Operando chemo-mechanical evolution in LiNi0.8Co0.1Mn0.1O2 cathode

Abstract

Abstract Ni-rich LiNixCoyMnzO2 (NCMxyz, x + y + z = 1, x ≥ 0.8) layered oxide materials are considered as the main cathode materials for high energy density Li-ion batteries. However, the endless cracks of polycrystalline NCM materials caused by stress accelerate the loss of active materials and electrolyte decomposition, limiting the cycle life. Hence, understanding the chemo-mechanical evolution during (de)lithiation of NCM materials is crucial to the performance improvement. In this work, an optical fiber with με resolution is designed to in operando detect the stress evolution of polycrystalline LiNi0.8Co0.1Mn0.1O2 (P-NCM811) cathode during cycling. By integrating the sensor inside the cathode, the stress variation of P-NCM811 is completely transferred to the optical fiber. We find that the anisotropy of primary particles leads to the appearance of structural stress, inducing the formation of microcracks in polycrystalline particles, which is the main reason for capacity decay. The isotropy of primary particles reduces the structural stress of polycrystalline particles, eliminating the generation of microcracks. Accordingly, the P-NCM811 with the ordered arrangement structure deliver high electrochemical performance with capacity retention of 82% over 500 cycles. This work provides a brand-new view for understanding the operando chemo-mechanical evolution of NCM materials during battery operation and guiding the design of electrode materials for rechargeable batteries.