CN110690450A

CN110690450A - Carbon electrode and forming method and application thereof

Info

Publication number: CN110690450A
Application number: CN201911019402.5A
Authority: CN
Inventors: 邓辉辉; 曹浪; 祝媛; 孙佩玲; 张俊; 袁中直; 刘金成
Original assignee: Eve Energy Co Ltd
Current assignee: Eve Energy Co Ltd
Priority date: 2019-10-24
Filing date: 2019-10-24
Publication date: 2020-01-14
Anticipated expiration: 2039-10-24
Also published as: CN110690450B

Abstract

The invention relates to a carbon electrode and a forming method and application thereof, wherein isoparaffin is used as a solvent in the forming process of the carbon electrode, the isoparaffin is mixed with a binder and acetylene black to obtain mixed slurry, and then the mixed slurry is kneaded and extruded to form the carbon electrode.

Description

Carbon electrode and forming method and application thereof

Technical Field

The invention belongs to the field of battery materials, and relates to a carbon electrode and a forming method and application thereof.

Background

The main components of the positive electrode material of the lithium/thionyl chloride battery are acetylene black and a binder. At present, water is mostly adopted as a mixing solvent in the manufacturing process of the carbon anode, and acetylene black has the characteristic of strong hydrophobicity, so that in the mixing process, the acetylene black needs high stirring speed and long dispersion time for sufficient infiltration, and polytetrafluoroethylene emulsion serving as a binder is difficult to uniformly disperse in the acetylene black, so that the prepared carbon anode shows high powder dropping rate and poor conductivity, and the discharge performance of a battery core assembled by the carbon anode is influenced. In addition, ethanol or isopropanol is adopted as a mixing solvent in some processes, although acetylene black can be well infiltrated, the ethanol and the isopropanol both have low flash point and inflammability, and can be continuously volatilized in the carbon anode manufacturing process to cause instability of the carbon anode structure, and the carbon anode has certain safety risk in the drying process, so that the large-scale industrial production is not facilitated.

At present, domestic manufacturers mostly adopt high-speed mixing of hydrated powder in the preparation process of a carbon anode and prepare a granular anode material (with the diameter of 1-2mm) through a plurality of processes, the preparation steps are relatively complicated and high in energy consumption, the anode granules have certain static electricity, and if field control is not good, the anode granules are clamped between a side film and a cathode in the automatic assembly process of equipment, so that the internal micro short circuit of a battery is caused. In addition, the anode micro powder is easy to dissolve out of the electrolyte and migrate to the surface of the cathode, so that the risk of improving the self-discharge rate of the battery is caused, and the discharge capacity of the battery is seriously influenced.

CN109830687A discloses a lithium-thionyl chloride battery positive electrode and a powder method. It comprises the following steps: adding the acetylene black into a powder mixer to be mixed under the conditions that the room temperature is 25 +/-5 ℃ and the humidity is 50% +/-20%; mixing the polytetrafluoroethylene emulsion, isopropanol and deionized water in the weight ratio to obtain a mixed solution, adding half of the mixed solution in a powder mixer, and stirring and mixing to obtain mixed powder; after stirring for 15 minutes, discharging mixed powder with the total amount of about 20 percent from an outlet part at the bottom of the powder mixer; uniformly adding the metal powder with the weight into the powder mixing machine from the inlet part of the powder mixing machine, then adding the mixed powder obtained in the step three from the inlet part of the powder mixing machine, and finally adding the remaining half weight of the mixed solution; and mixing materials again, stirring for 15 minutes, and finishing the whole powder mixing process, wherein water and isopropanol are used as solvents in the scheme, the operation process is complex, and the preparation process has safety risk.

CN107910497A discloses a method for preparing a positive electrode of a lithium thionyl chloride power type battery, which comprises the steps of: 1) pretreating powder; mixing the materials into a semi-dry wet material and uniformly stirring; feeding the semi-dry wet material into a strip extruding machine with a sieve pore size of 0.5-1.5mm for extruding to obtain strip material with the length of 1-2 cm; feeding the strip-shaped material into a centrifugal pill making machine to obtain fine pill materials with the particle size of 0.5-1.5 mm; putting the fine pills into vacuum drying for 8-10 h; 2) screening fine pellets on a net; pulverizing the obtained dry fine pill material into fine powder material; uniformly mixing the fine powder with an aqueous solvent to obtain semi-dry powder; putting the semi-dry powder on a nickel net, and carrying out vacuum drying and fiberization; 3) forming the positive electrode; rolling by using a rolling mill to prepare a positive electrode body with required thickness; the solvents adopted in the preparation process of the scheme are ethanol and water, the preparation process is complex to operate, the dispersion uniformity of the binder in the product in the acetylene black is not sufficient, and potential safety hazards exist in the preparation process.

Therefore, the development of the preparation method of the carbon electrode, which is simple, has good dispersion uniformity of all components in the obtained carbon electrode and obviously improves the powder dropping rate, is still significant.

Disclosure of Invention

The invention aims to provide a carbon electrode and a forming method and application thereof, wherein isoparaffin is used as a solvent in the forming process of the carbon electrode, the isoparaffin is mixed with a binder and acetylene black to obtain mixed slurry, and then the mixed slurry is kneaded and extruded to form the carbon electrode.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the present invention provides a method for forming a carbon electrode, the method comprising mixing an isoparaffin as a solvent, the solvent, a binder and acetylene black to obtain a mixed slurry, and then kneading and extruding the mixed slurry to obtain the carbon electrode.

In the traditional preparation process of the carbon electrode, water, ethanol or isopropanol is used as a mixing solvent, so that the prepared carbon electrode has the problems of high powder falling rate and poor conductivity, and the discharge performance of a battery cell assembled by the carbon electrode is influenced; in the forming process of the carbon electrode, isoparaffin is used as a solvent, has surface active groups, can be well combined with a hydrophobic binder, such as polytetrafluoroethylene emulsion, and expands, the surface activity of the dispersed binder is obviously improved, and the dispersed binder can react with original chemical bonds on the surface of conductive carbon black to form a mutual cross-linking structure, so that the hydrophobic binder is dispersed in the conductive carbon black more uniformly. The isoparaffin of the invention has high flash point (45-65 ℃) and boiling point (160-200 ℃), and the material can be completely and efficiently dried at relatively low temperature.

The carbon electrode obtained by the forming method has the advantages that the uniformity of each component is obviously improved, the structure is more stable, and the powder dropping rate is less than 0.5%; compared with a carbon electrode obtained by taking water or ethanol as a solvent, the adsorption capacity and the ionic conduction capacity of the obtained carbon electrode to an electrolyte are obviously improved, and the discharge capacity deviation of a battery assembled by taking the carbon electrode as the positive electrode of the lithium/thionyl chloride battery under a constant current condition is obviously reduced.

In the method, a certain gas diffusion layer is formed in acetylene black in the kneading process of the mixed slurry, and then the mixed slurry is dried, so that isoparaffin and water are evaporated in the diffusion layer of the acetylene black, and a good pore-forming effect is achieved; the method can design the pore structure of the carbon electrode by controlling the addition and matching ratio of the raw materials, thereby strengthening the controllability of the preparation process.

In the extrusion molding process of the method, the discharging is more continuous, smooth and uniform, the weight uniformity of the carbon electrode obtained after cutting is within +/-3%, and the diameter uniformity of the carbon electrode obtained after cutting is within +/-1% when the carbon electrode is a carbon rod. And the carbon electrode is obtained by adopting a direct extrusion molding method, so that the risk that the diaphragm and the cathode clamp the anode particles in the traditional particle anode assembling process is reduced, and the problems of uneven compaction and poor current collecting capability of the anode are solved.

Preferably, the mass ratio of the acetylene black, the binder and the solvent is 1 (0.08-0.2) to (7-15), such as 1:0.1:14, 1:0.15:12 or 1:0.19:8, and the like, and preferably 1 (0.1-0.12) to (10-12).

Preferably, the frequency of kneading is 10-30Hz, such as 12Hz, 15Hz, 17Hz, 20Hz, 22Hz, 25Hz, or 28Hz, and the like.

Preferably, the kneading time is 5-10min, such as 6min, 7min, 8min or 9min, etc.

Preferably, the isoparaffin comprises isoundecane and/or isododecane.

Preferably, the isoparaffin is an isoparaffin miscella, such as Isopar H-type isoparaffin miscella.

The isoparaffin in the Isopar H-type isoparaffin solvent oil mainly comprises isoundecane and isododecane.

Preferably, the binder is a polytetrafluoroethylene emulsion.

Preferably, the polytetrafluoroethylene emulsion is an aqueous dispersion of polytetrafluoroethylene having a solids content of 55-65%, such as 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, or 64%, etc., preferably 60%.

Preferably, a conductive additive is further added during the mixing of the solvent, the binder and the acetylene black.

Preferably, the conductive additive comprises ketjen black and/or carbon nanotubes.

The conductive additive is Ketjen black and/or a carbon nano tube, and the conductive additive also has hydrophobicity, and the method adopts isoparaffin as a solvent, so that the mixing uniformity of the conductive additive and a binder can be obviously improved, and the performance of the carbon electrode prepared from the conductive additive is improved.

Preferably, the mass ratio of the acetylene black to the conductive additive is (5-10):1, such as 6:1, 7:1, 8:1 or 9:1, etc.

Preferably, the method for adding the additive comprises the steps of mixing the conductive additive with acetylene black, and then mixing the conductive additive with a solvent and a binder to obtain a mixed slurry.

Preferably, the process of mixing the conductive additive with acetylene black is carried out in a high speed mixing granulator.

Preferably, the carbon electrode is obtained by cutting and drying after the extrusion molding.

Preferably, the drying temperature is 120-180 ℃.

Preferably, the drying is step-temperature drying, for example, drying at 85 ℃ for 4h, then at 130 ℃ for 3h, and finally at 180 ℃ for 2 h.

The drying process can be directly dried at the temperature of 120-180 ℃, and can also adopt step heating drying.

As a preferred embodiment of the present invention, the method for forming a carbon electrode includes the steps of:

(1) adding a polytetrafluoroethylene solution into a solvent, and stirring and mixing to obtain a mixed solution, wherein the solvent is isoundecane and/or isododecane;

(2) adding the mixed liquid obtained in the step (1) into acetylene black, and stirring for 1-3min to obtain mixed slurry; or mixing acetylene black with a conductive additive to obtain a mixture, adding the mixed solution obtained in the step (1) into the mixture, and stirring for 1-3min, such as 1.5min, 2min or 2.5min, to obtain a mixed slurry;

(3) kneading the mixed slurry obtained in the step (2), wherein the kneading frequency is 10-30Hz, and the kneading time is 5-10min, then extruding, molding, cutting and drying to obtain the carbon electrode.

In a second aspect, the present invention provides a carbon electrode prepared by the method of the first aspect.

In a third aspect, the present invention provides a lithium/thionyl chloride battery, the positive electrode of which employs the carbon electrode of the second aspect.

Compared with the prior art, the invention has the following beneficial effects:

(1) according to the forming method of the carbon electrode, isoparaffin is used as a solvent, the isoparaffin has surface active groups, can be well combined with a hydrophobic binder and can expand, the surface activity of the dispersed binder is obviously improved, and the dispersed binder can act with original chemical bonds on the surface of acetylene black to form a mutual cross-linking structure, so that the binder is more uniformly dispersed in the acetylene black, the powder dropping rate of the prepared carbon electrode is obviously reduced, the powder dropping rate of the carbon electrode obtained by the forming method is less than 0.5%, and the self-discharge rate of a battery assembled by the carbon electrode is reduced;

(2) the carbon electrode obtained by the forming method of the invention has obviously improved adsorption capacity and ion conductivity to electrolyte; the lithium/thionyl chloride battery is used as the anode of the lithium/thionyl chloride battery, the discharge capacity deviation of the obtained lithium/thionyl chloride battery under the constant current condition is obviously reduced, and the constant current discharge capacity deviation is within +/-3.1% under the 2mA condition.

Detailed Description

The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.

Example 1

The carbon electrode forming method comprises the following steps:

(1) adding the polytetrafluoroethylene emulsion into an isoparaffin solvent, and uniformly dispersing under stirring in a stirrer to obtain a mixed solution, wherein the isoparaffin solvent is Isopar H-type isoparaffin solvent oil;

(2) uniformly dispersing acetylene black and a conductive additive in a high-speed mixing granulator, adding the mixed solution obtained in the step (1) in the dispersing process, stirring for 3min, and taking out to obtain mixed slurry, wherein the conductive additive is ketjen black;

(3) and (2) kneading the mixed slurry in a kneading machine, wherein the kneading frequency is 20Hz, the kneading time is 8min, then carrying out extrusion molding, cutting, and then drying at 85-180 ℃ in a gradient manner, namely drying at 85 ℃ for 4h, then at 130 ℃ for 3h, and finally at 180 ℃ for 2h to obtain the rod-shaped carbon electrode.

In the embodiment, the raw material ratio is that the mass ratio of acetylene black, ketjen black, polytetrafluoroethylene emulsion and isoparaffin is 1:0.1:0.1: 10; the polytetrafluoroethylene emulsion used was composed of (60% solids aqueous solution of polytetrafluoroethylene).

In the extrusion molding process of the carbon electrode molding method, the material is smoothly and uniformly discharged, the uniformity of the components in the obtained rod-shaped carbon electrode is good, the weight uniformity of the carbon electrode obtained by cutting is within +/-3%, and the diameter uniformity of the rod-shaped carbon electrode is within +/-1%.

After extrusion moulding, the carbon rod is cut into the rodlike carbon electrode with fixed length through an automatic cutting machine, an analytical balance is used for accurately weighing a sample, and the calculation mode of the weight uniformity degree of the carbon electrode is as follows: (M)_max-M_min)/M_ave。M_maxMass maximum of rod-shaped carbon electrode, M_minMass minimum of rod-shaped carbon electrode, M_aveThe number of samples for the above test procedure was 100 as the mass average value of the rod-shaped carbon electrode.

The carbon rod cuts into the carbon positive pole of fixed length through automatic guillootine, uses the diameter of slide caliper rule measurement positive pole, the even degree calculation mode of bar-shaped carbon electrode diameter is: (R)_max-R_min)/R_ave。R_maxIs the maximum value of the diameter of the rod-shaped carbon electrode, R_minIs the minimum diameter of the rod-shaped carbon electrode, R_aveThe average diameter of the rod-shaped carbon electrode.

Example 2

The present example is different from example 1 in that the conductive additive is replaced by equal-quality carbon nanotubes from ketjen black, and other conditions are completely the same as those of example 1.

Example 3

The difference between the present example and example 1 is that the raw material ratio is acetylene black, ketjen black, polytetrafluoroethylene emulsion and isoparaffin in the mass ratio of 1:0.2:0.1:14, and the other conditions are completely the same as those in example 1.

Example 4

The difference between the present example and example 1 is that the raw material ratio is acetylene black, ketjen black, polytetrafluoroethylene emulsion and isoparaffin in the mass ratio of 1:0.1:0.15:12, and the other conditions are completely the same as those in example 1.

Example 5

This example is different from example 1 in that the conductive additive was not added, and the other conditions were completely the same as those of example 1.

Comparative example 1

The carbon particle positive electrode is prepared by the following steps: (1) uniformly mixing acetylene black, polytetrafluoroethylene emulsion and water in a high-speed mixer according to the mass ratio of 1:0.1:4.5, and discharging; (2) extruding the mixture into strips by a granulator, and then rotating the strips in a shot blasting machine to prepare round particles; (3) and drying in an oven for 6h at 160 ℃ to obtain the carbon particle anode.

Comparative example 2

The comparative example is different from example 1 in that the solvent is replaced by isoquality ethanol from isoparaffin, and other conditions are completely the same as those in example 1.

And (3) performance testing:

the carbon electrodes prepared in examples 1 to 5 and comparative examples 1 to 2 were tested for powder dropping rate by the following test methods:

weighing 20 cut rod-shaped carbon electrodes with the recording mass of M₁Placing in friability tester equipment, setting program operation frequency and time, taking out the rod-shaped carbon electrode after the equipment program is completed, screening out fine powder, weighing the mass of the rest rod-shaped carbon electrode, and recording the mass as M₂The powder falling rate calculation formula is as follows: (M)₁-M₂)/M₁×100％。

The carbon electrodes prepared in examples 1 to 5 and comparative examples 1 to 2 were used as the positive electrode of a lithium/thionyl chloride battery, and the deviation of the discharge capacity of the assembled battery under a constant current condition was measured by the following operation method;

assembly of lithium/thionyl chloride cell: an ER14250 cell was assembled by using the carbon electrodes prepared in examples 1 to 5 and comparative examples 1 to 2 as a positive electrode, metal lithium as a negative electrode, an electrolyte solution of 15mol/L lithium tetrachloroaluminum in thionyl chloride, and a separator; testing the discharge capacity deviation of the lithium iron phosphate under the conditions of normal-temperature 2mA constant-current discharge and cut-off voltage of 2.0V;

the results of the test for the powder dropping rate of the carbon electrodes obtained in examples 1 to 5 and comparative examples 1 to 2 and the test for the deviation in the discharge capacity of the lithium/thionyl chloride cell assembled therefrom are shown in table 1;

TABLE 1

	Powder fall rate%	2mA constant current discharge capacity deviation
			Example 1	0.21	±2.1％
Example 2	0.25	±2.8％
			Example 3	0.32	±3.1％
Example 4	0.27	±2.4％
			Example 5	0.19	±2.3％
Comparative example 1	0.80	±3.7％
			Comparative example 2	0.53	±4.2％

The above table shows that the carbon electrode prepared by the method is used as the anode of the lithium/thionyl chloride battery, the obtained lithium/thionyl chloride battery discharges at a constant current of 2mA at normal temperature, the discharge capacity deviation under the condition of a cut-off voltage of 2.0V is within +/-3.1%, and the carbon electrode is obviously superior to the carbon electrode obtained by the method of the comparative example 1-2.

The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.

Claims

1. A carbon electrode forming method is characterized by comprising the steps of mixing an isoparaffin serving as a solvent, a binder and acetylene black to obtain mixed slurry, kneading, extruding and forming to obtain the carbon electrode.

2. The method of claim 1, wherein the mass ratio of the acetylene black, the binder and the solvent is 1 (0.08-0.2) to (7-15), preferably 1 (0.1-0.12) to (10-12);

preferably, the frequency of kneading is 10 to 30 Hz;

preferably, the kneading time is 5 to 10 min.

3. The method of claim 1 or 2, wherein the isoparaffins comprise isoundecane and/or isododecane;

preferably, the isoparaffin is isoparaffin solvent oil;

preferably, the binder is a polytetrafluoroethylene emulsion.

4. The method according to any one of claims 1 to 3, wherein a conductive additive is further added during the mixing of the solvent, the binder and the acetylene black;

5. The method of claim 4, wherein the method of adding the conductive additive comprises mixing the conductive additive with acetylene black, and then mixing the acetylene black with a solvent and a binder to obtain a mixed slurry;

preferably, the process of mixing the conductive additive with the acetylene black is performed in a high-speed mixing granulator.

6. The method of any one of claims 1-5, wherein the extrusion molding further comprises cutting and drying to obtain the carbon electrode.

7. The method of claim 6, wherein the temperature of said drying is from 120 ℃ to 180 ℃.

8. The method according to any one of claims 1 to 7, characterized in that it comprises the steps of:

(1) adding the polytetrafluoroethylene emulsion into a solvent, and stirring and mixing to obtain a mixed solution, wherein the solvent is isomeric undecane hydrocarbon and/or isomeric dodecane hydrocarbon;

(2) adding the mixed liquid obtained in the step (1) into acetylene black, and stirring for 1-3min to obtain mixed slurry; or mixing acetylene black with a conductive additive to obtain a mixture, adding the mixed solution obtained in the step (1) into the mixture, and stirring for 1-3min to obtain mixed slurry;

9. A carbon electrode prepared by the method of any one of claims 1 to 8.

10. A lithium/thionyl chloride battery characterized in that the carbon electrode as claimed in claim 9 is used as a positive electrode of the lithium/thionyl chloride battery.