Secondary battery and electrical apparatus

Abstract

The present disclosure provides a secondary battery and an electrical apparatus. The secondary battery comprises a negative electrode sheet, the negative electrode sheet comprises a negative current collector and a negative electrode film layer located on at least one surface of the negative current collector, and the negative electrode film layer comprises at least two kinds of strip-shaped film areas which are alternately and circularly arranged in a TD direction or an MD direction. Graphite in two adjacent strip-shaped film areas has different OI values, an included angle is formed between the extending direction of the at least two kinds of strip-shaped film areas and the TD direction, and the included angle is not 0 degree. The TD direction is the width direction of the negative electrode sheet, and the MD direction is the length direction of the negative electrode sheet.

Description

Secondary batteries and electrical devices

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure is based on and claims the priority of Chinese patent application with application number 202410397132.6, application date April 2, 2024, and invention name “Secondary Battery and Electrical Device”. The entire content of this Chinese patent application is hereby incorporated into this disclosure as a reference. Technical Field

[0003] The present disclosure relates to the field of battery technology, and in particular to a secondary battery and an electrical device. Background Art

[0004] In recent years, secondary batteries have been widely used in energy storage systems such as hydropower, thermal, wind, and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, and other fields. With the application and promotion of secondary batteries, people have increasingly higher requirements for their energy density, cycle performance, and high-rate charging performance. As a key component of secondary batteries, the performance of the anode material affects the performance of the secondary battery to a certain extent. Graphite has a regular layered structure and excellent conductivity. Its theoretical specific capacity is 372mAh / g, and it is highly efficient, making it the current mainstream anode material. However, graphite as a secondary battery anode material has a large expansion rate, making it difficult to penetrate the electrolyte in the late stages of the cycle, which affects the cycle performance and kinetic performance of the secondary battery.

[0005] Summary of the Invention

[0006] The present disclosure has been made in view of the above-mentioned problems, and an object of the present disclosure is to provide a secondary battery having improved cycle performance and kinetic performance, and an electric device using the secondary battery.

[0007] In order to achieve the above-mentioned purpose, the first aspect of the present disclosure provides a secondary battery, including a negative electrode plate, the negative electrode plate including a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector; the negative electrode film layer includes at least two strip film regions arranged alternately and cyclically along the TD direction or the MD direction; wherein the graphite included in two adjacent strip film regions has different OI values, and the extension direction of at least two strip film regions has an angle with the TD direction; the angle is not 0°; the TD direction is the width direction of the negative electrode plate, and the MD direction is the length direction of the negative electrode plate.

[0008] In the present disclosure, since the negative electrode film layer includes at least two strip-shaped film areas, and the graphite included in the two adjacent strip-shaped film areas has different OI values, and the graphite with different OI values ​​corresponds to different full-charge thickness rebound rates, the surface of the negative electrode film layer will appear grooved in the fully charged state, and the space on the lower film area (i.e., the film area with a smaller full-charge thickness rebound rate) can be used as a path for electrolyte infiltration, which is beneficial to improving the electrolyte infiltration ability and the dynamic performance of the secondary battery. On this basis, by setting the extension direction of at least two strip-shaped film areas to form an angle with the TD direction that is not 0°, the difficulty of electrolyte infiltration can be reduced when the battery cell is placed vertically, and the climbing ability of the electrolyte can be improved, which is beneficial to improving the cycle performance of the secondary battery.

[0009] In some embodiments, the angle is an acute angle. In the present disclosure, when the extension direction of at least two strip-shaped membrane regions forms an acute angle with the TD direction, it can further reduce the difficulty of electrolyte infiltration when the battery cell is placed vertically, improve the climbing ability of the electrolyte, facilitate electrolyte infiltration, and thus help improve the cycle performance and dynamic performance of the secondary battery.

[0010] In some embodiments, the angle is 23° to 67°. The angle between the extension direction of at least two strip-shaped membrane regions and the TD direction is within the above range, which can simultaneously take into account the electrolyte infiltration ability and the amount of liquid stored per unit area, and further help improve the cycle performance and dynamic performance of the secondary battery.

[0011] In some embodiments, the angle is 30° to 60°. The angle between the extension direction of at least two strip-shaped membrane regions and the TD direction is within the above range, which can simultaneously take into account the electrolyte infiltration ability and the amount of liquid stored per unit area, and further help improve the cycle performance and dynamic performance of the secondary battery.

[0012] In some embodiments, the at least two strip-shaped membrane regions include a first membrane region and a second membrane region; and the negative electrode film layer includes at least two groups of the first membrane region and the second membrane region, arranged alternately and cyclically along the TD direction. In the present disclosure, by providing the negative electrode film layer with at least two groups of the first membrane region and the second membrane region, the electrolyte infiltration capacity can be more effectively improved, thereby enhancing the cycling performance of the secondary battery.

[0013] In some embodiments, the first membrane region includes a first graphite; the second membrane region includes a second graphite; the OI value of the first graphite is less than the OI value of the second graphite, and the difference between the OI value of the second graphite and the OI value of the first graphite is 2 to 4. In the present disclosure, graphites with different OI values ​​correspond to different expansions. By setting the OI value of the first graphite in the first membrane region to be less than the OI value of the second graphite in the second membrane region, a height difference can be generated between the first membrane region and the second membrane region in a fully charged state, which is conducive to forming a gully structure, that is, forming an infiltration path for the electrolyte. On this basis, by setting the difference between the OI value of the first graphite and the OI value of the second graphite within the above range, it is beneficial to take into account both the infiltration ability of the electrolyte and the dynamic performance of the secondary battery.

[0014] In some embodiments, the OI value of the first graphite is less than or equal to 15, and the OI value of the second graphite is greater than or equal to 15.

[0015] In some embodiments, the full-charge thickness rebound rate of the negative electrode plate corresponding to the first film region is 10% to 16%.

[0016] In some embodiments, the full-charge thickness rebound rate of the negative electrode sheet corresponding to the second film region is 17% to 22%.

[0017] A second aspect of the present disclosure provides an electric device including the secondary battery according to the first aspect of the present disclosure.

[0018] The electric device of the present disclosure includes the secondary battery provided by the present disclosure, and thus has at least the same advantages as the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG1 is a schematic diagram of the surface structure of the negative electrode film layer after full charge according to one embodiment of the present disclosure.

[0020] FIG2 is a schematic structural diagram of a square selected area in a negative electrode plate according to an embodiment of the present disclosure.

[0021] FIG3 is a functional relationship curve of the angle θ and g(θ) according to one embodiment of the present disclosure.

[0022] FIG4 is a functional relationship curve of the angle θ and f(θ) according to one embodiment of the present disclosure.

[0023] FIG5 is a schematic diagram of the structure of the negative electrode plate after cold pressing and full charging according to one embodiment of the present disclosure.

[0024] FIG6 is a schematic structural diagram of the first graphite and the second graphite according to an embodiment of the present disclosure.

[0025] FIG. 7 is a schematic diagram of a battery cell according to an embodiment of the present disclosure.

[0026] FIG. 8 is an exploded view of the battery cell according to the embodiment of the present disclosure shown in FIG. 7 .

[0027] FIG. 9 is a schematic diagram of a battery module according to an embodiment of the present disclosure.

[0028] FIG. 10 is a schematic diagram of a battery pack according to an embodiment of the present disclosure.

[0029] FIG. 11 is an exploded view of the battery pack shown in FIG. 10 according to one embodiment of the present disclosure.

[0030] FIG. 12 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present disclosure as a power source.

[0031] Description of reference numerals:

[0032] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0033] Below, the embodiments of the secondary battery and the electrical device disclosed in the present invention are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matter described in the claims.

[0034] " scope " disclosed in the present disclosure is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and selected lower limit and upper limit define the boundary of special scope.The scope that this mode limits can be to include end value or not include end value, and can be combined arbitrarily, and promptly any lower limit can form a scope with any upper limit combination.For example, if the scope of 60-120 and 80-110 is listed for specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected.In addition, if the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 listed, then the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.In the present disclosure, unless otherwise specified, numerical range " ab " represents the abbreviation of any real number combination between a and b, and wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0035] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0036] Unless otherwise specified, all technical features and optional technical features disclosed herein can be combined with each other to form a new technical solution.

[0037] Unless otherwise specified, all steps of the present disclosure may be performed sequentially or randomly, preferably sequentially. For example, a method comprising steps (a) and (b) indicates that the method may comprise steps (a) and (b) performed sequentially, or may comprise steps (b) and (a) performed sequentially. For example, a method further comprising step (c) indicates that step (c) may be added to the method in any order, for example, the method may comprise steps (a), (b), and (c), or may comprise steps (a), (c), and (b), or may comprise steps (c), (a), and (b), etc.

[0038] Unless otherwise specified, the terms used in the present disclosure have the common meanings that are generally understood by those skilled in the art.

[0039] Unless otherwise specified, the numerical values ​​of the parameters mentioned in the present disclosure can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in the present disclosure.

[0040] Unless otherwise specified, in the present disclosure, the term "active ions" refers to ions that can be intercalated and extracted back and forth between the positive electrode and the negative electrode of a secondary battery, including but not limited to lithium ions.

[0041] The term "secondary battery" referred to herein refers to a battery cell, a battery module, or a battery pack.

[0042] The term “fully charged” mentioned herein means that the battery is fully charged and reaches 100% state of charge (SOC), that is, 100% SOC.

[0043] The term “fully discharged” mentioned herein means that the battery is completely discharged, ie, reaches 0% SOC.

[0044] The state of charge of a battery can be obtained by measuring the open circuit voltage (OCV) across the battery and comparing it with the OCV-SOC curve of the battery.

[0045] Typically, a secondary battery cell consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0046] Graphite, as a negative electrode material for secondary batteries, has a large expansion rate and is difficult to be penetrated by the electrolyte in the later stages of the cycle, which affects the cycle performance of the secondary battery.

[0047] Based on this, the present disclosure proposes a new secondary battery and an electrical device, wherein the secondary battery has excellent cycle performance.

[0048] A first aspect of an embodiment of the present disclosure provides a secondary battery, comprising a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector; the negative electrode film layer comprises at least two strip film regions alternately arranged in a cyclic manner along a TD direction or an MD direction; wherein the graphite included in two adjacent strip film regions has different OI values, and the extension direction of at least two strip film regions has an angle with the TD direction; the angle is not 0°; the TD direction is the width direction of the negative electrode plate, and the MD direction is the length direction of the negative electrode plate.

[0049] In response to the problem that the graphite negative electrode is difficult to be infiltrated by the electrolyte in the later stage of the cycle, the negative electrode film layer is provided in the present disclosure to include at least two strip film areas, and the graphite included in the two adjacent strip film areas has different OI values. The graphites with different OI values ​​have different thickness rebound rates under the fully charged state due to the different orientation strengths of their graphite particles. In this way, under the fully charged state, the surface of the negative electrode film layer will appear gully-shaped, and the film area with a lower thickness rebound rate will expand less (i.e., the height is small), which can be used as a path for electrolyte infiltration, which is beneficial to improving the infiltration ability of the electrolyte and the dynamic performance of the secondary battery. On this basis, by setting the extension direction of at least two strip film areas to be at an angle to the TD direction, the difficulty of electrolyte infiltration can be reduced when the battery cell is placed vertically, and the climbing ability of the electrolyte can be improved, which is beneficial to improving the cycle performance of the secondary battery.

[0050] It should be noted that the OI value of graphite is the ratio of the diffraction peak intensity of the (004) crystal plane to the diffraction peak intensity of the (110) crystal plane in the X-ray diffraction pattern of graphite.

[0051] In the present disclosure, the OI value of graphite can be tested using instruments and methods known in the art. For example, an X-ray diffractometer (such as Bruker D8Discover) can be used for testing. The test can refer to JIS K 0131-1996 and JB / T 4220-2011 to obtain an X-ray diffraction pattern of the powder sample, and the powder OI value of the sample is calculated according to OI value = I004 / I110. I004 is the integral area of ​​the diffraction peak of the 004 crystal plane of crystalline carbon in the powder sample, and I110 is the integral area of ​​the diffraction peak of the 110 crystal plane of crystalline carbon in the powder sample. In the X-ray diffraction analysis test of the present disclosure, a copper target can be used as an anode target, CuKα rays can be used as a radiation source, the ray wavelength scan 2θ angle range is 20°-80°, and the scanning rate is 4° / min.

[0052] In some embodiments, the negative electrode film layer may include three strip-shaped film regions, four strip-shaped film regions, or more strip-shaped film regions, wherein each strip-shaped film region includes graphite, and the OI values ​​of the graphite in adjacent strip-shaped film regions are different.

[0053] FIG1 is a schematic diagram of the surface structure of a negative electrode film layer after full charge provided by an embodiment of the present disclosure. As shown in FIG1 , the negative electrode film layer includes an A film region and a B film region located on the surface of the current collector 100 and arranged alternately along the TD direction or the MD direction. During the charging process, the A film region expands in a direction at a certain angle to the current collector 100 (i.e., in the direction indicated by the arrow f), and expands less in the direction perpendicular to the current collector. The B film region expands in a direction perpendicular to the current collector 100 (i.e., in the direction indicated by the arrow e), and expands more in the direction perpendicular to the current collector. Therefore, in the fully charged state, the surface of the A film region is lower, and the surface of the B film region is higher. The surface of the negative electrode film layer composed of the A film region and the B film region has a gully-like structure. In addition, since the extension direction c of the A film region and the B film region has an angle θ with the TD direction that is not 0°, the electrolyte can be infiltrated by climbing in the direction indicated by the arrow c in FIG1 , which reduces the difficulty of infiltration compared to the infiltration process parallel to the TD direction.

[0054] In some embodiments, the included angle is an acute angle.

[0055] It should be noted that, in the present disclosure, an acute angle includes a case where the angle is an obtuse angle, and the obtuse angle is complementary to the acute angle.

[0056] In the present disclosure, when the angle between the extension direction of at least two strip-shaped membrane areas and the TD direction is an acute angle, the difficulty of electrolyte infiltration can be further reduced when the battery cell is placed vertically, the climbing ability of the electrolyte can be improved, which is beneficial to the infiltration of the electrolyte, thereby helping to improve the cycle performance and dynamic performance of the secondary battery.

[0057] In some embodiments, the angle is 23° to 67°.

[0058] In some embodiments, the angle is 30° to 60°.

[0059] In the present disclosure, the angle between the extension direction of at least two strip-shaped membrane regions and the TD direction is within the above range, which can take into account both the electrolyte infiltration ability and the liquid storage capacity per unit area, and is more conducive to improving the cycle performance of the secondary battery.

[0060] Below, taking a square selected area in the negative electrode sheet as an example, the influence of the angle on the performance of the secondary battery is explained.

[0061] As shown in Figure 2, assuming that the side length of the square selection area is a, in the plane where the strip film area is located, the size of at least two strip film areas perpendicular to the extension direction of the strip film area (i.e., the membrane area spacing) is d, the length of the membrane area falling within the square selection area is L, and the angle between the extension direction of the strip film area and the TD direction is θ, then a, d, L, and θ satisfy the following equations (1) to (3):

[0062] Combining formulas (1) and (2), we can obtain formula (3);

[0063] According to formula (3), the ratio of the membrane area length L to the membrane area spacing d within the square selection, g(θ), is a function of the angle θ. The functional relationship curve of g(θ) and the angle θ is shown in Figure 3. It can be seen that when the membrane area spacing d is constant, adjusting the angle θ can make the membrane area within the square selection longer, thereby achieving the purpose of higher liquid retention. As can be seen from Figure 3, when the angle θ is 0°, 45°, and 90°, the function reaches its maximum. That is, when the membrane area spacing d is constant, the stripe length L falling within the square selection is the largest when the angle θ between the extension direction of the stripe membrane area and the TD direction is 0°, 45°, and 90°.

[0064] Furthermore, formula (4) defines the amount of liquid stored in the negative electrode per unit area:

[0065] According to formula (4), when the membrane area spacing d is constant, the ratio f(θ) of the membrane area length L within the square selection area to the selection area unit is a function of the angle θ. The functional relationship curve between the angle θ and f(θ) is shown in Figure 4. As can be seen from Figure 4, the curve is axially symmetrical along θ at 45°, and the function reaches its maximum when the angle θ is 45°. Therefore, the angle θ in the embodiment of the present disclosure is preferably 45°.

[0066] Since the theoretical results of formula (3) and formula (4) are slightly different, the following further illustrates the liquid storage capacity within a unit selected area based on the rebound rate of each membrane area in the fully filled state and the width of the membrane area in the direction perpendicular to the extension, combined with Figure 5.

[0067] Assume that the negative electrode plate includes two strip-shaped membrane areas, namely membrane area 1 and membrane area 2, and both membrane area 1 and membrane area 2 contain graphite, and the OI value of the graphite in membrane area 1 is smaller than the OI value of the graphite in membrane area 2. That is, under the same cold pressing thickness, membrane area 1 is a membrane area with low full charge rebound rate, the width of membrane area 1 (i.e., the dimension perpendicular to its extension direction) is t1, and the full charge rebound rate of membrane area 1 is The second membrane area is a high full charge rebound rate membrane area. The width of the second membrane area is t2, and the full charge rebound rate of the second membrane area is Then t1+t2=d (as shown in Figure 5); the initial cold pressing thickness of the two membrane area electrodes is THK, and the height difference between the different membrane areas of the electrode after full charge is Then the liquid storage volume H in the unit selection area satisfies the following formula (5):

[0068] According to formula (5), the liquid storage volume H is related to the height difference caused by the difference in the rebound rate of the membrane area on the one hand, and to the width of the membrane area and the angle θ between the extension direction of the strip membrane area and the TD direction on the other hand. Combining the above formulas (4) and (5), the following formula (6) can be obtained:

[0069] According to formula (6), it can be seen that the liquid storage capacity H is positively correlated with f(θ). Therefore, when the width of the membrane area is determined, when the angle θ between the extension direction of the strip membrane area and the TD direction is 45°, f(θ) is maximized, that is, the liquid storage capacity in the unit selection area is the largest.

[0070] In addition, in the embodiment of the present disclosure, the size of the theoretical liquid storage capacity within the unit selection area needs to be within an appropriate range to take into account the cycle performance of the secondary battery and the compatibility of the low injection system.

[0071] In some embodiments, according to formula (4) and FIG. 4 , the theoretical liquid storage capacity within a unit selected area is defined to meet the requirements when f(θ) is greater than 0.8. In this case, the corresponding θ is between 30° and 60°.

[0072] In some embodiments, according to formula (4) and FIG4 , the theoretical liquid storage capacity within a unit selected area is defined to meet the requirements when f(θ) is greater than 0.7. In this case, the corresponding θ is between 23° and 67°.

[0073] In some embodiments, the at least two membrane regions include a first membrane region and a second membrane region; and the negative electrode membrane layer includes at least two groups of the first membrane region and the second membrane region alternately and cyclically arranged along the TD direction.

[0074] In the present disclosure, by providing the negative electrode film layer with at least two groups of first film regions and second film regions, the infiltration ability of the electrolyte can be more effectively improved, which is beneficial to improving the cycle performance of the secondary battery.

[0075] In some embodiments, the first film region includes a first graphite; the second film region includes a second graphite; the OI value of the first graphite is less than the OI value of the second graphite, and the difference between the OI value of the second graphite and the OI value of the first graphite is 2-4.

[0076] It should be noted that the OI value of the first graphite is the ratio of the diffraction peak intensity of the (004) crystal plane to the diffraction peak intensity of the (110) crystal plane in the X-ray diffraction pattern of the first graphite. The OI value of the second graphite is the ratio of the diffraction peak intensity of the (004) crystal plane to the diffraction peak intensity of the (110) crystal plane in the X-ray diffraction pattern of the second graphite.

[0077] In the present disclosure, the OI value of a material (e.g., the first graphite, the second graphite) is a well-known meaning in the art and can be tested using instruments and methods known in the art. For example, an X-ray diffractometer (e.g., Bruker D8 Discover) can be used for testing. The test can refer to JIS K 0131-1996 and JB / T 4220-2011 to obtain an X-ray diffraction pattern of a powder sample, and the powder OI value of the sample is calculated according to OI value = I004 / I110. I004 is the integral area of ​​the diffraction peak of the 004 crystal plane of crystalline carbon in the powder sample, and I110 is the integral area of ​​the diffraction peak of the 110 crystal plane of crystalline carbon in the powder sample. In the X-ray diffraction analysis test of the present disclosure, a copper target can be used as an anode target, CuKα rays can be used as a radiation source, the ray wavelength scan 2θ angle range is 20°-80°, and the scanning rate is 4° / min.

[0078] FIG6 shows a schematic diagram of the structure of the first graphite A and the second graphite B. As shown in FIG6 , due to the small OI value of the first graphite A, it can be seen that the graphite particles in the first graphite A exhibit a weak orientation, that is, the direction of the 004 crystal plane of the graphite particles is partially parallel to the current collector, and partially at a certain angle to the current collector. Among them, the graphite particles parallel to the current collector are easier to insert lithium, and the graphite particles at a certain angle to the current collector expand perpendicular to the 004 crystal plane after inserting lithium, that is, the expansion direction forms a certain angle with the current collector (as shown in the direction of arrow f in FIG6 ). Therefore, the first graphite A expands less in the direction perpendicular to the current collector surface. Due to the large OI value of the second graphite B, it can be seen that the graphite particles in the second graphite B exhibit a strong orientation, that is, the direction of the 004 crystal plane of the graphite particles is mostly parallel to the current collector, and its expansion after inserting lithium is perpendicular to the 004 crystal plane, that is, perpendicular to the surface of the current collector (as shown in the direction of arrow e in FIG6 ). Therefore, the second graphite B expands more in the direction perpendicular to the current collector surface.

[0079] In the present disclosure, since graphites with different OI values ​​correspond to different full-fill thickness rebound rates, by setting the OI value of the first graphite in the first film area to be smaller than the OI value of the second graphite in the second film area, a height difference can be generated between the first film area and the second film area in the full-fill state, which is conducive to the formation of a groove structure, that is, the formation of an infiltration path for the electrolyte.

[0080] On this basis, by setting the difference between the OI value of the first graphite and the OI value of the second graphite within the above range, the thickness difference between the two membrane areas when fully charged can be within an appropriate range, which can not only meet the fast charging effect of the membrane area corresponding to the lower rebound rate, but also enable the active ions to have a suitable diffusion path. For secondary batteries with a small initial electrolyte injection volume (for example, 2.6g / Ah), the electrolyte can also completely fill the groove space formed by the two membrane areas, and the diffusion path of the active ions will not be cut off by the gas, which is beneficial to taking into account both the wetting ability of the electrolyte and the dynamic performance of the secondary battery.

[0081] In addition, in the present disclosure, the surface of the first graphite with low OI is the main entrance for lithium insertion. Here, because the electrode rebound is small, the electrolyte is sufficient, and the liquid-phase active ions migrate faster; at the interface between the first graphite and the second graphite, the active ions can diffuse in the solid phase through the exposed side walls of the second graphite, which is beneficial to improving the rate performance of the secondary battery.

[0082] In some embodiments, the OI value of the first graphite is less than or equal to 15, and the OI value of the second graphite is greater than or equal to 15. For example, the OI value of the first graphite is 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, etc., and the OI value of the second graphite is 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, etc.

[0083] In some embodiments, the full-charge thickness rebound rate of the negative electrode sheet corresponding to the first membrane region is 10% to 16%. In some embodiments, the full-charge thickness rebound rate of the negative electrode sheet corresponding to the second membrane region is 17% to 22%.

[0084] It should be noted that the cold-pressed thicknesses of the first film region and the second film region in the initial state are the same.

[0085] In some embodiments, the full charge thickness rebound rate can be reversed by the following test method: take two secondary batteries from the same batch, disassemble one of the secondary batteries after fully discharging, obtain the negative electrode sheet, and measure the thickness H0 of the negative electrode sheet at this time; disassemble the other secondary battery after fully charging, obtain the negative electrode sheet, and measure the thickness H1 of the first film area and the thickness H2 of the second film area of ​​the negative electrode sheet at this time; the full charge thickness rebound rate of the first film area is Full filling thickness rebound rate of the second film area

[0086] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0087] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one 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).

[0088] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0089] The present disclosure does not particularly limit the content of the binder and / or other auxiliary agents, if any, in the negative electrode film layer. A person skilled in the art can determine the appropriate content of the binder and / or other auxiliary agents through routine experiments in the relevant field.

[0090] In some 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 base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0091] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the first graphite, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry for the first membrane region, the second graphite, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry for the second membrane region, and the first slurry and the second slurry are simultaneously coated on the negative electrode current collector using a coating machine with a special structure. After drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0092] The above embodiments are described only by taking the composition of the negative electrode film layer on the surface of one side of the negative electrode current collector as an example. It should be understood that the negative electrode current collector has two surfaces opposite to each other in the direction of its thickness, and the negative electrode film layer described in the above embodiments is arranged on any one or both of the two opposite surfaces of the negative electrode current collector. It should be noted that the various negative electrode film layer parameters (such as compaction density, surface density, porosity, thickness, etc.) given in the present disclosure refer to the parameters of the negative electrode film layer on a single side of the negative electrode current collector. When the negative electrode film layer is arranged on both sides of the negative electrode current collector, the parameters of the negative electrode film layer on either side meet the requirements of the present disclosure and are considered to fall within the scope of protection of the present disclosure.

[0093] In the present disclosure, the negative electrode sheet may include other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode sheet further includes a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode sheet further includes a protective layer covering the surface of the negative electrode film layer.

[0094] [Positive electrode]

[0095] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0096] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0097] 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 and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0098] In some embodiments, the positive electrode active material may be a positive electrode active material for lithium ion batteries that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present disclosure 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 oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.01 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0099] The battery's charge and discharge processes involve the intercalation and deintercalation of lithium, leading to different molar Li contents at different discharge states. The molar Li contents listed in this disclosure for positive electrode active materials refer to the material's initial state, i.e., before addition. When a positive electrode active material is used in a battery system, its molar Li content will change over the course of charge and discharge cycles.

[0100] The molar oxygen content in the positive electrode active materials listed in this disclosure is only a theoretical value. Lattice oxygen release can cause the molar oxygen content to change, and the actual molar oxygen content will fluctuate. The molar content of other elements may also change after battery manufacturing and during use. Therefore, the molar ratios of the elements in the molecular formulas of the positive electrode active materials above are the molar ratios at the time of preparation.

[0101] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0102] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0103] In some embodiments, the positive electrode sheet can be prepared by the following method: 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 (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0104] [Electrolytes]

[0105] The electrolyte conducts ions between the positive and negative electrodes. The present disclosure does not specifically limit the type of electrolyte, and the electrolyte can be selected based on needs. For example, the electrolyte can be liquid.

[0106] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0107] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0108] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, 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.

[0109] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0110] [Isolation film]

[0111] In some embodiments, the battery cell further includes a separator. The present disclosure has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0112] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can 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 can be the same or different, without particular limitation.

[0113] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a lamination process.

[0114] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0115] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0116] The present disclosure has no particular limitation on the shape of the battery cell, which may be cylindrical, square, or any other shape. For example, FIG7 shows a battery cell 5 with a square structure as an example.

[0117] In some embodiments, referring to Figure 8, the outer packaging may include a shell 51 and a top cover assembly 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the top cover assembly 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0118] In some embodiments, battery cells may be assembled into a battery module. The battery module may contain one or more battery cells. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0119] Figure 9 shows an example battery module 4. Referring to Figure 9 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0120] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0121] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0122] Figures 10 and 11 illustrate an exemplary battery pack 1. Referring to Figures 10 and 11 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be positioned over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0123] A second aspect of the embodiments of the present disclosure provides an electrical device, which includes the secondary battery provided in each of the above embodiments. 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, but is not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0124] As an electrical device, a battery cell, battery module or battery pack can be selected according to its usage requirements.

[0125] Figure 12 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0126] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0127] Example

[0128] The following examples are provided. The examples described below are illustrative and are intended only to explain the present disclosure and are not to be construed as limiting the present disclosure. Where specific techniques or conditions are not specified in the examples, the methods were performed according to those described in the literature in the art or according to the product specifications. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0129] Example 1

[0130] Preparation of negative electrode sheet: The first graphite (OI value is 14) is mixed with conductive agent carbon black, binder SBR and viscosity agent CMC in a weight ratio of 94.5:1:2.25:2.25, and an appropriate amount of solvent deionized water is added and stirred to obtain a first slurry; the second graphite (OI value is 17) is mixed with conductive agent carbon black, binder SBR and viscosity agent CMC in a weight ratio of 94.5:1:2.25:2.25, and an appropriate amount of solvent deionized water is added and stirred to obtain a second slurry; the third The first slurry and the second slurry are evenly coated on the surface of the copper foil, and after drying and cold pressing, a negative electrode sheet is obtained in which the first film area (corresponding to the first slurry) and the second film area (corresponding to the second slurry) are alternately arranged three times, wherein the width t1 of the first film area is 20 mm, the width t2 of the second film area is 20 mm, and during the coating process, the angle θ between the extension direction (i.e., the coating direction) of the first film area and the second film area and the TD direction is 45 degrees, and the initial thickness THK of the negative electrode sheet after cold pressing is 180 μm.

[0131] Preparation of positive electrode sheet: LiFePO4, conductive agent acetylene black, and binder PVDF are mixed in a weight ratio of 96:2:2, and an appropriate amount of solvent NMP is added and stirred evenly to obtain positive electrode slurry; the positive electrode slurry is coated on aluminum foil, and after coating, it is dried and cold pressed to obtain positive electrode sheet.

[0132] Separator film: 12 μm polyethylene film.

[0133] Electrolyte: Dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) were mixed in a mass ratio of 1:1:1 to obtain an organic solvent, and then LiPF6 was dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L.

[0134] Preparation of lithium-ion secondary battery: Place the positive electrode sheet, separator, and negative electrode sheet prepared above in order, so that the separator is placed between the positive and negative electrode sheets to play an isolating role, process and shape them, package them in aluminum-plastic bags, inject electrolyte, and then package them for capacity formation to obtain a soft-pack battery.

[0135] Anode film characterization

[0136] First, the secondary battery was fully charged at 0.3C. After full charge, the battery was disassembled and the thicknesses of the first and second membrane regions were measured, denoted as H1 and H2, respectively. The thickness rebound rate of the first membrane region was (H1-THK) / THK×100%, and the thickness rebound rate of the second membrane region was (H2-THK) / THK×100%, where THK is the initial cold-pressed thickness of the negative electrode.

[0137] In Example 1 of the present disclosure, during the coating process, the angle θ between the extension direction (i.e., coating direction) of the first and second film regions and the TD direction is 45 degrees, so f(θ) is 1 (calculated according to the aforementioned formula (4)). After cold pressing, the initial thickness THK of the negative electrode sheet is 180 μm. After full charge, the full charge thickness rebound rate of the first film region can be measured according to the above-mentioned full charge thickness rebound rate test. The full thickness rebound rate of the second film area is 16.0%. is 22.0%, then the difference in full thickness rebound rate between the first and second membrane areas is 6%, The width t1 of the first membrane area is 20 mm, the width t2 of the second membrane area is 20 mm, and t1 / (t1+t2) is 0.5. The theoretical liquid storage capacity per unit area is

[0138] Lithium-ion secondary battery performance test

[0139] 1) 2C charging capacity retention rate

[0140] At 25°C, the following steps were performed on the secondary battery:

[0141] ① Set aside for 30 minutes;

[0142] ②0.33C constant current charging to 3.65V;

[0143] ③Set aside for 30 minutes;

[0144] ④Discharge at a constant current of 0.33C to 2.5V and record the discharge capacity C0;

[0145] ⑤Set aside for 30 minutes;

[0146] ⑥2C constant current charging to 3.65V;

[0147] ⑦Set aside for 30 minutes;

[0148] ⑧Discharge at 0.33C constant current to 2.5V and record the discharge capacity C1;

[0149] ⑨Set aside for 30 minutes;

[0150] 2C charge capacity retention rate (%) = C0 / C1*100%.

[0151] 2) Cycle performance

[0152] Use a test fixture for fixing, the test fixture pressure is 0.65MPa, and perform the following test steps at 25℃:

[0153] ① Set aside for 30 minutes;

[0154] ②1C constant current charging to 3.65V;

[0155] ③Set aside for 30 minutes;

[0156] ④Discharge at 1C constant current to 2.5V and record the discharge capacity D0;

[0157] ⑤Set aside for 30 minutes;

[0158] ⑥ Cycle steps ②-⑤ and record the discharge capacity Dn in each full cycle;

[0159] The test cutoff condition is: the capacity retention ratio D0 / Dn*100% is less than 80%.

[0160] The number of cycles when the cycle capacity retention rate is less than 80% is the number of cycles when the test is cut off.

[0161] Comparative Example 1

[0162] A lithium-ion secondary battery was prepared in the same manner as in Example 1, except that the OI values ​​of the graphite in the first and second film regions of the negative electrode film layer in the negative electrode sheet were the same, both being 14. For details, please see Table 1 below.

[0163] The parameters of the negative electrode sheets prepared in Example 1 and Comparative Example 1 are shown in Table 1 below, and the test results of the lithium-ion secondary battery are shown in Table 2 below.

[0164] Table 1:

[0165] Table 2:

[0166] As can be seen from Table 1 above, compared with Comparative Example 1 (the OI value of the graphite in the first membrane area and the second membrane area is the same), in Example 1, by setting the graphite in the first membrane area and the second membrane area to have a suitable OI difference, the kinetic performance and cycle performance of the secondary battery can be significantly improved.

[0167] Examples 2-4

[0168] A lithium-ion secondary battery was prepared in the same manner as in Example 1, except that the angles θ between the extension directions of the first and second film regions in the negative electrode sheet and the TD direction were different. For details, please see Table 3 below.

[0169] Comparative Example 2

[0170] A lithium-ion secondary battery was prepared in the same manner as in Example 1, except that the angle θ between the extension direction of the first film region and the second film region in the negative electrode plate and the TD direction was 0°. For details, please see Table 3 below.

[0171] The test results of the lithium ion secondary batteries prepared in Examples 2-4 and Comparative Example 2 are shown in Table 3 below.

[0172] Table 3:

[0173] As can be seen from Table 3 above, relative to Comparative Example 2 (the angle between the extension direction of the first membrane area and the second membrane area and the TD direction is 0°), when the extension direction of the first membrane area and the second membrane area is an acute angle with the TD direction, the difficulty of electrolyte infiltration is reduced and the climbing ability of the electrolyte is improved. Therefore, the dynamic performance and cycle performance of the secondary battery can be significantly improved. In addition, although the theoretical liquid storage capacity per unit area of ​​Example 4 and Comparative Example 2 is the same, in Example 4, in the fully charged state, the infiltration path formed by the space above the first membrane area extends horizontally. In this way, when the battery is placed vertically, the electrolyte will flow to the bottom of each infiltration path, rather than to the bottom of the entire battery. Therefore, the difficulty of electrolyte infiltration is lower, and its cycle performance is better than that of Comparative Example 2.

[0174] It should be noted that the present disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present disclosure, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present disclosure. In addition, within the scope of the present disclosure, various modifications that can be imagined by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present disclosure.

Claims

1. A secondary battery comprising a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector; the negative electrode film layer comprising at least two strip-shaped film regions alternately arranged in a TD direction or an MD direction; The graphite included in two adjacent strip-shaped film regions has different OI values, and the extension direction of the at least two strip-shaped film regions forms an angle with the TD direction; the angle is not 0°; The TD direction is the width direction of the negative electrode sheet, and the MD direction is the length direction of the negative electrode sheet.

2. The secondary battery according to claim 1, wherein The included angle is an acute angle.

3. The secondary battery according to claim 1 or 2, wherein The angle is 23° to 67°.

4. The secondary battery according to any one of claims 1 to 3, wherein The angle is 30° to 60°.

5. The secondary battery according to any one of claims 1 to 4, wherein The at least two strip-shaped membrane regions include a first membrane region and a second membrane region; The negative electrode film layer includes at least two groups of the first film regions and the second film regions that are alternately and cyclically arranged along the TD direction.

6. The secondary battery according to claim 5, wherein The first film region includes a first graphite; the second film region includes a second graphite; The OI value of the first graphite is smaller than the OI value of the second graphite, and the difference between the OI value of the second graphite and the OI value of the first graphite is 2-4.

7. The secondary battery according to claim 6, wherein The OI value of the first graphite is less than or equal to 15, and the OI value of the second graphite is greater than or equal to 15.

8. The secondary battery according to any one of claims 5 to 7, wherein The full-charge thickness rebound rate of the negative electrode plate corresponding to the first film area is 10% to 16%.

9. The secondary battery according to any one of claims 5 to 8, wherein The full-charge thickness rebound rate of the negative electrode sheet corresponding to the second film region is 17% to 22%. 10 . An electric device comprising the secondary battery according to claim 1 .

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