Electrochemical Energy Storage with Graphene-Enabled Materials

Graphene is a one-atom-thick sheet of carbon atoms arranged in a honeycomb lattice. The exceptional physical properties of graphene have attracted enormous interest since its experimental isolation and initial characterisation in 2004, notably its intrinsically high surface area and its unique electronic properties, as manifested by through its high conductivity. Amongst the myriad applications foreseen for this material, exploitation in electrochemical energy storage with supercapacitors or batteries ranks as one of the most prominent.

De-carbonising the national, and indeed global, energy supply is a goal driven by rising fossil fuel prices and concerns over air pollution and anthropogenic climate change. For such de-carbonisation to make greater use of "renewable" energy sources requires new methods of storing and converting that energy. This general background, along with the widespread increase in usage of personal electronic apparatus (mobile phones, lap-tops) has driven an enormous renewal of interest and development of electrochemical (battery and supercapacitor based) energy storage, which is the technological motivation for this project. Ironically, such (potentially) de-carbonised energy stores are highly dependent on carbon as a constituent storage material. Supercapacitors are based on the storage of electrical energy within the electrical double-layer formed at high surface area electrodes, whereas certain types of battery are dependent on carbon, either as one of the electrodes or as a conducting additive used to complete the circuit to the electrodes.

There are considerable challenges to be addressed en route to incorporating graphene into these energy storage devices however: two specific problems, apparent in much of the vast body of recent work on graphene and energy storage, are: (a) the "graphene" is generally of poor quality and variable dimensions, and (b) frequently only minimal effort is made to control the architecture of the graphene in the resultant device. Consequently, we are still some way off the routine incorporation of graphene within battery and supercapacitor electrodes, as either composites for immobilisation or conductivity, or as primary electrode materials. The goal of this proposal is to remedy these deficiencies by iteratively designing, manufacturing and testing graphene-based batteries and supercapacitors.

The proposed research is in the area of material developemnt of graphene for supercapacitor and battery applications and will have considerable industrial and academic impact, both nationally and internationally.

The world-wide market for lithium-ion batteries alone is expected to increase from an estimated $8bn in 2008 to $30bn by 2017, according to independent market analyst Takeshita. For supercapacitors TechNavio projects the global market for supercapacitors to grow from an estimated value of $470 million in 2010, reaching a value of $1.2 billion in 2015. The energy storage needs of society in the long-term are likely to demand batteries for both stationary power storage, to collect unwanted energy generated from wind farms, and batteries and supercapacitors to power electric vehicles. The success of energy storage technologies, such as supercapacitors, Li-ion and Li-oxygen batteries underpins the UK's drive to a lower carbon and greener economy which is less reliant on carbon dioxide generating fossil fuel. Advances in supercapacitor and battery research would impact on the battery industry and the enormous portable electronics industry (laptops, cameras, mobile phones and other hand-held devices). Lithium batteries in particular have found, and will continue to find, important and diverse technological applications.

Optimisation of a technology usually derives from an understanding of the processes that underpin that technology. The primary aim of this proposal is therefore to make fundamental advances in the understanding of the structure and interactions occurring at electrochemical interfaces. Advances in the understanding of electrode interfaces would be most strongly felt by the supercapacitor and battery industry and, from there on, all users of supercapacitors and batteries. Our proposal seeks to incorporate graphene into such devices, building on the UK's fundamental expertise in this revolutionary material. Our work is based on a scaleable method of producing high quality graphene with tailored properties: the cost of electrochemical production has been independently estimated at £20/kg. Currently carbon blacks cost in the region of £3-4.50/kg (for use in batteries as conductivity enhancers) and £0.6-4.50/kg (for supercapacitor carbon, depending on the application). Therefore if graphene-enabled materials markedly improve the performance of either supercapacitors or batteries, the five fold difference in price with graphene should not present an insurmountable barrier to adoption if the performance/lifetime enhancement is sufficient.

A very important area for new batteries and supercapacitors technologies is in helping to meet the energy challenges of the 21st century, by contributing to energy storage requirements and also "electromobility". EPSRC has a strong energy theme, with relevant details laid out in the section "Underpinning Energy Research in Energy Storage Materials". A quarter of all man-made carbon dioxide emissions arise from transportation, any breakthroughs in battery or supercapacitor technology regarding significant increases in energy density (and therefore driving range) would allow future electric vehicles (EVs) to become a more attractive option for consumers. As a consequence our research will have a major impact on the automotive industry in the UK and worldwide. Moreover the UK will depend on more and more intermittent electricity supply from, for example, wind, wave and solar power. Energy storage will become crucial for the smoothing out of supply and demand and allowing for a less centralised grid. Improvements in battery performance will have significant impact on this nascent application and will allow greater adoption of green power and lower dependence on fossil fuel power stations, which will lower carbon dioxide emissions in this sector (approximately 30% of total UK emissions).