Transitional Metal Catalytic Pyrite Cathode Enables Ultrastable Four-Electron-Based All-Solid-State Lithium Batteries.

All-solid-state batteries can enable reversible four lithium ion storage for pyrite (FeS) at a cutoff voltage of 1.0-3.0 V. However, strain/stress concentration generating electrode pulverization and sluggish electrochemical reaction of lithium sulfide and sulfur will affect the long cycling stability of the battery. Through experiments and density functional theory (DFT) calculations, it is proved that nanostructure engineering and electronic conduction improvement with introduction of catalytic cobalt can effectively improve the electrochemical activity of FeS. The optimized loose structured CoFeS based all-solid-state lithium batteries show reversible capacities of 860.5, 797.7, 685.8, and 561.8 mAh g after five cycles at 100, 200, 500, and 1000 mA g, respectively, and a stable capacity of 543.5 mAh g can be maintained after cycling at a current density of 500 mA g for 100 cycles. TEM and Raman results reveal that, after the first cycle, the reversible reaction 2LiS + Fe ↔ FeS + (2 - )S + 4Li + 4 proceeds from the following cycles onward, while nanocrystalline mackinawite FeS, Fe(III)-containing mackinawite FeS, and FeS are generated after the first discharge-charge process. This work provides a facile method for improving the electrochemical performance for multi-electron reaction mechanism based all-solid-state lithium batteries.