Pole piece, battery, pole piece preparation method and pole piece preparation device

Abstract

The application discloses a pole piece, a battery, a preparation method of the pole piece, and a preparation device of the pole piece. The pole piece comprises a current collector and a coating arranged on the surface of the current collector. The coating has at least one recess structure. The recess structure is recessed from the surface of the coating to the direction where the current collector is located. The recess structure extends along the length direction of the pole piece. The pole piece has good structural performance and is beneficial to improving the fast-charging performance of the battery cell.

Description

Technical Field

[0001] This application relates to the field of batteries, and in particular to an electrode, a battery, a method for preparing the electrode, and an apparatus for preparing the electrode. Background Technology

[0002] With the development of lithium-ion battery technology, the requirements for energy density and fast charging capability of battery cells are becoming increasingly stringent, making the realization of fast charging under high areal density design an urgent need. However, fast charging under high areal density design is prone to lithium plating, which leads to the degradation of cell performance.

[0003] Therefore, how to improve the structure of the electrode to improve the fast charging performance of the battery cell is a technical problem that needs to be solved by those skilled in the art. Summary of the Invention

[0004] The purpose of this application is to provide an electrode sheet, a battery, a method for preparing the electrode sheet, and an apparatus for preparing the electrode sheet. This electrode sheet possesses good structural performance and is beneficial for improving the fast-charging performance of the battery cell. The preparation method and apparatus for this electrode sheet are simple to implement, do not involve material waste, and are conducive to mass production.

[0005] To solve the above-mentioned technical problems, this application provides an electrode sheet including a current collector and a coating disposed on the surface of the current collector. The coating has at least one recessed structure, which is recessed from the surface of the coating toward the current collector and extends along the length direction of the electrode sheet.

[0006] In one feasible embodiment, the coating has two or more of the recessed structures, and the recessed structures are spaced apart along the width direction of the electrode.

[0007] In one feasible solution, the recess depths of two adjacent recess structures are different along the width direction of the electrode; or, in the same recess structure, at least two regions of the recess structure have different recess depths.

[0008] In one feasible solution, the recessed structure is a through groove, and the extension length of the through groove is consistent with the length of the electrode sheet;

[0009] Alternatively, each of the recessed structures includes two or more grooves; in the same recessed structure, the grooves are arranged at intervals along the length of the electrode.

[0010] This application also provides a battery, including a negative electrode sheet, wherein the negative electrode sheet is any of the electrode sheets described above.

[0011] This application also provides a method for preparing an electrode sheet, applicable to the electrode sheets described in any of the above claims, the preparation method comprising:

[0012] Preparation of current collectors and slurries;

[0013] Adjusting the discharge flow rate of the slurry: At least one adjustment position is provided in the discharge chamber of the slurry to reduce the discharge flow rate of the discharge chamber at the adjustment position;

[0014] Coating: Controlling the slurry to be extruded from the adjusted discharge slit of the discharge chamber and coated onto the current collector.

[0015] In one feasible solution, the discharge chamber has two or more adjustment positions, and each adjustment position is arranged at intervals along the extension direction of the discharge gap.

[0016] In one feasible solution, the discharge flow rate of the discharge chamber at the adjustment position is adjusted by moving a baffle in a direction perpendicular to the discharge surface, the baffle being disposed at the adjustment position of the discharge chamber.

[0017] This application embodiment also provides an electrode preparation apparatus, applicable to the electrode as described in any of the above claims. The preparation apparatus includes a coating die head, the coating die head including a discharge cavity with a discharge gap, and at least one baffle is inserted into the upper die head of the coating die head. The baffles are spaced apart along the extension direction of the discharge gap, and the baffles are movable relative to the upper die head in a direction perpendicular to the discharge surface.

[0018] In one feasible embodiment, the preparation apparatus further includes a controller and a drive unit, the drive unit being used to drive the stop member to move relative to the upper die head, and the controller being communicatively connected to the drive unit.

[0019] The electrode sheet provided in this application can be used in batteries as the negative electrode sheet. By setting a concave structure on the coating of the electrode sheet, the coating can be non-uniformly distributed on the current collector, achieving a non-uniform areal density distribution of the coating. This increases the contact area between the electrode sheet and the electrolyte, which is beneficial for improving the lithium plating state of the electrode sheet, thereby improving the fast charging performance of the battery cell.

[0020] In the electrode preparation method and apparatus provided in this application, an adjustment position is set in the discharge chamber. By adjusting the discharge flow rate of the adjustment position, the coating applied to the current collector forms a concave structure, thereby forming a non-uniform electrode, which is beneficial to improve the lithium plating state of the electrode. The preparation method and apparatus are simple to operate, facilitate the mass production of the electrode, do not waste materials, and can ensure the structural performance of the electrode. Attached Figure Description

[0021] Figure 1 This is a structural diagram of the electrode sheet provided in one embodiment of this application;

[0022] Figure 2 for Figure 1 The bottom view of the electrode shown;

[0023] Figure 3 This is a structural diagram of the electrode sheet in another embodiment provided in this application;

[0024] Figure 4 This is a structural diagram of the preparation apparatus provided in one embodiment of this application;

[0025] Figure 5 for Figure 4 Internal structure diagram of the coating die shown;

[0026] Figure 6 This is a schematic diagram illustrating the implementation principle of the preparation apparatus and preparation method according to embodiments of this application.

[0027] Explanation of reference numerals in the attached figures:

[0028] Electrode 100, current collector 110, connecting area 111, coating 120, recessed structure 121, groove 1211;

[0029] Coating die head 200, upper die head 210, lower die head 220, discharge cavity 230, and baffle 240;

[0030] Host computer 300. Detailed Implementation

[0031] To enable those skilled in the art to better understand the present application, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] The ordinal numbers used in this article, such as first and second, are used to distinguish different parts with the same name and do not indicate a specific order or primary / secondary relationship.

[0033] For ease of understanding and description, this paper defines three directions based on the electrode sheet: the length direction (x), the width direction (y), and the thickness direction (z).

[0034] Please refer to Figure 1 and Figure 2 , Figure 1 This is a structural diagram of the electrode sheet provided in one embodiment of this application. Figure 2 for Figure 1 The bottom view of the electrode shown.

[0035] This embodiment provides an electrode 100 that can be applied to a battery, specifically as the negative electrode of the battery. The electrode 100 includes a current collector 110 and a coating 120 disposed on the surface of the current collector 110. It can be understood that the current collector 110 and the coating 120 are stacked in the thickness direction z of the electrode 100.

[0036] The coating 120 of the electrode 100 has at least one recessed structure 121, which is recessed from the surface 120A of the coating 120 toward the current collector 110, and extends along the length direction x of the electrode 100.

[0037] By adopting the above scheme, by setting a recessed structure 121 on the coating 120 of the electrode 100, the coating 120 can be non-uniformly distributed on the current collector 110, thereby achieving a non-uniform surface density distribution of the coating 120. This can increase the contact area between the electrode 100 and the electrolyte, which is beneficial to improving the lithium plating state of the electrode 100, and thus beneficial to improving the fast charging performance of the battery cell.

[0038] In some implementation schemes, the coating 120 of the electrode 100 can be provided with two or more recessed structures 121, and the two or more recessed structures 121 are arranged at intervals along the width direction y of the electrode 100.

[0039] In practical applications, the dimensions of the recessed structure 121 in the width direction y of the electrode 100, as well as the spacing between two adjacent recessed structures 121 in the width direction y of the electrode 100, can be set according to the performance requirements of the electrode 100, and can be determined through experiments or simulations. No specific limitations are placed on the relevant parameter values ​​of the recessed structure 121 here.

[0040] like Figure 2 and Figure 3 In the embodiment shown, the coating 120 of the electrode 100 is provided with two recessed structures 121, which are arranged at intervals along the width direction y of the electrode 100.

[0041] The recessed structure 121 can be implemented in a variety of ways.

[0042] For example, in Figure 2 and Figure 3 In the illustrated embodiment, each recessed structure 121 is a through groove, the extension length of which is consistent with the length of the electrode 100. In other words, both ends of the recessed structure 121 penetrate the two opposite sides of the electrode 100 in the length direction x. This helps to reduce the processing difficulty of the electrode 100.

[0043] For example, refer to Figure 3 ,exist Figure 3 In the illustrated embodiment, each recessed structure 121 of the coating 120 includes two grooves 1211 spaced apart along the length x of the electrode 100. It can be understood that the grooves 1211 in the same recessed structure 121 are arranged in a straight line or a crisscross pattern. This allows for flexible arrangement of the positions of the recessed structures 121 of the electrode 100 as needed.

[0044] contrast Figure 1 and Figure 3 It can be considered Figure 1 In the embodiment shown, the recessed structure 121 is a continuous groove structure extending along the length x direction of the electrode 100. Figure 3 In the embodiment shown, the recessed structure 121 is a discontinuous groove structure extending along the length x direction of the electrode 100.

[0045] In specific implementation, such as Figure 3 As shown, the grooves 1211 in two adjacent recessed structures 121 can be staggered in the width direction y of the electrode 100.

[0046] In other implementations, the grooves 1211 in two adjacent recessed structures 121 may also correspond in position along the width direction y of the electrode 100.

[0047] In other implementations, each recessed structure 121 may have three or more grooves 1211 along the length x of the electrode 100.

[0048] In application, the number of grooves 1211 provided in each recessed structure 121 of the coating 120 can be the same, such as Figure 3 As shown, the number of grooves 1211 provided in each recessed structure 121 can also be different.

[0049] In other implementations, in schemes where the coating 120 of the electrode 100 has two or more recessed structures 121, some of the recessed structures 121 may be similar to Figure 1 The through-slot shown can also have a partial recessed structure 121 similar to... Figure 3 The structure shown has two or more grooves 1211.

[0050] In some embodiments, the recess depths of two adjacent recess structures 121 of the electrode 100 can be set differently to accommodate different performance requirements of the electrode 100. In other embodiments, the recess depths of all recess structures 121 of the electrode 100 can also be set the same.

[0051] In some embodiments, within the same recessed structure 121 of the electrode 100, at least two regions of the recessed structure 121 have different recess depths. The recess depth of the recessed structure 121 varies along the length x of the electrode 100. This variation in recess depth can be continuous or discontinuous. For example, the recess depth of a through-groove, which is a recessed structure 121, can gradually decrease or increase from one end of the electrode 100 along the length x, or it can first decrease and then increase. As another example, the through-groove, which is a recessed structure 12, can be divided into several segments along the length x of the electrode 100, each segment having the same recess depth, with at least two segments having different recess depths. As yet another example, in an embodiment where the recessed structure 121 includes two or more grooves 1211, the recess depth of the different grooves 1211 is different. Furthermore, in an embodiment where the recessed structure 121 includes two or more grooves 1211, the recess depth of a single groove 1211 varies along the length x of the electrode 100.

[0052] Of course, in practical applications, the recess depth of the same recessed structure 121 of the electrode 100 can be consistent. This helps to reduce the difficulty of processing.

[0053] The current collector 110 of the electrode 100 may have a blank connection area 111 without the coating 120 to facilitate the connection of the tab (not shown in the figure). In practical applications, the tab can be welded to the connection area 111 of the current collector 110 by means of laser welding or other methods.

[0054] The electrode 100 provided in this embodiment has a relatively low areal density at the concave structure 121 of the coating 120 and a relatively high areal density at the non-concave structure 121. This electrode 100 is a non-uniform electrode. By setting a non-uniform low areal density region, it is beneficial to improve the fast charging performance of the battery cell. However, the areal density at the concave structure 121 should not be too low to avoid having the opposite effect. In practical applications, the magnitude of the areal density at the concave structure 121 of the coating 120 can be determined through experiments or simulations to improve the lithium plating state of the electrode 100 and enhance the fast charging performance of the battery cell.

[0055] This application also provides a battery including a negative electrode sheet, which adopts the above-described electrode sheet 100 structure. Using the above-described electrode sheet 100 structure as the negative electrode sheet increases the contact area between the electrolyte and the electrode sheet 100, improves the lithium plating state of the electrode sheet 100, and thus provides technical conditions for improving the fast-charging performance of the battery cell.

[0056] For example, the battery can be a lithium battery.

[0057] For example, the current collector 110 of the negative electrode can be made of copper foil.

[0058] For example, the coating 120 of the negative electrode sheet may include negative electrode active materials such as graphite, conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber.

[0059] This application provides a method for preparing an electrode sheet, applicable to the electrode sheet 100 described in the above embodiments. Taking the electrode sheet 100 as a negative electrode sheet as an example, the method for preparing the electrode sheet 100 includes:

[0060] Preparation of current collector 110 and slurry;

[0061] Adjust the discharge flow rate of the slurry: Set at least one adjustment position in the discharge chamber of the slurry to reduce the discharge flow rate of the discharge chamber at the adjustment position;

[0062] Coating: Control the slurry to be extruded from the adjusted discharge cavity through the discharge gap and coated onto the current collector 110.

[0063] The slurry can be formulated with appropriate active materials based on the performance requirements of the negative electrode sheet; no specific formulation is specified here. The negative electrode slurry can be obtained through existing negative electrode formulation processes.

[0064] Typically, the slurry is conveyed to the discharge chamber through the feeding section, and then extruded and coated onto the current collector 110 through the discharge slit in the discharge chamber. In application, the extension direction of the discharge slit in the discharge chamber is consistent with the width direction y of the current collector 110, and the extrusion direction of the slurry can be considered to be consistent with the length direction x of the current collector 110.

[0065] Using the above preparation method, by setting at least one adjustment position in the discharge chamber and reducing the discharge flow rate at that adjustment position, the amount of slurry extruded from the discharge gap at the position corresponding to the adjustment position is less than that at other positions. After coating, the coating 120 formed on the current collector 110 will form a recessed structure 121 at the location corresponding to the adjustment position. During the coating process, by setting the size of the adjustment position in the extension direction of the discharge gap and adjusting the discharge flow rate, recessed structures 121 of different widths and depths can be formed. This preparation method is convenient to operate, conducive to mass production, eliminates material waste, and ensures the structural performance of the electrode 100.

[0066] The preparation method provided in this application will not increase additional material costs or cause material loss.

[0067] The preparation method provided in this application forms a concave structure 121 on the electrode 100. The electrode 100 has no break points, which can ensure the structural strength of the electrode 100 and is highly feasible.

[0068] In practice, during the step of adjusting the discharge flow rate of the slurry, two or more adjustment positions can be set in the discharge chamber of the slurry, and each adjustment position can be arranged at intervals along the extension direction of the discharge gap. In this way, the discharge flow rate of two or more adjustment positions can be adjusted to form two or more recessed structures 121 in the width direction y of the formed electrode 100.

[0069] In practice, the discharge flow rate of the discharge chamber at the adjustment position can be adjusted by a baffle, which is positioned at the adjustment position of the discharge chamber. This baffle occupies space in the discharge chamber at the adjustment position, thereby reducing the discharge flow rate at that position. In application, the discharge flow rate can be adjusted by moving the baffle in a direction perpendicular to the discharge surface.

[0070] In practical applications, the space occupied by the baffle in the adjustment position can be set according to the structure of the recessed structure 121 to be formed. It can be understood that the dimension of the baffle in the extension direction of the discharge gap affects the dimension of the recessed structure 121 in the width direction y of the electrode 100, and the dimension occupied by the baffle in the height direction (or depth direction) of the discharge cavity affects the recess depth of the recessed structure 121. The extension direction of the discharge gap and the discharge direction of the discharge cavity can construct a discharge surface, with the height direction of the discharge cavity perpendicular to the discharge surface.

[0071] Please refer to this as well. Figure 4 and Figure 5 , Figure 4 This is a structural diagram of the preparation apparatus provided in one embodiment of this application. Figure 5 for Figure 4 The diagram shows the internal structure of the coating die.

[0072] This application provides an apparatus for preparing an electrode 100, applicable to the electrode 100 described in the above embodiments. The apparatus includes a coating die 200, which comprises an upper die 210 and a lower die 220. The coating die 200 has a closed state and an open state. In the closed state, the upper die 210 and the lower die 220 are fitted together, forming a discharge cavity 230 with a discharge gap (not shown in the figure) between them.

[0073] The direction of the discharge gap is in Figure 4 Marked as s1, the slurry is discharged in the discharge direction of the discharge chamber 230. Figure 4 The symbol 's2' indicates the discharge direction, with a solid arrow pointing to it.

[0074] The upper die head 210 is fitted with at least one stopper 240. When there are two or more stoppers 240, they are spaced apart along the extension direction s1 of the discharge gap. The stoppers 240 can move relative to the upper die head 210 in a direction perpendicular to the discharge surface. Here, the discharge surface refers to the plane formed by the extension direction s1 of the discharge gap and the discharge direction s2. It can be understood that the movement direction of the stopper 240 relative to the upper die head 210 is consistent with the mold closing direction of the upper die head 210 and the lower die head 220. The extension direction s1 of the discharge gap is consistent with the width direction of the electrode sheet 100.

[0075] exist Figure 4 and Figure 5 In the diagram, the direction of movement of the stop 240 is indicated by D. It can be understood that the stop 240 can move relative to the upper die head 210 towards the discharge cavity 230, or it can move relative to the upper die head 210 away from the discharge cavity 230. The height direction of the discharge cavity 230 is consistent with the direction of movement D of the stop 240.

[0076] The preparation apparatus can be used to manufacture the electrode 100 described in the aforementioned embodiments using the aforementioned preparation method. The preparation apparatus can conveniently manufacture the aforementioned electrode 100, which is conducive to mass production, does not cause material waste, and can ensure the structural performance of the electrode 100.

[0077] Combination Figure 4 and Figure 5 In practical applications, the position of the discharge cavity 230 corresponding to the baffle 240 is the adjustment position described in the aforementioned preparation method. By controlling the movement of the baffle 240 relative to the upper die head 210, the relative position of the baffle 240 in the height direction of the discharge cavity 230 can be adjusted, thereby adjusting the depth of the baffle 240 extending into the discharge cavity 230. This, in turn, adjusts the discharge flow rate at the position where the baffle 240 extends, resulting in the coating 120 applied to the collector 110 forming a recessed structure 121. It can be understood that after the baffle 240 extends into the discharge cavity 230, it is equivalent to reducing the gap value of the discharge slit at the position where the baffle 240 is located.

[0078] When the discharge chamber 230 is in a position where the baffle 240 is not installed, and when the baffle 240 does not extend into the discharge chamber 230, the discharge flow rate of the slurry is relatively maximum. A coating 120 with a thickness consistent with the height of the discharge chamber 230 can be formed on the collector 110. When the baffle 240 extends into the discharge chamber 230, the discharge flow rate is reduced due to the obstruction of the baffle 240. The thickness of the coating 120 finally coated onto the collector 110 is reduced, and a recessed structure 121 can be formed on the coating 120.

[0079] The shape and size of the baffle 240 are related to the structure of the recessed structure 121 of the coating 120. In practical applications, they can be configured as needed.

[0080] Figure 4 and Figure 5 In the example shown, five baffles 240 are provided on the upper die head 210 along the extension direction s1 of the discharge gap. In practical applications, some or all of the baffles 240 can be selected to extend into the discharge cavity 230 as needed, and the depth of the baffles 240 extending into the discharge cavity 230 can also be selected as needed.

[0081] by Figure 5 As shown, from left to right, the first, third and fifth baffles 240 extend into the discharge chamber 230. The coating 120 applied to the current collector 110 through the discharge chamber 230 can form three recessed structures 121.

[0082] In practical applications, during the coating process, the position of each baffle 240 relative to the discharge cavity 230 can be adjusted as needed to form a concave structure 121 with a through groove structure, or a concave structure 121 with multiple grooves 1211, or a concave structure 121 with different recess depths, etc.

[0083] In some embodiments, the apparatus for preparing the electrode 100 further includes a controller and a drive unit, wherein the drive unit is used to drive the stop member 240 to move relative to the upper die head 210, and the controller is communicatively connected to the drive unit. In this way, during the preparation of the electrode 100, the controller can send instructions to the drive unit to adjust the position of the stop member 240, thereby achieving automated preparation of the electrode 100 and improving the quality of the prepared electrode 100.

[0084] In a specific implementation, the preparation device may include a host computer 300, and the controller may be built into the host computer 300.

[0085] In a specific implementation, the driving component can control the movement of the stopper 240 by changing the pressure. For example, the driving component can be in the form of a telescopic cylinder, and the stopper 240 can be installed on the telescopic end of the telescopic cylinder. The controller drives the stopper 240 to move by controlling the pressure of the telescopic cylinder.

[0086] The implementation principle of the aforementioned preparation apparatus and method can be referred to Figure 6 understand, Figure 6 (a) illustrates the pressure change applied by the drive member to the baffle 240. It can be assumed that when the pressure increases, the baffle 240 extends into the discharge chamber 230 to reduce the discharge flow rate at the corresponding adjustment position, or in other words, to reduce the gap value of the discharge slit at the corresponding position. The gap value of the discharge slit responds to the positional change of the baffle 240 as follows: Figure 6 As shown in (b), the final result is as follows: Figure 6As shown in (c), the slurry discharge beam at the corresponding position of the baffle 240 is reduced, and a concave structure 121 with a lower coating surface density is formed at the corresponding position of the electrode 100.

[0087] The following comparison uses a battery cell assembled with a traditional electrode structure as a comparative example, and compares it with a battery cell assembled with an electrode 100 made using the preparation method or preparation device provided in this embodiment. This illustrates that the electrode 100 provided in this embodiment has a better lithium plating suppression effect, which is beneficial to improving the performance of the battery cell.

[0088] In the battery cells used as comparative examples and embodiments of this application, the structure is identical except for the negative electrode plate.

[0089] The separator of the battery cell is consistent. Specifically, the separator may include a 5um PE base film, a 2um ceramic layer, and 1um adhesive layers on both sides.

[0090] The positive electrode of the battery cell has a consistent structure. The positive electrode active material formulation is as follows: 98.2 wt% high-voltage lithium cobalt oxide, 0.8 wt% conductive carbon black, 0.4 wt% single-walled carbon nanotubes, and 0.6 wt% PVDF (polyvinylidene fluoride). The positive electrode active layer density is 13.1 mg / cm³. 2 The compacted density is 4.05 g / cm³. 3 .

[0091] The electrolyte of the battery cell is 1 mol / L LiPF6, the solvent is EC:DEC:EMC=3:5:3, and the additives are a certain proportion of VC, FEC, AND and HTCN.

[0092] In the comparative examples and embodiments, the negative electrode active material formulations of the negative electrode sheets were the same, consisting of 96.8 wt% graphite, 0.5 wt% conductive carbon black, 1.3 wt% sodium carboxymethyl cellulose, and 1.4% styrene-butadiene rubber. The negative electrode slurry was obtained using a conventional negative electrode formulation process, with a solid content of 48 ± 2% and a viscosity range of 4000-8000 cp.

[0093] In the comparative examples and embodiments, the density of the negative electrode active layer in the default normally coated area is 7.32 mg / cm³. 2 The compacted density is 1.75 g / cm³. 3 。 In the embodiments, based on the electrode 100 structure of this scheme, five embodiments are provided according to the different surface densities of the non-uniform surface density region, as detailed in Table 1 below.

[0094] After the cells for the comparative example and the five embodiments were fabricated, they were subjected to 10 cycles of low-temperature rate charge-discharge. The charging strategy was as follows: 5C constant current charging to 4.25V, 4C constant current charging to 4.35V, 3C constant current charging to 4.45V, 2C constant current charging to 4.48V, and constant voltage charging to the cutoff current of 0.05C, followed by a 10-minute rest period. Then, the cells were sequentially discharged at 1C constant current to 3.0V, followed by a 0.5C constant current discharge to 3.0V, and then rested for 10 minutes. This constituted one cycle. The above cycle was repeated 100 times to test the battery capacity retention rate. Subsequently, the cells were fully charged and disassembled to determine the electrode condition. The comparative results are shown in Table 1.

[0095] Table 1 - Comparison results between the comparative examples and embodiments using this implementation scheme

[0096] The surface density design values ​​in Table 1 refer to the surface density, with units of mg / cm³. 2 Low areal density region refers to a region with low areal density. For the electrode 100 provided in this embodiment, the region where the recessed structure 121 is located is a low areal density region. NP ratio refers to the ratio of negative electrode capacity to positive electrode capacity, used to ensure that the negative electrode material has sufficient capacity to accept lithium ions released by the positive electrode material during charging. Capacity retention rate refers to the capacity retention rate of the battery cell, which is the proportion of the initial capacity that the cell retains after a period of use. A higher capacity retention rate indicates better battery stability.

[0097] Based on the above comparison results, it can be seen that in Examples 1, 2, and 3, which were fabricated according to the principle of this scheme, the fast-charging performance of the battery cell can be effectively improved by setting a non-uniform low areal density region and reasonably setting the areal density of the low areal density region. After 100 cycles at low temperature, the capacity retention rate of the battery cell is higher than that of Comparative Example 1, and there is no lithium plating state. It can be seen that a reasonable non-uniform low areal density region can improve the conductivity of the electrolyte. Examples 4 and 5, fabricated according to the principle of this scheme, show that if the areal density of the non-uniform region is too low, especially when the negative electrode excess ratio is lower than 0.96, the insufficient negative electrode active material will lead to performance degradation. Therefore, in practical applications, the areal density of the non-uniform region can be reasonably set while taking into account the negative electrode excess ratio.

[0098] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this application. It should be noted that those skilled in the art can make several improvements and modifications to this application without departing from the principles of this application, and these improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. An electrode, characterized in that, The electrode includes a current collector and a coating disposed on the surface of the current collector, the coating having at least one recessed structure that is recessed from the surface of the coating toward the current collector and extends along the length of the electrode.

2. The electrode sheet according to claim 1, characterized in that, The coating has two or more recessed structures, and the recessed structures are spaced apart along the width direction of the electrode.

3. The electrode sheet according to claim 2, characterized in that, Along the width direction of the electrode, the recess depths of two adjacent recess structures are different; or, in the same recess structure, at least two regions of the recess structure have different recess depths.

4. The electrode sheet according to any one of claims 1-3, characterized in that, The recessed structure is a through groove, and the extension length of the through groove is the same as the length of the electrode sheet; Alternatively, each of the recessed structures includes two or more grooves; in the same recessed structure, the grooves are arranged at intervals along the length of the electrode.

5. A battery, characterized in that, Includes a negative electrode sheet, wherein the negative electrode sheet is the electrode sheet described in any one of claims 1-4.

6. A method for preparing an electrode sheet, characterized in that, The electrode is applicable to any one of claims 1-4, and the preparation method comprises: Preparation of current collectors and slurries; Adjusting the discharge flow rate of the slurry: At least one adjustment position is provided in the discharge chamber of the slurry to reduce the discharge flow rate of the discharge chamber at the adjustment position; Coating: Controlling the slurry to be extruded from the adjusted discharge slit of the discharge chamber and coated onto the current collector.

7. The method for preparing the electrode according to claim 6, characterized in that, The discharge chamber has two or more adjustment positions, and each adjustment position is arranged at intervals along the extension direction of the discharge gap.

8. The method for preparing the electrode according to claim 6 or 7, characterized in that, The discharge flow rate of the discharge chamber at the adjustment position is adjusted by moving a baffle in a direction perpendicular to the discharge surface. The baffle is located at the adjustment position of the discharge chamber.

9. An apparatus for preparing electrode sheets, characterized in that, The electrode preparation apparatus is applicable to any one of claims 1-4, wherein the coating die head includes a discharge cavity having a discharge gap, and at least one baffle is inserted into the upper die head of the coating die head, wherein each baffle is spaced apart along the extension direction of the discharge gap, and the baffle is movable relative to the upper die head in a direction perpendicular to the discharge surface.

10. The apparatus for preparing an electrode according to claim 9, characterized in that, The preparation apparatus further includes a controller and a drive unit. The drive unit is used to drive the stop member to move relative to the upper die head, and the controller is communicatively connected to the drive unit.

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