An electrolyte assembly optimization method for sodium-ion hybrid capacitors

Abstract

The application discloses an electrolyte assembly optimization method for a sodium ion hybrid capacitor and belongs to the technical field of electrochemical energy storage. The assembly method is to use an ester electrolyte which is more resistant to oxidation for pre-sodium treatment, form a film on the surface of a negative electrode material, and then assemble the sodium ion hybrid capacitor through an ether electrolyte. Through the ingenious design, the voltage window of the ether electrolyte can be widened to a certain extent, the problem of low oxidation potential of the ether is solved, and different electrode materials can be adapted by selecting different ester and ether electrolytes. In addition, the method does not need to modify the original ether electrolyte, and many tedious difficulties are saved. When the method is applied to the assembly of the sodium ion hybrid capacitor, excellent electrochemical performance can be exhibited, a new idea is provided for solving the electrolyte problem of the sodium ion hybrid capacitor, and a new way is opened up.

Description

TECHNICAL FIELD

[0001] The application relates to an electrolyte assembly optimization method for a sodium-ion hybrid capacitor and belongs to the technical field of electrochemical energy storage. BACKGROUND

[0002] With the huge demand for energy and carbon neutralization, the use of green energy such as solar energy and wind energy is rapidly increasing. However, the power transmission of green energy is intermittent and unstable, and a powerful energy storage system is needed to ensure the continuous output of electricity. Therefore, electrochemical energy storage (EES) devices are rapidly developing and being applied to homes and industries. At present, batteries and supercapacitors are the two most widely used energy storage devices in the world. Lithium-ion batteries are widely used in mobile electronic products, electric vehicles and other fields due to their high energy density. However, there are also some limitations, such as low power density and unsatisfactory cycle life. Supercapacitors can be ultra-fast charged in seconds, providing high power density (>10 kW kg -1 ) and stable operation for tens of thousands of times, and are applied to hybrid electric vehicles, subway train energy recovery, etc. However, due to the double-layer-based energy storage mechanism, the energy density of traditional supercapacitors is limited. Therefore, the development direction of the next generation of EES devices is to realize high energy and high power density, ultra-long cycle life and low cost.

[0003] Therefore, in advanced EES devices, the combination of batteries and supercapacitors, i.e. hybrid capacitors, is proposed. Hybrid capacitors are a combination of battery-type negative electrodes and capacitor-type positive electrodes, involving two different charge storage mechanisms during charging / discharging. Battery-type negative electrodes realize energy storage through the Faraday reaction of cations and can be divided into intercalation-type, alloying-type and conversion-type reactions, while capacitor-type positive electrodes store charges through physical adsorption / desorption or rapid reversible redox reactions on or near the surface. Based on this mixed charge storage mechanism, battery-type negative electrodes can provide high energy density, while capacitor-type positive electrodes can ensure high power density, which makes hybrid capacitors a competitive potential candidate for high-performance energy storage devices.

[0004] In recent years, due to the gradual rise in the price of lithium ore, people have focused on sodium, which is abundant in resources. Sodium-ion hybrid capacitors (SIHCs) have emerged as the times require. Due to the abundance of sodium resources, the standard Na / Na + redox potential is low, and the solvation Na + radius is smaller than the solvation Li +And achieved the expected key achievements. At present, the balance of the capacity and kinetics difference between the positive electrode and the battery type anode is still the key challenge for the existence of SIHCs. For this reason, researchers are committed to developing and exploring high-rate performance negative electrode materials. Due to the high theoretical capacity of multi-electron reaction, metal chalcogenides have been explored as potential negative electrode materials for sodium-ion hybrid capacitors. Compared with their corresponding metal oxides, metal chalcogenides exhibit excellent reversible capacity and better Na + Dynamics. This is mainly due to the different electronegativity of sulfur and oxygen, which causes the metal chalcogenide bond energy to be weaker than the corresponding metal oxide, and the weaker metal-sulfur bond can better promote the kinetics of electrochemical reaction. In addition, it is found that the use of ether-based electrolyte for metal chalcogenides can fully exert their electrochemical performance, but it is limited by the narrow redox window of ether-based electrolyte when assembling sodium-ion hybrid capacitors.

[0005] Therefore, the development of high-rate performance negative electrode materials and the research of high-performance electrolyte matching them are of great significance for the successful application of sodium-ion hybrid capacitors. SUMMARY

[0006] In the experiment, we found that the use of ester-based electrolyte in sodium-ion hybrid capacitors can cause the energy attenuation of the device to be particularly serious, which is due to the low cycle life of the positive and negative electrode materials in the ester-based electrolyte. Although the use of ether-based electrolyte can improve the cycle stability, the intrinsic low oxidation potential of ether-based electrolyte causes the voltage window of the hybrid capacitor to be reduced, thereby greatly reducing the overall energy density and power density. Based on this, researchers hope to solve this problem by designing high-voltage ether-based electrolyte. However, although the voltage window of the ether-based electrolyte can be expanded by certain modification strategies, due to the matching problem of the positive and negative electrode materials and the electrolyte, the modified electrolyte often affects the electrochemical performance of the positive and negative electrode materials. In addition, the research on the electrolyte of sodium-based energy storage devices is far from mature compared with lithium batteries, and there is still a long way to go to design ether-based electrolyte with high-voltage characteristics and matching positive and negative electrode materials.

[0007] Therefore, the purpose of the present application is to provide a simple and easy-to-use optimization assembly process method for sodium-ion hybrid capacitor electrolyte based on the defects existing in the current sodium-ion hybrid capacitor electrolyte.

[0008] The method of the present application comprises the following steps:

[0009] (1) The negative electrode material, conductive agent, binder and mixing solvent are uniformly mixed to obtain a mixed slurry, which is then coated on a copper foil. Vacuum drying at 65℃ for 12h, and then cutting into a 14mm diameter disc;

[0010] (2) The positive electrode material, conductive agent, and binder are mixed with a sizing solvent to obtain a mixed slurry, which is then coated on an aluminum foil. The coated aluminum foil is vacuum dried at 65°C for 12 hours, and then cut into a 14mm diameter disc;

[0011] (3) The negative electrode sheet obtained in step (2) is assembled into a CR2032 button-type half cell in a glove box. The electrolyte used is an ester-based electrolyte, the counter electrode is a metal sodium sheet, and the separator is GF / D. The assembled battery is pre-circulated at a small current density, and then sodiumized.

[0012] (4) The pre-sodiumized negative electrode sheet and the positive electrode sheet prepared in step (2) are assembled into a sodium-ion hybrid capacitor in a glove box, using an ether-based electrolyte as the electrolyte and a GF / D separator.

[0013] Further, in step (1), the negative electrode material is a sulfide with a conversion reaction or alloying reaction mechanism, including VS2, NbS2, FeS2, CoS2, NiS2, CuS2, ZnS2, MoS2, WS2, SnS2, InS2, etc., but is not limited to these.

[0014] Further, in step (2), the positive electrode material can include one of activated carbon, porous carbon, and graphene.

[0015] Further, in steps (1) and (2), the mass ratio of the negative electrode material / positive electrode material, conductive agent, and binder is (60-90):(5-20):(5-20). The conductive agent can include one or a mixture of several of acetylene black, Super-P, carbon nanotubes, Ketjen black, carbon fibers, and graphene. The binder can include an oil-based binder or a water-based binder. The oil-based binder can include polyvinylidene fluoride, and the water-based binder can include one or a mixture of several of styrene butadiene rubber, LA132, PAA-Li, sodium carboxymethyl cellulose, and sodium alginate. When the binder is an oil-based binder, the sizing solvent can include N-methyl pyrrolidone. When the binder is a water-based binder, the sizing solvent can include deionized water.

[0016] Further, in step (3), the ester-based electrolyte solute can include one or a mixture of several of NaPF6, NaClO4, NaCF3SO3, NaBH4, NaFSI, NaTFSI, and NaNO3. The ester-based electrolyte solvent can include one or a mixture of several of EC, DEC, PC, DMC, EMC, FEC, VC, MPC, AEC, AMC, VEC, EA, VA, ADV, and TAC.

[0017] Further, in the step (3), the current density used is 0.05-0.2 A g -1 , the pre-circulation is 3-10 times, and the sodiumization voltage is 0.01-0.3 V.

[0018] Further, in the step (4), the ether electrolyte solute can include one or more of NaPF6, NaClO4, NaCF3SO3, NaBH4, NaFSI, NaTFSI, and NaNO3; and the ether electrolyte solvent can include one or more of DME, DIGLYME, TETRAGLYME, G4, TTE, and HFE.

[0019] The present application has the following advantages:

[0020] (1) The method of the present application is universal and suitable for various positive and negative electrode materials.

[0021] (2) Different materials match different electrolytes, and the present application can flexibly combine the ester electrolyte and the ether electrolyte suitable for the positive and negative electrode materials.

[0022] (3) Compared with other inventions, the present application widens the electrochemical window without changing the excellent electrochemical performance of the ether electrolyte, and has excellent energy density, power density, and cycle stability when applied to a sodium ion hybrid capacitor.

[0023] (4) The method has simple experimental steps and easy operation, can be realized on a large scale, and provides a new idea for solving the electrolyte problem of the sodium ion hybrid capacitor. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 Figure is a long cycle performance test diagram of the sodium ion hybrid capacitor assembled according to the present application, Example 1, Comparative Example 1, and Comparative Example 2.

[0025] Figure 2 Figure is the first circle charge-discharge curve of the sodium ion hybrid capacitor assembled according to the present application, Example 1.

[0026] Figure 3 Figure is the first circle charge-discharge curve of the sodium ion hybrid capacitor assembled according to the present application, Comparative Example 2.

[0027] Figure 4 Figure is the first circle charge-discharge curve of the sodium ion hybrid capacitor assembled according to the present application, Comparative Example 3. DETAILED DESCRIPTION

[0028] The present application will be further described below through specific examples. Those skilled in the art should understand that the examples are only to help understand the present application and should not be regarded as specific limitations of the present application.

[0029] Example 1

[0030] (1) Vanadium disulfide, acetylene black, polyvinylidene fluoride were mixed in N-methyl pyrrolidone in the ratio of 7:2:1, then coated on copper foil. Vacuum dried at 65°C for 12h, then cut into a 14mm diameter disc;

[0031] (2) Activated carbon, acetylene black, polyvinylidene fluoride were mixed in N-methyl pyrrolidone in the ratio of 7:2:1, then coated on aluminum foil. Vacuum dried at 65°C for 12h, then cut into a 14mm diameter disc;

[0032] (3) The electrode sheet obtained in step (1) was assembled into a CR2032 button half-battery in a glove box, the electrolyte used was 1M NaClO4 in EC:DEC=1:1 Vol% with 5% FEC, the counter electrode was a piece of metallic sodium, and the separator was GF / D. The assembled battery was first pre-cycled at 0.1 Ag -1 for 3 times, and finally sodiumized to 0.3V;

[0033] (4) The electrode sheet of step (3) was used as the negative electrode and the electrode sheet prepared in step (2) was used as the positive electrode, the electrolyte was 1M NaPF6 in DME=100 Vol%, and the separator was GF / D. A sodium-ion hybrid capacitor was assembled in a glove box.

[0034] Example 2

[0035] (1) Molybdenum disulfide, acetylene black, polyvinylidene fluoride were mixed in N-methyl pyrrolidone in the ratio of 8:1:1, then coated on copper foil. Vacuum dried at 65°C for 12h, then cut into a 14mm diameter disc;

[0036] (2) Activated carbon, acetylene black, polyvinylidene fluoride were mixed in N-methyl pyrrolidone in the ratio of 8:1:1, then coated on aluminum foil. Vacuum dried at 65°C for 12h, then cut into a 14mm diameter disc;

[0037] (3) The electrode sheet obtained in step (1) was assembled into a CR2032 button half-battery in a glove box, the electrolyte used was 1M NaClO4 in EC:DMC=1:1 Vol% with 5% FEC, the counter electrode was a piece of metallic sodium, and the separator was GF / D. The assembled battery was first pre-cycled at 0.05 Ag -1 for 5 times, and finally sodiumized to 0.3V;

[0038] (4) Take the electrode prepared in step (3) as the negative electrode and the electrode prepared in step (2) as the positive electrode, and use 1M NaPF6 in DIGLYME = 100 Vol% as the electrolyte and GF / D as the separator to assemble a sodium-ion hybrid capacitor in a glove box.

[0039] Example 3

[0040] (1) Cobalt disulfide, acetylene black and polyvinylidene fluoride were mixed in a ratio of 8:1:1 in N-methylpyrrolidone, and then coated on a copper foil. Vacuum drying was performed at 65°C for 12h, and then the copper foil was cut into a circular sheet with a diameter of 14mm;

[0041] (2) Graphene, acetylene black and polyvinylidene fluoride were mixed in a ratio of 8:1:1 in N-methylpyrrolidone, and then coated on an aluminum foil. Vacuum drying was performed at 65°C for 12h, and then the aluminum foil was cut into a circular sheet with a diameter of 14mm;

[0042] (3) The electrode prepared in step (1) was assembled into a CR2032 button-type half-cell in a glove box, and 1M NaPF6, 0.2M NaNO3 in EC:PC = 1:1 Vol% with 5% FEC was used as the electrolyte, a piece of metallic sodium was used as the counter electrode, and GF / D was used as the separator. The assembled battery was first pre-cycled at 0.1Ag -1 for 3 times, and then sodiumized to 0.3V;

[0043] (4) Take the electrode prepared in step (3) as the negative electrode and the electrode prepared in step (2) as the positive electrode, and use 1M NaPF6 in DME = 100 Vol% with 5% TTE as the electrolyte and GF / D as the separator to assemble a sodium-ion hybrid capacitor in a glove box.

[0044] Example 4

[0045] The same steps (1) and (2) as in Example 1 were selected; (3) The electrode prepared in step (1) was assembled into a CR2032 button-type half-cell in a glove box, and 1M NaFSI, 0.2M NaNO3 in EC:PC:EMC = 1:1:1 Vol% was used as the electrolyte, a piece of metallic sodium was used as the counter electrode, and GF / D was used as the separator. The assembled battery was first pre-cycled at 0.1Ag -1 for 3 times, and then sodiumized to 0.3V; (4) The electrolyte used to assemble a sodium-ion hybrid capacitor was 1M NaFSI in DME.

[0046] Example 5

[0047] The same steps (1) and (2) as in Example 1 were selected; (3) Assembled CR2032 type button half cell, the electrolyte used was 1M NaClO4 in EC:DEC:EMC=1:1:1 Vol%. The assembled battery was first pre-cycled at 0.1Ag -1 3 times, and finally sodiumized to 0.3V; (4) Assembled sodium ion hybrid capacitor, the ether electrolyte used was 1M NaClO4 in DME=100 Vol%.

[0048] Example 6

[0049] The same steps (1), (2) and (3) as in Example 2 were selected, except that the assembled battery was pre-cycled at 0.1Ag -1 5 times, and finally sodiumized to 0.3V. Assembled sodium ion hybrid capacitor, the ether electrolyte used was 1M NaPF6 in DME=100 Vol%.

[0050] Comparative Example 1

[0051] The same steps (1), (2) and (3) as in Example 1 were selected. In step (4), the electrolyte for assembling the sodium ion hybrid capacitor was still selected as 1M NaClO4 in EC:DEC=1:1 Vol% with 5% FEC.

[0052] Comparative Example 2

[0053] The same steps (1), (2), (3) and (4) as in Example 1 were selected. Except that the electrolyte used for pre-sodiumization was changed to 1M NaPF6 in DME=100 Vol%, and the test voltage range of the sodium ion hybrid capacitor was 1-3.8V.

[0054] Comparative Example 3

[0055] The same steps as in Comparative Example 2 were taken. Except that the test voltage range of the sodium ion hybrid capacitor was 1-4V.

[0056] Except for Comparative Example 2, the test voltage of the sodium ion hybrid capacitor assembled in all other examples was 1-4V, and the current density was 1Ag -1 . The performance of the prepared sodium ion hybrid capacitor is shown in Table 1.

[0057] The above merely describes preferred embodiments of the present application, and is not intended to limit the present application in any form. Any person skilled in the art can make many possible changes and modifications to the technical solutions of the present application, or make equivalent embodiments with equivalent changes, without departing from the scope of the technical solutions of the present application, by using the technical contents described above. Therefore, any person skilled in the art should understand that any improvement, equivalent replacement of each raw material of the product of the present application, addition of auxiliary ingredients, selection of specific modes, etc. of the present application all fall within the protection scope and disclosure scope of the present application.

[0058] Table 1

[0059] Energy density (Wh Kg -1 ) Power density (W Kg -1 ) 1000 th Post energy density (Wh Kg -1 )]]> 1000 th Energy retention (%)]] Example 1 84.1 2803.3 77.8 92.5 Example 2 81.5 1191.7 71.8 88.1 Example 3 90.9 2272.5 79.6 87.6 Example 4 86.2 2155.0 78.0 90.5 Example 5 75.5 2516.7 72.6 96.2 Example 6 77.8 2593.3 73.3 94.2 Comparative Example 1 85.4 1708.0 42.8 50.1 Comparative Example 2 66.7 952.9 61.1 91.6 Comparative Example 3 \ \ \ \

[0060] Table 1 and Figure 1 It can be seen that the sodium ion hybrid capacitor assembled by the electrolyte optimization method of the present application can operate stably and exhibits excellent electrochemical performance. Comparative Example 1 has particularly serious energy attenuation during the cycle process compared with other examples. Comparative Example 2 exhibits excellent energy retention rate, but due to the limitation of the voltage window, the energy density and power density are much lower. In combination with Figure 3 , Figure 4 the charge-discharge curves, it is found that Comparative Example 3, which is the same as Comparative Example 2, is adjusted to 4V in voltage, and obvious electrolyte oxidation and decomposition phenomenon is observed, and the assembled sodium ion hybrid capacitor cannot operate normally.

[0061] In summary, the use of lipid electrolyte in sodium ion hybrid capacitors leads to serious energy attenuation of the device, and although the use of ether electrolyte can improve the cycle stability, the ether electrolyte has a low intrinsic oxidation potential, and there is obvious electrolyte decomposition phenomenon at a higher voltage, which leads to the need to reduce the voltage window of the hybrid capacitor, thereby greatly reducing the overall energy density and power density. The optimized electrolyte assembly method of the present application does not change the excellent electrochemical performance of the ether electrolyte, widens its electrochemical window, and has excellent energy density, power density and cycle stability when applied to sodium ion hybrid capacitors. Moreover, this method does not add additional complex experimental steps, can be applied on a large scale, and opens up a new way to solve the electrolyte problem of sodium ion hybrid capacitors.

[0062] Although the present application has been described above by combining exemplary embodiments, it should be clear to those skilled in the art that various modifications and changes can be made to the exemplary embodiments of the present application without departing from the spirit and scope defined by the claims.

Claims

1. A method for electrolyte assembly optimization for sodium-ion hybrid capacitors, characterized by: The negative electrode material is pre-sodiumized using an ester electrolyte, and then a sodium ion hybrid capacitor is assembled using an ether electrolyte; The negative electrode material is a sulfide with a conversion reaction or alloying reaction mechanism, including VS2, NbS2, FeS2, CoS2, NiS2, CuS2, ZnS2, MoS2, WS2, SnS2, or InS2.

2. The method for electrolyte assembly optimization for sodium-ion hybrid capacitors according to claim 1, wherein The specific steps are: (1) The negative electrode material, conductive agent, and binder are mixed with a sizing solvent to obtain a mixed slurry, which is then coated on a copper foil; vacuum drying is performed at 65°C for 12h, and then the copper foil is cut into a 14mm diameter disc; (2) The positive electrode material, conductive agent, and binder are mixed with a sizing solvent to obtain a mixed slurry, which is then coated on an aluminum foil; vacuum drying is performed at 65°C for 12h, and then the aluminum foil is cut into a 14mm diameter disc; (3) The obtained negative electrode sheet is assembled into a CR2032 button-type half battery in a glove box, the electrolyte used is an ester electrolyte, the counter electrode is a metal sodium sheet, and the separator is GF / D. The assembled battery is first subjected to pre-circulation at a current density of 0.05-0.2 Ag -1 Finally, sodiumization is performed again; (4) The pre-sodiumized electrode is used as the negative electrode, the electrode prepared in step (2) is used as the positive electrode, an ether electrolyte is selected as the electrolyte, and a GF / D separator is used to assemble a sodium ion hybrid capacitor in a glove box.

3. The method for electrolyte assembly optimization for sodium-ion hybrid capacitors according to claim 2, wherein: In step (2), the positive electrode material includes one of activated carbon, porous carbon, and graphene.

4. The method for electrolyte assembly optimization for sodium-ion hybrid capacitors according to claim 2, wherein: In steps (1) and (2), the mass ratio of the negative electrode material / positive electrode material, conductive agent, and binder is (60-90):(5-20):(5-20), the conductive agent includes one or a mixture of several of acetylene black, Super-P, carbon nanotubes, Ketjen black, carbon fibers, and graphene, the binder includes an oil-based binder or a water-based binder, the oil-based binder includes polyvinylidene fluoride, the water-based binder includes one or several of styrene-butadiene rubber, LA132, PAA-Li, sodium carboxymethyl cellulose, and sodium alginate, the sizing solvent includes N-methyl pyrrolidone when the binder is an oil-based binder, and the sizing solvent includes deionized water when the binder is a water-based binder.

5. The method for electrolyte assembly optimization for sodium-ion hybrid capacitors according to claim 2, wherein: In step (3), the pre-cycling includes 3-10 times, and the sodiumization voltage includes 0.01-0.3V.

6. The method for electrolyte assembly optimization for sodium-ion hybrid capacitors according to claim 2, wherein: In step (3), the ester electrolyte solute includes one or several of NaPF6, NaClO4, NaCF3SO3, NaBH4, NaFSI, NaTFSI, and NaNO3; the ester electrolyte solvent includes one or a mixture of several of EC, DEC, PC, DMC, EMC, FEC, VC, MPC, AEC, AMC, VEC, EA, VA, ADV, and TAC.

7. The method for electrolyte assembly optimization for sodium-ion hybrid capacitors according to claim 2, wherein: In step (4), the ether electrolyte solute includes one or several of NaPF6, NaClO4, NaCF3SO3, NaBH4, NaFSI, NaTFSI, and NaNO3; the ether electrolyte solvent includes one or several of DME, DIGLYME, TETRAGLYME, G4, TTE, and HFE.

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