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 quantity distribution of secondary particles of a positive electrode active material in a positive electrode plate, the volume average particle size of a negative electrode active material and the specific discharge capacity of the positive electrode active material and the negative electrode active material are controlled to meet the following relation: Y is greater than or equal to 1 and less than or equal to 40; y = (n1 / n2). Dv50. (C1 / C2), so that the positive pole piece and the negative pole piece are better matched, thereby effectively reducing the interface side reaction, reducing the gas production of the secondary battery, improving the diffusion path of lithium ions, improving the stability of the positive active material in the tabletting process, obviously improving the crushing resistance of particles, and improving the performance of the secondary battery. And meanwhile, the specific discharge capacity of the positive electrode active material and the specific discharge capacity of the negative electrode active material have good adaptability, so that the cycle performance and the rate capability of the secondary battery are effectively improved.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly relates to a secondary battery and an electrical device using the same. Background Art

[0002] Secondary batteries have become the main power source for electric vehicles due to their high energy density and long cycle life. As a key new high-performance cathode active material for secondary batteries, extensive research has been carried out.

[0003] Among them, lithium nickel oxide has become the mainstream cathode active material for high-performance electric vehicles due to its superior specific capacity, high voltage platform, and high tap density. In order to further improve the energy density of lithium nickel oxide, the Ni content needs to be further increased. However, as the Ni content increases, Ni located in the octahedron tends to enter the Li sites in the lattice, resulting in a decrease in electrochemical activity. Lithium nickel oxide is usually charged to a high voltage to achieve a high energy density, but at the same time, many mechanical problems are introduced, such as cracking due to lattice collapse, gas release, and structural reconstruction (or surface densification). These adverse phenomena may occur simultaneously, resulting in poor battery cycle performance and voltage decay.

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

[0005] The purpose of the present application is to overcome the deficiencies of the prior art and provide a secondary battery and an electrical device using the same, so as to improve the cycle performance and rate performance of the secondary battery.

[0006] To achieve the above purpose, a first aspect of the present application provides a secondary battery, including a positive electrode sheet, a negative electrode sheet, and an electrolyte. The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes secondary particles. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material.

[0007] The secondary battery satisfies: 1 ≤ Y ≤ 40, where Y = (n1 / n2)·Dv50·(C1 / C2);

[0008] where n1 particles / 0.01 mm 2 is the number of the secondary particles with an inner diameter ≥ 8 μm of the positive electrode active material in the positive electrode active material layer in the SEM image, within 0.01 mm 2 ;

[0009] n2 particles / 0.01 mm 2For the positive electrode active material in the positive electrode active material layer, in the SEM image, 0.01 mm 2 the number of the secondary particles with an inner diameter < 8 μm;

[0010] Dv50 μm is the volume average particle diameter of the negative electrode active material;

[0011] C1 mAh / g is the discharge specific capacity of the positive electrode active material measured in the voltage range of 2.8 V to 4.3 V;

[0012] C2 mAh / g is the discharge specific capacity of the negative electrode active material measured in the voltage range of 0.01 V to 2 V.

[0013] As an embodiment of the present application, at least one of the following (a) to (e) is satisfied:

[0014] (a) 8 ≤ n1 ≤ 42;

[0015] (b) 6 ≤ n2 ≤ 35;

[0016] (c) 5 ≤ Dv50 ≤ 16;

[0017] (d) 204 ≤ C1 ≤ 222;

[0018] (e) 364 ≤ C2 ≤ 655.

[0019] As an embodiment of the present application, 0.2 ≤ n1 / n2 ≤ 7 is satisfied.

[0020] As an embodiment of the present application, the positive electrode active material includes lithium nickel oxide, and the lithium nickel oxide includes at least one of compounds with the chemical formula Li 1+a [Ni x Co y Mn z M b O2, where M includes at least one of Ti, Zr, Sr, Sb, Ta, Ru, Nd, V, Ce, Mo. Among them, 0.5 ≤ x < 1, 0 ≤ y < 0.3, 0 ≤ z < 0.3, -0.1 ≤ a < 0.2, 0 ≤ b < 0.3, and x + y + z + b = 1.

[0021] As an embodiment of the present application, the positive electrode active material further includes lithium-containing phosphate, and the lithium-containing phosphate includes a compound with the chemical formula Li n Mn t Fe u A sAt least one of the compounds of PO4, wherein A includes one or more of Al, Ni, Co, Ti, La, Ce, Cr, Mo, Ca, Ga, V, Nb, Zr, In, Zn, and Y, 0.95 < n < 1.15, t + u + s = 1, 0 ≤ t < 1, 0 < u ≤ 1, 0 ≤ s ≤ 0.02.

[0022] As an embodiment of the present application, the mass percentage of the lithium-containing phosphate in the positive electrode active material is 5% to 30%.

[0023] As an embodiment of the present application, the electrolyte includes a fluorine-containing additive, and the secondary battery satisfies: 0.5 ≤ m2 / m1 ≤ 5;

[0024] Wherein, m1% is the mass percentage of the M element in the lithium nickel oxide;

[0025] m2% is the mass percentage of the fluorine-containing additive in the electrolyte.

[0026] As an embodiment of the present application, at least one of the following (f) to (h) is satisfied:

[0027] (f) 0.5 ≤ m1 ≤ 3;

[0028] (g) 1 ≤ m2 ≤ 5;

[0029] (h) The fluorine-containing additive includes one or more of hexafluoroglutaric anhydride, fluorinated ethylene carbonate, difluoroethylene carbonate, and diethyl fluoromalonate.

[0030] As an embodiment of the present application, the negative electrode active material includes graphite and silicon oxide material, and the mass percentage of the silicon oxide material in the negative electrode active material is 1% to 30%.

[0031] As an embodiment of the present application, the porosity of the positive electrode sheet is 20% to 30%; and / or

[0032] The porosity of the negative electrode sheet is 30% to 45%.

[0033] The second aspect of the present application provides an electrical device including the secondary battery described above.

[0034] The beneficial effects of the present application are as follows: By controlling the distribution of the number of large and small particles of the positive active material secondary particles in the SEM image of the positive electrode sheet, the volume average particle size of the negative active material, and the discharge specific capacities of the positive active material and the negative active material, the following relationship is satisfied: 1 ≤ Y ≤ 40, Y = (n1 / n2)·Dv50·(C1 / C2); the particle size distribution of the positive active material shows a multi-level grading, the particle pores of the positive active material are maximally filled, effectively improving the tap density and specific capacity per gram of the positive active material, enhancing the wettability of the electrolyte to the secondary particles, being able to effectively reduce the interfacial side reactions, reduce the gas generation of the secondary battery, improve the diffusion path of lithium ions, improve the stability of the positive active material particles and the negative active material particles, and enhance the anti-crushing ability of the particles. At the same time, the discharge specific capacities of the positive active material and the negative active material have good compatibility, thereby effectively improving the cycle performance and rate performance of the secondary battery. Detailed implementation manners

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. Apparently, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without making creative efforts shall fall within the protection scope of the present application.

[0036] In the present application, among the technical features described in an open-ended manner, there are included closed technical solutions composed of the listed features, as well as open technical solutions including the listed features.

[0037] In the present application, regarding the numerical range, unless otherwise specified, the above numerical range is considered continuous and includes the minimum and maximum values of this range, as well as each value between such minimum and maximum values. Further, when the range refers to an integer, it includes each integer between the minimum and maximum values of this range. In addition, when multiple ranges are provided to describe features or characteristics, these ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0038] The reagents or instruments used in the present application that are not specified by the manufacturer can all be conventional products obtained through commercial purchase.

[0039] The inventors of the present application have found through research that among the two relatively common designs of cathode active materials on the current market, one is composed of one or very few primary particles, that is, single-crystal materials. Single-crystal cathodes do not contain smaller grains, so there are no grain boundaries and no intergranular cracks will occur. In addition, their relatively low surface-to-volume ratio can minimize interfacial side reactions, such as gas evolution, transition metal dissolution, and side reactions with the electrolyte, thus achieving excellent thermal stability. However, in the case of single-crystal cathodes, their micron size results in longer Li + diffusion paths, leading to poor reaction kinetics and low capacity. Although the mechanical strength of single-crystal materials is high, the compaction ability of the materials is low, and the compaction of the cathode electrode sheet composed of single-crystal materials is low, which is not conducive to improving the energy density of the battery system. The other is secondary particle materials composed of many primary particles, and this material also has many problems. For example, in secondary particle materials of the same particle size, a large number of primary particles will make the primary particles too small, with a large specific surface area and serious side reactions with the electrolyte, resulting in serious gas production; this secondary particle material is easily broken during the tablet pressing process, with poor cycling performance, poor thermal stability, and poor safety. There are also different considerations in the design of the particle size of secondary particles. The particle size of the cathode active material has an important impact on the overall electrochemical performance of the battery. Small-particle materials have better kinetics and can match battery systems with high requirements for fast charging performance, but small particles are not pressure-resistant and are easily broken during cycling. Large particles can have higher compaction ability and significantly improve the anti-breaking ability of the particles, but the disadvantage is poor kinetic performance.

[0040] Therefore, based on the above problems, the embodiments of the present application provide a secondary battery and an electrical device using the same. The secondary battery includes a cathode electrode sheet, an anode electrode sheet, and an electrolyte. The cathode electrode sheet includes a cathode current collector and a cathode active material layer provided on at least one surface of the cathode current collector. The cathode active material layer includes a cathode active material, and the cathode active material includes secondary particles; the anode electrode sheet includes an anode current collector and an anode active material layer provided on at least one surface of the anode current collector. The anode active material layer includes an anode active material;

[0041] The secondary battery satisfies: 1 ≤ Y ≤ 40, Y = (n1 / n2)·Dv50·(C1 / C2);

[0042] where n1 pieces / 0.01 mm 2 is the number of the secondary particles with an inner diameter ≥ 8 μm in the cathode active material in the cathode active material layer in the SEM image within 0.01 mm 2 ;

[0043] n2 pieces / 0.01 mm 2For the positive electrode active material in the positive electrode active material layer, in the SEM image, 0.01 mm 2 the number of the secondary particles with an inner diameter < 8 μm;

[0044] Dv50 μm is the volume average particle size of the negative electrode active material;

[0045] C1 mAh / g is the discharge specific capacity of the positive electrode active material measured in the voltage range of 2.8 V to 4.3 V;

[0046] C2 mAh / g is the discharge specific capacity of the negative electrode active material measured in the voltage range of 0.01 V to 2 V.

[0047] The inventors of the present application have found through research that controlling the diameter of the secondary particles of the positive electrode active material in the SEM image, the volume average particle size of the negative electrode active material, and the discharge specific capacities of the positive electrode active material and the negative electrode active material can affect the performance of the secondary battery. In the present application, by controlling the diameter of the secondary particles in the SEM image, the volume average particle size of the negative electrode active material, and the discharge specific capacities of the positive electrode active material and the negative electrode active material to satisfy the following relationship: 1 ≤ Y ≤ 40, Y = (n1 / n2)·Dv50·(C1 / C2); the particle size distribution of the positive electrode active material presents a multi-stage grading, the particle pores of the positive electrode active material are maximally filled, effectively improving the tap density and gram capacity of the positive electrode active material, enhancing the wettability of the electrolyte to the secondary particles, effectively reducing the interfacial side reactions, reducing the gas generation of the secondary battery, improving the diffusion path of lithium ions, improving the stability of the positive electrode active material particles and the negative electrode active material particles, and enhancing the anti-crushing ability of the particles. At the same time, the discharge specific capacities of the positive electrode active material and the negative electrode active material have good adaptability, thereby effectively improving the cycle performance and rate performance of the secondary battery.

[0048] In one of the embodiments, 4 ≤ Y ≤ 20. In particular, when Y is controlled within this range, the cycle performance and rate performance can be further improved. For example, Y can also be one of 4, 8, 10, 13, 19, 20 or the range value of any two of them.

[0049] Among them, for the positive electrode active material in the positive electrode plate, 0.01 mm 2 the number (n1) of the secondary particles with an inner diameter ≥ 8 μm and 0.01 mm 2The testing method for the number (n2) of the secondary particles with an inner diameter < 8 μm is as follows: A sample containing the cross-section of the positive electrode active material layer is prepared using a cross-section polishing instrument (such as the IB-09010CP type argon ion cross-section polishing instrument of JEOL Ltd., Japan). After performing scanning electron microscope testing on the sample, a cross-section SEM image of the positive electrode active material particles in the positive electrode active material layer is obtained. The diameter of the secondary particles in a certain area SEM image (area: 0.01 mm 2 ) of the tested sample is measured using the measurement function built into the testing software or other tools with measurement capabilities (such as Nanomeature). The number of secondary particles with an inner diameter ≥ 8 μm and the number of secondary particles with a diameter < 8 μm within 0.01 mm 2 are counted to obtain the values of n1 and n2.

[0050] Among them, the specific testing method for the discharge specific capacity of the positive electrode active material measured in the voltage range of 2.8 V to 4.3 V is as follows: The positive electrode active material is mixed into a slurry according to the formulation ratio of active material: conductive agent: binder = 90:5:5, and after processes such as coating and rolling, a positive electrode sheet is obtained. Using a lithium sheet as the negative electrode, PP polypropylene as the separator, and the electrolyte prepared by dissolving EC:PC:DMC in a mass ratio of 30:30:40 in 1 mol / L LiPF6, a coin cell half-cell is assembled and tested to obtain the discharge specific capacity of the sample. The specific testing method is: The assembled coin cell half-cell is charged at a constant current of 0.1 C to the upper limit voltage of 4.3 V, left standing for 5 minutes, then charged at a constant voltage until the current ≤ 0.05 mA at the upper limit voltage, left standing for 5 minutes, and then discharged at a constant current of 0.1 C to the lower limit voltage of 2.8 V.

[0051] Among them, the specific testing method for the discharge specific capacity of the negative electrode active material measured in the voltage range of 0.01 V to 2 V is as follows: The negative electrode active material is mixed into a slurry according to the formulation ratio of active material: conductive agent: binder = 90:5:5, and after processes such as coating and rolling, a negative electrode sheet is obtained. Using a lithium sheet as the reference negative electrode, PP polypropylene as the separator, and the electrolyte prepared by dissolving EC:PC:DMC in a mass ratio of 30:30:40 in 1 mol / L LiPF6, a coin cell half-cell is assembled and tested to obtain the discharge specific capacity of the sample. The specific testing method is: The assembled coin cell is discharged at a constant current of 0.05 C to 0.01 V, then discharged at currents of 40 μA and 10 μA to 0.005 V, left standing for 5 min, and then charged at a constant current of 0.1 C to 2 V.

[0052] In one embodiment, 8 ≤ n1 ≤ 42. For example, it can be 8, 10, 12, 14, 16, 22, 26, 30, 34, 38, 42, or a range composed of any two of these values. By controlling n1 within this range, the interfacial side reactions can be effectively reduced, the stability of the positive electrode active material during the tablet pressing process can be effectively improved, the anti - fragmentation ability of the particles can be significantly enhanced, thereby improving the cycle performance and rate performance of the secondary battery.

[0053] In one embodiment, 6 ≤ n2 ≤ 35. For example, it can be 6, 8, 10, 12, 14, 20, 24, 28, 31, 35, or a range composed of any two of these values. By controlling n2 within this range, the diffusion distance of lithium ions in the secondary particles can be effectively reduced, the insertion and extraction speed of lithium ions can be improved, the contact area with the electrolyte can be increased, the electrochemical reactivity of the secondary battery can be enhanced, thereby improving the cycle performance and rate performance of the secondary battery.

[0054] In one embodiment, 5 ≤ Dv50 ≤ 16. For example, it can be 5, 6, 8, 10, 12, 14, 15, 16, or a range composed of any two of these values. By controlling the volume - average particle size of the negative electrode active material within this range, the insertion and extraction of lithium ions are further promoted, it can contact the electrolyte more fully, form more active sites, relieve the volume expansion and mechanical stress caused by the insertion and extraction of lithium ions, reduce the risk of particle cracking. At the same time, the discharge specific capacity of the positive electrode active material and the negative electrode active material has good adaptability, thereby effectively improving the cycle performance and rate performance of the secondary battery.

[0055] Among them, the volume - average particle size Dv50 of the negative electrode active material has the meaning well - known in the art, which represents the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 50%. The Dv50 of the negative electrode active material can be obtained by performing particle size analysis and testing using a Malvern laser particle size analyzer. The reference standard for particle size analysis and testing is: GB - T 19077 - 2016. The specific method includes: obtaining the negative electrode sheet of the secondary battery and placing it in a beaker, adding pure water to ultrasonically dissolve the binder for 1 h, pouring off the upper liquid, and repeating the above ultrasonic dissolution step 2 - 3 times. Taking out the current collector and filtering to obtain a solid powder sample, drying the powder sample and transferring it to a box furnace, and calcining at 450 °C for 3 h - 5 h to obtain a calcined powder sample, and then performing particle size analysis and testing on the calcined powder sample using a Malvern laser particle size analyzer, the Dv50 of the negative electrode active material in the negative electrode sheet can be obtained.

[0056] In one embodiment, 204 ≤ C1 ≤ 222. For example, it can be 204, 208, 210, 215, 220, 222 or a range composed of any two of these values. By controlling C1 within this range, the lithium extraction amount of the positive electrode and the structural stability of the positive electrode can be improved, enabling the secondary battery to have both high energy density and long-term life performance, thereby meeting the long-range and slow-decay requirements of electric vehicles.

[0057] In one embodiment, 208 ≤ C1 ≤ 218.

[0058] In one embodiment, 210 ≤ C1 ≤ 215.

[0059] In one embodiment, 364 ≤ C2 ≤ 655. For example, it can be 364, 380, 400, 420, 450, 460, 480, 500, 520, 550, 580, 600, 620, 640, 650, 655 or a range composed of any two of these values. By controlling C2 within this range, the secondary battery has both high energy density and long-term life performance, thereby meeting the long-range and slow-decay requirements of electric vehicles.

[0060] In one embodiment, 380 ≤ C2 ≤ 560.

[0061] In one embodiment, it satisfies: 0.2 ≤ n1 / n2 ≤ 7. For example, it can be 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7 or a range composed of any two of these values. By controlling the ratio of n1 / n2 within the above range, the filling effect of the pores of the particles of the positive electrode active material is further optimized, effectively improving the tap density and specific capacity of the positive electrode active material, enhancing the wettability of the electrolyte to the secondary particles, effectively reducing the interfacial side reactions, and reducing the gas generation of the secondary battery.

[0062] In one embodiment, the positive electrode active material includes lithium nickel oxide, and the lithium nickel oxide includes the chemical formula Li 1+a [Ni x Co y Mn z M bAt least one of the compounds of O2, M includes at least one of Ti, Zr, Sr, Sb, Ta, Ru, Nd, V, Ce, Mo, where 0.5 ≤ x < 1, 0 ≤ y < 0.3, 0 ≤ z < 0.3, -0.1 ≤ a < 0.2, 0 ≤ b < 0.3, and x + y + z + b = 1. In this embodiment, the lithium nickel oxide is a secondary particle, which is formed by the aggregation of primary particles of lithium nickel oxide. When the positive electrode active material is the above lithium nickel oxide containing M, the above doping elements can broaden the lithium layer spacing, promote the transport of lithium ions, play a role in inhibiting the migration of nickel ions to the lithium layer, reduce cation mixing, thereby improving the structural stability of the positive electrode active material. At the same time, it can strengthen the transition metal-oxygen bond, inhibit harmful phase changes during cycling, and inhibit oxygen release. Therefore, the secondary battery composed of the positive electrode active material has excellent rate performance and cycling performance.

[0063] In one embodiment, the element M in the lithium nickel oxide can be at least one of Zr, Sr, Ti, Sb, Nb, Y, Mo. By selecting the above elements for M, it can effectively inhibit the lattice distortion of lithium nickel oxide during charge and discharge, enhance the structural stability of the material, reduce the capacity loss caused by volume change and structural degradation during long-term cycling of the material, and can extend the cycle life of the battery. It can improve the electronic conductivity of the material and the transport rate of lithium ions, and improve the charge and discharge efficiency and power performance of the secondary battery.

[0064] In one embodiment, the element M in the lithium nickel oxide can include Zr and Sr. Zr and Sr can inhibit the migration of Ni at the transition metal site of lithium nickel oxide 2+ and effectively reduce the degree of ion mixing, promoting the transport of lithium ions. On the other hand, Zr and Sr form Zr-O bonds and Sr-O bonds with higher bond energies through bonding with lattice oxygen, effectively inhibiting the lattice distortion of the material during charge and discharge and enhancing the structural stability of the material.

[0065] In one embodiment, the element M in the lithium nickel oxide can include Nb and Y. Nb and Y can improve the conductivity of lithium nickel oxide, and at the same time can expand the lattice parameters, broaden the lithium ion migration path, lower the lithium ion migration energy barrier, thereby accelerating the migration of lithium ions. It can slow down the anisotropic mechanical strain and inhibit the formation and expansion of microcracks, inhibit the erosion of the electrolyte, and reduce the occurrence of side reactions.

[0066] In one embodiment, the positive electrode active material further includes a lithium-containing phosphate, and the lithium-containing phosphate includes a chemical formula of Li n Mn t Fe u A sAt least one of the compounds of PO4, wherein A comprises one or more of Al, Ni, Co, Ti, La, Ce, Cr, Mo, Ca, Ga, V, Nb, Zr, In, Zn, and Y, 0.95 < n < 1.15, t + u + s = 1, 0 ≤ t < 1, 0 < u ≤ 1, 0 ≤ s ≤ 0.02. In this embodiment, the lithium-containing phosphate is primary particles. In one embodiment, the element A of the above lithium-containing phosphate comprises one or more of Ti and Al. Ti doping can improve the thermal stability and cycling performance of the material, and Al doping can improve the electronic conductivity of the material, optimizing the comprehensive performance of the lithium-containing phosphate.

[0067] In one embodiment, the mass percentage of the lithium-containing phosphate in the positive electrode active material is 5% to 30%, for example, it can be 5%, 6%, 8%, 10%, 12%, 15%, 16%, 18%, 20%, 22%, 24%, 25%, 26%, 28%, 30% or the range composed of any two of these values. By using a combination of lithium nickel oxide and lithium-containing phosphate as the positive electrode active material in this application, it is beneficial to improve electron conductivity and ion diffusion, improve the polarization phenomenon during the charging / discharging process of the secondary battery, enhance the power performance of the secondary battery under low SOC conditions, improve the safety performance of the secondary battery and reduce costs, taking into account the high energy density of the secondary battery.

[0068] In one embodiment, the electrolyte comprises a fluorine-containing additive, and the secondary battery satisfies: 0.5 ≤ m2 / m1 ≤ 5, for example, it can be the range composed of any two of 0.5, 1, 2, 3, 4, 5.

[0069] Wherein, m1% is the mass percentage of the M element in the lithium nickel oxide;

[0070] m2% is the mass percentage of the fluorine-containing additive in the electrolyte.

[0071] By controlling the value of m2 / m1 within the above range in this application, the interfacial stability between the positive and negative electrodes and the electrolyte can be further improved, a stable and dense interfacial film can be formed, the stability of the positive electrode active material can be further improved, the metal dissolution of the positive electrode active material and the electrolyte decomposition can be effectively inhibited, the integrity of the positive electrode sheet can be maintained, and the volume expansion of the negative electrode active material can be alleviated, thereby further improving the cycling performance and rate performance of the secondary battery.

[0072] The test method for the type and content of the M element is as follows: Using the energy-dispersive X-ray spectroscopy (SEM-EDS) of a scanning electron microscope, perform surface analysis / line analysis on the cross-sectional composition of the secondary particles with different particle sizes, and the composition and content of the element M of the secondary polycrystalline particles with different particle sizes can be determined.

[0073] In one embodiment, 0.5 ≤ m1 ≤ 3. For example, it can be 0.5, 0.6, 0.8, 1, 1.2, 1.5, 1.6, 1.8, 2, 2.2, 2.4, 2.5, 2.6, 2.8, 3, or a range composed of any two of these values.

[0074] In one embodiment, 1 ≤ m2 ≤ 5. For example, it can be 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or a range composed of any two of these values.

[0075] In one embodiment, the fluorine-containing additive includes one or more of hexafluoroglutaric anhydride, fluorinated ethylene carbonate, difluoroethylene carbonate, and diethyl fluoromalonate.

[0076] In one embodiment, the negative electrode active material includes graphite and silicon-oxygen material. The mass percentage of the silicon-oxygen material in the negative electrode active material is 1% - 30%. For example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 16%, 20%, 30%, or a range composed of any two of these values. The negative electrode active material composed of graphite and silicon-oxygen material adopted in this application has excellent compatibility with the positive electrode active material. While maintaining the stability of graphite, it utilizes the high-capacity characteristics of silicon-oxygen to improve the capacity and energy density of the negative electrode active material, alleviate the pulverization of the negative electrode active material during repeated charge and discharge processes, provide a stable electron conduction path, improve the stability of the negative electrode active material, and thus further improve the cycle performance and rate performance of the secondary battery.

[0077] In one embodiment, the porosity of the positive electrode sheet is 20% - 30%. For example, it can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, or a range composed of any two of these values. When the porosity of the positive electrode sheet is within this range, the wettability of the electrolyte is better, resulting in lower polarization of the secondary battery, faster lithium-ion transmission rate, lower internal resistance of the secondary battery, better cycle performance of the battery, and moderate tightness degree of the combination between the primary particles. Furthermore, the secondary particles composed of the primary particles have relatively high compressive strength, strong ability to resist particle breakage, and are not easily broken during long-term cycling, reducing the side reactions between the active surface and the electrolyte, thereby making the comprehensive performance of the secondary battery better.

[0078] In one of the embodiments, the porosity of the negative electrode sheet is 30% to 45%, for example, it can be 30%, 32%, 34%, 35%, 36%, 38%, 40%, 42%, 44%, 45% or a range composed of any two of these values. When the porosity of the negative electrode sheet is within the above range, it can effectively reduce the swelling of the negative electrode material during the cycling process and improve the long cycling life of the battery. At the same time, it can keep the material with a lower impedance and effectively improve the fast charging performance of the material. When the porosity of the negative electrode sheet does not meet the target range, it will increase the contact and consumption between the material and the electrolyte, form a relatively thick SEI film, reduce the amount of electrolyte, resulting in a significant decrease in the cycling life of the material, an increase in the swelling rate of the electrode sheet. At the same time, when there are relatively large pore diameters, it may lead to a reduction in the mechanical stability of the electrode material, thus affecting the cycling life and safety of the battery.

[0079] An embodiment of the present application provides an electrical device, including the secondary battery described above, and the secondary battery serves as the power supply of the electrical device.

[0080] Exemplarily, the above electrical device 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, satellites, energy storage systems, etc., but is not limited thereto.

[0081] The following further elaborates the present application with specific embodiments:

[0082] Example 1

[0083] A method for preparing a secondary battery includes the following steps:

[0084] (1) Preparation of the positive electrode active material:

[0085] S1. Nickel sulfate, manganese sulfate, and cobalt sulfate are added to deionized water, and a mixed solution is prepared and added to the first reaction kettle and mixed evenly, where the molar ratio of nickel element, manganese element, and cobalt element is Ni:Co:Mn = 90:5:5; then, a metering pump is used to introduce ammonia water (concentration 0.4 mol / L) and sodium hydroxide aqueous solution (concentration 1 mol / L) into the first reaction kettle, and the pH of the reaction system is adjusted to 11.3 and stirred evenly to obtain a mixed solution.

[0086] S2. Nb2O5 is added to a certain volume of ethanol solution to obtain a mixture A, and the addition amount of Nb2O5 is such that the molar amount of Nb element in the active material particles is in a ratio of Nb:Me = 0.002:0.996 to the total molar amount of nickel element, cobalt element, and manganese element (denoted as Me).

[0087] S3. Add Y2O3 into an ethanol solution of a certain volume to obtain a mixture B. The addition amount of Y2O3 is such that the molar ratio of Y element to the total molar amount of Ni element, Co element and Mn element in the active material particles is Y:Me = 0.002:0.996.

[0088] S4. Add the mixture A obtained in step 2 and the mixture B obtained in step 3 into a second reaction kettle; then add the mixed solution obtained in step 1 into the second reaction kettle, continuously stir, and carry out a co-precipitation reaction. The co-precipitation reaction is divided into a first stage and a second stage. The stirring speed in the first stage is 400 rpm, the pH value of the reaction solution is 12.5, the ammonia value is 14 g / L, and the reaction is carried out for 2.5 h; the stirring speed in the second stage is 500 rpm, the pH value of the reaction solution is 12.0, the ammonia value is 8 g / L, and at the same time, stop adding the mixtures obtained in steps 2 and 3, and react for 3 h to obtain a solid-liquid mixture;

[0089] S5. Filter the solid-liquid mixture obtained in step 4, wash, dry, screen and demagnetize the obtained filter cake to obtain a ternary cathode active material precursor with a variety of particle size distributions and in-situ doping of particle orientation elements (Ni 0.90 Co 0.05 Mn 0.05 ) 0.996 Nb 0.002 Y 0.002 (OH)2.

[0090] S6. Mix the lithium salt Li2CO3 and the cathode active material precursor (Ni 0.90 Co 0.05 Mn 0.05 ) 0.996 Nb 0.002 Y 0.002 (OH)2, and then carry out mechanical mixing. Among them, the addition amounts of lithium carbonate and the cathode active material precursor are such that the molar ratio of lithium element to the total molar amount of Ni element, Co element and Mn element is Li:Me = 1.08:1, Me = Ni + Co + Mn. Put the mixed material into a tube furnace, heat it up to 750 °C at a rate of 5 °C / min in an air atmosphere and sinter for 13 h, then cool it to room temperature with the furnace, and crush to obtain Li with different particle size gradings 1.08 (Ni 0.90 Co 0.05 Mn 0.05 ) 0.996 Nb 0.002 Y 0.002 O2.

[0091] S7. The lithium nickel oxide Li prepared in step S6 1.08 (Ni 0.90 Co 0.05 Mn0.05 ) 0.996 Nb 0.002 Y 0.002 O₂ is mixed uniformly with a lithium-containing phosphate (specifically LiMn 0.6 Fe 0.4 PO₄) in a mass ratio of 80:20 to obtain the positive electrode active material.

[0092] (2) Preparation of the positive electrode sheet

[0093] The positive electrode active material prepared above, a conductive agent carbon black, and a binder polyvinylidene fluoride are added to a high-speed vacuum mixer in a mass ratio of 97.3:1.8:0.9 and mixed uniformly. Subsequently, N-methylpyrrolidone is added as a solvent, and after stirring for 12 h, a slurry is obtained. The obtained slurry is uniformly coated on an aluminum foil positive electrode current collector by a coater, placed in an oven, and dried at a high temperature of 110 °C. Subsequently, through processes such as rolling, cutting, and slitting, the positive electrode sheet can be prepared, wherein the sheet compact density of the positive electrode sheet is designed to be 3.5 g / cm 3 .

[0094] (3) Preparation of the negative electrode sheet

[0095] Graphite with Dv50 = 12.5 μm and SiO₂ with Dv50 = 8.5 μm are mixed uniformly in a mass ratio of 95:5 to obtain the negative electrode active material;

[0096] The negative electrode active material, a conductive agent acetylene black, a binder styrene-butadiene rubber, and a negative electrode thickener sodium carboxymethyl cellulose are added to a high-speed vacuum mixer in a mass ratio of 96:2:1:1 and mixed uniformly. Subsequently, deionized water is added as a solvent, and after stirring for 12 h, a slurry is obtained. The obtained slurry is uniformly coated on a copper foil negative electrode current collector by a coater, placed in an oven, and dried at a high temperature of 120 °C. Subsequently, through processes such as rolling, cutting, and slitting, the negative electrode sheet can be prepared, wherein the sheet compact density of the negative electrode sheet is designed to be 1.6 g / cm 3 .

[0097] (4) Preparation of the separator

[0098] A polyethylene polymer film is selected as the separator.

[0099] (5) Preparation of the electrolyte

[0100] Ethylene carbonate and dimethyl carbonate are mixed in a volume ratio of 1:1 to obtain an organic solvent. Then, lithium salt lithium hexafluorophosphate is dissolved in the above organic solvent, and hexafluoroglutaric anhydride with a mass ratio of 2.5% is added as a fluorine-containing additive to prepare the electrolyte, wherein the concentration of lithium salt lithium hexafluorophosphate is 1 mol / L.

[0101] (6) Preparation of secondary battery

[0102] The positive electrode sheet, negative electrode sheet, and separator obtained above are wound in a predetermined order to prepare a bare battery cell. The bare battery cell is placed in an outer packaging aluminum plastic film, baked to remove moisture, a certain amount of electrolyte is injected, and then vacuum packaged to prepare a secondary battery.

[0103] Among them, the relevant parameters of Example 1 are shown in Tables 1, 2, and 3.

[0104] Examples 2-5

[0105] The differences between Examples 2-5 and Example 1 are that in Examples 2-5, by adjusting the mixing mass ratio of lithium nickel oxide Li 1.08 (Ni 0.90 Co 0.05 Mn 0.05 ) 0.996 Nb 0.002 Y 0.002 O2 and lithium-containing phosphate (wherein the lithium-containing phosphate is selected as LiMn 0.6 Fe 0.38 Ti 0.01 Al 0.01 PO4) in the preparation process of the positive active material in step (1), the value of C1 is adjusted.

[0106] Examples 6-9

[0107] The differences between Examples 6-9 and Example 1 are that in Examples 6-9, by adjusting the mixing mass ratio of graphite and SiO2 in the preparation process of the negative electrode sheet in step (3), the value of C2 is adjusted.

[0108] Examples 10-13

[0109] The differences between Examples 10-13 and Example 1 are that in Examples 10-13, by adjusting the types of doping sources added in S2 and S3 in the preparation process of the positive active material in step (1), positive active materials doped with different types of M elements are obtained.

[0110] Examples 14-17

[0111] The differences between Examples 14-17 and Example 1 are that in Examples 14-17, by adjusting the reaction times of the first and second stages of the co-precipitation reaction in step S4 of the preparation process of the positive active material in step (1), ternary positive active material precursors with different particle size distributions are obtained.

[0112] Examples 18-20

[0113] Examples 18 to 20 are different from Example 1 in that, in Examples 18 to 20, by adjusting the Dv50 of the graphite and SiO2 anode materials used in the preparation process of the anode electrode in step (3), anode active materials with different Dv50 are obtained through adjustment.

[0114] Examples 21 to 23

[0115] Examples 21 to 23 are different from Example 1 in that, in Examples 21 to 23, by adjusting the doping source ratio added in S2 and S3 in the preparation process of the cathode active material in step (1), cathode active materials with different doping M element contents are obtained through adjustment.

[0116] Examples 24 to 26

[0117] Examples 24 to 26 are different from Example 1 in that, in Examples 24 to 26, by adjusting the content of hexafluoroglutaric anhydride added in the preparation process of the electrolyte in step (5), electrolytes with different fluorine-containing additive contents are obtained through adjustment.

[0118] Examples 27 to 28

[0119] Examples 27 to 28 are different from Example 1 in that, in Examples 27 to 28, by adjusting the types of fluorine-containing additives added in the preparation process of the electrolyte in step (5), electrolytes with different types of fluorine-containing additives are obtained through adjustment.

[0120] Comparative Examples 1 to 2

[0121] Comparative Examples 1 to 2 are different from Example 1 in that, in Comparative Examples 1 to 2, by adjusting the reaction times of the first and second stages of the coprecipitation reaction in step S4 of the preparation process of the cathode active material to obtain a ternary cathode active material precursor with different particle size distributions, by adjusting the mixing mass ratio of lithium nickel oxide Li 1.08 (Ni 0.90 Co 0.05 Mn 0.05 ) 0.996 Nb 0.002 Y 0.002 O2 and the mixing mass ratio of LiMn 0.6 Fe 0.4 PO4 (lithium iron manganese phosphate), and by adjusting the mixing mass ratio of graphite and SiO2 in the preparation process of the anode electrode in step (3), a secondary battery system with different Y values is obtained through adjustment.

[0122] Table 1

[0123]

[0124] Table 2

[0125]

[0126]

[0127] Table 3

[0128]

[0129]

[0130] Performance Test

[0131] 1. Test Method for 1 / 3C Capacity of Secondary Battery

[0132] The secondary battery is left standing for 2 h in a constant temperature environment of 25 °C, and then charged at a constant current of 1 / 3C to 4.25 V between 2.8 V and 4.25 V, then charged at a constant voltage of 4.25 V until the current ≤ 0.05 mA, left standing for 5 min, and then discharged at a constant current of 1C to 2.8 V, and the capacity of the secondary battery is recorded; the capacity test value is divided by the mass of the positive active material in the battery, which is the 1 / 3C specific capacity of the secondary battery. The test results are shown in Table 4.

[0133] 2. Test Method for Cycle Performance of Secondary Battery

[0134] In a constant temperature environment of 45 °C, charged at a constant current of 1C to 4.25 V between 2.8 V and 4.25 V, then charged at a constant voltage of 4.25 V until the current ≤ 0.05 mA, left standing for 5 min, and then discharged at a constant current of 1C to 2.8 V, and the capacity is denoted as Dn (n = 0, 1, 2...), and the previous process is repeated until the capacity decays to 80% of the initial capacity, and the number of cycles of the lithium-ion secondary battery is recorded. The test results are shown in Table 4.

[0135] 3. Test Method for High-Temperature Gas Generation of Secondary Battery

[0136] After the secondary battery is fully charged at a constant current of 1C to 4.25 V, it is left standing in a constant temperature oven at 70 °C for 30 days. And the initial volume and the volume after standing for 30 days of the secondary battery are measured by the water displacement method to obtain the volume expansion rate of the secondary battery.

[0137] Volume expansion rate of secondary battery (%) = (Volume after standing for 30 days / Initial volume - 1) × 100%.

[0138] Table 4

[0139]

[0140]

[0141] As can be seen from Table 1, in this application, by controlling the diameter of the secondary particles in the SEM image, the volume average particle size of the negative active material, and the discharge specific capacities of the positive and negative active materials to satisfy the following relationship: 1 ≤ Y ≤ 40, Y = (n1 / n2)·Dv50·(C1 / C2); the cycle performance and rate performance of the secondary battery can be effectively improved.

[0142] By comparing Example 17 and 14 with Examples 1 to 13, 15 to 16, 18 to 28, it can be seen that by controlling 4 ≤ Y ≤ 20, the cycle performance and rate performance of the secondary battery can be further improved.

[0143] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and not to limit the protection scope of this application. Although this application has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of this application can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of this application.

Claims

1. A secondary battery, comprising a positive electrode plate, a negative electrode plate, and an electrolyte, characterized in that, The positive electrode plate includes a positive current collector and a positive active material layer provided on at least one surface of the positive current collector. The positive active material layer includes a positive active material, and the positive active material includes secondary particles. The negative electrode plate includes a negative current collector and a negative active material layer provided on at least one surface of the negative current collector. The negative active material layer includes a negative active material. The secondary battery satisfies: 1 ≤ Y ≤ 40, where Y = (n1 / n2)·Dv50·(C1 / C2). Among them, n1 pieces per 0.01 mm 2 For the positive electrode active material in the positive electrode active material layer, in the SEM image, 0.01 mm 2 The number of the secondary particles with an inner diameter ≥ 8 μm n2 pieces / 0.01 mm 2 For the positive electrode active material in the positive electrode active material layer, in the SEM image, 0.01 mm 2 The number of the secondary particles with an inner diameter < 8 μm Dv50 μm is the volume average particle size of the negative active material. C1 mAh / g is the discharge specific capacity of the positive active material measured in the voltage range of 2.8 V to 4.3 V. C2 mAh / g is the discharge specific capacity of the negative active material measured in the voltage range of 0.01 V to 2 V.

2. The secondary battery according to claim 1, wherein It satisfies at least one of the following (a) to (e): (a) 8 ≤ n1 ≤ 42; (b) 6 ≤ n2 ≤ 35; (c) 5 ≤ Dv50 ≤ 16 (d) 204 ≤ C1 ≤ 222; (e) 364 ≤ C2 ≤ 655.

3. The secondary battery according to claim 1, wherein, It satisfies: 0.2 ≤ n1 / n2 ≤ 7.

4. The secondary battery according to claim 1, characterized in that, The positive electrode active material includes lithium nickel oxide, and the lithium nickel oxide includes at least one of compounds with the chemical formula Li 1+a [Ni x Co y Mn z M b O2, where M includes at least one of Ti, Zr, Sr, Sb, Ta, Ru, Nd, V, Ce, and Mo. Among them, 0.5 ≤ x < 1, 0 ≤ y < 0.3, 0 ≤ z < 0.3, -0.1 ≤ a < 0.2, 0 ≤ b < 0.3, and x + y + z + b = 1.

5. The secondary battery according to claim 4, wherein The positive electrode active material further includes a lithium-containing phosphate, and the lithium-containing phosphate includes at least one of compounds with the chemical formula Li n Mn t Fe u A s PO4, where A includes one or more of Al, Ni, Co, Ti, La, Ce, Cr, Mo, Ca, Ga, V, Nb, Zr, In, Zn, and Y, 0.95 < n < 1.15, t + u + s = 1, 0 ≤ t < 1, 0 < u ≤ 1, and 0 ≤ s ≤ 0.

02.

6. The secondary battery according to claim 5, characterized in that, The mass percentage of the lithium-containing phosphate in the positive active material is 5% to 30%.

7. The secondary battery according to claim 4 or 5, characterized in that, The electrolyte includes a fluorine-containing additive, and the secondary battery satisfies: 0.5 ≤ m2 / m1 ≤ 5; where m1% is the mass percentage of the M element in the lithium nickel oxide. m2% is the mass percentage of the fluorine-containing additive in the electrolyte.

8. The secondary battery according to claim 7, wherein, It satisfies at least one of the following (f) to (h): (f) 0.5 ≤ m1 ≤ 3; (g) 1 ≤ m2 ≤ 5; (h) The fluorine-containing additive includes one or more of hexafluoroglutaric anhydride, fluorinated ethylene carbonate, difluoroethylene carbonate, and diethyl fluoromalonate.

9. The secondary battery according to claim 1, characterized in that, The negative active material includes graphite and silicon-oxygen material, and the mass percentage of the silicon-oxygen material in the negative active material is 1% to 30%.

10. The secondary battery according to claim 1, wherein The porosity of the positive electrode plate is 20% to 30%; and / or The porosity of the negative electrode plate is 30% to 45%.

11. An electrical device, characterized in that, It includes the secondary battery according to any one of claims 1 to 10.

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