Aqueous electrolyte of zinc-sulfur battery as well as preparation method and application of aqueous electrolyte

Abstract

The invention belongs to the technical field of batteries, and relates to an aqueous electrolyte of a zinc-sulfur battery as well as a preparation method and application of the aqueous electrolyte. The aqueous electrolyte is prepared from zinc salt, phosphomolybdate, N-formyl piperidine and water, in the aqueous electrolyte, the mass fraction of the phosphomolybdate is 0.01-0.2% w / w, and the volume fraction of the N-formyl piperidine is 5-20% v / v. The phosphomolybdate and the N-formyl piperidine are added into the aqueous electrolyte of the zinc-sulfur battery to serve as electrolyte additives, so that cooperative regulation and control of a positive electrode and a negative electrode can be achieved, and preparation of the aqueous zinc-sulfur battery with high electrochemical performance is expected to be achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries and relates to an aqueous electrolyte for a zinc-sulfur battery and a preparation method and application thereof. Background Art

[0002] With the rapid development of the global economy and the continuous growth of population, the global energy demand has shown a rising trend. Lithium-ion batteries have become the main force in the energy storage market due to their remarkable characteristics such as green, clean, and stable cycles. However, the further development of lithium-ion batteries faces severe challenges: the distribution of lithium resources on the earth is extremely uneven, mainly concentrated in a few countries and regions; and with the continuous expansion of the lithium-ion battery market, the demand for lithium resources is increasing day by day, resulting in lithium resources becoming increasingly scarce and prices rising. The limited resources and high prices have seriously restricted the widespread application of lithium-ion batteries in the field of large-scale energy storage.

[0003] In comparison, aqueous zinc-ion batteries (AZIBs) have many advantages as a potential alternative technology in the field of large-scale energy storage due to their abundant resources, low cost, high safety and environmental protection, making them a highly potential alternative technology in the field of large-scale energy storage. Among the cathode materials currently developed and applied to AZIBs, such as manganese-based compounds, vanadium-based compounds, Prussian blue and organic compounds, all have the problem of low theoretical specific capacity, and their values ​​are all less than 400 mAh / g. This low theoretical specific capacity limits the energy density of the battery and cannot meet the current market's urgent demand for high-energy-density batteries, especially in terms of long driving range of electric vehicles and high energy storage capacity of large energy storage power stations. The limitations of these traditional cathode materials are becoming more and more obvious. In contrast, sulfur cathode materials with conversion reactions stand out and have many significant advantages. First, from an electrochemical point of view, the sulfur cathode benefits from the double electron transfer mechanism during the reaction process and has an extremely high theoretical capacity of about 1675mAh / g. High theoretical capacity means that the battery can store more electrical energy at the same mass or volume, thereby significantly improving the battery's energy density and meeting the market's demand for high-energy-density batteries. Secondly, from the perspective of cost and environmental protection, sulfur is abundant in nature, widely available, and relatively cheap, which makes sulfur cathode materials have obvious cost advantages when used on a large scale. At the same time, sulfur itself is safe and non-toxic, and is environmentally friendly during production and use, and will not cause environmental problems such as heavy metal pollution.

[0004] Although zinc-sulfur batteries have great potential for being green, low-cost, and having high energy density, there are still many problems that need to be solved in aqueous zinc-sulfur batteries. On the positive electrode side, the conversion reaction kinetics of the sulfur positive electrode are slow, which limits the electrode reaction rate during the battery charging and discharging process, resulting in low battery charging and discharging efficiency and inability to achieve rapid charging and discharging, which seriously affects the actual application performance of the battery. On the zinc negative electrode side, the hydrogen evolution side reaction is more serious. During the battery charging and discharging process, water is reduced on the negative electrode surface to produce hydrogen, which not only consumes the water in the electrolyte and reduces the coulomb efficiency of the battery, but also may cause the internal pressure of the battery to increase, causing safety problems. In addition, there is also the problem of dendrite growth at the zinc negative electrode during the cycle. As the number of charge and discharge cycles increases, zinc dendrites gradually grow and may pierce the diaphragm, causing a short circuit in the battery, greatly shortening the battery's cycle life and safety. These problems have seriously hindered the commercialization of aqueous zinc-sulfur batteries. Therefore, it is urgent to further develop aqueous zinc-sulfur batteries by regulating the positive and negative electrodes. Summary of the invention

[0005] In order to solve the above problems existing in the prior art, the purpose of the present invention is to provide an aqueous electrolyte for a zinc-sulfur battery and a preparation method and application thereof, so as to overcome the shortcomings of the prior art.

[0006] One object of the present invention is achieved by the following technical solutions: An aqueous electrolyte for a zinc-sulfur battery comprises a zinc salt, a phosphomolybdate, N-formylpiperidine and water; in the aqueous electrolyte, the mass fraction of the phosphomolybdate is 0.01-0.2% w / w, and the volume fraction of the N-formylpiperidine is 5-20% v / v.

[0007] Preferably, the zinc salt is zinc trifluoromethanesulfonate and / or zinc sulfate.

[0008] Preferably, the phosphomolybdate is one or more of ammonium phosphomolybdate, sodium phosphomolybdate, and potassium phosphomolybdate.

[0009] Preferably, the concentration of zinc salt in the aqueous electrolyte is 0.5-5 mol / L.

[0010] Preferably, the mass fraction of phosphomolybdate is 0.03-0.1% w / w.

[0011] Preferably, the volume fraction of N-formylpiperidine is 8-15% v / v.

[0012] The second object of the present invention is achieved by the following technical solutions: A method for preparing an aqueous electrolyte for a zinc-sulfur battery comprises the following steps: Dissolve zinc salt in water and stir until the zinc salt is dissolved to obtain a mixed solution; add phosphomolybdate and N-formylpiperidine to the mixed solution in sequence and stir evenly to obtain an aqueous electrolyte.

[0013] The third object of the present invention is achieved by the following technical solutions: An aqueous zinc-sulfur battery comprises a positive electrode material, a negative electrode material, a diaphragm and the aqueous electrolyte.

[0014] Preferably, the positive electrode material comprises a positive electrode active material, a conductive agent and a binder, wherein the positive electrode active material comprises sulfur or sulfur carbon.

[0015] Preferably, the negative electrode material is zinc foil.

[0016] The fourth object of the present invention is achieved by the following technical solutions: A method for preparing an aqueous zinc-sulfur battery comprises the following steps: The positive electrode materials are mixed and ground evenly, coated on a current collector, and dried to obtain a positive electrode sheet; Dissolving zinc salt in water and stirring until the zinc salt is dissolved to obtain a mixed solution; adding phosphomolybdate and N-formylpiperidine to the mixed solution in sequence and stirring evenly to obtain an aqueous electrolyte; The positive electrode sheet, zinc metal, aqueous electrolyte and separator are assembled into a battery.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention adds phosphomolybdate and N-formylpiperidine as electrolyte additives to the aqueous electrolyte of the zinc-sulfur battery to achieve coordinated regulation of the positive and negative electrodes. On the positive electrode, phosphomolybdate reduces the conversion energy barrier and promotes the conversion reaction; on the negative electrode, N-formylpiperidine can promote Zn 2+ The uniform deposition of ZnS can inhibit the growth of dendrites. Therefore, this synergistic regulation strategy is expected to achieve aqueous ZnS batteries with high electrochemical performance.

[0018] 2. The zinc-sulfur battery prepared using the electrolyte of the present invention has excellent electrochemical properties. At a current density of 0.5 A / g, the specific capacity of the battery can reach more than 1480 mAh / g. At a current density of 5 A / g, after 300 cycles, the battery can still maintain more than 70% of its capacity.

[0019] 3. By changing the electrolyte composition, the present invention is expected to improve the electrochemical performance of aqueous zinc-sulfur batteries, achieve the preparation of higher-performance aqueous zinc-sulfur batteries, and expand their application range in large-scale energy storage, electric vehicles and portable devices. DETAILED DESCRIPTION

[0020] Hereinafter, embodiments will be described in detail with respect to the aqueous electrolyte of the zinc-sulfur battery of the present invention, and the preparation method and application thereof. However, these embodiments are exemplary and the present disclosure is not limited thereto.

[0021] In some embodiments of the present invention, an aqueous electrolyte for a zinc-sulfur battery is provided, comprising a zinc salt, a phosphomolybdate, N-formylpiperidine and water.

[0022] The present invention adds phosphomolybdate and N-formylpiperidine as electrolyte additives to the aqueous electrolyte of the zinc-sulfur battery to improve the conductivity of the electrolyte, reduce the contact resistance between the electrode and the electrolyte, and improve the cycle stability of the zinc-sulfur battery at high current density. Specifically, phosphomolybdate can be specifically combined with the active substance, and can be used as a catalyst to reduce the conversion energy barrier of the active substance and inhibit the generation of by-products, thereby improving the conversion kinetics and cycle reversibility of the sulfur positive electrode. As an organic compound, the oxygen atoms in the molecules of N-formylpiperidine are expected to be affinity with the surface of the zinc metal negative electrode, thereby forming a layer of hydrophobic solid electrolyte interface film. With the protection of this film, the zinc metal negative electrode can reduce contact with active water molecules, thereby inhibiting the occurrence of hydrogen evolution reaction. Secondly, N-formylpiperidine is expected to participate in the Zn 2+ Solvation structure, replacing part of the water molecules in the solvation shell, the regulated solvation structure guides Zn 2+ It is uniformly deposited on the negative electrode, thereby inhibiting the growth of negative electrode dendrites.

[0023] Preferably, in the aqueous electrolyte, the mass fraction of phosphomolybdate is 0.01-0.2% w / w. Too little addition of phosphomolybdate has no significant effect, while too much addition increases the cost on the one hand, and also causes some side reactions on the other hand, which reduces the capacity retention of the battery. The mass fraction of phosphomolybdate is further preferably 0.03-0.1% w / w, for example, it can be any value among 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, and 0.1 mol / L.

[0024] Preferably, in the aqueous electrolyte, the volume fraction of N-formyl piperidine is 5-20% v / v. Addition of too much N-formyl piperidine may excessively change the composition and structure of the solvation sheath, which may reduce the battery capacity and cycle life. The volume fraction of N-formyl piperidine is further preferably 8-15% v / v, for example, it can be any value among 8, 9, 10, 11, 12, 13, 14, 15% v / v.

[0025] Preferably, the concentration of zinc salt in the aqueous electrolyte is 0.5-5 mol / L, more preferably 1-3 mol / L. For example, it can be any value among 1, 1.2, 1.5, 1.8, 2, 2.3, 2.5, 2.7, 3 mol / L.

[0026] Preferably, the zinc salt is zinc trifluoromethanesulfonate (Zn(CF3SO3)2) and / or zinc sulfate. Preferably, the phosphomolybdate is one or more of ammonium phosphomolybdate, sodium phosphomolybdate, and potassium phosphomolybdate.

[0027] In some embodiments of the present invention, an aqueous zinc-sulfur battery is provided, comprising a positive electrode material, a negative electrode material, a separator and the aqueous electrolyte.

[0028] Preferably, the positive electrode material comprises a positive electrode active material, a conductive agent and a binder, wherein the positive electrode active material comprises sulfur or sulfur-carbon, etc. Sulfur-carbon is a composite of sulfur and carbon material.

[0029] The conductive agent is not particularly limited, and any conductive agent that can be used in a battery can be used, and can be listed as one or more of activated carbon, carbon nanotubes, acetylene black, and graphite. The binder is also not particularly limited, and any binder that can be used in a battery can be used, and can be listed as one or more of polyvinylidene fluoride (PVDF), styrene rubber, nitrile rubber, styrene butadiene rubber (SBR), polyacrylamide (PAA), and polytetrafluoroethylene (PTFE).

[0030] In the positive electrode material, the mass fractions of the positive electrode active material, the conductive agent and the binder are 60-90%, 5-20% and 5-20% respectively.

[0031] Preferably, the negative electrode material is zinc foil.

[0032] Preferably, the diaphragm is a polyethylene diaphragm, a polypropylene diaphragm or glass fiber.

[0033] In some embodiments of the present invention, a method for preparing an aqueous zinc-sulfur battery is provided, comprising the following steps: The positive electrode materials are mixed and ground evenly, coated on a current collector, and dried to obtain a positive electrode sheet; Dissolving zinc salt in water and stirring until the zinc salt is dissolved to obtain a mixed solution; adding phosphomolybdate and N-formylpiperidine to the mixed solution in sequence and stirring evenly to obtain an aqueous electrolyte; The positive electrode sheet, zinc metal, aqueous electrolyte and separator are assembled into a battery.

[0034] Preferably, the current collector is one of carbon paper, carbon cloth, nickel foam, metal foil and the like.

[0035] The technical scheme of the present invention is further described below by specific embodiments. It should be understood that the specific embodiments described herein are only used to help understand the present invention and are not intended to be used for specific limitations of the present invention. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used raw materials in the art, and the methods used in the embodiments are all conventional methods in the art.

[0036] The potassium phosphomolybdate used in the following examples and comparative examples is homemade, and the steps are as follows: dissolving phosphomolybdic acid in water to form a 3 mg / mL phosphomolybdic acid solution; weighing KCl and dissolving it in water to form a 6 mg / mL KCl solution; adding an equal volume of the phosphomolybdic acid solution to the KCl solution and stirring evenly; then transferring the mixed solution to a hydrothermal reactor, reacting at 100° C. for 10 hours, and finally centrifugally washing and collecting with deionized water and ethanol, and drying to obtain potassium phosphomolybdate.

[0037] Example 1

[0038] The aqueous electrolyte provided in this embodiment is composed of Zn(CF3SO3)2, potassium phosphomolybdate, N-formylpiperidine, and water, wherein the concentration of Zn(CF3SO3)2 is 2 mol / L, the mass fraction of potassium phosphomolybdate is 0.05%w / w, and the volume fraction of N-formylpiperidine is 10%v / v.

[0039] Weigh each raw material according to the raw material addition amount, then dissolve Zn(CF3SO3)2 in water, and continue stirring at 400rpm with a magnetic stirrer at room temperature until the solution is completely clear and transparent without precipitation, to obtain a mixed solution; potassium phosphomolybdate and N-formylpiperidine are added to the mixed solution in sequence, and continue stirring under a magnetic stirrer until the electrolyte additive is completely dissolved, to obtain the aqueous electrolyte.

[0040] Example 2

[0041] The difference between Example 2 and Example 1 is that the mass fraction of potassium phosphomolybdate in Example 2 is 0.03% w / w, and the others are the same as Example 1.

[0042] Example 3

[0043] The difference between Example 3 and Example 1 is that the mass fraction of potassium phosphomolybdate in Example 3 is 0.08% w / w, and the others are the same as Example 1.

[0044] Example 4

[0045] The difference between Example 4 and Example 1 is that the volume fraction of N-formylpiperidine in Example 4 is 8% v / v, and the others are the same as Example 1.

[0046] Example 5

[0047] The difference between Example 5 and Example 1 is that the volume fraction of N-formylpiperidine in Example 5 is 15% v / v, and the others are the same as Example 1.

[0048] Example 6

[0049] The aqueous electrolyte provided in this embodiment is composed of zinc sulfate, potassium phosphomolybdate, N-formylpiperidine, and water, wherein the concentration of zinc sulfate is 3 mol / L, the mass fraction of potassium phosphomolybdate is 0.07% w / w, and the volume fraction of N-formylpiperidine is 12% v / v.

[0050] The preparation method of the aqueous electrolyte is the same as that of Example 1.

[0051] Comparative Example 1 The aqueous electrolyte of Comparative Example 1 consists of Zn(CF3SO3)2 and water, wherein the concentration of Zn(CF3SO3)2 is 2 mol / L.

[0052] Dissolve Zn(CF3SO3)2 in water and continue stirring at room temperature using a magnetic stirrer at 400 rpm until the solution is completely clear and transparent without precipitation, thereby obtaining an aqueous electrolyte.

[0053] Comparative Example 2 The aqueous electrolyte of Comparative Example 2 consists of Zn(CF3SO3)2, N-formylpiperidine and water, wherein the concentration of Zn(CF3SO3)2 is 2 mol / L and the volume fraction of N-formylpiperidine is 10% v / v.

[0054] Weigh each raw material according to the amount of raw material added, then dissolve Zn(CF3SO3)2 in water, and continue stirring at 400rpm with a magnetic stirrer at room temperature until the solution is completely clear and transparent without precipitation, to obtain a mixed solution; add N-formylpiperidine to the mixed solution, and continue stirring under a magnetic stirrer until the electrolyte additive is completely dissolved, to obtain an aqueous electrolyte.

[0055] Comparative Example 3 The aqueous electrolyte of Comparative Example 3 consists of Zn(CF3SO3)2, potassium phosphomolybdate and water, wherein the concentration of Zn(CF3SO3)2 is 2 mol / L and the mass fraction of potassium phosphomolybdate is 0.05% w / w.

[0056] Weigh each raw material according to the amount of raw material added, then dissolve Zn(CF3SO3)2 in water, and continue stirring at 400rpm with a magnetic stirrer at room temperature until the solution is completely clear and transparent without precipitation, to obtain a mixed solution; add potassium phosphomolybdate to the mixed solution, and continue stirring under a magnetic stirrer until the electrolyte additive is completely dissolved, to obtain an aqueous electrolyte.

[0057] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that the mass fraction of potassium phosphomolybdate in Comparative Example 4 is 0.3% w / w, and the others are the same as Example 1.

[0058] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that the volume fraction of N-formylpiperidine in Comparative Example 5 is 30% v / v, and the others are the same as Example 1.

[0059] The electrolytes of Examples 1-6 and Comparative Examples 1-5 are used to assemble the battery, and the specific steps are as follows: (1) 50% sulfur carbon powder, acetylene black and polyvinylidene fluoride are uniformly mixed in a mass ratio of 8:1:1, alcohol is added, and the mixture is fully ground and stirred to obtain a positive electrode slurry, and the slurry is scraped onto carbon paper, dried and baked to obtain a positive electrode sheet; (2) Assemble the positive electrode, zinc metal, aqueous electrolyte and separator glass fiber into a button battery.

[0060] The button cells composed of the electrolytes of Examples 1-6 and Comparative Examples 1-5 are respectively marked as button cells 1-11.

[0061] The above battery was subjected to constant current charge and discharge test, and its specific capacity was measured at a current density of 0.5 A / g; the cycle capacity retention rate was tested after 300 cycles at a current density of 5 A / g; the experimental results are shown in Table 1: Table 1 Capacity and cycle stability of button batteries 1-11

[0062] As can be seen from Table 1, the cycle stability of battery 7 is poor when using an electrolyte composed only of zinc salts, and a single zinc salt electrolyte cannot provide sufficient electrochemical stability. When using an electrolyte composed only of N-formylpiperidine as an additive, the capacity retention rate of battery 8 after 300 cycles is very low, which shows that the addition of N-formylpiperidine alone does not improve the battery cycle performance much; when using an electrolyte composed only of phosphomolybdate as an additive, the capacity retention rate of battery 9 is low, indicating that although the addition of a single phosphomolybdate has a certain improvement on the battery performance, the effect is very limited. The battery assembled using the electrolyte of Examples 1-6 shows excellent specific capacity and cycle stability, and the capacity retention rate still reaches more than 70% after 300 cycles at a current density of 5A / g.

[0063] It can be seen from the experimental data of button batteries 1, 10, and 11 that when the amount of phosphomolybdate and N-formylpiperidine added to the electrolyte is too much, the capacity and capacity retention rate of the battery will be reduced.

[0064] The various aspects, embodiments, and features of the present invention should be considered to be illustrative in all aspects and not limiting of the present invention, the scope of which is defined solely by the claims. Other embodiments, modifications, and uses will be apparent to those skilled in the art without departing from the spirit and scope of the claimed invention.

[0065] In the preparation method of the present invention, the order of each step is not limited to the order listed. For those skilled in the art, without creative work, the order of each step is also within the protection scope of the present invention. In addition, two or more steps or actions can be performed simultaneously.

[0066] Finally, it should be noted that the specific embodiments described herein are merely examples of the present invention, and are not intended to limit the implementation methods of the present invention. A person skilled in the art of the present invention may make various modifications or supplements to the specific embodiments described, or replace them in a similar manner. It is not necessary and impossible to provide all examples of all implementation methods here. However, these obvious changes or modifications derived from the essential spirit of the present invention still fall within the scope of protection of the present invention, and interpreting them as any additional limitation is contrary to the spirit of the present invention.

Claims

1. An aqueous electrolyte for a zinc-sulfur battery, characterized in that: The invention comprises zinc salt, phosphomolybdic acid salt, N-formylpiperidine and water; in the aqueous electrolyte, the mass fraction of phosphomolybdic acid salt is 0.01-0.2% w / w, and the volume fraction of N-formylpiperidine is 5-20% v / v.

2. The aqueous electrolyte according to claim 1, characterized in that The zinc salt is zinc trifluoromethanesulfonate and / or zinc sulfate.

3. The aqueous electrolyte according to claim 1, characterized in that The phosphomolybdate is one or more of ammonium phosphomolybdate, sodium phosphomolybdate and potassium phosphomolybdate.

4. The aqueous electrolyte according to claim 1, characterized in that In the aqueous electrolyte, the concentration of zinc salt is 0.5-5 mol / L.

5. The aqueous electrolyte according to claim 1, characterized in that: The mass fraction of phosphomolybdate is 0.03~0.1%w / w.

6. The aqueous electrolyte according to claim 1, characterized in that The volume fraction of N-formylpiperidine is 8-15% v / v.

7. The method for preparing an aqueous electrolyte for a zinc-sulfur battery according to claim 1, characterized in that: The following steps are involved: Dissolve zinc salt in water and stir until the zinc salt is dissolved to obtain a mixed solution; add phosphomolybdate and N-formylpiperidine to the mixed solution in sequence and stir evenly to obtain an aqueous electrolyte.

8. An aqueous zinc-sulfur battery, characterized in that: The invention comprises a positive electrode material, a negative electrode material, a separator and the aqueous electrolyte as claimed in claim 1.

9. The aqueous zinc-sulfur battery according to claim 8, characterized in that: The positive electrode material comprises a positive electrode active material, a conductive agent and a binder, and the positive electrode active material comprises sulfur or sulfur carbon; The negative electrode material is zinc foil.

10. The method for preparing an aqueous zinc-sulfur battery according to claim 8, characterized in that: The following steps are involved: The positive electrode materials are mixed and ground evenly, coated on a current collector, and dried to obtain a positive electrode sheet; Dissolving zinc salt in water and stirring until the zinc salt is dissolved to obtain a mixed solution; adding phosphomolybdate and N-formylpiperidine to the mixed solution in sequence and stirring evenly to obtain an aqueous electrolyte; The positive electrode sheet, zinc metal, aqueous electrolyte and separator are assembled into a battery.

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