Solvation Structure Design for Aqueous Zn Metal Batteries

Abstract

Aqueous Zn batteries are promising energy storage devices for large-scale energy-storage due to low cost and high energy density. However, their lifespan is limited by the water decomposition and Zn dendrite growth. Here, we suppress water reduction and Zn dendrite growth in dilute aqueous electrolyte by adding dimethyl sulfoxide (DMSO) into ZnCl2–H2O, in which DMSO replaces the H2O in Zn2+ solvation sheath due to a higher Gutmann donor number (29.8) of DMSO than that (18) of H2O. The preferential solvation of DMSO with Zn2+ and strong H2O–DMSO interaction inhibit the decomposition of solvated H2O. In addition, the decomposition of solvated DMSO forms Zn12(SO4)3Cl3(OH)15·5H2O, ZnSO3, and ZnS enriched-solid electrolyte interphase (SEI) preventing Zn dendrite and further suppressing water decomposition. The ZnCl2–H2O–DMSO electrolyte enables Zn anodes in Zn||Ti half-cell to achieve a high average Coulombic efficiency of 99.5% for 400 cycles (400 h), and the Zn||MnO2 full cell with a low capacity ratio of Zn:MnO2 at 2:1 to deliver a high energy density of 212 Wh/kg (based on both cathode and anode) and maitain 95.3% of the capacity over 500 cycles at 8 C.

Non-concentrated aqueous electrolytes with organic solvent additives for stable zinc batteries

“…For the S 2p spectra, the signals of sulfide ( e.g. , ZnS) 35,37 apparently appear as the Ar + sputtering time increases, further confirming the decomposition of the Zn 2+ –OTf − coordination and the involvement of decomposed species in the SEI formation. Additionally, the intensifying of the Zn peak coincides with the evolution of C and F signals, suggesting the enrichment of ZnCO 3 and ZnF 2 components in the inner SEI layer.…”

“…In a conventional aqueous electrolyte (concentration generally below 2 mol L −1 ), the typical solvation structure of Zn[H 2 O] 6 2+ without anion coordination makes it infeasible to form a protective SEI from the reductive decomposition of anions before Zn deposition. 35,36 Instead, competitive water decomposition with H 2 evolution occurred (H 2 O → H 2 + OH − ), which increases the local pH and induces the generation of Zn hydroxides or zincates to passivate the Zn anode. 35,38 Therefore, it is desirable to stabilize the Zn electrochemistry in non-concentrated aqueous electrolytes.…”

“… 35,36 Instead, competitive water decomposition with H 2 evolution occurred (H 2 O → H 2 + OH − ), which increases the local pH and induces the generation of Zn hydroxides or zincates to passivate the Zn anode. 35,38 Therefore, it is desirable to stabilize the Zn electrochemistry in non-concentrated aqueous electrolytes.…”

Simultaneous Regulation on Solvation Shell and Electrode Interface for Dendrite‐Free Zn Ion Batteries Achieved by a Low‐Cost Glucose Additive

“…As shown in Figures 4 c and S17, the Zn//Zn symmetric coin cell using ZnSO 4 ‐glucose electrolyte can stably cycle for over 2000 h at 1 mA cm −2 with 1 mAh cm −2 and 740 h at 2 mA cm −2 with 2 mAh cm −2 , while those using pure ZnSO 4 electrolyte are short‐circuited after 300 and 200 h of cycling under the same conditions. More attractively, even employing a high current of 5 mA cm −2 and a high capacity of 5 mAh cm −2 , this novel electrolyte system still supports stably reversible Zn plating/stripping for around 270 h (Figure 4 d), which is much superior to that using pure ZnSO 4 (around 20 h) and better than most of previous work (Table S1) [11, 13, 14, 21, 23–26, 36, 44, 45] …”

“…Previously, researchers added a small amount of solute like polyacrylamide or tetrabutylammonium sulfate into ZnSO 4 electrolyte, which are able to absorb on Zn surface, thus ensuring uniform deposition of Zn layer [21, 24, 33] . Furthermore, introducing various solvents such as succinonitrile, dimethyl sulfoxide or antisolvents into pure aqueous electrolyte is helpful for modulating the solvated structure of Zn hydration layer, thus suppressing the generation of by‐products [22, 23, 25] . Thus, it should be a charming idea to simultaneously optimize the solvation configuration around Zn ions in the electrolyte and control the environment on electrode‐electrolyte interface for achieving uniform nucleation on metal Zn surface.…”