Secondary battery and electric device

Abstract

The invention discloses a secondary battery and a power utilization device, and belongs to the technical field of batteries, the secondary battery is charged to 4.53 V at 0.5 C and the cut-off current is 0.05 C at 45 DEG C, the secondary battery is discharged to 3.0 V at 0.7 C and the cut-off current is 0.05 C, circulation is performed for 300 cls, and the thickness of a reaction layer is smaller than or equal to 500 nm; the secondary battery comprises a negative electrode plate, the negative electrode plate comprises a negative electrode active material, the negative electrode active material comprises an inner core and a carbon coating layer arranged on the outer surface of the inner core, the inner core comprises a porous carbon material and silicon particles deposited in pores of the porous carbon material, the porous carbon material contains doping elements, and the doping elements are doped in the silicon particles. The doping elements comprise at least two of N, P, S and B. The negative electrode active material disclosed by the invention can inhibit volume expansion of the negative electrode active material, and the cycling stability of the secondary battery is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a secondary battery and an electrical device. Background Art

[0002] Lithium-ion secondary batteries are the primary energy storage device in today's new energy sector. Carbon materials are the primary commercial anode material, and the thermal stability of silicon-carbon anode materials in battery cells is a key issue in current research and application. While silicon-carbon anodes offer advantages such as high energy density and fast charging performance, their thermal stability remains challenging, particularly due to potential safety issues in high-temperature environments.

[0003] Silicon expands by about 300% in volume during the charging and discharging process, which is much higher than the 16% of graphite. This will cause the electrode structure to rupture, the active material to pulverize, and increase the risk of local hot spots, thereby affecting the overall thermal stability.

[0004] In view of this, this application is filed. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a secondary battery and an electrical device. The negative electrode active material described in this application can inhibit the volume expansion of the negative electrode active material and significantly improve the cycle stability of the secondary battery.

[0006] To achieve the above objectives, the first aspect of the present application provides a secondary battery, which is charged to 4.53V at 0.5C at 45°C, with a cut-off current of 0.05C, discharged to 3.0V at 0.7C, with a cut-off current of 0.05C, and cycled for 300cls, with a reaction layer thickness of ≤500nm.

[0007] The secondary battery includes a negative electrode plate, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the negative electrode active material layer includes a negative electrode active material, the negative electrode active material includes a core and a carbon coating layer disposed on the outer surface of the core, the core includes a porous carbon material and silicon particles deposited in the pores of the porous carbon material, the porous carbon material contains a doping element, and the doping element includes at least two of N, P, S, and B;

[0008] The negative electrode active material satisfies: 1.1≤X / M≤3;

[0009] Wherein, X% is the mass percentage of the doping element in the core;

[0010] Mg / cm 3 is the compaction density of the negative electrode active material layer.

[0011] As an embodiment of the present application, at least one of the following (I) to (II) is satisfied:

[0012] (Ⅰ)2≤X≤5;

[0013] (Ⅱ)1.5≤M≤1.9.

[0014] As an embodiment of the present application, the doping elements include N, P and A elements, the A element includes at least S and B, and the mass ratio of N, P and A elements in the core is 2: (1~2): (1~2).

[0015] The mass ratio of N, P and A elements in the core is 2:(1):(1).

[0016] As an implementation scheme of the present application, the following conditions are satisfied: 2≤X / Y≤5.05;

[0017] Wherein, Y is the sphericity of the negative electrode active material.

[0018] As an implementation scheme of the present application, Y satisfies: 0.8≤Y≤1.

[0019] As an embodiment of the present application, the negative electrode active material satisfies: 0.04≤X / Z≤0.12;

[0020] Wherein, Z% is the mass percentage of the silicon particles in the core.

[0021] As an implementation scheme of the present application, Z satisfies: 45≤Z≤52.

[0022] As an embodiment of the present application, the D of the negative electrode active material V 50 particle size of 5 to 10 μm; and / or

[0023] The thickness of the carbon coating layer is 30-35 nm.

[0024] A second aspect of the present application provides an electrical device, comprising the secondary battery described above, wherein the secondary battery serves as a power supply for the electrical device.

[0025] The beneficial effects of the present invention are as follows: the negative electrode active material of the present application is a core-shell structure, the core is a porous carbon material containing at least two elements of N, P, S, and B and silicon particles deposited in the pores of the porous carbon material, and the outer shell is a carbon coating layer. By controlling 1.1≤X / M≤3, the reaction active sites can be effectively increased, and the conductivity and conductivity uniformity of the negative electrode active material can be effectively improved. At the same time, at 45°C, the battery is charged to 4.53V at 0.5C, the cutoff current is 0.05C, and the battery is discharged to 3.0V at 0.7C. The cutoff rate is 0.05C and the cycle is repeated for 300cls. The thickness of the reaction layer is ≤500nm, which reduces the polarization during the charge and discharge process and improves the reaction uniformity, improves the continuity of the heat conduction path, thereby enhancing the heat conduction capacity, avoiding cracks, thereby avoiding internal short circuits, reducing the risk of local overheating, and improving the thermal stability of the silicon-carbon negative electrode. The stress distribution during the charge and discharge process is more uniform, inhibiting the volume expansion of the negative electrode active material, and significantly improving the cycle stability of the secondary battery. DETAILED DESCRIPTION

[0026] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0027] In this 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.

[0028] In this application, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0029] In the present application, there is no particular limitation on the specific dispersion and stirring treatment methods.

[0030] Unless otherwise specified, the components, raw materials or instruments used in the embodiments and comparative examples of the present invention are all commercially available raw materials or instruments, and the components and raw materials used in each parallel experiment are all of the same kind.

[0031] The embodiment of the application provides a secondary battery, which is charged at 0.5C to 4.53V at 45 DEG C, the cutoff current is 0.05C, discharged at 0.7C to 3.0V, the cutoff current is 0.05C, and the reaction layer thickness is less than or equal to 500nm.

[0032] The secondary battery comprises a negative electrode sheet, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector, the negative electrode active material layer comprises a negative electrode active material, the negative electrode active material comprises a core and a carbon coating layer arranged on the outer surface of the core, the core comprises a porous carbon material and silicon particles deposited in the pores of the porous carbon material, and the porous carbon material contains a doping element, and the doping element comprises at least two of N, P, S and B.

[0033] The negative electrode active material satisfies 1.1 <= X / M <= 3.

[0034] X% is the mass percentage content of the doping element in the core.

[0035] Mg / cm 3 The compaction density of the negative electrode active material layer.

[0036] The negative electrode active material of the application is a core-shell structure, the core comprises a porous carbon material containing at least two of N, P, S and B and silicon particles deposited in the pores of the porous carbon material, and the shell is a carbon coating layer; by controlling 1.1 <= X / M <= 3, the reaction active sites can be effectively improved, the conductivity and the uniformity of the negative electrode active material can be effectively improved, the polarization in the charging and discharging process can be reduced, the reaction uniformity can be improved, the continuity of the heat conduction path can be improved, the heat conduction capacity can be enhanced, cracks can be avoided, internal short circuits can be avoided, the risk of local overheating can be reduced, the thermal stability of the silicon-carbon negative electrode can be improved, the stress distribution is more uniform in the charging and discharging process, the volume expansion of the negative electrode active material can be inhibited, and the cycle stability of the secondary battery can be significantly improved.

[0037] In some embodiments, 2.06 <= X / M <= 2.35.

[0038] In some embodiments, 2≤X≤5, for example, it can be 2, 2.5, 3, 3.5, 4, 4.5, 5 or a range consisting of any two values ​​therein. By controlling the mass percentage of the doping element in the core within this range, more active sites can be provided, the conductivity and hydrophilicity of the negative electrode active material can be improved, the volume expansion of the negative electrode active material can be inhibited, the conductivity of the negative electrode active material can be improved, more lithium ion storage space can be provided, and the cycle stability of the secondary battery can be further improved.

[0039] In some embodiments, 1.5≤M≤1.9, for example, it can be 1.5, 1.6, 1.7, 1.8, 1.9 or a range consisting of any two values ​​therein. By controlling the compaction density of the negative electrode active material layer within this range, the stability of the negative electrode active material can be further improved, and breakage during the rolling process can be avoided. The electrical and thermal conductivity continuity of the negative electrode active material can be improved, the thermal conductivity performance can be improved, cracks can be avoided, local overheating can be reduced, and the thermal stability of the negative electrode active material can be further improved, thereby effectively improving the cycle stability of the secondary battery.

[0040] In some embodiments, 1.5≤M≤1.8.

[0041] The test method for the compaction density of the negative electrode active material layer is:

[0042] (1) Use a cutting tool (circular or square mold) to cut a standard sample (such as a 14mm diameter circular electrode) from the rolled electrode. The coating area is S. Use a precision electronic balance (accuracy 0.1mg) to weigh the total mass m of the cut electrode. 总 (Note: If the electrode coating amount is low, multiple pieces can be measured to improve accuracy).

[0043] (2) Use a micrometer (accuracy 1 μm) or a laser thickness gauge to measure the thickness at multiple locations (at least 5 points) on the electrode and take the average value T 总 . Measure the thickness of the blank current collector (copper foil / aluminum foil) alone.

[0044] T 集流体 , then the compacted thickness of the negative electrode active material layer t = T 总 -T 集流体 ;

[0045] (3) Calculate the mass of the negative electrode active material layer (m): Given the mass of the current collector m 集流体 (obtained by weighing the blank foil) m = mtotal - m 集流体 .

[0046] (4) Calculate the compacted density M: M = m / (S*t);

[0047] t: thickness of the negative electrode active material layer after compaction (cm);

[0048] S: Area of ​​negative electrode active material layer coating (cm 2 );

[0049] m: mass of the negative electrode active material layer (g).

[0050] The doping elements include N, P and A elements, the A element includes at least S and B, and the mass ratio of the N, P and A elements in the core is 2: (1-2): (1-2). By controlling the mass ratio of the N, P and A elements in the core within this range, the charge transport effect is improved through the synergistic effect of the N, P and A elements, and more effective reaction sites are generated, thereby overcoming the steric hindrance effect, suppressing the volume expansion of the negative electrode active material, and significantly improving the cycle stability of the secondary battery.

[0051] The test method for the mass percentage of N, P and A elements in the kernel is as follows:

[0052] The negative electrode was immersed in N-methylpyrrolidone (NMP) (60°C with ultrasonication for 1-2 hours) to dissolve the PVDF and other binders. Residual NMP was removed by washing with acetone or ethanol. After drying, the sample was sintered at 600°C. X-ray photoelectron spectroscopy (XPS) was used to analyze the doping elements.

[0053] In some embodiments, the following is satisfied: 2≤X / Y≤5.05, for example, it can be 2, 3, 4, 5, 5.05 or a range consisting of any two values ​​therein. By controlling X / Y within this range, the fluidity of the negative electrode active material can be improved, which is beneficial to subsequent coating and rolling, and the chemical bonding between the silicon-carbon material and the binder (such as PVDF, CMC) is enhanced. At the same time, a higher sphericity is controlled to reduce the gaps between the active material particles. The two work together to greatly improve the adhesion of the slurry, reduce peeling after coating and drying, and thus improve the cycle stability of the secondary battery.

[0054] Wherein, Y is the sphericity of the negative electrode active material.

[0055] In some embodiments, 2.11≤X / Y≤4.71 is satisfied.

[0056] In some embodiments, Y satisfies: 0.8≤Y≤1, for example, it can be 0.8, 0.85, 0.9, 0.95, 1 or a range consisting of any two values ​​therein. By controlling Y within this range, the cycle stability of the secondary battery can be further improved.

[0057] In some embodiments, Y satisfies: 0.85≤Y≤0.99.

[0058] The sphericity of the negative electrode active material is tested as follows:

[0059] First, the lithium-ion battery is disassembled, the negative electrode sheet is taken out, and it is soaked and rinsed with dimethyl carbonate solvent to remove the lithium salt and electrolyte solvent on the negative electrode sheet. After drying, the cross-section of the negative electrode sheet is obtained by argon ion cutting. Under the backscattering mode of the scanning electron microscope, the silicon-carbon particles show a brighter contrast, and the graphite particles are darker. Therefore, the image of each bright spot particle in the SEM backscattering mode photo of the negative electrode sheet at a certain magnification (such as 2500 times) can be calculated by image processing software (such as ImagePro Plus) to obtain the perimeter and area of ​​each silicon-carbon particle. The perimeter equivalent radius r1 and area equivalent radius r2 of each particle are calculated respectively, and the sphericity of each particle Y = r2 / r1. The sphericity of each particle is then weighted averaged to obtain the average sphericity of the silicon-carbon particles in the cross-section of the negative electrode sheet.

[0060] In some embodiments, the following is satisfied: 0.04≤X / Z≤0.12, for example, it can be 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12 or a range consisting of any two values ​​therein. By controlling X / Z within this range, the silicon particles can be deposited more evenly, increasing the silicon content can increase the capacity, promote the rapid insertion / deinsertion of lithium ions, optimize the lithium ion migration path, promote the uniform distribution of lithium ions, reduce lithium plating caused by excessive local current density, effectively reduce the formation of lithium dendrites, and improve the cycle stability of the secondary battery.

[0061] Wherein, Z% is the mass percentage of the silicon particles in the core.

[0062] In some embodiments, the Z satisfies: 45≤Z≤52, for example, it can be 45, 46, 47, 48, 49, 50, 51, 52 or a range consisting of any two values ​​therein. By controlling Z within this range, the capacity of the secondary battery can be effectively increased, the insertion / deinsertion of lithium ions can be promoted, and the cycle stability of the secondary battery can be further improved.

[0063] The test method for the mass percentage of silicon particles in the core is as follows:

[0064] The mass content of elemental silicon in the silicon-carbon particles of the present invention, based on the total mass of the silicon-carbon particles, can be obtained by SEM-EDS analysis of the cross section of the silicon-carbon particles.

[0065] In some embodiments, the D of the negative electrode active material VThe particle size is 5 to 10 μm, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or a range consisting of any two values ​​thereof. By controlling the D V 50 Particle size is within this range, and appropriate Dv50 enhances the bonding force between particles and binder, improving structural stability and electrochemical performance.

[0066] It should be noted that the test of Dv50 mentioned in this application refers to GB-T 19077-2016 and is tested using a particle size analysis laser diffractometer.

[0067] In some embodiments, the thickness of the carbon coating layer is 30-35 nm, for example, 30 nm, 31 nm, 32 nm, 33 nm, 34 nm, 35 nm, or a range consisting of any two of these values. By controlling the thickness of the carbon coating layer within this range, electronic conductivity can be improved and electrode polarization can be reduced. A moderate carbon layer thickness (e.g., 20-40 nm) can provide a buffer space and inhibit particle breakage.

[0068] In some embodiments, the preparation method of the negative electrode active material is:

[0069] (1) Add phenol and formaldehyde solution into a beaker, use hydrochloric acid as a catalyst, stir and heat to reflux state, react for 1 hour, add dispersant polyvinyl alcohol aqueous solution, stir and disperse for 40 minutes at a speed of 300 r / min, then add curing agent hexamethylenetetramine, stop heating when yellow particles appear, cool, filter, wash with water and dry after the reaction is completed to obtain yellow phenolic resin balls.

[0070] (2) The phenolic resin is spheroidized into carbon material.

[0071] (3) uniformly mixing the carbon material, potassium hydroxide, ammonium dihydrogen phosphate, potassium carbonate, and thiourea, sintering, washing, and drying to obtain a precursor;

[0072] (4) introducing a first mixed gas, performing a first heat treatment, introducing a second mixed gas, performing a second heat treatment, and sintering to obtain a negative electrode active material.

[0073] In some embodiments, the molar ratio of the carbon material, potassium hydroxide, ammonium dihydrogen phosphate, potassium carbonate, and thiourea / boric acid is 1:1:(0.01-0.07):(0.01-0.07):(0.01-0.07).

[0074] In some embodiments, the molar ratio of phenol to formaldehyde in step (1) is 1:(0.6-0.95).

[0075] In some embodiments, the carbonization temperature in step (2) is 800-1200° C., and the time is 1-5 hours.

[0076] In some embodiments, washing is performed with a 0.5-5 mol / L hydrochloric acid solution until the solution becomes neutral.

[0077] In some embodiments, the drying temperature is 60-80° C., and the drying time is 10-24 hours.

[0078] In some embodiments, the first mixed gas includes monosilane gas and shielding gas, the volume ratio of the monosilane gas to the shielding gas is 1:1, and the flow rate of the first mixed gas is 100-200 sccm.

[0079] In some embodiments, the first heat treatment temperature is 400-600°C and the time is 8-20 hours.

[0080] In some embodiments, the second mixed gas includes acetylene gas and shielding gas, the volume ratio of the acetylene gas to the shielding gas is 1:1, and the flow rate of the second mixed gas is 50-200 sccm.

[0081] In some embodiments, the second heat treatment temperature is 500-600°C and the time is 10h. In some embodiments, the sintering temperature in step (3) is 700°C and the time is 2h.

[0082] In some embodiments, the carbon material is prepared by carbonizing a phenolic resin, washing it, and drying it to obtain the carbon material.

[0083] In some embodiments, the carbonization temperature is 800-1200°C and the time is 1-5 hours.

[0084] In some embodiments, washing is performed with a 0.5-5 mol / L hydrochloric acid solution until the solution becomes neutral.

[0085] In some embodiments, the drying temperature is 60-80° C., and the drying time is 10-24 hours.

[0086] In the present application, there is no particular limitation on the negative electrode current collector, as long as it can achieve the purpose of the present application. For example, it can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or a composite current collector.

[0087] In some embodiments, the negative electrode active material layer further includes a conductive agent and a negative electrode binder.

[0088] In some embodiments, the secondary battery further includes a positive electrode sheet, the positive electrode sheet including a positive electrode collector and a positive electrode active material layer disposed on at least one surface of the positive electrode collector, the positive electrode active material layer including a positive electrode active material.

[0089] In some embodiments, the positive electrode active material may be a positive electrode active material for a secondary battery that is well known in the art. As non-limiting examples, the positive electrode active material may include lithium-containing phosphates, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials or substances, and other traditional materials or substances that can be used as positive electrode active materials for secondary batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, non-limiting examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds.

[0090] In some embodiments, the type of the positive electrode current collector is not particularly limited, and the positive electrode current collector can be any material known to be suitable for use as a positive electrode current collector.

[0091] In some embodiments, the positive electrode current collector includes metal materials such as aluminum, stainless steel, nickel plating, titanium, tantalum, and carbon materials such as carbon cloth and carbon paper.

[0092] The form of the positive electrode current collector is not particularly limited. When the positive electrode current collector is a metal material, the positive electrode current collector may be in the form of metal foil, metal cylinder, metal strip coil, metal plate, metal foil, metal mesh, stamped metal, foamed metal, etc. When the positive electrode current collector is a carbon material, the positive electrode current collector may be in the form of, but not limited to, carbon plate, carbon film, carbon cylinder, etc.

[0093] In some embodiments, the positive electrode active material layer further includes a conductive agent and a positive electrode binder.

[0094] In some embodiments, the type of the conductive agent mentioned in the present application is not limited, and known conductive agents can be used.

[0095] In some embodiments, the conductive agent includes at least one of carbon materials such as acetylene black, needle coke, carbon nanotubes, and graphene.

[0096] In some embodiments, the type of the binder mentioned in this application is not limited, and known binders can be used.

[0097] In some embodiments, the positive electrode binder and the negative electrode binder mentioned independently include at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose, styrene-butadiene rubber, nitrile rubber, fluororubber, isoprene rubber, polybutadiene rubber, ethylene-propylene rubber, styrene-butadiene-styrene block copolymer or its hydride, ethylene-propylene-diene terpolymer, styrene-ethylene-butadiene-ethylene copolymer, styrene-isoprene-styrene block copolymer, syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymer.

[0098] In some embodiments, a separator is typically disposed between the positive and negative electrode plates to prevent short circuits. The type of separator is not particularly limited and can be selected based on actual needs. The separator can be a polypropylene film, a polyethylene film, a polyvinylidene fluoride film, a spandex film, an aramid film, or a multilayer composite film modified with a coating.

[0099] In some embodiments, the secondary battery further comprises an electrolyte, and the type of the electrolyte is not specifically limited. The electrolyte comprises an electrolyte salt and an organic solvent, and the specific types of the electrolyte salt and the organic solvent are not specifically limited and can be selected according to actual needs.

[0100] In one embodiment, the organic solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0101] In one embodiment, the lithium salt includes but is not limited to at least one of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium fluoride (LiF), and lithium trifluoromethanesulfonate (LiCF3SO3).

[0102] In one embodiment, the lithium salt comprises LiPF6.

[0103] In one embodiment, the concentration of the lithium salt in the electrolyte can be 0.5 to 2 mol / L, for example, 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L or a range consisting of any two values ​​therein.

[0104] In one embodiment, the electrolyte may further include additives. The type of the additives is not particularly limited and may be film-forming additives for the positive electrode and / or negative electrode, or additives that can improve certain battery properties, such as additives that improve the high or low temperature performance of the battery.

[0105] In some embodiments, the secondary battery may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0106] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0107] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or other shapes.

[0108] An embodiment of the present application provides an electric device, comprising the secondary battery described above, wherein the secondary battery serves as a power supply for the electric device.

[0109] Exemplarily, the above-mentioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.

[0110] The present application is further described below with specific examples:

[0111] Example 1

[0112] A method for preparing a secondary battery comprises the following steps:

[0113] (1) Preparation of negative electrode active materials:

[0114] S1: Add phenol and formaldehyde solution into a beaker, use hydrochloric acid as a catalyst (the amount is 10wt% of the formaldehyde solution), stir and heat to reflux state, react for 1 hour, add dispersant polyvinyl alcohol aqueous solution, stir and disperse for 40 minutes at a speed of 300r / min, then add 10at.% curing agent hexamethylenetetramine, the molar ratio of formaldehyde to phenol is 1:0.9, stop heating when yellow particles appear, cool, filter, wash with water, and dry after the reaction is completed to obtain phenolic resin balls with a sphericity of 0.99.

[0115] S2: The phenolic resin balls were carbonized at 1000°C for 2 h, cooled to room temperature, washed with 1 mol / L HCl until neutral, and vacuum dried at 70°C for 20 h to obtain the carbon material;

[0116] S3: The above carbon material was mixed with KOH, NH4H2PO4, potassium carbonate (K2CO3), and CH4N2S in a mortar at a substance amount of 1:1:0.046:0.046:0.046, and the mixed powder was transferred to an alumina crucible. The crucible was then transferred to a tube furnace, and protective gas N2 was introduced at a flow rate of 100 sccm. The mixture was sintered at 800°C for 2h, cooled to room temperature, washed with 1 mol / L HCl to neutrality, and vacuum dried at 70°C for 16h to obtain a precursor;

[0117] S4: The precursor prepared above was transferred to a fluidized bed, and SiH4 gas and protective gas N2 (volume ratio of 1:1) were introduced at a flow rate of 100 sccm, 500°C, and 10 h. The gas flow rate was controlled to uniformly deposit silicon into the porous carbon.

[0118] S5: Continue to introduce C2H2 and protective gas N2 (volume ratio of 1:1) into the above materials at a flow rate of 100 sccm and a temperature control of 500℃ for 1 hour for high-temperature carbon pre-coating. Then transfer the materials to a rotary kiln for high-temperature carbon secondary coating at a flow rate of 100 sccm and a temperature control of 500℃ for 6 hours to obtain the negative electrode active material.

[0119] The parameters of the negative electrode active materials are shown in Tables 1 and 2.

[0120] (2) Preparation of negative electrode sheet: The negative electrode active material, graphite, and binder PVDF (polyvinylidene fluoride) were mixed in a mass ratio of 9:90:1, and solvent NMP was added. The solid content of the negative electrode slurry was 40%. The mixture was stirred in a vacuum mixer until the system became uniform. The negative electrode slurry was evenly coated on a copper foil (6 μm), vacuum dried at 70 ° C for 24 h, and rolled with a roller press until the compaction density of the negative electrode active material layer was 1.70 g / cm 3 , cold pressing and cutting to obtain the negative electrode sheet.

[0121] (3) Preparation of positive electrode sheets: The positive electrode active material LiCoO2, the conductive agent acetylene black, and the binder PVDF were mixed in a mass ratio of 97:2:1, and the solvent NMP was added. The positive electrode slurry with a solid content of 74% was stirred under the action of a vacuum mixer until the system became uniform to obtain a positive electrode slurry; the solid content was 74%, and the positive electrode slurry was evenly coated on the current collector aluminum foil (9μm), vacuum dried at 70°C overnight, cold pressed, and cut to obtain positive electrode sheets.

[0122] (4) Preparation of electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a LiPF6 concentration of 1 mol / L.

[0123] (5) The diaphragm uses a ceramic coating diaphragm with a total thickness of 6.5μm and 0.75μm double-sided Al2O3 coated PE diaphragm.

[0124] (6) Assembly of secondary batteries: stack the above-mentioned positive electrode sheets, separators, and negative electrode sheets in order, with the separators being placed between the positive and negative electrode sheets to serve as an isolation layer, and then wind the sheets to obtain a bare cell. Place the bare cell in an outer packaging shell, dry it, and inject the electrolyte. After vacuum packaging, standing, forming, and shaping, a secondary battery is obtained.

[0125] Examples 2 to 5

[0126] The difference between Examples 2 to 5 and Example 1 is that Examples 2 to 5 adjust the mass percentage of the doping element in the core by changing S2.

[0127] Example 2: Carbon material is used in combination with KOH, NH4H2PO4, potassium carbonate (K2CO3), and CH4N2S in a substance ratio of 1:1:0.03:0.015:0.015, and the total content of N, P, and S is 2 wt.%.

[0128] Example 3: Carbon material is used in combination with KOH, NH4H2PO4, potassium carbonate (K2CO3), and CH4N2S in a substance ratio of 1:1:0.044:0.022:0.022, and the total content of N, P, and S is 3 wt.%.

[0129] Example 4: Carbon material is used in combination with KOH, NH4H2PO4, potassium carbonate (K2CO3), and CH4N2S in a substance ratio of 1:1:0.06:0.03:0.03, and the total content of N, P, and S is 4 wt.%.

[0130] Example 5: Carbon material is used in combination with KOH, NH4H2PO4, potassium carbonate (K2CO3), and CH4N2S in a substance ratio of 1:1:0.07:0.035:0.035, and the total content of N, P, and S is 5 wt.%.

[0131] Examples 6 to 9

[0132] The difference between Examples 6 to 9 and Examples 2 to 5 lies in the difference in compaction density and the total doping amount of N, P, and S. Examples 6 to 9 adjust the compaction density of the negative electrode active material by changing the ratio of the preparation of the S5 negative electrode sheet and the total doping amount of the S3 element.

[0133] The difference between Example 6 and Example 5 is that the negative electrode sheet compaction density is adjusted to 1.8 g / cm by adjusting the roller press pressure. 3 , change the total amount of S3 element doping to 5wt.%.

[0134] The difference between Example 7 and Example 4 is that the negative electrode sheet compaction density is adjusted to 1.6 g / cm by adjusting the roller press pressure. 3 , change the total amount of S3 element doping to 4wt.%.

[0135] The difference between Example 8 and Example 3 is that the negative electrode sheet compaction density is adjusted to 1.8 g / cm by adjusting the roller press pressure. 3 , change the total amount of S3 element doping to 3wt.%.

[0136] The difference between Example 9 and Example 2 is that the negative electrode sheet compaction density is adjusted to 1.5 g / cm by adjusting the roller press pressure. 3 , change the total amount of S3 element doping to 2wt.%.

[0137] Comparative Examples 1 to 3

[0138] Comparative Example 1 differs from Example 1 in that the compaction density and the amount of doping elements are different. The total amount of doping element S3 is changed to 5 wt.%, and the compaction density of the negative electrode sheet is adjusted to 1.5 g / cm by adjusting the roller press pressure in step S5. 3 , other conditions remain unchanged;

[0139] Comparative Example 2 differs from Example 1 in that the compaction density and the amount of doping elements are different. The total amount of doping element S3 is changed to 2 wt.%, and the compaction density of the negative electrode sheet is adjusted to 1.9 g / cm by adjusting the roller press pressure in step S5. 3 , other conditions remain unchanged;

[0140] The difference between Comparative Example 3 and Example 1 is that the types of doping elements are different. By changing the S2 step, only one element, nitrogen, is doped. The carbon material is used in combination with KOH, potassium carbonate (K2CO3), and C3H6N6 in a material amount of 1:1:0.05, and the total N content is 3.5wt.%.

[0141] Examples 10 to 13

[0142] The difference between Examples 10 to 13 and Examples 2 to 5 is that the sphericity of the silicon-carbon material is different. Examples 10 to 13 adjust the sphericity of the negative electrode active material by changing the ratio of S1 phenol to formaldehyde.

[0143] The difference between Example 10 and Example 5 is that the molar ratio of phenol to formaldehyde in S1 is adjusted to 1:0.6, while other conditions remain unchanged, and the sphericity is 0.74.

[0144] The difference between Example 11 and Example 4 is that the molar ratio of phenol to formaldehyde in S1 is adjusted to 1:0.7, while other conditions remain unchanged, and the sphericity is 0.85.

[0145] The difference between Example 12 and Example 3 is that the molar ratio of phenol to formaldehyde in S1 is adjusted to 1:0.8, while other conditions remain unchanged, and the sphericity is 0.91.

[0146] Example 13 differs from Example 2 in that the molar ratio of phenol to formaldehyde in S1 is adjusted to 1:0.95, while other conditions remain unchanged, and the sphericity is 0.95.

[0147] Examples 14 to 17

[0148] The difference between Examples 14 to 17 and Examples 2 to 5 is that the silicon content is different. Examples 14 to 17 change the flow rate and deposition time in step S4, thereby changing the mass percentage of silicon particles in the core.

[0149] The difference between Example 14 and Example 5 is that SiH4 gas and protective gas N2 (volume ratio 1:1) are introduced with a flow rate of 200 sccm, 500°C, and 8 hours to uniformly deposit silicon into the porous carbon, with a silicon content of 45.2%.

[0150] Example 15 The difference from Example 4 is that SiH4 gas and protective gas N2 (volume ratio 1:1) are introduced with a flow rate of 150 sccm, 500°C, and 12 hours to uniformly deposit silicon into the porous carbon, with a silicon content of 47.6%.

[0151] Example 16 is different from Example 3 in that SiH4 gas and protective gas N2 (volume ratio 1:1) are introduced with a flow rate of 100 sccm, 500°C, and 16 hours to uniformly deposit silicon into the porous carbon, with a silicon content of 49.4%.

[0152] Example 17 The difference between Example 2 is that SiH4 gas and protective gas N2 (volume ratio 1:1) are introduced with a flow rate of 100 sccm, 500°C, and 20 hours to uniformly deposit silicon into the porous carbon, with a silicon content of 52%.

[0153] Examples 18-19

[0154] The difference between Example 18 and Example 1 is that the types of doping elements are different. Example 18 changes the S2 step and uses carbon material in combination with KOH, NH4H2PO4, and potassium carbonate (K2CO3) in a substance amount of 1:1:0.046:0.046, and the total content of N and P is 3.5wt.%.

[0155] The difference between Example 19 and Example 1 is that the types of doping elements are different. Example 19 changes the S2 step by using carbon material in combination with KOH, potassium carbonate (K2CO3), CH4N2S, and H3B in a substance amount of 1:1:0.07:0.07, and the total content of N and S is 3.5wt.%.

[0156] Table 1

[0157]

[0158] Table 2

[0159]

[0160]

[0161] Performance Testing

[0162] 1. Cycle retention rate test

[0163] ① Charge the battery to 4.53V at 0.5C at 45℃, with a cut-off current of 0.05C, and leave it for 5 minutes;

[0164] ②Measure the discharge capacity of the battery at this time, recorded as D before;

[0165] ③Discharge the battery at 0.7C to 3V and leave it for 5 minutes;

[0166] ④ Charge the battery to 4.53V at 1.5C, with a cut-off current of 0.05C, and leave it for 5 minutes;

[0167] ⑤ Repeat the above steps ③ and ④ 300 times, and then measure the discharge capacity of the battery at this time, which is recorded as D;

[0168] Cycle retention rate = D after / D before * 100%.

[0169] 2. Cyclic thickness change rate

[0170] ① Charge the battery to 4.53V at 0.5C at 45℃, with a cut-off current of 0.05C, and leave it for 5 minutes;

[0171] ②Measure the thickness of the battery at this time and record it as dfront;

[0172] ③Discharge the battery at 0.7C to 3V and leave it for 5 minutes;

[0173] ④ Charge the battery to 4.53V at 1.5C, with a cut-off current of 0.05C, and leave it for 5 minutes;

[0174] ⑤ Repeat steps ③ and ④ above 300 times, and then measure the thickness of the battery at this time, which is recorded as d;

[0175] Cycle thickness retention rate = (d after - d before) / d before * 100%.

[0176] 3. Reaction layer thickness:

[0177] SEI film thickness test: At 45°C, the battery was charged to 4.53V at 0.5C, with a cutoff current of 0.05C, and discharged to 3.0V at 0.7C. After 300 cycles under the condition of a cutoff current of 0.05C, the battery was disassembled, the negative electrode sheet was taken out, the corresponding position in the negative electrode sheet was selected, the cross section was cut for electron microscopy testing, and the thickness of the reaction layer on the surface of 35 silicon material particles in each corresponding area was counted, and the average value was taken and recorded as the reaction layer thickness.

[0178] Table 3

[0179] Reaction layer thickness nm Cycle retention rate / % Thickness growth rate / % Example 1 201 93 7.2 Example 2 350 86 9.1 Example 3 323 87 9.4 Example 4 245 88 8.5 Example 5 323 85 9.1 Example 6 362 83 12.8 Example 7 388 86 12.6 Example 8 302 85 8.9 Example 9 392 84 11.3 Example 10 353 80 14.4 Example 11 321 86 10.2 Example 12 135 82 8.7 Example 13 385 85 9.8 Example 14 238 83 8.1 Example 15 279 86 8.6 Example 16 342 85 10.3 Example 17 384 81 11.9 Example 18 270 89 8 Example 19 253 91 7.6 Comparative Example 1 430 76 14.1 Comparative Example 2 545 70 14.7 Comparative Example 3 670 62 16.5

[0180] As can be seen from Table 3, the negative electrode active material of the present application is a core-shell structure, the core is a porous carbon material containing at least two elements of N, P, S, and B and silicon particles deposited in the pores of the porous carbon material, and the outer shell is a carbon coating layer. By controlling 1.1≤X / M≤3, the reaction active sites can be effectively increased, and the conductivity and conductivity uniformity of the negative electrode active material can be effectively improved. At the same time, at 45°C, the battery is charged to 4.53V at 0.5C, the cut-off current is 0.05C, and the battery is discharged to 3.0V at 0.7C. The cut-off rate is 0.05C and the cycle is 300cls. The thickness of the reaction layer is ≤500nm, which reduces the polarization during the charge and discharge process and improves the reaction uniformity, improves the continuity of the heat conduction path, thereby enhancing the heat conduction capacity, avoiding cracks, thereby avoiding internal short circuits, reducing the risk of local overheating, and improving the thermal stability of the silicon-carbon negative electrode. The stress distribution during the charge and discharge process is more uniform, suppressing the volume expansion of the negative electrode active material, and significantly improving the cycle stability of the secondary battery.

[0181] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A secondary battery, characterized in that: At 45°C, the secondary battery was charged to 4.53V at 0.5C, with a cut-off current of 0.05C, and discharged to 3.0V at 0.7C, with a cut-off current of 0.05C, for 300 cycles, and the reaction layer thickness was ≤500nm; The secondary battery includes a negative electrode plate, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the negative electrode active material layer includes a negative electrode active material, the negative electrode active material includes a core and a carbon coating layer disposed on the outer surface of the core, the core includes a porous carbon material and silicon particles deposited in the pores of the porous carbon material, the porous carbon material contains a doping element, and the doping element includes at least two of N, P, S, and B; The negative electrode active material satisfies: 1.1≤X / M≤3; Wherein, X% is the mass percentage of the doping element in the core; Mg / cm 3 is the compaction density of the negative electrode active material layer.

2. The secondary battery according to claim 1, wherein Satisfy at least one of the following (I) to (II): (Ⅰ)2≤X≤5； (Ⅱ)1.5≤M≤1.9。 3. The secondary battery according to claim 1, wherein The doping elements include N, P and A elements, the A element includes at least S and B, and the mass ratio of the N, P and A elements in the core is 2: (1-2): (1-2).

4. The secondary battery according to claim 1, wherein Satisfy: 2≤X / Y≤5.05; Wherein, Y is the sphericity of the negative electrode active material.

5. The secondary battery according to claim 4, wherein The Y satisfies: 0.8≤Y≤1.

6. The secondary battery according to claim 1, wherein The negative electrode active material satisfies: 0.04≤X / Z≤0.12; Wherein, Z% is the mass percentage of the silicon particles in the core.

7. The secondary battery according to claim 6, characterized in that The Z satisfies: 45≤Z≤52.

8. The secondary battery according to claim 1, wherein The negative electrode active material D V 50 particle size of 5 to 10 μm; and / or The thickness of the carbon coating layer is 30-35 nm.

9. The secondary battery according to claim 1, wherein The thickness of the reaction layer is 150-400 nm.

10. An electrical device, characterized in that: The secondary battery comprises the secondary battery according to any one of claims 1 to 9, wherein the secondary battery serves as a power supply for the electrical device.

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