Silicon-carbon composite material, method for preparing silicon-carbon composite material, negative electrode sheet, and electrochemical device

Abstract

The present application provides a silicon-carbon composite material, a method for preparing a silicon-carbon composite material, a negative electrode sheet, and an electrochemical device. The silicon-carbon composite material comprises a core portion and a shell layer on the surface of the core portion, wherein the core portion comprises a silicon-based material and / or graphite, and the shell layer comprises a silicon-carbon composite, the silicon-carbon composite comprising a silicon oxide compound SiO x wherein 0

Description

Technical Field

[0001] This application belongs to the field of electrochemical technology, specifically relating to a silicon-carbon composite material, a method for preparing the silicon-carbon composite material, a negative electrode sheet, and an electrochemical device. Background Technology

[0002] Electrochemical devices, such as lithium-ion batteries, are widely used in all aspects of modern life due to their advantages, including no memory effect, small size, light weight, and environmental friendliness. In recent years, electrochemical devices have seen rapid development in the fields of new energy vehicles and large-scale energy storage. However, among the negative electrode materials of traditional commercial electrochemical devices, taking lithium-ion batteries as an example, carbon-based materials such as graphite have low capacity, resulting in low energy density of lithium-ion batteries; while silicon-based materials are prone to expansion, leading to poor cycle performance of lithium-ion batteries. This greatly limits their large-scale application in electrochemical devices. Summary of the Invention

[0003] The purpose of this application is to provide a silicon-carbon composite material, a method for preparing the silicon-carbon composite material, a negative electrode, and an electrochemical device, which aims to enable the electrochemical device to simultaneously have high energy density and long cycle life.

[0004] A first aspect of this application provides a silicon-carbon composite material, comprising: a core and a shell layer on the surface of the core, wherein the core comprises a silicon-based material and / or graphite, and the shell layer comprises a silicon-carbon composite, the silicon-carbon composite comprising a silicon oxide compound SiO₂. x , of which 0 <x<2。

[0005] In any embodiment of this application, the silicon-based material includes elemental silicon and / or silicon suboxide.

[0006] In any embodiment of this application, the silicon-carbon composite further includes amorphous carbon.

[0007] The silicon-carbon composite material of this application includes a core and a shell. The core, due to including silicon-based materials and / or graphite, is able to provide high energy density for the negative electrode of a lithium-ion battery. The shell includes a silicon-carbon composite, which helps to buffer the volume expansion of the core during the reversible insertion and extraction of lithium ions, enhances the conductivity of the silicon-carbon composite material, and enhances its cycle performance.

[0008] In any embodiment of this application, the elemental silicon includes at least one of silicon nanoparticles and silicon microparticles, wherein the median particle size of the silicon nanoparticles is 200 nm to 1000 nm.

[0009] In any embodiment of this application, the material used to prepare the silicon-carbon composite includes an organosilicon source.

[0010] In any embodiment of this application, the thickness of the shell layer is from 5 nm to 100 nm.

[0011] In any embodiment of this application, the weight percentage of amorphous carbon in the shell is 2% to 30% based on the total weight of the shell.

[0012] In the silicon-carbon composite material of this application, the thickness of the shell layer is within a suitable range, which enables the silicon-carbon composite material to have a high energy density and also suppresses the volume expansion of the silicon-based material in the core, thus giving it excellent cycle performance.

[0013] In any embodiment of this application, the silicon oxide compound SiO x The silicon oxide compound SiO is dispersed in the amorphous carbon in the form of nanoparticles. x The particle size ranges from 2 nm to 5 nm.

[0014] In any embodiment of this application, the weight ratio of the core to the shell is 10 to 200.

[0015] In the silicon-carbon composite material of this application, the weight ratio of the core to the shell is within a suitable range, which is beneficial to improving the energy density and cycle performance of lithium-ion batteries.

[0016] In any embodiment of this application, the median particle size of the silicon nanoparticles is 300 nm to 800 nm.

[0017] In any embodiment of this application, the thickness of the shell layer is 5 nm to 20 nm.

[0018] In any embodiment of this application, the weight percentage of amorphous carbon in the shell is 3% to 10% based on the total weight of the shell.

[0019] In any embodiment of this application, the silicon oxide compound SiO x The particle size is 3nm to 4nm.

[0020] In any embodiment of this application, the weight ratio of the core to the shell is 20 to 90.

[0021] A second aspect of this application provides a method for preparing the silicon-carbon composite material described in the first aspect of this application, comprising:

[0022] The coating step includes coating a silicon-based material core and / or a graphite core with an organosilicon source, and converting the organosilicon source into polysilsesquioxane to obtain polysilsesquioxane-coated core particles.

[0023] The carbonization step includes carbonizing the polysilsesquioxane coating the nuclei to obtain the silicon-carbon composite material.

[0024] In the method for preparing silicon-carbon composite materials described in this application, an organosilicon source undergoes an in-situ condensation reaction on the surface of silicon-based materials and / or graphite under the catalysis of an alkali to obtain core particles coated with a polysilsesquioxane layer. The resulting product is then calcined at high temperature in an inert gas atmosphere, during which the organic groups in the polysilsesquioxane layer are converted into amorphous carbon, ultimately yielding the silicon-carbon composite material with excellent electrochemical performance described in this application.

[0025] In any embodiment of this application, the organosilicon source includes at least one of vinyltriethoxysilane, vinyltrimethoxysilane, propyltriethoxysilane, propyltrimethoxysilane, ethyltriethoxysilane, ethyltrimethoxysilane, methyltriethoxysilane, methyltrimethoxysilane, phenyltriethoxysilane, and ureapropyltriethoxysilane.

[0026] A third aspect of this application provides a negative electrode sheet, comprising: a current collector, and a negative electrode active material layer formed on the surface of the current collector, wherein the negative electrode active material layer comprises the silicon-carbon composite material described in the first aspect of this application or a silicon-carbon composite material prepared by the method described in the second aspect of this application.

[0027] The fourth aspect of this application discloses an electrochemical device comprising the negative electrode plate described in the third aspect of this application. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the preparation process of an embodiment of the silicon-carbon composite material of this application.

[0029] Figure 2 This is an XRD pattern of an embodiment of the silicon-carbon composite material of this application.

[0030] Figure 3 This is a TEM image of an embodiment of the silicon-carbon composite material of this application. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. The embodiments described herein are illustrative in nature and are used to provide a basic understanding of this application. The embodiments of this application should not be construed as limiting this application.

[0032] For the sake of brevity, this article only discloses some specific numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0033] In this description, unless otherwise stated, "above" and "below" include the stated number.

[0034] Unless otherwise stated, the terms used in this application have their common meanings as commonly understood by those skilled in the art. Unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0035] The term "about" is used to describe and indicate small variations. When used in conjunction with an event or situation, the term may refer to examples in which the event or situation occurred precisely or in examples in which the event or situation occurred very approximately. For example, when used in conjunction with numerical values, the term may refer to a range of variation less than or equal to ±10% of the numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. Additionally, quantities, ratios, and other numerical values ​​are sometimes presented in range format herein. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only numerical values ​​explicitly specified as range limits but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0036] The list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another instance, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0037] Currently, in the anode materials of traditional commercial lithium-ion batteries, graphite has hindered its further application in lithium-ion batteries due to its low capacity (372 mAh / g) and the safety hazard of lithium dendrites. Developing anode materials for lithium-ion batteries with high energy density and high safety is the focus of the current development of lithium battery technology. Compared with carbon-based materials such as graphite, silicon-based materials (including silicon oxides) are considered to be the most promising anode materials for lithium batteries that can replace graphite due to their low price, high specific capacity, and suitable working voltage.

[0038] Among them, compared with elemental silicon, silicon oxides (SiO x , 0 < x < 2) also have the following advantages in the field of anode materials for lithium-ion batteries: (1) The inert Li2O and lithium silicate generated during the first lithium intercalation process can effectively alleviate the volume change during charge and discharge, contributing to the maintenance of structural stability; (2) The natural amorphous form helps to reduce the pulverization of the material caused by uneven stress during the lithium intercalation / deintercalation process. However, the large volume expansion and poor conductivity still limit the large-scale application of silicon-based materials in lithium-ion batteries.

[0039] Although carbon materials have a small specific capacity as anode materials, due to their low price, good conductivity, outstanding chemical and thermal stability, etc., they can be used as good conductive media and buffer matrices for silicon-based materials. Therefore, the inventors found that combining silicon oxides and carbon by carbon coating to prepare silicon-carbon composite anode materials is a good method. However, the inventors also found that although the carbon coating method can improve the conductivity of the composite material to a certain extent and buffer the volume expansion of the silicon-based material, on the one hand, the thin carbon layer cannot effectively inhibit the huge volume expansion of the silicon-based material; on the other hand, the thick carbon layer will significantly reduce the energy density of the composite material.

[0040] To solve the above problems, the inventors proposed a silicon-carbon composite material that can both inhibit volume expansion and has a high capacity through a large amount of research. Using this silicon-carbon composite material can enable an electrochemical device to have a high energy density and cycling performance.

[0041] Silicon-carbon composite materials

[0042] In the first aspect of the embodiments of the present application, a silicon-carbon composite material is provided, including: a core part, and a shell layer on the surface of the core part, wherein the core part includes a silicon-based material and / or graphite, and the shell layer includes a silicon-carbon composite, and the silicon-carbon composite includes a silicon oxide SiO x , where 0 < x < 2.

[0043] The silicon-carbon composite material of this application includes a core and a shell. The core, by comprising silicon-based materials and / or graphite, can improve the energy density of the electrochemical device. The shell comprises a silicon-carbon composite that helps buffer the volume expansion of the core during the reversible insertion and extraction of active ions such as lithium ions, enhances the conductivity of the silicon-carbon composite material, and improves the cycle performance of the electrochemical device.

[0044] In some embodiments, the silicon-based material includes elemental silicon and / or silicon suboxide. Elemental silicon and silicon suboxide have high capacity, which can improve the energy density of electrochemical devices.

[0045] In some embodiments, elemental silicon includes at least one of silicon nanoparticles and silicon microparticles, preferably silicon nanoparticles.

[0046] In some embodiments, the median particle size of the silicon nanoparticles is between 200 nm and 1000 nm. For example, the median particle size of the silicon nanoparticles is a range consisting of 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, or any value above that. Preferably, the median particle size of the silicon nanoparticles is between 300 nm and 800 nm. In this application, the median particle size of the silicon-carbon nanoparticles is within a suitable range, which ensures that the silicon-carbon composite material has high capacity and controls the volume expansion of the silicon-carbon composite material during cycling, while also facilitating the coating treatment of the shell. The median particle size of the silicon nanoparticles is the particle size corresponding to the cumulative particle size distribution percentage of silicon nanoparticles reaching 50%. Physically, this means that particles larger than the median particle size account for 50%, and particles smaller than the median particle size also account for 50%. Particle size can be measured using a laser particle size analyzer (NanoBrook90Plus).

[0047] In some embodiments, the median particle size of the silicon microparticles can be 2000 nm.

[0048] In some embodiments, the material used to prepare the silicon-carbon composite includes an organosilicon source, which includes at least one of vinyltriethoxysilane, vinyltrimethoxysilane, propyltriethoxysilane, propyltrimethoxysilane, ethyltriethoxysilane, ethyltrimethoxysilane, methyltriethoxysilane, methyltrimethoxysilane, phenyltriethoxysilane, and ureapropyltriethoxysilane.

[0049] In this application, the organosilicon source can undergo an in-situ condensation reaction on the surface of a silicon-based material under the catalysis of an alkaline solution, thereby obtaining silicon-based material particles coated with a polysilsesquioxane layer. The organic groups in the polysilsesquioxane layer can be converted into amorphous carbon during subsequent carbonization treatment, thus obtaining the silicon oxide compound SiO. xSilicon-carbon composites distributed in amorphous carbon.

[0050] In some embodiments, the silicon-carbon composite in the shell comprises a silicon oxide compound SiOx and amorphous carbon, wherein the silicon oxide compound SiOx... x The silicon oxide compound SiO is dispersed in the amorphous carbon in the form of nanoparticles. x The particle size is 2nm to 5nm, for example, the silicon oxide compound SiO x The particle size is within the range of 2nm, 3nm, 4nm, 5nm, or higher. Preferably, the silicon oxide compound SiO x The particle size is 3nm to 4nm.

[0051] In this application, the silicon oxide compound SiO x The shell formed by silicon oxides and amorphous carbon in the form of nanoparticles has the advantages of good chemical stability and high conductivity. It can constrain the volume expansion of the core of silicon-carbon composite material during the reversible insertion and extraction of active ions such as lithium ions, and enhance the conductivity of silicon-carbon composite material.

[0052] In some embodiments, the thickness of the shell layer is 5 nm to 100 nm, for example, the thickness of the shell layer is 5 nm to 95 nm, 10 nm to 90 nm, 15 nm to 85 nm, 20 nm to 80 nm, 35 nm to 75 nm, 40 nm to 70 nm, or 55 nm to 65 nm. Preferably, the thickness of the shell layer is 5 nm to 20 nm.

[0053] In this application, the thickness of the silicon-carbon composite shell is primarily determined from a feasibility perspective. Because the interaction between the organosilicon source and the silicon-based material is weak during the coating process, the thickness of the coating layer needs to be controlled within 100 nm. This facilitates obtaining the aforementioned silicon-carbon composite material. Furthermore, a shell thickness within this range not only enables the silicon-carbon composite material to possess high capacity but also suppresses the volume expansion of the silicon-based material in the core, thereby improving the cycle performance of the electrochemical device.

[0054] In some embodiments, based on the total weight of the shell, the weight percentage of amorphous carbon in the shell is 2% to 30%, for example, the weight percentage of amorphous carbon is within the range of any value consisting of 5%, 10%, 15%, 20%, 25%, 30%, or higher. Preferably, the weight percentage of amorphous carbon is 3% to 10%. The content of amorphous carbon in the shell is mainly determined by the type of organosilicon source. After the organosilicon source undergoes an in-situ condensation reaction, a polysilsesquioxane layer is obtained. The silicon-carbon bonds in the polysilsesquioxane layer can break during subsequent carbonization to form amorphous carbon.

[0055] In some embodiments, the weight ratio of the core to the shell is 10 to 200, for example, 15 to 195, 30 to 180, 45 to 165, 60 to 150, 75 to 135, or 90 to 120. Preferably, the weight ratio of the core to the shell is 20 to 90.

[0056] In this application, the weight ratio of the core to the shell of the silicon-carbon composite material is within the aforementioned range, which is beneficial for improving the energy density and cycle performance of the electrochemical device. If the weight ratio of the core to the shell is small, the thick coating shell will reduce the capacity of the silicon-carbon composite material to some extent; if the weight ratio of the core to the shell is large, the thin coating shell will have difficulty suppressing the volume expansion of the silicon-based material in the core, which will affect the cycle performance of the silicon-carbon composite material.

[0057] A second aspect of this application provides a method for preparing the silicon-carbon composite material described in the first aspect of this application, comprising:

[0058] S10, Coating step, including coating a silicon-based material core and / or a graphite core with an organosilicon source, and converting the organosilicon source into polysilsesquioxane to obtain polysilsesquioxane-coated core particles.

[0059] S20, the carbonization step, includes carbonizing the polysilsesquioxane coating the nucleus particles to obtain the silicon-carbon composite material.

[0060] In some embodiments, silicon nanoparticles are used as the core. For example, the preparation process of the silicon-carbon composite material provided in the second aspect of this application is implemented as follows: Figure 1 As shown. Figure 2 As shown, XRD confirmed the presence of elemental silicon, silicon oxides, and amorphous carbon in the prepared silicon-carbon composite material. Figure 3 As shown in the TEM image, the silicon-carbon composite material has a distinct core-shell structure, with the core being silicon nanoparticles and the outer shell consisting of a composite of silicon oxides and uniformly distributed carbon.

[0061] In some embodiments, in step S10 above, the organosilicon source includes at least one selected from vinyltriethoxysilane, vinyltrimethoxysilane, propyltriethoxysilane, propyltrimethoxysilane, ethyltriethoxysilane, ethyltrimethoxysilane, methyltriethoxysilane, methyltrimethoxysilane, phenyltriethoxysilane, and ureapropyltriethoxysilane. Preferably, the organosilicon source is vinyltriethoxysilane.

[0062] In some embodiments, the concentration of the organosilicon source is from 0.1 mol / L to 2 mol / L, for example, from 0.2 mol / L to 1.8 mol / L, 0.4 mol / L to 1.6 mol / L, 0.6 mol / L to 1.4 mol / L, or 0.8 mol / L to 1.2 mol / L. Controlling the concentration of the organosilicon source within a suitable range facilitates obtaining a shell of appropriate thickness. By controlling the shell thickness within a suitable range, the volume expansion of the silicon-carbon composite core can be suppressed through the shell, while ensuring that the silicon-carbon composite material possesses high capacity.

[0063] In some embodiments, the coating step in S10 above further includes:

[0064] S100. In an alcohol-water solution, the organosilicon source is brought into contact with the silicon-based material core and / or graphite core to coat the silicon-based material core and / or graphite core.

[0065] S110. By adding alkali to the alcohol-water solution, the polysilsesquioxane precursor is polymerized into polysilsesquioxane to obtain the polysilsesquioxane-coated nuclei.

[0066] In some embodiments, in step S100 above, the volume ratio of alcohol to water in the alcohol-water solution is from 0.1 to 10. For example, the volume ratio of alcohol to water in the alcohol-water solution is within the range of 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, or any of the above values. Preferably, the volume ratio of alcohol to water in the alcohol-water solution is from 0.5 to 8. By adjusting the volume ratio of alcohol to water, the concentration of the alcohol-water solution can be adjusted, which in turn facilitates the adjustment of the shell thickness in the silicon-carbon composite material, thereby obtaining a silicon-carbon composite material with excellent electrochemical performance. An alcohol-water volume ratio within a suitable range is beneficial for obtaining a shell of appropriate thickness, thus enabling the silicon-carbon composite material to possess high capacity while suppressing core volume expansion, resulting in excellent cycle performance of the electrochemical device.

[0067] In some embodiments, the type of alcohol in the aqueous alcohol solution is not limited and can be a conventional alcohol known in the art, such as ethanol, methanol, ethylene glycol, glycerol, etc.

[0068] In some embodiments, in step S110 above, the pH of the system obtained after adding the alkali to the alcohol-water solution is 9 to 14, for example, the pH of the system is a range of 9, 10, 11, 12, 13 or any of the above values. Preferably, the pH of the system is 10 to 13.

[0069] In some embodiments, the base is selected from ammonia. The concentration of the ammonia is from 0.1 mol / L to 2 mol / L, for example, from 0.2 mol / L to 1.8 mol / L, from 0.4 mol / L to 1.6 mol / L, from 0.6 mol / L to 1.4 mol / L, or from 0.8 mol / L to 1.2 mol / L.

[0070] The pH value of the system can be adjusted by regulating the ammonia concentration. This pH adjustment allows for control over the thickness of the shell layer in the silicon-carbon composite material, thereby regulating its electrochemical performance. A suitable pH range facilitates obtaining a shell layer of appropriate thickness. By controlling the shell layer thickness within this range, the volume expansion of the silicon-carbon composite core can be suppressed, while ensuring the composite material possesses high capacity.

[0071] In some embodiments, the reaction temperature of the above-mentioned coating step S10 is 25°C to 80°C, for example, the reaction temperature is 30°C to 75°C, 35°C to 70°C, 40°C to 65°C, 45°C to 60°C or 50°C to 55°C.

[0072] In some embodiments, the reaction time of the above-described coating step S10 is 2 hours to 10 hours, for example, the reaction time is a range consisting of 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours or any of the above values.

[0073] In this application, the thickness of the shell layer in the silicon-carbon composite material can be adjusted by regulating the reaction temperature and time of the coating step. Maintaining a suitable reaction temperature and time for the coating step helps control the shell layer thickness within an appropriate range. Therefore, the shell layer can suppress the volume expansion of the silicon-carbon composite material's core while ensuring the composite material possesses high capacity.

[0074] In some embodiments, the carbonization process in step S20 above includes:

[0075] S200: The polysilsesquioxane-coated nuclei are heat-treated under an inert atmosphere.

[0076] In some embodiments, the heat treatment in step S200 includes: heating the silsesquioxane-coated nuclei particles from room temperature to 300°C to 400°C at a heating rate of 5°C / min to 10°C / min and holding at that temperature for 2h to 5h, then heating them to 600°C to 1200°C at a heating rate of 1°C / min to 5°C / min and holding at that temperature for 4h to 12h to obtain the silicon-carbon composite material.

[0077] In some embodiments, the thickness of the shell layer in the silicon-carbon composite material can be adjusted by regulating the carbonization temperature. Maintaining a suitable carbonization temperature helps control the shell layer thickness within an appropriate range. This allows the shell layer to suppress volume expansion of the silicon-carbon composite core while ensuring the composite material possesses high capacity.

[0078] In some embodiments, the type of inert atmosphere in step S200 is not limited and can be any inert atmosphere known in the art, such as nitrogen atmosphere, argon atmosphere, helium atmosphere, etc.

[0079] In this application, an organosilicon source can undergo an in-situ condensation reaction on the surface of silicon-based materials and / or graphite under the catalysis of an alkali to prepare polysilsesquioxane-coated core particles. The resulting product is then calcined at high temperature in an inert gas atmosphere, during which the organic groups in the polysilsesquioxane layer can be converted into amorphous carbon, ultimately yielding the silicon-carbon composite material with excellent electrochemical performance described in this application. By adjusting the volume ratio of alcohol to water in the alcohol-water solution, the pH value of the system obtained after adding an alkali to the alcohol-water solution, the concentration of the organosilicon source, and the reaction temperature of the coating reaction, the shell layer of the silicon-carbon composite material can be adjusted within the range of 5 nm to 100 nm. By adjusting the thickness of the shell layer, the capacity and other properties of the silicon-carbon composite material can be controlled, thereby enabling the silicon-carbon composite material to possess excellent electrochemical performance.

[0080] Negative electrode sheet

[0081] A third aspect of the embodiments of this application provides a negative electrode sheet, comprising: a current collector and a negative electrode active material layer formed on the surface of the current collector, wherein the negative electrode active material layer comprises the silicon-carbon composite material described in the first aspect of this application or a silicon-carbon composite material prepared by the method described in the second aspect of this application.

[0082] In some embodiments, the negative electrode active material layer does not exclude other negative electrode active materials besides silicon-carbon composite materials. The specific types of other negative electrode active materials are not specifically limited and can be selected according to requirements. As examples, other negative electrode active materials include, but are not limited to, natural graphite, artificial graphite, mesophase carbon microspheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, SiO, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured Li4Ti5O. 12 At least one of Li-Al alloys.

[0083] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0084] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0085] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0086] However, this application is not limited to the above-mentioned materials. The negative electrode sheet of this application may also use other known materials that can be used as negative electrode active materials, conductive agents, binders and thickeners.

[0087] In some embodiments, the current collector is a negative electrode current collector, which has two surfaces opposite each other in its thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0088] The negative electrode current collector can be made of metal foil or porous metal plate, such as foil or porous plate of metals or alloys thereof, such as copper, aluminum, nickel, titanium, iron, etc. As an example, the negative electrode current collector is copper foil.

[0089] The negative electrode sheet in this application can be prepared according to conventional methods in the art. For example, the silicon-carbon composite material described in the first aspect of this application or the silicon-carbon composite material prepared by the method described in the second aspect of this application, and other optional negative electrode active materials, conductive agents, binders and thickeners are dispersed in a solvent, which can be N-methylpyrrolidone (NMP) or deionized water, to form a uniform negative electrode slurry. The negative electrode slurry is coated on the negative electrode current collector, and the negative electrode sheet is obtained through processes such as drying and cold pressing.

[0090] The negative electrode sheet in this application does not exclude additional functional layers besides the negative electrode active material layer. For example, in some embodiments, the negative electrode sheet of this application further includes a conductive undercoat (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode active material layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of this application further includes a protective layer covering the surface of the negative electrode active material layer.

[0091] Electrochemical device

[0092] A fourth aspect of the embodiments of this application provides an electrochemical device, including any device in which an electrochemical reaction occurs to convert chemical energy into electrical energy, such as including but not limited to: a lithium-ion battery or a sodium-ion battery.

[0093] In some embodiments, the electrochemical device of this application includes a positive electrode, a negative electrode, a separator, and an electrolyte.

[0094] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0095] The electrochemical device of this application also includes an outer packaging for encapsulating the electrode assembly and electrolyte. In some embodiments, the outer packaging can be a rigid shell, such as a rigid plastic shell, an aluminum shell, a steel shell, etc., or it can be a flexible package, such as a pouch. The material of the flexible package can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0096] [Negative electrode plate]

[0097] The negative electrode used in the electrochemical device of this application is the negative electrode of the third aspect of the embodiments of this application.

[0098] [Positive electrode plate]

[0099] The materials, composition, and manufacturing methods of the positive electrode used in the electrochemical device of this application may include any techniques known in the prior art.

[0100] The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector and comprising a positive active material. As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0101] In some embodiments, the positive electrode active material layer includes a positive electrode active material, and the specific type of positive electrode active material is not specifically limited and can be selected according to needs. For example, the positive electrode active material may include one or more of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds. In the electrochemical device of this application, the modified compounds of the above-mentioned positive electrode active materials may be used to modify the positive electrode active material by doping, surface coating, or doping and surface coating.

[0102] As examples, lithium transition metal oxides may include one or more of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their modified compounds. As examples, olivine-structured lithium phosphates may include one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their modified compounds. These positive electrode active materials may be used alone or in combination of two or more.

[0103] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, super-P, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0104] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0105] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, the positive electrode current collector may be aluminum foil. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may be selected from one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may be selected from polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.

[0106] The positive electrode sheet in this application can be prepared according to conventional methods in the art. For example, the positive electrode active material layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to it.

[0107] The positive electrode sheet of this application does not exclude other additional functional layers besides the positive electrode active material layer. For example, in some embodiments, the positive electrode sheet of this application further includes a conductive undercoat (e.g., composed of a conductive agent and a binder) sandwiched between the positive electrode current collector and the positive electrode active material layer and disposed on the surface of the positive electrode current collector. In other embodiments, the positive electrode sheet of this application further includes a protective layer covering the surface of the positive electrode active material layer.

[0108] Electrolyte

[0109] The electrolyte acts as a conductor of active ions between the positive and negative electrodes. The electrolyte used in the electrochemical device of this application can be any electrolyte known in the prior art.

[0110] In some embodiments, the electrolyte includes an organic solvent, a lithium salt, and optional additives. The types of organic solvent, lithium salt, and additives are not specifically limited and can be selected as needed.

[0111] In some embodiments, as examples, the lithium salt includes, but is not limited to, at least one of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiBOB (lithium dioxalate borate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorodioxalate phosphate), and LiTFOP (lithium tetrafluorooxalate phosphate). One of the above lithium salts may be used alone, or two or more may be used simultaneously.

[0112] In some embodiments, as examples, the organic solvent includes, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE). One of the above organic solvents may be used alone, or two or more may be used simultaneously. Optionally, two or more of the above organic solvents may be used simultaneously.

[0113] In some embodiments, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0114] As an example, the additives include, but are not limited to, at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), vinyl sulfate (DTD), propylene sulfate, vinyl sulfite (ES), 1,3-propanesulfonate lactone (PS), 1,3-propenesulfonate lactone (PST), sulfonate cyclic quaternary ammonium salts, succinic anhydride, succinic anhydride (SN), adiponitrile (AND), tris(trimethylsilane) phosphate (TMSP), and tris(trimethylsilane) borate (TMSB).

[0115] The electrolyte can be prepared according to conventional methods in the art. For example, an organic solvent, a lithium salt, and optional additives can be mixed evenly to obtain an electrolyte. There are no particular restrictions on the order of addition of the materials; for example, the lithium salt and optional additives can be added to the organic solvent and mixed evenly to obtain an electrolyte; or, the lithium salt can be added to the organic solvent first, and then the optional additives can be added to the organic solvent and mixed evenly to obtain an electrolyte.

[0116] [Isolation membrane]

[0117] The separator is positioned between the positive and negative electrodes, primarily serving to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through. This application does not impose any particular restriction on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0118] In some embodiments, the material of the separator can be selected from one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride, but is not limited to these. The separator can be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different. In some embodiments, a ceramic coating or a metal oxide coating may also be provided on the separator.

[0119] electronic devices

[0120] A fifth aspect of the present application provides an electronic device that includes the electrochemical device of the fourth aspect of the present application, wherein the electrochemical device can be used as a power source in the electronic device.

[0121] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0122] Example

[0123] The following examples describe the disclosure of this invention in more detail. These examples are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of this disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized by conventional methods and can be used directly without further processing. The instruments used in the examples are also commercially available.

[0124] Example 1

[0125] Preparation of silicon-carbon composite materials

[0126] (1) 1g of silicon nanoparticles with a median particle size of 500nm were uniformly dispersed in a mixture of 50ml ethanol and 5mL deionized water. 1mL of vinyltriethoxysilane (1mol / L) was added dropwise, and the mixture was stirred for 0.5h. Then, 1mL of ammonia solution (1mol / L) was added and the mixture was stirred at 50℃ for 6h. After centrifugation, washing and drying, silicon nanoparticles coated with vinyl polysilsesquioxane were obtained.

[0127] (2) The dried vinyl polysilsesquioxane-coated silicon nanoparticles were placed in a tube furnace and heated from room temperature to 400°C at a heating rate of 5°C / min under an argon atmosphere and held for 2 hours. Then, the temperature was increased to 1000°C at a heating rate of 3°C / min and held for 8 hours to obtain a black silicon-carbon composite material.

[0128] Preparation of negative electrode sheet

[0129] Silicon-carbon composite material, conductive agent acetylene black, and binder sodium alginate were mixed in a mass ratio of 70:20:10, and an appropriate amount of deionized water was added. The mixture was stirred under vacuum to obtain a negative electrode slurry. The negative electrode slurry was then uniformly coated onto both surfaces of the negative electrode current collector copper foil. After vacuum drying at 70℃ for 12 hours, the slurry was punched into a circular electrode sheet with a diameter of 10 mm to obtain the negative electrode sheet. The loading of the silicon-carbon composite material was approximately 1.0 mg / cm³. 2 Up to 1.5 mg / cm 2 .

[0130] Preparation of positive electrode sheet

[0131] The positive electrode active material LiFePO4, conductive agent Super-P, and binder PVDF were mixed at a mass ratio of 70:20:10, and an appropriate amount of solvent NMP was added. The mixture was stirred in a vacuum mixer to obtain a positive electrode slurry. The positive electrode slurry was then uniformly coated onto both surfaces of the positive electrode current collector aluminum foil. After vacuum drying at 70℃ for 12 hours, the slurry was punched into a circular electrode sheet with a diameter of 10 mm to obtain the positive electrode sheet. The loading of the positive electrode active material LiFePO4 was approximately 4.0 mg / cm³. 2 Up to 6.0 mg / cm 2 .

[0132] Preparation of electrolyte

[0133] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a weight ratio of 1:1:1 to obtain an organic solvent. LiPF6 was dissolved in the organic solvent, and then fluoroethylene carbonate (FEC) was added and mixed thoroughly to obtain the electrolyte. Based on the mass of the electrolyte, the mass percentage of LiPF6 was 12.5%, and the mass percentage of fluoroethylene carbonate was 5%.

[0134] Preparation of the separating membrane

[0135] A porous polypropylene membrane (from Celgard) was used as the separator.

[0136] Preparation of lithium-ion batteries

[0137] In a dry Ar glove box, the prepared negative electrode sheet, separator, and positive electrode sheet are placed in the negative electrode shell of a CR2016 stainless steel battery in a bottom-up order. After injecting an appropriate amount of electrolyte, the positive electrode shell of the CR2016 stainless steel battery is covered, sealed with a sealing machine, and then removed from the glove box to obtain a lithium-ion battery.

[0138] Examples 2 to 5

[0139] The preparation method of the lithium-ion battery is similar to that in Example 1, except that the median particle size of the Si nanoparticles is adjusted.

[0140] Examples 6 to 9

[0141] The preparation method of the lithium-ion battery is similar to that in Example 1, except that the volume ratio of ethanol to deionized water, the concentration of vinyltriethoxysilane and ammonia solution, and the reaction temperature and time are adjusted during the preparation process.

[0142] In Example 6, 5 ml of ethanol and 50 ml of deionized water were used; in Example 7, 2 mol / L of vinyltriethoxysilane and 2 mol / L of ammonia solution were used; in Example 8, 2 mol / L of vinyltriethoxysilane, 2 mol / L of ammonia solution and the reaction temperature were 80°C; in Example 9, 2 mol / L of vinyltriethoxysilane, 2 mol / L of ammonia solution, the reaction temperature was 80°C and the reaction time was 10 h.

[0143] Examples 10 to 11

[0144] The preparation method of the lithium-ion battery is similar to that of Example 1, except that methyltriethoxysilane and propyltriethoxysilane are used instead of vinyltriethoxysilane in Example 1 during the preparation process.

[0145] Examples 12 to 14

[0146] The preparation method of the lithium-ion battery is similar to that of Example 1, except that silicon micron particles, SiO particles, and graphite are used instead of Si nanoparticles in Example 1 during the preparation process.

[0147] Comparative Example 1

[0148] The preparation method of the lithium-ion battery is similar to that in Example 1, except that dopamine is used instead of vinyltriethoxysilane in the preparation process, and a silicon-carbon composite material with carbon (C) shell is finally obtained. The specific preparation process is as follows:

[0149] (1) Take 50 ml of 0.02 mol / L tris(hydroxymethyl)aminomethane solution, add 14.7 ml of 0.02 mol / L HCl solution, and then add 35.3 ml of deionized water to prepare a 0.01 mol / L Tris buffer solution with a pH of 8.5 in 100 ml.

[0150] (2) Add 1g of silicon nanoparticles to the buffer solution, stir magnetically for 10min, add 0.4g of dopamine, continue stirring for 24h until the solution turns black, and obtain polydopamine-coated silicon nanoparticles after centrifugation, washing and drying.

[0151] (3) The polydopamine-coated silicon nanoparticles were placed in a tube furnace and heated from room temperature to 400°C at a heating rate of 5°C / min under an argon atmosphere and held for 2 hours. Then, the temperature was increased to 800°C at a heating rate of 3°C / min and held for 3 hours to finally obtain a silicon-carbon composite material with a shell of C.

[0152] Comparative Example 2

[0153] Comparative Example 2 consists of pure Si nanoparticles without any coating treatment.

[0154] The specific parameters of the above embodiments and comparative examples are detailed in Table 1, where " / " indicates that the corresponding component was not added, "SiO" x "-C" indicates silicon-carbon composite material.

[0155] Table 1

[0156]

[0157] Test section

[0158] (1) Initial discharge capacity and cycle capacity retention test of button half-cell

[0159] In a dry Ar glove box, lithium metal sheets, negative electrode sheets and separators made of silicon-carbon composite materials prepared in Examples 1 to 14 and Comparative Examples 1 to 2 are placed in the negative electrode shell of a CR2016 stainless steel battery in a bottom-up order. After injecting an appropriate amount of electrolyte, the positive electrode shell of the CR2016 stainless steel battery is covered, sealed with a sealing machine, and removed from the glove box to obtain a button half-cell.

[0160] Under normal temperature and pressure conditions, each coin cell prepared above was discharged at a constant current rate of 0.1C to 0.01V, then allowed to stand for 5 minutes. The discharge capacity at this point was recorded as the initial discharge capacity. The cells were then charged at a constant current rate of 0.1C to 1.5V, followed by constant voltage charging to a current of 0.05C, and then allowed to stand for 5 minutes. This constituted one charge-discharge cycle, and the charging capacity at this point was recorded as the initial charging capacity. The coin cells were subjected to 50 charge-discharge cycles using the above method, and the discharge capacity of each cycle was recorded.

[0161] The capacity retention rate (%) of a button cell is calculated as: (50th discharge capacity / 2nd discharge capacity) × 100%.

[0162] The performance of the coin cell reflects the performance of the silicon-carbon composite material prepared in this application.

[0163] (2) Energy density and cycle capacity retention test of lithium-ion batteries

[0164] Under normal temperature and pressure conditions, the lithium-ion batteries of Examples 1 to 14 and Comparative Examples 1 to 2 were charged at a constant current rate of 0.1C to 3.8V, then charged at a constant voltage rate to a current of 0.05C, and then allowed to stand for 5 minutes. The charging capacity at this point was recorded as the initial charging capacity. The batteries were then discharged at a constant current rate of 0.1C to 2.5V, and then allowed to stand for another 5 minutes. This constituted one charge-discharge cycle, and the discharge capacity at this point was recorded as the initial discharge capacity. The lithium-ion batteries were subjected to 100 charge-discharge cycles using the above method, and the discharge capacity was recorded for each cycle.

[0165] The gravimetric energy density (Wh / kg) of a lithium-ion battery = initial discharge capacity / weight of the negative electrode.

[0166] The capacity retention rate (%) of a lithium-ion battery = (100th discharge capacity / first discharge capacity) × 100%.

[0167] (3) Test of expansion rate of negative electrode sheet

[0168] Before cycling the lithium-ion battery, observe the cross-section of the negative electrode sheet using SEM and measure its thickness, denoted as a. Cycle the lithium-ion battery 100 times according to the above charge-discharge process, disassemble the lithium-ion battery, remove the cycled negative electrode sheet, rinse it with deionized water, and measure its thickness using the same method, denoted as b. The expansion rate of the negative electrode sheet is: (ba) / a×100%.

[0169] Table 2 presents the performance test results of Examples 1 to 14 and Comparative Examples 1 to 2.

[0170] Table 2

[0171]

[0172] Comparative analysis of the above embodiments and comparative examples shows that the silicon-carbon composite material proposed in this application has high capacity and low expansion rate. Using the silicon-carbon composite material of this application can improve the energy density of lithium-ion batteries, reduce the expansion rate of negative electrode sheets, and improve the cycle performance of lithium-ion batteries.

[0173] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A silicon-carbon composite material, comprising: a core, and a shell layer on a surface of the core, The core comprises a silicon-based material and / or graphite, the shell layer comprises a silicon-carbon composite, and the silicon-carbon composite comprises a silicon oxide compound SiO x wherein 0 < x < 2 x < 2; the silicon-based material comprises silicon nanoparticles, the silicon nanoparticles have a median particle size of 200 nm to 800 nm; the shell layer has a thickness of 5 nm to 20 nm, and the core and the shell layer have a weight ratio of 12 to 83.

2. The silicon-carbon composite material of claim 1, wherein, the silicon-carbon composite comprises amorphous carbon.

3. The silicon-carbon composite material of claim 2, wherein, the shell layer has a weight percentage of the amorphous carbon of 2% to 30% based on the total weight of the shell layer.

4. The silicon-carbon composite material of claim 2, wherein, The silicon-carbon composite includes amorphous carbon, the silicon oxide compound SiO x dispersed in the amorphous carbon, the particle size of the silicon oxide compound SiO x is 2 nm to 5 nm. 5.The silicon-carbon composite material according to any one of claims 1 to 4, satisfying at least one of conditions (1) to (4): (1) the silicon nanoparticles have a median particle size of 300 nm to 800 nm; (2) the shell layer has a weight percentage of the amorphous carbon of 3% to 10% based on the total weight of the shell layer; (3) the silicon oxide compound SiO x having a particle size of 3 nm to 4 nm; (4) the core and the shell layer have a weight ratio of 20 to 83. 6.A method for preparing the silicon-carbon composite material according to claim 1, comprising: a coating step of coating a silicon-based material core and / or a graphite core with an organosilicon source and converting the organosilicon source into a polysilsequioxane to obtain a polysilsequioxane-coated core particle; a carbonization step of performing a carbonization treatment on the polysilsequioxane coating the core particle to obtain the silicon-carbon composite material.

7. The method of claim 6, wherein, the organosilicon source comprises at least one of vinyltriethoxysilane, vinyltrimethoxysilane, propyltriethoxysilane, propyltrimethoxysilane, ethyltriethoxysilane, ethyltrimethoxysilane, methyltriethoxysilane, methyltrimethoxysilane, phenyltriethoxysilane, and ureidopropyltriethoxysilane. 8.An electrochemical device comprising a negative electrode sheet, the negative electrode sheet comprising a current collector and a negative electrode active material layer formed on a surface of the current collector, the negative electrode active material layer containing the silicon-carbon composite material according to any one of claims 1 to 5 or prepared by the method according to claim 6 or 7.

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