Solid-State Lithium Batteries: Advances, Challenges, and Future Perspectives

Abstract

Solid-state lithium-ion batteries are gaining attention as a promising alternative to traditional lithium-ion batteries. By utilizing a solid electrolyte instead of a liquid, these batteries offer the potential for enhanced safety, higher energy density, and longer life cycles. The solid electrolyte typically consists of a polymer matrix integrated with ceramic fillers, which can significantly boost ionic conductivity. Research efforts are currently focused on advancing materials for the battery’s three primary components: the electrolyte, anode, and cathode. Furthermore, innovative strategies are being developed to optimize the interfaces between these components, addressing key challenges in performance and durability. Cutting-edge manufacturing techniques are also being explored to improve production efficiency and reduce costs. With continued advancements, solid-state lithium-ion batteries are poised to become integral to next-generation technologies, including electric vehicles and wearable electronics.

1. Introduction

The production of lithium-ion batteries (LIBs) has grown exponentially, surging from 26 GWh in 2011 to a remarkable 747 GWh in 2020, with China contributing 76% of this capacity. This rapid expansion in battery technology and its widespread adoption have amplified concerns about battery safety, particularly as battery-related incidents draw significant public attention. As battery capacities increase, the risk of accidents also rises, highlighting the urgent need to enhance safety standards. Solid-state batteries (SSBs) are emerging as a key solution, offering safer alternatives that support the deeper integration of advanced energy storage technologies into society [1].

The rising energy demand, coupled with growing concerns about environmental pollution, underscores the need for renewable, efficient, and reliable energy storage systems. To support the transition from fossil fuels to renewable energy, energy storage solutions must effectively store surplus energy and release it during peak consumption. Solid-state lithium-ion batteries (SSLIBs) meet these criteria, offering high energy capacity, rapid response times, and exceptional energy conversion efficiency. Their versatility allows them to adapt to diverse power and energy requirements, making them a cornerstone technology for the future [2]. SSBs can be categorized into two types: quasi-solid-state batteries (QSSBs) and all-solid-state batteries (ASSBs). QSSBs combine liquid electrolytes with a solid matrix, enhancing performance, while ASSBs use solid electrolytes exclusively, providing superior safety, reduced weight, higher energy density, and better volumetric efficiency. These batteries often incorporate micro- or nano-structured silicon anodes, further enhancing their performance. While this technology is still in development, it holds immense promise as a safer, more efficient alternative to conventional LIBs, addressing the growing need for high-energy-density solutions [3,4]. A notable advancement in solid-state technology is the solid-state lithium-metal battery, which replaces the polymer separator in traditional LIBs with a solid separator. In conventional designs, repeated charge and discharge cycles can lead to the formation of lithium dendrites that pierce the polymer separator, eventually reaching the cathode. This causes short-circuiting, rapid discharge, and a significant fire risk due to the flammable liquid electrolyte. SSBs mitigate this risk by using a solid electrolyte, which is impermeable to dendrites, enabling the use of a lithium-metal anode instead of the carbon or silicon anodes found in traditional batteries [5]. Table 1 highlights the key differences between LIBs and SSBs.

Despite their promise, SSBs face many challenges, including scaling up to large-format cells [10]. The significant volume changes in Li-ion and especially in Li-metal anodes during charge and discharge cycles present a major challenge for interface stability in SSLIBs [11]. Material properties and interface compatibility must be optimized to achieve the desired performance at a larger scale. Figure 1 illustrates the key stability challenges in SSBs, including chemical, electrochemical, mechanical, and thermal stability, each linked to the fundamental battery chemistry. Chemical degradation occurs when solid electrolytes react with lithium metal or cathode materials, leading to phase decomposition and reduced performance. Electrochemical instability arises from interfacial reactions that form resistive layers, increasing internal resistance and limiting ion transport. Mechanical stress from volume changes in the electrodes can cause cracks in the solid electrolyte, resulting in contact loss and higher resistance. Although SSBs are generally safer than liquid-electrolyte batteries, thermal instability at high temperatures can still lead to electrolyte decomposition and interfacial degradation, impacting battery lifespan and safety [12,13]. Overcoming these challenges is essential for advancing SSB technology to the next level.

Figure 2 illustrates the key components and enhanced strategies provided by solid-state batteries, emphasizing their safety, stability, and mechanical versatility compared to conventional liquid-electrolyte batteries. As research continues to address these challenges, SSBs are poised to become a transformative force in energy storage, driving advancements in electric vehicles (EVs), renewable energy integration, and beyond.

When comparing conventional LIBs to SSBs, several key differences emerge, driven primarily by their distinct chemical compositions. These differences significantly affect safety, lifespan, energy density, and overall performance. LIBs rely on liquid electrolytes, which are flammable and hazardous and contribute to the overall cost and weight of the battery. Over time, these liquid electrolytes degrade, leading to reduced performance in terms of charge retention and energy capacity. Furthermore, while LIBs can achieve high energy densities, they are prone to instability and safety risks if the stored energy exceeds their capacity [16]. Although conventional LIBs are more commercially available and cost-effective than SSBs, the advantages of SSBs—such as enhanced safety, longer lifespan, and higher energy density—are increasingly evident, particularly in demanding applications.

Modern EVs typically demand gravimetric energy densities of 250–350 Wh/kg and volumetric energy densities exceeding 600 Wh/L to compete with or surpass conventional LIBs [17]. Recent laboratory tests on SSB parameters have demonstrated significant advancements. Recent SSB advancements featuring lithium-metal anodes have demonstrated energy densities exceeding 400 Wh/kg, significantly improving the driving range [18]. Lithium-metal pouch cells with a specific energy of 300 Wh/kg have also been validated, showcasing their potential for improved electrode materials and precise cell performance assessments [10]. Experimental setups, such as coin cells, are pivotal in accelerating the development of SSB materials. These setups allow researchers to investigate parameters like electrolyte volume, cathode loading, lithium anode thickness, current density, and voltage range. The cycle life of lithium-metal anodes can be significantly influenced by adjustments to these variables [19]. However, maintaining strict control over testing conditions is essential to derive meaningful insights that can guide the development of high-energy battery systems.

As shown in Table 2, transitioning to ASSB packs offers numerous advantages, including reduced material consumption, fewer hazardous components, and simplified system architecture. These factors result in battery packs that are approximately 40% smaller and lighter than conventional lithium-ion counterparts [20]. The benefits of SSBs continue to grow as research advances in their manufacturing processes. In key areas such as weight, safety, size, capacity, and performance potential, SSBs consistently outperform LIBs. Companies like Toyota and QuantumScape have reported SSB prototypes that achieve a higher cycle life, faster charging, and superior thermal stability, positioning SSBs as the next-generation solution for EVs [21,22]. Table 2 provides a clear visual comparison, highlighting these advantages through a representative example of battery design and form.

The implementation of SSBs holds significant promise for creating safer, more energy-dense, cost-effective, and environmentally friendly energy storage solutions [16]. By leveraging solid electrolytes, these batteries can achieve higher energy densities and superior performance metrics while offering enhanced safety compared to conventional LIBs. The inherent advantages of SSBs—such as improved stability, extended cycle life, and potential cost-effectiveness—position them as transformative technologies within the rechargeable battery industry [19].

One critical area of research focuses on the development of composite electrolyte systems to improve the energy density and kinetics of lithium-metal SSBs. For instance, studies on lithium-ion conductive polyethylene oxide (PEO) matrices have explored how electrolyte processing affects the mesostructure and overall cell kinetics. A notable composite electrolyte system, LLZO–PEO (LiTFSI), integrates lithium-ion-conductive doped-Li₇La₃Zr₂O₁₂ (LLZO) garnet fillers within the PEO matrix. This configuration offers design principles that aim to meet the practical demands of SSBs for industrial applications [23]. By advancing such composite electrolytes, researchers aim to overcome current challenges in SSB performance and accelerate their commercialization. These efforts underscore the pivotal role SSBs could play in addressing the growing energy demands of modern society, with applications ranging from EVs to renewable energy storage systems and beyond.

2. Materials for Solid-State Electrolytes

2.1. Types of Solid Electrolytes: Ceramic, Polymer, and Composite

The electrolyte is a critical component in batteries, facilitating the transfer of ions between the electrodes, which is essential for the charge–discharge cycles. To overcome the safety and performance limitations of liquid electrolytes, the LIB industry is increasingly turning to solid-state electrolytes. Among the emerging solutions are ceramic, polymer, and composite electrolytes, each offering distinct advantages and challenges. Table 3 provides an overview of commonly used solid-state electrolytes categorized by type.

Ceramic electrolytes—also known as inorganic solid electrolytes (ISEs)—have a long history, with early research on strong ionic conductors like PbF₂ and Ag₂S dating back to the 1830s [13]. Modern ceramic electrolytes include garnet-, NASICON-, perovskite-, and sulfide-based materials. These electrolytes exhibit high ionic conductivity, excellent thermal stability, mechanical strength, and non-flammability. However, their inherent brittleness poses challenges, such as cracking during battery expansion and high interfacial impedance between the electrolyte and electrodes [24,25].

Solid polymer electrolytes (SPEs) are composed of lithium salts dissolved in polymer matrices. Ideal polymers for this application possess high dielectric constants and polar functional groups, while lithium salts should exhibit low lattice energy [25]. Among various options, PEO has emerged as the most promising candidate. SPEs are lightweight, cost-effective, and flexible, which improves interfacial contact between the electrolyte and electrodes—a common issue with ceramic electrolytes. However, polymer electrolytes suffer from lower mechanical strength and ionic conductivity compared to their ceramic counterparts [24].

Composite electrolytes aim to combine the best properties of ceramic and polymer electrolytes while minimizing their individual limitations. Structurally, composite electrolytes resemble polymer electrolytes but incorporate ceramic fillers. These fillers enhance lithium-ion transport, leading to higher ionic conductivity [24]. Ceramic fillers in composite electrolytes can be categorized as active or inert: Active fillers (e.g., garnet, perovskite, and LISICON) directly conduct ions, achieving high conductivity (>10⁻⁴ S/cm). Inert fillers (e.g., TiO₂, Al₂O₃, SiO₂, and ZrO₂) function as plasticizers, improving the electrolyte’s mechanical properties and stability [26]. Shrinking these fillers to the nanoscale has been a focus of research as it enhances electrochemical performance and mechanical strength [27]. Advanced designs, such as multi-layered composite electrolytes, optimize performance by tailoring the properties of each layer to the specific needs of the anode and cathode. For instance, the electrolyte near the anode requires high voltage tolerance, while the cathode-side electrolyte must exhibit chemical stability. Intermediate layers further enhance mechanical properties and mitigate dendrite formation, improving the overall durability and safety of the battery system [25]. By leveraging these innovative materials, researchers are addressing key challenges in SSB development, paving the way for safer, more efficient, and commercially viable energy storage solutions.

2.2. Ionic Conductivity and Stability Considerations

Ionic conductivity measures the ability of a substance to conduct electricity through the movement of ions within a material, and it can occur in both solids and liquids. While ionic conductivity is generally higher in liquids than in solids, SSLBs compensate for this limitation by utilizing a lithium-metal anode, which offers a significantly higher energy density—up to 3860 mAh/g—compared to conventional graphite anodes [28]. Efforts are underway to enhance the ionic conductivity of solid electrolytes through innovative approaches such as irradiation and quenching at low temperatures [29]. Optimizing the composition of the electrolyte is a critical factor in achieving the highest possible ionic conductivity in solid-state electrolytes (SSEs).

SSEs come in various types, including garnet-based, sulfide-based, and others, each with unique properties [30]. These differences often relate to their ionic conductivity and reactivity to environmental conditions. Environmental factors, such as humidity or exposure to air, can negatively impact SSE performance, potentially leading to reduced ionic conductivity, structural damage, or the release of harmful gases [31]. However, SSEs are inherently more stable and less reactive than liquid electrolytes. For example, the adverse effects of atmospheric exposure on some sulfide-based SSEs can be nearly reversed through restoration techniques [29]. Additionally, incorporating lithium iodide in sulfide electrolytes has been shown to suppress the release of toxic hydrogen sulfide gas.

Recently, solid-state lithium–sulfur (Li-S) batteries have gained significant attention due to their high theoretical energy density and the inherent safety advantages of solid electrolytes over liquid counterparts. Sulfide solid electrolytes, owing to their high Li-ion conductivity (1–25 mS cm⁻¹), are suitable for the preparations of ASSBs with higher energy density [32]. Recent advancements focus on addressing key challenges, such as the poor ionic conductivity of solid electrolytes. Researchers have developed sulfide-based and polymer-composite electrolytes with enhanced ionic conductivity and better interfacial stability. Additionally, novel cathode architectures, such as nanostructured sulfur hosts and solid-state interlayers, have been introduced to suppress polysulfide diffusion and improve cycle life [33,34].

The stability of ionic conductivity is a significant advantage of SSEs over liquid electrolytes. While liquid electrolytes degrade quickly under extreme conditions such as severe temperatures, ultraviolet (UV) exposure, or water ingress, SSEs demonstrate greater resilience. This stability ensures that batteries maintain their charge capacity longer and are less prone to catastrophic failure. Furthermore, SSEs exhibit slower dendrite formation compared to liquid electrolytes. Dendrites, which are lithium deposits that grow within the electrolyte, can cause battery failure and short circuits. Advances in material science and new processing techniques continue to reduce dendrite formation, further improving the performance and safety of SSBs [35].

2.3. Challenges in Electrolyte Synthesis and Fabrication

Although SSBs are widely regarded as the future of battery technology, scaling their production to meet industrial demands presents significant challenges. These obstacles contribute to high costs, which is one of the primary reasons why solid-state electrolyte batteries (SSEBs) are not yet widely adopted across industries. While SSEBs can be produced reliably in laboratory settings, scaling these processes for mass production remains infeasible with current technologies [20]. One commonly used laboratory method is powder pressing, where electrolyte pellets are compressed into brick-like shapes. Although suitable for laboratory-scale testing, this method does not yield durable SSBs capable of prolonged use [20,36]. Recent advancements, such as hot rolling, have improved upon this technique by reducing porosity and increasing ionic conductivity while also enhancing the structural stability of the electrolyte “bricks” [36]. Despite these improvements, the scalability of production remains a critical bottleneck. Historically, most research has focused on optimizing the composition of electrolytes rather than the scalability of manufacturing processes; however, cost and production-scale analyses are now becoming more prominent areas of investigation.

Mechanochemical synthesis is one promising fabrication technique that uses mechanical force to drive chemical synthesis without relying on heat [37]. This approach is significant because the application of heat during electrolyte fabrication can adversely affect its desirable properties. Furthermore, mechanochemical synthesis avoids the use of harsh solvents, which could also degrade electrolyte performance. While promising, this method faces challenges in scaling up for industrial production [37,38].

A major complication in scaling the production of SSEBs lies in the sheer number of possible combinations of electrolyte materials and fabrication techniques. Each combination must be rigorously tested to determine how the chosen process affects the electrolyte’s properties. This trial-and-error approach is time-consuming but necessary to ensure the resulting batteries are both safe and effective. Moving forward, a combined focus on scalable manufacturing methods and optimal material compositions will be essential to overcome these challenges and bring SSEBs closer to widespread commercial adoption.

3. Electrode Materials and Interfaces

3.1. Cathode and Anode Materials in Solid-State Systems

In conventional lithium-ion batteries, cathodes are typically composed of multi-metal oxides containing lithium, cobalt, nickel, and manganese. However, these materials face significant challenges, particularly regarding the sustainability and ethical concerns associated with lithium mining [39,40]. In recent years, there has been a growing interest in organic cathode materials comprising abundant elements like carbon, hydrogen, oxygen, nitrogen, and sulfur. These organic materials offer several advantages, including lower material costs and higher theoretical energy density and capacity [40]. One of the primary challenges of using organic cathode materials in traditional liquid electrolyte systems is their tendency to dissolve, which compromises battery performance [41]. SSEs address this issue by providing a stable environment that prevents dissolution, making the combination of organic cathodes and solid-state systems particularly promising.

For anodes, traditional LIBs commonly use graphite due to its stability; however, graphite has a low specific capacity, necessitating thicker anodes to achieve comparable performance. In solid-state systems, lithium metal is considered the most effective anode material due to its high theoretical capacity and energy density. The primary challenge with lithium anodes lies in uncontrolled dendrite growth, which can compromise battery safety and performance [42]. It is known that thicker lithium anodes can store more lithium; however, they also significantly increase the battery weight and volume without proportionally improving energy output. Furthermore, thick anodes exacerbate volume change issues during charge and discharge cycles, resulting in increased internal stress, delamination, and more risk of dendrite formation. This necessitates the utilization of thin lithium foils, which can offer several advantages. Thin anodes help to minimize mechanical stress and mitigate volume change effects, thereby enhancing interface stability [43,44,45].

Silicon is another promising anode material being explored for use with SSEs. While silicon has shown limited effectiveness in traditional liquid electrolyte systems, it demonstrates better compatibility with solid electrolytes, offering high theoretical energy density. However, silicon anodes also face interfacial compatibility challenges when paired with solid electrolytes [42].

An emerging innovation in solid-state systems is the development of anode-free lithium-metal batteries (AF-LMBs). In these designs, the anode is not included during manufacturing but forms during the first charge when lithium ions migrate from the lithiated cathode [46,47]. By eliminating the use of a host anode, AF-LMBs can exploit the full potential of the lithium-containing cathode system, achieving the highest retrievable energy densities, simplifying anode processing, and reducing the overall cost of cell production and maintenance. However, this design introduces several challenges, with dendrite growth remaining a major concern, especially due to the significantly lower critical current density (CCD) of solid-state electrolytes compared to their liquid counterparts. Other issues include interfacial contact resistance, limited ion pathways, and the formation of dead lithium, all of which contribute to poor cation utilization during repetitive cycling. These factors collectively impair the long-term performance endurance and practical applicability of AF-LMBs [46,48].

SSB development also explores less conventional materials, such as glass and glass–ceramic cathodes, which have demonstrated some potential in specific applications [49,50]. The choice of cathode and anode materials, as well as their interactions with the electrolyte, creates a complex web of possibilities. This complexity necessitates extensive testing to predict and optimize the performance of SSBs.

Table 4 provides a simplified summary of potential materials for cathodes and anodes used in SSBs, highlighting their advantages and limitations in the context of solid-state technology. Combinations of these materials, along with others not listed, may also be utilized as cathode and anode materials for SSBs. For cathode materials, multi-metal oxides remain the traditional choice due to their high energy density and long cycle life; however, their reliance on materials like cobalt and nickel poses sustainability issues, including environmental impacts from mining and high material costs [40]. In contrast, organic cathodes have gained attention due to their natural abundance and cost-effectiveness. These materials are particularly well-suited for integration with SSEs due to their structural flexibility. However, their low energy density is a hurdle to overcome in comparison with inorganic materials [41]. The selection of anode materials for SSBs should account for factors such as high energy or power density and stable cycling performance. However, different materials present challenges like limited specific capacity, dendrite formation, interfacial compatibility issues, and rapid capacity degradation. Balancing these factors is crucial for optimizing battery performance and longevity. Understanding the synergistic effects between materials remains critical for advancing SSB technology.

3.2. Interface Engineering for Enhanced Performance

One of the critical challenges in SSB technology is the poor interfacial contact between the solid electrolyte and the electrodes. This issue leads to high energy barriers, limited ion transport channels, and compromised battery performance [51]. Unlike traditional liquid electrolyte batteries, where the liquid ensures uniform contact with the solid electrode surfaces, solid electrolytes often contain undesirable pores and cracks. These flaws reduce the contact area, negatively affecting the battery’s performance, durability, safety, and longevity. To address these challenges, several interface-engineering methods have been developed to enhance the contact between the electrolyte and electrodes:

• (a). Hot and Cold Pressing:

These techniques involve compressing small electrolyte pellets into dense, solid structures. Cold pressing is conducted at room temperature. This method uses mechanical force to form the solid electrolyte. Hot pressing is performed at elevated temperatures (typically 30–150 °C). This approach helps reduce porosity and improve contact at the interface [36]. Both methods aim to create a more compact and uniform electrolyte structure, mitigating cracks and voids that hinder ionic transport;

• (b). Buffer Layer Creation:

This method introduces a thin interfacial layer, typically a film of oxide, between the solid electrolyte and the electrode. The buffer layer acts like an adhesive, improving the mechanical and chemical compatibility between the two surfaces. Key benefits include reducing interfacial stress caused by lithium metal formation and minimizing dendrite growth, a common issue arising from poor interfacial contact [52]. This method also enhances specific capacity, ionic conductivity, and lithium-ion migration through improved mechanical properties [53]. The buffer layer has proven to be particularly effective in stabilizing the interface and is relatively straightforward to integrate into most SSB designs.

3.3. Issues of Dendrite Formation and Mitigation Strategies

Dendrite formation in solid-state lithium batteries presents a significant safety challenge, hindering their widespread adoption. Dendrites are needle-like structures that can form within batteries due to repeated ion movement during charging and discharging cycles. These structures can grow large enough to pierce the electrolyte or reach the anode, causing short circuits. However, SSBs are inherently more resistant to dendrite penetration than their liquid electrolyte counterparts. Even in the rare event of penetration, the absence of liquid electrolytes eliminates the risk of spillage, and the solid electrolytes are generally less flammable [54].

Although dendrite formation is less prevalent in solid-state electrolyte batteries (SSEBs), it is not entirely eliminated. Poor interfacial contact between the electrolyte and electrode, as discussed in the previous section, contributes significantly to dendrite formation. Techniques such as adding a buffer layer have shown promise in mitigating dendrite growth but additional work is needed to fully understand and address this issue. The exact mechanisms of how relatively soft dendrites grow through much harder solid electrolytes remain under investigation, though mechanical imperfections such as cracks and pores in the electrolyte are widely considered contributing factors [55].

A variety of strategies have been proposed to address dendrite formation, each with varying degrees of success, outlined below:

• (a). Buffer Layer Addition:

Adding a thin interfacial layer between the electrolyte and electrode improves contact and reduces stress points that contribute to dendrite initiation. As mentioned earlier, this method has shown significant promise in mitigating dendrite formation;

• (b). Surface Modification:

Modifying the surface of the electrolyte by adding materials—such as sodium-containing sulfur dioxide—has been found to slow dendrite growth. This technique enhances the electrolyte’s resistance to dendritic penetration by improving surface stability and uniformity [56];

• (c). Electrolyte Composition Optimization:

Research into the chemical composition of solid electrolytes has identified that some formulations are more resistant to dendrite formation than others. For example, electrolytes containing lithium hexafluorophosphate have been observed to promote faster dendrite growth, indicating the need to avoid or modify such compounds [57].

The most effective strategy for addressing dendrite formation will likely involve combining these methods. By integrating buffer layers, optimizing electrolyte composition, and implementing surface modifications, researchers can enhance the mechanical integrity and chemical stability of SSEBs, significantly reducing the risk of dendrite growth. Continued innovation in these areas is essential for enabling the safe and reliable large-scale adoption of solid-state lithium batteries.

4. Manufacturing Techniques and Scalability

4.1. Solid-State Battery Fabrication Methods

The fabrication of SSBs involves unique processes distinct from those used for conventional LIBs due to many factors, including the necessity of solidifying the electrolyte. As discussed in Section 1, the choice of anode, cathode, and electrolyte materials not only dictates the electrochemical performance of SSLBs but also significantly influences the selection of manufacturing techniques. Factors such as thermal stability, mechanical strength, ionic conductivity, and interfacial compatibility determine the feasibility of different fabrication approaches. Among the available methods, thin-film batteries represent a prominent approach. Thin-film batteries are created by stacking a thin-film electrolyte onto electrodes in a vacuum. While they store relatively small amounts of energy, they compensate with an extended cycle life and simplified manufacturing requirements.

There are challenges in SSB fabrication. The transition from liquid to solid electrolytes introduces significant manufacturing complexities. Many solid electrolytes, particularly those based on sulfides, are highly sensitive to moisture. Exposure to air can lead to their rapid deterioration, necessitating tightly controlled manufacturing environments with strict moisture regulation. Dedicated facilities are required to ensure the integrity of these sensitive materials [58]. The brittleness of ceramic electrolytes often necessitates high-temperature sintering or spark plasma sintering, while polymer electrolytes allow for solution casting or extrusion-based processing. Yao et al. [59] have identified several critical challenges associated with fabricating composite polymer electrolyte (CPE) films for SSBs, including the following: excessive use of organic solvents, slower production timelines, protocol mismatches, and precise temperature control requirements [60]. These constraints complicate the fabrication process and often impact scalability and cost-effectiveness.

To address these challenges, Yao and colleagues developed a rapid electrophoretic deposition (EPD) method for creating ultra-thin electrolyte layers. In this process, charged particles migrate toward an electrode of the opposite charge, where they deposit to form a uniform film. The resulting layer typically ranges in thickness from 20 to 50 μm. This thin layer, composed of lithium-conducting solid-state polymer-composite electrolytes, is subsequently paired with a lithium-metal anode to fabricate the all-solid-state lithium-metal battery [61]. This innovation offers a more efficient and precise fabrication method while producing a robust electrolyte layer with improved performance.

Despite advancements, existing manufacturing processes for SSBs still present notable drawbacks. For instance, the use of polymer binders, though convenient, can negatively impact charge transport within composite cathodes, reducing overall battery efficiency [62]. These limitations highlight the need for further optimization and innovation in fabrication techniques to achieve high-performing SSBs. As SSB technology continues to advance, addressing fabrication challenges remains crucial for their large-scale adoption. Research is focused on developing scalable, cost-effective, and environmentally friendly methods to enhance manufacturing efficiency while ensuring the performance and durability of the final product. Figure 3 presents a schematic comparison between an LIB and an SSB, highlighting their structural differences and unique features.

4.2. Challenges in Scaling up Production

Scaling up the production of SSBs presents significant challenges centered on cost, safety, and performance. These hurdles must be addressed for SSBs to achieve widespread commercial adoption across diverse applications, including consumer electronics, EVs, and grid storage. A major obstacle to scaling SSB production is the financial investment required. The manufacturing process often necessitates specialized facilities with stringent environmental controls, driving up initial capital costs. Despite these challenges, companies like LG Energy Solution, Panasonic, and Toyota are actively working to commercialize SSBs for various applications [63]. Additionally, the high cost of LIBs adds to the financial burden. A battery pack costing less than 100 USD per kilowatt-hour (kWh) is considered a competitive benchmark. However, SSBs currently face up to 30% higher costs driven by several factors related to materials and manufacturing complexities [64]. The fabrication of solid-state electrolytes requires precise control over thickness, uniformity, and purity, which increases production complexity. Achieving the necessary densification and interface stability in SSBs often requires prolonged processing times under controlled environments. These extended production cycles lead to lower throughput and increased operational costs [18]. Unlike LIBs, which benefit from established supply chains and economies, SSB technology is still in its early commercialization stages, facing scale-up challenges that further contribute to its higher production costs [65].

One promising strategy to lower costs involves increasing the energy density of SSBs. Batteries with an energy density of 400 Wh/kg could significantly reduce the cost per kWh, making them more affordable for widespread use [66]. According to Baranova et al. [67], achieving an energy density of at least 250 Wh/kg and maintaining a maximum cost of 120 USD per kWh would be crucial for enabling broader adoption. Meeting this benchmark would make SSBs economically viable for both consumers and corporations, justifying the higher upfront investment through long-term value and performance.

Another critical challenge lies in translating lab-scale developments into scalable industrial processes. Key gaps exist in the following areas: (a) electrolyte preparation: ensuring uniformity and quality during large-scale production; (b) layer fabrication: addressing issues such as cracks, porosity, and consistency; (c) assembly processes: optimizing automation for precision and cost-effectiveness; and (d) cell design: refining configurations to improve performance and durability at scale. Overcoming these gaps will require significant innovation and collaboration between researchers and manufacturers. Advances in materials science, engineering, and process optimization are essential to close the gap between experimental prototypes and commercially viable products [68].

To successfully scale up SSB production, the industry must address both technical and economic challenges. Innovations that increase energy density, improve manufacturing efficiency, and reduce production costs are critical. With continued investment and research, these efforts can help SSBs achieve market competitiveness, enabling their integration into a wide range of applications while fostering a sustainable energy future.

4.3. Innovations in Manufacturing Processes

Significant advancements have been made in manufacturing processes for next-generation batteries, including the development of SSBs. One notable achievement comes from Samsung, where researchers achieved a lifespan of over 1000 cycles for a practical pouch cell by employing silver–carbon-composite anodes [69]. This innovation enhanced heat conduction and performance, demonstrating the potential of composite materials in improving battery efficiency.

The resurgence of lithium-metal anodes has drawn considerable attention to improving metal interfaces. Efforts include the following: (a) protective layers: implementing protective coatings to enhance durability; (b) lithiophilization: using artificial interlayers to improve compatibility and stability; and (c) low-volume-change anodes: reducing volumetric changes during cycling to improve ion transport and suppress instability. These advancements aim to address persistent challenges such as dendrite formation, poor cycling performance, and limited ion transport, leading to batteries with higher energy densities and improved longevity.

ASSBs, which eliminate liquid electrolytes, are gaining traction despite challenges related to poor contact interfaces and scalability. To overcome these issues, Wang’s group proposed a “bottom-up” synthesis approach. This method involves assembling materials from basic components to form a nanocomposite by dissolving Li₂S, PVP, and Li₆PS₅Cl [70]. The resulting structure addresses common problems like poor cycle life, low rate performance, and insufficient electronic and ionic conductivity.

As traditional LIBs approach their physical limits in terms of mass and volumetric energy densities, the industry is shifting toward new breakthroughs in battery technology [67]. Companies like Nissan are at the forefront, expecting to produce an SSB with twice the energy density of conventional LIBs, a charging time reduced by two-thirds, and costs as low as 65 USD per kWh by 2028 [71]. Other next-generation batteries under development include Nickel–Cobalt–Manganese (NCM) LIBs, offering improved energy density and performance, and Lithium Iron Phosphate (LFP) batteries, which are a cost-effective alternative, with expected cost reductions exceeding 30% compared to NCM counterparts. These alternatives provide diverse options tailored to specific applications, balancing performance and affordability. Innovations in ultra-thin Li-conducting composite polymer electrolytes (CPEs) have further enhanced battery performance. Improvements include the following: (a) superior interfacial contact: reducing resistance at the electrolyte–electrode interface; (b) interfacial stability: minimizing degradation over repeated cycles; (c) increased ionic conductivity: enabling faster charge and discharge rates; and (d) enhanced mechanical properties: improving durability and structural integrity [72]. As advancements continue to push the boundaries of battery technology, innovations in materials, interfaces, and manufacturing methods are paving the way for a new generation of energy storage solutions. These breakthroughs promise to deliver batteries with greater energy density, faster charging, lower costs, and improved sustainability, positioning them as transformative tools in the global transition toward cleaner energy systems.

5. Performance, Safety, and Reliability

As the world transitions from fossil fuels as its primary energy source, LIBs have emerged as a leading alternative, driving advancements across public and private sectors. One of the most prominent applications of this technology has been in the automotive industry, where LIBs power EVs. However, despite their widespread adoption, the performance, safety, and sustainability of traditional LIBs have often been scrutinized. A key concern lies in their reliance on liquid electrolytes, which present challenges such as thermal instability, flammability, and limited energy density. The recent advancements in SSLIBs have addressed many of these issues, paving the way for next-generation energy storage solutions. SSLIBs replace liquid electrolytes with solid counterparts, significantly enhancing thermal stability, safety, and overall reliability. These innovations have unlocked the potential for longer-lasting, safer batteries, making them a critical component in pushing sustainable energy solutions.

5.1. Energy Density, Charge/Discharge Rates, and Cycle Life

Energy density in SSBs refers to the amount of energy stored per unit mass or volume. In these batteries, energy density is typically measured in milliampere-hours (mAh) per micron of cathode material thickness and per square centimeter of footprint area. Thin-film SSLIBs, for instance, exhibit an energy density of approximately 50 mAh per micron of cathode thickness and per square centimeter [73]. While promising, this value is considered a low volumetric energy density and remains one of the key challenges for SSLIBs.

Conventional LIBs dominate the energy storage market but are constrained by the limitations associated with liquid electrolytes. This can hinder the development of denser batteries. SSLIBs, by incorporating solid electrolytes, have the potential to overcome these challenges. They can achieve higher energy storage capacities in smaller, lighter designs, enabling increased energy and power output at reduced costs [74]. Charge rate, defined as the time required to fully charge a battery, is another critical parameter. For example, a charge rate of 0.03 C means it would take approximately 33 h to fully charge the battery, whereas a 1 C rate signifies full charging in one hour. Faster charging rates, however, tend to degrade battery performance, while slower rates help preserve battery health. To address these trade-offs, researchers are experimenting with various materials. Tin (Sn) powder electrodes in SSB cells, for instance, support a high capacity of 600 mAh g⁻¹ for over 100 cycles at low charge rates of around 0.03 C, showing good charge/discharge behavior [75]. However, as charge and discharge rates increase, capacity declines—a persistent challenge in battery engineering. Notably, silicon-based thin films demonstrate superior performance and rate capabilities compared to Sn powder electrodes, underscoring the importance of material selection in optimizing charge/discharge behavior [76].

Integrating LIBs in automotive applications to combat climate change and reduce fossil fuel reliance has also brought attention to battery longevity. Research highlights that SSLIBs with cobalt sulfide-Li₇P₃S₁₁ nanocomposite electrodes can achieve exceptional cycle life. These batteries maintain a discharge capacity of 421 mAh g⁻¹ even after 1000 cycles at a high current density of 1.27 mA cm⁻² [77]. This performance is enabled by innovative interfacial architectures, where Li₇P₃S₁₁ electrolyte particles are anchored to cobalt sulfide nanosheets through a liquid-based fabrication process. This design enhances the contact between the cathode and solid electrolyte, facilitating efficient lithium-ion transfer—a critical factor for maintaining long-term performance [78]. These advancements demonstrate that SSLIBs can achieve significantly longer cycle lives than traditional LIBs, paving the way for more durable and sustainable energy storage solutions [79].

5.2. Thermal Management and Safety Considerations

LIBs face two critical thermal challenges: overheating and extreme cold. Both high and low temperatures can degrade battery performance, reduce capacity, and shorten overall lifespan [80]. Overheating in LIBs can trigger a phenomenon known as “thermal runaway”, where lithiated carbons react with the solvents in the liquid electrolytes, initiating a chain reaction. This reaction generates excessive heat, potentially causing the battery to ignite or explode. To address this, modern battery designs incorporate safety mechanisms such as vents, thermal fuses, and automatic shutoff features to mitigate excessive heat buildup and prevent catastrophic failures [81]. Given these risks, safety in battery design has been a longstanding concern. Regulatory agencies worldwide have established rigorous standards that battery manufacturers must adhere to before products can be sold or integrated into applications. These standards include comprehensive testing procedures, such as overcharge, over-discharge, thermal abuse, short-circuit, and penetration tests, ensuring that batteries perform safely under various conditions [82].

SSBs offer enhanced thermal stability compared to their liquid-based counterparts but they are not without risks. One emerging safety concern is the issue of battery expansion, which can occur due to several factors, including gas generation during operation. Expansion can lead to internal short circuits and potentially dangerous failures, such as battery rupture or explosions. These challenges highlight the importance of further research and innovation to ensure SSBs meet stringent safety requirements while delivering superior performance and durability. Figure 4 depicts various outcomes under different safety scenarios within the battery.

Degradation mechanisms encompass a variety of processes that contribute to the performance decline in batteries over time. Table 5 summarizes the battery degradation mechanism and its outcomes. Key mechanisms include the following:

• (a). Diffusion-Induced Stress:

This occurs when volume changes happen as lithium ions intercalate into the electrode material during charging and discharging cycles. These expansions and contractions generate internal stress, potentially damaging the electrode structure [84];

• (b). Phase Changes and Interface Issues:

Slow ionic diffusion and poor contact at the electrode–electrolyte interface, or dissolution of transition metals, can lead to capacity loss [85];

• (c). Lithium Creep:

Intense heat can cause lithium metal to deform (creep), resulting in internal volume changes that may lead to short circuits. Lithium creep is a challenge due to the metal’s chemical aggressiveness and susceptibility to stress [85];

• (d). Interfacial Decomposition:

Chemical, electrochemical, and mechanical instabilities at the interface can degrade the battery, impacting operating temperatures and increasing costs. Differences in the way solids and liquids screen electric fields at the interface also contribute to decomposition [86];

• (e). Gas Generation:

Deterioration at the electrode–electrolyte interface can result in the release of gases such as hydrogen, carbon monoxide, and hydrocarbons. This issue, exacerbated by high temperatures, overcharging, or mechanical stress, raises safety concerns due to the potential for pressure buildup and thermal runaway [87].

Reliability testing ensures battery performance and safety. Various methods are used to evaluate durability, thermal stability, and lifespan:

• (a). Mechanical testing: simulates real-world conditions such as crushing, puncturing, and vibration to assess durability and structural integrity [88];

• (b). Thermal testing: evaluates the battery’s performance across a range of temperatures, from extreme heat to cold [89];

• (c). End-of-line testing: verifies functionality and performance under simulated operating conditions, including temperature cycling and charge–discharge scenarios [90];

• (d). Accelerated life testing: simulates long-term usage in a shorter time frame to identify power fade and capacity loss [91];

• (e). State of health (SOH) assessment: Conducted before the battery is sold to determine its overall condition after undergoing all previous tests. This helps manufacturers identify areas for improvement to enhance safety and longevity.

LIBs, while effective, face safety concerns due to their use of flammable liquid solvents in electrolytes. Replacing these solvents with solid electrolytes in SSBs mitigates flammability risks and reduces side reactions that accelerate degradation. SSBs also exhibit higher energy density, translating to longer lifespans and extended ranges. For instance, while traditional LIBs can last approximately 2000 cycles, SSBs can endure up to 10,000 cycles, demonstrating their potential for superior reliability and performance [79].

6. Current Challenges and Future Research Directions

6.1. Technical and Economic Barriers to Commercialization

Solid-state lithium batteries hold great promise but their development faces significant challenges. A key issue arises from the solid-state nature of both the electrodes and the electrolyte, which leads to poor contact between the two, particularly during battery expansion. Furthermore, electrochemical reactions at the electrode–electrolyte interface can result in electrolyte decomposition and dendritic growth [92]. These dendrites can penetrate the solid electrolyte, causing short circuits that may lead to battery fires or explosions. Another challenge is the formation of solid-electrolyte interphase (SEI) and cathode-electrolyte interphase (CEI) layers on the anode and cathode surfaces. These layers result from redox reactions with the electrolyte. While they can reduce dendrite growth, they also act as bottlenecks for current flow, diminishing overall battery performance [93].

Economic barriers further hinder the large-scale production of SSBs. Processes such as electrolyte manufacturing remain complex and inefficient, often yielding low volumes. While such limitations are manageable in research environments, they pose a significant obstacle to commercial viability. To enable cost-effective mass production, these processes must be streamlined and optimized [94].

Future research must address several critical areas to overcome these challenges. Optimizing both the anode and cathode materials and their interactions is essential for enhancing battery performance and longevity. Additionally, developing stable and robust electrolytes is crucial as interactions at the electrode–electrolyte interface are often responsible for capacity fade or failure [14]. While SSBs are generally considered safer than conventional lithium-ion batteries, ensuring consistent safety across all operational scenarios remains a priority. Finally, a deeper understanding of the governing physics behind SSBs is necessary to fully exploit their potential and drive technological advancements [69].

6.2. Recent Advances in Solid-State Battery Research

Recent advancements in SSBs primarily focus on optimizing their key components—the electrodes, the electrolyte, and the interfaces between them—to enhance performance and stability. Researchers are addressing the unique challenges associated with the anode, cathode, and their interactions [95].

One notable breakthrough is the development of flexible composite electrolyte membranes, which combine high mechanical strength with exceptional ionic conductivity. This improvement is attributed to the net structure of the electrolyte, which promotes uniform lithium-ion distribution. However, increasing the pore size within these membranes remains a challenge. This flexible technology holds great potential for applications in wearable electronics, where adaptability and reliability are critical [96].

In manufacturing, UV-curable electrolytes have emerged as a promising innovation. These electrolytes, composed of photoluminescent polymer gels, are applied directly to electrodes and cured in place using UV light. This process significantly reduces interfacial resistance on the cathode, enhancing electrochemical performance and manufacturing efficiency. However, the resistance at the electrolyte–anode interface remains an issue that requires further optimization [97]. To improve stability at these interfaces, buffer layers are being developed to regulate the solid-electrolyte interphase (SEI) and cathode-electrolyte interphase (CEI) films as demonstrated in Figure 5. For instance, a polyethylene oxide (PEO) layer applied to the cathode and a polypropylene carbonate (PPC) layer on the anode demonstrated enhanced interface stability, with batteries retaining 94.5% of their capacity after 150 cycles [98].

Another emerging technology is the electrospun fiber nanocomposite electrolyte, which is fabricated using polymers such as PMMA, PVDF-CO-HFP, and PEO, with titanium oxide (TiO₂) as a filler to boost ionic conductivity. When these fibers overlap, they form a 60-micrometer-thick membrane with a well-optimized pore diameter. This electrolyte exhibits excellent thermal resistance and high ionic conductivity, making it a promising candidate for next-generation SSBs [99].

Gel polymer electrolytes represent another exciting development, acting as a hybrid between solid and liquid electrolytes to leverage the benefits of both. These gels offer improved ionic conductivity and reduced interfacial resistance while minimizing the leakage risks associated with liquid electrolytes; however, their relatively low mechanical strength remains a limitation that requires further refinement [100,101].

6.3. Prospects for Next-Generation Solid-State Batteries

Next-generation SSBs must achieve higher capacities and lighter weights to meet the demands of emerging technologies, particularly the rapidly growing EV market [102]. To this end, researchers are exploring innovative approaches to enhance the performance and scalability of SSBs.

Sulfide-based electrolytes are a promising avenue due to their exceptional ionic conductivity and mechanical properties; however, their large-scale production faces significant challenges. The synthesis process is energy-intensive and time-consuming, making commercial viability difficult at present. Moreover, the underlying synthesis mechanisms remain only partially understood, necessitating further research to optimize their production [103].

Oxide-based solid electrolytes also hold considerable potential. Known for their excellent stability due to robust crystal structures, these materials exhibit high ionic conductivity and low porosity [104]. Their mechanical strength and conductivity can be further enhanced by incorporating inorganic fillers. Additionally, hybrid manufacturing techniques—combining methods like electrospinning with traditional fabrication approaches—offer a pathway to balance performance with cost efficiency [105].

While solid-state lithium batteries represent a transformative leap forward in battery technology, it is essential to recognize their current limitations. Despite significant advancements in safety and ionic conductivity, these batteries still face challenges in achieving high energy densities and rapid charge/discharge rates. Addressing these barriers will be critical for realizing their full potential in next-generation applications [106].

7. Applications and Market Potential

7.1. Use Cases in Electric Vehicles and Consumer Electronics

In the EV industry, scalability and cost-efficiency are critical. Any component designed for EVs must be capable of enduring mass production while maintaining financial and engineering feasibility. Transitioning to SSB technology in EVs requires material developers, production engineers, and battery manufacturers to optimize layer thickness and conduct extensive experiments on the fabrication, processing, and management of electrode and solid-electrolyte layers. EV companies are increasingly supporting advancements in scaling up large-format SSBs with enhanced energy density and safety [20].

A key determinant of success in the EV industry is the battery pack, with safety being a paramount consideration. Central to this safety is the battery thermal management system (BTMS), which ensures batteries operate within optimal temperature ranges to prevent overheating, mitigate damage, and extend battery lifespan. Temperature imbalances within battery packs can lead to irregular cell performance, reducing efficiency. Traditional cooling methods—air, liquid, or phase-change material cooling—have been effective but for SSBs, a newer approach is emerging: thermoelectric coolers (TECs). TECs, based on the Peltier effect, have been widely used in aerospace, military, industrial instruments, and commercial products. They are also utilized for climate control in EVs and hybrid vehicles (HVs) [107]. TEC systems offer precise temperature control by adjusting input current, allowing efficient regulation of surface temperatures. This technology offers several advantages over conventional BTMS solutions, such as no moving parts, compact size and lightweight design, maintenance-free operation, silent and electrically stable performance, dual functionality to heat and cool including temperature cycling, wide operating temperature range, highly accurate temperature control, functionality in any orientation including zero gravity and high G-forces, environmentally friendly design, and the capability to cool to very low temperatures (as low as −80 °C) [108]. In consumer electronics, TECs are already utilized in devices such as laser diodes, blood analyzers, CCD cameras, microprocessors, car seat climate control systems, and portable coolers.

The development of SSLIBs for EVs holds tremendous promise, offering faster charging and discharging, longer lifespans, higher energy density, lower costs, and improved safety. One of the key advantages of SSBs is their replacement of flammable liquid electrolytes with solid electrolytes, significantly reducing safety risks. This innovation has attracted automakers seeking to enhance both performance and safety [109]. Additionally, sensitivity analyses indicate that large-scale production of SSBs can significantly reduce environmental impacts. Key factors include reducing the energy required for manufacturing and minimizing the thickness of the ion-selective electrolyte (ISE) layers, which further enhances production efficiency [110].

7.2. Market Trends and Industry Adoption

Recent market analyses have identified significant momentum in the adoption of ASSBs. To better understand this trend, Google searches were conducted using specific keywords and relevant countries to gather the latest information on entities involved in ASSB activities. Drawing from corporate websites, scientific publications, marketing reports, and media coverage, researchers compiled a comprehensive list of 93 companies and institutions actively contributing to the development of the global ASSB market [111]. By exploring expert insights, market trends, and pricing scenarios, it becomes evident how emerging technologies like ASSBs are poised to disrupt the market, driving long-term cost reductions and reshaping the trajectory of LIB pricing. These findings represent a significant methodological advancement in technology forecasting [112]. Advancements in battery technology are crucial for supporting the growth of the EV market. Projections estimate an installed base of 100 million EVs by 2028. James Hodgson, a principal analyst at ABI Research, highlights lithium–silicon and solid-state batteries as the future of EV technology. These advancements promise enhanced performance, higher energy density, extended lifespans, and reduced costs. Even the integration of silicon anodes alone is projected to significantly impact the market, with the installed EV base expected to grow from 8 million in 2019 to 40 million by 2025, alleviating concerns about the driving range [109].

One pressing challenge in the industry is the sustainable recycling of batteries. As ASSBs gain traction, innovative recycling approaches are essential. Current research into fabrication techniques for ASSBs and LIB regeneration has introduced promising concepts that can be adapted for ASSB recycling. A hybrid approach, combining hydrometallurgical processes with direct recycling methods, shows significant potential. This strategy addresses chemical stability issues, ensures safe processing, and offers an effective pathway for recycling next-generation batteries [20].

7.3. Policy and Economic Impacts on Adoption

The adoption of SSBs is closely tied to advancements in recycling and reuse strategies, particularly as the industry confronts challenges posed by economic and technological barriers. Established recycling methods, including mechanical, pyrometallurgical, and hydrometallurgical processes, are being re-evaluated alongside emerging technologies designed to overcome these obstacles. These efforts aim to enhance the sustainability and economic viability of battery recycling systems [113]. ASSBs with solid oxide electrolytes are increasingly recognized for their potential to deliver safer, high-energy-density solutions for the future. A detailed cost analysis of manufacturing oxide-based ASSBs has been conducted, leveraging insights from technologies employed in solid oxide fuel cells (SOFCs) and multi-layer ceramic capacitors (MLCCs) [114]. This cross-industry assessment underscores the importance of drawing from established manufacturing techniques to optimize costs for next-generation batteries [115].

7.4. Future Research Directions

As global energy consumption rises and environmental pollution intensifies, the demand for renewable, efficient, and reliable energy solutions has become paramount. To address these challenges, advanced energy storage systems are essential for capturing energy and delivering electricity during peak usage periods. SSLIBs represent a transformative step in this evolution, offering significant advantages over traditional LIBs, including enhanced safety, higher energy density, and superior resistance to extreme conditions such as high pressure and low temperatures [116]. The transition from conventional LIBs to ASSBs reflects a collective effort by industry stakeholders to push the boundaries of energy storage technology. This progression is expected to yield substantial improvements in related sectors, such as EVs and sophisticated electronic devices. However, realizing the full potential of ASSBs will require overcoming key obstacles, including scaling production and achieving the economic feasibility of these cutting-edge designs.

The demand for high-performance energy storage solutions is particularly urgent for applications in extreme environments, such as deep-sea conditions where high pressure and low temperatures prevail. Lithium batteries are already employed in powering marine scientific instruments but future developments must focus on enhancing performance and safety under such conditions. Composite solid electrolytes (CSEs)—which integrate the strength and conductivity of solid inorganic electrolytes (SIEs) with the processability of solid polymer electrolytes (SPEs)—emerge as promising candidates for next-generation solid electrolytes [116].

Future advancements will likely be driven by the integration of material genome engineering and machine learning (ML). Combining experimental validation with computational models will accelerate material screening and design processes, enabling the discovery of novel materials for anodes, cathodes, and electrolytes. Additionally, the development of supplementary components or interfacial layers at the electrode–electrolyte junctions will be critical to optimizing performance and addressing challenges such as interfacial stability and ion transport.

8. Conclusions

The development and adoption of SSLIBs represent a pivotal advancement in energy storage technology, driven by the growing demand for safer, more efficient, and environmentally friendly solutions. SSBs offer significant advantages over traditional LIBs, including improved energy density, enhanced safety, and better performance under extreme conditions. These features make them highly promising for applications in EVs, consumer electronics, and specialized environments such as deep-sea and aerospace settings. However, the transition to ASSB technology is not without challenges. Scaling up production, ensuring economic feasibility, and optimizing material performance are critical hurdles that need to be addressed. The integration of advanced manufacturing techniques, material genome engineering, and machine learning will play a crucial role in overcoming these barriers, enabling the discovery of novel materials and improving interfacial stability and ion conductivity. The global market trends indicate a strong push toward adopting ASSBs, with significant investments in research, development, and infrastructure. Recycling and reuse strategies, along with innovations in battery manufacturing processes, are essential to support the sustainability and scalability of this technology. Policy frameworks and economic incentives will further facilitate the widespread adoption of SSBs, ensuring alignment with global environmental goals and energy demands. Thus, SSLIBs have the potential to revolutionize energy storage systems across various sectors, paving the way for a more sustainable and efficient future. Continued collaboration among researchers, industry stakeholders, and policymakers will be essential to realize the full potential of this transformative technology.

Conflicts of Interest

The authors declare no conflict of interest.

Footnotes

Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Figures and Tables

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Figure 1. Key stability challenges in SSBs. Reproduced from [14], open access, MDPI, 2024.

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Figure 2. Enhancement strategies for all-solid-state lithium batteries. Reproduced with permission from [15].

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Figure 3. SSB vs. LIB: structural comparison.

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Figure 4. Different outcomes to different safety scenarios within the battery. Adapted from [83].

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Figure 5. Electrode buffer and sacrificial layers. Reproduced with permission from [98].

Table 1

Comparison between lithium-ion and solid-state batteries [6,7,8,9].

Feature	Lithium-Ion Battery	Solid-State Battery
Energy density	~150–250 Wh/kg	~300–500 Wh/kg (higher theoretical potential)
Cycle life	500–2000 cycles	1000–5000 cycles (depends on material choice)
Safety	Lower (flammable liquid electrolyte)	Higher (non-flammable solid electrolyte)
Charging	Moderate charging rates (limited by liquid electrolyte diffusion)	Faster charging due to higher ion conductivity in solid electrolytes
Thermal stability	Moderate (risk of thermal runaway)	High (resistant to overheating)
Cost	Lower (mature production and supply chain)	higher (due to materials and processing)

Table 2

Conventional lithium-ion vs. ASSB pack build [20].

Conventional Lithium-Ion Battery	All-Solid-State BatteryYe
Material Component
Current collector Porous anode Porous separator Porous cathode	Bipolar current collector Dense lithium anode Dense solid electrolyte Dense cathode composite
Build Phases
1. Galvanic cell
Parallel stacking Welding joints for current collectors	Serial stacking Dense packaging
2. Cell stack
Serial connection Cooling system	Parallel connection No cooling system
3. Battery pack
[Image omitted. Please see PDF.]	[Image omitted. Please see PDF.]

Table 3

Common solid-state electrolytes by type [24].

Ceramic Electrolytes	Polymer Electrolytes
NASICON (Sodium superionic conductor)	Poly(ethylene oxide)
LISICON (Lithium superionic conductor)	Polyvinylidene fluoride
Garnet	Polyacrylonitrile
Perovskite	Poly(methyl methacrylate)
Li3N	Poly(ethyl methacrylate)
LiPON	Poly(acrylic acid)
Thio-LISICON	Polyvinyl chloride
Argyrodite	Poly(propylene oxide)
Sulfide glass–ceramic	Poly(caprolactone)
Anti-perovskite	Poly(trimethylene carbonate)
Li halide	Polypropylene carbonate
Other oxides	Polyethylene carbonate
Other sulfides	Poly(ethylene glycol)
	Poly(1,3-dioxolane)

Table 4

Materials for cathodes and anodes with advantages and disadvantages.

Electrode	Material	Advantages	Disadvantages	Reference
Cathode	Multi-metal oxide	High energy density, long-lasting, traditional material	Sustainability issues, expensive, dangerous mining	[40]
	Organic cathode	Natural abundance, cost-effective, suitable for SSEs	Reduced energy density	[40,41]
Anode	Graphite	High power density	Low specific capacity	[46]
	Lithium	High energy density, requires only a thin plate	Dendrite growth, high cost	[42,46]
	Silicon	Very high theoretical energy density	Interfacial compatibility issues	[42]
	Anode-free	Cost-effective, simplified production, ideal for SSEs	Rapid capacity degradation	[46]

Table 5

Battery degradation mechanisms and their outcomes.

Degradation Type	Outcome	Reference
1. Mechanical stress	Cracking of electrodes, which can compromise structural integrity and reduce battery capacity.	[84]
2. Phase changes	Disordering of electrode materials, leading to reduced efficiency and capacity loss.	[85]
3. Lithium creep (caused by elevated temperatures)	Volume changes resulting in internal deformation and potential short circuits.	[85]
4. Interfacial decomposition (between electrodes and electrolytes)	Electrochemical changes due to temperature variations, degrading performance and stability.	[86]
5. Gas generation (from electrode deterioration)	Release of gases (e.g., hydrogen, carbon monoxide), causing pressure buildup and safety risks.	[87]

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