In-situ polymerized composite polymer electrolyte with cesium-ion additive enables dual-interfacial compatibility in...

Solid composite polymer electrolytes (CPEs) that combine the advantages of inorganic and organic electrolytes are regarded as the most appealing candidates for all-solid-state lithium-metal batteries (ASSLMBs). Nonetheless, the interfacial incompatibility issues resulting from poor cathode/electrolyte contact and uncontrolled dendrite growth on Li anode are fundamentally challenging for the development of ASSLMBs. Herein, we design a solid CPE with dual-interface compatibility based on in-situ thermal polymerization of a precursor solution containing polymer monomer, cesium-ion (Cs⁺), and inorganic Li⁺ conductor. The resultant Cs⁺ containing CPE creates intimate interface contact with the cathode while achieving high interfacial stability with the Li-metal anode. Accordingly, this solid electrolyte can perform reversible Li plating/stripping over 750 h at 0.3 mA cm^-2 and a critical current density (CCD) of 0.8 mA cm^-2, in sharp contrast with its Cs⁺-free counterpart (failure after 11 h and a CCD of 0.5 mA cm^-2). Furthermore, the full ASSLMBs (Li|LiFePO₄) enable decent capacity retention of 90% over 100 cycles at 0.5C and high Coulombic efficiency of nearly 100%. Therefore, constructing solid-state electrolytes with dual-interfacial compatibility may be an effective avenue to achieve high-performance ASSLMBs.