Silicon nanowires for high energy lithium-ion battery negative electrodes

Samples of silicon nanowire materials, produced by Merck KGaA via a batched supercritical fluid method, were evaluated within composite electrodes for use as the active component in future lithium-ion battery negative electrodes. A comprehensive literature review of silicon based negative electrodes with a focus on silicon based composite type electrodes is provided. Characterisation of the nanowire materials was conducted via electron microscopy. Composite type electrodes were prepared utilising poly-acrylic acid as a binder material. Insight into the interaction of poly-acrylic acid with batch-1 nanowire material was achieved via a FTIR spectroscopy study, evidence for the formation of a binding interaction was observed.Composite electrodes containing nanowire material were electrochemically evaluated via the use of half-cells. The performance of the nanowire material samples was found to be significantly different and attributed to the use of differing precursor chemicals for synthesis. The structural variation of silicon nanowire particles within a composite electrode was investigated throughout an initial cycle and extended cycling. The electrochemical performance of composite electrodes containing the nanowire materials was found to depend critically on the composite electrode formulation and the electrolyte solution used. The rate performance was also observed to be influenced by the electrode formulation, suggesting the electronic and ionic conductivity of the composite electrode to be the rate limiting factors of the composite electrodes tested. Through the optimisation of composite electrode formulation and electrolyte, extended cycling at a capacity of over 600 mA h g-1(Composite) for 200 electrochemical cycles at a C-rate of C/10 was achieved, the highest number of cycles reported for SFLS silicon nanowire materials to date