Method for testing leveling property of battery slurry

Abstract

The invention belongs to the field of batteries, and particularly relates to a method for testing the leveling property of battery slurry, which is used for comprehensively judging the viscosity, the solid content, the recovery time of a three-stage test, the thixotropic ring test area, the contact angle and the phase angle difference of an oscillation scanning test. According to the technical scheme, the leveling property of the slurry is comprehensively evaluated by testing the viscosity, the solid content, the three-section type, the thixotropic ring, the contact angle and the oscillation scanning of the slurry, and the six test results are mutually proved, so that the problem of relatively large error caused by leveling property judgment according to a single test result is avoided, the yield of an electrode process is improved, and the production cost is reduced. And the battery manufacturing cost is saved.

Description

Technical Field

[0001] The invention belongs to the field of batteries, and in particular relates to a method for testing the leveling property of battery slurry. Background Art

[0002] With the development of science and technology and the progress of energy technology, lithium batteries are widely used in electric vehicles, special power supplies, portable electronic products and other fields, which are profoundly changing our production and lifestyle. As the first process of battery production, the performance of slurry plays a vital role in the quality of the battery. The leveling property of the slurry directly affects the coating process of battery processing.

[0003] Poor leveling will lead to uneven coating thickness, thus affecting the capacity, thickness and other performance of the battery; excessive leveling will cause the slurry at the edge of the foil to dry too fast during the coating process, and the slurry will continue to spread to both sides of the foil, resulting in black and bright edges during the rolling process, affecting the subsequent laser cutting process of battery production; the core coating process index in the power battery is the CPK value. The higher the value, the higher the yield and the better the consistency of the process. Adjusting the slurry during the homogenization process to give it the best leveling property can improve the CPK value of the coating process.

[0004] Among the existing slurry leveling test technologies, one method is to examine the slurry through the shear rate curve, and judge the leveling of the slurry according to the change of the slurry viscosity within the set shear rate range. This method is not intuitive enough; another method uses a paint sag detector to test the leveling of the slurry, but considering that the battery slurry is a non-Newtonian fluid with high solid content and high viscosity, the sag meter method for testing the leveling of the battery slurry has a relatively large error. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for testing the leveling property of battery slurry.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for judging the leveling property of battery slurry is provided, which makes a comprehensive judgment through viscosity, solid content, recovery time of a three-stage test, thixotropic ring test area, contact angle, and phase angle difference of an oscillation scanning test.

[0008] Use the following formula to judge: L C =(η*SC*(θ C -60)*10) / ((10+t)*(1000+S)*δ); where η is viscosity, SC is solid content, t is recovery time of three-stage test, S is thixotropic ring test area, θ Cis the contact angle, and δ is the phase angle difference of the oscillation scanning test;

[0009] Preferably, the judgment standard is that when Lc is less than 0.05, the slurry has too strong leveling property; when 0.05≤Lc≤1, the slurry has too strong leveling property; when Lc>1, the slurry has poor leveling property.

[0010] The viscosity test equipment is a rotational viscosity tester; preferably, a No. 3 rotor is selected and the rotation speed is set to 50 r / min.

[0011] The solid content is calculated by drying and weighing method; preferably, the method specifically comprises the following steps: taking 2-4 g of battery slurry, drying at 150° C. for 20 min, and calculating the weight loss ratio, solid content = 1-weight loss ratio.

[0012] The three-stage test equipment is a Malvern rheometer. Preferably, the test method is to set the 0.1s -1 Shear rate test 180s, then set 200s -1 Shear rate test 60s, final setting 0.1s -1 The shear rate test lasted for 600 s.

[0013] The thixotropic ring test equipment is a Malvern rheometer, and the shear rate variation range is 0.01s -1 ~200s -1 .

[0014] The oscillation sweep test is performed using a Malvern rheometer, preferably with a frequency setting of 1H. Z .

[0015] The contact angle test equipment is a Biolin surface tension meter. Preferably, the needle is 50 mm long and has an inner diameter of 0.26 mm. The contact plane is a flat smooth foil with a dyne value of 38. The contact angle data is recorded at 10 s.

[0016] The battery slurry meets the following parameters: a) viscosity η is limited to between 1500mpa·s-20000mpa·s, b) solid content SC is limited to between 40%-65%, c) t range is limited to between 1s-15s, d) S range is limited to between 100-1000, e) θ C The range is limited to 60°-90°, and the f)δ range is limited to 45°-85°.

[0017] The battery slurry performance test should be carried out within 24 hours after the slurry is discharged; the slurry needs to be stirred during the slurry performance test, and the stirring method is to stir clockwise with a glass rod; preferably, stirring for 1 minute; the test environment needs to be temperature controlled, and the temperature is controlled between 23°C±2°C.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The technical solution of the present application comprehensively evaluates the leveling of the slurry by testing six properties, namely, slurry viscosity, solid content, three-stage, thixotropic ring, contact angle, and oscillation scanning. The six test results corroborate each other, avoiding the problem of large errors caused by judging the leveling according to a single test result, thereby improving the yield rate of the electrode process and saving the cost of battery production. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Example 1 battery slurry test results diagram;

[0021] Figure 2 Example 2 battery slurry test result diagram;

[0022] Figure 3 Example 3 battery slurry test results diagram;

[0023] Figure 4 Example 4 battery slurry test result diagram;

[0024] Figure 5 Example 5 battery slurry test results diagram. DETAILED DESCRIPTION

[0025] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and the best embodiments.

[0026] A method for judging the leveling property of battery slurry is provided, which makes a comprehensive judgment through viscosity, solid content, recovery time of a three-stage test, thixotropic ring test area, contact angle, and phase angle difference of an oscillation scanning test.

[0027] The following formula can be used for specific judgment: L C =(η*SC*(θ C -60)*10) / ((10+t)*(1000+S)*δ); where η is viscosity, SC is solid content, t is recovery time of three-stage test, S is thixotropic ring test area, θ C is the contact angle, and δ is the phase angle difference of the oscillation scanning test (δ = 0° is an ideal solid, 45° < δ < 90° the test sample exhibits liquid phase behavior, and δ = 90° is an ideal liquid);

[0028] The judgment criteria are: when Lc is less than 0.05, the slurry has too strong leveling properties; when 0.05≤Lc≤1, the slurry has too good leveling properties; when Lc>1, the slurry has poor leveling properties.

[0029] It should be noted that the test methods for the various parameters in this application are all standard test methods. If other test methods are used, they are also applicable to the technical solution of this application, and the formulas are fine-tuned according to actual conditions.

[0030] The test of each parameter in this embodiment can be carried out in the following manner:

[0031] The viscosity test equipment is a rotary viscosity tester; preferably, rotor No. 3 is selected and the speed is set to 50r / min. The solid content calculation method adopts the drying weighing method; preferably, it specifically includes the following steps: take 2-4g of battery slurry, dry at 150℃ for 20min, calculate the weight loss ratio, solid content = 1-weight loss ratio. The three-stage test equipment is a Malvern rheometer. Preferably, the test method is to set 0.1s -1 Shear rate test 180s, then set 200s -1 Shear rate test 60s, final setting 0.1s -1 The shear rate test lasted for 600s. The thixotropic ring test equipment was a Malvern rheometer, and the shear rate change range was 0.01s. -1 ~200s -1 The oscillation sweep test was performed using a Malvern rheometer, preferably with a frequency of 1H. Z The contact angle test equipment is a Biolin surface tension meter. Preferably, the needle is 50 mm long and has an inner diameter of 0.26 mm. The contact plane is a flat foil with a dyne value of 38. The contact angle data is recorded at 10 seconds.

[0032] When using the above formula for judgment, each parameter test has a certain range: the battery slurry meets the following parameters: a) viscosity η is limited to between 1500mpa·s-20000mpa·s, b) solid content SC is limited to between 40%-65%, c) t range is limited to between 1s-15s, d) S range is limited to between 100-1000, e) θ C The range is limited to 60°-90°, and the f)δ range is limited to 45°-85°.

[0033] The following points should be noted during the test process: the battery slurry performance test should be carried out within 24 hours after the slurry is discharged; the slurry needs to be stirred during the slurry performance test, and the stirring method is to stir clockwise with a glass rod; preferably, stirring for 1 minute; the test environment needs to be temperature controlled, and the temperature is controlled between 23℃±2℃. If an abnormal situation is encountered during the test, the test needs to be re-tested after pausing, otherwise the curve will have breakpoints, affecting the accuracy of the test data.

[0034] This application uses the wet mechanical stirring method as an example for homogenization, and the system is graphite + binder. The empirical formula method is also applicable to other homogenization methods and slurry systems.

[0035] The negative electrode slurry of lithium battery was tested. The homogenization method was wet mechanical stirring. The system was graphite + binder. The solid content was set to 40%, 45%, 50%, 55%, and 60%, respectively. Within 24 hours after the slurry was discharged, the slurry was tested for viscosity, solid content, three-stage, thixotropic ring, contact angle, and oscillation scanning. The test results of three-stage, thixotropic ring, contact angle, and oscillation scanning are shown in Figure 1-Figure 5 , statistical test results, according to the empirical formula: Lc = (η * SC * (θ C -60)*10) / ((10+t)*(1000+S)*δ) is used for calculation. The judgment standard is that when Lc<0.05, the slurry leveling is too strong; when 0.05≤Lc≤1, the slurry leveling is too strong and good; when Lc>1, the slurry leveling is poor. The implementation results are shown in the following table.

[0036] Table 1

[0037]

[0038] The slurry is coated, the indoor temperature is 23±2℃, the humidity is ≤10%, the drying temperature is 105℃, the fan frequency is 30HZ, the belt speed is 5m / s, and the surface density of the electrode during the coating process is monitored by an X-ray surface density meter. In the coating process of Example 1, due to the excessive leveling of the slurry, the drying speed of the slurry at the edge of the foil is too fast. The slurry continues to spread to both sides during the coating and drying process, resulting in the thickness of the foil edge exceeding the standard. The problem of black and bright edges appeared in the subsequent rolling process. The black and bright edges will be judged as leaking foil in the subsequent laser cutting process, which will cause the laser cutting process to be unable to proceed, directly reducing the pass rate of the electrode process. No problems were found in the coating, rolling, and laser cutting processes of the electrode in Examples 2 to 4. In Example 5, the slurry has poor leveling, and the consistency of the coating amount is difficult to control. The X-ray surface density meter frequently alarms during the coating process.

[0039] In summary, the technical solution of the present application comprehensively evaluates the leveling properties of the slurry by testing six properties, namely, slurry viscosity, solid content, three-stage, thixotropic ring, contact angle, and oscillation scanning. The six test results support each other, avoiding the problem of large errors caused by judging the leveling properties based on a single test result, thereby improving the yield rate of the electrode process and saving the cost of battery production.

[0040] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for judging the leveling property of battery slurry, characterized in that: A comprehensive judgment is made based on viscosity, solid content, recovery time of the three-stage test, thixotropic ring test area, contact angle, and phase angle difference of the oscillation scanning test.

2. The method for judging the leveling property of battery slurry according to claim 1, characterized in that: Use the following formula to judge: L C =(η*SC*(θ C -60)*10) / ((10+t)*(1000+S)*δ); where η is viscosity, SC is solid content, t is recovery time of three-stage test, S is thixotropic ring test area, θ C is the contact angle, and δ is the phase angle difference of the oscillation scanning test; Preferably, the judgment standard is that when Lc is less than 0.05, the slurry has too strong leveling property; when 0.05≤Lc≤1, the slurry has too strong leveling property; when Lc>1, the slurry has poor leveling property.

3. The method for testing the leveling property of battery slurry according to claim 1, characterized in that: The viscosity test equipment is a rotation viscosity tester; preferably, a No. 3 rotor is selected and the rotation speed is set to 50r / min.

4. The method for testing the leveling property of battery slurry according to claim 1, characterized in that: The solid content is calculated by drying and weighing method; preferably, the method specifically comprises the following steps: taking 2-4 g of battery slurry, drying at 150° C. for 20 min, and calculating the weight loss ratio, solid content = 1-weight loss ratio.

5. The method for testing the leveling property of battery slurry according to claim 1, characterized in that: The three-stage test equipment is a Malvern rheometer. Preferably, the test method is to set the 0.1s -1 Shear rate test 180s, then set 200s -1 Shear rate test 60s, final setting 0.1s -1 The shear rate test lasted for 600 s.

6. The method for testing the leveling property of battery slurry according to claim 1, characterized in that: The thixotropic ring test equipment is a Malvern rheometer, and the shear rate variation range is 0.01s -1 ~200s -1 .

7. The method for testing the leveling property of battery slurry according to claim 1, characterized in that: The oscillation sweep test is performed using a Malvern rheometer, preferably with a frequency setting of 1H. Z .

8. The method for testing the leveling property of battery slurry according to claim 1, characterized in that: The contact angle test equipment is a Biolin surface tension meter. Preferably, the needle is 50 mm long and has an inner diameter of 0.26 mm. The contact plane is a flat smooth foil with a dyne value of 38. The contact angle data is recorded at 10 s.

9. The method for testing the leveling property of battery slurry according to claim 1, characterized in that: The battery slurry meets the following parameters: a) viscosity η is limited to between 1500mpa·s-20000mpa·s, b) solid content SC is limited to between 40%-65%, c) t range is limited to between 1s-15s, d) S range is limited to between 100-1000, e) θ C The range is limited to 60°-90°, and the f)δ range is limited to 45°-85°.

10. The method for testing the leveling property of battery slurry according to claim 1, characterized in that: The battery slurry performance test should be carried out within 24 hours after the slurry is discharged; the slurry needs to be stirred during the slurry performance test, and the stirring method is to stir clockwise with a glass rod; preferably, stirring for 1 minute; the test environment needs to be temperature controlled, and the temperature is controlled between 23°C±2°C.

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