Exploring the synthesis conditions and formation mechanisms of Li-rich layered oxides via solid-state method

Abstract

Li- and Mn-rich layered oxides are receiving considerable attentions for the next-generation commercial lithium ion batteries owing to their high capacity and low cost. However, there is still some dispute about the ideal synthesis protocol to obtain the optimum electrochemical performances. Herein, we deeply explore the decomposition/lithiation mechanisms of sodium-contained Ni1/6Co1/6Mn4/6CO3 precursor (NCM-P) during calcination process, and highlight the effects of heat treatment temperature and the lithium to NCM-P molar ratio (Li/TM) on Li- and Mn-rich layered oxides. The results demonstrate that Ni1/6Co1/6Mn4/6CO3 can be initially lithiated to LiNi1/6Co1/6Mn4/6O2, then gradually lithiated/decomposed to 0.1/6Li4Mn5O12·2.5/6Li2MnO3·0.5LiNi1/3Co1/3Mn1/3O2 material. The cathode crystal crystallization and the components are significantly affected by heat treatment temperature and the Li/TM ratios. The optimized synthetic conditions for Li- and Mn-rich cathode materials is in 500 °C for 4 h, 750 °C for 4 h, and 840 °C for 10 h under Li/TM = 1.4. Under this condition, the synthesized Li- and Mn-rich oxides can deliver a first discharge capacity of 259.4 mAh·g−1 at 25 mA g−1 with 84.00% coulombic efficiency, and 218.2 mAh·g−1 at 250 mA g−1 with 90.97% capacity retention after 100 cycles. This study would give some guidance for the synthesis of Li-rich layered oxides.