Enhanced cycle performance and air stability in Ti‐doped P2‐type layered oxide enabled by crystal structure modification and Jahn–Teller effect tailoring

Abstract Layered oxide cathode materials have attracted significant attention due to their high energy density. However, their practical commercialization in sodium‐ion batteries has been hindered by drawbacks such as poor air stability and cycle performance. Herein, we present a simple strategy to address these obstacles through Ti doping. Interestingly, Ti doping can increase the Na layer spacing while decreasing the transition metal layer spacing. The modified interlayer space ensures a greater Na + diffusion coefficient and improved rate performance. Moreover, the high‐spin Mn 3+ content decreases after Ti doping, which mitigates the Jahn–Teller effect and improves structural stability. As a result, the Na 0.55 Ni 0.1 Fe 0.1 Mn 0.65 Ti 0.15 O 2 cathode material delivers a capacity retention of 77.11% after 150 cycles at 1C, which is much higher than 55.02% of Na 0.55 Ni 0.1 Fe 0.1 Mn 0.8 O 2 . Meanwhile, the air stability evaluation reveals that carbon dioxide and water promote the formation of the hydrate phase. Ti doping can inhibit the exchange of H + and Na + , as well as the formation of residual sodium species. Furthermore, the electrochemical performance deterioration caused by the water will be alleviated. These findings provide valuable insight into the development of layered oxide cathode materials with needed cycling performance and air stability for the commercialization of SIBs.