In situ conversion reaction of magnesium fluoride to boost the performance of the sulfide-based electrolyte Li6PS5Cl for all-solid-state lithium metal batteries†

Among the solid electrolytes of all-solid-state lithium metal batteries being pursued globally, Li₆PS₅Cl is one of the most promising candidates owing to its high ionic conductivity and easy processibility. However, Li₆PS₅Cl is vulnerable to the lithium anode because lithium can not only reduce Li₆PS₅Cl to generate passive interfaces but can also lead to the growth of lithium dendrites, which could penetrate the Li₆PS₅Cl bulk and eventually short-circuit the battery. Herein, we report that the electrochemical performance of Li₆PS₅Cl could be greatly enhanced by compositing it with MgF₂, which was the most effective metal fluoride among five studied materials. Specifically, critical current density was increased by 4.7 times, cycling durability in Li|electrolyte|Li symmetric cells was extended by 19 times, capacity retention in Li|electrolyte|LiNi_0.7Co_0.2Mn_0.1O₂ full cells was enhanced from 76% to 86%, and rate capability was boosted from 0.2C to 1C. Combination studies involving experimental characterizations and theoretical computations revealed that the performance-improving mechanism involved a sustained-release effect of capsule medicines, meaning during the charging/discharging cycles, MgF₂ could timely scavenge lithium dendrites to generate Li_xMg alloy and LiF, wherein Li_xMg could reversibly release/uptake Li and LiF could suppress the nucleation of lithium dendrites.