Functional Surface Coating to Enhance the Stability of LiNi_0.6Mn_0.2Co_0.2O₂

Parasitic reactions are responsible for continuous performance loss during the normal operation and storage of lithium-ion batteries, particularly for those using nickel-rich cathode materials. Among many contributors, residual Li2CO3 on the surface of nickel-rich cathodes plays a detrimental role in promoting parasitic reactions, and hence accelerates the performance loss of those cathode materials. In this work, a wet impregnation process was utilized to convert the detrimental Li2CO3 and LiOH impurities into a beneficial functional surface coating comprising phosphates. Specifically, hydro-phosphates were used as the functional surface modification agents to mitigate the detrimental effect of surface residuals. The best electrochemical performance was achieved by modifying LiNi0.6Mn0.2Co0.2O2 with a diluted dihydro-phosphate solution (pKa = 7.2), while the metal cation had a negligible impact on the electrochemical performance. This work provides a cheap and simple method for enabling the high performance of nickel-rich cathodes.