Enhancing the structure stability of Ni-rich LiNi0.6Co0.2Mn0.2O2 cathode via encapsulating in negative thermal expansion nanocrystalline shell

Abstract

Ni-rich cathode materials have attracted considerable attention due to the high electrochemical capacities and prominent price advantage, while their extensive applications are still impeded by the poor structure stability induced by the intrinsic Li+/Ni2+ cation mixing and mechanical stress accumulation upon cycling. To address these issues, a typical negative thermal expansion (NTE) material ZrV2O7 (ZVO) is firstly employed as coating layer on LiNi0.6Co0.2Mn0.2O2 (NCM622) particles to promote the electrochemical performances through enhancing the structure stability upon repeated cycling and operating at high temperature. The [email protected] wt% ZVO sample exhibits excellent cyclability (71.0% capacity retension after 500 cycles under 25 °C and 67.0% capacity retension after 200 cycles under 55 °C) and rate capability (60.7% at 5 C). Further in-situ XRD analysis confirms that the structure stability of NCM622 could be prominently stabilized both under electrochemical and thermal treatments after ZVO decoration. Intensive investigation implies the unique functionalities of ZVO in restraining the stress accumulation and volume expansion, thus contributing to the bulk structure stability and interface compatibility of modified NCM622, besides the traditional effect of surface deposition layers (physical separation between solid electrode/electrolyte and inhibited irreversible surface side reactions).