Negative pole piece, secondary battery and electric device

Abstract

The invention provides a negative pole piece, a secondary battery and an electric device. The negative electrode plate comprises a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, the negative electrode film layer is internally provided with a negative electrode active material, and the negative electrode active material comprises graphite; the negative electrode film layer comprises a first region, a second region and a third region, and the first region, the second region and the third region are sequentially arranged in the first direction; the negative pole piece meets at least one of the following conditions: the graphitization degree of graphite in the first region and the third region is greater than the graphitization degree of graphite in the second region; the graphite volume particle size distribution Dv50 in the first area and the third area is greater than the graphite Dv50 in the second area; the OI value of graphite in the first area and the third area is greater than the OI value of graphite in the second area; when the secondary battery is assembled by taking the first direction as the width direction of the negative pole piece disclosed by the invention, lithium precipitation in the middle of the negative pole piece in the use process of the secondary battery can be relieved, and the cycle performance of the secondary battery is improved.

Description

Technical Field

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

[0002] In recent years, as the application scope of secondary batteries becomes wider and wider, secondary batteries are widely used in energy storage power supply systems such as hydropower, thermal power, wind power and solar power stations, as well as in many fields such as electric tools, electric bicycles, electric motorcycles and electric vehicles.

[0003] As secondary batteries have made great progress, higher requirements have been put forward for their cycle performance. Batteries with excellent cycle performance have very high requirements for negative electrode plates. During the use of current secondary batteries, lithium deposition is prone to occur on the negative electrode plates. If the deposited lithium continues to accumulate on the negative electrode plates, it is easy to cause the isolation membrane to be punctured, affecting the cycle performance of the secondary battery.

[0004] Therefore, seeking for secondary batteries with better cycle performance is one of the key areas of focus for those skilled in the art. Summary of the invention

[0005] The present application is made in view of the above-mentioned problems, and one of its purposes is to provide a negative electrode plate, which can alleviate the lithium plating of the negative electrode plate during the use of the secondary battery, thereby improving the cycle performance of the secondary battery.

[0006] In order to achieve the above-mentioned object, the first aspect of the present application provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer has a negative electrode active material, and the negative electrode active material comprises graphite; the negative electrode film layer comprises a first region, a second region and a third region, and the first region, the second region and the third region are arranged in sequence in a first direction;

[0007] Wherein, the negative electrode plate satisfies at least one of the following:

[0008] (1) The graphitization degree of the graphite in the first region and the third region is greater than the graphitization degree of the graphite in the second region;

[0009] (2) the volume particle size distribution Dv50 of the graphite in the first region and the third region is greater than the volume particle size distribution Dv50 of the graphite in the second region;

[0010] (3) The OI values ​​of the graphite in the first region and the third region are both greater than the OI value of the graphite in the second region.

[0011] The present application divides the negative electrode film layer into multiple regions along a first direction, and sets the graphitization degree of the negative electrode active material graphite in the first region and the third region at both ends to be greater than the graphitization degree of the graphite in the second region in the middle, and / or the volume particle size distribution Dv50 of the graphite in the first region and the third region is greater than the volume particle size distribution Dv50 of the graphite in the second region, and / or the OI value of the graphite in the first region and the third region is greater than the OI value of the graphite in the second region; when the first direction is used as the width direction of the negative electrode plate to be assembled into a battery, the secondary battery is not prone to lithium deposition in the middle of the negative electrode plate during the cycle process, thereby effectively alleviating the problem of easy lithium deposition in the middle of the negative electrode plate and improving the cycle performance of the secondary battery.

[0012] In any embodiment, the graphitization degree of the graphite in the first region is a1, the graphitization degree of the graphite in the third region is a2, the graphitization degree of the graphite in the second region is b, 0<a1-b<40%, 0<a2-b<40%. In this way, the cycle performance of the secondary battery can be further improved.

[0013] In any embodiment, 5%<a1-b<20%; 5%<a2-b<20%, which can further improve the cycle performance of the secondary battery.

[0014] In any embodiment, the graphitization degree of the graphite in the first region and the third region is independently 65% ​​to 100%; the graphitization degree of the graphite in the second region is 60% to 90%. In this way, the cycle performance of the secondary battery can be effectively improved.

[0015] In any embodiment, the volume particle size distribution Dv50 of the graphite in the first region is c1, the volume particle size distribution Dv50 of the graphite in the third region is c2, and the volume particle size distribution Dv50 of the graphite in the second region is d, 0<c1-d<10.0μm, 0<c2-d<10.0μm. In this way, the lithium deposition problem in the middle of the negative electrode sheet can be better improved, and the cycle performance of the secondary battery can be further improved.

[0016] In any embodiment, 2 μm<c1-d<8.0 μm, and 2 μm<c2-d<8.0 μm. In this way, the cycle performance of the secondary battery can be further improved.

[0017] In any embodiment, the volume particle size distribution Dv50 of the graphite in the first region and the third region is independently 7 μm to 15 μm, and the volume particle size distribution Dv50 of the graphite in the second region is 6 μm to 14.5 μm. In this way, the cycle performance of the secondary battery can be effectively improved.

[0018] In any embodiment, the OI value of the graphite in the first region is e1, the OI value of the graphite in the third region is e2, and the OI value of the graphite in the second region is f, 0<e1-f<9, 0<e2-f<9. In this way, the cycle performance of the secondary battery can be further improved.

[0019] In any embodiment, 1.5<e1-f<3.0, 1.5<e2-f<3.0. In this way, the cycle performance of the secondary battery can be further improved.

[0020] In any embodiment, the OI value of the graphite in the first region and the third region is independently 5.0 to 10.0, and the OI value of the graphite in the second region is 2.5 to 4.5. In this way, the cycle performance of the secondary battery can be effectively improved.

[0021] In any embodiment, the sizes of the first region, the second region and the third region in the first direction are g, h and i respectively, the size of the negative electrode sheet in the first direction is j, 0.1≤h / j≤0.75, 0.125≤g / j≤0.45, 0.125≤i / j≤0.45. In this way, the rapid lithium insertion ability of the negative electrode active material in the negative electrode film layer along the first direction can be more reasonably distributed, further improving the cycle performance of the secondary battery.

[0022] In any embodiment, the thickness of the negative electrode sheet is 50 μm to 400 μm.

[0023] The second aspect of the present application provides a secondary battery, comprising the negative electrode sheet of the first aspect of the present application, wherein the secondary battery is a wound battery, and the secondary battery is wound with the first direction being the width direction of the negative electrode sheet. The secondary battery has good cycle performance.

[0024] In any embodiment, the negative electrode plate has a first overhang area and a second overhang area at both end edges in the first direction respectively; the range of the first area covers the first overhang area; the range of the third area covers the second overhang area.

[0025] In any embodiment, a size of the first region in the first direction is greater than a size of the first overhang region in the first direction.

[0026] In any embodiment, a size of the third region in the first direction is greater than a size of the second overhang region in the first direction.

[0027] A third aspect of the present application provides an electrical device, comprising the secondary battery of the second aspect of the present application.

[0028] The negative electrode plate of the present application is formed by dividing the negative electrode film layer into multiple regions along a first direction, and making the graphitization degree of the negative electrode active material graphite in the first region and the third region on both sides greater than the graphitization degree of the graphite in the second region in the middle, and / or the volume particle size distribution Dv50 of the graphite in the first region and the third region is greater than the volume particle size distribution Dv50 of the graphite in the second region, and / or the OI value of the graphite in the first region and the third region is greater than the OI value of the graphite in the second region; when the first direction is used as the width direction of the negative electrode plate to be assembled to form a secondary battery, the secondary battery is not prone to lithium deposition in the middle of the negative electrode plate during the cycle process, which can improve the cycle performance of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a plan view of a negative electrode sheet according to an embodiment of the present application;

[0030] Figure 2 is a cross-sectional view of a negative electrode sheet along the thickness direction according to an embodiment of the present application;

[0031] Figure 3 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0032] Figure 4 yes Figure 3 An exploded view of a secondary battery according to an embodiment of the present application is shown;

[0033] Figure 5 FIG. 1 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present application as a power source.

[0034] Description of reference numerals:

[0035] 1. Negative electrode plate; 11. Negative electrode current collector; 12. Negative electrode film layer; 121. First region; 122. Second region; 123. Third region; 124. First overhang region; 125. Second overhang region; 5. Secondary battery; 51. Shell; 52. Electrode assembly; 53. Cover plate; 6. Electrical device. DETAILED DESCRIPTION

[0036] Below, some embodiments of the isolation membrane, secondary battery and electrical device of the present application are described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0037] The "range" disclosed in the present application can be defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The range defined in this way can be inclusive or exclusive of the end values, and any end value can be included or excluded independently, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a specific parameter, it is understood that the range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are also listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to listing the parameter as, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0038] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0039] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments. The "implementation methods" mentioned herein have a similar understanding.

[0040] Those skilled in the art will appreciate that, in the methods of each embodiment or example, the order in which each step is written does not mean a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible internal logic. If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) can be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0041] In the present application, in the open technical features or technical solutions described by the words "contain", "include", "comprise", etc., unless otherwise specified, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions including additional members in addition to the listed members. For example, A includes a1, a2 and a3. Unless otherwise specified, it may also include other members or may not include additional members. It can be regarded as providing both the feature or solution of "A consists of a1, a2 and a3" and the feature or solution of "A not only includes a1, a2 and a3, but also includes other members". In the present application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0042] In this application, "optionally", "optional", and "optional" mean optional, that is, any one of the two parallel schemes of "yes" or "no". If there are multiple "options" in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "option" is independent.

[0043] The weights described in the embodiments of the present application may be μg, mg, g, kg, or other weight units known in the chemical industry.

[0044] At present, lithium deposition is easy to occur on the negative electrode sheet of secondary batteries during use. If the lithium deposited on the negative electrode sheet continues to accumulate on the negative electrode sheet, it is easy to cause the separator to be punctured, which brings great safety hazards to the secondary battery and affects the cycle performance of the secondary battery. In this regard, the present application proposes a negative electrode sheet, which can effectively improve the lithium deposition phenomenon on the negative electrode sheet of the secondary battery during use, thereby improving the safety performance and cycle performance of the secondary battery.

[0045] See also Figure 1 and Figure 2 In one embodiment of the present application, there is provided a negative electrode plate 1, which includes a negative electrode current collector 11 and a negative electrode film layer 12 arranged on at least one surface of the negative electrode current collector 11, wherein the negative electrode film layer 12 contains a negative electrode active material, and the negative electrode active material includes graphite; the negative electrode film layer 12 includes a first region 121, a second region 122 and a third region 123; the first region 121, the second region 122 and the third region 123 are arranged in sequence in a first direction; and the graphitization degree of the negative electrode active material graphite in the first region 121 and the third region 123 is greater than the graphitization degree of the graphite in the second region 122; and / or the volume particle size distribution Dv50 of the graphite in the first region 121 and the third region 123 is greater than the volume particle size distribution Dv50 of the graphite in the second region 122; and / or the OI value of the graphite in the first region 121 and the third region 123 is greater than the OI value of the graphite in the second region 122.

[0046] During the cycle of the secondary battery, the uneven temperature and expansion force of different parts of the negative electrode plate 1 will lead to uneven polarization distribution in the width direction of the negative electrode plate 1. Specifically, in the wound negative electrode plate, due to the influence of heat dissipation, the temperature in the middle of the negative electrode plate 1 is generally higher, the expansion force is larger, and the polarization is smaller; while the two ends of the negative electrode plate 1 along the width direction have lower temperatures, smaller expansion forces, and larger polarization. Affected by the above uneven polarization distribution, lithium ions tend to diffuse and embed lithium in the middle of the negative electrode plate 1 during the cycle of the secondary battery, so that the amount of lithium embedded in the two ends of the negative electrode plate 1 along the width direction is lower than that in the middle, making it easy for lithium precipitation to occur in the middle of the negative electrode plate 1, affecting the cycle performance of the secondary battery.

[0047] The negative electrode film layer 12 of the negative electrode plate 1 mentioned above in the present application includes a first region 121, a second region 122 and a third region 123; the first region 121, the second region 122 and the third region 123 are arranged in sequence in the first direction, and the graphitization degree of the negative electrode active material graphite in the first region 121 and the third region 123 is greater than the graphitization degree of the graphite in the second region 122; and / or the volume particle size distribution Dv50 of the graphite in the first region 121 and the third region 123 is greater than the volume particle size distribution Dv50 of the graphite in the second region 122; and / or the OI value of the graphite in the first region 121 and the third region 123 is greater than the OI value of the graphite in the second region 122. In this way, when the first direction is used as the width direction of the negative electrode plate 1 to assemble a secondary battery, the rapid lithium insertion capability in the second region in the middle of the negative electrode plate 1 can be improved, so that the secondary battery is not prone to lithium deposition in the middle of the negative electrode plate 1 during the cycle process, thereby effectively alleviating the problem of easy lithium deposition in the middle of the negative electrode plate 1 and improving the cycle performance of the secondary battery.

[0048] In some of the embodiments, the graphitization degree of the graphite in the first region 121 and the third region 123 is greater than the graphitization degree of the graphite in the second region 122. The degree of graphitization of the negative electrode active material graphite has a significant effect on the rapid lithium insertion ability of the graphite. Carbon materials will form an ordered layered structure after graphitization, and lithium ions can be embedded in the graphite interlayer when used as negative electrode active materials. Generally speaking, the lower the graphitization degree of the graphite, the higher the disorder between the material layers, and the better its fast charging performance. By setting the graphitization degree of the graphite in the first region 121 and the third region 123 of the negative electrode plate 1 to be greater than the graphitization degree of the graphite in the second region 122, the fast charging performance of the graphite in the second region 122 can be made greater than the fast charging capacity of the graphite in the first region 121 and the third region 123, thereby improving the lithium precipitation problem in the middle of the negative electrode plate 1 and improving the cycle performance of the secondary battery.

[0049] In some embodiments, the graphite degree of the graphite in the first region 121 is a1, the graphite degree of the graphite in the third region 123 is a2, the graphite degree of the graphite in the second region 122 is b, 0<a1-b<40%, 0<a2-b<40%. In this way, the lithium deposition problem in the middle of the negative electrode plate 1 can be further improved, and the cycle performance of the secondary battery can be further improved.

[0050] In some embodiments, 5%<a1-b<20%; 5%<a2-b<20%. In this way, the lithium deposition problem in the middle of the negative electrode plate 1 can be further improved, and the cycle performance of the secondary battery can be further improved.

[0051] In some embodiments, the graphitization degree of the graphite in the first region 121 and the third region 123 is independently 65% ​​to 100%; the graphitization degree of the graphite in the second region 122 is 60% to 90%. The graphitization degree of the graphite in the first region 121, the second region 122, and the third region 123 is within the above range, which can further improve the lithium deposition problem in the middle of the negative electrode plate 1 and further improve the cycle performance of the secondary battery.

[0052] In some of the embodiments, the volume particle size distribution Dv50 of the graphite in the first region 121 and the third region 123 is greater than the volume particle size distribution Dv50 of the graphite in the second region 122. The particle size of the negative electrode active material graphite has a significant effect on the rapid lithium insertion ability of the graphite. Within a certain particle size range, the smaller the volume particle size distribution Dv50 of the graphite, the greater its rapid lithium insertion ability. By setting the volume particle size distribution Dv50 of the graphite in the first region 121 and the third region 123 of the negative electrode plate 1 to be greater than the volume particle size distribution Dv50 of the graphite in the second region 122, the rapid lithium insertion ability of the graphite in the second region 122 can be made greater than the rapid lithium insertion ability of the graphite in the first region and the third region, thereby improving the lithium precipitation problem in the middle of the negative electrode plate 1 and improving the safety and cycle performance of the secondary battery.

[0053] It should be noted that the volume particle size distribution Dv50 refers to the value of the particle size at which the cumulative volume of the material particles reaches 50% from the small particle size side in the volume-based particle size distribution.

[0054] In some embodiments, the graphite volume particle size distribution Dv50 in the first region 121 of the negative electrode plate 1 is c1, the graphite volume particle size distribution Dv50 in the third region 123 is c2, and the graphite volume particle size distribution Dv50 in the second region 122 is d, and 0<c1-d<10.0μm, 0<c2-d<10.0μm. The relative size of the graphite volume particle size distribution Dv50 in the first region 121, the second region 122, and the third region 123 of the negative electrode plate 1 is within the above range, which can better improve the lithium deposition problem in the middle of the negative electrode plate 1 and further improve the cycle performance of the secondary battery.

[0055] In some embodiments, 2 μm<c1-d<8.0 μm, 2 μm<c2-d<8.0 μm. In this way, the lithium deposition problem in the middle of the negative electrode plate 1 can be further improved, and the cycle performance of the secondary battery can be further improved.

[0056] In some embodiments, the graphite volume particle size distribution Dv50 in the first region 121 and the third region 123 is independently 7 μm to 15 μm; the graphite volume particle size distribution Dv50 in the second region 122 is 6 μm to 14.5 μm. The graphite volume particle size distribution Dv50 in the first region 121, the second region 122, and the third region 123 is within the above range, which can further improve the lithium deposition problem in the middle of the negative electrode plate 1 and further improve the cycle performance of the secondary battery.

[0057] In some of the embodiments, the OI value of the graphite in the first region 121 and the third region 122 is greater than the OI value of the graphite in the second region 122. Generally, the smaller the OI value of the graphite material, the more conducive it is to the diffusion and embedding of lithium ions, and the larger the OI value, the less conducive it is to the diffusion and embedding of lithium ions. The present application sets the OI value of the graphite in the first region 121 and the third region 122 to be greater than the OI value of the graphite in the second region 122, so that the lithium ion diffusion and rapid lithium insertion capabilities of the active material in the second region located in the middle of the electrode are better than those on both sides of the first direction, thereby improving the problem of lithium precipitation in the middle of the negative electrode 1 and improving the safety and cycle performance of the secondary battery.

[0058] It should be noted that the OI value of graphite refers to the graphite orientation index, which represents the peak intensity ratio of the 004 peak to the 110 peak of the graphite material (i.e., I 004 / I 110 ). Among them, I 004 It represents the peak intensity of (004) crystal plane of graphite material in X-ray diffraction, I 110 It represents the peak intensity of the (110) crystal plane of graphite material during X-ray diffraction.

[0059] In some embodiments, the OI value of graphite in the first region 121 is e1, the OI value of graphite in the third region 123 is e2, and the OI value of graphite in the second region 122 is f, 0<e1-f<9, 0<e2-f<9. In this way, the lithium deposition problem in the middle of the negative electrode plate 1 can be further improved, and the cycle performance of the secondary battery can be further improved.

[0060] In some embodiments, 1.5<e1-f<3.0, 1.5<e2-f<3.0. In this way, the lithium deposition problem in the middle of the negative electrode plate 1 can be further improved, and the cycle performance of the secondary battery can be further improved.

[0061] In some embodiments, the OI value of the graphite in the first region 121 and the third region 123 is independently 5.0 to 10.0; the OI value of the graphite in the second region 122 is 2.5 to 4.5. The OI values ​​of the graphite in the first region 121, the second region 122, and the third region 123 are within the above range, which can further improve the lithium deposition problem in the middle of the negative electrode plate 1 and further improve the cycle performance of the secondary battery.

[0062] In some embodiments, the size of the first region 121 along the first direction is g, the size of the second region 122 along the first direction is h, the size of the third region 123 along the first direction is i, the size of the negative electrode plate 1 along the first direction is j, 0.1≤h / j≤0.75, 0.125≤g / j≤0.45, 0.125≤i / j≤0.45. The ratio of the size of the first region 121, the second region 122 and the third region 123 along the first reverse direction to the size of the negative electrode plate 1 along the first direction is within the above range, which can make the distribution of the rapid lithium insertion ability of the negative electrode active material in the negative electrode film layer 12 along the first direction more reasonable, further improve the lithium precipitation problem in the middle of the negative electrode plate 1, and further improve the cycle performance of the secondary battery.

[0063] In some embodiments, the thickness of the negative electrode plate 1 is 50 μm to 400 μm. It can be understood that the thickness of the negative electrode plate 1 includes the thickness of the negative electrode current collector 11 and the sum of the thickness of the negative electrode film layer 12 on the upper and lower surfaces of the negative electrode current collector 11. The thickness of the negative electrode plate 1 can be, but is not limited to, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 120 μm, 140 μm, 160 μm, 180 μm, 200 μm, 220 μm, 240 μm, 260 μm, 280 μm, 300 μm, 320 μm, 340 μm, 360 μm, 380 μm, 400 μm.

[0064] The second aspect of the present application also provides a secondary battery, which includes the negative electrode sheet 1 of the first aspect of the present application, and the secondary battery is a wound battery, and the secondary battery is wound with the first direction being the width direction of the negative electrode sheet. Therefore, the secondary battery has good safety and cycle performance.

[0065] See also Figure 1 In some embodiments, the negative electrode plate 1 has a first overhang area 124 and a second overhang area 125 at both end edges along the first direction respectively; the range of the first area 121 covers the first overhang area 124, and the range of the third area 123 covers the second overhang area 125.

[0066] Furthermore, in some embodiments, the size of the first region 121 along the first direction is larger than the size of the first overhang region 124 along the first direction; the size of the third region 123 along the first direction is larger than the size of the second overhang region 125 along the first direction.

[0067] In other words, the first region 121 of the negative electrode plate 1 in the secondary battery of the present application includes the first overhang region 124 and part of the non-overhang region; similarly, the third region 123 includes the second overhang region 125 and part of the non-overhang region; and the second region 122 is within the non-overhang region.

[0068] It should be noted that the overhang area refers to the area on the negative electrode sheet 1 that does not overlap with the positive electrode sheet after the negative electrode sheet 1 and the positive electrode sheet are wound together, and the non-overhang area refers to the area on the negative electrode sheet 1 that overlaps with the positive electrode sheet after the negative electrode sheet 1 and the positive electrode sheet are wound together.

[0069] The third aspect of the present application further provides an electrical device, which comprises the secondary battery of the second aspect of the present application.

[0070] The secondary battery and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0071] Unless otherwise specified, the components, material types or contents of the batteries mentioned are applicable to both lithium-ion secondary batteries and sodium-ion secondary batteries.

[0072] In one embodiment of the present application, a secondary battery is provided.

[0073] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0074] Positive electrode

[0075] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector.

[0076] 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 any one or both of the two opposite surfaces of the positive electrode current collector.

[0077] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material on a polymer material substrate. Among them, the metal material includes but is not limited to aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc. Polymer material substrate (such as substrates of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.)

[0078] In some embodiments, the positive electrode active material may include a positive electrode active material for a battery known in the art.

[0079] As an example, the positive electrode active material of a lithium-ion secondary battery may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt 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 0.15 Al 0.05O2) and its modified compounds, etc. Examples of lithium-containing phosphates with an olivine structure 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.

[0080] As an example, the positive electrode active material of the sodium ion secondary battery may include at least one of the following materials: at least one of a sodium transition metal oxide, a polyanionic compound, and a Prussian blue compound. However, the present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium ion batteries may also be used.

[0081] As an optional technical solution of the present application, in the sodium transition metal oxide, the transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. The sodium transition metal oxide is, for example, Na x MO2, wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0<x≤1.

[0082] As an optional technical solution of the present application, the polyanionic compound can be a compound having sodium ions, transition metal ions and tetrahedral (YO4) n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; Y can be at least one of P, S and Si; n represents (YO4) n- valence state.

[0083] Polyanionic compounds can also be those with sodium ions, transition metal ions, tetrahedral (YO4) n- A class of compounds containing anion units and halogen anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; Y can be at least one of P, S and Si, and n represents (YO4) n- valence state; the halogen may be at least one of F, Cl and Br.

[0084] Polyanionic compounds can also be sodium ions, tetrahedral (YO4) n- Anion unit, polyhedral unit (ZO y ) m+ and an optional halogen anion. Y can be at least one of P, S and Si, and n represents (YO4) n-valence state; Z represents a transition metal, which may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; m represents (ZO y ) m+ valence state; the halogen may be at least one of F, Cl and Br.

[0085] Polyanionic compounds include NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2 (P2O7), NaM'PO4F (M' is one or more of V, Fe, Mn and Ni) and Na3(VO y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0086] Prussian blue compounds can be sodium ions, transition metal ions and cyanide ions (CN - ). The transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Prussian blue compounds are, for example, Na a Me b Me' c (CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0<a≤2, 0<b<1, 0<c<1.

[0087] The weight ratio of the positive electrode active material in the positive electrode film layer is 80 to 100 weight %, based on the total weight of the positive electrode film layer.

[0088] In some embodiments, the positive electrode film layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin. The weight ratio of the binder in the positive electrode film layer is 0 to 20 weight%, based on the total weight of the positive electrode film layer.

[0089] In some embodiments, the positive electrode film layer may further include a conductive agent. As an 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. The weight ratio of the conductive agent in the positive electrode film layer is 0-20% by weight, based on the total weight of the positive electrode film layer.

[0090] 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, wherein the positive electrode slurry has a solid content of 40wt% to 80wt%, and the viscosity at room temperature is adjusted to 5000mPa·s to 25000mPa·s, the positive electrode slurry is coated on the surface of the positive electrode collector, and after drying, the positive electrode sheet is formed by cold rolling; the positive electrode powder coating unit surface density is 150mg / m 2 ~350 mg / m 2 The compaction density of the positive electrode is 3.0g / cm 3 ~3.6g / cm 3 , optional 3.3g / cm 3 ~3.5g / cm 3 .

[0091] The calculation formula of the compacted density is:

[0092] Compacted density = coating surface density / (thickness of the electrode after extrusion - thickness of the current collector).

[0093] The mass M of the positive electrode active material per unit area of ​​the positive electrode film can be obtained by weighing using a standard balance.

[0094] The thickness T of the positive electrode film can be measured by using a micrometer, for example, a Mitutoyo 293-100 micrometer with an accuracy of 0.1 μm. It should be noted that the thickness of the positive electrode film described in this application refers to the thickness of the positive electrode film in the positive electrode sheet used for assembling the battery after cold pressing.

[0095] Negative electrode

[0096] The negative electrode plate in the secondary battery of the present application adopts the negative electrode plate of the first aspect of the present application.

[0097] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0098] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0099] 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 material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material on a polymer material substrate. Among them, the metal material includes but is not limited to copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc., and the polymer material substrate includes but is not limited to polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE) and other substrates.

[0100] 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). The weight ratio of the binder in the negative electrode film layer is 0 to 30% by weight, based on the total weight of the negative electrode film layer.

[0101] In some embodiments, the negative electrode film layer may further include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. The weight ratio of the conductive agent in the negative electrode film layer is 0 to 20 weight %, based on the total weight of the negative electrode film layer.

[0102] In some embodiments, the negative electrode film layer may further include other additives, such as a thickener (such as sodium carboxymethyl cellulose (CMC-Na)), etc. The weight ratio of the other additives in the negative electrode film layer is 0 to 15 weight %, based on the total weight of the negative electrode film layer.

[0103] 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 negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry, wherein the solid content of the negative electrode slurry is 30wt% to 70wt%, and the viscosity at room temperature is adjusted to 2000mPa·s to 10000mPa·s; the obtained negative electrode slurry is coated on the negative electrode collector, and after a drying process, cold pressing such as rolling, a negative electrode sheet is obtained. The negative electrode powder coating unit area density is 75mg / m 2 ~220 mg / m 2 , the compaction density of the negative electrode is 1.2g / m 3 ~2.0g / m 3 .

[0104] The mass M of the negative electrode active material per unit area of ​​the negative electrode film can be obtained by weighing using a standard balance.

[0105] The thickness T of the negative electrode film can be measured by using a micrometer, for example, a Mitutoyo 293-100 micrometer with an accuracy of 0.1 μm. It should be noted that the thickness of the negative electrode film described in this application refers to the thickness of the negative electrode film in the negative electrode sheet used for assembling the battery after cold pressing.

[0106] Electrolytes

[0107] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0108] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0109] In some embodiments, the electrolyte salt of the lithium ion secondary battery can be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0110] The electrolyte salt of the sodium ion secondary battery can be selected from one or more of sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium difluorophosphate, sodium perchlorate, and sodium chloride.

[0111] The concentration of the electrolyte salt is generally 0.1 mol / L to 5 mol / L.

[0112] In some embodiments, the solvent can be selected from one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

[0113] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0114] Isolation film

[0115] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0116] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0117] In some embodiments, the isolation film has a thickness of 6 μm to 40 μm, and may be 12 μm to 20 μm.

[0118] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0119] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0120] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0121] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 3 The secondary battery 5 is a square structure as an example.

[0122] In some embodiments, reference Figure 4 , the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0123] In some embodiments, the secondary batteries 5 can be assembled into a battery module. The number of secondary batteries 5 contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0124] In the battery module, the plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

[0125] Optionally, the battery module may further include a housing having a housing space, and the plurality of secondary batteries 5 are housed in the housing space.

[0126] 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 according to the application and capacity of the battery pack.

[0127] The battery pack may include a battery box and a plurality of battery modules disposed in the battery box. The battery box includes an upper box body and a lower box body, and the upper box body can be covered on the lower box body to form a closed space for accommodating the battery modules. The plurality of battery modules can be arranged in the battery box in any manner.

[0128] In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device may include 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., but are not limited thereto.

[0129] As the electrical device, a secondary battery, a battery module or a battery pack may be selected according to its usage requirements.

[0130] Figure 5 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the power consumption device for the secondary battery, a battery pack or a battery module can be used.

[0131] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0132] The following are some examples.

[0133] In order to make the technical problems, technical solutions and beneficial effects solved by the present application clearer, the present application will be further described in detail below in conjunction with the embodiments and drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present application and its applications. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0134] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the field or the product instructions are used. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0135] 1. Battery Example

[0136] Embodiment 1:

[0137] 1) Preparation of negative electrode

[0138] The negative electrode active material artificial graphite (gram capacity of 340mAh / g, volume particle size distribution Dv50=15.0μm), the conductive agent acetylene black, the binder SBR (styrene butadiene latex), and the binder CMC (carboxymethyl cellulose) are mixed in a weight ratio of 95:1.5:3.1:0.4, and the solvent deionized water is added, and the mixture is stirred and mixed to obtain negative electrode slurry 1; the negative electrode active material artificial graphite (gram capacity of 340mAh / g, volume particle size distribution Dv50=14.3μm), the conductive agent acetylene black, the binder SBR, and the binder CMC are mixed in a weight ratio of 95:1.5:3.1:0.4, and the solvent deionized water is added, and the mixture is stirred and mixed to obtain negative electrode slurry 2;

[0139] The negative electrode slurry 1 is applied to the two ends of the negative electrode current collector copper foil in the width direction, and the negative electrode slurry 2 is applied to the middle of the negative electrode current collector copper foil in the width direction; after drying and cold pressing, the negative electrode sheet is obtained. Among them, the area where the negative electrode slurry 1 is applied in the negative electrode film layer of the negative electrode sheet is the first area and the third area, and the area where the negative electrode slurry 2 is applied is the second area. The coating weight of the negative electrode film layer is 0.108g / 1540.25mm 2 (measured by weight excluding solvent). The width of the first region is 60 mm, the width of the second region is 60 mm, the width of the third region is 60 mm, the thickness of the negative electrode collector is 6 μm, the total thickness of the negative electrode sheet is 110 μm, and the thickness of the negative electrode film layer on the upper and lower sides of the negative electrode collector is equal.

[0140] 2) Preparation of positive electrode

[0141] The positive electrode active material lithium iron phosphate (gram capacity of 139 mAh / g), the conductive agent acetylene black, and the binder PVDF (polyvinylidene fluoride) were mixed in a weight ratio of 96:2:2, and the solvent N-methylpyrrolidone was added, and the mixture was stirred and mixed to obtain a positive electrode slurry. The positive electrode slurry was then coated on the positive electrode current collector aluminum foil, wherein the coating weight of the negative electrode slurry was 0.224 g / 1540.25 mm 2 (measured by weight excluding solvent), and then dried and cold pressed to obtain a positive electrode sheet.

[0142] 3) Preparation of electrolyte

[0143] In an argon atmosphere glove box with a water content of <10ppm, EC (ethylene carbonate), PC (propylene carbonate), and DMC (dimethyl carbonate) are mixed in a weight ratio of EC:PC:DMC=3:3:3, and then LiPF6, VC (vinylene carbonate), DTD (vinyl sulfate), and PS (propylene sulfite) are added to the mixed organic solvent and stirred evenly to obtain an electrolyte, wherein the concentration of LiPF6 in the lithium-ion battery electrolyte is 1 mol / L, and the mass percentages of VC, DTD, and PS are 3%, 1%, and 1%, respectively.

[0144] 4) Isolation film

[0145] A polyethylene porous membrane was used as the isolation membrane.

[0146] 5) Battery assembly

[0147] The positive electrode sheet, the separator and the negative electrode sheet are stacked in order, the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wound to obtain a bare cell. The bare cell is placed in an outer package, the prepared electrolyte is injected, and the package is packaged for formation to obtain a lithium-ion secondary battery.

[0148] Embodiment 2:

[0149] This embodiment is basically the same as embodiment 1, except that the volume particle size distribution Dv50 of the negative electrode active material graphite in the second region of the negative electrode film layer is different. In this embodiment, the volume particle size distribution Dv50 of the negative electrode active material graphite in the second region is 12.5 μm.

[0150] Embodiment 3:

[0151] This embodiment is basically the same as embodiment 1, except that the volume particle size distribution Dv50 of the negative electrode active material graphite in the second region of the negative electrode film layer is different. In this embodiment, the volume particle size distribution Dv50 of the negative electrode active material graphite in the second region is 11.7 μm.

[0152] Embodiment 4:

[0153] This embodiment is basically the same as embodiment 1, except that the volume particle size distribution Dv50 of the negative electrode active material graphite in the second region of the negative electrode film layer is different. In this embodiment, the volume particle size distribution Dv50 of the negative electrode active material graphite in the second region is 10.3 μm.

[0154] Embodiment 5:

[0155] This embodiment is basically the same as embodiment 1, except that the volume particle size distribution Dv50 of the negative electrode active material graphite in the second region of the negative electrode film layer is different. In this embodiment, the volume particle size distribution Dv50 of the negative electrode active material graphite in the second region is 8.6 μm.

[0156] Embodiment 6:

[0157] This embodiment is basically the same as embodiment 1, except that the volume particle size distribution Dv50 of the negative electrode active material graphite in the second region of the negative electrode film layer is different. In this embodiment, the volume particle size distribution Dv50 of the negative electrode active material graphite in the second region is 6.8 μm.

[0158] Embodiment 7:

[0159] 1) Preparation of negative electrode

[0160] The negative electrode active material artificial graphite (gram capacity of 340mAh / g, degree of graphitization = 90%), the conductive agent acetylene black, the binder SBR, and the binder CMC are mixed according to a weight ratio of 95:1.5:3.1:0.4, and a solvent deionized water is added, and the mixture is stirred and mixed to obtain negative electrode slurry 1; the negative electrode active material artificial graphite (gram capacity of 340mAh / g, degree of graphitization = 86%), the conductive agent acetylene black, the binder SBR, and the binder CMC are mixed according to a weight ratio of 95:1.5:3.1:0.4, and a solvent deionized water is added, and the mixture is stirred and mixed to obtain negative electrode slurry 2;

[0161] The negative electrode slurry 1 is applied to the two ends of the negative electrode current collector copper foil in the width direction, and the negative electrode slurry 2 is applied to the middle of the negative electrode current collector copper foil in the width direction; after drying and cold pressing, the negative electrode sheet is obtained. Among them, the area where the negative electrode slurry 1 is applied in the negative electrode film layer of the negative electrode sheet is the first area and the third area, and the area where the negative electrode slurry 2 is applied is the second area. The coating weight of the negative electrode film layer is 0.108g / 1540.25mm 2 (measured by weight excluding solvent). The width of the first region is 60 mm, the width of the second region is 60 mm, the width of the third region is 60 mm, the thickness of the negative electrode collector is 6 μm, the total thickness of the negative electrode sheet is 110 μm, and the thickness of the negative electrode film layer on the upper and lower sides of the negative electrode collector is equal.

[0162] 2) Preparation of positive electrode

[0163] The positive electrode active material lithium iron phosphate (gram capacity of 139 mAh / g), the conductive agent acetylene black, and the binder PVDF were mixed in a weight ratio of 96:2:2, and the solvent N-methylpyrrolidone was added, and the mixture was stirred and mixed to obtain a positive electrode slurry. The positive electrode slurry was then coated on the positive electrode current collector aluminum foil, wherein the coating weight of the negative electrode slurry was 0.224 g / 1540.25 mm 2 (measured by weight excluding solvent), and then dried and cold pressed to obtain a positive electrode sheet.

[0164] 3) Preparation of electrolyte

[0165] In an argon atmosphere glove box with a water content of <10ppm, EC, PC, and DMC were mixed in a weight ratio of EC:PC:DMC=3:3:3, and then LiPF6, VC, DTD, and PS were added to the mixed organic solvent and stirred evenly to obtain an electrolyte, wherein the concentration of LiPF6 in the lithium-ion battery electrolyte was 1 mol / L, and the mass percentages of VC, DTD, and PS were 3%, 1%, and 1%, respectively.

[0166] 4) Isolation film

[0167] A polyethylene porous membrane was used as the isolation membrane.

[0168] 5) Battery assembly

[0169] The positive electrode sheet, the separator and the negative electrode sheet are stacked in order, the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wound to obtain a bare cell. The bare cell is placed in an outer package, the prepared electrolyte is injected, and the package is packaged for formation to obtain a lithium-ion secondary battery.

[0170] Embodiment 8:

[0171] This embodiment is basically the same as Embodiment 7, except that the graphitization degree of the negative electrode active material graphite in the second region of the negative electrode film layer is different. In this embodiment, the graphitization degree of the negative electrode active material graphite in the second region is 81%.

[0172] Embodiment 9:

[0173] This embodiment is basically the same as embodiment 7, except that the graphitization degree of the negative electrode active material graphite in the second region of the negative electrode film layer is different. In this embodiment, the graphitization degree of the negative electrode active material graphite in the second region is 78%.

[0174] Embodiment 10:

[0175] This embodiment is basically the same as the embodiment 7, except that the graphitization degree of the negative electrode active material graphite in the second region of the negative electrode film layer is different. In this embodiment, the graphitization degree of the negative electrode active material graphite in the second region is 76%.

[0176] Embodiment 11:

[0177] This embodiment is basically the same as the embodiment 7, except that the graphitization degree of the negative electrode active material graphite in the second region of the negative electrode film layer is different. In this embodiment, the graphitization degree of the negative electrode active material graphite in the second region is 72%.

[0178] Embodiment 12:

[0179] This embodiment is basically the same as the embodiment 7, except that the graphitization degree of the negative electrode active material graphite in the second region of the negative electrode film layer is different. In this embodiment, the graphitization degree of the negative electrode active material graphite in the second region is 65%.

[0180] Embodiment 13:

[0181] 1) Preparation of negative electrode

[0182] The negative electrode active material artificial graphite (gram capacity of 340mAh / g, OI=5.22), the conductive agent acetylene black, the binder SBR, and the binder CMC are mixed according to a weight ratio of 95:1.5:3.1:0.4, and a solvent deionized water is added, and the mixture is stirred and mixed to obtain negative electrode slurry 1; the negative electrode active material artificial graphite (gram capacity of 340mAh / g, OI=4.36), the conductive agent acetylene black, the binder SBR, and the binder CMC are mixed according to a weight ratio of 95:1.5:3.1:0.4, and a solvent deionized water is added, and the mixture is stirred and mixed to obtain negative electrode slurry 2;

[0183] The negative electrode slurry 1 is applied to the two ends of the negative electrode current collector copper foil in the width direction, and the negative electrode slurry 2 is applied to the middle of the negative electrode current collector copper foil in the width direction; after drying and cold pressing, the negative electrode sheet is obtained. Among them, the area where the negative electrode slurry 1 is applied in the negative electrode film layer of the negative electrode sheet is the first area and the third area, and the area where the negative electrode slurry 2 is applied is the second area. The coating weight of the negative electrode film layer is 0.108g / 1540.25mm 2 (measured by weight excluding solvent). The width of the first region is 60 mm, the width of the second region is 60 mm, the width of the third region is 60 mm, the thickness of the negative electrode collector is 6 μm, the total thickness of the negative electrode sheet is 110 μm, and the thickness of the negative electrode film layer on the upper and lower sides of the negative electrode collector is equal.

[0184] 2) Preparation of positive electrode

[0185] The positive electrode active material lithium iron phosphate (gram capacity of 139 mAh / g), the conductive agent acetylene black, and the binder PVDF were mixed in a weight ratio of 96:2:2, and the solvent N-methylpyrrolidone was added, and the mixture was stirred and mixed to obtain a positive electrode slurry. The positive electrode slurry was then coated on the positive electrode current collector aluminum foil, wherein the coating weight of the negative electrode slurry was 0.224 g / 1540.25 mm 2 (measured by weight excluding solvent), and then dried and cold pressed to obtain a positive electrode sheet.

[0186] 3) Preparation of electrolyte

[0187] In an argon atmosphere glove box with a water content of <10ppm, EC, PC, and DMC were mixed in a weight ratio of EC:PC:DMC=3:3:3, and then LiPF6, VC, DTD, and PS were added to the mixed organic solvent and stirred evenly to obtain an electrolyte, wherein the concentration of LiPF6 in the lithium-ion battery electrolyte was 1 mol / L, and the mass percentages of VC, DTD, and PS were 3%, 1%, and 1%, respectively.

[0188] 4) Isolation film

[0189] A polyethylene porous membrane was used as the isolation membrane.

[0190] 5) Battery assembly

[0191] The positive electrode sheet, the separator and the negative electrode sheet are stacked in order, the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wound to obtain a bare cell. The bare cell is placed in an outer package, the prepared electrolyte is injected, and the package is packaged for formation to obtain a lithium-ion secondary battery.

[0192] Embodiment 14:

[0193] This embodiment is basically the same as embodiment 13, except that the OI value of the negative electrode active material graphite in the second region of the negative electrode film layer is different. In this embodiment, the OI value of the negative electrode active material graphite in the second region is 3.89.

[0194] Embodiment 15:

[0195] This embodiment is basically the same as embodiment 13, except that the OI value of the negative electrode active material graphite in the second region of the negative electrode film layer is different. In this embodiment, the OI value of the negative electrode active material graphite in the second region is 3.45.

[0196] Embodiment 16:

[0197] This embodiment is basically the same as embodiment 13, except that the OI value of the negative electrode active material graphite in the second region of the negative electrode film layer is different. In this embodiment, the OI value of the negative electrode active material graphite in the second region is 3.21.

[0198] Embodiment 17:

[0199] This embodiment is basically the same as embodiment 13, except that the OI value of the negative electrode active material graphite in the second region of the negative electrode film layer is different. In this embodiment, the OI value of the negative electrode active material graphite in the second region is 2.99.

[0200] Embodiment 18:

[0201] This embodiment is basically the same as embodiment 13, except that the OI value of the negative electrode active material graphite in the second region of the negative electrode film layer is different. In this embodiment, the OI value of the negative electrode active material graphite in the second region is 2.12.

[0202] Embodiment 19:

[0203] 1) Preparation of negative electrode

[0204] The negative electrode active material artificial graphite (gram capacity of 340mAh / g, volume particle size distribution Dv50=15.0μm, graphitization degree=90%, OI value=5.22), conductive agent acetylene black, binder SBR (styrene butadiene latex), binder CMC (carboxymethyl cellulose) are mixed according to a weight ratio of 95:1.5:3.1:0.4, and deionized water is added as a solvent, and the mixture is stirred and mixed to obtain negative electrode slurry 1; the negative electrode active material artificial graphite (gram capacity of 340mAh / g, volume particle size distribution Dv50=10.3μm, graphitization degree=76%, OI value=3.21), conductive agent acetylene black, binder SBR, binder CMC are mixed according to a weight ratio of 95:1.5:3.1:0.4, and deionized water is added as a solvent, and the mixture is stirred and mixed to obtain negative electrode slurry 2;

[0205] The negative electrode slurry 1 is applied to the two ends of the negative electrode current collector copper foil in the width direction, and the negative electrode slurry 2 is applied to the middle of the negative electrode current collector copper foil in the width direction; after drying and cold pressing, the negative electrode sheet is obtained. Among them, the area where the negative electrode slurry 1 is applied in the negative electrode film layer of the negative electrode sheet is the first area and the third area, and the area where the negative electrode slurry 2 is applied is the second area. The coating weight of the negative electrode film layer is 0.108g / 1540.25mm 2 (Based on weight excluding solvent) The width of the second region / the width of the negative electrode sheet h / j=0.05, the thickness of the negative electrode collector is 6 μm, the total thickness of the negative electrode sheet is 110 μm, and the thickness of the negative electrode film layers on the upper and lower sides of the negative electrode collector is equal.

[0206] 2) Preparation of positive electrode

[0207] The positive electrode active material lithium iron phosphate (gram capacity of 139 mAh / g), the conductive agent acetylene black, and the binder PVDF (polyvinylidene fluoride) were mixed in a weight ratio of 96:2:2, and the solvent N-methylpyrrolidone was added, and the mixture was stirred and mixed to obtain a positive electrode slurry. The positive electrode slurry was then coated on the positive electrode current collector aluminum foil, wherein the coating weight of the negative electrode slurry was 0.224 g / 1540.25 mm 2 (measured by weight excluding solvent), and then dried and cold pressed to obtain a positive electrode sheet.

[0208] 3) Preparation of electrolyte

[0209] In an argon atmosphere glove box with a water content of <10ppm, EC (ethylene carbonate), PC (propylene carbonate), and DMC (dimethyl carbonate) are mixed in a weight ratio of EC:PC:DMC=3:3:3, and then LiPF6, VC (vinylene carbonate), DTD (vinyl sulfate), and PS (propylene sulfite) are added to the mixed organic solvent and stirred evenly to obtain an electrolyte, wherein the concentration of LiPF6 in the lithium-ion battery electrolyte is 1 mol / L, and the mass percentages of VC, DTD, and PS are 3%, 1%, and 1%, respectively.

[0210] 4) Isolation film

[0211] A polyethylene porous membrane was used as the isolation membrane.

[0212] 5) Battery assembly

[0213] The positive electrode sheet, the separator and the negative electrode sheet are stacked in order, the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wound to obtain a bare cell. The bare cell is placed in an outer package, the prepared electrolyte is injected, and the package is packaged for formation to obtain a lithium-ion secondary battery.

[0214] Embodiment 20:

[0215] This embodiment is basically the same as Embodiment 19, the only difference being that the ratio of the second region of the negative electrode film layer to the negative electrode film region is different. In this embodiment, the width of the second region / the width of the negative electrode sheet h / j=0.1.

[0216] Embodiment 21:

[0217] This embodiment is basically the same as Embodiment 19, except that the ratio of the second region of the negative electrode film layer to the negative electrode film region is different. In this embodiment, the width of the second region / the width of the negative electrode plate h / j=0.25.

[0218] Embodiment 22:

[0219] This embodiment is basically the same as Embodiment 19, except that the ratio of the second region of the negative electrode film layer to the negative electrode film region is different. In this embodiment, the width of the second region / the width of the negative electrode plate h / j=0.5.

[0220] Embodiment 23:

[0221] This embodiment is basically the same as Embodiment 19, except that the ratio of the second region of the negative electrode film layer to the negative electrode film region is different. In this embodiment, the width of the second region / the width of the negative electrode plate h / j=0.75.

[0222] Embodiment 24:

[0223] This embodiment is basically the same as Embodiment 19, except that the ratio of the second region of the negative electrode film layer to the negative electrode film region is different. In this embodiment, the width of the second region / the width of the negative electrode plate h / j=0.85.

[0224] 2. Battery comparison

[0225] Comparative Example 1:

[0226] 1) Preparation of negative electrode

[0227] The negative electrode active material artificial graphite (gram capacity of 340 mAh / g, volume particle size distribution Dv50 = 15.0 μm, graphitization degree = 90%, OI = 5.22), conductive agent acetylene black, binder SBR, binder CMC are mixed in a weight ratio of 95:1.5:3.1:0.4, solvent deionized water is added, and the mixture is stirred and mixed to obtain a negative electrode slurry;

[0228] The negative electrode slurry is coated on the entire upper and lower surfaces of the negative electrode current collector copper foil; after drying and cold pressing, the negative electrode sheet is obtained. The coating weight of the negative electrode film layer is 0.108g / 1540.25mm 2 (measured by weight excluding solvent). The thickness of the negative electrode current collector is 6 μm, the total thickness of the negative electrode sheet is 110 μm, and the thickness of the negative electrode film layers on the upper and lower sides of the negative electrode current collector is equal.

[0229] 2) Preparation of positive electrode

[0230] The positive electrode active material lithium iron phosphate (gram capacity of 139 mAh / g), the conductive agent acetylene black, and the binder PVDF were mixed in a weight ratio of 96:2:2, and the solvent N-methylpyrrolidone was added, and the mixture was stirred and mixed to obtain a positive electrode slurry. The positive electrode slurry was then coated on the positive electrode current collector aluminum foil, wherein the coating weight of the negative electrode slurry was 0.224 g / 1540.25 mm 2 (measured by weight excluding solvent), and then dried and cold pressed to obtain a positive electrode sheet.

[0231] 3) Preparation of electrolyte

[0232] In an argon atmosphere glove box with a water content of <10ppm, EC, PC, and DMC were mixed in a weight ratio of EC:PC:DMC=3:3:3, and then LiPF6, VC, DTD, and PS were added to the mixed organic solvent and stirred evenly to obtain an electrolyte, wherein the concentration of LiPF6 in the lithium-ion battery electrolyte was 1 mol / L, and the mass percentages of VC, DTD, and PS were 3%, 1%, and 1%, respectively.

[0233] 4) Isolation film

[0234] A polyethylene porous membrane was used as the isolation membrane.

[0235] 5) Battery assembly

[0236] The positive electrode sheet, the separator and the negative electrode sheet are stacked in order, the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wound to obtain a bare cell. The bare cell is placed in an outer package, the prepared electrolyte is injected, and the package is packaged for formation to obtain a lithium-ion secondary battery.

[0237] Comparative Example 2:

[0238] This comparative example is basically the same as comparative example 1, except that the volume particle size distribution Dv50, graphitization degree and OI value of the negative electrode active material artificial graphite in the negative electrode slurry are different. In this comparative example, the volume particle size distribution Dv50 of the artificial graphite is 12.5 μm, the graphitization degree is 86%, and the OI is 4.36.

[0239] Comparative Example 3:

[0240] This comparative example is basically the same as comparative example 1, except that the volume particle size distribution Dv50, graphitization degree and OI value of the negative electrode active material artificial graphite in the negative electrode slurry are different. In this comparative example, the volume particle size distribution Dv50 of the artificial graphite is 10.3 μm, the graphitization degree is 81%, and the OI is 2.99.

[0241] Comparative Example 4:

[0242] 1) Preparation of negative electrode

[0243] The negative electrode active material artificial graphite (gram capacity of 340mAh / g, volume particle size distribution Dv50=14.3μm), the conductive agent acetylene black, the binder SBR (styrene butadiene latex), and the binder CMC (carboxymethyl cellulose) are mixed in a weight ratio of 95:1.5:3.1:0.4, and the solvent deionized water is added, and the mixture is stirred and mixed to obtain negative electrode slurry 1; the negative electrode active material artificial graphite (gram capacity of 340mAh / g, volume particle size distribution Dv50=15μm), the conductive agent acetylene black, the binder SBR, and the binder CMC are mixed in a weight ratio of 95:1.5:3.1:0.4, and the solvent deionized water is added, and the mixture is stirred and mixed to obtain negative electrode slurry 2;

[0244] The negative electrode slurry 1 is applied to the two ends of the negative electrode current collector copper foil in the width direction, and the negative electrode slurry 2 is applied to the middle of the negative electrode current collector copper foil in the width direction; after drying and cold pressing, the negative electrode sheet is obtained. Among them, the area where the negative electrode slurry 1 is applied in the negative electrode film layer of the negative electrode sheet is the first area and the third area, and the area where the negative electrode slurry 2 is applied is the second area. The coating weight of the negative electrode film layer is 0.108g / 1540.25mm 2(measured by weight excluding solvent). The width of the first region is 60 mm, the width of the second region is 60 mm, the width of the third region is 60 mm, the thickness of the negative electrode collector is 6 μm, the total thickness of the negative electrode sheet is 110 μm, and the thickness of the negative electrode film layer on the upper and lower sides of the negative electrode collector is equal.

[0245] 2) Preparation of positive electrode

[0246] The positive electrode active material lithium iron phosphate (gram capacity of 139 mAh / g), the conductive agent acetylene black, and the binder PVDF (polyvinylidene fluoride) were mixed in a weight ratio of 96:2:2, and the solvent N-methylpyrrolidone was added, and the mixture was stirred and mixed to obtain a positive electrode slurry. The positive electrode slurry was then coated on the positive electrode current collector aluminum foil, wherein the coating weight of the negative electrode slurry was 0.224 g / 1540.25 mm 2 (measured by weight excluding solvent), and then dried and cold pressed to obtain a positive electrode sheet.

[0247] 3) Preparation of electrolyte

[0248] In an argon atmosphere glove box with a water content of <10ppm, EC (ethylene carbonate), PC (propylene carbonate), and DMC (dimethyl carbonate) are mixed in a weight ratio of EC:PC:DMC=3:3:3, and then LiPF6, VC (vinylene carbonate), DTD (vinyl sulfate), and PS (propylene sulfite) are added to the mixed organic solvent and stirred evenly to obtain an electrolyte, wherein the concentration of LiPF6 in the lithium-ion battery electrolyte is 1 mol / L, and the mass percentages of VC, DTD, and PS are 3%, 1%, and 1%, respectively.

[0249] 4) Isolation film

[0250] A polyethylene porous membrane was used as the isolation membrane.

[0251] 5) Battery assembly

[0252] The positive electrode sheet, the separator and the negative electrode sheet are stacked in order, the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wound to obtain a bare cell. The bare cell is placed in an outer package, the prepared electrolyte is injected, and the package is packaged for formation to obtain a lithium-ion secondary battery.

[0253] Comparative Example 5:

[0254] This comparative example is basically the same as comparative example 4, except that the volume particle size distribution Dv50 of the active material graphite in the negative electrode slurry 1 is different. In this embodiment, the volume particle size distribution Dv50 of the negative electrode active material graphite in the negative electrode slurry 1 is 12.5 μm.

[0255] Comparative Example 6:

[0256] This comparative example is basically the same as comparative example 4, except that the volume particle size distribution Dv50 of the active material graphite in the negative electrode slurry 1 is different. In this embodiment, the volume particle size distribution Dv50 of the negative electrode active material graphite in the negative electrode slurry 1 is 10.3 μm.

[0257] Comparative Example 7:

[0258] 1) Preparation of negative electrode

[0259] The negative electrode active material artificial graphite (gram capacity of 340mAh / g, degree of graphitization = 86%), the conductive agent acetylene black, the binder SBR, and the binder CMC are mixed according to a weight ratio of 95:1.5:3.1:0.4, and the solvent deionized water is added, and the mixture is stirred and mixed to obtain negative electrode slurry 1; the negative electrode active material artificial graphite (gram capacity of 340mAh / g, degree of graphitization = 90%), the conductive agent acetylene black, the binder SBR, and the binder CMC are mixed according to a weight ratio of 95:1.5:3.1:0.4, and the solvent deionized water is added, and the mixture is stirred and mixed to obtain negative electrode slurry 2;

[0260] The negative electrode slurry 1 is applied to the two ends of the negative electrode current collector copper foil in the width direction, and the negative electrode slurry 2 is applied to the middle of the negative electrode current collector copper foil in the width direction; after drying and cold pressing, the negative electrode sheet is obtained. Among them, the area where the negative electrode slurry 1 is applied in the negative electrode film layer of the negative electrode sheet is the first area and the third area, and the area where the negative electrode slurry 2 is applied is the second area. The coating weight of the negative electrode film layer is 0.108g / 1540.25mm 2 (measured by weight excluding solvent). The width of the first region is 60 mm, the width of the second region is 60 mm, the width of the third region is 60 mm, the thickness of the negative electrode collector is 6 μm, the total thickness of the negative electrode sheet is 110 μm, and the thickness of the negative electrode film layer on the upper and lower sides of the negative electrode collector is equal.

[0261] 2) Preparation of positive electrode

[0262] The positive electrode active material lithium iron phosphate (gram capacity of 139 mAh / g), the conductive agent acetylene black, and the binder PVDF were mixed in a weight ratio of 96:2:2, and the solvent N-methylpyrrolidone was added, and the mixture was stirred and mixed to obtain a positive electrode slurry. The positive electrode slurry was then coated on the positive electrode current collector aluminum foil, wherein the coating weight of the negative electrode slurry was 0.224 g / 1540.25 mm 2 (measured by weight excluding solvent), and then dried and cold pressed to obtain a positive electrode sheet.

[0263] 3) Preparation of electrolyte

[0264] In an argon atmosphere glove box with a water content of <10ppm, EC, PC, and DMC were mixed in a weight ratio of EC:PC:DMC=3:3:3, and then LiPF6, VC, DTD, and PS were added to the mixed organic solvent and stirred evenly to obtain an electrolyte, wherein the concentration of LiPF6 in the lithium-ion battery electrolyte was 1 mol / L, and the mass percentages of VC, DTD, and PS were 3%, 1%, and 1%, respectively.

[0265] 4) Isolation film

[0266] A polyethylene porous membrane was used as the isolation membrane.

[0267] 5) Battery assembly

[0268] The positive electrode sheet, the separator and the negative electrode sheet are stacked in order, the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wound to obtain a bare cell. The bare cell is placed in an outer package, the prepared electrolyte is injected, and the package is packaged for formation to obtain a lithium-ion secondary battery.

[0269] Comparative Example 8:

[0270] This comparative example is basically the same as comparative example 7, except that the graphitization degree of the active material graphite in the negative electrode slurry 1 is different. In this embodiment, the graphitization degree of the negative electrode active material graphite in the negative electrode slurry 1 is 81%.

[0271] Comparative Example 9:

[0272] This comparative example is basically the same as comparative example 7, except that the graphitization degree of the active material graphite in the negative electrode slurry 1 is different. In this embodiment, the graphitization degree of the negative electrode active material graphite in the negative electrode slurry 1 is 76%.

[0273] Comparative Example 10:

[0274] 1) Preparation of negative electrode

[0275] The negative electrode active material artificial graphite (gram capacity of 340mAh / g, OI=4.36), the conductive agent acetylene black, the binder SBR, and the binder CMC are mixed in a weight ratio of 95:1.5:3.1:0.4, and the solvent deionized water is added, and the mixture is stirred and mixed to obtain negative electrode slurry 1; the negative electrode active material artificial graphite (gram capacity of 340mAh / g, OI=5.22), the conductive agent acetylene black, the binder SBR, and the binder CMC are mixed in a weight ratio of 95:1.5:3.1:0.4, and the solvent deionized water is added, and the mixture is stirred and mixed to obtain negative electrode slurry 2;

[0276] The negative electrode slurry 1 is applied to the two ends of the negative electrode current collector copper foil in the width direction, and the negative electrode slurry 2 is applied to the middle of the negative electrode current collector copper foil in the width direction; after drying and cold pressing, the negative electrode sheet is obtained. Among them, the area where the negative electrode slurry 1 is applied in the negative electrode film layer of the negative electrode sheet is the first area and the third area, and the area where the negative electrode slurry 2 is applied is the second area. The coating weight of the negative electrode film layer is 0.108g / 1540.25mm 2 (measured by weight excluding solvent). The width of the first region is 60 mm, the width of the second region is 60 mm, the width of the third region is 60 mm, the thickness of the negative electrode collector is 6 μm, the total thickness of the negative electrode sheet is 110 μm, and the thickness of the negative electrode film layer on the upper and lower sides of the negative electrode collector is equal.

[0277] 2) Preparation of positive electrode

[0278] The positive electrode active material lithium iron phosphate (gram capacity of 139 mAh / g), the conductive agent acetylene black, and the binder PVDF were mixed in a weight ratio of 96:2:2, and the solvent N-methylpyrrolidone was added, and the mixture was stirred and mixed to obtain a positive electrode slurry. The positive electrode slurry was then coated on the positive electrode current collector aluminum foil, wherein the coating weight of the negative electrode slurry was 0.224 g / 1540.25 mm 2 (measured by weight excluding solvent), and then dried and cold pressed to obtain a positive electrode sheet.

[0279] 3) Preparation of electrolyte

[0280] In an argon atmosphere glove box with a water content of <10ppm, EC, PC, and DMC were mixed in a weight ratio of EC:PC:DMC=3:3:3, and then LiPF6, VC, DTD, and PS were added to the mixed organic solvent and stirred evenly to obtain an electrolyte, wherein the concentration of LiPF6 in the lithium-ion battery electrolyte was 1 mol / L, and the mass percentages of VC, DTD, and PS were 3%, 1%, and 1%, respectively.

[0281] 4) Isolation film

[0282] A polyethylene porous membrane was used as the isolation membrane.

[0283] 5) Battery assembly

[0284] The positive electrode sheet, the separator and the negative electrode sheet are stacked in order, the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wound to obtain a bare cell. The bare cell is placed in an outer package, the prepared electrolyte is injected, and the package is packaged for formation to obtain a lithium-ion secondary battery.

[0285] Comparative Example 11:

[0286] This comparative example is basically the same as comparative example 7, except that the OI value of the active material graphite in the negative electrode slurry 1 is different. The OI value of the negative electrode active material graphite in the negative electrode slurry 1 in this embodiment is 3.89.

[0287] Comparative Example 12:

[0288] This comparative example is basically the same as comparative example 7, except that the graphitization degree of the active material graphite in the negative electrode slurry 1 is different. In this embodiment, the graphitization degree of the negative electrode active material graphite in the negative electrode slurry 1 is 3.45.

[0289] 3. Test Method

[0290] 1) Volume particle size distribution Dv50 test

[0291] Unless otherwise specified, the particle size distribution parameter Dv50 of the negative electrode active material determined by the particle size distribution measurement value in this application is determined by a particle size analyzer-laser diffraction method. Specifically, reference can be made to the standard GB / T19077-2016, using a laser diffraction scattering particle size analyzer and measuring according to the manufacturer's instructions.

[0292] 2) Graphitization degree test

[0293] The crystal unit cell parameters are calculated by X-ray polycrystalline diffraction, and the peak positions of C004 and Si311 of two parallel samples are obtained by peak search using the center of gravity method, and the value of graphite layer spacing d002 is calculated by substituting the obtained d002 into the Mering-Maire formula: g = [(3.440-d002) / (3.440-3.354)]*100%, and the graphitization degree g is obtained. The graphitization degree g of the negative active material can be determined by referring to the standards JB / T4220-2011 and JISK0131-1996 and by using the XRD diffraction method through the lattice parameters of the carbon crystal.

[0294] 3) OI value test

[0295] According to the embodiments of the present application, the OI value GOI of the negative electrode active material powder can be determined by XRD testing with reference to JIS K0131-1996. Specifically, according to the embodiments of the present application, the OI value of the active material powder can be calculated according to the formula GOI=C004 / C110, wherein C004 is the peak area of ​​the 004 characteristic diffraction peak in the X-ray diffraction spectrum of the negative electrode, and C110 is the peak area of ​​the 110 characteristic diffraction peak in the X-ray diffraction spectrum of the negative electrode.

[0296] 4) Battery room temperature cycle performance test

[0297] At 25°C, the lithium-ion secondary battery is first charged at a constant current of 1C (i.e., the current value that completely discharges the theoretical capacity within 1 hour) to a voltage of 3.65V, then charged at a constant voltage of 3.65V to a current of 0.05C. After standing for 5 minutes, the lithium-ion secondary battery is discharged at a constant current of 1C to a voltage of 2.5V. This is a charge and discharge cycle process, and the discharge capacity this time is the discharge capacity of the first cycle. The lithium-ion secondary battery is subjected to multiple cycle charge and discharge tests according to the above method until the discharge capacity of the lithium-ion secondary battery decays to 80%, and the number of cycles of the lithium-ion secondary battery is recorded.

[0298] 5) Battery high temperature cycle performance test

[0299] At 60°C, the lithium-ion secondary battery is first charged at a constant current of 1C (i.e., the current value that completely discharges the theoretical capacity within 1 hour) to a voltage of 3.65V, then charged at a constant voltage of 3.65V to a current of 0.05C. After standing for 5 minutes, the lithium-ion secondary battery is discharged at a constant current of 1C to a voltage of 2.5V. This is a charge and discharge cycle process, and the discharge capacity this time is the discharge capacity of the first cycle. The lithium-ion secondary battery is subjected to multiple cycle charge and discharge tests according to the above method, and the discharge capacity of the 500th cycle is detected.

[0300] Capacity retention rate of the lithium ion secondary battery after 500 cycles at 60° C.=(discharge capacity at the 500th cycle / discharge capacity at the first cycle)×100%.

[0301] The parameters and performance test data of the embodiments and comparative examples of the present application are shown in Table 1, Table 2 and Table 3.

[0302] Table 1

[0303]

[0304]

[0305]

[0306] Table 2

[0307]

[0308]

[0309] Table 3

[0310]

[0311]

[0312]

[0313] It can be seen from Examples 1 to 6 and Comparative Examples 1 to 6 that by controlling the volume particle size distribution Dv50 of graphite in the middle region (i.e., the second region) of the negative electrode plate to be smaller than that in the outer region (i.e., the first region and the third region), the fast charging capacity of graphite in the middle region can be greater than that in the outer region, and the difference in volume particle size distribution Dv50 is within a suitable range, which is conducive to improving the consistency of polarization performance between the middle region and the outer region. Among them, when c1-d ≥ 8 μm or c2-d ≥ 8 μm, the graphite kinetics in the outer region are too slow, which will increase the probability of lithium precipitation in the outer region.

[0314] It can be seen from Examples 7 to 12 and Comparative Examples 1 to 3 and 7 to 9 that by controlling the graphitization degree of the graphite in the middle region of the negative electrode to be less than that in the outer region, the fast charging capacity of the graphite in the middle region is greater than that in the outer region, and the difference in graphitization degree is within a suitable range, which is conducive to improving the consistency of the polarization performance of the middle region and the outer region. Among them, when a1-b ≥ 20% or a2-b ≥ 20%, the graphite kinetics in the outer region are too slow, which will increase the probability of lithium precipitation in the outer region.

[0315] It can be seen from Examples 13 to 18 and Comparative Examples 1 to 3 and 10 to 12 that by controlling the OI value of the graphite in the middle region of the negative electrode to be smaller than that in the outer region, the fast charging capacity of the graphite in the middle region is greater than that in the outer region, and the difference in the OI value is within a suitable range, which is conducive to improving the consistency of the polarization performance of the middle region and the outer region. Among them, when e1-f≥3.0 or e2-f≥3.0, the graphite kinetics in the outer region is too slow, which will increase the probability of lithium precipitation in the outer region.

[0316] It can be seen from Examples 19 to 24 and Comparative Examples 1 to 3 that the ratio of the width of the middle region in the width direction of the negative electrode plate to the width of the negative electrode plate affects the effect of improving lithium deposition in the middle. When h / j is less than 1 / 10, the middle region is narrow and lithium deposition still occurs in local areas. When h / j is greater than 3 / 4, the middle region is too wide and lithium deposition also occurs in local areas.

[0317] To summarize, in view of the phenomenon that the temperature of the middle part of the electrode is high, the expansion force is large, and the positive polarization is small, while the temperature of the head and bottom of the electrode is low, the expansion force is small, and the positive polarization is large during the battery cell cycle; the present application proposes a new differentiated design of the negative electrode electrode, which improves the rapid lithium insertion ability of the graphite in the middle area (the second area) of the negative electrode by adjusting the fast charging capacity of the graphite in the middle area (the first area and the third area) to be greater than that in the outer areas (the first area and the third area), thereby alleviating the problem of mismatch between the positive and negative electrodes during the battery cell cycle and improving lithium deposition in the middle of the battery cell.

[0318] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A negative electrode plate, characterized in that: The invention comprises a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer has a negative electrode active material, and the negative electrode active material comprises graphite; the negative electrode film layer comprises a first region, a second region and a third region, and the first region, the second region and the third region are arranged in sequence in a first direction; Wherein, the negative electrode plate satisfies at least one of the following: (1) The graphitization degree of the graphite in the first region and the third region is greater than the graphitization degree of the graphite in the second region; (2) the volume particle size distribution Dv50 of the graphite in the first region and the third region is greater than the volume particle size distribution Dv50 of the graphite in the second region; (3) The OI values ​​of the graphite in the first region and the third region are both greater than the OI value of the graphite in the second region.

2. The negative electrode sheet according to claim 1, characterized in that: The graphitization degree of the graphite in the first region is a1, the graphitization degree of the graphite in the third region is a2, and the graphitization degree of the graphite in the second region is b, 0<a1-b<40%, 0<a2-b<40%.

3. The negative electrode sheet according to claim 2, characterized in that: 5%<a1-b<20%, 5%<a2-b<20%.

4. The negative electrode sheet according to any one of claims 1 to 3, characterized in that: The graphitization degree of the graphite in the first region and the third region is independently 65% ​​to 100%; the graphitization degree of the graphite in the second region is 60% to 90%.

5. The negative electrode sheet according to any one of claims 1 to 3, characterized in that: The volume particle size distribution Dv50 of the graphite in the first region is c1, the volume particle size distribution Dv50 of the graphite in the third region is c2, and the volume particle size distribution Dv50 of the graphite in the second region is d, 0<c1-d<10.0μm, 0<c2-d<10.0μm.

6. The negative electrode sheet according to claim 5, characterized in that: 2μm<c1-d<8.0μm, 2μm<c2-d<8.0μm.

7. The negative electrode sheet according to any one of claims 1 to 3 and 6, characterized in that: The volume particle size distribution Dv50 of the graphite in the first region and the third region is independently 7 μm to 15 μm; the volume particle size distribution Dv50 of the graphite in the second region is 6 μm to 14.5 μm.

8. The negative electrode sheet according to any one of claims 1 to 3 and 6, characterized in that: The OI value of the graphite in the first region is e1, the OI value of the graphite in the third region is e2, and the OI value of the graphite in the second region is f, 0<e1-f<9, 0<e2-f<9.

9. The negative electrode sheet according to claim 8, characterized in that: 1.5<e1-f<3.0, 1.5<e2-f<3.

0.

10. The negative electrode sheet according to any one of claims 1 to 3, 6 and 9, characterized in that: The OI values ​​of the graphite in the first region and the third region are independently 5.0 to 10.0; the OI value of the graphite in the second region is 2.5 to 4.

5.

11. The negative electrode sheet according to any one of claims 1 to 3, 6 and 9, characterized in that: The sizes of the first region, the second region and the third region in the first direction are g, h and i respectively, and the size of the negative electrode plate in the first direction is j, 0.1≤h / j≤0.75, 0.125≤g / j≤0.45, 0.125≤i / j≤0.

45.

12. The negative electrode sheet according to any one of claims 1 to 3, 6 and 9, characterized in that: The thickness of the negative electrode plate is 50 μm to 400 μm.

13. A secondary battery, characterized in that: The negative electrode sheet comprises the negative electrode sheet according to any one of claims 1 to 12, wherein the secondary battery is a wound battery, and the secondary battery is wound with the first direction being the width direction of the negative electrode sheet.

14. The secondary battery according to claim 13, characterized in that: The negative electrode sheet has a first overhang area and a second overhang area at both end edges in the first direction respectively; the first area covers the first overhang area; the third area covers the second overhang area; Optionally, a size of the first area in the first direction is greater than a size of the first overhang area in the first direction; Optionally, a size of the third area in the first direction is greater than a size of the second overhang area in the first direction.

15. An electrical device, characterized in that: A secondary battery comprising the secondary battery according to claim 13 or 14.

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