Electrode assembly and preparation method therefor, battery, and electric device

Abstract

An electrode assembly and a preparation method therefor, a battery, and an electric device. The electrode assembly comprises an electrode plate. The electrode plate comprises a current collector, an active layer, and a tab. The active layer is arranged on at least one side of the current collector in the thickness direction thereof, and the tab is arranged on one side of the current collector in the height direction thereof. In the direction from the side of the current collector where the tab is arranged to the opposite side and in the direction from the current collector to the side away from the current collector, the liquid absorption capacity of the active layer decreases gradually. By enabling the active layer to have different liquid absorption capacities for an electrolyte in a specific direction, the electrolyte wettability of the electrode assembly can be effectively improved. Moreover, the problem of reduced electrolyte wettability of the electrode plate due to the volume expansion or contraction of the electrode plate squeezing out the electrolyte during charging and discharging can also be addressed, thereby improving the electrolyte wettability of the electrode assembly.

Description

Electrode assembly and preparation method thereof, battery, and electrical device

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on November 20, 2023, with application number 202311548956.0 and invention name “Electrode assembly and preparation method thereof, battery, and electrical device”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of battery technology, and in particular to an electrode assembly and a preparation method thereof, a battery, and an electrical device. Background Art

[0003] Batteries, as carriers of electrical energy, are widely used in various fields. Depending on their application, batteries have various requirements. For example, batteries used in the power sector, providing power for devices such as automobiles and electric two-wheelers, must have high energy density and excellent cycle performance.

[0004] The battery assembly is the core component of the battery. During long-term storage and use of the battery, the electrolyte wettability of the electrode assembly will usually gradually deteriorate, affecting the performance of the battery.

[0005] Application Contents

[0006] The purpose of the embodiments of the present application is to provide an electrode assembly and its preparation method, a battery, and an electrical device that can solve the problem of poor wettability of the electrode assembly, thereby reducing battery resistance and improving battery cycle performance. Technical Solutions

[0007] The technical solution adopted in the embodiment of this application is:

[0008] In a first aspect, an embodiment of the present application provides an electrode assembly, the electrode assembly comprising a pole piece, the pole piece comprising a current collector, an active layer, and a pole tab, wherein the active layer is disposed on at least one side in a thickness direction of the current collector, and the pole tab is disposed on one side in a height direction of the current collector;

[0009] In the direction from the tab side of the current collector to the opposite side, the liquid absorption capacity of the active layer near the tab side is greater than or equal to the liquid absorption capacity of the opposite side, and the liquid absorption capacity of at least one area of ​​the active layer near the tab side is greater than the liquid absorption capacity of the opposite side;

[0010] In the direction from the current collector to the direction away from the current collector, the liquid absorption capacity of the area of ​​the active layer close to the current collector is greater than or equal to the liquid absorption capacity of the area on the opposite side, and the liquid absorption capacity of at least one area of ​​the active layer close to the current collector is greater than the liquid absorption capacity of the area on the opposite side.

[0011] The present application specifically distributes the liquid absorption capacity of the active layer in the direction from the side of the current collector where the tab is located to the opposite side, and from the current collector to the direction away from the current collector. Specifically, the liquid absorption capacity of the active layer near the tab (or near the current collector) is greater than or equal to the liquid absorption capacity of the opposite side, and the liquid absorption capacity of at least one area of ​​the active layer near the tab (or near the current collector) is greater than the liquid absorption capacity of the opposite side. This allows for the formation of an electrode assembly with a three-dimensional matrix distribution structure. In an electrode assembly with this structure, the active layer has a higher liquid absorption capacity near the tab than on the opposite side. Since the tab is typically near the top of the electrode assembly, after the electrode assembly is wetted with electrolyte, the amount of electrolyte absorbed by the top of the active layer will be greater than that at the bottom of the active layer. During long-term storage and use of the electrode assembly, even if the electrolyte at the top tends to accumulate downward due to gravity, a relatively large amount of electrolyte can still be retained, resulting in more uniform electrolyte wettability of the active layer in this direction. This can compensate for the problem of poor wettability caused by the concentration of electrolyte at the bottom of the active layer due to gravity.

[0012] At the same time, in the direction from the current collector to the side away from the current collector, the area of ​​the active layer close to the current collector has a higher liquid absorption capacity. After the electrolyte is infiltrated, the area closer to the current collector in the active layer will have a higher amount of electrolyte, which can compensate for the problem of reduced electrolyte wettability or difficulty in infiltration of the electrode due to the volume expansion or contraction of the electrode during the charge and discharge process, which squeezes out the electrolyte.

[0013] Therefore, the embodiment of the present application can effectively improve the electrolyte wettability of the active layer by specifically designing the distribution of the liquid absorption capacity of the active layer in the direction from the side of the current collector where the pole ear is set to the opposite other side, and from the current collector to the direction away from the current collector, so that the active layer can be evenly wetted in different directions. The electrolyte wettability of the electrode assembly is mainly reflected by the active layer, so the improvement of the electrolyte wettability of the active layer is beneficial to the improvement of the electrolyte wettability of the electrode assembly as a whole. The improvement of electrolyte wettability will help reduce battery resistance and improve the cycle performance of the battery.

[0014] In some embodiments, in a direction from the tab side of the current collector to the opposite side, the liquid absorption capacity of the separator contained in the electrode assembly near the tab side is greater than or equal to the liquid absorption capacity of the opposite side, and the liquid absorption capacity of at least one area of ​​the separator near the tab side is greater than the liquid absorption capacity of the opposite side;

[0015] In the direction from the current collector to the direction away from the current collector, the liquid absorption capacity of the active layer is greater than the liquid absorption capacity of the separator contained in the electrode assembly.

[0016] By changing the design of the liquid absorption capacity of the diaphragm in the direction from the side where the electrode tab of the current collector is set to the opposite side, the liquid absorption capacity of the diaphragm can be made higher on the side close to the electrode tab, further improving the electrolyte wettability of the electrode assembly in this direction.

[0017] At the same time, in the direction from the current collector to the direction away from the current collector, the liquid absorption capacity of the active layer is greater than the liquid absorption capacity of the diaphragm contained in the electrode assembly, which can reduce the situation where the diaphragm absorbs a large amount of electrolyte and causes insufficient electrolyte in the active layer, and improve the electrolyte wettability of the electrode in this direction.

[0018] In some embodiments, at least one of the active layer and the separator included in the electrode assembly includes at least two adjacent gradient units, extending from one side of the current collector where the tab is located to the opposite side, wherein the gradient unit on the side closer to the tab has a higher liquid absorption capacity than the gradient unit on the opposite side. Optionally, the number of gradient units is 2 to 10.

[0019] By providing multiple gradient units in the direction from one side of the current collector where the tab is provided to the opposite side, the liquid absorption capacity of the active layer and / or diaphragm in this direction can be gradually reduced layer by layer. The lower gradient units can provide a buffer for the downward movement of the electrolyte in the adjacent, higher gradient units, thereby helping to solve the problem of the electrolyte concentrating at the bottom of the electrode assembly due to gravity during long-term storage and use of the electrode assembly, and improving the electrolyte wettability of the electrode assembly in this direction. At the same time, experiments in the embodiments of the present application show that, within a certain range, the more gradient units are provided in this direction, the better the effect of improving the electrolyte wettability of the electrode assembly.

[0020] In some embodiments, the difference in liquid absorption capacity between two adjacent gradient units is 1.1 to 5 times, optionally 1.2 to 2 times.

[0021] The difference in liquid absorption capacity between two adjacent gradient units is a certain multiple, so that the lower gradient unit can provide a good buffering effect for the downward movement of the electrolyte in the adjacent, higher gradient unit, thereby improving the electrolyte wettability in the direction from the active layer close to the electrode ear to the opposite side.

[0022] In some embodiments, in a direction from one side of the current collector where the tab is provided to the other opposite side, the height of any gradient unit accounts for 10% to 60% of the total height of the active layer or the separator, and optionally 10% to 50%.

[0023] Setting the height of the gradient units in the direction from the electrode tab side of the current collector to the opposite side within a suitable range is beneficial to increasing the number of gradient units, thereby improving the electrolyte wettability of the electrode assembly in this direction.

[0024] In some embodiments, the active layer includes at least two adjacent liquid-absorbing layers arranged in a direction away from the current collector, wherein the liquid-absorbing layer on the side closest to the current collector has a higher liquid-absorbing capacity than the liquid-absorbing layer on the opposite side. Optionally, the number of liquid-absorbing layers is 2 to 10.

[0025] By providing multiple liquid-absorbing layers in the direction from the current collector to the direction away from the current collector, the liquid-absorbing capacity of the active layer in this direction can be gradually reduced layer by layer. When the volume of the electrode changes and the electrolyte is squeezed out, the liquid-absorbing layer on the side away from the current collector can provide a buffer for the electrolyte overflow tendency of the adjacent liquid-absorbing layer on the side closer to the current collector. This helps to solve the problem of reduced electrolyte wettability or difficulty in wetting the electrode due to the volume expansion or contraction of the electrode during the charge and discharge process, thereby improving the electrolyte wettability of the electrode assembly in this direction. At the same time, experiments have shown that within a certain range, the greater the number of liquid-absorbing layers provided in the direction from the current collector to the direction away from the current collector, the better the improvement effect on the electrolyte wettability of the electrode assembly.

[0026] In some embodiments, in a direction from the current collector to away from the current collector, the thickness of any one liquid absorbing layer accounts for 10% to 60% of the total thickness of the active layer on one side of the current collector, and optionally 10% to 50%.

[0027] Setting the thickness of the liquid absorption layer in the direction from the current collector to the direction away from the current collector within an appropriate range is beneficial to increasing the number of liquid absorption layers, thereby improving the electrolyte wettability of the electrode assembly in this direction.

[0028] In some embodiments, the active layer comprises a first electrolyte absorber;

[0029] In a direction from one side of the current collector where the tab is provided to the other opposite side, the mass content of the first electrolyte absorber in the region of the active layer close to the tab is greater than or equal to the mass content of the first electrolyte absorber in the region on the other opposite side, and the mass content of the first electrolyte absorber in at least one region of the active layer close to the tab is greater than the mass content of the first electrolyte absorber in the region on the other opposite side;

[0030] In the direction from the current collector to the direction away from the current collector, the mass content of the first electrolyte absorber in the area of ​​the active layer close to the current collector is greater than or equal to the mass content of the first electrolyte absorber in the area on the other side, and the mass content of the first electrolyte absorber in at least one area of ​​the active layer close to the current collector is greater than the mass content of the first electrolyte absorber in the area on the other side.

[0031] By adding an electrolyte absorber to the active layer and adjusting the mass content of the electrolyte absorber to change along a certain direction, the electrode assembly can have different absorption and retention capabilities for the electrolyte in different areas, and present a certain distribution pattern of liquid absorption along a specific direction, which is beneficial to improving the electrolyte wettability of the electrode assembly.

[0032] In some embodiments, the separator included in the electrode assembly comprises a base membrane and a separator coating disposed on at least one side of the base membrane; the separator coating comprises a second electrolyte absorbent;

[0033] In the direction from the side of the current collector where the pole tab is set to the other opposite side, the mass content of the second electrolyte absorber in the area of ​​the diaphragm coating close to the pole tab is greater than or equal to the mass content of the second electrolyte absorber in the area on the other opposite side, and the mass content of the second electrolyte absorber in at least one area of ​​the diaphragm coating close to the pole tab is greater than the mass content of the second electrolyte absorber in the area on the other opposite side.

[0034] In some embodiments, in a direction from the current collector to away from the current collector, the mass content of the first electrolyte absorber in the active layer is greater than the mass content of the second electrolyte absorber in the separator coating.

[0035] By adding an electrolyte absorber to the diaphragm coating and adjusting the mass content of the electrolyte absorber to change along a certain direction, the electrode assembly can have different absorption and retention capabilities for the electrolyte in different areas, and present a certain distribution pattern of liquid absorption along a specific direction, further improving the electrolyte wettability of the electrode assembly.

[0036] In some embodiments, the first electrolyte absorber and the second electrolyte absorber independently include one or more of polymethyl methacrylate, polymethyl acrylate, polyethyl acrylate, polyvinyl acetate, polyacrylamide, polyacrylic acid, and polyacrylonitrile.

[0037] These polymers have a high affinity for electrolytes and swell to absorb the electrolyte into a gel upon contact. By using these polymers as electrolyte absorbers and adjusting their distribution within the active layer and separator coating, the electrode assembly can be effectively designed to exhibit a gradient or gradual change in liquid absorption along specific directions, thereby improving the electrolyte wettability of the electrode assembly.

[0038] In some embodiments, the mass content of the first electrolyte absorber in the active layer and the mass content of the second electrolyte absorber in the diaphragm coating are independently greater than 0 and less than or equal to 8%; optionally greater than or equal to 1% and less than or equal to 6%.

[0039] Setting the mass content of the electrolyte absorber in the active layer and diaphragm coating within an appropriate range is not only beneficial for adjusting the liquid absorption capacity of different areas of the electrode assembly, but also does not cause a significant reduction in the active material in the active layer, thereby maintaining the stability of the electrode capacity.

[0040] In a second aspect, the present application provides a method for preparing an electrode assembly, comprising:

[0041] An active layer is prepared on at least one side of the current collector in the thickness direction, and a tab is provided on one side of the current collector in the height direction;

[0042] In the direction from the tab side to the opposite side of the current collector, the liquid absorption capacity of the active layer near the tab side is controlled to be greater than or equal to the liquid absorption capacity of the opposite side, and the liquid absorption capacity of at least one area of ​​the active layer near the tab side is greater than the liquid absorption capacity of the opposite side;

[0043] In the direction from the current collector to the direction away from the current collector, the liquid absorption capacity of the area of ​​the active layer close to the current collector is controlled to be greater than or equal to the liquid absorption capacity of the area on the opposite side, and the liquid absorption capacity of at least one area of ​​the active layer close to the current collector is greater than the liquid absorption capacity of the area on the opposite side.

[0044] By making the active layer have different absorption capacities for the electrolyte in specific directions, it is possible to compensate for the problem of poor electrolyte wettability of the electrode assembly caused by gravity during long-term storage and use, which tends to concentrate the electrolyte at the bottom of the electrode assembly. It can also compensate for the problem of reduced electrolyte wettability of the electrode sheet caused by the expansion or contraction of the electrode volume squeezing out the electrolyte during the charge and discharge process, thereby improving the electrolyte wettability of the electrode assembly.

[0045] In some embodiments, the method for preparing an electrode assembly further comprises:

[0046] In the direction from the tab side to the opposite side of the current collector, the liquid absorption capacity of the region of the separator contained in the control electrode assembly near the tab side is greater than or equal to the liquid absorption capacity of the opposite side region, and the liquid absorption capacity of at least one region of the separator near the tab side is greater than the liquid absorption capacity of the opposite side region;

[0047] In the direction from the current collector to the direction away from the current collector, the liquid absorption capacity of the active layer is controlled to be greater than the liquid absorption capacity of the separator.

[0048] By varying the separator's liquid absorption capacity from the current collector's tab side to the opposite side, the separator's liquid absorption capacity is increased near the tab side, further improving the electrode assembly's electrolyte wettability in that direction. Simultaneously, from the current collector toward the direction away from the current collector, the active layer's liquid absorption capacity is greater than that of the separator within the electrode assembly. This reduces the risk of electrolyte starvation in the active layer caused by the separator absorbing large amounts of electrolyte, thereby improving the electrode's electrolyte wettability in that direction.

[0049] In a third aspect, the present application provides a battery comprising the electrode assembly of the first aspect.

[0050] The above-mentioned electrode assembly has good electrolyte wettability. During long-term storage and use, its top and the active layer of the electrode near the inner side of the current collector can be well wetted by the electrolyte. After applying it to the battery, the battery will exhibit low resistance and excellent cycle performance.

[0051] In a fourth aspect, the present application provides an electrical device, which includes the battery of the third aspect.

[0052] The battery disclosed in the embodiments of this application can be used in electrical devices that use batteries as power sources, or in various energy storage systems that use batteries as energy storage elements, to provide electrical energy. The battery exhibits the advantages of low resistance and good cycle performance. Therefore, its application in various electrical devices can improve the user experience of various electrical devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or exemplary technical descriptions. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0054] FIG1 is a schematic diagram showing changes in the liquid absorption capacity of an electrode assembly according to one embodiment of the present application;

[0055] FIG2 is a schematic diagram of the gradient structure of the negative electrode sheet and the separator in Example 1 of the present application;

[0056] FIG3 is a schematic diagram of the gradient structure of the negative electrode sheet in Example 2 of the present application;

[0057] FIG4 is a schematic diagram of the gradient structure of the positive electrode sheet in Example 3 of the present application;

[0058] FIG5 is a schematic diagram of the gradient structure of the positive electrode sheet in Example 4 of the present application;

[0059] FIG6 is a schematic diagram of the gradient structure of the negative electrode sheet in Example 5 of the present application;

[0060] FIG7 is a schematic diagram of the gradient structure of the positive electrode sheet in Example 5 of the present application;

[0061] FIG8 is a schematic diagram of the gradient structure of the negative electrode sheet in Comparative Example 2 of the present application;

[0062] FIG9 is a schematic diagram of the gradient structure of the positive electrode sheet in Comparative Example 2 of the present application;

[0063] FIG10 is a schematic diagram of the gradient structure of the electrode assembly in Comparative Example 3 of the present application;

[0064] FIG11 is a schematic diagram of a battery cell according to an embodiment of the present application;

[0065] FIG12 is an exploded view of the battery cell according to one embodiment of the present application shown in FIG11 ;

[0066] FIG13 is a schematic diagram of a battery module according to an embodiment of the present application;

[0067] FIG14 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0068] FIG15 is an exploded view of the battery pack according to one embodiment of the present application shown in FIG14 ;

[0069] FIG16 is a schematic diagram of an electrical device using a battery as a power source according to an embodiment of the present application;

[0070] Figure markings: D1-direction from one side of the current collector where the pole ear is set to the opposite other side, D2-direction from the current collector to the direction away from the current collector; 10-negative current collector, 11-first negative active layer, 111-first gradient unit, 112-second gradient unit, 113-third gradient unit, 114-fourth gradient unit, 115-fifth gradient unit, 116-sixth gradient unit; 20-positive current collector, 21-first positive active layer, 211-ath gradient unit, 212-bth gradient unit, 213-cth gradient unit, 214-dth gradient unit, 215-eth gradient unit, 216-fth gradient unit; 30-diaphragm, 31-diaphragm coating; 01-shell, 02-cover plate, 03-electrode assembly, 04-battery cell, 05-battery module, 06-upper box, 07-lower box. DETAILED DESCRIPTION

[0071] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0072] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0073] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0074] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0075] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0076] In the description of the embodiments of the present application, the term "at least one" refers to one or more, and "plurality" refers to two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple, respectively.

[0077] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. Some or all of the steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0078] The weights of the relevant components mentioned in the examples of this application may not only refer to the specific content of each component, but also represent the weight ratio between the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the examples of this application, it is within the scope disclosed in the examples of this application. Specifically, the mass described in the examples of this application may be a mass unit known in the chemical industry, such as μg, mg, g, kg, etc.

[0079] Batteries, as carriers of electrical energy, are widely used in various fields. Depending on their application, the market places various demands on batteries. For example, batteries used in the power sector, providing power for devices such as automobiles and electric two-wheelers, require high energy density and excellent cycle performance.

[0080] Among various batteries, the most widely used ones are those that use liquid as the electrolyte. This type of battery usually includes electrodes (positive electrode and negative electrode), with a separator provided between the positive electrode and the negative electrode. The positive electrode, negative electrode and separator are wound or stacked into an electrode assembly (battery cell JR), and the electrode assembly is filled with electrolyte. Common electrode assemblies are placed in the vertical direction, that is, in the direction of gravity. After the electrolyte is injected into the casing containing the electrode assembly, the electrolyte infiltrates the positive electrode, negative electrode and separator. However, during long-term storage and use of the battery, due to the effect of gravity, the electrolyte usually tends to concentrate at the bottom of the electrode assembly, while having poor wettability on the top of the electrode assembly.

[0081] At the same time, to increase energy density, related technologies usually try to increase the compaction density of the electrode as much as possible. However, the increase in compaction density will reduce the porosity of the electrode, making it difficult for the electrolyte to penetrate the electrode, especially the inner side of the electrode near the current collector.

[0082] Furthermore, during the battery's charge and discharge cycles, active metal ions, such as lithium and sodium ions, repeatedly escape and embed in the active material of the electrode, causing the active material to expand and contract. During this expansion and contraction process, the electrode surface pressure increases, squeezing out the electrolyte stored within the electrode, reducing the electrode's electrolyte wettability. In particular, the electrolyte wettability of the electrode's inner layer near the current collector is lower than that of the electrode's surface layer.

[0083] Poor electrolyte infiltration in the electrode assembly will increase the migration resistance of active metal ions, causing increased battery impedance, increased electrode polarization, lithium deposition, etc., thereby causing battery capacity decay and reducing battery cycle performance.

[0084] To address the problem of poor electrolyte wettability of the electrode assembly, the embodiment of the present application designs an electrode assembly with a three-dimensional matrix gradient structure. The electrode assembly has a specific distribution pattern of liquid absorption capacity along two specific directions, that is, the liquid absorption capacity of the area on the side of the active layer close to the pole ear (or close to the current collector) is greater than or equal to the liquid absorption capacity of the opposite area on the other side, and the liquid absorption capacity of at least one area of ​​the active layer close to the pole ear (or close to the current collector) is greater than the liquid absorption capacity of the opposite area on the other side. In this way, the electrode assembly can achieve guided electrolyte infiltration, compensate for the problem of uneven electrolyte distribution at the top and bottom of the electrode assembly caused by gravity, and improve the problem of difficult electrolyte infiltration of the inner layer of the electrode sheet close to the current collector, which is beneficial to reducing battery resistance and improving battery cycle performance.

[0085] The electrode assembly designed in the embodiment of the present application can be used to make batteries, and then used in various electrical devices, including but not limited to mobile phones, tablets, laptops, electric toys, electric tools, electric vehicles, electric cars, ships, spacecraft, etc.

[0086] The present application will be further described below with reference to the following examples. It should be understood that these examples are only used to illustrate the present application and are not intended to limit the scope of the present application.

[0087] [Electrode assembly]

[0088] In a first aspect, an embodiment of the present application provides an electrode assembly, comprising a pole piece, the pole piece comprising a current collector, an active layer, and a tab, wherein the active layer is disposed on at least one side in a thickness direction of the current collector, and the tab is disposed on one side in a height direction of the current collector;

[0089] In the direction from the tab side of the current collector to the opposite side, the liquid absorption capacity of the active layer near the tab side is greater than or equal to the liquid absorption capacity of the opposite side, and the liquid absorption capacity of at least one area of ​​the active layer near the tab side is greater than the liquid absorption capacity of the opposite side;

[0090] In the direction from the current collector to the direction away from the current collector, the liquid absorption capacity of the area of ​​the active layer close to the current collector is greater than or equal to the liquid absorption capacity of the area on the opposite side, and the liquid absorption capacity of at least one area of ​​the active layer close to the current collector is greater than the liquid absorption capacity of the area on the opposite side.

[0091] The detailed characteristics of the direction and liquid absorption capacity are as follows.

[0092] 1) Direction

[0093] The current collector is usually made of a thin metal sheet or a composite material sheet with a small thickness, and an active layer is provided on one or both sides in the thickness direction. The height direction of the current collector refers to the direction perpendicular to the thickness direction of the current collector, which can be the width direction or length direction of the plane perpendicular to the thickness direction of the current collector. The tab is set on one side of the height direction of the current collector, so the direction from the side where the tab is set to the other side of the current collector is consistent with the height direction of the current collector. At the same time, the tab is usually close to the top of the electrode assembly, and the electrode assembly is usually in a standing state, so the height direction of the current collector is usually consistent with the height direction of the electrode assembly, and is also consistent with the direction of gravity. Therefore, the direction from the side where the tab is set to the other side of the current collector is usually also the direction of gravity.

[0094] The direction from the current collector to the side away from the current collector is consistent with the thickness direction of the current collector, and more specifically, it can be the direction from the side of the active layer close to the current collector to the side of the active layer away from the current collector.

[0095] 2) Liquid absorption capacity

[0096] The liquid absorption capacity of a sample reflects the sample's ability to absorb and wet liquids. In the embodiments of this application, the liquid absorption capacity of a sample refers to the sample's ability to absorb and wet electrolytes. Samples with different liquid absorption capacities exhibit different liquid absorption speeds on a macroscopic scale. Therefore, the liquid absorption capacity can be tested using the following methods:

[0097] Take a certain area (for example 2*2cm 2 ) Weigh the sample to be tested to obtain M1. Soak it in electrolyte at a certain temperature (e.g., room temperature, 25°C) for a certain time, t (e.g., 1 hour). Remove the sample, wipe off any excess electrolyte on the surface with a dust-free paper, and then weigh it to obtain M2. This gives the sample's liquid absorption rate, or the amount of liquid absorbed per unit time: m = (M2 - M1) / t. The liquid absorption capacity, F, then = σ*m / THK. Where σ is the porosity of the sample, and THK is the sample thickness. A larger F indicates a faster absorption rate and a stronger absorption capacity.

[0098] For electrodes with double-sided active layers, they need to be wiped into a single side for testing in actual operation to prevent the situation where the test results are difficult to compare due to different designs on the two sides.

[0099] For the difference in liquid absorption capacity of different areas of the active layer in the direction from the side where the electrode ear of the current collector is set to the opposite side, the liquid absorption capacity of different areas can be tested by taking the same electrode, sampling different areas in this direction, and then using the above method to test the liquid absorption capacity of different areas.

[0100] For the difference in liquid absorption capacity of different areas of the active layer in the direction from the current collector to the direction away from the current collector, that is, in the thickness direction of the electrode, it is necessary to compare the liquid absorption capacity F of the complete electrode. totalAnd the liquid absorption capacity of the inner layer after scraping off the surface of the electrode F inner (The thickness after scraping is confirmed by the step thickness gauge) to distinguish, if F inner >F total This indicates that in this direction, the liquid absorption capacity of the active layer area close to the current collector is greater than that of the opposite area.

[0101] The F of the pole piece is usually between 0.1 and 3.

[0102] It can be understood that the electrodes in the electrode assembly generally include positive electrodes and negative electrodes. Then, in a certain direction, the distribution of the liquid absorption capacity of the active layer is "the liquid absorption capacity of the area of ​​the active layer close to the electrode tab (or close to the current collector) is greater than or equal to the liquid absorption capacity of the area on the other side, and the liquid absorption capacity of at least one area of ​​the active layer close to the electrode tab (or close to the current collector) is greater than the liquid absorption capacity of the area on the other side", including that the liquid absorption capacity of at least one of the positive active layer and the negative active layer in this direction has the above distribution.

[0103] In a certain direction, "the liquid absorption capacity of the region of the active layer near the tab (or near the current collector) is greater than or equal to the liquid absorption capacity of the region on the opposite side, and the liquid absorption capacity of at least one region of the active layer near the tab (or near the current collector) is greater than the liquid absorption capacity of the region on the opposite side" includes various situations, including but not limited to: 1) the liquid absorption capacity of the active layer decreases gradually in that direction; 2) the liquid absorption capacity of the active layer gradually decreases within a certain region in that direction, then remains unchanged within a certain region; 3) the liquid absorption capacity of the active layer remains unchanged within a certain region in that direction, then gradually decreases, and then remains unchanged. The decreasing liquid absorption capacity of the active layer can include one or both of the following distribution forms: a gradient decrease or a gradual decrease. A gradient decrease means that in that direction, the active layer can be divided into two or more gradient units, each gradient unit having a uniform or nearly uniform liquid absorption capacity, and the liquid absorption capacity of two adjacent gradient units gradually decreases in that direction. A gradual decrease means that in that direction, the liquid absorption capacity of each region of the active layer shows a continuous decreasing trend. Among them, the situation where the liquid absorption capacity of the active layer decreases gradually from one side of the current collector to the other side of the opposite side can be referred to Figure 1a, and the situation where the liquid absorption capacity of the active layer gradually decreases can be referred to Figure 1b. The darker the color in the figure, the higher the liquid absorption capacity.

[0104] In the embodiment of the present application, a specific distribution design of the liquid absorption capacity of the active layer is performed in the direction from the side of the current collector where the tab is provided to the opposite side, and from the current collector to the direction away from the current collector. That is, the liquid absorption capacity of the active layer area near the tab (or near the current collector) is greater than or equal to the liquid absorption capacity of the opposite side, and the liquid absorption capacity of at least one area of ​​the active layer near the tab (or near the current collector) is greater than the liquid absorption capacity of the opposite side. This can form an electrode assembly with a three-dimensional matrix distribution structure. The electrode assembly with this structure has a higher liquid absorption capacity near the tab than on the opposite side. The tab is usually near the top of the electrode assembly. After the electrode assembly is wetted with electrolyte, the amount of electrolyte retained at the top of the active layer will be greater than the amount at the bottom of the active layer. During long-term storage and use of the electrode assembly, even if the electrolyte at the top tends to accumulate downward due to gravity, a large amount of electrolyte can still be retained, making the electrolyte wettability of the active layer in this direction more uniform, which can compensate for the problem of poor wettability caused by the concentration of electrolyte at the bottom of the active layer due to gravity.

[0105] At the same time, in the direction from the current collector to the side away from the current collector, the area of ​​the active layer close to the current collector has a higher liquid absorption capacity. After the electrolyte is infiltrated, the area closer to the current collector in the active layer will have a higher electrolyte retention. This can make up for the problem that the electrolyte wettability of the electrode is reduced or difficult to infiltrate due to the volume expansion or contraction of the electrode during the charge and discharge process, which squeezes out the electrolyte.

[0106] Therefore, the embodiment of the present application can effectively improve the electrolyte wettability of the active layer by specifically designing the distribution of the liquid absorption capacity of the active layer in the direction from the side of the current collector where the pole ear is set to the opposite other side, and from the current collector to the direction away from the current collector, so that the active layer can be evenly wetted in different directions. The electrolyte wettability of the electrode assembly is mainly reflected by the active layer, so the improvement of the electrolyte wettability of the active layer is beneficial to the improvement of the electrolyte wettability of the electrode assembly as a whole. The improvement of electrolyte wettability will help reduce battery resistance and improve the cycle performance of the battery.

[0107] In some embodiments, in a direction from the side of the current collector where the tab is provided to the opposite side, the liquid absorption capacity of the separator contained in the electrode assembly near the tab side is greater than or equal to the liquid absorption capacity of the opposite side area, and the liquid absorption capacity of at least one area of ​​the separator near the tab side is greater than the liquid absorption capacity of the opposite side area;

[0108] In the direction from the current collector to the direction away from the current collector, the liquid absorption capacity of the active layer is greater than the liquid absorption capacity of the separator.

[0109] Typically, an electrode assembly includes a separator and electrode sheets. The electrode sheets include positive and negative electrodes. The separators and electrode sheets are arranged alternately, more specifically in the order of positive electrode sheet, separator, and negative electrode sheet. For laminated electrode assemblies, the electrodes are stacked in this order. For wound electrode assemblies, the electrode sheets and separators are arranged in this order before winding.

[0110] For the test method of the liquid absorption capacity of different regions of the separator, reference can be made to the liquid absorption capacity test method and the method for determining the difference in liquid absorption capacity of different regions of the active layer described above. Generally, the liquid absorption capacity of the separator is between 1 and 15.

[0111] By changing the design of the liquid absorption capacity of the diaphragm in the direction from the side where the electrode tab of the current collector is set to the opposite side, the liquid absorption capacity of the diaphragm can be made higher on the side close to the electrode tab, further improving the electrolyte wettability of the electrode assembly in this direction.

[0112] At the same time, in the direction from the current collector to the direction away from the current collector, the liquid absorption capacity of the active layer is greater than the liquid absorption capacity of the diaphragm contained in the electrode assembly, which can reduce the situation where the diaphragm absorbs a large amount of electrolyte and causes insufficient electrolyte in the active layer, and improve the electrolyte wettability of the electrode in this direction.

[0113] It can be understood that, in the direction from the current collector to the direction away from the current collector, the liquid absorption capacity of the area of ​​the active layer close to the current collector is greater than or equal to the liquid absorption capacity of the area on the opposite side, and the liquid absorption capacity of at least one area of ​​the active layer close to the current collector is greater than the liquid absorption capacity of the area on the opposite side. At the same time, the liquid absorption capacity of the active layer is greater than the liquid absorption capacity of the diaphragm. Then, in this direction, the liquid absorption capacity of the electrode assembly is in the following relationship: the area of ​​the active layer close to the current collector > the area of ​​the active layer close to the diaphragm > the diaphragm, as shown in Figure c of Figure 1. The darker the color in the figure, the higher the liquid absorption capacity.

[0114] At the same time, combined with the distribution of the liquid absorption capacity of the active layer and the diaphragm in the direction from the side of the current collector where the pole tab is set to the other opposite side, it can be understood that the active layer has the highest liquid absorption capacity in the area close to the current collector and close to the pole tab, while the diaphragm has the lowest liquid absorption capacity in the area away from the pole tab.

[0115] In some embodiments, at least one of the active layer and the separator included in the electrode assembly includes at least two adjacent gradient units, extending from one side of the current collector where the tab is located to the opposite side, wherein the gradient unit on the side closest to the tab has a higher liquid absorption capacity than the gradient unit on the opposite side. Optionally, the number of gradient units is 2 to 10, for example, any one of 2, 3, 4, 5, 6, 7, 8, 9, or 10, or a range therebetween.

[0116] By providing multiple gradient units in the direction from one side of the current collector where the tab is provided to the opposite side, the liquid absorption capacity of the active layer and / or diaphragm in this direction can be gradually reduced layer by layer. The lower gradient units can provide a buffer for the downward movement of the electrolyte in the adjacent, higher gradient units, thereby helping to solve the problem of the electrolyte concentrating at the bottom of the electrode assembly due to gravity during long-term storage and use of the electrode assembly, and improving the electrolyte wettability of the electrode assembly in this direction. At the same time, experiments in the embodiments of the present application show that, within a certain range, the more gradient units are provided in this direction, the better the effect of improving the electrolyte wettability of the electrode assembly.

[0117] In some embodiments, the difference in liquid absorption capacity between two adjacent gradient units is 1.1 times to 5 times, optionally 1.2 times to 2 times, for example, it can be any point value of 1.1 times, 1.2 times, 1.4 times, 1.6 times, 1.8 times, 2 times, 2.5 times, 3 times, 3.5 times, 4 times, 4.5 times, 5 times, or a range value between any two of them.

[0118] The difference in liquid absorption capacity between two adjacent gradient units is a certain multiple, so that the lower gradient unit can provide a good buffering effect for the downward movement of the electrolyte in the adjacent, higher gradient unit, thereby improving the electrolyte wettability in the direction from the active layer close to the electrode ear to the opposite side.

[0119] In some embodiments, the height of any gradient unit in the direction from one side of the current collector where the pole ear is set to the other opposite side accounts for 10% to 60% of the total height of the active layer or the diaphragm, and can optionally be 10% to 50%. For example, it can be any point value among 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or a range value between any two of them.

[0120] Setting the height of the gradient units in the direction from the electrode tab side of the current collector to the opposite side within a suitable range is beneficial to increasing the number of gradient units, thereby improving the electrolyte wettability of the electrode assembly in this direction.

[0121] In some embodiments, the active layer includes at least two adjacent liquid-absorbing layers in a direction away from the current collector, wherein the liquid-absorbing layer on the side closest to the current collector has a higher liquid-absorbing capacity than the liquid-absorbing layer on the opposite side. Optionally, the number of liquid-absorbing layers is 2 to 10, for example, any one of 2, 3, 4, 5, 6, 7, 8, 9, or 10, or a range therebetween.

[0122] Considering that the active layer can include at least two adjacent gradient units in the direction from the current collector's tab to the opposite side, the gradient unit near the tab has a higher liquid absorption capacity than the gradient unit on the opposite side. Therefore, under certain conditions, a liquid absorption layer in the direction from the current collector to the direction away from the current collector may overlap with a gradient unit in the direction from the current collector's tab to the opposite side.

[0123] By providing multiple liquid-absorbing layers in the direction from the current collector to the direction away from the current collector, the liquid-absorbing capacity of the active layer in this direction can be gradually reduced layer by layer. When the volume of the electrode changes and the electrolyte is squeezed out, the liquid-absorbing layer on the side away from the current collector can provide a buffer for the electrolyte overflow tendency of the adjacent liquid-absorbing layer on the side closer to the current collector. This helps to solve the problem of reduced electrolyte wettability or difficulty in wetting the electrode due to the volume expansion or contraction of the electrode during the charge and discharge process, thereby improving the electrolyte wettability of the electrode assembly in this direction. At the same time, experiments have shown that within a certain range, the greater the number of liquid-absorbing layers provided in the direction from the current collector to the direction away from the current collector, the better the improvement effect on the electrolyte wettability of the electrode assembly.

[0124] In some embodiments, the thickness of any one liquid absorption layer in the direction from the current collector to the direction away from the current collector accounts for 10% to 60% of the total thickness of the active layer on one side of the current collector, and can be optionally 10% to 50%. For example, it can be any point value among 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or a range value between any two of them.

[0125] Setting the thickness of the liquid absorption layer in the direction from the current collector to the direction away from the current collector within an appropriate range is beneficial to increasing the number of liquid absorption layers, thereby improving the electrolyte wettability of the electrode assembly in this direction.

[0126] In some embodiments, the active layer comprises a first electrolyte absorber;

[0127] In a direction from one side of the current collector where the tab is provided to the other opposite side, the mass content of the first electrolyte absorber in the region of the active layer close to the tab is greater than or equal to the mass content of the first electrolyte absorber in the region on the other opposite side, and the mass content of the first electrolyte absorber in at least one region of the active layer close to the tab is greater than the mass content of the first electrolyte absorber in the region on the other opposite side;

[0128] In the direction from the current collector to the direction away from the current collector, the mass content of the first electrolyte absorber in the area of ​​the active layer close to the current collector is greater than or equal to the mass content of the first electrolyte absorber in the area on the other side, and the mass content of the first electrolyte absorber in at least one area of ​​the active layer close to the current collector is greater than the mass content of the first electrolyte absorber in the area on the other side.

[0129] An electrolyte absorber refers to a material capable of absorbing electrolyte. The active layer contains the electrolyte absorber, which, along with other components such as the active material, conductive agent, and binder, forms the active layer. The mass content of the electrolyte absorber in the active layer can be determined using a combination of inductively coupled plasma (ICP), energy dispersive X-ray spectroscopy (EDS), hydrogen spectrometry, and carbon spectrometry.

[0130] By adding an electrolyte absorber to the active layer and adjusting the mass content of the electrolyte absorber to change along a certain direction, the electrode assembly can have different absorption and retention capabilities for the electrolyte in different areas, and present a certain distribution pattern of liquid absorption along a specific direction, which is beneficial to improving the electrolyte wettability of the electrode assembly.

[0131] In some embodiments, the separator included in the electrode assembly comprises a base membrane and a separator coating disposed on at least one side of the base membrane; the separator coating comprises a second electrolyte absorbent;

[0132] In the direction from the side of the current collector where the pole tab is set to the other opposite side, the mass content of the second electrolyte absorber in the area of ​​the diaphragm coating close to the pole tab is greater than or equal to the mass content of the second electrolyte absorber in the area on the other opposite side, and the mass content of the second electrolyte absorber in at least one area of ​​the diaphragm coating close to the pole tab is greater than the mass content of the second electrolyte absorber in the area on the other opposite side.

[0133] In some embodiments, in a direction from the current collector to away from the current collector, the mass content of the first electrolyte absorber in the active layer is greater than the mass content of the second electrolyte absorber in the separator coating.

[0134] The separator coating contains an electrolyte absorbent, meaning the electrolyte absorbent and other materials form a coating on at least one side of the base membrane. By adding the electrolyte absorbent to the separator coating and adjusting the mass content of the electrolyte absorbent along a specific direction, the electrode assembly can have different electrolyte absorption and retention capabilities in different areas, and exhibit a certain distribution of electrolyte absorption capacity along a specific direction, further improving the electrolyte wettability of the electrode assembly.

[0135] In some embodiments, the first electrolyte absorber and the second electrolyte absorber independently include one or more of polymethyl methacrylate, polymethyl acrylate, polyethyl acrylate, polyvinyl acetate, polyacrylamide, polyacrylic acid, and polyacrylonitrile.

[0136] These polymers have a high affinity for electrolytes and swell to absorb the electrolyte into a gel upon contact. By using these polymers as electrolyte absorbers and adjusting their distribution within the active layer and separator coating, the electrode assembly can be effectively designed to exhibit a gradient or gradual change in liquid absorption along specific directions, thereby improving the electrolyte wettability of the electrode assembly.

[0137] In some embodiments, the mass content of the first electrolyte absorber in the active layer and the mass content of the second electrolyte absorber in the separator coating are each independently greater than 0 and less than or equal to 8%, and optionally greater than or equal to 1% and less than or equal to 6%. For example, the mass content can be any of 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, or 8%, or a range therebetween.

[0138] Setting the mass content of the electrolyte absorber in the active layer and diaphragm coating within an appropriate range is not only beneficial for adjusting the liquid absorption capacity of different areas of the electrode assembly, but also does not cause a significant reduction in the active material in the active layer, thereby maintaining the stability of the electrode capacity.

[0139] The electrode assembly includes a positive electrode and a negative electrode, with a separator positioned between the positive and negative electrodes to separate them. For detailed technical features of the positive and negative electrodes, separators, and methods for preparing the electrode assembly, please refer to the following.

[0140] 1. Positive electrode

[0141] The positive electrode sheet may include a positive electrode current collector and a positive electrode active layer provided on at least one side of the positive electrode current collector and comprising a positive electrode active material, a binder, and a conductive agent.

[0142] The positive electrode active material is the key substance involved in the battery chemical reaction in the positive electrode sheet. The conductive agent is used to collect microcurrents between the positive electrode active materials and between the positive electrode active materials and the positive electrode current collector, thereby improving electronic conductivity. At the same time, the conductive agent can also promote the infiltration of the electrolyte into the positive electrode sheet. The binder can improve the bonding strength between the various substances in the positive electrode active layer and between the positive electrode active layer and the positive electrode current collector. The thickener is helpful in increasing the viscosity of the positive electrode slurry and improving the processing performance of the positive electrode slurry. The positive electrode current collector is used to transmit electrons.

[0143] 1.1. Positive electrode active material

[0144] Depending on the type of battery the electrode assembly is used for, the positive electrode sheet can use different positive electrode active materials. The electrode assembly of the embodiment of the present application can be used in both lithium-ion batteries and sodium-ion batteries.

[0145] When the electrode assembly is applied to a lithium-ion battery, the positive electrode active material may include one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium nickel oxide, lithium cobalt oxide, and lithium ferrite.

[0146] In the case where the electrode assembly is applied to a sodium ion battery, the positive electrode active material may include one or more of a layered oxide, a polyanion compound, and a Prussian blue compound. For example, the layered oxide may include Na x MO2, M=Fe, Mn, Ni, Co, Cr, Sc, Ti, V, Cr, Cu, Zn and combinations thereof, 0.4≤x≤1. The polyanion compound may include one or more of phosphate, pyrophosphate, sulfate, and anion-doped types.

[0147] The mass content of the positive electrode active material in the positive electrode active layer is 80% to 98%, and may include, but is not limited to, any one of 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, and 98%, or a range therebetween. It is understood that setting the mass content of the positive electrode active material in the active layer of the positive electrode sheet at a higher level can increase the energy density of the battery.

[0148] 1.2. Conductive agent

[0149] The conductive agent may include one or more of acetylene black (SP), carbon nanotubes, conductive carbon black (super-P), Ketjen black, carbon fiber, and graphene.

[0150] The mass content of the conductive agent in the positive electrode active layer can be 0.5% to 5%, for example, any one of 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range between any two of them, and can also be set to other contents as needed.

[0151] 1.3. Binder

[0152] The binder includes but is not limited to one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, polyimide, polytetrafluoroethylene, polybutyl acrylate, polyacrylonitrile, carboxymethyl cellulose, carboxymethyl cellulose salt, polyacrylic acid, polyacrylate, polyvinyl alcohol, sodium alginate, cyclodextrin, styrene-butadiene rubber, vinyl acetate resin, acrylic resin, and chlorinated rubber.

[0153] The mass content of the binder in the positive electrode active layer is 0.5% to 5%, for example, any one of 0.5%, 1%, 2%, 3%, 4%, and 5%, or a range between any two of them.

[0154] 1.4. Cathode Current Collector

[0155] The positive electrode active layer is disposed on at least one side of the positive electrode current collector, and optionally on both sides of the positive electrode current collector. The positive electrode current collector may include, but is not limited to, a metal current collector, a carbon current collector, a conductive resin current collector, a metal-resin composite current collector, and more specifically, aluminum, copper, nickel, titanium, iron, and alloys thereof, stainless steel, carbon fiber, carbon nanotubes (CNTs), graphite, and the like. Optionally, the positive electrode current collector includes aluminum.

[0156] 2. Negative electrode

[0157] The negative electrode sheet may include a negative electrode current collector and a negative electrode active layer disposed on at least one side of the negative electrode current collector and comprising a negative electrode active material, a binder, and a conductive agent.

[0158] The negative electrode active material may include one or more of graphite, hard carbon, soft carbon, mesophase carbon microbeads, graphene, silicon, and silicon dioxide. The mass content of the negative electrode active material in the negative electrode active layer may include, but is not limited to, 90% to 98%, for example, any one of 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, and 98%, or a range therebetween.

[0159] The types of conductive agents and binders in the negative electrode sheet, and their mass contents in the negative electrode active layer can be referred to the positive electrode sheet and will not be repeated here.

[0160] The negative electrode active layer may also optionally include a thickener, such as carboxymethyl cellulose (CMC). The mass content of the thickener in the active layer includes, but is not limited to, 0.5% to 5%, for example, any one of 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, and 5%, or any range therebetween.

[0161] The negative electrode current collector may include but is not limited to a metal current collector, a carbon current collector, a conductive resin current collector, a composite current collector of metal and resin, and more specifically copper, nickel, titanium, iron and their respective alloys, stainless steel, carbon fiber, carbon nanotubes (CNT), graphite, and the like.

[0162] 3. Diaphragm

[0163] The separator in the electrode assembly includes a base membrane and a separator coating layer disposed on at least one side of the base membrane.

[0164] The base membrane can be any porous structure membrane with electrochemical stability and mechanical stability, such as a single layer or multilayer film of one or more of glass fiber, non-woven fabric, polyethylene (PE), polypropylene (PP) and polyvinylidene fluoride (PVDF).

[0165] The membrane coating typically also includes one or more inorganic and organic materials. Inorganic materials may include one or more of alumina and boehmite, which can improve the membrane's heat resistance, hardness, chemical stability, and flame retardancy. Organic materials may include one or more of aramid, polyvinylidene fluoride, and polymethyl methacrylate (PMMA), which can act as a binder to enhance adhesion or improve the membrane's chemical stability and heat resistance.

[0166] [Method for preparing electrode assembly]

[0167] The electrode assembly of the embodiment of the present application can be prepared by the following method.

[0168] A second aspect of this embodiment provides a method for preparing an electrode assembly, comprising:

[0169] An active layer is prepared on at least one side of the current collector in the thickness direction, and a tab is provided on one side of the current collector in the height direction;

[0170] In the direction from the tab side to the opposite side of the current collector, the liquid absorption capacity of the active layer near the tab side is controlled to be greater than or equal to the liquid absorption capacity of the opposite side, and the liquid absorption capacity of at least one area of ​​the active layer near the tab side is greater than the liquid absorption capacity of the opposite side;

[0171] In the direction from the current collector to the direction away from the current collector, the liquid absorption capacity of the area of ​​the active layer close to the current collector is controlled to be greater than or equal to the liquid absorption capacity of the area on the opposite side, and the liquid absorption capacity of at least one area of ​​the active layer close to the current collector is greater than the liquid absorption capacity of the area on the opposite side.

[0172] By making the active layer have different absorption capacities for the electrolyte in specific directions, it is possible to compensate for the problem of poor electrolyte wettability of the electrode assembly caused by gravity during long-term storage and use, which tends to concentrate the electrolyte at the bottom of the electrode assembly. It can also compensate for the problem of reduced electrolyte wettability of the electrode sheet caused by the expansion or contraction of the electrode volume squeezing out the electrolyte during the charge and discharge process, thereby improving the electrolyte wettability of the electrode assembly.

[0173] The variation trend of the active layer's liquid absorption capacity in different directions can be controlled by the following methods:

[0174] preparing an active layer comprising a first electrolyte absorbent;

[0175] From one side of the current collector where the tab is provided to the other opposite side, the mass content of the first electrolyte absorber in the region of the active layer close to the tab is controlled to be greater than or equal to the mass content of the first electrolyte absorber in the region on the other opposite side, and the mass content of the first electrolyte absorber in at least one region of the active layer close to the tab is greater than the mass content of the first electrolyte absorber in the region on the other opposite side;

[0176] In the direction from the current collector to the direction away from the current collector, the mass content of the first electrolyte absorber in the active layer is controlled to decrease gradually, and the mass content of the first electrolyte absorber in the area of ​​the active layer close to the current collector is controlled to be greater than or equal to the mass content of the first electrolyte absorber in the area on the other side, and the mass content of the first electrolyte absorber in at least one area of ​​the active layer close to the current collector is greater than the mass content of the first electrolyte absorber in the area on the other side.

[0177] By adding an electrolyte absorber to the active layer and adjusting the mass content of the electrolyte absorber to change along a certain direction, the active layer can have different absorption and retention capabilities for the electrolyte in different areas, and exhibit varying liquid absorption capabilities along a specific direction, thereby improving the electrolyte wettability of the electrode assembly.

[0178] In some embodiments, the method for preparing an electrode assembly further comprises:

[0179] In the direction from the tab side to the opposite side of the current collector, the liquid absorption capacity of the region of the separator contained in the control electrode assembly near the tab side is greater than or equal to the liquid absorption capacity of the opposite side region, and the liquid absorption capacity of at least one region of the separator near the tab side is greater than the liquid absorption capacity of the opposite side region;

[0180] In the direction from the current collector to the direction away from the current collector, the liquid absorption capacity of the active layer is controlled to be greater than the liquid absorption capacity of the separator.

[0181] By varying the separator's liquid absorption capacity from the current collector's tab side to the opposite side, the separator's liquid absorption capacity is increased near the tab side, further improving the electrode assembly's electrolyte wettability in that direction. Simultaneously, from the current collector toward the direction away from the current collector, the active layer's liquid absorption capacity is greater than that of the separator within the electrode assembly. This reduces the risk of electrolyte starvation in the active layer caused by the separator absorbing large amounts of electrolyte, thereby improving the electrode's electrolyte wettability in that direction.

[0182] The liquid absorption capacity of the separator can be set by the following method: preparing a separator coating on at least one side of the base film to obtain the separator; the separator coating comprises a second electrolyte absorbent;

[0183] From the side of the current collector where the tab is provided to the opposite side, the mass content of the second electrolyte absorber in the region of the diaphragm coating close to the tab is controlled to be greater than or equal to the mass content of the second electrolyte absorber in the region on the opposite side, and the mass content of the second electrolyte absorber in at least one region of the diaphragm coating close to the tab is greater than the mass content of the second electrolyte absorber in the region on the opposite side;

[0184] In the direction from the current collector to the direction away from the current collector, the mass content of the first electrolyte absorber in the active layer is controlled to be greater than the mass content of the second electrolyte absorber in the diaphragm coating.

[0185] By adding an electrolyte absorber to the diaphragm coating and adjusting the mass content of the electrolyte absorber to change along a certain direction, the electrode assembly can have different absorption and retention capabilities for the electrolyte in different areas, and exhibit varying liquid absorption capabilities along a specific direction, further improving the electrolyte wettability of the electrode assembly.

[0186] In the above preparation method, the method for preparing the active layer may include: mixing the active material, the conductive agent, the binder, the first electrolyte absorber (other components may be added as needed) with the solvent to obtain the electrode slurry; coating the electrode slurry on at least one side of the current collector, drying and compacting.

[0187] Since the mass content of the first electrolyte absorber in the active layer varies along a certain direction, electrode slurries containing different first electrolyte absorber contents can be prepared in advance and applied in layers and regions in sequence to form an active layer whose liquid absorption capacity varies according to a certain rule.

[0188] Similarly, for the preparation of the separator coating, the second electrolyte absorber can be formed into a slurry with the other components and solvent in the separator coating, and then coated on at least one side of the base membrane. Because the mass content of the second electrolyte absorber in the separator coating varies along a certain direction, slurries containing different electrolyte absorber contents can be prepared in advance and applied in layers and regions in sequence, thereby forming a separator coating with a liquid absorption capacity that varies according to a certain pattern.

[0189] In addition, the preparation method of the electrode assembly further includes: arranging the electrode sheets and the separator in sequence, stacking or winding them, and obtaining the electrode assembly. It can be understood that the electrode sheets of the electrode assembly include positive and negative electrode sheets, and the separator is disposed between the positive and negative electrode sheets to separate the positive and negative electrode sheets. Therefore, arranging the electrode sheets and the separator in sequence, and performing the stacking or winding step, more specifically, includes alternatingly arranging the positive and negative electrode sheets, disposing the separator between the positive and negative electrode sheets to separate the two, and stacking or winding them to form the electrode assembly.

[0190] [Battery]

[0191] A third aspect of an embodiment of the present application provides a battery, which includes the electrode assembly of the first aspect described above.

[0192] The above-mentioned electrode assembly has good electrolyte wettability. During long-term storage and use, its top and the active layer of the electrode near the inner side of the current collector can be well wetted by the electrolyte. After applying it to the battery, the battery will exhibit low resistance and excellent cycle performance.

[0193] The electrode assembly of the embodiment of the present application can be a laminated electrode assembly or a wound electrode assembly. Therefore, the battery can also be one or both of a laminated battery and a wound battery.

[0194] Typically, a battery includes, in addition to an electrode assembly, an electrolyte, an outer packaging, etc. Meanwhile, the battery of the embodiment of the present application may include one or more of a battery cell, a battery module, and a battery pack.

[0195] 1. Electrolytes

[0196] The electrolyte can serve as a carrier for ion transport in the battery. In the battery of the embodiment of the present application, the electrolyte used can be a solid electrolyte, such as a polymer electrolyte, an inorganic solid electrolyte, etc., but is not limited thereto; the electrolyte can also be an electrolyte solution.

[0197] The electrolyte solution includes a solvent and a metal salt dissolved in the solvent.

[0198] The solvent may be a non-aqueous organic solvent, for example, one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB) and ethyl butyrate (EB), preferably two or more.

[0199] The battery of the embodiment of the present application may include one or both of a lithium-ion battery and a sodium-ion battery. For a lithium-ion battery, the metal salt in its electrolyte includes a lithium salt; for a sodium-ion battery, the metal salt in its electrolyte includes a sodium salt.

[0200] The lithium salt may include one or more of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bisfluorosulfonyl imide), LiTFSI (lithium bistrifluoromethanesulfonyl imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalatoborate), LiBOB (lithium bisoxalatoborate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorooxalatophosphate) and LiTFOP (lithium tetrafluorooxalatophosphate).

[0201] Sodium salts may include sodium hexafluorophosphate (NaPF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium trifluoromethanesulfonate (NaOTf), sodium sulfide (Na2S), sodium chloride (NaCl), sodium fluoride (NaF), sodium sulfate (Na2SO4), sodium carbonate (Na2CO3), sodium phosphate (Na3PO4), sodium nitrate (NaNO3), sodium difluorooxalatoborate (NaDFOB), sodium pyrophosphate (Na4P2O7), sodium dodecylbenzenesulfonate (SDBS), sodium dodecyl sulfate (SDS), trisodium citrate, sodium metaborate (NaBO2), sodium borate One or more of sodium tungstate (Na2B4O7), sodium molybdate (Na2MoO4), sodium tungstate (Na2WO4), sodium bromide (NaBr), sodium nitrite (NaNO2), sodium iodate (NaIO3), sodium iodide (NaI), sodium silicate (Na2SiO3), sodium lignin sulfonate, sodium oxalate (Na2C2O4), sodium aluminate (NaAlO2), sodium methane sulfonate, sodium acetate (CH3COONa), sodium dichromate (Na2Cr2O7), sodium hexafluoroarsenate (NaAsF6), sodium tetrafluoroborate (NaBF4), and sodium perchlorate (NaClO4).

[0202] The electrolyte may also optionally contain other additives, such as vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), succinonitrile (SN), adiponitrile (ADN), glutaronitrile (GLN), hexanetrinitrile (HTN), 1,3-propane sultone (1,3-PS), vinyl sulfate (DTD), methylene disulfonate (MMDS), 1-propylene-1,3-sultone (PST), 4-methylethylene sulfate (PCS), 4-ethylethylene sulfate (PES), 4-propylethylene sulfate (PEGLST), propylene sulfate (TS), 1,4-butane sultone (1,4-BS), ethylene sulfite (DTO), dimethyl sulfite (DMS), diethyl sulfite (DES), sulfonate cyclic quaternary ammonium salt, tris(trimethylsilyl) phosphate (TMSP) and tris(trimethylsilyl) borate (TMSB), but are not limited thereto.

[0203] The electrolyte may also include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0204] The amount of electrolyte injected into the battery can be determined based on the designed injection coefficient. The injection coefficient is the mass of electrolyte injected per unit capacity. The amount of electrolyte injected = battery cell design capacity * injection coefficient.

[0205] In an embodiment of the present application, the filling coefficient of the battery can be set to 1g / Ah to 5g / Ah, optionally 1.2g / Ah to 2g / Ah, for example, any one of 1g / Ah, 1.2g / Ah, 1.4g / Ah, 1.6g / Ah, 1.8g / Ah, 2g / Ah, 2.2g / Ah, 2.4g / Ah, 2.6g / Ah, 2.8g / Ah, 3g / Ah, 3.2g / Ah, 3.4g / Ah, 3.6g / Ah, 3.8g / Ah, 4g / Ah, 4.2g / Ah, 4.4g / Ah, 4.6g / Ah, 4.8g / Ah, and 5g / Ah, or a range of values ​​therebetween. The electrode assembly of the embodiment of the present application can guide the infiltration of the electrolyte and has good electrolyte wettability even at a lower filling coefficient. Therefore, when the electrode assembly of the embodiment of the present application is applied to a battery, it is beneficial to reduce the battery's filling coefficient and reduce the amount of electrolyte injection. In addition, experiments have shown that the electrode assembly of the embodiment of the present application has an excellent effect on improving the electrochemical performance of batteries with low filling coefficients.

[0206] 2. Outer packaging

[0207] The battery may include an outer packaging that can be used to encapsulate an electrode assembly including a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte.

[0208] The battery outer packaging can be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell; or a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0209] The outer package shape can be cylindrical, square or any other shape. For example, FIG11 is an example of a battery cell with an outer package shape of a square structure.

[0210] Referring to Figure 12 , the outer packaging may include a housing 01 and a cover plate 02 . Housing 01 may include a base plate and side plates connected to the base plate, which together form a housing cavity. Housing 01 has an opening communicating with the housing cavity, and cover plate 02 can be positioned over the opening to seal the housing cavity. The positive electrode sheet, negative electrode sheet, and separator may be wound or laminated to form an electrode assembly 03 . One or more electrode assemblies 03 are encapsulated within the housing cavity. Electrolyte is impregnated within electrode assembly 03 .

[0211] 3.Battery cells, battery modules, and battery packs

[0212] The battery of the embodiment of the present application may be at least one of a battery cell, a battery module, and a battery pack. According to different packaging forms, batteries are divided into battery cells, battery modules, and battery packs. Among them, the battery cell is the most basic unit of a secondary battery, including an electrode assembly and an electrolyte. The electrode assembly is usually composed of a positive electrode sheet, a negative electrode sheet, and an isolating member. The positive electrode sheets and the negative electrode sheets are alternately stacked, and a diaphragm is provided between the positive electrode sheet and the negative electrode sheet to play an isolating role to obtain a bare cell, or a bare cell can be obtained after winding. The cell is placed in a casing, the electrolyte is injected, and the casing is sealed to obtain a battery cell. The battery cell mainly relies on the movement of metal ions in the electrolyte between the positive electrode sheet and the negative electrode sheet to work.

[0213] In some battery packaging technologies, one or more battery cells can be first integrated into a battery module, and then one or more battery modules can be assembled into a battery pack. In other battery packaging technologies, one or more battery cells can be directly installed in a box to form a battery pack, eliminating the intermediate state of the battery module, thereby reducing the weight of the battery pack and improving the energy density of the battery.

[0214] Referring to Figure 13 , which illustrates an exemplary battery module, multiple battery cells 04 may be arranged sequentially along the length of the module. Alternatively, they may be arranged in any other manner. Furthermore, the multiple battery cells 04 may be secured together using fasteners.

[0215] Optionally, the battery module may further include a housing having a receiving space, and the plurality of battery cells 04 are received in the receiving space.

[0216] Refer to Figures 14 and 15 , which illustrate an example battery pack. The battery pack may include a battery box and multiple battery modules 05 disposed within the battery box. The battery box includes an upper box body 06 and a lower box body 07 . The upper box body 06 can be placed over the lower box body 07 to form an enclosed space for accommodating the battery modules 05 . The multiple battery modules 05 can be arranged in any manner within the battery box.

[0217] [Electrical devices]

[0218] An embodiment of the present application further provides an electrical device, which includes the battery of the third aspect described above.

[0219] The battery disclosed in the embodiments of this application can be used in electrical devices that use batteries as power sources, or in various energy storage systems that use batteries as energy storage elements, to provide electrical energy. The battery exhibits the advantages of low resistance and good cycle performance. Therefore, its application in various electrical devices can improve the user experience of various electrical devices.

[0220] Electrical devices may include, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, and the like. Electric toys may include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys. Spacecraft may include airplanes, rockets, space shuttles, and spacecraft. The electrical devices may be selected from batteries consisting of single cells, battery modules, or battery packs based on their intended use.

[0221] Figure 16 shows an example of an electric device. This device can be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of this device, a battery pack or battery module can be used.

[0222] The following embodiments of the present application are described in detail. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0223] In the following examples and comparative examples, for simplicity, D1 is used to refer to the direction from the side of the current collector where the tab is located to the opposite side. For positive electrode sheets, D1 refers to the direction from the side of the positive electrode current collector where the tab is located to the opposite side. For negative electrode sheets, D1 refers to the direction from the side of the negative electrode current collector where the tab is located to the opposite side. D2 is used to refer to the direction from the current collector to the direction away from the current collector. For positive electrode sheets, D2 refers to the direction from the positive electrode current collector to the direction away from the positive electrode current collector. For negative electrode sheets, D2 refers to the direction from the negative electrode current collector to the direction away from the negative electrode current collector.

[0224] Furthermore, considering that the active layer in the D1 direction can include at least two adjacent gradient units with decreasing liquid absorption capacity, and in the D2 direction, the active layer can include at least two adjacent absorbent layers with decreasing liquid absorption capacity, a certain absorbent layer in the D2 direction may overlap with a gradient unit in the D1 direction. Therefore, in the following embodiments and comparative examples, the term "gradient unit" is used to uniformly represent regions with different liquid absorption capacities.

[0225] Example 1

[0226] This embodiment provides a lithium-ion battery comprising an electrode assembly consisting of a positive electrode sheet, a negative electrode sheet, and a separator, as well as an electrolyte and an outer packaging. The negative electrode sheet and the separator include polyethyl acrylate (electrolyte absorbent) with a gradient content. The electrode assembly is placed in the outer packaging and is impregnated with the electrolyte.

[0227] The electrode assembly comprises:

[0228] 1) Negative electrode

[0229] The negative electrode sheet includes a negative electrode current collector copper foil with a thickness of 8 μm and a negative electrode active layer with a total thickness of 60 μm arranged on both surfaces of the negative electrode current collector. At the same time, a negative electrode ear is arranged on one side of the negative electrode current collector in the height direction.

[0230] In this embodiment, the negative electrode active layer on one side of the negative electrode sheet is provided with a plurality of gradient units with a decreasing mass content of polyethyl acrylate in directions D1 and D2, ie, a single-sided gradient design.

[0231] As shown in Figure 2, the negative electrode active layer (first negative electrode active layer 11, 30 μm thick) on one side of the negative electrode current collector 10 in the negative electrode sheet includes, along the thickness direction of the negative electrode sheet, a stacked first gradient unit 111 and a second gradient unit 112, as well as a stacked third gradient unit 113 and a fourth gradient unit 114. The first gradient unit 111 and the third gradient unit 113 are located close to the negative electrode current collector 10 and are arranged side by side along the height direction of the negative electrode current collector 10, with the first gradient unit 111 located close to the top of the negative electrode current collector 10. The second gradient unit 112 and the fourth gradient unit 114 are arranged side by side along the height direction of the negative electrode current collector 10, with the second gradient unit 112 located close to the top of the negative electrode current collector 10.

[0232] The first gradient unit 111, the second gradient unit 112, the third gradient unit 113 and the fourth gradient unit 114 have the same size (same length, width and thickness), and all contain polyethyl acrylate, graphite, 2.5wt% styrene-butadiene rubber (SBR), 0.5wt% acetylene black (SP) and 1.2wt% carboxymethyl cellulose (CMC), wherein the total mass content of polyethyl acrylate and graphite is 95.8wt%, and the mass content of polyethyl acrylate in the first gradient unit 111, the second gradient unit 112, the third gradient unit 113 and the fourth gradient unit 114 is 5%, 4%, 4% and 3%, respectively.

[0233] The negative electrode active layer on the other side of the negative electrode current collector 10 (the second negative electrode active layer, with a thickness of 30 μm, not shown in FIG. 2 ) contains 95.8 wt % graphite, 2.5 wt % SBR, 0.5 wt % SP, and 1.2 wt % CMC.

[0234] The negative electrode sheet can be prepared as follows:

[0235] Four negative electrode slurries corresponding to the first gradient unit 111, the second gradient unit 112, the third gradient unit 113 and the fourth gradient unit 114 are prepared respectively, and the first gradient unit 111 and the third gradient unit 113 are coated on one side of the negative electrode current collector 10 by an LOM (laminated entity manufacturing or layered entity manufacturing) extrusion coating device, followed by drying. Then, the second gradient unit 112 and the fourth gradient unit 114 are coated side by side next to the first gradient unit 111 and the third gradient unit 113 by an LOM extrusion coating device, and dried again.

[0236] The negative electrode slurry corresponding to the other side of the negative electrode current collector 10 is coated and dried.

[0237] After coating and drying, cold pressing is performed to obtain a negative electrode sheet.

[0238] 2) Positive electrode

[0239] The positive electrode sheet includes a positive electrode collector aluminum foil with a thickness of 15 μm and a positive electrode active layer with a total thickness of 80 μm arranged on both surfaces of the positive electrode collector. The positive electrode active layer contains 96 wt% lithium nickel cobalt manganese oxide NCM111, 3 wt% polyvinylidene fluoride PVDF and 1 wt% acetylene black SP.

[0240] Mix NCM111, PVDF, and SP, add N-methylpyrrolidone, stir, and disperse to obtain a positive electrode slurry. Apply the positive electrode slurry onto aluminum foil, dry, and cold press to obtain a positive electrode sheet.

[0241] 3) Diaphragm

[0242] The separator includes a base film (a 12μm thick PE film) and a 3μm thick separator coating disposed on one side of the base film. Referring to Figure 2 , the separator coating 31 comprises two gradient units with polyethyl acrylate content of 2% and 1% by weight, respectively. Separator coating 31 also includes 3% by weight PVDF and the balance alumina. The polyethyl acrylate content increases from bottom to top along the height of the negative electrode current collector 10. That is, the gradient unit with a 2% polyethyl acrylate content is located near the top of the negative electrode current collector 10.

[0243] 4) Lithium-ion batteries

[0244] The positive electrode sheet, separator, and negative electrode sheet are arranged in sequence, with the separator positioned between the positive and negative electrodes to provide isolation, and the first negative active layer 11 of the negative electrode sheet adjacent to the separator coating 13. After arrangement, the electrode assembly is wound. The electrode assembly is placed in an outer package and filled with the prepared electrolyte (1M LiPF6, EMC:EC volume ratio of 7:3, injection coefficient of 1.2g / Ah). The battery is then packaged, filled, formed, and vented to produce a wound hard-shell lithium-ion battery.

[0245] Example 2

[0246] The difference between this embodiment and embodiment 1 is that the negative electrode active layers on both sides of the negative electrode sheet are provided with multiple gradient units with decreasing polyethyl acrylate mass content in the D1 and D2 directions, with a double-sided gradient design.

[0247] That is, in this embodiment, the second negative electrode active layer of the negative electrode sheet has the same structure as the first negative electrode active layer, and includes four gradient units with polyethyl acrylate mass contents of 5%, 4%, 4%, and 3%, respectively. The distribution positions of the four gradient units in the second negative electrode active layer are symmetrical with the first gradient unit 111, the second gradient unit 112, the third gradient unit 113, and the fourth gradient unit 114, as shown in Figure 3.

[0248] Example 3

[0249] The difference between this embodiment and embodiment 2 is that the positive electrode active layer on one side of the positive electrode sheet is provided with multiple gradient units with a decreasing mass content of polyethyl acrylate in the D1 and D2 directions, having a single-sided gradient design.

[0250] Specifically, in this embodiment, the positive electrode sheet includes a positive electrode current collector aluminum foil with a thickness of 15 μm and a positive electrode active layer with a total thickness of 80 μm provided on both surfaces of the positive electrode current collector, and a positive electrode tab is provided on one side of the positive electrode current collector in the height direction.

[0251] 4 , the positive electrode active layer (first positive electrode active layer 21, 40 μm thick) on one side of the positive electrode current collector 20 includes, along the thickness direction of the positive electrode sheet, a stacked a-th gradient unit 211 and b-th gradient unit 212, as well as a stacked c-th gradient unit 213 and d-th gradient unit 214. The a-th gradient unit 211 and the c-th gradient unit 213 are located near the positive electrode current collector 20 and are arranged side by side along the height direction of the positive electrode current collector 20, with the a-th gradient unit 211 located near the top of the positive electrode current collector 20. The b-th gradient unit 212 and the d-th gradient unit 214 are arranged side by side along the height direction of the positive electrode current collector 20, with the b-th gradient unit 212 located near the top of the positive electrode current collector 20.

[0252] The ath gradient unit 211, the bth gradient unit 212, the cth gradient unit 213 and the dth gradient unit 214 have the same size (same length, width and thickness), and all contain polyethyl acrylate, NCM111, 3wt% PVDF and 1wt% SP, wherein the total mass content of polyethyl acrylate and NCM111 is 96wt%, and the mass content of polyethyl acrylate in the ath gradient unit 211, the bth gradient unit 212, the cth gradient unit 213 and the dth gradient unit 214 are 5%, 4%, 4% and 3% respectively.

[0253] The positive electrode active layer on the other side of the positive electrode current collector (the second positive electrode active layer, with a thickness of 40 μm, not shown in FIG4 ) contains 96 wt % NCM111, 3 wt % PVDF, and 1 wt % SP.

[0254] Example 4

[0255] The difference between this embodiment and embodiment 3 is that the positive electrode active layers on both sides of the positive electrode sheet are provided with multiple gradient units with a decreasing mass content of polyethyl acrylate in the D1 and D2 directions, with a double-sided gradient design.

[0256] That is, in this embodiment, the second positive electrode active layer of the positive electrode sheet has the same structure as the first positive electrode active layer, and includes four gradient units with polyethyl acrylate mass contents of 5%, 4%, 4%, and 3%, respectively. The distribution positions of the four gradient units in the positive electrode sheet are symmetrical with the a-th gradient unit 211, the b-th gradient unit 212, the c-th gradient unit 213, and the d-th gradient unit 214, as shown in Figure 5.

[0257] Example 5

[0258] The difference between this embodiment and embodiment 4 is that, in the negative electrode sheet, the first negative electrode active layer and the second negative electrode active layer both have two additional gradient units with polyethyl acrylate mass contents of 6% and 5% respectively; at the same time, in the positive electrode sheet, the first positive electrode active layer and the second positive electrode active layer both have two additional gradient units with polyethyl acrylate mass contents of 6% and 5% respectively.

[0259] Specifically, the structures of the negative electrode sheet and the positive electrode sheet of this embodiment are as follows:

[0260] 1) Negative electrode

[0261] 6 , in this embodiment, the first negative active layer 11 (30 μm thick) on one side of the negative current collector 10 includes, along the thickness direction of the negative electrode sheet, a stacked first gradient unit 111, a second gradient unit 112, a stacked third gradient unit 113, a stacked fourth gradient unit 114, and a stacked fifth gradient unit 115 and a sixth gradient unit 116. The first, third, and fifth gradient units 111, 113, and 115 are located near the negative current collector 10 and are arranged sequentially along the height direction of the negative current collector 10, with the first gradient unit 111 located near the top of the negative current collector 10. The second, fourth, and sixth gradient units 112, 114, and 116 are arranged side by side along the height direction of the negative current collector 10, with the second gradient unit 112 located near the top of the negative current collector 10.

[0262] The first gradient unit 111, the second gradient unit 112, the third gradient unit 113, the fourth gradient unit 114, the fifth gradient unit 115 and the sixth gradient unit 116 have the same size (same length, width and thickness), and all contain polyethyl acrylate, graphite, 2.5wt% SBR, 0.5wt% SP and 1.2wt% CMC, wherein the total mass content of polyethyl acrylate and graphite is 95.8wt%, and the mass content of polyethyl acrylate in the first gradient unit 111, the second gradient unit 112, the third gradient unit 113, the fourth gradient unit 114, the fifth gradient unit 115 and the sixth gradient unit 116 is 6%, 5%, 5%, 4%, 4% and 3%, respectively.

[0263] The second negative electrode active layer on the other side of the negative electrode current collector 10 has a symmetrical structure to the first negative electrode active layer.

[0264] 2) Positive electrode

[0265] 7 , in the positive electrode sheet of this embodiment, the positive electrode active layer (first positive electrode active layer 21, 40 μm thick) on one side of the positive electrode current collector 20 includes, along the thickness direction of the positive electrode sheet, stacked a-th gradient unit 211 and b-th gradient unit 212, stacked c-th gradient unit 213 and d-th gradient unit 214, and stacked e-th gradient unit 215 and f-th gradient unit 216. The a-th gradient unit 211, c-th gradient unit 213, and e-th gradient unit 215 are located near the positive electrode current collector 20 and are arranged sequentially along the height direction of the positive electrode current collector 20, with the a-th gradient unit 211 located near the top of the positive electrode current collector 20. The b-th gradient unit 212, d-th gradient unit 214, and d-th gradient unit 214 are arranged side by side along the height direction of the positive electrode current collector 20, with the b-th gradient unit 212 located near the top of the positive electrode current collector 20.

[0266] The ath gradient unit 211, the bth gradient unit 212, the cth gradient unit 213, the dth gradient unit 214, the eth gradient unit 215 and the fth gradient unit 216 have the same size and all contain polyethyl acrylate, NCM111, 3wt% PVDF and 1wt% SP, wherein the total mass content of polyethyl acrylate and NCM111 is 96wt%, and the mass content of polyethyl acrylate in the ath gradient unit 211, the bth gradient unit 212, the cth gradient unit 213, the dth gradient unit 214, the eth gradient unit 215 and the fth gradient unit 216 are 6%, 5%, 5%, 4%, 4% and 3% respectively.

[0267] The second positive electrode active layer on the other side of the positive electrode current collector 20 has a symmetrical structure to the first positive electrode active layer.

[0268] Example 6

[0269] The difference between this embodiment and embodiment 4 is that the injection coefficient of the electrolyte is 2 g / Ah.

[0270] Comparative Example 1

[0271] The difference between this comparative example and Examples 1 to 5 is that the negative electrode sheet, the positive electrode sheet and the separator do not contain polyethyl acrylate.

[0272] That is, in this comparative example, the negative electrode sheet includes an 8μm-thick copper foil and negative electrode active layers disposed on both surfaces of the copper foil. The two negative electrode active layers have a total thickness of 60μm and each contains 95.8wt% graphite, 2.5wt% styrene-butadiene rubber (SBR), 0.5wt% SP, and 1.2wt% CMC.

[0273] The positive electrode sheet includes a 15 μm thick aluminum foil and positive electrode active layers disposed on both surfaces of the aluminum foil. The total thickness of the two positive electrode active layers is 80 μm, and each contains 96 wt% NCM111, 3 wt% PVDF, and 1 wt% SP.

[0274] Comparative Example 2

[0275] The difference between this comparative example and Example 5 is that both the negative electrode active layer and the positive electrode active layer are provided with multiple gradient units with a decreasing mass content of polyethyl acrylate only in the D1 direction, while there are no multiple gradient units with a decreasing mass content of polyethyl acrylate in the D2 direction; at the same time, the diaphragm coating of the diaphragm does not contain polyethyl acrylate.

[0276] The structures of the negative electrode and positive electrode of this comparative example are as follows:

[0277] 1) Negative electrode

[0278] 8 , in this comparative example, the first negative electrode active layer 11 (30 μm thick) on one side of the negative electrode current collector 10 of the negative electrode sheet includes a first gradient unit 111 , a third gradient unit 113 , and a fifth gradient unit 115 . The first gradient unit 111 , the third gradient unit 113 , and the fifth gradient unit 115 are arranged side by side along the height direction of the negative electrode current collector 10 , with the first gradient unit 111 being close to the top of the negative electrode current collector 10 .

[0279] The first gradient unit 111, the third gradient unit 113, and the fifth gradient unit 115 have the same size (same length, width, and thickness), and all contain polyethyl acrylate, graphite, 2.5wt% SBR, 0.5wt% SP, and 1.2wt% CMC, wherein the total mass content of polyethyl acrylate and graphite is 95.8wt%, and the mass content of polyethyl acrylate in the first gradient unit 111, the third gradient unit 113, and the fifth gradient unit 115 is 6%, 5%, and 4%, respectively.

[0280] The second negative electrode active layer on the other side of the negative electrode current collector 10 has a symmetrical structure to the first negative electrode active layer.

[0281] 3) Positive electrode

[0282] 9 , in the positive electrode sheet of this comparative example, the positive electrode active layer (the first positive electrode active layer 21 , having a thickness of 40 μm) on one side of the positive electrode current collector 20 includes the a-th gradient unit 211 , the c-th gradient unit 213 , the d-th gradient unit 214 , and the e-th gradient unit 215 , and the a-th gradient unit 211 , the c-th gradient unit 213 , and the e-th gradient unit 215 are arranged in sequence along the height direction of the positive electrode current collector 20 , with the a-th gradient unit 211 being close to the top of the positive electrode current collector 20 .

[0283] The a-th gradient unit 211, the c-th gradient unit 213 and the e-th gradient unit 215 have the same size and all contain polyethyl acrylate, NCM111, 3wt% PVDF and 1wt% SP, wherein the total mass content of polyethyl acrylate and NCM111 is 96wt%, and the mass content of polyethyl acrylate in the a-th gradient unit 211, the c-th gradient unit 213 and the e-th gradient unit 215 are 6%, 5% and 4% respectively.

[0284] The second positive electrode active layer on the other side of the positive electrode current collector 20 has a symmetrical structure to the first positive electrode active layer.

[0285] Comparative Example 3

[0286] The difference between this comparative example and Example 5 is that both the negative electrode active layer and the positive electrode active layer are provided with multiple gradient units with a decreasing mass content of polyethyl acrylate only in the D2 direction, while there are no multiple gradient units with a decreasing mass content of polyethyl acrylate in the D1 direction; at the same time, the diaphragm coating of the diaphragm contains uniformly distributed polyethyl acrylate.

[0287] Specifically, the structures of the negative electrode sheet, positive electrode sheet, and diaphragm of this comparative example are as follows:

[0288] 1) Negative electrode

[0289] 10 , in this comparative example, the first negative active layer 11 (30 μm thick) on one side of the negative current collector 10 includes a first gradient unit 111 and a second gradient unit 112 stacked in the thickness direction of the negative electrode sheet, wherein the first gradient unit 111 is close to the negative current collector 10 .

[0290] The first gradient unit 111 and the second gradient unit 112 have the same size and both contain polyethyl acrylate, graphite, 2.5 wt% SBR, 0.5 wt% SP and 1.2 wt% CMC, wherein the total mass content of polyethyl acrylate and graphite is 95.8 wt%, and the mass content of polyethyl acrylate in the first gradient unit 111 and the second gradient unit 112 is 4% and 3%, respectively.

[0291] The second negative electrode active layer on the other side of the negative electrode current collector 10 has a symmetrical structure to the first negative electrode active layer.

[0292] 2) Positive electrode

[0293] 10 , in the positive electrode sheet of this comparative example, the first positive electrode active layer 21 (with a thickness of 40 μm) on one side of the positive electrode current collector 20 includes stacked a-th gradient unit 211 and b-th gradient unit 212 in the thickness direction of the positive electrode sheet, wherein the a-th gradient unit 211 is close to the positive electrode current collector 20 .

[0294] The a-th gradient unit 211 and the b-th gradient unit 212 have the same size and both contain polyethyl acrylate, NCM111, 3wt% PVDF and 1wt% SP, wherein the total mass content of polyethyl acrylate and NCM111 is 96wt%, and the mass content of polyethyl acrylate in the a-th gradient unit 211 and the b-th gradient unit 212 is 4% and 3%, respectively.

[0295] The second positive electrode active layer on the other side of the positive electrode current collector 20 has a symmetrical structure to the first positive electrode active layer.

[0296] 3) Diaphragm

[0297] 10 , the separator of this comparative example includes a base film (a PE film having a thickness of 12 μm) and a separator coating layer having a thickness of 3 μm provided on one side of the base film. The separator coating layer 31 includes polyethyl acrylate having a mass content of 2%.

[0298] Comparative Example 4

[0299] The difference between this comparative example and comparative example 1 is that the injection coefficient of the electrolyte is 2 g / Ah.

[0300] The gradient unit designs of the positive electrode sheet, positive electrode sheet and separator in each embodiment and comparative example are shown in the following table.

[0301] [Table 1]

[0302] In Table 1, “gradient design direction” refers to the gradient distribution direction of the mass content of polyethyl acrylate in the positive electrode sheet or the negative electrode sheet, including D1 and D2.

[0303] "Single-sided" means that the active layer on one side of the positive electrode sheet or the negative electrode sheet is designed with gradient units with a gradient distribution of the mass content of polyethyl acrylate, and "double-sided" means that the active layers on both sides of the positive electrode sheet or the negative electrode sheet are designed with gradient units with a gradient distribution of the mass content of polyethyl acrylate.

[0304] "Polyethyl acrylate Gradient Mass Content" represents the mass content of polyethyl acrylate within each gradient unit in the positive electrode sheet, negative electrode sheet, or separator. In Table 1, the vertical data within the "Polyethyl acrylate Gradient Mass Content" cell represents the distribution of polyethyl acrylate mass content along direction D1, and the horizontal data represents the distribution of polyethyl acrylate mass content along direction D2.

[0305] [Liquid absorption capacity]

[0306] The liquid absorption capacity of gradient units containing different amounts of polyethyl acrylate in the positive electrode sheet, negative electrode sheet, and separator was tested. To facilitate the test and provide more intuitive results, the following test was conducted by first preparing a complete positive electrode sheet, negative electrode sheet, or separator corresponding to each gradient unit, and then conducting the liquid absorption capacity test. The test method is as follows.

[0307] Sample preparation:

[0308] 1) Polyethyl acrylate, graphite, SBR, SP, CMC, and water were mixed to form a negative electrode slurry. The negative electrode slurry was coated on both surfaces of a copper foil (8 μm thick), dried, and cold pressed to form a negative electrode active layer with a thickness of 30 μm on both surfaces of the copper foil. The components in the negative electrode slurry were 2.5 wt% SBR, 0.5 wt% SP, and 1.2 wt% CMC. The total weight content of polyethyl acrylate and graphite was 95.8 wt%. The weight content of polyethyl acrylate was 6%, 5%, 4%, 3%, and 0%, respectively. Samples 1, 2, 3, 4, and 5 were obtained, corresponding to gradient units containing different weight contents of polyethyl acrylate in the negative electrode sheet. The weight of each sample was the same.

[0309] 2) NCM111, PVDF, SP, and NMP (N-methylpyrrolidone) were mixed to form a positive electrode slurry. The positive electrode slurry was coated on both surfaces of an aluminum foil (15 μm thick), dried, and cold pressed to form a positive electrode active layer with a thickness of 40 μm on both surfaces of the aluminum foil. The components in the positive electrode slurry were 3 wt% PVDF and 1 wt% SP. The total mass content of polyethyl acrylate and NCM111 was 96 wt%, and the mass content of polyethyl acrylate was 6%, 5%, 4%, 3%, and 0%, respectively. Samples a, b, c, d, and e corresponding to the gradient units containing different mass contents of polyethyl acrylate in the positive electrode sheet were obtained. The mass of each sample was the same.

[0310] 3) A 3 μm thick diaphragm coating was applied on a 12 μm thick PE film, and the mass content of polyethyl acrylate in the diaphragm coating was controlled to be 2%, 1%, and 0%, to obtain samples A, B, and C corresponding to each gradient unit containing different polyethyl acrylate mass contents in the diaphragm, and the mass of each sample was the same.

[0311] Liquid absorption capacity test:

[0312] Cut the sample to be tested into 2*2cm 2 The sample was weighed to obtain a mass M1 and then immersed in an electrolyte (the electrolyte composition is the same as in Example 1) at room temperature (25°C) for 1 hour. The sample was removed and the excess electrolyte on the surface was wiped off with a dust-free paper. The sample was then weighed to obtain M2, and the amount of liquid absorbed per unit time (1 hour) was obtained as m (g) = M2 - M1. The liquid absorption capacity F = σ*m / THK. Where σ is the porosity of the sample, THK is the sample thickness (mm), and F is in g / mm.

[0313] [Table 2]

[0314] The test results show that samples with different polyethyl acrylate mass contents have different electrolyte absorption capacities. Therefore, in Examples 1-5, the positive electrode sheet, negative electrode sheet, and separator contain polyethyl acrylate mass contents in a gradient distribution, and thus have gradient-distributed electrolyte absorption capacities.

[0315] Specifically, in Examples 1-5, the positive electrode sheet, negative electrode sheet, and separator contained polyethyl acrylate in a gradient-decreasing mass content along direction D1. The mass content of polyethyl acrylate was higher at the top of each of the positive electrode sheet, negative electrode sheet, and separator than at their respective bottoms. Accordingly, the liquid absorption capacity of each of the positive electrode sheet, negative electrode sheet, and separator was higher at their respective bottoms, and the liquid absorption capacity of each of the positive electrode sheet, negative electrode sheet, and separator gradually decreased along direction D1.

[0316] Furthermore, in Examples 1-5, the positive electrode sheets, negative electrode sheets, and separators contained polyethyl acrylate in a gradient distribution along the D2 direction, with the polyethyl acrylate content in the positive and / or negative electrode active layers on the side closest to the current collector being higher than in the separator. Accordingly, the liquid absorption capacity of the positive electrode sheets, negative electrode sheets, and separators was gradient along the D2 direction.

[0317] [Electrochemical Performance]

[0318] 1. The electrochemical performance of the lithium-ion batteries of Examples 1 to 5 and Comparative Examples 1 to 3 (all with a liquid injection coefficient of 1.2 g / Ah) was tested. The test results are shown in Tables 3 and 4 below.

[0319] [Table 3]

[0320] [Table 4]

[0321] The performance change rates in Table 4 refer to the change rates calculated based on Table 3 compared with those in Comparative Example 1.

[0322] Test results show that compared to Comparative Example 1, which lacked a gradient design for liquid absorption capacity in both the D1 and D2 directions, Examples 1-5 simultaneously incorporate gradient units containing polyethyl acrylate in the positive electrode sheet, negative electrode sheet, and separator along both D1 and D2, resulting in the electrode assembly having a gradient-decreasing liquid absorption capacity along both directions. This reduces the battery's internal resistance and DC impedance, increases the number of battery cycles, and improves battery cycling performance. Furthermore, as the number of gradient units increases, the battery's internal resistance and DC impedance decrease, and the battery's cycling performance improves.

[0323] The improvement in battery performance in Examples 1 to 5 is primarily due to the fact that the positive electrode sheet, negative electrode sheet, and separator have greater liquid absorption capacity at the top than at the bottom. This can compensate for the problem of poor wettability of the top of the electrode assembly due to gravity, which causes the electrolyte to tend to concentrate at the bottom of the electrode assembly due to long-term storage and use. Furthermore, the positive electrode sheet and / or negative electrode sheet have greater liquid absorption capacity on the side near the current collector than on the side near the separator. This improves the electrolyte wettability inside the electrode sheet, compensating for the problem of reduced or difficult electrolyte wettability on the side of the electrode sheet near the current collector due to volume expansion or contraction of the positive and negative electrode sheets during charge and discharge, which squeezes out the electrolyte. This improvement in electrolyte wettability helps promote electrochemical reactions in the battery, accelerates the transfer of lithium ions, and thus reduces the battery's internal resistance and DC impedance. Furthermore, after long-term cycling, both the top of the electrode assembly and the interior of the electrode sheet maintain good electrolyte wettability, thereby improving the battery's cycling performance.

[0324] 2. The electrochemical performance of the lithium-ion batteries of Example 6 and Comparative Example 4 (both with a liquid filling coefficient of 2 g / Ah) was tested. The test results are shown in Tables 5 and 6 below.

[0325] [Table 5]

[0326] [Table 6]

[0327] The performance change rates in Table 6 refer to the change rates calculated from Table 5 compared with those of Comparative Example 4.

[0328] The test results show that at a high injection coefficient, the internal resistance, DC impedance and cycle performance of the battery of Example 6 are also improved compared with those of Comparative Example 4.

[0329] Furthermore, a combined analysis of Table 6 and Table 4 shows that, at a low injection coefficient of 1.2 g / Ah, the internal resistance of the battery in Example 4 was reduced by 64.8%, the DC impedance was reduced by 29.0%, and the number of cycles increased by 17.2% compared to Comparative Example 1. While, with the same electrode assembly structure, Example 6, which adopted a higher injection coefficient of 2 g / Ah, reduced the internal resistance of the battery by 5.9%, the DC impedance by 5.3%, and the number of cycles by 2.7% compared to Comparative Example 4. The improvement in battery performance at the low injection coefficient of 1.2 g / Ah in Example 4 was more significant than that at the high injection coefficient of 2 g / Ah, indicating that by designing the positive electrode sheet, negative electrode sheet, and separator to have a gradient distribution of liquid absorption capacity in a specific direction, the electrochemical performance of the battery with a low injection coefficient is better improved.

[0330] [Electrochemical performance test method]

[0331] 1. Battery internal resistance IMP

[0332] At 25°C, charge the battery at a constant current of 0.33C to 4.2V, then switch to a constant voltage charge of 4.2V until the current reaches 0.05C, and then discharge at 0.33C for 30 minutes. Then, use the positive and negative test leads of the TH2523A AC impedance tester to touch the positive and negative terminals of the battery respectively. Test under 1000Hz AC current and read the battery internal resistance (IMP) directly from the tester.

[0333] 2. DC impedance

[0334] At 25°C, the battery was charged at a constant current of 0.33C to 4.2V. It was then switched to a constant voltage charge of 4.2V until the current reached 0.05C. The battery was then discharged at 0.33C to 2.5V, and the discharge capacity (C0) was recorded. Discharge was continued at 0.33C to 30% of the battery's discharge capacity (C0), and the voltage (V1) was recorded. The battery was then discharged at 2C (I1) for 30s, and the voltage (V2) was recorded. The DC resistance (DCR) was calculated by dividing the voltage drop during this discharge period by the current: (30% SOC DCR @ 2C 30s) = (V1 - V2) / I1.

[0335] 3. Cycle performance

[0336] At 25°C, charge the battery at a constant current of 0.5C to 4.2V, then charge at a constant voltage of 4.2V until the current reaches 0.05C, and then discharge at 1C to 2.5V. Record the initial discharge capacity C1. This is one charge and discharge process. Repeat the charge and discharge cycle until the capacity retention rate decays to 80% of the initial discharge capacity C1. Stop the test and record the number of cycles.

[0337] 4. Porosity

[0338] The porosity σ test method for the sample involved in the liquid absorption capacity test is as follows: Cut the sample into 20 circular pieces with a diameter of 14mm, record the weight and thickness, and calculate the bulk density. The circular sample is placed in the sample cup of the true density porosity tester. Using helium displacement, the true volume of the electrode is calculated by combining Archimedes' principle and Bohr's law, and the true density is then calculated. Porosity is equal to (1 - bulk density / true density) * 100%.

[0339] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. An electrode assembly, characterized in that: The electrode assembly comprises a pole piece, the pole piece comprises a current collector, an active layer and a pole ear, the active layer is arranged on at least one side in the thickness direction of the current collector, and the pole ear is arranged on one side in the height direction of the current collector; In the direction from the side of the current collector where the tab is provided to the other side opposite thereto, the liquid absorption capacity of the region of the active layer close to the tab side is greater than or equal to the liquid absorption capacity of the region on the other side opposite thereto, and the liquid absorption capacity of at least one region of the active layer close to the tab side is greater than the liquid absorption capacity of the region on the other side opposite thereto; In the direction from the current collector to away from the current collector, the liquid absorption capacity of the area of ​​the active layer close to the current collector is greater than or equal to the liquid absorption capacity of the other side area, and the liquid absorption capacity of at least one area of ​​the active layer close to the current collector is greater than the liquid absorption capacity of the other side area.

2. The electrode assembly according to claim 1, characterized in that: In the direction from the side of the current collector where the tab is provided to the other side opposite thereto, the liquid absorption capacity of the region near the tab side of the separator contained in the electrode assembly is greater than or equal to the liquid absorption capacity of the region on the other side opposite thereto, and the liquid absorption capacity of at least one region of the separator near the tab side is greater than the liquid absorption capacity of the region on the other side opposite thereto; In a direction from the current collector to away from the current collector, the liquid absorption capacity of the active layer is greater than the liquid absorption capacity of the separator.

3. The electrode assembly according to claim 1 or 2, characterized in that: In the direction from one side of the electrode ear where the current collector is set to the other opposite side, at least one of the active layer and the diaphragm contained in the electrode assembly includes at least two adjacently arranged gradient units, wherein the liquid absorption capacity of the gradient unit close to the electrode ear is higher than the liquid absorption capacity of the gradient unit on the other opposite side; optionally, the number of the gradient units is 2 to 10.

4. The electrode assembly according to claim 3, characterized in that: The difference in liquid absorption capacity between two adjacent gradient units is 1.1 to 5 times, and optionally 1.2 to 2 times.

5. The electrode assembly according to claim 3 or 4, characterized in that: In the direction from one side of the current collector where the pole ear is arranged to the other opposite side, the height of any one of the gradient units accounts for 10% to 60% of the total height of the active layer or the separator, and optionally 10% to 50%.

6. The electrode assembly according to any one of claims 1 to 5, characterized in that: In the direction from the current collector to away from the current collector, the active layer includes at least two adjacently arranged liquid absorption layers, wherein the liquid absorption capacity of the liquid absorption layer close to the current collector is higher than the liquid absorption capacity of the liquid absorption layer on the other opposite side; optionally, the number of the liquid absorption layers is 2 to 10.

7. The electrode assembly according to claim 6, characterized in that: In the direction from the current collector to away from the current collector, the thickness of any one of the liquid absorbing layers accounts for 10% to 60% of the total thickness of the active layer arranged on one side of the current collector, and optionally 10% to 50%.

8. The electrode assembly according to any one of claims 1 to 7, characterized in that: The active layer comprises a first electrolyte absorber; in a direction from one side of the current collector where the pole ear is provided to the other side opposite thereto, the mass content of the first electrolyte absorber in a region of the active layer close to one side of the pole ear is greater than or equal to the mass content of the first electrolyte absorber in a region on the other side opposite thereto, and the mass content of the first electrolyte absorber in at least one region of the active layer close to one side of the pole ear is greater than the mass content of the first electrolyte absorber in a region on the other side opposite thereto; In the direction from the current collector to away from the current collector, the mass content of the first electrolyte absorber in the region of the active layer close to one side of the current collector is greater than or equal to the mass content of the first electrolyte absorber in the region on the other side, and the mass content of the first electrolyte absorber in at least one region of the active layer close to one side of the current collector is greater than the mass content of the first electrolyte absorber in the region on the other side.

9. The electrode assembly according to claim 8, characterized in that: The diaphragm contained in the electrode assembly comprises a base film and a diaphragm coating disposed on at least one side of the base film; the diaphragm coating comprises a second electrolyte absorbent; In the direction from one side of the pole ear to the other opposite side of the current collector, the mass content of the second electrolyte absorber in the area close to one side of the pole ear of the diaphragm coating is greater than or equal to the mass content of the second electrolyte absorber in the area on the other opposite side, and the mass content of the second electrolyte absorber in at least one area close to one side of the pole ear of the diaphragm coating is greater than the mass content of the second electrolyte absorber in the area on the other opposite side.

10. The electrode assembly according to claim 9, characterized in that: In a direction from the current collector to away from the current collector, the mass content of the first electrolyte absorber in the active layer is greater than the mass content of the second electrolyte absorber in the diaphragm coating.

11. The electrode assembly according to claim 9 or 10, characterized in that: The first electrolyte absorbent and the second electrolyte absorbent independently include one or more of polymethyl methacrylate, polymethyl acrylate, polyethyl acrylate, polyvinyl acetate, polyacrylamide, polyacrylic acid, and polyacrylonitrile.

12. The electrode assembly according to any one of claims 9 to 11, characterized in that: The mass content of the first electrolyte absorber in the active layer and the mass content of the second electrolyte absorber in the diaphragm coating are independently greater than 0 and less than or equal to 8%; optionally greater than or equal to 1% and less than or equal to 6%.

13. A method for preparing an electrode assembly, characterized in that: include: An active layer is prepared on at least one side of the current collector in the thickness direction, and a tab is provided on one side of the current collector in the height direction; In the direction from the side of the current collector where the tab is provided to the other side opposite thereto, the liquid absorption capacity of the region of the active layer close to the tab side is controlled to be greater than or equal to the liquid absorption capacity of the region on the other side opposite thereto, and the liquid absorption capacity of at least one region of the active layer close to the tab side is greater than the liquid absorption capacity of the region on the other side opposite thereto; In the direction from the current collector to away from the current collector, the liquid absorption capacity of the area of ​​the active layer close to the current collector is controlled to be greater than or equal to the liquid absorption capacity of the other side area, and the liquid absorption capacity of at least one area of ​​the active layer close to the current collector is greater than the liquid absorption capacity of the other side area.

14. The method for preparing an electrode assembly according to claim 13, characterized in that: The method for preparing the electrode assembly further includes: In the direction from the side of the current collector where the electrode tab is provided to the other side opposite thereto, the liquid absorption capacity of the region near the electrode tab of the diaphragm contained in the electrode assembly is controlled to be greater than or equal to the liquid absorption capacity of the region on the other side opposite thereto, and the liquid absorption capacity of at least one region of the diaphragm near the electrode tab is greater than the liquid absorption capacity of the region on the other side opposite thereto; In a direction from the current collector to away from the current collector, the liquid absorption capacity of the active layer is controlled to be greater than the liquid absorption capacity of the separator.

15. A battery, characterized in that: The battery comprises the electrode assembly according to any one of claims 1 to 12.

16. An electrical device, characterized in that: The electrical device comprises the battery according to claim 15.

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