Composite silicon-based material and preparation method thereof, negative electrode sheet and lithium-ion battery

Abstract

This application relates to a composite silicon-based material, a preparation method thereof, a negative electrode plate, and a lithium-ion battery. The composite silicon-based material comprises a porous nitrogen-doped carbon shell and a silicon-based material encapsulated within the porous nitrogen-doped carbon shell; the porous nitrogen-doped carbon shell is formed by carbonizing a nitrogen-containing organic carbon source polymer. The solution provided in this application, when the porous nitrogen-doped carbon-encapsulated silicon-based material is applied to the negative electrode of a lithium battery, increases the tap density of the silicon negative electrode, inhibits volume expansion, and improves the battery's energy density and cycle performance.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a composite silicon-based material and a preparation method thereof, a negative electrode sheet and a lithium-ion battery. Background Art

[0002] With the rapid development of lithium-ion battery technology, the continuous upgrading of electronic devices, and the widespread adoption of electric vehicles, market demand for battery energy density continues to increase. Among battery anode materials, traditional graphite, due to its low theoretical specific capacity, has hindered further improvements in energy density. Silicon, on the other hand, is currently considered the most promising alternative to traditional graphite anodes due to its high theoretical specific capacity and abundant reserves, leading to its development and application in lithium-ion batteries.

[0003] However, when silicon is fully lithiated with lithium ions, its volume expansion can exceed 300%, leading to a series of problems. The volume effect causes silicon particles to pulverize, impairing their adhesion to the current collector. It also increases interparticle contact resistance, accelerating battery capacity decay. Furthermore, this significant volume expansion causes the SEI layer to continuously rupture and reform, consuming lithium ions and leading to increased irreversible capacity loss, severely deteriorating the battery's cycling performance. Summary of the Invention

[0004] In order to solve or partially solve the problems existing in the related art, the present application provides a composite silicon-based material and its preparation method, a negative electrode plate and a lithium-ion battery, which can increase the tap density of the silicon negative electrode, inhibit volume expansion, and improve the energy density and cycle performance of the battery.

[0005] In a first aspect, the present application provides a composite silicon-based material, which includes a porous nitrogen-doped carbon shell and a silicon-based material encapsulated in the porous nitrogen-doped carbon shell; wherein the porous nitrogen-doped carbon shell is formed by carbonizing an organic carbon source polymer containing nitrogen elements.

[0006] In some embodiments, the nitrogen-containing organic carbon source polymer is 4-(2-aminoethyl)-1,2-benzenediol hydrochloride; and / or the particle size D50 of the silicon-based material is selected from 3μm to 15μm; and / or the pore shape of the porous nitrogen-doped carbon shell layer includes hexagonal pores, square pores, conical pores or other irregular pores; and / or the silicon-based material is selected from silicon-carbon materials.

[0007] A second aspect of the present application provides a method for preparing a composite silicon-based material, comprising:

[0008] Adding a surfactant and a pore-forming agent into a mixed solution containing a silicon-based material and dispersing them evenly to obtain a silicon-based material with a treated surface;

[0009] Adding a nitrogen-containing organic carbon source to a mixed solution containing the surface-treated silicon-based material and dispersing the mixture uniformly to obtain a silicon-based material whose surface is coated with a nitrogen-containing organic carbon source polymer;

[0010] removing the surfactant and the pore-forming agent, and drying to obtain silicon-based material particles whose surfaces are coated with a nitrogen-containing organic carbon source polymer;

[0011] The silicon-based material particles whose surfaces are coated with the organic carbon source polymer containing nitrogen elements are subjected to a first carbonization and a second carbonization respectively, and the organic carbon source polymer containing nitrogen elements forms a porous nitrogen-doped carbon shell layer to prepare the composite silicon-based material.

[0012] In some embodiments, the surfactant and the pore-forming agent are the same substance;

[0013] Preferably, the surfactant and the pore-forming agent have hydrophilicity and lipophilicity;

[0014] More preferably, the surfactant and the pore-forming agent are selected from one or more of polyvinyl pyrrolidone, cetyltrimethylammonium chloride, cetyltrimethylammonium bromide, polyether F127 and polyether P123.

[0015] In some embodiments, the removing of the surfactant and the pore-forming agent comprises:

[0016] The silicon-based material with the surface coated with the nitrogen-containing organic carbon source polymer is washed with ethanol and water respectively to remove the surfactant and the pore-forming agent.

[0017] In some embodiments, the mass ratio of the silicon-based material, the surfactant, the pore-forming agent, and the nitrogen-containing organic carbon source is 100:(5-40):(1-20).

[0018] In some embodiments, after adding the nitrogen-containing organic carbon source to the mixed solution containing the surface-treated silicon-based material, the process further comprises:

[0019] An alkaline solution is added to adjust the mixed solution to alkaline; preferably, the pH value of the mixed solution after adjustment is 8-10; more preferably, the alkaline solution is selected from one of ammonia water, sodium hydroxide or potassium hydroxide.

[0020] In some embodiments, the temperature of the first carbonization is lower than the temperature of the second carbonization, and the duration of the first carbonization is longer than the duration of the second carbonization;

[0021] Preferably, the temperature of the first carbonization is 550°C to 750°C, and the temperature of the second carbonization is 650°C to 900°C.

[0022] The third aspect of the present application provides a negative electrode plate, which includes a current collector and a negative electrode material coated on at least one side of the current collector; the negative electrode material includes the composite silicon-based material of the first aspect or the composite silicon-based material prepared by the preparation method of the second aspect.

[0023] A fourth aspect of the present application provides a lithium-ion battery comprising the above-mentioned negative electrode plate.

[0024] The technical solution provided by this application may have the following beneficial effects:

[0025] The composite silicon-based material of the present application, when used as the negative electrode material of a lithium-ion battery, can effectively inhibit the volume expansion of silicon, improve the conductivity and tap density of the silicon negative electrode material, reduce lithium ion loss, and improve the energy density and cycle stability of the battery.

[0026] The composite silicon-based material prepared by the preparation method of the present application uses the same substance as a surfactant and a pore-forming agent to ensure that the shell of the organic carbon source forms a more ordered porous channel; and the surfactant and the pore-forming agent are both hydrophilic and lipophilic, and can adhere tightly to the silicon-based material when forming pores, and can then be easily removed without residue by washing with water and ethanol; in addition, the organic carbon source containing nitrogen elements of a specific material is used, and no additional initiator is required for polymerization. Under appropriate alkaline conditions, it can be efficiently polymerized on the surface of the silicon-based material to form a preliminary shell, and then the porous morphology is stabilized by the first carbonization, and a stable porous nitrogen-doped carbon shell is formed by the second carbonization.

[0027] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. DETAILED DESCRIPTION

[0028] To facilitate understanding of the present invention, the present invention will be described in detail below. However, before describing the present invention in detail, it should be understood that the present invention is not limited to the specific embodiments described. It should also be understood that the terminology used herein is for the purpose of describing specific embodiments only and is not intended to be limiting.

[0029] Where a numerical range is provided, it will be understood that each intervening value between the upper and lower limits of the range and any other specified or intervening values ​​in the specified range is encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included in smaller ranges and are also encompassed within the present invention, subject to any explicitly excluded limits in the specified range. Where a specified range includes one or two limits, ranges excluding either or both of those included limits are also encompassed within the present invention. It will also be understood that the term "and / or" as used herein refers to and includes any or all possible combinations of one or more associated listed items. In the description of this application, "a plurality of" means two or more, unless otherwise specifically defined. "One or more" means one or more, unless otherwise specifically defined.

[0030] Unless otherwise defined, all terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although any methods and materials or equivalents to those described herein may also be used in the practice or testing of the present invention, preferred methods and materials are now described.

[0031] In the related art, during the recycling of lithium-ion batteries, when the silicon material of the negative electrode is embedded with lithium ions and is fully lithiated, the volume will expand severely and cause various problems. In order to suppress the expansion of silicon materials, the related art helps to suppress the expansion rate by making composite silicon-based materials. When preparing composite silicon-based materials, the conventional method is to deposit the silicon material inside the porous carbon, but there will be floating silicon on the surface of the obtained material, which will cause the reaction to produce gas in the subsequent slurrying process of the negative electrode material, thereby affecting the quality of the subsequent coating process. In other related technologies, if the silicon material is first completely coated and then pores are made by acid-base etching or other methods, the preparation process is complicated and has certain safety risks.

[0032] The present application provides a composite silicon-based material and a preparation method thereof, which can produce a porous nitrogen-doped carbon-coated silicon-based material for application in the negative electrode of a lithium battery, thereby increasing the tap density of the silicon negative electrode, inhibiting volume expansion, and improving the energy density and cycle performance of the battery.

[0033] A composite silicon-based material provided in one embodiment of the present application includes a porous nitrogen-doped carbon shell and a silicon-based material encapsulated in the porous nitrogen-doped carbon shell; wherein the porous nitrogen-doped carbon shell is formed by carbonizing an organic carbon source polymer containing nitrogen elements.

[0034] The porous nitrogen-doped carbon shell is located on the outer layer of the silicon-based material, which then encapsulates the silicon-based material, thereby limiting the silicon-based material's expansion rate during actual use. At the same time, the porous channels formed allow lithium ions to pass through the nitrogen-doped carbon shell and enter the inner silicon-based material for insertion and deinsertion.

[0035] In some embodiments, the organic carbon source polymer containing nitrogen elements is 4-(2-aminoethyl)-1,2-benzenediol hydrochloride. On the one hand, by adopting 4-(2-aminoethyl)-1,2-benzenediol hydrochloride, polymerization can occur only by pH adjustment, and there is no need to add an additional initiator to initiate the polymerization reaction, thereby avoiding the introduction of impurity residues and affecting the material properties, and there is no need to generate an additional step of removing the initiator during the preparation process, thereby improving production efficiency. On the other hand, by using small molecules containing organic nitrogen / carbon sources, a thin shell can be polymerized on the surface of the silicon-based material. While the shell effectively limits the expansion of the silicon-based material, it avoids the shell being too thick and affecting the migration efficiency of lithium ions.

[0036] In some embodiments, the particle size D50 of the silicon-based material is selected from 3μm to 15μm. For example, the particle size D50 of the silicon-based material can be selected from 3μm to 12μm, etc. In the granular state of the silicon-based material in powder form, particles of the same mass but different particle sizes have different corresponding specific surface areas; accordingly, when the specific surface area is larger, the content of the corresponding raw material required to form a porous nitrogen-doped carbon shell of the same thickness is also larger, thereby increasing the cost of raw materials. In addition, the larger the specific surface area, the better. The larger the specific surface area, the more severe the reaction on the surface of the material during the charge and discharge process of the lithium battery, which ultimately affects the capacity retention rate of the battery. By limiting the particle size of the silicon-based material, the corresponding specific surface area can be controlled, and then when applied to the battery, it is beneficial to improve the capacity retention rate of the battery during use.

[0037] In some embodiments, the pore shape of the porous nitrogen-doped carbon shell includes hexagonal pores, square pores, tapered pores, or other irregular pores. It is understood that the pore shape is determined by the micelle aggregation morphology of the pore-forming agent during the preparation process, and different types of pore-forming agents will produce different effects. In the present application, a variety of pore channels of different shapes can be formed in the porous nitrogen-doped carbon shell, which can help adjust the migration efficiency of lithium ions.

[0038] In some embodiments, the silicon-based material is selected from a silicon-carbon material. By selecting a silicon-based material containing carbon, the advantages of both carbon and silicon anodes can be achieved while reducing the volume expansion caused by pure silicon.

[0039] The composite silicon-based material of the present application, by coating the silicon-based material with a porous nitrogen-doped carbon shell layer, can improve the conductivity and tap density of the silicon negative electrode material, inhibit volume expansion, enhance the rate charge and discharge performance of the silicon negative electrode, and thus help improve the cycle performance of the battery; at the same time, reduce the consumption of lithium ions during the use of the battery and maintain the energy density of the battery.

[0040] An embodiment of the present application further provides a method for preparing a composite silicon-based material, which comprises the following steps:

[0041] S110, adding a surfactant and a pore-forming agent into a mixed solution containing a silicon-based material, and dispersing them evenly to obtain a silicon-based material with a treated surface.

[0042] The mixed liquid containing the silicon-based material can be prepared in advance by adding powdered silicon-based material particles to water and mixing and dispersing them. A surfactant and a pore-forming agent are then added to the mixed liquid containing the silicon-based material and uniformly dispersed to obtain a surface-treated silicon-based material. The surface-treated silicon-based material can be particles having the surfactant and pore-forming agent adsorbed on their surfaces.

[0043] In one specific embodiment, ultrasonic dispersion can be used to obtain a uniformly dispersed mixture containing the silicon-based material. Furthermore, after adding a surfactant and a pore-forming agent to the mixture containing the silicon-based material, ultrasonic dispersion is continued to uniformly disperse the surfactant and pore-forming agent, so that the surfactant and pore-forming agent are adsorbed on the surface of the silicon-based material particles.

[0044] In some embodiments, the surfactant and the pore-forming agent are the same substance, that is, the same substance can be used as a surfactant and a pore-forming agent. Preferably, the same substance as the surfactant and the pore-forming agent has both hydrophilicity and lipophilicity. Such a design, on the one hand, uses the same substance and one end of the substance is hydrophilic and the other end is lipophilic, that is, the lipophilic end will be adsorbed on the surface of the silicon-based material, and the other end is exposed to water, which is conducive to the organic carbon source in the subsequent steps to form ordered pores on the surface of the silicon-based material during polymerization, and then the organic carbon source can form a stable and reliable shell on the surface of the silicon-based material. If different substances are used for the surfactant and the pore-forming agent, the organic carbon source will form disordered pores during polymerization, resulting in the organic carbon source not being able to completely adhere to the silicon-based material, and the porous nitrogen-doped shell formed after carbonization will easily fall off, and it will not play a role in constraining the expansion of the silicon-based material. On the other hand, the surfactant and pore-forming agent with both hydrophilicity and lipophilicity can be easily removed in the subsequent steps, and the impurity removal is quickly completed without residue, thereby improving production efficiency.

[0045] In some specific embodiments, the surfactant and the pore-forming agent are selected from one or more of polyvinyl pyrrolidone, hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, polyether F127, and polyether P123. That is, only one substance can be used as both a surfactant and a pore-forming agent; or multiple substances can be used, each of which can be used as both a surfactant and a pore-forming agent. When only one substance is used as a surfactant and a pore-forming agent, the organic carbon source can form relatively ordered pores in subsequent steps; when two different substances are used as surfactants and pore-forming agents, the organic carbon source can form composite pores during the polymerization process, and the composite pores can more effectively change the migration of lithium ions at the material interface, while also ensuring that the formed shell is firmly wrapped around the silicon-based material.

[0046] S120, adding a nitrogen-containing organic carbon source to a mixed solution containing a surface-treated silicon-based material, and dispersing the mixture uniformly to obtain a silicon-based material whose surface is coated with a nitrogen-containing organic carbon source polymer.

[0047] In this step, a nitrogen-containing organic carbon source is added to the mixed solution. Preferably, ultrasonic dispersion is used for uniform dispersion. During the dispersion process, the organic carbon source polymerizes outside the silicon-based material, and corresponding pores are formed due to the aggregation of the pore-forming agent micelles.

[0048] In some embodiments, the nitrogen-containing organic carbon source is 4-(2-aminoethyl)-1,2-benzenediol hydrochloride. When this substance is used as the conductive organic carbon source, no initiator is required when the polymerization reaction occurs on the surface of the silicon-based material.

[0049] In order to cause the polymerization reaction of 4-(2-aminoethyl)-1,2-benzenediol hydrochloride, in some embodiments, an alkaline solution is added to the mixed solution to adjust the mixed solution to alkaline; preferably, the pH value of the adjusted mixed solution is 8 to 10. It can be understood that if the alkalinity of the mixed solution is too weak, the polymerization rate of the organic carbon source is too slow, which will increase production energy consumption; if the alkalinity of the mixed solution is too strong, although the polymerization rate is faster, it is not allowed to form channels, and the shell coating after polymerization will also be uneven. In the present application, by adjusting the mixed solution to the appropriate alkalinity, the polymerization efficiency can be ensured while the organic carbon source forms a uniform shell.

[0050] In some embodiments, the alkaline solution is selected from ammonia, sodium hydroxide, or potassium hydroxide. This design uses a readily available alkaline solution to adjust the pH of the mixed solution, reducing raw material costs.

[0051] In some embodiments, the mass ratio of the silicon-based material, surfactant and pore-forming agent, and nitrogen-containing organic carbon source is 100:(5-40):(1-20). With this design, through the appropriate mass ratio, the surfactant and pore-forming agent of the same substance can promote the organic carbon source to form an appropriate number of porous channels. The appropriate mass of the organic carbon source can form a shell layer of appropriate thickness, achieving the optimal coating thickness without excessive thickness and resulting in excessively long pore channels, thereby ensuring the efficient migration of lithium ions.

[0052] S130, removing the surfactant and the pore-forming agent, and drying to obtain silicon-based material particles whose surfaces are coated with the organic carbon source polymer containing nitrogen elements.

[0053] After the organic carbon source completes the polymerization reaction, in this step, the surfactant and pore-forming agent that form micelle agglomeration are removed, so that the organic carbon source polymer generates porous channels on the surface of the silicon-based material particles.

[0054] In some embodiments, when the surfactant and pore-forming agent are the same substance and possess both hydrophilic and lipophilic properties, the silicon-based material coated with a nitrogen-containing organic carbon source polymer is washed with ethanol and water, respectively, to remove the surfactant and pore-forming agent. It is understood that due to the hydrophilic nature of surfactant molecules, one end is hydrophilic and the other is lipophilic. When washing with water, the hydrophilic end drags the surfactant molecules with it, while when washing with ethanol, the lipophilic end drags the surfactant molecules with it. Alternating washes facilitate the removal of the surfactant. Furthermore, when the surfactant is shaken in water, a large number of bubbles are generated. During washing with water, the presence of bubbles can be used to determine whether there is residual surfactant.

[0055] Furthermore, after removing the surfactant and the pore-forming agent, filtering out the residual liquid, and drying, the silicon-based material particles with the surface coated with the nitrogen-containing organic carbon source polymer can be obtained.

[0056] S140, performing a first carbonization and a second carbonization on silicon-based material particles whose surfaces are coated with an organic carbon source polymer containing nitrogen elements, respectively, so that the organic carbon source polymer containing nitrogen elements forms a porous nitrogen-doped carbon shell layer to obtain a composite silicon-based material.

[0057] In some embodiments, the temperature of the first carbonization is 550°C to 750°C, and the temperature of the second carbonization is 650°C to 900°C. In this step, different reaction conditions are successively adopted for the first carbonization and the second carbonization. Particularly, through the first carbonization, the polymer formed by the organic carbon source is converted into graphite-phase nitrogen-doped carbon, thereby stabilizing the resulting porous morphology. Then, through the second carbonization, a stable porous nitrogen-doped carbon shell is formed. Particularly, the temperature of the first carbonization is lower than the temperature of the second carbonization, thereby avoiding high temperature from destroying the pore structure during the first carbonization, and the high temperature during the second carbonization can eliminate the structural stress and stabilize the formed shell.

[0058] As can be seen from this example, the composite silicon-based material prepared by the preparation method of the present application uses the same substance as a surfactant and a pore-forming agent to ensure that the shell of the organic carbon source forms a more ordered porous channel; and the surfactant and the pore-forming agent are both hydrophilic and lipophilic, and can be tightly adhered to the silicon-based material when forming a porous structure, and can then be easily removed by washing with water and ethanol without residue; In addition, an organic carbon source containing nitrogen elements of a specific material is used, and no additional initiator is required for polymerization. Under appropriate alkaline conditions, it can be efficiently polymerized on the surface of the silicon-based material to form a preliminary shell, and then the porous morphology is stabilized by the first carbonization, and a stable porous nitrogen-doped carbon shell is formed by the second carbonization. With such a design, the composite silicon-based material obtained can effectively inhibit the volume expansion of silicon when applied to the negative electrode material of a lithium-ion battery, improve the conductivity and tap density of the silicon negative electrode material, reduce lithium ion loss, and improve the energy density and cycle stability of the battery.

[0059] The following is a further description of a method for preparing a composite silicon-based material according to a specific embodiment. The method comprises:

[0060] S210, dispersing 100 parts by weight of the silicon-based material in 1L to 2L of water for 1 hour to 1.5 hours to obtain a mixed solution containing the silicon-based material.

[0061] Preferably, the silicon-based material may be a silicon-carbon material.

[0062] S220, adding 5 to 40 parts of surfactant and pore-forming agent of the same substance into the mixed solution containing the silicon-based material, and dispersing for 1 hour to 1.5 hours to obtain a silicon-based material with a surface treated.

[0063] Preferably, the surfactant and pore-forming agent can be selected from one or more of polyvinylpyrrolidone, cetyltrimethylammonium chloride, cetyltrimethylammonium bromide, polyether F127, and polyether P123. In other words, if multiple of the aforementioned materials are used simultaneously, each material can simultaneously function as both a surfactant and a pore-forming agent.

[0064] As you can understand, silicon-based materials are solid and difficult to disperse in water, while pore-forming agents / surfactants are easily soluble in water. Adding the pore-forming agent / surfactant first increases the liquid viscosity, making it even more difficult to evenly disperse the silicon-based material. Therefore, the pore-forming agent / surfactant should be added after the silicon-based material is evenly dispersed in S210. Increasing the liquid viscosity helps stabilize the dispersed mixture.

[0065] S230, adding 1 to 20 parts of an organic carbon source containing a nitrogen element to a mixed solution containing a surface-treated silicon-based material, dispersing for 0.5 h to 1 h, adding an alkaline solution to the mixed solution, adjusting the pH value of the mixed solution to 8 to 10, and dispersing for 6 h to 24 h, and then centrifuging to obtain a silicon-based material whose surface is coated with an organic carbon source polymer containing a nitrogen element.

[0066] The nitrogen-containing organic carbon source is 4-(2-aminoethyl)-1,2-benzenediol hydrochloride. Preferably, the alkaline solution is selected from ammonia water, sodium hydroxide or potassium hydroxide.

[0067] Among them, 4-(2-aminoethyl)-1,2-benzenediol hydrochloride can complete the polymerization reaction in an alkaline environment without adding an initiator.

[0068] It should be noted that in the negative electrode materials of the related art, the polymerization of the conductive polymer requires a chain initiator. The chain initiator is generally a persulfate, but persulfate is easy to decompose and has strong oxidizing properties, which will then deteriorate the safety of the reaction. In the embodiment of the present application, a conductive material that does not require the addition of an initiator, namely 4-(2-aminoethyl)-1,2-benzenediol hydrochloride, is used to ensure safety during the production process.

[0069] S240, washing the silicon-based material whose surface is coated with the organic carbon source polymer containing nitrogen elements with ethanol and water respectively, removing the surfactant and the pore-forming agent and then drying to obtain dry silicon-based material particles whose surface is coated with the organic carbon source polymer containing nitrogen elements.

[0070] S250, in an inert atmosphere, carbonizing the silicon-based material particles whose surfaces are coated with an organic carbon source polymer containing nitrogen at 550° C. to 750° C. for a first time for 1.5 hours to 2 hours.

[0071] In this step, the organic carbon source polymer containing nitrogen is carbonized to form graphite-phase nitrogen-doped carbon through a first carbonization in an inert atmosphere such as nitrogen, and the obtained porous morphology is stabilized.

[0072] S260, in an inert atmosphere, carbonizing the silicon-based material particles whose surfaces are coated with an organic carbon source polymer containing nitrogen at 650° C. to 900° C. for a first time for 1 hour to 1.5 hours.

[0073] In this step, a firmly bonded porous nitrogen-doped carbon shell is formed on the surface of the silicon-based material particles using a higher temperature and a shorter time than the first carbonization.

[0074] As can be seen from this example, in the preparation process, a direct synthesis method is used to form pores, which has a simple preparation process and saves production costs. Surfactants are used as pore-forming agents to create more ordered pore channels, providing channels for rapid diffusion of lithium ions, thereby increasing electrochemical reaction activity and improving electrochemical performance. A conductive material that does not require the addition of an initiator is found to be polymerized and coated on the surface of the silicon-based material, and a stable porous shell is formed through the first carbonization and second carbonization under different conditions, so that the conductivity of the prepared silicon-based material is improved. The ordered porous channels can enhance the migration ability of lithium ions, which is conducive to rapid charging and discharging, and further improves the rate performance. The shell wrapping can increase the tap density of the silicon negative electrode, inhibit volume expansion, and then improve the energy density and cycle stability of the battery. In addition, when applied to negative electrode materials, the surface of the silicon negative electrode contains hydroxyl groups, which can form hydrogen bonds with the carboxyl groups in the binder, enhance the bonding force, strengthen the combination of the silicon negative electrode and the binder, and improve the bonding properties.

[0075] An embodiment of the present application further provides a negative electrode plate, which includes a current collector and a negative electrode material coated on at least one side of the current collector; the negative electrode material includes the composite silicon-based material of any of the above embodiments.

[0076] In some specific embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode material disposed on the negative electrode current collector. The negative electrode material may include a negative electrode active material, a conductive agent, a binder, a thickener, and a solvent. Composite silicon-based materials can be used as the negative electrode active material. According to relevant technologies, the negative electrode active material, conductive agent, binder, thickener, and solvent are mixed in a predetermined mass ratio to prepare a negative electrode slurry. This slurry is then coated on the negative electrode current collector, dried, rolled, and cut into pieces to produce a negative electrode sheet of a predetermined size.

[0077] An embodiment of the present application further provides a lithium-ion battery, and the lithium-ion battery of the present application includes the negative electrode sheet in any of the above embodiments.

[0078] In a specific embodiment, the lithium-ion battery of the present application includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein the separator is placed between the positive electrode sheet and the negative electrode sheet. After being prepared into a bare cell through a lamination process, a finished battery is produced through relevant processes. For example, the bare cell is placed in an aluminum-plastic film for encapsulation, and then vacuum encapsulation, static standing, formation, shaping, and other processes are performed to complete the preparation of the lithium-ion battery. The specific preparation process can be selected according to relevant technologies and will not be described in detail here.

[0079] In some embodiments, the positive electrode material further comprises a conductive agent, a binder, and a solvent. Specifically, the positive electrode active material, the conductive agent, the binder, and the solvent can be mixed in a predetermined mass ratio to prepare a positive electrode slurry, which is then coated on a positive electrode current collector, dried, roll-pressed, and cut into pieces to obtain positive electrode sheets of a predetermined size.

[0080] The materials for the current collector, conductive agent, binder, solvent, and other components of the positive and negative electrode sheets can be selected based on relevant technologies and are not limited here. The separator can be made of, for example, polyethylene, polypropylene, self-woven fabric, non-woven fabric, or a synthetic resin microporous membrane, and can be selected based on relevant technologies and are not limited here.

[0081] One embodiment of the present application further provides an electronic device comprising the above-mentioned lithium-ion battery. The lithium-ion battery serves as a power source for the electronic device and can also be used as an energy storage unit for the electronic device. The electronic device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc.

[0082] To make the present invention easier to understand, the present invention will be further described in detail below with reference to the following examples. These examples are merely illustrative and do not limit the scope of application of the present invention. Unless otherwise specified, the raw materials or components used in the present invention can be obtained through commercial channels or conventional methods.

[0083] Composite silicon-based materials are prepared according to different embodiments below.

[0084] Example 1

[0085] (1) Ultrasonic dispersion of 50 g of silicon-based material in 1 L of deionized water for 1 h.

[0086] (2) Add 10 g of polyvinyl pyrrolidone (surfactant / pore-forming agent) and disperse by ultrasonic for 1 hour.

[0087] (3) Add 10 g of 4-(2-aminoethyl)-1,2-benzenediol hydrochloride (organic carbon source), disperse for 0.5 h, adjust the pH to 9.0 with ammonia water, disperse for 24 h, and then centrifuge to obtain a silicon-based material with a surface coated with a nitrogen-containing organic carbon source polymer.

[0088] (4) The product of step (3) is washed with ethanol and water and then dried to obtain a silicon-based material whose surface is coated with an organic carbon source polymer containing nitrogen elements.

[0089] (5) The silicon-based material of step (4) is calcined at 600° C. in a high-purity nitrogen atmosphere for 2 h to obtain a preliminarily carbonized silicon-based material.

[0090] (6) The silicon-based material after the first carbonization in step (5) is calcined at 800° C. in a high-purity nitrogen atmosphere for 1.5 hours to obtain a porous nitrogen-doped carbon-coated composite silicon-based material.

[0091] Example 2

[0092] (1) Ultrasonic dispersion of 50 g of silicon-based material in 1 L of deionized water for 1 h.

[0093] (2) Add 10 g of hexadecyltrimethylammonium chloride (surfactant / pore-forming agent) and disperse by ultrasonic for 1 hour.

[0094] (3) Add 10 g of 4-(2-aminoethyl)-1,2-benzenediol hydrochloride (organic carbon source), disperse for 0.5 h, adjust the pH to 9.0 with ammonia water, disperse for 24 h, and then centrifuge to obtain a silicon-based material with a surface coated with a nitrogen-containing organic carbon source polymer.

[0095] (4) The product of step (3) is washed with ethanol and water and then dried to obtain a silicon-based material whose surface is coated with an organic carbon source polymer containing nitrogen elements.

[0096] (5) The silicon-based material of step (4) is calcined at 600° C. in a high-purity nitrogen atmosphere for 2 h to obtain a preliminarily carbonized silicon-based material.

[0097] (6) The silicon-based material after the first carbonization in step (5) is calcined at 800° C. in a high-purity nitrogen atmosphere for 1.5 hours to obtain a porous nitrogen-doped carbon-coated composite silicon-based material.

[0098] Example 3

[0099] (1) Ultrasonic dispersion of 100 g of silicon-based material in 2 L of deionized water was performed for 1 h.

[0100] (2) Add 20 g of hexadecyltrimethylammonium bromide (surfactant / pore-forming agent) and disperse by ultrasonic for 1 hour.

[0101] (3) Add 20 g of 4-(2-aminoethyl)-1,2-benzenediol hydrochloride (organic carbon source), disperse for 0.5 h, adjust the pH to 9.0 with ammonia water, disperse for 24 h, and then centrifuge to obtain a silicon-based material with a surface coated with a nitrogen-containing organic carbon source polymer.

[0102] (4) The product of step (3) is washed with ethanol and water and then dried to obtain a silicon-based material whose surface is coated with an organic carbon source polymer containing nitrogen elements.

[0103] (5) The silicon-based material of step (4) is calcined at 600° C. in a high-purity nitrogen atmosphere for 2 h to obtain a preliminarily carbonized silicon-based material.

[0104] (6) The silicon-based material after the first carbonization in step (5) is calcined at 800° C. in a high-purity nitrogen atmosphere for 1.5 hours to obtain a porous nitrogen-doped carbon-coated composite silicon-based material.

[0105] Example 4

[0106] (1) Ultrasonic dispersion of 100 g of silicon-based material in 2 L of deionized water was performed for 1 h.

[0107] (2) Add again 10g polyvinyl pyrrolidone and 10g polyether F127 (surfactant / pore-forming agent), ultrasonic dispersion for 1 h.

[0108] (3) Add 20 g of 4-(2-aminoethyl)-1,2-benzenediol hydrochloride (organic carbon source), disperse for 0.5 h, adjust the pH to 9.0 with ammonia water, disperse for 24 h, and then centrifuge to obtain a silicon-based material with a surface coated with a nitrogen-containing organic carbon source polymer.

[0109] (4) The product of step (3) is washed with ethanol and water and then dried to obtain a silicon-based material whose surface is coated with an organic carbon source polymer containing nitrogen elements.

[0110] (5) The silicon-based material of step (4) is calcined at 600° C. in a high-purity nitrogen atmosphere for 2 h to obtain a preliminarily carbonized silicon-based material.

[0111] (6) The silicon-based material after the first carbonization in step (5) is calcined at 800° C. in a high-purity nitrogen atmosphere for 1.5 hours to obtain a porous nitrogen-doped carbon-coated composite silicon-based material.

[0112] Example 5

[0113] (1) Ultrasonic dispersion of 50 g of silicon-based material in 1 L of deionized water for 1 h.

[0114] (2) Add 10 g of polyether F127 (surfactant / pore-forming agent) and disperse by ultrasonic for 1 hour.

[0115] (3) Add 10 g of 4-(2-aminoethyl)-1,2-benzenediol hydrochloride (organic carbon source), disperse for 0.5 h, adjust the pH to 9.0 with ammonia water, disperse for 24 h, and then centrifuge to obtain a silicon-based material with a surface coated with a nitrogen-containing organic carbon source polymer.

[0116] (4) The product of step (3) is washed with ethanol and water and then dried to obtain a silicon-based material whose surface is coated with an organic carbon source polymer containing nitrogen elements.

[0117] (5) The silicon-based material of step (4) is calcined at 600° C. in a high-purity nitrogen atmosphere for 2 h to obtain a preliminarily carbonized silicon-based material.

[0118] (6) The silicon-based material after the first carbonization in step (5) is calcined at 800° C. in a high-purity nitrogen atmosphere for 1.5 hours to obtain a porous nitrogen-doped carbon-coated composite silicon-based material.

[0119] Example 6

[0120] (1) Ultrasonic dispersion of 100 g of silicon-based material in 2 L of deionized water was performed for 1 h.

[0121] (2) Add 20 g of polyether P123 (surfactant / pore-forming agent) and disperse by ultrasonic for 1 hour.

[0122] (3) Add 20 g of 4-(2-aminoethyl)-1,2-benzenediol hydrochloride (organic carbon source), disperse for 0.5 h, adjust the pH to 9.0 with ammonia water, disperse for 24 h, and then centrifuge to obtain a silicon-based material with a surface coated with a nitrogen-containing organic carbon source polymer.

[0123] (4) The product of step (3) is washed with ethanol and water and then dried to obtain a silicon-based material whose surface is coated with an organic carbon source polymer containing nitrogen elements.

[0124] (5) The silicon-based material of step (4) is calcined at 600° C. in a high-purity nitrogen atmosphere for 2 h to obtain a preliminarily carbonized silicon-based material.

[0125] (6) The silicon-based material after the first carbonization in step (5) is calcined at 800° C. in a high-purity nitrogen atmosphere for 1.5 hours to obtain a porous nitrogen-doped carbon-coated composite silicon-based material.

[0126] Example 7

[0127] (1) Ultrasonic dispersion of 50 g of silicon-based material in 1 L of deionized water for 1 h.

[0128] (2) Add 10 g of polyvinyl pyrrolidone (surfactant / pore-forming agent) and disperse by ultrasonic for 1 hour.

[0129] (3) Add 10 g of 4-(2-aminoethyl)-1,2-benzenediol hydrochloride (organic carbon source), disperse for 0.5 h, adjust the pH to 10.0 with ammonia water, disperse for 24 h, and then centrifuge to obtain a silicon-based material with a surface coated with a nitrogen-containing organic carbon source polymer.

[0130] (4) The product of step (3) is washed with ethanol and water and then dried to obtain a silicon-based material whose surface is coated with an organic carbon source polymer containing nitrogen elements.

[0131] (5) The silicon-based material of step (4) is calcined at 600° C. in a high-purity nitrogen atmosphere for 2 h to obtain a preliminarily carbonized silicon-based material.

[0132] (6) The silicon-based material after the first carbonization in step (5) is calcined at 800° C. in a high-purity nitrogen atmosphere for 1.5 hours to obtain a porous nitrogen-doped carbon-coated composite silicon-based material.

[0133] Example 8

[0134] (1) Ultrasonic dispersion of 100 g of silicon-based material in 2 L of deionized water was performed for 1 h.

[0135] (2) Add 20 g of polyether F127 (surfactant / pore-forming agent) and disperse by ultrasonic for 1 hour.

[0136] (3) Add 20 g of 4-(2-aminoethyl)-1,2-benzenediol hydrochloride (organic carbon source), disperse for 0.5 h, adjust the pH to 9.0 with sodium hydroxide, disperse for 24 h, and then centrifuge to obtain a silicon-based material with a surface coated with a nitrogen-containing organic carbon source polymer.

[0137] (4) The product of step (3) is washed with ethanol and water and then dried to obtain a silicon-based material whose surface is coated with an organic carbon source polymer containing nitrogen elements.

[0138] (5) The silicon-based material of step (4) is calcined at 600° C. in a high-purity nitrogen atmosphere for 2 h to obtain a preliminarily carbonized silicon-based material.

[0139] (6) The silicon-based material after the first carbonization in step (5) is calcined at 800° C. in a high-purity nitrogen atmosphere for 1.5 hours to obtain a porous nitrogen-doped carbon-coated composite silicon-based material.

[0140] Example 9

[0141] (1) Ultrasonic dispersion of 100 g of silicon-based material in 2 L of deionized water was performed for 1 h.

[0142] (2) Add again 10g polyvinyl pyrrolidone and 10g polyether F127 (surfactant / pore-forming agent), ultrasonic dispersion for 1 h.

[0143] (3) Add 20 g of 4-(2-aminoethyl)-1,2-benzenediol hydrochloride (organic carbon source), disperse for 0.5 h, adjust the pH to 9.0 with potassium hydroxide, disperse for 24 h, and then centrifuge to obtain a silicon-based material with a surface coated with a nitrogen-containing organic carbon source polymer.

[0144] (4) The product of step (3) is washed with ethanol and water and then dried to obtain a silicon-based material whose surface is coated with an organic carbon source polymer containing nitrogen elements.

[0145] (5) The silicon-based material of step (4) is calcined at 600° C. in a high-purity nitrogen atmosphere for 2 h to obtain a preliminarily carbonized silicon-based material.

[0146] (6) The silicon-based material after the first carbonization in step (5) is calcined at 800° C. in a high-purity nitrogen atmosphere for 1.5 hours to obtain a porous nitrogen-doped carbon-coated composite silicon-based material.

[0147] Example 10

[0148] (1) Ultrasonic dispersion of 100 g of silicon-based material in 2 L of deionized water was performed for 1 h.

[0149] (2) Add again 20g polyvinyl pyrrolidone and 20g polyether F127 (surfactant / pore-forming agent), ultrasonic dispersion for 1 h.

[0150] (3) Add 20 g of 4-(2-aminoethyl)-1,2-benzenediol hydrochloride (organic carbon source), disperse for 0.5 h, adjust the pH to 9.0 with ammonia water, disperse for 24 h, and then centrifuge to obtain a silicon-based material with a surface coated with a nitrogen-containing organic carbon source polymer.

[0151] (4) The product of step (3) is washed with ethanol and water and then dried to obtain a silicon-based material whose surface is coated with an organic carbon source polymer containing nitrogen elements.

[0152] (5) The silicon-based material of step (4) is calcined at 600° C. in a high-purity nitrogen atmosphere for 2 h to obtain a preliminarily carbonized silicon-based material.

[0153] (6) The silicon-based material after the first carbonization in step (5) is calcined at 800° C. in a high-purity nitrogen atmosphere for 1.5 hours to obtain a porous nitrogen-doped carbon-coated composite silicon-based material.

[0154] Example 11

[0155] (1) Ultrasonic dispersion of 100 g of silicon-based material in 2 L of deionized water was performed for 1 h.

[0156] (2) Add again 10g polyvinyl pyrrolidone and 10g polyether F127 (surfactant / pore-forming agent), ultrasonic dispersion for 1 h.

[0157] (3) Add 40 g of 4-(2-aminoethyl)-1,2-benzenediol hydrochloride (organic carbon source), disperse for 0.5 h, adjust the pH to 9.0 with ammonia water, disperse for 24 h, and then centrifuge to obtain a silicon-based material with a surface coated with a nitrogen-containing organic carbon source polymer.

[0158] (4) The product of step (3) is washed with ethanol and water and then dried to obtain a silicon-based material whose surface is coated with an organic carbon source polymer containing nitrogen elements.

[0159] (5) The silicon-based material of step (4) is calcined at 600° C. in a high-purity nitrogen atmosphere for 2 h to obtain a preliminarily carbonized silicon-based material.

[0160] (6) The silicon-based material after the first carbonization in step (5) is calcined at 800° C. in a high-purity nitrogen atmosphere for 1.5 hours to obtain a porous nitrogen-doped carbon-coated composite silicon-based material.

[0161] Performance Testing

[0162] 1. Testing the specific surface area of ​​composite silicon-based materials

[0163] The specific surface areas of the composite silicon-based materials of the above-mentioned embodiments were tested by nitrogen adsorption method. The test results are shown in Table 1 below.

[0164] 2. Rate discharge test

[0165] The composite silicon-based materials prepared in the above embodiments are respectively used to prepare corresponding negative electrode sheets, and then the negative electrode sheets are assembled with positive electrode sheets, separators and electrolytes according to relevant technologies to prepare corresponding lithium-ion batteries.

[0166] At room temperature, the lithium-ion batteries corresponding to each example were subjected to discharge tests at different rates. Specifically, the discharge capacity at 0.2C was used as a benchmark, and the discharge capacity at 2C was calculated. By comparing the discharge capacity ratios at 2C, the discharge capacity ratios of each lithium-ion battery were obtained. The test results are shown in Table 1 below.

[0167] 2. Thickness Expansion Rate and Capacity Retention Rate Test

[0168] The lithium-ion batteries corresponding to each example were subjected to charge and discharge cycle testing at room temperature. The initial thickness (unit: mm) of the lithium-ion battery was used as a benchmark, and the discharge capacity in the third week after initial stabilization was taken as 100%. The subsequent weekly capacity was compared with the third week capacity to obtain the thickness expansion rate and capacity retention rate at the 200th week.

[0169] Table 1

[0170]

[0171]

[0172] In the above embodiments, different surfactants and pore-forming agents were used for comparison in embodiments 1, 2, 3, 4, 5, and 6. The test results show that the battery using both polyvinyl pyrrolidone and polyether F127 has the best performance.

[0173] Different alkaline solutions were compared in Examples 5 and 8 with Examples 4 and 9. The test results showed that the battery performance was slightly different when pH was adjusted with different alkaline solutions, but the difference was not large. Considering the low cost and performance of ammonia water, it has the greatest application prospect.

[0174] Comparison of different pH values ​​between Examples 1 and 7 shows that the battery performance is best when the pH is around 9.

[0175] Examples 4 and 10 were compared for the pore-forming agent content. The results showed that increasing the pore-forming agent content increases the number of pores in the negative electrode sheet, meaning that more pore-forming agent is not necessarily better. As the pore volume increases, on the one hand, the resistance to lithium ion intercalation and deintercalation during charge and discharge decreases, increasing the rate discharge ratio. On the other hand, the number of channels for lithium ion intercalation increases, making the concentration distribution of lithium ions more uniform during intercalation, reducing the risk of excessive lithium ion intercalation in local areas, which can lead to excessive interlayer gaps and expansion of the material, resulting in material rupture, gaps between silicon-carbon materials, and between silicon-carbon and graphite, ultimately causing the electrode sheet to expand excessively and even separate from the current collector. Furthermore, the material's specific surface area increases, leading to severe side reactions during cycling and a significant loss of active lithium, which reduces the retention rate.

[0176] Comparison of the 4-(2-aminoethyl)-1,2-benzenediol hydrochloride content in Examples 4 and 11 shows that excessively high 4-(2-aminoethyl)-1,2-benzenediol hydrochloride content can actually reduce the battery's capacity retention. This is because excessively high 4-(2-aminoethyl)-1,2-benzenediol hydrochloride content increases the thickness of the carbon coating on the silicon-based material, affecting the material's capacity.

[0177] The above test results show that Example 7 has the worst performance, while Example 4 has the best overall performance. When the composite silicon-based material is used in a battery, a larger specific surface area is not necessarily better. A larger specific surface area results in more severe surface reactions during battery charge and discharge, ultimately affecting capacity retention.

[0178] Regarding the above embodiment, its specific implementation has been described in detail in the embodiment of the method, and will not be elaborated again here.

[0179] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0180] It should be noted that the embodiments described above are only used to explain the present application and do not constitute any limitation to the present application. The present application has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present application may be modified as specified within the scope of the claims of the present application, and the present application may be revised without departing from the scope and spirit of the present application. Although the present application described therein relates to specific methods, materials and embodiments, it does not mean that the present application is limited to the specific examples disclosed therein. On the contrary, the present application can be extended to all other methods and applications with the same function.

Claims

1. A method for preparing a composite silicon-based material, characterized in that: include: Adding a surfactant to a mixed solution containing a silicon-based material and dispersing the mixture uniformly to obtain a silicon-based material with a treated surface; The surfactant is used as a pore-forming agent, and the surfactant is selected from multiple groups of polyvinyl pyrrolidone, hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, polyether F127 and polyether P123; Adding a nitrogen-containing organic carbon source to a mixed solution containing the surface-treated silicon-based material and dispersing the mixture uniformly to obtain a silicon-based material whose surface is coated with a nitrogen-containing organic carbon source polymer; removing the surfactant and drying to obtain silicon-based material particles whose surfaces are coated with a nitrogen-containing organic carbon source polymer; The silicon-based material particles whose surfaces are coated with a nitrogen-containing organic carbon source polymer are subjected to a first carbonization and a second carbonization, respectively, and the nitrogen-containing organic carbon source polymer forms a porous nitrogen-doped carbon shell to obtain the composite silicon-based material; the nitrogen-containing organic carbon source polymer is 4-(2-aminoethyl)-1,2-benzenediol hydrochloride, and the mass ratio of the silicon-based material, the surfactant, and the nitrogen-containing organic carbon source is 100:(5~40):(1~20); wherein the temperature of the first carbonization is lower than the temperature of the second carbonization, the duration of the first carbonization is longer than the duration of the second carbonization, the temperature of the first carbonization is 550℃~750℃, and the temperature of the second carbonization is 650℃~900℃.

2. The preparation method according to claim 1, characterized in that The removing of the surfactant comprises: The silicon-based material with the surface coated with the nitrogen-containing organic carbon source polymer is washed with ethanol and water respectively to remove the surfactant.

3. The preparation method according to claim 1, characterized in that After adding the nitrogen-containing organic carbon source to the mixed solution containing the surface-treated silicon-based material, the method further comprises: An alkaline solution is added to adjust the mixture to alkaline.

4. The preparation method according to claim 3, wherein: The alkaline solution is selected from one of ammonia water, sodium hydroxide or potassium hydroxide.

5. The preparation method according to claim 3, wherein: The pH value of the mixed solution after adjustment is 8-10.

6. A composite silicon-based material obtained according to the preparation method according to any one of claims 1 to 5, characterized in that: It comprises a porous nitrogen-doped carbon shell layer and a silicon-based material coated in the porous nitrogen-doped carbon shell layer; wherein the porous nitrogen-doped carbon shell layer is formed by carbonizing an organic carbon source polymer containing nitrogen elements.

7. The composite silicon-based material according to claim 6, characterized in that: The particle size D50 of the silicon-based material is selected from 3 μm to 15 μm; and / or The pore shape of the porous nitrogen-doped carbon shell layer includes hexagonal pores, square pores, tapered pores or other irregular pores; and / or The silicon-based material is selected from silicon-carbon materials.

8. A negative electrode plate, characterized in that: It comprises a current collector and a negative electrode material coated on at least one side of the current collector; the negative electrode material comprises a composite silicon-based material prepared by the preparation method of any one of claims 1 to 5, or a composite silicon-based material according to claim 6 or 7.

9. A lithium-ion battery, characterized in that: Including the negative electrode sheet according to claim 8.

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