Positive pole piece, negative pole piece, secondary battery and electric device

Abstract

The invention relates to a positive pole piece, a negative pole piece, a secondary battery and an electric device. The positive pole piece comprises a positive middle coating area and a positive side coating area located on at least one side of the positive middle coating area, and the resistance R1 of a film layer of the positive side coating area is smaller than the resistance R2 of a film layer of the positive middle coating area. According to the positive pole piece, the positive middle coating area and the positive side coating area are set as follows: the resistance R1 of the film layer of the positive side coating area is smaller than the resistance R2 of the film layer of the positive middle coating area, so that the lithium removal rate of the positive middle coating area is smaller than the lithium removal rate of the positive side coating area in the charging process; correspondingly, lithium is not easy to separate out in the middle area of the negative electrode opposite to the middle coating area of the positive electrode on the negative electrode plate, so that the problem of serious lithium separation in the middle area of the negative electrode can be relieved to a certain extent, and the cycle performance of the secondary battery is improved.

Description

Technical Field

[0001] The present application relates to the field of new energy technologies, and particularly to a positive electrode sheet, a negative electrode sheet, a secondary battery, and an electrical device using the same. Background Art

[0002] The statements herein only provide background information related to the present application and do not necessarily constitute prior art.

[0003] In recent years, with the increasingly wide application range of lithium-ion batteries, lithium-ion batteries are widely used in energy storage power systems such as hydroelectric, thermal, wind, and solar power stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. Lithium-ion batteries have achieved great development, and thus higher requirements are also put forward for their cycle performance and lithium plating problems. Summary of the Invention

[0004] The present application provides a positive electrode sheet or a negative electrode sheet that can improve the cycle performance of a secondary battery and alleviate the lithium plating problem.

[0005] In addition, a secondary battery and an electrical device including at least one of the above positive electrode sheet and negative electrode sheet are also provided.

[0006] To achieve the above object, a first aspect of the present application provides a positive electrode sheet, including a positive electrode middle coating area and a positive electrode edge coating area located on at least one side of the positive electrode middle coating area, and a resistance R of the film layer of the positive electrode edge coating area 1 is less than a resistance R of the film layer of the positive electrode middle coating area 2 .

[0007] Without wishing to be limited to any theory, by setting the positive electrode middle coating area and the positive electrode edge coating area such that the resistance R of the film layer of the positive electrode edge coating area 1 is less than the resistance R of the film layer of the positive electrode middle coating area 2 , during the charging process, the lithium deintercalation rate of the positive electrode middle coating area is less than the lithium deintercalation rate of the positive electrode edge coating area, and correspondingly, it is not easy for the middle area of the negative electrode (or the negative electrode middle coating area) opposite to the positive electrode middle coating area on the negative electrode sheet to deposit lithium, thereby alleviating the serious lithium plating problem in the middle area of the negative electrode to a certain extent and improving the cycle performance of the secondary battery.

[0008] In some embodiments of the present application, R 1 =(0.1 - 0.95)R 2 ; optionally, R 1 =(0.1 - 0.9)R 2 Optionally, R 1 =(0.1 - 0.8)R 2 .

[0009] In some embodiments of the present application, the total thickness of the film layer in the positive electrode middle coating area is less than the total thickness of the film layer in the positive electrode side coating area.

[0010] In some embodiments of the present application, at least one of the following conditions is met:

[0011] (1) The ratio a of the total thickness of the film layer of the positive electrode edge coating area to the total thickness of the film layer of the positive electrode middle coating area satisfies: 1<a≤1.4, and a can be selected from 1.008 to 1.4, further selected from 1.05 to 1.4, and more preferably selected from 1.05 to 1.2;

[0012] (2) The total thickness of the film layer in the positive electrode coating area is 80 μm to 240 μm;

[0013] (3) With the direction from the positive electrode middle coating area to the positive electrode side coating area as the width direction, the total width of the positive electrode side coating area accounts for 10% to 90% of the total width of the positive electrode middle coating area and the positive electrode side coating area, and can be 20% to 80%, and more preferably 30% to 60%;

[0014] (4) The positive electrode side coating areas are provided on opposite sides of the positive electrode middle area.

[0015] In some embodiments of the present application, the film layer of the positive electrode edge coating area includes a positive electrode current collector and a positive electrode base coating layer and a positive electrode active layer stacked in sequence on the positive electrode current collector; the positive electrode middle coating area includes a positive electrode current collector and a positive electrode active layer arranged on the positive electrode current collector.

[0016] In some embodiments of the present application, (1) the difference between the total thickness of the film layer of the positive electrode edge coating area and the positive electrode middle coating area is the thickness of the positive electrode bottom coating layer;

[0017] (2) The thickness of the positive electrode bottom coating is 0.5 to 20 μm, and can be 1 to 10 μm;

[0018] (3) The positive electrode current collector of the positive electrode middle coating area and the positive electrode side coating area is the same current collector, and the thickness of the positive electrode active layer of the positive electrode middle coating area and the positive electrode side coating area is the same;

[0019] (4) The components of the positive electrode bottom coating layer include a conductive agent and a binder; optionally, in the positive electrode bottom coating layer, the mass content of the conductive agent is 50% to 80%; optionally, in the positive electrode bottom coating layer, the mass content of the binder is 20% to 50%.

[0020] In a second aspect of the present application, a negative electrode plate is provided, comprising a negative electrode middle coating region and a negative electrode side coating region located at least on one side of the negative electrode middle coating region, wherein the resistance R 3 Greater than the resistance R of the film layer in the negative electrode coating area4 .

[0021] Without wishing to be limited to any theory, the negative electrode plate is configured such that the negative electrode middle coating area and the negative electrode side coating area are: the resistance R of the film layer in the negative electrode side coating area 3 Greater than the resistance R of the film layer in the negative electrode coating area 4 In this way, during the charging process, the kinetic performance of the negative electrode middle coating area is better than that of the negative electrode side coating area, which makes the negative electrode middle coating area relatively less prone to lithium deposition, thereby alleviating the serious lithium deposition problem in the middle area of ​​the negative electrode to a certain extent and improving the cycle performance of the secondary battery.

[0022] In some embodiments of the present application, R 3 =(1.1~7)R 4 ;

[0023] Optionally, R 3 =(1.1~5)R 4 ; More optionally, R 3 =(2~5)R 4 .

[0024] In some embodiments of the present application, the total thickness of the film layer in the negative electrode middle coating area is less than the total thickness of the film layer in the negative electrode side coating area.

[0025] In some embodiments of the present application, at least one of the following conditions is met:

[0026] (1) The ratio c of the total thickness of the film layer of the negative electrode edge coating area to the total thickness of the film layer of the negative electrode middle coating area satisfies: 1<c≤1.4, and c can be selected from 1.008 to 1.4, further selected from 1.05 to 1.4, and more preferably selected from 1.05 to 1.2;

[0027] (2) The total thickness of the film layer in the negative electrode middle coating area is 50 μm to 300 μm;

[0028] (3) With the direction from the negative electrode middle coating area to the negative electrode side coating area as the width direction, the total width of the negative electrode side coating area accounts for 10% to 90% of the total width of the negative electrode middle coating area and the negative electrode side coating area, and can be 20% to 80%, and more preferably 30% to 60%;

[0029] (4) The negative electrode side coating areas are provided on opposite sides of the negative electrode middle area.

[0030] In some embodiments of the present application, the film layer of the negative electrode edge coating area includes a negative electrode current collector and a negative electrode bottom coating layer and a negative electrode active layer stacked in sequence on the negative electrode current collector; the negative electrode middle coating area includes a negative electrode current collector and a negative electrode active layer arranged on the negative electrode current collector.

[0031] In some embodiments of the present application, at least one of the following conditions is met:

[0032] (1) The difference between the total thickness of the film layer of the negative electrode edge coating area and the negative electrode middle coating area is the thickness of the negative electrode bottom coating layer;

[0033] (2) The thickness of the negative electrode bottom coating is 0.5 to 20 μm, and can be 1 to 10 μm;

[0034] (3) The negative electrode current collector of the negative electrode middle coating area and the negative electrode side coating area is the same current collector, and the thickness of the negative electrode active layer of the negative electrode middle coating area and the negative electrode side coating area is the same;

[0035] (4) The components of the negative electrode bottom coating include a conductive agent and a binder; optionally, in the negative electrode bottom coating, the mass content of the conductive agent is 10% to 30%; optionally, in the negative electrode bottom coating, the mass content of the binder is 70% to 90%.

[0036] In a third aspect of the present application, a secondary battery is provided, comprising at least one of any of the above-mentioned positive electrode sheets and any of the above-mentioned negative electrode sheets.

[0037] In a fourth aspect of the present application, there is provided an electrical device comprising any of the above-mentioned positive electrode sheets, any of the above-mentioned negative electrode sheets, and at least one of the above-mentioned secondary batteries.

[0038] The electric device of the present application includes the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery.

[0039] The details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to better describe and illustrate the embodiments or examples provided by the present application, reference may be made to one or more drawings. The additional details or examples used to describe the drawings should not be considered as limiting the scope of the disclosed application, the embodiments or examples currently described, and any of the best modes of these applications currently understood. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0041] Figure 1 This is a schematic diagram of the structure of a positive electrode plate according to one embodiment of the present application.

[0042] Figure 2 It is a schematic diagram of a battery cell according to an embodiment of the present application.

[0043] Figure 3for Figure 2 An exploded view of a battery cell according to an embodiment of the present application is shown.

[0044] Figure 4 It is a schematic diagram of a battery module according to one embodiment of the present application.

[0045] Figure 5 A schematic diagram of a battery pack according to an embodiment of the present application.

[0046] Figure 6 for Figure 5 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0047] Figure 7 FIG. 1 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0048] Description of reference numerals:

[0049] 510, positive electrode plate; 501, positive electrode middle coating area; 502, positive electrode side coating area; 511, positive electrode current collector; 512, positive electrode bottom coating layer; 513, positive electrode active layer;

[0050] 1. Battery pack; 2. Upper box; 3. Lower box; 4. Battery module; 5. Battery cell; 51. Shell; 52. Electrode assembly; 53. Cover plate; 6. Electrical device. DETAILED DESCRIPTION

[0051] Below, some embodiments of the positive electrode sheet, negative electrode sheet, secondary battery and electrical device of the present application are described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0052] "Scope" disclosed in the present application can be limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or excluding end values, and any end value can be included or not included independently, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 listed, and if the maximum range values ​​3,4 and 5 are also listed, the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation for these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to listing the parameter as, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is expressed as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9 and 10.

[0053] In the present application, "plurality", "multiple" and the like, unless otherwise specified, refer to a number greater than or equal to 2. For example, "one or more" means one or greater than or equal to two.

[0054] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0055] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments. The "implementation methods" mentioned herein have a similar understanding.

[0056] Those skilled in the art will appreciate that, in the methods of each embodiment or example, the order in which each step is written does not mean a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible internal logic. If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) can be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0057] In the present application, in the open technical features or technical solutions described by the words "contain", "include", "comprise", etc., unless otherwise specified, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions including additional members in addition to the listed members. For example, A includes a1, a2 and a3. Unless otherwise specified, it may also include other members or may not include additional members. It can be regarded as providing both the feature or solution of "A consists of a1, a2 and a3" and the feature or solution of "A not only includes a1, a2 and a3, but also includes other members". In the present application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0058] In this application, "optionally", "optional", and "optional" mean optional, that is, any one of the two parallel schemes of "yes" or "no". If there are multiple "options" in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "option" is independent.

[0059] The secondary battery and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0060] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, and an electrolyte. The electrolyte is located between the positive electrode sheet and the negative electrode sheet. During the battery charging and discharging process, active ions are embedded and extracted back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet.

[0061] Taking lithium ions as an example, during the charging process, Li + The discharge process is just the opposite, Li is released from the negative electrode to form Li+ , return to the positive electrode.

[0062] In addition, an isolation membrane may also be included. The isolation membrane is arranged between the positive electrode plate and the negative electrode plate. The main function of the isolation membrane is to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0063] Generally speaking, as the battery is repeatedly charged and discharged during use, serious lithium plating problems are prone to occur in the central area of ​​the electrode, which causes the battery's cycle performance to plummet and even causes safety problems.

[0064] An embodiment of the present application provides a positive electrode sheet, a negative electrode sheet, and a secondary battery, wherein the secondary battery includes one or both of the above-mentioned positive electrode sheet and negative electrode sheet to improve the cycle performance of the secondary battery and improve the lithium plating problem of the secondary battery.

[0065] In one embodiment of the present application, a positive electrode plate is provided, comprising a positive electrode middle coating region and a positive electrode side coating region located at least on one side of the positive electrode middle coating region, wherein the resistance R 1 Less than the resistance R of the film layer in the positive electrode coating area 2 .

[0066] In this paper, the resistance R 1 And the resistance R of the film layer in the positive electrode coating area 2 Both refer to the resistance value of the corresponding area including the positive electrode current collector and all the film layers on both surfaces of the positive electrode current collector. For example, the resistance R 1 It refers to the overall resistance value of the positive electrode current collector at the positive electrode edge coating area and all the film layers located on both surfaces of the positive electrode current collector. The pole sheet resistance is an important component of the internal resistance of lithium batteries. It is composed of the coating resistance, the current collector resistance and the interface resistance between the current collector and the coating.

[0067] Resistance R of the film layer in the positive electrode coating area 1 And the resistance R of the film layer in the positive electrode coating area 2 The following test method can be used to measure: first cut the positive electrode sheet into sections and test the resistance R of the film layer in the positive electrode edge coating section. 1 And the resistance R of the film layer in the positive electrode coating area 2 The specific resistance test method includes but is not limited to at least one of a four-probe, a two-probe, and an ohmmeter test method.

[0068] As an example, the method of using the four-probe method to test the diaphragm resistance through a diaphragm resistance meter is as follows: the instrument has 14mm diameter copper terminals at the upper and lower ends. During the test, the upper and lower ends are combined to clamp the cut and partitioned electrode film layer in the middle, squeeze and force, and read the diaphragm resistance of the device. Furthermore, the resistance values ​​of more than 15 positions can be monitored and the average value can be taken.

[0069] Due to the differences in parameters such as the composition and thickness of the film layer in the edge coating area and the middle coating area of the positive electrode, the resistance of the film layer in the edge coating area of the positive electrode is different from that of the film layer in the middle coating area of the positive electrode.

[0070] Without wishing to be limited to any theory, the positive electrode tab is configured such that the middle coating area and the edge coating area of the positive electrode are set so that the resistance R of the film layer in the edge coating area of the positive electrode 1 is less than the resistance R of the film layer in the middle coating area of the positive electrode 2 . In this way, during the charging process, the rate of lithium deintercalation in the middle coating area of the positive electrode is less than the rate of lithium deintercalation in the edge coating area of the positive electrode. Correspondingly, it is less likely for lithium to deposit in the middle area (or the middle coating area of the negative electrode) of the negative electrode opposite to the middle coating area of the positive electrode, thereby alleviating to a certain extent the serious lithium deposition problem in the middle area of the negative electrode and improving the cycling performance of the secondary battery.

[0071] Please refer to Figure 1 , the positive electrode tab 510 includes a middle coating area 501 of the positive electrode and edge coating areas 502 of the positive electrode located on both sides of the middle coating area 501 of the positive electrode. The resistance R of the edge coating area 502 of the positive electrode 1 is less than the resistance R of the middle coating area 501 of the positive electrode 2 .

[0072] In some embodiments, R 1 =(0.1 - 0.95)R 2 ; optionally, R 1 =(0.1 - 0.9)R 2 . Optionally, R 1 =(0.1 - 0.8)R 2 , or optionally, R 1 =(0.1 - 0.7)R 2 , or optionally, R 1 =(0.1 - 0.5)R 2 , or optionally, R 1 =(0.1 - 0.3)R 2 .

[0073] As an example, R 1 can be 0.1R 2 , 0.2R 2 , 0.3R 2 , 0.4R 2 , 0.5R 2 , 0.6R 2 , 0.7R 2 , 0.8R 2 , 0.9R 2 , 0.95R 2 , or can also be a range formed by any two of the above point values. The same applies hereinafter. Further controlling R 1 and R2 This relationship can further improve the lithium plating problem of secondary batteries and enhance the cycle performance of secondary batteries.

[0074] Optionally, R 2 =0.01~2Ω.

[0075] Generally, as the battery continues to expand during use, the thickness of the pole piece increases, the porosity decreases, and the electrolyte is squeezed out during the charging process. During discharge, the electrolyte needs to flow back. Due to the large expansion force in the later stage, the electrolyte reflux is difficult, resulting in a lack of electrolyte in the central area of ​​the pole piece, which can also lead to lithium precipitation problems, thereby causing the battery's cycle performance to plummet and even cause safety problems. In some embodiments, the total thickness of the film layer in the positive electrode middle coating area is less than the total thickness of the film layer in the positive electrode side coating area. Therefore, the liquid storage capacity of the positive electrode middle coating area can be increased, thereby improving the ability of the electrolyte to flow back to the positive electrode middle coating area, thereby further improving the lithium precipitation problem of the secondary battery and improving the cycle performance of the secondary battery. In some embodiments, the ratio a of the total thickness of the film layer in the positive electrode side coating area to the positive electrode middle coating area satisfies: 1 < a ≤ 1.4. Optionally, a is 1.008 to 1.4, further optionally 1.01 to 1.2, and more optionally 1.05 to 1.1. As an example, the total thickness ratio may be 1.008, 1.01, 1.05, 1.07, 1.1, 1.2, 1.3, 1.4, or a range consisting of any two point values.

[0076] In this article, the thickness test method can be tested by methods known in the art, for example, it can be tested by a step meter test method. The stylus of the step meter gently rubs the surface of the sample with a very small force, and the micron or even nanometer level of the surface of the sample is amplified millions of times by the sensor connected to the stylus, and then converted into an electronic signal, input into the computer software, and finally displayed in the form of digital and graphical data. Further, the thickness can be tested at more than 15 locations and the average value can be taken.

[0077] In some of the embodiments, the total thickness of the film layer in the positive electrode midcoat region is 80 μm to 240 μm.

[0078] In some embodiments, the direction from the positive electrode middle coating area to the positive electrode edge coating area is the width direction (eg Figure 1The total width of the positive electrode side coating area accounts for 10% to 90% of the total width of the positive electrode middle coating area and the positive electrode side coating area. As an example, the ratio can be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%. As the total width of the positive electrode side coating area accounts for the total width of the positive electrode middle coating area and the positive electrode side coating area, the cycle performance of the secondary battery first increases and then decreases. The total width of the positive electrode side coating area accounts for the total width of the positive electrode middle coating area and the positive electrode side coating area. The ratio can be selected from 20% to 80%, and can be more selectively selected from 30% to 60%.

[0079] In some of the embodiments, positive electrode side coating regions are disposed on opposite sides of the positive electrode mid-region.

[0080] In some embodiments, the film layer of the positive electrode edge coating area includes a positive electrode current collector and a positive electrode base coating layer and a positive electrode active layer stacked in sequence on the positive electrode current collector; the positive electrode middle coating area includes a positive electrode current collector and a positive electrode active layer arranged on the positive electrode current collector.

[0081] Please continue reading Figure 1 In one embodiment, the film layer of the positive electrode edge coating area 502 of the positive electrode plate 510 includes a positive electrode current collector 511, a positive electrode bottom coating layer 512 and a positive electrode active layer 513 stacked in sequence on the negative electrode current collector 511; the positive electrode middle coating area 501 of the positive electrode plate 510 includes a positive electrode current collector 511 and a positive electrode active layer 513 arranged on the positive electrode current collector 511.

[0082] In some of the embodiments, the difference between the total thickness of the film layer in the positive electrode edge coating region and the positive electrode middle coating region is the thickness of the positive electrode bottom coating layer.

[0083] Furthermore, the thickness of the positive electrode bottom coating layer is 0.5-20 μm, and can be 1-10 μm. Controlling the thickness of the positive electrode bottom coating layer within this range can not only meet the above resistance requirements, but also substantially not affect the energy density of the secondary battery.

[0084] By first forming a positive electrode bottom coating with low surface resistance on the positive electrode current collector in the positive electrode edge coating area, and then forming a positive electrode active layer on the positive electrode bottom coating, the overall resistance R 1 Reduced, lower than the resistance R of the film layer in the positive electrode coating area 2 .

[0085] In some embodiments, the components of the positive electrode bottom coating include a conductive agent and a binder. Further, in the positive electrode bottom coating, the mass content of the conductive agent is 50% to 80%; further, the mass content of the binder is 20% to 50%.

[0086] In some embodiments, the positive electrode current collectors in the positive electrode middle coating area and the positive electrode side coating area are the same current collector, and the thickness of the positive electrode active layer in the positive electrode middle coating area and the positive electrode side coating area is the same.

[0087] As a non-limiting example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode active layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0088] In some of the embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the positive electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0089] In some of the embodiments, the positive electrode active material may be a positive electrode active material for a battery known in the art, including but not limited to at least one of a lithium ion active material and a sodium ion active material.

[0090] As non-limiting examples of lithium ion active materials, the positive electrode active material may include one or more of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO 2 ), one or more of lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and modified compounds thereof. Non-limiting examples of lithium phosphates containing an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. Non-limiting examples of lithium cobalt oxides may include LiCoO 2 Non-limiting examples of lithium nickel oxides may include LiNiO 2 Non-limiting examples of lithium manganese oxides may include LiMnO 2 、LiMn2 O 4 etc.; Non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (Also referred to as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O 2 (Also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O 2 (Also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O 2 (Also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O 2 (Also referred to as NCM 811 ) etc. Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.8 Co 0.15 Al 0.05 O 2 .

[0091] As non-limiting examples of sodium ion active materials, the sodium ion active materials may include one or more of the following materials: sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. However, the present application is not limited to these materials, and other conventionally known materials that can be used as positive active materials for sodium ion batteries may also be used.

[0092] As an optional technical solution of the present application, in the sodium transition metal oxide, the transition metal may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Non-limiting examples of sodium transition metal oxides may include Na x MO 2 , where M may include one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0<x≤1.

[0093] As an optional technical solution of the present application, the polyanionic compound can be a compound having sodium ions, transition metal ions and tetrahedral (YO 4 ) n-A class of compounds with anionic units. The transition metal can include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be one or more of P, S, and Si; n represents the valence state of (YO 4 ) n- .

[0094] The polyanionic compound can also be a class of compounds with sodium ions, transition metal ions, tetrahedral (YO 4 ) n- anionic units, and halogen anions. The transition metal can include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be one or more of P, S, and Si, n represents the valence state of (YO 4 ) n- ; the halogen can be one or more of F, Cl, and Br.

[0095] The polyanionic compound can also be a class of compounds with sodium ions, tetrahedral (YO 4 ) n- anionic units, polyhedral units (ZO y ) m+ , and optional halogen anions. Y can be one or more of P, S, and Si, n represents the valence state of (YO 4 ) n- ; Z represents a transition metal, which can include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, m represents the valence state of (ZO y ) m+ ; the halogen can be one or more of F, Cl, and Br.

[0096] The polyanionic compound can include NaFePO 4 , Na 3 V 2 (PO 4 ) 3 (sodium vanadium phosphate, abbreviated as NVP), Na 4 Fe 3 (PO 4 ) 2 (P 2 O 7 ), NaM’PO 4 F, and Na 3 (VO y ) 2 (PO 4 ) 2 F 3-2y (0 ≤ y ≤ 1), one or more of them. Among them, NaM’PO4 M' in F may include one or more of V, Fe, Mn and Ni.

[0097] Prussian blue compounds can be sodium ions, transition metal ions and cyanide ions (CN - ). The transition metal may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Non-limiting examples of Prussian blue compounds may include Na a Me b Me' c (CN) 6 , wherein Me and Me' can each independently be one or more of Ni, Cu, Fe, Mn, Co and Zn, 0<a≤2, 0<b<1, 0<c<1.

[0098] It can be understood that, taking lithium ions as active ions, the battery will be accompanied by the deintercalation and consumption of lithium (Li) during the charging and discharging process, and the content of Li in the positive electrode sheet is different when the battery is discharged to different states. In the enumeration of positive electrode materials in this application, unless otherwise specified, the content of Li is the initial state of the material. The positive electrode material is applied to the positive electrode sheet in the battery system, and after the charge and discharge cycle, the content of Li in the positive electrode material contained in the electrode sheet usually changes. Among them, the content of Li can be measured by molar content, but is not limited to this. Regarding "the content of Li is the initial state of the material", the initial state of the material refers to the state before the material is added to the positive electrode slurry. It can be understood that the new material obtained by appropriate modification on the basis of the listed positive electrode materials is also within the scope of the positive electrode material. The aforementioned appropriate modification refers to the acceptable modification method for the positive electrode material, and non-limiting examples include coating modification. In the enumeration of positive electrode materials in this application, the content of oxygen (O) is only a theoretical state value. The release of lattice oxygen will cause the molar content of oxygen to change, and the actual content of O will fluctuate. The content of O may be measured by molar content, but is not limited thereto.

[0099] In some of these embodiments, the positive electrode active layer may also optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0100] In some embodiments, the positive electrode active layer may further include a conductive agent. As non-limiting examples, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0101] In some embodiments, the positive electrode sheet can be prepared by the following method:

[0102] A conductive agent, a binder and any other components are dispersed in a solvent to form a primer slurry; the primer slurry is applied to the edge area on at least one side of the width direction of the positive electrode current collector surface, and the primer slurry is not applied to the middle area, and dried to form a positive electrode primer layer on at least one side of the positive electrode current collector surface.

[0103] Dispersing the above components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components in a solvent to form a positive electrode slurry;

[0104] The positive electrode slurry is coated on the surface of the positive electrode bottom coating of the positive electrode collector, including the positive electrode bottom coating and the exposed positive electrode collector area in the middle. After drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0105] The type of solvent can be selected from but not limited to any one of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode collector. The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode collector. The solid content of the positive electrode slurry can be 40wt% to 80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000-25000mPa·s. When coating the positive electrode slurry, the coating unit surface density on a dry weight basis (excluding the solvent) can be 15-35mg / cm 2 The compaction density of the positive electrode sheet can be 3.0 to 3.6 g / cm 3 , can be selected as 3.3~3.5g / cm 3 .

[0106] Negative electrode

[0107] Another embodiment of the present application provides a negative electrode plate, including a negative electrode middle coating area and a negative electrode side coating area located at least on one side of the negative electrode middle coating area, and the resistance R 3 Greater than the resistance R of the film layer in the negative electrode coating area 4 .

[0108] Without wishing to be limited to any theory, the negative electrode plate is configured such that the negative electrode middle coating area and the negative electrode side coating area are: the resistance R of the film layer in the negative electrode side coating area 3 Greater than the resistance R of the film layer in the negative electrode coating area 4In this way, during the charging process, the kinetic performance of the negative electrode middle coating area is better than that of the negative electrode side coating area, which makes the negative electrode middle coating area relatively less prone to lithium deposition, thereby alleviating the serious lithium deposition problem in the middle area of ​​the negative electrode to a certain extent and improving the cycle performance of the secondary battery.

[0109] It can be understood that the structures of the middle coating area and the side coating area of ​​the negative electrode plate can be the same or similar to those of the positive electrode plate. The main difference is that the resistance of the film layer in the middle coating area and the side coating area of ​​the negative electrode plate is different.

[0110] In some embodiments, R 3 =(1.1~7)R 4 ; Optionally, R 3 =(1.1~6)R 4 , optionally, R 3 =(1.1~5)R 4 , or R 3 =(3~5)R 4 As an example, R 3 Can be 1.1R 4 , 1.5R 4 , 2R 4 、3R 4 , 3.5R 4 、4R 4 , 4.5R 4 , 5.5R 4 、6R 4 、6.5R 4 ,7R 4 , or it can be a range consisting of any two of the above point values. Further control R 3 and R 4 This relationship can further improve the lithium plating problem of secondary batteries and enhance the cycle performance of secondary batteries.

[0111] Optionally, R 4 ≤0.01Ω.

[0112] Generally, as the battery continues to expand during use, the thickness of the electrode increases, the porosity decreases, and the electrolyte is squeezed out during the charging process. During discharge, the electrolyte needs to flow back. Due to the large expansion force in the later stage, it is difficult for the electrolyte to flow back, resulting in a lack of electrolyte in the central area of ​​the electrode, which can also lead to lithium precipitation problems, thereby causing the battery's cycle performance to plummet and even cause safety problems. In some of the embodiments, the total thickness of the film layer in the negative electrode middle coating area is less than the total thickness of the film layer in the negative electrode side coating area. Therefore, the liquid storage capacity of the negative electrode side coating area can be increased, thereby improving the ability of the electrolyte to flow back to the negative electrode side coating area, thereby further improving the lithium precipitation problem of the secondary battery and improving the cycle performance of the secondary battery.

[0113] In some embodiments, the total thickness ratio c of the film layer of the negative electrode edge coating area and the negative electrode middle coating area satisfies: 1<c≤1.4, and c can be 1.008~1.4, 1.01~1.4, 1.01~1.2, or 1.05~1.4, or 1.05~1.2. As an example, the total thickness ratio can be 1.008, 1.01, 1.05, 1.07, 1.1, 1.2, 1.3, 1.4, or a range consisting of any two point values.

[0114] In some of the embodiments, the total thickness of the film layer in the negative electrode middle coating region is 50 μm to 300 μm.

[0115] In some embodiments, the total width of the negative electrode side coating area accounts for 10% to 90% of the total width of the negative electrode middle coating area and the negative electrode side coating area, with the direction from the negative electrode middle coating area to the negative electrode side coating area as the width direction. As an example, the ratio can be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%. As the ratio increases, the cycle performance of the secondary battery first increases and then decreases. The ratio can be selected from 20% to 80%, and more preferably from 30% to 60%.

[0116] Optionally, the negative electrode middle coating area is arranged opposite to the positive electrode middle coating area; the negative electrode side coating area is arranged opposite to the positive electrode side coating area.

[0117] In some embodiments, negative electrode side coating regions are disposed on opposite sides of the negative electrode middle region.

[0118] In some embodiments, the film layer of the negative electrode edge coating area includes a negative electrode current collector and a negative electrode bottom coating layer and a negative electrode active layer stacked in sequence on the negative electrode current collector; the negative electrode middle coating area includes a negative electrode current collector and a negative electrode active layer arranged on the negative electrode current collector.

[0119] In some embodiments, the difference between the total thickness of the film layer in the negative electrode edge coating region and the negative electrode middle coating region is the thickness of the primer layer.

[0120] In some of the embodiments, the thickness of the negative electrode bottom coating layer is 1-10 μm. By controlling the thickness of the negative electrode bottom coating layer within this range, in addition to meeting the above resistance requirement, the energy density of the secondary battery is not substantially affected.

[0121] By first forming a negative electrode bottom coating with a large surface resistance on the negative electrode current collector in the negative electrode edge coating area, and then forming a negative electrode active layer on the negative electrode bottom coating, the overall resistance R 3 Increased, greater than the resistance R of the film layer in the negative electrode coating area 4 .

[0122] In some embodiments, the components of the negative electrode bottom coating include a conductive agent and a binder. Further, in the negative electrode bottom coating, the mass content of the conductive agent is 10% to 30%; further, the mass content of the binder is 70% to 90%.

[0123] In some embodiments, the negative electrode current collectors in the negative electrode middle coating region and the negative electrode side coating region are the same current collector, and the thickness of the negative electrode active layer in the negative electrode middle coating region and the negative electrode side coating region is the same.

[0124] The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active layer includes a negative electrode active material.

[0125] As a non-limiting example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode active layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0126] In some of the embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the negative electrode current collector, non-limiting examples of the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the negative electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0127] In some of the embodiments, the negative electrode active material may adopt the negative electrode active material for batteries known in the art. As a non-limiting example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include one or more of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0128] In some of these embodiments, the negative electrode active layer may also optionally include a binder. The binder may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0129] In some of these embodiments, the negative electrode active layer may also optionally include a conductive agent. The conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0130] In some of these embodiments, the negative electrode active layer may also optionally include other additives, such as a thickening agent (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0131] In some of these embodiments, the negative electrode plate can be prepared by the following method:

[0132] Disperse the conductive agent, binder, and any other components in a solvent to form a primer slurry; coat the primer slurry on at least one edge region on the width direction side of the negative electrode current collector surface, control the middle region not to be coated with the primer slurry, and dry to form a negative electrode primer layer on at least one side of the negative electrode current collector surface.

[0133] Disperse the components for preparing the negative electrode plate, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry;

[0134] Coat the negative electrode slurry on the surface of the negative electrode current collector where the negative electrode primer layer is located, including the negative electrode primer layer and the middle exposed negative electrode current collector region, and after processes such as drying and cold pressing, the negative electrode plate can be obtained.

[0135] The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or two surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40wt% - 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000 - 10000 mPa·s. When coating the negative electrode slurry, the coating unit surface density in terms of dry weight (deducting the solvent) can be 75 - 220 g / m 2 . The compaction density of the negative electrode plate can be 1.0 g / cm 3 ~1.8 g / cm 3 .

[0136] Electrolyte

[0137] The electrolyte functions to conduct ions between the positive electrode plate and the negative electrode plate. There are no particular restrictions on the type of electrolyte in this application, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or all-solid-state.

[0138] In some of these embodiments, the electrolyte uses an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0139] In some of these embodiments, the electrolyte salt may include lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluorooxalate borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP), or one or more of them.

[0140] In some of these embodiments, the solvent may include 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), butenyl carbonate, fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone, or one or more of them.

[0141] In some of these embodiments, the electrolytic solution may also optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performances, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, etc.

[0142] In some embodiments, the additives in the electrolytic solution may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethyl carbonate (TFPC), etc.

[0143] Separator

[0144] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0145] In some embodiments, the material of the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0146] In some embodiments, the thickness of the separator is 6-40 μm, and can be 12-20 μm. In some embodiments, the positive electrode sheet, the negative electrode sheet and the separator can be made into an electrode assembly by a winding process or a lamination process.

[0147] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0148] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, and further, non-limiting examples of plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0149] The secondary battery includes at least one battery cell. The secondary battery may include one or more battery cells.

[0150] In this application, unless otherwise specified, "battery cell" refers to a basic unit that can realize the mutual conversion of chemical energy and electrical energy, and further, generally speaking, at least includes a positive electrode sheet, a negative electrode sheet and an electrolyte. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting active ions between the positive electrode sheet and the negative electrode sheet.

[0151] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 2 The battery cell 5 is a square structure as an example.

[0152] In some of these embodiments, reference Figure 3, the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to actual needs.

[0153] The secondary battery may be a battery module 4 or a battery pack 1 .

[0154] The battery module includes at least one battery cell. The number of battery cells contained in the battery module can be one or more, and those skilled in the art can select a suitable number according to the application and capacity of the battery module.

[0155] Figure 4 4 is an example of a battery module. Figure 4 In the battery module 4, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by fasteners.

[0156] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0157] In some of the embodiments, the battery modules may be assembled into a battery pack. The battery pack may contain one or more battery modules. Those skilled in the art may select a suitable number according to the application and capacity of the battery pack.

[0158] Figure 5 and Figure 6 1 is a battery pack 1 as an example. Figure 5 and Figure 6 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0159] In addition, the present application also provides an electrical device, which includes a secondary battery provided by the present application. The secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto. Among them, the mobile device may be, for example, a mobile phone, a laptop computer, etc.; the electric vehicle may be, for example, a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but are not limited thereto.

[0160] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0161] Figure 7 The power consumption device 6 is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the power consumption device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module can be used.

[0162] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0163] Hereinafter, the embodiments of the present application will be described. 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. If the 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. The reagents or instruments used that do not specify the manufacturer are all conventional products that can be obtained commercially.

[0164] 1. Preparation Example

[0165] Example 1

[0166] 1) Preparation of positive electrode

[0167] Both sides of the positive electrode current collector aluminum foil are divided along its width direction, including a middle area A and edge areas B of equal width located on both sides of the middle area A, wherein the total width of the edge areas B on both sides accounts for 50% of the total width of the middle area A and the edge areas B on both sides (the width of the base coating accounts for 50%).

[0168] Conductive carbon black SP and binder PVDF were dispersed in solvent NMP at a weight ratio of 5:5 and mixed evenly to obtain a primer slurry. The primer slurry was applied to the edge area B on both sides of the positive electrode current collector, and the middle area A was not coated with the primer slurry, and dried to form a positive electrode primer layer of the same thickness on both sides.

[0169] The positive electrode active material LiNi 0.5 Co0.2 Mn 0.3 O 2 (abbreviated as NCM 523 ), conductive carbon black SP and binder PVDF are dispersed in solvent NMP in a weight ratio of 98:1:1 and mixed evenly to obtain a positive electrode slurry.

[0170] The positive electrode slurry is coated (the coating amount per unit area is 0.27g / 1540.25mm 2 ) On both sides of the positive current collector with the positive bottom coating formed thereon (including the positive bottom coating and the exposed positive current collector area in the middle), after drying, cold pressing and other processes, a positive active layer is formed to obtain a positive electrode sheet. The positive electrode sheet forms a positive electrode side coating area in the edge area and a positive electrode middle coating area in the middle area. The positive electrode middle coating area refers to the total thickness A2 of the positive current collector layer and the positive active layer on both sides, and its thickness is 120μm.

[0171] 2) Preparation of negative electrode sheet

[0172] The negative electrode active material graphite, the thickener sodium carboxymethyl cellulose, the adhesive styrene butadiene rubber, and the conductive agent acetylene black are mixed in a mass ratio of 97:1:1:1, and deionized water is added to obtain a negative electrode slurry under the action of a vacuum mixer; the negative electrode slurry is evenly coated on both sides of the copper foil; the copper foil is dried at room temperature and then transferred to a 120°C oven for drying for 1 hour, and then super-cold pressed and cut to obtain a negative electrode sheet with a total thickness of 138 μm, wherein the coating amount per unit area of ​​both sides is 0.17 g / 1540.25 mm 2 .

[0173] 3) Isolation film

[0174] A 12μm thick polypropylene isolation film was selected.

[0175] 4) Preparation of electrolyte

[0176] The organic solvent is a mixed solution containing ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC), wherein the volume ratio of EC, EMC and DEC is 20:20:60. In an argon atmosphere glove box with a water content of <10ppm, fully dried lithium salt LiPF6 is dissolved in the organic solvent and mixed evenly to obtain an electrolyte. The concentration of the lithium salt is 1 mol / L.

[0177] 5) Preparation of batteries

[0178] The positive electrode sheet, isolation film, and negative electrode sheet are stacked in order, so that the isolation film is placed between the positive and negative electrode sheets to play an isolating role. Then, they are wound into a square bare battery cell, loaded with aluminum-plastic film, and then baked at 80°C to remove water. After that, 10g of the corresponding non-aqueous electrolyte is injected and sealed. After standing, hot and cold pressing, formation, clamping, capacity division and other processes, a finished battery with a capacity of 4000mAh is obtained.

[0179] The secondary batteries of Examples 2 to 16 and Comparative Examples 1 to 2 are prepared in a similar manner to the secondary battery of Example 1, but the preparation process of the positive electrode sheet is different. Specifically, in the positive electrode sheet, the thickness of the primer layer, the total width of the edge regions B on both sides accounted for the total width of the middle region A and the edge regions B on both sides, and the composition of the primer layer are different (which leads to R 1 / R 2 Different), as shown in Table 1. Among them, the total thickness A2 of the positive electrode coating area remains unchanged.

[0180] Among them, no primer layer is provided in the positive electrode sheet in Comparative Example 1.

[0181] Among them, R in Comparative Example 2 1 / R 2 >1, that is, the resistance R of the film layer in the positive electrode coating area 1 >Resistance R of the film layer in the positive electrode coating area 2 .

[0182] Examples 17 to 20

[0183] The secondary batteries of Examples 17 to 20 are prepared in a similar manner to the secondary battery of Example 4, but in Examples 17 to 20, a primer layer is provided on the negative electrode sheet, and no primer layer is provided on the positive electrode sheet. The difference between Examples 17 to 20 is that the composition of the primer layer in the negative electrode sheet is different (which results in R 3 / R 4 Different), as shown in Table 2. Among them, the thickness of the negative electrode middle coating area of ​​the negative electrode plate is 138 μm.

[0184] The preparation process of the positive electrode sheet and the negative electrode sheet of Example 17 is as follows:

[0185] 1) Preparation of positive electrode

[0186] The positive electrode active material LiNi 0.5 Co 0.2 Mn 0.3 O 2 (abbreviated as NCM 523 ), conductive carbon black SP and binder PVDF are dispersed in solvent NMP in a weight ratio of 98:1:1 and mixed evenly to obtain a positive electrode slurry.

[0187] The positive electrode slurry is coated (the coating amount per unit area is 0.27g / 1540.25mm 2 ) After drying, cold pressing and other processes, a positive electrode active layer is formed on both sides of the positive electrode current collector aluminum foil to obtain a positive electrode sheet.

[0188] 2) Preparation of negative electrode sheet

[0189] Both sides of the negative electrode current collector copper foil are divided along its width direction, including a middle area A and edge areas B of equal width located on both sides of the middle area A, wherein the total width of the edge areas B on both sides accounts for 50% of the total width of the middle area A and the edge areas B on both sides (the width of the base coating accounts for 50%).

[0190] The conductive agent acetylene black and the adhesive styrene butadiene rubber are mixed in a mass ratio of 3:7, and deionized water is added to obtain a primer slurry under the action of a vacuum mixer. The primer slurry is applied to the edge area B on both sides of the negative electrode current collector, and the middle area A is not coated with the primer slurry, and dried to form a negative electrode primer layer of the same thickness on both sides.

[0191] The negative electrode active material graphite, the thickener sodium carboxymethyl cellulose, the binder styrene butadiene rubber, and the conductive agent acetylene black were mixed in a mass ratio of 97:1:1:1, deionized water was added, and the negative electrode slurry was obtained under the action of a vacuum mixer.

[0192] The negative electrode slurry was coated (the coating amount per unit area was 0.17 g / 1540.25 mm 2 ) On both sides of the negative electrode current collector formed with the negative electrode bottom coating (including the negative electrode bottom coating and the exposed negative electrode current collector area in the middle), the copper foil is dried at room temperature and then transferred to a 120°C oven for drying for 1 hour, and then supercooled pressed and cut to form a negative electrode active layer to obtain a negative electrode pole piece. The negative electrode pole piece forms a negative electrode side coating area in the edge area and a negative electrode middle coating area in the middle area.

[0193] Comparative Example 3

[0194] The secondary battery of Comparative Example 3 is prepared in a similar manner to the secondary battery of Example 17, but R 3 / R 4 <1, that is, the resistance R of the film layer in the negative electrode coating area 3 <Resistance R of the film layer in the negative electrode intermediate coating area 4 .

[0195] Embodiment 21

[0196] The secondary battery of Example 21 is prepared in a similar manner to the secondary battery of Example 17, but the positive electrode sheet of Example 1 is used to replace the positive electrode sheet in Example 17, that is, the positive electrode sheet of Example 1 and the negative electrode sheet in Example 17 are used in combination.

[0197] 2. Performance Test

[0198] (1) Test the cycle stability of the battery

[0199] At 25°C, charge at a constant current of 1 / 3C (nominal capacity) to a termination voltage of 4.4V, then charge at a constant voltage of 0.05C, leave for 5 minutes, and then discharge at a 1 / 3C to a discharge cut-off voltage of 2.5V to obtain the discharge energy E and capacity C, which is recorded as the initial capacity C0. Repeat the above steps for the same battery cell, and simultaneously record the discharge capacity Cn of the battery after the nth cycle, then the battery capacity retention rate Pn after each cycle = Cn / C0 × 100%. During this test, the first cycle corresponds to n = 1, the second cycle corresponds to n = 2, ... the 1500th cycle corresponds to n = 1500. The corresponding battery capacity retention rate data in Tables 1 and 2 are the data measured after 1500 cycles under the above test conditions.

[0200] (2) Lithium deposition test

[0201] (II) Lithium deposition performance test

[0202] After the cycle test process is terminated, each secondary battery that reaches 100% SOC is disassembled to observe whether lithium is deposited at the interface of the negative electrode plate.

[0203] The evaluation method of lithium precipitation degree is as follows:

[0204] Level 0 lithium deposition: There is no lithium deposition area on the entire negative electrode;

[0205] Level 1 lithium deposition: The maximum area of ​​a single lithium deposition area of ​​the entire negative electrode is ≤ 2*2mm 2 , the number of lithium deposition areas of the entire negative electrode is ≤5;

[0206] Level 2 lithium plating: 2*2mm 2 <The maximum area of ​​a single lithium deposition area of ​​the entire negative electrode is ≤5*5mm 2 , the number of lithium deposition areas of the entire negative electrode is ≤10;

[0207] Level 3 lithium deposition: lithium deposition occurs and the judgment criteria for level 1 and level 2 lithium deposition are not met.

[0208] The above performance test results of each embodiment and comparative example are shown in Table 1 and Table 2.

[0209] In Table 1, the total thickness ratio a of the film layer of the positive electrode edge coating area and the positive electrode middle coating area refers to the ratio of the total thickness A1 of the positive electrode collector, the double-sided positive electrode base coating and the double-sided positive electrode active layer in the positive electrode edge coating area to the total thickness A2 of the positive electrode collector layer and the double-sided positive electrode active layer in the positive electrode middle coating area.

[0210] Table 1

[0211]

[0212]

[0213] It should be noted that the resistance of the positive electrode bottom coating can be adjusted by adjusting the thickness of the positive electrode bottom coating and the mass content of the conductive agent in the positive electrode bottom coating, thereby adjusting R 1 / R 2 The negative electrode is similar.

[0214] It can be seen from Table 1 that, compared with Comparative Examples 1 to 2, the cycle performance of the battery in each embodiment is improved and the degree of lithium plating is reduced.

[0215] From Examples 1 to 8, it can be seen that as the thickness of the bottom coating of the positive electrode sheet increases in the range of 0.5 to 20 μm, that is, the depression of the middle coating of the positive electrode sheet is more obvious, the thickness of the bottom coating is in the range of 0.5 to 10 μm, the electrolyte reflux is improved, the capacity retention rate is increased, the cycle performance is improved, and the degree of lithium precipitation is reduced; when the thickness of the bottom coating increases to 20 μm, the thickness of the bottom coating is too large, which affects the energy density, and the conductive agent content in the bottom coating accounts for 80% and has reached the boundary, and the resistance ratio R 1 / R 2 The ratio a of the total thickness of the film layer of the positive electrode edge coating area to the positive electrode middle coating area is 1.008 to 1.4. In the optional range of 1.05 to 1.4 or 1.05 to 1.2, the cycle performance is further improved and the degree of lithium precipitation is further reduced.

[0216] It can be seen from Examples 4 and 9 to 12 that as the proportion of the bottom coating width increases, the capacity of the battery first increases and then decreases. This is because the proportion of the bottom coating is too small to achieve the maximum effect, and the proportion of the bottom coating is too large to achieve the effect of the intermediate difference. The proportion of the bottom coating width can be selected between 30% and 70%.

[0217] From Examples 4 and 13 to 16, it can be seen that as R 1 / R 2 The smaller the ratio, the faster the lithium removal on both sides, the slower the lithium removal in the middle, and the more difficult it is to deposit lithium in the middle. 1 / R 2 The ratio of , the improvement of lithium precipitation is not obvious, and a lower R 1 / R 2 The ratio is more difficult.

[0218] In Table 2, the total thickness ratio c of the film layer of the negative electrode edge coating area and the negative electrode middle coating area refers to the ratio of the total thickness C1 of the negative electrode current collector, the double-sided negative electrode base coating and the double-sided negative electrode active layer in the negative electrode edge coating area to the total thickness C2 of the negative electrode current collector layer and the double-sided negative electrode active layer in the negative electrode middle coating area.

[0219] Table 2

[0220]

[0221] As can be seen from Table 2, compared with Comparative Examples 1 and 3, the cycle performance of the battery in Examples 17 to 21 is improved and the degree of lithium plating is reduced.

[0222] From Examples 17 to 20, it can be seen that the undercoat layer is provided on the negative electrode sheet. 3 / R 4 The larger the ratio of R, the greater the battery capacity will be. The further the kinetic difference between the two sides is, the worse the cycle will be. 3 =(2~5)R 4 , the battery’s cycle performance is further improved and the degree of lithium plating is further reduced.

[0223] It can be seen from Example 1, Example 17 and Example 21 that the cycle performance of the battery prepared by combining the positive electrode plate of the embodiment of the present application and the negative electrode plate of the embodiment of the present application is better.

[0224] The above description of various embodiments tends to emphasize the differences between the various embodiments. The same or similar aspects can be referenced to each other, and for the sake of brevity, they will not be repeated herein.

[0225] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A positive electrode sheet, It is characterized in that The positive electrode coating layer includes a positive electrode middle coating area and a positive electrode side coating area located at at least one side of the positive electrode middle coating area. The resistance R 1 Less than the resistance R of the film layer in the positive electrode coating area 2 .

2. The positive electrode sheet according to claim 1, It is characterized in that R 1 =(0.1~0.95)R 2 ; Optionally, R 1 =(0.1~0.9)R 2 Optionally, R 1 =(0.1~0.8)R 2 .

3. The positive electrode sheet according to claim 1 or 2, It is characterized in that The total thickness of the film layer in the positive electrode middle coating area is less than the total thickness of the film layer in the positive electrode side coating area.

4. The positive electrode sheet according to claim 3, It is characterized in that At least one of the following conditions is met: (1) The ratio a of the total thickness of the film layer of the positive electrode edge coating area to the total thickness of the film layer of the positive electrode middle coating area satisfies: 1<a≤1.4, and a can be selected from 1.008 to 1.4, further selected from 1.05 to 1.4, and more preferably selected from 1.05 to 1.2; (2) The total thickness of the film layer in the positive electrode coating area is 80 μm to 240 μm; (3) With the direction from the positive electrode middle coating area to the positive electrode side coating area as the width direction, the total width of the positive electrode side coating area accounts for 10% to 90% of the total width of the positive electrode middle coating area and the positive electrode side coating area, and can be 20% to 80%, and more preferably 30% to 60%; (4) The positive electrode side coating areas are provided on opposite sides of the positive electrode middle area.

5. The positive electrode sheet according to claim 1, 2 or 4, It is characterized in that The film layer of the positive electrode edge coating area includes a positive electrode current collector and a positive electrode bottom coating layer and a positive electrode active layer stacked in sequence on the positive electrode current collector; the positive electrode middle coating area includes a positive electrode current collector and a positive electrode active layer arranged on the positive electrode current collector.

6. The positive electrode sheet according to claim 5, It is characterized in that At least one of the following conditions is met: (1) The difference between the total thickness of the film layer of the positive electrode edge coating area and the positive electrode middle coating area is the thickness of the positive electrode bottom coating layer; (2) The thickness of the positive electrode bottom coating is 0.5 to 20 μm, and can be 1 to 10 μm; (3) The positive electrode current collector of the positive electrode middle coating area and the positive electrode side coating area is the same current collector, and the thickness of the positive electrode active layer of the positive electrode middle coating area and the positive electrode side coating area is the same; (4) The components of the positive electrode bottom coating layer include a conductive agent and a binder; optionally, in the positive electrode bottom coating layer, the mass content of the conductive agent is 50% to 80%; optionally, in the positive electrode bottom coating layer, the mass content of the binder is 20% to 50%.

7. A negative electrode sheet, It is characterized in that The negative electrode coating layer includes a negative electrode middle coating area and a negative electrode side coating area located at at least one side of the negative electrode middle coating area. The resistance R 3 Greater than the resistance R of the film layer in the negative electrode coating area 4 .

8. The negative electrode sheet according to claim 7, It is characterized in that R 3 =(1.1~7)R 4 ; Optionally, R 3 =(1.1~5)R 4 ; More optionally, R 3 =(2~5)R 4 .

9. The negative electrode sheet according to claim 7 or 8, It is characterized in that The total thickness of the film layer in the negative electrode middle coating area is less than the total thickness of the film layer in the negative electrode side coating area.

10. The negative electrode sheet according to claim 9, It is characterized in that At least one of the following conditions is met: (1) The ratio c of the total thickness of the film layer of the negative electrode edge coating area to the total thickness of the film layer of the negative electrode middle coating area satisfies: 1<c≤1.4, and c can be selected from 1.008 to 1.4, further selected from 1.05 to 1.4, and more preferably selected from 1.05 to 1.2; (2) The total thickness of the film layer in the negative electrode middle coating area is 50 μm to 300 μm; (3) With the direction from the negative electrode middle coating area to the negative electrode side coating area as the width direction, the total width of the negative electrode side coating area accounts for 10% to 90% of the total width of the negative electrode middle coating area and the negative electrode side coating area, and can be 20% to 80%, and more preferably 30% to 60%; (4) The negative electrode side coating areas are provided on opposite sides of the negative electrode middle area.

11. The negative electrode sheet according to claim 7, 8 or 10, It is characterized in that The film layer of the negative electrode edge coating area includes a negative electrode current collector and a negative electrode bottom coating layer and a negative electrode active layer stacked in sequence on the negative electrode current collector; the negative electrode middle coating area includes a negative electrode current collector and a negative electrode active layer arranged on the negative electrode current collector.

12. The negative electrode sheet according to claim 11, It is characterized in that At least one of the following conditions is met: (1) The difference between the total thickness of the film layer of the negative electrode edge coating area and the negative electrode middle coating area is the thickness of the negative electrode bottom coating layer; (2) The thickness of the negative electrode bottom coating is 0.5 to 20 μm, and can be 1 to 10 μm; (3) The negative electrode current collector of the negative electrode middle coating area and the negative electrode side coating area is the same current collector, and the thickness of the negative electrode active layer of the negative electrode middle coating area and the negative electrode side coating area is the same; (4) The components of the negative electrode bottom coating include a conductive agent and a binder; optionally, in the negative electrode bottom coating, the mass content of the conductive agent is 10% to 30%; optionally, in the negative electrode bottom coating, the mass content of the binder is 70% to 90%.

13. A secondary battery, It is characterized in that The invention comprises at least one of the positive electrode sheet according to any one of claims 1 to 6 and the negative electrode sheet according to any one of claims 7 to 12.

14. An electrical device, It is characterized in that The invention comprises at least one of the positive electrode sheet according to any one of claims 1 to 6, the negative electrode sheet according to any one of claims 7 to 12, and the secondary battery according to claim 13.

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