Negative electrode binder for lithium battery, preparation method of negative electrode binder, negative electrode slurry, negative electrode plate and lithium battery

Abstract

The invention relates to a negative electrode binder for a lithium battery. The negative electrode binder is prepared from the following components in parts by mass: 15-20 parts of rosin resin, 5-13 parts of a solvent, 2-5 parts of an emulsifier and 18-25 parts of deionized water. According to the binder provided by the invention, the rosin resin is used, the rosin resin is a tricyclic diterpenoid compound and has good corrosion resistance, film-forming property and adhesiveness, so that the binder has better viscosity, and when the binder is used for preparing the negative electrode slurry, the use amount of the binder can be reduced, and meanwhile, the performance of a battery cell cannot be attenuated; meanwhile, the rosin resin has very high oxidation resistance, so that the oxidation resistance of the binder is improved, the electrical performance of the battery can be widened, and the improvement of the overall performance of the battery cell is facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a negative electrode binder for lithium batteries, a preparation method thereof, a negative electrode slurry, a negative electrode sheet, and a lithium battery. Background Art

[0002] In lithium-ion batteries, binders are an important factor affecting the stability of electrode structures. Negative electrode binders mainly play the role of bonding negative electrode active materials, conductive agents and dispersants to the current collector. Currently, most lithium battery manufacturers still use SBR (polystyrene butadiene copolymer) or its modified products as negative electrode binders. SBR has good bonding properties. Using SBR as a negative electrode binder can reduce the phenomenon of electrode film stripping and decarbonization during the coating, cutting, stripping and winding of electrode production, optimize the processing performance of the electrode, and the resulting electrode has good flexibility.

[0003] However, SBR itself is not resistant to electrolyte solvents, and SBR emulsion is mainly made of butadiene-styrene-acrylic acid through low-temperature emulsion polymerization. There is still an unsaturated double bond -C=C- left on the main chain of the polymer after free polymerization of butadiene, which is not resistant to aging and oxidation. In order to eliminate the unsaturated double bond and improve the aging resistance, the cross-linking degree is very large, which loses flexibility and makes the low-temperature resistance relatively poor, thus affecting the low-temperature performance of lithium batteries; the SBR production process is complicated, and it is not easy to modify the continuous production method; the emulsifier used is an inert emulsifier, which does not participate in the polymer chain, and it is easy to frost the polymer in the future, affecting the performance; too many additives in the low-temperature synthesis of SBR may affect the performance of the battery. Summary of the invention

[0004] Based on this, the purpose of the present invention is to provide a negative electrode binder for a lithium battery and a preparation method thereof, a negative electrode slurry, a negative electrode sheet, and a lithium battery. The negative electrode binder for a lithium battery of the present invention has better viscosity and antioxidant ability. When the binder of the present invention is used to prepare the negative electrode slurry, the amount of the binder can be reduced without causing a decrease in the performance of the battery cell.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The invention provides a negative electrode binder for a lithium battery, which is prepared from the following components in parts by mass: 15-20 parts of rosin resin, 5-13 parts of solvent, 2-5 parts of emulsifier, and 18-25 parts of deionized water.

[0007] The binder provided by the present invention uses rosin resin, which is a tricyclic diterpene compound with excellent corrosion resistance, film-forming property and adhesion, so that the binder has better viscosity. When the binder of the present invention is used to prepare negative electrode slurry, the amount of the binder can be reduced without causing attenuation of battery performance.

[0008] As a further improvement of the above solution of the present invention, the rosin resin is a low softening point rosin resin or a high softening point rosin resin. The melting point of the low softening point rosin resin is 60-90°C, and the melting point of the high softening point rosin resin is 172-175°C.

[0009] As a further improvement of the above scheme of the present invention, the solvent is at least one of ethyl acetate, ethanol, benzene, chloroform, ether, acetone, and carbon disulfide.

[0010] As a further improvement of the above scheme of the present invention, the emulsifier is at least one of Tween8, Tween10, Tween80, AT-11, AT-25, AT50, AT80, Span80, FES993, AT10500, Lanette E, Eumulgin prismas, EumulginA-BO, and Tamol-9104.

[0011] The present invention also provides a method for preparing the negative electrode binder for lithium battery as described above, which comprises the following steps:

[0012] S1. Mix the rosin resin and the solvent in proportion to obtain an oil phase and heat the oil phase to 45-55°C;

[0013] S2. Mix the emulsifier and deionized water in proportion to obtain an aqueous phase and heat the aqueous phase to 45-55°C;

[0014] S3. The oil phase is added to the water phase and emulsified and homogenized by homogenization. The homogenization temperature is 45°C-95°C, the time is 8-15min, and the stirring speed is 8000-12000rpm to obtain a negative electrode binder for a lithium battery.

[0015] The present invention also provides a method for preparing the negative electrode binder for lithium battery as described above, which comprises the following steps:

[0016] S1. Mix rosin resin, emulsifier and solvent in proportion to obtain an oil phase and heat the oil phase to 50-65°C;

[0017] S2. Heat the deionized water to 50-65°C;

[0018] S3. The oil phase is added to deionized water and emulsified and homogenized by homogenization. The homogenization temperature is 45°C-95°C, the time is 8-15min, and the stirring speed is 8000-12000rpm to obtain a negative electrode binder for a lithium battery.

[0019] The present invention also provides a negative electrode slurry for a lithium battery, which includes a negative electrode active material, a conductive agent, a binder and a thickener. The binder is the negative electrode binder for a lithium battery as described above or the negative electrode binder for a lithium battery prepared by the preparation method as described above.

[0020] The present invention also provides a negative electrode sheet, which includes a current collector and a negative electrode active material layer covering the current collector, wherein the negative electrode active material layer is formed by coating a negative electrode slurry on the current collector, and is characterized in that the negative electrode slurry adopts the negative electrode slurry for lithium battery as described above.

[0021] The present invention also provides a lithium battery, which comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the negative electrode sheet is the negative electrode sheet as described above.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The binder provided by the present invention uses rosin resin, which is a tricyclic diterpene compound with good corrosion resistance, film-forming property and adhesion. Therefore, compared with the traditional SBR emulsion, the binder provided by the present invention has better viscosity. When the binder of the present invention is used to prepare the negative electrode slurry, the amount of the binder can be reduced, and the performance of the battery cell will not be attenuated; at the same time, the rosin resin has a high antioxidant property, which improves the antioxidant capacity of the binder, can broaden the electrical properties of the battery, and is conducive to improving the overall performance of the battery cell. The binder provided by the present invention uses rosin resin, which contains a large number of double bonds and carboxyl groups, is prone to disproportionation reactions and other reactions, provides the possibility for subsequent modification, and is convenient for adjustment and operation. For example, when the adhesion of the binder is to be increased, its polyhydroxyl capacity and medium acrylic monomer can be used to improve its adhesion; when the dynamic properties of the binder are to be improved, more ester groups can be grafted to enhance the swelling properties and accelerate the transmission of lithium ions. DETAILED DESCRIPTION

[0024] For ease of understanding of the present invention, the present invention will be described more fully below in conjunction with specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0026] Preparation sample 1

[0027] This embodiment proposes a negative electrode binder for a lithium battery, which includes the following components by mass: 20 parts of low softening point rosin resin (melting point 60-90°C), 10 parts of ethyl acetate, 0.5 parts of emulsifier Eumulgin prismas, 1.5 parts of emulsifier Tween80, and 20 parts of deionized water. The preparation method of the negative electrode binder for a lithium battery in this embodiment includes the following steps:

[0028] S1. Add low softening point rosin resin and ethyl acetate to a beaker in proportion, and place the beaker on a 45°C constant temperature platform and heat to completely dissolve the rosin resin. Keep heating to obtain an oil phase for later use;

[0029] S2. Add emulsifier Eumulgin prismas, emulsifier Tween80 and deionized water to a beaker in proportion, and heat the beaker in a constant temperature water bath at 45°C to obtain an aqueous phase for later use;

[0030] S3. Heat the rotor of the homogenizer with hot water, then place it in a suitable position in the water phase. After it is firmly fixed, turn on the homogenizer at a speed of 10000 rpm / min, and then quickly pour the oil phase obtained in step S1 into the water phase while it is still hot. Start timing for 10 minutes. When the time is up, turn off the homogenizer to obtain a milky white negative electrode binder for lithium batteries.

[0031] Preparation sample 2

[0032] This embodiment proposes a negative electrode binder for a lithium battery, which includes the following components by mass: 20 parts of high softening point rosin resin (melting point 172-175°C), 10 parts of ethyl acetate, 0.5 parts of emulsifier Eumulgin prismas, 1.5 parts of emulsifier Tween80, and 20 parts of deionized water. The preparation method of the negative electrode binder for a lithium battery in this embodiment includes the following steps:

[0033] S1. Add high softening point rosin resin and ethyl acetate to a beaker in proportion, and place the beaker on a constant temperature platform at 80 ° C to heat the rosin resin completely, keep heating, and obtain the oil phase for standby;

[0034] S2. Add emulsifier Eumulgin prismas, emulsifier Tween80 and deionized water to a beaker in proportion, and heat the beaker in a constant temperature water bath at 80°C to obtain an aqueous phase for later use;

[0035] S3. Heat the rotor of the homogenizer with hot water, then place it in a suitable position in the water phase. After it is firmly fixed, turn on the homogenizer at a speed of 10000 rpm / min, and then quickly pour the oil phase obtained in step S1 into the water phase while it is still hot. Start timing for 10 minutes. When the time is up, turn off the homogenizer to obtain a milky white negative electrode binder for lithium batteries.

[0036] Example 1

[0037] The present embodiment provides a negative electrode slurry for a lithium battery, which includes the following raw materials in mass percentage: 28% silicon dioxide (SIO), 66% graphite, 1.5% conductive carbon black, 3% acrylic binder (PAA), 1.1% negative electrode binder for lithium batteries prepared in Preparation Sample 1, and 0.4% carboxymethyl cellulose CMC. The preparation method of the negative electrode slurry for lithium batteries in the present embodiment is: 28% silicon oxide, 66% graphite, 1.5% conductive carbon black, and 0.4% carboxymethyl cellulose CMC are added to a slurry tank and mixed uniformly, and then an appropriate amount of deionized water (converted according to the solid content of the discharge) and 3% acrylic binder (PAA) are added, and finally 1.1% of the negative electrode binder for lithium batteries prepared in Preparation Sample 1 is added, and the final slurry discharge solid content is 35%. This embodiment also provides a negative electrode sheet: the negative electrode slurry prepared in this embodiment is coated on a 8 μm copper foil and baked at 90° C. to obtain a coating with a surface density of 41.1 g / m 2 The negative electrode sheet is then rolled and compacted to 1.55g / m 3 .

[0038] Example 2

[0039] This embodiment adopts the same implementation as Example 1, and the difference from Example 1 is that the negative electrode slurry for lithium battery in this embodiment includes the following component raw materials in percentage by mass: 28% SIO, 66% graphite, 1.5% conductive carbon black, 3% acrylic binder (PAA), 1.1% negative electrode binder for lithium battery prepared by Preparation Sample 2, and 0.4% CMC.

[0040] Example 3

[0041] This embodiment adopts the same implementation as Example 1, and the difference from Example 1 is that the negative electrode slurry for lithium battery in this embodiment includes the following component raw materials in percentage by mass: 28% SIO, 66.5% graphite, 1.5% conductive carbon black, 3% acrylic binder (PAA), 0.6% negative electrode binder for lithium battery prepared in Preparation Sample 1, and 0.4% CMC.

[0042] Example 4

[0043] This embodiment adopts the same implementation as Example 1, and the difference from Example 1 is that the negative electrode slurry for the lithium battery in this embodiment includes the following component raw materials in percentage by mass: 28% SIO, 66.5% graphite, 1.5% conductive carbon black, 3% acrylic binder (PAA), 0.6% negative electrode binder for the lithium battery prepared in Example 2, and 0.4% CMC.

[0044] Comparative Example

[0045] This comparative example adopts the same implementation as Example 1, and the difference from Example 1 is that the negative electrode slurry for lithium battery in this example includes the following component raw materials in parts by mass: 28% SIO, 66% graphite, 1.5% conductive carbon black, 3% acrylic binder (PAA), 1.1% SBR, and 0.4% CMC.

[0046] Test Case

[0047] The negative electrode sheets of Examples 3-6 and the comparative example were used to prepare lithium batteries respectively: the positive electrode was made of NCM811: conductive carbon black: PVDF = 97: 1.2: 1.8, and the slurry was coated to prepare the positive electrode sheet, and the coating surface density was 112 g / m 2 , compacted to 3.6g / m 3 The positive electrode sheet is cut into 15×15cm size with a cutting machine, and the ear is 1.5×4.5cm long and wide; all the negative electrode sheets are cut into 15.6×15.6cm size negative electrode sheets, and the ear is 1.5×4.5cm long and wide; then a 18×18cm, 12μm thick separator is placed between the positive and negative electrode sheets, and the positive and negative electrode sheets are fixed with tape so that the negative electrode sheet can completely cover the size of the positive electrode sheet, and finally the ear is welded and packaged into a soft-pack battery cell; the electrolyte is injected with conventional commercial electrolyte.

[0048] The prepared lithium batteries were subjected to performance tests respectively, and the test conditions were room temperature cycling and 0.5C charge and discharge.

[0049] The test results are shown in the following table.

[0050]

[0051] It can be seen from the results in the above table that compared with the conventional SBR+PAA+CMC system, the binder emulsion prepared using rosin resin in the embodiment of the present application under the high silicon system has better advantages in long circulation, and the emulsions finally formed by the rosin resins with low softening points and high softening points have similar performances, and both can provide good binding force on silicon particles, thereby achieving the ability to enhance the circulation performance.

[0052] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0053] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A negative electrode binder for a lithium battery, characterized in that: The invention is prepared from the following components in parts by weight: 15-20 parts of rosin resin, 5-13 parts of solvent, 2-5 parts of emulsifier and 18-25 parts of deionized water.

2. The negative electrode binder for lithium battery according to claim 1, characterized in that: The rosin resin is a rosin resin with a low softening point or a rosin resin with a high softening point.

3. The negative electrode binder for lithium battery according to claim 1, characterized in that The solvent is at least one of ethyl acetate, ethanol, benzene, chloroform, ether, acetone and carbon disulfide.

4. The negative electrode binder for lithium battery according to claim 1, characterized in that The emulsifier is at least one of TO-8, Tween10, Tween80, AT-11, AT-25, AT50, AT80, Span80, FES993, AT10500, Lanette E, Eumulgin prismas, Eumulgin A-BO, and Tamol-9104.

5. A method for preparing a negative electrode binder for a lithium battery as claimed in any one of claims 1 to 4, characterized in that: It includes the following steps: S1. Mix the low softening point rosin resin and the solvent in proportion to obtain an oil phase and heat the oil phase to 45-55°C; S2. Mix the emulsifier and deionized water in proportion to obtain an aqueous phase and heat the aqueous phase to 45-55°C; S3. The oil phase is added to the water phase and emulsified and homogenized by homogenization. The homogenization temperature is 45°C-95°C, the time is 8-15min, and the stirring speed is 8000-12000rpm to obtain a negative electrode binder for a lithium battery.

6. A method for preparing a negative electrode binder for a lithium battery as claimed in any one of claims 1 to 4, characterized in that: It includes the following steps: S1. Mix the high softening point rosin resin, emulsifier and solvent in proportion to obtain an oil phase and heat the oil phase to 50-65°C; S2. Heat the deionized water to 50-65°C; S3. The oil phase is added to deionized water and emulsified and homogenized by homogenization. The homogenization temperature is 45°C-95°C, the time is 8-15min, and the stirring speed is 8000-12000rpm to obtain a negative electrode binder for a lithium battery.

7. A negative electrode slurry for a lithium battery, comprising a negative electrode active material, a conductive agent, a binder and a thickener, characterized in that: The binder is the negative electrode binder for a lithium battery as described in any one of claims 1 to 4 or the negative electrode binder for a lithium battery prepared by the preparation method as described in any one of claims 5 to 6.

8. A negative electrode sheet, comprising a current collector and a negative electrode active material layer coated on the current collector, wherein the negative electrode active material layer is formed by coating a negative electrode slurry on the current collector, characterized in that: The negative electrode slurry is the negative electrode slurry for lithium battery as claimed in claim 7.

9. A lithium battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, characterized in that: The negative electrode sheet is the negative electrode sheet as claimed in claim 8.

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