Self-Supporting SiOxCy/C-F Electrodes Modified by Surface Fluorination to Enhance Lithium-Ion Battery Performance

Lithium batteries are a widely used energy source not only for portable electronics, but also for electric mobility. The ever-increasing demand for higher power density is driving further research into electrode materials to make batteries more efficient, durable and safe. To outperform graphite (372 mAh/g), research has focused on anode materials such as silicon (4200 mAh/g for Li₄.₄Si), which leads to a 300% volume expansion during alloy formation. Silicon oxide, with less volume variation (150%) but lower performance (1965 mAh/g for SiO₂), has therefore become a material of interest. However, these materials need to be combined with carbons to achieve sufficient electrical conductivity. In addition, surface passivation by fluorination is known to stabilize the Solid Electrolyte Interface (SEI) [1]. Both the nature of the materials involved, and processing of the electrodes therefore have a role to play in the overall performance of the battery.In this work, we have produced sol–gel composite lithium battery anode materials made from an intimate mixture of SiO₂ and carbon, nanostructured and self-supported by biomass-derived carbon fibers [2]. The versatility of the synthesis process has enabled us to obtain a wide range of textures, with micropores, mesopores and macropores in variable quantities depending on the synthesis conditions. In addition, variable quantities of SiO₂ were obtained, up to 80 by weight with respect to carbon. Thanks to its self-supporting nature, electrodes were cut directly from the material. We have thus demonstrated that it is possible to use it as an electrode material without going through the formulation stage, without adding binder or conductive carbon, and without using a current collector in button cell tests. The electrochemical performance of the cut material (Fig. 1) was superior to that of the formulated material, with a discharge capacity of 1070 mAh/g compared with 943 mAh/g for the formulated material after 100 cycles at C/25 (Fig. 2). Similarly, fluorination treatment of the electrode from the cut material resulted in better performance with a discharge capacity of 1786 mAh/g after 100 cycles at C/25.