Determining the effect of a varying carbon concentration on the cycling stability of a a-SiCx:H anode

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Lithium-ion batteries are currently most commonly used in most electronic devices. These batteries are used because of their superiority in gravimetric energy and cyclability compared to other battery technologies. The most common anode used in lithium-ion batteries is currently graphite. Graphite has proven to be a very stable cycling material. However, with a specific capacity of 372 mAh/g, there are alternatives with higher specific capacities.
One of those alternatives is silicon, which has a theoretic capacity of 3000 mAh/g. However, a volume change of 200-300% occurs when a pure silicon anode is cycled. Thereby cracking the material and losing the majority of this theoretic capacity. The capacity retention of a silicon-based anode can be increased by various techniques. Of those techniques, two are used in this
work, alloying the silicon with carbon and creating a porous material.
This research aims to evaluate the effect of carbon concentration and porosity in the hydrogenated amorphous silicon carbide (a-SiCx:H) on the cycling performance of Li-ion batteries when this material is used for the anode. The a-SiCx:H used in this research is deposited on carbon fiber paper (CFP) using Plasma Enhanced Chemical Vapour Deposition (PECVD). By varying the precursor gas flows used during the PECVD the structure of the a-SiCx:H is changed and
samples with varying porosity and carbon concentration are obtained. These anodes are then tested using coin-cell batteries in a half-cell configuration. The results of a stability test indicated that the sample with an estimated carbon concentration of 8% and a porosity of 29% had the best capacity retention, retaining 61% of the initial 1800 mAh/g during 60 cycles at 0.3C.
This result is achieved with the sample having the highest carbon concentration and porosity that was researched in this work, suggesting that both a high carbon concentration and a high porosity value increase the capacity retention of the a-SiCx:H anode. Individual contributions of the carbon concentration and the porosity to the capacity retention have not been researched.
Therefore, conclusions to these individual contributions cannot be drawn.