Porous carbon negative electrode material, preparation method thereof and lithium ion battery

Abstract

The application relates to the technical field of lithium ion batteries, in particular to a preparation method of a porous carbon negative electrode material, which comprises the following steps: mixing starch and a eutectic solvent at 60-80 DEG C to obtain a precursor; and performing grinding on the precursor after calcination of the precursor at 300-400 DEG C and 800-900 DEG C under an inert atmosphere to obtain the porous carbon negative electrode material. The preparation method of the porous carbon negative electrode material provided by the application introduces a eutectic solvent, which can destroy the hydrogen bonds between and in starch molecules, change the arrangement of the starch molecules from close order to disorder, homogeneously disperse the starch and prevent the agglomeration of the starch; on the other hand, the gas generated in the calcination process of the eutectic solvent can realize the porosity of the carbon material, improve the specific surface area and lithium storage performance of the carbon negative electrode material and improve the initial efficiency.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a porous carbon anode material, its preparation method, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries are currently important energy storage devices. Due to their advantages of high energy density and long cycle life, they have been widely used in smartphones, portable appliances, medical electronics, power tools, and electric vehicles in recent years.

[0003] Among them, the anode material is an important component of lithium-ion batteries and one of the key factors determining the overall performance of lithium-ion batteries. Lithium-ion battery anode materials are generally graphite, amorphous carbon, etc., especially hard carbon among amorphous carbons, which generally have higher lithium storage capacity than graphite materials due to the presence of many nanopores, and have become an increasingly popular research hotspot in anode materials in recent years.

[0004] Common raw materials for the industrial production of hard carbon anode materials mainly include non-renewable fossil resources such as coal, resin, and pitch. Preparation methods primarily include pyrolysis and emulsion methods. These methods are not only complex in terms of process conditions or procedures, but also detrimental to environmental protection. Starch, a typical representative of polysaccharides, is a widely available and inexpensive renewable natural carbon source, making it an important raw material for carbon material preparation. However, due to the unique structure of starch, starch-based hard carbon anode materials prepared using starch as a carbon source have relatively low initial efficiency, failing to fully utilize their lithium storage capacity.

[0005] Therefore, improving the initial efficiency of starch-based hard carbon anode materials is a technical problem that urgently needs to be solved. Summary of the Invention

[0006] To address the issue of low initial efficiency in existing starch-based hard carbon anode materials, this invention provides a method for preparing porous carbon anode materials. This method synthesizes porous carbon anode materials using a low eutectic solvent, thereby improving the specific surface area and lithium storage performance of carbon anode materials and solving the problem of low initial efficiency in existing amorphous carbon anode materials.

[0007] The technical solution adopted by this invention to solve its technical problem is:

[0008] A method for preparing a porous carbon anode material includes the following steps: mixing starch with a eutectic solvent at 60-80°C to obtain a precursor; calcining the precursor sequentially at 350-550°C and 750-950°C under an inert atmosphere, followed by grinding to obtain the porous carbon anode material.

[0009] Optionally, the mass ratio of the starch to the eutectic solvent is (0.8-1.5):1.

[0010] Optionally, the eutectic solvent is a hydrogen bond donor-choline halide-lithium halide.

[0011] Optionally, the hydrogen bond donor-halogenated choline-lithium halide is obtained by mixing the hydrogen bond donor, choline halide, and lithium halide at 70-90°C.

[0012] Optionally, the molar ratio of the hydrogen bond donor, the choline halide, and the lithium halide is 1:2:1.

[0013] Optionally, the hydrogen bond donor is selected from at least one of oxalic acid and glycerol.

[0014] Optionally, the halogenated choline is selected from at least one of fluorinated choline, choline chloride, and choline bromide.

[0015] Optionally, the lithium halide is selected from at least one of lithium fluoride, lithium chloride, and lithium bromide.

[0016] Another object of the present invention is to provide a porous carbon anode material, which is prepared by the method for preparing porous carbon anode materials as described above.

[0017] Another object of the present invention is to provide a lithium-ion battery comprising the porous carbon anode material as described above.

[0018] The beneficial effects of this invention are:

[0019] The method for preparing porous carbon anode materials provided by this invention introduces a eutectic solvent, which on the one hand breaks the hydrogen bonds between and within starch molecules, changing the arrangement of starch molecules from tightly ordered to scattered and disordered, thus homogeneously dispersing the starch and preventing starch agglomeration; on the other hand, the gas generated during the calcination of the eutectic solvent is used to realize the porosity of the carbon material, thereby improving the specific surface area and lithium storage performance of the carbon anode material and increasing the first-pass efficiency. Detailed Implementation

[0020] The present invention will now be described in further detail. The embodiments described below are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0021] Currently, the primary efficiency of starch-based hard carbon anode materials is typically improved through porosimetry. A common process for preparing porous starch involves using amylase to corrode starch granules, starting from the amorphous regions and working inwards to create pores, resulting in irregular pits or even holes on the starch surface. However, this enzymatic method, when using small doses of enzyme, only corrodes the starch granule surface to create pits. These pits are often amorphous regions with poor uniformity, thus offering limited improvement to the electrochemical performance of the anode material.

[0022] To address the problem of low initial efficiency in existing starch-based hard carbon anode materials, this invention provides a method for preparing a porous carbon anode material. The method includes the following steps: mixing starch with a eutectic solvent at 60-80°C, preferably at 65°C, to obtain a precursor; calcining the precursor sequentially at 350-550°C and 750-950°C under an inert atmosphere, preferably at 350°C and 850°C, followed by grinding to obtain the porous carbon anode material.

[0023] Starch is typically a mixture of amylopectin and amylose, a highly crystalline substance with numerous hydrogen bonds between and within molecules, making it difficult to dissolve in water. This invention mixes starch with a eutectic solvent at 60-80°C. The eutectic solvent acts as a gelatinization solvent for the starch, homogeneously dispersing it and dominating the gelatinization process, thus preventing starch agglomeration. Further calcination utilizes the gas generated during the calcination process to create pores through corrosion, resulting in porous carbon materials. This improves the specific surface area and lithium storage performance of carbon anode materials, enhancing their initial efficiency.

[0024] The method for preparing porous carbon anode materials provided by this invention introduces a eutectic solvent, which on the one hand breaks the hydrogen bonds between and within starch molecules, changing the arrangement of starch molecules from tightly ordered to scattered and disordered, thus homogeneously dispersing the starch and preventing starch agglomeration; on the other hand, the gas generated during the calcination of the eutectic solvent is used to realize the porosity of the carbon material, thereby improving the specific surface area and lithium storage performance of the carbon anode material and increasing the first-pass efficiency.

[0025] Compared to the existing technology that uses amylase to corrode starch granules to prepare porous starch, and then further prepares porous starch-based anode materials, the anode material prepared in this invention first gelatinizes the starch with a eutectic solvent, and then further porousens the carbon material by using the gas generated by the eutectic solvent during calcination. Therefore, in the carbon anode material provided by this invention, the porous structure is generated from the inside of the carbon material to the outside, and the porous distribution is more uniform, which is more conducive to improving the electrochemical performance of the anode material.

[0026] To balance the specific capacity and initial efficiency of the carbon anode material, the present invention preferably uses a mass ratio of starch to eutectic solvent of (0.8-1.5):1, and further preferably a mass ratio of starch to eutectic solvent of 1:1.

[0027] To ensure the electrochemical performance of the porous carbon anode material, the present invention preferably uses a eutectic solvent of hydrogen bond donor-choline halide-lithium halide.

[0028] Among them, the hydrogen bond donor in the eutectic solvent can bind with the precursor, namely starch, through hydrogen bonds, making the eutectic solvent difficult to be washed away by deionized water. In the subsequent calcination process, it can effectively inhibit the agglomeration of starch particles, which is beneficial to the porosity of carbon materials. The gas produced after the carbonization of choline halide is an acidic component such as nitrogen oxides, hydrohalic acids, carbon dioxide, and carbon monoxide, which produces a corrosion and pore-forming effect, thereby increasing the specific surface area and lithium storage performance of carbon anode materials. Furthermore, the carbon dioxide gas produced by the thermal decomposition of hydrogen bond donor in the hydrogen bond donor-choline halide-lithium halide group will further promote the porosity of carbon materials. The lithium halide in the eutectic solvent can be embedded in the micropores of porous carbon during the pore-forming process, playing a role in lithium replenishment, which is beneficial to the formation of SEI film.

[0029] The present invention preferably obtains the hydrogen bond donor-halogenated choline-lithium halide by mixing the hydrogen bond donor, choline halide, and lithium halide at 70-90°C, and more preferably by mixing the hydrogen bond donor, choline halide, and lithium halide at 80°C.

[0030] Specifically, the preferred molar ratio of hydrogen bond donor, choline halide, and lithium halide in the eutectic solvent is 1:2:1.

[0031] To ensure the initial efficiency of the porous carbon anode material, the hydrogen bond donor is preferably selected from at least one of oxalic acid and glycerol; and the halogenated choline is preferably selected from at least one of fluorinated choline, choline chloride, and choline bromide.

[0032] To facilitate the formation of the SEI film, the lithium halide of the present invention is preferably selected from at least one of lithium fluoride, lithium chloride, and lithium bromide.

[0033] The starch used in this invention is preferably selected from at least one of cereal starch, potato starch, and legume starch.

[0034] Specifically, the preparation method of the porous carbon anode material in this invention can be carried out according to the following process:

[0035] S1: First, stir the hydrogen bond donor, choline halide, and lithium halide in a molar ratio of 1:2:1 in a stirrer at 70-90℃ for 3-5 hours to obtain a eutectic solvent hydrogen bond donor-choline halide-lithium halide.

[0036] S2: Weigh starch and eutectic solvent at a mass ratio of (0.8-1.5):1 and stir in a stirrer at 60-80℃ for 3-5 hours. Then sonicate the resulting mixture for 1-2 hours to obtain the precursor.

[0037] S3: Heat the precursor to 350-550℃ in an inert gas protective atmosphere in a tube furnace, remove tar and gas, and then heat it again to 750-950℃ and hold it for 5-8 hours.

[0038] S4: Grind the product from step S3 to obtain the target product of the present invention, namely, porous carbon anode material.

[0039] Another object of the present invention is to provide a porous carbon anode material, which is prepared by the method for preparing porous carbon anode materials as described above.

[0040] The porous carbon anode material provided by this invention introduces a eutectic solvent during the preparation process. On the one hand, this breaks the hydrogen bonds between and within starch molecules, changing the arrangement of starch molecules from tightly ordered to scattered and disordered, thus homogeneously dispersing the starch and preventing starch agglomeration. On the other hand, the gas generated during the calcination of the eutectic solvent is used to achieve porosity of the carbon material, thereby increasing the specific surface area and lithium storage performance of the carbon anode material and improving the first-pass efficiency.

[0041] Another object of the present invention is to provide a lithium-ion battery comprising the porous carbon anode material as described above.

[0042] The lithium-ion battery provided by this invention uses a porous carbon anode material in which a eutectic solvent is introduced during the preparation process. On the one hand, this breaks the hydrogen bonds between and within starch molecules, changing the arrangement of starch molecules from tightly ordered to scattered and disordered, thus homogeneously dispersing the starch and preventing starch agglomeration. On the other hand, the gas generated during the calcination of the eutectic solvent is used to achieve porosity of the carbon material, thereby increasing the specific surface area and lithium storage performance of the carbon anode material and improving the initial efficiency.

[0043] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0044] Example 1

[0045] This embodiment provides a method for preparing a porous carbon anode material, which includes the following steps:

[0046] S1: First, oxalic acid, choline chloride, and lithium chloride are stirred in a stirrer at 80°C for 5 hours in a molar ratio of 1:2:1 to obtain the eutectic solvent oxalic acid-choline chloride-lithium chloride.

[0047] S2: Weigh corn starch and eutectic solvent oxalic acid-choline chloride-lithium chloride at a mass ratio of 1:1 and stir in a stirrer at 65°C for 3 hours. Then sonicate the resulting mixture for 2 hours to obtain the precursor.

[0048] S3: Heat the precursor to 350°C in an argon protective atmosphere in a tube furnace, hold for 7 hours, remove tar and gas, and then heat to 850°C again and hold for 6 hours.

[0049] S4: Grind the product from step S3 to obtain the target product of the present invention, namely, porous carbon anode material.

[0050] Example 2

[0051] This embodiment provides a method for preparing a porous carbon anode material, which includes the following steps:

[0052] S1: First, glycerol, fluorinated choline, and lithium fluoride are stirred in a stirrer at 80°C for 4 hours in a molar ratio of 1:2:1 to obtain the eutectic solvent glycerol-fluorinated choline-lithium fluoride.

[0053] S2: Weigh wheat starch and eutectic solvent glycerol-fluorinated choline-lithium fluoride in a mass ratio of 1:1 and stir in a stirrer at 65°C for 4 hours. Then sonicate the resulting mixture for 1 hour to obtain the precursor.

[0054] S3: Heat the precursor to 450°C in an argon protective atmosphere in a tube furnace, hold for 6 hours, remove tar and gas, and then heat to 950°C again and hold for 8 hours.

[0055] S4: Grind the product from step S3 to obtain the target product of the present invention, namely, porous carbon anode material.

[0056] Example 3

[0057] This embodiment provides a method for preparing a porous carbon anode material, which includes the following steps:

[0058] S1: First, glycerol, choline bromide and lithium bromide are stirred in a stirrer at 80°C for 3 hours in a molar ratio of 1:2:1 to obtain the eutectic solvent glycerol-choline bromide-lithium bromide;

[0059] S2: Weigh potato starch and eutectic solvent glycerol-choline bromide-lithium bromide at a mass ratio of 1:1, stir in a stirrer at 65°C for 4 hours, and then sonicate the resulting mixture for 2 hours to obtain the precursor;

[0060] S3: Heat the precursor to 550°C in an argon protective atmosphere in a tube furnace, hold for 5 hours, remove tar and gas, and then heat to 850°C again and hold for 5-8 hours.

[0061] S4: Grind the product from step S3 to obtain the target product of the present invention, namely, porous carbon anode material.

[0062] Example 4

[0063] This embodiment provides a method for preparing a porous carbon anode material, which includes the following steps:

[0064] S1: First, oxalic acid, choline chloride and lithium chloride are stirred in a stirrer at 80°C for 3 hours in a molar ratio of 1:2:1 to obtain the eutectic solvent oxalic acid-choline chloride-lithium chloride.

[0065] S2: Weigh wheat starch and eutectic solvent oxalic acid-choline chloride-lithium chloride at a mass ratio of 1:1 and stir in a stirrer at 65°C for 4 hours. Then sonicate the resulting mixture for 2 hours to obtain the precursor.

[0066] S3: Heat the precursor to 350°C in an argon protective atmosphere in a tube furnace, hold for 7 hours, remove tar and gas, and then heat to 750°C again and hold for 6 hours.

[0067] S4: Grind the product from step S3 to obtain the target product of the present invention, namely, porous carbon anode material.

[0068] Example 5

[0069] This embodiment provides a method for preparing a porous carbon anode material, which includes the following steps:

[0070] S1: First, oxalic acid, choline chloride, and lithium chloride are stirred in a stirrer at 80°C for 5 hours in a molar ratio of 1:2:1 to obtain the eutectic solvent oxalic acid-choline chloride-lithium chloride.

[0071] S2: Weigh corn starch and eutectic solvent oxalic acid-choline chloride-lithium chloride at a mass ratio of 0.8:1 and stir in a stirrer at 65°C for 3 hours. Then sonicate the resulting mixture for 2 hours to obtain the precursor.

[0072] S3: Heat the precursor to 350°C in an argon protective atmosphere in a tube furnace, hold for 8 hours, remove tar and gas, and then heat to 850°C again and hold for 6 hours.

[0073] S4: Grind the product from step S3 to obtain the target product of the present invention, namely, porous carbon anode material.

[0074] Example 6

[0075] This embodiment provides a method for preparing a porous carbon anode material, which includes the following steps:

[0076] S1: First, oxalic acid, choline chloride, and lithium chloride are stirred in a stirrer at 80°C for 5 hours in a molar ratio of 1:2:1 to obtain the eutectic solvent oxalic acid-choline chloride-lithium chloride.

[0077] S2: Weigh corn starch and eutectic solvent oxalic acid-choline chloride-lithium chloride at a mass ratio of 1.5:1 and stir in a stirrer at 65°C for 3 hours. Then sonicate the resulting mixture for 2 hours to obtain the precursor.

[0078] S3: Heat the precursor to 350°C in an argon protective atmosphere in a tube furnace, hold for 7 hours, remove tar and gas, and then heat to 850°C again and hold for 6 hours.

[0079] S4: Grind the product from step S3 to obtain the target product of the present invention, namely, porous carbon anode material.

[0080] Comparative Example 1

[0081] This comparative example provides a method for preparing a negative electrode material, including the following steps:

[0082] S1: The corn starch is heated to 350°C in a tube furnace under an argon protective atmosphere and held for 7 hours to remove tar and gas. Then, it is heated to 850°C again and held for 6 hours.

[0083] S2: Grind the product from step S1 to obtain the negative electrode material.

[0084] Comparative Example 2

[0085] This comparative example provides a method for preparing a negative electrode material, including the following steps:

[0086] S1: First, oxalic acid and choline chloride are stirred in a stirrer at 80°C for 5 hours in a molar ratio of 1:2 to obtain the eutectic solvent oxalic acid-choline chloride.

[0087] S2: Weigh corn starch and eutectic solvent oxalic acid-choline chloride at a mass ratio of 1:1 and stir in a stirrer at 65°C for 3 hours. Then sonicate the resulting mixture for 2 hours to obtain the precursor.

[0088] S3: Heat the precursor to 350°C in an argon protective atmosphere in a tube furnace, hold for 7 hours, remove tar and gas, and then heat to 850°C again and hold for 6 hours.

[0089] S4: Grind the product from step S3 to obtain the negative electrode material.

[0090] Comparative Example 3

[0091] This comparative example provides a method for preparing a negative electrode material, including the following steps:

[0092] S1: First, choline chloride and lithium chloride are stirred in a stirrer at 80°C for 5 hours in a molar ratio of 2:1 to obtain the eutectic solvent choline chloride-lithium chloride.

[0093] S2: Weigh corn starch and eutectic solvent choline chloride-lithium chloride at a mass ratio of 1:1 and stir in a stirrer at 65°C for 3 hours. Then sonicate the resulting mixture for 2 hours to obtain the precursor.

[0094] S3: Heat the precursor to 350°C in an argon protective atmosphere in a tube furnace, hold for 7 hours, remove tar and gas, and then heat to 850°C again and hold for 6 hours.

[0095] S4: Grind the product from step S3 to obtain the negative electrode material.

[0096] Comparative Example 4

[0097] This comparative example provides a method for preparing a negative electrode material, including the following steps:

[0098] S1: First, oxalic acid and lithium chloride are stirred in a stirrer at 80°C for 5 hours in a molar ratio of 1:1 to obtain a mixture of oxalic acid and lithium chloride.

[0099] S2: Weigh corn starch and the mixture of oxalic acid-lithium chloride at a mass ratio of 1:1 and stir in a stirrer at 65°C for 3 hours. Then sonicate the resulting mixture for 2 hours to obtain the precursor.

[0100] S3: Heat the precursor to 350°C in an argon protective atmosphere in a tube furnace, hold for 7 hours, remove tar and gas, and then heat to 850°C again and hold for 6 hours.

[0101] S4: Grind the product from step S3 to obtain the negative electrode material.

[0102] The negative electrode materials prepared in the above embodiments and comparative examples were used to prepare coin cells using the coin cell process, and the results were tested. The test results are shown in Table 1.

[0103] The manufacturing process of button cells is as follows:

[0104] The negative electrode materials prepared in the above embodiments and comparative examples were used as negative electrode active materials. They were mixed with vinylidene fluoride (PVDF) (dissolved in N-methylpyrrolidone) and conductive carbon black in a mass ratio of 90:5:5. The mixture was coated into an electrode film and dried in a vacuum drying oven at 120°C for 12 hours. After rolling and punching, the negative electrode sheet was obtained. Using PP film as the coin cell separator and lithium metal sheet as the counter electrode, the hard carbon negative electrode sheet obtained above was assembled into a 2430 button cell in a glove box. Its electrochemical performance was tested (test voltage (0-3) V, current 0.05 C). The results are shown in Table 1.

[0105] Table 1

[0106]

[0107] As can be seen from the data in the table above, the anode materials prepared in each embodiment of the present invention all have high specific capacity and excellent first-pass efficiency.

[0108] The technical solution provided in Comparative Example 1 involves directly calcining starch. Due to severe starch agglomeration and the inability to achieve porosity, the specific capacity and initial efficiency of the prepared negative electrode material are significantly reduced.

[0109] The technical solution provided in Comparative Example 2 does not add lithium halide to the eutectic solvent. Although it can achieve corrosion and pore formation during calcination, it cannot simultaneously replenish lithium during the pore formation process. As a result, the prepared anode material has a high specific capacity but a low initial efficiency.

[0110] The technical solution provided in Comparative Example 3 uses choline chloride and lithium chloride as eutectic solvents. However, it cannot break the hydrogen bonds between starch molecules and cannot effectively alleviate starch agglomeration. As a result, the pores are insufficient, and although the initial efficiency of the prepared negative electrode material is improved compared with Comparative Example 1, the specific capacity and initial efficiency are significantly different from those of Example 1.

[0111] The technical solution provided in Comparative Example 4 uses a mixture of oxalic acid and lithium chloride to replace the eutectic solvent. Although oxalic acid is beneficial for porosimetry, due to the lack of choline chloride, lithium chloride has no effective linkage. As a result, although the specific capacity of the prepared negative electrode material is significantly improved compared with Comparative Example 1, the specific capacity and initial efficiency are significantly different from those of Example 1 because lithium chloride cannot be effectively retained in the channels.

[0112] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for preparing a porous carbon negative electrode material, characterized by, The method comprises the following steps: mixing starch and a eutectic solvent at 60-80 DEG C to obtain a precursor; and performing calcination on the precursor at 350-550 DEG C and 750-950 DEG C in an inert atmosphere, and then performing grinding to obtain a porous carbon negative electrode material. The eutectic solvent is a hydrogen bond donor-halogenated choline-halogenated lithium. The hydrogen bond donor is at least one of oxalic acid and glycerol.

2. The method for preparing a porous carbon negative material according to claim 1, wherein, The mass ratio of the starch to the eutectic solvent is (0.8-1.5):

1.

3. The method for preparing a porous carbon negative electrode material according to claim 1, wherein The hydrogen bond donor-halogenated choline-halogenated lithium is obtained by mixing a hydrogen bond donor, halogenated choline and halogenated lithium at 70-90 DEG C.

4. The method for preparing a porous carbon negative electrode material according to claim 3, characterized by, The molar ratio of the hydrogen bond donor, the halogenated choline and the halogenated lithium is 1:2:

1.

5. The method for preparing a porous carbon negative electrode material according to claim 3, wherein The halogenated choline is at least one of fluorinated choline, chlorinated choline and brominated choline.

6. The method for preparing a porous carbon negative material according to claim 3, wherein The halogenated lithium is at least one of fluorinated lithium, chlorinated lithium and brominated lithium.

7. A porous carbon negative electrode material, characterized by, The porous carbon negative electrode material is prepared by the method of any one of claims 1-6.

8. A lithium-ion battery, characterized by, The porous carbon negative electrode material of claim 7.

Images