Regulation on electrochemical performance of LiNi0.5Mn1.5O4 cathode material via lithium silicate coating with different Li/Si ratio

Abstract

Surface coating is regarded as an effective means to alleviate the rapid capacity fading of LiNi0.5Mn1.5O4 material. Lithium silicate, as an ideal coating material, combines the advantages of high ionic conductivity, chemical inertness, and HF capture. Considering the influence of Li/Si ratios on Li+ ions diffusion in lithium silicate, the effects of different Li/Si lithium silicate coatings on the structural and electrochemical performance of LiNi0.5Mn1.5O4 material are investigated. The results show that lithium silicate coatings increase the cation disordering degree, improve the crystallinity, stabilize the electrode/electrolyte interface, and improve Li+ diffusion kinetics. Li/Si ratio greatly affects the composition of lithium silicate coating, which changes from Li2Si2O5 + Li2SiO3 (1:1), Li2Si2O5 + Li4SiO4 (2:1, 3:1) to pure Li4SiO4 phase (4:1). First principles calculation manifests that Li+ migration energy barriers decrease with the increase of Li/Si ratio in lithium silicate. At Li/Si = 4:1, the coated sample shows the best electrochemical performance, with specific discharge capacity of 126.7 mAh g−1 at 10 C rate and capacity retention rate of 91.25% after 200 cycles at 1 C rate. The composition of lithium silicate coating can be controlled by changing Li/Si ratio, which in turn regulates the electrochemical performance of LiNi0.5Mn1.5O4 material.