Aqueous electrolyte for zinc secondary battery and zinc secondary battery comprising same

Abstract

An embodiment of the present invention provides an aqueous electrolyte for a zinc secondary battery, comprising: a metal salt comprising zinc; water; and a glycol-based co-solvent, wherein the glycol-based co-solvent is included in an amount of 5 to 150 parts by weight based on 100 parts by weight of the water.

Description

Aqueous electrolyte for zinc secondary batteries and zinc secondary batteries containing the same

[0001] The present invention relates to an aqueous electrolyte for a zinc secondary battery and a zinc secondary battery comprising the same, and more particularly, to a zinc secondary battery utilizing the electrolyte for a zinc secondary battery that suppresses hydrogen generation reaction on the surface of an anode by including an appropriate co-solvent and further significantly improves life characteristics.

[0002]

[0003] Aqueous zinc-ion batteries (AZIBs) have a structure that uses Zn metal as the negative electrode and water as the electrolyte solvent. However, there is a problem that corrosion and hydrogen evolution reaction (HER) occur when Zn metal and water come into direct contact. In particular, H in the electrolyte during the charge and discharge process + As ions increase, HER is promoted, generating hydrogen gas. This increases internal cell pressure and can lead to a shortened battery life and reduced safety in the long term. Therefore, electrolyte composition and protection strategies are essential to address these issues.

[0004] As a strategy to solve this problem, one can consider a method to disrupt and weaken the strong hydrogen bonding network in the existing electrolyte. In particular, introducing a specific cosolvent can control the electrolyte environment, thereby reducing the direct reactivity between Zn metal and water, and H + It can be expected that the effect of suppressing the occurrence of Zn in the electrolyte 2+ It can effectively suppress corrosion and HER of Zn metal by changing the solvation structure and reducing the number and activity of free water molecules. In addition, it can be applied by a simple mixing method, so the manufacturing process is simple and it has the advantage of improving the properties of the electrolyte without additional complex synthesis processes.

[0005] However, due to the nature of the cosolvent, an increase in its concentration can affect the physical and chemical properties of the electrolyte, especially the ionic conductivity. Therefore, it is important to establish optimal conditions that consider the balance between the HER inhibition effect and the conductivity of the electrolyte. When a cosolvent with an appropriate composition is applied, a protective layer is formed on the electrode surface during the charge and discharge process, alleviating local current concentration and providing a more uniform Zn 2+ Reversible deposition / desorption of zinc can be induced. This effect can contribute to suppressing dendrite formation, reducing the risk of battery short-circuiting, and improving long-term stability. This enables the design of a co-solvent-based electrolyte that is easy to manufacture while improving the performance of aqueous zinc-ion batteries, and has a high possibility of leading to the development of practical batteries with long-life characteristics, leading to the present invention.

[0006]

[0007] The present invention has been devised to solve the above-mentioned problem, and one embodiment of the present invention provides an electrolyte for a zinc secondary battery.

[0008] In addition, another embodiment of the present invention provides a zinc secondary battery including the electrolyte for the zinc secondary battery.

[0009] The technical problems to be solved by the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present invention belongs from the description below.

[0010]

[0011] As a technical means for achieving the aforementioned technical task, one aspect of the present invention is,

[0012] A zinc secondary battery aqueous electrolyte is provided, comprising a metal salt containing zinc; water; and a glycol solvent, characterized in that the glycol solvent is included in an amount of 5 to 150 parts by weight per 100 parts by weight of the water.

[0013] The above glycol cosolvents are ethylene glycol, propylene glycol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, dimethylene glycol, diethylene glycol (DEG), triethylene glycol (TEG), tetraethylene glycol (TetraEG), methyl glycol (Methyl Glycol, 2-Methoxyethanol), ethyl glycol (Ethyl Glycol, 2-Ethoxyethanol), and butyl glycol. (Butyl Glycol, 2-Butoxyethanol) may be at least one selected from the group consisting of.

[0014] The above metal salt may include at least one selected from the group consisting of zinc sulfate (ZnSO₄), zinc trifluoromethanesulfonate (Zn(OTf)₂), zinc nitrate (Zn(NO₃)₂), zinc chloride (ZnCl₂), zinc acetate (Zn(CH₃COO)₂), zinc perchlorate (Zn(ClO₄)₂), zinc bromide (ZnBr₂), zinc fluorophosphate (ZnF₂), zinc tetrafluoroborate (Zn(BF₄)₂), zinc hexafluorophosphate (Zn(PF6)₂), zinc methanesulfonate (Zn(CH₃SO₃)₂), zinc triflate (Zn(TFSI)₂), and zinc citrate (Zn₃(C6H5O7)₂).

[0015] The above glycol solvent may be propylene glycol, and the metal salt may be zinc trifluoromethanesulfonate (Zn(OTf)₂).

[0016] The above aqueous electrolyte may have a molar concentration of the metal salt of 1 to 5 M.

[0017] The viscosity of the above aqueous electrolyte may be 7 to 240 cP.

[0018] After the above charge / discharge process, when X-ray diffraction analysis was performed on the zinc metal surface, the ratio of peak intensities for the (002), (101), and (102) planes was I (002) / I (101) This 0.4 to 1.5, I (002) / I (102) This may satisfy 1.95 to 3.0.

[0019]

[0020] Another aspect of the present invention is:

[0021] A zinc secondary battery is provided, comprising: a positive electrode; a negative electrode; and the aqueous electrolyte.

[0022] The above positive electrode may include a positive electrode active material, a conductive material, and a binder.

[0023] The above cathode active material may be one selected from the group consisting of manganese dioxide (MnO₂), vanadium trioxide (V₂O₃), vanadium pentoxide (V₂O5), vanadium dioxide (VO₂), and molybdenum trioxide (MoO₃).

[0024] The above cathode active material may have a composite structure on a layered material including at least MXene.

[0025] The above negative electrode may include zinc as a negative electrode active material.

[0026] The above zinc ion secondary battery may further include a separator.

[0027] The above separation membrane may include at least one selected from the group consisting of filter paper, glass fiber, hydrophilic polymer, and polymer-inorganic oxide hybrid materials.

[0028] The above electrolyte may be such that the absolute value of the bond energy formed between zinc ions and water molecules is less than 2.0 eV.

[0029] During charging / discharging of the above zinc secondary battery, the coordination number of water molecules coordinated to the zinc ion with the highest frequency may be 4.

[0030]

[0031] According to an embodiment of the present invention, by controlling the electrolyte environment of aqueous zinc-ion batteries (AZIBs) using a cosolvent, corrosion of Zn metal and hydrogen evolution reaction (HER) can be effectively suppressed. This allows excessive H generated during the charge and discharge process to be effectively suppressed. + It can prevent the increase of internal pressure and solve the problem of battery performance deterioration due to hydrogen gas. In addition, by introducing a co-solvent, Zn 2+ The solvation structure of Zn is adjusted, reducing the activity of free water molecules and creating a more stable electrode environment. This reduces unnecessary reactions between Zn metal and electrolyte, which can improve long-term electrode life and battery safety.

[0032] Furthermore, according to one embodiment of the present invention, the co-solvent-based electrolyte can be manufactured through a simple mixing process, making it easily applicable without a separate, complex synthesis process. Accordingly, stable performance can be maintained under various current densities and charge / discharge conditions, and dendrite formation can be suppressed, thereby reducing the risk of battery short-circuiting. Through these effects, the present invention can contribute to the development of high-performance, long-life AZIBs and provide a practical, commercially viable electrolyte technology.

[0033] The effects of the present invention are not limited to the above-described effects, and should be understood to include all effects that can be inferred from the composition of the invention described in the description or claims of the present invention.

[0034]

[0035] Figure 1 shows an electrical surface potential (ESP) map of a PG (Propylene Glycol) molecule.

[0036] Figure 2 shows the dielectric constant (left axis, green bar) and dipole moment (right axis, purple bar) of various solvents, such as methanol (MeOH), ethylene glycol (EG), polyethylene glycol (PEG 200), and PG.

[0037] Figure 3 is a photograph of the appearance of electrolyte samples manufactured by increasing the PG content from 0% to 90% in 10% increments according to one embodiment of the present invention.

[0038] Figure 4 shows the FT-IR spectra of PG 00, PG 30, PG 50, and PG 80 samples in the electrolyte according to one embodiment of the present invention, at 1400 to 1800 cm -1 It shows the section.

[0039] Figure 5 shows the electrolyte according to one embodiment of the present invention, 2600 to 3800 cm of the same samples. -1 It shows the interval FT-IR spectrum.

[0040] Figure 6 is a bar graph showing the relative absorption intensities of strong hydrogen bonds (Strong HBs) and weak hydrogen bonds (Weak HBs) according to PG concentration in an electrolyte according to one embodiment of the present invention.

[0041] Figures 7(a) to 7(d) show FT-IR spectra of 2600 to 3800 cm for each of PG 00, PG 30, PG 50, and PG 80 samples in the electrolyte according to one embodiment of the present invention. -1This shows the results of fitting the interval by dividing it into four Gaussian components (G1, G2, G3, G4).

[0042] Figure 8 shows the viscosity (red graph) and ionic conductivity (blue graph) of PG 00, PG 30, PG 50, and PG 80 samples in an electrolyte according to one embodiment of the present invention.

[0043] Figure 9 shows an electrolyte according to one embodiment of the present invention, with a current density of 0.5 mA cm -2 and capacity 2.0 mAh cm -2 Coulomb efficiency is shown along with the charge / discharge curve under the conditions.

[0044] Figure 10 shows an electrolyte according to an embodiment of the present invention, with a current density of 2.0 mA cm -2 Same capacity (2.0 mAh cm) under increased conditions -2 ) is presented as a result of charging / discharging.

[0045] Figure 11 shows the Zn in the electrolyte according to one embodiment of the present invention through DFT simulation. 2+ It shows the process of ions sequentially coordinating with water molecules.

[0046] Figure 12 shows the Zn calculated through DFT calculation in an electrolyte according to an embodiment of the present invention. 2+ - This is a graph comparing H2O binding energies.

[0047] Figures 13 and 14 are AIMD simulation results for the electrolyte according to one embodiment of the present invention, Zn 2+ It shows the distribution of the number of water molecules distributed around it.

[0048] Figure 15 shows LSV curves for observing hydrogen evolution (HER) and oxygen evolution (OER) potentials in PG 00 and PG 30 electrolytes according to one embodiment of the present invention.

[0049] Figure 16 is a comparison of Tafel plots for confirming corrosion potential on the Zn surface in an electrolyte according to an embodiment of the present invention.

[0050] Figure 17 shows the results of measuring by-products formed on the surface of a Zn metal foil immersed in an electrolyte for 5 days according to an embodiment of the present invention using XRD.

[0051] Figure 18 shows an electrolyte according to an embodiment of the present invention, with a current density of 1.0 mA cm -2 , capacity 1.0 mAh cm -2 Graph showing the Zn nucleation overpotential (NOP) over time under conditions.

[0052] Figure 19 shows the reciprocal of the reverse charge transfer resistance (1 / R) obtained using the Arrhenius equation in an electrolyte according to an embodiment of the present invention. ct ) and the reciprocal of temperature (1 / T) are shown in a graph.

[0053] FIG. 20 and FIG. 21 show the surface energy of each Zn crystal plane (002, 100, 101) under W / PG (FIG. 20, blue graph) and W / O PG (FIG. 21, red graph) conditions in an electrolyte according to one embodiment of the present invention.

[0054] Figure 22 shows an electrolyte according to an embodiment of the present invention, with a current density of 7 mA cm -2 , area capacity 7 mAh cm -2 This is the result of measuring the crystal plane peak of the Zn deposition layer in PG 00 and PG 30 electrolytes by XRD after performing 3 cycles of charge / discharge under the conditions.

[0055] Figure 23 shows the results of observing the Zn deposition process using an in situ optical microscope using PG 00 (left) and PG 30 (right) samples in an electrolyte according to one embodiment of the present invention (top) and the results of observing the surface using SEM after 60 minutes (bottom).

[0056] Figure 24 shows the results of measuring the XPS spectrum (C 1s, F 1s, S 2p, O 1s) of a PG 30 sample according to a sputtering time (0 s, 90 s, 180 s) in an electrolyte according to an embodiment of the present invention.

[0057] Figure 25 shows the results of measuring a PG 00 sample using XPS under the same conditions in an electrolyte according to an embodiment of the present invention.

[0058] Figure 26 shows the TOF-SIMS 3D distribution of a PG 30 sample in an electrolyte according to one embodiment of the present invention.

[0059] Figure 27 shows the results of TOF-SIMS measurement performed on a PG 00 sample in an electrolyte according to an embodiment of the present invention.

[0060] FIG. 28 and FIG. 29 show the results of measuring the coulombic efficiency while charging / discharging a ZnCu asymmetric cell in PG 00 (red curve) and PG 30 (blue curve) electrolytes according to one embodiment of the present invention.

[0061] Figures 30 and 31 show the electrolyte according to one embodiment of the present invention, 0.5 mA cm in a ZnZn symmetric cell. -2 , 0.5 mAh cm -2 (Fig. 30) and 2.0 mA cm -2 , 2.0 mAh cm -2 This is the result of a long-term (hundreds to thousands of hours) reversible deposition / deposition test of Zn² conducted by applying the conditions of (Fig. 31).

[0062] Figure 32 shows an electrolyte according to an embodiment of the present invention, which comprises a ZnZn symmetrical cell and has an areal capacity of 1 mAh cm. -2 In the fixed state, the current density is 0.5 →1 → 2 → 5 → 7 → 10 → 20 → 30 mA cm -2 After sequentially increasing to the initial current density of 0.5 mA cm -2The long-term stability of the cell was evaluated by returning it to the original state.

[0063] Figure 33 shows an electrolyte according to an embodiment of the present invention, after applying a deep discharge rate (80% DOD) to a Zn∥Zn symmetric cell, 1.0 mA cm -2 4.68 mAh cm -2 This is a graph that observes the change in voltage while exchanging capacity.

[0064] Figure 34 shows the current density stepwise (0.1 → 0.5 → 1 → 2 → 4 → 6 → 8 → 10 → 15 A g) for each of the PG 00 (red) and PG 30 (blue) electrolytes in a full cell using VO₂@V-MXene (9:1) as a cathode material according to one embodiment of the present invention. -1 ) shows the discharge capacity measured by increasing the voltage.

[0065] Figure 35 shows an electrolyte according to an embodiment of the present invention, with a current density of 1 A g. -1 This is the result of operating a full cell using VO₂@V-MXene (9:1) as a cathode material for approximately 2,000 cycles under these conditions.

[0066] Figure 36 shows an electrolyte according to an embodiment of the present invention, which has a higher current density (5 A g -1 ) is the result of driving a full cell using VO₂@V-MXene (9:1) cathode material for approximately 3,600 cycles.

[0067] Figure 37 shows an electrolyte according to an embodiment of the present invention, with a current density of 10 A g. -1 This is the result of performing repeated charge / discharge cycles of approximately 5,000 or more under extreme conditions.

[0068]

[0069] Hereinafter, the present invention will be described in more detail. However, the present invention may be implemented in various different forms, and the present invention is not limited to the embodiments described herein, but is defined only by the claims set forth below.

[0070] Additionally, the terminology used herein is solely for the purpose of describing specific embodiments and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. Throughout the specification of the present invention, the term "including" or "comprising" a component does not exclude other components, but rather implies the inclusion of other components, unless specifically stated otherwise.

[0071] Throughout the specification, when a part is said to be "connected (connected, contacted, joined)" to another part, this includes not only cases where the two parts are "directly connected," but also cases where the two parts are "indirectly connected" with other elements in between. Furthermore, when a part is said to "include" a component, this does not mean that the other components are excluded, but rather that the other components may be included, unless otherwise specifically stated.

[0072] As used herein, “%” may mean “weight%” or “wt%” in terms of content, unless otherwise specified.

[0073] The terminology used in this specification is for the purpose of describing specific embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0074]

[0075] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0076]

[0077] Structural characteristics of PG molecules and their interaction with Zn2+

[0078] Figure 1 shows the electric surface potential (ESP) map of a PG (Propylene Glycol) molecule. The red area in this figure corresponds to oxygen atoms, which have high electronegativity and are more electronegative than Zn 2+ It shows that the oxygen atoms in the PG molecule can form strong interactions with Zn ions. 2+ It suggests that it can replace water molecules in the solvation structure and simultaneously reduce the amount of free water molecules.

[0079] Also, this phenomenon is due to the presence of oxygen atoms in Zn 2+ Within the solvation structure, it can be inferred that existing water molecules can be easily desolvated. This suggests that PG acts as an effective cosolvent to improve electrochemical properties compared to water alone, as confirmed by the following experiments.

[0080] Figure 2 shows the dielectric constant (left axis, green bars) and dipole moment (right axis, purple bars) of various solvents, including methanol (MeOH), ethylene glycol (EG), polyethylene glycol (PEG 200), and PG. PG has a high dielectric constant and dipole moment compared to other alcohol-based (-OH group) organic solvents, and these characteristics are attributed to Zn 2+ can play an important role in controlling the behavior of PG. The high dielectric constant of Zn 2+ It can contribute to promoting the dissociation of Zn salts and improving ion mobility by weakening the electrostatic attraction between Zn and anions. In addition, the high dipole moment of PG can contribute to improving the ion mobility of Zn 2+ This suggests that the formation of strong coordination bonds with Zn² increases the likelihood of replacing some water molecules in the existing solvation structure. This change may contribute to promoting the dissociation of Zn² and anions and improving electrochemical stability in the electrolyte by adjusting the solvation structure.

[0081]

[0082] Example 1: Preparation of electrolytes with different PG contents and optical observation

[0083] Figure 3 is a photograph of the appearance of electrolyte samples manufactured by increasing the PG content from 0% to 90% in 10% increments according to one embodiment of the present invention. First, the PG 00 sample was manufactured by dissolving 2 M Zn(OTf)2 using only water (H2O) as the sole solvent, and the PG 30 sample was manufactured by simply stirring water and PG in a 7:3 weight ratio (wt.%) to make a co-solvent, and then adding the same concentration of Zn(OTf)2 salt.

[0084] While no precipitate was formed up to 80% PG content, as the content increased above 80%, precipitate began to form in the sample. In particular, it was confirmed that precipitate was clearly formed in the PG 90 sample, which resulted in a decrease in solubility. These results showed that adding too much PG did not sufficiently dissolve Zn(OTf)2, and it was confirmed that it is desirable to select around PG 80 as the maximum concentration for actual process application.

[0085]

[0086] Example 2: Analysis of FT-IR spectra (1400 to 1800 cm-1, 2600 to 3800 cm-1)

[0087] Figure 4 shows the FT-IR spectra of PG 00, PG 30, PG 50, and PG 80 samples in the electrolyte according to one embodiment of the present invention, at 1400 to 1800 cm -1 This section shows the spectrum. In this spectrum, it was confirmed that the peak positions of the CH bending vibration (β) and the OH bending vibration (β) varied depending on the PG content. As the PG concentration increased, the CH bending vibration peak tended to shift to a lower waveband, which is interpreted as a result of the PG molecules causing changes in the existing hydrogen bonding network through their interaction with water molecules.

[0088] Figure 5 shows the electrolyte according to one embodiment of the present invention, 2600 to 3800 cm of the same samples. -1 The FT-IR spectrum is shown. Looking at the peak positions of ν and ν, as the PG concentration increases, ν shifts to a lower wavenumber and ν(OH) shifts to a higher wavenumber. This indicates that PG is Zn 2+ Zn forms a new coordination within the solvation structure 2+ - This means that the H2O interaction is weakened, and as a result, the strong hydrogen bonds between water molecules are gradually broken down.

[0089]

[0090] Example 3: Interpreting FT-IR Peak Decomposition (Gaussian Fit) Results

[0091] Figure 6 is a bar graph showing the relative absorption intensities of strong hydrogen bonds (Strong HBs) and weak hydrogen bonds (Weak HBs) at different PG concentrations in an electrolyte according to one embodiment of the present disclosure. As the PG content increases, the relative proportion of strong hydrogen bonds decreases, while the proportion of weak hydrogen bonds increases. This suggests that PG disrupts the bonding network of water molecules, favoring bonding states with relatively low energy over strong bonds between H2O molecules. Specific data are as follows.

[0092]

[0093] In addition to the above data, FIGS. 7(a) to 7(d) show FT-IR spectra of 2600 to 3800 cm for each of PG 00, PG 30, PG 50, and PG 80 samples in the electrolyte according to one embodiment of the present invention. -1This shows the fitting results by dividing the interval into four Gaussian components (G1, G2, G3, and G4). G1 and G2 mainly correspond to strong hydrogen bonding regions, and G3 and G4 correspond to weak hydrogen bonding regions. In fact, it is quantitatively confirmed that the overall number of hydrogen bonds tends to decrease as the PG content increases, and the proportion of strong hydrogen bonds (G1 + G2) decreases from 59.2% to 36.8%, while the proportion of weak hydrogen bonds (G3 + G4) increases from 40.8% to 63.2%.

[0094]

[0095] Example 4: Measurement of viscosity and ionic conductivity

[0096] Fig. 8 shows the viscosity (red graph) and ionic conductivity (blue graph) of PG 00, PG 30, PG 50, and PG 80 samples in the electrolyte according to one embodiment of the present invention. As can be seen in the graph, as the PG concentration increases, the viscosity increases rapidly, while the ionic conductivity tends to decrease. Specifically, the viscosity of PG 00, which does not contain PG, was 6.0 cP, the viscosity of PG 10, which contains the least PG, was 7.4 cP, and the viscosity of 80, which contains the most PG, was 218.5 cP. This suggests that selecting an appropriate PG content is important because an increase in the viscosity of the electrolyte may inhibit ion mobility, which may negatively affect the electrochemical performance.

[0097]

[0098] Example 5: Charge / discharge characteristics of Zn||Cu asymmetric cell

[0099] Figure 9 shows an electrolyte according to one embodiment of the present invention, with a current density of 0.5 mA cm -2 and capacity 2.0 mAh cm -2The Coulombic efficiency is shown along with the charge / discharge curve under the conditions. As a result of comparing the PG 00, PG 30, PG 50, and PG 80 samples, both PG 30 and PG 50 showed a Coulombic efficiency of about 97.9%. This indicates that the PG content is within the appropriate range of Zn 2+ This suggests that it favors the reversible deposition / deposition of .

[0100] Figure 10 shows an electrolyte according to an embodiment of the present invention, with a current density of 2.0 mA cm -2 Same capacity (2.0 mAh cm) under increased conditions -2 ) are presented. Under these conditions, ionic conductivity becomes a more important factor as the current density increases. In fact, the PG 30 sample showed the most stable charge / discharge characteristics, and its coulombic efficiency was also superior to other concentrations (e.g., PG 30 was 99.4%, PG 00 was 97.5%, PG 80 was 86.8%, etc.). This result shows that the PG 30 concentration, which has a good balance of viscosity and ionic conductivity, exhibits excellent electrochemical performance in various operating environments.

[0101] Consequently, if the PG concentration is excessively high, electrochemical performance deteriorates due to decreased ion mobility caused by increased viscosity. Furthermore, if the PG concentration is excessively low, the electrolyte exhibits characteristics similar to water, making it difficult to control Zn precipitation. Therefore, it was confirmed that PG 30 provides an optimal balance between viscosity and ionic conductivity, enabling excellent performance under various operating conditions.

[0102]

[0103] Example 6: DFT - Simulation of the sequential solvation process of Zn2+

[0104] Figure 11 shows the Zn in the electrolyte according to one embodiment of the present invention through DFT simulation. 2+ It shows the process of sequential coordination bonding of ions with water molecules. In electrolyte without PG (W / O PG), Zn 2+It formed the most stable solvation structure by coordinating with up to six water molecules. On the other hand, in the case of the electrolyte containing PG (W / PG), Zn 2+ The coordination with four water molecules was shown to be the most stable, which means that the remaining positions are replaced by PG molecules to create a new solvation environment.

[0105]

[0106] Example 7: DFT - Binding energy between Zn2+ and water molecules

[0107] Figure 12 shows the Zn calculated through DFT calculation in an electrolyte according to an embodiment of the present invention. 2+ - This is a graph comparing the H2O binding energy. In the electrolyte without PG, the binding energy is approximately -2.54 eV, which is lower than that of Zn. 2+ - It was confirmed that the H2O interaction was maintained strongly. However, in the electrolyte where PG exists, the corresponding binding energy decreased to -1.58 eV, indicating that water molecules and Zn 2+ It can be seen that the interaction between them is relatively weakened. This is interpreted as a result of the overall coordination structure and bond stability changing as PG molecules partially replace water molecules.

[0108]

[0109] Example 8: AIMD - Water molecule coordination number distribution in the Zn2+ solvation structure

[0110] Figures 13 and 14 are AIMD simulation results for the electrolyte according to one embodiment of the present invention, Zn 2+ It shows the distribution of the number of water molecules coordinated around the PG. In the electrolyte without PG (W / O PG), the state of coordinating 6 water molecules was predominant at about 77.3%, but in the electrolyte containing PG (W / PG), Zn 2+ The state of coordinating four water molecules and one PG molecule was found to be predominant at a ratio of about 93.7%. This means that PG replaces some of the existing water molecules to form Zn2+ This reaffirms that changing the solvation environment of ions is a factor that ultimately influences the hydrogen bonding network changes and ion transport characteristics observed in previous experiments.

[0111]

[0112] Example 9: LSV (Liner Sweep Voltammetry) Analysis

[0113] Figure 15 shows LSV curves for observing hydrogen evolution (HER) and oxygen evolution (OER) potentials in PG 00 and PG 30 electrolytes according to one embodiment of the present invention. Current density 0.1 mA cm -2 The hydrogen evolution potential (HER) measured in the vicinity shifted from -0.90 V for PG 00 to -0.99 V for PG 30, confirming the effect of slightly slowing down hydrogen evolution. The oxygen evolution potential (OER) was 0.01 mA cm -2 At the branch point, the voltage increased from 1.67 V for PG 00 to 1.73 V for PG 30, indicating a wider voltage stability of up to 2.72 V (vs. Ag / AgCl). This suggests that, compared to the PG 00 sample, side reactions (hydrogen and oxygen evolution) occurring at the interface were suppressed, improving the overall electrochemical stability.

[0114]

[0115] Example 11: Evaluation of corrosion behavior using Tafel plot

[0116] Figure 16 is a comparison of Tafel plots for confirming the corrosion potential on the Zn surface in the electrolyte according to one embodiment of the present invention. The corrosion potential (E) of the PG 00 sample corr ) is approximately -923.3 mV, and the corrosion current density (I corr ) is 5.02 mA cm -2However, in the PG 30 sample, the corrosion potential slightly increased to -920.8 mV, and the corrosion current density was 2.35 mA cm -2 This result quantitatively supports the fact that PG 30 electrolyte suppresses the corrosion reaction that proceeds on the Zn metal surface.

[0117] In particular, the significant decrease in corrosion current density suggests that Zn metal can exist in a more stable state within the electrolyte. This can be interpreted as having the advantage of improving electrode life by reducing unnecessary byproduct formation on the Zn surface in addition to the HER suppression effect.

[0118]

[0119] Example 12: Confirmation of by-product formation through XRD analysis

[0120] Figure 17 shows the results of measuring byproducts formed on the surface of a Zn metal foil immersed in an electrolyte for 5 days according to an embodiment of the present invention using XRD. Zn observed in a PG 00 sample x OTf y (OH) 2x-y ·Related peaks such as nH2O were relatively attenuated in the PG 30 sample, which is interpreted as a result of the effective suppression of the hydrogen evolution reaction (HER) and corrosion reaction on the Zn surface.

[0121] Consequently, the use of PG 30 electrolyte improved the corrosion resistance of Zn metal over a wide voltage stability range, suppressed HER and OER, and reduced byproduct formation. These characteristics provide favorable conditions for application in high-performance Zn batteries and related electrochemical systems.

[0122]

[0123] Example 13: Nucleation Overpotential (NOP) Analysis

[0124] Figure 18 shows an electrolyte according to an embodiment of the present invention, with a current density of 1.0 mA cm -2 , capacity 1.0 mAh cm -2 This graph shows the Zn nucleation overpotential (NOP) over time under different conditions. The initial overpotential in the PG 00 electrolyte remained high at approximately 118.4 mV, while it decreased significantly to approximately 92.6 mV in the PG 30 electrolyte. This indicates that the Zn 2+ This means that the initial energy required for ions to form nuclei on the electrode surface is reduced, leading to a more stable deposition process.

[0125] Example 14: Desolvation energy measurement

[0126] Figure 19 is a graph showing the relationship between the reciprocal of the reverse charge transfer resistance (1 / Rct) obtained using the Arrhenius equation and the reciprocal of the temperature (1 / T) in an electrolyte according to an embodiment of the present invention, where the slope is Zn 2+ The desolvation activation energy (Ea) was estimated. The desolvation activation energy of PG 00 electrolyte is approximately 26.0 kJ mol -1 , whereas PG 30 electrolyte showed a high value of 23.3 kJ mol -1 Zn as low as 2+ It was confirmed that the energy required for the ion to escape from the solvent shell was reduced. This is because Zn 2+ The reduced desolvation energy of means that water molecules within the solvated structure can be more easily removed, which allows Zn 2+ This means that it induces an easier deposition process.

[0127]

[0128] Example 15: Comparison of surface energy by crystal plane

[0129] Figures 20 and 21 show the surface energy of Zn crystal planes (002, 100, 101) under W / PG (top, blue graph) and W / O PG (bottom, red graph) conditions in the electrolyte according to one embodiment of the present invention. In the presence of PG 30 electrolyte, the (002) plane shows the highest surface energy, suggesting that it acts as the most unstable crystal plane. Accordingly, Zn 2+ The ions grow preferentially along the unstable (002) plane to stabilize it, resulting in uniform Zn on the Zn cathode surface. 2+ It can be interpreted that it contributes to inducing deposition and suppressing dendrite formation.

[0130]

[0131] Example 16: XRD (peak by crystal plane) analysis

[0132] Fig. 22 shows the results of XRD measurement of the crystal plane peaks of the Zn deposition layer in the PG 00 and PG 30 electrolytes according to one embodiment of the present invention. As a result of comparing the relative intensities of the (002), (100), (101), and (102) planes, it was confirmed that the (002) plane grew dominantly in the actual deposition process in PG 30 as the peak ratio corresponding to the (002) plane increased. In addition, the (002) / (101) or (002) / (102) ratio was significantly different from that of PG 00, indicating that the PG 30 electrolyte uniformly deposited Zn on the Zn cathode surface. 2+ It can be interpreted that it contributes to inducing deposition and suppressing dendrite formation.

[0133]

[0134] Example 17: In situ optical image observation and SEM analysis

[0135] Figure 23 shows the results of observing the Zn deposition process using an in situ optical microscope using a PG 00 sample in an electrolyte according to one embodiment of the present invention (top) and the results of observing the surface using an SEM after 60 minutes (bottom). As time passes, dendrites are clearly formed on the electrode surface, and numerous sharp, irregular crystals are also observed in the SEM image.

[0136] Figure 23 shows the results of observing the PG 30 sample under the same conditions. From the beginning, dendrites were noticeably suppressed on the surface, and a relatively dense and flat crystal structure was formed even after a long period of deposition. This is because the (002) plane grew preferentially, uniformly expanding the crystal, and PG uniformly distributed Zn on the Zn cathode surface. 2+ It can be interpreted that it contributes to inducing deposition and suppressing dendrite formation.

[0137]

[0138] Example 18: Analysis of SEI layer composition using XPS

[0139] Figure 24 shows the XPS spectra (C 1s, F 1s, S 2p, O 1s) of a PG 30 sample measured according to sputtering time (0 s, 90 s, 180 s) in an electrolyte according to an embodiment of the present invention. At the initial surface (0 s), C=O (290.9 eV), ZnF₂ (686.0 eV), CF₃ (690.2 eV), SO3 2- (163.5 eV), CO3 2- / SO3 2- (533.0 eV) etc. were detected, indicating that a composite SEI layer with mixed organic and inorganic bonding species was formed. As sputtering progressed, the peak of ZnO / Zn(OH)₂(531.4 eV) also became more prominent. Based on all of the above analysis results, it is interpreted that each organic and inorganic bonding species constituting the SEI layer was formed uniformly over the entire thickness region.

[0140] Figure 25 shows the results of measuring PG 00 sample by XPS under the same conditions in the electrolyte according to one embodiment of the present invention, showing C=O (291.0 eV), ZnF₂ (685.6 eV), SO3 2- (163.7 eV) and so on appear from the initial surface, but the SEI layer characteristics with a uniform mixture of organic and inorganic components are relatively less observed compared to the PG 30 sample. This suggests that the SEI layer formed in the PG 00 electrolyte is non-uniform, which may increase the possibility of local current concentration and dendrite formation during the Zn deposition process.

[0141]

[0142] Example 19: Ion distribution and structure observed by TOF-SIMS

[0143] Figure 26 shows the TOF-SIMS 3D distribution of a PG 30 sample in an electrolyte according to one embodiment of the present invention. ZnCO3 - , ZnF2 - , ZnS - , ZnSO3 - It can be seen that various ion species are uniformly distributed in the depth direction, which means that an organic-inorganic mixed layer is formed throughout the SEI layer. This mixed layer is Zn 2+ It contributes to suppressing non-uniform crystal growth by alleviating local deposition and delamination.

[0144] Figure 27 shows the results of TOF-SIMS measurement performed on a PG 00 sample in an electrolyte according to an embodiment of the present invention. ZnCO3 - , ZnF2 - , ZnS - , ZnSO3 - Although some paper has been confirmed, its distribution appears relatively irregular. This suggests that the composition and thickness of the SEI layer are not uniform, and that the risk of dendrite formation may increase during long-term charge and discharge cycles.

[0145]

[0146] Example 20: Comparison of Zn∥Cu cell coulombic efficiencies

[0147] Figures 28 and 29 show the results of measuring the Coulombic efficiency while charging / discharging a Zn∥Cu asymmetric cell in PG 00 (red curve) and PG 30 (blue curve) electrolytes according to one embodiment of the present invention. From the initial to the 10th, 50th, and 100th cycles, the PG 30 sample maintained a higher Coulombic efficiency overall, and even after discharging, Zn deposition and desorption proceeded uniformly, resulting in less damage to the electrode surface.

[0148] These results suggest that, as previously confirmed in previous experiments, the dendrite and side reaction suppression effects are expressed within the PG 30 electrolyte, allowing high efficiency to be maintained even over long cycles.

[0149]

[0150] Example 21: Zn∥Zn Cell Plating / Stripping Longevity Evaluation

[0151] Figures 30 and 31 show the electrolyte according to one embodiment of the present invention, 0.5 mA cm in a Zn∥Zn symmetric cell. -2 , 0.5 mAh cm -2 (Fig. 30) and 2.0 mA cm -2 , 2.0 mAh cm -2 (Fig. 31) Applying the conditions for a long time (hundreds to thousands of hours) Zn 2+ This is the result of a reversible deposition / desorption test.

[0152] Referring to Fig. 30, the results of the voltage profile by PG electrolyte fraction were analyzed, and as the PG content increased, the voltage range tended to increase, and in the case of PG 00, PG 10, PG 20, PG 40, and PG 60, it was confirmed that normal cell operation did not occur before 3000 hours. On the other hand, PG 30, PG 50, PG 70, and PG 80 were operated normally for 3000 hours, and among them, PG 30 (blue) maintained the smallest voltage range and showed consistent behavior. In particular, since it was confirmed that in cases containing PG overall, cell operation for a long time was possible compared to PG 00, the effect of the technical configuration of the present invention can be confirmed.

[0153] The voltage profile appears to be more stable for a longer period of time in the PG 30 sample compared to the PG 00, indicating that Zn 2+ This means that it suppresses dendrite growth by inducing uniform deposition and detachment of lithium, and significantly delays the short-circuit phenomenon that occurs during the charge and discharge process.

[0154]

[0155] Example 22: Rate performance characteristics

[0156] Figure 32 shows an electrolyte according to an embodiment of the present invention, in which the areal capacity is fixed at 1 mAh cm-2 and the current density is 0.5 → 1 → 2 → 5 → 7 → 10 → 20 → 30 mA cm -2 and then increased to the initial current density of 1 mA cm -2 The rate performance of the Zn∥Zn symmetric cell was measured by lowering the current density to 0.5 mA cm. The PG 00 sample was well maintained under high current conditions and then lowered to the initial current density of 0.5 mA cm. -2After returning to the initial current density, the voltage became rapidly unstable or a short-circuit phenomenon occurred, whereas the PG 30 sample maintained a relatively constant voltage behavior even in the high current density range and after returning to the initial density.

[0157] These rate characteristic evaluations reflect the electrolyte performance in high-power driving or rapid charging situations and provide evidence that the PG 30 electrolyte exhibits excellent stability under various operating conditions.

[0158]

[0159] Example 23: Long-term charge / discharge at 80% depth of discharge (DOD)

[0160] Figure 33 shows an electrolyte according to an embodiment of the present invention, after applying a deep discharge rate (80% DOD) to a Zn∥Zn symmetric cell, 1.0 mA cm -2 4.68 mAh cm -2 This graph observes voltage changes as capacities are exchanged. For the PG 00 sample, voltage became unstable around 50 hours, and a cell short-circuit phenomenon appeared around 130 hours. However, for the PG 30 sample, stable charging / discharging was maintained for a much longer period, up to 220 hours.

[0161] This supports the fact that PG 30 electrolyte effectively protects the Zn surface and suppresses dendrites and side reactions, thereby improving electrode life and performance even under conditions of high Zn utilization.

[0162] Consequently, the application of the PG 30 electrolyte exhibits high Coulombic efficiency under various current density and areal capacity conditions, and enables stable operation for long periods of time even during deep discharge. This can be understood as the combined effect of the previously confirmed voltage stability enhancement (HER / OER suppression) and dendrite formation inhibition.

[0163]

[0164] Example 24: Electrochemical performance evaluation

[0165] Figure 34 shows the current density stepwise (0.1 → 0.5 → 1 → 2 → 4 → 6 → 8 → 10 → 15 A g) for each of the PG 00 (red) and PG 30 (blue) electrolytes in a full cell using VO₂@V-MXene (9:1) as a cathode material according to an embodiment of the present invention. -1 ) shows the discharge capacity measured while increasing the current density. Although PG 00 shows slightly higher discharge capacity overall, a tendency for the capacity to gradually decrease at the last 0.1 A g¹ current density was observed, whereas PG 30 sample maintains relatively high discharge capacity even when the current density increases, and when it is returned to a low current (0.1 A g -1 ) also showed excellent responsiveness and reversibility by recovering the capacity to almost the initial level.

[0166] These results suggest that the PG 30 electrolyte forms good interactions not only with the Zn cathode but also with the VO₂@V-MXene anode, minimizing side reactions and resistance increase at the electrode interface.

[0167] Figure 35 shows an electrolyte according to an embodiment of the present invention, with a current density of 1 A g. -1 These are the results of long-term charge / discharge cycles exceeding 2,000 cycles under these conditions. Compared to the PG 00 sample, the PG 30 sample exhibited significantly more stable capacity retention and Coulombic efficiency, maintaining approximately 80.0% of the initial capacity. Referring to Figures 34 and 35, it can be confirmed that PG 30 exhibited superior electrochemical performance.

[0168] This suggests that the PG 30 electrolyte effectively suppresses electrolyte decomposition and dendrite formation on the electrode surface, thereby maintaining the electrolyte-electrode interface stable even during long-term charge / discharge. In addition, 1 A g -1The current density corresponds to a relatively low current density, and it is generally difficult for aqueous zinc batteries to be operated stably for a long time under such low current density conditions. However, it can be confirmed that the above problem can be improved by using PG 30.

[0169] Figure 36 shows an electrolyte according to an embodiment of the present invention, which has a higher current density (5 A g -1 ) is the result of operating a full cell using VO₂@V-MXene(9:1) cathode material for approximately 3,600 cycles. The capacity of the PG 00 sample rapidly decreased as the cycle progressed, dropping to approximately 33%, but the PG 30 sample maintained a capacity of over 80% and maintained stable operation for a long period of time even during high-speed charge / discharge.

[0170] The reason for such a large difference appears to be that the PG 30 electrolyte is excellent in ion transfer and suppression of side reactions at the Zn cathode, which means that it can guarantee high reliability even when applied to large-capacity, high-power batteries in the future.

[0171] Figure 37 shows an electrolyte according to an embodiment of the present invention, with a current density of 10 A g. -1 This is the result of performing repeated charge / discharge cycles for more than approximately 5,000 cycles under very high current density conditions. While the PG 30 sample stably maintained 80% of the initial capacity, the PG 00 sample's capacity decreased by approximately 31%, reaching its practical lifespan limit.

[0172] These outstanding lifespan characteristics can be interpreted as a positive interaction between the extended voltage stability range and the dendrite suppression effect with the cathode material. Ultimately, this confirms that PG-containing co-solvent electrolytes in aqueous ion batteries are a key technology that significantly enhances their commercial viability.

[0173]

[0174] The first aspect of this article is,

[0175] A zinc secondary battery aqueous electrolyte is provided, comprising a metal salt containing zinc; water; and a glycol solvent, characterized in that the glycol solvent is included in an amount of 5 to 150 parts by weight per 100 parts by weight of the water.

[0176]

[0177] Hereinafter, the aqueous electrolyte for a zinc secondary battery according to the first aspect of the present invention will be described in detail.

[0178]

[0179] In one embodiment of the present invention, the metal salt may include at least one selected from the group consisting of zinc sulfate (ZnSO₄), zinc trifluoromethanesulfonate (Zn(OTf)₂), zinc nitrate (Zn(NO₃)₂), zinc chloride (ZnCl₂), zinc acetate (Zn(CH₃COO)₂), zinc perchlorate (Zn(ClO₄)₂), zinc bromide (ZnBr₂), zinc fluorophosphate (ZnF₂), zinc tetrafluoroborate (Zn(BF₄)₂), zinc hexafluorophosphate (Zn(PF6)₂), zinc methanesulfonate (Zn(CH₃SO₃)₂), zinc triflate (Zn(TFSI)₂), and zinc citrate (Zn₃(C6H5O7)₂). The metal salt described above can be selected based on its solubility and stability in the electrolyte, as well as its charge-discharge reactivity. Furthermore, various combinations of metal salts can be applied to meet the required performance, taking into account processability and environmental impact. Preferably, the metal salt is zinc trifluoromethanesulfonate (Zn(OTf)₂).

[0180] In one embodiment of the present invention, the aqueous electrolyte may have a molar concentration of the metal salt of 0.45 M or more, 0.75 M or more, 1.125 M or more, 1.35 M or more, 1.5 M or more, or 1.8 M or more, 12.5 M or less, 10 M or less, 7.5 M or less, 7.5 M or less, 6.25 M or less, or 5 M or less. If it is less than the above range, the ion concentration in the electrolyte may be insufficient, which may lower the ionic conductivity, and thus the charge / discharge efficiency or output characteristics may be lowered. In addition, there may be a concern that the cycle life may be shortened because a uniform reaction does not occur on the electrode surface. On the other hand, if it is more than the above range, the electrolyte viscosity may increase due to excessively high ion concentration, which may hinder ion diffusion, promote corrosion reaction, or form unnecessary by-products on the electrode surface, which may lower the battery performance. Furthermore, internal resistance increases, causing heat generation to worsen and potentially damaging electrode stability during long-term operation.

[0181] In one embodiment of the present invention, the glycol cosolvent is ethylene glycol, propylene glycol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, dimethylene glycol, diethylene glycol (DEG), triethylene glycol (TEG), tetraethylene glycol (TetraEG), methyl glycol (Methyl Glycol, 2-Methoxyethanol), ethyl glycol (Ethyl Glycol, 2-Ethoxyethanol), and butyl glycol (Butyl Glycol, 2-Butoxyethanol). The glycol cosolvent may be selected to control the viscosity in the electrolyte and increase the interfacial stability with the electrode surface, and may suppress the hydrogen generation reaction that may occur on the negative electrode surface while minimizing the coordination number of water molecules of zinc ions during the charge / discharge process. In addition, an appropriate material among various types of glycols may be optimized and applied according to the targeted physical and chemical properties (e.g., flame retardancy, boiling point, etc.). Preferably, the glycol cosolvent may be propylene glycol.

[0182] In one embodiment of the present invention, with respect to 100 parts by weight of the water, the content of the glycol co-solvent may be 0.1 parts by weight or more, 1 part by weight or more, 5 parts by weight or more, 6 parts by weight or more, 7.5 parts by weight or more, 10 parts by weight or more, 12 parts by weight or more, 20 parts by weight or more, 30 parts by weight or more, 36 parts by weight or more, 40 parts by weight or more, or 48 parts by weight or more, 400 parts by weight or less, 250 parts by weight or less, 150 parts by weight or less, 120 parts by weight or less, 90 parts by weight or less, 80 parts by weight or less, 75 parts by weight or less, or 60 parts by weight or less. If it is below the above range, the glycol cosolvent may not be sufficiently added, making it difficult to secure the viscosity and interfacial stability of the aqueous electrolyte and the ability to suppress hydrogen evolution reaction at the desired levels. As a result, there may be concerns that the uniform reaction on the electrode surface may be inhibited or the cycle performance may deteriorate. On the other hand, if it is exceeded, the electrolyte viscosity may excessively increase due to the excess of the glycol cosolvent, the ion transfer path may be obstructed, and some side reactions or by-products may increase, which may reduce long-term reliability and output.

[0183] In one embodiment of the present invention, the viscosity of the aqueous electrolyte may be 5 cP or more, 6 cP or more, 7 cP or more, 9 cP or more, 10 cP or more, 20 cP or more, 30 cP or more, 36 cP or more, 40 cP or more, or 48 cP or more, and may be 450 cP or less, 360 cP or less, 270 cP or less, 240 cP or less, 225 cP or less, or 180 cP or less. If it is less than the above range, the additive may be contained in an extremely small amount, and the effects of the additive, such as suppressing hydrogen ion generation and suppressing dendrite formation, may not be sufficiently exerted, and there is a concern that the long-term stability of the battery may be reduced during the charge / discharge process. On the other hand, if the above range is exceeded, the electrolyte viscosity may become excessively high, which may impede ion diffusion and electron movement paths, thereby delaying electrochemical reactions, deteriorating the output and cycle characteristics of the battery, and increasing the possibility of heat generation and side reactions.

[0184] In one embodiment of the present invention, after charging and discharging zinc metal in the aqueous electrolyte, the surface can be characterized by performing X-ray diffraction analysis. Specifically, according to one embodiment, the current density is 7 mA cm -2 , area capacity 7 mAh cm -2 It can be a characterization after 3 cycles of charge and discharge under the conditions. For example, the first to fourth diffraction peaks corresponding to representative crystal planes [(002), (101), (100), (102), etc.] of zinc (Zn) having a hexagonal (hcp) structure can be observed around 2θ = 35 to 37°, 37 to 39°, 42 to 44°, 53 to 55°, etc. Specifically, the relative intensity ratio (I) of the peak corresponding to the (002) plane and the (101) plane peak(002) / I (101) ), and the relative intensity ratio of the (002) and (102) plane peaks (I (002) / I (102) ) varies depending on the sample, and growth toward the (002) plane is more dominant than other crystal planes, which allows confirmation of the dendrite growth inhibition effect. Preferably, in one embodiment of the present invention, the ratio of peak intensities for the (002), (101), and (102) planes I (002) / I (101) This may be satisfied from 0.4 to 2.0, preferably from 0.4 to 1.5, more preferably from 0.4 to 1.0, I (002) / I (102) This may be satisfied in the range of 1.95 to 4.0, preferably 1.95 to 3.0, and more preferably 2.0 to 2.5. By satisfying the above-described range, it can be seen that the electrolyte according to one embodiment of the present invention has a unique effect of suppressing dendrite formation while allowing preferential growth toward the (002) plane.

[0185]

[0186] The second aspect of the original text is,

[0187] A zinc secondary battery is provided, comprising: a positive electrode; a negative electrode; and the aqueous electrolyte.

[0188]

[0189] Detailed explanations of parts that overlap with the first aspect of the present application have been omitted, but the explanations of the first aspect of the present application may be applied equally even if the explanations are omitted in the second aspect.

[0190]

[0191] Hereinafter, a zinc secondary battery according to the second aspect of the present invention will be described in detail.

[0192]

[0193] In one embodiment of the present invention, the positive electrode may include a positive electrode active material, a conductive material, and a binder.

[0194] In one embodiment of the present invention, the absolute value of the bond energy formed between the zinc ion and the water molecule may be 0.0003 eV or more, 0.0005 eV or more, 0.00075 eV or more, 0.0009 eV or more, 0.001 eV or more, or 0.0012 eV or more, and may be 2.5 eV or less, 2.4 eV or less, 2.3 eV or less, 2.2 eV or less, 2.2 eV or less, or 2 eV or less. If the above range is exceeded, the bond between the zinc ion and the water molecule is excessively strong, so that the desolvation energy of the zinc ion with respect to water increases, thereby increasing the side reaction on the electrode surface due to water, which may possibly lower the long-term stability of the cell.

[0195] In one embodiment of the present invention, during charge / discharge of the zinc secondary battery, the coordination number of water molecules coordinated to the zinc ion with the highest frequency may be 4. Considering that the zinc ion in a typical aqueous electrolyte has a coordination number of 6 with water molecules with the highest frequency, the coordination number can be lowered due to the action of the substance added to the electrolyte according to one embodiment of the present invention, and such a technical configuration can significantly reduce the hydrogen evolution reaction on the negative electrode surface.

[0196] In one embodiment of the present invention, a zinc secondary battery has a structure capable of electrochemical charging and discharging, and various materials can be applied as positive electrode active materials. For example, representative examples include metal oxides or metal complexes including manganese compounds (manganese dioxide (MnO₂), manganese trioxide (Mn₂O₃), manganese tetraoxide (Mn₃O₄), manganese composite oxides and sulfides), vanadium compounds (V₂O₃, V₂O5, VO₂, vanadium phosphate (vanadium phosphate)), molybdenum compounds (MoO₃), iodine (I₂) or iodide compounds, nickel compounds (NiOOH, nickel hexacyanoferrate), Prussian blue analogues (including CuHCF), organic compounds, or mixtures thereof. In addition, to increase the electron transport within the anode, a carbon-based conductive material (carbon black, acetylene black, etc.) is mixed in an appropriate ratio, and the active material can be implemented in various forms such as powder, thin film, nanostructure, etc. In addition, the positive electrode active material may have a structure complexed on a layered material including at least MXene. Preferably, the MXene may be a vanadium-based MXene.

[0197] In one embodiment of the present invention, the cathode mainly uses zinc (Zn) metal or a zinc alloy, and when discharging, Zn → Zn 2++ 2e oxidation reaction occurs and a reduction reaction is considered to proceed in the reverse direction during charging. In the zinc anode, there is a possibility that dendrites (metal dendritic structures) may form or a hydrogen evolution reaction may occur during the charge / discharge cycle, so various electrolyte compositions or anode surface treatments can be applied to suppress this. For example, there is a method of suppressing dendrite formation by doping small amounts of aluminum (Al), indium (In), magnesium (Mg), etc. into the anode metal, or applying a protective coating (e.g. nickel plating, carbon coating) to the anode surface to reduce corrosion and side reactions. In addition, current density control or three-dimensionalization of the anode structure (porous structure, etc.) is being studied to uniformly induce zinc peeling and plating, and through these, it is possible to increase the cycle life and efficiency.

[0198] In one embodiment of the present invention, the separator is considered to be composed of a material selected to prevent direct contact between the anode and cathode while allowing free movement of ions. For example, the separator may include at least one selected from the group consisting of filter paper, glass fiber, hydrophilic polymer, and polymer-inorganic oxide hybrid materials. In addition, a porous membrane of the polyolefin series, such as polypropylene (PP) or polyethylene (PE), may be representatively used, and a cellulose series paper or glass fiber separator may also be considered. The separator must maintain chemical stability when in contact with the electrolyte, and must have a uniform pore structure so as not to impede ion conductivity. In some embodiments, a method of coating inorganic particles (alumina, zirconia, etc.) may be used to enhance heat resistance and chemical resistance.

[0199] In one embodiment of the present invention, the current collector is considered to play a role in supporting the equal exchange of current between the positive and negative electrodes. In a zinc secondary battery, materials such as titanium (Ti), nickel (Ni), and stainless steel (including special alloys) with good corrosion resistance and electrical conductivity can be considered as positive current collectors. Carbon-based materials (carbon cloth, carbon paper, carbon nanotubes, etc.) can also be utilized. The positive current collectors described above can be used on the negative electrode side, and preferably, a zinc plate or a zinc-plated metal foil can be directly utilized, and copper (Cu)-based materials can also be used as an additional support. It is also possible to use metal surface treatment or a protective coating together to prevent corrosion or oxidation problems during long-term charge and discharge.

[0200] In one embodiment of the present invention, the conductive agent is considered a material added to secure an electron conduction path within the electrode. Carbon black, acetylene black, graphite powder, carbon nanotubes (CNTs), graphene, and other materials can be used. These materials facilitate electron transfer between active materials, thereby enhancing electrode performance. Since the internal resistance of the electrode varies significantly depending on the content and dispersion state of the conductive agent, it is crucial to precisely control the preprocessing and mixing conditions to ensure uniform dispersion.

[0201] In one embodiment of the present invention, the binder is considered to play a role in maintaining the physical structure by binding the electrode active material and the conductive material, and absorbing and alleviating the volume change that may occur during the charge / discharge process. Generally, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) are widely used, and the appropriate type and mixing ratio are determined according to requirements such as chemical stability with the electrolyte, adhesive properties, and pore control within the electrode. When manufacturing with an aqueous process, aqueous binders such as CMC and SBR are often selected, and PVDF series are often selected for an organic solvent-based process.

[0202] In one embodiment of this invention, a zinc secondary battery manufactured by combining these components exhibits low toxicity and high safety, making it applicable to a wide range of fields, from large-scale ESSs to portable electronic devices and military power supplies. In particular, the battery's marketability is high due to its utilization of zinc, which is relatively abundant and price-competitive. Furthermore, active research into nanostructure design and surface treatment processes is expected to further improve energy density, cycle life, and output characteristics.

[0203]

[0204] According to an embodiment of the present invention, by controlling the electrolyte environment of aqueous zinc-ion batteries (AZIBs) using a cosolvent, corrosion of Zn metal and hydrogen evolution reaction (HER) can be effectively suppressed. This allows excessive H generated during the charge and discharge process to be effectively suppressed. + It can prevent the increase of internal pressure and solve the problem of battery performance deterioration due to hydrogen gas. In addition, by introducing a co-solvent, Zn 2+The solvation structure of ZnO is adjusted to reduce the activity of free water molecules and create a more stable electrode environment. This reduces unnecessary reactions between Zn metal and the electrolyte, and can improve long-term electrode life and battery safety, suggesting industrial potential for use in aqueous zinc-ion batteries.

Claims

1. Metal salt containing zinc; water; and Contains glycol co-solvents; An aqueous electrolyte for a zinc secondary battery, characterized in that it comprises 5 to 150 parts by weight of the glycol co-solvent for 100 parts by weight of the water.

2. In paragraph 1, The above glycol cosolvents are ethylene glycol, propylene glycol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, dimethylene glycol, diethylene glycol (DEG), triethylene glycol (TEG), tetraethylene glycol (TetraEG), methyl glycol (Methyl Glycol, 2-Methoxyethanol), ethyl glycol (Ethyl Glycol, 2-Ethoxyethanol), and butyl glycol. An aqueous electrolyte for a zinc secondary battery, characterized in that it comprises at least one selected from the group consisting of (Butyl Glycol, 2-Butoxyethanol).

3. In paragraph 1, An aqueous electrolyte for a zinc secondary battery, characterized in that the metal salt comprises at least one selected from the group consisting of zinc sulfate (ZnSO₄), zinc trifluoromethanesulfonate (Zn(OTf)₂), zinc nitrate (Zn(NO₃)₂), zinc chloride (ZnCl₂), zinc acetate (Zn(CH₃COO)₂), zinc perchlorate (Zn(ClO₄)₂), zinc bromide (ZnBr₂), zinc fluorozinc acid (ZnF₂), zinc tetrafluoroborate (Zn(BF₄)₂), zinc hexafluorophosphate (Zn(PF6)₂), zinc methanesulfonate (Zn(CH₃SO₃)₂), zinc triflate (Zn(TFSI)₂), and zinc citrate (Zn₃(C6H5O7)₂).

4. In paragraph 1, The above glycol solvent is propylene glycol, An aqueous electrolyte for a zinc secondary battery, characterized in that the metal salt is zinc trifluoromethanesulfonate (Zn(OTf)₂).

5. In paragraph 1, The aqueous electrolyte for a zinc secondary battery is characterized in that the molar concentration of the metal salt is 1 to 5 M.

6. In paragraph 1, An aqueous electrolyte for a zinc secondary battery, characterized in that the viscosity of the aqueous electrolyte is 7 to 240 cP.

7. In paragraph 1, After the above charging and discharging, when X-ray diffraction analysis was performed on the zinc metal surface, the ratio of peak intensities for the (002), (101), and (102) planes was I (002) / I (101) This 0.4 to 1.5, I (002) / I (102) An aqueous electrolyte for a zinc secondary battery, characterized in that it satisfies 1.95 to 3.

0.

8. Bipolar; cathode; and Aqueous electrolyte of the first paragraph; A zinc secondary battery comprising:

9. In paragraph 8, A zinc secondary battery characterized in that the positive electrode includes a positive electrode active material, a conductive material, and a binder.

10. In paragraph 8, The above cathode active material is a manganese compound such as manganese dioxide (MnO₂), manganese trioxide (Mn₂O₃), or manganese tetraoxide (Mn₃O₄). manganese complex oxides or complex sulfides, Vanadium compounds, such as V₂O₃, V₂O5, or VO₂, Vanadium phosphate, molybdenum compounds (MoO₃), Iodine (I₂) or iodide compounds, A zinc secondary battery characterized by being an organic compound or a mixture thereof.

11. In paragraph 8, A zinc secondary battery, characterized in that the positive electrode active material has a composite structure formed on a layered material including at least MXene.

12. In paragraph 8, A zinc ion secondary battery characterized in that the negative electrode contains zinc as a negative electrode active material.

13. In paragraph 8, A zinc secondary battery characterized in that the zinc ion secondary battery further includes a separator.

14. In paragraph 8, A zinc secondary battery, characterized in that the electrolyte has an absolute value of the bond energy formed between zinc ions and water molecules of less than 2.0 eV.

15. In paragraph 8, A zinc secondary battery, characterized in that the coordination number of water molecules coordinated to the zinc ion with the highest frequency during charge and discharge of the zinc secondary battery is 4.

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