Composite cathode material preparation method based on dry mixing and wet mixing and application thereof

Abstract

The application relates to a preparation method and application of a composite positive electrode material based on dry mixing and wet mixing of slurry. It is found for the first time that the early addition of a conductive agent into ball milling accelerates the side reaction of a high-nickel positive electrode and a sulfide electrolyte, and influences the battery performance. Based on this, the application adopts step-by-step ball milling in dry mixing, that is, the high-nickel positive electrode material is first ball milled with the sulfide electrolyte, so that the sulfide electrolyte is uniformly coated on the surface of the high-nickel positive electrode material in situ, the agglomeration is reduced, and the mixing uniformity is improved, then the conductive agent is added for rapid ball milling, the generation of side reactions is reduced, and the cycle stability and rate performance of the battery are improved; meanwhile, the application also adopts gradient mixing of slurry, that is, the binder is first dissolved in an organic solvent, then the binder is mixed with the above dry mixing and the organic solvent in a wet mixing mode of slurry, the uniformity and stability of the slurry are improved, the binder caking and "jelly effect" phenomena are avoided, and the cycle stability and rate performance of the battery are further improved.

Description

Technical Field

[0001] This invention belongs to the field of all-solid-state battery technology, and relates to a method for preparing composite cathode materials based on dry mixing and wet mixing, and their application. Background Technology

[0002] The large-scale preparation of high-nickel ternary composite cathode materials currently faces the following technical bottlenecks, severely impacting battery energy density and cycle life. First, ball milling damages the particle structure. Traditional ball milling (>500 rpm) results in a breakage rate of >30% for single-crystal ternary particles, leading to an abnormally large specific surface area and exacerbating side reactions. Simultaneously, dry mixing uniformity is insufficient, and manual milling is inefficient (taking 60 min / batch), with a mixing uniformity of only 75-80%, and a coating surface density deviation of ±3.5%. Second, residual alkali control and slurry stability are issues. The residual alkali (Li2CO3 / LiOH) content on the surface of high-nickel ternary cathode materials is as high as 2500-6000 ppm. During wet mixing, it easily reacts with polar solvents to form viscous lithium salt polymers, causing a sharp increase in slurry viscosity and triggering a "jelly effect," thus making coating difficult and resulting in an electrode thickness uniformity deviation >3 μm. Third, during wet mixing, some binder agglomerates without dissolving, leading to lower slurry viscosity and affecting the battery's electrochemical performance.

[0003] Therefore, how to solve the problem of traditional ball milling easily damaging the particle structure, while avoiding binder agglomeration and the "jelly effect" phenomenon, and improving the electrochemical performance of the battery, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for preparing composite cathode materials based on dry mixing and wet slurry mixing, and its application.

[0005] The objective of this invention can be achieved through the following methods:

[0006] In a first aspect, the present invention provides a method for preparing composite cathode materials based on dry mixing and wet slurry mixing, comprising the following steps: S1. First, the high-nickel cathode material and sulfide electrolyte are ball-milled in the first stage, and then a conductive agent is added for ball-milling in the second stage to obtain composite cathode powder. S2. Dissolve the adhesive in an organic solvent to obtain a premixed solution; S3. Add organic solvent and premix to the composite positive electrode powder, then ball mill and sieve to obtain a slurry; S4. Coat the slurry onto the substrate and dry it to obtain the composite cathode material.

[0007] In one embodiment of the present invention, in step S1, the high-nickel cathode material (NCM) includes NCM622, NCM811, and LiNi. 0.92 Co 0.05 Mn 0.03 One or more of O2.

[0008] As one embodiment of the present invention, in step S1, the sulfide electrolyte (SE) includes Li6PS5Cl and Li 5.6 PS 4.4 Cl、Li 5.5 PS 4.5 One or more of Cl.

[0009] As one embodiment of the present invention, in step S1, the conductive agent includes one or more of VGCF, conductive carbon black, and acetylene black.

[0010] In one embodiment of the present invention, in step S1, the mass ratio of the high-nickel cathode material, the sulfide electrolyte, and the conductive agent is 70-85:14-29:1.

[0011] In one embodiment of the present invention, in step S1, the rotation speed of the first or second stage ball milling is 200-400 rpm, and the ball-to-material ratio is 1-5:1; wherein the ball milling time of the first stage is 2-6 hours, and the ball milling time of the second stage is 2-4 hours. The reason why the present invention uses two-stage ball milling is that adding the conductive agent too early during ball milling will accelerate the side reaction between the high-nickel cathode and the sulfide electrolyte, affecting the battery performance. Therefore, the conductive agent is added in the later stage of ball milling, and the ball milling time should not be too long. At the same time, by using staged ball milling, the high-nickel cathode material and the sulfide electrolyte are ball milled first. Under ball milling, the sulfide electrolyte will uniformly coat the surface of the high-nickel cathode material in situ, thereby improving the mixing uniformity. Adding the conductive agent too early will, to some extent, disrupt the uniform in-situ coating of the high-nickel cathode material by the sulfide electrolyte.

[0012] As one embodiment of the present invention, in step S2, the adhesive includes one or more of polyisobutylene (PIB), styrene-butadiene rubber (BR), and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP).

[0013] As one embodiment of the present invention, in step S2 or S3, the organic solvent is independently selected from one or more of toluene, xylene, and dibutyl ether.

[0014] In one embodiment of the present invention, in step S2, the concentration of the binder in the premixed liquid is 6-10 wt%.

[0015] In one embodiment of the present invention, in step S3, the mass ratio of the premixed liquid, the organic solvent and the composite positive electrode powder is 1-3:30-40:100.

[0016] As one embodiment of the present invention, in step S3, the ball mill rotates at a speed of 400-600 rpm for 2-6 hours, and the ball-to-material ratio is 5-10:1.

[0017] In the wet gradient mixing process of this invention, the addition of the organic solvent in the first stage is to prepare the binder into a premixed solution of a certain concentration, and the addition of the organic solvent in the second stage is to adjust the overall viscosity of the slurry. Since the binder is similar to a glue after dissolving in the solvent, it needs to be dissolved in the organic solvent in advance and dispersed evenly before it can be wet-mixed with the composite cathode powder. Otherwise, it will cause large-area agglomeration of the slurry and produce a "jelly effect".

[0018] Secondly, the present invention provides a composite cathode material obtained by the method described above.

[0019] Thirdly, the present invention provides an application of the composite cathode material in the preparation of all-solid-state batteries.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention is the first to discover that premature addition of the conductive agent during ball milling accelerates side reactions between the high-nickel cathode and the sulfide electrolyte, affecting battery performance. Based on this, this invention employs stepwise ball milling in the dry mixing process. First, the high-nickel cathode material and the sulfide electrolyte are ball-milled, allowing the sulfide electrolyte to uniformly coat the surface of the high-nickel cathode material in situ, reducing agglomeration and improving mixing uniformity. Then, the conductive agent is added and rapidly ball-milled to reduce the generation of side reactions, thereby improving the battery's cycle stability and rate performance. Simultaneously, this invention also employs gradient slurry mixing. The binder is pre-dissolved in an organic solvent, and then wet-mixed with the aforementioned dry mixture and the organic solvent. This results in a slurry with appropriate viscosity, while simultaneously avoiding binder clumping and the "jelly effect," further improving the battery's cycle stability and rate performance.

[0021] 2. This invention effectively solves the problems of mixing uniformity and electrochemical performance of high-nickel ternary composite cathodes by combining dry segmented ball milling and wet gradient mixing, and is suitable for the industrial production of high-nickel ternary composite cathode materials. Attached Figure Description

[0022] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a SEM image of the dry composite cathode obtained by dry segmented ball milling in Example 1. Detailed Implementation

[0023] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The following examples are implemented under the premise of the technical solution of the present invention, providing detailed implementation methods and specific operating procedures, which will help those skilled in the art to further understand the present invention. It should be noted that the scope of protection of the present invention is not limited to the following embodiments; any adjustments and improvements made under the concept of the present invention are all within the scope of protection of the present invention.

[0024] Example 1 This embodiment provides a method for preparing composite cathode materials based on dry mixing and wet slurry mixing, including the following steps: 1. Dry segmented ball milling mixing (dry composite cathode preparation) 425mg of LiNi 0.92 Co 0.05 Mn 0.03 O2 and 70 mg of Li6PS5Cl were placed in a 25 mL ball mill jar, and 2 g of milling beads (3 mm) were added. The mixture was milled at 300 rpm for 2 hours using a planetary ball mill, and then scraped off. This process was repeated three times for a total of 6 hours (the three repetitions were to ensure the uniformity of the mixture). 5 mg of conductive agent (VGCF) was added, and the mixture was milled for another 2 hours to complete the dry composite cathode mixing.

[0025] like Figure 1 As shown, it is a SEM image of the dry composite cathode obtained by dry segmented ball milling. It can be seen that through dry segmented ball milling, the sulfide electrolyte is uniformly coated on the surface of the high-nickel cathode material in situ.

[0026] 2. Wet slurry mixing (wet composite cathode preparation) Dissolve the BR adhesive in xylene solution to prepare an 8wt% adhesive solution; Weigh out the pre-composite cathode powder, 10mm and 5mm ball milling beads (1:1, ball-to-powder ratio 10:1), add xylene solution (35% of composite cathode powder), add 8wt% premixed liquid (2% of composite cathode powder), ball mill at 500rpm for 4h, test the slurry viscosity to be 2000 cP (this viscosity is appropriate, proving that no "jelly effect" has occurred), and sieve the slurry through a 250 mesh screen; The slurry is transferred to a coating device and uniformly coated onto the aluminum foil current collector, wherein the loading of the positive electrode is 25 mg / cm³. 2 The coated electrode was transferred to a vacuum drying oven and vacuum dried at 60°C for 12 hours to ensure complete removal of the solvent, thus obtaining a wet-process composite positive electrode.

[0027] 3. Performance advantages: Assembly of the pressure cell: Take 100 mg of Li5.5 PS 4.5 Cl powder is cold-pressed on a tablet press (2MPa); the composite positive electrode sheet prepared in the above steps is cold-pressed on a tablet press (6MPa); 10mg of lithium silicon alloy material is cold-pressed on a tablet press (8MPa), and copper foil is placed in it as a current collector to obtain an all-solid-state lithium battery.

[0028] The all-solid-state lithium battery was subjected to cycle stability and rate performance tests. The test methods and results are as follows: Cyclic stability: 0.5C charge-discharge (2.5-4.3V), 0.5C discharge specific capacity is 195.86 mAh / g, and capacity retention is 96.34% after 100 cycles (compared to <90% for traditional high-nickel ternary cathodes).

[0029] Comparative Example 1 The preparation method of this comparative example is basically the same as that of Example 1, except that in step 1, LiNi is used... 0.92 Co 0.05 Mn 0.03 O2, Li6PS5Cl and conductive agent (VGCF) were added together to a ball mill jar, along with 2g of milling beads (3mm). The mixture was then milled at 300rpm for 8 hours using a planetary ball mill to complete the composite cathode mixing.

[0030] The all-solid-state lithium battery obtained in Comparative Example 1 has a discharge specific capacity of 176.34 mAh / g at 0.5C and a capacity retention rate of 80.58% after 100 cycles, which is much lower than that of Example 1.

[0031] Comparative Example 2 The preparation method of this comparative example is basically the same as that of Example 1, except that in step 2, pre-composite cathode powder, 10 mm and 5 mm ball milling beads (1:1, ball-to-powder ratio 10:1) are weighed, xylene solution (35% of composite cathode powder) is added, BR binder (2% of composite cathode powder) is added, and the mixture is ball milled at 500 rpm for 4 hours. The slurry is then sieved through a 250 mesh sieve, and it is found that some binder clumps in the slurry have not dissolved. This is because the binder was not dissolved in an organic solvent beforehand, resulting in a low slurry viscosity. The tested slurry viscosity is 1500 cP.

[0032] The all-solid-state lithium battery obtained in Comparative Example 2 has a discharge specific capacity of 168.45 mAh / g at 0.5C and a capacity retention rate of 78.43% after 100 cycles, which is much lower than that of Example 1.

[0033] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing composite cathode materials based on dry mixing and wet slurry mixing, characterized in that, Includes the following steps: S1. First, the high-nickel cathode material and sulfide electrolyte are ball-milled in the first stage, and then a conductive agent is added for ball-milling in the second stage to obtain composite cathode powder. S2. Dissolve the adhesive in an organic solvent to obtain a premixed solution; S3. Add organic solvent and premix to the composite positive electrode powder, then ball mill and sieve to obtain a slurry; S4. Coat the slurry onto the substrate and dry it to obtain the composite cathode material.

2. The method according to claim 1, characterized in that, In step S1, the high-nickel cathode material includes NCM622, NCM811, and LiNi. 0.92 Co 0.05 Mn 0.03 One or more of O2; the sulfide electrolyte includes Li6PS5Cl, Li 5.6 PS 4.4 Cl、Li 5.5 PS 4.5 One or more of Cl; the conductive agent includes one or more of VGCF, conductive carbon black, and acetylene black.

3. The method according to claim 1, characterized in that, In step S1, the mass ratio of the high-nickel cathode material, sulfide electrolyte, and conductive agent is 70-85:14-29:

1.

4. The method according to claim 1, characterized in that, In step S1, the rotation speed of the first or second ball mill is 200-400 rpm, and the ball-to-material ratio is 1-5:1; wherein the time of the first ball mill is 2-6 h, and the time of the second ball mill is 2-4 h.

5. The method according to claim 1, characterized in that, In step S2, the adhesive includes one or more of polyisobutylene, styrene-butadiene rubber, and polyvinylidene fluoride-hexafluoropropylene.

6. The method according to claim 1, characterized in that, In step S2 or S3, the organic solvent is independently selected from one or more of toluene, xylene, and dibutyl ether.

7. The method according to claim 1, characterized in that, In step S2, the concentration of the binder in the premixed liquid is 6-10 wt%.

8. The method according to claim 1, characterized in that, In step S3, the mass ratio of the premixed liquid, organic solvent and composite cathode powder is 1-3:30-40:

100.

9. A composite cathode material obtained by the method according to any one of claims 1-8.

10. The application of the composite cathode material as described in claim 9 in the preparation of an all-solid-state battery.

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