Local ionic structure unit design in sulfide solid electrolyte flakes by improving pressing process

The rapid development of electric vehicles and energy storage facilities requires novel secondary batteries with higher energy density and increased safety. Sulfide solid electrolyte, especially lithium thiophosphate (LPS), has become a research hotspot due to its non-flammability and high structural strength. The high-performance LPS powders need to be prepared into flakes before practical application. However, the widely used cold pressing process for the preparation of LPS flakes have fatal defects such as low density and high interface resistance. This work systematically studied the differences in the body defects, density and crystallization process of electrolyte flakes obtained by different tableting processes. The nucleation is inhibited in the high-density sulfide solid electrolyte samples. In addition, based on the improvement of pressurizing equipment, it was discovered for the first time that glass transition process (the secondary hot pressing at glass transition temperature) can significantly improve the distribution of local structured ions. Notably, the content of P₂S₇^4- and P₂S₆^4- has doubled after glass transition, resulting in improving the ionic conductivity and stability, respectively. The HP-GT (the electrolyte flakes after glass transition) exhibits extremely high relative density (99 ± 1%), low ion activation energy (14.4 kJ/mol) and extremely high ion conductivity (3.48 mS/cm). On the other hand, a specific discharge capacity of ∼ 680 mAh g⁻¹ is still maintained for the Li|HP-GT|MoS₂ solid-state battery after 30 cycles. This work confirms the feasibility of the sulfide solid electrolyte after the second hot-pressing in the application of high-safety, high-energy density solid-state lithium batteries.