CN113121823A

CN113121823A - Conductive adhesive for lithium ion battery and preparation method thereof

Info

Publication number: CN113121823A
Application number: CN201911401865.8A
Authority: CN
Inventors: 钱超; 路广明; 蔡旺; 何家齐; 张艺
Original assignee: Shenzhen Yanyi New Materials Co Ltd
Current assignee: Shenzhen Yanyi New Materials Co Ltd
Priority date: 2019-12-31
Filing date: 2019-12-31
Publication date: 2021-07-16

Abstract

The invention provides a polyamide-imide conductive adhesive which is used for a lithium ion battery and can improve the electrochemical properties of the lithium ion battery, such as multiplying power, high-low temperature charge and discharge, cycle life and the like. The conductive adhesive disclosed by the invention has the following beneficial effects: the solution state is realized, and the solution is not needed to be dissolved in the using process, so that the production efficiency is improved; the phenomenon that the polymer adhesive is easy to gel after HF (hydrogen fluoride) removal in water environment is improved; the proportion of active substances in the electrode material is increased; the conductive substance is polymerized in the molecular weight of the binder in an in-situ polymerization mode, so that the dispersibility of the conductive substance is improved, and the transmission rate of electrons is improved; the electrochemical properties of the lithium ion battery such as multiplying power, high-low temperature charge and discharge, cycle life and the like are improved.

Description

Conductive adhesive for lithium ion battery and preparation method thereof

Technical Field

The invention relates to the field of lithium ion batteries, in particular to a conductive adhesive for a lithium ion battery and a preparation method thereof.

Background

Lithium Ion Batteries (LIBs) are considered to be one of the most promising energy storage systems, and are currently widely used in portable energy storage systems and automobile power systems, especially in hybrid and pure electric vehicles, and the market requirements for energy density, fast charging, safety and the like of lithium ion batteries are further increased. The binder for the lithium battery is used as an important component of the lithium battery and is a main source of the mechanical property of the whole electrode.

The binders for lithium batteries are various, and currently, the binders applied to lithium batteries are generally high molecular compounds, and the commonly used binders mainly include polyvinylidene fluoride (PVDF), Styrene Butadiene Rubber (SBR) emulsion and hydroxymethyl cellulose (CMC), and in addition, aqueous binders containing polyacrylic acid (PAA) and Polyacrylonitrile (PAN) as main components also have a certain market. Among them, polyvinylidene fluoride (PVDF) is currently most widely used. Polyvinylidene fluoride is a semi-crystalline polymer, the crystallinity is generally 65-78%, and the crystallization melting temperature is about 170 ℃. With the advancement of use, researchers have pointed out that, although high crystallinity implies high adhesion, the presence of a crystalline state is detrimental to the penetration of the liquid electrolyte and thus affects the Li + mobility; in addition, since PVDF has a high degree of crystallinity, which results in a large difference in shrinkage between the PVDF binder and the current collector, the internal stress of the electrode increases as the degree of crystallinity of PVDF increases, and during use, the internal stress of the electrode partially or entirely peels off the electrode active material layer from the current collector over time, causing capacity deterioration.

PVDF is used as a binder for a lithium battery, and the moisture content needs to be strictly controlled in the slurry mixing process because free amine exists in an NMP solvent, the pH value of the system is increased after water absorption, basic groups can attack adjacent C-F, C-H bonds in PVDF molecular chains to generate elimination reaction, partial double bonds can be generated in the PVDF molecular chains, the viscosity of the slurry system is increased, and a gel state can be generated in severe cases, so that the coating is difficult.

At present, in addition to a binder and an active material, a conductive agent is also added in the preparation process of battery slurry, and the proportion of the active material is usually about 93%. Patent documents CN104282912A and CN109742402A disclose that it is difficult to ensure uniform dispersion of the conductive agent in the slurry, to ensure good contact of the conductive agents of the components, and to achieve ideal conductive effect, and to increase the process and cost due to multiple dispersions, by physically blending the conductive particles and the active material and continuously ball-milling the mixture for 12 hours in a ball mill.

Disclosure of Invention

The invention provides a polyamide-imide conductive adhesive which is used for a lithium ion battery and can improve the electrochemical properties of the lithium ion battery, such as multiplying power, high-low temperature charge and discharge, cycle life and the like.

In a first aspect, the present invention provides a conductive adhesive, characterized by having the following structural formula:

wherein A, C are each one of the following structures:

wherein B, D are each one of the following structures:

wherein a, b, c and d are respectively one of 11, 10, 6, 5, 3 and 0.

Optionally, the conductive binder has the following structural formula:

in a second aspect, the invention provides the use of a conductive binder in the preparation of a lithium ion battery.

The third aspect of the present invention provides a method for preparing the conductive adhesive, comprising the following steps:

adding a catalyst into a high-efficiency selective solvent to perform a dehydration condensation reaction on a diacid monomer containing an imide structure and diamine;

and adding a high-efficiency selective solvent containing a conductive substance after the dehydration condensation reaction to carry out a secondary reaction, thereby obtaining the conductive adhesive.

Optionally, the diamine is an aromatic diamine or a p-phenylenediamine,

optionally, the mole ratio of the diacid monomer containing the imide structure to the diamine is 1: 1-1.05.

Optionally, the highly efficient selective solvent is N-methylpyrrolidone.

Optionally, the catalyst is a mixture of pyridine and triphenyl phosphite.

Optionally, the volume ratio of pyridine to triphenyl phosphite is 0.5-1, and is further preferably 3: 4;

optionally, the dehydration condensation reaction conditions are: 8-12 hours at 60-120 ℃;

optionally, the dehydration condensation reaction conditions are: reacting at 60 ℃ for 1 hour, gradually heating to 120 ℃ at the heating rate of 10 ℃ per hour, and reacting for 11 hours;

optionally, the addition amount of pyridine and triphenyl phosphite is 0.5-1 times of the mass of diacid monomer, and the solid content of the system is controlled between 13% and 30%.

Optionally, the conductive substance is one or more of a carboxylated carbon nanotube and graphene oxide;

optionally, the conductive material is a carboxylated carbon nanotube;

optionally, the dehydration condensation reaction generates polyamide imide, the addition amount of the carboxylated carbon nanotube is 1-10% of the mass of the polyamide imide,

optionally, the mass concentration of the conductive substance in the N-methylpyrrolidone solution is 0.1% -0.5%;

optionally, the conditions for the re-reaction are: reacting for 3-5 hours at 80-140 ℃;

optionally, the conditions for the re-reaction are: reacting for 4 hours at 120 ℃;

optionally, after the secondary reaction, the by-product and the catalyst are evaporated out under negative pressure at 100-120 ℃ to obtain the uniform and stable conductive adhesive.

Optionally, the preparation method of the diacid monomer containing the imide structure comprises the following steps: anhydride and amino acid are dehydrated and condensed in acetic acid solvent under the catalysis of pyridine through a chemical dehydration mode to generate diacid monomer containing imide structure.

The invention has the following beneficial effects:

the invention provides a high molecular weight polyamide imide conductive adhesive, which improves the phenomenon that the high molecular adhesive is easy to gel after HF (hydrogen fluoride) is removed in water environment; the proportion of active substances in the electrode material is increased; the conductive substance is polymerized in the molecular weight of the binder in an in-situ polymerization mode, so that the dispersibility of the conductive substance is improved, and the transmission rate of electrons is improved; the electrochemical properties of the lithium ion battery such as multiplying power, high-low temperature charge and discharge, cycle life and the like are improved.

Drawings

Fig. 1 shows the rheology curve of a battery slurry prepared with the conductive binder of example 1, with shear rate on the abscissa and shear viscosity on the ordinate.

Fig. 2 shows the rheological characteristics of the battery slurry prepared with the conductive binder of example 1 and the prior art, respectively, with shear stress on the abscissa and modulus on the ordinate.

Fig. 3 shows the electrochemical performance of a battery prepared using the conductive adhesive of example 1, the electrochemical performance of the battery measured using an impedance tester and CV, with voltage on the abscissa and current on the ordinate, the outer line corresponding to the PCB-L of example 1, and the inner line corresponding to the PVDF of the prior art.

Fig. 4 shows the ac resistance of the battery prepared with the conductive adhesive of example 1, tested with an impedance tester and CV, both the abscissa and ordinate being impedance, represented by the long line corresponding to the PVDF of the prior art, and the short line corresponding to the PCR-L of example 1.

Fig. 5 shows the conductive adhesive of example 1 to prepare a positive electrode sheet, and the distribution of SWCNTs on the sheet was observed by SEM.

Detailed Description

In order to better explain the problems to be solved, the technical solutions adopted and the beneficial effects achieved by the technical solutions of the present invention, further description will be given with reference to specific embodiments. It should be noted that the technical solutions of the present invention include, but are not limited to, the following embodiments.

The specific techniques or conditions not specified in the examples of the present invention are performed according to the techniques or conditions described in the literature in the art or according to the product specification. The instruments used are not indicated by manufacturers, and are all conventional products which can be obtained commercially, and the reagents used are not indicated by manufacturers or concentrations, and are all analytically pure which can be obtained conventionally.

The application provides a preparation method of a conductive adhesive for a lithium ion battery, which comprises the following steps:

(1) preparing diacid monomer containing imide structure;

anhydride and amino acid are dehydrated and condensed in acetic acid solvent under the catalysis of pyridine through a chemical dehydration mode to generate diacid monomer containing imide structure.

(2) Adding a catalyst into a high-efficiency selective solvent to react with diacid monomer (DIDA) containing an imide structure and diamine;

the method comprises the following steps of carrying out phosphorylation reaction on diacid monomer containing an imide structure and aromatic diamine (also can be p-phenylenediamine), wherein the charging ratio (molar ratio) of the diacid monomer containing the imide structure to the aromatic diamine is 1: (1-1.05) and dehydrating and condensing the mixture at the temperature of 60-120 ℃ for 8-12 hours in NMP solvent and catalyst (more preferably, 60 ℃ for 1 hour, gradually raising the temperature to 120 ℃ at the temperature raising rate of 10 ℃ per hour, and keeping the total reaction time for 11 hours), wherein the catalyst can be a mixture of pyridine and triphenyl phosphite, the volume ratio of the pyridine to the triphenyl phosphite is 0.5-1, and the ratio is more preferably 3:4, the addition amount of the pyridine and the triphenyl phosphite is 0.5-1 times of the mass of the diacid monomer, and the solid content of the system is controlled between 13-30%.

(3) And adding a conductive substance after the reaction to react again to obtain the conductive adhesive.

Adding N-methyl pyrrolidone solution containing conductive substances after dehydration condensation, reacting for 3-5 hours at 80-140 ℃, and evaporating (preferably spirally evaporating at 100-120 ℃) reaction byproducts and catalysts to obtain the uniform and stable conductive adhesive. The conductive substance comprises one or more combinations of carboxylated single-walled carbon nanotubes, carboxylated multi-walled carbon nanotubes and graphene oxide, and is further preferably carboxylated carbon nanotubes, the mass concentration of the carboxylated carbon nanotubes in an N-methylpyrrolidone solution is 0.1% -0.5%, the dehydration condensation reaction generates polyamideimide, the addition amount of the carboxylated carbon nanotubes is 1% -10% of the mass of the Polyamideimide (PAI), and the hydroxylated carbon nanotubes comprise one or more of multi-walled carbon nanotubes and single-walled carbon nanotubes.

The conductive adhesive for the lithium battery prepared by the invention is in a solution state, does not need to be dissolved in the using process, and improves the production efficiency.

The prepared conductive adhesive does not have elimination reaction similar to PVDF (the existing mainstream adhesive for the positive electrode, non-conductive type), and does not have gel state after being placed for a long time.

The conductive adhesive prepared by the invention has the advantages that the conductive carbon nano tube and the polymer have in-situ polymerization, and the dispersion of conductive substances is facilitated.

The addition amount of the prepared binder in the battery slurry is 0.5-5%, and the proportion of active substances is 95-99.5%, so that the energy density of the lithium battery is greatly improved.

Example 1

The embodiment provides a preparation method of a conductive adhesive for a lithium ion battery, which comprises the following steps:

(1) feeding amino undecanoic Acid (AU) and diphenyl ether dianhydride (ODPA) according to a molar ratio of 2:1, dissolving in a mixed solvent of glacial acetic acid (with a purity of 99.5%) and pyridine (pyridine accounts for 8% -15% of the total volume), refluxing at 120 ℃ for 8 hours, cooling to room temperature to separate out a product, filtering, washing with deionized water to neutralize, and vacuum drying at 90 ℃ to obtain an imide diacid monomer (DIDA monomer).

(2) 0.01mol (6.768g) of the DIDA monomer obtained in step (1) and 0.01mol (1.081g) of p-phenylenediamine were charged in a 100ml three-necked flask, 50ml of an NMP solvent having a purity of 98% (i.e., N-methylpyrrolidone) was added, and a catalyst (i.e., 6ml of pyridine and 8ml of triphenyl phosphite) was added. Reacting at 60 ℃ for 1 hour, gradually increasing the temperature to 120 ℃ at the temperature increasing rate of 10 ℃ per hour, and reacting at 120 ℃ for 5 hours, wherein the total reaction time is 11 hours.

(3) The carboxylated carbon nanotubes (purchased from Nanjing Gingo nanotechnology Co., Ltd., JCST-90) were dispersed in a solvent of NMP with a purity of 98% at a ratio of five thousandths (mass concentration of carbon nanotubes in NMP solution) using a high pressure homogenizer, and injected into the reacted system of step (2) by a syringe in an amount of 78ml to 100ml, and the reaction was completed at 120 ℃ for 4 hours. Negative pressure rotary evaporation of reaction by-product H at 100-120 deg.C₂O and a catalyst to obtain a uniform and stable conductive binder, wherein the structural formula is as follows:

the present embodiment also provides for the use of a conductive adhesive: and preparing the lithium ion battery by using the obtained conductive adhesive, and detecting the lithium ion battery.

(1) Preparing the anode of the lithium ion battery: respectively adding 0.3g of the conductive adhesive (PCB-L) and 9.7g of lithium iron phosphate (LFP) into a closed container, then adding 11g of NMP, wherein the solid content is about 42%, stirring at a high speed of 2000rpm/min for 10min, uniformly mixing the slurry, and judging the slurry to be in a glossy state macroscopically.

(2) And (2) uniformly coating the battery slurry obtained in the step (1) on a common aluminum foil in a coating mode, and drying the coated pole piece in a forced air oven at 100 ℃ for 2 hours.

(3) The pole piece manufactured in the step (2) is compacted according to the compaction density of 2.2g/mm³And (5) cold pressing, weighing the compacted electrode slice pieces, and baking for 2 hours in vacuum to prepare the button cell. The diaphragm is a 12+4um ceramic coated diaphragm.

Testing a rheological characteristic curve of battery slurry through detection; and (3) detecting the charge-discharge cycle characteristics of the battery by using a Xinwei battery test cabinet: the first charge efficiency of the battery was tested by charging and discharging at a charge and discharge rate of 0.1C in a voltage range of 1.9V to 3.75V. After 1 cycle of charge and discharge, the battery was charged to a half-charge state, the ac resistance (fig. 4) and electrochemical performance (fig. 3) of the battery were measured with an impedance tester and CV, and the distribution of SWCNTs on the pole piece was observed by SEM (fig. 5).

And (4) analyzing results:

fig. 1 and 2 represent the cell slurry rheological characteristic curve, the cell slurry flow characteristic of 3% PCB-L conductive adhesive content and the viscoelasticity, and it can be seen from fig. 1 that as the shear rate increases, the cell slurry plateaus when the shear rate reaches 1251/S, indicating that the slurry flowability is better, and it can be seen from fig. 2 that when the shear rate reaches 5Pa, the gel point appears, meaning that when the shear force is greater than 5Pa, the viscous behavior of the cell slurry is dominant, which is beneficial to the uniformity of slurry application.

The button cell performance test results are shown in table 1. In the shown embodiment, the peel strength of the pole piece is more than 5N/m (the general use requirement of the peel strength of the positive pole piece), and the first coulombic efficiency is more than 97%.

Example 2

Example 2 differs from example 1 in that: the proportion of the active material of the cell is 98%, and the performance test results of the button cell are shown in table 1.

Example 3

Example 3 differs from example 1 in that: the percentage of the active material in the cell is 98.5%, and the performance test results of the button cell are shown in table 1.

TABLE 1

Example 4

The conductive adhesive prepared in example 1 is used for preparing a soft package battery, and the soft package battery is detected by the method shown in example 1, wherein the method is different from charging and discharging in a voltage range of 2.0V-3.7V.

And (3) positive electrode: the active material is lithium iron phosphate (LFP), the content of the active material is 97%, and the content of a conductive adhesive (PCB-L, namely the conductive adhesive in the embodiment 1 of the invention) is 3%; the control was PVDF5130 (suwei PVDF5130), as shown in table 2.

Negative electrode: 96% of active material graphite, 1% of conductive carbon black and 3% of negative electrode binder (CMC).

A diaphragm: the 16um ceramic coated diaphragm, design capacity is 1000 mAh.

The results of the measurements are shown in tables 2 and 3. Under the condition that no conductive Substance (SP) is added, the first efficiency of the battery is 2.88% higher than that of a comparative sample, which shows that the addition of the conductive adhesive is more favorable for lithium removal and lithium insertion reactions of the lithium battery, the internal resistance is small after capacity grading, and the conductive adhesive of the PCB-L is more favorable for electron transmission. Table 3 shows that the comparison of the charge and discharge efficiencies at different magnifications also confirms that the PCB-L conductive adhesive exhibits better electrochemical properties.

TABLE 2

TABLE 3

Claims

1. An electrically conductive adhesive having the formula:

wherein A, C are each one of the following structures:

wherein B, D are each one of the following structures:

wherein a, b, c and d are respectively one of 11, 10, 6, 5, 3 and 0.

2. The conductive adhesive of claim 1, having the formula:

3. use of the electrically conductive binder according to claim 1 or 2 for the preparation of a lithium ion battery.

4. The method for preparing a conductive adhesive according to claim 1 or 2, comprising the steps of:

and (3) after dehydration condensation reaction, adding a high-efficiency selective solvent containing a conductive substance to react again to obtain the conductive adhesive as claimed in claim 1.

5. The method for producing a conductive adhesive according to claim 4,

the diamine is aromatic diamine or p-phenylenediamine,

the mole ratio of the diacid monomer containing the imide structure to the diamine is 1: 1-1.05.

6. The method of claim 4, wherein the highly efficient selective solvent is N-methylpyrrolidone.

7. The method for producing a conductive adhesive according to claim 4,

the catalyst is a mixture of pyridine and triphenyl phosphite;

optionally, the volume ratio of pyridine to triphenyl phosphite is 0.5 to 1, and more preferably 3: 4.

8. The method for producing a conductive adhesive according to claim 4,

the dehydration condensation reaction conditions are as follows: 8-12 hours at 60-120 ℃;

the dehydration condensation reaction conditions are as follows: reacting at 60 ℃ for 1 hour, gradually heating to 120 ℃ at the heating rate of 10 ℃ per hour, and reacting for 11 hours;

wherein the addition amount of pyridine and triphenyl phosphite is 0.5-1 times of the mass of diacid monomer, and the solid content of the system is controlled between 13-30%.

9. The method for producing a conductive adhesive according to claim 4,

the conductive substance is one or more of a carboxylated carbon nanotube and graphene oxide;

the conductive substance is a carboxylated carbon nanotube;

the dehydration condensation reaction generates polyamide imide, and the addition amount of the carboxylated carbon nanotube is 1-10% of the mass of the polyamide imide;

the mass concentration of the conductive substance in the N-methyl pyrrolidone solution is 0.1-0.5%;

the conditions for the secondary reaction are as follows: reacting for 3-5 hours at 80-140 ℃;

the conditions for the secondary reaction are as follows: reacting for 4 hours at 120 ℃;

after the secondary reaction, the by-product and the catalyst are evaporated out under the negative pressure at the temperature of 100-120 ℃ to obtain the uniform and stable conductive adhesive.

10. The method for preparing the conductive adhesive according to claim 4, wherein the method for preparing the diacid monomer containing the imide structure comprises the following steps: anhydride and amino acid are dehydrated and condensed in acetic acid solvent under the catalysis of pyridine through a chemical dehydration mode to generate diacid monomer containing imide structure.