A method for detecting moisture content in lithium batteries

Abstract

The present invention provides a method for detecting moisture levels in lithium batteries, comprising: filling a baking chamber with dry inert gas until the pressure inside the chamber exceeds standard atmospheric pressure, then stopping the filling; heating and maintaining the pressure for a predetermined period of time to ensure thorough mixing of the gases within the baking chamber; initially evacuating the baking chamber, controlling the vacuum value within the baking chamber to 0.5 to 0.8 times the standard atmospheric pressure, and then heating and maintaining the pressure for a predetermined period of time; evacuating the baking chamber again, each time decreasing the vacuum value within the baking chamber until the vacuum value decreases to between 100 and 150 Pa, and then heating and maintaining the pressure for a predetermined period of time; collecting pressure values ​​corresponding to different time points and fitting them into a pressure-time curve. When the pressure curve meets preset conditions, recording the measured humidity value of a dew point meter placed within the baking chamber, and outputting a compensated humidity value based on the measured humidity value. By alternating the baking chamber between positive and negative pressures, the present invention improves water removal efficiency, making the moisture detection value closer to the actual value.

Description

Technical Field

[0001] The present invention generally relates to the field of lithium battery technology. More specifically, the present invention relates to a method for detecting the moisture content of a lithium battery. Background Art

[0002] Lithium batteries are a type of battery that uses lithium metal or lithium alloys as the positive and negative electrode materials and a non-aqueous electrolyte solution. They have advantages such as high energy density, long cycle life, and low self-discharge rate. Domestic lithium battery technology is mainly used in the new energy vehicle industry and the energy storage industry.

[0003] The negative pressure baking process for lithium batteries is a manufacturing process designed to improve battery safety and performance. This process is primarily used in the drying process of lithium battery cells during production. Its purpose is to effectively remove moisture from the cells, preventing it from reacting with the electrolyte during subsequent high-temperature processing or use, generating harmful gases or degrading battery performance. Before baking, baking equipment must set fixed baking parameters based on the characteristics of the material being baked, such as baking temperature, maximum vacuum, minimum vacuum, and baking time. Due to the large pressure fluctuations within the baking chamber during the baking process, it is impossible to use equipment such as a dew point meter to directly monitor the moisture concentration in the chamber in real time.

[0004] One current method for detecting moisture content is to remove the test batteries from the tray after baking and test their moisture content. The battery can only proceed to the next production process if the moisture content is lower than the expected value. This is the most traditional method for detecting moisture content. Another method for determining moisture content is to collect the pressure value in the baking chamber and establish a mathematical model based on the pressure value to determine whether the moisture value after baking meets the standard. However, this method cannot directly obtain the specific moisture value. Due to the superposition of various objective factors, this judgment method cannot exempt the moisture content value from detection, but only makes an advance judgment in theory. Therefore, in order to ensure that the moisture content value after baking meets the requirements, the moisture content value still needs to be tested after baking, and it does not actually improve production efficiency.

[0005] In view of this, there is an urgent need to provide a method for detecting the moisture content of a lithium battery to solve the above problems. Summary of the Invention

[0006] In order to at least solve one or more technical problems in the above background technology, the present invention proposes a method for detecting the moisture value of a lithium battery.

[0007] To this end, the present invention provides the following technical solutions.

[0008] The present invention discloses a method for detecting the moisture content of a lithium battery, comprising:

[0009] S1: Keeping the baking chamber sealed, and filling it with dry inert gas until the pressure inside the chamber exceeds the standard atmospheric pressure, then stopping the filling; heating the baking chamber to a first preset temperature and maintaining it for a first preset time to allow the gas in the baking chamber to be fully mixed;

[0010] S2: evacuating the baking chamber for the first time, controlling the vacuum value in the baking chamber to be 0.5 to 0.8 times the standard atmospheric pressure, heating to a second preset temperature and maintaining the temperature for a second preset time; thereafter, filling the baking chamber with dry inert gas until the pressure therein exceeds the standard atmospheric pressure, and then stopping the filling;

[0011] S3: Evacuating the baking chamber again, with each vacuuming step decreasing the vacuum value in the baking chamber compared to the previous vacuuming step, heating the chamber to a second preset temperature and maintaining the temperature for a second preset time; thereafter, filling the baking chamber with dry inert gas until the pressure therein exceeds standard atmospheric pressure, and then stopping the filling;

[0012] S4: Repeat step S3;

[0013] S5: until the vacuum value decreases to between 100 and 150 Pa, and the vacuum value of the next vacuuming does not decrease compared to the previous vacuuming value; the baking chamber is heated to a second preset temperature and maintained for a second preset time; thereafter, dry inert gas is filled into the baking chamber until the pressure therein exceeds standard atmospheric pressure, and then the filling is stopped;

[0014] S6: continuing to evacuate the baking chamber until the vacuum value is controlled between 100 and 150 Pa, heating the baking chamber to a second preset temperature and maintaining the temperature for a second preset time; thereafter, filling the baking chamber with dry inert gas until the pressure therein exceeds standard atmospheric pressure, and then stopping the filling;

[0015] S7: collecting the pressure values ​​corresponding to different time points in the above steps to obtain continuously changing discrete pressure-time data points, and fitting the discrete data points into a pressure-time curve using a mathematical method;

[0016] S8: On the pressure-time curve, obtain the current acquisition time point and the previous acquisition time point and their corresponding pressure values;

[0017] S9: When a preset condition is met, a test humidity value of a dew point meter placed in the baking chamber is recorded, and a compensation humidity value is output according to the test humidity value.

[0018] Preferably, in each of the aforementioned steps, dry inert gas is filled into the baking chamber until the pressure therein is higher than the standard atmospheric pressure. After heating to the first preset temperature and maintaining the first preset time, the maximum pressure value in the baking chamber does not exceed 1.05 times the standard atmospheric pressure.

[0019] Preferably, the first preset temperature is 50-60 degrees Celsius, and the first preset time does not exceed 5 minutes; if the pressure value in the baking chamber is about to reach 1.05 times the standard atmospheric pressure during heating within the first preset time, heating is stopped and the baking chamber is vacuumed.

[0020] Preferably, in step S3, the decreasing trend is that the vacuum value of each vacuuming is 0.5 to 0.8 times the vacuum value of the previous vacuuming.

[0021] Preferably, the second preset temperature is 100-120 degrees Celsius, and the second preset time is 15 minutes.

[0022] Preferably, satisfying the preset condition in step S9 includes: calculating the pressure change rate based on the data collected in step S8, and when the pressure change rate is not greater than a preset value, it is considered that the preset condition is satisfied;

[0023] Alternatively, according to the data collected in step S8, the changing trend of the pressure value is monitored. If the pressure value in the baking chamber does not reach the set pressure upper limit within the set time, it is also considered that the preset condition is met.

[0024] Preferably, the preset value is 0.04.

[0025] Preferably, the set time is 5 minutes, and the set pressure upper limit is 1.1 times the last vacuum value.

[0026] Preferably, the compensation humidity value is outputted by establishing a humidity conversion function:

[0027] ;in, is the test humidity value recorded by the dew point meter, To record the real-time pressure in the baking chamber when the humidity value is tested, is the molar mass of water vapor, is the molar constant of the gas, is the temperature inside the baking chamber;

[0028] Substitute the test humidity value into the above function to obtain the compensated humidity value.

[0029] The technical solution provided by this application may have the following beneficial effects:

[0030] By utilizing the device described in the above-mentioned embodiments of the present invention and its multiple schemes, that is, the present invention can repeatedly evacuate the vacuum and then fill the baking chamber with dry inert gas again until the pressure value therein is higher than the standard atmospheric pressure, and then stop filling the gas. Moreover, each time the vacuum is evacuated, the vacuum value in the baking chamber tends to decrease compared with the value of the previous vacuum evacuation. That is, the entire baking process includes vacuum evacuation and intermittent filling of excess dry inert gas, which can effectively reduce the probability of leakage from the outside into the baking chamber under the negative pressure state during the entire baking process, and effectively reduce the heavy burden on the baking equipment itself caused by the continuous negative pressure state in the baking chamber; each time the vacuum is evacuated, the vacuum value in the baking chamber tends to decrease compared with the value of the previous vacuum evacuation. The decreasing trend of the vacuum value can improve the equipment's tolerance to negative pressure environments and reduce the probability of box leakage; intermittent overfilling of dry inert gas can fully mix water vapor with the overfilled dry inert gas, so that during the next negative pressure extraction process, as much water vapor as possible can be carried out of the baking chamber. That is, the advantage of filling the baking chamber with excessive dry inert gas to periodically put it in a positive pressure state is that the overfilled inert gas can be used to carry as much water vapor in the baking chamber as possible; intermittent negative pressure extraction, so that the baking chamber is in a negative pressure state, helps the liquid water in the lithium battery to evaporate faster even in a non-heated high-temperature state, and then be carried out of the baking chamber by the subsequent overfilled dry inert gas.

[0031] The moisture value detection method proposed in the present invention improves the water removal effect by alternating the baking chamber between positive pressure and negative pressure, making the moisture detection value closer to the actual value; in addition, the method proposed in the present invention helps to quickly remove water during the moisture value detection process to improve the moisture value detection efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The above and other objects, features and advantages of the exemplary embodiments of the present invention will become readily understood by reading the detailed description below with reference to the accompanying drawings. In the accompanying drawings, several embodiments of the present invention are shown in an exemplary and non-limiting manner, and the same or corresponding reference numerals represent the same or corresponding parts.

[0033] Figure 1 It is a flow chart showing one embodiment of the present invention. DETAILED DESCRIPTION

[0034] The embodiments will now be described with reference to the accompanying drawings. It should be understood that for simplicity and clarity of explanation, reference numerals may be repeated in the accompanying drawings to indicate corresponding or similar elements, where deemed appropriate. In addition, the present invention sets forth many specific details in order to provide a thorough understanding of the embodiments described herein. However, one of ordinary skill in the art will understand that the embodiments described herein can be practiced without these specific details. In other cases, well-known methods, processes, and components are not described in detail so as not to obscure the embodiments described herein. Moreover, this description should not be construed as limiting the scope of the embodiments described herein.

[0035] According to one embodiment of the present invention, a method for detecting the moisture content of a lithium battery is provided, comprising the following steps:

[0036] S1: Keeping the baking chamber sealed, and filling it with dry inert gas until the pressure inside exceeds the standard atmospheric pressure, then stopping the filling; heating the baking chamber to a first preset temperature and maintaining it for a first preset time to allow the gas in the baking chamber to be fully mixed;

[0037] S2: evacuating the baking chamber for the first time, controlling the vacuum value in the baking chamber to be 0.5 to 0.8 times the standard atmospheric pressure, heating to a second preset temperature and maintaining the temperature for a second preset time; thereafter, filling the baking chamber with dry inert gas until the pressure therein exceeds the standard atmospheric pressure, and then stopping the filling;

[0038] S3: Evacuating the baking chamber again, with each vacuuming step decreasing the vacuum value in the baking chamber from the previous vacuuming value, heating the chamber to a second preset temperature and maintaining the temperature for a second preset time; thereafter, filling the baking chamber with dry inert gas until the pressure therein exceeds standard atmospheric pressure, and then stopping the filling;

[0039] S4: Repeat step S3;

[0040] S5: until the vacuum value decreases to between 100 and 150 Pa, and the vacuum value of the next vacuuming does not decrease compared to the previous vacuuming value; heating the baking chamber to a second preset temperature and maintaining it for a second preset time; thereafter, filling the baking chamber with dry inert gas until the pressure therein exceeds standard atmospheric pressure, and then stopping the filling;

[0041] S6: continuing to evacuate the baking chamber until the vacuum value is controlled between 100 and 150 Pa, heating the baking chamber to a second preset temperature and maintaining the temperature for a second preset time; thereafter, filling the baking chamber with dry inert gas until the pressure therein exceeds standard atmospheric pressure, and then stopping the filling;

[0042] S7: collecting the pressure values ​​corresponding to different time points in the above steps to obtain continuously changing pressure-time discrete data points, and fitting the discrete data points into a pressure-time curve using mathematical methods;

[0043] S8: On the pressure-time curve, obtain the current acquisition time point and the previous acquisition time point and their corresponding pressure values;

[0044] S9: When the preset conditions are met, the test humidity value of the dew point meter placed in the baking chamber is recorded, and a compensation humidity value is output according to the test humidity value.

[0045] The inert dry gas mentioned in step S1 of the above embodiment and other embodiments of this specification may be dry nitrogen.

[0046] In the foregoing and subsequent steps, dry inert gas is filled into the baking chamber until the pressure therein is higher than the standard atmospheric pressure. After heating to a first preset temperature and maintaining it for a first preset time, the maximum pressure value in the baking chamber does not exceed 1.05 times the standard atmospheric pressure.

[0047] Since the baking chamber of the baking equipment is in a state of alternating positive and negative pressure when implementing the method of the present invention, in order to reduce the impact of pressure changes in the baking chamber on the baking equipment and reduce the stringent structural requirements of the baking equipment, during the process of filling with dry inert gas and heating and maintaining the first preset time, it is necessary to control the pressure value in the baking chamber to not exceed 1.05 times the standard atmospheric pressure, thereby reducing the manufacturing cost of the baking equipment.

[0048] In one embodiment, the first preset temperature is 50-60 degrees Celsius, and the first preset time is no more than 5 minutes. The heating method can be to use an aluminum heating plate for heating, and when the inert dry gas is introduced, it is passed through the heating coil to achieve heating of the baking chamber. The main purpose of heating and maintaining the first preset time after the inert dry gas is first filled into the baking chamber is to fully mix the gas in the baking chamber so as to carry as much water vapor and oxygen and other interfering gases that affect baking as possible when the negative pressure is pumped. Therefore, when heating, the first preset temperature is set at about 50-60 degrees Celsius and work is done on the gas in the baking chamber to increase its internal energy, thereby increasing the molecular kinetic energy of the gas in the baking chamber, and then fully mixing the gas; the first preset temperature should not be too high to avoid the baked lithium battery or battery cell pole coil being oxidized by the oxygen in the baking chamber.

[0049] It should be noted that if the pressure value in the baking chamber is about to reach 1.05 times the standard atmospheric pressure during heating within the first preset time, heating is stopped and the baking chamber is evacuated.

[0050] In step S2, the baking chamber is vacuumed for the first time, and the vacuum value in the baking chamber is controlled to be 0.5 to 0.8 times the standard atmospheric pressure. This step is the beginning of decreasing the vacuuming of the baking chamber.

[0051] In the subsequent step S3, each time the vacuum is pumped, the vacuum value in the baking chamber shows a decreasing trend compared with the previous vacuum value, and the decreasing trend is also that the vacuum value of each vacuum is 0.5 to 0.8 times the previous vacuum value, until the vacuum value at the last vacuum is reduced to between 100 and 150 Pa. In the subsequent vacuuming, the vacuum value in the baking chamber will no longer decrease compared with the vacuum value at the last vacuum, and can maintain the same value as the vacuum value at the last vacuum, or can control the vacuum value between 100 and 150 Pa when continuing to vacuum.

[0052] In one embodiment, the second preset temperature is 100-120 degrees Celsius, and the second preset time is 15 minutes.

[0053] Since the baking chamber is gradually vacuumed until the vacuum value reaches about 100 Pa, there is no medium such as inert gas in the baking chamber or the amount of inert gas present is very small. In order to heat the baking chamber to a second preset temperature of 100-120 degrees Celsius, the heating method here can be contact heating, that is, heating using an aluminum heating plate. The second preset time of 15 minutes is maintained in order to fully evaporate the liquid water in the lithium battery under the negative pressure state. Since the liquid water can evaporate faster under the negative pressure state even at a high temperature without heating, the high temperature of 100-120 degrees Celsius is further conducive to improving the water escape effect. In steps S2, S3, S5 and S6, the key action is to fill the baking chamber with an excess of dry inert gas until the pressure value therein is higher than the standard atmospheric pressure and then stop the gas filling. In this way, each time the escaped water can be carried out of the baking chamber as much as possible by the subsequent overfill of dry inert gas.

[0054] In some embodiments, satisfying the preset condition in step S9 can be calculating the pressure change rate based on the data collected in step S8. When the pressure change rate is not greater than a preset value, it is considered to satisfy the preset condition. Specifically, the preset value can be 0.04. When the water content value is detected using the method mentioned in the background art, the corresponding pressure change rate when the lithium battery baking meets the requirements is calculated by the recorded pressure-time curve and is not higher than 0.04. Therefore, the value of 0.04 is used here to limit the requirement of the moisture value detection method of the present invention on the pressure change rate.

[0055] In other embodiments, the predetermined condition in step S9 may be satisfied by monitoring the pressure trend based on the data collected in step S8. If the pressure in the baking chamber does not reach a set upper pressure limit within a set time, the predetermined condition is also considered satisfied. Specifically, the set time may be 5 minutes, and the set upper pressure limit may be 1.1 times the last vacuum value. For example, if the last vacuum value was 110 Pa, then the set upper pressure limit may be 121 Pa. As long as the pressure in the baking chamber does not reach 121 Pa within the set 5 minutes, the predetermined condition is satisfied, and step S9 may be executed.

[0056] In one embodiment, the compensated humidity value may be outputted by first establishing a humidity conversion function:

[0057] ;

[0058] in, is the test humidity value recorded by the dew point meter, To record the real-time pressure in the baking chamber when testing the humidity value, is the molar mass of water vapor, is the molar constant of the gas, is the temperature inside the baking chamber;

[0059] Then substitute the test humidity value into the above function to obtain the compensated humidity value.

[0060] Specifically, according to the ideal gas equation ,get:

[0061]

[0062] in is the average atmospheric pressure during the sampling period, in Pa ; Represents volume in units of ; is the molar amount of the substance; The molar gas constant is 8.314472, with the unit of (J / (mol.K)); Represents thermodynamic temperature in K. The volume of 1 mol of gas is:

[0063]

[0064] The mass of water vapor is calculated based on the volume ratio of water vapor. Represents the volume ratio of water vapor, which is also the test humidity value recorded by the dew point meter; is the molar mass of water vapor, which is a constant of 18.015 and is expressed in kg / mol. The mass of water vapor thus calculated is:

[0065]

[0066] use Indicates the case of humidity compensation,

[0067]

[0068] in, is the test humidity value recorded by the dew point meter, To record the real-time pressure in the baking chamber when testing the humidity value, is the molar mass of water vapor, is the molar constant of the gas, is the temperature inside the baking chamber, and The ratio is a constant.

[0069] Substituting the test humidity value recorded by the dew point meter and the real-time pressure value in the baking chamber into the above formula, a compensated humidity value is obtained. This compensated humidity value can more accurately represent the measured moisture value of the lithium battery.

[0070] It should be understood that the terms "first" or "second" and the like in the claims, specifications, and drawings disclosed herein are used to distinguish between different objects, rather than to describe a specific order. The terms "include" and "comprising" used in the specifications and claims disclosed herein indicate the presence of the described features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or combinations thereof.

[0071] It should also be understood that the terminology used in this disclosure is for the purpose of describing specific embodiments only and is not intended to limit the disclosure. As used in the disclosure and claims, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly indicates otherwise. It should further be understood that the term "and / or" as used in the disclosure and claims refers to any and all possible combinations of one or more of the associated listed items, including and including these combinations.

[0072] Although the embodiments of the present invention are as described above, the contents are only examples used to facilitate understanding of the present invention and are not intended to limit the scope and application scenarios of the present invention. Any person skilled in the art of the present invention may make any modifications and changes in the form and details of the implementation without departing from the spirit and scope disclosed by the present invention, but the scope of patent protection of the present invention shall still be based on the scope defined by the attached claims.

Claims

1. A method for detecting moisture content in a lithium battery, characterized in that: include: S1: Keeping the baking chamber sealed, and filling it with dry inert gas until the pressure inside the chamber exceeds the standard atmospheric pressure, then stopping the filling; heating the baking chamber to a first preset temperature and maintaining it for a first preset time to allow the gas in the baking chamber to be fully mixed; S2: evacuating the baking chamber for the first time, controlling the vacuum value in the baking chamber to be 0.5 to 0.8 times the standard atmospheric pressure, heating to a second preset temperature and maintaining the temperature for a second preset time; thereafter, filling the baking chamber with dry inert gas until the pressure therein exceeds the standard atmospheric pressure, and then stopping the filling; S3: Evacuating the baking chamber again, with each vacuuming step decreasing the vacuum value in the baking chamber compared to the previous vacuuming step, heating the chamber to a second preset temperature and maintaining the temperature for a second preset time; thereafter, filling the baking chamber with dry inert gas until the pressure therein exceeds standard atmospheric pressure, and then stopping the filling; S4: Repeat step S3; S5: until the vacuum value decreases to between 100 and 150 Pa, and the vacuum value of the next vacuuming does not decrease compared to the previous vacuuming value; the baking chamber is heated to a second preset temperature and maintained for a second preset time; thereafter, dry inert gas is filled into the baking chamber until the pressure therein exceeds standard atmospheric pressure, and then the filling is stopped; S6: continuing to evacuate the baking chamber until the vacuum value is controlled between 100 and 150 Pa, heating the baking chamber to a second preset temperature and maintaining the temperature for a second preset time; thereafter, filling the baking chamber with dry inert gas until the pressure therein exceeds standard atmospheric pressure, and then stopping the filling; S7: collecting the pressure values ​​corresponding to different time points in the above steps to obtain continuously changing discrete pressure-time data points, and fitting the discrete data points into a pressure-time curve using a mathematical method; S8: On the pressure-time curve, obtain the current acquisition time point and the previous acquisition time point and their corresponding pressure values; S9: When a preset condition is met, a test humidity value of a dew point meter placed in the baking chamber is recorded, and a compensation humidity value is output according to the test humidity value.

2. A method for detecting moisture content in a lithium battery according to claim 1, characterized in that: In the aforementioned steps, dry inert gas is filled into the baking chamber until the pressure value therein is higher than the standard atmospheric pressure. After heating to the first preset temperature and maintaining the first preset time, the maximum pressure value in the baking chamber does not exceed 1.05 times the standard atmospheric pressure.

3. A method for detecting moisture content in a lithium battery according to claim 2, characterized in that: The first preset temperature is 50-60 degrees Celsius, and the first preset time does not exceed 5 minutes; if the pressure value in the baking chamber is about to reach 1.05 times the standard atmospheric pressure during heating within the first preset time, heating is stopped and the baking chamber is vacuumed.

4. A method for detecting moisture content in a lithium battery according to claim 1, characterized in that: In step S3, the decreasing trend is specifically that the vacuum value of each vacuuming is 0.5 to 0.8 times the vacuum value of the previous vacuuming.

5. The method for detecting moisture content in a lithium battery according to claim 1, wherein: The second preset temperature is 100-120 degrees Celsius, and the second preset time is 15 minutes.

6. A method for detecting moisture content in a lithium battery according to claim 1, characterized in that: The satisfying of the preset condition in step S9 includes: calculating the pressure change rate based on the data collected in step S8, and when the pressure change rate is not greater than a preset value, it is considered that the preset condition is satisfied; Alternatively, according to the data collected in step S8, the changing trend of the pressure value is monitored. If the pressure value in the baking chamber does not reach the set pressure upper limit within the set time, it is also considered that the preset condition is met.

7. A method for detecting moisture content in a lithium battery according to claim 6, characterized in that: The preset value is 0.

04.

8. A method for detecting moisture content in a lithium battery according to claim 6, characterized in that: The set time is 5 minutes, and the set pressure upper limit is 1.1 times the last vacuum value.

9. A method for detecting moisture content in a lithium battery according to claim 1, characterized in that: The output method of the compensated humidity value is to establish a humidity conversion function: ;in, is the test humidity value recorded by the dew point meter, To record the real-time pressure in the baking chamber when the humidity value is tested, is the molar mass of water vapor, is the molar constant of the gas, is the temperature inside the baking chamber; Substitute the test humidity value into the above function to obtain the compensated humidity value.

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