Multi-Layered Fluorinated Graphene Cathode Materials for Lithium and Sodium Primary Batteries: Effect of Interlayer Distance on Rate Capability

Abstract

Fluorinated graphene has a promising application prospect in lithium primary batteries (LPBs) and sodium primary batteries (SPBs). Herein, five fluorinated graphene materials with different fluorine contents (FG-x) are prepared by a large-scale gas fluorination process. It is found that the structural characteristics of FG-x strongly depend on the fluorination temperature: the fluorine content (i.e. F/C ratio) gradually increases with the rising fluorination temperature, resulting in the enlargement of interlayer spacing and the increasing of C–F bond strength. The middle sample of FG-0.75 achieves the maximum energy densities in LPBs (2239.8 Wh kg⁻¹) and SPBs (1939.2 Wh kg⁻¹). The interlayer distance is critical to the rate capability of FG-x, and the FG-0.95 with a largest lattice spacing exhibits the best rate performance in both Li/CF_x and Na/CF_x batteries. The electrochemical reaction mechanism and the structural evolution of FG-x revealed by ex-situ X-ray photoelectron spectroscopy, X-ray diffraction characterization, and in-situ Raman spectra further confirm the effect of interlayer distance.

Keywords: Lithium Batteries, Sodium Batteries, Fluorocarbon, Fluorinated Graphene