Abstract
The electrochemical behaviour of the binary transition metal phosphide Cu3P towards lithium is investigated through galvano- and potentiostatic measurements. Obtained through high-temperature synthesis, this system shows a better volumetric capacity than graphite and a good capacity retention. In situ X-ray diffraction and first-principles electronic structure calculations are combined with the electrochemical results to show that the complete insertion of 3LiC in the Cu3P electrode proceeds with the formation of three intermediate phases of lithium composition LixCu(3Kx)P (xZ1,2,3). The extra capacity previously observed in discharge is now clearly assigned to lithium insertion into the CuP2 impurity and to SEI reactions.