Fast kinetics in free-standing porous Cu₃P anode for Li-ion batteries

Anode materials for Li-ion batteries based on a conversion mechanism show very high theoretical specific capacities. In particular, phosphide materials display volumetric and gravimetric capacities far beyond graphite, approaching those of silicon-based materials. However, the slow kinetics and large mechanical strain during the conversion process are challenging issues toward enabling phosphide-based anode materials. Here, we synthesize a copper phosphide free-standing membrane and show the benefits of this approach, which provides lighter electrodes with faster kinetics during lithiation and delithiation. The Cu₃P membrane is both binder-free and carbon black-free, and its synthetic process involves a simple chemical vapor deposition of phosphorus on a composite polymer-copper membrane at a moderate temperature of 429 °C. Microscopic and other methods show the purity of the phase and of the porous structure within the membrane. Galvanostatic cycling reveals an initial discharge reaching the theoretical capacity, high reversible capacity of 320 mAh/g_electrode (including the current collector), and good kinetics for phosphide-based materials at C/5 rate.