Zinc-air battery acidic electrolyte and preparation method and application thereof

Abstract

The invention relates to a zinc-air battery acidic electrolyte and a preparation method and application thereof, and belongs to the technical field of electrolyte preparation. The preparation method of the acidic electrolyte of the zinc-air battery comprises the following steps: mixing a ZnSO4 solution and an H2SO4 solution, and uniformly stirring to obtain the acidic electrolyte. The combination of ZnSO4 and H2SO4 is used in the electrolyte, and the non-noble metal catalyst MnO2 is used as an air cathode catalyst, so that the growth of zinc dendrites can be effectively inhibited, the cycle life of the battery is remarkably prolonged, the cost of the battery is reduced, and meanwhile, the efficient and stable operation of the battery is realized; the electrolyte provided by the invention overcomes many defects of an alkaline electrolyte, has good electrochemical activity and long-term stability, and is expected to realize large-scale application of the zinc-air battery.

Description

Technical Field

[0001] The present application relates to the technical field of electrolyte preparation, and particularly to an acidic electrolyte for a zinc-air battery, a preparation method thereof, and an application thereof. Background Art

[0002] Zinc-air batteries typically use alkaline electrolytes (such as KOH and NaOH) to ensure the high activity of the zinc anode and the air cathode. However, alkaline electrolytes have various limitations in practical applications, especially being prone to react with CO in the air 2 to form carbonates or bicarbonates, thereby significantly reducing the conductivity of the electrolyte. The deposition of these carbonates not only clogs the pores of the air electrode and reduces its performance, but also causes the gradual deterioration of the overall performance of the battery. In addition, the growth of zinc dendrites in alkaline electrolytes is also one of the key factors limiting the cycle life of zinc-air secondary batteries.

[0003] The growth of zinc dendrites is usually caused by the non-uniform deposition of zinc ions during the electroplating / stripping process. These dendrites will gradually pierce the separator, thereby triggering a short-circuit accident, which not only seriously affects the life and safety of the battery, but also may cause the battery to suddenly fail during the cycle. To inhibit the growth of zinc dendrites, researchers have proposed various methods, including changing the electrode structure, adding electrolyte additives to change the deposition characteristics, and protecting the zinc metal anode through surface coating, etc. However, these methods usually have problems such as high cost and complex processes, and it is difficult to achieve large-scale application.

[0004] Currently, the noble metal catalysts (such as Pt, PtRu) widely used in alkaline electrolytes show good activity in the oxygen reduction reaction (ORR), but are prone to passivation during the oxygen evolution reaction (OER) process, resulting in catalyst deactivation, which significantly reduces the overall efficiency of the battery. In addition, most of the literature and research focus on the inhibition of zinc dendrites in alkaline electrolytes, and the research on neutral or acidic electrolyte environments is relatively scarce, which further limits the application of zinc-air batteries in these environments.

[0005] In recent years, some researchers have begun to focus on neutral and acidic electrolytes in order to improve the electrochemical performance while inhibiting the growth of zinc dendrites. In an acidic environment, the lower risk of zinc electrode corrosion and the stability of the acidic electrolyte in the reaction with CO 2 make the acidic system show the potential to be superior to the alkaline system in some aspects. However, the current research on acidic electrolytes mainly focuses on zinc-ion batteries, and the application of acidic electrolytes in zinc-air batteries is still blank, especially there are still great challenges in achieving efficient inhibition of zinc dendrite growth and extending the battery cycle life. Summary of the Invention

[0006] In view of this, the present application provides an acidic electrolyte for a zinc-air battery, a preparation method and an application thereof. By using a combination of ZnSO 4 and H 2 SO 4 in the electrolyte and adopting a non-noble metal catalyst MnO 2 as the air cathode catalyst, the growth of zinc dendrites can be effectively inhibited, the cycle life of the battery can be significantly extended, the cost of the battery can be reduced, and at the same time, the efficient and stable operation of the battery is realized; the electrolyte of the present application overcomes many disadvantages of the alkaline electrolyte, has good electrochemical activity and long-term stability, is expected to realize the large-scale application of zinc-air batteries, and can effectively overcome the defects existing in the above-mentioned prior art.

[0007] The first aspect of the present application provides a preparation method for an acidic electrolyte of a zinc-air battery, comprising the following steps:

[0008] Mix the ZnSO 4 solution and the H 2 SO 4 solution, stir evenly to obtain an acidic electrolyte.

[0009] Preferably, the volume ratio of the ZnSO 4 solution to the H 2 SO 4 solution is 1:1.

[0010] Preferably, the preparation process of the H 2 SO 4 solution is: use a pipette to measure concentrated sulfuric acid, and slowly add it to deionized water, stirring evenly while adding to obtain the H 2 SO 4 solution.

[0011] Preferably, the concentration of the H 2 SO 4 solution is 0.05 M; the concentration of the concentrated sulfuric acid is 95%.

[0012] Preferably, the preparation process of the ZnSO 4 solution is: dissolve ZnSO 4 ·7H 2 O in deionized water, stir until completely dissolved, then transfer the solution to a volumetric flask and make up the volume with deionized water to obtain the ZnSO 4 solution.

[0013] Preferably, the concentration of the ZnSO 4 solution is 1 M.

[0014] Preferably, the ZnSO 4 ·7H 2The purity of O ≥ 99%.

[0015] Preferably, the stirring time ≥ 10 minutes.

[0016] The second aspect of the present application also provides an acidic electrolyte for a zinc-air battery, which is the acidic electrolyte for a zinc-air battery prepared by the above method.

[0017] The third aspect of the present application also provides the application of the above acidic electrolyte for a zinc-air battery in inhibiting the growth of zinc dendrites.

[0018] Compared with the prior art, the present application has the following beneficial effects:

[0019] 1. The acidic electrolyte of the present application undergoes zinc plating / stripping cycle experiments at a current density of 2 mA / cm 2 and exhibits stable electrochemical performance, with a cycle life exceeding 200 hours.

[0020] 2. The acidic electrolyte of the present application is more stable than traditional alkaline electrolytes and is not prone to reacting with CO in the air. 2 This avoids the situation where carbonates are generated and block the pores of the air electrode, which greatly improves the stability of the battery and extends the service life of the battery.

[0021] 3. The present application uses MnO 2 as a non-noble metal catalyst, replacing traditional noble metal catalysts, with lower costs, and MnO 2 exhibits good durability in acidic electrolytes and is suitable for large-scale applications.

[0022] 4. Compared with alkaline electrolytes, the zinc electrode in the acidic electrolyte of the present application has a lower corrosion risk, enhancing the safety and long-term use performance of the battery. Description of the Drawings

[0023] In order to more clearly illustrate the technical solutions in the present application or the prior art, the following will briefly introduce the drawings required for the description of the present application or the prior art. Obviously, the drawings in the following description are some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0024] Figure 1 Figure for the constant current zinc electroplating / stripping voltage-time of a symmetric cell using 1.0 M ZnSO 2 at a current density of 2 mA / cm 4 + 0.05 M H 2 SO 4 as the electrolyte;

[0025] Figure 2For the scanning electron microscope (SEM) image of zinc foil after 1 hour of plating / stripping cycle in 1.0 M ZnSO 4 + 0.05 M H 2 SO 4 electrolyte;

[0026] Figure 3 For the galvanostatic zinc plating / stripping voltage - time plots at different current densities in a symmetric cell with 1.0 M ZnSO 4 + 0.05 M H 2 SO 4 as the electrolyte;

[0027] Figure 4 For the ORR and OER current density plots of (a) PtRu / C, (b) MnO 2 as catalysts at different electrolyte concentrations;

[0028] Figure 5 For the results plot of the galvanostatic test of Zn / PtRu cell using 1.0 M ZnSO 4 + 0.05 M H 2 SO 4 as the electrolyte;

[0029] Figure 6 For the scanning electron microscope (SEM) image of zinc foil after more than 100 charge - discharge cycles in a Zn / PtRu cell with 1.0 M ZnSO 4 + 0.05 M H 2 SO 4 electrolyte; Detailed implementation manners

[0030] To make the objectives, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be clearly and completely described below in conjunction with the accompanying drawings in the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without making creative efforts belong to the scope of protection of the present application.

[0031] The experimental methods used in the embodiments of the present application are all conventional methods unless otherwise specified.

[0032] In the following embodiments, unless otherwise specified, all raw materials can be obtained through commercial purchase or conventional methods.

[0033] Example 1

[0034] 1.1 Preparation of electrolyte

[0035] Prepare 1 M ZnSO4 Solution: Material preparation of ZnSO 4 ·7H 2 O (zinc sulfate heptahydrate, purity ≥ 99%), H 2 SO 4 (concentrated sulfuric acid, concentration 95%), deionized water: used to dissolve ZnSO 4 and dilute H 2 SO 4 , ensuring the electrolyte is pure and free of impurities.

[0036] (1) Weigh 14.39 g of ZnSO 4 ·7H 2 O, which is the required mass for a 1 M ZnSO 4 solution in 100 mL of water. (2) Pipette approximately 0.28 mL of concentrated sulfuric acid (concentration 95%) and slowly add it to 100 mL of deionized water while stirring. Be careful to avoid adding it too quickly to prevent the solution from splashing due to rapid heat release during the reaction. Stir evenly to obtain a 0.05 M H 2 SO 4 dilution solution. (3) Add the weighed ZnSO 4 ·7H 2 O to a clean beaker, add 80 mL of deionized water, and stir until the ZnSO 4 is completely dissolved. Then transfer the solution to a 100 mL volumetric flask and make up to the mark with deionized water to ensure the accuracy of the solution concentration. (4) Mix the prepared 1 M ZnSO 4 solution and 0.05 M H 2 SO 4 solution in a 1:1 volume ratio and stir evenly to form the target acidic electrolyte 1 M ZnSO 4 + 0.05 M H 2 SO 4 . This mixed solution should be stirred for at least 10 minutes to ensure uniform distribution of the electrolyte.

[0037] 1.2 Electrode materials

[0038] (1) Anode: Use high-purity zinc foil (Zn, purity ≥ 99.98%, thickness 0.01 inches) as the anode material. Take a 1 cm × 1 cm high-purity zinc sheet, wash it with deionized water to remove oxides and impurities, and then gently polish the surface with sandpaper to make it smoother, in order to achieve uniform zinc deposition and stripping and thus inhibit dendrite growth. Wash the zinc sheet with deionized water, then wash it with anhydrous ethanol and dry it. (2) Cathode: Use carbon paper (1.5 cm × 1.5 cm, 0.2 mm thick) as the conductive substrate, select MnO 2 as the non-noble metal catalyst, and use MnO2 The catalyst was mixed with Nafion solution to prepare a catalyst ink, which was uniformly coated on carbon paper using a spraying technique. The coated carbon paper was dried at 60 °C for 30 minutes to ensure the adhesion and stability of the catalyst on the carbon paper.

[0039] 1.3 Assembly of the battery

[0040] Assembly of the symmetric battery: (1) High-purity zinc foil (Zn, purity ≥ 99.98%, thickness 0.01 inches) was used as the anode and cathode of the symmetric battery. A 1 cm × 1 cm zinc sheet was taken, and after cleaning with deionized water, the surface was gently polished with sandpaper to ensure uniform zinc deposition and stripping. Subsequently, it was washed with absolute ethanol and dried to ensure that the electrode surface was free of contamination. (2) 1 M ZnSO 4 + 0.05 M H 2 SO 4 electrolyte was injected between the anode and cathode to ensure that the electrolyte fully wetted the electrode surface and optimized the electrochemical reaction efficiency. (3) A Nafion membrane was placed between the anode and cathode to ensure a smooth conduction path for zinc ions in the electrolyte, while effectively isolating the electrodes to prevent short circuits. (4) The assembled symmetric battery was sealed to reduce the contact between the electrolyte and air and avoid the performance degradation of the electrolyte caused by the reaction of ZnSO 4 with CO 2 . (5) A constant current zinc deposition / dissolution cycle test was carried out using a battery tester. Each cycle included 1 hour of charging (deposition) and 1 hour of discharging (dissolution) to evaluate the cycle life and electrochemical stability of the battery. The current density was 2 mA / cm 2 .

[0041] Assembly of the full battery: (1) The pretreated zinc foil was installed as the anode, and the carbon paper coated with MnO 2 catalyst was installed as the cathode. Carbon paper (1.5 cm × 1.5 cm, 0.2 mm thick) was used as the conductive substrate, and MnO 2 was used as the non-noble metal catalyst. The MnO 2 catalyst was mixed with Nafion solution to form a catalyst ink, which was sprayed on the carbon paper to form a uniform catalytic layer and dried for 30 minutes. (2) 1 M ZnSO 4 + 0.05 M H 2 SO 4 electrolyte was injected between the anode and cathode to ensure that the electrolyte fully wetted the electrode surface and optimized the electrochemical reaction efficiency. (3) A Nafion membrane was placed between the anode and cathode to ensure a smooth conduction path for zinc ions in the electrolyte, while effectively isolating the electrodes to prevent short circuits. (4) The assembled battery components were sealed in a battery case to reduce the contact between the electrolyte and the outside air and prevent ZnSO in the electrolyte 4React with CO 2 to ensure the long-term stable operation of the battery. (5) Use a battery tester to perform a constant current zinc deposition / dissolution cycle test. Each cycle includes 1 hour of charging (deposition) and 1 hour of discharging (dissolution) at a current density of 2 mA / cm 2 to evaluate the stability and cycle life of the battery. The test results show that the all-battery cycle life using MnO 2 as the air cathode is longer, with small voltage fluctuations and is suitable for long-term use.

[0042] Example 2

[0043] The acidic electrolyte and its preparation method provided in this example can refer to Example 1, except that the concentration of H 2 SO 4 is 0.005 M.

[0044] Example 3

[0045] The acidic electrolyte and its preparation method provided in this example can refer to Example 1, except that the concentration of H 2 SO 4 is 0.0005 M.

[0046] Electrochemical performance test

[0047] 1. Test of the constant current zinc deposition / dissolution symmetric cell with acidic electrolytes of different concentrations. Test the electrochemical stability of 1.0 M ZnSO 2 and acidic electrolytes with different concentrations of H 4 SO 2 under constant current conditions at a current density of 2 mA / cm 4 to evaluate the inhibitory effect of each concentration of electrolyte on the growth of zinc dendrites. The specific steps are as follows:

[0048] (1) Current density: 2 mA / cm 2 .

[0049] (2) Electrolyte concentration: 1.0 M ZnSO 4 + 0.05 M H 2 SO 4 , 1.0 M ZnSO 4 + 0.005 M H 2 SO 4 , 1.0 MZnSO 4 + 0.0005 M H 2 SO 4 .

[0050] (3) Cycling process: Set each cycle to include a 1-hour charging process (zinc deposition) and a 1-hour discharging process (zinc dissolution).

[0051] (4) Data recording and analysis: Record the voltage change of the battery during the test, calculate the voltage gap, polarization voltage change rate, and stable cycle times at different concentrations, and obtain the voltage-time curve under different concentrations of electrolyte. The test results are shown in Table 1 and Figure 1 as follows. The results show that the battery using 1.0M ZnSO 4 +0.05M H 2 SO 4 as the electrolyte performs the best, with the smallest voltage gap and the lowest voltage change rate. Table 1 shows the test results of the constant current zinc deposition / dissolution symmetric battery in different electrolytes.

[0052] Table 1 Test results of the constant current zinc deposition / dissolution symmetric battery in different electrolytes

[0053]

[0054]

[0055] (5) After the cycle test, take out the zinc anode from the battery, clean and dry it, and use SEM scanning electron microscopy to image the surface of the zinc foil and analyze its surface morphology and the growth of zinc dendrites. The test results are as Figure 2 follows. Comparing the growth of dendrites under different electrolyte conditions, the 1.0M ZnSO 4 +0.05M H 2 SO 4 acidic electrolyte has a significant effect on inhibiting dendrite growth.

[0056] 2. Test of the constant current zinc deposition / dissolution symmetric battery at different current densities. Evaluate the electrochemical stability of the acidic electrolyte for the zinc deposition / dissolution process at different current densities to further confirm the applicability of the optimal electrolyte concentration combination at higher current densities. The specific steps are as follows:

[0057] (1) Electrolyte: 1.0M ZnSO 4 +0.05M H 2 SO 4 .

[0058] (2) Current density: 2mA / cm 2 , 5mA / cm 2 , 10mA / cm 2 .

[0059] (3) Data recording and analysis: Record the voltage fluctuations of the battery at different current densities and calculate the voltage change rate at each current density. The test results are as Figure 3As shown, it can be clearly seen that compared with other current densities, at 2 mA / cm 2 current density, the charge-discharge potential gap of the battery is smaller and the battery performance is very stable. At 10 mA / cm 2 , the voltage shows wavy fluctuations, which may be caused by the self-corrosion of zinc under acidic conditions.

[0060] 3. Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) tests of the half-cell. Test the ORR and OER activities of the non-precious metal catalyst MnO 2 in acidic electrolyte to compare its electrochemical performance with that of the traditional precious metal catalyst PtRu. The specific steps are as follows:

[0061] (1) Electrolyte: 1.0 M ZnSO 4 + 0.05 M H 2 SO 4 、1.0 M ZnSO 4 + 0.005 M H 2 SO 4 、1.0 MZnSO 4 + 0.0005 M H 2 SO 4 .

[0062] (2) Three-electrode system: The working electrode is the MnO 2 air cathode, the counter electrode is the Pt mesh, and the reference electrode is the Zn wire.

[0063] (3) Scanning parameter settings: Set the potential scanning range to be from 0.5 V to 2.4 V, and the scanning rate to be 1 mV / s.

[0064] (4) Data recording and analysis: Use linear sweep voltammetry (LSV) to measure the current density at different potentials and analyze the activities of the MnO 2 and PtRu catalysts during the ORR and OER processes. The test results are as Figure 4 shown. The results show that MnO 2 has excellent catalytic activity in ORR and OER. When using 1.0 M ZnSO 4 + 0.05 M H 2 SO 4 as the electrolyte, the two catalysts show almost similar activities, indicating the potential to replace precious metal catalysts in acidic electrolytes.

[0065] 4. Charge-discharge test of the full cell. In 1.0 M ZnSO 4 + 0.05 M H 2 SO 4 electrolyte, 2 mA / cm2 Under the current density, the charge-discharge performance of the Zn / PtRu and Zn / MnO 2 electrode combinations in acidic electrolyte was tested to evaluate the long-term effect of the electrolyte on dendrite inhibition and the cycle life of the battery. The specific steps are as follows:

[0066] (1) Electrolyte: 1.0M ZnSO 4 +0.05M H 2 SO 4 .

[0067] (2) Current density: 2mA / cm 2 .

[0068] (3) Data recording and analysis: Connect the battery to a battery tester, conduct cyclic tests on the battery, and record the voltage fluctuations and discharge times of each cycle. Remove the zinc anode from the battery after the cyclic test, clean and dry it. Use SEM to image the surface of the zinc foil and analyze its surface morphology and the growth of zinc dendrites. The test results are as Figure 5 and Figure 6 shown. Figure 5 The results show that the Zn / MnO 2 combination maintained a stable voltage output within 200 hours, while the voltage of the battery using the PtRu electrode dropped sharply after 60 hours. Figure 6 The results show that in 1.0M ZnSO 4 +0.05M H 2 SO 4 electrolyte, at a current density of 2mA / cm 2 , the surface of the zinc in the Zn / MnO 2 battery was relatively flat, and the growth of dendrites was significantly inhibited.

[0069] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing an acidic electrolyte for a zinc-air battery, characterized in that: The following steps are involved: The ZnSO4 solution and the H2SO4 solution are mixed and stirred evenly to obtain an acidic electrolyte.

2. The method for preparing an acidic electrolyte for a zinc-air battery according to claim 1, characterized in that: The volume ratio of the ZnSO4 solution to the H2SO4 solution is 1:

1.

3. The method for preparing an acidic electrolyte for a zinc-air battery according to claim 1, characterized in that: The preparation process of the H2SO4 solution is as follows: using a pipette to measure concentrated sulfuric acid, and slowly adding it into deionized water, stirring evenly while adding, to obtain the H2SO4 solution.

4. The method for preparing an acidic electrolyte for a zinc-air battery according to claim 3, characterized in that: The concentration of the H2SO4 solution is 0.05M; the concentration of the concentrated sulfuric acid is 95%.

5. The method for preparing an acidic electrolyte for a zinc-air battery according to claim 1, characterized in that: The preparation process of the ZnSO4 solution is as follows: dissolving ZnSO4·7H2O in deionized water, stirring until completely dissolved, then transferring the solution to a volumetric flask, and making up the volume with deionized water to obtain the ZnSO4 solution.

6. The method for preparing an acidic electrolyte for a zinc-air battery according to claim 5, characterized in that: The concentration of the ZnSO4 solution is 1M.

7. The method for preparing an acidic electrolyte for a zinc-air battery according to claim 5, characterized in that: The purity of the ZnSO4·7H2O is ≥99%.

8. The method for preparing an acidic electrolyte for a zinc-air battery according to claim 1, characterized in that: The stirring time is ≥10 minutes.

9. A zinc-air battery acid electrolyte, characterized in that: A zinc-air battery acid electrolyte prepared by the method described in any one of claims 1 to 8.

10. Use of the zinc-air battery acid electrolyte according to claim 9 in inhibiting zinc dendrite growth.

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