WO2021127929A1

WO2021127929A1 - Preparation method for secondary battery

Info

Publication number: WO2021127929A1
Application number: PCT/CN2019/127643
Authority: WO
Inventors: 董宇洋; 闫东阳; 曾巧
Original assignee: 宁德新能源科技有限公司
Priority date: 2019-12-23
Filing date: 2019-12-23
Publication date: 2021-07-01
Also published as: CN113316864B; CN113316864A

Abstract

The present application provides a preparation method for a secondary battery, comprising the following steps: providing an electrode assembly; placing the electrode assembly in a housing and injecting an electrolyte, and obtaining a battery cell; and performing formation processing on the battery cell, the formation processing being performed under the pressure of 0.5 MPa-3.0 MPa, thereby obtaining the secondary battery. By adopting the preparation method, the thickness expansion rate of the secondary battery in a cycle can be improved.

Description

Preparation method of secondary battery

Technical field

This application relates to the field of batteries, and in particular to a method for preparing secondary batteries.

Background technique

Nowadays, portable mobile terminal devices are generally equipped with a battery-centric energy supply system. With the development of portable devices in a smaller and thinner direction, people have higher and higher requirements for the thickness of the battery core. In addition, since most portable devices are not for one-time use, in addition to the requirements for the initial thickness of the battery, the same requirements are also imposed on the thickness of the battery during the entire service life of the portable device, that is, the battery is used for a long time. The expansion cannot exceed the predetermined range.

Generally speaking, the battery core can be encapsulated by a steel shell and a reinforced structure. Although the thickness of the battery core can be limited, the disadvantage is that it will increase the weight of the portable device. In addition, the effect of improving the cyclic expansion of the battery can be achieved by adjusting the battery material system, such as matching the particle size of different components in the anode formula to maximize the space utilization to achieve the purpose of improving the thickness, but the disadvantages are The modification of the material system will increase the cost and technical difficulty.

Summary of the invention

In view of the above, it is necessary to propose a method for preparing a secondary battery, which can improve the cyclic expansion of the secondary battery without increasing the weight of the battery, and without increasing the cost and technical difficulty.

A preferred embodiment of the present application provides a method for preparing a secondary battery, which includes the following steps: providing an electrode assembly; placing the electrode assembly in a casing and injecting electrolyte to obtain a battery unit; A chemical conversion treatment is performed, and the chemical conversion treatment is performed under a pressure of 0.5 MPa to 3.0 MPa, thereby obtaining the secondary battery.

In some embodiments of the present application, the pressure is obtained by clamping the battery cell with a clamp and/or pressurizing in the housing.

In some embodiments of the present application, the chemical conversion treatment is performed at a temperature of 40°C to 90°C.

In some embodiments of the present application, the temperature is obtained by heating the battery cell, fluid heat exchange, and/or heat radiation.

In some embodiments of the present application, the chemical conversion treatment includes a first charging stage, and the charging current of the first charging stage is 0.1C-0.8C.

In some embodiments of the present application, the charging time of the first charging stage is 4min-20min.

In some embodiments of the present application, the chemical conversion treatment further includes a second charging stage after the first charging stage, and the charging current of the second charging stage is greater than the charging current of the first charging stage.

In some embodiments of the present application, both the first charging stage and the second charging stage are performed under the pressure.

In some embodiments of the present application, the electrode assembly is prepared by the following steps: providing a positive electrode current collector and a negative electrode current collector; coating the positive electrode active material and the negative electrode active material on the positive electrode current collector and the negative electrode current collector, respectively, A positive pole piece and a negative pole piece are obtained; and a separator is placed between the positive pole piece and the negative pole piece, and is wound or stacked to obtain the electrode assembly.

In some embodiments of the present application, after 400 charge-discharge cycles are performed on the secondary battery, the thickness expansion rate of the secondary battery is less than or equal to 7%.

The embodiment of the application chemically forms the battery cell under high pressure, which can improve the arrangement and orientation of the negative electrode active material on the negative electrode current collector, and make the negative electrode active material expand in the direction of the length and width of the electrode assembly during the cycle. Transfer, thereby reducing the particle gap between the negative active material, improving the space utilization rate, and achieving the purpose of improving the thickness expansion rate of the secondary battery. Moreover, the embodiments of the present application can also improve the cyclic expansion of the secondary battery without increasing the weight of the battery, and without increasing the cost and technical difficulty.

Description of the drawings

FIG. 1 is a flowchart of a method for manufacturing a secondary battery provided by an embodiment of the application.

Fig. 2 is a state change diagram of the active material of the secondary battery in the manufacturing method shown in Fig. 1.

FIG. 3 is a graph showing changes in thickness expansion ratio of secondary batteries prepared in Examples 2, 4-6 and Comparative Example 2-3 of the application as a function of the number of cycles.

4 is a graph showing changes in thickness expansion ratio of secondary batteries prepared in Examples 1-3 and Comparative Example 1 of the application with the number of cycles.

Fig. 5 is a graph showing the variation of the thickness expansion rate of the secondary batteries prepared in Examples 5, 7-8 and Comparative Example 4-5 of the application as a function of the number of cycles.

The following specific embodiments will further illustrate this application in conjunction with the above-mentioned drawings.

Detailed ways

Referring to FIG. 1, an embodiment of the present application provides a method for preparing a secondary battery, which includes the following steps:

Step S1: Provide an electrode assembly.

In this embodiment, first, the positive electrode current collector and the negative electrode current collector are provided. Then, the positive electrode active material and the negative electrode active material are respectively coated on the positive electrode current collector and the negative electrode current collector to obtain a positive electrode pole piece and a negative electrode pole piece. Then, the separator is placed between the positive pole piece and the negative pole piece, and is wound or stacked to obtain the electrode assembly.

Wherein, the positive electrode active material may include common positive electrode active materials, binders and additives. The negative active material may include common negative active materials, binders, and additives.

Step S2: placing the electrode assembly in the casing and injecting electrolyte to obtain a battery cell. The electrolyte may be an electrolyte commonly used in this field.

Step S3: chemical conversion treatment is performed on the battery unit, and the chemical conversion treatment is performed under a pressure of 0.5 MPa-3.0 MPa, thereby obtaining the secondary battery.

Among them, the expansion of the secondary battery during the cycle is mainly caused by the expansion of the positive electrode active material or the negative electrode active material in the thickness direction of the electrode assembly. After the formation, the thickness change of the positive pole piece reaches the maximum value, and its thickness does not change significantly during the subsequent cycles, while the thickness of the negative pole piece continues to increase during the cycle. Therefore, the secondary battery is in the cycle The main source of swelling is the swelling of the negative electrode active material. The embodiment of the application is formed into the battery cell under a high pressure of 0.5Mpa～3.0Mpa. As shown in Figure 2, the arrangement and orientation of the negative electrode active material (such as graphite, etc.) on the negative electrode current collector can be improved, so that the negative electrode The direction of the expansion of the active material during the cycle transfers to the length and width directions of the electrode assembly, thereby reducing the particle gap between the negative active material, improving the space utilization rate, and achieving the purpose of improving the thickness expansion rate of the secondary battery.

In some embodiments, the chemical conversion treatment may be performed under a pressure of 0.5 MPa-2.0 MPa, so that the battery cell has a smaller thickness expansion rate. In some embodiments, the chemical conversion treatment may be performed under a pressure of 1.0 MPa-2.0 MPa.

Among them, the inventor of the present application found that when the pressure is less than 0.5Mpa, the negative electrode active material is not easily compressed; and when the pressure is greater than 3.0Mpa, the negative electrode active material particles will be broken, or the surface morphology of the negative electrode current collector will be affected. This leads to undesirable phenomena such as stress concentration.

In some embodiments, the pressure is obtained by clamping the battery cell with a clamp and/or pressurizing in the housing.

In some embodiments, the chemical conversion treatment is performed at a temperature of 40°C to 90°C. In this temperature range, the reaction activity of the active substance in the chemical conversion process remains the highest, and the entire chemical conversion process is more efficient. Among them, the inventor of the present application found that when the temperature is greater than 90° C., the electrolyte in the electrolyte will decompose, and the active material will lose its activity at high temperatures, resulting in degradation of the performance of the secondary battery. In some embodiments, the chemical conversion treatment is performed at a temperature of 40°C to 70°C. In some embodiments, the chemical conversion treatment is performed at a temperature of 40°C-60°C.

In some embodiments, the temperature may be obtained by heating the battery cell, fluid heat exchange, and/or heat radiation.

In some embodiments, the chemical conversion treatment includes a first charging stage, and the charging current of the first charging stage is 0.1C-0.8C. In some embodiments, the charging current in the first charging stage is 0.2C-0.6C. In some embodiments, the charging current in the first charging stage is 0.2C-0.5C.

In some embodiments, the chemical conversion treatment may further include a second charging phase after the first charging phase, and the charging current of the second charging phase is greater than the charging current of the first charging phase. The first charging stage and the second charging stage are both performed under the same preset pressure, that is, the charging voltage of the entire charging stage remains unchanged.

In the embodiments of the application, a higher pressure and a lower charging current are used at the same time during the formation, which can make the negative electrode active material more fully change the arrangement and orientation, and at the same time make the SEI film formed on the surface of the negative electrode more uniform, which is beneficial to Increase first-time capacity. Among them, the inventor of the present application found that when the charging current is greater than 0.8C, the rearrangement of the negative electrode active material will be disturbed, and the SEI film formation reaction during the formation process will be too violent to ensure its uniformity, and it will be accompanied by side effects. When the reaction occurs, the electrolyte in the secondary battery will also be consumed; and when the charging current is less than 0.1C, the SEI film is formed unevenly, and the subsequent increase in the current in the second charging stage will cause a thicker SEI film to be locally formed. As a result, the thickness of the battery cell is locally increased.

In some embodiments, the charging time of the first charging stage is 4min-20min. Among them, the inventor of the present application found that when the charging time of the first charging stage is less than 4 minutes, the formation is incomplete due to the short time; and when the charging time is greater than 20 minutes, the active material will lose activity due to the long time. , Forming a by-product, thereby increasing the thickness of the battery cell.

In this embodiment, after 400 charge and discharge cycles are performed on the battery cell, the thickness expansion rate of the secondary battery is less than or equal to 7%.

The technical solution of the present application will be described below in conjunction with embodiments.

Example 1

The electrode assembly is made, the electrode assembly is placed in the casing and the electrolyte is injected to obtain the battery cell.

The battery cell is placed in the battery placement mechanism of the chemical conversion equipment, and the battery cell is subjected to a chemical conversion treatment at a temperature of 40° C., and an external pressure of 1.0 Mpa is applied to the battery cell during the chemical conversion treatment. Wherein, the current in the first charging stage of the chemical conversion treatment is set to 0.4C, and the time is set to 4 minutes. After the chemical conversion treatment, the battery cells are subjected to a standard charging and discharging process at room temperature to achieve capacity activation, and then degassing treatment is performed to complete the preparation of secondary batteries. The standard charging and discharging process may include: constant current charging of the battery cell with a current of 0.2C to its rated upper limit voltage, and constant voltage charging of the battery cell with the upper limit voltage to a cut-off current (such as 0.02C) to complete the charging Process: The battery cell is discharged with a constant current of 0.2C to a cut-off voltage (such as 3.0V) to complete the discharge process.

Example 2

It is almost the same as Example 1, except that the chemical conversion treatment is performed at a temperature of 60°C.

Example 3

It is almost the same as Example 1, except that the chemical conversion treatment is performed at a temperature of 90°C.

Example 4

It is almost the same as Example 2, except that the chemical conversion treatment is carried out under a pressure of 0.5Mpa.

Example 5

It is roughly the same as Example 4, except that the chemical conversion treatment is carried out under a pressure of 2.0 Mpa.

Example 6

It is roughly the same as Example 4, except that the chemical conversion treatment is performed under a pressure of 3.0Mpa.

Example 7

It is roughly the same as Embodiment 5, except that the current in the first charging stage of the chemical conversion treatment is 0.1C.

Example 8

It is roughly the same as Embodiment 5, except that the current in the first charging stage of the chemical conversion treatment is 0.8C.

Example 9

It is roughly the same as Embodiment 5, except that: the time of the first charging stage of the chemical conversion treatment is 8 minutes.

Comparative example 1

It is almost the same as Example 1, except that the chemical conversion treatment is performed at a temperature of 100°C.

Comparative example 2

It is roughly the same as Example 2, except that the chemical conversion treatment is performed under a pressure of 0.1Mpa.

Comparative example 3

It is almost the same as Example 2, except that the chemical conversion treatment is carried out under a pressure of 4.0Mpa.

Comparative example 4

It is roughly the same as Embodiment 5, except that the current in the first charging stage of the chemical conversion treatment is 0.05C.

Comparative example 5

It is roughly the same as Embodiment 5, except that the current in the first charging stage of the chemical conversion treatment is 1.0C.

Comparative example 6

It is roughly the same as Comparative Example 5, except that: the time of the first charging stage of the chemical conversion treatment is 16 minutes.

Comparative example 7

It is roughly the same as Comparative Example 5, except that: the time of the first charging stage of the chemical conversion treatment is 25 minutes.

The thickness expansion rate of the secondary batteries prepared in Examples 1-9 and Comparative Examples 1-6 were measured respectively as follows: ① Charging step: charge the secondary battery with a constant current of 0.8C to the charging limit voltage (such as 4.4V), measure the thickness of the secondary battery and record it as the initial thickness T ₀ ; ②discharge step: discharge the secondary battery with a constant current of 1C to a cut-off voltage (such as 3.0V); ③repeat the charging step ① and discharge Step ② 400 times each, record the thickness T of the secondary battery after 100 charging steps per cycle, and calculate the thickness expansion rate of the secondary battery. The ratio of the difference between the thickness T and the initial thickness T ₀ to the initial thickness T ₀ is the thickness expansion rate λ of the secondary battery, that is, λ=(TT ₀ )/T ₀ .

The measurement is repeated 8 times for each group of secondary batteries according to the above method, and the average value of the corresponding thickness expansion rate λ is calculated as the final thickness expansion rate, and the measurement results of each embodiment and comparative example are listed in Table 1.

Table 1 The formation parameters and thickness expansion rate of the secondary batteries of each embodiment and each comparative example

Combining Table 1 and Figure 3, it can be seen that compared to Comparative Examples 2-3, after 400 charge-discharge cycles of the secondary batteries of Examples 2, 4-6, the thickness expansion rate of the secondary batteries is smaller. The thickness expansion rate corresponding to Example 6 is slightly larger than 7% (the pressure is 3Mpa, which is at a critical value and is caused by the fluctuation of the measurement data), and the thickness expansion rates of Examples 2 and 4-5 are both less than 7%. Furthermore, in conjunction with Table 1 and Figure 4, it can be seen that compared with Comparative Example 1, after 400 charge and discharge cycles of the secondary battery of Examples 1-3, the thickness expansion rate of the secondary battery is less than 7%. In addition, in conjunction with Table 1 and Figure 5, it can be seen that compared with Comparative Examples 4-5, after 400 charge and discharge cycles of the secondary batteries of Examples 5 and 7-8, the thickness expansion rate of the secondary batteries is less than 7%. . This respectively indicates that appropriate external pressure, temperature and low current in the chemical conversion process can achieve the purpose of improving the thickness expansion rate of the secondary battery without increasing the weight of the battery or increasing the cost, and it can also make the entire chemical conversion process more efficient.

Finally, compared with Comparative Examples 5-6, after 400 charge-discharge cycles of the secondary battery of Comparative Example 7, the thickness expansion rate of the secondary battery is higher, indicating that the first charging phase is too long and is not conducive to control. The thickness expansion rate of the secondary battery is described.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the application and not to limit them. Although the application has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the application can be Make modifications or equivalent replacements without departing from the spirit and scope of the technical solution of the present application.

Claims

A method for preparing a secondary battery is characterized in that it comprises the following steps:

Provide electrode assembly;

Placing the electrode assembly in the casing and injecting electrolyte to obtain a battery cell; and

The battery cell is subjected to chemical conversion treatment, and the chemical conversion treatment is performed under a pressure of 0.5 MPa to 3.0 MPa, thereby obtaining the secondary battery.
The method for manufacturing a secondary battery according to claim 1, wherein the pressure is obtained by clamping the battery cell with a clamp and/or pressing in the casing.
The method for manufacturing a secondary battery according to claim 1, wherein the chemical conversion treatment is performed at a temperature of 40°C to 90°C.
8. The method for manufacturing a secondary battery according to claim 3, wherein the temperature is obtained by heating the battery cell, fluid heat exchange and/or heat radiation.
8. The method for manufacturing a secondary battery according to claim 1, wherein the chemical conversion treatment includes a first charging stage, and the charging current in the first charging stage is 0.1C-0.8C.
8. The method for preparing a secondary battery according to claim 5, wherein the charging time of the first charging stage is 4min-20min.
The method for manufacturing a secondary battery according to claim 5 or 6, wherein the chemical conversion treatment further comprises a second charging stage after the first charging stage, and the charging current of the second charging stage is greater than The charging current of the first charging stage.
8. The method for manufacturing a secondary battery according to claim 7, wherein the first charging stage and the second charging stage are both performed under the pressure.
8. The method for manufacturing a secondary battery according to claim 1, wherein the electrode assembly is prepared by the following steps:

Provide positive electrode current collector and negative electrode current collector;

Coating the positive electrode active material and the negative electrode active material on the positive electrode current collector and the negative electrode current collector respectively to obtain positive electrode pieces and negative electrode pieces; and

The separator is placed between the positive pole piece and the negative pole piece, and is wound or stacked to obtain the electrode assembly.
2. The method for manufacturing a secondary battery according to claim 1, wherein after 400 charge-discharge cycles of the secondary battery, the thickness expansion rate of the secondary battery is less than or equal to 7%.