Lithium battery diaphragm, preparation method of lithium battery diaphragm, battery cell and preparation method of battery cell
The lithium battery separator, with its multi-layer composite structure and optimized process, solves the problem of separator wrinkling after electrolyte wetting, achieving high-efficiency anti-wrinkle performance and low-cost production, thus improving battery safety and lifespan.
Patent Information
- Application Number
- CN202511199296.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-26
- Publication Date
- 2025-11-28
AI Technical Summary
Existing lithium battery separators are prone to wrinkling after being soaked in electrolyte, leading to performance degradation. Existing solutions are costly or introduce side effects.
The lithium battery separator adopts a multi-layer composite structure, including a base film layer, a discontinuous anti-wrinkle functional layer and an interface reinforcement layer. By designing the anti-wrinkle functional layer and stacking the interface reinforcement layer, a multi-layer composite structure with different moduli is formed. Combined with segmented winding tension control and hot pressing pre-pressing process, wrinkles are avoided in the separator during the cell forming process.
It significantly improves the anti-wrinkle performance of lithium battery separators, reducing the wrinkle rate of separators to below 1% after electrolyte impregnation. The cells show no deformation after 1000 cycles, improving battery safety and cycle life, and reducing production costs.
Smart Images
Figure CN121035531A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of lithium batteries, and particularly relates to a lithium battery separator, a preparation method thereof, a battery cell and a preparation method thereof. BACKGROUND
[0002] The lithium battery separator is a key component affecting the performance and safety of the battery, and needs to have good ion conductivity, mechanical strength and wrinkle resistance after electrolyte immersion. In the prior art, the separator wrinkle problem is mainly caused by the following reasons: Uneven material stress: the traditional PP / PE separator is prone to swelling after electrolyte immersion, resulting in uneven interlayer stress and causing wrinkles; process defects: such as uneven winding tension, improper heat pressing parameters, etc., resulting in deformation of the separator during the formation of the battery cell; single structure: the modulus distribution of the single-layer separator is single, and cannot offset the local stress after electrolyte immersion.
[0003] The existing solutions such as adjusting the electrolyte formula or adding a coating layer have problems such as high cost, complex process or introducing side effects (such as increased self-discharge). SUMMARY
[0004] In view of the above problems, the application provides a lithium battery separator, a preparation method thereof, a battery cell and a preparation method thereof.
[0005] A first object of the application is to provide a lithium battery separator, which comprises a base film layer, a discontinuous anti-wrinkle functional layer coated on the base film layer, and an interface strengthening layer superimposed on the side of the base film layer on which the discontinuous anti-wrinkle functional layer is coated. The anti-wrinkle functional layer is an inorganic particle coating layer, and the total area of the anti-wrinkle functional layer accounts for 25%-70% of the area of the base film layer.
[0006] Further, the thickness of the anti-wrinkle functional layer is 5-15 pm.
[0007] Further, the anti-wrinkle functional layer is composed of inorganic nanoparticles and a binder.
[0008] Further, the particle size of the inorganic nanoparticles is 0.1-1 pm.
[0009] Further, the inorganic nanoparticles are one of alumina nanoparticles and silica nanoparticles.
[0010] Further, the mass ratio of the inorganic nanoparticles to the binder is 7-9:1-3, and preferably, the mass ratio of the inorganic nanoparticles to the binder is 9:1.
[0011] Further, the binder is polyvinylidene fluoride.
[0012] Further, the interface reinforcing layer is made of a film of ultra-high molecular weight polyethylene and mineral oil mixed and bidirectionally stretched.
[0013] Further, the mass ratio of the ultra-high molecular weight polyethylene to the mineral oil is 6-8:2-4, preferably, the mass ratio of the ultra-high molecular weight polyethylene to the mineral oil is 7:3.
[0014] Further, the thickness of the interface reinforcing layer is 20-30 μm, preferably, the thickness of the interface reinforcing layer is 20 μm.
[0015] Further, the bidirectional stretching is performed at a longitudinal stretching ratio of 3 and a transverse stretching ratio of 2.
[0016] Further, the base film layer is a PP film or a PE film, and the thickness of the base film layer is 20-50 μm, preferably, the thickness of the base film layer is 30 μm.
[0017] Further, the anti-wrinkle functional layer is distributed on one side or both sides of the base film layer.
[0018] Further, when the anti-wrinkle functional layer is coated on one side of the base film layer, the interface reinforcing layer is stacked on the side of the base film layer on which the discontinuous anti-wrinkle functional layer is coated.
[0019] Further, when the anti-wrinkle functional layer is coated on both sides of the base film layer, the interface reinforcing layer is stacked on both sides of the base film layer on which the discontinuous anti-wrinkle functional layer is coated.
[0020] The second object of the present application is to provide a preparation method of the lithium battery separator, comprising: After the base film layer coated with the anti-wrinkle functional layer and the interface reinforcing layer are stacked, cold stretching, laminated hot pressing and hot stretching are performed to obtain the anti-wrinkle separator, wherein, during the stacking, the interface reinforcing layer is close to the anti-wrinkle functional layer.
[0021] Further, the cold stretching is performed at a temperature of -10-20 ℃ and a stretching ratio of 1.05-1.2.
[0022] Further, the laminated hot pressing is performed at a temperature of 100-150 ℃ and a pressure of 2-8 MPa.
[0023] Further, in the hot stretching, the stretching ratio is 3-5.
[0024] The third object of the present application is to provide a lithium battery cell comprising the lithium battery separator.
[0025] The fourth object of the present application is to provide a preparation method of the lithium battery cell, comprising: The positive electrode sheet, the negative electrode sheet and the anti-wrinkle diaphragm are wound into a core, and an elastic layer is wrapped outside the core, then the core is subjected to hot-pressing pre-pressing, after the hot-pressing pre-pressing, the elastic layer wrapped outside is removed, and a hot-pressing pre-pressed core is obtained; The hot-pressing pre-pressed core is subjected to liquid injection and formation, and an electric core is obtained.
[0026] Further, the winding into the core is controlled by segmented tension.
[0027] Further, the hot-pressing pre-pressing is performed under the conditions of temperature 100-110 DEG C, pressure 1-3 t and time 50-70 s.
[0028] Further, in the liquid injection and formation process, the liquid injection is performed by restraint force, and the formation is performed in stages; wherein the restraint force is 0.3-0.5 MPa, and the current parameter in the formation in stages is 0.1 C-0.5 C.
[0029] Further, the thickness of the elastic layer is 1-3 mm, and the elastic layer is made of an elastic material known in the art, such as a silica gel pad, and the material of the elastic layer is not limited in the present application.
[0030] The present application has the following advantages: The lithium battery diaphragm, the preparation method thereof, the electric core and the preparation method thereof, the anti-wrinkle diaphragm is combined by the base film layer, the discontinuous anti-wrinkle functional layer coated on the base film layer, and the interface strengthening layer (the interface strengthening layer is stacked on the side of the base film layer on which the discontinuous anti-wrinkle functional layer is coated), a multi-layer composite structure with different modulus is formed, stress dispersion and interface strengthening are realized, and wrinkles caused by stress concentration of a single material are avoided; wherein the anti-wrinkle functional layer is an inorganic particle coating layer, the total area of the anti-wrinkle functional layer accounts for 25%-70% of the area of the base film layer, a local stress buffer zone is formed on the base film layer, the anti-wrinkle performance of the obtained anti-wrinkle diaphragm is further improved, the anti-wrinkle performance of the finally obtained anti-wrinkle diaphragm is that the wrinkle rate of the diaphragm after electrolyte immersion is reduced to below 1%, the electric core does not have "S" type deformation after 1000 cycles, and has no side effects.
[0031] The present application also has the following advantages: The interface strengthening layer adopts a UHMWPE and mineral oil blending system, the uniformity of micropores is improved, and the swelling deformation after electrolyte immersion is reduced; When the anti-wrinkle functional layer is coated, an intermittent spraying method is adopted for coating, the amount of coating material is reduced by 30%-50%, and the comprehensive cost is reduced by 15%; The electric core and the preparation method thereof provided by the application further avoid the wrinkle of the anti-wrinkle diaphragm formed in the winding process on the basis of the anti-wrinkle diaphragm, improve the process stability, and make the wrinkle rate of the final obtained electric core less than 0.5%.
[0032] The anti-wrinkle diaphragm and the preparation method thereof and the electric core and the preparation method thereof provided by the application have high compatibility with the original production line, can be upgraded on the existing production line, and do not need to replace the core equipment. The application integrates the structure optimization and the process innovation, can significantly improve the safety and the cycle life of the lithium battery, and is suitable for large-scale industrial production.
[0033] Other features and advantages of the present application will be set forth in the following description, and in part will become apparent to those skilled in the art from the following description, or can be learned by practice of the present application. The objects and other advantages of the present application can be achieved and obtained by the structure indicated in the specification, claims and drawings. BRIEF DESCRIPTION OF DRAWINGS
[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.
[0035] Figure 1 A structure schematic diagram of a lithium battery diaphragm according to an embodiment of the present application is shown; Figure 2 A structure schematic diagram of a lithium battery diaphragm according to an embodiment of the present application is shown; In the figure: 10, base film layer; 20, anti-wrinkle functional layer; 30, interface strengthening layer. DETAILED DESCRIPTION
[0036] In order to make the objects, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.
[0037] A method for preparing a lithium battery separator according to some embodiments of the present application, comprising a base film layer 10, a discontinuous wrinkle-resistant functional layer 20 coated on the base film layer 10, and an interface strengthening layer 30 superimposed on the side of the base film layer 10 coated with the discontinuous wrinkle-resistant functional layer 20.
[0038] In some embodiments of the present application, the discontinuous wrinkle-resistant functional layer 20 is distributed on one side of the base film layer 10, and the interface strengthening layer 30 is superimposed on the side of the base film layer 10 coated with the discontinuous wrinkle-resistant functional layer 20, as shown in Figure 1
[0039] In some embodiments of the present application, the discontinuous wrinkle-resistant functional layer 20 is distributed on both sides of the base film layer 10, and the interface strengthening layer 30 is superimposed on both sides of the base film layer 10 coated with the discontinuous wrinkle-resistant functional layer 20, as shown in Figure 2
[0040] A method for preparing a lithium battery separator according to some embodiments of the present application, comprising: After the base film layer coated with the wrinkle-resistant functional layer and the interface strengthening layer are laminated, cold stretching, laminated hot pressing, and hot stretching are performed to obtain a wrinkle-resistant separator, wherein during lamination, the interface strengthening layer is close to the wrinkle-resistant functional layer.
[0041] In some embodiments of the present application, the cold stretching is performed at a temperature of -10-20°C and a stretching ratio of 1.05-1.2.
[0042] In some embodiments of the present application, the laminated hot pressing is performed at a temperature of 100-150°C and a pressure of 2-8 MPa.
[0043] In some embodiments of the present application, the hot stretching is performed at a stretching ratio of 3-5.
[0044] Example 1 Preparation of the separator: Preparation of the base film: PP resin with a melt index of 1.2 g / 10 min is melt-extruded, cast, and cooled to crystallize, to obtain a base film with a thickness of 30 μm; Coating of the wrinkle-resistant functional layer: alumina particles (particle size 0.5 μm) are mixed with PVDF binder (mass ratio 9:1), and then mixed with solvent (NMP) to form a coating solution, which is coated on one side of the base film by intermittent spraying, with a coating area ratio of 50%; Preparation of the interface strengthening layer: UHMWPE is blended with mineral oil (mass ratio 7:3) and extruded to form a microporous film with a thickness of 20 μm by bidirectional stretching (3 times in the longitudinal direction and 2 times in the transverse direction); Composite lamination: the base film and the interface strengthening film are laminated, the film is stretched under the condition of temperature -10-20℃ and stretching ratio 1.05-1.2, the cold stretching mainly utilizes the elastic deformation characteristics of the material at low temperature to form the initial morphology of the microporous structure. After cold stretching, hot pressing (temperature 130℃, pressure 5MPa) is carried out for 40s, and then hot stretching is carried out to form the final microporous structure (the stretching ratio is 3 times), to obtain the separator with total thickness 55μm.
[0045] Example 2 Preparation of the separator: Preparation of the base film: PE resin with melt index 1.2g / 10min is melt extruded, and then casted and cooled to crystallize, to obtain the base film with thickness 25μm; Coating of the anti-wrinkle functional layer: alumina particles (particle size 0.3μm) are mixed with PVDF binder (mass ratio 8:1), and then mixed with solvent (NMP) to form the coating solution, which is coated on one side of the base film by intermittent spraying, and the coating area accounts for 25%; Preparation of the interface strengthening layer: UHMWPE is blended with mineral oil (mass ratio 8:2) and extruded, and then bidirectional stretched (3 times in longitudinal direction and 2 times in transverse direction) to form the microporous film with thickness 30μm; Composite lamination: the base film and the interface strengthening film are laminated, the film is stretched under the condition of temperature -10-20℃ and stretching ratio 1.05-1.2, the cold stretching mainly utilizes the elastic deformation characteristics of the material at low temperature to form the initial morphology of the microporous structure. After cold stretching, hot pressing (temperature 130℃, pressure 5MPa) is carried out for 40s, and then hot stretching is carried out to form the final microporous structure (the stretching ratio is 3 times), to obtain the separator with total thickness 55μm.
[0046] Example 3 Preparation of the separator: Preparation of the base film: PP resin with melt index 1.2g / 10min is melt extruded, and then casted and cooled to crystallize, to obtain the base film with thickness 45μm; Coating of the anti-wrinkle functional layer: alumina particles (particle size 0.5μm) are mixed with PVDF binder (mass ratio 9:1), and then mixed with solvent (NMP) to form the coating solution, which is coated on one side of the base film by intermittent spraying, and the coating area accounts for 50%; Preparation of the interface strengthening layer: UHMWPE is blended with mineral oil (mass ratio 7:3) and extruded, and then bidirectional stretched (3 times in longitudinal direction and 2 times in transverse direction) to form the microporous film with thickness 20μm; Composite lamination: cold stretching: laminating the base film with the interface strengthening film, stretching the film under the condition of temperature -10-20℃, stretching ratio 1.05-1.2, the cold stretching is mainly to use the elastic deformation characteristics of the material at low temperature to form the initial form of the microporous structure. After cold pressure stretching, heat pressure (temperature 150℃, pressure 2MPa) for 40s, then heat stretching setting (stretching ratio 5 times), the total thickness of the separator is 70μm.
[0047] Comparative Example 1 Preparation of the separator: compared with Example 1, the functional layer was deleted, and the rest was the same.
[0048] Comparative Example 2 Preparation of the separator: compared with Example 1, the interface strengthening layer was deleted, and the rest was the same.
[0049] Comparative Example 3 provided the separator of the base film in Example 1.
[0050] Example 4 Preparation of the battery cell: Winding: the positive sheet, the negative sheet and the separator obtained in Example 1 were wound into a core according to the segmented tension control; Specific segmented control process: positive sheet winding tension: 750g for the first circle, and then decreased by 4g for each circle, and finally adjusted on site according to the effect; Negative sheet winding tension: 700g for the first circle, and then decreased by 4g for each circle, and finally adjusted on site according to the effect; Separator tension: 150g, constant tension, and finally adjusted on site according to the effect.
[0051] Pre-pressing: wrapping 1mm silicone elastic layer outside the core, heat pressing (temperature 100℃, pressure 2t, time 60s); Liquid injection and formation: using restrained force injection (fixture pressure 0.3MPa) and staged formation (0.1C-0.5C), and the final battery cell has a wrinkle rate of <0.5%.
[0052] Performance test: The separators obtained in Example 1-Example 3 and Comparative Example 1-3 were subjected to electrolyte immersion experiment (immersion conditions: temperature 45℃, immersion time 48h), and the experimental results are shown in Table 1.
[0053] Table 1
[0054] As can be seen from Table 1, the separators obtained in Example 1-3 have better anti-wrinkle performance, and the wrinkle rate of the separator after electrolyte immersion is reduced to below 1%, and the core is deformed.
[0055] Although the present application has been described in detail with reference to the foregoing embodiments, it should be understood that modifications can be made to the foregoing embodiments, or additional implementations of the present application can be implemented, without departing from the spirit or scope of the application. Accordingly, the present application is not limited except as by the appended claims.
Claims
1. A lithium battery separator, characterized in that, It includes a base film layer, a discontinuous anti-wrinkle functional layer coated on the base film layer, and an interface reinforcement layer, wherein the interface reinforcement layer is superimposed on the side of the base film layer coated with the discontinuous anti-wrinkle functional layer. The anti-wrinkle functional layer is an inorganic particle coating, and the total area of the anti-wrinkle functional layer accounts for 25%-70% of the area of the base film layer.
2. The lithium battery separator according to claim 1, characterized in that, The thickness of the anti-wrinkle functional layer is 5-15 μm.
3. A lithium battery separator according to claim 1, characterized in that, The anti-wrinkle functional layer is composed of inorganic nanoparticles and a binder.
4. A lithium battery separator according to claim 1, characterized in that, The interface reinforcement layer is composed of ultra-high molecular weight polyethylene and mineral oil.
5. A lithium battery separator according to claim 1, characterized in that, The base film layer is a PP film or a PE film, and the thickness of the base film layer is 20-50 μm.
6. A lithium battery separator according to any one of claims 1-5, characterized in that, The anti-wrinkle functional layer is distributed on one or both sides of the base film layer; The interface reinforcement layer is superimposed on one side of the base film layer where a discontinuous anti-wrinkle functional layer is coated, or the interface reinforcement layer is superimposed on both sides of the base film layer where a discontinuous anti-wrinkle functional layer is coated.
7. A method for preparing a lithium battery separator according to any one of claims 1-6, characterized in that, include: After laminating a base film layer coated with an anti-wrinkle functional layer and an interface reinforcement layer, cold stretching, hot pressing, and hot stretching and shaping are performed to obtain an anti-wrinkle diaphragm. During lamination, the interface reinforcement layer is close to the anti-wrinkle functional layer.
8. The method for preparing a lithium battery separator according to claim 7, characterized in that, The conditions for cold stretching are: temperature -10 to 20°C, stretching ratio 1.05 to 1.2; The conditions for the lamination hot pressing are: temperature 100-150℃, pressure 2-8MPa.
9. A lithium battery cell, characterized in that, Includes a lithium battery separator as described in any one of claims 1-6.
10. A method for preparing a lithium battery cell, characterized in that, The battery cell includes a lithium battery separator as described in any one of claims 1-6, comprising: The positive electrode sheet, negative electrode sheet and anti-wrinkle separator are wound into a core, and an elastic layer is wrapped around the outer layer of the core. The core is then hot-pressed and pre-pressed. After hot-pressing and pre-pressing, the outer elastic layer is removed to obtain the core after hot-pressing and pre-pressing. The hot-pressed core is injected with liquid and formed to obtain the battery cell.
11. The method for preparing a lithium battery cell according to claim 10, characterized in that, When winding the core, segmented tension control is used; The conditions for hot pressing pre-compression are: temperature 100-110℃, pressure 1-3t, time 50-70s; During the injection and formation process, a restraining force injection and a staged formation are adopted, wherein the restraining force is 0.3-0.5MPa and the current parameter in the staged formation is 0.1C-0.5C.