Composite diaphragm for battery cell, cell structure and lithium ion battery
By adopting a composite separator design in lithium-ion batteries, high heat-resistant materials cover the negative electrode sheet area and heat-shrinkage material cover the empty foil area, forming an asymmetric structure, solving the thermal runaway problem caused by short circuit in the needle puncture test, and improving the battery safety and needle puncture pass rate.
Patent Information
- Application Number
- CN202510395363.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-31
- Publication Date
- 2025-08-12
AI Technical Summary
In the needle puncture test, existing lithium-ion batteries are prone to severe short circuits due to foreign matter puncture, causing heat out of control, and thus causing fire or explosion. The existing technology is difficult to effectively improve the needle puncture pass rate and reduce the risk of fire and explosion.
The composite separator design is adopted, including the first area covering the negative electrode sheet area with high heat resistance materials such as polyimide or polyether etherketone, and the second area covering the empty foil area of the negative electrode sheet using heat shrinkable materials such as acrylonitrile-butadiene-styrene copolymer, polyethylene, polyvinyl chloride or polytetrafluoroethylene to form an asymmetric structure, guiding the short-circuit point to concentrate in the empty foil area with lower resistance, sharing heat and current.
The probability of short circuit in the pole sheet material area is significantly reduced. By concentrating the short circuit point to the empty foil area, the heat release of the battery is reduced, the needle puncture pass rate is improved, the risk of battery fire and explosion is reduced, and the safety is improved.
Smart Images
Figure CN120473579A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of lithium ion batteries, in particular to a composite diaphragm for a battery cell, a cell structure and a lithium ion battery. Background Art
[0002] Lithium-ion batteries have been widely used in civil and power applications. Existing lithium-ion batteries have complex internal structures, including tightly wound or stacked layers of materials, such as the positive electrode, negative electrode, and separator. When a lithium-ion battery is punctured by a foreign object, the foreign object can penetrate the electrode and separator, causing contact between the positive and negative electrodes and a short circuit. Common safety tests for lithium-ion batteries include overcharging, over-discharging, extrusion, and needle penetration. The main purpose of the needle penetration test is to observe the safety of lithium-ion batteries under simulated internal short-circuit conditions. When the foreign object piercing the battery is a steel needle used in the needle penetration test, the metal needle can cause the internal short circuit to be more severe. Once an internal short circuit occurs in a battery, the entire battery discharges through the short-circuit point and releases energy. The rapid release of large amounts of heat can easily lead to thermal runaway. Due to the high exothermicity of the chemical reactions within the battery, once thermal runaway is triggered, the temperature rises rapidly, which can cause the battery to catch fire or explode, resulting in serious safety accidents. Therefore, a solution is urgently needed to improve the needle penetration pass rate of lithium-ion batteries and reduce the risk of fire and explosion in lithium-ion batteries to address the above problems. Summary of the Invention
[0003] In view of the above problems existing in the prior art, the object of the present invention is to provide a composite diaphragm for a battery cell, a cell structure and a lithium ion battery.
[0004] To achieve the above object, the present invention adopts the following technical solutions:
[0005] The present invention provides a battery core structure, comprising a positive electrode sheet, a negative electrode sheet and a composite separator; the head and tail of the positive electrode sheet and the negative electrode sheet are both provided with a hollow foil area;
[0006] The composite diaphragm includes a first region and two second regions respectively connected to the head and tail of the first region; the first region completely covers the material area of the negative electrode sheet, and the two second regions respectively cover the two empty foil areas at the head and tail of the negative electrode sheet;
[0007] The material used in the first region includes at least one of polyimide and polyetheretherketone;
[0008] The material used for the second region includes at least one of acrylonitrile-butadiene-styrene copolymer, polyethylene, polyvinyl chloride, and polytetrafluoroethylene.
[0009] In some embodiments, the second region includes a head region and a tail region; the head region is arranged corresponding to the head empty foil region of the negative electrode plate, and the tail region is arranged corresponding to the tail empty foil region of the negative electrode plate; the length of the head region is smaller than the length of the tail region.
[0010] In some embodiments, the composite separator includes a first separator and a second separator, wherein the first separator, the negative electrode sheet, the second separator, and the positive electrode sheet are sequentially arranged from the inside to the outside and wound into a core;
[0011] The winding core includes a first protection section, a functional section, and a second protection section arranged in sequence from the inside to the outside;
[0012] The first protection section includes, arranged from inside to outside, the head area of the first diaphragm, the empty foil area of the negative electrode plate, the head area of the second diaphragm, and the empty foil area of the positive electrode plate;
[0013] The functional section includes the first region of the first diaphragm, the material region of the negative electrode sheet, the first region of the second diaphragm, and the material region of the positive electrode sheet, which are sequentially arranged from the inside to the outside;
[0014] The second protection section includes the tail area of the first diaphragm, the empty foil area of the negative electrode plate, the tail area of the second diaphragm and the empty foil area of the positive electrode plate, which are arranged in sequence from the inside to the outside.
[0015] In some embodiments, the length of the first protection segment is at least enough to wrap around the innermost layer of the winding core.
[0016] In some embodiments, the length of the second protection segment is at least enough to wrap around the outermost layer of the winding core.
[0017] The present invention also provides a composite diaphragm for a battery cell, comprising: a first region;
[0018] Two second regions, respectively connected to the head and tail of the first region;
[0019] The material used in the first region is at least one of polyimide and polyetheretherketone;
[0020] The material used for the second region is at least one of acrylonitrile-butadiene-styrene copolymer, polyethylene, polyvinyl chloride, and polytetrafluoroethylene.
[0021] In some embodiments, the length of the second region is smaller than the length of the first region.
[0022] In some embodiments, the second region includes a head region and a tail region; the length of the head region is smaller than the length of the tail region.
[0023] In some embodiments, the head region and the tail region are made of at least partially the same material.
[0024] The present invention further provides a lithium-ion battery comprising the above-mentioned battery core structure or the above-mentioned composite diaphragm.
[0025] Compared with the prior art, the present invention has the following beneficial effects:
[0026] The composite diaphragm in the present invention adopts a material with thermal ductility or a material that does not rebound after being stretched under force in the first area of the middle section, and adopts a material with thermal shrinkage or a material that rebounds after being stretched under force in the second area of the head and tail sections. No matter which part of the electrode is punctured, the probability of short circuit in the electrode material area can be reduced, so that the short circuit occurs more in the empty foil area at the head and tail of the positive and negative electrode sheets. Since the resistance of the collector is smaller than the resistance of the material area, the empty foil area will share most of the current and reduce the heat of the electrode material area. The present invention does not need to add additional additives or apply a protective layer, so that the short circuit occurs more in the empty foil area of the collector, reduces the reaction heat of the electrode material area, reduces the risk of battery fire and explosion, and improves the needle puncture pass rate of the battery. BRIEF DESCRIPTION OF THE DRAWINGS
[0027] Figure 1 is a cross-sectional schematic diagram of the battery cell structure of the present invention in an expanded state;
[0028] Figure 2 is a schematic cross-sectional view of the battery cell structure of the present invention in a needle-punctured state;
[0029] Figure 3 It is a schematic longitudinal cross-sectional view of the battery cell structure of the present invention;
[0030] Figure 4 1 is a schematic diagram of the temperature monitoring results of the acupuncture test in Example 1 of the present invention;
[0031] Figure 5 Schematic diagram of temperature monitoring results of acupuncture test in Example 2 of the present invention. DETAILED DESCRIPTION
[0032] To make the technical solutions and advantages of the present invention more clear, the present invention and its beneficial effects will be further described in detail below in conjunction with specific implementation methods, but the implementation methods of the present invention are not limited thereto.
[0033] See also Figure 1 , Figure 1 2 is a cross-sectional schematic diagram of the battery cell structure of the present invention in an unfolded state, wherein the battery cell structure includes a positive electrode sheet, a negative electrode sheet and a composite separator; the head and tail of the positive electrode sheet and the negative electrode sheet are both provided with a hollow foil area;
[0034] The composite diaphragm includes a first region and two second regions connected to the head and tail of the first region respectively; the first region completely covers the material area of the negative electrode sheet, and the two second regions respectively cover the two empty foil areas at the head and tail of the negative electrode sheet;
[0035] The materials used in the first area include at least one of polyimide and polyetheretherketone; the first area uses engineering plastic materials with excellent heat resistance and high mechanical strength, which can maintain a stable structure under extreme working conditions and is not easy to deform, thereby ensuring the thermal stability and insulation effect of the material area during winding and use.
[0036] The second region is made of at least one of acrylonitrile-butadiene-styrene copolymer, polyethylene, polyvinyl chloride, and polytetrafluoroethylene. The flexible heat-shrinkable material in this region not only absorbs stress but also shrinks appropriately when heated, helping to shift the short-circuit point toward the bare foil area. This creates a thermal channel, distributing heat and current while maintaining core tightness, further suppressing the triggering of thermal runaway.
[0037] Unlike the prior art that only uses a single diaphragm material, the present invention introduces a partitioned covering structure of the empty foil area and the composite diaphragm in the structural design. This structure ensures that when the battery cell is mechanically damaged (such as needle puncture), the short-circuit point is preferentially concentrated in the empty foil area with lower resistance, significantly reducing the reaction heat in the material area and improving battery safety.
[0038] Specifically, the second region includes a head region and a tail region; the head region corresponds to the head hollow foil area of the negative electrode, and the tail region corresponds to the tail hollow foil area of the negative electrode; the length of the head region is shorter than that of the tail region. The second region, formed by the head and tail regions, has a different design length, with the tail region being longer than the head region. This design allows the tail protection section to provide greater buffer space and heat transfer capabilities, given that the innermost and outermost layers of the core structure are susceptible to stress concentration and ambient heat. This asymmetric structure further enhances the overall heat release directionality of the battery cell, facilitating a safe and controllable energy release process.
[0039] Specifically, the composite diaphragm includes a first diaphragm and a second diaphragm, wherein the first diaphragm, the negative electrode sheet, the second diaphragm and the positive electrode sheet are arranged in sequence from the inside to the outside and wound into a core;
[0040] The winding core includes a first protection section, a functional section, and a second protection section arranged in sequence from the inside to the outside;
[0041] The first protection section includes, from the inside to the outside, the head area of the first diaphragm, the empty foil area of the negative electrode sheet, the head area of the second diaphragm, and the empty foil area of the positive electrode sheet;
[0042] The functional section includes the first region of the first diaphragm, the material region of the negative electrode sheet, the first region of the second diaphragm, and the material region of the positive electrode sheet, which are arranged in sequence from the inside to the outside;
[0043] The second protection section includes the tail area of the first diaphragm, the empty foil area of the negative electrode sheet, the tail area of the second diaphragm and the empty foil area of the positive electrode sheet, which are arranged in sequence from the inside to the outside.
[0044] The composite diaphragm in the present invention is arranged in sequence from the inside to the outside with a first diaphragm, a negative electrode sheet, a second diaphragm and a positive electrode sheet, and is wound to form a three-section structure (a first protection section, a functional section and a second protection section). This structure clarifies the spatial boundary between the functional area and the protection area, distinguishes and guides stress and heat, effectively prevents heat diffusion caused by randomization of short-circuit points, and improves the pass rate of the puncture test.
[0045] According to the actual winding process, the first and second protection sections of the present invention are designed to cover the innermost circle and the outermost circle respectively, which not only enhances the initial structural stability of the battery cell, but also provides better basic insulation and protection conditions for subsequent packaging, liquid injection and other processes, and effectively prevents the stress accumulation points in the starting / ending sections from becoming potential sources of thermal runaway.
[0046] Example 1
[0047] This embodiment 1 provides a cylindrical battery comprising a cell structure and a composite separator. During the coating stage, bare foil areas are reserved at the head and tail of the positive and negative electrode sheets. During the winding process, the bare foil areas at the head and tail of the positive and negative electrode sheets are each reserved for a length of no less than 20 mm and no less than 100 mm, respectively, to ensure that the bare foil areas have sufficient current release capability in the event of a short circuit.
[0048] The composite diaphragm consists of a first region and two second regions connected to the head and tail of the first region, respectively. The material used in the first region is polyimide (PI), and the material used in the second region is polytetrafluoroethylene (PTFE). The total length of the composite diaphragm meets normal production requirements. PI has high thermal stability and good mechanical strength. When used as a diaphragm material, it has excellent heat resistance and deformation retention, making it suitable for thermal insulation protection of the battery core material area. PTFE has good elasticity and certain thermal shrinkage, which helps to guide short-circuit current to concentrate in the bare foil area and achieve rapid heat dissipation. The total length of the composite diaphragm is customized according to the selected pole piece length to ensure complete coverage during the winding process. Specifically, the length of the first region formed by PI material should not be less than the length of the pole piece material area to ensure that it provides sufficient insulation and structural support in the functional section. The second region formed by PTFE material is located at the head and tail ends of the composite diaphragm, and the length matches the bare foil area, ensuring precise overlap with the bare foil area of the pole piece when the battery cell is wound, thereby forming the first and second protection sections respectively.
[0049] The core after winding is as follows Figure 2 As shown, the longitudinal section diagram of the core is shown in Figure 3 As shown in the figure, the innermost layer is the first protective section, the middle is the functional section, and the outermost layer is the second protective section. This structural design not only enhances the battery cell's overall puncture resistance but also, through the gradient coordination of material properties, achieves targeted heat transfer and dissipation, significantly improving safety while maintaining battery performance.
[0050] Example 2
[0051] Example 2 provides a cylindrical battery, including a battery cell structure and a composite diaphragm. The only difference between Example 2 and Example 1 is that the material used in the first area is polyetheretherketone (PEEK), and the material used in the second area is polyvinyl chloride (PVC). Compared with PI, PEEK material has higher mechanical strength and chemical corrosion resistance, and is suitable for application scenarios requiring stronger structural support and environmental stability. In particular, it can still maintain a good physical form under high-rate charge and discharge or complex stress environments to prevent diaphragm deformation from causing local heat accumulation. PVC has certain heat shrinkage properties and flexible wrapping capabilities, which can effectively guide the short-circuit area to transfer to the empty foil area under extreme impacts such as acupuncture, and form a local closed area during the recovery stage to limit heat diffusion.
[0052] Comparative Example 1
[0053] Specifically, Comparative Example 1 provides a cylindrical battery. In this battery structure, the positive and negative electrodes do not have empty foil areas at the beginning and end. The electrode material always passes through the inner and outermost layers of the battery cell during the winding process. At the same time, the separator used is a single polyolefin material without a partitioning design.
[0054] Test Case
[0055] The cylindrical batteries obtained in Example 1, Example 12 and Comparative Example 1 were subjected to needle penetration tests. The test results of Example 1, Example 2 and Comparative Example 1 are shown in Table 1. Figure 4 and Figure 5 . The test results show that the maximum temperature reached by the battery in Example 1 after acupuncture is slightly lower than that of the battery in Comparative Example 1, and because the short-circuit points are mainly concentrated in the empty foil area, under the synergy of the thermal conductivity of the steel shell and the external convection heat dissipation, the overall heat dissipation efficiency is higher, the temperature drops faster, and the accumulation of heat in the electrode material area is effectively suppressed. Although the maximum temperature of the battery in Example 2 after acupuncture is slightly higher than the maximum temperature of the battery in Comparative Example 1 after acupuncture, its temperature rise rate is relatively slow, and the duration of the temperature peak is significantly shortened. This shows that although the heat generated in a short period of time is slightly high, because the composite diaphragm structure effectively guides the short-circuit area to the empty foil area, the heat is quickly dispersed through the metal current collector, and the overall thermal runaway risk is significantly reduced. In contrast, the traditional diaphragm used in Comparative Example 1 cannot effectively limit the short-circuit area during the acupuncture process. The short-circuit points are randomly distributed and concentrated in large quantities inside the active material area, resulting in rapid accumulation of local heat and triggering thermal runaway. At the same time, the single material diaphragm is unable to guide the stress release path after being subjected to force, and it is difficult to disperse heat through structural deformation. Not only does the temperature rise rapidly and last for a long time, there is a major safety hazard.
[0056] In addition, in the tests of Examples 1 and 2, the battery cell structure remained intact, with no signs of bulging, rupture, or fire. However, the sample in Comparative Example 1 showed obvious expansion and even deformation in multiple tests. This is because the internal thermal resistance of the battery cell is uneven under this structure, and uncontrollable thermal expansion is very likely to occur under high-rate operation or physical impact conditions, which forms a significant safety difference with the solution of the present invention, further verifying the significant advantages of the design of the present invention in improving battery safety.
[0057] The above are only some or preferred embodiments of the present invention. Neither the text nor the drawings can limit the scope of protection of the present invention. All equivalent structural transformations made by using the contents of the present invention description and drawings under the overall concept of the present invention, or direct / indirect application in other related technical fields are included in the scope of protection of the present invention.
Claims
1. A battery cell structure, characterized in that: It includes a positive electrode sheet, a negative electrode sheet and a composite separator; the head and tail of the positive electrode sheet and the negative electrode sheet are both provided with an empty foil area; The composite diaphragm includes a first region and two second regions respectively connected to the head and tail of the first region; the first region completely covers the material area of the negative electrode sheet, and the two second regions respectively cover the two empty foil areas at the head and tail of the negative electrode sheet; The material used in the first region includes at least one of polyimide and polyetheretherketone; The material used for the second region includes at least one of acrylonitrile-butadiene-styrene copolymer, polyethylene, polyvinyl chloride, and polytetrafluoroethylene.
2. The battery cell structure according to claim 1, characterized in that: The second region includes a head region and a tail region; the head region is arranged corresponding to the head empty foil region of the negative electrode plate, and the tail region is arranged corresponding to the tail empty foil region of the negative electrode plate; the length of the head region is smaller than the length of the tail region.
3. The battery core structure according to claim 2, characterized in that: The composite diaphragm includes a first diaphragm and a second diaphragm, wherein the first diaphragm, the negative electrode sheet, the second diaphragm and the positive electrode sheet are sequentially arranged from the inside to the outside and wound into a winding core; The winding core includes a first protection section, a functional section, and a second protection section arranged in sequence from the inside to the outside; The first protection section includes, arranged from inside to outside, the head area of the first diaphragm, the empty foil area of the negative electrode plate, the head area of the second diaphragm, and the empty foil area of the positive electrode plate; The functional section includes the first region of the first diaphragm, the material region of the negative electrode sheet, the first region of the second diaphragm, and the material region of the positive electrode sheet, which are sequentially arranged from the inside to the outside; The second protection section includes the tail area of the first diaphragm, the empty foil area of the negative electrode plate, the tail area of the second diaphragm and the empty foil area of the positive electrode plate, which are arranged in sequence from the inside to the outside.
4. The battery core structure according to claim 3, characterized in that: The length of the first protection section is at least sufficient to surround the innermost layer of the winding core.
5. The battery core structure according to claim 3 or 4, characterized in that: The length of the second protection section is at least sufficient to surround the outermost layer of the winding core.
6. A composite diaphragm for a battery cell, characterized in that: include: First Area; two second areas; connected to the head and tail of the first region respectively; The material used in the first region is at least one of polyimide and polyetheretherketone; The material used for the second region is at least one of acrylonitrile-butadiene-styrene copolymer, polyethylene, polyvinyl chloride, and polytetrafluoroethylene.
7. The composite diaphragm for battery cells according to claim 6, characterized in that: The length of the second region is smaller than the length of the first region.
8. The composite diaphragm for battery cells according to claim 7, characterized in that: The second region includes a head region and a tail region; the length of the head region is smaller than the length of the tail region.
9. The composite diaphragm for battery cells according to claim 8, characterized in that: The head region and the tail region are made of at least partially the same material.
10. A lithium ion battery, characterized in that: A composite separator for a battery cell comprising the battery cell structure according to any one of claims 1 to 5 or any one of claims 6 to 9.