Secondary battery and electric device

Abstract

The invention provides a secondary battery and a power utilization device, the secondary battery comprises a negative electrode piece, the negative electrode piece comprises 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 kinds of strip-shaped film areas which are alternately and circularly arranged along the TD direction or the MD direction; wherein graphite contained in two adjacent strip-shaped film areas has different OI values, and an included angle is formed between the extending direction of the at least two strip-shaped film areas and the TD direction; the included angle is not 0 degree; the TD direction is the width direction of the negative pole piece, and the MD direction is the length direction of the negative pole piece. The secondary battery provided by the invention has excellent cycle performance and dynamic performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a secondary battery and a power consumption device. BACKGROUND

[0002] In recent years, secondary batteries are widely used in energy storage power systems such as hydroelectric, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, etc. With the application and promotion of secondary batteries, people have higher and higher requirements for the energy density, cycle performance and large-rate charging performance of secondary batteries, and the performance of the negative electrode material, as an important component of the secondary battery, to some extent, affects the performance of the secondary battery. Graphite has a regular layered structure and excellent electrical conductivity, and its theoretical specific capacity is 372 mAh / g, which is high in efficiency and is currently the mainstream negative electrode material. However, as a negative electrode material for secondary batteries, graphite expands greatly, and it is difficult for the electrolyte to infiltrate in the later cycle, which affects the cycle performance and kinetic performance of the secondary battery. SUMMARY

[0003] The present application is made in view of the above-mentioned problems, and aims to provide a secondary battery with improved cycle performance and kinetic performance, and a power consumption device using the same.

[0004] To achieve the above-mentioned purpose, the first aspect of the present application provides a secondary battery, comprising a negative electrode sheet, the negative electrode sheet 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 arranged alternately in a TD direction or an MD direction; wherein the graphite included in adjacent two strip-shaped film regions has different OI values, and the extension direction of the at least two strip-shaped film regions has an included angle with the TD direction; the included 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.

[0005] In the present application, since the negative electrode film layer comprises at least two strip-shaped film regions, and the graphite included in adjacent two strip-shaped film regions has different OI values, and the graphite with different OI values corresponds to different full charge thickness rebound rates, so that in the full charge state, the surface of the negative electrode film layer will present a gully shape, and the space on the lower film region (i.e. the film region with smaller full charge thickness rebound rate) can be used as a path for electrolyte infiltration, which is beneficial to improve the infiltration ability of the electrolyte and the kinetic performance of the secondary battery. On this basis, by setting the extension direction of the at least two strip-shaped film regions to have an included angle with the TD direction which 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 improve the cycle performance of the secondary battery.

[0006] In some embodiments, the included angle is an acute angle. In the present application, when the included angle between the extension direction of the at least two strip-shaped film regions and the TD direction is an acute angle, the wettability of the electrolyte can be further reduced when the battery cell is vertically placed, the climbing ability of the electrolyte is improved, the wettability of the electrolyte is improved, and thus the cycle performance and dynamic performance of the secondary battery are improved.

[0007] In some embodiments, the included angle is 23°-67°. When the included angle between the extension direction of the at least two strip-shaped film regions and the TD direction is within the above range, the wettability of the electrolyte and the liquid storage capacity per unit area can be simultaneously considered, and the cycle performance and dynamic performance of the secondary battery are more improved.

[0008] In some embodiments, the included angle is 30°-60°. When the included angle between the extension direction of the at least two strip-shaped film regions and the TD direction is within the above range, the wettability of the electrolyte and the liquid storage capacity per unit area can be simultaneously considered, and the cycle performance and dynamic performance of the secondary battery are more improved.

[0009] In some embodiments, the at least two strip-shaped film regions include a first film region and a second film region; and the negative electrode film layer includes at least two groups of the first film region and the second film region arranged in the TD direction in an alternating cycle. In the present application, by arranging the negative electrode film layer to include at least two groups of the first film region and the second film region, the wettability of the electrolyte can be more effectively improved, and the cycle performance of the secondary battery is improved.

[0010] 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. In the present application, different OI values of the graphite correspond to different expansions. By arranging the OI value of the first graphite of the first film region to be less than the OI value of the second graphite of the second film region, a height difference between the first film region and the second film region can be generated under the full charge state, which is conducive to forming a gully structure, i.e., forming a wettability path of the electrolyte. On this basis, by arranging the difference between the OI value of the first graphite and the OI value of the second graphite to be within the above range, the wettability of the electrolyte and the dynamic performance of the secondary battery can be simultaneously considered.

[0011] 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.

[0012] In some embodiments, the full charge thickness rebound rate of the negative electrode sheet corresponding to the first film region is 10%-16%.

[0013] In some embodiments, the second film region corresponds to a full charge thickness rebound rate of the negative electrode tab of 17% to 22%.

[0014] A second aspect of the present application provides a power consuming device comprising the secondary battery of the first aspect of the present application.

[0015] The power consuming device of the present application comprises the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 A schematic diagram of the surface structure of the negative electrode film layer after full charging according to an embodiment of the present application.

[0017] Figure 2 A schematic diagram of a square selected region in the negative electrode tab according to an embodiment of the present application.

[0018] Figure 3 A curve of the function relationship between the included angle θ and g(θ) according to an embodiment of the present application.

[0019] Figure 4 A curve of the function relationship between the included angle θ and f(θ) according to an embodiment of the present application.

[0020] Figure 5 A schematic diagram of the structure of the negative electrode tab after cold pressing and after full charging according to an embodiment of the present application.

[0021] Figure 6 A schematic diagram of the structure of the first graphite and the second graphite according to an embodiment of the present application.

[0022] Figure 7 A schematic diagram of a battery cell according to an embodiment of the present application.

[0023] Figure 8 A schematic diagram of a battery cell according to an embodiment of the present application. Figure 7 A schematic diagram of a battery cell according to an embodiment of the present application.

[0024] Figure 9 A schematic diagram of a battery module according to an embodiment of the present application.

[0025] Figure 10 A schematic diagram of a battery pack according to an embodiment of the present application.

[0026] Figure 11 A schematic diagram of a battery pack according to an embodiment of the present application. Figure 10 A schematic diagram of a battery pack according to an embodiment of the present application.

[0027] Figure 12 A schematic diagram of a power consuming device using the secondary battery as a power source according to an embodiment of the present application.

[0028] REFERENCE SIGNS

[0029] 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 battery cell; 51 case; 52 electrode assembly; 53 top cap assembly. DETAILED DESCRIPTION

[0030] Hereinafter, specific embodiments of a secondary battery and an electric device according to the present application are described in detail with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters known to those skilled in the art, repeated description of substantially identical structures are omitted. This is to avoid the following description becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0031] The "ranges" disclosed in the present application are defined in the form of lower and upper limits, 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 ranges defined in this way can include or exclude the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if the ranges 60-120 and 80-110 are listed for a particular parameter, it is understood that the ranges 60-110 and 80-120 are also contemplated. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise stated, a numerical range "a-b" represents a shorthand manner of describing the arbitrary combination of real numbers 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" have been listed herein, and "0-5" is just a shorthand notation for these numerical combinations. In addition, when it is stated that a certain parameter is an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0032] If not specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0033] If not specifically stated, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0034] If not otherwise specified, all steps of the present application can be performed in any order, preferably in the order as specified. For example, the method comprising steps (a) and (b) means that the method can comprise steps (a) and (b) in the order as specified, or the method can comprise steps (b) and (a) in the order as specified. For example, the method comprising step (c) means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or the method can comprise steps (a), (c) and (b), or the method can comprise steps (c), (a) and (b), etc.

[0035] If not otherwise specified, the terms used in the present application have the commonly understood meanings by those skilled in the art.

[0036] If not otherwise specified, the values of the parameters mentioned in the present application can be measured by various testing methods commonly used in the art, for example, the testing methods given in the present application.

[0037] If not otherwise specified, in the present application, the term "active ion" means ions that can be reversibly intercalated and deintercalated between the positive electrode and the negative electrode of a secondary battery, including but not limited to lithium ions.

[0038] The term "secondary battery" as mentioned herein refers to a battery cell, a battery module or a battery pack.

[0039] The term "full charge" as mentioned herein refers to a battery being fully charged, reaching 100% State of Charge (SOC), i.e. 100% SOC.

[0040] The term "full discharge" as mentioned herein refers to a battery being fully discharged, i.e. reaching 0% SOC.

[0041] The State of Charge (SOC) of a battery can be obtained by measuring the Open Circuit Voltage (OCV) across the battery and comparing it to the OCV-SOC curve of the battery.

[0042] Generally, a secondary battery cell comprises a positive electrode, a negative electrode, an electrolyte and a separator. During the charging and discharging of the battery, active ions are reversibly intercalated and deintercalated between the positive electrode and the negative electrode. The electrolyte serves as a conductor of ions between the positive electrode and the negative electrode. The separator is arranged between the positive electrode and the negative electrode and serves to prevent short circuiting of the positive and negative electrodes, while allowing the passage of ions.

[0043] The expansion of graphite as a negative electrode material for secondary batteries is large, and the electrolyte is difficult to infiltrate in the later stage of the cycle, which affects the cycle performance of the secondary battery.

[0044] Based on this, the application provides a new secondary battery and a power consumption device, which has excellent cycle performance.

[0045] The first aspect of the application provides a secondary battery, comprising a negative electrode sheet, the negative electrode sheet 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 arranged in an alternating cycle in a TD direction or an MD direction; wherein the graphite included in adjacent two strip-shaped film regions has different OI values, and the extension direction of the at least two strip-shaped film regions has an included angle with the TD direction; the included 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.

[0046] In view of the problem that the electrolyte is difficult to infiltrate in the later stage of the cycle of the graphite negative electrode, the negative electrode film layer in the application comprises at least two strip-shaped film regions, and the graphite included in adjacent two strip-shaped film regions has different OI values. Because the graphite with different OI values has different strengths of orientation of graphite particles, the thickness rebound rate in the full charge state is different. In the full charge state, the surface of the negative electrode film layer appears in a gully shape, and the film region with a lower thickness rebound rate has a smaller expansion (i.e., a smaller height), which can be used as a path for electrolyte infiltration, and is beneficial to improve the infiltration capacity of the electrolyte and the kinetic performance of the secondary battery. On this basis, by setting the extension direction of the at least two strip-shaped film regions to have an included angle with the TD direction, the infiltration difficulty of the electrolyte can be reduced when the battery cell is vertically placed, the climbing ability of the electrolyte is improved, and the cycle performance of the secondary battery is improved.

[0047] It should be noted that the OI value of the 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 graphite.

[0048] In the application, the OI value of the graphite can be tested by instruments and methods known in the art. For example, an X-ray diffractometer (such as Bruker D8Discover) can be used for testing, and the X-ray diffraction pattern of the powder sample can be obtained by referring to JIS K0131-1996 and JB / T 4220-2011, and the powder OI value of the sample can be calculated according to OI value = I004 / I110. I004 is the integral area of the diffraction peak of the 004 crystal plane of the crystalline carbon in the powder sample, and I110 is the integral area of the diffraction peak of the 110 crystal plane of the crystalline carbon in the powder sample. In the X-ray diffraction analysis test in the application, a copper target can be used as an anode target, CuKα ray is used as a radiation source, the scanning range of the ray wavelength is 20°-80°, and the scanning rate is 4° / min.

[0049] 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.

[0050] Figure 1 A schematic diagram of the surface structure of a negative electrode film layer after full charge provided in an embodiment of the present application is shown in FIG. Figure 1 As shown, the negative electrode film layer includes film regions A and B 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 film region A 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 film region B 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 film region A is lower, and the surface of the film region B is higher. The surface of the negative electrode film layer composed of the film regions A and B has a gully-like structure. In addition, since the extension direction c of the film region A and the film region B has an angle θ with the TD direction that is not 0°, the electrolyte can be discharged along the Figure 1 Climbing the slope in the direction indicated by the arrow c reduces the difficulty of infiltration compared to the infiltration process parallel to the TD direction.

[0051] In some embodiments, the angle is an acute angle.

[0052] It should be noted that, in the present application, an acute angle includes a case where the angle is an obtuse angle, and the obtuse angle is complementary to the acute angle.

[0053] In the present application, 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.

[0054] In some embodiments, the angle is 23° to 67°.

[0055] In some embodiments, the angle is 30° to 60°.

[0056] In the present application, 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.

[0057] 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.

[0058] like Figure 2As shown, assuming the side length of the square selection region is a, the dimension of at least two strip-shaped membrane regions in the plane where the strip-shaped membrane regions are located (i.e., the membrane region spacing) is d, the length of the membrane region falling in the square selection region is L, and the angle between the extension direction of the strip-shaped membrane region and the TD direction is θ, then a, d, L, and θ satisfy the following formulas (1) to (3):

[0059]

[0060]

[0061] Combining formulas (1) and (2), formula (3) can be obtained;

[0062]

[0063] According to formula (3), the ratio g(θ) of the length L of the membrane region falling in the square selection region to the membrane region spacing d is a function of the angle θ, and the functional relationship curve of g(θ) and the angle θ is shown in FIG. 3. Figure 3 It can be seen that when the membrane region spacing d is constant, adjusting the angle θ can make the length of the membrane region falling in the square selection region larger, so as to achieve the purpose of higher liquid retention. From Figure 3 It can be seen that when the angle θ is 0°, 45°, or 90°, the function takes the maximum value, that is, when the extension direction of the strip-shaped membrane region is 0°, 45°, or 90° relative to the TD direction, the length L of the strip-shaped membrane region falling in the square selection region is the largest.

[0064] Further, formula (4) defines the size of the liquid storage amount of the negative pole piece per unit selection region area:

[0065]

[0066] According to formula (4), when the membrane region spacing d is constant, the ratio f(θ) of the length L of the membrane region falling in the square selection region to the unit selection region is a function of the angle θ, and the functional relationship curve of the angle θ and f(θ) is shown in FIG. 4. Figure 4 It can be seen that the curve is symmetrically distributed along θ=45°, and the function takes the maximum value when the angle θ is 45°, so the angle θ in the embodiments of the present application is preferably 45°. Figure 4 Since the theoretical results of formula (3) and formula (4) are slightly different, the following further explains the liquid storage amount per unit selection region according to the rebound rate of each membrane region in the full charge state and the width of the membrane region in the direction perpendicular to the extension direction.

[0067] Figure 5

[0068] ​​Assuming that the negative electrode sheet comprises two strip-shaped film regions, namely film region one and film region two, both of which comprise graphite, and the OI value of the graphite in the film region one is less than that of the graphite in the film region two, i.e. under the same cold-pressed thickness, the film region one is a low full-charge rebound rate film region, the width (i.e. the size in the direction perpendicular to the extension direction) of the film region one is t1, and the full-charge rebound rate of the film region one is The film region two is a high full-charge rebound rate film region, the width of the film region two is t2, and the full-charge rebound rate of the film region two is Then t1+t2=d (as shown in Figure 5 ); the initial cold-pressed thickness of the electrode sheet of the two film regions is THK, and the height difference between different film regions of the electrode sheet after full charging is Then the liquid storage amount H in the unit selected region satisfies the following formula (5):

[0069]

[0070] According to formula (5), it can be seen that the liquid storage amount H is related to the height difference caused by the rebound rate difference of the film regions, and is related to the width of the film regions and the angle θ between the extension direction of the strip-shaped film region and the TD direction. Combining the above formula (4) and formula (5), the following formula (6) can be obtained:

[0071]

[0072] According to formula (6), it can be seen that the liquid storage amount H is positively correlated with f(θ), and therefore, when the width of the film region is determined, the liquid storage amount in the unit selected region is the largest when the angle θ between the extension direction of the strip-shaped film region and the TD direction is 45°, i.e. f(θ) takes the maximum value.

[0073] In addition, in the embodiments of the present application, the size of the theoretical liquid storage amount in the unit selected region needs to be in a suitable range to take into account the cycle performance of the secondary battery and the compatibility of the low liquid injection system.

[0074] In some embodiments, according to formula (4) and Figure 4 , it is defined that the size of the theoretical liquid storage amount in the unit selected region when f(θ) is greater than 0.8 meets the requirements, and at this time, the corresponding θ is between 30° and 60°.

[0075] In some embodiments, according to formula (4) and Figure 4 , it is defined that the size of the theoretical liquid storage amount in the unit selected region when f(θ) is greater than 0.7 meets the requirements, and at this time, the corresponding θ is between 23° and 67°.

[0076] In some embodiments, the at least two film regions comprise a first film region and a second film region; and the negative electrode film layer comprises at least two groups of the first film region and the second film region arranged in an alternating cycle along the TD direction.

[0077] In the present application, by setting the negative electrode film layer to include at least two groups of first film regions and second film regions, the wettability of the electrolyte can be more effectively improved, and the cycle performance of the secondary battery can be improved.

[0078] In some embodiments, the first film regions include a first graphite; the second film regions include 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.

[0079] It should be noted that the OI value of the first graphite is the ratio of the diffraction peak intensity of the (004) crystal face to the diffraction peak intensity of the (110) crystal face 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 face to the diffraction peak intensity of the (110) crystal face in the X-ray diffraction pattern of the second graphite.

[0080] In the present application, the OI value of the material (such as the first graphite, the second graphite) is the meaning known in the art, which can be tested by instruments and methods known in the art. For example, an X-ray diffractometer (such as Bruker D8 Discover) can be used for testing, and the test can refer to JIS K 0131-1996, JB / T 4220-2011 to obtain the 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 face of the crystalline carbon in the powder sample, and I110 is the integral area of the diffraction peak of the 110 crystal face of the crystalline carbon in the powder sample. In the X-ray diffraction analysis test of the present application, a copper target can be used as an anode target, CuKα ray is used as the radiation source, the scanning range of the ray wavelength is 20°-80°, and the scanning rate is 4° / min.

[0081] Figure 6 The structural schematic diagrams of the first graphite A and the second graphite B are shown as follows, Figure 6 As shown in the figure, since the OI value of the first graphite A is small, it can be seen that the graphite particles in the first graphite A have weak orientation, i.e., the direction of the 004 crystal face of the graphite particles is partially parallel to the current collector and partially at a certain angle with the current collector. Among them, the graphite particles parallel to the current collector are easier to be embedded with lithium, and the graphite particles at a certain angle with the current collector expand perpendicular to the 004 crystal face after being embedded with lithium, i.e., at a certain angle with the expansion direction and the current collector (such as Figure 6the arrow f direction in FIG. 1B), and thus the first graphite A has a smaller expansion in the direction perpendicular to the surface of the current collector. Since the second graphite B has a larger OI value, it can be seen that the graphite particles in the second graphite B have a stronger orientation, i.e., the direction of the 004 crystal plane of the graphite particles is mostly parallel to the current collector, and the expansion after lithium intercalation is perpendicular to the 004 crystal plane, i.e., perpendicular to the surface of the current collector (as shown by the arrow e direction in FIG. 1B). Figure 6 Thus, the second graphite B has a larger expansion in the direction perpendicular to the surface of the current collector.

[0082] In the present application, since the graphite with different OI values corresponds to different full-charge thickness rebound rates, by setting the OI value of the first graphite in the first film region to be smaller than the OI value of the second graphite in the second film region, a height difference between the first film region and the second film region in the full-charge state can be generated, which is beneficial to form a gully structure, i.e., to form an infiltration path of the electrolyte.

[0083] On this basis, by setting the difference between the OI value of the first graphite and the OI value of the second graphite to be within the above range, the thickness difference between the two film regions in the full-charge state can be within a suitable range, which can not only satisfy the fast-charging effect of the film region corresponding to a lower rebound rate, but also enable the active ions to have a suitable diffusion path, and for a secondary battery with a small initial electrolyte injection amount (e.g., 2.6 g / Ah), the electrolyte can also completely fill the gully space formed by the two film regions, and the diffusion path of the active ions will not be interrupted by gas, which is beneficial to simultaneously consider the infiltration ability of the electrolyte and the kinetic performance of the secondary battery.

[0084] In addition, in the present application, the surface of the first graphite with a low OI value is the main entrance for lithium intercalation, and here the electrode tab has a small rebound, the electrolyte is sufficient, and the liquid-phase active ions migrate quickly; on the interface between the first graphite and the second graphite, the active ions can perform solid-phase diffusion through the exposed side wall of the second graphite, which is beneficial to improve the rate performance of the secondary battery.

[0085] 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.

[0086] In some embodiments, the full-charge thickness rebound rate of the negative electrode tab corresponding to the first film region is 10% to 16%. In some embodiments, the full-charge thickness rebound rate of the negative electrode tab corresponding to the second film region is 17% to 22%.

[0087] It should be noted that the cold-pressed thickness of the first film region and the second film region in the initial state is the same.

[0088] In some embodiments, the full-charge thickness rebound rate can be tested in reverse as follows: take two secondary batteries of the same batch, disassemble one of the secondary batteries after full charging, obtain the negative electrode sheet, and measure the thickness H0 of the negative electrode sheet at this time; disassemble the other secondary battery after full charging, obtain the negative electrode sheet, and measure the thickness H1 of the first film region and the thickness H2 of the second film region of the negative electrode sheet at this time; the full-charge thickness rebound rate of the first film region φ1 = (H1 - H0) / H0 * 100%; the full-charge thickness rebound rate of the second film region φ2 = (H2 - H0) / H0 * 100%.

[0089] In some embodiments, the negative electrode film layer can further optionally comprise a conductive agent. The conductive agent can be selected from at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0090] In some embodiments, the negative electrode film layer can further optionally comprise a binder. The binder can 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).

[0091] In some embodiments, the negative electrode film layer can further optionally comprise other auxiliary agents, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0092] The content of the binder and / or other auxiliary agents, if any, in the negative electrode film layer is not particularly limited in the present application. A person skilled in the art can determine a suitable content of the binder and / or other auxiliary agents through routine experiments in the art.

[0093] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as a metal foil, a copper foil can be used. The composite current collector can comprise 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 can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material base layer (such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0094] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the first graphite, the conductive agent, the binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry of the first film region, dispersing the second graphite, the conductive agent, the binder and any other components in a solvent (e.g., deionized water) to form a negative electrode slurry of the second film region, simultaneously coating the first slurry and the second slurry on the negative electrode current collector using a special structure coating machine, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0095] The above embodiments are described by way of example with respect to the composition of the negative electrode film layer on one side surface of the negative electrode current collector. It should be understood that the negative electrode current collector has two opposite surfaces in the thickness direction thereof, 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 parameters (e.g., the compacted density, the area density, the porosity, the thickness, etc.) of each negative electrode film layer given in the present application refer to the parameters of the negative electrode film layer on one 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 any one side thereof meet the present application, and it is considered to fall within the protection scope of the present application.

[0096] In the present application, the negative electrode sheet described above does not exclude that other additional functional layers can be included in addition to the above-mentioned 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) arranged on the surface of the above-mentioned negative electrode current collector and sandwiched between the above-mentioned negative electrode current collector and the above-mentioned negative electrode film layer; in some embodiments, the negative electrode sheet further includes a protective layer covering the surface of the above-mentioned negative electrode film layer.

[0097] [Positive electrode sheet]

[0098] 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.

[0099] As an example, the positive electrode current collector has two opposite surfaces in the thickness direction thereof, and the positive electrode film layer is arranged on any one or both of the two opposite surfaces of the positive electrode current collector.

[0100] In some embodiments, the cathode current collector can employ a metal foil or a composite current collector. For example, as a metal foil, an aluminum foil can be employed. The composite current collector can 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 can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0101] In some embodiments, the cathode active material can employ a cathode active material for a lithium ion battery known in the art. As an example, the cathode active material can include at least one of a lithium-containing phosphate of an olivine structure, a lithium transition metal oxide, and a modified compound of each thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery cathode active material can also be used. These cathode active materials can be used alone only one or in combination of two or more. Among them, examples of the lithium transition metal oxide can include, but are not limited to, lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., 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 (e.g., LiNi 0.85 Co 0.01 Al 0.05O2) and modified compounds thereof, etc. Examples of the lithium-containing phosphate having an olivine structure can include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (which can also be referred to as LFP)), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite of lithium manganese iron phosphate and carbon.

[0102] The battery will be accompanied by Li de-intercalation and consumption during charging and discharging, and the molar content of Li is different when the battery is discharged to different states. In the enumeration of the positive electrode active material in the present application, the molar content of Li is the initial state of the material, i.e., the state before feeding. When the positive electrode active material is applied to the battery system, the molar content of Li will change after charging and discharging cycles.

[0103] In the enumeration of the positive electrode active material in the present application, the molar content of oxygen is only the theoretical state value, and the release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of oxygen will fluctuate. The molar content of other elements also changes after the battery is manufactured and used. Therefore, the ratio of the molar amounts of the elements in the molecular formula of the above positive electrode active material is the ratio of the molar amounts when prepared.

[0104] In some embodiments, the positive electrode film layer can also optionally include a binder. As an example, the binder can 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.

[0105] In some embodiments, the positive electrode film layer can also optionally include a conductive agent. As an example, the conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0106] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode sheet can be obtained.

[0107] [Electrolyte]

[0108] The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The present application does not have specific limitations on the type of electrolyte, which can be selected as needed. For example, the electrolyte can be liquid.

[0109] In some embodiments, the electrolyte employs an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0110] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoroboric oxalate, lithium bisoxalate borate, lithium difluorophosphate bisoxalate, and lithium tetrafluorophosphate oxalate.

[0111] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl 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, cyclobutane sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0112] In some embodiments, the electrolyte solution can further optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive capable of improving certain performance of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0113] [Separator]

[0114] In some embodiments, the battery cell further includes a separator. The type of the separator is not particularly limited in the present application, and any known porous structure separator having good chemical stability and mechanical stability can be used.

[0115] 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, and is not particularly limited. When the separator is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0116] In some embodiments, the positive electrode tab, the negative electrode tab, and the separator can be made into an electrode assembly through a lamination process.

[0117] In some embodiments, the battery cell can include an outer package. The outer package can be used to package the electrode assembly and the electrolyte described above.

[0118] In some embodiments, the outer package of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the battery cell can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, etc. can be listed.

[0119] The shape of the battery cell is not particularly limited, and can be cylindrical, square, or any other shape. For example, Figure 7 is a square structure battery cell 5 as an example.

[0120] In some embodiments, referring to Figure 8 , the outer package can include a shell 51 and a top cover assembly 53. The shell 51 can 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 communicating with 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 separator film can form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and the skilled person in the art can select according to the specific actual demand.

[0121] In some embodiments, the battery cell can be assembled into a battery module, and the number of battery cells contained in the battery module can be one or more, and the specific number can be selected by the skilled person in the art according to the application and capacity of the battery module.

[0122] Figure 9 is a battery module 4 as an example. Referring to Figure 9 , in the battery module 4, a plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, it can also be arranged in any other way. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0123] Optionally, the battery module 4 can also include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0124] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by the skilled person in the art according to the application and capacity of the battery pack.

[0125] Figure 10 and Figure 11 is a battery pack 1 as an example. Referring to Figure 10 and Figure 11 , the battery pack 1 can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be covered on the lower box body 3 to form a closed space for accommodating the battery module 4. The plurality of battery modules 4 can be arranged in the battery box in any way.

[0126] A second aspect of the embodiments of the present application provides a power consuming device including the secondary battery provided by each of the above embodiments. The secondary battery can be used as a power source of the power consuming device, or can be used as an energy storage unit of the power consuming device. The power consuming device can include a mobile device (e.g., a cell phone, a notebook computer, etc.), an electric vehicle (e.g., 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.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0127] As the power consuming device, a battery cell, a battery module, or a battery pack can be selected according to the use requirement thereof.

[0128] Figure 12 The power consuming device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the requirement of high power and high energy density of the secondary battery for the power consuming device, a battery pack or a battery module can be used.

[0129] The device as another example can be a cell phone, a tablet computer, a notebook computer, etc. The device generally requires thinness, and a battery cell can be used as a power source.

[0130] Embodiments

[0131] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are for the purpose of explanation of the present application, and should not be understood as a limitation of the present application. In the embodiments, unless a specific technique or condition is specified, the technique or condition described in the literature in the art or according to the product manual is used. Unless the manufacturer of the reagent or instrument is specified, it is a general product that can be obtained on the market.

[0132] Example 1

[0133] Preparation of the negative electrode sheet: the first graphite (OI value of 14) and the conductive agent carbon black, the binder SBR and the thickening agent CMC were added in a weight ratio of 94.5:1:2.25:2.25, and an appropriate amount of solvent deionized water was added, stirred uniformly to obtain the first slurry; the second graphite (OI value of 17) and the conductive agent carbon black, the binder SBR and the thickening agent CMC were added in a weight ratio of 94.5:1:2.25:2.25, and an appropriate amount of solvent deionized water was added, stirred uniformly to obtain the second slurry; the first slurry and the second slurry were uniformly coated on the surface of the copper foil, and dried, cold-pressed to obtain the negative electrode sheet composed of the first film area (corresponding to the first slurry) and the second film area (corresponding to the second slurry) arranged alternately 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 in 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.

[0134] Preparation of the positive electrode sheet: LiFePO4 and the conductive agent acetylene black, the binder PVDF were added in a weight ratio of 96:2:2, and an appropriate amount of solvent NMP was added, stirred uniformly to obtain the positive electrode slurry; the positive electrode slurry was coated on the aluminum foil, and after coating, dried, cold-pressed to obtain the positive electrode sheet.

[0135] Separator film: a polyethylene film of 12 μm.

[0136] Electrolyte: dimethyl carbonate (DMC), methyl ethyl 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.

[0137] Preparation of the lithium ion secondary battery: the above prepared positive electrode sheet, the separator film and the negative electrode sheet were placed in order, with the separator film between the positive and negative electrode sheets to play a separating role, and were processed and molded, packaged with an aluminum plastic bag, injected with the electrolyte, and after packaging, the formation capacity was measured to prepare a soft package battery.

[0138] Characterization of the negative electrode film layer

[0139] Firstly, the above secondary battery was fully charged with a current of 0.3 C, and after full charging, the thickness of the first film area and the second film area after full charging was measured, and was recorded as H1 and H2 respectively. The thickness rebound rate of the first film area was (H1-THK) / THK×100%, and the thickness rebound rate of the second film area was (H2-THK) / THK×100%, wherein THK was the initial cold-pressed thickness of the negative electrode sheet.

[0140] In Embodiment 1 of the present application, the angle θ between the extension direction (i.e. the coating direction) of the first film region and the second film region and the TD direction is 45 degrees during the coating process, so f(θ) is 1 (calculated according to the aforementioned formula (4)). After cold pressing, the initial thickness THK of the negative electrode tab is 180 μm, and after full charging, the full charging thickness rebound rate of the first film region is 16.0% according to the aforementioned full charging thickness rebound rate test, and the full charging thickness rebound rate of the second film region is 22.0%, so the difference between the full charging thickness rebound rates of the first film region and the second film region is 6%, and the full charging thickness rebound rate of the second film region is 22.0%, so the difference between the full charging thickness rebound rates of the first film region and the second film region is 6%, and the full charging thickness rebound rate of the second film region is 22.0%, so the difference between the full charging thickness rebound rates of the first film region and the second film region is 6%,

[0141] Lithium ion secondary battery performance test

[0142] 1) 2C charge capacity retention rate

[0143] The following steps were performed on the aforementioned secondary battery at 25°C:

[0144] ① Stand for 30 minutes;

[0145] ② 0.33C constant current charging to 3.65V;

[0146] ③ Stand for 30 minutes;

[0147] ④ 0.33C constant current discharging to 2.5V, and record the discharge capacity CO;

[0148] ⑤ Stand for 30 minutes;

[0149] ⑥ 2C constant current charging to 3.65V;

[0150] ⑦ Stand for 30 minutes;

[0151] ⑧ 0.33C constant current discharging to 2.5V, and record the discharge capacity CI;

[0152] ⑨ Stand for 30 minutes;

[0153] 2C charge capacity retention rate (%) = CO / CI * 100%.

[0154] 2) Cycle performance

[0155] Fixed using a test fixture, the pressure of the test fixture was 0.65 MPa, and the following test steps were performed at 25°C:

[0156] ① Stand for 30 minutes;

[0157] ​​②1C constant current charging to 3.65V;

[0158] ③Rest for 30 minutes;

[0159] ④1C constant current discharging to 2.5V, record the discharge capacity D0;

[0160] ⑤Rest for 30 minutes;

[0161] ⑥Cycle ②-⑤, and record the discharge capacity Dn in each full cycle;

[0162] The test end condition is that the capacity retention rate D0 / Dn*100% is less than 80%.

[0163] The cycle number when the cycle capacity retention rate is less than 80% is the cycle number at the test end.

[0164] Comparative Example 1

[0165] The lithium ion secondary battery was prepared according to the same method as in Example 1, except that the OI values of the graphites in the first film region and the second film region in the negative electrode film layer in the negative electrode sheet were the same, both being 14. See Table 1 below for details.

[0166] The parameters of the negative electrode sheets prepared in the above Example 1 and Comparative Example 1 are shown in Table 1 below, and the test results of the lithium ion secondary batteries are shown in Table 2 below.

[0167] Table 1:

[0168]

[0169] Table 2:

[0170]

[0171] From Table 1 above, it can be seen that, compared with Comparative Example 1 (the OI values of the graphites in the first film region and the second film region are the same), by setting the graphites in the first film region and the second film region in Example 1 to have a suitable OI difference, the kinetic performance and cycle performance of the secondary battery can be significantly improved.

[0172] Examples 2-4

[0173] The lithium ion secondary battery was prepared according to the same method as in Example 1, except that the angles θ between the extension directions of the first film region and the second film region and the TD direction in the negative electrode sheet were different. See Table 3 below for details.

[0174] Comparative Example 2

[0175] The lithium ion secondary battery was prepared according to the same method as in Example 1, except that the angle θ between the extension directions of the first film region and the second film region and the TD direction in the negative electrode sheet was 0°. See Table 3 below for details.

[0176] The test results of the lithium ion secondary batteries prepared in Examples 2-4 and Comparative Example 2 are shown in Table 3 below.

[0177] Table 3:

[0178]

[0179] As can be seen from Table 3, compared with Comparative Example 2 (the angle between the extension direction of the first film region and the second film region and the TD direction is 0°), when the angle between the extension direction of the first film region and the second film region and the TD direction is an acute angle, the wettability of the electrolyte is reduced and the climbing ability of the electrolyte is improved, thus the dynamic performance and the cycle performance of the secondary battery can be obviously improved. In addition, although the theoretical liquid storage capacity in the unit selected region of Example 4 and Comparative Example 2 is the same, in Example 4, the wettability of the electrolyte is lower and the cycle performance is better than that of Comparative Example 2, because the wettability path formed by the space above the first film region extends horizontally in the full charged state, so that when the battery is placed vertically, the electrolyte will flow to the bottom of each wettability path, but not to the bottom of the entire battery.

[0180] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration and exerting the same effects as the technical idea within the scope of the technical solutions of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications that can be thought of by those skilled in the art, other modes constructed by combining part of the elements of the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery comprising a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector; characterized in that: The negative electrode film layer includes 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, characterized in that The angle is 23° to 67°.

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

5. The secondary battery according to any one of claims 1 to 4, characterized in that: 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, characterized in that 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, characterized in that 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, characterized in that: 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, characterized in that: The full-charge thickness rebound rate of the negative electrode sheet corresponding to the second film region is 17% to 22%.

10. An electrical device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 1 to 9.

Images