Silver Vanadium Bronze, Beta-Ag0.33v2o5: Crystal-Water-Free High-Capacity Cathode Material For Rechargeable Ca-Ion Batteries

Calcium-ion batteries (CIBs) are getting increasing attention as post-lithium-ion batteries owing to their theoretical and potential advantages in terms of energy density and cost-effectiveness. However, most of the reported cathode materials suffer from low capacity or cyclability in dried nonaqueous electrolytes. So far, all of the materials with high capacity (>100 mA h g(-1)) contain crystal water, which was considered to be crucial to the structural stability, enabling facile Ca diffusion. Here, we report beta-Ag0.33V2O5 as a high-capacity cathode material for CIBs without crystal water. After the initial activation process, the material exhibited a capacity of 179 mA h g(-1) at approximately 2.8 V (vs. Ca2+/Ca) in the ninth cycle and showed a modest cycling performance. The capacity is the highest among the Ca cathode materials without crystal water reported to date. We revealed that the activation process was caused by a replacement reaction between the silver and calcium ions. This material demonstrates that crystal water is not an essential component of CIB electrode materials for a high capacity, stimulating the ongoing research for developing higher-performance materials.