CN102637906B - Preparation method of winding-structure lithium ion battery - Google Patents

Abstract

The invention belongs to the technical field of lithium ion batteries, and in particular relates to a preparation method of a wound lithium ion battery, comprising the following steps: coating the positive electrode slurry on the positive electrode current collector, cold pressing the positive electrode slurry after drying, and then bending Fold into a V shape; the negative electrode is treated in the same way, place the bent positive electrode sheet and negative electrode sheet crosswise, and place a separator between the positive electrode sheet and the negative electrode sheet, then weld the positive electrode sheet through the positive electrode lug, and the negative electrode sheet through the negative electrode Ears are welded and connected to obtain the pole piece group; the pole piece group is wound into a battery cell, the battery cell is placed in a packaging bag, and the lithium-ion battery is obtained after liquid injection and formation. Compared with the prior art, the present invention adopts the method of bending the pole piece to reduce the resistance of the pole piece, reduces the ohmic polarization during the charge and discharge process, improves the consistency of the battery, and can significantly reduce the Joule heat during the charge and discharge process. And the gas production rate of side reactions, thereby improving the rate performance and cycle life of lithium-ion batteries and lithium-ion battery packs.

Description

Preparation method of winding structure lithium ion battery

technical field

The invention belongs to the technical field of lithium-ion batteries, and in particular relates to a preparation method of a winding-type lithium-ion battery with a large rate.

Background technique

Lithium-ion batteries have been widely used in consumer electronics, such as laptops, smartphones, tablets, and power tools (such as electric vehicles), because of their advantages such as high energy density, excellent cycle performance, environmental friendliness, and no memory effect. a wide range of applications. General consumer electronic products are charged by DC power supply, and the charging time generally ranges from 3 hours to 10 hours. In a low-temperature environment, in order to prevent lithium deposition in the battery, the charge-discharge current density is generally reduced to one-third or one-fifth of that at normal temperature. With the acceleration of the pace of life, end consumers hope that the charging and discharging speed of electronic products will be accelerated, especially in low temperature environments, high current charging and discharging can also be used. We all know that the inside of a lithium-ion battery is mainly a chemical system. Large current density and low temperature environment will cause polarization inside the battery. raise security issues.

General electrical appliances will have a shutdown voltage, generally ranging from 3.0V to 3.6V, while the normal charge and discharge voltage range of lithium-ion batteries is 3.0V to 4.2V. If the discharge is carried out in a high current density and low temperature environment, in the initial stage of discharge, the battery discharge voltage will drop sharply due to the existence of polarization, which will cause the battery discharge platform voltage to be very low, reaching the shutdown voltage of the electrical appliance, resulting in electrical failure. normal work.

Traditional lithium-ion battery structures mainly include winding structure and laminated structure. The winding structure is: positive and negative electrodes, and the separator is long strip, and the separator is placed between the positive and negative electrodes to prevent short circuit. During assembly, the positive and negative electrodes and the diaphragm are wound into a lithium-ion battery by a reel, and then the production process is completed through packaging, liquid injection, activation and other processes.

Compared with the winding structure, the lamination structure is different in that the pole pieces of the lamination are welded together by n positive and negative electrodes respectively, and the subsequent process is the same as that of the winding structure lithium-ion battery. Therefore, compared with the winding structure, the lithium-ion battery with the stacked structure has the advantages of low resistance and high rate performance because the pole pieces are connected in parallel. The disadvantage is that the production efficiency of the stacked structure is relatively low, especially in the punching of the pole pieces. When it is used, the edge is easy to drop powder, causing micro-short circuit or even overheating inside the battery. In addition, because the positive and negative pole pieces in the laminated structure are welded in parallel with tabs, it is necessary to reserve a certain space at the top seal or the seal to store the welding area, which also leads to a decrease in the energy density of the battery. Therefore, lithium-ion batteries with winding structures are widely used in the market.

The pole pieces of the wound structure battery are connected together in series, so compared with the laminated battery, its resistance is higher, which leads to an increase in the ohmic polarization of the battery and affects the rate performance of the battery. At the same time, a large resistance value will also lead to an increase in the temperature rise of the battery when charging and discharging at a high rate, resulting in an increase in the internal side reactions of the battery and deteriorating the performance of the lithium-ion battery.

However, the lithium-ion batteries used in electric vehicles generally have a large capacity, and the requirements for the resistance of the battery are relatively high. Because the battery capacity used in electric vehicles is very large, the capacity of a general single cell is tens to hundreds of amperes, and multiple batteries are connected in series and parallel, so the resistance of the lithium-ion battery is required to be as small as possible. To reduce the Joule heat of the entire battery system, ensure that the internal temperature of the battery system is as close to room temperature as possible, and ensure the electrical performance of the lithium-ion battery. Otherwise, under the condition of poor heat dissipation, the side reaction inside the lithium-ion battery will intensify as the charge and discharge progress. Lithium-ion batteries have a chemical system inside, and in a high-temperature environment, the side reaction speed inside the battery will become faster. The side reactions will cause more gas to be generated inside the battery, resulting in an increase in the internal pressure of the battery and destroying the interface inside the battery. Charging and discharging under such circumstances will lead to a decrease in battery capacity and deterioration of cycle performance. In severe cases, it may cause lithium deposition on the surface of the negative electrode, and the battery may overheat or even explode, increasing the safety hazard of lithium-ion batteries.

In view of this, it is indeed necessary to provide a preparation method of a lithium-ion battery with a wound structure to improve the high-rate performance and cycle performance of the battery.

Contents of the invention

The purpose of the present invention is to: aim at the deficiencies of the prior art, and provide a kind of preparation method of the lithium-ion battery of winding structure, to improve the large rate performance of the battery, cycle performance and the temperature rise when charging and discharging with large current, and solve The problem that the battery discharge platform drops too fast, thereby reducing the risk of overheating of the lithium-ion battery.

In order to achieve the above object, the present invention adopts following technical scheme:

A preparation method of a winding structure lithium ion battery, comprising the following steps:

The first step, the preparation of the positive electrode sheet: apply the positive electrode slurry on the positive electrode current collector, reserve a blank area of the positive electrode sheet on both sides of the positive electrode current collector in the length direction when coating, and cold press the positive electrode slurry after drying. Then bend into a V shape;

Preparation of the negative electrode sheet: apply the negative electrode slurry on the negative electrode current collector, reserve a blank area of the negative electrode sheet on both sides of the negative electrode current collector in the length direction when coating, cold press the negative electrode slurry after drying, and then bend it into V-shaped; the positive and negative pole pieces of this bent structure can reduce the resistance of the pole pieces, improve the performance of high-rate charge and discharge, reduce the temperature rise during charge and discharge, and improve the cycle life and electrochemical performance of lithium-ion batteries.

In the second step, place the bent positive electrode sheet and negative electrode sheet crosswise so that the blank area of the positive electrode sheet is opposite to the blank area of the negative electrode sheet, and place a diaphragm between the positive electrode sheet and the negative electrode sheet, and then place the positive electrode sheet at both ends of the V shape The blank area is connected by welding the positive pole tab, and the blank area of the negative electrode sheet located at both ends of the V shape is connected by welding the negative electrode tab to obtain the pole piece group;

In the third step, the pole piece group is wound into a battery cell, and the battery cell is placed in a packaging bag, and the lithium-ion battery is obtained after liquid injection, standing, formation, and capacity.

After the pole piece is bent, the resistance of the pole piece can be reduced, because after the pole piece is bent, the resistance of the pole piece is reduced to one-nth of the original (n is the number of bending times of the pole piece). According to the Joule heat formula Q=I ² Rt, after the resistance is reduced to one-nth of the original, the Joule’s heat will also be reduced to one-nth of the original, which in turn can reduce the Joule’s heat in the charging and discharging process and reduce lithium The side reaction inside the ion battery also reduces the ohmic polarization during the charge and discharge process and improves the high rate charge and discharge performance.

As an improvement to the preparation method of the wound structure lithium ion battery of the present invention, when the positive electrode sheet is coated, lateral blank areas are reserved on both sides in the width direction of the positive electrode current collector.

As an improvement to the preparation method of the winding structure lithium-ion battery of the present invention, the width of the lateral blank area is 2 mm to 5 mm.

As an improvement to the preparation method of the wound structure lithium ion battery of the present invention, the bending of the positive electrode sheet is performed along the center line of the positive electrode sheet in the length direction.

As an improvement to the preparation method of the wound structure lithium ion battery of the present invention, the bending of the negative electrode sheet is carried out along the centerline of the length direction of the negative electrode sheet.

As an improvement to the preparation method of the winding structure lithium-ion battery of the present invention, the blank area of the positive electrode sheet is arranged on both sides of the positive electrode sheet; the blank area of the negative electrode sheet is arranged on the front and back sides of the negative electrode sheet.

As an improvement to the preparation method of the winding structure lithium-ion battery of the present invention, the horizontal blank area is arranged on one side of the positive electrode sheet, and when winding, the horizontal blank area is opposite to the negative electrode sheet.

As an improvement to the preparation method of the winding structure lithium ion battery of the present invention, multiple V shapes are provided on the positive electrode sheet, and multiple V shapes are provided on the negative electrode sheet.

As an improvement to the preparation method of the winding structure lithium ion battery of the present invention, the number of V-shaped on the positive electrode sheet is equal to the number of V-shaped on the negative electrode sheet.

Compared with the prior art, the invention adopts the method of bending the pole piece to reduce the resistance of the pole piece, and solves the problem of large resistance of the traditional wound lithium ion. The battery pole piece in the present invention is wound after being bent n times, which can reduce the resistance of the pole piece to one nth of that of the traditional battery, greatly reducing the resistance of the pole piece, and reducing the ohmic resistance in the charging and discharging process. Polarization improves battery consistency. The method of bending the pole pieces used in the present invention can significantly reduce the gas production rate of Joule heat and side reactions in the charging and discharging process, thereby improving the rate performance and cycle life of lithium-ion batteries and lithium-ion battery packs, and also Reduces the risk of overheating of Li-ion cells and Li-ion battery packs.

The use of the bent pole piece of the present invention also improves the efficiency of the winding process. For a battery with the same capacity, the length of the pole piece can be reduced to a fraction of that of a traditional battery, and the efficiency of the coating process, cold pressing process, and winding process can be doubled, reducing the process cost and improving the efficiency of the lithium-ion battery. Product competitiveness. In addition, because the electrode bending reduces the electrode resistance and ohmic polarization, the coating weight can be increased according to the actual performance requirements, and the energy density of the battery can be improved without affecting the electrical performance of the battery.

Description of drawings

Fig. 1 is a schematic view of the structure of the positive pole piece of the present invention;

Fig. 2 is a schematic diagram of the structure of the negative electrode sheet of the present invention;

Fig. 3 is a schematic diagram of the structure of the positive pole piece after bending in the present invention;

Fig. 4 is a schematic diagram of the structure of the negative pole piece after bending in the present invention;

Fig. 5 is a schematic diagram of the structure of positive and negative pole pieces before winding in the present invention;

Fig. 6 is a schematic diagram of the winding structure of the lithium-ion battery of the present invention;

Fig. 7 is the low temperature (-10 ℃) 2C discharge curve of the battery of embodiment 1 of the present invention and comparative example 1;

Fig. 8 is the cycle curve when the batteries of Example 1 of the present invention and Comparative Example 1 are charged at 1C and discharged at 1C at 25C;

FIG. 9 is the 2C rate curves of the batteries of Example 1 and Comparative Example 1 of the present invention at normal temperature (25° C.).

Detailed ways

The present invention and its beneficial effects will be described in detail below in conjunction with specific embodiments and accompanying drawings, but the invention is not limited thereto.

As shown in Fig. 1, Fig. 3, Fig. 5 and Fig. 6, the positive electrode sheet 10 of the present invention comprises a positive electrode current collector 1, a positive electrode membrane 2 coated on the positive electrode current collector 1 and reserved on the positive electrode current collector 1 The blank area 3 of the positive electrode sheet, the positive electrode sheet 10 is bent into a V shape, and the blank area 3 of the positive electrode sheet is connected through the positive electrode tab 4 . There is at least one V shape (as shown in Figure 3).

As shown in Fig. 2, Fig. 4, Fig. 5 and Fig. 6, the negative electrode sheet 20 of the present invention includes a negative electrode current collector 5, a negative electrode diaphragm 6 coated on the negative electrode current collector 5 and a reserved The blank area 7 of the negative electrode sheet, the negative electrode sheet 20 is bent into a V shape, and the blank area 7 of the negative electrode sheet is connected through the negative electrode tab 8 . There is at least one V shape (as shown in Figure 4). As shown in Figure 6, the lithium ion battery of the present invention comprises positive electrode sheet 10, negative electrode sheet 20, separator 30 spaced between positive electrode sheet 10 and negative electrode sheet 20, and electrolyte, positive electrode sheet 10 and negative electrode sheet 20 are respectively The positive electrode sheet 10 and the negative electrode sheet 20 mentioned above.

Example 1

The following is an example of bending once along the center line of the length of the pole piece (that is, only one V shape is provided on the positive pole piece 10 and the negative pole piece 20) to illustrate the specific process:

Preparation of positive electrode sheet 10:

Mix LiCoO ₂ (lithium cobaltate), Super-P (conductive carbon black), PVDF (polyvinylidene fluoride) and NMP (N,N-dimethylpyrrolidone) in a mass ratio of 95:2:3 and stir evenly Obtain positive electrode slurry. Viscosity was adjusted by NMP during stirring. Then the slurry is evenly coated on both sides of the 14 micron thick positive electrode current collector 1 (aluminum foil) according to a certain width, and the coating adopts interval coating instead of continuous coating. The positive electrode sheet blank area 3 is reserved on both sides of the aluminum foil (as shown in Figure 1), and the horizontal blank area 9 is reserved in the width direction of one side of the aluminum foil. The width of the horizontal blank area 9 is 2 mm to 5 mm. , and then bend the positive electrode sheet into a V-shape close to 180° through a V-shaped mold, the bending edge is the center line of the positive electrode sheet along the length direction, and at the same time ensure that the horizontal blank area 9 in the width direction is inside the bent positive electrode sheet , to prepare the positive electrode sheet 10. When the positive electrode is coated, the blank area 3 of the positive electrode sheet is reserved in the length direction to reserve the welding area of the positive electrode tab, and the horizontal blank area 9 is reserved in the width direction to ensure that the positive electrode active material area is not larger than the negative electrode active material area after the positive electrode sheet is bent. , in order to prevent the occurrence of lithium precipitation phenomenon.

Preparation of negative electrode sheet 20: artificial graphite, Super-P (conductive carbon black), CMC (water-based binder, carboxymethyl cellulose), SBR (Styrene Butadiene Rubber a kind of rubber) according to mass ratio 94: 1: 2:3 mixed with deionized water and stirred evenly to obtain negative electrode coating slurry. The viscosity was adjusted by deionized water during stirring. Then the slurry is coated on both sides of the 9 micron thick negative electrode current collector 5 (copper foil) according to a certain width, and the two sides of the length direction of the front and back sides of the copper foil are reserved for welding the negative electrode tab during coating. 8, the blank area 7 of the negative electrode sheet (as shown in Figure 2), after the negative electrode slurry is dried, it is cold-pressed, and then the positive electrode sheet is bent into a V shape close to 180° through a V-shaped mold, and the bending edge is the length of the negative electrode sheet. The center line of the direction, the negative electrode sheet 20 is made.

Diaphragm 30 is made of polypropylene porous membrane. As shown in Figure 5, then the positive electrode sheet 10 and the negative electrode sheet 20 after bending are intersected (that is, one end of the positive electrode sheet 10 is inserted in the V-shape of the negative electrode sheet 20, and the inserted end is close to the center of the negative electrode sheet 20 along the length direction line and parallel to the center line; at the same time, one end of the negative electrode sheet 20 is inserted into the V shape of the positive electrode sheet 10, and the inserted end is close to the center line of the positive electrode sheet 10 along the length direction and parallel to the center line), so that the blank area of the positive electrode sheet 3 Opposite to the blank area 7 of the negative electrode sheet, and place a separator 30 between the positive electrode sheet 10 and the negative electrode sheet 20, then connect the blank area 3 of the positive electrode sheet located at both ends of the V shape by welding the positive electrode tab 4, and the negative electrode sheet located at both ends of the V shape The blank area 7 is welded and connected through the negative pole tab 8 to obtain the pole piece group;

The pole piece group is wound into a battery cell with a rolling needle, the battery cell is placed in a packaging bag, and the lithium-ion battery is obtained after liquid injection, standing, formation, and capacity.

Lithium-ion batteries with this structure can reduce the resistance of the electrode sheet to half of the original.

Of course, the positive electrode sheet can also be provided with multiple V-shaped shapes, and the negative electrode sheet can also be provided with multiple (n) V-shaped shapes. The number of V-shaped shapes on the positive electrode sheet should be equal to the number of V-shaped shapes provided on the negative electrode sheet. The resistance of the lithium-ion battery with this structure will be reduced to one-nth of the original.

Comparative example 1

The difference from Example 1 is that the lithium-ion battery is prepared by the traditional method, that is, the positive electrode sheet and the negative electrode sheet are not bent, but the positive electrode sheet, the negative electrode sheet and the separator are directly wound after cold pressing to obtain Electrode set. The rest are the same as in Embodiment 1, and will not be repeated here.

The lithium ion battery of embodiment 1 and comparative example 1 is tested as follows:

(1) The batteries of Example 1 and Comparative Example 1 were placed in a low temperature environment of 10°C and discharged at a discharge rate of 2C, and the discharge curves of the two were recorded. The results obtained are shown in FIG. 7 .

It can be seen from FIG. 7 that the voltage of the battery of Comparative Example 1 drops very quickly under the condition of low temperature and large rate, that is, the discharge voltage plateau of the battery drops too fast, which is obviously faster than the voltage drop of the battery of Example 1 of the present invention. It shows that the lithium-ion battery prepared by the method of the present invention has better low-temperature high-rate discharge performance, and can avoid the risk of battery overheating.

(2) The batteries of Example 1 and Comparative Example 1 were placed in a normal temperature environment of 25°C for cycle tests at a charge rate of 1C and a discharge rate of 1C, and the cycle curves of the two were recorded. The results obtained are shown in FIG. 8 .

It can be seen from FIG. 8 that under the same test conditions, after 500 cycles, the capacity retention rate of the battery of Example 1 of the present invention reaches as much as 90%, while that of the battery of Comparative Example 1 is only 80%. This shows that the lithium ion battery prepared by the invention has better cycle performance at normal temperature.

At the same time, the temperature rise of the battery surface during the cycle was measured, and the results showed that the temperature rise of the battery of Comparative Example 1 reached as high as 120°C, while the temperature rise of the present invention was only about 80°C.

(3) The batteries of Example 1 and Comparative Example 1 were placed in a normal temperature environment of 25° C. to test the 2C rate curve of the batteries, and the obtained results are shown in FIG. 9 .

It can be seen from FIG. 9 that the lithium-ion battery prepared by the method of the present invention has better rate performance.

In summary, the method of the present invention can significantly improve the rate performance and cycle performance of the battery, the temperature rise during high-current charge and discharge, and solve the problem of the battery discharge platform dropping too fast, thereby reducing the overheating risk of the lithium-ion battery .

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 (7)

1. A preparation method of wound structure lithium ion battery, is characterized in that, comprises the following steps: The first step, the preparation of the positive electrode sheet: apply the positive electrode slurry on the positive electrode current collector, reserve a blank area of the positive electrode sheet on both sides of the positive electrode current collector in the length direction when coating, and cold press the positive electrode slurry after drying. Then bend into a V shape; Preparation of the negative electrode sheet: apply the negative electrode slurry on the negative electrode current collector, reserve a blank area of the negative electrode sheet on both sides of the negative electrode current collector in the length direction when coating, cold press the negative electrode slurry after drying, and then bend it into V-shaped; In the second step, place the bent positive electrode sheet and negative electrode sheet crosswise so that the blank area of the positive electrode sheet is opposite to the blank area of the negative electrode sheet, and place a diaphragm between the positive electrode sheet and the negative electrode sheet, and then place the positive electrode sheet at both ends of the V shape The blank area is connected by welding the positive pole tab, and the blank area of the negative electrode sheet located at both ends of the V shape is connected by welding the negative electrode tab to obtain the pole piece group; The third step is to wind the pole piece group into a battery cell, put the battery cell in a packaging bag, inject liquid, stand still, form, and capacity to obtain a lithium-ion battery; When the positive electrode sheet is coated, a horizontal blank area is reserved on both sides of the width direction of the positive electrode current collector; the width of the horizontal blank area is 2 mm to 5 mm, so as to ensure that the positive active material area of the positive electrode sheet is not larger than Negative electrode active material area to prevent the occurrence of lithium precipitation. 2 . The method for preparing a wound structure lithium ion battery according to claim 1 , wherein the bending of the positive electrode sheet is along the centerline of the positive electrode sheet in the longitudinal direction. 3 . 3 . The method for preparing a wound structure lithium ion battery according to claim 1 , wherein the bending of the negative electrode sheet is along the centerline of the length direction of the negative electrode sheet. 4 . 4. The preparation method of the winding structure lithium ion battery according to claim 1, characterized in that: the blank area of the positive electrode sheet is arranged on both sides of the positive electrode sheet; the blank area of the negative electrode sheet is arranged on the positive and negative sides of the negative electrode sheet. Conversely. 5 . The method for preparing a winding structure lithium ion battery according to claim 2 , wherein the lateral blank area is arranged on one side of the positive electrode sheet, and when winding, the horizontal blank area is opposite to the negative electrode sheet. 6 . 6 . The method for preparing a winding structure lithium ion battery according to claim 1 , wherein the positive electrode sheet is provided with multiple V shapes, and the negative electrode sheet is provided with multiple V shapes. 7 . 7 . The method for preparing a winding structure lithium ion battery according to claim 6 , wherein the number of V-shaped on the positive electrode sheet is equal to the number of V-shaped on the negative electrode sheet. 8 .