Secondary battery and electric device

Abstract

This invention provides a secondary battery and an electrical device, wherein the secondary battery provided by this invention satisfies: 10 < 0.1 × exp (B) ×(M×K / P) 0.5 <142; where, B m 2 / g represents the specific surface area of ​​the positive electrode active material, P g / L represents the tap density of the conductive agent, M g / mol represents the molar mass of the binder, and K represents the ratio of open pores to closed pores in the positive electrode active material. By matching the specific surface area of ​​the positive electrode active material, the ratio of open pores to closed pores, the tap density of the conductive agent powder, and the molar mass of the binder to satisfy the above relationships, an effective conductive network for the electrode is constructed, improving the ionic and electronic conductivity of the positive electrode, thereby effectively improving the discharge rate performance and preparing a secondary battery with excellent fast discharge performance.

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 positive electrode sheet, as a crucial component of secondary batteries, has dynamic performance that is a key factor affecting battery performance. Existing technologies, particularly electric vehicles, place higher demands on the rapid discharge performance of secondary batteries; however, current secondary batteries exhibit inadequate rapid discharge performance, failing to effectively meet the need for superior rapid discharge capabilities.

[0003] Therefore, there is an urgent need to provide a positive electrode with excellent kinetic performance to improve the rapid discharge performance of secondary batteries. Summary of the Invention

[0004] 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 discharge performance of existing secondary batteries.

[0005] To solve the above problems, the present invention is achieved through the following technical solution:

[0006] This invention proposes a secondary battery, comprising a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive active material layer disposed on the positive current collector, the positive active material layer comprising a positive active material, a conductive agent and a binder, the positive active material having a porous structure;

[0007] The secondary battery satisfies: 10 < 0.1 × exp (B) ×(M×K / P) 0.5 <142;

[0008] Among them, B m 2 / g represents the specific surface area of ​​the positive electrode active material;

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

[0010] M g / mol is the molar mass of the binder;

[0011] K is the ratio of open pores to closed pores in the positive electrode active material.

[0012] Furthermore, in the secondary battery, the positive 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 30 to 50.

[0013] Furthermore, in the aforementioned secondary battery, K is 2 to 3.

[0014] Furthermore, in the aforementioned secondary battery, the specific surface area Bm of the positive electrode active material is... 2 / g is 0.5~1.5.

[0015] Furthermore, in the secondary battery, the tap density P of the conductive agent is 50-600 g / L.

[0016] Furthermore, in the secondary battery, the molar mass M of the binder is 1,000,000 to 2,000,000 g / mol.

[0017] Furthermore, in the secondary battery, the positive electrode active material includes one or more crystals of P2 and O3 type layered oxides.

[0018] Furthermore, in the aforementioned secondary battery, the areal density of the positive electrode sheet is 200–250 g / m³. 2 The resistance is 200–500 mΩ.

[0019] Furthermore, the secondary battery meets at least one of the following conditions:

[0020] a. The conductive agent includes at least one of conductive carbon black, Ketjen black, acetylene black, carbon nanotubes, and graphene;

[0021] b. The adhesive includes at least one of styrene-butadiene rubber, polytetrafluoroethylene, and polyvinylidene fluoride.

[0022] Furthermore, in the secondary battery, the positive electrode current collector includes an aluminum foil layer and a carbon layer disposed on the aluminum foil layer, and the tensile strength of the positive electrode current collector is 30-60 kN and the elongation is 0.6%-0.8%.

[0023] The present invention also proposes an electrical device, wherein the aforementioned secondary battery is provided as the power supply for the electrical device.

[0024] Compared with the prior art, the embodiments of the present invention have the following advantages:

[0025] In this embodiment of the invention, the provided secondary battery includes a positive electrode sheet, which 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, a conductive agent, and a binder. The secondary battery satisfies: 10 < 0.1 × exp (B) ×(M×K / P) 0.5 <142; where, B m 2 / g represents the specific surface area of ​​the positive electrode active material, P g / L represents the tap density of the conductive agent, and M g / mol represents the molar mass of the binder. In this embodiment of the invention, by controlling the specific surface area of ​​the positive electrode active material, the ratio of open pores to closed pores, the tap density of the conductive agent powder, and the molar mass of the binder to satisfy the above relationships, an electrode conductive network is effectively constructed, improving the ionic conductivity and electronic conductivity of the positive electrode, thereby effectively improving the discharge rate performance and preparing a secondary battery with excellent fast discharge performance.

[0026] 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. Detailed Implementation

[0027] 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.

[0028] The applicant of this invention discovered that in secondary batteries, such as sodium-ion batteries, sodium ions are released from the negative electrode and then embedded in the positive electrode during discharge. Therefore, the dynamic performance of the positive electrode of a sodium-ion battery is closely related to the battery's rapid discharge performance. However, the rapid discharge performance of existing secondary batteries such as sodium-ion batteries is not good.

[0029] To address the aforementioned problems, this invention provides a secondary battery comprising a positive electrode sheet, which 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, a conductive agent, and a binder, and the positive active material has a porous structure.

[0030] The above secondary battery satisfies: 10 < 0.1 × exp (B) ×(M×K / P) 0.5 <142;

[0031] Among them, B m 2 / g represents the specific surface area of ​​the positive electrode active material;

[0032] P g / L is the tap density of the conductive agent;

[0033] M g / mol is the molar mass of the binder;

[0034] K is the ratio of open pores to closed pores in the positive electrode active material.

[0035] The applicant discovered that the kinetic performance of the positive electrode is related to the physicochemical properties of its constituent materials; and the kinetic performance of the positive electrode is closely related to the fast discharge performance of the battery. Therefore, by optimizing the physicochemical properties of the constituent materials of the positive electrode and matching them appropriately, the kinetic performance of the positive electrode can be effectively improved, thereby improving the fast discharge performance of the battery.

[0036] Because the specific surface area of ​​the positive electrode active material, the tap density of the conductive agent powder, the molar mass of the binder, and the ratio of open pores to closed pores in the positive electrode active material have a strong influence on the positive electrode dynamics, in this embodiment of the invention, based on the interaction and mutual influence relationship between the positive electrode active material, the conductive agent powder, and the binder, the specific surface area of ​​the positive electrode active material, the ratio of open pores to closed pores, the tap density of the conductive agent powder, and the molar mass of the binder are controlled to satisfy the above-mentioned relationship, so as to exert a synergistic effect, effectively construct the conductive network of the positive electrode sheet, improve the ionic conductivity and electronic conductivity of the positive electrode sheet, effectively improve the discharge rate performance, and prepare a secondary battery with excellent fast discharge performance.

[0037] Optionally, 0.1×exp (B) ×(M×K / P) 0.5 The value can be one or any two of the following: 10.6, 20, 30, 40, 60, 70, 80, 85, 90, 100, 110, 120, 130, 141.7.

[0038] Optionally, in one embodiment, the specific surface area B m of the above-mentioned positive electrode active material 2 / g is 0.5~1.5m 2 The particle size is moderate, which facilitates rapid ion movement between particles for fast discharge, while avoiding excessive liquid absorption and low solids content in the slurry during stirring, which could lead to coating cracks, bulging, and other processing problems, thus ensuring processing performance. In some embodiments, the specific surface area of ​​the above-mentioned positive electrode active material can be 0.5 m². 2 / g, 0.6m 2 / g, 0.8m 2 / g, 1.0m 2 / g, 1.2m 2 / g, 1.4m 2 / g, 1.5m 2 The range of one or both of the values ​​in / g.

[0039] Optionally, in one embodiment, the tap density P of the conductive agent is 50-600 g / L, which effectively balances the wetting effect with the electrolyte and the contact performance with the positive electrode active material, forming a dense conductive network with high ionic conductivity and low conductivity, thus achieving excellent rapid discharge performance. In some embodiments, the tap density of the conductive agent is within the range of one or any two of 50 g / L, 60 g / L, 80 g / L, 100 g / L, 150 g / L, 200 g / L, 300 g / L, 400 g / L, 500 g / L, and 600 g / L.

[0040] Optionally, in one embodiment, the molar mass M of the binder is 1,000,000 to 2,000,000 g / mol. This ensures that the binder network layer formed on the surface of the positive electrode active material has high porosity, avoiding insufficient liquid absorption that would affect rate performance. It also prevents dispersion problems such as folding and clumping of binder molecules, allowing the positive electrode active material and conductive agent to be uniformly dispersed, thus forming a good conductive network and effectively balancing rate performance and fast discharge performance. In some embodiments, the molar mass of the binder is within the range of one or both of the following: 1,000,000 g / mol, 1,050,000 g / mol, 1,100,000 g / mol, 1,200,000 g / mol, 1,500,000 g / mol, 1,800,000 g / mol, 1,900,000 g / mol, and 2,000,000 g / mol. In practical applications, the molar mass of the binder can be determined by mass spectrometry, dilute solution viscosity method, and volume exclusion chromatography.

[0041] In the secondary battery provided by this invention, the positive 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 30 to 50, which can effectively balance the initial coulombic efficiency and rate performance, and is less likely to cause gas generation during cycling. Optionally, in some embodiments, the number N of primary particles in a single secondary particle can be one or any combination of 30, 32, 35, 38, 40, 42, 45, 48, and 50.

[0042] In practical applications, this N value can be adjusted by adding surfactants during the precursor preparation process. The N value can be calculated by measuring the primary and secondary particle sizes and volume ratios using SEM and TEM.

[0043] Optionally, in one embodiment, the positive electrode active material has a porous structure, and the ratio K of open pores to closed pores in the positive 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 positive 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.

[0044] In practical applications, the above-mentioned K value can be obtained by adjusting the sintering temperature, the closed pore size can be obtained by testing according to GB / T 10799-2008, and the open pore size can be measured by gas adsorption method.

[0045] Optionally, in one embodiment, the above-mentioned positive electrode active material includes one or more of P2, O3 type, and crystalline layered oxides. The chemical formula of the layered oxide is Na. x MO2, wherein M is selected from at least one of Fe, Ni, Li, Cu, Zn, Co, Ti, and Mn, and 0.90 ≥ x ≥ 0.70. Wherein, when x > 0.9, the crystal structure of the layered cathode material is a single O3 type, while when x < 0.7, the crystal structure of the layered cathode material is a single P2 type.

[0046] In practical applications, the ratio of P2-type crystal structure layered oxides to O3-type crystal structure layered oxides can be adjusted by the sodium content x. When x is large, the O3 phase accounts for a larger proportion, and when x is small, the P2 phase accounts for a larger proportion.

[0047] Optionally, in one specific embodiment, the sodium ion layered oxide is composed of a mixture of P2-type and O3-type sodium ion layered metal oxides, wherein the space group of the O3-type sodium ion layered metal oxide is R-3m, and its molar percentage in the mixed phase is 20-98%; the space group of the P2-type sodium ion layered metal oxide is P63 / mmc, and its molar percentage in the mixed phase is 2-80%.

[0048] Optionally, in the secondary battery provided in this embodiment of the invention, the areal density of the positive electrode sheet is 200-250 g / m². 2 The resistance of the positive electrode is 200–500 mΩ. In some embodiments, the areal density of the positive electrode is 200 g / m³. 2 205g / m 2 210g / m 2 220g / m 2 250g / m 2The resistance of the positive electrode is within one or both of the following ranges, resulting in a higher compaction density and thus improving the energy density of the battery. In some embodiments, the resistance of the positive electrode is within one or both of the following ranges: 200mΩ, 205mΩ, 220mΩ, 250mΩ, 300mΩ, 400mΩ, and 500mΩ. A resistance within these ranges indicates lower resistance and higher conductivity, which is beneficial for improving the rate performance of the battery.

[0049] Optionally, in one embodiment, the conductive agent may include at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, carbon fibers, and carbon microspheres. These conductive agents are widely available and exhibit excellent conductivity.

[0050] Optionally, in one embodiment, the adhesive includes at least one of styrene-butadiene rubber, polytetrafluoroethylene, and polyvinylidene fluoride. The adhesive can bond and fix the positive electrode active material and the conductive agent, and can also fix the positive electrode active material layer to the positive electrode current collector, reducing powder shedding.

[0051] Optionally, in one specific embodiment, the positive electrode current collector includes an aluminum foil layer and a carbon layer disposed on the aluminum foil layer. The tensile strength of the positive electrode current collector is 30-60 kN, and the elongation is 0.6%-0.8%. In some embodiments, the tensile strength of the positive electrode current collector is a value within the range of one or both of 30 kN, 32 kN, 35 kN, 40 kN, 50 kN, and 60 kN. In some embodiments, the elongation is a value within the range of one or both of 0.6%, 0.7%, and 0.8%.

[0052] 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 including the above-mentioned positive electrode material, binder and 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 electrode current collector such as aluminum foil; after drying, rolling, die cutting and other processes, the positive electrode sheet can be obtained.

[0053] The secondary battery provided by the present invention also includes a negative electrode and an upper electrolyte.

[0054] In this process, the electrolyte in the electrolyte solution plays a role in conducting ions between the positive and negative electrode plates.

[0055] 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 can be a negative active material used in batteries, such as a metal negative electrode material or a non-metal negative electrode material. The metal negative electrode material is preferably a metal foil or alloy compound such as sodium, sodium alloy, tin, or antimony. The non-metal negative electrode material is preferably any one or a combination of at least two of hard carbon, soft carbon, graphite, and silicon suboxide.

[0056] In some embodiments, the negative electrode material includes hard carbon. Compared to other negative electrode materials, hard carbon has a disordered internal crystal arrangement and a larger interlayer spacing, which is more conducive to the formation of a protective film on its surface and further optimizes the stability of the protective film. In some embodiments, the hard carbon is in the form of spherical or near-spherical particles, further improving the stability of the film formed between the negative electrode material and the electrolyte.

[0057] 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.

[0058] Understandably, the secondary battery provided in the embodiments of the present invention also includes a separator.

[0059] 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.

[0060] The present invention also proposes an electrical device, wherein the aforementioned secondary battery is provided as the power supply for the electrical device.

[0061] 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.

[0062] 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.

[0063] The present invention will be described in detail below through embodiments.

[0064] (1) Discharge rate performance test:

[0065] At room temperature, a fully charged battery (voltage 3.65V) was discharged to 1.5V at a current density of 0.33C, and the capacity was recorded as C1.

[0066] Then, at room temperature, the fully charged battery (voltage 3.65V) was discharged to 1.5V at a current density of 5C, and the capacity was recorded as C2.

[0067] Calculate the capacity retention ratio C2 / C1 as a test indicator of discharge rate performance.

[0068] (2) Coating crack test:

[0069] Randomly cut a 1 square decimeter section from the baked positive electrode sheet and record the number of cracks on this area.

[0070] Example 1

[0071] (1) Preparation of positive electrode sheet

[0072] NaNi, the positive electrode active material 0.33 Fe 0.33 Mn 0.33 O2, sodium carboxymethyl cellulose (CMC) thickener, carbon black conductive agent, and styrene-butadiene rubber (SBR) binder are mixed in a mass ratio of 80:7.5:7.5:5. NMP solvent is added, and the mixture is stirred under vacuum to obtain a positive electrode slurry. The positive electrode slurry is then uniformly coated onto both sides of a carbon-coated aluminum foil current collector. After air-drying at room temperature, it is transferred to an oven for further drying. The resulting material is then rolled and cut to obtain the positive electrode sheet. The carbon-coated aluminum foil has a tensile strength of 45 kN, an elongation of 0.7%, and a specific surface area of ​​1.5 m² for the positive electrode active material. 2 / g, the number of primary particles in a single secondary particle of the positive electrode active material is 40, the ratio of open pores to closed pores is 2.5, the tap density of the conductive agent is 300g / L, and the molar mass of the binder is 1500000g / mol.

[0073] (2) Preparation of negative electrode sheet

[0074] The negative electrode active material hard carbon, conductive agent acetylene black (Super P) and binder SBR are mixed evenly in a mass ratio of 97:1:2 and evenly dispersed in deionized water to form a uniform black slurry. The mixed slurry is coated on both sides of copper foil, and then baked, rolled, and cut into sheets to obtain the negative electrode sheet.

[0075] (3) Preparation of electrolyte

[0076] 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.

[0077] (4) Preparation of sodium-ion batteries

[0078] The positive electrode, separator (glass fiber 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, liquid injection, formation, sorting and other processes, a sodium-ion battery is obtained.

[0079] Example 2

[0080] The difference between Example 2 and Example 1 is that, in step (1), the tap density of the conductive agent is adjusted to 600 g / L and the specific surface area of ​​the positive electrode active material is adjusted to 0.5 m². 2 / g, the molar mass of the binder is 1,000,000 g / mol.

[0081] Example 3

[0082] The difference between Example 3 and Example 1 is that, in step (1), the tap density of the conductive agent is adjusted to 50 g / L and the specific surface area of ​​the positive electrode active material is adjusted to 1.5 m². 2 / g, the molar mass of the binder is 2,000,000 g / mol.

[0083] Example 4

[0084] The difference between Example 4 and Example 1 is that in step (1), the molar mass of the adhesive is adjusted to 1,000,000 g / mol.

[0085] Example 5

[0086] The difference between Example 5 and Example 1 is that in step (1), the molar mass of the adhesive is adjusted to 2,000,000 g / mol.

[0087] Example 6

[0088] The difference between Example 6 and Example 1 is that in step (1), the conductive agent is adjusted to acetylene black, the tap density is 50 g / L, and the binder is adjusted to polytetrafluoroethylene (PTFE).

[0089] Example 7

[0090] The difference between Example 7 and Example 1 is that in step (1), the conductive agent is adjusted to Ketjen Black, the tap density is 600 g / L, and the binder is adjusted to polytetrafluoroethylene (PTFE).

[0091] Example 8

[0092] The difference between Example 8 and Example 1 is that, in step (1), the specific surface area of ​​the positive electrode active material is adjusted to 0.5 m². 2 / g.

[0093] Example 9

[0094] The difference between Example 9 and Example 1 is that, in step (1), the specific surface area of ​​the positive electrode active material is adjusted to 1.5 m². 2 / g.

[0095] Example 10

[0096] The difference between Example 10 and Example 1 is that in step (1), the number of primary particles in a single secondary particle of the positive electrode active material is adjusted to 30.

[0097] Example 11

[0098] The difference between Example 11 and Example 1 is that in step (1), the number of primary particles in a single secondary particle of the positive electrode active material is adjusted to 50.

[0099] Example 12

[0100] The difference between Example 12 and Example 1 is that in step (1), the ratio of open pores to closed pores in the positive electrode active material is adjusted to 2.

[0101] Example 13

[0102] The difference between Example 13 and Example 1 is that in step (1), the ratio of open pores to closed pores of the positive electrode active material is adjusted to 3.

[0103] Example 14

[0104] The difference between Example 14 and Example 1 is that in step (1), the tensile strength of the carbon-coated aluminum foil is adjusted to 32KN and the elongation is 0.6%, and the ratio of open pores to closed pores of the positive electrode active material is adjusted to 3.

[0105] Example 15

[0106] The difference between Example 15 and Example 1 is that in step (1), the tensile strength of the carbon-coated aluminum foil is adjusted to 58KN and the elongation rate is 0.8%, and the ratio of open pores to closed pores of the positive electrode active material is adjusted to 3.

[0107] Examples 16-18

[0108] The preparation process is the same as in Example 1, except that the weight of the positive electrode slurry is adjusted to obtain positive electrode sheets with different areal densities.

[0109] Comparative Example 1

[0110] The difference between Comparative Example 1 and Example 1 is that, in step (1), the tap density of the conductive agent was adjusted to 700 g / L and the specific surface area of ​​the positive electrode active material was adjusted to 0.4 m². 2 / g, the molar mass of the binder is 900000g / mol.

[0111] Comparative Example 2

[0112] The difference between Comparative Example 2 and Example 1 is that, in step (1), the tap density of the conductive agent was adjusted to 30 g / L and the specific surface area of ​​the positive electrode active material was adjusted to 1.3 m². 2 / g, the molar mass of the binder is 2500000g / mol.

[0113] The process parameters for each embodiment and comparative example are shown in Table 1.

[0114] Table 1

[0115]

[0116]

[0117] Where, x = 0.1 × exp (B) ×(M×K / P) 0.5 .

[0118] The areal density and resistance of the prepared positive electrode sheets of each embodiment and comparative example were tested, and the test data are shown in Table 2.

[0119] The batteries prepared in each embodiment and comparative example were subjected to discharge rate performance tests and coating crack tests. The test data are shown in Table 2.

[0120] Table 2

[0121]

[0122]

[0123] In summary, in this embodiment, the specific surface area of ​​the positive electrode active material, the ratio of open pores to closed pores, the tap density of the conductive agent powder, and the molar mass of the binder are matched to satisfy 10 < 0.1 × exp[…]. (B) ×(M×K / P) 0.5 <142 can effectively construct a conductive network for the positive electrode, improve the conductivity of the positive electrode, reduce the resistance of the positive electrode, and also improve the toughness of the positive electrode, making it less prone to cracking under high temperature conditions. This can effectively improve the discharge rate performance and produce a secondary battery with excellent fast discharge performance. Its 5C discharge capacity retention rate is greater than 80%, thus solving the problem of poor fast discharge performance of existing secondary batteries.

[0124] 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.

[0125] 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 invention includes a positive electrode sheet, which 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, a conductive agent, and a binder. The positive active material has a porous structure. The secondary battery satisfies: 10 < 0.1×exp (B) ×(M×K / P) 0.5 < 142; Among them, B m 2 / g represents the specific surface area of ​​the positive electrode active material, and B is 0.5~1.5; P g / L is the tap density of the conductive agent, where P is 50~600; M g / mol is the molar mass of the binder, where M is 1,000,000 to 2,000,000; K is the ratio of open pores to closed pores in the positive electrode active material, and K is 2 to 3.

2. The secondary battery according to claim 1, characterized in that, The positive 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 30 to 50.

3. The secondary battery according to claim 1, characterized in that, The areal density of the positive electrode sheet is 200~250 g / m³. 2 The resistance of the positive electrode is 200~500 mΩ.

4. The secondary battery according to claim 1, characterized in that, At least one of the following conditions must be met: a. The conductive agent includes at least one of conductive carbon black, Ketjen black, acetylene black, carbon nanotubes, and graphene; b. The adhesive includes at least one of styrene-butadiene rubber, polytetrafluoroethylene, and polyvinylidene fluoride.

5. The secondary battery according to claim 1, characterized in that, The positive electrode current collector includes an aluminum foil layer and a carbon layer disposed on the aluminum foil layer. The tensile strength of the positive electrode current collector is 30~60KN and the elongation is 0.6%~0.8%.

6. An electrical appliance, characterized in that, The device includes the secondary battery as described in any one of claims 1 to 5, wherein the secondary battery serves as the power supply for the electrical equipment.

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