CN101882693A - Lithium ion secondary battery and preparation method of negative plate thereof - Google Patents

Abstract

The invention discloses a lithium ion secondary battery, which comprises: the negative plate comprises a negative current collector and negative diaphragms distributed on two sides of the negative current collector, and printing layers are distributed on the surface of each negative diaphragm at intervals. In the lithium ion secondary battery, the printing layers are distributed on the surface of the negative electrode diaphragm at intervals, so that the safety performance of the battery is improved, the increase of the thickness of the battery is reduced, and the battery has ideal safety performance and high energy density. In addition, the invention also discloses a preparation method of the lithium ion secondary battery negative plate.

Description

Preparation method of lithium ion secondary battery and negative electrode sheet thereof

technical field

The invention relates to the technical field of lithium ion batteries, in particular to a lithium ion secondary battery with good safety performance and high energy density and a method for preparing the negative electrode sheet thereof.

Background technique

With the development of modern society, mobile devices such as camcorders, notebook computers, portable DVD and digital cameras have been more and more widely used, and the demand for high-energy batteries is also increasing. The miniaturization of modern mobile devices has also put forward higher requirements for the safety performance of high-energy batteries.

Lithium-ion secondary battery is a kind of green and environment-friendly battery. During the preparation process, the positive electrode sheet, the negative electrode sheet, and the separator between the positive electrode sheet and the negative electrode sheet are generally wound to make the cell. In order to increase energy density, lithium-ion secondary batteries usually use thinner separators. Although thinner separators can increase energy density, they also pose safety hazards. In order to improve the safety performance of the lithium-ion secondary battery, a layer of surface printing paste is usually printed on the surface of the negative electrode sheet to form a printing layer.

In the current preparation method of the printing layer, a layer of negative electrode slurry is respectively coated on both sides of the negative electrode collector of the negative electrode sheet according to the data measured in advance to form the negative electrode diaphragm, and then respectively coated on the negative electrode diaphragm after cold pressing and slitting. A layer of surface printing paste is printed on the entire surface to form a printing layer. Although this can effectively improve the safety performance of the lithium-ion secondary battery, the printed surface printing layer has a certain thickness, which is not conducive to improving the energy density of the lithium-ion secondary battery.

Contents of the invention

An object of the present invention is to provide a lithium ion secondary battery with good safety performance and high energy density.

In order to achieve the above-mentioned purpose of the invention, the present invention provides a lithium ion secondary battery, which includes: a positive electrode sheet, a negative electrode sheet, a separator spaced between the positive electrode sheet and the negative electrode sheet, and an electrolyte, wherein the negative electrode sheet includes a negative electrode A current collector and negative electrode membranes distributed on both surfaces of the negative electrode current collector, and printing layers are distributed on the surface of the negative electrode membrane at intervals.

Compared with the prior art, in the lithium ion secondary battery of the present invention, the surface of the negative electrode diaphragm is distributed with printed layers at intervals, which not only improves the safety performance of the battery, but also reduces the increase in battery thickness, so that the battery has ideal safety performance and high energy density.

As an improvement of the lithium ion secondary battery of the present invention, the printing layer is distributed on the head, tail and winding bend of the negative electrode sheet.

As an improvement of the lithium-ion secondary battery of the present invention, the width of the printed layer at the turning point of the winding is less than 5 mm.

As an improvement of the lithium-ion secondary battery of the present invention, the total thickness of the printing layers distributed on both sides of the winding bend is 3-4 μm.

As an improvement of the lithium ion secondary battery of the present invention, the negative electrode diaphragm is formed by coating the negative electrode slurry. Mixed evenly with deionized water.

As an improvement of the lithium ion secondary battery of the present invention, the printing layer is formed by coating the surface printing paste at intervals, and the surface printing paste is formed by mixing aluminum oxide, sodium carboxymethyl cellulose, The rubber is evenly mixed with deionized water.

Another object of the present invention is to provide a method for preparing a negative electrode sheet of a lithium ion secondary battery.

In order to achieve the above-mentioned purpose of the invention, the present invention provides a method for preparing a negative electrode sheet of a lithium ion secondary battery, which includes the following steps: providing a negative electrode current collector; coating negative electrode slurry on both sides of the negative electrode current collector to form a negative electrode diaphragm; And, the surface printing paste is coated at intervals on the surface of the negative electrode film to form a printing layer.

As an improvement to the preparation method of the lithium-ion secondary battery negative electrode sheet of the present invention, the negative electrode slurry is uniformly mixed with graphite, conductive carbon powder, sodium carboxymethyl cellulose, styrene-butadiene rubber and deionized water.

As an improvement to the preparation method of the lithium-ion secondary battery negative plate of the present invention, the surface printing paste is prepared by uniformly mixing aluminum oxide, sodium carboxymethyl cellulose, styrene-butadiene rubber and deionized water.

As an improvement to the preparation method of the negative electrode sheet of the lithium ion secondary battery of the present invention, the surface printing paste is coated on the head, tail and winding corner of the negative electrode sheet.

Description of drawings

Below in conjunction with the accompanying drawings and specific embodiments, the preparation method of the lithium ion secondary battery and the negative electrode sheet thereof of the present invention will be described in detail, wherein:

FIG. 1 is a schematic structural view of a negative electrode sheet of a lithium-ion secondary battery of a comparative example.

Fig. 2 is a schematic structural view of the surface of the lithium ion secondary battery negative electrode sheet coated with a printing layer at intervals according to the present invention.

Fig. 3 is a graph comparing cycle curves of the lithium ion secondary battery of the comparative example and the lithium ion secondary battery of the present invention charged at 0.5 rate and discharged at 1.0 rate at 45°C.

Detailed ways

comparative example

Preparation of negative electrode sheet: mix graphite, conductive carbon powder (Super-P), sodium carboxymethylcellulose (CMC), styrene-butadiene rubber (SBR) with deionized water in a mass ratio of 94.5:1.5:1.5:2.5, and stir Obtain the negative electrode slurry evenly, and adjust the viscosity with deionized water during the stirring process; then, evenly coat the negative electrode slurry on both sides of the copper foil of the negative electrode current collector to form a negative electrode diaphragm; after cold pressing, carry out stripping and cutting and welding the tabs to obtain the negative electrode sheet 10' shown in FIG.

Preparation of the positive electrode sheet: lithium cobalt oxide (LiCoO ₂ ), polyvinylidene fluoride (PVDF), conductive carbon powder (Super-P) and N,N-dimethylpyrrolidone (NMP) at a mass ratio of 96:2.0:2.0 Mix and stir evenly to obtain the positive electrode slurry, and adjust the viscosity by NMP during the stirring process; then, evenly coat the positive electrode slurry on both sides of the aluminum foil of the positive electrode current collector to form a positive electrode diaphragm; after cold pressing, carry out stripping and cutting And weld the tabs to get the positive plate.

Preparation of lithium-ion secondary battery: Wind the positive electrode sheet, negative electrode sheet and ED12 (PP/PE/PP) separator prepared according to the aforementioned process to make a bare battery cell, after top sealing, side sealing, vacuum drying, and electrolysis Liquid, vacuum encapsulation, chemical formation and aging processes, etc., to prepare the lithium-ion secondary battery of the comparative example.

Example

Preparation of negative electrode sheet: mix graphite, conductive carbon powder (Super-P), sodium carboxymethylcellulose (CMC), styrene-butadiene rubber (SBR) with deionized water in a mass ratio of 94.5:1.5:1.5:2.5, and stir Obtain the negative electrode slurry evenly, and adjust the viscosity with deionized water during the stirring process; then, evenly coat the negative electrode slurry on both sides of the copper foil of the negative electrode current collector to form a negative electrode diaphragm; after cold pressing, carry out stripping and cutting and welding the tabs to obtain the negative electrode sheet.

The preparation of the negative electrode sheet with the printing layer distributed at intervals on the surface: aluminum oxide (Al ₂ O ₃ ), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were mixed with deionized Mix with water, stir evenly to obtain the surface printing paste of the negative electrode sheet, adjust the viscosity by deionized water during the stirring process; then, print the surface printing paste on both sides of the aforementioned negative electrode sheet at intervals by gravure printing to form a printing layer distributed at intervals , during the printing process, the printing thickness is controlled by controlling the viscosity of the slurry, the printing spacing is controlled by controlling the tape speed and printing frequency, the printing width is controlled by adjusting the gravure printing machine, and the printing is printed according to the calculated position and size during printing. The printing length is the same as the width of the negative film. In this way, the negative electrode sheet 10 shown in FIG. 2 with the surface coated with a spaced printing layer is obtained, wherein 102 is a negative electrode current collector, 104 is a negative electrode tab, 106 is a negative electrode film, and 108 is a printing layer.

It should be noted that: please refer to FIG. 2 , according to an embodiment of the present invention, when the gravure printing method is used to print the surface printing paste on both sides of the negative electrode sheet 10, it is not printed on both sides of the negative electrode sheet 10 respectively. Instead of printing one layer, spacer printing is used. The printing position is selected at the head 110, tail 112 and winding bend 114 of the negative electrode sheet 10, the printing width at the winding bend 114 is controlled within 5 mm, and the total printing thickness on both sides of the winding bend 114 is controlled at 3-4 μm. In the battery structure, there is a relatively high tension at the winding bend 114, and the separator here is easily damaged. In addition, the copper foils at the head 110 and the tail 112 of the negative electrode sheet 10 are relatively prone to internal short circuits. Coating printing layer 108 on both sides of the head 110, tail portion 112 and winding turning 114 of the negative electrode sheet 10, and controlling the position and width of the printing layer 108, can minimize the increase of battery thickness, and at the same time due to the use of thinner Safety problems caused by the isolation film.

Preparation of the positive electrode sheet: lithium cobalt oxide (LiCoO ₂ ), polyvinylidene fluoride (PVDF), conductive carbon powder (Super-P) and N,N-dimethylpyrrolidone (NMP) at a mass ratio of 96:2.0:2.0 Mix and stir evenly to obtain the positive electrode slurry, and adjust the viscosity by NMP during the stirring process; then, evenly coat the positive electrode slurry on both sides of the positive electrode current collector aluminum foil to form a positive electrode diaphragm; after cold pressing, carry out stripping and cutting And weld the tabs to get the positive plate.

Preparation of lithium-ion secondary battery: The positive electrode sheet, negative electrode sheet and ED12 (PP/PE/PP) separator prepared according to the aforementioned process are wound into a bare cell, which is top-sealed, side-sealed, vacuum-dried, and injected with electrolyte , vacuum encapsulation, formation and aging processes to produce the lithium-ion secondary battery of the embodiment of the present invention. The performance contrast of table 1 comparative example lithium ion secondary battery and lithium ion secondary battery of the present invention

Table 1 is the performance comparison between the lithium-ion secondary battery of the comparative example and the lithium-ion secondary battery of the present invention. 1.0 rate discharge cycle curve comparison chart. It can be seen from Table 1 and Figure 3 that compared with the lithium ion secondary battery using the negative electrode sheet without the printed layer on the surface, the thickness of the lithium ion secondary battery using the negative electrode sheet with the printed layer distributed on the surface is slightly increased, and the cycle Performance remains essentially the same level, but security features are much improved. Compared with the lithium-ion secondary battery using the negative electrode sheet whose surface is completely coated with the printing layer, the lithium-ion secondary battery using the negative electrode sheet with the printing layer distributed on the surface at intervals can obtain good safety performance and energy density at the same time.

According to the disclosure and teaching of the above specification, those skilled in the art to which the present invention pertains can also make appropriate changes and modifications to the above embodiment. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention. In addition, although some specific terms are used in this specification, these terms are only for convenience of description and do not constitute any limitation to the present invention.

Claims (10)

1. lithium rechargeable battery, it comprises: positive plate, negative plate, be interval in the barrier film between positive plate and the negative plate, and electrolyte, wherein, negative plate comprises negative current collector and the cathode membrane that is distributed on the negative current collector two sides, and it is characterized in that: the spaced surface of described cathode membrane is distributed with printed layers.

2. lithium rechargeable battery according to claim 1 is characterized in that: described printed layers is distributed in head, afterbody and the coiling corner of described negative plate.

3. lithium rechargeable battery according to claim 2 is characterized in that: the width of the printed layers of described coiling corner is less than 5mm.

4. lithium rechargeable battery according to claim 2 is characterized in that: the gross thickness that is distributed in the printed layers on two sides, described coiling corner is 3-4 μ m.

5. lithium rechargeable battery according to claim 1, it is characterized in that: described cathode membrane is to be formed by the cathode size coating, and cathode size is by graphite, conductive carbon powder, sodium carboxymethylcellulose, butadiene-styrene rubber and deionized water are evenly mixed.

6. lithium rechargeable battery according to claim 1, it is characterized in that: described printed layers is to be coated with at interval by the surface printing slurry to form, and the surface printing slurry is by alundum (Al, sodium carboxymethylcellulose, butadiene-styrene rubber and deionized water are evenly mixed.

7. the preparation method of a lithium ion secondary battery negative pole sheet, it may further comprise the steps:

Negative current collector is provided;

At the two sided coatings cathode size of negative current collector, form cathode membrane; And

At cathode membrane spaced surface coating surface printing slurry, form printed layers.

8. the preparation method of lithium ion secondary battery negative pole sheet according to claim 7 is characterized in that: described cathode size is by graphite, conductive carbon powder, sodium carboxymethylcellulose, butadiene-styrene rubber and deionized water are evenly mixed.

9. the preparation method of lithium ion secondary battery negative pole sheet according to claim 7 is characterized in that: described surface printing slurry is by alundum (Al, sodium carboxymethylcellulose, butadiene-styrene rubber and deionized water are evenly mixed.

10. the preparation method of lithium ion secondary battery negative pole sheet according to claim 7 is characterized in that: described surface printing slurry is coated head, afterbody and the coiling corner of negative plate.

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