Aqueous zinc-iodine battery

Abstract

The invention discloses an aqueous zinc-iodine battery which comprises an iodine positive electrode, a zinc negative electrode, a diaphragm and an electrolyte solution, the electrolyte solution comprises a zinc sulfate solution and erythritol; the problems of side reaction and growth of electrode dendrites in the prior art are solved.

Description

Technical Field

[0001] The invention relates to the technical field of zinc ion batteries, and in particular to an aqueous zinc-iodine battery. Background Art

[0002] Aqueous zinc-ion batteries (AZIBs) have a high theoretical capacity (820 mAh g -1 and 5855mAhcm -3 ), low electrochemical potential (-0.76V relative to standard hydrogen electrode), wide sources and high safety have been greatly developed. However, before the practical application of AZIBs, some problems still need to be solved, including the unrestricted growth of zinc dendrites, side reactions triggered by highly active water molecules, the electrochemical stability window limited by hydrogen evolution and oxygen evolution reactions, and byproducts such as basic zinc sulfate. To date, various strategies have been adopted to inhibit the appearance of zinc dendrites and the generation of byproducts. These strategies can be summarized into four categories: electrode structure design, surface coating technology, diaphragm modification engineering and selection of electrolyte additives. Since the electrolyte is crucial to the electrochemical stability window and reaction mechanism, the electrolyte additive strategy is considered to be the most effective method. The advantages of the electrolyte additive strategy also lie in its economy, easy availability and simple preparation.

[0003] Zinc sulfate (ZnSO4) is a widely used electrolyte in AZIBs. In a 2M ZnSO4 aqueous solution, six water molecules bond with zinc to form Zn[(H2O)6] 2+ The solvation structure of Zn 2+ Electrostatic interaction between Zn[(H2O)6] and water molecules 2+ The activity of the OH bond in ZnO is higher than that of pure water. Therefore, it may induce the side reaction of hydrogen evolution reaction (HER), resulting in Zn 2+ The deposition / stripping efficiency is low. In addition, Zn[(H2O)6] 2+ The solvation structure hinders the migration of electrons and ions, which has an adverse effect on the stripping process of the zinc electrode. To avoid these problems, it is crucial to adjust the electrolyte environment. So far, a large number of inorganic salts and organic molecules have been used as electrolyte additives. For example, the Chinese patent with publication number CN118630341A discloses a degradable aqueous biomass zinc-iodine battery and its preparation method, and the electrolyte solution additive is sodium alginate colloid; although significant progress has been made in the use of electrolyte additives to improve the performance of AZIBs, many key issues such as HER and corrosion side reactions, imbalance between "network water" and "free water", and the inability of additives to inhibit the growth of electrode dendrites still exist. Summary of the invention

[0004] The invention provides an aqueous zinc-iodine battery, which solves the problems of side reactions and electrode dendrite growth in the prior art.

[0005] In order to solve this technical problem, the present invention provides the following technical solution:

[0006] An aqueous zinc-iodine battery, comprising: an iodine positive electrode, a zinc negative electrode, a separator and an electrolyte solution;

[0007] The electrolyte solution includes zinc sulfate solution and erythritol.

[0008] Preferably, the concentration of erythritol is 0.1-0.3M.

[0009] Preferably, the concentration of erythritol is 0.2M.

[0010] Preferably, the concentration of the zinc sulfate solution is 2M.

[0011] Preferably, the iodine positive electrode is obtained by coating positive electrode slurry on carbon paper and drying it; the positive electrode slurry comprises an active material, a conductive agent and a binder; and the active material comprises iodine monomer and activated carbon.

[0012] Preferably, the conductive agent is acetylene black.

[0013] Preferably, the adhesive is PVDF.

[0014] Preferably, the weight ratio of the active material, the conductive agent and the binder is 8:1:1.

[0015] Preferably, the weight ratio of iodine monomer to activated carbon is 3:7.

[0016] Preferably, the separator is glass fiber.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] Food sweetener erythritol (four-carbon polyol, C4H 12 O4) is introduced into ZnSO4 electrolyte due to its unique characteristics of miscibility with water, non-toxicity and inertness to obtain ZnSO4+erythritol electrolyte. 2+ The coordination of Zn 2+ The H2O molecules in the solvation shell can be reduced and the decomposition of active water can be reduced, thereby alleviating HER and corrosion side reactions.

[0019] At the same time, due to the polar groups of erythritol, the hydrogen bond network of ZnSO4+erythritol electrolyte can be reconfigured, resulting in a balance between “network water” and “free water”, which can inhibit side reactions without reducing ion transport.

[0020] In addition, due to the rich polar groups, the erythritol additive is preferentially adsorbed on the surface of the zinc anode, thereby effectively protecting the zinc anode and inhibiting the crazy growth of dendrites.

[0021] The Coulombic efficiency (CE) value of the Ti||Zn battery using ZnSO4+erythritol electrolyte (99%) is significantly higher than that of pure ZnSO4 electrolyte (97%). -2 and 0.5mAhcm -2 Under the same conditions, the lifespan of the Zn||Zn symmetric battery and Ti||Zn asymmetric battery with erythritol added is 6 times and 7 times longer than that of the pure ZnSO4 battery, respectively. -1 and 1.0Ag -1 At a current density of , the Zn-I2 battery using ZnSO4+erythritol electrolyte also has better stability than the battery using ZnSO4. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0023] Figure 1 (a) Cyclic voltammetry curves of Zn-I2 full cells using ZnSO4 and ZnSO4 + erythritol;

[0024] Figure 1 (b) is the electrochemical impedance spectroscopy of the Zn-I2 full cell using ZnSO4 and ZnSO4+erythritol;

[0025] Figure 1 (c) Rate performance of Zn-I2 full cells using ZnSO4 and ZnSO4+erythritol at different current densities;

[0026] Figure 1 (d) is the constant current charge and discharge curve;

[0027] Figure 1 (e) Zn-I2 full battery using ZnSO4+erythritol at 0.2Ag -1 Constant current charge and discharge curves of different cycles;

[0028] Figure 1 (f) is at 0.2Ag -1 Long-term cycling performance of Zn-I2 full batteries using ZnSO4 and ZnSO4+erythritol under 40 %;

[0029] Figure 2 (a) is the electrostatic potential diagram;

[0030] Figure 2(b) LUMO-HOMO energy band gap and schematic diagram of water and erythritol molecules, blue represents the positive region and yellow represents the negative region;

[0031] Figure 2 (c) H2O-H2O, erythritol-H2O, H2O-Zn 2+ and erythritol-Zn 2+ The binding energy of

[0032] Figure 2 (d) NMR spectra of different electrolytes in D2O;

[0033] Figure 2 (e) FTIR of ZnSO4 and ZnSO4+erythritol electrolyte;

[0034] Figure 2 (f) Raman spectra of ZnSO4 and ZnSO4+erythritol electrolytes;

[0035] Figure 3 (a) is a three-dimensional snapshot of ZnSO4-H2O;

[0036] Figure 3 (b) ZnSO4-H2O-erythritol and Zn obtained by molecular dynamics simulation 2+ A partially magnified snapshot of the solvated structure;

[0037] Figure 3 (c) Zn in ZnSO4 and ZnSO4+erythritol electrolytes obtained by molecular dynamics simulation 2+ - Radial distribution function and coordination number of O;

[0038] Figure 3 (d) is the electrostatic potential diagram;

[0039] Figure 3 (e) is [Zn(H2O)6] 2+ and [Zn(H2O)5-erythritol] 2+ LUMO-HOMO energy band gap and schematic diagram;

[0040] Figure 4 (a) is the adsorption energy of water, zinc and erythritol molecules on the Zn(002) surface;

[0041] Figure 4 (b) The charge density difference along the Z axis of the zinc plate containing erythritol molecules (placed horizontally) and water and the corresponding equipotential surface (the yellow and cyan translucent clusters represent the increase and decrease of electron density, respectively);

[0042] Figure 4(c) Nyquist plot of Zn||Zn battery using ZnSO4 and ZnSO4+erythritol electrolyte;

[0043] Figure 4 (d) is the differential capacitance of Na2SO4 and Na2SO4+erythritol electrolytes;

[0044] Figure 4 (e) is the linear sweep voltammetry (LSV) curve; Figure 4 (f) is at 5mVs -1 Below, Tafel plots of zinc anode in ZnSO4 and ZnSO4 + erythritol electrolytes;

[0045] Figure 5 (a) is a schematic diagram of the effect of ZnSO4+erythritol and ZnSO4 electrolyte;

[0046] Figure 5 (b) is at 0.1mVs -1 Cyclic voltammetry curves of nucleation overpotential on titanium foil in different electrolytes.

[0047] Figure 5 (c) Chronoamperometric curves of Zn||Zn batteries with two different electrolytes;

[0048] Figure 5 (d) is at 1.0 mA cm -2 、0.5mAhcm -2 Long-term cycling performance of Zn||Zn batteries with two different electrolytes; Figure 5 (e) is at 4.0 mA cm -2 、0.5mAhcm -2 Long-term cycling performance of Zn||Zn batteries with two different electrolytes;

[0049] Figure 6 (a) Coulombic efficiency curves of Ti||Zn batteries using ZnSO4 and ZnSO4+erythritol electrolytes;

[0050] Figure 6 (b) is the potential-capacity curve of the Ti||Zn battery using ZnSO4+erythritol electrolyte;

[0051] Figure 6 (c) XRD comparison of zinc anode after cycling in different electrolytes;

[0052] Figure 6 (d) is the scanning electron microscope image of the zinc anode after cycling in ZnSO4 electrolyte;

[0053] Figure 6(e) is a scanning electron microscope image of the zinc anode after cycling in ZnSO4+erythritol electrolyte;

[0054] Figure 6 (f) is an in-situ optical microscopy image of the zinc deposition process in ZnSO4 electrolyte;

[0055] Figure 6 (g) In situ optical microscopy image of the zinc deposition process in ZnSO4+erythritol electrolyte. DETAILED DESCRIPTION

[0056] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. The illustrative embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0057] Example 1

[0058] (a) Preparation of electrolyte

[0059] 5.7512 g ZnSO4·7H2O was added to 10 mL deionized water to obtain ZnSO4 electrolyte. 2M ZnSO4+0.2M erythritol electrolyte was obtained by adding 0.2442 g erythritol to 10 mL ZnSO4 solution.

[0060] (b) Preparation of I2 / AC electrode

[0061] First, iodine monomer and activated carbon were mixed in a mortar at a mass ratio of 3:7. Then, the mixture was loaded into a glass tube and heated at 90°C for 4 hours to obtain I2 / AC material. Next, a positive electrode slurry was prepared according to the ratio of I2 / AC material: acetylene black: PVDF = 8:1:1, which was then coated on carbon paper and vacuum dried at 90°C for 4 hours to obtain an I2 / AC electrode. The mass loading of I2 is about 1.0 mg cm -2 .

[0062] (c) Assembly of Zn-I2 battery

[0063] CR2032 button cells were assembled with I2 / AC electrode as positive electrode, zinc foil as negative electrode, glass fiber as separator, pure ZnSO4 and ZnSO4+erythritol as electrolyte, and their electrochemical performance was tested and evaluated. The diameters of the negative electrode, positive electrode and separator were 14 mm, 14 mm and 19 mm respectively. The specific capacity of the battery was calculated based on the mass of iodine.

[0064] Example 2

[0065] The preparation process of the electrolyte is as follows: 5.7512 g ZnSO4·7H2O is added to 10 mL deionized water to obtain ZnSO4 electrolyte. 2M ZnSO4+0.1M erythritol electrolyte is obtained by adding 0.1221 g erythritol to 10 mL ZnSO4 solution.

[0066] The preparation of I2 / AC electrode and the assembly of Zn-I2 battery are the same as those in Example 1.

[0067] Example 3

[0068] The preparation process of the electrolyte is as follows: 5.7512g ZnSO4·7H2O is added to 10mL deionized water to obtain ZnSO4 electrolyte. 2M ZnSO4+0.3M erythritol electrolyte is obtained by adding 0.3663g erythritol to 10mL ZnSO4 solution.

[0069] The preparation of I2 / AC electrode and the assembly of Zn-I2 battery are the same as those in Example 1.

[0070] Comparative Example 1

[0071] The difference between Comparative Example 1 and Example 1 is that erythritol is not added to the electrolyte; the preparation process of the electrolyte of Comparative Example 1 is: 5.7512 g of ZnSO4·7H2O is added to 10 mL of deionized water to obtain a 2M ZnSO4 electrolyte.

[0072] The preparation of I2 / AC electrode and the assembly of Zn-I2 battery are the same as those in Example 1.

[0073] In order to verify the practicality of erythritol additives in improving the performance of the whole battery, the performance of Zn-I2 batteries assembled with I2 / AC as the positive electrode and zinc foil as the negative electrode in Examples 1-3 and Comparative Example 1 was tested. The results show that the battery performance using the ZnSO4+erythritol electrolyte of Examples 1-3 is significantly better than the battery performance of the ZnSO4 electrolyte of Comparative Example 1. In order to illustrate the effect of erythritol, the best performing Example 1 (electrolyte with an erythritol concentration of 0.2M) and Comparative Example 1 without erythritol were selected as the test results for comparison. Therefore, unless otherwise specified, the text describing "ZnSO4+erythritol" below refers to 0.2M erythritol.

[0074] Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were measured using an electrochemical workstation (Autolab M204). The scan rate of the CV test of the Zn-I2 battery was 2.0 mVs -1The EIS was measured in the frequency range of 100kHz to 0.1Hz with an AC voltage amplitude of 5mV at open circuit voltage. The constant current charge and discharge tests were performed on a Xinwei BTS-51 battery test system.

[0075] exist Figure 1 In a, the cyclic voltammetry curve shows that the battery containing erythritol additive in Example 1 can obtain a higher current density than that in Comparative Example 1. This is attributed to the fact that the erythritol molecules adsorbed on the electrode surface are beneficial to the zinc deposition process and accelerate the reaction rate. Figure 1 In b, the electrochemical impedance spectrum shows that the battery using ZnSO4+erythritol electrolyte in Example 1 has a lower impedance, which indicates that it has a faster charge transfer rate.

[0076] The rate performance and long-term cycle stability were further tested. Figure 1 c shows that the full battery using ZnSO4+erythritol electrolyte has a -1 To 4.0Ag -1 They have similar rate performance and discharge capacity in the current density range. Figure 1 d, the battery using ZnSO4+erythritol electrolyte in Example 1 shows a slightly higher discharge platform, which means that the erythritol additive has a beneficial effect. The operating voltage platform of about 1.2V corresponds to the redox reaction of I2 / I-. Importantly, Figure 1 ef in 0.2Ag -1 The long-term cycle stability under the conditions of 1.5 % α-H2O2 and 1.5 % α-H2O2 showed that the battery using ZnSO4+erythritol electrolyte in Example 1 exhibited stable cycle performance, with the capacity maintained at 185 mAh g after more than 1800 cycles. -1 The capacity retention rate is 88%. In contrast, the battery using ZnSO4 electrolyte in Comparative Example 1 has a capacity of 210 mAhg / cm2 after 805 cycles. -1 Down to 147mAhg -1 , the capacity decay is faster, and the capacity retention rate is only 70%. In addition, at 1.0Ag -1 At a current density of 1.3 Å, the battery using ZnSO4+erythritol electrolyte can run for more than 10,000 cycles, which is almost twice the number of cycles of the battery using ZnSO4 electrolyte under the same test conditions. This shows that the erythritol additive can not only guide the uniform deposition of zinc anode, but also improve the stability of the battery.

[0077] In order to further clarify the mechanism of erythritol, X-ray diffraction (XRD, Bruker AXS GmbH, Germany) and scanning electron microscopy (SEM, Hitachi SU8100) were used to analyze the crystal structure and morphology of the samples on zinc foil. Raman spectroscopy (WiTechalpha300R), Fourier transform infrared spectroscopy (FTIR, NioletiN10) and hydrogen nuclear magnetic resonance imaging (NMR, Bruker 600MHz, Germany) were used to study the changes in the solution. Cyclic voltammetry curves (CV) and electrochemical impedance spectroscopy (EIS) were measured using an electrochemical workstation (AutolabM204). Zn||Zn symmetric cells, Ti||Zn and Zn-I2 batteries were constructed using ZnSO4 and ZnSO4+erythritol electrolytes, respectively, and the CV test scan rate was 2.0mVs -1 . EIS was measured in the frequency range of 100kHz to 0.1Hz, with an AC voltage amplitude of 5mV at open circuit voltage. HER and oxygen evolution reaction (OER) were tested using linear sweep voltammetry (LSV) in a three-electrode system: Ag / AgCl as reference electrode, platinum foil as counter electrode, and titanium foil as working electrode. Constant current charge and discharge tests were performed on a Xinwei BTS-51 battery test system.

[0078] 1. Electrolyte characterization results:

[0079] The molecular structure affects its properties, and the properties of the additive molecules affect the properties of the solution, especially the solvation structure of the ions and the hydrogen bond network in the solution. First, the intrinsic properties of the additive were calculated using density functional theory (DFT). Compared with the H2O molecule, the O atom in the erythritol molecule has a more positive charge, which means that the erythritol molecule is more likely to transfer Zn 2+ Donate electrons to reduce the transition from H2O to Zn 2+ electron transfer, which may change Zn[(H2O)6] 2+ The solvation structure of Figure 2 From the electrostatic potential diagram of H2O and erythritol molecules in a, the -OH group in the erythritol molecule has a higher electronegativity than that in the H2O molecule, which means that they are 2+ and H + This is consistent with previous speculation that erythritol additives may change the Zn[(H2O)6] 2+ The solvation structure.

[0080] The redox properties of erythritol and H2O molecules were evaluated by calculating the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels. The HOMO energy level indicates the ability to donate electrons, while the LUMO energy level reflects the ability to accept electrons. Figure 2b shows that erythritol molecules have higher HOMO and lower LUMO energy levels than H2O molecules, indicating a stronger interaction between erythritol molecules and the zinc anode. The lower LUMO energy indicates that erythritol molecules may be reduced on the surface of the zinc anode to form a solid electrolyte interface (SEI) layer, thereby alleviating water decomposition in the electrolyte. The lower orbital energy gap (ΔE = E LUMO -E HOMO ) values ​​confirm this. Based on these findings, the binding energies between various substances were further calculated (calculation details: Theoretical calculations were completed using Dmol3 and molecular dynamics software package (MaterialsStudio2020). The Perdew-Burke-Ernzerhof (PBE) functional method with generalized gradient approximation (GGA) was used for geometry optimization and calculation. The orbital occupation and global orbital cutoffs were 0.005Ha and To achieve accurate electronic convergence, a self-consistent field (SCF) procedure was used with a total energy convergence criterion of 1 × 10 -6 Ha. The maximum force and displacement are 0.002 and The binding energy (Ebinding) between Zn atoms, H2O molecules and erythritol molecules is obtained by the following formula:

[0081] E binding =E tot -E A -E B

[0082] Among them, E tot is the total energy of the system, E A is the energy of the erythritol molecule, E B is the energy of Zn atoms and H2O molecules in the system). Figure 2 As shown in c, the binding energy of erythritol-H2O is greater than that of H2O-H2O, which means that erythritol molecules may destroy the hydrogen bonds in H2O-H2O. 2+ The binding energy is higher than that of Zn 2+ -H2O, which indicates that erythritol molecules can enter Zn[(H2O)6] 2+ The solvation sheath structure replaces some H2O molecules. This may form a layer of [Zn(H2O)x-(erythritol)y] 2+ The electrostatic protection layer is used to regulate the electric field on the zinc electrode, thereby mitigating the formation of random dendrites and side reactions.

[0083] The effect of erythritol additive on Zn[(H2O)6] was investigated using NMR, FTIR and Raman spectroscopy. 2+ The solvation structure and hydrogen bond network in aqueous electrolytes. Figure 2As shown in d, the addition of ZnSO4 to D2O leads to a significant chemical shift of the 1H peak, which means that the hydrated Zn[(H2O)6] 2+ From H2O to Zn in the cluster 2+ The charge transfer of Zn[(H2O)6] 2+ The solvation sheath structure of the electrolyte can be reconfigured to change the coordination environment and side reactions of the zinc ion. Figure 2 From the FTIR spectrum of e, with the increase of erythritol content, strong hydrogen bonds gradually decreased and weak hydrogen bonds increased, which shows that erythritol additives can reduce the number of "network water" and "free water" molecules in the electrolyte, thereby reducing the diffusion of hydrogen ions and weakening side reactions and corrosion. The reason is that the O atoms in the erythritol molecules have a higher negative charge density than those in H2O. They form weak hydrogen bonds with H2O as hydrogen bond acceptors. This induction effect can enhance the OH covalent bonds in water. However, SO4 2- According to the classical Eigen-Tamm mechanism, the ion association in ZnSO4 solution can be decomposed into solvent-separated ion pairs (Zn 2+ (H2O)6·SO4 2- , SSIP) and contact ion pairs (Zn 2+ (H2O)5·OSO3 2- , CIP). SSIP represents Zn 2+ The ion coordinates with six H2O molecules to form SO4 2- In contrast, CIP represents the Zn 2+ ion with five H2O molecules and one SO4 2- Anion coordination formation and SO4 2- In order to explore more characteristics of ZnSO4 solution containing erythritol additive, Raman spectroscopy analysis was further performed. When erythritol was introduced into the electrolyte, ν(SO4 2- ) band frequency decreases, and the contribution of CIP decreases from 81.81% to 52.10% ( Figure 2 f). This is because erythritol and Zn 2+ The strong interaction between them makes it easy for erythritol to insert into CIP and replace the original SO4 2- groups, thereby preventing the formation of Zn4(OH)6SO4·xH2O byproducts. In conclusion, erythritol additives are beneficial to changing the Zn 2+The solvation sheath structure of ZnO2 and the disruption of the hydrogen bond network lead to a balance between “network water” and “free water”, which can synergistically affect the activity of water and ZnO2. 2+ The deposition environment is likely to slow down the growth of Zn dendrites and inhibit the bypass reaction.

[0084] In order to further study the effect of erythritol molecules on ZnSO4 electrolyte, molecular dynamics (MD) simulations were performed to simulate the Zn 2+ A model system consisting of 2400 H2O, 198 ZnSO4 and 8 erythritol molecules was constructed. The model system was firstly geometrically optimized and subjected to five annealing cycles from 300K to 500K. Then a 1ns NPT ensemble was performed at 1atm and 298K. The system temperature and pressure were controlled using a Nose thermostat and a Berendsen barostat. The electrostatic interactions were calculated using the Ewald summation. The van der Waals interaction cutoff radius is Finally, a 10 ns NVT combination was performed and the Zn 2+ Coordination. ). The statistical results show that typical hydrated ion solvation structures are detected in both electrolytes, such as Figure 3 a and Figure 3 By analyzing the radial distribution functions (RDFs), two key parameters describing the geometric arrangement of solvent molecules, namely the coordination number and the average bond length, can be obtained. Figure 3 c shows that in pure ZnSO4 electrolyte, Zn 2+ The coordination number of -H2O coordination is 5.4, corresponding to about In ZnSO4+erythritol electrolyte, Zn 2+ The corresponding coordination number with H2O is reduced to 5.2. 2+ The coordination number with erythritol is 0.05, and the Zn-O peak is near In addition, Zn 2+ With SO4 2- The coordination number of the oxygen atom in ZnSO4 is about 0.78, and this value drops to 0.74 after the introduction of erythritol molecules. 2+ The solvation structures of Zn 2+ -(H2O) 5.4 ·(SO4 2- ) 0.78 and Zn 2+ -(H2O) 5.2 ·(Erythritol) 0.05 ·(SO4 2- ) 0.74These findings are consistent with the above view that when erythritol additives are added to the electrolyte, Zn 2+ Some H2O molecules and SO4 in the solvation sheath structure 2- Replaced by erythritol molecules.

[0085] In order to study the reconstructed Zn 2+ The chemical properties of the solvated sheath structures were investigated using density functional theory (DFT) calculations to obtain their electrostatic potentials and HOMO-LUMO band gaps. In ZnSO4 and ZnSO4+erythritol electrolytes, the stoichiometric ratios are simplified to [Zn(H2O)6] 2+ and [Zn(H2O)5-erythritol] 2+ . Figure 3 d shows that the formed [Zn(H2O)5-erythritol] 2+ The electrostatic potential of Zn is lower, which means that 2+ The surrounding electrostatic repulsion is weakened, and Zn 2+ The diffusion of

[0086] [Zn(H2O)5-erythritol] 2+ The HOMO-LUMO band gap difference decreases, and the HOMO energy level moves upward ( Figure 3 e), which proves that [Zn(H2O)5-erythritol] 2+ It makes the charge transfer on the electrode surface easier and promotes the Zn 2+ Deposition / stripping.

[0087] 2. Electrode-electrolyte interface properties of zinc anode

[0088] Since different solvation structures directly affect the interfacial behavior of electrodes, the interfacial experimental study aims to obtain some new observations. First, the wettability of the electrolyte on Zn foil was evaluated by contact angle measurement. The results show that the contact angle of ZnSO4+erythritol electrolyte on Zn foil (98.17°) is smaller than that of ZnSO4 electrolyte (100.75°), which means that the introduction of erythritol molecules effectively reduces the free energy of the interfacial reaction and achieves Zn 2+ Secondly, the Zn foil was immersed in different electrolytes for 20 days to study the intrinsic stability between the Zn electrode surface and the electrolyte. The results showed that the Zn anode immersed in ZnSO4+erythritol electrolyte presented a relatively dense, smooth surface with tiny protrusions. In contrast, sharp and messy protrusions were observed on the surface of the Zn anode using ZnSO4 electrolyte, which indicates that due to the Zn 2+The Zn electrode is extremely unstable in this electrolyte due to the non-directional deposition and tip effect. The erythritol molecules in the electrolyte can reduce the generation of alkaline zinc sulfate byproducts on the surface of the Zn negative electrode. For Zn foil in ZnSO4+erythritol electrolyte, the (002) crystal plane and the (101) crystal plane (I 002 / 101 ) and (100) planes (I 002 / 100 ) are 2.32 and 0.49, respectively, exceeding the values ​​in ZnSO4 electrolyte ((I 002 / 101 =1.75,I 002 / 100 =0.38). This indicates that the erythritol additive is beneficial to the growth of the (002) crystal plane, forming a dense and smooth layer and inhibiting the crazy growth of dendrites, thereby improving the stability of the Zn negative electrode.

[0089] In order to reveal the effect of erythritol molecules on the electrode interface, DFT calculations were used again to compare the adsorption energies of erythritol, H2O, and Zn on the Zn(002) crystal plane (calculation details: the adsorption energies between Zn(002) and different substances were constructed). Supercell. Set along the Z direction The vacuum layer is used to eliminate the influence of periodic Zn atoms. During the structural relaxation process, the top two layers of Zn atoms are allowed to relax, while the bottom Zn atoms are fixed. The adsorption energy (E) of substance A on the Zn (002) crystal plane is adsorption ) is calculated by the following formula:

[0090] E adsorption =E A-Zn -E A -E Zn ;

[0091] Among them, E Zn is the energy of the Zn(002) crystal plane, E A-Zn is the total energy of the Zn(002) crystal surface after adsorption of substances, and EA is the energy of the adsorbed substances. These substances include Zn atoms, H2O molecules, and erythritol molecules). Figure 4 As shown in a, the adsorption energies of H2O and Zn are -0.45eV and -0.52eV, respectively, which are both smaller than the adsorption energy between erythritol molecules and Zn (002) (E vertical =-1.12eV, when placed horizontally horizontal =-1.30 eV), regardless of whether the erythritol molecules are placed vertically or horizontally. In other words, the erythritol molecules are preferentially adsorbed on the Zn electrode surface to guide the Zn deposition process. In order to reveal the electron flow and density distribution between the Zn electrode interface and H2O or erythritol, the charge density difference is further fitted, such as Figure 4As shown in b. The overlapping electron clouds imply the trend of electron transfer, which indicates the existence of chemical adsorption between the molecule and the Zn atom. In the erythritol (horizontally placed)-Zn (002) model, the area of ​​the overlapping electron cloud between erythritol and the Zn atom is larger than that in the H2O-Zn (002) model and the erythritol (vertically placed)-Zn (002) model. These results confirm that the erythritol molecule can be preferentially and strongly adsorbed on the Zn electrode surface, regulating the environment of the Zn deposition process through the newly formed, water-reduced double electrical layer (EDL). Figure 4 c shows the Nyquist plots of Zn||Zn batteries using ZnSO4 and ZnSO4+erythritol electrolytes, respectively. The charge transfer resistance of the Zn||Zn battery using ZnSO4+erythritol electrolyte is smaller than that using ZnSO4 electrolyte, which is attributed to the adsorption of erythritol molecules on the electrode surface accelerating the Zn 2+ The adsorption behavior of erythritol molecules on the EDL surface was detected by differential capacitance (DC) measurement. Figure 4 d shows that the capacitance value decreases after adding erythritol molecules to the sodium sulfate electrolyte, which indicates that the erythritol molecules participate in the EDL structure on the Zn electrode surface, which is consistent with the conclusion of theoretical calculation.

[0092] In aqueous electrolytes, hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and corrosion problems on the electrode surface are inevitable. These problems may be improved given the altered EDL interface of the electrode. Therefore, linear sweep voltammetry (LSV) was used to evaluate the HER and OER of Na2SO4 and Na2SO4+erythritol electrolytes. Figure 4 As shown in Figure e, the HER and OER overpotentials in the Na2SO4+erythritol electrolyte are larger, indicating that the erythritol additive can effectively inhibit the decomposition of water to produce hydrogen and oxygen. In addition, the inhibition of HER and OER is also attributed to the changes in the solvation structure and hydrogen bond network by the erythritol molecule, because the mobility of free water is reduced and [Zn(H2O)5-erythritol] 2+ The formation of an electrostatic protective layer isolates free water. Based on these changes, it is speculated that the corrosion problem of the electrode may also be alleviated. The corrosion problem of the Zn electrode in ZnSO4 and ZnSO4+erythritol electrolytes was evaluated by measuring the linear polarization curves ( Figure 4 f). The results show that the corrosion current of Zn foil in ZnSO4+erythritol electrolyte (0.162 mA cm -2 ) is significantly smaller than the corrosion current in ZnSO4 electrolyte (0.219 mA cm -2 ), which proves that the corrosion rate is reduced, which is consistent with the inferred results.

[0093] Therefore, the role of erythritol molecules can be summarized into three aspects: regulating the interaction between "network water" and "free water" by weakening hydrogen bonds, reconstructing Zn 2+ The solvation structure of Zn 2+ diffusion environment, and adsorbed on the zinc surface to form a protective layer to prevent hydrogen evolution reaction and zinc corrosion caused by free water, such as Figure 5 As shown in a. 2+ The deposition behavior of Zn depends on the deposition kinetics, and 2+ The first deposition of Zn is crucial to the stability of subsequent cycles. A Ti||Zn asymmetric battery was assembled and the initial nucleation process of the Ti||Zn battery was studied by cyclic voltammetry (CV). Figure 5 As shown in b, the nucleation overpotential (NOP) in ZnSO4+erythritol electrolyte is slightly higher than that in ZnSO4 electrolyte. The higher the nucleation overpotential, the smaller the nucleus, which is beneficial to alleviate the local aggregation of zinc ions and make them deposited uniformly. Therefore, it is more likely that fine particles will be deposited uniformly in ZnSO4+erythritol electrolyte. In addition to CV, chronoamperometry (CA) measurement is also a good way to explore the changes in electrochemically active surfaces and understand the Zn 2+ The Zn||Zn symmetric cells using ZnSO4 and ZnSO4+erythritol electrolytes were prepared and tested, such as Figure 5 As shown in Figure 3, when an overpotential of -150 mV is applied to the Zn||Zn battery using ZnSO4+erythritol electrolyte, the current increases rapidly within the first 50 s. This period is associated with a rapid and intensive growth of the effective electrode area, indicating the presence of an initial zinc nucleation process. Thereafter, the current density is maintained at 5 mA cm -2 , which indicates that Zn 2+ The nucleation behavior of Zn is transformed from two-dimensional (2D) to three-dimensional (3D) diffusion, which is beneficial to the 2+ In contrast, for Zn||Zn batteries using ZnSO4 electrolyte, due to the 2+ The two-dimensional diffusion on the surface of the zinc anode intensifies the continuous increase in flow density, resulting in uneven electric field distribution on the surface of the zinc anode, which inevitably triggers dendrite growth.

[0094] Next, to evaluate the Zn 2+ Reversible cycling stability during the deposition / stripping process. Zn||Zn symmetric cells using ZnSO4 and ZnSO4+erythritol electrolytes were prepared and tested at different current densities. Figure 5 d. Figure 5 e recorded the Zn||Zn battery using ZnSO4 and ZnSO4+erythritol electrolyte at a current density of 0.5 mA cm -2、1.0mAcm -2 and 4.0mAcm -2 The potential-time curve of the Zn||Zn battery using ZnSO4+erythritol electrolyte can run more than 1000 hours longer than the battery using ZnSO4 electrolyte. In addition, the Zn||Zn battery using ZnSO4+erythritol electrolyte has a higher current density of 10.0mAcm -2 、20.0mAcm -2 and 30.0mAcm -2 In contrast, the Zn||Zn battery using ZnSO4 electrolyte failed within 50 hours of cycling. Figure 5 d- Figure 5 In e, the Zn||Zn battery using ZnSO4 electrolyte exhibits obvious polarization behavior at around 200 h, which is mainly attributed to the Zn 2+ The irreversible redox reaction of Zn leads to uneven deposition / stripping and related side reactions. Nevertheless, the life of Zn||Zn battery using ZnSO4+erythritol electrolyte exceeds 1300 h, which indicates that erythritol additive can effectively enhance the Zn 2+ uniform deposition / stripping, thereby improving the stability of the zinc anode.

[0095] In order to evaluate Zn 2+ The deposition / stripping behavior of Ti||Zn asymmetric cells was assembled for Coulombic efficiency (CE) test. The CE value η is determined by the formula η=td / tc, where td and tc represent the duration (s) of electroplating and stripping, respectively. -2 、2.0mAcm -2 and 4.0mAcm -2 CE tests were performed at a current density of . As can be seen from 6a, the CE values ​​of the Ti||Zn batteries using ZnSO4 electrolyte are unstable, and these batteries fail within 100 cycles. The CE values ​​of the Ti||Zn batteries using ZnSO4+erythritol electrolyte are stable and as high as nearly 99%, and these batteries can be cycled for more than 500 times. In addition, Figure 6 The potential-capacity curves in b show that the Ti||Zn battery using ZnSO4+erythritol electrolyte exhibits stable capacity and lower polarization potential during repeated cycling compared with the battery using ZnSO4 electrolyte. These findings suggest that erythritol molecular additives can promote the Zn 2+ deposition / stripping, thus helping to prolong the stability of the zinc anode.

[0096] Generally, it is necessary to optimize the growth of the (002) crystal plane to obtain a dense and smooth zinc deposit layer, thereby inhibiting the crazy growth of dendrites and stabilizing the zinc anode. 2+ The effect of directional deposition was investigated by XRD analysis of the surface crystal structure of the zinc anode after cycling for 100 h in ZnSO4 electrolyte and ZnSO4 + erythritol electrolyte. Figure 6 c). In ZnSO4+erythritol electrolyte, the intensity ratio of (002) crystal plane to (101) crystal plane (I 002 / 101 ) is 0.68, which is almost twice the intensity ratio (0.36) in ZnSO4 electrolyte. This indicates that the erythritol additive is conducive to the preferential growth of Zn(002) crystal plane. In addition, the evolution of the surface morphology of the zinc anode cycled in ZnSO4 electrolyte and ZnSO4+erythritol electrolyte for 100 hours was studied by scanning electron microscopy. The surface of the zinc anode cycled in ZnSO4 electrolyte showed a fluffy, disordered stacking ( Figure 6 d), while the surface of the zinc anode cycled in ZnSO4+erythritol electrolyte is compact, flat, and uniformly stacked ( Figure 6 e). In addition, in situ optical microscopy was used to monitor the -2 The zinc deposition behavior under Figure 6 As shown in f, due to Zn 2+ The random deposition of Zn in ZnSO4 electrolyte rapidly led to the emergence of Zn dendrites on the surface of Zn foil, especially at the tip. 2+ The deposited surface is basically smooth, with almost no visible protrusions ( Figure 6 g), which is due to the change of the electrode-electrolyte interface. This may be related to the formation of the electrostatic protective layer [Zn(H2O)5-erythritol] 2+ This layer can make the electric field on the surface of the zinc anode uniform, promote the uniform deposition of zinc ions, thereby greatly inhibiting the formation of zinc dendrites and providing long-term stability of the zinc anode.

[0097] In summary, an environmentally friendly erythritol additive with multiple hydroxyl groups was added to the ZnSO4 electrolyte, and the erythritol molecules could enter the solvation layer of hydrated zinc ions and replace some water molecules. At the same time, density functional theory (DFT) calculations showed that erythritol molecules could destroy the original hydrogen bond network structure of the ZnSO4 solution. These results indicate that the erythritol additive caused changes in "network water" and "free water", which may change the properties of the ZnSO4 electrolyte. In addition, DFT calculations also revealed that erythritol molecules can be preferentially adsorbed on the surface of the zinc electrode, thereby changing the deposition environment of Zn ions and inhibiting the growth of dendrites. Spectral experiments confirmed the reconstruction of hydrated zinc ions and hydrogen bond network structures after the addition of erythritol molecules. The results of electrochemical experiments showed that the side reactions at the zinc anode were reduced and the protrusion of dendrites was alleviated. Charge and discharge experiments further demonstrated that Ti||Zn batteries and Zn||Zn batteries using ZnSO4+erythritol electrolytes had significantly higher Coulombic efficiency values ​​and longer life than batteries using pure ZnSO4 electrolytes. Moreover, the Zn-I2 full battery using ZnSO4+erythritol electrolyte also has better stability than the battery using ZnSO4.

[0098] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An aqueous zinc-iodine battery, characterized in that: include: It includes an iodine positive electrode, a zinc negative electrode, a separator and an electrolyte solution; The electrolyte solution includes zinc sulfate solution and erythritol.

2. The aqueous zinc-iodine battery according to claim 1, characterized in that: The concentration of erythritol is 0.1-0.3M.

3. The aqueous zinc-iodine battery according to claim 2, characterized in that: The concentration of erythritol was 0.2M.

4. The aqueous zinc-iodine battery according to claim 1, characterized in that: The concentration of the zinc sulfate solution is 2M.

5. The aqueous zinc-iodine battery according to claim 1, characterized in that: The iodine positive electrode is obtained by coating positive electrode slurry on carbon paper and drying it; the positive electrode slurry comprises active materials, conductive agents and adhesives; the active materials comprise iodine monomers and activated carbon.

6. The aqueous zinc-iodine battery according to claim 5, characterized in that: The conductive agent is acetylene black.

7. The aqueous zinc-iodine battery according to claim 5, characterized in that: The adhesive is PVDF.

8. The aqueous zinc-iodine battery according to claim 5, characterized in that: The weight ratio of the active material, the conductive agent and the binder is 8:1:

1.

9. The aqueous zinc-iodine battery according to claim 5, characterized in that: The weight ratio of iodine monomer to activated carbon is 3:

7.

10. The aqueous zinc-iodine battery according to claim 5, characterized in that: The diaphragm is fiberglass.

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