Engineering Thermal Stability of Binary Manganese-Based Layered Oxide Cathodes Toward Advanced Sodium-Ion Batteries

The thermal stability is vital for layered oxide cathodes to boost the operation safety of rechargeable batteries, in particular, the highly enriched transition metal Na-based layered oxides for sodium-ion batteries (SIBs). Transition metals significantly influence catalysis, chemical/electrochemical reactions with electrolytes, yet the catalysis capability of different transition metals remains unclear. Here, the thermal stability of three types of binary manganese-based layered oxides (Na_0.78TM_0.33Mn_0.67O₂, TM = Cu, Ni, and Fe) is revealed. The CuMn-based layered oxide has the minimum catalytic effect on electrolyte decomposition when charged to high voltages, delivering a good thermal stability, as revealed by combining density function theoretic calculations, thermogravimetry, and differential scanning calorimetry measurements. Further promotion of thermal stability and electrochemical performance is performed by MgTi co-doping to suppress irreversible phase transition and enhance superior Na⁺ diffusion kinetics. Consequently, the highest onset temperature (269.5 °C) and the lowest heat generation (106.8 J g^-1) are achieved for the MgTi co-doped cathode, as well as the remarkable capacity retention of 91.7% upon 500 cycles at 1C. The results provide a new insight into constructing high-efficiency layered oxide cathode materials for SIBs.