CoxP compounds: electrochemical conversion/partial recombination reaction and partially disproportionated nanocomposite for Li-ion battery anodes

Abstract

Co_xP binary compounds, CoP and Co₂P, were synthesized using simple solid-state synthetic routes, and their potential as anode materials for Li-ion batteries was investigated. Electrochemical Li reactivity was possible on the CoP electrode, whereas the Co₂P electrode did not react with Li. The electrochemically driven partial recombination reaction of the CoP electrode was thoroughly demonstrated using ex situ X-ray diffraction and extended X-ray absorption fine structure analyses. To enhance the electrochemical performances of CoP, its carbon-modified nanocomposite was prepared. The nanocomposite consisted of well-dispersed CoP (active with Li) and Co₂P (inactive with Li) nanocrystallites, as well as amorphous P within the amorphous carbon matrix. The partially disproportionated CoP/C nanocomposite electrode exhibited good electrochemical performance with a high initial charge capacity of 531 mA h g⁻¹ (or 855 mA h cm⁻³), a cycling durability of 407 mA h g⁻¹ (or 655 mA h cm⁻³) over 200 cycles, a good initial coulombic efficiency of ca. 75%, and a fast rate capability (2C: 435 mA h g⁻¹, 3C: 410 mA h g⁻¹).