Speaker

Peter Bruce, Professor, Departments of Materials and Chemistry
University of Oxford 

Talk Abstract:

Solid State Batteries

The solid-state battery is widely regarded as the next frontier in battery technology, offering a stepchange in energy density and safety. Of the challenges facing realisation of the all-solid-state battery, solid/solid interfaces rank high. At the lithium metal / ceramic electrolyte interface, dendrites (fingers of lithium) can form on charging and penetrate the ceramic leading to short circuit and cell failure.

Typically, for relatively dense ceramics, this occurs above a critical charging current (CCD). It has often been suggested that densification of the ceramic electrolyte should benefit charging. However, not all changes in microstructure on densification are predicted to lead to an increase in CCD, some changes are positive while others are negative. The relationship between the ceramic microstructure, densification and the CCD will be considered with particular reference to the highly conducting Argyrodite solid electrolyte, Li6PS5Cl.

Lithium-rich Cathodes

Li-ion battery cathodes that can store more energy than those in use today are an important target for materials research. The challenge has proved formidable and demands a deeper understanding of the science underpinning intercalation cathodes.

For over 20 years it has been known that on charging, more Li+ can be removed from layered compounds such as Li[Li0.2Ni0.2Mn0.6]O2 or Li[Li0.2Ni0.13Co0.13Mn0.54]O2 than is charge compensated by transition metal oxidation. The additional electrons are removed from the O2- ions. Many excellent contributions have been made in an endeavour to understand oxygen redox, the nature of the hole states and their link to the resulting structural changes.

We have shown that oxidation of O2- forms O2 that is either evolved from the surface of the particles or trapped in nano-voids formed in the bulk by reorganisation of the Li vacancies on the transition metal sites within the structure. Although O2 in these nano-voids can be reduced back to O2-, the process is not energetically reversible, resulting in the 1st cycle voltage hysteresis (approx. 1eV is lost). This mechanism also has implications which play out over extended cycling. The voids grow in size and O2 cannot be fully reduced, rationalising the well known problem of voltage fade in Li rich materials. It is possible to suppress O2 formation, trapping hole states on O2- and obtaining energetic (voltage) and structural reversibility. The electron holes are not localised on oxygen but itinerant. Such behaviour may point the way towards practical high energy density cathodes for Li-ion batteries.

Bio:
Professor Sir Peter G Bruce, FRS, FRSE, FRSC, MAE, IoM, ML, is Wolfson Professor of Materials at the University of Oxford, UK. He co-founded the Faraday Institution, the UK’s centre of excellence for research on electrochemical energy storage, and serves as its Chief Scientist. From 2018-2023 he served as Physical Secretary and Vice President of the Royal Society (UK Academy of Sciences).

Peter’s research interests embrace materials chemistry and electrochemistry, especially lithium and sodium batteries. Recent efforts have focused on the synthesis and understanding of new high capacity cathode materials for lithium-ion batteries, the processes taking place in solid-state batteries and the challenges of the lithium-air battery.

Peter’s research has been recognised by a number of awards and fellowships. He has received the Tilden Prize, the Liversidge Award and the Longstaff Prize from the Royal Society nof Chemistry, the Carl Wagner Award of the Electrochemical Society (USA) and the Hughes Medal of the Royal Society. He has been named as a Highly Cited Researcher by Thomson Reuters/Clarivate every year since 2015. Peter was elected as a member of the Chinese Academy of Sciences in 2023 and the German Academy of Sciences, Leopoldina, in 2024. In the 2022 Queen’s Birthday Honours List, Peter received a knighthood for his services to science and innovation.