Secondary battery and electric device

Abstract

The application provides a secondary battery and an electric device, wherein the secondary battery comprises a negative electrode sheet, and a conductive agent in the negative electrode sheet is composed of at least two different conductive materials, and the secondary battery satisfies: 10 < [100000*(Dv50)] / [P 2 *(lnM)] < 34; wherein P is the tap density of the conductive agent, g / L; Dv50 is the particle size corresponding to the volume cumulative distribution percentage of the negative electrode active material being equal to 50%, μm; and M is the molar mass of the binder, g / mol. By setting the conductive agent to be composed of at least two different conductive materials, and matching the relationship among the Dv50 of the negative electrode active material, the tap density of the conductive agent and the molar mass of the binder, the conductive network of the electrode sheet is effectively constructed, the ionic conductivity and the electronic conductivity of the negative electrode sheet are improved, the charging rate performance is effectively improved, and the secondary battery with excellent fast charging performance is prepared.

Description

Technical Field

[0001] This invention relates to the field of battery manufacturing technology, and in particular to a secondary battery and electrical equipment. Background Technology

[0002] Currently, the negative electrode sheet is an important component of secondary batteries, and its kinetic performance is a key factor affecting the performance of secondary batteries.

[0003] In the current technology, electric vehicles have placed higher demands on the fast discharge performance of secondary batteries. However, the fast discharge performance of existing secondary batteries is not good and cannot effectively meet the demand for excellent fast charging of secondary batteries.

[0004] Therefore, there is an urgent need to provide a negative electrode with excellent kinetic performance to improve the fast charging performance of secondary batteries. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a secondary battery and an electrical device to solve the problem of poor fast charging performance of existing secondary batteries.

[0006] To solve the above problems, the present invention is achieved through the following technical solution:

[0007] This invention proposes a secondary battery, comprising a negative electrode sheet, the negative electrode sheet comprising 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 comprising a negative electrode active material, a conductive agent and a binder; the conductive agent is composed of at least two different conductive materials;

[0008] The secondary battery satisfies: 10 < [100000 * (Dv50)] / [P] 2 *(lnM)]<34;

[0009] Wherein, P g / L is the tap density of the conductive agent;

[0010] Dv50μm is the particle size corresponding to a cumulative volume distribution percentage of 50% for the negative electrode active material.

[0011] M g / mol is the molar mass of the binder.

[0012] Furthermore, in the secondary battery, the conductive agent includes at least two of the following: zero-dimensional point conductive agent, one-dimensional linear conductive agent, and two-dimensional planar conductive agent.

[0013] Furthermore, in the secondary battery, the conductive agent includes zero-dimensional point conductive agent, one-dimensional linear conductive agent, and two-dimensional planar conductive agent.

[0014] Furthermore, based on the total content of the conductive agent, the mass percentage of the zero-dimensional point conductive agent is 25-40%, the mass percentage of the one-dimensional linear conductive agent is 30-50%, and the mass percentage of the two-dimensional planar conductive agent is 10-45%.

[0015] Furthermore, in the secondary battery, the conductive agent includes at least conductive carbon black as the zero-dimensional point conductive agent, at least carbon nanotubes and carbon fibers as the one-dimensional linear conductive agent, and at least graphene as the two-dimensional planar conductive agent.

[0016] Furthermore, in the secondary battery, the tap density P of the conductive agent is 120-210, the Dv50 of the negative electrode active material is 40-100, and the molar mass M of the binder is 1,200,000-1,900,000.

[0017] Furthermore, the secondary battery meets at least one of the following conditions:

[0018] a. The Dv50 of the zero-dimensional point conductive agent is 30-100 μm, the Dv50 of the one-dimensional linear conductive agent is 4-20 μm, and the Dv50 of the two-dimensional planar conductive agent is 0.5-3 μm.

[0019] b. The adhesive is one or more of styrene-butadiene latex, polytetrafluoroethylene, and PVDF.

[0020] Furthermore, in the secondary battery, the negative electrode active material has a porous structure, and the ratio K of the open pores to closed pores of the negative electrode active material is 2 to 3.

[0021] Furthermore, in the secondary battery, the negative electrode active material includes secondary particles formed by the aggregation of primary particles, and the number N of primary particles in a single secondary particle is 40 to 60.

[0022] The present invention also proposes an electrical device, wherein the aforementioned secondary battery is provided as the power supply for the electrical device.

[0023] Compared with the prior art, the embodiments of the present invention have the following advantages:

[0024] In this embodiment of the invention, the provided secondary battery includes a negative electrode sheet, which includes a negative current collector and a negative active material layer disposed on the negative current collector. The negative active material layer includes a negative active material, a conductive agent, and a binder; the conductive agent is composed of at least two different conductive materials; the secondary battery satisfies: 10 < [100000*(Dv50)] / [P] 2*(lnM)]<34; where P g / L is the tap density of the conductive agent; Dv50μm is the particle size corresponding to a volumetric cumulative distribution percentage of 50% for the negative electrode active material; and M g / mol is the molar mass of the binder. In this embodiment of the invention, by setting the conductive agent to be composed of at least two different conductive materials, and matching the above-mentioned relationship between the Dv50 of the negative electrode active material, the tap density of the conductive agent powder, and the molar mass of the binder, an electrode conductive network is effectively constructed, improving the ionic conductivity and electronic conductivity of the negative electrode, thereby effectively improving the charging rate performance.

[0025] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit the invention. Detailed Implementation

[0026] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to specific embodiments.

[0027] The applicant of this invention discovered that during the charging process of a sodium-ion battery, sodium ions are deintercalated from the positive electrode and intercalated into the negative electrode through the electrolyte. Therefore, the dynamic performance of the negative electrode of a sodium-ion battery is closely related to the battery's fast charging performance. However, the fast charging performance of existing secondary batteries such as sodium-ion batteries is not good.

[0028] To address the aforementioned problems, this invention provides a secondary battery comprising a negative electrode sheet, which includes 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 includes a negative electrode active material, a conductive agent, and a binder; the conductive agent is composed of at least two different conductive materials.

[0029] The secondary battery satisfies: 10 < [100000 * (Dv50)] / [P] 2 *(lnM)]<34;

[0030] Wherein, Pg / L is the tap density of the conductive agent;

[0031] Dv50μm is the particle size corresponding to a cumulative volume distribution percentage of 50% for the negative electrode active material.

[0032] M g / mol is the molar mass of the binder.

[0033] The applicant discovered that the kinetic performance of the negative electrode depends on the matching of the physicochemical properties among the constituent materials of the negative electrode; at the same time, the kinetic performance of the negative electrode is closely related to the fast charging performance of the battery. Therefore, by optimizing the physicochemical properties among the constituent materials of the negative electrode and making reasonable matching, the kinetic performance of the negative electrode can be effectively improved, thereby improving the fast charging performance of the battery.

[0034] Because the three parameters of the negative electrode active material Dv50, the tap density of the conductive agent powder, and the molar mass of the binder play a decisive role in the negative electrode dynamics, in this embodiment of the invention, based on the interaction and mutual influence relationship between the negative electrode active material, the conductive agent powder, and the binder, the conductive agent is set to be composed of at least two different conductive materials, and the Dv50 of the negative electrode active material, the tap density of the conductive agent powder, and the molar mass of the binder satisfy the above-mentioned relationship, effectively constructing an electrode conductive network, improving the ionic conductivity and electronic conductivity of the negative electrode, thereby effectively improving the charging rate performance and preparing a secondary battery with excellent fast charging performance.

[0035] Optionally, [100000*(Dv50)] / [P 2 The value of *(lnM)] can be a range of 11, 15, 20, 30, 33 or any two of them.

[0036] Optionally, in one embodiment, the conductive agent includes at least two of the following: zero-dimensional point conductive agent, one-dimensional linear conductive agent, and two-dimensional planar conductive agent. Under the combined action of at least two conductive agents of different dimensions, a three-dimensional conductive network can be constructed, which greatly improves the dynamic performance of the battery.

[0037] Optionally, in one specific embodiment, the specific surface area of ​​the zero-dimensional point-like conductive agent in the secondary battery provided by the present invention is 30-200 m². 2 / g, the specific surface area of ​​the one-dimensional linear conductive agent is 300-1000m². 2 / g, the specific surface area of ​​the two-dimensional planar conductive agent is 2000-3000m². 2 / g. In some embodiments, the specific surface area of ​​the zero-dimensional point-like conductive agent is 30m². 2 / g、35m 2 / g、40m 2 / g、60m 2 / g、80m 2 / g, 100m 2 / g, 150m 2 / g、200m 2 The range of one or both of the values ​​in / g, the specific surface area of ​​the one-dimensional linear conductive agent is 300m². 2 / g, 350m2 / g、400m 2 / g、500m 2 / g、700m 2 / g、900m 2 / g, 1000m 2 The specific surface area of ​​the two-dimensional planar conductive agent is 2000 m², which is within the range of one or both of the values ​​in / g. 2 / g、2100m 2 / g、2200m 2 / g、2400m 2 / g、2500m 2 / g、2600m 2 / g、2800m 2 / g、3000m 2 The range of one or both of the values ​​in / g.

[0038] Optionally, in one specific embodiment, in the secondary battery provided by the present invention, the Dv50 of the zero-dimensional point conductive agent is 30-100 μm, the Dv50 of the one-dimensional linear conductive agent is 4-20 μm, and the Dv50 of the two-dimensional planar conductive agent is 0.5-3 μm; in some embodiments, the Dv50 of the zero-dimensional point conductive agent can be one or any two of 30 μm, 40 μm, 50 μm, 60 μm, 80 μm, and 100 μm. The Dv50 of one-dimensional linear conductive agents can be one or any two of the following values: 4μm, 5μm, 8μm, 10μm, 15μm, 20μm. The Dv50 of two-dimensional planar conductive agents can be one or any two of the following values: 0.5μm, 0.6μm, 0.8μm, 1μm, 1.5μm, 2μm, 3μm. This ensures that the size of the conductive agent in each dimension is appropriate, which can give full play to the performance advantages of the conductive agent in each dimension and improve the fast charging performance.

[0039] Optionally, in one specific embodiment, in the secondary battery provided by the present invention, the tap density of the zero-dimensional point conductive agent is 200-500 g / L, the tap density of the one-dimensional linear conductive agent is 100-250 g / L, and the tap density of the two-dimensional planar conductive agent is 10-100 g / L. This effectively balances the wetting effect with the electrolyte and the contact performance with the negative electrode active material, forming a dense conductive network with high ionic conductivity and achieving excellent fast charging performance. In some embodiments, the tap density of the zero-dimensional point conductive agent is a range of 200 g / L, 250 g / L, 350 g / L, 500 g / L or any two of these values; the tap density of the one-dimensional linear conductive agent is a range of 100 g / L, 120 g / L, 150 g / L, 160 g / L, 180 g / L, 200 g / L, 220 g / L, 250 g / L or any two of these values; and the tap density of the two-dimensional planar conductive agent is a range of 10 g / L, 20 g / L, 40 g / L, 60 g / L, 80 g / L, 100 g / L or any two of these values.

[0040] In practical applications, the tap density is tested using the tap density measurement method specified in GB / T 31057.2-2018. The specific steps include:

[0041] The weighed powder is loaded into the measuring cylinder of the compaction device and fixed on the support. The cam is rotated, and the directional rod drives the support to slide up and down and strike the anvil. The vibration is performed at 250±15 times per minute for 12 minutes. The volume of powder in the measuring cylinder is measured, and the ratio of powder mass to volume is the compaction density of the powder.

[0042] Optionally, in one embodiment, the conductive agent in the secondary battery includes a zero-dimensional point conductive agent, a one-dimensional linear conductive agent, and a two-dimensional planar conductive agent. Based on the total content of the conductive agent, the mass percentage of the zero-dimensional point conductive agent is 25-40%, the mass percentage of the one-dimensional linear conductive agent is 30-50%, and the mass percentage of the two-dimensional planar conductive agent is 10-45%. This more rationally constructs a three-dimensional conductive network and achieves fast charging performance.

[0043] Optionally, in one embodiment, the zero-dimensional dot-shaped conductive agent includes at least conductive carbon black, the one-dimensional linear conductive agent includes at least one of carbon nanotubes and carbon fibers, and the two-dimensional planar conductive agent includes at least graphene.

[0044] Optionally, in one embodiment, the tap density P of the conductive agent is 120 to 210 g / L. The tap density P of the conductive agent is the tap density of a mixed conductive agent after mixing at least two of the following: zero-dimensional point conductive agent, one-dimensional linear conductive agent, and two-dimensional planar conductive agent. The tap density of the conductive agent within the above range can effectively balance the wetting effect with the electrolyte and the contact performance with the negative electrode active material, forming a dense conductive network with high ionic conductivity and achieving excellent fast discharge performance.

[0045] In one embodiment, the Dv50 of the negative electrode active material is 40-100μm, which makes the particle size moderate. This facilitates the rapid shuttle of active ions between particles to achieve rapid charging, and also avoids excessive liquid absorption and low solid content in the slurry during the stirring process, which can lead to coating cracks, bulging edges and other process problems, thus ensuring processing performance.

[0046] In one embodiment, the molar mass M of the binder is 1,200,000 to 1,900,000 g / mol. This ensures that the binder network layer formed on the surface of the negative electrode active material has a high porosity, avoiding excessively low liquid absorption that would affect the rate performance. It also avoids dispersion problems such as folding and clumping of binder molecules, allowing the negative electrode active material and conductive agent to be uniformly dispersed, thereby forming a good conductive network and effectively balancing rate performance and fast discharge performance.

[0047] In some embodiments, the tap density P g / L of the conductive agent can be one or any two of the following values: 120 g / L, 110 g / L, 120 g / L, 140 g / L, 150 g / L, 160 g / L, 180 g / L, 200 g / L, 210 g / L; the Dv50 of the negative electrode active material can be one or any two of the following values: 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm; and the molar mass of the binder is one or any two of the following values: 1200000 g / mol, 1050000 g / mol, 1100000 g / mol, 1200000 g / mol, 1500000 g / mol, 1800000 g / mol, 1900000 g / mol.

[0048] Optionally, in one specific embodiment, the adhesive is one or more of styrene-butadiene latex, polytetrafluoroethylene, and PVDF.

[0049] Optionally, in one embodiment, the negative electrode active material has a porous structure, and the ratio K of open pores to closed pores in the negative electrode active material is 2 to 3. The proportion of open pores is moderate, resulting in a suitable active surface area, which effectively balances the initial coulombic efficiency and rate performance, ensuring the wetting effect of the electrolyte. In some embodiments, the ratio K of open pores to closed pores in the negative electrode active material is a range of one or both of 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, and 3.0.

[0050] In practical applications, the above-mentioned K value can be obtained by adjusting the sintering temperature, the closed-pore ratio can be obtained by testing according to GB / T 10707-2008, and the open-pore porosity can be measured by gas adsorption method.

[0051] In the secondary battery provided by this invention, the negative electrode active material includes secondary particles formed by the aggregation of primary particles. The number N of primary particles in a single secondary particle is 40 to 60, which can effectively balance the initial coulombic efficiency and rate performance, and reduce gas production during cycling. Optionally, in some embodiments, the number N of primary particles in a single secondary particle can be one or any combination of 40, 42, 45, 48, 50, 52, 55, 58, and 60.

[0052] In practical applications, the N value can be adjusted by the calcination time during the hard carbon preparation process. The N value can be calculated by measuring the primary and secondary particle sizes and volume ratios using SEM and TEM.

[0053] The aforementioned negative electrode active material layer can be a negative electrode active material used in batteries, such as a metal negative electrode active material or a non-metal negative electrode active material; the metal negative electrode active material is preferably a metal foil or alloy compound such as sodium, sodium alloy, tin, or antimony; the non-metal negative electrode active material is preferably any one or a combination of at least two of hard carbon, soft carbon, graphite, and silicon suboxide.

[0054] Optionally, in one specific embodiment, the negative electrode active material includes hard carbon, and the precursor of the hard carbon is one or more of biomass, resin, and coal. This results in a disordered crystal arrangement and larger interlayer spacing within the negative electrode active material, which is more conducive to the formation of a protective film on its surface by additives in the electrolyte, further optimizing the stability of the protective film. In this embodiment, the resin may include phenolic resin, epoxy resin, polyfurfuryl alcohol, etc.

[0055] Optionally, in one specific embodiment, the negative electrode current collector is one or more of copper foil, aluminum foil, carbon-coated copper foil, and carbon-coated aluminum foil.

[0056] 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, binder and 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 copper foil; after baking, rolling, cutting and other processes, the negative electrode sheet can be obtained.

[0057] The secondary battery provided by the present invention also includes a positive electrode and an electrolyte.

[0058] In this process, the electrolyte in the electrolyte solution plays a role in conducting ions between the positive and negative electrode plates.

[0059] The aforementioned positive electrode sheet includes a positive current collector and a positive active material layer disposed on the aforementioned positive current collector. The aforementioned positive active material layer includes a positive active material, which includes at least one of sodium ion transition metal oxides, sodium ion transition metal phosphates and variants, sodium ion transition metal sulfates, and Prussian blue compounds.

[0060] Optionally, in one embodiment, the above-mentioned positive electrode active material comprises NaCoO2, NaMnO2, and NaNi. 0.33 Fe 0.33 Mn 0.33 One or more of O2, NaFePO4, NaCoPO4, and Na3V2(PO4)3.

[0061] Optionally, in one embodiment, the positive electrode sheet further includes an adhesive and a conductive agent. The adhesive may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, and tetrafluoroethylene-hexafluoropropylene copolymer. The conductive agent may be acetylene black, carbon fiber, carbon nanotubes, Ketjen black, artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, graphene, etc.

[0062] In some embodiments, the positive electrode sheet is prepared as follows: the components used to prepare the positive electrode sheet, such as the positive active material, binder and any other components, are dispersed in a solvent such as N-methylpyrrolidone to form a positive electrode slurry; the positive electrode slurry is coated on both sides of a positive electrode current collector such as an aluminum foil; after baking, rolling, cutting and other processes, the positive electrode sheet can be obtained.

[0063] Understandably, the secondary battery provided in the embodiments of the present invention also includes a separator.

[0064] In practical applications, the negative electrode sheet, separator and positive electrode sheet are stacked in sequence and wound to obtain a core. The core is then packaged to obtain a bare cell. After baking, the bare cell is injected with electrolyte, formed, resealed and sorted to obtain the above-mentioned secondary battery.

[0065] The present invention also proposes an electrical device, wherein the aforementioned secondary battery is provided as the power supply for the electrical device.

[0066] The above-described secondary battery embodiments and electrical device embodiments include the electrolyte described above and can achieve the same technical effect. To avoid repetition, they will not be repeated here. For relevant details, please refer to the description of the positive electrode material embodiments.

[0067] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention 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 the invention.

[0068] The present invention will be described in detail below through embodiments.

[0069] (1) Charging rate performance test:

[0070] At room temperature, the cell with a state of charge of 0% (SOC) was charged to 4.0V at a current density of 0.33C, and the capacity was recorded as C1.

[0071] Then, at room temperature, the cell with SOC=0% charge is charged to 4.0V at a current density of 5C. The capacity at this time is C2, and the capacity is recorded as C2.

[0072] Calculate the capacity retention ratio C2 / C1 as a test indicator of charging rate performance.

[0073] (2) Coating crack test: Randomly cut 1 square decimeter from the baked negative electrode sheet and record the number of cracks on this area.

[0074] (3) Test of ionic conductivity of negative electrode: The constant current intermittent titration (GITT) method was used. The voltage range was 2.5V to 4.2V, the pulse time was 10 minutes, the pulse current was 0.33C, and the relaxation time was 3 hours.

[0075] (4) Electron conductivity test of negative electrode: Electron conductivity = 1 / Electrode film resistance. Film resistance is tested using the four-probe method. A four-probe instrument is used to contact the probes with the sample to be tested and measure its resistance.

[0076] (5) Moisture absorption test of negative electrode sheet: Place a 1 square decimeter negative electrode sheet in an environment with a humidity of 70% for 7 days. The increase in the mass of the electrode sheet within 7 days is the moisture absorption.

[0077] (6) First Coulomb efficiency test:

[0078] The battery was discharged at a constant current of 0.33C to 2.5V, allowed to rest for 30 minutes, then charged at a constant current of 0.33C to 4.2V, and finally charged at a constant voltage until the current reached 0.05C. This yielded the battery's initial charge capacity. After resting for 30 minutes, it was discharged at a constant current of 0.33C to 2.5V, yielding the initial discharge capacity. The initial efficiency = (initial discharge capacity / initial charge capacity) * 100%. The initial coulombic efficiency of the battery was then calculated.

[0079] Example 1

[0080] (1) Preparation of positive electrode sheet

[0081] NaNi 0.33 Fe 0.33 Mn 0.33 O2, sodium carboxymethyl cellulose (CMC), conductive carbon black, and styrene-butadiene latex (SBR) were mixed in a mass ratio of 80:7.5:7.5:5. N-methylpyrrolidone solvent was added, and the mixture was stirred under vacuum to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on both sides of carbon-coated aluminum foil, dried at room temperature, and then transferred to an oven for further drying. The positive electrode sheet was then obtained by rolling and cutting.

[0082] (2) Preparation of negative electrode sheet

[0083] Preparation of hard carbon: Under an inert atmosphere, phenolic resin with a molecular weight of approximately 1000 g / mol was heated to 1300 °C at 10 °C / min and calcined at high temperature for 12 hours, then cooled to room temperature to obtain hard carbon. Hard carbon with a Dv50 of 6 μm, a conductive agent with a tap density of 160 g / L (a mixture of conductive carbon black, carbon nanotubes, and graphene in a mass ratio of 30:40:30), and styrene-butadiene latex (SBR) with a molar mass of 1,500,000 g / mol were mixed evenly in a 97:1:2 mass ratio and uniformly dispersed in deionized water to prepare a uniform black slurry. The slurry was coated on both sides of a copper foil, then baked, rolled, and cut to obtain the negative electrode sheet.

[0084] The hard carbon particle size Dv50 is 68μm, the number of primary particles in a single secondary particle is 50, and the ratio of open pores to closed pores is 2.5.

[0085] The specific surface area of ​​conductive carbon black in the conductive agent is 100m². 2 The carbon nanotubes have a density of 60 μm, a Dv50 of 60 μm, a tap density of 260 g / L, and a specific surface area of ​​600 m². 2 The graphene has a density of 10 μm, a tap density of 180 g / L, and a specific surface area of ​​2500 m². 2 / g, Dv50 is 2μm, and tap density is 60g / L.

[0086] (3) Preparation of electrolyte

[0087] Ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1. Then, 1 mol / L NaPF6 was dissolved in the mixed organic solvent and mixed thoroughly to prepare an electrolyte.

[0088] (4) Battery manufacturing

[0089] The positive electrode, separator, and negative electrode are stacked in sequence, then wound into a bare cell and packed into a soft-pack casing. After top-side sealing, electrolyte injection, formation, and sorting, a sodium-ion battery is obtained.

[0090] Examples 2-4

[0091] The preparation method is the same as in Example 1, except that the ratio of conductive carbon black, carbon nanotubes and graphene is adjusted during the preparation of the negative electrode.

[0092] Examples 5-8

[0093] The preparation method is the same as in Example 1, except that the particle size Dv50 of conductive carbon black, carbon nanotubes, and graphene is adjusted during the preparation of the negative electrode.

[0094] In Example 5, the particle sizes Dv50 of the conductive carbon black, carbon nanotubes, and graphene were 62 μm, 12 μm, and 3 μm, respectively.

[0095] The particle sizes Dv50 of the conductive carbon black, carbon nanotubes, and graphene in Example 6 are 65 μm, 14 μm, and 4 μm, respectively.

[0096] The particle sizes Dv50 of the conductive carbon black, carbon nanotubes, and graphene in Example 7 are 57 μm, 8 μm, and 1.5 μm, respectively.

[0097] The particle sizes Dv50 of the conductive carbon black, carbon nanotubes, and graphene in Example 8 are 55 μm, 7 μm, and 1 μm, respectively.

[0098] Examples 9-12

[0099] The preparation method is the same as in Example 1. The difference is that, during the preparation of hard carbon, the particle size of the negative electrode material is changed by adjusting the molecular weight of the precursor phenolic resin. The larger the molecular weight, the larger the particle size.

[0100] Examples 13-16

[0101] The preparation method is the same as in Example 1, except that the calcination time during the hard carbon preparation process is adjusted to obtain negative electrode active materials with different N values. This is achieved by adjusting the hard carbon calcination time; the longer the time, the smaller the N value.

[0102] Examples 17-20

[0103] The preparation method is the same as in Example 1, except that the calcination temperature during the hard carbon preparation process is adjusted to obtain negative electrode active materials with different K values. The higher the temperature, the larger the K value.

[0104] Examples 21-23

[0105] The preparation method is the same as in Example 1, except that different molar masses of binder are used as the binder for the negative electrode.

[0106] Examples 24-26

[0107] The preparation method is the same as in Example 1, except that the components and proportions of the conductive agent are changed, as shown in Table 1.

[0108] Comparative Examples 1-2

[0109] The preparation process is the same as in Example 1, except that the mixing ratio of conductive carbon black, carbon nanotubes and graphene is adjusted during the preparation of the negative electrode sheet.

[0110] Comparative Example 3

[0111] The preparation process is the same as in Example 1, except that the conductive agent used in the preparation of the negative electrode is only carbon nanotubes.

[0112] The process parameters for each embodiment and comparative example are shown in Table 1 and Table 2.

[0113] Table 1

[0114]

[0115]

[0116]

[0117] Where x = [100000*(Dv50)] / [P 2 *(lnM)].

[0118] The negative electrode sheets prepared in each embodiment and comparative example were subjected to ionic conductivity test, electronic conductivity test and moisture absorption test. The batteries prepared in each embodiment and comparative example were subjected to the first coulombic efficiency test, charging rate performance test and coating crack test. The test data are shown in Table 3.

[0119] Table 3

[0120]

[0121] In summary, in this embodiment, by setting the conductive agent to consist of at least two different conductive materials, and matching the Dv50 of the negative electrode active material, the tap density of the conductive agent powder, and the molar mass of the binder to satisfy the above-mentioned relationship, an electrode conductive network is effectively constructed, improving the ionic conductivity and electronic conductivity of the negative electrode, thereby effectively improving the charging rate performance and preparing a secondary battery with excellent fast charging performance.

[0122] Although preferred embodiments of the present invention 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 invention.

[0123] The present invention has been described in detail above. Specific examples have been used to illustrate the principle and implementation of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation and application scope based on the idea of ​​the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A secondary battery, characterized in that, The device includes a negative electrode sheet, which comprises 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 comprises a negative electrode active material, a conductive agent, and a binder. The conductive agent is composed of at least two conductive materials of different dimensions. The secondary battery satisfies: 10 < [100000 * (Dv50)] / [P] 2 *(lnM)]<34; Wherein, P g / L is the tap density of the conductive agent, and P is 120~210; Dv50 μm is the particle size corresponding to a cumulative volume distribution percentage of 50% for the negative electrode active material, where Dv50 is 40~100. M g / mol is the molar mass of the binder, where M is 1,200,000 to 1,900,000.

2. The secondary battery according to claim 1, characterized in that, The conductive agent includes at least two of the following: zero-dimensional point conductive agent, one-dimensional linear conductive agent, and two-dimensional planar conductive agent.

3. The secondary battery according to claim 2, characterized in that, The conductive agent includes zero-dimensional point conductive agent, one-dimensional linear conductive agent and two-dimensional planar conductive agent.

4. The secondary battery according to claim 3, characterized in that, Based on the total content of the conductive agent, the mass percentage of the zero-dimensional point conductive agent is 25-40%, the mass percentage of the one-dimensional linear conductive agent is 30-50%, and the mass percentage of the two-dimensional planar conductive agent is 10-45%.

5. The secondary battery according to any one of claims 2 to 4, characterized in that, The conductive agent includes, in the case of, at least one of the following: zero-dimensional point conductive agent, conductive carbon black; one-dimensional linear conductive agent, carbon nanotubes and carbon fibers; and two-dimensional planar conductive agent, graphene.

6. The secondary battery according to claim 2, characterized in that, At least one of the following conditions must be met: a. The Dv50 of the zero-dimensional point conductive agent is 30~100μm, the Dv50 of the one-dimensional linear conductive agent is 4~20μm, and the Dv50 of the two-dimensional planar conductive agent is 0.5~3μm. b. The adhesive is one or more of styrene-butadiene latex, polytetrafluoroethylene, and PVDF.

7. The secondary battery according to claim 1, characterized in that, The negative electrode active material has a porous structure, and the ratio K of the open pores to closed pores of the negative electrode active material is 2 to 3.

8. The secondary battery according to claim 1, characterized in that, The negative electrode active material includes secondary particles formed by the aggregation of primary particles, wherein the number N of primary particles in a single secondary particle is 40 to 60.

9. An electrical appliance, characterized in that, The device includes the secondary battery as described in any one of claims 1 to 8, wherein the secondary battery serves as the power supply for the electrical equipment.

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