Biomass-based lithium ion battery negative electrode conductive agent with stress dispersion effect as well as preparation method and application of biomass-based lithium ion battery negative electrode conductive agent

Abstract

The invention discloses a biomass-based lithium ion battery negative electrode conductive agent with a stress dispersion effect as well as a preparation method and application thereof, and relates to the field of lithium ion battery conductive agents. The biomass-based lithium ion battery negative electrode conductive agent with the stress dispersion effect is biomass carbon fiber and is of a hollow tubular structure, and micropores are formed in the surface of the biomass-based lithium ion battery negative electrode conductive agent. The biomass-based conductive agent prepared by the invention has a stress dispersion effect. Movement of charges in an electrode can be promoted, and strain caused by volume expansion of the silicon nanoparticles can be effectively relieved, so that the specific discharge capacity and the cycling stability are improved. Compared with the traditional granular conductive carbon black, the hollow tubular biomass-based lithium ion battery negative electrode conductive agent prepared by the invention can effectively relieve expansion / shrinkage stress and service life attenuation caused by the volume change.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery conductive agent technology, specifically relating to a biomass-based lithium-ion battery negative electrode conductive agent with stress dispersion effect, its preparation method and application. Background Technology

[0002] With the rapid development of new energy vehicles, portable electronic devices, and energy storage power stations, higher requirements are being placed on the energy density, rate performance, and cycle life of lithium-ion batteries. As the core energy storage unit of lithium-ion batteries, the conductivity, ion diffusion rate, and structural stability of the active material directly affect the overall performance of the battery. However, traditional commercially available anode active materials (such as graphite-based anodes and silicon-based anodes) suffer from inherently low conductivity (e.g., graphite's room temperature conductivity is approximately 10). -3 Problems such as S / cm, volume expansion (silicon-based expansion rate is 300%), and single ion transport path severely restrict its application in high-power scenarios (such as fast charging and high-rate discharge).

[0003] To address the aforementioned problems of active materials, existing technologies mainly include carbon coating / composite techniques, metal doping, and nanostructural fabrication. However, large-scale preparation is costly and difficult to implement for industrial application.

[0004] The conductive carbon black used in traditional materials has a granular structure with a large specific surface area but low mechanical strength. It cannot suppress the expansion of silicon anodes, and its poor dispersibility makes it prone to agglomeration, affecting the uniformity of electron conduction and making it impossible to maintain a stable structure during cycling.

[0005] Based on the above background, this invention proposes a biomass-based lithium-ion battery negative electrode conductive agent with stress dispersion effect and its preparation method. The development of this material not only provides a new option for lithium battery conductive agents, but also has the potential to promote the high-value utilization of biomass resources in the new energy field. Summary of the Invention

[0006] The purpose of this invention is to provide a biomass-based lithium-ion battery negative electrode conductive agent with stress-dispersing properties, its preparation method, and its application. This improves problems such as volume expansion and insufficient conductivity of active materials, thereby enhancing battery cycle performance. The raw materials are widely available, inexpensive, and the synthesis conditions are simple, meeting the requirements of industrial production.

[0007] The present invention adopts the following technical solution: A method for preparing a biomass-based lithium-ion battery negative electrode conductive agent with stress-dispersing effect includes the following steps: S1. Cleaning of pollutants on the surface of biomass fibers: Cleaning water-soluble and oil-soluble impurities from the surface of biomass fibers, and drying to obtain the precursor; S2, Carbonization: The precursor is first pre-carbonized in an air atmosphere, cooled to room temperature, and then carbonized at high temperature in a nitrogen atmosphere to obtain biomass carbon fiber, which is the biomass-based lithium-ion battery negative electrode conductive agent with stress dispersion effect. In S1, the biomass fiber is derived from one or more of poultry and mammals.

[0008] Furthermore, the poultry include chickens, ducks, and geese; the mammals include sheep, camels, rabbits, cattle, horses, mink, and foxes.

[0009] Furthermore, in S1, the reaction temperature for cleaning water-soluble impurities is 30-90°C for 30-240 minutes; the reaction temperature for cleaning oil-soluble impurities is 20-100°C for 12-48 hours, using one or more of hydrocarbons, alcohols, esters, and ketones.

[0010] Furthermore, in S2, the temperature for pre-carbonization in the air atmosphere is 80-1100℃; the temperature for high-temperature carbonization in the nitrogen atmosphere is 200-2200℃, and the heating rate is 1-60℃ / min.

[0011] A biomass-based lithium-ion battery negative electrode conductive agent with stress-dispersing effect is obtained by any of the preparation methods described herein.

[0012] Furthermore, the conductive agent is biomass carbon fiber, which has a hollow tubular structure with micropores on its surface. The conductive agent can be mixed with the active material to form a three-dimensional topological framework conductive network structure.

[0013] Furthermore, the active material is a graphite-based anode material, a silicon-based anode material, a silicon-oxygen-based anode material, or a silicon-carbon-based anode material.

[0014] Furthermore, the biomass carbon fiber has an outer diameter of 0.01 μm to 70 μm, an inner diameter of 0.00001 μm to 30 μm, and a length of 0.2 μm to 100 mm, with an aspect ratio of not less than 2; preferably, the biomass carbon fiber has an outer diameter of 1 μm to 20 μm, an inner diameter of 0.01 μm to 5 μm, and a length of 10 μm to 500 μm; the similar diameters of the biomass carbon fibers provide stable chemical bonding, which helps to achieve uniform dispersion.

[0015] A lithium-ion battery negative electrode slurry, wherein the negative electrode slurry contains a biomass-based lithium-ion battery negative electrode conductive agent with stress-dispersing effect prepared by any one of the methods described above, or any one of the biomass-based lithium-ion battery negative electrode conductive agents with stress-dispersing effect.

[0016] Furthermore, the negative electrode slurry also includes active materials, traditional conductive agents, and binders; The active material is one or more of graphite-based anode materials, silicon-based anode materials, siloxy-based anode materials, and silicon-carbon-based anode materials; the conventional conductive agent is conductive carbon black; and the binder is one or more of polyvinyl alcohol, polytetrafluoroethylene, polyolefin, polyvinylidene fluoride, polyurethane, polyacrylic acid, styrene-butadiene rubber, sodium carboxymethyl cellulose, and sodium alginate. The conductive agent is present in the negative electrode slurry at a weight percentage of 0.1-10%.

[0017] The beneficial effects of this invention are detailed below: (1) The biomass-based lithium-ion battery negative electrode conductive agent with stress dispersion function in this invention is biomass carbon fiber, with an outer diameter of 0.01 μm to 70 μm and an inner diameter of 0.00001 μm to 30 μm. It has a hollow tubular structure with micropores on the surface. This material has a large specific surface area, abundant active sites, uniform tube diameter distribution, and excellent conductivity. The biomass carbon fiber can be mixed with the active material to form a three-dimensional topological framework network structure. When subjected to external force, the fiber directly bears the stress and transfers it to other fibers through interfacial interactions (such as mechanical interlocking, chemical bonding, etc.), thereby reducing the stress burden on the matrix. It can effectively alleviate the expansion / contraction stress and lifespan decay caused by the volume change of silicon nanoparticles, thereby improving cycle stability.

[0018] (2) Animal biomass fibers have a natural hollow structure and contain N, P and S elements. No further chemical doping is required. The N, P and S doped carbon materials derived from animal biomass fibers exhibit high conductivity and can be used to improve the performance of lithium-ion batteries.

[0019] (3) Carbonizing biomass fibers allows them to retain mechanical strength while also possessing a certain degree of conductivity, which can expand the conductive network and promote the capacity utilization of the battery. It can also promote the movement of charges in the electrodes, reduce the use of conductive carbon black, and improve the discharge specific capacity and cycle stability.

[0020] (4) The raw materials of this invention are green and environmentally friendly, the preparation process is simple and convenient, and the high-energy graphitization process in traditional methods is avoided, which significantly reduces production costs and makes it easy to achieve large-scale production. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the synthesis steps according to an embodiment of the present invention; Figure 2The images show electron micrographs (SEM) of the original sample and the embodiments of the present invention. In the images, (a) is the original sample, (b) is Example 1, (c) is Example 2, and (d) is Example 3.

[0022] Figure 3 This is a comparison diagram of the conductivity of biomass carbon fibers under different pressures using four-point probes in Examples 1-3 of the present invention.

[0023] Figure 4 The images show cross-sectional views of the negative electrode of the half-cell in Embodiment 4 and Comparative Examples 1 and 2 of the present invention before cycling, at the 50th cycle, and at the 100th cycle.

[0024] Figure 5 The images show the surface views of the negative electrode sheet of the half-cell in Example 4 and Comparative Examples 1 and 2 of the present invention before cycling, at the 50th cycle, and at the 100th cycle.

[0025] Figure 6 These are battery long-cycle test diagrams for Embodiment 4 and Comparative Examples 1 and 2 of the present invention.

[0026] Figure 7 The battery rate test diagrams are for Embodiment 4 and Comparative Examples 1 and 2 of the present invention. Detailed Implementation

[0027] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0028] Example 1 A biomass-based lithium-ion battery negative electrode conductive agent with stress-dispersing effect is prepared as follows: Weigh 2 g of rabbit hair fiber, put it into 100 mL of deionized water, stir at 60 ℃ for 2 h, then wash with ethanol and dry in a forced-air oven at 60 ℃ for 12 h to obtain the precursor. The precursor was heated to 250 °C in air at a heating rate of 2 °C / min and held for 2 h. After cooling to room temperature, it was transferred to a nitrogen atmosphere and heated to 700 °C at a heating rate of 5 °C / min and held for 3 h. The resulting biomass carbon fiber is a biomass-based lithium-ion battery negative electrode conductive agent with stress dispersion properties. Its SEM image is shown below. Figure 2 As shown in (b).

[0029] Example 2 Unlike Example 1, in step (2), the heating rate from 5 °C / min to 700 °C under a nitrogen atmosphere was changed to 5 °C / min to 600 °C. The SEM image of the biomass carbon fiber prepared in Example 2 is shown below. Figure 2 As shown in (c).

[0030] Example 3 Unlike Example 1, in step (2), the heating rate from 5 °C / min to 700 °C under a nitrogen atmosphere was changed to 5 °C / min to 800 °C. The SEM image of the biomass carbon fiber prepared in Example 3 is shown below. Figure 2 As shown in (d).

[0031] Examples 4-6 The lithium-ion battery conductive agents obtained in Examples 1-3 were mixed in water at a mass ratio of silicon-carbon anode material: fiber conductive agent: sodium carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR) = 80%: 10%: 5%: 5% to form three uniform anode slurries based on Examples 1-3. These slurries were then coated onto copper foil and dried to form anode sheets. The silicon-carbon mass loading of the anode material was approximately 2 mg·cm³. -2 .

[0032] Battery Assembly: The CR2025 coin cells were assembled entirely in an argon-atmospheric glove box. For the coin half-cell, a pure lithium metal sheet was used as the counter electrode, a Celgard 2325 separator was used, and the electrolyte was a mixed solution containing 1.2 M lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC), diethyl carbonate (DEC) (where EC / DEC = 1 / 1, v / v), and 25 vo 1% fluoroethylene carbonate (FEC). Charge-discharge tests were conducted on the LAND electrochemical testing system in Wuhan, China. For the half-cell, the charge-discharge voltage window was 0.005–1.5 V.

[0033] Comparative Example 1 Replace the mass ratio of silicon-carbon anode material: fiber conductive agent: sodium carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR) = 80%: 10%: 5%: 5% in Example 4 with silicon-carbon anode material: conductive carbon black (SP): sodium carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR) = 80%: 10%: 5%: 5%, while keeping all other aspects the same.

[0034] Comparative Example 2 Replace the mass ratio of silicon-carbon anode material: fiber conductive agent: sodium carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR) in Example 4 (80%: 10%: 5%: 5%) with silicon-carbon anode material: fiber conductive agent: conductive carbon black (SP): sodium carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR) (80%: 5%: 5%: 5%), and keep all other ratios the same.

[0035] Performance testing Conductivity testing: Based on the Kelvin four-wire method, the conductivity is tested using a four-probe powder conductivity meter.

[0036] Long-cycle and rate performance testing: After the assembled half-cells were left to stand at room temperature for 12 hours, constant current charge-discharge tests and rate performance tests were conducted. The constant current charge-discharge tests were performed at 30 °C and 0.3 C, and the rate performance tests were performed at 0.03 C, 0.1 C, 0.3 C, 0.5 C, 1 C, and 2 C, respectively. The battery cycle performance and rate performance test results of Example 4 and Comparative Examples 1 and 2 are as follows: Figure 6 , Figure 7 .

[0037] Testing the expansion rate of silicon-carbon electrodes after lithium intercalation: In a half-cell, a silicon-carbon electrode was used as the positive electrode, with the thickness of the positive electrode sheet before battery assembly defined as L1. After the battery underwent 30 and 50 charge-discharge cycles, it was disassembled. The thickness L2 of the positive electrode sheet at the same location was measured. Figure 4 The images show cross-sectional views of the positive electrode sheets of Example 4 and Comparative Examples 1 and 2 before and after cycling, and the expansion rate is calculated using the formula: expansion rate % after lithium insertion = (L2-L1) / L1×100%.

[0038] Results Analysis Table 1. Diameter of rabbit hair before treatment and materials from Examples 1-3 of the present invention. like Figure 2 As shown, (a) is an SEM image of rabbit hair before treatment, and (b), (c), and (d) are SEM images of the rabbit hair precursor after treatment with the carbonization methods described in Examples 1-3, respectively. All images are randomly selected locations, and the overall morphology in each example is basically as shown in the corresponding images. It can be seen that the rabbit hair fibers before treatment have a hollow tubular structure. After high-temperature carbonization, the hollow tubular structure is still maintained, with a uniform tube diameter distribution of approximately 5-15 μm. However, as the carbonization temperature increases, the diameter and length of the carbon fibers decrease. This is because when the carbonization temperature increases, the pyrolysis reaction intensifies, and a large amount of volatile substances are generated and released, leading to shrinkage and defects in the internal structure of the fiber, resulting in a reduction in fiber diameter.

[0039] like Figure 3 The diagram shows the conductivity of the original sample and Examples 1-3. The original sample is not conductive, while the biomass carbon material after high-temperature carbonization is conductive, and the conductivity gradually increases with increasing carbonization temperature. This is because as the carbonization temperature increases, the material carbonizes more completely, the degree of graphitization increases, impurities decrease, and the carbon structure becomes more ordered, thus facilitating electron migration and increasing conductivity.

[0040] like Figure 4The figures show cross-sectional views of the electrode in Example 4 and Comparative Examples 1 and 2 before cycling, at the 50th cycle, and at the 100th cycle. The electrode expansion rates are shown in Table 2. It can be seen that the electrode expansion rate of Example 4 before and after cycling is significantly lower than that of Comparative Examples 1 and 2. The main reason is that the biomass-based lithium-ion battery negative electrode conductive agent with stress-dispersing properties prepared in this invention exhibits a hollow tubular structure, which, together with the silicon-carbon-based negative electrode material in the electrode, can form a reinforced concrete structure. This facilitates the dispersion of stress generated by electrode expansion, thereby reducing the stress burden on the matrix, alleviating the expansion / contraction stress and lifespan decay caused by volume changes, and thus improving cycle stability. Furthermore, the prepared biomass carbon fiber possesses a certain degree of conductivity, which can expand the conductive network and promote battery capacity utilization. It can promote charge movement in the electrode, thereby increasing the discharge specific capacity.

[0041] Table 2. Electrode expansion rates before and after half-cell cycling in Example 4 and Comparative Examples 1 and 2 like Figure 5 The images show electrode surface images of the half-cells in Example 4 and Comparative Examples 1 and 2 before, after 50, and after 100 cycles. It can be seen that before cycling, the content of hollow tubular fibers in the electrode increases with the increase in the proportion of biomass carbon fiber added. After 50 and 100 cycles, the electrode image in Comparative Example 1 shows deeper cracks, while the electrode images of Example 4 and Comparative Example 2 after cycling show smaller cracks. This indicates that the hollow tubular fibers can effectively disperse the stress generated by electrode expansion, acting as a "patchwork" in the electrode. Furthermore, the number of cracks in Example 4 is less than that in Comparative Example 2, indicating that with the increase in biomass carbon fiber content, more stress expansion can be alleviated, resulting in better cycling stability.

[0042] like Figure 6 The table shows the long-cycle test results of the batteries in Example 4 and Comparative Examples 1 and 2. The capacity retention rates after 150 and 200 cycles are shown in the table. It can be seen that the capacity retention rate of Example 4 is significantly higher than that of Comparative Examples 1 and 2. This is because the carbonized fibers maintain a hollow tubular structure, mitigating the expansion / contraction stress and lifespan decay caused by volume changes. Furthermore, the fibers have strong conductivity, forming a better conductive network, thus effectively improving the cycle stability and discharge specific capacity of the half-cell. In contrast, the biomass carbon fiber content in Comparative Example 2 is lower than that in Example 4, resulting in the failure to form a good conductive network in certain areas of the electrode, leading to a decrease in cycle performance.

[0043] Table 3. Long-cycle capacity retention rates of Example 4 and Comparative Examples 1 and 2 like Figure 7The diagram shows the battery rate test results for Example 4 and Comparative Examples 1 and 2. It can be seen that the rate performance of Example 4 and Comparative Example 2 is higher than that of Comparative Example 1. This further verifies the high conductivity and cycle stability of the biomass carbon fiber in this invention, and that it can cycle stably at high current rates.

Claims

1. A method for preparing a biomass-based lithium-ion battery negative electrode conductive agent with stress-dispersing effect, characterized in that, Includes the following steps: S1. Cleaning of pollutants on the surface of biomass fibers: Cleaning water-soluble and oil-soluble impurities from the surface of biomass fibers, and drying to obtain the precursor; S2. Carbonization: The precursor is pre-carbonized in an air atmosphere, cooled to room temperature, and then carbonized at high temperature in a nitrogen atmosphere to obtain biomass carbon fiber, which is the biomass-based lithium-ion battery negative electrode conductive agent with stress dispersion effect. In S1, the biomass fiber is derived from one or more of poultry and mammals.

2. The method for preparing the biomass-based lithium-ion battery negative electrode conductive agent with stress-dispersing effect according to claim 1, characterized in that, The poultry include chickens, ducks, and geese; the mammals include sheep, camels, rabbits, cattle, horses, mink, and foxes.

3. The method for preparing the biomass-based lithium-ion battery negative electrode conductive agent with stress-dispersing effect according to claim 1, characterized in that, In S1, the reaction temperature for cleaning water-soluble impurities is 30-90℃ for 30-240 minutes; the reaction temperature for cleaning oil-soluble impurities is 20-100℃ for 12-48 hours, using one or more of hydrocarbons, alcohols, esters, and ketones.

4. The method for preparing the biomass-based lithium-ion battery negative electrode conductive agent with stress-dispersing effect according to claim 1, characterized in that, In S2, the temperature for pre-carbonization in air atmosphere is 80-1100℃; the temperature for high-temperature carbonization in nitrogen atmosphere is 200-2200℃, and the heating rate is 1-60℃ / min.

5. A biomass-based lithium-ion battery negative electrode conductive agent with stress-dispersing effect, characterized in that, It is obtained by the preparation method described in any one of claims 1-4.

6. The biomass-based lithium-ion battery negative electrode conductive agent with stress-dispersing effect according to claim 5, characterized in that, The conductive agent is biomass carbon fiber, which has a hollow tubular structure with micropores on its surface. The conductive agent can be mixed with active materials to form a three-dimensional topological framework conductive network structure.

7. The biomass-based lithium-ion battery negative electrode conductive agent with stress-dispersing effect according to claim 6, characterized in that, The active material is a graphite-based anode material, a silicon-based anode material, a silicon-oxygen-based anode material, or a silicon-carbon-based anode material.

8. The biomass-based lithium-ion battery negative electrode conductive agent with stress-dispersing effect according to claim 6, characterized in that, The biomass carbon fiber has an outer diameter of 0.01 μm to 70 μm, an inner diameter of 0.00001 μm to 30 μm, a length of 0.2 μm to 100 mm, and an aspect ratio of not less than 2.

9. A lithium-ion battery negative electrode slurry, characterized in that, The negative electrode slurry contains a biomass-based lithium-ion battery negative electrode conductive agent with stress-dispersing effect prepared by the method described in any one of claims 1-4, or a biomass-based lithium-ion battery negative electrode conductive agent with stress-dispersing effect as described in any one of claims 5-8.

10. The lithium-ion battery negative electrode slurry according to claim 9, characterized in that, The negative electrode slurry also includes active materials, traditional conductive agents, and binders; The active material is one or more of graphite-based anode materials, silicon-based anode materials, siloxy-based anode materials, and silicon-carbon-based anode materials; the conventional conductive agent is conductive carbon black. The adhesive is one or more of the following: polyvinyl alcohol, polytetrafluoroethylene, polyolefin, polyvinylidene fluoride, polyurethane, polyacrylic acid, styrene-butadiene rubber, sodium carboxymethyl cellulose, and sodium alginate. The conductive agent is present in the negative electrode slurry at a weight percentage of 0.1-10%.

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