Interface Stability of Sulfide/PVDF-HFP Solid Composite Electrolyte with High Voltage NMC Cathode

Abstract

Solid composite electrolytes (SCEs) have attracted serious attention for solid-state Li metal batteries. In particular, SCEs that incorporate inorganic sulfide into polymer electrolytes provide a feasible approach to address the air sensitivity and (electro)chemical instability of sulfides. Nevertheless, there is still little research on pairing sulfide-SCEs with high-voltage cathodes. In this work, reports on efforts to synthesize and compare SCEs that embedding sulfides (Li₇PS₆ and Li₃PS₄) into PVDF/HFP polymer using a strong polar solvent (DMF). Two sulfides show distinct behaviors when dispersed in the DMF solvent. The Li₇PS₆-SCE exhibits an ionic conductivity of 2.5 × 10⁻⁴ S cm⁻¹ at room temperature, higher than the Li₃PS₄-SCE (1.75 × 10⁻⁴ S cm⁻¹). Moreover, Li₇PS₆-SCE displays better electrochemical cycling performance in solid-state Li metal batteries with LiNi_1/3Mn_1/3Co_1/3O₂ (NMC 111) cathode.. When increasing upper cut-off voltages from 4.0 to 4.4 V, Li| Li₇PS₆-SCE |NMC111 cells deliver higher discharge capacities but exhibit worse cycling stability. Interface analysis using X-ray photoelectron spectroscopy (XPS) reveals the formation of LiF under a high voltage of 4.4 V, while t not present with 4.0 V. This work explores the synthesis of SCEs with different sulfides in a strong polar solvent and highlights the interface reactions between sulfide/PVDF-HFP SCEs with oxide cathodes.