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The materials used in the construction of a battery's components must be chosen carefully to optimize battery performance for the specific application.
The lithium-ion battery is an incredibly complex batch reactor, with solids, liquids, and gases reacting in a system that combines organic and inorganic chemistry, heterogeneous catalysis, and electronic physics. Yet, despite its complexity, this reactor is expected to cycle reversibly hundreds or perhaps thousands of times.
It is important to recognize that the lithium-ion battery is a system, where all components and interactions between components affect the performance of the battery, and in turn the performance of the device it powers. The materials used in the construction of the battery's components vary significantly by application. And these materials must be carefully chosen to ensure that the characteristics of the operating battery are consistent with the expectations of the user. Table 1 summarizes the most common materials for the battery's main components - the cathode, anode, electrolyte, and separator.
Because lithium-ion batteries are used across a wide range of applications, cell manufacturers must choose materials that perform best on the metrics that are most important for the application. The key attributes that must be considered regardless of the application are: energy density, power density, safety, lifetime, and cost. Figure 1 shows the impacts of material choices on these metrics.
The energy density of the battery governs the amount of electricity that can be delivered by a battery of a specific size. For automotive applications, more energy allows the vehicle to go farther on a single charge. In general, the cathode has a large effect on energy density because the choice of cathode material determines the capacity (lithium content) of the battery and contributes to the operating voltage.
Power density refers to the rate at which the battery delivers current. As a battery discharges during use, lithium ions move out of the anode into the electrolyte, across the separator, and back into the cathode at the opposite terminal. The rate at which these processes occur throttles the power of the cell. As a result, the electrolyte materials and the electrode (anode and cathode) materials are all important choices when tuning the power of the battery design.
Many components influence battery lifetime, some dramatically. This...