Improving the Electrochemical Performance and Structural Stability of the LiNi_0.8Co_0.15Al_0.05O₂ Cathode Material at High-Voltage Charging through Ti Substitution

LiNi_0.8Co_0.15Al_0.05O₂ (NCA) has been proven to be a good cathode material for lithium-ion batteries (LIBs), especially in electric vehicle applications. However, further elevating energy density of NCA is very challenging. Increasing the charging voltage of NCA is an effective method, but its structural instability remains a problem. In this work, we revealed that titanium substitution could improve cycle stability of NCA under high cutoff voltage significantly. Titanium ions with a relatively larger ion radius could modify the oxygen lattice and change the local coordination environment of NCA, leading to decreased cation migration, better kinetic and thermodynamic properties, and improved structural stability. As a result, the Ti-substituted NCA cathode exhibits impressive reversible capacity (198 mA h g^-1 at 0.1C) with considerable cycle stability under a cutoff voltage up to 4.7 V. It is also revealed that Ti could suppress oxygen release in the high-voltage region, benefitting cycle and thermal stabilities. This work provides valuable insight into the design of high-voltage layered cathode materials for high-energy-density LIBs.