A kind of aqueous electrolyte and the zinc ion hybrid capacitor comprising the aqueous electrolyte

Abstract

The application discloses a water-based electrolyte and a zinc ion hybrid capacitor comprising the water-based electrolyte. The water-based electrolyte is a water-based electrolyte for a zinc ion hybrid capacitor, and comprises a zinc salt, an electrolyte additive and water. The electrolyte additive comprises a first additive and a second additive. The first additive is an organic antifreezing agent, and the second additive is a heterocyclic nonane. The volume fraction of the organic antifreezing agent in the water-based electrolyte is greater than 0.1% and less than 40%. The water-based electrolyte of the application uses the organic antifreezing agent and the heterocyclic nonane as additives, and the two cooperate with each other. The water-based electrolyte can not only prevent freezing and avoid ice formation, but also modify the zinc negative electrode interface, reduce the Zn 2+ reduction rate, alleviate concentration polarization, thereby facilitating inhibition of dendrite growth, and can also inhibit the side reaction of the zinc negative electrode, thereby improving the low-temperature cycle performance of the zinc ion hybrid capacitor.

Description

Technical Field

[0001] This invention relates to the field of zinc ion hybrid capacitor technology, and to an aqueous electrolyte and a zinc ion hybrid capacitor containing the aqueous electrolyte. Background Technology

[0002] Zinc-ion hybrid capacitors, as an emerging energy storage device, have attracted considerable attention in the energy sector in recent years. They cleverly combine the advantages of batteries and supercapacitors, exhibiting unique performance characteristics. In terms of working principle, a zinc-ion hybrid capacitor has one battery-type electrode and one capacitor-type electrode. During charging and discharging, charge storage is achieved through the insertion / deintercalation of zinc ions on the battery-type electrode and the adsorption / desorption of zinc ions on the capacitor-type electrode. This unique electrode system allows it to possess both the high energy density characteristics of batteries and the high power density characteristics of supercapacitors.

[0003] Compared to traditional energy storage devices, zinc-ion hybrid capacitors offer significant advantages. Firstly, they possess higher energy density, meeting power supply needs for longer periods. Secondly, their rapid charging and discharging speeds greatly reduce charging and discharging time. Furthermore, zinc resources are abundant, relatively inexpensive, and environmentally friendly, making zinc-ion hybrid capacitors a promising candidate for large-scale energy storage applications. With ongoing research and technological advancements, zinc-ion hybrid capacitors are expected to play an even more crucial role in future energy storage, providing new and effective solutions to energy challenges.

[0004] Although zinc-ion hybrid capacitors have many advantages, problems such as zinc anode dendrite growth, electrolyte freezing, and interfacial side reactions seriously affect the stable operation of zinc-ion hybrid capacitors in low-temperature environments.

[0005] On the one hand, during the zinc electrodeposition process, rapid Zn deposition... 2+ Reduction reaction kinetics and slow Zn 2+ Mass transfer kinetics will accelerate dendrite growth. Typically, zinc-ion hybrid capacitors need to operate at high rates, and high-rate operation implies rapid Zn deposition. 2+ The reduction reaction will rapidly consume the Zn at the solid-liquid interface. 2+ However, at low temperatures, the electrolyte viscosity increases sharply and the ionic conductivity decreases, affecting Zn. 2+ The mass transfer rate is relatively slow, and the Zn consumed at the interface... 2+ The inability to replenish immediately will create a strong interfacial concentration gradient, which in turn promotes zinc dendrite growth.

[0006] On the other hand, due to the high freezing point of water, aqueous electrolytes may freeze in low-temperature environments. This will lead to loss of electrolyte fluidity, obstruction of ion transport, and even separation of the solid-liquid interface, resulting in battery failure.

[0007] In addition, the Zn metal anode is accompanied by interfacial side reactions such as hydrogen evolution and corrosion during the circulation of aqueous electrolyte, which also limits the cycle life of aqueous zinc ion mixed capacitors.

[0008] Therefore, it is necessary to provide an electrolyte suitable for zinc-ion hybrid capacitors that can prevent electrolyte freezing and dendrite growth on the zinc anode at low temperatures, ensuring good mass transfer kinetics of the zinc-ion hybrid capacitor and thus excellent low-temperature cycling performance. This is a technical problem that urgently needs to be solved. Summary of the Invention

[0009] To address the aforementioned technical problems in the prior art, the present invention aims to provide an aqueous electrolyte and a zinc-ion hybrid capacitor containing the aqueous electrolyte. The electrolyte provided by the present invention can prevent electrolyte freezing and dendrite growth on the zinc negative electrode at low temperatures, ensuring good mass transfer kinetics in the zinc-ion hybrid capacitor, thereby exhibiting excellent low-temperature cycling performance.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] In a first aspect, the present invention provides an aqueous electrolyte for use in zinc-ion hybrid capacitors. The aqueous electrolyte comprises zinc salt, electrolyte additives, and water. The electrolyte additives include a first additive and a second additive. The first additive is an organic antifreeze, and the second additive is heterocyclic nonane. The volume fraction of the organic antifreeze in the aqueous electrolyte is greater than 0.1% and less than 40%.

[0012] In this invention, by way of example, the volume fraction of the organic antifreeze can be, for example, 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, 5.5%, 6%, 7%, 7.5%, 8%, 9%, 10%, 12%, 14%, 15%, 16%, 18%, 20%, 22%, 23%, 25%, 26%, 27%, 28%, 30%, 32%, 35%, 36%, 38%, 39%, or 39.5%.

[0013] The aqueous electrolyte of this invention uses water as the main component and adds an organic antifreeze agent. According to the colligative properties of the solution, when the organic antifreeze agent dissolves in water to form a solution, it will lower the freezing point of water. This is mainly because: at low temperatures, water molecules are supposed to form ice crystals, but the presence of organic molecules in the organic antifreeze agent disrupts the original orderly arrangement of water molecules, hindering the aggregation of water molecules. This makes it necessary to have a lower temperature for water molecules to form a stable ice crystal structure, thereby lowering the freezing point of water.

[0014] However, the aforementioned organic antifreeze agents typically have high viscosity, and the introduction of organic molecules as additives into the electrolyte hinders the absorption of Zn. 2+ The rapid transfer to the zinc anode exacerbates concentration polarization at the interface, which further promotes dendrite growth. To address the drawback of organic antifreeze agents exacerbating interfacial concentration polarization, heterocyclic nonane is introduced into the aqueous electrolyte of this invention. First, the highly symmetrical cyclic structure of heterocyclic nonane allows it to be stably adsorbed on the zinc anode surface, modifying the interfacial electric double layer. Second, the larger molecular volume of heterocyclic nonane broadens the interfacial electric double layer, and the steric hindrance effect prolongs the electron migration path, allowing Zn... 2+ When Zn migrates to the zinc anode surface, the resistance to electron binding increases. 2+ The reduction rate decreases. Therefore, even with organic antifreeze, the reduction rate of Zn decreases. 2+ Under mass transfer kinetics, the introduction of heterocyclic nonane reduces Zn 2+ The reduction rate still effectively alleviated concentration polarization at the interface, which is beneficial for suppressing dendrite growth. Furthermore, the heterocyclic nonane replacing H₂O adsorbed on the electrode surface isolates the active water from direct contact with zinc metal, effectively suppressing interfacial side reactions.

[0015] It is important to note that the volume fraction of the organic antifreeze in the aqueous electrolyte of this invention should not be too small or too large. If the volume fraction is too small, it will not effectively prevent freezing, and the electrolyte may freeze at low temperatures. If the volume fraction is too large, it will cause a sharp decrease in the ionic conductivity of the bulk electrolyte, restricting the mass transfer kinetics of zinc ions, increasing diffusion resistance, and resulting in a decrease in the low-temperature cycling capacity retention of the zinc ion mixed capacitor. The aqueous electrolyte of this invention has a simple formulation, is safe and reliable, environmentally friendly, and suitable for large-scale production.

[0016] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0017] Preferably, the organic antifreeze agent includes at least one of ethylene glycol butyl ether, propylene glycol butyl ether, ethylene glycol butyl ether acetate, ethylene glycol, propylene glycol, polyethylene glycol, dimethyl sulfoxide, and formamide, and is preferably ethylene glycol butyl ether.

[0018] Ethylene glycol butyl ether exhibits good antifreeze properties, primarily due to its molecular structure, which gives it good solubility and a low freezing point. Under low-temperature conditions, ethylene glycol butyl ether can effectively lower the freezing point of water, thereby improving the antifreeze performance of aqueous electrolytes.

[0019] Preferably, the organic antifreeze in the aqueous electrolyte has a volume fraction of 5%-40% and does not exceed 40%, for example, it can be 5%, 7%, 8%, 10%, 12%, 15%, 16%, 18%, 20%, 23%, 25%, 27%, 30%, 32%, 34%, 36%, 38%, or 39%, etc., preferably 15%-30%. The volume fraction of the organic antifreeze should not be too high, otherwise it will cause a sharp decrease in the ionic conductivity in the bulk electrolyte, restrict the mass transfer kinetics of zinc ions, increase the diffusion resistance, and lead to a decrease in the cycle capacity retention rate of the zinc ion mixed capacitor.

[0020] Preferably, the heterocyclic nonane includes at least one of 1,4,7-triazacyclononane, 1,4,7-trithiocyclononane, and 1,4,7-triazacyclononane-1,4,7-triacetic acid, with 1,4,7-triazacyclononane-1,4,7-triacetic acid being the most preferred. These substances have highly symmetrical cyclic structures. 1,4,7-triazacyclononane and 1,4,7-trithiocyclononane are adsorbed onto the zinc anode surface through N or S atoms on the ring, while 1,4,7-triazacyclononane-1,4,7-triacetic acid is adsorbed through three carboxyl groups outside the ring. Therefore, 1,4,7-triazacyclononane-1,4,7-triacetic acid can generate a thicker interfacial double layer, resulting in a more significant steric hindrance effect and better improving the performance of the zinc ion hybrid capacitor.

[0021] Preferably, the molar concentration of heterocyclic nonane in the aqueous electrolyte is 5 mmol / L-50 mmol / L, for example, it can be 5 mmol / L, 7 mmol / L, 8 mmol / L, 10 mmol / L, 12 mmol / L, 15 mmol / L, 20 mmol / L, 25 mmol / L, 30 mmol / L, 35 mmol / L, 40 mmol / L, 45 mmol / L or 50 mmol / L, etc., preferably 20 mmol / L-35 mmol / L.

[0022] Preferably, the zinc salt is a soluble zinc salt, which includes at least one of zinc sulfate, zinc acetate, zinc chloride, and zinc trifluoromethanesulfonate.

[0023] Preferably, the molar concentration of zinc salt in the aqueous electrolyte is 0.5 mol / L-4 mol / L, for example, it can be 0.5 mol / L, 0.7 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, 2.3 mol / L, 2.5 mol / L, 2.8 mol / L, 3 mol / L, 3.3 mol / L, 3.6 mol / L, or 4 mol / L, and more preferably 1 mol / L-3 mol / L.

[0024] As a preferred technical solution of the aqueous electrolyte of the present invention, the aqueous electrolyte is composed of zinc salt, organic antifreeze, heterocyclic nonane and water;

[0025] The molar concentration of zinc salt in the aqueous electrolyte is 0.5 mol / L-4 mol / L;

[0026] The organic antifreeze has a volume fraction of 5%-40% in the aqueous electrolyte;

[0027] The molar concentration of heterocyclic nonane in the aqueous electrolyte is 5 mmol / L-50 mmol / L.

[0028] This invention does not limit the preparation method of aqueous electrolyte. Exemplarily, the preparation method includes the following steps:

[0029] Zinc salts are dissolved in water to obtain zinc salt solutions;

[0030] Add the first additive to the zinc salt solution and mix well to form the precursor solution;

[0031] Add the second additive to the first solution and mix well to obtain an aqueous electrolyte.

[0032] In a second aspect, the present invention provides a zinc-ion hybrid capacitor, the zinc-ion hybrid capacitor comprising a battery-type electrode, a capacitor-type electrode, a separator, and an electrolyte, wherein the separator is located between the battery-type electrode and the capacitor-type electrode, and the electrolyte is the aqueous electrolyte described in the first aspect.

[0033] Preferably, the battery-type electrode is a zinc-containing electrode (hereinafter referred to as a zinc electrode). Exemplarily, the zinc-containing electrode can be commercial zinc foil, zinc metal alloy, or other zinc-containing solid electrodes. However, it is not limited to the types listed above; other zinc-containing electrodes commonly used in the art are also suitable for this invention.

[0034] Preferably, the capacitive electrode is made of carbon material. Exemplarily, the carbon material can be commercially available activated carbon (AC) or other porous carbon materials. However, it is not limited to the types listed above; other carbon materials commonly used in the art are also suitable for this invention.

[0035] In one embodiment, the diaphragm is a glass fiber diaphragm (GF / D).

[0036] In one embodiment, the zinc ion hybrid capacitor uses a CR2032 type housing.

[0037] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0038] Compared with existing technologies, the present invention has the following beneficial effects:

[0039] (1) The aqueous electrolyte of the present invention utilizes organic antifreeze and heterocyclic nonane as additives. The two work synergistically to prevent the electrolyte from freezing and to modify the zinc anode interface, thereby reducing the Zn content. 2+ The reduction rate alleviates concentration polarization, which helps suppress dendrite growth and can also suppress side reactions of the zinc anode, thereby improving the low-temperature cycling performance of zinc ion hybrid capacitors.

[0040] (2) The aqueous electrolyte of the present invention has a simple formula, is safe and reliable, green and environmentally friendly, and is suitable for large-scale production. Detailed Implementation

[0041] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0042] In the following embodiments, the concentration of zinc salt refers to the molar concentration of zinc salt in the aqueous electrolyte; the volume fraction of organic antifreeze refers to the volume fraction of organic antifreeze in the aqueous electrolyte; and the concentration of heterocyclic nonane refers to the molar concentration of heterocyclic nonane in the aqueous electrolyte.

[0043] Example 1

[0044] This embodiment provides an aqueous electrolyte composed of zinc salt, organic antifreeze, heterocyclic nonane, and water; the zinc salt is ZnSO4, and the concentration of the zinc salt is 2 mol / L.

[0045] The organic antifreeze is ethylene glycol butylene, and the volume fraction of the organic antifreeze is 20%.

[0046] The heterocyclic nonane is 1,4,7-triazacyclononane-1,4,7-triacetic acid, and the concentration of the heterocyclic nonane is 25 mmol / L.

[0047] This embodiment also provides a method for preparing the above-mentioned aqueous electrolyte, including the following steps:

[0048] First, weigh 57.512g of zinc sulfate heptahydrate in air and pre-dissolve it in 60mL of deionized water to form solution A.

[0049] Next, measure 20 mL of ethylene glycol butylene and add it to the above solution A, stirring until well mixed to form solution B.

[0050] Next, dilute solution B to 100 mL with deionized water and shake well to form solution C.

[0051] Finally, 0.7583 g of 1,4,7-triazacyclononane-1,4,7-triacetic acid was weighed and added to solution C, and stirred until homogeneous to obtain the aqueous electrolyte.

[0052] Examples 2-9 and Comparative Examples 1-3

[0053] The differences from Example 1 are shown in Table 1, and all other operations are the same as in Example 1.

[0054] Experimental Example

[0055] The electrolytes of Examples 1-9 and Comparative Examples 1-4 were applied to an aqueous zinc-ion hybrid capacitor. The preparation method of the aqueous zinc-ion hybrid capacitor includes the following steps:

[0056] Commercial activated carbon, conductive carbon black, and PVDF were dissolved in an appropriate amount of NMP at a mass ratio of 8:1:1. After stirring evenly, the solution was coated onto a 10mm thick commercial titanium foil, dried, and then stamped into a 16mm diameter circular electrode sheet to serve as a capacitive electrode. The activated carbon material loading was 5mg / cm³. 2 .

[0057] Commercial zinc foil with a thickness of 0.08 mm was cleaned with ethanol and then stamped into a circular electrode with a diameter of 16 mm to serve as a battery electrode.

[0058] A zinc-ion hybrid capacitor, also known as a Zn / / AC zinc-ion hybrid capacitor, is assembled in the following order: negative electrode shell - battery-type electrode - separator - electrolyte (0.15 mL) - capacitor-type electrode - steel sheet - spring sheet - positive electrode shell.

[0059] Low-temperature cycling performance test:

[0060] The cycling performance of the Zn / / AC zinc ion hybrid capacitor assembled in the experimental example was tested at a low temperature of -20℃ using a constant current charge-discharge instrument. The current density was set to 8A / g, and the voltage window was set to 0.2-1.8V. The capacitance retention rate after 15,000 cycles was obtained. The results are shown in Table 1.

[0061] Table 1. Composition of different electrolytes and corresponding performance test results of zinc ion hybrid capacitors.

[0062]

[0063]

[0064] As shown in Table 1, this invention utilizes organic antifreeze and heterocyclic nonane as additives. The synergistic effect of these two additives not only prevents the electrolyte from freezing and avoids icing, but also modifies the zinc anode interface, alleviates concentration polarization, helps suppress dendrite growth, and inhibits side reactions at the zinc anode, thereby improving the low-temperature cycling performance of the zinc-ion hybrid capacitor. The hybrid capacitor made with the electrolyte of this invention retains a capacity of over 62.4% after 15,000 cycles at -20℃. Furthermore, by optimizing the volume fraction of the organic antifreeze in the aqueous electrolyte, the concentration of heterocyclic nonane, and the type of heterocyclic nonane, the hybrid capacitor can retain a capacity of over 72.5% after 15,000 cycles at -20℃.

[0065] By comparing Example 1 with Comparative Examples 1, 2, and 3, it can be seen that the addition of organic antifreeze and heterocyclic nonane can significantly improve the cycle capacity retention of zinc ion mixed capacitors compared with mixed capacitors that do not contain organic antifreeze and / or heterocyclic nonane.

[0066] Comparative examples 1-3 show that a concentration of heterocyclic nonane in the range of 20 mmol / L-35 mmol / L is more conducive to synergistic effects with organic antifreeze agents to improve the low-temperature cycling performance of zinc ion hybrid capacitors.

[0067] A comparison of Examples 1 and 5 shows that an organic antifreeze in the aqueous electrolyte with a volume fraction of 15%-30% is more beneficial for improving the low-temperature cycling performance of the zinc ion hybrid capacitor.

[0068] Comparing Example 1 and Example 7, it can be seen that ethylene glycol butyl ether is more beneficial for synergistic cooperation with heterocyclic nonane to improve the low-temperature cycling performance of zinc ion mixed capacitors compared to propylene glycol butyl ether.

[0069] A comparison of Examples 1 and 8 shows that, compared to 1,4,7-triazacyclononane, 1,4,7-triazacyclononane-1,4,7-triacetic acid is more conducive to synergistic effects with organic antifreeze agents to improve the low-temperature cycling performance of zinc ion hybrid capacitors.

[0070] A comparison of Examples 1 and 9 shows that if the molar concentration of heterocyclic nonane is too high, a thicker electrical double layer will form at the interface, reducing the Zn content. 2+ The deposition efficiency on the zinc anode leads to a decrease in the low-temperature cycling performance of the zinc-ion hybrid capacitor.

[0071] In summary, the aqueous electrolyte provided by this invention is an antifreeze electrolyte, which also contains an organic antifreeze agent and heterocyclic nonane. The two have a synergistic effect. This electrolyte can simultaneously alleviate the dendrite growth of zinc anode at low temperatures and inhibit electrolyte freezing. Zinc ion hybrid capacitors containing this electrolyte have excellent cycling performance in low-temperature environments.

[0072] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A zinc-ion hybrid capacitor with a capacitance retention of over 72.5% after 15,000 cycles at -20℃, characterized in that... The zinc-ion hybrid capacitor includes a battery-type electrode, a capacitor-type electrode, a separator, and an electrolyte. The battery-type electrode is a zinc-containing electrode, the capacitor-type electrode is made of carbon material, and the separator is located between the battery-type electrode and the capacitor-type electrode. The electrolyte is an aqueous electrolyte composed of zinc salt, electrolyte additives, and water. The electrolyte additives include an organic antifreeze agent and heterocyclic nonane. The organic antifreeze agent is ethylene glycol butyl ether, and the heterocyclic nonane is 1,4,7-triazacyclononane-1,4,7-triacetic acid. The volume fraction of ethylene glycol butyl ether in the aqueous electrolyte is 15%-30%. The molar concentration of 1,4,7-triazacyclononane-1,4,7-triacetic acid in the aqueous electrolyte is 20 mmol / L-35 mmol / L; The molar concentration of zinc salt in the aqueous electrolyte is 1 mol / L to 3 mol / L.

2. The zinc-ion hybrid capacitor according to claim 1, characterized in that, The zinc salt is a soluble zinc salt, which includes at least one of zinc sulfate, zinc acetate, zinc chloride, and zinc trifluoromethanesulfonate.

Images