Preparation and properties of Li₇P₂S₈I solid electrolyte by wet-chemical method

For advanced all-solid-state lithium batteries, the solid electrolyte is one of the most critical factors that significantly affect the performance of batteries. The Li7P2S8I solid-state electrolyte was successfully prepared by wet-chemical synthesis and subsequent vacuum heat-treatment method, taking P2S5, Li2S and LiI as the raw materials and tetrahydrofuran as the reaction solvent. The morphology, elements distribution, and phase composition of the electrolyte sample were studied by means of simultaneous thermal analysis, powder X-ray diffraction, Raman spectroscopy, scanning electron microscope, and energy dispersive spectrometer. The electrochemical properties of Li7P2S8I solid electrolyte were analyzed by AC impedance measurements, cyclic voltammetry, and DC polarization test. The results show that the optimal heat-treatment temperature of Li7P2S8I solid electrolyte is 230 ℃ and the obtained sample has nanoporous structure and each kind of elements is uniformly distributed in it. Electrochemical tests show that the ionic conductivity of the electrolyte at 25 ℃ is 1.63×10-4 S·cm-1, the activation energy is 0.388 eV, the electrochemical window reaches 5 V and the lithium ion transport number is larger than 0.999. In addition, the symmetrical cell assembled with the electrolyte and lithium metal can be charged and discharged stably for more than 262 cycles (525 h). This proves that the Li7P2S8I solid electrolyte prepared by this method has excellent electrochemical stability and chemical compatibility with the metal lithium anode