High initial efficiency hard carbon composite material, preparation method and application thereof

Abstract

The application relates to the technical field of secondary batteries, in particular to a hard carbon composite material with high initial efficiency and a preparation method and application thereof. The preparation method comprises the following steps: S1. adding lithium carboxymethyl cellulose into a hydrocarbon aqueous solution and uniformly dispersing, continuously adding a boron-based crosslinking agent and a pore-forming agent, vacuum drying the mixture, and obtaining a precursor material; S2. heating the precursor material to obtain a porous precursor material; and S3. transferring the porous precursor material into a tube furnace, introducing a carbon source mixed gas, and obtaining a hard carbon composite material. The lithium carboxymethyl cellulose is doped in the material and carbonized, the irreversible capacity of the material is reduced, the initial efficiency and the lithium ion conductivity are improved, the shell of the material is coated with heteroatoms, the electronic conductivity of the material is improved, the power performance is improved, the microwave heating is adopted, the porous structure is formed in the material, the sodium storage / lithium storage of the material is improved, and the energy density is improved.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, and in particular to a high-efficiency hard carbon composite material, its preparation method, and its application. Background Technology

[0002] Hard carbon refers to carbon materials that are difficult to graphitize, formed by the thermal decomposition of polymers. Hard carbon possesses an interlaced layered structure with large interlayer spacing, allowing lithium ions to intercalate and deintercalate from different angles, thus increasing the diffusion rate of lithium ions and enabling rapid charge-discharge. The presence of numerous micropores further enhances the lithium intercalation space, resulting in a reversible specific capacity typically ranging from 300 to 800 mAh / g, far exceeding the theoretical capacity of graphite (372 mAh / g). Hard carbon exhibits structural stability and minimal volume expansion during charge-discharge, contributing to excellent long-cycle performance. Its lithium intercalation potential can exceed 0.2V, ensuring good safety. Due to these superior properties, hard carbon is used in HEVs, 48V start-stop batteries, PHEV power batteries, and consumer batteries. However, the fabrication process generates numerous lattice defects within the hard carbon structure, leading to a higher irreversible capacity and reducing the material's initial efficiency. The main measures to improve the initial efficiency of hard carbon materials include increasing the carbonization temperature to reduce porosity, but this will reduce the specific capacity; doping with elements such as phosphorus, but this will increase the voltage plateau and reduce the energy density; while lithium supplementation can not only reduce the irreversible capacity of the material and improve the initial efficiency and energy density, but also improve the lithium ion insertion and extraction rate during charging and discharging, thereby improving the rate capability and cycle performance.

[0003] Chinese patent CN107240680B discloses a hard carbon-metal oxide-soft carbon composite material, its preparation method and application, with an initial coulombic efficiency of 72%. Chinese patent CN113594461B discloses a carbon-silicon composite material, its preparation method and application, with an initial efficiency of up to 87.9%. It can be seen that the initial efficiency of materials in the prior art is difficult to exceed 90%. Summary of the Invention

[0004] To improve the first-pass efficiency of hard carbon materials, this invention involves doping lithium carboxymethyl cellulose into a hard carbon precursor and then carbonizing it to obtain lithium-containing amorphous carbon. This reduces irreversible capacity and heteroatom doping, thereby improving the electronic conductivity of the material and reducing defects, thus enhancing the first-pass efficiency.

[0005] The first aspect of the present invention provides a method for preparing a hard carbon composite material with high first-pass efficiency, the method comprising the following steps:

[0006] S1. Add lithium carboxymethyl cellulose to an aqueous hydrocarbon solution and disperse it evenly. Continue to add boron-based crosslinking agent and pore-forming agent. Vacuum dry the mixture to obtain the precursor material.

[0007] S2. Heat the precursor material to obtain a porous precursor material;

[0008] S3. The porous precursor material is transferred into a tube furnace, and a carbon source mixed gas is introduced to obtain a hard carbon composite material.

[0009] In some embodiments, the hydrocarbon may be selected from at least one of glucose, sucrose, lignin, cellulose, starch, phenolic resin, polyacrylonitrile, and epoxy resin, or may be selected from other water-soluble hydrocarbons, and is not limited thereto. The concentration of the aqueous solution of the hydrocarbon is 1-10 wt%.

[0010] In some embodiments, the mass ratio of lithium carboxymethyl cellulose, hydrocarbon, boron-based crosslinking agent, and pore-forming agent is (10-30):100:(5-15):(1-5).

[0011] The applicant discovered in its research that the addition of lithium carboxymethyl cellulose can reduce the irreversible capacity of the material, improve the first efficiency and lithium-ion conductivity, and enhance the electronic conductivity and power performance by coating it with heteroatoms. When the content of lithium carboxymethyl cellulose is too low, the improvement in the first efficiency of the material is not obvious, while when the amount added is too high, it will increase the alkalinity of the material and reduce the processing performance. Further synergistic addition of boron-based crosslinking agent and pore-forming agent can improve the power performance and specific capacity. In particular, when the mass ratio of the two is (5-15):(1-5), the specific capacity and power performance of the material can be improved more effectively.

[0012] In some embodiments, the pore-forming agent includes at least one selected from calcium ascorbate, magnesium ascorbate, potassium ascorbate, and sodium ascorbate. The specific selection of the above-mentioned pore-forming agent within the system of the present invention can further improve the specific capacity.

[0013] In some embodiments, the boron-based crosslinking agent is prepared by mixing boric acid, p-hydroxybenzaldehyde, sodium carbonate, and cyclohexane under an inert gas atmosphere, heating and stirring to obtain the boron-based crosslinking agent.

[0014] Furthermore, the boron-based crosslinking agent is prepared by mixing boric acid, p-hydroxybenzaldehyde, sodium carbonate, and cyclohexane under an inert gas atmosphere, heating to 50-100°C, and stirring for 6-24 hours to obtain the boron-based crosslinking agent. The boron-based crosslinking agent prepared by the method of this invention relies on its boric acid to create pores and improve specific capacity, while the pores formed after the carbonization of sodium carbonate further enhance specific capacity.

[0015] In some embodiments, the mass ratio of boric acid, p-hydroxybenzaldehyde, sodium carbonate, and cyclohexane is (10-50):(10-50):(1-5):(500-1000).

[0016] Further, S1 includes adding lithium carboxymethyl cellulose to an aqueous hydrocarbon solution and dispersing it evenly, then adding a boron-based crosslinking agent and a pore-forming agent, and reacting it hydrothermally at a temperature of 100-200℃ for 12-24 hours. The mixture is then vacuum dried to obtain the precursor material.

[0017] Furthermore, the heating methods in S2 include, but are not limited to, microwave heating.

[0018] In some embodiments, the carbon source gas mixture includes at least one of ammonia, boron trifluoride, phosphorus trifluoride, and hydrogen sulfide, and at least one of methane, acetylene, ethylene, and ethane.

[0019] Furthermore, the volume ratio of at least one gas selected from ammonia, boron trifluoride, phosphorus trifluoride, and hydrogen sulfide to at least one gas selected from methane, acetylene, ethylene, and ethane is (1-5):10.

[0020] Furthermore, S3 includes transferring the porous precursor material into a tube furnace, introducing an inert gas to purge the air inside the tube, then introducing a mixed gas containing a carbon source at a flow rate of 10-100 mL / min, a temperature of 700-1100℃, and a purging time of 60-600 min, and cooling to room temperature (25℃) to obtain a hard carbon composite material.

[0021] A second aspect of the present invention provides a hard carbon composite material with high first-pass efficiency obtained by the preparation method described above.

[0022] In some embodiments, the initial charge-discharge efficiency of the hard carbon composite material is higher than 96.0%.

[0023] A third aspect of the invention provides the application of the preparation method or the hard carbon composite material in the field of secondary batteries.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1) By doping lithium carboxymethyl cellulose into the material and carbonizing it, the irreversible capacity of the material is reduced, the first efficiency and lithium-ion conductivity are improved; and the electronic conductivity of the material is improved by coating it with heteroatoms to improve the power performance; at the same time, the sodium / lithium storage of the material is improved by using microwave heating to form a porous structure inside, thereby improving the energy density.

[0026] 2) By crosslinking crosslinking agents, pore-forming agents and hydrocarbons to form pores, the amount of lithium or sodium stored in the material is increased. Carboxymethyl cellulose lithium doping reduces defects on the material surface during the crosslinking process and improves the first efficiency. Carboxymethyl cellulose lithium has a binding effect to improve the dispersion performance. Attached Figure Description

[0027] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0028] Figure 1 The image shows a SEM image of the high first-pass efficiency hard carbon composite material prepared in Example 1. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Preparation method of boron-based crosslinking agent in the examples and comparative examples: Under nitrogen protection, 30g boric acid, 30g p-hydroxybenzaldehyde, 3g sodium carbonate and 500g cyclohexane were mixed, heated to 80℃ and stirred for 12h to obtain boron-based crosslinking agent.

[0031] Example 1

[0032] The first aspect of this embodiment provides a method for preparing a hard carbon composite material with high initial efficiency, the method comprising the following steps:

[0033] S1: 20g of lithium carboxymethyl cellulose was added to 200g of 5wt% glucose aqueous solution and dispersed evenly. Then, 10g of boron-based crosslinking agent and 3g of pore-forming agent were added. The mixture was subjected to hydrothermal reaction at 150℃ for 18h. The mixture was then vacuum dried to obtain the precursor material. The pore-forming agent was calcium ascorbate.

[0034] S2: Transfer the precursor material to a microwave oven and heat it at 400W for 30 minutes to obtain a porous precursor material.

[0035] S3: The porous precursor material is transferred into a tube furnace, and argon inert gas is introduced to remove the air in the tube. Then, a mixed gas containing carbon source is introduced at a flow rate of 50 mL / min, a temperature of 800℃, and a time of 300 min. The mixture is then cooled to room temperature (25℃) to obtain a hard carbon composite material. The mixed gas containing carbon source is boron trifluoride and methane in a volume ratio of 3:10.

[0036] The second aspect of this embodiment provides a high first-pass efficiency hard carbon composite material obtained by the preparation method described above.

[0037] The third aspect of this embodiment provides the application of the aforementioned hard carbon composite material in the field of secondary batteries.

[0038] Example 2

[0039] The first aspect of this embodiment provides a method for preparing a hard carbon composite material with high initial efficiency, the method comprising the following steps:

[0040] S1: 10g of lithium carboxymethyl cellulose was added to 100g of 10wt% sucrose aqueous solution and dispersed evenly. Then, 5g of boron-based crosslinking agent and 1g of pore-forming agent were added. The mixture was subjected to hydrothermal reaction at 100℃ for 24h. The mixture was then vacuum dried to obtain the precursor material. The pore-forming agent was magnesium ascorbate.

[0041] S2: Transfer the precursor material to a microwave oven and heat it at 300W for 60 minutes to obtain a porous precursor material.

[0042] S3: The porous precursor material is transferred into a tube furnace, and argon inert gas is introduced to remove the air in the tube. Then, a mixed gas containing carbon source is introduced at a flow rate of 10 mL / min, a temperature of 700℃, and a time of 600 min. The mixture is then cooled to room temperature (25℃) to obtain a hard carbon composite material. The mixed gas containing carbon source is phosphorus trifluoride and acetylene in a volume ratio of 1:10.

[0043] The second aspect of this embodiment provides a high first-pass efficiency hard carbon composite material obtained by the preparation method described above.

[0044] The third aspect of this embodiment provides the application of the aforementioned hard carbon composite material in the field of secondary batteries.

[0045] Example 3

[0046] The first aspect of this embodiment provides a method for preparing a hard carbon composite material with high initial efficiency, the method comprising the following steps:

[0047] S1: 30g of lithium carboxymethyl cellulose was added to 1000g of 1wt% starch aqueous solution and dispersed evenly. Then, 15g of boron-based crosslinking agent and 5g of pore-forming agent were added. The mixture was subjected to hydrothermal reaction at 200℃ for 12h. The mixture was then vacuum dried to obtain the precursor material. The pore-forming agent was potassium ascorbate.

[0048] S2: Transfer the precursor material to a microwave oven and heat it at 500W for 10 minutes to obtain a porous precursor material.

[0049] S3: The porous precursor material is transferred into a tube furnace, and argon inert gas is introduced to remove the air in the tube. Then, a mixed gas containing carbon source is introduced at a flow rate of 100 mL / min, a temperature of 1100℃, and a time of 600 min. The mixture is then cooled to room temperature (25℃) to obtain a hard carbon composite material. The mixed gas containing carbon source is ammonia and ethylene in a volume ratio of 5:10.

[0050] The second aspect of this embodiment provides a high first-pass efficiency hard carbon composite material obtained by the preparation method described above.

[0051] The third aspect of this embodiment provides the application of the aforementioned hard carbon composite material in the field of secondary batteries.

[0052] Comparative Example 1

[0053] This comparative example provides a method for preparing a hard carbon composite material with high first-pass efficiency, the method comprising the following steps:

[0054] S1: 20g of lithium carboxymethyl cellulose was added to 200g of 5wt% glucose aqueous solution and dispersed evenly. Then, 10g of boron-based crosslinking agent and 3g of pore-forming agent were added. The mixture was subjected to hydrothermal reaction at 150℃ for 18h. The mixture was then vacuum dried to obtain the precursor material. The pore-forming agent was calcium ascorbate.

[0055] S2: The precursor material is transferred to a tube furnace, argon inert gas is introduced to remove the air inside the tube, and the material is heated to 800℃ for carbonization for 3 hours to obtain a hard carbon composite material.

[0056] Comparative Example 2

[0057] This comparative example provides a method for preparing a high first-time efficiency hard carbon composite material. The specific implementation method is the same as that in Example 3, except that S1 includes: mixing 100g of glucose and 5g of calcium ascorbate evenly and reacting at a temperature of 280℃ for 6h to obtain the precursor material.

[0058] Performance testing

[0059] (1) SEM testing

[0060] The morphology of the hard carbon composite material in Example 1 was characterized using scanning electron microscopy, such as... Figure 1 As shown, the material exhibits a granular structure with a particle size between 10-15 μm and uniform size.

[0061] (2) Physicochemical performance testing

[0062] The oil absorption values ​​of the hard carbon composite materials prepared in Examples 1-3 and Comparative Examples 1-2 were tested to characterize the materials' ability to absorb electrolyte. The absorption values ​​were determined according to the method in GB / T 7046-2003 "Determination of Absorption Value of Pigment Carbon Black Dibutyl Phthalate". Simultaneously, the specific surface area, tap density, and OI value of the powder material of the composite materials were tested according to GB / T 24533-2019 "Graphite Anode Materials for Lithium-ion Batteries".

[0063] Table 1

[0064]

[0065] As can be seen from Table 1, the tap density and specific surface area of ​​the composite materials prepared in Examples 1-3 are significantly higher than those in Comparative Examples 1-2. This is because adding a pore-forming agent to the hydrothermal reaction can improve the density and porosity of the materials in the examples, thereby further increasing the specific surface area and oil absorption value of the materials.

[0066] (3) Charge and discharge performance test

[0067] The hard carbon composite materials prepared in Examples 1-3 and Comparative Examples 1-2 were assembled into button cells. The assembly method included: adding a binder and solvent to the composite material, stirring to form a slurry, then coating it onto copper foil (120 μm thick on one side), and drying and rolling to obtain the electrode sheet. The binder used was PVDF binder, and the solvent was NMP, with a ratio of graphene:PVDF:NMP = 80 g:20 g:300 mL. The electrolyte was LiPF6 / EC+DEC (EC and DEC volume ratio 1:1, LiPF6 concentration 1.3 mol / L), a lithium metal sheet was used as the counter electrode, and a polyethylene propylene (PEP) composite membrane was used as the separator. Assembly was carried out in an argon-filled glove box.

[0068] Electrochemical performance was tested using a Wuhan Landian 5V / 10mA battery tester, with a charge / discharge voltage range of 0.005V to 2.0V and a charge / discharge rate of 0.1C. The rate capability and cycle performance of the material were also tested at discharge rates of 0.1C / 0.2C / 0.5C / 1C / 2C, and the 2C / 0.1C retention rate was calculated. The coin cell cycle performance at 0.2C / 0.2C, 0.005V-2V, and 25±3℃ was also tested. The room-temperature DCR of the material was also measured using the coin cell. The test results are shown in Table 2.

[0069] Table 2

[0070]

[0071] As can be seen from Table 2, the batteries made using the hard carbon composite materials obtained in Examples 1-3 have significantly higher discharge specific capacity and initial efficiency than the comparative examples. This is because the materials in the examples are doped with lithium carboxymethyl cellulose and carbonized, which reduces the irreversible capacity of the material, improves the initial efficiency, increases the number of lithium ions during charging and discharging, improves the rate capability, and coats the outer shell with heteroatoms to improve the electronic conductivity of the material, further improving the rate performance.

[0072] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a hard carbon composite material, characterized in that, The preparation method includes the following steps: S1. Add lithium carboxymethyl cellulose to an aqueous hydrocarbon solution and disperse it evenly. Continue to add boron-based crosslinking agent and pore-forming agent. Vacuum dry the resulting mixture to obtain the precursor material. S2. Heat the precursor material to obtain a porous precursor material; S3. The porous precursor material is transferred into a tube furnace, a carbon source mixed gas is introduced, and hard carbon composite material is obtained by high-temperature carbonization. The mass ratio of lithium carboxymethyl cellulose, hydrocarbon, boron-based crosslinking agent and pore-forming agent is (10-30):100:(5-15):(1-5); The boron-based crosslinking agent is prepared by mixing boric acid, p-hydroxybenzaldehyde, sodium carbonate and cyclohexane in an inert gas atmosphere, heating and stirring to obtain the boron-based crosslinking agent.

2. The method for preparing a hard carbon composite material according to claim 1, characterized in that, The pore-forming agent includes at least one of calcium ascorbate, magnesium ascorbate, potassium ascorbate, and sodium ascorbate.

3. The method for preparing a hard carbon composite material according to claim 1, characterized in that, The mass ratio of boric acid, p-hydroxybenzaldehyde, sodium carbonate, and cyclohexane is (10-50):(10-50):(1-5):(500-1000).

4. The method for preparing a hard carbon composite material according to claim 1, characterized in that, The carbon source gas mixture includes at least one of ammonia, boron trifluoride, phosphorus trifluoride, and hydrogen sulfide, and at least one of methane, acetylene, ethylene, and ethane.

5. The method for preparing a hard carbon composite material according to claim 1, characterized in that, The mass concentration of the aqueous hydrocarbon solution is 1-10%.

6. A hard carbon composite material obtained by the preparation method according to claim 1.

7. A hard carbon composite material according to claim 6, characterized in that, The initial charge-discharge efficiency of the hard carbon composite material is higher than 96.0%.

8. The preparation method according to any one of claims 1-5 or the application of the hard carbon composite material according to claim 6 in the field of secondary batteries.

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