Graphene Quantum Dots as an Electrode Material for Hybrid Battery-Supercapacitors

电池-超级电容器混合体(BSH)是一种很有前途的储能装置，它结合了电池和超级电容器的优点，使它们能够受益于高能量密度、高功率密度、长生命周期、快速充电和高温能力1。然而，制造具有高性能的可靠的BSH仍然是非常具有挑战性的，研究还很少。本项目旨在通过利用石墨烯量子点(GQD)的独特性质来弥补这一研究空白，即合成石墨烯量子点并将其嵌入到可控的BSH电极的制造中，以低成本的工艺。为了实现BSHS的高性能潜力，人们正在寻找进一步改善其性能的方法，使其具有与先进电池和传统超级电容器的竞争力。一种选择是将石墨烯量子点(GQD，具有可调电子性质的纳米尺寸半导体颗粒)集成到设备的两个电极上。GQD保留了石墨烯的特性(快速移动的电子、高热导率、量子隧道效应等)，但表现出量子限制效应，导致材料的禁带打开，使它们除了尺寸和边缘效应外，还具有半导体的行为。此外，GQD对多种电解液离子表现出很强的吸附能力，包括锂、钠等常规储能设备中常用的离子。在超级电容型电极中加入GQD提高了能量密度和电容电位2，而在电池型电极上加入GQD的优点包括高可逆比容量、改进的倍率能力和更长的寿命周期3。与标准锂离子电池相比，没有添加GQD的BSHS有可能保持相当于4000%的生命周期1，4。加入GQD将进一步延长生命周期，因为它们可以调节电极的内部结构，防止损坏，从而减少对它们的频繁更换、广泛的矿产开采、生产过程中的二氧化碳排放和围绕废锂离子电池处置的环境问题。尽管GQD的潜力很高，但据我所知，到目前为止，还没有关于可靠的BSHS将GQD集成到两个电极中的报告。此外，GQD结构(锯齿形和扶手椅边缘，以及官能化程度)对GQD性质的作用和影响，以及由此产生的电极和器件还没有定义。因此，本项目旨在填补这一空白，并通过开发用于BSH应用的可靠的GQD基电极。我们的目标是：(I)通过对GQD和电极行为的系统表征来建立GQD和电极的结构和性能之间的关系；(Ii)使用分子动力学模拟来优化实验设计并预测所产生的装置的响应；(Iii)基于最有希望的模拟和实验结果制造混合动力装置的原型演示器。

A battery-supercapacitor hybrid (BSH) is a promising type of energy storage device that combines the advantages of both batteries and supercapacitors, allowing them to benefit from high energy density, high power density, long life cycle, fast charging times and high-temperature capabilities1. However, fabricating reliable BSH exhibiting high performance remains very challenging and little studied. This project aims to address this research gap by exploiting the unique properties of graphene quantum dots (GQDs), i.e. to synthesise and embed them in the fabrication of BSH electrodes controllably in a low-cost process. To realise the potential high for performance BSHs, the search for methods to improve their properties further, making them competitive against advanced batteries and conventional supercapacitors, is ongoing. One option is to integrate graphene quantum dots (GQDs, nanometre-sized semiconductor particles with tuneable electronic properties) onto both electrodes of the device. GQDs retain the characteristics of graphene (fast-moving electrons, high thermal conductivity, quantum tunnelling, etc.), but exhibit the quantum confinement effect, resulting in an opening of the material's bandgap, allowing them to behave as a semiconductor, in addition to size and edge effects. Furthermore, GQDs display a strong adsorption capacity for a wide range of electrolyte ions, including lithium, sodium and other ions commonly used in conventional energy storage devices. The incorporation of GQDs into a supercapacitor-type electrode increases the energy density and capacitance potential2, while the advantages to including GQDs on a battery-type electrode include high reversible specific capacity, improved rate capability, and longer life cycle3. BSHs without the addition of GQDs have the potential to maintain a life cycle equal to 4000% versus that of a standard lithium-ion battery1,4. The inclusion of GQDs will result in a further increase of the life cycle since they can regulate the internal structure of the electrodes, preventing damage and therefore reducing the need for their frequent replacement, extensive mineral mining, CO2 emissions during production and environmental issues surrounding the disposal of spent lithium-ion batteries. Despite the high potential of GQDs, to the best of my knowledge, so far, there are no reports on reliable BSHs where GQDs are integrated into both electrodes. Moreover, the role and effect of GQD structure (zigzag and armchair edges, and functionalisation degree) on the properties of the GQDs, and the resulting electrodes and device are not defined yet. Therefore, this project aims to fill this gap and by developing reliable GQD-based electrodes for BSH applications. We aim to: (i) Establish the relationship between the structure and properties of the GQDs and electrodes produced using a systematic characterisation of the GQDs and electrode behaviours; (ii) use molecular dynamic simulations to optimise the experimental design and to predict the response of the device produced; (iii) produce a prototype demonstrator of a hybrid power device based on the most promising simulation and experimental results.