CN112072106A - Conductive adhesive material, preparation method thereof, negative electrode plate and lithium ion battery - Google Patents
Conductive adhesive material, preparation method thereof, negative electrode plate and lithium ion battery Download PDFInfo
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- CN112072106A CN112072106A CN202010887642.3A CN202010887642A CN112072106A CN 112072106 A CN112072106 A CN 112072106A CN 202010887642 A CN202010887642 A CN 202010887642A CN 112072106 A CN112072106 A CN 112072106A
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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
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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
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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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
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
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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
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
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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
- H01M2220/00—Batteries for particular applications
- H01M2220/30—Batteries in portable systems, e.g. mobile phone, laptop
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- 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 provides a conductive adhesive material, a preparation method thereof, a negative pole piece and a lithium ion battery, and relates to the field of batteries. The conductive adhesive material comprises a polymer carbon dot aqueous solution prepared by taking polymers rich in hydroxyl, carboxyl and amino, such as polyvinyl alcohol, sodium carboxymethylcellulose, sodium alginate, chitosan, polyethyleneimine and the like as raw materials and processing the raw materials at high temperature and high pressure or by microwaves. The conductive adhesive material can solve the problems that in the prior art, when a silicon-based material is taken as a negative active material, the silicon-based material is poor in conductivity and easy to fall off from a pole piece, and the purposes of improving the conductivity of the pole piece and the adhesive force of the pole piece material and further improving the energy density of the silicon negative pole piece are achieved.
Description
Technical Field
The invention relates to the field of batteries, in particular to a conductive adhesive material, a preparation method thereof, a negative pole piece and a lithium ion battery.
Background
Currently, in commercial lithium ion batteries, the active material of the anode is mainly graphite. However, the graphite has a limited specific mass capacity and a small specific volume capacity lifting space, and a lithium ion battery using the graphite as an anode active material cannot meet the use requirements of future high-capacity and small-volume electronic equipment.
Through research, silicon is found to be the most promising material for anodes of lithium ion batteries. The theoretical gram capacity of the silicon-based material is up to 4200mAh/g, and the theoretical volume specific capacity is up to 7200mAh/cm3. However, the silicon-based material has poor conductivity, and conductive carbon black must be added when the material is used, so that the stability and energy density of the pole piece are influenced. In addition, in the lithium removal/insertion process, the volume change of the silicon-based material is large, and the silicon-based material is easy to crack, so that the silicon-based material is easy to fall off from a current collector copper foil to cause electrode film pulverization, the cycle performance of the lithium ion battery is deteriorated, and the commercial application of the lithium ion battery is limited.
Disclosure of Invention
The invention aims to provide a conductive binder material, which has both conductive and adhesive functions and solves the problems that in the prior art, when a silicon-based material is taken as a negative electrode active material, the silicon-based material has poor conductivity, the adhesion fails in a circulating process and the silicon-based material is easy to pulverize.
A second object of the present invention is to provide a method for preparing a conductive adhesive material.
The third objective of the present invention is to provide a negative electrode plate to improve the cycle stability of the lithium ion battery.
The fourth purpose of the invention is to provide a lithium ion battery containing the negative pole piece.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a conductive adhesive material is a polymer carbon dot aqueous solution prepared by using a polymer rich in hydroxyl, carboxyl and/or amino as a raw material and performing high-temperature high-pressure or microwave treatment, wherein the material contains a condensation polymerizable functional group.
Furthermore, the raw material is one or more of polyvinyl alcohol, sodium carboxymethylcellulose, sodium alginate, chitosan, polyethyleneimine and the like.
Further, the polymer carbon dot particles are nano materials with 0-dimensional carbon as the main component and are formed by sp2And sp3The carbon skeleton, rich functional groups and polymer chains are observed under a transmission electron microscope, the diameter of the carbon skeleton is 0.1 nm-50 nm, the carbon skeleton is uniformly distributed in an aqueous solution, crystal lattice stripes can be seen in particle cores, and the particle size can be changed along with factors such as raw materials, high-temperature high-pressure treatment time, solution concentration and the like.
Furthermore, the reaction temperature is 25-950 ℃, the pressure is 0.1-5.5 MPa, and the microwave power is 5-5000W.
A process for preparing electrically conductive adhesive includes such steps as loading the aqueous solution of polymer in hydrothermal reactor, heating in baking oven, full reaction, and natural cooling. Or placing the polymer aqueous solution in microwave equipment, carrying out microwave treatment under certain power, and naturally cooling to obtain the binder material.
Further, the mass fraction of the polymer aqueous solution can be adjusted between 0.01% and 80%.
Furthermore, the reaction time of the polymer water solution in the hydrothermal kettle is 4-32 hours, and the microwave heating time is 5 s-24 hours.
The polymer carbon dot aqueous solution prepared by the invention shows obvious light absorption in a UV-vis region, and particularly shows strong absorption in an ultraviolet region.
The polymer carbon dot aqueous solution can be used as a binder for a negative pole piece to prepare a lithium ion battery.
Compared with the prior art, the technical scheme of the invention has the advantages that:
the conductive adhesive material of the invention is characterized in that after the high-temperature high-pressure treatment of the polymer, the polar group is dehydrated and condensed to form a polymer dot which has SP2The conjugated structure constructs a conductive network on a polymer molecular chain, so that the conductivity of the binder is improved, and the use of conductive carbon black in the negative electrode slurry can be reduced when the conductive carbon black is used as the negative electrode slurry, so that the stability and the energy density of the silicon negative electrode material are improved. At the same time, the user can select the desired position,the surface of the polymer carbon dot has rich polar groups, and has strong hydrogen bond effect with a silicon-based material, so that the problems of bonding failure and pulverization of the silicon-based material in the circulation process can be effectively solved.
The preparation method of the conductive adhesive material is simple, easy to implement, low in cost and easy for large-scale industrial production.
According to the negative pole piece provided by the invention, the binder material is adopted as the binder, the binder has good conductivity, the use of conductive carbon black is reduced, the energy density of the pole piece is improved, and the high binding power exists between the binder and the silicon-based material layer, so that the structural stability of the negative pole piece can be improved, and the negative pole piece can be used in a lithium ion battery and can effectively improve the energy density and the cycle performance of the lithium ion secondary battery.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
Drawings
Fig. 1 is a transmission electron microscope photograph of the prepared conductive adhesive a1(a), a2 (b).
FIG. 2 is a TEM photograph of the prepared electrode sheets N1(a), N2 (b).
Fig. 3 is a graph of the cycle performance of the battery of example 3.
Fig. 4 is a graph of the cycle performance of the battery of example 6.
Fig. 5 is a graph comparing the cycle performance of batteries using a3 as a binder and PVA as a binder.
FIG. 6 is a scanning electron microscope image before and after cycling of the pole piece using A3 as binders (a), (c) and PVA as binders (b), (d).
Detailed Description
Embodiments of the present invention will be described in detail below with reference to examples, but it will be understood by those skilled in the art that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
It should be noted that: in the present invention, all the embodiments and preferred methods mentioned herein can be combined with each other to form a new technical solution, if not specifically stated. In the present invention, all the technical features mentioned herein and preferred features may be combined with each other to form a new technical solution, if not specifically stated. In the present invention, the percentage (%) or parts means the weight percentage or parts by weight with respect to the composition, if not otherwise specified. In the present invention, the components referred to or the preferred components thereof may be combined with each other to form a novel embodiment, if not specifically stated. In the present invention, unless otherwise stated, the numerical range "a-b" represents a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "6 to 22" means that all real numbers between "6 to 22" have been listed herein, and "6 to 22" is simply a shorthand representation of the combination of these values. The "ranges" disclosed herein may have one or more lower limits and one or more upper limits, respectively, in the form of lower limits and upper limits. In the present invention, unless otherwise specified, the individual reactions or operation steps may or may not be performed in sequence. Preferably, the reaction processes herein are carried out sequentially.
Unless otherwise defined, technical and scientific terms used herein have the same meaning as is familiar to those skilled in the art. In addition, any methods or materials similar or equivalent to those described herein can also be used in the present invention.
On one hand, the invention provides a conductive adhesive material, which comprises polymer dots generated by polymers rich in hydroxyl, carboxyl and amino groups, such as polyvinyl alcohol, sodium carboxymethyl cellulose, sodium alginate, chitosan, polyethyleneimine and the like, wherein the polymer dots, namely the adhesive material, are obtained after the polymers are subjected to high-temperature and high-pressure treatment.
According to the negative pole piece provided by the invention, the conductive adhesive material is adopted as the adhesive, the adhesive has good conductivity, the use of conductive carbon black is reduced, the energy density of the pole piece is improved, and the adhesive and the silicon-based material layer have high adhesive force, so that the structural stability of the negative pole piece can be improved, and the negative pole piece is used in a lithium ion battery and can effectively improve the energy density and the cycle performance of the lithium ion secondary battery.
The raw materials for preparing the conductive adhesive material in the invention are commercial hydroxyl, carboxyl and amino-rich polymers. Specifically, the polymer can be polyvinyl alcohol, sodium alginate, sodium carboxymethylcellulose, polyethyleneimine, chitosan, etc.
In some embodiments of the present invention, the polymer raw materials used each contain polar groups such as hydroxyl, carboxyl or amino groups, and these polar groups undergo a series of reactions such as dehydration condensation under high temperature and pressure or microwave treatment, thereby forming polymer carbon dot particles in the polymer solution.
Tests prove that the polymer carbon dot particles uniformly distributed in the polymer aqueous solution can effectively improve the conductivity and the adhesive property of the pole piece using the polymer carbon dot particles as the adhesive, so that the stability and the cycle performance of the negative pole piece are improved.
In a second aspect, the invention provides a method for preparing a conductive adhesive material, wherein the adhesive material is obtained by naturally cooling after the polymer solution is subjected to high-temperature and high-pressure or microwave treatment.
The preparation method of the conductive adhesive material is simple, easy to implement, low in cost and easy for large-scale industrial production.
It should be noted that, in the present invention, there are many methods for high-temperature high-pressure treatment of the polymer, including but not limited to oven heating, microwave heating, etc. In some preferred embodiments of the present invention, the polymer aqueous solution is filled into a hydrothermal kettle, and the hydrothermal kettle is placed in an oven, and after sufficient reaction at a certain temperature, the hydrothermal kettle is naturally cooled to obtain the binder material.
In some preferred embodiments of the invention, the mass fraction of the polymer solution is 5%, 10% or 20%.
The polymer solution had a volume of 10mL, 50mL, 100mL, 200mL, or 500 mL.
Alternatively, the time for the high-temperature high-pressure treatment of the polymer solution in the hydrothermal kettle is 6h, 10h, 16h, 24h or 32 h.
Alternatively, the polymer solution is heated by microwave for 5s, 60s, 10min, 30min, 1h, and 24 h.
Optionally, the treatment temperature is 25-950 ℃, the treatment pressure is 0.1-5.5 MPa, and the microwave power is 5-5000W.
In addition, during the high-temperature high-pressure treatment, certain catalysts (such as sodium hydroxide, potassium hydroxide and the like) can be optionally added to promote the formation of carbon points and simultaneously reduce the time and temperature of the treatment.
A negative pole piece comprises the conductive adhesive material.
The conductive adhesive has good conductive performance, reduces the use of conductive carbon black, improves the energy density of a pole piece, and has higher adhesive force with a silicon-based material layer, so that the structural stability of a negative pole piece can be improved, and the conductive adhesive is used in a lithium ion battery and can effectively improve the energy density and the cycle performance of the lithium ion secondary battery.
A lithium ion battery comprises the negative pole piece.
Because the lithium ion battery comprises the negative pole piece, the lithium ion battery has all the advantages of the negative pole piece, and the description is omitted.
The present invention will be described in further detail with reference to examples and comparative examples.
Example 1
S1) preparation of binder material a 1:
preparing 10ml of 5% polyvinyl alcohol aqueous solution, putting the polyvinyl alcohol aqueous solution into a 50ml of hydrothermal kettle with a polytetrafluoroethylene lining, putting the hydrothermal kettle into a drying oven at 160 ℃, taking out the hydrothermal kettle after 6 hours, and naturally cooling the hydrothermal kettle in the air to obtain the binder material, wherein the binder material is marked as A1.
S2) manufacturing a pole piece N1:
1 part by mass of A1 and 9 parts by mass of active material nano siliconUniformly mixing the materials by using a mortar, adding 0.2ml of deionized water to obtain negative electrode slurry, coating the negative electrode slurry on a copper foil, wherein the solid coating mass is 1mg/cm2Then dried in a vacuum oven at 100 ℃ for 12 hours, cut into pieces, weighed and the resulting pole piece was designated as N1.
S3) preparation of lithium ion half cell C1:
the diaphragm is a 25 mu m polypropylene film;
the electrolyte consists of a non-aqueous organic solvent and LiPF6Composition of, wherein, LiPF6The molar concentration in the electrolyte is 1M, and the nonaqueous organic solvent comprises a solvent with a volume ratio of 1:1, and simultaneously contains 10% of fluoroethylene carbonate by volume;
and transferring the prepared negative pole piece into an inert atmosphere glove box, stacking the pole piece N1, a diaphragm and a lithium piece in sequence, and filling electrolyte for assembly to finish the assembly of the lithium ion half battery, wherein the obtained lithium ion secondary battery is recorded as C1.
Example 2
S1) preparation of binder material a 2:
preparing 10ml of 8% polyvinyl alcohol aqueous solution, putting the polyvinyl alcohol aqueous solution into a 100ml of hydrothermal kettle with a polytetrafluoroethylene lining, putting the hydrothermal kettle into a drying oven at 200 ℃, taking out the hydrothermal kettle after 24 hours, and naturally cooling the hydrothermal kettle in the air to obtain the binder material, wherein the binder material is marked as A2.
S2) manufacturing a pole piece N2:
uniformly mixing 1 part by mass of A2 and 9 parts by mass of active material nano-silicon by using a mortar, adding 0.2ml of deionized water to obtain negative electrode slurry, coating the negative electrode slurry on copper foil, wherein the solid coating mass is 1mg/cm2Then dried in a vacuum oven at 100 ℃ for 12 hours, cut into pieces, weighed and the resulting pole piece was designated as N2.
S3) preparation of lithium ion half cell C2:
the diaphragm is a 25 mu m polypropylene film;
the electrolyte consists of a non-aqueous organic solvent and LiPF6Composition of, wherein, LiPF6The molar concentration of the electrolyte is 1M, and the electrolyte is non-aqueous organic solutionThe agent comprises the following components in a volume ratio of 1:1, and simultaneously contains 10% of fluoroethylene carbonate by volume;
and transferring the prepared negative pole piece into an inert atmosphere glove box, stacking the pole piece N2, a diaphragm and a lithium piece in sequence, and filling electrolyte for assembly to finish the assembly of the lithium ion half battery, wherein the obtained lithium ion secondary battery is recorded as C2.
Example 3
S1) preparation of binder material A3:
preparing 50ml of 20% polyvinyl alcohol aqueous solution, putting the polyvinyl alcohol aqueous solution into a 200ml of hydrothermal kettle with a polytetrafluoroethylene lining, putting the hydrothermal kettle into an oven at 250 ℃, taking out the hydrothermal kettle after 12 hours, and naturally cooling the hydrothermal kettle in the air to obtain the binder material, wherein the binder material is marked as A3.
S2) manufacturing a pole piece N3:
uniformly mixing 1 part by mass of A3 and 9 parts by mass of active material nano-silicon by using a mortar, adding 0.2ml of deionized water to obtain negative electrode slurry, coating the negative electrode slurry on copper foil, wherein the solid coating mass is 1mg/cm2Then dried in a vacuum oven at 100 ℃ for 12 hours, cut into pieces, weighed and the resulting pole piece was designated as N3.
S3) preparation of lithium ion half cell C3:
the diaphragm is a 25 mu m polypropylene film;
the electrolyte consists of a non-aqueous organic solvent and LiPF6Composition of, wherein, LiPF6The molar concentration in the electrolyte is 1M, and the nonaqueous organic solvent comprises a solvent with a volume ratio of 1:1, and simultaneously contains 10% of fluoroethylene carbonate by volume;
and transferring the prepared negative pole piece into an inert atmosphere glove box, stacking the pole piece N3, a diaphragm and a lithium piece in sequence, and filling electrolyte for assembly to finish the assembly of the lithium ion half battery, wherein the obtained lithium ion secondary battery is recorded as C3.
Example 4
S1) preparation of binder material a 4:
preparing 10ml of 5% polyethyleneimine aqueous solution, putting the polyethyleneimine aqueous solution into a 50ml of hydrothermal kettle with a polytetrafluoroethylene lining, putting the hydrothermal kettle into a 160 ℃ oven, taking out after 8 hours, putting the hydrothermal kettle into air, and naturally cooling to obtain the binder material, wherein the binder material is marked as A4.
S2) manufacturing a pole piece N4:
uniformly mixing 1 part by mass of A4 and 9 parts by mass of active material nano-silicon by using a mortar, adding 0.2ml of deionized water to obtain negative electrode slurry, coating the negative electrode slurry on copper foil, wherein the solid coating mass is 1mg/cm2Then dried in a vacuum oven at 100 ℃ for 12 hours, cut into pieces, weighed and the resulting pole piece was designated as N4.
S3) preparation of lithium ion half cell C4:
the diaphragm is a 25 mu m polypropylene film;
the electrolyte consists of a non-aqueous organic solvent and LiPF6Composition of, wherein, LiPF6The molar concentration in the electrolyte is 1M, and the nonaqueous organic solvent comprises a solvent with a volume ratio of 1:1, and simultaneously contains 10% of fluoroethylene carbonate by volume;
and transferring the prepared negative pole piece into an inert atmosphere glove box, stacking the pole piece N4, a diaphragm and a lithium piece in sequence, and filling electrolyte for assembly to finish the assembly of the lithium ion half battery, wherein the obtained lithium ion secondary battery is recorded as C4.
Example 5
S1) preparation of binder material a 5:
preparing 10ml of 3% chitosan aqueous solution, putting the chitosan aqueous solution into a 100ml of hydrothermal kettle with a polytetrafluoroethylene lining, putting the hydrothermal kettle into a 200 ℃ oven, taking out the hydrothermal kettle after 10 hours, and naturally cooling the hydrothermal kettle in the air to obtain the binder material, wherein the binder material is marked as A5.
S2) manufacturing a pole piece N5:
uniformly mixing 1 part by mass of A5 and 9 parts by mass of active material nano-silicon by using a mortar, adding 0.2ml of deionized water to obtain negative electrode slurry, coating the negative electrode slurry on copper foil, wherein the solid coating mass is 1mg/cm2And subsequently dried in a vacuum drying oven at 100 deg.CThe pieces were dried for 12 hours, cut and weighed, and the resulting pole piece was designated N5.
S3) preparation of lithium ion half cell C5:
the diaphragm is a 25 mu m polypropylene film;
the electrolyte consists of a non-aqueous organic solvent and LiPF6Composition of, wherein, LiPF6The molar concentration in the electrolyte is 1M, and the nonaqueous organic solvent comprises a solvent with a volume ratio of 1:1, and simultaneously contains 10% of fluoroethylene carbonate by volume;
and transferring the prepared negative pole piece into an inert atmosphere glove box, stacking the pole piece N5, a diaphragm and a lithium piece in sequence, and filling electrolyte for assembly to finish the assembly of the lithium ion half battery, wherein the obtained lithium ion secondary battery is recorded as C5.
Example 6
S1) preparation of binder material a 6:
preparing 20ml of 8% sodium carboxymethylcellulose aqueous solution, filling the sodium carboxymethylcellulose aqueous solution into a 200ml of hydrothermal kettle with a polytetrafluoroethylene lining, placing the hydrothermal kettle in an oven at 250 ℃, taking out after 6 hours, and placing in the air for natural cooling to obtain the binder material, wherein the binder material is marked as A6.
S2) manufacturing a pole piece N6:
uniformly mixing 1 part by mass of A6 and 9 parts by mass of active material nano-silicon by using a mortar, adding 0.2ml of deionized water to obtain negative electrode slurry, coating the negative electrode slurry on copper foil, wherein the solid coating mass is 1mg/cm2Then dried in a vacuum oven at 100 ℃ for 12 hours, cut into pieces, weighed and the resulting pole piece was designated as N6.
S3) preparation of lithium ion half cell C6:
the fabrication process was the same as for the lithium-ion half cell C1, except that the pole piece N1 was changed to N6, and the resulting lithium-ion half cell was designated C6.
Example 7
S1) preparation of Binder A7
Preparing 20ml of 8% sodium carboxymethylcellulose aqueous solution, placing the solution in a microwave oven, heating for 4 minutes under the power condition of 100W, naturally cooling, taking out, and changing the solution from colorless to brown yellow to obtain the binder material, which is recorded as A7.
S2) manufacturing a pole piece N7:
uniformly mixing 1 part by mass of A7 and 9 parts by mass of active material nano-silicon by using a mortar, adding 0.2ml of deionized water to obtain negative electrode slurry, coating the negative electrode slurry on copper foil, wherein the solid coating mass is 1mg/cm2Then dried in a vacuum oven at 100 ℃ for 12 hours, cut into pieces, weighed and the resulting pole piece was designated as N7.
S3) preparation of lithium ion half cell C7:
the fabrication process was the same as for the lithium-ion half cell C1, except that the pole piece N1 was changed to N7, and the resulting lithium-ion half cell was designated C7.
Example 8
S1) preparation of Binder A8
Preparing a 5% PVA aqueous solution and a 5% chitosan aqueous solution, uniformly mixing the PVA aqueous solution and the chitosan aqueous solution according to the mass ratio of 1:1, taking 10mL of the mixed solution, putting the mixed solution into a 200mL hydrothermal kettle, heating for 6h at 230 ℃, naturally cooling and taking out to obtain the binder material, which is marked as A8.
S2) manufacturing a pole piece N8:
uniformly mixing 1 part by mass of A8 and 9 parts by mass of active material nano-silicon by using a mortar, adding 0.2ml of deionized water to obtain negative electrode slurry, coating the negative electrode slurry on copper foil, wherein the solid coating mass is 1mg/cm2Then dried in a vacuum oven at 100 ℃ for 12 hours, cut into pieces, weighed and the resulting pole piece was designated as N8.
S3) preparation of lithium ion half cell C8:
the fabrication process was the same as for the lithium-ion half cell C1, except that the pole piece N1 was changed to N8, and the resulting lithium-ion half cell was designated C8.
Comparative example 1
The specific steps and the raw material ratio are the same as those of example 1, except that in the comparative example, when the pole piece is manufactured, a polyvinyl alcohol aqueous solution is used as a binder, and the obtained lithium ion battery is marked as DC 1.
Comparative example 2
The specific steps and the raw material ratio are the same as those in example 4, except that in the comparative example, when the pole piece is manufactured, a polyethyleneimine aqueous solution is used as a binder, and the obtained lithium ion battery is marked as DC 2.
Comparative example 3
The specific steps and the raw material ratio are the same as those in example 5, except that in the comparative example, when the pole piece is manufactured, a chitosan aqueous solution is used as a binder, and the obtained lithium ion battery is marked as DC 3.
Comparative example 4
The specific steps and the raw material ratio are the same as those in example 6, except that in the comparative example, a sodium carboxymethylcellulose aqueous solution is used as a binder when the pole piece is manufactured, and the obtained lithium ion battery is marked as DC 4.
Among them, in the above examples and comparative examples, polyvinyl alcohol was obtained from Mecline and had a molecular weight of 1775. Sodium alginate was purchased from alatin with a molecular weight of 30000. Polyethyleneimine is available from alatin and has a molecular weight of 10000. Carboxylated chitosan was purchased from alatin, molecular weight 50000.
Topography characterization
The prepared A1, A2 was observed using a field emission transmission electron microscope, the photograph of which is shown in FIG. 1; uniformly distributed spheroidal particles can be observed from a transmission electron microscope photo, the diameter of the particles is 3-20 nm, and the particles are the synthesized polymer carbon dots.
When the prepared N1 and N2 pole pieces are observed by using a field emission transmission electron microscope, as shown in fig. 2, it can be seen from fig. 2 that the conductive adhesive is in close contact with the nano silicon particles, and not only is the surface contact between the polymer and the silicon particles, but also the point contact between the polymer carbon points and the nano silicon particles exists. The combination of point contact and surface contact effectively improves the bonding performance of the conductive adhesive.
Performance testing
The method for testing the cycle capacity retention rate of the half-cell in the C1-C8 and the DC 1-DC 4 respectively comprises the following steps:
and (3) taking each battery, standing and activating for 12 hours, then carrying out constant-current charge and discharge at a rate of 0.1C, and recording discharge capacities of 10 th, 20 th, 30 th, 40 th and 50 th times of circulation respectively.
The capacity retention ratio of the battery at the N-th time was the discharge capacity at the N-th time/the discharge capacity at the first time × 100%.
The test results are shown in table 1.
TABLE 1 Capacity Retention ratio for 50 cycles of different batteries
As can be seen from the data in Table 1, the capacity retention rate of the batteries C1-C8 adopting the technical scheme of the invention is far higher than that of the batteries DC 1-DC 4 after 50 cycles. The polymer carbon dots are generated through high-temperature and high-pressure treatment, so that the conductivity and the binding property of the polymer carbon dots serving as the cathode binder are effectively improved, and the stability and the cycle performance of the cathode are improved.
Using the adhesive A3 of example 3, a load of 1.5mg/cm was made2And assembling the half cell by using the nano silicon and the pole piece N3 with the mass ratio of A3 being 9:1, and then testing under the multiplying power condition of 0.5C. Fig. 3 is a test result, and it can be seen from the test result that the first efficiency of the battery is 89.7%, the problem of low first efficiency (generally 60-70%) of the nano-silicon is effectively overcome, after 50 cycles, the capacity is stabilized at 2536.2mAh/g, the coulombic efficiency is basically maintained at above 99.5%, the cycle retention rate is 85.2%, and excellent electrochemical performance is shown.
Using the adhesive A6 of example 6, a load of 1.5mg/cm was made2And assembling the half cell by using the nano silicon and the pole piece N6 with the mass ratio of A6 being 9:1, and then testing under the multiplying power condition of 0.5C. FIG. 4 is a test result, and it can be seen from the test result that the first efficiency of the battery is 85.9%, the problem of low first efficiency of nano-silicon is effectively overcome, after 50 cycles, the capacity is stabilized at 1870.6mAh/g, and the coulombic efficiency is basically highThe electrochemical performance is excellent when the cycle retention rate is kept above 99.5% and 83.5%.
We prepared a pole piece using PVA as a binder for comparison, the mass ratio of nanosilicon to PVA in the pole piece being "9: 1", under the same loading and the same test conditions, as compared to the half cell using binder A3 in example 3 as a binder, and as a result, as shown in fig. 5, it was found that the half cell using A3 as a binder maintained stable cycling capacity after 50 cycles at 0.5C, while the half cell using PVA as a binder had failed. This further demonstrates the effectiveness of a3 in promoting pole piece conductivity and cycle stability.
In addition, the difference of the appearance of the pole piece using PVA as the binder and the pole piece using A3 as the binder after 30 cycles under the condition of 0.5C is observed through a scanning electron microscope, and the loading capacity of the pole piece is 1.0mg/cm2The shapes before and after circulation are shown in fig. 6, and it is obvious from the figure that the pole piece using a3 as the binder still maintains a relatively regular shape after circulation, the particles are uniformly distributed, and the pole piece using PVA as the binder has obvious agglomeration after circulation, which affects the electrochemical performance of the pole piece. The effectiveness of a3 in promoting pole piece adhesion was further demonstrated by scanning electron microscope pictures.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (8)
1. The conductive adhesive material is characterized in that a polymer with hydroxyl, carboxyl and/or amino is used as a raw material and is subjected to high-temperature high-pressure or microwave treatment to obtain a polymer carbon dot aqueous solution, wherein polymer carbon dot particles are uniformly distributed in the aqueous solution, and the diameter of the polymer carbon dot particles is 0.1-50 nm.
2. The conductive adhesive material as claimed in claim 1, wherein the raw material is one or more of polyvinyl alcohol, sodium carboxymethyl cellulose, sodium alginate, chitosan, and polyethyleneimine.
3. The conductive adhesive material according to claim 1, wherein the reaction temperature is 25 to 950 ℃, the reaction pressure is 0.1 to 5.5MPa, and the microwave power is 5 to 5000W.
4. The conductive adhesive material as claimed in claim 1, wherein the material is prepared by a method comprising: putting the polymer aqueous solution into a hydrothermal kettle, sealing the hydrothermal kettle, putting the hydrothermal kettle into an oven, heating for full reaction, and naturally cooling; or putting the polymer aqueous solution into microwave equipment, starting microwaves to perform full reaction, and naturally cooling.
5. The conductive adhesive material according to claim 3, wherein the mass fraction of the aqueous polymer solution is 0.01 to 80%.
6. The conductive adhesive material according to claim 3, wherein the reaction time in the hydrothermal reactor is 0.1 to 240 hours, and the microwave treatment time is 5s to 24 hours.
7. A negative electrode plate, characterized in that it is made of the conductive adhesive material of any one of claims 1 to 6 as an adhesive.
8. A lithium ion battery comprising the negative electrode tab of claim 7.
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