Vacancy Engineering in Anode Materials for High-Power K-Ion Batteries

Energy storage is a tremendous research focus of our time and plays a vital role in tackling climate change and enabling a low carbon economy. It is the technology that will accelerate the transition to electric vehicles and facilitate the efficient utilisation of renewable energy in the grid scale applications. Today's massive production of Li-ion batteries (LIBs) has resulted in the supply risk of Li and Co, which would place future UK battery industry subject to external market and geopolitical forces. There is an immediate need to exempt from the over-reliance on LIBs through developing the next generation batteries that are based on earth-abundant elements. K-ion batteries (KIBs) offer cost-effectiveness and environmental sustainability, as they are based on K (2.09% abundance in the earth's crust, vs. 0.002% Li) and a Co-free system. KIBs possess the advantages of K having the closest reduction potential to Li (-2.92 V vs. -3.04 V) and being able to reversibly intercalate into graphite, which makes it possible to achieve high energy density and directly utilise the existing LIB manufacturing facilities. In practical applications such as grid-level storage where considerations of cell weight and size take a back seat to cost-per-kWh, KIBs represent a very attractive candidate.

Building on our previous work on KIBs, our ambition is to develop high-performance KIBs and unlock the potential of KIBs as the next generation batteries. The major challenge of developing KIBs is the large size of K-ion because it causes kinetic difficulties to store K-ion. This project presents the design of electrode materials' structural defects, in accordance with the time scales of K-ion kinetics, to achieve high performance of KIBs. We will study crystalline structures that have directional pathways for K-ion insertion and diffusion at a long-range time scale, which allows to achieve high energy density. More importantly, we will investigate the approach of creating oxygen vacancies that allows a fast K-ion knetics at a short-range time scale and therefore a high power density. Simultaneously, developing KIBs requires the understanding of the complex processes occurring within the electrodes. We will perform materials characterisation and chemical analysis to understand the benefits of oxygen vacancies, especially the spatial effect of the vacancies, and acquire much-needed clarity on the fundamental chemistry of reversible K-ion storage, which is important as the development of KIBs is still in its infancy. This will suggest promising avenues for the improvement of KIB electrode materials in a wide range and generate the knowledge that could be transferred to other energy applications. The novelty in the approach is fundamentally different from the previous considerations of enhancing charge transport in the field of KIBs. The project includes the following:

(i) Explore titanium niobium oxides (TNOs) as a new type of KIB anodes to reversibly store K-ion, which will identify promising materials put through as the model materials for the design of OVs.
(ii) Create and control oxygen vacancies located in the surface or towards the bulk of TNOs and investigate the spatial effect of the vacancies on the enhancement of electrode power density.
(iii) Perform in-situ and ex-situ characterisations of anodes with and without oxygen vacancies to best characterise, understand and explain the K-ion kinetics upon the designed structural engineering.
(iv) Demonstrate KIB full-cell prototypes in a lab scale based on the advantages of performance, low-cost and environmental sustainability of the anodes (TNOs) developed in the project and the state-of-the-art cathodes (Prussian blue analogues).
(v) Engage with all stakeholders in the UK's battery industry and be an advocate for KIBs.

This project and its outcomes will have major impact on the following aspects:

Economy
To achieve the ambitious 2040 goal to out-sale petrol and diesel vehicles, it is imperative to develop low-cost and high-performing batteries that can be put into use in a foreseeable future. The successful delivery of this project will lead to prototypes of K-ion batteries (KIBs) based on earth abundant elements, attract academic and industrial interest, and preparation for future commercialisation. It is also envisaged that besides electric vehicles, KIBs are an affordable solution for stationary energy storage and integrate renewables energy (e.g., wind and solar) into grid for off-peak consumption. In a medium term of 4-10-year window, the outcome of this project will have impact through potential intellectual property generated in the field of KIB technology, focused academic and industrial collaborations on KIB materials exploitation and cell management, and employment opportunities in battery production. This will boost the UK's capability in various strategically relevant scientific and technological domains. In a long term of 10-50-year window, the outcome of this project will change the supply chain of KIBs in the UK and around the world and stimulate global knowledge transfer across various energy applications.

Society
This project aims to make significant development in KIB technology by tuning materials' structural defects and enabling high battery performance. As the UK government has now a legally binding target to bring all greenhouse gas emission to net zero by 2050, KIB is an immediate cost-effective and environmentally sustainable energy storage solution and its development will reinforce the transition to electric vehicles and reduce CO2 emission within the UK energy landscape. Damaging effects of transport emissions on the health of the public will be minimised in an affordable low carbon society. The development of KIBs will contribute to large employment of renewable energies in the UK and be used in large-scale stationary energy storage. The ability to store energy at a large scale will have significant influence on providing energy to remote areas and helping aid organisations in the regions where power grid may be damaged by natural disasters. In addition, the increase of the UK's capacity in energy storage will generate large saving on power bills for the public.

People
In a short term of 3 years, this project will provide highly skilled researchers, i.e., the PRDA and PhD student involved in the project, who will have gained experimental and technical skills as well as knowledge in electrochemical energy storage. They will be exposed to different disciplines to better understand how to bridge fundamental science and practical applications as well as the associated societal and economic issues. The knowledge, skills and experience will be important for these researchers to work in academia and hi-tech sectors with the goal of market innovation for battery technologies and beyond. This project will be a platform for MSci, MSc and BSc students to work on mini-projects. It will help them to engage with nanomaterials, analytical equipment tools, electrochemical technologies, and will therefore enhance their employability.

Knowledge
This project will deliver understanding of the limiting issues of enhancing battery performance and the solutions to these issues. It will also generate insights into the (physio)chemical processes that may occur in battery reactions and even be initially unknown. The understanding and insights will be applicable across many topics, from electrochemical applications to nanotechnology and further to materials sciences. The project will also produce titanium niobium oxides and Prussian blue analogues with structural/compositional features and low production cost. These materials can be used in a wide range of applications, such as medicine, pathology, machinery, etc.