Hierarchically-structured electrodes for Li-air batteries

Li-air batteries are secondary batteries with the highest theoretical energy density of any battery system. In order to achieve this in practice, many technical problems must first be resolved. One key issue limiting the discharge capacity at higher rates is that of oxygen diffusion through the cathode material. At higher discharge rates, oxygen from the air side of the cathode does not have time to diffuse throughout the whole electrode before being consumed, resulting in a build up of discharge product at the air side. This results in eventual pore blockage and the underutilisation of the cathode volume. Another issue affecting the energy efficiency of these batteries is the high overpotentials caused by the slow kinetics of the oxygen reduction and evolution reactions on discharge and charge. One of the main goals of this project is to develop an understanding of the relationship between oxygen diffusivity and discharge capacity of Li-air batteries at high discharge rates. In this project, the oxygen diffusivity through the cathode will initially be controlled via laser processing of carbon nanotube (CNT) mats. Building from this, more advanced material synthesis methods can be employed, such as nano-lithography to define a patterned catalyst followed by CNT forest growth. The material properties and electrochemical performance of this cathode material will be characterised, and correlated with the effective oxygen diffusivity through the electrode. Using this system as an experimental basis, operando XRD and gas pressure monitoring will be used to study the effects of varying oxygen diffusivity and cycling rate on cell kinetics in detail. Following this, cathodes functionalised with catalytic nanoparticles will be synthesised and have their electrochemical performance characterised. The operando techniques developed earlier in the project will be used to study the effects of heterogeneous catalysis on discharge product formation in Li-air batteries. These studies will help improve the cell capacity and efficiency of Li-air batteries, particularly athigh discharge rates, relevant for commercial applications.

Our main impacts will be:
- a new generation of interdisciplinary nano researchers with expertise across science and innovation, fluent in the combination of approaches and technologies
- strategic developments in the study and control of nano-interfaces connecting complex architectures, for advances in emerging scientific grand challenges across vital areas of energy, health and ICT
- integration of new functional nanotechnologies together by harnessing nano-interfaces within larger application systems, and their translation into innovative products and services through our industry partners and student-led spin-outs
- a paradigm change of collaborative outlook in this science and technology
- a strong interaction with stakeholders including outreach and public engagement with cutting edge nano research
- improved use of interdisciplinary working tools including management, discipline bridging and IT

Economic impact of the new CDT is focused through our industrial engagement programme, as well as our innovation training. Our partner companies include - NPL, Hitachi, Oxford Nanopore, TWI, ARM, Eight19, Mursla, Britvic, Nokia Bell Labs, IBM, Merck, Oxford Instruments, Aixtron, Cambridge Display Technologies, Fluidic Analytics, Emberion, Schlumberger, Applied Materials and others. Such partnerships are crucial for the UK to revive high value manufacturing as the key pillar to lead for future technologies. We evidence this via the large number of CDT projects resulting in patents, with their exploitation supported by Cambridge Enterprise and our Industry Partners, and direct economic impact has also resulted from the large proportion of our students/alumni joining industry (a key outcome), or founding startups including: Echion Technologies (battery materials), Inkling Cambridge (Graphene inks and composites), HexagonFab (2D materials), Simprints (low-cost biometrics), Cortirio (rapid diagnosis of brain injury).

Training impact emerges through not just the vast array of Nano techniques and ideas that our cohorts and associated students are exposed to, but also the interdisciplinary experience that accrues to all the academics. In particular the younger researchers coming into the University are plugged into a thriving programme that connects their work to many other sciences, applications, and societal challenges. Interactions with external partners, including companies, are also strong and our intern programme will greatly strengthen training outcomes.

Academic impact is fostered by ensuring strong coherent plans for research in the early years, and also the strong focus of the whole CDT on study and control of nano-interfaces connecting complex architectures. Our track record for CDT student-led publications is already strong, including 4 Nature/Science, 6 Nature Chem/Nano/Mat, 13 Nat. Comm., with student publications receiving >6000 citations in total, including 16 papers with >100 citations each and high altmetric scores. Students have also given talks and posters at international conferences and won numerous awards/fellowships for research excellence.

Societal impacts arise from both the progression of our cohorts into their careers as well as their interaction with the media, public, and sponsors. We directly encourage a wide variety of engagement, including interaction with >5000 members of the public each year (mostly pre-university) through Nano exhibits during public events such as the Cambridge Science Festival and Royal Society Summer Science Exhibition, and also art-science collaborations to reach new audiences. We also run public policy and global challenges workshops, and will further develop this aspect with external partners. Our efforts to bring societal challenges to students' awareness frames their view of what a successful career looks like. Longer term societal impact comes directly from our engagement with partner companies creating jobs and know-how in the UK.