Cosolvent-involved hybrid solvation models for aqueous Zn-ion electrolytes: a case study of ethylene glycol-H₂O-ZnSO₄ system

Abstract

Tuning electrolyte bulk properties, fundamentally the Zn-ion solvation structures, is key to addressing degradation issues in aqueous Zn-ion batteries (AZIBs). The common practice is to add water-soluble organics as a cosolvent. However, a comprehensive fundamental understanding of the cosolvent effect on electrolyte bulk properties is still lacking. In this work, using ethylene glycol (EG) as the cosolvent and 2M ZnSO₄ as the base aqueous Zn-ion electrolyte, we report from a computational perspective how the cosolvent affects aqueous electrolyte bulk properties such as conductivity and pH. To ensure reliability of the computational results, we have used experimental ion conductivity data to validate our computing methods. Further, we show new hybrid solvation models that encompass H₂O, cosolvent and anion, e.g., EG-Zn(H₂O)₅²⁺ and EG-Zn(H₂O)₄²⁺-SO₄^2-. Based on these cosolvent-involved Zn-ion solvation models, the experimental pH trending has been successfully explained. Our work offers new insights into the cosolvent effect on aqueous Zn-ion electrolyte bulk properties and solvation structures.

Keywords

Cosolvent-involved hybrid solvation models / 2M ZnSO₄ / ethylene glycol / pH / conductivity

References

[1] Rajabi R,Billings A,Khan J.Insights into chemical and electrochemical interactions between Zn anode and electrolytes in aqueous Zn−ion batteries.J Electrochem Soc2022;169:110536

[2] Pan H,Yan P.Reversible aqueous zinc/manganese oxide energy storage from conversion reactions.Nat Energy2016;1:BFnenergy201639

[3] Guo X,Bai C,Fang G.Zn/MnO₂ battery chemistry with dissolution-deposition mechanism.Mater Today Energy2020;16:100396

[4] Lu Y,van den Bergh W,Huang K.A high performing Zn-ion battery cathode enabled by in situ transformation of V₂O₅ atomic layers.Angew Chem Int Ed Engl2020;59:17004-11

[5] Wang L,Chen J.Ultralong cycle stability of aqueous zinc-ion batteries with zinc vanadium oxide cathodes.Sci Adv2019;5:eaax4279 PMCID:PMC6984968

[6] Zhao W,Wu X.ε-MnO₂@C cathode with high stability for aqueous zinc-ion batteries.Appl Surf Sci2022;605:154685

[7] Chen C,Zhao Y,Zhao L.Al-intercalated MnO₂ cathode with reversible phase transition for aqueous Zn-ion batteries.Chem Eng J2021;422:130375

[8] Li G,Zhang S.Developing cathode materials for aqueous zinc ion batteries: challenges and practical prospects.Adv Funct Mater2024;34:2301291

[9] Wu F,Chen Y.Achieving highly reversible zinc anodes via N, N-dimethylacetamide enabled Zn-ion solvation regulation.Small2022;18:e2202363

[10] Hao J,Ye C.Boosting zinc electrode reversibility in aqueous electrolytes by using low-cost antisolvents.Angew Chem Int Ed Engl2021;60:7366-75

[11] Hou Z,Gao Y,Lu Z.Tailoring desolvation kinetics enables stable zinc metal anodes.J Mater Chem A2020;8:19367-74

[12] Qin R,Zhang M.Tuning Zn²⁺ coordination environment to suppress dendrite formation for high-performance Zn-ion batteries.Nano Energy2021;80:105478

[13] Chang N,Li R.An aqueous hybrid electrolyte for low-temperature zinc-based energy storage devices.Energy Environ Sci2020;13:3527-35

[14] Jia H,Wang Y,Shi S.Hybrid Co‐solvent‐induced high‐entropy electrolyte: regulating of hydrated Zn²⁺ solvation structures for excellent reversibility and wide temperature adaptability.Adv Energy Mater2024;14:2304285

[15] Zenodo. GROMACS 2019.6 Source code. 2020.

[16] Gaussian 16. 2016. https://gaussian.com/gaussian16/. (accessed 2025-02-07)

[17] Lu T.Multiwfn: a multifunctional wavefunction analyzer.J Comput Chem2012;33:580-92

[18] Lu T.A comprehensive electron wavefunction analysis toolbox for chemists, Multiwfn.J Chem Phys2024;161:082503

[19] Sobtop: A tool of generating forcefield parameters and GROMACS topology file. http://sobereva.com/soft/Sobtop. (accessed 2025-02-07)

[20] Bayly CI,Cornell W.A well-behaved electrostatic potential based method using charge restraints for deriving atomic charges: the RESP model.J Phys Chem1993;97:10269-80

[21] Wang J,Caldwell JW,Case DA.Development and testing of a general amber force field.J Comput Chem2004;25:1157-74

[22] Jiang Y,He X.Fine-tuning electrolyte concentration and metal-organic framework surface toward actuating fast Zn²⁺ dehydration for aqueous Zn-ion batteries.Angew Chem Int Ed Engl2023;62:e202307274

[23] Yue J,Yang J.Multi-ion engineering strategies toward high performance aqueous zinc-based batteries.Adv Mater2024;36:e2304040

[24] Sun S,Billings A.Understanding the critical bulk properties of Zn-salt solution electrolytes for aqueous Zn-ion batteries.Chem Mater2024;36:6805-15

[25] Bullerjahn JT,Heidari M,Hummer G.Unwrapping NPT simulations to calculate diffusion coefficients.J Chem Theory Comput2023;19:3406-17 PMCID:PMC10269326

[26] von Bülow S, Bullerjahn JT, Hummer G. Systematic errors in diffusion coefficients from long-time molecular dynamics simulations at constant pressure.J Chem Phys2020;153:021101

[27] Huang K. Transport of charged particles in a solid oxide fuel cell (SOFC). In: Solid oxide fuel cell technology. Elsevier; 2009. pp. 41-66. https://books.google.com/books?hl=zh-CN&lr=&id=c46kAgAAQBAJ&oi=fnd&pg=PP1&dq=Solid+oxide+fuel+cell+technology.&ots=BaY0QiCZiL&sig=Vj11zv61FcxKTCHjzITGhj9uVXo#v=onepage&q=Solid%20oxide%20fuel%20cell%20technology.&f=false. (accessed 2025-02-07)

[28] Cao X,Zhong A,Liu S.Molecular acidity: an accurate description with information-theoretic approach in density functional reactivity theory.J Comput Chem2018;39:117-29

[29] Liu S.Estimation of molecular acidity via electrostatic potential at the nucleus and valence natural atomic orbitals.J Phys Chem A2009;113:3648-55 PMCID:PMC2670071

[30] Liu S,Pedersen LG.Molecular acidity: a quantitative conceptual density functional theory description.J Chem Phys2009;131:164107 PMCID:PMC2855715

[31] Szwajczakaf E.On the relation between mobility of lons and viscosity. the Walden’s Rule.Mol Cryst Liq Cryst1986;139:253-61

[32] Wang J,Wu J.Interfacial “single-atom-in-defects” catalysts accelerating Li⁺ desolvation kinetics for long-lifespan lithium-metal batteries.Adv Mater2023;35:e2302828

[33] Elliott GR,Webber GB,Craig VSJ.Dynamic ion correlations and ion-pair lifetimes in aqueous alkali metal chloride electrolytes.J Phys Chem B2024;128:7438-44

[34] Yu X,Li Z.Unlocking dynamic solvation chemistry and hydrogen evolution mechanism in aqueous zinc batteries.J Am Chem Soc2024;146:17103-13

[35] Zhang H,Guo Y.Unraveling the mechanisms of aqueous zinc ion batteries via first-principles calculations.ACS Energy Lett2024;9:4761-84