Compound additive-containing composite electrolyte for aqueous zinc ion battery

Abstract

The invention belongs to the technical field of aqueous zinc ion batteries, and particularly discloses a compound additive-containing composite electrolyte for an aqueous zinc ion battery, the composite electrolyte is composed of a water-soluble zinc salt, deionized water and a compound additive, and the compound additive is formed by compounding tetrahydrofuran and phosphoric acid. The tetrahydrofuran and phosphoric acid compounded additive can effectively adjust the pH value of the electrolyte and keep the electrolyte stable in the electrochemical cycle process, the tetrahydrofuran additive changes a zinc ion solvated structure and meanwhile can partially open a ring under the induction of phosphoric acid, more stable linear polyether is formed and anchored on the surface of a zinc negative electrode, and the electrolyte is more stable in performance. Therefore, hydrogen evolution reaction and corrosion of the zinc negative electrode are inhibited, zinc ions are guided to be uniformly deposited, the problems of zinc dendrite growth and the like are solved, and finally the cycling stability of the zinc negative electrode is improved to a great extent.

Description

Technical Field

[0001] The invention relates to the technical field of aqueous zinc ion batteries, and in particular to a composite electrolyte for aqueous zinc ion batteries containing a composite additive. Background Art

[0002] Electrochemical energy storage technologies (such as secondary batteries, supercapacitors, and hydrogen production by water electrolysis) are characterized by low cost, high efficiency, and low environmental dependence, and have great application potential in the fields of smart grids, new energy electric vehicles, and consumer electronics. Therefore, large-scale electrochemical energy storage and conversion technologies have become a hot research area.

[0003] At present, lithium-ion batteries have good energy density (150-300Wh / kg) and stability, and occupy 95% of the electrochemical energy storage market. However, they have problems such as low power density (160-340W / kg), long charging and discharging time, and high potential safety risks caused by the flammability of organic electrolytes. Therefore, the high cost caused by the scarcity of lithium resources and the safety problems caused by organic electrolytes have seriously restricted their further development.

[0004] As an emerging energy storage technology, aqueous zinc-ion batteries have attracted widespread attention for their low cost, high safety, good environmental sustainability and high energy density. However, problems such as zinc anode dendrite growth, electrolyte decomposition and cathode dissolution limit their commercial application. Adding additives to the electrolyte is one of the more convenient and effective means to improve the performance of zinc-ion batteries. Electrolyte additives (such as ionic additives, inorganic additives, organic additives and metal additives) can effectively regulate the distribution of zinc ions on the surface of the metal zinc anode, thereby inhibiting the formation and growth of zinc dendrites. Most of the current research directions focus on using only one additive, which may not be able to simultaneously and efficiently play the role of building a stable anode / electrolyte interface, guiding zinc ion desolvation, accelerating ion transport, uniform nucleation and directional deposition. Therefore, it is crucial to design a composite electrolyte additive that can simultaneously build a stable anode / electrolyte interface, regulate zinc ion high-speed desolvation, accelerate ion transport, uniform nucleation and directional deposition. Summary of the invention

[0005] The object of the present invention is to provide a composite electrolyte for an aqueous zinc ion battery containing a composite additive, so as to solve the technical problems existing in the existing aqueous zinc ion batteries, such as low pH value of the electrolyte, instability during the electrochemical cycle, susceptibility to hydrogen evolution reaction and corrosion of the zinc negative electrode, and zinc dendrite growth.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention firstly provides a composite electrolyte for an aqueous zinc ion battery containing a composite additive. The composite electrolyte consists of a water-soluble zinc salt, deionized water and the composite additive. The composite additive is compounded of tetrahydrofuran and phosphoric acid.

[0008] Furthermore, in the composite electrolyte, the concentration of the water-soluble zinc salt is 0.1-3.0 mol / L, the concentration of tetrahydrofuran is 1-15 mmol / L, and the concentration of phosphoric acid is 1-15 mmol / L.

[0009] Furthermore, the water-soluble zinc salt is at least one of zinc sulfate, zinc acetate, zinc trifluoromethanesulfonate, zinc chloride and zinc perchlorate.

[0010] The method for preparing the composite electrolyte for aqueous zinc ion batteries of the present invention comprises the following steps:

[0011] Step 1: dissolving a water-soluble zinc salt in deionized water to obtain a basic electrolyte;

[0012] Step 2: Add the composite additive to the basic electrolyte, stir until completely dissolved, and let stand to obtain a composite electrolyte for an aqueous zinc ion battery containing the composite additive.

[0013] The present invention further provides an aqueous zinc ion battery, wherein the electrolyte of the aqueous zinc ion battery adopts the composite electrolyte containing the composite additive.

[0014] The aqueous zinc ion battery can be a symmetrical battery, a half-cell or a full battery.

[0015] Furthermore, the symmetrical battery is composed of zinc foil, a glass fiber separator and the composite electrolyte.

[0016] Furthermore, the half-cell is composed of zinc foil, glass fiber separator, copper foil and the composite electrolyte.

[0017] Furthermore, the full battery consists of a zinc foil negative electrode, a glass fiber separator, a polyaniline, manganese dioxide or vanadium pentoxide positive electrode and the composite electrolyte.

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

[0019] (1) The present invention uses tetrahydrofuran and phosphoric acid as a composite additive for the aqueous zinc ion battery electrolyte. In the presence of the H3PO4 additive, some tetrahydrofuran molecules undergo a ring-opening reaction to generate a stable linear polyether, which is preferentially adsorbed on the surface of the zinc negative electrode, thereby inhibiting the corrosion of the zinc negative electrode, accelerating the desolvation of zinc ions at the anode / electrolyte interface, accelerating the transmission of zinc ions, further promoting nucleation and inhibiting the formation and growth of dendrites, refining the grains, and ensuring that the zinc negative electrode has high reversibility and stability during the cycle process, thereby improving the cycle performance of the aqueous zinc ion battery and improving the cycle life of the aqueous zinc ion battery; and the unopened tetrahydrofuran molecules have a low reversibility to Zn 2+ Has a strong affinity and can change Zn[(H2O)6] 2+ The solvation structure of H2O can be reduced and the activity of H2O can be reduced, thereby inhibiting side reactions such as hydrogen evolution.

[0020] (2) The present invention uses tetrahydrofuran and phosphoric acid as a composite additive for the aqueous zinc ion battery electrolyte. The composite additive can effectively adjust the pH value of the electrolyte and keep it stable during the electrochemical cycle, thereby solving the side reactions such as hydrogen evolution and corrosion caused by excessively high or low pH, thereby greatly improving the cycle stability of the zinc ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the chronoamperometric (CA) curve of Zn / / Zn symmetric cells assembled with different electrolytes;

[0022] Figure 2 The Zn / / Zn symmetric battery assembled with different electrolytes at 5 mA cm -2 Cyclic voltage curves under current density;

[0023] Figure 3 The symmetrical battery assembled from the electrolyte obtained in Comparative Example 1 was -2 Scanning electron microscope (SEM) image of the zinc electrode after cycling for 100 h at a current density of ;

[0024] Figure 4 The symmetrical battery assembled from the electrolyte obtained in Example 1 was -2 Scanning electron microscope (SEM) image of the zinc electrode after 100 cycles at a current density of ;

[0025] Figure 5 The symmetrical battery assembled from the electrolyte obtained in Example 4 was -2 Scanning electron microscope (SEM) image of the zinc electrode after 100 cycles at a current density of .

[0026] Figure 6 It is a pH diagram of different electrolytes.

[0027] Figure 7 1 is the Raman spectra of the electrolytes obtained in Comparative Example and Example 4. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention are further explained in conjunction with specific embodiments below. The following embodiments are implemented on the premise of the technical solutions of the present invention, and detailed implementation methods and specific operating processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0029] Example 1

[0030] In this embodiment, a composite electrolyte for aqueous zinc batteries is prepared according to the following steps:

[0031] Step 1: dissolving zinc sulfate heptahydrate powder in deionized water to obtain a basic electrolyte;

[0032] Step 2: Add tetrahydrofuran to the basic electrolyte, stir at 800 rpm for 2 hours, and let stand for 12 hours to obtain a composite electrolyte, in which the concentration of zinc sulfate is 2.0 mol / L and the concentration of tetrahydrofuran is 10 mmol / L.

[0033] Example 2

[0034] In this embodiment, a composite electrolyte for aqueous zinc batteries is prepared according to the following steps:

[0035] Step 1: dissolving zinc sulfate heptahydrate powder in deionized water to obtain a basic electrolyte;

[0036] Step 2: Add tetrahydrofuran and phosphoric acid to the basic electrolyte, stir at 800 rpm for 2 hours, and let stand for 12 hours to obtain a composite electrolyte, in which the concentration of zinc sulfate is 2.0 mol / L, the concentration of tetrahydrofuran is 10 mmol / L, and the concentration of phosphoric acid is 5 mmol / L.

[0037] Example 3

[0038] In this embodiment, a composite electrolyte for aqueous zinc batteries is prepared according to the following steps:

[0039] Step 1: dissolving zinc sulfate heptahydrate powder in deionized water to obtain a basic electrolyte;

[0040] Step 2: Add tetrahydrofuran and phosphoric acid to the basic electrolyte, stir at 800 rpm for 2 hours, and let stand for 12 hours to obtain a composite electrolyte, in which the concentration of zinc sulfate is 2.0 mol / L, the concentration of tetrahydrofuran is 10 mmol / L, and the concentration of phosphoric acid is 15 mmol / L.

[0041] Example 4

[0042] In this embodiment, a composite electrolyte for aqueous zinc batteries is prepared according to the following steps:

[0043] Step 1: dissolving zinc sulfate heptahydrate powder in deionized water to obtain a basic electrolyte;

[0044] Step 2: Add tetrahydrofuran and phosphoric acid to the basic electrolyte, stir at 800 rpm for 2 hours, and let stand for 12 hours to obtain a composite electrolyte, in which the concentration of zinc sulfate is 2.0 mol / L, the concentration of tetrahydrofuran is 10 mmol / L, and the concentration of phosphoric acid is 10 mmol / L.

[0045] Comparative Example

[0046] The electrolyte provided in this comparative example is a basic electrolyte obtained by dissolving zinc sulfate heptahydrate powder in deionized water, wherein the concentration of zinc sulfate is 2.0 mol / L.

[0047] In order to test the practical performance of the electrolytes prepared in the above embodiments and comparative examples, batteries were assembled and battery performance tests were performed according to the following method:

[0048] Put the zinc sheet into the positive electrode shell, add appropriate amount of electrolyte, then put in the glass fiber separator. After adding appropriate amount of electrolyte, stack the zinc negative electrode, gasket and shrapnel in sequence, cover the negative electrode shell, and finally put it into the button battery packaging machine to seal it into a symmetrical battery.

[0049] Figure 1 The chronoamperometric (CA) curves of Zn / / Zn symmetric cells assembled with different electrolytes. Figure 1 It can be concluded that the current density of the symmetrical battery assembled with the electrolyte without additives in the comparative example continues to increase rapidly, while the current density of the symmetrical battery assembled with the electrolyte containing the composite additives in each embodiment tends to be stable after a short nucleation process of ~30s, and a stable and continuous three-dimensional diffusion process occurs. The stable low current density means uniform deposition of zinc.

[0050] Figure 2 The Zn / / Zn symmetric battery assembled with different electrolytes at 5 mA cm -2 Cyclic voltage curve under current density. Figure 2It can be concluded that the symmetrical battery assembled with the electrolyte without additives in the comparative example was cycled only for about 85 hours, and the polarization began to decrease rapidly until a large oscillation appeared, indicating that the uneven deposition / dissolution was accompanied by the aggravation of corrosion and hydrogen evolution, resulting in the generation of a large number of dendrites and other byproducts, and finally causing the battery to fail. However, the symmetrical battery assembled with the electrolyte containing the composite additive in Example 4, due to the ring-opening reaction of some tetrahydrofuran molecules, a stable linear polyether was generated, and it was preferentially adsorbed on the zinc anode, forming a "shielding effect", blocking the direct contact between water and zinc, inhibiting hydrogen evolution and corrosion reactions, and achieving dendrite-free zinc deposition. The final symmetrical battery can be cycled to 640 hours. This shows that the application of the electrolyte containing the composite additive of phosphoric acid and tetrahydrofuran of the present invention allows the battery to avoid the "tip effect", inhibit the formation of dendrites, and alleviate the occurrence of side reactions, and finally enables the aqueous zinc ion symmetrical battery to achieve a higher cycle stability. At the same time, it can be seen from the performance comparison of Examples 1 to 4 that the concentration of phosphoric acid has a great influence on the performance of the battery.

[0051] Symmetrical cells assembled from the electrolytes of Comparative Example, Example 1, and Example 4 were -2 The scanning electron microscope (SEM) images of the zinc electrode after 100 cycles at a current density of Figure 3 , Figure 4 and Figure 5 As shown, it can be seen that Figure 3 (Comparative Example) and Figure 4 The zinc electrode surface of (Example 1) forms severe flaky zinc dendrites, and Figure 5 The results of (Example 4) show that the surface of the zinc electrode using the electrolyte containing the composite additive is smooth and no obvious dendrites are formed.

[0052] Figure 6 The pH values ​​of different electrolytes are shown, and it can be found that the electrolyte of the comparative example presents a weakly acidic environment with a pH value of 4.03; after adding the THF additive, the pH value of the electrolyte of Example 1 drops to 3.93. The acidic electrolyte environment will accelerate the dissolution and corrosion reaction of zinc metal. The electrolyte of Example 4 is added with the H3PO4 additive to form a pH regulator composed of THF and H3PO4, and the pH value is adjusted to a value close to neutral, thereby reducing the HER and corrosion reactions, and improving the reversibility of the zinc anode, reducing the growth of zinc dendrites.

[0053] Figure 7 : is the Raman spectrum of the electrolyte obtained in the comparative example and the example 4. In the example 4, the Raman spectrum is at ~1120cm -1 An obvious band appeared at , which can be considered as the CO / COC stretching vibration of polyether, further proving the formation of polyether in ZnSO4 / THF / H3PO4 electrolyte.

[0054] From the above content, it can be seen that the composite electrolyte additive provided by the present invention can adjust the pH value of the electrolyte, and tetrahydrofuran can partially open the ring to form a stable chain polyether anchored on the surface of the zinc negative electrode, effectively solving the problems of zinc dendrites, zinc metal corrosion and hydrogen evolution, thereby greatly improving the cycle performance of the zinc negative electrode.

[0055] The above embodiments describe the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for illustrating the principles of the present invention. Without departing from the scope of the principles of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of protection of the present invention.

Claims

1. A composite electrolyte for aqueous zinc ion batteries containing a composite additive, characterized in that: The composite electrolyte is composed of water-soluble zinc salt, deionized water and a compound additive, and the compound additive is compounded from tetrahydrofuran and phosphoric acid.

2. The composite electrolyte for aqueous zinc ion batteries according to claim 1, characterized in that In the composite electrolyte, the concentration of water-soluble zinc salt is 0.1-3.0 mol / L, the concentration of tetrahydrofuran is 1-15 mmol / L, and the concentration of phosphoric acid is 1-15 mmol / L.

3. The composite electrolyte for aqueous zinc ion batteries according to claim 1, characterized in that: The water-soluble zinc salt is at least one of zinc sulfate, zinc acetate, zinc trifluoromethanesulfonate, zinc chloride and zinc perchlorate.

4. A method for preparing a composite electrolyte for an aqueous zinc ion battery according to any one of claims 1 to 3, characterized in that: The following steps are involved: Step 1: dissolving a water-soluble zinc salt in deionized water to obtain a basic electrolyte; Step 2: Add the composite additive to the basic electrolyte, stir until completely dissolved, and let stand to obtain a composite electrolyte for an aqueous zinc ion battery containing the composite additive.

5. An aqueous zinc ion battery, characterized in that: The composite electrolyte according to any one of claims 1 to 3 is used.

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