Gel electrolyte, method for preparing gel electrolyte, and zinc-air battery

Abstract

The application relates to the technical field of zinc-air batteries, and discloses a gel electrolyte, a preparation method of the gel electrolyte and a zinc-air battery, wherein the gel electrolyte comprises the following components: a water-soluble monomer, water, an electrolyte salt, a first electrolyte additive, a crosslinking agent and an initiator; the first electrolyte additive comprises dipropylene glycol and zinc trifluoromethyl sulfonate. Through optimization of the composition and the preparation method of the gel electrolyte, the application effectively solves the key technical problems in the zinc-air battery, and improves the performance and the cycle life of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of zinc-air batteries, in particular to a gel electrolyte, a preparation method of the gel electrolyte and a zinc-air battery. BACKGROUND

[0002] With the continuous growth of global energy demand and the serious environmental problems and energy crisis caused by fossil energy, it is urgent to develop efficient, environmentally friendly and sustainable new energy technologies. In this context, zinc-air batteries have attracted widespread attention from the scientific community and industry due to their high energy density, high safety performance, environmental characteristics and relatively low cost.

[0003] Quasi-solid-state zinc-air batteries mainly include three parts: air cathode, zinc anode and gel electrolyte. In an alkaline environment, the working principle of the battery is based on a series of electrochemical reactions. During discharge, metallic zinc (Zn) acts as the negative electrode, loses electrons and is oxidized to zinc ions (Zn²⁺); at the same time, oxygen (O2) in the air diffuses to the air cathode and undergoes an oxygen reduction reaction (ORR) there to generate hydroxyl ions (OH⁻); and during charging, the air cathode undergoes an oxygen evolution reaction (OER), i.e. hydroxyl ions lose electrons and release oxygen.

[0004] Among them, there are still some problems to be solved in the existing technology of zinc-air batteries. One of the primary problems is dendrite formation. Due to the unevenness of the initial substrate surface of the zinc anode, the electric field strength increases at locations with higher curvature, and these sites have relatively high activity. Therefore, zincate is preferentially reduced at these low-energy sites and attracts more zincate accumulation. With the progress of charge and discharge cycles, this accumulation effect gradually intensifies, eventually forming dendrites, which seriously affects the performance and life of the battery.

[0005] Another important problem is the hydrogen evolution reaction. On the surface of the zinc anode, in addition to the main zinc oxidation reaction, other competitive electrochemical reactions may also occur. Among them, the hydrogen evolution reaction is a non-negligible side reaction. When hydrogen ions in the electrolyte solution obtain enough electrons, they will combine to form hydrogen gas. This reaction is particularly significant in zinc-air batteries because it competes with zinc oxidation for the same electrons. The hydrogen evolution reaction not only reduces the coulombic efficiency of the battery, but also can cause damage to the structure and performance of the battery.

[0006] In summary, although quasi-solid-state zinc-air batteries have broad application prospects, dendrite problems and hydrogen evolution problems are still key factors that restrict their further development and application. Therefore, research on technical innovations and solutions to these problems has important practical significance and scientific value. SUMMARY

[0007] The gel electrolyte, the preparation method and the application thereof overcome the deficiencies in the prior art.

[0008] The present application is achieved by the following technical solutions.

[0009] The gel electrolyte comprises the following components: a water-soluble monomer, water, an electrolyte salt, a first electrolyte additive, a crosslinking agent and a thermal initiator.

[0010] The first electrolyte additive comprises dipropylene glycol and zinc trifluoromethyl sulfonate.

[0011] Further, the mass ratio of the dipropylene glycol, the zinc trifluoromethyl sulfonate and the water is (1-3):(6-8):10.

[0012] Further, the gel electrolyte further comprises a second electrolyte additive, and the second electrolyte additive comprises zinc acetate.

[0013] Further, the water-soluble monomer is an acrylamide monomer.

[0014] Further, the electrolyte salt is at least one of potassium hydroxide, sodium hydroxide and lithium hydroxide.

[0015] Further, the crosslinking agent is at least one of methylene bisacrylamide, N-methylol acrylamide and acrylamide-PEG-hydroxyl.

[0016] Further, the initiator is at least one of potassium persulfate, ammonium persulfate, azobisisobutyronitrile and azobisisoheptyl cyanide.

[0017] Further, the gel electrolyte further comprises a third electrolyte additive, and the third electrolyte additive is modified porous zinc oxide nanorod.

[0018] The present application further provides a preparation method of the gel electrolyte, comprising the following steps.

[0019] S1: the first electrolyte additive is added into the water in proportion, and first stirring is performed to obtain a first mixed solution;

[0020] S2: the water-soluble monomer is added into the first mixed solution in proportion, and second stirring is performed; the crosslinking agent and the initiator are continuously added, and third stirring is performed to obtain a gel precursor solution;

[0021] S3: the gel precursor solution is injected into a mold, and drying is performed under certain conditions; then the mold containing the gel is immersed into an electrolyte salt solution, and soaking is performed; then the gel is taken out from the mold to obtain the gel electrolyte.

[0022] Further, the mass concentration of the water-soluble monomer in the mixed solution in the S2 step is 0.25 g / mL to 0.3 g / mL.

[0023] Further, in the S2 step, the third stirring is to stir the crosslinking agent and the initiator until they are fully dissolved.

[0024] Further, the drying condition in the S3 step is 40°C to 85°C for 4 hours to 12 hours.

[0025] Further, the molar concentration of the electrolyte salt solution is 2 mol / L to 8 mol / L.

[0026] Further, zinc acetate is added in the preparation process of the electrolyte salt solution in the S3 step, and the molar concentration of the zinc acetate in the electrolyte salt solution is 0.1 mol / L to 0.5 mol / L. The zinc acetate is a weak acid and a strong base salt, and can hydrolyze to generate hydroxyl ions (OH⁻) in the aqueous solution, which helps to maintain the alkaline environment of the gel electrolyte during the soaking process. Further, the zinc acetate can affect the deposition behavior on the surface of the zinc negative electrode, which helps to form a more uniform zinc deposition layer, thereby reducing the formation of dendrites. Meanwhile, the zinc deposition layer can reduce the direct contact between the zinc negative electrode and the electrolyte, thereby reducing the hydrogen evolution reaction.

[0027] Further, in the S1 step, the first electrolyte additive and the third electrolyte additive are added into the water in a certain proportion, and the first mixed solution is obtained through the first stirring.

[0028] Further, the third electrolyte additive is modified porous zinc oxide nanorods, and the mass ratio of the modified porous zinc oxide nanorods to water is (0.05 to 0.2) to 10.

[0029] Further, the modified porous zinc oxide nanorods are prepared by the following steps:

[0030] The zinc acetate ethanol solution and the oxalic acid dihydrate ethanol solution are mixed uniformly in a certain proportion to obtain a second mixed solution;

[0031] The second mixed solution is placed in a reaction kettle and reacted at 70 to 90°C for 4 to 6 hours to obtain a reaction product. The reaction product is washed to neutral with water or ethanol, and then dried;

[0032] The dried reaction product is annealed at 400 to 500°C for 100 to 180 minutes to obtain the porous zinc oxide nanorods.

[0033] The porous zinc oxide nanorods are dispersed in a PEG-2000 solvent, filtered and dried after ultrasonic treatment to obtain modified porous zinc oxide nanorods.

[0034] Further, the gel electrolyte is a gel electrolyte layer, and the thickness of the gel electrolyte layer is 1-5 mm.

[0035] The gel electrolyte prepared by the application can be applied to a zinc-air battery to improve the electrochemical performance of the zinc-air battery.

[0036] Compared with the prior art, the application has at least the following advantages:

[0037] 1. The application adds specific first electrolyte additives, i.e., dipropylene glycol and zinc trifluoromethyl sulfonate, to the gel electrolyte, because dendrites are easy to form under uneven electric fields, and the synergistic effect of dipropylene glycol and zinc trifluoromethyl sulfonate can effectively regulate the electric field distribution on the surface of the zinc negative electrode, reduce the problem of increased electric field strength caused by uneven surface, thereby inhibiting the growth of dendrites, and thus improving the stability and cycle life of the zinc-air battery.

[0038] 2. The application uses dipropylene glycol as the first electrolyte additive, which has the functions of improving the performance of the electrolyte and inhibiting the growth of dendrites, and also plays the role of a plasticizer, which can improve the elasticity and flexibility of the gel electrolyte, help to improve the mechanical strength of the gel electrolyte, so that it is not easy to break, thereby enhancing the stability and durability of the gel electrolyte.

[0039] 3. The stability of the electrolyte is enhanced: the application selects specific water-soluble monomers, electrolyte salts, first electrolyte additives, cross-linking agents and initiators, and the synergistic effect of these components makes the gel electrolyte have excellent electrical conductivity, mechanical strength and chemical stability. This helps to improve the working performance and long-term stability of the battery under high current density. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 The charge-discharge cycle curve of Example 1 of the application;

[0041] Figure 2 The charge-discharge cycle curve of Example 3 of the application. DETAILED DESCRIPTION

[0042] In order to facilitate the understanding of the application, the application will be described more fully below with reference to the related drawings. The preferred embodiments of the application are shown in the drawings. However, the application can be realized in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the application more thorough and comprehensive.

[0043] Example 1

[0044] S1: dipropylene glycol and zinc trifluoromethyl sulfonate were added into pure water (the mass ratio of dipropylene glycol, zinc trifluoromethyl sulfonate and water was 2.5:7.5:10), first stirring was performed to obtain a first mixed solution;

[0045] S2: 2.5 g of acrylamide was added into 10 ml of the first mixed solution, second stirring was performed, 2.5 mg of methylene bisacrylamide and 7.5 mg of potassium persulfate were continuously added, and third stirring was performed until complete dissolution to obtain a gel precursor solution;

[0046] S3: the gel precursor solution was injected into a mold, drying was performed at 60℃ for 12 h, then the mold with the gel was immersed into an electrolyte salt solution (the electrolyte salt solution was a mixed solution of 6M potassium hydroxide solution and 0.2M zinc acetate), normal temperature soaking was performed for 48 h, then the gel was taken out from the mold to obtain a gel electrolyte.

[0047] Example 2

[0048] S1: dipropylene glycol and zinc trifluoromethyl sulfonate were added into pure water (the mass ratio of dipropylene glycol, zinc trifluoromethyl sulfonate and water was 5:7.5:10), first stirring was performed to obtain a first mixed solution;

[0049] The remaining S2 and S3 steps were the same as those in Example 1.

[0050] Example 3

[0051] S1: dipropylene glycol and zinc trifluoromethyl sulfonate were added into pure water (the mass ratio of dipropylene glycol, zinc trifluoromethyl sulfonate and water was 2.5:10:10), first stirring was performed to obtain a first mixed solution;

[0052] The remaining S2 and S3 steps were the same as those in Example 1.

[0053] Example 4

[0054] S1: 0.5M zinc acetate ethanol solution and 0.5M oxalic acid dihydrate ethanol solution were mixed uniformly according to equal volume ratio to obtain a second mixed solution; the second mixed solution was placed in a reaction kettle, and reaction was performed at 80℃ for 5 hours to obtain a reaction product, the reaction product was washed to neutral with ethanol, and then the reaction product was dried; the dried reaction product was annealed at 450℃ for 150 minutes to obtain porous zinc oxide nanorods; the porous zinc oxide nanorods were dispersed in a PEG-2000 solvent, and after ultrasonic treatment, filtration and drying were performed to obtain modified porous zinc oxide nanorods;

[0055] S2: add dipropylene glycol, zinc triflate, modified porous zinc oxide nanorods into pure water (the mass ratio of dipropylene glycol, zinc triflate, modified porous zinc oxide nanorods and water is 2.5:7.5:0.1:10), perform first stirring to obtain a first mixed solution;

[0056] S3: add 2.5 g of acrylamide into 10 ml of the first mixed solution, perform second stirring, continue to add 2.5 mg of methylene bisacrylamide and 7.5 mg of potassium persulfate, perform third stirring until fully dissolved to obtain a gel precursor solution;

[0057] S4: inject the gel precursor solution into a mold, perform drying at 60°C for 12 h, then immerse the mold with the gel into an electrolyte salt solution (the electrolyte salt solution is a mixed solution of 6M potassium hydroxide solution and 0.2M zinc acetate), soak at room temperature for 48 h, then take out the gel from the mold to obtain a gel electrolyte.

[0058] Comparative Example 1

[0059] S1: add zinc triflate into pure water (the mass ratio of zinc triflate and water is 7.5:10), perform first stirring to obtain a first mixed solution;

[0060] The remaining steps S2 and S3 are the same as those in Example 1.

[0061] Comparative Example 2

[0062] S1: add dipropylene glycol into pure water (the mass ratio of dipropylene glycol and water is 2.5:10), perform first stirring to obtain a first mixed solution;

[0063] The remaining steps S2 and S3 are the same as those in Example 1.

[0064] Comparative Example 3

[0065] S1: add glycerol and zinc triflate into pure water (the mass ratio of glycerol, zinc triflate and water is 2.5:7.5:10), perform first stirring to obtain a first mixed solution;

[0066] The remaining steps S2 and S3 are the same as those in Example 1.

[0067] Comparative Example 4

[0068] S1: add dipropylene glycol and zinc triflate into pure water (the mass ratio of dipropylene glycol, zinc triflate and water is 2.5:7.5:10), perform first stirring to obtain a first mixed solution;

[0069] The remaining steps S2 and S3 are the same as those in Example 1.

[0070] Comparative Example 5

[0071] The commercially available zinc oxide nanoparticles (particle size < 100 nm) were used to replace the modified porous zinc oxide nanorods, and the remaining steps were the same as those of Example 4.

[0072] Conductivity test: The gel electrolytes prepared in different examples and comparative examples were cut into the same size and then subjected to conductivity test using a conductivity meter. The specific results are shown in Table 1.

[0073] Cycle test: The gel electrolytes prepared in different examples and comparative examples were cut into the same size (5 cm x 5 cm x 2 mm) and then subjected to cycle test after being assembled into a "sandwich" structure battery with a positive electrode (using a commercial Pt / C catalyst) and a negative electrode (using a zinc sheet), wherein the charging and discharging conditions were as follows: charging for 1 h and discharging for 1 h, and the charging and discharging current was 5 mA / cm 2 . The specific test results are shown in Table 1.

[0074] Table 1. Test results of different examples and comparative examples

[0075] Group Conductivity (S / cm) Cycling time (h) Example 1 0.685 160 Example 2 0.427 142 Example 3 0.401 128 Example 4 0.769 173 Comparative Example 1 0.389 84 Comparative Example 2 0.285 102 Comparative Example 3 Too high viscosity to be removed completely Comparative Example 4 0.364 137 Comparative Example 5 0.484 146

[0076] Please refer to Table 1 and Figure 1 , Figure 2 , the gel electrolyte of the present application uses dipropylene glycol and zinc triflate as the first electrolyte additive. As can be seen from the data of Examples 1 to 3, the cycle time of the zinc-air battery using the prepared gel electrolyte can be stably maintained at more than 120 h. Meanwhile, Example 1 is a preferred example, and the mass ratio of dipropylene glycol, zinc triflate and water in the preparation process is controlled in the range of (1-3):(6-8):10, so that the conductivity of the prepared gel electrolyte can reach more than 0.6 S / cm, and the cycle time can reach more than 160 h. However, the amount of dipropylene glycol and zinc triflate in Examples 2 and 3 exceeds the optimal proportion range, resulting in a slight decrease in the test data. It can be seen that, after the component proportion of dipropylene glycol and zinc triflate is optimized, the electrochemical performance of the zinc-air battery can be significantly improved.

[0077] Among them, Example 4 is to add modified porous zinc oxide nanorods in the preparation process of the gel. As can be seen from the data, the conductivity and cycle time are obviously improved after adding the modified porous zinc oxide nanorods. It is possible that the modified porous zinc oxide nanorods have a rich pore structure, and these pores can act as ion transmission channels to promote the rapid migration of ions in the gel electrolyte, thereby improving the ion conductivity. At the same time, the modified porous zinc oxide nanorods can be embedded in the matrix of the gel electrolyte to form a stable network structure, thereby improving the overall mechanical strength and stability of the gel electrolyte.

[0078] The gel electrolyte in Comparative Example 1 is not added with dipropylene glycol, and the gel electrolyte in Comparative Example 2 is not added with zinc trifluoromethyl sulfonate. It can be seen from the data that, compared with Example 1, the conductivity of the gel electrolyte in Comparative Example 1 and Comparative Example 2 is significantly reduced, and the cycle time is reduced by about 50%. It can be seen that the combination of dipropylene glycol and zinc trifluoromethyl sulfonate can significantly improve the electrochemical performance of the battery, and the use of either of them alone cannot achieve the test results of Example 1.

[0079] The gel electrolyte in Comparative Example 3 is prepared by replacing dipropylene glycol with glycerol in the preparation process. The prepared gel electrolyte cannot be completely taken out from the mold due to too much viscosity. It can be seen that dipropylene glycol has the function of adjusting the viscosity and fluidity of the gel electrolyte in the present application, and has a certain plasticizing effect on the gel electrolyte, thereby improving the flexibility of the gel electrolyte. The experimental results of Comparative Example 3 show that dipropylene glycol plays a crucial role in the gel electrolyte formula system and cannot be simply replaced.

[0080] The gel electrolyte in Comparative Example 4 is prepared by replacing zinc trifluoromethyl sulfonate with zinc methanesulfonate in the preparation process. It can be known from the test results that, compared with Example 1, the conductivity and cycle time of Comparative Example 4 are significantly reduced. It may be due to the fact that zinc trifluoromethyl sulfonate has a fluorinated group, which can provide better electrochemical performance, especially in inhibiting the growth of zinc dendrites. Therefore, zinc trifluoromethyl sulfonate cannot be simply replaced in the gel electrolyte system.

[0081] The difference between Comparative Example 5 and Example 4 is that commercially available zinc oxide nanoparticles (particle size <100 nm) are used to replace the modified porous zinc oxide nanorods. It can be seen from the test data (compared with Example 1) that the zinc oxide nanoparticles have limited performance improvement on the gel electrolyte. It may be due to the fact that although the zinc oxide nanoparticles have a large specific surface area, the electrons need to pass through more interfaces when transmitting between the particles, which slows down the electron transmission rate and increases the possibility of electron recombination. At the same time, the nanoparticles may agglomerate, and the gap between the particles is small, which is not conducive to electron transmission. The modified porous zinc oxide nanorods provided by the present application are one-dimensional nanostructures, which have fewer contact interfaces when electrons transmit, avoid electron recombination with other ions, and enable electrons to transmit at a higher speed. Therefore, the modified porous zinc oxide nanorods have better electron transmission performance.

[0082] The above examples only express several embodiments of the present application, and the description is more specific and detailed, but it cannot be understood as a limitation on the scope of the patent. It should be noted that, for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the scope of protection of the present application. Therefore, the protection scope of the present application patent should be subject to the appended claims.

Claims

1. A gel electrolyte characterized by, The gel electrolyte comprises the following components: water-soluble monomers, water, electrolyte salt, first electrolyte additive, cross-linking agent and initiator. The first electrolyte additive comprises dipropylene glycol and zinc trifluoromethyl sulfonate. The mass ratio of the dipropylene glycol, zinc trifluoromethyl sulfonate and water is (1-3):(6-8):

10. The gel electrolyte further comprises a second electrolyte additive, and the second electrolyte additive comprises zinc acetate. The water-soluble monomers are acrylamide monomers. The gel electrolyte further comprises a third electrolyte additive, and the third electrolyte additive is modified porous zinc oxide nanorods, and the mass ratio of the modified porous zinc oxide nanorods and water is (0.05-0.2):

10. The modified porous zinc oxide nanorods are prepared by the following steps: The zinc acetate ethanol solution and the ethanol solution of oxalic acid dihydrate are mixed uniformly at a certain ratio to obtain a second mixed solution. The second mixed solution is placed in a reaction kettle and reacted at 70-90°C for 4-6 hours to obtain a reaction product, which is washed to neutral with water or ethanol, and then dried. The dried reaction product is annealed at 400-500°C for 100-180 minutes to obtain porous zinc oxide nanorods. The porous zinc oxide nanorods are dispersed in a PEG-2000 solvent, ultrasonically treated, filtered and dried to obtain modified porous zinc oxide nanorods. The electrolyte salt is at least one of potassium hydroxide, sodium hydroxide and lithium hydroxide.

2. The gel electrolyte according to claim 1, characterized by, The cross-linking agent is at least one of methylene bisacrylamide, N-methylol acrylamide and acrylamide-PEG-hydroxyl, and the initiator is at least one of potassium persulfate, ammonium persulfate, azobisisobutyronitrile and azobisisoheptyl nitrile.

3. The method for producing a gel electrolyte according to any one of claims 1 to 2, characterized by, The method comprises the following steps: S1: The first electrolyte additive and the third electrolyte additive are added to the water in a certain proportion, and first stirring is performed to obtain a first mixed solution; S2: The water-soluble monomers are added to the first mixed solution in a certain proportion, and second stirring is performed, and the cross-linking agent and the initiator are continuously added, and third stirring is performed to obtain a gel precursor solution; S3: The gel precursor solution is injected into a mold, dried under certain conditions, and then the mold containing the gel is immersed in an electrolyte salt solution, soaked, and then the gel is taken out of the mold to obtain a gel electrolyte.

4. The method for preparing a gel electrolyte according to claim 3, wherein In the S2 step, the mass concentration of the water-soluble monomers in the mixed solution is 0.25g / mL-0.3g / mL.

5. The method of claim 3, wherein the gel electrolyte is prepared by mixing the polymer, the electrolyte solution, and the inorganic particles. In the S3 step, the electrolyte salt solution contains a second electrolyte additive.

6. A zinc-air battery characterized by comprising: The gel electrolyte of any one of claims 1-2. The gel electrolyte of any one of claims 1-2.

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