A winding core and a battery cell

Abstract

The utility model belongs to battery technical field discloses the roll core and battery monomer, the roll core includes positive sheet and negative sheet, and the positive sheet and negative sheet are overlaid and are rolled along the winding direction, along the winding direction, the both ends of positive sheet are positive starting end and positive end in proper order, along the winding direction, the both ends of negative sheet are negative starting end and negative end in proper order, the area density of positive starting end is greater than the area density of positive end, the area density of negative starting end is greater than the area density of negative end, to make the winding starting area of roll core can independently heat dissipation, or, the area density of positive starting end is less than the area density of positive end, the area density of negative starting end is less than the area density of negative end, to make the winding starting area of roll core can independently heat.

Description

Technical Field

[0001] This utility model relates to the field of battery technology, and in particular to a winding core and a battery cell. Background Technology

[0002] Lithium batteries require temperature control during charging and discharging, and the specific heating or cooling measures should be selected based on the ambient temperature.

[0003] In existing technologies, temperature control devices such as liquid cooling plates are often used to control the temperature of lithium batteries. For example, in hot regions with high ambient temperatures, the temperature control device cools the lithium battery, while in cold regions with low ambient temperatures, the temperature control device heats the lithium battery.

[0004] The above-mentioned solutions are not effective in controlling the temperature of cylindrical lithium batteries. Therefore, it is urgent to propose a new type of core and battery cell to solve the above-mentioned technical problems. Utility Model Content

[0005] The first objective of this invention is to provide a winding core that can independently dissipate heat or independently heat itself at the winding start area.

[0006] To achieve this objective, the present invention adopts the following technical solution:

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

[0008] Along the winding direction, the two ends of the positive electrode sheet are the positive electrode start end and the positive electrode end, respectively.

[0009] Along the winding direction, the two ends of the negative electrode sheet are the negative electrode start end and the negative electrode end, respectively.

[0010] The surface density at the beginning of the positive electrode is greater than that at the end of the positive electrode, and the surface density at the beginning of the negative electrode is greater than that at the end of the negative electrode.

[0011] Alternatively, the surface density at the positive electrode starting end is less than the surface density at the positive electrode ending end, and the surface density at the negative electrode starting end is less than the surface density at the negative electrode ending end.

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

[0013] Optionally, the thickness of the positive electrode remains unchanged along the winding direction, and the thickness of the negative electrode remains unchanged.

[0014] Optionally, the areal density at the starting end of the positive electrode is a, and the areal density at the ending end of the positive electrode is b, both being 5 g / m³. 2 ≤|ab|≤105g / m 2 .

[0015] Optionally, the areal density at the starting end of the negative electrode is c, and the areal density at the ending end of the negative electrode is d, 5 g / m³. 2 ≤|cd|≤125g / m 2 .

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

[0017] Alternatively, the compaction density at the beginning of the positive electrode is less than the compaction density at the end of the positive electrode, and the compaction density at the beginning of the negative electrode is less than the compaction density at the end of the negative electrode.

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

[0019] Optionally, the compaction density at the starting end of the positive electrode is e, and the compaction density at the ending end of the positive electrode is f, 0.05 g / cm³. 3 ≤|ef|≤4g / cm 3 .

[0020] Optionally, the compaction density at the starting end of the negative electrode is g, and the compaction density at the ending end of the negative electrode is h, 0.05 g / cm³. 3 ≤|gh|≤2g / cm 3 .

[0021] The second objective of this invention is to provide a battery cell whose winding start area of ​​the core can independently dissipate heat or independently heat up.

[0022] To achieve this objective, the present invention adopts the following technical solution:

[0023] A battery cell includes a battery casing and the aforementioned winding core, with the winding core disposed inside the battery casing.

[0024] The beneficial effects of this utility model are:

[0025] The winding core provided by this utility model has a greater areal density at the positive electrode starting end than at the positive electrode ending end, and a greater areal density at the negative electrode starting end than at the negative electrode ending end. For ease of description, the winding core located at the positive and negative electrode starting ends will be referred to as the winding starting region, and the winding core located at the positive and negative electrode ending ends will be referred to as the winding ending region. In the battery casing, this structure allows the electrolyte in the winding ending region to be more abundant than that in the winding starting region. Therefore, the internal resistance of the winding ending region is less than that of the winding starting region, resulting in less heat generation in the winding ending region than in the winding starting region. This creates a temperature difference between the winding ending region and the winding starting region, which facilitates the transfer of heat from the winding starting region to the winding ending region, achieving the effect of self-heating in the winding starting region.

[0026] The winding core provided by this utility model has a smaller areal density at the positive electrode starting end than at the positive electrode ending end, and a smaller areal density at the negative electrode starting end than at the negative electrode ending end. In the battery casing, this structure allows the electrolyte in the winding ending area to be less than that in the winding starting area. Therefore, the internal resistance of the winding ending area is greater than that of the winding starting area, and consequently, the heat generation in the winding ending area is greater than that in the winding starting area. This creates a temperature difference between the winding ending area and the winding starting area, which facilitates the transfer of heat from the winding ending area to the winding starting area, achieving the effect of self-heating in the winding starting area. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the core provided in Embodiment 1 of this utility model;

[0028] Figure 2 This is a schematic diagram of the structure of the positive electrode sheet provided in Embodiment 1 of this utility model before the positive electrode active material layer is compacted;

[0029] Figure 3 This is a schematic diagram of the structure of the positive electrode sheet provided in Embodiment 1 of this utility model after the positive electrode active material layer has been compacted;

[0030] Figure 4 This is a schematic diagram of the structure of the negative electrode sheet provided in Embodiment 1 of this utility model before the negative electrode active material layer is compacted;

[0031] Figure 5 This is a schematic diagram of the structure of the negative electrode sheet provided in Embodiment 1 of this utility model after the negative electrode active material layer has been compacted;

[0032] Figure 6 This is a schematic diagram of the structure of the positive electrode sheet provided in Embodiment 2 of this utility model before the positive electrode active material layer is compacted;

[0033] Figure 7 This is a schematic diagram of the structure of the positive electrode sheet provided in Embodiment 2 of this utility model after the positive electrode active material layer has been compacted;

[0034] Figure 8 This is a schematic diagram of the structure of the negative electrode sheet provided in Embodiment 2 of this utility model before the negative electrode active material layer is compacted;

[0035] Figure 9 This is a schematic diagram of the structure of the negative electrode sheet provided in Embodiment 2 of this utility model after the negative electrode active material layer has been compacted.

[0036] In the picture:

[0037] 10. 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 Implementation

[0038] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, not the entire structure.

[0039] In the description of this utility model, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0040] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0041] In the description of this embodiment, the terms "upper," "lower," "right," etc., refer to the orientation or positional relationship shown in the accompanying drawings. They are used only for ease of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model. In addition, the terms "first" and "second" are only used for distinction in description and have no special meaning.

[0042] In existing technologies, temperature control devices such as liquid cooling plates are often used to control the temperature of individual battery cells. The temperature control device is located outside the battery casing, while the battery cell is located inside the battery casing. The temperature control device located outside the battery casing heats or cools the battery cell located inside the battery casing.

[0043] Cylindrical battery cells are in a coiled shape (hereinafter referred to as coiled cores). A coiled core is typically formed by stacking and winding positive and negative electrode sheets in sequence. For example... Figure 1 As shown, in the radial direction of the core 10, the core 10 closer to the axis 11 is the winding start area 12, and the core 10 farther from the axis 11 is the winding end area 13. It is evident that the distance between the winding start area 12 and the temperature control device is larger than that of the winding end area 13, resulting in poor temperature control of the winding start area 12 by the temperature control device. When the battery cell is used in hot regions with high ambient temperatures, the poor cooling effect of the temperature control device on the winding start area 12 poses a significant risk of thermal runaway to the battery cell. Furthermore, the uneven temperature distribution in the radial direction of the core 10 reduces the conductivity of the battery cell. When the battery cell is used in cold regions with low ambient temperatures, the poor heating effect of the temperature control device on the winding start area 12 leads to uneven temperature distribution in the radial direction of the core 10, further reducing the conductivity of the battery cell.

[0044] Therefore, this invention proposes a winding core 10 and a battery cell, aiming to improve the cooling or heating effect of the winding start area 12. This winding core 10 is mainly used in lithium battery structures.

[0045] Example 1

[0046] This embodiment provides a winding core 10, the winding start area 12 of which can dissipate heat independently.

[0047] Specifically, such as Figures 1 to 5 As shown, the core 10 includes a positive electrode sheet 100 and a 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, the two ends of the positive electrode sheet 100 are the positive electrode start end 110 and the positive electrode end 120, respectively. Along the winding direction, the two ends of the negative electrode sheet 200 are the negative electrode start end 210 and the negative electrode end 220, respectively. The areal density of the positive electrode start end 110 is greater than that of the positive electrode end 120, and the areal density of the negative electrode start end 210 is greater than that of the negative electrode end 220.

[0048] In this embodiment, the winding direction is Figures 2 to 5 The x1 direction in the middle.

[0049] In this embodiment, the winding direction of the core 10 is from the positive starting end 110 to the positive ending end 120, and the winding direction is from the negative starting end 210 to the negative ending end 220. Therefore, the positions of the core 10 corresponding to the positive starting end 110 and the negative starting end 210 are the winding starting area 12, and the positions of the core 10 corresponding to the positive ending end 120 and the negative ending end 220 are the winding ending area 13. 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, in the battery casing, this structure allows for more electrolyte in the winding ending region 13 than in the winding starting region 12. Consequently, the internal resistance of the winding ending region 13 is lower than that of the winding starting region 12, and the heat generation in the winding ending region 13 is lower than that in the winding starting region 12. This achieves the effect that the temperature of the winding ending region 13 is lower 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 starting region 12 to the winding ending region 13, achieving the effect of self-heating of the winding starting region 12. This structural design can reduce the risk of thermal runaway in battery cells, improve the safety of battery cells, and also improve the radial temperature distribution uniformity of the core 10, which is beneficial to improving the conductivity of battery cells.

[0050] 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.

[0051] 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.

[0052] Furthermore, 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. That is, in this embodiment, the areal density of the positive electrode 100 gradually decreases along the winding direction, and the areal density of the negative electrode 200 gradually decreases along the winding direction. This structural design is beneficial for further reducing the risk of thermal runaway in individual battery cells and improving the radial temperature uniformity of the core 10. Specifically, this structure allows the electrolyte in the battery case to gradually increase along the winding direction. Therefore, along the winding direction, the internal resistance of the core 10 gradually decreases, the heat generation of the core 10 gradually decreases, and the temperature of the core 10 gradually decreases. This results in a temperature difference along the winding direction of the entire core 10. This temperature difference allows the heat from the winding start area 12 to be transferred along the winding direction to the winding end area 13. This temperature difference also allows the heat from the winding start area 12 to be transferred radially to the outer periphery of the core 10. It is evident that this structure increases the heat transfer path of the winding start region 12, thereby improving its heat dissipation efficiency. Furthermore, when the winding start region 12 and the winding end region 13 do not overlap radially in the core 10, this structure also shortens the heat transfer path of the winding start region 12, further improving its heat dissipation efficiency. Moreover, this structure causes the temperature of the entire core 10 to gradually decrease along the winding direction. Therefore, the core 10 located between the winding start region 12 and the winding end region 13 can also dissipate heat independently, and the heat transfer path in this region includes both the winding direction and the radial direction, achieving highly efficient heat dissipation in this area.

[0053] On the other hand, this structural design helps to reduce the difficulty of preparing the positive electrode 100 and the negative electrode 200. Specifically, before the active material layer on the current collector is compacted, the areal density of the electrode is mainly reflected in the thickness of the active material layer. Along the winding direction, the areal density of the positive electrode 100 gradually changes. That is, before the positive active material layer 132 is compacted, the thickness of the positive active material layer 132 on the positive current collector 131 gradually changes along the winding direction. Compared with the abrupt change in the thickness of the positive active material layer 132 at a certain position on the positive current collector 131, this structure with gradually changing thickness helps to reduce the difficulty of preparing the positive active material layer 132 on the positive current collector 131. Similarly, along the winding direction, the areal 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 abrupt change in the thickness of the negative electrode active material layer 232 at a certain position on the negative electrode current collector 231, this structure with gradually changing thickness is beneficial to reducing the difficulty of preparing the negative electrode active material layer 232 on the negative electrode current collector 231.

[0054] Optionally, 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 being 5 g / m³. 2 ≤|ab|≤105g / m 2 For example, |ab| could be 5g / m 2 10g / m 2 35g / m 2 50g / m 2 83g / m 2 100g / m 2 Or 105g / m 2 This allows the winding start area 12 to have high heat dissipation efficiency while reducing the expansion of the core 10 and increasing the energy storage capacity of the core 10.

[0055] Optionally, 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 For example, |cd| could be 5g / m 2 10g / m 2 55g / m 2 60g / m 2 100g / m 2 120g / m 2 Or 125g / m 2 This allows the winding start area 12 to have high heat dissipation efficiency while reducing the expansion of the core 10 and increasing the energy storage capacity of the core 10.

[0056] Optionally, the thickness of the positive electrode 100 and the thickness of the negative electrode 200 remain unchanged along the winding direction. This structure can improve the overall structural consistency of the core 10, prevent radial deformation of the core 10, and improve the dimensional consistency of the core 10 in different radial directions.

[0057] Furthermore, the compaction density of the positive electrode starting end 110 is greater than that of the positive electrode ending end 120, so that the porosity of the positive electrode active material layer 132 in the positive electrode ending end 120 is greater than that in the positive electrode starting end 110. When the battery cell discharges, the positive electrode ending end 120 has sufficient expansion space compared to the positive electrode starting end 110. Therefore, the expansion amount and expansion stress of the positive electrode ending end 120 can be reduced, that is, the expansion amount and expansion stress of the winding ending region 13 are reduced. The compaction density of the negative electrode starting end 210 is greater than that of the negative electrode ending end 220, so that the porosity of the negative electrode active material layer 232 at the negative electrode ending end 220 is greater than that at the negative electrode starting end 210. When the battery cell discharges, the negative electrode ending end 220 has sufficient expansion space compared to the negative electrode starting end 210. Therefore, the expansion amount and expansion stress of the negative electrode ending end 220 can be reduced, which in turn reduces the expansion amount and expansion stress of the winding ending region 13. It is evident that this structural design is beneficial in reducing the expansion amount and expansion stress of the winding ending region 13 during battery cell charging and discharging, thereby achieving the effect of reducing the expansion amount and expansion stress of the core 10.

[0058] On the other hand, 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. This can further improve the kinetic performance of the positive electrode ending end 120 and the negative electrode ending end 220, thereby further improving the charge / discharge efficiency and rate performance of the winding core 10. Furthermore, during battery cell charging, the negative electrode ending end 220 preferentially inserts lithium before the negative electrode starting end 210, further reducing the expansion of the negative electrode starting end 210, i.e., reducing the expansion of the winding starting region 12. During battery cell discharging, the positive electrode ending end 120 preferentially inserts lithium before the positive electrode starting end 110, further reducing the expansion of the positive electrode starting end 110, i.e., reducing the expansion of the winding starting region 12. Therefore, this structural design is beneficial in reducing the expansion of the winding starting region 12 during battery cell charging and discharging, achieving the effect of further reducing the expansion of the winding core 10.

[0059] On the other hand, 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. This can further increase the loading and utilization of active materials at the positive electrode starting end 110 and the negative electrode starting end 210, thereby further increasing the electrical energy stored in the core 10 when the volume or weight of the battery cell is the same.

[0060] On the other hand, 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. This can further increase the electrolyte in the winding ending region 13, thereby increasing the temperature difference between the winding ending region 13 and the winding starting region 12, which has the effect of improving the thermal conductivity from the winding starting region 12 to the winding ending region 13.

[0061] Optionally, the compaction density of the positive electrode 100 gradually changes along the winding direction; that is, in this embodiment, the compaction density of the positive electrode 100 gradually decreases along the winding direction. In this embodiment, the areal density of the positive electrode 100 gradually decreases along the winding direction, and the thickness of the positive electrode 100 remains constant along the winding direction. Therefore, when the positive electrode active material layer 132 on the positive electrode current collector 131 is compacted, ensuring that the thickness of the positive electrode active material layer 132 remains consistent along the winding direction achieves a gradual decrease in the compaction density of the positive electrode 100 along the winding direction. This design helps reduce the manufacturing difficulty of the positive electrode 100, thereby improving the production efficiency and reducing the production cost of the positive electrode 100. Similarly, in this embodiment, the compaction density of the negative electrode 200 gradually changes along the winding direction; that is, in this embodiment, the compaction density of the negative electrode 200 gradually decreases along the winding direction. In this embodiment, the areal density of the negative electrode 200 gradually decreases along the winding direction, and the thickness of the negative electrode 200 remains unchanged along the winding direction. Therefore, when the negative electrode active material layer 232 on the negative electrode current collector 231 is compressed, the thickness of the negative electrode active material layer 232 remains consistent along the winding direction, thus achieving a gradual decrease in the compaction density of the negative electrode 200 along the winding direction. It can be seen that this design helps to reduce the manufacturing difficulty of the negative electrode 200, thereby improving the production efficiency of the negative electrode 200 and reducing the production cost of the negative electrode 200.

[0062] In addition, when the battery cell is charged and discharged, this structure can make the expansion stress of the core 10 more uniform and dispersed along the winding direction, reducing the probability of a sudden increase in expansion stress in a certain area of ​​the core 10, which is beneficial to extending the cycle life of the battery cell.

[0063] Optionally, 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 / cm3 For example, |ef| can be 0.05 g / cm³. 3 0.1g / cm 3 2g / cm 3 3.5g / cm 3 Or 4g / cm 3 While reducing the expansion amount and expansion stress of the core 10, it improves the heat conduction efficiency from the winding start area 12 to the winding end area 13 and increases the energy storage capacity of the core 10.

[0064] Optionally, 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 For example, |gh| can be 0.05 g / cm³. 3 0.1g / cm 3 0.5g / cm 3 1g / cm 3 1.5g / cm 3 Or 2g / cm 3 While reducing the expansion amount and expansion stress of the core 10, it improves the heat conduction efficiency from the winding start area 12 to the winding end area 13 and increases the energy storage capacity of the core 10.

[0065] In this embodiment, the areal density of the positive electrode 100 and the negative electrode 200 of the wound core 10 gradually decreases along the winding direction, and the compaction density of the positive electrode 100 and the negative electrode 200 also gradually decreases along the winding direction. This improves the charge and discharge efficiency and rate performance of the wound core 10. The maximum charging current of the wound core 10 is increased to 6C, the wound core 10 can reach 80% capacity after 10 minutes of charging, the internal resistance of the wound core 10 is reduced to 1.5mΩ, the capacity retention rate is above 80%, and the cycle life of the wound core 10 can reach 1500 cycles. Furthermore, the winding start region 12 of the wound core 10 can dissipate heat independently. Therefore, during fast charging, the temperature rise of the wound core 10 is reduced by about 25%, and the thermal runaway trigger time is delayed to 300s.

[0066] This embodiment also provides a method for preparing a core, which includes the following steps:

[0067] S1, providing positive current collector 131 and negative current collector 231;

[0068] S2. Prepare a positive electrode active material layer 132 on the positive electrode current collector 131, and take the two ends of the positive electrode current collector 131 in the first direction as the first positive electrode end and the second positive electrode end in sequence. 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.

[0069] A negative electrode active material layer 232 is prepared on the negative electrode current collector 231, and 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.

[0070] S3. Compact the positive electrode active material layer 132 on the positive electrode current collector 131 to form the positive electrode sheet 100;

[0071] The negative electrode active material layer 232 on the negative electrode current collector 231 is compacted to form the negative electrode sheet 200;

[0072] 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.

[0073] 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.

[0074] 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.

[0075] Secondly, by using this method to prepare the core 10, 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, thereby improving the charge / discharge efficiency and rate performance of the core 10. Furthermore, during charging, the negative electrode termination 220 preferentially inserts lithium before the negative electrode initiation 210, reducing the expansion of the negative electrode initiation 210, which in turn reduces the expansion of the winding initiation region 12. During discharging, the positive electrode termination 120 preferentially inserts lithium before the positive electrode initiation 110, reducing the expansion of the positive electrode initiation 110, which in turn reduces the expansion of the winding initiation region 12. Therefore, this core preparation method is beneficial for reducing the expansion of the winding initiation region 12, thus achieving the effect of reducing the overall expansion of the core 10.

[0076] Furthermore, by using this method to prepare the core 10, the loading and utilization of the positive and negative active materials in the winding start region 12 are greater than those in the winding end region 13. Under the condition that the volume or weight of the battery cell is the same, the core 10 stores more electrical energy, which is beneficial to improving the energy density of the battery cell.

[0077] Furthermore, in step S2, a positive electrode active material layer 132 is prepared on the positive electrode current collector 131 using a dry electrode process. The dry electrode process eliminates the need for solvents, allowing direct mixing of the positive electrode active material, conductive agent, and solid binder, followed by composite formation with the positive electrode current collector 131 to form the positive electrode sheet 100. Compared to the wet electrode process, the dry electrode process eliminates evaporation, recovery, and drying processes and related equipment, reducing equipment investment and operating costs. Process energy consumption can be reduced by approximately 40%, and the production cost of a single core 10 can be reduced by approximately 25%. Secondly, the dry electrode process ensures uniform distribution of the components in the positive electrode active material layer 132, avoiding the problem of uneven distribution caused by solvent evaporation. Thirdly, the positive electrode sheet 100 prepared using the dry electrode process can achieve higher compaction density; under the same conditions, the energy density of the positive electrode sheet 100 prepared using the dry electrode process can be increased by approximately 20%. Similarly, in step S2, a negative electrode active material layer 232 is prepared on the negative electrode current collector 231 using a dry electrode process. The technical effect is the same as that of the positive electrode 100, and will not be described in detail here.

[0078] It should be noted that the dry electrode process is a relatively mature electrode production process in this technical field, and its specific preparation method will not be described in detail here.

[0079] Optionally, in step S2, the thickness of the positive electrode active material layer 132 and the thickness of the negative electrode active material layer 232 are gradually changed along the first direction. That is, the thickness of the positive electrode active material layer 132 and the thickness of the negative electrode active material layer 232 are gradually reduced along the first direction, resulting in a gradual decrease in the areal density of both the positive electrode sheet 100 and the negative electrode sheet 200 along the first direction. This reduces the difficulty of implementing step S2. Furthermore, during charging and discharging, the heat from the winding start region 12 can be transferred not only along the winding direction to the winding end region 13, but also along the radial direction of the core 10 to the outer periphery of the core 10, improving the heat dissipation efficiency of the winding start region 12. In addition, during charging and discharging, the core 10 located between the winding start region 12 and the winding end region 13 can also dissipate heat independently, and the heat transfer path of the core 10 in this region includes both the winding direction and the radial direction, achieving efficient heat dissipation of the core 10 in this region.

[0080] Optionally, in step S3, the thickness of the positive electrode 100 and the negative electrode 200 are kept consistent along the first direction. This causes the compaction density of both the positive and negative electrode 100 to gradually decrease along the first direction, further increasing the electrolyte volume in the winding termination region 13. This improves the temperature difference between the winding termination region 13 and the winding start region 12, thereby increasing the heat dissipation efficiency of the winding start region 12. Furthermore, it further improves the dynamic performance of the positive electrode termination 120 and the negative electrode termination 220, achieving the effects of further improving the charge / discharge efficiency and rate performance of the winding core 10, further reducing the expansion amount in the winding start region 12, and further reducing the expansion amount and expansion stress in the winding termination region 13. Finally, this method can increase the loading and utilization of the positive and negative active materials in the winding start region 12, thereby increasing the energy storage capacity of the winding core 10 while maintaining the same volume or weight of the battery cell.

[0081] It should be noted that the above-described compaction method for maintaining the thickness of the positive electrode 100 along the first direction is prior art in this technical field. For example, a positive current collector 131 with an uncompacted positive electrode active material layer 132 is placed on a conveyor belt, and a pressure roller is positioned above the conveyor belt. The axis 11 of the pressure roller is perpendicular to the conveying direction of the conveyor belt. Along the axis 11 of the pressure roller, the distance between each position of the pressure roller and the conveyor belt is the same. The uncompacted positive electrode current collector 131 with the positive electrode active material layer 132 moves with the transmission of the conveyor belt, and the positive electrode active material layer 132 is compacted by the pressure roller, thereby maintaining the thickness of the positive electrode 100 along the first direction. The method for maintaining the thickness of the negative electrode 200 along the first direction is the same as that for the positive electrode 100, and will not be described again here.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] Example 2

[0086] 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.

[0087] 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.

[0088] On the other hand, the areal density of the positive electrode starting end 110 is less than that of the positive electrode ending end 120, and the areal density of the negative electrode starting end 210 is less than that of the negative electrode ending end 220. Therefore, the kinetic performance of both 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 performance of the winding core 10. Furthermore, during battery cell charging, the negative electrode starting end 210 preferentially inserts lithium before the negative electrode ending end 220, thus reducing the expansion of the negative electrode ending end 220, which in turn reduces the expansion of the winding ending region 13. During battery cell discharging, the positive electrode starting end 110 preferentially inserts lithium before the positive electrode ending end 120, thus reducing the expansion of the positive electrode ending end 120, which in turn reduces the expansion of the winding ending region 13. It is evident that this structure reduces the expansion of the winding ending region during battery cell charging and discharging, which is beneficial for reducing the expansion of the winding core 10.

[0089] On the other hand, the areal density of the positive electrode starting end 110 is less than that of the positive electrode ending end 120, and the areal density of the negative electrode starting end 210 is less than that of the negative electrode ending end 220. Therefore, the loading and efflux of the active material at the positive electrode ending end 120 and the negative electrode ending end 220 are greater than those at the positive electrode starting end 110 and the negative electrode starting end 210. 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.

[0090] Furthermore, the areal density of the positive electrode 100 gradually increases along the winding direction, as does the areal density of the negative electrode 200. This structure allows the electrolyte in the battery case to gradually decrease along the winding direction. Therefore, along the winding direction, the internal resistance of the core 10 gradually increases, the heat generation of the core 10 gradually increases, and the temperature of the core 10 gradually rises. This creates a temperature difference along the winding direction of the entire core 10. This temperature difference allows the heat from the winding end region 13 to be transferred along the winding direction to the winding start region 12. It also allows the heat from the outer periphery of the core 10 to be transferred radially towards the winding start region. Thus, this structure increases the heat transfer path and improves the heating efficiency of the winding start region. Furthermore, when the winding start region 12 and the winding end region 13 do not overlap radially in the core 10, this structure also shortens the heat absorption path of the winding start region 12, further improving the heating efficiency of the winding start region. Furthermore, this structure allows the temperature of the entire core 10 to gradually increase along the winding direction. Therefore, the core 10 located between the winding start area 12 and the winding end area 13 can also be heated autonomously. Moreover, the heat transfer path of the core 10 in this area includes two paths: along the winding direction and along the radial direction, thus achieving the effect of efficient heating of the core 10 in this area.

[0091] Furthermore, 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 at the positive electrode starting end 110 is greater than that at the positive electrode ending end 120. During discharge, the positive electrode starting end 110 has more expansion space than the positive electrode ending end 120, thus reducing the expansion amount and expansion stress of the positive electrode starting end 110, i.e., reducing the expansion amount and expansion stress of the winding starting region 12. 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 at the negative electrode starting end 210 is greater than that at 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, thus reducing the expansion amount and expansion stress of the negative electrode starting end 210, i.e., reducing the expansion amount and expansion stress of the winding starting region 12. It is evident that during the charging and discharging of a single battery cell, this structural design helps to reduce the expansion amount and expansion stress of the winding start area 12, thereby achieving the effect of reducing the expansion amount and expansion stress of the core 10.

[0092] Secondly, the compaction density of the positive electrode starting end 110 is lower than that of the positive electrode ending end 120, so that the porosity of the positive electrode active material layer 132 at the positive electrode starting end 110 is greater than that at the positive electrode ending end 120. This further improves the kinetic performance of the positive electrode starting end 110 and the negative electrode starting end 210, thereby enhancing the charge / discharge efficiency and rate performance of the winding core 10. Furthermore, during charging, the negative electrode starting end 210 preferentially inserts lithium before the negative electrode ending end 220 to reduce the expansion of the negative electrode ending end 220, which in turn reduces the expansion of the winding ending region 13. During discharging, the positive electrode starting end 110 preferentially inserts lithium before the positive electrode ending end 120 to reduce the expansion of the positive electrode ending end 120, which in turn reduces the expansion of the winding ending region 13. Therefore, this structural design is beneficial in reducing the expansion of the winding ending region 13 during the charging and discharging of a single battery cell, thus further reducing the expansion of the winding core 10.

[0093] Furthermore, 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 at the positive electrode starting end 110 is greater than that at the positive electrode ending end 120. This can further increase the loading and utilization of the active material at the positive electrode ending end 120 and the negative electrode ending end 220, thereby further increasing the electrical energy stored in the core 10 when the volume or weight of the battery cell is the same.

[0094] Furthermore, 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 at the positive electrode starting end 110 is greater than that at the positive electrode ending end 120. This can further increase the electrolyte in the winding starting region 12, thereby increasing the temperature difference between the winding starting region 12 and the winding ending region 13, which has the effect of improving the self-heating efficiency of the winding starting region 12.

[0095] This embodiment also provides a core preparation method, which differs from the first embodiment in that: in step S4, the electrode structure is wound along a second direction, which is opposite to the first direction in the first embodiment.

[0096] In this embodiment, the second direction is the winding direction, that is... Figures 6 to 9 In the x2 direction, the x2 direction is opposite to the x1 direction, that is, the second direction is opposite to the first direction. The first positive end is the positive terminal 120, the second positive end is the positive starting end 110, the first negative end is the negative terminal 220, and the second negative end is the negative starting end 210.

[0097] In step S2, the thickness of the positive active material layer 132 at the positive electrode starting end 110 is less 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 less than the thickness of the negative active material layer 232 at the negative electrode ending end 220. This forms a structure in which the areal density of the positive electrode starting end 110 of the positive electrode sheet 100 is less 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 less than the areal density of the negative electrode ending end 220. This achieves the effect of self-heating of the winding starting area 12 of the core 10, and also reduces the expansion of the core 10 during charging and discharging. Under the condition that the volume or weight of the battery cell is the same, it is beneficial to improve the energy density of the battery cell.

[0098] 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 be self-heated, so that the battery cell has high conductivity.

[0099] 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 be heated independently, so that the battery cell has high conductivity.

[0100] Example 3

[0101] This embodiment provides a core 10. The following mainly describes the differences between this embodiment and Embodiment 1, while the similarities will not be repeated.

[0102] In this embodiment, the areal density of the positive electrode starting end 110 is greater than that of the positive electrode ending end 120, the areal density of the negative electrode starting end 210 is greater than that of the negative electrode ending end 220, the compaction density of the positive electrode starting end 110 is less than that of the positive electrode ending end 120, and the compaction density of the negative electrode starting end 210 is less than that of the negative electrode ending end 220, thereby realizing heat transfer between the winding starting area 12 and the winding ending area 13.

[0103] It should be noted that in this embodiment, the areal density and compaction density of the positive electrode 100 exhibit opposite trends. This structure can be achieved by changing the thickness of the positive current collector 131 and the thickness of the positive active material layer 132. The principle by which the areal density and compaction density of the negative electrode 200 exhibit opposite trends is the same as that of the positive electrode 100, and will not be repeated here.

[0104] It should also be noted that the areal density and compaction density of the electrode both determine the amount of electrolyte. Therefore, in this embodiment, the direction of heat transfer between the winding start area 12 and the winding end area 13 can be determined by changing the magnitude relationship between |ab| and |ef|, and the magnitude relationship between |cd| and |gh|.

[0105] Example 4

[0106] This embodiment provides a core 10. The following mainly describes the differences between this embodiment and Embodiment 1, while the similarities will not be repeated.

[0107] The areal density of the positive electrode starting end 110 is less than that of the positive electrode ending end 120, the areal density of the negative electrode starting end 210 is less than that of the negative electrode ending end 220, 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, thereby realizing the heat transfer between the winding starting region 12 and the winding ending region 13.

[0108] It should be noted that in this embodiment, the areal density and compaction density of the positive electrode 100 exhibit opposite trends. This structure can be achieved by changing the thickness of the positive current collector 131 and the thickness of the positive active material layer 132. The principle by which the areal density and compaction density of the negative electrode 200 exhibit opposite trends is the same as that of the positive electrode 100, and will not be repeated here.

[0109] It should also be noted that the areal density and compaction density of the electrode both determine the amount of electrolyte. Therefore, in this embodiment, the direction of heat transfer between the winding start area 12 and the winding end area 13 can be determined by changing the magnitude relationship between |ab| and |ef|, and the magnitude relationship between |cd| and |gh|.

[0110] Obviously, the above embodiments of this utility model are merely examples for clearly illustrating the present utility model, and are not intended to limit the implementation of the present utility model. Those skilled in the art can make various obvious changes, readjustments, and substitutions without departing from the protection scope of this utility model. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this utility model should be included within the protection scope of the claims of this utility model.

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 .

5. The winding core according to claim 1, characterized in that, 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 .

6. The winding core according to any one of claims 1-5, 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).

7. The winding core according to claim 6, 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.

8. The winding core according to claim 6, 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 .

9. The winding core according to claim 6, characterized in that, 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 .

10. A single battery cell, characterized in that, It includes a battery casing and a winding core (10) as described in any one of claims 1-9, wherein the winding core (10) is disposed within the battery casing.

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