A porous hollow carbon microsphere / nanodiamond lithium ion battery negative electrode material and a preparation method thereof

Abstract

The application provides a kind of porous hollow carbon microspheres / nanometer diamond lithium ion battery negative electrode material and its preparation method, belong to lithium ion battery negative electrode material technical field, the biomass soapberry peel is used as carbon source in the application, and the method of adding nanometer diamond hydrothermal treatment and potassium hydroxide activation, porous hollow carbon microspheres composite nanometer diamond (PHCS-ND) is synthesized.When PHCS-ND is applied to the negative electrode of lithium ion battery, good cycle stability is shown.At 2C current density, after 1500 cycles, the specific capacity can reach 700-800mA h g ‑1 At 5C current density, after 6000 cycles, the specific capacity can reach 350-450mA h g ‑1 Even at 20C current density, after 13000 cycles, the specific capacity can still reach 100-120mA h g ‑1 , with long cycle stability and high capacity performance.The preparation method used in the application has the advantages of simple process, easy to realize, easy to enlarge, etc., and is expected to be mass-produced in the future.

Description

Technical Field

[0001] This invention belongs to the technical field of lithium-ion battery anode materials, specifically relating to a porous hollow carbon microsphere / nanodiamond lithium-ion battery anode material and its preparation method. Background Technology

[0002] Lithium-ion batteries have revolutionized portable electronics and electric vehicles due to their superior energy density, extended cycle life, and minimal self-discharge rate. The appropriate selection of the anode material significantly impacts lithium-ion battery performance. To date, carbonaceous materials commonly used for energy storage include graphite, graphene, carbon nanotubes, and carbon nanofibers. Among these, graphite has become a widely used anode material for lithium-ion batteries due to its low cost, good thermal conductivity, and excellent chemical stability; however, its theoretical capacity is only 372 mAh. -1 Furthermore, graphite structures are easily damaged and exfoliated during lithium encapsulation due to the introduction of solvent molecules, leading to severe capacity decay and decreased stability. Although some non-graphite materials of Sn, SnO2, and Si exhibit capacities of 994, 1965, and 4200 mA hg, respectively... -1 While these materials offer high theoretical specific capacity, their high cost and relatively poor conductivity and cycle stability lead to subsequent capacity decay during lithium-ion battery cycling. To date, designing suitable electrode structures or surface modifications have been effective strategies to overcome these problems and improve the overall performance of lithium-ion batteries.

[0003] Among the various structures of carbon anodes, hollow porous structures are advantageous for adapting to volume deformation during repeated ion insertion and extraction. High surface area and open porous channels promote surface charge storage and a large number of active sites for catalytic reactions, while the thin shell and void spaces help alleviate structural strain caused by lithium-ion insertion. However, the design and fabrication of these structures always involve complex methods and multiple synthetic steps, in which various surfactants, block copolymers, and hard templates are indispensable, thus hindering large-scale continuous industrial production. Therefore, designing a convenient, cost-effective, and template-free method to synthesize highly efficient structures with enhanced energy storage is of paramount importance. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art by introducing nanodiamond combined with biomass carbon materials to synthesize porous hollow carbon microsphere materials and applying them to lithium-ion battery anode materials, thereby providing a lithium-ion battery anode material with high capacity, long cycle stability and high safety performance and its preparation method.

[0005] The specific technical solution of the present invention is as follows:

[0006] A method for preparing a porous hollow carbon microsphere / nanodiamond lithium-ion battery anode material, comprising the following steps:

[0007] 1) After removing the seeds from the biomass soapberry, wash it with deionized water and ethanol, dry it, and then mechanically grind it to obtain biomass powder;

[0008] 2) Add nanodiamond powder to the biomass powder at a ratio of 0.1wt% to 1wt%, grind and mix to obtain nanodiamond / biomass mixed powder; the particle size of the nanodiamond powder is 5 to 20 nm;

[0009] 3) Soak the nanodiamond / biomass mixed powder obtained in step 2) in deionized water with a concentration of 1.5 to 2.5 wt% in the deionized water, and place it in a high-pressure reactor lined with polytetrafluoroethylene. Perform a hydrothermal reaction at 120°C to 240°C for 8 to 24 hours. After the reactor cools down naturally, take it out and dry the sample.

[0010] 4) Mix potassium hydroxide with the sample obtained in step 3) at a mass ratio of 1:(1-3), disperse in deionized water for activation, and then transfer to an oven to dry at 80°C;

[0011] 5) Carbonize the sample treated in step 4) at 700–900°C for 1.5–2.5 hours in a protective atmosphere;

[0012] 6) The composite material is treated with hydrochloric acid to remove inorganic impurities, then washed with deionized water until the solution becomes neutral, and dried and ground at 60-100℃ to obtain porous hollow carbon microspheres / nanodiamond lithium-ion battery anode material.

[0013] Step 4) The concentration of potassium hydroxide in the dispersed deionized water is 1.4wt% to 4.9wt%; the activation time of potassium hydroxide is 6 to 12 hours.

[0014] Step 5) The heating rate during carbonization is 5℃ / min.

[0015] The specific steps for hydrochloric acid treatment in step 6) are as follows: Immerse the composite material in 1.0-5.0M hydrochloric acid for 3-6 hours.

[0016] The method for preparing lithium-ion battery anodes using porous hollow carbon microspheres / nanodiamond lithium-ion battery anode materials is as follows:

[0017] 10 wt% binder, 80 wt% porous hollow carbon microspheres / nanodiamond anode material, and 10 wt% conductive agent were mixed and solvent was added. The mixture was stirred with a magnetic stirrer to form a viscous fluid. The viscous fluid was coated onto a current collector and dried under vacuum. Finally, it was cut into electrode shapes and compacted to obtain a lithium-ion battery anode.

[0018] The porous hollow carbon microspheres / nanodiamond lithium-ion battery anode material obtained by the method of the present invention has a porous and hollow structure on the surface of the carbon spheres, with the size of a single carbon sphere being 2 to 6 μm, and nanodiamonds distributed on the surface of the carbon spheres to form a porous hollow carbon microsphere / nanodiamond composite structure.

[0019] The beneficial effects of this invention are:

[0020] The porous hollow carbon microspheres / nanodiamond lithium-ion battery anode material prepared by this invention exhibits excellent electrochemical performance. Lithium-ion batteries prepared using this porous hollow carbon microspheres / nanodiamond lithium-ion battery anode material achieve a specific capacity of 700–800 mA hg after 1500 cycles at a 2C current density. -1 At a current density of 5C, after 6000 cycles, the specific capacitance can reach 350-450 mA hg. -1 Even at a current density of 20C, after 13,000 cycles, the specific capacitance can still reach 100-120 mA hg. -1 It features long-term cycle stability and high capacity performance.

[0021] This invention applies nanodiamond to the synthesis of porous hollow carbon sphere anode materials. Its preparation method has the advantages of simple process, easy implementation and easy scale-up, and is expected to be mass-produced in the future. Attached Figure Description

[0022] Figure 1 Scanning electron microscope (SEM) and high-resolution transmission electron microscope (HTEM) images of the porous hollow carbon microspheres / nanodiamond anode material (PHCS-ND) prepared in Example 1.

[0023] Figure 2 The porous hollow carbon microspheres / nanodiamond anode material (PHCS-ND) prepared in Example 1 is shown in the transmission electron microscope (TEM) image.

[0024] Figure 3 The image shown is a scanning electron microscope (SEM) image of the #PBC sample without nanodiamond carbon material in Comparative Example 1.

[0025] Figure 4 The images show transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HTEM) images of the #PBC sample without nanodiamond carbon material in Comparative Example 1.

[0026] Figure 5 To utilize carbon materials, the porous hollow carbon microspheres / nanodiamond anode material prepared in Example 1 was applied to a lithium-ion battery, and the voltage-to-capacity curve at 0.2C was shown.

[0027] Figure 6 To utilize carbon materials, the porous hollow carbon microspheres / nanodiamond anode material prepared in Example 1 was applied to lithium-ion batteries at constant rates of 2C, 5C, and 20C, as shown in the charge-discharge cycle curves.

[0028] Figure 7 To utilize carbon materials, the porous hollow carbon microspheres / nanodiamond anode material prepared in Example 1 is shown in the charge-discharge cycle curves of a lithium-ion battery at varying rates.

[0029] Figure 8 Impedance diagram of a lithium-ion battery using the porous hollow carbon microspheres / nanodiamond anode material prepared in Example 1, for the purpose of using carbon materials. Detailed Implementation

[0030] The present application will be described in further detail below with reference to the accompanying drawings and embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present application and are not intended to limit it in any way.

[0031] Example 1: Preparation of porous hollow carbon microspheres / nanodiamond anode material (PHCS-ND)

[0032] 1) The biomass precursor is selected from soapberry peel (rich in cellulose, hemicellulose, tea saponin, saponins, etc.). After removing the seeds from the soapberry, it is washed and dried, and then crushed into soapberry peel powder by a pulverizer. Nanodiamond powder (ND) is added to the soapberry peel powder at a ratio of 0.1wt% to 1wt% and then ground and mixed to obtain nanodiamond / biomass mixed powder; wherein, the particle size of the nanodiamond powder is 5 to 20 nm.

[0033] 2) Soak the obtained nanodiamond / biomass mixed powder in deionized water (the concentration of nanodiamond / biomass mixed powder in deionized water is 2wt%), and put it into a high-pressure reactor lined with polytetrafluoroethylene. Perform hydrothermal reaction at 120℃~240℃ for 8~24 hours. After the reactor cools down naturally, take it out and dry the sample.

[0034] 3) Mix potassium hydroxide with the sample obtained in step 3) at a mass ratio of 1:(1-3), disperse in deionized water for activation, and then transfer to an oven to dry at 80°C; the concentration of potassium hydroxide in the deionized water after dispersion is 1.4wt% to 4.9wt%, and the activation time is 6 to 12h;

[0035] 4) High-temperature carbonization and pyrolysis in an argon protective atmosphere (99.99% argon gas, passing through the chamber at 50 sccm), heating to 700-900℃ at a heating rate of 5℃ / min, and cooling to room temperature under argon flow to obtain nanodiamond and soapberry peel-derived carbon composite materials.

[0036] 5) Immerse the composite material in 1.0-5.0M HCl solution for 3-6 hours to remove inorganic impurities, then wash with deionized water until the solution becomes neutral, dry and grind at 60-100℃ to obtain porous hollow carbon microspheres / nanodiamond anode material, denoted as PHCS-ND.

[0037] Comparative Example 1: Carbon material (PBC) without added nanodiamonds

[0038] For comparison, the same method as in Example 1 was used in the comparative example, except that no nano-diamond powder was added, and the resulting carbon material was designated as the comparative sample #PBC.

[0039] The scanning electron microscope (SEM) image of the porous hollow carbon microspheres / nanodiamond anode material (PHCS-ND) obtained in Example 1 is shown below. Figure 1 Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) images are shown below. Figure 2 ;like Figure 1 and Figure 2 As shown, the porous hollow carbon microspheres / nanodiamond anode material has a size of 2-6 μm, with the nanodiamonds distributed on the carbon material substrate. The SEM image of the carbon material sample #PBC in Comparative Example 1 without added nanodiamonds is shown below. Figure 3 TEM and HRTEM Figure 4 Compared to sample #PHCS-ND, sample #PBC exhibits less spherical formation.

[0040] Example 2: Fabrication of lithium-ion battery components using carbon anode and porous hollow carbon microspheres / nanodiamond anode materials

[0041] The negative electrode of the lithium-ion battery is composed of 80 wt% active material (PHCS-ND), 10 wt% binder (polyvinylidene fluoride, PVDF), and 10 wt% conductive agent carbon black. After mixing and grinding the three components for 30 minutes, the mixture is placed in a container, and a certain amount of 1-methyl-2-pyrrolidone (NMP) solvent is added. The container is then placed on a magnetic stirrer and stirred at a constant speed for 4–8 hours until the mixture becomes a viscous fluid. Using copper foil as the current collector, the above viscous mixture is coated onto the copper foil, ensuring a uniform coating density. The temperature of a vacuum drying oven is set to 120°C, and the copper foil coating is placed inside the drying oven for 12 hours. After 12 hours, it is removed and ready for use. The prepared copper foil coating is cut into several electrode discs using a special cutting die. The active material on the electrode discs is then compacted using a pressing machine to ensure full contact with the current collector and prevent material detachment. Before assembly, the mass of the electrode discs is weighed for subsequent calculations of specific capacity parameters, etc.

[0042] Example 3: Fabrication and Performance of Lithium-ion Batteries

[0043] The lithium-ion batteries assembled during testing were CR-2025 button cells. A bio-carbon and nanodiamond composite material was used as the negative electrode, and a lithium sheet as the reference electrode. The battery, along with its corresponding positive and negative electrode shells, gaskets, springs, separators, and electrolytes, was manufactured according to lithium-ion battery production specifications. The batteries were encapsulated in an anhydrous and oxygen-free environment, and their electrochemical performance was then tested using the Blue Electric testing system. The lithium-ion half-cells prepared using sample #PBC and sample #PHCS-ND were labeled S1 and S2, respectively.

[0044] 1) Charge and discharge performance test

[0045] Batteries S1 and S2 prepared in Example 5 were tested in the Blue Electricity Test System. At 25°C, the batteries were discharged to 0.01V at a certain current density. After the discharge was completed, the batteries were left to stand for 3 minutes. Then, they were charged to 3V at a certain current density. After the charging was completed, the batteries were left to stand for 3 minutes and then discharged to 0.01V at the same constant current density. After the batteries were discharged, they were left to stand for 3 minutes and then charged under the same conditions.

[0046] A charge-discharge test was conducted on a half-cell with PHCS-ND as the negative electrode at a current density of 0.2C, and the results are as follows. Figure 5 As shown, at a current density of 0.2C, the capacity of the PHCS-ND battery is higher than that of the pure bio-carbon lithium-ion battery.

[0047] Cyclic performance tests were conducted on the half-cell with PHCS-ND as the negative electrode at current densities of 2C, 5C, and 20C. The results are as follows: Figure 6 As shown, at a current density of 2C, after 1500 cycles, the capacity of the battery containing PHCS-ND reaches 798.8 mA hg as the structure gradually activates. -1 Its high reversible capacity exceeds that of pure bio-carbon batteries (448.8 mA hg). -1 After 6000 cycles at a current density of 5C, the reversible capacity of the PHCS-ND composite material, with gradual structural activation, is 430.9 mA hg. -1 It has a higher capacity than pure bio-carbon lithium-ion batteries (225.1 mA hg). -1 After 13,000 cycles at a high current density of 20C, the reversible capacity of the PHCS-ND composite material is 113.7 mA hg. -1 It has a higher capacity than pure bio-carbon lithium-ion batteries (73.6 mA hg). -1 ).

[0048] Variable-rate discharge was performed at 0.2C, 0.5C, 2C, 5C, and 10C to test the reversible specific capacity of the nanodiamond / carbon anode battery. Figure 7As shown, it exhibits superior rate performance, with capacities of 729.3, 597.1, 431.3, 327.5, and 256.5 mA hg at 0.2C, 0.5C, 2C, 5C, and 10C rates, respectively. -1 Furthermore, its capacity was higher than that of non-diamond batteries at every rate testing stage. When the current density returned to 0.2C, its capacity remained at 691.1 mA hg. -1 The performance is superior to that of bio-based carbon anode materials. This demonstrates that nanodiamond / carbon composite anode material batteries possess high capacity and high stability.

[0049] 2) Electrochemical impedance spectroscopy

[0050] The impedance spectra of batteries prepared using samples #PBC and #PHCS-ND as negative electrode materials are as follows: Figure 8 As shown, the voltage range is 0-3V. Obviously, the impedance of the porous hollow carbon microsphere / nanodiamond anode material is less than that of the pure biomass carbon anode material. This indicates that the introduction of ND increases the conductivity of ions and improves the cycle performance of lithium-ion batteries.

Claims

1. A porous hollow carbon microsphere / nanodiamond lithium-ion battery anode material, characterized in that, The carbon microspheres in the material have a porous and hollow surface, with individual carbon microspheres ranging in size from 2 to 6 µm. Nanodiamonds are distributed on the surface of the carbon microspheres, forming a porous and hollow carbon microsphere / nanodiamond composite structure. The preparation method of the material is as follows: 1) After removing the seeds from the biomass soapberry, wash it with deionized water and ethanol, dry it, and then mechanically grind it to obtain biomass powder; 2) Add nanodiamonds to the biomass powder at a ratio of 0.1wt% to 1wt%, grind and mix to obtain nanodiamond / biomass mixed powder; the particle size of the nanodiamonds is 5 to 20 nm; 3) Soak the nanodiamond / biomass mixed powder obtained in step 2) in deionized water, with a concentration of 1.5~2.5wt% in the deionized water; place it in a high-pressure reactor lined with polytetrafluoroethylene and perform a hydrothermal reaction at 120℃~240℃ for 8~24 hours. After the reactor cools down naturally, take it out and dry the sample. 4) Mix potassium hydroxide with the sample obtained in step 3) at a mass ratio of 1:(1~3), disperse in deionized water for activation, and then transfer to an oven to dry at 80°C; 5) Carbonize the sample treated in step 4) at 700~900℃ for 1.5~2.5 hours in a protective atmosphere; 6) The composite material is treated with hydrochloric acid to remove inorganic impurities, then washed with deionized water until the solution becomes neutral, dried and ground at 60~100℃ to obtain porous hollow carbon microspheres / nanodiamond lithium-ion battery anode material.

2. The porous hollow carbon microsphere / nanodiamond lithium-ion battery anode material according to claim 1, characterized in that, Step 4) The concentration of potassium hydroxide in the deionized water after dispersion is 1.4wt%~4.9wt%.

3. The porous hollow carbon microsphere / nanodiamond lithium-ion battery anode material according to claim 1, characterized in that, Step 4) The activation treatment with potassium hydroxide takes 6 to 12 hours.

4. The porous hollow carbon microsphere / nanodiamond lithium-ion battery anode material according to claim 1, characterized in that, Step 5) The heating rate during carbonization is 5℃ / min.

5. The porous hollow carbon microsphere / nanodiamond lithium-ion battery anode material according to claim 1, characterized in that, The specific steps for hydrochloric acid treatment in step 6) are as follows: Immerse the composite material in 1.0~5.0 M hydrochloric acid for 3~6 h.

6. The use of the porous hollow carbon microspheres / nanodiamond lithium-ion battery anode material as described in claim 1 for preparing lithium-ion battery anodes.

7. The use of the porous hollow carbon microspheres / nanodiamond lithium-ion battery anode material according to claim 6, characterized in that, 10 wt% binder, 80 wt% of the porous hollow carbon microspheres / nanodiamond lithium-ion battery anode material, and 10 wt% conductive agent were mixed and solvent was added. The mixture was stirred with a magnetic stirrer to form a viscous fluid. The viscous fluid was coated onto a current collector and dried under vacuum. Finally, it was cut into electrode shapes and compacted to obtain the lithium-ion battery anode.

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