CN118299511A - A cathode sheet and secondary battery - Google Patents

A cathode sheet and secondary battery Download PDF

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Publication number
CN118299511A
CN118299511A CN202410219491.2A CN202410219491A CN118299511A CN 118299511 A CN118299511 A CN 118299511A CN 202410219491 A CN202410219491 A CN 202410219491A CN 118299511 A CN118299511 A CN 118299511A
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active coating
active
coating layer
coating
current collector
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蒋世权
高云雷
杨洁
曾力
于子龙
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Huizhou Liwinon Energy Technology Co Ltd
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Huizhou Liwinon Energy Technology Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Manufacturing & Machinery (AREA)
  • Battery Electrode And Active Subsutance (AREA)
  • Secondary Cells (AREA)

Abstract

本发明公开了一种阴极片及二次电池，该阴极片包括集流体和设置在所述集流体至少一侧表面的活性材料层，所述活性材料层包括第一活性涂层和第二活性涂层，所述第一活性涂层和第二活性涂层并列设置在所述集流体的同一侧表面，且所述第二活性涂层设在集流体沿Y轴方向边缘两侧；所述第一活性涂层与所述第二活性涂层满足关系：2≤D1(L1+H)/D2(L2+h)＜30；相比于现有技术，本发明从源头上减少极片析锂的发生，避免内阻增加影响电池极化，能够保持传输通道畅通。第一涂层与第二涂层的厚度差以及晶粒度的大小都会影响锂离子的的传输效率，在锂离子电池循环的过程中，从涂层脱出的锂离子速度较慢，降低了阳极片表面的锂离子堆积，避免析锂的发生。

The present invention discloses a cathode sheet and a secondary battery, the cathode sheet comprises a current collector and an active material layer arranged on at least one side surface of the current collector, the active material layer comprises a first active coating and a second active coating, the first active coating and the second active coating are arranged in parallel on the same side surface of the current collector, and the second active coating is arranged on both sides of the edge of the current collector along the Y-axis direction; the first active coating and the second active coating satisfy the relationship: 2≤D 1 (L 1 +H)/D 2 (L 2 +h)＜30; compared with the prior art, the present invention reduces the occurrence of lithium plating of the pole sheet from the source, avoids the increase of internal resistance affecting the polarization of the battery, and can keep the transmission channel unobstructed. The thickness difference between the first coating and the second coating and the size of the grain size will affect the transmission efficiency of lithium ions. During the cycle of the lithium-ion battery, the lithium ions released from the coating are slow, which reduces the accumulation of lithium ions on the surface of the anode sheet and avoids the occurrence of lithium plating.

Description

Cathode sheet and secondary battery
Technical Field
The invention relates to the field of secondary batteries, in particular to a cathode sheet and a secondary battery
Background
The lithium ion battery is used as a novel secondary battery, has the advantages of high working voltage, high energy density, long service life, wide working temperature range, environmental friendliness and the like, and becomes a main energy storage device of mainstream electronic products. With the increasing demands of the market for battery performance, lithium ion batteries with excellent performance are required to have higher energy density and also have excellent long cycle life.
In the design and manufacturing process of lithium ion batteries, for safety and to prevent lithium precipitation from the negative electrode, the area of the negative electrode sheet is larger than that of the positive electrode sheet, i.e., the edge of the negative electrode sheet exceeds the size of the positive electrode sheet by 1-3 mm in the length or width direction, so-called Overhang region is formed. However, there are several reasons for causing edge precipitation: ① Since the battery has overhang areas, excessive lithium ions are caused at the edge of the positive electrode, so that the negative electrode Overhang area cannot intercalate excessive lithium ions from the positive electrode during charging, and lithium precipitation occurs. ② The Overhang area pole piece of the battery pole piece is uneven, the contact of the positive pole piece and the negative pole piece is poor, the transmission path of lithium ions is influenced, lithium is easy to separate out from the edge of the battery core, and the service life of the battery is shortened. ③ The surface density mismatch caused by the thick edge effect at the edge of the positive and negative electrode plate coating process, such as overlarge surface density at the edge of the positive electrode or overlarge surface density at the edge of the negative electrode, can cause lithium precipitation.
In order to reduce negative effects caused by edge lithium deposition, a method is currently available to paste a glue on the edge surface of the active material layer to inhibit lithium precipitation, but after multiple charge and discharge cycles, the phenomenon of lithium precipitation still exists at the corresponding position of the glue, so that the safety performance of the battery is affected.
In view of the foregoing, it is necessary to provide a solution to the above-mentioned problems.
Disclosure of Invention
One of the objects of the present invention is: aiming at the defects of the prior art, a cathode sheet is provided to solve the problem of lithium precipitation at the edges of the two sides of the head and the tail of the current battery.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
The cathode sheet comprises a current collector and an active material layer arranged on at least one side surface of the current collector, wherein the active material layer comprises a first active coating and a second active coating, the first active coating and the second active coating are arranged on the same side surface of the current collector in parallel, and the second active coating is arranged on two sides of the edge of the current collector along the Y-axis direction; the first active coating and the second active coating satisfy the relation: d 1(L1+H)/D2(L2 +h) is less than or equal to 2 and less than 30;
wherein H is the thickness of the first active coating, H is the thickness of the second active coating, and the unit is mu m;
L 1 is the grain size of the active material of the first active coating, L 2 is the grain size of the active material of the second active coating in nm;
d 1 is the lithium ion diffusion coefficient of the first active coating, and D 2 is the lithium ion diffusion coefficient of the second active coating, cm/s.
Preferably, the thicknesses of the first and second active coatings satisfy the relationship: h is more than or equal to 0.97 and less than or equal to H.
Preferably, the thickness of the second active coating layer and the grain size of the active material of the second active coating layer satisfy the relationship: h/L 2 is more than or equal to 0.35 and less than or equal to 1.8.
Preferably, the thickness H of the first active coating is 25-100 μm.
Preferably, the grain size of the first active coating active material is smaller than the grain size of the second active coating active material, and the relationship is satisfied: 1.2L 1≤L2≤4L1.
Preferably, the grain sizes of the active materials of the first active coating layer and the second active coating layer are respectively 10-100 nm.
Preferably, the lithium ion diffusion coefficients of the first active coating and the second active coating are respectively 1×10 -10～1×10-7 cm/s, and the relation is satisfied: 3D 2≤D1≤50.2D2.
Preferably, the coating width of one side of the second active coating layer is 2-5 mm.
Preferably, the current collector material is at least one selected from metallic aluminum, metallic nickel, stainless steel, nickel-titanium alloy, and carbon fiber.
Preferably, the thickness of the current collector is 6 to 20 μm.
The second object of the invention is to provide a secondary battery, which comprises a cathode plate, an anode plate, a diaphragm and electrolyte, wherein the cathode plate is the cathode plate in any section.
Compared with the prior art, the invention has the beneficial effects that: according to the cathode plate provided by the invention, the thickness of the active coating is limited, the grain size of the active material and the diffusion coefficient of lithium ions meet the relation 2- 1(L1+H)/D2(L2 +h & lt 30, the occurrence of lithium precipitation of the cathode plate is reduced from the source, the bonding between the cathode plate and the diaphragm can be ensured to be good, the influence of the increase of internal resistance on the polarization of a battery is avoided, and the smoothness of a transmission channel can be kept. The thickness difference between the first coating and the second coating and the size of the grain size can influence the transmission efficiency of lithium ions, and in the process of lithium ion battery circulation, the grain size of the second active coating is larger than that of the first active coating, so that the lithium ion speed of the coating is slower, the lithium ion accumulation on the surface of the anode sheet is reduced, and the occurrence of lithium precipitation is avoided.
Drawings
Fig. 1 is a plan view of a cathode sheet according to example 1 of the present invention.
Fig. 2 is a schematic cross-sectional structure of the cathode sheet according to embodiment 1 of the present invention.
In the figure, 11-a first active coating; 12-a second active coating; 13-current collector.
Detailed Description
In order to make the technical scheme and advantages of the present invention more apparent, the present invention and its advantageous effects will be described in further detail below with reference to the detailed description and the accompanying drawings, but the embodiments of the present invention are not limited thereto.
The terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature. In the description of the present invention, the meaning of "a plurality" is two or more, unless explicitly defined otherwise.
1. Cathode plate
The first aspect of the present invention is directed to a cathode sheet comprising a current collector and an active material layer disposed on at least one side surface of the current collector, the active material layer comprising a first active coating layer and a second active coating layer, the first active coating layer and the second active coating layer being disposed in parallel on the same side surface of the current collector, and the second active coating layer being disposed on both sides of an edge of the current collector in a Y-axis direction; the first active coating and the second active coating satisfy the relation: d 1(L1+H)/D2(L2 +h) is less than or equal to 2 and less than 30;
wherein H is the thickness of the first active coating, H is the thickness of the second active coating, and the unit is mu m;
L 1 is the grain size of the active material of the first active coating, L 2 is the grain size of the active material of the second active coating in nm; d 1 is the lithium ion diffusion coefficient of the first active coating, and D 2 is the lithium ion diffusion coefficient of the second active coating, cm/s.
The inventors found that controlling the thickness, grain size, and lithium ion diffusion coefficient of the first active coating and the second active coating in the above relation can reduce the negative effects caused by lithium metal deposition at the edge of the lithium ion battery pole piece. The lithium is easy to be separated from the head and tail parts (refer to two sides of the edge of the electrode plate), and the cathode active material is arranged on two sides of the cathode plate close to the edge and adopts a second coating with large grain size; the cathode active material of the second coating has large grain size, and lithium ions released from the second coating have slower speed in the process of cycling the lithium ion battery, so that the lithium ion accumulation on the surfaces of the two sides of the edge of the anode sheet is reduced, and the occurrence of lithium precipitation is avoided.
Wherein the thicknesses of the first and second active coatings satisfy the relationship: h is more than or equal to 0.97 and less than or equal to H. The thickness of the second coating is as close as possible to that of the first coating, if the second coating is thinner, the contact between the cathode and anode plates and the diaphragm is insufficient, and lithium ions are easy to separate out; if the second coating is thicker, more lithium ions are released, and the anode cannot accommodate the lithium ions, which also causes lithium precipitation.
Wherein the thickness of the second active coating layer and the grain size of the active material of the second active coating layer satisfy the relationship: h/L 2 is more than or equal to 0.35 and less than or equal to 1.8. Meanwhile, on the premise that the above relation can be met, the thickness and the grain size in the second active coating can meet the above relation, so that the material has certain stability.
In some embodiments, the first active coating thickness H is 25 to 100 μm. Specifically, the thickness of the first active coating layer may be 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 85 μm, 90 μm, 95 μm, 100 μm.
Wherein, the grain size of the first active coating active material is smaller than that of the second active coating active material, and the relation is satisfied: 1.2L 1≤L2≤4L1. The lithium is easy to be separated from the head and tail parts (refer to two sides of the edge of the electrode plate), and the cathode active material is arranged on two sides of the cathode plate close to the edge and adopts a second coating with large grain size; the cathode active material of the second coating has large grain size, and lithium ions which are removed from the second coating have slower speed in the process of cycling the lithium ion battery, so that the lithium ion accumulation on the surfaces of the two sides of the edge of the anode sheet is reduced, and the occurrence of lithium precipitation is avoided; meanwhile, the grain sizes of the first coating and the second coating are not suitable to be too large, and the larger the grain size is, the slower the lithium ions are extracted, so that the battery capacity is lower, and the energy density is affected.
In some embodiments, the active materials of the first and second active coatings have a grain size of 10 to 100nm, respectively.
Wherein, the lithium ion diffusion coefficients of the first active coating and the second active coating are respectively 1X 10 -10～1×10-7 cm/s, and the relation is satisfied: 3D 2≤D1≤50.2D2. Two active material layers with different lithium ion diffusion rates are arranged on at least one side surface of the positive electrode current collector, and the second active coating position row and the two sides of the first active coating are arranged on the same side; the second coating has a lithium ion diffusion rate that is less than the lithium ion diffusion rate of the first coating. The second coating has slow lithium ion diffusion rate, and can reduce the accumulation of lithium ions in the edge area of the anode sheet in the process of battery core circulation, thereby effectively avoiding the occurrence of lithium precipitation.
In some embodiments, the single side of the second active coating layer has a coating width of 2 to 5mm, specifically 2mm, 3mm, 4mm, 5mm, which may include but is not limited to the values exemplified above, preferably 3mm.
In some embodiments, the current collector material is selected from at least one of metallic aluminum, metallic nickel, stainless steel, nickel titanium alloy, carbon fiber.
Wherein the cathode active material is selected from one or more of lithium cobaltate, ternary material, lithium-rich material or other positive electrode materials.
In some embodiments, the cathode active material is a lithium cobaltate material, the grain size of which is measured and calculated by an X-ray diffractometer (XRD), and the sample is tested by using the XRD, the scanning range is 5-90 °, the scanning speed is 5 °/min, and the characteristic peak (003) corresponding crystal plane appears in the diffraction angle range of 15-25 °. The grain size is a crystal grain size describing a direction perpendicular to the (hkl) plane, and the smaller the grain size, the more crystal planes of the material, and the faster the lithium ion diffusion rate. The calculation formula of the grain size is as follows:
L＝Kλ/βcosθ
where K is the Scherrer constant, which takes on a value of 0.89, β is the half-height width of the diffraction peak (hkl), θ is the diffraction angle, and λ is the angle of incidence.
2. Secondary battery
A second aspect of the present invention is directed to a secondary battery including a cathode tab, an anode tab, and a separator interposed between the cathode tab and the anode tab, wherein the cathode tab is the above-described cathode tab.
The anode sheet comprises an anode current collector and an anode active material layer coated on at least one surface of the anode current collector, wherein the anode active material layer can be one or more of graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microsphere, silicon-based material, tin-based material, lithium titanate or other metals capable of forming alloy with lithium. Wherein, the graphite can be selected from one or more of artificial graphite, natural graphite and modified graphite; the silicon-based material can be one or more selected from simple substance silicon, silicon oxygen compound, silicon carbon compound and silicon alloy; the tin-based material can be selected from one or more of elemental tin, tin oxide and tin alloy. While the anode current collector is typically a structure or part that collects current, the anode current collector may be of various materials suitable in the art for use as a lithium ion battery anode current collector, for example, the anode current collector may be a material including, but not limited to, metal foil, etc., and more particularly may be a material including, but not limited to, copper foil, etc.
The separator may be a variety of materials suitable for lithium ion battery separators in the art, and may be, for example, a combination of one or more of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, natural fibers, and the like.
The secondary battery further includes an electrolyte including an organic solvent, an electrolyte lithium salt, and an additive. Wherein, the electrolyte lithium salt can be LiPF 6 and/or LiBOB adopted in the high-temperature electrolyte; at least one kind of LiBF 4、LiBOB、LiPF6 used in the low-temperature electrolyte may be used; at least one of LiBF 4、LiBOB、LiPF6 and LiTFSI adopted in the overcharge-preventing electrolyte can be adopted; but may also be at least one of LiClO 4、LiAsF6、LiCF3SO3、LiN(CF3SO2)2. And the organic solvent may be a cyclic carbonate, including PC, EC; chain carbonates, including DFC, DMC, or EMC; carboxylic esters, including MF, MA, EA, MP, and the like, are also possible. And the additive includes, but is not limited to, at least one of a film forming additive, a conductive additive, a flame retardant additive, an overcharge preventing additive, an additive for controlling the contents of H 2 O and HF in the electrolyte, an additive for improving low temperature performance, and a multifunctional additive.
In order to make the technical scheme and advantages of the present invention more apparent, the present invention and its advantageous effects will be described in further detail below with reference to the detailed description and the accompanying drawings, but the embodiments of the present invention are not limited thereto.
Example 1
As shown in fig. 1 to 2, the cathode sheet provided in this embodiment includes a current collector 13 and active material layers disposed on two side surfaces of the current collector 13, the active material layers include a first active coating 11 and a second active coating 12, the first active coating 11 and the second active coating 12 are disposed in parallel on the same side surface of the current collector 13, and the second active coating 12 is disposed on two sides of the first active coating 11; the first reactive coating 11 and the second reactive coating 12 satisfy the relationship: d 1(L1+H)/D2(L2 +h) is less than or equal to 2 and less than 30; wherein H is the thickness of the first active coating, H is the thickness of the second active coating, and the unit is mu m; l 1 is the grain size of the active material of the first active coating, L 2 is the grain size of the active material of the second active coating in nm; d 1 is the lithium ion diffusion coefficient of the first active coating, and D 2 is the lithium ion diffusion coefficient of the second active coating, cm/s.
The preparation method of the cathode plate comprises the following steps:
Fully dispersing a cathode active substance LiCoO 2, a conductive agent acetylene black, a conductive carbon nano tube and a binder polyvinylidene fluoride (PVDF) in a weight ratio of 97.6:0.5:0.6:1.3 in an N-methyl pyrrolidone solvent system to obtain cathode active material layer slurry, uniformly coating the active material layer slurry on a cathode current collector to form a first active coating and a second active coating respectively, and then carrying out cold pressing and slitting to obtain a cathode pole piece. Wherein the specific design parameters of the first and second active coatings are shown in table 1.
Anode pole piece: anode active material, conductive agent (SP and CNT are mixed in a mass ratio of 0.45:0.05), binder (SBR and PAALi are mixed in a mass ratio of 0.5:1.8) are mixed according to a weight ratio of 97.7:1.1:1.2, anode active material slurry is prepared and uniformly coated on an anode current collector, and then the anode current collector is subjected to cold pressing and slitting to obtain an anode plate.
Isolation film: and coating the PE surface with a ceramic mixture as a separation film.
Electrolyte solution: ethylene Carbonate (EC), propylene Carbonate (PC), diethyl carbonate (DEC) and Propyl Propionate (PP) are mixed according to the volume ratio of 1.2:1:4:4, and then fully dried lithium salt LiPF 6 is dissolved in a mixed organic solvent according to the proportion of 1mol/L to prepare the electrolyte.
Full cell preparation: and winding or laminating the cathode pole piece, the isolating film and the anode pole piece to manufacture a bare cell, and then packaging and injecting electrolyte to manufacture the finished lithium ion battery.
Example 2
Different from example 1, the grain size L 2 and the diffusion coefficient D 2 of the second active coating are shown in table 1.
The remainder is the same as embodiment 1 and will not be described here again.
Example 3
Different from example 1, the grain size L 2 and the diffusion coefficient D 2 of the second active coating are shown in table 1.
The remainder is the same as embodiment 1 and will not be described here again.
Example 4
Different from example 1, the grain size L 2 and the diffusion coefficient D 2 of the second active coating are shown in table 1.
The remainder is the same as embodiment 1 and will not be described here again.
Example 5
Different from example 4, the grain size L 1 and the diffusion coefficient D 1 of the first active coating are shown in Table 1.
The remainder is the same as embodiment 4 and will not be described here again.
Example 6
Different from example 1, the grain size L 1 of the first active coating layer and its lithium ion diffusion coefficient D 1, and the grain size L 2 of the second active coating layer and its lithium ion diffusion coefficient D 2 are shown in table 1.
The remainder is the same as embodiment 1 and will not be described here again.
Example 7
Different from example 1, the thickness h of the second reactive coating layer was varied and the specific parameters are shown in Table 1.
The remainder is the same as embodiment 1 and will not be described here again.
Example 8
Different from example 1, the thickness H of the first reactive coating layer and the thickness H of the second reactive coating layer are shown in table 1.
The remainder is the same as embodiment 1 and will not be described here again.
Example 9
Different from example 1, the thickness H of the first reactive coating layer and the thickness H of the second reactive coating layer are shown in table 1.
The remainder is the same as embodiment 1 and will not be described here again.
Example 10
Different from example 1, the thickness H of the first reactive coating layer and the thickness H of the second reactive coating layer are shown in table 1.
The remainder is the same as embodiment 1 and will not be described here again.
Example 11
Different from example 1, the thickness H of the first reactive coating layer and the thickness H of the second reactive coating layer are shown in table 1.
The remainder is the same as embodiment 1 and will not be described here again.
Example 12
Different from example 3, the thickness H of the first reactive coating and the thickness H of the second reactive coating are specified in table 1.
The remainder is the same as embodiment 3 and will not be described here again.
Comparative example 1
Different from example 1, the grain size L 2 and the diffusion coefficient D 2 of the second active coating are shown in table 1.
The remainder is the same as embodiment 1 and will not be described here again.
Comparative example 2
Different from example 1, the thickness h of the second reactive coating layer was varied and the specific parameters are shown in Table 1.
The remainder is the same as embodiment 1 and will not be described here again.
Comparative example 3
Different from example 1, the grain size L 2 and the diffusion coefficient D 2 of the second active coating are shown in table 1.
The remainder is the same as embodiment 1 and will not be described here again.
Examples 1 to 12 and comparative examples 1 to 3 were arranged as shown in Table 1.
TABLE 1
The cathode sheets and secondary batteries obtained in examples 1 to 12 and comparative examples 1 to 3 were tested. The test results are shown in Table 2 below.
The cyclic test method comprises the following steps: the cycle test was performed at 25℃or 45℃according to the following method,
Charging system ：3.6C CC to 4.25V,2.8C CC to 4.35V,CV to 1.8C,1.8C CC to 4.4V,CV to 1.5C,1.5C CC to 4.5V,CV to 1.2C,1.2C CC to 4.55V,CV to 0.26C;
Discharge system: 0.7C DC to 3.0V.
500 Week capacity retention = 500 th week discharge capacity/1 st week discharge capacity 100%;
500-week expansion= (thickness at 500 weeks-initial half-electric thickness)/initial half-electric thickness 100%;
initial half-electric thickness: constant current charging at 0.5C to 3.96V constant voltage to 0.02C, all cell thicknesses were tested using 600 PPG.
And (3) multiplying power performance test: capacity measurement was performed in the following manner in an environment of 25 ℃ with 0.5C charged to 4.5V, and 0.02C cut off; then, 1C is discharged to 3.0V.
Rate performance = discharge capacity/rated capacity × 100%
The test results are shown in table 2 below.
TABLE 2
From examples 1 to 12, it can be seen that by providing active material layers with different lithium ion diffusion rates on both sides of the cathode sheet, the cyclic expansion rate and the capacity retention rate at 25 ℃ are effectively improved, and the phenomenon of thickness expansion of the battery caused by head-to-tail lithium precipitation is avoided, thus preventing the service life of the product. The larger the grain size of the second active coating layer, the more favorable the lithium ion extraction is slowed down, but the exertion of the battery capacity is also affected, so that the selection of the proper grain size is particularly important.
From the test results of examples 1, 7 to 11 and comparative example 2, it can be seen that the difference in thickness between the first active coating layer and the second active coating layer affects insufficient contact between the electrode sheet and the separator, increases internal resistance of the battery, and affects expansion rate, capacity retention rate and rate capability of the battery in circulation. The thinner the coating thickness, the higher the cell cycle swell ratio and capacity retention ratio, and the better the rate capability, as in example 8.
From the test results of examples 1 to 6 and comparative example 3, it is apparent that the diffusion coefficient of the second active coating layer is greater than that of the first active coating layer, significantly affecting the rate performance of the battery. The cathode current collector has the advantages that the active material layers with two different lithium ion diffusion rates are arranged on the surface of at least one side of the cathode current collector, and only the lithium ion diffusion rate of the second active coating is smaller than that of the first active coating, the lithium ion diffusion rate of the second active coating is slow, and the accumulation of lithium ions in the edge area of the anode sheet can be reduced in the process of battery core circulation, so that the occurrence of lithium precipitation is effectively avoided.
From the test results of example 3 and example 12, it is understood that example 3 satisfying the relationship 0.35.ltoreq.h/L 2.ltoreq.1.8 has better expansion rate and retention rate and rate capability at 25℃for 500 cycles than example 12, whereas example 12 has a second active coating layer with a smaller grain size, resulting in unstable structure of the second active coating layer and affecting rate capability of the battery.
In summary, the cathode sheet provided by the invention has the advantages that the thickness of the active coating is limited, the grain size of the active material and the diffusion coefficient of lithium ions meet the relation 2 which is less than or equal to D 1(L1+H)/D2(L2 +h) and less than 30, the occurrence of lithium precipitation of the cathode sheet is reduced from the source, the bonding between the cathode sheet and a diaphragm is ensured to be good, the influence of the increase of internal resistance on the polarization of a battery is avoided, and the smoothness of a transmission channel is kept. The thickness difference between the first coating and the second coating and the size of the grain size can influence the transmission efficiency of lithium ions, the lithium ion speed of the lithium ion battery in the circulating process is lower, the lithium ion accumulation on the surface of the anode sheet is reduced, and the occurrence of lithium precipitation is avoided. Meanwhile, the grain size and the coating thickness are in an interaction relation, the small multiplying power performance of the grains is improved, but the influence caused by the small multiplying power performance is that the material structure is unstable; the large-grain coating has a thin multiplying power performance lower than that of small grains, but has a better structure stability, so that the first active coating and the second active coating are respectively matched with different grain sizes, and the material can have stability on the premise of ensuring the multiplying power performance.
Variations and modifications of the above embodiments will occur to those skilled in the art to which the invention pertains from the foregoing disclosure and teachings. Therefore, the present invention is not limited to the above-described embodiments, but is intended to be capable of modification, substitution or variation in light thereof, which will be apparent to those skilled in the art in light of the present teachings. In addition, although specific terms are used in the present specification, these terms are for convenience of description only and do not limit the present invention in any way.

Claims (11)

1.一种阴极片，其特征在于，包括集流体和设置在所述集流体至少一侧表面的活性材料层，所述活性材料层包括第一活性涂层和第二活性涂层，所述第一活性涂层和第二活性涂层并列设置在所述集流体的同一侧表面，且所述第二活性涂层设在集流体沿Y轴方向边缘两侧；所述第一活性涂层与所述第二活性涂层满足关系：2≤D1(L1+H)/D2(L2+h)＜30；1. A cathode sheet, characterized in that it comprises a current collector and an active material layer disposed on at least one side of the current collector, the active material layer comprises a first active coating layer and a second active coating layer, the first active coating layer and the second active coating layer are disposed side by side on the same side of the current collector, and the second active coating layer is disposed on both sides of the edge of the current collector along the Y-axis direction; the first active coating layer and the second active coating layer satisfy the relationship: 2≤D 1 (L 1 +H)/D 2 (L 2 +h)＜30; 其中，H为第一活性涂层的厚度，h为第二活性涂层的厚度，单位为μm；Wherein, H is the thickness of the first active coating, h is the thickness of the second active coating, in μm; L1为第一活性涂层的活性材料的晶粒度，L2为第二活性涂层的活性材料的晶粒度，单位为nm； L1 is the grain size of the active material of the first active coating, L2 is the grain size of the active material of the second active coating, in nm; D1为第一活性涂层的锂离子扩散系数，D2为第二活性涂层的锂离子扩散系数，cm/s。 D1 is the lithium ion diffusion coefficient of the first active coating, and D2 is the lithium ion diffusion coefficient of the second active coating, cm/s. 2.根据权利要求1所述的阴极片，其特征在于，所述第一活性涂层和所述第二活性涂层的厚度满足关系：0.97H≤h≤H。2 . The cathode sheet according to claim 1 , wherein the thickness of the first active coating layer and the second active coating layer satisfy the relationship: 0.97H≤h≤H. 3.根据权利要求1所述的阴极片，其特征在于，所述第二活性涂层的厚度和第二活性涂层的活性材料的晶粒度满足关系：0.35≤h/L2≤1.8。3 . The cathode sheet according to claim 1 , wherein the thickness of the second active coating layer and the grain size of the active material of the second active coating layer satisfy the relationship: 0.35≤h/L 2 ≤1.8. 4.根据权利要求2所述的阴极片，其特征在于，所述第一活性涂层厚度H为25～100μm。4 . The cathode sheet according to claim 2 , wherein a thickness H of the first active coating is 25 to 100 μm. 5.根据权利要求1所述的阴极片，其特征在于，所述第一活性涂层活性材料的晶粒度小于第二活性涂层活性材料的晶粒度，且满足关系：1.2L1≤L2≤4L1。5 . The cathode sheet according to claim 1 , wherein the grain size of the active material of the first active coating layer is smaller than the grain size of the active material of the second active coating layer, and the relationship is satisfied: 1.2L 1 ≤L 2 ≤4L 1 . 6.根据权利要求5所述的阴极片，其特征在于，所述第一活性涂层和所述第二活性涂层的活性材料的晶粒度分别为10～100nm。6 . The cathode sheet according to claim 5 , wherein the grain sizes of the active materials of the first active coating layer and the second active coating layer are respectively 10 to 100 nm. 7.根据权利要求1所述的阴极片，其特征在于，所述第一活性涂层和第二活性涂层的锂离子扩散系数分别为1×10-10～1×10-7cm/s，且满足关系：3D2≤D1≤50.2D2。7 . The cathode sheet according to claim 1 , wherein the lithium ion diffusion coefficients of the first active coating layer and the second active coating layer are respectively 1×10 −10 ˜1×10 −7 cm/s and satisfy the relationship: 3D 2 ≤D 1 ≤50.2D 2 . 8.根据权利要求1所述的阴极片，其特征在于，所述第二活性涂层的单侧的涂布宽度为2～5mm。8 . The cathode sheet according to claim 1 , wherein the coating width of one side of the second active coating is 2 to 5 mm. 9.根据权利要求1所述的阴极片，其特征在于，所述集流体选自金属铝、金属镍、不锈钢、镍钛合金、碳纤维中的至少一种。9 . The cathode sheet according to claim 1 , wherein the current collector is selected from at least one of metal aluminum, metal nickel, stainless steel, nickel-titanium alloy, and carbon fiber. 10.根据权利要求1所述的阴极片，其特征在于，所述集流体的厚度为6～20μm。10 . The cathode sheet according to claim 1 , wherein the thickness of the current collector is 6 to 20 μm. 11.一种二次电池，包括阴极片、阳极片、隔膜和电解液，其特征在于，所述阴极片为权利要求1～10任一项所述的阴极片。11. A secondary battery comprising a cathode sheet, an anode sheet, a separator and an electrolyte, wherein the cathode sheet is the cathode sheet according to any one of claims 1 to 10.
CN202410219491.2A 2024-02-27 2024-02-27 A cathode sheet and secondary battery Pending CN118299511A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN119786513A (en) * 2024-12-13 2025-04-08 浙江锂威能源科技有限公司 Negative electrode sheet, preparation method thereof and lithium ion battery

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN119786513A (en) * 2024-12-13 2025-04-08 浙江锂威能源科技有限公司 Negative electrode sheet, preparation method thereof and lithium ion battery

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