Design of negative pole piece of low-internal-resistance lithium ion capacitor

Abstract

The invention discloses a design method of a negative pole piece of a low-internal-resistance lithium ion capacitor, and relates to a design method which takes a microporous copper current collector as a pole piece base material and regulates and controls the viscosity and the conductivity of slurry to solve the problem of high internal resistance of the lithium ion capacitor, so that the internal resistance of the capacitor is reduced, and the rate capability and the cycling stability of a monomer can be effectively improved. The pore diameter and density of the microporous copper foil influence the transmission speed of interface ions, which is specifically reflected in the diffusion speed of lithium ions and the embedding degree of lithium. The binding agent and the conductive agent influence the loading capacity of the active substance and the transmission speed of electrons, and the manufacturing of the low-internal-resistance lithium ion capacitor pole piece is achieved by regulating and controlling the influence factors.

Description

Technical Field

[0001] The invention relates to an energy storage device, in particular to the design of a negative electrode plate of a lithium ion capacitor and the production of a soft package monomer thereof. Background Art

[0002] Lithium-ion capacitor (Li-ion capacitor) is an energy storage device between lithium-ion battery and supercapacitor. It uses capacitive positive electrode material and battery-like negative electrode material, which makes it have the performance characteristics of both lithium-ion battery and capacitor: high power density, capable of charging and discharging more than 100C; more than 500,000 cycles, 100 times higher than lithium battery; high energy density, 3 to 5 times that of traditional supercapacitor. Due to its outstanding comprehensive performance, lithium-ion capacitors have a broad potential market in rail transportation, new energy vehicles, port machinery, smart grid, military industry and other fields.

[0003] The lithium ion capacitor involved in the present invention has a capacitor active material as the positive electrode and a lithium deintercalation compound as the negative electrode. During charging, under the action of the electric field, the anions in the electrolyte migrate to the positive electrode and are adsorbed on the surface of the positive electrode capacitor active material to produce a double electric layer, while the lithium ions in the electrolyte are embedded in the negative electrode material to form a lithium intercalation compound, and the electrons are transferred from the positive electrode to the negative electrode through an external circuit to participate in the formation of the lithium intercalation compound. During discharge, the opposite is true. Therefore, the positive and negative electrodes of the lithium ion capacitor, the selection of the electrolyte material, and the effect of pre-intercalation of lithium in the negative electrode are crucial to the electrochemical performance of the lithium ion capacitor.

[0004] The development of lithium-ion capacitors has been going on for nearly 30 years, and the performance of its positive and negative active materials, such as activated carbon, graphite, lithium titanium oxide and other materials, has become stable and can meet the industry's requirements for the performance of key materials for lithium-ion capacitors. Therefore, the pre-embedding of negative lithium in the lithium-ion capacitor system has become a key parameter for the realization of high-performance lithium-ion capacitors. The use of microporous foil as the current collector in lithium-ion capacitors is the key to pre-embedding lithium at the negative electrode. The lithium source pre-assembled in the capacitor can only complete the pre-lithiation process quickly through the pore channels of the microporous foil. Moreover, microporous foil can effectively carry electrode active materials, accelerate the transfer rate of charge, and reduce the electrochemical polarization internal resistance. Therefore, the negative electrode sheet based on microporous foil plays a vital role in the realization of low internal resistance of lithium-ion capacitors. Summary of the invention

[0005] The internal resistance of the negative electrode sheet of the lithium ion capacitor currently used is relatively high, which has an adverse effect on the assembly of high-performance lithium ion capacitor monomers. Based on this, it is necessary to provide a design method for a lithium ion capacitor negative electrode sheet that can quickly and efficiently complete pre-embedded lithium to achieve low resistance, and a lithium ion capacitor monomer prepared using the above negative electrode sheet.

[0006] A negative electrode plate of a lithium ion capacitor comprises a negative electrode current collector and a negative electrode active layer coated on the negative electrode current collector. The negative electrode current collector is a microporous copper foil, and the negative electrode active layer comprises a carbon material, a binder and a conductive agent.

[0007] The current collector is a microporous metal foil having a plurality of through holes extending from the surface of the foil layer to the back surface, and having a density of the through holes of 1000 / cm2.

[0008] Microporous metal foil is a type of rolled copper foil or electrolytic copper foil, with a pore size ranging from 10 to 30 um and a thickness ranging from 8 to 20 um.

[0009] The negative electrode active layer slurry is prepared from a carbon material, a conductive agent and an aqueous binder solution.

[0010] The carbon material is at least one of soft carbon, hard carbon, mesophase carbon microspheres and graphite.

[0011] The conductive agent is one or a mixture of Ketjen black, acetylene black, graphene and carbon nanotubes.

[0012] The binder is one or a mixture of polyvinylidene fluoride, ethylene acrylic acid, ethylene vinyl acetate, styrene-butadiene rubber and carboxymethyl cellulose.

[0013] The negative electrode active layer material ratio is 6-20% by mass of conductive agent, 70-92% by mass of active negative electrode material, and 2-10% by mass of binder. The thickness of the negative electrode active layer is 30-50 um.

[0014] A method for preparing the above-mentioned negative electrode plate of a lithium ion capacitor comprises the following steps: Applying negative electrode slurry on the negative electrode current collector to form a negative electrode active layer, rolling and then cutting, wherein the negative electrode slurry includes an activated carbon material, a binder and a conductive agent; A lithium ion capacitor monomer comprises a laminated battery core, an electrolyte and a capacitor housing; the laminated battery core is formed by sequentially stacking a positive electrode sheet, a diaphragm and a negative electrode sheet; the negative electrode sheet is the negative electrode sheet of the lithium ion capacitor prepared above, and the electrolyte and the laminated battery core are both placed inside the capacitor housing. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 SEM image of microporous copper foil with a pore size of 15um Figure 2 SEM image of microporous copper foil with a pore size of 25um Figure 3 The electrode sheet of Example 1 is used as the negative electrode to assemble a lithium ion capacitor monomer to test its internal resistance and rate performance; Figure 4The electrode sheet of Example 3 is used as the negative electrode to assemble a lithium ion capacitor monomer to test its internal resistance and rate performance; Implementation

[0016] In order to more clearly illustrate the purpose, features and advantages of the present invention, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. The accompanying drawings described below are some embodiments of the present invention, and those skilled in the art can make similar improvements without violating the connotation of the present invention. The present invention is not limited by the specific implementation disclosed below. Example

[0017] The present embodiment provides a design of a negative electrode sheet for a lithium ion capacitor, including the selection of a current collector and the configuration of a negative electrode coating slurry, and the specific implementation steps are as follows: (1) Add 3% binder into ultrapure water, stir for a certain period of time until it is completely dissolved, then add 87% carbon material and 10% conductive agent, stir evenly to obtain an aqueous slurry; (2) Coating the slurry on the copper foil current collector with a pore size of about 15 μm, and drying for later use; (3) Roll the negative electrode and cut it into a certain size of electrode sheet, stack it with the positive electrode sheet and pre-embedded lithium into a monomer, and seal it with an aluminum-plastic film; (4) Liquid injection, chemical formation, and sample retention for testing. Example

[0018] The present embodiment provides a design of a negative electrode sheet for a lithium ion capacitor, including the selection of a current collector and the configuration of a negative electrode coating slurry, and the specific implementation steps are as follows: (1) Add 6% binder into ultrapure water, stir for a certain period of time until it is completely dissolved, then add 86% carbon material and 8% conductive agent, stir evenly to obtain an aqueous slurry; (2) Coating the slurry on the copper foil current collector with a pore size of about 15 μm, and drying for later use; (3) Roll the negative electrode and cut it into a certain size of electrode sheet, stack it with the positive electrode sheet and pre-embedded lithium into a monomer, and seal it with an aluminum-plastic film; (4) Liquid injection, chemical formation, and sample retention for testing. Example

[0019] The present embodiment provides a design of a negative electrode sheet for a lithium ion capacitor, including the selection of a current collector and the configuration of a negative electrode coating slurry, and the specific implementation steps are as follows: (1) Add 3% binder into ultrapure water, stir for a certain period of time until it is completely dissolved, then add 87% carbon material and 10% conductive agent, stir evenly to obtain an aqueous slurry; (2) Coat the slurry on the copper foil current collector with a pore size of about 25 μm, and dry it for later use; (3) Roll the negative electrode and cut it into a certain size of electrode sheet, stack it with the positive electrode sheet and pre-embedded lithium into a monomer, and seal it with an aluminum-plastic film; (4) Liquid injection, chemical formation, and sample retention for testing. Example

[0020] (1) Add 6% binder into ultrapure water, stir for a certain period of time until it is completely dissolved, then add 86% carbon material and 8% conductive agent, stir evenly to obtain an aqueous slurry; (2) Coat the slurry on the copper foil current collector with a pore size of about 25 μm, and dry it for later use; (3) Roll the negative electrode and cut it into a certain size of electrode sheet, stack it with the positive electrode sheet and pre-embedded lithium into a monomer, and seal it with an aluminum-plastic film; (4) Liquid injection, chemical formation, and sample retention for testing.

[0021] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A method for designing a negative electrode plate of a low internal resistance lithium ion capacitor, characterized in that: include: Low internal resistance, the internal resistance value is 2~4mΩ; A negative electrode sheet, which is a soft electrode sheet loaded with carbon active material; The design method includes the selection of current collectors, and the regulation of conductive agents and adhesives.

2. The negative electrode sheet according to claim 1, characterized in that: The negative electrode plate is formed by coating and drying an aqueous slurry on a microporous current collector.

3. The design method according to claim 1 is characterized in that the aqueous slurry is regulated by changing the contents of the conductive agent, the active negative electrode material, and the binder, and the microporous current collector is selected according to the pore size.

4. The aqueous slurry according to claim 2, characterized in that It is made by using water as solvent, adding conductive agent, binder and carbon material, and stirring at high and low speeds.

5. The coating and drying method according to claim 2, characterized in that: The aqueous slurry is dried in a drying oven by extrusion coating to form an electrode sheet.

6. The conductive agent according to claim 3, characterized in that: The conductive agent is one or a mixture of Ketjen black, acetylene black, graphene and carbon nanotubes.

7. The active negative electrode material according to claim 3, characterized in that: The negative electrode carbon material is at least one of soft carbon, hard carbon, mesophase carbon microspheres and graphite.

8. The adhesive according to claim 3, characterized in that The binder is one or a mixture of polyvinylidene fluoride, ethylene acrylic acid, ethylene vinyl acetate, styrene-butadiene rubber and carboxymethyl cellulose.

9. The content according to claim 3, characterized in that The mass fractions of conductive agent are 6~20%, active negative electrode material is 70~92%, and binder is 2~10%.

10. The microporous current collector according to claim 3, characterized in that: The microporous current collector is a rolled copper foil or an electrolytic copper foil, with a pore size in the range of 10 to 30 um and a thickness in the range of 8 to 20 um.

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