Battery electrolyte wetting judgment method

Abstract

This application discloses a method for determining electrolyte wetting in a battery, comprising: acquiring a first electrode, a second electrode, and a lithium strip of the battery under test and pre-treating them; constructing a first battery model using the pre-treated first electrode as the positive electrode and the lithium strip as the negative electrode; constructing a second battery model using the pre-treated second electrode as the positive electrode and the lithium strip as the negative electrode; calculating the voltage difference between the first and second battery models after stabilization; and using the voltage difference as a threshold voltage to determine the degree of electrolyte wetting in the battery under test. This method constructs a first battery model and a second battery model using two different electrodes of the battery under test, and calculates the voltage difference between the first and second battery models to determine the degree of wetting. The determination result is not affected by the battery's structure and has high accuracy and efficiency.

Description

Technical Field

[0001] The embodiments of this application relate to the field of battery manufacturing technology, and in particular to a method for determining battery electrolyte wetting. Background Technology

[0002] Lithium-ion batteries, characterized by high energy density, long cycle life, and sustainable energy utilization, are widely used in mobile phones, computers, drones, power tools, new energy vehicles, and grid storage. Therefore, the safety performance of lithium-ion batteries has received greater attention, and higher requirements have been placed on their energy density and fast-charging performance. In the manufacturing process of lithium-ion batteries, the degree of electrolyte wetting is undoubtedly a key factor affecting their safety performance and energy density. Sufficient electrolyte wetting directly impacts the quality of the passivation film. Insufficient wetting and uneven distribution of the electrolyte on the electrodes lead to varying lithium-ion migration impedances during film formation and different reduction reaction mechanisms, resulting in uneven film formation at different locations on the negative electrode. This ultimately causes poor electrical performance and insufficient cycle life in the later stages of cell formation. Currently, the main methods for assessing whether electrolyte wetting is sufficient include: 1) testing the wetting status of different locations in the battery cell using ultrasonic waves, and judging whether wetting is sufficient by the color difference in different locations inside the battery cell; however, the accuracy of this method is affected by the thickness of the battery cell casing; 2) testing the AC impedance during the battery cell wetting process, and judging whether wetting is sufficient by the change in ohmic impedance value at different times during the wetting process until it reaches a stable value; however, this method takes a long time and is inefficient.

[0003] Chinese patent CN113991198A discloses a method for detecting electrolyte wetting in lithium-ion batteries. Specifically, it discloses the process of isolating the positive and negative electrode sheets with a separator, welding positive and negative electrode tabs to form a bare cell, encapsulating the bare cell in a casing to form a pre-assembled cell, and injecting electrolyte for testing to measure the membrane potential to obtain the degree of cell wetting.

[0004] However, the applicant discovered that the measured degree of electrolyte wetting in this technology was inaccurate. Summary of the Invention

[0005] The embodiments of this application provide a method for judging electrolyte wetting in batteries, in order to solve the technical problem that the test results are greatly affected by the structure of the battery cell itself and the judgment efficiency is low in the prior art.

[0006] To address the aforementioned technical problems, embodiments of this application disclose the following technical solutions:

[0007] This application provides a method for determining battery electrolyte wetting, including:

[0008] Obtain the first electrode, second electrode, and lithium strip of the battery under test and perform pretreatment;

[0009] The first battery model is constructed by using the pre-treated first electrode as the positive electrode and the lithium strip as the negative electrode.

[0010] The second battery model is constructed by using the pretreated second electrode as the positive electrode and the lithium strip as the negative electrode.

[0011] The difference between the stable voltages of the first battery model and the second battery model is calculated.

[0012] The difference in voltage is used as a threshold voltage to determine the degree of electrolyte wetting in the tested battery.

[0013] Furthermore, the method for determining the degree of electrolyte wetting of the tested battery by using the voltage difference as a threshold voltage includes:

[0014] Obtain the positive and negative electrode voltages of the battery under test;

[0015] The voltage difference is obtained by subtracting the negative voltage from the positive voltage.

[0016] The voltage difference is compared with the threshold voltage, and the degree of wetting of the tested battery is determined based on the comparison result.

[0017] Furthermore, the method for calculating the difference in the stabilized voltage between the first battery model and the second battery model includes:

[0018] Monitor the voltage change of the first battery model during the aging process, and record it as the first voltage after the voltage stabilizes;

[0019] Monitor the voltage change of the second battery model during the aging process, and record it as the second voltage after the voltage stabilizes;

[0020] The threshold voltage is obtained by subtracting the first voltage from the second voltage.

[0021] Furthermore, the method for obtaining the first electrode, the second electrode, and the lithium strip of the battery and performing pretreatment includes:

[0022] Obtain the first electrode of the battery under test, and cut the first electrode;

[0023] Obtain the second electrode of the battery under test, and cut the second electrode;

[0024] Obtain the lithium strip of the battery under test and cut the lithium strip;

[0025] The first electrode sheet after cutting has a first area S1mm.2 The cut second electrode has a second area S2mm. 2 The cut lithium strip has a third area S3mm. 2 The second area is S2mm 2 Greater than or equal to the third area S3mm 2 The third area S3mm 2 Larger than the first area S1mm 2 The first area S1mm 2 The second area S2mm 2 The third area S3mm 2 The relationship is satisfied as follows:

[0026] 1≤S2 / S3≤1.2;

[0027] 1≤S3 / S1≤1.5.

[0028] Furthermore, the determination method also includes obtaining the electrode tabs and cutting the electrode tabs;

[0029] The tabs are used to connect the first electrode, the second electrode, and the lithium strip, respectively; the cut tabs have a fourth area of ​​S4mm. 2 The first area S1mm 2 and the fourth area S4mm 2 The following condition is satisfied: 2≤S1 / S4≤3.

[0030] Furthermore, the first electrode is the positive electrode of the battery under test, and the material is NCM; the second electrode is the negative electrode of the battery under test, and the material is Gr; and the lithium strip is a copper-lithium composite strip.

[0031] Furthermore, the method for constructing the first battery model includes:

[0032] The first electrode is used as the positive terminal of the first battery model, and the two lithium strips are used as the negative terminals of the first battery model. The positive and negative terminals are separated by a separator.

[0033] After the first electrode and the lithium strip are connected to their respective tabs, they are packaged into a casing and sealed after electrolyte is injected.

[0034] Furthermore, the method for constructing the second battery model includes:

[0035] The second electrode is used as the positive terminal of the second battery model, and the two lithium strips are used as the negative terminals of the second battery model. The positive and negative terminals are separated by a separator.

[0036] The second electrode and the lithium strip are connected to their respective tabs and then encapsulated in a housing, and sealed after electrolyte is injected.

[0037] Furthermore, the electrolyte injected into the first battery model and the second battery model is the same as the electrolyte of the battery under test;

[0038] The electrolyte ratio is DMC:EMC:EC = 1:1:1, 2% VC, 1 mol / L.

[0039] Furthermore, the determination method also includes aging treatment of the first battery model and the second battery model:

[0040] Place the first battery model and the second battery model into the aging device;

[0041] The aging equipment accelerates the aging of the first battery model and the second battery model by controlling temperature, humidity and pressure;

[0042] The temperature range is 40-45℃, while the ambient dew point temperature is below -35℃.

[0043] One of the above technical solutions has the following advantages or beneficial effects:

[0044] Compared with existing technologies, this application provides a battery electrolyte wetting determination method, comprising: acquiring a first electrode, a second electrode, and a lithium strip of the battery under test and pre-treating them; constructing a first battery model by using the pre-treated first electrode as the positive electrode and the lithium strip as the negative electrode; constructing a second battery model by using the pre-treated second electrode as the positive electrode and the lithium strip as the negative electrode; calculating the difference in voltage between the first battery model and the second battery model after stabilization; and using the voltage difference as a threshold voltage to determine the degree of electrolyte wetting in the battery under test. This method constructs a first battery model and a second battery model using two different electrodes of the battery under test, and calculates the voltage difference between the first battery model and the second battery model to determine the degree of wetting in the battery under test. The determination result is not affected by the battery's structure itself, and has high accuracy and efficiency. Attached Figure Description

[0045] The technical solution and other beneficial effects of this application will become apparent from the following detailed description of specific embodiments in conjunction with the accompanying drawings.

[0046] Figure 1 This is a schematic diagram of the method flow provided in the embodiments of this application;

[0047] Figure 2 This is a schematic diagram of the first battery model structure provided in an embodiment of this application;

[0048] Figure 3 This is a schematic diagram of the second battery model structure provided in an embodiment of this application;

[0049] Figure 4 This is a schematic diagram of the potential change of the positive electrode-battery model provided in Embodiment 1 of this application;

[0050] Figure 5 This is a schematic diagram of the potential change of the negative electrode-battery model provided in Embodiment 1 of this application;

[0051] Figure 6 This is a schematic diagram of the full cell potential change provided in Embodiment 1 of this application;

[0052] Figure 7 This is a schematic diagram of the potential change of the positive electrode-battery model provided in Embodiment 2 of this application;

[0053] Figure 8 This is a schematic diagram of the potential change of the negative electrode-battery model provided in Embodiment 2 of this application;

[0054] Figure 9 This is a schematic diagram of the full cell potential change provided in Embodiment 2 of this application.

[0055] The attached figures are labeled as follows:

[0056] 1-Lithium strip, 2-First electrode, 3-Separator, 4-Second electrode. Detailed Implementation

[0057] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0058] The applicant noted that two methods are commonly used to measure the degree of electrolyte wetting in batteries: ultrasonic measurement and AC impedance measurement. The ultrasonic method requires an ultrasonic testing setup, including an ultrasonic transmitter and receiver. The transmitter emits ultrasonic waves into the battery cell, which penetrate the metal casing and are received by the receiver. The degree of wetting inside the cell is then determined by the received signal. However, as the cell casing thickens, the ultrasonic penetration effect is significantly reduced, and the signal at the receiver is also greatly weakened. Therefore, the ultrasonic method is not suitable for all types of batteries and cannot accurately measure the electrolyte wetting condition inside the cell. In contrast, the AC impedance measurement method measures the high-frequency ohmic resistance during battery wetting. As wetting deepens, the high-frequency ohmic resistance gradually decreases and reaches a stable value, indicating sufficient electrolyte wetting. While this method is simpler than the ultrasonic method and is not affected by the battery's structure, it requires continuous measurement of the cell's ohmic resistance, resulting in a long measurement time and low efficiency.

[0059] The specific implementation methods of this application are illustrated below through examples:

[0060] like Figure 1 As shown in the figure, this application discloses a method for determining battery electrolyte wetting, including:

[0061] S1: Obtain the first electrode, second electrode, and lithium strip of the battery under test and perform preprocessing.

[0062] In this embodiment, the method for preprocessing the first electrode, the second electrode, and the lithium strip includes: obtaining the first electrode of the battery under test and cutting it; obtaining the second electrode of the battery under test and cutting it; obtaining the lithium strip of the battery under test and cutting it; wherein the cut first electrode has a first area S1mm. 2 The cut second electrode has a second area S2mm. 2 The cut lithium strip has a third area S3mm 2 Second area S2mm 2 Greater than or equal to the third area S3mm 2 The third area is S3mm. 2 Greater than the first area S1mm 2 Understandably, cutting the first electrode, second electrode, and lithium strip into different sizes facilitates subsequent assembly. These components can be cut from the battery under test or from the same material. To create an environment identical to the battery under test, the dimensions of the first electrode, second electrode, and lithium strip need to be designed to make the calculation results closer to reality.

[0063] In this embodiment of the application, the first area S1mm 2 Second area S2mm 2 The third area is S3mm 2 The following relationships are satisfied: 1 ≤ S2 / S3 ≤ 1.2; 1 ≤ S3 / S1 ≤ 1.5. It should be noted that the second area of ​​the second electrode is S2 mm. 2 The third area of ​​the lithium strip is S3mm 2 The ratios between these values ​​include, but are not limited to: 1.0, 1.05, 1.10, 1.15, and 1.20, with the third area of ​​the lithium strip being 3mm. 2 and the first area S1mm of the first electrode 2 The ratios between them include, but are not limited to, 1.0, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, and 1.50. It is conceivable that in some other embodiments, to construct other types of test structures, the dimensions of the first electrode, the second electrode, and the lithium strip can be designed differently, resulting in larger ratios between the first electrode, the second electrode, and the lithium strip.

[0064] In this embodiment, the method further includes obtaining and cutting the electrode tabs; wherein the electrode tabs are used to connect the first electrode, the second electrode, and the lithium strip respectively; the cut electrode tabs have a fourth area S4mm. 2 The first area is S1mm 2 and the fourth area S4mm 2 The relationship 2 ≤ S1 / S4 ≤ 3 must be satisfied. It's understandable that the tabs are used to connect the first electrode, the second electrode, and the lithium strip. For ease of measurement, current needs to be drawn out through the tabs. Since the tabs are generally smaller than the electrode plates, their area can be one-tenth to one-fifth of the area of ​​the first electrode plate. It should be noted that the first area of ​​the first electrode plate is S1 mm. 2 The fourth area of ​​the electrode is S4mm. 2 The ratios between these ratios include, but are not limited to, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, and 3.0. It is conceivable that in some other embodiments, to meet different application scenarios, the area of ​​the tab can be designed to be smaller or larger, and regardless of the size of the tab, it is for the purpose of facilitating connection with the first electrode, the second electrode, and the lithium strip.

[0065] In this embodiment, the first electrode is the positive electrode of the battery under test, made of NCM, and the second electrode is the negative electrode of the battery under test, made of Gr. The lithium strip is a copper-lithium composite strip. NCM is an abbreviation for nickel (Ni), cobalt (Co), and manganese (Mn) in the ternary materials of the battery. The first electrode is composed of these three materials. Gr is the code for 4Cr3Mo3W4VNb steel, a hot-work die steel, a high-heat-strength steel for high-speed hammer forging dies. This steel has good hot strength, hot hardness, wear resistance, resistance to thermal fatigue, forging performance, and machinability. It also has a wide range of quenching heating temperatures, low overheat sensitivity, and high hardenability. By using the same materials as the positive and negative electrodes of the battery under test, the real environment of the battery under test is reproduced, avoiding errors caused by different materials in the constructed test structure, which could lead to incorrect judgments on the degree of electrolyte wetting.

[0066] In this embodiment, the length of the first electrode after cutting is 90mm-100mm and the width is 45mm-55mm, wherein the optimal length is 95mm and the width is 50mm; the length of the second electrode after cutting is 90mm-100mm and the width is 50mm-60mm, wherein the optimal length is 95mm and the width is 55mm; the length of the lithium strip after cutting is 90mm-100mm and the width is 50mm-60mm, wherein the optimal length is 95mm and the width is 55mm; the length and width of the tab after cutting are both 8-12mm, wherein the preferred length and width are 10mm. To facilitate connection and measurement, the first electrode is designed as a rectangular structure, while the second electrode and lithium strip are the same size for better measurement. The tabs are smaller to facilitate the extraction of current from the test structure and connection to the first, second, and lithium strips. Before cutting, the dimensions of the first, second, lithium strips, and tabs can be measured on the electrode plate using calipers or a ruler, and the outlines can be drawn on the electrode plate with a marker. Then, the first, second, lithium strips, and tabs can be cut out using a cutting device; alternatively, laser cutting equipment can be used to cut the electrodes after setting the corresponding cutting dimensions.

[0067] S2: A first battery model is obtained by using the pre-treated first electrode as the positive electrode and the lithium strip as the negative electrode. The construction method of the first battery model includes: using the first electrode as the positive terminal and two lithium strips as the negative terminals, with the positive and negative terminals separated by a separator; connecting the first electrode and lithium strips to their respective tabs and then encapsulating them in a casing, followed by electrolyte injection and sealing. It can be understood that by using the first electrode as the positive electrode and the lithium strip as the negative electrode, and connecting the first electrode and lithium strip to their respective tabs, they are stacked according to the manufacturing process of the battery under test. The resulting structure is as follows... Figure 2As shown, after stacking, the cells are placed into a casing, electrolyte is injected, and the casing is sealed to prevent electrolyte leakage. Since the material of the first electrode is the same as the positive electrode material of the battery under test, the first battery model constructed in this way can be regarded as a scaled-down version of the battery under test, used to simulate the operating environment of the positive terminal of the battery under test. Therefore, by testing the first battery model, relevant data of the battery under test can be obtained.

[0068] S3: A second battery model is obtained by using the pre-treated second electrode as the positive electrode and the lithium strip as the negative electrode. The construction method of the second battery model includes: using the second electrode as the positive terminal and two lithium strips as the negative terminals, with the positive and negative terminals separated by a separator; connecting the second electrode and lithium strips to their respective tabs, then encapsulating them in a casing, and sealing after electrolyte injection. It can be understood that by using the second electrode as the positive electrode and the lithium strip as the negative electrode, and connecting the second electrode and lithium strip to their respective tabs, they are stacked according to the manufacturing process of the battery under test. The resulting structure is as follows... Figure 3 As shown, after stacking, the electrode is placed in the casing, filled with electrode liquid, and sealed to prevent the internal electrolyte from leaking out. Since the material of the second electrode is the same as that of the negative electrode of the battery under test, the second battery model constructed in this way can be regarded as a scaled-down version of the battery under test, used to simulate the operating environment of the negative terminal of the battery under test. Therefore, by testing the second battery model, the relevant data of the battery under test can be obtained.

[0069] In this embodiment, after constructing the first and second battery models, to accelerate the electrolyte wetting speed and thus improve testing efficiency, the first and second battery models also need to undergo aging treatment. The treatment steps include: placing the first and second battery models into an aging device; the aging device accelerating the aging of the first and second battery models by controlling temperature, humidity, and pressure; wherein the temperature range is 40-45℃, and the ambient dew point temperature is below -35℃. It is understood that in a normal operating environment, complete electrolyte wetting of the battery interior requires tens of hours. Therefore, to accelerate the aging speed of the batteries and reduce testing time, the first and second battery models are placed in an aging device to accelerate their aging. It is conceivable that, in addition to increasing the ambient temperature, other environmental parameters can be changed in some other embodiments, such as controlling humidity at 20%-60% and pressure at 0.5-2.5 MPa.

[0070] In this embodiment, the electrolyte injected into the first and second battery models is the same as the electrolyte in the battery under test; the electrolyte ratio is DMC:EMC:EC = 1:1:1, 2% VC, 1 mol / L. In this embodiment, DMC is dimethyl carbonate, EMC (Epoxy Molding Compound), EC is ethyl cellulose, and VC is vinylene carbonate. It is understood that in order to construct a structure identical to the battery under test and obtain the parameters after complete electrolyte wetting, the same electrolyte is injected into the first and second battery models to reproduce the real-world usage scenario and improve the accuracy of the data after complete electrolyte wetting.

[0071] S4: Calculate the difference in voltage between the first battery model and the second battery model after they have stabilized.

[0072] In this embodiment, the voltage change of the first battery model during the aging process is monitored and recorded as the first voltage after the voltage stabilizes; the voltage change of the second battery model during the aging process is monitored and recorded as the second voltage after the voltage stabilizes; the difference between the first voltage and the second voltage is obtained. It is understood that since the electrolyte gradually permeates the inside of the battery, the voltage output by the battery is not yet stable during this process. Therefore, when the voltage in the first and second battery models no longer changes, it indicates that the electrolyte in the first and second battery models has been fully permeated. The first battery model simulates the usage scenario of the positive terminal of the battery under test, while the second battery model simulates the usage scenario of the negative terminal of the battery under test. By calculating the voltages of the first and second battery models respectively and then subtracting them, the voltage difference between the first and second battery models can be obtained. This voltage difference also reflects the voltage difference between the positive and negative terminals of the battery under test after complete permeation. Therefore, this voltage difference can be used to determine whether the electrolyte in the battery under test has been fully permeated.

[0073] S5: Use the voltage difference as the threshold voltage to determine the degree of electrolyte wetting in the tested battery.

[0074] In this embodiment, the positive and negative electrode voltages of the battery under test are obtained; the voltage difference is obtained by subtracting the negative electrode voltage from the positive electrode voltage; the voltage difference is compared with a threshold voltage, and the degree of wetting of the battery under test is determined based on the comparison result. It is understood that after obtaining the voltage difference value after the first and second battery models have stabilized, this voltage difference value can be used as the threshold voltage for determining the degree of wetting of the battery under test. To avoid misjudgment, the first and second battery models can be constructed multiple times to obtain multiple threshold voltages, and corresponding range values ​​can be set for these multiple threshold voltages. When the obtained voltage difference between the positive and negative terminals of the battery under test is within the threshold voltage range, it indicates that the battery under test has been sufficiently wetting; otherwise, it indicates that the battery has not been sufficiently wetting.

[0075] The electrolyte wetting determination method in this application is further illustrated by the following examples:

[0076] Example 1

[0077] Taking a ternary lithium battery as an example, using NCM811 as the positive electrode material, Gr as the negative electrode, and an electrolyte formulation of (DMC:EMC:EC = 1:1:1, 2% VC, 1mol / L), the specific implementation steps for testing whether the battery system is sufficiently wetted are as follows:

[0078] Step A1: Cut the positive electrode sheet of the ternary system battery into 50mm*95mm size sheets, and cut the positive electrode tabs into 10mm*10mm size sheets;

[0079] Step A2: Cut the negative electrode sheet of the ternary system battery into 55mm*100mm size sheets, and cut the negative electrode tabs into 10mm*10mm size sheets;

[0080] Step A3: Cut the lithium strip to a size of 55mm*100mm, and the size of the cut lithium strip tabs is 10mm*10mm;

[0081] Step A4: Using one positive electrode sheet as the positive electrode and two lithium strips as the negative electrode, the electrodes are separated by a separator. Following the cell stacking process, the electrodes are stacked, tabs are welded, the casing is installed, electrolyte is injected, and finally the casing is sealed to obtain the positive electrode-battery model. Similarly, using one negative electrode sheet as the positive electrode and two lithium strips as the negative electrode, the electrodes are separated by a separator. Following the same steps, the negative electrode-battery model is obtained.

[0082] Step A5: After the positive electrode-battery model is filled with electrolyte, it is placed in a 45℃ constant temperature chamber. Voltage changes during the high-temperature static period of the cell are collected using a data acquisition device. The voltage changes are as follows: Figure 4 As shown. When the electrolyte is fully wetted, the voltage will remain constant, and the final stable voltage value of the positive electrode-cell model is V. 正极 =3.118V;

[0083] Step A6: After the negative electrode-battery model is filled with electrolyte, it is placed in a 45℃ constant temperature chamber. Voltage changes during the high-temperature static period of the cell are collected using a data acquisition device. The voltage changes are as follows: Figure 5 As shown. When the electrolyte is fully wetted, the voltage will remain constant, and the final stable voltage value of the negative electrode-cell model is V. 负极 =2.964V;

[0084] Step A7: According to formula V 全电池 =V 正极 -V 负极 The voltage V after full immersion of the full cell was calculated. 全电池 =0.154V.

[0085] After the test, the results were verified. A soft-pack cell was fabricated using NCM811 as the positive electrode material, Gr as the negative electrode, and an electrolyte formulation of (DMC:EMC:EC = 1:1:1, 2% VC, 1 mol / L). After electrolyte injection, the cell was placed at 45°C for static treatment, and the change in the full-cell voltage during the static treatment process was monitored. Figure 6 As shown, when the voltage reaches 0.154V, it indicates that the cell wetting is complete. Tests show that after 10 hours of wetting, the full cell voltage reaches 0.154V, indicating complete wetting. To verify whether wetting was complete, cell structures were disassembled after 5 hours, 10 hours, and 20 hours of wetting. The results show that after 10 hours, the electrolyte wetting was sufficient.

[0086] Example 2

[0087] Taking the lithium iron phosphate (LFP) battery system as an example, the positive electrode material is LFP (lithium iron phosphate, LiFePO4), the negative electrode is Gr, and the electrolyte formula is (DMC:EMC:EC = 1:1:1, 2% VC, 1mol / L). The specific implementation steps for testing whether the battery system is sufficiently wetted are as follows:

[0088] Step B1: Cut the positive electrode sheet of the lithium iron phosphate battery into 50mm*95mm size sheets, and cut the positive electrode tabs into 10mm*10mm size sheets;

[0089] Step B2: Cut the negative electrode sheet of the lithium iron phosphate battery into 55mm*100mm size sheets, and cut the negative electrode tabs into 10mm*10mm size sheets;

[0090] Step B3: Cut the lithium strip to a size of 55mm*100mm, and the size of the cut lithium strip tabs is 10mm*10mm;

[0091] Step B4: Using one positive electrode sheet as the positive electrode and two lithium strips as the negative electrode, the electrodes are separated by a separator. Following the cell stacking process, the electrodes are stacked, tabs are welded, the casing is installed, electrolyte is injected, and finally the casing is sealed to obtain the positive electrode-battery model. Similarly, using one negative electrode sheet as the positive electrode and two lithium strips as the negative electrode, the electrodes are separated by a separator. The same steps are followed to obtain the negative electrode-battery model.

[0092] Step B5: After the positive electrode-battery model is filled with electrolyte, it is placed in a 45℃ constant temperature chamber. The voltage changes during the high-temperature static period of the cell are collected using Xinwei equipment. The voltage changes are as follows: Figure 7 As shown. When the battery is fully wetted, the voltage will remain constant, and the final stable voltage value of the positive electrode-battery model is V. 正极 =3.233V;

[0093] Step B6: After the negative electrode-battery model is filled with electrolyte, it is placed in a 45℃ constant temperature chamber. The voltage changes during the high-temperature static period of the cell are collected using Xinwei equipment. The voltage changes are as follows: Figure 8 As shown. When the battery is fully wetted, the voltage will remain constant, and the final stable voltage value of the negative electrode-battery model is V. 负极 =2.964V;

[0094] Step B7: According to formula V 全电池 =V 正极 -V 负极 The voltage V after full immersion of the full cell was calculated. 全电池 =0.269V.

[0095] After the test, the results were verified. A soft-pack cell was fabricated using LFP as the positive electrode material, Gr as the negative electrode, and an electrolyte formulation of (DMC:EMC:EC = 1:1:1, 2% VC, 1 mol / L). After electrolyte injection, the cell was placed at 45°C for static treatment, and the change in the full cell voltage during the static treatment process was monitored. Figure 9 As shown, when the voltage reaches 0.269V, it indicates that the cell wetting is complete. Tests show that after 15 hours of wetting, the full battery voltage of the lithium iron phosphate cell reaches 0.269V, indicating complete wetting. To verify whether wetting was complete, cell structures were disassembled after 5 hours, 15 hours, and 20 hours of wetting, respectively. The results show that the electrolyte wetting was sufficient after 15 hours.

[0096] The above provides a detailed description of a battery electrolyte wetting determination method provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the technical solutions and core ideas of this application. Those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for determining battery electrolyte wetting, characterized in that, include: Obtain the first electrode, second electrode, and lithium strip of the battery under test and perform pretreatment; The first battery model is constructed by using the pre-treated first electrode as the positive electrode and the lithium strip as the negative electrode. The second battery model is constructed by using the pretreated second electrode as the positive electrode and the lithium strip as the negative electrode. The difference between the stable voltages of the first battery model and the second battery model is calculated. The method of using the voltage difference as a threshold voltage to determine the electrolyte wetting degree of the tested battery includes: Obtain the positive and negative electrode voltages of the battery under test; The voltage difference is obtained by subtracting the negative voltage from the positive voltage. The voltage difference is compared with the threshold voltage, and the degree of wetting of the tested battery is determined based on the comparison result.

2. The battery electrolyte wetting determination method as described in claim 1, characterized in that, The method for calculating the difference in stable voltage between the first battery model and the second battery model includes: Monitor the voltage change of the first battery model during the aging process, and record it as the first voltage after the voltage stabilizes; Monitor the voltage change of the second battery model during the aging process, and record it as the second voltage after the voltage stabilizes; The difference between the first voltage and the second voltage is obtained.

3. The battery electrolyte wetting determination method as described in claim 1, characterized in that, The method for obtaining the first electrode, second electrode, and lithium strip of the battery and performing pretreatment includes: Obtain the first electrode of the battery under test, and cut the first electrode; Obtain the second electrode of the battery under test, and cut the second electrode; Obtain the lithium strip of the battery under test and cut the lithium strip; The first electrode sheet after cutting has a first area S1mm. 2 The cut second electrode has a second area S2mm. 2 The cut lithium strip has a third area S3mm. 2 The second area is S2mm 2 Greater than or equal to the third area S3mm 2 The third area S3mm 2 Larger than the first area S1mm 2 The first area S1mm 2 The second area S2mm 2 The third area S3mm 2 The relationship is satisfied as follows: 1≤S2 / S3≤1.2; 1≤S3 / S1≤1.

5.

4. The battery electrolyte wetting determination method as described in claim 3, characterized in that, The determination method further includes obtaining the electrode tabs and cutting the electrode tabs; The tabs are used to connect the first electrode, the second electrode, and the lithium strip, respectively; the cut tabs have a fourth area of ​​S4mm. 2 The first area S1mm 2 and the fourth area S4mm 2 The following condition is satisfied: 2≤S1 / S4≤3.

5. The battery electrolyte wetting determination method as described in claim 4, characterized in that, The first electrode is the positive electrode of the battery under test, and the material is NCM. The second electrode is the negative electrode of the battery under test, and the material is Gr. The lithium strip is a copper-lithium composite strip.

6. The battery electrolyte wetting determination method as described in claim 4, characterized in that, The method for constructing the first battery model includes: The first electrode is used as the positive terminal of the first battery model, and the two lithium strips are used as the negative terminals of the first battery model. The positive and negative terminals are separated by a separator. After the first electrode and the lithium strip are connected to their respective tabs, they are packaged into a casing and sealed after electrolyte is injected.

7. The battery electrolyte wetting determination method as described in claim 6, characterized in that, The construction method of the second battery model includes: The second electrode is used as the positive terminal of the second battery model, and the two lithium strips are used as the negative terminals of the second battery model. The positive and negative terminals are separated by a separator. The second electrode and the lithium strip are connected to their respective tabs and then encapsulated in a housing, and sealed after electrolyte is injected.

8. The battery electrolyte wetting determination method as described in claim 7, characterized in that, The electrolyte injected into the first battery model and the second battery model is the same as the electrolyte of the battery under test; The electrolyte ratio is DMC:EMC:EC = 1:1:1, 2% VC, 1 mol / L.

9. The battery electrolyte wetting determination method as described in claim 1, characterized in that, The judgment method further includes aging treatment of the first battery model and the second battery model: Place the first battery model and the second battery model into the aging device; The aging equipment accelerates the aging of the first battery model and the second battery model by controlling temperature, humidity and pressure; The temperature range is 40-45℃, while the ambient dew point temperature is below -35℃.

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