Periodic Reporting for period 2 - BATNMR (Development and Application of New NMR Methods for Studying Interphases and Interfaces in Batteries)
Berichtszeitraum: 2021-04-01 bis 2022-09-30
The use of lithium metal as a negative electrode in a lithium-ion rechargeable battery can increase its energy density, but so far, its use is limited due to uncontrolled and inhomogeneous electrodeposition on cycling the battery due to rapid battery fade and safety issues. To solve the Li metal problem and prevent battery degradation in batteries more generally, we must understand both how the electrolyte – the liquid that transports the ions in a battery from the anode to cathode and vice versa – and the passivation layers that protect both the anode and cathode function and fail. Clearly this work is important because the development of better batteries underpin European and Global goals to reduce CO2 emissions. We must develop more sustainable batteries that last longer before failing and have higher energy densities (i.e. can run longer on a single charge).
An important tool to improve battery technology is nuclear magnetic resonance (NMR) spectroscopy because it allows chemical species to be identified. We have been pushing the use of operando methods to do this so as to understand how the different components of the battery operate synergistically. A challenge however with this method is its low sensitivity. This means it is difficult to pick up minor components – be in the molecules formed during degradation or at the interfaces in and between the various layers that make up the battery. We have thus been developing new methods to enhance the NMR signals and have applied them to look at battery reactions and Li metal dendrite formation. The overall objectives are to develop new NMR metrologies specifically designed to target key reactions or species in batteries and then to apply them to understand function and provide insight into how improve battery performance.
An important tool to improve battery technology is nuclear magnetic resonance (NMR) spectroscopy because it allows chemical species to be identified. We have been pushing the use of operando methods to do this so as to understand how the different components of the battery operate synergistically. A challenge however with this method is its low sensitivity. This means it is difficult to pick up minor components – be in the molecules formed during degradation or at the interfaces in and between the various layers that make up the battery. We have thus been developing new methods to enhance the NMR signals and have applied them to look at battery reactions and Li metal dendrite formation. The overall objectives are to develop new NMR metrologies specifically designed to target key reactions or species in batteries and then to apply them to understand function and provide insight into how improve battery performance.
Our work has centered on the development of Overhauser Dynamic Nuclear Polarization (DNP) methods for lithium ion batteries. This approach as allowed us to enhance the Li metal by as much as a factor of 8 in our original experiment, and more recently by a factor of 50 in the new facility funded as part of the ERC grant. We have worked on the theory that underpins this experiment and have applied it to understand how Li dendrites grow in the batteries. We has also performed detailed studies of how the battery electrolytes degrade and how the reactions at the cathode differ from those at the anode, and how they “talk to each other” via cross-over reactions where one species formed at one electrode migrates and reacts at the other. We have used new NMR methods to quantify how the ions move through the layers that protect the Li metal from further reaction with the electrolyte, which ultimately will help us design methods to use Li metal in batteries. Finally, we have performed studies of anode materials that are suitable for fast charging of batteries. Dissemination has been performed via speaking at multiple battery conferences. For example, I gave a talk to the Falling Walls Conference in Berlin in November 2021 "Breaking the Walls on Fast Charging", https://www.youtube.com/watch?v=0pBKV1LGoRo also giving a more detailed science presentation and contributing to a round table discussion. As part of my Koerber Award, in 2021, I discussed the role of batteries in mitigating climate change (https://www.koerber-stiftung.de/en/koerber-european-science-prize/previous-prizewinners/2021). I will also give invited talks and plenary lectures in a series of batteries conference in person on 2022. I also disseminate my work via a start-up company that I helped to co-found which specialises in fast-charging batteries.