A vacuum drying method for large square lithium battery electrode groups

Abstract

This application discloses a vacuum drying method for a large square lithium battery electrode assembly, comprising the following steps: performing a first vacuum drying on unassembled positive and negative electrode sheets, and detecting the water content on the surface of the positive and negative electrode sheets; assembling the square battery cell in the order of positive electrode sheet, separator, and negative electrode sheet, and after electrolyte injection, performing a second vacuum drying on the battery cell; the second vacuum drying is divided into two stages: a constant vacuum drying stage and a variable vacuum drying stage based on the constant vacuum drying, wherein the variable vacuum drying stage is achieved by introducing inert gas into the drying equipment; preset the first vacuum drying task value and the second vacuum drying task value, wherein the first vacuum drying task value is greater than the second vacuum drying task value, and the time of the second vacuum drying can be controlled by setting the second vacuum drying task value, thereby controlling the overall vacuum drying time.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to a vacuum drying method for a large square lithium battery electrode assembly. Background Technology

[0002] Three key factors in lithium-ion battery manufacturing processes are moisture, dust, and aging. Among these, moisture control is particularly crucial. Moisture can easily lead to increased internal resistance, low capacity, poor cycle life, and deteriorated electrical performance, directly impacting battery performance. The baking process before electrolyte injection into the electrode assembly is a critical step in controlling battery moisture. Researching how to improve baking efficiency and reduce electrode assembly moisture has become a key concern for lithium-ion battery manufacturers.

[0003] Currently, lithium battery manufacturers generally use vacuum ovens to bake the electrode assembly. The baking efficiency of the electrode assembly is greatly affected by temperature, vacuum level, and time. The higher the temperature, the faster the moisture evaporation rate and the higher the baking efficiency. However, excessively high temperatures can cause the separator in the lithium battery to shrink due to heat, resulting in short circuits and poor battery performance. Therefore, conventional vacuum baking must control the baking temperature within 85±3℃, and the baking effect is not ideal. Increasing the vacuum level can lower the boiling point of moisture, increase the moisture vaporization rate, and improve baking efficiency. However, conventional baking vacuum levels are only controlled below -85Kpa, so the improvement in baking efficiency is limited. Summary of the Invention

[0004] One of the objectives of this invention is to remove moisture from the electrode assembly of a large square lithium-ion battery.

[0005] To achieve the above objectives, this application provides a vacuum drying method for a large square lithium battery electrode assembly, comprising the following steps:

[0006] The unassembled positive and negative electrode sheets were subjected to a first vacuum drying process, and the water surface content of the positive and negative electrode sheets was measured.

[0007] The square battery cell is assembled in the order of positive electrode, separator, and negative electrode. After liquid injection, the battery cell is subjected to a second vacuum drying.

[0008] The second vacuum drying is divided into two stages: a constant vacuum drying stage and a variable vacuum drying stage based on the constant vacuum drying. The variable vacuum drying stage is achieved by introducing an inert gas into the drying equipment.

[0009] The first vacuum drying task value and the second vacuum drying task value are preset, wherein the first vacuum drying task value is greater than the second vacuum drying task value.

[0010] Furthermore, the specific steps of the variable vacuum drying include introducing a drying inert gas into the vacuum drying equipment to adjust the vacuum level of the equipment to atmospheric pressure, and continuously heating with nitrogen gas for 40 to 60 minutes.

[0011] Furthermore, the temperature of the first vacuum drying is not lower than 150°C, and the vacuum degree of the first vacuum drying is not lower than -0.09 MPa.

[0012] Preferably, the temperature of the first vacuum drying is 150–200°C.

[0013] Furthermore, by controlling the first vacuum drying task value, the time of the first vacuum drying is 3-5 hours.

[0014] Furthermore, the temperature of the second vacuum drying is not higher than 85°C, and the vacuum degree of the second vacuum drying is not higher than -0.09 MPa.

[0015] Preferably, the temperature of the first vacuum drying is 85±3℃.

[0016] Furthermore, by controlling the second vacuum drying task value, the time of the second vacuum drying is 3 to 5 hours.

[0017] Furthermore, the first vacuum drying task is to achieve complete drying.

[0018] Further, dry nitrogen gas is introduced into the vacuum baking oven to de-vacuum the oven to atmospheric pressure, and nitrogen gas is introduced during heating for 40 to 60 minutes.

[0019] Furthermore, the entire vacuum drying time is 24–30 hours.

[0020] Furthermore, the preset value for the second vacuum task is no higher than 300 ppm.

[0021] Compared with the prior art, this application has the following technical effects:

[0022] The drying time can be controlled by setting the vacuum task value for the first drying stage. Because there is no high temperature affecting the separator, the first vacuum drying can achieve complete drying. However, during the assembly process after the first vacuum drying, moisture from the air can still enter the positive and negative electrode plates. Therefore, the first vacuum drying can only shorten the time of the second vacuum drying to a certain extent, and cannot completely eliminate this step. The second vacuum drying needs to control the water content in the battery within a certain range to ensure normal battery use. In addition, the reason for using two vacuum drying stages is that the separator in the middle of the cell cannot be heated to too high a temperature. Excessive temperature and vacuum will damage the separator. Performing a single vacuum drying on the positive and negative electrode plates eliminates the concern about separator damage and allows for complete drying of the positive and / or negative electrode plates. Increasing the temperature and vacuum level of the first vacuum drying stage and adding a vacuum level variation stage makes the entire drying process safer and reduces sudden voltage changes that could cause sudden changes in the drying environment, thus affecting the drying effect. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application are described in further detail below. Exemplary embodiments will be described in detail here. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the claims.

[0024] Example 1

[0025] In this embodiment, a vacuum drying method for a large square lithium battery electrode assembly is provided, comprising the following steps:

[0026] Unassembled positive and negative electrode sheets were subjected to a first vacuum drying process, and the water surface content of the positive and negative electrode sheets was measured. The temperature of the first vacuum drying was 150°C, and the vacuum degree of the first vacuum drying was -0.090 MPa.

[0027] The square battery cell is assembled in the order of positive electrode, separator, and negative electrode. After liquid injection, the battery cell is subjected to a second vacuum drying. The temperature of the first vacuum drying is 85°C and the vacuum degree of the first vacuum drying is -0.090 MPa.

[0028] The second vacuum drying is divided into two stages: a constant vacuum drying stage and a variable vacuum drying stage based on the constant vacuum drying. The variable vacuum drying stage is achieved by introducing an inert gas into the drying equipment. The specific steps of the variable vacuum drying include introducing a drying inert gas into the vacuum drying equipment to adjust the vacuum level of the equipment to normal pressure, and continuously heating with nitrogen for 40 min to 60 min. By controlling the second vacuum drying task value, the time of the first vacuum drying is controlled to be 5 h.

[0029] Initial measurement process: By controlling the time of the first vacuum drying, adjusting the temperature and vacuum level of the first vacuum drying, the target value of the first vacuum drying is measured;

[0030] For the second vacuum drying, adjust the temperature range to 85.3℃, continuously measure the value required to achieve the second vacuum drying task, the water content should not exceed 300ppm, and the time value.

[0031] Example 2

[0032] In this embodiment, a vacuum drying method for a large square lithium battery electrode assembly is provided, comprising the following steps:

[0033] Based on Example 1, the time for the first vacuum drying is further shortened, and the specific steps are as follows:

[0034] Unassembled positive and negative electrode sheets are subjected to a first vacuum drying process, and the water content on the surface of the positive and negative electrode sheets is measured. The temperature of the first vacuum drying is 150°C, and the vacuum degree of the first vacuum drying is -0.090 MPa.

[0035] The square battery cell is assembled in the order of positive electrode, separator, and negative electrode. After electrolyte filling, the battery cell undergoes a second vacuum drying. The temperature of the first vacuum drying is 85°C, and the vacuum degree of the first vacuum drying does not exceed -0.085 MPa.

[0036] The second vacuum drying is divided into two stages: a constant vacuum drying stage and a variable vacuum drying stage based on the constant vacuum drying. The variable vacuum drying stage is achieved by introducing an inert gas into the drying equipment. The specific steps of the variable vacuum drying include introducing a drying inert gas into the vacuum drying equipment to adjust the vacuum level of the equipment to normal pressure, and continuously heating with nitrogen for 40 min to 60 min. By controlling the second vacuum drying task value, the time of the first vacuum drying is controlled to be 4.5 h.

[0037] The system presets a first vacuum drying value and a second vacuum drying value, wherein the first vacuum drying value is greater than the second vacuum drying value. The first vacuum drying is mainly for processing the positive / negative electrode sheets. By controlling the first vacuum drying value, the water content is controlled to be no more than 300 ppm, and the first vacuum drying time is controlled to be 5 hours.

[0038] Example 3

[0039] In this embodiment, a vacuum drying method for a large square lithium battery electrode assembly is provided, comprising the following steps:

[0040] Based on Example 2, the time for the first vacuum drying is further shortened. The specific steps are as follows:

[0041] Unassembled positive and negative electrode sheets are subjected to a first vacuum drying process, and the water surface content of the positive and negative electrode sheets is measured. The temperature of the first vacuum drying is 180°C, and the vacuum degree of the first vacuum drying is -0.100 MPa.

[0042] The square battery cell is assembled in the order of positive electrode, separator, and negative electrode. After liquid injection, the battery cell is subjected to a second vacuum drying. The temperature of the first vacuum drying is 84.7℃, and the vacuum degree of the second vacuum drying is -0.084 MPa.

[0043] The second vacuum drying is divided into two stages: a constant vacuum drying stage and a variable vacuum drying stage based on the constant vacuum drying. The variable vacuum drying stage is achieved by introducing an inert gas into the drying equipment. The specific steps of the variable vacuum drying include introducing a drying inert gas into the vacuum drying equipment to adjust the vacuum degree of the equipment to normal pressure, and continuously heating with nitrogen for 40 min to 60 min. By controlling the second vacuum drying task value, the water content is not greater than 300 ppm, and the time of the first vacuum drying is controlled to be 5 h.

[0044] The first vacuum drying task value and the second vacuum drying task value are preset, wherein the first vacuum drying task value is greater than the second vacuum drying task value. The first vacuum drying mainly processes the positive / negative electrode sheets. By controlling the first vacuum drying task value, the time of the first vacuum drying is controlled to be 3 to 5 hours.

[0045] Example 4

[0046] In this embodiment, a vacuum drying method for a large square lithium battery electrode assembly is provided, comprising the following steps:

[0047] Based on Example 3, the time for the first vacuum drying is further shortened. The specific steps are as follows:

[0048] The unassembled positive and negative electrode sheets were subjected to a first vacuum drying, and the water surface content of the positive and negative electrode sheets was measured. The temperature of the first vacuum drying was 190°C, and the vacuum degree of the first vacuum drying was -0.101 MPa.

[0049] The square battery cell is assembled sequentially in the order of positive electrode, separator, and negative electrode. After electrolyte injection, the battery cell undergoes a second vacuum drying process. The temperature of the first vacuum drying process does not exceed 84.7℃, and the vacuum degree of the first vacuum drying process is -0.082 MPa.

[0050] The second vacuum drying is divided into two stages: a constant vacuum drying stage and a variable vacuum drying stage based on the constant vacuum drying. The variable vacuum drying stage is achieved by introducing an inert gas into the drying equipment. The specific steps of the variable vacuum drying include introducing a drying inert gas into the vacuum drying equipment to adjust the vacuum level of the equipment to normal pressure, and continuously heating with nitrogen for 40 min to 60 min. By controlling the second vacuum drying task value, the time of the first vacuum drying is controlled to be 3 hours.

[0051] The first vacuum drying task value and the second vacuum drying task value are preset, wherein the first vacuum drying task value is greater than the second vacuum drying task value. The first vacuum drying mainly processes the positive / negative electrode sheets. By controlling the first vacuum drying task value, the time of the first vacuum drying is controlled to be 4 hours.

[0052] Example 5

[0053] Based on Example 1, the time for the first vacuum drying is further shortened, and the specific steps are as follows:

[0054] In this embodiment, a vacuum drying method for a large square lithium battery electrode assembly is provided, comprising the following steps:

[0055] Unassembled positive and negative electrode sheets were subjected to a first vacuum drying process, and the water surface content of the positive and negative electrode sheets was measured. The temperature of the first vacuum drying was 200°C, and the vacuum degree of the first vacuum drying was -0.09 MPa.

[0056] The square battery cell is assembled in the order of positive electrode, separator, and negative electrode. After liquid injection, the battery cell is subjected to a second vacuum drying. The temperature of the first vacuum drying is 85°C and the vacuum degree of the first vacuum drying is -0.110 MPa.

[0057] The second vacuum drying is divided into two stages: a constant vacuum drying stage and a variable vacuum drying stage based on the constant vacuum drying. The variable vacuum drying stage is achieved by introducing an inert gas into the drying equipment. The specific steps of the variable vacuum drying include introducing a drying inert gas into the vacuum drying equipment to adjust the vacuum level of the equipment to normal pressure, and continuously heating with nitrogen for 40 min to 60 min. By controlling the second vacuum drying task value, the time of the first vacuum drying is controlled to be 3 hours.

[0058] The first vacuum drying task value and the second vacuum drying task value are preset, wherein the first vacuum drying task value is greater than the second vacuum drying task value. The first vacuum drying mainly processes the positive / negative electrode sheets. By controlling the first vacuum drying task value, the time of the first vacuum drying is controlled to be 3 to 5 hours.

[0059] The drying times in Examples 1-5 were statistically analyzed, and the results are shown in the table below:

[0060] Table 1. Statistical results of drying time

[0061]

[0062] As shown in Table 1, in Examples 1 to 5, the first vacuum drying time can be controlled within 3 to 6 hours, and the second vacuum drying time can be controlled within 3 to 6 hours.

[0063] The time for the first and second vacuum drying processes is 6 to 10 hours; the target value for the second vacuum drying is usually no higher than 300 ppm.

[0064] Increasing the temperature of the first vacuum drying can shorten the first vacuum drying time. In addition, decreasing the first vacuum degree can also shorten the first vacuum time. This is mainly because the boiling point of water under vacuum is inversely proportional to the vacuum degree. Maximizing the vacuum degree of electrode baking reduces the boiling point of water under vacuum conditions and improves the water vaporization efficiency. Without increasing the baking temperature, the water inside the electrode can be quickly evaporated and discharged, thus improving the baking efficiency.

[0065] The initial drying temperature in Example 5 was too high, which increased overall energy consumption and damage to the substrate under such high temperature conditions.

[0066] In summary, the optimal experimental scheme in this application is Example 4, where the first vacuum drying temperature is 190℃ and the vacuum degree is -0.101 MPa, the second vacuum drying temperature is 84.7℃ and the vacuum degree is -0.082, and the first and second vacuum drying times are 7 hours.

[0067] Although preferred embodiments of the present application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of the present application.

[0068] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or terminal device that includes said element.

[0069] The above provides a detailed description of a vacuum drying method for a large square lithium battery electrode assembly. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this application. At the same time, those skilled in the art will recognize that there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A vacuum drying method for a large square lithium battery electrode assembly, characterized in that, Includes the following steps: The unassembled positive and negative electrode sheets are subjected to a first vacuum drying process, and the water content on the surface of the positive and negative electrode sheets is measured. The temperature of the first vacuum drying is not lower than 150°C, and the vacuum degree of the first vacuum drying is not lower than -0.09 MPa. The square battery cell is assembled in the order of positive electrode, separator, and negative electrode. After electrolyte injection, the battery cell is subjected to a second vacuum drying. The temperature of the second vacuum drying is not higher than 85°C, and the vacuum degree of the second vacuum drying is not higher than -0.09 MPa. The second vacuum drying is divided into two stages: a constant vacuum drying stage and a variable vacuum drying stage based on the constant vacuum drying. The variable vacuum drying stage is achieved by introducing an inert gas into the drying equipment. The specific steps of the variable vacuum drying include: introducing dry nitrogen into the vacuum baking oven to de-vacuum the vacuum baking oven to atmospheric pressure, and maintaining nitrogen heating for 40 min to 60 min. The first vacuum drying task has a preset drying value and a second vacuum drying task has a preset drying value, wherein the first vacuum drying task value is greater than the second vacuum drying task value; the first vacuum drying task value is preset to be completely dried.

2. The vacuum drying method for the large square lithium battery electrode assembly according to claim 1, characterized in that, By controlling the first vacuum drying task value, the time of the first vacuum drying is 3 to 5 hours.

3. The vacuum drying method for the large square lithium battery electrode assembly according to claim 1, characterized in that, By controlling the value of the second vacuum drying task, the time of the second vacuum drying is 3 to 5 hours.

4. The vacuum drying method for the large square lithium battery electrode assembly according to claim 1, characterized in that, The entire vacuum drying time is 24–30 hours.

5. The vacuum drying method for the large square lithium battery electrode assembly according to claim 1, characterized in that, The preset value for the second vacuum drying task is no higher than 300 ppm.

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