Negative pole piece, battery cell, preparation method of battery cell and battery

Abstract

The invention relates to the technical field of batteries, in particular to a negative pole piece, a battery cell, a preparation method of the battery cell and a battery. The negative pole piece provided by the invention comprises a region which is overlapped with the positive pole piece after being overlapped and a region which is not overlapped with the positive pole piece after being overlapped, the non-overlapped region at least comprises a first outer edge region and a second outer edge region which is positioned on the opposite side of the first outer edge region, and the overlapped region at least comprises a first inner edge region which is adjacent to the first outer edge region; the first outer edge area is adjacent to the first inner edge area, the second inner edge area is adjacent to the second outer edge area, and the first outer edge area, the first inner edge area, the second outer edge area and the second inner edge area are each provided with a concave structure. The negative pole piece provided by the invention can improve the cycle capacity retention ratio of the battery to a certain extent while reducing the lithium precipitation of the negative pole piece and ensuring the safety of the battery, thereby effectively improving the performance of the battery and prolonging the service life of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a negative electrode sheet, a battery cell, a method for preparing the battery cell, and a battery. Background Art

[0002] Secondary batteries, particularly lithium-ion batteries, have been widely used in electric vehicles and consumer electronics due to their high energy density, excellent output power, and long cycle life. The battery cell, the core component of a secondary battery responsible for the electrochemical reaction, is primarily composed of a wound or stacked positive and negative electrode sheets, with a separator between them to ensure proper battery operation. During battery assembly design, the negative electrode sheet is often designed to extend beyond the positive electrode sheet by a certain length and width, creating a so-called "overhang" region. This occurs because during charging, lithium ions from the positive electrode migrate to the negative electrode and embed within it. If the negative electrode lacks sufficient space to accommodate these lithium ions, they precipitate on the negative electrode surface, forming lithium dendrites. These dendrites can pierce the separator, causing an internal short circuit and potentially leading to safety issues such as thermal runaway. The overhang region provides additional negative electrode area, reducing the risk of lithium ion precipitation on the negative electrode surface. However, excessive overhang can reduce the battery's initial efficiency and capacity, and increase self-discharge capacity, thereby affecting battery performance. Therefore, a balance needs to be found between security and performance.

[0003] At present, there are mainly the following ways to treat the overhang area: (1) Strip groove treatment in the overhang area: Through laser etching process, strip grooves are made in the overhang area to regulate the dynamics of the area and improve the lithium deposition problem in the overhang area; (2) Surface coating treatment in the overhang area: A layer of high swelling, high liquid absorption and liquid retention material is coated on the overhang area to regulate the dynamics of the area and improve the lithium deposition problem in the overhang area; (3) Coating different materials in the overhang area: Different dynamic materials are coated on the overhang area and the main coating area to improve the lithium deposition problem in the overhang area through the dynamic difference of the materials.

[0004] Although the existing treatment methods can improve the lithium plating problem to a certain extent and balance the safety and performance of the battery, there are still some shortcomings: (1) Laser etching will generate dust, which will affect the self-discharge of the battery cell, and the equipment cost is high. The width of the overhang area is usually between 0.5mm and 3mm, and the precision requirements for laser dwell time, distance control, etc. are very high, and the amount of dust is large; (2) The surface coating treatment requires secondary coating, and the coating film width and thickness window are extremely narrow, which makes the actual operation very difficult; (3) Different materials are coated in the overhang area, and the processing window is also narrow, and there is a fusion zone between the two materials. If the fusion zone is too thick, the bulge edge will be rolled up later, and if it is too thin, the NP ratio (the ratio of the negative electrode capacity to the positive electrode capacity) will be reduced, and lithium plating will be easy during the cycle process.

[0005] Therefore, the art needs a new technical solution that can effectively solve the lithium plating problem and balance the safety and performance of the battery. Summary of the Invention

[0006] The present invention aims to solve the above technical problem, that is, to solve the technical problem that lithium is easily deposited on existing electrode plates.

[0007] In a first aspect, the present invention provides a negative electrode plate, comprising an area overlapping with the positive electrode plate after stacking and an area not overlapping, the non-overlapping area comprising at least a first outer edge region, and a second outer edge region located opposite the first outer edge region, the overlapping area comprising at least a first inner edge region adjacent to the first outer edge region, and a second inner edge region adjacent to the second outer edge region, wherein a recessed structure is provided in the first outer edge region, the first inner edge region, the second outer edge region, and the second inner edge region.

[0008] In a preferred embodiment of the above-mentioned negative electrode plate, the non-overlapping area also includes a third outer edge area and a fourth outer edge area, the fourth outer edge area is arranged opposite to the third outer edge area, and is constructed as a frame structure with the first outer edge area and the second outer edge area, the overlapping area also includes a third inner edge area adjacent to the third outer edge area, and a fourth inner edge area adjacent to the fourth outer edge area, wherein the third outer edge area, the third inner edge area, the fourth outer edge area, and the fourth inner edge area are all provided with a recessed structure.

[0009] In a preferred embodiment of the above-mentioned negative electrode plate, the recessed structure is a plurality of micropores.

[0010] In a preferred embodiment of the above-mentioned negative electrode sheet, some or all of the plurality of micropores are non-through micropores, or all of the plurality of micropores are through micropores.

[0011] In the preferred embodiment of the above-mentioned negative electrode sheet, the pore diameter r of the micropores is 20 μm≤r≤60 μm; and / or

[0012] The micropores are evenly distributed, and the pore spacing d of the micropores is 30 μm≤d≤100 μm.

[0013] In a preferred embodiment of the above-mentioned negative electrode plate, the negative electrode plate includes an active material layer, the micropores are formed on the active material layer, the thickness of the active material layer is H, the depth of the micropores is h, and 1 / 4≤h / H≤3 / 4.

[0014] In the preferred embodiment of the above-mentioned negative electrode sheet, the width of the first inner edge region is 0.5 mm to 5 mm; and / or

[0015] The width of the second inner edge area is 0.5 mm to 5 mm; and / or

[0016] The width of the third inner edge area is 0.5mm-5mm; and / or

[0017] The width of the fourth inner edge area is 0.5 mm to 5 mm.

[0018] In a preferred embodiment of the above-mentioned negative electrode sheet, the shape of the micropores is at least one of circular, elliptical, and polygonal.

[0019] The negative electrode plate provided by the present invention, when applied to a wound battery, provides a recessed structure, such as a microporous structure, in the first outer edge region, the first inner edge region, the second outer edge region, and the second inner edge region, so that the hierarchical dynamic performance of these regions is improved, thereby increasing the rate of lithium ion release in these regions during the subsequent discharge process of the battery cell, thereby avoiding the accumulation of lithium in these regions during the charge and discharge process. This can not only effectively reduce lithium plating of the negative electrode plate and ensure battery safety, but also improve the battery's cycle capacity retention rate to a certain extent, thereby effectively improving the performance and life of the battery using the negative electrode plate.

[0020] In a second aspect, the present invention further provides a battery cell comprising the negative electrode sheet described in any one of the aforementioned technical solutions.

[0021] In a third aspect, the present invention further provides a method for preparing a battery cell, the method comprising:

[0022] preparing a positive electrode sheet;

[0023] Prepare a negative electrode sheet, wherein the negative electrode sheet is the negative electrode sheet described in any one of the above items;

[0024] The positive electrode sheet, the separator and the negative electrode sheet are stacked in sequence.

[0025] In some feasible embodiments of the above-mentioned method for preparing the battery cell, the micropores are formed by needle roller extrusion.

[0026] Micro-hole processing is performed in the above-mentioned areas by using a needle roller instead of a laser. This has the advantages of no dust generation, small fluctuation in the thickness of the pole piece, simple processing process, and compatibility with rolling, die-cutting, winding and other equipment. It has strong mass production operability and significant performance improvement.

[0027] In a fourth aspect, the present invention further provides a battery, comprising the battery cell described in any one of the aforementioned technical solutions.

[0028] In a fourth aspect, the present invention further provides a battery, comprising at least one battery cell, wherein the battery cell is manufactured by the battery cell preparation method described in any one of the aforementioned technical solutions.

[0029] Those skilled in the art will understand that, since the battery cell, the method for preparing the battery cell, and the battery provided by the present invention include the aforementioned negative electrode sheet, they have all the technical effects that can be obtained by the aforementioned negative electrode sheet, which will not be elaborated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The preferred embodiments of the present invention are described below with reference to the accompanying drawings, in which:

[0031] Figure 1 A schematic top view of the structure of a battery cell for a laminated battery provided in an embodiment of the present invention;

[0032] Figure 2 for Figure 1 AA section view;

[0033] Figure 3 for Figure 1 A partial enlarged schematic diagram of point B in the middle;

[0034] Figure 4 A schematic structural diagram of a negative electrode sheet in a battery cell for a laminated battery provided by an embodiment of the present invention;

[0035] Figure 5 A schematic diagram of the structure of a stacked battery cell provided in an embodiment of the present invention, wherein the separator is not shown;

[0036] Figure 6 A schematic structural diagram of a negative electrode sheet in a wound battery cell provided by an embodiment of the present invention;

[0037] Figure 7 A schematic structural diagram of a wound battery cell according to an embodiment of the present invention, wherein the separator is not shown;

[0038] Figure 8 A schematic top view of a battery cell for a laminated battery according to another embodiment of the present invention;

[0039] List of reference numerals:

[0040] 1. Diaphragm; 2. Negative electrode plate; 21. First edge region; 211. First outer edge region; 212. First inner edge region; 22. Second edge region; 221. Second outer edge region; 222. Second inner edge region; 23. Third edge region; 231. Third outer edge region; 232. Third inner edge region; 24. Fourth edge region; 241. Fourth outer edge region; 242. Fourth inner edge region; 25. Middle region; 26. Micropore; 3. Positive electrode plate; 31. Positive electrode edge insulating layer; 4. Positive electrode tab; 5. Negative electrode tab. DETAILED DESCRIPTION

[0041] Preferred embodiments of the present invention are described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are intended only to illustrate the technical principles of the present invention and are not intended to limit the scope of protection of the present invention. Those skilled in the art may adjust these embodiments as needed to suit specific applications.

[0042] In order to better illustrate the present invention, numerous specific details are given in the following detailed description. It should be understood by those skilled in the art that the present invention can also be implemented without certain specific details.

[0043] In the description of the present invention, terms such as "upper," "lower," "inner," "outer," "front," and "back" indicating directions or positional relationships are based on the directions or positional relationships shown in the figures. This is for ease of description only and does not indicate or imply that the device to be protected must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, the orientations described in the following embodiments should not be construed as limitations on the present invention. Furthermore, ordinal numbers such as "first" and "second" are used for convenience only and are not intended to indicate or imply relative importance.

[0044] Furthermore, it should be noted that, in the description of the present invention, unless otherwise expressly specified or limited, the terms "mounted" and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; and direct or indirect connections through an intermediary. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0045] Reference below Figures 1 to 8 The negative electrode sheet provided in the embodiments of the present invention and the battery cell and battery made of the negative electrode sheet are described.

[0046] The battery cell provided by the embodiment of the present invention includes a positive electrode sheet 3, a negative electrode sheet 2, a separator 1, an electrolyte (not shown), etc. Figure 1 and Figure 2 As shown in the figure, the positive electrode sheet 3, the separator 1 and the negative electrode sheet 2 are stacked in sequence to form a battery cell. The battery cell can be formed into a battery in a winding manner or in a stacking manner. The stacking manner is further divided into bag-making stacking and Z-shaped stacking. Figure 1 FIG. 1 shows a schematic diagram of a cell structure suitable for forming a battery by bag-making lamination, as shown in FIG. Figure 1 As shown in , the negative electrode sheet 2 exceeds the positive electrode sheet 3 by a certain range in both the length and width directions, and the diaphragm 1 exceeds the negative electrode sheet 2 by a certain range in both the length and width directions to ensure that the positive electrode sheet 3 and the negative electrode sheet 2 can be fully isolated. This type of battery cell is called a negative-electrode-in-positive battery cell. In addition, a positive electrode edge insulation layer 31 is provided on one side of the positive electrode sheet 3, which is used to prevent short circuits and improve battery safety. The positive electrode sheet 3 is connected to a positive electrode tab 4, and the negative electrode sheet 2 is connected to a negative electrode tab 5. As shown in Figure 1 As shown in , the positive electrode tab and the negative electrode tab are located on the same side of the battery cell. Alternatively, it can also be as follows Figure 8 As shown in , the positive electrode tab and the negative electrode tab are located on different sides of the battery cell. When preparing a battery, the battery cell is placed in a shell, liquid is injected into the shell, and the battery is manufactured after the formation and capacity separation processes.

[0047] like Figure 2 and Figure 4 As shown in , the negative electrode plate 2 provided in the embodiment of the present invention includes an area overlapping with the positive electrode plate 3 and an area not overlapping, wherein the area of ​​the overlapping area is equal to the area of ​​the positive electrode plate, and the area of ​​the non-overlapping area is the excess area of ​​the negative electrode plate over the positive electrode plate. Figure 1 and Figure 4 As shown, the non-overlapping area is the outer edge area of ​​the negative electrode sheet, including the first outer edge area 211, the second outer edge area 221, the third outer edge area 231 and the fourth outer edge area 241. The first outer edge area 211 and the third outer edge area 231 are arranged opposite to each other, and the second outer edge area 221 and the fourth outer edge area 241 are arranged opposite to each other. The first outer edge area 211, the second outer edge area 221, the third outer edge area 231 and the fourth outer edge area 241 are connected and form a Figure 4 The box structure shown in . Figure 1 、 Figure 2 and Figure 4As shown, the overlapping area includes an inner edge area and a middle area 25. The inner edge area is an area adjacent to the outer edge area, including a first inner edge area 212, a second inner edge area 222, a third inner edge area 232 and a fourth inner edge area 242. The first inner edge area 212 and the third inner edge area 232 are arranged opposite to each other, and the second inner edge area 222 and the fourth inner edge area 242 are arranged opposite to each other. The first inner edge area 212 is adjacent to the first outer edge area 211, and together they constitute the first edge area 21; the second inner edge area 222 is adjacent to the second outer edge area 221, and together they constitute the second edge area 22; the third inner edge area 232 is adjacent to the third outer edge area 231, and together they constitute the third edge area 23; the fourth inner edge area 242 is adjacent to the fourth outer edge area 241, and together they constitute the fourth edge area 24. The first inner edge area 212, the second inner edge area 222, the third inner edge area 232 and the fourth inner edge area 242 are connected and form as shown in the figure. Figure 4 The size of the frame structure shown is smaller than the size of the frame structure formed by connecting the outer edge areas. Figure 4 As shown in , the overlapping area also includes a middle area 25. In this embodiment, the sum of the area of ​​the middle area 25 and the area of ​​the inner edge area is equal to the area of ​​the positive electrode sheet.

[0048] In order to reduce the problem of lithium plating of the negative electrode 2 and to balance the safety and performance of the battery, in the embodiment of the present invention, the first outer edge area 211, the second outer edge area 221, the third outer edge area 231 and the fourth outer edge area 241, as well as the first inner edge area 212, the second inner edge area 222, the third inner edge area 232 and the fourth inner edge area 242 are all provided with a recessed structure. Specifically, the recessed structure in the embodiment of the present invention is a plurality of micropores 26. Figure 3 As shown in FIG, all the micropores 26 in the embodiment of the present invention are through micropores 26, the pore diameter r of the micropores 26 is 20 μm ≤ r ≤ 60 μm, the micropores 26 are evenly distributed, and the pore spacing d between each micropore 26 is 30 μm ≤ d ≤ 100 μm. The pore spacing refers to the distance between the centers of adjacent micropores 26. The pore spacing d is as shown in FIG. Figure 3 As shown in .

[0049] Specifically, the negative electrode sheet 2 primarily comprises a negative electrode current collector and an active material layer. The negative electrode current collector, typically made of copper foil, is used to support the negative electrode active material and conduct current. The active material, typically composed of active materials such as graphite and silicon, as well as a conductive agent and a binder, is coated on the surface of the negative electrode current collector. These active materials undergo a reduction reaction during discharge, releasing energy. The micropores 26 in this embodiment of the present invention are formed in the active material layer.

[0050] Alternatively, the micropores 26 may be partially or completely non-through. Specifically, if the thickness of the active material layer is H and the depth of the micropores 26 is h, then 1 / 4 ≤ h / H ≤ 3 / 4, where the depth h of the micropores 26 refers to the depth of the active material layer's surface away from the current collector recessed toward the current collector.

[0051] Here, “penetrating” means penetrating the active material layer of the negative electrode sheet but not penetrating the current collector, and “non-penetrating” means not penetrating the active material layer.

[0052] Furthermore, in this embodiment, the widths of the first inner edge zone 212, the second inner edge zone 222, the third inner edge zone 232, and the fourth inner edge zone 242 are the same, and the corresponding widths are 0.5 mm to 5 mm. Alternatively, the widths of the respective inner edge zones may be different. Specifically, the width of the first inner edge zone 212 is 0.5 mm to 5 mm, the width of the second inner edge zone 222 is 0.5 mm to 5 mm, the width of the third inner edge zone 232 is 0.5 mm to 5 mm, and the width of the fourth inner edge zone 242 is 0.5 mm to 5 mm. For example, the first inner edge zone 212 and the second inner edge zone 222 have the same width and are both 4 mm, and the third inner edge zone 232 and the fourth inner edge zone 242 have the same width and are both 3 mm, etc.

[0053] It should be noted that the numerical values ​​in the above examples are merely exemplary and should not be construed to limit the scope of protection of the present invention.

[0054] In this embodiment, the shape of the micropores 26 is circular. Alternatively, the shape of the micropores 26 can also be at least one of an ellipse and a polygon. Preferably, the plurality of micropores 26 are evenly distributed, such as Figure 3 As shown in FIG, the sizes and spacings of the micro-holes 26 are the same.

[0055] Alternatively, the recessed structure in the present invention may also be a plurality of strip-shaped groove structures that are arranged continuously or discontinuously, and each strip-shaped groove structure may be through-hole or non-through-hole.

[0056] The stacked battery cells are as follows Figure 5 As shown in Figure 5 The diaphragm is hidden in the figure, and it can be seen that in the battery cell, the shape of the negative electrode plate is no different from the shape before lamination.

[0057] In another embodiment of the present invention, the battery is formed in a wound manner. Figure 6 and Figure 7As shown in , when the battery is formed in a winding manner, the non-overlapping area of ​​the corresponding negative electrode sheet only includes the first outer edge area 211 and the second outer edge area 221, and the first outer edge area 211 and the second outer edge area 221 are arranged opposite to each other. Accordingly, the overlapping area includes the first inner edge area 212 adjacent to the first outer edge area 211, and the second inner edge area 222 adjacent to the second outer edge area 221, and the middle area 25 between the first inner edge area 212 and the second inner edge area 222. This is because the winding method is based on Figure 6 The width direction of the winding is the axis, and the wound battery cell is as follows Figure 7 As shown in .

[0058] It should be noted that when the above-mentioned battery cell is used to prepare a wound battery, whether the tab arrangement shown in 1 is adopted or Figure 8 The arrangement of the tabs shown only requires Figure 6 or Figure 7 The first edge region 21 and the second edge region 22 of the negative electrode sheet are provided with micropores 26. When preparing a laminated battery, whether the tab arrangement shown in FIG. 1 or the tab arrangement shown in FIG. Figure 8 The arrangement of the tabs shown in the figure requires Figure 4 or Figure 5 The first edge region 21 , the second edge region 22 , the third edge region 23 and the fourth edge region 24 of the negative electrode sheet shown in FIG are all provided with micropores 26 .

[0059] A method for preparing a battery cell comprising the above-mentioned negative electrode sheet is provided below.

[0060] Specifically, the method for preparing the battery cell in this embodiment includes:

[0061] S10, preparing a positive electrode sheet.

[0062] A positive electrode sheet generally refers to an electrode sheet with a high potential that contains an active substance that undergoes a reduction reaction during discharge. It consists of a positive electrode current collector and a positive electrode active material layer, with the positive electrode active material layer being coated on the surface of the positive electrode current collector. In some cases, the positive electrode current collector not coated with the positive electrode active material layer protrudes from the positive electrode current collector coated with the positive electrode active material layer, and this portion serves as the positive electrode tab for connection to an external circuit. In this embodiment, a positive electrode edge insulation layer is further provided on one side of the positive electrode current collector not coated with the positive electrode active material layer, and the positive electrode edge insulation layer is interposed between the positive electrode tab and the positive electrode current collector coated with the positive electrode active material layer.

[0063] Common cathode current collector materials are metals, such as aluminum foil. Aluminum foil has good conductivity and mechanical strength, meeting the battery's current collector requirements. In some cases, other elements, such as silicon, may be added to the aluminum foil to improve its performance.

[0064] The positive electrode active material is a key component in the battery's chemical reactions. Common positive electrode active materials include lithium cobalt oxide, lithium iron phosphate, ternary lithium (such as lithium nickel cobalt manganese oxide), and lithium manganese oxide. These active materials have different electrochemical properties and cost-effectiveness, so the choice can be based on specific application requirements.

[0065] Specifically, in this embodiment, the preparation process of the positive electrode sheet is as follows:

[0066] S101. LiFePO4 (lithium iron phosphate or lithium ferrous phosphate), SP (superconductive powder), and PVDF (polyvinylidene fluoride) are uniformly dispersed in NMP (N-Methylpyrrolidone) at a mass ratio of 96.5%:1.5%:2% to form a positive electrode slurry. SP is used to improve the battery's conductivity and is typically employed in the form of carbon black or conductive fibers. PVDF acts as a binder, uniformly dispersing the positive electrode material (such as LiFePO4) and the conductive agent in the slurry and ensuring the coated electrode has good mechanical strength and electrochemical properties. NMP serves as a slurry solvent, acting as a carrier for the conductive agent and positive electrode material. Through stirring and mixing with NMP, the conductive agent and positive electrode material are uniformly dispersed in the slurry. NMP also has a stable chemical structure, maintaining the stability of the slurry and reducing the probability of battery fire or explosion.

[0067] S102: coating.

[0068] Specifically, coating refers to evenly applying the positive electrode slurry to the current collector (such as aluminum foil) to form a wet coating of a certain thickness. Taking the positive electrode sheet of a lithium-ion battery as an example, the coating method of the positive electrode sheet is: using a tool such as a four-sided film applicator, the positive electrode slurry is evenly applied to the aluminum foil and then scraped from top to bottom with the desired film thickness.

[0069] S103: Drying.

[0070] Specifically, drying refers to removing solvents (such as NMP) from the wet coating, allowing the coating to dry and solidify. Drying methods include static drying or hot air drying. Static drying uses an electrically heated constant-temperature forced-air drying oven, while hot air drying uses a hot air dryer with adjustable drying temperature and air speed.

[0071] S104: Roller pressing.

[0072] Specifically, rolling refers to compacting the electrode sheet using a roller press to improve its density and mechanical strength. Rolling method: Use a roller press to roll the electrode sheet, adjust the roller pressure according to the characteristics of the electrode material, maintain a stable rolling speed, and monitor the electrode thickness and compaction density.

[0073] S105, die-cutting and slicing to make positive electrode sheets.

[0074] Specifically, die-cutting and slicing refers to cutting the rolled electrode sheets into specific shapes and sizes according to design requirements. Die-cutting and slicing method: Use a die-cutting machine to die-cut and slice the rolled electrode sheets. According to the design requirements, the appropriate mold and cutting parameters are selected to form the positive electrode sheets required for battery cell production.

[0075] S20, preparing a negative electrode sheet.

[0076] Specifically, the steps for preparing the negative electrode sheet are as follows:

[0077] S201. Artificial graphite, SP (Superconductive Powder), CMC (Carboxymethyl Cellulose Sodium), and styrene-butadiene rubber are evenly dispersed in deionized water at a mass ratio of 96%:1.2%:1%:1.8% to form a negative electrode slurry. Artificial graphite serves as the negative electrode active material, providing the majority of the battery's capacity. SP is used to increase the conductivity of the negative electrode material, ensuring smooth current flow within the battery. CMC acts as a binder, securing the active material, conductive agent, etc. to the negative electrode current collector and maintaining the structural stability of the negative electrode sheet. Styrene-butadiene rubber has excellent physical and chemical properties, such as wear resistance and aging resistance, which can enhance the durability and stability of the negative electrode sheet. Deionized water serves as a solvent to help evenly disperse the various components.

[0078] S202: coating.

[0079] Specifically, the coating of the negative electrode sheet is similar to that of the positive electrode sheet, and will not be described in detail here.

[0080] S203: Drying.

[0081] Specifically, the drying of the negative electrode sheet is similar to that of the positive electrode sheet, and will not be described in detail here.

[0082] S204: Rolling.

[0083] Specifically, the rolling process of the negative electrode sheet is similar to that of the positive electrode sheet, and will not be described in detail here.

[0084] S205, punching, die-cutting and slicing to make negative electrode sheets.

[0085] It can be die-cutting followed by punching, or die-cutting and punching can be performed simultaneously. Taking die-cutting followed by punching as an example, specifically, according to the design requirements, the appropriate mold and cutting parameters are selected to form the required negative electrode sheet. When preparing the negative electrode sheet for making a laminated battery, it is necessary to punch the first outer edge area, the first inner edge area, the second outer edge area, the second inner edge area, the third outer edge area, the third inner edge area, the fourth outer edge area, and the fourth inner edge area by needle roller extrusion to form the following: Figure 3 When preparing a negative electrode sheet for a wound battery, the first outer edge region, the first inner edge region, the second outer edge region, and the second inner edge region are perforated using needle roller extrusion. For example, the width of the first inner edge region, the second inner edge region, the third inner edge region, and the fourth inner edge region can be 3 mm, and the micropores in each edge region can be formed in one step using needle roller extrusion.

[0086] S30, stacking the positive electrode sheet, the separator and the negative electrode sheet in sequence.

[0087] Specifically, when preparing a wound battery, the positive electrode sheet, separator, and negative electrode sheet are first stacked in order and then wound to form the cylindrical structure of the battery cell. When preparing a laminated battery, the sheets can be stacked in a Z-shaped stack or in a bag-making manner (the battery cells are pre-assembled to form individual cells). Among them, polyethylene film is selected as the separator, the positive electrode sheet is provided with a positive electrode tab, and the negative electrode sheet is provided with a negative electrode tab.

[0088] The wound or stacked cells can be made into batteries after assembly, liquid injection, aging, formation, capacity division and other processes. The negative electrode plates in the batteries are negative electrode plates with corresponding micropores.

[0089] The performance of batteries including the negative electrode sheets provided by the embodiments of the present invention are compared and verified below with reference to the charts.

[0090] Specifically, in the following experiment, taking the laminated battery as an example, whether it is the control group or the experimental group, the width of the frame structure composed of the first outer edge area, the second outer edge area, the third outer edge area and the fourth outer edge area is the same, and the width of the frame structure composed of the first inner edge area, the second inner edge area, the third inner edge area and the fourth inner edge area is different. The battery performance is verified by comparing the lithium plating area and the cycle capacity retention rate.

[0091] (1) The cycle capacity retention rate test process is as follows:

[0092] At 25°C, the battery was cycled according to the following steps:

[0093] S1: Charge the battery at a constant current of 0.5C with a charge rate and a charge cut-off voltage of 3.65V.

[0094] S2: Charge the battery at a constant voltage of 3.65V and a charge cut-off current of 0.05C;

[0095] S3: Let the battery rest for 5 minutes;

[0096] S4: The battery is discharged at a constant current at a discharge rate of 0.5C, and the discharge cut-off voltage is 2.5V;

[0097] S5: Let the battery sit for 5 minutes.

[0098] The above charge and discharge process is considered one cycle. The discharge capacity of the first cycle is recorded as the initial capacity of the battery. After completing all the planned cycles, the ratio of the discharge capacity of the last cycle to the initial capacity is calculated to obtain the cycle capacity retention rate, that is, cycle capacity retention rate = discharge capacity / initial capacity × 100%.

[0099] (2) Lithium deposition test:

[0100] After 1000 cycles of the above charge and discharge process, the fully charged battery was disassembled to obtain the negative electrode sheet. The ratio of the area of ​​the negative electrode sheet where lithium deposition occurred to the area of ​​the entire negative electrode sheet was measured.

[0101] The inner edge region in the table below refers to the combination of the first inner edge region, the second inner edge region, the third inner edge region, and the fourth inner edge region. The specific experimental results are shown in the table below: Inner edge area width / mm Lithium deposition area Cycle capacity retention rate Reference group / 5.6％ 88.6％ Experimental Group 1 3 0 94.3％ Experimental Group 2 0.5 0 94.1％ Experimental Group 3 5 0 94.6％ Experimental Group 4 8 0.5％ 92.5％ Experimental Group 5 10 4.2％ 90.8％

[0102] Among them, the experimental group refers to the reference group with a width of 0 in the inner edge area, that is, no micropores are set in the part of the negative electrode sheet facing the positive electrode sheet. In this case, after 1000 cycles of charge and discharge, the lithium deposition area accounts for 5.6% of the area of ​​the entire negative electrode sheet, and the cycle capacity retention rate is 88.6%.

[0103] In experimental group 1, the width of the inner edge area was set to 3 mm. In this case, after 1000 cycles of charge and discharge, the lithium deposition area was 0 and the cycle capacity retention rate was 94.3%.

[0104] In experimental group 2, the width of the inner edge area was set to 0.5 mm. In this case, after 1000 cycles of charge and discharge, the lithium deposition area was 0 and the cycle capacity retention rate was 94.1%.

[0105] In experimental group 3, the width of the inner edge area was set to 5 mm. In this case, after 1000 cycles of charge and discharge, the lithium deposition area was 0 and the cycle capacity retention rate was 94.6%.

[0106] In experimental group 4, the width of the inner edge area was set to 8 mm. In this case, after 1000 cycles of charge and discharge, the lithium deposition area was 0.5%, and the cycle capacity retention rate was 92.5%.

[0107] In experimental group 5, the width of the inner edge area was set to 10 mm. In this case, after 1000 cycles of charge and discharge, the lithium deposition area was 4.2%, and the cycle capacity retention rate was 90.8%.

[0108] Combined with the experiment, the principle that the scheme of the present invention can reduce lithium plating is explained: a part of the lithium will diffuse into the Overhang area during the charging process, and cannot be completely released during the discharge process, and this effect has a cumulative effect, which has a certain deteriorating effect on the battery capacity and the cycle capacity retention rate. Therefore, by punching in the Overhang area, the Overhang electrode dynamics can be improved, so that lithium ions can be quickly removed from the Overhang area during the discharge process, offsetting the adverse effects of the Overhang area to a certain extent. However, due to the existence of the Overhang area, the liquid phase potential is the highest at the junction of the Overhang area and the third area, and the lithium plating problem is most likely to occur in this area. The present invention punches the interface area (inner edge area) to improve the dynamics of this area, which can effectively avoid the lithium plating problem in the interface area (inner edge area) under high coating amount and high pressure compaction system. In other words, punching in the Overhang area can avoid the attenuation of the cycle capacity retention rate caused by the accumulation of lithium diffusion during long-term charge and discharge, and punching in the inner edge area can avoid the lithium plating problem caused by the excessively high liquid phase potential and weak mismatch of the anode dynamics in this area during long-term charge and discharge, thereby further reducing the lithium plating phenomenon.

[0109] It can be seen that compared with the scheme of setting micropores only in the outer edge area (the first outer edge area and the second outer edge area in the winding case, and the first outer edge area, the second outer edge area, the third outer edge area and the fourth outer edge area in the stacking case), the scheme in the embodiment of the present invention, that is, the scheme of setting micropores in the outer edge area and the inner edge area at the same time, can further reduce the lithium plating problem of the negative electrode sheet and improve the cycle capacity retention rate of the battery to a certain extent, thereby effectively improving the performance and life of the battery.

[0110] Thus far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art may make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will fall within the scope of protection of the present invention.

Claims

1. A negative electrode plate, characterized in that: The negative electrode plate includes an area that overlaps with the positive electrode plate after being stacked and an area that does not overlap, the non-overlapping area includes at least a first outer edge area and a second outer edge area located on the opposite side of the first outer edge area, and the overlapping area includes at least a first inner edge area adjacent to the first outer edge area and a second inner edge area adjacent to the second outer edge area. Wherein, recessed structures are provided in the first outer edge region, the first inner edge region, the second outer edge region, and the second inner edge region.

2. The negative electrode sheet according to claim 1, characterized in that: The non-overlapping area also includes a third outer edge area and a fourth outer edge area. The fourth outer edge area is arranged opposite to the third outer edge area and is configured as a frame structure with the first outer edge area and the second outer edge area. The overlapping area also includes a third inner edge area adjacent to the third outer edge area and a fourth inner edge area adjacent to the fourth outer edge area. Wherein, recessed structures are provided in the third outer edge region, the third inner edge region, the fourth outer edge region, and the fourth inner edge region.

3. The negative electrode sheet according to claim 2, characterized in that: The recessed structure is a plurality of micropores.

4. The negative electrode sheet according to claim 3, characterized in that: Some or all of the plurality of micropores are non-through micropores, or all of the plurality of micropores are through micropores.

5. The negative electrode sheet according to claim 3, characterized in that: The pore size r of the micropores is 20 μm≤r≤60 μm; and / or The micropores are evenly distributed, and the pore spacing d of the micropores is 30 μm≤d≤100 μm.

6. The negative electrode sheet according to claim 3, characterized in that: The negative electrode sheet includes an active material layer, the micropores are formed on the active material layer, the thickness of the active material layer is H, the depth of the micropores is h, and 1 / 4≤h / H≤3 / 4.

7. The negative electrode sheet according to claim 3, characterized in that: The width of the first inner edge area is 0.5 mm to 5 mm; and / or The width of the second inner edge area is 0.5 mm to 5 mm; and / or The width of the third inner edge area is 0.5mm-5mm; and / or The width of the fourth inner edge area is 0.5 mm to 5 mm.

8. The negative electrode sheet according to claim 3, characterized in that: The shape of the micropores is at least one of circular, elliptical, and polygonal.

9. A battery cell, characterized in that: The battery cell comprises the negative electrode sheet according to any one of claims 1 to 8.

10. A method for preparing a battery cell, characterized in that: The preparation method comprises: preparing a positive electrode sheet; Prepare a negative electrode sheet, wherein the negative electrode sheet is the negative electrode sheet according to any one of claims 3 to 8; The positive electrode sheet, the separator and the negative electrode sheet are stacked in sequence.

11. The method for preparing a battery cell according to claim 10, wherein: The micropores are formed by needle roller extrusion.

12. A battery, characterized in that: The battery comprises the battery cell according to claim 9; or The battery comprises at least one battery cell, which is manufactured by the battery cell preparation method according to claim 10 or 11.

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