Enabling Excellent Thermal Stability of an Ultrahigh Nickel-Rich Cathode (LiNi_0.90Co_0.05Mn_0.05O₂) by a Magnesium and Titanium Codoping Strategy

Layered nickel-rich transition metal oxides have received much attention with their advantages of high specific energy density and reasonable cost. However, the large volume changes of nickel-rich materials with alternate repetition of delithiation and lithiation processes lead to particle microcracks and even fracture with severe surface reconstruction and thermal stability degradation during long-term charge–discharge cycling. Herein, we propose a codoping strategy of Mg and Ti in Li[Ni 0.90 Co 0.05 Mn 0.05 ]O 2 (NCM90), achieving excellent cyclability (98.9% versus 86.6%) after 100 cycles. The enhanced electrochemical performance is further confirmed by the ameliorated cyclability shown in the testing of an NCM∥graphite full cell. In situ X-ray diffraction and high-resolution transmission electron microscopy results reveal that cation mixing and particle fragmentation of the modified materials resulted from volume changes from the H2–H3 phase transition at a high charged state can be availably mitigated. Furthermore, the codoped NCM cathodes exhibit a well-controlled exothermic behavior at an elevated temperature, with suppressed heat release and delayed oxygen evolution. This study provides a valuable strategic guideline for the application of high-nickel cathodes in lithium-ion batteries with ideal cycling and thermal stability.