Ti-Modification of Grain Boundaries for Enhanced High Voltage Cycling Stability of NCM811

Polycrystalline Ni-rich layered lithium transition metal oxides are one of the most promising cathode materials for next-generation high energy density lithium-ion batteries, yet they are still facing many challenges, especially for the cycling induced structural degradations. Intergranular cracking has been identified as one of the most crucial degradations, and grain boundary (GB) engineering has been demonstrated to be an effective countering strategy. Herein, we report a GB modification protocol that can realize not only improved GB stability but also interfacial reaction kinetics, realizing much improved cycling performance of NCM811. The simple and effective solution method can incorporate Ti-dopant into GBs and secondary particle surface, realizing the increase of the capacity retention from 79.5% to 93.5% at 3.0–4.5 V after 100 cycles, and its high voltage (4.7 V) and high temperature (55 °C) cycling stability are also significantly improved. Comprehensive microstructure and electrochemical characterizations of the samples before and after cycling are conducted to reveal the underlying mechanisms, validating that both interfacial degradations and bulk failures have been effectively mitigated. This work provides an effective protocol in the modification of GBs and interfaces of polycrystalline battery materials, which is promising and feasible for industrial mass-production application.