Method for rapidly testing stability of lithium ion battery slurry

Abstract

The invention belongs to the technical field of battery manufacturing, and particularly discloses a method for rapidly testing the stability of lithium ion battery slurry, which comprises the following steps: adding a solvent into the slurry after slurry mixing, diluting through primary centrifugation, stopping suspension when the suspension appears, and then reducing the rotating speed for secondary centrifugation; and respectively testing and drawing kinetic index TSI curves of the mixed slurry and the slurry subjected to secondary centrifugation, and comparing the two curves to judge the stability of the slurry. The time for judging the stability of the lithium ion battery slurry can be shortened, the operation is simple, and the practicability is high.

Description

Technical Field

[0001] The invention belongs to the technical field of battery manufacturing, and in particular relates to a method for quickly testing the stability of lithium-ion battery slurry. Background Art

[0002] As the policy of energy conservation and emission reduction is gradually intensified, in order to reduce fuel consumption, the demand for combined power batteries is increasing, and the proportion of power lithium-ion batteries is increasing. The combination of single cells in series and parallel has put forward higher requirements for the consistency of single cells. In the production and manufacturing process of lithium-ion batteries, slurry mixing is the first and most important step, which directly determines the quality of the process. The main purpose of this process is to form a solid suspension system with uniform particle dispersion and stability of active materials, conductive agents, binders and solvents by stirring. The stability of battery slurry directly affects the stability of subsequent coating and the distribution of different materials on the current collector, which seriously affects the performance of the obtained battery. Therefore, evaluating the stability of slurry is the key to ensuring the performance of lithium battery manufacturing.

[0003] The usual method for measuring stability is to determine whether the slurry has settled by testing the change in solid content and viscosity of the slurry at different times. The above test method takes a long time. With the increasing requirements for the solid content of the slurry, the test takes a long time and the values ​​are inaccurate in actual production, which makes it lack of practical application significance. Summary of the invention

[0004] In view of this, the present invention provides a method for quickly testing the stability of lithium-ion battery slurry, which reduces the time required for judging the stability of lithium-ion battery slurry, is simple to operate, and is highly practical.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] A method for quickly testing the stability of lithium-ion battery slurry comprises the following steps: adding a solvent to the slurry after mixing and diluting it through the first centrifugation, stopping when a suspension appears, and then reducing the speed for the second centrifugation; testing and drawing the kinetic index TSI curve of the mixed slurry and the slurry after the second centrifugation respectively, and judging the stability of the slurry by comparing the two curves.

[0007] Preferably, the solvent is of the same type as the solvent added to the slurry during slurry mixing.

[0008] Preferably, the volume ratio of the added solvent to the mixed slurry is 7 to 10:40.

[0009] Preferably, the first centrifugation speed is 1200-1800 rpm, and the centrifugation time is 1-80 min.

[0010] Preferably, the second centrifugation speed is 400-600 rpm and the centrifugation time is 1-5 min.

[0011] Preferably, the stability of the slurry is determined by the difference in TSI values ​​between the two curves and / or the degree of overlap of the curves. The smaller the difference in TSI values ​​and / or the higher the degree of overlap of the curves, the more stable the slurry.

[0012] Preferably, the mixed slurry is a positive electrode slurry or a negative electrode slurry of lithium ions.

[0013] It can be seen from the above technical solutions that compared with the prior art, the present invention has the following excellent effects:

[0014] Since the solid content of lithium ion slurry is high and the viscosity is large in current actual production, the solid content of the slurry can be reduced by adding a solvent for dilution in the present invention, so that the slurry can be separated quickly. The present invention performs a first centrifugation after adding the solvent, so that the solvent is dispersed in the slurry to form a suspension state; the second centrifugation accelerates the stratification and sedimentation of the slurry and accelerates the change of TSI. The present invention can shorten the judgment time of the slurry stability, and then quickly guide production. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0016] Figure 1 The TSI curves of the three groups of slurries A, B and C drawn in Example 1;

[0017] Figure 2 The TSI curves of the three groups of slurries A, B and C drawn for Example 2;

[0018] Figure 3 The solid content change curve of the slurry of group A prepared in Example 1 and Example 2. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] Example 1

[0021] The preparation method of positive electrode slurry is as follows: ternary (NCM111), conductive agent (super-p), PVDF (polyvinylidene fluoride), first PVDF and solvent NMP (N-methylpyrrolidone) are mixed and stirred to obtain a uniform transparent liquid, and at the same time, ternary (NCM111) and conductive agent (super-p) are dry mixed, the above NCM: super-p: PVDF = 95%: 3%: 2%, and stirred for 5 hours in a double planetary slurry mixer, and finally the two are mixed and stirred to obtain positive electrode slurry. The slurry solid content is 48.3%, and the slurry viscosity is 2250mpa.s.

[0022] The slurry was placed in centrifugal glasses with scales. There were 9 samples, divided into 3 groups, A, B, and C. The slurry height in each glass was 40 mm. Several milliliters of NMP were drawn and injected into the glasses in groups B and C, so that the total height of the two glasses reached 47 mm, and the slurry was diluted.

[0023] The six samples in the above two groups B and C were centrifuged at a speed of 1500 rpm for 3 minutes, so that the solvent was dispersed in the glass cup and a diluted suspension appeared on the upper layer. All the above nine samples were scanned by the stability analyzer for six times, and the TSI formula was calculated at a height of 35 mm-47 mm. The TSI average curve B and curve A of the centrifuged group B and the non-centrifuged group A were drawn respectively, as shown in the figure. Figure 1 Middle curve B and curve A.

[0024] Take three samples from group C and perform a second centrifugal rotation at a centrifugal speed of 500 rpm for 1 min to accelerate the stratification and sedimentation of the slurry. Perform a stability analyzer scan test on the samples of group C for 6 times and draw a curve C of the average TSI value of group C, as shown in Figure 1 Middle curve C.

[0025]

[0026] The TSI measurement method of the stability analyzer test instrument is to put the glass into the stability analyzer for testing and record TSI1. The TSI calculation formula is as follows;

[0027] TSI stands for Stability Kinetic Index

[0028] Scan represents the light intensity value (when there is transmitted light, it is the transmitted light intensity value, when there is no transmitted light, it is the backscattered light intensity value)

[0029] h means that the scanning range for determining a light intensity value is 40μm or a light intensity value can be determined every 40μm

[0030] H represents the height of the sample

[0031] n represents the number of scans (that is, the nth scan), and N represents the total number of scans.

[0032] Usually the scanning times are 1-100 times, the sample height H is 10-50 mm, and the selected calculated TSI sample height is 0-50 mm. The present invention selects the scanning times to be 6 times, the sample height H is 47 mm, and the selected calculated TSI sample height is 35 mm-47 mm.

[0033] Example 2

[0034] The preparation method of positive electrode slurry is as follows: ternary (NCM523), conductive agent (super-p), PVDF (polyvinylidene fluoride), first PVDF and solvent NMP (N-methylpyrrolidone) are mixed and stirred to obtain a uniform transparent liquid, and at the same time, ternary (NCM523) and conductive agent (super-p) are dry mixed, the above NCM: super-p: PVDF = 95.5%: 3.5%: 1%, and stirred for 5 hours in a double planetary slurry mixer, and finally the two are mixed and stirred to obtain positive electrode slurry. The slurry solid content is 49.0%, and the slurry viscosity is 2500mpa.s.

[0035] The rest is the same as in Example 1, and the TSI curve is measured in groups, such as Figure 2 Middle curves A, B, C.

[0036] In the above Examples 1-2, the TSI value of Group A in Example 1 was relatively low and rose gradually and gently. After adding solvent to Group B for centrifugal rotation, the TSI value increased, but the rising trend did not change significantly. Group C continued to centrifuge to accelerate sedimentation and stratification, and the TSI value initially showed significant changes. As the number of scans increased, the trend of the value changes before and after was close.

[0037] In Example 2, the TSI value of Group A was relatively low and rose gradually. After adding solvent to Group B for centrifugal rotation, the TSI value increased and the upward trend changed slightly. Group C continued to centrifuge to accelerate sedimentation and stratification, and significant changes appeared initially. As the number of scans increased, the difference in the trend of value changes before and after became increasingly greater.

[0038] In the above description, TSI represents the kinetic stability coefficient. The greater the change in its value, the faster the slurry settles or the internal particles agglomerate, and the worse the slurry stability. The slurry stability in Example 2 is relatively poor.

[0039] The slurries of Group A of Examples 1 and 2 were tested using the traditional method of changing solid content over time. The results are shown in Figure 3As shown in Table 1, after standing for 36 hours, in Example 1, the solid content of the slurry changed from 48.3% to 47.2%, with a change rate of 2.2%. In Example 2, the solid content of the slurry changed from 49% to 46.7%, with a change rate of 4.6%. The results show that the slurry stability in Example 2 is poor, which is consistent with the results of the method of the present invention.

[0040] Table 1

[0041]

[0042] In summary, the slurry dilution method and the test of the change of the kinetic stability index of the present invention can shorten the judgment time of the slurry stability and thus quickly guide the production.

[0043] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for quickly testing the stability of lithium-ion battery slurry, characterized in that: The following steps are involved: The slurry after slurrying is added with solvent and diluted by the first centrifugation, and the suspension stops when the suspension appears, and then the speed is reduced to perform the second centrifugation; The kinetic index TSI curves of the combined slurry and the slurry after the second centrifugation were tested and drawn respectively, and the stability of the slurry was judged by comparing the two curves.

2. A method for rapidly testing the stability of lithium-ion battery slurry according to claim 1, characterized in that: The solvent is of the same type as the solvent added to the slurry during slurry mixing.

3. The method for quickly testing the stability of lithium-ion battery slurry according to claim 1, characterized in that: The volume ratio of the added solvent to the mixed slurry is 7 to 10:

40.

4. The method for quickly testing the stability of lithium-ion battery slurry according to claim 1, characterized in that: The first centrifugation speed is 1200-1800rpm, and the centrifugation time is 1-80min.

5. The method for quickly testing the stability of lithium-ion battery slurry according to claim 1, characterized in that: The second centrifugation speed is 400-600 rpm and the centrifugation time is 1-5 min.

6. A method for quickly testing the stability of lithium-ion battery slurry according to any one of claims 1 to 5, characterized in that: The stability of the slurry can be judged by the difference in TSI values ​​between the two curves and / or the degree of curve overlap. The smaller the difference in TSI values ​​and / or the higher the degree of curve overlap, the more stable the slurry.

7. A method for quickly testing the stability of lithium-ion battery slurry according to any one of claims 1 to 5, wherein the mixed slurry is a positive electrode slurry or a negative electrode slurry of lithium ions.

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