Periodic Reporting for period 2 - CATHDFENS (CATHode Development For Enhanced iNterfacial Studies (CATH-DFENS))
Reporting period: 2018-09-01 to 2019-08-31
Li-ion batteries (LIB) possess higher energy densities than many other rechargeable batteries (specific energy 100-150 Wh kg−1) with high availability and proven performance. One of the greatest challenges for improving LIB performance is the development of suitable cathode materials; able to accept and release Li+ ions repeatedly (for recharging) and quickly (for high rate). LIB cathode materials are currently worth EUR 10 B industry and this is predicted to increase in the years to come; so there is a race to find the next commercial-grade cathodes. This has attracted sizable investment from materials manufactures as well and significant interest from the academic sector. Whilst the search continues for new materials, there are real and significant enhancements that can be made to proven technologies and existing materials.
It is known that the battery cathode/electrolyte interface is the location of multiple degradation processes which lead to battery failure however as these processes occur on very short length scales and batteries geometries are complex, with multiple materials within close proximity to one another, it is challenging to deconvolute these processes during operations. In this work, simpler model systems are made with defined cathode surfaces. This is done by making very thin films single crystals of commercially used cathodes materials on flat substrates and then studying these surfaces and the interface they have with electrolyte during operation.
The proposed research will improve our fundamental understanding of the role of the cathode/electrolyte interface in Li-ion battery degradation, essential to underpin improved battery design and manufacture. With this better understanding, the outputs of the project are to define new processes to improve the cathode surface which can be used commercially for better batteries with improved lifetime.
The first 2 years of this work were performed at Lawrence Berkeley National Laboratory in California, USA. The UK host institution is University College London where the third and last year will be performed.
It is known that the battery cathode/electrolyte interface is the location of multiple degradation processes which lead to battery failure however as these processes occur on very short length scales and batteries geometries are complex, with multiple materials within close proximity to one another, it is challenging to deconvolute these processes during operations. In this work, simpler model systems are made with defined cathode surfaces. This is done by making very thin films single crystals of commercially used cathodes materials on flat substrates and then studying these surfaces and the interface they have with electrolyte during operation.
The proposed research will improve our fundamental understanding of the role of the cathode/electrolyte interface in Li-ion battery degradation, essential to underpin improved battery design and manufacture. With this better understanding, the outputs of the project are to define new processes to improve the cathode surface which can be used commercially for better batteries with improved lifetime.
The first 2 years of this work were performed at Lawrence Berkeley National Laboratory in California, USA. The UK host institution is University College London where the third and last year will be performed.
A new high-throughput pulsed laser deposition system was designed, built, commissioned and exploited by the fellow. This new method permitted a 15-fold increase in throughput for making thin films, increasing from 4 films a day to 60 films per day; allowing better optimisation on materials. This also had knock on effects on the way that materials optimisation is approached. Funding of $100 k was awarded to the candidate from the Science Support Office at Advance Light Source.
A model system was developed of current commercial cathodes NMC 532 and LiMn2O4 on metal and single crystal supports. These thin films had low roughness (below 1 nm r.m.s. roughness).
A soluble buffer layer was optimised from which low roughness crystalline NMC films could be grown and subsequent “lifted off”. This means that it was possible to make free-standing thin films of NMC 532 with dimensions 10 mm x 10 mm x 5 nm. This is a world’s first battery cathode materials.
These model systems were investigated by several highly surface/interface specific laboratory and synchrotron based techniques, including Near Field Spectroscopy, AFM, X-Ray Reflectivity, X-Ray Photoemission Spectroscopy.
The combination of the above allowed for development of a new understanding of surface degradation processes which occur and the types of changes to the cathode surface which occur during cycling.
A simple surface technique was created and it was demonstrated on thin films that this could reduce these negative effects, in particular interfacial impedance rise over long-term cell cycling. It was then demonstrated that this could be directly applied to bulk cathode materials (before making the cell) and interestingly after making the cell.
A model system was developed of current commercial cathodes NMC 532 and LiMn2O4 on metal and single crystal supports. These thin films had low roughness (below 1 nm r.m.s. roughness).
A soluble buffer layer was optimised from which low roughness crystalline NMC films could be grown and subsequent “lifted off”. This means that it was possible to make free-standing thin films of NMC 532 with dimensions 10 mm x 10 mm x 5 nm. This is a world’s first battery cathode materials.
These model systems were investigated by several highly surface/interface specific laboratory and synchrotron based techniques, including Near Field Spectroscopy, AFM, X-Ray Reflectivity, X-Ray Photoemission Spectroscopy.
The combination of the above allowed for development of a new understanding of surface degradation processes which occur and the types of changes to the cathode surface which occur during cycling.
A simple surface technique was created and it was demonstrated on thin films that this could reduce these negative effects, in particular interfacial impedance rise over long-term cell cycling. It was then demonstrated that this could be directly applied to bulk cathode materials (before making the cell) and interestingly after making the cell.
The project has developed new know-how and knowledge in the areas of i) thin film deposition equipment, ii) thin film deposition and iii) battery cathode interface.
The high throughput PLD systems is a first and offers significant improvements over the state-of-the-art in terms of the number of films which can be produced in a given time. It is currently used as a user facility under the Advance Light Source at LBNL, meaning that it can be accessed for free through a simple proposal procedure. There have been numerous users and staff trained on the equipment from a variety of institutions around USA and Europe. The equipment has resulted in the fellow being direct involved and influential in ongoing projects and has attached new funding (totalling $1 M over 3 years) to the Lab in collaboration with Stanford Linear Acceleration Center (SLAC) as the lead for investigations into battery materials.
The NMC thin films have lower roughness than in the literature meaning they can be used to studying processes on the nm length-scale and making useful for surface/ interface investigations.
The lift-off is a world first for battery cathode materials and has implications for new type of experiments removing constraints of the thick solid substrates. Opening new possibilities to look at the effect of stress and strains and their effect on de/lithiation which has not previously been possible due to the direct bond with the millimetre-thick substrates.
The Intellectual Property generated in this project will be protected during the final stage of this project duration so that it can be commercialised.
The high throughput PLD systems is a first and offers significant improvements over the state-of-the-art in terms of the number of films which can be produced in a given time. It is currently used as a user facility under the Advance Light Source at LBNL, meaning that it can be accessed for free through a simple proposal procedure. There have been numerous users and staff trained on the equipment from a variety of institutions around USA and Europe. The equipment has resulted in the fellow being direct involved and influential in ongoing projects and has attached new funding (totalling $1 M over 3 years) to the Lab in collaboration with Stanford Linear Acceleration Center (SLAC) as the lead for investigations into battery materials.
The NMC thin films have lower roughness than in the literature meaning they can be used to studying processes on the nm length-scale and making useful for surface/ interface investigations.
The lift-off is a world first for battery cathode materials and has implications for new type of experiments removing constraints of the thick solid substrates. Opening new possibilities to look at the effect of stress and strains and their effect on de/lithiation which has not previously been possible due to the direct bond with the millimetre-thick substrates.
The Intellectual Property generated in this project will be protected during the final stage of this project duration so that it can be commercialised.