Copper-Stabilized P′2-Type Layered Manganese Oxide Cathodes for High-Performance Sodium-Ion Batteries

Layered sodium manganese oxides are promising low-cost and high-capacity cathode materials for commercialization of sodium-ion batteries (SIBs). P′2-type Na0.67MnO2 with an orthorhombic structure has been considered as a significant candidate for SIBs. However, the Jahn–Teller distortion and undesired phase transitions will lead to poor structural stability and unsatisfactory cycling performance. Herein, a systematic investigation on partially copper-doped P′2-type Na0.67Cu x Mn1–x O2 (x = 0, 0.05, 0.1, and 0.2) series as cathodes for SIBs reveals the relationship between doping concentrations and Na storage properties. With proper copper content, P′2 Na0.67Cu0.1Mn0.9O2 exhibits a suppressed Jahn–Teller effect as well as relatively less phase transitions, which can deliver a high specific capacity of 222.7 mA h g–1 at 10 mA g–1 within 1.5–4.2 V, with a capacity retention of 76% at 1 A g–1 after 300 cycles. The electrochemical mechanism is systematically investigated via in situ X-ray diffraction observations and density functional theory calculations, which provide fundamental guidelines for developing high-performance cathodes for SIBs.