CN114256563A

CN114256563A - Conductive adhesive, electrochemical device, and electronic device

Info

Publication number: CN114256563A
Application number: CN202111565774.5A
Authority: CN
Inventors: 胡克文
Original assignee: Dongguan Amperex Technology Ltd
Current assignee: Dongguan Amperex Technology Ltd
Priority date: 2021-12-20
Filing date: 2021-12-20
Publication date: 2022-03-29

Abstract

The present application relates to a conductive paste, an electrochemical device, and an electronic device. The conductive adhesive comprises a matrix and a conductive filler, wherein the matrix comprises modified epoxy resin, polyurethane and polyimide. The conductive adhesive can replace laser welding to be used for an electrochemical device, can improve the production efficiency of the electrochemical device, and also improves the quality of the electrochemical device.

Description

Conductive adhesive, electrochemical device, and electronic device

Technical Field

The application relates to the field of energy storage, in particular to conductive adhesive, an electrochemical device and an electronic device.

Background

Lithium ion batteries are widely used in various electronic products such as mobile terminals, electric tools, electric vehicles, and the like. Button cell who uses in wearing equipment such as bluetooth headset usually adopts laser welding to fix utmost point ear and utmost point post. However, during laser welding, bad welding products are easily generated, and the production efficiency of the battery is affected. To solve this problem, the prior art attempts to use conductive paste instead of laser welding.

However, the conductive paste in the prior art has the following problems: (1) the shear strength after bonding to metals such as Al, Cu or Ni is low, and<5 MPa; (2) in the electrolyte system, the swelling rate and the dissolution rate are high, so that the battery is circulatedThe phenomena of capacity attenuation acceleration and thickness expansion acceleration appear in the process, and even black spots or purple spots are generated; (3) the conductivity is poor, and the conductivity of laser welding cannot be replaced; (4) some conductive particles are susceptible to oxidation, e.g. Al, to Al₂O₃Insulating, and Al³⁺The content of the impurity ions exceeds the standard; (5) the rheological parameters do not satisfy the dispensing process.

Therefore, there is a need to develop an improved conductive paste for electrochemical devices to achieve conductive bonding instead of laser welding.

Disclosure of Invention

In view of the deficiencies of the prior art, the present application provides a conductive paste, an electrochemical device and an electronic device including the conductive paste. The conductive adhesive is used for the electrochemical device instead of laser welding, can improve the production efficiency of the electrochemical device, and improves the quality of the electrochemical device.

In a first aspect, the present application provides a conductive paste comprising a matrix and a conductive filler, wherein the matrix comprises a modified epoxy, a polyurethane, and a polyimide.

In the application, the conductive adhesive matrix can form a molecular skeleton of the conductive adhesive, provide mechanical properties and a bonding effect, enable conductive filler particles to form channels, enable the conductive filler particles to be mutually contacted, and enable the particles to form a certain current path through a tunnel effect. The matrix of the application simultaneously comprises three components of modified epoxy resin, polyurethane and polyimide, and the modified epoxy resin can overcome the defects of high brittleness and poor toughness of the epoxy resin; the polyurethane improves the impact damage resistance and has good shock absorption effect; the polyimide has high temperature resistance up to 400 ℃ and can be used for a long time at the temperature of 200-300 ℃.

According to some embodiments of the present application, the modified epoxy resin includes a carboxyl group and/or a cyano group. The carboxyl of the active functional group can react with the epoxy group in the epoxy resin; the cyano (-CN group) has strong polarity and can have better miscibility with the epoxy resin.

According to some embodiments of the present application, the matrix is present in an amount of 50 to 85% by mass, based on the mass of the conductive paste. The higher the mass ratio of the matrix, the higher the viscosity of the conductive adhesive, the higher the thixotropic index and the shear strength. The shear strength of the conductive adhesive is increased, the reliability of a bonding interface can be improved, and the conductivity of the electrochemical device is further improved. According to some embodiments of the present application, the matrix has a mass content of 55%, 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, 82%, 85% or a range of any two thereof, based on the mass of the conductive paste.

According to some embodiments of the present application, the conductive filler is present in an amount of 10 to 45% by mass, based on the mass of the conductive paste. The higher the mass ratio of the conductive filler, the lower the resistance and the better the conductivity. According to some embodiments of the present application, the conductive filler is present in an amount ranging from 10%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 35%, 38%, 40%, 45% by mass or any two thereof, based on the mass of the conductive paste.

According to some embodiments of the present application, the modified epoxy resin is present in an amount of 70 to 90% by mass, based on the mass of the matrix. The higher the proportion of modified epoxy resin, the greater the shear strength. According to some embodiments of the present application, the modified epoxy resin is present in an amount ranging from 70%, 72%, 75%, 77%, 80%, 83%, 85%, 88%, 90% by mass or any two thereof, based on the mass of the matrix.

According to some embodiments of the present application, the polyurethane is present in an amount of 5 to 20% by mass, based on the mass of the matrix. The higher the polyurethane proportion is, the higher the impact damage resistance is, the better the shock absorption effect of the conductive adhesive is, and further the shock resistance, the falling resistance and the roller performance of the electrochemical device can be improved.

According to some embodiments of the present application, the polyimide is present in an amount of 5 to 20% by mass, based on the mass of the substrate. The higher the polyimide proportion is, the better the temperature resistance of the conductive adhesive is, and further the high-temperature safety performance of the electrochemical device can be improved.

According to some embodiments of the present application, at least one of the following conditions (x) to (z) is satisfied: (x) The weight average molecular weight of the modified epoxy resin is 300 to 8000; (y) the weight average molecular weight of the polyurethane is 10000 to 150000; and (z) the weight average molecular weight of the polyimide is 13000 to 200000. According to some embodiments of the present application, the modified epoxy resin has a weight average molecular weight in a range of 500, 1000, 2000, 3000, 3500, 4000, 5000, 6000, 7000 or any two thereof. According to some embodiments of the application, the weight average molecular weight of the polyurethane is in the range of 10000, 20000, 30000, 40000, 50000, 60000, 70000, 80000, 90000, 100000, 130000, 150000, or any two thereof. According to some embodiments of the present application, the weight average molecular weight of the polyimide is 13000, 20000, 40000, 50000, 80000, 100000, 120000, 150000, 180000, 200000, or a range consisting of any two thereof.

According to some embodiments of the present application, the conductive filler includes one or more of Au, Ag, Ni, Cu, Zn, graphite, or graphene.

According to some embodiments of the present application, the conductive filler satisfies at least one of the following conditions (i) to (iii): (i) the surface morphology of the conductive filler comprises one or more of flake, sphere or branch; (ii) the particle size of the conductive filler is 0.1-100 μm; and (iii) the conductive filler has a bulk density of 2g/cm³To 15g/cm³. The conductivity of the conductive adhesive can be improved by regulating and controlling the surface appearance, the particle size distribution and the stacking density of the conductive filler, so that the quality of the electrochemical device is improved. According to some preferred embodiments of the present application, the conductive filler has a spherical surface morphology.

According to some embodiments of the present application, the conductive paste further comprises other ingredients including one or more of a curing agent, a diluent, an accelerator, a stress modifier, or a filler.

According to some embodiments of the present application, the curing agent comprises one or more of an aromatic amine curing agent, an aliphatic amine curing agent, an alicyclic amine curing agent, a polyetheramine curing agent, or an anhydride curing agent. According to some embodiments of the present application, the diluent comprises one or more of toluene, xylene, benzene, or acetone. According to some embodiments of the present application, the stress modifier comprises one or more of polysulfide rubber, vinyl resin, nitrile rubber. According to some embodiments of the present application, the accelerator comprises one or more of diglycidyl ether, polyglycidyl ether, propylene oxide butyl ether, propylene oxide phenyl ether, propylene oxide ethyl ether, or propylene oxide propyl ether. According to some embodiments of the present application, the filler comprises one or more of alumina, boron nitride or silica, titania.

According to some embodiments of the present application, the content of the other component is 15% by mass or less based on the mass of the conductive paste. According to some embodiments of the present application, the content of the other component is 10% by mass or less based on the mass of the conductive paste.

According to some embodiments of the present application, the conductive paste has at least one of the following characteristics (a) to (e): (a) the viscosity of the conductive adhesive is 50Pa.s to 300 Pa.s; (b) the thixotropic index of the conductive adhesive is 1 to 5; (c) the curing temperature of the conductive adhesive is less than or equal to 150 ℃; (d) the line width change rate of the conductive adhesive is less than or equal to 75 percent; and (e) the thermal weight loss rate of the conductive adhesive is less than or equal to 0.2 percent. According to some embodiments of the present application, the viscosity is determined using the viscosity measurement method of GB/T10247-. The thixotropic index is the ratio of the viscosity under different rotating speeds, namely the ratio of the low-speed viscosity (such as 0.1r/min) to the high-speed viscosity (such as 1r/min), and reflects the quality of the capability of the fluid to recover the original structure after the structure is damaged under the action of shear force. According to some embodiments of the present application, the thixotropic index is the ratio of the viscosity at a test temperature of 200 ℃ at a rotational speed of 0.1r/min to the viscosity at a rotational speed of 1 r/min. The line width change rate of the conductive adhesive refers to the line width change rate of the conductive adhesive before and after curing, i.e. the line width change rate of the adhesive is (width after curing-width before curing)/width before curing × 100%.

According to some embodiments of the present application, the conductive paste has at least one of the following characteristics (a) to (G): (A) the tensile shear bonding strength of the conductive adhesive is 5MPa to 10 MPa; (B) the volume resistance of the conductive adhesive is 0.01 omega cm to 0.1 omega cm; (C) the contact resistance of the conductive adhesive is less than or equal to 0.5 omega cm; (D) the total resistance of the conductive adhesive is less than or equal to 1m omega; (E) the swelling rate of the electrolyte of the conductive adhesive is less than or equal to 0.1 percent; and (F) the dissolution rate of the electrolyte of the conductive adhesive is less than or equal to 2 percent.

In the present application, the swelling ratio of the electrolyte indicates the weight change rate of the conductive adhesive before and after soaking in the electrolyte solvent, and the calculation formula may be (weight after soaking-weight before soaking)/weight before soaking × 100%. The electrolyte dissolution rate represents a weight change rate of the conductive adhesive after being soaked in the electrolyte solvent and dried, and the calculation formula may be (weight before soaking-weight after drying)/weight before soaking × 100%. The temperature of soaking may be 50 ℃ to 70 ℃, and the time of soaking may be 5 days to 8 days. The drying time may be 5 days to 8 days, and the drying temperature may be 80 ℃ to 90 ℃. The electrolyte solvent includes Ethylene Carbonate (EC), Propylene Carbonate (PC), diethyl carbonate (DEC) and Ethyl Propionate (EP) in a mass ratio of, for example, EC: PC: DEC: EP ═ 3: 1: 3.

In a second aspect, the present application provides an electrochemical device comprising an electrode assembly and a housing, the housing being provided with a terminal, the electrode assembly being provided with a tab, wherein the terminal is connected to the tab by a conductive adhesive according to the first aspect of the present application.

In a third aspect, the present application provides an electronic device comprising an electrochemical device according to the second aspect of the present application.

The conductive adhesive provided by the application has high shearing strength after being bonded, so that the reliability of a bonding interface can be ensured; on the other hand, the electrochemical performance is stable, and the use requirement of the lithium ion battery can be met. The conductive adhesive provided by the application is used for replacing laser welding for the electrochemical device, so that the production efficiency of the electrochemical device can be improved, and the cost is reduced.

Drawings

Fig. 1 is a schematic diagram of an application position of a conductive adhesive in a button cell according to an embodiment of the present application, where in fig. 1, 1 is a case cover, 2 is a PP adhesive, 3 is a terminal, 4 is a conductive adhesive, 5 is a bare cell, and 6 is a case.

Detailed Description

The present application is further described below in conjunction with the detailed description. It should be understood that these specific embodiments are merely illustrative of the present application.

In the application, the conductive adhesive matrix can form a molecular skeleton of the conductive adhesive, provide mechanical properties and a bonding effect, enable conductive filler particles to form channels, enable the conductive filler particles to be mutually contacted, and enable the particles to form a certain current path through a tunnel effect. The matrix of the application simultaneously comprises three components of modified epoxy resin, polyurethane and polyimide, and the modified epoxy resin can overcome the defects of high brittleness and poor toughness of the epoxy resin; the polyurethane improves the impact damage resistance and has good shock absorption effect; the polyimide has high temperature resistance up to 400 deg.c and may be used at 200-300 deg.c for long period.

Polyurethane, known as polyurethane PU, is a heterochain polymer with-NH-COO-characteristic groups. Synthesized from two raw materials: isocyanate plays a role of a hard segment, contains 2 or more-NCO characteristic groups, has a highly unsaturated bond structure with overlapped double bond arrangement, and can react with various compounds containing active hydrogen. Such as hexamethylene diisocyanate (MDI), Naphthalene Diisocyanate (NDI), and the like. ② the polyhydric alcohol plays the role of soft segment, such as butanediol, polyether glycol, polyester glycol, etc. The glass transition temperature, melting point, modulus, elasticity, tensile strength and the like of the polyurethane are controlled by adjusting the proportion and the type of the soft segment and the soft segment. According to some embodiments of the present application, the polyurethane includes soft segments of polyether diol or polyester diol and hard segments of isocyanate. According to some embodiments of the application, the weight average molecular weight of the polyurethane is 10000 to 150000.

The polyimide is a polycondensate of dianhydride and diamine, and refers to a polymer with a main chain containing-CO-NH-CO-characteristic groups, is high-temperature resistant and can be used for a long time at the temperature of 200-300 ℃. According to some embodiments of the present application, the polyimide has a weight average molecular weight of 13000 to 200000.

According to some embodiments of the present application, the modified epoxy resin includes a carboxyl group and/or a cyano group. The carboxyl of the active functional group can react with the epoxy group in the epoxy resin; the cyano (-CN group) has strong polarity and can have better miscibility with the epoxy resin. The epoxy resin is a high molecular polymer and refers to a generic name of a polymer containing more than two epoxy groups in a molecule. It is a polycondensation product of epichlorohydrin and bisphenol A or a polyol, and has a weight average molecular weight of 300 to 7000.

According to some embodiments of the present application, the modified epoxy resin is an epoxy resin toughened with liquid carboxyl terminated nitrile butadiene rubber (CTBN).

According to some embodiments of the present application, the polyurethane is present in an amount of 5 to 20% by mass, based on the mass of the matrix. The higher the polyurethane proportion is, the higher the impact damage resistance is, the better the shock absorption effect of the conductive adhesive is, and further the shock resistance, falling resistance and roller performance of the electrochemical device can be improved.

According to some embodiments of the present application, the conductive filler satisfies at least one of the following conditions (i) to (iii): (i) the surface morphology of the conductive filler comprises one or more of flake, sphere or branch; (ii) the particle size of the conductive filler is 0.1-100 μm; and (iii) the bulk density of the conductive filler is 2g/cm³To 15g/cm³. The conductivity of the conductive adhesive can be improved by regulating and controlling the surface appearance, the particle size distribution and the stacking density of the conductive filler, so that the quality of the electrochemical device is improved. According to some preferred embodiments of the present application, the conductive filler has a spherical surface morphology.

According to some embodiments of the present application, the conductive paste has at least one of the following characteristics (a) to (e): (a) the viscosity of the conductive adhesive is 50Pa.s to 300 Pa.s; (b) the thixotropic index of the conductive adhesive is 1 to 5; (c) the curing temperature of the conductive adhesive is less than or equal to 150 ℃; and (d) the line width variation rate of the glue is less than or equal to 75 percent; (e) the thermal weight loss rate of the conductive adhesive is less than or equal to 0.2 percent. According to some embodiments of the present application, the viscosity is determined using the viscosity measurement method of GB/T10247-. The thixotropic index is the ratio of the viscosity at different rotating speeds, namely the ratio of the low-speed viscosity (such as 0.1r/min) to the high-speed viscosity (such as 1r/min), and reflects the quality of the capability of the fluid to restore the original structure after the structure is damaged under the action of shear force. According to some embodiments of the present application, the thixotropic index is the ratio of the viscosity at a test temperature of 200 ℃ at a rotational speed of 0.1r/min to the viscosity at a rotational speed of 1 r/min. The glue line width change rate refers to the width change rate of the conductive glue before and after curing, i.e. the glue line width change rate is (width after curing-width before curing)/width before curing × 100%.

According to some embodiments of the present application, the conductive paste has at least one of the following characteristics (a) to (G): (A) the tensile shear bonding strength of the conductive adhesive is 5MPa to 10 MPa; (B) the volume resistance of the conductive adhesive is 0.01 omega cm to 0.1 omega cm; (C) the contact resistance of the conductive adhesive is less than or equal to 0.5 omega cm; (D) the total resistance of the conductive adhesive is less than or equal to 1m omega; and (E) the swelling ratio of the electrolyte of the conductive adhesive is less than or equal to 0.1 percent; (F) the dissolution rate of the electrolyte of the conductive adhesive is less than or equal to 2 percent.

The utility model provides a conducting resin solidifies below 150 ℃, and the back is glued to perpendicular point, glues the line and can not slide downwards or spread out, guarantees to have the clearance between the gluey line, ensures that the lithium ion between utmost point ear and the utmost point post freely shuttles back and forth, satisfies some requirement of gluing processing technology.

The electronic device or apparatus of the present application is not particularly limited. In some embodiments, the electronic device of the present application includes, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a cellular phone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a handheld cleaner, a portable CD player, a mini-disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power source, a motor, an automobile, a motorcycle, a moped, a bicycle, a lighting fixture, a toy, a game machine, a clock, a power tool, a flashlight, a camera, or a large household battery, and the like.

The present application is further illustrated below with reference to examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present application.

Test method

1. Viscosity measuring method GB/T10247-

The device name: viscometer, manufacturer: boomera flyer, model: DV 2T. Measurement range: 1.5mpa.s, precision: . + -. 1% FS.

Measurement of viscosity by rotational method: the conductive adhesive is placed in a cylinder at 200 ℃, and a Bohler fly 51# rotor rotating at 1rpm is selected. The viscometer is started, and after the reading is stabilized, the measurement is repeated three times, and the maximum difference from the mean value is not more than 1.5 percent of the mean value. The final viscosity results were taken as the average of three measurements.

2. Thixotropic index test

The thixotropic index is the ratio of the viscosity at different rotational speeds, i.e., the ratio of the low-speed viscosity to the high-speed viscosity. Reflecting the quality of the fluid in the ability of restoring the original structure after the structure is damaged under the action of shearing force.

The testing steps are as follows:

a) the container with the sample is placed in a thermostatic bath which is heated to 200 ℃ and the temperature is kept uniform.

b) The Bohler fly 51# rotor was immersed vertically into the sample and allowed to reach the rotor level mark.

c) The rotational speed was set to 0.1r/min and the viscometer was started and the first reading taken after the rotating pointer was stabilized. And restarting twice after the motor is closed, respectively reading the stable readings of the pointer for the second time and the third time, and taking the average value as eta 0.1.

d) And changing the rotating speed from 0.1r/min to 1r/min, repeating the steps, measuring the reading of the stabilized pointer for three times, and taking the average value as eta 1.

The thixotropic index It should be calculated as follows, taking two significant figures, and noting the temperature of the experiment:

It＝η0.1/η1

3. shear test

Shear strength: the glue joint can bear the maximum load parallel to the glue joint surface in unit area. The testing steps are as follows:

three samples of an Al sheet, a Cu sheet and a Ni sheet are made into a sheet specification of 12.7mm multiplied by 25.4mm, then three samples of the Al sheet and the Cu sheet, the Al sheet and the Ni sheet and the Cu sheet and the Ni sheet are selected to be combined, and conductive adhesive is coated on the boundary surface of the samples. After curing for 2h at 100 ℃ the test was carried out in a universal tester at a shear rate of 10mm/min until the interface was broken. And (3) testing 5 samples in each sample combination, wherein the arithmetic average value of the tensile shear strength is the shear strength of the bonded conductive glue.

4. Resistance testing method

Four-probe resistivity tester, manufacturer: reko, type: FT-340. The needle points of the four probes are on the same straight line, the distances are equal and are all S, the distance of 0.5mm is generally adopted, and the corresponding correction needs to be carried out on the measurement result at different probe distances. And calculating the influence of different sample thicknesses on the resistivity through the setting of the thickness value.

The volume resistance comprises the following specific steps: and (3) filling conductive adhesive into a die with the depth of 202.54mm and the depth of 50 mu m, putting the sample into an environment of color-changing water-absorbing silica gel particles, curing for 2h at 100 ℃, inversely buckling the sample on a self-made four-probe die, and pressing downwards to enable the probes to be in close contact with the adhesive tape to obtain a resistance value so as to calculate the volume resistance.

The contact resistance comprises the following specific steps: coating 202mm of conductive glue on the joint parts of the Al sheet and the Cu sheet, curing for 2h at 100 ℃, marking test areas on the Al sheet and the Cu sheet respectively, and testing the resistance value.

The total resistance comprises the following specific steps: and (3) coating the conductive glue between the polar ear and the polar pole of the naked electric core to obtain a sample with the thickness of 202mm and the thickness of 50 mu m, and testing the resistance value.

5. Thermal weight loss test method

The device name: thermal mass spectrometer DSC/TG-MS, model number: STA449F3-QMS403C, test basis: the thermal analysis method for the thermal stability of GB/T13464-: the temperature is between room temperature and 800 ℃, the heating rate is 0.1-50 ℃/min, and the TG resolution is 0.1 ug.

The method comprises the following specific steps: heating rate to 100 deg.C/min, maintaining for 2.5h, and testing thermal weight loss.

6. Dissolution rate test

And (3) preparing the conductive glue into a glue block, and soaking the glue block in lithium salt-free electrolyte to ensure that the electrolyte completely submerges the glue block. Soaking at 60 deg.C for 7 days, and baking at 85 deg.C for 7 days.

Wherein the organic solvent of the lithium salt-free electrolyte is Ethylene Carbonate (EC), Propylene Carbonate (PC), diethyl carbonate (DEC) and Ethyl Propionate (EP), and the mass ratio of EC to PC to DEC to EP is 3: 1: 3.

Swelling ratio (weight after 7 days soaking-weight before soaking)/weight before soaking 100%.

The dissolution rate (weight before soaking-weight after drying)/weight before soaking 100%.

7. Glue line width change rate

And (3) dispensing the conductive adhesive on the glass sheet by using a dispenser, standing for 10min at room temperature to ensure the stable viscosity of the adhesive line, and recording the width of the adhesive line before curing by using a CCD (charge coupled device).

Curing for 2h at 100 ℃ to ensure that the glue line is kept in a vertical state in the whole curing process, wherein the width of the glue line can change under the self gravity, and the CCD records the width of the glue line after measurement.

The line width change rate of the adhesive is (width after curing-width before curing)/width before curing 100%.

Second, examples and comparative examples

1. Preparation of conductive glue

1) And pre-reaction: adding CTBN (carboxyl-terminated liquid nitrile rubber) with the mass ratio of 10-15% and epoxy resin (weight-average molecular weight of 3500) with the mass ratio of 85-90% into a reactor, heating to 150 ℃, and carrying out N reaction₂Stirring for 12h in a protective atmosphere.

The mechanism is as follows: CNBT is a telechelic high polymer, active functional groups of carboxyl are arranged at two ends of a molecular chain, can react with epoxy groups in epoxy resin, has-CN groups with strong polarity, and has good miscibility with the epoxy resin.

2) And adding a curing agent (such as an aromatic amine curing agent, an aliphatic amine curing agent, an alicyclic amine curing agent, a polyether amine curing agent, an anhydride curing agent and the like) into the pre-reacted epoxy-CTBN-epoxy adduct, and curing for 2 hours to obtain the modified epoxy resin.

3) And 50-85% of modified epoxy resin, polyurethane (weight average molecular weight is 80000) and polyimide (weight average molecular weight is 10000) in mass proportion (70-90%): (5% to 20%): (5-20%) adding into reactor, adding 10-45% of conductive filler (one or more of Au, Ag, Ni, Cu, Al, Zn, graphite, and graphene), heating to 200 deg.C under N₂Stirring was carried out for 12h under a protective atmosphere.

4) And then adding other components (curing agent, diluent, stress modifier, accelerator and oxide) with the mass ratio of 5-10%, and curing for 2h to obtain the conductive glue.

See table 1 for example and comparative example specific components.

2. Battery preparation method

Positive pole piece: mixing the positive electrode active material lithium cobaltate, acetylene black and polyvinylidene fluoride (PVDF) according to a mass ratio of 94: 3: 3, adding N-methyl pyrrolidone (NMP) as a solvent to prepare slurry with the solid content of 75%, and uniformly stirring. And uniformly coating the slurry on an Al foil of a positive current collector, drying at 90 ℃, cold-pressing to obtain a positive pole piece with the thickness of a positive active material layer of 100 mu m, and repeating the steps on the other surface of the positive pole piece to obtain the positive pole piece with the positive active material layer coated on two surfaces.

Negative pole piece: preparing a negative electrode active material of artificial graphite, acetylene black, styrene butadiene rubber and sodium carboxymethyl cellulose according to a mass ratio of 96: 1: 1.5: 1.5, adding deionized water as a solvent to prepare slurry with the solid content of 70%, and uniformly stirring. And uniformly coating the slurry on a copper foil of a negative current collector, drying at 110 ℃, performing cold pressing to obtain a negative pole piece with a negative active material layer of which the thickness is 150 mu m and one surface is coated with the negative active material layer, and repeating the coating steps on the other surface of the negative pole piece to obtain the negative pole piece with the two surfaces coated with the negative active material layer.

And (3) isolation film: PE separator film with a thickness of 7 μm.

The organic solvent of the electrolyte is Ethylene Carbonate (EC), Propylene Carbonate (PC), diethyl carbonate (DEC) and Ethyl Propionate (EP), the mass ratio of EC to PC to DEC to EP is 3: 1: 3, and the solute is lithium hexafluorophosphate (LiPF)₆)，LiPF₆The concentration of (2) is 1 mol/L.

Preparing a battery: and respectively positioning the positive pole piece and the negative pole piece on two sides of the isolating membrane for winding to obtain the bare cell. The bare cell is put into a steel shell, the bare cell tab and the pole are connected and fixed by conductive adhesive (specifically, a certain amount of the prepared conductive adhesive is sprayed or coated at the cell tab by a dispenser, then the cell is put into the shell, finally the pole is covered at the tab, and reliable bonding is formed after the conductive adhesive is cured). And then the lithium ion button cell is prepared by the processes of top side sealing, vacuum baking, liquid injection, formation, capacity, air extraction and the like.

Third, test results

Table 1 shows the compositions of the conductive pastes in examples 1 to 49 and comparative examples 1 to 5. Table 2 shows the results of the performance test of the conductive pastes in examples 1 to 49 and comparative examples 1 to 5.

TABLE 1

TABLE 2

As can be seen from tables 1 and 2,

1. when the total mass ratio of the matrix is 40%, the shear strength of the conductive adhesive is only 4.35MPa, and reliable bonding cannot be realized. When the total mass ratio of the matrix is 95%, the thixotropic index of the conductive adhesive is 7.90, the dispensing processability is poor, and the mass ratio of the conductive filler is low, so that the resistance is large. Therefore, the mass proportion of the matrix is 50-85%, and the use requirement can be met.

2. Example 1 and comparative example 5 show that the shear strength of the conductive adhesive can be improved from 2.80MPa to 5.20MPa, and the modified epoxy resin has better toughness than the epoxy resin. Therefore, the matrix needs to be modified epoxy resin to meet the use requirement.

3. The matrix only contains epoxy resin or modified epoxy resin, which can cause the conductive adhesive to have high viscosity, high thixotropic index and poor dispensing processability.

4. The matrix is only polyurethane, which can cause the conductive adhesive to have high viscosity, large thixotropic index and poor dispensing processability. And the swelling rate, the dissolution rate and the glue line width change rate are all high, so that the electrochemical risk exists.

5. The matrix only contains polyimide, which can cause the conductive adhesive to have high viscosity, large thixotropic index and poor dispensing processability. And the swelling rate, the dissolution rate and the glue line width change rate are all high, so that the electrochemical risk exists.

6. Modified epoxy resin in the matrix: polyurethane: the composition of the polyimide is (70-90%): (5-20%): (5% -20%) and can implement conductive reliable adhesion.

The above embodiments are only used for illustrating the technical solutions of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; such modifications or substitutions do not depart from the spirit and scope of the present disclosure.

Claims

1. A conductive adhesive comprises a matrix and a conductive filler, wherein the matrix comprises modified epoxy resin, polyurethane and polyimide.

2. The conductive paste according to claim 1, wherein the matrix is contained in an amount of 50 to 85% by mass and the conductive filler is contained in an amount of 10 to 45% by mass, based on the mass of the conductive paste.

3. The conductive paste according to claim 1, wherein the modified epoxy resin is contained in an amount of 70 to 90% by mass, the polyurethane is contained in an amount of 5 to 20% by mass, and the polyimide is contained in an amount of 5 to 20% by mass, based on the mass of the base.

4. The conductive paste of claim 1, wherein the modified epoxy resin comprises a carboxyl group and/or a cyano group.

5. The conductive paste of claim 1, wherein the conductive filler comprises one or more of Au, Ag, Ni, Cu, Zn, graphite, or graphene.

6. The conductive paste according to claim 1, wherein the conductive filler satisfies at least one of the following conditions (i) to (iii):

(i) the surface morphology of the conductive filler comprises one or more of flake, sphere or branch;

(ii) the particle size of the conductive filler is 0.1-100 μm;

(iii) the conductive filler has a bulk density of 2g/cm³To 15g/cm³。

7. The conductive paste according to claim 1, wherein the conductive paste has at least one of the following characteristics (a) to (e):

(a) the viscosity of the conductive adhesive is 50Pa.s to 300 Pa.s;

(b) the thixotropic index of the conductive adhesive is 1 to 5;

(c) the curing temperature of the conductive adhesive is less than or equal to 150 ℃;

(d) the line width change rate of the conductive adhesive is less than or equal to 75 percent;

(e) the thermal weight loss rate of the conductive adhesive is less than or equal to 0.2 percent.

8. The conductive paste according to claim 1, wherein the conductive paste has at least one of the following characteristics (a) to (F):

(A) the tensile shear bonding strength of the conductive adhesive is 5MPa to 10 MPa;

(B) the volume resistance of the conductive adhesive is 0.01 omega cm-0.1 omega cm;

(C) the contact resistance of the conductive adhesive is less than or equal to 0.5 omega cm;

(D) the total resistance of the conductive adhesive is less than or equal to 1m omega;

(E) the swelling rate of the electrolyte of the conductive adhesive is less than or equal to 0.1 percent;

(F) the dissolution rate of the electrolyte of the conductive adhesive is less than or equal to 2 percent.

9. An electrochemical device comprising an electrode assembly and a housing, the housing being provided with a terminal, the electrode assembly being provided with a tab, wherein the terminal is connected to the tab by the conductive adhesive of any one of claims 1 to 8.

10. An electronic device comprising the electrochemical device according to claim 9.