A zinc-iodine battery electrolyte additive with pH buffering and multi-iodide shuttle effect inhibition capability

Abstract

The application belongs to the technical field of secondary batteries, and particularly relates to a zinc-iodine battery electrolyte additive with pH buffering and multi-iodide shuttle effect inhibition capabilities. In order to effectively improve the performance and service life of a zinc ion battery, the application provides a water-based zinc ion battery electrolyte additive. The electrolyte additive is a zwitterionic polyelectrolyte, which can inhibit hydrogen evolution and buffer pH value, and can also reduce the shuttle effect of multi-iodide. At the same time, after the zwitterionic polyelectrolyte is introduced into the electrolyte to assemble a water-based zinc-iodine battery, the cycle life of the water-based zinc-iodine battery can be greatly improved, and the stable coulomb efficiency of the water-based zinc-iodine battery can be ensured.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of secondary batteries, and particularly relates to a zinc-iodine battery electrolyte additive with pH buffering and multi-iodide shuttle effect inhibition capabilities. BACKGROUND

[0002] Electrochemical energy storage, especially lithium-ion battery energy storage, has advantages such as no pollution, high efficiency, flexible power, long service life, and has developed very rapidly in recent years. Since 1990, lithium-ion batteries have been dominant in the fields of portable electronic devices, electric vehicles and the like. However, the key problems such as lack of lithium resources, high manufacturing cost, and unsafe organic electrolyte limit their application in large-scale energy storage systems. Therefore, researchers have turned their attention to the research and development of new non-lithium secondary battery technologies, such as zinc-ion batteries.

[0003] In recent years, aqueous zinc-iodine batteries have become one of the most promising new energy storage technologies due to their superior electrochemical performance and extremely high safety. Compared with other metal elements, zinc metal has significant advantages in resource reserves, chemical stability, electrochemical stability, safety, etc. For example, zinc metal can be stably operated in medium and weak acid electrolyte. In addition, compared with the organic electrolyte widely used in lithium-ion batteries, the aqueous electrolyte used in aqueous zinc-ion batteries not only has ultra-high conductivity, but also has the safety advantages of non-toxicity and non-flammability. The above characteristics make aqueous zinc-ion batteries very promising for application in future large-scale energy storage fields.

[0004] However, due to the chemical properties of zinc negative electrode in aqueous electrolyte and the corrosion problem caused by multi-iodine ions, zinc-iodine batteries are still difficult to be widely used in large-scale energy storage. The main reason is that zinc negative electrode not only produces side reactions in aqueous electrolyte to cause hydrogen evolution and passivation, but also causes zinc ion tip deposition on the electrode surface to gradually evolve into zinc dendrites due to the change of electrode / electrolyte interface concentration. In addition, there is also the problem of dissolution and shuttle effect of multi-iodide. The high concentration of multi-iodine ion intermediates produced by the conversion between I2 and I - will cause serious shuttle effect, causing self-discharge reaction of negative electrode (I3 - + Zn → Zn 2+ + I - ), which further aggravates the corrosion reaction of zinc negative electrode, resulting in irreversible loss of active mass of zinc-iodine battery and significant decrease in cycle life. Therefore, developing a high-performance aqueous zinc-iodine battery electrolyte with pH buffering and multi-iodide shuttle effect inhibition capabilities is the key to effectively improving the performance and life of zinc-ion batteries. SUMMARY

[0005] In order to overcome the above-mentioned deficiencies of the prior art, the present application provides an electrolyte with pH buffering and multi-iodide shuttle effect inhibition capacity, which uses a zwitterionic polyelectrolyte as an additive, and a water-based zinc-iodine battery assembled from the electrolyte has the advantages of long cycle life and high coulomb efficiency.

[0006] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is:

[0007] The present application provides, in a first aspect, the use of a zwitterionic polyelectrolyte as an electrolyte additive in the preparation of a water-based zinc ion battery, wherein the zwitterionic polyelectrolyte is polyvinyl alcohol ammonium phosphate.

[0008] Preferably, the working current density of the battery is 1-50 mA·cm -2 .

[0009] Preferably, the water-based zinc ion battery is a battery assembled in the form of "negative electrode-separator-positive electrode" using a zinc metal material as the negative electrode and a halogen element iodine as the positive electrode.

[0010] More preferably, the zinc metal material is one of zinc sheet, zinc powder, electroplated zinc, foamed zinc or zinc elemental material.

[0011] More preferably, the positive electrode is composed of active material, activated carbon, conductive agent and binder in a mass ratio of 4:4:1:1; and the battery separator includes but is not limited to a glass fiber separator.

[0012] The present application provides, in a second aspect, a water-based zinc ion battery electrolyte, which comprises a soluble zinc salt, polyvinyl alcohol ammonium phosphate and water.

[0013] Preferably, the concentration of the polyvinyl alcohol ammonium phosphate is 0.02-0.20 g / L.

[0014] Preferably, the soluble zinc salt comprises at least one of zinc sulfate, zinc chloride, zinc nitrate, zinc acetate, zinc fluoride and zinc trifluoromethane sulfonate.

[0015] Preferably, the concentration of the soluble zinc salt is 1-3 mol / L.

[0016] Compared with the prior art, the present application has the following beneficial effects:

[0017] The present application adds zwitterionic polyelectrolyte in aqueous zinc ion battery electrolyte, which can alleviate the shuttle effect of polyiodide by buffering pH during battery cycling, thereby protecting zinc ion battery electrode and significantly improving the cycle life of zinc ion battery. At the same time, the aqueous zinc ion battery prepared by using the electrolyte of the present application has a significant improvement in the effect of inhibiting hydrogen evolution. In addition, the aqueous zinc-iodine battery assembled by introducing zwitterionic polyelectrolyte into the electrolyte can greatly improve the cycle life of the aqueous zinc ion battery and ensure its stable coulombic efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 LSV curve of three-electrode device assembled using blank electrolyte and electrolyte added with polyvinyl alcohol ammonium phosphate;

[0019] Figure 2 pH change graph of symmetrical battery during cycling using blank electrolyte and electrolyte added with polyvinyl alcohol ammonium phosphate;

[0020] Figure 3 Scanning electron microscope graph of zinc electrode surface after 200 cycles at a current density of 5 mA·cm -2 and a fixed capacity of 1 mAh·cm -2 using blank electrolyte and electrolyte added with polyvinyl alcohol ammonium phosphate;

[0021] Figure 4 Time-voltage curve of zinc symmetrical battery at a current density of 5 mA·cm -2 and a fixed capacity of 1 mAh·cm -2 using blank electrolyte and electrolyte added with polyvinyl alcohol ammonium phosphate;

[0022] Figure 5 Cycle number-coulombic efficiency curve of zinc-copper asymmetrical battery at a current density of 5 mA·cm -2 and a fixed capacity of 1 mAh·cm -2 using blank electrolyte and electrolyte added with polyvinyl alcohol ammonium phosphate;

[0023] Figure 6 Cycle number-discharge specific capacity curve of zinc-iodine full battery at a current density of 2 A·g -1 using blank electrolyte and electrolyte added with polyvinyl alcohol ammonium phosphate. DETAILED DESCRIPTION

[0024] The specific embodiments of the present application are further described below. It is to be understood that the description of these embodiments is intended to help understand the present application and is not intended to limit the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0025] The experimental methods in the following examples are all conventional methods unless otherwise specified. The test materials used in the following examples are all commercially available unless otherwise specified.

[0026] Example:

[0027] An electrolyte for protecting an aqueous zinc-ion battery, the electrolyte is composed of a soluble salt, a zwitterionic polyelectrolyte and deionized water, the soluble salt is zinc sulfate (ZnSO4), wherein the concentration of zinc sulfate (ZnSO4) is 2 mol / L, the zwitterionic polyelectrolyte is polyvinyl alcohol ammonium phosphate, wherein the concentration of polyvinyl alcohol ammonium phosphate is 0.1 g / L, and the rest is deionized water. Dissolve 5.75 g of ZnSO4 in 0.5 mL of polyvinyl alcohol ammonium phosphate aqueous solution (0.1 g / L) and 9.5 mL of deionized water, stir for 10 h to obtain the target electrolyte (denoted as ZS+PVAP).

[0028] Comparative Example:

[0029] Dissolve 5.75 g of ZnSO4 in 10 mL of deionized water, stir for 10 h to obtain a blank electrolyte (denoted as ZS).

[0030] Experimental Example:

[0031] (1) Assemble a three-electrode battery device including a working electrode (an electrode clamp for clamping zinc sheets), a reference electrode (Ag / AgCl), and a counter electrode (a platinum electrode) using the blank electrolyte and the electrolyte added with polyvinyl alcohol ammonium phosphate, and then draw an LSV curve to compare the inhibition of hydrogen evolution. As shown in Figure 1 Compared with the battery using the blank electrolyte, the overpotential of the battery using the electrolyte added with polyvinyl alcohol ammonium phosphate is more negative, which indicates that the electrolyte is significantly inhibited after being modified by polyvinyl alcohol ammonium phosphate.

[0032] (2) Assemble a zinc symmetric battery (Zn / / Zn) using the blank electrolyte and the electrolyte added with polyvinyl alcohol ammonium phosphate, and then compare the pH of the zinc symmetric battery under beaker device during the cycle process, and draw a pH change curve. As shown in Figure 2As shown, the pH value of the zinc symmetric cell using the zincate electrolyte with added polyvinyl ammonium phosphate has a stable pH value during charge and discharge, while the pH value of the zinc symmetric cell using the blank electrolyte varies greatly. It shows that after the electrolyte is modified by polyvinyl ammonium phosphate, the generation of hydrogen and basic zinc salt is significantly inhibited, thereby improving the performance of the zinc ion battery.

[0033] (3) Zinc symmetric cells were assembled using the blank electrolyte and the electrolyte with added polyvinyl ammonium phosphate, and then the zinc dendrite growth on the surface of the zinc electrode after 200 cycles at a current density of 5 mA·cm -2 and a fixed capacity of 1 mAh·cm -2 was measured. As shown in FIG. 3, a large number of dendrites can be observed on the surface of the zinc electrode when the blank electrolyte is used, while almost no dendrites are generated on the surface of the zinc electrode when the electrolyte with added polyvinyl ammonium phosphate is used, and the surface is very smooth. Figure 3

[0034] (4) Zinc symmetric cells were assembled using the blank electrolyte and the electrolyte with added polyvinyl ammonium phosphate, and then the time-voltage curve of the battery at a current density of 5 mA·cm -2 and a fixed capacity of 1 mAh·cm -2 was measured to evaluate the cycle life of the battery. As shown in FIG. 4, at a current density of 5 mA·cm -2 and a fixed capacity of 1 mAh·cm -2 , the zinc symmetric cell using the blank electrolyte has a short circuit after 200 h of cycling, while the zinc symmetric cell using the electrolyte with added polyvinyl ammonium phosphate can be stably cycled to 4400 h. It shows that after the electrolyte is modified by polyvinyl ammonium phosphate, the cycle life of the zinc symmetric cell is significantly improved. Figure 4

[0035] (5) Zinc-copper asymmetric cells were assembled using the blank electrolyte and the electrolyte with added polyvinyl ammonium phosphate, and then the cycle number-coulombic efficiency curve of the battery at a current density of 5 mA·cm -2 and a fixed capacity of 1 mAh·cm -2 was measured to evaluate the coulombic efficiency of the battery. As shown in FIG. 5, the coulombic efficiency of the zinc-copper asymmetric cell using the blank electrolyte decreases rapidly after 200 cycles, while the zinc-copper asymmetric cell using the electrolyte with added polyvinyl ammonium phosphate can be stably cycled to 5200 cycles, and the average coulombic efficiency can be as high as 99.6%. It shows that after the electrolyte is modified by polyvinyl ammonium phosphate, the cycle number and coulombic efficiency of the zinc-copper asymmetric cell are significantly improved. Figure 5

[0036] ​​​(6) Zinc-iodine full cells were assembled using blank electrolyte and electrolyte with added polyvinyl alcohol ammonium phosphate, and then their performance at 2 A·g was measured. -1 The cycle count-discharge specific capacity curves at current densities were used to evaluate the performance of the zinc-iodine full cell. Figure 6 As shown, the zinc-iodine full cell using the blank electrolyte experienced a rapid decrease in discharge specific capacity and coulombic efficiency after 2000 cycles, while the zinc-iodine full cell with the electrolyte containing polyvinyl alcohol ammonium phosphate could cycle stably up to 8000 cycles with a capacity retention rate as high as 98%. This indicates that the capacity retention rate and coulombic efficiency of the zinc-iodine full cell were significantly improved after the electrolyte was modified with polyvinyl alcohol ammonium phosphate.

[0037] In summary, introducing a zwitterionic polyelectrolyte (ammonium polyvinyl phosphate) into the electrolyte can suppress hydrogen evolution and buffer pH, while also mitigating the shuttle effect of polyiodides. Furthermore, assembling an aqueous zinc-iodine battery by introducing the zwitterionic polyelectrolyte into the electrolyte can significantly improve the cycle life of the aqueous zinc-iodine battery and ensure stable coulombic efficiency.

[0038] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. The application of zwitterionic polyelectrolytes as electrolyte additives in the preparation of aqueous zinc-ion batteries, characterized in that, The zwitterionic polyelectrolyte is polyvinyl alcohol ammonium phosphate, and the concentration of polyvinyl alcohol ammonium phosphate is 0.02-0.20 g / L; the aqueous zinc-ion battery is a battery assembled in the form of "negative electrode-separator-positive electrode" with zinc metal material as negative electrode and halogen element iodine as positive electrode.

2. The application according to claim 1, characterized in that, The battery's operating current density is 1–50 mA·cm⁻¹ -2 .

3. The application according to claim 1, characterized in that, The zinc metal material is one of zinc sheet, zinc powder, electroplated zinc, or zinc foam.

4. An aqueous zinc-ion battery electrolyte, characterized in that, The electrolyte includes soluble zinc salt, polyvinyl alcohol ammonium phosphate and water; the concentration of polyvinyl alcohol ammonium phosphate is 0.02-0.20 g / L; the aqueous zinc-ion battery is a battery assembled in the form of "negative electrode-separator-positive electrode" with zinc metal material as negative electrode and halogen element iodine as positive electrode.

5. The aqueous zinc-ion battery electrolyte according to claim 4, characterized in that, The soluble zinc salt includes at least one of zinc sulfate, zinc chloride, zinc nitrate, zinc acetate, zinc fluoride, and zinc trifluoromethanesulfonate.

6. The aqueous zinc-ion battery electrolyte according to claim 4, characterized in that, The concentration of the soluble zinc salt is 1–3 mol / L.

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