CN108520959B - Water-based polymer-isocyanate-based electrode composite material and preparation method thereof - Google Patents

Water-based polymer-isocyanate-based electrode composite material and preparation method thereof Download PDF

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CN108520959B
CN108520959B CN201810229403.1A CN201810229403A CN108520959B CN 108520959 B CN108520959 B CN 108520959B CN 201810229403 A CN201810229403 A CN 201810229403A CN 108520959 B CN108520959 B CN 108520959B
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composite material
isocyanate
water
electrode
electrode composite
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CN108520959A (en
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胡宏玖
李爽
郭晶
张柯烽
贺耀龙
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University of Shanghai for Science and Technology
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/043—Processes of manufacture in general involving compressing or compaction
    • H01M4/0433—Molding
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention discloses a water-based polymer-isocyanate-based electrode composite material and a preparation method thereof, which can be applied to secondary battery electrode composite materials and forming thereof. The preparation method is characterized in that based on an aqueous solution mixing and coating method, 3.0-15.0% of water-based polymer, 80.5-95.7% of electrode active particles, 2.0-8.0% of conductive auxiliary agent and 0.5-1.5% of water emulsion polymerization isocyanate cross-linking agent are used for preparing a composite material, and then the composite material is coated on a current collector to obtain a negative electrode. The electrode composite material prepared by the method has excellent electrochemical behavior and mechanical property, and the forming process is simple, the production efficiency is high, and the electrode composite material meets the requirements of environmental protection.

Description

Water-based polymer-isocyanate-based electrode composite material and preparation method thereof
Technical Field
The invention relates to an electrode composite material and a preparation method thereof, in particular to a water-based polymer-based negative electrode composite material and a preparation method thereof, which are applied to the technical field of lithium and sodium secondary batteries and the technical field of new energy materials and forming processes.
Background
Although the current global main energy is still based on fossil fuels such as petroleum, coal and natural gas, the fossil fuels have the characteristic of non-renewable energy, gases such as carbon dioxide, nitrous oxide and sulfur dioxide released in the combustion process cause air pollution, and the development and utilization of wind energy, solar energy, geothermal energy and the like are therefore the key points of continuous attention in the field of energy for over thirty years. However, these renewable clean energy sources are restricted by environmental factors, and cannot be stably and continuously supplied, and a high-capacity energy storage and conversion device needs to be developed to realize effective storage and distribution, i.e. the energy storage technology is a strategic support for future energy structure transformation and power production and consumption mode change. Although electrochemical energy storage systems such as lithium, sodium secondary batteries, fuel cells and super capacitors have been rapidly developed in recent years, graphite-based lithium ion batteries have been widely applied to consumer electronics devices such as mobile communication, portable computers and video cameras, and are also acknowledged as the first choice for power supply and storage of renewable energy, but the capacity and power of the graphite-based lithium ion batteries still cannot meet the actual engineering requirements. Compared with graphite with the theoretical capacity of only 372mAh/g, the novel negative electrode material such as silicon, germanium, tin, ternary transition metal oxide and the like has higher energy density, but the electrode active particles are accompanied with severe volume change in the charge and discharge cycles of the electrode, the deformation is restricted by a surrounding matrix, the electrode is easy to damage due to the generated large stress, and the cycle life of the battery is obviously shorter than that of the existing commercial product. How to improve the service performance of the high-capacity secondary battery is a common challenge in the chemical, mechanical and material industries in recent years.
The electrode of the lithium and sodium battery is formed by coating a composite material prepared from active particles, a conductive auxiliary agent and a bonding material on the surface of a metal current collector. The polymer binder is a key component of the binder and is intended to tightly connect the active particles and conductive materials (carbon black, acetylene black, nickel powder, etc.) to the current collector, maintaining the integrity of the conductive path. Polyvinylidene fluoride (PVdF) used as a common binder of the graphite negative electrode has mechanical properties which are difficult to meet the service requirements of high-capacity electrode materials in an electrolyte environment. Not only is the adhesive polymer body easily damaged, but also the debonding phenomenon with the active particles and the current collector is significant, so that the complete electron movement channel cannot be maintained, thereby becoming one of the main factors of the battery capacity degradation. In addition, PVdF electrodes require the use of large amounts of N-methyl pyrrolidone (NMP) during the formation process, and the organic solvent is not only expensive and toxic, but also evaporates slowly, resulting in long slurry drying time and low electrode production efficiency. The aqueous bonding system has the advantages of low cost, no pollution and no need of pretreatment to control humidity, and hydroxyl or carboxyl-containing aqueous polymers such as carboxymethyl cellulose (CMC), carboxylic styrene-butadiene emulsion (SBR), polyvinyl alcohol (PVA), polyacrylic acid (PAA) and sodium alginate gradually replace PVdF in recent years and become main bonding agents of negative electrode materials of lithium and sodium secondary batteries. Although the cycle capacity, the coulombic efficiency and the rate capability of the high-power battery prepared based on the water-based polymer are obviously improved, the high-power battery still has a larger distance from the engineering requirement.
Disclosure of Invention
In order to solve the problems of the prior art, the invention aims to overcome the defects in the prior art and provide the water-based polymer-isocyanate-based electrode composite material and the preparation method thereof.
In order to achieve the purpose, the invention adopts the following technical scheme:
an aqueous polymer-isocyanate-based electrode composite material is prepared by combining aqueous polymer containing hydroxyl or carboxyl, electrode active particles, a conductive additive and water-emulsified polymeric isocyanate as raw material components, wherein the raw material components are as follows according to the dry mass percentage:
3.0-15.0 wt% of water-based polymer;
80.5-95.7 wt% of active particles;
1.0-3.0 wt% of conductive additive;
0.3-1.5 wt% of water-emulsified polymeric isocyanate.
The above-mentioned aqueous polymer preferably adopts any one polymer or mixture of any several polymers of carboxymethyl cellulose, carboxyethyl cellulose, carboxylic styrene-butadiene emulsion, polyvinyl alcohol, polyacrylic acid, sodium alginate and vinyl acetate homopolymerized and copolymerized emulsion.
The electrode active particles are preferably made of any one material or a mixture of any several materials of graphite, silicon, germanium, tin, transition metal oxide and nano zinc ferrite.
The conductive auxiliary agent preferably adopts any one material or a mixture of any several materials of carbon black, acetylene black, carbon fiber, carbon nano sheet and nickel powder.
The water-emulsified polymeric isocyanate is preferably a polymeric polyisocyanate modified with a nonionic surfactant.
In a preferred embodiment of the present invention, the aqueous polymer is used as the adhesive material, the crosslinking adhesive system of the aqueous polymer and the water-emulsified polymeric isocyanate is formed, the water-emulsified polymeric isocyanate crosslinking electrode particles and the conductive assistant form a firm chemical linking structure, and the aqueous polymer, the electrode active particles, the conductive assistant and the water-emulsified polymeric isocyanate form the aqueous polymer-isocyanate-based electrode composite material with a three-dimensional network structure.
A preparation method of an electrode composite material adopts an aqueous solution casting method or an aqueous solution mixing and coating method, wherein the raw material components are prepared according to the dry mass percentage of the components, 3.0-15 wt% of waterborne polymer, 80.5-95.7 wt% of electrode active particles, 1.0-3.0 wt% of conductive additive and 0.3-1.5 wt% of water emulsion polymerization isocyanate are used as raw materials to prepare the waterborne polymer-isocyanate-based electrode composite material, and the preparation method comprises the following steps:
a. adding the water-based polymer and deionized water into a reaction kettle according to the mass ratio of 2:100, slowly heating to 60-90 ℃, and mechanically stirring for 1-2 hours to obtain a uniformly distributed water-based polymer solution;
b. cooling to 50 ℃, slowly adding a conductive aid into the aqueous polymer solution prepared in the step a, and mixing for 2-3 hours under the combined action of ultrasonic waves and mechanical stirring to uniformly disperse the conductive aid in the aqueous polymer solution;
c. continuously cooling to 30-40 ℃, gradually adding the electrode active particles into the mixed solution of the aqueous polymer and the conductive agent prepared in the step b, and mechanically stirring for 1-2 hours to disperse the active particles into the mixed solution; as a preferred technical scheme of the invention, the temperature is continuously reduced to 30-35 ℃, the electrode active particles are gradually added into the mixed solution of the aqueous polymer and the conductive agent, and mechanical stirring is carried out, so that the active particles are dispersed in the mixed solution;
d. c, dropwise adding water-emulsified polymeric isocyanate into the mixed solution prepared in the step c, and stirring for 15-30 minutes to obtain slurry;
e. d, coating the slurry prepared in the step d on a metal current collector with the thickness of not less than 8 mu m, and then carrying out a three-stage drying and forming process:
drying at 40-60 deg.C for 30-60 min to obtain initial stage drying treatment; then drying at the temperature of 110-140 ℃ for 20-50 minutes to carry out intermediate-stage drying treatment; and carrying out final drying treatment for 60-120 minutes at 30-60 ℃ in vacuum to obtain the cathode electrode sheet composite material.
As the preferred technical scheme of the invention, the three-stage drying and forming process is carried out:
drying at 50-60 deg.C for 45-60 min to perform initial stage drying treatment; then drying at the temperature of 110-140 ℃ for 30-50 minutes to carry out intermediate-stage drying treatment; and carrying out final drying treatment for 60-120 minutes at 30-60 ℃ in vacuum to obtain the cathode electrode sheet composite material.
As a preferred technical scheme, the preparation method of the electrode composite material adopts the raw material components of the water-based polymer, the electrode active particles, the conductive auxiliary agent and the water-emulsified polymeric isocyanate according to the dry mass ratio of (3-6) to 90:3: 1.
Compared with the prior art, the invention has the following obvious and prominent substantive characteristics and remarkable advantages:
1. the electrode composite material substrate prepared by the invention is a cross-linking bonding system of the water-based polymer and the polyisocyanate, wherein hydrogen bond acting force exists between the water-based polymer main glue and the electrode active particles, so that excellent toughness and self-repairing function are provided for the composite material; the isocyanate group-NCO in the water-emulsified polymeric isocyanate not only forms a chemical bond with hydroxyl or carboxyl in the water-based polymer, but also can react with free hydroxyl on the surfaces of the cross-linked electrode particles and the conductive additive to form firm chemical connection, an effective three-dimensional network structure is formed among the components of the composite material, and the macroscopic mechanical property of the composite material is obviously improved;
2. in the coating and forming process of the composite material slurry prepared by the invention, water or metal oxide hydrate is adsorbed on the metal surface of a current collector, urea bonds generated by the reaction of-NCO and water are chelated with metal oxides due to hydrogen bonds to form ureides, namely metal oxide complexes; in addition, the group can also form a covalent bond with a metal hydrate and the like, so that the dried composite material and the current collector have excellent bonding strength;
3. when the-NCO of the bonding system is chemically crosslinked with a solvent and carboxyl contained in the component, a certain amount of carbon dioxide can be released, and a small amount of micropores are generated in the gas escape process, so that the volume change generated by the desorption of lithium/sodium from electrode active particles can be buffered, the internal stress is reduced, and the diffusion of electrolyte in a composite material is facilitated, so that the internal resistance is reduced, and the rate capability of a battery is improved;
4. in the prior art, in order to improve the production efficiency of the electrode plate, a common solution is to increase the drying temperature, but the capillary effect causes the polymer content in the composite material to present gradient distribution along the coating thickness, namely, the adhesive close to the collector side is less, and the surface of the active layer is enriched, so that the layered damage is easily generated, the motion resistance of active ions in the electrolyte is increased, and based on the nonlinear characteristic of the solvent evaporation process in the composite material during electrode forming and the strong correlation with the mechanical property of a cured film; the invention designs a three-section drying temperature-changing and time-changing molding process, realizes the sectional temperature and time control, controls the initial temperature and the tail end temperature at the lower temperature range of 40-60 ℃ and 30-60 ℃, and only raises the drying temperature of the middle stage to 110-140 ℃, thereby not only improving the molding efficiency, but also increasing the crosslinking degree of the composite material and better solving the problem of the non-uniformity of the distribution of the polymer adhesive therein;
5. the water-based polymer-isocyanate-based electrode composite material prepared by the method has excellent electrochemical and mechanical properties;
6. compared with the existing preparation method of the cathode of the lithium secondary battery, the method of the invention not only has more excellent product performance and higher production efficiency, but also avoids the release of organic solvent.
Drawings
Fig. 1 is a specific capacity performance curve diagram of a battery made of the aqueous polymer-isocyanate-based electrode composite material as a negative electrode material according to an embodiment of the present invention.
Detailed Description
The above-described scheme is further illustrated below with reference to specific embodiments, which are detailed below:
the first embodiment is as follows:
in this embodiment, a preparation method of an electrode composite material adopts an aqueous solution casting method or an aqueous solution mixing and coating method, adopts raw material components of sodium carboxymethylcellulose, styrene-butadiene rubber emulsion, electrode zinc ferrite nanoparticles, conductive carbon black and polymeric polyisocyanate modified by a nonionic surfactant according to a ratio of 3:3:90:3:1 in parts by dry mass, and includes the following steps:
a. adding sodium carboxymethylcellulose and deionized water into a reaction kettle according to the mass ratio of 2:100, slowly heating to 80 ℃ at the heating speed of 10 ℃/min, and mechanically stirring for 1 hour to obtain a uniformly distributed sodium carboxymethylcellulose solution;
b. cooling to 50 ℃, slowly adding 30 parts by dry mass of conductive carbon black into 30 parts by dry mass of the sodium carboxymethyl cellulose solution prepared in the step a, and mixing for 2 hours under the combined action of ultrasonic waves and mechanical stirring to uniformly disperse the conductive carbon black in the sodium carboxymethyl cellulose solution;
c. continuously cooling to 35 ℃, gradually adding 900 parts by dry mass of electrode zinc ferrite nanoparticles into the mixed solution of sodium carboxymethylcellulose and conductive carbon black prepared in the step b, and mechanically stirring for 1 hour to disperse active particles in the mixed solution;
d. gradually adding 30 parts of styrene-butadiene rubber emulsion with dry content into the mixed solution prepared in the step c, adding 30 parts of deionized water, and mechanically stirring for 30 minutes to disperse the mixture into the mixed solution;
e. cooling to 25 ℃, dropwise adding 10 parts by dry mass of polymeric polyisocyanate modified by nonionic surfactant into the mixed solution prepared in the step c, and stirring for 15 minutes to obtain slurry;
f. and e, coating the slurry prepared in the step e on a copper foil metal current collector with the thickness of 8 microns, and then performing a three-stage drying and forming process: drying at 50 deg.C for 45 min to obtain initial stage drying treatment; then drying at 110 ℃ for 30 minutes for intermediate stage drying treatment; and finally drying the mixture at 30 ℃ for 60 minutes in vacuum to obtain the cathode electrode plate composite material.
Experimental test analysis:
the aqueous polymer-isocyanate-based electrode composite material prepared in the embodiment is used as a negative electrode plate, and experimental detection is carried out, so that the areal density of the composite material is 12.5mg/cm2Tensile strength of 5.46MPa and adhesive strength of 0.81N/cm, see Table 1.
Example two:
this embodiment is substantially the same as the first embodiment, and is characterized in that:
in this embodiment, a preparation method of an electrode composite material, which adopts an aqueous solution casting method or an aqueous solution mixing and coating method, adopts raw material components of polyvinyl alcohol, electrode graphite particles, conductive carbon black and polymeric polyisocyanate modified by a nonionic surfactant according to a ratio of 6:90:3:1 in parts by dry mass, and includes the following steps:
a. adding polyvinyl alcohol and deionized water into a reaction kettle according to the mass ratio of 2:100, slowly heating to 80 ℃ at the heating speed of 10 ℃/min, and mechanically stirring for 1 hour to obtain uniformly distributed polyvinyl alcohol solution;
b. cooling to 50 ℃, slowly adding 30 parts by dry mass of conductive carbon black into 60 parts by dry mass of the polyvinyl alcohol solution prepared in the step a, and mixing for 2 hours under the combined action of ultrasonic waves and mechanical stirring to uniformly disperse the conductive carbon black in the polyvinyl alcohol solution;
c. continuously cooling to 30 ℃, gradually adding 900 parts by dry mass of electrode graphite particles into the mixed solution of the polyvinyl alcohol and the conductive carbon black prepared in the step b, and mechanically stirring for 1 hour to disperse the active particles into the mixed solution;
d. cooling to 25 ℃, dropwise adding 10 parts by dry mass of polymeric polyisocyanate modified by nonionic surfactant into the mixed solution prepared in the step c, and stirring for 15 minutes to obtain slurry;
e. d, coating the slurry prepared in the step d on a copper foil metal current collector with the thickness of 8 microns, and then performing a three-stage drying and forming process: drying at 50 deg.C for 45 min to obtain initial stage drying treatment; then drying at 110 ℃ for 30 minutes for intermediate stage drying treatment; and finally drying the mixture at 30 ℃ for 60 minutes in vacuum to obtain the cathode electrode plate composite material.
Experimental test analysis:
the aqueous polymer-isocyanate-based electrode composite material prepared in the embodiment is used as a negative electrode plate, and experimental detection is carried out, so that the areal density of the composite material is 13.8mg/cm2The tensile strength was 4.50MPa, and the adhesive strength was 0.80N/cm. Although the tensile strength of the waterborne polymer-isocyanate-based electrode composite prepared in this example is slightly lower than that of the waterborne polymer-isocyanate-based electrode composite prepared in the first example, the areal density of the waterborne polymer-isocyanate-based electrode composite is higher, and the composite and the current collector have excellent bonding strength equivalent to that of the first example, see table 1.
Example three:
this embodiment is substantially the same as the previous embodiment, and is characterized in that:
in this embodiment, a preparation method of an electrode composite material, which adopts an aqueous solution casting method or an aqueous solution mixing and coating method, adopts raw material components of polyvinyl alcohol, electrode graphite particles, conductive carbon black and polymeric polyisocyanate modified by a nonionic surfactant according to a ratio of 6:90:3:1 in parts by dry mass, and includes the following steps:
a. adding polyvinyl alcohol and deionized water into a reaction kettle according to the mass ratio of 2:100, slowly heating to 60 ℃ at the heating speed of 10 ℃/min, and mechanically stirring for 2 hours to obtain uniformly distributed polyvinyl alcohol solution;
b. cooling to 50 ℃, slowly adding 30 parts by dry mass of conductive carbon black into 60 parts by dry mass of the polyvinyl alcohol solution prepared in the step a, and mixing for 3 hours under the combined action of ultrasonic waves and mechanical stirring to uniformly disperse the conductive carbon black in the polyvinyl alcohol solution;
c. continuously cooling to 40 ℃, gradually adding 900 parts by dry mass of electrode graphite particles into the mixed solution of the polyvinyl alcohol and the conductive carbon black prepared in the step b, and mechanically stirring for 3 hours to disperse the active particles into the mixed solution;
d. cooling to 30 ℃, dropwise adding 10 parts by dry mass of polymeric polyisocyanate modified by nonionic surfactant into the mixed solution prepared in the step c, and stirring for 30 minutes to obtain slurry;
e. d, coating the slurry prepared in the step d on a copper foil metal current collector with the thickness of 8 microns, and then performing a three-stage drying and forming process:
drying at 40 deg.C for 60 min to obtain initial stage drying treatment; then drying at 140 ℃ for 20 minutes for intermediate stage drying treatment; and finally drying the mixture at 60 ℃ for 60 minutes in vacuum to obtain the cathode electrode plate composite material.
Experimental test analysis:
the aqueous polymer-isocyanate-based electrode composite material prepared in the embodiment is used as a negative electrode plate, and experimental detection is carried out, so that the areal density of the composite material is 13.7mg/cm2The tensile strength was 4.48MPa, and the adhesive strength was 0.82N/cm. The waterborne polymer-isocyanate-based electrode composite prepared in this example, although having a slightly lower areal density than the waterborne polymer-isocyanate-based electrode composite prepared in example two, had excellent tensile strength and adhesive strength comparable to those of example two, see table 1.
Example four:
this embodiment is substantially the same as the previous embodiment, and is characterized in that:
in this embodiment, a method for preparing an electrode composite material, which uses an aqueous solution casting method or an aqueous solution mixing and coating method, includes the following steps that raw material components, namely polyvinyl alcohol, graphite particles, conductive carbon black and polymeric polyisocyanate modified by a nonionic surfactant, are mixed according to a ratio of 6:90:3:1 in parts by dry mass:
a. adding polyvinyl alcohol and deionized water into a reaction kettle according to the mass ratio of 2:100, slowly heating to 90 ℃ at the heating speed of 15 ℃/min, and mechanically stirring for 1 hour to obtain uniformly distributed polyvinyl alcohol solution;
b. cooling to 50 ℃, slowly adding 30 parts by dry mass of conductive carbon black into 60 parts by dry mass of the polyvinyl alcohol solution prepared in the step a, and mixing for 2 hours under the combined action of ultrasonic waves and mechanical stirring to uniformly disperse the conductive carbon black in the polyvinyl alcohol solution;
c. continuously cooling to 40 ℃, gradually adding 900 parts by dry mass of electrode graphite particles into the mixed solution of the polyvinyl alcohol and the conductive carbon black prepared in the step b, and mechanically stirring for 2 hours to disperse the active particles into the mixed solution;
d. cooling to 30 ℃, dropwise adding 10 parts by dry mass of polymeric polyisocyanate modified by nonionic surfactant into the mixed solution prepared in the step c, and stirring for 30 minutes to obtain slurry;
e. d, coating the slurry prepared in the step d on a copper foil metal current collector with the thickness of 8 microns, and then performing a three-stage drying and forming process:
drying at 60 ℃ for 30 minutes for an initial stage; then drying for 50 minutes at 110 ℃ for intermediate stage drying treatment; and finally drying the mixture at 120 ℃ for 30 minutes in vacuum to obtain the cathode electrode plate composite material.
Experimental test analysis:
the aqueous polymer-isocyanate-based electrode composite material prepared in the embodiment is used as a negative electrode plate, and experimental detection shows that the area density is 13.5mg/cm2, the tensile strength is 4.51MPa, and the bonding strength is 0.79N/cm. The aqueous polymer-isocyanate-based electrode composite prepared in this example has a slightly lower areal density than the aqueous polymer-isocyanate-based electrode composites prepared in the second and third examples, but has the same excellent tensile strength and adhesion strength to the current collector.
Comparative example one:
in the comparative example, the preparation method of the electrode composite material adopts an aqueous solution casting method or an aqueous solution mixing and coating method, adopts the raw material components of sodium carboxymethylcellulose, styrene-butadiene rubber emulsion, electrode zinc ferrite nano particles and conductive carbon black according to the proportion of 3.5:3.5:90:3 in parts by dry mass, and comprises the following steps:
a. adding sodium carboxymethylcellulose and deionized water into a reaction kettle according to the mass ratio of 2:100, slowly heating to 80 ℃ at the heating speed of 10 ℃/min, and mechanically stirring for 1 hour to obtain a uniformly distributed sodium carboxymethylcellulose solution;
b. cooling to 50 ℃, slowly adding 30 parts by dry mass of conductive carbon black into 35 parts by dry mass of the sodium carboxymethyl cellulose solution prepared in the step a, and mixing for 2 hours under the combined action of ultrasonic waves and mechanical stirring to uniformly disperse the conductive carbon black in the sodium carboxymethyl cellulose solution;
c. continuously cooling to 35 ℃, gradually adding 900 parts by dry mass of electrode zinc ferrite nanoparticles into the mixed solution of sodium carboxymethylcellulose and conductive carbon black prepared in the step b, and mechanically stirring for 1 hour to disperse active particles in the mixed solution;
d. cooling to 25 ℃, dropwise adding 35 parts of styrene-butadiene rubber emulsion in dry mass into the mixed solution prepared in the step d, adding 30 parts of deionized water, and mechanically stirring for 30 minutes to obtain slurry;
e. d, coating the slurry prepared in the step d on a copper foil metal current collector with the thickness of 8 microns, and then performing a three-stage drying and forming process: drying at 50 deg.C for 45 min to obtain initial stage drying treatment; then drying at 110 ℃ for 30 minutes for intermediate stage drying treatment; and finally drying the mixture at 30 ℃ for 60 minutes in vacuum to obtain the cathode electrode plate composite material.
Experimental test analysis:
the electrode composite material prepared by the comparative example is used as a negative electrode slice to carry out experimental detection, and the areal density of the electrode composite material is 10.5mg/cm2The tensile strength was 3.45MPa, and the adhesive strength was 0.51N/cm. Example one preparationCompared with the aqueous polymer-based electrode composite material prepared by the comparative example, the aqueous polymer-isocyanate-based electrode composite material has obviously improved surface density, tensile strength and bonding strength.
Comparative example two:
in the comparative example, the preparation method of the electrode composite material adopts an aqueous solution casting method or an aqueous solution mixing and coating method, adopts the raw material components of polyvinyl alcohol, electrode zinc ferrite nano particles and conductive carbon black according to the proportion of 7:90:3 in parts by dry mass, and comprises the following steps:
a. adding polyvinyl alcohol and deionized water into a reaction kettle according to the mass ratio of 2:100, slowly heating to 80 ℃ at the heating speed of 10 ℃/min, and mechanically stirring for 1 hour to obtain uniformly distributed polyvinyl alcohol solution;
b. cooling to 50 ℃, slowly adding 30 parts by dry mass of conductive carbon black into 60 parts by dry mass of the polyvinyl alcohol solution prepared in the step a, and mixing for 2 hours under the combined action of ultrasonic waves and mechanical stirring to uniformly disperse the conductive carbon black in the polyvinyl alcohol solution;
c. continuously cooling to 30 ℃, gradually adding 900 parts by dry mass of electrode zinc ferrite nanoparticles into the mixed solution of polyvinyl alcohol and conductive carbon black prepared in the step b, and mechanically stirring for 1 hour to disperse active particles in the mixed solution;
d. cooling to 25 ℃, and adding 30 parts of
Mechanically stirring the deionized water for 30 minutes to obtain slurry;
e. d, coating the slurry prepared in the step d on a copper foil metal current collector with the thickness of 8 microns, and then performing a three-stage drying and forming process: drying at 50 deg.C for 45 min to obtain initial stage drying treatment; then drying at 110 ℃ for 30 minutes for intermediate stage drying treatment; and finally drying the mixture at 30 ℃ for 60 minutes in vacuum to obtain the cathode electrode plate composite material.
Experimental test analysis:
the waterborne polymer-isocyanate-based electrode composite material prepared in the example was used as a negative electrodeThe pole piece is tested by experiments, and the surface density of the pole piece is 13.0mg/cm2Tensile strength of 3.21MPa and adhesive strength of 0.55N/cm, see Table 1. The surface density, tensile strength and adhesive strength of the waterborne polymer-isocyanate-based electrode composite materials prepared in the second, third and fourth examples are obviously improved compared with those of the waterborne polymer-isocyanate-based electrode composite material prepared in the comparative example.
TABLE 1 comparison of the main physical and mechanical properties of the electrode composites prepared in the inventive and comparative examples
Figure BDA0001602284650000091
As can be seen from table 1 and fig. 1, the composite material prepared by the above embodiment of the present invention based on the waterborne polymer-isocyanate bonding system has good electrochemical behavior and excellent mechanical properties, and can be widely applied to the industrial field of lithium ion or sodium ion secondary batteries. Compared with the electrode composite material prepared in the comparative example, which is used as a negative electrode material, the aqueous polymer-isocyanate-based electrode composite material prepared in the example I is used for preparing a battery, and the battery prepared from the aqueous polymer-isocyanate-based electrode composite material prepared in the example I has higher coulombic efficiency and battery capacity for the first time. The aqueous polymer-isocyanate-based electrode composite prepared in example two has the same excellent initial coulombic efficiency and battery capacity as those of the batteries prepared from the electrode composites prepared in examples three and four, and the initial coulombic efficiency and battery capacity of the battery prepared from the aqueous polymer-isocyanate-based electrode composite prepared in example two are higher than those of the battery prepared from the electrode composite prepared in comparative example two as a negative electrode material. And compared with the battery prepared by using the electrode composite material prepared in the first embodiment as a negative electrode material, the capacity of the battery prepared in the second embodiment is improved by more than two times. The composite material prepared by the waterborne polymer-isocyanate bonding system prepared by the embodiment of the invention has good electrochemical behavior and excellent mechanical property, and can be widely applied to the industrial field of lithium ion or sodium ion secondary batteries.
In a word, the substrate of the electrode composite material prepared by the embodiment of the invention is a cross-linking bonding system of the water-based polymer and the polyisocyanate, wherein a hydrogen bond acting force exists between the water-based polymer main glue and the electrode active particles, so that excellent toughness and a self-repairing function are provided for the composite material; the isocyanate group-NCO in the water-emulsified polymeric isocyanate not only forms a chemical bond with hydroxyl or carboxyl in the water-based polymer, but also can react with free hydroxyl on the surfaces of the cross-linked electrode particles and the conductive additive to form firm chemical connection, an effective three-dimensional network structure is formed among the components of the composite material, and the macroscopic mechanical property of the composite material is obviously improved; in the coating and forming process of the composite material slurry prepared in the embodiment, water or metal oxide hydrate is adsorbed on the metal surface of the current collector, urea bonds generated by the reaction of-NCO and water and metal oxides are chelated due to hydrogen bonds to form ureides, namely metal oxide complexes; in addition, the group can also form a covalent bond with a metal hydrate and the like, so that the dried composite material and the current collector have excellent bonding strength; according to the bonding system, when the-NCO in the bonding system is chemically crosslinked with the solvent and the carboxyl contained in the component, a certain amount of carbon dioxide can be released, and a small amount of micropores are generated in the gas escape process, so that the volume change generated by the release of lithium/sodium from electrode active particles can be buffered, the internal stress is reduced, the diffusion of electrolyte in a composite material is facilitated, the internal resistance is reduced, and the rate capability of the battery is improved.
In the prior art, in order to improve the production efficiency of the electrode plate, a common solution is to increase the drying temperature, but the capillary effect causes the polymer content in the composite material to present gradient distribution along the coating thickness, namely, the adhesive close to the collector side is less, and the surface of the active layer is enriched, so that the layered damage is easily generated, the motion resistance of active ions in the electrolyte is increased, and based on the nonlinear characteristic of the solvent evaporation process in the composite material during electrode forming and the strong correlation with the mechanical property of a cured film; the embodiment of the invention adopts a three-section drying temperature-changing and time-changing molding process to realize the sectional temperature and time control, controls the initial temperature and the terminal temperature at the lower temperature interval of 40-60 ℃ and 30-60 ℃, and only raises the drying temperature of the middle stage to 110-140 ℃, thereby not only improving the molding efficiency, but also increasing the crosslinking degree of the composite material and better solving the problem of the non-uniformity of the distribution of the polymer adhesive therein; the water-based polymer-isocyanate-based electrode composite material prepared by the method of the embodiment of the invention has excellent electrochemical and mechanical properties; compared with the existing preparation method of the cathode of the lithium secondary battery, the method provided by the embodiment of the invention has the advantages that the product performance is more excellent, the production efficiency is higher, and the release of an organic solvent is avoided. In the embodiment of the invention, the aqueous solution mixing and coating method is adopted, the composite material is prepared by the aqueous polymer, the electrode active particles, the conductive auxiliary agent and the water-emulsified polymeric isocyanate cross-linking agent, and then the composite material is coated on the current collector to obtain the negative electrode. The electrode composite material prepared by the method of the embodiment of the invention has excellent electrochemical behavior and mechanical property, and the forming process is simple, the production efficiency is high and the electrode composite material meets the requirements of environmental protection.
The embodiments of the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made according to the purpose of the invention, and any changes, modifications, substitutions, combinations or simplifications made according to the spirit and principle of the technical solution of the present invention shall be equivalent substitution patterns, so long as the object of the present invention is met, and the present invention shall fall within the protection scope of the present invention without departing from the technical principle and inventive concept of the aqueous polymer-isocyanate based electrode composite material and the preparation method thereof.

Claims (10)

1. The preparation method of the electrode composite material is characterized by adopting an aqueous solution casting method or an aqueous solution mixing and coating method, wherein 3.0-15 wt% of hydroxyl or carboxyl-containing aqueous polymer, 80.5-95.7 wt% of electrode active particles, 1.0-3.0 wt% of conductive additive and 0.3-1.5 wt% of water-emulsified polymeric isocyanate are used as raw materials to prepare the aqueous polymer-isocyanate-based electrode composite material according to the dry mass percentage of the components, and the preparation method comprises the following steps:
a. adding the water-based polymer and deionized water into a reaction kettle according to the mass ratio of 2:100, slowly heating to 60-90 ℃, and mechanically stirring for 1-2 hours to obtain a uniformly distributed water-based polymer solution;
b. cooling to 50 ℃, slowly adding a conductive aid into the aqueous polymer solution prepared in the step a, and mixing for 2-3 hours under the combined action of ultrasonic waves and mechanical stirring to uniformly disperse the conductive aid in the aqueous polymer solution;
c. continuously cooling to 30-40 ℃, gradually adding the electrode active particles into the mixed solution of the aqueous polymer and the conductive agent prepared in the step b, and mechanically stirring for 1-2 hours to disperse the active particles into the mixed solution;
d. cooling to be not higher than 30 ℃, dropwise adding water to the mixed solution prepared in the step c to emulsify polymeric isocyanate, and stirring for 15-30 minutes to obtain slurry;
e. d, coating the slurry prepared in the step d on a metal current collector with the thickness of not less than 8 mu m, and then carrying out a three-stage drying and forming process:
drying at 40-60 deg.C for 30-60 min to obtain initial stage drying treatment; then drying at the temperature of 110-140 ℃ for 20-50 minutes to carry out intermediate-stage drying treatment; and then carrying out vacuum drying at 30-60 ℃ for 60-120 minutes to carry out final stage drying treatment to obtain the cathode electrode piece composite material.
2. The method for preparing the electrode composite material according to claim 1, wherein: the raw material components of the water-based polymer, the electrode active particles, the conductive additive and the water-emulsified polymeric isocyanate are (3-6) in dry mass ratio to 90:3: 1.
3. The method for preparing the electrode composite material according to claim 1, wherein: and c, continuously cooling to 30-35 ℃, gradually adding the electrode active particles into the mixed solution of the aqueous polymer and the conductive agent, and mechanically stirring to disperse the active particles in the mixed solution.
4. The method for preparing the electrode composite material according to claim 1, wherein: in the step e, a three-stage drying and forming process is carried out:
drying at 50-60 deg.C for 45-60 min to perform initial stage drying treatment; then drying at the temperature of 110-140 ℃ for 30-50 minutes to carry out intermediate-stage drying treatment; and carrying out final drying treatment for 60-120 minutes at 30-60 ℃ in vacuum to obtain the cathode electrode sheet composite material.
5. The aqueous polymer-isocyanate-based electrode composite material is prepared by the preparation method of the electrode composite material according to claim 1, and is characterized in that the prepared aqueous polymer-isocyanate-based electrode composite material is prepared by combining hydroxyl-or carboxyl-containing aqueous polymer, electrode active particles, a conductive auxiliary agent and water-emulsified polymeric isocyanate as raw material components, wherein the raw material components are as follows according to the dry mass percentage ratio of the components:
Figure FDA0002957028000000021
6. the aqueous polymer-isocyanate-based electrode composite of claim 5, wherein: the water-based polymer is any one polymer or a mixture of any several polymers in homopolymerization and copolymerization emulsion of carboxymethyl cellulose, carboxyethyl cellulose, carboxylic styrene-butadiene emulsion, polyvinyl alcohol, polyacrylic acid, sodium alginate and vinyl acetate.
7. The aqueous polymer-isocyanate-based electrode composite of claim 5, wherein: the electrode active particles are made of any one material or a mixture of any several materials of graphite, silicon, germanium, tin, transition metal oxide and nano zinc ferrite.
8. The aqueous polymer-isocyanate-based electrode composite of claim 5, wherein: the conductive auxiliary agent is any one material or a mixture of any several materials of carbon black, carbon fiber, carbon nanosheet and nickel powder.
9. The aqueous polymer-isocyanate-based electrode composite of claim 5, wherein: the water-emulsified polymeric isocyanate adopts polymeric polyisocyanate modified by nonionic surfactant.
10. The aqueous polymer-isocyanate-based electrode composite according to any one of claims 5 to 9, wherein: the water-based polymer-isocyanate-based electrode composite material with a three-dimensional network structure is formed by using a water-based polymer aqueous solution as a bonding material, forming a cross-linked bonding system with water-emulsified polymeric isocyanate, forming a firm chemical linking structure by using water-emulsified polymeric isocyanate cross-linked electrode particles and a conductive auxiliary agent, and forming the water-based polymer-isocyanate-based electrode composite material with the three-dimensional network structure by using the water-based polymer aqueous solution, the electrode active particles, the conductive auxiliary agent and the water-emulsified polymeric isocyanate.
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