Computational Investigation of Copper Phosphides as Conversion Anodes for Lithium-Ion Batteries.

ABSTRACT: Using first-principles structure searching with density-functional theory (DFT), we identify a novel Fm3?m phase of Cu2P and two low-lying metastable structures, an I4?3d-Cu3P phase and a Cm-Cu3P11 phase. The computed pair distribution function of the novel Cm-Cu3P11 phase shows its structural similarity to the experimentally identified Cm-Cu2P7 phase. The relative stability of all Cu-P phases at finite temperatures is determined by calculating the Gibbs free energy using vibrational effects from phonon modes at 0 K. From this, a finite-temperature convex hull is created, on which Fm3?m-Cu2P is dynamically stable and the Cu3-x P (x < 1) defect phase Cmc21-Cu8P3 remains metastable (within 20 meV/atom of the convex hull) across a temperature range from 0 to 600 K. Both CuP2 and Cu3P exhibit theoretical gravimetric capacities higher than contemporary graphite anodes for Li-ion batteries; the predicted Cu2P phase has a theoretical gravimetric capacity of 508 mAh/g as a Li-ion battery electrode, greater than both Cu3P (363 mAh/g) and graphite (372 mAh/g). Cu2P is also predicted to be both nonmagnetic and metallic, which should promote efficient electron transfer in the anode. Cu2P's favorable properties as a metallic, high-capacity material suggest its use as a future conversion anode for Li-ion batteries; with a volume expansion of 99% during complete cycling, Cu2P anodes could be more durable than other conversion anodes in the Cu-P system, with volume expansions greater than 150%. The structures and figures presented in this paper, and the code used to generate them, can be interactively explored online using Binder.

SUBMITTER: Harper AF 

PROVIDER: S-EPMC7469244 | biostudies-literature | 2020 Aug

REPOSITORIES: biostudies-literature