Negative pole piece, secondary battery and electric equipment

Abstract

The utility model discloses a negative pole piece, a secondary battery and electric equipment. The negative pole piece comprises a negative current collector, a first active material layer and a second active material layer, wherein the first active material layer and the second active material layer are sequentially stacked on the surface of the negative current collector; a plurality of hole structures are formed in the second active material layer; wherein the porosity of the first active material layer is larger than that of the second active material layer, and the compaction density of the first active material layer is smaller than that of the second active material layer. When the negative pole piece disclosed by the utility model is used in the secondary battery, the battery has high rate performance and better cycle performance.

Description

TECHNICAL FIELD

[0001] The utility model belongs to the battery technical field, concretely relates to a negative pole piece, secondary battery and electric equipment. BACKGROUND

[0002] Lithium ion battery has been widely applied to digital products and power supply because of its advantages of high energy density, high charging efficiency, superior cycle performance and large output power. With the continuous progress of science and technology, higher requirements are put forward for the structure and performance of lithium ion battery. High rate performance and good cycle performance have become the focus of the development of lithium ion battery. However, the conventional negative pole piece cannot meet the requirements of high rate performance and good cycle performance of the battery at the same time, which affects the application of the battery to some extent. SUMMARY

[0003] The utility model discloses at least one of the technical problems existing in the prior art. To this end, the utility model provides a negative pole piece, which is used in a secondary battery, and the battery has high rate performance and good cycle performance.

[0004] The utility model also provides a secondary battery.

[0005] The utility model also provides an electric equipment.

[0006] In the first aspect, the utility model provides a negative pole piece, which comprises a negative current collector, a first active material layer and a second active material layer which are sequentially stacked on the surface of the negative current collector, and the second active material layer is provided with a plurality of hole structures.

[0007] The negative pole piece according to the utility model has at least the following beneficial effects:

[0008] In the utility model, the second active material layer (upper layer) is a low-porosity high-compaction-density active material layer, and the first active material layer (lower layer) is a high-porosity low-compaction-density active material layer. Combined with the setting of the hole structure, the high-compaction active material layer of the upper layer with a relatively slow lithium extraction rate forms an ion high-speed channel due to the hole structure, which can effectively accelerate the lithium ion transmission, and the lower layer of high-porosity active material layer itself has a very fast lithium ion transmission rate. The progressive design of the utility model from the high-compaction active material layer to the high-porosity active material layer can well balance the lithium extraction speed of the upper and lower layers, so that the lithium ion can be extracted from the negative pole piece as quickly as possible. This not only guarantees the high energy density requirement but also guarantees the high power requirement, and the battery has excellent cycle and rate performance.

[0009] And in the rolling step of the tab preparation process, the upper layer of high-density active material layer can withstand greater pressure and is not easy to be crushed, thereby ensuring the integrity of the active material layer structure and being beneficial to improving the cycle performance of the applied battery.

[0010] In this document, unless otherwise specified, the volume of the material in the active material layer in the natural state is not included in the calculation of the porosity of the first active material layer and the porosity of the second active material layer.

[0011] In some embodiments of the present application, the width of the cross section of the hole structure decreases in the direction of the second active material layer towards the first active material layer. The shape of the cross section of the hole structure is not limited, such as not limited to circular, but also various geometric shapes such as oval, sector, regular or irregular polygon, etc. The width of the cross section of the hole structure, unless otherwise specified, refers to the size of the cross section of the hole structure in the vertical direction of the second active material layer towards the first active material layer.

[0012] In some embodiments of the present application, the width of the cross section of the hole structure is 20-140 μm.

[0013] In some embodiments of the present application, the hole structure includes a plurality of columns of continuous repeating hole units along the width direction of the tab.

[0014] In some embodiments of the present application, the hole structure includes continuous repeating hole units along the width direction of the tab; the average distance d from the center of the hole unit to the edge, the center distance L between adjacent repeating hole units, L and d satisfy: 3.5d≥L>0. Wherein, it can be understood that the center distance L between adjacent repeating hole units refers to the center distance between adjacent hole units in a column of continuous repeating hole units along the width direction of the tab.

[0015] The shape of the hole unit in the present application is not limited, such as but not limited to rectangular, circular, and preferably circular. Taking a circular hole unit as an example: when L tends to 0, it becomes a rectangular slot as shown in Figure 2 , at this time the fast charging rate performance is more excellent; when L=2d, the circular hole unit just connects; when L>2d, the tab unit is a continuous non-connected point hole structure, and the active material layer has a relatively smaller punching area, which is more beneficial to retaining the ED of the battery. Compared with L>2d, the lithium ion transmission channel of the tab is more when L≤2d, and the fast charging rate capability of the applied battery is stronger.

[0016] In some embodiments of the present application, the center distance between adjacent repeating hole units along the length direction of the tab is 0.5-4 mm.

[0017] In some embodiments of the utility model, in the second active material layer, adjacent hole units are connected or not connected.

[0018] In some embodiments of the utility model, along the direction of the second active material layer towards the first active material layer, the depth of the hole structure is greater than or equal to the thickness of the second active material layer.

[0019] In some embodiments of the utility model, along the direction of the second active material layer towards the first active material layer, the depth of the hole structure is equal to the thickness of the second active material layer.

[0020] Through the above-mentioned embodiment, compared with the depth of the hole structure being greater than the thickness of the second active material layer, the depth of the hole structure being equal to the thickness of the second active material layer can not only effectively accelerate the transmission of lithium ions, but also is more difficult to cause capacity loss.

[0021] In some embodiments of the utility model, the first active material layer is a first carbon material layer, and the second active material layer is a second carbon material layer.

[0022] In some embodiments of the utility model, the first material layer includes but is not limited to one or more carbon materials such as graphite, hard carbon, silicon-carbon material, etc.

[0023] In some embodiments of the utility model, the second material layer includes but is not limited to one or more carbon materials such as graphite, hard carbon, silicon-carbon material, etc.

[0024] In some embodiments of the utility model, the porosity of the first active material layer is 25% to 50%, such as optionally 30% to 45%.

[0025] In some embodiments of the utility model, the porosity of the second active material layer is 5% to 25%, such as optionally 10% to 20%.

[0026] In some embodiments of the utility model, the compaction density of the first active material layer is 1.40 to 1.70 g / cm 3 , such as optionally 1.45 to 1.65 g / cm 3 .

[0027] In some embodiments of the utility model, the compaction density of the second active material layer is 1.60 to 1.85 g / cm 3 , such as optionally 1.65 to 1.80 g / cm 3 . In some embodiments of the utility model, the compaction density of the second active material layer is optionally 1.70 to 1.80 g / cm 3 .

[0028] In some embodiments of the present application, the thickness ratio of the second active material layer to the first active material layer is 4:1 to 3:2.

[0029] In some embodiments of the present application, the thickness of the first active material layer is 5 to 150 μm.

[0030] In some embodiments of the present application, the thickness of the second active material layer is 5 to 150 μm.

[0031] In some embodiments of the present application, the volume of the hole structure is V1, the sum of the volumes of the first active material layer and the second active material layer is V2, and the ratio of V1 to V2 is 1:(30 to 110).

[0032] According to the above embodiments, when the thickness ratio of the second active material layer to the first active material layer is 4:1 to 3:2 and the center distance between adjacent repeated hole units is 0.5 mm to 4 mm, the lithium ions can have a faster deintercalation rate in the negative electrode sheet, the demand for high power can be met, and better cycle and rate performance can be obtained.

[0033] In some embodiments of the present application, the two side surfaces of the negative current collector are sequentially stacked with the first active material layer and the second active material layer, respectively.

[0034] In a second aspect of the present application, a secondary battery is provided, which comprises the above negative electrode sheet.

[0035] In a third aspect of the present application, an electric device is provided, which comprises the above secondary battery, and the battery is used as a power supply of the electric device. BRIEF DESCRIPTION OF DRAWINGS

[0036] The present application will be further described below in conjunction with the drawings and examples, in which:

[0037] Figure 1 FIG. 1 is a cross-sectional view of a negative electrode sheet according to an embodiment of the present application;

[0038] Figure 2 FIG. 2 is a distribution diagram of hole structures in an active material layer of the negative electrode sheet according to the embodiment of the present application;

[0039] Figure 3 FIG. 8 is a distribution diagram of hole structures in an active material layer of the negative electrode sheet according to an embodiment of the present application.

[0040] FIG. 1 is a cross-sectional view of a negative electrode sheet according to an embodiment of the present application; DETAILED DESCRIPTION

[0041] The concept and the technical effects of the present application will be described clearly and completely in combination with the embodiments, so as to fully understand the purpose, features and effects of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0042] The utility model provides a negative pole piece, include;Negative current collector and first active material layer and second active material layer of surface of negative current collector are set gradually in sequence, the second active material layer is equipped with a plurality of hole structure;Wherein, the porosity of first active material layer is greater than the porosity of second active material layer, and the compaction density of first active material layer is less than the compaction density of second active material layer.

[0043] In some embodiments of the utility model, along the direction of the second active material layer towards the first active material layer, the width of the cross section of the hole structure shows a decreasing trend. The shape of the cross section of the hole structure is not limited, such as not limited to circular, but also various geometric shapes such as oval, sector, regular or irregular polygon. The width of the cross section of the hole structure, unless otherwise specified, refers to the size of the cross section of the hole structure in the vertical direction of the direction of the second active material layer towards the first active material layer. Through the above-mentioned embodiments, the width of the cross section of the hole structure shows a decreasing trend, so that the side of the hole structure close to the negative current collector can occur capillary action, which is beneficial to the infiltration of electrolyte, increases the liquid retention of the battery cell, and improves the cycle life of the battery cell.

[0044] In some embodiments of the utility model, the width of the cross section of the hole structure is 20-140 μm.

[0045] In some embodiments of the utility model, the hole structure includes a plurality of continuous repeating hole units along the column in the width direction of the pole piece.

[0046] In some embodiments of the utility model, the hole structure includes continuous repeating hole units along the width direction of the pole piece; the average distance d from the center of the hole unit to the edge, the center distance L of the adjacent repeating hole units, L and d satisfy: 3.5d≥L>0. Wherein, it can be understood that the center distance L of the adjacent repeating hole units refers to the center distance of the adjacent hole units in a column of continuous repeating hole units along the width direction of the pole piece.

[0047] The shape of the hole unit in the utility model is not limited, such as including but not limited to rectangular, circular, and preferably circular. Taking the circular hole unit as an example: when L tends to 0 infinitely, it will become as Figure 2rectangular slot position, at this time, the fast charging rate performance is more excellent, when L = 2d, the circular hole unit just connects, when L > 2d, the pole piece unit is a continuous non-connected point aperture structure, and the material active layer has a relatively smaller punching area, which is more beneficial to retain the ED of the battery.

[0048] In some embodiments of the utility model, the center distance of adjacent repeated hole units along the length direction of the pole piece is 0.5-4mm.

[0049] In some embodiments of the utility model, the second active material layer is connected or not connected with each other.

[0050] In some embodiments of the utility model, the depth of the hole structure is greater than or equal to the thickness of the second active material layer along the direction of the second active material layer to the first active material layer.

[0051] In some embodiments of the utility model, the depth of the hole structure is equal to the thickness of the second active material layer along the direction of the second active material layer to the first active material layer.

[0052] Compared with the depth of the hole structure being greater than the thickness of the second active material layer, the depth of the hole structure being equal to the thickness of the second active material layer can effectively accelerate the transmission of lithium ions and is less likely to cause capacity loss.

[0053] In some embodiments of the utility model, the porosity of the first active material layer is 25%-50%, such as 30%-45%.

[0054] In some embodiments of the utility model, the porosity of the second active material layer is 5%-25%, such as 10%-20%.

[0055] In some embodiments of the utility model, the compaction density of the first active material layer is 1.40-1.70g / cm 3 , such as 1.45-1.65g / cm 3 .

[0056] In some embodiments of the utility model, the compaction density of the second active material layer is 1.60-1.85g / cm 3 , such as 1.65-1.80g / cm 3In some embodiments of the present application, the compacted density of the second active material layer can be selected from 1.70 to 1.80 g / cm 3 .

[0057] In some embodiments of the present application, the thickness ratio of the second active material layer to the first active material layer is 4:1 to 3:2.

[0058] In some embodiments of the present application, the thickness of the first active material layer is 5 to 150 μm.

[0059] In some embodiments of the present application, the thickness of the second active material layer is 5 to 150 μm.

[0060] In some embodiments of the present application, the volume of the hole structure is V1, the sum of the volumes of the first active material layer and the second active material layer is V2, and the ratio of V1 to V2 is 1:(30 to 110).

[0061] In some embodiments of the present application, the two side surfaces of the negative electrode current collector are sequentially stacked with the first active material layer and the second active material layer, respectively.

[0062] In some embodiments of the present application, the first active material layer is a first carbon material layer, and the second active material layer is a second carbon material layer.

[0063] In some embodiments of the present application, the first active material layer comprises a first negative electrode active material, a first conductive agent and a first binder.

[0064] In some embodiments of the present application, the first negative electrode active material comprises, but is not limited to, one or more of graphite, hard carbon, silicon-carbon material, etc.

[0065] In some embodiments of the present application, the material of the first conductive agent is not limited, and can be selected from one or more of acetylene black, carbon nanotube, etc.

[0066] In some embodiments of the present application, the material of the first binder is not limited, and can be selected from one or more of polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), etc.

[0067] In some embodiments of the present application, the first active material layer further comprises a first thickening agent. Optionally, the type of the first thickening agent is not limited, and can be selected from sodium carboxymethyl cellulose (CMC).

[0068] In some embodiments of the utility model, the weight ratio of the first negative active material, the first conductive agent, the first binder and the first thickening agent is 85-99.5:0.1-2:0.1-5:0.1-5, which can be 98.1:0.5:0.7:0.7.

[0069] In some embodiments of the utility model, the second active material layer comprises a second negative active material, a second conductive agent and a second binder.

[0070] In some embodiments of the utility model, the second negative active material comprises but is not limited to one or more of graphite, hard carbon, silicon-carbon material and the like.

[0071] In some embodiments of the utility model, the material of the second conductive agent is not limited, which can be one or more of acetylene black, carbon nanotube and the like.

[0072] In some embodiments of the utility model, the material of the second binder is not limited, which can be polyvinylidene fluoride (PVDF) and the like.

[0073] In some embodiments of the utility model, the second active material layer further comprises a second thickening agent. Optionally, the type of the second thickening agent is not limited, which can be sodium carboxymethyl cellulose (CMC).

[0074] In some embodiments of the utility model, the weight ratio of the second negative active material, the second conductive agent, the second binder and the second thickening agent is 85-99.5:0.1-2:0.1-5:0.1-5, which can be 98.1:0.5:0.7:0.7.

[0075] In some embodiments of the utility model, the hole structure is formed on the second active material layer of the pole piece by laser etching, and / or the hole structure is formed on the first active material layer of the pole piece by laser etching. Optionally, the laser etching field mirror can be at least one of a continuous aperture or a point aperture.

[0076] The second aspect of the utility model provides a secondary battery comprising the negative pole piece.

[0077] The third aspect of the utility model provides a power-using device comprising the secondary battery, wherein the battery is used as the power supply of the power-using device.

[0078] In the following examples and comparative examples, the experimental methods not specified with specific conditions are generally according to the conventional conditions in the field or according to the suggested conditions of the manufacturers; the raw materials, reagents and the like used, if not specially specified, are all raw materials and reagents that can be obtained from the conventional market or the like commercial channels.

[0079] Graphite A200, graphite A100, purchased from Jiangxi Zichen Technology Co., Ltd.

[0080] Example 1

[0081] The embodiment discloses a negative electrode sheet, comprising a negative electrode current collector, a first active material layer (i.e. a first carbon material layer) and a second active material layer (i.e. a second carbon material layer) which are sequentially arranged on both sides of the negative electrode current collector respectively; wherein the porosity of the first active material layer is greater than the porosity of the second active material layer, and the compaction density of the first active material layer is less than the compaction density of the second active material layer. Specifically, the porosity of the first active material layer is 40%, and the compaction density P1 is 1.50 g / cm3; the porosity of the second active material layer is 15%, and the compaction density P2 is 1.70 g / cm3. 3 3 .

[0082] The thickness ratio of the second active material layer to the first active material layer is 4:1. The thickness H1 of the first active material layer is 28.8 μm. The thickness H2 of the second active material layer is 115.2 μm.

[0083] The pore structure comprises a plurality of columns of continuously repeated pore units along the width direction of the sheet. The pore structure comprises continuously repeated pore units along the width direction of the sheet; the average distance d of the pore unit center to the edge, and the center distance L of adjacent repeated pore units, wherein L < 2d. The continuously repeated pore units are continuous holes formed by laser etching, and a column of holes forms a hole groove. In the direction of the second active material layer towards the first active material layer, the depth of the hole groove (115.2 μm) is equal to the thickness of the second active material layer. The distance between adjacent hole grooves is 2 mm (i.e. the center distance of adjacent repeated pore units along the length direction of the sheet). In the direction of the second active material layer towards the first active material layer, the width of the hole groove cross-section decreases, specifically, the width of the hole groove cross-section is 20-140 μm. The width of the hole groove cross-section, i.e. the width of the hole structure cross-section, refers to the size of the hole structure cross-section in the vertical direction of the direction of the second active material layer towards the first active material layer.

[0084] The volume of the pore structure is V1, the sum of the volumes of the first active material layer and the second active material layer is V2, and the ratio of V1 and V2 is α = 1:50.

[0085] The negative electrode sheet is prepared by a method comprising the following steps:

[0086] ​​​The first active material layer (lower slurry) is obtained by mixing graphite A200, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), thickening agent sodium carboxymethyl cellulose (CMC) in a mass ratio of 98.1:0.5:0.7:0.7 in a deionized water solvent system and fully stirring to mix uniformly. The second active material layer (upper slurry) is obtained by mixing graphite A100, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), thickening agent sodium carboxymethyl cellulose (CMC) in a mass ratio of 98.1:0.5:0.7:0.7 in a deionized water solvent system and fully stirring to mix uniformly.

[0087] Then, the upper and lower slurries are simultaneously and uniformly coated on a 6-micron-thick copper foil in a thickness ratio of 4:1, followed by cold pressing, slitting, and laser etching (the holes formed by laser etching have a center spacing of 2 mm along the length direction of the pole piece, and a depth of 115.2 microns) to obtain a negative pole piece.

[0088] The embodiment discloses a lithium ion battery, which comprises the negative pole piece and the positive pole piece of the embodiment, an electrolyte, and a separator.

[0089] The preparation method of the positive pole piece comprises the following steps: uniformly dispersing active material LiCoO2, conductive agent acetylene black, conductive carbon nanotube, and binder polyvinylidene fluoride (PVDF) in a weight ratio of 98.2:0.5:0.3:1.0 in an N-methylpyrrolidone solvent system, coating the mixture on a 10-micron-thick aluminum foil, and then cold pressing and slitting to obtain the positive pole piece.

[0090] The separator: 2-micron-thick aluminum oxide ceramic mixture is coated on the surface of a 5-micron-thick PE layer as a separator.

[0091] The electrolyte: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) are mixed in a volume ratio of 1:1:4:4, and then fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent in a proportion of 1 mol / L to prepare the electrolyte.

[0092] The full battery is prepared: the positive pole piece, the separator, and the negative pole piece are wound or laminated to make a bare cell, and then the electrolyte is injected after packaging to make a lithium ion battery.

[0093] The embodiment discloses a consumer electronic device, which comprises the secondary battery in the embodiment, and the secondary battery is used as the power supply of the consumer electronic device.

[0094] Examples 1-8 and Comparative Examples 1-3 disclose a series of negative electrode sheets and lithium ion batteries. Among them, the difference between the negative electrode sheets of Examples 1-8 and Comparative Examples 1-3 and Example 1 is only that the negative electrode sheets adopt the design parameters in Table 1. Among them, the laser etching field mirror used in Example 8 is a point aperture, and a hole structure is formed on the second active material layer. In Comparative Example 1, the upper and lower two layers in Example 1 are interchanged, and a traditional double-layer coating form (high compaction of the lower layer + high porosity of the upper layer) is adopted. In Comparative Example 2, the negative electrode sheet does not contain the second active material layer, i.e., the high compaction active layer is used entirely. In Comparative Example 3, the negative electrode sheet does not contain the first active material layer, i.e., the high porosity active layer is used entirely. The others are the same as Example 1.

[0095] The lithium ion batteries in Examples 1-8 and Comparative Examples 1-3 differ from Example 1 only in that the negative electrode sheets in Examples 1-8 and Comparative Examples 1-3 are used instead of the negative electrode sheet in Example 1, and the others are the same as Example 1.

[0096] Table 1

[0097]

[0098] Test Example

[0099] In this test example, the batteries obtained in the examples and comparative examples are subjected to performance tests, specifically including:

[0100] Lithium ion diffusion rate: the rate of lithium ion insertion and extraction in the electrode material, which largely determines the reaction rate, which can be determined by the GITT method. The larger the lithium ion diffusion rate, the faster the lithium ion diffuses in the electrode sheet, which is beneficial to the rate and cycle performance.

[0101] GITT test method: first, the negative electrode sheet coated with graphite on one side is cleaned with NMP and deionized water, and is flushed to the size required for assembling a button cell. Then, in a glove box, a metal lithium sheet is used as a counter electrode, and a ceramic-coated PE film is used as a separator, and the three are assembled into a button cell. The button cell is subjected to constant current pulse charging / discharging at 0.1C (the button cell is charged at 0.1C for 10 min, and is left for 1 h). The voltage curve of the charging and discharging process is fitted to obtain the lithium ion diffusion coefficient at this SOC. The next round of pulse charging / discharging at 0.1C is continued for 10 min until the battery reaches the upper and lower voltage limits.

[0102] RT cycle test method: the cell is placed in a test environment at room temperature (25°C), and is subjected to cycle test according to the cycle specification of 5.0C CC to 4.25V, CV to 2.8C, CC to 4.35V, CV to 1.8C, CC to 4.53V, CV to 0.02C, until the battery capacity attenuation is greater than 20% or the swelling is greater than 10%.

[0103] Rate capability test method: the three-electrode cell is charged to 4.53V at 0.5C constant current and constant voltage, and discharged to 3.0V at 0.2C constant current for 2 cycles; finally, it is charged to 4.53V at different rates (1C-10C), and the potential change of the negative electrode (vs. reference electrode) is monitored at the same time. The test is carried out from low rate to high rate, and the charging rate when the voltage is <0 is the rate capability.

[0104] The test results are shown in Table 2:

[0105] Table 2

[0106]

[0107] The active material layer in the negative electrode sheet of Comparative Example 3 is a high-porosity material layer containing pore structures, and compared with the examples, the active material is largely consumed and the ED loss is extremely large.

[0108] In the utility model, the second active material layer (upper layer) of the negative electrode sheet is a high-compaction-density low-porosity graphite layer with a compaction density of 1.60-1.80 g / cm 3 , and a porosity of 5%-25%, and the first active material layer (lower layer) is a low-compaction high-porosity graphite layer with a compaction density of 1.40-1.70 g / cm 3 , and a porosity of 25%-50%, and the obtained battery has good high-rate performance and high energy density. In the utility model, the negative electrode sheet has a progressive change from high compaction to high porosity from top to bottom, and is combined with the laser etching technology. Alternatively, in the utility model, the laser etching depth and the upper layer thickness are further limited, when the laser etching depth is greater than or equal to the upper layer thickness (high-compaction layer), the upper layer of high-compaction graphite can be etched through, lithium ions can quickly reach and leave the upper layer of graphite, and the lower layer of high-porosity graphite has a very fast lithium extraction speed without laser etching, can well match the lithium extraction speed of the upper layer, ensure sufficient ion high-speed channels, and enable the negative electrode to achieve a larger lithium extraction speed. Optionally, compared with a laser etching interval of greater than 4 mm, when the laser etching interval is 0.5 mm-4 mm, more sufficient lithium ion transmission channels can be met, and the lithium extraction speed can better meet the high-power demand. Compared with a laser etching interval of less than 0.5 mm, when the laser etching interval is 0.5 mm-4 mm, the electrode sheet is less likely to be damaged.

[0109] In the aspect of laser etching field mirrors, it can be known from Comparative Example 3 and Example 8 that when a continuous aperture field mirror is used for laser etching, the lithium ion transmission path is more than that of a point-shaped aperture, and thus the rate and cycle performance are better.

[0110] Unless otherwise specified, "about" as used herein is meant to encompass a range of values + / - 2% of the stated value. For example, about 100 is 100 + / - 2% x 100. Unless otherwise specified, "room temperature" and "ambient temperature" as used herein are about 20-30°C. "Between" as used herein includes the endpoints, for example, "between 2-3" includes the endpoints 2 and 3.

[0111] The embodiments of the present application have been described in detail above with reference to the drawings, but the present application is not limited to the above-described embodiments, and various changes can be made within the scope of knowledge of those skilled in the art without departing from the spirit of the present application. Furthermore, the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

Claims

1. A negative electrode sheet, characterized by, The negative electrode current collector and the first active material layer and the second active material layer arranged in sequence on the surface of the negative electrode current collector, the second active material layer is provided with a plurality of hole structures; wherein the porosity of the first active material layer is greater than the porosity of the second active material layer, and the compaction density of the first active material layer is less than the compaction density of the second active material layer.

2. The negative electrode sheet according to claim 1, characterized by, Along the direction of the second active material layer towards the first active material layer, the width of the hole structure cross section shows a decreasing trend.

3. The negative electrode sheet according to claim 1, wherein The hole structure includes a continuous and repeated hole unit along the width direction of the pole piece; the average distance d from the center of the hole unit to the edge, the center distance L of the adjacent repeated hole unit, L and d satisfy: 3.5d≥L>0.

4. The negative electrode sheet according to claim 3, characterized by Along the direction of the second active material layer towards the first active material layer, the depth of the hole structure is greater than or equal to the thickness of the second active material layer.

5. The negative electrode sheet according to claim 1, wherein The first active material layer is a first carbon material layer, and the second active material layer is a second carbon material layer.

6. The negative electrode sheet according to claim 1, wherein The porosity of the first active material layer is 25% to 50%, and the porosity of the second active material layer is 5% to 25%.

7. The negative electrode sheet according to claim 1, wherein The first active material layer has a compacted density of 1.40 to 1.70 g / cm 3 ; and the second active material layer has a compacted density of 1.60 to 1.85 g / cm 3 .

8. The negative electrode sheet according to claim 1, wherein The thickness ratio of the second active material layer to the first active material layer is 4:1 to 3:

2.

9. The negative electrode plate of claim 1, wherein, The volume of the hole structure is V1, the sum of the volumes of the first active material layer and the second active material layer is V2, and the ratio of V1 to V2 is 1:(30-110).

10. The negative electrode plate of claim 1, wherein, The two side surfaces of the negative electrode current collector are sequentially arranged with the first active material layer and the second active material layer.

11. A secondary battery characterized by comprising: The negative electrode pole piece of any one of claims 1-10.

12. An electrical device, characterized by The secondary battery of claim 11, the battery is used as a power supply for the electrical equipment. The secondary battery of claim 11, the battery is used as a power supply for the electrical equipment.

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