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.