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Title: Enhanced strength and temperature dependence of mechanical properties of Li at small scales and its implications for Li metal anodes

Most next-generation Li ion battery chemistries require a functioning lithium metal (Li) anode. However, its application in secondary batteries has been inhibited because of uncontrollable dendrite growth during cycling. Mechanical suppression of dendrite growth through solid polymer electrolytes (SPEs) or through robust separators has shown the most potential for alleviating this problem. Studies of the mechanical behavior of Li at any length scale and temperature are limited because of its extreme reactivity, which renders sample preparation, transfer, microstructure characterization, and mechanical testing extremely challenging. We conduct nanomechanical experiments in an in situ scanning electron microscope and show that micrometer-sized Li attains extremely high strengths of 105 MPa at room temperature and of 35 MPa at 90 °C. We demonstrate that single-crystalline Li exhibits a power-law size effect at the micrometer and submicrometer length scales, with the strengthening exponent of –0.68 at room temperature and of –1.00 at 90 °C. We also report the elastic and shear moduli as a function of crystallographic orientation gleaned from experiments and first-principles calculations, which show a high level of anisotropy up to the melting point, where the elastic and shear moduli vary by a factor of ~4 between the stiffest and most compliant orientations.more » In conclusion, the emergence of such high strengths in small-scale Li and sensitivity of this metal’s stiffness to crystallographic orientation help explain why the existing methods of dendrite suppression have been mainly unsuccessful and have significant implications for practical design of future-generation batteries.« less
Authors:
ORCiD logo [1] ;  [2] ;  [1] ; ORCiD logo [2] ;  [1]
  1. California Inst. of Technology (CalTech), Pasadena, CA (United States)
  2. Carnegie Mellon Univ., Pittsburgh, PA (United States)
Publication Date:
Grant/Contract Number:
SC0006599; EE006799
Type:
Published Article
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 114; Journal Issue: 1; Journal ID: ISSN 0027-8424
Publisher:
National Academy of Sciences, Washington, DC (United States)
Research Org:
California Inst. of Technology (CalTech), Pasadena, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
25 ENERGY STORAGE; dendrite; size effect; elastic anisotropy; dislocation; elevated temperature
OSTI Identifier:
1336848
Alternate Identifier(s):
OSTI ID: 1465395

Xu, Chen, Ahmad, Zeeshan, Aryanfar, Asghar, Viswanathan, Venkatasubramanian, and Greer, Julia R. Enhanced strength and temperature dependence of mechanical properties of Li at small scales and its implications for Li metal anodes. United States: N. p., Web. doi:10.1073/pnas.1615733114.
Xu, Chen, Ahmad, Zeeshan, Aryanfar, Asghar, Viswanathan, Venkatasubramanian, & Greer, Julia R. Enhanced strength and temperature dependence of mechanical properties of Li at small scales and its implications for Li metal anodes. United States. doi:10.1073/pnas.1615733114.
Xu, Chen, Ahmad, Zeeshan, Aryanfar, Asghar, Viswanathan, Venkatasubramanian, and Greer, Julia R. 2016. "Enhanced strength and temperature dependence of mechanical properties of Li at small scales and its implications for Li metal anodes". United States. doi:10.1073/pnas.1615733114.
@article{osti_1336848,
title = {Enhanced strength and temperature dependence of mechanical properties of Li at small scales and its implications for Li metal anodes},
author = {Xu, Chen and Ahmad, Zeeshan and Aryanfar, Asghar and Viswanathan, Venkatasubramanian and Greer, Julia R.},
abstractNote = {Most next-generation Li ion battery chemistries require a functioning lithium metal (Li) anode. However, its application in secondary batteries has been inhibited because of uncontrollable dendrite growth during cycling. Mechanical suppression of dendrite growth through solid polymer electrolytes (SPEs) or through robust separators has shown the most potential for alleviating this problem. Studies of the mechanical behavior of Li at any length scale and temperature are limited because of its extreme reactivity, which renders sample preparation, transfer, microstructure characterization, and mechanical testing extremely challenging. We conduct nanomechanical experiments in an in situ scanning electron microscope and show that micrometer-sized Li attains extremely high strengths of 105 MPa at room temperature and of 35 MPa at 90 °C. We demonstrate that single-crystalline Li exhibits a power-law size effect at the micrometer and submicrometer length scales, with the strengthening exponent of –0.68 at room temperature and of –1.00 at 90 °C. We also report the elastic and shear moduli as a function of crystallographic orientation gleaned from experiments and first-principles calculations, which show a high level of anisotropy up to the melting point, where the elastic and shear moduli vary by a factor of ~4 between the stiffest and most compliant orientations. In conclusion, the emergence of such high strengths in small-scale Li and sensitivity of this metal’s stiffness to crystallographic orientation help explain why the existing methods of dendrite suppression have been mainly unsuccessful and have significant implications for practical design of future-generation batteries.},
doi = {10.1073/pnas.1615733114},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
number = 1,
volume = 114,
place = {United States},
year = {2016},
month = {12}
}

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