Development of Graphene Silicon-Lithium Ion Battery Anodes

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This project is in collaboration with Applied Graphene Materials UK Ltd (AGM). It focuses on the synthesis of a graphene-silica composite for anodes within lithium-ion batteries and the advancement of industrial-scale production. With an ever-present pressure and awareness for sustainability and net-zero carbon emissions, our reliance on hydrocarbons must be replaced with that of renewable energy sources. However, the intermittency of renewables and inability to regulate energy production to meet peak demands force the requirement to improve energy-storage solutions. Away from the energy grid, the UK government aims to ban the production of internal combustion engine vehicles by 2030. This deadline causes the need to improve battery performance to meet consumer expectations for matters such as range, lifespan and charge rate. In recent years, lithium-ion batteries have been demonstrated as the most promising energy-storage devices due to their high working voltage and energy densities (150Wh/kg), long life cycle and safe performance for consumer goods. Silicon-based anodes have recently become an attractive replacement for traditionally low performing graphite anodes, due to their extremely high theoretical capacity for lithium (4200 mAhg-1) and low working voltage (~0.2VvsLi/Li+). However, silicon suffers from poor electrical conductivity, excessive volume expansion (~300%) and structural deformation with the introduction of lithium. The latter two result in a considerable reduction in capacity over a multi-cycle period (upwards of 40% after the first cycle alone). The introduction of graphene coatings and nanostructures around silica molecules is the most promising solution to overcome silicon's limitations. The coatings/nanostructures aim to absorb the observed expansion and reduce the severity of fracturing, all whilst having the additional benefit of introducing graphene's high electrical conductivity. Figure 1: Graphene cages around silicon microparticles comparison However, the synthesis of graphene-silica anodes, alone, is a very hot topic and widely covered by previous research. What this project aims to achieve is the novel enhancement of a scalable technique that can be replicated in industrial-scale production. With this aim, multiple objectives must be achieved throughout the project: To synthesize graphene-silica composites and aerogels with AGM, through techniques such as chemical vapour deposition (CVD) and freeze-drying, to produce an effective battery anode material. To characterize the composites through multiple full-cycle (charge and discharge) periods and record the capacity retention and coulombic efficiency throughout. To characterize the composites by observing the extent of silica fracturing over the course of multi-cycle periods. To characterize the crystallinity of the graphene nanostructures/coatings to better understand how the variance of graphene formation affects the performance of the anode and formation of the solid electrolyte interface (SEI). To evaluate the potential of the given manufacturing technique(s) based on the characterisation/efficiency of the composite, and the time and cost of the production technique. To investigate how the variable conditions of the synthesis process, such as working temperature, vapour density and the distance from the vapour outlet to the base silica material, affects the morphology of the graphene layer.