Negative electrode sheet, secondary battery, and electric device

Abstract

The application provides a negative electrode sheet, a secondary battery and a power utilization device. The negative electrode sheet 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 comprises 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 a first direction. The negative electrode sheet satisfies at least one of the following conditions: 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; the volume particle size distribution Dv50 of the graphite in the first region and the third region is greater than the Dv50 of the graphite in the second region; 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; and when the secondary battery is assembled in the first direction as the width direction of the negative electrode sheet, the lithium precipitation in the middle of the negative electrode sheet during the use 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, in particular to a negative electrode sheet, a secondary battery and an electric device. BACKGROUND

[0002] In recent years, with the application range of secondary batteries becoming more and more extensive, secondary batteries are widely used in energy storage power supply systems such as hydraulic, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles and electric vehicles.

[0003] Due to the great development of secondary batteries, higher requirements are put forward for the cycle performance thereof. Batteries with excellent cycle performance have high requirements for negative electrode sheets. The current secondary batteries are prone to lithium precipitation on the negative electrode sheet during use, and if the precipitated lithium continuously accumulates on the negative electrode sheet, the separator film is easily punctured, affecting the cycle performance of the secondary battery.

[0004] Therefore, seeking a secondary battery with more excellent cycle performance is one of the directions that the person skilled in the art focuses on. SUMMARY

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

[0006] In order to achieve the above-mentioned purpose, 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, the negative electrode film layer having a negative electrode active material therein, the negative electrode active material comprising graphite; the negative electrode film layer comprises a first region, a second region and a third region, the first region, the second region and the third region are sequentially arranged in a first direction;

[0007] Wherein, the negative electrode sheet 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 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.

[0011] The present application can effectively alleviate the problem of lithium precipitation in the middle of the negative electrode sheet during the cycle process of the secondary battery, improve the cycle performance of the secondary battery, and the like.

[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, and the graphitization degree of the graphite in the second region is b, 0

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

[0014] In any embodiment, the graphitization degree of the graphite in the first region and the third region is independently 65% to 100%; and 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 < 10.0 μm, and 0 < c2-d < 10.0 μm. In this way, the problem of lithium precipitation 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 of the embodiments, 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, and 0 < e2-f < 9. In this way, the cycle performance of the secondary battery can be further improved.

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

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

[0021] In any of the embodiments, the size of the first region, the second region, and the third region in the first direction is g, h, and i, respectively, and the size of the negative electrode tab in the first direction is j, 0.1 ≤ h / j ≤ 0.75, 0.125 ≤ g / j ≤ 0.45, and 0.125 ≤ i / j ≤ 0.45. In this way, the distribution of the fast lithium intercalation capacity of the negative electrode active material in the negative electrode film layer along the first direction can be more reasonable, and the cycle performance of the secondary battery can be further improved.

[0022] In any of the embodiments, the thickness of the negative electrode tab is 50-400 μm.

[0023] The second aspect of the present application provides a secondary battery comprising the negative electrode tab of the first aspect of the present application, the secondary battery being a roll battery, and the secondary battery being rolled in the first direction as the width direction of the negative electrode tab. The secondary battery has good cycle performance.

[0024] In any of the embodiments, the negative electrode tab has a first overhang region and a second overhang region at both end edges in the first direction, respectively; the first region covers the first overhang region; and the third region covers the second overhang region.

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

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

[0027] The third aspect of the present application provides a power consuming device comprising the secondary battery of the second aspect of the present application.

[0028] The negative electrode tab of the present application divides the negative electrode film layer into multiple regions along the first direction, and makes the graphitization degree of the graphite of the negative electrode active material in the first region and the third region on both sides greater than that 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 that in the second region, and / or the OI value of the graphite in the first region and the third region is greater than that in the second region. When the first direction is taken as the width direction of the negative electrode tab to assemble the secondary battery, the secondary battery is less likely to have lithium precipitation in the middle of the negative electrode tab during the cycle process, and the cycle performance of the secondary battery can be improved. BRIEF DESCRIPTION OF DRAWINGS

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

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

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

[0032] Figure 4 is a schematic view of a power consuming device using the secondary battery of an embodiment of the present application as a power source. Figure 3

[0033] Figure 5 is a schematic view of a power consuming device using the secondary battery of an embodiment of the present application as a power source.

[0034] BRIEF DESCRIPTION OF DRAWINGS

[0035] 1, negative electrode tab; 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, power consuming device. DETAILED DESCRIPTION

[0036] ​Some embodiments of the separator, secondary battery, and electrical device of the present application are described in detail below, with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed explanation is omitted. For example, there will be cases where detailed explanation of matters known well, repeated explanation of substantially identical configurations, is omitted. This is to avoid the following description from becoming unnecessarily lengthy, and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to sufficiently understand the present application, and are not intended to define the subject matter of the claims.

[0037] The "ranges" disclosed herein can be defined with both a lower and an upper limit, and a given range is defined with a selected lower limit and a selected upper limit, which define the boundaries of the particular range. Ranges defined by such limits can be either inclusive or exclusive of the end values, either end value can be included or excluded independently, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if a minimum range value of 1 and 2 are listed, and if a maximum range value of 3, 4, and 5 are also listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise stated, a numerical range "a-b" indicates a shorthand way of describing each and every intervening real number, with a and b both being real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed herein, "0-5" is merely a shorthand way of describing these numerical combinations. Also, when it is stated that a parameter is an integer ≥ 2, it is equivalent to listing the parameter as, for example, integer 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 new technical solutions.

[0039] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment or implementation of the present application. The appearance of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive or alternative embodiments to other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. Reference herein to "an implementation" has a similar understanding.

[0040] It is understood by those skilled in the art that the order of writing each step in the method of each embodiment or example does not mean a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. If not specifically stated, all steps of the present application can be performed in sequence or randomly, preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method also comprises step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0041] In the present application, the open technical features or technical solutions described by the words "containing", "including", "comprising" and the like do not exclude additional members other than the listed members, and can be regarded as providing both a closed feature or solution composed of the listed members and an open feature or solution including additional members in addition to the listed members. For example, A includes a1, a2 and a3, and unless otherwise specified, it can also include other members or can not include additional members, and can be regarded as providing both the feature or solution that "A is composed of a1, a2 and a3" and the feature or solution that "A includes a1, a2 and a3, and 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 the present application, "optionally", "optional" and "optional" mean that it can or can not be, that is, it can be selected from either of the two parallel solutions "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 weight described in the specification of the embodiments of the present application can be μg, mg, g, kg and other weight units commonly known in the chemical industry.

[0044] At present, lithium precipitation phenomenon is prone to occur on the negative electrode sheet during the use of the secondary battery. If the lithium precipitated on the negative electrode sheet continuously accumulates on the negative electrode sheet, it is easy to cause the isolation film to be pierced, which brings great safety hazard to the secondary battery and affects the cycle performance of the secondary battery. In view of this, the present application provides a negative electrode sheet which can effectively improve the lithium precipitation phenomenon on the negative electrode sheet during the use of the secondary battery, thereby improving the safety performance and cycle performance of the secondary battery.

[0045] Please refer toFigure 1 and Figure 2 In an embodiment, the application provides a negative electrode tab 1, which comprises a negative electrode current collector 11 and a negative electrode film layer 12 provided on at least one surface of the negative electrode current collector 11, the negative electrode film layer 12 comprising a negative electrode active material, the negative electrode active material comprising graphite; the negative electrode film layer 12 comprising 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 being sequentially arranged in a first direction; and the graphitization degree of the graphite in the first region 121 and the third region 123 being 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 being 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 being greater than the OI value of the graphite in the second region 122.

[0046] In the cycle process of the secondary battery, due to the non-uniformity of the temperature and the expansion force of different parts of the negative electrode tab 1, the polarization distribution in the width direction of the negative electrode tab 1 is non-uniform. Specifically, in the wound negative electrode tab, due to the influence of heat dissipation, the temperature of the middle part of the negative electrode tab 1 is generally high, the expansion force is large, and the polarization is small; while the temperature of the two ends of the negative electrode tab 1 along the width direction is low, the expansion force is small, and the polarization is large. Affected by the above non-uniform polarization distribution, lithium ions are more inclined to diffuse and intercalate lithium in the middle part of the negative electrode tab 1 in the cycle process of the secondary battery, so that the intercalation amount of lithium in the two ends of the negative electrode tab 1 along the width direction is lower than that in the middle part, and the middle part of the negative electrode tab 1 is prone to lithium precipitation, which affects the cycle performance of the secondary battery.

[0047] The negative electrode film layer 12 of the negative electrode tab 1 described above comprises 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 sequentially arranged in a first direction, and 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; 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 taken as the width direction of the negative electrode tab 1 to assemble a secondary battery, the rapid intercalation capacity of the second region in the middle part of the negative electrode tab 1 can be improved, and the secondary battery is less likely to have lithium precipitation in the middle part of the negative electrode tab 1 in the cycle process, thereby effectively alleviating the problem that the middle part of the negative electrode tab 1 is prone to lithium precipitation, and improving the cycle performance of the secondary battery.

[0048] In some 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 graphitization degree of the negative electrode active material graphite has a significant impact on the fast lithium intercalation capability of the graphite. After graphitization, the carbon material forms an ordered layered structure, and lithium ions can be intercalated between the graphite layers when the material is used as a negative electrode active material. Generally, the lower the graphitization degree of the graphite, the higher the disorder between the layers of the material, and the better the 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 sheet 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 greater than that 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 sheet 1 and improving the cycle performance of the secondary battery.

[0049] In some embodiments, the graphitization degree of the graphite in the first region 121 is a1, the graphitization degree of the graphite in the third region 123 is a2, and the graphitization degree of the graphite in the second region 122 is b, 0 < a1-b < 40%, and 0 < a2-b < 40%. In this way, the lithium precipitation problem in the middle of the negative electrode sheet 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 precipitation problem in the middle of the negative electrode sheet 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%; and 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 within the above range can further improve the lithium precipitation problem in the middle of the negative electrode sheet 1, and further improve the cycle performance of the secondary battery.

[0052] In some 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 influence on the rapid lithium intercalation capacity of the graphite. Within a certain particle size range, the smaller the volume particle size distribution Dv50 of the graphite, the greater the rapid lithium intercalation capacity of the graphite. 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 sheet 1 to be greater than the volume particle size distribution Dv50 of the graphite in the second region 122, the rapid lithium intercalation capacity of the graphite in the second region 122 can be greater than the rapid lithium intercalation capacity of the graphite in the first region and the third region, thereby improving the lithium precipitation problem in the middle of the negative electrode sheet 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 particle size value at which the cumulative volume of the material particles reaches 50% from the small particle size side in the particle size distribution on a volume basis.

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

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

[0057] In some 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 intercalation of lithium ions, and the greater the OI value, the less conducive it is to the diffusion and intercalation of lithium ions. By setting 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, the present application can make the lithium ion diffusion and fast intercalation capacity of the active material in the second region in the middle of the pole piece better than on both sides of the first direction, thereby improving the lithium precipitation problem in the middle of the negative pole piece 1 and improving the safety and cycle performance of the secondary battery.

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

[0059] In some embodiments, the OI value of the graphite in the first region 121 is e1, the OI value of the graphite in the third region 123 is e2, and the OI value of the graphite in the second region 122 is f, 0 < e1-f < 9, and 0 < e2-f < 9. In this way, the lithium precipitation problem in the middle of the negative pole piece 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, and 1.5 < e2-f < 3.0. In this way, the lithium precipitation problem in the middle of the negative pole piece 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 5.0-10.0; and the OI value of the graphite in the second region 122 is 2.5-4.5. The OI value of the graphite in the first region 121, the second region 122 and the third region 123 is in the above range, which can further improve the lithium precipitation problem in the middle of the negative pole piece 1, and further improve the cycle performance of the secondary battery.

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

[0063] In some embodiments, the thickness of the negative electrode tab 1 is 50 μm to 400 μm. It can be understood that the thickness of the negative electrode tab 1 includes the sum of the thickness of the negative electrode current collector 11 and 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 tab 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, or 400 μm.

[0064] The second aspect of the present application also provides a secondary battery including the negative electrode tab 1 of the first aspect of the present application. The secondary battery is a winding battery, and the secondary battery is wound in the first direction as the width direction of the negative electrode tab. Thus, the secondary battery has good safety and cycle performance.

[0065] Please refer to Figure 1 In some embodiments, the negative electrode tab 1 has a first overhang region 124 and a second overhang region 125 at the two end edges along the first direction, respectively; the first region 121 covers the first overhang region 124, and the third region 123 covers the second overhang region 125.

[0066] Further, in some embodiments, the dimension of the first region 121 along the first direction is greater than the dimension of the first overhang region 124 along the first direction, and the dimension of the third region 123 along the first direction is greater than the dimension of the second overhang region 125 along the first direction.

[0067] In other words, the first region 121 of the negative electrode tab 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 region refers to the region on the negative electrode tab 1 that does not overlap with the positive electrode tab after the negative electrode tab 1 and the positive electrode tab are wound, and the non-overhang region refers to the region on the negative electrode tab 1 that overlaps with the positive electrode tab after the negative electrode tab 1 and the positive electrode tab are wound.

[0069] The third aspect of the present application also provides a power consuming device comprising the secondary battery of the second aspect of the present application.

[0070] The secondary battery and the power consuming device of the present application are described below with appropriate reference to the accompanying drawings.

[0071] Unless otherwise specified, the components, material types or contents of the battery 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 tab, a negative electrode tab, an electrolyte and a separator. During the charging and discharging process of the battery, active ions are inserted and extracted between the positive electrode tab and the negative electrode tab. The electrolyte plays a role in conducting ions between the positive electrode tab and the negative electrode tab. The separator is arranged between the positive electrode tab and the negative electrode tab, mainly to prevent short circuiting of the positive and negative electrodes, while allowing ions to pass through.

[0074] Positive electrode tab

[0075] The positive electrode tab 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 opposite surfaces in the thickness direction of itself, and the positive electrode film layer is arranged on either one or both of the two opposite surfaces of the positive electrode current collector.

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

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

[0079] As an example, the positive electrode active material of the lithium ion secondary battery can include at least one of a lithium-containing phosphate of an olivine structure, a lithium transition metal oxide, and a modified compound of each thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive electrode active material for a battery can also be used. These positive electrode active materials can be used alone only one or two or more can be used in combination. Examples of the lithium transition metal oxide can include, but are not limited to, lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (which can also be referred to simply as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which can also be referred to simply as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (which can also be referred to simply as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (which can also be referred to simply as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (which can also be referred to simply as NCM 811 ), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0080] As an example, the positive electrode active material of a sodium-ion secondary battery may include at least one of the following materials: sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. However, this 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 in this application, the transition metal in the sodium transition metal oxide can be at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. For example, the sodium transition metal oxide is Na. x MO2, where 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 in this application, the polyanionic compound can be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. 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- The price state.

[0083] Polyanionic compounds can also contain sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds containing anionic units and halide 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- The valence state; the halogen can be at least one of F, Cl and Br.

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

[0085] Polyanionic compounds are, for example, NaFePO4, Na3V2(PO4)3(Na3V2P04, NVP for short), 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 (0≤y≤1) at least one.

[0086] Prussian blue compounds can be a class of compounds having sodium ions, transition metal ions, and cyanide ions (CN - ). The transition metal can 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, and 0 < c < 1.

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

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

[0089] In some embodiments, the positive electrode film layer further optionally includes a conductive agent. As an example, the conductive agent can include at least one of super P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The weight ratio of the conductive agent in the positive electrode film layer is 0-20 wt.%, based on the total weight of the positive electrode film layer.

[0090] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, in a solvent (e.g., N-methyl pyrrolidone) to form a positive electrode slurry, wherein the solid content of the positive electrode slurry is 40 wt% to 80 wt%, the viscosity at room temperature is adjusted to 5000 mPa·s to 25000 mPa·s, the positive electrode slurry is coated on the surface of the positive electrode current collector, and the positive electrode sheet is formed after drying and cold pressing by a cold rolling machine; the unit area surface density of the positive electrode powder coating is 150 mg / m 2 to 350 mg / m 2 , the compaction density of the positive electrode sheet is 3.0 g / cm 3 to 3.6 g / cm 3 , and optionally 3.3 g / cm 3 to 3.5 g / cm 3 .

[0091] The formula for calculating the compaction density is as follows:

[0092] Compaction density = coating surface density / (thickness of the sheet 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 measured using a standard balance.

[0094] The thickness T of the positive electrode film can be measured using a micrometer, for example, a micrometer with a model number of Mitutoyo 293-100 and an accuracy of 0.1 μm. It should be noted that the thickness of the positive electrode film as described in the present application refers to the thickness of the positive electrode film in the positive electrode sheet that has been cold-pressed and used for assembling the battery.

[0095] Negative electrode sheet

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

[0097] The negative electrode sheet comprises 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 comprises a negative electrode active material.

[0098] As an example, the negative electrode current collector has two opposite surfaces in the thickness direction of itself, 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 current collector can be a metal foil or a composite current collector. For example, as a metal foil, a copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material on a polymer material base layer. The metal material can include, but is not limited to, copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, and the like, and the polymer material base layer can include, but is not limited to, a polypropylene (PP) base layer, a polyethylene terephthalate (PET) base layer, a polybutylene terephthalate (PBT) base layer, a polystyrene (PS) base layer, a polyethylene (PE) base layer, and the like.

[0100] In some embodiments, the negative electrode film layer can further optionally include a binder. The binder can be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). The weight ratio of the binder in the negative electrode film layer is 0-30% by weight, based on the total weight of the negative electrode film layer.

[0101] In some embodiments, the negative electrode film layer can further optionally include a conductive agent. The conductive agent can 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 0-20% by weight, based on the total weight of the negative electrode film layer.

[0102] In some embodiments, the negative electrode film layer can further optionally include other auxiliary agents, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like. The weight ratio of the other auxiliary agents in the negative electrode film layer is 0-15% by weight, based on the total weight of the negative electrode film layer.

[0103] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry, wherein the solid content of the negative electrode slurry is 30-70% by weight, and the viscosity at room temperature is adjusted to 2000-10000 mPa·s; coating the obtained negative electrode slurry on a negative electrode current collector, and performing a drying process, cold pressing (e.g., against a roller), to obtain the negative electrode sheet. The negative electrode powder coating unit area density is 75-220 mg / m 2 . 2 The negative electrode sheet compaction density is 1.2-2.0 g / m 3 . 3 .

[0104] The mass M of the negative active material in the negative film per unit area can be measured using a standard balance.

[0105] The thickness T of the negative film can be measured using a micrometer, for example, a micrometer with a model number of Mitutoyo 293-100 and a precision of 0.1 μm. It should be noted that the thickness of the negative film as described herein refers to the thickness of the negative film in the negative electrode sheet after being cold-pressed and compacted and used to assemble a battery.

[0106] Electrolyte

[0107] The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The type of the electrolyte is not particularly limited and can be selected as needed. For example, the electrolyte can be in a liquid state, a gel state, or a full solid state.

[0108] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution 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 bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalato borate (LiDFOB), lithium dioxalato borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalato phosphate (LiDFOP), and lithium tetrafluorodioxalato phosphate (LiTFOP).

[0110] The electrolyte salt of the sodium ion secondary battery can be selected from one or more of sodium hexafluorophosphate, sodium bisfluorosulfonylimide, sodium bis-trifluoromethanesulfonylimide, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium difluorophosphate, sodium perchlorate, 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), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0113] In some embodiments, the electrolyte solution can further optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive capable of improving certain properties of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0114] Separator film

[0115] In some embodiments, the secondary battery further includes a separator film. The type of the separator film is not particularly limited in the present application, and any known porous structure separator film having good chemical stability and mechanical stability can be used.

[0116] In some embodiments, the material of the separator film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0117] In some embodiments, the thickness of the separator film is 6 μm to 40 μm, and can be selected from 12 μm to 20 μm.

[0118] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator film can be used to manufacture an electrode assembly by a winding process or a stacking process.

[0119] In some embodiments, the secondary battery can include an outer package. The outer package can be used to package the above-described electrode assembly and the electrolyte solution.

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

[0121] The shape of the secondary battery is not particularly limited, and can be cylindrical, square, or any other shape. For example, Figure 3 is a square structure as an example of a secondary battery 5.

[0122] In some embodiments, referring to Figure 4 , the outer package can include a housing 51 and a cover plate 53. The housing 51 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be provided on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator can form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and the skilled person can select according to the specific actual needs.

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

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

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

[0126] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by the skilled person according to the application and capacity of the battery pack.

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

[0128] In addition, the application also provides a power utilization device, which comprises at least one of the secondary battery, the battery module, or the battery pack provided by the application. The secondary battery, the battery module, or the battery pack can be used as a power supply of the power utilization device, and can also be used as an energy storage unit of the power utilization device. The power utilization device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0129] As the power utilization device, the secondary battery, the battery module, or the battery pack can be selected according to the use requirement thereof.

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

[0131] The device as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and the secondary battery can be used as a power supply.

[0132] The following are some embodiments.

[0133] In order to make the technical problems, technical solutions and beneficial effects solved by the application clearer, the application will be further described in detail below in combination with embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the application, but not all the embodiments. The description of the at least one exemplary embodiment is actually only illustrative, but not as any limitation on the application and its application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the application.

[0134] The specific technology or condition not mentioned in the embodiments is carried out according to the technology or condition described in the literature in the art or according to the product instruction. The reagent or instrument not mentioned by the manufacturer is a conventional product that can be obtained by market purchase.

[0135] I. Battery Embodiment

[0136] Embodiment 1:

[0137] 1) Preparation of negative electrode sheet

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

[0139] The negative electrode slurry 1 is coated on both end edges of the negative electrode current collector copper foil in the width direction, and the negative electrode slurry 2 is coated on the middle position of the negative electrode current collector copper foil in the width direction; after drying and cold pressing, a negative electrode sheet is obtained. The area of the negative electrode film layer of the negative electrode sheet, which is coated with the negative electrode slurry 1, is a first area and a third area, and the area coated with the negative electrode slurry 2 is a second area. The coating weight of the negative electrode film layer is 0.108 g / 1540.25 mm 2 (in the weight excluding the solvent). The width of the first area is 60 mm, the width of the second area is 60 mm, the width of the third area is 60 mm, the thickness of the negative electrode current collector is 6 μm, the total thickness of the negative electrode sheet is 110 μm, and the thicknesses of the negative electrode film layers on the upper and lower sides of the negative electrode current collector are equal.

[0140] 2) Preparation of a positive electrode sheet

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

[0142] 3) Preparation of an electrolyte

[0143] In an argon atmosphere glove box with water content <10 ppm, EC (ethylene carbonate), PC (propylene carbonate), DMC (dimethyl carbonate) were mixed in a weight ratio of EC:PC:DMC=3:3:3, then LiPF6, VC (vinylene carbonate), DTD (vinyl sulfate), PS (propylene sulfite) were added to the mixed organic solvent, and after stirring uniformly, an electrolyte was obtained, 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.

[0144] 4) Separator film

[0145] A polyethylene porous film was used as the separator film.

[0146] 5) Battery assembly

[0147] The positive electrode sheet, the separator film, and the negative electrode sheet were stacked in order, with the separator film between the positive electrode sheet and the negative electrode sheet to play a separating role, and were wound to obtain a bare battery cell. The bare battery cell was placed in an outer package, injected with prepared electrolyte, and packaged for formation to obtain a lithium ion secondary battery.

[0148] Example 2:

[0149] This example is basically the same as Example 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 example, the volume particle size distribution Dv50 of the negative electrode active material graphite in the second region is 12.5 μm.

[0150] Example 3:

[0151] This example is basically the same as Example 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 example, the volume particle size distribution Dv50 of the negative electrode active material graphite in the second region is 11.7 μm.

[0152] Example 4:

[0153] This example is basically the same as Example 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 example, the volume particle size distribution Dv50 of the negative electrode active material graphite in the second region is 10.3 μm.

[0154] Example 5:

[0155] This example is basically the same as Example 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 example, the volume particle size distribution Dv50 of the negative electrode active material graphite in the second region is 8.6 μm.

[0156] Example 6:

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

[0158] Example 7:

[0159] 1) Negative electrode sheet preparation

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

[0161] The above negative electrode slurry 1 was coated on the two end edges of the negative electrode current collector copper foil in the width direction, and the negative electrode slurry 2 was coated on the middle position of the negative electrode current collector copper foil in the width direction; after drying and cold pressing, a negative electrode sheet was obtained. Among them, the region of the negative electrode film layer coated with the negative electrode slurry 1 is the first region and the third region, and the region coated with the negative electrode slurry 2 is the second region. The coating weight of the negative electrode film layer is 0.108 g / 1540.25 mm 2 (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 current collector is 6 μm, the total thickness of the negative electrode sheet is 110 μm, and the thicknesses of the negative electrode film layers on the upper and lower sides of the negative electrode current collector are equal.

[0162] 2) Positive electrode sheet preparation

[0163] The positive active material lithium iron phosphate (gravimetric capacity 139 mAh / g), conductive agent acetylene black, and binder PVDF were mixed in a weight ratio of 96:2:2, and the solvent N-methyl pyrrolidone was added, and the mixture was thoroughly stirred and mixed to obtain a positive electrode slurry, and then the positive electrode slurry was 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 (weight excluding solvent), and then dried and cold pressed to obtain a positive electrode sheet.

[0164] 3) Electrolyte preparation

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

[0166] 4) Isolation film

[0167] A polyethylene porous film is used as the isolation film.

[0168] 5) Battery assembly

[0169] The positive electrode sheet, the isolation film, and the negative electrode sheet are stacked in order, with the isolation film between the positive electrode sheet and the negative electrode sheet to play a role of isolation, and a bare battery cell is obtained by winding. The bare battery cell is placed in an outer package, injected with prepared electrolyte, and packaged for formation to obtain a lithium ion secondary battery.

[0170] Example 8:

[0171] This example is basically the same as Example 7, with the only difference being that the graphitization degree of the negative active material graphite in the second region of the negative electrode film layer is different. In this example, the graphitization degree of the negative active material graphite in the second region is 81%.

[0172] Example 9:

[0173] This example is basically the same as Example 7, with the only difference being that the graphitization degree of the negative active material graphite in the second region of the negative electrode film layer is different. In this example, the graphitization degree of the negative active material graphite in the second region is 78%.

[0174] Example 10:

[0175] This example is basically the same as Example 7, with the only difference being that the graphitization degree of the negative active material graphite in the second region of the negative electrode film layer is different. In this example, the graphitization degree of the negative active material graphite in the second region is 76%.

[0176] Example 11:

[0177] This example is basically the same as Example 7, with the only difference being that the graphitization degree of the negative active material graphite in the second region of the negative electrode film layer is different. In this example, the graphitization degree of the negative active material graphite in the second region is 72%.

[0178] Example 12:

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

[0180] Example 13:

[0181] 1) Negative electrode sheet preparation

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

[0183] The negative electrode slurry 1 described above was coated on the two end edges of the negative electrode current collector copper foil in the width direction, and the negative electrode slurry 2 was coated on the middle position of the negative electrode current collector copper foil in the width direction. After drying and cold pressing, a negative electrode sheet was obtained. In the negative electrode film layer of the negative electrode sheet, the region coated with the negative electrode slurry 1 was the first region and the third region, and the region coated with the negative electrode slurry 2 was the second region. The coating weight of the negative electrode film layer was 0.108 g / 1540.25 mm 2 (in terms of the weight excluding the solvent). The width of the first region was 60 mm, the width of the second region was 60 mm, the width of the third region was 60 mm, the thickness of the negative electrode current collector was 6 μm, the total thickness of the negative electrode sheet was 110 μm, and the thicknesses of the negative electrode film layers on the upper and lower sides of the negative electrode current collector were equal.

[0184] 2) Positive electrode sheet preparation

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

[0186] 3) Electrolyte preparation

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

[0188] 4) Separator film

[0189] A polyethylene porous film is used as the separator film.

[0190] 5) Battery assembly

[0191] The positive electrode sheet, the separator film, and the negative electrode sheet are stacked in order, with the separator film between the positive electrode sheet and the negative electrode sheet to play a separating role, and the naked battery cell is obtained by winding. The naked battery cell is placed in an outer package, the prepared electrolyte is injected, and the package is sealed for formation to obtain a lithium ion secondary battery.

[0192] Example 14:

[0193] This example is basically the same as Example 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 example, the OI value of the negative electrode active material graphite in the second region is 3.89.

[0194] Example 15:

[0195] This example is basically the same as Example 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 example, the OI value of the negative electrode active material graphite in the second region is 3.45.

[0196] Example 16:

[0197] This example is basically the same as Example 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 example, the OI value of the negative electrode active material graphite in the second region is 3.21.

[0198] Example 17:

[0199] This example is basically the same as Example 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 example, the OI value of the negative electrode active material graphite in the second region is 2.99.

[0200] Example 18:

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

[0202] Example 19:

[0203] 1) Negative electrode sheet preparation

[0204] The negative active material artificial graphite (gravimetric capacity of 340 mAh / g, volume particle size distribution Dv50 = 15.0 pm, graphitization degree = 90%, OI value = 5.22), conductive agent acetylene black, binder SBR (styrene-butadiene rubber), and binder CMC (carboxymethyl cellulose) were mixed in a weight ratio of 95:1.5:3.1:0.4, and a solvent, deionized water, was added. After sufficient stirring and mixing, negative electrode slurry 1 was obtained. The negative active material artificial graphite (gravimetric capacity of 340 mAh / g, volume particle size distribution Dv50 = 10.3 pm, graphitization degree = 76%, OI value = 3.21), conductive agent acetylene black, binder SBR, and binder CMC were mixed in a weight ratio of 95:1.5:3.1:0.4, and a solvent, deionized water, was added. After sufficient stirring and mixing, negative electrode slurry 2 was obtained.

[0205] The negative electrode slurry 1 described above was coated on both end edges of the negative current collector copper foil in the width direction, and the negative electrode slurry 2 was coated on the middle position of the negative current collector copper foil in the width direction. After drying and cold pressing, a negative electrode sheet was obtained. In the negative electrode film layer of the negative electrode sheet, the region coated with the negative electrode slurry 1 was the first region and the third region, and the region coated with the negative electrode slurry 2 was the second region. The coating weight of the negative electrode film layer was 0.108 g / 1540.25 mm 2 (in terms of the weight excluding the solvent). The width of the second region / width of the negative electrode sheet h / j = 0.05, the thickness of the negative current collector was 6 pm, the total thickness of the negative electrode sheet was 110 pm, and the thicknesses of the negative electrode film layers on the upper and lower sides of the negative current collector were equal.

[0206] 2) Positive electrode sheet preparation

[0207] The positive active material lithium iron phosphate (gravimetric capacity of 139 mAh / g), conductive agent acetylene black, and binder PVDF (polyvinylidene fluoride) were mixed in a weight ratio of 96:2:2, and a solvent, N-methylpyrrolidone, was added. After sufficient stirring and mixing, a positive electrode slurry was obtained. The positive electrode slurry was then coated on a positive current collector aluminum foil, and the coating weight of the positive electrode slurry was 0.224 g / 1540.25 mm 2 (in terms of the weight excluding the solvent). After drying and cold pressing, a positive electrode sheet was obtained.

[0208] 3) Electrolyte preparation

[0209] In an argon atmosphere glove box with water content <10 ppm, EC (ethylene carbonate), PC (propylene carbonate), DMC (dimethyl carbonate) were mixed in a weight ratio of EC:PC:DMC = 3:3:3, and then LiPF6, VC (vinylene carbonate), DTD (vinyl sulfate), PS (propylene sulfite) were added to the mixed organic solvent. After stirring uniformly, an electrolyte was obtained, 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.

[0210] 4) Isolation film

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

[0212] 5) Battery assembly

[0213] The positive electrode sheet, the isolation film, and the negative electrode sheet were stacked in order, with the isolation film between the positive electrode sheet and the negative electrode sheet to play a role of isolation, and were wound to obtain a bare battery cell. The bare battery cell was placed in an outer package, injected with prepared electrolyte, and packaged for formation to obtain a lithium ion secondary battery.

[0214] Example 20:

[0215] This example is basically the same as Example 19, except that the ratio of the second area of the negative electrode film layer / the negative electrode film area is different. In this example, the width of the second area / the width of the negative electrode sheet h / j = 0.1.

[0216] Example 21:

[0217] This example is basically the same as Example 19, except that the ratio of the second area of the negative electrode film layer / the negative electrode film area is different. In this example, the width of the second area / the width of the negative electrode sheet h / j = 0.25.

[0218] Example 22:

[0219] This example is basically the same as Example 19, except that the ratio of the second area of the negative electrode film layer / the negative electrode film area is different. In this example, the width of the second area / the width of the negative electrode sheet h / j = 0.5.

[0220] Example 23:

[0221] This example is basically the same as Example 19, except that the ratio of the second area of the negative electrode film layer / the negative electrode film area is different. In this example, the width of the second area / the width of the negative electrode sheet h / j = 0.75.

[0222] Example 24:

[0223] This example is basically the same as example 19, the only difference is that the ratio of the second area of the negative electrode film layer / the negative electrode film area is different. In this example, the width of the second area / the width of the negative electrode sheet h / j = 0.85.

[0224] II. Battery Comparative Example

[0225] Comparative Example 1

[0226] 1) Preparation of negative electrode sheet

[0227] The negative electrode active material artificial graphite (gravimetric capacity 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 were mixed in a weight ratio of 95:1.5:3.1:0.4, deionized water was added, and the mixture was thoroughly stirred and mixed to obtain a negative electrode slurry.

[0228] The above negative electrode slurry was coated on the entire upper and lower surfaces of the negative electrode current collector copper foil; after drying and cold pressing, a negative electrode sheet was obtained. The coating weight of the negative electrode film layer was 0.108 g / 1540.25 mm 2 (not including the weight of the solvent). The thickness of the negative electrode current collector was 6 μm, and the total thickness of the negative electrode sheet was 110 μm. The thickness of the negative electrode film layer on the upper and lower sides of the negative electrode current collector was equal.

[0229] 2) Preparation of positive electrode sheet

[0230] The positive electrode active material lithium iron phosphate (gravimetric capacity 139 mAh / g), conductive agent acetylene black, and binder PVDF were mixed in a weight ratio of 96:2:2, N-methyl pyrrolidone was added as a solvent, and the mixture was thoroughly stirred and mixed to obtain a positive electrode slurry. The positive electrode slurry was then coated on the positive electrode current collector aluminum foil, with a coating weight of 0.224 g / 1540.25 mm 2 (not including the weight of the 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 <10 ppm, EC, PC, DMC were mixed in a weight ratio of EC:PC:DMC = 3:3:3, then LiPF6, VC, DTD, PS were added to the mixed organic solvent, and stirred uniformly to obtain an electrolyte. 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) Separation film

[0234] A porous polyethylene film is used as the separator.

[0235] 5) Battery assembly

[0236] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order with the separator between the positive electrode sheet and the negative electrode sheet to play a role of separation, and are wound to obtain a bare battery cell. The bare battery cell is placed in an outer package, injected with prepared electrolyte, and 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 artificial graphite as the negative active material 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 artificial graphite as the negative active material 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 sheet

[0243] The artificial graphite (gravimetric capacity 340 mAh / g, volume particle size distribution Dv50 = 14.3 μm) as the negative active material, the conductive agent acetylene black, the binder SBR (styrene-butadiene rubber), 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 to obtain the negative electrode slurry 1 after sufficient stirring and mixing. The artificial graphite (gravimetric capacity 340 mAh / g, volume particle size distribution Dv50 = 15 μm) as the negative active material, 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 to obtain the negative electrode slurry 2 after sufficient stirring and mixing.

[0244] The negative electrode slurry 1 is coated on the two end edges of the negative current collector copper foil in the width direction, and the negative electrode slurry 2 is coated on the middle position of the negative current collector copper foil in the width direction. After drying and cold pressing, the negative electrode sheet is obtained. In the negative electrode film layer of the negative electrode sheet, the region coated with the negative electrode slurry 1 is the first region and the third region, and the region coated with the negative electrode slurry 2 is the second region. The coating weight of the negative electrode film layer is 0.108 g / 1540.25 mm 2(Excluding the weight of the solvent). The width of the first region was 60 mm, the width of the second region was 60 mm, the width of the third region was 60 mm, the thickness of the negative current collector was 6 μm, the total thickness of the negative electrode tab was 110 μm, and the thicknesses of the negative electrode film layers on the upper and lower sides of the negative current collector were equal.

[0245] 2) Preparation of the positive electrode tab

[0246] The positive electrode active material lithium iron phosphate (gravimetric 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, a solvent N-methyl pyrrolidone was added, and the mixture was stirred thoroughly to obtain a positive electrode slurry. The positive electrode slurry was then coated on the positive current collector aluminum foil, wherein the coating weight of the negative electrode slurry was 0.224 g / 1540.25 mm 2 (Excluding the weight of the solvent), and then dried and cold-pressed to obtain the positive electrode tab.

[0247] 3) Preparation of the electrolyte

[0248] In an argon atmosphere glove box with a water content of <10 ppm, EC (ethylene carbonate), PC (propylene carbonate), and DMC (dimethyl carbonate) were 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) were added to the mixed organic solvent. After stirring uniformly, the electrolyte was obtained, 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.

[0249] 4) Separation film

[0250] A polyethylene porous film was used as the separation film.

[0251] 5) Battery assembly

[0252] The positive electrode tab, the separation film, and the negative electrode tab were stacked in order, with the separation film between the positive electrode tab and the negative electrode tab to play a separation role, and were wound to obtain a bare cell. The bare cell was placed in an outer package, the prepared electrolyte was injected, and the package was sealed for formation to obtain a lithium ion secondary battery.

[0253] Comparative Example 5:

[0254] This comparative example was 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 was different. In this example, the volume particle size distribution Dv50 of the negative electrode active material graphite in the negative electrode slurry 1 was 12.5 μm.

[0255] Comparative Example 6:

[0256] This comparative example is basically the same as Comparative Example 4, with the only difference being that the volume particle size distribution Dv50 of the active material graphite in the negative electrode slurry 1 is different. In this example, 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) Negative electrode sheet preparation

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

[0260] The above negative electrode slurry 1 was coated on both ends of the negative electrode current collector copper foil in the width direction, and the negative electrode slurry 2 was coated on the middle position of the negative electrode current collector copper foil in the width direction; after drying and cold pressing, a negative electrode sheet was obtained. Among them, the area of the negative electrode film layer coated with the negative electrode slurry 1 is the first area and the third area, and the area coated with the negative electrode slurry 2 is the second area. The coating weight of the negative electrode film layer is 0.108 g / 1540.25 mm 2 (weight excluding solvent). The width of the first area is 60 mm, the width of the second area is 60 mm, the width of the third area is 60 mm, 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 layer on the upper and lower sides of the negative electrode current collector is equal.

[0261] 2) Positive electrode sheet preparation

[0262] The positive electrode active material lithium iron phosphate (gravimetric capacity 139 mAh / g), conductive agent acetylene black, and binder PVDF were mixed in a weight ratio of 96:2:2, and a solvent N-methyl pyrrolidone was added, and the mixture was thoroughly stirred and mixed to obtain a positive electrode slurry. Then, the positive electrode slurry was 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 (weight excluding solvent), and then dried and cold pressed to obtain a positive electrode sheet.

[0263] 3) Electrolyte preparation

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

[0265] 4) Isolation film

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

[0267] 5) Battery assembly

[0268] The positive electrode sheet, the isolation film, and the negative electrode sheet were stacked in order, with the isolation film between the positive electrode sheet and the negative electrode sheet to play a role of isolation, and a bare battery cell was obtained by winding. The bare battery cell was placed in an outer package, injected with the prepared electrolyte, and packaged for formation to obtain a lithium ion secondary battery.

[0269] Comparative Example 8:

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

[0271] Comparative Example 9:

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

[0273] Comparative Example 10:

[0274] 1) Preparation of negative electrode sheet

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

[0276] The negative electrode slurry 1 is coated on both end edges of the negative electrode current collector copper foil in the width direction, and the negative electrode slurry 2 is coated on the middle position of the negative electrode current collector copper foil in the width direction; after drying and cold pressing, a negative electrode sheet is obtained. Among them, the area of the negative electrode film layer coated with the negative electrode slurry 1 is the first area and the third area, and the area coated with the negative electrode slurry 2 is the second area. The coating weight of the negative electrode film layer is 0.108 g / 1540.25 mm 2 (Excluding the weight of the solvent). The width of the first area is 60 mm, the width of the second area is 60 mm, the width of the third area is 60 mm, the thickness of the negative electrode current collector is 6 μm, and the total thickness of the negative electrode sheet is 110 μm. The thicknesses of the negative electrode film layers on the upper and lower sides of the negative electrode current collector are equal.

[0277] 2) Preparation of positive electrode sheet

[0278] The positive electrode active material lithium iron phosphate (specific capacity 139 mAh / g), the conductive agent acetylene black, and the binder PVDF are mixed in a weight ratio of 96:2:2, a solvent N-methyl pyrrolidone is added, and the mixture is stirred and mixed uniformly to obtain a positive electrode slurry. Then, the positive electrode slurry is coated on the positive electrode current collector aluminum foil, wherein the coating weight of the negative electrode slurry is 0.224 g / 1540.25 mm 2 (Excluding the weight of the 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 <10 ppm, EC, PC, and DMC are mixed in a weight ratio of EC:PC:DMC=3:3:3, and then LiPF6, VC, DTD, and PS are added to the mixed organic solvent. After stirring uniformly, an electrolyte is obtained, 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.

[0281] 4) Separation film

[0282] A polyethylene porous film is used as the separation film.

[0283] 5) Battery assembly

[0284] The positive electrode sheet, the separation film, and the negative electrode sheet are stacked in order, with the separation film between the positive electrode sheet and the negative electrode sheet to play a separation role, and are wound to obtain a bare cell. The bare cell is placed in an outer package, injected with the prepared electrolyte, and 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. In this example, the OI value of the negative electrode active material graphite in the negative electrode slurry 1 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 example, the graphitization degree of the negative electrode active material graphite in the negative electrode slurry 1 is 3.45.

[0289] III. Test Methods

[0290] 1) Dv50 test of volume particle size distribution

[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 the particle size analyzer-laser diffraction method. Specifically, it can be measured according to the manufacturer's instructions using a laser diffraction scattering particle size analyzer in accordance with the standard GB / T19077-2016.

[0292] 2) Graphitization degree test

[0293] The crystal cell parameters are calculated by X-ray polycrystalline diffraction, and the C004 and Si311 peak positions of two parallel samples are obtained by the barycentric method. The value of the graphite interlayer spacing d002 is calculated by substituting the crystal face spacing formula. The obtained d002 is substituted into the Mering-Maire formula: g = [(3.440-d002) / (3.440-3.354)]*100%, to obtain the graphitization degree value g. The graphitization degree g of the negative electrode active material can be determined by the XRD diffraction method through the lattice parameters of carbon crystals according to the standards JB / T4220-2011 and JIS K0131-1996.

[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 test according 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 normal temperature cycle performance test

[0297] The lithium ion secondary battery was first charged at 1C (i.e. the current value of the theoretical capacity completely discharged within 1 h) to a voltage of 3.65 V at 25 °C, and then charged at 3.65 V to a current of 0.05C, and after standing for 5 min, the lithium ion secondary battery was discharged at 1C to a voltage of 2.5 V, which was one charge-discharge cycle process, and the discharge capacity of this time was the discharge capacity of the first cycle. The lithium ion secondary battery was subjected to multiple cycle charge-discharge tests according to the above method until the discharge capacity of the lithium ion secondary battery decayed to 80%, and the cycle number of the lithium ion secondary battery was recorded.

[0298] 5) Battery high temperature cycle performance test

[0299] The lithium ion secondary battery was first charged at 1C (i.e. the current value of the theoretical capacity completely discharged within 1 h) to a voltage of 3.65 V at 60 °C, and then charged at 3.65 V to a current of 0.05C, and after standing for 5 min, the lithium ion secondary battery was discharged at 1C to a voltage of 2.5 V, which was one charge-discharge cycle process, and the discharge capacity of this time was the discharge capacity of the first cycle. The lithium ion secondary battery was subjected to multiple cycle charge-discharge tests according to the above method, and the discharge capacity of the 500th cycle was detected.

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

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

[0302] Table 1

[0303]

[0304]

[0305]

[0306] Table 2

[0307]

[0308]

[0309] Table 3

[0310]

[0311]

[0312]

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

[0314] As can be seen from Examples 7 to 12 and Comparative Examples 1 to 3 and 7 to 9, by controlling the graphitization degree of the graphite in the middle region of the negative electrode tab to be less than that in the outer regions, the fast charging capability of the graphite in the middle region can be greater than that in the outer regions, while the difference in the 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 regions. When a1-b≥20% or a2-b≥20%, the kinetics of the graphite in the outer regions is too slow, which can increase the probability of lithium precipitation in the outer regions.

[0315] As can be seen from Examples 13 to 18 and Comparative Examples 1 to 3 and 10 to 12, by controlling the OI value of the graphite in the middle region of the negative electrode tab to be less than that in the outer regions, the fast charging capability of the graphite in the middle region can be greater than that in the outer regions, while 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 regions. When e1-f≥3.0 or e2-f≥3.0, the kinetics of the graphite in the outer regions is too slow, which can increase the probability of lithium precipitation in the outer regions.

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

[0317] In summary, in view of the phenomenon that the middle region of the electrode tab has high temperature, large swelling force, and small positive polarization during the cycle process of the battery cell, while the head and bottom regions of the electrode tab have low temperature, small swelling force, and large positive polarization, a novel differential design of the negative electrode tab is proposed, which adjusts the fast charging capability of the graphite in the middle region (the second region) of the negative electrode tab to be greater than that in the outer regions (the first region and the third region), so as to improve the fast lithium intercalation capability of the graphite in the middle region, thereby relieving the mismatch between the positive and negative electrodes during the cycle process of the battery cell and improving the middle lithium precipitation of the battery cell.

[0318] Note that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration, function, and effect as the technical idea of the present application are included in the technical scope of the present application. Furthermore, other modes constructed by applying various modifications to the embodiments, or by combining part of the configurations of the embodiments, which can be conceived by those skilled in the art, without departing from the spirit of the present application, are also included in the scope of the present application.

Claims

1. A negative electrode sheet, characterized by, The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, the negative electrode film layer comprising a negative electrode active material, the negative electrode active material comprising graphite; the negative electrode film layer comprises a first region, a second region and a third region, the first region, the second region and the third region being sequentially arranged in a first direction; the first direction is a width direction of the negative electrode sheet. At least one of the following conditions is satisfied by the negative electrode sheet: (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; 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, 5% < a1-b < 40%, 5% < a2-b < 40%; (2) 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; 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, 1.33 ≤ e1-f < 9, 1.33 ≤ e2-f < 9; the OI value of the graphite in the first region and the third region is independently 5.0-10.0; the OI value of the graphite in the second region is 2.5-4.

5.

2. The negative electrode sheet according to claim 1, characterized by 5% < a1-b < 20%, 5% < a2-b < 20%.

3. The negative electrode sheet according to claim 1, wherein The graphitization degree of the graphite in the first region and the third region is independently 65%-100%; the graphitization degree of the graphite in the second region is 60%-90%.

4. The negative electrode sheet according to claim 1, wherein 1.5 < e1-f < 3.0, 1.5 < e2-f < 3.

0.

5. The negative electrode sheet according to any one of claims 1 to 4, wherein The size of the first region, the second region and the third region in the first direction is g, h and i respectively, and 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.

6. The negative electrode sheet according to any one of claims 1 to 4, wherein The thickness of the negative electrode sheet is 50 μm-400 μm.

7. A secondary battery characterized by comprising: The secondary battery comprises the negative electrode sheet of any one of claims 1-6.

8. The secondary battery according to claim 7, characterized by The negative electrode sheet has a first overhang region and a second overhang region at both ends in the first direction respectively; the range of the first region covers the first overhang region; the range of the third region covers the second overhang region.

9. The secondary battery according to claim 8, characterized by The size of the first region in the first direction is greater than the size of the first overhang region in the first direction.

10. The secondary battery according to claim 8, characterized by The size of the third region in the first direction is greater than the size of the second overhang region in the first direction.

11. An electrical device, characterized by The secondary battery comprises the negative electrode sheet of any one of claims 7-10.

Images