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

Abstract

The present application relates to the technical field of negative electrode materials, in particular to a silicon-carbon negative electrode material, a preparation method thereof, a negative electrode sheet and a lithium ion battery. The silicon-carbon negative electrode material comprises a porous carbon matrix with a pore structure, the pore structure containing elemental silicon, the outer surface of the porous carbon matrix being coated with a loose carbon layer, and the outer surface of the loose carbon layer being coated 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 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 present application has a small volume change during the embedding / detaching of lithium, and has a better capacity, first coulomb efficiency and cycle performance.

Description

Technical Field

[0001] This invention relates to the field of anode material technology, and more specifically, to a silicon-carbon anode material, its preparation method, anode sheet, and a lithium-ion battery. Background Technology

[0002] Compared to graphite anode materials, silicon-based anode materials have a higher theoretical specific capacity (4200mAh / g), and batteries made with silicon-based anode materials have a relatively higher energy density, thereby improving battery life and range.

[0003] However, silicon undergoes a volume change of approximately 300% during lithium insertion / extraction, which causes a series of problems during cycling. For example, silicon-based anode materials may crack and eventually pulverize; the volume change prevents the formation of a stable SEI layer on the electrode surface, leading to repeated SEI layer breakage and formation, consuming a large number of lithium ions. This results in a decrease in battery capacity, initial coulombic efficiency, and cycle performance.

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

[0005] The primary objective of this invention is to provide a silicon-carbon anode material having a specific structure, wherein the pore volume P of the porous carbon matrix, the mass fraction A of silicon in the silicon-carbon anode material, and the true density B of the silicon-carbon anode material satisfy a specific relationship: 30≤100×A / (2.26-B) / P≤70. This significantly reduces the volume change of the silicon-carbon anode material during lithium insertion / extraction, thereby improving the capacity, initial coulombic efficiency, and cycle performance of the silicon-carbon anode material.

[0006] The second objective of this invention is to provide a method for preparing silicon-carbon anode materials that is simple and easy to operate, can be mass-produced, and the silicon-carbon anode materials prepared by this method exhibit small volume changes during lithium insertion / extraction processes and have excellent electrochemical performance.

[0007] The third objective of this invention is to provide a negative electrode sheet.

[0008] The fourth objective of this invention is to provide a lithium-ion battery.

[0009] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0010] This invention first provides a silicon-carbon anode material, comprising a porous carbon matrix with a porous structure containing elemental silicon, the outer surface of the porous carbon matrix being coated with a loose carbon layer, and the outer surface of the loose carbon layer being coated with a dense carbon layer; the pore volume of the porous carbon matrix is ​​P, measured in cm³. 3 / g; the mass fraction of silicon in the silicon-carbon anode material is A; the true density of the silicon-carbon anode material is B, in g / cm³. 3 Where P, A, and B satisfy 30≤100×A / (2.26-B) / P≤70.

[0011] Furthermore, the pore volume P of the porous carbon matrix is ​​1.4–1.8 cm³. 3 / g.

[0012] Furthermore, the mass fraction A of silicon in the silicon-carbon anode material is 40% to 55%.

[0013] Furthermore, the true density B of the silicon-carbon anode material is 1.5–1.8 g / cm³. 3 .

[0014] Furthermore, the loose carbon layer in the silicon-carbon anode material accounts for 5% to 10% of the total mass.

[0015] Furthermore, the dense carbon layer in the silicon-carbon anode material accounts for 2% to 5% of the total mass.

[0016] This invention further provides a method for preparing silicon-carbon anode materials, comprising the following steps:

[0017] Porous carbon, a silicon source, and a solvent are mixed and reacted, allowing the silicon dioxide generated by the hydrolysis of the silicon source to enter the pore structure of the porous carbon. Then, solid-liquid separation is performed to obtain a first intermediate.

[0018] The first intermediate is mixed with a reducing agent and heated to carry out a reduction reaction, so that the silicon dioxide in the porous structure is reduced to elemental silicon, thus obtaining the second intermediate.

[0019] The second intermediate, dispersant, and organic carbon source are mixed and coated to form a coating layer on the outer surface of the porous carbon. Then, solid-liquid separation and calcination are performed to form a loose carbon layer from the coating layer, thus obtaining the third intermediate.

[0020] The third intermediate is mixed with an acid solution and reacted to remove the reducing agent and / or the product formed after the reducing agent reaction. Then, solid-liquid separation is performed to obtain the fourth intermediate.

[0021] A gaseous carbon source is introduced into a system containing the fourth intermediate, and chemical vapor deposition is performed to obtain the silicon-carbon anode material.

[0022] Furthermore, before mixing the porous carbon, silicon source, and solvent, the porous carbon is first calcined at 250–400°C.

[0023] Furthermore, the calcination time is 2 to 8 hours.

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

[0025] Furthermore, the porous carbon has a pore volume of 1.4–1.8 cm³. 3 / g;

[0026] Furthermore, the specific surface area of ​​the porous carbon is 800–1000 m². 2 / g, microporosity 8%~15%, pore size <50nm.

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

[0028] Furthermore, the solvent includes a mixture of ethanol and water.

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

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

[0031] Furthermore, the step of mixing porous carbon, silicon source and solvent includes: firstly, ultrasonically dispersing the porous carbon in the solvent, then adding an alkaline solution to adjust the pH of the mixture to 10.5-11.5, and then adding the silicon source thereto.

[0032] Furthermore, the alkaline solution includes at least one of ammonia solution, sodium hydroxide solution, potassium hydroxide solution, and sodium carbonate solution.

[0033] Furthermore, the reaction time for mixing and reacting porous carbon, silicon source and solvent is 12 to 24 hours.

[0034] Furthermore, the reducing agent includes at least one of metallic magnesium, metallic aluminum, and magnesium-aluminum alloys.

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

[0036] Furthermore, the atmosphere for the reduction reaction includes an inert atmosphere.

[0037] Furthermore, the heating temperature for the reduction reaction is 550–650°C, and the holding time is 10–24 h.

[0038] Furthermore, the dispersant comprises a mixed solvent of ethanol and water.

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

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

[0041] Furthermore, the mass ratio of the second intermediate to the organic carbon source is 1:0.15 to 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 alkaline solution to adjust the pH of the mixture to 10.5-11.5, and then adding the organic carbon source thereto.

[0043] Furthermore, the alkaline solution includes at least one of ammonia solution, sodium hydroxide solution, potassium hydroxide solution, and sodium carbonate solution.

[0044] Furthermore, the coating time is 12 to 24 hours.

[0045] Furthermore, the roasting atmosphere includes an inert atmosphere.

[0046] Furthermore, the calcination temperature is 550–650°C, and the holding time is 3–8 hours.

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

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

[0049] Furthermore, the reaction time for mixing and reacting the third intermediate with the acid solution is 5 to 12 hours.

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

[0051] Furthermore, the flow rate of the gaseous carbon source is 0.1–0.4 L / min.

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

[0053] Furthermore, the chemical vapor deposition temperature is 600–700°C, and the time is 1–3 hours.

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

[0055] The present invention also 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 anode material provided by this invention has a specific structure, and the pore volume P of the porous carbon matrix, the mass fraction A of silicon in the silicon-carbon anode material, and the true density B of the silicon-carbon anode material satisfy a specific relationship: 30≤100×A / (2.26-B) / P≤70. This can significantly reduce the volume change of the silicon-carbon anode material during the lithium insertion / extraction process and improve the capacity, first coulombic efficiency, and cycle performance of the silicon-carbon anode material. Attached Figure Description

[0058] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0059] Figure 1 This is a schematic diagram of the structure of the silicon-carbon anode material provided by the present invention. Detailed Implementation

[0060] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0061] Unless otherwise specified, in this invention, terms such as "first aspect," "second aspect," "third aspect," and "fourth aspect" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, terms such as "first," "second," "third," and "fourth" serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0062] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

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

[0064] In a first aspect, the present invention provides a silicon-carbon anode material, such as... Figure 1 The diagram shown is a schematic representation of the silicon-carbon anode material, specifically a cross-sectional view. The silicon-carbon anode material includes a porous carbon matrix with several pore structures containing elemental silicon. The porous carbon matrix is ​​coated with a loose carbon layer, and the loose carbon layer is coated with a dense carbon layer.

[0065] It is understandable that the porous structure of the porous carbon matrix provides free space for the expansion of the elemental silicon within it.

[0066] It is understandable that the density of a loose carbon layer is lower than that of a dense carbon layer.

[0067] In some implementations, 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, measured in cm³. 3 / g.

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

[0070] The true density of the silicon-carbon anode material is B, with units of g / cm³. 3 .

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

[0072] The silicon-carbon anode material provided by this invention has a specific structure, and the pore volume P of the porous carbon matrix, the mass fraction A of silicon in the silicon-carbon anode material, and the true density B of the silicon-carbon anode material satisfy a specific relationship: 30≤100×A / (2.26-B) / P≤70. This can significantly reduce the volume change of the silicon-carbon anode material during the lithium insertion / extraction process and improve the capacity, first coulombic efficiency (hereinafter referred to as first efficiency) and cycle performance of the silicon-carbon anode material.

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

[0074] Meanwhile, this invention controls the pore volume P of the porous carbon matrix, the mass fraction A of silicon in the silicon-carbon anode material, and the true density B of the silicon-carbon anode material to satisfy the relationship 30≤100×A / (2.26-B) / P≤70. The size of the porous carbon pore volume P affects the size of the silicon mass fraction A; the larger the pore volume, the larger the silicon mass fraction that can penetrate. The size of the silicon mass fraction A affects the true density B of the silicon-carbon material; the larger the silicon mass fraction A, 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 cm³. 3 / g, for example, 1.5cm 3 / g, 1.6cm 3 / g or 1.7cm 3 / g.

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

[0077] In some specific embodiments, the true density B of the silicon-carbon anode material is 1.5–1.8 g / cm³. 3 ; including but not limited to 1.5g / cm 3 1.55g / cm 3 1.6g / cm 3 1.65g / cm 3 1.7g / cm 3 1.75g / cm 3 1.8g / cm 3 The value can be any one of the points or any range between the two. The silicon-carbon anode material provided by this invention has low true density, low expansion, and good cycle performance.

[0078] In some specific embodiments, the loose carbon layer in the silicon-carbon anode material accounts for 5% to 10% by mass, for example, 6%, 7%, 8% or 9%.

[0079] In some specific embodiments, the dense carbon layer in the silicon-carbon anode material accounts for 2% to 5% by mass, for example 3% or 4%.

[0080] Secondly, the present invention provides a method for preparing the silicon-carbon anode 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 the silicon source is hydrolyzed enters the pore structure of the porous carbon. Then, solid-liquid separation is performed to obtain a first intermediate.

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

[0083] Then, the first intermediate is mixed with a reducing agent and heated to carry out a reduction reaction, reducing the silicon dioxide within the porous structure to elemental silicon, thus obtaining the 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 within its porous structure.

[0084] Subsequently, the second intermediate, dispersant, and organic carbon source are mixed and coated to form a coating layer on the outer surface of the porous carbon. Then, solid-liquid separation and calcination are performed to form a loose carbon layer, yielding the third intermediate. The organic carbon source includes liquid and / or solid carbon sources. During the coating process, the organic carbon source or the product of its polymerization coats the outer surface of the second intermediate, forming a coating layer. Calcination of this coating layer forms the loose carbon layer. In other words, the third intermediate is porous carbon with a loose carbon layer on its outer surface, and the porous carbon also contains elemental silicon within its pore structure.

[0085] In some specific implementations, the organic carbon source is a monomeric carbon source. After the materials are mixed, the monomeric carbon source undergoes a polymerization reaction to generate a polymer, which is then coated on the outer surface of the second intermediate. Alternatively, the organic carbon source can be a polymer material directly.

[0086] Further, the third intermediate is mixed with an acid solution and reacted (i.e., acid washing to remove impurities) to remove the reducing agent and / or the product formed after the reducing agent reaction. Then, solid-liquid separation is performed to obtain the fourth intermediate. This invention employs a method of first coating and calcining followed by acid washing to remove impurities. The remaining space after impurity removal provides free space for the expansion of silicon during the lithiation process. If acid washing is performed before coating, the carbon used for coating will occupy the remaining space after impurity removal, hindering the free change in silicon volume.

[0087] In some specific embodiments, the reducing agent includes an active metal. It is understood that an active metal 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 any unreacted or excessive active metal.

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

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

[0090] It is understandable that by controlling the pore volume of the porous carbon raw material, the amount of silicon source and organic carbon source added during the reaction process, the flow rate of the gaseous carbon source, and the time of chemical vapor deposition, the final silicon-carbon anode material can be controlled to satisfy the relationship 30≤100×A / (2.26-B) / P≤70.

[0091] The method for preparing silicon-carbon anode material provided by this invention is simple and easy to operate, and can be mass-produced. Furthermore, the silicon-carbon anode material prepared by this method exhibits small volume change during lithium insertion / extraction processes and has excellent electrochemical performance.

[0092] It is understandable that the true density of silicon-carbon anode materials can be controlled by adjusting the pore volume of porous carbon and the mass fraction of silicon.

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

[0094] Calcination of porous carbon before its reaction with silicon source increases the number of oxygen-containing functional groups in the porous carbon, promoting its bonding with silicon source and / or silicon dioxide (since the calcination temperature of the porous carbon before the reaction is low, this operation has almost no effect on the pore volume of the porous carbon).

[0095] Preferably, the calcination time is 2 to 8 hours; including but not limited to any one of 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, and 8 hours, or any range between 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 cm³. 3 / g, for example, 1.5cm 3 / g, 1.6cm 3 / g or 1.7cm 3 / g.

[0098] In some specific embodiments, the specific surface area of ​​the porous carbon is 800–1000 m². 2 / g, for example 850m 2 / g、900m 2 / g or 950m 2 / g; the microporosity of the porous carbon is 8% to 15%, for example 9%, 10%, 11%, 12%, 13% or 14%, and the pore size of the porous carbon is <50nm (i.e. all pore sizes are less than 50nm).

[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 mixture of ethanol and water. Preferably, the volume ratio of ethanol to water is 3 to 5:1, for example, 4:1.

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

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

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

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

[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 one of 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8 or any range between the two.

[0106] In some specific embodiments, the atmosphere for the reduction reaction includes an inert atmosphere. This inert atmosphere includes, but is not limited to, nitrogen atmosphere, argon atmosphere, etc.

[0107] In some specific embodiments, the heating temperature of the reduction reaction is 550-650℃, including but not limited to any one of 550℃, 560℃, 580℃, 600℃, 630℃, and 650℃, or any range between two of them; the holding time of the reduction reaction is 10-24h, including but not limited to any one of 10h, 12h, 15h, 18h, 20h, 22h, and 24h, or any range between two of them.

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

[0109] In some specific embodiments, the dispersant comprises a mixed solvent of ethanol and water; preferably, the volume ratio of ethanol to water is 3 to 5:1, for example 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, so that dopamine polymerizes into polydopamine, and then 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 one of 1:0.15, 1:0.17, 1:0.20, 1:0.23, 1:0.25 or any range between the two.

[0113] In some specific embodiments, 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 alkaline solution to adjust the pH of the mixture to 10.5–11.5 (including but not limited to any one of 10.5, 10.8, 11, 11.2, and 11.5, or a range between any two); and then adding the organic carbon source thereto. Preferably, the alkaline solution includes at least one of ammonia solution, sodium hydroxide solution, potassium hydroxide solution, and sodium carbonate solution.

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

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

[0116] In some specific embodiments, the roasting temperature is 550-650℃, including but not limited to any one of 550℃, 560℃, 580℃, 600℃, 630℃, and 650℃ or any range between two of them; the roasting holding time is 3-8h, including but not limited to any one of 3h, 4h, 5h, 6h, 7h, and 8h or any range between two of them.

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

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

[0119] In some specific embodiments, the concentration of the acid solution is 0.5 to 2 mol / L; including but not limited to 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 any range between 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 hours, including but not limited to any one of 5 hours, 6 hours, 8 hours, 10 hours, and 12 hours, or any range between two of them.

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

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

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

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

[0125] The chemical vapor deposition time is 1 to 3 hours, for example, 1 hour, 1.5 hours, 1.7 hours, 2 hours, 2.5 hours or 3 hours.

[0126] Thirdly, the present invention provides a negative electrode sheet comprising the silicon-carbon negative electrode material.

[0127] The battery made from this negative electrode exhibits excellent electrochemical performance, with high capacity, high initial efficiency, and long cycle life.

[0128] Optionally, the negative electrode sheet may further include a binder and / or a conductive agent, which is not limited in this invention.

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

[0130] The lithium-ion battery provided by this invention has high capacity, high initial coulombic efficiency, and excellent cycle performance.

[0131] Optionally, the lithium-ion battery may further include a positive electrode, a separator, and an electrolyte, which are not limited in this invention.

[0132] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0133] Example 1

[0134] The method for preparing the silicon-carbon anode material provided in this embodiment includes the following steps:

[0135] (1) Take 5 kg of porous carbon (specific surface area 936 m²) 2 / g, pore volume 1.6cm 3 / g, microporosity 10%, pore size <50nm, minimum pore size 0.5nm), and calcined in a muffle furnace (air atmosphere) at 300℃ for 2h.

[0136] (2) Take 1 kg of calcined porous carbon and ultrasonically disperse it evenly in 10 L of alcohol-water mixed solvent (ethanol to water volume ratio of 4:1). Add ammonia water to adjust the pH of the mixed solution to 11. After dispersing and stirring for 0.5 h, add 5 kg of tetraethyl orthosilicate (i.e., the mass ratio of porous carbon to silicon source is 1:5). Stir and react for 12 h. Filter and wash repeatedly 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 (i.e., the mass ratio of the first intermediate to the reducing agent is 1:0.6). Mix the two evenly and place them in a box furnace under an argon atmosphere. Heat the furnace to 600°C at a heating rate of 1°C / min to carry out the reduction reaction. After holding the temperature for 10 hours, take out the product to obtain the second intermediate.

[0138] (4) Take 1 kg of the second intermediate and ultrasonically disperse it evenly in 10 L of alcohol-water mixed solvent (ethanol to water volume ratio of 4:1). Then add ammonia water to adjust the pH 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, filter and wash repeatedly until the filtrate is neutral to obtain the third intermediate.

[0139] (5) Take 1 kg of the third intermediate and calcine it in a box furnace under an argon atmosphere. Heat it to 600°C at a heating rate of 5°C / min and keep it at that temperature for 3 hours. Then take it out to obtain the third intermediate. Place it in 10 L of hydrochloric acid solution with a molar concentration of 1 mol / L to remove impurities (remove magnesium and / or magnesium oxide). Stir for 5 hours and then filter and wash it repeatedly 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 kiln. Evacuate the kiln at room temperature and introduce N2 to replace the air with N2. Under nitrogen atmosphere protection, heat the kiln to 650℃ at 5℃ / min and introduce C2H2 (acetylene) at a flow rate of 1L / min to perform chemical vapor deposition. After holding the reaction at this temperature for 2 hours, close the C2H2 valve to obtain the final silicon-carbon anode material.

[0141] The silicon-carbon anode material prepared in this embodiment includes a porous carbon matrix with a porous structure containing 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.

[0142] Example 2

[0143] The preparation method of the silicon-carbon anode material provided in this embodiment is basically the same as that in Example 1. The difference is 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 anode material provided in this embodiment is basically the same as that in Example 1. The difference is 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 anode material provided in this embodiment is basically the same as that in Example 1. The difference is 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 anode material provided in this embodiment is basically the same as that in Example 1. The difference is 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 anode material provided in this embodiment is basically the same as that in Example 1. The difference is that in step (6), the reaction time of chemical vapor deposition is 1.7h.

[0152] Example 7

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

[0154] Example 8

[0155] The preparation method of the silicon-carbon anode material provided in this embodiment is basically the same as that in Example 1, except that in step (1), the pore volume of the porous carbon is 1.4 cm³. 3 / g, specific surface area is 805m² 2 / g, microporosity 11%, pore size <50nm.

[0156] Example 9

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

[0158] Example 10

[0159] The preparation method of the silicon-carbon anode material provided in this embodiment is basically the same as that in Example 1. The difference is 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 embodiment 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 order of operations in steps (4) and (5) is different. In this comparative example, acid washing to remove impurities is performed first, followed by coating and calcination. The specific preparation method of the silicon-carbon anode material provided in this comparative example includes:

[0164] (1)-(3): Same as steps (1)-(3) in Example 1;

[0165] (4) Take 1 kg of the second intermediate and place it in 10 L of hydrochloric acid solution with a molar concentration of 1 mol / L to remove impurities (remove magnesium and / or magnesium oxide). After stirring for 5 h, filter and wash repeatedly until the filtrate is neutral to obtain the third intermediate.

[0166] (5) Take 1 kg of the third intermediate and ultrasonically disperse it uniformly in 10 L of alcohol-water mixed solvent (ethanol to water volume ratio of 4:1). Then add ammonia water to adjust the pH 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. Stir for 12 h and filter and wash repeatedly until the filtrate is neutral to obtain semi-finished product B. Take another 1 kg of semi-finished product B and calcine it in a box furnace under an argon atmosphere. Heat it to 600 °C at a heating rate of 5 °C / min and hold for 3 h to obtain the fourth intermediate.

[0167] (6): Same as step (6) in 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 in Example 1, except that step (4) is not performed, but step (5) is performed directly, that is, 1 kg of the second intermediate is calcined. 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 in Example 1. The difference is that step (6) is not performed. That is, the silicon-carbon anode material in this comparative example is the fourth intermediate obtained by step (5) in Example 1, without a dense carbon layer.

[0172] The pore volume of the porous carbon matrix of the silicon-carbon anode materials prepared in each embodiment and comparative example is P, in cm³. 3 / g, the mass fraction of silicon in the silicon-carbon anode material is A, and the true density of the silicon-carbon anode material is B, in g / cm³. 3 The values ​​of P, A, B, and A / (2.26-B) / P are shown in Table 1. The mass fraction of the loose carbon layer (hereinafter referred to as loose carbon layer mass fraction) and the mass fraction of the dense carbon layer (hereinafter referred to as dense carbon layer mass fraction) in the silicon-carbon anode materials prepared in each embodiment and comparative example are shown in Table 1.

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

[0174]

[0175]

[0176] Furthermore, the silicon-carbon anode materials prepared in each embodiment and comparative example were used as anode active materials. Anode slurry was prepared by mixing the anode active material, binder, and conductive agent in a mass ratio of 70:20:10 with a solvent. The anode slurry was coated onto copper foil and dried to obtain anode sheets. A lithium sheet was used as the counter electrode, and a polypropylene microporous membrane separator and 1 mol / L LiPF6 dissolved in a four-component mixed solvent were used as the electrolyte. The volume ratio of ethylene carbonate (EC): dimethyl carbonate (DMC): vinylene carbonate (VC): fluoroethylene carbonate (FEC) in the four-component solvent was 1:1:1:1. CR2032 coin cell half-cells were assembled, and the capacity, initial efficiency, and capacity retention of each cell were tested. The results are shown in Table 2.

[0177] The test methods for capacity, first-time efficiency, and capacity retention are as follows: After standing for 10 minutes, discharge to 5mV at a constant current of 0.1C; after standing for 5 minutes, discharge to 5mV at a constant current of 0.02C; after standing for 5 minutes, discharge to 5mV at a constant current of 0.01C; after standing for 10 minutes, charge to 2.0V at a constant current of 0.1C. Repeat this cycle 100 times.

[0178] Table 2 Electrochemical performance of each battery

[0179]

[0180]

[0181] As can be seen from Tables 1 and 2, the silicon-carbon anode materials prepared in each embodiment satisfy the relationship 30≤100×A / (2.26-B) / P≤70, and the battery has better capacity, initial coulombic efficiency and cycle performance.

[0182] If the ratios do not satisfy the relationship 30≤100×A / (2.26-B) / P≤70, the battery capacity, initial coulombic efficiency, or cycle performance are poor.

[0183] By comparing Example 1 and Comparative Example 1, it can be seen that the method of coating first and then acid washing can obtain silicon-carbon particles with lower true density. The pores in the particles provide free space for the volume expansion of silicon, thus exhibiting good cycle stability.

[0184] By comparing Example 1 and Comparative Example 2, it can be seen that the silicon-carbon anode material of Comparative Example 2 has no loose carbon layer, resulting in a high true density of silicon-carbon particles. The particles are unable to buffer the volume change of silicon, thus resulting in poor electrochemical performance.

[0185] Comparing Example 1 and Comparative Example 3, it can be seen that the silicon-carbon anode material in Comparative Example 3 lacks a dense carbon layer, leading to direct contact between the electrolyte and silicon particles, causing silicon oxidation and electrolyte decomposition. During the repeated changes in the volume of the silicon particles, the solid electrolyte interface layer generated by electrolyte decomposition gradually increases on their surface, resulting in increasingly deteriorated electrical performance.

[0186] In summary, the silicon-carbon anode material provided by this invention has a specific structure and satisfies the specific relationship 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 coulombic efficiency and cycle performance of the silicon-carbon anode material and the battery made from it.

[0187] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions 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 substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A silicon-carbon anode material, characterized in that, The invention includes a porous carbon matrix having a porous structure containing elemental silicon, the outer surface of the porous carbon matrix being coated with a loose carbon layer, and the outer surface of the loose carbon layer being coated with a dense carbon layer. The pore volume of the porous carbon matrix is ​​P, measured in cm³. 3 / g; the mass fraction of silicon in the silicon-carbon anode material is A; the true density of the silicon-carbon anode material is B, in g / cm³. 3 Where P, A, and B satisfy 30 ≤ 100 × A / (2.26 - B) / P ≤ 70; The porous carbon matrix has a pore volume P of 1.6~1.8 cm³. 3 / g; The porous carbon layer in the silicon-carbon anode material accounts for 5% to 10% of the total mass. The preparation method of the silicon-carbon anode material includes the following steps: Porous carbon, a silicon source, and a solvent are mixed and reacted, allowing the silicon dioxide generated by the hydrolysis of the silicon source to enter the porous structure of the porous carbon. Then, solid-liquid separation is performed to obtain a first intermediate. The first intermediate is mixed with a reducing agent and heated to carry out a reduction reaction, so that the silicon dioxide in the porous structure is reduced to elemental silicon to obtain the second intermediate. The second intermediate, dispersant, and organic carbon source are mixed and coated to form a coating layer on the outer surface of the porous carbon. Then, solid-liquid separation and calcination are performed to form a loose carbon layer from the coating layer, thus obtaining the third intermediate. The third intermediate is mixed with an acid solution and reacted to remove the reducing agent and / or the product formed after the reaction of the reducing agent. Then, solid-liquid separation is performed to obtain the fourth intermediate. A gaseous carbon source is introduced into a system containing the fourth intermediate, and chemical vapor deposition is performed to obtain the silicon-carbon anode material.

2. The silicon-carbon anode material according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The mass fraction A of silicon in the silicon-carbon anode material is 40%~55%; (2) The true density B of the silicon-carbon anode material is 1.5~1.8 g / cm³. 3 ; (3) The mass fraction of the dense carbon layer in the silicon-carbon anode material is 2% to 5%.

3. The silicon-carbon anode material according to claim 1, characterized in that, At least one of the following conditions must be met: (1) Before mixing the porous carbon, silicon source and solvent, the porous carbon is calcined at 250~400℃; the calcination time is 2~8h; the calcination atmosphere includes air atmosphere or oxygen atmosphere; (2) The specific surface area of ​​the porous carbon is 800~1000 m². 2 / g, microporosity 8%~15%, pore size <50nm; (3) The silicon source includes at least one of tetraethyl orthosilicate, trimethoxysilane, tetraethylsilane, phenyltrimethoxysilane and tetrachlorosilane; (4) The solvent includes a mixture of ethanol and water; the volume ratio of ethanol to water is 3~5:1; (5) The mass ratio of the porous carbon to the silicon source is 1:4~6; (6) The step of mixing porous carbon, silicon source and solvent includes: firstly, ultrasonically dispersing the porous carbon in the solvent, then adding an alkaline solution to adjust the pH of the mixture to 10.5~11.5, and then adding the silicon source thereto; the alkaline solution includes at least one of ammonia solution, sodium hydroxide solution, potassium hydroxide solution and sodium carbonate solution; (7) The reaction time for mixing and reacting porous carbon, silicon source and solvent is 12~24h.

4. The silicon-carbon anode material according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The reducing agent includes at least one of metallic magnesium, metallic aluminum, and 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℃ and the holding time is 10~24h.

5. The silicon-carbon anode material according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The dispersant comprises a mixed solvent of ethanol and water; the volume ratio of ethanol to water is 3~5:1; (2) The organic carbon source includes 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 includes: firstly, ultrasonically dispersing the second intermediate in the dispersant, then adding an alkaline solution to adjust the pH of the mixture to 10.5~11.5, and then adding the organic carbon source thereto; the alkaline solution includes at least one of ammonia solution, sodium hydroxide solution, potassium hydroxide solution and sodium carbonate solution; (5) The coating time is 12~24h; (6) The roasting atmosphere includes an inert atmosphere; (7) The roasting temperature is 550~650℃ and the holding time is 3~8h.

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

7. The silicon-carbon anode material according to claim 1, characterized in that, At least one of the following conditions must be 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 0.1~0.4 L / min; (3) The atmosphere for the chemical vapor deposition includes an inert atmosphere; (4) The temperature of the chemical vapor deposition is 600~700℃ and the time is 1~3h.

8. A negative electrode sheet, characterized in that, Includes the silicon-carbon anode material as described in any one of claims 1 to 7.

9. A lithium-ion battery, characterized in that, Includes the negative electrode as described in claim 8.

Images