Improvement of silicon powder negative electrodes by copper electroless deposition for lithium secondary batteries

In order to enhance the electrical conductivity of Si powder, which shows a poor cycleabilty as the anode in lithium secondary batteries due to low electrical conductivity and a severe volume change on cycling, Cu is deposited on the Si surface by a electroless deposition method. As Cu deposition on bare Si powder is found to be unsatisfactory, Si powder is etched to roughen the surface, on to which a large amount of Cu deposit with a uniform coverage is obtained. The resulting anode material exhibits improved cycle performance as a result of conductivity enhancement. The long-term cycleability is, however, still unsatisfactory due to detachment of Cu from the Si surface that is caused by a severe volume change of the Si particles on cycling. The detachment of Cu is greatly suppressed by annealing at 400 °C in an inert atmosphere and, thereby, delivers better cycle performance. The improvement in interfacial stability exhibited by the annealed samples is ascribed to the formation of a Cu3Si alloy phase at the interface and diffusion of Cu atoms into the Si particles.