Exploring tailored electrolytes to regulate lithium-ion battery performance by operando transmission electron microscopy
- Abstract number
- 73
- Presentation Form
- Submitted Talk
- Corresponding Email
- [email protected]
- Session
- Stream 1: EMAG - Energy and Energy Storage Materials
- Authors
- Mr Chen Gong (2), Mr Shengda Pu (2), Dr Xiangwen Gao (2), Dr Sixie Yang (2), Dr Junliang Liu (2), Mr Ziyang Ning (2), Dr Gregory Rees (2), Dr Isaac Capone (2), Dr Liquan Pi (2), Dr Boyang Liu (2), Dr Gareth Hartley (2), Mr Jack Fawdon (2), Prof Jun Luo (1), Prof Mauro Pasta (2), Prof Chris Grovenor (2), Prof Peter Bruce (2), Dr Alex Robertson (2)
- Affiliations
-
1. Tianjin University of Technology
2. University of Oxford
- Keywords
liquid-cell TEM; operando TEM; batteries; solid electrolyte interphase; SEI;
- Abstract text
In Li-ion batteries the solid electrolyte interphase (SEI) has a crucial role in controlling the structural evolution of the electrode during battery operation. For lithium metallic anodes, an anode that is arguably the ideal for making more effective Li-based batteries instead of the current graphite anodes, engineering this SEI is seen as one of the best ways to avoid cell degradation over many cycles.[1] Understanding how different SEIs that form on the anode can alter the structural dynamics of charge cycling remains only partly understood, yet will be important for designing suitable SEIs.
Here, we use operando liquid-cell transmission electron microscopy (TEM) to image lithium electrodeposition and dissolution at electrode surfaces with different SEIs.[2] The electrochemical changes that occur at an operating battery electrolyte-electrolyte interface are notoriously complex, especially for those battery chemistries governed by an additional SEI intermediary. This means that post-mortem imaging of an operated electrode risks not revealing the complete picture of the dynamic processes that occurred, and thus ideally warrants operando imaging to fully understand and diagnose.
We performed operando scanning-mode (S)TEM imaging of electrodes electrically cycled in a commonly used electrolyte - 1M LiPF6 salt dissolved in 1:1 EC:DMC solvent, also called LP30 - and compared with electrodes cycled with the same electrolyte but with an additional 10% volume of fluoroethylene carbonate additive. The FEC additive lead to a fluoride-rich interphase layer forming on the electrode surface after electrochemical cycling, which we confirmed by secondary ion mass spectrometry in a plasma focus ion beam (PFIB) system, with an atmospheric transfer system used to prevent air contamination of the lithium.
Our results revealed that a fluoride-rich SEI gave a distinct, denser lithium deposition structure that was easier to dissolve uniformly, and thus reduced the chances of lithium loss. In conjunction with quantitative composition measurement by mass spectrometry, we identified that the fluoride-rich SEI reduces lithium loss by reducing dead lithium formation (where lithium deposits detach from the anode and thus become electrically isolated, unable to take part in further electrochemistry), and by preventing electrolyte decomposition.
These findings highlight the importance of appropriately tailoring the SEI for facilitating consistent and uniform lithium dissolution, and its potent role in governing the plated lithium’s structure.
- References
[1] M. D. Tikekar, S. Choudhury, Z. Tu, L. A. Archer, Nat. Energy 2016, 1, 16114.
[2] C. Gong et al. Adv. Energy Mat. 2021, 11, 1003118.