“Water in Ionic Liquid” Electrolyte Toward Supercapacitors With High Operation Voltage, Long Lifespan, and Wide Temperature Compatibility

Abstract

Aqueous electrolytes, with their inherent safety, low cost, and eco-friendliness, provide a promising alternative for energy storage devices, but their application is limited due to the narrow electrochemical stability window of water. Using super-concentrated electrolytes has been demonstrated effectives in expanding the electrochemical window of aqueous electrolytes. However, this approach also brings in several challenges, including decreased ionic conductivity, poor wettability, and increased temperature sensitivity due to the near-saturated salt concentrations. In this study, we employed a water-miscible ionic liquid (i.e., 1-butyl-3-methylimidazolium trifluoromethanesulfonate) to break the solubility limitations faced in super-concentrated electrolytes and created a new “water in ionic liquid” electrolyte that simultaneously featured with broad electrochemical window, decent ionic conductivity, and wide temperature compatibility. Moreover, a prototype of electrochemical double-layer supercapacitor utilizing the “water in ionic liquid” electrolyte demonstrates outstanding performance characteristics, including a high operating voltage (2.6 V), excellent rate capability with 81% capacitance retention from 0.5 to 30 A g^-1, remarkable cyclic stability with 75% capacitance retention after 120,000 cycles, along with broad temperature compatibility from -20°C to 60°C. These findings not only provide new insights into electrolyte engineering but also offer a pathway for designing innovative aqueous electrolytes for energy storage devices with balanced electrochemical performance.

Keywords

aqueous electrolytes / electrolyte engineering / solvation structures / supercapacitor / “water in ionic liquid” electrolyte

References

[1] P. Simon and Y. Gogotsi, “Materials for Electrochemical Capacitors,” Nature Materials 7, no. 11 (2008): 845-854.

[2] P. Simon and Y. Gogotsi, “Perspectives for Electrochemical Capacitors and Related Devices,” Nature Materials 19, no. 11 (2020): 1151-1163.

[3] F. Béguin, V. Presser, A. Balducci, and E. Frackowiak, “Carbons and Electrolytes for Advanced Supercapacitors,” Advanced Materials 26, no. 14 (2014): 2219-2251.

[4] C. Zhong, Y. Deng, W. Hu, J. Qiao, L. Zhang, and J. Zhang, “A Review of Electrolyte Materials and Compositions for Electrochemical Supercapacitors,” Chemical Society Reviews 44, no. 21 (2015): 7484-7539.

[5] L. Chen, H. Wu, X. Ai, Y. Cao, and Z. Chen, “Toward Wide-Temperature Electrolyte for Lithium-Ion Batteries,” Battery Energy 1 (2022): 20210006.

[6] M. Dong, H. Q. Fu, Y. Xu, et al., “Nico Alloy-Anchored Self-Supporting Carbon Foam as a Bifunctional Oxygen Electrode for Rechargeable and Flexible Zn-Air Batteries,” Battery Energy 2 (2023): 20220063.

[7] Y. S. Meng, V. Srinivasan, and K. Xu, “Designing Better Electrolytes,” Science 378, no. 6624 (2022): 1065.

[8] O. Borodin, J. Self, K. A. Persson, C. Wang, and K. Xu, “Uncharted Waters: Super-Concentrated Electrolytes,” Joule 4, no. 1 (2020): 69-100.

[9] D. Chao, W. Zhou, F. Xie, et al., “Roadmap for Advanced Aqueous Batteries: From Design of Materials to Applications,” Science Advances 6, no. 21 (2020): eaba4098.

[10] J. Yu, C. Yu, X. Song, et al., “Microscopic-Level Insights Into Solvation Chemistry for Nonsolvating Diluents Enabling High-Voltage/Rate Aqueous Supercapacitors,” Journal of the American Chemical Society 145, no. 25 (2023): 13828-13838.

[11] H. Kim, J. Hong, K. Y. Park, H. Kim, S. W. Kim, and K. Kang, “Aqueous Rechargeable Li and Na Ion Batteries,” Chemical Reviews 114, no. 23 (2014): 11788-11827.

[12] D. Chao and S. Z. Qiao, “Toward High-Voltage Aqueous Batteries: Super- or Low-Concentrated Electrolyte?,” Joule 4, no. 9 (2020): 1846-1851.

[13] J. Park, J. Lee, and W. Kim, “Water-in-Salt Electrolyte Enables Ultrafast Supercapacitors for AC Line Filtering,” ACS Energy Letters 6, no. 2 (2021): 769-777.

[14] L. Suo, O. Borodin, T. Gao, et al., ‘Water-in-Salt’ Electrolyte Enables High-Voltage Aqueous Lithium-Ion Chemistries,” Science 350, no. 6263 (2015): 938-943.

[15] L. Suo, O. Borodin, Y. Wang, et al., ‘Water-in-Salt’ Electrolyte Makes Aqueous Sodium-Ion Battery Safe, Green, and Long-Lasting,” Advanced Energy Materials 7, no. 21 (2017): 1701189.

[16] L. Jiang, Y. Lu, C. Zhao, et al., “Building Aqueous K-Ion Batteries for Energy Storage,” Nature Energy 4, no. 6 (2019): 495-503.

[17] Y. Yamada, K. Usui, K. Sodeyama, S. Ko, Y. Tateyama, and A. Yamada, “Hydrate-Melt Electrolytes for High-Energy-Density Aqueous Batteries,” Nature Energy 1 (2016): 16129.

[18] M. H. Lee, S. J. Kim, D. Chang, et al., “Toward a Low-Cost High-Voltage Sodium Aqueous Rechargeable Battery,” Materials Today 29 (2019): 26-36.

[19] M. R. Lukatskaya, J. I. Feldblyum, D. G. Mackanic, et al., “Concentrated Mixed Cation Acetate ‘Water-in-Salt’ Solutions as Green and Low-Cost High Voltage Electrolytes for Aqueous Batteries,” Energy & Environmental Science 11, no. 10 (2018): 2876-2883.

[20] L. Jiang, L. Liu, J. Yue, et al., “High-Voltage Aqueous Na-Ion Battery Enabled by Inert-Cation-Assisted Water-in-Salt Electrolyte,” Advanced Materials 32, no. 2 (2020): 1904427.

[21] D. Reber, R. Grissa, M. Becker, R. S. Kühnel, and C. Battaglia, “Anion Selection Criteria for Water-in-Salt Electrolytes,” Advanced Energy Materials 11, no. 5 (2021): 2002913.

[22] D. P. Leonard, Z. Wei, G. Chen, F. Du, and X. Ji, “Water-in-Salt Electrolyte for Potassium-Ion Batteries,” ACS Energy Letters 3, no. 2 (2018): 373-374.

[23] J. Park, J. Lee, and W. Kim, “Redox-Active Water-in-Salt Electrolyte for High-Energy-Density Supercapacitors,” ACS Energy Letters 7, no. 4 (2022): 1266-1273.

[24] J. Yue, L. Lin, L. Jiang, et al., “Interface Concentrated-Confinement Suppressing Cathode Dissolution in Water-in-Salt Electrolyte,” Advanced Energy Materials 10, no. 36 (2020): 2000665.

[25] Y. Zhang, J. Xu, Z. Li, et al., “All-Climate Aqueous Na-Ion Batteries Using ‘Water-in-Salt’ Electrolyte,” Science Bulletin 67, no. 2 (2022): 161-170.

[26] J. J. Xu, X. Ji, J. X. Zhang, et al., “Aqueous Electrolyte Design for Super-Stable 2.5 V LiMn₂O₄ || Litio Pouch Cells,” Nature Energy 7, no. 2 (2022): 186-193.

[27] Z. Hou, M. Dong, Y. Xiong, X. Zhang, Y. Zhu, and Y. Qian, “Formation of Solid-Electrolyte Interfaces in Aqueous Electrolytes by Altering Cation-Solvation Shell Structure,” Advanced Energy Materials 10, no. 15 (2020): 1903665.

[28] H. Bi, X. Wang, H. Liu, et al., “A Universal Approach to Aqueous Energy Storage via Ultralow-Cost Electrolyte With Super-Concentrated Sugar as Hydrogen-Bond-Regulated Solute,” Advanced Materials 32, no. 16 (2020): 2000074.

[29] L. Geng, J. Meng, X. Wang, et al., “Eutectic Electrolyte With Unique Solvation Structure for High-Performance Zinc-Ion Batteries,” Angewandte Chemie International Edition 61, no. 31 (2022): 2206717.

[30] J. N. Hao, L. B. Yuan, Y. L. Zhu, et al., “Low-Cost and Non-Flammable Eutectic Electrolytes for Advanced Zn-I Batteries,” Angewandte Chemie International Edition 62, no. 39 (2023): 2310284.

[31] Y. Zhu, X. Guo, Y. Lei, et al., “Hydrated Eutectic Electrolytes for High-Performance Mg-Ion Batteries,” Energy & Environmental Science 15, no. 3 (2022): 1282-1292.

[32] R. Chen, C. Zhang, J. Li, et al., “A Hydrated Deep Eutectic Electrolyte With Finely-Tuned Solvation Chemistry for High-Performance Zinc-Ion Batteries,” Energy & Environmental Science 16, no. 6 (2023): 2540-2549.

[33] J. P. Xie, D. W. Lin, H. Lei, et al., “Electrolyte and Interphase Engineering of Aqueous Batteries Beyond ‘Water-in-Salt’ Strategy,” Advanced Materials 36 (2023): 2306508.

[34] J. Ren, M. Shen, Z. Li, et al., “Towards High-Performance All-Solid-State Asymmetric Supercapacitors: A Hierarchical Doughnut-Like Ni₃S₂@PPy Core−Shell Heterostructure on Nickel Foam Electrode and Density Functional Theory Calculations,” Journal of Power Sources 501 (2021): 230003.

[35] L. Zheng, Y. Zhao, P. Xu, et al., “Copper Doped CoS_X@Co(OH)₂ Hierarchical Mesoporous Nanosheet Arrays as Binder-Free Electrodes for Superior Supercapacitors,” Journal of Alloys and Compounds 911 (2022): 165115.

[36] T. Zhu, J. Pan, Z. An, R. Zhe, Q. Ou, and H. E. Wang, “Bifunctional Nicuo_X Photoelectrodes to Promote Pseudocapacitive Charge Storage by In Situ Photocharging,” Journal of Materials Chemistry A 10, no. 38 (2022): 20375-20385.

[37] P. Wang, X. Ding, R. Zhe, et al., “Synchronous Defect and Interface Engineering of NiMoO₄ Nanowire Arrays for High-Performance Supercapacitors,” Nanomaterials 12, no. 7 (2022): 1094.

[38] S. Wu, B. Su, M. Sun, et al., “Dilute Aqueous-Aprotic Hybrid Electrolyte Enabling a Wide Electrochemical Window Through Solvation Structure Engineering,” Advanced Materials 33, no. 41 (2021): 2102390.

[39] F. Chi, C. Li, Q. Zhou, et al., “Graphene-Based Organic Electrochemical Capacitors for AC Line Filtering,” Advanced Energy Materials 7, no. 19 (2017): 1700591.

[40] J. Xie, Z. Liang, and Y. C. Lu, “Molecular Crowding Electrolytes for High-Voltage Aqueous Batteries,” Nature Materials 19, no. 9 (2020): 1006-1011.

RIGHTS & PERMISSIONS

2025 The Author(s). Battery Energy published by Xijing University and John Wiley & Sons Australia, Ltd.