Effect of calcination temperature on interlayer spacing and oxygen vacancies concentration of NaCu0.2Fe0.3Mn0.5O2 layered materials for sodium-ion batteries

• Higher calcination temperatures expand Na layer spacing, enhancing Na⁺ diffusion kinetics and rate performance. • Elevated calcination temperatures reduce oxygen vacancies, improving crystallinity and cyclic stability. • Optimized NCFM delivers an initial discharge capacity of 143.3 mA·h/g at 0.1C and retains 79.28% after 100 cycles at 1C. • Calcination temperature control is a key strategy for tuning interlayer spacing and oxygen vacancies in layered oxide cathodes.