Pouch-type lithium ion battery

Abstract

The utility model relates to the field of lithium ion battery preparation discloses a kind of soft package lithium ion batteries. Battery includes: aluminium plastic film casing and internal electric core, the aluminium plastic film casing has the chamber formed by sealing, the electric core is encapsulated in the chamber, the aluminium plastic film casing includes the positive edge of electrode extraction with, and side edge without electrode extraction, the side edge is bent at least twice, forms a folded edge structure, in the folded edge structure, between each adjacent two the folded edge area of stacking, between the folded edge area of innermost layer and the side of the electric core, all are bonded by hot melt adhesive layer. The scheme is especially suitable for improving the sealing reliability of ultrathin soft package lithium ion battery.

Description

Technical Field

[0001] This utility model relates to the field of lithium-ion battery packaging technology, specifically to the aluminum-plastic film sealing structure of thin soft-pack lithium-ion batteries, and particularly to a soft-pack lithium-ion battery. Background Technology

[0002] Thin-pack lithium-ion batteries are widely used in wearable devices and flexible electronic products due to their advantages such as lightweight and flexibility. However, the aluminum-plastic film sealing process for thin-pack lithium-ion batteries has long faced a dilemma: See Figure 1 As shown, in the prior art, the folding process involves folding the cut edge of the aluminum-plastic film towards the side of the battery. To prevent the folded edge from exceeding the body's dimensions, the effective sealing width of the heat-sealed edge is compressed (typically ≤1mm, while the heat-sealing density of conventional soft-pack batteries is at least 3mm), resulting in insufficient heat-sealing bond strength of the heat-sealed edge in thin soft-pack batteries.

[0003] Existing technology 2, flattening process: Keep the aluminum-plastic film flat and extended. Since traditional heat sealing requires ≥3mm to ensure bonding strength, the existing technology needs to retain the standard sealing width (about 3-5mm). However, this technology requires additional space in the width direction of the battery, resulting in a decrease in volume utilization of about 8-12%, which seriously restricts the improvement of battery energy density. Summary of the Invention

[0004] One of the objectives of this utility model embodiment is to provide a soft-pack lithium-ion battery, which is particularly suitable for improving the sealing reliability of ultra-thin soft-pack lithium-ion batteries.

[0005] In a first aspect, this embodiment provides a soft-pack lithium-ion battery, comprising: an aluminum-plastic film casing and an internal battery cell. The aluminum-plastic film casing has a sealed chamber, and the battery cell is encapsulated within the chamber. The aluminum-plastic film casing includes a front sealing edge with electrode leads and a side sealing edge without electrode leads. The side sealing edge is bent at least twice to form a layered folded edge structure. Within the folded edge structure, the two adjacent folded edge areas stacked together, and the innermost folded edge area and the side of the battery cell, are all bonded together by a hot melt adhesive layer.

[0006] Optionally, the folded edge structure includes a first folded edge area and a second folded edge area that are stacked and attached together. The first folded edge area is a heat-sealed edge strip along the side of the battery cell between a first fold line and a second fold line, wherein the second fold line is parallel to the first fold line. The second folded area is the heat-sealed edge strip between the second fold line and the outer edge of the side seal.

[0007] Optionally, the first folded edge area is the innermost layer of the folded edge structure and is in contact with the side of the battery cell. The second folded edge area is bent from the second fold line and attached to the outside of the side of the first folded edge area.

[0008] Optionally, the outer edge of the heat-sealed edge attached to the side of the battery cell and the end face of the hot melt adhesive layer thereon are cut end faces. A waterproof adhesive layer is fully covered on the cut end face, and the waterproof adhesive layer extends to both sides to form a waterproof adhesive extension edging on the outer surface of the folded structure.

[0009] Optionally, the waterproof adhesive layer is a silicone-modified epoxy resin adhesive.

[0010] Optionally, the silicone-modified epoxy resin adhesive contains boron nitride with a surface modified by a silane coupling agent, wherein the mass fraction of the boron nitride is 1.5-2.5%.

[0011] Optionally, the second folded edge area is bent from the second crease line and attached between the first folded edge area and the side of the battery cell, forming the innermost layer of the folded edge structure.

[0012] Optionally, the hot melt adhesive layer is a polyolefin-based hot melt adhesive with a melt viscosity of 1500-3000 cps and an interfacial bonding force with the aluminum-plastic film of ≥15N / 15mm.

[0013] Optionally, the hot melt adhesive layer penetrates into the micropores on the surface of the aluminum-plastic film it is bonded to, with a penetration depth of 5-10 μm, and forms a physical riveting structure after curing.

[0014] Optionally, the thickness of the pouch lithium-ion battery is less than or equal to 3 mm.

[0015] Optionally, the bottom and top surfaces of the aluminum-plastic film casing are respectively arc surfaces that are in contact with the bottom and top surfaces of the arc-shaped battery cell. The bottom and top of the folded edge structure are parallel to the arc surface, respectively.

[0016] Optionally, the crease lines between two adjacent folded areas within the folded structure are arc lines parallel to the arc surface.

[0017] As can be seen from the above, adopting this technical solution has the following beneficial effects: The folded edge structure is bonded using a thin layer of hot melt adhesive, increasing the total thickness by ≤0.1mm, significantly improving the battery's volumetric energy density. The layers within the folded edge structure are bonded together with hot melt adhesive, which provides mechanical anchoring and sealing for the folded edge structure, improving the sealing reliability of the heat-sealed edge. The hot melt adhesive penetrates the micropores of the aluminum-plastic film to form a "physical riveting," resulting in high interfacial bonding strength and effectively inhibiting interfacial delamination after cycling. This solution is easily implemented by modifying existing production lines, facilitating widespread adoption. Attached Figure Description

[0018] The accompanying drawings, which are provided to further illustrate the present invention and form part of this application, do not constitute an undue limitation of the present invention.

[0019] Figure 1 A three-dimensional structural diagram of an arc-shaped soft-pack lithium-ion battery using a single-folding edge process; Figure 2 A three-dimensional structural schematic diagram of a single-ended outgoing electrode tab with a double-folded edge structure on both sides, provided for the first embodiment of this utility model; Figure 3 A three-dimensional structural diagram of a second type of arc-shaped soft-pack lithium-ion battery with a single-ended output tab having a double-folded edge structure on both sides, provided for an embodiment of this utility model; Figure 4 A three-dimensional structural diagram of a third type of arc-shaped soft-pack lithium-ion battery with a single-ended output tab having a double-folded edge structure on both sides, provided for an embodiment of this utility model; Figure 5 A three-dimensional structural diagram of a fourth type of arc-shaped soft-pack lithium-ion battery with a single-ended output tab having a double-folded edge structure on both sides, provided for an embodiment of this utility model; Figure 6 A three-dimensional structural diagram of the first type of arc-shaped soft-pack lithium-ion battery with a double-folded edge structure on one side and tabs at both ends provided for the embodiment of this utility model; Figure 7 A three-dimensional structural diagram of a second type of arc-shaped soft-pack lithium-ion battery with a double-folded edge structure on one side and tabs at both ends provided for the present utility model embodiment; Figure 8 A three-dimensional structural diagram of a third type of arc-shaped soft-pack lithium-ion battery with a double-folded edge structure on one side and tabs at both ends provided for the present utility model embodiment; Figure 9 This is a three-dimensional structural diagram of a fourth type of arc-shaped soft-pack lithium-ion battery with a double-folded edge structure on one side and tabs at both ends, provided as an embodiment of the present utility model.

[0020] 1: Aluminum-plastic film casing; 11: Chamber; 12: Front sealing edge; 13: Side sealing edge; 2: Folded edge structure; 21: First folded edge area; 22: Second folded edge area; 3: Electrode; 4: Electrode adhesive. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The illustrative embodiments and descriptions of the present invention are used to explain the present invention, but are not intended to limit the present invention.

[0022] Examples of embodiments of the present invention are shown in the accompanying drawings in a detailed description below, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout.

[0023] The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention. In the description of the present invention, it should be understood that terms such as "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the drawings and are only for the convenience of describing the present invention and simplifying the description, 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, and therefore should not be construed as limiting the present invention.

[0024] Furthermore, the terms "" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "" or "second" may explicitly or implicitly include one or more of that feature. In the description of this utility model, "a plurality of" means two or more, unless otherwise explicitly specified.

[0025] In this utility model, unless otherwise explicitly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., 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 according to the specific circumstances.

[0026] See Figures 1-9 As shown.

[0027] This embodiment provides a structure for a pouch lithium-ion battery, which is particularly suitable for the design of ultra-thin pouch lithium-ion batteries with a thickness of ≤3mm.

[0028] The ultra-thin soft-pack lithium-ion battery mainly includes: a battery cell (not shown in the figure) and an aluminum-plastic film casing 1 for sealing the battery cell.

[0029] The main body of the battery cell consists of a positive electrode, a negative electrode, a separator, and an electrolyte. External tabs 3 are welded onto the positive and negative electrode sheets to serve as external electrodes.

[0030] A separator is provided between each positive and negative electrode. The positive electrode includes an aluminum foil current collector and positive polar active material layers coated on both sides of the aluminum foil current collector. The positive polar active material may be, but is not limited to, lithium iron phosphate, ternary materials, etc. The negative electrode includes a copper foil current collector and negative polar active material layers coated on both sides of the copper foil current collector. The negative polar active material may be, but is not limited to, graphite, silicon carbide, etc.

[0031] Referring to the illustration, this embodiment uses an ultra-thin arc-shaped lithium-ion battery as an example. Specifically, the bottom and top surfaces of the battery cell are parallel arc surfaces. The battery cell can be manufactured using a winding process or a stacking process.

[0032] Taking the lamination process as an example, the laminated battery cell consists of sheet-like positive electrode plates, separator layers, and negative electrode plates stacked together. After lamination, the middle of the laminated battery cell along its length is initially fixed to prevent it from spreading out. In its natural state, the laminated battery cell is placed in a support mold of different shapes. Under the action of gravity, each electrode plate and separator layer of the laminated battery cell adheres tightly to the top surface of the support mold, and the laminated battery cell takes on the same shape as the current support mold.

[0033] For example, when the top surface of the support mold is a raised arc along the length direction, the two wide ends of the stacked battery cell placed on it naturally droop under the action of gravity. The stacked battery cell on the support mold is naturally arc-shaped along the length direction, with the middle part of the arc protruding and the two ends drooping. The inner arc of the side of the stacked battery cell is close to the support mold, and the outer arc is located on the top surface of the arc-shaped battery.

[0034] When the supporting mold is a concave arc shape along the length direction, the stacked battery cell on it is an arc shape that can only be concave in the middle and rise at both ends. The outer arc of the side of the stacked battery cell is in close contact with the supporting mold, and the inner arc is located on the top surface of the arc-shaped battery.

[0035] A recess matching the arc shape of the battery cell is pre-stamped into the aluminum-plastic film. The inner surface of the bottom of the recess is an arc shape along its length. This recess serves as a mold for the battery cell, and the shape of the inner surface of the bottom of the recess determines the shape of the battery cell placed inside the recess. In this embodiment, the two long edges of the recess opening are arcs parallel to its bottom surface, and the two wide edges of the recess opening can, but are not limited to, be straight lines. An integral aluminum-plastic film extends from all four sides of the recess opening in the aluminum-plastic film. Aluminum-plastic film is pre-reserved for heat sealing along the two wide edges and the long edges of the recess opening. This recess serves as a chamber 11 for accommodating the arc-shaped battery cell. After the battery cell is placed into the recess, along one wide end of the recess (e.g., ... Figures 2-5 ) or along a length of the recessed end (e.g. Figures 6-9 The bottom aluminum-plastic film is folded over to become the top aluminum-plastic film of the aluminum-plastic film shell 1. The top aluminum-plastic film completely covers the top of the opening of the recess and is attached to the bottom aluminum-plastic film. At this time, the polypropylene layer surfaces of the two aluminum-plastic films are facing each other, serving as the inner surface of the aluminum-plastic film shell 1.

[0036] For the heat-sealed edge (referred to as the positive sealing edge 13) of the aluminum-plastic film shell 1 with electrode leads, electrode adhesive 4 is applied to the front and back sides of the electrode 3 section located between the heat-sealed edges of the two electrode tabs 3 of the battery cell body. The electrode adhesive 4 pre-covers the welding section before entering the aluminum-plastic film shell 1 to avoid welding burrs piercing the aluminum-plastic film and affecting the sealing reliability of the aluminum-plastic film shell 1. During heat sealing, a heat sealing machine is used to apply a certain amount of heat and pressure to the positive sealing edge 13 to be heat-sealed. On the positive sealing edge 13, the polypropylene layers on the inner surfaces of the upper and lower layers of aluminum-plastic film melt and bond together under the action of pressure and heat, and are sealed together after cooling and solidification. At the same time, the electrode adhesive 4 on the front and back sides of the electrode tab 3 melts and flows with the adhesive layer on the opposite surfaces of the lower and upper layers to fill the micro gaps between the aluminum-plastic film and the electrode 3 section on the top and bottom surfaces. The electrode adhesive 4 melts and fully bonds together with the aluminum-plastic film on the bottom and top surfaces. After holding pressure and cooling, the middle section of the electrode tab 3 is sealed together in the heat-sealed edge at this end.

[0037] For the heat-sealed edge (referred to as the side seal edge) of the aluminum-plastic film shell 1 without electrode leads, a heat-sealing machine is used to apply a certain pressure and heat to the side seal edge to be heat-sealed. This causes the polypropylene layers on the opposing inner surfaces of the upper and lower layers of the aluminum-plastic film to melt and bond together under pressure and heat. After pressure holding, cooling, and solidification, the layers are sealed together to form the heat-sealed edge. The heat-sealing conditions are 180℃ / 3MPa / 10s.

[0038] In their research on this invention, the inventors discovered that traditional processes face fundamental challenges when the battery thickness is ≤3mm: Since the thickness of ultra-thin soft-pack lithium-ion batteries is ≤3mm, the bending radius of the folded edge is ≤0.5mm due to the thickness limitation. The polypropylene layer of aluminum-plastic film is prone to micro-cracks under ultra-small curvature, which can easily lead to problems such as leakage and water vapor infiltration.

[0039] Generally, to ensure the corrosion resistance of aluminum-plastic film, the aluminum layer exposure ratio of the battery is required to be ≤5%. However, after heat sealing, the heat-sealed edge of the ultra-thin soft-pack lithium-ion battery needs to be cut and folded, which exposes the aluminum layer of the aluminum-plastic film. The aluminum layer exposure ratio is ≥15%, which easily leads to the corrosion of the aluminum layer and accelerates the penetration of electrolyte. The corrosion rate of aluminum-plastic film is increased by at least 3 times.

[0040] The effective heat-sealing edge width of ultra-thin soft-pack lithium-ion batteries is ≤1mm, while traditional aluminum-plastic film heat sealing generally requires a width of ≥3mm to ensure heat-sealing bond strength.

[0041] Therefore, in this embodiment, the aluminum-plastic film shell 1 is further processed as follows: the side sealing edge without the tab 3 protruding is bent at least twice (this embodiment uses two bends as an illustration) to form a layered folded edge structure 2, in which the layers within the structure are bonded together and the innermost layer is bonded to the side of the battery cell by a hot melt adhesive layer.

[0042] The adoption of this technical solution has the following beneficial effects: The folded edge structure 2 is bonded using a thin layer of hot melt adhesive, increasing the total thickness by ≤0.1mm, significantly improving the battery's volumetric energy density. The layers within the folded edge structure 2 are bonded together with hot melt adhesive, which provides mechanical anchoring and sealing for the folded edge structure 2 formed by bending, improving the sealing reliability of the heat-sealed edge. The hot melt adhesive penetrates into the micropores of the aluminum-plastic film to form a "physical riveting," resulting in high interfacial bonding strength and effectively inhibiting interfacial delamination after cycling. This solution is easily implemented by modifying existing production lines, facilitating widespread adoption.

[0043] It should be noted that, Figures 2-9 To facilitate the display of the battery's folded edge structure 2, the hot melt adhesive and waterproof adhesive are not shown. For the location, structure, and coating process of the hot melt adhesive and waterproof adhesive, please refer to the text description in the instruction manual.

[0044] Example 1: Outward-folding double-sided battery.

[0045] This embodiment uses an ultra-thin battery (2.1mm thick) for the smartwatch. Figure 2 The outward-folded structure shown has two electrodes extending from the same width end of the arc-shaped battery. Folded edge structures 2 are provided on both sides of the battery. In the folded edge structure 2, the second folded edge area 22 connecting the outer edge is attached to the outer side of the first folded edge area 21.

[0046] Cell fabrication: A 100mAh rated capacity cell is fabricated using conventional stacking technology.

[0047] The cathode is made of LiCoO2 coated aluminum foil with a surface density of 20 mg / cm²; the anode is made of graphite coated copper foil with a surface density of 10 mg / cm²; the stack consists of 14 layers with dimensions of 28 × 36 × 2.1 mm.

[0048] Aluminum-plastic film stamping shell: DART® 3μm (Nylon 15μm / Aluminum 40μm / PP 58μm), stamping depth: 1.8mm.

[0049] The battery cell body is placed inside the aluminum-plastic film chamber 11. The two electrodes of the battery cell body extend from one wide end, and the aluminum-plastic film is folded up along the edge of the other wide end opposite to the tab 3 as the top layer of aluminum-plastic film, covering the opening of the chamber 11.

[0050] The liquid injection and aluminum-plastic film heat sealing steps can be implemented using existing technologies.

[0051] In this embodiment, the heat sealing parameters are 180℃×5s and pressure 0.6MPa.

[0052] Electrolyte: 1M LiPF6 in EC / DMC (1:1), injection volume: 0.8g / Ah.

[0053] Adhesive application and folding: Apply molten polyolefin hot melt adhesive (Technomelt PS 8308, melt viscosity 2000cps) to a predetermined area of ​​the side sealing edge (e.g., but not limited to, at a position approximately 0.3 mm from the predetermined fold line). The adhesive application location includes both surfaces of the aluminum-plastic film that will form the first folding area 21. Subsequently, the side seal is bent outward from the bottom edge of the side of the battery cell as the first fold line, so that the side seal is located outside the side of the battery cell and the outer edge of the side seal extends beyond the top surface of the battery cell. Then, it is bent outward further along the second fold line flush with the top surface of the battery cell, so that the second folded edge area 22 is tightly attached to the outside of the first folded edge area 21. It is pressed for 5 seconds at a pressure of 0.3MPa and a temperature of 65℃, so that the hot melt adhesive can be fully leveled and wetted into the two interfaces. The hot melt adhesive layer penetrates into the micropores on the surface of the aluminum-plastic film it is bonded to, with a penetration depth of 5-10μm. After curing, it forms a physical riveting structure. The entire mechanism is tightly attached to the outside of the side of the battery cell.

[0054] The hot melt adhesive is cured by pressing it at room temperature for 5 seconds, allowing it to cool and solidify. After curing, the hot melt adhesive forms a physical riveting structure with the two interfaces it is bonded to.

[0055] Edge trimming: A laser precision cutting system is used to remove the outer edge of the heat-sealed edge that extends beyond the bottom surface of the battery cell, forming a flat cut end face flush with the bottom surface of the battery cell.

[0056] Apply waterproof adhesive: Spray silicone-modified epoxy resin waterproof adhesive (such as, but not limited to, Dow Corning SE9187L, which contains 2wt% KH550 modified boron nitride modified with a silane coupling agent) onto the cut end face, and extend the waterproof adhesive to the outer surface of the folded edge structure 2 on both sides by about 0.3mm each to form an edge.

[0057] In ultra-thin soft-pack lithium-ion batteries, the application of hot melt adhesive and waterproof adhesive is not a simple superposition of technical effects. By using the hot melt adhesive edge pressing of this utility model in this embodiment, the waterproof layer fully covers the cut end face, and the width of the waterproof layer extending to the surface facing outward of the edge is >=0.2mm. It also fully covers the hot melt adhesive overflow area, which can achieve an unexpected effect of 1+1>2.

[0058] It should be noted that, in the research of this utility model, the inventors discovered that the extension width of the waterproof layer is 0.2 mm, which is the critical value for blocking capillary penetration. When the extension width is ≤0.2 mm, the water vapor permeability increases sharply, and the capillary penetration blocking fails.

[0059] Curing: First, use UV curing (900mW / cm², 365nm, 2.5s), then cure at room temperature for 24 hours.

[0060] It should be noted that in this embodiment, hot melt adhesive is first applied and the edges are folded and pressed to ensure that the folded edges are tightly attached to the battery cell before the edges are cut. This provides a complete base surface for the cut edges and ensures that the waterproof adhesive completely covers the cross-section.

[0061] If the hot melt adhesive is omitted, the gap between the folded edge and the battery cell can easily lead to unevenness at the cut end, and the waterproof adhesive applied in the subsequent process cannot effectively cover the aluminum layer.

[0062] Experiments have shown that even after applying a waterproof adhesive layer to the cut end face of the folded edge without hot melt adhesive, the exposed aluminum layer area of ​​the cut end face is still >40%; furthermore, there are micro gaps (>10μm) between the folded edge without hot melt adhesive and the side of the battery cell, and the waterproof adhesive cannot fill these micro gaps due to its viscosity limitations, resulting in poor waterproof and anti-corrosion effects.

[0063] In summary, the process of first folding and pressing the edges to form a folded structure that is bonded to the battery cell, followed by edge trimming, not only provides rigid support for the trimmed edges but also creates an anchoring surface for subsequent waterproof adhesive extension through the formation of a hot melt adhesive overflow area (0.1-0.15mm wide). This sequence is the cornerstone of the process for solving the "three difficulties in sealing thin batteries" (small space + high sealing + low cost).

[0064] Example 2: Outward-folding double-sided battery (no glue applied after cutting the edges): The preparation process for folded structure 2 is exactly the same as that in Example 1, except that the steps of applying waterproof adhesive and subsequent curing are omitted.

[0065] Example 3: Outward-folding double-sided battery (cut before folding, comparative example): The folded edge structure 2 is the same as that in Example 1, and the preparation process is similar to that in Example 1, but the difference is that: laser cutting is performed first, followed by the processes of applying glue, bending and pressing to cure.

[0066] Example 4: Inward-folding double-sided battery (hidden cut design): This embodiment provides a method such as Figure 3 The core of the inward-folding double-sided battery structure shown lies in its unique bending sequence and structural design, which completely covers the cut end of the aluminum-plastic film inside, thereby achieving a physical seal.

[0067] S1: Edge trimming. First, the side sealing edge without electrode leads is laser-cut to pre-form a smooth, flat cut end face. This step precedes any bending operation, ensuring the processing accuracy and quality of the cut.

[0068] S2: Apply hot melt adhesive. Pre-apply molten polyolefin hot melt adhesive to the planned bending area. Adhesive application locations include: The inner surface of the aluminum-plastic film that will form the first folded edge area 21 in the future (i.e. the side facing the battery cell in the future). The corresponding position on the side of the battery cell.

[0069] S3: First bend: Bend the side seal inward along the first crease line (L1) (towards the battery cell) so that the side seal is roughly parallel to the side of the battery cell, forming a preset gap between them. At this time, the side coated with hot melt adhesive faces the battery cell.

[0070] S4: Second bending and pressing. The far end of the vertical edge formed after the first bending (i.e., the first folded edge area 21) is bent inward again along the second crease line (L2). This second crease line (L2) is designed to be flush with the top surface of the cell. Through this bending, the second folded edge area 22 (the part from the second crease line to the cut end face) is inserted into the "U-shaped" gap formed in step S3, between the first folded edge area 21 and the side of the cell, until its outer edge (i.e., the pre-cut end face) is tightly attached to the bottom end of the U-shaped gap. Then, pressing is performed (conditions: 0.3MPa, 60℃, 5s). Under pressure, the pre-applied hot melt adhesive flows and impregnates, firmly bonding the second folded edge area 22 to the side of the cell, while the outer edge of the second folded edge area 22 is also bonded to the first folded edge area 21 by hot melt adhesive.

[0071] S5: Curing, the hot melt adhesive layer is cooled and cured under pressure (conditions: 0.3MPa, room temperature, 5s).

[0072] The resulting folded structure 2 is stacked in the following order from the inside out: cell side → second folded area 22 (innermost layer) → first folded area 21. The cut end face of the outer edge of the heat-sealed edge is covered inside, closely attached to the bottom end of the U-shaped gap, and not exposed to the external environment.

[0073] This embodiment relies entirely on the mechanical bonding and sealing effect of the hot melt adhesive layer. The cut is hidden, and no waterproof adhesive layer is applied.

[0074] Comparative Example 1, Flattening Process: The side seals are completely straight and flat, with an effective sealing width of 4.0mm.

[0075] Comparative Example 2: Traditional one-step folding process: The side sealing edge is bent only once and stands on the outside of the battery cell without being coated with any hot melt adhesive or waterproof adhesive.

[0076] Comparative Example 3: One-time folding and application of hot melt adhesive only: The side sealing edge is bent once and bonded to the side of the battery cell with hot melt adhesive. The cut end face is not waterproofed.

[0077] Comparative Example 4: One-time folding and application of waterproof adhesive only: The side sealing edge is bent once, without using hot melt adhesive; only waterproof adhesive is applied to the cut end face.

[0078] Multiple performance tests were conducted on the batteries of the above embodiments and comparative examples, and the results are shown in the table below: Failure rate at 85℃ / 85%RH for 500 hours 0% 15% 38% 2% 100% 65% 18% 95% <![CDATA[Helium leak detection rate (×10⁻ 9 Pa·m³ / s)]]> 5.3 12.5 25.0 8.1 150 320 80 280 Thickness expansion rate after 1500 cycles ≤3% ≤4% ≤4% ≤4% N / A >8% ≤5% N / A Volumetric energy density (Wh / L) 382 382 382 378 320 345 375 340 Thickening at the folded edge (mm) 0.10 0.10 0.10 0.08 N / A N / A 0.10 N / A Capacity retention rate after 1000 cycles at 60℃ and 1C 88.5% 83.2% 80.5% 85.1% N / A 75.3% 84.5% N / A 28-day capacity retention rate after full charge storage at 60℃ 95.2% 90.1% 88.3% 92.8% N / A 85.0% 91.5% N / A .

[0079] As can be seen from the above, Example 1 showed the best performance in all tests, verifying that it is the optimal technical approach.

[0080] Comparing Example 1 and Example 2, the waterproof adhesive reduced the rate of damp heat failure from 15% to 0%, demonstrating that its chemical barrier is crucial for improving long-term reliability.

[0081] Comparing Example 1 (folding before cutting, 0% failure) with Example 3 (cutting before folding, 38% failure), the same structure exhibits significant performance differences due to different process sequences, demonstrating that "folding before cutting" is crucial for ensuring cut quality and avoiding micro-damage.

[0082] All comparative examples are far inferior to the embodiments of this utility model, proving that traditional flat, single-edge folding, or single-adhesive sealing solutions cannot solve the sealing problem of ultra-thin batteries.

[0083] In particular, in the high-temperature cycle life test (60°C, 1C 1000 cycles capacity retention), Example 1 exhibits a capacity retention rate of 88.5%, demonstrating optimal long-term cycle life. This is attributed to its excellent airtightness, which effectively mitigates electrolyte consumption and side reactions under high-flux cycling.

[0084] The capacity retention rate of Example 2 was 83.2%, and that of Example 4 was 85.1%, both of which were better than all comparative examples, but lower than that of Example 1, demonstrating that the durability of single protection (hot melt adhesive only or structural protection only) is weaker than that of double protection.

[0085] The capacity retention rate of Example 3 was 80.5%. Due to the micro-damage caused by the pre-cutting and post-folding process, its cycle life was even lower than that of Comparative Example 3 (84.5%), which once again proves the importance of advanced processes.

[0086] In high-temperature storage (28-day capacity retention rate after full charge storage at 60℃), This test assessed the battery's chemical stability and gas production.

[0087] Example 1 leads by a wide margin with a capacity retention rate of 95.2%, indicating that its packaging structure can most effectively maintain the stability of the internal environment of the battery and suppress chemical degradation at high temperatures.

[0088] The capacity retention rate of Example 4 was 92.8%, which was better than the capacity retention rate of 90.1% of Example 2, indicating that even without waterproof adhesive, the physical concealment of the cut in the inward folding structure can effectively slow down storage aging.

[0089] Comparative Example 2 had the lowest capacity retention rate (85.0%) because it was most susceptible to interface degradation and electrolyte oxidation caused by high temperatures.

[0090] The technical solution of this embodiment not only solves the problem of short-term sealing failure, but also significantly improves the long-term service life of the battery under harsh conditions, fully meeting the high reliability requirements of power supply for high-end consumer electronics products.

[0091] In summary, this embodiment is particularly suitable for ultra-thin lithium-ion batteries with a thickness of ≤3mm. In the context of mainstream technologies focusing on improving single performance without recognizing the coupled failure mechanism of mechanical seals and chemical protection in thin-film applications, the technical solution of this embodiment solves the dual sealing failure problem of folded boundary peeling and edge corrosion.

[0092] The embodiments described above do not constitute a limitation on the scope of protection of this technical solution. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the above embodiments should be included within the scope of protection of this technical solution.

Claims

1. A soft-pack lithium-ion battery, comprising: An aluminum-plastic film casing and an internal battery cell, wherein the aluminum-plastic film casing has a sealed cavity, and the battery cell is encapsulated within the cavity; the aluminum-plastic film casing includes a front sealing edge with electrode leads and a side sealing edge without electrode leads, characterized in that... The side sealing edge is bent at least twice to form a layered folded edge structure. Within the folded edge structure, each pair of adjacent folded edge areas, and the innermost folded edge area, are bonded together with the side of the battery cell by a hot melt adhesive layer.

2. The soft-pack lithium-ion battery according to claim 1, characterized in that, The folded edge structure includes a first folded edge area and a second folded edge area that are stacked and attached together. The first folded edge area is a heat-sealed edge strip along the side of the battery cell between a first fold line and a second fold line, wherein the second fold line is parallel to the first fold line. The second folded area is the heat-sealed edge strip between the second fold line and the outer edge of the side seal.

3. The soft-pack lithium-ion battery according to claim 2, characterized in that, The first folded edge area is the innermost layer of the folded edge structure and is in contact with the side of the battery cell. The second folded edge area is bent from the second fold line and attached to the outside of the side of the first folded edge area.

4. The soft-pack lithium-ion battery according to claim 3, characterized in that, The outer edge of the heat-sealed edge, which is attached to the side of the battery cell, and the end face of the hot melt adhesive layer to which they are bonded are cut end faces. A waterproof adhesive layer is fully covered on the cut end face, and the waterproof adhesive layer extends to both sides to form a waterproof adhesive extension edging on the outer surface of the folded structure.

5. The soft-pack lithium-ion battery according to claim 4, characterized in that, The waterproof adhesive layer is a silicone-modified epoxy resin adhesive.

6. The soft-pack lithium-ion battery according to claim 2, characterized in that, The second folded edge area is bent from the second fold line and attached between the first folded edge area and the side of the battery cell, forming the innermost layer of the folded edge structure.

7. The soft-pack lithium-ion battery according to claim 1, characterized in that, The hot melt adhesive layer is a polyolefin-based hot melt adhesive with a melt viscosity of 1500-3000 cps and an interfacial bonding force with the aluminum-plastic film of ≥15N / 15mm.

8. The soft-pack lithium-ion battery according to claim 1, characterized in that, The hot melt adhesive layer penetrates into the micropores on the surface of the aluminum-plastic film it is bonded to, with a penetration depth of 5-10 μm, and forms a physical riveting structure after curing.

9. The soft-pack lithium-ion battery according to claim 1, characterized in that, The thickness of the soft-pack lithium-ion battery is less than or equal to 3 mm.

10. The soft-pack lithium-ion battery according to claim 1, characterized in that, The bottom and top surfaces of the aluminum-plastic film casing are respectively arc surfaces that are in contact with the bottom and top surfaces of the arc-shaped battery cell. The bottom and top of the folded edge structure are parallel to the arc surface, respectively.

11. The soft-pack lithium-ion battery according to claim 10, characterized in that, The crease lines between any two adjacent folded areas within the folded structure are arc lines parallel to the arc surface.

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