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

[Image: see text] Using first-principles structure searching with density-functional theory (DFT), we identify a novel Fm3̅m phase of Cu(2)P and two low-lying metastable structures, an I4̅3d–Cu(3)P phase and a Cm–Cu(3)P(11) phase. The computed pair distribution function of the novel Cm–Cu(3)P(11) phase shows its structural similarity to the experimentally identified Cm–Cu(2)P(7) 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 Fm3̅m–Cu(2)P is dynamically stable and the Cu(3–x)P (x < 1) defect phase Cmc2(1)–Cu(8)P(3) remains metastable (within 20 meV/atom of the convex hull) across a temperature range from 0 to 600 K. Both CuP(2) and Cu(3)P exhibit theoretical gravimetric capacities higher than contemporary graphite anodes for Li-ion batteries; the predicted Cu(2)P phase has a theoretical gravimetric capacity of 508 mAh/g as a Li-ion battery electrode, greater than both Cu(3)P (363 mAh/g) and graphite (372 mAh/g). Cu(2)P is also predicted to be both nonmagnetic and metallic, which should promote efficient electron transfer in the anode. Cu(2)P’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, Cu(2)P 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.