In situ conversion reaction of magnesium fluoride to boost the performance of the sulfide-based electrolyte Li 6 PS 5 Cl for all-solid-state lithium metal batteries

Among the solid electrolytes of all-solid-state lithium metal batteries being pursued globally, Li 6 PS 5 Cl is one of the most promising candidates owing to its high ionic conductivity and easy processibility. However, Li 6 PS 5 Cl is vulnerable to the lithium anode because lithium can not only reduce Li 6 PS 5 Cl to generate passive interfaces but can also lead to the growth of lithium dendrites, which could penetrate the Li 6 PS 5 Cl bulk and eventually short-circuit the battery. Herein, we report that the electrochemical performance of Li 6 PS 5 Cl could be greatly enhanced by compositing it with MgF 2 , 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 0.7 Co 0.2 Mn 0.1 O 2 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, MgF 2 could timely scavenge lithium dendrites to generate Li x Mg alloy and LiF, wherein Li x Mg could reversibly release/uptake Li and LiF could suppress the nucleation of lithium dendrites.