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Efficacy of Stabilizing Calcium Battery Electrolytes through Salt-Directed Coordination Change

Journal Article · · Journal of Physical Chemistry. C
 [1];  [1];  [1];  [1]
  1. Joint Center for Energy Storage Research, Lemont, IL (United States); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
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Achieving practical, high-energy-density calcium batteries requires controlling the stability of Ca2+ electrolytes during calcium metal cycling. Because of the highly reactive nature of calcium, most typical electrolyte constituents are unstable, leading to electrode passivation and low Coulombic efficiency. Among various commercially available salts, calcium bis(trifluoromethylsulfonyl)imide (Ca(TFSI)2) is attractive because of its oxidative stability and high solubility in a variety of solvents. However, this salt does not allow for calcium metal plating, and it has been proposed that TFSI– instability induced by Ca2+ coordination is to blame. In this work, we test the ability of strongly coordinating Ca2+ cosalts such as halides and borohydrides to displace TFSI– from the first coordination shell of Ca2+ and thereby stabilize TFSI-based electrolytes to enable calcium plating. Through spectroscopic analysis, we find that the effectiveness of these cosalts at displacing the TFSI– anion is dependent on the solvent’s coordination strength toward Ca2+. Surprisingly, electrochemical calcium deposition behavior is not correlated to the population of bound or free TFSI–. Instead, the nature of the coordination interaction between Ca2+ and the cosalt anion is more important for determining stability. Our findings indicate that TFSI– anions are inherently unstable during calcium deposition even in the nominally free state. Furthermore, strategies aimed at eliminating the interactions of these anions with the electrode surface via interface/interphase design are required.

Research Organization:
Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE National Nuclear Security Administration (NNSA)
Grant/Contract Number:
NA0003525
OSTI ID:
1877146
Report Number(s):
SAND2022-8815J; 707728
Journal Information:
Journal of Physical Chemistry. C, Journal Name: Journal of Physical Chemistry. C Journal Issue: 25 Vol. 126; ISSN 1932-7447
Publisher:
American Chemical SocietyCopyright Statement
Country of Publication:
United States
Language:
English

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Related Subjects

25 ENERGY STORAGE
Anions
Deposition
Electrolytes
Salts
Solvents