Plating and Stripping Calcium at Room Temperature in an Ionic-Liquid Electrolyte

Biria, Saeid; Pathreeker, Shreyas; Genier, Francielli S.; Li, Hansheng; Hosein, Ian D.

doi:10.1021/acsaem.9b02529

“…Since the publication of Ponrouch et al, there have been numerous reports of viable Ca-ion electrolytes, ranging from organic solvents [10][11][12][13][14] to ionic liquids [15,16] and polymers [17]. With several examples of successful Ca-ion cathodes [18][19][20][21], a cyclable Ca-ion rocking chair battery is within reach; in fact, there are already some functional examples of such a setup [14,22].…”

Section: Introductionmentioning

confidence: 99%

A Computational Comparison of Ether and Ester Electrolyte Stability on a Ca Metal Anode

Liepinya

¹

,

Smeu

²

2021

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Ca-ion batteries (CIBs) have the potential to provide inexpensive energy storage, but their realization is impeded by the lack of suitable electrolytes. Motivated by recent experimental progress, we perform ab initio molecular dynamics simulations to investigate early decomposition reactions at the anode-electrolyte interface. By examining different combinations of solvent—tetrahydrofuran (THF) or ethylene carbonate (EC)—and salt—Ca(BH4)2, Ca(BF4)2, Ca(BCl4)2, and Ca(ClO4)2—we identify a variety of behavioral trends between electrolyte solutions. Next, we perform a separate trajectory with pure THF and gradually increased negative charge; despite an addition of -32e, no THF decomposition is detected. Charge analysis reveals that in a reductive environment, THF distributes excess charge evenly across its hydrocarbon backbone, while EC concentrates charge on its ester oxygens and carbonyl carbon, resulting in decomposition. Graphs of charge vs. time for both solvents reveal that EC decomposition products can be reduced by up to five electrons, while those of THF are limited to a single electron. Ultimately, we find Ca(BH4)2 and THF to be the most stable solution investigated herein, corroborating experimental evidence of its suitability as a CIB electrolyte.

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“…Challenges meeting the above conditions are in part owing to the unique solvation and solubility properties of divalent ions, entailing strong coordination to its environment (be it through ion pairing or solvation) as well as the strong reducing nature of multivalent metals. Thus far, studies that have elicited Ca redox activity or proposed Ca battery architectures have explored electrolytes composed of solvents such as alkyl carbonates (e.g., EC, PC), [11][12][13] THF, 14 DME, [15][16] ionic liquids, [17][18][19] , and glymes. [20][21] Salts that have been explored with these solvents have included Ca(BF4)2, Ca(TFSI)2, Ca(TFS)2, Ca(ClO4)2, Ca(BH4)2, Ca[B(hfip)4]2, as well as Ca(PF6)2.…”

Section: Introductionmentioning

confidence: 99%

A Computational Study on the Ca2+ Solvation, Coordination Environment, and Mobility in Electrolytes for Calcium Ion Batteries

Biria

¹

,

Pathreeker

²

,

Hosein

³

2021

Preprint

Self Cite

1

0

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Calcium (ion) batteries are promising next-generation energy storage systems, owing to their numerous benefits in terms of performance metrics, low-cost, mineral abundance, and economic sustainability. A central and critical area to the advancement of the technology is the development of suitable eletrolytes that allow for good salt solubility, ion mobility, electrochemical stability, and reversible redox activity. At this time, the study of different solvent-salt combinations is very limited. Here, we present a computational study on the coordination environment, solvation energetics, and diffusivity of calcium ions over a range of pertinent ionic liquids, cyclic and acylic alkyl carbonates, and specific alkyl nitriles and alkyl formamides, using the salts calcium bis(trifluoromethylsulfonyl)imide (Ca(TFSI)2) and calcium perchlorate (Ca(ClO4)2). Key findings are that several solvents from different solvent classes present comparable solvation environments and mobilities. Ca(TFSI)2 is prefered over Ca(ClO4)2 owing to the former’s mix coordination of Ca2+ to O and N atoms. Ionic liquids with alkyl sulfonate anions provide better coordation over TFSI, which leads to greater diffusivity. Binary organic mixtures (carbonates) provide the best solvation of Ca2+, however, single organic solvents also provide good solvation, such as EC, THF and DMF, as well as some acyclic carbonates. Ion pairing with the salt anion is always present, but can be mitigated through solvent selection, which also correlates to greater mobility; however, there are examples in which strong ion pairing is not significantly adverse to diffusivity. The solvent incorporate into the solvation structure with binary organic mixtures correlates well with the solvation capabilities of the individual solvents. Finally, we show that ionic liquids (specifically alkyl imidazole (cation) alkyl sulfonate (anion) ionic liquids) do not decompose when coordinating at a Ca metal interface, which indicates its promising stability. Overall, this study contributes further generalized understanding of the correlation between solvent and salt and the resultant Ca2+ complexes and Ca2+ mobility in a range of electrolytes, and reveals a range of possible solvents suitable for exploration in calcium (ion) batteries.

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“…Furthermore, 1000 fs is sufficient for all reaction dynamics to occur at the surface, as has been shown previously for ethylene carbonate on calcium metal. 31 17 As such, further studies should focus on investigating Ca 2+ transport across these solvent-metal interfaces to possibly elucidate the ease of reversible deposition and dissolution of Calcium from bulk electrolyte.…”

Section: Ca 2+ Self-diffusivitymentioning

confidence: 99%

A Computational Study on the Ca2+ Solvation, Coordination Environment, and Mobility in Electrolytes for Calcium Ion Batteries

Biria

¹

,

Pathreeker

²

,

Hosein

³

2021

Preprint

Self Cite

0

View full text Add to dashboard Cite

Calcium (ion) batteries are promising next-generation energy storage systems, owing to their numerous benefits in terms of performance metrics, low-cost, mineral abundance, and economic sustainability. A central and critical area to the advancement of the technology is the development of suitable eletrolytes that allow for good salt solubility, ion mobility, electrochemical stability, and reversible redox activity. At this time, the study of different solvent-salt combinations is very limited. Here, we present a computational study on the coordination environment, solvation energetics, and diffusivity of calcium ions over a range of pertinent ionic liquids, cyclic and acylic alkyl carbonates, and specific alkyl nitriles and alkyl formamides, using the salts calcium bis(trifluoromethylsulfonyl)imide (Ca(TFSI)2) and calcium perchlorate (Ca(ClO4)2). Key findings are that several solvents from different solvent classes present comparable solvation environments and mobilities. Ca(TFSI)2 is prefered over Ca(ClO4)2 owing to the former’s mix coordination of Ca2+ to O and N atoms. Ionic liquids with alkyl sulfonate anions provide better coordation over TFSI, which leads to greater diffusivity. Binary organic mixtures (carbonates) provide the best solvation of Ca2+, however, single organic solvents also provide good solvation, such as EC, THF and DMF, as well as some acyclic carbonates. Ion pairing with the salt anion is always present, but can be mitigated through solvent selection, which also correlates to greater mobility; however, there are examples in which strong ion pairing is not significantly adverse to diffusivity. The solvent incorporate into the solvation structure with binary organic mixtures correlates well with the solvation capabilities of the individual solvents. Finally, we show that ionic liquids (specifically alkyl imidazole (cation) alkyl sulfonate (anion) ionic liquids) do not decompose when coordinating at a Ca metal interface, which indicates its promising stability. Overall, this study contributes further generalized understanding of the correlation between solvent and salt and the resultant Ca2+ complexes and Ca2+ mobility in a range of electrolytes, and reveals a range of possible solvents suitable for exploration in calcium (ion) batteries.

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Plating and Stripping Calcium at Room Temperature in an Ionic-Liquid Electrolyte

Cited by 43 publications

References 31 publications

A Computational Comparison of Ether and Ester Electrolyte Stability on a Ca Metal Anode

A Computational Comparison of Ether and Ester Electrolyte Stability on a Ca Metal Anode

A Computational Study on the Ca2+ Solvation, Coordination Environment, and Mobility in Electrolytes for Calcium Ion Batteries

A Computational Study on the Ca2+ Solvation, Coordination Environment, and Mobility in Electrolytes for Calcium Ion Batteries

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