Understanding an Exceptionally Fast and Stable Li-Ion Charging of Highly Fluorinated Graphene with Fine-Controlled...

Fluorine (F) atoms with the highest electronegativity and low polarizability can easily modify the surface and composition of carbon-based electrode materials. However, this is accompanied by complete irreversibility and uncontrolled reactivity, thus hindering their use in rechargeable electronic devices. Therefore, understanding the electrochemical effects of the C-F configuration might lead to achieving superior electrochemical properties. Here, we demonstrate that the fluorinated and simultaneously reduced graphene oxide (FrGO) was easily synthesized through direct gas fluorination. The as-prepared 11%-FrGO electrode exhibited a high capacity (1365 mAh g^-1 at 0.1 A g^-1), remarkable rate capability, and good stability (64% retention after 1000 cycles at 5 A g^-1). Furthermore, the annealed FrGO (11%-FrGO(A)) electrode in which the C-F bond configurations were controlled by facile thermal treatment shows long-term stability (80% retention after 1000 cycles at 5 A g^-1). Above a certain content, F atoms enhance Li-ion adsorption and electron transfer, accelerate Li-ion diffusion, and facilitate the formation of a solid electrolyte interphase layer. In particular, the C-F configuration plays a significant role in retaining the capacity under harsh recharging conditions. The results in this study could provide valuable insights into the field of rechargeable devices.