Negative active material and preparation method thereof, negative pole piece and secondary battery

Abstract

The invention relates to a negative active material and a preparation method thereof, a negative pole piece and a secondary battery. The negative electrode active material comprises silicon particles, a one-dimensional carbon material, a graphene carbon cage and polymer pyrolytic carbon, the one-dimensional carbon material forms a three-dimensional carbon skeleton, the graphene carbon cage coats at least part of the surface of the three-dimensional carbon skeleton, and at least part of the polymer pyrolytic carbon anchors the silicon particles on the three-dimensional carbon skeleton. According to the negative electrode active material provided by the invention, by utilizing the synergistic effect among the silicon particles, the one-dimensional carbon material, the graphene carbon cage and the polymer pyrolytic carbon, the conductivity and the structural stability of the negative electrode active material are improved, and the cycle performance of the battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a negative electrode active material and a preparation method thereof, a negative electrode sheet, and a secondary battery. Background Art

[0002] In recent years, as the application scope of secondary batteries has become more and more extensive, secondary batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles and electric vehicles. With the continuous improvement of battery energy density, the traditional graphite anode can no longer meet the demand, and the silicon-based anode has great application prospects with its lower voltage and higher theoretical specific capacity.

[0003] At present, the silicon particles are accompanied by obvious volume changes during the charging and discharging process, which can easily cause the silicon particles to break and pulverize, thereby increasing the internal resistance of the battery and deteriorating the cycle performance. The pulverization of silicon particles makes it impossible to form a stable and uniform SEI film on its surface, and a new SEI film needs to be continuously generated, which consumes active ions and further causes the battery capacity to decay. In addition, the poor conductivity of silicon negative electrode materials also affects the rate performance and capacity utilization of silicon negative electrodes.

[0004] In traditional technology, new carbon materials such as carbon fiber, carbon nanotubes, and graphene are introduced into silicon-based materials to prepare composite materials.

[0005] However, on the one hand, the structural design of some composite materials has major defects, which cannot ensure continuous electrical contact during the cycle process, or cannot maintain the structural integrity of the material during long cycles, and cannot form a stable solid electrolyte interface, which leads to poor cycle performance; on the other hand, the synthesis of some composite materials is relatively cumbersome and the synthesis cost is high, and they cannot be prepared at low cost and on a large scale, which hinders further industrial production and practical application. Summary of the invention

[0006] Based on this, it is necessary to provide a negative electrode active material and its preparation method, a negative electrode plate, and a secondary battery to ensure continuous electrical contact during the cycle process, improve the conductivity and structural stability of the material, and thereby improve the cycle stability of the battery; simplify the synthesis steps, reduce costs, and facilitate large-scale preparation, industrial production, and practical applications.

[0007] The first aspect of the present application provides a negative electrode active material, which includes silicon particles, one-dimensional carbon material, graphene carbon cage and polymer pyrolytic carbon, the one-dimensional carbon material constitutes a three-dimensional carbon skeleton, the graphene carbon cage is coated on at least part of the surface of the three-dimensional carbon skeleton, and at least part of the polymer pyrolytic carbon anchors the silicon particles on the three-dimensional carbon skeleton.

[0008] In some embodiments, at least a portion of the polymer pyrolytic carbon is dispersed within the graphene carbon cages.

[0009] In some embodiments, the negative electrode active material further includes a coupling agent, and the coupling agent includes an amino group and an alkoxy group.

[0010] In some embodiments, the mass ratio of silicon particles to coupling agent is 100:(1-5).

[0011] In some embodiments, the polymer pyrolytic carbon is selected from the pyrolytic carbonization product of at least one of polyacrylonitrile, polyacrylic acid, polyethylene glycol, polyethylene oxide, polyvinyl alcohol, polyacrylamide, poly(methyl methacrylate), poly(methyl ether acrylate), their derivatives, and their copolymers.

[0012] In some embodiments, the mass ratio of silicon particles, one-dimensional carbon material, graphene carbon cage and polymer pyrolytic carbon is (5-7.5):1:1:(0.5-3).

[0013] In some embodiments, the particle size D of the negative electrode active material is v 50 is 2nm~30nm.

[0014] The second aspect of the present application provides a method for preparing a negative electrode active material, which comprises the following steps: adding silicon particles, one-dimensional carbon materials and polymers to a solvent for mixing, spray drying and granulation, and then performing pyrolysis and carbonization treatment to obtain core particles; coating at least part of the surface of the core particles with graphene carbon cages to obtain a negative electrode active material; wherein the polymer is subjected to pyrolysis and carbonization treatment to form polymer pyrolytic carbon, the one-dimensional carbon material constitutes a three-dimensional carbon skeleton, the graphene carbon cage is coated on at least part of the surface of the three-dimensional carbon skeleton, and at least part of the polymer pyrolytic carbon anchors the silicon particles to the three-dimensional carbon skeleton.

[0015] The third aspect of the present application provides a negative electrode plate, which includes the negative electrode active material provided by the first aspect above, or the negative electrode active material prepared by the preparation method provided by the second aspect above.

[0016] A fourth aspect of the present application provides a secondary battery, which includes the negative electrode plate provided by the third aspect.

[0017] Compared with the traditional technology, this application has at least the following beneficial effects:

[0018] The negative electrode active material provided by the present application, through the synergistic effect of silicon particles, one-dimensional carbon materials, graphene carbon cages and polymer pyrolytic carbon, on the one hand, the one-dimensional carbon material has excellent electrical conductivity, which improves the electron migration rate of the material, and the polymer pyrolytic carbon anchors the silicon particles on the three-dimensional carbon skeleton composed of the one-dimensional carbon material, so that the three-dimensional carbon skeleton can maintain continuous electrical contact with the silicon particles during the cycle, thereby improving the conductivity of the negative electrode active material, and the pores of the three-dimensional carbon skeleton provide space for the volume expansion of silicon particles during the lithium insertion process, thereby improving the structural stability of the negative electrode active material, and further improving the cycle performance of the battery; on the other hand, the graphene carbon cage further enhances the conductivity of the negative electrode active material by utilizing the excellent conductivity of graphene, and the graphene carbon cage, as an encapsulated carbon cage, has high mechanical strength and good elasticity, and plays a good role as a buffer layer. During the cycle, the silicon particles are allowed to maintain the connectivity between the silicon particles and the electrode during the volume expansion and contraction process. In addition, the graphene carbon cage can also construct a stable surface interface layer on the surface, which is conducive to the formation of a stable solid electrolyte interface during the battery cycle, reducing the consumption of active lithium in the battery, and further improving the cycle stability of the battery.

[0019] The preparation method of the negative electrode active material provided in the present application is synthesized by industrial technologies such as spray drying and high-temperature pyrolysis. The preparation method is simple, low in cost, high in repeatability, can be prepared on a large scale, and has certain industrial prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of a process for preparing a negative electrode active material in one embodiment of the present application.

[0021] Figure 2 Schematic diagram of the preparation steps of the negative electrode active material in Example 1 of the present application.

[0022] Figure 3 This is a SEM test image of the negative electrode active material in Example 1 of the present application.

[0023] Figure 4 This is a test chart of lithium insertion capacity of a button battery 2032 assembled with negative electrode active materials of Examples 1-2 and Comparative Example 1 of the present application after 100 cycles at 0.5C. DETAILED DESCRIPTION

[0024] References to embodiments of the present application will now be provided in detail, one or more examples of which are described below. Each example is provided as an explanation rather than a limitation of the present application. In fact, it will be apparent to those skilled in the art that various modifications and variations may be made to the present application without departing from the scope or spirit of the present application. For example, a feature described or described as part of one embodiment may be used in another embodiment to produce a further embodiment.

[0025] Therefore, it is intended that the present application covers such modifications and variations that fall within the scope of the appended claims and their equivalents. Other objects, features and aspects of the present application are disclosed in or are apparent from the following detailed description. It will be appreciated by those of ordinary skill in the art that this discussion is merely a description of exemplary embodiments and is not intended to limit the broader aspects of the present application.

[0026] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0027] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0028] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0029] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0030] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, it is mentioned that the method may also include step (c), which means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0031] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0032] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0033] The first aspect of the present application provides a negative electrode active material, which includes silicon particles, one-dimensional carbon material, graphene carbon cage and polymer pyrolytic carbon, the one-dimensional carbon material constitutes a three-dimensional carbon skeleton, the graphene carbon cage is coated on at least part of the surface of the three-dimensional carbon skeleton, and at least part of the polymer pyrolytic carbon anchors the silicon particles on the three-dimensional carbon skeleton.

[0034] The negative electrode active material provided by the present application, through the synergistic effect of silicon particles, one-dimensional carbon materials, graphene carbon cages and polymer pyrolytic carbon, on the one hand, the one-dimensional carbon material has excellent electrical conductivity, which improves the electron migration rate of the material, and the polymer pyrolytic carbon anchors the silicon particles on the three-dimensional carbon skeleton composed of the one-dimensional carbon material, so that the three-dimensional carbon skeleton can maintain continuous electrical contact with the silicon particles during the cycle, thereby improving the conductivity of the negative electrode active material, and the pores of the three-dimensional carbon skeleton provide space for the volume expansion of silicon particles during the lithium insertion process, thereby improving the structural stability of the negative electrode active material, and further improving the cycle performance of the battery; on the other hand, the graphene carbon cage further enhances the conductivity of the negative electrode active material by utilizing the excellent conductivity of graphene, and the graphene carbon cage, as an encapsulated carbon cage, has high mechanical strength and good elasticity, and plays a good role as a buffer layer. During the cycle, the silicon particles are allowed to maintain the connectivity between the silicon particles and the electrode during the volume expansion and contraction process. In addition, the graphene carbon cage can also construct a stable surface interface layer on the surface, which is conducive to the formation of a stable solid electrolyte interface during the battery cycle, reducing the consumption of active lithium in the battery, and further improving the cycle stability of the battery.

[0035] In summary, the negative electrode active material provided in the present application utilizes the synergistic effect between silicon particles, one-dimensional carbon materials, graphene carbon cages and polymer pyrolytic carbon to improve the conductivity and structural stability of the negative electrode active material and improve the cycle performance of the battery.

[0036] It can be understood that polymer pyrolytic carbon has a conductive effect and can anchor and adsorb silicon particles on the three-dimensional carbon skeleton to ensure continuous electrical contact between the silicon particles and the three-dimensional carbon skeleton.

[0037] In some embodiments, the polymer pyrolytic carbon is selected from the pyrolytic carbonization product of at least one of polyacrylonitrile, polyacrylic acid, polyethylene glycol, polyethylene oxide, polyvinyl alcohol, polyacrylamide, poly(methyl methacrylate), poly(methyl ether acrylate), derivatives thereof, and copolymers thereof. During the pyrolytic carbonization process, the polymer molecular chains and the three-dimensional carbon skeleton are cross-linked with each other. At the same time, since the polymer has nitrogen-containing functional groups or oxygen-containing functional groups, these polar functional groups generate strong interaction forces with silicon particles during the pyrolytic carbonization process, thereby anchoring the silicon particles to the three-dimensional carbon skeleton, ensuring continuous electrical contact between the silicon particles and the three-dimensional carbon skeleton.

[0038] In some embodiments, at least a portion of the polymer pyrolytic carbon is dispersed in the graphene carbon cage. The polymer pyrolytic carbon is dispersed in the graphene carbon cage, which is beneficial to improving the structural stability and coating stability of the graphene carbon cage.

[0039] In some embodiments, the particle size D of the silicon particles is v 50 is 50 nm to 200 nm. For example, the particle size D of the silicon particles is v 50 can be, but is not limited to, 50 nm, 75 nm, 100 nm, 125 nm, 150 nm, 175 nm, or 200 nm.

[0040] In some embodiments, the negative electrode active material further includes a coupling agent, and the coupling agent includes an amino group and an alkoxy group.

[0041] Generally speaking, one-dimensional carbon materials are modified with carboxyl functional groups, and silicon particles are modified with hydroxyl functional groups. The amino group of the coupling agent is connected to the carboxyl group of the one-dimensional carbon material through an amidation reaction, and the alkoxy group of the coupling agent is connected to the hydroxyl group of the silicon particle through a hydrolysis polymerization reaction, so that the coupling agent establishes a chemical bond between the one-dimensional carbon material and the silicon particle, and at least part of the coupling agent bridges the one-dimensional carbon material and the silicon particle, thereby improving the mechanical properties of the material and further improving the structural stability of the negative electrode active material. In addition, the graphene carbon cage is usually modified with a carboxyl functional group, and at least part of the coupling agent bridges the silicon particle and the graphene carbon cage. The amino group of the coupling agent is connected to the carboxyl group of the graphene carbon cage through an amidation reaction, and the alkoxy group of the coupling agent is connected to the hydroxyl group of the silicon particle through a hydrolysis polymerization reaction, thereby the coupling agent establishes a chemical bond between the graphene carbon cage and the silicon particle, thereby improving the coating stability of the graphene carbon cage, improving the mechanical stability of the material, and further improving the structural stability of the negative electrode active material.

[0042] In some embodiments, the mass ratio of silicon particles to coupling agent is 100:(1-5). For example, the mass ratio of silicon particles to coupling agent can be, but is not limited to, 100:1, 100:2, 100:3, 100:4, 100:5.

[0043] In some embodiments, the coupling agent is selected from at least one of γ-aminopropyltriethoxysilane (KH-550), γ-aminopropyltrimethoxysilane (KH-540) and N-(β-aminoethyl)-γ-aminopropyltriethoxysilane (KH-791).

[0044] Furthermore, the coupling agent is γ-aminopropyltriethoxysilane (KH-550). The hydrolysis product of KH-550 is ethanol, which is environmentally friendly and is conducive to improving the dispersibility of the solution during the preparation process.

[0045] In some embodiments, the mass ratio of silicon particles, one-dimensional carbon material, graphene carbon cage and polymer pyrolytic carbon is (5-7.5):1:1:(0.5-3). Exemplarily, the mass ratio of silicon particles, one-dimensional carbon material, graphene carbon cage and polymer pyrolytic carbon can be, but is not limited to, 5:1:1:0.5, 5.5:1:1:1, 6:1:1:1.5, 6:1:1:2, 6.5:1:1:2, 7:1:1:2.5, 7.25:1:1:2.75, 7.5:1:1:3.

[0046] In some embodiments, the particle size D of the negative electrode active material is v 50 is 2nm~30nm. Exemplarily, the particle size D of the negative electrode active material v 50 can be but is not limited to 2nm, 4nm, 6nm, 8nm, 10nm, 12nm, 14nm, 16nm, 18nm, 20nm, 22nm, 24nm, 26nm, 28nm, 30nm.

[0047] The second aspect of the present application provides a method for preparing a negative electrode active material, such as Figure 1 As shown, the preparation method comprises the following steps:

[0048] S1. Silicon particles, one-dimensional carbon materials and polymers are added into a solvent and mixed, spray-dried and granulated, and then pyrolyzed and carbonized to obtain core particles.

[0049] S2. Coating at least a portion of the surface of the core particles with graphene carbon cages to obtain negative electrode active materials.

[0050] The polymer is subjected to pyrolysis and carbonization treatment to form polymer pyrolytic carbon, the one-dimensional carbon material forms a three-dimensional carbon skeleton, the graphene carbon cage is coated on at least part of the surface of the three-dimensional carbon skeleton, and at least part of the polymer pyrolytic carbon anchors the silicon particles on the three-dimensional carbon skeleton.

[0051] The preparation method of the negative electrode active material provided in the present application is synthesized by industrial technologies such as spray drying and high-temperature pyrolysis. The preparation method is simple, low in cost, high in repeatability, can be prepared on a large scale, and has certain industrial prospects.

[0052] It can be understood that the addition of polymer is beneficial to improving the material strength of spray-dried granulation and provides a precursor compound for the subsequent formation of polymer pyrolytic carbon; during the pyrolytic carbonization process, the polymer anchors and adsorbs the silicon particles and the three-dimensional carbon skeleton, thereby anchoring the silicon particles on the three-dimensional carbon skeleton.

[0053] In some embodiments, in step S1, a coupling agent is added to a solvent and mixed with silicon particles, a one-dimensional carbon material and a polymer, and the solvent includes water. The coupling agent includes an amino group and an alkoxy group. Generally speaking, the one-dimensional carbon material is modified with a carboxyl functional group, and the silicon particles are modified with a hydroxyl functional group. The amino group of the coupling agent is connected to the carboxyl group of the one-dimensional carbon material through an amidation reaction, and the alkoxy group of the coupling agent is connected to the hydroxyl group of the silicon particles through a hydrolysis polymerization reaction, so that the coupling agent establishes a chemical bond between the one-dimensional carbon material and the silicon particles, thereby improving the mechanical properties of the material and further improving the structural stability of the negative electrode active material.

[0054] In some of the embodiments, in step S1, the inlet air temperature of the spray drying is 160°C~200°C, the outlet air temperature is 80°C~100°C, the spray pressure is 0.5MPa~1.5MPa, and the feed rate is 0.4L / h~0.8L / h.

[0055] In some embodiments, in step S1, the temperature of the pyrolysis carbonization treatment is 400° C. to 800° C., and the time is 4 h to 10 h.

[0056] In some embodiments, step S2 specifically includes the following steps: adding core particles, graphene and polymer into a solvent for mixing, spray drying and granulation, and then performing pyrolysis and carbonization treatment to obtain a negative electrode active material.

[0057] In some embodiments, the graphene is a graphene microplatelet, and the diameter of the graphene microplatelet is 5 μm to 10 μm. For example, the diameter of the graphene microplatelet may be, but is not limited to, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm.

[0058] In some embodiments, in step S2, a coupling agent is added to a solvent and mixed with the core particles, graphene and polymer, and the solvent includes water. The coupling agent includes an amino group and an alkoxy group. Graphene is usually modified with a carboxyl group, and silicon particles are usually modified with a hydroxyl group. The amino group of the coupling agent is connected to the carboxyl group of the graphene carbon cage through an amidation reaction, and the alkoxy group of the coupling agent is connected to the hydroxyl group of the silicon particles through a hydrolysis polymerization reaction, so that the coupling agent establishes a chemical bond between the graphene carbon cage and the silicon particles, thereby improving the coating stability of the graphene carbon cage, improving the mechanical stability of the material, and further improving the structural stability of the negative electrode active material.

[0059] The third aspect of the present application provides a negative electrode plate, which includes the negative electrode active material provided by the first aspect above, or the negative electrode active material prepared by the preparation method provided by the second aspect above.

[0060] Typically, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is disposed on at least one side of the negative electrode current collector. The negative electrode active material layer includes the negative electrode active material provided by the first aspect above, or the negative electrode active material prepared by the preparation method provided by the second aspect above.

[0061] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0062] In some embodiments, the negative electrode active material layer may further include a binder. The binder may include 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), or carboxymethyl chitosan (CMCS).

[0063] In some embodiments, the negative electrode active material layer may further include a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0064] In some of the embodiments, the negative electrode active material layer may further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0065] A fourth aspect of the present application provides a secondary battery, which includes the negative electrode plate provided by the third aspect.

[0066] In some embodiments, the battery comprises a lithium ion battery or a sodium ion battery. The battery of the present application comprises a battery cell form, a battery module form and a battery pack form.

[0067] Typically, a battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the battery charge and discharge process, active ions are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0068] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer is disposed on at least one side of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material.

[0069] As an example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is disposed on any one or both of the two facing surfaces of the positive electrode current collector.

[0070] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0071] In some embodiments, the positive electrode active material layer may further include a positive electrode active material. The positive electrode active material may be a positive electrode active material for a battery known in the art.

[0072] As an example, when the positive electrode plate is used in a lithium-ion battery, the positive electrode active material may be a positive electrode active material for lithium-ion batteries known in the art. Furthermore, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO 2 ), lithium nickel oxide (such as LiNiO 2 ), lithium manganese oxide (such as LiMnO 2 、LiMn 2 O 4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.8 Co 0.15 Al 0.05 O 2 ) or at least one of its modified compounds, etc. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, lithium iron phosphate (such as LiFePO 4 (also referred to as LFP), composite materials of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), at least one of a composite material of lithium manganese phosphate and carbon, a composite material of lithium iron manganese phosphate and a composite material of lithium iron manganese phosphate and carbon.

[0073] In some embodiments, the positive electrode active material layer may further include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0074] In some of the embodiments, based on the total mass of the positive electrode active material layer, the mass proportion of the binder is 0.5% to 3%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, etc.

[0075] In some embodiments, the positive electrode active material layer may further include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0076] In some of the embodiments, based on the total mass of the positive electrode active material layer, the mass proportion of the conductive agent is 0.8% to 4%, for example, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, etc.

[0077] In some of the embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0078] The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0079] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0080] In some of the embodiments, when the battery is a lithium ion battery, the electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0081] In some embodiments, the solvent may include at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, ethylene glycol dimethyl ether, methyl ethyl sulfone and diethyl sulfone.

[0082] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0083] The present application has no particular limitation on the type of isolation membrane, and any known porous isolation membrane with good chemical stability and mechanical stability can be selected.

[0084] In some embodiments, the material of the isolation membrane may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene or polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0085] In some embodiments, the positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode assembly by a winding process or a lamination process.

[0086] In some embodiments, the battery cell may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0087] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and the plastic may be polypropylene, polybutylene terephthalate, polybutylene succinate, etc.

[0088] Secondary batteries can be used as power sources for electrical devices or as energy storage units for electrical devices. Electrical devices may include, but are not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to these.

[0089] The present application will be further described below with reference to specific embodiments and comparative examples.

[0090] Embodiments 1 to 14

[0091] The negative electrode active materials of Examples 1 to 14 were prepared as follows:

[0092] (1) Silicon particles, one-dimensional carbon materials and polymers are dispersed in an aqueous solution, 5 g of anhydrous ethanol is added to assist dispersion, a coupling agent is added, and the mixture is stirred and ultrasonicated to be uniformly dispersed to prepare a precursor solution.

[0093] The particle size D of silicon particles v 50 is 50 nm, and the coupling agent is γ-aminopropyltriethoxysilane (KH-550).

[0094] (2) The core particle precursor solution is spray dried and granulated.

[0095] The inlet air temperature of the spray drying was 180°C, the outlet air temperature was 90°C, the spray pressure was 1.0 MPa, and the feed rate was 0.6 L / h.

[0096] (3) The collected secondary particles are placed in a tubular furnace, argon gas is introduced into the tubular furnace, and pyrolysis and carbonization treatment is performed in the argon atmosphere. The pyrolysis and carbonization treatment temperature is 600°C and the pyrolysis and carbonization treatment time is 6 hours to obtain core particles.

[0097] (4) The core particles, graphene and polymer are dispersed in an aqueous solution, 5 g of anhydrous ethanol is added to assist the dispersion, 0.6 g of a coupling agent is added, and the mixture is stirred and ultrasonicated to be uniformly dispersed to prepare a negative electrode active material precursor solution.

[0098] The graphene is a graphene microsheet with a sheet diameter of 5 μm, the coupling agent is γ-aminopropyltriethoxysilane (KH-550), and the mass ratio of the polymer in step (1) to that in step (4) is 1:1.

[0099] (5) The negative electrode active material precursor solution is spray dried and granulated.

[0100] The inlet air temperature of the spray drying was 180°C, the outlet air temperature was 90°C, the spray pressure was 1.0 MPa, and the feed rate was 0.6 L / h.

[0101] (6) The collected particles are placed in a tubular furnace, argon gas is introduced into the tubular furnace, and pyrolysis and carbonization treatment is performed in the argon atmosphere, wherein the pyrolysis and carbonization treatment temperature is 600°C and the pyrolysis and carbonization treatment time is 6 hours, thereby obtaining a negative electrode active material.

[0102] Table 1 lists in detail the material amounts and material parameters in each embodiment.

[0103] Table 1

[0104]

[0105] In short, the preparation methods of Examples 1 to 14 are basically the same, and the only difference is the type and quality of the one-dimensional carbon material, the type and quality of the polymer pyrolytic carbon, the quality of the silicon particles, and the quality of the coupling agent.

[0106] like Figure 2 As shown, Figure 2 Schematic diagram of the preparation steps of the negative electrode active material in Example 1 of the present application.

[0107] like Figure 3 As shown, Figure 3 This is a SEM test image of the negative electrode active material in Example 1 of the present application.

[0108] Embodiment 15

[0109] The preparation method and material parameters of the negative electrode active material in this embodiment are basically the same as those in Embodiment 1, with the only difference being:

[0110] In step (4), no polymer and coupling agent are added. In this embodiment, the Dv50 of the negative electrode active material is 20 μm.

[0111] Example 16

[0112] The preparation method and material parameters of the negative electrode active material in this embodiment are basically the same as those in Embodiment 1, with the only difference being:

[0113] In step (1) and step (4), no coupling agent is added.

[0114] Comparative Example 1

[0115] This comparative example provides a negative electrode active material.

[0116] Negative electrode active material: Silicon particles (particle size D v 50 is 50 nm, which is the same as the silicon particles in Example 1); Manufacturer: Zhejiang Zhongning Silicon Industry Co., Ltd.

[0117] Comparative Example 2

[0118] This comparative example provides a negative electrode active material and a preparation method thereof.

[0119] (1) Disperse silicon particles, carbon fibers and polymers in an aqueous solution, add 5 g of anhydrous ethanol to aid dispersion, add a coupling agent, stir and ultrasonicate to uniformly disperse them, and prepare a core particle precursor solution.

[0120] The particle size D of silicon particles v 50 is 50 nm, and the coupling agent is γ-aminopropyltriethoxysilane (KH-550).

[0121] (2) The core particle precursor solution is spray-dried and granulated to obtain core particles.

[0122] The inlet air temperature of the spray drying was 180°C, the outlet air temperature was 90°C, the spray pressure was 1.0 MPa, and the feed rate was 0.6 L / h.

[0123] (3) The core particles, graphene and polymer are dispersed in an aqueous solution, 5 g of anhydrous ethanol is added to assist the dispersion, 0.6 g of a coupling agent is added, and the mixture is stirred and ultrasonicated to be uniformly dispersed to prepare a negative electrode active material precursor solution.

[0124] The graphene is a graphene microsheet with a sheet diameter of 5 μm, the coupling agent is γ-aminopropyltriethoxysilane (KH-550), and the mass ratio of the polymer in step (1) to that in step (4) is 1:1.

[0125] (4) The negative electrode active material precursor solution is spray dried and granulated to prepare the negative electrode active material.

[0126] The inlet air temperature of the spray drying was 180°C, the outlet air temperature was 90°C, the spray pressure was 0.5MPa, and the feed rate was 0.6L / h.

[0127] The specific material parameters are shown in Table 1.

[0128] Performance Testing

[0129] The negative electrode active materials of the above embodiments and comparative examples are prepared into slurry according to m(negative electrode active material): m(CMC, sodium carboxymethyl cellulose): m(SBR, styrene-butadiene latex): m(acetylene black) = 80:3:7:10; the slurry is coated on Cu foil, placed in an oven at 80°C, and baked in air atmosphere for 4 hours. The pole piece after drying is cut into discs with a diameter of 14 mm, and the mass of the negative electrode active material is 1.5 mg~2.5 mg. (The mass of the negative electrode active material: the pole piece after drying is weighed, then the mass of the copper foil is subtracted, and then multiplied by the mass percentage of the active substance).

[0130] The prepared disc was used as the positive electrode, the Li sheet was used as the negative electrode, and the electrolyte model was 3003F (commercial), and the button battery 2032 was assembled for testing. The above button battery was tested on a Land tester (manufacturer: Wuhan Xinnuo Electronics Co., Ltd.) at a test temperature of 25°C, with a constant current of 0.5C for charge and discharge, and a cut-off voltage of 0.005V-2.0V. Then, the lithium insertion capacity of the button battery at a constant current of 0.5C and the stability of 100 charge and discharge cycles were evaluated.

[0131] The test results are shown in Table 2 and Figure 4 .

[0132] Table 2

[0133]

[0134] As shown in Table 2, by comparing Examples 1 to 16 with Comparative Examples 1 to 2, it can be seen that the negative electrode active material provided in the present application improves the cycle capacity retention rate of the battery while ensuring the battery capacity performance and coulombic efficiency.

[0135] As shown in Table 2, by comparing Examples 1 to 16 with Comparative Example 1, it can be seen that silicon particles, as negative electrode active materials, have better discharge capacity at the initial stage of discharge, as shown by higher first-cycle reversible capacity and first-cycle coulombic efficiency; Figure 4 As shown, as the cycle progresses, the volume of the silicon particle material expands, causing the electrode to crack and pulverize, and the conductive connectivity between the silicon particles deteriorates, resulting in rapid capacity decay.

[0136] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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.

[0137] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the technical concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A negative electrode active material, characterized in that: The invention comprises silicon particles, one-dimensional carbon material, graphene carbon cage and polymer pyrolytic carbon, wherein the one-dimensional carbon material constitutes a three-dimensional carbon skeleton, the graphene carbon cage is coated on at least part of the surface of the three-dimensional carbon skeleton, and at least part of the polymer pyrolytic carbon anchors the silicon particles on the three-dimensional carbon skeleton.

2. The negative electrode active material according to claim 1, characterized in that At least a portion of the polymer pyrolytic carbon is dispersed within the graphene carbon cage.

3. The negative electrode active material according to claim 1, characterized in that Also included are coupling agents including amino groups and alkoxy groups.

4. The negative electrode active material according to claim 3, characterized in that The mass ratio of the silicon particles to the coupling agent is 100:(1-5).

5. The negative electrode active material according to any one of claims 1 to 4, characterized in that: The polymer pyrolytic carbon is a pyrolytic carbonization product of at least one of polyacrylonitrile, polyacrylic acid, polyethylene glycol, polyethylene oxide, polyvinyl alcohol, polyacrylamide, poly(methyl methacrylate), poly(methyl ether acrylate), derivatives thereof, and copolymers thereof.

6. The negative electrode active material according to any one of claims 1 to 4, characterized in that: The mass ratio of the silicon particles, the one-dimensional carbon material, the graphene carbon cage and the polymer pyrolytic carbon is (5-7.5):1:1:(0.5-3).

7. The negative electrode active material according to any one of claims 1 to 4, characterized in that: The particle size D of the negative electrode active material v 50 is 2nm~30nm.

8. A method for preparing a negative electrode active material, characterized in that: The following steps are involved: Silicon particles, one-dimensional carbon materials and polymers are added to a solvent and mixed, spray-dried and granulated, and then pyrolyzed and carbonized to obtain core particles; Coating at least a portion of the surface of the core particles with graphene carbon cages to obtain a negative electrode active material; The polymer is subjected to pyrolysis and carbonization treatment to form polymer pyrolytic carbon, the one-dimensional carbon material forms a three-dimensional carbon skeleton, the graphene carbon cage is coated on at least part of the surface of the three-dimensional carbon skeleton, and at least part of the polymer pyrolytic carbon anchors the silicon particles on the three-dimensional carbon skeleton.

9. A negative electrode plate, characterized in that: The invention comprises the negative electrode active material according to any one of claims 1 to 7, or the negative electrode active material prepared by the preparation method according to claim 8.

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

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