Self-assembled hydrated copper coordination compounds as ionic conductors for room temperature solid-state batteries

As the core component of solid-state batteries, neither current inorganic solid-state electrolytes nor solid polymer electrolytes can simultaneously possess satisfactory ionic conductivity, electrode compatibility and processability. By incorporating efficient Li⁺ diffusion channels found in inorganic solid-state electrolytes and polar functional groups present in solid polymer electrolytes, it is conceivable to design inorganic-organic hybrid solid-state electrolytes to achieve true fusion and synergy in performance. Herein, we demonstrate that traditional metal coordination compounds can serve as exceptional Li⁺ ion conductors at room temperature through rational structural design. Specifically, we synthesize copper maleate hydrate nanoflakes via bottom-up self-assembly featuring highly-ordered 1D channels that are interconnected by Cu²⁺/Cu⁺ nodes and maleic acid ligands, alongside rich COO^- groups and structural water within the channels. Benefiting from the combination of ion-hopping and coupling-dissociation mechanisms, Li⁺ ions can preferably transport through these channels rapidly. Thus, the Li⁺-implanted copper maleate hydrate solid-state electrolytes shows remarkable ionic conductivity (1.17 × 10^-4 S cm^-1 at room temperature), high Li⁺ transference number (0.77), and a 4.7 V-wide operating window. More impressively, Li⁺-implanted copper maleate hydrate solid-state electrolytes are demonstrated to have exceptional compatibility with both cathode and Li anode, enabling long-term stability of more than 800 cycles. This work brings new insight on exploring superior room-temperature ionic conductors based on metal coordination compounds.