CN111525105B - Negative electrode material of lithium iron phosphate battery and preparation method of negative electrode plate - Google Patents

Abstract

The invention discloses a negative electrode material of a lithium iron phosphate battery, which comprises a mixed graphite negative electrode material with a weight percentage of 95-98%, a conductive agent with a weight percentage of 0-2% matched with the negative electrode material, and a weight percentage of 2 to 3% binder. In addition, the invention also discloses a method for preparing the negative electrode sheet of the lithium iron phosphate battery. The invention discloses a negative electrode material and a negative electrode sheet preparation method of a lithium iron phosphate battery, which can optimize the particle size distribution, the porosity of the electrode sheet, etc. through the optimized mixing and compounding of two different types of negative electrode materials and functional negative electrode materials In this way, negative electrode materials with improved high-temperature cycle performance and negative electrode sheets with optimized parameters such as pole piece porosity and liquid absorption performance can be obtained, thereby improving the high-temperature cycle performance of lithium iron phosphate batteries, which has great practical significance in production.

Description

A negative electrode material for a lithium iron phosphate battery and a preparation method for a negative electrode sheet

technical field

The invention relates to the technical field of lithium ion batteries, in particular to a negative electrode material of a lithium iron phosphate battery and a preparation method for a negative electrode sheet.

Background technique

At present, in the field of electric buses, most power batteries use lithium iron phosphate. The cycle performance of lithium iron phosphate battery at room temperature (25°C) is more than 2000 times; however, the working environment of electric vehicles is relatively complicated. 55°C) is much higher than the normal temperature environment of 25°C. Although there is a liquid cooling device, the internal temperature of the battery must be around 50°C. It is an inevitable application condition for lithium-ion batteries to be used at high temperatures. However, in a high temperature environment, the cycle attenuation of the lithium iron phosphate battery is accelerated, thereby greatly reducing the battery life, so it is imminent to improve the high temperature cycle life of the lithium iron phosphate battery.

Contents of the invention

The object of the present invention is to provide a negative electrode material and a negative electrode sheet preparation method of a lithium iron phosphate battery in view of the technical defects existing in the prior art.

For this reason, the present invention provides a negative electrode material of a lithium iron phosphate battery, comprising a graphite negative electrode material mixed with 95% to 98% by weight, a conductive agent with a weight percentage of 0% to 2% matched with the negative electrode material, and The weight percentage is 2-3% binder.

Among them, two kinds of artificial graphite negative electrode materials with different properties, A and B, are mixed and compounded to form a mixed graphite negative electrode material;

Material A is artificial graphite of needle coke type, which is a secondary bonding particle, with a particle size D50 of 10-18 μm;

Material B includes artificial graphite of one or two kinds of petroleum coke or coal coke, and the particle size D50 is 12-16 μm.

In addition, the present invention also provides a method for preparing a negative pole piece of a lithium iron phosphate battery, comprising the following steps:

In the first step, according to the preset weight ratio, add two negative electrode materials A and B in the planetary mixer in turn, and mix and stir through the planetary mixer, so that the two negative electrode materials A and B are fully mixed and evenly , to obtain a mixed graphite negative electrode material C;

Wherein, the weight ratio of negative electrode material A is 0-80%, and the weight ratio of negative electrode material B is 20-100%;

In the second step, for the blended graphite negative electrode material C obtained in the first step, screen the blended graphite negative electrode material C whose particle size D50 is within a preset value range;

In the third step, according to the preset weight ratio, for the blended graphite negative electrode material C whose particle size D50 is within the preset value range, sequentially add a preset ratio of conductive agent and sodium carboxymethylcellulose CMC as a binder , and then fully stir and mix evenly with a planetary mixer;

Wherein, the weight proportions are: 95-98% graphite negative electrode material C, 0-2% conductive agent and 2-3% sodium carboxymethyl cellulose CMC as a binder;

The fourth step is to continue to add water, so that the solid content of the formed negative electrode slurry is 40% to 50%, and the viscosity is in the range of 2000cP to 4000cP;

The fifth step, after adjusting the viscosity, continue to add the binder styrene-butadiene rubber SBR, and stir until there is no floating blue and white emulsion on the surface of the negative electrode slurry;

In the sixth step, continue to apply the negative electrode slurry finally prepared in the fifth step evenly on the copper foil negative electrode current collector, and obtain the finished negative electrode sheet of the lithium iron phosphate battery after drying.

Wherein, in the first step, the stirring speed of the planetary mixer is 10-25 r/min, and the rotation speed is 500-1000 r/min.

Wherein, in the second step, the particle size D50 of the graphite negative electrode material C is 12-14 μm, or 15-17 μm, or 17-18 μm.

Wherein, in the second step, the particle size D50 of the graphite negative electrode material C is 15-17 μm.

Wherein, in the third step, the conductive agent is one or both of carbon black or graphitized conductive agent.

It can be seen from the above technical solutions provided by the present invention that, compared with the prior art, the present invention provides a negative electrode material and a negative electrode sheet preparation method for a lithium iron phosphate battery, which can be used by two different types of negative electrode materials and functional negative electrode materials. Optimized mixing and compounding, while optimizing particle size distribution, pole piece porosity, etc., so as to obtain negative electrode materials with improved high-temperature cycle performance and negative electrode pole pieces with optimized parameters such as pole piece porosity and liquid absorption performance, thereby improving the high temperature of lithium iron phosphate batteries. Cyclic performance has great practical significance in production.

Description of drawings

Fig. 1 is the flow chart of the preparation method of the negative electrode sheet of a kind of lithium iron phosphate battery provided by the present invention;

Figure 2a, Figure 2b, and Figure 2c are the composite negative electrode materials with three different particle sizes D50, the final prepared lithium iron phosphate battery, and the transmission electron microscope images of the negative pole piece obtained by dissecting after precharging. It can be seen from the figure : Composite negative electrode material C2 has a relatively uniform SEI film on the surface of the negative electrode particles after pre-charging due to the high porosity of the pole piece and strong liquid absorption capacity;

Figure 3 shows the 1C cycle curve of the final prepared lithium iron phosphate battery with three different particle sizes D50 at a high temperature of 45°C. It can be seen from the figure that the high temperature cycle performance of the composite negative electrode material C2 is better .

Detailed ways

In order to enable those skilled in the art to better understand the solution of the present invention, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

The invention provides a negative electrode material for a lithium iron phosphate battery, which comprises a mixed graphite negative electrode material with a weight percentage of 95-98%, a conductive agent with a weight percentage of 0-2% matched with the negative electrode material, and a weight percentage of 2-3% binder.

In the present invention, in terms of specific implementation, two artificial graphite negative electrode materials with different properties, A and B, are mixed and compounded to form a mixed graphite negative electrode material (namely, C material).

In terms of specific implementation, material A is energy-type artificial graphite of needle coke type, which is a secondary bonded particle, and the particle size D50 is 10-18 μm, so as to ensure the capacity of the final composite negative electrode material (namely C material);

In terms of specific implementation, the B material includes one or two types of low-energy artificial graphite of petroleum coke or coal coke, and the particle size D50 is 12-16 μm.

In terms of specific implementation, the material A may specifically be an existing high-capacity, high-compression artificial graphite material with secondary particles.

In terms of specific implementation, the B material can specifically be an existing low-capacity artificial graphite material with good isotropic primary particles or secondary particles.

It should be noted that, for the present invention, the negative electrode material of the lithium iron phosphate battery provided is a graphite negative electrode material for a lithium iron phosphate battery, and the negative electrode material includes a mixed graphite negative electrode material, and a conductive material matched with the negative electrode material. Agents and binders, the components are optimized and combined to obtain the best negative electrode interface and porosity of the electrode sheet. In the present invention, the present invention mixes two negative electrode materials with different properties, A and B, to form C material, which can improve the interface between the negative electrode sheet and the electrolyte, ensure the proper kinetic performance of the material, reduce the internal resistance of the battery, and The porosity of the negative electrode sheet is improved, the wettability of the electrolyte is increased, and the high-temperature cycle performance of the lithium iron phosphate battery is improved.

It should be noted that, after a large amount of data research, the applicant found that the part that first fails during the high-temperature cycle of the lithium iron phosphate battery is: the SEI film formed at the interface between the graphite negative electrode and the electrolyte solution ruptures and forms repeatedly, resulting in increased polarization , the internal resistance increases, and the active lithium is lost too much. Therefore, improving the film-forming quality of the SEI film on the surface of the graphite negative electrode of the battery is of great significance for improving the high-temperature cycle performance of lithium iron phosphate. The film-forming quality of SEI film has an important relationship with parameters such as the morphology of the negative electrode material, the porosity of the electrode sheet, and the ratio of the negative electrode.

In addition, referring to Fig. 1, the present invention also provides a method for preparing a negative pole piece of a lithium iron phosphate battery, which is used to produce a negative pole piece of a lithium iron phosphate battery, and the negative pole piece includes the above-mentioned lithium iron phosphate battery. Negative material.

The method specifically includes the following steps:

In the first step, according to the preset weight ratio, add two negative electrode materials A and B in the planetary mixer in turn, and mix and stir through the planetary mixer, so that the two negative electrode materials A and B are fully mixed and evenly , to obtain a mixed graphite negative electrode material C;

Wherein, the weight ratio of negative electrode material A is 0-80%, and the weight ratio of negative electrode material B is 20-100%;

For example, in the graphite negative electrode material C1, the weight ratio of A is 80%, and the weight ratio of B is 20%;

In the graphite negative electrode material C2, the weight ratio of A is 0-40%, and the weight ratio of B is 100%-60%;

In graphite negative electrode material C3, the weight ratio of A is 50%, and the weight ratio of B is 50%

In the present invention, in the first step, the stirring speed of the planetary mixer is 10-25r/min, and the rotation speed is 500-1000r/min, so that the two negative materials A and B are completely mixed evenly.

In the second step, for the blended graphite negative electrode material C obtained in the first step, screen the blended graphite negative electrode material C whose particle size D50 is within a preset value range;

In the present invention, in the second step, for the blended graphite negative electrode material C obtained in the first step, specifically, the mixed graphite negative electrode material C whose particle size D50 is within a preset numerical range can be screened through a sieve .

In the present invention, in the second step, the particle size D50 of the graphite negative electrode material C may be 12-14 μm, or 15-17 μm, or 17-18 μm. Among them, 15 to 17 μm is preferable.

In the third step, according to the preset ratio, for the mixed graphite negative electrode material C whose particle size D50 is within the preset value range, the conductive agent of the preset ratio and sodium carboxymethyl cellulose CMC as the binder are sequentially added, Then fully stir and mix evenly with a planetary mixer;

In the third step, the mixed graphite negative electrode material C, the conductive agent and the sodium carboxymethyl cellulose CMC as the binder with the particle size D50 within the preset value range, the specific weight ratio is: 95-98% Graphite negative electrode material C, 0-2% conductive agent and 2-3% sodium carboxymethyl cellulose CMC as binder.

It should be noted that, in the present invention, in the third step, the conductive agent is one or several kinds of small spherical particles with a particle size of 20-100nm. During the stirring process, the spherical particles are bonded into chains and coated on the The C surface of the graphite negative electrode material improves the conductivity and uniformity of the negative electrode sheet.

Specifically, the conductive agent is one or both of carbon black or graphitized conductive agent.

The fourth step is to continue to add water, so that the solid content of the formed negative electrode slurry is 40% to 50%, and the viscosity is in the range of 2000cP to 4000cP;

It should be noted that in the present invention, in the third step and the fourth step, after the CMC dry powder is added, it can be more evenly adhered to the surface of the negative electrode particles after being stirred, and the CMC long chain can be better formed after adding water and dissolving. Adsorbed on the surface of graphite negative electrode particles.

The fifth step, after adjusting the viscosity, continue to add the binder styrene-butadiene rubber SBR, and stir until there is no floating blue and white emulsion on the surface of the negative electrode slurry;

The sixth step is to continue to apply the negative electrode slurry finally prepared in the fifth step evenly on the copper foil negative electrode current collector, and dry (for example, through an oven) to obtain the finished negative electrode sheet of the lithium iron phosphate battery.

It should be noted that, in the present invention, in the second step, as shown in Fig. 2a, Fig. 2b, Fig. 2c, Fig. 3 and Table 1, for the graphite negative electrode material C with particle size D50 in different composite ratios, it can be selected respectively Different particle size D50 value ranges, wherein, the particle size D50 range of the graphite composite material C1 is 12-14 μm, the particle size D50 range of the graphite composite material C2 is 15-17 μm, and the particle size D50 range of the graphite composite material C3 is 17-18 μm.

It should be noted that, for the present invention, for three kinds of graphite composite materials C1, C2, and C3 with different particle sizes D50, the third step to the sixth step above are respectively carried out sequentially, and for the final negative pole piece finished product, test the pole piece respectively. Table 1 shows the compaction, cohesive force, electrical resistance, porosity and liquid absorption rate of the electrode sheet. It can be seen from Table 1 that the C2 particle size D50 of the graphite composite material is 15-17 μm, the electrode piece has a higher adhesion, and the porosity and liquid absorption are better.

Table 1:

In addition, see Figure 2a, Figure 2b, and Figure 2c. Figure 2a, Figure 2b, and Figure 2c show three graphite composite materials C1, C2, and C3 with different particle sizes D50. Using the same process, three negative electrodes are finally prepared. The lithium iron phosphate battery assembled by the lithium iron phosphate battery, the transmission electron microscope image of the negative pole piece dissected after precharging, can be seen from Figure 2a, Figure 2b, and Figure 2c: the graphite composite material C2 has a high porosity due to the high porosity of the pole piece and liquid absorption Strong ability, after pre-charging, the film formation of SEI film on the surface of negative electrode particles is relatively uniform.

In addition, see Figure 3. Figure 3 shows three graphite composite materials C1, C2, and C3 with different particle sizes D50. Using the same process, the battery assembled from the three composite negative pole pieces finally prepared was tested at a high temperature of 45°C. It can be seen from Figure 3 that the 1C cycle curve of graphite composite material C2 has better high temperature cycle performance

Therefore, based on the above statement, it can be seen that compared with the prior art, the negative electrode material and negative electrode sheet preparation method of a lithium iron phosphate battery provided by the present invention can be optimized by two different types of negative electrode materials and functional negative electrode materials. Mixing and compounding, while optimizing particle size distribution, pole piece porosity, etc., to obtain negative electrode materials with improved high-temperature cycle performance and negative electrode pole pieces with optimized parameters such as pole piece porosity and liquid absorption performance, thereby improving the high-temperature cycle performance of lithium iron phosphate batteries , which has great practical significance in production.

The above is only a preferred embodiment of the present invention, it should be pointed out that, for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications can also be made. It should be regarded as the protection scope of the present invention.

Claims (4)

1. A negative electrode material for a lithium iron phosphate battery, characterized in that, comprising a graphite negative electrode material that is 95 to 98% by weight, a conductive agent that is 0 to 2% by weight and a weight percent that matches the negative electrode material Binder with a percentage of 2~3%; Two kinds of artificial graphite negative electrode materials with different properties, A and B, are mixed and compounded to form a mixed graphite negative electrode material; Wherein, the weight ratio of negative electrode material A is 0-40% and not 0, and the weight ratio of negative electrode material B is 60-100% and not 100%; Material A is needle-like coke-like artificial graphite, which is a secondary bonded particle, with a particle size D50 of 10-18 μm, and material A is a high-capacity, high-compression secondary particle artificial graphite material; Material B includes artificial graphite of one or two kinds of petroleum coke or coal coke, with a particle size D50 of 12-16 μm, and material B is a low-capacity, isotropic primary particle or secondary particle artificial graphite material; The obtaining method of the graphite negative electrode material of described blending, comprises the steps: In the first step, according to the preset weight ratio, add two negative electrode materials A and B in the planetary mixer in turn, and mix and stir through the planetary mixer, so that the two negative electrode materials A and B are fully mixed and evenly , to obtain a mixed graphite negative electrode material; In the second step, for the mixed graphite negative electrode material obtained in the first step, the mixed graphite negative electrode material whose particle size D50 is within 15-17 μm is screened. 2. A method for preparing a negative electrode pole piece of a lithium iron phosphate battery, characterized in that, comprising the following steps: In the first step, according to the preset weight ratio, add two negative electrode materials A and B in the planetary mixer in turn, and mix and stir through the planetary mixer, so that the two negative electrode materials A and B are fully mixed and evenly , to obtain a mixed graphite negative electrode material C; Wherein, the weight ratio of negative electrode material A is 0-40% and not 0, and the weight ratio of negative electrode material B is 60-100% and not 100%; In the second step, for the mixed graphite negative electrode material C obtained in the first step, screen the mixed graphite negative electrode material C whose particle size D50 is within 15-17 μm; In the third step, according to the preset weight ratio, for the blended graphite negative electrode material C with a particle size D50 within 15-17 μm, sequentially add a preset ratio of conductive agent and sodium carboxymethylcellulose CMC as a binder, Then fully stir and mix evenly with a planetary mixer; Among them, the weight proportions are: 95-98% of mixed graphite negative electrode material C with particle size D50 within 15-17 μm, 0-2% of conductive agent and 2-3% of carboxymethyl fiber as binder Sodium Sodium CMC; The fourth step is to continue to add water so that the solid content of the formed negative electrode slurry is 40%~50%, and the viscosity is in the range of 2000cP~4000cP; The fifth step, after adjusting the viscosity, continue to add the binder styrene-butadiene rubber SBR, and stir until there is no floating blue and white emulsion on the surface of the negative electrode slurry; The sixth step is to continue to evenly coat the negative electrode slurry finally prepared in the fifth step on the copper foil negative electrode current collector, and obtain the finished negative electrode sheet of the lithium iron phosphate battery after drying; Among them, two kinds of artificial graphite negative electrode materials with different properties, A and B, are mixed and compounded to form a mixed graphite negative electrode material; Material A is needle-like coke-like artificial graphite, which is a secondary bonded particle, with a particle size D50 of 10-18 μm, and material A is a high-capacity, high-compression secondary particle artificial graphite material; Material B includes one or two artificial graphites of petroleum coke or coal coke, with a particle size D50 of 12-16 μm, and material B is a low-capacity, isotropic primary particle or secondary particle artificial graphite material. 3. The method for preparing negative pole pieces as claimed in claim 2, wherein in the first step, the stirring speed of the planetary mixer is 10~25r/min, and the rotation speed is 500~1000r/min. 4. The preparation method of the negative pole piece as claimed in claim 2, characterized in that, in the third step, the conductive agent is one or both of carbon black or graphitized conductive agent.

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