The electrochemical performance and mechanism of cobalt (II) fluoride as anode material for lithium and sodium ion batteries

• The as-prepared CoF2 shows excellent electrochemical performance as anode material for lithium ion batteries.
• The Li insertion/extraction mechanism of CoF2 below 1.2 V was firstly proposed.
• The electrochemical performance of CoF2 as anode material in sodium ion batteries was firstly studied.

Cobalt (II) fluoride begins to enter into the horizons of people along with the research upsurge of metal fluorides. It is very significative and theoretically influential to make certain its electrochemical reaction mechanism. In this work, we discover a new and unrevealed reversible interfacial intercalation mechanism reacting below 1.2 V for cobalt (II) fluoride electrode material, which contributes a combined discharge capacity of about 400 mA h g−1 with the formation of SEI film at the initial discharge process. A highly reversible storage capacity of 120 mA h g−1 is observed when the cell is cycled over the voltage of 0.01-1.2 V at 0.2 C, and the low-potential voltage reaction process has a significant impact for the whole electrochemical process. Electrochemical analyses suggest that pure cobalt (II) fluoride shows better electrochemical performance when it is cycled at 3.2-0.01 V compared to the high range (1.0-4.5 V). So, we hold that cobalt (II) fluoride is more suitable to serve as anode material for lithium ion batteries. In addition, we also try to reveal the relevant performance and reaction mechanism, and realize the possibility of cobalt (II) fluoride as anode material for sodium ion batteries.