CN114824208A - Lithium battery negative electrode slurry formula, lithium battery negative electrode and preparation method thereof, and lithium battery - Google Patents

Abstract

The invention discloses a lithium battery cathode slurry formula, a lithium battery cathode, a preparation method thereof and a lithium battery, wherein the lithium battery cathode comprises 65-80% of graphite, 1-10% of hard carbon, 0.5-5% of high compaction auxiliary agent, and the balance of sodium carboxymethylcellulose and a binder by mass percentage. According to the invention, hard carbon and a high compaction auxiliary agent are added into the negative pole piece, and the high compaction auxiliary agent is specifically high anisometric crystalline flake graphite, so that the compaction density of the pole piece can be improved without influencing the capacity of the negative pole, the multiplying power performance of the battery is improved, the internal resistance is reduced, and the rebound of the pole piece is reduced.

Description

Lithium battery negative electrode slurry formula, lithium battery negative electrode and preparation method thereof, and lithium battery

Technical Field

The invention relates to the technical field of lithium battery manufacturing, in particular to a lithium battery negative electrode slurry formula, a lithium battery negative electrode, a preparation method of the lithium battery negative electrode and a lithium battery.

Background

The lithium ion battery has the advantages of high voltage, high capacity, long cycle life, low self-discharge efficiency, good safety performance and the like, and is widely applied to the fields of 3C digital products, electric automobiles, start-stop power supplies, models, energy storage and the like. At present, although the power lithium battery for the vehicle can meet the driving mileage of 500km, the charging time of several hours is usually required when the battery is fully charged, and the requirement of a customer can not be met; meanwhile, for digital consumer lithium batteries, consumers hope to further reduce the charging time of the lithium battery on the basis of improving the capacity of the lithium battery, and the consumption experience is improved. Therefore, the capacity and the charging time of the lithium battery become one of the primary consideration factors influencing the decision of consumers, and the lithium battery with higher compaction and higher multiplying power can be the next market explosion point of the lithium ion lithium battery.

The traditional quick-charging graphite material generally increases the ionic conductivity by reducing the particle size of powder, but greatly reduces the compaction density of a graphite cathode and the processing performance of the material while limiting the yield and the productivity. And other graphite cathode preparation methods can reduce the quick charge performance or have higher requirements on process equipment.

Disclosure of Invention

The invention aims to provide a lithium battery negative electrode slurry formula, a lithium battery negative electrode, a preparation method of the lithium battery negative electrode and a lithium battery, which can improve the compaction density of a pole piece, improve the rate capability of the lithium battery, reduce the internal resistance and reduce the rebound of the pole piece while not influencing the capacity of the lithium battery negative electrode.

The invention discloses a lithium battery cathode slurry formula which comprises, by mass, 65-80% of graphite, 1-10% of hard carbon, 0.5-5% of a high compaction auxiliary agent, and the balance of sodium carboxymethylcellulose and a binder.

Optionally, by mass percentage, 75% to 80% of graphite, 5% to 10% of hard carbon, 3% to 5% of high compaction aid, sodium carboxymethylcellulose and the balance binder.

Optionally, by mass percentage, 80% of graphite, 5% of hard carbon, 3% of high compaction aid, sodium carboxymethyl cellulose and the balance of binder.

Optionally, by mass percentage, 80% of graphite, 10% of hard carbon, 5% of high compaction aid, sodium carboxymethyl cellulose and the balance of binder.

Optionally, the high compaction aid is highly anisometric flake graphite.

Optionally, the particle size D50 of the graphite is 8-15 μm.

Optionally, the hard carbon particle size D50 is 3 to 9 μm.

The invention also discloses a lithium battery cathode which is prepared by adopting the lithium battery cathode slurry formula.

The invention also discloses a preparation method of the lithium battery cathode, which is applied to the preparation of the lithium battery cathode and comprises the following steps:

dry-mixing hard carbon, graphite and a high compaction auxiliary agent to obtain a mixture;

adding water into the mixture to mix to obtain pre-slurry, wherein the solid content is controlled at 50-70%;

kneading the pre-slurry into balls, adding sodium carboxymethylcellulose for pre-dispersion, then adding water for dispersion, and adding N-methylpyrrolidone;

adding a binder, stirring, performing vacuum defoaming, and waiting until the cathode slurry is obtained;

and coating the negative electrode slurry on a negative electrode current collector, and drying the negative electrode of the lithium battery.

The invention also discloses a lithium battery which comprises the lithium battery cathode.

According to the invention, hard carbon and a high compaction auxiliary agent are added into the negative pole piece, and the high compaction auxiliary agent is specifically high anisometric crystalline flake graphite, so that the compaction density of the pole piece can be improved without influencing the capacity of the negative pole, the multiplying power performance of the battery is improved, the internal resistance is reduced, and the rebound of the pole piece is reduced.

Detailed Description

It is to be understood that the terminology, the specific structural and functional details disclosed herein are for the purpose of describing particular embodiments only, and are representative, but that the present invention may be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein.

The invention is described in detail below with reference to alternative embodiments.

The invention discloses a lithium battery cathode slurry formula which comprises, by mass, 65-80% of graphite, 1-10% of hard carbon, 0.5-5% of a high compaction auxiliary agent, and the balance of sodium carboxymethylcellulose and a binder. Specifically, the graphite may be 65%, 70%, 73%, 75%, 78%, 80%; the hard carbon can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%; the high compaction aid may be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%.

Preferably, by mass percentage, 75-80% of graphite, 5-10% of hard carbon, 3-5% of high compaction auxiliary agent, and the balance of sodium carboxymethylcellulose and binder.

Preferably, in one embodiment, the graphite is 80% by mass, the hard carbon is 5% by mass, the high compaction aid is 3% by mass, the sodium carboxymethyl cellulose and the binder are the rest by mass, the compaction density is high, the compaction effect is the best, and the high-rate and high-pressure effect is the best. In another embodiment, the battery comprises 80% of graphite, 10% of hard carbon, 5% of high compaction auxiliary agent, the balance of sodium carboxymethyl cellulose and binder, the rebound degree of the pole piece is minimum, the thickness change of the pole piece is minimum, the whole volume of the battery is small, the battery is not easy to expand and deform, and the safety performance is high.

Preferably, the high compaction aid is highly anisometric flake graphite.

Preferably, the hard carbon particle diameter D50 is 3 to 9 μm.

Preferably, the particle size D50 of the graphite is 8-15 μm. More preferably, the particle size D50 of the graphite is 9-12 μm, and the quick charging performance is good.

The embodiment also discloses a lithium battery cathode which is prepared by adopting the lithium battery cathode slurry formula.

The embodiment also discloses a preparation method of the lithium battery cathode, which is applied to the preparation of the lithium battery cathode and comprises the following steps:

s100: dry-mixing hard carbon, graphite and a high compaction auxiliary agent to obtain a mixture;

s200: adding water into the mixture to mix to obtain pre-slurry, wherein the solid content is controlled at 50-70%;

s300: kneading the pre-slurry into balls, adding sodium carboxymethylcellulose for pre-dispersion, then adding water for dispersion, and adding N-methylpyrrolidone;

s400: adding a binder, stirring, performing vacuum defoaming, and waiting until the cathode slurry is obtained;

s500: and coating the negative electrode slurry on a negative electrode current collector, and drying the negative electrode of the lithium battery.

Specifically, in the step S100, the hard carbon and the high compaction aid are dry-mixed first, and then the graphite is dry-mixed. According to the sequence, the hard carbon with small particles and the high compaction auxiliary agent are mixed firstly, so that the dispersion is easy, and then the graphite with large particles is added for mixing, so that the final dispersion effect is good. In the step S200, the water added into the mixture is deionized water, and the mixture is stirred after the deionized water is added, revolves at 10-30 rpm and rotates at 150-300 rpm. In step S300, the pre-slurry is kneaded twice, and the pre-slurry is kneaded into a spherical shape with a bright surface and a wet interior. In the step S200, adding sodium carboxymethylcellulose, stirring, revolving at 10-30 rpm, and rotating at 300-800 rpm; the added N-methyl pyrrolidone accounts for 0.03 to 0.1 percent of the weight of the graphite. And in the step S400, adding a binder, stirring for 30-60 min, and then performing vacuum defoaming, wherein the viscosity of the negative electrode slurry is controlled to be 2000-4500 mpa.s. In the step S500, the density of a coating surface of the negative electrode slurry coated on the negative electrode current collector is 60-100 g/m ² 。

The embodiment also discloses a lithium battery which comprises the lithium battery negative electrode. Specifically, the lithium battery further comprises a positive plate, a lithium battery diaphragm and electrolyte. The positive plate comprises a positive current collector and a positive slurry coating positioned on the positive current collector. Wherein the positive active slurry layer comprises a positive active material selected from lithium cobaltate (LiCoO) ₂ ) Lithium nickel manganese cobalt ternary material, lithium iron phosphate (LiFePO) ₄ ) Lithium manganate (LiMn) ₂ O ₄ ) One or more of (a).

According to the invention, hard carbon and a high compaction auxiliary agent are added into the negative pole piece, and the high compaction auxiliary agent is specifically high anisometric crystalline flake graphite, so that the compaction density of the pole piece can be improved without influencing the capacity of the negative pole, the multiplying power performance of the battery is improved, the internal resistance is reduced, and the rebound of the pole piece is reduced. Specifically, the hard carbon is added, and the interlaced layered structure of the hard carbon enables lithium ions to be inserted and extracted from various angles of the material, so that the diffusion speed of the lithium ions is increased, and the rapid charge and discharge of the material can be realized; the high compaction additive is added, the high compaction additive is specifically high anisometric crystalline flake graphite, and the high compaction additive can be stressed to slide in the negative pole rolling process and rearrange the artificial graphite particles with irregular shapes, so that the pole piece compaction density is improved, and the high compaction additive and the artificial graphite particles jointly act on the graphite negative pole.

Examples of the experiments

And (3) manufacturing a negative electrode:

according to the formula of the negative electrode slurry for the lithium battery, the components are mixed with water, stirred and dispersed to prepare the negative electrode slurry, the negative electrode slurry is coated on a smooth copper foil or a carbon-coated copper foil through an extrusion coating machine or a transfer coating machine, the coating temperature is controlled to be between 80 ℃ and 150 ℃, and the negative electrode can be obtained through drying and cold pressing. The serial number relationship of the obtained negative electrode samples is shown in table 1 by changing the mixture ratio of the high compaction additive and the hard carbon.

Cathode number	Hard carbon	High compaction additive	Density of compaction
				Comparative example A1	0wt.％	0wt.％	1.60g/cc
Comparative example A2	3wt.％	0wt.％	1.55g/cc
				Comparative example A3	0wt.％	1wt.％	1.64g/cc
Comparative example A4	3wt.％	2wt.％	1.68g/cc
				Comparative example A5	5wt.％	3wt.％	1.73g/cc
Comparative example A6	10wt.％	5wt.％	1.69g/cc

TABLE 1

As in the above table, as the amount of hard carbon and high compaction additive increases, the compaction density is normally distributed and begins to decrease after reaching the highest point. Among them, A5 has the highest compaction density, the best compaction effect, and the best high-rate high-pressure effect. The compacted densities of a4 and a6 are reduced compared with a5, but are still far higher than a1 without the addition of hard carbon and high compaction additive, a2 with the addition of only hard carbon or A3 with the addition of only high compaction additive, and the high-magnification high-compaction effects are better than those of a1 to A3, which shows that the high-magnification high-compaction effects of the high compaction additive and the hard carbon are better in the mixture ratio of the invention.

And (3) manufacturing a positive electrode:

fully stirring and mixing a positive electrode active material lithium cobaltate LCO, a conductive agent SP and a binder polyvinylidene fluoride PVDF in an N-methylpyrrolidone solvent NMP according to the weight ratio of 97:1.7:1.3 to form uniform positive electrode slurry. And coating the slurry on a positive current collector foil, drying and cold pressing to obtain the positive plate.

Manufacturing the lithium ion battery:

the positive pole piece, the isolating membrane and the negative pole in the table 1 are sequentially stacked, so that the isolating membrane is positioned between the positive pole and the negative pole to play an isolating role, and then the bare cell can be wound. Placing the bare cell into an aluminum plastic film outer packaging bag, and completing the preparation of the lithium ion battery through the procedures of liquid injection, vacuum packaging, standing, formation, shaping and the like to obtain batteries B1-B6 in sequence, as shown in Table 2:

cathode number	Battery numbering
		Comparative example A1	B1
Comparative example A2	B2
		Comparative example A3	B3
Comparative example A4	B4
		Comparative example A5	B5
Comparative example A6	B6

TABLE 2

And (3) testing the rebound of the negative electrode of the battery:

when the negative electrode is rolled, an on-line thickness gauge is used for recording the thickness of the pole piece and recording the thickness as 0 hour (0H), then the thickness is recorded after 48H, the recording thickness of the half-electrode disassembled pole piece, the recording thickness of the full-electrode disassembled pole piece, the recording thickness of the pole piece disassembled through high-temperature circulation for 20 weeks, the recording thickness of the pole piece disassembled through high-temperature circulation for 100 weeks, and the recording thickness of the pole piece disassembled through high-temperature circulation for 300 weeks.

The test conditions described above: the charging multiplying power is 5C, the discharging multiplying power is 1C, the cut-off multiplying power is 0.05C, and the charging voltage is 2.5-4.48V in an environment of 45 +/-2 ℃. The pole piece thickness variation test conditions are as in table 3:

TABLE 3

As can be seen from Table 3, the rebound degree of the pole pieces in the batteries B4-B6 is less than that of the battery B1-B3, and the thickness change of the pole pieces is smaller. The rebound degree of the pole piece in the B6 battery is minimum, the thickness change of the pole piece is minimum, the whole size of the battery is small, the expansion deformation is not easy to occur, the safety performance is high, and the safety accidents such as explosion are not easy to occur.

Battery rate discharge test

Test methods and conditions: discharging the battery to 3.0V at constant current of 0.2C at normal temperature, and standing for 10 min; charging the battery to 4.45V at constant current and constant voltage of 0.2C, stopping current at 0.05C, and standing for 10 min; discharging the battery to 3.0V at constant current of 0.2C, and standing for 10 min; charging the battery to 4.45V at constant current and constant voltage of 0.2C, stopping current at 0.05C, and standing for 10 min; discharging the battery to 3.0V at constant current of 0.5C, and standing for 10 min; charging the battery to 4.45V at constant current and constant voltage of 0.2C, stopping current at 0.05C, and standing for 10 min; discharging the battery to 3.0V at a constant current of 1.0C, and standing for 10 min; charging the battery to 4.45V at constant current and constant voltage of 0.2C, stopping current at 0.05C, and standing for 10 min; charging the battery to 4.45V at constant current and constant voltage of 0.2C, stopping current at 0.05C, and standing for 10 min; discharging the battery to 3.0V at constant current of 3.0C, and standing for 10 min; charging the battery to 4.45V at constant current and constant voltage of 0.2C, stopping current at 0.05C, and standing for 10 min; discharging the battery to 3.0V at constant current of 4.0C, and standing for 10 min; charging the battery to 4.45V at constant current and constant voltage of 0.2C, stopping current at 0.05C, and standing for 10 min; discharging the battery to 3.0V at constant current of 5.0C, and standing for 10 min; charging the battery to 4.45V at constant current and constant voltage of 0.2C, stopping current at 0.05C, and standing for 10 min; the battery was discharged to 3.0V at a constant current of 6.0C and left for 10 min.

The battery rate discharge test results are shown in table 4 below:

as can be seen from table 4 above, the B5 cell exhibited the best electrochemical performance and the best rate performance. The proportion of the B5 hard carbon and the high compaction additive is an optimal scheme in terms of the electrochemical performance of the battery.

It should be noted that, the limitations of the steps involved in the present disclosure are not considered to limit the order of the steps without affecting the implementation of the specific embodiments, and the steps written in the foregoing may be executed first, or executed later, or even executed simultaneously, and as long as the present disclosure can be implemented, all should be considered to belong to the protection scope of the present disclosure.

The foregoing is a more detailed description of the invention in connection with specific alternative embodiments, and the practice of the invention should not be construed as limited to those descriptions. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.

Claims (10)

1. The formula of the lithium battery cathode slurry is characterized by comprising 65-80% of graphite, 1-10% of hard carbon, 0.5-5% of high compaction auxiliary agent, and the balance of sodium carboxymethylcellulose and a binder by mass percentage.

2. The negative electrode paste formulation for lithium batteries according to claim 1, wherein the graphite is 75 to 80% by mass, the hard carbon is 5 to 10% by mass, the high compaction aid is 3 to 5% by mass, and the sodium carboxymethyl cellulose and the binder are the rest by mass.

3. The lithium battery negative electrode paste formulation of claim 2, wherein the graphite is 80% by mass, the hard carbon is 5% by mass, the high compaction aid is 3% by mass, the sodium carboxymethyl cellulose and the binder are the balance.

4. The lithium battery negative electrode paste formulation of claim 2, wherein the graphite is 80% by mass, the hard carbon is 10% by mass, the high compaction aid is 5% by mass, the sodium carboxymethyl cellulose, and the balance of the binder.

5. The lithium battery negative electrode slurry formulation of any one of claims 1 to 4, wherein the high compaction aid is highly anisometric flake graphite.

6. The negative electrode slurry formulation for lithium batteries according to any one of claims 1 to 4, wherein the particle size D50 of the graphite is 8 to 15 μm.

7. The negative electrode paste formulation for lithium batteries according to any one of claims 1 to 4, wherein the hard carbon has a particle diameter D50 of 3 to 9 μm.

8. A negative electrode for a lithium battery, characterized by being prepared using the negative electrode slurry formulation for a lithium battery according to any one of claims 1 to 7.

9. A method for preparing a negative electrode for a lithium battery, which is applied to the preparation of the negative electrode for a lithium battery as claimed in claim 8, comprising the steps of:

dry-mixing the hard carbon, the graphite and the high compaction aid to obtain a mixture;

adding water into the mixture to mix to obtain pre-slurry, wherein the solid content is controlled at 50-70%;

kneading the pre-slurry into balls, adding sodium carboxymethylcellulose for pre-dispersion, then adding water for dispersion, and adding N-methylpyrrolidone;

adding a binder, stirring, performing vacuum defoaming, and waiting until the cathode slurry is obtained;

and coating the negative electrode slurry on a negative electrode current collector, and drying the negative electrode of the lithium battery.

10. A lithium battery comprising the negative electrode for a lithium battery according to claim 8.