In situ Conversion Reaction of Magnesium Fluoride to Boost the Performance of Sulfide-Based Electrolyte Li6PS5Cl for All-Solid-State Lithium Metal Batteries

For solid electrolytes of all-solid-state lithium metal batteries being pursued globally, Li6PS5Cl is one of the most promising candidates due 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 also grow lithium dendrites to penetrate through the Li6PS5Cl bulk and eventually short-circuit the battery. Herein this paper reports that the electrochemical performance of Li6PS5Cl can be greatly enhanced by compositing it with MgF2, which is the most effective metal fluoride among five studied materials. Specifically, the critical current density is increased by 4.7 times; the cycling durability in Li|electrolyte|Li symmetric cells is extended by 19 times; the capacity retention in Li|electrolyte|LiNi0.7Co0.2Mn0.1O2 full cells is enhanced from 76% to 86%; and the rate capability is boosted from 0.2 C to 1 C. The combinatory studies of experimental characterizations and theoretical computations find that the performance-improving mechanism is like a sustained-release effect of capsular medicines. That is, during the charging/discharging cycles can MgF2 timely scavenge lithium dendrites to generate LixMg alloy and LiF, wherein LixMg can reversibly release/uptake Li and LiF can suppress the nucleation of lithium dendrites.