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%.