A preparation method and application of a composite conductive additive for high-load electrodes

Abstract

A method for preparing and applying a composite conductive additive for high-load electrodes is disclosed. Carbon nanofibers are mixed with conductive carbon black to obtain a composite conductive additive for high-load electrodes where carbon nanofibers construct a continuous and efficient three-dimensional electron conduction pathway between the conductive carbon black and active particles. This composite conductive additive is applied to high-load electrode sheets in lithium-ion batteries. In preparing the positive electrode sheet, the positive electrode material, the composite conductive additive, and a binder are uniformly mixed in a mass ratio of 90:5:5 to form a slurry. The slurry is then coated onto an aluminum foil current collector using a scraper and dried in a vacuum oven. The advantages are: the preparation method is simple; this conductive additive is suitable for increasing the thickness of high-load, high-voltage lithium-rich positive electrodes; it possesses excellent mechanical properties to inhibit cracking and detachment of high-load electrodes; and it can construct a three-dimensional conductive network to improve the electrochemical performance of thick electrodes.

Description

Technical Field

[0001] This invention is applied to the field of new energy secondary batteries, specifically to conductive additives for lithium-ion battery lithium-manganese-rich cathode materials, and more specifically to a method for preparing and applying a composite conductive additive for high-load electrodes. Background Technology

[0002] With the rapid development of the electric vehicle industry, higher demands are being placed on the specific capacity, rate of change, and cycle stability of lithium-ion batteries. Increasing the areal loading of electrode active materials to fabricate "thick electrodes" is one effective way to improve the energy density of individual battery cells. However, as electrode thickness increases (e.g., ternary cathodes exceeding 50 micrometers), effective lithium-ion and electron conduction becomes difficult, directly affecting the electrochemical performance of lithium-ion batteries. Electron conduction relies on a continuous porous solid network composed of active material particles and conductive additives. Conductive additives with high electron transport can improve the electrochemical performance of thick electrodes. An ideal conductive network structure requires: high electronic conductivity to ensure rapid electron transport; a continuous and uniform structure spanning the entire electrode thickness; and good mechanical strength to maintain the integrity of the electrode structure during cycling. Traditional electrode designs struggle to form a uniform, continuous, and robust conductive network in thick electrodes.

[0003] Traditional conductive agents, such as conductive carbon black (Super P), are zero-dimensional nanoparticles with low electronic conductivity and a tendency to agglomerate, making it difficult to achieve uniform dispersion on the surface of active material particles. This results in point-to-point contact between the agent and the active material, hindering the formation of a continuous three-dimensional conductive network structure. One-dimensional conductive materials, such as carbon nanofibers (CNFs), possess excellent electronic conductivity, electrochemical stability, superior compatibility, and robust mechanical properties, demonstrating great potential in the fabrication of flexible and self-supporting electrodes. Leveraging their high aspect ratio, entangled network structure, and abundant surface hydroxyl groups, carbon nanofibers have been developed as flexible building blocks for preparing self-supporting and sandwich-structured cathode materials with high surface mass loading. Carbon nanofibers typically have a diameter of 5–10 micrometers; the high aspect ratio of carbon fibers can construct an interpenetrating 3D conductive network framework, thereby enhancing the stability of the electrode structure. The carbon network of carbon nanofibers can also provide a three-dimensional pathway for electron transport. However, at the microscale, carbon nanofiber networks may still suffer from uneven distribution or insufficient contact with some small-sized active particles. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing and applying a composite conductive additive for high-load electrodes. The preparation method is simple, and the conductive additive is suitable for increasing the thickness of high-load, high-voltage lithium-rich cathodes. It has excellent mechanical properties to inhibit cracking and shedding of high-load electrodes, and can also construct a three-dimensional conductive network to improve the electrochemical performance of thick electrodes.

[0005] The technical solution of this invention is: A method for preparing a composite conductive additive for high-load electrodes includes the following steps: mixing carbon nanofibers with conductive carbon black at a mass ratio of 3:7, and then grinding the mixture; resulting in a composite conductive additive for high-load electrodes in which carbon nanofibers construct a continuous and efficient three-dimensional electron conduction pathway between the conductive carbon black and active particles. This composite conductive additive of carbon nanofibers and conductive carbon black can be used as a conductive additive for thick electrodes, helping to form a more efficient conductive network. Simultaneously, the construction of a three-dimensional conductive framework improves the mechanical stability of the electrode and controls costs, making it more suitable for industrial applications.

[0006] Furthermore, the length of the carbon nanofibers is 5μm-50μm.

[0007] Furthermore, the diameter of the carbon nanofibers is 200nm-600nm.

[0008] Furthermore, the conductive carbon black is Super P.

[0009] Application of a composite conductive additive prepared by the above method in high-load electrode sheets of lithium-ion batteries.

[0010] Furthermore, in preparing the positive electrode sheet, the positive electrode material, the composite conductive additive, and the binder are uniformly mixed in a mass ratio of 90:5:5 to form a slurry. The slurry is then coated onto the aluminum foil current collector using an 800μm scraper and dried in a vacuum oven at 80℃ for 12 hours.

[0011] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention uses carbon nanofibers (CNF) and conventional conductive agent conductive carbon black (Super P). When used in combination, a triple continuous conductive interface of "fiber-carbon black-active material" can be constructed through a simple manual grinding and mixing process. The preparation process is simple, low-cost, and easy to scale up, and has good prospects for industrial application.

[0012] (2) Carbon nanofibers (CNFs) have a high aspect ratio, excellent electrical conductivity and mechanical strength. They can form a three-dimensional network skeleton structure inside the electrode, which significantly enhances the structural integrity and crack resistance of thick electrodes and improves the bonding strength between the electrode and the current collector. The results show that when the CNF addition is 2.5 wt%, the electrode peel strength can reach 7.6 N, and the mechanical properties are significantly better than those of traditional electrodes.

[0013] (3) Carbon nanofibers (CNFs) are rich in polar functional groups such as hydroxyl groups on their surface. They can promote the adsorption and uniform dispersion of conductive carbon black (Super P) particles through hydrogen bonding and other interactions, forming a stable and continuous conductive network with the active material. This effectively reduces the interfacial contact resistance and improves the overall electronic conduction efficiency of the electrode.

[0014] (4) This invention is applicable to thick electrode systems with high areal loading, and the active material loading can reach 18 mg·cm³. -2 In conclusion, the introduction of carbon nanofibers (CNFs) not only enhances the electronic conductivity of the electrode, but also buffers volume changes during charge and discharge processes through its three-dimensional network structure, suppressing electrode pulverization and significantly improving the cycling stability of thick electrodes.

[0015] (5) In terms of electrochemical performance, the lithium-rich manganese-based thick electrode using this composite conductive agent can achieve a reversible specific capacity of 249.42 mAh g at 0.1C. -1 It approaches the level of a thin electrode; it maintains high capacity and good capacity retention during 1C cycling, while still exhibiting 110 mAh g⁻¹ at high 2C rates. -1 Its capacity performance demonstrates excellent rate performance and cycle durability, making it suitable for lithium-ion battery systems with high energy density and high power requirements. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the conductive additives used in this invention forming an electrode sheet; Figure 2 This is a 50,000x SEM image of the high-load lithium-rich manganese-based electrode sheet based on composite conductive additives, as described in Comparative Example 1 of this invention. Figure 3 This is a SEM image of the highly loaded lithium-rich manganese-based electrode sheet based on composite conductive additives in Embodiment 1 of the present invention, magnified at 50,000 times. Figure 4 This is a 50,000x SEM image of the high-load lithium-rich manganese-based electrode sheet based on composite conductive additives, as described in Comparative Example 2 of this invention. Figure 5 This is a 50,000x SEM image of the high-load lithium-rich manganese-based electrode sheet based on composite conductive additives, which is a comparative example of the present invention. Figure 6 The stress-strain curves of the high-load lithium-rich manganese-based electrode sheet based on composite conductive additives in the present invention (comparative examples 1, 2, and 3) are obtained from the 90° tensile test. Figure 7 Comparison curves of electronic conductivity of high-load lithium-rich manganese-based electrode sheets based on composite conductive additives in the present invention (comparative examples 1, 2, and 3). Figure 8 The first charge-discharge curves of the battery assembled with the high-load lithium-rich manganese-based cathode material based on composite conductive additives according to the present invention (comparative examples 1, 2, and 3) at 30°C and 0.1C rate. Figure 9 The discharge specific capacity decay diagram is shown for the battery assembled with the high-load lithium-rich manganese-based cathode material based on composite conductive additives according to the present invention (comparative examples 1, 2, and 3) after 50 cycles at 30°C and 1C. Figure 10 The image shows the cycling curves of the battery assembled with the high-load lithium-rich manganese-based cathode material based on composite conductive additives according to the present invention (comparative examples 1, 2, and 3) under different rate conditions (0.1C, 0.2C, 0.5C, 1C, 2C, and 0.1C). Detailed Implementation

[0017] The specific implementation methods of the present invention will be further described below with reference to examples. It should be noted that the specific implementation methods described herein are only for illustration and explanation of the present invention and are not intended to limit the scope of protection of the present invention.

[0018] The carbon nanofibers (CNFs) used in the embodiments and comparative examples of this invention have a diameter of 200nm-600nm and a length of 5μm-50μm.

[0019] Comparative Example 1 Step 1: First, weigh 24 mg of conductive carbon black (Super P) and 6 mg of carbon nanofibers (CNF), and place them in an agate mortar. At room temperature, manually grind for 30 minutes to mix the conductive carbon black (Super P) and carbon nanofibers (CNF) evenly to obtain a conductive carbon black-carbon nanofiber composite conductive additive.

[0020] Step 2: Add 0.18g of sodium carboxymethyl cellulose to 9.82g of deionized water, stir and mix thoroughly at room temperature for 12 hours to prepare a transparent and uniform sodium carboxymethyl cellulose aqueous solution as a binder.

[0021] Step 3: Apply lithium-rich manganese cathode material 0.5Li2MnO3·0.5LiNi 0.33 Co 0.33 Mn 0.33O2, conductive carbon black-carbon nanofiber composite conductive additive, and sodium carboxymethyl cellulose aqueous solution binder are uniformly mixed in a mass ratio of 90:5:5 to form a slurry. The slurry is coated onto an aluminum foil current collector using an 800 μm doctor blade. After drying in a vacuum oven at 80 °C for 12 h, the slurry is cut into sheets to obtain lithium-rich manganese-based positive electrode sheets. The product is denoted as LRMO-CNF 1.0 wt.

[0022] Example 1 Step 1: First, weigh 21 mg of conductive carbon black (Super P) and 9 mg of carbon nanofibers (CNF), and place them in an agate mortar. At room temperature, manually grind for 30 minutes to mix the conductive carbon black (Super P) and carbon nanofibers (CNF) evenly to obtain a conductive carbon black-carbon nanofiber composite conductive additive.

[0023] Step 2: Add 0.18g of sodium carboxymethyl cellulose to 9.82g of deionized water, stir and mix thoroughly at room temperature for 12 hours to prepare a transparent and uniform sodium carboxymethyl cellulose aqueous solution as a binder.

[0024] Step 3: Apply lithium-rich manganese cathode material 0.5Li2MnO3·0.5LiNi 0.33 Co 0.33 Mn 0.33 O2, conductive carbon black-carbon nanofiber composite conductive additive, and sodium carboxymethyl cellulose aqueous solution binder are uniformly mixed in a mass ratio of 90:5:5 to form a slurry. The slurry is coated onto an aluminum foil current collector using an 800μm doctor blade. After drying in a vacuum oven at 80℃ for 12 hours, the slurry is cut into sheets to obtain lithium-rich manganese-based positive electrode sheets. The product is denoted as LRMO-CNF 1.5 wt.

[0025] Comparative Example 2 Step 1: First, weigh 18 mg of conductive carbon black (Super P) and 12 mg of carbon nanofibers (CNF), and place them in an agate mortar. At room temperature, manually grind for 30 minutes to mix the conductive carbon black (Super P) and carbon nanofibers (CNF) evenly to obtain a conductive carbon black-carbon nanofiber composite conductive additive.

[0026] Step 2: Add 0.18g of sodium carboxymethyl cellulose to 9.82g of deionized water, stir and mix thoroughly at room temperature for 12 hours to prepare a transparent and uniform sodium carboxymethyl cellulose aqueous solution as a binder.

[0027] Step 3: Apply lithium-rich manganese cathode material 0.5Li2MnO3·0.5LiNi 0.33 Co 0.33 Mn 0.33O2, conductive carbon black-carbon nanofiber composite conductive additive, and sodium carboxymethyl cellulose aqueous solution binder are uniformly mixed in a mass ratio of 90:5:5 to form a slurry. The slurry is coated onto an aluminum foil current collector using an 800μm scraper. After drying in a vacuum oven at 80℃ for 12h, the slurry is cut into sheets to obtain lithium-rich manganese-based positive electrode sheets. The product is denoted as LRMO-CNF 2.0 wt.

[0028] Comparative Example 3 Step 1: First, weigh 15mg of conductive carbon black (Super P) and 15mg of carbon nanofibers (CNF) and place them in an agate mortar. At room temperature, manually grind for 30 minutes to mix the conductive carbon black (Super P) and carbon nanofibers (CNF) evenly to obtain a conductive carbon black-carbon nanofiber composite conductive additive.

[0029] Step 2: Add 0.18g of sodium carboxymethyl cellulose to 9.82g of deionized water, stir and mix thoroughly at room temperature for 12 hours to prepare a transparent and uniform sodium carboxymethyl cellulose aqueous solution as a binder.

[0030] Step 3: Apply lithium-rich manganese cathode material 0.5Li2MnO3·0.5LiNi 0.33 Co 0.33 Mn 0.33 O2, conductive carbon black-carbon nanofiber composite conductive additive, and sodium carboxymethyl cellulose aqueous solution binder are uniformly mixed in a mass ratio of 90:5:5 to form a slurry. The slurry is coated onto an aluminum foil current collector using an 800μm scraper. After drying in a vacuum oven at 80℃ for 12 hours, the slurry is cut into sheets to obtain lithium-rich manganese-based positive electrode sheets. The product is denoted as LRMO-CNF 2.5 wt.

[0031] Test Analysis The lithium-rich manganese-based positive electrode sheet was cut into uniformly sized circular sheets, dried, and then assembled into 2025 button cells in an argon-filled glove box with oxygen and water content of less than 0.01 ppm. The button cells were then placed in an oven for long-term activation treatment at a temperature of 45°C for 40 hours. After removal, the cells were activated for 3 cycles at a current density of 0.1C, and then the battery cycle performance was tested at a current density of 1C.

[0032] Electrochemical performance was tested using 2025 coin cells on a Xinwei testing system. A Li metal sheet was used as the reference and counter electrode, a Celgard-2400 separator, and Xinzhoubang 3045I electrolyte. The test voltage window was 2.0–4.8 V. The test temperature was 27 ± 1 °C. The performance test results are shown in Table 1.

[0033] Table 1. Initial charge-discharge and cycle data of LRMO thick electrodes with carbon nanofiber (CNF) contents of 1.0 wt%, 1.5 wt%, 2.0 wt%, and 2.5 wt%. As shown in Table 1, at the same surface loading of active material (approximately 18 mg / cm³), 2 Under the conditions of ) and slurry coating process, the content of carbon nanofibers (CNF) in the composite conductive agent has a significant impact on the electrochemical performance of the thick electrode. Figure 8 The initial charge-discharge curves and the data in Table 1 together show that when the carbon nanofiber (CNF) content is 1.5 wt% (Example 1), the electrode exhibits the highest reversible specific capacity (249.42 mAh / g) at 0.1C, closest to the capacity level of thin electrodes. Simultaneously, its first-cycle discharge capacity at 1C also reaches 197.61 mAh / g, demonstrating excellent rate performance. However, the electrochemical performance does not increase monotonically with increasing carbon nanofiber (CNF) content. (Comparison) Figure 9 The cycling performance curves and capacity retention data in Table 1 show that: Comparative Example 1 (CNF 1.0 wt%) has the highest capacity retention rate after 50 cycles (91.74%), but its absolute capacity value is the lowest; while Comparative Example 3 (CNF 2.5 wt%) exhibits the most severe capacity decay at 1C cycling, with a capacity retention rate of only 64.32% after 50 cycles. Example 1 (CNF 1.5 wt%) achieves the best balance between high capacity (197.61 mAh / g) and good cycling stability (86.79% retention rate).

[0034] like Figures 2-5 The image shows SEM morphology images of thick electrodes with different carbon nanofiber (CNF) contents. As the CNF content increases, the fibrous network structure in the electrode becomes more pronounced. When the carbon nanofiber (CNF) content is appropriate (1.5 wt% in Example 1), its high aspect ratio allows for the construction of continuous and efficient three-dimensional electronic conduction pathways between active particles (such as...). Figure 1 (As shown in the schematic diagram), and enhances electrode integrity through its mechanical strength, thereby simultaneously improving capacity and cycle performance. Figure 10 The rate performance test further confirmed this, and the electrode of Example 1 was able to maintain a capacity of about 110 mAh / g at a high rate of 2C, demonstrating optimal charge transport kinetics.

[0035] However, when the carbon nanofiber (CNF) content is too high (2.5 wt% in Comparative Example 3), excessive fibers may cause the electrode structure to be too dense. On the one hand, this crowds out the pores required for lithium-ion transport, increasing the resistance to ion migration; on the other hand, it may cause some active materials to be over-encapsulated or isolated, reducing the effective electrochemical reaction interface. Ultimately, although the electronic conductivity may still be high (supporting its high first-cycle capacity), ion transport is restricted and structural stress increases, leading to accelerated capacity decay during cycling.

[0036] in conclusion: In summary, this invention successfully prepared a composite conductive additive suitable for high-load thick electrodes by combining carbon nanofibers (CNF) with traditional conductive carbon black (Super P). The lithium-rich manganese-based thick electrode exhibits the best overall performance when the CNF content in the composite conductive agent is 1.5 wt% (corresponding to a total conductive agent content of 5 wt% in the electrode). This electrode maintains a high surface loading of active material (~13 mg / cm²). 2 While possessing high specific capacity (~249.4 mAh / g at 0.1C), excellent rate performance (~110 mAh / g at 2C), and good cycling stability (86.79% capacity retention after 50 cycles at 1C), this is mainly attributed to the fact that carbon nanofibers (CNFs) can excellently construct a synergistic network of "three-dimensional mechanical framework-continuous electronic pathway" at this ratio, effectively solving the core problems of difficult electron conduction, poor mechanical stability, and the need to balance ion transport in thick electrodes.

[0037] The above-described specific embodiments and data fully illustrate the effectiveness and advantages of the present invention, but the scope of protection of the present invention is not limited to the above embodiments. For those skilled in the art, any equivalent modifications, substitutions, or improvements made to the present invention without departing from the principles and spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a composite conductive additive for high loading electrodes, characterized by, Includes the following steps: Carbon nanofibers are mixed with conductive carbon black at a mass ratio of 3:7, and then ground. A composite conductive additive was developed to obtain a high-load electrode in which carbon nanofibers construct a continuous and efficient three-dimensional electronic conduction pathway between conductive carbon black and active particles.

2. The method of claim 1, wherein the high conductivity composite additive is prepared by the steps of: The length of the carbon nanofibers is 5μm-50μm. ​ 3. The method of claim 1, wherein the high conductivity composite additive is prepared by the steps of: The diameter of the carbon nanofibers is 200nm-600nm. ​ 4. The method of claim 1, wherein the high conductivity composite additive is prepared by the steps of: The conductive carbon black is Super P. ​ 5. The application of a composite conductive additive prepared by the preparation method as described in claim 1 in a high-load electrode sheet of a lithium-ion battery.

6. Use according to claim 5, characterized in that, When preparing the positive electrode sheet, the positive electrode material, the composite conductive additive, and the binder are uniformly mixed in a mass ratio of 90:5:5 to form a slurry. The slurry is coated onto the aluminum foil current collector using an 800μm scraper and dried in a vacuum oven at 80℃ for 12 hours.

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