Forging Inspired Processing of Sodium‐Fluorinated Graphene Composite as Dendrite‐Free Anode for Long‐Life Na–CO2 Cells

Abstract

Na–CO2 batteries recently are emerging as promising energy‐storage devices due to the abundance of Na in the earth's crust and the clean utilization of greenhouse gas CO2. However, similar to metallic Li, metallic Na also suffers from a serious issue of dendrite growth upon repeated cycling, while a facile method to solve this issue is still lacking. In this work, we report an effective, environmentally friendly method to inhibit Na dendrite growth by in situ constructing a stable, NaF‐rich solid electrolyte interface (SEI) layer on metallic Na via adding a small amount (~3 wt%) of fluorinated graphene (FG) in bulk Na. Inspired by the forging processing, a uniform Na/FG composite was obtained by melting and repetitive FG‐adsorbing/hammering processes. The Na/FG–Na/FG half cell exhibits a low voltage hysteresis of 110–140 mV over 700 h at a current density up to 5 mA cm−2 with an areal capacity as high as 5 mAh cm−2. Na–CO2 full cell with the Na/FG anode is able to sustain a stable cycling of 391 cycles at a limited capacity of 1000 mAh g−1. Long cycle life of the cell can be attributed to the protecting effect of the in situ fabricated NaF‐rich SEI layer on metallic Na. Both experiments and density functional theory (DFT) calculations confirm the formation of the NaF‐rich SEI layer. The inhibition effect of the NaF‐rich SEI layer for Na dendrites is verified by in situ optical microscopy observations.