A method of baking a lithium-ion battery cell

Abstract

The application provides a baking method of a lithium ion battery cell, comprising the following steps: (1) placing the lithium ion battery cell into a vacuum drying box; (2) vacuumizing; (3) heating; (4) continuously feeding nitrogen into the lithium ion battery cell, and controlling the absolute pressure in the lithium ion battery cell to be a first pressure, wherein the first pressure is lower than one standard atmosphere; (5) controlling the absolute pressure in the lithium ion battery cell to be a second pressure, wherein the second pressure is lower than the first pressure; (6) repeating step (5) for 1-6 times; (7) keeping the lithium ion battery cell in the vacuum state; (8) feeding nitrogen into the vacuum drying box, stopping heating, and completing baking. The application effectively improves the baking efficiency of the battery.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of battery manufacturing process, and relates to a baking method of a lithium ion battery cell. BACKGROUND

[0002] As a kind of electrochemical component with high energy density, the performance of lithium ion battery is seriously affected by internal moisture. In order to control the moisture content in the lithium ion battery, the lithium ion battery cell after assembly and before liquid injection is usually baked to make the internal moisture content lower than a certain threshold. The baking process takes a long time, and more baking equipment is often needed, which increases the manufacturing cost of lithium ion battery and hinders the improvement of the production efficiency of lithium ion battery.

[0003] The existing battery baking technology usually alternately carries out vacuum heating (60-120 min) and nitrogen charging and exhaust (1-2 min) at a heating temperature. The purpose of vacuum heating is to vaporize the moisture in the battery into water vapor, and the purpose of nitrogen charging and exhaust is to exhaust the water vapor formed in the heating process to improve the baking efficiency of the next stage of vacuum heating. Usually, vacuum heating is carried out for 120 min, and then nitrogen is charged and exhausted once, which needs to be alternately carried out for about 6 times, and takes about 12 hours.

[0004] For the baking process, researchers have proposed improvement measures from the aspects of equipment and process. For example, Chinese patent application CN106785066A proposes a lithium battery baking jig, which can contact multiple surfaces of the battery and provide heating conditions at the same time, thereby improving the efficiency of battery baking; Chinese patent application CN115014045A provides a lithium battery cell baking process, which realizes the reduction of battery moisture by multiple cycles of vacuum pumping and nitrogen charging at a heating temperature, and provides a nitrogen atmosphere during the heating and cooling processes to avoid the influence of water vapor and oxygen in the box on the cell materials.

[0005] However, battery baking is still one of the longest steps in the battery manufacturing process, and it is necessary to develop a new baking process to improve the efficiency of battery baking and thus improve the production efficiency of batteries. SUMMARY

[0006] The purpose of the present application is to shorten the baking process time of the cell as much as possible under the premise of ensuring the baking effect of the cell, to improve the baking efficiency of the cell, and thus to improve the production efficiency of the battery.

[0007] Specifically, the present application provides a baking method of a lithium ion battery cell, comprising the following steps:

[0008] (1) placing the lithium ion battery cell into a vacuum drying box, wherein the shell of the lithium ion battery cell has a gas inlet and a gas outlet;

[0009] (2) vacuumizing the vacuum drying oven so that the absolute pressure in the vacuum drying oven reaches 500 Pa or less;

[0010] (3) heating the lithium ion battery cell to 80-120°C and holding the temperature;

[0011] (4) continuously introducing nitrogen into the lithium ion battery cell through the gas inlet and discharging through the gas outlet to control the absolute pressure in the lithium ion battery cell to a first pressure, which is lower than one standard atmosphere, and holding the temperature and pressure for 30-60 min;

[0012] (5) adjusting the nitrogen introduction flow rate and the gas discharge flow rate to control the absolute pressure in the lithium ion battery cell to a second pressure, which is lower than the first pressure, and holding the temperature and pressure for 30-60 min;

[0013] (6) repeating step (5) 1-6 times, wherein the absolute pressure in the lithium ion battery cell is controlled to an (n+2)th pressure in the n-th repetition of step (5), which is lower than an (n+1)th pressure;

[0014] (7) stopping the introduction of nitrogen into the lithium ion battery cell, so that the lithium ion battery cell is in a vacuum state in the vacuum drying oven, and holding the temperature for 30-60 min;

[0015] (8) introducing nitrogen into the vacuum drying oven, stopping heating, and cooling the lithium ion battery cell to complete the baking.

[0016] In one or more embodiments, the gas inlet and the gas outlet of the lithium ion battery cell are connected to a gas inlet channel and a gas outlet channel, respectively, and the gas inlet channel and the gas outlet channel are in communication through a connecting passage outside the vacuum drying oven, and a drying device is arranged on the connecting passage.

[0017] In one or more embodiments, in step (4), the first pressure is 30±5 kPa, for example, 30±2 kPa.

[0018] In one or more embodiments, in step (5), the second pressure is 5-25 kPa, for example, 8-22 kPa.

[0019] In one or more embodiments, in step (6), the absolute pressure in the lithium ion battery cell is controlled to 5±1 kPa in the last repetition of step (5).

[0020] In one or more embodiments, in step (6), step (5) is repeated 1 or 2 times.

[0021] In one or more embodiments, in step (5), the second pressure is 10 ± 2 kPa; in step (6), step (5) is repeated once, and the third pressure is 5 ± 1 kPa.

[0022] In one or more embodiments, in step (5), the second pressure is 20 ± 5 kPa, for example, 20 ± 2 kPa; in step (6), step (5) is repeated twice, and the third pressure is 10 ± 2 kPa, and the fourth pressure is 5 ± 1 kPa.

[0023] In one or more embodiments, in step (7), the absolute pressure in the vacuum drying oven is below 500 Pa.

[0024] In one or more embodiments, in step (8), the heating is stopped after the absolute pressure in the vacuum drying oven reaches one standard atmosphere. DETAILED DESCRIPTION

[0025] To enable persons skilled in the art to understand the features and effects of the present application, the following is a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific words used in the text are of the usual meaning understood by those skilled in the art of the present application, and in the event of a conflict, the definition in the specification shall prevail.

[0026] Theories or mechanisms described and disclosed herein, whether correct or not, should not be considered limiting the scope of the present application, i.e., the present application can be implemented without regard to any particular theory or mechanism.

[0027] In this text, "comprising", "including", "containing", and similar phrases cover the meanings of "consisting essentially of" and "consisting of", for example, when this text discloses "A comprising B and C", "A consisting essentially of B and C" and "A consisting of B and C" should be considered to have been disclosed herein.

[0028] In this text, all features defined in the form of numerical ranges or percentage ranges, such as values, quantities, contents and concentrations, are for the sake of brevity and convenience. Therefore, the description of numerical ranges or percentage ranges should be considered to have covered and specifically disclosed all possible sub-ranges and individual values within the range (including integers and fractions).

[0029] In this text, unless otherwise specified, percentages refer to mass percentages, and ratios refer to mass ratios.

[0030] In the description herein, it is to be understood that the embodiments or examples are not intended to limit the present application to such embodiments or examples. Rather, all alternatives, modifications, and equivalents of the methods and materials described herein, made in the light of the present application, are to be included within the scope of claims.

[0031] In the description herein, all possible combinations between technical features in various embodiments or examples are not described in order to simplify the description. Therefore, as long as the combinations of technical features do not contradict each other, the technical features in various embodiments or examples can be combined in any manner, and all possible combinations should be considered as the scope described in the specification.

[0032] In the present application, during the baking process of the lithium ion battery cell, nitrogen is introduced into the cell while vacuum is applied, so as to realize the dynamic nitrogen negative pressure inside the cell. Firstly, the negative pressure is a nitrogen negative pressure, which does not hinder the vaporization of water in the battery; secondly, the negative pressure is a dynamic negative pressure, the water vapor generated by the vaporization of water in the cell is immediately taken away by the dynamic nitrogen, avoiding the decrease of the baking efficiency due to the retention of water vapor, thus the baking efficiency can be improved and the baking time can be shortened. Further, the gas inlet and the exhaust outlet on the shell of the lithium ion battery cell are connected with the gas inlet channel and the exhaust outlet channel respectively, the gas inlet channel and the exhaust outlet channel are connected outside the vacuum drying box, and a drying device is arranged on the connecting passage, so as to form an air flow loop between the internal space of the battery and the external nitrogen channel, and realize the recycling of nitrogen.

[0033] The baking method of the lithium ion battery cell of the present application comprises the following steps:

[0034] (1) placing the lithium ion battery cell into a vacuum drying box, wherein the shell of the lithium ion battery cell has a gas inlet and an exhaust outlet;

[0035] (2) vacuumizing the vacuum drying box, so as to make the absolute pressure in the vacuum drying box reach 500 Pa or below;

[0036] (3) heating the lithium ion battery cell to 80-120℃ and keeping the temperature;

[0037] (4) continuously introducing nitrogen into the lithium ion battery cell through the gas inlet, and discharging through the exhaust outlet, so as to control the absolute pressure in the lithium ion battery cell to a first pressure, wherein the first pressure is lower than one standard atmosphere, and keeping the temperature and pressure for 30-60 min;

[0038] (5) adjusting the nitrogen inlet flow and the exhaust flow to control the absolute pressure in the lithium ion battery cell to a second pressure, wherein the second pressure is lower than the first pressure, and keeping the temperature and pressure for 30-60 min;

[0039] (6) repeating step (5) 1-6 times, wherein the absolute pressure in the lithium ion battery cell in the nth repetition of step (5) is controlled to be a (n+2)th pressure, which is lower than a (n+1)th pressure;

[0040] (7) stopping the introduction of nitrogen into the lithium ion battery cell, allowing the lithium ion battery cell to be in a vacuum state of the vacuum drying box, and keeping the temperature for 30-60 min;

[0041] (8) introducing nitrogen into the vacuum drying box, stopping heating, and allowing the lithium ion battery cell to cool down, thereby completing the baking.

[0042] In the present application, the lithium ion battery cell has a gas inlet and a gas outlet on the shell of the lithium ion battery cell, which are used for introducing nitrogen into the lithium ion battery cell and discharging nitrogen, respectively. In a preferred embodiment, the gas inlet and the gas outlet on the shell of the lithium ion battery cell are connected to a gas inlet channel and a gas outlet channel, respectively, and the gas inlet channel and the gas outlet channel are connected through a connecting passage outside the vacuum drying box, and a drying device is arranged on the connecting passage, thereby forming a gas flow loop between the internal space of the lithium ion battery cell and the external nitrogen channel, and achieving the recycling of nitrogen.

[0043] In step (1), the assembled lithium ion battery cell can be first placed in a clamp and then placed in the vacuum drying box.

[0044] In step (2), the vacuum drying box is pre-evacuated to a vacuum degree of 500 Pa or less, for example, 0-500 Pa. In this document, the pressure value is absolute pressure unless otherwise specified.

[0045] In steps (3)-(7), the temperature of the lithium ion battery cell is maintained at 80-120°C, for example, 90°C, 100°C, or 110°C.

[0046] In step (4), nitrogen gas is continuously introduced into the interior of the lithium-ion battery cell to maintain a dynamic nitrogen gas negative pressure P1 (i.e., a first pressure) in the interior of the lithium-ion battery cell. Herein, the dynamic nitrogen gas negative pressure refers to that the absolute pressure in the interior of the lithium-ion battery cell is lower than one standard atmosphere, and the pressure is maintained by dynamic nitrogen gas. The present application removes water vapor formed by water vaporization in time by providing a dynamic nitrogen gas negative pressure in the interior of the cell. In some embodiments, the gas inlet channel and the gas outlet channel are connected to the gas inlet and the gas outlet of the lithium-ion battery cell, respectively, and nitrogen gas is circulated to maintain a dynamic nitrogen gas negative pressure P1 in the interior of the battery. In some preferred embodiments, the dynamic nitrogen gas negative pressure P1 (i.e., the first pressure) is 30±5 kPa, preferably 30±2 kPa, for example, 26 kPa, 27 kPa, 28 kPa, 29 kPa, 30 kPa, 31 kPa, 32 kPa, 33 kPa, or 34 kPa. Controlling the dynamic nitrogen gas negative pressure P1 in the above range is advantageous for improving the cell baking efficiency. In step (4), the dynamic nitrogen gas negative pressure P1 and the temperature in the cell are preferably maintained for 30-60 min, for example, 40 min or 50 min. Controlling the time for maintaining the pressure in step (4) in the range of 30-60 min is advantageous for improving the cell baking efficiency.

[0047] In step (5), the nitrogen gas flow rate and the gas outlet flow rate are adjusted to maintain a dynamic nitrogen gas negative pressure P2 (i.e., a second pressure) in the interior of the lithium-ion battery cell. In some embodiments, the nitrogen gas flow rate in the gas inlet channel and the gas outlet channel is adjusted to reduce the dynamic nitrogen gas negative pressure in the interior of the battery to P2. The dynamic nitrogen gas negative pressure P2 is lower than the dynamic nitrogen gas negative pressure P1, which is advantageous for improving the cell baking efficiency. In some preferred embodiments, the dynamic nitrogen gas negative pressure P2 (i.e., the second pressure) is 5-25 kPa, preferably 8-22 kPa, for example, 8 kPa, 10 kPa, 12 kPa, 15 kPa, 18 kPa, 20 kPa, or 22 kPa. Controlling the dynamic nitrogen gas negative pressure P2 in the above range is advantageous for improving the cell baking efficiency. In step (5), the dynamic nitrogen gas negative pressure P2 and the temperature in the cell are preferably maintained for 30-60 min, for example, 40 min or 50 min. Controlling the time for maintaining the pressure in step (5) in the range of 30-60 min is advantageous for improving the cell baking efficiency.

[0048] In step (6), step (5) can be repeated 1, 2, 3, 4, 5 or 6 times. Each time step (5) is performed, the nitrogen flow in the cell is gradually reduced by adjusting the nitrogen inlet flow and the exhaust flow, so that the dynamic nitrogen negative pressure in the cell is lower than that in the previous step (5). Specifically, the absolute pressure in the lithium ion battery cell in the nth repeated step (5) is the (n+2)th pressure, and the (n+2)th pressure needs to be lower than the (n+1)th pressure, i.e. the third pressure is lower than the second pressure, the fourth pressure is lower than the third pressure, and so on. Gradually reducing the dynamic nitrogen negative pressure in the cell is beneficial to improve the cell baking efficiency. The time for holding pressure in each repeated step (5) is preferably controlled at 30-60 min, for example 40 min, 50 min, which is beneficial to improve the cell baking efficiency. The number of times step (5) is repeated and the dynamic nitrogen negative pressure value in each repetition can be set as needed. For example, the difference between the dynamic nitrogen negative pressure in the two repeated steps (5) can be 1-20 kPa, for example 2-15 kPa, 2-10 kPa, which is beneficial to improve the cell baking efficiency. Preferably, the dynamic nitrogen negative pressure in the lithium ion battery cell in the last repeated step (5) is controlled to be 5±1 kPa, which is beneficial to improve the cell baking efficiency.

[0049] In step (6), step (5) is repeated only once, the second pressure in step (5) is preferably 10±2 kPa. In step (6), step (5) is repeated 2 or more times, the second pressure in step (5) is preferably 20±5 kPa, for example 20±2 kPa.

[0050] In some preferred embodiments, in step (6), step (5) is repeated 1 or 2 times, which is beneficial to shorten the baking time while ensuring the baking effect and improve the production efficiency. When step (5) is repeated only once, preferably, the second pressure in step (5) is 10±2 kPa, and the third pressure in the first repeated step (5) in step (6) is 5±1 kPa, which is beneficial to improve the cell baking efficiency. When step (5) is repeated only twice, preferably, the second pressure in step (5) is 20±5 kPa, preferably 20±2 kPa, the third pressure in the first repeated step (5) in step (6) is 10±2 kPa, preferably 10±1 kPa, and the fourth pressure in the second repeated step (5) is 5±1 kPa, which is beneficial to improve the cell baking efficiency.

[0051] In step (7), the gas inlet channel and the exhaust channel can be removed, so that the cell is in a vacuum environment of the drying box. The absolute pressure in the vacuum drying box is preferably below 500 Pa, for example 0-500 Pa. The cell is kept at the heating temperature for 30-60 min in the vacuum environment.

[0052] In step (8), nitrogen is introduced into the vacuum drying oven, preferably after the absolute pressure in the vacuum drying oven reaches one standard atmosphere, heating is stopped, the battery cell is cooled, and the baking process is completed.

[0053] In some embodiments, the baking method of the lithium ion battery cell of the present application comprises the following steps:

[0054] (1) The assembled lithium ion battery cell is placed in a clamp and then placed in a vacuum drying oven;

[0055] (2) The vacuum drying oven is pre-evacuated to a vacuum degree of 500 Pa or less;

[0056] (3) The lithium ion battery cell is heated to a temperature of 80-120°C and then kept at this temperature;

[0057] (4) The gas inlet and the gas outlet of the lithium ion battery cell are connected to the gas inlet channel and the gas outlet channel, respectively, and nitrogen is circulated to maintain a certain dynamic nitrogen negative pressure P1 in the lithium ion battery cell, P1 is less than one standard atmosphere, and the process is maintained for 30-60 min;

[0058] (5) The nitrogen flow in the gas inlet channel and the gas outlet channel is adjusted to reduce the nitrogen negative pressure in the lithium ion battery cell to P2, P2 is less than P1, and the process is maintained for 30-60 min;

[0059] (6) Step (5) is repeated 1-6 times to gradually reduce the nitrogen flow and reduce the nitrogen negative pressure in the lithium ion battery cell;

[0060] (7) The gas inlet channel and the gas outlet channel are removed, the lithium ion battery cell is placed in the vacuum environment of the vacuum drying oven, and the heating temperature is maintained for 30-60 min;

[0061] (8) Nitrogen is introduced into the vacuum drying oven, heating is stopped, the lithium ion battery cell is cooled, and the baking process is completed.

[0062] The baking efficiency of the prior art decreases in the second half of the vacuum heating. Compared with the prior art, the lithium ion battery cell baking process provided by the present application can provide a dynamic nitrogen negative pressure in the battery cell, which can immediately remove the water vapor generated by the vaporization of the water in the battery cell, thereby avoiding the decrease in baking efficiency caused by the retention of water vapor, and improving the battery production efficiency.

[0063] The present application will be described in detail below with specific examples. It should be understood that these examples are merely illustrative and are not intended to limit the scope of the present application. The methods, reagents and materials used in the examples are conventional in the art unless otherwise specified. The raw compounds in the examples can be purchased through commercial channels.

[0064] Example 1

[0065] The lithium ion battery cell is baked by the following process in this example:

[0066] (1) Put the assembled lithium ion battery cell into the fixture and into the vacuum drying oven;

[0067] (2) Pre-evacuate the vacuum drying oven to make its vacuum degree (absolute pressure) reach below 500 Pa;

[0068] (3) Heat the lithium ion battery cell to make it reach 90℃ and keep the temperature;

[0069] (4) Connect the charging passage and the exhaust passage to the charging port and the exhaust port on the lithium ion battery cell shell respectively, and make the charging passage and the exhaust passage communicate through the connecting passage outside the vacuum drying oven, set the drying device on the connecting passage, and circulate nitrogen to make the internal dynamic nitrogen negative pressure (absolute pressure) of the lithium ion battery cell reach 30 kPa and keep for 60 min;

[0070] (5) Adjust the nitrogen flow in the charging passage and the exhaust passage to reduce the internal dynamic nitrogen negative pressure of the lithium ion battery cell to 10 kPa and keep for 60 min;

[0071] (6) Adjust the nitrogen flow in the charging passage and the exhaust passage to reduce the internal dynamic nitrogen negative pressure of the lithium ion battery cell to 5 kPa and keep for 60 min;

[0072] (7) Remove the charging passage and the exhaust passage to make the lithium ion battery cell in the vacuum environment (absolute pressure below 500 Pa) of the vacuum drying oven and keep the heating temperature for 60 min;

[0073] (8) Fill nitrogen in the vacuum drying oven to make it reach one standard atmosphere, stop heating, and make the lithium ion battery cell cool down to complete the baking.

[0074] Example 2

[0075] The lithium ion battery cell is baked by the following process in this example:

[0076] (1) Put the assembled lithium ion battery cell into the fixture and into the vacuum drying oven;

[0077] (2) Pre-evacuate the vacuum drying oven to make its vacuum degree reach below 500 Pa;

[0078] (3) Heat the lithium ion battery cell to make it reach 80℃ and keep the temperature;

[0079] (4) connect the gas inlet and the exhaust outlet on the lithium ion battery cell shell with the gas inlet channel and the exhaust outlet channel respectively, and make the lithium ion battery cell maintain a dynamic nitrogen negative pressure of 30 kPa for 60 min by connecting the gas inlet channel and the exhaust outlet channel through a connecting passage outside the vacuum drying box, setting a drying device on the connecting passage, and circulating nitrogen;

[0080] (5) adjust the nitrogen flow in the gas inlet channel and the exhaust outlet channel, reduce the dynamic nitrogen negative pressure in the lithium ion battery cell to 20 kPa, and maintain for 60 min;

[0081] (6) adjust the nitrogen flow in the gas inlet channel and the exhaust outlet channel, reduce the dynamic nitrogen negative pressure in the lithium ion battery cell to 10 kPa, and maintain for 60 min;

[0082] (7) adjust the nitrogen flow in the gas inlet channel and the exhaust outlet channel, reduce the dynamic nitrogen negative pressure in the lithium ion battery cell to 5 kPa, and maintain for 60 min;

[0083] (8) remove the gas inlet channel and the exhaust outlet channel, and make the lithium ion battery cell in the vacuum environment (absolute pressure below 500 Pa) of the vacuum drying box, and maintain the heating temperature for 60 min;

[0084] (9) fill nitrogen in the vacuum drying box to reach a standard atmospheric pressure, stop heating, and cool down the lithium ion battery cell to complete the baking.

[0085] Example 3

[0086] The lithium ion battery cell is baked by the following process in this example:

[0087] (1) place the assembled lithium ion battery cell in the clamp, and put it into the vacuum drying box;

[0088] (2) pre-evacuate the vacuum drying box to make the vacuum degree below 500 Pa;

[0089] (3) heat the lithium ion battery cell to 110℃, and maintain the temperature;

[0090] (4) connect the gas inlet and the exhaust outlet on the lithium ion battery cell shell with the gas inlet channel and the exhaust outlet channel respectively, and make the lithium ion battery cell maintain a dynamic nitrogen negative pressure of 30 kPa for 30 min by connecting the gas inlet channel and the exhaust outlet channel through a connecting passage outside the vacuum drying box, setting a drying device on the connecting passage, and circulating nitrogen;

[0091] (5) adjust the nitrogen flow in the gas inlet channel and the exhaust outlet channel, reduce the dynamic nitrogen negative pressure in the lithium ion battery cell to 20 kPa, and maintain for 30 min;

[0092] (6) Adjust the nitrogen flow in the charging channel and the exhaust channel, reduce the dynamic nitrogen negative pressure in the lithium ion battery cell to 10 kPa, and maintain for 30 min;

[0093] (7) Adjust the nitrogen flow in the charging channel and the exhaust channel, reduce the dynamic nitrogen negative pressure in the lithium ion battery cell to 5 kPa, and maintain for 30 min;

[0094] (8) Remove the charging channel and the exhaust channel, so that the lithium ion battery cell is in a vacuum environment (absolute pressure below 500 Pa) in the vacuum drying box, and maintain the heating temperature for 60 min;

[0095] (9) Fill nitrogen in the vacuum drying box to reach a standard atmospheric pressure, stop heating, and cool down the lithium ion battery cell to complete the baking.

[0096] Example 4

[0097] The lithium ion battery cell is baked by the following process in this example:

[0098] (1) Put the assembled lithium ion battery cell into the clamp and into the vacuum drying box;

[0099] (2) Pre-evacuate the vacuum drying box to make its vacuum degree reach below 500 Pa;

[0100] (3) Heat the lithium ion battery cell to make it rise to 120℃, and perform temperature maintenance;

[0101] (4) Connect the charging channel and the exhaust channel with the charging port and the exhaust port on the lithium ion battery cell shell respectively, and the charging channel and the exhaust channel are connected through the connecting passage outside the vacuum drying box, a drying device is arranged on the connecting passage, and nitrogen circulation is performed to make the internal dynamic nitrogen negative pressure of the lithium ion battery cell maintain at 30 kPa for 30 min;

[0102] (5) Adjust the nitrogen flow in the charging channel and the exhaust channel, reduce the dynamic nitrogen negative pressure in the lithium ion battery cell to 10 kPa, and maintain for 30 min;

[0103] (6) Adjust the nitrogen flow in the charging channel and the exhaust channel, reduce the dynamic nitrogen negative pressure in the lithium ion battery cell to 5 kPa, and maintain for 30 min;

[0104] (7) Remove the charging channel and the exhaust channel, so that the lithium ion battery cell is in a vacuum environment (absolute pressure below 500 Pa) in the vacuum drying box, and maintain the heating temperature for 60 min;

[0105] (7) The vacuum drying oven is filled with nitrogen to reach one standard atmosphere, heating is stopped, and the lithium ion battery cell is cooled to complete the baking.

[0106] Comparative Example 1

[0107] The lithium ion battery cell is baked by the following process in the present comparative example:

[0108] (1) The assembled lithium ion battery cell is placed in a clamp and put into a vacuum drying oven;

[0109] (2) The vacuum drying oven is pre-evacuated to a vacuum degree of 500 Pa or less;

[0110] (3) The lithium ion battery cell is heated to 90°C and kept at this temperature;

[0111] (4) Nitrogen is filled in the vacuum drying oven to reach 90 kPa, and the pressure is maintained for 2 min;

[0112] (5) The vacuum drying oven is evacuated to a vacuum degree of 500 Pa or less, and the pressure is maintained for 120 min;

[0113] (6) Steps (4) to (5) are repeated 6 times;

[0114] (7) The vacuum drying oven is filled with nitrogen to reach one standard atmosphere, heating is stopped, and the lithium ion battery cell is cooled to complete the baking.

[0115] Comparative Example 2

[0116] The lithium ion battery cell is baked by the following process in the present comparative example:

[0117] (1) A nitrogen inlet, a gas permeable baffle and a heating device are arranged at the bottom of the vacuum drying oven, and a nitrogen outlet is arranged at the top;

[0118] (2) The assembled lithium ion battery cell is placed in the vacuum drying oven, and the vacuum is extracted to 500 Pa. The temperature in the vacuum drying oven is heated to 90°C by the heating device;

[0119] (3) Nitrogen is introduced into the vacuum drying oven through the nitrogen inlet, and the vacuum degree in the hollow drying oven is maintained at 5 kPa. The temperature in the vacuum drying oven is maintained at 90°C for 4 h;

[0120] (4) Nitrogen is introduced into the vacuum drying oven to one standard atmosphere, and heating is stopped to cool the lithium ion battery cell to complete the baking.

[0121] Test Example

[0122] Take in the shell after welding 50 Ah battery 30, divided into 6 groups, each group 5, respectively according to the process of example 1-4 and comparative example 1-2 is baked, and the mass m1 before baking and the mass m2 after baking are weighed. According to the mass m1 and m2, the average relative weight loss of the battery after baking is calculated, as shown in table 1. Relative weight loss = (m1-m2) / m1*100%.

[0123] Table 1: relative weight loss of battery after baking

[0124]

[0125] As shown in table 1, comparative example 1 uses the method of vacuum baking and nitrogen charging exhaust alternately. In the later stage of vacuum baking, due to the water vaporization, the baking efficiency is not high, and after 6 cycles, the final relative weight loss is 0.0148%. Examples 1-4 use dynamic nitrogen negative pressure at different temperatures for baking, and the water vapor formed by water vaporization can be immediately discharged, so it is always in a high-efficiency baking state. The relative weight loss after baking is higher than that of comparative example 1, indicating the effectiveness of examples 1-4. At the same time, it can be seen that the baking time of examples 1-4 is much lower than that of comparative example 1, indicating that the baking process of the present application can significantly improve the baking efficiency and production efficiency.

[0126] Comparative example 2 uses a single dynamic negative pressure to maintain the whole oven for battery baking. Compared with comparative example 1, it uses dynamic nitrogen negative pressure to discharge the water vapor formed during battery baking, so the baking efficiency is better than that of comparative example 1. But in the baking process, the water content in the battery gradually decreases, and the water vapor formation rate gradually decreases, so a single dynamic negative pressure cannot match the exhaust demand of each stage in the baking process. Examples 1-4 use a ladder dynamic negative pressure, in the early stage of baking, the water content in the battery is high, and the water vapor formed is more, so a larger nitrogen negative pressure is used to quickly discharge the water vapor formed. With the progress of baking, the water vapor formation rate slows down, so a lower nitrogen negative pressure is used for exhaust. Compared with comparative example 2, examples 1-4 use a ladder nitrogen negative pressure for exhaust according to the water vapor formation rate, which can more effectively improve the baking efficiency and reduce the baking process time. And unlike comparative example 2, which maintains nitrogen negative pressure on the whole oven, examples 1-4 can directly control the dynamic nitrogen negative pressure inside the battery shell through the air inlet and exhaust outlet, so they have better exhaust effect and higher baking efficiency.

Claims

1. A method of baking a lithium-ion battery cell, characterized by, The method comprises the following steps: (1) placing a lithium ion battery cell into a vacuum drying oven, the lithium ion battery cell having a gas inlet and a gas outlet; (2) vacuumizing the vacuum drying oven to make the absolute pressure in the vacuum drying oven reach 500 Pa or less; (3) heating the lithium ion battery cell to 80-120 ℃ and keeping the temperature; (4) continuously feeding nitrogen into the lithium ion battery cell through the gas inlet and discharging gas through the gas outlet to control the absolute pressure in the lithium ion battery cell to a first pressure, the first pressure being lower than one standard atmosphere, and keeping the temperature and pressure for 30-60 min; (5) adjusting the nitrogen feeding flow and the gas discharging flow to control the absolute pressure in the lithium ion battery cell to a second pressure, the second pressure being lower than the first pressure, and keeping the temperature and pressure for 30-60 min; (6) repeating step (5) for 1-6 times, wherein the absolute pressure in the lithium ion battery cell is controlled to an n+2th pressure in the nth repeating step (5), the n+2th pressure being lower than the n+1th pressure; (7) stopping feeding nitrogen into the lithium ion battery cell, keeping the lithium ion battery cell in the vacuum state of the vacuum drying oven, and keeping the temperature for 30-60 min; (8) feeding nitrogen into the vacuum drying oven, stopping heating, and cooling the lithium ion battery cell to complete the baking; in step (4), the first pressure is 30±5 kPa; in step (5), the second pressure is 5-25 kPa; in step (6), the absolute pressure in the lithium ion battery cell is controlled to 5±1 kPa in the last repeating step (5).

2. The method of baking a lithium-ion battery cell of claim 1, wherein, The gas inlet and the gas outlet of the lithium ion battery cell are connected with a gas feeding channel and a gas discharging channel respectively, the gas feeding channel and the gas discharging channel are communicated through a connecting passage outside the vacuum drying oven, and a drying device is arranged on the connecting passage.

3. The method of baking a lithium-ion battery cell of claim 1, wherein, in step (4), the first pressure is 30±2 kPa.

4. The method of baking a lithium-ion battery cell of claim 1, wherein, in step (5), the second pressure is 8-22 kPa.

5. The method of baking a lithium-ion battery cell of claim 1, wherein, in step (6), step (5) is repeated for 1 or 2 times.

6. The method of baking a lithium-ion battery cell of claim 1, wherein, in step (5), the second pressure is 10±2 kPa; in step (6), step (5) is repeated for 1 time, and the third pressure is 5±1 kPa.

7. The method of baking a lithium-ion battery cell of claim 1, wherein, in step (5), the second pressure is 20±5 kPa; in step (6), step (5) is repeated for 2 times, the third pressure is 10±2 kPa, and the fourth pressure is 5±1 kPa.

8. The method of baking a lithium-ion battery cell of claim 1, wherein, in step (5), the second pressure is 20±2 kPa; in step (6), step (5) is repeated for 2 times, the third pressure is 10±2 kPa, and the fourth pressure is 5±1 kPa.

9. The method of baking a lithium-ion battery cell of claim 1, wherein, in step (7), the absolute pressure in the vacuum drying oven is 500 Pa or less.

10. The method of baking a lithium-ion battery cell of claim 1, wherein, in step (8), the heating is stopped after the absolute pressure in the vacuum drying oven reaches one standard atmosphere.

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