KR102659129B1 - Quantitative analytical method for solubility of polyvinylidenefluoride(pvdf) - Google Patents

Abstract

The present invention includes the steps of 1) preparing a solution of polyvinylidene fluoride (PVDF) dissolved in a solvent; 2) Flowing the polyvinylidene fluoride (PVDF) solution at a constant speed and measuring the number of particles for each polyvinylidene fluoride (PVDF) particle size from an image file obtained by high-speed photography; 3) Polyvinylidene fluoride (PVDF) particles having a specific particle size or less are classified as dissolved polyvinylidene fluoride (PVDF), and polyvinylidene fluoride (PVDF) particles having a specific particle size or more are classified as undissolved. Classifying polyvinylidene fluoride (PVDF) as dissolved polyvinylidene fluoride (PVDF) and evaluating the solubility of polyvinylidene fluoride (PVDF) through the number of dissolved and undissolved polyvinylidene fluoride (PVDF) particles; It relates to an analysis method for quantifying fluoride (PVDF) solubility.

Description

Polyvinylidene fluoride (PVDF) solubility quantification analysis method {QUANTITATIVE ANALYTICAL METHOD FOR SOLUBILITY OF POLYVINYLIDENEFLUORIDE(PVDF)}

The present invention relates to an analysis method for quantifying polyvinylidene fluoride (PVDF) solubility.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among such secondary batteries, lithium secondary batteries exhibit high energy density and operating potential, long cycle life, and low self-discharge rate. Batteries have been commercialized and are widely used.

A lithium secondary battery generally consists of a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator, and an electrolyte, and is a secondary battery in which charging and discharging are performed by intercalation-decalation of lithium ions. Lithium secondary batteries have the advantages of high energy density, large electromotive force, and high capacity, so they are applied in various fields.

Polyvinylidene fluoride (PVDF), which is widely used as a binder for the positive and negative electrodes of lithium secondary batteries, has large limitations in the solvents in which it can be dissolved and does not have high solubility. If polyvinylidene fluoride (PVDF) does not dissolve well, the polyvinylidene fluoride (PVDF) aggregates and is not evenly distributed on the electrode, which causes an increase in resistance within the electrode, a decrease in adhesion, and further life resistance of the lithium secondary battery cell.

Accordingly, to improve the solubility of polyvinylidene fluoride (PVDF), a method of controlling the particle size and dissolution temperature of polyvinylidene fluoride (PVDF) is used, and the method of evaluating the solubility is visual observation. This method is widely used. However, the conventional method of evaluating the solubility of polyvinylidene fluoride (PVDF) with the naked eye had limitations in accurately and reliably evaluating the solubility of polyvinylidene fluoride (PVDF). There has been a need for a method to evaluate the solubility of PVDF.

Japanese Patent Publication No. 2013-217818

The present invention seeks to provide a method for quantifying the solubility of polyvinylidene fluoride (PVDF), which can quantitatively evaluate the solubility of polyvinylidene fluoride (PVDF), which is used as an electrode binder for lithium secondary batteries.

The present invention includes the steps of 1) preparing a solution of polyvinylidene fluoride (PVDF) dissolved in a solvent; 2) Flowing the polyvinylidene fluoride (PVDF) solution at a constant speed and measuring the number of particles for each polyvinylidene fluoride (PVDF) particle size from an image file obtained by high-speed photography; 3) Polyvinylidene fluoride (PVDF) particles having a specific particle size or less are classified as dissolved polyvinylidene fluoride (PVDF), and polyvinylidene fluoride (PVDF) particles having a specific particle size or more are classified as undissolved. Classifying polyvinylidene fluoride (PVDF) as dissolved polyvinylidene fluoride (PVDF) and evaluating the solubility of polyvinylidene fluoride (PVDF) through the number of dissolved and undissolved polyvinylidene fluoride (PVDF) particles; An analysis method for quantifying fluoride (PVDF) solubility is provided.

According to the present invention, the solubility of polyvinylidene fluoride (PVDF), which is used as a binder for electrodes of lithium secondary batteries, can be quantitatively evaluated. By using the polyvinylidene fluoride (PVDF) solubility quantification analysis method of the present invention, the solubility of polyvinylidene fluoride (PVDF) can be evaluated more precisely and reliably compared to the conventional method of evaluating solubility with the naked eye. , it can prevent an increase in resistance, a decrease in adhesion, and further a decrease in the lifespan of a lithium secondary battery cell due to agglomeration of the polyvinylidene fluoride (PVDF) binder in the electrode.

Hereinafter, the present invention will be described in more detail to facilitate understanding of the present invention. At this time, the terms or words used in this specification and claims should not be construed as limited to their usual or dictionary meanings, and the inventor should appropriately define the concept of the term in order to explain his or her invention in the best way. It must be interpreted with meaning and concept consistent with the technical idea of the present invention based on the principle that it can be done.

The present invention includes the steps of 1) preparing a solution of polyvinylidene fluoride (PVDF) dissolved in a solvent; 2) Flowing the polyvinylidene fluoride (PVDF) solution at a constant speed and measuring the number of particles for each polyvinylidene fluoride (PVDF) particle size from an image file obtained by high-speed photography; 3) Polyvinylidene fluoride (PVDF) particles having a specific particle size or less are classified as dissolved polyvinylidene fluoride (PVDF), and polyvinylidene fluoride (PVDF) particles having a specific particle size or more are classified as undissolved. Classifying polyvinylidene fluoride (PVDF) as dissolved polyvinylidene fluoride (PVDF) and evaluating the solubility of polyvinylidene fluoride (PVDF) through the number of dissolved and undissolved polyvinylidene fluoride (PVDF) particles; An analysis method for quantifying fluoride (PVDF) solubility is provided.

The polyvinylidene fluoride (PVDF) solubility quantification analysis method of the present invention will be described in detail step by step.

First, in step 1), a polyvinylidene fluoride (PVDF) solution dissolved in a solvent is prepared.

The polyvinylidene fluoride (PVDF) may be used as a binder for electrodes of lithium secondary batteries, and the binder serves to improve adhesion between electrode active material particles and adhesion between the electrode active material and the electrode current collector.

The solvent is not particularly limited, but solvents commonly used in preparing electrode slurries for lithium secondary batteries can be used, for example, dimethyl sulfoxide (DMSO), isopropyl alcohol, N -Methylpyrrolidone (NMP), acetone, or water may be used, and one of these may be used alone or a mixture of two or more may be used.

The polyvinylidene fluoride (PVDF) is a polymer that exists rolled up in a spherical shape, but when dissolved in a solvent, it unfolds linearly and is distributed in the solution. Polyvinylidene fluoride (PVDF) used as a binder for electrodes of lithium secondary batteries may be, for example, spherical particles with an average particle diameter (D ₅₀ ) of 1 to 500 ㎛, more preferably 10 to 200 ㎛. It may be a spherical particle, but is not limited thereto.

In the present invention, the average particle size (D ₅₀ ) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. The average particle diameter (D ₅₀ ) can be measured using, for example, a laser diffraction method. For example, the method for measuring the average particle diameter (D ₅₀ ) of the positive electrode active material is to disperse the particles of the positive electrode active material in a dispersion medium and then introduce them into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000) to measure approximately After irradiating 28 kHz ultrasonic waves with an output of 40 W, the average particle diameter (D ₅₀ ) corresponding to 50% of the volume accumulation in the measuring device can be calculated.

Solubility can be adjusted by adjusting the time and dissolution temperature for dissolving the polyvinylidene fluoride (PVDF) in the solvent, and the solubility can be quantitatively evaluated through the polyvinylidene fluoride (PVDF) solubility quantification analysis method of the present invention. You can.

Next, in step 2), the polyvinylidene fluoride (PVDF) solution is flowed at a constant speed and the number of particles for each polyvinylidene fluoride (PVDF) particle size is measured from the image file obtained by high-speed photography.

High-speed imaging of the polyvinylidene fluoride (PVDF) solution can be performed using a high-speed image analysis device, for example, Sympatec's QICPIC equipment. In addition, high-speed imaging can be performed while flowing the polyvinylidene fluoride (PVDF) solution at a rate of 1 to 1,000 ml/min, more preferably at a rate of 10 to 500 ml/min, and even more preferably at a rate of 50 to 300 ml/min. You can shoot at high speed while streaming. By flowing in the above speed range and shooting at high speed, the effect of analyzing the distribution of particles in the solution by size can be excellent without duplication of frames.

The number of polyvinylidene fluoride (PVDF) particles can be measured by particle size in the range of 1 to 5000㎛ from the image file obtained by the high-speed shooting, but is not limited to this, and the polyvinylidene fluoride (PVDF) dissolved in step 1) above ( PVDF) The particle size range to be measured can be adjusted appropriately by considering the average particle size of the particles and the degree of solubility according to the solvent. More specifically, the number of polyvinylidene fluoride (PVDF) particles in each particle size interval of 5㎛ to 1000㎛ in the range of 1 to 5000㎛ can be measured from the image file obtained by the high-speed shooting, but is not limited thereto. The range of particle diameter intervals to be measured can be adjusted appropriately by considering the average particle diameter of the polyvinylidene fluoride (PVDF) particles dissolved in step 1) and the degree of solubility according to the solvent. For example, if the number of polyvinylidene fluoride (PVDF) particles in each section is measured at 5㎛ intervals, the number of polyvinylidene fluoride (PVDF) particles having a particle diameter of greater than 0㎛ to 5㎛, greater than 5㎛ to The number of particles in each particle size section can be measured in the same way as the number of polyvinylidene fluoride (PVDF) particles with a particle diameter of 10㎛, and the number of polyvinylidene fluoride (PVDF) particles with a particle diameter of more than 10㎛ to 15㎛. If the number of polyvinylidene fluoride (PVDF) particles in each section is measured at 100㎛ intervals, the number of polyvinylidene fluoride (PVDF) particles having a particle diameter of more than 0㎛ to 100㎛, more than 100㎛ to 200 The number of particles in each particle size section can be measured in the same way as the number of polyvinylidene fluoride (PVDF) particles with a particle size of ㎛, and the number of polyvinylidene fluoride (PVDF) particles with a particle size of more than 200㎛ to 300㎛. there is. Meanwhile, considering the average particle diameter of the polyvinylidene fluoride (PVDF) particles dissolved in step 1) and the degree of solubility according to the solvent, the particle size interval can be set by adjusting the particle size interval differently depending on the particle size. For example, the particle size section may be set at 5㎛ intervals up to 100㎛, the particle size section may be set at 20㎛ intervals up to 1000㎛, and the particle size section may be set at 1000㎛ intervals up to 5000㎛.

Next, 3) polyvinylidene fluoride (PVDF) particles having a certain particle size or less are classified as dissolved polyvinylidene fluoride (PVDF), and polyvinylidene fluoride (PVDF) particles having a certain particle size or more are classified as dissolved polyvinylidene fluoride (PVDF). is classified as undissolved polyvinylidene fluoride (PVDF), and the solubility of polyvinylidene fluoride (PVDF) is evaluated through the number of dissolved and undissolved polyvinylidene fluoride (PVDF) particles.

The specific particle size that serves as the basis for classification of the dissolved and undissolved polyvinylidene fluoride (PVDF) may be based on the average particle size of the polyvinylidene fluoride (PVDF) particles dissolved in step 1). For example, if polyvinylidene fluoride (PVDF) with an average particle diameter (D ₅₀ ) of 150㎛ was dissolved in step 1), polyvinylidene fluoride (PVDF) particles with a particle diameter of 150㎛ or less were dissolved. Polyvinylidene fluoride (PVDF) particles with a particle diameter exceeding 150㎛ can be classified as undissolved. Afterwards, solubility can be quantitatively calculated through the number ratio of dissolved and undissolved polyvinylidene fluoride (PVDF) particles.

Meanwhile, when evaluating solubility in this step, based on the average particle diameter of the polyvinylidene fluoride (PVDF) particles dissolved in step 1), a weight is given to the number of measured particles for particle sizes that are more than twice the average particle diameter. So you can calculate solubility. For example, when polyvinylidene fluoride (PVDF) with an average particle diameter (D ₅₀ ) of 150㎛ is dissolved in step 1) above. Observation of polyvinylidene fluoride (PVDF) particles with a particle size of 300㎛ or more can be viewed as being formed by two or more polyvinylidene fluoride (PVDF) particles agglomerating, and this is weighted to reflect this in the quantitative calculation of solubility. will be. The weight can be determined by considering the average particle diameter of the polyvinylidene fluoride (PVDF) particles dissolved in step 1) and the degree of solubility according to the solvent. For example, when the average particle diameter (D ₅₀ ) of the polyvinylidene fluoride (PVDF) particles dissolved in step 1) above is 150㎛, the particle size when measuring solubility in this step is greater than 300㎛ to 360㎛. is calculated by giving 2 times the weight to the measured number of particles, and if the particle size is over 360㎛ to 400㎛, it is calculated by giving 3 times the weight to the measured number of particles, and if the particle size is over 400㎛ to 5000㎛. In this case, it can be calculated by giving 5 times the weight to the measured number of particles.

According to the polyvinylidene fluoride (PVDF) solubility quantification analysis method of the present invention, the solubility of polyvinylidene fluoride (PVDF), which is used as a binder for electrodes of lithium secondary batteries, can be quantitatively evaluated. Compared to conventional evaluations of solubility with the naked eye, the solubility of polyvinylidene fluoride (PVDF) can be evaluated more precisely and reliably. As a result, resistance increases due to agglomeration of the polyvinylidene fluoride (PVDF) binder in the electrode, It is possible to prevent a decrease in adhesion and further reduce the lifespan of a lithium secondary battery cell.

Example

For 100 parts by weight of solvent N-methyl-2-pyrrolidone (NMP), 6 parts by weight of polyvinylidene fluoride (PVDF) with an average particle diameter (D ₅₀ ) of 150㎛ was dissolved at 25°C for 1 hour and 4 hours, respectively. , 12 hours and 24 hours were dissolved to prepare a polyvinylidene fluoride (PVDF) solution.

The polyvinylidene fluoride (PVDF) solution was flowed at a rate of 100 ml/min and image files were obtained by high-speed shooting at 500 fps using Sympatec's QICPIC equipment, and the number of particles was measured for each particle size section as shown in Table 1 below.

In addition, for particle sizes larger than 300㎛, solubility was evaluated by calculating the weighted number of particle sizes measured as shown in Table 2 below.

Particle size (㎛) Dissolution time (particle number ratio (%)) 1h 4h 12h 24h Exceeds 0~5 0.00 0.00 0.00 0.00 Exceeding 5~10 35.99 37.97 38.12 41.21 Exceeding 10~15 25.71 26.01 28.46 28.58 Exceeding 15~20 12.04 11.43 12.99 12.39 Exceeding 20~25 8.70 7.20 7.71 7.73 Exceeding 25~30 7.07 5.59 5.32 4.95 Over 30~35 3.08 2.69 2.03 1.53 Over 35~40 2.21 2.51 1.91 1.05 Over 40~45 1.07 1.79 1.13 0.64 Exceeding 45~50 0.83 1.37 0.70 0.43 Over 50~55 0.72 0.79 0.56 0.21 Over 55~60 0.52 0.57 0.31 0.15 Over 60~65 0.35 0.43 0.16 0.15 Over 65~70 0.28 0.29 0.16 0.12 Exceeding 70~75 0.19 0.21 0.18 0.11 Exceeding 75~80 0.13 0.19 0.14 0.11 Exceeding 80~85 0.12 0.30 0.05 0.21 Exceeding 85~90 0.09 0.14 0.02 0.07 Exceeding 90~95 0.09 0.09 0.01 0.03 Exceeding 95~100 0.09 0.06 0.00 0.03 Exceeding 100~110 0.18 0.08 0.00 0.14 Exceeding 110~120 0.12 0.05 0.00 0.11 Exceeding 120~130 0.09 0.09 0.00 0.03 Exceeding 130~140 0.04 0.09 0.00 0.01 Exceeding 140~150 0.03 0.03 0.00 0.01 Exceeding 150~160 0.04 0.02 0.00 0.00 Exceeding 160~170 0.00 0.00 0.00 0.00 Exceeding 170~180 0.00 0.00 0.00 0.00 Exceeding 180~190 0.02 0.00 0.00 0.00 Exceeding 190~200 0.04 0.01 0.00 0.00 Exceeding 200~220 0.01 0.00 0.00 0.00 Exceeding 220~240 0.03 0.00 0.00 0.00 Exceeding 240~260 0.01 0.00 0.00 0.00 Exceeding 260~280 0.01 0.00 0.00 0.00 Exceeding 280~300 0.02 0.01 0.00 0.00 Exceeding 300~320 0.02 0.00 0.00 0.00 Exceeding 320~340 0.00 0.00 0.00 0.00 Exceeding 340~360 0.00 0.00 0.00 0.00 Exceeding 360~380 0.00 0.00 0.00 0.00 Exceeding 380~400 0.01 0.00 0.00 0.00 Exceeding 400~1000 0.01 0.00 0.00 0.00 Exceeding 1000~2000 0.00 0.00 0.00 0.00 Exceeding 2000~3000 0.00 0.00 0.00 0.00 Exceeding 3000~4000 0.00 0.00 0.00 0.00 Exceeding 4000~5000 0.00 0.00 0.00 0.00

Particle size (㎛) weight Dissolution time 1h 1h*weight 4h 4h*weight 12h 12h*weight 24h 24h*weight Exceeding 150~160 One 0.04 0.04 0.02 0.02 0.00 0.00 0.00 0.00 Exceeding 160~170 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Exceeding 170~180 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Exceeding 180~190 0.02 0.02 0.00 0.00 0.00 0.00 0.00 0.00 Exceeding 190~200 0.04 0.04 0.01 0.01 0.00 0.00 0.00 0.00 Exceeding 200~220 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00 Exceeding 220~240 0.03 0.03 0.00 0.00 0.00 0.00 0.00 0.00 Exceeding 240~260 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00 Exceeding 260~280 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00 Exceeding 280~300 0.02 0.02 0.01 0.01 0.00 0.00 0.00 0.00 Exceeding 300~320 2 0.02 0.05 0.00 0.00 0.00 0.00 0.00 0.00 Exceeding 320~340 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Exceeding 340~360 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Exceeding 360~380 3 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 Exceeding 380~400 0.01 0.02 0.00 0.00 0.00 0.00 0.00 0.00 Exceeding 400~1000 5 0.01 0.04 0.00 0.00 0.00 0.00 0.00 0.00 Exceeding 1000~2000 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Exceeding 2000~3000 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Exceeding 3000~4000 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Exceeding 4000~5000 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Sum*1000 - 325.1 - 31.05 - 0.00 - 0.00

* Sum*1000: The Sum value is small, so it is expressed by multiplying by 1000.

Referring to Tables 1 and 2 above, it can be seen that the number of particles exceeding 150㎛ decreases as the dissolution time increases, making it possible to quantitatively evaluate the solubility of polyvinylidene fluoride (PVDF) according to the dissolution time. there was.

In particular, referring to Table 2, when the dissolution time is 1 hour, the value calculated by reflecting the weight for the number of particles exceeding 150㎛ is 325.1, and when the dissolution time is 4 hours, the number of particles exceeding 150㎛ is 325.1. The value calculated by reflecting the weight is 31.05, and when the dissolution time is 12 and 24 hours, the value calculated by reflecting the weight for the number of particles exceeding 150㎛ is 0.00, respectively, and the polyvinylidene fluoride ( The solubility of PVDF) could be evaluated more precisely and quantitatively.

[ Experiment example : Adhesion evaluation]

450 parts by weight of lithium cobalt composite oxide as positive electrode active material particles for 100 parts by weight of polyvinylidene fluoride (PVDF) solution prepared by dissolving for 1 hour, 4 hours, 12 hours, and 24 hours, respectively, as in the above example. , a positive electrode active material slurry was prepared by mixing 25 parts by weight of carbon black as a conductive material. The prepared positive electrode active material slurry was applied to the positive electrode current collector, dried, and then roll pressed to prepare a positive electrode composite with an average thickness of 90㎛. An aluminum (Al) thin film with a thickness of 20 μm was used as the positive electrode current collector.

To measure electrode adhesion, an electrode specimen was manufactured to a size of 2 cm in width and 20 cm in height, and double-sided tape was attached to a glass measuring 2.5 cm in width and length 7.5 cm, and then the prepared specimen was attached to the double-sided tape to prepare an evaluation specimen. The prepared specimen was pulled at a 90° angle at a speed of 300 mm/min, and the force measured was measured, and this was evaluated as the adhesion of the electrode. The results are shown in Table 3.

Dissolution time (h) One 4 12 24 Adhesion (N/m) 88.3 115.1 122.7 121.3

Referring to Table 3, it was confirmed that the adhesion increased as the dissolution time increased, which was consistent with the results inferred from the results of the solubility evaluation of polyvinylidene fluoride (PVDF) according to the present invention.

Claims (8)

1) Preparing a polyvinylidene fluoride (PVDF) solution dissolved in a solvent;
2) Flowing the polyvinylidene fluoride (PVDF) solution at a constant speed and measuring the number of particles for each polyvinylidene fluoride (PVDF) particle size from an image file obtained by high-speed photography;
3) Polyvinylidene fluoride (PVDF) particles having a specific particle size or less are classified as dissolved polyvinylidene fluoride (PVDF), and polyvinylidene fluoride (PVDF) particles having a specific particle size or more are classified as undissolved. Classifying polyvinylidene fluoride (PVDF) as dissolved polyvinylidene fluoride (PVDF) and evaluating the solubility of polyvinylidene fluoride (PVDF) through the number of dissolved and undissolved polyvinylidene fluoride (PVDF) particles;
Polyvinylidene fluoride (PVDF) solubility quantification analysis method comprising.
According to paragraph 1,
Polyvinylidene fluoride, characterized in that the dissolved and undissolved polyvinylidene fluoride (PVDF) in step 3) is classified based on the average particle diameter of the polyvinylidene fluoride (PVDF) particles dissolved in step 1). PVDF solubility quantification analysis method.
According to paragraph 1,
Step 2) is a polyvinylidene fluoride (PVDF) solubility quantification analysis method characterized in that the number of polyvinylidene fluoride (PVDF) particles is measured by particle size in the range of 1 to 5000㎛ from an image file.
According to paragraph 1,
Based on the average particle diameter of the polyvinylidene fluoride (PVDF) particles dissolved in step 1), when measuring solubility in step 3), a weight is given to the number of measured particles for particle sizes that are more than twice the average particle diameter. Polyvinylidene fluoride (PVDF) solubility quantification analysis method characterized by calculating.
According to paragraph 1,
When the average particle diameter (D ₅₀ ) of the polyvinylidene fluoride (PVDF) particles dissolved in step 1) is 150㎛, when measuring solubility in step 3), if the particle size is greater than 300㎛ to 360㎛, It is calculated by giving a weight of 2 times to the number of particles measured, and if the particle size is over 360㎛ to 400㎛, it is calculated by giving a weight of 3 to the measured number of particles, and if the particle size is over 400㎛ to 5000㎛. A polyvinylidene fluoride (PVDF) solubility quantification analysis method, characterized in that it is calculated by giving a weight of 5 times to the number of measured particles.
According to paragraph 1,
Step 2) is a method for quantifying the solubility of polyvinylidene fluoride (PVDF), characterized in that high-speed imaging is performed while flowing the polyvinylidene fluoride (PVDF) solution at a rate of 1 to 1,000 ml/min.
According to paragraph 1,
Step 2) is a polyvinylidene fluoride (PVDF) solubility quantification analysis method, characterized in that the polyvinylidene fluoride (PVDF) solubility is obtained by high-speed imaging of the polyvinylidene fluoride (PVDF) solution with a high-speed image analysis device.
According to paragraph 1,
A method for quantifying the solubility of polyvinylidene fluoride (PVDF), characterized in that the polyvinylidene fluoride (PVDF) is used as a binder for electrodes of lithium secondary batteries.