Mitigating Jahn–Teller Effect of Mn-Based Layered Oxide Cathodes for Sodium-Ion Batteries by Regulation of Coordination Chemistry
Lingyun Li, Ming‐Yuan Shen, Jingsong Wang, Tao Wu, Wen‐Cui Li
Abstract
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, MnO 6 octahedra centered around Mn 3+ 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 Na 0.8 Li 0.17 Mg 0.18 Mn 0.66 O 2 (LMM) cathode. The as-synthesized cathode material, Na 0.8 Li 0.17 Ca 0.025 Mg 0.12 Ni 0.05 Mn 0.66 O 2 (LMCNM), conforms to the standard P 63/ 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 Mn 3+ to Mn 4+ . Furthermore, partial reversible anionic redox has been achieved through codoping with Ca and Ni to harmonize expressive stability and high capacity.