Mitigating Jahn–Teller Effect of Mn-Based Layered Oxide Cathodes for Sodium-Ion Batteries by Regulation of Coordination Chemistry

P2-type Mn-based layered oxide cathode materials are competitive candidates for sodium-ion batteries (SIBs), which are expected to be widely used in large-scale electrochemical energy storage applications due to their easy availability. However, MnO6 octahedra centered around Mn3+ are inclined to adverse phase transitions and lattice oxygen loss under high operating voltages, which markedly compromise the capacity and cycling stability. Here, a configurational entropy tuning strategy was proposed to optimize the P2-type Na0.8Li0.17Mg0.18Mn0.66O2 (LMM) cathode. The as-synthesized cathode material, Na0.8Li0.17Ca0.025Mg0.12Ni0.05Mn0.66O2 (LMCNM), conforms to the standard P63/mmc crystal phase. Impressively, this material exhibits a capacity retention rate of 92% after 100 cycles at a 0.4C rate (where 1C = 125 mA h g-1) and demonstrates minimal volume change (0.94%) during charge-discharge cycles at higher working voltages (2.0-4.3 V). In situ X-ray powder diffraction (XRD), ex situ X-ray photoelectron spectroscopy (XPS), and computational analyses collectively indicate that through the charging and discharging processes of LMCNM, there is no obvious Jahn-Teller distortion, while there is clear evidence for charge compensation from Mn3+ to Mn4+. Furthermore, partial reversible anionic redox has been achieved through codoping with Ca and Ni to harmonize expressive stability and high capacity.