Hybrid covalent organic-framework-based electrolytes for optimizing interface resistance in solid-state lithium-ion batteries

Abstract

High ion conductivity and low electrode-electrolyte interface resistance are intensively pursued topics for the development of solid-state Li-ion batteries with high safety and energy density. Here, we propose a design using keto-enamine covalent organic frameworks (TPBD) and polyethylene oxide (PEO) to prepare a solid-state electrolyte (TPBD-LiPF 6 @PEO), achieving a high ion conductivity of 0.543 mS cm −1 at 25°C and optimizing the electrode-electrolyte interface resistance in Li-ion batteries. Solid-state nuclear magnetic resonance experiments and density functional theory calculations show that the strong interaction between the –C=O site in TPBD and Li + ions promotes the dissociation of LiPF 6 . The assembled LiFePO 4 |TPBD-LiPF 6 @PEO|Li batteries without using liquid electrolytes offer a specific capacity of nearly 140 mAh g −1 at 0.2 C with a columbic efficiency of 99.6% after 200 cycles at 25°C. This strategy for preparing solid-state electrolytes provides practical ideas and suggestions in the development of solid-state energy devices. • The –C=O groups in TPBD frameworks promote the dissociation of LiPF 6 • TPBD reduces the crystallinity of PEO and enhances mechanical strength of the electrolyte • Fast ion conduction is achieved due to the optimized interface resistance • Solid-state Li-ion batteries can operate at 25°C without adding any liquid electrolyte The low conductivity of solid electrolytes and the interface resistance of solid-state batteries have long been scientific problems that plague the development of solid-state Li-ion batteries. Cheng et al. report a fibrous covalent organic framework TPBD that can promote the dissociation of LiPF 6 , combining with flexible PEO to prepare an inorganic/polymer solid electrolyte. The results show that the electrode-electrolyte interface impedance is greatly reduced, realizing the operation of solid-state battery at room temperature without the addition of liquid electrolyte.