CN115579475A - Lithium ion battery cathode slurry and preparation method thereof - Google Patents

Abstract

The invention discloses a lithium ion battery cathode slurry, which comprises a cathode active substance, an oxygen-containing lithium oxide, a binder and a conductive agent, wherein the cathode active substance comprises the following components in percentage by mass: 93.5-96.4%, wherein the mass percent of the oxygen-containing lithium oxide is as follows: 0.2% -0.4%, wherein the mass percentage of the binder is as follows: 1.7-4.2%, wherein the conductive agent comprises the following components in percentage by mass: 0.5% -1.2%; the lithium-containing compound is used for increasing the content of lithium ions in the battery, providing more lithium ion resources, delaying the loss of active lithium, depositing additional active lithium on the negative electrode, and serving as a lithium library in subsequent cycles to improve the first-effect performance and rate capability of the lithium battery.

Description

Lithium ion battery cathode slurry and preparation method thereof

Technical Field

The invention relates to the technical field of lithium ion batteries, in particular to a lithium ion battery cathode slurry and a preparation method thereof.

Background

The lithium ion battery is widely used in industries such as mobile phones, electric vehicles, electric tools, digital cameras and the like as a green energy source, and has high mass and volume specific energy, so that the lithium ion battery is increasingly applied to energy storage equipment, electric vehicles and the like in recent years, and higher requirements are provided for the performance of the lithium ion battery.

In the manufacturing process of the lithium ion battery, the composition and the preparation method of the negative electrode slurry are very critical influencing factors of the cycle life of the lithium ion. The preparation of the traditional negative electrode slurry generally selects single graphite or a plurality of blended graphites as negative electrode active substances, when the slurry is prepared, the binder, the conductive agent and the negative electrode graphite are sequentially added into a solvent to be uniformly stirred, the slurry obtained after stirring cannot meet the performance requirement of the lithium ion battery on circulation under high multiplying power, the stripping force of a pole piece is low, and the internal resistance of the battery is high. Therefore, new battery negative electrode components and proportions need to be found, a new preparation method of the negative electrode slurry is found, the peel strength of the pole piece is improved, and the long-cycle requirement of the lithium ion battery, especially the requirement of the cycle life under high multiplying power, is met.

We believe that the concept of prelithiation may play a central role in this respect. In conventional lithium ion batteries, prelithiation is generally considered to be a particularly attractive technique for compensating for the high active lithium loss caused by the solid electrolyte interface (membrane) formation during the first cycle.

In a traditional negative electrode slurry preparation formula, a styrene butadiene rubber type emulsion adhesive becomes a negative electrode mainstream adhesive for a long time due to good cohesion, elasticity and adhesion. However, this adhesive also has several significant disadvantages: 1. the dynamic performance and the low-temperature performance are poor; 2. the thickened CMC needs to be matched, so the total consumption is high; 3, SBR floating is serious, and the bonding efficiency is low. The internal resistance is high and the dynamic performance of the battery is poor, and lithium ions in a system are irreversibly consumed in the formation process, so that the first efficiency of the battery is low.

Disclosure of Invention

The invention aims to provide a lithium ion battery cathode slurry and a preparation method thereof, which aim to solve the problems in the background technology.

In order to achieve the purpose, the invention provides the following technical scheme: the lithium ion battery negative electrode slurry comprises a negative electrode active material, an oxygen-containing lithium compound, a binder and a conductive agent, wherein the negative electrode active material comprises the following components in percentage by mass: 93.5-96.4%, wherein the mass percent of the oxygen-containing lithium oxide is as follows: 0.2% -0.4%, wherein the mass percentage of the binder is as follows: 1.7-4.2%, wherein the conductive agent comprises the following components in percentage by mass: 0.5 to 1.2 percent.

Preferably, the chemical formula of the lithium-containing oxide is LixMyNz;

m is germanium, antimony, tin or a compound of two elements of the germanium, the antimony and the tin, and N is oxygen, sulfur, fluorine or a compound of two elements of the fluorine;

x =0.5 to 2, Y =1, Z =2 to 6.

A preparation method of lithium ion battery negative electrode slurry comprises the following steps:

step 1: further grinding the lithium-containing compound powder, and then drying in vacuum to remove moisture;

and 2, step: weighing a certain amount of negative electrode graphite material, and fully stirring the negative electrode graphite material and lithium-containing compound powder to obtain a mixture;

and step 3: dispersing the mixture obtained in the step 2, a pre-prepared water-based binder (sodium carboxymethyl cellulose) and a conductive agent in water, controlling the solid content of the slurry to be 52%, and rapidly stirring the slurry in vacuum for 2 h to obtain a homogeneous solution;

and 4, step 4: adding quantitative SBR, slowly stirring for 0.5 h, adjusting the pH to be 5.5-6.5, adjusting the viscosity to be 3000-5000mpa · s, and discharging to obtain the cathode slurry.

Preferably, the lithium-containing compound in step 1 is milled by a sand mill, and the grain diameter after milling is 50nm to 1 μm.

Preferably, the aqueous binder prepared in advance in step 3 is prepared by adding sodium carboxymethyl cellulose into distilled water to prepare a solution and stirring; wherein the concentration of sodium carboxymethylcellulose is 1.5%, and the pH value of distilled water is 7.

Preferably, the pH value of the cathode slurry in the step 4 is adjusted to ensure the consistency of the battery performance;

the pH value adjustment is to adjust the pH value by adding ethanolamine, weak acid in organic acid or a mixture thereof;

the weak acid includes acetic acid, formic acid, and acetic acid.

Compared with the prior art, the invention has the beneficial effects that: according to the invention, the lithium-containing compound is utilized to increase the lithium ion content in the battery, so that more lithium ion resources are provided, the loss of active lithium can be delayed, extra active lithium can be deposited on the negative electrode, and the extra active lithium can be used as a lithium library in subsequent cycles to improve the first-effect performance and rate capability of the lithium battery;

the sodium carboxymethyl cellulose adopted in the invention has better dynamic performance, can obviously reduce the direct current internal resistance of the battery, and prolongs the cycle life of the battery.

Drawings

FIG. 1 is a graph comparing internal resistance of batteries before and after discharge according to the present invention;

FIG. 2 is a comparison of internal resistance of the battery before and after the improvement of the present invention;

FIG. 3 is a comparison of battery cycle life before and after improvement in accordance with the present invention;

FIG. 4 is a graph comparing the rate performance of the battery before and after the improvement of the present invention;

FIG. 5 is a graph comparing the rate performance of the battery before and after the improvement of the present invention;

fig. 6 is a comparison of the first-pass performance of the cells before and after the improvement of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The invention provides a technical scheme that: the lithium ion battery negative electrode slurry comprises a negative electrode active material, an oxygen-containing lithium oxide, a binder and a conductive agent, wherein the negative electrode active material can be a negative electrode graphite material, and the chemical formula of the oxygen-containing lithium oxide is LixMyNz;

in the chemical formula, M is germanium, antimony, tin or a compound of two elements thereof, and N is oxygen, sulfur, fluorine or a compound of two elements thereof; x =0.5 to 2, y =1, z =2 to 6.

The mass percentage of the negative active material is as follows: 93.5-96.4%, wherein the mass percent of the oxygen-containing lithium oxide is as follows: 0.2% -0.4%, wherein the mass percentage of the binder is as follows: 1.7-4.2%, wherein the conductive agent comprises the following components in percentage by mass: 0.5 to 1.2 percent.

The preparation method of the lithium ion battery cathode slurry comprises the following steps:

step 1: the particle size of the lithium-containing compound powder is too low, so that the agglomeration and structural defects of the slurry become more, and the functionality is reduced; too high leads to poor surface coating effect, so lithium-containing compound powder needs to be further ground, the sample grinding is mainly carried out by using sanding equipment, the grain diameter after the sample grinding is 50nm-1 μm, and then the vacuum drying is carried out to remove moisture;

step 2: weighing a certain amount of negative electrode graphite material, and fully stirring the negative electrode graphite material and lithium-containing compound powder to obtain a mixture;

and step 3: dispersing the mixture obtained in the step 2, a pre-prepared water-based binder (sodium carboxymethyl cellulose) and a conductive agent in water, controlling the solid content of the slurry to be 52%, and rapidly stirring the slurry in vacuum for 2 h to obtain a homogeneous solution;

the aqueous binder prepared in advance in the step 3 is prepared by adding sodium carboxymethyl cellulose into distilled water to prepare a solution and stirring the solution; wherein, the concentration of the sodium carboxymethylcellulose is 1.5 percent, and the pH value of the distilled water is 7, so that the contact between the adhesive and the graphite can be increased, and the dispersibility is improved;

and 4, step 4: adding quantitative SBR, slowly stirring for 0.5 h, adjusting the pH to be 5.5-6.5, adjusting the viscosity to be 3000-5000mpa · s, and discharging to obtain cathode slurry;

in the step 4, the pH must be adjusted to be between 5.5 and 6.5, and if the pH is too high or too low, the slurry is likely to settle, so that the uniformity of slurry coating is not good, and the consistency of battery performance is affected;

wherein the weak acid comprises acetic acid, formic acid and acetic acid.

The invention will be further illustrated with reference to the following examples:

preparing negative electrode slurry: weighing a 19 kg negative electrode graphite material, 0.08 kg Li0.5Ge0.5Sb0.5O2, 23.73 kg CMC-Na of a solution with the concentration of 1.5% and 0.24 kg as a conductive agent, stirring in a stirring cylinder, finally adding 0.2 kg SBR, stirring for 0.5 h, and adjusting the solid content to be about 50%, thereby obtaining a negative electrode slurry;

and finally, applying the negative electrode slurry to the soft package lithium ion battery, and carrying out electrical property test.

For the test of the resistance performance in the lithium battery before and after the improvement, as shown in fig. 1 and fig. 2, the direct current internal resistance before and after the improvement of the lithium battery can be found to be remarkably reduced by observation;

as shown in fig. 3, in the working condition of 1C/1C, after 1500 weeks of circulation, the capacity retention rate before improvement is 79%, and the capacity retention rate after improvement is 88%, so that the cycle life is significantly prolonged;

for the tests on the rate capability of the lithium battery before and after the improvement, as shown in fig. 4 and 5, the charge-discharge rate capability of 1C/2C/3C is remarkably improved;

for the test of the first effect performance of the lithium battery before and after the improvement, as shown in fig. 6, it can be obviously seen that the first effect after the improvement is improved by about 3%.

Through tests, compared with the traditional scheme of binding agent SBR + CMC + negative graphite material, the direct current internal resistance of the battery is reduced, the first-effect performance is improved, and the cycle life and the rate capability of the battery are improved.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims (6)

1. The lithium ion battery negative electrode slurry comprises a negative electrode active material, an oxygen-containing lithium compound, a binder and a conductive agent, and is characterized in that: the mass percentage of the negative active material is as follows: 93.5-96.4%, wherein the mass percent of the oxygen-containing lithium oxide is as follows: 0.2% -0.4%, wherein the mass percentage of the binder is as follows: 1.7-4.2%, wherein the conductive agent comprises the following components in percentage by mass: 0.5 to 1.2 percent.

2. The lithium ion battery negative electrode slurry according to claim 1, wherein: the chemical formula of the oxygen-containing lithium oxide is LixMyNz;

m is germanium, antimony, tin or a compound of two elements thereof, and N is oxygen, sulfur, fluorine or a compound of two elements thereof;

x =0.5 to 2, Y =1, Z =2 to 6.

3. The preparation method of the lithium ion battery negative electrode slurry according to claim 1, characterized in that: the method comprises the following steps:

step 1: further grinding the lithium-containing compound powder, and then drying in vacuum to remove moisture;

step 2: weighing a certain amount of negative electrode graphite material, and fully stirring the negative electrode graphite material and lithium-containing compound powder to obtain a mixture;

and step 3: dispersing the mixture obtained in the step 2, a pre-prepared water-based binder (sodium carboxymethyl cellulose) and a conductive agent in water, controlling the solid content of the slurry to be 52%, and rapidly stirring the slurry in vacuum for 2 h to obtain a homogeneous solution;

and 4, step 4: adding quantitative SBR, slowly stirring for 0.5 h, adjusting the pH to be 5.5-6.5, adjusting the viscosity to be 3000-5000mpa · s, and discharging to obtain the cathode slurry.

4. The preparation method of the lithium ion battery negative electrode slurry according to claim 3, characterized in that: the lithium-containing compound in the step 1 is subjected to sample grinding by using sanding equipment, and the grain diameter after sample grinding is 50nm-1 mu m.

5. The preparation method of the lithium ion battery negative electrode slurry according to claim 3, characterized by comprising the following steps: the pre-prepared aqueous binder in the step 3 is prepared by adding sodium carboxymethyl cellulose into distilled water to prepare a solution and stirring the solution; wherein the concentration of the sodium carboxymethylcellulose is 1.5 percent, and the PH value of the distilled water is 7.

6. The preparation method of the lithium ion battery negative electrode slurry according to claim 3, characterized in that: adjusting the pH value of the cathode slurry in the step 4 to ensure the consistency of the battery performance;

the pH value adjustment is to adjust the pH value by adding ethanolamine, weak acid in organic acid or a mixture thereof;

the weak acid includes acetic acid, formic acid, and acetic acid.

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