AMorphous Silicon Alloy Anodes for Multiple Battery Systems - "AMorpheuS"

Carbon anodes for Li-ion batteries (LIBs) are regarded as one limiting factor preventing Li-ion batteries from being a viable option for transport applications (which require higher capacity for extended driving ranges) or grid storage applications (which require long cycle life). Compared to carbon, silicon has a much higher energy density and has been the focus of considerable research effort in recent years, stimulating the formation of high-profile, high-investment university spin-out companies such as Amprius and Nexeon. Silicon is the second most abundant element in the earth's crust and is thus a sustainable battery material candidate from a cost and availability perspective. However, despite its desirable properties for Li-ion batteries, it is also renowned for its drawbacks, namely large volume expansion, pulverisation and continued lithium loss through chemical reactions with the electrolyte (which the lithium ions diffuse in). Such phenomena have hindered the successful widespread uptake of this material in commercial Li-ion batteries, despite the myriad of global research groups working on finding ways to make it viable, e.g. by nano-structuring.

Project AMorpheuS presents an alternative way to fabricate Si anodes that does not rely on complex, costly nanostructuring or attempting to control electrode architectures. The approach is simply to deposit from solution using electrodeposition methods and to passivate the amorphous thin films with polymer chemistries that have already been shown to be effective as binders for Si electrodes. A fundamental understanding of the structural and surface properties of these electrodes will be obtained during realistic battery operation so as to identify the optimum Si alloy and polymer chemistry and optimise performance rationally. This project will develop Si electrodes that are not exclusively destined for use in Li-ion systems but can also be reversibly cycled in Na-ion and Li-S batteries. A variety of Si-alloy chemistries will be explored, including Si-Sn alloys, since these show considerable promise as anodes for Na-ion batteries. A goal is to develop the first Si-based Na anode.

This flexibility opens up numerous technology transfer opportunities in a variety of emerging battery systems focused on higher energy, sustainable, and safer technologies (e.g. Li-ion, Na-ion and LiS, respectively). The new batteries will be tested in the UK's first full battery prototyping line in a non-commercial environment.

Fully understanding what occurs in a battery as it is charged / discharged is complex. The battery is a closed system with constantly changing domains. Central to the success of this project is the application of in-situ characterisation techniques for analysing real-time, dynamic structural and surface changes that occur as Li ions pass back and forth between the anode and cathode (or why they do not). This knowledge will subsequently guide continued improvements in electrode designs. The major techniques proposed to gain a comprehensive understanding of the chemistry occurring in the battery as it is charged/discharged are multinuclear NMR and X-ray computed tomography. These techniques have provided battery researchers with a wealth of vital, real-time insight - especially regarding failure mechanisms in silicon materials.

Project AMorpheuS's approach will reduce the need for additional processing of materials in the electrodes, e.g., (i) high surface area carbons (which need energy-intense mixing processes) and (ii) industry-standard binders (which require toxic solvents to enable them to be processed into coatings). This strategy will reduce production time and eliminate toxic chemicals. These improvements will significantly reduce manufacturing cost and increase the UK's energy security.

AMorpheuS will prepare a novel amorphous Si-alloy anode with inherent degradation resistance that can be deployed in a number of Li-ion & beyond- Li-ion battery types and will positively impact the UK's "Energy Trilemma" around cost, environmental concerns and energy security.

The demand for rechargeable lithium-ion batteries (LIBs) has grown significantly since 1991, increases in Li consumption having grown at a rate of ca. 22% per annum since 2000. Despite its maturity in portable electronics, analysts foresee a continued boom in sales revenues across all industry sectors, from consumer electronics and EVs to grid storage. More recently, Na-ion batteries (NIBs) have gained recognition as promising candidates for next-generation, large-scale energy storage systems. Unlike Li, sodium is an abundant and inexpensive element that shares many properties with Li as an energy storage material. This means that Na-ion batteries can be successfully developed using approaches previously used with LIBs and represent a more sustainable technology than Li. LiS systems are also gaining more attention, having demonstrated higher energy density than LiCoO2-graphite LIBs, and show great potential for transport applications. The ability to inexpensively develop, at scale, an anode that could be used in all of these types of battery will simplify manufacturing routes and stimulate growth within the UK.

Society: Energy production and storage are now central paradigms to our quality of life. The traditional grid system (macrogrid) is costly, inefficient and carries risks of localized incidents being able to disturb the "whole". Microgrids, on the other hand, are obviously smaller and combine power generation, load management and energy storage assets - all controlled in a coordinated network. Having the ability to locally store renewable solar energy, for example, will significantly impact domestic energy costs and reduce issues relating to intermittency.

Environment: Legislation-driven goals such as the EU's 20-20-20 strategy are striving for a 20% reduction in CO2 emissions, a 20% increase energy efficiency, and a 20% increase in renewable energy systems by 2020. This project can deliver in all three of these areas. According to the IEA's Energy Technology Perspectives scenario, PV-harnessed energy is forecast to save 30 Gt of potential CO2 emissions by 2050, and the capability to incorporate longer-lasting, efficient energy storage into renewable energy technologies is essential for this to be achieved. By eliminating the need to use conventional anode components such as conductive additives and polymer binder systems, there will be a reduction in the use of toxic battery solvents such as N-methyl pyrrolidone (NMP), a known teratogen.

Economy: The market for energy storage on the grid (ESG) alone is forecast to surpass $30bn by 2022. Long duration energy storage by advanced batteries will multiply the technology options available to make this viable. Considerable market opportunities also exist in the transport and portable electronics sectors. Technology transfer and commercial exploitation of this research to produce a new range of longer-lasting, higher energy density batteries, (with better design-through-innovation manufacturing) would create market share and generate significant economic benefits for the UK in these three areas.

Knowledge: New understanding of the structural dynamics and surface evolution established in novel a-Si anodes for several competing battery technologies. New approaches in electrode fabrication will generate degradation-resistant anodes and develop and disseminate expertise. Advancing knowledge within electrodeposition will allow exploitation possibilities not only in energy storage but within surface science innovations for other research areas, e.g. corrosion inhibition. Technology transfer opportunities exist with UK battery companies such as Sharp, Faradion, QinetiQ, JLR and Oxis Energy.