The Development of Recyclable Hybrid Solid Electrolytes for Battery Applications

The exponential growth in rechargeable battery technologies over the last 20 years is due to the rising demand for portable electronics, but more recently, batteries have become an increasingly important means of storing energy, to drive the use of renewable energy resources and decrease the impact of human activity on the environment.

Since their development in the 1970s-80s, lithium ion (Li-ion) batteries have dominated the field, exhibited by the award of the Nobel Prize in Chemistry in 2019 to Goodenough, Whittingham and Yoshino. Li-ion batteries have enabled the development of electric vehicles and the storage of energy from renewable sources, such as solar and wind power. Their significant downfall, however, is the use of lithium salts in organic solvents as the cell's electrolyte, which are highly flammable and pose potential safety risks, such as fires and explosions. An explored alternative to these dangerous solvents are solid or semi-crystalline electrolytes (SEs), which have shown to improve the safety of Li-ion batteries, producing what is known as an all-solid-state battery (ASSB).

This PhD research encompasses the development of recyclable hybrid solid electrolytes for implementation into solid-state battery systems, with the hybrid element being a polymer/ceramic combination. Some polymers are capable of functioning effectively as electrolytes, and display the robust mechanical properties required for use in everyday devices, i.e., poly(ethylene oxide)s (PEO) displays considerable flexibility and chemical stability, making them excellent candidate materials for SEs. Yet, their commercialisation alone isn't feasible due to their inability to meet the practical conductivities required (~10-3 S cm-1) due to the frustrated transport of ions through the material. Therefore, polymer electrolytes can be combined with ceramic fillers such as Al2O3 or TiO2, drastically improving the ionic conductivity of the SEs, without affecting their mechanical strength.

The project explores the potential of such poly(acetals) in hybrid electrolytes, assessing their ion transport mechanisms using a combination of conventional and in situ solid-state NMR spectroscopy, in conjunction with impedance measurements and muon spin relaxation spectroscopy studies. The effects of structural parameters of the polymers such as monomer composition and degree of polymerisation on the resultant mechanical properties will be assessed, to enable the production of robust electrolytes. A range of different inorganic ceramics will also be evaluated to determine the optimal poly(acetal):ceramic combination. Key research in this area will be to evaluate the performance of the hybrid electrolytes prepared relative to current PEO-based electrolytes, to determine their standing within the community of solid electrolytes. Additionally, computational techniques, including atomistic modelling and DFT calculations will be utilised to understand the ion mobility within the new SE materials.

This project spans multiple EPSRC research areas including materials for energy applications, energy storage, polymer materials, materials engineering (ceramics), computational chemistry, and functional ceramics and inorganics, with the work falling under the themes of energy and manufacturing the future, as well as circular economy.

ReNU's enhanced doctoral training programme delivered by three uniquely co-located major UK universities, Northumbria (UNN), Durham (DU) and Newcastle (NU), addresses clear skills needs in small-to-medium scale renewable energy (RE) and sustainable distributed energy (DE). It was co-designed by a range of companies and is supported by a balanced portfolio of 27 industrial partners (e.g. Airbus, Siemens and Shell) of which 12 are small or medium size enterprises (SMEs) (e.g. Enocell, Equiwatt and Power Roll). A further 9 partners include Government, not-for-profit and key network organisations. Together these provide a powerful, direct and integrated pathway to a range of impacts that span whole energy systems.

Industrial partners will interact with ReNU in three main ways: (1) through the Strategic Advisory Board; (2) by providing external input to individual doctoral candidate's projects; and (3) by setting Industrial Challenge Mini-Projects. These interactions will directly benefit companies by enabling them to focus ReNU's training programme on particular needs, allowing transfer of best practice in training and state-of-the-art techniques, solution approaches to R&D challenges and generation of intellectual property. Access to ReNU for new industrial partners that may wish to benefit from ReNU is enabled by the involvement of key networks and organisations such as the North East Automotive Alliance, the Engineering Employer Federation, and Knowledge Transfer Network (Energy).

In addition to industrial partners, ReNU includes Government organisations and not for-profit-organisations. These partners provide pathways to create impact via policy and public engagement. Similarly, significant academic impact will be achieved through collaborations with project partners in Singapore, Canada and China. This impact will result in research excellence disseminated through prestigious academic journals and international conferences to the benefit of the global community working on advanced energy materials.