Battery cell and secondary battery

Abstract

Embodiments of the present application provide an electric core and a secondary battery. The electric core includes a winding core, a positive pole and a negative pole, a fastening ring, and at least one filler. The positive pole and the negative pole are each electrically connected to the winding core. The fastening ring is disposed around at least a portion of the winding core and is adjacent to the positive pole and the negative pole. The fastening ring includes at least one elastic portion adapted to provide an elastic force to tighten the fastening ring. The at least one filler is arranged between the fastening ring and the winding core and is adjacent to the positive pole to press the winding core. Thus, the electrical performance and safety performance of the secondary battery can be improved.

Description

Technical Field

[0001] The exemplary embodiments of this application generally relate to the field of secondary batteries, and particularly to battery cells and secondary batteries. Background Technology

[0002] With the continuous development of new energy technologies, secondary batteries (such as lithium batteries) have been widely used in power, energy storage, and 3C fields due to their core technological advantages such as high energy density, excellent rate performance, long cycle life, and high voltage. However, there are still some problems in the processing and assembly of secondary batteries, which affect their electrical and safety performance. Summary of the Invention

[0003] In a first aspect of this application, a battery cell is provided. The battery cell includes: a core; a positive terminal and a negative terminal, each electrically connected to the core; a fastening ring disposed around at least a portion of the core and adjacent to the positive and negative terminals, the fastening ring including at least one elastic portion adapted to provide an elastic force to tighten the fastening ring; and at least one filler disposed between the fastening ring and the core and adjacent to the positive terminal to compress the core.

[0004] In some embodiments, a pair of elastic portions are provided, and the pair of elastic portions are respectively arranged on opposite sides along the length direction of the core.

[0005] In some embodiments, the fastening ring further includes a pair of rigid portions, which are respectively arranged on opposite sides along the thickness direction of the core, the thickness direction being perpendicular to the length direction.

[0006] In some embodiments, at least one filler is disposed in at least one of a pair of rigid portions facing the inner side of the core, and protrudes from the inner side of at least one rigid portion in the thickness direction.

[0007] In some embodiments, along the thickness direction, the size of each of the pair of elastic portions in its natural, unstretched form is smaller than the size of the core.

[0008] In some embodiments, along the length direction, the size of each of a pair of rigid portions is equal to the size of the core.

[0009] In some embodiments, the fastening ring is made of insulating material, and the filler is also made of insulating material.

[0010] In some embodiments, the filler material is selected from at least one of the following: polycarbonate, polystyrene, polyoxymethylene, and nylon.

[0011] In some embodiments, the fastening ring includes at least one insulating elastic band wound around the outside of the core.

[0012] In this embodiment, the fastening ring of the battery cell surrounds the outside of the wound core, so that the elastic portion of the fastening ring can provide elastic force to tighten the fastening ring. A filler is arranged between the fastening ring and the wound core, adjacent to the positive electrode post of the battery cell. This allows the fastening ring to apply pressure towards the wound core to the filler. Because the filler is arranged adjacent to the positive electrode post of the battery cell, the filler can compress multiple electrodes in the wound core, keeping the multiple electrodes in close contact at least near the positive electrode post. That is, the gap between the multiple electrodes can be reduced. On the one hand, this reduces the ion migration distance and lowers the internal resistance of the wound core. On the other hand, it can also improve the uniformity of active ion migration, reduce lithium plating on the negative electrode, and thus reduce the risk of puncturing the separator due to lithium dendrite extension. In this way, the electrical performance and safety performance of the secondary battery can be improved.

[0013] In a second aspect of this application, a secondary battery is provided. The secondary battery includes a battery cell according to the first aspect.

[0014] It should be understood that the content described in this content section is not intended to limit the key or essential features of the embodiments of this application, nor is it intended to restrict the scope of this application. Other features of this application will become readily apparent from the following description. Attached Figure Description

[0015] The above and other features, advantages, and aspects of the embodiments of this application will become more apparent from the accompanying drawings and the following detailed description. In the drawings, the same or similar reference numerals denote the same or similar elements, wherein: Figure 1 A schematic diagram of the structure of a battery cell according to some embodiments of this application is shown; Figure 2 A schematic diagram of a fastening ring and a filler according to some embodiments of this application is shown; Figure 3A A schematic diagram of the negative electrode obtained after disassembling a battery cell after it has been fully charged, according to some embodiments of this application, is shown. Figure 3B A schematic diagram of the negative electrode sheet obtained by disassembling a battery cell according to some embodiments of this application after 50 supercharge (6C) cycles is shown. Figure 4A This diagram shows the negative electrode plate obtained after disassembling a conventional battery cell after it has been fully charged; and Figure 4B The diagram shows the negative electrode obtained after disassembling a conventional battery cell after 50 supercharge (6C) cycles. Detailed Implementation

[0016] Embodiments of this application will now be described in more detail with reference to the accompanying drawings. While some embodiments of this application are shown in the drawings, it should be understood that this application can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of this application. It should be understood that the drawings and embodiments of this application are for illustrative purposes only and are not intended to limit the scope of protection of this application.

[0017] It should be noted that the headings of any section / subsection provided herein are not limiting. Various embodiments are described throughout this document, and embodiments of any type may be included under any section / subsection. Furthermore, embodiments described in any section / subsection may be combined in any way with any other embodiments described in the same section / subsection and / or different sections / subsections.

[0018] In the description of embodiments of this application, the term "comprising" and similar terms should be understood as open-ended inclusion, i.e., "including but not limited to". The term "based on" should be understood as "at least partially based on". The term "one embodiment" or "the embodiment" should be understood as "at least one embodiment". The term "some embodiments" should be understood as "at least some embodiments". Other explicit and implicit definitions may also be included below. The terms "first", "second", etc., may refer to different or the same objects. Other explicit and implicit definitions may also be included below.

[0019] It should be noted that, in the description of the embodiments of this application, any one of the length direction L, thickness direction T, and extension direction E is not coplanar with the other two, thereby defining a three-dimensional space for placing the battery cell and secondary battery. In some specific embodiments, any two of the length direction L, thickness direction T, and extension direction E can be perpendicular to each other, corresponding to the length, thickness, and height of the battery cell, respectively.

[0020] In the core of a secondary battery, the tabs of the same electrode sheet are usually arranged on the same side along the length of the core. These tabs of the same electrode sheet are electrically connected to the corresponding terminals of the cell by welding. To facilitate welding and subsequent assembly into the casing, the tabs are usually designed with appropriate length redundancy. Especially for the positive electrode sheet, since the positive electrode sheet is more rigid, the redundancy reserved at the positive electrode tab is correspondingly increased to avoid damage to the positive electrode sheet during assembly.

[0021] However, during cell assembly and casing, the downward pressure from the cell insertion compresses the redundant portions of the electrode tabs, causing them to bend. This bending of the redundant portions partially separates the negative electrode from the adjacent positive electrode. Particularly for the negative electrode in the first or last layer of the electrode stack, the compression from the redundant portions creates a noticeable gap between the negative electrode and the adjacent positive electrode in a portion of the positive electrode tab. Furthermore, during cell charging, the side of the negative electrode facing the positive electrode expands due to a chemical reaction, and the outward force generated by this expansion further increases the aforementioned gap.

[0022] Excessive gaps between electrodes can prevent ions (e.g., lithium ions) released from the positive electrode from fully embedding into the corresponding negative electrode. These unembedded ions accumulate in the corresponding area of ​​the negative electrode, forming visible purple spots and affecting the battery's electrochemical performance. Furthermore, in fast-charging scenarios, unembedded lithium ions can undergo lithium plating at the purple spots. The lithium dendrites generated by this plating can pierce the battery's internal separator, causing a short circuit within the cell and potentially leading to thermal runaway, fire, or even explosion—serious safety incidents that pose a significant threat to the safety of lithium-ion batteries.

[0023] According to embodiments of this application, a battery cell and a secondary battery are provided to solve or at least partially solve the aforementioned technical defects or other potential technical defects. In this embodiment, a fastening ring of the battery cell surrounds the outside of the wound core, so that the elastic portion of the fastening ring can provide elastic force to tighten the fastening ring. A filler is arranged between the fastening ring and the wound core, adjacent to the positive electrode post of the battery cell, which allows the fastening ring to apply pressure towards the wound core to the filler. Because the filler is arranged adjacent to the positive electrode post of the battery cell, the filler can compress multiple electrodes in the wound core, keeping the multiple electrodes in close contact at least near the positive electrode post. That is, the gap between the multiple electrodes can be reduced. In this way, on the one hand, the ion migration distance can be reduced, and the internal resistance of the wound core can be lowered. On the other hand, the uniformity of active ion migration can be improved, reducing lithium plating on the negative electrode, thereby reducing the risk of puncturing the separator due to lithium dendrite extension. Therefore, the electrical performance and safety performance of the secondary battery can be improved.

[0024] Figure 1 A schematic diagram of the structure of a battery cell according to some embodiments of this application is shown. Figure 2 A schematic diagram of a fastening ring and filler according to some embodiments of this application is shown. Figure 1 and Figure 2As shown, the battery cell described herein generally includes a core 1, a positive electrode post 2, and a negative electrode post 3. The positive electrode post 2 and the negative electrode post 3 are electrically connected to the core 1. The core 1 includes a positive electrode sheet, a negative electrode sheet, and a separator film stacked together. The core 1 can be assembled through processes such as winding and packaging. In some embodiments, the core 1 can be wound into a shape of predetermined specifications and / or dimensions. Exemplarily, the core 1 can be an elliptical cylindrical shape or an oblong cylindrical shape. The positive electrode post 2 and the negative electrode post 3 are arranged on the same side of the core 1 along the extending direction E, and the positive electrode post 2 is electrically connected to the tab of the positive electrode sheet by welding or other means, and the negative electrode post 3 is electrically connected to the tab of the negative electrode sheet by welding or other means. In some embodiments, the positive electrode post 2 and the negative electrode post 3 can be arranged along the length direction L of the core 1. Correspondingly, the positive electrode tab of the positive electrode sheet and the negative electrode tab of the negative electrode sheet are arranged along the length direction L.

[0025] The battery cell also includes a fastening ring 4 disposed on the outside of the core 1 and a filler 5 disposed between the fastening ring 4 and the core 1. The fastening ring 4 is arranged adjacent to the positive electrode post 2 and the negative electrode post 3, and the fastening ring 4 at least partially surrounds the outside of the core 1. The fastening ring 4 includes an elastic portion 41. During the period when the fastening ring 4 surrounds the outside of the core 1, the elastic portion 41 can provide an elastic force (e.g., a tensile force) so that the fastening ring 4 can be tightened on the outer surface of the core 1. During the period when the fastening ring 4 is tightened on the outer surface of the core 1, the tightening force of the fastening ring 4 can compress the filler 5, so that the filler 5 compresses the core 1 along the thickness direction T. The multiple electrode sheets wound in the core 1 can remain in close contact after being compressed by the filler 5, thereby effectively reducing the gap between the electrode sheets, improving the transfer efficiency and uniformity of ions between the positive and negative electrode sheets, and thus improving the electrical performance and safety performance of the secondary battery.

[0026] The filler 5 is arranged adjacent to the positive electrode post 2. For example, the filler 5 can be aligned with the positive electrode post 2 along the extension direction E, so that the filler 5 can be squeezed to the weak points in the electrode sheet where gaps are prone to occur. As a result, the gap in the region of the negative electrode sheet near the positive electrode post 2 can be reduced, effectively shortening the ion transport path, reducing the overall impedance of the core 1, and suppressing local lithium plating in the negative electrode sheet, reducing the risk of internal short circuit caused by lithium dendrites piercing the separator.

[0027] In some embodiments, the fastening ring 4 includes a pair of elastic portions 41, which are respectively arranged on opposite sides of the winding core 1 along the length direction L. Thus, the pair of elastic portions 41 can provide a uniform elastic force to the fastening ring 4 and tighten it.

[0028] In some embodiments, the fastening ring 4 further includes a pair of rigid portions 42, which are respectively arranged on opposite sides of the core 1 along the thickness direction T. Each rigid portion 42 has its two ends connected to a pair of elastic portions 41. In some embodiments, the battery cell may include at least a pair of fillers 5, each pair of fillers 5 being arranged on opposite sides of the core 1 along the thickness direction T. Each filler 5 is arranged on the inner side of the same side rigid portion 42 facing the core 1, and the filler 5 protrudes from the rigid portion 42 along the thickness direction T towards one side of the core 1. In this way, the elastic force provided by the pair of elastic portions 41 can bring each rigid portion 42 closer together along the thickness direction T, and the fillers 5 can accurately compress weak points on the core 1 where gaps are prone to occur in the electrode sheets, thereby effectively controlling the gaps between the electrode sheets.

[0029] In some embodiments, the elastic portion 41 can be stretched in a predetermined direction, and after being stretched, the elastic portion 41 can generate an elastic force that drives it to return to its natural shape. Specifically, in the thickness direction T, the size of the elastic portion 41 in its unstretched natural shape is smaller than the size of the core 1. When the fastening ring 4 is fitted over the outer side of the core 1, the elastic portion 41 is stretched, thereby providing an elastic force to the connected pair of rigid portions 42, and allowing the pair of rigid portions 42 to compress the core 1 through at least one pair of fillers 5.

[0030] In some embodiments, the contact surface of the filler 5 facing the core 1 can be a plane, an inclined plane, or a suitable curved surface. In some embodiments, the size of the filler 5 protruding from the rigid portion 42 can be specifically designed for the position of the filler 5 on the core 1. Thus, the core 1 can be compressed with appropriate extrusion pressure according to the winding method and position of the internal electrode sheets, thereby ensuring the extrusion effect. As an example only, the size of the filler 5 protruding from the rigid portion 42 on the side closer to the positive electrode post 2 can be larger than the size of the filler 5 protruding from the rigid portion 42 on the side farther from the positive electrode post 2. In some other embodiments, multiple pairs of fillers 5 can be arranged on the fastening ring 4 along the extension direction E, and the size of each filler 5 protruding from the rigid portion 42 can also be arbitrarily and appropriately adjusted according to its position on the core 1, which is not limited in this application.

[0031] In some embodiments, the size of each rigid part 42 along the length direction L is equal to the size of the core 1. This allows the elastic force generated by the elastic part 41 to be as parallel as possible to the thickness direction T, so that a pair of rigid parts 42 can clamp the core 1 along the thickness direction T. This reduces the influence of the fastening ring 4 on other sides of the core 1, thereby ensuring the winding effect and reducing the risk of excessive local stress on the electrode or separator caused by excessive compression of the sides of the core 1 along the length direction L by the elastic part 41, which could lead to breakage or damage.

[0032] In some embodiments, the fastening ring 4 and / or the filler 5 may be made of insulating material. For example, the filler 5 may be made of polycarbonate, polystyrene, polyoxymethylene, or nylon. In some other embodiments, the rigid portion 42 of the fastening ring 4 may be made of polyetheretherketone, polyimide, or the like. In some optional embodiments, the elastic portion 41 of the fastening ring 4 may be made of silicone rubber, fluororubber, or the like. It should be noted that the above description of the material selection for the fastening ring 4 and / or the filler 5 is merely exemplary. In fact, other suitable materials may be selected based on the material properties of the fastening ring 4 and / or the filler 5, raw material costs, processing difficulty, etc., and this application does not impose any limitations on this.

[0033] In some embodiments, the fastening ring 4 can be a closed annular structure. For example, the fastening ring 4 can be composed of a pair of elastic portions 41 and a pair of rigid portions 42 connected end to end. The fastening ring 4 can be sleeved on the outer peripheral surface of the core 1 and tightly adhered to the outer peripheral surface of the core 1 under the elastic force provided by the elastic portions 41. In some other embodiments, the fastening ring 4 can also be a partial annular structure, where the fastening ring 4 can partially surround the outside of the core 1. For example, the fastening ring 4 can be generally C-shaped, and the C-shaped fastening ring 4 can be arranged on the side of the core 1 along the length direction L and tightly adhered to three sides of the core 1. In this C-shaped structure, the elastic portion 41 can be arranged in the middle of the fastening ring 4 and located on one side of the core 1 along the length direction L. The elastic portion 41 can provide elastic force, allowing the two ends of the fastening ring 4 to be clamped on opposite sides of the core 1 along the thickness direction T.

[0034] In some embodiments, the fastening ring 4 may also be formed by wrapping an insulating elastic strip around the outside of the core 1. Specifically, the filler 5 may be placed at a weak location on the core 1 where gaps are likely to occur, and the insulating elastic strip may be wrapped around the outside of the core 1 in the extending direction E. The insulating elastic strip is moderately stretched during winding, thereby allowing the formed fastening ring 4 to tighten on the surface of the core 1 and causing the filler 5 to compress the core 1.

[0035] In the actual production and testing of battery cells, the reliability of a batch of cells can be determined by disassembling the cells and inspecting the surface condition of the negative electrode. Typically, the surface of the disassembled negative electrode is a uniform golden-gray color (the color may vary depending on the active coating on the negative electrode surface). The purple spots mentioned earlier usually refer to localized dark purple, blue, or iridescent patches on the coating. The formation of purple spots is essentially an optical interference phenomenon, fundamentally caused by the formation of a solid electrolyte interface film with abnormal composition, thickness, or structure on the surface of the negative electrode, leading to changes in light reflection and interference.

[0036] In other words, the formation of purple spots indicates inhomogeneity in the microstructure and chemical state of the electrode, which can have a series of negative impacts on cell performance, and these impacts are usually irreversible. Specifically, the formation of purple spots can affect the electrical and cycle performance of the cell. For example, the formation of purple spots may lead to capacity decay and reduced initial charge-discharge efficiency; it may also shorten the cycle life of the cell and increase temperature rise, etc.

[0037] Furthermore, after multiple charge-discharge cycles, lithium plating may occur in the purple-spotted areas of the battery cell. This means that lithium ions can more easily gain electrons directly on the graphite surface and be reduced to metallic lithium (lithium plating). Lithium plating not only consumes active lithium but also forms lithium dendrites, which can pierce the separator, cause internal short circuits, and pose serious safety hazards.

[0038] Therefore, by checking the condition of the negative electrode, the operational reliability of this batch of battery cells can be determined, and the stability of such battery cells over a long period of time can be predicted to some extent.

[0039] In some specific embodiments, the positive electrode, separator, and negative electrode can be stacked and wound sequentially to form a core. Then, a fastening ring is wrapped around the outside of the core and filler is installed to obtain a battery cell. The tightening force of the fastening ring compresses the core, keeping the positive electrode, separator, and negative electrode tightly attached. The battery cell is placed in an outer packaging shell, vacuum dried, and then injected with electrolyte. After settling, formation, shaping, and capacity testing, a secondary battery is obtained. After charging the secondary battery to full capacity, the battery cell is disassembled, and the condition of the negative electrode is inspected. The secondary battery is then subjected to 50 overcharge-discharge cycles at a 6C rate, after which the battery cell is disassembled, and the condition of the negative electrode is inspected.

[0040] Figure 3A A schematic diagram of the negative electrode obtained after disassembling a battery cell after it has been fully charged, according to some embodiments of this application, is shown. Figure 3B A schematic diagram of the negative electrode sheet obtained by disassembling a battery cell according to some embodiments of this application after 50 overcharge (6C) cycles is shown. Figure 3A and Figure 3B As shown, the surface of the negative electrode sheet of the battery cell provided in this application embodiment is complete and uniform, and no purple spots or lithium plating were found on the surface. It should be noted that... Figure 3A and Figure 3B In the process, the ring-shaped purple area located at the edge of the negative electrode is a normal phenomenon caused by the negative electrode being designed to have a slightly larger area than the positive electrode, and it does not belong to the purple spots mentioned in this application.

[0041] In contrast, conventional battery cells (i.e., those without a fastening ring around the outside of the core and without filler) can be placed in an outer packaging shell, vacuum dried, and then injected with electrolyte. After settling, formation, shaping, and capacity testing, a secondary battery is obtained. This secondary battery is then fully charged, and the conventional battery cells within it are disassembled to inspect the condition of the negative electrode. The secondary battery is then overcharged and discharged at a 6C rate for 50 cycles, after which the conventional battery cells are disassembled and the condition of the negative electrode is inspected. Figure 4A This diagram shows the negative electrode sheet obtained after disassembling a conventional battery cell (without fastening rings and fillers) after full charging. Figure 4B The diagram shows a schematic of the negative electrode obtained after disassembling a conventional battery cell (without fastening ring 4 and filler 5) after 50 overcharge (6C) cycles. Figure 4A and Figure 4B As shown, Figure 4A In the middle section, after the negative electrode plate was fully charged, purple spots 410 appeared in the area near the positive electrode post 2. Compared to Figure 3A A well-defined, ring-shaped purple area at the center edge. Figure 4A The width of the purple spot 410 increased significantly, and it showed a tendency to spread towards the center region of the negative electrode. Meanwhile... Figure 4B In the process, after multiple charge-discharge cycles, the purple spot 410 further deteriorated, and a bright silver spot 420 appeared (that is, lithium plating occurred in this area).

[0042] By comparison Figure 3A , 3B As can be seen from 4A and 4B, the battery cell provided in this application embodiment can significantly reduce the gap between the electrodes in the cell, thereby suppressing the formation of purple spots on the negative electrode and the development of lithium plating. This greatly improves the electrical performance and safety performance of the secondary battery.

[0043] The various implementations of this application have been described above. The foregoing description is exemplary and not exhaustive, nor is it limited to the disclosed implementations. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described implementations. The terminology used herein is chosen to best explain the principles, practical applications, or improvements to technology in the market, or to enable others skilled in the art to understand the various implementations disclosed herein.

Claims

1. A battery cell, characterized in that, include: Core (1); The positive terminal (2) and the negative terminal (3) are each electrically connected to the winding core (1); A fastening ring (4) is disposed around at least a portion of the winding core (1) and adjacent to the positive terminal post (2) and the negative terminal post (3). The fastening ring (4) includes at least one elastic portion (41) adapted to provide an elastic force to tighten the fastening ring (4). as well as At least one filler (5) is arranged between the fastening ring (4) and the core (1) and adjacent to the positive electrode post (2) to compress the core (1).

2. The battery cell according to claim 1, characterized in that, The elastic part (41) is provided in a pair, and the pair of elastic parts (41) are respectively arranged on opposite sides along the length direction (L) of the core (1).

3. The battery cell according to claim 2, characterized in that, The fastening ring (4) further includes a pair of rigid parts (42), which are respectively arranged on opposite sides along the thickness direction (T) of the core (1), the thickness direction (T) being perpendicular to the length direction (L).

4. The battery cell according to claim 3, characterized in that, The at least one filler (5) is disposed in at least one of the pair of rigid portions (42) facing the inner side of the core (1) and protruding from the inner side of the at least one rigid portion (42) along the thickness direction (T).

5. The battery cell according to claim 4, characterized in that, Along the thickness direction (T), the size of each of the pair of elastic portions (41) in its natural form without stretching is smaller than the size of the core (1).

6. The battery cell according to claim 4, characterized in that, Along the length direction (L), the size of each of the pair of rigid portions (42) is equal to the size of the core (1).

7. The battery cell according to claim 1, characterized in that, The fastening ring (4) is made of insulating material, and the filler (5) is made of insulating material.

8. The battery cell according to claim 7, characterized in that, The filler (5) is made of at least one of the following: polycarbonate, polystyrene, polyoxymethylene and nylon.

9. The battery cell according to claim 1, characterized in that, The fastening ring (4) includes at least one insulating elastic strip wrapped around the outside of the core (1).

10. A secondary battery, characterized in that, include: The battery cell according to any one of claims 1-9.

Images