Secondary battery and electric device

Abstract

The invention provides a secondary battery and an electric device. The secondary battery comprises a negative electrode piece, the negative electrode piece comprises a negative electrode current collector and a negative electrode active layer located on at least one surface of the negative electrode current collector, the negative electrode current collector comprises an empty foil area and an active area, the negative electrode active layer is located in the active area, and the negative electrode active layer is located in the direction from the empty foil area to the active area. The negative electrode active layer comprises a first active part, a second active part and a third active part which are distributed in sequence; the thicknesses of the first active part, the second active part and the third active part are T1, T2 and T3 respectively, T1 is greater than T2, and T3 is greater than T2.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a secondary battery and an electrical device. Background Art

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

[0003] During the charging process of a secondary battery, the negative electrode plate usually expands to a certain extent. Since there is limited space for the negative electrode plate to expand inside the battery shell, when the negative electrode plate expands, the electrolyte infiltrated inside the negative electrode plate may be squeezed out. During the discharge process, the squeezed electrolyte needs to re-enter the negative electrode plate. Since the electrolyte has a large movement distance when it re-enters the negative electrode plate, it is difficult for the electrolyte to quickly flow back to the negative electrode plate during the discharge process, which will make the electrolyte's wettability to the negative electrode plate worse, thereby reducing the battery's cycle performance. Summary of the invention

[0004] In order to achieve the above-mentioned object, the first aspect of the present application provides a secondary battery, comprising a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a negative electrode active layer located on at least one surface of the negative electrode current collector, the negative electrode current collector comprising an empty foil area and an active area, the negative electrode active layer being located in the active area, and in the direction from the empty foil area to the active area, the negative electrode active layer comprising a first active portion, a second active portion and a third active portion distributed in sequence. When the secondary battery is in a fully charged state, the thicknesses of the first active portion, the second active portion and the third active portion are T1, T2 and T3 respectively, wherein T1>T2, T3>T2.

[0005] In the above-mentioned secondary battery, there are certain differences in thickness between the first active portion, the second active portion, and the third active portion, so that a certain accommodation space can be formed in the middle of the negative electrode plate. In this way, during the charging process, the squeezed electrolyte can be temporarily stored in the accommodation space, which can increase the overall liquid retention of the negative electrode plate during the charging process. During the discharge process, the electrolyte temporarily stored in the accommodation space can quickly flow back to the negative electrode plate, which is beneficial to improve the cycle performance of the battery.

[0006] In some embodiments, 1.01≤T1 / T2≤1.2; and / or, 1.01≤T3 / T2≤1.2. T1 / T2 and T3 / T2 within the corresponding range can make the accommodation space formed in the middle of the negative electrode plate have a more appropriate size, and maintain a high space utilization rate of the battery housing on the basis of making the negative electrode plate as a whole have an appropriate liquid retention amount.

[0007] In some embodiments, T1≤T3. In this case, more electrolyte can be retained in the first active portion and the second active portion, reducing the risk of lithium deposition in the first active portion and the second active portion due to lack of electrolyte. Optionally, 0.8≤T1 / T3≤1.

[0008] In some embodiments, 150 μm ≤ T1 ≤ 200 μm; and / or, 160 μm ≤ T2 ≤ 220 μm; and / or, 170 μm ≤ T3 ≤ 250 μm. T1, T2, and T3 being within the corresponding ranges can make the amount of active material used within a suitable range, thereby making the battery have both good cycle performance and high energy density.

[0009] In some embodiments, the expansion rate η1 of the active material of the first active part is greater than the expansion rate η2 of the active material of the second active part, and the expansion rate η3 of the active material of the third active part is greater than the expansion rate η2 of the active material of the second active part. When the expansion rate of the active material of the first active part, the expansion rate of the active material of the second active part, and the expansion rate of the active material of the third active part satisfy this relationship, it is beneficial to promote the formation of the accommodation space in the middle of the negative electrode sheet, thereby improving the cycle performance of the battery.

[0010] In some embodiments, 1.01≤η1 / η2≤2; and / or, 1.01≤η3 / η2≤3. The expansion of the active materials of the first active portion, the second active portion, and the third active portion during the charging process can be better matched, so that when a suitable size of accommodation space is formed, the negative electrode plate maintains a relatively stable structure, and the adverse effect of the expansion of the active materials on the structural stability of the negative electrode plate is reduced.

[0011] In some embodiments, η1≤η3. In this case, during the battery charging process, the extrusion of the electrolyte in the third active part can be promoted, so that the first active part and the second active part can retain more electrolyte, further reducing the risk of lithium precipitation in the first active part and the second active part due to lack of electrolyte. Optionally, 0.6≤η1 / η3≤1.

[0012] In some embodiments, 15%≤η1≤25%; and / or, 10%≤η2≤18%; and / or, 20%≤η3≤30%.

[0013] In some embodiments, the graphitization degree G1 of the active material of the first active part is greater than the graphitization degree G2 of the active material of the second active part, and the graphitization degree G3 of the active material of the third active part is greater than the graphitization degree G2 of the active material of the second active part. When the graphitization degrees of the active materials of the first active part, the second active part, and the third active part satisfy this relationship, on the one hand, the formation of the accommodation space in the middle of the negative electrode sheet can be promoted by the difference in volume change of the active materials during the charging process, and on the other hand, the graphitization degree of the active material of the second active part is relatively low, the interlayer spacing is relatively large, and it has good compressive resistance, which can improve the overall mechanical strength of the negative electrode sheet.

[0014] In some embodiments, 0.95≤G2 / G1<1; and / or, 1.01≤G3 / G2≤1.1. G2 / G1 and G3 / G2 are within the corresponding ranges, which can make the interlayer spacing of the materials between the first active part, the second active part and the third active part better matched, which is beneficial to improve the efficiency of ion insertion and extraction, and promote the improvement of battery cycle performance.

[0015] In some embodiments, G1≤G3; optionally, 0.95≤G1 / G3≤1. Active materials with high graphitization may exhibit higher expansion, and active materials with low graphitization may exhibit lower expansion. During the battery charging process, the expansion of the third active part can promote the extrusion of the electrolyte in the third active part, thereby allowing the first active part and the second active part to retain more electrolyte, further reducing the risk of lithium precipitation in the first active part and the second active part due to lack of electrolyte.

[0016] In some embodiments, 93%≤G1≤94.5%; and / or, 89%≤G2≤93.5%; and / or, 94%≤G3≤95%. G1, G2, and G3 within the corresponding range can make the active material have a smaller powder resistivity and reduce the resistance of the negative electrode sheet.

[0017] In some embodiments, the OI value OI1 of the first active portion is greater than the OI value OI2 of the second active portion, and the OI value OI3 of the third active portion is greater than the OI value OI2 of the second active portion. In this case, lithium ions have a higher transmission rate in the negative electrode sheet, which is beneficial to improving the cycle performance of the battery.

[0018] In some embodiments, 1.05≤OI1 / OI2≤2.5; and / or, 1.5≤OI3 / OI2≤4.

[0019] In some embodiments, OI1≤OI3; optionally, 0.8≤OI1 / OI3≤1.

[0020] In some embodiments, 12≤OI1≤25; and / or, 8≤OI2≤15; and / or, 15≤OI3≤35.

[0021] In some embodiments, in the direction from the empty foil area to the active area, the widths of the first active portion, the second active portion, and the third active portion are D1, D2, and D3, respectively; 0.2≤D2 / (D1+D2+D3)≤0.8. When D1, D2, and D3 satisfy this relationship, the accommodation space in the negative electrode sheet can have a suitable size, so that the negative electrode sheet as a whole has a suitable liquid retention amount. Optionally, D1=D3.

[0022] In some embodiments, 20 mm ≤ D1 ≤ 100 mm; and / or, 20 mm ≤ D2 ≤ 60 mm; and / or, 20 mm ≤ D3 ≤ 200 mm.

[0023] In some embodiments, the active material of the first active portion, the active material of the second active portion, and the active material of the third active portion all include graphite.

[0024] In some embodiments, the active material of the first active portion, the active material of the second active portion, and the active material of the third active portion all include silicon-based materials.

[0025] In some embodiments, the mass percentage w1 of silicon in the active material of the first active portion is greater than the mass percentage w2 of silicon in the active material of the second active portion, and the mass percentage w3 of silicon in the active material of the third active portion is greater than the mass percentage w2 of silicon in the active material of the second active portion.

[0026] In some embodiments, 1.01≤w1 / w2≤5; and / or, 1.01≤w3 / w2≤10.

[0027] In some embodiments, w1≤w3; optionally, 0.7≤w1 / w3≤1.

[0028] In some embodiments, 1%≤w1≤15%; and / or, 0<w2≤10%; and / or, 2%≤w3≤25%.

[0029] A second aspect of the present application provides an electric device, wherein the electric device comprises the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] 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:

[0031] Figure 1 It is a schematic diagram of a secondary battery according to one embodiment of the present application.

[0032] Figure 2 for Figure 1 An exploded view of a secondary battery according to an embodiment of the present application is shown.

[0033] Figure 3 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.

[0034] Figure 4 A top view of a negative electrode sheet in a secondary battery according to an embodiment of the present application.

[0035] Figure 5 for Figure 4 The corresponding negative electrode is viewed from the left at another angle.

[0036] Description of reference numerals:

[0037] 1. Secondary battery; 11. Shell; 12. Electrode assembly; 13. Cover plate; 2. Power-consuming device; 3. Negative electrode plate; 31. Empty foil area; 32. Active area; 33. Negative electrode active layer; 331. First active part; 332. Second active part; 333. Third active part. DETAILED DESCRIPTION

[0038] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present application are given in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present application belongs. The terms used herein in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0040] The "range" disclosed in the present application can be defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The range defined in this way can be inclusive or exclusive of the end values, and any end value can be included or excluded independently, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a specific parameter, it is understood that the range of 60 to 110 and 80 to 120 is also expected. 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 can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation 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 listed in this document, and "0-5" is just an abbreviation of 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.

[0041] 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.

[0042] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0043] 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.

[0044] 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.

[0045] In this application, in the open technical features or technical solutions described by the words "contain", "include", "include", etc., if there is no other explanation, 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. If there is no other explanation, 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 includes not only a1, a2 and a3, but also other members".

[0046] In this 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.

[0047] 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.

[0048] An embodiment of the present application provides a secondary battery, including a negative electrode plate, the negative electrode plate including a negative electrode current collector and a negative electrode active layer located on at least one surface of the negative electrode current collector, the negative electrode current collector including a hollow foil area and an active area, the negative electrode active layer is located in the active area, and in the direction from the hollow foil area to the active area, the negative electrode active layer includes a first active portion, a second active portion, and a third active portion distributed in sequence. When the secondary battery is fully charged, the thicknesses of the first active portion, the second active portion, and the third active portion are T1, T2, and T3, respectively, wherein T1>T2, and T3>T2.

[0049] In the secondary battery of this embodiment, there is a certain difference in thickness between the first active portion, the second active portion, and the third active portion, so that a certain accommodation space can be formed in the middle of the negative electrode plate. In this way, during the charging process, the squeezed electrolyte can be temporarily stored in the accommodation space, which can increase the overall liquid retention of the negative electrode plate during the charging process. During the discharge process, the electrolyte temporarily stored in the accommodation space can quickly flow back to the negative electrode plate, which is beneficial to improve the cycle performance of the battery.

[0050] It is understood that the empty foil area of ​​the negative electrode current collector can be used as a tab, or a tab can be connected to the empty foil area. The active area of ​​the negative electrode current collector is used to form a negative electrode active layer. Optionally, the negative electrode active layer can be formed in the active area of ​​the negative electrode current collector by coating.

[0051] See also Figure 4 and Figure 5 , in which the structure of the negative electrode plate in the secondary battery is schematically shown. The negative electrode plate 3 includes a negative electrode current collector and a negative electrode active layer 33 located on at least one surface of the negative electrode current collector. The negative electrode current collector includes a hollow foil area 31 and an active area 32. The negative electrode active layer 33 is located in the active area 32. In the direction from the hollow foil area 31 to the active area 32, the negative electrode active layer 33 is divided into a first active part 331, a second active part 332 and a third active part 333 which are distributed in sequence.

[0052] exist Figure 4 and Figure 5 In the example shown, the direction from the empty foil area 31 to the active area 32 is represented as the Y direction, and the thickness direction is represented as the Z direction. Optionally, the Y direction represents the width direction of the negative electrode sheet, the Z direction represents the thickness direction of the negative electrode sheet, and the X direction represents the length direction of the negative electrode sheet.

[0053] exist Figure 4 and Figure 5 In the illustrated example, the thickness T1 of the first active portion, the width D1 of the first active portion, the thickness T2 of the second active portion, the width D2 of the second active portion, the thickness T3 of the third active portion, and the width D3 of the third active portion are shown.

[0054] In some embodiments, 1.01≤T1 / T2≤1.2. Optionally, T1 / T2 may be 1.01, 1.05, 1.08, 1.1, 1.12, 1.15, 1.18, 1.2, etc. 1.01≤T3 / T2≤1.2. Optionally, T3 / T2 may be 1.01, 1.05, 1.08, 1.1, 1.12, 1.15, 1.18, 1.2, etc. T1 / T2 and T3 / T2 within the corresponding range can make the accommodation space formed in the middle of the negative electrode plate have a more suitable size, and the battery housing can maintain a high space utilization rate on the basis of making the negative electrode plate as a whole have a suitable liquid retention amount.

[0055] In some embodiments, T1≤T3. In this case, more electrolyte can be maintained in the first active portion and the second active portion, reducing the risk of lithium precipitation in the first active portion and the second active portion due to lack of electrolyte. Optionally, 0.8≤T1 / T3≤1. Further optionally, T1 / T3 can be 0.8, 0.85, 0.9, 0.95, 1, etc.

[0056] In some embodiments, 150 μm ≤ T1 ≤ 200 μm; and / or, 160 μm ≤ T2 ≤ 220 μm; and / or, 170 μm ≤ T3 ≤ 250 μm. T1, T2, and T3 being within the corresponding ranges can make the amount of active material used within a suitable range, thereby making the battery have both good cycle performance and high energy density.

[0057] Alternatively, T1 may be 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm, etc. T2 may be 160 μm, 170 μm, 180 μm, 190 μm, 200 μm, 210 μm, 220 μm, etc. T3 may be 170 μm, 180 μm, 190 μm, 200 μm, 210 μm, 220 μm, 230 μm, 240 μm, 250 μm, etc.

[0058] In some embodiments, the expansion rate η1 of the active material of the first active part is greater than the expansion rate η2 of the active material of the second active part, and the expansion rate η3 of the active material of the third active part is greater than the expansion rate η2 of the active material of the second active part. When the expansion rate of the active material of the first active part, the expansion rate of the active material of the second active part, and the expansion rate of the active material of the third active part satisfy this relationship, it is beneficial to promote the formation of the accommodation space in the middle of the negative electrode sheet, thereby improving the cycle performance of the battery.

[0059] It is understandable that the expansion rate of the active material can be tested by the following method: prepare the active material into a negative electrode sheet, test the thickness of 20 points on the negative electrode sheet, and take the average value as the initial thickness of the negative electrode sheet, recorded as H0. Then assemble the negative electrode sheet into a battery and disassemble it after full charge, measure the thickness of the corresponding 20 points on the fully charged negative electrode sheet, and take the average value as the thickness of the fully charged negative electrode sheet, recorded as H1. The expansion rate of the active material η = (H1-H0) / H0.

[0060] Optionally, 1.01≤η1 / η2≤2; and / or, 1.01≤η3 / η2≤3. When η1 / η2 and η3 / η2 are within the corresponding range, the expansion of the active materials of the first active portion, the second active portion, and the third active portion during the charging process can be better matched, and when a suitable size of accommodation space is formed, the negative electrode sheet maintains a relatively stable structure, reducing the adverse effects of the expansion of the active materials on the structural stability of the negative electrode sheet. Further optionally, η1 / η2 can be 1.01, 1.05, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, etc. η3 / η2 can be 1.01, 1.05, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, etc.

[0061] In some embodiments, η1≤η3. At this time, during the battery charging process, the extrusion of the electrolyte in the third active part can be promoted, so that the first active part and the second active part can retain more electrolyte, further reducing the risk of lithium precipitation in the first active part and the second active part due to lack of electrolyte. Optionally, 0.6≤η1 / η3≤1. Further optionally, η1 / η3 can be 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, etc. Optionally, 15%≤η1≤25%; and / or, 10%≤η2≤18%; and / or, 20%≤η3≤30%. Further optionally, η1 can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, etc. η2 can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, etc. η3 can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, etc.

[0062] In some embodiments, the graphitization degree G1 of the active material of the first active part is greater than the graphitization degree G2 of the active material of the second active part, and the graphitization degree G3 of the active material of the third active part is greater than the graphitization degree G2 of the active material of the second active part. When the graphitization degrees of the active materials of the first active part, the second active part, and the third active part satisfy this relationship, on the one hand, the formation of the accommodation space in the middle of the negative electrode sheet can be promoted by the difference in volume change of the active materials during the charging process, and on the other hand, the graphitization degree of the active material of the second active part is relatively low, the interlayer spacing is relatively large, and it has good compressive resistance, which can improve the overall mechanical strength of the negative electrode sheet.

[0063] It is understood that the graphitization degree of the active material is well known in the art and can be tested by methods known in the art. For example, an X-ray diffractometer (such as Bruker D8 Discover) can be used for testing. The test can refer to JISK0131-1996 and JB / T 4220-2011, and the d 002 The size of the G is then calculated according to the formula G = (0.344-d 002 ) / (0.344-0.3354)×100% to calculate the graphitization degree. 002 The interlayer spacing in the graphite crystal structure is measured in nm. In X-ray diffraction analysis, CuK α The radiation source is a ray, the ray wavelength scans a 2θ angle range of 20° to 80°, and the scanning rate is 4° / min.

[0064] In some embodiments, 0.95≤G2 / G1<1; and / or, 1.01≤G3 / G2≤1.1. G2 / G1 and G3 / G2 are within the corresponding ranges, which can better match the interlayer spacing of the materials between the first active portion, the second active portion, and the third active portion, which is beneficial to improve the efficiency of ion insertion and extraction and promote the improvement of battery cycle performance. Optionally, G2 / G1 can be 0.95, 0.96, 0.97, 0.98, 0.99, 1, etc. G3 / G2 can be 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, etc.

[0065] In some embodiments, G1≤G3. Active materials with high graphitization may show higher expansion, and active materials with low graphitization may show lower expansion. When G1≤G3, during the battery charging process, the expansion of the third active part can promote the extrusion of the electrolyte in the third active part, so that the first active part and the second active part can retain more electrolyte, further reducing the risk of lithium precipitation in the first active part and the second active part due to lack of electrolyte. Optionally, 0.95≤G1 / G3≤1. Further optionally, G1 / G3 can be 0.95, 0.96, 0.97, 0.98, 0.99, 1, etc.

[0066] In some embodiments, 93% ≤ G1 ≤ 94.5%; and / or, 89% ≤ G2 ≤ ​​93.5%; and / or, 94% ≤ G3 ≤ 95%. G1, G2, and G3 can make the active material have a smaller powder resistivity within the corresponding range, thereby reducing the resistance of the negative electrode sheet. In addition, G1, G2, and G3 can make the negative electrode active layer have better adhesion within the corresponding range, which is conducive to maintaining a stable structure of the negative electrode sheet. Optionally, G1 can be 93%, 93.2%, 93.5%, 93.8%, 94%, 94.2%, 94.5%, etc. G2 can be 89%, 90%, 91%, 92%, 93%, 93.5%, etc. G3 can be 94%, 94.1%, 94.2%, 94.5%, 94.8%, 95%, etc.

[0067] In some embodiments, the OI value OI1 of the first active portion is greater than the OI value OI2 of the second active portion, and the OI value OI3 of the third active portion is greater than the OI value OI2 of the second active portion. In this case, lithium ions have a higher transmission rate in the negative electrode sheet, which is beneficial to improving the cycle performance of the battery.

[0068] It is understood that the OI value of the active part has a well-known meaning in the art and can be measured by methods known in the art. For example, according to the general principles of X-ray diffraction analysis and the method for determining the lattice parameters of graphite JIS K0131-1996 and JB / T4220-2011, an X-ray diffraction spectrum can be obtained by using an X-ray powder diffractometer (X'pert PRO), and then according to OI value = C 004 / C 110 The OI value of the negative electrode film can be calculated, where C 004 is the peak area of ​​the 004 characteristic diffraction peak, C 110 is the peak area of ​​the 110 characteristic diffraction peak.

[0069] In some embodiments, 1.05≤OI1 / OI2≤2.5; and / or, 1.5≤OI3 / OI2≤4. Optionally, OI1 / OI2 can be 1.05, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, etc. OI3 / OI2 can be 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, etc.

[0070] In some embodiments, OI1≤OI3. Optionally, 0.8≤OI1 / OI3≤1. Optionally, OI1 / OI3 may be 0.8, 0.82, 0.85, 0.88, 0.9, 0.92, 0.95, 0.98, 1, etc.

[0071] In some embodiments, 12≤OI1≤25; and / or, 8≤OI2≤15; and / or, 15≤OI3≤35. Optionally, OI1 may be 12, 15, 18, 20, 22, 25, etc., and OI2 may be 8, 9, 10, 11, 12, 13, 14, 15, etc.

[0072] In some embodiments, in the direction from the empty foil area to the active area, the widths of the first active portion, the second active portion, and the third active portion are D1, D2, and D3, respectively; 0.2≤D2 / (D1+D2+D3)≤0.8. When D1, D2, and D3 satisfy this relationship, the accommodation space in the negative electrode sheet can have a suitable size, so that the negative electrode sheet as a whole has a suitable liquid retention amount. Optionally, D2 / (D1+D2+D3) can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, etc. Further optionally, D1=D3.

[0073] In some embodiments, 20 mm ≤ D1 ≤ 100 mm; and / or, 20 mm ≤ D2 ≤ 60 mm; and / or, 20 mm ≤ D3 ≤ 200 mm. Optionally, D1 may be 20 mm, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm, 100 mm, etc. D2 may be 20 mm, 30 mm, 40 mm, 50 mm, 60 mm, etc. D3 may be 20 mm, 40 mm, 50 mm, 70 mm, 80 mm, 100 mm, 120 mm, 140 mm, 150 mm, 170 mm, 180 mm, 200 mm, etc.

[0074] In some embodiments, the active material of the first active part, the active material of the second active part, and the active material of the third active part all include graphite. It is understood that the graphite may include one or more of artificial graphite, natural graphite, and modified natural graphite. It is also understood that the graphite in the active material of the first active part, the active material of the second active part, and the active material of the third active part may be the same or different.

[0075] Further, the active material of the first active part, the active material of the second active part, and the active material of the third active part all include silicon-based materials. It is understood that the silicon-based material may include one or more of elemental silicon, silicon-oxygen compounds, silicon-carbon compounds, silicon-nitrogen compounds, and silicon alloys. It is also understood that the silicon-based materials in the active material of the first active part, the active material of the second active part, and the active material of the third active part may be the same or different.

[0076] In some embodiments, the mass percentage w1 of silicon in the active material of the first active portion is greater than the mass percentage w2 of silicon in the active material of the second active portion, and the mass percentage w3 of silicon in the active material of the third active portion is greater than the mass percentage w2 of silicon in the active material of the second active portion.

[0077] Optionally, 1.01≤w1 / w2≤5; and / or, 1.01≤w3 / w2≤10. Further optionally, w1 / w2 can be 1.01, 1.1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, etc. w3 / w2 can be 1.01, 1.1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, etc.

[0078] In some embodiments, w1≤w3. Optionally, 0.7≤w1 / w3≤1. For example, w1 / w3 can be 0.7, 0.8, 0.9, 1, etc.

[0079] In some embodiments, 1%≤w1≤15%; and / or, 0<w2≤10%; and / or, 2%≤w3≤25%. Alternatively, w1 can be 1%, 3%, 5%, 8%, 10%, 12%, 15%, etc. w2 can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, etc. w3 can be 3%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, etc.

[0080] In some embodiments, the active material of the first active portion includes a silicon-based material and graphite, the active material of the third active portion includes a silicon-based material and graphite, and the active material of the second active portion does not include a silicon-based material.

[0081] Another embodiment of the present application provides an electric device, which includes the secondary battery mentioned above.

[0082] The secondary battery and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0083] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. 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 ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0084] Positive electrode

[0085] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0086] 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 material layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0087] In some 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.

[0088] In some of the embodiments, the positive electrode active material may be a positive electrode active material for a battery known in the art. As a non-limiting example, 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 、LiMn 2 O 4 etc.; Non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3 Co1 / 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 .

[0089] In some of these embodiments, the positive electrode active material 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.

[0090] In some embodiments, the positive electrode active material 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.

[0091] In some of the embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent to form a positive electrode slurry; the positive electrode slurry is coated on at least one side of the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained. 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 applying the positive electrode slurry, the coating unit area density based on dry weight (excluding solvent) can be 15-35 mg / 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 .

[0092] Negative electrode

[0093] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0094] 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 material layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0095] 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.

[0096] 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.

[0097] In some embodiments, the negative electrode active material layer may further 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).

[0098] In some embodiments, the negative electrode active material layer may further include a conductive agent, which may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0099] In some of the embodiments, the negative electrode active material layer may further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0100] In some of the embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one side of the surface of the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained. The surface of the negative electrode collector coated with the negative electrode slurry can be on a single surface of the negative electrode collector or on both surfaces of the negative electrode collector. The solid content of the negative electrode slurry can be 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000-10000mPa·s. When coating the negative electrode slurry, the coating unit surface density on a dry weight basis (excluding the solvent) can be 75-220g / m 2 The compaction density of the negative electrode sheet can be 1.0g / cm 3 ~1.8g / cm 3 .

[0101] Electrolytes

[0102] The electrolyte has the function of conducting ions between the positive electrode and the negative electrode. The present application has no particular restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0103] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0104] In some 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 ), one or more of lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0105] 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), butylene carbonate One or more of fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0106] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0107] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), and the like.

[0108] Isolation film

[0109] 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.

[0110] 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.

[0111] In some embodiments, the isolation film has a thickness of 6 to 40 μm, and may be 12 to 20 μm.

[0112] In some of the embodiments, the positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode assembly by a winding process or a lamination process.

[0113] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0114] 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.

[0115] The secondary battery includes at least one battery cell. The secondary battery may include one or more battery cells.

[0116] 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.

[0117] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 1 The battery cell 1 is a square structure as an example.

[0118] In some of these embodiments, reference Figure 2, the outer packaging may include a shell 11 and a cover plate 13. Among them, the shell 11 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 11 has an opening connected to the receiving cavity, and the cover plate 13 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 12 through a winding process or a lamination process. The electrode assembly 12 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 12. The number of electrode assemblies 12 contained in the battery cell 1 can be one or more, and those skilled in the art can select according to actual needs.

[0119] The secondary battery may be a battery module or a battery pack.

[0120] 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.

[0121] In the battery module, the plurality of battery cells may be arranged in sequence along the length direction of the battery module. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells may be fixed by fasteners.

[0122] Optionally, the battery module may further include a housing having an accommodation space, and the plurality of battery cells are accommodated in the accommodation space.

[0123] 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.

[0124] The battery pack may include a battery box and a plurality of battery modules disposed in the battery box. The battery box includes an upper box body and a lower box body, and the upper box body can be covered on the lower box body to form a closed space for accommodating the battery modules. The plurality of battery modules can be arranged in the battery box in any manner.

[0125] 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.

[0126] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0127] Figure 3 The power consumption device 2 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.

[0128] Another example of a device may be a mobile phone, a tablet computer, a laptop computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0129] In order to make the technical problems, technical solutions and beneficial effects solved by the present application clearer, the present application will be further described in detail below in conjunction with the embodiments and drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present application and its applications. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0130] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the field or the product instructions are used. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0131] Example 1

[0132] (1) Preparation of positive electrode sheet

[0133] The positive electrode active material LiNi 0.9 Co 0.05 Mn 0.05 O 2 , conductive carbon black, binder PVDF and solvent N-methylpyrrolidone (NMP) were uniformly stirred at a weight ratio of 96:2:2:100 to obtain a uniformly mixed positive electrode slurry. The positive electrode slurry was coated on an aluminum foil current collector with a thickness of 13 μm, and then dried and cold pressed to obtain a positive electrode sheet.

[0134] (2) Preparation of negative electrode sheet

[0135] High expansion artificial graphite, conductive carbon black, binder carboxymethyl cellulose (CMC) and solvent water are uniformly mixed in a weight ratio of 95:2:3:100, and stirred to obtain a uniform first negative electrode slurry. The third negative electrode slurry is the same as the first negative electrode slurry.

[0136] Low expansion artificial graphite, conductive carbon black, binder carboxymethyl cellulose (CMC) and solvent water are uniformly mixed in a weight ratio of 95:2:3:100, and stirred to obtain a uniform negative electrode and second negative electrode slurry.

[0137] The first negative electrode slurry, the second negative electrode slurry and the third negative electrode slurry are coated on a copper foil current collector with a thickness of 6 μm, and the negative electrode sheet is obtained after drying and cold pressing. In the negative electrode sheet, the first negative electrode slurry, the second negative electrode slurry and the third negative electrode slurry respectively form the first active part, the second active part and the third active part, and the first active part, the second active part and the third active part are arranged in sequence in the direction from the empty foil area to the active area of ​​the current collector.

[0138] (3) Preparation of electrolyte

[0139] Ethylene carbonate (EC), polycarbonate (PC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1:1, and then LiPF 6 is uniformly dissolved in the above solution to obtain an electrolyte. In the electrolyte, LiPF 6 The concentration is 1 mol / L.

[0140] (4) Isolation film

[0141] A polyethylene film (PE) with a thickness of 12 μm was used as the separator.

[0142] (5) Preparation of secondary batteries

[0143] The positive electrode sheet, the separator, and the negative electrode sheet are stacked and wound in order to obtain an electrode assembly; the electrode assembly is placed in a shell, an electrolyte is added, and a secondary battery is obtained after packaging, standing, forming, aging and other processes. The forming method is to place the battery cell in a forming device at 40°C, charge it with a small current, and charge it to 30% to 50% SOC of the battery cell design capacity. The width D1 of the first active part, the width D2 of the second active part, and the width D3 of the third active part are 40mm, 30mm and 50mm respectively. The relevant parameters of the negative electrode sheet of the secondary battery are shown in Table 1.

[0144] Example 2

[0145] Compared with Example 1, the difference of Example 2 is that low expansion artificial graphite, silicon oxide, conductive carbon black, binder carboxymethyl cellulose (CMC) and solvent water are uniformly mixed in a weight ratio of 93:2:2:3:100, and stirred to obtain a uniform negative electrode first negative electrode slurry.

[0146] Embodiment 3 to Embodiment 8

[0147] Compared with Example 1, the difference between Examples 3 to 8 and Comparative Examples 1 to 3 is that different graphites are used. The relevant parameters of the negative electrode sheet are shown in Table 1.

[0148] Test Case

[0149] (1) Secondary battery energy density test

[0150] The weight M of all active materials loaded per unit area of ​​the positive electrode sheet of the secondary battery in the embodiment and the comparative example was measured respectively. Each battery was charged at a rate of 0.33C to a voltage of 4.25V at room temperature, and then discharged at a rate of 0.33C to a voltage of 2.5V, and the discharge energy S0 was measured. The battery mass energy density is calculated as follows: battery mass energy density = S0 / M. The results are shown in Table 1.

[0151] (2) Secondary battery cycle life test

[0152] Five secondary batteries in each embodiment and comparative example were respectively tested in parallel. Each battery was charged at a rate of 0.33C to a voltage of 4.25V at room temperature, and then discharged at a rate of 0.33C to a voltage of 2.5V. The reversible capacity was measured as C0. The charging and discharging were repeated until the discharge capacity Cn / C0 of a certain cycle was ≤80%. The number of cycles of each battery was taken as the cycle life of the battery. The results are shown in Table 1.

[0153] (3) Secondary battery negative electrode thickness test

[0154] The battery in the embodiment and the comparative example was charged to 4.25V using 0.33Cn, and then charged at a constant voltage until the current was less than 0.02Cn. The battery was disassembled, the negative electrode sheet was taken out, and the thickness was randomly measured at 20 points on the first active part and the second active part using a micrometer, and the thickness was averaged. The results are shown in Table 1.

[0155] Table 1

[0156]

[0157]

[0158] In Table 1, T1 represents the thickness of the first active part, in μm. η1 represents the expansion rate of the active material of the first active part, in %. G1 represents the degree of graphitization of the active material of the first active part, in %. OI1 represents the OI value of the first active part. T2 represents the thickness of the second active part, in μm. η2 represents the expansion rate of the active material of the second active part, in %. G2 represents the degree of graphitization of the active material of the second active part, in %. OI2 represents the OI value of the second active part. T3 represents the thickness of the third active part, in μm. η3 represents the expansion rate of the active material of the third active part, in %. G3 represents the degree of graphitization of the active material of the third active part, in %. OI3 represents the OI value of the third active part. Energy density represents the mass energy density of the battery, in Wh / kg. Cycle life represents the cycle life of the battery, in cycles.

[0159] It can be seen from Examples 1 to 8 and Comparative Examples 1 to 3 that when T1>T2, T3>T2, the battery has a higher energy density and a longer cycle life.

[0160] It can be seen from Example 1 and Example 2 that when the active materials of the first active portion and the third active portion include silicon oxide, the energy density and cycle life of the battery are better.

[0161] It can be seen from Example 1, Example 3, Example 5 and Example 6 that when T1 / T2 is more appropriate, the energy density and cycle life of the battery are better.

[0162] It can be seen from Examples 1, 4, 7 and 8 that when the expansion rate of the active material, the degree of graphitization of the active material and the OI value of the active part are appropriate, the energy density and cycle life of the battery are better.

[0163] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0164] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A secondary battery, characterized in that: The secondary battery comprises a negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer located on at least one surface of the negative electrode current collector, wherein the negative electrode current collector comprises a hollow foil area and an active area, wherein the negative electrode active layer is located in the active area, and in a direction from the hollow foil area to the active area, the negative electrode active layer comprises a first active portion, a second active portion and a third active portion distributed in sequence; when the secondary battery is in a fully charged state, the thicknesses of the first active portion, the second active portion and the third active portion are T1, T2 and T3 respectively, wherein T1>T2, and T3>T2.

2. The secondary battery according to claim 1, characterized in that: 1.01≤T1 / T2≤1.2; and / or, 1.01≤T3 / T2≤1.

2.

3. The secondary battery according to claim 1 or 2, characterized in that: T1≤T3; optionally, 0.8≤T1 / T3≤1.

4. The secondary battery according to any one of claims 1 to 3, characterized in that: 150μm≤T1≤200μm; and / or, 160μm≤T2≤220μm; and / or, 170μm≤T3≤250μm.

5. The secondary battery according to any one of claims 1 to 4, characterized in that: The expansion rate η1 of the active material of the first active portion is greater than the expansion rate η2 of the active material of the second active portion, and the expansion rate η3 of the active material of the third active portion is greater than the expansion rate η2 of the active material of the second active portion.

6. The secondary battery according to claim 5, characterized in that: 1.01≤η1 / η2≤2; and / or, 1.01≤η3 / η2≤3.

7. The secondary battery according to claim 5 or 6, characterized in that: η1≤η3; optionally, 0.6≤η1 / η3≤1.

8. The secondary battery according to any one of claims 5 to 7, characterized in that: 15%≤η1≤25%; and / or, 10%≤η2≤18%; and / or, 20%≤η3≤30%.

9. The secondary battery according to any one of claims 1 to 8, characterized in that The graphitization degree G1 of the active material of the first active portion is greater than the graphitization degree G2 of the active material of the second active portion, and the graphitization degree G3 of the active material of the third active portion is greater than the graphitization degree G2 of the active material of the second active portion.

10. The secondary battery according to claim 9, characterized in that: 0.95≤G2 / G1<1; and / or, 1.01≤G3 / G2≤1.

1.

11. The secondary battery according to claim 9 or 10, characterized in that: G1≤G3; optionally, 0.95≤G1 / G3≤1.

12. The secondary battery according to any one of claims 9 to 11, characterized in that: 93%≤G1≤94.5%; and / or, 89%≤G2≤93.5%; and / or, 94%≤G3≤95%.

13. The secondary battery according to any one of claims 1 to 12, characterized in that: The OI value OI1 of the first active portion is greater than the OI value OI2 of the second active portion, and the OI value OI3 of the third active portion is greater than the OI value OI2 of the second active portion.

14. The secondary battery according to claim 13, characterized in that: 1.05≤OI1 / OI2≤2.5; and / or, 1.5≤OI3 / OI2≤4.

15. The secondary battery according to claim 13 or 14, characterized in that: OI1≤OI3; optionally, 0.8≤OI1 / OI3≤1.

16. The secondary battery according to any one of claims 13 to 15, characterized in that: 12≤OI1≤25; and / or, 8≤OI2≤15; and / or, 15≤OI3≤35.

17. The secondary battery according to any one of claims 1 to 16, characterized in that: In the direction from the empty foil area to the active area, the widths of the first active portion, the second active portion and the third active portion are D1, D2 and D3 respectively; 0.2≤D2 / (D1+D2+D3)≤0.8; optionally, D1=D3.

18. The secondary battery according to claim 17, characterized in that: 20mm≤D1≤100mm; and / or, 20mm≤D2≤60mm; and / or, 20mm≤D3≤200mm.

19. The secondary battery according to any one of claims 1 to 18, characterized in that: The active material of the first active portion, the active material of the second active portion, and the active material of the third active portion all include graphite.

20. The secondary battery according to claim 19, characterized in that: The active material of the first active portion, the active material of the second active portion, and the active material of the third active portion all include silicon-based materials.

21. The secondary battery according to claim 20, characterized in that: The mass percentage w1 of silicon in the active material of the first active portion is greater than the mass percentage w2 of silicon in the active material of the second active portion, and the mass percentage w3 of silicon in the active material of the third active portion is greater than the mass percentage w2 of silicon in the active material of the second active portion.

22. The secondary battery according to claim 21, characterized in that: 1.01≤w1 / w2≤5; and / or, 1.01≤w3 / w2≤10.

23. The secondary battery according to claim 21 or 22, characterized in that: w1≤w3; optionally, 0.7≤w1 / w3≤1.

24. The secondary battery according to any one of claims 21 to 23, characterized in that: 1%≤w1≤15%; and / or, 0<w2≤10%; and / or, 2%≤w3≤25%.

25. An electrical device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 1 to 24.

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