Aqueous electrolyte and zinc ion hybrid capacitor containing aqueous electrolyte

Abstract

The invention discloses an aqueous electrolyte and a zinc ion hybrid capacitor containing the same. The aqueous electrolyte is used for the zinc ion hybrid capacitor, the aqueous electrolyte 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, the second additive is heterocyclic nonane, and the zinc salt is an organic antifreezing agent. The volume fraction of the organic antifreezing agent in the aqueous electrolyte is greater than 0.1% and less than 40%. According to the aqueous electrolyte disclosed by the invention, the organic anti-freezing agent and the heterocyclic nonane are used as additives, and the organic anti-freezing agent and the heterocyclic nonane are synergistically matched, so that the electrolyte is anti-freezing and is prevented from freezing, a zinc negative electrode interface can be modified, the reduction rate of Zn < 2 + > is reduced, and concentration polarization is relieved, thereby being beneficial to inhibiting dendritic crystal growth and inhibiting side reaction of a zinc negative electrode; and the low-temperature cycle performance of the zinc ion hybrid capacitor is improved.

Description

Technical Field

[0001] The invention relates to the technical field of zinc ion hybrid capacitors, and in particular to an aqueous electrolyte and a zinc ion hybrid capacitor comprising the aqueous electrolyte. Background Art

[0002] As an emerging energy storage device, zinc ion hybrid capacitors have attracted much attention in the energy field in recent years. It cleverly combines the advantages of batteries and supercapacitors, showing unique performance characteristics. From the working principle, zinc ion hybrid capacitors have a battery-type electrode and a capacitor-type electrode. During the charging and discharging process, they rely on the embedding / de-embedding process of zinc ions on the battery-type electrode side and the adsorption / desorption process on the capacitor-type electrode side to achieve charge storage. This unique electrode system enables it to have both the high energy density characteristics of batteries and the high power density characteristics of supercapacitors.

[0003] Compared with traditional energy storage devices, zinc-ion hybrid capacitors have obvious advantages. On the one hand, their energy density is high, which can meet the power supply needs for a longer time; on the other hand, their charging and discharging speed is fast, which greatly shortens the charging and discharging time. In addition, zinc resources are abundant, the cost is low, and it is relatively environmentally friendly, which makes zinc-ion hybrid capacitors have broad prospects in large-scale energy storage applications. With the continuous deepening of research and the continuous advancement of technology, zinc-ion hybrid capacitors are expected to play a more important role in the field of energy storage in the future and provide a new and effective way to solve energy problems.

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

[0005] On the one hand, during the zinc electrodeposition process, the rapid Zn 2+ Reduction kinetics and slow Zn 2+ Mass transfer kinetics will accelerate dendrite growth. Generally speaking, zinc ion hybrid capacitors need to operate at high rate conditions, and high rate operation means fast Zn 2+ reduction reaction, which will rapidly consume Zn at the solid-liquid interface 2+ However, under low temperature conditions, the electrolyte viscosity increases sharply and the ionic conductivity decreases. 2+ The mass transfer rate is relatively slow, and the Zn consumed at the interface 2+ Unable to be replenished immediately, this will form a strong interfacial concentration gradient, which in turn promotes the growth of zinc dendrites.

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

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

[0008] Therefore, it is necessary to provide an electrolyte suitable for zinc ion hybrid capacitors, which can avoid electrolyte freezing and dendrite growth of zinc negative electrode at low temperatures, ensure that the zinc ion hybrid capacitor has good mass transfer kinetics, and thus has excellent low-temperature cycle performance. This is a technical problem that needs to be solved urgently. Summary of the invention

[0009] In view of the above technical problems existing in the prior art, the purpose of the present invention is 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 of the zinc negative electrode at low temperatures, ensuring that the zinc ion hybrid capacitor has good mass transfer kinetics, thereby having excellent low-temperature cycle performance.

[0010] To achieve the above object, the present invention adopts the following technical solutions:

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

[0012] In the present invention, illustratively, 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 the present invention uses water as the main component, to which an organic antifreeze is added. According to the colligative properties of the solution, when the organic antifreeze is dissolved in water to form a solution, the freezing point of water will be lowered. This is mainly because: at low temperatures, water molecules are supposed to form ice lattices, but the presence of organic molecules in the organic antifreeze disrupts the original regular arrangement of water molecules, hinders the aggregation of water molecules, and requires a lower temperature for the water molecules to form a stable ice crystal structure, thereby lowering the freezing point of water.

[0014] However, the above-mentioned organic antifreeze agents usually have high viscosity, and the introduction of organic molecules into the electrolyte as additives hinders the Zn 2+ The rapid transfer to the zinc negative electrode exacerbates the concentration polarization at the interface, which further promotes dendrite growth. In order to solve the problem that organic antifreeze exacerbates the concentration polarization at the interface, heterocyclic nonane is introduced into the aqueous electrolyte of the present invention. First, the highly symmetrical ring structure of heterocyclic nonane allows it to be stably adsorbed on the surface of the zinc negative electrode and modify the interfacial double layer. Secondly, the larger molecular volume of heterocyclic nonane widens the interfacial double layer, and the steric hindrance effect prolongs the electron migration path. When Zn 2+ When it migrates to the surface of the zinc negative electrode, its resistance to combining with electrons increases, and Zn 2+ Therefore, even if the organic antifreeze reduces the Zn 2+ In the case of mass transfer kinetics, the introduction of heterocyclononane reduces the Zn 2+ The reduction rate is still effectively alleviated the concentration polarization at the interface, which is beneficial to inhibit dendrite growth. In addition, heterocyclononane replaces H2O and adsorbs on the electrode surface, isolating the direct contact between active water and zinc metal, and effectively inhibiting the interface side reaction.

[0015] It should be noted that the volume fraction of the organic antifreeze in the aqueous electrolyte of the present invention should not be too small or too large. If the volume fraction is too small, it cannot effectively prevent freezing, and the electrolyte may freeze under low temperature conditions; if the volume fraction is too large, it will cause the ionic conductivity in the bulk electrolyte to drop sharply, the mass transfer kinetics of zinc ions will be limited, the diffusion resistance will increase, and the low-temperature cycle capacity retention rate of the zinc ion hybrid capacitor will decrease. The aqueous electrolyte of the present invention has a simple formula, is safe and reliable, is green and environmentally friendly, and is 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. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[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, preferably ethylene glycol butyl ether.

[0018] The antifreeze effect of ethylene glycol butyl ether is good, which is mainly due to its molecular structure, which makes ethylene glycol butyl ether have good solubility and low freezing point. Under low temperature conditions, ethylene glycol butyl ether can effectively reduce the freezing point of water, thereby improving the antifreeze performance of aqueous electrolytes.

[0019] Preferably, the volume fraction of the organic antifreeze in the aqueous electrolyte is 5%-40% and does not contain 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 the ionic conductivity in the bulk electrolyte to decrease sharply, the mass transfer kinetics of zinc ions will be limited, the diffusion resistance will increase, and the cycle capacity retention rate of the zinc ion hybrid capacitor will decrease.

[0020] Preferably, the heterocyclononane includes at least one of 1,4,7-triazacyclononane, 1,4,7-trithiacyclononane and 1,4,7-triazacyclononane-1,4,7-triacetic acid, preferably 1,4,7-triazacyclononane-1,4,7-triacetic acid. These substances have highly symmetrical ring structures, 1,4,7-triazacyclononane and 1,4,7-trithiacyclononane are adsorbed on the surface of the zinc negative electrode through the N atoms or S atoms on the ring, and 1,4,7-triazacyclononane-1,4,7-triacetic acid is adsorbed through three carboxyl groups outside the ring, so 1,4,7-triazacyclononane-1,4,7-triacetic acid can produce a thicker interfacial double layer, the steric hindrance effect is more significant, and the performance of the zinc ion hybrid capacitor can be better improved.

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

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

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

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

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

[0028] The present invention does not limit the preparation method of the aqueous electrolyte. Exemplarily, the preparation method comprises the following steps:

[0029] Dissolving a zinc salt in water to obtain a zinc salt solution;

[0030] Adding the first additive to the zinc salt solution and mixing evenly to form a precursor solution;

[0031] The second additive is added to the first solution and mixed evenly to obtain an aqueous electrolyte.

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

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

[0034] Preferably, the capacitive electrode is a carbon material. For example, the carbon material may be commercial activated carbon (AC) and other porous carbon materials. However, it is not limited to the types listed above, and other commonly used carbon materials in the art are also applicable to the present invention.

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

[0036] In one embodiment, the housing model used for the zinc ion hybrid capacitor is CR2032.

[0037] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The aqueous electrolyte of the present invention uses an organic antifreeze agent and a heterocyclic nonane as additives. The two cooperate with each other to prevent the electrolyte from freezing and to avoid ice formation, and to modify the zinc negative electrode interface, thereby reducing the Zn 2+ The reduction rate can be reduced, and concentration polarization can be alleviated, thereby inhibiting dendrite growth. It can also inhibit the side reactions of the zinc negative electrode and improve the low-temperature cycle performance of the zinc ion hybrid capacitor.

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

[0041] The technical solution of the present invention is further illustrated below through specific implementation methods.

[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; the concentration of heterocyclononane refers to the molar concentration of heterocyclononane in the aqueous electrolyte.

[0043] Example 1

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

[0045] The organic antifreeze agent is ethylene glycol butyl ether, and the volume fraction of the organic antifreeze agent is 20%;

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

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

[0048] First, under air atmosphere, 57.512 g of zinc sulfate heptahydrate was weighed and pre-dissolved in 60 mL of deionized water to form solution A.

[0049] Secondly, 20 mL of ethylene glycol butyl ether was measured and added to the above solution A and stirred evenly to form solution B.

[0050] Again, dilute solution B to 100 mL with deionized water and shake 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 evenly 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 the other operations are consistent with Example 1.

[0054] Experimental example

[0055] The electrolytes of Examples 1-9 and Comparative Examples 1-4 are applied to aqueous zinc ion hybrid capacitors. The preparation method of the aqueous zinc ion hybrid capacitors comprises the following steps:

[0056] Commercial activated carbon, conductive carbon black and PVDF were dissolved in an appropriate amount of NMP in a mass ratio of 8:1:1, stirred evenly and coated on a commercial titanium foil with a thickness of 10 mm. After drying, they were punched into circular electrodes with a diameter of 16 mm as capacitive electrodes, in which the loading amount of activated carbon material was 5 mg / cm 2 .

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

[0058] The zinc ion hybrid capacitor, also known as Zn / / AC zinc ion hybrid capacitor, is assembled in the order of negative electrode shell - battery type electrode - diaphragm - electrolyte (injection volume 0.15mL) - capacitor type electrode - steel sheet - spring - positive electrode shell.

[0059] Low temperature cycle performance test:

[0060] At a low temperature of -20°C, the cycle performance of the Zn / / AC zinc ion hybrid capacitor assembled in the experimental example was tested using a constant current charge and discharge instrument, with the current density set to 8A / g and the voltage window set to 0.2-1.8V, and the capacity 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] Combined with Table 1, it can be seen that the present invention uses organic antifreeze and heterocyclic nonane as additives. The two work together to prevent the electrolyte from freezing and avoid ice formation, and can also modify the zinc negative electrode interface, alleviate concentration polarization, and help inhibit dendrite growth. It can also inhibit the side reaction of the zinc negative electrode and improve the low-temperature cycle performance of the zinc ion hybrid capacitor. The hybrid capacitor made of the electrolyte of the present invention has a capacity retention rate of more than 62.4% after 15,000 cycles at -20°C. Further, by optimizing the volume fraction of the organic antifreeze in the aqueous electrolyte, the concentration of the heterocyclic nonane, and the type of the heterocyclic nonane, the capacity retention rate of the hybrid capacitor can be made to be more than 72.5% after 15,000 cycles at -20°C.

[0065] By comparing Example 1 and Comparative Example 1, Comparative Example 2, and Comparative Example 3, it can be seen that compared with the hybrid capacitor without organic antifreeze and / or heterocyclic nonane, the addition of organic antifreeze and heterocyclic nonane can significantly improve the cycle capacity retention rate of the zinc ion hybrid capacitor.

[0066] By comparing Examples 1-3, it can be seen that the concentration of heterocyclononane in the range of 20 mmol / L-35 mmol / L is more conducive to cooperating with the organic antifreeze agent to improve the low-temperature cycle performance of the zinc ion hybrid capacitor.

[0067] By comparing Example 1 with Example 5, it can be seen that the volume fraction of the organic antifreeze agent in the aqueous electrolyte is in the range of 15%-30%, which is more conducive to improving the low-temperature cycle performance of the zinc ion hybrid capacitor.

[0068] By comparing Example 1 with Example 7, it can be seen that compared with propylene glycol butyl ether, ethylene glycol butyl ether is more conducive to cooperating with heterocyclononane to improve the low-temperature cycle performance of zinc ion hybrid capacitors.

[0069] By comparing Example 1 with Example 8, it can be seen that compared with 1,4,7-triazacyclononane, 1,4,7-triazacyclononane-1,4,7-triacetic acid is more conducive to cooperating with organic antifreeze to improve the low-temperature cycle performance of zinc ion hybrid capacitors.

[0070] By comparing Example 1 with Example 9, it can be seen that if the molar concentration of heterocyclononane is too high, a thicker double electrical layer will be formed at the interface, reducing the Zn 2+ The deposition efficiency on the zinc negative electrode leads to the decrease of low-temperature cycling performance of zinc ion hybrid capacitors.

[0071] In summary, the aqueous electrolyte provided by the present invention is an antifreeze electrolyte, and organic antifreeze agent and heterocyclic nonane are added at the same time, and the two have a synergistic effect. The electrolyte can simultaneously alleviate the growth of zinc negative electrode dendrites at low temperatures and inhibit the freezing of the electrolyte. The zinc ion hybrid capacitor containing the electrolyte has excellent cycle performance in a low temperature environment.

[0072] The applicant declares that the present invention illustrates the detailed method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed method, that is, it does not mean that the present invention must rely on the above-mentioned detailed method to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various 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. An aqueous electrolyte, characterized in that An aqueous electrolyte for a zinc ion hybrid capacitor, the aqueous electrolyte comprising a zinc salt, an electrolyte additive and water, the electrolyte additive comprising a first additive and a second additive, the first additive being an organic antifreeze, the second additive being a heterocyclic nonane, and the volume fraction of the organic antifreeze in the aqueous electrolyte being greater than 0.1% and less than 40%.

2. The aqueous electrolyte according to claim 1, characterized in that 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, preferably ethylene glycol butyl ether.

3. The aqueous electrolyte according to claim 1 or 2, characterized in that: The volume fraction of the organic antifreeze agent in the aqueous electrolyte is 5%-40% and excluding 40%, preferably 15%-30%.

4. The aqueous electrolyte according to any one of claims 1 to 3, characterized in that: The heterocyclononane includes at least one of 1,4,7-triazacyclononane, 1,4,7-trithiacyclononane and 1,4,7-triazacyclononane-1,4,7-triacetic acid, and preferably 1,4,7-triazacyclononane-1,4,7-triacetic acid.

5. The aqueous electrolyte according to any one of claims 1 to 4, characterized in that: The molar concentration of heterocyclononane in the aqueous electrolyte is 5 mmol / L-50 mmol / L, preferably 20 mmol / L-35 mmol / L.

6. The aqueous electrolyte according to any one of claims 1 to 5, characterized in that: The zinc salt is a soluble zinc salt, and the soluble zinc salt includes at least one of zinc sulfate, zinc acetate, zinc chloride and zinc trifluoromethanesulfonate.

7. The aqueous electrolyte according to any one of claims 1 to 6, characterized in that: The molar concentration of the zinc salt in the aqueous electrolyte is 0.5 mol / L-4 mol / L, preferably 1 mol / L-3 mol / L.

8. The aqueous electrolyte according to any one of claims 1 to 7, characterized in that: The aqueous electrolyte is composed of zinc salt, organic antifreeze, heterocyclononane and water; the molar concentration of the zinc salt in the aqueous electrolyte is 0.5 mol / L-4 mol / L; The volume fraction of the organic antifreeze in the aqueous electrolyte is 5%-40%; The molar concentration of heterocyclononane in the aqueous electrolyte is 5 mmol / L-50 mmol / L.

9. A zinc ion hybrid capacitor, characterized in that: The zinc ion hybrid capacitor comprises a battery-type electrode, a capacitor-type electrode, a diaphragm and an electrolyte. The diaphragm is located between the battery-type electrode and the capacitor-type electrode. The electrolyte is the aqueous electrolyte according to any one of claims 1 to 8.

10. The zinc ion hybrid capacitor according to claim 9, characterized in that: The battery-type electrode is a zinc-containing electrode; Preferably, the capacitive electrode is made of carbon material.

Images