Roll core, roll core preparation method and battery monomer

Abstract

The invention belongs to the technical field of batteries, and discloses a roll core, a roll core preparation method and a battery monomer, the roll core comprises a positive plate and a negative plate, the positive plate and the negative plate are stacked and are wound along a winding direction, two ends of the positive plate are a positive starting end and a positive ending end in sequence along the winding direction, and the positive starting end and the positive ending end are wound along the winding direction. The two ends of the negative plate are a negative starting end and a negative ending end in sequence, the surface density of the positive starting end is larger than that of the positive ending end, and the surface density of the negative starting end is larger than that of the negative ending end, so that the winding starting area of the winding core can automatically dissipate heat, or the surface density of the positive starting end is smaller than that of the positive ending end, and the surface density of the negative starting end is smaller than that of the negative ending end. The surface density of the cathode starting end is smaller than that of the cathode ending end, so that the winding starting area of the winding core can be automatically heated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a winding core, a winding core preparation method and a battery cell. BACKGROUND

[0002] Lithium batteries need to control temperature during charging and discharging, and specific heating or cooling measures are selected according to the ambient temperature.

[0003] In the prior art, a temperature control device such as a liquid cooling plate is often used to control the temperature of lithium batteries, for example, in hot areas with high ambient temperature, the temperature control device cools the lithium battery, and in cold areas with low ambient temperature, the temperature control device heats the lithium battery.

[0004] The above scheme has poor temperature control effect on cylindrical lithium batteries, therefore, it is urgent to provide a winding core, a winding core preparation method and a battery cell to solve the above technical problems. SUMMARY

[0005] The first object of the present application is to provide a winding core, the winding start area of which can be self-heated or self-cooled.

[0006] To achieve this object, the present application adopts the following technical scheme:

[0007] A winding core, comprising a positive electrode sheet and a negative electrode sheet, the positive electrode sheet and the negative electrode sheet are stacked and wound along a winding direction;

[0008] Along the winding direction, the two ends of the positive electrode sheet are a positive electrode start end and a positive electrode end end in sequence;

[0009] Along the winding direction, the two ends of the negative electrode sheet are a negative electrode start end and a negative electrode end end in sequence;

[0010] The area density of the positive electrode start end is greater than the area density of the positive electrode end end, and the area density of the negative electrode start end is greater than the area density of the negative electrode end end;

[0011] Alternatively, the area density of the positive electrode start end is less than the area density of the positive electrode end end, and the area density of the negative electrode start end is less than the area density of the negative electrode end end.

[0012] Optionally, along the winding direction, the area density of the positive electrode sheet gradually changes, and the area density of the negative electrode sheet gradually changes.

[0013] Optionally, along the winding direction, the thickness of the positive electrode sheet is constant, and the thickness of the negative electrode sheet is constant.

[0014] Optionally, the area density of the positive electrode start end is a, the area density of the positive electrode end end is b, 5g / m 2 ≤|a-b|≤105g / m 2 ;

[0015] And / or, the surface density of the negative electrode starting end is c, the surface density of the negative electrode ending end is d, 5g / m 2 ≤|c-d|≤125g / m 2 .

[0016] Optionally, the compaction density of the positive electrode starting end is greater than the compaction density of the positive electrode ending end, and the compaction density of the negative electrode starting end is greater than the compaction density of the negative electrode ending end.

[0017] Or, the compaction density of the positive electrode starting end is less than the compaction density of the positive electrode ending end, and the compaction density of the negative electrode starting end is less than the compaction density of the negative electrode ending end.

[0018] Optionally, along the winding direction, the compaction density of the positive electrode sheet gradually changes, and the compaction density of the negative electrode sheet gradually changes.

[0019] Optionally, the compaction density of the positive electrode starting end is e, the compaction density of the positive electrode ending end is f, 0.05g / cm 3 ≤|e-f|≤4g / cm 3 ;

[0020] And / or, the compaction density of the negative electrode starting end is g, the compaction density of the negative electrode ending end is h, 0.05g / cm 3 ≤|g-h|≤2g / cm 3 .

[0021] The second object of the application is to provide a core preparation method, and the winding starting area of the core prepared by the method can be self-heated or self-cooled.

[0022] To achieve this object, the application adopts the following technical solutions:

[0023] The core preparation method comprises the following steps:

[0024] S1, providing a positive electrode current collector and a negative electrode current collector;

[0025] S2, preparing a positive electrode active material layer on the positive electrode current collector, taking the two ends of the positive electrode current collector in the first direction as a positive electrode first end and a positive electrode second end in sequence, and the thickness of the positive electrode active material layer of the positive electrode first end is greater than the thickness of the positive electrode active material layer of the positive electrode second end;

[0026] Preparing a negative electrode active material layer on the negative electrode current collector, taking the two ends of the negative electrode current collector in the first direction as a negative electrode first end and a negative electrode second end in sequence, and the thickness of the negative electrode active material layer of the negative electrode first end is greater than the thickness of the negative electrode active material layer of the negative electrode second end;

[0027] S3, compacting the positive electrode active material layer on the positive electrode current collector to form a positive electrode sheet;

[0028] The negative active material layer on the negative current collector is compacted to form a negative electrode sheet;

[0029] S4, stacking the positive electrode sheet and the negative electrode sheet, and making the positive electrode first end and the negative electrode first end face the same direction to form an electrode sheet structure;

[0030] The electrode sheet structure is wound along a first direction;

[0031] Alternatively, the electrode sheet structure is wound along a second direction opposite to the first direction.

[0032] Optionally, in step S2, the thickness of the positive active material layer is gradually changed along the first direction, and the thickness of the negative active material layer is gradually changed along the first direction.

[0033] Optionally, in step S3, the thickness of the positive electrode sheet is kept consistent along the first direction, and the thickness of the negative electrode sheet is kept consistent along the first direction.

[0034] A third object of the present application is to provide a battery monomer, the winding starting area of the winding core of which can be autonomously cooled or heated.

[0035] To achieve the above object, the present application adopts the following technical solutions:

[0036] The battery monomer comprises a battery shell and the winding core, and the winding core is arranged in the battery shell.

[0037] A fourth object of the present application is to provide a battery monomer, the winding starting area of the winding core of which can be autonomously cooled or heated.

[0038] To achieve the above object, the present application adopts the following technical solutions:

[0039] The battery monomer comprises a battery shell and the winding core prepared by the winding core preparation method, and the winding core is arranged in the battery shell.

[0040] The present application has the following beneficial effects:

[0041] The volume core provided by the present application is characterized in that the surface density of the starting end of the positive electrode is greater than that of the ending end of the positive electrode, and the surface density of the starting end of the negative electrode is greater than that of the ending end of the negative electrode. For the convenience of description, the volume core located in the starting end of the positive electrode and the starting end of the negative electrode is referred to as the winding starting area, and the volume core located in the ending end of the positive electrode and the ending end of the negative electrode is referred to as the winding ending area. In the battery shell, the structure can make the electrolyte of the winding ending area more than that of the winding starting area, so that the internal resistance of the winding ending area is less than that of the winding starting area, and the heat production of the winding ending area is less than that of the winding starting area, thereby forming a temperature difference between the winding ending area and the winding starting area. The temperature difference is beneficial to the heat transfer from the winding starting area to the winding ending area, and achieves the effect of self-heat dissipation of the winding starting area.

[0042] The volume core provided by the present application is characterized in that the surface density of the starting end of the positive electrode is greater than that of the ending end of the positive electrode, and the surface density of the starting end of the negative electrode is greater than that of the ending end of the negative electrode. For the convenience of description, the volume core located in the starting end of the positive electrode and the starting end of the negative electrode is referred to as the winding starting area, and the volume core located in the ending end of the positive electrode and the ending end of the negative electrode is referred to as the winding ending area. In the battery shell, the structure can make the electrolyte of the winding ending area more than that of the winding starting area, so that the internal resistance of the winding ending area is less than that of the winding starting area, and the heat production of the winding ending area is less than that of the winding starting area, thereby forming a temperature difference between the winding ending area and the winding starting area. The temperature difference is beneficial to the heat transfer from the winding starting area to the winding ending area, and achieves the effect of self-heat dissipation of the winding starting area. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 FIG. 1 is a structural schematic diagram of the volume core provided by the first embodiment of the present application;

[0044] Figure 2 FIG. 2 is a structural schematic diagram of the positive electrode sheet before the positive active material layer is compacted according to the first embodiment of the present application;

[0045] Figure 3 FIG. 3 is a structural schematic diagram of the positive electrode sheet after the positive active material layer is compacted according to the first embodiment of the present application;

[0046] Figure 4 FIG. 4 is a structural schematic diagram of the negative electrode sheet before the negative active material layer is compacted according to the first embodiment of the present application;

[0047] Figure 5 FIG. 5 is a structural schematic diagram of the negative electrode sheet after the negative active material layer is compacted according to the first embodiment of the present application;

[0048] Figure 6 FIG. 6 is a structural schematic diagram of the positive electrode sheet before the positive active material layer is compacted according to the second embodiment of the present application;

[0049] Figure 7 FIG. 7 is a structural schematic diagram of the positive electrode sheet after the positive active material layer is compacted according to the second embodiment of the present application;

[0050] Figure 8 is a structure schematic diagram of the negative electrode sheet before the negative electrode active material layer is compacted according to the second embodiment of the present application;

[0051] Figure 9 is a structure schematic diagram of the negative electrode sheet after the negative electrode active material layer is compacted according to the second embodiment of the present application.

[0052] In the figure:

[0053] 10, winding core; 11, axis; 12, winding start area; 13, winding end area; 100, positive electrode sheet; 110, positive electrode start end; 120, positive electrode end end; 131, positive electrode current collector; 132, positive electrode active material layer; 200, negative electrode sheet; 210, negative electrode start end; 220, negative electrode end end; 231, negative electrode current collector; 232, negative electrode active material layer. DETAILED DESCRIPTION

[0054] The present application will be further described below in conjunction with the drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the present application, but not to limit the present application. In addition, it should be noted that, for the convenience of description, only the parts related to the present application are shown in the drawings, but not all the structures.

[0055] In the description of the present application, unless otherwise explicitly specified and limited, the terms "connected", "connected", "fixed" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0056] In the present application, unless otherwise explicitly specified and limited, the "upper" or "lower" of the first feature to the second feature can include that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, the "upper", "above" and "on" of the first feature to the second feature includes that the first feature is directly above and obliquely above the second feature, or only indicates that the horizontal height of the first feature is higher than that of the second feature. The "below", "under" and "under" of the first feature to the second feature includes that the first feature is directly below and obliquely below the second feature, or only indicates that the horizontal height of the first feature is less than that of the second feature.

[0057] In the description of the present embodiment, the terms "upper", "lower", "right", "left", and the like, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first" and "second" are only used to distinguish in description and have no special meaning.

[0058] In the prior art, a temperature control device such as a liquid cooling plate is often used to control the temperature of the battery monomer. The temperature control device is arranged outside the battery shell, and the cell is arranged inside the battery shell. The temperature control device outside the battery shell heats or cools the cell inside the battery shell.

[0059] The cell of the cylindrical battery monomer is in the form of a roll (hereinafter referred to as a roll cell). The roll cell is usually formed by stacking and winding positive and negative electrode sheets in sequence. As shown in Figure 1 In the radial direction of the roll cell 10, the roll cell 10 close to the axis 11 is the winding start area 12, and the roll cell 10 away from the axis 11 is the winding end area 13. It can be seen that compared with the winding end area 13, the winding start area 12 has a larger distance from the temperature control device, which results in poor temperature control effect of the temperature control device on the winding start area 12. When the battery monomer is applied to a hot area with high ambient temperature, the cooling effect of the temperature control device on the winding start area 12 is poor, which increases the risk of thermal runaway of the battery monomer. In addition, due to the uneven temperature distribution in the radial direction of the roll cell 10, the conductivity of the battery monomer is reduced. When the battery monomer is applied to a cold area with low ambient temperature, the heating effect of the temperature control device on the winding start area 12 is poor, which results in uneven temperature distribution in the radial direction of the roll cell 10, and reduces the conductivity of the battery monomer.

[0060] Therefore, the present application provides a roll cell 10, a roll cell preparation method and a battery monomer, which aims to improve the cooling effect or heating effect of the winding start area 12. The roll cell 10 and the roll cell preparation method are mainly applied to lithium battery structures.

[0061] Embodiment one

[0062] The present embodiment provides a roll cell 10, which can autonomously dissipate heat at the winding start area 12.

[0063] Specifically, as shown in Figures 1 to 5As shown, the winding core 10 includes the positive electrode sheet 100 and the negative electrode sheet 200, the positive electrode sheet 100 and the negative electrode sheet 200 are stacked and wound along the winding direction, along the winding direction, two ends of the positive electrode sheet 100 are the positive electrode starting end 110 and the positive electrode ending end 120 in sequence, along the winding direction, two ends of the negative electrode sheet 200 are the negative electrode starting end 210 and the negative electrode ending end 220 in sequence, the surface density of the positive electrode starting end 110 is greater than the surface density of the positive electrode ending end 120, and the surface density of the negative electrode starting end 210 is greater than the surface density of the negative electrode ending end 220.

[0064] In this embodiment, the winding direction is Figures 2 to 5 x1 direction in the formula (1).

[0065] The winding core 10 provided in this embodiment, the direction of the positive electrode starting end 110 pointing to the positive electrode ending end 120 is the winding direction, and the direction of the negative electrode starting end 210 pointing to the negative electrode ending end 220 is the winding direction, therefore, the position of the winding core 10 corresponding to the positive electrode starting end 110 and the negative electrode starting end 210 is the winding starting area 12, and the position of the winding core 10 corresponding to the positive electrode ending end 120 and the negative electrode ending end 220 is the winding ending area 13. The surface density of the positive electrode starting end 110 is greater than the surface density of the positive electrode ending end 120, and the surface density of the negative electrode starting end 210 is greater than the surface density of the negative electrode ending end 220, therefore, in the battery shell, this structure can make the electrolyte of the winding ending area 13 more than the electrolyte of the winding starting area 12, and then the internal resistance of the winding ending area 13 is less than the internal resistance of the winding starting area 12, the heat production of the winding ending area 13 is less than the heat production of the winding starting area 12, and the effect of the temperature of the winding ending area 13 being lower than the temperature of the winding starting area 12 is achieved, thereby forming a temperature difference between the winding ending area 13 and the winding starting area 12, which is beneficial to the heat transfer from the winding starting area 12 to the winding ending area 13, and realizes the effect of self-heat dissipation of the winding starting area 12. This structure design can reduce the risk of thermal runaway of the battery monomer, improve the safety of the battery monomer, and the structure design also improves the uniformity of the temperature distribution in the radial direction of the winding core 10, which is beneficial to improving the conductivity of the battery monomer.

[0066] On the other hand, the areal density of the positive electrode starting end 110 is greater than that of the positive electrode ending end 120, and the areal density of the negative electrode starting end 210 is greater than that of the negative electrode ending end 220. Therefore, the kinetic performance of both the positive electrode ending end 120 and the negative electrode ending end 220 is better than that of the positive electrode starting end 110 and the negative electrode starting end 210. The lithium-ion diffusion resistance of the winding ending region 13 is small, which enables faster transport between the active material and the electrolyte, which helps to alleviate lithium-ion concentration polarization, thereby improving the charge and discharge efficiency and rate performance of the winding core 10. Furthermore, the kinetic performance of the positive electrode termination 120 and the negative electrode termination 220 is superior to that of the positive electrode initiation 110 and the negative electrode initiation 210. During battery cell charging, the negative electrode termination 220 preferentially inserts lithium compared to the negative electrode initiation 210, thereby reducing the expansion of the negative electrode initiation 210, which in turn reduces the expansion of the winding initiation region 12. During battery cell discharging, the positive electrode termination 120 preferentially inserts lithium compared to the positive electrode initiation 110, thereby reducing the expansion of the positive electrode initiation 110, which in turn reduces the expansion of the winding initiation region 12. Therefore, this structural design is beneficial in reducing the expansion of the winding initiation region 12 during battery cell charging and discharging, thus achieving the effect of reducing the expansion of the core 10.

[0067] On the other hand, the areal density of the positive electrode starting end 110 is greater than that of the positive electrode ending end 120, and the areal density of the negative electrode starting end 210 is greater than that of the negative electrode ending end 220. Therefore, the loading and efflux of the active material at the positive electrode starting end 110 and the negative electrode starting end 210 are both greater than those at the positive electrode ending end 120 and the negative electrode ending end 220. Under the condition that the volume or weight of the battery cell is the same, the core 10 provided in this embodiment stores more electrical energy, which is beneficial to improving the energy density of the battery cell.

[0068] Further, the area density of the positive electrode sheet 100 gradually changes along the winding direction, and the area density of the negative electrode sheet 200 gradually changes, that is, in the present embodiment, the area density of the positive electrode sheet 100 gradually decreases along the winding direction, and the area density of the negative electrode sheet 200 gradually decreases along the winding direction. This structural design is conducive to further reducing the risk of battery cell thermal runaway and improving the temperature uniformity of the jelly-roll 10 in the radial direction. Specifically, this structure can gradually increase the amount of electrolyte in the battery shell along the winding direction, so that the internal resistance of the jelly-roll 10 gradually decreases along the winding direction, the heat generation of the jelly-roll 10 gradually decreases, and the temperature of the jelly-roll 10 gradually decreases, thereby forming a temperature difference along the winding direction of the entire jelly-roll 10. This temperature difference can make the heat of the winding start area 12 transfer along the winding direction to the winding end area 13, and the temperature difference can also make the heat of the winding start area 12 transfer along the radial direction of the jelly-roll 10 to the outer periphery of the jelly-roll 10. It can be seen that this structure increases the heat transfer path of the winding start area 12, which has the effect of improving the heat dissipation efficiency of the winding start area 12. Moreover, when the winding start area 12 and the winding end area 13 do not overlap in the radial direction of the jelly-roll 10, this structure also shortens the heat transfer path of the winding start area 12, further improving the heat dissipation efficiency of the winding start area 12. Again, this structure makes the temperature of the entire jelly-roll 10 gradually decrease along the winding direction, so that the jelly-roll 10 located between the winding start area 12 and the winding end area 13 can also dissipate heat autonomously, and the heat transfer path of the jelly-roll 10 in this region includes two paths along the winding direction and along the radial direction, achieving the effect of efficient heat dissipation of the jelly-roll 10 in this region.

[0069] On the other hand, this structural design is conducive to reducing the difficulty of preparing the positive electrode sheet 100 and the negative electrode sheet 200. Specifically, before the active material layer on the current collector is compacted, the area density of the electrode sheet is mainly reflected in the thickness of the active material layer. Along the winding direction, the area density of the positive electrode sheet 100 gradually changes, that is, before the positive electrode active material layer 132 is compacted, the thickness of the positive electrode active material layer 132 on the positive electrode current collector 131 gradually changes along the winding direction. Compared with the thickness of the positive electrode active material layer 132 suddenly changing at a certain position on the positive electrode current collector 131, this gradually changing thickness structure is conducive to reducing the difficulty of preparing the positive electrode active material layer 132 on the positive electrode current collector 131. Similarly, along the winding direction, the area density of the negative electrode sheet 200 gradually changes, that is, before the negative electrode active material layer 232 is compacted, the thickness of the negative electrode active material layer 232 on the negative electrode current collector 231 gradually changes along the winding direction. Compared with the thickness of the negative electrode active material layer 232 suddenly changing at a certain position on the negative electrode current collector 231, this gradually changing thickness structure is conducive to reducing the difficulty of preparing the negative electrode active material layer 232 on the negative electrode current collector 231.

[0070] Optionally, the area density of the positive electrode start end 110 is a, the area density of the positive electrode end 120 is b, 5g / m2 ≤|a-b|≤105g / m 2 For example, |a-b| can be 5g / m 2 , 10g / m 2 , 35g / m 2 , 50g / m 2 , 83g / m 2 , 100g / m 2 or 105g / m 2 , etc. In this way, the winding start area 12 has higher heat dissipation efficiency, the expansion amount of the winding core 10 is reduced, and the power storage capacity of the winding core 10 is increased.

[0071] Optionally, the surface density of the negative electrode start end 210 is c, the surface density of the negative electrode end 220 is d, and 5g / m 2 ≤|c-d|≤125g / m 2 For example, |c-d| can be 5g / m 2 , 10g / m 2 , 55g / m 2 , 60g / m 2 , 100g / m 2 , 120g / m 2 or 125g / m 2 , etc. In this way, the winding start area 12 has higher heat dissipation efficiency, the expansion amount of the winding core 10 is reduced, and the power storage capacity of the winding core 10 is increased.

[0072] Optionally, along the winding direction, the thickness of the positive electrode sheet 100 is constant, and the thickness of the negative electrode sheet 200 is constant. This structure can improve the overall structural consistency of the winding core 10, avoid radial deformation of the winding core 10, and improve the consistency of the size of the winding core 10 in different radial directions.

[0073] Further, the compaction density of the positive electrode starting end 110 is greater than the compaction density of the positive electrode ending end 120, so that the porosity of the positive electrode active material layer 132 of the positive electrode ending end 120 is greater than the porosity of the positive electrode active material layer 132 of the positive electrode starting end 110. When the battery cell is discharging, the positive electrode ending end 120 has sufficient expansion space compared with the positive electrode starting end 110, so that the expansion amount and expansion stress of the positive electrode ending end 120 can be reduced, i.e., the expansion amount and expansion stress of the winding ending area 13 are reduced. The compaction density of the negative electrode starting end 210 is greater than the compaction density of the negative electrode ending end 220, so that the porosity of the negative electrode active material layer 232 of the negative electrode ending end 220 is greater than the porosity of the negative electrode active material layer 232 of the negative electrode starting end 210. When the battery cell is discharging, the negative electrode ending end 220 has sufficient expansion space compared with the negative electrode starting end 210, so that the expansion amount and expansion stress of the negative electrode ending end 220 can be reduced, i.e., the expansion amount and expansion stress of the winding ending area 13 are reduced. It can be seen that the structural design is beneficial to reduce the expansion amount and expansion stress of the winding ending area 13, so as to reduce the expansion amount and expansion stress of the winding core 10 when the battery cell is charging and discharging.

[0074] On the other hand, the compaction density of the positive electrode starting end 110 is greater than the compaction density of the positive electrode ending end 120, and the compaction density of the negative electrode starting end 210 is greater than the compaction density of the negative electrode ending end 220. Therefore, the kinetic performance of the positive electrode ending end 120 and the negative electrode ending end 220 can be further improved, so as to further improve the charging and discharging efficiency and rate performance of the winding core 10. In addition, when the battery cell is charging, the lithium is preferentially embedded in the negative electrode ending end 220 than in the negative electrode starting end 210, so as to further reduce the expansion amount of the negative electrode starting end 210, i.e., the expansion amount of the winding starting area 12 is reduced. When the battery cell is discharging, the lithium is preferentially embedded in the positive electrode ending end 120 than in the positive electrode starting end 110, so as to further reduce the expansion amount of the positive electrode starting end 110, i.e., the expansion amount of the winding starting area 12 is reduced. It can be seen that the structural design is beneficial to reduce the expansion amount of the winding starting area 12 when the battery cell is charging and discharging, so as to further reduce the expansion amount of the winding core 10.

[0075] In another aspect, the compaction density of the positive electrode starting end 110 is greater than the compaction density of the positive electrode ending end 120, and the compaction density of the negative electrode starting end 210 is greater than the compaction density of the negative electrode ending end 220. Therefore, the load amount and play amount of the active material of the positive electrode starting end 110 and the negative electrode starting end 210 can be further increased, so as to further improve the stored electric energy of the winding core 10 under the condition that the volume or weight of the battery cell is the same.

[0076] In another aspect, the compaction density of the positive electrode starting end 110 is greater than the compaction density of the positive electrode ending end 120, and the compaction density of the negative electrode starting end 210 is greater than the compaction density of the negative electrode ending end 220, which can further increase the electrolyte in the winding ending area 13, thereby increasing the temperature difference between the winding ending area 13 and the winding starting area 12, and improving the heat conduction efficiency from the winding starting area 12 to the winding ending area 13.

[0077] Optionally, the compaction density of the positive electrode sheet 100 gradually changes along the winding direction, that is, in the embodiment, the compaction density of the positive electrode sheet 100 gradually decreases along the winding direction. In the embodiment, the area density of the positive electrode sheet 100 gradually decreases along the winding direction, and the thickness of the positive electrode sheet 100 is constant along the winding direction. Therefore, when the positive electrode active material layer 132 on the positive electrode current collector 131 is compacted, the thickness of the positive electrode active material layer 132 along the winding direction is kept constant, so that the compaction density of the positive electrode sheet 100 gradually decreases along the winding direction. It can be seen that this design is beneficial to reduce the preparation difficulty of the positive electrode sheet 100, thereby improving the production efficiency of the positive electrode sheet 100 and reducing the production cost of the positive electrode sheet 100. Similarly, in the embodiment, the compaction density of the negative electrode sheet 200 gradually changes along the winding direction, that is, in the embodiment, the compaction density of the negative electrode sheet 200 gradually decreases along the winding direction. In the embodiment, the area density of the negative electrode sheet 200 gradually decreases along the winding direction, and the thickness of the negative electrode sheet 200 is constant along the winding direction. Therefore, when the negative electrode active material layer 232 on the negative electrode current collector 231 is compacted, the thickness of the negative electrode active material layer 232 along the winding direction is kept constant, so that the compaction density of the negative electrode sheet 200 gradually decreases along the winding direction. It can be seen that this design is beneficial to reduce the preparation difficulty of the negative electrode sheet 200, thereby improving the production efficiency of the negative electrode sheet 200 and reducing the production cost of the negative electrode sheet 200.

[0078] In addition, when the battery monomer is charged and discharged, the structure can make the expansion stress of the winding core 10 along the winding direction more uniform and dispersed, reduce the probability of sudden increase of the expansion stress of the winding core 10 in a certain area, and be beneficial to prolong the cycle life of the battery monomer.

[0079] Optionally, the compaction density of the positive electrode starting end 110 is e, the compaction density of the positive electrode ending end 120 is f, and 0.05g / cm 3 ≤|e-f|≤4g / cm 3 . For example, |e-f| can be 0.05g / cm 3 , 0.1g / cm 3 , 2g / cm 3 , 3.5g / cm 3 or 4g / cm 3and the like, while reducing the expansion amount and expansion stress of the winding core 10, improve the heat conduction efficiency from the winding start area 12 to the winding end area 13, and increase the power storage capacity of the winding core 10.

[0080] Optionally, the compaction density of the negative electrode start end 210 is g, the compaction density of the negative electrode end end 220 is h, and 0.05g / cm 3 ≤|g-h|≤2g / cm 3 For example, |g-h| can be 0.05g / cm 3 , 0.1g / cm 3 , 0.5g / cm 3 , 1g / cm 3 , 1.5g / cm 3 or 2g / cm 3 and the like, while reducing the expansion amount and expansion stress of the winding core 10, improve the heat conduction efficiency from the winding start area 12 to the winding end area 13, and increase the power storage capacity of the winding core 10.

[0081] The winding core 10 provided in the embodiment has a gradually decreasing surface density of the positive electrode sheet 100 and the negative electrode sheet 200 along the winding direction, and a gradually decreasing compaction density of the positive electrode sheet 100 and the negative electrode sheet 200 along the winding direction, thereby improving the charge-discharge efficiency and rate performance of the winding core 10, increasing the maximum charge current of the winding core 10 to 6C, reaching 80% of the power of the winding core 10 after 10 minutes of charging, reducing the internal resistance of the winding core 10 to 1.5mΩ, and achieving a cycle life of the winding core 10 of 1500 times when the capacity retention rate is more than 80%. In addition, the winding start area 12 of the winding core 10 can autonomously dissipate heat, so that the temperature rise of the winding core 10 is reduced by about 25% during rapid charging of the winding core 10, and the thermal runaway trigger time is delayed to 300s.

[0082] The embodiment further provides a winding core preparation method, which comprises the following steps:

[0083] S1, providing a positive electrode current collector 131 and a negative electrode current collector 231;

[0084] S2, preparing a positive electrode active material layer 132 on the positive electrode current collector 131, taking the two ends of the positive electrode current collector 131 in the first direction as a positive electrode first end and a positive electrode second end in sequence, and the thickness of the positive electrode active material layer 132 at the positive electrode first end is greater than the thickness of the positive electrode active material layer 132 at the positive electrode second end;

[0085] S3, preparing a negative electrode active material layer 232 on the negative electrode current collector 231, taking the two ends of the negative electrode current collector 231 in the first direction as a negative electrode first end and a negative electrode second end in sequence, and the thickness of the negative electrode active material layer 232 at the negative electrode first end is greater than the thickness of the negative electrode active material layer 232 at the negative electrode second end;

[0086] S3. Compact the positive electrode active material layer 132 on the positive electrode current collector 131 to form the positive electrode sheet 100;

[0087] The negative electrode active material layer 232 on the negative electrode current collector 231 is compacted to form the negative electrode sheet 200;

[0088] S4. Stack the positive electrode 100 and the negative electrode 200 so that the first end of the positive electrode and the first end of the negative electrode face the same direction to form an electrode structure, and wind the electrode structure along the first direction.

[0089] In this embodiment, the first direction is the winding direction, i.e. Figures 2 to 5 In the x1 direction, the first positive electrode end is the positive electrode starting end 110, the second positive electrode end is the positive electrode ending end 120, the first negative electrode end is the negative electrode starting end 210, and the second negative electrode end is the negative electrode ending end 220. In step S4, the electrode structure is wound along the first direction to form a core 10. The region of the core 10 radially close to the axis 11 corresponds to the positive electrode starting end 110 and the negative electrode starting end 210, i.e., the winding starting region 12 of the core 10. The region of the core 10 radially away from the axis 11 corresponds to the positive electrode ending end 120 and the negative electrode ending end 220, i.e., the winding ending region 13 of the core 10.

[0090] In step S2, the thickness of the positive active material layer 132 at the positive electrode starting end 110 is greater than the thickness of the positive active material layer 132 at the positive electrode ending end 120, and the thickness of the negative active material layer 232 at the negative electrode starting end 210 is greater than the thickness of the negative active material layer 232 at the negative electrode ending end 220. This forms a structure where the areal density of the positive electrode starting end 110 of the positive electrode sheet 100 is greater than the areal density of the positive electrode ending end 120, and the areal density of the negative electrode starting end 210 of the negative electrode sheet 200 is greater than the areal density of the negative electrode ending end 220. That is, the positive electrode layer 132 at the starting region 12 is... The areal density of electrode 100 and negative electrode 200 are greater than those of positive electrode 100 and negative electrode 200 in the winding termination region 13, respectively. Consequently, in the battery casing, the electrolyte in the winding termination region 13 is more than that in the winding start region 12, and the internal resistance of the winding termination region 13 is less than that of the winding start region 12. During charging and discharging, the heat generated in the winding termination region 13 is less than that generated in the winding start region 12, resulting in a lower temperature in the winding termination region 13 compared to the winding start region 12. This allows heat to be transferred from the winding start region 12 to the winding termination region 13. Therefore, this core preparation method enables the winding start region 12 to dissipate heat autonomously during charging and discharging, which not only reduces the risk of thermal runaway in the battery cell and improves the safety of the battery cell, but also improves the radial temperature uniformity of the core 10 and enhances the conductivity of the battery cell.

[0091] Secondly, the prepared jelly-roll 10 can make the kinetic performance of the positive electrode tail end 120 and the negative electrode tail end 220 better than the kinetic performance of the positive electrode start end 110 and the negative electrode start end 210, thereby improving the charge-discharge efficiency and rate capability of the jelly-roll 10. In addition, during charging, the negative electrode tail end 220 preferentially embeds lithium to the negative electrode start end 210, thereby reducing the expansion amount of the negative electrode start end 210, i.e., reducing the expansion amount of the winding start area 12. During discharging, the positive electrode tail end 120 preferentially embeds lithium to the positive electrode start end 110, thereby reducing the expansion amount of the positive electrode start end 110, i.e., reducing the expansion amount of the winding start area 12. It can be seen that the jelly-roll preparation method is beneficial to reducing the expansion amount of the winding start area 12, thereby reducing the expansion amount of the jelly-roll 10.

[0092] Thirdly, the prepared jelly-roll 10 can make the loading amount and the amount of active substances of the positive electrode active material and the negative electrode active material in the winding start area 12 greater than those in the winding end area 13, and in the case of the same volume or weight of the battery monomer, the jelly-roll 10 can store more electric energy, thereby being beneficial to improving the energy density of the battery monomer.

[0093] Further, in step S2, the positive electrode active material layer 132 is prepared on the positive electrode current collector 131 by using a dry electrode process. The dry electrode process does not need a solvent, and can directly mix the positive electrode active material, the conductive agent and the solid-state binder to form the positive electrode sheet 100 by compounding with the positive electrode current collector 131. Compared with the wet electrode process, the dry electrode process saves the processes and related equipment such as evaporation, recovery and drying, thereby reducing the equipment investment and operation cost, and the process energy consumption can be reduced by about 40%, and the production cost of a single jelly-roll 10 can be reduced by about 25%. Secondly, the dry electrode process can make the components in the positive electrode active material layer 132 uniformly distributed, thereby avoiding the problem of uneven distribution of the components in the positive electrode active material layer 132 caused by solvent evaporation. Thirdly, the positive electrode sheet 100 prepared by using the dry electrode process can achieve a higher compaction density, and under the same conditions, the energy density of the positive electrode sheet 100 prepared by using the dry electrode process can be improved by about 20%. Similarly, in step S2, the negative electrode active material layer 232 is prepared on the negative electrode current collector 231 by using the dry electrode process, and the technical effects are the same as those of the positive electrode sheet 100, which will not be described herein again.

[0094] It should be pointed out that the dry electrode process is a relatively mature electrode sheet production process in the technical field, and the specific preparation method will not be described herein again.

[0095] Optionally, in step S2, the thickness of the positive active material layer 132 is gradually changed along the first direction, and the thickness of the negative active material layer 232 is gradually changed along the first direction, that is, the thickness of the positive active material layer 132 gradually decreases along the first direction, and the thickness of the negative active material layer 232 gradually decreases along the first direction, so that the area density of the positive sheet 100 gradually decreases along the first direction, and the area density of the negative sheet 200 gradually decreases along the first direction. Thus, the difficulty of implementing step S2 is reduced. And during charging and discharging, the heat of the winding starting area 12 can not only be transferred to the winding ending area 13 along the winding direction, but also be transferred to the outer periphery of the winding core 10 along the radial direction of the winding core 10, thereby improving the heat dissipation efficiency of the winding starting area 12. In addition, during charging and discharging, the winding core 10 located between the winding starting area 12 and the winding ending area 13 can also dissipate heat autonomously, and the heat transfer path of the winding core 10 in this region includes two paths along the winding direction and along the radial direction, thereby achieving the effect of high-efficiency heat dissipation of the winding core 10 in this region.

[0096] Optionally, in step S3, the thickness of the positive sheet 100 is kept consistent along the first direction, and the thickness of the negative sheet 200 is kept consistent along the first direction. Thus, the compaction density of the positive sheet 100 gradually decreases along the first direction, and the compaction density of the negative sheet 200 gradually decreases along the first direction, further increasing the amount of electrolyte in the winding ending area 13, so as to increase the temperature difference between the winding ending area 13 and the winding starting area 12, thereby improving the heat dissipation efficiency of the winding starting area 12. Moreover, the kinetic performance of the positive ending end 120 and the negative ending end 220 can be further improved, thereby achieving the effects of further improving the charging and discharging efficiency and rate capability of the winding core 10, further reducing the expansion amount of the winding starting area 12, further reducing the expansion amount and expansion stress of the winding ending area 13. Finally, the method can improve the loading amount and the amount of active material of the positive active material and the negative active material in the winding starting area 12, thereby improving the storage capacity of the winding core 10 under the condition that the volume or weight of the battery cell is the same.

[0097] It should be noted that the above-mentioned compaction method for keeping the thickness of the positive sheet 100 consistent along the first direction is a prior art in the technical field, and exemplarily, the positive current collector 131 with the positive active material layer 132 (not compacted) is placed on a conveyor belt, a compression roller is arranged above the conveyor belt, the axis 11 of the compression roller is perpendicular to the conveying direction of the conveyor belt, the spacing between each position of the compression roller and the conveyor belt is the same along the axis 11 of the compression roller, the positive current collector 131 with the positive active material layer 132 (not compacted) moves along with the transmission of the conveyor belt, and the positive active material layer 132 is compacted by the compression roller, thereby keeping the thickness of the positive sheet 100 consistent along the first direction. The method for keeping the thickness of the negative sheet 200 consistent along the first direction is the same as that of the positive sheet 100, which will not be described here.

[0098] Optionally, in step S2, the positive electrode active material layer 132 is made of a high-nickel ternary material, the nickel content of the positive electrode 100 is greater than or equal to 80%, the negative electrode active material layer 232 is made of a silicon-carbon composite material, and the specific capacity of the silicon-carbon composite material in the negative electrode 200 is greater than 1200mAh / g.

[0099] This embodiment also provides a battery cell, which includes a battery casing and the aforementioned winding core 10. The winding core 10 is disposed inside the battery casing. The battery cell uses the aforementioned winding core 10, and the winding start area 12 of the winding core 10 can dissipate heat independently, so that the battery cell has high safety and conductivity.

[0100] This embodiment also provides a battery cell, which includes a battery casing and a core 10 prepared by the above-described core preparation method. The core 10 is disposed inside the battery casing. The core 10 of the battery cell is made by the above-described core preparation method. The winding start area 12 of the core 10 can dissipate heat independently, so that the battery cell has high safety and conductivity.

[0101] Example 2

[0102] This embodiment provides a core 10, a core preparation method, and a battery cell. The following mainly describes the differences between this embodiment and Embodiment 1, while the similarities will not be repeated.

[0103] like Figures 6 to 9 As shown, the areal density of the positive electrode starting end 110 is less than the areal density of the positive electrode ending end 120, and the areal density of the negative electrode starting end 210 is less than the areal density of the negative electrode ending end 220. In other words, in this embodiment, the winding direction is... Figures 6 to 9 In the x2 direction, the core 10 corresponding to the positive electrode starting end 110 and the negative electrode starting end 210 is the winding starting region 12, and the core 10 corresponding to the positive electrode ending end 120 and the negative electrode ending end 220 is the winding ending region 13. In the battery casing, this structure allows the electrolyte in the winding ending region 13 to be less than that in the winding starting region 12. Consequently, the internal resistance of the winding ending region 13 is greater than that of the winding starting region 12, and the heat generation in the winding ending region 13 is greater than that in the winding starting region 12. This achieves the effect that the temperature of the winding ending region 13 is higher than that of the winding starting region 12, thus creating a temperature difference between the winding ending region 13 and the winding starting region 12. This temperature difference facilitates the transfer of heat from the winding ending region 13 to the winding starting region 12, achieving the effect of self-heating of the winding starting region 12. This structural design improves the radial temperature uniformity of the core 10, which is beneficial for improving the conductivity of the battery cells.

[0104] In another aspect, the surface density of the positive electrode starting end 110 is less than the surface density of the positive electrode ending end 120, and the surface density of the negative electrode starting end 210 is less than the surface density of the negative electrode ending end 220, so the kinetic performance of the positive electrode starting end 110 and the negative electrode starting end 210 is better than that of the positive electrode ending end 120 and the negative electrode ending end 220, thereby improving the charge-discharge efficiency and rate capability of the winding core 10. In addition, when the battery cell is charging, lithium is preferentially inserted into the negative electrode starting end 210 than the negative electrode ending end 220, thereby reducing the expansion amount of the negative electrode ending end 220, i.e., reducing the expansion amount of the winding ending area 13. When the battery cell is discharging, lithium is preferentially inserted into the positive electrode starting end 110 than the positive electrode ending end 120, thereby reducing the expansion amount of the positive electrode ending end 120, i.e., reducing the expansion amount of the winding ending area 13. It can be seen that when the battery cell is charging and discharging, the structure can reduce the expansion amount of the winding ending area, which is beneficial to reduce the expansion amount of the winding core 10.

[0105] In another aspect, the surface density of the positive electrode starting end 110 is less than the surface density of the positive electrode ending end 120, and the surface density of the negative electrode starting end 210 is less than the surface density of the negative electrode ending end 220, so the kinetic performance of the positive electrode starting end 110 and the negative electrode starting end 210 is better than that of the positive electrode ending end 120 and the negative electrode ending end 220, thereby improving the charge-discharge efficiency and rate capability of the winding core 10. In addition, when the battery cell is charging, lithium is preferentially inserted into the negative electrode starting end 210 than the negative electrode ending end 220, thereby reducing the expansion amount of the negative electrode ending end 220, i.e., reducing the expansion amount of the winding ending area 13. When the battery cell is discharging, lithium is preferentially inserted into the positive electrode starting end 110 than the positive electrode ending end 120, thereby reducing the expansion amount of the positive electrode ending end 120, i.e., reducing the expansion amount of the winding ending area 13. It can be seen that when the battery cell is charging and discharging, the structure can reduce the expansion amount of the winding ending area, which is beneficial to reduce the expansion amount of the winding core 10.

[0106] Further, the surface density of the positive electrode sheet 100 gradually increases along the winding direction, and the surface density of the negative electrode sheet 200 gradually increases along the winding direction. This structure can make the electrolyte in the battery case gradually decrease along the winding direction, so the internal resistance of the winding core 10 gradually increases along the winding direction, the heat generation amount of the winding core 10 gradually increases, and the temperature of the winding core 10 gradually increases, thereby forming a temperature difference along the winding direction of the entire winding core 10. This temperature difference can make the heat of the winding ending area 13 transfer to the winding starting area 12 along the winding direction, and the temperature difference can also make the outer peripheral area of the winding core 10 transfer to the starting area of the winding core 10 along the radial direction of the winding core 10. It can be seen that this structure increases the heat transfer path and has the effect of improving the heating efficiency of the starting area of the winding core 10. In addition, when the winding starting area 12 and the winding ending area 13 do not overlap in the radial direction of the winding core 10, this structure also shortens the path of the winding starting area 12 to absorb heat, further improving the heating efficiency of the starting area of the winding core 10. Again, this structure makes the temperature of the entire winding core 10 gradually increase along the winding direction, so the winding core 10 located between the winding starting area 12 and the winding ending area 13 can also be heated independently, and the heat transfer path of the winding core 10 in this area includes two paths along the winding direction and along the radial direction, achieving the effect of efficient heating of the winding core 10 in this area.

[0107] Further, the compaction density of the positive electrode starting end 110 is less than that of the positive electrode ending end 120, so that the porosity of the positive electrode active material layer 132 of the positive electrode starting end 110 is greater than that of the positive electrode ending end 120. During discharging, the positive electrode starting end 110 has more expansion space than the positive electrode ending end 120, so that the expansion amount and expansion stress of the positive electrode starting end 110 can be reduced, i.e., the expansion amount and expansion stress of the winding starting area 12 are reduced. The compaction density of the negative electrode starting end 210 is less than that of the negative electrode ending end 220, so that the porosity of the negative electrode active material layer 232 of the negative electrode starting end 210 is greater than that of the negative electrode ending end 220. During charging, the negative electrode starting end 210 has more expansion space than the negative electrode ending end 220, so that the expansion amount and expansion stress of the negative electrode starting end 210 can be reduced, i.e., the expansion amount and expansion stress of the winding starting area 12 are reduced. It can be seen that the structure design is beneficial to reduce the expansion amount and expansion stress of the winding starting area 12 during charging and discharging of the battery cell, and the effect of reducing the expansion amount and expansion stress of the winding core 10 is achieved.

[0108] Secondly, the compaction density of the positive electrode starting end 110 is less than that of the positive electrode ending end 120, so that the porosity of the positive electrode active material layer 132 of the positive electrode starting end 110 is greater than that of the positive electrode ending end 120. Thus, the kinetic performance of the positive electrode starting end 110 and the negative electrode starting end 210 can be further improved, so that the charging and discharging efficiency and rate capability of the winding core 10 can be improved. In addition, during charging, lithium is preferentially inserted into the negative electrode starting end 210 than the negative electrode ending end 220, so that the expansion amount of the negative electrode ending end 220 is reduced, i.e., the expansion amount of the winding ending area 13 is reduced. During discharging, lithium is preferentially inserted into the positive electrode starting end 110 than the positive electrode ending end 120, so that the expansion amount of the positive electrode ending end 120 is reduced, i.e., the expansion amount of the winding ending area 13 is reduced. It can be seen that the structure design is beneficial to reduce the expansion amount of the winding ending area 13 during charging and discharging of the battery cell, and the effect of further reducing the expansion amount of the winding core 10 is achieved.

[0109] Thirdly, the compaction density of the positive electrode starting end 110 is less than that of the positive electrode ending end 120, so that the porosity of the positive electrode active material layer 132 of the positive electrode starting end 110 is greater than that of the positive electrode ending end 120. Thus, the load amount and play amount of the active material of the positive electrode ending end 120 and the negative electrode ending end 220 can be further increased, and the stored electric energy of the winding core 10 is further improved under the condition that the volume or weight of the battery cell is the same.

[0110] Fourthly, the compaction density of the positive electrode starting end 110 is less than that of the positive electrode ending end 120, so that the porosity of the positive electrode active material layer 132 of the positive electrode starting end 110 is greater than that of the positive electrode ending end 120. Thus, the electrolyte of the winding starting area 12 can be further increased, and the temperature difference between the winding starting area 12 and the winding ending area 13 is further increased, so that the effect of improving the self-heating efficiency of the winding starting area 12 is achieved.

[0111] The embodiment also provides a winding core preparation method, which is different from the winding core preparation method of the first embodiment in that, in step S4, the pole piece structure is wound in a second direction opposite to the first direction in the first embodiment.

[0112] In the embodiment, the second direction is the winding direction, i.e., the x2 direction in the formula (1), and the x2 direction is opposite to the x1 direction, i.e., the second direction is opposite to the first direction. The positive electrode first end is the positive electrode end 120, the positive electrode second end is the positive electrode start end 110, the negative electrode first end is the negative electrode end 220, and the negative electrode second end is the negative electrode start end 210. Figures 6 to 9

[0113] In step S2, the thickness of the positive electrode active material layer 132 of the positive electrode start end 110 is less than the thickness of the positive electrode active material layer 132 of the positive electrode end 120, and the thickness of the negative electrode active material layer 232 of the negative electrode start end 210 is less than the thickness of the negative electrode active material layer 232 of the negative electrode end 220, so that the face density of the positive electrode start end 110 of the positive electrode piece 100 is less than the face density of the positive electrode end 120, and the face density of the negative electrode start end 210 of the negative electrode piece 200 is less than the face density of the negative electrode end 220. Thus, the winding start area 12 of the winding core 10 can be self-heated, and the expansion amount of the winding core 10 can be reduced during charging and discharging. In the case of the same volume or weight of the battery monomer, the energy density of the battery monomer can be improved.

[0114] The embodiment also provides a battery monomer, which comprises a battery shell and the winding core 10 described above, and the winding core 10 is arranged in the battery shell. The winding core 10 described above is used in the battery monomer, and the winding start area 12 of the winding core 10 can be self-heated, so that the battery monomer has high conductivity.

[0115] The embodiment also provides a battery monomer, which comprises a battery shell and the winding core 10 prepared by the winding core preparation method described above, and the winding core 10 is arranged in the battery shell. The winding core 10 prepared by the winding core preparation method described above is used in the battery monomer, and the winding start area 12 of the winding core 10 can be self-heated, so that the battery monomer has high conductivity.

[0116] Embodiment Three

[0117] The embodiment provides a winding core 10, and the differences between the embodiment and the first embodiment will be mainly described below, and the same parts will not be described again.

[0118] ​The winding core 10 provided by the embodiment has the following characteristics: the surface density of the positive electrode starting end 110 is greater than the surface density of the positive electrode ending end 120, the surface density of the negative electrode starting end 210 is greater than the surface density of the negative electrode ending end 220, the compaction density of the positive electrode starting end 110 is less than the compaction density of the positive electrode ending end 120, and the compaction density of the negative electrode starting end 210 is less than the compaction density of the negative electrode ending end 220, so that heat transfer between the winding starting area 12 and the winding ending area 13 is realized.

[0119] It should be noted that, in the embodiment, the surface density and the compaction density of the positive electrode sheet 100 have opposite change trends, and the structure can be realized by changing the thickness of the positive electrode current collector 131 and the thickness of the positive electrode active material layer 132. The principle of realizing the opposite change trends of the surface density and the compaction density of the negative electrode sheet 200 is the same as that of the positive electrode sheet 100, and will not be described here.

[0120] It should be further noted that the surface density of the sheet and the compaction density of the sheet simultaneously determine the amount of electrolyte, and therefore, in the embodiment, the direction of heat transfer between the winding starting area 12 and the winding ending area 13 can be determined by changing the size relationship between |a-b| and |e-f| and the size relationship between |c-d| and |g-h|.

[0121] Embodiment Four

[0122] The embodiment provides a winding core 10, and the differences between the embodiment and Embodiment One will be mainly described below, and the same parts will not be described here.

[0123] The surface density of the positive electrode starting end 110 is less than the surface density of the positive electrode ending end 120, the surface density of the negative electrode starting end 210 is less than the surface density of the negative electrode ending end 220, the compaction density of the positive electrode starting end 110 is greater than the compaction density of the positive electrode ending end 120, and the compaction density of the negative electrode starting end 210 is greater than the compaction density of the negative electrode ending end 220, so that heat transfer between the winding starting area 12 and the winding ending area 13 is realized.

[0124] It should be noted that, in the embodiment, the surface density and the compaction density of the positive electrode sheet 100 have opposite change trends, and the structure can be realized by changing the thickness of the positive electrode current collector 131 and the thickness of the positive electrode active material layer 132. The principle of realizing the opposite change trends of the surface density and the compaction density of the negative electrode sheet 200 is the same as that of the positive electrode sheet 100, and will not be described here.

[0125] It should be further noted that the surface density of the sheet and the compaction density of the sheet simultaneously determine the amount of electrolyte, and therefore, in the embodiment, the direction of heat transfer between the winding starting area 12 and the winding ending area 13 can be determined by changing the size relationship between |a-b| and |e-f| and the size relationship between |c-d| and |g-h|.

[0126] Obviously, the above embodiments of the present application are merely exemplary but not intended to limit the embodiments of the present application. Various obvious changes, re-adjustments and substitutions can be made by those skilled in the art without departing from the scope of the present application. It is not necessary or possible to enumerate all the embodiments. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. A type of winding core, characterized in that, It includes a positive electrode (100) and a negative electrode (200), wherein the positive electrode (100) and the negative electrode (200) are stacked and wound along the winding direction; Along the winding direction, the two ends of the positive electrode sheet (100) are the positive electrode start end (110) and the positive electrode end end (120) respectively; Along the winding direction, the two ends of the negative electrode sheet (200) are the negative electrode starting end (210) and the negative electrode ending end (220) respectively; The surface density of the positive electrode starting end (110) is greater than the surface density of the positive electrode ending end (120), and the surface density of the negative electrode starting end (210) is greater than the surface density of the negative electrode ending end (220). Alternatively, the areal density of the positive electrode starting end (110) is less than the areal density of the positive electrode ending end (120), and the areal density of the negative electrode starting end (210) is less than the areal density of the negative electrode ending end (220).

2. The winding core according to claim 1, characterized in that, Along the winding direction, the areal density of the positive electrode (100) gradually changes, and the areal density of the negative electrode (200) also gradually changes.

3. The winding core according to claim 1, characterized in that, Along the winding direction, the thickness of the positive electrode (100) remains unchanged, and the thickness of the negative electrode (200) remains unchanged.

4. The winding core according to claim 1, characterized in that, The areal density of the positive electrode starting end (110) is a, and the areal density of the positive electrode ending end (120) is b, both 5 g / m³. 2 ≤|ab|≤105g / m 2 ; And / or, the areal density of the negative electrode starting end (210) is c, and the areal density of the negative electrode ending end (220) is d, 5 g / m³. 2 ≤|cd|≤125g / m 2 .

5. The winding core according to any one of claims 1-4, characterized in that, The compaction density of the positive electrode starting end (110) is greater than that of the positive electrode ending end (120), and the compaction density of the negative electrode starting end (210) is greater than that of the negative electrode ending end (220). Alternatively, the compaction density of the positive electrode starting end (110) is less than the compaction density of the positive electrode ending end (120), and the compaction density of the negative electrode starting end (210) is less than the compaction density of the negative electrode ending end (220).

6. The winding core according to claim 5, characterized in that, Along the winding direction, the compaction density of the positive electrode (100) gradually changes, and the compaction density of the negative electrode (200) also gradually changes.

7. The winding core according to claim 5, characterized in that, The compaction density of the positive electrode starting end (110) is e, and the compaction density of the positive electrode ending end (120) is f, 0.05 g / cm³. 3 ≤|ef|≤4g / cm 3 ; And / or, the compaction density of the negative electrode starting end (210) is g, and the compaction density of the negative electrode ending end (220) is h, 0.05 g / cm³. 3 ≤|gh|≤2g / cm 3 .

8. A method for preparing a core, characterized in that, Includes the following steps: S1, providing a positive current collector (131) and a negative current collector (231); S2. A positive electrode active material layer (132) is prepared on the positive electrode current collector (131). The two ends of the positive electrode current collector (131) in the first direction are successively used as the first positive electrode end and the second positive electrode end. The thickness of the positive electrode active material layer (132) at the first positive electrode end is greater than the thickness of the positive electrode active material layer (132) at the second positive electrode end. A negative electrode active material layer (232) is prepared on the negative electrode current collector (231). The two ends of the negative electrode current collector (231) in the first direction are successively used as the first negative electrode end and the second negative electrode end. The thickness of the negative electrode active material layer (232) at the first negative electrode end is greater than the thickness of the negative electrode active material layer (232) at the second negative electrode end. S3. Compact the positive electrode active material layer (132) on the positive electrode current collector (131) to form a positive electrode sheet (100); The negative electrode active material layer (232) on the negative electrode current collector (231) is compacted to form a negative electrode sheet (200); S4. Stack the positive electrode (100) and the negative electrode (200) so that the first end of the positive electrode and the first end of the negative electrode face the same direction to form an electrode structure; The electrode structure is wound along the first direction; Alternatively, the electrode structure may be wound in a second direction, which is opposite to the first direction.

9. The method for preparing the core according to claim 8, characterized in that, In step S2, the thickness of the positive electrode active material layer (132) is gradually changed along the first direction, and the thickness of the negative electrode active material layer (232) is gradually changed along the first direction.

10. The method for preparing the core according to claim 8, characterized in that, In step S3, the thickness of the positive electrode (100) is kept consistent along the first direction, and the thickness of the negative electrode (200) is kept consistent along the first direction.

11. A single battery cell, characterized in that, It includes a battery casing and a winding core (10) as described in any one of claims 1-7, wherein the winding core (10) is disposed within the battery casing.

12. A single battery cell, characterized in that, The battery casing includes a core (10) prepared by the method of preparing the core (10) as described in any one of claims 8-10, wherein the core (10) is disposed within the battery casing.

Images