Enabling High-Voltage and Long Lifespan Sodium Batteries via Single-Crystal Layer-Structured Oxide Cathode Material

Abstract

Manganese-based layer-structured transition metal oxides are considered promising cathode materials for future sodium batteries owing to their high energy density potential and industrial feasibility. The grain-related anisotropy and electrode/electrolyte side reactions, however, constrain their energy density and cycling lifespan, particularly at high voltages. Large-sized single-crystal O3-typed Na[Ni_0.3Mn_0.5Cu_0.1Ti_0.1]O₂ was thus designed and successfully synthesized toward high-voltage and long-lifespan sodium batteries. The grain-boundary-free single-crystal structure and unidirectional Na⁺ diffusion channels enable a faster Na⁺ diffusion rate and high electronic conductivity. Meanwhile, the large-area exposed (003) crystal plane can not only exhibit a higher energy barrier for electrode–electrolyte side reactions but also alleviate the interlayer sliding and structural collapse during charge–discharge processes. The lattice oxygen in contact with the electrolyte was stabilized, and the TMO₆ octahedral structure integrity was maintained as well. A high specific capacity of 160.1 mAh g^–1 at a current density of 0.1 C was demonstrated. Coupled with hard carbon as the anode, the full cell can also demonstrate an excellent capacity and cycling stability, achieving a high specific capacity of 141.1 mAh g^–1 at 0.1 C. After 100 cycles at 2 C, the capacity retention rate is 97.3%.