Method for preparing hard carbon material, negative electrode sheet, and sodium ion battery

Abstract

The application discloses a preparation method of a hard carbon material, a negative plate and a sodium ion battery. The preparation method comprises the following steps: mixing a lignin solution and pitch powder, the mass ratio of the pitch to the lignin being 1:0.025-0.15, to obtain a pretreated precursor; placing the pretreated precursor in a reaction atmosphere containing oxygen, and performing a heating reaction, the heating reaction temperature being capable of dehydrogenating the pitch to obtain an intermediate product; and performing carbonization treatment on the intermediate product to obtain the hard carbon. The method can make the synthesized hard carbon material have more sodium storage active sites, thereby improving the sodium storage capacity of the sodium ion battery, and can reduce the decomposition reaction of the lignin in the heating process, thereby improving the yield of the hard carbon material.

Description

TECHNICAL FIELD

[0001] The present application particularly relates to a preparation method of hard carbon material, negative electrode sheet and sodium ion battery. BACKGROUND

[0002] Lithium ion batteries have been commercialized due to their excellent electrochemical performance, but the limited lithium resources and uneven distribution in the world, as well as the price fluctuation of lithium salt affected by the market, will limit its development to a certain extent. Especially, the storage amount of lithium resources in China is small and the demand is increasing, so it is urgent to find a substitute for lithium ion batteries. Sodium and lithium have similar physical and chemical properties, and the crust abundance of sodium is more than 400 times that of lithium, so sodium ion battery becomes the most promising commercial substitute for lithium ion battery. The key to the commercialization of sodium ion battery is to develop low-cost and high-performance electrode materials. At present, the development of positive electrode materials for sodium ion batteries is relatively mature, and the commercialization process is limited by the slow development of negative electrode materials. Among the many negative electrode materials for sodium ion batteries, hard carbon with disordered structure and abundant source stands out.

[0003] As a raw material of hard carbon negative electrode material, pitch-based has the advantages of high residual carbon rate, etc., and the preparation process of pitch-based hard carbon material is generally to add crosslinking agent or oxidizing agent to prevent the generation of ordered structure in the high temperature process. However, the amount of additive used in the preparation of pitch-based is small due to cost and other factors, and the oxidation and crosslinking degree of pitch caused by the additive is far from enough compared with the relatively large amount of pitch, which leads to low capacity of pitch-based hard carbon, and the obtained pitch-based is more inclined to soft body ordered structure, thereby limiting the development of pitch-based hard carbon material. In addition, lignin, as one of the precursors of hard carbon negative electrode material, is an amorphous polymer formed by connecting propane units through carbon-carbon bonds and ether bonds. The hard carbon material prepared therefrom has the characteristics of rich pore structure, etc., and has advantages in improving battery capacity, but due to the rich oxygen-containing functional groups on its surface, it is easy to cause water absorption of the battery and consume a large amount of electrolyte, thereby leading to low first coulomb efficiency (generally 75-80%) and other shortcomings. In addition, the high temperature carbonization process of lignin mainly goes through dehydration, thermal cracking and polycondensation aromatization process. The hard carbon prepared by this method has the problems of low yield (generally 20-30%) and is not conducive to the commercialization of the material. SUMMARY

[0004] The technical problem solved by the present application is to overcome the problems of low capacity of hard carbon material prepared by the existing preparation method of pitch-based hard carbon and low yield of hard carbon material prepared from lignin, and to provide a preparation method of hard carbon material, negative electrode sheet and sodium ion battery. The hard carbon material prepared by the method of the present application has high capacity and yield.

[0005] The present application solves the above technical problems by the following technical solutions:

[0006] The present application provides a preparation method of hard carbon material, which comprises the following steps:

[0007] (1) mixing a lignin solution with pitch powder, the mass ratio of the pitch to the lignin being 1:0.025-0.15, to obtain a pretreated precursor;

[0008] (2) placing the pretreated precursor in a reaction atmosphere containing oxygen, and performing a heating reaction, the heating reaction temperature being capable of dehydrogenating the pitch to obtain an intermediate product;

[0009] (3) performing carbonization treatment on the intermediate product to obtain a hard carbon material.

[0010] In the present application, the lignin can be a conventional lignin with p-hydroxyphenylpropane structure, guaiacylpropane structure or syringylpropane structure in the art; preferably, the molecular mass of phenolic hydroxyl and alcoholic hydroxyl in the lignin accounts for 50-80% of the total molecular mass, for example 70%.

[0011] In the present application, in step (1), the preparation of the lignin solution comprises: dissolving lignin in caprolactone to obtain a lignin solution.

[0012] Preferably, the mass ratio of the lignin to the caprolactone is 1:1.

[0013] After mixing the lignin with the caprolactone, a stirring step can also be performed.

[0014] The stirring can employ a conventional stirring device in the art, such as a stirrer.

[0015] The stirring speed can be a conventional speed in the art capable of completely dissolving lignin in caprolactone, preferably 50-500 r / min, for example 200 r / min.

[0016] The stirring time can be a conventional time in the art capable of completely dissolving lignin in caprolactone, preferably 1-10 h, for example 2 h.

[0017] In the present application, in step (1), the pitch can be a conventional pitch used in the art, preferably one or more of coal tar pitch, petroleum pitch and natural pitch, and the softening point of the pitch is 120-280°C.

[0018] In the present application, in step (1), the mass ratio of the pitch to the lignin is preferably 1:0.075.

[0019] In the present application, in step (1), the D50 particle size of the asphalt powder is preferably 3-20 μm.

[0020] In the present application, in step (1), the lignin solution and the asphalt powder can be mixed by using a conventional mechanical mixing method in the art.

[0021] The mixing device can be a conventional device in the art, such as a high-speed mixer.

[0022] The rotation speed of the mixing is preferably 500-3000 r / min, for example 2000 r / min.

[0023] The mixing time is preferably 10-60 min, for example 20 min.

[0024] In the present application, in step (2), the oxygen-containing reaction atmosphere can be a conventional oxygen-containing atmosphere capable of causing the asphalt to undergo a dehydrogenation reaction in the art, such as an air atmosphere or an oxygen atmosphere.

[0025] In the present application, in step (2), the gas flow of the oxygen-containing reaction atmosphere can be determined according to the mass of the pretreated precursor; the greater the mass of the pretreated precursor, the greater the gas flow; preferably, the ratio of the gas flow of the oxygen-containing reaction atmosphere to the mass of the pretreated precursor is (0.5-2.5) m 3 / h:(1-20) kg.

[0026] In the present application, in step (2), the heating reaction temperature is preferably 280-380℃, for example 360℃.

[0027] In the present application, in step (2), the heating rate in the heating reaction is preferably 0.5-5℃ / min, for example 0.5℃ / min.

[0028] In the present application, in step (2), the holding time at the heating reaction temperature is preferably 1-4 h, for example 3 h.

[0029] In the present application, in step (2), the device used in the heating reaction process can be a conventional asphalt dehydrogenation reaction device in the art, such as a reaction kettle.

[0030] In the present application, in step (2), the heating reaction process can further include a stirring step.

[0031] The rotation speed of the stirring is preferably 30-200 r / min, for example 50 r / min.

[0032] In the present application, in step (3), before the carbonization treatment of the intermediate product, a crushing step can be further included.

[0033] Preferably, the particle size D50 of the pulverized intermediate product is 3-10 μm, for example 5-6 μm.

[0034] In the present application, the carbonization process in step (3) can be a conventional process in the art.

[0035] Preferably, the carbonization temperature is 1000-1500 °C, for example 1300 °C.

[0036] Preferably, the heating rate of the carbonization process is 1-10 °C / min, for example 5 °C / min.

[0037] Preferably, the holding time at the carbonization temperature is 2-6 h, for example 4 h.

[0038] In the present application, the equipment used for the carbonization process in step (3) can be a conventional equipment in the art, such as a tube furnace.

[0039] In the present application, after the carbonization process in step (3), the intermediate product can further be sieved.

[0040] Preferably, the sieve used for the sieving has a mesh size of 200.

[0041] The present application also provides a hard carbon material prepared by the method for preparing a hard carbon material.

[0042] Preferably, the interlayer distance of the hard carbon material is 0.36-0.39 nm, more preferably 0.37-0.39 nm, for example 0.367 nm, 0.369 nm, 0.374 nm, 0.377 nm, 0.381 nm or 0.383 nm.

[0043] Preferably, the specific surface area of the hard carbon material is 2.3-4.8 m 2 / g, more preferably 2.4-4.7 m 2 / g, for example 2.42 m 2 / g, 2.72 m 2 / g, 2.92 m 2 / g, 3.68 m 2 / g, 3.89 m 2 / g or 4.62 m 2 / g.

[0044] Preferably, the yield of the hard carbon material is 69.6-72.4%, for example 69.6%, 70.9%, 71.6%, 71.7%, 71.8% or 72.4%.

[0045] The application also provides a negative electrode sheet comprising the hard carbon material.

[0046] In the application, preferably, the negative electrode sheet comprises a current collector and a negative electrode material coated on the current collector; the raw material of the negative electrode material comprises the hard carbon material, a conductive agent and a binder.

[0047] Preferably, the mass ratio of the hard carbon material, the conductive agent and the binder is a:b:c, wherein 90≤a≤95, 2≤b≤5 and 2≤c≤5.

[0048] Preferably, the conductive agent can be a conductive agent commonly used in battery materials, such as SP.

[0049] Preferably, the binder can be a binder commonly used in battery materials, such as PVDF.

[0050] In the application, the raw material of the negative electrode material can further comprise a solvent.

[0051] Preferably, the solvent can be a solvent commonly used in the art which can dissolve the binder, such as N-methyl pyrrolidone.

[0052] Preferably, the amount of the solvent added can be an amount commonly used in the art which can make the slurry be coated into the electrode sheet smoothly.

[0053] The application also provides a sodium ion battery comprising the negative electrode sheet.

[0054] On the basis of common sense in the art, the above-mentioned preferred conditions can be combined arbitrarily, thereby obtaining each preferred example of the application.

[0055] The positive progress effect of the application is that:

[0056] (1) The application makes the pitch and the lignin solution fully contact, makes the pitch fully dehydrogenate under the heating reaction condition and introduces more oxygen-containing functional groups through the lignin solution, avoids the problem of insufficient pitch oxidation, improves the crosslinking degree of the pitch in the oxidation process, prevents the occurrence of pitch structure ordering, makes the synthesized hard carbon material have more sodium storage active sites, and further improves the sodium storage capacity of the sodium ion battery.

[0057] (2) The preparation method of the application further makes the hydroxyl on the benzene ring of the lignin react with the ester group of the caprolactone under certain temperature conditions, makes the caprolactone ring-opening form an ester chain on the lignin, which is conducive to the generation of the hard carbon material disorder degree to obtain a three-dimensional structure and improve the sodium storage performance of the hard carbon material; at the same time, the preparation method of the application can reduce the decomposition reaction of the lignin in the heating process, thereby improving the yield of the hard carbon material. BRIEF DESCRIPTION OF DRAWINGS

[0058] Figure 1 is the SEM image of the hard carbon material of Example 3.

[0059] Figure 2 is the XRD comparison chart of the hard carbon materials of Example 3 and Comparative Example 1.

[0060] Figure 3 is the hard carbon material half-cell charge-discharge curve chart of Example 3. DETAILED DESCRIPTION

[0061] The application will be further described in the following examples without limiting the application to the examples described. The experimental methods in the following examples, if not otherwise specified, are selected according to the conventional methods and conditions, or according to the commercial instructions.

[0062] The reagents and raw materials used in the following examples are commercially available.

[0063] Example 1

[0064] (1) 25 g of lilac phenylpropanol structure lignin (molecular mass of phenolic hydroxyl and alcoholic hydroxyl accounts for 70% of the total molecular mass) was added to 25 g of caprolactone solution, the stirring speed was 200 r / min, and the stirring time was 2 h, to obtain a mixed solution A of lignin and caprolactone;

[0065] (2) The mixed solution A was mixed with 1 kg of crushed petroleum pitch powder (D50 is 3-20 μm, softening point is 250℃) in a high-speed mixer at a speed of 2000 r / min for 20 min, to obtain a pretreated precursor B;

[0066] (3) The pretreated precursor B was placed in a 30 L reaction kettle, air was introduced, the gas flow rate was 1.5 m 3 / h, and the pretreated precursor B was heated and stirred at a stirring speed of 50 r / min, the temperature was raised at a rate of 0.5℃ / min, the final temperature was 360℃, and the holding time was 3 h, to obtain an intermediate product C;

[0067] (4) The intermediate product C was crushed to a D50 particle size of 5-6 μm, and was placed in a tube furnace for carbonization treatment, the temperature was raised at a rate of 5℃ / min, the carbonization temperature was 1300℃, and the holding time was 4 h; the obtained sample was sieved with a 200 mesh sieve, to obtain a hard carbon material.

[0068] Example 2

[0069] The specific process is the same as that of Example 1, except that the mass ratio of pitch to lignin is 1:0.05.

[0070] Example 3

[0071] The specific process is the same as that in Example 1, except that the mass ratio of pitch to lignin is 1:0.075.

[0072] Example 4

[0073] The specific process is the same as that in Example 1, except that the mass ratio of pitch to lignin is 1:0.10.

[0074] Example 5

[0075] The specific process is the same as that in Example 1, except that the mass ratio of pitch to lignin is 1:0.125.

[0076] Example 6

[0077] The specific process is the same as that in Example 1, except that the mass ratio of pitch to lignin is 1:0.15.

[0078] Example 7

[0079] The specific process is the same as that in Example 1, except that the caprolactone solution is changed to water.

[0080] Comparative Example 1

[0081] In this comparative example, no lignin and caprolactone are added, and the pitch powder is subjected to steps (2) to (4) in Example 1.

[0082] Comparative Example 2

[0083] In this comparative example, the lignin is directly pulverized to a D50 particle size of 5-6 μm, and is subjected to carbonization treatment in a tube furnace at a heating rate of 5°C / min and a carbonization temperature of 1300°C for 4 h. The obtained sample is sieved through a 200-mesh screen to obtain a hard carbon finished material.

[0084] Comparative Example 3

[0085] The specific process is the same as that in Example 1, except that no caprolactone is added, and the lignin powder is directly mixed with the pitch powder.

[0086] Effect Example

[0087] Measurement of electrochemical performance:

[0088] Preparation of negative electrode sheet: The hard carbon materials prepared in each example and comparative example, the conductive agent SP, the binder PVDF and N-methyl pyrrolidone are mixed uniformly and coated on a current collector to prepare a sodium ion battery negative electrode sheet; wherein the mass ratio of the hard carbon material, the conductive agent and the binder is 92:3:5 (90≤a≤95; 2≤b≤5; 2≤c≤5), and the current collector is a copper foil.

[0089] The positive electrode sheet is a sodium sheet, the separator is a glass fiber separator, and the electrolyte is NaPF6 (EC: DMC = 1:1). A button cell (model CR2032) is assembled.

[0090] The charge-discharge test of the battery was performed on a battery test system. The test conditions were as follows: the current density was 20 mA / g, the voltage range was 0-2 V, and the test temperature was room temperature.

[0091] Determination of specific surface area:

[0092] The nitrogen adsorption-desorption test was performed on the hard carbon material prepared in each example and comparative example to obtain the specific surface area of the hard carbon material.

[0093] Determination of interlayer spacing:

[0094] The d-spacing of the hard carbon material prepared in each example and comparative example was obtained by XRD. 002 .

[0095] The test results are shown in Table 1.

[0096] Table 1

[0097]

[0098]

[0099] Figure 1 The structure of the hard carbon material prepared in Example 3 is shown in the schematic diagram. As can be seen, the particle surface is relatively full, and the particle morphology is relatively regular.

[0100] Figure 2 The XRD comparison diagram of the hard carbon material prepared in Example 3 and the hard carbon material prepared in Comparative Example 1 is shown. As can be seen from the diagram, the D002 peak of the hard carbon material obtained in Example 3 is shifted to the left and the peak shape is wider compared with Comparative Example 1, indicating that the hard carbon material obtained in Example 3 has a higher degree of disorder, i.e., a good crosslinking effect.

[0101] Figure 3 The half-cell charge-discharge curve of the hard carbon material prepared in Example 3 is shown. The charge-discharge curve is a typical charge-discharge curve of a hard carbon material half-cell, which is composed of a slope section above 0.1 V and a platform section below 0.1 V.

Claims

1. A method for producing a hard carbon material, characterized by, It comprises the following steps: (1) mixing the lignin solution with the asphalt powder, the mass ratio of the asphalt to the lignin being 1:(0.025-0.15), to obtain a pretreatment precursor; The preparation of the lignin solution comprises: dissolving lignin in caprolactone to obtain a lignin solution; (2) placing the pretreatment precursor in an oxygen-containing reaction atmosphere and performing a heating reaction, the temperature of the heating reaction being capable of dehydrogenating the asphalt, to obtain an intermediate product; (3) performing carbonization treatment on the intermediate product to obtain a hard carbon material.

2. The method for producing a hard carbon material according to claim 1, wherein The lignin is lignin with a p-hydroxyphenylpropane structure, lignin with a guaiacylpropane structure or lignin with a syringylpropane structure; And / or, the mass ratio of the lignin to the caprolactone is 1:1; And / or, after mixing the lignin with the caprolactone, a stirring step is further included.

3. The method for producing a hard carbon material according to claim 2, wherein The molecular mass of the phenolic hydroxyl and alcoholic hydroxyl in the lignin accounts for 50-80% of the total molecular mass; And / or, the stirring speed is 50-500 r / min; And / or, the stirring time is 1-10 h.

4. The method of producing a hard carbon material according to claim 1, wherein In step (1), the asphalt is one or more of coal tar pitch, petroleum pitch and natural asphalt, and the softening point of the asphalt is 120-280℃; And / or, in step (1), the D50 particle size of the asphalt powder is 3-20 μm; And / or, in step (1), the mixing speed is 500-3000 r / min; And / or, in step (1), the mixing time is 10-60 min.

5. The method of producing a hard carbon material according to claim 1, wherein In step (2), the oxygen-containing reaction atmosphere is an air atmosphere or an oxygen atmosphere; And / or, in step (2), the gas flow rate of the oxygen-containing reaction atmosphere to the mass of the pretreated precursor is (0.5-2.5) m 3 / h: (1-20) kg; And / or, in step (2), the temperature of the heating reaction is 280-380℃; And / or, in step (2), the temperature rising rate in the heating reaction is 0.5-5℃ / min; And / or, in step (2), the holding time at the temperature of the heating reaction is 1-4 h; And / or, in step (2), the equipment used in the process of the heating reaction is a reaction kettle; And / or, in step (2), the process of the heating reaction further includes a stirring step.

6. The method for producing a hard carbon material according to claim 5, wherein The stirring speed is 30-200 r / min.

7. The method of producing a hard carbon material according to claim 1, wherein In step (3), before performing carbonization treatment on the intermediate product, a crushing step is further included; And / or, in step (3), the temperature of the carbonization treatment is 1000-1500℃; And / or, in step (3), the temperature rising rate of the carbonization treatment is 1-10℃ / min; And / or, in step (3), the holding time at the temperature of the carbonization treatment is 2-6 h; And / or, in step (3), the equipment used in the carbonization treatment is a tube furnace; And / or, in step (3), after performing the carbonization treatment on the intermediate product, a screening step is further included.

8. The method for producing a hard carbon material according to claim 7, wherein The particle size D50 of the crushed intermediate product is 3-10 μm; And / or, the screen used in the screening is a 200-mesh screen.

9. The method of producing a hard carbon material according to claim 1, wherein The lignin is lignin with a syringylpropane structure; And / or, the asphalt is petroleum pitch. And / or, in step (1), the mass ratio of the pitch to the lignin is 1:0.

075.

10. The hard carbon material prepared by the method of any one of claims 1 to 9.

11. The hard carbon material of claim 10, wherein, The hard carbon material has an interlayer spacing of 0.36-0.39 nm. and / or the specific surface area of the hard carbon material is 2.3 to 4.8 m 2 / g; And / or, the yield of the hard carbon material is 69.6-72.4%.

12. The hard carbon material of claim 11, wherein, The hard carbon material has an interlayer spacing of 0.37-0.39 nm. and / or the specific surface area of the hard carbon material is 2.4 to 4.7 m 2 / g.

13. A negative electrode sheet characterized by comprising: The battery includes the hard carbon material of any one of claims 10 to 12.

14. The negative electrode sheet according to claim 13, wherein The negative electrode sheet includes a current collector and a negative electrode material coated on the current collector; the raw material of the negative electrode material includes the hard carbon material, a conductive agent and a binder.

15. The negative electrode sheet according to claim 14, wherein The mass ratio of the hard carbon material, the conductive agent and the binder is a:b:c, wherein 90≤a≤95, 2≤b≤5 and 2≤c≤5.

16. A sodium-ion battery, characterized in that, The battery includes the negative electrode sheet of any one of claims 13 to 15.

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