METHOD FOR MEASURING OIL CONTENT OF LITHIUM BATTERY SEPARATOR BY USING DSC

Abstract

A method for measuring the oil content of a lithium battery separator by using DSC includes the following steps: taking 5-10 mg of an oil-containing separator sample from the lithium battery separator, and taking 5-10 mg of an oil-free separator sample from an oil-free separator; performing an enthalpy test on the oil-free separator sample at room temperature by using a differential scanning calorimeter to obtain a first enthalpy value, and performing an enthalpy test on the oil-containing separator sample by using the differential scanning calorimeter to obtain a second enthalpy value; subtracting the second enthalpy value from the first enthalpy value to obtain a difference, and then dividing the difference by the first enthalpy value to obtain the oil content of the oil-containing separator sample.

Claims

1. A method for measuring an oil content of a lithium battery separator by using DSC, comprising the following steps: taking 5-10 mg of an oil-containing separator sample from the lithium battery separator, taking 5-10 mg of an oil-free separator sample from an oil-free separator, and performing an enthalpy test on the oil-free separator sample at room temperature by using a differential scanning calorimeter to obtain a first enthalpy value; performing first heating on the oil-containing separator sample from the room temperature to a temperature of 160-240° C. at a heating rate of 3-30 K/min, maintaining the temperature for 5-15 min, and then cooling the oil-containing separator sample to the room temperature at a cooling rate of 3-30 K/min; and performing second heating on the oil-containing separator sample from the room temperature to the temperature of 160-240° C. at the heating rate of 3-30 K/min, and then naturally cooling the oil-containing separator sample to the room temperature; performing an enthalpy test on the oil-containing separator sample by using the differential scanning calorimeter to obtain a second enthalpy value, subtracting the second enthalpy value from the first enthalpy value to obtain a difference, and then dividing the difference by the first enthalpy value to obtain the oil content of the oil-containing separator sample.

2. The method according to claim 1, wherein, a weight of the oil-containing separator sample is equal to a weight of the oil-free separator sample.

3. The method according to claim 2, wherein, the heating rate of the first heating is 10 K/min, and a heating time of the first heating is 17.5 min.

4. The method according to claim 3, wherein, the cooling rate after the first heating is 20 K/min.

5. The method according to claim 4, wherein, the heating rate of the second heating is 10 K/min, and a heating time of the second heating is 17.5 min.

6. The method according to claim 1, wherein, the room temperature is 25° C.

7. The method according to claim 2, wherein, the room temperature is 25° C.

8. The method according to claim 3, wherein, the room temperature is 25° C.

9. The method according to claim 4, wherein, the room temperature is 25° C.

10. The method according to claim 5, wherein, the room temperature is 25° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The detailed description of the preferred embodiments below clearly shows the advantages and superiority of the present invention to those of ordinary skill in the art. The drawings are only used to illustrate the preferred embodiments, and should not be construed as limiting the present invention. In addition, throughout the drawings, the same reference designators are used to denote the same components.

[0015] FIGURE is a graph showing curves of the enthalpy values obtained from the differential scanning calorimeter during the measurement process.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0016] In order to clearly illustrate the technical solutions in the embodiments of the present invention, the experimental process is described in detail hereinafter. Specifically, a conventional separator with a thickness of 12 μm and a porosity of 40% is selected, then the oil content of the separator in different processes, including die head (fetching the separator from the die head for DSC), cast, machine direction orientation (MDO), transverse direction orientation (TDO)1, and TDO2, is measured by two methods, which are compared as the following.

[0017] (1) Traditional Method

[0018] A separator with a weight m1 is ultrasonically cleaned in an ultrasonic cleaner (power: 300 W) with dichloromethane for 20 min. During the ultrasonic cleaning process, the separator is shaken constantly by using a tweezer. After 20 min, the separator is again ultrasonically cleaned in the ultrasonic cleaner (power: 300 W) with new dichloromethane for 10 min to extract the mineral oil in the separator thoroughly. After being cleaned 2 times, the separator is removed from the ultrasonic cleaner by using the tweezer, and placed in a watch glass. Then, the separator is placed and dried in a dryer at a temperature of 70° C. for 20 min. When the time is up, the separator is fetched from the dryer, and then cooled in a crucible for 10 min. Subsequently, the separator is weighed by using a scale to obtain its weight m2. The difference between m1 and m2 is the weight of the mineral oil, such that the content of the mineral oil can be obtained.

TABLE-US-00001 TABLE 1 Original Weight separator Extraction Drying Drying Cooling after White oil Total weight time temperature time time extraction content duration No. Process (g) (min) (° C.) (min) (min) (g) (%) (min) 1 Die head 1.363 30 70 20 10 0.488 64.20% 75 2 CAST 0.922 30 70 20 10 0.348 62.26% 75 3 MDO 0.797 30 70 20 10 0.326 59.10% 75 4 TDO1 0.657 30 70 20 10 0.228 65.30% 75 5 TDO2 0.294 30 70 20 10 0.293 0.34% 75

[0019] (2) The Method of the Present Invention

[0020] 5-10 mg of an oil-containing separator sample is taken from the lithium battery separator, and 5-10 mg of an oil-free separator sample is taken from an oil-free separator. An enthalpy test is performed on the oil-free separator sample at room temperature by using a differential scanning calorimeter to obtain a first enthalpy value. First heating is performed on the oil-containing separator sample from the room temperature to a temperature of 160-240° C. at a heating rate of 3-30 K/min. The temperature is maintained for 5-15 min, and then the oil-containing separator sample is cooled to the room temperature at a cooling rate of 3-30 K/min. Second heating is performed on the oil-containing separator sample from room temperature to the temperature of 160-240° C. at a heating rate of 3-30 K/min, and then the oil-containing separator sample is naturally cooled to room temperature. An enthalpy test is performed on the oil-containing separator sample by using the differential scanning calorimeter to obtain a second enthalpy value, the second enthalpy value is subtracted from the first enthalpy value to obtain a difference, and then the difference is divided by the first enthalpy value to obtain the oil content of the oil-containing separator sample.

TABLE-US-00002 TABLE 2 Original separator Blank White oil Total weight Enthalpy enthalpy content duration No. Process (g) (J/g) (J/g) (%) (min) 1 Die head 0.0086 70.85 198.7 64.34% 54 2 CAST 0.0074 75.22 198.7 62.14% 54 3 MDO 0.0068 81.35 198.7 59.06% 54 4 TDO1 0.0092 68.55 198.7 65.50% 54 5 TDO2 0.0062 198.1 198.7 0.30% 54

[0021] Table 1 and Table 2 show the results of the two test methods. Specifically, Table 1 shows the test data obtained by using the traditional method to detect the oil content of the lithium battery separator according to the embodiment of the present invention, and Table 2 shows the test data obtained by using DSC to detect the oil content of the lithium battery separators according to the embodiment of the present invention. FIGURE is a graph showing curves of the enthalpy values obtained from the differential scanning calorimeter during the measurement process.

[0022] Obviously, those skilled in the art can make various modifications and changes to the present invention without departing from the spirit and scope of the present invention. Therefore, if these modifications and changes of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and changes.