Secondary battery and electric device

Abstract

The invention relates to 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 first lithium supplementing layer and the second lithium supplementing layer are sequentially arranged on at least one surface of the positive electrode current collector, the first lithium supplementing layer comprises the first lithium supplementing agent, the second lithium supplementing layer comprises the second lithium supplementing agent, and the average particle size P1 of the first lithium supplementing agent is smaller than the average particle size P2 of the second lithium supplementing agent. The first lithium supplementing layer and the second lithium supplementing layer are arranged on the surface layer of the positive electrode current collector, so that a lithium supplementing agent can be prevented from reacting with slurry to generate gel, the stripping force of a pole piece is improved, and the compaction density of the lithium supplementing layer can be improved while the conductivity of the lithium supplementing layer is ensured, so that the first coulombic efficiency of the battery can be effectively improved, and the service life of the battery is prolonged. And the energy density and the cycle performance are improved.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a secondary battery and an electrical device. Background Technology

[0002] Lithium replenishment technology is an important way to improve the energy density of lithium batteries. Currently, the main methods for replenishing active lithium are negative electrode replenishment and positive electrode replenishment. Compared with the difficult and costly negative electrode replenishment process, positive electrode replenishment involves adding a small amount of positive electrode replenishing agent during the positive electrode homogenization process. During charging, excess Li elements are extracted from these high-capacity positive electrode materials and intercalated into the negative electrode to replenish the irreversible capacity during the first charge and discharge. However, positive electrode replenishment is less efficient than negative electrode replenishment, and positive electrode replenishment is prone to reacting with the homogenized slurry, leading to gelation, reducing the battery's initial coulombic efficiency, and affecting the battery's energy density and cycle performance. Summary of the Invention

[0003] The purpose of this application is to solve the problems of low initial coulombic efficiency, low energy density, and poor cycle performance in the existing technology of positive electrode lithium replenishment, and to provide a secondary battery and power device that can improve initial coulombic efficiency, energy density, and cycle performance.

[0004] To achieve the above objectives, a first aspect of this application provides a secondary battery, including a positive electrode sheet, the positive electrode sheet including a current collector and a first lithium replenishing layer and a second lithium replenishing layer sequentially disposed on at least one surface of the current collector; the first lithium replenishing layer includes a first lithium replenishing agent, the second lithium replenishing layer includes a second lithium replenishing agent, and the average particle size P1 of the first lithium replenishing agent is smaller than the average particle size P2 of the second lithium replenishing agent.

[0005] As an embodiment of this application, the surface of the current collector is provided with a groove, and the thickness T of the current collector and the maximum depth D of the groove satisfy: 0.1T≤D≤0.25T.

[0006] As an embodiment of this application, the total projected area S1 of the groove in the thickness direction of the current collector and the total area S2 of the current collector satisfy: S1≤0.2S2.

[0007] As an embodiment of this application, the length L of the groove is 3μm~15μm, the width W of the groove is 1μm~15μm, and the thickness T of the current collector is 6μm~20μm.

[0008] As an embodiment of this application, the groove has a curved profile along the direction perpendicular to the current collector plane.

[0009] As an embodiment of this application, the average particle size P2 of the second lithium replenishing agent and the average particle size P1 of the first lithium replenishing agent satisfy the following condition: 10≤P2 / P1≤100.

[0010] As an embodiment of this application, the average particle size P1 of the first lithium replenishing agent satisfies: 30nm≤P1<2μm.

[0011] As an embodiment of this application, the average particle size P2 of the second lithium supplement meets the following condition: 2μm≤P2≤20μm.

[0012] As an embodiment of this application, the first lithium supplement includes at least one of Li3N, LiF, LiS, Li2O, and Li2O2.

[0013] As an embodiment of this application, the second lithium supplement includes Li5FeO4, Li x At least one of NiO2, Li6CoO4, Li2RuO3, Li2MoO3, Li2MoO4, and Li5ReO6, wherein the Li x In NiO2, 0 < x ≤ 1.

[0014] As an embodiment of this application, the thickness T1 of the first lithium replenishment layer and the thickness T of the current collector satisfy: T≤T1≤2T.

[0015] As an embodiment of this application, the thickness T2 of the second lithium replenishment layer and the thickness T of the current collector satisfy: T / 2≤T2≤T.

[0016] As an embodiment of this application, the surface of the second lithium replenishment layer is provided with protrusions, and the height H of the protrusions does not exceed the thickness T2 of the second lithium replenishment layer.

[0017] As an embodiment of this application, the tangential profile of the protrusion along the direction perpendicular to the current collector plane is a curve.

[0018] As an embodiment of this application, the total projected area of ​​the protrusion along the direction perpendicular to the plane of the second lithium replenishment layer does not exceed 30% of the total area of ​​the second lithium replenishment layer.

[0019] As an embodiment of this application, the first lithium replenishing layer further includes a first conductive agent, and the second lithium replenishing layer further includes a second conductive agent, wherein the average particle size of the first conductive agent is smaller than the average particle size of the second lithium replenishing agent.

[0020] As an embodiment of this application, the first conductive agent includes at least one of acetylene black, Ketjen black, carbon nanotubes, carbon nanofibers, and graphene.

[0021] As an embodiment of this application, the second conductive agent includes at least one of metal powder, conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, carbon nanofibers, graphene, and conductive graphite.

[0022] As an embodiment of this application, the surface of the second lithium replenishment layer is further provided with a positive electrode active material layer, the positive electrode active layer including a positive electrode active material, the positive electrode active material including at least one of lithium iron phosphate, lithium manganese iron phosphate, and ternary positive electrode material.

[0023] In a second aspect of this application, an electrical device is provided, including the aforementioned secondary battery.

[0024] The beneficial effects of this application are as follows: The secondary battery provided in this application comprises a first lithium replenishing layer and a second lithium replenishing layer sequentially disposed on at least one surface of the positive electrode current collector. The first lithium replenishing layer includes a first lithium replenishing agent, and the second lithium replenishing layer includes a second lithium replenishing agent. The average particle size of the first lithium replenishing agent is smaller than that of the second lithium replenishing agent. By disposing of the first and second lithium replenishing layers on the surface of the positive electrode current collector, it is possible to avoid the lithium replenishing agent reacting with the slurry to form a gel, thereby improving the peeling force of the electrode sheet. Furthermore, it is possible to improve the compaction density of the lithium replenishing layer while ensuring its conductivity, thereby effectively improving the initial coulombic efficiency of the battery, and enhancing its energy density and cycle performance. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of the positive electrode sheet in an embodiment of this application. Detailed Implementation

[0026] To better illustrate the purpose, technical solution, and advantages of this application, the following will provide further explanation of this application in conjunction with specific embodiments.

[0027] Unless otherwise specified, the reagents, methods and equipment used in this application are all conventional reagents, methods and equipment in the field.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] In one embodiment of this application, a secondary battery is provided, including a positive electrode sheet, the positive electrode sheet including a current collector and a first lithium replenishing layer and a second lithium replenishing layer sequentially disposed on at least one surface of the current collector; the first lithium replenishing layer includes a first lithium replenishing agent, the second lithium replenishing layer includes a second lithium replenishing agent, and the average particle size P1 of the first lithium replenishing agent is smaller than the average particle size P2 of the second lithium replenishing agent.

[0032] The secondary battery provided in this application has a first lithium replenishing layer and a second lithium replenishing layer sequentially disposed on at least one surface of the positive electrode current collector. The first lithium replenishing layer includes a first lithium replenishing agent, and the second lithium replenishing layer includes a second lithium replenishing agent. The average particle size of the first lithium replenishing agent is smaller than the average particle size of the second lithium replenishing agent. By disposing the first and second lithium replenishing layers on the surface of the positive electrode current collector, it is possible to avoid the lithium replenishing agent reacting with the slurry to form a gel, thereby improving the peeling force of the electrode sheet. Furthermore, it is possible to improve the compaction density of the lithium replenishing layer while ensuring its conductivity, thereby effectively improving the initial coulombic efficiency of the battery, and enhancing its energy density and cycle performance.

[0033] In one embodiment, the surface of the current collector is provided with a groove, and the thickness T of the current collector and the maximum depth D of the groove satisfy: 0.1T≤D≤0.25T.

[0034] This study found that setting grooves on the surface of the current collector can improve the peel force between the current collector foil and the coating, and can accommodate additional lithium replenishment, further improving the first coulombic efficiency of the battery. When the thickness T of the current collector and the maximum depth D of the groove satisfy 0.1T≤D≤0.25T, the strength of the current collector can be guaranteed and it is beneficial to improve the first coulombic efficiency and energy density of the battery.

[0035] It should be noted that the thickness of the current collector mentioned in this application refers to the thickness of the current collector where the groove is not provided, and the maximum depth of the groove refers to the vertical distance from the surface of the current collector to the deepest point of the bottom of the groove.

[0036] In one embodiment, the first lithium replenishment layer fills the groove.

[0037] In one embodiment, the thickness T of the current collector is 6 μm to 20 μm.

[0038] For example, the thickness T of the current collector can be any point value or any two-point range value between 6μm and 20μm, such as one or any two of the following: 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm.

[0039] In one embodiment, the total projected area S1 of the groove in the thickness direction of the current collector and the total area S2 of the current collector satisfy: S1≤0.2S2.

[0040] This application research found that reducing the total projected area S1 of the groove in the thickness direction of the current collector can effectively improve the mechanical strength of the current collector, improve the processing capability during electrode processing, and improve the structural stability of the electrode during cycling. Limiting the total projected area S1 of the groove in the thickness direction of the current collector and the total area S2 of the current collector to the range of S1≤0.2S2 can ensure the mechanical strength of the current collector, improve the stability of the electrode, and further improve the cycle performance of the battery.

[0041] In one embodiment, the length L of the groove is 3μm to 15μm, and the width W of the groove is 1μm to 15μm.

[0042] This application research found that the length and width of the groove affect the flatness of the current collector surface and the volume of the groove. Within the above range, the length and width of the groove can make the peel force between the current collector and the first lithium replenishment layer high, and the current collector has good mechanical strength, which is beneficial to improving the battery's first coulombic efficiency and energy density.

[0043] For example, the length L of the groove can be any point value or any two-point range value between 3μm and 15μm, such as one or any two of the following: 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm; the width W of the groove can be any point value or any two-point range value between 1μm and 15μm, such as one or any two of the following: 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm.

[0044] In one embodiment, the groove has a curved profile along a cross-sectional profile perpendicular to the current collector plane.

[0045] This application research found that the groove's sectional profile along the direction perpendicular to the current collector plane is curved, which can have a higher volume utilization rate than a straight surface, which is beneficial for accommodating more lithium replenishing agent and improving the battery's first coulombic efficiency and energy density.

[0046] It should be noted that when the groove has a curved profile along the cross-sectional contour perpendicular to the current collector plane, the groove is irregular in shape. The length and width of the groove refer to the length and width of the smallest bounding rectangle of the irregular shape.

[0047] In one embodiment, the average particle size P2 of the second lithium supplement agent and the average particle size P1 of the first lithium supplement agent satisfy the following condition: 10 ≤ P2 / P1 ≤ 100.

[0048] This application research found that when the average particle size P2 of the second lithium replenishing agent and the average particle size P1 of the first lithium replenishing agent satisfy the above-mentioned relationship, the conductivity and compaction density of the first and second lithium replenishing layers can be further improved, thereby effectively improving the first coulombic efficiency of the battery, and enhancing the energy density and cycle performance.

[0049] For example, P2 / P1 can be any point value or any two-point range value between 10 and 120, such as one or any two of the range values ​​of 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, and 120.

[0050] It should be noted that the test method for the average particle size of the first lithium replenishing agent is as follows: high-temperature tape is used to stick to the surface of the current collector coating, the first lithium replenishing layer and the second lithium replenishing layer are peeled off respectively, and the particle size of at least 100 lithium replenishing agent particles is measured using a scanning electron microscope. A particle size distribution fitting diagram is made to obtain the average particle size value.

[0051] In one embodiment, the average particle size P1 of the first lithium supplement satisfies: 30nm ≤ P1 < 2μm.

[0052] For example, the average particle size P1 of the first lithium supplement can be any point value or any two-point range value between 30nm and 2μm, such as one or any two range values ​​of 30nm, 50nm, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, and 2μm.

[0053] In one embodiment, the average particle size P2 of the second lithium supplement satisfies: 2μm≤P2≤20μm.

[0054] For example, the average particle size P1 of the second lithium supplement can be any point value or any two-point range value between 2μm and 20μm, such as one or any two of the following: 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm.

[0055] In one embodiment, the first lithium replenishing agent includes at least one of Li3N, LiF, LiS, Li2O, and Li2O2.

[0056] This application research found that the above-mentioned first lithium replenishing agent has high capacity and high lithium replenishment efficiency, which can significantly improve the first efficiency, energy density and cycle performance of the battery. At the same time, the first lithium replenishing agent has a small average particle size, which can improve the conductivity of the first lithium replenishing layer and make it easy to fill the groove, thereby improving battery performance.

[0057] In one embodiment, the second lithium supplement includes Li5FeO4 and Li x At least one of NiO2, Li6CoO4, Li2RuO3, Li2MoO3, Li2MoO4, and Li5ReO6, wherein the Li x In NiO2, 0 < x ≤ 1.

[0058] This application research found that the above-mentioned second lithium replenishing agent has high air stability, can isolate the first lithium replenishing agent from contact with air to prevent side reactions, reduce environmental sensitivity, and is suitable for industrial production. At the same time, the second lithium replenishing agent has a large average particle size, which is beneficial to improving the compaction density of the lithium replenishing layer.

[0059] In one embodiment, the thickness T1 of the first lithium replenishment layer and the thickness T of the current collector satisfy: T≤T1≤2T.

[0060] This application research found that when the thickness T1 of the first lithium replenishment layer and the thickness T of the current collector satisfy T≤T1≤2T, it can accommodate more first lithium replenishment agents with high lithium replenishment efficiency, effectively improving the lithium replenishment effect.

[0061] It should be noted that the thickness of the first lithium replenishment layer in this application can be obtained by measuring TEM images.

[0062] In one embodiment, the thickness T2 of the second lithium replenishment layer and the thickness T of the current collector satisfy: T / 2 ≤ T2 ≤ T.

[0063] This application research found that limiting the thickness T2 of the second lithium replenishment layer and the thickness T of the current collector to the range of T / 2≤T2≤T allows the second lithium replenishment layer to reduce its mass and volume while isolating the first lithium replenishment layer from the external environment, thus improving the overall lithium replenishment effect.

[0064] It should be noted that the thickness of the second lithium replenishment layer in this application can be obtained by measuring TEM images.

[0065] In one embodiment, the surface of the second lithium replenishment layer is provided with a protrusion, the height H of which does not exceed the thickness T2 of the second lithium replenishment layer.

[0066] This application research found that setting protrusions on the surface of the second lithium replenishment layer can improve the peel force between the current collector containing the lithium replenishment layer and the positive electrode active material layer. The height H of the protrusion does not exceed the thickness T2 of the second lithium replenishment layer, which is beneficial to maintaining the stability of the protrusion structure and the current collector winding efficiency.

[0067] In one embodiment, the protrusion has a curved cross-sectional profile along a direction perpendicular to the current collector plane.

[0068] This application research found that the tangential profile of the protrusion along the direction perpendicular to the plane of the current collector is curved, which is beneficial for the current collector to be rolled up and less prone to damage.

[0069] In one embodiment, the total projected area of ​​the protrusion along the direction perpendicular to the plane of the second lithium replenishment layer does not exceed 30% of the total area of ​​the second lithium replenishment layer.

[0070] This application research found that if the total projected area of ​​the protrusion along the direction perpendicular to the plane of the second lithium replenishment layer does not exceed 30% of the total area of ​​the second lithium replenishment layer, the surface flatness of the second lithium replenishment layer can be kept within a suitable range and the lithium replenishment efficiency can be guaranteed.

[0071] In one embodiment, the first lithium replenishment layer further includes a first conductive agent, and the second lithium replenishment layer further includes a second conductive agent, wherein the average particle size of the first conductive agent is smaller than the average particle size of the second lithium replenishment agent.

[0072] This application research found that setting a first conductive agent with a small average particle size in the first lithium replenishment layer can further improve the conductivity of the first lithium replenishment layer.

[0073] In one embodiment, the first conductive agent includes at least one of acetylene black, Ketjen black, carbon nanotubes, carbon nanofibers, and graphene.

[0074] In one embodiment, the second conductive agent includes at least one of metal powder, conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, carbon nanofibers, graphene, and conductive graphite.

[0075] In one embodiment, the first lithium replenishment layer further includes a first binder, the first lithium replenishment layer comprising the following components by mass percentage: 80%~90% first lithium replenishing agent, 5%~11% first conductive agent, and 5%~9% first binder.

[0076] In one embodiment, the second lithium replenishing layer further includes a second binder, and the first lithium replenishing layer comprises the following components by mass percentage: 84% to 94% second lithium replenishing agent, 3% to 9% second conductive agent, and 3% to 7% second binder.

[0077] In one embodiment, the current collector comprises an aluminum current collector.

[0078] In one embodiment, the method of forming grooves on the surface of the current collector includes at least one of stamping, rolling, and etching; optionally, the method of forming grooves on the surface of the current collector is stamping or rolling.

[0079] In one embodiment, the method of forming protrusions on the surface of the second lithium replenishment layer includes at least one of stamping, rolling, and etching; optionally, the method of forming grooves on the surface of the current collector is stamping or rolling.

[0080] This application does not limit the first and second adhesives, and any known adhesive can be used. Exemplarily, the first and second adhesives may each be independently at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), sodium polyacrylate (PAANa), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and sodium alginate (SA).

[0081] In one embodiment, the surface of the second lithium replenishment layer is further provided with a positive electrode active material layer, the positive electrode active layer comprising a positive electrode active material, the positive electrode active material comprising at least one of lithium iron phosphate, lithium manganese iron phosphate, and ternary positive electrode materials.

[0082] In one embodiment, the positive electrode coating further includes a positive electrode binder and a positive electrode conductive agent.

[0083] This application does not limit the positive electrode binder and positive electrode conductive agent; any known positive electrode binder and positive electrode conductive agent can be used. For example, the positive electrode binder may be at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), sodium polyacrylate (PAANa), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and sodium alginate (SA); the positive electrode conductive agent may be at least one selected from Super P, carbon nanotubes, and graphene.

[0084] In one embodiment, the secondary battery further includes a negative electrode, an electrolyte, and a separator.

[0085] In one embodiment, the separator of the secondary battery is disposed between the positive electrode and the negative electrode.

[0086] In one embodiment, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector; the negative active material layer includes a negative active material. This application does not limit the negative active material; any known negative active material can be used. As an example, the negative active material can be at least one of artificial graphite, natural graphite, silicon-carbon composite material, elemental silicon, silicon suboxide, and hard carbon.

[0087] In one embodiment, the negative electrode current collector can be made of a material with good conductivity and mechanical strength, serving both as a conductor and a current collector. In another embodiment, the negative electrode current collector can be a metal foil or a composite current collector (a composite current collector can be formed by depositing a metal material on a polymer substrate). As an example, copper foil is used as the negative electrode current collector.

[0088] In one embodiment, the electrolyte comprises an organic solvent and a lithium salt.

[0089] This application does not limit the use of organic solvents and lithium salts; any known organic solvents and lithium salts may be used.

[0090] For example, the organic solvent includes at least one of ethylene carbonate (EC), propylene carbonate, diethyl carbonate, ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC); the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

[0091] In one embodiment of this application, an electrical device is provided, which includes the secondary battery described in this application.

[0092] 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.

[0093] Example 1 This application provides a secondary battery, the preparation method of which includes the following steps: (1) Preparation of positive electrode sheet S1. Mix Li3N, acetylene black, and PVDF in N-methylpyrrolidone (NMP) at a mass ratio of 85:8:7 to obtain a first lithium replenishing layer slurry. Apply the first lithium replenishing layer slurry to both sides of the current collector aluminum foil with grooves, and bake and dry to obtain the first lithium replenishing layer. The method for setting the grooves on the surface of the current collector aluminum foil is as follows: when the aluminum foil stamping roll is opened, design a protrusion with a height of 1.7μm, a length of 8.5μm, and a width of 2.7μm on the roll, and stamp out the pit-shaped grooves on the surface of the aluminum foil through the protrusion pattern.

[0094] S2. Li5FeO4:acetylene black:PVDF are mixed evenly in NMP at a mass ratio of 89:6:5 to obtain a second lithium replenishment layer slurry. The obtained second lithium replenishment layer slurry is coated on the surface of the obtained first lithium replenishment layer. A pit with a depth of 4μm is set on the surface of the roller press. The current collector coated with the lithium replenishment layer produces arc-shaped protrusions after being rolled by the roller press. After baking and drying, the second lithium replenishment layer is obtained. The structural schematic diagram of the electrode at this time is shown in the figure. Figure 1 As shown; S3. Mix LiFePO4, acetylene black, PVDF, and carbon nanotubes in NMP at a mass ratio of 96.5:1:2:0.5 to obtain a positive electrode active material slurry. Coat the obtained positive electrode active material slurry onto the surface of the obtained second lithium replenishment layer, and bake and dry to obtain the positive electrode sheet. The parameters of the obtained positive electrode sheet are shown in Tables 1-2. (2) Preparation of negative electrode sheet Artificial graphite, conductive carbon black, binder styrene-butadiene rubber, and sodium carboxymethyl cellulose are mixed evenly on copper foil in a mass ratio of 96:1:1.5:1.5 to obtain a negative electrode sheet; (3) Preparation of secondary batteries The negative electrode sheet was die-cut into a size of 45*58mm using a die-cutting machine, and the positive electrode sheet was die-cut into a size of 43*56mm using a die-cutting machine. Celgard 2500 was used as the separator, and 1M lithium hexafluorophosphate was dissolved in a mixed solvent of EC:DMC:EMC in a volume ratio of 1:1:1 as the electrolyte. The rechargeable battery was then assembled.

[0095] Examples 2-5 This application provides a secondary battery, which differs from Embodiment 1 in that the parameters in Tables 1-2 are achieved by adjusting the maximum depth of the groove.

[0096] Examples 6-8 This application provides a secondary battery, which differs from Embodiment 1 in that the parameters in Tables 1-2 are achieved by adjusting the width and length of the groove.

[0097] Examples 9-16 This application provides a secondary battery, which differs from Embodiment 1 in that the parameters in Tables 1-2 are achieved by adjusting the thickness of the first lithium replenishment layer and the second lithium replenishment layer, as well as the types of the first lithium replenishing agent and the second lithium replenishing agent.

[0098] Examples 17-23 This application provides a secondary battery, which differs from Embodiment 1 in that the parameters in Tables 1-2 are achieved by adjusting the average particle size of the first and second lithium supplements.

[0099] Example 24 This application provides a secondary battery, which differs from Embodiment 1 in that it does not have grooves on the surface of the current collector aluminum foil to achieve the parameters in Tables 1-2.

[0100] Example 25 This application provides a secondary battery, which differs from Embodiment 1 in that it does not have protrusions on the surface of the second lithium replenishment layer to achieve the parameters in Tables 1-2.

[0101] Example 26 This application provides a secondary battery, which differs from Embodiment 1 in that the groove shown has a straight sectional profile along the direction perpendicular to the current collector plane, and the protrusion has a straight sectional profile along the direction perpendicular to the current collector plane.

[0102] Comparative Example 1 This application provides a secondary battery in comparison. The difference between the secondary battery and Embodiment 1 is that the groove is not provided on the surface of the current collector aluminum foil and the first lithium replenishment layer and the second lithium replenishment layer are not provided to achieve the parameters in Tables 1-2.

[0103] Comparative Example 2 This application provides a secondary battery in comparison, the difference between the secondary battery and Embodiment 1 is that a second lithium replenishment layer is not provided to achieve the parameters in Tables 1-2.

[0104] Comparative Example 3 This application provides a secondary battery in comparison, the difference between the secondary battery and Embodiment 1 is that the first lithium replenishment layer is not provided to achieve the parameters in Tables 1-2.

[0105] Comparative Example 4 This application provides a secondary battery in comparison, which differs from Example 1 in that the parameters in Tables 1-2 are achieved by adjusting the average particle size of the first and second lithium supplements.

[0106] Comparative Example 5 This application provides a secondary battery as a comparative example. The difference between the secondary battery and Example 1 is that the parameters in Tables 1-2 are achieved by adjusting the type and average particle size of the second lithium replenishing agent.

[0107] The thickness T of the current collector, the maximum depth D of the groove, the length L of the groove, the width W of the groove, the total projected area S1 of the groove in the thickness direction of the current collector, the thickness T1 of the first lithium replenishing layer, the thickness T2 of the second lithium replenishing layer, the average particle size P1 of the first lithium replenishing agent, the average particle size P2 of the second lithium replenishing agent, the type of the first lithium replenishing agent, the type of the second lithium replenishing agent, the height H of the protrusion, and the total projected area S3 of the protrusion along the direction perpendicular to the plane of the second lithium replenishing layer are shown in Tables 1-2.

[0108] Table 1. Parameters of Secondary Batteries Table 2 Secondary Battery Parameter Table The secondary batteries of the examples and comparative examples were subjected to performance tests. The test results are shown in Table 3. The performance test method was as follows: charge and discharge cycles were performed at a rate of 1C at 25°C within a voltage range of 2-3.8V.

[0109] Table 3 Performance Data of Secondary Batteries As can be seen from Table 3, the technical solution provided in this application has excellent first coulombic efficiency, energy density and cycle performance, with a first efficiency of not less than 92.3%, an energy density of not less than 248.1 Wh / kg and a capacity retention of not less than 91.2% after 1000 cycles.

[0110] The results of Examples 1-26 and Comparative Example 1 of this application show that not setting a lithium replenishment layer on the current collector surface will lead to a significant decrease in battery performance.

[0111] The results of Examples 1-26 and Comparative Examples 2-3 of this application show that simply setting a single lithium replenishment layer on the current collector surface does not significantly improve the performance of the battery, and the energy density, initial efficiency and capacity retention of the battery are all reduced.

[0112] The results of Examples 1-26 and Comparative Examples 4-5 of this application show that when the average particle size of the first lithium replenishing agent in the first lithium replenishing layer is greater than or equal to the average particle size of the second lithium replenishing agent, it will lead to a decrease in battery performance, and the battery's initial coulombic efficiency, energy density and cycle performance will all decrease.

[0113] 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, The device includes a positive electrode sheet, which includes a current collector and a first lithium replenishing layer and a second lithium replenishing layer sequentially disposed on at least one surface of the current collector; the first lithium replenishing layer includes a first lithium replenishing agent, and the second lithium replenishing layer includes a second lithium replenishing agent, wherein the average particle size P1 of the first lithium replenishing agent is smaller than the average particle size P2 of the second lithium replenishing agent.

2. The secondary battery according to claim 1, characterized in that, The surface of the current collector is provided with a groove, and the thickness T of the current collector and the maximum depth D of the groove satisfy: 0.1T≤D≤0.25T.

3. The secondary battery according to claim 2, characterized in that, The total projected area S1 of the groove in the thickness direction of the current collector and the total area S2 of the current collector satisfy: S1≤0.2S2; And / or, the length L of the groove is 3μm~15μm, the width W of the groove is 1μm~15μm, and the thickness T of the current collector is 6μm~20μm; And / or, the groove has a curved profile along its cross-sectional contour perpendicular to the current collector plane.

4. The secondary battery according to claim 1, characterized in that, The average particle size P2 of the second lithium supplement agent and the average particle size P1 of the first lithium supplement agent satisfy the following condition: 10≤P2 / P1≤100.

5. The secondary battery according to claim 1 or 4, characterized in that, The average particle size P1 of the first lithium supplement meets the following condition: 30nm ≤ P1 < 2μm; And / or, the average particle size P2 of the second lithium supplement satisfies: 2μm≤P2≤20μm.

6. The secondary battery according to claim 1, characterized in that, The first lithium supplement includes at least one of Li3N, LiF, LiS, Li2O, and Li2O2; And / or, the second lithium supplement includes Li5FeO4, Li x At least one of NiO2, Li6CoO4, Li2RuO3, Li2MoO3, Li2MoO4, and Li5ReO6, wherein the Li x In NiO2, 0 < x ≤ 1.

7. The secondary battery according to claim 1, characterized in that, The thickness T1 of the first lithium replenishment layer and the thickness T of the current collector satisfy: T≤T1≤2T; And / or, the thickness T2 of the second lithium replenishment layer and the thickness T of the current collector satisfy: T / 2≤T2≤T.

8. The secondary battery according to claim 1, characterized in that, The surface of the second lithium replenishment layer is provided with protrusions, and the height H of the protrusions does not exceed the thickness T2 of the second lithium replenishment layer.

9. The secondary battery according to claim 8, characterized in that, The protrusion has a curved profile along the direction perpendicular to the current collector plane; And / or, the total projected area of ​​the protrusion along the direction perpendicular to the plane of the second lithium replenishment layer does not exceed 30% of the total area of ​​the second lithium replenishment layer.

10. The secondary battery according to claim 1, characterized in that, The first lithium replenishment layer further includes a first conductive agent, and the second lithium replenishment layer further includes a second conductive agent, wherein the average particle size of the first conductive agent is smaller than the average particle size of the second lithium replenishment agent.

11. The secondary battery according to claim 10, characterized in that, The first conductive agent includes at least one of acetylene black, Ketjen black, carbon nanotubes, carbon nanofibers, and graphene. And / or, the second conductive agent includes at least one of metal powder, conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, carbon nanofibers, graphene, and conductive graphite.

12. The secondary battery according to claim 1, characterized in that, The surface of the second lithium replenishment layer is further provided with a positive electrode active material layer, wherein the positive electrode active material includes at least one of lithium iron phosphate, lithium manganese iron phosphate, and ternary positive electrode materials.

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

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