The structure and properties of a new type of nanostructured composite Si/C electrodes for lithium ion accumulators

Abstract

The results obtained in studies of the structure and electrochemical properties of film electrodes prepared by magnetron plasma sputtering of silicon and graphite and working under the conditions of lithium injection and extraction are generalized. Composite silicon-carbon electrodes synthesized by depositing silicon and carbon nanolayers with the use of a magnetron plasma were films 100–500 nm thick. Part of them exhibited highly uniform nanogranular structure based on a carbon matrix with inserted silicon clusters of size below 6 nm. The nanogranular structure of Si/C composites was observed for the first time; such a morphology was not characteristic of not structured silicon layers deposited under equal conditions. The factors that determined the electrochemical charging-discharging behavior of new composites were the degree of uniformity of the nanogranular structure, the ratio between the silicon and carbon components, and film thickness. For two thin films, the initial composite capacitance was higher than that corresponding to the Li4.4Si stoichiometry for the silicon component and LiC6 stoichiometry for the carbon component, which was related to the special nanostructured state of silicon and carbon. The effects (luminescence band and absorption bands in the visible range) characteristic of nanosized silicon particles were observed.