Jahn‐Teller Effect in Sodium Layered Oxide Cathodes: Inducement Mechanisms, Mitigation Strategies, and Rational Utilizations

Abstract The sodium‐layered transition metal oxides (Na_xTMO₂) are regarded as the promising cathode for sodium‐ion batteries (SIBs) relying on their high theory capacity and cost‐effectiveness. Nevertheless, the intrinsic lattice distortions caused by Jahn‐Teller active ions significantly degrade the structural stability of Na_xTMO₂, generally resulting in unsatisfactory electrochemical properties. In this review, begins by introducing the inducement mechanisms of Jahn‐Teller effect for the transition metal (TM) ions. Subsequently, the restraining strategies as well as corresponding mechanisms for Jahn‐Teller effect by using element doping/substitutions, surface reconstructions, polyphase symbiosis, as well as TM/oxygen/Na⁺ vacancy manipulations are summarized in detail. Specifically, the influences of such mitigation strategies for Jahn‐Teller deformation on the electrochemical properties, phase evolution behaviors, TM dissolution characteristics, and crystal lattice stability of Na_xTMO₂ are comprehensively discussed. Furthermore, the sensible utilization of Jahn‐Teller distortion is summarized to build Na_xTMO₂ cathodes with high capacity and/or repaid ion transport kinetics as well. In the end, the challenges faced by amelioration methods are overviewed and put forward corresponding research directions in the future to trenchantly constrain the TMO₆ octahedron Jahn‐Teller deformation. This work will provide more perceptions for further studies of Na_xTMO₂ cathodes in SIBs.