Fabrication Of Sulfide Electrolyte Based All-solid-state Lithium-ion Batteries By Ink Coating Method

Abstract:Sulfide electrolytes have been known for excellent electrochemical performance. In this thesis, methods for fabricating sulfide electrolyte were investigated. An ink coating method for electrolyte film was developed. The results are summarized as follows:1. Sulfide electrolytes were synthesized respectively by high energy ball milling, hot-injection and high-temperature sintering methods. The high-temperature sintering method was chosen by comparing the physical structure of the final products. The sulfide was annealed at550℃and argon atmosphere for12hours to obtain crystalline Li8P2S9.2. An ink coating method is developed to prepare sulfide solid electrolyte for all-solid-state lithium ion batteries. The Li8P2S9is dispersed in N-methyl-2-pyrrolidone (NMP) solvent to form a homogeneous ink. Under the action of NMP, the particle size of Li8P2S9decreases from10μm to1μm while the crystalline structure of Li8P2S9is unchanged that benefits contacts between Li8P2S9particles. Through adding a certain amount of poly(vinylidene fluoride)(PVDF) as an organic binder, the ink is directly dropped on LiFePO4cathode sheet and then heated at120℃to remove NMP. When Li8P2S9:PVDF=10:1(w/w), the solid electrolyte has an ionic conductivity of2.03×10-4S cm-1at30℃and an electrochemical window of5.15V at25℃. In addition, the LiFePO4/electrolyte/Li batteries assembled by such facile method show good charge/discharge performance. At the rate of0.2C, the average specific capacities of around113.7mAh g-1for100cycles are delivered at25℃with the Coulombic efficiencies of99%for each cycle. These results suggest that the ink coating method is an alternative way for sulfide electrolyte based all-solid-state lithium ion batteries.