Negative electrode active material, secondary battery and electric equipment

Abstract

The embodiment of the invention provides a negative electrode active material, a secondary battery and electric equipment, and the negative electrode active material provided by the embodiment of the invention meets the following conditions: P = (V / S) / (1 / 6 * Dv50), V = 1 / 6 * pi * D (4, 3) * D (4, 3) * D (4, 3), S = pi * D (3, 2) * D (3, 2), pi = 3.14, 1.2 < = P < = 1.9, wherein Dv50 represents the corresponding particle size when the accumulated particle volume of the negative electrode active material reaches 50%, D (3, 2) represents the surface area average particle size of the negative electrode active material, and D (4, 3) represents the volume average particle size of the negative electrode active material. Wherein the Dv50, the surface area average particle size and the volume average particle size of the negative electrode active material are controlled to meet the relational expression, so that the particles are close to a spherical shape under the action of pressure, the liquid phase diffusion impedance is small, the normal-temperature power performance is relatively good, and the performance of the material can be improved on the premise of ensuring the reaction area to improve the dynamic performance of the material. The size of the pores is restrained to reduce side reactions, thereby improving storage life.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a negative electrode active material, a secondary battery, and an electrical device. Background Technology

[0002] Currently, electric vehicles are placing higher demands on the power performance and cycle life of secondary batteries.

[0003] However, when faced with external forces such as rolling, the particles of the negative electrode active material in the existing technology are prone to deformation, which leads to the deterioration of the electrode pore structure, increases the liquid phase diffusion resistance, and thus seriously degrades the power performance of the battery. At the same time, the damage to the surface of the negative electrode active material particles will aggravate the side reactions, thereby shortening the battery life. In addition, the pore structure inside the negative electrode active material particles is prone to side reactions, which will lead to a more significant decrease in the battery's storage life. Summary of the Invention

[0004] The technical problem to be solved by this application is to provide a negative electrode active material, a secondary battery and an electrical device to solve the problem that existing negative electrode active material particles are prone to deformation after being subjected to pressure, which damages the active ion transport channels and surface structure, resulting in the deterioration of battery power performance and storage life.

[0005] To solve the above problems, this application provides the following technical solution: This application proposes a negative electrode active material, wherein the negative electrode active material satisfies: P=(V / S) / (1 / 6×Dv50), V=1 / 6×π×D(4,3)×D(4,3)×D(4,3), S=π×D(3,2)×D(3,2), π=3.14, 1.2≤P≤1.9; Wherein, Dv50 represents the particle size corresponding to when the cumulative particle volume of the negative electrode active material reaches 50%, D(3,2) is the surface area average particle size of the negative electrode active material, and D(4,3) is the volume average particle size of the negative electrode active material.

[0006] Furthermore, the particle size of the negative electrode active material satisfies at least one of the following: (1) Dv50 is 4~8μm; (2) D(4,3) is 4~9μm; (3) D(3,2) is 3~8μm.

[0007] Furthermore, the particles of the negative electrode active material have pores inside.

[0008] Furthermore, the pore volume of the argon adsorption test opening in the negative electrode active material is 0.003~0.015 cm³. 3 / g; and / or, the volume percentage of pores with a diameter of less than 1 nm is less than 15%.

[0009] Furthermore, the specific surface area of ​​the negative electrode active material is 3.0~7.0 m². 2 / g.

[0010] Furthermore, the oil absorption value of the negative electrode active material is 40~65 mL dibutyl phthalate / 100g.

[0011] Furthermore, the negative electrode active material includes a core and a shell disposed on the surface of the core, the core comprising natural graphite and the shell comprising amorphous carbon.

[0012] Furthermore, in the negative electrode active material, the mass ratio of the amorphous carbon to the natural graphite is 0.01:1 to 0.1:1.

[0013] Furthermore, in the aforementioned negative electrode active material, the core has a Dv50 of 3~8μm, and the shell has a thickness of 3~30nm.

[0014] This application also proposes a secondary battery, which includes a negative electrode sheet, the negative electrode sheet including a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, the negative electrode active material layer including the negative electrode active material as described above.

[0015] Furthermore, in the secondary battery, the negative electrode sheet satisfies at least one of the following (1) to (3): (1) The compaction density of the negative electrode sheet is 1.1~1.4 g / cm³. 3 ; (2) The coating surface density of the negative electrode sheet is 2~5 mg / cm³. 2 ; (3) The tortuosity of the negative electrode sheet is 2~9.

[0016] This application also proposes an electrical device, which includes the aforementioned secondary battery, wherein the secondary battery serves as the power supply for the electrical device.

[0017] Compared with the prior art, the embodiments of this application have the following advantages: In this embodiment, the provided negative electrode active material satisfies: P=(V / S) / (1 / 6×Dv50), V=1 / 6×π×D(4,3)×D(4,3)×D(4,3), S=π×D(3,2)×D(3,2), π=3.14, 1.2≤P≤1.9; where Dv50 represents the particle size corresponding to when the cumulative particle volume of the negative electrode active material reaches 50%, D(3,2) is the surface area average particle size of the negative electrode active material, and D(4,3) is the volume average particle size of the negative electrode active material. Controlling the Dv50, surface area average particle size, and volume average particle size of the negative electrode active material to satisfy the above relationships makes the particles nearly spherical under pressure, resulting in low liquid phase diffusion resistance, good power performance at room temperature, and, while ensuring the reaction area to improve the material's kinetic performance, constraining the pore size to reduce side reactions, thereby improving storage life.

[0018] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0019] Figure 1 This is a scanning electron microscope image of the negative electrode active material in Example 1 of this application. Detailed Implementation

[0020] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] The applicant of this application discovered that, when faced with external forces, the particles of the prior art negative electrode active material are prone to deformation, leading to the deterioration of the electrode pore structure, increasing the liquid phase diffusion resistance, and thus severely degrading the power performance of the battery. At the same time, damage to the surface of the negative electrode active material particles will exacerbate side reactions, thereby shortening the battery life. In addition, the pore structure inside the negative electrode active material particles is prone to side reactions, resulting in a more significant decrease in the battery's storage life.

[0022] The existing technologies cannot effectively improve the above problems, and there is an urgent need to develop a new type of negative electrode active material that can maintain the integrity of the particle structure and the stability of the morphology under the action of external force, and effectively suppress the generation of harmful micropores, thereby comprehensively improving the high-rate performance and life of the battery.

[0023] To address the aforementioned problems, this application provides a negative electrode active material that satisfies the following conditions: P = (V / S) / (1 / 6 × Dv50), V = 1 / 6 × π × D(4,3) × D(4,3) × D(4,3), S = π × D(3,2) × D(3,2), π = 3.14, 1.2 ≤ P ≤ 1.9; where Dv50 represents the particle size corresponding to when the cumulative particle volume of the negative electrode active material reaches 50%, D(3,2) is the surface area average particle size of the negative electrode active material, and D(4,3) is the volume average particle size of the negative electrode active material.

[0024] Among them, the closer the morphology index P is to 1, the closer the negative electrode active material is to a sphere after stirring, slurry preparation, coating, and rolling. Particles that are close to a sphere are more likely to be densely packed. When the same compaction density is achieved, the pressure required is too small, and the reconstruction effect on the surface structure is not obvious, which affects the power performance. On the other hand, the more the morphology index P deviates from 1, the more irregular the shape of the negative electrode active material is after stirring, slurry preparation, coating, and rolling. The deformation is more severe. The deformation of the particles blocks the lithium ion diffusion channels, increases the tortuosity of the electrode, and deteriorates the power performance.

[0025] In this embodiment, the Dv50, average surface area particle size, and average volume particle size of the negative electrode active material are controlled to satisfy the above-mentioned relationship, so that the particles are close to spherical after being subjected to pressure. The liquid phase diffusion resistance is small, the power performance at room temperature is good, and the size of the pores can be constrained to reduce side reactions while ensuring the reaction area to improve the material kinetic performance, thereby improving the storage life.

[0026] Therefore, the negative electrode active material provided in this application embodiment solves the problem that existing negative electrode active material particles are prone to deformation after being compressed, which damages the active ion transport channels and surface structure, leading to the deterioration of battery power performance and storage life.

[0027] Optionally, in some embodiments, the particle size of the above-mentioned negative electrode active material satisfies: Dv50 is 4~8μm. Controlling the size of Dv50 within this range allows the negative electrode active material to have a suitable specific surface area, effectively balancing the solid-phase diffusion path and the chemical reaction area, thereby improving the battery's kinetic performance, storage performance, and power performance.

[0028] Optionally, in some embodiments, the particle size of the above-mentioned negative electrode active material satisfies that D(4,3) is 4~9 μm. Controlling the size of D(4,3) within the above range enables the negative electrode active material to have a suitable specific surface area, effectively balancing the solid-phase diffusion path and the chemical reaction area, thereby improving the battery's kinetic performance, storage performance, and power performance.

[0029] Optionally, in some embodiments, the particle size of the above-mentioned negative electrode active material satisfies that D(3,2) is 3~8 μm. Controlling the size of D(3,2) within the above range enables the negative electrode active material to have a suitable specific surface area, effectively balancing the solid-phase diffusion path and the chemical reaction area, thereby improving the battery's kinetic performance, storage performance, and power performance.

[0030] Optionally, in some embodiments, the particles of the aforementioned negative electrode active material have pores inside. Provided that P is between 1.2 and 1.9, the pores inside the negative electrode active material particles, although causing particle deformation or even destruction of the accumulated active ion diffusion channels under pressure, thereby worsening the liquid phase diffusion impedance and leading to a decrease in power performance, can significantly increase the reaction area by reconstructing the particle surface structure under pressure, thus effectively improving power performance.

[0031] Optionally, the aforementioned pores are elongated pores. In some specific embodiments, the pore volume of the argon adsorption test opening of the above-mentioned negative electrode active material is 0.003~0.015 cm³. 3 / g can reduce the tortuosity of the diffusion path of active ions while ensuring storage performance, effectively increasing the electrochemical reaction area and improving kinetic, power and storage performance.

[0032] In some specific embodiments, the pore volume of the argon adsorption test aperture of the above-mentioned negative electrode active material can be 0.003 cm³. 3 / g, 0.004cm 3 / g, 0.005cm 3 / g, 0.006cm 3 / g, 0.007cm 3 / g, 0.008cm 3 / g, 0.009cm 3 / g, 0.010cm 3 / g, 0.011cm 3 / g, 0.012cm 3 / g, 0.013cm 3 / g, 0.014cm 3 / g, 0.015cm 3 The range of values ​​in / g, either one or both.

[0033] Optionally, in some embodiments, in the argon adsorption test of the above-mentioned negative electrode active material, the proportion of the pore volume with a pore size of less than 1 nm is less than 15%. Having an open pore volume proportion of less than 1 nm within the above range can reduce the tortuosity of the active ion diffusion path while ensuring storage performance, effectively increasing the electrochemical reaction area and improving kinetic, power, and storage performance.

[0034] In some specific embodiments, in the argon adsorption test of the above-mentioned negative electrode active material, the proportion of the pore volume with a pore size of less than 1 nm can be one of 2%, 5%, 8%, 10%, 12%, 14% or any value between two of them.

[0035] Optionally, in some embodiments, the specific surface area of ​​the above-mentioned negative electrode active material is 3.0~7.0 m². 2 / g, which can effectively balance the electrochemical reaction area and side reactions, thus achieving a balance between power performance and storage performance. In some specific embodiments, the specific surface area of ​​the negative electrode active material can be 3.0m². 2 / g, 4.0m 2 / g, 5.0m 2 / g, 6.0m 2 / g, 7.0m 2 The range of values ​​in / g, either one or both.

[0036] Optionally, in some embodiments, the oil absorption value of the above-mentioned negative electrode active material is 40~65 mL dibutyl phthalate / 100g, which ensures that the liquid phase diffusion resistance of the material is small so as to have better kinetic performance, and makes the material easy to process and reduces the amount of binder used, thereby ensuring battery capacity.

[0037] Optionally, in some embodiments, the aforementioned negative electrode active material includes a core and a shell layer disposed on the surface of the core. The core includes natural graphite, and the shell layer includes amorphous carbon. In this embodiment, by utilizing the characteristics of natural graphite particles being loose and porous internally and spherical externally, an amorphous carbon shell layer is formed on its exterior through coating or other means. This can improve kinetic performance while maintaining high capacity, thereby effectively improving the rate performance and cycle life of the battery.

[0038] Optionally, in some embodiments, the mass ratio of amorphous carbon to natural graphite in the above-mentioned negative electrode active material is 0.01:1 to 0.1:1, which can effectively balance kinetic performance and storage performance.

[0039] In some specific embodiments, the mass ratio of amorphous carbon to natural graphite in the above-mentioned negative electrode active material can be one of 0.01:1, 0.02:1, 0.05:1, 0.08:1, 0.1:1 or any value between two of them.

[0040] Optionally, in some embodiments, the core Dv50 of the above-mentioned negative electrode active material is 3~8μm and the shell thickness is 3~30nm, which can avoid deterioration of the first-efficiency and high-temperature performance, and also make the solid-phase diffusion path shorter, thus ensuring kinetic performance.

[0041] In some specific implementations, the Dv50 of the kernel can be one of 3μm, 4μm, 5μm, 6μm, 7μm, 8μm or any value between two of them, and the thickness of the shell can be one of 3nm, 5nm, 10nm, 20nm, 30nm or any value between two of them.

[0042] This application also provides a method for preparing a negative electrode active material, including steps 101 to 104: Step 101: Shape natural graphite into spherical graphite with a Dv50 of 3~8μm.

[0043] In step 101 above, flake natural graphite is crushed and shaped for 90-180 minutes to prepare spherical graphite with a Dv50 of 3-8 μm. The particle morphology can be controlled by the shaping time. The shorter the shaping time, the more irregular the particles; the longer the shaping time, the closer the particles are to spherical shapes. However, if the shaping time is too long, the effect of the shaping time on the particle morphology weakens, the yield decreases rapidly, and the cost increases.

[0044] Step 102: Pressurize the spherical graphite at a pressure of 100~400MPa for 30~70min.

[0045] In step 102 above, the spherical natural graphite is subjected to pressure treatment using a cold isostatic press or a warm isostatic press. The medium is water, inert gas, or other liquid, the pressure is 100~400MPa, and the pressurization time is 30~70min. During the pressure application process, the particles flow, come into contact and compress with each other, and the particle surface is damaged to a certain extent, further reshaping the particle morphology. The pressure transforms the large pores inside the particles into small pores, reducing the pore volume to 0.015 cm³. 3 The pressure is below / g, making the particles more compact. At the same time, the pressure increases the number of pores with a diameter of <1nm and the proportion of open pores with a diameter of less than 1nm. Therefore, it is necessary to control the appropriate pressure and time.

[0046] Step 103: Crush the pressure-treated spherical graphite to a Dv50 of 3~8μm.

[0047] In step 103 above, the spherical graphite after pressure treatment is crushed and dispersed to a Dv50 of 3~8μm to facilitate subsequent coating with carbon source coating agent.

[0048] Step 104: Mix spherical graphite and carbon source coating agent evenly, and carbonize at 1000~1500℃ under protective gas to form an amorphous carbon layer on the surface, thus obtaining the negative electrode active material.

[0049] In step 104 above, spherical graphite is uniformly mixed with a coating agent and carbonized at 1000-1500℃ under a protective gas such as nitrogen or argon. This forms an amorphous carbon layer with moderate order on the surface, resulting in lower electrochemical reaction impedance and improved kinetic performance. Simultaneously, the carbon source penetrates into the particle pores at high temperature, exerting a secondary regulatory effect on the pore volume and distribution within the particles. During the carbonization process of the carbon source itself, the volatilization of volatiles also creates pores, affecting the pore volume and distribution of the negative electrode active material.

[0050] In step 104 above, the coating agent can be selected from coal tar pitch, petroleum pitch, phenolic resin, epoxy resin, etc., and the amount of coating agent added is 5wt%~15wt%.

[0051] In step 104 above, the carbonized product is sieved and demagnetized to obtain the finished negative electrode active material.

[0052] This application also proposes a secondary battery, including a negative electrode sheet, wherein the negative electrode sheet includes a negative current collector and a negative active material layer disposed on the negative current collector, the negative active material layer including the negative active material as described above.

[0053] The negative electrode active material layer of the negative electrode sheet in the secondary battery provided in this application uses the above-mentioned negative electrode active material. Its particles are close to spherical after being subjected to pressure. It has low liquid phase diffusion resistance and good power performance. It can also constrain the size of the pores to reduce side reactions while ensuring the reaction area to improve the material kinetic performance, thereby improving the storage life.

[0054] Optionally, in some embodiments, the compaction density of the negative electrode sheet is 1.1~1.4 g / cm³. 3 This ensures that the contact between the electrode particles is sufficiently close, facilitating electron transport and guaranteeing the performance of the kinetics. It also ensures that the particles have sufficient porosity, which facilitates the diffusion of the electrolyte into the liquid phase.

[0055] In some embodiments, the compaction density of the negative electrode sheet can be 1.1 g / cm³. 3 1.2g / cm 3 1.3g / cm 3 1.4g / cm 3 The range of values ​​between one or any two of them.

[0056] Optionally, in some embodiments, the coating surface density of the negative electrode sheet is 2~5 mg / cm³. 2 This not only reduces internal resistance and polarization loss, thereby extending the cycle life of the battery, but also facilitates the insertion and extraction of lithium ions, ensuring the battery's dynamic performance.

[0057] In some embodiments, the coating surface density of the negative electrode sheet can be 2 g / cm³. 2 3g / cm 2 4g / cm 2 5g / cm 2 The range of values ​​between one or any two of them.

[0058] Optionally, in some embodiments, the tortuosity of the negative electrode sheet is 2 to 9, resulting in a short ion diffusion path and low impedance, which helps to improve the battery dynamics performance.

[0059] In some embodiments, the tortuosity of the negative electrode sheet can be one of 2, 3, 4, 5, 6, 7, 8, 9 or any value between two of them.

[0060] The secondary battery may include a lithium-ion secondary battery.

[0061] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on the negative current collector. The negative active material layer contains the negative active material or a mixture of the negative active material and one or more of artificial graphite, hard carbon, soft carbon, silicon carbon material, and silicon oxide material.

[0062] In the secondary battery provided in this application embodiment, the negative electrode sheet further includes a second conductive agent and a second binder; optionally, the second conductive agent includes one or more of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene, and the second binder includes carboxymethyl cellulose-based binders and resin-based binders.

[0063] Optionally, in one embodiment, the carboxymethyl cellulose-based adhesive includes one or more of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose; and / or the resin-based adhesive includes one or more of styrene-butadiene rubber, polyacrylic acid, and polyacrylonitrile.

[0064] In some embodiments, the negative electrode sheet is prepared as follows: the components used to prepare the negative electrode sheet, such as the negative electrode active material, the second binder and the second conductive agent, are dispersed in a solvent such as deionized water to form a negative electrode slurry; the negative electrode slurry is coated on both sides of a negative electrode current collector such as a copper foil; after baking, rolling, cutting and other processes, the negative electrode sheet can be obtained.

[0065] The battery provided in this application embodiment also includes a positive electrode, a separator, and an electrolyte.

[0066] The aforementioned positive electrode sheet includes a positive current collector and a positive active material layer disposed on the positive current collector. The positive active material layer includes a positive active material, which includes a lithium-ion transition metal oxide, selectable from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium phosphates with an olivine structure. Optionally, the aforementioned lithium-ion transition metal oxide includes at least one of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium manganese oxide, and lithium iron phosphate.

[0067] In some embodiments of this application, the positive electrode further includes a first conductive agent, which includes at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, hard carbon, carbon fiber, and carbon microspheres.

[0068] In some embodiments of this application, the positive electrode sheet further includes a first adhesive, which includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0069] In some embodiments of this application, the positive electrode sheet is prepared as follows: the components used to prepare the positive electrode sheet, such as the positive active material including the above-mentioned positive active material, the first binder and the first conductive agent, are dispersed in a solvent such as N-methylpyrrolidone to form a positive electrode slurry; the positive electrode slurry is coated on a positive current collector such as an aluminum foil; after drying, rolling, die cutting and other processes, the positive electrode sheet can be obtained.

[0070] In this embodiment, the electrolyte acts as a conductor of ions between the positive and negative electrodes. The electrolyte can be liquid, gel-like, or entirely solid. In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent, wherein the electrolyte salt is a lithium salt.

[0071] Optionally, the aforementioned secondary battery includes any one of liquid lithium-ion batteries, quasi-solid-state lithium-ion batteries, quasi-solid-state lithium metal batteries, all-solid-state lithium-ion batteries, and solid-state lithium metal batteries.

[0072] This application also proposes an electrical device, which includes the aforementioned secondary battery, serving as the power supply for the aforementioned electrical device.

[0073] For the above-described secondary battery embodiments and electrical device embodiments, the positive electrode sheet includes a positive electrode active material layer, which includes the aforementioned positive electrode active material and can achieve the same technical effect. To avoid repetition, it will not be described again here. For relevant details, please refer to the description of the positive electrode active material embodiments.

[0074] To make the inventive objectives, technical solutions, and beneficial effects of this application clearer, the application is further described below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of this application.

[0075] The present application will be described in detail below through embodiments.

[0076] Test methods (1) Particle size and distribution test Add 0.1g of negative electrode active material powder to deionized water, add 3-5 drops of surfactant, and sonicate at 53KHz and 120W for 3min. Inject the entire mixture into the sample and test the particle size and distribution using a laser particle size analyzer (Malvern MasterSizer 3000). The surfactant can be nonylphenol polyoxyethylene ether, the solvent refractive index is 1.33, the sample refractive index is 2.42, and the opacity is 8-12%.

[0077] (2) Aperture distribution test Referring to the national standard GB / T 21650.2-2008, the negative electrode active material was heated to 250℃ at a rate of 10℃ / min and then held at that temperature for 2 hours for degassing. The adsorbate was argon gas, and the relative pressure P / P0 was selected within a range of 10. -9 ~0.99, the number of selected points is 80, and the data processing method is DFT (density functional theory).

[0078] (3) Electrode tortuosity test Two rolled negative electrode sheets were used to fabricate a symmetrical cell. The electrochemical impedance spectroscopy (EIS) was measured using an electrochemical workstation with a perturbation voltage of 5 mV and a test frequency of 5 MHz to 0.2 Hz. The ionic impedance R was obtained. ion Calculate tortuosity = ion / 2d, where A: electrode cross-sectional area, unit m 2 ; Electrolyte conductivity, in S / m; Porosity (%): Porosity (%): Electrode thickness (m). Porosity is calculated by measuring the true volume of a certain number of regularly shaped electrodes using a true density meter, and is obtained from (apparent volume - true volume) / apparent volume. The apparent volume is the volume of the regularly shaped electrodes.

[0079] (4) Lithium-ion battery Imax test: At 25±5℃ and 50% SOC, discharge with a test current of I for 10 seconds until the final voltage is V. 下限 ~(V)下限 Within the range of -0.05), the maximum current satisfying the above conditions is the discharge Imax, where V 下限 The lower limit of battery discharge voltage is 2.8V; At 25±5℃, with 50% SOC, charge with a test current I for 10 seconds until the final voltage is V. 上限 ~(V) 上限 Within the range of +0.05), the maximum current satisfying the above conditions is the charging current Imax, where V 上限 The maximum charging voltage for the battery is 4.2V.

[0080] (5) Storage performance test: The battery was charged at 25°C at 1C to the upper voltage limit of 4.2V, and then charged at a constant voltage to 0.05C; after resting for 10 minutes, it was discharged at 1C to the lower voltage limit of 2.8V, and the discharge capacity was recorded as C0; after resting for 10 minutes, 1C0 was charged to the upper voltage limit, and then charged at a constant voltage to 0.05C0; after resting for 10 minutes, 1C0 was discharged for 12 minutes to adjust to 80% SOC; The above batteries were stored in a 60℃ oven for 30 days, then removed and left to stand at 25℃ for 4 hours. The 1C0 cells were charged to the upper voltage limit of 4.2V, and then charged at a constant voltage to 0.05C0. After standing for 10 minutes, the 1C0 cells were discharged to the lower voltage limit of 2.8V, and the discharge capacity was recorded as C1. Calculate the recovery volume retention rate = (C1 / C0) × 100% Example 1 (1) Preparation of negative electrode active material ①Powder and shape flake natural graphite for 120 min to prepare spherical graphite with Dv50 of 3μm; ② Pressurize the spherical graphite using a cold isostatic press, with water as the medium, a pressure of 200 MPa, and a pressurization time of 60 minutes.

[0081] ③ The pressurized spherical graphite is crushed and dispersed until the Dv50 is 3μm.

[0082] ④ Mix the spherical graphite with the asphalt coating agent evenly and carbonize it at 1200℃ under nitrogen. The amount of coating agent added is 7wt%.

[0083] ⑤ Screening and demagnetization yield the finished negative electrode active material.

[0084] (2) Preparation of negative electrode sheet The above-mentioned negative electrode active material, conductive carbon black, thickener CMC, and binder SBR are mixed in a mass ratio of 95:2:1.2:1.8. Deionized water is added as a solvent, and the mixture is stirred under the action of a stirrer until the system is homogeneous to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated on the negative electrode current collector copper foil, dried in an oven, rolled and cut to obtain a negative electrode sheet.

[0085] (3) Preparation of positive electrode sheet Nickel-cobalt-manganese ternary material (NCM523), conductive carbon black, and binder PVDF are mixed at a mass ratio of 95:3:2. Solvent NMP is added, and the mixture is stirred until the system is homogeneous to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated on the positive electrode current collector aluminum foil, dried in an oven, rolled, and slit to obtain the positive electrode sheet.

[0086] (4) Preparation of electrolyte Ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed in a volume ratio of 1:1:1. Then, 1 mol / L LiPF6 was dissolved in the mixed organic solvent and mixed thoroughly to prepare an electrolyte.

[0087] (5) Preparation of lithium-ion batteries The above-mentioned positive electrode sheet, separator, and negative electrode sheet are wound in sequence to obtain a bare cell; the bare cell is placed in an outer packaging shell, vacuum dried, and then injected with electrolyte. After standing, formation, shaping, and capacity testing, a lithium-ion battery is obtained.

[0088] Examples 2-13 The preparation method is the same as in Example 1, except that the preparation process parameters of the negative electrode active material are adjusted.

[0089] Comparative Examples 1 to 2 The preparation method is the same as in Example 1, except that the crushing and shaping time of the flake natural graphite during the preparation of the negative electrode active material is adjusted.

[0090] The preparation process and performance parameters of the negative electrode active materials in each embodiment and comparative example are shown in Table 1.

[0091] Table 1

[0092] Scanning electron microscopy was performed on the negative electrode active material in Example 7, and the results are as follows: Figure 1 As shown, the particle shape is mainly irregular with a small number of spherical particles. The particles are relatively dense inside and contain a small number of narrow pores.

[0093] The compaction density and areal density of the negative electrode sheets in each embodiment and comparative example were tested, and the results are shown in Table 2.

[0094] The secondary batteries in each embodiment and comparative example were subjected to Imax test and storage performance test, and the results are shown in Table 2.

[0095] Table 2

[0096] Among them, P=(V / S) / (1 / 6×Dv50), V=1 / 6×π×D(4,3)×D(4,3)×D(4,3), S=π×D(3,2)×D(3,2), π=3.14.

[0097] In summary, in this embodiment, the negative electrode active material satisfies: P = (V / S) / (1 / 6 × Dv50), V = 1 / 6 × π × D(4,3) × D(4,3) × D(4,3), S = π × D(3,2) × D(3,2), π = 3.14, 1.2 ≤ P ≤ 1.9; where Dv50 represents the particle size corresponding to when the cumulative particle volume of the negative electrode active material reaches 50%, D(3,2) is the surface area average particle size of the negative electrode active material, and D(4,3) is the volume average particle size of the negative electrode active material. Controlling the Dv50, surface area average particle size, and volume average particle size of the negative electrode active material to satisfy the above relationships makes the particles nearly spherical under pressure, resulting in low liquid phase diffusion resistance, good power performance at room temperature, and, while ensuring the reaction area to improve the material's kinetic performance, constraining the pore size to reduce side reactions, thereby improving storage life.

[0098] Although preferred embodiments of the present application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of the present application.

[0099] The above provides a detailed description of the negative electrode active material, secondary battery, and electrical device provided in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A negative electrode active material, characterized in that, The negative electrode active material satisfies: P=(V / S) / (1 / 6×Dv50), V=1 / 6×π×D(4,3)×D(4,3)×D(4,3), S=π×D(3,2)×D(3,2), π=3.14, 1.2≤P≤1.9; Wherein, Dv50 represents the particle size corresponding to when the cumulative particle volume of the negative electrode active material reaches 50%, D(3,2) is the surface area average particle size of the negative electrode active material, and D(4,3) is the volume average particle size of the negative electrode active material.

2. The negative electrode active material according to claim 1, characterized in that, The particle size of the negative electrode active material satisfies at least one of the following: (1) Dv50 is 4~8μm; (2) D(4,3) is 4~9μm; (3) D(3,2) is 3~8μm.

3. The negative electrode active material according to claim 1, characterized in that, The particles of the negative electrode active material have pores inside.

4. The negative electrode active material according to claim 3, characterized in that, The pore volume of the argon adsorption test aperture of the negative electrode active material is 0.003~0.015 cm³. 3 / g; and / or, the volume percentage of pores with a diameter of less than 1 nm is less than 15%.

5. The negative electrode active material according to claim 1, characterized in that, The specific surface area of ​​the negative electrode active material is 3.0~7.0 m². 2 / g.

6. The negative electrode active material according to claim 1, characterized in that, The oil absorption value of the negative electrode active material is 40~65mL dibutyl phthalate / 100g.

7. The negative electrode active material according to any one of claims 1 to 6, characterized in that, The negative electrode active material includes a core and a shell disposed on the surface of the core. The core includes natural graphite and the shell includes amorphous carbon.

8. The negative electrode active material according to claim 7, characterized in that, The mass ratio of the amorphous carbon to the natural graphite is 0.01:1 to 0.1:

1.

9. The positive electrode material according to claim 7, characterized in that, The core has a Dv50 of 3~8μm and the shell has a thickness of 3~30nm.

10. A secondary battery, comprising a negative electrode, characterized in that, The negative electrode sheet includes a negative current collector and a negative active material layer disposed on the negative current collector, wherein the negative active material layer includes the negative active material as described in any one of claims 1 to 9.

11. The secondary battery according to claim 10, characterized in that, The negative electrode sheet satisfies at least one of the following (1) to (3): (1) The compaction density of the negative electrode sheet is 1.1~1.4 g / cm³. 3 ; (2) The coating surface density of the negative electrode sheet is 2~5 mg / cm³. 2 ; (3) The tortuosity of the negative electrode sheet is 2~9.

12. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 10 or 11, wherein the secondary battery serves as the power supply for the electrical device.

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