Positive electrode slurry as well as homogenizing method and application thereof

Abstract

The invention relates to a positive electrode slurry and a homogenizing method and application thereof, and the homogenizing method comprises the following steps: (1) carrying out first mixing on an acrylic polymer dispersant, a first solvent and lithium manganese iron phosphate to obtain a first component; carrying out second mixing on a binder and a second solvent to obtain a second component; and (2) performing solid-phase mixing on a ternary main body material and a conductive agent to obtain a dry powder mixture, performing third mixing on the dry powder mixture and the first component to obtain a half-step slurry, and performing fourth mixing on the half-step slurry and the second component to obtain the positive electrode slurry. According to the homogenizing method of the positive electrode slurry provided by the invention, the design of a step-by-step mixing mode is combined with the pre-dispersion of the lithium manganese iron phosphate by adopting the acrylic polymer dispersing agent, so that the agglomeration phenomenon of the lithium manganese iron phosphate during homogenizing is inhibited, and the dispersity of the lithium manganese iron phosphate introduced into the ternary main body material is improved; the stability and the safety of the ternary positive electrode material are effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a positive electrode slurry and a homogenization method and application thereof. Background Art

[0002] Lithium-ion batteries are the core components of new energy vehicles and energy storage systems, and have experienced explosive growth worldwide. With the rapid expansion of the electric vehicle market, the demand for high-performance, long-life lithium-ion batteries has surged, driving the continuous advancement of battery technology and a significant reduction in costs. In addition, lithium-ion batteries are increasingly used in portable electronic devices, drones, power tools and other fields, becoming an indispensable energy source in modern society.

[0003] The ternary positive electrode material of nickel, cobalt and manganese contained in lithium-ion batteries has become a research hotspot at home and abroad due to its high energy density, long cycle life and good rate performance. For example, the prior art CN109244431A discloses a nickel-cobalt-manganese ternary positive electrode material, which is a core-shell structure, the core layer is a hollow structure of Li2MnO3, and the shell material is a nickel-cobalt-manganese ternary material; wherein the content of Mn in the shell material is a gradient distribution, gradually decreasing from the inner layer to the outer layer. The nickel-cobalt-manganese ternary positive electrode material is a hollow core-shell structure, the core layer is a hollow structure of Li2MnO3, the shell material is a nickel-cobalt-manganese ternary material, and the Mn content in the shell material decreases in a gradient. This structure shortens the diffusion path of lithium ions, improves the rate performance of the material, and at the same time maintains the spherical morphology of the material, and has no significant effect on the tap density of the material.

[0004] However, the nickel-cobalt-manganese ternary positive electrode material still has problems such as high cost, poor stability and poor safety, which will affect the application of ternary positive electrode materials in lithium-ion batteries and hinder the development of lithium-ion batteries. In order to improve the stability and safety of nickel-cobalt-manganese ternary positive electrode materials and reduce the cost of batteries, lithium iron manganese phosphate is generally introduced into nickel-cobalt-manganese ternary positive electrode materials. Compared with traditional lithium iron phosphate, lithium iron manganese phosphate has a higher voltage platform and improved energy density, which is close to the energy density level of ternary materials, but the cost is lower; secondly, the introduction of small lithium iron manganese phosphate particles between large particles of nickel-cobalt-manganese ternary positive electrode materials can build a stable structure, reduce impedance, and improve cycle life; in addition, the introduction of lithium iron manganese phosphate can effectively suppress the risk of thermal runaway of nickel-cobalt-manganese ternary materials under high temperature and high pressure, and can improve the stability and safety of nickel-cobalt-manganese ternary positive electrode materials. However, due to the large difference in specific surface area between the small particles of lithium iron manganese phosphate and the main nickel-cobalt-manganese ternary positive electrode material, the lithium iron manganese phosphate particles are easily adsorbed on the surface of the main material during the mixing process, and agglomerate at the same time, thereby affecting the performance of lithium-ion batteries.

[0005] Therefore, how to improve the stability and safety of ternary positive electrode materials and avoid the agglomeration and uneven dispersion of lithium manganese iron phosphate has become a technical problem that needs to be solved urgently. Summary of the invention

[0006] In order to solve the above technical problems, the purpose of the present invention is to provide a positive electrode slurry and a homogenization method and application thereof. The homogenization method of the positive electrode slurry provided by the present invention suppresses the agglomeration phenomenon of the lithium iron manganese phosphate during the homogenization process by designing a step-by-step mixing process combined with the use of an acrylic polymer dispersant to pre-disperse the lithium iron manganese phosphate, improves the dispersibility of the lithium iron manganese phosphate introduced into the ternary main material, and effectively improves the stability and safety of the ternary positive electrode material.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for homogenizing a positive electrode slurry, the homogenizing method comprising the following steps:

[0009] (1) mixing an acrylic polymer dispersant, a first solvent, and lithium manganese iron phosphate to obtain a first component;

[0010] performing a second mixing of the binder and the second solvent to obtain a second component;

[0011] (2) solid-phase mixing the ternary main material and the conductive agent to obtain a dry powder mixture, performing a third mixing of the dry powder mixture and the first component to obtain a half-step slurry, and performing a fourth mixing of the half-step slurry and the second component to obtain the positive electrode slurry.

[0012] The positive electrode slurry homogenization method of the present invention adopts a step-by-step mixing method, firstly introducing a specific acrylic polymer dispersant and pre-mixing with lithium iron manganese phosphate to achieve sufficient dispersion of small particles of lithium iron manganese phosphate, and then mixing the dry powder mixture consisting of the ternary main material and the conductive agent with the components consisting of the lithium iron manganese phosphate dispersion and the components consisting of the binder dispersion in sequence, which can inhibit the agglomeration of lithium iron manganese phosphate during the homogenization process, improve the dispersibility of the lithium iron manganese phosphate introduced in the ternary positive electrode material, and effectively improve the stability and safety of the ternary positive electrode material.

[0013] Preferably, the acrylic polymer in the acrylic polymer dispersant of step (1) comprises a polymer and / or a copolymer composed of monomer units, and the monomer units comprise any one of methacrylic acid, methacrylate, methacrylate, methacrylamide or methacrylonitrile, or a combination of at least two thereof.

[0014] Preferably, the chemical formula of the lithium manganese iron phosphate in step (1) is LiMn x Fe 1-xPO4, wherein x is 0.6-0.7, for example, 0.6, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69 or 0.7, etc.

[0015] Preferably, the particle size D50 of the lithium manganese iron phosphate in step (1) is 0.5-3 μm, such as 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm or 3 μm, etc., preferably 0.5-2 μm.

[0016] Preferably, in the first mixing process of step (1), the mass ratio of the acrylic polymer dispersant to the first solvent is (3-4):(6-7), such as 3:7, 3.5:6.5 or 4:6.

[0017] Preferably, in the first mixing process of step (1), the added amount of the acrylic polymer dispersant is 0.4-5wt% of the mass of the lithium manganese iron phosphate, for example, 0.4wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt% or 5wt%, etc.

[0018] In the present invention, if the amount of acrylic polymer dispersant added is too low, it will lead to the inability to effectively disperse the lithium manganese iron phosphate, affecting the coating effect and thus affecting the battery performance; if the amount of acrylic polymer dispersant added is too high, a large amount of acrylic polymer residue will remain during coating, which will affect the battery performance.

[0019] Preferably, the rotation speed of the first mixing in step (1) is 700-1000 rpm, for example, 700 rpm, 750 rpm, 800 rpm, 850 rpm, 900 rpm, 950 rpm or 1000 rpm, etc.

[0020] In the present invention, the first mixing can be performed using a high-speed disperser.

[0021] The present invention can effectively improve the dispersibility of lithium iron manganese phosphate by regulating the rotation speed of the first mixing. If the rotation speed is too low, the dispersion effect of lithium iron manganese phosphate will be poor, resulting in the presence of agglomerated lithium iron manganese phosphate in the positive electrode slurry after homogenization, affecting the electrochemical properties of the positive electrode material; if the rotation speed is too high, a large number of bubbles will be generated in the resulting slurry, affecting the consistency of subsequent coating, and a too high rotation speed will also lead to increased energy consumption and costs.

[0022] Preferably, the first mixing time in step (1) is 0.5-3 h, for example, 0.5 h, 0.75 h, 1 h, 1.25 h, 1.5 h, 1.75 h, 2 h, 2.25 h, 2.5 h, 2.75 h or 3 h.

[0023] Preferably, the first mixing in step (1) comprises: firstly mixing the acrylic polymer dispersant with the first solvent to obtain an acrylic polymer dispersion, and then further mixing the acrylic polymer dispersion with the lithium manganese iron phosphate to obtain a first component.

[0024] Preferably, the acrylic polymer dispersant and the first solvent are mixed for 0.2-1.8 h, for example, 0.2 h, 0.4 h, 0.6 h, 0.8 h, 1 h, 1.2 h, 1.4 h, 1.6 h or 1.8 h.

[0025] Preferably, the acrylic polymer dispersion and the lithium manganese iron phosphate are mixed for 0.2-2 h, for example, 0.2 h, 0.4 h, 0.6 h, 0.8 h, 1 h, 1.2 h, 1.4 h, 1.6 h, 1.8 h or 2 h.

[0026] Preferably, in step (1), the first solvent comprises N-methylpyrrolidone.

[0027] Preferably, the binder in step (1) comprises polyvinylidene fluoride (PVDF).

[0028] Preferably, in step (1), the second solvent comprises N-methylpyrrolidone.

[0029] Preferably, the solid content of the second component in step (1) is 1-1.3wt%, for example, 1wt%, 1.05wt%, 1.1wt%, 1.15wt%, 1.2wt%, 1.25wt% or 1.3wt%, etc.

[0030] Preferably, the second mixing method in step (1) includes stirring.

[0031] Preferably, the stirring revolution is 60-100 rpm, for example, 60 rpm, 65 rpm, 70 rpm, 75 rpm, 80 rpm, 85 rpm, 90 rpm, 95 rpm or 100 rpm, etc.

[0032] Preferably, the stirring speed is 1000-2000 rpm, for example, 1000 rpm, 1200 rpm, 1400 rpm, 1600 rpm, 1800 rpm or 2000 rpm.

[0033] Preferably, the second mixing time is 0.5-2 h, for example 0.5 h, 0.75 h, 1 h, 1.25 h, 1.5 h, 1.75 h or 2 h, etc.

[0034] Preferably, the mass ratio of the ternary host material to the conductive agent in step (2) is (45-55):1, for example, 45:1, 46:1, 47:1, 48:1, 49:1, 50:1, 51:1, 52:1, 53:1, 54:1 or 55:1, etc.

[0035] Preferably, the chemical formula of the ternary host material in step (2) is LiNi a Co b Mn 1-a-b O2, wherein a is 0.6-0.9, such as 0.6, 0.65, 0.7, 0.75, 0.8, 0.85 or 0.9, and b is 0.1-0.2, such as 0.1, 0.12, 0.14, 0.16, 0.18 or 0.2, etc.

[0036] Preferably, the conductive agent in step (2) includes a first conductive agent and a second conductive agent.

[0037] Preferably, the first conductive agent includes conductive carbon black.

[0038] Preferably, the second conductive agent comprises multi-walled carbon nanotubes.

[0039] The homogenization method provided by the present invention introduces two specific conductive agent combinations. First, the conductive carbon black can form point-to-point contact with the active material, which is beneficial to the adsorption of the electrolyte. Second, the multi-walled carbon nanotubes have a fibrous structure and can form point-to-line contact with the active material to form a continuous conductive network in the active material of the electrode. The two conductive agents cooperate with each other to form a complete conductive network.

[0040] Preferably, the mass ratio of the first conductive agent to the second conductive agent is 2:(0.5-1), for example, 2:0.5, 2:0.6, 2:0.7, 2:0.8, 2:0.9 or 2:1.

[0041] Preferably, the rotation speed of the solid phase mixing in step (2) is 30-60 rpm, for example, 30 rpm, 35 rpm, 40 rpm, 45 rpm, 50 rpm, 55 rpm or 60 rpm.

[0042] In the present invention, the rotation speed during the mixing process of the ternary main material and the conductive agent is relatively low, mainly to avoid the destruction of the structure and quality of the ternary main material under excessively high rotation speed conditions, and to avoid the floating of dust during the mixing process and the waste of dry powder materials, thereby affecting the quality and composition of the substances in the positive electrode slurry.

[0043] In the present invention, lithium iron manganese phosphate is dispersed separately from the ternary main body material and the conductive agent, and the respective mixing speeds can be regulated to meet the requirement of setting a higher speed during the dispersion of lithium iron manganese phosphate, while a lower speed is used for mixing the ternary main body material and the conductive agent, thereby avoiding the problem that during the simultaneous mixing of the three, the low speed leads to poor dispersion of lithium iron manganese phosphate, while the high speed leads to poor quality of the ternary main body material and inaccurate composition content.

[0044] Preferably, the solid phase mixing time in step (2) is 0.5-1 h, such as 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h or 1 h.

[0045] Preferably, in the third mixing process of step (2), the mass ratio of the ternary main material in the dry powder mixture to the lithium manganese iron phosphate in the first component is (5-9):(1-5), for example, 5:5, 6:4, 7:3, 8:2 or 9:1, etc.

[0046] The positive electrode slurry homogenization method provided by the present invention can meet a relatively wide range of relative contents between lithium iron manganese phosphate and the ternary main material. On the basis of ensuring the electrochemical properties of the subsequently obtained positive electrode material, even if too much lithium iron manganese phosphate is added, it can still have excellent dispersibility, which effectively solves the problem in the prior art that too much lithium iron manganese phosphate cannot be added to the ternary main material due to poor dispersibility and serious agglomeration of lithium iron manganese phosphate, thereby failing to effectively improve the stability of the positive electrode material.

[0047] Preferably, the third mixing method in step (2) includes stirring.

[0048] Preferably, during the third mixing process, the stirring revolution is 60-100 rpm, for example, 60 rpm, 65 rpm, 70 rpm, 75 rpm, 80 rpm, 85 rpm, 90 rpm, 95 rpm or 100 rpm.

[0049] Preferably, during the third mixing process, the stirring rotation speed is 1000-2000 rpm, for example, 1000 rpm, 1200 rpm, 1400 rpm, 1600 rpm, 1800 rpm or 2000 rpm.

[0050] Preferably, the third mixing time is 1-2 h, for example, 1 h, 1.2 h, 1.4 h, 1.6 h, 1.8 h or 2 h.

[0051] Preferably, in the fourth mixing process of step (2), the amount of the second component added satisfies that the proportion of the binder in the second component in the solid matter of the positive electrode slurry is 1-2.5wt%, for example, 1wt%, 1.2wt%, 1.4wt%, 1.6wt%, 1.8wt%, 2wt%, 2.2wt%, 2.4wt% or 2.5wt%, etc., and the solid matter in the positive electrode slurry includes the ternary main material, the lithium manganese iron phosphate, the acrylic polymer dispersant, the binder and the conductive agent.

[0052] Preferably, the fourth mixing method in step (2) includes stirring.

[0053] Preferably, during the fourth mixing process, the stirring revolution is 100-200 rpm, for example, 100 rpm, 120 rpm, 140 rpm, 160 rpm, 180 rpm or 200 rpm.

[0054] Preferably, during the fourth mixing process, the stirring rotation is 3000-5000 rpm, for example, 3000 rpm, 3200 rpm, 3400 rpm, 3600 rpm, 3800 rpm, 4000 rpm, 4200 rpm, 4400 rpm, 4600 rpm, 4800 rpm or 5000 rpm.

[0055] Preferably, the fourth mixing time in step (2) is 3-4 h, for example, 3 h, 3.2 h, 3.4 h, 3.6 h, 3.8 h or 4 h.

[0056] Preferably, after the fourth mixing in step (2), the third solvent is added to the slurry obtained by the fourth mixing for a fifth mixing, and the viscosity of the obtained positive electrode slurry is adjusted to 4000-6000mPa·s, for example, 4000mPa·s, 4200mPa·s, 4400mPa·s, 4600mPa·s, 4800mPa·s, 5000mPa·s, 5200mPa·s, 5400mPa·s, 5600mPa·s, 5800mPa·s or 6000mPa·s, etc.

[0057] The present invention does not specifically limit the content of the third solvent added in the fifth mixing process. It is only necessary to adjust the viscosity of the obtained positive electrode slurry within a specific range during the mixing process at a specific rotation speed.

[0058] Preferably, during the fifth mixing process, the stirring revolution is 100-200 rpm, for example, 100 rpm, 120 rpm, 140 rpm, 160 rpm, 180 rpm or 200 rpm.

[0059] Preferably, during the fifth mixing process, the stirring rotation is 3000-5000 rpm, for example, 3000 rpm, 3200 rpm, 3400 rpm, 3600 rpm, 3800 rpm, 4000 rpm, 4200 rpm, 4400 rpm, 4600 rpm, 4800 rpm or 5000 rpm, etc.

[0060] Preferably, the fifth mixing time is 1-4 h, for example, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 or 4 h, etc.

[0061] Preferably, the third solvent comprises N-methylpyrrolidone.

[0062] In a second aspect, the present invention provides a positive electrode slurry, which is prepared by the homogenization method described in the first aspect, and the positive electrode slurry includes a solid substance and a solvent, and the solid substance includes a ternary main material, lithium manganese iron phosphate, an acrylic polymer dispersant, a binder and a conductive agent.

[0063] The positive electrode slurry provided by the present invention has excellent dispersibility and stability. Through the interaction of the ternary main material, lithium manganese iron phosphate, acrylic polymer dispersant, binder, conductive agent and solvent, the positive electrode material obtained by the positive electrode slurry can have excellent electrochemical properties while also having the advantages of good stability and safety performance.

[0064] Preferably, the solvent comprises N-methylpyrrolidone.

[0065] Preferably, the viscosity of the positive electrode slurry is 4000-6000 mPa·s, for example, 4000 mPa·s, 4200 mPa·s, 4400 mPa·s, 4600 mPa·s, 4800 mPa·s, 5000 mPa·s, 5200 mPa·s, 5400 mPa·s, 5600 mPa·s, 5800 mPa·s or 6000 mPa·s, etc.

[0066] In a third aspect, the present invention provides a positive electrode plate, which is obtained by coating the positive electrode slurry described in the second aspect on the surface of a positive electrode collector, followed by drying and rolling.

[0067] The positive electrode plate provided by the present invention is obtained by coating, drying and rolling a specific positive electrode slurry, and has good internal material dispersibility and high stability, and has excellent electrochemical performance.

[0068] In a fourth aspect, the present invention provides a lithium-ion battery, wherein the lithium-ion battery comprises the positive electrode sheet described in the third aspect.

[0069] The lithium ion battery provided by the present invention has good stability and safety, as well as excellent electrochemical performance.

[0070] Compared with the prior art, the present invention has at least the following beneficial effects:

[0071] (1) The positive electrode slurry homogenization method of the present invention adopts a step-by-step mixing method, firstly introducing a specific acrylic polymer dispersant and pre-mixing with lithium iron manganese phosphate to achieve sufficient dispersion of small particles of lithium iron manganese phosphate, and then mixing the dry powder mixture consisting of the ternary main material and the conductive agent with the components consisting of the lithium iron manganese phosphate dispersion and the components consisting of the binder dispersion in sequence, which can inhibit the agglomeration of lithium iron manganese phosphate during the homogenization process, improve the dispersibility of the lithium iron manganese phosphate introduced in the ternary positive electrode material, and effectively improve the stability and safety of the ternary positive electrode material.

[0072] (2) The positive electrode slurry provided by the present invention has excellent dispersibility and stability. Through the interaction of the ternary main material, lithium manganese iron phosphate, acrylic polymer dispersant, binder, conductive agent and solvent, the positive electrode material obtained by the positive electrode slurry has excellent electrochemical properties and also has the advantages of good stability and safety performance. DETAILED DESCRIPTION

[0073] For the convenience of understanding the present invention, the present invention lists the following embodiments. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0074] Example 1

[0075] This embodiment provides a method for homogenizing a positive electrode slurry, and the specific steps of the homogenizing method include the following steps:

[0076] S1. A polymethyl methacrylate dispersant (molecular weight of about 15,000) and N-methyl pyrrolidone are mixed at a speed of 800 rpm for 30 minutes using a high-speed disperser, wherein the mass ratio of the polymethyl methacrylate dispersant to the N-methyl pyrrolidone is 3:7, to obtain a polymethyl methacrylate dispersion, and then, the polymethyl methacrylate dispersion and lithium iron manganese phosphate are further mixed at a speed of 800 rpm using a high-speed disperser for 30 minutes to obtain a first component, wherein the amount of the polymethyl methacrylate dispersant added to the first component is 2wt% of the mass of the lithium iron manganese phosphate, and the chemical formula of the lithium iron manganese phosphate is LiMn 0.6 Fe 0.4 PO4, particle size D50 is 1μm.

[0077] S2. Stir polyvinylidene fluoride and N-methylpyrrolidone at an orbital speed of 80 rpm and an autorotational speed of 1500 rpm for 1 h to obtain a second component with a solid content of 1 wt%.

[0078] S3. LiNi 0.8 Co 0.1 Mn 0.1 The O2 main material and the conductive agent were mixed at a rotation speed of 50 rpm for 1 h. The conductive agent consisted of conductive carbon black and multi-walled carbon nanotubes with a mass ratio of 2:1. 0.8 Co 0.1 Mn 0.1 The mass ratio of the O2 main material to the conductive agent is 50:1, and a dry powder mixture is obtained.

[0079] S4. The dry powder mixture obtained in step S3 and the first component obtained in step S1 were stirred at a revolution speed of 80 rpm and a rotation speed of 1500 rpm for 1 h to obtain a half-step slurry, wherein LiNi 0.8 Co 0.1 Mn 0.1 O2 host material and LiMn 0.6 Fe 0.4 The mass ratio of PO4 is 8:2.

[0080] S5. The half-step slurry obtained in step S4 and the second component obtained in step S2 are stirred at an orbital speed of 150 rpm and an autorotation speed of 4000 rpm for 3 h, and the amount of the second component added satisfies that the PVDF in the second component accounts for 2 wt% of the total mass of the solid matter in the positive electrode slurry. N-methylpyrrolidone is then added to the stirred product and stirred at an orbital speed of 150 pm and an autorotation speed of 4000 rpm for 3 h to obtain a positive electrode slurry with a viscosity of 5000 mPa·s. The solid matter in the obtained positive electrode slurry includes polymethyl methacrylate dispersant, LiMn 0.6 Fe 0.4 PO4, polyvinylidene fluoride, LiNi 0.8 Co 0.1 Mn 0.1 O2 host material, conductive carbon black and multi-walled carbon nanotubes.

[0081] Example 2

[0082] This embodiment provides a method for homogenizing a positive electrode slurry, and the specific steps of the homogenizing method include the following steps:

[0083] S1. Stir polyvinylidene fluoride and N-methylpyrrolidone at an orbital speed of 100 rpm and an autorotational speed of 1000 rpm for 0.5 h to obtain a first component with a solid content of 1.2 wt%.

[0084] S2. The polymethyl methacrylate dispersant (molecular weight of about 15,000) and N-methyl pyrrolidone were mixed at a speed of 700 rpm for 40 min using a high-speed disperser, wherein the mass ratio of the polymethyl methacrylate dispersant to the N-methyl pyrrolidone was 4:6 to obtain a polymethyl methacrylate dispersion, and then the polymethyl methacrylate dispersion was mixed with lithium iron manganese phosphate (chemical formula LiMn 0.7 Fe 0.3 PO4) continue to use a high-speed disperser to mix at a speed of 700 rpm for 2 hours to obtain a second component, wherein the amount of polymethyl methacrylate dispersant added in the second component is 5wt% of the mass of lithium manganese iron phosphate, and the chemical formula of lithium manganese iron phosphate is LiMn 0.7 Fe 0.3 PO4, particle size D50 is 2μm.

[0085] S3. LiNi 0.6 Co 0.2 M 0.2 The O2 main material and the conductive agent were mixed at a rotation speed of 30 rpm for 1 h. The conductive agent consisted of conductive carbon black and multi-walled carbon nanotubes with a mass ratio of 2:0.5. 0.6 Co 0.2 M 0.2 The mass ratio of the O2 main material to the conductive agent is 55:1, and a dry powder mixture is obtained.

[0086] S4. The dry powder mixture obtained in step S3 and the second component obtained in step S2 were stirred at a revolution speed of 60 rpm and a rotation speed of 2000 rpm for 1 h to obtain a half-step slurry, wherein LiNi 0.6 Co 0.2 M 0.2 O2 host material and LiMn 0.7 Fe 0.3 The mass ratio of PO4 is 9:1.

[0087] S5. The half-step slurry obtained in step S4 and the first component obtained in step S1 are stirred at an orbital speed of 100 rpm and an autorotation speed of 3000 rpm for 4 hours, and the amount of the first component added satisfies that the PVDF in the first component accounts for 2.5 wt% of the total mass of the solid matter in the positive electrode slurry. N-methylpyrrolidone is then added to the stirred product and stirred at an orbital speed of 100 pm and an autorotation speed of 3000 rpm for 1 hour to obtain a positive electrode slurry with a viscosity of 6000 mPa·s. The solid matter in the obtained positive electrode slurry includes polymethyl methacrylate dispersant, LiMn 0.7 Fe 0.3 PO4, polyvinylidene fluoride, LiNi 0.6 Co 0.2 M 0.2O2 host material, conductive carbon black and multi-walled carbon nanotubes.

[0088] Example 3

[0089] This embodiment provides a method for homogenizing a positive electrode slurry, and the specific steps of the homogenizing method include the following steps:

[0090] S1. A polymethyl methacrylate dispersant (molecular weight of about 15,000) and N-methyl pyrrolidone are mixed at a speed of 1000 rpm for 20 minutes using a high-speed disperser, wherein the mass ratio of the polymethyl methacrylate dispersant to the N-methyl pyrrolidone is 3:7, to obtain a polymethyl methacrylate dispersion, and then the polymethyl methacrylate dispersion and lithium iron manganese phosphate are further mixed at a speed of 1000 rpm using a high-speed disperser for 1 hour to obtain a first component, wherein the amount of the polymethyl methacrylate dispersant added to the first component is 0.45wt% of the mass of the lithium iron manganese phosphate, and the chemical formula of the lithium iron manganese phosphate is LiMn 0.6 Fe 0.4 PO4, particle size D50 is 0.5μm.

[0091] S2. The polyvinylidene fluoride and N-methylpyrrolidone were stirred at an orbital speed of 60 rpm and an autorotational speed of 2000 rpm for 2 h to obtain a second component with a solid content of 1.3 wt%.

[0092] S3. LiNi 0.7 Co 0.2 Mn 0.1 The O2 main material and the conductive agent were mixed at a rotation speed of 60 rpm for 0.5 h. The conductive agent consisted of conductive carbon black and multi-walled carbon nanotubes with a mass ratio of 2:1. 0.7 Co 0.2 Mn 0.1 The mass ratio of the O2 main material to the conductive agent is 45:1, and a dry powder mixture is obtained.

[0093] S4. The dry powder mixture obtained in step S3 and the first component obtained in step S1 were stirred at a revolution speed of 100 rpm and a rotation speed of 1000 rpm for 2 h to obtain a half-step slurry, wherein LiNi 0.7 Co 0.2 Mn 0.1 O2 host material and LiMn 0.6 Fe 0.4 The mass ratio of PO4 is 6:4.

[0094] S5. The half-step slurry obtained in step S4 and the second component obtained in step S2 are stirred at an orbital speed of 200 rpm and an autorotation speed of 5000 rpm for 3 h, and the amount of the second component added satisfies that the PVDF in the second component accounts for 1 wt% of the total mass of the solid matter in the positive electrode slurry. N-methylpyrrolidone is then added to the stirred product and stirred at an orbital speed of 200 pm and an autorotation speed of 5000 rpm for 1 h to obtain a positive electrode slurry with a viscosity of 4000 mPa·s. The solid matter in the obtained positive electrode slurry includes polymethyl methacrylate dispersant, LiMn 0.6 Fe 0.4 PO4, polyvinylidene fluoride, LiNi 0.7 Co 0.2 Mn 0.1 O2 host material, conductive carbon black and multi-walled carbon nanotubes.

[0095] Example 4

[0096] The difference between this embodiment and embodiment 1 is that: in the homogenization method provided in this embodiment, step S4 of the ternary main material LiNi 0.8 Co 0.1 Mn 0.1 O2 and LiMn 0.6 Fe 0.4 The mass ratio of PO4 is 5:5. The rest of the contents are the same as those in Example 1.

[0097] Example 5

[0098] The difference between this embodiment and embodiment 1 is that: in the homogenization method provided in this embodiment, the LiNi 0.8 Co 0.1 Mn 0.1 O2 host material and LiMn 0.6 Fe 0.4 The mass ratio of PO4 is 4:6. The rest of the contents are the same as those in Example 1.

[0099] Example 6

[0100] The difference between this embodiment and embodiment 1 is that: in the homogenization method provided in this embodiment, the LiNi 0.8 Co 0.1 Mn 0.1 O2 host material and LiMn 0.6 Fe 0.4 The mass ratio of PO4 is 9.5:0.5. The rest of the contents are the same as those in Example 1.

[0101] Example 7

[0102] The difference between this embodiment and embodiment 1 is that in the homogenization method provided in this embodiment, the amount of polymethyl methacrylate dispersant added is 0.1 wt % of the mass of lithium manganese iron phosphate. The rest of the contents are the same as those in embodiment 1.

[0103] Example 8

[0104] The difference between this embodiment and embodiment 1 is that in the homogenization method provided in this embodiment, the amount of polymethyl methacrylate dispersant added is 6 wt % of the mass of lithium manganese iron phosphate. The rest of the contents are the same as those in embodiment 1.

[0105] Example 9

[0106] The difference between this embodiment and embodiment 1 is that the rotation speed of the homogenization method provided in this embodiment during the preparation of the first component is controlled to 600 rpm, that is, the polymethyl methacrylate dispersant and N-methyl pyrrolidone are mixed at a high speed dispersing machine at a rotation speed of 600 rpm for 30 minutes, and then the polymethyl methacrylate dispersion is mixed with lithium iron manganese phosphate (chemical formula LiMn 0.6 Fe 0.4 PO4) Continue to use the high-speed disperser to mix at a speed of 600 rpm for 30 min. The rest of the contents are the same as in Example 1.

[0107] Example 10

[0108] The difference between this embodiment and embodiment 1 is that the rotation speed of the homogenization method provided in this embodiment during the preparation of the first component is controlled to be 1100 rpm, that is, the polymethyl methacrylate dispersant and N-methyl pyrrolidone are mixed at a high speed dispersing machine at a rotation speed of 1100 rpm for 30 minutes, and then the polymethyl methacrylate dispersion is mixed with lithium iron manganese phosphate (chemical formula LiMn 0.6 Fe 0.4 PO4) Continue to use the high-speed disperser to mix at a speed of 1100 rpm for 30 min. The rest of the contents are the same as in Example 1.

[0109] Embodiment 11

[0110] The difference between this embodiment and embodiment 1 is that in the homogenization method provided in this embodiment, the conductive agent used is only conductive carbon black, and multi-walled carbon nanotubes are omitted. The rest of the contents are the same as those in embodiment 1.

[0111] Example 12

[0112] The difference between this embodiment and embodiment 1 is that in the homogenization method provided in this embodiment, the conductive agent used is only multi-walled carbon nanotubes, and conductive carbon black is omitted. The rest of the contents are the same as those in embodiment 1.

[0113] Example 13

[0114] The difference between this embodiment and embodiment 1 is that in the homogenization method provided in this embodiment, step S3 is to treat the ternary main material LiNi 0.8 Co 0.1 Mn 0.1 O2 and the conductive agent were mixed at a rotation speed of 20 rpm for 1 hour. The rest of the contents were the same as in Example 1.

[0115] Embodiment 14

[0116] The difference between this embodiment and embodiment 1 is that in the homogenization method provided in this embodiment, step S3 is to treat the ternary main material LiNi 0.8 Co 0.1 Mn 0.1 O2 and the conductive agent were mixed at a rotation speed of 70 rpm for 1 hour. The rest of the contents were the same as in Example 1.

[0117] Comparative Example 1

[0118] The difference between this comparative example and Example 1 is that in the homogenization method provided in this comparative example, the addition of the acrylic polymer dispersant in step S1 is omitted, that is, the addition of the polymethyl methacrylate dispersant is omitted. The rest of the contents are the same as in Example 1.

[0119] Comparative Example 2

[0120] The difference between this comparative example and Example 1 is that in the homogenization method provided in this comparative example, the polymethyl methacrylate dispersant is replaced by polyvinyl pyrrolidone. The rest of the contents are the same as those in Example 1.

[0121] Comparative Example 3

[0122] The difference between this comparative example and Example 1 is that in the homogenization method provided in this comparative example, the preparation process of the dry powder mixture in step S3 is omitted, and LiNi 0.8 Co 0.1 Mn 0.1 The O2 main material and the conductive agent are added to the mixing process of the polymethyl methacrylate dispersion and lithium manganese iron phosphate in step S1, that is, LiNi 0.8 Co 0.1 Mn 0.1 The O2 main material, the conductive agent, the polymethyl methacrylate dispersion and the lithium iron manganese phosphate were mixed at a speed of 800 rpm for 30 minutes using a high-speed disperser to obtain a half-step slurry, and the obtained half-step slurry was mixed with the second component composed of polyvinylidene fluoride and N-methylpyrrolidone prepared in step S2. The rest of the contents are the same as in Example 1.

[0123] Comparative Example 4

[0124] The difference between this comparative example and Example 1 is that in the homogenization method provided in this comparative example, all materials are added at once according to the proportion and homogenized at a revolution speed of 150 pm and a rotation speed of 4000 rpm for 3 hours. The rest of the contents are the same as Example 1.

[0125] The positive electrode slurries provided in Examples 1-14 and Comparative Examples 1-4 were sealed and placed at room temperature of 25° C. for 4 hours, and the viscosity increase Δγ (mPa·s) of the positive electrode slurries before and after 4 hours was tested. The test results are shown in Table 1.

[0126] Table 1

[0127]

[0128]

[0129] Application Example 1-14 and Comparative Application Example 1-4

[0130] Application Examples 1-14 and Comparative Application Examples 1-4 provide soft-pack lithium-ion batteries, wherein the positive electrode sheet preparation process is as follows: the positive electrode slurry prepared in Examples 1-14 and Comparative Examples 1-4 is coated on a 15 μm aluminum foil, and then dried and rolled to obtain a positive electrode sheet, wherein the loading amount of the active material in the positive electrode sheet is 400 g / m 2 The preparation process of the negative electrode sheet is as follows: ordinary artificial graphite is used as the negative electrode main material, and the mass ratio of the artificial graphite main material, the conductive carbon black conductive agent, and the sodium carboxymethyl cellulose (CMC) binder is 95:1:4 and mixed in water as a solvent to prepare a negative electrode slurry, and the obtained negative electrode slurry is coated on a 6μm copper foil, and after drying and rolling, a negative electrode sheet is obtained. The loading amount of the active material in the negative electrode sheet is 200g / m 2 ; Electrolyte: commercial lithium ion electrolyte (1 mol / L LiPF6, EC / EMC=3 / 7wt%); The above-mentioned positive electrode sheet, negative electrode sheet and electrolyte are assembled into a soft-pack lithium ion battery.

[0131] The soft-pack lithium-ion batteries obtained from Example 1-14 and Comparative Application Example 1-4 were tested:

[0132] (1) Cycle test: Under the environmental condition of 25°C, the voltage range is set to 2.8-4.2V, and at 1C, the soft-pack lithium-ion batteries of corresponding use cases 1-14 and comparative application examples 1-4 are cycled and the number of cycles at which the capacity retention rate is above 90% is recorded.

[0133] (2) Safety test: A needle puncture test was performed on the lithium-ion batteries of Example 1-14 and Comparative Example 1-4 to test the safety performance of the batteries. The specific test adopted the national standard GB / T31485-2015.

[0134] The test results are shown in Table 2.

[0135] Table 2

[0136] Number of cycles with capacity retention rate above 90% (n) acupuncture Application Example 1 874 pass Application Example 2 798 pass Application Example 3 801 pass Application Example 4 786 pass Application Example 5 472 pass Application Example 6 772 fail Application Example 7 516 fail Application Example 8 482 pass Application Example 9 513 pass Application Example 10 441 pass Application Example 11 571 pass Application Example 12 563 pass Application Example 13 752 pass Application Example 14 743 pass Comparative application example 1 402 fail Comparative Application Example 2 526 fail Comparative Application Example 3 342 fail Comparative Application Example 4 198 fail

[0137] Note that the "pass" in Table 2 means that the assembled soft-pack lithium-ion battery has passed the puncture test of the national standard GB / T31485-2015, that is, during the puncture test, the steel needle stays in the battery for less than 1 hour, and no fire, smoke or explosion occurs; the "fail" means that the assembled soft-pack lithium-ion battery has not passed the puncture test of the national standard GB / T31485-2015, that is, during the puncture test, the steel needle stays in the battery for less than 1 hour, and there is smoke or open flame or even explosion.

[0138] The test results show that:

[0139] (1) It can be seen from Examples 1 to 4 and Application Examples 1 to 4 that the positive electrode slurry homogenization method provided by the present invention suppresses the agglomeration of lithium iron manganese phosphate during the homogenization process by designing a step-by-step mixing process combined with the use of an acrylic polymer dispersant to pre-disperse lithium iron manganese phosphate, thereby improving the dispersibility of the lithium iron manganese phosphate introduced into the ternary main material, thereby effectively improving the stability and safety of the ternary positive electrode material.

[0140] (2) By comparing Example 1, Example 4 and Examples 5-6, and Application Example 1, Application Example 4 and Application Example 5-6, it can be seen that if the mass ratio of the ternary main material to lithium iron manganese phosphate is too low, and the amount of lithium iron manganese phosphate added is too high, the slurry dispersion performance will be reduced and the battery performance will deteriorate; if the mass ratio of the two is too high, and the amount of lithium iron manganese phosphate added is too low, the safety of the battery will deteriorate. In addition, it can be seen from Example 4 that the slurry method provided by the present invention is effective in the case of LiNi8Co1Mn1O2 main material and LiMn 0.6 Fe 0.4 The mass ratio of PO4 is 5:5, and more LiMn is added to the positive electrode slurry. 0.6 Fe 0.4 PO4 still has relatively excellent electrochemical properties.

[0141] (3) By comparing Example 1 with Examples 7-8, and Application Example 1 with Application Examples 7-8, it can be seen that if the amount of acrylic polymer dispersant added is too low, effective dispersion of lithium manganese iron phosphate will not be achieved, and the viscosity of the resulting positive electrode slurry will change significantly after being placed under closed conditions at room temperature for a period of time, and the cycle performance and safety performance when used in the battery will deteriorate; if the amount of acrylic polymer dispersant added is too high, a large amount of acrylic polymer residue will remain during coating, which will affect the battery performance.

[0142] (4) By comparing Example 1 with Examples 9-10, and Application Example 1 with Application Examples 9-10, it can be seen that if the rotation speed in the first component mixing process of the present invention is too low, the dispersion effect of lithium manganese iron phosphate will be poor, and agglomerated lithium manganese iron phosphate will still exist. The viscosity of the obtained positive electrode slurry will change significantly after being placed under normal temperature and closed conditions for a period of time; if the rotation speed is too high, bubbles will be generated, resulting in poor coating effect of the positive electrode slurry, thereby affecting the cycle performance of the assembled battery.

[0143] (5) By comparing Example 1 with Examples 11-12, and Application Example 1 with Application Examples 11-12, it can be seen that if the present invention only uses conductive carbon black as the conductive agent, the cycle performance of the battery will be poor; if only multi-walled carbon nanotubes are used as the conductive agent, the cycle performance of the battery will also deteriorate.

[0144] (6) By comparing Example 1 with Examples 13-14, and Application Example 1 with Application Examples 13-14, it can be seen that if the mixing speed during the solid-phase mixing of the conductive agent and the ternary main material in the present invention is too low, the mixing effect between the conductive agent and the ternary main material will be poor, affecting the electrochemical performance of the battery; if the mixing speed during the solid-phase mixing of the conductive agent and the ternary main material is too high, the structure and quality of the ternary main material will be destroyed, and dust will be raised during the mixing process, and the dry powder material will be wasted, thereby affecting the quality and composition of the main material in the positive electrode slurry.

[0145] (7) It can be seen from the comparison between Example 1 and Comparative Examples 1-2, and between Application Example 1 and Comparative Application Examples 1-2 that the present invention fully achieves the dispersion of small particles of lithium iron manganese phosphate by introducing a specific acrylic polymer dispersant and pre-mixing it with lithium iron manganese phosphate. When the acrylic polymer dispersant is missing or the acrylic polymer dispersant is replaced by conventional polyvinyl pyrrolidone, the dispersion of small particles of lithium iron manganese phosphate will deteriorate. After the obtained positive electrode slurry is left for a period of time, its viscosity changes significantly, and the electrochemical performance and safety performance when used in the battery will deteriorate.

[0146] (8) By comparing Example 1 with Comparative Example 3, and Application Example 1 with Comparative Application Example 3, it can be seen that the step-by-step mixing design process adopted by the present invention can ensure the quality and composition content of the main material while improving the dispersibility of lithium iron manganese phosphate. If the main material and the conductive agent are mixed together with the dispersion liquid and lithium iron manganese phosphate in a high-speed disperser, firstly, in the high-speed disperser, the multi-walled carbon nanotubes are easily broken up, affecting their conductive properties. Secondly, the particle structure of the ternary main material may be destroyed during high-speed dispersion, affecting its circulation and safety performance.

[0147] (9) By comparing Application Example 1 with Comparative Application Example 4, it can be seen that if the present invention adopts a process of adding raw materials at one time and homogenizing, the homogenization effect will be poor, the dispersion of lithium manganese iron phosphate inside will be poor, and the viscosity of the obtained positive electrode slurry will change significantly after being placed for a period of time, thereby causing the electrochemical performance of the obtained lithium ion battery to deteriorate.

[0148] In summary, the homogenization method of the positive electrode slurry of the present invention adopts a step-by-step mixing method, firstly introducing a specific acrylic polymer dispersant and pre-mixing with lithium iron manganese phosphate to achieve sufficient dispersion of small particles of lithium iron manganese phosphate, and then mixing the dry powder mixture composed of the ternary main material and the conductive agent with the components composed of the lithium iron manganese phosphate dispersion and the components composed of the binder dispersion in sequence, which can inhibit the agglomeration of lithium iron manganese phosphate during the homogenization process, improve the dispersibility of the lithium iron manganese phosphate introduced in the ternary positive electrode material, and effectively improve the stability and safety of the ternary positive electrode material.

[0149] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for homogenizing a positive electrode slurry, characterized in that: The homogenization method comprises the following steps: (1) mixing an acrylic polymer dispersant, a first solvent, and lithium manganese iron phosphate to obtain a first component; performing a second mixing of the binder and the second solvent to obtain a second component; (2) solid-phase mixing the ternary main material and the conductive agent to obtain a dry powder mixture, performing a third mixing of the dry powder mixture and the first component to obtain a half-step slurry, and performing a fourth mixing of the half-step slurry and the second component to obtain the positive electrode slurry.

2. The homogenization method according to claim 1, characterized in that The acrylic polymer in the acrylic polymer dispersant of step (1) comprises a polymer and / or a copolymer composed of monomer units, wherein the monomer units comprise any one or a combination of at least two of methacrylic acid, methacrylate, methacrylate, methacrylamide or methacrylonitrile; Preferably, the chemical formula of the lithium manganese iron phosphate in step (1) is LiMn x Fe 1-x PO4, where x is 0.6-0.7; Preferably, the particle size D50 of the lithium manganese iron phosphate in step (1) is 0.5-3 μm, preferably 0.5-2 μm; Preferably, in the first mixing process of step (1), the mass ratio of the acrylic polymer dispersant to the first solvent is (3-4):(6-7); Preferably, in the first mixing process of step (1), the amount of the acrylic polymer dispersant added is 0.4-5wt% of the mass of the lithium manganese iron phosphate; Preferably, the rotation speed of the first mixing in step (1) is 700-1000 rpm; Preferably, the first mixing time in step (1) is 0.5-3h; Preferably, the first mixing in step (1) comprises: firstly mixing the acrylic polymer dispersant with the first solvent to obtain an acrylic polymer dispersion, and then further mixing the acrylic polymer dispersion with the lithium manganese iron phosphate to obtain a first component; Preferably, in step (1), the first solvent comprises N-methylpyrrolidone.

3. The homogenization method according to claim 1 or 2, characterized in that: The binder in step (1) comprises polyvinylidene fluoride; Preferably, the second solvent in step (1) comprises N-methylpyrrolidone; Preferably, the solid content of the second component in step (1) is 1-1.3 wt %; Preferably, the second mixing method in step (1) includes stirring; Preferably, the revolution of the stirring is 60-100 rpm; Preferably, the stirring speed is 1000-2000 rpm; Preferably, the second mixing time is 0.5-2h.

4. The homogenization method according to any one of claims 1 to 3, characterized in that: In step (2), the mass ratio of the ternary main material to the conductive agent is (45-55):1; Preferably, the chemical formula of the ternary host material in step (2) is LiNi a Co b Mn 1-a-b O2, where a is 0.6-0.9 and b is 0.1-0.2; Preferably, the conductive agent in step (2) includes a first conductive agent and a second conductive agent; Preferably, the first conductive agent comprises conductive carbon black; Preferably, the second conductive agent comprises multi-walled carbon nanotubes; Preferably, the mass ratio of the first conductive agent to the second conductive agent is 2:(0.5-1); Preferably, the rotation speed of the solid phase mixing in step (2) is 30-60 rpm; Preferably, the solid phase mixing time in step (2) is 0.5-1 h.

5. The homogenization method according to any one of claims 1 to 4, characterized in that: In the third mixing process of step (2), the mass ratio of the ternary main material in the dry powder mixture to the lithium manganese iron phosphate in the first component is (5-9):(1-5); Preferably, the third mixing method in step (2) includes stirring; Preferably, during the third mixing process, the revolution of the stirring is 60-100 rpm; Preferably, during the third mixing process, the stirring speed is 1000-2000 rpm; Preferably, the third mixing time is 1-2 hours.

6. The homogenization method according to any one of claims 1 to 5, characterized in that: In the fourth mixing process of step (2), the amount of the second component added satisfies that the proportion of the solid matter of the binder in the second component in the positive electrode slurry is 1-2.5wt%, and the solid matter in the positive electrode slurry includes the ternary main material, the lithium manganese iron phosphate, the acrylic polymer dispersant, the binder and the conductive agent; Preferably, the fourth mixing method in step (2) includes stirring; Preferably, during the fourth mixing process, the revolution of the stirring is 100-200 rpm; Preferably, during the fourth mixing process, the stirring speed is 3000-5000 rpm; Preferably, the fourth mixing time in step (2) is 3-4 hours; Preferably, after the fourth mixing in step (2), the third solvent is added to the slurry obtained by the fourth mixing to perform a fifth mixing, and the viscosity of the obtained positive electrode slurry is adjusted to 4000-6000 mPa·s; Preferably, during the fifth mixing process, the revolution of the stirring is 100-200 rpm; Preferably, during the fifth mixing process, the stirring speed is 3000-5000 rpm; Preferably, the fifth mixing time is 1-4h; Preferably, the third solvent comprises N-methylpyrrolidone.

7. A positive electrode slurry, characterized in that: The positive electrode slurry is prepared by the homogenization method according to any one of claims 1 to 6, and the positive electrode slurry comprises a solid substance and a solvent, wherein the solid substance comprises a ternary main material, lithium manganese iron phosphate, an acrylic polymer dispersant, a binder and a conductive agent.

8. The positive electrode slurry according to claim 7, characterized in that: The solvent includes N-methylpyrrolidone; Preferably, the viscosity of the positive electrode slurry is 4000-6000 mPa·s.

9. A positive electrode sheet, characterized in that: The positive electrode sheet is obtained by coating the positive electrode slurry described in claim 7 or 8 on the surface of the positive electrode current collector, followed by drying and rolling.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode sheet according to claim 9.

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