Secondary battery and electric device

Abstract

The invention discloses a secondary battery and an electric device, and belongs to the technical field of batteries. According to the secondary battery provided by the invention, the numerical values of the ratio of the D peak intensity at 1350 + / -20 cm <-1 > to the G peak intensity at 1580 + / -20 cm <-1 > of the Raman spectrum of the negative electrode active material layer, the tortuosity of the negative electrode plate and the ratio of the open pore volume to the closed pore volume of the negative electrode active material layer are simultaneously controlled to be within a specific range, so that the three can be mutually influenced and synergistically acted; therefore, the conductivity of the pole piece and the first-circle coulombic efficiency and rate capability of the secondary battery are effectively improved.

Description

Technical Field

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

[0002] As the market for electrochemical devices (such as sodium-ion batteries) continues to expand, the performance requirements for batteries in electric vehicles and power tools are also constantly increasing. Furthermore, the power market places extremely high demands on the cost of rechargeable batteries, requiring them to be low-cost, while production time significantly impacts cost. Therefore, developing inexpensive and high-performance electrodes is crucial for the commercialization of rechargeable batteries. However, current conventional electrode designs offer very limited improvements in electrode conductivity, initial coulombic efficiency, and rate performance, thus restricting the development of rechargeable batteries. Summary of the Invention

[0003] The purpose of this application is to solve the technical problems of poor electrode conductivity, poor first-cycle coulombic efficiency and rate performance of secondary batteries in the prior art, and to provide a secondary battery and power supply device.

[0004] To achieve the above objectives, a first aspect of this application provides a secondary battery, including a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer disposed on at least a portion of the surface of the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material, and the Raman spectrum of the negative electrode active material layer being at 1350±20 cm⁻¹. -1 The D peak intensity at 1580±20cm -1 The ratio of the G peak intensities at point G, x, satisfies 0.84 ≤ x ≤ 1.20; The tortuosity y of the negative electrode sheet satisfies 0.14≤y≤0.60; The ratio z of the open-pore volume to the closed-pore volume of the negative electrode active material layer satisfies 0.070≤z≤0.095.

[0005] As an embodiment of this application, the secondary battery satisfies: 1.68 ≤ Q ≤ 7.13; Where Q = x × y ÷ z.

[0006] As an embodiment of this application, the pore volume Vo of the negative electrode active material layer satisfies 10.3 ≤ Vo ≤ 15.1, in μm. 3 .

[0007] As an embodiment of this application, the closed-pore volume Vc of the negative electrode active material layer satisfies 110.2≤Vc≤215.9, in μm. 3 .

[0008] As an embodiment of this application, the compaction density PD of the single layer of the negative electrode active material layer satisfies 1.2≤PD≤1.8, with the unit being g / cm³.

[0009] As an embodiment of this application, the particle size Dv99 of the negative electrode active material satisfies 3.9≤Dv99≤10.7, where the unit is μm.

[0010] As an embodiment of this application, the particle size Dv50 of the negative electrode active material satisfies 1.16≤Dv50≤2.68, with units of μm.

[0011] As an embodiment of this application, the porosity α of the single layer of the negative electrode active material layer satisfies 24% ≤ α ≤ 41%.

[0012] As an embodiment of this application, the thickness L of a single layer of the negative electrode active material layer satisfies 20≤L≤60, with units of μm.

[0013] As an embodiment of this application, the resistivity of the negative electrode is 10.4 mΩ·m to 15.1 mΩ·m.

[0014] As an embodiment of this application, the negative electrode active material includes hard carbon, and the graphitization degree g of the hard carbon satisfies 10.0% ≤ g ≤ 20.0%.

[0015] As an implementation of this application, g and x satisfy 0.74≤xg≤1.00.

[0016] As an embodiment of this application, the (Dv90-Dv10) / Dv50 of the negative electrode active material satisfies 2.50≤(Dv90-Dv10) / Dv50≤3.40.

[0017] A second aspect of this application provides an electrical device including the secondary battery described in this application.

[0018] Compared with the prior art, the beneficial effects of this application are: The secondary battery provided in this application achieves this by simultaneously controlling the Raman spectrum of the negative electrode active material layer at 1350±20 cm⁻¹. -1 The D peak intensity at 1580±20cm -1 Within a specific range, the ratio of G peak intensity, the tortuosity of the negative electrode sheet, and the ratio of open-pore volume to closed-pore volume in the negative electrode active material layer can influence and synergistically improve the conductivity of the electrode sheet, the first-cycle coulombic efficiency of the secondary battery, and the rate performance. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0021] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0022] According to a first aspect of this application, a secondary battery is provided, comprising a negative electrode sheet, the negative electrode sheet including a negative electrode current collector and a negative electrode active material layer disposed on at least a portion of the surface of the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material, and the Raman spectrum of the negative electrode active material layer being at 1350±20 cm⁻¹. -1 The D peak intensity at 1580±20cm -1 The ratio of the G peak intensities at point G, x, satisfies 0.84 ≤ x ≤ 1.20; The tortuosity y of the negative electrode sheet satisfies 0.14≤y≤0.60; The ratio z of the open-pore volume to the closed-pore volume of the negative electrode active material layer satisfies 0.070≤z≤0.095.

[0023] The secondary battery provided in this application achieves this by simultaneously controlling the Raman spectrum of the negative electrode active material layer at 1350±20 cm⁻¹. -1 The D peak intensity at 1580±20cm -1 Within a specific range, the ratio of G peak intensity, the tortuosity of the negative electrode sheet, and the ratio of open-pore volume to closed-pore volume in the negative electrode active material layer can influence and synergistically improve the conductivity of the electrode sheet, the first-cycle coulombic efficiency of the secondary battery, and the rate performance.

[0024] In this application, the Raman spectrum of the negative electrode active material layer is controlled at 1350±20 cm⁻¹. -1 The D peak intensity at 1580±20cm-1 Within a specific range, the ratio of the G peak intensities can increase the number of active sites inside the negative electrode active material layer, improve the capacity for storing metal ions, suppress side reactions between the negative electrode active material layer and the electrolyte, reduce irreversible capacity, and thus improve the conductivity of the electrode, the first-cycle coulombic efficiency of the secondary battery, and the rate performance.

[0025] This application controls the tortuosity of the negative electrode sheet within a specific range, so that the negative electrode active material layer has suitable compaction density, porosity and disorder. This not only improves the capacity of the active material and the wetting degree of the electrolyte, but also facilitates the solid-phase migration of sodium ions inside the negative electrode active material layer, thereby improving the conductivity of the electrode sheet, the first-cycle coulombic efficiency and rate performance of the secondary battery.

[0026] This application, by controlling the ratio of open-pore volume to closed-pore volume in the negative electrode active material layer within a specific range, can not only improve the capacity of the active material, but also give the negative electrode active material layer a suitable degree of disorder, which is conducive to the extraction and insertion of sodium ions, thereby improving the conductivity of the electrode, the first-cycle coulombic efficiency of the secondary battery, and the rate performance.

[0027] It should be noted that the Raman spectrum of the negative electrode active material layer described in this application is at 1350±20 cm⁻¹. -1 The D peak intensity at 1580±20cm -1 The test method for the ratio x of the G peak intensity at the point is as follows: the secondary battery is discharged at a current of 0.1C to the lower voltage limit of 2.0V, the negative electrode sheet is obtained after disassembly, dried, the negative electrode active material layer is removed from the negative electrode sheet, and the negative electrode active material layer is placed under a Raman spectrometer at a constant temperature of 25℃. After obtaining the data, it is fitted and the corresponding x value is calculated.

[0028] For example, the Raman spectrum of the negative electrode active material layer is at 1350±20 cm⁻¹. -1 The D peak intensity at 1580±20cm -1 The ratio x of the G peak intensities can be any point value between 0.84 and 1.20 or a range between any two points. For example, it can be one of 0.84, 0.85, 0.88, 0.90, 0.93, 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, 1.13, 1.15, 1.18, 1.20 or a range between any two.

[0029] It should be noted that the tortuosity of the negative electrode sheet described in this application is y = L' / L, where L' = 2 × PD × Dv99 × (1-a); where L' represents the shortest path for active ions (electrolyte) to travel in the monolayer negative electrode active material layer, in μm; L represents the thickness of the monolayer negative electrode active material layer, in μm; and PD represents the compaction density of the monolayer negative electrode active material layer, in g / cm³.3 Dv99 represents the particle size corresponding to a cumulative volume distribution percentage of 99% of the negative electrode active material particles in a single-layer negative electrode active material layer, in μm; a represents the porosity of the single-layer negative electrode active material layer.

[0030] The compaction density PD (in g / cm³) of the single-layer negative electrode active material layer described in this application 3 = Aspect density of a single-layer negative electrode active material layer / Thickness of a single-layer negative electrode active material layer. The method for testing the surface density of the single-layer negative electrode active material layer is as follows: Discharge the secondary battery at a 0.1C current to the lower voltage limit of 2.0V, disassemble to obtain the negative electrode sheet, dry it, weigh the total mass of the negative electrode sheet, remove the negative electrode active material layer from the negative electrode sheet, weigh the mass of the negative electrode current collector, and calculate the mass of the single-layer negative electrode active material layer. Then measure the effective area of ​​the single-layer negative electrode active material layer projected onto the negative electrode current collector. Divide the mass of the single-layer negative electrode active material layer by its effective area projected onto the negative electrode current collector to obtain the surface density of the single-layer negative electrode active material layer. The thickness L of the single-layer negative electrode active material layer is obtained by observation and measurement using a scanning electron microscope (SEM).

[0031] The Dv99 test method for the single-layer negative electrode active material layer described in this application is as follows: According to the GB / T19077-2016 standard "Particle Size Analysis by Laser Diffraction", the secondary battery is discharged at a current of 0.1C to the lower voltage limit of 2.0V. After disassembly, the negative electrode sheet is obtained. It is first cleaned with dimethyl carbonate (DMC) to remove residual electrolyte. Then, the negative electrode active material layer is peeled off from the negative electrode sheet with insulating tape. The negative electrode active material layer is then placed in a pure argon atmosphere and calcined at 700℃ for 9 hours to remove binder, moisture and volatile impurities, thereby obtaining the negative electrode active material powder of the negative electrode active material layer. The particle size distribution of the negative electrode active material is measured using a laser diffractometer, and the particle size Dv99 value corresponding to the cumulative volume distribution percentage of the negative electrode active material reaching 99% is obtained by analysis.

[0032] The porosity α of the single-layer negative electrode active material layer described in this application is as follows: the secondary battery is discharged to the lower voltage limit of 2.0V at a current of 0.1C. After disassembly, the negative electrode sheet is obtained. It is first cleaned with dimethyl carbonate (DMC) to remove residual electrolyte. Then, the negative electrode active material layer is peeled off from the negative electrode sheet with insulating tape. The porosity α of the single-layer negative electrode active material layer is tested by nitrogen adsorption-desorption method.

[0033] For example, the tortuosity y of the negative electrode can be any point value between 0.14 and 0.60 or a range between any two points. For instance, it can be one of 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.22, 0.23, 0.25, 0.27, 0.28, 0.30, 0.32, 0.33, 0.35, 0.37, 0.38, 0.40, 0.42, 0.43, 0.45, 0.47, 0.48, 0.50, 0.52, 0.53, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60 or a range between any two.

[0034] It should be noted that the test method for the ratio z of open-pore volume to closed-pore volume of the negative electrode active material layer described in this application is as follows: the secondary battery is discharged at a current of 0.1C to the lower voltage limit of 2.0V, and the negative electrode sheet is obtained after disassembly. It is first cleaned with dimethyl carbonate (DMC) to remove residual electrolyte, and then the negative electrode active material layer is peeled off from the negative electrode sheet with insulating tape. Under constant temperature of 25°C, the density ρ and true density ρ of the negative electrode active material layer are measured with a densitometer and a true density meter, respectively. s Then, according to the formulas z=Vo / Vc, Vo=Vt-Vc, Vc = Vt (1-ρ / ρ s The z value is calculated, where Vo represents the open pore volume of the negative electrode active material layer, Vc represents the closed pore volume of the negative electrode active material layer, and Vt represents the total volume of the negative electrode active material layer.

[0035] For example, the ratio z of the open pore volume to the closed pore volume of the negative electrode active material layer can be any point value between 0.070 and 0.095 or a range between any two points, such as one of 0.070, 0.073, 0.075, 0.078, 0.080, 0.083, 0.085, 0.088, 0.090, 0.093, 0.095 or a range between any two.

[0036] As an embodiment of this application, the secondary battery satisfies: 1.68 ≤ Q ≤ 7.13; Where Q = x × y ÷ z.

[0037] For example, Q can be any point value between 1.68 and 7.13 or a range value between any two points, such as 1.68, 1.69, 1.70, 1.80, 1.81, 1.82, 1.83, 1.84, 1.85, 1.90, 2.00, 2.20, 2.30, 2.50, 2.70, 2.80, 3.00, 3.20, 3.30, 3.50, 3.70, 3.80, 40, 4.20, 4.30, 4... The range of values ​​between one or any two of the following: 0.50, 4.70, 4.80, 5.00, 5.20, 5.30, 5.50, 5.70, 5.80, 6.00, 6.20, 6.30, 6.40, 6.50, 6.60, 6.65, 6.66, 6.67, 6.70, 6.80, 6.90, 7.00, 7.02, 7.05, 7.07, 7.08, 7.09, 7.10, 7.11, 7.12, and 7.13.

[0038] When Q is within the above range, the defect degree of the negative electrode active material and the conductivity of the negative electrode sheet are in a state of mutual balance, which is conducive to further improving the conductivity of the negative electrode sheet, the first-cycle coulombic efficiency and rate performance of the secondary battery.

[0039] As an embodiment of this application, the pore volume Vo of the negative electrode active material layer satisfies 10.3 ≤ Vo ≤ 15.1, in μm. 3 .

[0040] For example, Vo can be any point value between 10.3 and 15.1 or a range value between any two points. For instance, it can be one of 10.3, 10.5, 10.8, 11.0, 11.3, 11.5, 11.8, 12.0, 12.3, 12.5, 12.8, 13.0, 13.3, 13.5, 13.8, 14.0, 14.3, 14.5, 14.8, 15.0, 15.1 or a range value between any two.

[0041] When Vo is within the above range, it is beneficial to further improve the conductivity of the electrode, the first-cycle coulombic efficiency of the secondary battery, and the rate performance.

[0042] As an embodiment of this application, the closed-pore volume Vc of the negative electrode active material layer satisfies 110.2≤Vc≤215.9, in μm. 3 .

[0043] For example, Vc can be any point value between 110.2 and 215.9 or a range value between any two points, such as 110.2, 110.3, 110.5, 110.8, 111.0, 115.0, 120.0, 125.0, 130.0, 135.0, 140.0, 145.0, 150.0, 155.0, and 160.0. The range of values ​​between one and any two of the following: 165.0, 170.0, 175.0, 180.0, 185.0, 190.0, 195.0, 200.0, 205.0, 210.0, 215.0, 215.1, 215.2, 215.3, 215.4, 215.5, 215.6, 215.7, 215.8, and 215.9.

[0044] When Vc is within the above range, it is beneficial to further improve the conductivity of the electrode, the first-cycle coulombic efficiency of the secondary battery, and the rate performance.

[0045] As an embodiment of this application, the compaction density PD of the single layer of the negative electrode active material layer satisfies 1.2≤PD≤1.8, with the unit being g / cm³.

[0046] For example, the PD can be any point value between 1.2 and 1.8 or a range value between any two points, such as one of 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8 or a range value between any two of them.

[0047] When the PD is within the above range, it is beneficial to balance the defect degree of the negative electrode active material and the conductivity of the electrode, thereby further improving the conductivity of the electrode, the first-cycle coulombic efficiency and rate performance of the secondary battery.

[0048] As an embodiment of this application, the particle size Dv99 of the negative electrode active material satisfies 3.9≤Dv99≤10.7, where the unit is μm.

[0049] For example, Dv99 can be any point value between 3.9 and 10.7 or a range value between any two points. For example, it can be one of 3.9, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0, 10.5, 10.6, 10.7 or a range value between any two.

[0050] When Dv99 is within the above range, it can promote the rapid migration of metal ions and make the SEI layer more uniform, which is beneficial to further improve the conductivity of the negative electrode, the first-cycle coulombic efficiency and rate performance of the secondary battery.

[0051] As an embodiment of this application, the particle size Dv50 of the negative electrode active material satisfies 1.16≤Dv50≤2.68, with units of μm. Here, Dv50 represents the particle size corresponding to when the cumulative volume distribution percentage of the negative electrode active material particles in a single-layer negative electrode active material layer reaches 50%.

[0052] The Dv50 test method for the single-layer negative electrode active material in this application is as follows: According to the GB / T19077-2016 standard "Particle Size Analysis by Laser Diffraction", the secondary battery is discharged at a current of 0.1C to the lower voltage limit of 2.0V. After disassembly, the negative electrode sheet is obtained. It is first cleaned with dimethyl carbonate (DMC) to remove residual electrolyte. Then, the negative electrode active material layer is peeled off from the negative electrode sheet with insulating tape. The negative electrode active material layer is then placed in a pure argon atmosphere and calcined at 700℃ for 9 hours to remove binder, moisture and volatile impurities, thus obtaining the negative electrode active material powder. The particle size distribution of the negative electrode active material is measured using a laser diffractometer, and the particle size Dv50 value corresponding to the cumulative volume distribution percentage of the negative electrode active material reaching 50% is obtained by analysis.

[0053] For example, Dv50 can be any point value between 1.16 and 2.68 or a range value between any two points. For example, it can be one of 1.16, 1.20, 1.30, 1.40, 1.50, 1.60, 1.70, 1.80, 1.90, 2.00, 2.10, 2.20, 2.30, 2.40, 2.50, 2.60, 2.65, 2.66, 2.67, 2.68 or a range value between any two of them.

[0054] When Dv50 is within the above range, it is beneficial to further improve the conductivity of the electrode, the first-cycle coulombic efficiency of the secondary battery, and the rate performance.

[0055] As an embodiment of this application, the porosity α of the single layer of the negative electrode active material layer satisfies 24% ≤ α ≤ 41%.

[0056] For example, 'a' can be any point value between 24% and 41% or a range value between any two points, such as one of 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41% or a range value between any two.

[0057] When 'a' is within the above range, it is beneficial to further improve the conductivity of the negative electrode, the first-cycle coulombic efficiency of the secondary battery, and the rate performance.

[0058] As an embodiment of this application, the thickness L of a single layer of the negative electrode active material layer satisfies 20≤L≤60, with units of μm.

[0059] For example, L can be any point value between 20 and 60 or a range value between any two points, such as one of 20, 23, 25, 28, 30, 35, 40, 45, 50, 55, 56, 57, 58, 59, 60 or a range value between any two.

[0060] When L is within the above range, it is beneficial to further improve the conductivity of the negative electrode, the first-cycle coulombic efficiency of the secondary battery, and the rate performance.

[0061] It should be noted that the test method for the thickness L of the single layer of negative electrode active material layer described in this application is as follows: the secondary battery is discharged at a current of 0.1C to the lower voltage limit of 2.0V, the negative electrode sheet is obtained after disassembly, dried, and the negative electrode sheet is observed under a scanning electron microscope (SEM) to measure the thickness L of the single layer of negative electrode active material layer.

[0062] In this application, the term "single layer of negative electrode active material layer" refers to the negative electrode active material layer coated on one side of the negative electrode current collector. It can be understood that the thickness of a single layer of negative electrode active material layer refers to the thickness of the negative electrode active material layer coated on one side of the negative electrode current collector.

[0063] As an embodiment of this application, the resistivity of the negative electrode is 10.4 mΩ·m to 15.1 mΩ·m.

[0064] It should be noted that the resistivity test method of the negative electrode sheet described in this application is as follows: the secondary battery is discharged at a current of 0.1C to the lower voltage limit of 2.0V, the negative electrode sheet is obtained after disassembly, dried, and the negative electrode active material layer is peeled off from the negative electrode sheet with insulating tape. Then, four equally spaced metal probes are used to contact the negative electrode active material layer. Among them, a current I (in mA) is passed between the two metal probes that are separated by two metal probes in the middle and located on the outer side. The other two adjacent metal probes located on the inner side are used to measure the voltage U (in V). The resistivity of the negative electrode sheet is calculated according to the resistivity formula ρ=ηW(U / I), where W is the thickness L of a single layer of negative electrode active material (in μm), and η is a correction coefficient related to the material properties. Here, η is taken as 1.

[0065] For example, the resistivity of the negative electrode can be any point value or a range between any two points between 10.4 mΩ·m and 15.1 mΩ·m. For instance, it can be one of 10.4 mΩ·m, 10.5 mΩ·m, 11.0 mΩ·m, 11.5 mΩ·m, 12.0 mΩ·m, 12.5 mΩ·m, 13.0 mΩ·m, 13.5 mΩ·m, 14.0 mΩ·m, 14.5 mΩ·m, 15.0 mΩ·m, and 15.1 mΩ·m, or a range between any two.

[0066] As an embodiment of this application, the negative electrode active material includes hard carbon, and the graphitization degree g of the hard carbon satisfies 10.0% ≤ g ≤ 20.0%.

[0067] It should be noted that the test method for the graphitization degree g of the hard carbon described in this application is as follows: the secondary battery is discharged at a current of 0.1C to the lower voltage limit of 2.0V, the negative electrode sheet is obtained after disassembly, dried, the negative electrode active material layer is removed from the negative electrode sheet, and it is ground to a particle size of less than 0.075mm to obtain the sample to be tested; then, under constant temperature of 25℃, the d of the sample to be tested is measured using a high-precision X-ray diffractometer (XRD). 002 The formula g=(0.3440-d) is used to calculate the result. 002 The graphitization degree g of hard carbon is calculated as (0.3440-0.3354)×100%, where 0.3440 nm is the interlayer spacing of non-graphitized carbon and 0.3354 nm is the interlayer spacing of ideal graphite.

[0068] For example, g can be any point value between 10.0% and 20.0% or a range value between any two points, such as one of 10.0%, 11.0%, 12.0%, 13.0%, 14.0%, 15.0%, 16.0%, 17.0%, 18.0%, 19.0%, 20.0% or a range value between any two.

[0069] When g is within the above range, it is beneficial to further improve the conductivity of the electrode, the first-cycle coulombic efficiency of the secondary battery, and the rate performance.

[0070] As an implementation of this application, g and x satisfy 0.74≤xg≤1.00.

[0071] For example, xg can be any point value between 0.74 and 1.00 or a range value between any two points. For instance, it can be one of 0.74, 0.75, 0.76, 0.77, 0.78, 0.80, 0.83, 0.85, 0.88, 0.90, 0.93, 0.95, 0.96, 0.97, 0.98, 0.99, 1.00 or a range value between any two of them.

[0072] When xg is within the above range, the graphitization degree and defect degree of the negative electrode active material are in a balanced state, which is conducive to further improving the conductivity of the negative electrode sheet, the first-cycle coulombic efficiency and rate performance of the secondary battery.

[0073] As an embodiment of this application, the ratio (Dv90-Dv10) / Dv50 of the negative electrode active material satisfies 2.50≤(Dv90-Dv10) / Dv50≤3.40. Here, Dv90 represents the particle size corresponding to a cumulative volume distribution percentage of 90% for the negative electrode active material in a single-layer negative electrode active material layer, and Dv10 represents the particle size corresponding to a cumulative volume distribution percentage of 10% for the negative electrode active material in a single-layer negative electrode active material layer. The testing methods for Dv90 and Dv10 of the negative electrode active material are the same as those for Dv99 or Dv50 of the negative electrode active material.

[0074] For example, (Dv90-Dv10) / Dv50 can be any point value between 2.50 and 3.40 or a range value between any two points, such as one of 2.50, 2.60, 2.70, 2.80, 2.90, 3.00, 3.10, 3.20, 3.30, 3.40 or a range value between any two of them.

[0075] When (Dv90-Dv10) / Dv50 is within the above range, the particle size distribution of the negative electrode active material is relatively uniform, which is beneficial to further improve the conductivity of the electrode, the first-cycle coulombic efficiency of the secondary battery, and the rate performance.

[0076] As an embodiment of this application, the negative electrode active material layer further includes at least one of a negative electrode conductive agent and a negative electrode binder.

[0077] This application does not impose any particular restrictions on the selection of the negative electrode conductive agent; conventional negative electrode conductive agents in the art can be used. For example, the negative electrode conductive agent includes at least one of conductive carbon black, acetylene black, graphene, and carbon nanotubes (CNTs).

[0078] This application does not impose any particular restrictions on the selection of the negative electrode binder; conventional negative electrode binders in the art can be used. Exemplarily, the negative electrode binder includes at least one of polyvinylidene fluoride (PVDF) and styrene-butadiene rubber (SBR).

[0079] As an embodiment of this application, the secondary battery further includes a positive electrode and an electrolyte.

[0080] As an embodiment of this application, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least a portion of the surface of the positive current collector.

[0081] As an embodiment of this application, the positive electrode active material layer includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder.

[0082] This application does not impose any particular restrictions on the selection of the positive electrode active material, and conventional positive electrode active materials in the art can be used. For example, the positive electrode active material may be Na3V2(PO4)3(NVP), NaFePO4(NFP), Na3V2(PO4)2F3(NVPF), etc.

[0083] This application does not impose any particular restrictions on the selection of the positive electrode conductive agent; conventional positive electrode conductive agents in the art can be used. For example, the positive electrode conductive agent includes at least one of conductive carbon black, acetylene black, SuperP, graphene, and carbon nanotubes (CNTs).

[0084] This application does not impose any particular restrictions on the selection of the positive electrode binder; conventional positive electrode binders in the art can be used. Exemplarily, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), sodium polyacrylate (PAANa), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR).

[0085] As an embodiment of this application, the electrolyte includes an organic solvent and a sodium salt.

[0086] This application does not impose any particular restrictions on the selection of organic solvents, and conventional organic solvents in the art can be used. Exemplarily, the organic solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate, ethyl methyl carbonate, diethyl carbonate, and dimethyl carbonate.

[0087] This application does not impose any particular restrictions on the selection of sodium salts, and conventional sodium salts in the art can be used. Exemplarily, the sodium salt includes at least one of NaClO4 (sodium perchlorate), NaPF6 (sodium hexafluorophosphate), NaTFSI (sodium bis(trifluoromethanesulfonyl)imide), and NaBF4 (sodium tetrafluoroborate).

[0088] As an embodiment of this application, the method for preparing the secondary battery includes the following steps: (1) Preparation of negative electrode sheet: The negative electrode active material, negative electrode conductive agent and negative electrode binder are mixed and added to water to obtain negative electrode slurry. The negative electrode slurry is coated on at least one surface of the negative electrode current collector, and then dried, rolled, slit and cut to obtain negative electrode sheet. (2) Preparation of positive electrode sheet: The positive electrode active material, positive electrode conductive agent and positive electrode binder are mixed and then added to N-methylpyrrolidone to obtain positive electrode slurry. The positive electrode slurry is coated on at least one surface of the positive electrode current collector, and then dried, rolled, slit and cut into sheets to obtain positive electrode sheet. (3) Preparation of electrolyte: Sodium salt is added to organic solvent to obtain electrolyte; (4) Preparation of secondary battery: The positive electrode, negative electrode, separator and other components are assembled and then subjected to processes such as winding, hot pressing, super welding, core assembly, casing, baking, liquid injection, high temperature immersion, formation, aging, sealing and capacity testing to obtain secondary battery.

[0089] It should be noted that the x and z values ​​can be controlled by adjusting the calcination temperature and holding time in step (1), as well as the mass ratio of the negative electrode active material, negative electrode conductive agent, and negative electrode binder. For example, increasing the calcination temperature and / or holding time can make both the x and z values ​​increase first and then decrease. For example, by increasing the amount of negative electrode active material and decreasing the amount of negative electrode conductive agent and negative electrode binder in relation to the mass ratio of the negative electrode active material, negative electrode conductive agent, and negative electrode binder, both the x and z values ​​can be increased.

[0090] It should be noted that the values ​​of Dv99, PD, a, and y can be controlled by adjusting the mesh size of the sieve used in step (1); for example, increasing the mesh size of the sieve used in sieving can decrease Dv99, increase PD, increase a, and decrease y.

[0091] It should be noted that the values ​​of Dv99, PD, a, L and y can be controlled by adjusting the rolling pressure in step (1); for example, increasing the rolling pressure in the rolling process can keep Dv99 unchanged, increase PD, keep a unchanged, decrease L and increase y.

[0092] According to a second aspect of this application, an electrical device is provided, including the secondary battery described in this application.

[0093] For example, the aforementioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0094] Example 1 This application provides a secondary battery, the preparation method of which includes the following steps: (1) Preparation of negative electrode: Phenolic resin and ethanol solution with a volume fraction of 99% (solvent is water) were mixed at a solid-liquid ratio of 100g:400mL, air-dried at 25℃, and then calcined at 900℃ under argon atmosphere protection for 4h to obtain hard carbon as the negative electrode active material. Hard carbon was sieved through a double-layer 2400-mesh sieve. Then, the negative electrode active material (hard carbon), negative electrode conductive agent (conductive carbon black), and negative electrode binder (polyvinylidene fluoride, PVDF) were mixed at a mass ratio of 95:2.5:2.5 and then thoroughly mixed in water to obtain a negative electrode slurry with a solid content of 50%. The negative electrode slurry was coated on both surfaces of a 4.5 μm negative electrode current collector (copper foil) at a flow rate of 1 m / min. The electrode sheet was then dried, rolled, slit, and cut to obtain the negative electrode sheet. The drying temperature was 100℃, and the rolling pressure was 40t during the rolling process. (2) Preparation of the positive electrode: The positive electrode active material [Na3V2(PO4)3, NVP], positive electrode conductive agent (conductive carbon black), and positive electrode binder (polyvinylidene fluoride, PVDF) were mixed in a mass ratio of 85:7.5:7.5, and then thoroughly mixed in N-methylpyrrolidone to obtain a positive electrode slurry with a solid content of 68%. The positive electrode slurry was coated on both surfaces of a 13μm positive electrode current collector (aluminum foil) at a flow rate of 2m / min. The electrode sheet was then dried, rolled, slit, and cut to obtain the positive electrode sheet. The drying temperature was 100℃, and the rolling pressure was 40t during the rolling process. (3) Preparation of electrolyte: Sodium salt is added to organic solvent to obtain electrolyte; Ethylene carbonate (EC) and propylene carbonate (PC) were mixed in a mass ratio of 1:1 to obtain an organic solvent. Then, NaClO4 (sodium perchlorate) was added and mixed evenly to obtain an electrolyte. The concentration of sodium perchlorate was 1 mol / L. (4) Preparation of secondary battery: The positive electrode, negative electrode, separator and other components are assembled and then subjected to processes such as winding, hot pressing, super welding, core assembly, casing, baking, liquid injection, high temperature immersion, formation, aging, sealing and capacity testing to obtain secondary battery.

[0095] Examples 2-6 Examples 2-6 provide different secondary batteries. The difference between their preparation methods and those of Example 1 is that the calcination temperature and holding time in step (1) are different. By adjusting the calcination temperature and holding time in step (1), the x-value and z-value of Examples 2-6 are shown in Table 1. The rest are the same as those of Example 1.

[0096] Examples 7-10 Examples 7-10 provide different secondary batteries. The difference between their preparation methods and those of Example 1 is that the mesh size of the sieve used in step (1) is different. By adjusting the mesh size of the sieve used in step (1), the parameters such as Dv99, PD, a and y values ​​of Examples 7-10 are shown in Table 1. The rest are the same as those of Example 1.

[0097] Examples 11-14 Examples 11-14 provide different secondary batteries. The difference between their preparation methods and those of Example 1 is that the rolling pressure in step (1) is different. By adjusting the rolling pressure in step (1), the parameters such as PD, a and y values ​​of Examples 11-14 are shown in Table 1. The rest are the same as those of Example 1.

[0098] Examples 15-18 Examples 15-18 provide different secondary batteries. The difference between their preparation methods and those of Example 1 is that the mass ratio of negative electrode active material (hard carbon), negative electrode conductive agent (conductive carbon black), and negative electrode binder (polyvinylidene fluoride, PVDF) in step (1) is different. By adjusting the mass ratio of negative electrode active material, negative electrode conductive agent, and negative electrode binder in step (1), the x-value and z-value of Examples 15-18 are shown in Table 1. The rest are the same as those of Example 1.

[0099] Comparative Examples 1-4 Comparative Examples 1-4 provide different secondary batteries. The difference between their preparation methods and those of Example 1 is that the calcination temperature and holding time in step (1), the mesh size of the sieve used for sieving, and the rolling pressure during the rolling process are different. By adjusting the calcination temperature and holding time in step (1), the mesh size of the sieve used for sieving, and the rolling pressure during the rolling process, the x, y, and z values ​​of Comparative Examples 1-4 are shown in Table 1. The rest are the same as those of Example 1.

[0100] The parameters in the embodiments and comparative examples are shown in Table 1-2: Table 1 Table 2 Performance testing The performance of the secondary batteries prepared in the examples and comparative examples was tested, including the following aspects: 1. Resistivity test of the negative electrode: The secondary battery was discharged at a current of 0.1C to the lower voltage limit of 2.0V. After disassembly, the negative electrode sheet was obtained, dried, and the negative electrode active material layer was peeled off from the negative electrode sheet with insulating tape. Then, four equally spaced metal probes were used to contact the negative electrode active material layer. A current I (in mA) was passed between the two metal probes that were separated by two metal probes in the middle and located on the outer side. The other two adjacent metal probes located on the inner side were used to measure the voltage U (in V). The resistivity of the negative electrode sheet was calculated according to the resistivity formula ρ=ηW(U / I), where W is the thickness L of a single layer of negative electrode active material (in μm), and η is a correction coefficient related to the material properties. Here, η is taken as 1. 2. First-lap Coulomb efficiency test: The secondary battery was subjected to its first charge-discharge test at 25°C, being charged at a constant current of 0.33C until the upper limit of the cutoff voltage V. max Then in V max Charge at constant voltage until the current is less than 0.05C, let stand for 5 minutes, then discharge at a current of 0.33C until the lower cutoff voltage V. min Record the first discharge capacity and first charge capacity of the secondary battery during the first charge-discharge test, where V max =3.8V, V min =2V, calculate the first-round coulomb efficiency (%) using the following formula: First-cycle coulombic efficiency (%) = (first discharge capacity / first charge capacity) × 100%; 3. Ratio Performance Test: The secondary battery was subjected to charge-discharge tests at 25°C, and was charged at a constant current of 0.33C until the upper limit of the cutoff voltage V. max Then in V max Charge at constant voltage until the current is less than 0.05C, let stand for 5 minutes, then discharge at a current of 5C until the lower cutoff voltage V. min This is considered one charge-discharge cycle. Repeat this process 10 times, recording the discharge capacity of the first and tenth cycles, where V... max =3.8V, V min =2V, calculate the 5C rate retention rate (%) using the following formula: 5C rate retention (%) = Discharge capacity of the 10th charge-discharge cycle / Discharge capacity of the 1st charge-discharge cycle × 100%; The experimental results are shown in Table 3: Table 3 As shown in Table 3, the secondary battery of this application has high electrode conductivity, high first-cycle coulombic efficiency and high rate performance. Specifically, the resistivity of the negative electrode is ≤15.1 mΩ·m, the first-cycle coulombic efficiency of the secondary battery is ≥81%, and the rate performance (5C rate retention rate) of the secondary battery is ≥68.5%.

[0101] Furthermore, as can be seen from Examples 1-18 and Comparative Examples 1-4, when the Raman spectrum of the negative electrode active material layer is at 1350±20 cm⁻¹... -1 The D peak intensity at 1580±20cm -1 When the values ​​of the ratio of G peak intensity, the tortuosity of the negative electrode sheet, and the ratio of open pore volume to closed pore volume of the negative electrode active material layer are within a specific range in this application, the conductivity of the electrode sheet, the first-cycle coulombic efficiency of the secondary battery, and the rate performance can be effectively improved.

[0102] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of this application and not to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. 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 at least a portion of the surface of the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material, characterized in that, The Raman spectrum of the negative electrode active material layer is at 1350±20 cm⁻¹. -1 The D peak intensity at 1580±20cm -1 The ratio of the G peak intensities at point G, x, satisfies 0.84 ≤ x ≤ 1.20; The tortuosity y of the negative electrode sheet satisfies 0.14≤y≤0.60; The ratio z of the open-pore volume to the closed-pore volume of the negative electrode active material layer satisfies 0.070≤z≤0.

095.

2. The secondary battery as described in claim 1, characterized in that, The secondary battery satisfies: 1.68 ≤ Q ≤ 7.13; Where Q = x × y ÷ z.

3. The secondary battery as described in claim 1, characterized in that, The pore volume Vo of the negative electrode active material layer satisfies 10.3 ≤ Vo ≤ 15.1, in μm. 3 .

4. The secondary battery as described in claim 1, characterized in that, The closed-pore volume Vc of the negative electrode active material layer satisfies 110.2≤Vc≤215.9, in μm. 3 .

5. The secondary battery as described in claim 1, characterized in that, The compaction density PD of a single layer of the negative electrode active material layer satisfies 1.2≤PD≤1.8, with units of g / cm³.

6. The secondary battery as described in claim 1, characterized in that, The particle size Dv99 of the negative electrode active material satisfies 3.9≤Dv99≤10.7, where the unit is μm; And / or, the particle size Dv50 of the negative electrode active material satisfies 1.16≤Dv50≤2.68, in μm.

7. The secondary battery as described in claim 1, characterized in that, The porosity α of the single layer of the negative electrode active material layer satisfies 24% ≤ a ≤ 41%.

8. The secondary battery as described in claim 1, characterized in that, The thickness L of a single layer of the negative electrode active material layer satisfies 20≤L≤60, and the unit is μm.

9. The secondary battery as described in claim 1, characterized in that, The resistivity of the negative electrode is 10.4 mΩ·m to 15.1 mΩ·m.

10. The secondary battery as described in claim 1, characterized in that, The negative electrode active material includes hard carbon, and the degree of graphitization g of the hard carbon satisfies 10.0%≤g≤20.0%.

11. The secondary battery as described in claim 10, characterized in that, The condition g and x satisfy 0.74≤xg≤1.

00.

12. The secondary battery as described in claim 1, characterized in that, The ratio of (Dv90-Dv10) / Dv50 of the negative electrode active material satisfies 2.50≤(Dv90-Dv10) / Dv50≤3.

40.

13. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 1-12.

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