Negative pole piece, preparation method of negative pole piece, secondary battery and electric device

Abstract

The invention relates to a negative pole piece and a preparation method thereof, a secondary battery and an electric device. The negative pole piece comprises a negative current collector and a lithium agent metal layer, the negative current collector is provided with a plurality of open pore structures, the edges of the open pore structures are provided with bulges, the average roughness of the edges of the open pore structures is 0.2-3, and the maximum roughness of the edges of the open pore structures is 2.5-6.1; the lithium-based metal layer is arranged on at least one surface of the negative electrode current collector and covers the open pore structure, and the bulge is embedded into the lithium-based metal layer and is coated by the lithium-based metal layer. According to the negative pole piece provided by the invention, the battery has relatively high energy density and good cycle life.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and particularly to a negative electrode sheet, a preparation method thereof, a secondary battery, and an electrical device. 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 hydro, 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. Due to the great development of lithium-ion batteries, higher requirements are also put forward for their energy density, cycle performance, and safety performance. Metallic lithium has an extremely high theoretical specific capacity (3860 mAh / g) and an extremely low reduction potential (-3.04 V vs standard hydrogen electrode), so metallic lithium is considered to be a preferred negative electrode material for next-generation high-energy-density lithium-ion batteries.

[0004] However, due to the volume expansion and dendrite deposition problems of the metallic lithium negative electrode during the battery cycle, and restricted by the characteristics of metallic lithium and the processing level, a support skeleton needs to be provided for metallic lithium to prepare a high-performance negative electrode sheet. Currently, the negative electrode of a lithium metal battery (i.e., a lithium-ion battery using a negative electrode sheet) is mainly a lithium-copper composite tape formed by mechanically rolling a continuous copper foil and a lithium strip. Although it can be used as a negative electrode, its performance is far from the expectation. The density of the copper foil is about 16 times greater than that of metallic lithium, resulting in a significant reduction in the energy density of the battery. Related technologies mostly use a porous copper current collector to improve the specific energy of the negative electrode, but this leads to a decrease in the bonding force between metallic lithium and the copper foil and a poor structural stability of the negative electrode sheet, thereby affecting the cycle life of the battery. Therefore, traditional negative electrode sheets still need to be improved. Summary of the Invention

[0005] The present application provides a negative electrode sheet, a preparation method thereof, a secondary battery, and an electrical device, which can enable the battery to have both high energy density and good cycle life.

[0006] To achieve the above object, the first aspect of the present application provides a negative electrode sheet, including:

[0007] A negative electrode current collector, the negative electrode current collector having a plurality of opening structures, the edges of the opening structures having protrusions, the average roughness of the edges of the opening structures being 0.2 to 3, and the maximum roughness of the edges of the opening structures being 2.5 to 6;

[0008] A lithium-based metal layer, the lithium-based metal layer being compounded on at least one surface of the negative electrode current collector and covering at least a part of the opening region at least,

[0009] Wherein, the protrusions are embedded in the lithium-based metal layer.

[0010] Thus, in this application, by providing an opening structure on the negative electrode current collector, the weight of the negative electrode current collector is reduced to improve the battery energy density. And by providing protrusions at the edge of the opening structure and embedding the protrusions in the lithium-based metal layer, the bonding strength between the lithium-based metal layer and the negative electrode current collector is improved, thereby improving the structural stability of the negative electrode sheet. Further, the edge roughness of the opening structure caused by these granular protrusions is maintained within a specific range, so that while these protrusions can be embedded in the lithium metal layer, the risk of puncturing and short-circuiting the separator is avoided. The negative electrode sheet provided by this application enables the battery to have both a relatively high energy density and good cycle life.

[0011] In some embodiments of the first aspect of this application, the average edge roughness of the opening structure is 1.1 - 2.6, and / or the maximum edge roughness of the opening structure is 2.5 - 6.1.

[0012] In some embodiments of the first aspect of this application, the size of the opening structure is 0.01 mm - 2 mm, and can be optionally 0.01 mm - 0.08 mm; and / or,

[0013] The hole pitch between two adjacent opening structures is 0.01 mm - 0.6 mm, and can be optionally 0.01 mm - 0.05 mm.

[0014] In some embodiments of the first aspect of this application, the opening ratio of the negative electrode current collector is 20% - 50%, and can be optionally 20% - 35%.

[0015] In some embodiments of the first aspect of this application, the thickness of the negative electrode current collector is 5 μm - 15 μm, and can be optionally 5 μm - 8 μm; and / or,

[0016] The thickness of the lithium-based metal layer on one side is 10 μm - 50 μm, and can be optionally 10 μm - 25 μm.

[0017] In some embodiments of the first aspect of this application, the opening structure includes one or more of a round hole, an oval hole, a trapezoidal hole, a quadrilateral hole, and a triangular hole.

[0018] In some embodiments of the first aspect of this application, the negative electrode current collector includes a main body region and an edge region. The opening structure is provided in the main body region, the lithium-based metal layer is provided on the main body region, and the edge region is located on at least one side of the main body region;

[0019] Optionally, the edge region is a non-opening structure;

[0020] Optionally, the ratio of the area of the edge region to the area of the negative current collector is 0.1 to 0.3, and further optionally 0.1 to 0.2.

[0021] In some embodiments of the first aspect of the present application, the negative current collector is a copper foil.

[0022] In some embodiments of the first aspect of the present application, the tensile strength of the negative current collector is greater than or equal to 150 MPa, and optionally 250 MPa to 350 MPa; and / or,

[0023] The elongation rate of the negative current collector is greater than or equal to 2.5%, and optionally 3.5% to 4.5%.

[0024] The second aspect of the present application further provides a method for preparing the negative electrode plate, including the following steps:

[0025] S10, etching a continuous copper foil by a chemical etching template method to prepare the negative current collector; and

[0026] S20, disposing a lithium-based metal on at least one surface of the negative current collector; optionally, laminating the lithium-based metal on at least one surface of the negative current collector by a rolling method.

[0027] Thus, the method for preparing the negative electrode plate provided by the present application is obtained by etching a commercial continuous copper foil, which is convenient and easy to operate and has a low cost.

[0028] In some embodiments of the second aspect of the present application, step S10 includes:

[0029] Coating an anti-corrosion protective agent on the continuous copper foil, positioning a photosensitive tool with pins to expose the pattern on both sides of the continuous copper foil, and then corroding the continuous copper foil synchronously from both sides using a double-sided process.

[0030] The third aspect of the present application further provides a secondary battery, including the negative electrode plate or the negative electrode plate prepared by the preparation method.

[0031] Thus, the secondary battery of the present application can have both high energy density and good cycle life due to including the above negative electrode plate.

[0032] The fourth aspect of the present application provides an electrical device, including the secondary battery of the first aspect of the present application.

[0033] The electrical 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.

[0034] 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 specification, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] For a better description and illustration of the embodiments or examples provided in this application, one or more drawings can be referred to. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments or examples, and the best mode of these applications currently understood. Moreover, in all the drawings, the same reference numerals are used to represent the same components. In the drawings:

[0036] Figure 1 FIG. is a schematic structural diagram of a negative electrode plate according to an embodiment of the present application.

[0037] Figure 2 FIG. is a schematic structural diagram of a negative electrode current collector according to an embodiment of the present application.

[0038] Figure 3 FIG. is a photograph of an opening structure according to an embodiment of the present application.

[0039] Figure 4 FIG. is a schematic structural diagram of a negative electrode current collector according to another embodiment of the present application.

[0040] Figure 5 FIG. is a schematic diagram of a battery cell according to an embodiment of the present application.

[0041] Figure 6 is Figure 5 an exploded view of the battery cell shown in FIG. according to an embodiment of the present application.

[0042] Figure 7 FIG. is a schematic diagram of a battery module according to an embodiment of the present application.

[0043] Figure 8 FIG. is a schematic diagram of a battery pack according to an embodiment of the present application.

[0044] Figure 9 is Figure 8 an exploded view of the battery pack shown in FIG. according to an embodiment of the present application.

[0045] Figure 10 FIG. is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present application.

[0046] DESCRIPTION OF REFERENCE NUMERALS:

[0047] 10 Negative electrode current collector; 20 Lithium-based metal layer; 12 Opening structure; 13 Main body area; 14 Edge area; 1 Battery pack; 2 Upper box body; 3 Lower box body; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Cover plate; 6 Electrical device. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] Hereinafter, some embodiments of the negative electrode sheet, its preparation method, secondary battery, and electrical device of the present application will be described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary details are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the accompanying drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0049] The "range" disclosed in the present application can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The range defined in this way can include or not include the end values. Any end value can be independently included or not included, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are also listed, the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In the present application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" are fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when it is stated that a certain parameter is an integer ≥2, it is equivalent to listing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when it is stated that a certain parameter is an integer selected from "2 - 10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0050] In the present application, when it comes to "a plurality of", "a variety of", etc., unless otherwise specifically defined, it means greater than 2 or equal to 2 in quantity. For example, "one or more" means one or greater than or equal to two.

[0051] If there is no special instruction, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0052] As used herein, the reference to "embodiment" means that the specific features, structures or characteristics described in connection with the embodiment may be included in at least one embodiment or implementation of the present application. The phrase appearing at various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein may be combined with other embodiments. The reference to "implementation" herein has a similar understanding.

[0053] Those skilled in the art can understand that in the methods of various embodiments or implementations, the written order of each step does not mean a strict execution order that constitutes any limitation to the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. If there is no special description, all steps of the present application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) carried out sequentially, or may also include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may also include steps (a), (c) and (b), or may also include steps (c), (a) and (b), etc.

[0054] In the present application, in an open technical feature or technical solution described by words such as "containing", "comprising", "including", etc., without other instructions, additional members other than the listed members are not excluded, and it can be regarded as providing both a closed feature or solution composed of the listed members and an open feature or solution that further includes additional members outside the listed members. For example, A includes a1, a2 and a3. Without other instructions, it may further include other members or may not include additional members, and it can be regarded as providing both a feature or solution that "A is composed of a1, a2 and a3" and a feature or solution that "A not only includes a1, a2 and a3, but also includes other members". In the present application, without other instructions, A (such as B) means that B is a non-limiting example in A, and it can be understood that A is not limited to B.

[0055] In the present application, "optionally", "optional", "option" mean that it is optional, that is, it refers to any one of two parallel options of "having" or "not having". If the word "optional" appears multiple times in a technical solution, without special instructions and without contradictions or mutual constraints, each "optional" is independent of each other.

[0056] In the present application, a "lithium metal battery" refers to a lithium-ion battery using a negative electrode sheet.

[0057] At present, as the supporting framework for metallic lithium in the negative electrode tab, there are commercial continuous copper foil current collectors, copper wire woven copper mesh current collectors, copper foam current collectors, and three-dimensional nanoporous copper current collectors. Compared with other current collectors, the biggest advantage of commercial continuous copper foil current collectors is their convenience in application and low cost. However, there are also many problems, and the most prominent problem is that the energy density of the battery is reduced due to the high density of copper. If the commercial continuous copper foil current collector can still be used as the raw material and the problem of energy density decline can be solved on this basis, it will greatly promote the application and development of the negative electrode tab.

[0058] Based on this, please refer to Figure 1 , the first aspect of the present application provides a negative electrode tab, including a negative electrode current collector 10 and a lithium-based metal layer 20.

[0059] Please refer to Figure 2 and Figure 3 , the negative electrode current collector 10 includes a plurality of opening structures 12, as Figure 3 shown, the edge of the opening structure 12 has a protrusion, the average roughness of the edge of the opening structure 12 is 0.2 - 3, and the maximum roughness of the edge of the opening structure 12 is 2.5 - 6.1;

[0060] The lithium-based metal layer 20 is disposed on at least one surface of the negative electrode current collector 10 and covers the opening structure 12, and the protrusion is embedded in the lithium-based metal layer 20 and is coated by the lithium-based metal layer 20.

[0061] The above negative electrode tab reduces the weight of the negative electrode current collector by providing an opening structure on the negative electrode current collector to improve the energy density of the battery, and improves the bonding strength between the lithium-based metal layer and the negative electrode current collector by providing a protrusion at the edge of the opening structure and embedding the protrusion in the lithium-based metal layer, thereby improving the structural stability of the negative electrode tab; further, the roughness of the edge of the opening structure caused by these protrusions is maintained within a specific range, so that these protrusions can be embedded in the lithium metal layer while avoiding the risk of puncturing and short-circuiting the separator. This negative electrode tab can enable the battery to have both high energy density and good cycle life.

[0062] It should be noted that the opening structure 12 in the present application is a through hole.

[0063] Understandably, the average roughness Ra of the edge of the opening structure 12 can be 1.1, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6 and any value between them; in some embodiments, the average roughness of the edge of the opening structure 12 is 1.1 - 2.6.

[0064] Understandably, the maximum edge roughness Rz of the perforated structure 12 can be 2.5, 2.8, 3.0, 3.2, 3.4, 3.6, 3.8, 4.0, 4.2, 4.4, 4.6, 4.8, 5.0, 5.2, 5.4, 5.6, 5.8, 6.0, 6.1, and any value therebetween. In some embodiments, the maximum edge roughness of the perforated structure is 2.5 to 6.1.

[0065] The average edge roughness Ra of the perforated structure 12 has the meaning well-known in the art and can be obtained by using conventional instruments and methods in the art. For example, using a surface roughness measuring instrument, a diamond stylus with a tip radius of curvature of about 2 microns is slowly slid along the surface to be measured. The up and down displacement of the diamond stylus is converted into an electrical signal by an electrical length sensor, and after amplification, filtering, and calculation, the surface roughness value is indicated by a display instrument. Automatically calculating the arithmetic mean deviation of the profile (the arithmetic mean of the absolute values of the distances between the points on the profile line in the measurement direction and the reference line within the sampling length) by the instrument is the average edge roughness Ra of the perforated structure 12, and automatically calculating the maximum height of the profile (the distance between the highest peak line and the lowest valley bottom line of the maximum profile within the sampling length) by the instrument is the maximum edge roughness Rz.

[0066] The shape of the perforated structure 12 can be various. The perforated structure 12 can include one or more of round holes, oval holes, trapezoidal holes, square holes, and triangular holes. The square hole can be a rectangular hole or a square hole. Optionally, the perforated structure 12 is a round hole and / or an oval hole, and the structural stability of the negative electrode plate is better.

[0067] In some embodiments, the size of the perforated structure 12 is 0.01 mm, 0.02 mm, 0.04 mm, 0.05 mm, 0.06 mm, 0.08 mm, 0.1 mm, 0.2 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.4 mm, 1.6 mm, 1.8 mm, 2 mm, and any value therebetween. Optionally, the size of the perforated structure 12 is 0.01 mm to 0.08 mm.

[0068] The size of the perforated structure 12 refers to the size of the maximum dimension of the perforated structure 12. For example, when the perforated structure 12 is a round hole, the size of the perforated structure 12 takes its diameter; when the perforated structure 12 is an oval hole, the size of the perforated structure 12 takes the length of its major axis, that is, the major diameter; when the perforated structure 12 is a trapezoidal hole, a square hole, or a triangular hole, the size of the perforated structure 12 takes the size of its longest side. The size of the perforated structure 12 is the average value calculated after microscopically measuring more than 30 perforated structures 12.

[0069] The size of the above-mentioned opening structure 12 has better mechanical strength within this range, further improving the structural stability of the negative electrode plate.

[0070] In some embodiments, the hole spacing between two adjacent opening structures 12 is 0.01 mm, 0.015 mm, 0.020 mm, 0.028 mm, 0.030 mm, 0.05 mm, 0.1 mm, 0.2 mm, 0.3 mm, 0.35 mm, 0.40 mm, 0.45 mm, 0.50 mm, 0.55 mm, 0.60 mm, and any value therebetween. Optionally, the hole spacing of the opening structure 12 is 0.01 mm to 0.05 mm.

[0071] The hole spacing between two adjacent opening structures 12 refers to the distance between the edge of one opening structure 12 and the edge of another opening structure 12 among two adjacent opening structures 12. The hole spacing between two adjacent opening structures 12 is the average value calculated after measuring more than 30 opening structures 12 by an optical microscope.

[0072] The hole spacing of the above-mentioned opening structure 12 has better mechanical strength within this range, further improving the structural stability of the negative electrode plate.

[0073] In some embodiments, the opening ratio of the negative electrode current collector 10 is 20%, 25%, 30%, 35%, 40%, 45%, 50%, and any value therebetween. Optionally, the opening ratio of the negative electrode current collector is 20% to 35%.

[0074] The opening ratio of the negative electrode current collector 10 refers to the ratio of the area of a plurality of opening structures 12 to the area of the negative electrode current collector. The opening ratio of the negative electrode current collector 10 can be measured by the following method:

[0075] Taking the opening structure 12 as a circular hole, observing the opening size on the surface of the negative electrode plate under an optical microscope, measuring the diameter R and the hole spacing L of the opening, the length l and the width w of the negative electrode plate, the formula for calculating the opening ratio is: opening ratio = π(R / 2) 2 *n / (l*w), where n is the number of opening structures 12. Both R and L are the average values calculated after measuring more than 30 opening structures 12 according to the above measurement method.

[0076] In some embodiments, the thickness of the negative electrode current collector 10 is 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, and any value therebetween. Optionally, the thickness of the negative electrode current collector is 5 μm to 8 μm.

[0077] The thickness of the negative electrode current collector 10 can be measured with a micrometer. For example, a micrometer with the model Mitutoyo 293-100 and an accuracy of 0.1 μm can be used for measurement. When the thickness of the negative electrode current collector is within this range, the structural stability of the negative electrode sheet is better.

[0078] Please refer to Figure 4 , in some embodiments, the negative electrode current collector 10 includes a main body region 13 and an edge region 14. The opening structure 12 is provided in the main body region 13, the lithium-based metal layer 20 is provided in the main body region 13, and the edge region 14 is located on at least one side of the main body region 13. Optionally, the edge region 14 is a non-opening structure, such as a continuous copper foil, which does not have a hole structure, for example, does not have the above-mentioned opening structure 12. Providing the edge region 14 in the negative electrode current collector 10 can further improve the structural stability of the negative electrode sheet.

[0079] Optionally, the ratio of the area of the edge region 14 to the area of the negative electrode current collector 10 is 0.1 to 0.3 and any value therebetween. The smaller the area of the edge region 14, the higher the energy density of the battery. The larger the area of the edge region 14, the better the structural stability of the negative electrode sheet. When the ratio of the area of the edge 14 to the area of the negative electrode current collector 10 is within this range, the comprehensive performance of the battery is better. Further optionally, the ratio of the area of the edge region 14 to the area of the negative electrode current collector 10 is 0.1 to 0.2. In some embodiments, the negative electrode current collector 10 is a copper foil.

[0080] In some embodiments, the tensile strength of the negative electrode current collector is greater than or equal to 150 MPa. Optionally, the tensile strength of the negative electrode current collector is 250 MPa to 350 MPa.

[0081] In some embodiments, the elongation rate of the negative electrode current collector is greater than or equal to 2.5%. Optionally, the elongation rate of the negative electrode current collector is 3.5% to 4.5%.

[0082] In some embodiments, the lithium-based metal layer includes one or more of metallic lithium and lithium alloys. The content of lithium element in the lithium alloy can be selected as more than 30 wt%, more than 50 wt%, more than 70 wt%, more than 90 wt%, more than 95 wt%, more than 97 wt%, or more than 99 wt%. The lithium alloy can include, but is not limited to, one or more of lithium indium alloy, lithium zinc alloy, lithium magnesium alloy, lithium tin alloy, and lithium silver alloy.

[0083] In some embodiments, the thickness of the single-sided lithium-based metal layer is 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, and any value therebetween.

[0084] The second aspect of the present application provides a method for preparing a negative electrode sheet, including the following steps:

[0085] S10. Etch the continuous copper foil by chemical etching template method to prepare the negative electrode current collector 10; and

[0086] S20. Compose the negative electrode current collector 10 and the lithium-based metal by rolling method.

[0087] In some embodiments, the chemical etching template method etches the continuous copper foil by coating an anti-etching protective agent on the continuous copper foil, positioning the photosensitive tool with pins to expose the pattern on both sides of the continuous copper foil, and then using a double-sided process to etch the continuous copper foil synchronously from both sides. The anti-etching protective agent and the etching solution are both conventional reagents in the art. The etching time of the chemical etching template method is determined according to actual needs. For example, if it is actually necessary to obtain an opening structure 12 with an average edge roughness of 1.3 and a maximum edge roughness of 4.2, the opening structure 12 can be obtained through a finite number of tests, and then the corresponding etching time can be determined.

[0088] In some embodiments, the etching solution used to etch the continuous copper foil is FeCl 3 solution.

[0089] In some embodiments, the pressure for composing the negative electrode current collector 10 and the lithium-based metal by rolling method is 1.5T - 3T, and can be optionally 2.5T - 3T.

[0090] In some embodiments, the lithium-based metal includes one or more of metallic lithium and lithium alloys. The content of lithium element in the lithium alloy can be optionally above 30wt%, above 50wt%, above 70wt%, above 90wt%, above 95wt%, above 97wt%, or above 99wt%. The lithium alloy can include, but is not limited to, one or more of lithium indium alloy, lithium zinc alloy, lithium magnesium alloy, lithium tin alloy, and lithium silver alloy.

[0091] The third aspect of the present application provides a secondary battery, including the negative electrode sheet of any embodiment of the first aspect of the present application or the negative electrode sheet prepared by the preparation method of any embodiment of the second aspect of the present application. Further, the fourth aspect of the present application provides an electrical device, including at least one of the secondary batteries of the third aspect of the present application.

[0092] In addition, the secondary battery and the electrical device of the present application are described below with appropriate reference to the drawings.

[0093] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charge and discharge process of the battery, active ions are embedded and extracted back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly playing a role in preventing short circuit between the positive and negative electrodes, and at the same time allowing ions to pass through.

[0094] The positive electrode plate includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material.

[0095] As a non-limiting example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode active material layer is provided on any one or both of the two opposite surfaces of the positive electrode current collector.

[0096] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector can include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on the polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material can include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc. In the positive electrode current collector, non-limiting examples of the polymer material substrate can include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0097] In some embodiments, the positive electrode active material can be a positive electrode active material for batteries well-known in the art. As a non-limiting example, the positive electrode active material can include one or more of the following materials: lithium-containing phosphates with olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials can also be used. These positive electrode active materials can be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides can include, but are not limited to, lithium cobalt oxide (such as LiCoO 2 ), 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 their modified compounds, etc. Non-limiting examples of lithium-containing phosphates with olivine structure can include, but are not limited to, lithium iron phosphate, composite materials of lithium iron phosphate and carbon, lithium manganese phosphate, composite materials of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and composite materials of lithium manganese iron phosphate and carbon. Non-limiting examples of lithium cobalt oxide can include LiCoO 2 ; non-limiting examples of lithium nickel oxide can include LiNiO 2 ; non-limiting examples of lithium manganese oxide can include LiMnO 2 , LiMn 2 O 4 etc.; non-limiting examples of lithium nickel cobalt manganese oxide can include LiNi 1 / 3 Co1 / 3 Mn 1 / 3 O 2 (which can also be abbreviated as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O 2 (which can also be abbreviated as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O 2 (which can also be abbreviated as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O 2 (which can also be abbreviated as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O 2 (which can also be abbreviated as NCM 811 ) etc. Non-limiting examples of lithium nickel cobalt aluminum oxide can include LiNi 0.8 Co 0.15 Al 0.05 O 2 .

[0098] In some of these embodiments, the positive electrode active material layer may optionally further include a binder. As non-limiting examples, the binder can include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0099] In some of these embodiments, the positive electrode active material layer may optionally further include a conductive agent. As non-limiting examples, the conductive agent can include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0100] In some of these embodiments, the positive electrode sheet can be prepared in the following manner: dispersing the above-mentioned 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; coating the positive electrode slurry on at least one surface of the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode sheet can be obtained. The type of the solvent can be selected from, but not limited to, any one of the foregoing embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface of the positive electrode current collector or two surfaces of the positive electrode current collector. The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface of the positive electrode current collector or two surfaces of the positive electrode current 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 - 25000 mPa·s. When coating the positive electrode slurry, the coating unit surface density in terms of dry weight (deducting the solvent) can be 15 - 35 mg / cm 2 . The tap density of the positive electrode sheet can be 3.0 - 3.6 g / cm 3 , and can be optionally 3.3 - 3.5 g / cm 3 .

[0101] Negative electrode sheet

[0102] The negative electrode sheet provided in the first aspect of the present application.

[0103] It should be noted that in some embodiments, in the secondary battery, the main region 13 of the negative electrode sheet is opposite to the region covered by the positive electrode active material layer.

[0104] Electrolyte

[0105] The electrolyte has the function of conducting ions between the positive electrode sheet and the negative electrode sheet. The present application does not have any particular limitation on the type of the electrolyte, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or all-solid-state.

[0106] In some of these embodiments, the electrolyte adopts an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0107] In some of these embodiments, the electrolyte salt can 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) one or more of lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluoro(bis(oxalato))phosphate (LiDFOP), and lithium tetrafluoro(oxalato)phosphate (LiTFOP).

[0108] In some 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), ethylene carbonate fluorinated ethylene 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.

[0109] In some embodiments, the electrolyte 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 performance, 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.

[0110] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluorinated ethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethyl carbonate (TFPC), etc.

[0111] Separator

[0112] In some embodiments, the secondary battery further includes a separator. The present application does not particularly limit the type of the separator, and any well-known porous structure separator with good chemical stability and mechanical stability can be selected.

[0113] In some embodiments, the material of the separator may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0114] In some embodiments, the thickness of the separator is 6-40 μm, and may be optionally 12-20 μm.

[0115] 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 stacking process.

[0116] In some embodiments, the secondary battery may include an outer package. The outer package may be used to encapsulate the above-mentioned electrode assembly and electrolyte.

[0117] In some embodiments, the outer package of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The outer package of the secondary battery may also be a soft package, such as a pouch soft package. The material of the soft package may be plastic. Further, non-limiting examples of the plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate, etc.

[0118] The secondary battery includes at least one battery cell. The secondary battery may include one or more battery cells.

[0119] In this application, unless otherwise specified, a "battery cell" refers to a basic unit capable of converting chemical energy and electrical energy into each other. Further, generally, it includes at least a positive electrode plate, a negative electrode plate, and an electrolyte. During the charging and discharging process of the battery, active ions are embedded and removed back and forth between the positive electrode plate and the negative electrode plate. The electrolyte plays a role in conducting active ions between the positive electrode plate and the negative electrode plate.

[0120] This application does not particularly limit the shape of the battery cell, and it may be cylindrical, square, or any other arbitrary shape. For example, Figure 5 is a battery cell 5 with a square structure as an example.

[0121] In some embodiments, referring to Figure 6 , the outer package may include a housing 51 and a cover plate 53. Among them, the housing 51 may include a bottom plate and side plates connected to the bottom plate. The bottom plate and the side plates enclose to form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode plate, the negative electrode plate, and the separator may be formed into an electrode assembly 52 through a winding process or a stacking 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 included in the battery cell 5 may be one or more, and those skilled in the art can select according to actual needs.

[0122] The secondary battery may be a battery module 4 or a battery pack 1.

[0123] The battery module includes at least one battery cell. The number of battery cells included in the battery module may 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.

[0124] Figure 7 is a battery module 4 as an example. Referring to Figure 7, in the battery module 4, multiple battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other way. Further, the multiple battery cells 5 can be fixed by fasteners.

[0125] Optionally, the battery module 4 can further include a housing having an accommodation space, and the multiple battery cells 5 are accommodated in the accommodation space.

[0126] In some embodiments, the above battery module can also be assembled into a battery pack. The number of battery modules included in the battery pack 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 pack.

[0127] Figure 8 and Figure 9 is a battery pack 1 as an example. Refer to Figure 8 and Figure 9 , in the battery pack 1, it can include a battery box and multiple 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 multiple battery modules 4 can be arranged in the battery box in any way.

[0128] In addition, the present application also provides an electrical device. The electrical device includes the secondary battery provided by the present application. The secondary battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can include mobile devices, electric vehicles, electric trains, ships, satellites, energy storage systems, etc., but is not limited thereto. Among them, the mobile device can be, for example, a mobile phone, a laptop computer, etc.; the electric vehicle can 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 is not limited thereto.

[0129] As the electrical device, the secondary battery can be selected according to its usage requirements.

[0130] Figure 10 is an electrical device 6 as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the electrical device for the secondary battery, a battery pack or a battery module can be adopted.

[0131] As another example of the device, it can be a mobile phone, a tablet computer, a laptop computer, etc. This device usually requires being thin and light, and a secondary battery can be used as the power source.

[0132] Embodiment

[0133] The embodiments of the present application will be described below. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as a limitation to the present application. For those technologies or conditions not specified in the embodiments, they shall be carried out according to the technologies or conditions described in the literature in the art or according to the product specifications. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0134] Example 1

[0135] 1) Preparation of the positive electrode sheet

[0136] The positive active material NCM811, conductive carbon black SP, and binder PVDF were dispersed in the solvent NMP in a weight ratio of 98:1:1 and mixed evenly to obtain a positive electrode slurry; the positive electrode slurry was evenly coated on both sides of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet was obtained, where the coating amount per unit area on both sides was 0.27 g / 1540.25 mm 2 .

[0137] 2) Preparation of the negative electrode sheet

[0138] The negative electrode current collector was prepared by chemically etching a 15-μm-thick commercially available continuous copper foil using a chemical etching template method; specifically, an anti-corrosion protective agent was coated on the continuous copper foil, the pattern was exposed on both sides of the continuous copper foil using a pin-positioned photosensitive tool, and then the continuous copper foil was etched synchronously from both sides using a double-sided process. Multiple through-round holes with a diameter of 2 mm and a hole pitch of 2.5 mm were formed on the negative electrode current collector, and the opening ratio was 50%.

[0139] The above negative electrode current collector and lithium foil were roll-pressed at a pressure of 2.5 T by a rolling method, and lithium metal was loaded on both sides of the negative electrode current collector, with a single-sided lithium metal thickness of 20 μm. The formed negative electrode sheet was divided into a main body area and an edge area, the opening structure was arranged in the main body area, the edge area was a non-opening structure, and the ratio of the area of the edge area to the area of the negative electrode current collector was 0.1.

[0140] 3) Separator

[0141] A 12-μm-thick polypropylene separator was selected.

[0142] 4) Preparation of the electrolyte

[0143] The organic solvent was a mixed solution containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), where the volume ratio of EC, EMC, and DEC was 20:20:60. In a glove box filled with argon with a water content < 10 ppm, the fully dried lithium salt LiPF6 was dissolved in the organic solvent and mixed evenly to obtain the electrolyte. Among them, the concentration of the lithium salt was 1 mol / L.

[0144] 5) Preparation of the battery

[0145] Stack the positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator placed between the positive and negative electrode sheets to play an insulating role. After winding into a square bare battery cell, it is placed into an aluminum-plastic film, then baked at 80°C to remove moisture, injected with 10 g of the corresponding non-aqueous electrolyte, sealed, and after processes such as standing, hot and cold pressing, formation, jigging, and grading, a finished battery with a capacity of 4000 mAh is obtained.

[0146] Examples 2 to 12 and Comparative Examples 1 to 2

[0147] The secondary batteries of Examples 2 - 12 and the secondary batteries of Comparative Examples 1 to 2 are prepared in a similar manner to the secondary battery of Example 1, except that the relevant parameters of the negative electrode sheet are different, and the specific relevant parameters are listed in Table 1.

[0148] Comparative Example 3

[0149] The secondary battery of Comparative Example 3 is prepared in a similar manner to the secondary battery of Example 1, except that the preparation method of the negative electrode current collector in the negative electrode sheet of Comparative Example 5 is as follows: commercially available continuous copper foil with a thickness of 15 μm and lithium foil are roll-pressed at a pressure of 2.5 T by a rolling method, and lithium metal is loaded on both sides of the negative electrode current collector, with a thickness of 20 μm of lithium metal on one side.

[0150] Testing methods

[0151] 1. Average roughness Ra and maximum roughness Rz

[0152] Using a surface roughness measuring instrument, a diamond stylus with a tip radius of curvature of about 2 μm slides slowly along the measured surface. The up and down displacement of the diamond stylus is converted into an electrical signal by an electrical length sensor, and after amplification, filtering, and calculation, the surface roughness value is indicated by a display instrument. The arithmetic mean deviation of the profile (the arithmetic mean of the absolute values of the distances between the points on the profile line in the sampling length along the measurement direction and the reference line) is calculated automatically by the instrument as Ra, and the maximum height of the profile (the distance between the highest peak line and the lowest valley bottom line of the maximum profile in the sampling length) is calculated automatically by the instrument as Rz.

[0153] 2. Battery energy density and cycle life test

[0154] The cycle test temperature is 25°C. The battery is charged at a constant current of 3C to the upper limit voltage, then charged at a constant voltage to 0.05C, left standing for 5 minutes, and then discharged at 0.33C to the lower limit voltage. The capacity obtained from this step is taken as the initial capacity. The initial capacity is multiplied by the average discharge voltage and then divided by the weight of the battery cell to obtain the weight energy density; a 3C charge / 0.33C discharge cycle test is carried out until the capacity decays to 80% SOH, and the corresponding number of cycle turns is recorded to obtain the corresponding life data.

[0155] Table 1

[0156]

[0157]

[0158] It should be noted that the energy density gradually increases with the weight reduction. However, when the weight reduction is greater than 35%, the cycle performance decreases significantly. Therefore, it is preferred that the 8um copper foil has a weight reduction of about 35%, which can maintain the structural stability of the battery cell and achieve a cycle performance close to that of the unperforated copper foil.

[0159] The descriptions of the above embodiments tend to emphasize the differences between the embodiments. Their similarities or commonalities can be referred to each other. For the sake of brevity, they will not be elaborated herein.

[0160] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples. Embodiments having the same composition and the same effect as the technical idea within the technical scope of this application are included in the technical scope of this application. In addition, within the scope not departing from the gist of this application, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways constructed by combining some constituent elements of the embodiments are also included in the scope of this application.

Claims

1. A negative electrode plate, characterized in that: include: A negative electrode current collector, wherein the negative electrode current collector has a plurality of open pore structures, the edges of the open pore structures have protrusions, the average roughness of the edges of the open pore structures is 0.2 to 3, and the maximum roughness of the edges of the open pore structures is 2.5 to 6.1; A lithium-based metal layer is disposed on at least one surface of the negative electrode current collector and covers the open hole structure, and the protrusion is embedded in the lithium-based metal layer and covered by the lithium-based metal layer.

2. The negative electrode sheet according to claim 1, characterized in that: The average roughness of the edge of the open-pore structure is 1.1 to 2.6, and / or the maximum roughness of the edge of the open-pore structure is 2.5 to 6.

1.

3. The negative electrode sheet according to claim 1, characterized in that: The size of the open hole structure is 0.01 mm to 2 mm, and can be 0.01 mm to 0.08 mm; and / or, The hole spacing between two adjacent open hole structures is 0.01 mm to 0.6 mm, and can be optionally 0.01 mm to 0.05 mm.

4. The negative electrode sheet according to any one of claims 1 to 3, characterized in that: The porosity of the negative electrode current collector is 20% to 50%, and can be optionally 20% to 35%.

5. The negative electrode sheet according to claim 1, characterized in that: The thickness of the negative electrode current collector is 5 μm to 15 μm, and can be 5 μm to 8 μm; and / or, The thickness of the lithium-based metal layer on one side is 10 μm to 50 μm, and can be optionally 10 μm to 25 μm.

6. The negative electrode sheet according to any one of claims 1 to 5, characterized in that: The open hole structure includes one or more of a circular hole, an elliptical hole, a trapezoidal hole, a quadrilateral hole and a triangular hole.

7. The negative electrode sheet according to any one of claims 1 to 5, characterized in that: The negative electrode current collector includes a main region and an edge region, the open hole structure is arranged in the main region, the lithium-based metal layer is arranged on the main region, and the edge region is located on at least one side of the main region; Optionally, the edge area is a non-opening structure; Optionally, the ratio of the area of ​​the edge region to the area of ​​the negative electrode current collector is 0.1 to 0.3, and further optionally 0.1 to 0.

2.

8. The negative electrode sheet according to any one of claims 1 to 5, characterized in that: The negative electrode current collector is copper foil.

9. The negative electrode sheet according to any one of claims 1 to 5, characterized in that: The tensile strength of the negative electrode current collector is greater than or equal to 150 MPa, and may be 250 MPa to 350 MPa; and / or, The elongation rate of the negative electrode current collector is greater than or equal to 2.5%, and can be optionally 3.5% to 4.5%.

10. A method for preparing a negative electrode sheet according to any one of claims 1 to 9, characterized in that: The following steps are involved: S10, etching the continuous copper foil using a chemical etching template method to prepare the negative electrode current collector; and S20, disposing a lithium-based metal on at least one surface of the negative electrode current collector; optionally, the lithium-based metal is compounded on at least one surface of the negative electrode current collector by a rolling method.

11. The method for preparing a negative electrode sheet according to claim 10, characterized in that: Step S10 includes: A resist is applied to the continuous copper foil, a photosensitive tool is positioned with pins to expose the pattern on both sides of the continuous copper foil, and then a double-sided process is used to simultaneously etch the continuous copper foil from both sides.

12. A secondary battery, characterized in that: The invention comprises the negative electrode sheet according to any one of claims 1 to 9 or the negative electrode sheet prepared by the preparation method according to claim 10 or 11.

13. An electrical device, characterized in that: Includes the secondary battery as claimed in claim 12.

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