Current collector-free electrode with carbon nanotube flexible skeleton and preparation method thereof

Abstract

The invention discloses a current collector-free electrode with a carbon nanotube flexible framework and a preparation method of the current collector-free electrode, and belongs to the technical field of lithium batteries, the current collector-free electrode is prepared by taking a carbon nanotube dispersion liquid, an electrode active material and a binder as raw materials through a wet method, and the preparation method comprises the following steps: firstly, weighing the active material; the preparation method comprises the following steps: putting the raw materials into deionized water, carrying out ultrasonic dispersion, adding a carbon nanotube dispersion liquid, carrying out ultrasonic dispersion, fully mixing in a mixer, adding a binder, continuously fully mixing, finally removing a redundant solvent, and drying, thereby obtaining the carbon nanotube composite material. The pole piece does not need a current collector as a carrier, can be directly used as a positive pole piece and a negative pole piece, is simple to use, can reduce the weight of the battery, greatly improves the energy density of the battery, adopts a one-step forming method to prepare a current collector-free electrode, is simpler and more efficient, and is suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and particularly to a current collector-free electrode with a carbon nanotube flexible skeleton and a preparation method thereof. Background Art

[0002] As the current mainstream energy storage technology, lithium-ion batteries are widely used in fields such as consumer electronics, electric vehicles, and energy storage systems. Conventional lithium-ion battery electrodes generally require the use of current collectors for current collection, supporting active materials, and enhancing the mechanical properties of the electrodes. However, such battery electrodes using current collectors are structurally unstable during mechanical deformation and charge / discharge processes, and active materials, conductive agents, binders, etc. are likely to fall off from the current collector, and even cause the electrode sheet to break, seriously affecting the service life of lithium-ion batteries.

[0003] To address the above problems, generally two methods are mainly adopted at present. One is to use a new type of binder with better bonding ability, and the other is to develop new carbon-based current collectors (including carbon fabrics, carbon nanotube papers, graphene sheets, etc.) to replace metal current collectors. However, these methods often require complex and expensive manufacturing processes and costs, and cannot be used for large-scale actual production. In addition, generally, polymer fabrics with metal deposition or pretreatment are also used to replace traditional current collectors, and progress has been made in mechanical flexibility. However, the problem of active materials falling off from the current collector has not been effectively solved, and ultimately the battery capacity remains at a low level.

[0004] Therefore, the field has begun to explore battery designs without current collectors or with reduced current collector usage to further improve the energy density and performance of batteries. For example, Chinese Patent Application CN116470009A discloses a dry preparation method for a current collector-free electrode. The preparation method is to first prepare an electrode composite powder and then press it into shape. The mechanism is that the prepared electrode composite powder is pressed into shape by dry pressing, so that the powder particles approach each other in the mold and are firmly combined by internal friction to form a green body with a certain shape. Using this method to prepare a current collector-free electrode, the manufacturing process is relatively complex, and it is necessary to precisely control steps such as powder mixing, pressing, and heat treatment, increasing the difficulty and cost of production; in addition, the electrode sheet prepared by this method is relatively thick (200 - 3000 μm), and an overly thick electrode may cause an increase in internal resistance and affect the charge and discharge performance of the battery. Summary of the Invention

[0005] One of the objectives of the present invention is to provide a current collector-free electrode with a carbon nanotube flexible skeleton to solve the above problems.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows: A current collector-free electrode with a carbon nanotube flexible skeleton is prepared by a wet method using a carbon nanotube dispersion, an electrode active material, and a binder as raw materials.

[0007] As a preferred technical solution, the content of carbon nanotubes in the carbon nanotube dispersion accounts for 2-30% of the mass of all raw materials; the concentration range of the carbon nanotube dispersion is: 0.1-5 wt.%.

[0008] As a preferred technical solution, the diameter of the carbon nanotubes in the carbon nanotube dispersion is 0.5-20 nm, and the length is 5-100 μm. Generally speaking, the longer the length of the carbon nanotubes and the thinner the diameter, the better the performance. In this patent, the carbon nanotubes not only serve as a conductive agent but also as a self-supporting skeleton for the active material, so this range is selected. Carbon nanotubes with too high a length-to-diameter ratio are prone to agglomeration, which is not conducive to the good dispersion of the active material; carbon nanotubes with too low a length-to-diameter ratio are not conducive to the formation of a three-dimensional flexible skeleton.

[0009] As a preferred technical solution, the binder is selected from at least one of polyvinylidene fluoride, polyacrylic acid, carboxymethyl cellulose, styrene-butadiene rubber, polytetrafluoroethylene, polyvinyl alcohol, fluororubber, or polyurethane.

[0010] As a preferred technical solution, the active material includes a positive electrode active material and a negative electrode active material; the positive electrode active material is selected from at least one of lithium cobaltate, lithium manganate, lithium titanate, lithium vanadate, LiMn x Ni y Co z O 2 (x + y + z = 1), LiNi x Co y Al z O 2 (x + y + z = 1); the negative electrode active material is selected from at least one of silicon, silicon carbide, SiO x , graphite, graphene, carbon nanotubes, MCMB, or carbon fiber.

[0011] The second object of the present invention is to provide a preparation method of the above-mentioned current collector-free electrode with a carbon nanotube flexible skeleton. The technical solution adopted is as follows: The method includes the following steps:

[0012] (1) After weighing the active material, it is placed in deionized water with a concentration of 5-50 g / L and ultrasonically dispersed for 5-60 min;

[0013] (2) Add the carbon nanotube dispersion to the material obtained in step (1), ultrasonically disperse for 5-60 min, and then place it in a mixer and compound at a high speed of 500-1000 rpm for 2-24 h to fully mix;

[0014] (3) Add a binder to the material obtained in step (2) and continue to compound it at a low speed of 50 - 500 rpm for 2 - 24 h to make it fully mixed;

[0015] (4) After the mixing is completed, use a solvent removal device to remove the excess solvent (the solvent includes deionized water and the dispersant in the carbon nanotube dispersion). After the material is dried at 60 - 150 °C for 6 - 24 h, it is obtained.

[0016] Compared with the dry preparation of the prior art, the present application adopts wet preparation, and the electrode plate is formed in one step, which is simpler and more efficient and is suitable for industrial production; the mechanism of the present invention is: the electrode active material, carbon nanotubes, and binder are dispersed in a solvent to form a uniform solution, and the obtained electrode plate after removing the solvent has flexibility due to the interconnected network structure of the carbon nanotubes.

[0017] As a preferred technical solution, the mixer is selected from any one of a V-type mixer, a planetary power mixer, a double-shaft blade mixer, a ball mill mixer, a countercurrent mixer, and a high-low speed mixer.

[0018] As a preferred technical solution, the solvent removal device is selected from any one of a rotary evaporator, a nitrogen blowing dryer, a vacuum filter, a thin film evaporator, a hot plate evaporator, a pneumatic dryer, and a microwave dryer.

[0019] On the one hand, the present invention uses a carbon nanotube dispersion instead of other conductive agents (such as conductive carbon black Super P, acetylene black, Ketjen black, etc.) for the preparation of battery electrode plates, and optimizes the preparation process, which can form an interconnected network structure with the active material and the binder, and can form a good flexible electrode plate without the support of a current collector, which can greatly improve the energy density of the battery;

[0020] The amount of the carbon nanotube dispersion added determines whether a flexible electrode plate can be formed and the hardness of the electrode plate. If the amount of the carbon nanotube dispersion is too small, the carbon nanotubes are not enough to form an interconnected 3D network structure to bind the active material; if the amount of the carbon nanotube dispersion is too large, the battery capacity will be reduced; therefore, the addition of an appropriate amount of the carbon nanotube dispersion is crucial;

[0021] The carbon nanotubes have a tubular bundle structure and are easy to form a branched conductive network on the surface of the active material, improving the Li ＋ insertion / extraction ability during charge and discharge, and having more surface defects than conductive carbon black SP, increasing the lithium storage sites; conductive carbon black Super P has a point-contact conductive network, which is difficult to completely cover the active material and will also cause Li ＋ diffusion difficulties, as Figure 1 shown, Figure 1In the left figure, the conductive carbon black Super P is a rigid nanoparticle, which has point-to-point contact with the active material. In the right figure, the carbon nanotube is a flexible long chain, which has line-to-point contact with the active material.

[0022] Compared with the prior art, the advantages of the present invention are as follows:

[0023] (1) For the electrode sheet of the present invention, there is no need for a current collector as a carrier, and it can be directly used as the positive and negative electrode sheets. It is not only simple to use, but also can reduce the weight of the battery and greatly improve the energy density of the battery;

[0024] (2) The electrode sheet of the present invention forms a three-dimensional conductive network under the connection of the flexible long chains of carbon nanotubes, with excellent flexibility and elasticity, and the mechanical strength is significantly improved;

[0025] (3) The electrode sheet provided by the present invention uses the three-dimensional conductive network composed of carbon nanotubes as a flexible support, which can not only serve as a good ion and electron transmission channel for active particles, but also be closely distributed around the active material to buffer the volume change during charge and discharge, maintain the overall stability of the electrode sheet, and improve the service life of the battery;

[0026] (4) The preparation method of the present invention does not use volatile solvents, reduces pollution, and is green and environmentally friendly;

[0027] (5) The present invention adopts a one-step forming method to prepare a current collector-free electrode, which is more simple and efficient and is suitable for industrial production. Description of the Drawings

[0028] Figure 1 It is a principle comparison between the present invention and the prior art;

[0029] Figure 2 It is a photo of the flexible electrode prepared in Example 1 of the present invention. Detailed Embodiments

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

[0031] In the following embodiments and comparative examples, the concentration of the carbon nanotube dispersion used is 0.4 wt.%, and its preparation method is as follows: First, 0.01 g of polyvinyl alcohol (PVA) is dissolved in 33 mL of dimethyl sulfoxide (DMSO) at room temperature, and ultrasonically dispersed for 30 min. Then, 0.15 g of carbon nanotubes and 4.49 g of deionized water are added, and after ultrasonically dispersing for 30 min, the mixture is mixed by a mixer for 8 h to obtain a uniformly dispersed slurry.

[0032] The concentration of the Super P dispersion used was 0.4 wt.%, and its preparation method was as follows: First, 0.01 g of polyvinyl alcohol (PVA) was dissolved in 33 mL of dimethyl sulfoxide (DMSO) at room temperature and ultrasonically dispersed for 30 min. Then, 0.15 g of Super P and 4.49 g of deionized water were added, and after ultrasonically dispersing for 30 min, the mixture was mixed with a mixer for 8 h to obtain a uniformly dispersed slurry.

[0033] Example 1:

[0034] Weigh 2 g of silicon-carbon negative electrode (theoretical specific capacity is 650 mAh / g), add 20 mL of deionized water, ultrasonically disperse for 30 min, then add 107.0 g of carbon nanotube dispersion, ultrasonically disperse for 30 min, then stir at a speed of 800 rpm for 12 h, then add 7.13 g of polyacrylic acid solution, and then stir at a speed of 300 rpm for 8 h; after stirring, remove the excess solvent with a vacuum filter and dry at 80 °C for 8 h to obtain a current collector-free electrode with a carbon nanotube flexible skeleton. (In this example, the content of carbon nanotubes in the carbon nanotube dispersion accounts for 15% of the mass of all raw materials).

[0035] Example 2:

[0036] Weigh 2 g of silicon-carbon negative electrode (theoretical specific capacity is 650 mAh / g), add 20 mL of deionized water, ultrasonically disperse for 30 min, then add 10.4 g of carbon nanotube dispersion, ultrasonically disperse for 30 min, then stir at a speed of 800 rpm for 12 h, then add 0.69 g of polyacrylic acid solution, and then stir at a speed of 300 rpm for 8 h. After stirring, remove the excess solvent with a vacuum filter and dry at 80 °C for 8 h to obtain a current collector-free electrode with a carbon nanotube flexible skeleton. (In this example, the content of carbon nanotubes in the carbon nanotube dispersion accounts for 2% of the mass of all raw materials).

[0037] Example 3:

[0038] Weigh 2 g of silicon-carbon negative electrode (theoretical specific capacity is 650 mAh / g), add 20 mL of deionized water, ultrasonically disperse for 30 min, then add 299.4 g of carbon nanotube dispersion, ultrasonically disperse for 30 min, then stir at a speed of 800 rpm for 12 h, then add 13.3 g of polyacrylic acid solution, and then stir at a speed of 300 rpm for 8 h. After stirring, remove the excess solvent with a vacuum filter and dry at 80 °C for 8 h to obtain a current collector-free electrode with a carbon nanotube flexible skeleton. (In this example, the content of carbon nanotubes in the carbon nanotube dispersion accounts for 30% of the mass of all raw materials).

[0039] Comparative Example 1:

[0040] Compared with Example 1, in this comparative example, only the "107.0 g of carbon nanotube dispersion" in Example 1 was replaced with "107.0 g of Super P conductive carbon black dispersion", and the solid content of the Super P conductive carbon black dispersion was still 0.4 wt.%. The remaining materials, conditions, and parameters were the same as those in Example 1.

[0041] Comparative Example 2:

[0042] This comparative example refers to the dry preparation method of CN116470009A, and the specific steps are as follows:

[0043] Take 2 g of silicon-carbon negative electrode and 7.13 g of polyacrylic acid, put them into a mixer, and process them at a speed of 600 rpm for 10 h to disperse the binder on the surface of the electrode active material, obtaining a composite material of the electrode active material and the binder; add 107.0 g of carbon nanotube dispersion to the composite material of the electrode active material and the binder, process it at a speed of 600 rpm for 10 h, then remove the excess solvent with a vacuum filter, and dry it at 80 °C for 8 h to obtain a composite material of the electrode active material, the binder, and the conductive agent; pass the prepared composite material of the electrode active material, the binder, and the conductive agent through a 150-mesh sieve to obtain a composite powder of the electrode active material, the binder, and the conductive agent with the same morphological structure; take 2 g of the prepared composite powder of the electrode active material, the binder, and the conductive agent with the same morphological structure, put it into a mold, press it into shape under a pressure of 150 MPa, and then put it into an oven at 80 °C for heat treatment for 10 h to obtain a current collector-free electrode.

[0044] Comparative Example 3

[0045] Weigh 2 g of silicon-carbon negative electrode, add 20 mL of deionized water, ultrasonically disperse for 30 min, then add 107.0 g of carbon nanotube dispersion, ultrasonically disperse for 30 min, then stir at a speed of 800 rpm for 12 h, then add 7.13 g of polyacrylic acid, and stir at a speed of 300 rpm for 8 h; after the stirring is completed, coat the slurry on the copper current collector, with the same thickness as the current collector-free electrode with a carbon nanotube flexible skeleton in Example 1, and dry it at 80 °C for 8 h to remove the excess solvent.

[0046] The current collector-free electrodes prepared in Examples 1-3 and Comparative Examples 1-2 and the current collector electrodes prepared in Comparative Example 3 were respectively cut into circular electrodes with a diameter of 12 mm (taking the product prepared in Example 1 as an example, the weight of a circular electrode with a diameter of 12 mm was only 1.45 mg (Xingyun electronic analytical balance, 0.01~220 g), and the electrode thickness was only 23 μm (Shangshen electronic micrometer, 0~25 mm)), and button batteries were assembled with lithium sheets as the counter electrodes;

[0047] After the assembled batteries were left standing for 8 h, a multi-channel battery test system (Neware battery test station) was used to test all the batteries in the voltage range of 0.01 - 3 V (vs. Li / Li + ). The test results are shown in Table 1.

[0048] Table 1 Battery performance of different examples and comparative examples

[0049] Initial charge capacity (mAh / g) Initial Coulombic efficiency (%) Capacity retention rate after 100 cycles (%) Example 1 639 88.3 85.9 Example 2 613 81.2 83.9 Example 3 606 85.4 84.5 Comparative Example 1 258 45.3 20.1 Comparative Example 2 622 83.5 73.9 Comparative Example 3 600 76.9 83.7

[0050] In terms of physical properties, the electrode sheet prepared in Example 1 (as Figure 2 shown) has good flexibility and can be used independently as a battery electrode sheet without a current collector;

[0051] However, for the electrode material prepared in Comparative Example 1, due to the absence of the three-dimensional network structure of carbon nanotubes, the electrode structure cannot be maintained stable during the charge / discharge process of the battery. After several cycles, the electrode structure collapses quickly, resulting in a rapid decay of the battery capacity.

[0052] For the electrode material prepared in Comparative Example 2, the electrode composite powder was first prepared, and then the electrode sheet without a current collector was formed by dry pressing. The formed electrode is combined by the friction between powder particles, lacking the continuity of the network structure connected by carbon nanotubes, and its electrochemical performance is also inferior to that of Example 1.

[0053] For the electrode material prepared in Comparative Example 3, the test was carried out with a current collector. Since the presence of the current collector will increase the interfacial impedance and contact impedance, which greatly affects the battery performance, its electrochemical performance is instead inferior to that of Example 1. That is, the electrode of the present invention is more suitable for applications without a current collector, thus saving more in terms of cost, etc., and the weight of the whole battery is also lighter, and the overall energy density of the manufactured battery is higher.

[0054] The test results show that the flexible electrode sheet prepared by the carbon nanotube dispersion liquid of the present invention can be directly used as a battery electrode sheet without a current collector carrier, which not only reduces the steps of preparing the battery electrode sheet, but also, without a current collector, the battery weight will be reduced and the overall energy density of the battery will be increased.

[0055] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A current collector-free electrode having a carbon nanotube flexible skeleton, characterized in that: The invention is prepared by a wet method using carbon nanotube dispersion, electrode active material and binder as raw materials.

2. The current collector-free electrode with a carbon nanotube flexible skeleton according to claim 1, characterized in that: The content of carbon nanotubes in the carbon nanotube dispersion accounts for 2-30% of the mass of all raw materials; the concentration range of the carbon nanotube dispersion is: 0.1-5wt.%.

3. The current collector-free electrode with a carbon nanotube flexible skeleton according to claim 1, characterized in that: The carbon nanotubes in the carbon nanotube dispersion have a diameter of 0.5 to 20 nm and a length of 5 to 100 μm.

4. The current collector-free electrode with a carbon nanotube flexible skeleton according to claim 1, characterized in that: The binder is selected from at least one of polyvinylidene fluoride, polyacrylic acid, carboxymethyl cellulose, styrene-butadiene rubber, polytetrafluoroethylene, polyvinyl alcohol, fluorinated rubber or polyurethane.

5. The current collector-free electrode with a carbon nanotube flexible skeleton according to claim 1, characterized in that: The active material includes a positive electrode active material and a negative electrode active material; the positive electrode active material is selected from lithium cobalt oxide, lithium manganese oxide, lithium titanate, lithium vanadate, LiMn x Ni y Co z O2(x+y+z=1), LiNi x Co y Al z O2 (x+y+z=1); the negative electrode active material is selected from silicon, silicon carbon, SiO x , graphite, graphene, carbon nanotubes, MCMB or carbon fiber.

6. The method for preparing a current collector-free electrode having a carbon nanotube flexible skeleton according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) Weigh the active substance and place it in deionized water at a concentration of 5 to 50 g / L, and ultrasonically disperse it for 5 to 60 minutes; (2) adding the carbon nanotube dispersion to the material obtained in step (1), ultrasonically dispersing for 5 to 60 minutes, and then placing in a mixer at 500 to 1000 rpm for 2 to 24 hours to fully mix; (3) Adding a binder to the material obtained in step (2) and continuing to compound at a low speed of 50 to 500 rpm for 2 to 24 hours to fully mix; (4) After mixing, excess solvent is removed using a solvent removal device, and the material is dried at 60 to 150°C for 6 to 24 hours to obtain the product.

7. The preparation method according to claim 6, characterized in that: The mixer is selected from any one of a V-type mixer, a planetary power mixer, a double-shaft blade mixer, a ball mill mixer, a countercurrent mixer, and a high-speed or low-speed mixer.

8. The preparation method according to claim 6, characterized in that: The solvent removal device is selected from any one of a rotary evaporator, a nitrogen blow dryer, a vacuum filter, a thin film evaporator, a hot plate evaporator, an air flow dryer, and a microwave dryer.

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