Silicon-carbon negative electrode material, preparation method thereof and battery

Abstract

The invention provides a silicon-carbon negative electrode material, a preparation method thereof and a battery. The method for preparing the silicon-carbon negative electrode material comprises the following steps: carrying out first carbonization treatment on thermoplastic resin to obtain resin carbon; uniformly mixing the resin carbon with an activating agent, and performing activated pore-forming to obtain resin-based porous carbon; performing second carbonization treatment on the resin-based porous carbon to obtain a porous carbon precursor; performing silicon vapor deposition on the porous carbon precursor to obtain silicon deposition porous carbon; and forming a carbon coating material on the surface of the silicon deposition porous carbon to obtain the silicon-carbon negative electrode material. Therefore, through the preparation method, the porous carbon precursor with high specific surface area, high pore volume and low resistivity can be prepared, so that the silicon-carbon negative electrode material with relatively high specific capacity and relatively low resistivity can be obtained.

Description

Technical Field

[0001] The present invention relates to the field of material technology, and in particular to a silicon-carbon negative electrode material and a preparation method thereof and a battery. Background Art

[0002] The theoretical capacity of traditional graphite is 372mAh / g, and the current product has reached 340-360mAh / g, which is close to the theoretical value. In order to improve the energy density of lithium batteries, it is necessary to develop negative electrode materials with higher specific capacity. The theoretical specific capacity of silicon negative electrode materials is as high as 4200mAh / g, which is about 10 times that of graphite negative electrode, and is the negative electrode material with the highest known specific capacity for lithium-ion batteries. However, when silicon is fully lithiated, its volume will expand by more than 300%. The huge volume change will lead to a series of negative effects, such as causing high internal stress in the battery, easy squeezing of the pole piece, and causing cracks in the silicon negative electrode material until it pulverizes. In order to relieve stress, silicon-carbon negative electrode materials can be modified and prepared by dispersing nano-silicon on porous carbon materials.

[0003] Resin-based porous carbon has attracted much attention due to its low impurity content, high batch stability, and relatively easy industrial preparation. However, conventional resin-based porous carbon has the disadvantage of high resistivity, which leads to greater obstruction of the transmission of electrons and ions inside the material, affecting the specific capacity, initial efficiency, and cycle efficiency of lithium batteries. The macroscopic manifestation is accelerated battery aging and a significant problem of insufficient battery life. Based on the above difficulties, it is necessary to develop a resin-based porous carbon with high specific surface area, rich pore structure, and low resistivity. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, one object of the present invention is to provide a method for preparing a silicon-carbon negative electrode material, which can effectively prepare a silicon-carbon negative electrode material with high specific capacity and low resistivity.

[0005] In one aspect of the present invention, the present invention provides a method for preparing a silicon-carbon negative electrode material. According to an embodiment of the present invention, the method for preparing a silicon-carbon negative electrode material comprises: subjecting a thermoplastic resin to a first carbonization treatment to obtain resin carbon; mixing the resin carbon and an activator evenly, activating and forming pores to obtain resin-based porous carbon; subjecting the resin-based porous carbon to a second carbonization treatment to obtain a porous carbon precursor; subjecting the porous carbon precursor to vapor deposition of silicon to obtain silicon-deposited porous carbon; and forming a carbon-coated material on the surface of the silicon-deposited porous carbon to obtain the silicon-carbon negative electrode material. Thus, by the above-mentioned preparation method, a porous carbon precursor having a high specific surface area, a high pore volume and a low resistivity can be prepared, which is conducive to obtaining a silicon-carbon negative electrode material with a high specific capacity and a low resistivity.

[0006] According to an embodiment of the present invention, the second carbonization treatment is microwave carbonization.

[0007] According to an embodiment of the present invention, the temperature of the second carbonization treatment is 1300° C. to 1600° C., and the carbonization time is 5 min to 20 min.

[0008] According to an embodiment of the present invention, the resistivity of the porous carbon precursor is 55 mΩ·cm to 225 mΩ·cm.

[0009] According to an embodiment of the present invention, the temperature of the first carbonization treatment is 500° C. to 700° C., and the time is 0.5 to 2 hours.

[0010] According to an embodiment of the present invention, the activated pore formation satisfies at least one of the following conditions: the mass ratio of the resin carbon to the activator is 1:(2-4); the treatment is carried out in an inert atmosphere at 650°C-800°C for 1-2h.

[0011] According to an embodiment of the present invention, the specific surface area of ​​the resin-based porous carbon is 1500 m 2 / g~2600m 2 / g, pore volume is 0.6cm 3 / g~1.4cm 3 / g.

[0012] According to an embodiment of the present invention, the vapor deposited silicon satisfies at least one of the following conditions: the temperature is 400°C to 500°C, the time is 5 to 8 hours; the flow rate of the silane / nitrogen mixed gas is 20L / min to 35L / min; the volume ratio of silane and nitrogen is 1:(2 to 4).

[0013] According to an embodiment of the present invention, the method for preparing a silicon-carbon negative electrode material also includes at least one of the following steps: crushing the porous carbon precursor to obtain the porous carbon precursor with a particle size D50 of 2 to 12 μm; after the activation and pore formation to obtain the resin-based porous carbon, the resin-based porous carbon is cleaned.

[0014] In another aspect of the present invention, the present invention provides a silicon-carbon negative electrode material. According to an embodiment of the present invention, the silicon-carbon negative electrode material is prepared by the method described above. As a result, the silicon-carbon negative electrode material has a higher specific capacity and a lower resistivity. It can be understood by those skilled in the art that the silicon-carbon negative electrode material has all the features and advantages described above, and will not be described in detail here.

[0015] In another aspect of the present invention, the present invention provides a battery. According to an embodiment of the present invention, the battery includes a negative electrode plate, and the negative electrode plate includes the silicon-carbon negative electrode material described above. As a result, the battery has good specific capacity, better first efficiency and cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0017] Figure 1 It is a flow chart of a method for preparing a silicon-carbon negative electrode material in one embodiment of the present invention. DETAILED DESCRIPTION

[0018] The scheme of the present invention will be explained below in conjunction with the embodiments. It will be appreciated by those skilled in the art that the following embodiments are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. Where specific techniques or conditions are not indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used are not indicated by the manufacturer and are all conventional products that can be obtained commercially.

[0019] The present invention is described below with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present invention in any way.

[0020] In one aspect of the present invention, the present invention provides a method for preparing a silicon-carbon negative electrode material. Figure 1 , the method for preparing the silicon-carbon negative electrode material comprises:

[0021] S100: subjecting the thermoplastic resin to a first carbonization treatment to obtain resin carbon.

[0022] According to some embodiments of the present invention, there are no special requirements for the specific type of thermoplastic resin, and those skilled in the art can flexibly select it according to actual needs. For example, it can be at least one of polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polyamide (PA), polyoxymethylene (POM), polycarbonate (PC), acrylic resin, saturated polyester, fluoroplastic, polysulfone resin, polyether ketone resin, polyphenylene ether resin, etc.

[0023] According to some embodiments of the present invention, the temperature of the first carbonization treatment is 500°C to 700°C, such as 500°C, 550°C, 600°C, 650°C, 700°C, etc., and the time is 0.5 to 2h, such as 0.5h, 0.8h, 1h, 1.2h, 1.5h, 1.8h, 2h, etc. In this way, the carbonization temperature of the first carbonization treatment can effectively carbonize the thermoplastic resin and remove volatile impurities in the thermoplastic resin, but cannot completely carbonize the thermoplastic resin, which is conducive to obtaining resin-based porous carbon with a high specific surface area after the subsequent activation pore-forming treatment.

[0024] In some embodiments of the present invention, after the first carbonization treatment, the thermoplastic resin can be carbonized to more than 90%, but will not be completely carbonized.

[0025] In some embodiments of the present invention, the first carbonization process may be performed in a rotary kiln.

[0026] In some embodiments of the present invention, before the subsequent step S200 is performed, the resin carbon may be further crushed and the resin carbon of the target particle size may be collected by screening. In some embodiments, the resin carbon may be crushed by a double roll crusher and / or an ultrafine stone mill and screened to obtain the resin carbon of the target particle size ≤ 80 μm.

[0027] S200: The resin carbon and the activator are mixed evenly, and activated to form pores to obtain resin-based porous carbon. Through this step, resin-based porous carbon with a rich pore structure can be obtained.

[0028] According to some embodiments of the present invention, the mass ratio of resin carbon to activator is 1:(2-4), for example, the mass ratio of resin carbon to activator is 1:2, 1:2.5, 1:3, 1:3.5, 1:4, etc. The above ratio can make the carbon react with the activator to obtain a rich pore structure, increase the specific surface area of ​​the resin-based porous carbon, and thus facilitate the subsequent deposition of silicon, and solve the problem of large volume expansion of silicon materials during lithium extraction; if the amount of activator is relatively small (mass ratio greater than 1:1), the resulting pore structure is relatively reduced, which is not conducive to the improvement of its specific surface area; if the amount of activator is relatively large (mass ratio less than 1:4), the excess activator will further etch the carbon atoms of the previously formed pore skeleton, so that some of the original microporous structures become mesopores or even macropores, and even cause the original pore structure to collapse, which relatively reduces the specific surface area and pore volume of the resin-based porous carbon.

[0029] According to some embodiments of the present invention, the activation pore-forming conditions may be an activation treatment at 650°C to 800°C (e.g., 650°C, 700°C, 750°C, 800°C) in an inert atmosphere for 1 to 2 hours. Under the above conditions, resin-based porous carbon with a higher specific surface area and pore volume can be obtained.

[0030] According to some embodiments of the present invention, the activation pore making can be performed in a rotary kiln, and the air in the rotary kiln is replaced with an inert gas, wherein the inert gas includes but is not limited to nitrogen, argon, helium and the like.

[0031] According to some embodiments of the present invention, the material of the activator includes at least one of potassium hydroxide and sodium hydroxide.

[0032] According to some embodiments of the present invention, after the resin-based porous carbon is obtained by activation and pore formation, the resin-based porous carbon is cleaned. In some specific embodiments, the cleaning process may include steps such as pickling, water washing, and drying. Among them, the pickling may be carried out by acid washing such as hydrochloric acid and nitric acid to remove the reaction products of the unreacted activator activation and pore formation process, and then washed with water until neutral.

[0033] According to some embodiments of the present invention, the specific surface area of ​​the resin-based porous carbon is 1500 m 2 / g~2600m 2 / g (for example, the specific surface area is 1500m 2 / g、1600m 2 / g、1700m 2 / g、1800m 2 / g、1900m 2 / g, 2000m 2 / g, 2100m 2 / g, 2200m 2 / g, 2300m 2 / g, 2400m 2 / g、2500m 2 / g, 2600m 2 / g, etc.), and the pore volume is 0.6cm 3 / g~1.3cm 3 / g (for example, 0.6cm 3 / g, 0.7cm 3 / g, 0.8cm 3 / g, 0.9cm 3 / g, 1.0cm 3 / g, 1.1cm 3 / g, 1.2cm 3 / g, 1.3cm 3 / g, 1.4cm 3 / g, etc.). It can be seen that resin-based porous carbon with a large specific surface area and pore volume can be prepared, which is beneficial to obtain a porous carbon precursor with a high specific surface area and pore volume.

[0034] S300: performing a second carbonization treatment on the resin-based porous carbon to obtain a porous carbon precursor. Through further carbonization, the resistivity of the resin-based porous carbon can be effectively reduced to obtain a porous carbon precursor with low resistivity.

[0035] According to some embodiments of the present invention, the second carbonization treatment is microwave carbonization. In this way, carbonization by microwave method can make the sample evenly heated and efficiently carbonized, and the original porous carbon structure will not be excessively damaged during the carbonization process, so that the resin-based porous carbon still maintains a high specific surface area and pore volume after carbonization, and microwave heating can quickly form heat inside the entire object, greatly shortening the time required for heating. In some specific embodiments, the second carbonization treatment can be performed in a microwave carbonization furnace.

[0036] According to some embodiments of the present invention, the temperature of the second carbonization treatment is 1300°C to 1600°C, such as 1300°C, 1350°C, 1400°C, 1450°C, 1500°C, 1550°C, 1600°C, etc., the heating rate is 40 to 50°C / min, such as 40°C / min, 45°C / min, 50°C / min, and the carbonization time (i.e., the holding time after reaching the temperature of the second carbonization treatment) is 5min to 20min, such as 5min, 8min, 10min, 12min, 15min, 18min, 20min, etc. Under the above conditions, the second carbonization can be well achieved, and the resistivity of the porous carbon precursor can be effectively reduced.

[0037] According to some embodiments of the present invention, the resistivity of the porous carbon precursor is 55mΩ·cm to 225mΩ·cm, such as 55mΩ·cm, 60mΩ·cm, 70mΩ·cm, 80mΩ·cm, 90mΩ·cm, 100mΩ·cm, 110mΩ·cm, 120mΩ·cm, 130mΩ·cm, 140mΩ·cm, 50mΩ·cm, 160mΩ·cm, 170mΩ·cm, 180mΩ·cm, 190mΩ·cm, 200mΩ·cm, 210mΩ·cm, 220mΩ·cm, 225mΩ·cm, etc. It can be seen that the porous carbon precursor prepared by the present invention has a lower resistivity, which is conducive to obtaining a silicon-carbon negative electrode material with a lower resistivity.

[0038] According to some embodiments of the present invention, the porous carbon precursor may be further crushed to obtain a porous carbon precursor having a particle size D50 of 2 to 12 μm (e.g., 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, etc.). The porous carbon precursor having the above particle size is conducive to the preparation of silicon-carbon negative electrode materials with good electrical properties.

[0039] According to some embodiments of the present invention, the crushing process can be performed using a jet mill crushing device.

[0040] The specific surface area and pore volume of the porous carbon precursor for preparing silicon-carbon negative electrode materials can directly affect the amount of subsequent deposited silicon, and are one of the factors that determine the electrochemical properties of the material. Therefore, it is crucial to regulate the specific surface area and pore volume of the porous carbon precursor. According to some embodiments of the present invention, as described above, the resin-based porous carbon obtained by activation and pore formation in the present invention has a rich pore structure, a high specific surface area and pore volume. On this basis, through the second microwave carbonization treatment, the resistivity of the porous carbon precursor is further reduced, and it can penetrate into the interior of the heated object, so that the inside and outside of the object are heated at the same time. Different from the traditional heat conduction (rotary kiln, box furnace, heating rate of 5-10°C / min) which gradually transfers heat from the surface of the object to the inside, microwave heating (in some examples, the heating rate of microwave heating is 40-50°C / min) can form heat very quickly inside the entire object, greatly shortening the time required for heating. Therefore, the specific surface area and pore volume of the porous carbon are substantially not affected. Therefore, through the above method of the present invention, a porous carbon precursor with a higher specific surface area, pore volume and lower resistivity can be obtained, which is beneficial to the subsequent deposition of nano-silicon.

[0041] S400: vapor-depositing silicon on the porous carbon precursor to obtain silicon-deposited porous carbon. This step can achieve the deposition of nano-silicon in the pores of the porous carbon precursor, thereby increasing the specific capacity of the silicon-carbon negative electrode material, and the pore structure can provide a certain expansion space for silicon to buffer the volume expansion effect of silicon in the process of lithium embedding, thereby preventing the silicon-carbon negative electrode material from cracking and other undesirable phenomena.

[0042] According to some embodiments of the present invention, the temperature of vapor-deposited silicon is 400°C to 500°C (for example, 400°C, 420°C, 450°C, 480°C, 500°C, etc.), and the time is 5 to 8 hours (for example, 5 hours, 6 hours, 7 hours, 8 hours); the flow rate of the silane / nitrogen mixed gas is 20L / min to 35L / min (for example, 20L / min, 22L / min, 25L / min, 27L / min, 30L / min, 32L / min, 35L / min, etc.); the volume ratio of silane and nitrogen is 1:(2 to 4) (for example, the volume ratio is 1:2, 1:3, 1:4, etc.). Under the above conditions, nano-silicon can be effectively deposited in the pores of the porous carbon precursor to obtain silicon-deposited porous carbon.

[0043] According to some embodiments of the present invention, vapor deposition of silicon may be performed in an inert atmosphere, and the inert gas may include at least one of nitrogen, helium, and argon.

[0044] According to some embodiments of the present invention, the step of vapor depositing silicon may be performed in a rotary kiln.

[0045] S500: forming a carbon coating material on the surface of silicon-deposited porous carbon to obtain a silicon-carbon negative electrode material.

[0046] According to some embodiments of the present invention, the process steps for forming a carbon-coated material on the surface of silicon-deposited porous carbon may include: introducing 15 to 30 L / min of acetylene / nitrogen mixed gas into the furnace, keeping it warm for 3 to 5 hours, and obtaining a product silicon-carbon negative electrode material.

[0047] According to some embodiments of the present invention, the carbon coating process can be carried out in a rotary kiln, so that after the nano-silicon deposition is completed, the introduction of silane is stopped, and acetylene is introduced to continue the carbon coating process.

[0048] According to an embodiment of the present invention, a porous carbon precursor having a high specific surface area, a high pore volume and a low resistivity can be prepared by the above-mentioned preparation method, which is conducive to obtaining a silicon-carbon negative electrode material with a high specific capacity and a low resistivity.

[0049] In another aspect of the present invention, the present invention provides a silicon-carbon negative electrode material. According to an embodiment of the present invention, the silicon-carbon negative electrode material is prepared by the method described above. As a result, the silicon-carbon negative electrode material has a higher specific capacity and a lower resistivity. It can be understood by those skilled in the art that the silicon-carbon negative electrode material has all the features and advantages described above, and will not be described in detail here.

[0050] In another aspect of the present invention, the present invention provides a battery. According to an embodiment of the present invention, the battery includes a negative electrode plate, and the negative electrode plate includes the silicon-carbon negative electrode material described above. As a result, the battery has good specific capacity, better first efficiency and cycle performance.

[0051] According to some embodiments of the present invention, in addition to the above-mentioned silicon-carbon negative electrode material, the negative electrode sheet may further include at least one of a negative electrode current collector, graphite, a conductive agent and a binder. The silicon-carbon negative electrode material, graphite, a conductive agent, a binder and a solvent are mixed to form a slurry and coated on the negative electrode current collector to obtain a negative electrode sheet, wherein the silicon-carbon negative electrode material and graphite are used as active materials of the negative electrode sheet. In some embodiments, the negative electrode current collector may be a metal foil, for example, a copper foil; in some embodiments, the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS); in some embodiments, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0052] According to some embodiments of the present invention, the battery may be a lithium ion battery or a sodium ion battery.

[0053] According to some embodiments of the present invention, the battery includes, in addition to the aforementioned negative electrode sheet, a positive electrode sheet, an electrolyte solution and a separator. According to some embodiments of the present invention, the positive electrode sheet, the negative electrode sheet and the separator can be made into an electrode assembly by a winding process or a lamination process.

[0054] According to some embodiments of the present invention, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material, a conductive agent, and a binder.

[0055] In some embodiments, the positive electrode current collector may be a metal foil, such as an aluminum foil.

[0056] In some embodiments, the positive electrode active material may be a positive electrode active material for a lithium ion battery or a sodium ion battery known in the art. Taking a lithium ion battery as an example, the positive electrode active material may include at least one of the following materials: a lithium phosphate containing an olivine structure, a lithium transition metal oxide, wherein examples of the lithium transition metal oxide may include but are not limited to lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811)), lithium nickel cobalt aluminum oxide (such as LiNi 0.8 Co 0.15 Al 0.05 O2) and its modified compounds, etc.; examples of lithium-containing phosphates with olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0057] In some embodiments, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0058] In some embodiments, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0059] According to some embodiments of the present invention, the electrolyte solution includes an electrolyte salt and a solvent, and the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate and lithium tetrafluorooxalate phosphate. In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0060] According to some embodiments of the present invention, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0061] Example

[0062] Example 1

[0063] First, 10 kg of thermoplastic resin was weighed and placed in a rotary kiln for carbonization. The initial temperature was 25 °C, the heating rate was 5 °C / min, the carbonization temperature was 600 °C, and the carbonization time was 1 h. The carbonized resin carbon was crushed using a double roll crusher and an ultrafine stone mill, and the resin carbon with a particle size of less than 80 μm was screened and collected.

[0064] Then, 1 kg of resin carbon was mixed with KOH in a mass ratio of 1:2, and placed in a rotary kiln for activation and pore formation. The activation temperature was 700°C and the activation time was 2 h. After the activation, 2 M HCl was used for acid washing for 5 h, and then washed with water until neutral, and dried to obtain resin-based porous carbon.

[0065] The resin-based porous carbon was sent into a microwave carbonization furnace for secondary high-temperature microwave carbonization. The carbonization temperature was 1300°C, the heating rate was 50°C / min, and the carbonization time was 10min to obtain a porous carbon precursor. The porous carbon precursor was crushed again to obtain a particle size range of D V 50 is a porous carbon precursor of 2 to 12 μm;

[0066] The porous carbon precursor is placed in a rotary kiln, the air in the furnace is replaced with an inert gas, the furnace is heated to 450°C, a silane / nitrogen mixed gas is introduced at a flow rate of 25 L / min, and the mixture is kept warm for 6 hours to obtain silicon-deposited porous carbon;

[0067] Stop introducing silane, introduce acetylene / nitrogen mixed gas at 20 L / min, keep warm for 4 hours, and obtain the product silicon-carbon negative electrode material.

[0068] Example 2

[0069] The steps are basically the same as those in Example 1, except that 1 kg of resin carbon is mixed with KOH in a mass ratio of 1:3 and placed in a rotary kiln for activation and pore formation.

[0070] Example 3

[0071] The steps are basically the same as those in Example 1, except that 1 kg of resin carbon is mixed with KOH in a mass ratio of 1:4 and placed in a rotary kiln for activation and pore formation.

[0072] Example 4

[0073] The steps are basically the same as those in Example 2, except that the carbonization temperature during the secondary high-temperature microwave carbonization is 1400°C.

[0074] Example 5

[0075] The steps are basically the same as those in Example 2, except that during the secondary high-temperature microwave carbonization process, the carbonization temperature is 1500°C.

[0076] Example 6

[0077] The steps are basically the same as those in Example 2, except that in the secondary high-temperature microwave carbonization process, the carbonization temperature is 1600°C.

[0078] Example 7

[0079] The steps are basically the same as those in Example 2, except that during the secondary high-temperature carbonization process, the second carbonization treatment is carried out in a rotary kiln with a heating rate of 5°C / min.

[0080] Comparative Example 1

[0081] First, 10 kg of thermoplastic resin was weighed and placed in a rotary kiln for carbonization. The initial temperature was 25 °C, the heating rate was 5 °C / min, the carbonization temperature was 600 °C, and the carbonization time was 1 h. The carbonized resin carbon was crushed using a double roll crusher and an ultrafine stone mill, and the resin carbon with a particle size of less than 80 μm was screened and collected.

[0082] Then, 1 kg of resin carbon was mixed with KOH in a mass ratio of 1:2, and placed in a rotary kiln for activation and pore formation. The activation temperature was 700°C and the activation time was 2 h. After the activation, 2 M HCl was used for acid washing for 5 h, and then washed with water until neutral, and dried to obtain resin-based porous carbon.

[0083] The resin-based porous carbon is crushed again to obtain a particle size range of D V 50 is a porous carbon precursor of 2 to 12 μm;

[0084] The porous carbon precursor is placed in a rotary kiln, the air in the furnace is replaced with an inert gas, the furnace is heated to 450°C, a silane / nitrogen mixed gas is introduced at a flow rate of 25 L / min, and the mixture is kept warm for 6 hours to obtain silicon-deposited porous carbon;

[0085] Stop introducing silane, introduce acetylene / nitrogen mixed gas at 20 L / min, keep warm for 4 hours, and obtain the product silicon-carbon negative electrode material.

[0086] Comparative Example 2

[0087] The steps are basically the same as those in Comparative Example 1, except that 1 kg of resin carbon is mixed with KOH in a mass ratio of 1:3 and placed in a rotary kiln for activation and pore formation.

[0088] Comparative Example 3

[0089] The steps are basically the same as those in Comparative Example 1, except that 1 kg of resin carbon is mixed with KOH in a mass ratio of 1:4 and placed in a rotary kiln for activation and pore formation.

[0090] The specific surface area, pore volume, microporosity, average pore diameter and resistivity of the porous carbon precursors obtained in the above embodiments and comparative examples were tested. The test data can be seen in Table 1.

[0091] The silicon-carbon negative electrode materials obtained in the above embodiments and comparative examples were used to prepare test cells (CR2025 lithium ion half-cells), and the data of the first lithium insertion and extraction specific capacity, the first coulombic efficiency, the capacity retention rate and the like of the tests can be found in Table 1. The preparation method of the CR2025 lithium ion half-cell includes:

[0092] The silicon-carbon negative material prepared above was mixed with carbon nanotubes and polyacrylic acid LA136D in a mass ratio of 90:5:5, and an appropriate amount of deionized water was added, and a homogenizer was used to prepare a paste. The paste was evenly scraped on the copper foil to a thickness of 180 μm, and then baked in a drying oven to prepare a pole piece.

[0093] The baked electrode pieces were pressed and cut into circular electrodes with a diameter of 16 mm. The circular electrodes were neatly stacked in the order of negative electrode shell, spring sheet, gasket, lithium sheet, diaphragm, circular electrode, and positive electrode shell in a glove box, and the electrolyte was injected and packaged to obtain a CR2025 lithium-ion half-cell.

[0094] Performance Testing:

[0095] Unless otherwise specified, the first lithium insertion and extraction specific capacity, the first coulombic efficiency and the capacity retention rate of the present invention are obtained by performing charge and discharge tests on the above-mentioned CR2025 lithium-ion half-cells using a Blue Electric series battery testing system.

[0096] 1. First lithium removal specific capacity

[0097] The battery was discharged to 0V with a current of 0.05C, left to stand for 3 minutes, and then discharged to 0V with a current of 50μA to obtain the first lithium insertion capacity of the silicon-carbon material. The battery was then discharged with a current of 0.05C until the voltage was ≥1.5V to obtain the first lithium removal capacity.

[0098] 2. First Coulombic efficiency

[0099] The first coulombic efficiency is calculated based on the first lithium desorption specific capacity and the first lithium insertion specific capacity. The first coulombic efficiency = first lithium desorption specific capacity / first lithium insertion specific capacity.

[0100] 3. Capacity retention rate

[0101] The battery was charged and discharged cyclically with a current of 0.2C, and the first cycle capacity C1 and the 200th cycle capacity C2 were recorded respectively. The capacity retention rate = C2 / C1.

[0102] Table 1

[0103]

[0104] Example 1-Example 3 and Comparative Example 1-Example 3 (the difference between Comparative Example 1-Example 3 and Example 1-Example 3 is that no microwave high temperature carbonization step is performed) are used to explore the effect of different carbon-alkali ratios on the specific surface area and pore structure of porous carbon precursors. The carbon-alkali ratios of Examples 1, 2 and 3 are 1:2, 1:3 and 1:4, respectively. The specific surface area and pore volume of the prepared porous carbon precursor are 1533.53 m 2 / g, 2497.47m2 / g, 2117.89m 2 / g and 0.6094cm 3 / g, 1.2465cm 3 / g, 0.9643cm 3 / g, the carbon-base ratios of Comparative Examples 1, 2 and 3 are also 2, 3 and 4 respectively, and the specific surface area and pore volume of the prepared porous carbon precursor are 1690.72 m 2 / g, 2637.98m 2 / g, 2264.09m 2 / g and 0.7048cm 3 / g, 1.3090cm 3 / g, 1.0263cm 3 / g. It can be seen that appropriately increasing the carbon-base ratio can promote a more intense reaction between the carbon atoms in the sample and KOH, induce the formation of a richer pore structure, increase the specific surface area, facilitate the deposition of nano-silicon, and solve the problem of large volume expansion of silicon materials during lithium extraction. As shown in Table 1, the specific capacity of Example 2 after depositing nano-silicon is increased to 2497.47 mAh / g, significantly higher than 1533.53 mAh / g of Example 1; the specific capacity of Comparative Example 2 after depositing nano-silicon is increased to 2033 mAh / g, significantly higher than 1690.72 mAh / g of Comparative Example 1.

[0105] However, when the carbon-alkali ratio was increased to 1:4, the specific surface area and pore volume of Example 3 decreased to 2117.89 m 2 / g and 0.9643cm 3 / g; Compared with comparative example 2, the specific surface area and pore volume of comparative example 3 decreased to 2264.09m 2 / g and 1.0263cm 3 / g. This is because too much KOH etches the previously formed skeleton carbon atoms, and some original micropores become mesopores or even macropores, causing the original pore structure to collapse, reducing the specific surface and pore volume of the porous carbon precursor, which is not conducive to the deposition of nano-silicon.

[0106] In view of the problem of high resistivity of thermoplastic resin-based porous carbon, the present invention designs microwave secondary high-temperature carbonization to reduce the resistivity of the porous carbon precursor and improve the first coulomb efficiency and cycle capacity retention rate of the silicon-carbon material. According to the data of Comparative Examples 1-3, the resistivity of the activated resin-based porous carbon is about 220mΩ.cm. According to the data of Examples 1-3, it can be seen that after microwave secondary carbonization at 1300°C, it is significantly reduced to 140-150mΩ.cm. Compared with Comparative Examples 1-3, the specific surface area of ​​the porous carbon of Examples 1-3 is only slightly reduced, which has little effect on the subsequent deposition of nano-silicon.

[0107] It can be seen from the data of Example 2, Example 4, Example 5 and Example 6 that by increasing the temperature of microwave carbonization, the resistivity of the porous carbon precursor shows a downward trend, the first efficiency and cycle performance are improved, and the electrochemical performance of the silicon-carbon negative electrode material is improved.

[0108] By comparing Example 2 and Example 7, it can be seen that microwave carbonization can better reduce the resistivity of the porous carbon precursor while maintaining its good pore structure.

[0109] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0110] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0111] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a silicon-carbon negative electrode material, characterized in that: include: The thermoplastic resin is subjected to a first carbonization treatment to obtain resin carbon; The resin carbon and the activator are mixed evenly, and activated to form pores to obtain resin-based porous carbon; Performing a second carbonization treatment on the resin-based porous carbon to obtain a porous carbon precursor; vapor-depositing silicon on the porous carbon precursor to obtain silicon-deposited porous carbon; A carbon coating material is formed on the surface of the silicon-deposited porous carbon to obtain the silicon-carbon negative electrode material.

2. The method according to claim 1, characterized in that The second carbonization treatment is microwave carbonization.

3. The method according to claim 1 or 2, characterized in that: The temperature of the second carbonization treatment is 1300° C. to 1600° C., and the carbonization time is 5 min to 20 min.

4. The method according to claim 1 or 2, characterized in that: The resistivity of the porous carbon precursor is 55 mΩ·cm to 225 mΩ·cm.

5. The method according to claim 1 or 2, characterized in that: The temperature of the first carbonization treatment is 500° C. to 700° C., and the time is 0.5 to 2 hours.

6. The method according to claim 1 or 2, characterized in that: The activation pore formation satisfies at least one of the following conditions: The mass ratio of the resin carbon to the activator is 1:(2-4); Treat in an inert atmosphere at 650°C to 800°C for 1 to 2 hours.

7. The method according to claim 6, characterized in that The specific surface area of ​​the resin-based porous carbon is 1500 m 2 / g~2600m 2 / g, pore volume is 0.6cm 3 / g~1.4cm 3 / g.

8. The method according to claim 1 or 2, characterized in that: The vapor deposited silicon satisfies at least one of the following conditions: The temperature is 400℃~500℃, and the time is 5~8h; The flow rate of silane / nitrogen mixed gas is 20L / min~35L / min; The volume ratio of silane to nitrogen is 1:(2-4).

9. The method according to claim 1 or 2, characterized in that: Also includes at least one of the following steps: The porous carbon precursor is crushed to obtain the porous carbon precursor with a particle size D50 of 2 to 12 μm; After the resin-based porous carbon is obtained by the activation and pore creation, the resin-based porous carbon is cleaned.

10. A silicon-carbon negative electrode material, characterized in that: The invention is prepared by the method according to any one of claims 1 to 9.

11. A battery, characterized in that: It comprises a negative electrode plate, and the negative electrode plate comprises the silicon-carbon negative electrode material according to claim 10.

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