Fluorine-free salts for aqueous lithium-ion and sodium-ion battery electrolytes

Hosseini-Bab-Anari, Elham; Boschin, Andrea; Mandai, Toshihiko; Masu, Hyuma; Moth‐Poulsen, Kasper; Johansson, Patrik

doi:10.1039/c6ra19623c

Cited by 18 publications

(11 citation statements)

References 67 publications

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“…In particular, nitrates, perchlorates, and acetates have been studied, and concentrations up to 40m have been achieved for eutectic mixtures of two acetate salts. [ 22–28 ] Still, even at such high concentrations, most of these electrolytes do not nearly reach the electrochemical stability of lithium perfluorinated sulfonylimide/triflate electrolytes. In the case of sodium electrolytes, they are even outperformed by the much‐lower‐concentrated 9m NaOTf electrolyte.…”

Section: Introductionmentioning

confidence: 99%

Anion Selection Criteria for Water‐in‐Salt Electrolytes

Reber

Grissa

Becker

et al. 2020

Advanced Energy Materials

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Water‐in‐salt electrolytes have enabled the development of novel high‐voltage aqueous lithium‐ion batteries. This study explores the reasons why analogous sodium electrolytes have struggled to reach the same level of electrochemical stability. Solution structure and electrochemical stability are compared for 11 sodium salts, selected among the major classes of salts proposed for highly concentrated electrolytes. The water environment established for each anion is related to its position in the Hofmeister series and a surprisingly strong correlation between the chaotropicity of the anion and the resulting electrochemical stability of the electrolyte is found. The search for suitable sodium salts is complicated by the fact that higher salt concentrations are needed than for their lithium equivalents. Reaching such a high concentration of >25 mol kg−1 with one or a combination of multiple sodium salts that have the desired properties remains a major challenge. Hence, alternative approaches such as multisolvent systems should be explored. The water solubility of NaTFSI can be increased from 8 to 30 mol kg−1 in the presence of ionic liquids. Such a ternary electrolyte enables stable cycling of a 2 V class sodium‐ion battery based on the NaTi2(PO4)3/Na2Mn[Fe(CN)6] electrode couple for 300 cycles at 1C with a Coulombic efficiency of >99.5%.

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Section: Introductionmentioning

confidence: 99%

Anion Selection Criteria for Water‐in‐Salt Electrolytes

Reber

Grissa

Becker

et al. 2020

Advanced Energy Materials

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“…The ionic conductivity of this Li-based aqueous electrolyte is 30 mS cm À 1 and the electrochemical stability window is 2 V, higher than the thermodynamic stability of water but still very much limited by water decomposition. [108] Other reported examples are the synthesis and crystal structure of borate anions, such as bis(2,3-oxy-pyrazine)borate (LiPOB; 9, Figure 5) [109] anion and bis[1,2-benzenediolato(2-)-O,O']borate (Li[Bcat 2 ]; 10, Figure 5). [110] However, there is no information about their solubility, conductivity or other relevant properties for Li-ion batteries.…”

Section: Other Saltsmentioning

confidence: 99%

Fluorine‐Free Electrolytes for Lithium and Sodium Batteries

Hernández

Mogensen

Younesi

et al. 2022

Batteries & Supercaps

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Fluorinated components in the form of salts, solvents and/or additives are a staple of electrolytes for high‐performance Li‐ and Na‐ion batteries, but this comes at a cost. Issues like potential toxicity, corrosivity and environmental concerns have sparked interest in fluorine‐free alternatives. Of course, these electrolytes should be able to deliver performance that is on par with the electrolytes being in use today in commercial batteries. This begs the question: Are we there yet? This review outlines why fluorine is regarded as an essential component in battery electrolytes, along with the numerous problems it causes and possible strategies to eliminate it from Li‐ and Na‐ion battery electrolytes. The examples provided demonstrate the possibilities of creating fully fluorine‐free electrolytes with similar performance as their fluorinated counterparts, but also that there is still a lot of room for improvement, not least in terms of optimizing the fluorine‐free systems independently of their fluorinated predecessors.

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“…In particular, nitrates, perchlorates, and acetates have been studied, and concentrations up to 40m have been achieved for eutectic mixtures of two acetate salts. [22][23][24][25][26][27][28] Still, even at such high concentrations, most of these electrolytes do not nearly reach the electrochemical stability of lithium perfluorinated sulfonylimide/triflate electrolytes. In the case of sodium electrolytes, they are even outperformed by the much-lower-concentrated 9m NaOTf electrolyte.…”

Section: Introductionmentioning

confidence: 99%

Anion Selection Criteria for Water-in-Salt Electrolytes

Reber¹,

Grissa²,

Becker³

et al. 2022

Meet. Abstr.

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Water-in-salt electrolytes have enabled the development of novel high-voltage aqueous lithium-ion batteries due to their wide electrochemical stability window. Here, we explore why analogous sodium electrolytes have struggled to reach the same level of electrochemical stability and compare solution structure and electrochemical stability for eleven sodium salts, selected among the major classes of salts proposed for highly concentrated electrolytes.[1-3] We relate the water environment established for each anion to its position in the Hofmeister series, finding a strong correlation between the chaotropicity of the anion and the resulting electrochemical stability of the electrolyte. We discuss the importance of the solid-electrolyte interphase for stable battery performance, how it relates to the choice of anion, and further show that the search for suitable sodium salts is complicated by the fact that higher salt concentrations are needed than for their lithium equivalents.[4] Reaching such a high concentration of 25 to 30 mol/kg with one or a combination of multiple sodium salts that have the desired properties remains a major challenge. We conclude that alternative approaches such as mixed water/organic solvent or dual-cation electrolytes should be pursued to enable the development of high-voltage aqueous sodium-ion batteries. We demonstrate the potential of the mixed-solvent approach by showing that the water solubility of NaTFSI can be increased from 8 to 30 mol/kg in the presence of ionic liquids. Such a ternary electrolyte, based on highly chaotropic anions, enables stable cycling of a 2 V-class sodium-ion battery based on the NaTi2(PO4)3/Na2Mn[Fe(CN)6] electrode couple for 300 cycles at 1C with a Coulombic efficiency of >99.5%.[5] References: [1] Kühnel, R.-S.; Reber, D.; Battaglia, C., A High-Voltage Aqueous Electrolyte for Sodium-Ion Batteries. ACS Energy Lett. 2017, 2, 2005-2006. [2] Reber, D.; Kühnel, R.-S.; Battaglia, C., Suppressing Crystallization of Water-in-Salt Electrolytes by Asymmetric Anions Enables Low-Temperature Operation of High-Voltage Aqueous Batteries. ACS Materials Letters 2019, 1, 44-51. [3] Reber, D.; Takenaka, N.; Kühnel, R.-S., Yamada, A.; Battaglia, C., Impact of Anion Asymmetry on Local Structure and Supercooling Behavior of Water-in-Salt Electrolytes. J. Phys. Chem. Lett. 2020, 11, 4720 [4] Reber, D.; Kühnel, R.-S.; Battaglia, C., Stability of aqueous electrolytes based on LiFSI and NaFSI. Electrochim. Acta 2019, 321, 134644 [5] Reber, D.; Grissa, R.; Becker, M.; Kühnel, R.-S.; Battaglia, C., Anion Selection Criteria for Water-in-Salt Electrolytes. Adv. Energy Mater. 2021, 11, 2002913

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Fluorine-free salts for aqueous lithium-ion and sodium-ion battery electrolytes

Abstract: Novel fluorine-free salts for aqueous lithium-ion and sodium-ion battery electrolytes.

Cited by 18 publications

References 67 publications

Anion Selection Criteria for Water‐in‐Salt Electrolytes

Anion Selection Criteria for Water‐in‐Salt Electrolytes

Fluorine‐Free Electrolytes for Lithium and Sodium Batteries

Anion Selection Criteria for Water-in-Salt Electrolytes

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