An innovative dehydrofluorinated composite gel electrolyte for enhanced solid-state batteries

Improving the ionic conductivity by increasing the concentration of mobile Li-ions and the number of available Li-ion conduction sites poses significant challenges in organic-inorganic composite electrolytes. In this study, the single-ion conducting composite gel electrolyte (CGE-Li₃OCl) composed of PVDF-Li₃OCl-FEC is prepared through a dehydrofluorination reaction of PVDF. This reaction is prompted by the oxygen atoms in Li₃OCl, which create a Lewis-basic environment. The formation of unsaturated CC bonds enhances the interactions between the organic and inorganic phases, thereby facilitating faster Li-ion conduction. CGE40-Li₃OCl, identified as the optimal experimental group, achieves an ionic conductivity of 2.73 × 10^-4 S cm^-1. The Li-ion transference number (T_Li+) is 0.90, the electrochemical window exceeds 4.78 V (vs. Li⁺/Li), the CCD of the CGE40-Li₃OCl is 0.85 mA cm^-2, and the Young's modulus of CGE40- Li₃OCl reaches 892.53 MPa. When CGE40-Li₃OCl is used as the separator, the Li/Li symmetric cell operates stably for over 2500 h at a current density of 0.1 mA cm^-2. This indicates that CGE40-Li₃OCl effectively suppresses lithium dendrite growth due to its single-ion conducting property. After 350 cycles at a rate of 1C, the Li/CGE40-Li₃OCl/LiNi_0.8Co_0.15Al_0.05O₂ (NCA) cell exhibited a capacity retention of 84.15 %. In contrast, the Li/CGE40-LLZTO/NCA cell experienced severe capacity fading, retaining only 72.01 % of its initial capacity. Furthermore, a lithiated hard carbon/CGE40-Li₃OCl/NCA cell retains 80 % of its initial capacity after 300 cycles at a 1C rate. In summary, the innovative dehydrofluorination reaction not only enhances the interactions between the organic and inorganic phases but also significantly achieves the fast ionic conductivity and wide electrochemical window of the electrolyte, making it a promising candidate for high-performance solid-state batteries.