P2-Type Cathodes Enabled by Oxygen Vacancies and Lattice Stabilization for High-Rate and Low-Temperature Performance

Abstract

Layered transition-metal oxides are promising cathodes for sodium-ion batteries, but their performance is often complicated by oxygen vacancy (OV) formation and management. Intrinsic OVs, induced by external factors such as doping, play a pivotal role in regulating their physicochemical properties. However, precisely how these OVs can be strategically leveraged to concurrently optimize both the kinetics and structural stability remains a key challenge. In this work, a synergistic strategy combining the construction of a Na-rich P2 structure with Mg/Ti co-doping is proposed to synthesize Na0.8Mg0.05Ni0.25Mn0.65Ti0.05O2 (NMNMTO-1). Experimental and theoretical results suggest that Mg/Ti co-doping is associated with intrinsic OV-related local configurations through coupled charge compensation, which, together with the expanded Na-layer spacing, lowers the Na+ migration barrier. Meanwhile, Mg/Ti-assisted lattice stabilization increases the oxygen-vacancy formation energy, helping reinforce the oxygen framework and mitigate irreversible oxygen loss and unfavorable P2-O2 transition. This dual-regulation mechanism promotes reversible P2-OP4 structural evolution during cycling. The NMNMTO-1 cathode delivers enhanced electrochemical performance, retaining 110 mAh g–1 at 10 C and 87.3% capacity after 100 cycles at 2 C, while also showing improved sodium-storage performance at –25 °C.