Multiscale modelling of mechanical deterioration in lithium-ion batteries

Identifying cheap and efficient methods to store clean electrical energy is one of the key hurdles that must be overcome on the path to achieving a low carbon economy. An important component of this is developing commercially attractive battery packs for use in electric vehicles; around one half of the total cost of these vehicles is currently the battery. Recent legislation to ban the sale of combustion engines across large parts of the world over the next few decades means that this goal must be achieved as a matter of urgency.

Lithium-ion batteries are currently the best candidates to meet these demands. They are both energy and power dense, and only slowly lose their charge when not in use. Although their lifetime is already reasonable in relatively mild applications, such as consumer electronics where they can be used for upwards of 1000 cycles, they are plagued by rather more rapid degradation in the abusive high-current regimes that are common in electric vehicles. Reduced longevity is directly responsible for inflated consumer cost, and so extending battery cyclability is of paramount importance in realizing a healthy market for lithium-ion technology.

The root cause of a significant portion of battery degradation is the pulverisation of the internal electrode microstructure by the swelling/contraction of constituent material when the device is in use. This mechanical degradation can in turn accelerate chemical degradation of the cell. To combat this, new materials and architectures must be identified to mitigate this source of damage. The search for improved design can be effectively guided by a coherent modelling framework that can be used to (i) benchmark novel designs without the need to construct and test them, and (ii) identify optimal configurations for manufacturers to target. The development of such a tool is predicated on overcoming some significant mathematical challenges related to resolving the accurate model equations describing the interaction of the variety of different materials (a liquid electrolyte and several different solids) over the vastly differing relevant lengthscales (from microns to centimeters).

This program of work will overcome these challenges by applying systematic mathematical methods and deliver a tool to tackle the task of accurately modelling the evolution of the damage sustained by the internal components of a battery over its lifetime. This will significantly accelerate the development of more robust batteries and pave the way to realizing a sustainable future.

The overarching goal of this work is to provide a theoretical framework that empowers manufacturers to build lithium-ion batteries (LIBs) that are more long-lived, safer, and better able to cope in abusive high rate applications. The challenges that need to be addressed en route to realizing this goal were identified in collaboration with the industrialists, chemists and engineering who work in the areas where the impact of this work will be felt. Continued communication, and impact in the form of cross-pollination of ideas with these areas, will be ensured by holding regular meetings with members of the Faraday Institute's modelling team (with whom JF has a fruitful working relationship), with industrial collaborators (see their letter of support), and with academics in chemistry and engineering. Impact outside this network will be ensured by producing open source publications, attending judiciously chosen conferences, and perhaps most importantly, distributing user-friendly open source code to access and make use of the theoretical tools that we develop.

Taking these steps will ensure that the mechanical models and solution methods that we develop will equip both academia and industry with a bespoke tool capable of both (i) carrying out virtual testing of the structural integrity of materials and device architectures (reducing the need for time consuming and costly prototyping), and (ii) identifying optimal materials and microstructures to serve as target that should be aimed for in practice. This will provide a significant benefit for economic success by accelerating the development of improved battery packs, thereby directly decreasing the overall cost of mobile energy storage. The largest impact is expected to be felt in the area of transport, where around one half of the overall cost of an electric vehicle (EV) is due to the battery. Enhancing the commercial viability of LIBs will enhance the rate of adoption of EVs and strongly contribute towards meeting the recent policies to ban the sale of combustion engines across large portions of the world in the next few decades. This, in turn, will ultimately make a contribution towards societal improvement by decreasing CO2, NOx and particulate emissions; mitigating climate change; and enhancing quality of life.

The importance of delivering this impact is reflected in the myriad of bodies pledging strong support towards this, and related, causes. For example, the EPSRC's Strategic Plan and Productive and Resilient Nation outcome, the NERC's UK Climate Resilience program and the government's Grand Challenges laid out in their Industrial Strategy. Lastly, impact in the form of effective public engagement will be generated by the PI first being trained in, and then delivering presentations to the public on progress in this highly topical area.