Zinc-iodine battery electrolyte additive with pH buffering and multi-iodide shuttle effect inhibiting capabilities

Abstract

The invention 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 inhibiting capabilities. In order to effectively improve the performance of the zinc ion battery and prolong the service life of the zinc ion battery, the invention provides an aqueous zinc ion battery electrolyte additive, and the electrolyte additive is a zwitterionic polyelectrolyte, can inhibit hydrogen evolution and buffer the pH value, and also can reduce the shuttle effect of polyiodide. Meanwhile, the zwitterionic polyelectrolyte is introduced into the electrolyte to assemble the water-based zinc-iodine battery, so that the cycle life of the water-based zinc-iodine battery can be greatly prolonged, and the stable coulombic efficiency of the water-based zinc-iodine battery can be ensured.

Description

Technical Field

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

[0002] Electrochemical energy storage, especially lithium-ion battery energy storage, has the advantages of being pollution-free, highly efficient, flexible in power, and having a long lifespan, and has developed very rapidly in recent years. Since 1990, lithium-ion batteries have dominated the fields of portable electronic devices, electric vehicles, and the like. However, key issues such as the lack of lithium resources, high manufacturing costs, and unsafe organic electrolytes 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 properties and extremely high safety. Compared with other metal elements, zinc metal has significant advantages in resource reserves, chemical stability, electrochemical stability, and safety. For example, metallic zinc can operate stably in both neutral and weak acid electrolytes. In addition, compared with the organic electrolytes widely used in lithium-ion batteries, the aqueous electrolytes used in aqueous zinc-ion batteries not only have ultra-high conductivity, but also have safety advantages such as being non-toxic and non-flammable. The above characteristics make aqueous zinc-ion batteries very promising for use in the future large-scale energy storage field.

[0004] However, due to the chemical properties of the zinc negative electrode in the aqueous electrolyte and the corrosion problem caused by polyiodide ions, zinc-iodine batteries are still difficult to promote and apply in large-scale energy storage. This is mainly because the zinc negative electrode is not only prone to side reactions in the aqueous electrolyte, causing hydrogen evolution and passivation, but the concentration change at the electrode / electrolyte interface will also cause the zinc ion tip deposition on the electrode surface to gradually evolve into zinc dendrites. In addition, there are also problems with the dissolution and shuttle effect of polyiodides. Among them, I2 and I - The high concentration of polyiodide ion intermediates produced by the conversion between the two will lead to a serious shuttle effect, causing the negative electrode to self-discharge (I3 - +Zn→Zn 2+ +I - ), which further aggravates the corrosion reaction of the zinc negative electrode, leading to irreversible loss of the active quality of the zinc-iodine battery and a significant decrease in the 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 improve the performance and life of zinc-ion batteries. Summary of the invention

[0005] In order to overcome the above-mentioned deficiencies of the prior art, the present invention proposes an electrolyte with pH buffering and polyiodide shuttle effect inhibition capabilities, the electrolyte uses a zwitterionic polyelectrolyte as an additive, and the aqueous zinc-iodine battery assembled with the electrolyte has the advantages of long cycle life and high coulombic efficiency.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

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

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

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

[0010] More preferably, the zinc metal material is one of zinc flakes, zinc powder, electroplated zinc, foamed zinc or zinc single substance 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; the battery separator includes but is not limited to glass fiber separator.

[0012] A second aspect of the present invention provides an aqueous zinc ion battery electrolyte, the electrolyte comprising a soluble zinc salt, polyvinyl ammonium phosphate and water.

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

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

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

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

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

[0018] Figure 1 LSV curves of the three-electrode device assembled using a blank electrolyte and an electrolyte added with polyvinyl ammonium phosphate;

[0019] Figure 2 The pH change diagram of the symmetrical battery assembled using the blank electrolyte and the electrolyte added with polyvinyl ammonium phosphate during the cycle process;

[0020] Figure 3 The symmetric zinc cell assembled with blank electrolyte and electrolyte added with polyvinyl ammonium phosphate at 5 mA cm -2 The current density and 1 mAh cm -2 Electron microscopy image of the zinc electrode surface after 200 cycles at a fixed capacity;

[0021] Figure 4 The symmetric zinc cell assembled with blank electrolyte and electrolyte added with polyvinyl ammonium phosphate at 5 mA cm -2 The current density and 1 mAh cm -2 The time-voltage curve under fixed capacity;

[0022] Figure 5 The results of the Zn-Cu asymmetric cell assembled with blank electrolyte and electrolyte added with polyvinyl ammonium phosphate at 5 mA cm -2 The current density and 1 mAh cm -2 The cycle number-Coulomb efficiency curve at a fixed capacity;

[0023] Figure 6 The Zn-iodine full cell assembled with blank electrolyte and electrolyte added with polyvinyl ammonium phosphate was tested at 2A·g -1 The cycle number-discharge specific capacity curve at the current density. DETAILED DESCRIPTION

[0024] The specific embodiments of the present invention are further described below. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in each embodiment of the present invention 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 conventional methods unless otherwise specified, and the experimental materials used in the following examples are 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. 5.75 g ZnSO4 is dissolved in 0.5 mL of polyvinyl alcohol ammonium phosphate aqueous solution (0.1 g / L) and 9.5 mL of deionized water, and stirred for 10 hours to obtain a target electrolyte (referred to as ZS+PVAP).

[0028] Comparative Example:

[0029] 5.75 g ZnSO4 was dissolved in 10 mL deionized water and stirred for 10 h to obtain a blank electrolyte (denoted as ZS).

[0030] Experimental example:

[0031] (1) A three-electrode battery device including a working electrode (electrode clip for zinc sheet), a reference electrode (Ag / AgCl), and a counter electrode (platinum electrode) was assembled using a blank electrolyte and an electrolyte with polyvinyl alcohol ammonium phosphate added, and then an LSV curve was drawn to compare the inhibition of hydrogen evolution. Figure 1 As shown in the figure, compared with the battery using blank electrolyte, the overpotential of the battery using the electrolyte added with polyvinyl alcohol ammonium phosphate is more negative, which indicates that the HER is significantly suppressed after the electrolyte is modified by polyvinyl alcohol ammonium phosphate.

[0032] (2) A zinc symmetric battery (Zn / / Zn) was assembled using a blank electrolyte and an electrolyte with polyvinyl alcohol ammonium phosphate added, and then the pH of the zinc symmetric battery under the beaker device during the cycle was compared and a pH change curve was drawn. Figure 2As shown in the figure, the pH value of the zinc symmetric battery using polyvinyl alcohol ammonium phosphate electrolyte has a stable pH value during charge and discharge, while the pH value of the zinc symmetric battery using blank electrolyte varies greatly. This shows that after the electrolyte is modified by polyvinyl alcohol ammonium phosphate, the generation of hydrogen and basic zinc salt is significantly inhibited, thereby improving the performance of zinc ion batteries.

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

[0034] (4) Zinc symmetric cells were assembled using blank electrolyte and electrolyte with polyvinyl ammonium phosphate added, and then their conductivity at 5 mA cm -2 The current density and 1 mAh cm -2 The time-voltage curve at a fixed capacity is used to evaluate the cycle life of the battery. Figure 4 As shown, at 5 mA cm -2 The current density and 1 mAh cm -2 At a fixed capacity, the zinc symmetric battery using a blank electrolyte short-circuited after 200 hours of cycling, while the zinc symmetric battery using an electrolyte with polyvinyl alcohol ammonium phosphate added could stably cycle to 4400 hours. This shows that the cycle life of the zinc symmetric battery has been significantly improved after the electrolyte was modified by polyvinyl alcohol ammonium phosphate.

[0035] (5) A Zn-Cu asymmetric cell was assembled using a blank electrolyte and an electrolyte with polyvinyl alcohol ammonium phosphate added, and then its current at 5 mA cm -2 The current density is 1 mAh cm -2 The cycle number-Coulomb efficiency curve at a fixed capacity is used to evaluate the Coulomb efficiency of the battery. Figure 5 As shown in the figure, the coulombic efficiency of the zinc-copper asymmetric battery using a blank electrolyte drops rapidly after 200 cycles, while the zinc-copper asymmetric battery using an electrolyte added with polyvinyl alcohol ammonium phosphate can stably cycle up to 5200 cycles, and the average coulombic efficiency can reach 99.6%. This shows that after the electrolyte is modified by polyvinyl alcohol ammonium phosphate, the cycle number and coulombic efficiency of the zinc-copper asymmetric battery are significantly improved.

[0036] (6) A zinc-iodine full cell was assembled using a blank electrolyte and an electrolyte with polyvinyl alcohol ammonium phosphate added, and then its conductivity at 2 A·g -1 The discharge capacity curve of the cycle number at the current density is used to evaluate the performance of the zinc-iodine full battery. Figure 6 As shown in the figure, the discharge capacity and coulombic efficiency of the zinc-iodine full battery using blank electrolyte dropped sharply after 2000 cycles, while the zinc-iodine full battery with polyvinyl alcohol ammonium phosphate electrolyte could stably cycle up to 8000 cycles, and the capacity retention rate could reach 98%. This shows that after the electrolyte was modified by polyvinyl alcohol ammonium phosphate, the capacity retention rate and coulombic efficiency of the zinc-iodine full battery were significantly improved.

[0037] In summary, by introducing zwitterionic polyelectrolytes (polyvinyl ammonium phosphate) into the electrolyte, hydrogen evolution can be suppressed and pH can be buffered, while the shuttling effect of polyiodides can be reduced. At the same time, by introducing zwitterionic polyelectrolytes into the electrolyte and assembling them into aqueous zinc-iodine batteries, the cycle life of aqueous zinc-iodine batteries can be greatly improved, and their stable coulombic efficiency can be guaranteed.

[0038] The embodiments of the present invention are 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 of these embodiments are made without departing from the principles and spirit of the present invention, and still fall within the protection scope of the present invention.

Claims

1. Application of zwitterionic polyelectrolyte as electrolyte additive in the preparation of aqueous zinc ion battery, characterized in that: The zwitterionic polyelectrolyte is polyvinyl ammonium phosphate.

2. The use according to claim 1, characterized in that: The working current density of the battery is 1~50mA·cm -2 .

3. The use according to claim 1, characterized in that: The aqueous zinc ion battery is a battery that uses zinc metal material as the negative electrode and halogen element iodine as the positive electrode, and is assembled into a "negative electrode-diaphragm-positive electrode" form.

4. The use according to claim 3, characterized in that: The zinc metal material is one of zinc flakes, zinc powder, electroplated zinc, foamed zinc or zinc single substance material.

5. An aqueous zinc ion battery electrolyte, characterized in that: The electrolyte includes soluble zinc salt, polyvinyl ammonium phosphate and water.

6. An aqueous zinc ion battery electrolyte according to claim 5, characterized in that: The concentration of the polyvinyl ammonium phosphate is 0.02-0.20 g / L.

7. An aqueous zinc ion battery electrolyte according to claim 5, characterized in that: The soluble zinc salt includes at least one of zinc sulfate, zinc chloride, zinc nitrate, zinc acetate, zinc fluoride and zinc trifluoromethane sulfonate.

8. An aqueous zinc ion battery electrolyte according to claim 5, characterized in that: The concentration of the soluble zinc salt is 1-3 mol / L.

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