Cobalt-free system, cathode slurry, homogenization method and use thereof

Abstract

The present invention provides a cobalt-free system, a cathode slurry, and its homogenization method and use, which includes a cobalt-free material, an adhesive, a conductive agent, and a pH adjuster, and can reduce the viscosity rebound of the slurry after standing to the same level as that of ternary 811 single crystal, and improve the coating surface density stability of the cobalt-free material to the same level as that of ternary material.

Description

[Technical Field]

[0001] The present invention relates to the field of battery technology, for example, to cobalt-free systems, cathode slurries, homogenization methods and uses thereof. [Background technology]

[0002] With the depletion of conventional energy sources and increasing environmental problems, the development of lithium-ion batteries as a new clean energy source is receiving increasing attention, and research and development into more practical and efficient lithium-ion batteries is being carried out.

[0003] Compared with other batteries, lithium-ion batteries have advantages such as high energy density, long cycle life, high open-circuit voltage, no memory effect, safety, and pollution-free operation. After more than two decades of rapid development, lithium-ion batteries are widely used in fields such as laptops, mobile phones, digital cameras, and energy storage. In recent years, with people's growing awareness of environmental protection, environmental pollution and global warming caused by automobile exhaust have attracted widespread attention. To eradicate these issues and mitigate the energy crisis caused by dwindling oil resources, the research, development, and commercialization of energy-saving, environmentally friendly electric vehicles have become a global concern. Compared with other mobile devices, electric vehicles place higher requirements on battery performance, such as cycle life, battery consistency, and high-current discharge capacity.

[0004] Slurry homogenization is a critical step in the lithium battery industry, and the quality of the slurry determines the quality of the subsequent application and final battery performance. Currently, there are two homogenization processes for lithium-ion battery cathode slurries. The first is the wet process, which involves first mixing a solvent and adhesive, then adding and stirring a conductive agent, and then adding and stirring an active material to prepare the cathode slurry. This process takes a long time, significantly impacting production efficiency. Furthermore, the slurry has a low solids content, which makes it prone to poor stability and prone to layer separation after standing. The second is the dry process, which involves first dry-blending and stirring the adhesive, conductive agent, and active material together in a homogenizer, followed by adding and stirring a solvent to prepare the cathode slurry. However, in this process, adding the solvent after dry-blending the adhesive makes it difficult to dissolve, resulting in poor dispersion of the slurry, which in turn affects the uniformity of the slurry.

[0005] Currently, cobalt-free materials are still new materials, and there are no suitable systems or homogenization processes for them. If they are produced based on the existing ternary material system and homogenization process, the resulting slurry will have a large change in viscosity after standing, which is unfavorable for subsequent use.

[0006] Therefore, there is a great need to provide a homogenization process that can be applied to cobalt-free systems. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention provides a cobalt-free system, a cathode slurry, and a homogenization method and use thereof, which can reduce the viscosity rebound of the slurry after standing to the same level as that of ternary 811 single crystal, and improve the coating surface density stability of the cobalt-free material to the same level as that of ternary materials, thereby ensuring battery quality. [Means for solving the problem]

[0008] In one embodiment of the present invention, there is provided a cobalt-free composition in a positive electrode slurry for a lithium ion battery, the composition comprising a cobalt-free material, an adhesive, a conductive agent, and a pH adjuster, The cobalt-free material is Li x Ni y Mn z O2, x is 1 to 1.1, y is 0.5 to 0.8, z is 0.2 to 0.5, and y + z = 1; the adhesive is polyvinylidene fluoride, and the number average molecular weight of the polyvinylidene fluoride is 500,000 to 1,500,000; the conductive agent includes a combination of a first conductive agent and a second conductive agent, the first conductive agent is conductive carbon black, and the second conductive agent is single-walled carbon nanotubes; and the pH adjuster includes oxalic acid and / or maleic acid; When calculated based on 100 parts by weight of the cobalt-free composition, The amount of the cobalt-free material added is 95.4 to 97.8 parts by weight, and the amount of the adhesive added is 1 to 1.8 parts by weight, the amount of the first conductive agent added is 1 to 2 parts by weight, and the amount of the second conductive agent added is 0.2 to 0.8 parts by weight; The amount of the pH adjuster added is 0.1 to 0.5% of the total mass of the dry powder in the cobalt-free material, adhesive, and conductive agent. the law of nature, The positive electrode slurry for the lithium ion battery includes a paste liquid and the cobalt-free composition dispersed in the paste liquid, and the paste liquid is obtained by preparing a paste from an adhesive and a solvent, The adhesive is polyvinylidene fluoride, and the number average molecular weight of the polyvinylidene fluoride is 500,000 to 1,500,000; the solvent includes any one or a combination of at least two of N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide; The amount of the solvent added is 80 to 95 parts by weight, and the amount of the adhesive added is 5 to 20 parts by weight. The present invention provides a cobalt-free composition.

[0009] By combining cobalt-free materials, adhesives, conductive agents, and pH adjusters, the cobalt-free system, when used in a slurry, has good dispersibility and a short swelling time, can reduce the viscosity rebound of the slurry after standing to the same level as that of ternary 811 single crystal, and can improve the stability of the coating surface density of the cobalt-free material to the same level as that of ternary materials.

[0010] In one embodiment, the cobalt-free material is Li x Ni y Mn z O2, where x is 1 to 1.1, y is 0.5 to 0.8, z is 0.2 to 0.5, and y + z = 1. For example, x may be 1, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, etc., y may be 0.5, 0.52, 0.55, 0.58, 0.6, 0.62, 0.65, 0.68, 0.7, 0.72, 0.75, 0.78, 0.8, etc., and z may be 0.2, 0.22, 0.25, 0.28, 0.3, 0.32, 0.35, 0.37, 0.4, 0.42, 0.45, 0.48, 0.5, etc.

[0011] In one embodiment, the cobalt-free material is Li x Ni 0.75 Mn 0.25 O2, where x is 1 to 1.1.

[0012] In one embodiment, the adhesive is polyvinylidene fluoride, and the number average molecular weight of the polyvinylidene fluoride is 500,000 to 1,500,000, for example, 500,000, 600,000, 700,000, 800,000, 900,000, 1,000,000, 1,100,000, 1,200,000, 1,300,000, 1,400,000, 1,500,000, etc. In this embodiment, the adhesive uses low molecular weight polyvinylidene fluoride, which has good dispersibility and a short swelling time.

[0013] In one embodiment, when the amount of the cobalt-free material added is 95.4 to 97.8 parts by weight, the amount of the adhesive added is 1 to 1.8 parts by weight. For example, the amount of the cobalt-free material added may be 95.4 parts by weight, 95.8 parts by weight, 96 parts by weight, 96.2 parts by weight, 96.5 parts by weight, 96.8 parts by weight, 97 parts by weight, 97.2 parts by weight, 97.5 parts by weight, 97.8 parts by weight, etc., and the amount of the adhesive added may be 1 part by weight, 1.1 parts by weight, 1.2 parts by weight, 1.3 parts by weight, 1.4 parts by weight, 1.5 parts by weight, 1.6 parts by weight, 1.7 parts by weight, 1.8 parts by weight, etc.

[0014] In one embodiment, the conductive agent comprises a combination of a first conductive agent and a second conductive agent, the first conductive agent being conductive carbon black, and the second conductive agent comprising single-walled carbon nanotubes.

[0015] The single-walled carbon nanotubes have a better conductive effect than the carbon nanotubes, which can compensate for the poor conductivity of the cobalt-free material, and can reduce the amount of the single-walled carbon nanotubes added to make the dispersion more uniform.

[0016] In one embodiment, when the amount of the cobalt-free material added is calculated as 95.4 to 97.8 parts by weight, the amount of the first conductive agent added is 1 to 2 parts by weight, and the amount of the second conductive agent added is 0.2 to 0.8 parts by weight. For example, the amount of the cobalt-free material added may be 95.4 parts by weight, 95.8 parts by weight, 96 parts by weight, 96.2 parts by weight, 96.5 parts by weight, 96.8 parts by weight, 97 parts by weight, 97.2 parts by weight, 97.5 parts by weight, 97.8 parts by weight, etc.; the amount of the first conductive agent added may be 1 part by weight, 1.1 parts by weight, 1.2 parts by weight, 1.3 parts by weight, 1.4 parts by weight, 1.5 parts by weight, 1.6 parts by weight, 1.7 parts by weight, 1.8 parts by weight, 1.9 parts by weight, 2 parts by weight, etc.; and the amount of the second conductive agent added may be 0.2 parts by weight, 0.3 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 0.6 parts by weight, 0.7 parts by weight, 0.8 parts by weight, etc.

[0017] In one embodiment, the pH adjuster includes oxalic acid and / or maleic acid, which can neutralize the high pH of the cobalt-free material itself, while also absorbing moisture to prevent the slurry from clumping and make the slurry more uniformly dispersed.

[0018] In one embodiment, the amount of the pH adjuster added is 0.1 to 0.5% of the total mass of the dry powder in the cobalt-free material, adhesive, and conductive agent, for example, 0.1%, 0.12%, 0.15%, 0.17%, 0.2%, 0.22%, 0.25%, 0.27%, 0.3%, 0.32%, 0.35%, 0.38%, 0.4%, 0.42%, 0.45%, 0.47%, 0.5%, etc.

[0019] In one embodiment of the present invention, a positive electrode slurry is provided that includes a paste liquid and the cobalt-free system dispersed in the paste liquid.

[0020] In one embodiment, the method for preparing the paste liquid includes preparing a paste from adhesive A and a solvent to obtain the paste liquid.

[0021] In one embodiment, the paste is produced in a paste production machine, and the time for producing the paste is 200 to 300 minutes, for example, 200 minutes, 210 minutes, 220 minutes, 230 minutes, 240 minutes, 250 minutes, 260 minutes, 270 minutes, 280 minutes, 290 minutes, 300 minutes, etc.

[0022] In one embodiment, the adhesive A is polyvinylidene fluoride, and the number average molecular weight of the polyvinylidene fluoride is 500,000 to 1,500,000, for example, 500,000, 600,000, 700,000, 800,000, 900,000, 1,000,000, 1,100,000, 1,200,000, 1,300,000, 1,400,000, 1,500,000, etc.

[0023] In one embodiment, the solvent comprises any one or a combination of at least two of N-methylpyrrolidone, N,N-dimethylformamide, or dimethyl sulfoxide.

[0024] In one embodiment, assuming that the amount of the solvent is 80 to 95 parts by weight, the amount of the adhesive A is 5 to 20 parts by weight. For example, the amount of the solvent may be 80 parts by weight, 81 parts by weight, 82 parts by weight, 83 parts by weight, 84 parts by weight, 85 parts by weight, 86 parts by weight, 87 parts by weight, 88 parts by weight, 89 parts by weight, 90 parts by weight, 91 parts by weight, 92 parts by weight, 93 parts by weight, 94 parts by weight, 95 parts by weight, etc., and the amount of the adhesive A may be 5 parts by weight, 8 parts by weight, 10 parts by weight, 12 parts by weight, 15 parts by weight, 18 parts by weight, 20 parts by weight, etc.

[0025] In one embodiment of the present invention, there is provided a method for homogenizing the positive electrode slurry, which includes adding and dispersing a cobalt-free system into a paste liquid to obtain the positive electrode slurry.

[0026] In one embodiment, the homogenization method comprises: (1) adding an adhesive, a first conductive agent, and a pH adjuster in a cobalt-free system to a paste liquid and mixing them to obtain a conductive paste A; (2) adding a second conductive agent in a cobalt-free system to the conductive paste A obtained in step (1) and mixing to obtain a conductive paste B; (3) adding and mixing the cobalt-free material in the cobalt-free system to the conductive paste B obtained in step (2) to obtain the positive electrode slurry; Includes:

[0027] In one embodiment, the mixing in step (1) is carried out under stirring conditions, wherein the linear velocity of the stirring is 15 to 16 m / s, for example, 15 m / s, 15.1 m / s, 15.2 m / s, 15.3 m / s, 15.4 m / s, 15.5 m / s, 15.6 m / s, 15.7 m / s, 15.8 m / s, 15.9 m / s, 16 m / s, etc., and the stirring time is 40 to 80 min, for example, 40 min, 45 min, 50 min, 55 min, 60 min, 65 min, 70 min, 75 min, 80 min, etc.

[0028] In one embodiment, the mixing in step (2) is carried out under stirring conditions, wherein the linear velocity of the stirring is 15 to 16 m / s, for example, 15 m / s, 15.1 m / s, 15.2 m / s, 15.3 m / s, 15.4 m / s, 15.5 m / s, 15.6 m / s, 15.7 m / s, 15.8 m / s, 15.9 m / s, 16 m / s, etc., and the stirring time is 40 to 80 min, for example, 40 min, 45 min, 50 min, 55 min, 60 min, 65 min, 70 min, 75 min, 80 min, etc.

[0029] In one embodiment, the mixing in step (3) is performed under stirring conditions, and the linear velocity of the stirring is 19 to 20 m / s, for example, 19 m / s, 19.1 m / s, 19.2 m / s, 19.3 m / s, 19.4 m / s, 19.5 m / s, 19.6 m / s, 19.7 m / s, 19.8 m / s, 19.9 m / s, 20 m / s, etc., and the stirring time is 100 to 140 min, for example, 100 min, 102 min, 105 min, 107 min, 110 min, 112 min, 115 min, 117 min, 120 min, 122 min, 125 min, 127 min, 130 min, 132 min, 135 min, 137 min, 140 min, etc.

[0030] In one embodiment of the present invention, a positive electrode sheet is provided, which includes a positive electrode current collector and a slurry layer formed on the outer surface of the positive electrode current collector, wherein the slurry used in the slurry layer is the positive electrode slurry.

[0031] In one embodiment of the present invention, there is provided a lithium ion battery comprising a positive electrode sheet, a negative electrode sheet, and a separator, wherein the positive electrode sheet is the positive electrode sheet. [Brief explanation of the drawings]

[0032] The drawings are intended to provide a further understanding of the technical solution of the present invention, constitute a part of the specification, and are used to interpret the technical solution of the present invention together with the embodiments of the present invention, but are not intended to limit the technical solution of the present invention.

[0033] [Figure 1]1 is a graph showing the change in viscosity with shear rate of slurries obtained in Example 1 of the present invention and Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0034] In an embodiment of the present invention, a cobalt-free system is provided, which includes a cobalt-free material, an adhesive, a conductive agent, and a pH adjuster, wherein the cobalt-free material is Li x Ni y Mn z O2, x is 1 to 1.1, y is 0.5 to 0.8, z is 0.2 to 0.5, and y+z=1.

[0035] The cobalt-free system of the present invention can reduce the degree of viscosity rebound of the slurry after it has been left to stand. In some examples, the viscosity of the slurry before it was left to stand was 5260-6980 cp, and after it had been left to stand for 12 hours, the viscosity of the slurry rebounded to 12120-14950 cp, reaching the same level as that of ternary 811 single crystal. At the same time, the stability of the coating surface density of the cobalt-free material can be improved, with the variation of the coating surface density being as low as ±1.03%, reaching the same level as that of ternary materials.

[0036] In one embodiment, the cobalt-free material is prepared by the following method, which includes the following steps:

[0037] In S100, precursor Ni y Mn z (OH)2, the lithium source LiOH, and the dopant are mixed under stirring conditions at a mixing speed of 600 to 1000 rpm, for example, 600 rpm, 700 rpm, 800 rpm, 900 rpm, or 1000 rpm, for a mixing time of 10 to 40 minutes, for example, 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, or 40 minutes, to obtain a mixture.

[0038] In one embodiment, the dopant element is any one or a combination of at least two selected from Ti, Zr, and Al, and the doping amount is 2000 to 5000 ppm, for example, 2000 ppm, 2500 ppm, 3000 ppm, 4000 ppm, 4500 ppm, or 5000 ppm, and the doping amount is Li / transition metal in dopant=1.04 to 1.06, for example, 1.04, 1.05, or 1.06.

[0039] In S200, the mixture obtained in step S100 is subjected to primary firing under conditions of an oxygen gas concentration of 90 to 100 vol%. During the primary firing process, the temperature is first raised to 930 to 950 degrees at a rate of 1 to 4 degrees / min, and then maintained at that temperature for 5 to 15 hours to obtain a primary fired material.

[0040] In S300, the primary fired material obtained in step S200 is roll-crushed and polished, and then sieved through a 325 mesh sieve to obtain the sieved material.

[0041] In S400, the sieved material obtained in step S300 is dry-coated with nano-Zr and Al oxide (of which Zr content is 0.1% to 0.3 wt%, Al content is 0.1% to 0.2 wt%) and mixed at a high temperature with a rotation speed of 800 to 1200 rpm for 10 to 30 minutes, for example, 800 rpm, 850 rpm, 900 rpm, 1000 rpm, 1100 rpm, or 1200 rpm, for a time of 10 minutes, 15 minutes, 20 minutes, or 30 minutes, to obtain a coating.

[0042] In S500, the coated product obtained in step S400 is subjected to secondary baking, and the temperature is raised to 400 to 700°C at a rate of 2 to 4 degrees / min and maintained for 5 to 8 hours to obtain a secondary baked product.

[0043] In S600, the secondary fired product obtained in step S500 is sieved through a 325 mesh or 350 mesh sieve to obtain a cobalt-free material.

[0044] Cobalt-free material LiNi 0.75 Mn 0.25 O2, LiNi 0.8 Mn 0.2 O2 and LiNi 0.5 Mn 0.5 O2 can be prepared by the above method, and LiNi 0.8 Mn 0.2 Taking O2 as an example, in one embodiment, LiNi 0.8 Mn 0.2 The preparation method of O2 includes the following steps:

[0045] In S100, precursor Ni 0.8 Mn 0.2 (OH)2, a lithium source LiOH, and a dopant (a combination of at least one of Ti, Zr, and Al, with a doping amount of 5000 ppm and a Li / transition metal in the dopant ratio of 1.06) are mixed under stirring conditions at a mixing speed of 1000 rpm for 10 minutes to obtain a mixture.

[0046] In S200, the mixture obtained in step S100 is subjected to primary firing under conditions of an oxygen gas concentration of 90%. During the primary firing process, the temperature is first raised to 950°C at a rate of 2°C / min, and then held at that temperature for 12 hours to obtain the primary fired material.

[0047] In S300, the primary fired material obtained in step S200 is roll-crushed and polished, and then sieved through a 325 mesh sieve to obtain the sieved material.

[0048] In S400, the sieved material obtained in step S300 is dry-coated with nano-Zr and Al oxide (of which Zr content is 0.2 wt% and Al content is 0.1 wt%) and mixed at a high temperature with a rotation speed of 1000 rpm for 15 minutes to obtain a coating material.

[0049] In S500, the coated product obtained in step S400 is subjected to secondary baking, and the temperature is raised to 500° C. at a rate of 3° C. / min and maintained at this temperature for 6 hours to obtain a secondary baked product.

[0050] In S600, the secondary fired product obtained in step S500 is sieved through a 325 mesh sieve to obtain a cobalt-free material. [Example]

[0051] This example provides a cobalt-free system including 96.5 parts by weight of cobalt-free material, 1.5 parts by weight of adhesive, 1.5 parts by weight of first conductive agent, 0.5 parts by weight of second conductive agent, and a pH adjuster (the amount added is 0.3% of the dry powder amount in the cobalt-free material, adhesive, first conductive agent, and second conductive agent), where the cobalt-free material is LiNi 0.75 Mn 0.25 O2, the adhesive was polyvinylidene fluoride having a number average molecular weight of 1 million, the conductive agent included a first conductive agent and a second conductive agent, the first conductive agent was conductive carbon black, the second conductive agent was single-walled carbon nanotubes, and the pH adjuster was oxalic acid.

[0052] This example provides a positive electrode slurry including a paste liquid and the above-described cobalt-free system dispersed in the paste liquid. The paste liquid was prepared by adding 90 parts by weight of N-methylpyrrolidone and 10 parts by weight of polyvinylidene fluoride having a number average molecular weight of 1,000,000 to a paste making machine and producing the paste for 240 minutes to obtain the paste liquid.

[0053] This example provides a method for homogenizing a cathode slurry, which includes the following steps:

[0054] (1) The adhesive in the cobalt-free system, the first conductive agent, and the pH adjuster were added to the paste liquid and mixed with a stirrer. The linear stirring speed was 15.7 m / s and the stirring time was 60 minutes, and conductive paste A was obtained.

[0055] (2) The second conductive agent in the cobalt-free system was added to the conductive paste A obtained in step (1) and mixed with a stirrer at a linear stirring speed of 15.7 m / s for a stirring time of 60 min to obtain conductive paste B.

[0056] (3) The cobalt-free material in the cobalt-free system was added to the conductive paste B obtained in step (2) and mixed with a stirrer at a linear stirring speed of 19.7 m / s for a stirring time of 120 min to obtain the positive electrode slurry.

[0057] By conducting a viscosity test on the slurry obtained in this example, it was found that the viscosity of the slurry was 5660 cp, and after standing for 12 hours, the viscosity rebounded to 13000 cp, indicating that the viscosity rebound of the slurry after standing for 12 hours was relatively small.

[0058] The slurry obtained in this example was applied to a positive electrode sheet, and a long electrode sheet 1 m long was cut out. Sampling was performed every 20 cm, with 8 data points sampled each time, for a total of 48 data points. The 48 data points were calculated, and the variation in the applied surface density was ±1.03%, where the calculation method for the surface density variation (SD) included the following:

[0059]

number

[0060] This example provides a cobalt-free system including 95.4 parts by weight of cobalt-free material, 1.8 parts by weight of adhesive, 2 parts by weight of first conductive agent, 0.8 parts by weight of second conductive agent, and a pH adjuster (the amount added is 0.1% of the dry powder amount in the cobalt-free material, adhesive, first conductive agent, and second conductive agent), wherein the cobalt-free material is Li 1.1 Ni 0.8 Mn 0.2 O2, the adhesive was polyvinylidene fluoride with a number average molecular weight of 500,000, the conductive agent included a first conductive agent and a second conductive agent, the first conductive agent was conductive carbon black, the second conductive agent was single-walled carbon nanotubes, and the pH adjuster was maleic acid.

[0061] This example provides a positive electrode slurry including a paste liquid and the cobalt-free system dispersed in the paste liquid. The paste liquid was prepared by adding 95 parts by weight of N-methylpyrrolidone and 5 parts by weight of polyvinylidene fluoride having a number average molecular weight of 500,000 to a paste making machine and producing the paste for 200 minutes to obtain the paste liquid.

[0062] This example provides a method for homogenizing a cathode slurry, which includes the following steps:

[0063] (1) The adhesive, the first conductive agent, and the pH adjuster in the cobalt-free system were added to the paste liquid and mixed with a stirrer. The linear stirring speed was 15 m / s and the stirring time was 80 min, and conductive paste A was obtained.

[0064] (2) The second conductive agent in the cobalt-free system was added to the conductive paste A obtained in step (1) and mixed with a stirrer at a linear stirring speed of 15 m / s for a stirring time of 80 min to obtain conductive paste B.

[0065] (3) The cobalt-free material in the cobalt-free system was added to the conductive paste B obtained in step (2) and mixed with a stirrer at a linear stirring speed of 19 m / s for a stirring time of 140 min to obtain the positive electrode slurry.

[0066] By conducting a viscosity test on the slurry obtained in this example, it was found that the viscosity of the slurry was 5260 cp, and after standing for 12 hours, the viscosity rebounded to 12770 cp, indicating that the viscosity rebound of the slurry after standing for 12 hours was relatively small.

[0067] In this example, the same test method for coating surface density as in Example 1 was employed, and it was found that the variation in coating surface density was ±1.05%. [Example]

[0068] This example provides a cobalt-free system including 97.8 parts by weight of cobalt-free material, 1 part by weight of adhesive, 1 part by weight of first conductive agent, 0.2 parts by weight of second conductive agent, and a pH adjuster (the amount added is 0.5% of the dry powder amount in the cobalt-free material, adhesive, first conductive agent, and second conductive agent), wherein the cobalt-free material is LiNi 0.5 Mn 0.5 O2, the adhesive was polyvinylidene fluoride with a number average molecular weight of 1.5 million, the conductive agent included a first conductive agent and a second conductive agent, the first conductive agent was conductive carbon black, the second conductive agent was single-walled carbon nanotubes, and the pH adjuster was oxalic acid.

[0069] This example provides a positive electrode slurry including a paste liquid and the cobalt-free system dispersed in the paste liquid. The paste liquid was prepared by adding 80 parts by weight of N-methylpyrrolidone and 20 parts by weight of polyvinylidene fluoride having a number average molecular weight of 1.5 million to a paste making machine and producing a paste for 300 minutes to obtain the paste liquid.

[0070] This example provides a method for homogenizing a cathode slurry, which includes the following steps:

[0071] (1) The adhesive, the first conductive agent, and the pH adjuster in the cobalt-free system were added to the paste liquid and mixed with a stirrer. The linear stirring speed was 16 m / s and the stirring time was 40 min, and conductive paste A was obtained.

[0072] (2) The second conductive agent in the cobalt-free system was added to the conductive paste A obtained in step (1) and mixed with a stirrer at a linear stirring speed of 16 m / s for a stirring time of 40 min to obtain conductive paste B.

[0073] (3) The cobalt-free material in the cobalt-free system was added to the conductive paste B obtained in step (2) and mixed with a stirrer at a linear stirring speed of 20 m / s for a stirring time of 100 min to obtain the positive electrode slurry.

[0074] By conducting a viscosity test on the slurry obtained in this example, it was found that the viscosity of the slurry was 6640 cp, and after standing for 12 hours, the viscosity rebounded to 12120 cp, indicating that the viscosity rebound of the slurry after standing for 12 hours was relatively small.

[0075] In this example, the same test method for coating surface density as in Example 1 was employed, and it was found that the variation in coating surface density was ±1.306%. [Example]

[0076] The only difference from Example 1 is that the conductive agent in the cobalt-free system was the first conductive agent; other compositions and preparation methods were the same as those of Example 1.

[0077] By conducting a viscosity test on the slurry obtained in this example, it was found that the viscosity of the slurry was 6230 cp, and after standing for 12 hours, the viscosity rebounded to 12130 cp, indicating that the viscosity rebound of the slurry after standing for 12 hours was relatively small.

[0078] In this example, the same test method for coating surface density as in Example 1 was employed, and it was found that the variation in coating surface density was ±1.446%.

[0079] A comparison of Example 1 and Example 4 showed that when the cobalt-free system contained only the first conductive agent, the variation in coating area density was relatively large. [Example]

[0080] The only difference from Example 1 is that the conductive agent was the second conductive agent, and the other components and preparation method were the same as those of Example 1.

[0081] By conducting a viscosity test on the slurry obtained in this example, it was found that the viscosity of the slurry was 6210 cp, and after standing for 12 hours, the viscosity rebounded to 13250 cp, indicating that the viscosity rebound of the slurry after standing for 12 hours was relatively small.

[0082] In this example, the same test method for coating surface density as in Example 1 was employed, and it was found that the variation in coating surface density was ±1.485%.

[0083] Comparison of Example 1 and Example 5 showed that when the cobalt-free system contained only the second conductive agent, the variation in coating area density was relatively large. [Example]

[0084] The only difference from Example 1 is that the single-walled carbon nanotubes in the cobalt-free system were replaced with carbon nanotubes; the other compositions and preparation methods were the same as those of Example 1.

[0085] By conducting a viscosity test on the slurry obtained in this example, it was found that the viscosity of the slurry was 6980 cp, and after standing for 12 hours, the viscosity rebounded to 13260 cp, indicating that the viscosity rebound of the slurry after standing for 12 hours was relatively small.

[0086] In this example, the same test method for coating surface density as in Example 1 was employed, and it was found that the variation in coating surface density was ±1.37%.

[0087] Comparison between Example 1 and Example 6 revealed that when carbon nanotubes were used instead of single-walled carbon nanotubes, the variation in the surface density of the slurry was relatively large. [Example]

[0088] The only difference from Example 1 was that the number average molecular weight of the adhesive, polyvinylidene fluoride, was 5,000,000; the other components and preparation methods were the same as those of Example 1.

[0089] By conducting a viscosity test on the slurry obtained in this example, it was found that the viscosity of the slurry was 6350 cp, and after standing for 12 hours, the viscosity rebounded to 14950 cp, indicating that the viscosity rebound of the slurry after standing for 12 hours was relatively small.

[0090] In this example, the same test method for coating surface density as in Example 1 was employed, and it was found that the variation in coating surface density was ±1.32%.

[0091] A comparison between Example 1 and Example 7 revealed that when the adhesive used was high molecular weight polyvinylidene fluoride, the viscosity repulsion of the slurry was relatively large, and the variation in coating surface density was relatively large.

[0092] [Comparative Example 1] The only difference from Example 1 is that the cobalt-free system did not contain oxalic acid as a pH adjuster; other components and preparation methods were the same as those of Example 1.

[0093] By conducting a viscosity test on the slurry obtained in this comparative example, it was found that the viscosity of the slurry was 5630 cp, and after standing for 12 hours, the viscosity rebounded to 47000 cp, indicating that the viscosity rebound of the slurry was relatively large after standing for 12 hours.

[0094] In this comparative example, the same test method for coating surface density as in Example 1 was employed, and it was found that the variation in coating surface density was ±2.02%.

[0095] Comparing Example 1 with Comparative Example 1, it was found that when oxalic acid was not included in the cobalt-free system, the viscosity of the slurry rebounded significantly and the coating surface density varied significantly, which was disadvantageous for practical application.

[0096] Comparative Example 2 This comparative example provides a homogenization method, which includes the following steps:

[0097] (1) 6.25 parts by weight of polyvinylidene fluoride (number average molecular weight 800,000) and 93.75 parts by weight of N-methylpyrrolidone were added to a paste production machine, and paste production was carried out for 240 minutes to obtain a paste liquid.

[0098] (2) 1.2 parts by weight of polyvinylidene fluoride (number average molecular weight 800,000) and 0.7 parts by weight of carbon nanotubes were added to a stirrer and stirred to obtain a conductive paste 1.

[0099] (3) 1.8 parts by weight of conductive carbon black and the conductive paste 1 obtained in step (2) were added to a stirrer and stirred to obtain a conductive paste 2.

[0100] (4) 96.3 parts by weight of the cobalt-free material and the conductive paste 2 obtained in step (3) were added to a stirrer and stirred to obtain a slurry.

[0101] By conducting a viscosity test on the slurry obtained in this comparative example, it was found that the viscosity of the slurry was 6850 cp, and after standing for 12 hours, the viscosity rebounded to 70000 cp, indicating that the viscosity rebound of the slurry was relatively large after standing for 12 hours.

[0102] In this comparative example, the same test method for coating surface density as in Example 1 was employed, and it was found that the variation in coating surface density was ±2.28%.

[0103] Comparing Example 1 and Comparative Example 2, it was found that when the ternary homogenization method was applied, the viscosity of the obtained slurry was highly repulsive and the coating surface density also varied significantly, which was disadvantageous for practical application.

[0104] 1 is a graph showing the change in viscosity with shear rate at different rotational speeds (from 0 to 300 r / min and from 300 to 0 r / min) of the slurries obtained in Example 1 and Comparative Example 2. As can be seen from FIG. 1, in Comparative Example 2, when the rotational speed changed from 0 to 300 r / min, the viscosity of the slurry was 133,000 cp at 1 r / min, and when the rotational speed changed from 300 to 0 r / min, the viscosity of the slurry was 10,901 cp at 1 r / min. In Example 1, when the rotational speed changed from 0 to 300 r / min, the viscosity of the slurry was 24,544 cp at 1 r / min, and when the rotational speed changed from 300 to 0 r / min, the viscosity of the slurry was 12,311 cp at 1 r / min. Comparing Comparative Example 2 with Example 1, it was found that in Example 1, when the rotation speed was changed from 300 to 0 r / min, the viscosity of the slurry at 1 r / min decreased significantly, and the thixotropy loop area (i.e., the area between the two viscosity curves from 0 to 300 r / min and from 300 to 0 r / min) became significantly smaller. This means that the slurry formed in Example 1 has stronger fluidity and ability to return to its initial state, which contributes to coating leveling. This means that homogenizing the cobalt-free system in Example 1 is a method that significantly optimizes and improves the effect.

Claims

1. A positive electrode slurry for a lithium ion battery, comprising: a paste liquid; and a cobalt-free material, an adhesive, a conductive agent, and a pH adjuster dispersed in the paste liquid, the cobalt-free material is LixNiyMnzO2, where x is 1 to 1.1, y is 0.5 to 0.8, z is 0.2 to 0.5, and y+z=1; the adhesive is polyvinylidene fluoride, and the number average molecular weight of the polyvinylidene fluoride is 500,000 to 1,500,000; the conductive agent includes a combination of a first conductive agent and a second conductive agent, the first conductive agent being conductive carbon black, and the second conductive agent being single-walled carbon nanotubes; and the pH adjuster includes oxalic acid and / or maleic acid; When the cobalt-free material, the adhesive, the conductive agent, and the pH adjuster are calculated as 100 parts by weight, The amount of the cobalt-free material added is 95.4 to 97.8 parts by weight, and the amount of the adhesive added is 1 to 1.8 parts by weight; the amount of the first conductive agent added is 1 to 2 parts by weight, and the amount of the second conductive agent added is 0.2 to 0.8 parts by weight; the amount of the pH adjuster added is 0.1 to 0.5% of the total mass of the dry powders in the cobalt-free material, the adhesive, and the conductive agent; The paste liquid is obtained by manufacturing a paste from an adhesive and a solvent, The adhesive is polyvinylidene fluoride, and the number average molecular weight of the polyvinylidene fluoride is 500,000 to 1,500,000; the solvent includes any one or a combination of at least two of N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide; The positive electrode slurry for a lithium ion battery, wherein the amount of the solvent added is 80 to 95 parts by weight, and the amount of the adhesive added is 5 to 20 parts by weight.

2. 2. The lithium ion battery positive electrode slurry of claim 1, wherein the cobalt-free material is LixNi0.75Mn0.25O2, where x is 1 to 1.

1.

3. 3. The homogenization method for producing a positive electrode slurry for a lithium ion battery according to claim 1 or 2, comprising: (1) adding an adhesive, a first conductive agent, and a pH adjuster to a paste liquid and mixing them to obtain a conductive paste A; (2) adding a second conductive agent to the conductive paste A obtained in step (1) and mixing to obtain a conductive paste B; (3) adding and mixing a cobalt-free material into the conductive paste B obtained in step (2) to obtain the positive electrode slurry; Including, The homogenization method, wherein the first conductive agent is conductive carbon black and the second conductive agent is single-walled carbon nanotubes.

4. The mixing described in step (1) is carried out under stirring conditions, the linear velocity of the stirring is 15 to 16 m / s, and the stirring time is 40 to 80 min; The mixing described in step (2) is carried out under stirring conditions, the linear velocity of the stirring is 15 to 16 m / s, and the stirring time is 40 to 80 min; 4. The homogenization method according to claim 3, wherein the mixing in step (3) is carried out under stirring conditions, the linear velocity of the stirring being 19-20 m / s, and the stirring time being 100-140 min.

5. A positive electrode sheet comprising a positive electrode current collector and a slurry layer provided on the outer surface of the positive electrode current collector, wherein the slurry used in the slurry layer is the positive electrode slurry for a lithium ion battery according to claim 1 or 2.

6. A lithium ion battery comprising a positive electrode sheet, a negative electrode sheet, and a separator, wherein the positive electrode sheet is the positive electrode sheet according to claim 5.

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