Engineering Well-Connected Ion-Conduction Network and Interface Chemistry for High-Performance Pvdf-Based Polymer-in-Salt Electrolytes

Abstract

The challenges posed by the low ionic conductivity at room temperature and the poor compatibility of the Li metal/electrolyte interface restrict the practical application of solid-state polymer electrolytes. Herein, a bifunctional heptafluorobutyric anhydride (HFA) additive has been proposed to overcome the abovementioned problems of the polyvinylidene fluoride (PVDF)-based polymer-in-salt solid electrolyte. The experimental data and the molecular dynamics (MD) simulations demonstrate the HFA additive can promote the formation of nanometric aggregates (n-AGGs), which can construct a continuous and fast Li+ ion transport network in the solid electrolyte. Meanwhile, HFA additive exhibits a lower LUMO energy level, and then it can contribute a LiF-rich SEI at the Li metal/electrolyte interface. As a result, the fabricated solid electrolytes with HFA additive can deliver an improved ion conductivity of 2.41×10-4 S cm-1 at room temperature, which renders the symmetric Li||Li batteries to show an ultra-long cycle life (≈1700 h at 0.1 mAh cm-2). Besides, the HFA-containing solid electrolytes show greatly enhanced cycle stability than those of the pristine electrolyte in the full cells when paired with LiFePO4 cathode or high-voltage LiNi0.6Co0.2Mn0.2O2 (NCM622) cathode. This work provides a critical insight into the mechanism of new additive to enhance the electrochemical performances of PVDF-based polymer-in-salt solid-state electrolytes.

Keywords: solid-state batteries, polymer-in-salt electrolytes, ionic conductivity, interface chemistry, ion transport mechanism