High Performance Aluminium-graphene Battery Materials

Aluminium-ion battery is a novel energy storage device using aluminium metal anode and aluminium-based ionic liquid electrolyte.It have unique advantages of high anodic capacity,safety and low-cost.However,the progress of Al-ion battery is now restricted by its cathodic performance such as low capacity and insufficient cycling stability,which impede its further pratical application in the future.Hence finding a matched cathode material(especially well-performed graphene-based cathode material)and study the cathodic reation mechanism to improve its electrochemical performance is of vital importance.Graphene is a novel two dimensional nano-carbon material with excellent mechanical strength and flexibility,outstanding optical property and ultrahigh electronic conductivity.Such excellent electronic conductivity,ultra-large aspect ratio and surface area enables great application potential of graphene in energy storage material field.Exploring the relationship between key indexes of graphene and important factors during electrode reaction is the crux of the promoting graphene's application in energy storage field.Accordingly,this thesis presented systemic studies on "high-quality graphene design" with the break point of "short lab" graphene cathode of Al-ion battery,studied relation between the fundamental "defect-free","few-stack" characteristic and electrode performance to significantly improve the electrochemical performances of graphene cathode of Al-ion battery and expand the"high-quality graphene design" to other battery systems.The main results are listed as follows.1.Propose the primary "defect-free princi(?)le" for graphene cathode of Al-ion battery:the fewer the defects,the better the performance.We successfully fabricated a large-scale producible defect-free graphene aerogel cathode affording excellent performances:high specific capacity of 100 mAh g-1,fast charge in 7.2 seconds(highest current densities of 100 A g-1),stable cycling performance within 25,000 cycles.Such Al-graphene aerogel battery can deliver moderate energy density of 60 Wh kg-1 and power density of 30 kW kg-1,achieving or surpassing the commercialized supercapacitors.We demonstrated that the defects in graphene leads to the degradation and decay of performance.We also proved the fast charge/slow discharge,flexible and foldable,fire-resistance and safe advantages of Al-graphene battery,exhibiting its great potential as future wearable,high power density and safe energy storage devices.2.Propose the "high-quality graphene design".We achieved a scalable defect-free,few-stack and highly continuous graphene microflower powder material by inducing key technologie such as targeted crumple and high temperature annealing.We also explained the decisive effect of the "defect-free" and"few-stack" characteristic on graphene cathode of Al-ion battery.The defect-free GmF3000 cathode of Al-ion battery can deliever high and stable specific capacity of 100 mAh g-1 withing 5,000 cycles,and can be fast charged in 18 seconds(highest current densities of 20 A g-1),far surpassing those of low-quality graphene cathode.We also expand the "high-quality graphene design" to sulfur cathode of Li-S battery.The defect-free GmF3000-S composite cathode can achieve a high areal capacity of 5.2 mAh cm-2 also surpassing those of low-quality graphene-sulfur control composites,demonstrating the general applicability of"high-quality graphene design".3.Demonstrate the existance of aluminium dendrites in Al-ion battery using room temperature ionic liquid electrolyte and aluminum metal anode.We discover the vital role of native oxide film in preventing dendrite growth and maintaing the intergrity of Al metal anode;explain the reaction mechanism of Al metal with ionic liquid electrolyte under the full-scale surficial protection of native oxide film,which can promote further deep thought and practical development of Al-ion battery.