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From ion to atom to dendrite: Formation and nanomechanical behavior of electrodeposited lithium

Citrin, Michael A. and Yang, Heng and Nieh, Simon K. and Berry, Joel and Gao, Wenpei and Pan, Xiaoqing and Srolovitz, David J. and Greer, Julia R. (2020) From ion to atom to dendrite: Formation and nanomechanical behavior of electrodeposited lithium. MRS Bulletin . ISSN 0883-7694. (In Press) https://resolver.caltech.edu/CaltechAUTHORS:20200713-102704003

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Abstract

Development of high energy density solid-state batteries with Li metal anodes has been limited by uncontrollable growth of Li dendrites in liquid and solid electrolytes (SEs). This, in part, may be caused by a dearth of information about mechanical properties of Li, especially at the nano- and micro-length scales and microstructures relevant to Li batteries. We investigate Li electrodeposited in a commercial LiCoO₂/LiPON/Cu solid-state thin-film cell, grown in situ in a scanning electron microscope equipped with nanomechanical capabilities. Experiments demonstrate that Li was preferentially deposited at the LiPON/Cu interface along the valleys that mimic the domain boundaries of underlying LiCoO₂ (cathode). Cryogenic electron microscopy analysis of electrodeposited Li revealed a single-crystalline microstructure, and in situ nanocompression experiments on nano-pillars with 360–759 nm diameters revealed their average Young's modulus to be 6.76 ± 2.88 GPa with an average yield stress of 16.0 ± 6.82 MPa, ~24x higher than what has been reported for bulk polycrystalline Li. We discuss mechanical deformation mechanisms, stiffness, and strength of nano-sized electrodeposited Li in the framework of its microstructure and dislocation-governed nanoscale plasticity of crystals, and place it in the parameter space of existing knowledge on small-scale Li mechanics. The enhanced strength of Li at small scales may explain why it can penetrate and fracture through much stiffer and harder SEs than theoretically predicted. Lithium is an ideal battery anode, with a theoretical specific capacity of 3860 mAh/g; replacing the conventional graphitic anode in Li-ion batteries with Li can increase energy density by ~50%. A significant drawback of Li anodes is dendrite formation during cycling, which can lead to short circuiting (a safety hazard and cell death) and to “dead Li,” which drastically reduces cycle life. Virtually all approaches to supress Li dendrite growth have not proven to be consistently successful. Preventing electrolyte and cell failure requires a more sophisticated understanding of Li dendrite growth kinetics and mechanics. Few experiments that probe mechanical behavior of electrodeposited Li exist. Most experiments on mechanical properties have focused on thin films, Li foils, and focused ion beam-carved Li. We developed in situ experimental methodology that allows one to electrochemically charge small-scale battery cells and to observe, in real-time, the formation of Li dendrites and to probe their mechanical response. Experiments reveal: (1) Li nano-deposits are single crystalline and typically shaped as faceted pillars with 300-800nm diameters, and (2) strengths of Li nanopillars are 16.0 ± 6.82 MPa, which is 24x greater than bulk. This strength enhancement can be explained in terms of the ubiquitous “smaller is stronger size effect” in nano-sized single-crystalline metals. This work expands the existing strength versus size property space for Li and helps explain why dendrites can penetrate through much stiffer and harder ceramic solid electrolytes, than what has been theorized.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1557/mrs.2020.148DOIArticle
ORCID:
AuthorORCID
Citrin, Michael A.0000-0001-8183-5437
Yang, Heng0000-0001-7431-932X
Gao, Wenpei0000-0002-2776-2676
Pan, Xiaoqing0000-0002-0965-8568
Srolovitz, David J.0000-0001-6038-020X
Greer, Julia R.0000-0002-9675-1508
Additional Information:© 2020 Materials Research Society. Published online by Cambridge University Press: 09 July 2020. The authors would like to acknowledge the generous financial support from the ARPA-E IDEAS Grant #DE-AR0000884. Part of JB's contribution was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. We also acknowledge Andrey Malyutin and Shrawan Mageswaran for their help and discussions on performing TEM, and Ottman Tertuliano, Carlos Portela, and Jane Zhang for their invaluable help and discussions about the mechanical experiments. The authors acknowledge Xiaoxing Xia for his help with the SEM electrochemical experiments. JB acknowledges useful discussions with Alta Fang.
Funders:
Funding AgencyGrant Number
Advanced Research Projects Agency-Energy (ARPA-E)DE-AR0000884
Department of Energy (DOE)DE-AC52-07NA27344
Record Number:CaltechAUTHORS:20200713-102704003
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20200713-102704003
Official Citation:Citrin, M., Yang, H., Nieh, S., Berry, J., Gao, W., Pan, X., . . . Greer, J. (2020). From ion to atom to dendrite: Formation and nanomechanical behavior of electrodeposited lithium. MRS Bulletin, 1-14. doi:10.1557/mrs.2020.148
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:104353
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:13 Jul 2020 19:01
Last Modified:11 Nov 2020 00:30

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