Improved cycling performance of high capacity spinel cathode material for Li-ion batteries

Abstract

In the face of growing clean energy needs and strengthened environmental regulations, Lithium ion batteries (LIBs) are spotlighted as the sustainable energy alternatives. Recently, with growing interest in electric vehicles and energy storage systems, large scale batteries are focused. For these large scale applications of LIBs, many researchers have attempted to develop the cathode material with high thermal stability, excellent cycling retention, low cost, high power and energy density. The mostly used cathode materials in the early commercialized EVs are the low portion of Ni-rich layered and the high portion of cation-doped spinel material composite. The reason why the spinel is more proper is that it has many advantages of low cost, abundance, nontoxicity and good thermal stability, which is suitable for requirement of EVs. However, it also has serious problem of manganese dissolution in elevated temperatures. Thus, the portion of Ni-rich layered material (170 mAh g-1) is raised to increase driving range recently. However, the changing composition of cathode materials causes increasing battery cost resulting in the hindrance of widely commercializing EVs because the price of Ni-rich materials is approximately 3 times higher than that of spinel material. Therefore, the spinel cathode material toward high stability and capacity (>120 mAh g-1) should be developed. In this paper, we tried to develop high capacity and high stability spinel material for EVs. We synthesized Al doped spinel as bare and optimized it for the best cycling performance. The discharge capacity of this optimized bare was 125.4mAhg-1 and the cycling retention after 100cycles at 60 oC was 82.2% of its initial capacity. And then we proceed with coating and doping simultaneously. The coating layer can protect the surface of bare from being directly exposed to the HF in electrolyte and suppress the dissolution of Mn ions. Also fluorine is doped into vacant oxygen site on the surface for structural stability. Accordingly, the cycle performance at elevated temperature is significantly improved. This coated LiMn2O4 exhibited a discharge capacity of 120.1 mAh g-1 and retained 94% of its initial capacity at 60℃ after 100 cycles.