Insight into the microscopic morphology and electrochemical performance correlation mechanism upon calcination at different temperatures of a novel spherical cobalt-free 0.6Li2MnO3·0.4Li[Fe1/3Ni1/3Mn1/3]O2 cathode

Abstract

The performance of a cathode depends on its microscopic morphology and crystal structure, which are usually affected by the calcination temperature. Herein, we systematically studied the effect of calcination temperature on a novel spherical cobalt-free 0.6Li₂MnO₃·0.4Li[Fe_1/3Ni_1/3Mn_1/3]O₂ (LFNMO) cathode on the three scales of particles, crystal grains and unit cells. The results show that the LFNMO prepared at 850 °C exhibits the highest tap density (2.11 g cm⁻³), the largest I₍₀₀₃₎/I₍₁₀₄₎ (1.3175) and c/a (4.9881) ratios, and the most well-developed layered structure with the least lithium/transition metal (Li/TM) cation mixing. The LFNMO prepared at a lower calcination temperature (800 °C) exhibits low crystallinity, an unbalanced phase ratio, and the poorest layered structure with serious Li/TM cation mixing. The higher temperature (900 °C) causes the overgrowth of primary particles, leading to the growth of ion transport paths and a poorer layered structure with more Li/TM cation mixing, which shows low discharge specific capacity and poor rate capability. The LFNMO cathode prepared at 850 °C shows the best electrochemical performance and exhibits a discharge specific capacity of 213 mA h g⁻¹ at C/10, and the capacity retention rate is 88.3% after 200 cycles. The findings highlight the importance of calcination temperature for the preparation and development of cobalt-free lithium-rich manganese-based cathode materials.