Lithiated Prussian blue analogues as positive electrode active materials for stable non-aqueous lithium-ion batteries

Abstract

Prussian blue analogues (PBAs) are appealing active materials for post-lithium electrochemical energy storage. However, PBAs are not generally suitable for non-aqueous Li-ion storage due to their instability upon prolonged cycling. Herein, we assess the feasibility of PBAs with various lithium content for non-aqueous Li-ion storage. We determine the crystal structure of the lithiated PBAs via neutron powder diffraction measurements and investigate the influence of water on structural stability and Li-ion migration through operando X-ray diffraction measurements and bond valence simulations. Furthermore, we demonstrate that a positive electrode containing Li_2-xFeFe(CN)₆⋅nH₂O (0 ≤ x ≤ 2) active material coupled with a Li metal electrode and a LiPF₆-containing organic-based electrolyte in coin cell configuration delivers an initial discharge capacity of 142 mAh g⁻¹ at 19 mA g⁻¹ and a discharge capacity retention of 80.7% after 1000 cycles at 1.9 A g⁻¹. By replacing the lithium metal with a graphite-based negative electrode, we also report a coin cell capable of cycling for more than 370 cycles at 190 mA g⁻¹ with a stable discharge capacity of about 105 mAh g⁻¹ and a discharge capacity retention of 98% at 25 °C.

Prussian blue analogues (PBAs) are appealing materials for aqueous Na- and K- ion batteries but are limited for non-aqueous Li-ion storage. Here, the authors report the synthesis of various lithiated PBAs and discuss critical factors for improving the non-aqueous electrochemical storage of Li ions.