Patent Application
20240014370
The present disclosure belongs to the technical field of batteries, and relates to an electrode sheet, a preparation method thereof, and a battery.
With the advancement of science and technology, lithium batteries are more and more widely used in life; they can be found in various fields from small household appliances to new energy vehicles and to large-scale energy storage. At present, the mainstream cathode systems include LCO, NCM, NCA, LFP, LMO, etc. The anode systems include artificial graphite, natural graphite, LTO, Si—C composite, artificial and natural composite systems, etc., and its structure is diverse, including square, cylindrical and button-type lithium battery; according to the outsourcing material, it is divided into aluminum shell, steel shell and soft-pack lithium battery.
Square aluminum shell batteries are widely used in lithium power and energy storage due to their advantages of simple structure, high energy density, flexible size, simple pack grouping, and high packaging reliability. Among them, LiFePO4 with olivine structure has the advantages of good structural stability, stable discharge platform, good cycle performance, wide source of raw materials, low price and no environmental pollution, it has been widely used in the two fields of power and energy storage, and the square aluminum shell LFP battery is the most common.
The positive electrode sheet material is an important factor that determines the performance and cost of lithium batteries, and it is a key technological breakthrough direction for improving battery energy density; the negative electrode with excellent performance has high specific energy, low electrode potential, and good lithium-deintercalation stability, and it is the key to affecting the performance of the battery; the main function of the diaphragm is to separate the positive and negative electrode of the lithium battery, prevent the two electrodes from contacting and short circuit, and allow the ions of the electrolyte to pass through; the electrolyte is the “blood” of the lithium battery, and through the electrolyte, Li+ is deintercalated back-and-forth between the positive and negative electrodes, and affects the key performance of the battery at the same time, such as safety, high and low temperature performance, and power performance. The electrolyte is generally composed of solvents, lithium salts and additives in a certain proportion, and the composition is different according to different electrical performance requirements. During the use of the battery, the electrolyte will be consumed, especially for batteries with long cycle life. The amount of liquid retention is as large as possible to satisfy the consumption of electrolyte during the cycle.
In the current electrode sheet preparation process, the main problems are: 1. the distribution of pores inside an electrode sheet is not uniform, resulting in different current densities in different regions of an electrode sheet during the battery discharge process, which cannot maximize the discharge capacity of the battery; 2. the depth of discharge in different regions of an electrode sheet is different, and the expansion situation is also different. During the discharge process of the battery, the resistance of the battery is likely to increase due to the separation of the active material and the current collector (powder dropping), and the pulse capacity in the final stage decreases rapidly; in serious cases, there may be an internal short circuit in the battery caused by partial powder dropping.
CN107919459A discloses a preparation method of a lithium ion battery negative electrode sheet, a lithium ion battery negative electrode sheet and a lithium ion battery, which belongs to the technical field of lithium ion batteries. The preparation method of the negative electrode sheet of the lithium ion battery comprises the following steps: mixing the negative electrode material with water uniformly to prepare the negative electrode slurry; the negative electrode material comprises a negative electrode active material, a conductive agent, a binder, and an additive. The mass ratio of the negative electrode active material, the conductive material agent, the binder and the additive is 85.5-95.5:1-3:1.5-3.5:2-8; the additive is at least one of ethylene carbonate and propylene carbonate; the prepared negative slurry material is coated on the negative electrode current collector and dried to obtain the material.
CN103531811A discloses a method for preparing a positive electrode sheet for a lithium ion battery, comprising the following steps: according to a solid-liquid ratio of (0.1-2 g):100 mL, refluxing a carbon material in a mixed acid composed of concentrated nitric acid and concentrated sulfuric acid to obtain the carboxylated carbon material; according to the solid-liquid ratio of (0.1-2 g):100 mL, refluxing the carboxylated carbon material in diphenol chloride to obtain the carbon material of acyl chloride; according to the solid-liquid ratio of (0.1-1 g): 100 mL: 200 mL, the acyl-chlorinated carbon material and ethylenediamine are refluxed in anhydrous toluene to obtain an amidated carbon material; the amidated carbon material is dissolved in water to form a dispersion; the current collector is soaked in the dispersion liquid, and then the current collector is alternately soaked in the dispersion liquid and Li2C6O6 solution, and dried to obtain the positive electrode sheet for the lithium ion battery. However, the above methods all have the problems of uneven thickness of the electrode sheet and poor discharge capacity at large currents.
The purpose of the present disclosure is to provide an electrode sheet, a preparation method thereof, and a battery. The preparation method of the electrode sheet provided by the present disclosure can improve the consistency of the thickness of the diaphragm in the process of diaphragm-forming, and can make the distribution of the inner hole of the electrode sheet more uniform, the porosity is better, and the discharge capacity of the battery can be improved.
In order to achieve the above object, the present disclosure provides the technical solutions described below.
In a first aspect, a production method for preparing an electrode sheet, including the following steps:
In the preparation method provided by the present disclosure, the purpose of making uniform particles is achieved by mixing and granulating described in step (1), a laminating machine with multiple rollers is used to first form the mixed particles into sheet described in step (2), and then press the sheet on a current collector to improve uniformity. The mutual cooperation of the above two steps enables the electrode sheet obtained by the method of the present disclosure to have better porosity under the condition of maintaining a higher compaction density, so that the battery prepared by these steps has better discharge capacity, especially in larger current and lower temperature conditions.
In the present disclosure, the numbers of rolls of the laminating machine is 3, 4, or 5, etc. When the numbers of rolls of the laminating machine is 3 or more, because the diaphragm is formed in advance, the adhesion between the active substances and the thickness uniformity can be improved, so the effect is much better than that of using a two-roll laminating machines (2 rolls).
The following are optional technical solutions of the present disclosure, but not as limitations of the technical solutions provided by the present disclosure. Through the following technical solutions, the technical purposes and advantages of the present disclosure can be better achieved and realized.
As an optional technical solution of the present disclosure, the electrode sheet is a positive electrode sheet or a negative electrode sheet.
Optionally, the active material described in step (1) includes any one or a combination of at least two of manganese dioxide, lithium manganate, lithium cobaltate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium iron phosphate, graphite and silicon carbon material. Typical but non-limiting combinations are: a combination of manganese dioxide and lithium manganate, a combination of lithium manganate and lithium cobaltate, a combination of lithium cobaltate and lithium nickel cobalt manganate, a combination of graphite and silicon carbon materials, etc.
Optionally, the conductive agent described in step (1) includes any one or a combination of at least two of carbon black, graphite, graphene or carbon nanotubes. Typical but non-limiting combinations are: a combination of carbon black and graphene, a combination of graphite and graphene, a combination of graphene and carbon nanotubes, etc.
Optionally, the binder described in step (1) includes any one or a combination of at least two of styrene-butadiene rubber, polytetrafluoroethylene, polyvinyl fluoride, sodium carboxymethyl cellulose, polyvinylidene fluoride or lithium polyacrylate. Typical but non-limiting combinations are: a combination of styrene-butadiene rubber and polytetrafluoroethylene, a combination of polytetrafluoroethylene and polyvinyl fluoride, a combination of polyvinyl fluoride and sodium carboxymethyl cellulose, a combination of polyvinylidene fluoride and lithium polyacrylate, etc.
Optionally, the solvent described in step (1) is any one or a combination of at least two of water, ethanol, ethylene glycol, glycerol, isopropanol, n-butanol, 1-methyl pyrrolidone (NMP) or N, N-dimethylformamide (DMF). Typical but non-limiting combinations are: a combination of water and ethanol, a combination of water and isopropanol, a combination of water and ethylene glycol, etc.
As an optional technical solution of the present disclosure, the mass ratio of the active material, conductive agent, solvent and binder described in step (1) is (58-88):(1-6):(10-30):(1-6), such as 58:6:30:6; 61:6:27:6; 66:6:22:6; 70:6:18:6; 75:2:18:5; 80:3:12:5 or 88:1:10:1.
As an optional technical solution of the present disclosure, the mixing and granulation described in step (1) is performed with a granulator.
Optionally, the rotational speed of the granulator is 50-1200 rpm, such as 50 rpm, 100 rpm, 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, 1100 rpm or 1200 rpm.
Optionally, the mixing and granulating time of step (1) is 1-10 min, such as 1 min, 1.5 min, 2 min, 2.5 min, 3 min, 3.5 min, 4 min, 4.5 min, 5 min, 5.5 min, 6 min, 6.5 min, 7 min, 7.5 min, 8 min, 8.5 min, 9 min, 9.5 min or 10 min, but it is not limited to the listed values, other unlisted values within the numerical range are also applicable.
By using the above-mentioned granulator rotation speed and mixing granulation time, the uniformity of the particles can be controlled, further, the consistency of the thickness of the composite diaphragm and the pore distribution of the electrode sheet can be controlled.
As an optional technical solution of the present disclosure, the current collector described in step (2) includes any one or a combination of at least two of steel mesh, aluminum mesh, copper mesh, nickel mesh, aluminum foil and copper foil combination.
As an optional technical solution of the present disclosure, the temperature of the diaphragm forming described in step (2) is 15-35° C., that is, the diaphragm forming at room temperature.
Optionally, the laminating machine described in step (2) is a three-roll laminating machine or a four-roll laminating machine.
As an optional technical solution of the present disclosure, the distance between the rolls of the laminating machine described in step (2) is 0.05-0.5 mm, such as 0.05 mm, 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm or 0.5 mm, in the present disclosure, if the roller spacing is too large, it will lead to weak adhesion between the diaphragm and the current collector; if the roller spacing is too small, it will cause jamming.
Optionally, the rotational speed of the rollers of the laminating machine described in step (2) is 1-10 r/min, such as 1 r/min, 2 r/min, 3 r/min, 4 r/min, 5 r/min, 6 r/min, 7 r/min, 8 r/min, 9 r/min or 10 r/min. In the present disclosure, if the rotational speed of the rollers of the laminating machine is too high, the uniformity of the electrode sheet will be deteriorated; if the rotational speed of the rollers of the laminating machine is too low, it will cause material jamming.
Optionally, step (2) further includes baking the product obtained after the diaphragm forming.
Optionally, the temperature of the baking is 100-300° C., such as 100° C., 120° C., 140° C., 160° C., 200° C., 250° C. or 300° C., but it is not limited to the values listed, other unlisted values within the range of values are also applicable.
Optionally, the baking time is 5-28 h, such as 5 h, 8 h, 12 h, 16 h, 20 h, 24 h, 26 h, 27 h or 28 h, but it is not limited to the values listed, other unlisted values within the range of values are also applicable.
As a further optional technical solution of the method described in the present disclosure, the method comprises the following steps:
In a second aspect, the present disclosure provides an electrode sheet prepared by the preparation method described in the first aspect.
Optionally, on the electrode sheet, the thickness of the diaphragm is 0.2-1.0 mm; Optionally, the compaction density of the electrode sheet is 1.5-3.0 g/cm3.
In a third aspect, the present disclosure provides a battery comprising the electrode sheet according to the second aspect.
Compared with the prior art, the present disclosure has the advantages described below:
In order to better illustrate the present disclosure and facilitate the understanding of the technical solutions of the present disclosure, the present disclosure will be described in further detail below. The following embodiments are only simple examples of the present disclosure, and do not represent or limit the protection scope of the present disclosure. The protection scope of the present disclosure is subject to the claims.
The following are typical but non-limiting examples of the present disclosure:
This embodiment was prepared according to the following method:
The schematic flow diagram of the preparation method of this embodiment is shown in
The schematic diagram of the laminating machine in this embodiment is shown in
The test results of the positive electrode sheet prepared in this example are shown in Table 1
This embodiment is prepared according to the following method:
The schematic diagram of the laminating machine in this embodiment is shown in
The test results of the positive electrode sheet prepared in this example are shown in Table 1.
This embodiment is prepared according to the following method:
The test results of the positive electrode sheet prepared in this example are shown in Table 1.
This embodiment was prepared according to the following method:
The test results of the negative electrode sheets prepared in this example are shown in Table 1.
The preparation method of the electrode sheet of this comparative example was the same as that of Example 1 in other aspects, except that the three-roll laminating machine was not used described in step (2), but two-roll laminating machine (2 rolls) was used.
The schematic diagram of the laminating machine of this comparative example is shown in
The test results of the positive electrode sheet prepared in this comparative example are shown in Table 1.
The preparation method of the electrode sheet of this comparative example was the same as that of Example 4 in other aspects, except that described in step (2), a three-roll laminating machine was not used instead of a two-roll laminating machine (2 rolls) was used.
The test results of the positive electrode sheet prepared in this comparative example are shown in Table 1.
Testing Method
The electrode sheets provided in each example and comparative example were tested.
A micrometer was used to test the consistency of the thickness of the electrode sheet (characterized by the overall standard deviation of the thickness of three electrode sheets prepared in a certain Example or Comparative Example).
The electrolyte was used to test the liquid absorption under dry conditions (dew point≤−45° C.). At −10° C. and normal temperature (25° C.) the 1 C capacity retention rate of the battery was tested with the Neware test cabinet using standard steps.
Test Standard Steps:
The electrolyte of Examples 1-3, Comparative Example 1 was composed of solvents (EC, PC, EMC, FB), additives (VC, MMDS), and lithium salt (LiPF6), and the electrolyte of Example 4 was: ethylene glycol dimethyl ether and propylene carbonate solution of lithium perchlorate; the negative electrode sheets of Examples 1-3 is graphite, and the negative electrode sheet of Example 4 is lithium metal.
The test results are shown in the following table:
12%
13%
10%
Combining the above examples and comparative examples, it can be seen that the preparation method of the example can obtain the electrode sheet with relatively good porosity under the condition of maintaining a relatively high compaction density (1.5-3.0 g/cm3) by using a suitable laminating machine cooperating with a granulation process. So that the battery has a better discharge capacity, especially under the conditions of large current and low temperature, and the thickness consistency of the electrode sheet is good.
In Comparative Example 1, because the diaphragm lamination equipment used was not suitable, particles were generated on both sides of the current collector, the uniformity was poor, and the pores formed after rolling were not uniform. Moreover, the diaphragm lamination equipment has a high requirement on the strength of the current collector.
The applicant declares that the above is only the specific implementation of the present disclosure, but the scope of protection of the present disclosure is not limited to this.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202110035611.X | Jan 2021 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2021/140823 | 12/23/2021 | WO |
