P2 ‐type Na x TmO 2 oxides as cathodes for non‐aqueous sodium‐ion batteries—Structural evolution and commercial prospects

First-generation sodium-ion batteries (SIBs) are commercially launched by Faradion Ltd., UK, and HiNa Battery Technology Company Ltd., China, utilizing the transition metal oxide-based cathodes. Currently, the commercial Faradion cells deliver ~1000 cycles at an energy density of ~140 to 150 Wh kg−1, whereas HiNa SIB cells deliver ~120 Wh kg−1. P2-type, O3-type, and composite P-O and P-P type transition metal oxide cathodes have generated much interest in the last few years. P2-type layered oxides are critical as cathodes in achieving higher energy and power density in SIB technology, along with better C-rate capabilities. Compared to their O3-type counterparts, P2-type layered transition metal oxides encounter lower activation energy barriers, enabling improved rate kinetics. However, P2-type cathodes often face poor cycle stability due to undesirable phase changes during charge-discharge cycles and structural instability to air and moisture. This review evaluates all the P2-type layered oxide compounds as SIB cathodes, highlighting the strategies followed to meet the challenges and offers aspects of their successful commercialization.