Li-ion Battery Cathode Materials Free of Cobalt

Lead Research Organisation: University of Oxford
Department Name: OxICFM CDT

Abstract

As the effects of climate change become increasingly evident, the reliance of humanity on fossil fuels fails to lessen at a sufficient rate. The discovery of sustainable, safe and effective battery materials is vital for a shift in the energy-economy towards renewable energy sources. Much of this research focusses around cathode materials for lithium-ion batteries, where it is perceived the greatest improvements can be made- although electrolyte research also represents a significant contribution. Lithium-ion batteries have applications in a vast range of technologies, from mobile phones to remote-controlled drones. The UK plans to ban all-but electric car sales by 2035, a feat which will require significant further development of battery technologies.
Currently consumer-available cathode materials all present some issues, slowing down further adoption. The most widely adopted of these materials, lithium cobalt oxide has significant issues with material supply. 70% of cobalt is mined in the Democratic Republic of the Congo, of which, a portion is mined in locations linked to modern slavery and human rights abuses. There have been international calls to reduce production reliance on cobalt from these sources or remove cobalt from battery materials entirely. A global call was made by Amnesty International in 2019 to "clean up" battery supply chains, although insufficient changes have been made in many industries.
Research targeting battery materials free of cobalt focusses around 2 areas of new material synthesis- substituted, layered oxide materials and polyanionic materials. Research in this project shall focus on the latter, which expects to produce a new generation of safe, cheap cathode materials. These materials feature large polyanions on some crystal sites, resulting in a sacrifice of energy density due to the "dead weight" of the polyanions. As such, recent work has trialled the use of anion-redox to boost the voltage produced in these battery materials. These anion-redox processes free up additional electrons from the material upon discharge, increasing the voltage and energy density of the material over that provided by just cation-redox.
A further advantage of polyanion materials is provided by their chemical stability. At high voltage, oxide materials may form oxygen, which can in-turn interfere with the electrolyte. However, the oxygen atoms in polyanion materials are covalently bonded to the anion core, suppressing O2 formation and allowing for access of higher voltages.
This project shall utilise these new anion-redox methods to improve the properties of polyanion cathode materials, including boosting energy density. Target materials shall include transition metal polyanion species, such as sulfates, phosphates, oxalates, peroxodisulfates and their thio-substituted analogues. Discharge processes will involve reduction of the polyanion, in addition to the transition metal centre. A wide range of synthesis and analysis methods shall be used in collaboration with other groups.
This research aims to produce new generations of safe, cheap, high energy density cathode materials, using recently discovered methods to produce and improve new materials. Applications are vast and have potential to revolutionise large-scale industries, including electric vehicles and renewable energy.
This project falls within the EPSRC Energy Storage research area, under the theme of Energy. Research is aligned with the Faraday Institution project- "Lithium Ion Cathode Materials - FutureCat". Collaboration with the group of D. O. Scanlon (UCL) will assess potential synthetic targets through computational methods. Battery testing will be carried out in collaboration with the University of Sheffield.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/S023828/1 01/04/2019 30/09/2027
2404181 Studentship EP/S023828/1 01/10/2020 30/09/2024 Katherine Steele