Method for evaluating stability and slurry mixing process of negative electrode slurry

Abstract

The invention relates to a negative electrode slurry stability and slurry mixing process evaluation method, which comprises the following steps of: putting negative electrode slurry to be detected into a sample bottle, and extracting a plurality of slurry samples at different height positions from the sample bottle; testing the particle size distribution of each slurry sample at different standing times by using a laser particle size tester, and calculating the particle size dispersion index of each slurry sample at different standing times; calculating the particle size dispersion coefficient of each slurry sample at different standing times, and judging the stability of the negative electrode slurry to be detected; calculating the particle size dispersion coefficient of each slurry sample at different height positions in the same standing time, and judging the dispersion uniformity of the negative electrode slurry to be detected; and judging the advantages and disadvantages of the cathode slurry mixing process according to the particle size dispersion coefficients of the slurry samples at different standing times and the particle size dispersion coefficients of the slurry samples at different height positions at the same standing time. According to the invention, the dispersion uniformity and stability of the slurry can be judged, and the advantages and disadvantages of the slurry mixing process can be judged.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery slurry mixing technology, and in particular to a method for evaluating negative electrode slurry stability and slurry mixing technology. Background Art

[0002] With the development of new energy, the requirements for battery performance are getting higher and higher, and the stability of the positive and negative electrode slurry of the battery is one of the important factors that determine the battery performance. The positive and negative electrode slurry is usually a suspended dispersion system formed by dispersing active materials, conductive agents, binders, stabilizers, etc. in a solvent through high-speed stirring. There are huge differences in the particle sizes of different substances in the slurry, and the affinity of their surface groups to the solvent is also different. In addition, agglomeration will occur between the particles, resulting in uneven dispersion of particles of different substances in the slurry, and the stability of the slurry will deteriorate. Slurries with poor stability will settle during the coating process, and severe cases will cause slurry stratification, resulting in unstable coating amount of active materials on the current collector, which will result in poor consistency of the manufactured battery cells and serious impact on battery performance. Therefore, the stability of battery slurry is crucial to battery production.

[0003] In traditional technology, the stability of slurry is determined by testing the shear rate-viscosity curve of slurry with a rheometer. Although this method is simple and convenient, it can only reflect the overall stability of the slurry, but cannot qualitatively determine the uniformity of slurry dispersion. The scraper fineness meter can detect the particle size of dispersed slurry, but the fineness scraper is limited by the sampling technique and the influence of individual differences in visual observation, and it is difficult to achieve the requirements of accurate evaluation.

[0004] The patent with publication number CN111811920A discloses a method for testing the uniformity and stability of slurry dispersion, using a laser particle size analyzer to detect the slurry particle size and judging the stability of the slurry by the D50 parameter. The patent with publication number CN102539294A discloses a method for testing the stability of negative electrode slurry, using a laser particle size analyzer to detect the slurry particle size and judging the stability of the slurry by the D90 difference change parameter between the upper and lower layers of the slurry. Both of these judgment methods cannot accurately reflect the changes in particle size in the slurry due to sedimentation, and cannot evaluate the slurry mixing process. Summary of the invention

[0005] Based on this, the purpose of the present invention is to provide a method for evaluating the stability of negative electrode slurry and the slurry mixing process, which can judge the dispersion uniformity and stability of the slurry and can judge the quality of the slurry mixing process.

[0006] To achieve the above object, the present invention adopts the following technical solutions: The present invention first provides a method for evaluating the stability of negative electrode slurry and slurry mixing process, which comprises the following steps: S1. Take the negative electrode slurry to be tested in a sample bottle, and extract several slurry samples at different heights from the sample bottle; S2. Using a laser particle size tester to test the particle size distribution of each slurry sample at different standing times, and calculating the particle size dispersion index of each slurry sample at different standing times; S3. Calculate the particle size dispersion coefficient of each slurry sample at different standing times and determine the stability of the negative electrode slurry to be tested; S4. Calculate the particle size dispersion coefficient of each slurry sample at different height positions at the same standing time and determine the dispersion uniformity of the negative electrode slurry to be tested; S5. The quality of the negative electrode slurry mixing process is judged based on the particle size dispersion coefficient of each slurry sample at different standing times and the particle size dispersion coefficient of each slurry sample at different height positions at the same standing time.

[0007] As a further improvement of the above solution of the present invention, in step S1, extracting h1 , h2, …, hm Slurry sample at location, h1 , h2, …, hm Increase successively, m is a positive integer and m ≥2.

[0008] As a further improvement of the above solution of the present invention, in step S1, m =2, , , H is the liquid level of negative electrode slurry in the sample bottle.

[0009] As a further improvement of the above solution of the present invention, in step S1, the solid content of the negative electrode slurry is 49%-55%, and the viscosity is 3000-6500 mPa·s.

[0010] As a further improvement of the above scheme of the present invention, in step S2, a laser particle size tester is used to test the static state of each slurry sample. t1, t2, …, tn After the particle size, t1, t2, …, tn Increase successively, n is a positive integer and n ≥2; According to the formula Calculate the slurry sample t1, t2, …, tn Particle size dispersion index P hm tn .

[0011] As a further improvement of the above scheme of the present invention, n=3, t1=0 hours, t2=4 hours, t3=24 hours.

[0012] As a further improvement of the above solution of the present invention, in step S3, according to the formula Calculate the particle size dispersion coefficient of each slurry sample at different standing times L hn tn ; if 0<| L hm tn |<1%, the stability of the negative electrode slurry to be tested is judged to be good; if | L hm tn |≥1%, it is judged that the stability of the negative electrode slurry to be tested is poor.

[0013] As a further improvement of the above solution of the present invention, in step S4, according to the formula Calculate the particle size dispersion coefficient of each slurry sample at different heights at the same standing time H hm tn ; if 0<| H hm tn |<1%, the dispersion uniformity of the negative electrode slurry to be tested is determined; if | H hm tn |≥1%, the dispersion uniformity of the negative electrode slurry to be tested is determined.

[0014] As a further improvement of the above solution of the present invention, in step S5, if 0<| L hm tn |<1%, 0<| H hm tn |<1%, the slurry mixing process of the negative electrode slurry to be tested is determined to be the optimal process.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention utilizes a laser particle size analyzer to detect the change in particle size of the slurry at different times, calculates the slurry dispersion coefficient at different times and positions based on the dispersion index of the negative electrode slurry, and judges the dispersion uniformity and stability of the slurry; determines the narrowness of the particle size distribution of the slurry through the dispersion index, the smaller the value, the more uniform the particle size, the more concentrated the particle size distribution, and the better the stability; the larger the value changes with the standing time, the agglomeration of particles, the wider the particle size distribution, and the worse the stability; calculates the slurry dispersion coefficient at different times and in the upper and lower layers based on the dispersion index of the slurry, judges the dispersion uniformity and stability of the slurry, and can judge the quality of the slurry mixing process.

[0016] The invention has simple operation, low detection limit and good repeatability, plays a good monitoring role in the lithium ion battery manufacturing process and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The present invention is a flowchart of a method for evaluating the stability of negative electrode slurry and slurry mixing process in an embodiment of the present invention. DETAILED DESCRIPTION

[0018] For ease of understanding of the present invention, the present invention will be described more fully below in conjunction with specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0020] Reference Figure 1 This embodiment provides a method for evaluating the stability of negative electrode slurry and slurry mixing process, which includes the following steps: S1. Put the negative electrode slurry to be tested into a sample bottle, extract several slurry samples at different heights from the sample bottle and place them in different small beakers, seal them and store them.

[0021] Specifically, the solid content of the negative electrode slurry to be tested is 49%-55%, the viscosity is 3000-6500mPa·s, and the height of the sample is drawn from the sample bottle. h1 , h2, …, hm The slurry sample at h1 , h2, …, hm Increase successively, m is a positive integer and m ≥2. In this embodiment, m =2, , , H is the liquid level of negative electrode slurry in the sample bottle.

[0022] S2. Use a laser particle size tester to test the particle size distribution of each slurry sample at different standing times, and calculate the particle size dispersion index of each slurry sample at different standing times.

[0023] Specifically, the laser particle size tester was used to test the slurry samples. t1, t2, …, tn After the particle size distribution, t1, t2, …, tn Increase successively, n is a positive integer and n ≥2. And according to the formula Calculate the slurry sample t1, t2, …, tn Particle size dispersion index P hm tnIn this embodiment, n=3, t1=0 hours, t2=4 hours, and t3=24 hours.

[0024] S3. Calculate the particle size dispersion coefficient of each slurry sample at different standing times and determine the stability of the negative electrode slurry to be tested.

[0025] Specifically, according to the formula Calculate the particle size dispersion coefficient of each slurry sample at different standing times L hn tn ; if 0<| L hm tn |<1%, the stability of the negative electrode slurry to be tested is judged to be good; if | L hm tn |≥1%, it is judged that the stability of the negative electrode slurry to be tested is poor.

[0026] S4. Calculate the particle size dispersion coefficient of each slurry sample at different height positions at the same standing time and determine the dispersion uniformity of the negative electrode slurry to be tested.

[0027] Specifically, according to the formula Calculate the particle size dispersion coefficient of each slurry sample at different heights at the same standing time H hm tn ; if 0<| H hm tn |<1%, it is judged that the dispersion uniformity of the negative electrode slurry to be tested is good; if | H hm tn |≥1%, it is judged that the dispersion uniformity of the negative electrode slurry to be tested is poor, which means that the storage and standing time of the negative electrode slurry should be less than this time tn .

[0028] S5. The quality of the negative electrode slurry mixing process is judged based on the particle size dispersion coefficient of each slurry sample at different standing times and the particle size dispersion coefficient of each slurry sample at different height positions at the same standing time.

[0029] If 0<| L hm tn |<1%, 0<| H hm tn |<1%, the slurry mixing process of the negative electrode slurry to be tested is determined to be the optimal process.

[0030] The present invention will be further described below in conjunction with specific embodiments.

[0031] Case 1: Graphite (discreteness of particle size distribution 1.31), superconducting carbon black, SBR emulsion (purity 48%), CMC and deionized water mixture were pulped using a twin-screw pulping machine according to the weight percentage of 96.5%: 0.5%: 1.8%: 1.2%, and the side feed solid content was 70%, and finally a negative electrode slurry with uniform dispersion, good stability and solid content of 54% was obtained. Take 200mL of negative electrode slurry in a sample bottle, and the liquid level of the negative electrode slurry is 100mm. Use a syringe to draw 1 mL of slurry sample at heights of h1=20mm and h2=80mm and place them in different small beakers, seal them and store them separately, record them as lower layer samples and upper layer samples respectively. Use a laser particle size tester to test the particle size distribution of the lower layer samples and upper layer samples after t1=0 hour, t2=4 hours and t3=24 hours, respectively, and obtain the Dmin, D10, D50, D90 and Dmax of the lower layer samples and upper layer samples at different standing times.

[0032] According to the formula Calculate the particle size dispersion index of the lower sample (height h1=20mm) and the upper sample (height h2=80mm) at different standing times (t1=0 hours, t2=4 hours, t3=24 hours). For example, calculate the particle size dispersion index of the lower sample (height h1=20mm) at t2=4 hours and t3=24 hours. , The particle size dispersion index of the upper sample (height h2 = 80 mm) after standing for t2 = 4 hours and t3 = 24 hours is , .

[0033] The results are shown in Table 1.

[0034] Table 1

[0035] Case 2: Graphite (discreteness of particle size distribution 1.31), superconducting carbon black, SBR emulsion (purity 48%), CMC and deionized water mixture were pulped using a twin-screw pulping machine according to the weight percentage of 96.5%: 0.5%: 1.8%: 1.2%, and the side feed solid content was 71%, and finally a negative electrode slurry with uniform dispersion, good stability and solid content of 54% was obtained. Take 200mL of negative electrode slurry in a sample bottle, and the liquid level of the negative electrode slurry is 100mm. Use a syringe to draw 1 mL of slurry sample at heights of h1=20mm and h2=80mm and place them in different small beakers, seal them and store them separately, record them as lower layer samples and upper layer samples respectively. Use a laser particle size tester to test the particle size distribution of the lower layer samples and upper layer samples after t1=0 hour, t2=4 hours and t3=24 hours, respectively, and obtain the Dmin, D10, D50, D90 and Dmax of the lower layer samples and upper layer samples at different standing times.

[0036] According to the formula Calculate the particle size dispersion index of the lower sample (height h1=20mm) and the upper sample (height h2=80mm) at t1=0 hours, t2=4 hours, and t3=24 hours. For example, calculate the particle size dispersion index of the lower sample (height h1=20mm) at t2=4 hours and t3=24 hours. , The particle size dispersion index of the upper sample (height h2 = 80 mm) after standing for t2 = 4 hours and t3 = 24 hours is , .

[0037] The results are shown in Table 2.

[0038] Table 2

[0039] Case 3: Graphite (discreteness of particle size distribution 1.31), superconducting carbon black, SBR emulsion (purity 48%), CMC and deionized water mixture were pulped using a twin-screw pulping machine according to the weight percentage of 96.5%: 0.5%: 1.8%: 1.2%, and the side feed solid content was 72%, and finally a negative electrode slurry with uniform dispersion, good stability and solid content of 54% was obtained. Take 200mL of negative electrode slurry in a sample bottle, and the liquid level of the negative electrode slurry is 100mm. Use a syringe to draw 1 mL of slurry sample at heights of h1=20mm and h2=80mm and place them in different small beakers, seal them and store them separately, record them as lower layer samples and upper layer samples respectively. Use a laser particle size tester to test the particle size distribution of the lower layer samples and upper layer samples after t1=0 hour, t2=4 hours and t3=24 hours, respectively, and obtain the Dmin, D10, D50, D90 and Dmax of the lower layer samples and upper layer samples at different standing times.

[0040] According to the formula Calculate the particle size dispersion index of the lower sample (height h1=20mm) and the upper sample (height h2=80mm) at t1=0 hours, t2=4 hours, and t3=24 hours. For example, calculate the particle size dispersion index of the lower sample (height h1=20mm) at t2=4 hours and t3=24 hours. , The particle size dispersion index of the upper sample (height h2 = 80 mm) after standing for t2 = 4 hours and t3 = 24 hours is , .

[0041] The results are shown in Table 3.

[0042] Table 3

[0043] The viscosity and fineness data of the negative electrode slurry in each case are shown in Table 4.

[0044] Table 4

[0045] By formula Calculate the particle size dispersion coefficient of the lower sample (height h1=20mm) and the upper sample (height h2=80mm) at t1=0 hours, t2=4 hours, and t3=24 hours in each case. For example, calculate the particle size dispersion coefficient of the lower sample (height h1=20mm) and the upper sample (height h2=80mm) at t2=4 hours. , The results are shown in Table 5.

[0046] Table 5

[0047] By formula Calculate the particle size dispersion coefficient of the lower sample (height h1=20mm) and the upper sample (height h2=80mm) at the same standing time in each case. For example, calculate the particle size dispersion coefficient at standing time t2=4 hours. The results are shown in Table 6.

[0048] Table 6

[0049] According to the results in Table 5 and Table 6, the negative electrode slurries made by the slurry combination process in Case 2 and Case 3 have better stability after standing for 24 hours. Compared with Case 2, the dispersion coefficient of the negative electrode slurry particle size in Case 3 is smaller, the slurry viscosity and fineness are smaller, the slurry dispersion is more uniform, and the stability is higher. The slurry combination process in Case 3 is the best; in Case 1, the dispersion coefficient of the negative electrode slurry gradually increases with the increase of standing time, indicating that the stability of the negative electrode slurry gradually deteriorates with time; in Case 1, the absolute value of the upper and lower layer particle size coefficient is greater than 1% at 4 hours, indicating that the stability of the negative electrode slurry combined by the Case 1 process deteriorates after 4 hours. It is recommended that the negative electrode slurry of the Case 1 process be stored for less than 4 hours.

[0050] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0051] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for evaluating the stability of negative electrode slurry and slurry mixing process, characterized in that: It includes the following steps: S1. Take the negative electrode slurry to be tested in a sample bottle, and extract several slurry samples at different heights from the sample bottle; S2. Using a laser particle size tester to test the particle size distribution of each slurry sample at different standing times, and calculating the particle size dispersion index of each slurry sample at different standing times; S3. Calculate the particle size dispersion coefficient of each slurry sample at different standing times and determine the stability of the negative electrode slurry to be tested; S4. Calculate the particle size dispersion coefficient of each slurry sample at different height positions at the same standing time and determine the dispersion uniformity of the negative electrode slurry to be tested; S5. The quality of the negative electrode slurry mixing process is judged based on the particle size dispersion coefficient of each slurry sample at different standing times and the particle size dispersion coefficient of each slurry sample at different height positions at the same standing time.

2. The negative electrode slurry stability and slurry mixing process evaluation method according to claim 1, characterized in that: In step S1, extract from the sample bottle h1 , h2, …, hm Slurry sample at location, h1 , h2, …, hm Increase successively, m is a positive integer and m ≥2.

3. The negative electrode slurry stability and slurry mixing process evaluation method according to claim 2, characterized in that: In step S1, m =2, , , H is the liquid level of negative electrode slurry in the sample bottle.

4. The negative electrode slurry stability and slurry mixing process evaluation method according to claim 1, characterized in that: In step S1, the solid content of the negative electrode slurry is 49%-55%, and the viscosity is 3000-6500 mPa·s.

5. The negative electrode slurry stability and slurry mixing process evaluation method according to claim 2, characterized in that: In step S2, the laser particle size tester is used to test the slurry samples. t1, t2, …, tn After the particle size, t1, t2, …, tn Increase successively, n is a positive integer and n ≥2; According to the formula Calculate the slurry sample t1, t2, …, tn Particle size dispersion index P hm tn .

6. The negative electrode slurry stability and slurry mixing process evaluation method according to claim 5, characterized in that: n=3, t1=0 hours, t2=4 hours, t3=24 hours.

7. The negative electrode slurry stability and slurry mixing process evaluation method according to claim 5, characterized in that: In step S3, according to the formula Calculate the particle size dispersion coefficient of each slurry sample at different standing times L hn tn ; if 0<| L hm tn |<1%, the stability of the negative electrode slurry to be tested is judged to be good; if | L hm tn |≥1%, it is judged that the stability of the negative electrode slurry to be tested is poor.

8. The negative electrode slurry stability and slurry mixing process evaluation method according to claim 7, characterized in that: In step S4, according to the formula Calculate the particle size dispersion coefficient of each slurry sample at different heights at the same standing time H hm tn ; if 0<| H hm tn |<1%, the dispersion uniformity of the negative electrode slurry to be tested is determined; if | H hm tn |≥1%, the dispersion uniformity of the negative electrode slurry to be tested is determined.

9. The negative electrode slurry stability and slurry mixing process evaluation method according to claim 5, characterized in that: In step S5, if 0<| L hm tn |<1%, 0<| H hm tn |<1%, the slurry mixing process of the negative electrode slurry to be tested is determined to be the optimal process.

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