1:25 PM - CT02.03.02
Revealing Reaction Dynamics of Battery Electrolyte-Electrode Interfaces via In Situ Electrochemical TEM
Alex Robertson1,Shengda Pu1,Chen Gong1,Xiangwen Gao1,Ziyang Ning1,Sixie Yang1,John-Joseph Marie1,Boyang Liu1,Robert House1,Gareth Hartley1,Jun Luo2,Peter Bruce1
University of Oxford1,Tianjin University of Technology2
The critical area for understanding and progressing battery technology is the interface between the electrode and the electrolyte. The electrochemistry occurring at this interface, including the formation and evolution of an intermediate solid-electrolyte interphase (SEI) layer, is notoriously complex. Applying in-situ characterisation techniques to illuminate these dynamics will help with the diagnosis of the specific interfacial processes, and thus facilitate the design of better electrolytes. In this talk I will discuss some of our recent work using in-situ liquid-cell TEM to probe the evolving electrode interface in real time.
Multivalent electrolytes, using chemistries based on Ca or Mg ions, are promising candidates for next-generation batteries. Recent breakthroughs are beginning to overcome the longstanding problem of devising effective multivalent electrolytes, yet a major challenge remains in designing electrolytes that yield a stable SEI that does not inhibit cycling. We performed extensive in-situ TEM characterisation of one of the more promising new electrolytes, a calcium borohydride salt in tetrahydrofuran (THF), capturing the real-time nucleation, growth, and dissolution of calcium under various current density conditions. In-situ TEM imaging demonstrates the existence of a critical current density, beyond which adverse dendritic calcium plating morphologies dominate, and yielding detached isolated calcium deposits on stripping.
Several other next-generation batteries are based on Li ion chemistries, and to attain peak performance desire a lithium metal anode. Yet ensuring that they remain stable over many cycles has proven challenging. One of the most effective avenues to combat this has been tailoring the SEI by adjusting the electrolyte composition with additives. These fluoride-rich interphases significantly improve cycling efficiency, yet diagnosing how they alter the structural dynamics of Li electroplating and stripping is difficult without in-situ imaging. I will discuss how using in-situ TEM can provide unique insights into the distinct morphological changes that occur to Li plated from electrolytes tailored to form a fluoride-rich interphase. Our observations reveal that the fluoride-rich SEI favours the formation of a densely interwoven Li deposit, as opposed to the more dendritic structures formed from standard electrolyte. This denser structure proved more amenable to uniform dissolution, leaving behind fewer isolated dead Li fragments, and thus yielding superior efficiency.
 Pu, S.; Gong, C.; Robertson, A. W. Liquid Cell Transmission Electron Microscopy and its Applications. Royal Society Open Science, 2020, 7, 191204.
 Wang, D.; Gao, X.; Chen, Y.; Jin, L.; Kuss, C.; Bruce, P. G. Plating and Stripping Calcium in Organic Electrolyte. Nature Materials, 2018, 17, 16-20.
 Pu, S.; Gong, C.; Gao, X.; Ning, Z.; Yang, S.; Marie, J. J.; Liu, B.; House, R. A.; Hartley, G. O.; Luo, J.; Bruce, P. G.; Robertson, A. W. Current-Density-Dependent Electroplating in Ca Electrolytes; From Globules to Dendrites. ACS Energy Letters, 2020, 5, 2283-2290.