Fluorinated carbon nitride with a hierarchical porous structure ameliorating PEO for high-voltage, high-rate solid lithium metal batteries

Abstract

Instability caused by lithium dendrites and low oxidation potentials hinders the commercialization of poly(ethylene oxide) (PEO) based all-solid-state lithium metal batteries (ASSLBs). Herein, fluorinated carbon nitride (FCN) with a hierarchical porous structure was designed and fabricated to modify a PEO-based electrolyte. The resultant FCN effectively suppressed the lithium dendrite growth in ASSLBs and elevated the oxidation potential of the PEO-based electrolyte to as high as 5.2 V. The fluorine and nitrogen in the FCN resulted in the formation of a LiF- and Li₃N-rich composite solid electrolyte interface (SEI) that prevented continuous side reactions between the Li metal anode and the electrolyte. The produced hierarchical structure has abundant mesopores, which provided fluent channels for Li ion diffusion without extra resistance and greatly promoted the cycling and rate performance of the batteries. By using this porous FCN modified electrolyte, Li–Li symmetrical cells exhibited an ultra-long lifespan of more than 2500 h at a current density of 0.1 mA cm⁻². The ASSLBs combined with a high-voltage ternary cathode can work stably at high rates of 2C and 5C with capacity retentions of 87.8% after 150 cycles and 92.1% after 50 cycles, respectively. This work presents a facile and effective strategy for the design of polymer based electrolytes for high-voltage, high-rate ASSLBs.