Method for detecting moisture value of lithium battery

Abstract

The invention provides a method for detecting the moisture value of a lithium battery. The method comprises the following steps: filling a baking chamber with dry inert gas until the pressure value in the baking chamber is higher than the standard atmospheric pressure; heating and keeping for a certain period of time so that gas in the baking chamber is fully mixed; the baking chamber is vacuumized for the first time, the vacuum value in the baking chamber is controlled to be 0.5-0.8 time of the standard atmospheric pressure value, and the baking chamber is heated and kept for a certain period of time; vacuumizing the baking chamber again, enabling the vacuum value in the baking chamber to be gradually reduced compared with the last vacuumizing value during each vacuumizing until the vacuumizing value is gradually reduced to 100-150Pa, and heating and keeping for a certain period of time; pressure values corresponding to different time points are collected and fitted into a pressure-time curve, when the pressure curve meets a preset condition, a test humidity value of a dew-point meter arranged in the baking chamber is recorded, and a compensation humidity value is output according to the test humidity value. The baking chamber is alternately changed between the positive pressure and the negative pressure, the dewatering effect is improved, and the moisture detection value is closer to the actual value.

Description

Technical Field

[0001] The present invention generally relates to the technical field of lithium batteries, and more specifically, 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 alloy as positive / negative electrode materials and non-aqueous electrolyte solutions. They have the advantages of 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 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 mainly used in the drying process of battery cells in lithium battery production. The purpose is to effectively remove moisture from the battery cells to prevent moisture from reacting with the electrolyte during subsequent high-temperature processing or use to generate harmful gases or reduce battery performance. Before baking, the baking equipment must set fixed baking parameters according to the characteristics of the baking material, such as baking temperature, maximum vacuum value, minimum vacuum value, baking time, etc. During the baking process, due to the large pressure changes in the baking chamber, it is impossible to use related equipment such as a dew point meter to directly detect the moisture concentration in the chamber in real time.

[0004] At present, one method for detecting water content is to take out the test battery in the tray after baking to detect the moisture value. The next production process can only be entered if the detected moisture value is lower than the expected value. This is the most traditional method for detecting water content. Another method for judging water value is to collect the pressure value in the baking chamber and establish a mathematical model based on it to judge whether the moisture value after baking meets the standard. The specific value of the moisture value cannot be directly obtained. Due to the superposition of various objective factors, this judgment method cannot exempt the water content value from detection, but only makes an advance judgment in theory. Therefore, in order to ensure that the water content value after baking meets the requirements, the water content value still needs to be tested after baking, and it cannot 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-mentioned background technology, the present invention proposes a method for detecting the moisture value of a lithium battery. To this end, the present invention provides the following technical solutions.

[0007] The present invention discloses a method for detecting the moisture value of a lithium battery, comprising: S1: Keep the baking chamber in a sealed state, and fill it with dry inert gas until the pressure inside is higher than the standard atmospheric pressure, and then stop filling; heat the baking chamber to a first preset temperature and keep it for a first preset time, so that the gas in the baking chamber is fully mixed; S2: evacuating the baking chamber for the first time, controlling the vacuum value in the baking chamber to be 0.5-0.8 times the standard atmospheric pressure value, heating 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 value therein is higher than the standard atmospheric pressure and then stopping the filling; S3: evacuating the baking chamber again, with each evacuation making the vacuum value in the baking chamber decrease gradually compared with the last evacuation value, 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 is higher than the standard atmospheric pressure, and then stopping the filling; S4: repeat step S3; S5: until the vacuum value decreases to between 100 and 150 Pa, the vacuum value of the next vacuuming will no longer decrease compared with 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 value therein is higher than the standard atmospheric pressure and the filling is stopped; S6: continue to evacuate the baking chamber to control the vacuum value between 100 and 150 Pa, heat the baking chamber to a second preset temperature and maintain it for a second preset time; thereafter, fill the baking chamber with dry inert gas until the pressure value therein is higher than the standard atmospheric pressure and then stop filling; 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 a mathematical method; S8: on the pressure-time curve, taking the current acquisition time point and the previous acquisition time point and their corresponding pressure values; 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.

[0008] Preferably, in the aforementioned steps, dry inert gas is filled into the baking chamber until the pressure therein is higher than the standard atmospheric pressure, and 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.

[0009] 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 evacuated.

[0010] 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.

[0011] Preferably, the second preset temperature is 100-120 degrees Celsius, and the second preset time is 15 minutes.

[0012] Preferably, satisfying the preset condition in step S9 includes: calculating the pressure change rate according to 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, and if the pressure value in the baking chamber does not reach the set pressure upper limit within the set time, it is also regarded as meeting the preset condition.

[0013] Preferably, the preset value is 0.04.

[0014] Preferably, the set time is 5 minutes, and the set pressure upper limit is 1.1 times the last vacuum value.

[0015] Preferably, the compensation humidity value is outputted by establishing 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 in the baking chamber; Substitute the test humidity value into the above function to obtain the compensated humidity value.

[0016] The technical solution provided by this application may have the following beneficial effects: 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 chamber 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 chamber with dry inert gas. Moreover, each time the chamber is evacuated, the vacuum value in the baking chamber tends to decrease compared with the value of the previous evacuation. That is, the entire baking process includes evacuating the chamber and intermittently filling the chamber with excessive 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 chamber is evacuated, the vacuum value in the baking chamber tends to decrease compared with the value of the previous evacuation. The decreasing trend of the vacuum value can improve the tolerance of the equipment to the negative pressure environment and reduce the probability of box leakage; intermittent overfilling of dry inert gas can make the water vapor and the overfilled dry inert gas fully mixed, so that in the next negative pressure extraction process, the water vapor can be carried out of the baking chamber as much as possible, that is, the benefit of filling with excessive dry inert gas to make the baking chamber in a positive pressure state in stages 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 makes the baking chamber in a negative pressure state, which 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.

[0017] 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, so that the moisture detection value is 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

[0018] By reading the following detailed description with reference to the accompanying drawings, the above and other objects, features and advantages of the exemplary embodiments of the present invention will become readily understood. 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, wherein: Figure 1 It is a flow chart showing one embodiment of the present invention. DETAILED DESCRIPTION

[0019] 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, it will be appreciated by those of ordinary skill in the art that the embodiments described herein may be practiced without these specific details. In other cases, well-known methods, processes, and components are not described in detail to avoid obscuring the embodiments described herein. Moreover, the description should not be construed as limiting the scope of the embodiments described herein.

[0020] According to one embodiment of the present invention, a method for detecting moisture content in a lithium battery is provided, comprising the following steps: S1: Keep the baking chamber in a sealed state, and fill it with dry inert gas until the pressure inside is higher than the standard atmospheric pressure, and then stop filling; heat the baking chamber to a first preset temperature and keep it for a first preset time, so that the gas in the baking chamber is fully mixed; S2: evacuating the baking chamber for the first time, controlling the vacuum value in the baking chamber to be 0.5-0.8 times the standard atmospheric pressure value, heating 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 value therein is higher than the standard atmospheric pressure, and then stopping the filling; S3: evacuating the baking chamber again, with each evacuation making the vacuum value in the baking chamber decrease gradually compared with the last evacuation value, 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 is higher than the standard atmospheric pressure, and then stopping the filling; S4: repeat step S3; S5: until the vacuum value decreases to between 100 and 150 Pa, the vacuum value of the next vacuuming will no longer decrease compared with 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 value therein is higher than the standard atmospheric pressure and then stopping the filling; S6: continue to evacuate the baking chamber to control the vacuum value between 100 and 150 Pa, heat the baking chamber to a second preset temperature and maintain it for a second preset time; thereafter, fill the baking chamber with dry inert gas until the pressure value therein is higher than the standard atmospheric pressure and then stop filling; 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 a mathematical method; S8: On the pressure-time curve, take the current acquisition time point and the previous acquisition time point and their corresponding pressure values; S9: When the preset conditions are met, the test humidity value of the dew point meter placed in the baking chamber is recorded, and the compensation humidity value is output according to the test humidity value.

[0021] The inert dry gas mentioned in step S1 of the above embodiment and other embodiments of this specification may be dry nitrogen.

[0022] 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 a first preset time, the maximum pressure value in the baking chamber does not exceed 1.05 times the standard atmospheric pressure.

[0023] Since the baking chamber of the baking equipment is in a state of alternating positive pressure and negative pressure when the method of the present invention is implemented, in order to reduce the impact of the pressure change in the baking chamber on the baking equipment and reduce the stringent requirements on the structure of the baking equipment, during the process of filling with dry inert gas and heating up 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.

[0024] In one embodiment, the first preset temperature is 50-60 degrees Celsius, and the first preset time does not exceed 5 minutes. The heating method can be heating by an aluminum heating plate, and when the inert dry gas is introduced, it passes through the heating coil, thereby achieving heating of the baking chamber. Since 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 drawn. 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.

[0025] 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, the heating is stopped and the baking chamber is evacuated.

[0026] In step S2, the baking chamber is evacuated for the first time, and the vacuum value in the baking chamber is controlled to be 0.5-0.8 times the standard atmospheric pressure value. This step is the beginning of the decreasing evacuation of the baking chamber.

[0027] In the subsequent step S3, each time the vacuum is evacuated, the vacuum value in the baking chamber decreases compared with the previous vacuum value, and the decreasing trend is also that the vacuum value of each vacuum is 0.5~0.8 times the previous vacuum value, until the vacuum value at the last vacuum decreases to between 100~150Pa. In the subsequent vacuuming, the vacuum value in the baking chamber will no longer decrease compared with the vacuum value at the last vacuuming, and can maintain the same value as the vacuum value at the last vacuuming, or can control the vacuum value between 100~150Pa when the vacuuming continues.

[0028] In one embodiment, the second preset temperature is 100-120 degrees Celsius, and the second preset time is 15 minutes.

[0029] Since the baking chamber is evacuated and gradually reduced until the vacuum value is about 100Pa, there is no medium such as inert gas in the baking chamber or the amount of inert gas is very small, in order to heat to the second preset temperature of 100-120 degrees Celsius, the heating method here can be contact heating, that is, heating with an aluminum heating plate; and the second preset time of 15 minutes is to fully evaporate the liquid water in the lithium battery under the negative pressure state. Since the liquid water can be evaporated faster even at a non-heating high temperature under the negative pressure state, coupled with heating to a high temperature of 100-120 degrees Celsius, it is more helpful to improve 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 inside the baking chamber is higher than the standard atmospheric pressure and stop the gas filling, so that each escaped water can be carried out of the baking chamber as much as possible by the subsequent overfilled dry inert gas.

[0030] In some embodiments, satisfying the preset condition in step S9 may be 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, the preset condition is deemed to be satisfied. Specifically, the preset value may be 0.04. When the water content value is detected using the method mentioned in the background technology, the corresponding pressure change rate when the lithium battery baking meets the requirements calculated by the recorded pressure-time curve is not higher than 0.04. Therefore, the value of 0.04 is used here to limit the requirements of the water content detection method of the present invention on the pressure change rate.

[0031] In other embodiments, the preset condition in step S9 can also be satisfied by monitoring the change trend of the pressure value according to the data collected in step S8. If the pressure value in the baking chamber does not reach the set pressure upper limit within the set time, it is also considered to meet the preset condition. Specifically, the set time can be 5 minutes, and the set pressure upper limit value is 1.1 times the last vacuum value. For example, if the vacuum value of the last vacuum value is 110Pa, then the set pressure upper limit value is 121Pa. As long as the pressure value in the baking chamber does not reach 121Pa within the set 5 minutes, the preset condition is satisfied and step S9 can be executed.

[0032] In one embodiment, the compensation humidity value may be outputted by first establishing 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 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; Then substitute the test humidity value into the above function to obtain the compensated humidity value.

[0033] Specifically, according to the ideal gas equation ,get:

[0034] 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. Then the volume of 1 mol of gas is:

[0035] 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, in kg / mol. The mass of water vapor calculated from this is:

[0036] use Indicates the case of humidity compensation,

[0037] 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 in the baking chamber, and The ratio is a constant.

[0038] The test humidity value recorded by the dew point meter and the real-time pressure value in the baking chamber are substituted into the above formula to obtain a compensated humidity value, which can more accurately represent the measured moisture value of the lithium battery.

[0039] It should be understood that the possible terms "first" or "second" etc. in the claims, specifications and drawings disclosed in the present invention are used to distinguish different objects rather than to describe a specific order. The terms "include" and "comprise" used in the specifications and claims disclosed in the present invention indicate the presence of the described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or their collections.

[0040] It should also be understood that the terms used in this disclosure are only for the purpose of describing specific embodiments and are not intended to limit the disclosure. As used in the disclosure and claims, the singular forms of "a", "an", and "the" are intended to include the plural forms unless the context clearly indicates otherwise. It should also be further understood that the term "and / or" used in the disclosure and claims refers to any combination of one or more of the associated listed items and all possible combinations, including these combinations.

[0041] 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 technician in the technical field of the present invention can 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 the moisture value of a lithium battery, characterized in that: include: S1: Keep the baking chamber in a sealed state, and fill it with dry inert gas until the pressure inside is higher than the standard atmospheric pressure, and then stop filling; heat the baking chamber to a first preset temperature and keep it for a first preset time, so that the gas in the baking chamber is fully mixed; S2: evacuating the baking chamber for the first time, controlling the vacuum value in the baking chamber to be 0.5-0.8 times the standard atmospheric pressure value, heating 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 value therein is higher than the standard atmospheric pressure and then stopping the filling; S3: evacuating the baking chamber again, with each evacuation making the vacuum value in the baking chamber decrease gradually compared with the last evacuation value, 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 is higher than the standard atmospheric pressure, and then stopping the filling; S4: repeat step S3; S5: until the vacuum value decreases to between 100 and 150 Pa, the vacuum value of the next vacuuming will no longer decrease compared with 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 value therein is higher than the standard atmospheric pressure and the filling is stopped; S6: continue to evacuate the baking chamber to control the vacuum value between 100 and 150 Pa, heat the baking chamber to a second preset temperature and maintain it for a second preset time; thereafter, fill the baking chamber with dry inert gas until the pressure value therein is higher than the standard atmospheric pressure and then stop filling; 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 a mathematical method; S8: on the pressure-time curve, taking the current acquisition time point and the previous acquisition time point and their corresponding pressure values; 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.

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 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 evacuated.

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. A method for detecting moisture content in a lithium battery according to claim 1, characterized in that: 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: Meeting the preset condition in step S9 includes: calculating the pressure change rate according to 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 met; Alternatively, according to the data collected in step S8, the changing trend of the pressure value is monitored, and if the pressure value in the baking chamber does not reach the set pressure upper limit within the set time, it is also regarded as meeting the preset condition.

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: 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 in the baking chamber; Substitute the test humidity value into the above function to obtain the compensated humidity value.

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