Conductive additive suitable for dry-method electrode preparation and preparation method of conductive additive

Abstract

The invention discloses a conductive additive suitable for dry-method electrode preparation and a preparation method of the conductive additive, and aims to overcome the defect that in the prior art, carbon nano tube rubber master batch cannot be applied to dry-method electrode preparation to solve the problem of expansion of an electrode material in the application process. The conductive additive comprises a conductive carbon material and a lubricating auxiliary agent capable of lubricating and dispersing the conductive carbon material under the action of shearing force, the mass ratio of the conductive carbon material to the lubricating additive is (10-95): 1; the conductive carbon material contains 0-20% of a dispersing agent; the lubricating additive comprises a plasticizer A which is liquid at normal temperature; according to the conductive additive disclosed by the invention, the added lubricating auxiliary agent can lubricate the conductive carbon material under the action of shearing force, so that the conductive carbon material is uniformly dispersed in the processing process, the effective exertion of the conductive performance is ensured, and the problem of expansion of an electrode plate material in the application process can be effectively inhibited.

Description

Technical Field

[0001] The present invention relates to the field of conductive materials, and particularly to a conductive additive suitable for dry electrode preparation and a preparation method thereof. Background Art

[0002] Conductive carbon materials include carbon nanotubes, graphene, conductive carbon black, graphite, carbon fiber, etc. As high-performance conductive materials, conductive carbon materials are widely used in lithium batteries, conductive plastics, conductive coatings, conductive films, etc. However, conductive carbon materials are generally nanomaterials, and there is an attractive force between nanomaterials, which easily leads to conditions such as agglomeration, entanglement, and stacking, resulting in the inability to effectively and uniformly disperse the conductive carbon materials during application and affecting the exertion of their conductive performance.

[0003] To solve the above problems, in the prior art, surface functionalization modification is performed on conductive carbon materials such as carbon nanotubes to improve the interfacial bonding between carbon nanotubes and mixed materials such as polymer polymers, and to achieve the uniform dispersion of carbon nanotubes. Based on this method, the Chinese patent with the publication number CN 104513410 A discloses a variety of methods in the background art, but all have defects. To overcome these defects, this patent proposes "a preparation method of a pre-dispersed carbon nanotube rubber masterbatch". After mixing carbon nanotubes, rubber, wax, dispersion aids, and other rubber aids evenly and granulating, a carbon nanotube masterbatch with regular appearance and convenient for storage / transportation is obtained, which is convenient to use, has good dispersion effect, and also has advantages such as less pollution, low mixing energy consumption, and good mechanical properties, meeting the development needs of the green economy and can be applied to the processing of rubber products, plastic products, etc.

[0004] However, the above technical solutions are limited to applying the obtained conductive masterbatch containing carbon nanotubes to the processing of rubber products and plastic products, and cannot expand the application scope to the dry electrode preparation process. The dry electrode preparation technology is an electrode manufacturing method that does not require a solvent and directly presses the electrode material powder onto a metal current collector to form an electrode. During the dry electrode preparation process, it is necessary to solve not only the dispersion problem of conductive carbon materials under the action of shear force and the firmness problem of the combination of conductive carbon materials and the main material, but also the problem of electrode material expansion during application. Summary of the Invention

[0005] Although the conductive masterbatch containing carbon nanotubes in the prior art can solve the dispersion problem of conductive carbon materials (carbon nanotubes) and improve the firmness of the combination of conductive carbon materials and the main material, it cannot solve the problem of electrode material expansion during application and is not suitable for the preparation of dry electrodes. The present invention overcomes the above defects and provides a conductive additive suitable for dry electrode preparation and a preparation method thereof.

[0006] The technical solution adopted by the present invention to achieve the first invention objective is as follows: A conductive additive suitable for dry electrode preparation, comprising: a conductive carbon material and a lubricating aid capable of lubricating and dispersing the conductive carbon material under the action of shear force; the mass ratio of the conductive carbon material to the lubricating aid is (10 - 95):1; the conductive carbon material is a conductive carbon material containing 0 - 20% of a dispersant. The lubricating aid includes: a plasticizer that is liquid at room temperature.

[0007] In the conductive additive of the present invention, the added lubricating aid can lubricate the conductive carbon material under the action of shear force, making the conductive carbon material evenly dispersed during the processing, and ensuring the effective exertion of the conductive performance. The conductive carbon material applied can be one or several of: carbon nanotubes, graphene, conductive carbon black, graphite, carbon fiber. In the conductive carbon material, a dispersant can be added or not added; when a dispersant is added to the conductive carbon material, the content of the dispersant is at most 20%, generally 10% - 17%. The dispersant for dispersing the conductive carbon material generally selects polyvinylpyrrolidone (PVP). The addition of the dispersant improves the dispersion degree of the conductive carbon material and does not affect its conductive performance, which is conducive to the application of the dry electrode preparation process.

[0008] The lubricating aid of the present invention includes: a plasticizer A that is liquid at room temperature. The conductive carbon material is generally a nanomaterial with a large specific surface area, which can adsorb the liquid plasticizer A at room temperature, forming a liquid film of the plasticizer A on the surface of the conductive carbon material. In this way, during the high-speed dispersion process of dry electrode preparation, the liquid film exists between the conductive carbon material and the polymer for dry electrodes. Under the condition of high shear force, it plays a lubricating role, and after the dispersion process ends, this liquid film is adsorbed on the surface of the main electrode material particles through capillary action, binding more tightly, effectively inhibiting the swelling problem that occurs when the electrode material is applied; and it will not fall off under subsequent processing, such as under high shear force and high centrifugal force again.

[0009] Preferably, the applied plasticizer A includes: one or several of PEG400, phthalic acid esters (such as: DBP, DOP, DIDP), aliphatic dibasic acid esters (such as: dioctyl adipate DOA, dioctyl sebacate DOS), phosphate esters (such as: tricresyl phosphate TCP, chlorodiphenyl phosphate CDP), epoxy compounds (such as: epoxidized soybean oil, butyl epoxy oleate), polymeric plasticizers (such as: propylene glycol adipate polyester), benzene polycarboxylic acid esters (such as: triisooctyl 1,2,4 - trimellitate), chlorine-containing plasticizers (such as: chlorinated paraffin, methyl pentachlorostearate), alkyl sulfonic acid esters, polyol esters.

[0010] Preferably, the lubricating aid of the present invention further comprises: a polymer B that is easy to chain slip and / or a plasticizer A' with a melting point ≤ 60°C; when the polymer B that is easy to chain slip and / or the plasticizer A' with a melting point ≤ 60°C is added, by weight, the parts of each component in the lubricating aid are: 2-10 parts of plasticizer A that is liquid at room temperature, 5-10 parts of polymer that is easy to chain slip, and / or 2-5 parts of plasticizer A' with a melting point ≤ 60°C.

[0011] The polymer B that is easy to chain slip is easily mixed with the conductive carbon material, and further increases the dispersion degree of the conductive carbon material under the action of shear force, making it easy to process; moreover, by combining plasticizer A with polymer B, plasticizer A can reduce the force between polymer molecular chains, lower the melting point and glass transition temperature of the polymer. During the high-speed dispersion process of the dry electrode process, the temperature is usually > 50°C, and the viscoelasticity of the polymer is improved due to the action of plasticizer A, making it easier to adhere to the surface of the main material, further ensuring the bonding degree between the conductive additive and the electrode main material.

[0012] The plasticizer A' with a melting point ≤ 60°C, as a low-melting-point plasticizer, can also increase the dispersion degree of the conductive carbon material under the action of shear force. Plasticizer A and plasticizer A' can form a mixture. In the presence of plasticizer A, A' can better adsorb to the conductive carbon material, such as carbon nanotubes; and plasticizer A' can adjust the viscosity of plasticizer A, increase the viscosity of plasticizer A, and further improve the adsorption ability between the lubricating aid in the conductive additive and the conductive carbon material.

[0013] In addition, if the polymer B that is easy to chain slip and plasticizer A' are combined and applied, plasticizer A' and polymer B are easily blended, and plasticizer A' is dispersed in the molecular chains of polymer B, which can further lower the melting point of polymer B.

[0014] Preferably, the polymer B that is easy to chain slip used is: PP wax and / or PE wax. PP wax and PE wax have low melting points, can become molten states at high-speed dispersion temperatures; and their surface energy is low, molecular chains are easy to slip, and they are easily mixed with non-polar conductive carbon materials; their electrical properties are stable, and their application to electrodes has little impact on battery performance.

[0015] Preferably, the plasticizer A' is a hydrocarbon mixture plasticizer, such as: paraffin wax. The hydrocarbon mixture plasticizer is easily blended with polymer B and dispersed in the polymer chains, further lowering the melting point of polymer B; and it also has the advantages of stable electrical properties and little impact on battery performance when applied to electrodes.

[0016] In order to further improve the application performance of the conductive additive of the present invention, preferably, the lubricating aid further comprises: 1-2 parts of perfluoroalkylated compound and / or 1-2 parts of curing agent. Adding perfluoroalkylated compound can reduce the surface energy at the interface between the conductive carbon material and the polymer, improve the interfacial slip between the conductive carbon material and the polymer material, and reduce the friction coefficient; moreover, it can prevent the aggregation of conductive carbon materials; in addition, the perfluoroalkylated compound partially covers the surface of the conductive carbon material without affecting its conductivity. The curing agent is used to react with the hydroxyl groups on the surface of the positive electrode active main material to improve the binding ability between the conductive additive and the positive electrode active main material.

[0017] Preferably, the perfluoroalkylated compound is one or more of: perfluorooctane, perfluorooctanoic acid, perfluorooctanesulfonic acid. Preferably, the curing agent is one or more of: isocyanate, organotitanium, organozirconium, polycarbodiimide, which can undergo a curing reaction with hydroxyl groups at 50-1220 °C.

[0018] Among the components of the lubricating aid of the present invention, plasticizer A is adsorbed by the conductive carbon material to form a liquid film, which is beneficial to the dispersion and adsorption of carbon nanotubes, and is also a good solvent for perfluoroalkylated compound, plasticizer A', curing agent, and polymer B, which is beneficial to the combination of each component in the lubricant with the conductive carbon material.

[0019] The technical solution adopted by the present invention to achieve the second invention objective is: a preparation method of the conductive additive applicable to dry electrode preparation described in the above technical solution, comprising the following steps:

[0020] S1. Pretreat the conductive carbon material described in the above technical solution to improve the dispersion degree of the conductive carbon material, and obtain a conductive carbon material powder with improved dispersion degree;

[0021] S2. Add the conductive carbon material powder obtained in step S1 to a mixer or a twin-screw extruder, and mix it with the components of the lubricating aid described in the above technical solution in proportion to obtain a conductive additive applicable to dry electrode preparation.

[0022] Preferably, in step S1, the method for pretreating the conductive carbon material is: mixing the conductive carbon material and a dispersant in a solvent, dispersing them by sand grinding or a homogenizer, and then drying to obtain a conductive carbon material powder with improved dispersion degree. The dispersant is generally selected as polyvinylpyrrolidone (PVP), and the solvent is water or alcohol.

[0023] The beneficial effects of the present invention are as follows: (1) In the conductive additive of the present invention, a lubricating auxiliary agent is added between the conductive carbon materials, and the conductive carbon materials are prone to slip. Under the shearing force of the dry process, the conductive carbon materials depolymerize by slipping and adsorb on the surface of the active material. Moreover, it can be seen from the SEM diagram of the prepared electrode that the conductive additive can uniformly cover the surface of the active material, which not only facilitates the exertion of the conductive performance but also can further inhibit the swelling problem that occurs when the electrode material is applied.

[0024] (2) The conductive additive of the present invention can solve the problems that the dispersant for the dry process, the nano-carbon material and the main electrode material are not firmly combined, and cannot inhibit the swelling of the electrode material, as well as the problem that the secondary particles of the conductive carbon material are agglomerated and dispersed in the electrode.

[0025] The following further illustrates and verifies the technical solution of the present invention through the drawings and specific embodiments. Description of the Drawings

[0026] Att Figure 1 It is the SEM diagram of conductive additive 1.

[0027] Att Figure 2 It is the SEM diagram of conductive additive 3.

[0028] Att Figure 3 It is the SEM diagram of the positive electrode prepared by applying the dry electrode process with conductive additive 1 added.

[0029] Att Figure 4 It is the SEM diagram of the positive electrode prepared by applying the dry electrode process with conductive additive 2 added.

[0030] Att Figure 5 It is the SEM diagram of the positive electrode prepared by applying the dry electrode process with conductive additive 4 added. Specific Embodiments

[0031] The following further illustrates and verifies the technical solution of the present invention through Examples 1-3 and Comparative Examples 1 and 2.

[0032] Before applying the conductive carbon material, it is generally pre-dispersed first. The following are the pre-dispersion methods when the conductive carbon material is selected as carbon nanotube (CNT) or graphene:

[0033] 1. Pre-disperse carbon nanotubes: Mix carbon nanotubes: PVP: water in a ratio of 50:10:940 using a homogenizing emulsifying pump at a rotational speed of 20,000 RPM. For example, the amounts of carbon nanotubes, PVP, and water can be 50 g, 10 g, and 940 g respectively to obtain a pre-dispersed solution of carbon nanotubes. Then, use a high-pressure homogenizer to mix the pre-dispersed solution evenly at 100 MPa to obtain a carbon nanotube slurry. After that, place the carbon nanotube slurry in an oven and dry it at 80 °C for 24 hours. Then, mechanically crush the obtained solid to obtain carbon nanotube powder with improved dispersion, where the mass fraction of CNT is 83.3%.

[0034] 2. Pre-disperse graphene: Mix graphene: PVP: alcohol in a ratio of 25:5:470 using a homogenizing emulsifying pump at a rotational speed of 20,000 RPM. For example, the amounts of graphene, PVP, and alcohol can be 25 g, 5 g, and 470 g respectively to obtain a pre-dispersed solution of graphene. Then, use a high-pressure homogenizer to mix the pre-dispersed solution evenly at 100 MPa to obtain a graphene slurry. After that, place the graphene slurry in an oven and dry it at 50 °C for 24 hours. Then, mechanically crush the obtained solid to obtain graphene powder with improved dispersion, where the mass fraction of graphene is 83.3%.

[0035] Apply the composite carbon nanotube powder or composite graphene powder with improved dispersion obtained by the above pre-dispersion method to the following examples, and prepare a conductive additive according to the formula and steps of the present invention.

[0036] Example 1

[0037] After preheating the internal mixer to 70 °C, first add 8 g of PE polyethylene wax, 2 g of paraffin wax, 2 g of dimethyl phthalate, 1 g of perfluorooctanoic acid, and 1 g of blocked isocyanate curing agent to the internal mixer. After mixing evenly, add 60 g of composite carbon nanotube powder, mix evenly, and then cool to obtain Conductive Additive 1 (as shown in the attachment Figure 1 ), where the carbon nanotubes are 67.6 wt%.

[0038] Example 2

[0039] After preheating the internal mixer to 70 °C, first add 18 g of PE polyethylene wax, 5 g of paraffin wax, 5 g of polyethylene glycol 400, 2 g of perfluorooctane, and 2 g of organic zirconium cross-linking agent (curing temperature is 90 °C) to the internal mixer. After mixing evenly, add 60 g of composite carbon nanotube powder, mix evenly, and then cool to obtain Conductive Additive 2, where the content of carbon nanotubes is 54.3 wt%.

[0040] Example 3

[0041] After the twin-screw extruder is preheated to 80 °C, 5 g of PP polypropylene wax, 5 g of polyethylene wax, 3 g of paraffin wax, 10 g of tricresyl phosphate, 1 g of perfluorooctanesulfonic acid, 1 g of polycarbodiimide, and 60 g of composite graphene powder are first added to the internal mixer. After mixing evenly, it is cooled to obtain Conductive Additive 3 (as shown in Figure 2 ), where graphene is 58.8 wt%.

[0042] Comparative Example 1

[0043] Take: the amounts of carbon nanotubes, PVP, and water are 50 g, 10 g, and 940 g respectively. According to the above pre-dispersion method, 60 g of carbon nanotube powder with improved dispersion is obtained as Conductive Additive 4.

[0044] Comparative Example 2

[0045] For example, the amounts of graphene, PVP, and alcohol can be taken as 25 g, 5 g, and 470 g respectively. According to the above pre-dispersion method, 30 g of graphene powder with improved dispersion is obtained as Conductive Additive 5.

[0046] Using the above five conductive additive samples, dry dispersion processes are respectively used to prepare electrode sheets. The mass of the effective conductive carbon material applied is 5 g, and the addition amounts of the respective conductive additives are converted based on the mass of the conductive carbon material.

[0047] Characterize the morphologies of the electrode sheets prepared with Conductive Additive 1, Conductive Additive 2, and Conductive Additive 4 (as shown in Figure 3 , 4 , and 5). After comparative analysis, it can be seen that: when using the conductive additives of the present invention, compared with directly using the conductive carbon material containing a dispersant, the conductive additives of the present invention can make the conductive carbon material uniformly cover the active material of the electrode sheet. Due to the uniform coating of the conductive additive, the expansion during the application of the electrode sheet material can also be inhibited, thereby improving the performance of the lithium battery.

[0048] Test the resistivity of the electrode sheets obtained by the above conductive additives through the dry electrode preparation process. The test results are shown in Table 1:

[0049] Table 1 Resistivity of the electrode sheets prepared with five conductive additives

[0050]

[0051]

[0052] Analyzing Table 1, it can be seen that: when preparing electrode sheets by the dry electrode method, at the same content of the conductive carbon material, the resistivity of the electrode sheets obtained by using the conductive additives of the present invention is lower, indicating that the conductive additives of the present invention can enable the conductive carbon material to fully and effectively exert its conductivity.

Claims

1. A conductive additive suitable for dry electrode preparation, characterized in that: The conductive additive comprises: a conductive carbon material and a lubricating agent capable of lubricating and dispersing the conductive carbon material under shear force; the mass ratio of the conductive carbon material to the lubricating agent is (10-95):1; The conductive carbon material is a conductive carbon material containing 0-20% dispersant; The lubricating auxiliary agent includes: a plasticizer A which is liquid at room temperature.

2. A conductive additive suitable for dry electrode preparation according to claim 1, characterized in that: The lubricating aid further comprises: a polymer B that facilitates chain slippage and / or a plasticizer A′ with a melting point ≤ 60°C; The components of the lubricating auxiliary agent include, by weight: 2-10 parts of a plasticizer A which is liquid at room temperature, 5-10 parts of a polymer B which is easy for chain slippage, and / or 2-5 parts of a plasticizer A' with a melting point ≤ 60°C.

3. The conductive additive suitable for dry electrode preparation according to claim 1, characterized in that: The plasticizer A is one or more of PEG400, phthalate, aliphatic dibasic acid ester, phosphate, epoxy compound, polymeric plasticizer, benzene polyester, chlorine-containing plasticizer, alkyl sulfonate, and polyol ester.

4. A conductive additive suitable for dry electrode preparation according to claim 2, characterized in that: The polymer B that is easy to chain slip is: PP wax and / or PE wax.

5. The conductive additive suitable for dry electrode preparation according to claim 2, characterized in that: The plasticizer A' is a hydrocarbon mixture plasticizer.

6. A conductive additive suitable for dry electrode preparation according to claim 2, characterized in that: The lubricating agent further comprises: 1-2 parts of perfluoroalkyl compound and / or 1-2 parts of curing agent.

7. A conductive additive suitable for dry electrode preparation according to claim 6, characterized in that: The perfluoroalkyl compound is one or more of perfluorooctane, perfluorooctane carboxylic acid and perfluorooctane sulfonic acid; the curing agent is one or more of isocyanate, organic titanium, organic zirconium and polycarbodiimide.

8. The conductive additive suitable for dry electrode preparation according to claim 1, characterized in that: The conductive carbon material is one or more of carbon nanotubes, graphene, conductive carbon black, graphite, and carbon fiber; the dispersant contained in the conductive carbon material is PVP.

9. A method for preparing a conductive additive suitable for dry electrode preparation according to any one of claims 1 to 8, characterized in that: The preparation method comprises the following steps: S1. Pretreating the conductive carbon material according to any one of claims 1 to 8 to improve the dispersion of the conductive carbon material to obtain a conductive carbon material powder with improved dispersion; S2. Add the conductive carbon material powder obtained in step S1 into an internal mixer or a twin-screw extruder, and mix it with the components of the lubricating agent described in any one of claims 1 to 8 in proportion to obtain a conductive additive suitable for dry electrode preparation.

10. The method for preparing a conductive additive suitable for dry electrode preparation according to claim 9, characterized in that: In the step S1, the method for pretreating the conductive carbon material is: mixing the conductive carbon material and the dispersant in a solvent, dispersing by sand milling or homogenizer, and drying to obtain a conductive carbon material powder with improved dispersion.

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