An All-Solid-State Battery Based on Sulfide and PEO Composite Electrolyte.

Replacing liquid electrolytes with solid polymer electrolytes (SPEs) is considered as a vital approach to developing sulfur (S)-based cathodes. However, the polysulfides shuttle and the growth of lithium (Li) dendrites are still the major challenges in polyethylene oxide (PEO)-based electrolyte. Here, an all-solid-state Li metal battery with flexible PEO-Li10 Si0.3 PS6.7 Cl1.8 (LSPSCl)-C-lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) composite cathode (FCC) and PEO-LSPSCl-LiTFSI composite electrolyte (S-CPE) is designed. The initial capacity of the Li|S-CPE|FCC battery is 414 mAh g-1 with 97.8% capacity retention after 100 cycles at 0.1 A g-1 . Moreover, the battery displays remarkable capacity retention of 80% after 500 cycles at 0.4 A g-1 . Cryo-transmission electron microscopy (Cryo-TEM) reveals rich large-sized Li2 CO3 particles at the Li/PEO interface blocking the Li+ transport, but the layer with rich Li2 O nanocrystals, amorphous LiF and Li2 S at the Li/S-CPE interface suppresses the growth of lithium dendrite and stabilizes the interface. In situ optical microscopy demonstrates that the excellent cyclic stability of FCC is ascribed to the reversible shuttle of P-S-P species, resulting from the movement of ether backbone in PEO. This study provides strategies to mitigate the polysulfide shuttle effect and Li dendrite formation in designing high energy density solid-state Li-S-based batteries.

Cryo-EM Revealing the Origin of Excessive Capacity of the Se Cathode in Sulfide-Based All-Solid-State Li-Se Batteries.

Selenium (Se), whose electronic conductivity is nearly 25 orders higher than that of sulfur (S) and whose theoretical volumetric capacity is 3254 mAh cm-3, is considered as a potential alternative to S to overcome the poor electronic conductivity issue of the S cathode in the lithium (Li)-S battery. However, the study of the Li-Se battery, particularly a Li-Se all-solid-state battery (ASSB), is still in its infancy. Herein, we report the performance of Li-Se ASSBs at both room temperature (RT) and high temperature (HT, 50 °C), using a Li10Si0.3PS6.9Cl1.8 (LSPSCl) solid-state electrolyte and Li-In anode. With a Se loading of 7.6 mg cm-2, the Li-Se battery displayed a record high reversible capacity of 6.8 mAh cm-2 after 50 cycles at HT, which exceeds the theoretical areal capacity of 5.2 mAh cm-2 for Se. Moreover, the RT Li-Se ASSB delivered an initial areal capacity of about 2 mAh cm-2 at a current density of 1 A g-1 for 1200 cycles with a capacity retention of 67%. Cryo-electron microscopy revealed that the excessive capacity of Se at HT can be attributed to the formation of a previously unknown S5Se4 phase during charging, which participated reversibly in a subsequent redox reaction. The formation of the S5Se4 phase originated from the reaction of Se with S, which was generated by the decomposition of LSPSCl at HT. These results unlock the electrochemistry of a Li-Se ASSB, suggesting that a Li-Se ASSB is a viable alternative to a Li-S battery for energy storage applications.