Development of Graphene Silicon-Lithium Ion Battery Anodes

该项目是与英国应用石墨烯材料有限公司(AGM)合作的。重点研究了锂离子电池负极用石墨烯-二氧化硅复合材料的合成及其工业化生产的进展。随着对可持续性和净零碳排放的压力和意识一直存在，我们对碳氢化合物的依赖必须被可再生能源所取代。然而，可再生能源的间歇性以及无法调节能源生产以满足高峰需求，迫使人们要求改进储能解决方案。除了能源电网，英国政府的目标是在2030年前禁止生产内燃机汽车。这一最后期限导致需要提高电池性能，以满足消费者对续航里程、寿命和充电率等问题的期望。近年来，锂离子电池以其高的工作电压和能量密度(150Wh/kg)、长的使用周期和消费品的安全性能而被证明是最有前途的储能装置。硅基阳极因其极高的锂理论容量(4200mAhg-1)和低工作电压(~0.2VvsLi/Li+)而成为传统低性能石墨阳极的有吸引力的替代品。然而，由于锂的引入，硅存在导电性差、体积膨胀过大(~300%)和结构变形等问题。后两者导致在多个周期内产能大幅下降(仅在第一个周期后就减少了40%以上)。在二氧化硅分子周围引入石墨烯涂层和纳米结构是克服硅限制的最有前途的解决方案。涂层/纳米结构旨在吸收观察到的膨胀并降低破裂的严重程度，同时还具有引入石墨烯的高导电性的额外好处。图1：硅微粒周围的石墨烯笼子比较然而，单是石墨烯-二氧化硅阳极的合成，就是一个非常热门的话题，并且被以前的研究广泛覆盖。该项目旨在实现对可扩展技术的新颖增强，该技术可在工业规模生产中复制。为了实现这一目标，整个项目必须实现多个目标：通过化学气相沉积(CVD)和冷冻干燥等技术，利用AGM合成石墨烯-二氧化硅复合材料和气凝胶，以生产有效的电池负极材料。通过多个全循环(充放电)对复合材料进行表征，并记录整个过程中的容量保持率和库仑效率。通过观察多循环过程中二氧化硅断裂的程度来表征复合材料。表征石墨烯纳米结构/涂层的结晶度，以更好地了解石墨烯形成的差异如何影响阳极的性能和固体电解质界面(SEI)的形成。根据复合材料的特性/效率以及生产技术的时间和成本来评估给定制造技术(S)的潜力。研究合成过程中的可变条件，如工作温度、蒸气密度和从蒸气出口到基二氧化硅材料的距离，如何影响石墨烯层的形貌。

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.