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

Abstract

The invention relates to the technical field of negative electrode materials, in particular to a silicon-carbon negative electrode material and a preparation method thereof, a negative electrode plate and a lithium ion battery. The silicon-carbon negative electrode material comprises a porous carbon matrix with a pore structure, monatomic silicon is contained in the pore structure, the outer surface of the porous carbon matrix is coated with a loose carbon layer, and the outer surface of the loose carbon layer is coated with a compact carbon layer; the pore volume of the porous carbon matrix is P, and the unit is cm < 3 > / g; the mass fraction of the silicon element in the silicon-carbon negative electrode material is A; the true density of the silicon-carbon negative electrode material is B, and the unit is g / cm < 3 >; p, A, and B satisfy 30 < = 100 * A / (2.26-B) / P < = 70. The silicon-carbon negative electrode material provided by the invention has small volume change in the lithium intercalation / deintercalation process, and has better capacity, first coulombic efficiency and cycle performance.

Description

Technical Field

[0001] The present invention relates to the technical field of anode materials, and in particular, to a silicon-carbon anode material, a preparation method thereof, an anode sheet, and a lithium-ion battery. Background Art

[0002] Compared with graphite anode materials, silicon-based anode materials have a higher theoretical specific capacity (4200 mAh / g). The energy density of the battery prepared from the silicon-based anode material is relatively higher, thereby improving the battery life and mileage.

[0003] However, silicon undergoes a volume change of about 300% during the lithium insertion / extraction process, which will cause a series of problems during the cycling process. For example, cracks will occur in the silicon-based anode material until it pulverizes; the volume change causes an unstable SEI layer to form on the electrode surface. The SEI layer repeatedly breaks and regenerates, consuming a large amount of lithium ions, resulting in a decrease in the capacity, initial Coulomb efficiency, and cycling performance of the battery.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] The first object of the present invention is to provide a silicon-carbon anode material, which has a specific structure, and the pore volume P of the porous carbon matrix, the mass fraction A of silicon element in the silicon-carbon anode material, and the true density B of the silicon-carbon anode material satisfy a specific relational expression: 30 ≤ 100×A / (2.26 - B) / P ≤ 70, which can significantly reduce the volume change of the silicon-carbon anode material during the lithium insertion / extraction process, and improve the capacity, initial Coulomb efficiency, and cycling performance of the silicon-carbon anode material.

[0006] The second object of the present invention is to provide a preparation method of a silicon-carbon anode material, which is simple and easy to operate, can be mass-produced, and the silicon-carbon anode material prepared by this method has a small volume change during the lithium insertion / extraction process and excellent electrochemical performance.

[0007] The third object of the present invention is to provide an anode sheet.

[0008] The fourth object of the present invention is to provide a lithium-ion battery.

[0009] In order to achieve the above objects of the present invention, the following technical solutions are specifically adopted:

[0010] The present invention first provides a silicon-carbon anode material, which includes a porous carbon matrix having a pore structure, the pore structure contains elemental silicon, the outer surface of the porous carbon matrix is coated with a loose carbon layer, and the outer surface of the loose carbon layer is coated with a dense carbon layer; the pore volume of the porous carbon matrix is P, with the unit of cm 3 / g; The mass fraction of silicon element in the silicon-carbon negative electrode material is A; The true density of the silicon-carbon negative electrode material is B, with the unit of g / cm 3 ; where P, A, and B satisfy 30 ≤ 100×A / (2.26 - B) / P ≤ 70.

[0011] Further, the pore volume P of the porous carbon matrix is 1.4 - 1.8 cm 3 / g.

[0012] Further, the mass fraction A of silicon element in the silicon-carbon negative electrode material is 40% - 55%.

[0013] Further, the true density B of the silicon-carbon negative electrode material is 1.5 - 1.8 g / cm 3 。

[0014] Further, the mass fraction of the loose carbon layer in the silicon-carbon negative electrode material is 5% - 10%.

[0015] Further, the mass fraction of the dense carbon layer in the silicon-carbon negative electrode material is 2% - 5%.

[0016] The present invention further provides a preparation method of the silicon-carbon negative electrode material, including the following steps:

[0017] Mix porous carbon, a silicon source, and a solvent and react to make the silicon dioxide generated by the hydrolysis of the silicon source enter the pore structure of the porous carbon, and then perform solid-liquid separation to obtain a first intermediate.

[0018] Mix the first intermediate with a reducing agent and heat for a reduction reaction to reduce the silicon dioxide in the pore structure to elemental silicon, obtaining a second intermediate.

[0019] Mix the second intermediate, a dispersant, and an organic carbon source and perform coating to form a coating layer on the outer surface of the porous carbon, then perform solid-liquid separation and calcination to make the coating layer form a loose carbon layer, obtaining a third intermediate.

[0020] Mix the third intermediate with an acid solution and react to remove the reducing agent and / or the product formed after the reaction of the reducing agent, and then perform solid-liquid separation to obtain a fourth intermediate.

[0021] Introduce a gaseous carbon source into the system containing the fourth intermediate for chemical vapor deposition to obtain the silicon-carbon negative electrode material.

[0022] Further, before mixing the porous carbon, the silicon source, and the solvent, first calcine the porous carbon at 250 - 400 °C.

[0023] Further, the calcination time is 2 - 8 h.

[0024] Further, the calcination atmosphere includes an air atmosphere or an oxygen atmosphere;

[0025] Further, the pore volume of the porous carbon is 1.4 - 1.8 cm 3 / g;

[0026] Further, the specific surface area of the porous carbon is 800 - 1000 m 2 / g, the microporosity is 8% - 15%, and the pore diameter < 50 nm.

[0027] Further, the silicon source includes at least one of tetraethyl orthosilicate, trimethoxysilane, tetraethylsilane, phenyltrimethoxysilane, and tetrachlorosilane.

[0028] Further, the solvent includes a mixed solvent of ethanol and water.

[0029] Further, the volume ratio of the ethanol to the water is 3 - 5:1.

[0030] Further, the mass ratio of the porous carbon to the silicon source is 1:4 - 6.

[0031] Further, the step of mixing the porous carbon, the silicon source, and the solvent includes: first ultrasonically dispersing the porous carbon in the solvent, then adding an alkali solution to adjust the pH of the mixed system to 10.5 - 11.5, and then adding the silicon source thereto.

[0032] Further, the alkali solution includes at least one of an ammonia water solution, a sodium hydroxide solution, a potassium hydroxide solution, and a sodium carbonate solution.

[0033] Further, the reaction time for mixing and reacting the porous carbon, the silicon source, and the solvent is 12 - 24 h.

[0034] Further, the reducing agent includes at least one of metallic magnesium, metallic aluminum, and a magnesium-aluminum alloy.

[0035] Further, the mass ratio of the first intermediate to the reducing agent is 1:0.4 - 0.8.

[0036] Further, the atmosphere of the reduction reaction includes an inert atmosphere.

[0037] Further, the heating temperature of the reduction reaction is 550 - 650 °C, and the heat preservation time is 10 - 24 h.

[0038] Further, the dispersant includes a mixed solvent of ethanol and water.

[0039] Further, the volume ratio of the ethanol to the water is 3 - 5:1;

[0040] Further, the organic carbon source includes at least one of dopamine, phenolic resin, glucose, citric acid, and polypyrrole.

[0041] Further, the mass ratio of the second intermediate to the organic carbon source is 1:0.15 - 0.25.

[0042] Further, the step of mixing the second intermediate, the dispersant, and the organic carbon source includes: first ultrasonically dispersing the second intermediate in the dispersant, then adding an alkali solution to adjust the pH of the mixed system to 10.5 - 11.5, and then adding the organic carbon source thereto.

[0043] Further, the alkali solution includes at least one of ammonia water solution, sodium hydroxide solution, potassium hydroxide solution, and sodium carbonate solution.

[0044] Further, the coating time is 12 - 24 h.

[0045] Further, the atmosphere for roasting includes an inert atmosphere.

[0046] Further, the roasting temperature is 550 - 650 °C, and the heat preservation time is 3 - 8 h.

[0047] Further, the acid solution includes at least one of hydrochloric acid solution, nitric acid solution, sulfuric acid solution, and perchloric acid solution.

[0048] Further, the concentration of the acid solution is 0.5 - 2 mol / L.

[0049] Further, the reaction time for mixing and reacting the third intermediate with the acid solution is 5 - 12 h.

[0050] Further, the gaseous carbon source includes at least one of acetylene, methane, ethylene, propylene, toluene, and benzene.

[0051] Further, the inlet flow rate of the gaseous carbon source is 0.1 - 0.4 L / min.

[0052] Further, the atmosphere for chemical vapor deposition includes an inert atmosphere.

[0053] Further, the temperature for chemical vapor deposition is 600 - 700 °C, and the time is 1 - 3 h.

[0054] The present invention also provides a negative electrode sheet including the silicon-carbon negative electrode material.

[0055] The present invention further provides a lithium-ion battery including the negative electrode sheet.

[0056] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0057] The silicon-carbon negative electrode material provided by the present invention has a specific structure, and the pore volume P of the porous carbon matrix, the mass fraction A of silicon element in the silicon-carbon negative electrode material, and the true density B of the silicon-carbon negative electrode material satisfy a specific relational expression: 30 ≤ 100×A / (2.26 - B) / P ≤ 70, which can significantly reduce the volume change of the silicon-carbon negative electrode material during the lithium insertion / extraction process, and improve the capacity, first Coulomb efficiency, and cycling performance of the silicon-carbon negative electrode material. Brief Description of the Drawings

[0058] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0059] Figure 1 It is a schematic structural diagram of the silicon-carbon negative electrode material provided by the present invention. Detailed Embodiments

[0060] The technical solutions of the present invention will be clearly and completely described below in conjunction with the drawings and specific embodiments. However, those skilled in the art will understand that the following described embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0061] If there is no special indication, in the present invention, "the first aspect", "the second aspect", "the third aspect", "the fourth aspect", etc. are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "the first", "the second", "the third", "the fourth", etc. only serve the purpose of non-exhaustive listing and description, and it should be understood that they do not constitute a closed limitation on the quantity.

[0062] If there is no special indication, "including" and "comprising" mentioned in the present invention mean open-ended or can also be closed-ended. For example, the said "including" and "comprising" can mean that other components not listed can also be included, or can only include the listed components.

[0063] Unless otherwise specified, in the present invention, "one or more" or "at least one" refers to any one, any two, or any two or more of the listed items. Among them, "several" refers to any two or more.

[0064] In a first aspect, the present invention provides a silicon-carbon negative electrode material, as Figure 1 shown in the schematic structural diagram of the silicon-carbon negative electrode material, specifically a sectional view. The silicon-carbon negative electrode material includes a porous carbon matrix having a plurality of pore structures, the pore structures contain elemental silicon, the outer surface of the porous carbon matrix is coated with a loose carbon layer, and the outer surface of the loose carbon layer is coated with a dense carbon layer.

[0065] It can be understood that the pore structures of the porous carbon matrix can provide free space for the expansion of the elemental silicon therein.

[0066] It can be understood that the density of the loose carbon layer is lower than that of the dense carbon layer.

[0067] In some embodiments, the density of the loose carbon layer is significantly lower than that of the dense carbon layer.

[0068] The pore volume of the porous carbon matrix is P, with the unit of cm 3 / g.

[0069] The mass fraction of silicon element in the silicon-carbon negative electrode material is A.

[0070] The true density of the silicon-carbon negative electrode material is B, with the unit of g / cm 3 .

[0071] The above P, A, and B satisfy the following relationship: 30 ≤ 100×A / (2.26 - B) / P ≤ 70. Among them, the value of 100×A / (2.26 - B) / P includes but is not limited to any point value among 30, 35, 40, 45, 50, 55, 60, 65, 70 or the range value between any two of them.

[0072] The silicon-carbon negative electrode material provided by the present invention has a specific structure, and the pore volume P of the porous carbon matrix, the mass fraction A of silicon element in the silicon-carbon negative electrode material, and the true density B of the silicon-carbon negative electrode material satisfy a specific relationship: 30 ≤ 100×A / (2.26 - B) / P ≤ 70, which can significantly reduce the volume change of the silicon-carbon negative electrode material during the lithium insertion / extraction process and improve the capacity, first Coulomb efficiency (abbreviated as first efficiency), and cycling performance of the silicon-carbon negative electrode material.

[0073] Specifically, the pore structure in the porous carbon matrix provides a buffer space for the expansion of elemental silicon in the pore structure, significantly reducing the volume change during the cycling of the silicon-carbon anode material, and the elemental silicon provides a high capacity; the loose carbon layer provides a buffer space for silicon expansion, and the dense carbon layer provides a good electron transport path and avoids direct contact between the electrolyte and elemental silicon.

[0074] Meanwhile, in the present invention, by controlling the pore volume P of the porous carbon matrix, the mass fraction A of silicon element in the silicon-carbon anode material, and the true density B of the silicon-carbon anode material to satisfy the relational expression 30 ≤ 100×A / (2.26 - B) / P ≤ 70, wherein the size of the pore volume P of the porous carbon affects the size of the mass fraction A of infiltrated silicon. The larger the pore volume, the larger the mass fraction of infiltrated silicon. The size of the mass fraction A of silicon affects the true density B of the silicon-carbon material. The larger the mass fraction A of silicon, the smaller the true density B.

[0075] In some specific embodiments, the pore volume P of the porous carbon matrix is 1.4 - 1.8 cm 3 / g, such as 1.5 cm 3 / g, 1.6 cm 3 / g or 1.7 cm 3 / g.

[0076] In some specific embodiments, the mass fraction A of silicon element in the silicon-carbon anode material is 40% - 55%; including but not limited to any point value of 40%, 42%, 43%, 45%, 48%, 50%, 53%, 55% or the range value between any two of them.

[0077] In some specific embodiments, the true density B of the silicon-carbon anode material is 1.5 - 1.8 g / cm 3 ; including but not limited to any point value of 1.5 g / cm 3 、1.55 g / cm 3 、1.6 g / cm 3 、1.65 g / cm 3 、1.7 g / cm 3 、1.75 g / cm 3 、1.8 g / cm 3 or the range value between any two of them. The silicon-carbon anode material provided by the present invention has a low true density, low expansion of the silicon-carbon anode material, and good cycling effect.

[0078] In some specific embodiments, the mass fraction of the loose carbon layer in the silicon-carbon anode material is 5% - 10%, such as 6%, 7%, 8% or 9%.

[0079] In some specific embodiments, the mass fraction of the dense carbon layer in the silicon-carbon negative electrode material is 2% to 5%, such as 3% or 4%.

[0080] In a second aspect, the present invention provides a method for preparing the silicon-carbon negative electrode material, comprising the following steps:

[0081] First, porous carbon, a silicon source, and a solvent are mixed and reacted, so that the silicon dioxide generated after hydrolysis of the silicon source enters the pore structure of the porous carbon, and then solid-liquid separation is performed to obtain a first intermediate.

[0082] It can be understood that the porous carbon has a pore structure. The silicon source undergoes a hydrolysis reaction in the solvent, and the generated silicon dioxide enters the internal pore structure of the porous carbon. After solid-liquid separation, porous carbon with silicon dioxide inside the pore structure is obtained, that is, the first intermediate.

[0083] Then, the first intermediate and a reducing agent are mixed and heated for a reduction reaction to reduce the silicon dioxide in the pore structure to elemental silicon, obtaining a second intermediate. It can be understood that the role of the reducing agent is to reduce silicon dioxide to elemental silicon. The second intermediate is porous carbon with elemental silicon inside the pore structure.

[0084] After that, the second intermediate, a dispersant, and an organic carbon source are mixed and coated to form a coating layer on the outer surface of the porous carbon, and then solid-liquid separation and calcination are performed to make the coating layer form a loose carbon layer, obtaining a third intermediate. Among them, the organic carbon source includes a liquid carbon source and / or a solid carbon source. During the coating process, the organic carbon source or the product after polymerization of the organic carbon source is coated on the outer surface of the second intermediate to form a coating layer, and the coating layer is calcined to form a loose carbon layer. That is, the third intermediate is porous carbon with a loose carbon layer on the outer surface, and at the same time, there is also elemental silicon inside the pore structure of the porous carbon.

[0085] In some specific embodiments, the organic carbon source is a monomer carbon source. After mixing the materials, the monomer carbon source undergoes a polymerization reaction to generate a polymer, and then the polymer is coated on the outer surface of the second intermediate. Or the organic carbon source directly uses a polymer material.

[0086] Further, the third intermediate is mixed and reacted with an acid solution (i.e., pickling for impurity removal) to remove the reducing agent and / or the product formed after the reaction of the reducing agent, and then solid-liquid separation is performed to obtain a fourth intermediate. The present invention adopts pickling for impurity removal after coating and calcination. The remaining free space after impurity removal can provide free space for the expansion of silicon during the lithiation process. If pickling is performed first and then coating, the carbon used for coating will occupy the free space left after impurity removal, hindering the free change of the silicon volume.

[0087] In some specific embodiments, the reducing agent includes active metals. It can be understood that active metals and silicon dioxide can react under certain conditions to produce elemental silicon and metal oxides. Adding an acid solution can remove the metal oxides generated after the reduction reaction, as well as the unreacted or excessive active metals.

[0088] Subsequently, a gaseous carbon source is introduced into the system containing the fourth intermediate for chemical vapor deposition, and the silicon-carbon negative electrode material is obtained after the reaction is completed.

[0089] Through chemical vapor deposition, a dense carbon layer can be further coated (formed) on the outer surface of the porous carbon layer of the fourth intermediate. That is, the silicon-carbon negative electrode material has a double-layer carbon structure, where the outermost layer is a dense carbon layer, the second outermost layer is a porous carbon layer, and the interior is porous carbon (i.e., a porous carbon matrix), and the pore structure of the porous carbon also contains elemental silicon.

[0090] It can be understood that by controlling the pore volume of the porous carbon raw material, the addition amounts of the silicon source and the organic carbon source during the reaction, the flow rate of the gaseous carbon source introduced, and the time of chemical vapor deposition, the finally prepared silicon-carbon negative electrode material can be regulated to satisfy the relationship 30 ≤ 100×A / (2.26 - B) / P ≤ 70.

[0091] The preparation method of the silicon-carbon negative electrode material provided by the present invention is simple and easy to operate, can realize batch production, and the silicon-carbon negative electrode material prepared by this method has a small volume change during the lithium insertion / extraction process and excellent electrochemical performance.

[0092] It can be understood that by regulating the pore volume of the porous carbon and the mass fraction of silicon, the true density of the silicon-carbon negative electrode material can be controlled.

[0093] In some specific embodiments, before mixing the porous carbon, the silicon source and the solvent, the porous carbon is first calcined at 250 - 400 °C; wherein, the calcination temperature includes but is not limited to any point value of 250 °C, 280 °C, 300 °C, 330 °C, 350 °C, 370 °C, 400 °C or the range value between any two of them.

[0094] Calcining the porous carbon before the reaction with the silicon source can increase the oxygen-containing functional groups in the porous carbon and promote its combination with the silicon source and / or silicon dioxide (since the calcination temperature of the porous carbon before the reaction is relatively low, this operation has little effect on the pore volume of the porous carbon).

[0095] Preferably, the calcination time is 2 - 8 h; including but not limited to any point value of 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h or the range value between any two of them.

[0096] Preferably, the calcination atmosphere includes an air atmosphere or an oxygen atmosphere.

[0097] In some specific embodiments, the pore volume of the porous carbon is 1.4 - 1.8 cm 3 / g, such as 1.5 cm 3 / g, 1.6 cm 3 / g or 1.7 cm 3 / g.

[0098] In some specific embodiments, the specific surface area of the porous carbon is 800 - 1000 m 2 / g, such as 850 m 2 / g, 900 m 2 / g or 950 m 2 / g; the microporosity of the porous carbon is 8% - 15%, such as 9%, 10%, 11%, 12%, 13% or 14%, and the pore diameter of the pore structure of the porous carbon < 50 nm (i.e., all pore diameters are less than 50 nm).

[0099] In some specific embodiments, the silicon source includes at least one of tetraethyl orthosilicate, trimethoxysilane, tetraethylsilane, phenyltrimethoxysilane, and tetrachlorosilane.

[0100] In some specific embodiments, the solvent includes a mixed solvent of ethanol and water. Preferably, the volume ratio of ethanol to water is 3 - 5:1, such as 4:1.

[0101] In some specific embodiments, the mass ratio of the porous carbon to the silicon source is 1:4 - 6, including but not limited to any point value of 1:4, 1:4.5, 1:5, 1:5.5, 1:6 or the range value between any two of them.

[0102] In some specific embodiments, the step of mixing the porous carbon, the silicon source, and the solvent includes: first ultrasonically dispersing the porous carbon in the solvent, then adding an alkali solution to adjust the pH of the mixed system to 10.5 - 11.5 (including but not limited to any point value of 10.5, 10.8, 11, 11.2, 11.5 or the range value between any two of them), and then adding the silicon source thereto; preferably, the alkali solution includes at least one of an ammonia water solution, a sodium hydroxide solution, a potassium hydroxide solution, and a sodium carbonate solution.

[0103] In some specific embodiments, the reaction time for mixing and reacting the porous carbon, the silicon source, and the solvent is 12 - 24 h, including but not limited to any point value of 12 h, 15 h, 18 h, 20 h, 22 h, 24 h or the range value between any two of them.

[0104] In some specific embodiments, the reducing agent includes at least one of metallic magnesium, metallic aluminum, and magnesium aluminum alloy.

[0105] In some specific embodiments, the mass ratio of the first intermediate to the reducing agent is 1:0.4 to 0.8, including but not limited to any point value among 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8 or the range value between any two of them.

[0106] In some specific embodiments, the atmosphere of the reduction reaction includes an inert atmosphere. Among them, the inert atmosphere includes but not limited to nitrogen atmosphere, argon atmosphere, etc.

[0107] In some specific embodiments, the heating temperature of the reduction reaction is 550 to 650 °C, including but not limited to any point value among 550 °C, 560 °C, 580 °C, 600 °C, 630 °C, 650 °C or the range value between any two of them; the heat preservation time of the reduction reaction is 10 to 24 h, including but not limited to any point value among 10 h, 12 h, 15 h, 18 h, 20 h, 22 h, 24 h or the range value between any two of them.

[0108] In some specific embodiments, the heating rate of the heating is 0.5 to 5 °C / min, including but not limited to any point value among 0.5 °C / min, 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min or the range value between any two of them.

[0109] In some specific embodiments, the dispersant includes a mixed solvent of ethanol and water; preferably, the volume ratio of the ethanol to the water is 3 to 5:1, such as 4:1.

[0110] In some specific embodiments, the organic carbon source includes at least one of dopamine, phenolic resin, glucose, citric acid, and polypyrrole.

[0111] When dopamine is used, the pH of the reaction system is adjusted to be alkaline to polymerize dopamine into polydopamine, and then the polydopamine forms a coating layer.

[0112] In some specific embodiments, the mass ratio of the second intermediate to the organic carbon source is 1:0.15 to 0.25, including but not limited to any point value among 1:0.15, 1:0.17, 1:0.20, 1:0.23, 1:0.25 or the range value between any two of them.

[0113] In some specific embodiments, the step of mixing the second intermediate, the dispersant and the organic carbon source includes: first, ultrasonically disperse the second intermediate in the dispersant, then add an alkali solution to adjust the pH of the mixed system to 10.5-11.5 (including but not limited to the point values of any one of 10.5, 10.8, 11, 11.2, 11.5 or the range values between any two of them), and then add the organic carbon source thereto; preferably, the alkali solution includes at least one of an ammonia water solution, a sodium hydroxide solution, a potassium hydroxide solution and a sodium carbonate solution.

[0114] In some specific embodiments, the reaction time for the coating is 12-24 h; including but not limited to the point values of any one of 12 h, 15 h, 18 h, 20 h, 22 h, 24 h or the range values between any two of them.

[0115] In some specific embodiments, the atmosphere for the calcination includes an inert atmosphere; wherein, the inert atmosphere includes but not limited to a nitrogen atmosphere, an argon atmosphere, etc.

[0116] In some specific embodiments, the temperature for the calcination is 550-650 °C, including but not limited to the point values of any one of 550 °C, 560 °C, 580 °C, 600 °C, 630 °C, 650 °C or the range values between any two of them; the heat preservation time for the calcination is 3-8 h, including but not limited to the point values of any one of 3 h, 4 h, 5 h, 6 h, 7 h, 8 h or the range values between any two of them.

[0117] In some specific embodiments, the heating rate for the calcination is 1-10 °C / min, including but not limited to the point values of any one of 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 8 °C / min, 10 °C / min or the range values between any two of them.

[0118] In some specific embodiments, the acid solution includes at least one of a hydrochloric acid solution, a nitric acid solution, a sulfuric acid solution and a perchloric acid solution.

[0119] In some specific embodiments, the concentration of the acid solution is 0.5-2 mol / L; including but not limited to the point values of any one of 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.3 mol / L, 1.5 mol / L, 1.7 mol / L, 2 mol / L or the range values between any two of them.

[0120] In some specific embodiments, the reaction time for mixing and reacting the third intermediate with the acid solution is 5 to 12 h, including but not limited to any point value among 5 h, 6 h, 8 h, 10 h, 12 h or the range value between any two of them.

[0121] In some specific embodiments, the gaseous carbon source includes at least one of acetylene, methane, ethylene, propylene, toluene and benzene.

[0122] In some specific embodiments, the flow rate of the gaseous carbon source introduced is 0.1 to 0.4 L / min; including but not limited to any point value among 0.1 L / min, 0.2 L / min, 0.3 L / min, 0.4 L / min or the range value between any two of them.

[0123] In some specific embodiments, the atmosphere for chemical vapor deposition includes an inert atmosphere; wherein, the inert atmosphere includes but not limited to a nitrogen atmosphere, an argon atmosphere, etc.

[0124] In some specific embodiments, the temperature for chemical vapor deposition is 600 to 700 °C, including but not limited to any point value among 600 °C, 620 °C, 630 °C, 650 °C, 680 °C, 700 °C or the range value between any two of them.

[0125] The time for chemical vapor deposition is 1 to 3 h, such as 1 h, 1.5 h, 1.7 h, 2 h, 2.5 h or 3 h.

[0126] In the third aspect, the present invention provides a negative electrode sheet including the silicon-carbon negative electrode material.

[0127] The battery prepared from the negative electrode sheet has excellent electrochemical performance, with high capacity, high initial efficiency and long cycle life.

[0128] Optionally, the negative electrode sheet further includes a binder and / or a conductive agent, and the present invention does not make any limitation thereto.

[0129] In the fourth aspect, the present invention provides a lithium-ion battery including the negative electrode sheet.

[0130] The lithium-ion battery provided by the present invention has a high capacity, a high initial Coulomb efficiency and excellent cycling performance.

[0131] Optionally, the lithium-ion battery further includes a positive electrode sheet, a separator and an electrolyte, and the present invention does not make any limitation thereto.

[0132] The implementation scheme of the present invention will be described in detail below in combination with embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0133] Example 1

[0134] The preparation method of the silicon-carbon anode material provided in this example includes the following steps:

[0135] (1) Take 5 kg of porous carbon (specific surface area 936 m 2 / g, pore volume 1.6 cm 3 / g, microporosity 10%, pore diameter <50 nm, the lowest pore diameter is 0.5 nm), and place it in a muffle furnace at 300 °C (air atmosphere) for calcination for 2 h.

[0136] (2) Take 1 kg of the calcined porous carbon, ultrasonically disperse it evenly in 10 L of an alcohol-water mixed solvent (the volume ratio of ethanol to water is 4:1), and add ammonia water to adjust the pH value of the mixed solution to 11. After dispersing and stirring for 0.5 h, then add 5 kg of tetraethyl orthosilicate (that is, the mass ratio of porous carbon to silicon source is 1:5), stir and react for 12 h, and then perform multiple suction filtration and washing until the filtrate is neutral to obtain the first intermediate.

[0137] (3) Take 1 kg of the first intermediate and 0.6 kg of magnesium powder (that is, the mass ratio of the first intermediate to the reducing agent is 1:0.6), evenly mix the two, place them in a box furnace under an argon atmosphere, and heat up to 600 °C at a heating rate of 1 °C / min for reduction reaction. After holding for 10 h, take out the product to obtain the second intermediate.

[0138] (4) Take 1 kg of the second intermediate, ultrasonically disperse it evenly in 10 L of an alcohol-water mixed solvent (the volume ratio of ethanol to water is 4:1), and then add ammonia water to adjust the pH value of the mixed solution to 11. After dispersing and stirring for 0.5 h, add 0.2 kg of dopamine (that is, the mass ratio of the second intermediate to the organic carbon source is 1:0.2) for coating, stir for 12 h, and then perform multiple suction filtration and washing until the filtrate is neutral to obtain the third intermediate.

[0139] (5) Take 1 kg of the third intermediate, place it in a box furnace under an argon atmosphere for roasting, heat up to 600 °C at a heating rate of 5 °C / min, take it out after holding for 3 h to obtain the third intermediate, place it in 10 L of a hydrochloric acid solution with a molar concentration of 1 mol / L for impurity removal (removing magnesium and / or magnesium oxide), stir for 5 h, and then perform multiple suction filtration and washing until the filtrate is neutral to obtain the fourth intermediate.

[0140] (6) Take 1 kg of the fourth intermediate and place it in a rotary furnace. Evacuate the air and introduce N 2 to replace the air with N 2 . Under the protection of a nitrogen atmosphere, heat it to 650 °C at a rate of 5 °C / min, and at the same time introduce C 2 H 2 (acetylene) at a flow rate of 1 L / min for chemical vapor deposition. After maintaining the temperature for 2 h, close the C 2 H 2 gas valve to obtain the final silicon-carbon negative electrode material.

[0141] The silicon-carbon negative electrode material prepared in this example includes a porous carbon matrix with a pore structure. The pore structure contains elemental silicon. The outer surface of the porous carbon matrix is coated with a loose carbon layer, and the outer surface of the loose carbon layer is coated with a dense carbon layer.

[0142] Example 2

[0143] The preparation method of the silicon-carbon negative electrode material provided in this example is basically the same as that in Example 1, except that in step (2), the mass of tetraethyl orthosilicate is replaced with 4.5 kg.

[0144] Example 3

[0145] The preparation method of the silicon-carbon negative electrode material provided in this example is basically the same as that in Example 1, except that in step (2), the mass of tetraethyl orthosilicate is replaced with 5.5 kg.

[0146] Example 4

[0147] The preparation method of the silicon-carbon negative electrode material provided in this example is basically the same as that in Example 1, except that in step (4), the mass of dopamine is replaced with 0.18 kg.

[0148] Example 5

[0149] The preparation method of the silicon-carbon negative electrode material provided in this example is basically the same as that in Example 1, except that in step (4), the mass of dopamine is replaced with 0.23 kg.

[0150] Example 6

[0151] The preparation method of the silicon-carbon negative electrode material provided in this example is basically the same as that in Example 1, except that in step (6), the reaction time of chemical vapor deposition is 1.7 h.

[0152] Example 7

[0153] The preparation method of the silicon-carbon negative electrode material provided in this example is basically the same as that in Example 1, except that in step (6), the reaction time of chemical vapor deposition is 2.2 h.

[0154] Example 8

[0155] The preparation method of the silicon-carbon anode material provided in this example is basically the same as that in Example 1, except that in step (1), the pore volume of the porous carbon is 1.4 cm 3 / g, the specific surface area is 805 m 2 / g, the microporosity is 11%, and the pore diameter is <50 nm.

[0156] Example 9

[0157] The preparation method of the silicon-carbon anode material provided in this example is basically the same as that in Example 1, except that in step (1), it is calcined in a muffle furnace (air atmosphere) at 350 °C for 3 h.

[0158] Example 10

[0159] The preparation method of the silicon-carbon anode material provided in this example is basically the same as that in Example 1, except that in step (4), dopamine is replaced with an equal mass of phenolic resin.

[0160] Example 11

[0161] The preparation method of the silicon-carbon anode material provided in this example is basically the same as that in Example 1, except that in step (6), acetylene is replaced with ethylene.

[0162] Comparative Example 1

[0163] The preparation method of the silicon-carbon anode material provided in this comparative example is basically the same as that in Example 1, except that the operation order of steps (4) and (5) is different. In this comparative example, acid washing for impurity removal is carried out first, and then coating and roasting are carried out. The preparation method of the silicon-carbon anode material provided in this comparative example specifically includes:

[0164] (1)-(3): The same as steps (1)-(3) of Example 1;

[0165] (4) Take 1 kg of the second intermediate, place it in a 10 L hydrochloric acid solution with a molar concentration of 1 mol / L for impurity removal (removing magnesium and / or magnesium oxide), stir for 5 h, and then carry out multiple suction filtration and washing until the filtrate is neutral to obtain the third intermediate.

[0166] (5) Take 1 kg of the third intermediate and ultrasonically disperse it evenly in 10 L of an ethanol-water mixed solvent (the volume ratio of ethanol to water is 4:1). Then add ammonia water to adjust the pH value of the mixed solution to 11. After dispersing and stirring for 0.5 h, add 0.2 kg of dopamine (i.e., the mass ratio of the second intermediate to the organic carbon source is 1:0.2) for coating. After stirring for 12 h, perform multiple suction filtrations and washings until the filtrate is neutral to obtain semi-finished product B. Then take 1 kg of semi-finished product B and place it in a box furnace under an argon atmosphere for roasting. Heat it to 600 °C at a heating rate of 5 °C / min, hold for 3 h and then take it out to obtain the fourth intermediate.

[0167] (6): The same as step (6) of Example 1.

[0168] Comparative Example 2

[0169] The preparation method of the silicon-carbon anode material provided in this comparative example is basically the same as that of Example 1, except that the coating in step (4) is not carried out, but step (5) is directly carried out, that is, 1 kg of the second intermediate is roasted. The silicon-carbon anode material prepared in this comparative example has no loose carbon layer.

[0170] Comparative Example 3

[0171] The preparation method of the silicon-carbon anode material provided in this comparative example is basically the same as that of Example 1, except that step (6) is not carried out, that is, the silicon-carbon anode material in this comparative example is the fourth intermediate obtained in step (5) of Example 1 and has no dense carbon layer.

[0172] The pore volume of the porous carbon matrix of the silicon-carbon anode materials prepared in each example and each comparative example is P, with the unit of cm 3 / g, the mass fraction of silicon element in the silicon-carbon anode material is A, and the true density of the silicon-carbon anode material is B, with the unit of g / cm 3 , and the values of P, A, B and the value of A / (2.26 - B) / P are shown in Table 1 respectively. The mass fraction of the loose carbon layer (abbreviated as the loose carbon layer mass fraction) and the mass fraction of the dense carbon layer (abbreviated as the dense carbon layer mass fraction) in the silicon-carbon anode materials prepared in each example and each comparative example are shown in Table 1.

[0173] Table 1 Performance indicators of the silicon-carbon anode materials prepared in each example and each comparative example

[0174]

[0175]

[0176] Further, the silicon-carbon anode materials prepared in each of the examples and comparative examples were used as the anode active materials, and a negative electrode paste was prepared by mixing with a solvent according to a mass ratio of anode active material: binder: conductive agent of 70:20:10. The negative electrode paste was coated on a copper foil, and after drying, a negative electrode sheet was obtained. A lithium sheet was used as the counter electrode, and a polypropylene microporous membrane separator and 1 mol / L LiPF 6 dissolved in a four-component mixed solvent was used as the electrolyte. Among them, in the four-component solvent, the volume ratio of ethylene carbonate (EC): dimethyl carbonate (DMC): vinylene carbonate (VC): fluoroethylene carbonate (FEC) = 1:1:1:1. A CR2032 type coin-shaped half-cell was assembled, and the capacity, initial efficiency, and capacity retention rate of each battery were tested respectively. The results are shown in Table 2.

[0177] Among them, the test methods for capacity, initial efficiency, and capacity retention rate are as follows: Stand still for 10 min, discharge at a constant current of 0.1C to 5 mV, stand still for 5 min, then discharge at a constant current of 0.02C to 5 mV, stand still for 5 min, and then discharge at a constant current of 0.01C to 5 mV; stand still for 10 min, charge at a constant current of 0.1C to 2.0V. Cycle 100 times.

[0178] Table 2 Electrochemical performance of each battery

[0179]

[0180]

[0181] It can be seen from Table 1 and Table 2 that the silicon-carbon anode materials prepared in each of the examples satisfy the relationship 30 ≤ 100×A / (2.26 - B) / P ≤ 70, and the batteries have better capacity, initial Coulombic efficiency, and cycling performance.

[0182] However, each of the comparative examples does not satisfy the relationship 30 ≤ 100×A / (2.26 - B) / P ≤ 70, and the capacity, initial Coulombic efficiency, or cycling performance of the batteries is poor.

[0183] It can be seen by comparing Example 1 and Comparative Example 1 that the method of first coating and then pickling can obtain silicon-carbon particles with a lower true density. The pores in the particles provide free space for the volume expansion of silicon, thus showing good cycling stability.

[0184] It can be seen by comparing Example 1 and Comparative Example 2 that the silicon-carbon anode material of Comparative Example 2 has no loose carbon layer, resulting in a higher true density of the silicon-carbon particles. It is difficult to buffer the volume change of silicon inside the particles, and thus its electrochemical performance is poor.

[0185] It can be seen by comparing Example 1 with Comparative Example 3 that the silicon-carbon anode material of Comparative Example 3 has no dense carbon layer, resulting in direct contact between the electrolyte and silicon particles, causing oxidation of silicon and decomposition of the electrolyte. During the repeated volume change process of the silicon particles, the solid electrolyte interface layer generated by the decomposition of the electrolyte on its surface gradually increases, leading to further deterioration of its electrical properties.

[0186] In summary, the silicon-carbon anode material provided by the present invention has a specific structure and satisfies the specific relational expression 30 ≤ 100×A / (2.26 - B) / P ≤ 70, which can significantly reduce the volume change of the silicon-carbon anode material during lithium insertion / extraction, and improve the capacity, initial Coulomb efficiency, and cycling performance of the silicon-carbon anode material and the battery prepared therefrom.

[0187] Although the present invention has been illustrated and described with reference to specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; those of ordinary skill in the art should understand that: without departing from the spirit and scope of the present invention, the technical solutions described in the foregoing embodiments may be modified, or some or all of the technical features may be equivalently replaced; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A silicon-carbon negative electrode material, characterized in that: It comprises a porous carbon matrix with a pore structure, wherein the pore structure contains elemental silicon, the outer surface of the porous carbon matrix is ​​covered with a loose carbon layer, and the outer surface of the loose carbon layer is covered with a dense carbon layer; The pore volume of the porous carbon matrix is ​​P, in cm 3 / g; the mass fraction of silicon in the silicon-carbon negative electrode material is A; the true density of the silicon-carbon negative electrode material is B, in units of g / cm 3 ; Wherein P, A, and B satisfy 30≤100×A / (2.26-B) / P≤70.

2. The silicon-carbon negative electrode material according to claim 1, characterized in that: At least one of the following conditions is met: (1) The pore volume P of the porous carbon matrix is ​​1.4 to 1.8 cm 3 / g; (2) The mass fraction A of the silicon element in the silicon-carbon negative electrode material is 40% to 55%; (3) The true density B of the silicon-carbon negative electrode material is 1.5 to 1.8 g / cm 3 ; (4) The mass fraction of the loose carbon layer in the silicon-carbon negative electrode material is 5% to 10%; (5) The mass fraction of the dense carbon layer in the silicon-carbon negative electrode material is 2% to 5%.

3. The method for preparing the silicon-carbon negative electrode material according to claim 1 or 2, characterized in that: The steps include: The porous carbon, the silicon source and the solvent are mixed and reacted, so that the silicon dioxide generated by the hydrolysis of the silicon source enters the pore structure of the porous carbon, and then the solid-liquid separation is carried out to obtain a first intermediate; The first intermediate is mixed with a reducing agent and then heated to perform a reduction reaction, so that the silicon dioxide in the pore structure is reduced to elemental silicon to obtain a second intermediate; The second intermediate, a dispersant and an organic carbon source are mixed and coated to form a coating layer on the outer surface of the porous carbon, and then solid-liquid separation and roasting are performed to form a loose carbon layer on the coating layer to obtain a third intermediate; The third intermediate is mixed with an acid solution and reacted, the reducing agent and / or the product formed after the reducing agent reacts are removed, and then the solid-liquid separation is performed to obtain a fourth intermediate; A gaseous carbon source is introduced into the system containing the fourth intermediate to perform chemical vapor deposition to obtain the silicon-carbon negative electrode material.

4. The method for preparing the silicon-carbon negative electrode material according to claim 3, characterized in that: At least one of the following conditions is met: (1) Before mixing the porous carbon, the silicon source and the solvent, the porous carbon is first calcined at 250 to 400° C.; preferably, the calcination time is 2 to 8 hours; preferably, the calcination atmosphere includes an air atmosphere or an oxygen atmosphere; (2) The pore volume of the porous carbon is 1.4 to 1.8 cm 3 / g; (3) The specific surface area of ​​the porous carbon is 800 to 1000 m 2 / g, microporosity 8% to 15%, pore size <50nm; (4) The silicon source comprises at least one of tetraethyl orthosilicate, trimethoxysilane, tetraethylsilane, phenyltrimethoxysilane and tetrachlorosilane; (5) The solvent comprises a mixed solvent of ethanol and water; preferably, the volume ratio of the ethanol to the water is 3 to 5:1; (6) The mass ratio of the porous carbon to the silicon source is 1:4-6; (7) The step of mixing the porous carbon, the silicon source and the solvent comprises: firstly ultrasonically dispersing the porous carbon in the solvent, then adding an alkaline solution to adjust the pH of the mixed system to 10.5-11.5, and then adding the silicon source thereto; preferably, the alkaline solution comprises at least one of an aqueous ammonia solution, a sodium hydroxide solution, a potassium hydroxide solution and a sodium carbonate solution; (8) The reaction time of mixing and reacting the porous carbon, the silicon source and the solvent is 12 to 24 hours.

5. The method for preparing the silicon-carbon negative electrode material according to claim 3, characterized in that: At least one of the following conditions is met: (1) The reducing agent includes at least one of metallic magnesium, metallic aluminum and a magnesium-aluminum alloy; (2) The mass ratio of the first intermediate to the reducing agent is 1:0.4-0.8; (3) The atmosphere of the reduction reaction includes an inert atmosphere; (4) The heating temperature of the reduction reaction is 550-650° C., and the insulation time is 10-24 hours.

6. The method for preparing the silicon-carbon negative electrode material according to claim 3, characterized in that: At least one of the following conditions is met: (1) The dispersant comprises a mixed solvent of ethanol and water; preferably, the volume ratio of the ethanol to the water is 3 to 5:1; (2) the organic carbon source comprises at least one of dopamine, phenolic resin, glucose, citric acid and polypyrrole; (3) The mass ratio of the second intermediate to the organic carbon source is 1:0.15-0.25; (4) The step of mixing the second intermediate, the dispersant and the organic carbon source comprises: firstly dispersing the second intermediate in the dispersant by ultrasonication, then adding an alkali solution to adjust the pH of the mixed system to 10.5-11.5, and then adding the organic carbon source thereto; preferably, the alkali solution comprises at least one of an aqueous ammonia solution, a sodium hydroxide solution, a potassium hydroxide solution and a sodium carbonate solution; (5) The coating time is 12 to 24 hours; (6) The calcination atmosphere includes an inert atmosphere; (7) The calcination temperature is 550-650° C. and the heat preservation time is 3-8 hours.

7. The method for preparing the silicon-carbon negative electrode material according to claim 3, characterized in that: At least one of the following conditions is met: (1) The acid solution comprises at least one of a hydrochloric acid solution, a nitric acid solution, a sulfuric acid solution and a perchloric acid solution; (2) The concentration of the acid solution is 0.5 to 2 mol / L; (3) The reaction time of mixing and reacting the third intermediate with the acid solution is 5 to 12 hours.

8. The method for preparing the silicon-carbon negative electrode material according to claim 3, characterized in that: At least one of the following conditions is met: (1) The gaseous carbon source includes at least one of acetylene, methane, ethylene, propylene, toluene and benzene; (2) The flow rate of the gaseous carbon source is 0.1 to 0.4 L / min; (3) The atmosphere of the chemical vapor deposition includes an inert atmosphere; (4) The temperature of the chemical vapor deposition is 600-700° C. and the time is 1-3 hours.

9. A negative electrode sheet, characterized in that: Comprising the silicon-carbon negative electrode material as described in claim 1 or 2.

10. A lithium ion battery, characterized in that: Comprising the negative electrode sheet as claimed in claim 9.

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