Unlocking Superior Li+ Transport and Anodic Compatibility for Solid Polymer Electrolytes by Zwitterionic Metal-Organic Filler-Mediated Li+ Coordination Engineering

Abstract

Residual solvents such as DMF in vinylidene fluoride (VDF)-based solid polymer electrolytes (SPEs) promote lithium salt dissociation but trigger parasitic reactions with the Li metal anode, limiting interfacial stability. Here, we introduce a multifunctional zwitterionic filler (LS) into the poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) matrix to regulate Li⁺ coordination and suppress solvent-induced degradation. The LS filler contains borate groups that compete with DMF for Li⁺ binding, weakening Li⁺–DMF interactions, while Zn²⁺ sites in its metal-organic cage immobilize TFSI^– anions and establish a Li⁺-dominated, weakly coordinated solvation structure. This dual regulation accelerates Li⁺ transport and promotes the formation of an inorganic, F- and N-rich solid electrolyte interphase (SEI) on the Li metal anode. As a result, the optimized electrolyte (LSPH) delivers a high ionic conductivity of 0.641 mS cm^–1 and a Li-ion transference number of 0.83 at room temperature, outperforming the filler-free control. The Li|LSPH|Li symmetric cells exhibit a high critical current density of 3.4 mA cm^–2 and stable cycling for over 1000 h at 1.0 mA cm^–2. Furthermore, the Li|LSPH|NCM811 full cells deliver an outstanding discharge capacity of 136.3 mAh g^–1 at 5 C and retain 70% capacity after 1000 cycles at 1 C and 4.3 V. This strategy effectively overcomes the trade-off associated with residual solvents in VDF-based electrolytes and advances the development of high-performance solid polymer electrolytes for lithium metal batteries.