Secondary battery and electric device
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHEJIANG LIWINON ENERGY TECHNOLOGY CO LTD
- Filing Date
- 2024-12-12
- Publication Date
- 2026-06-05
Smart Images
Figure CN119650805B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of new energy technology, specifically to a secondary battery and electrical equipment. Background Technology
[0002] Currently, common methods to improve energy density include using thick electrodes to increase the loading of active material per unit area. However, simply increasing the electrode thickness increases the transport distance of ions and electrons, leading to severe polarization and poor electrochemical performance. Therefore, it is necessary to develop a technology to improve the electrode ion transport kinetics, reduce polarization, and enhance the battery's electrical performance. Summary of the Invention
[0003] Based on the deficiencies of the existing technology, the purpose of this application is to provide a secondary battery and an electrical device.
[0004] To achieve the above objectives, in a first aspect, this application provides a secondary battery, including a positive electrode, a separator, a negative electrode, and an electrolyte, wherein the positive electrode includes a positive current collector and a positive active material layer disposed on one or both sides of the positive current collector.
[0005] Along the direction away from the positive current collector, the positive active material layer sequentially includes a first active material layer and a second active material layer. Both the first active material layer and the second active material layer contain a conductive agent. The conductive agent in the first active material layer is a fibrous conductive agent, and the conductive agent in the second active material layer is a particulate conductive agent.
[0006] In some embodiments, the mass fraction of the fibrous conductive agent in the first active material layer is 0.5% to 1%.
[0007] In some embodiments, the mass fraction of the particulate conductive agent in the second active material layer is ≥1%. In one embodiment, the mass fraction of the particulate conductive agent in the second active material layer is 1% to 6%.
[0008] In some embodiments, the mass fraction of the conductive agent in the positive electrode active material layer is 0.5% to 3%.
[0009] In some embodiments, the positive electrode, the separator, and the negative electrode are arranged sequentially and wound together. The positive electrode has a flat region and a corner region. The first active material layer is located in the flat region and the corner region of the positive electrode, and the second active material layer is located in the flat region of the positive electrode.
[0010] In some embodiments, the thickness h2 of the first active material layer and the thickness h3 of the second active material layer satisfy: h2:h3=(4~10):1.
[0011] In some embodiments, the second active material layer h3 satisfies: 10μm≤h3≤30μm.
[0012] In some embodiments, the fibrous conductive agent has an average diameter of less than 150 nm and an average specific surface area of 10–250 m². 2 / g, with an average length of 5–30 μm. In one embodiment, the fibrous conductive agent has an average diameter of 10–20 nm and an average specific surface area of 150–250 m². 2 / g.
[0013] In some embodiments, the Dv50 of the particulate conductive agent is 30-50 nm.
[0014] In some embodiments, the fibrous conductive agent includes at least one of carbon nanotubes and carbon fibers.
[0015] In some embodiments, the particulate conductive agent includes at least one of Ketjen Black, acetylene black, and Super-P.
[0016] Secondly, this application provides an electrical device including the aforementioned secondary battery.
[0017] Compared with the prior art, the beneficial effects of this application are as follows: By setting the positive electrode active material layer to include a double-layer structure, and controlling the conductive agent in the first active material layer near the positive electrode current collector to be a fibrous conductive agent, and the conductive agent in the second active material layer away from the positive electrode current collector to be a particulate conductive agent, this application can promote the penetration of electrolyte into the positive electrode material, reduce polarization during the charging and discharging process, and make the electrochemical performance of the secondary battery, such as the initial coulombic efficiency and cycle performance, better. Attached Figure Description
[0018] Figure 1 This is a schematic diagram of a partial structure of the core in Example 1;
[0019] Figure 2 This is a schematic diagram of the gap coating in Example 1;
[0020] Figure 3 This is a microscopic schematic diagram of the double-layer structure in the straight region of the positive electrode sheet in Example 1;
[0021] Among them, 10-positive electrode sheet, 20-separator, 30-negative electrode sheet, 101-positive current collector, 102-first active material layer (i.e., lower layer), 103-second active material layer (i.e., upper layer), 301-negative current collector, 302-negative active material layer. Detailed Implementation
[0022] To better illustrate the purpose, technical solutions, and advantages of this application, the following description, in conjunction with specific embodiments and comparative examples, aims to provide a detailed understanding of the content of this application, rather than limiting it. All other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this application. Unless otherwise specified, the experimental reagents and instruments involved in the implementation of this application are commonly used reagents and instruments. In this application, the technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions that include the listed features.
[0023] According to a first aspect of this application, a secondary battery is provided, comprising a positive electrode, a separator, a negative electrode, and an electrolyte, wherein the positive electrode comprises a positive current collector and a positive active material layer disposed on one or both sides of the positive current collector.
[0024] Along the direction away from the positive electrode current collector, the positive electrode active material layer sequentially includes a first active material layer and a second active material layer. Both the first active material layer and the second active material layer contain a conductive agent. The conductive agent in the first active material layer is a fibrous conductive agent, and the conductive agent in the second active material layer is a particulate conductive agent.
[0025] By setting the positive electrode active material layer as a multi-layer structure, the conductive agent in the first active material layer near the positive electrode current collector is a fibrous conductive agent. The fibrous conductive agent has a high aspect ratio and a large specific surface area, which can promote the penetration of electrolyte into the positive electrode material and help reduce interfacial impedance. At the same time, the fibrous conductive agent can better improve the mechanical properties of the positive electrode material and help increase the adhesion between the positive electrode active material layer and the positive electrode current collector. The conductive agent in the second active material layer away from the positive electrode current collector is a particulate conductive agent. Since the active material containing particulate conductive agent is more likely to penetrate and diffuse into the active material containing fibrous conductive agent, the specific shape difference of the conductive agent in the first and second active material layers is conducive to improving the interfacial stability between the first and second active material layers, and improving the problems of microcracks and peeling of the positive electrode material during charging and discharging. In addition, the specific shape difference of the conductive agent in the first and second active material layers is more conducive to building a gradient distribution of electron transfer and ion diffusion, reducing polarization distribution, improving the utilization rate of the positive electrode active material, and further improving the dynamic performance of the electrode.
[0026] With the combined effect of a first active material layer containing fibrous conductive agents and a second active material layer containing particulate conductive agents, the positive electrode exhibits good electron and ion transport kinetics, low polarization, and good electrochemical performance such as initial coulombic efficiency and cycle performance of the secondary battery.
[0027] In some embodiments, the mass fraction of the fibrous conductive agent in the first active material layer is 0.5% to 1%. For example, the mass fraction of the fibrous conductive agent in the first active material layer is within the range formed by any two of the following values: 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%.
[0028] When the mass fraction of the fibrous conductive agent in the first active material layer is in the range of 0.5% to 1%, not only does the layer have good conductivity, but the fibrous conductive agent also has better dispersion in the slurry of the first active material layer. The slurry also has suitable viscosity, which makes the battery cycle performance better and the initial coulombic efficiency higher.
[0029] In some embodiments, the mass fraction of the particulate conductive agent in the second active material layer is ≥1%. For example, the mass fraction of the particulate conductive agent in the second active material layer is within the range formed by any two of the following values: 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, or more.
[0030] When the mass fraction of particulate conductive agent in the second active material layer is ≥1%, the conductivity of the layer is better.
[0031] In one embodiment, the mass fraction of the particulate conductive agent in the second active material layer is 1% to 6%.
[0032] In some embodiments, the mass fraction of the conductive agent in the positive electrode active material layer is 0.5% to 3%. For example, the mass fraction of the conductive agent in the positive electrode active material is within the range formed by any two of the following values: 0.5%, 0.7%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, or more.
[0033] When the mass fraction of the conductive agent in the positive electrode active material layer is in the range of 0.5% to 3%, it helps to reduce the electrode contact resistance, promote electrolyte wetting, and improve the toughness of the positive electrode sheet, thereby increasing the battery charge and discharge efficiency, while ensuring that the secondary battery has a high energy density.
[0034] In some embodiments, the positive electrode, the separator, and the negative electrode are arranged in sequence and wound together. The positive electrode has a flat region and a corner region. The first active material layer is located in the flat region and the corner region of the positive electrode, and the second active material layer is located in the flat region of the positive electrode.
[0035] A positive electrode, separator, and negative electrode are arranged sequentially and wound together to form a wound-type battery cell. For wound-type cells (i.e., coiled cells), simply increasing the electrode thickness can lead to an increase in the CB value in the corner region, increasing the risk of lithium plating. By simultaneously setting a first active material layer and a second active material layer in a specific order in the flat region of the positive electrode, the flat region can be ensured to have better electron and ion transport kinetics and facilitate a more stable interface. By setting the first active material layer in the corner region of the positive electrode without setting the second active material layer, the fibrous conductive agent has better conductivity and lower impedance than particulate conductive agents, and also has stronger liquid absorption and retention capabilities. This can better reduce the risk of lithium plating caused by the increased CB value difference in the corner region and improve cycle performance.
[0036] In one embodiment, the second active material layer is made by gap coating, where the gap is the length of the corner area of the positive electrode sheet, and the core satisfies ab=π*(h1+2*h2), where a is the length of the gap on the outside of the core, b is the length of the gap on the inside of the core, h1 is the thickness of the positive current collector, and h2 is the thickness of the first active material layer. The units of a, b, h1 and h2 are the same, such as mm.
[0037] In some embodiments, the thickness h2 of the first active material layer and the thickness h3 of the second active material layer satisfy the following: h2:h3 = (4 to 10):1. For example, h2:h3 is a range formed by any two values of 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1 or above.
[0038] Controlling h2:h3 within the range of (4-10):1 ensures a more suitable thickness ratio between the first and second active material layers, facilitating better performance of both and resulting in improved kinetic performance and interfacial adhesion of the secondary battery. When the positive electrode, separator, and negative electrode are arranged and wound sequentially, with the positive electrode having a flat region and a corner region, and the first active material layer located in both the flat and corner regions of the positive electrode, and the second active material layer located in the flat region of the positive electrode, controlling h2:h3 within the range of (4-10):1 also ensures higher active material capacity in the corner region of the positive electrode, better electrolyte wetting, better cycle performance, and higher initial coulombic efficiency.
[0039] In some embodiments, the second active material layer h3 satisfies: 10μm≤h3≤30μm. For example, h3 is a range formed by any two of the following values: 10μm, 12μm, 14μm, 16μm, 18μm, 20μm, 22μm, 24μm, 26μm, 28μm, 30μm, or more.
[0040] When h3 is in the range of 10μm to 30μm, it is beneficial to form gaps in the corner regions of the positive and negative electrode sheets, which can alleviate the compression between adjacent layers caused by the expansion of the electrode sheets in the corner regions. At the same time, it can also better promote the wetting and liquid retention capacity of the electrolyte in the corner regions. Moreover, the interface stability between the first active material layer and the second active material layer in the flat region is better, which can ensure the construction of the double-layer electron and ion transport gradient in the flat region, resulting in better cycle performance and higher initial coulombic efficiency.
[0041] In some embodiments, the fibrous conductive agent has an average diameter of less than 150 nm and an average specific surface area of 10–250 m². 2 / g, with an average length of 5–30 μm. For example, the average diameter of the fibrous conductive agent is within the range of any two values of 150 nm, 140 nm, 130 nm, 120 nm, 110 nm, 100 nm, 90 nm, 80 nm, 70 nm, 60 nm, 50 nm, 40 nm, 30 nm, 20 nm, 10 nm, or more; the average specific surface area is 10 m². 2 / g、20m 2 / g、30m 2 / g、40m 2 / g, 50m 2 / g、60m 2 / g、70m 2 / g、80m 2 / g、90m 2 / g, 100m 2 / g, 120m 2 / g, 140m 2 / g, 160m 2 / g、180m 2 / g、200m 2 / g、220m 2 / g、250m 2 / g or a range formed by any two values; a range formed by any two values with an average length of 5μm, 7μm, 10μm, 12μm, 15μm, 17μm, 20μm, 22μm, 25μm, 27μm, 30μm or more.
[0042] When the average diameter of the fibrous conductive agent is below 150 nm and the average specific surface area is between 10 and 250 m², 2 Within the range of / g and with an average length in the range of 5–30 μm, fibrous conductive agents possess a high specific surface area, good conductivity, and a high aspect ratio, which is beneficial for improving the tensile strength of the positive electrode and better mitigating problems such as microcracks and peeling caused by volume changes during charging and discharging. In one embodiment, the average diameter of the fibrous conductive agent is 10–20 nm, and the average specific surface area is 150–250 m² / g.2 / g, to improve its conductivity and to give the fibrous conductive agent better dispersion in the first active material layer, thereby improving battery cycle performance and increasing initial coulombic efficiency.
[0043] The average diameter and length of the fibrous conductive agent can be measured using transmission electron microscopy (TEM) or scanning electron microscopy (SEM). Software can be used to statistically analyze the diameter or length of the obtained samples and calculate the mean. Typically, 100–200 fibrous conductive agents are measured.
[0044] The average specific surface area was calculated using the BET test method, which measures the amount of nitrogen adsorbed by the sample under different relative pressures. The specific surface area of the material was then calculated using the BET formula.
[0045] In some embodiments, the Dv50 of the particulate conductive agent is 30 to 50 nm. For example, the Dv50 of the particulate conductive agent is a range formed by any two of the following values: 30 nm, 32 nm, 34 nm, 36 nm, 38 nm, 40 nm, 42 nm, 44 nm, 46 nm, 48 nm, 50 nm, or more.
[0046] When the Dv50 of the particulate conductive agent is in the range of 30 to 50 nm, the specific surface area is larger, making it easier to fill the small gaps between the positive electrode active materials, resulting in better continuity of the formed conductive network, and thus better improving the conductivity of the positive electrode sheet.
[0047] The Dv50 of a particulate conductive agent refers to the particle size corresponding to a cumulative volume percentage of 50%, i.e., the median particle size in the volume distribution. Particle size distribution is determined through laser particle size analysis. The particle size distribution of the sample is characterized using laser light scattering technology, and the Dv50 particle size is calculated.
[0048] In some embodiments, the fibrous conductive agent includes at least one of carbon nanotubes (CNTs) and carbon fibers (VGCF). In one embodiment, the fibrous conductive agent includes carbon nanotubes. Compared to carbon fibers, carbon nanotubes have a higher aspect ratio, a larger specific surface area, and higher tensile strength, which is beneficial for reducing impedance and improving mechanical properties; at the same time, they are more conducive to the construction of electron and ion transport gradient networks, promoting the penetration of electrolyte into the cathode material and improving kinetic performance.
[0049] In one embodiment, the carbon nanotubes have an average diameter of less than 20 nm and an average specific surface area of 150–250 m². 2 / g, with an average length of 5–30 μm. The average diameter of carbon nanotubes can be selected from any two ranges of 20 nm, 18 nm, 16 nm, 14 nm, 12 nm, 10 nm, or more; the average specific surface area is 150 m². 2 / g, 160m 2 / g、170m 2 / g、180m 2 / g、190m 2 / g、200m 2 / g、210m 2 / g、220m 2 / g、230m 2 / g、240m 2 / g、250m 2 / g or a range formed by any two values; a range formed by any two values with an average length of 5μm, 7μm, 10μm, 12μm, 15μm, 17μm, 20μm, 22μm, 25μm, 27μm, 30μm or more.
[0050] The average diameter of carbon nanotubes is controlled to be below 20 nm, and the average specific surface area is 150–250 m². 2 / g, especially controlling the average diameter of carbon nanotubes to 10–20 nm and the average specific surface area to 150–250 m² / g. 2 At / g, the conductivity is better while ensuring good dispersion of carbon nanotubes.
[0051] In one embodiment, the carbon fibers have an average diameter of 150 nm and an average specific surface area of 13 m². 2 / g, with an average length of 10–20 μm. Although carbon fiber has a lower specific surface area and aspect ratio than carbon nanotubes, its production is mature and its dispersibility is slightly better. When the first active material layer contains carbon nanotubes, the mass fraction of carbon fiber in the first active material layer can be selected as 1% to give the layer better conductivity.
[0052] In some embodiments, the particulate conductive agent includes at least one of Ketjen Black, acetylene black, and Super-P (i.e., SP).
[0053] In some embodiments, the first active material layer further comprises a positive electrode active material. The positive electrode active material in the first active material layer may be any commonly used positive electrode active material in the art. For example, the positive electrode active material in the first active material layer includes at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, transition metal phosphate, and lithium iron phosphate.
[0054] In some embodiments, the first active material layer further comprises a binder. The binder in the first active material layer may be any binder commonly used in the art. Exemplarily, the binder in the first active material layer includes at least one of polyvinylidene fluoride (PVDF) and carboxylated polyvinylidene fluoride (C-PVDF). The mass fraction of the binder in the first active material layer may be selected from 1% to 2%, such as 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, or any range formed by any two of the above values.
[0055] In some embodiments, the second active material layer further comprises a positive electrode active material. The positive electrode active material in the second active material layer can be any commonly used positive electrode active material in the art. For example, the positive electrode active material in the second active material layer includes at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, transition metal phosphates, and lithium iron phosphate.
[0056] In some embodiments, the second active material layer further comprises a binder. The binder in the second active material layer may be any binder commonly used in the art. Exemplarily, the binder in the second active material layer includes at least one of polyvinylidene fluoride (PVDF) and carboxylated polyvinylidene fluoride (C-PVDF). The mass fraction of the binder in the second active material layer may be selected from 1% to 2%, such as 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, or any range formed by any two of the above values.
[0057] The mass fraction of the positive electrode active material in the positive electrode active material layer can be selected as 96% to 98%, such as 96%, 96.2%, 96.4%, 96.6%, 96.8%, 97%, 97.2%, 97.4%, 97.6%, 97.8%, 98%, or any range formed by any two values above.
[0058] In some embodiments, the positive current collector may be any metal foil or composite current collector commonly used in the art, such as aluminum foil or composite aluminum foil.
[0059] In some embodiments, a conductive undercoat layer is further provided between the positive current collector and the positive active material layer to enhance the interfacial conductivity between the positive current collector and the positive active material layer and reduce the DC internal resistance. However, the conductive undercoat layer is not a necessary structure for the positive electrode sheet of this application.
[0060] In some embodiments, the compaction density of the positive electrode sheet is 3.4–4.3 g / cm³. 3 For example, the compaction density of the positive electrode sheet is 3.4 g / cm³.3 3.5g / cm 3 3.6g / cm 3 3.7g / cm 3 3.8g / cm 3 3.9g / cm 3 4g / cm 3 4.1g / cm 3 4.2g / cm 3 4.3g / cm 3 Or the range formed by any two of the above values.
[0061] In some embodiments, the method for preparing the positive electrode sheet includes the following steps:
[0062] The raw materials for preparing the first active material layer and the raw materials for preparing the second active material layer are mixed and dispersed to obtain the first active material layer slurry and the second active material layer slurry.
[0063] According to the structural design of the positive electrode sheet, the first active material layer slurry is coated on the positive current collector, dried, then the second active material layer slurry is coated, dried, and then rolled to obtain the positive electrode sheet.
[0064] In one embodiment, the first active material layer slurry has a solid content of 60 wt.% to 70 wt.%, such as the range formed by any two values of 60 wt.%, 62 wt.%, 64 wt.%, 66 wt.%, 68 wt.%, 70 wt.%, or above.
[0065] In one embodiment, the solvent for the first active material layer slurry includes at least one of N-methylpyridinone (NMP) and polyvinylidene fluoride (PVDF).
[0066] In one embodiment, the second active material layer slurry has a solid content of 60 wt.% to 70 wt.%, such as the range formed by any two values of 60 wt.%, 62 wt.%, 64 wt.%, 66 wt.%, 68 wt.%, 70 wt.%, or more.
[0067] In one embodiment, the solvent for the second active material layer slurry includes at least one of N-methylpyridinone (NMP) and polyvinylidene fluoride (PVDF).
[0068] The diaphragm can be any commonly used diaphragm material in the field.
[0069] The aforementioned negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. The negative electrode current collector can be any commonly used negative electrode current collector in the art; the negative electrode active material layer can be any commonly used negative electrode active material layer in the art.
[0070] The electrolyte can be any commonly used electrolyte in this field.
[0071] According to a second aspect of this application, an electrical device is provided, including the aforementioned secondary battery. The aforementioned secondary battery can be used as a power supply for the electrical device. Exemplarily, the electrical device includes at least one of an electric vehicle battery and a mobile phone battery.
[0072] The present application will be further described below with reference to specific embodiments.
[0073] Example 1
[0074] This embodiment provides a secondary battery, including a positive electrode 10, a separator 20, a negative electrode 30, and an electrolyte. The positive electrode 10, the separator 20, and the negative electrode 30 are arranged sequentially and wound together to form a core. A partial structural schematic diagram of the core is shown below. Figure 1 As shown;
[0075] The positive electrode 10 includes a positive current collector 101 and positive active material layers disposed on both sides of the positive current collector 101. The compaction density of the positive electrode 10 is 3.55 g / cm³. 3 ;
[0076] The positive electrode current collector 101 is an aluminum foil, and the thickness h1 of the positive electrode current collector 101 is 10 μm;
[0077] Along the direction away from the positive electrode current collector 101, the positive electrode active material layer sequentially includes a first active material layer 102 and a second active material layer 103;
[0078] The thickness h2 of the first active material layer 102 and the thickness h3 of the second active material layer 103 are shown in Table 1;
[0079] The core meets the requirements as shown in Table 1, where a is the outer gap length of the core (i.e., the length of the outer arc of the positive electrode corner area), and b is the inner gap length of the core (i.e., the length of the inner arc of the positive electrode corner area). The units of a and b are μm.
[0080] The negative electrode 30 is a graphite negative electrode, comprising a negative electrode current collector 301 and a negative electrode active material layer 302 disposed on both sides of the negative electrode current collector 301. The negative electrode current collector 301 is a copper foil with a thickness of 8 μm. The negative electrode active material layer 302 contains the following components by mass fraction: 95% artificial graphite, 1.5% conductive agent SP, 2% thickener CMC (sodium carboxymethyl cellulose), and 2% binder SBR (styrene-butadiene rubber). The compacted density of the negative electrode 30 is 1.6 g / cm³. 3 ;
[0081] Membrane 20 uses a PP-PE-PP composite membrane, Celgard 2325.
[0082] The electrolyte is a mixed solvent of EC / FEC / EMC / DMC (weight ratio 3:1:2:4) with 1.2 mol / L LiPF6 added.
[0083] The preparation method of the secondary battery in this embodiment includes the following steps:
[0084] The positive electrode active material, binder, and conductive agent were mixed with N-methylpyridinone (NMP) according to the formulations in Table 1, and dispersed by stirring to obtain a first active material layer 102 slurry with a solid content of 65 wt.% and a second active material layer 103 slurry with a solid content of 65 wt.%, wherein the positive electrode active material was NCA (LiNi). 0.8 Co 0.15 Al 0.05 O2), and the binder is polyvinylidene fluoride (PVDF);
[0085] The first active material layer 102 slurry is coated on both sides of the positive electrode current collector by roller coating, and dried at 85°C. Then, the second active material layer 103 slurry is coated according to the preset gap lengths a and b, and dried at 85°C and compacted to obtain the positive electrode sheet 10.
[0086] The positive electrode 10, separator 20 and negative electrode 30 are wound together to form a bare cell, placed in a soft-pack casing, injected with electrolyte, and then sealed and formed to obtain a lithium-ion secondary battery.
[0087] Table 1
[0088]
[0089] Table 2
[0090]
[0091] Examples 2-4
[0092] These embodiments all provide a secondary battery, and the differences between these secondary batteries and Embodiment 1 are as follows: the content of each component in the first active material layer 102 is different;
[0093] Furthermore, the preparation methods of these secondary batteries differ from those in Example 1 as follows: the proportions of positive electrode active material, binder, and conductive agent in the slurry of the first active material layer 102 are different, as detailed in Table 1.
[0094] Examples 5-8
[0095] These embodiments all provide a secondary battery. The differences between these secondary batteries and Embodiment 1 are as follows: the thickness h2 of the first active material layer 102 and the thickness h3 of the second active material layer 103 are different, as detailed in Table 1.
[0096] Furthermore, the preparation methods of these secondary batteries differ from those in Example 1 as follows: the coating amounts of the first active material layer 102 slurry and the second active material layer 103 slurry are adjusted accordingly.
[0097] Examples 9-12
[0098] These embodiments all provide a secondary battery, and the differences between these secondary batteries and Embodiment 1 are as follows: the thickness h3 of the second active material layer 103 is different, as detailed in Table 1;
[0099] Furthermore, the preparation methods of these secondary batteries differ from those in Example 1 as follows: the coating amount of the second active material layer 103 slurry is adjusted accordingly.
[0100] Example 13
[0101] This embodiment provides a secondary battery, which differs from Embodiment 1 as follows: a and b are different, as detailed in Table 1;
[0102] Furthermore, the preparation method of the secondary battery in this embodiment differs from that in Embodiment 1 as follows: the coating method of the second active material layer 103 slurry is different; in this embodiment, it is a continuous coating.
[0103] Examples 14-19
[0104] These embodiments all provide a secondary battery, which differs from Embodiment 1 as follows: the average diameter, average specific surface area, average length and / or type of the fibrous conductive agent are different, as detailed in Tables 1 and 2;
[0105] Furthermore, the preparation methods of these secondary batteries differ from those in Example 1 as follows: the fibrous conductive agent raw materials are adjusted accordingly.
[0106] Examples 20-21
[0107] These embodiments all provide a secondary battery, and the differences between these secondary batteries and Embodiment 1 are as follows:
[0108] The content of each component in the first active substance layer 102 is different.
[0109] The content of each component in the second active substance layer 103 is different.
[0110] The types, Dv50, and average specific surface areas of particulate conductive agents vary; see Tables 1 and 2 for details.
[0111] The contents of conductive agent and positive electrode active material in the positive electrode active material layer are different, as detailed in Tables 1 and 2;
[0112] The differences between the preparation methods of these secondary batteries and those in Example 1 are as follows:
[0113] The proportions of positive electrode active material, binder and conductive agent in the first active material layer 102 slurry are different, as detailed in Tables 1 and 2;
[0114] The proportions of positive electrode active material, binder and conductive agent in the second active material layer slurry 103 are different, as detailed in Tables 1 and 2;
[0115] The raw materials for the granular conductive agent used were adjusted accordingly.
[0116] Comparative Example 1
[0117] This comparative example provides a secondary battery, which differs from Example 1 as follows:
[0118] The conductive agent in the first active material layer 102 is different. In this comparative example, the conductive agent in the first active material layer 102 is the particulate conductive agent in Example 1.
[0119] Furthermore, the preparation method of this comparative secondary battery differs from that of Example 1 as follows: the conductive agent used in the slurry of the first active material layer 102 is adjusted accordingly.
[0120] Comparative Example 2
[0121] This comparative example provides a secondary battery, which differs from Example 1 as follows:
[0122] The conductive agent in the second active material layer 103 is different. In this comparative example, the conductive agent in the second active material layer 103 is the fibrous conductive agent in Example 1.
[0123] Furthermore, the preparation method of this comparative secondary battery differs from that of Example 1 as follows: the conductive agent used in the slurry of the second active material layer 103 is adjusted accordingly.
[0124] Comparative Example 3
[0125] This comparative example provides a secondary battery, which differs from Example 1 as follows:
[0126] The conductive agents in the first active material layer 102 and the second active material layer 103 are different. In this comparative example, the conductive agents in the first active material layer 102 and the second active material layer 103 are the same, which are a mixture of fibrous conductive agent and granular conductive agent. The weight ratio of fibrous conductive agent to granular conductive agent is 80:20. The fibrous conductive agent and granular conductive agent are the same as those in Example 1.
[0127] Furthermore, the preparation method of this comparative secondary battery differs from that of Example 1 as follows: the conductive agents used in the first active material layer 102 slurry and the second active material layer 103 slurry are adjusted accordingly.
[0128] Comparative Example 4
[0129] This comparative example provides a secondary battery, which differs from Example 1 as follows:
[0130] The conductive agents in the first active material layer 102 and the second active material layer 103 are different. In this comparative example, the conductive agent in the first active material layer 102 is a particulate conductive agent, and the conductive agent in the second active material layer 103 is a fibrous conductive agent. The fibrous conductive agent and the particulate conductive agent are the same as those in Example 1.
[0131] Furthermore, the preparation method of this comparative secondary battery differs from that of Example 1 as follows: the conductive agents used in the first active material layer 102 slurry and the second active material layer 103 slurry are adjusted accordingly.
[0132] The following performance tests were performed on the above-mentioned lithium-ion secondary batteries:
[0133] Initial coulombic efficiency: At 25°C, the lithium-ion secondary battery was charged at a constant current of 0.2C to 4.3V, then charged at a constant voltage of 4.3V until the current was less than 0.02C. After standing for 5 minutes, it was discharged at 0.2C to 2.8V. The initial coulombic efficiency of the battery was calculated after three cycles.
[0134] Impedance test: At 25℃, test the battery at 50% SOC, 10mHz~10 5 Calculate the ohmic impedance R0 from the AC impedance spectrum (EIS) in the Hz frequency range;
[0135] Cyclic test: At 45℃, the battery is charged at a constant current of 1C to 4.3V, then charged at a constant voltage of 4.3V until the current is less than 0.02C, left to stand for 5 minutes, and then discharged at 1C to 2.8V for cycling.
[0136] The test results are shown in Table 3.
[0137] Table 3
[0138]
[0139] As can be seen from the above data, the secondary batteries of each embodiment have high initial coulombic efficiency, low impedance and good cycle performance, such as initial coulombic efficiency above 81.9%, R0 below 0.392Ω, and capacity retention rate above 90% after 500 cycles at 45℃. Their overall performance is better than that of the comparative embodiments.
[0140] A comparison of Example 1 with Comparative Examples 1-4 shows that when the conductive agent in the first active material layer 102 is a fibrous conductive agent and the conductive agent in the second active material layer 103 is a particulate conductive agent, a lower impedance is achieved while significantly improving the initial coulombic efficiency and cycle performance. In Comparative Example 1, both the first active material layer 102 and the second active material layer 103 use particulate conductive agents, resulting in poor initial coulombic efficiency, impedance, and cycle performance. This is because the electrolyte has weak penetration in the positive electrode active material layer, leading to incomplete wetting. This results in numerous side reactions during cycling, especially in the initial cycling process. Furthermore, the adhesion between the first active material layer 102 and the positive electrode current collector is weak, and the interface stability between the first active material layer 102 and the second active material layer 103 is unstable, making the positive electrode active material layer prone to micro-deformation during charging and discharging. Problems such as cracks and peeling were observed, and the polarization of the positive electrode active material layer was also relatively large. Moreover, the conductivity of the particulate conductive agent was worse than that of the fibrous conductive agent. In Comparative Example 2, the conductive agents in the first active material layer 102 and the second active material layer 103 were both fibrous conductive agents, resulting in a deviation in the initial coulombic efficiency. This is because the uniformly distributed conductive agent cannot form a gradient structure for electron and ion conduction. During the charging and discharging process, there is an uneven distribution of lithium ions and electrons, which will cause more lithium ions to undergo side reactions at the interface to form an SEI film. In Comparative Example 3, the conductive agents in the first active material layer 102 and the second active material layer 103 were both a mixture of fibrous and particulate conductive agents, and the initial coulombic efficiency was still poor. In Comparative Example 4, the conductive agent in the first active material layer 102 was a particulate conductive agent, and the conductive agent in the second active material layer 103 was a fibrous conductive agent, resulting in a deviation in the initial coulombic efficiency.
[0141] Comparing Examples 1 to 4, it can be seen that when the mass fraction of the fibrous conductive agent in the first active material layer 102 is in the range of 0.5% to 1%, the conductivity of the conductive agent is higher and the viscosity and dispersibility of the slurry are better. The fibrous conductive agent is more evenly distributed in the first active material layer, the cycle performance is better, and the initial coulombic efficiency is higher.
[0142] Comparing Examples 1 and 5-8, it can be seen that when h2:h3 is in the range of (4-10):1, while ensuring high conductivity, the electrolyte wetting in the corner area is better, the cycle performance is better, and the initial coulombic efficiency is higher.
[0143] Comparing Examples 1 and 9-12, it can be seen that when h3 is in the range of 10μm to 30μm, the interface stability between the first active material layer and the second active material layer is better, which can ensure the construction of the flat region double-layer electron and ion transport gradient, resulting in better cycling performance and higher initial coulombic efficiency.
[0144] Comparing Example 1 and Example 13, it can be seen that when the first active material layer 102 is located in the flat area and corner area of the positive electrode sheet, and the second active material layer 103 is located in the flat area of the positive electrode sheet, that is, when the slurry of the second active material layer 103 is applied with gap coating, the cycle performance is significantly better, thus making the overall performance of the battery better.
[0145] Comparing Examples 1 and 14-17, it can be seen that when the average diameter of the fibrous conductive agent is in the range of 10-20 nm, the average specific surface area is in the range of 150-250 m². 2 Within the range of / g, the conductive agent has higher conductivity and better slurry viscosity and dispersibility. The fibrous conductive agent is more evenly distributed in the first active material layer, has better cycle performance, and has higher initial coulombic efficiency.
[0146] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended 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, characterized in that, It includes a positive electrode, a separator, a negative electrode, and an electrolyte. The positive electrode includes a positive current collector and a layer of positive active material disposed on one or both sides of the positive current collector. Along the direction away from the positive electrode current collector, the positive electrode active material layer sequentially includes a first active material layer and a second active material layer. Both the first active material layer and the second active material layer contain a conductive agent. The conductive agent in the first active material layer is a fibrous conductive agent, and the conductive agent in the second active material layer is a particulate conductive agent. The positive electrode, the separator, and the negative electrode are arranged in sequence and wound together. The positive electrode has a flat region and a corner region. The first active material layer is located in the flat region and the corner region of the positive electrode, and the second active material layer is located in the flat region of the positive electrode.
2. The secondary battery as described in claim 1, characterized in that, The mass fraction of the fibrous conductive agent in the first active material layer is 0.5%~1%; and / or The mass fraction of particulate conductive agent in the second active material layer is ≥1%.
3. The secondary battery as described in claim 1, characterized in that, The mass fraction of the particulate conductive agent in the second active material layer is 1% to 6%.
4. The secondary battery as described in claim 1, characterized in that, The mass fraction of the conductive agent in the positive electrode active material layer is 0.5% to 3%.
5. The secondary battery as described in claim 1, characterized in that, The thickness h2 of the first active material layer and the thickness h3 of the second active material layer satisfy: h2:h3 = (4~10):
1.
6. The secondary battery as described in any one of claims 1 to 5, characterized in that, The second active material layer h3 satisfies: 10μm≤h3≤30μm.
7. The secondary battery as described in any one of claims 1 to 5, characterized in that, The fibrous conductive agent has an average diameter of less than 150 nm and an average specific surface area of 10~250 m². 2 / g, with an average length of 5~30μm; and / or The particulate conductive agent has a Dv50 of 30~50nm.
8. The secondary battery as described in claim 7, characterized in that, The fibrous conductive agent has an average diameter of 10-20 nm and an average specific surface area of 150-250 m². 2 / g.
9. The secondary battery as described in any one of claims 1 to 5, characterized in that, The fibrous conductive agent includes at least one of carbon nanotubes and carbon fibers; and / or The particulate conductive agent includes at least one of Ketjen Black, acetylene black, and Super-P.
10. An electrical appliance, characterized in that, The electrical equipment includes a secondary battery as described in any one of claims 1 to 9.