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

Abstract

The invention relates to the technical field of batteries, in particular to a negative active material and a preparation method thereof, a negative pole piece and a secondary battery. The negative electrode active material comprises: a substrate having a three-dimensional network structure, the material of the substrate comprising diamond and polyolefin; and the silicon-based material particles are at least partially filled in the three-dimensional network structure. According to the negative electrode active material provided by the invention, the material comprises the substrate of the diamond and the polyolefin as the substrate of the silicon carbon material, so that the cost is reduced, the three-dimensional network structure of the substrate is filled with the silicon-based material particles, and the three-dimensional network structure has a confinement effect on the silicon-based active material; the substrate can effectively restrain volume expansion of silicon-based material particles in the charging and discharging process, damage and pulverization of the material structure are reduced, and the cycle performance of the battery is improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, 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] Secondary batteries are widely used in consumer electronics, energy storage devices, electric vehicles and other fields due to their high energy density, long cycle life and low self-discharge rate.

[0003] Silicon-based negative electrode materials have great potential for improving energy density due to their excellent theoretical specific capacity (about 4200 mAh / g). However, silicon has problems such as huge volume change (>300%) during charging and discharging, poor conductivity, and inability to form a stable solid electrolyte layer (SEI). Based on the above shortcomings, people began to study silicon-carbon composite materials.

[0004] In traditional technology, silicon particles are loaded on the surface of a carbon substrate as a silicon-carbon composite material to improve the material's electrical conductivity and the battery's cycle performance.

[0005] However, the carbon substrates currently used mainly include resin carbon substrates, phenolic carbon substrates and petroleum coke carbon substrates. Resin carbon substrates have defective macropores, which are prone to structural collapse in the later stages of the cycle, affecting the battery's cycle performance; although the pore formation of phenolic carbon substrates is controllable, their cost is high; petroleum coke carbon substrates are low in cost, but their pore uniformity is poor, the material strength is poor, and their ability to mitigate silicon expansion is poor. 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 inhibit the volume expansion of silicon-based materials during the cycle process, reduce the destruction and pulverization of the material structure, and control the deposition amount of silicon-based materials. On the basis of ensuring the battery capacity, prevent local expansion caused by uneven deposition or excessive expansion caused by excessive deposition, thereby improving the cycle performance of the battery.

[0007] A first aspect of the present application provides a negative electrode active material, which includes: a substrate having a three-dimensional network structure, wherein the material of the substrate includes diamond and polyolefin; and silicon-based material particles at least partially filled in the three-dimensional network structure.

[0008] In some embodiments, the material of the substrate further includes a silane coupling agent.

[0009] In some embodiments, the negative electrode active material further includes: a carbon coating layer coated on at least a portion of the surface of the substrate.

[0010] In some embodiments, the mass ratio of diamond to polyolefin is 1:(0.05-0.2).

[0011] In some embodiments, the diamond particle size D v 50 is 10 nm~20 nm.

[0012] In some embodiments, the porosity of the substrate is between 20% and 90%.

[0013] In some embodiments, the particle size D of the negative electrode active material is v 50 is 5 μm~10 μm.

[0014] In some embodiments, the specific surface area of ​​the negative electrode active material is 2 m² / g to 7 m² / g.

[0015] The second aspect of the present application provides a method for preparing a negative electrode active material, which comprises the following steps: preparing diamond and polyolefin into a substrate having a three-dimensional network structure; and filling at least part of silicon-based material particles in the three-dimensional network structure.

[0016] In some embodiments, diamond and polyolefin are prepared into a substrate having a three-dimensional network structure, which specifically includes the following steps: adding diamond and polyolefin into a solvent to obtain a spinning solution; and electrospinning the spinning solution to obtain a substrate having a three-dimensional network structure.

[0017] In some embodiments, filling at least a portion of silicon-based material particles in the three-dimensional network structure specifically includes the following steps: transferring the substrate to a tube furnace, and introducing a silicon precursor for chemical vapor deposition.

[0018] The third aspect of the present application provides a negative electrode plate, which includes: a negative electrode collector; and a negative electrode active material layer, which is arranged on at least one side surface of the negative electrode collector, and the negative electrode active material layer is 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.

[0019] A fourth aspect of the present application provides a secondary battery, which includes the negative electrode plate provided by the third aspect.

[0020] Compared with the traditional technology, this application has at least the following beneficial effects:

[0021] The negative electrode active material provided by the present application reduces the cost by using a substrate including diamond and polyolefin as a substrate for silicon-carbon material, and filling silicon-based material particles in the three-dimensional network structure of the substrate. On the one hand, since diamond has excellent physical and chemical properties, and has both hardness and elastic modulus, combined with the confinement effect of the three-dimensional network structure of the substrate on the silicon-based active material, the substrate can effectively constrain the volume expansion of the silicon-based material particles during the charge and discharge process, reduce the damage and pulverization of the material structure, improve the cycle stability of the material, and thus improve the cycle performance of the battery; on the other hand, diamond and polyolefin are used as the substrate of the material, and the pore uniformity of the three-dimensional network structure is good, which is conducive to controlling the deposition amount of silicon-based material particles. On the basis of ensuring the battery capacity, local expansion caused by uneven deposition or excessive expansion caused by excessive deposition is prevented, thereby improving the cycle performance of the battery.

[0022] In addition, diamond has a high hardness and is not easy to be directly processed into a substrate material. Polyolefin can provide functional chemical bonds, and with the help of its excellent flexibility and processability, it can be used as a substrate forming skeleton to be compounded with diamond materials to form a substrate with a three-dimensional network structure, which reduces the difficulty of preparing the diamond substrate and is conducive to large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of a process for preparing a negative electrode active material in one embodiment of the present application. 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 a substrate and silicon-based material particles. The substrate has a three-dimensional network structure, and the material of the substrate includes diamond and polyolefin. The silicon-based material particles are at least partially filled in the three-dimensional network structure.

[0034] The negative electrode active material provided by the present application reduces the cost by using a substrate including diamond and polyolefin as a substrate for silicon-carbon material, and filling silicon-based material particles in the three-dimensional network structure of the substrate. On the one hand, since diamond has excellent physical and chemical properties, and has both hardness and elastic modulus, combined with the confinement effect of the three-dimensional network structure of the substrate on the silicon-based active material, the substrate can effectively constrain the volume expansion of the silicon-based material particles during the charge and discharge process, reduce the damage and pulverization of the material structure, improve the cycle stability of the material, and thus improve the cycle performance of the battery; on the other hand, diamond and polyolefin are used as the substrate of the material, and the pore uniformity of the three-dimensional network structure is good, which is conducive to controlling the deposition amount of silicon-based material particles. On the basis of ensuring the battery capacity, local expansion caused by uneven deposition or excessive expansion caused by excessive deposition is prevented, thereby improving the cycle performance of the battery.

[0035] In addition, diamond has a high hardness and is not easy to be directly processed into a substrate material. Polyolefin can provide functional chemical bonds, and with the help of its excellent flexibility and processability, it can be used as a substrate forming skeleton to be compounded with diamond materials to form a substrate with a three-dimensional network structure, which reduces the difficulty of preparing the diamond substrate and is conducive to large-scale industrial production.

[0036] In some embodiments, the mass ratio of diamond to polyolefin is 1:(0.05-0.2). For example, the mass ratio of diamond to polyolefin can be, but is not limited to, 1:0.05, 1:0.075, 1:0.1, 1:0.15, 1:0.175, 1:0.2.

[0037] In some embodiments, the diamond particle size D v 50 is 10 nm to 20 nm. For example, the particle size D of the diamond v 50 can be but not limited to 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm. Within the above particle size range, the diamond is located at the nanoscale, which is conducive to building a uniform three-dimensional mesh pore structure, reducing the defects of the substrate, improving the mechanical strength of the substrate, and enhancing the confinement effect of the substrate on the expansion of silicon particles, which is conducive to controlling the deposition amount of silicon-based material particles and further improving the cycle performance of the battery.

[0038] In some embodiments, the polyolefin includes one or more of polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene. Further, the polyolefin includes polypropylene.

[0039] In some embodiments, the porosity of the substrate is 20% to 90%. For example, the porosity of the substrate may be, but is not limited to, 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 90%. Within the above porosity range, the filling of silicon-based material particles can be facilitated on the basis of ensuring the mechanical properties of the substrate, and the confinement effect of the three-dimensional network structure of the substrate can be brought into play, thereby improving the capacity performance and cycle performance of the battery.

[0040] In some embodiments, the material of the substrate also includes a silane coupling agent. When the silane coupling agent is introduced into the substrate, on the one hand, the silane coupling agent can improve the surface activity of the material, enhance the adhesion of the substrate, and help improve the interface bonding strength between the silicon-based material particles and the substrate, and improve the stability of the negative electrode active material; on the other hand, the silane coupling agent can form a chemical cross-linking network in the substrate, improving the mechanical strength and heat resistance of the material.

[0041] In some embodiments, the silane coupling agent includes one or more of vinyl trimethoxy silane, vinyl ethoxy silane, vinyl methyl dimethoxy silane, vinyl tri (2-methoxyethoxy) silane, and methacryloxypropyl trimethoxy silane. Further, the silane coupling agent includes vinyl trimethoxy silane.

[0042] In some embodiments, the mass ratio of diamond to silane coupling agent is 1:(0.15-0.6). For example, the mass ratio of diamond to silane coupling agent can be, but is not limited to, 1:0.15, 1:0.2, 1:0.25, 1:0.3, 1:0.35, 1:0.4, 1:0.45, 1:0.5, 1:0.55, 1:0.6.

[0043] In some embodiments, the negative electrode active material further includes a carbon coating layer. The carbon coating layer is coated on at least part of the surface of the substrate. The carbon material has good electrical conductivity. When the carbon coating layer is coated on the surface of the substrate, a conductive layer can be formed on the surface of the substrate, thereby improving the electrical conductivity of the material; at the same time, the carbon coating layer can serve as a protective layer on the surface of the negative electrode active material to prevent it from direct contact with the external environment and oxidation.

[0044] In some embodiments, the carbon coating layer includes a carbon material obtained by heat-treating one or more of acetylene, methane, propylene, pitch and resin as a carbon precursor.

[0045] In some embodiments, the thickness of the carbon coating layer is 5 nm to 15 nm. For example, the thickness of the carbon coating layer can be, but is not limited to, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, and 15 nm.

[0046] In some embodiments, the particle size D of the negative electrode active material is v 50 is 5 μm to 10 μm. For example, the particle size D of the negative electrode active material is v 50 includes but is not limited to 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, and 10 μm.

[0047] In some embodiments, the specific surface area of ​​the negative electrode active material is 2 m² / g to 7 m² / g. Exemplarily, the specific surface area of ​​the negative electrode active material includes but is not limited to 2 m² / g, 3 m² / g, 4 m² / g, 5 m² / g, 6 m² / g, and 7 m² / g.

[0048] 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:

[0049] S1. Diamond and polyolefin are prepared into a substrate having a three-dimensional network structure.

[0050] S2. Fill at least part of the silicon-based material particles in the three-dimensional network structure.

[0051] The preparation method of the negative electrode active material provided in the present application reduces the cost by preparing diamond and polyolefin into a substrate with a three-dimensional network structure, and fills the silicon-based material particles in the three-dimensional network structure of the substrate. On the one hand, since diamond has excellent physical and chemical properties, and has both hardness and elastic modulus, combined with the confinement effect of the three-dimensional network structure of the substrate on the silicon-based active material, the substrate can effectively constrain the volume expansion of the silicon-based material particles during the charge and discharge process, reduce the damage and pulverization of the material structure, improve the cycle stability of the material, and thus improve the cycle performance of the battery; on the other hand, diamond and polyolefin are used as the material substrate, and the pore uniformity of the three-dimensional network structure is good, which is conducive to controlling the deposition amount of the silicon-based material particles. On the basis of ensuring the battery capacity, local expansion caused by uneven deposition or excessive expansion caused by excessive deposition is prevented, thereby improving the cycle performance of the battery.

[0052] In addition, diamond has a high hardness and is not easy to be directly processed into a substrate material. Polyolefin can provide functional chemical bonds, and with the help of its excellent flexibility and processability, it can be used as a substrate forming skeleton to be compounded with diamond materials to form a substrate with a three-dimensional network structure, which reduces the difficulty of preparing the diamond substrate and is conducive to large-scale industrial production.

[0053] In some implementation modes, step S1 specifically includes the following steps:

[0054] S11. Add diamond and polyolefin into a solvent to obtain a spinning solution.

[0055] S12, electrospinning the spinning solution to obtain a substrate with a three-dimensional network structure.

[0056] In some embodiments, in step S11, the diamond particle size D v 50 is 10 nm to 20 nm. For example, the particle size D of the diamond v 50 can be but not limited to 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm. In the above particle size range, diamond is at the nanoscale and has a large specific surface area. Therefore, it is easier to be evenly dispersed in the polyolefin solution during the electrospinning process, which helps to form uniform and continuous nanofibers during the spinning process, and then helps to build a uniform three-dimensional network structure, reduce the defects of the substrate, improve the mechanical strength of the substrate, enhance the confinement effect of the substrate on the expansion of silicon particles, and help to control the deposition amount of silicon-based material particles, and further improve the cycle performance of the battery.

[0057] In some implementation modes, step S11 specifically includes the following steps:

[0058] S111, placing diamond and polyolefin into a ball mill for ball milling to obtain a functionalized diamond material.

[0059] S112, adding the functionalized diamond material into the solvent to obtain a spinning solution.

[0060] In some embodiments, in step S11, the solvent includes a polar solvent and a volatile solvent. The polar solvent has high polarity and stability and can effectively dissolve polyolefin materials, while the volatile solvent dissolves polymers and adjusts the viscosity and fluidity of the solution through its volatility, thereby affecting the formation and properties of the fiber; the combined effect of the polar solvent and the volatile solvent helps to obtain a three-dimensional network structure with uniform structure and good continuity, thereby improving the mechanical strength of the substrate.

[0061] In some embodiments, the polar solvent includes at least one of N,N-dimethylacetamide (DMA) and N,N-dimethylformamide (DMF).

[0062] In some embodiments, the volatile solvent includes one or more of acetone, ethyl acetate, isopropanol, acetonitrile, cyclohexane and dichloromethane. Further, the volatile solvent includes acetone.

[0063] In some implementation modes, step S1 specifically includes the following steps:

[0064] S11, adding diamond, polyolefin and silane coupling agent into a solvent to obtain a spinning solution.

[0065] S12, electrospinning the spinning solution to obtain a substrate with a three-dimensional network structure.

[0066] In this way, the silane coupling agent is introduced into the spinning solution, and then a three-dimensional network structure substrate is prepared by electrospinning. On the one hand, the silane coupling agent can improve the surface activity of the material and enhance the adhesion of the substrate, which is beneficial to improve the interface bonding strength between the silicon-based material particles and the substrate and improve the stability of the negative electrode active material; on the other hand, the silane coupling agent can form a chemical cross-linking network in the substrate to improve the mechanical strength and heat resistance of the material.

[0067] In some embodiments, in step S11, after adding diamond and polyolefin into a solvent to obtain a spinning solution, the method further comprises the following steps: subjecting the spinning solution to ultrasonic stirring treatment.

[0068] In some embodiments, the speed of the ultrasonic stirring treatment is 150 rpm to 850 rpm.

[0069] In some embodiments, the ultrasonic stirring treatment time is 0.5h~36h.

[0070] In some embodiments, the temperature of the ultrasonic stirring treatment is 25°C to 60°C.

[0071] In some of the embodiments, in step S12, the conditions for electrospinning are: a voltage of 12 kV to 22 kV, a distance between the needle and the receiving axis of 10 cm to 20 cm, and a propulsion speed of the spinning solution of 0.1 mL / h to 1 mL / h.

[0072] The present application does not limit the method for implementing step S2. Any method that can fill silicon-based material particles into a three-dimensional network structure, such as chemical vapor deposition, magnetron sputtering, etc., can be used.

[0073] In some embodiments, step S2 specifically includes the following steps: transferring the substrate to a tube furnace, introducing a silicon precursor for chemical vapor deposition. Further, in step S2, the temperature of the chemical vapor deposition is 700°C to 1200°C, and the time of the chemical vapor deposition is 1h to 2h. The preparation method using chemical vapor deposition can more evenly deposit silicon-based material particles into a three-dimensional network structure.

[0074] In some embodiments, the silicon precursor includes one or more of monosilane, disilane, trisilane, halogenated silane, trichlorosilane, silole and its derivatives, silanol and its derivatives.

[0075] In some embodiments, after step S2, the method for preparing the negative electrode active material further comprises the following step: performing carbon coating treatment on the substrate.

[0076] In some embodiments, the substrate is subjected to a carbon coating treatment, specifically comprising the following steps: a carbon precursor is introduced into a tube furnace to perform chemical vapor deposition. Further, in the carbon coating treatment, the temperature of the chemical vapor deposition is 300°C to 1000°C, and the time of the chemical vapor deposition is 1h to 50h. Further, in the carbon coating treatment, the temperature of the chemical vapor deposition is 400°C to 900°C, and the time of the chemical vapor deposition is 12h to 48h.

[0077] In some embodiments, after step S2, the method for preparing the negative electrode active material further comprises the following step: crushing the material.

[0078] In some embodiments, after step S2, the method for preparing the negative electrode active material further comprises the following step: performing a grading process on the material.

[0079] The third aspect of the present application provides a negative electrode plate, which 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, and the negative electrode active material layer is the negative electrode active material provided in the first aspect or the negative electrode active material prepared by the preparation method provided in the second aspect.

[0080] In some embodiments, the negative electrode active material layer further includes graphite.

[0081] 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.).

[0082] 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).

[0083] 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.

[0084] 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)).

[0085] A fourth aspect of the present application provides a secondary battery, which includes the negative electrode plate provided by the third aspect.

[0086] In some embodiments, the secondary battery includes a lithium ion battery, a sodium ion battery, or a potassium ion battery.

[0087] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the charge and discharge process of a secondary battery, 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.

[0088] 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.

[0089] 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.

[0090] 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.).

[0091] 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.

[0092] As an example, when the positive electrode plate is used in a lithium-ion battery, the positive electrode active material may adopt 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. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.8 Co 0.15 Al 0.05 O2) 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, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0100] In some of the embodiments, when the secondary 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] In some embodiments, the battery cell may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0107] 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.

[0108] In some embodiments, the secondary battery provided in the present application can be used as a power source for an electrical device, or as an energy storage unit for an electrical device. Electrical devices may include mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto. Among them, mobile devices may be, for example, mobile phones, laptop computers, 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 thereto.

[0109] The present application will be further described below with reference to specific embodiments and comparative examples.

[0110] Example 1

[0111] Negative electrode active material:

[0112] (1) Add 10 g of diamond, 2 g of polypropylene and 5 g of vinyltrimethoxysilane into a ball mill and mill for 6 h to obtain a functionalized diamond material.

[0113] Among them, the diamond particle size D v 50 is 15 nm, and the mass ratio of diamond to polyolefin is 1:0.2.

[0114] (2) 5 g of functionalized nanodiamond material was added to a mixed solvent of 2.5 g of N,N-dimethylformamide and 10 g of acetone to obtain a spinning solution, which was then subjected to ultrasonic stirring treatment (ultrasonic stirring treatment speed was 800 rpm; time was 30 min; temperature was 25 °C). After ultrasonic treatment, electrospinning was carried out under the conditions of a voltage of 15 kV, a distance between the needle and the receiving axis of 15 cm, and a propulsion speed of the spinning solution of 0.5 mL / h to obtain a substrate with a three-dimensional network structure.

[0115] Among them, the porosity of the substrate is 75%.

[0116] (3) 2 g of the substrate was added into a tube furnace, monosilane gas was introduced, and chemical vapor deposition was performed at 1000°C for 1.5 h to fill the silicon-based material particles into a three-dimensional network structure.

[0117] (4) Then, methane gas was introduced and chemical vapor deposition was carried out at 800°C for 24 hours to obtain a carbon coating layer. After cooling to room temperature, the obtained material was crushed and graded to obtain a negative electrode active material.

[0118] The thickness of the carbon coating layer is 10 nm.

[0119] Negative electrode:

[0120] Graphite, the above-mentioned negative electrode active material, PAA, and SBR are mixed in a mass ratio of 7.5:2.5:0.5:0.1, and deionized water is added. After stirring evenly and degassing, a negative electrode slurry is obtained. The negative electrode slurry is applied to copper foil, dried, and roll-pressed to obtain a negative electrode sheet.

[0121] Secondary battery:

[0122] Polyvinylidene fluoride, carbon nanotubes (CNT), conductive carbon black (SP), and positive electrode material NCM811 are added to N-methylpyrrolidone in a mass ratio of 1.1:0.6:1.1:97.2, and stirred evenly to obtain a positive electrode slurry; the positive electrode slurry is coated on an aluminum foil, and dried, cold pressed and punched in sequence to obtain a positive electrode plate; a polyethylene separator is placed between the positive electrode plate and the above-mentioned negative electrode plate, and stacked in a Z shape to obtain a battery cell, which is placed in a packaging shell, and an electrolyte (1 mol / L LiPF6 of ethylene carbonate, dimethyl carbonate, ethylene glycol propyl ether and ethyl methyl carbonate (wt% = 2:1:4:3) and 3.0% FEC) is injected to obtain a secondary battery.

[0123] Example 2

[0124] The preparation method of the negative electrode active material, negative electrode plate and secondary battery provided in this embodiment is basically the same as that in embodiment 1, except that:

[0125] In step (1), the amount of polypropylene is 0.5 g, the mass ratio of diamond to polyolefin is 1:0.05, and the porosity of the substrate is 85%.

[0126] Example 3

[0127] The preparation method of the negative electrode active material, negative electrode plate and secondary battery provided in this embodiment is basically the same as that in embodiment 1, except that:

[0128] In step (1), the diamond particle size D v 50 is 20 nm, and the porosity of the substrate is 23%.

[0129] Example 4

[0130] The preparation method of the negative electrode active material, negative electrode plate and secondary battery provided in this embodiment is basically the same as that in embodiment 1, except that:

[0131] In step (1), the diamond particle size D v 50 is 10 nm, and the porosity of the substrate is 82%.

[0132] Example 5

[0133] The preparation method of the negative electrode active material, negative electrode plate and secondary battery provided in this embodiment is basically the same as that in embodiment 1, except that:

[0134] In step (1), no vinyltrimethoxysilane was added and the porosity of the substrate was 20%.

[0135] Example 6

[0136] The preparation method of the negative electrode active material, negative electrode plate and secondary battery provided in this embodiment is basically the same as that in embodiment 1, except that:

[0137] In step (4), no methane gas is introduced, that is, no carbon coating is performed, and the material is directly crushed and graded to obtain the negative electrode active material.

[0138] Example 7

[0139] The preparation method of the negative electrode active material, negative electrode plate and secondary battery provided in this embodiment is basically the same as that in embodiment 1, except that:

[0140] In step (1), the amount of polypropylene is 3 g, the mass ratio of diamond to polyolefin is 1:0.3, and the porosity of the substrate is 15%.

[0141] Example 8

[0142] The preparation method of the negative electrode active material, negative electrode plate and secondary battery provided in this embodiment is basically the same as that in embodiment 1, except that:

[0143] In step (1), the diamond particle size D v 50 is 2 μm, and the porosity of the substrate is 93%.

[0144] Comparative Example 1

[0145] The preparation method of the negative electrode active material, negative electrode plate and secondary battery provided in this comparative example is basically the same as that in Example 1, except that:

[0146] Negative electrode active material:

[0147] Silicon-carbon material (manufacturer: Shenghua New Materials; model: SH-S02; substrate is biomass material).

[0148] Performance Testing

[0149] (1) Pole expansion rate test

[0150] The secondary batteries of the above-mentioned embodiments and comparative examples were charged at a constant current of 0.33C to a rated charging voltage of 4.2V, and then charged at a constant voltage to a current of 0.05C. After disassembly, the negative electrode expansion rate was tested, where the negative electrode expansion rate = (full electrode sheet thickness - rolled electrode sheet thickness) / (rolled electrode sheet thickness - foil thickness). The test results are shown in Table 1.

[0151] (2) Cycle life test

[0152] The secondary batteries prepared in the above examples and comparative examples were charged at a constant current of 1C to the rated charging voltage, then charged at a constant voltage to a current of 0.05C, left to stand for 10 minutes, and then discharged at a constant current of 1C to the rated discharge voltage, and the initial capacity was recorded as C0; then charged at a constant current of 1C0 to the rated charging voltage, then charged at a constant voltage to a current of 0.05C, left to stand for 10 minutes, and discharged at 1C0, and the discharge capacity C of each cycle was recorded. n , until the cycle capacity retention rate (C n / C0×100%) is 80%, and the number of cycles is recorded. The test results are shown in Table 1.

[0153] Table 1

[0154]

[0155] As shown in Table 1, by comparing Examples 1 to 8 with Comparative Example 1, it can be seen that the negative electrode active material provided in the present application reduces the expansion rate of the negative electrode sheet and improves the cycle performance of the battery.

[0156] 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.

[0157] 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: include: A substrate having a three-dimensional network structure, wherein the material of the substrate comprises diamond and polyolefin; as well as Silicon-based material particles are at least partially filled in the three-dimensional network structure.

2. The negative electrode active material according to claim 1, characterized in that The material of the substrate further includes a silane coupling agent.

3. The negative electrode active material according to claim 1, characterized in that Also includes: The carbon coating layer is coated on at least a portion of the surface of the substrate.

4. The negative electrode active material according to any one of claims 1 to 3, characterized in that: The substrate satisfies at least one of the following conditions: (1) The mass ratio of the diamond to the polyolefin is 1:(0.05-0.2); (2) The diamond particle size D v 50 is 10 nm~20 nm; (3) The porosity of the substrate is 20% to 90%.

5. The negative electrode active material according to any one of claims 1 to 3, characterized in that: At least one of the following conditions is met: (1) Particle size D of the negative electrode active material v 50 is 5 μm~10 μm; (2) The specific surface area of ​​the negative electrode active material is 2 m² / g to 7 m² / g.

6. A method for preparing a negative electrode active material, characterized in that: The following steps are involved: Diamond and polyolefin are prepared into a substrate having a three-dimensional network structure; At least part of the silicon-based material particles are filled in the three-dimensional network structure.

7. The preparation method according to claim 6, characterized in that: The diamond and polyolefin are prepared into a substrate having a three-dimensional network structure, specifically comprising the following steps: Adding diamond and polyolefin into a solvent to obtain a spinning solution; The spinning solution is subjected to electrostatic spinning to obtain a substrate with a three-dimensional network structure.

8. The preparation method according to claim 6, characterized in that: Filling at least part of the silicon-based material particles in the three-dimensional network structure specifically comprises the following steps: The substrate was transferred to a tube furnace and silicon precursor was introduced for chemical vapor deposition.

9. A negative electrode plate, characterized in that: include: Anode current collector; as well as A negative electrode active material layer is disposed on at least one side of the negative electrode current collector, wherein the negative electrode active material layer comprises the negative electrode active material according to any one of claims 1 to 5 or the negative electrode active material prepared by the preparation method according to any one of claims 6 to 8.

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

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