Hard carbon material, preparation method thereof, pole piece and application

Abstract

The invention discloses a hard carbon material, a preparation method thereof, a pole piece and application. The preparation method of the hard carbon material comprises the following steps: carbonizing oxidized asphalt and molecular sieves, and removing the molecular sieves to obtain the hard carbon material, the mass ratio of the oxidized asphalt to the molecular sieve is 1: (1-20). The hard carbon material prepared by the preparation method disclosed by the invention has relatively high true density and relatively high open pore volume ratio. The battery prepared from the hard carbon material has better first coulombic efficiency. The preparation method of the hard carbon material is simple to operate and beneficial to industrial production.

Description

Technical Field

[0001] The invention relates to a hard carbon material and a preparation method, a pole piece and application thereof. Background Art

[0002] As a new type of negative electrode material for lithium-ion batteries, hard carbon has abundant sources and low energy consumption in the production process. With the growing demand for high-performance batteries, the demand for hard carbon is also increasing. At present, the mainstream power battery market is mainly dominated by graphite, but the room for improvement of graphite is very limited, and the diffusion of lithium ions between graphite layers also restricts the development of battery rate performance. It can be seen that with the increasing demand for battery energy and power performance in downstream applications, pure graphite negative electrode materials have become stretched. As a new type of negative electrode material, hard carbon has a higher lithium storage capacity and excellent rate performance than the graphite negative electrode of lithium-ion batteries. As the market demand for higher-performance power batteries grows, it will also drive the release of demand for hard carbon negative electrode materials.

[0003] However, hard carbon as a negative electrode material for lithium-ion batteries faces the problem of low initial efficiency, which will affect the overall energy density of the battery cell, lead to rapid battery energy loss and cycle life decay, and increase the amount and cost share of positive electrode materials. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the defect of low first coulombic efficiency of hard carbon materials in the prior art, and provide a hard carbon material and its preparation method, pole piece and application. The hard carbon material prepared by the present invention has a higher true density and a higher open pore volume ratio. The battery prepared from the hard carbon material has a better first coulombic efficiency. The preparation method of the hard carbon material of the present invention is simple to operate and is conducive to industrial production.

[0005] The present invention solves the above technical problems through the following technical solutions.

[0006] The present invention provides a method for preparing a hard carbon material, which comprises the following steps: carbonizing oxidized asphalt and molecular sieve, removing the molecular sieve, and obtaining the hard carbon material; the mass ratio of the oxidized asphalt to the molecular sieve is 1:(1-20).

[0007] In the present invention, the oxidized asphalt can be prepared by conventional methods in the art, preferably by the following steps: subjecting the asphalt to oxidation treatment with an oxidant.

[0008] The types of asphalt may include one or more of petroleum asphalt, coal tar asphalt and natural asphalt, such as coal asphalt.

[0009] The D50 of the asphalt may be 1-100 μm, preferably 3-10 μm, such as 5, 6, 7, 8 or 9 μm.

[0010] The softening point of the asphalt may be 120-280°C, preferably 200-280°C, such as 240°C.

[0011] Wherein, the type of the oxidant can be conventional in the art, preferably including oxygen-containing gas, strong acid oxidant, hydrogen peroxide or sodium periodate. The oxygen-containing gas is preferably oxygen and / or air, such as air. The strong acid oxidant preferably includes nitric acid and / or sulfuric acid.

[0012] Wherein, when the oxidant is an oxygen-containing gas, the mass volume ratio of the asphalt to the oxidant is preferably 1 kg: (2-8) m 3 , for example 1kg: 3m 3 , 1kg: 4m 3 , 1kg: 5m 3 or 1kg: 6m 3 .

[0013] The temperature of the oxidation treatment may be 200-600°C, preferably 300-500°C, such as 400°C.

[0014] The oxidation treatment time may be 1-10 h, preferably 3-8 h, such as 4, 5 or 6 h.

[0015] The rate of heating from room temperature to the temperature of the oxidation treatment may be 0.5-5°C / min, preferably 0.8-2°C / min, for example 1°C / min.

[0016] In the present invention, the D50 of the asphalt after oxidation treatment may be 1-20 μm, preferably 3-10 μm, such as 5, 6, 7, 8 or 9 μm.

[0017] In the present invention, the applicant discovered during the research and development process that when molecular sieves are added during oxidation treatment, the asphalt will melt and mix with the molecular sieves to form agglomerates, and it is impossible to separate it from the asphalt during subsequent treatment, making it impossible to continue subsequent experiments.

[0018] In the present invention, the pore size of the molecular sieve can allow molecules with a diameter less than 15 angstroms to pass through, preferably allowing molecules with a diameter less than 13 angstroms to pass through, and more preferably 3A, 4A, 5A, 10X, 13X, Y or sodium mordenite type, such as 3A type.

[0019] In the present invention, the particle size of the molecular sieve may be 2-10 mm, preferably 4-7 mm, such as 5 mm.

[0020] In the present invention, the mass ratio of the oxidized asphalt to the molecular sieve is preferably 1:(1-6), such as 1:2, 1:3, 1:4 or 1:5.

[0021] In the present invention, the equipment for the carbonization treatment may be conventional in the art, such as a carbonization furnace.

[0022] In the present invention, the carbonization treatment is preferably carried out under an inert atmosphere, and the inert atmosphere is preferably nitrogen.

[0023] In the present invention, the temperature of the carbonization treatment may be 1000-1600°C, preferably 1000-1200°C, such as 1100°C.

[0024] In the present invention, the carbonization treatment time may be 2-6 hours, preferably 2-4 hours, such as 3 hours.

[0025] In the present invention, the rate of heating from room temperature to the temperature of carbonization treatment may be 1-10°C / min, preferably 1-5°C / min, such as 2, 3 or 4°C / min.

[0026] In the present invention, the method for removing the molecular sieve can be conventional in the art, such as sieving. The mesh size of the sieve used for sieving is preferably 100-400 mesh, such as 100 mesh.

[0027] The present invention also provides a hard carbon material, which is prepared by the hard carbon material preparation method as described above.

[0028] The present invention also provides a hard carbon material, wherein the open pore volume ratio is 10%-70%; the open pore volume ratio represents the percentage of the open pore volume to the sum of the open pore volume and the closed pore volume.

[0029] In the present invention, the open pores refer to pores different from closed pores, and refer to cavities and channels communicating with the outside world.

[0030] In the present invention, the open pore volume ratio of the hard carbon material is preferably 15%-60%, for example, 19.81%, 26.64%, 37.75%, 49.48%, 55.59% or 58.13%.

[0031] In the present invention, the true density of the hard carbon material can be 1.85-2.00 g / cm 3 , for example 1.89, 1.92, 1.93, 1.94 or 1.97 g / cm 3 .

[0032] In the present invention, the open pore volume of the hard carbon material may be 0.02-0.15 cm³ / g, for example, 0.0214, 0.0265, 0.0395, 0.0638, 0.0947 or 0.1088 cm³ / g.

[0033] In the present invention, the closed pore volume of the hard carbon material may be 0.07-0.09 cm³ / g, for example, 0.0866, 0.0730, 0.0651, 0.0757 or 0.0784 cm³ / g.

[0034] The present invention also provides a pole piece, which comprises the hard carbon material as described above.

[0035] The present invention also provides an application of the pole piece as described above in an electrochemical device.

[0036] In the present invention, the electrochemical device is preferably a lithium ion battery.

[0037] On the basis of being in accordance with the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0038] The reagents and raw materials used in the present invention are commercially available.

[0039] The positive and progressive effects of the present invention are:

[0040] (1) The hard carbon material prepared in the present application has a high true density and a high open pore volume ratio. The battery prepared from the hard carbon material has a high first coulombic efficiency.

[0041] (2) The preparation method of the hard carbon material of the present application is simple to operate and is conducive to industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is the SEM image of the hard carbon material obtained in Example 4.

[0043] Figure 2 This is the charge and discharge curve of the half-cell assembled with the hard carbon material obtained in Example 4. DETAILED DESCRIPTION

[0044] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0045] Example 1

[0046] A method for preparing a hard carbon material comprises the following steps:

[0047] (1) The coal tar pitch raw material with a softening point of 240°C is crushed, and the particle size D50 after crushing is 5 μm;

[0048] (2) 1 kg of the coal tar powder crushed in step (1) was placed in a reactor, the oxidation treatment temperature was 400°C, the heating rate from room temperature to the oxidation treatment temperature was 1°C / min, the oxidation treatment time was 5 hours, and the air flow rate was 1m 3 / h;

[0049] (3) crushing the coal tar pitch after oxidation treatment in step (2), and the particle size D50 after crushing is 5 μm;

[0050] (4) The coal tar pitch after the oxidation treatment after the crushing in step (3) is mixed with a 3A type molecular sieve with a particle size of 5 mm at a mass ratio of 1:1; after the mixture is evenly mixed, it is placed in a carbonization furnace and carbonized under a N2 atmosphere at a heating rate of 1°C / min, a carbonization temperature of 1000°C, and a carbonization treatment condition of 2h;

[0051] (5) The carbonized material obtained in step (4) is sieved through a 100-mesh sieve to remove the molecular sieve to obtain a hard carbon material.

[0052] The preparation methods of the hard carbon materials of Examples 2-6 and Comparative Example 1 are the same as those of Example 1, the only difference being the mass ratio of oxidized coal tar pitch to molecular sieve, as shown in Table 1 below.

[0053] Table 1

[0054]

[0055] Effect Example 1

[0056] The SEM image of the hard carbon material obtained in Example 4 is as follows Figure 1 As shown. Figure 1 It can be seen that the hard carbon material prepared in Example 4 has irregular granular shape and a smooth surface, which is a typical hard carbon material morphology.

[0057] The true density, open pore volume and closed pore volume of the hard carbon materials prepared in Examples 1-6 and Comparative Example 1 were tested. The results are shown in Table 2.

[0058] Among them, the true density can be obtained by testing with the gas solvent method;

[0059] Among them, the open pore volume can be obtained by using the surface area analyzer NOVA-Touch test; adsorbent: high-purity CO2; BET tube test;

[0060] Where, closed pore volume = 1 / ρ − 1 / 2.26; where ρ represents the true density.

[0061] Among them, the proportion of open pore volume = (open pore volume) / (open pore volume + closed pore volume) × 100%.

[0062] Table 2

[0063]

[0064] The hard carbon materials prepared in Examples 1-6 and Comparative Example 1 were assembled into batteries and the electrochemical performance was tested. The method of assembling the battery is as follows: the hard carbon materials, conductive agent (SP) and binder (PVDF) prepared in Examples 1-6 and Comparative Example 1 were mixed in a mass ratio of 94:1:5, and evenly mixed with N-methylpyrrolidone (the mass ratio of N-methylpyrrolidone to PVDF was 95:5) and coated on the current collector to prepare the negative electrode of the lithium-ion battery. The electrode was dried at 80°C in a vacuum oven for 12 hours and then cut into electrode discs. In an Ar atmosphere glove box, a lithium sheet was used as the counter electrode, and the electrolyte used 1 mol of LiPF6 electrolyte dissolved in a volume ratio of 1:1 ethylene carbonate (EC) and dimethyl carbonate solvent to assemble a CR2032 button battery.

[0065] The electrochemical performance test was carried out under the following conditions: the charge and discharge procedure was 0.2C discharge to 5mV, 0.02mA discharge to 0V, and 0.2C charge to 2V. The test results are shown in Table 3. The charge and discharge curves of the half-cell assembled with the hard carbon material obtained in Example 4 are shown in Figure 2 shown.

[0066] Table 3

[0067]

[0068] It can be seen from Table 2 and Table 3 that, compared with Comparative Example 1, in the process of preparing hard carbon materials in Examples 1-6, the use of molecular sieves can effectively absorb the gas overflowed from the oxidized asphalt during the heat treatment and carbonization process, so that the prepared hard carbon material has a higher open pore volume and open pore ratio, a lower closed pore volume and a higher true density, and the prepared battery has a higher reversible specific capacity and a higher first coulombic efficiency.

Claims

1. A method for preparing a hard carbon material, characterized in that: The method comprises the following steps: carbonizing the oxidized asphalt and molecular sieve, removing the molecular sieve, and obtaining the hard carbon material; the mass ratio of the oxidized asphalt and the molecular sieve is 1:(1-20).

2. The method for preparing a hard carbon material according to claim 1, characterized in that: The mass ratio of the oxidized asphalt to the molecular sieve is 1:(1-6), for example, 1:2, 1:3, 1:4 or 1:

5.

3. The method for preparing a hard carbon material according to claim 1, characterized in that: The oxidized asphalt is obtained by oxidizing asphalt and an oxidant.

4. The method for preparing a hard carbon material according to claim 3, characterized in that: The preparation method of the hard carbon material meets one or more of the following conditions: (1) The type of asphalt includes one or more of petroleum asphalt, coal tar asphalt and natural asphalt, such as coal tar; (2) The D50 of the asphalt is 1-100 μm, preferably 3-10 μm, such as 5, 6, 7, 8 or 9 μm; (3) The softening point of the asphalt is 120-280°C, preferably 200-280°C, for example 240°C; (4) The oxidant includes oxygen-containing gas, strong acid oxidant, hydrogen peroxide or sodium periodate; the oxygen-containing gas is preferably oxygen and / or air, such as air; the strong acid oxidant is preferably nitric acid and / or sulfuric acid; Wherein, when the oxidant is an oxygen-containing gas, the mass volume ratio of the asphalt to the oxidant is preferably 1 kg: (2-8) m 3 , for example 1kg: 3m 3 , 1kg: 4m 3 , 1kg: 5m 3 or 1kg: 6m 3 ; (5) The temperature of the oxidation treatment is 200-600°C, preferably 300-500°C, for example 400°C; (6) The oxidation treatment time is 1-10 hours, preferably 3-8 hours, such as 4, 5 or 6 hours; (7) The rate of heating from room temperature to the oxidation treatment temperature is 0.5-5°C / min, preferably 0.8-2°C / min, for example 1°C / min.

5. The method for preparing a hard carbon material according to claim 1, characterized in that: The preparation method of the hard carbon material meets one or more of the following conditions: (1) The D50 of the oxidized asphalt is 1-20 μm, preferably 3-10 μm, such as 5, 6, 7, 8 or 9 μm; (2) The molecular sieve has a pore size that allows molecules with a diameter of less than 15 angstroms to pass through, preferably allows molecules with a diameter of less than 13 angstroms to pass through, and more preferably is 3A, 4A, 5A, 10X, 13X, Y or sodium mordenite type, such as 3A type; (3) The particle size of the molecular sieve is 2-10 mm, preferably 4-7 mm, for example 5 mm; (4) The carbonization treatment equipment is a carbonization furnace; (5) The carbonization treatment is carried out under an inert atmosphere; the inert atmosphere is preferably nitrogen; (6) The temperature of the carbonization treatment is 1000-1600°C, preferably 1000-1200°C, for example 1100°C; (7) The carbonization treatment time is 2-6 hours, preferably 2-4 hours, for example 3 hours; (8) The rate of heating from room temperature to the carbonization temperature is 1-10°C / min, preferably 1-5°C / min, for example 2, 3 or 4°C / min.

6. A hard carbon material, characterized in that The hard carbon material is prepared by the method for preparing the hard carbon material as described in any one of claims 1 to 5.

7. A hard carbon material, characterized in that: The open pore volume ratio of the hard carbon material is 10%-70%; the open pore volume ratio represents the percentage of the open pore volume to the sum of the open pore volume and the closed pore volume.

8. The hard carbon material according to claim 7, characterized in that The hard carbon material satisfies one or more of the following conditions: (1) The open pore volume ratio of the hard carbon material is 15%-60%, such as 19.81%, 26.64%, 37.75%, 49.48%, 55.59% or 58.13%; (2) The true density of the hard carbon material is 1.85-2.00 g / cm 3 , for example 1.89, 1.92, 1.93, 1.94 or 1.97 g / cm 3 .

9. A pole piece, characterized in that: It comprises the hard carbon material as claimed in any one of claims 6 to 8.

10. Use of the electrode piece according to claim 9 in an electrochemical device.

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