CN111224063A

CN111224063A - Positive plate, aqueous electrode slurry and preparation method thereof

Info

Publication number: CN111224063A
Application number: CN202010040863.7A
Authority: CN
Inventors: 谭玉明; 薛建军; 夏明德
Original assignee: Guangzhou Great Power Energy & Technology Co ltd
Current assignee: Guangzhou Great Power Energy & Technology Co ltd
Priority date: 2020-01-14
Filing date: 2020-01-14
Publication date: 2020-06-02

Abstract

A positive plate, aqueous electrode slurry and a preparation method thereof belong to the field of batteries. The slurry includes a dispersant and a dispersoid. Wherein the dispersant is water; the dispersoid includes an electrode active material, a conductive agent, a binder, and a plasticizer, and the plasticizer includes a carbonate-based compound or a carboxylate-based compound. The carbonate compound and the carboxylate compound each independently contain a selective group. The selective group is an ester group and one or both selected from the group consisting of a hydroxyl group and a carboxyl group. The electrode sheet made from the slurry of the example has appropriate plasticity to enable a relatively higher compaction density, thereby facilitating an increase in energy density while maintaining life.

Description

Positive plate, aqueous electrode slurry and preparation method thereof

Technical Field

The application relates to the field of batteries, in particular to a positive plate, water-based electrode slurry and a preparation method thereof.

Background

Because of the advantages of high voltage, high specific energy density, long cycle life, small self-discharge, safety, no memory effect and the like, the lithium ion battery is widely applied to the fields of various portable electronic products, small power systems, aerospace and the like. With the development of technology, the demand for lithium ion batteries tends to high energy density.

In order to realize high energy density of lithium ion batteries, continuous innovation and breakthrough in battery raw materials are required, and continuous improvement and perfection of preparation processes are also required.

Disclosure of Invention

Based on the defects, the application provides the positive plate, the aqueous electrode slurry and the preparation method thereof, so as to partially or completely improve and even solve the problem that the electrode plate is easy to break when the compaction density is increased.

The application is realized as follows:

in a first aspect, examples of the present application provide an aqueous electrode slurry for application to a lithium ion battery.

The aqueous electrode slurry includes a dispersant and a dispersoid.

Wherein the dispersant is water.

The dispersoid comprises an electrode active material, a conductive agent, a binder and a plasticizer. The plasticizer comprises a carbonate compound or a carboxylate compound, and the carbonate compound and the carboxylate compound respectively and independently contain a functional group. The functional group is an ester group and an optional group, and the optional group includes one or both selected from the group consisting of a hydroxyl group and a carboxyl group.

In a second aspect, examples of the present application provide a method of making the aqueous electrode slurry described above. The method comprises the following steps: the dispersoid is uniformly mixed into the dispersant.

In a third aspect, examples of the present application provide a positive electrode sheet including a current collector and an electrode material layer.

Wherein, the current collector is made of aluminum foil or aluminum alloy foil.

The electrode material layer is obtained by transferring the aforementioned aqueous electrode slurry to a current collector and rolling.

In the implementation process, the aqueous electrode slurry provided by the embodiment of the application uses the plasticizer, so that the slurry has proper ductility, and the plasticity and toughness of the electrode sheet manufactured by the slurry are improved. The electrode sheet thus obtained can therefore withstand higher rolling pressures without being damaged, so that a higher compaction density of the electrode sheet is possible. Moreover, the electrode plate has improved toughness, so that the electrode plate can be bent and curled properly without powder falling and the like, thereby being beneficial to manufacturing and packaging of batteries. Meanwhile, by increasing the compaction density, the energy density of the electrode sheet can be increased without changing the electrode active material.

Detailed Description

Embodiments of the present application will be described in detail below with reference to examples, but those skilled in the art will appreciate that the following examples are only illustrative of the present application and should not be construed as limiting the scope of the present application. 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.

References to "and/or" in the examples indicate simultaneous or separate. E.g., a and/or B, indicates that a alone, B alone, or both A, B are present.

The following is a detailed description of the positive electrode sheet, the aqueous electrode slurry, and the preparation method thereof according to the embodiments of the present application:

at present, improving the compaction density of an electrode plate of a lithium ion battery is one of effective methods for optimizing the energy density of the lithium ion battery. Typically, the compaction operation is achieved by rolling. However, increasing the compaction density of the pole piece increases the risk of breaking the tape during rolling, which increases the brittleness of the pole piece and further causes the inner ring to break in the winding and hot-pressing process.

In view of the above, the present invention is particularly proposed.

In general, the present disclosure provides an option to increase the ductility of the electrode sheet so as to enable a higher compaction density of the electrode sheet, thereby increasing the energy density of the lithium ion battery fabricated thereby. In the example, the plasticizer is added into the electrode slurry to improve the plasticity of the electrode slurry, so that the brittleness of the pole piece is improved, and the flexibility of the pole piece is improved, thereby solving the processing problem (such as avoiding the powder falling of the pole piece) of the rolling process section of the positive pole piece, and simultaneously not influencing the conductivity of the pole piece.

The aqueous electrode slurry in the examples of the present application includes a dispersant and a dispersoid. Wherein the dispersant is water. The dispersoid comprises an electrode active material, a conductive agent, a binder and a plasticizer.

The plasticizer is selected from esters, and comprises carbonate compounds or carboxylic ester compounds. Further, the carbonate compound also has functional groups, and the functional groups are ester groups and optional groups. In other words, the above-mentioned two ester compounds may have only an ester group; alternatively, it has not only an ester group but also an optional group.

The optional group includes one or both selected from the group consisting of a hydroxyl group and a carboxyl group. I.e., the optional group includes both carboxyl and hydroxyl groups, or the optional group includes only carboxyl groups, or the optional group includes only hydroxyl groups. The carboxylic ester compound also contains a functional group, and the selective group is an ester group and one or both selected from the group consisting of a hydroxyl group and a carboxyl group. In other words, the plasticizer includes a carbonate-based compound, and the carbonate-based compound has an ester group and a hydroxyl group, or the carbonate-based compound has an ester group and a carboxyl group, or the carbonate-based compound has an ester group, a hydroxyl group, and a carboxyl group. For plasticizers with carboxylic ester compounds, the carboxylic ester compounds have similar radical design.

The plasticizers in the examples of the present application have polar groups and are soluble in water. When the plasticizer is mixed with the adhesive, polar functional groups in the molecular structure of the plasticizer can enter between molecular chains of the adhesive to form a bond site with the adhesive, so that the bond site between the molecular chains of the adhesive is replaced, the acting force between the molecular chains of the adhesive is reduced, the crystallinity and the rigidity of the adhesive are reduced, the flexibility of the adhesive is improved, and the flexibility of a pole piece is improved.

Illustratively, the plasticizer includes one or more of dimethyl phthalate, diethyl phthalate, dibutyl phthalate, lauryl alcohol ester, cetyl alcohol ester, polyol ester, dimethyl carbonate, diethyl carbonate, and propylene carbonate. In other examples, the plasticizer may be a combination of two of the above, such as a mixture of dimethyl phthalate and diethyl phthalate, a mixture of a dodecyl alcohol ester and a polyol ester. Alternatively, the plasticizer may be a combination of three of the above, such as a mixture of cetyl alcohol ester, polyol ester, and dimethyl carbonate, and the like.

Accordingly, the various components in the slurry can be selected as follows.

The electrode active material comprises one or more of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium vanadium phosphate, lithium manganese phosphate, lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide. For example, a mixture of lithium cobaltate and lithium manganate, a mixture of lithium manganate and lithium iron phosphate, a mixture of lithium manganate, lithium iron phosphate and lithium vanadium phosphate, and a mixture of lithium cobaltate, lithium manganate and lithium manganese phosphate.

The conductive agent includes any one or more of carbon black, ketjen black, acetylene black, KS-6, graphene, carbon fiber, and carbon nanotube, but is not limited thereto. For example, the conductive agent is a mixture of carbon black and ketjen black, a mixture of acetylene black and graphene, a mixture of carbon fibers and carbon nanotubes, a mixture of carbon black, acetylene black and carbon fibers, a mixture of carbon black, ketjen black, KS-6, carbon fibers and carbon nanotubes.

The binder may be selected from one or more of carbomer 941, carbomer 2020, carbomer TR-2, carbomer ETD2020, carbomer Ultrez20, carbomer Aqua SF-1, styrene butadiene rubber, hydroxypropyl methylcellulose, carboxymethylcellulose, acrylic acid copolymer, acrylonitrile copolymer, sodium alginate, chitosan, and chitosan derivatives.

In addition, in consideration of the operating environment and characteristics of the battery, particularly temperature limitation, the plasticizer needs to be selected according to circumstances so that it stably exists in its predetermined form. For example, in some instances, the boiling point and flash point of the plasticizer need to be specifically examined to avoid combustion, vaporization, etc. that may result. For example, in some examples, the plasticizer is selected from the above components while having a boiling point of not less than 150 ℃ and a flash point of not less than 100 ℃. Through the selection to boiling point and flash point, plasticizer flash point is high, the boiling point is high, and difficult volatility or flash combustion can not bring processing or safety problem at the in-process of anodal thick liquids coating or stoving.

Further, the amount of the plasticizer may also be limited to prevent adverse effects that may be caused by its excessive use. Such adverse effects include, for example, that if the amount of plasticizer contained in the slurry increases for the production of the same amount of slurry, the content of the electrode active material in the slurry decreases, which results in the production of an electrode having the same capacity requiring more slurry, which in turn causes problems such as inconvenience in packaging the produced battery, increase in the quality and volume of the battery, and the like. In the examples, the content of the plasticizer is 0.2 to 5.0 wt% based on the solid matter in the (aqueous electrode) slurry. In other examples, the plasticizer is present in an amount of 0.6 wt% to 4.5 wt%; alternatively, the content of the positive electrode plasticizer is 1.4 wt% to 3.6 wt%. Alternatively, the content of the positive electrode plasticizer is 2.2 wt% to 3.0 wt%.

In addition to the selection of the plasticizer content described above, in some examples, the content of each substance in the slurry may be defined as follows. The content of the electrode active material is 90 wt% to 95 wt%, the content of the conductive agent is 1.0 wt% to 3.0 wt%, the content of the binder is 2.0 wt% to 5.0 wt%, and the content of the positive electrode plasticizer is 0.2 wt% to 5.0 wt%, based on the solid matter in the slurry.

Based on the above, the aqueous electrode slurry can be obtained simply by dispersing the electrode active material, the conductive agent, the binder and the plasticizer as the dispersoids in water as the dispersant. For example, the components are added into water one by one and mixed evenly. Alternatively, the components are made into a solution with water, and then the solutions of the components are mixed. The preparation method of the aqueous electrode slurry in the application example comprises the following steps:

adding adhesive into dispersant in stirrer, and stirring to obtain glue solution.

And adding a conductive agent material into the glue solution, sequentially stirring at a low speed and a high speed, adding the electrode active material in batches, uniformly dispersing, adding a plasticizer, and mixing to obtain a mixture.

The mixture can be filtered to obtain a slurry with better fluidity, viscosity, etc., based on convenience of use and the presence of particulate matter in the components. In one example, the mixture is screened so that the size of the particles in the slurry is smaller than the size of the mesh openings of a 120 to 160 mesh screen. Therefore, the viscosity of the prepared aqueous electrode slurry can be controlled between 5000m & Pas and 8000m & Pas by controlling specific substances and dosage ratios in the components and combining sieving. Further, in various examples, the viscosity of the slurry can be 5400 m-Pas to 7600 m-Pas; alternatively, the viscosity of the slurry is from 6100 m-Pas to 7200 m-Pas; alternatively, the viscosity of the slurry is 6500 m-Pas to 6800 m-Pas. The viscosity of the slurry can be optionally adjusted with water. And through verification, the performance of the pole piece is influenced by the excessively high or excessively low viscosity of the slurry.

Further, as an application example of the aqueous electrode slurry, an electrode sheet, such as a positive electrode sheet (positive electrode sheet), may also be produced. The electrode comprises a current collector and an electrode material layer fixed on the surface of the current collector. Generally, the electrode material layer is wrapped on the outer surface of the current collector, and a part of the current collector is reserved for connecting a tab.

The current collector may be of sheet-type construction (thickness of, for example, 12 to 15 microns) and made of a metal material, such as aluminum foil or aluminum alloy foil.

The electrode material layer is prepared by using the aqueous electrode slurry, for example, the slurry is transferred to the surface of the current collector or the current collector is immersed in the slurry, and then the current collector wrapped with the slurry is rolled to obtain the electrode plate, and meanwhile, the preparation of the electrode plate is also completed. In some alternative embodiments, the positive electrode sheet may have a compacted density of 3.5cm³Rolling under the condition of/g to reach the elongation of more than 1%. Compared with the prior electrode slice, the compaction density of the prior electrode slice can only reach 3.1cm³G to 3.4cm³And/g, if the voltage is continuously increased, the performance of the electrode slice is reduced.

The present application is described in further detail with reference to examples below.

Example 1

The lithium ion battery anode material is prepared from the following raw materials in parts by mass: lithium iron phosphate: 93.8%, acrylic copolymer: 2.5%, acetylene black: 1.2%, carbon nanotubes: 1.5% and 1.0% of dodecyl alcohol ester.

The preparation steps are as follows:

s1, adding the prepared acrylic copolymer adhesive into a stirrer of the solvent, and stirring for 30 minutes at medium speed to prepare a glue solution;

s2, adding acetylene black and the carbon nano tube material, stirring at a medium speed for 10 minutes, and then stirring at a high speed for 1.5 hours;

s3, adding the lithium iron phosphate material in batches for multiple times, and stirring at a high speed for 3 hours to disperse uniformly;

s4, finally adding a plasticizer of dodecyl alcohol ester, and continuously stirring for 30 minutes to obtain the lithium ion battery anode slurry;

and S5, sieving the slurry obtained in the step S4 by a 150-mesh sieve, and testing the viscosity of the slurry to obtain the lithium ion battery aqueous anode slurry.

And S6, coating the two sides of the lithium ion battery aqueous positive electrode slurry coating machine on an aluminum foil with the thickness of 15 microns, and drying and rolling to obtain the lithium ion battery positive electrode sheet.

Example 2

The lithium ion battery anode material is prepared from the following raw materials in parts by mass: lithium iron phosphate: 93.8%, acrylic copolymer: 2.5%, acetylene black: 1.2%, carbon nanotubes: 1.5% and diethyl phthalate 1.0%.

The preparation steps are as follows:

s4, finally adding a plasticizer diethyl phthalate, and continuously stirring for 30 minutes to obtain the lithium ion battery anode slurry;

Example 3

The lithium ion battery anode material is prepared from the following raw materials in parts by mass: lithium iron phosphate: 93.8%, acrylic copolymer: 2.5%, acetylene black: 1.2%, carbon nanotubes: 1.5% and propylene carbonate 1.0%.

The preparation steps are as follows:

s4, finally adding a plasticizer propylene carbonate, and continuously stirring for 30 minutes to obtain the lithium ion battery anode slurry;

Example 4

The lithium ion battery anode material is prepared from the following raw materials in parts by mass: lithium nickel cobalt manganese oxide: 93.8%, carboxymethyl cellulose and acrylic acid copolymer: 3.5%, acetylene black: 1.2%, carbon nanotubes: 1.5% and 0.5% of dodecyl alcohol ester.

The preparation steps are as follows:

s1, adding the prepared adhesive into a stirrer of the solvent, and stirring for 30 minutes at medium speed to prepare a glue solution;

s3, adding the nickel cobalt lithium manganate material for multiple times in batches, and stirring at a high speed for 3 hours to disperse uniformly;

Example 5

The lithium ion battery anode material is prepared from the following raw materials in parts by mass: lithium manganate: 93.8%, carboxymethyl cellulose and acrylic acid copolymer: 3.5%, acetylene black: 1.2%, carbon nanotubes: 1.5% and 0.5% of dodecyl alcohol ester.

The preparation steps are as follows:

s3, adding the lithium manganate material for multiple times in batches, and stirring at a high speed for 3 hours to disperse uniformly;

Comparative example 1

The lithium ion battery anode material is prepared from the following raw materials in parts by mass: lithium iron phosphate: 93.8%, acrylic copolymer: 2.5%, acetylene black: 1.2% and carbon nanotubes: 1.5 percent.

The preparation steps are as follows:

s3, adding the lithium iron phosphate material for multiple times in batches, stirring at a high speed for 3 hours, and uniformly dispersing to obtain the lithium ion battery anode slurry;

and S4, sieving the slurry obtained in the step S3 by a 150-mesh sieve, and testing the viscosity of the slurry to obtain the lithium ion battery aqueous anode slurry.

And S5, coating the two sides of the lithium ion battery aqueous positive electrode slurry coating machine on an aluminum foil with the thickness of 15 microns, and drying and rolling to obtain the lithium ion battery positive electrode sheet.

Test example 1

The electrode slurry in each example was separately tested, and the solid content and the viscosity of the slurry prepared in each example and comparative example were measured as shown in table 1.

TABLE 1 solid content and viscosity of the slurries

Test example 2

The same aluminum foil was selected as a current collector, and the slurries prepared in each of examples and comparative examples were coated on the aluminum foil under the same coating conditions and at the same coating thickness to manufacture corresponding electrode sheets. And detecting the cracking condition of the coating (electrode material layer) on the surface of each electrode plate.

The coated and dried pole pieces were visually observed and the cracking of the coating was evaluated in the following manner.

If cracks with the length of more than 30cm and the width of more than 2mm exist on the surface of the pole piece, the cracks are serious;

if the crack is 5cm-30cm long and about 2mm wide, the crack is obviously cracked;

cracks with a length of 5cm or less and a width of 2mm or less are slightly cracked.

The positive electrode sheets prepared in examples 1 to 5 and comparative example 1 were evaluated for cracking according to the above criteria, and the evaluation results are shown in table 2.

TABLE 2 Pole piece cracking

The results in Table 2 show that the pole pieces of examples 1-5 exhibited no cracking upon drying compared to comparative example 1, examples 1-5, due to the addition of the plasticizer to the slurries of examples 1-5. In comparative example 1, the coating on the surface of the electrode sheet was slightly cracked because no plasticizer was added to the slurry.

Test example 3:

and testing the elongation of the pole piece. The specific test method is as follows:

rolling the positive plate to a compaction density of 3.5cm³(ii) in terms of/g. After the rolling was completed, the length of the substrate before the rolling (L1) and the length after the rolling (L2) were measured, and the elongation of the pole piece (L2/L1) was calculated and the results are reported in Table 3.

And testing the light transmittance of the pole piece. The specific test method is as follows:

for the positive electrode sheets (relating to the length and thickness of the current collector, the width, and the thickness of the coating) having the same specification prepared in examples 1 to 5 and comparative example 1, the positive electrode sheets were rolled back and forth three times in half with a press roller having a weight of 2Kg after being folded in half, and the light leakage in half was recorded, and the results are recorded in table 3.

TABLE 3 light transmission performance results

Numbering	Elongation of pole piece	Light leakage after doubling up	Post-coating processability
				Example 1	1.10％	Light-proof	Good effect
Example 2	1.08％	Light-proof	Good effect
				Example 3	1.03％	Light-proof	In general
Example 4	1.05％	Light-proof	Good effect
				Example 5	1.06％	Light-proof	Good effect
Comparative example 1	0.86％	Light transmission	Difference (D)

In the test of the positive electrode sheet, the elongation of the positive electrode sheet characterizes the degree of extension of the positive electrode sheet. Specifically, the greater the elongation percentage of the positive electrode sheet, the greater the degree of expansion.

Therefore, as can be seen from the results in table 3, the positive electrode sheets of examples 1 to 5 had significantly increased elongation and greatly reduced risk of process tape breakage at the same compaction density as compared with comparative example 1 containing no plasticizer.

Meanwhile, the flexibility of the positive pole piece is improved by the positive plasticizer used in the slurry. In the experiment, the pole pieces prepared in the examples 1 to 5 are opaque at the crease after being folded in half for three times and compacted in half, while the pole piece prepared in the comparative example 1 without the positive electrode plasticizer added in the slurry is transparent at the crease after being folded in half for three times and compacted in half.

The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An aqueous electrode slurry applied to a lithium ion battery is characterized by comprising a dispersant and a dispersoid, wherein the dispersant is water, the dispersoid comprises an electrode active material, a conductive agent, a binder and a plasticizer, the plasticizer comprises a carbonate compound or a carboxylate compound, the carbonate compound and the carboxylate compound respectively and independently contain functional groups, the functional groups are ester groups and optional groups, and the optional groups comprise one or both selected from the group consisting of hydroxyl groups and carboxyl groups.

2. The aqueous electrode slurry according to claim 1, wherein the plasticizer has a boiling point of not less than 150 ℃ and a flash point of not less than 100 ℃.

3. The aqueous electrode slurry according to claim 1, wherein the plasticizer is contained in an amount of 0.2 to 5.0 wt% based on the solid matter in the slurry;

optionally, the plasticizer is present in an amount of 0.6 wt% to 4.5 wt%;

optionally, the plasticizer is present in an amount of 1.4 wt% to 3.6 wt%;

optionally, the plasticizer is present in an amount of 2.2 wt% to 3.0 wt%.

4. The aqueous electrode slurry according to claim 3, wherein the content of the electrode active material is 90 to 95 wt%, the content of the conductive agent is 1.0 to 3.0 wt%, the content of the binder is 2.0 to 5.0 wt%, and the content of the plasticizer is 0.2 to 5.0 wt%, based on the solid matter in the slurry.

5. The aqueous electrode slurry according to any one of claims 1 to 4, characterized in that the viscosity of the slurry is from 5000 m-Pas to 8000 m-Pas;

optionally, the slurry has a viscosity of 5400 m-Pas to 7600 m-Pas;

optionally, the slurry has a viscosity of 6100 m-Pas to 7200 m-Pas;

optionally, the slurry has a viscosity of 6500 m-Pas to 6800 m-Pas.

6. The aqueous electrode slurry according to claim 1, wherein the slurry has the definition of any one or more of:

(I) the electrode active material comprises one or more of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium vanadium phosphate, lithium manganese phosphate, lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide;

(II) the conductive agent comprises any one or more of carbon black, ketjen black, acetylene black, KS-6, graphene, carbon fibers and carbon nanotubes;

(III) the binder comprises one or more of carbomer 941, carbomer 2020, carbomer TR-2, carbomer ETD2020, carbomer Ultrez20, carbomer Aqua SF-1, styrene butadiene rubber, hydroxypropyl methylcellulose, carboxymethylcellulose, acrylic acid copolymers, acrylonitrile copolymers, sodium alginate, chitosan, and chitosan derivatives;

(IV) the plasticizer comprises one or more of dimethyl phthalate, diethyl phthalate, dibutyl phthalate, lauryl alcohol ester, cetyl alcohol ester, polyol ester, dimethyl carbonate, diethyl carbonate and propylene carbonate;

(V) the particle size of the particulate matter in the slurry is smaller than the pore size of the mesh of a screen having a mesh number of 120 to 160.

7. A method of making the aqueous electrode slurry of any one of claims 1 to 6, comprising: the dispersoid is uniformly mixed into the dispersant.

8. The method of claim 7, wherein the method comprises:

adding the adhesive into the dispersant in a stirrer, and stirring to obtain a glue solution;

adding a conductive agent material into the glue solution, sequentially carrying out low-speed stirring and high-speed stirring, adding the electrode active material in batches, uniformly dispersing, and adding a plasticizer to mix to obtain a mixture;

the mixture is sieved, and undersize with a viscosity of 5000 m-Pas to 8000 m-Pas is taken, wherein the mesh number of the sieve is 120 to 160.

9. A positive electrode sheet, comprising:

a current collector made of aluminum foil or aluminum alloy foil;

a layer of electrode material obtained by transferring the aqueous electrode slurry from any one of claims 1 to 6 to the current collector and rolling.

10. The positive electrode sheet according to claim 9, wherein the current collector has a thickness of 12 to 15 μm;

and/or the positive plate is 3.5cm³Elongation of more than 1% per gram of compacted density.