Quick-charge negative plate and battery

Abstract

According to the fast-charging negative electrode plate, in the fast-charging negative electrode plate, two sides of a current collector are coated with first graphite layers; the second graphite layer is coated on the first graphite layer, the porosity of the second graphite layer is higher than that of the first graphite layer, and a plurality of lithium ion linear diffusion channels extending vertically are distributed on the top surface of the second graphite layer in an array manner. The fast-charging negative plate has a gradient pore structure with high surface porosity, low tortuosity and low internal porosity, gives consideration to rate capability and energy density, and has a cost advantage.

Description

Technical Field

[0001] The utility model relates to the technical field of lithium-ion batteries, and in particular to a fast-charging negative electrode sheet and a battery. Background Art

[0002] The preparation of batteries with higher energy density and shorter charging time requires not only improvements in the battery materials themselves, but also improvements from engineering perspectives such as controlling electrode thickness, increasing porosity, and reducing tortuosity. The production of electrodes requires processes such as slurry mixing, coating, and rolling, and finally a porous active material layer with a tortuous diffusion path for carrier transport is obtained. Although tortuosity is closely related to porosity, porosity only describes the proportion of pores, and tortuosity focuses more on describing effective ion paths. Therefore, high-porosity electrodes do not necessarily have low tortuosity, such as when there are a large number of dead ends. Based on the porous structure of the electrode, tortuosity can be defined as the effective length of the ion transport path. If the tortuosity τ of a straight ion migration path is set to 1, the larger the τ, the more tortuous the path and the more difficult the ion transport.

[0003] In the case of high-load thick electrodes, high-rate performance is limited by the diffusion path in the electrode microstructure. As an important limiting factor, high tortuosity will directly affect the cycle stability and energy density of the battery. Reducing the length of the ion diffusion path helps to obtain faster and more effective diffusion, increase the limiting current density, and ultimately improve the electrolyte overpotential on the negative electrode side to avoid lithium plating at the negative electrode during fast charging. At the same time, designing a gradient pore structure graphite thick electrode with high surface porosity and low tortuosity and low internal porosity can increase the contact surface between the electrode and the electrolyte while strengthening the electronic conduction between the electrode and the current collector, which is expected to take into account both rate performance and volume energy density.

[0004] Chinese invention patent CN111312985A discloses a pole piece with a graded porosity distribution, and its preparation method and use. The slurry is coated on the current collector and dried to obtain a first film layer, and the slurry is coated on the first film layer and dried to obtain a second film layer. The method uses a pore-forming agent to increase the porosity of the second film layer. Furthermore, the distribution window of the porosity is controlled in multiple dimensions through different particle size stacking, cold pressing and low-temperature vacuum baking processes, so that the porosity of the pole piece is improved, and the thickness of the pole piece is less affected. However, the voids obtained by pore formation with the pore-forming agent are non-directional, and there are a large number of invalid dead zone channels. At the same time, the thick pole piece prepared by two coatings has the problem of insufficient adhesion.

[0005] The Chinese patent with publication number CN112151743A discloses a method for making holes in a thick electrode, its products and uses. The method comprises coating a slurry on the surface of a current collector with a surface roughness of Ra≥1um, drying, and obtaining the thick electrode. However, the patent uses air flow to blow air under the electrode to make holes during coating. In this method, the current collector must have holes, the current collector is easy to break, and the actual operation technology is difficult.

[0006] The above information disclosed in the background technology section is only used to enhance the understanding of the background of the present invention and therefore may contain information that does not constitute the prior art known to ordinary technicians in this field. Utility Model Content

[0007] The purpose of the utility model is to provide a fast-charging negative electrode sheet and a battery. The fast-charging negative electrode sheet has a gradient pore structure with high porosity and low tortuosity on the surface and low porosity inside, taking into account both rate performance and energy density, and having cost advantages.

[0008] In order to achieve the above purpose, the utility model provides the following technical solutions:

[0009] A fast-charging negative electrode sheet of the utility model comprises:

[0010] current collector;

[0011] A first graphite layer coated on both sides of the current collector;

[0012] The second graphite layer is coated on the first graphite layer and has a higher porosity than the first graphite layer. A plurality of vertically extending lithium ion linear diffusion channels are distributed in an array on the top surface of the second graphite layer.

[0013] In the fast-charging negative electrode sheet, the thickness of the second graphite layer is greater than that of the first graphite layer.

[0014] In the fast-charging negative electrode sheet, both sides of the current collector are coated with a first graphite layer, and the two first graphite layers are respectively coated with a second graphite layer.

[0015] In the fast-charging negative electrode sheet, the fast-charging negative electrode sheet is a symmetrical structure relative to the current collector.

[0016] In the fast-charging negative electrode sheet, the depth of the lithium ion linear diffusion channel is no more than half the thickness of the second graphite layer, so as to take into account both fast-charging performance and energy density.

[0017] In the fast-charging negative electrode sheet, the thickness of the second graphite layer is 60-100 μm, and the thickness of the first graphite layer is 10-30 μm.

[0018] In the fast-charging negative electrode sheet, the linear diffusion channel of lithium ions is a circular channel.

[0019] In the fast-charging negative electrode sheet, the pore diameter of the lithium ion linear diffusion channel is 5-70 μm, and the pore density is 400 to 3000 per mm2.

[0020] In the fast-charging negative electrode sheet, the pore depth of the lithium ion linear diffusion channel is 1 μm to 50 μm.

[0021] A battery comprises the fast-charging negative electrode sheet.

[0022] In the above technical solution, the utility model provides a fast-charging negative electrode sheet, which has the following beneficial effects:

[0023] 1. The utility model creates vertical channels in the second graphite layer in a directionally manner, and the pores have the characteristics of low tortuosity, which avoids the problems of high tortuosity and a large number of dead ends in traditional high-porosity electrodes, helps to obtain faster and more effective diffusion, provides more lithium insertion active sites, and shortens Li + Increasing the solid-phase diffusion distance in the graphite negative electrode and the limiting current density can effectively improve the fast charging performance of lithium-ion batteries.

[0024] 2. The first graphite layer of the utility model is located near the current collector, and has the characteristics of low porosity and high conductivity, which can effectively reduce the contact resistance between the graphite layer and the current collector, and transfer the electrons transmitted from the upper layer to the current collector more quickly. It works synergistically with the second graphite layer to comprehensively improve the transmission rate of electrons and lithium ions.

[0025] 3. The utility model provides a fast-charging negative electrode sheet with a dual-gradient structure. The lithium insertion capacity of the negative electrode sheet gradually decreases from the electrolyte to the current collector, and a gradient reaction speed can be formed during fast charging to improve the overall lithium insertion capacity of the negative electrode sheet.

[0026] 4. The lithium battery of the present invention has high energy density and high rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present utility model. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0028] Figure 1 A schematic structural diagram of a fast-charging negative electrode sheet provided in an embodiment of the utility model.

[0029] Figure 2This is a SEM image of a fast-charging negative electrode sheet provided in an embodiment of the utility model.

[0030] Figure 3 A comparison diagram of a fast-charging negative electrode sheet provided in an embodiment of the utility model and a negative electrode sheet with a different structure provided in a comparative example, which are obtained by disassembling a negative electrode sheet after full charge after fast charging. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the implementation of the utility model clearer, the technical solution in the implementation of the utility model will be clearly and completely described below in conjunction with the drawings in the implementation of the utility model. Obviously, the described implementation is a part of the implementation of the utility model, not all of the implementations. Based on the implementation of the utility model, all other implementations obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0032] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

[0033] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0034] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0035] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present utility model, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0036] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0037] In the present utility model, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0038] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below in conjunction with the accompanying drawings.

[0039] See also Figure 1-3 As shown, in one embodiment, a fast-charging negative electrode sheet of the utility model includes:

[0040] current collector 1;

[0041] A first graphite layer 2, coated on both sides of the current collector 1;

[0042] The second graphite layer 3 is coated on the first graphite layer 2 and has a higher porosity than the first graphite layer 2 . A plurality of vertically extending lithium ion linear diffusion channels are distributed in an array on the top surface of the second graphite layer 3 .

[0043] In a preferred embodiment of the fast-charging negative electrode sheet, the first graphite layer contains a plurality of conductive agents, and the conductive agents in the first graphite layer include two or more of SP, KS-6, carbon nanotubes and graphene, etc.; the amount of the conductive agent is 2% to 5%. The obtained electrode has an efficient conductive network, which effectively improves the electronic conductivity between the bottom graphite layer and the bottom graphite layer and the current collector.

[0044] In a preferred embodiment of the fast-charging negative electrode sheet, the thickness of the second graphite layer 3 is greater than that of the first graphite layer 2 .

[0045] In a preferred embodiment of the fast-charging negative electrode sheet, both sides of the current collector 1 are coated with a first graphite layer 2 , and the two first graphite layers 2 are respectively coated with a second graphite layer 3 .

[0046] In a preferred embodiment of the fast-charging negative electrode sheet, the fast-charging negative electrode sheet is a symmetrical structure relative to the current collector 1.

[0047] In a preferred embodiment of the fast-charging negative electrode sheet, the depth of the lithium ion linear diffusion channel is no more than half the thickness of the second graphite layer 3 .

[0048] In a preferred embodiment of the fast-charging negative electrode sheet, the thickness of the second graphite layer 3 is 60-100 μm, and the thickness of the first graphite layer 2 is 10-30 μm.

[0049] In a preferred embodiment of the fast-charging negative electrode sheet, the linear diffusion channel of lithium ions is a circular channel.

[0050] In a preferred embodiment of the fast-charging negative electrode sheet, the pore diameter of the lithium ion linear diffusion channel is 5-70 μm, and the pore density is 400-3000 / mm 2 .

[0051] In a preferred embodiment of the fast-charging negative electrode sheet, the pore depth of the lithium ion linear diffusion channel is 1 μm to 50 μm.

[0052] A battery comprises the fast-charging negative electrode sheet.

[0053] In one embodiment, the structure of the fast-charging negative electrode sheet includes coating the first graphite layer 2 and the second electric graphite layer 3 on both sides of the current collector 1; the second graphite layer 3 is laser-engraved to obtain a linear diffusion channel for lithium ions; the graphite material of the first graphite layer 2 is low-cost graphite commonly found in the market. The graphite material of the second graphite layer 3 is fast-charging graphite commonly found in the market. The amount of the conductive agent used in the slurry of the first graphite layer 2 during the homogenization process is 2% to 5%; the conductive agent includes two or more of SP, KS-6, carbon nanotubes, and graphene. After the second graphite layer 3 is subjected to the rolling process, its thickness is 60-100 μm, and after the first graphite layer 2 is subjected to the rolling process, its thickness is 10-30 μm. The second graphite layer 3 and the first graphite layer 2 are simultaneously coated on the current collector 1 by extrusion coating. The vertical channels enable the negative electrode surface layer to form a highly porous and low-tortuosity linear diffusion channel for lithium ions. At the same time, it can also increase the penetration depth of the electrolyte, provide more active sites for lithium insertion, and effectively shorten the Li +The solid phase diffusion distance in the graphite negative electrode enhances the lithium ion embedding ability. The porosity of the first graphite layer 2 is lower than that of the second graphite layer 3, which matches the low lithium concentration in the bottom layer of the thick electrode and the fewer lithium embedding active sites required. Compared with randomly distributed and single gradient distributed electrodes, the dual gradient structure electrode has a higher utilization rate of active materials at high current density. The lithium embedding ability of the negative electrode sheet is gradually reduced from the electrolyte to the current collector 1, and a gradient reaction speed can be formed during fast charging, thereby improving the overall lithium embedding ability of the negative electrode sheet. At the same time, the first graphite layer 2 is a highly conductive graphite layer, which has a denser structure and more highly conductive substances, so that the second graphite layer 3 has excellent electronic conductivity. This layer is arranged near the current collector 1 side, which can effectively reduce the contact resistance between the graphite layer and the current collector 1 and reduce the internal resistance of the electrode sheet.

[0054] In order to further study the lithium plating of negative electrode sheets with different structures, the rate performance of the battery and the fast charging capacity retention rate during fast charging, we also provide examples and comparative examples.

[0055] Example 1: The negative electrode is coated with the above-mentioned double-layer coating technology. The first graphite layer 2 uses a low-cost graphite from BYD Company. The mass ratio of water, graphite, SP, carbon nanotubes, CMC and SBR in the prepared slurry is 100:94:2:2:1:1; the second graphite layer uses a fast-charging graphite from BYD Company. The mass ratio of water, graphite, SP, CMC and SBR in the prepared slurry is 100:96.5:1.5:1:1. After coating, baking, rolling, slitting and die-cutting, the thickness of the first graphite layer is 20μm, and the thickness of the second graphite layer is 80μm. The second graphite layer 2 is laser engraved to form holes, and the hole diameter of the laser engraved holes is controlled to be 35μm and the hole density is 800.

[0056] / mm 2 The hole depth is 20 μm. The prepared electrode was tested by SEM. Figure 1 As shown, holes of a certain depth are evenly distributed in the pole piece.

[0057] The prepared electrode is matched with the corresponding positive electrode, and the processes of lamination, packaging, liquid injection, and formation are completed. The prepared battery cell is subjected to rate charging test, 15-week fast charging cycle test, and 100-week fast charging cycle test under room temperature conditions.

[0058] Comparative Example 1: The negative electrode is extrusion coated, and only the fast-charging graphite layer is coated. A fast-charging graphite of BTR is used, and the mass ratio of water, graphite, SP, CMC and SBR in the prepared slurry is 100:96.5:1.5:1:1. After coating, baking, rolling, slitting and die-cutting, the thickness of the fast-charging graphite layer is 100μm.

[0059] The prepared electrode is matched with the corresponding positive electrode, and the processes of lamination, packaging, liquid injection, and formation are completed. The prepared battery cell is subjected to rate charging test, 15-week fast charging cycle test, and 100-week fast charging cycle test under room temperature conditions.

[0060] Rate charging test, the specific test conditions are as follows:

[0061] (1) Stand for 60 min; discharge at 1C constant current to 3.0V, and constant voltage to 0.1C;

[0062] (2) Stand for 60 min; charge at 1C constant current to 4.3 V, and constant voltage to 0.05C; stand for 60 min; discharge at 1C to 3.0 V, and constant voltage to 0.1C;

[0063] (3) Stand for 60 min; charge at 2C constant current to 4.3 V, and constant voltage to 0.05C; stand for 60 min; discharge at 1C to 3.0 V, and constant voltage to 0.1C;

[0064] (4) Stand for 60 min; charge at 4C constant current to 4.3 V, and constant voltage to 0.05C; stand for 60 min; discharge at 1C to 3.0 V, and constant voltage to 0.1C;

[0065] (5) Stand for 60 min; charge at 6C constant current to 4.3 V, and constant voltage to 0.05C; stand for 60 min; discharge at 1C to 3.0 V, and constant voltage to 0.1C;

[0066] Fast charging 15-week cycle test, the specific test conditions are as follows:

[0067] (1) Stand for 60 minutes; discharge at 1C to 3.0V;

[0068] (2) Stand for 60 min; charge at 6C to 4.1V, and then charge at constant voltage to 4C;

[0069] (3) 4C charging to 4.2V, constant voltage to 3C;

[0070] (4) 3C charging to 4.25V, constant voltage to 2C;

[0071] (5) 2C charging to 4.3V, constant voltage to 0.05C;

[0072] (6) The above steps are repeated 15 times.

[0073] Fast charging 100-week cycle test:

[0074] (1) Stand for 60 minutes; discharge at 1C to 3.0V;

[0075] (2) Stand for 60 min; charge at 6C to 4.1V, and then charge at constant voltage to 4C;

[0076] (3) 4C charging to 4.2V, constant voltage to 3C;

[0077] (4) 3C charging to 4.25V, constant voltage to 2C;

[0078] (5) 2C charging to 4.3V, constant voltage to 0.05C;

[0079] (6) The above steps are repeated 100 times.

[0080] Table 1 Performance test results comparison table

[0081]

[0082] As shown in Table 1, the rate charging performance of Example 1 is much better than that of Comparative Example 1. After 100 cycles of fast charging, the capacity retention rate of Example 1 is 97.6%, while Comparative Example 1 has severe capacity decay, with a capacity retention rate of only 69.1%. After 15 weeks of fast charging, the battery cell is disassembled. The disassembled pole piece corresponding to Example 1 has no lithium deposition, while the disassembled pole piece corresponding to Comparative Example 1 has lithium deposition.

[0083] Finally, it should be noted that the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making any creative work are within the scope of protection of the present application.

[0084] The above only describes some exemplary embodiments of the present invention by way of illustration. It is undoubted that those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A fast-charging negative electrode sheet, characterized in that: These include, current collector; A first graphite layer coated on both sides of the current collector; The second graphite layer is coated on the first graphite layer and has a higher porosity than the first graphite layer. A plurality of vertically extending lithium ion linear diffusion channels are distributed in an array on the top surface of the second graphite layer.

2. A fast-charging negative electrode sheet according to claim 1, characterized in that: The second graphite layer is thicker than the first graphite layer.

3. A fast-charging negative electrode sheet according to claim 1, characterized in that: Both sides of the current collector are coated with a first graphite layer, and the two first graphite layers are respectively coated with a second graphite layer.

4. A fast-charging negative electrode sheet according to claim 1, characterized in that: The fast-charging negative electrode sheet is a symmetrical structure relative to the current collector.

5. The fast-charging negative electrode sheet according to claim 1, characterized in that: The depth of the lithium ion linear diffusion channel is no more than half the thickness of the second graphite layer.

6. A fast-charging negative electrode sheet according to claim 1, characterized in that: The thickness of the second graphite layer is 60-100 μm, and the thickness of the first graphite layer is 10-30 μm.

7. The fast-charging negative electrode sheet according to claim 1, characterized in that: The linear diffusion channel of lithium ions is a circular channel.

8. A fast-charging negative electrode sheet according to claim 7, characterized in that: The pore diameter of the lithium ion linear diffusion channel is 5-70 μm, and the pore density is 400-3000 / mm 2 .

9. A fast-charging negative electrode sheet according to claim 7, characterized in that: The pore depth of the lithium ion linear diffusion channel is 1 μm to 50 μm.

10. A battery, characterized in that: It includes the fast-charging negative electrode sheet described in any one of claims 1 to 9.

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