Porous carbon material, silicon-carbon composite material, and preparation method and application thereof

Abstract

The present application relates to a kind of porous carbon material, silicon-carbon composite material and its preparation method and application.The preparation method of the porous carbon material includes the following steps: S1, after the mixture including carbon material and zinc chloride is heat treated and acid washed, porous carbon precursor is obtained;S2, porous carbon material is obtained after porous carbon precursor, nitric acid and polar solvent are mixed, soaked, dried.The preparation method of the present application greatly improves the yield of porous carbon preparation, reduces production cost.The battery prepared by using the above-mentioned porous carbon material to prepare silicon-carbon composite material has excellent electrochemical performance.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of porous carbon material, silicon-carbon composite material and its preparation method and application. BACKGROUND

[0002] Silicon-carbon composite material is widely concerned because of extremely high energy density, and is widely used in consumer battery field.The general preparation process of silicon-carbon composite material includes precursor preparation→ precursor carbonization→ precursor activation (porous carbon) → silane deposition→ carbon source coating, etc.Among them, porous carbon is crucial to silicon-carbon composite material.The main reason is that porous carbon material is used as the carrier of silicon-carbon composite material, and good void distribution and conductivity have influence on the rate, expansion and strength of silicon-carbon composite material.Because of the multiple problems such as great difficulty in preparing ideal porous carbon, low yield of carbonized and activated porous carbon, and small remaining amount of porous carbon after multiple processes, the price of porous carbon can reach 400000 rmb / t.Furthermore, CO2, alkali and steam are usually used for activation, which is mainly etching, and is the main reason for low yield of porous carbon, and also because of the activation method, various functional groups are easily produced in the porous carbon, which affects the rate performance, initial efficiency and strength of silicon-carbon composite material prepared based on porous carbon, and because of the high tap density of hard carbon material prepared based on precursor, the surface lacks necessary voids, which leads to low efficiency and high cost of active activation by gas adsorption, and if waste gas cannot be recycled, it will be a great waste of resources, and so on.

[0003] The porous carbon material prepared by zinc chloride activation has a high yield, and based on its activation principle, the mesoporous gap shape is more in the porous carbon formed, and the formed carbon has a similar layered structure, the degree of graphitization is increased, and the conductivity is improved to a certain extent.However, the specific surface area of the porous carbon material obtained by zinc chloride activation is usually low, and can only reach 1500 m 2 / g, which is obviously not conducive to the deposition of silane.In addition, the similar layered structure existing in the porous carbon is very unfavorable to the strength.In addition, zinc chloride activator is a heavy metal salt, and its voltage window range is narrow, and within the voltage window range of lithium ion battery, if the impurities in the porous carbon material activated by zinc chloride are not completely removed, it will cause a serious hidden danger in the repeated charging and discharging process of the battery, including the influence on performance and safety, which may reduce the service life and rate performance, and even cause short circuit, direct scrap, and even fire. SUMMARY

[0004] The present application is to solve the defects of low specific surface area, poor strength and incomplete impurity removal of the porous carbon material prepared by zinc chloride activation in the prior art, and further based on the problems that the rate performance, initial efficiency and the like of the silicon-carbon composite material prepared from the porous carbon material are not ideal, a porous carbon material, a silicon-carbon composite material, a preparation method and application thereof are provided. The porous carbon material prepared by the preparation method has low impurity content, high specific surface area and high strength, and the silicon-carbon composite material prepared by using the porous carbon material has excellent electrochemical performance in a lithium ion battery; and the preparation method greatly improves the yield of the porous carbon material and does not need to be tempered, thereby greatly reducing the production cost of the porous carbon material.

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

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

[0007] S1, obtaining a first precursor by heat treating and acid washing a mixture containing a carbon material and zinc chloride;

[0008] S2, mixing the first precursor, nitric acid and a polar solvent, soaking and drying.

[0009] In the present application, in step S1, the mass ratio of the carbon material to the zinc chloride is preferably 1:(1-10), more preferably 1:(3-5), for example 1:3.

[0010] In step S1, the temperature of the heat treatment is preferably 500-800℃, for example 600℃.

[0011] In step S1, the heating rate of the heat treatment is preferably 1-10℃ / min, for example 2℃ / min. Wherein, the meaning of the heating rate is the heating rate during the process of increasing from room temperature to the heat treatment temperature.

[0012] In step S1, the heat treatment can be carried out in a conventional heating device in the art, such as a rotary furnace, a fluidized bed, a push plate kiln, a tube furnace, a muffle furnace, a vacuum furnace or a microwave oven. In a specific embodiment, the heat treatment is carried out by using a rotary furnace, wherein the rotation speed of the rotary furnace is preferably 5-20r / min, for example 10r / min.

[0013] In step S1, the heat treatment can be carried out in an inert atmosphere. Wherein, the inert atmosphere is preferably nitrogen, helium or argon. Wherein, the gas supply rate of the inert atmosphere is preferably 1-10L·kg 1 min -1 , for example 2L·kg 1 min -1.

[0014] In step S1, the holding time of the heat treatment can be 1-5h, for example 3h.

[0015] In step S1, the acid washing can be performed by using a conventional acid. The concentration of the acid is preferably 0.1-5M, for example 1M. The acid washing is preferably performed by using hydrochloric acid.

[0016] In step S1, the acid washing can further include an operation of recovering the waste liquid for drying treatment.

[0017] In step S1, the particle size D 50 of the carbon material is preferably 5-10μm, for example 8.1μm.

[0018] In step S1, the water content of the first precursor can be 20%-80%, for example 50%. Wherein, the water content refers to the percentage of the mass of water in the first precursor to the total mass of the first precursor.

[0019] In step S2, the pH value of the mixture slurry of the first precursor, nitric acid and polar solvent is 2-6, for example 2.

[0020] In step S2, the nitric acid is preferably dilute nitric acid.

[0021] In step S2, the polar solvent can be one or more of N-methyl pyrrolidone (NMP), water, acetone, ethanol, chloroform, diethyl ether, acetic acid, acetonitrile, isopropanol and methanol, for example N-methyl pyrrolidone.

[0022] In step S2, the amount of the polar solvent can be 0.1%-5%, the percentage being the mass percentage of the polar solvent in the mixture slurry of the first precursor, nitric acid and polar solvent.

[0023] In step S2, during the soaking, zinc chloride reacts with nitric acid: ZnCl2+HNO3→Zn(NO3)2+HCl, and HCl escapes in the form of gas.

[0024] In step S2, the soaking can be performed at room temperature.

[0025] In step S2, the time of the soaking is preferably 5-20h, preferably 10h.

[0026] In step S2, the pressure of the soaking is preferably 10-50 kPa, for example 10 kPa. The pressure of the soaking refers to the pressure in the container during the soaking, which can be achieved by vacuumizing, and the purpose of the soaking under the pressure lower than the normal pressure is to reduce the tension of the bubbles (HCl gas) in the pores, to promote the reaction of the nitric acid with the ZnCI2 in the material, and to continuously make the reaction ZnCI2+HNO3→Zn(NO3)2+HCl proceed to the right.

[0027] In step S2, the drying is performed in the conventional equipment in the field, for example a vacuum drying oven, a rotary evaporator, a blast drying oven or a double-cone drying oven.

[0028] In step S2, the drying is preferably vacuum drying.

[0029] Preferably, the pressure of the vacuum drying is 10-50 kPa.

[0030] Preferably, the time of the vacuum drying is 5-20 h, for example 10 h.

[0031] Preferably, the temperature of the vacuum drying is 80-150℃, for example 100℃.

[0032] In the present application, preferably, the product obtained in step S2 is recorded as a second precursor, and after step S2, the following step is further included:

[0033] Step S3, the second precursor is subjected to a gas activation treatment.

[0034] In step S3, the gas source of the gas activation is preferably CO2.

[0035] In step S3, the time of the gas activation can be 1-10 h.

[0036] In step S3, the gas flow rate of the gas activation can be 0.5-5 L·kg 1 min -1 , preferably 2 L·kg 1 min -1 .

[0037] In step S3, the temperature of the gas activation can be 500-800℃, preferably 500-600℃, for example 600℃.

[0038] In the present application, preferably, before step S1, the following step is further included:

[0039] Step S0, carbonizing a mixture containing a carbon source to obtain a carbon material.

[0040] In step S0, the carbon source comprises one or more of resin, sucrose, glucose, fructose, starch, cellulose, triglyceride, fatty acid, hemicellulose, lignin, and pitch. Preferably, the carbon source is resin, more preferably phenol-formaldehyde resin.

[0041] In step S0, the carbonization can be performed by using a staged heat treatment. Preferably, the carbonization comprises the following stages:

[0042] First stage: heating at a heating rate of 0.1-20℃ / min to 50-300℃, and holding for 5-600 min;

[0043] Second stage: heating at a heating rate of 0.1-20℃ / min to 300-1000℃, and holding for 5-1200 min.

[0044] In one embodiment, the carbonization comprises the following steps: first heating at a heating rate of 4℃ / min to 200℃ for 50 min, and holding for 1 h; and then heating at a heating rate of 4℃ / min to 652℃ for 113 min, and holding for 1 h.

[0045] In step S0, the carbonization is performed in an inert atmosphere, which is one or more of nitrogen, helium, and argon. Preferably, the inert gas is supplied at a rate of 1-5 L·kg -1 min -1 .

[0046] In step S0, the mixture can further comprise a curing agent and a solvent.

[0047] Preferably, the curing agent is one or more of urotropine, ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, diethylaminopropylamine, hexamethylenetetramine, aniline, p-toluenesulfonic acid, formaldehyde, benzenesulfonyl chloride, p-toluenesulfonyl chloride, ethyl sulfate, petroleum sulfonic acid, dodecylbenzenesulfonic acid, polyformaldehyde, maleic anhydride, phthalic anhydride, isocyanate, pyridine, benzoyl peroxide, cumene hydroperoxide, t-butyl hydroperoxide, and cyclohexanone peroxide, for example urotropine.

[0048] Preferably, the solvent is one or more of water, N-methylpyrrolidone, water, acetone, ethanol, chloroform, diethyl ether, acetic acid, acetonitrile, isopropyl alcohol, and methanol.

[0049] Preferably, the ratio of the total mass of the curing agent and the solvent to the mass of the carbon source is (0.001-5):1.

[0050] In step S0, the mixture can be prepared by mixing the components.

[0051] The mixing can be performed in conventional equipment in the art, for example, in a high-speed dispersion homogenizer, a planetary dispersion, an ultrasonic cell crusher, or an ultrasonic cleaning machine.

[0052] The rotation speed of the mixing can be 1000-5000 r / min, for example, 2000 r / min.

[0053] The mixing time can be 1-600 min, for example, 60 min.

[0054] In step S0, the process further comprises a drying process before the carbonization.

[0055] The drying method can be conventional in the art, for example, spray drying, rotary evaporation, spray drying, or vacuum granulation.

[0056] In some preferred embodiments, the drying method is spray drying.

[0057] The temperature of the spray drying can be 50-200 ℃, for example, 130 ℃.

[0058] The particle diameter of the material after the spray drying can be 5-20 μm, for example, 8 μm.

[0059] The present application provides a porous carbon material prepared by the above method.

[0060] In the present application, preferably, the specific surface area of the porous carbon material is 1500-2000 m 2 / g, for example, 1535 m 2 / g, 1639 m 2 / g, 1867 m 2 / g, 1693 m 2 / g, 1832 m 2 / g, or 1935 m 2 / g.

[0061] Preferably, the micropore specific surface area ratio of the porous carbon material is more than 90%, wherein the micropore specific surface area ratio refers to the percentage of the specific surface area of the micropores in the total specific surface area of the porous carbon material.

[0062] Preferably, the mesopore specific surface area ratio of the porous carbon material is less than 10%, for example, 7.0%, 7.7%, 7.9%, 8.0%, 8.1%, 8.4%, 8.8%, 9.3%, or 9.8%, wherein the mesopore specific surface area ratio refers to the percentage of the specific surface area of the mesopores in the total specific surface area of the porous carbon material.

[0063] Preferably, the total pore volume of the porous carbon material is 0.6-1.2 cm3 / g, for example 1.12 cm 3 / g.

[0064] The present application provides a preparation method of a silicon-carbon composite material, comprising the following steps (denoted as step S4): sequentially performing silicon deposition and carbon coating on the above porous carbon material.

[0065] In step S4, the silicon source for the silicon deposition preferably comprises silane (general formula: Si n H 2n+2 ), which can be one or more of monosilane (SiH4), disilane (Si2H6), trisilane (Si3H8) and tetrasilane (Si4H 10 ).

[0066] In step S4, the flow rate of the silicon source for the silicon deposition can be 0.1-10 L·kg -1 min -1 , for example 0.5 L·kg -1 min -1 .

[0067] In step S4, preferably, the silicon source and the carrier gas are simultaneously introduced during the silicon deposition. The volume ratio of the silicon source to the carrier gas is 1:(2-6), for example 1:4.

[0068] In step S4, the temperature for the silicon deposition can be 400-800℃, for example 550℃.

[0069] In step S4, the time for the silicon deposition can be 3-16 h, for example 8 h.

[0070] In step S4, the carbon coating can be performed by a method conventional in the art.

[0071] In some preferred embodiments, the carbon coating is performed by a vapor deposition method.

[0072] The carbon source for the carbon coating can comprise one or more of acetylene, alkanes, alkenes, aromatic compounds (such as one or more of anthracene, naphthalene and lignin), and carbohydrates (such as one or more of glucose, cellulose and hemicellulose).

[0073] The flow rate of the carbon source can be 0.1-10 L·kg -1 min -1 , for example 2 L·kg -1 min -1 The temperature for the carbon coating can be 300-1000℃, for example 600℃.

[0074] The carbon coating time can be 60-1200 min, for example, 600 min.

[0075] The application provides a silicon-carbon composite material prepared by the above method.

[0076] In the application, the silicon-carbon composite material comprises, from inside to outside, a porous carbon framework, a silicon deposition layer and a carbon coating layer; and the silicon deposition layer is located on the pore wall of the porous carbon framework.

[0077] The silicon-carbon composite material is used as an electrode material in a battery.

[0078] The electrode material is preferably a negative electrode material.

[0079] On the basis of common sense in the art, the above preferred conditions can be combined arbitrarily, thereby obtaining preferred examples of the application.

[0080] The reagents and raw materials used in the application are commercially available.

[0081] The positive progress of the application is that:

[0082] 1. The application uses zinc chloride and nitric acid to improve the yield of the porous carbon material (from less than 20% in the prior art to more than 45%), greatly reducing the manufacturing cost of the porous carbon. At the same time, the content of zinc elements in the porous carbon is maximized, reducing the impurity content to less than 170 ppm.

[0083] 2. In the preferred scheme, further activation with CO2 can further improve the yield of the porous carbon material. The CO2 ventilation amount required by the method is only 0.5-5 L·kg 1 min -1 , and the ventilation time is only 1-10 h, which is much lower than the amount of CO2 used in the prior art, and can further reduce the production cost. Moreover, the preparation method of the porous carbon material can maximize the reduction of the influence on the equipment, and promote the development of large-scale production process.

[0084] 3. The porous carbon material has low impurity content, high specific surface area and high strength. The silicon-carbon composite material prepared by using the porous carbon material has excellent electrochemical performance in lithium ion batteries, especially the first efficiency (the first efficiency can be more than 83%) and the cycle performance (the 1C cycle failure parameter at 25℃ can be more than 55 cycles). DETAILED DESCRIPTION

[0085] The application will be further described in the following by way of examples without limiting the application to the examples described. The experimental methods in the following examples, unless otherwise specified, are carried out according to conventional methods and conditions, or according to the instructions of the commercial suppliers.

[0086] Phenolic resin, purchased from Hubei Hengye Technology Co., Ltd., model 2135.

[0087] Example 1

[0088] S0, Preparation of carbon material:

[0089] (1) 1 kg of phenolic resin, 2 kg of alcohol, and 60 g of urotropine (HMT) were mixed by a high-speed dispersion homogenizer at a dispersion speed of 2000 r / min for 60 min. Then, spray drying was performed at 130℃ until the particle diameter was 8 μm.

[0090] (2) The spray-dried powder was placed in a rotary furnace at a rotation speed of 10 r / min, and the nitrogen atmosphere was supplied at a rate of 1 L·kg -1 min -1 . Carbonization was performed: first stage, 4℃ / min, 50 min, to 200℃, 1 h, mainly to crosslink the phenolic resin; second stage, 4℃ / min, 113 min, to 652℃, 1 h. The prepared carbon material had a particle size D50 of 8.1 μm.

[0091] S1, Activation of carbon material: first, 10 kg of carbon material was mixed with 30 kg of zinc chloride, and the rotation speed of the rotary furnace was adjusted to 10 r / min, and the nitrogen supply rate was 2 L·kg -1 min -1 . The furnace was heated at a rate of 2℃ / min to 600℃, and then kept at this temperature for 3 h. After that, the temperature in the furnace was cooled to room temperature. Then, the material was taken out and washed with hydrochloric acid (concentration of 1 M) to obtain a first precursor (water content of 50%), and the waste liquid was recovered and dried.

[0092] S2, 35 kg of the first precursor was added to 7 kg of dilute nitric acid, and NMP was added to obtain a mixture slurry. The pH of the mixture slurry was 2, and the mass fraction of NMP in the mixture slurry was 5%. The mixture was soaked at room temperature for 10 h, and the pressure was continuously drawn to 10 kPa. Then, the material was filtered, and the filtered material was placed in a vacuum drying oven, the pressure inside the vacuum drying oven was kept at 10 kPa, the temperature was kept at 100℃, and the material was dried for 10 h to obtain a second precursor.

[0093] S3, then activated in a CO2 atmosphere in a rotary furnace, the supply rate was 2 L·kg 1 min-1 The porous carbon material is obtained by activating for 1 h at 600℃.

[0094] S4, preparation of the silicon-carbon composite material:

[0095] The atmosphere is switched to silane containing carrier gas (20% silane and 80% argon by volume percentage), and deposition is carried out at 550℃ for 8 h at a flow rate of 0.5 L·kg -1 min -1 .

[0096] Then acetylene is introduced at a flow rate of 2 L·kg -1 min -1 , and the silicon-carbon composite material is obtained by maintaining at 600℃ for 600 min.

[0097] Example 2

[0098] The difference from Example 1 is that the CO2 activation time in step S3 is 3 h; the rest of the conditions are the same as in Example 1.

[0099] Example 3

[0100] The difference from Example 1 is that the CO2 activation time in step S3 is 7 h; the rest of the conditions are the same as in Example 1.

[0101] Example 4

[0102] The difference from Example 1 is that the mass ratio of zinc chloride to carbon material in step S1 is 1:4, i.e. 10 kg of carbon material is used with 40 kg of zinc chloride; the rest of the conditions are the same as in Example 1.

[0103] Example 5

[0104] The difference from Example 4 is that the CO2 activation time in step S3 is 3 h; the rest of the conditions are the same as in Example 4.

[0105] Example 6

[0106] The difference from Example 4 is that the CO2 activation time in step S3 is 7 h; the rest of the conditions are the same as in Example 4.

[0107] Example 7

[0108] The difference from Example 1 is that the mass ratio of zinc chloride to carbon material in step S1 is 1:5, i.e. 10 kg of carbon material is used with 50 kg of zinc chloride; the rest of the conditions are the same as in Example 1.

[0109] Example 8

[0110] The difference between Example 7 and this example is that the CO2 activation time in step S3 is 3h; the rest of the conditions are the same as those in Example 7.

[0111] Example 9

[0112] The difference between Example 7 and this example is that the CO2 activation time in step S3 is 7h; the rest of the conditions are the same as those in Example 7.

[0113] Comparative Example 1

[0114] In Comparative Example 1, no zinc chloride is used for pore forming, i.e., steps S1 and S2 are not performed, and the carbon material obtained in step S0 is directly subjected to CO2 activation. The specific operation is as follows: the carbon material is transferred into a rotary furnace and activated in a CO2 atmosphere for 7h at a temperature of 600℃. Then, silicon deposition and carbon coating are performed according to step S4 of Example 1.

[0115] Comparative Example 2

[0116] The difference between Comparative Example 1 and this example is that the CO2 activation time is 8h; the rest of the conditions are the same as those in Comparative Example 1.

[0117] Comparative Example 3

[0118] The difference between Comparative Example 1 and this example is that the CO2 activation time is 9h; the rest of the conditions are the same as those in Comparative Example 1.

[0119] Comparative Example 4

[0120] The difference between Comparative Example 1 and this example is that the CO2 activation time is 10h; the rest of the conditions are the same as those in Comparative Example 1.

[0121] Comparative Example 5

[0122] The difference between Comparative Example 1 and this example is that the CO2 activation time is 11h; the rest of the conditions are the same as those in Comparative Example 1.

[0123] Comparative Example 6

[0124] The difference between this example and Example 1 is that no gas activation is performed, i.e., step S3 is not performed; the rest of the conditions are the same as those in Example 1.

[0125] Comparative Example 7

[0126] The difference between Comparative Example 1 and this example is that the CO2 activation time is 3h; the rest of the conditions are the same as those in Comparative Example 1.

[0127] Comparative Example 8

[0128] The difference between this example and Example 6 is that the process of treating with dilute nitric acid in step S2 is not performed; the rest of the conditions are the same as those in Example 6.

[0129] Example 1

[0130] 1. Particle size test: The D50 of the silicon-tin composite material was tested by a laser particle size analyzer. 50 The particle size was tested at 0 MPa, 5 MPa, 10 MPa, 15 MPa and 20 MPa, respectively.

[0131] 2. Element content test: The carbon content and sulfur content of each example and the comparative example were determined by a sulfur carbon instrument, and the silicon content was obtained by calculation, i.e., silicon content (%) = 100 - carbon content (%) - sulfur content (%).

[0132] 3. Porous carbon yield: The calculation method was to divide the mass of the prepared porous carbon by the amount of the input carbon material.

[0133] 4. Lithium intercalation expansion amount test: The following formula was used to calculate: (thickness of the electrode sheet after saturated lithium intercalation - thickness of the copper foil) / (thickness of the electrode sheet without lithium intercalation - thickness of the copper foil).

[0134] 5. Specific surface area test: The ASAP2020 of Mic was used.

[0135] 6. Impurity metal ion content test: The microwave digestion instrument, aqua regia, HF and other auxiliary detection, and liquid chromatography were used to detect the impurity metal ion content in the material.

[0136] Examples 1-9 and comparative examples 1-8 were tested according to the above test methods, and the test results are shown in Tables 1 and 2.

[0137] Table 1

[0138]

[0139]

[0140] Comparative Examples 1-5 and 7 are silicon-carbon composites prepared using a conventional CO2 activation method, while Examples 1-9 are silicon-carbon composites prepared using a ZnCl2 activation method. As can be seen from the table, the biggest advantage of the method based on the synergistic activation of ZnCl2 and CO2 is that the yield of porous carbon is greatly improved and the mesopore specific surface area is comparable to that of the silicon-carbon composite activated by CO2 for 11 h. This is mainly related to the activation method of ZnCl2 and the subsequent treatment with dilute nitric acid. The conventional porous carbon is usually etched by chemical etching, and most of the carbon material is discharged from the rotary kiln in the form of gas. The activation method using ZnCl2 allows the carbonized carbon material to grow around the ZnCl2 molecules and produce many mesopores, which opens all the internal pores of the porous carbon before further activation by CO2, greatly shortening the etching time and reducing the huge loss caused by opening the main channels and further deepening the etching during the preparation of the porous carbon. This method fully utilizes the advantages of ZnCl2, and the specific surface area of the porous carbon can reach more than 2000 m 2 / g.

[0141] The yield of the porous carbon of Examples 1-3 shows a decreasing trend, which is mainly due to the insufficient amount of ZnCl2. Some of the pores are opened by ZnCl2 and then etched away by CO2. However, as can be seen from Examples 4-9, when the amount of ZnCl2 added is within a suitable range, there is a large difference between 1 h and 3 h of CO2 activation, while the difference between 3 h and 7 h is small. This is mainly because the etching is basically completed at 3 h, and there are few active sites in the internal porous carbon that can adsorb CO2 molecules, so the development of the pores is no longer obvious.

[0142] As can be seen from Comparative Examples 1-5 and 7, the longer the CO2 activation time, the larger the specific surface area of the obtained silicon-carbon composite, the larger the mesopore specific surface area, and the more the silicon content of the obtained silicon-carbon composite, but the yield of the porous carbon material is lower. The lithium intercalation expansion amount of Comparative Examples 1-5 and 7 is close to the same, which is because of the mesopore expansion effect.

[0143] Compared with Examples 1-9, Comparative Example 6 has less micropore (small specific surface area) and thus less silicon content, and the development of micropores is not ideal.

[0144] Compared with Examples 1-9, Comparative Example 7 has very little silicon content, which is closer to the performance of hard carbon, so the expansion reduction effect is good.

[0145] Compared with Example 6, Comparative Example 8 is a sample that does not undergo the dilute nitric acid washing in step S2, and the silicon content is slightly lower, which may be because the impurities affect the development of micropores but do not affect the development of mesopores. Therefore, the lithium intercalation expansion amount is relatively lower than that of Example 6.

[0146] Table 2

[0147]

[0148] Compared with Comparative Example 8, Examples 1-9 further removed the generated Zn(NO3)2 under vacuum heating, greatly reducing the residual of Zn(NO3)2, making it possible for the porous carbon material prepared by the zinc chloride-based activation process to be applied in the field of battery applications. 2+

[0149] As can be seen from Examples 7-9, when the amount of zinc chloride reaches 5 times that of the porous carbon material, the proportion of mesopores in the material increases, which easily leads to a more obvious change in the particle size of the material at a lower pressure, resulting in a decrease in the overall strength of the material.

[0150] In addition, when the specific surface area of the mesopores is large, the lithium intercalation expansion amount of the silicon-carbon composite material decreases, which is mainly because the mesopores in the material, although they can alleviate expansion, also weaken the mechanical strength of the material. As can be seen from the above table, the silicon-carbon composite material obtained in Examples 1-9 of the present application achieves a balance between alleviating volume expansion and pressure resistance.

[0151] Effect Example 2

[0152] 1. Preparation of button cell

[0153] Preparation of negative electrode slurry and electrode sheet: 100 g of CMC, PAA, SBR, SP, CNTs, and silicon-carbon composite material with a mass ratio of 0.5:2.5:1:0.1:0.1:95.8 were added in the order of CMC, silicon-carbon composite material, SP, and CNTs. After dispersion for 3 h at a self-rotation speed of 300 r / min and a revolution speed of 1000 r / min using a planetary dispersing machine, 80% of the required deionized water with a solid content of 40% was injected at a self-rotation speed of 500 r / min and a revolution speed of 600 r / min for 1 h. PAA was added and dispersed at a self-rotation speed of 500 r / min and a revolution speed of 500 r / min for 1 h. The remaining 20% of the deionized water was injected, and SBR was finally added and dispersed at a self-rotation speed of 300 r / min and a revolution speed of 300 r / min for 1 h. The coated current collector used was a copper foil with a thickness of 8 μm, which was coated on both sides, with the coated surface facing the negative electrode of the button cell. The thickness of the single-side coated active material was about 40 μm, and the tap density was 1.7 g / cm 3 The coating speed was 40 cm / S, the baking temperature was 80°C, and the drying time was 400 s.

[0154] ​Formulation of electrolyte: the electrolyte is composed of EC 10%, PC 15%, DEC 20%, PP 30%, LiPF6 15%, FEC 6%, PS 2.5% and LiODFB 1.5% by mass percentage.

[0155] Half-cell assembly: the positive electrode uses the silicon-carbon composite material as above, the negative electrode uses lithium sheet, 0.5 g of the electrolyte as above is used to assemble a CR2032 button cell, and the voltage string port is 0-1.5V. The whole battery is assembled in a glove box to avoid contact with air.

[0156] 2. Electrochemical test

[0157] According to the following steps, the battery is tested for each silicon-carbon composite material.

[0158] (1) Test of first efficiency:

[0159] First, a CR2032 button cell is assembled, then discharged at 0.1V / h to 0.000V by using constant voltage discharge mode, and then charged at 0.1V / h to 1.5V, the charge and discharge capacity is recorded, and the first efficiency is calculated by the delithiation capacity / lithiation capacity.

[0160] (2) Test of 0.1C 0.8V gram capacity:

[0161] First, a CR2032 button cell is assembled, then discharged at 0.1V / h to 0.000V by using constant voltage discharge mode, and then charged at 0.1V / h to 0.8V, the charge capacity is recorded, and a CR2032 button cell is reassembled to record the 0.1C of the charge capacity, and then the constant current charge and discharge test is carried out, and the capacity is obtained after discharging to 0V and charging to 0.8V, and then the 0.1C 0.8V gram capacity is obtained by using the capacity / active mass in the electrode.

[0162] (3) Test of cycle failure parameters:

[0163] ① 1C 0.8V cycle failure parameters (measured at 25℃ and 45℃ respectively):

[0164] The above button cell is discharged at 0.1V / h to 0.000V by using constant voltage discharge mode, and then charged at 0.1V / h to 0.8V, and the charge capacity is recorded; a button cell is reassembled to record the 1C of the charge capacity, and then the constant current charge and discharge test is carried out, and the discharge capacity is recorded when repeatedly charged and discharged from 0V to 0.8V, and the cycle number is recorded when the discharge capacity is 60% of the 1C 0.8V gram capacity.

[0165] ② 2C 0.8V cycle failure parameters (measured at 25℃ and 45℃ respectively):

[0166] The above button cell is discharged at a constant voltage of 0.1 V / h to 0.000 V, and then charged at 0.1 V / h to 0.8 V, and the charge capacity is recorded; a button cell is reassembled, and a 2C constant current charge-discharge test is performed to record the charge capacity, and the discharge capacity is recorded repeatedly from 0 V to 0.8 V, and the cycle number is recorded when the discharge capacity is 60% of the 2C, 0.8 V gram capacity.

[0167] Examples 1-9 and Comparative Examples 1-8 were tested according to the above test method, and the test results are shown in Table 3.

[0168] Table 3

[0169]

[0170]

[0171] In Comparative Examples 1-5 and Comparative Example 7, the increase in specific surface area and the increase in mesopore specific surface area increase the silicon content of the obtained silicon-carbon composite material, and the first efficiency is improved, which is possibly because the filling of silicon reduces the appearance of ultramicropores in the porous carbon.

[0172] Compared with Examples 1-9, the first efficiency of Comparative Example 6 is higher, and the lithium intercalation expansion amount is low, but the 0.8 V gram capacity is small, which is because the specific surface area of the obtained silicon-carbon composite material is small, and the silicon content is small.

[0173] Compared with Examples 1-9, the first efficiency of Comparative Example 7 is higher, and the expansion is lower, but the 0.8 V gram capacity is only 660 mAh / g, which is because the specific surface area is very low, resulting in a small silicon content of the obtained silicon-carbon composite material, so the overall performance is biased towards that of hard carbon material.

[0174] Compared with Example 6, the specific surface area and silicon content of Comparative Example 8 are small, but the development of mesopores is not affected. However, because the impurity content is high, the zinc ion is greatly exceeded, affecting activation, causing the battery to self-discharge seriously, and the cycle performance drops sharply. The self-discharge is serious, so the cycle performance is particularly poor.

[0175] In summary, Examples 1-9 use multiple activation methods to synergistically control the development of porous carbon, reduce costs and increase efficiency, which is more conducive to reducing the production cost of silicon-carbon negative electrodes, so that silicon-carbon negative electrodes can be applied to power batteries, rather than being limited to the field of 3C consumer batteries.

Claims

1. A method for producing a porous carbon material, characterized by, It comprises the following steps: S1, after heat treatment and acid washing of a mixture containing carbon material and zinc chloride, a first precursor is obtained; the mass ratio of the carbon material to the zinc chloride is 1: (1-10); S2, mixing the first precursor, nitric acid and a polar solvent, soaking, drying to obtain a second precursor; S3, the second precursor is subjected to gas activation treatment; The gas source of the gas activation is CO2; The time of the gas activation is 1-10h; The gas activation is 0.5-5 L·kg 1 min -1 ; The temperature of the gas activation is 500-800℃; The specific surface area of the porous carbon material is 1500-2000 m 2 / g; the mesopore specific surface ratio of the porous carbon material is 10% or less.

2. The method for producing a porous carbon material according to claim 1, wherein Step S1 meets one or more of the following conditions a-h: a. The mass ratio of the carbon material to the zinc chloride is 1: (3-5); b. The temperature of the heat treatment is 500-800℃; c. The heating rate of the heat treatment is 1-10℃ / min; d. the heat treatment is carried out in an inert atmosphere, the inert atmosphere having a gas feed rate of 1-10 L·kg 1 min -1 ; e. The holding time of the heat treatment is 1-5h; f. The concentration of the acid used in the acid washing is 0.1-5M; g. the particle size D of the carbon material 50 is 5-10 μm; h. The water content of the first precursor is 20%-80%.

3. The method for producing a porous carbon material according to claim 2, wherein Step S1 meets one or more of the following conditions a-f: a. The temperature of the heat treatment is 600℃; b. The heating rate of the heat treatment is 2℃ / min; c. the inert atmosphere is supplied at a rate of 2 L·kg 1 min -1 ; d. The holding time of the heat treatment is 3h; e. The concentration of the acid used in the acid washing is 1M; f. the particle size D of the carbon material 50 was 8.1 pm.

4. The method for producing a porous carbon material according to claim 1, wherein Step S2 meets one or more of the following conditions a-f: a. The PH value of the mixture slurry of the first precursor, nitric acid and polar solvent is 2-6; b. The polar solvent is one or more of ethanol, N-methyl pyrrolidone, water, acetone, chloroform, diethyl ether, acetic acid, acetonitrile, isopropanol and methanol; c. The amount of the polar solvent is 0.1%-5%, the percentage being the mass percentage of the polar solvent in the mixture slurry of the first precursor, nitric acid and polar solvent; d. The soaking time is 5-20h; e. The soaking pressure is 10-50kPa; f. The drying is vacuum drying.

5. The method for producing a porous carbon material according to claim 4, wherein Step S2 meets one or more of the following conditions a-f: a. The soaking time is 10h; b. The soaking pressure is 10kPa; c. The vacuum drying pressure is 10-50kPa; d. The vacuum drying time is 5-20h; e. The vacuum drying temperature is 80-150℃.

6. The method of claim 1, wherein the porous carbon material is prepared by a process comprising: Step S3 meets one or more of the following conditions a-b: a. the gas activation of the gas feed rate is 2 L·kg 1 min -1 ; b. The temperature of the gas activation is 500-600℃.

7. The method for preparing porous carbon materials according to claim 1, characterized in that, Before step S1, it also includes: Step S0, carbonizing a mixture containing carbon source to obtain carbon material.

8. The method for producing a porous carbon material according to claim 7, wherein Step S0 meets one or more of the following conditions a-d: a. The carbon source contains one or more of resin, sucrose, glucose, fructose, starch, cellulose, triglyceride, fatty acid, hemicellulose, lignin and pitch; b. Before the carbonization, it also includes a drying step; c. The carbonization adopts segmented heat treatment; d. The carbonization is carried out in an inert atmosphere.

9. The method for producing a porous carbon material according to claim 8, wherein Step S0 meets one or more of the following conditions a-d: a. The carbon source is resin; b. The drying method is spray drying; c. The carbonization comprises the following stages: First stage: heating to 50-300℃ at a heating rate of 0.1-20℃ / min, and holding for 5-600 min; Second stage: heating to 300-1000℃ at a heating rate of 0.1-20℃ / min, and holding for 5-1200 min; d. The inert atmosphere is one or more of nitrogen, helium and argon.

10. The method for producing a porous carbon material according to claim 9, wherein The carbon source is phenolic resin.

11. A porous carbon material, characterized by, It is prepared by the preparation method of the porous carbon material in any one of claims 1-10.

12. The porous carbon material of claim 11, wherein, The porous carbon material satisfies the following conditions a and / or b: a. The micropore specific surface area ratio of the porous carbon material is more than 90%, wherein the micropore specific surface area ratio refers to the percentage of the specific surface area of the micropores to the total specific surface area of the porous carbon material; b. the total pore volume of the porous carbon material is 0.6-1.2 cm 3 / g.

13. The porous carbon material of claim 12, wherein, The total pore volume of the porous carbon material is 1.12 cm 3 / g.

14. The porous carbon material of claim 11, wherein, The porous carbon material satisfies the following conditions a and / or b: a. the specific surface area of the porous carbon material is 1535 m 2 / g, 1639 m 2 / g, 1867 m 2 / g, 1693 m 2 / g, 1832 m 2 / g or 1935 m 2 / g; b. The mesopore specific surface area ratio of the porous carbon material is 7.0%, 7.7%, 7.9%, 8.0%, 8.1%, 8.4%, 8.8%, 9.3% or 9.8%, wherein the mesopore specific surface area ratio refers to the percentage of the specific surface area of the mesopores to the total specific surface area of the porous carbon material.

15. A method of producing a silicon-carbon composite material, characterized by, It comprises the following steps: The porous carbon material in any one of claims 11-14 is sequentially subjected to silicon deposition and carbon coating; The silicon-carbon composite material comprises, from inside to outside, a porous carbon skeleton, a silicon deposition layer and a carbon coating layer; wherein the silicon deposition layer is located on the pore walls in the porous carbon skeleton.

16. The method of claim 15, wherein the silicon-carbon composite material is prepared by a process comprising: The preparation method satisfies one or more of the following conditions a-f: a. The silicon source for silicon deposition comprises silane; b. the aeration rate of the silicon deposition silicon source is 0.1-10 L·kg -1 min -1 ; c. In the process of silicon deposition, the silicon source and the carrier gas are simultaneously introduced; d. The temperature for silicon deposition is 400-800℃; e. The time for silicon deposition is 3-15h; f. The carbon coating is performed by gas phase deposition.

17. The method of claim 16, wherein the silicon-carbon composite material is prepared by a process comprising: The preparation method satisfies one or more of the following conditions a-i: a. The silane comprises one or more of monosilane, disilane, trisilane and tetrasilane; b. the aeration rate of the silicon deposition silicon source is 0.5 L-kg -1 min -1 ; c. The volume ratio of the silicon source to the carrier gas is 1:(2-6); d. The temperature for silicon deposition is 550℃; e. The time for silicon deposition is 8h; f. The carbon source for carbon coating by gas phase deposition comprises one or more of alkyne, alkane, alkene, aromatic compound and carbohydrate; g. The ventilation amount of the carbon source is 0.1-10 L·kg -1 min -1 ; h. The temperature for carbon coating is 300-1000℃; i. The time for carbon coating is 30-1200 min.

18. The method of claim 17, wherein the silicon-carbon composite material is prepared by a process comprising: The preparation method satisfies one or more of the following conditions a-d: a. The volume ratio of the silicon source to the carrier gas is 1:4; b. aeration rate of the carbon source 2 L-kg -1 min -1 ; c. The temperature for carbon coating is 600℃; d. The time for carbon coating is 600 min.

19. A silicon-carbon composite material, characterized by, The silicon-carbon composite material is prepared by the preparation method of the silicon-carbon composite material in any one of claims 15-18.

20. Use of the silicon-carbon composite material in claim 19 as an electrode material in a battery.

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