Improve the Internal and Interface Stability of Sulfide-Based Composite Electrolytes Through High Concentration Electrolyte and Continuous Li+ Conductive Frameworks.

Composite electrolytes have received widespread attention due to their potential to simultaneously integrate the advantages of different types of electrolytes. However, composite electrolytes based on sulfides and polymers electrolyte still face issues such as instability toward lithium metal, low ion transference number, and instability between polymers and sulfides. Based on this, a composite electrolyte based on a continuous conductive Li_5.4PS_4.4Cl_1.6(LPSC) framework with polytetrafluoroethylene (PTFE) is prepared as a binder (LPSC@PTFE) and gel electrolyte containing high concentration lithium salt. The gel electrolyte fills the pores in the LPSC@PTFE membrane and protects the interface between the sulfide electrolyte and lithium metal. In addition, high-concentration electrolytes exhibit better stability compared to low-concentration electrolytes, whether for lithium metal or sulfides. The improvement has been demonstrated in stability through analysis of in-situ electrochemical impedance spectroscopy (EIS) combined with relaxation time distribution (DRT), as well as characterization by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The mechanism behind the performance enhancement through theoretical calculations and simulations has also been speculated on. The optimized composite electrolyte membrane has an electrochemical window of 4.98 V, an increased ion transference number of 0.74, a critical current density of 1.8 mA cm^-2@0.1 mAh cm^-2, and can cycle for more than 4000 h at a current density of 0.1 mA cm^-2@0.1 mAh cm^-2. After matching with LiFePO₄ (LFP) cathode, the capacity retention rate is 94.1% after 150 cycles at a rate of 1C and 89.7% after 150 cycles at a rate of 2C.