Interfacial layer rich in organic fluoride enabling stable cycling of high-voltage PEO-based solid-state lithium batteries

Highlights: • Organic F-rich coating layer is in-situ constructed on the surface of LiCoO₂. • Side reactions of LiCoO₂ and PEO are effectively suppressed. • Li/LiCoO₂ cells show good cycling performance at 4.2 V and 4.35 V. • Designed liquid-state electrolyte plays crucial roles in forming the coating layer. • Formation mechanism of the coating layer is analyzed by DFT calculations. -- Abstract: Solid-state lithium batteries (SSLBs) are considered as next-generation electrochemical energy storage systems with superior safety performance and high energy density. It's difficult to improve the energy density of PEO-based SSLBs, due to the limited electrochemical window. It severely hinders their applications. Here, the coating layer with organic fluoride rich microstructure is in-situ constructed on the surface of LiCoO₂ by electrochemical method with a designed liquid-state electrolyte, which effectively suppresses the side reactions at the interface by physically blocking the contact between PEO and LiCoO₂. It shows improved electrochemical performance at 4.2 V and 4.35 V. In addition, this kind of method is extended to other two layered cathode materials (i.e., LiNi_1/3Co_1/3Mn_1/3O₂ and LiNi_0.5Co_0.2Mn_0.3O₂), and good battery performance is achieved as well. It indicates the universality of this method and important roles of the organic fluorides rich coating layer. The Results indicate that the designed liquid-state electrolyte plays an important role in forming organic fluoride rich coating layer. The formation mechanism of this kind of coating layer is analyzed by DFT calculations. It provides new ideas for interface protection between PEO and high-voltage layered cathode materials, meanwhile, it further improves the energy density of PEO-based SSLBs.