Sulfide solid electrolytes are widely regarded as one of the most promising technical routes to realize all-solid-state batteries (ASSBs) due to their high ionic conductivity and favorable deformability. However, the relatively high price of the crucial starting material, Li2S, results in high costs of sulfide solid electrolytes, limiting their practical application in ASSBs. To solve this problem, we develop a new synthesis route of Li2S via liquid-phase synthesis method, employing lithium and biphenyl in 1, 2-dimethoxyethane (DME) ether solvent to form a lithium solution as the lithium precursor. Because of the comparatively strong reducibility of the lithium solution, its reaction with sulfur proceeds effectively even at room temperature. This new synthesis route of Li2S starts with cheap precursors of lithium, sulfur, biphenyl and DME solvent, and the only remaining byproduct (DME solution of biphenyl) after the collection of Li2S product can be recycled and reused. Besides, the reaction can proceed effectively at room temperature with mild condition, reducing energy cost to a great extent. The as-synthesized Li2S owns uniform and extremely small particle size, proved to be feasible in synthesizing sulfide solid electrolytes (such as the solid-state synthesis of Li6PS5Cl). Spontaneously, this lithium solution can be directly employed in the synthesis of Li3PS4 solid electrolytes via liquid-phase synthesis method, in which the centrifugation and heat treatment processes of Li2S are not necessary, providing simplified production process. The as-synthesized Li3PS4 exhibits typical Li+ conductivity of 1.85×10−4 S⋅cm−1 at 30 °C.
Developing all solid-state lithium ion batteries (ASSBs) is a promising way to solve safety issues surrounding liquid-based batteries, yet the interfacial issues make ASSBs insufficient in providing long-term cycling performance or acceptable rate capabilities. Herein, we propose a new kind of electrolyte configuration, comprising a 3D ceramic framework filled with plastic crystals on the surface, to effectively enhance the interfacial Li diffusion kinetics. The soft plastic crystals enable not only excellent contact with the rigid framework and cathodes, but also rapid molecular reorganization to accommodate the interfacial Li, achieving ultrafast Li diffusion globally via the 3D framework. As a result, the ASSBs with the proposed electrolyte (i.e. garnet-succinonitrile composites) show an extremely low interfacial resistance, providing an initial discharge capacity of 165.3 mA h g−1 and a 95% capacity retention after 100 cycles when using a LiNi0.5Co0.2Mn0.3O2 (NCM) cathode. Furthermore, these NCM-ASSBs using the designed electrolyte even exhibit better cycling performance within a higher voltage range (2.8–4.5 V) than conventional lithium ion batteries (LIBs) using conventional liquid electrolytes (LEs). A capacity retention rate of 92% for 3DLLZO-PCE is demonstrated, against the 85% for LE-LIBs after 50 cycles. We believe that this strategy provides useful guidance for constructing high-performance ASSBs, which is important in their further commercialization.
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