CN109461937B

CN109461937B - Three-dimensional mixed conductive adhesive for lithium battery and battery comprising same

Info

Publication number: CN109461937B
Application number: CN201811223517.1A
Authority: CN
Inventors: 郭玉国; 李金熠; 孟庆海; 岳树伟; 李士成; 岳风树
Original assignee: Shenzhen Eubo New Material Technology Co ltd; Institute of Chemistry CAS
Current assignee: Shenzhen Eubo New Material Technology Co ltd; Institute of Chemistry CAS
Priority date: 2018-10-19
Filing date: 2018-10-19
Publication date: 2021-06-22
Anticipated expiration: 2038-10-19
Also published as: CN109461937A

Abstract

A three-dimensional hybrid conductive binder for a lithium battery and a battery including the same. The adhesive comprises: carbon nanotube, graphene, and a polymer having a chemical bonding effect with the carbon nanotube and the graphene. The carbon nano tubes and the graphene are mixed in a certain proportion to form a three-dimensional conductive network, and polymer groups and groups on the graphene carbon nano tubes can be effectively combined to improve the strength of the compound and can be well dispersed when electrode slurry is prepared. In the charging and discharging process, the three-dimensional composite conductive adhesive can better restrict the expansion and contraction of active substances of electrode plates, effectively improve the cycle stability and rate capability of high-capacity and high-volume change type electrode materials, such as silicon-based negative electrode materials and tin-based negative electrodes, and can be expanded to the high-volume change type electrode materials in new battery systems in the future.

Description

Three-dimensional mixed conductive adhesive for lithium battery and battery comprising same

Technical Field

The invention belongs to the field of lithium ion batteries, and relates to a three-dimensional mixed conductive binder for a lithium battery and a battery containing the binder.

Background art:

the lithium ion battery has the outstanding advantages of high specific energy, small self-discharge, long service life, greenness, no pollution and the like, and is widely applied to portable electronic products and electric automobiles. With the development and progress of the society, further application of the lithium ion battery urgently needs to improve energy density, and development of an electrode material with high specific capacity is one of effective approaches. Among negative electrode materials, carbon materials are mainly commercialized at present, and the theoretical specific capacity of the carbon materials is low and is about 372mA h g < -1 >. Silicon, which is receiving increasing attention due to its high theoretical specific capacity (about 3579mA h · g-1), is considered to be one of the most likely materials to replace graphite anodes. However, silicon undergoes a volume change of about 300% during lithium intercalation/deintercalation, and the large volume change causes pulverization and exfoliation of the silicon electrode, so that electrical contact between silicon particles and between silicon and a current collector is lost. Besides the structural design, the adhesive occupies an important position in the application of the silicon negative electrode, and the expansion effect of the pole piece can be effectively inhibited due to the strong cohesive force of the high molecular structure. Meanwhile, the silicon-based material has the characteristics of poor conductivity and rate capability, and the volume change in the lithium desorption process can be relieved and the rate capability of the active material and the electrode can be improved through the synergistic effect of the three-dimensional conductive network and the polymer by adding the conductive network into the binder. Therefore, the preparation of the adhesive which is less in dosage, strong in adhesive force, excellent in conductivity and capable of effectively inhibiting the expansion of the pole piece, particularly the expansion of the high-capacity electrode material through the synergistic effect is not only the development trend in the future, but also the urgent need of the market.

Currently, the binders mainly used for lithium ion battery electrode materials in the market mainly include polyvinylidene fluoride (PVDF), Styrene Butadiene Rubber (SBR)/sodium carboxymethylcellulose (CMC), and the like. PVDF has poor binding power and flexibility, very limited effect of inhibiting the expansion of a pole piece, difficult improvement of the capacity and the rate characteristic of the battery, and higher price of PVDF and a solvent thereof, which increases the cost of the lithium ion battery. The SBR/CMC aqueous binder is applied in the market on a large scale, but is difficult to be applied to the preparation of the positive pole piece due to the self reason, has mature application in the traditional graphite system, and still has poor expansion inhibition effect in high-capacity and especially high-volume change electrode materials. On the other hand, in order to increase the energy density of the battery, the amount of the conductive additive is also controlled to be within 5%, and it is difficult to achieve the performance of the material with high capacity and high rate.

Therefore, there is a need to develop a binder having three-dimensional conductivity and in which the polymer and the crosslinked conductive network act synergistically to effectively inhibit volume expansion and to improve capacity exertion and rate capability of high energy density battery systems.

Disclosure of Invention

In view of the defects of the prior art, one of the objects of the present invention is to provide a binder with three-dimensional conductivity, which has strong adaptability, strong mechanical properties, strong binding power, good effect of inhibiting expansion in an electrode with high volume change, and obviously improved capacity exertion and rate capability. One of the innovation points of the invention is that the conductive additive in the electrode material is creatively introduced into the binder, thereby reducing the usage amount of the binder and the conductive additive in the preparation process of the electrode material, correspondingly increasing the usage amount of active ingredients and further improving the battery performance; the second innovation point is that the polymer monomer and the conductive additive are mixed in the preparation process of the adhesive and then polymerized in situ, compared with the traditional technology, the acting force mode between the polymer and the conductive additive is changed, so that the dispersibility of the conductive additive in the polymer, the electrode conductivity and the mechanical property are improved; the third innovation point is that the combination of the carbon nanotube with the dotted line structure and the graphene with the two-dimensional surface layer structure is selected as the conductive additive, and the specific dosage range is controlled, so that the structure of the obtained binder has a multi-dimensional mixed microstructure, the conductive additive can be dispersed in the polymer more sufficiently, and the overall dosage of the polymer and the conductive additive playing a role in binding in the preparation process of the electrode material can be reduced more effectively; the innovation point is that the selected carbon nanotube is preferably a single-walled carbon nanotube, and the aspect ratio is more preferably 2000-3000; graphene is preferably a single layer, a double layer or a few layers (3-10 layers), and the graphene and the carbon nanotube can be grafted with groups by carboxylation, hydroxylation, amination, sulfonation and the like, preferably reactive groups such as hydroxyl, carboxyl, amino and the like.

Based on the above innovation, the application provides the following technical scheme:

a three-dimensional mixed conductive adhesive for a lithium battery comprises carbon nano tubes, graphene and an adhesive polymer, wherein the carbon nano tubes and/or the graphene are/is provided with a reactive group, and the reactive group can be chemically bonded with the adhesive polymer.

Preferably, in the preparation process of the binder, after the polymer monomer is mixed with the carbon nanotube and the graphene, the polymer monomer is polymerized in situ;

preferably, wherein the carbon nanotubes comprise one or more of the following: comprises multi-wall carbon nanotubes and single-wall carbon nanotubes, more preferably single-wall carbon nanotubes, wherein the aspect ratio is 100-10000, preferably 2000-5000, and most preferably 2000-3000.

Preferably, wherein the graphene comprises one or more of: graphene oxide, chemically reduced graphene oxide, single-layer graphene, double-layer graphene, few-layer graphene (3 to 10 layers), multi-layer graphene (10 layers or more), preferably single-layer or few-layer graphene.

Preferably, the mass ratio of the carbon nanotubes to the graphene is 10-90: 90-10, preferably 30-70: 70-30, most preferably 30-40: 60-70.

Preferably, wherein the reactable groups comprise one or more of: epoxy group, carboxyl, sulfonic group, hydroxyl, aldehyde group, amino group, cyano group, ester group, amide group, carbon-carbon double bond and carbon-carbon triple bond.

Preferably, the binding polymer comprises one or more of the following: cyanoacrylate, styrene-butadiene rubber, polyvinyl alcohol, isoprene rubber, polybutadiene rubber, ethylene propylene rubber, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyamic acid, polyetherimide, polyamide, sodium carboxymethylcellulose, starch, hydroxypropyl cellulose, phenol resin, epoxy resin, polyamideimide, polyacrylic acid, methacrylic acid, polymethacrylic acid, more preferably polymers having an amide group, an imide group, for example, polyamic acid, polyamide, polyetherimide, polyamideimide.

A method of making the binder, the method comprising:

adding an initiator or a catalyst A into a cohesive polymer or a polymerizable monomer material of the cohesive polymer to prepare a solution;

step (2), adding graphene with reactive groups and carbon nanotubes into the solution obtained in the step (1) to form a mixture;

step (3), uniformly mixing the mixture obtained in the step (2), and carrying out solution deoxygenation treatment;

step (4), vacuumizing, heating and stirring the solution obtained in the step (3);

and (5) reacting for a certain time to obtain the adhesive.

Preferably, step (4) comprises vacuum stirring and heating, wherein the stirring rate is controlled at 50-1000rpm, preferably 300-500 rpm; the heating reaction temperature is in the range of 40 to 200 deg.C, preferably 60 to 150 deg.C. The solid content of the adhesive obtained in the step (5) is 5-70%, preferably 10-60%; the product viscosity is from 10 to 6000 mPas, preferably from 500 to 4000 mPas.

Preferably, the catalyst/initiator in step (1) is selected from one or more of the following: ammonium persulfate, ethylene diamine tetraacetic acid, tetramethyl ethylene diamine, dithiothreitol, acrylamide-methylene acrylamide, sodium dodecyl sulfate and tris (hydroxymethyl) aminomethane.

A lithium battery comprising a positive electrode and a negative electrode, at least one of the negative electrode and the positive electrode comprising the binder according to any one of the above.

Preferably, in the lithium battery, the electrode material is prepared from the binder and the electrode active material described herein, and no conductive additive is additionally added. Wherein the binder is used in an amount of 1 to 5 parts by weight based on 100 parts by weight of the electrode.

Drawings

FIG. 1: with a schematic representation of a three-dimensional conductive network binder.

Detailed Description

The present invention will be further illustrated with reference to the following specific examples, but the present invention is not limited to the following examples. The test methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials, unless otherwise indicated, are commercially available.

Example 1

5g of carboxymethyl cellulose, 5g of acrylic acid, 0.025g of ammonium persulfate, 3.5g of few-layer graphene (3-7) of hydroxyl and carboxyl, 1.5g of single-walled carbon nanotube with the length-diameter ratio of 3000 and 200ml of deionized water to form a mixture, adding the mixture into a reaction kettle, stirring the mixture at 30 ℃ until the mixture is fully mixed, wherein the stirring revolution speed is 20rpm, the dispersion rotation speed is 2000rpm, and introducing high-purity nitrogen to drive oxygen for 2 hours. And (3) vacuumizing and degassing the reaction kettle, heating to 80 ℃, and reacting for 2 hours at a stirring speed of 20rpm to obtain the binder with the three-dimensional conductive network.

The composite binder is mixed with nano silicon particles for pulping, wherein the mass of the binder excluding water and the ratio of nano silicon powder are 3: 97. and uniformly coating the slurry on a copper foil current collector to obtain the electrode diaphragm. A button battery is assembled by using a metal lithium sheet as a counter electrode, a polypropylene microporous membrane (Celgard 2400) as a diaphragm and 1mol/L LiPF6 (a solvent is a mixed solution of ethylene carbonate and dimethyl carbonate with a volume ratio of 1: 1, wherein 5% of vinylidene fluoride carbonate is added) as an electrolyte in an argon-protected glove box, and a charge-discharge test is performed, wherein the test procedure is 100mA/g, and the charge-discharge voltage interval is 0.01-1.0V. The peel strength of the electrode sheet, the gram capacity exertion of the electrode material, the 50-cycle capacity retention rate of the battery, the rate capability of the electrode material and the expansion rate of the electrode sheet were respectively tested, and the results are shown in table 1.

Example 2

The difference from example 1 is that 10g of acrylamide, 0.025g of ammonium persulfate and 0.01g N-N methylene bisacrylamide were used as raw materials, and 0.025g of ethylenediaminetetraacetic acid was added before heating and stirring, and the test results are shown in Table 1.

Example 3

Compared with example 1, the difference is that the raw material adopts 10-15 layers of graphene. The test results are shown in Table 1.

Example 5

Compared with example 1, the difference is that the ratio of carbon nanotubes to graphene in the raw material is adjusted to 50: 50, the total mass of the conductive additive was unchanged, and the test results are shown in Table 1.

Example 6

Compared with the embodiment 1, the difference is that the raw material adopts 10-15 layers of graphene, the ratio of the composite binder to the nano silicon particles is 6: 94, the test results are shown in Table 1.

Example 7

Compared with the embodiment 2, the difference is that the ratio of the raw material graphene to the carbon nanotubes is changed to 30: 70, the test results are shown in Table 1.

Example 9

The difference compared to example 1 is that the raw materials used are carboxymethyl cellulose and a product after polyacrylic acid esterification, and the test results are shown in table 1.

Example 10

The difference from example 1 is that the polymer obtained by crosslinking acrylamide and methylene acrylamide was used as the starting material, and the test results are shown in Table 1.

Example 11

The difference from example 1 is that the aspect ratio of the carbon nanotube is 2000, and the test results are shown in table 1.

Comparative example 1

Compared with example 1, the difference is that the raw material does not use carbon nanotubes, the ratio of the binder to the graphene is kept unchanged, and the test results are listed in table 1.

Comparative example 2

Compared with example 1, the difference is that the raw material does not use graphene, the ratio of the binder to the carbon nanotubes is kept unchanged, and the test results are listed in table 1.

Comparative example 3

The difference compared to example 1 is that no chemically active polymer was used as the starting material, the ratio of binder to carbon nanotubes was kept constant and the test results are shown in table 1.

Comparative example 4

Compared with example 1, the difference is that the raw materials do not use graphene and carbon nanotubes, conductive carbon black is used, the ratio of the binder to the conductive carbon black is kept unchanged, and the test results are listed in table 1.

Comparative example 5

Compared with the embodiment 1, the difference is that only sodium carboxymethyl cellulose, styrene butadiene rubber and conductive carbon black are used as raw materials, and the nano silicon particles are changed: adhesive: the carbon material ratio is 94: 2: 4, the test results are shown in Table 1.

Comparative example 6

Compared with the example 1, the difference is that only polyacrylic acid, styrene butadiene rubber and conductive carbon black are used as raw materials, and the nano silicon particles are changed: adhesive: the carbon material ratio is 94: 2: 4, the test results are shown in Table 1.

Comparative example 7

The difference compared to example 1 is that the starting material was only polyacrylic acid and no other polymer, and the test results are listed in table 1.

Table 1 examples and comparative performance test results

Claims

1. A preparation method of a binder with a three-dimensional conductive network comprises the following steps: 5g of carboxymethyl cellulose, 5g of acrylic acid, 0.025g of ammonium persulfate, 3.5g of 3-7 layers of few-layer graphene with hydroxyl and carboxyl, 1.5g of single-walled carbon nanotubes with the length-diameter ratio of 3000 and 200ml of deionized water to form a mixture, adding the mixture into a reaction kettle, stirring the mixture at 30 ℃ until the mixture is fully mixed, wherein the stirring revolution speed is 20rpm, the dispersion rotation speed is 2000rpm, and introducing high-purity nitrogen to drive oxygen for 2 hours; and (3) vacuumizing and degassing the reaction kettle, heating to 80 ℃, and reacting for 2 hours at a stirring speed of 20rpm to obtain the binder with the three-dimensional conductive network.