Molecular coordination induced high ionic conductivity of composite electrolytes and stable LiF/Li3N interface in long-term cycling all-solid-state lithium metal batteries

Composite polymer/oxide electrolyte (CPE) is a promising candidate for all-solid-state lithium metal batteries (ASSLMBs), but controlling the interactions between components in CPEs to achieve high efficient Li+-transport and stable CPE/electrode interface is a challenge. Here, we report a mesoporous black LaxCoO3-δ nanofiber (NF) film with tunable cationic defects to regulate the molecular coordination with PEO/LiTFSI matrix and realize stable operations of ASSLMBs over 1000 cycles. By tuning the A-site defects from x = 1.0 to 0.8, the LaxCoO3-δ NFs show gradually enhanced coordination with PEO/LiTFSI, achieving a high ionic conductivity of 2.5 × 10−4 S/cm at 30 °C. Moreover, the defective La0.8CoO3-δ can catalyze the formation of stable LiF/Li3N interfacial layers, which possess high Li+-conduction kinetics and interfacial energy, thus enabling stable battery operations even at high currents. As a result, the LiFePO4-based ASSLMBs show a long life of >1000 cycles at 0.2 C with a capacity retention of >75%, and they can deliver a high discharge capacity of 142 mA h g−1 at 1 C with a capacity retention of 92.2% over 300 cycles. Importantly, this molecular coordination strategy is still effective when extended to other defective oxides, thus providing a universal method to design high-performance CPEs.