Boosting initial coulombic efficiency in cobalt-free Li-rich layered oxides via facile gas–solid interface modification

Abstract

Cobalt-free lithium-rich layered oxide cathode materials (Co-free LRLOs), while offering advantages such as high energy density and environmental friendliness, are constrained by challenges including unstable anionic redox processes, irreversible oxygen release, severe structural degradation, and low initial coulombic efficiency (ICE). This study proposes a method for simultaneously achieving surface Nb⁵⁺ doping and a surface spinel phase construction in Co-free LRLOs by modifying the gas–solid interface through the thermal decomposition of ammonium niobium oxalate. The surface spinel phase and Nb⁵⁺ doping synergistically suppress side reactions and enhance Li⁺ diffusion. The optimized Co-free LRLO delivers an ICE of 100.4% with a capacity of 306 mA h g⁻¹ at 0.1C. Furthermore, at the ultra-low temperature of −20 °C, the cell exhibits high cycling stability combined with a discharge capacity of 111 mA h g⁻¹ at 0.33C. This work presents a scalable strategy under mild conditions to overcome ICE limitations in Co-free LRLOs, providing promising pathways for practical high-performance Mn-based cathodes.