Synergistic coupling among Mg2B2O5, polycarbonate and N,N-dimethylformamide enhances the electrochemical performance of PVDF-HFP-based solid electrolyte

Abstract

Polymer solid electrolytes (SPEs) based on the [solvate-Li+] complex structure have promising prospects in lithium metal batteries (LMBs) due to their unique ion transport mechanism. However, the solvation structure may compromise the mechanical performance and safety, hindering practical application of SPEs. In this work, a composite solid electrolyte (CSE) is designed through the organic–inorganic synergistic interaction among N,N-dimethylformamide (DMF), polycarbonate (PC), and Mg2B2O5 in poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP). Flame-retardant Mg2B2O5 nanowires provide non-flammability to the prepared CSEs, and the addition of PC improves the dispersion of Mg2B2O5 nanowires. Simultaneously, the organic–inorganic synergistic action of PC plasticizer and Mg2B2O5 nanowires promotes the dissociation degree of LiTFSI and reduces the crystallinity of PVDF-HFP, enabling rapid Li ion transport. Additionally, Raman spectroscopy and DFT calculations confirm the coordination between Mg atoms in Mg2B2O5 and N atoms in DMF, which exhibits Lewis base-like behavior attacking adjacent C–F and C–H bonds in PVDF-HFP while inducing dehydrofluorination of PVDF-HFP. Based on the synergistic coupling of Mg2B2O5, PC, and DMF in the PVDF-HFP matrix, the prepared CSE exhibits superior ion conductivity (9.78 × 10−4 S cm−1). The assembled Li symmetric cells cycle stably for 3900 h at a current density of 0.1 mA cm−2 without short circuit. The LFP||Li cells assembled with PDL-Mg2B2O5/PC CSEs show excellent rate capability and cycling performance, with a capacity retention of 83.3% after 1000 cycles at 0.5 C. This work provides a novel approach for the practical application of organic–inorganic synergistic CSEs in LMBs.