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

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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.