Application of graphene quantum dots and zinc ion battery electrolyte and zinc ion battery

Abstract

The application discloses an application of graphene quantum dots, and a zinc ion battery electrolyte and a zinc ion battery. The application is specifically an application of graphene quantum dots with electronegative groups containing nitrogen, sulfur and oxygen on the surface as electrolyte additives of the zinc ion battery. The graphene quantum dots as the electrolyte additives can adsorb zinc ions in the electrolyte solution, uniformly co-deposit on the negative electrode surface, and then induce the zinc ions to preferentially deposit along the (002) crystal surface parallel to the electrode surface, so that the formation of zinc dendrites is fundamentally inhibited. In addition, the graphene quantum dots are light in mass, do not affect the energy density of the battery, are stable in performance, do not produce side reactions, can be recycled in the charging and discharging process, and achieve long-time performance improvement. The aqueous zinc ion battery with the graphene quantum dots added in the electrolyte can continuously light up an LED array, and has a good prospect in the field of high-energy-density zinc ion batteries.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to the application of graphene quantum dots, zinc-ion battery electrolyte, and zinc-ion batteries. Background Technology

[0002] Compared to flammable and explosive organic batteries, aqueous multivalent metal-ion batteries offer greater safety and are more environmentally friendly. Zinc, in particular, boasts abundant natural reserves, high theoretical capacity, and low electrochemical potential, making aqueous zinc-ion batteries a highly sought-after technology. However, the persistent problem of zinc dendrite formation severely hinders the practical application of zinc-ion batteries. Continuous dendrite growth on the negative electrode side can cause serious side reactions and may even puncture the separator, ultimately leading to reduced coulombic efficiency and shortened cycle life. The dendrite problem becomes even more severe with high positive electrode loading and low N / P ratios.

[0003] It is generally believed that the dendrite problem of zinc anodes stems from the uneven distribution of charge and ions on the zinc anode surface during battery cycling, and the vertical growth caused by the preferential deposition of the (101) facet with low surface energy. Therefore, researchers have conducted extensive exploratory studies to address the dendrite problem of zinc anodes, mainly through the following three methods: 1) Structural design: preparing three-dimensional and composite structures to suppress the volume expansion of zinc dendrites and induce uniform deposition of zinc ions. However, the increased specific surface area of ​​complex structures leads to more active sites, thereby accelerating the rate of side reactions; 2) Interface design: coating the zinc sheet surface with a modified layer to uniformly induce ions or electrons. However, interface modification usually increases internal resistance and reduces energy density, and the coating is easily damaged during repeated charge and discharge cycles; 3) Electrolyte additives: introducing organic or inorganic additives to achieve electrostatic shielding, artificial solid electrolyte interphase (SEI) layer, uniform electric field distribution, and induced crystal orientation. However, the consumption and decomposition of additives during charge and discharge cycles are still detrimental to the long-term cycling of the battery.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide an application of graphene quantum dots, as well as a zinc-ion battery electrolyte and a zinc-ion battery, to improve the above-mentioned technical problems.

[0006] This invention is implemented as follows:

[0007] In a first aspect, the present invention provides an application of graphene quantum dots as an electrolyte additive for zinc-ion batteries, wherein the surface of the graphene quantum dots has electronegative groups containing nitrogen, sulfur, and oxygen.

[0008] Secondly, the present invention also provides a zinc-ion battery electrolyte, the components of which include zinc salts and graphene quantum dots used in the above applications.

[0009] Thirdly, the present invention also provides a zinc-ion battery comprising the above-mentioned electrolyte.

[0010] This invention offers the following advantages: Graphene quantum dots containing nitrogen, oxygen, and sulfur on their surface, when used as an electrolyte additive, can adsorb zinc ions in the electrolyte solution and uniformly co-deposit on the negative electrode surface. This induces preferential deposition of zinc ions along the (002) crystal plane parallel to the electrode surface, fundamentally suppressing the formation of zinc dendrites. Furthermore, graphene quantum dots are lightweight, do not affect the battery's energy density, exhibit stable performance, do not produce side reactions, and can be recycled during charge and discharge processes, achieving long-term performance improvement. Aqueous zinc-ion batteries with this graphene quantum dot electrolyte can continuously illuminate LED arrays, showing promising prospects in the field of high-energy-density zinc-ion batteries. Attached Figure Description

[0011] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0012] Figure 1 This is a schematic flowchart of the preparation method of graphene quantum dots as an electrolyte additive in an embodiment of the present invention.

[0013] Figure 2 These are TEM and HRTEM images of the graphene quantum dots prepared in Example 1 of this invention;

[0014] Figure 3 The image shows the FTIR spectrum of the graphene quantum dots prepared in Example 1 of this invention.

[0015] Figure 4 XPS image of the graphene quantum dots prepared in Example 1 of this invention;

[0016] Figure 5 This is a schematic diagram of the deposition process of the electrolyte additive in Comparative Example 1 and Example 1 of the present invention on the zinc negative electrode;

[0017] Figure 6 For the symmetrical cells of Comparative Example 1 and Example 1 of this invention, at 1 mA / cm 2 SEM image of the morphology after 10 cycles;

[0018] Figure 7 For the symmetrical cells of Comparative Example 1 and Example 1 of this invention, at 1 mA / cm 2 The time-voltage curve below;

[0019] Figure 8 For Comparative Example 1 and Example 1 of the present invention, the full cell has an N / P ratio of 3.0 and a positive electrode loading of 4 mg / cm³. 2 The cycle number of cycles - specific capacity curve. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0021] The abbreviations used in this invention are all fixed abbreviations in the field, and some of the abbreviations are explained as follows: SEM image: Scanning Electron Imaging; TEM image: Transmission Electron Imaging; HRTEM image: High-Resolution Transmission Electron Imaging; FTIR image: Infrared Spectroscopy; XPS image: X-ray Photoelectron Spectroscopy.

[0022] The following is a detailed description of the application of graphene quantum dots proposed in this invention, as well as the zinc-ion battery electrolyte and zinc-ion battery.

[0023] Some embodiments of the present invention provide an application of graphene quantum dots as an electrolyte additive for zinc-ion batteries, wherein the surface of the graphene quantum dots has electronegative groups containing nitrogen, sulfur, and oxygen.

[0024] Through extensive research and practice, the inventors creatively proposed using graphene quantum dots with electronegative groups containing nitrogen, sulfur, and oxygen as an additive to solve the dendrite problem of zinc anodes. This also addresses the issues of consumption and decomposition of existing electrolyte additives during charge and discharge. The reason why these graphene quantum dots can solve the zinc anode dendrite problem is likely due to the fact that the numerous electronegative groups in the graphene quantum dots can adsorb zinc ions in solution, uniformly co-depositing them on the anode surface. This induces zinc ions to preferentially deposit along the (002) crystal plane parallel to the electrode surface, fundamentally inhibiting the formation of zinc dendrites. Simultaneously, graphene quantum dots are lightweight, do not affect the battery's energy density, have stable performance, do not produce side reactions, and can be recycled during charge and discharge, achieving long-term performance improvement. Furthermore, the synthesis method of these graphene quantum dots is simple, the process is easy to operate, has good controllability, low raw material costs, and is environmentally friendly and pollution-free, making it suitable for large-scale production.

[0025] Specifically, electronegative groups include, but are not limited to, OH, NH, C=O, C=C, CN, CO, C=S, and CS.

[0026] In some embodiments, in order to enable the graphene quantum dots to function stably and continuously in the electrolyte, the graphene quantum dots have a spherical microstructure with a diameter of 2 to 4 nm and a lattice spacing of 0.19 to 0.22 nm, for example, the lattice spacing can be 0.21 nm.

[0027] Specifically, some embodiments also provide a method for preparing the above-mentioned graphene quantum dots, see [link to documentation]. Figure 1 It is mainly prepared by the following steps: using hydroxy acids and nitrogen and sulfur sources as raw materials, a condensation reaction occurs during hydrothermal process. The hydroxy acids form graphene carbon cores through the condensation reaction, and a large number of hydroxy and carboxyl groups are formed on the surface. Then, nitrogen and sulfur are doped to form electronegative groups containing nitrogen, sulfur and oxygen on the surface of the graphene carbon cores.

[0028] Furthermore, to facilitate a better hydrothermal polycondensation reaction, in some embodiments, a homogeneous reaction solution is first prepared, followed by heating to carry out the reaction. The reaction solution is prepared as follows: a hydroxy acid and a nitrogen-sulfur source are dissolved in deionized water, and after continuous stirring for a period of time, a clear solution is formed. Sufficient dissolution of the reactants ensures that the subsequent hydrothermal reaction proceeds fully, orderly, and uniformly, resulting in carbon quantum dots of uniform morphology and size.

[0029] In some embodiments, the preparation method of graphene quantum dots specifically involves: pouring the reaction solution into a hydrothermal reactor, sealing it, transferring it to an oven, hydrothermally reacting it at high temperature for a period of time, and then cooling the reaction solution to room temperature after the reaction is completed.

[0030] The capacity of the hydrothermal reactor can be selected from 25 to 500 mL, and the temperature during the hydrothermal reaction can be selected from 120℃ to 200℃, for example, the temperature can be 120℃, 125℃, 130℃, 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, 195℃ or 200℃, etc., and the time can be selected from 3 to 5 hours, for example, 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours, etc.

[0031] Specifically, in the above embodiments, the molar ratio of hydroxy acid to nitrogen and sulfur source can be 1:1 to 5, for example 1:1, 1:2, 1:3, 1:4 or 1:5. The hydroxy acid includes, but is not limited to, at least one of citric acid, tartaric acid, malic acid and lactic acid. The concentration of hydroxy acid is 0.02 mol / L to 0.5 mol / L. The nitrogen and sulfur source includes, but is not limited to, at least one of thiourea and sulfonamide.

[0032] In some embodiments, in order to achieve better reaction results, the polycondensation reaction is carried out under stirring conditions, for example, the stirring speed can be selected from 100 rpm to 1500 rpm as needed.

[0033] In order to make the graphene quantum dots more stable in performance and more uniform in size, and more suitable for addition in electrolyte, some embodiments involve adjusting the pH with an alkaline reagent after the polycondensation reaction is completed, followed by dialysis purification.

[0034] Specifically, dialysis is performed using dialysis bags. In some implementations, the molecular weight cutoff of the dialysis bag is 3,000 to 4,000 Daltons, and the dialysis time is 8 to 16 hours.

[0035] The alkaline reagent is an alkaline solution. The solute in the alkaline solution includes, but is not limited to, at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate, as long as it can achieve the effect of adjusting the pH. In some embodiments, the concentration of the alkaline solution can be selected from 0.5 mol / L to 2 mol / L.

[0036] In some implementations, the pH of the reacted solution is adjusted to 5.5–6.5 before dialysis purification.

[0037] Furthermore, in some embodiments, after dialysis purification, the product is dried; specifically, the product is dried by freeze drying. The vacuum degree of freeze drying can be 1 Pa to 30 Pa, the cold trap temperature can be -60°C to -90°C, and the time can be 24 to 72 hours.

[0038] The graphene quantum dots are mainly used as additives in electrolytes containing zinc salts. Therefore, in order to achieve better adsorption of zinc ions and fully suppress the formation of zinc dendrites, in some embodiments, the concentration of zinc salt in the electrolyte is 1 mol / L to 3 mol / L, for example, 1 mol / L, 2 mol / L or 3 mol / L. The amount of graphene quantum dots added to the electrolyte of the zinc-ion battery is 0.01 wt% to 0.5 wt%, for example, 0.01 wt%, 0.02 wt%, 0.03 wt%, 0.04 wt%, 0.05 wt%, 0.06 wt%, 0.07 wt%, 0.08 wt%, 0.09 wt%, 0.1 wt%, 0.15 wt%, 0.20 wt%, 0.25 wt%, 0.3 wt%, 0.35 wt%, 0.4 wt%, 0.45 wt% or 0.5 wt%, etc., preferably 0.02 wt% to 0.1 wt%. Alternatively, carbon quantum dots can be added based on the mass fraction of zinc salt in the electrolyte, for example, by adding 0.02% to 0.5% of the mass of zinc salt.

[0039] In some embodiments, the zinc salt includes, but is not limited to, at least one of zinc sulfate, zinc chloride, zinc trifluoromethanesulfonate, and zinc bis(trifluoromethanesulfonyl)imide. That is, the zinc salt can be any one of zinc sulfate, zinc chloride, zinc trifluoromethanesulfonate, and zinc bis(trifluoromethanesulfonyl)imide, or a mixture of two or three of them, with no limit on the mixing ratio.

[0040] Some embodiments of the present invention also provide a zinc-ion battery electrolyte, the components of which include zinc salts and graphene quantum dots as described in any of the above embodiments.

[0041] Specifically, the concentration of zinc salt in the electrolyte is 1 mol / L to 3 mol / L, and the amount of graphene quantum dots added to the electrolyte of the zinc-ion battery is 0.01 wt to 0.5 wt, preferably 0.02 wt to 0.1 wt.

[0042] The zinc-ion battery electrolyte is prepared by adding graphene quantum dots to the electrolyte and stirring until the mixture is homogeneous at a stirring speed of 100–1500 rpm.

[0043] The present invention also provides a zinc-ion battery comprising the above-described electrolyte.

[0044] Specifically, in some embodiments, the zinc-ion battery is a Zn / Zn symmetrical battery, which uses a zinc sheet as the negative electrode and a zinc sheet as the positive electrode, Waterman glass fiber filter paper as the separator, and is assembled by adding the above-mentioned electrolyte.

[0045] Alternatively, the zinc-ion battery is a Zn / NVO full cell, which uses a zinc sheet as the negative electrode and Na2V6O. 16 ·3H2O(NVO) is used as the positive electrode, with a positive electrode loading of 3-5 mg / cm³. 2 The N / P ratio is adjusted to 2.5 to 3.5, and the electrolyte is added dropwise to form the electrolyte.

[0046] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0047] Example 1

[0048] This embodiment provides a zinc-ion battery electrolyte and its specific preparation method. The preparation method of the zinc-ion battery electrolyte specifically includes:

[0049] 0.21 g (1 mmol) of citric acid and 0.23 g (3 mmol) of thiourea were dissolved in 10 mL of deionized water and stirred continuously at 500 rpm to form a clear solution. The solution was then transferred to a 25 mL Teflon-lined reactor. The reactor was sealed and heated in an electric oven at 160 °C for 4 h. After cooling to room temperature, the product solution was alkalized to pH 6 with 1 mol / L sodium hydroxide solution, and then purified by dialyzing using a dialysis bag with a molecular weight cutoff of 3500 Daltons for 12 h. The dialyzed product was freeze-dried under a vacuum of 1 Pa at a cold trap temperature of -70 °C for 48 h. Graphene quantum dots were obtained after freeze-drying.

[0050] 20 mmol of zinc sulfate powder was dissolved in 10 mL of deionized water and stirred continuously at 500 rpm to form a clear solution, yielding a 2 mol / L zinc sulfate electrolyte. Graphene quantum dots were then added at 0.1% of the zinc sulfate mass fraction and stirred continuously at 500 rpm to form a clear solution, thus obtaining a zinc-ion battery electrolyte.

[0051] Example 2

[0052] This embodiment provides a zinc-ion battery electrolyte and its specific preparation method. The preparation method of the zinc-ion battery electrolyte specifically includes:

[0053] 0.13 g (1 mmol) of malic acid and 0.52 g (3 mmol) of sulfonamide were dissolved in 10 mL of deionized water and stirred continuously at 500 rpm to form a clear solution. The solution was then transferred to a 25 mL Teflon-lined reactor. The reactor was sealed and heated in an electric oven at 160 °C for 4 h. After cooling to room temperature, the product solution was alkalized to pH 6 with 1 mol / L sodium hydroxide solution, and then purified by dialyzing using a dialysis bag with a molecular weight cutoff of 3500 Daltons for 12 h. The dialyzed product was freeze-dried under a vacuum of 1 Pa at a cold trap temperature of -70 °C for 48 h. Graphene quantum dots were obtained after freeze-drying.

[0054] 20 mmol of zinc trifluoromethanesulfonate powder was dissolved in 10 mL of deionized water and stirred continuously at 500 rpm to form a clear solution, yielding a 2 mol / L zinc trifluoromethanesulfonate electrolyte. Graphene quantum dots were added at 0.2% of the mass fraction of zinc trifluoromethanesulfonate, and the solution was stirred continuously at 500 rpm to form a clear solution, thus obtaining a zinc-ion battery electrolyte.

[0055] Example 3

[0056] This embodiment provides a zinc-ion battery electrolyte and its specific preparation method. The preparation method of the zinc-ion battery electrolyte specifically includes:

[0057] 0.15 g (1 mmol) of tartaric acid and 0.347 g (2 mmol) of sulfonamide were dissolved in 10 mL of deionized water and stirred continuously at 500 rpm to form a clear solution. The solution was then transferred to a 25 mL Teflon-lined reactor. The reactor was sealed and heated in an electric oven at 190 °C for 3 h. After cooling to room temperature, the product solution was alkalized to pH 6 with 1 mol / L sodium hydroxide solution, and then purified by dialyzing using a dialysis bag with a molecular weight cutoff of 3000 Daltons for 10 h. The dialyzed product was freeze-dried under a vacuum of 10 Pa at a cold trap temperature of -90 °C for 24 h. Graphene quantum dots were obtained after freeze-drying.

[0058] 20 mmol of zinc trifluoromethanesulfonate powder was dissolved in 10 mL of deionized water and stirred continuously at 500 rpm to form a clear solution, yielding a 2 mol / L zinc trifluoromethanesulfonate electrolyte. Graphene quantum dots were added at 0.4% of the mass fraction of zinc trifluoromethanesulfonate, and the mixture was stirred continuously at 500 rpm to form a clear solution, thus obtaining a zinc-ion battery electrolyte.

[0059] Example 4

[0060] This embodiment provides a zinc-ion battery electrolyte and its specific preparation method. The preparation method of the zinc-ion battery electrolyte specifically includes:

[0061] 0.21 g (1 mmol) of citric acid and 0.304 g (4 mmol) of thiourea were dissolved in 10 mL of deionized water and stirred continuously at 500 rpm to form a clear solution. The solution was then transferred to a 25 mL Teflon-lined reactor. The reactor was sealed and heated in an electric oven at 140 °C for 5 h. After cooling to room temperature, the product solution was alkalized to pH 6 with 1 mol / L sodium hydroxide solution, and then purified by dialyzing using a dialysis bag with a molecular weight cutoff of 3500 Daltons for 12 h. The dialyzed product was freeze-dried under a vacuum of 20 Pa at a cold trap temperature of -60 °C for 72 h. Graphene quantum dots were obtained after freeze-drying.

[0062] 20 mmol of zinc sulfate powder was dissolved in 10 mL of deionized water and stirred continuously at 500 rpm to form a clear solution, yielding a 2 mol / L zinc sulfate electrolyte. Graphene quantum dots were then added at 0.7% of the zinc sulfate mass fraction and stirred continuously at 500 rpm to form a clear solution, thus obtaining a zinc-ion battery electrolyte.

[0063] Comparative Example 1

[0064] This comparative example provides a zinc-ion battery electrolyte and its specific preparation method. The preparation method of the zinc-ion battery electrolyte specifically includes:

[0065] 20 mmol of zinc sulfate powder was dissolved in 10 mL of deionized water and stirred continuously at 500 rpm to form a clear solution, thus obtaining a 2 mol / L zinc sulfate electrolyte.

[0066] Experimental Example 1

[0067] The graphene quantum dots prepared in Example 1 were analyzed:

[0068] Figure 2 The image shows a TEM image of the graphene quantum dots prepared in Example 1 of this invention. The graphene quantum dots have a spherical microstructure with a diameter of 2-4 nm, are uniformly dispersed, and show no obvious agglomeration. The HRTEM image shows the good crystallinity of the graphene quantum dots, with a lattice spacing of 0.21 nm.

[0069] Figure 3 The image shown is the FTIR spectrum of the graphene quantum dots prepared in Example 1 of this invention. The graphene quantum dots contain the following electronegative groups on their surface: OH, NH, C=O, C=C, CN, CO, C=S, and CS. These groups facilitate the uniform distribution of the graphene quantum dots in aqueous solution and enhance their adsorption capacity for zinc ions.

[0070] Figure 4 The image shown is the XPS image of the graphene quantum dots prepared in Example 1 of this invention. The surface of the graphene quantum dots contains the following electronegative groups: NH, C=O, CC, C=C, CN, CO, and CS, which is consistent with the conclusion of the FTIR image.

[0071] Experimental Example 2

[0072] The electrolytes prepared in Example 1 and Comparative Example 1 were used to assemble batteries, and the specific operations were as follows:

[0073] A Zn / Zn symmetrical cell was assembled using zinc sheets as both the negative and positive electrodes, with Waterman glass fiber filter paper as the separator, and 150 μL of electrolyte added. After standing for 6 hours, the current density was 1 mA / cm². 2 The discharge capacity is 1mAh / cm. 2 The long-cycle stability of the battery was tested under the charge and discharge mechanism.

[0074] Using zinc sheet as the negative electrode, Na2V6O 16 • 3H₂O(NVO₄) is used as the positive electrode, with a positive electrode loading of 4 mg / cm³. 2The N / P ratio was adjusted to 3.0, and Waterman glass fiber filter paper was used as the separator. 150 μL of the electrolyte prepared above was added, and a Zn / NVO full cell was assembled. After standing for 6 hours, the long-term cycle stability of the full cell was tested under the conditions of a test voltage range of 0.3-1.5V, a charge / discharge current of 1A / g, and 10,000 cycles.

[0075] Battery test results are as follows Figures 5-8 As shown, the battery test results of Example 1 and Comparative Example 1 are analyzed:

[0076] Figure 5 This is a schematic diagram illustrating the deposition process of the electrolyte additive in Comparative Example 1 and Example 1 on a zinc anode. When graphene quantum dots are absent, due to the inhomogeneity of the interfacial electric field, zinc ions undergo uneven nucleation; the tip effect exacerbates the uneven deposition, resulting in the growth of irregular dendrites. Graphene quantum dots, with their numerous electronegative groups, can adsorb zinc ions and further uniformly co-deposit on the anode surface; the graphene quantum dots deposited on the anode surface can continue to induce preferential deposition of zinc ions along the (002) crystal plane parallel to the electrode surface, fundamentally suppressing the formation of zinc dendrites.

[0077] Figure 6 For the symmetrical cells of Comparative Example 1 and Example 1 of this invention, at 1 mA / cm 2 SEM image of the morphology after 10 cycles. (Example) Figure 5 a) In Comparative Example 1, zinc ions are deposited unevenly and grow vertically on the negative electrode surface, with obvious dendrite formation. For example... Figure 5 b. In Example 1, zinc ions are deposited uniformly and densely on the negative electrode surface and grow parallel to the electrode surface without obvious dendrite formation.

[0078] Figure 7 For the symmetrical cells of Comparative Example 1 and Example 1 of this invention, at 1 mA / cm 2 The time-voltage curve below. For example... Figure 6 a. In Comparative Example 1, the symmetrical cell short-circuited after 54 hours, and the voltage curve fluctuated significantly. For example... Figure 6 b. The symmetrical battery in Example 1 can operate stably for 1450 hours, demonstrating excellent cycle stability.

[0079] Figure 8 For Comparative Example 1 and Example 1 of the present invention, the full cell has an N / P ratio of 3.0 and a positive electrode loading of 4 mg / cm³. 2 The cycle count-specific capacity curves are shown below. Comparative Example 1 exhibits rapid capacity decay and significant fluctuations after 250 cycles. Example 1 demonstrates excellent cycle stability and high energy density, maintaining 94.7% capacity retention after 620 cycles while achieving an energy density of 107.7 Wh / kg.

[0080] In summary, the embodiments of this invention utilize graphene quantum dots rich in nitrogen, oxygen, and sulfur. These quantum dots not only adsorb zinc ions for uniform co-deposition on the negative electrode surface but also induce preferential deposition of zinc ions along the (002) crystal plane parallel to the electrode surface, fundamentally suppressing the formation of zinc dendrites. This ultimately achieves a zinc metal negative electrode with high positive electrode loading and stable cycling at a low N / P ratio. Furthermore, graphene quantum dots are lightweight, do not affect the battery's energy density, exhibit stable performance, do not produce side reactions, and can be recycled during charge and discharge, achieving long-term performance improvement. In addition, the synthesis method of this graphene quantum dot is simple, the process is easy to operate, has good controllability, low raw material cost, and is environmentally friendly and pollution-free, making it suitable for large-scale production.

[0081] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An application of graphene quantum dots as an electrolyte additive in zinc-ion batteries, characterized in that, The surface of the graphene quantum dots has electronegative groups containing nitrogen, sulfur, and oxygen. The electronegative groups include OH, NH, C=O, C=C, CN, CO, C=S, and CS; The graphene quantum dots have a spherical microstructure with a diameter of 2-4 nm and a lattice spacing of 0.19-0.22 nm. The graphene quantum dots are prepared by the following steps: using hydroxy acids and nitrogen and sulfur sources as raw materials, a condensation reaction occurs during hydrothermal process; The molar ratio of the hydroxy acid to the nitrogen and sulfur source is 1:1 to 5. The hydroxy acid includes at least one of citric acid, tartaric acid, malic acid, and lactic acid, and the concentration of the hydroxy acid is 0.02 mol / L to 0.5 mol / L. The nitrogen and sulfur source includes at least one of thiourea and sulfonamide.

2. The application according to claim 1, characterized in that, The polycondensation reaction is carried out under stirring conditions, with a stirring speed of 100 rpm to 1500 rpm; The hydrothermal polycondensation reaction occurs at temperatures ranging from 120℃ to 200℃ and takes 3 to 5 hours.

3. The application according to claim 1, characterized in that, After the polycondensation reaction is completed, the pH is adjusted using an alkaline reagent and then purified by dialysis. The alkaline reagent is an alkaline solution, and the solute in the alkaline solution includes at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate, and the concentration of the alkaline solution is 0.5 mol / L to 2 mol / L. Adjust the pH to 5.5-6.5; Dialysis was performed using dialysis bags with a molecular weight cutoff of 3000-4000 Daltons, and the dialysis time was 8-16 hours. After dialysis purification, the product is freeze-dried at a vacuum of 1 Pa to 30 Pa, a cold trap temperature of -60°C to -90°C, and a time of 24 to 72 hours.

4. The application according to claim 1, characterized in that, The electrolyte comprises zinc salt, the concentration of which is 1 mol / L to 3 mol / L, and the amount of graphene quantum dots added to the electrolyte of the zinc-ion battery is 0.01 wt% to 0.5 wt%. The zinc salt includes at least one of zinc sulfate, zinc chloride, zinc trifluoromethanesulfonate, and zinc bis(trifluoromethanesulfonyl)imide.

5. The application according to claim 4, characterized in that, The amount of graphene quantum dots added to the electrolyte of the zinc-ion battery is 0.02wt~0.1wt.

6. A zinc-ion battery electrolyte, characterized in that, Its components include zinc salts and the graphene quantum dots used in any one of claims 1 to 5.

7. The zinc-ion battery electrolyte according to claim 6, characterized in that, The concentration of the zinc salt in the electrolyte is 1 mol / L to 3 mol / L, and the amount of graphene quantum dots added to the electrolyte of the zinc-ion battery is 0.01 wt to 0.5 wt.

8. The zinc-ion battery electrolyte according to claim 7, characterized in that, The amount of graphene quantum dots added to the electrolyte of the zinc-ion battery is 0.02wt~0.1wt.

9. A zinc-ion battery, characterized in that, It includes the electrolyte as described in any one of claims 6-8.

10. The zinc-ion battery according to claim 9, characterized in that, The zinc-ion battery is a Zn / Zn symmetrical battery, which uses a zinc sheet as the negative electrode and a zinc sheet as the positive electrode, Waterman glass fiber filter paper as the separator, and is assembled by adding the electrolyte. Alternatively, the zinc-ion battery is a Zn / NVO full cell, which uses a zinc sheet as the negative electrode and Na2V6O. 16 • 3H₂O (NVO) is used as the positive electrode, with a positive electrode loading of 3~5 mg / cm³. 2 The N / P ratio is adjusted to 2.5~3.5, and the electrolyte is added dropwise to form the electrolyte.

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