Porous silicon / carbon composite negative electrode material and preparation method and application thereof

Abstract

The invention provides a porous silicon / carbon composite negative electrode material and a preparation method and application thereof.The preparation method comprises the steps that firstly, polyamide acid is evenly distributed in pore structures in porous silicon particles through a low-concentration polyamide acid solution dipping method, and a polyamide acid / porous silicon compound is obtained; mixing the polyamic acid / porous silicon compound with a high-concentration polyamic acid solution, coating the mixture on a substrate, and curing to obtain a polyimide / porous silicon compound composite membrane loaded on the substrate; then, polyimide inside and on the surfaces of the porous silicon particles is converted into graphene in situ by utilizing a laser-induced composite film, the porous silicon / carbon composite negative electrode material has a spatial three-dimensional network conductive channel structure, the cycle performance of a battery can be improved, the volume expansion of the battery can be reduced, and the performance of the battery can be improved. And the conductivity of the porous silicon / carbon composite negative electrode material can be remarkably improved, the resistance of a negative electrode diaphragm of a battery is greatly reduced, and the rate capability and the first coulombic efficiency of the battery are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery negative electrode materials, and in particular to a porous silicon / carbon composite negative electrode material and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries, due to their advantages such as small size and high energy density, are widely used in various mobile electronic devices and new energy vehicles. Currently, the majority of commercial lithium-ion battery anode materials are graphite. While graphite offers excellent cycling stability when used as a negative electrode material, its theoretical capacity is relatively low, making it difficult to meet the energy endurance and charging time requirements of mobile electronic devices and new energy vehicles.

[0003] Silicon negative electrode has the advantages of high theoretical specific capacity (theoretical capacity at room temperature is 3579mAh / g) and low charge and discharge voltage (<0.5V), making it one of the candidates for new lithium-ion battery negative electrode materials. However, the silicon negative electrode will undergo severe volume expansion and contraction during the alloying and dealloying process. The stress generated during the volume change will cause the negative electrode material to pulverize and fall off from the current collector, resulting in rapid decay of battery capacity and poor cycle performance. Studies have found that porous silicon / carbon negative electrode materials can take into account high capacity and high initial efficiency while ensuring that the negative electrode sheet has a low expansion rate. However, the conductivity of porous silicon / carbon negative electrode materials is much worse than that of graphite negative electrode materials, which has a great impact on the overall rate performance and voltage platform of the battery.

[0004] To address this type of problem, current approaches mostly involve improving the carbon skeleton of porous silicon / carbon negative electrode materials and the vapor deposition of nanosilicon, such as adding conductive materials with strong conductivity to the carbon source for generating the carbon skeleton or improving the deposition process of nanosilicon. However, the effects of these improvements are not very significant. Summary of the Invention

[0005] In order to address the deficiencies of the prior art, the purpose of the present invention is to provide a porous silicon / carbon composite negative electrode material and its preparation method and application. The porous silicon / carbon composite negative electrode material provided by the present invention has a spatial three-dimensional network conductive channel structure, which can not only improve the cycle performance of the battery and reduce the volume expansion of the battery, but also significantly improve the conductive performance of the porous silicon / carbon composite negative electrode material, greatly reduce the resistance of the battery's negative electrode diaphragm, and significantly improve the battery's rate performance and first coulombic efficiency.

[0006] The object of the present invention is achieved through the following technical solutions:

[0007] A method for preparing a porous silicon / carbon composite negative electrode material comprises the following steps:

[0008] (1) mixing a diamine compound, a dianhydride compound, a catalyst and water, reacting to prepare a polyamic acid solution;

[0009] (2) mixing the porous silicon and the polyamic acid solution, impregnating, filtering, and drying to prepare a polyamic acid / porous silicon composite;

[0010] (3) mixing a polyamic acid / porous silicon composite and a polyamic acid solution and coating the mixture on a substrate, curing the mixture to obtain a polyimide / porous silicon composite film supported on the substrate, and in-situ constructing a porous silicon / graphene composite material on the substrate by laser induction of the composite film;

[0011] (4) scraping the porous silicon / graphene composite material prepared in step (3) from the substrate to obtain a porous silicon / graphene composite powder;

[0012] (5) The porous silicon / graphene composite powder obtained in step (4) is subjected to carbon coating and sintering treatment to prepare the porous silicon / carbon composite negative electrode material.

[0013] According to an embodiment of the present invention, in step (1), the diamine compound is selected from one or a mixture of p-phenylenediamine, 4,4'-diaminodiphenyl ether, p-phenylenediamine, m-p-phenylenediamine, 1,5-diaminonaphthalene, 1,4-diaminopyrene and 1,4-diaminoanthracene.

[0014] According to an embodiment of the present invention, in step (1), the catalyst is selected from one or a mixture of more than one of 1,2-dimethylimidazole, triethylamine and dodecyltrimethylammonium chloride.

[0015] According to an embodiment of the present invention, in step (1), the dianhydride compound is selected from one or a mixture of more than one of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 1,3-bis(3,4-dicarboxybenzene)hexafluoropropane dianhydride and 3,3',4,4'-benzophenonetetracarboxylic dianhydride.

[0016] According to an embodiment of the present invention, in step (1), the molar ratio of the diamine compound to the dianhydride compound is 1:1.

[0017] According to an embodiment of the present invention, in step (1), the molar ratio of the diamine compound to the catalyst is 1:(1.8-2.2), for example, 1:1.8, 1:1.9, 1:2, 1:2.1 or 1:2.2.

[0018] According to an embodiment of the present invention, in step (1), the mass ratio of the diamine compound to water is 100:(120-150), for example, 100:120, 100:130, 100:140 or 100:150.

[0019] According to an embodiment of the present invention, in step (1), the reaction temperature is 70-90°C, for example, 70°C, 75°C, 80°C, 85°C or 90°C; the reaction time is 3-48 hours, for example, 3 hours, 6 hours, 9 hours, 12 hours, 15 hours, 18 hours, 22 hours, 26 hours, 30 hours, 35 hours, 40 hours or 48 hours.

[0020] According to an embodiment of the present invention, in step (1), a diamine compound, a catalyst and water are mixed, heated to 40-50°C, and stirred for 30-120 minutes to obtain a mixed solution; then the temperature of the mixed solution is raised to 70-90°C, a dianhydride compound is added, and the mixture is stirred for 3-48 hours to react to obtain a polyamic acid solution.

[0021] According to an embodiment of the present invention, in step (1), the polyamic acid solution is an aqueous solution of polyamic acid.

[0022] According to an embodiment of the present invention, in step (1), the concentration of the polyamic acid solution is 1-30wt%, for example, 1wt%, 3wt%, 5wt%, 7wt%, 9wt%, 12wt%, 15wt%, 18wt%, 22wt%, 26wt%, 28wt% or 30wt%; the concentration of the polyamic acid solution can be controlled by controlling the reaction time.

[0023] According to an embodiment of the present invention, in step (2), the median particle size D of the porous silicon 50 5-10 μm, such as 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm.

[0024] According to an embodiment of the present invention, in step (2), the pore volume of the porous silicon is 0.4-1.0m 3 / g, such as 0.4m 3 / g, 0.5m 3 / g, 0.6m 3 / g, 0.7m 3 / g, 0.8m 3 / g, 0.9m 3 / g or 1.0m 3 / g; the average pore size of the porous silicon is 10-60nm, such as 10nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm or 60nm.

[0025] According to an embodiment of the present invention, in step (2), the mass ratio of the polyamic acid solution to the porous silicon is 100:(5-15), for example, 100:5, 100:8, 100:10, 100:12 or 100:15.

[0026] According to an embodiment of the present invention, in step (2), the concentration of the polyamic acid solution is 1-5wt%, for example, 1wt%, 2wt%, 3wt%, 4wt% or 5wt%. Selecting a low concentration of the polyamic acid solution is advantageous for impregnating the polyamic acid into the pores inside the porous silicon particles by the impregnation method, while also ensuring that the pores inside the porous silicon particles after impregnation still have a porous structure.

[0027] According to an embodiment of the present invention, in step (2), the immersion temperature is room temperature, and the immersion time is 30 min-120 min, for example, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min or 120 min.

[0028] According to an embodiment of the present invention, in step (2), the drying temperature is 60-100°C.

[0029] According to an embodiment of the present invention, in step (3), the mass ratio of the polyamic acid / porous silicon composite to the polyamic acid solution is 10:(10-20), for example, 10:10, 10:12, 10:14, 10:16, 10:18 or 10:20.

[0030] According to an embodiment of the present invention, in step (3), the concentration of the polyamic acid solution is 18-30wt%, for example, 18wt%, 20wt%, 22wt%, 24wt%, 25wt%, 26wt%, 27wt%, 28wt%, 29wt% or 30wt%. Selecting a high concentration of polyamic acid solution is beneficial for coating the surface of the porous silicon particles with polyamic acid, thereby in situ generating graphene with sufficient thickness and avoiding direct contact between the porous silicon and the electrolyte.

[0031] According to an embodiment of the present invention, in step (3), the substrate is selected from glass, carbon cloth, plastic, ceramic or metal.

[0032] According to an embodiment of the present invention, in step (3), the curing is performed in a vacuum oven.

[0033] According to an embodiment of the present invention, in step (3), the curing temperature is 100-200°C, for example, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C or 200°C; the curing time is 1-20 hours, for example, 2 hours, 3 hours, 5 hours, 6 hours, 8 hours, 10 hours, 12 hours, 15 hours or 18 hours.

[0034] According to an embodiment of the present invention, in step (3), during the curing process, polyamic acid generates polyimide through an imidization reaction.

[0035] According to an embodiment of the present invention, in step (3), the thickness of the composite film is 10-100 μm, for example, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm or 100 μm.

[0036] According to an embodiment of the present invention, in step (3), the laser-induced light source includes but is not limited to one or more of solid laser, liquid laser, gas laser, semiconductor laser, fiber laser, pulsed laser, continuous laser and excimer laser.

[0037] According to an embodiment of the present invention, in step (3), the control parameters of the laser induction include laser wavelength, laser power, scanning rate, scanning spacing, pulse frequency, focal length and voltage; preferably, the laser wavelength is 0.1-1000 μm, the laser power is 0.1-1000 W, the scanning rate is 0.1-5000 mm / s, the scanning spacing is 0.001-100 mm, the pulse frequency is 0.001-2000 kHz, the focal length is 0.1-1000 cm, and the voltage is 1-10000 kV.

[0038] According to an embodiment of the present invention, in step (4), the porous silicon / graphene composite material prepared in step (3) is scraped off from the substrate using a method known in the art to obtain a porous silicon / graphene composite powder.

[0039] According to an embodiment of the present invention, in step (4), the median particle size D of the porous silicon / graphene composite powder is 50 5-12 μm, such as 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm or 12 μm.

[0040] According to an embodiment of the present invention, in step (5), the carbon coating and sintering are carried out by methods known in the art, wherein the carbon coating method includes but is not limited to any one of chemical vapor deposition, solid phase mixing of carbon sources or liquid phase mixing of carbon sources.

[0041] Exemplarily, the carbon coating method is to uniformly mix the porous silicon / graphene composite powder obtained in step (4) with asphalt, so that the asphalt powder is coated on the surface of the porous silicon / graphene composite powder to obtain a mixture;

[0042] Illustratively, the sintering method is to carbonize the carbon-coated mixture, and then break it up and screen it after cooling to obtain the porous silicon / carbon composite negative electrode material.

[0043] The present invention provides a porous silicon / carbon composite negative electrode material prepared by the above method.

[0044] According to an embodiment of the present invention, the porous silicon / carbon composite negative electrode material includes graphene, porous silicon and amorphous carbon; preferably, the porous silicon / carbon composite negative electrode material is a composite of graphene, porous silicon and amorphous carbon.

[0045] According to an embodiment of the present invention, the porous silicon / carbon composite negative electrode material has a core-shell structure, including a core, a first coating layer and a second coating layer, the first coating layer is coated on the outer surface of the core, and the second coating layer is coated on the outer surface of the first coating layer; the core is graphene and porous silicon, and the graphene is uniformly distributed in the pores of the porous silicon; the first coating layer is graphene, and the second coating layer is amorphous carbon.

[0046] According to an embodiment of the present invention, the thickness of the first coating layer (graphene layer) is 25-80nm, for example, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm or 80nm; the thickness of the second coating layer (amorphous carbon layer) is 100-600nm, for example, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm or 600nm.

[0047] The present invention also provides the use of the porous silicon / carbon composite negative electrode material as a negative electrode of a lithium ion battery.

[0048] The present invention also provides a negative electrode sheet, which comprises the above-mentioned porous silicon / carbon composite negative electrode material.

[0049] The present invention also provides a lithium-ion battery, which comprises the above-mentioned porous silicon / carbon composite negative electrode material, or the above-mentioned negative electrode sheet.

[0050] Beneficial effects of the present invention:

[0051] The present invention firstly adopts a low-concentration polyamic acid solution impregnation method to uniformly distribute polyamic acid in the pore structure inside porous silicon particles to obtain a polyamic acid / porous silicon composite, wherein the porous silicon particles in the polyamic acid / porous silicon composite still retain part of the pore structure; then the polyamic acid / porous silicon composite is mixed with a high-concentration polyamic acid solution and coated on a substrate, and after curing, a polyimide / porous silicon composite film supported on the substrate is obtained; then, laser-induced composite film is used to in-situ convert polyimide inside and on the surface of the porous silicon particles into graphene, that is, graphene is in-situ generated in the pore structure inside the porous silicon particles and on the surface of the porous silicon particles to prepare a porous silicon / graphene composite material; finally, a layer of amorphous carbon is coated on the surface of the porous silicon / graphene composite material.

[0052] The porous silicon / carbon composite negative electrode material of the present invention also retains the porous structure of porous silicon. The three-dimensional graphene skeleton structure grown in situ in the internal pores and outer surface of the porous silicon particles can form a three-dimensional network conductive channel structure with high mechanical strength, structural stability, and a developed and robust structure. During the battery charge and discharge cycle, it can buffer the volume expansion of the porous silicon during the process of lithium ion insertion and extraction, thereby improving the battery's cycle performance. At the same time, the three-dimensional graphene network conductive channel structure can significantly enhance the conductivity of the porous silicon / carbon composite negative electrode material, greatly reducing the resistance of the negative electrode membrane and improving the battery's rate performance. In addition, the outermost amorphous carbon layer can also improve the battery's initial coulombic efficiency, further improving the cycle performance of the porous silicon / carbon composite negative electrode material. DETAILED DESCRIPTION

[0053] The preparation method of the present invention will be described in further detail below with reference to specific examples. It should be understood that the following examples are merely illustrative and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are encompassed within the scope of protection intended by the present invention.

[0054] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the reagents, materials, etc. used in the following examples are all commercially available unless otherwise specified.

[0055] Example 1

[0056] (1) 162 g of p-phenylenediamine, 288 g of 1,2-dimethylimidazole, and 200 g of water were added to a three-necked flask, heated to 40° C., and stirred for 60 min to obtain a mixed solution; then the temperature was raised to 75° C., 441 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride was added to the mixed solution in 5 portions, and the mixture was stirred for 4 h to react to obtain a polyamic acid solution (concentration of 2 wt%). A portion of the polyamic acid solution was taken out from the three-necked flask, cooled to room temperature, and sealed for storage; then the remaining polyamic acid solution was stirred for 15 h to obtain a polyamic acid solution (concentration of 18 wt%), cooled to room temperature, and sealed for storage;

[0057] (2) 8g of porous silicon (D 50 The pore volume is 0.54m 3 / g, with an average pore size of 30 nm) was immersed in 100 g of the polyamic acid solution (concentration of 2 wt%) of step (1), immersed for 50 min, filtered, and dried at 80 ° C to obtain a polyamic acid / porous silicon composite;

[0058] (3) After 10 g of the polyamic acid / porous silicon composite of step (2) was mixed evenly with 12 g of a polyamic acid solution (concentration of 18 wt%), the mixture was evenly coated on a copper foil and cured in a vacuum oven at 100° C. for 16 h to obtain a polyimide / porous silicon composite composite film (thickness of 50 μm) supported on the copper foil; the composite film was irradiated with a carbon dioxide infrared laser having a wavelength of 1064 nm, a laser power of 10 W, a scanning rate of 200 mm / s, a scanning spacing of 0.1 mm, a pulse frequency of 100 kHz, a focal length of 20 cm, and a voltage of 300 kV to in situ construct a porous silicon / graphene composite material on the copper foil;

[0059] (4) scraping the porous silicon / graphene composite material prepared in step (3) from the copper foil to obtain a porous silicon / graphene composite powder;

[0060] (5) Asphalt with a softening point of 100°C is crushed to 3 μm in an impact mill, mixed with the porous silicon / graphene composite powder prepared above at a mass ratio of 3:100, heat-treated at 1200°C for 4 hours under N2 protection, and then cooled to room temperature and then broken up, sieved, and demagnetized to obtain the porous silicon / carbon composite material.

[0061] The porous silicon / carbon composite negative electrode material has a core-shell structure, including a core, a first coating layer and a second coating layer, wherein the first coating layer is coated on the outer surface of the core, and the second coating layer is coated on the outer surface of the first coating layer; the core is graphene and porous silicon, and the graphene is uniformly distributed in the pores of the porous silicon; the first coating layer is graphene, and the second coating layer is amorphous carbon; the thickness of the first coating layer is 25 nm, and the thickness of the second coating layer is 280 nm.

[0062] Example 2

[0063] (1) 162 g of p-phenylenediamine, 288 g of 1,2-dimethylimidazole, and 200 g of water were added to a three-necked flask, heated to 40° C., and stirred for 60 min to obtain a mixed solution; then the temperature was raised to 80° C., 441 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride was added to the mixed solution in 5 portions, and the mixture was stirred for 6 h to react to obtain a polyamic acid solution (concentration of 3 wt%). A portion of the polyamic acid solution was taken out from the three-necked flask, cooled to room temperature, and sealed for storage; then the remaining polyamic acid solution was stirred for 20 h to obtain a polyamic acid solution (concentration of 24 wt%), cooled to room temperature, and sealed for storage;

[0064] (2) 8g of porous silicon (D 50 The pore volume is 0.65m 3 / g, with an average pore size of 40 nm) was immersed in 100 g of the polyamic acid solution (concentration of 3 wt%) of step (1), immersed for 80 min, filtered, and dried at 80 ° C to obtain a polyamic acid / porous silicon composite;

[0065] (3) 10 g of the polyamic acid / porous silicon composite of step (2) was mixed evenly with 14 g of a polyamic acid solution (concentration of 24 wt%), and then evenly coated on a copper foil. The mixture was cured in a vacuum oven at 140° C. for 10 h to obtain a polyimide / porous silicon composite film (thickness of 60 μm) supported on the copper foil. The composite film was irradiated with a carbon dioxide infrared laser having a wavelength of 1064 nm, a laser power of 10 W, a scanning rate of 200 mm / s, a scanning spacing of 0.1 mm, a pulse frequency of 100 kHz, a focal length of 20 cm, and a voltage of 300 kV to in-situ construct a porous silicon / graphene composite material on the copper foil.

[0066] (4) scraping the porous silicon / graphene composite material prepared in step (3) from the copper foil to obtain a porous silicon / graphene composite powder;

[0067] (5) 10 g of the porous silicon / graphene composite powder obtained in step (4) was placed in a rotary kiln, and methane was introduced at a flow rate of 1 L / min in an argon atmosphere at a flow rate of 100 L / min and an environment of 800°C for 3 hours. Then, the introduction of methane was stopped, and after cooling to room temperature, the powder was dispersed, sieved, and demagnetized to obtain the porous silicon / carbon composite negative electrode material.

[0068] The porous silicon / carbon composite negative electrode material has a core-shell structure, including a core, a first coating layer and a second coating layer, wherein the first coating layer is coated on the outer surface of the core, and the second coating layer is coated on the outer surface of the first coating layer; the core is graphene and porous silicon, and the graphene is uniformly distributed in the pores of the porous silicon; the first coating layer is graphene, and the second coating layer is amorphous carbon; the thickness of the first coating layer is 38 nm, and the thickness of the second coating layer is 420 nm.

[0069] Example 3

[0070] (1) 162 g of p-phenylenediamine, 288 g of 1,2-dimethylimidazole, and 200 g of water were added to a three-necked flask, heated to 40° C., and stirred for 60 min to obtain a mixed solution; then the temperature was raised to 85° C., 441 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride was added to the mixed solution in 5 portions, and the mixture was stirred for 5 h to react to obtain a polyamic acid solution (concentration of 4 wt %). A portion of the polyamic acid solution was taken out from the three-necked flask, cooled to room temperature, and sealed for storage; then the remaining polyamic acid solution was stirred for 26 h to obtain a polyamic acid solution (concentration of 26 wt %), cooled to room temperature, and sealed for storage;

[0071] (2) 8g of porous silicon (D 50 The pore volume is 10 μm and 0.75 m 3 / g, with an average pore size of 48 nm) was immersed in 100 g of the polyamic acid solution (concentration of 4 wt%) of step (1), immersed for 100 min, filtered, and dried at 80 ° C to obtain a polyamic acid / porous silicon composite;

[0072] (3) After 10 g of the polyamic acid / porous silicon composite of step (2) was mixed evenly with 15 g of a polyamic acid solution (concentration of 26 wt%), the mixture was evenly coated on glass and cured in a vacuum oven at 160° C. for 8 h to obtain a polyimide / porous silicon composite composite film (thickness of 80 μm) supported on glass; the composite film was irradiated with a carbon dioxide infrared laser having a wavelength of 1064 nm, a laser power of 10 W, a scanning rate of 200 mm / s, a scanning spacing of 0.1 mm, a pulse frequency of 100 kHz, a focal length of 20 cm, and a voltage of 300 kV to in situ construct a porous silicon / graphene composite material on the glass;

[0073] (4) scraping the porous silicon / graphene composite material prepared in step (3) from the glass to obtain a porous silicon / graphene composite powder;

[0074] (5) Asphalt with a softening point of 120°C was crushed to 3 μm in an impact mill, mixed with the porous silicon / graphene composite powder prepared above at a mass ratio of 5:100, heat treated at 1000°C for 8 hours under N2 protection, and then cooled to room temperature and then broken up, sieved, and demagnetized to obtain the porous silicon / carbon composite negative electrode material.

[0075] The porous silicon / carbon composite negative electrode material has a core-shell structure, including a core, a first coating layer and a second coating layer, wherein the first coating layer is coated on the outer surface of the core, and the second coating layer is coated on the outer surface of the first coating layer; the core is graphene and porous silicon, and the graphene is uniformly distributed in the pores of the porous silicon; the first coating layer is graphene, and the second coating layer is amorphous carbon; the thickness of the first coating layer is 50nm, and the thickness of the second coating layer is 470nm.

[0076] Example 4

[0077] (1) 162 g of p-phenylenediamine, 288 g of 1,2-dimethylimidazole, and 200 g of water were added to a three-necked flask, heated to 40° C., and stirred for 60 min to obtain a mixed solution; then the temperature was raised to 90° C., 441 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride was added to the mixed solution in 5 portions, and the mixture was stirred for 5 h to react to obtain a polyamic acid solution (concentration of 5 wt%). A portion of the polyamic acid solution was taken out from the three-necked flask, cooled to room temperature, and sealed for storage; then the remaining polyamic acid solution was stirred for 30 h to obtain a polyamic acid solution (concentration of 28 wt%), cooled to room temperature, and sealed for storage;

[0078] (2) 8g of porous silicon (D 50 The pore volume is 0.82m 3 / g, with an average pore size of 60 nm) was immersed in 100 g of the polyamic acid solution (concentration of 5 wt%) of step (1), immersed for 120 min, filtered, and dried at 80 ° C to obtain a polyamic acid / porous silicon composite;

[0079] (3) 10 g of the polyamic acid / porous silicon composite of step (2) was mixed evenly with 18 g of a polyamic acid solution (concentration of 28 wt%), and then evenly coated on a carbon cloth. The mixture was cured in a vacuum oven at 100° C. for 10 h to obtain a polyimide / porous silicon composite film (thickness of 100 μm) supported on the carbon cloth; the composite film was irradiated with a carbon dioxide infrared laser having a wavelength of 1064 nm, a laser power of 10 W, a scanning rate of 200 mm / s, a scanning spacing of 0.1 mm, a pulse frequency of 100 kHz, a focal length of 20 cm, and a voltage of 300 kV to in-situ construct a porous silicon / graphene composite material on the carbon cloth;

[0080] (4) scraping the porous silicon / graphene composite material prepared in step (3) from the carbon cloth to obtain a porous silicon / graphene composite powder;

[0081] (5) Asphalt with a softening point of 150°C was crushed to 3 μm in an impact mill, mixed with the porous silicon / graphene composite powder prepared above at a mass ratio of 8:100, heat-treated at 800°C for 10 hours under N2 protection, and then cooled to room temperature before being dispersed, sieved, and demagnetized to obtain the porous silicon / carbon composite negative electrode material.

[0082] The porous silicon / carbon composite negative electrode material has a core-shell structure, including a core, a first coating layer and a second coating layer, wherein the first coating layer is coated on the outer surface of the core, and the second coating layer is coated on the outer surface of the first coating layer; the core is graphene and porous silicon, and the graphene is uniformly distributed in the pores of the porous silicon; the first coating layer is graphene, and the second coating layer is amorphous carbon; the thickness of the first coating layer is 62nm, and the thickness of the second coating layer is 540nm.

[0083] Comparative Example 1

[0084] (1) 162 g of p-phenylenediamine, 288 g of 1,2-dimethylimidazole, and 200 g of water were added to a three-necked flask, heated to 40° C., and stirred for 60 min to obtain a mixed solution; then the temperature was raised to 75° C., 441 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride was added to the mixed solution in 5 portions, and the mixture was stirred for 19 h to react to obtain a polyamic acid solution (concentration of 18 wt%), which was then cooled to room temperature and sealed for storage;

[0085] (2) 10g of porous silicon (D 50 The pore volume is 0.54m 3 / g, with an average pore size of 30nm) was mixed evenly with 12g of polyamic acid solution (18wt%), and then evenly coated on a copper foil. The mixture was cured in a vacuum oven at 100°C for 16h to obtain a polyimide / porous silicon composite film (50μm thick) supported on the copper foil; the composite film was irradiated with a carbon dioxide infrared laser with a wavelength of 1064nm, a laser power of 10W, a scanning rate of 200mm / s, a scanning spacing of 0.1mm, a pulse frequency of 100kHz, a focal length of 20cm, and a voltage of 300kV to in situ construct a porous silicon / graphene composite material on the copper foil;

[0086] (3) scraping the porous silicon / graphene composite material prepared in step (2) from the copper foil to obtain a porous silicon / graphene composite powder;

[0087] (4) Asphalt with a softening point of 100°C was crushed to 3 μm in an impact mill, mixed with the porous silicon / graphene composite powder prepared above at a mass ratio of 3:100, and heat-treated at 1200°C for 4 hours under N2 protection. After cooling to room temperature, it was dispersed, sieved, and demagnetized to obtain a porous silicon / carbon composite negative electrode material.

[0088] The porous silicon / carbon composite negative electrode material has a core-shell structure, including a core, a first coating layer and a second coating layer, wherein the first coating layer is coated on the outer surface of the core, and the second coating layer is coated on the outer surface of the first coating layer; the core is porous silicon; the first coating layer is graphene, and the second coating layer is amorphous carbon; the thickness of the first coating layer is 25 nm, and the thickness of the second coating layer is 280 nm.

[0089] Comparative Example 2

[0090] (1) 162 g of p-phenylenediamine, 288 g of 1,2-dimethylimidazole, and 200 g of water were added to a three-necked flask, heated to 40° C., and stirred for 60 min to obtain a mixed solution; then the temperature was raised to 75° C., 441 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride was added to the mixed solution in 5 portions, and the mixture was stirred for 4 h to react to obtain a polyamic acid solution (concentration of 2 wt%). A portion of the polyamic acid solution was taken out from the three-necked flask, cooled to room temperature, and sealed for storage;

[0091] (2) 8g of porous silicon (D 50 The pore volume is 0.54m 3 / g, with an average pore size of 30 nm) was immersed in 100 g of the polyamic acid solution (concentration of 2 wt%) of step (1), and after immersion for 50 min, a polyamic acid / porous silicon composite solution was obtained;

[0092] (3) The polyamic acid / porous silicon composite solution of step (2) is uniformly coated on a copper foil, and cured in a vacuum oven at 100° C. for 16 h to obtain a polyimide / porous silicon composite film (50 μm thick) supported on the copper foil; the composite film is irradiated with a carbon dioxide infrared laser having a wavelength of 1064 nm, a laser power of 10 W, a scanning rate of 200 mm / s, a scanning spacing of 0.1 mm, a pulse frequency of 100 kHz, a focal length of 20 cm, and a voltage of 300 kV to in situ construct a porous silicon / graphene composite material on the copper foil;

[0093] (4) scraping the porous silicon / graphene composite material prepared in step (3) from the copper foil to obtain a porous silicon / graphene composite powder;

[0094] (5) Asphalt with a softening point of 100°C is crushed to 3 μm in an impact mill, mixed with the porous silicon / graphene composite powder prepared above at a mass ratio of 3:100, heat-treated at 1200°C for 4 hours under N2 protection, and then cooled to room temperature and then broken up, sieved, and demagnetized to obtain the porous silicon / carbon composite material.

[0095] The porous silicon / carbon composite negative electrode material has a core-shell structure, including a core and a coating layer, wherein the coating layer is coated on the outer surface of the core; the core is graphene and porous silicon, and the graphene is evenly distributed in the pores of the porous silicon, and a very small amount of graphene is distributed on the surface of the porous silicon; the coating layer is amorphous carbon; and the thickness of the coating layer is 280nm.

[0096] Electrochemical performance test

[0097] Semi-charge test method: The porous silicon / carbon composite negative electrode materials prepared in Examples 1-4 and Comparative Examples 1-2 were mixed uniformly in a mass ratio of conductive carbon black (SP): carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR) = 95:1:1.5:2.5, coated on copper foil, and dried in a vacuum drying oven at 120°C for 12 hours. Simulated battery assembly was performed in an argon-protected Braun glove box. The electrolyte consisted of 1M LiPF6 + EC:DEC:DMC (volume ratio of 1:1:1), with a metal lithium sheet as the counter electrode. Simulated battery testing was performed in a 5V, 10mA Xinwei battery test cabinet with charge and discharge voltages of 0.01-1.5V and charge and discharge rates of 0.1C and 1C. The initial capacity and initial coulombic efficiency obtained from the tests are listed in Table 1. The charge and discharge rate was 0.1C, and the capacity retention rate was calculated as the charge capacity at the Nth cycle of the battery test / the initial charge capacity * 100%. The test results are listed in Table 1.

[0098] Table 1. Electrochemical performance test results

[0099]

[0100] Compared with Example 1, the high concentration of the polyamic acid solution in Comparative Example 1 prevents the polyamic acid from entering the pore structure inside the porous silicon particles. During the subsequent laser induction process, a graphene coating is only generated on the surface of the porous silicon. The volume expansion of the porous silicon during the cycle can only be mitigated by the graphene layer on the outer surface. However, this structure is unstable and easily broken during the cycle, resulting in a significant decrease in the cycle performance of the obtained battery and a significant increase in the expansion rate of the electrode. At the same time, due to the lack of graphene inside the porous silicon particles, the conductivity of the porous silicon / carbon composite negative electrode material deteriorates, greatly increasing the resistance of the negative electrode membrane and reducing the rate performance of the battery.

[0101] Compared with Example 1, although the polyamic acid solution of Comparative Example 2 can enter the pore structure inside the porous silicon particles, due to the low concentration of the polyamic acid solution, it is unable to form a coating layer with a certain thickness on the surface of the porous silicon particles. In the subsequent laser induction process, only the polyamide in the pore structure inside the porous silicon particles can be induced into graphene. The surface of the porous silicon particles contains only a very small amount of graphene, resulting in the inability to form a complete graphene coating on the surface of the porous silicon particles. This structure is unstable and easily broken during the cycle process, resulting in reduced cycle performance of the obtained battery and increased pole piece expansion rate. At the same time, due to the absence of graphene on the surface of the porous silicon particles, the conductive properties of the porous silicon / carbon composite negative electrode material deteriorate, greatly increasing the resistance of the negative electrode membrane and reducing the rate performance of the battery.

[0102] As can be seen from Examples 1-4, the porous silicon / carbon composite negative electrode material prepared by the present invention retains the porous structure of porous silicon. The three-dimensional graphene skeleton structure grown in situ in the internal pores and outer surface of the porous silicon particles can form a three-dimensional network conductive channel structure with high mechanical strength, structural stability, and a developed and robust structure. During the battery charge and discharge cycle, it can buffer the volume expansion of porous silicon during the process of lithium ion insertion and extraction, thereby improving the battery's cycle performance. At the same time, the three-dimensional graphene network conductive channel structure can significantly improve the conductivity of the porous silicon / carbon composite negative electrode material, greatly reduce the resistance of the negative electrode membrane, and improve the battery's rate performance. In addition, the outermost amorphous carbon layer can also improve the battery's first coulombic efficiency, further improving the cycle performance of the porous silicon / carbon composite negative electrode material.

[0103] The above describes the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A method for preparing a porous silicon / carbon composite negative electrode material, comprising the following steps: (1) mixing a diamine compound, a dianhydride compound, a catalyst and water, reacting to prepare a polyamic acid solution; (2) mixing the porous silicon and the polyamic acid solution, impregnating, filtering, and drying to prepare a polyamic acid / porous silicon composite; (3) mixing a polyamic acid / porous silicon composite and a polyamic acid solution and coating the mixture on a substrate, curing the mixture to obtain a polyimide / porous silicon composite film supported on the substrate, and in-situ constructing a porous silicon / graphene composite material on the substrate by laser induction of the composite film; (4) scraping the porous silicon / graphene composite material prepared in step (3) from the substrate to obtain a porous silicon / graphene composite powder; (5) The porous silicon / graphene composite powder obtained in step (4) is subjected to carbon coating and sintering treatment to prepare the porous silicon / carbon composite negative electrode material.

2. The preparation method according to claim 1, wherein In step (1), the diamine compound is selected from one or more of p-phenylenediamine, 4,4'-diaminodiphenyl ether, p-phenylenediamine, m-p-phenylenediamine, 1,5-diaminonaphthalene, 1,4-diaminopyrene and 1,4-diaminoanthracene; the catalyst is selected from one or more of 1,2-dimethylimidazole, triethylamine and dodecyltrimethylammonium chloride; the dianhydride compound is selected from one or more of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 1,3-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride and 3,3',4,4'-benzophenonetetracarboxylic dianhydride; And / or, in step (1), the molar ratio of the diamine compound to the dianhydride compound is 1:1; the molar ratio of the diamine compound to the catalyst is 1:(1.8-2.2); the mass ratio of the diamine compound to water is 100:(120-150); And / or, in step (1), the reaction temperature is 70-90° C.; the reaction time is 3-48 hours.

3. The preparation method according to claim 1 or 2, wherein In step (2), the median particle size D of the porous silicon 50 The pore volume of the porous silicon is 0.4-1.0m 3 / g; the average pore size of the porous silicon is 10-60nm. And / or, in step (2), the mass ratio of the polyamic acid solution to the porous silicon is 100:(5-15). And / or, in step (2), the concentration of the polyamic acid solution is 1-5 wt %.

4. The preparation method according to any one of claims 1 to 3, wherein In step (3), the mass ratio of the polyamic acid / porous silicon composite to the polyamic acid solution is 10:(10-20); and / or, in step (3), the concentration of the polyamic acid solution is 18-30 wt %; And / or, in step (3), the curing temperature is 100-200° C.; the curing time is 1-20 hours; And / or, in step (3), the thickness of the composite film is 10-100 μm.

5. The preparation method according to any one of claims 1 to 4, wherein In step (3), the laser-induced light source includes but is not limited to one or more of a solid laser, a liquid laser, a gas laser, a semiconductor laser, a fiber laser, a pulsed laser, a continuous laser, and an excimer laser; And / or, in step (3), the control parameters of the laser induction include laser wavelength, laser power, scanning rate, scanning spacing, pulse frequency, focal length and voltage; the laser wavelength is 0.1-1000 μm, the laser power is 0.1-1000 W, the scanning rate is 0.1-5000 mm / s, the scanning spacing is 0.001-100 mm, the pulse frequency is 0.001-2000 kHz, the focal length is 0.1-1000 cm, and the voltage is 1-10000 kV.

6. A porous silicon / carbon composite negative electrode material prepared by the method according to any one of claims 1 to 5.

7. The porous silicon / carbon composite negative electrode material according to claim 6, wherein: The porous silicon / carbon composite negative electrode material includes graphene, porous silicon and amorphous carbon; preferably, the porous silicon / carbon composite negative electrode material is a composite of graphene, porous silicon and amorphous carbon.

8. The porous silicon / carbon composite negative electrode material according to claim 6 or 7, wherein: The porous silicon / carbon composite negative electrode material has a core-shell structure, including a core, a first coating layer and a second coating layer, wherein the first coating layer is coated on the outer surface of the core, and the second coating layer is coated on the outer surface of the first coating layer; the core is graphene and porous silicon, and the graphene is uniformly distributed in the pores of the porous silicon; the first coating layer is graphene, and the second coating layer is amorphous carbon. Preferably, the thickness of the first coating layer is 25-80 nm; the thickness of the second coating layer is 100-600 nm. 9 . A negative electrode sheet, comprising the porous silicon / carbon composite negative electrode material according to claim 6 . 10 . A lithium-ion battery comprising the porous silicon / carbon composite negative electrode material according to claim 6 , or the negative electrode sheet according to claim 9 .

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