Enhancing the air stability of LiNi0.6Co0.2Mn0.2O2 cathode through WO3/Li2WO4 surface modification

High-nickel cathode materials are widely applied in the field of electric vehicles because of their superior energy density. However, given their increased Ni content, these materials are susceptible to poor air stability and serious residual lithium growth. In this study, an Li2WO4/WO3 coating layer is first constructed on the surface of LiNi0.6Co0.2Mn0.2O2 (NCM622), and then the air stability of pristine and W-coated NCM622 is investigated. After being exposed to the air with a relative humidity of 80% for 7 days, the initial discharge capacity deterioration of NCM622 at 0.2 C decreases from 3.57% to 0.46% due to W coating. Furthermore, the discharge capacity of pristine NCM622 at 5 C over 3.0–4.5 V after air exposure decreases from 145.7 to 130.9 mAh g−1, while the 1% W-modified NCM622 maintains an excellent discharge capacity of about 155 mAh g−1. The significantly improved air stability is not only because of the physical barrier effect of the surface coating, but also because WO3 in the composite spontaneously reacts with LiOH during air exposure to form a thicker lithium-ion conductor, the Li2WO4 layer. These results provide a relevant basis for the selection of coating species in improving the storage stability of high-nickel cathode materials.