Designing ultrastable P2/O3-type layered oxides for sodium ion batteries by regulating Na distribution and oxygen redox chemistry

Abstract

P2/O3-type Ni/Mn-based layered oxides are promising cathode materials for sodium-ion batteries (SIBs) owing to their high energy density. However, exploring effective ways to enhance the synergy between the P2 and O3 phases remains a necessity. Herein, we design a P2/O3-type Na0.76Ni0.31Zn0.07Mn0.50Ti0.12O2 (NNZMT) with high chemical/electrochemical stability by enhancing the coupling between the two phases. For the first time, a unique Na+ extraction is observed from a Na-rich O3 phase by a Na-poor P2 phase and systematically investigated. This process is facilitated by Zn2+/Ti4+ dual doping and calcination condition regulation, allowing a higher Na+ content in the P2 phase with larger Na+ transport channels and enhancing Na+ transport kinetics. Because of reduced Na+ in the O3 phase, which increases the difficulty of H+/Na+ exchange, the hydrostability of the O3 phase in NNZMT is considerably improved. Furthermore, Zn2+/Ti4+ presence in NNZMT synergistically regulates oxygen redox chemistry, which effectively suppresses O2/CO2 gas release and electrolyte decomposition, and completely inhibits phase transitions above 4.0 V. As a result, NNZMT achieves a high discharge capacity of 144.8 mA h g−1 with a median voltage of 3.42 V at 20 mA g−1 and exhibits excellent cycling performance with a capacity retention of 77.3% for 1000 cycles at 2000 mA g−1. This study provides an effective strategy and new insights into the design of high-performance layered-oxide cathode materials with enhanced structure/interface stability for SIBs.