In Situ Construction of a LiF‐Enriched Interface for Stable All‐Solid‐State Batteries and its Origin Revealed by Cryo‐TEM

• Published in: Advanced materials (Weinheim) 2020-08, Vol.32 (34), p.e2000223-n/a
• Main Authors: Sheng, Ouwei, Zheng, Jianhui, Ju, Zhijin, Jin, Chengbin, Wang, Yao, Chen, Mei, Nai, Jianwei, Liu, Tiefeng, Zhang, Wenkui, Liu, Yujing, Tao, Xinyong
• Format: Article
• Language: English
• Subjects: cryo‐transmission electron microscopy; Electrolytes; Ethylene oxide; Interface reactions; Interface stability; interfaces; Lithium fluoride; lithium metal anodes; Lithium oxides; Materials science; Molecular dynamics; Molten salt electrolytes; Nanocrystals; Polyethylene oxide; polymer electrolytes; Polymers; Solid electrolytes; Transmission electron microscopy; Workability
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.202000223

The application of solid polymer electrolytes (SPEs) is still inherently limited by the unstable lithium (Li)/electrolyte interface, despite the advantages of security, flexibility, and workability of SPEs. Herein, the Li/electrolyte interface is modified by introducing Li2S additive to harvest stable all‐solid‐state lithium metal batteries (LMBs). Cryo‐transmission electron microscopy (cryo‐TEM) results demonstrate a mosaic interface between poly(ethylene oxide) (PEO) electrolytes and Li metal anodes, in which abundant crystalline grains of Li, Li2O, LiOH, and Li2CO3 are randomly distributed. Besides, cryo‐TEM visualization, combined with molecular dynamics simulations, reveals that the introduction of Li2S accelerates the decomposition of N(CF3SO2)2− and consequently promotes the formation of abundant LiF nanocrystals in the Li/PEO interface. The generated LiF is further verified to inhibit the breakage of CO bonds in the polymer chains and prevents the continuous interface reaction between Li and PEO. Therefore, the all‐solid‐state LMBs with the LiF‐enriched interface exhibit improved cycling capability and stability in a cell configuration with an ultralong lifespan over 1800 h. This work is believed to open up a new avenue for rational design of high‐performance all‐solid‐state LMBs. Based on the atomic visualization of the lithium (Li)/poly(ethylene oxide) (PEO) interface through cryo‐transmission electron microscopy, Li2S additive is revealed to promote the decomposition of LiN(CF3SO2)2 (LiTFSI) to generate uniform LiF nanocrystals in situ, rendering uniform Li deposition and preventing PEO bond cleavage. This optimized interface is promising for PEO‐electrolyte‐based Li metal batteries with significantly improved cycling lifespan.