Long-cycle-life Li2MnO3 thin-film cathode enabled by all-solid-state battery configuration

Li2MnO3 (LMO) is a key component in lithium-rich manganese-based oxides (LMROs) and has attracted great attention as a cathode for lithium-ion batteries (LIBs) due to its high theoretical capacity and cost-effectiveness. However, its severe capacity fading and discharge voltage decay during prolonged cycling greatly hinders its applications. In this study, an LMO film is prepared, followed by the fabrication and investigation of an LMO/LiPON/Li all-solid-state thin film lithium battery (LMO-TFLB). The results show that although the LiPON electrolyte deposition results in the formation of a disordered interface layer derived from the LMO layer, an LMO/LiPON interface with small interfacial resistance and good structural stability during cycling is obtained, allowing fast Li+ diffusion across the interface. Furthermore, in contrast to the half cell that uses liquid electrolyte (LMO-LIB), the LiPON electrolyte in the LMO-TFLB significantly aids in impeding the Mn dissolution to prevent active material loss. More importantly, although a structural transformation from a layered LMO phase to a spinel-like phase occurs in the cathode of the LMO-TFLB during cycling, the transformed spinel-like phase with a higher crystallinity than that in the LMO-LIB facilitates fast Li+ and electron transport to improve the LMO-TFLB's capacity. Consequently, the LMO-TFLB exhibits a long cycle life without any capacity loss after 1000 cycles, which outperforms that of the LMO-LIB (20% capacity retention after 450 cycles). This work demonstrates that all-solid-state battery configuration is highly promising for unlocking the full potential of LMROs cathode materials for LIBs.