A diaphragm, an electric core and an electric device using the same

Abstract

This invention provides a separator and a base membrane, the base membrane comprising a central region and a peripheral region adjacent to the central region, the peripheral region comprising a first region located above the central region and a second region located below the central region; a first coating coated on the central region of the base membrane; and a second coating coated on the first and second regions of the base membrane; the first coating comprising first ceramic particles, a first binder, and a wetting agent; the second coating comprising a fast ion conductor material, second ceramic particles, and a second binder; wherein the ceramic particles in the first coating constitute 80%~95% by mass in the second coating, the fast ion conductor material in the second coating constitutes 10%~30% by mass, and the thickness T2 of the second coating is greater than the thickness T1 of the first coating. The separator of this invention can significantly improve interfacial contact performance, reduce interfacial impedance, and avoid puncture damage to the separator from the electrode edges; it also solves the problem of insufficient electrolyte wetting in the central region.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and in particular to a separator, a battery cell, and an electrical device thereof. Background Technology

[0002] The separator is a key component of lithium-ion batteries, and its performance directly affects the cell's safety, cycle life, and power output. The separator is an electronically insulating, ion-permeable material with a certain porosity, providing channels for ions to shuttle after absorbing electrolyte in the battery. The separator's electrolyte absorption rate (absorption rate) and its electrolyte retention capacity (retention rate) directly influence the cell's cycle life and rate performance. Generally, for separators of the same material, a thicker separator results in a better retention rate, better cycle life, and better safety; conversely, a thinner separator results in a lower retention rate, better rate performance, but lower safety. Separator thickness and retention rate / safety performance present a contradiction. To address this contradiction, existing separators, while being thinner, incorporate a ceramic coating. The good wettability of ceramic particles improves both absorption and retention rates, while simultaneously enhancing safety.

[0003] Patent 202511352987.8 provides a battery separator, including a base film and a coating loaded on at least one side of the base film. The coating includes a first ceramic and a second ceramic, with the first ceramic filling the coating and the second ceramic including first particles filled in the coating and second particles embedded in the coating, wherein the ratio of the number of second particles to the number of first particles is 1.2 to 4.0. This coated separator allows for larger pores between the separator and the electrode sheet after winding, improving the electrolyte injection efficiency, providing space to release electrode sheet stress, and reducing lithium plating, thus significantly improving the cycle performance and capacity retention of the secondary battery. However, this separator still has shortcomings. The large pores initially between the separator and the electrode sheet increase the ion transport distance, affecting rate performance; furthermore, the pores occupy a certain proportion of the volume, affecting the battery energy density; and this separator is only suitable for cylindrical batteries.

[0004] Patent 202511754534.8 discloses a gradient-structured separator and its preparation method. The gradient-structured separator includes a separator base film and a coating layer. The coating layer comprises ceramic coatings with different particle sizes. Ceramic particles A with a particle size D50 ≤ 100 nm and ceramic particles B with a particle size 200-400 nm are used to coat both sides of the separator base film. This application designs a gradient-structured separator with low porosity near the positive electrode and high porosity near the negative electrode, which facilitates the formation of a smoother lithium-ion transport channel on the negative electrode side of the separator to meet higher lithium-ion flux requirements.

[0005] However, in practice, especially with wound cells, the uneven stress on the large surface of the core, with even greater stress at the center, makes it more difficult for the separator between the cell electrodes to absorb and retain liquid. In addition, the top and bottom of the core may have poor adhesion between the electrodes and separator due to overhang and insufficient hot pressing, which leads to rapid lithium deposition and degradation in these areas. This type of separator still cannot improve the lithium deposition problem. Summary of the Invention

[0006] This invention addresses the problems of existing technologies, such as difficulty in wetting the central separator of a large area of ​​the battery cell, low liquid retention rate, and poor kinetics leading to lithium deposition in the top and bottom regions of the battery cell due to loose adhesion between the separator and electrode. One aspect of this invention provides a separator, comprising: a base film including a central region and a peripheral region adjacent to the central region, the peripheral region including a first region above the central region and a second region below the central region; a first coating applied to the central region of the base film; and a second coating applied to the first and second regions of the base film; the first coating comprising first ceramic particles, a first binder, and a wetting agent; the second coating comprising a fast ion conductor material, second ceramic particles, and a second binder; wherein the mass fraction of the ceramic particles in the first coating in the second coating is 80%~95%, the mass fraction of the fast ion conductor material in the second coating is 10%~30%, and the thickness T2 of the second coating is greater than the thickness T1 of the first coating.

[0007] Furthermore, the first ceramic particle is one or more of zirconium oxide, aluminum oxide, and titanium oxide.

[0008] Furthermore, the first adhesive is a compound adhesive of styrene-butadiene rubber and polyacrylic acid, wherein the mass ratio of styrene-butadiene rubber to polyacrylic acid is 1:0.5~1.2.

[0009] Furthermore, the thickness T1 of the first coating is 0.5~3μm.

[0010] Furthermore, the fast ion conductor material is one or more of LATP, LZTP, and MXNE materials.

[0011] Furthermore, the thickness T2 of the second coating is 2.5~8μm.

[0012] Furthermore, the porosity of the second coating is 45% to 60%.

[0013] Furthermore, the width of the second coating is 8-15 mm.

[0014] In another aspect, the present invention provides a battery cell having the above-described separator.

[0015] A third aspect of the present invention provides an electrical device having the aforementioned diaphragm. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only one embodiment of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort. Figure 1 This is a schematic diagram of the structure of a single diaphragm of the present invention; Figure 2 This is a schematic diagram of the structure of the diaphragm assembly according to the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] like Figure 1 and 2As shown, the separator of the present invention comprises a base film and a coating coated on the base film, the coating being coated on at least one side of the separator. The separator and the positive electrode sheet and the negative electrode sheet are wound or stacked to form a core. The coating on any side of the separator is further divided into a first coating 10 and a second coating 20, which are coated on different regions of the base film respectively; the first coating 10 is coated on the central region of the separator; the second coating 20 is coated on the peripheral region of the separator away from the central region. Specifically, the base film includes a central region and a peripheral region adjacent to the central region, the peripheral region including a first region located above the central region and a second region located below the central region; the first coating 10 is coated on the central region of the base film; the second coating 20 is coated on the first region and the second region of the base film. The base membrane is a porous membrane, made from one or more composites of nanocellulose, aramid, polyethylene (PE), and polypropylene (PP). Its thickness is 3–20 μm, porosity is 35%–55%, pore size is 0.01–1 μm, longitudinal tensile strength is ≥150 MPa, transverse tensile strength is ≥120 MPa, and thermal shrinkage rate at 130℃ is ≤3% (1 h). It possesses excellent mechanical properties and thermal stability, effectively preventing short circuits caused by separator damage or thermal shrinkage during battery assembly and charging / discharging. The porous structure of the base membrane provides a basic channel for lithium-ion transport, and its pore size and porosity design synergize with the ion conductivity of subsequent coatings to ensure overall ion transport efficiency. The first coating 10 mainly consists of ceramic particles, a binder, and a wetting agent. The ceramic particles can be one or more of zirconium oxide, alumina, and titanium oxide, with a particle size of 0.05~1μm. The mass fraction of ceramic particles in the first coating 10 is 80%~95%, preferably 85%~90%, to ensure that the coating has sufficient heat resistance and mechanical strength. The binder is selected from one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polyacrylate, and polyvinylidene fluoride (PVDF), preferably a compound binder of SBR and polyacrylic acid (mass ratio 1:0.5~1.2), with a mass fraction of 5%~20%, preferably 10%~15%. The function of the binder is to firmly bond the ceramic particles to the surface of the base film, while also possessing a certain degree of flexibility to prevent the coating from falling off or cracking during winding or stacking. The compound binder can balance adhesion and electrolyte compatibility. The thickness T1 of the first coating 10 is 0.5~3μm, and the surface contact angle is <30°. The smaller the contact angle, the better the hydrophilicity of the coating, which can quickly absorb electrolyte and maintain electrolyte wetting, thus solving the problem of insufficient electrolyte wetting in the central area of ​​the core. The porosity of the first coating 10 is 30%~40%, which matches the porosity of the base film, ensuring that lithium ions can pass through smoothly. At the same time, the dense coating structure can effectively suppress the thermal shrinkage of the base film and improve the high-temperature safety of the battery.Specifically, the main components of coating 2 are fast ion conductor material, ceramic particles, and binder. The fast ion conductor material can be one or more of LATP, LZTP, MXNE, etc. The mass fraction of the fast ion conductor material in coating 2 is 10%~30%, preferably 15%~25%. Too much addition will increase the brittleness of the coating, while too little addition will not achieve the effect of improving ion transport efficiency. The ceramic particles can be one or more of zirconium oxide, alumina, titanium oxide, etc., with a particle size of 0.05~5μm. The mass fraction of ceramic particles in the second coating is 60%~75%, preferably 65%~70%, and its main function is to improve the mechanical strength and thermal stability of the coating, while providing a supporting framework for the fast ion conductor material. The binder uses the same binder system as the first coating 10, with a mass fraction of 1%~10%, preferably 1%~5%, to ensure good adhesion between the second coating 20 and the base film, and between the second coating 20 and the electrode, to prevent the coating from falling off during winding or stacking, while also possessing a certain degree of flexibility and electrolyte compatibility. The thickness T2 of the second coating 20 is greater than T1 + 1~5 μm, that is, the value of T2 is in the range of 2.5~8 μm, preferably 3~6 μm; the porosity of the second coating 20 is greater than 40%, preferably 45%~60%. The high porosity can accommodate more electrolyte and provide sufficient channels for lithium ion transport. Combined with the role of fast ion conductor material, it significantly reduces the ion transport resistance in the end region of the core; the ionic conductivity of the second coating 20 is ≥1.0×10⁻³ S / cm (25℃), and the electrochemical stability window is ≥4.5V (vs Li⁺ / Li). It is compatible with high-voltage cathode materials and improves the energy density and cycle stability of the battery. Specifically, the width of the coating 2 at the top and bottom of the separator is 5~20mm, preferably 8~15mm. The effect is better when the width of the second coating 20 is equal to the thinning width of the electrode. In this case, the coating 2 can completely cover the thinned area of ​​the electrode, effectively filling the interfacial gap caused by the thinning, improving interfacial contact performance, reducing interfacial impedance, and preventing puncture damage to the separator from the electrode edges, further improving battery safety and cycle life. The width of the first coating 10 is the total width of the base film minus the width of the second coating 20 on the top and bottom sides, ensuring that the first coating 10 completely covers the central main area of ​​the core, meeting the thermal stability and electrolyte wetting requirements of the central area.

[0019] The coating can be applied to only one side of the base film (the side facing the positive electrode or the side facing the negative electrode), or it can be applied to both sides of the base film. When applied to both sides, the coating partitioning, composition, and parameters are completely identical on both sides, which can further improve the interfacial compatibility between the separator and the positive and negative electrodes, and balance the overall ion transport efficiency and thermal stability of the battery. Of course, alternatively, the coating can also be applied to only one surface of the base film.

[0020] The embodiments and comparative examples of the present invention will be described in detail below as to how they are operated and implemented. Example 1

[0021] This embodiment provides a partitioned coated diaphragm, with the following specific parameters: 1. Base film: PP / PE / PP three-layer composite film with a thickness of 12μm, porosity of 45%, pore size of 0.2~0.5μm, longitudinal tensile strength of 180MPa, transverse tensile strength of 130MPa, and heat shrinkage rate of 3.5% (1h) at 130℃.

[0022] 2. Coating: Coated on both sides of the base film, the coating on both sides has the same partitioning method, composition and parameters, as detailed below: (1) First coating 10 (central area): The composition includes alumina and zirconium oxide composite ceramic particles (mass ratio 1:0.5) and styrene-butadiene rubber and polyacrylic acid composite adhesive (mass ratio 1:0.8), with a ceramic particle mass fraction of 80% and an adhesive mass fraction of 20%; the ceramic particle size is 0.1~0.5μm; the thickness of the first coating 10 is T1=1.5μm, the surface contact angle is 22°, and the porosity is 35%.

[0023] (2) Second coating 20 (upper and lower sides): The composition includes LATP and LZTP composite fast ion conductor material (mass ratio 1:1), zirconium oxide and titanium oxide composite ceramic particles (mass ratio 1:0.6), and styrene-butadiene rubber and polyacrylic acid composite binder (mass ratio 1:0.8). The fast ion conductor material has a mass fraction of 20%, the ceramic particles have a mass fraction of 65%, and the binder has a mass fraction of 15%. The ceramic particles have a particle size of 0.5~3μm. The coating 2 thickness T2=5μm (satisfying T2-T1>1~5μm), a porosity of 50%, and an ionic conductivity of 1.2×10 -3 S / cm (25℃), electrochemical stability window 4.8V (vs Li⁺ / Li).

[0024] 3. Partition size: The width of coating 2 is 10mm, which is equal to the thinning width of the electrode (10mm); the width of the first coating 10 is the total width of the base film (130mm) minus the width of the upper and lower coatings 2 (10mm×2), which is 110mm.

[0025] 4. Preparation method: (1) Preparation of the first coating 10 slurry: ceramic particles, binder and deionized water are mixed in proportion, 0.3% (mass fraction) of wetting agent is added, and the mixture is dispersed for 30 min using a high-speed disperser at a dispersion speed of 3000 r / min to obtain a uniform first coating 10 slurry with a solid content of 40%.

[0026] (2) Preparation of the second coating 20 slurry: Mix fast ion conductor material, ceramic particles, binder and deionized water in proportion, add 1.0% (mass fraction) of dispersant, disperse for 40 min using a high-speed disperser at a dispersion speed of 3500 r / min, and obtain a uniform second coating 2 slurry with a solid content of 35%.

[0027] (3) Partition coating: Using micro-concave roller coating technology, the first coating 10 slurry is coated on the central area of ​​the base film, and the coating 2 slurry is coated on the upper and lower sides of the base film. During the coating process, the coating speed is controlled at 5m / min to ensure that the first coating 10 and the second coating 20 do not overlap or have any omissions.

[0028] (4) Drying and curing: The coated diaphragm is sent into an oven and dried at 80°C for 10 minutes to remove most of the moisture. Then it is dried at 120°C for 20 minutes to complete the curing and obtain the partitioned coated diaphragm.

[0029] 5. Performance testing: The separator, positive electrode (NCM811), and negative electrode (graphite) were wound together to form a core and assembled into an 18650 lithium-ion battery. The performance test results are as follows: after 1000 cycles, the capacity retention rate is 88%, the battery internal resistance is 42mΩ, there is no thermal runaway after 2 hours of storage at 130℃, and the electrolyte wetting time is ≤30s. Example 2

[0030] This embodiment provides a partitioned coated diaphragm, with the following specific parameters: 1. Base membrane: PE wet-process membrane with a thickness of 8μm, porosity of 50%, pore size of 0.05~0.2μm, longitudinal tensile strength of 160MPa, transverse tensile strength of 125MPa, and heat shrinkage rate of 4.2% (1h) at 130℃.

[0031] 2. Coating: Coated on one side of the base film (the side facing the positive electrode), as detailed below: (1) First coating 10 (central area): The composition includes alumina ceramic particles and PVDF binder, with ceramic particles having a mass fraction of 75% and binder having a mass fraction of 25%; the ceramic particle size is 0.05~0.3μm; the thickness of the first coating 10 is T1=1μm, the surface contact angle is 18°, and the porosity is 32%.

[0032] (2) Coating 2 (upper and lower sides): The composition includes LATP fast ion conductor material, alumina ceramic particles, and PVDF binder. The mass fraction of fast ion conductor material is 15%, the mass fraction of ceramic particles is 70%, and the mass fraction of binder is 15%. The particle size of ceramic particles is 0.05~2μm. The thickness of coating 2 is T2=4μm (satisfying T2-T1>1~5μm), the porosity is 48%, the ionic conductivity is 1.0×10⁻³ S / cm (25℃), and the electrochemical stability window is 4.6V (vs Li⁺ / Li).

[0033] 3. Partition size: The width of coating 2 is 8mm, which is equal to the thinning width of the electrode (8mm); the width of the first coating 10 is the total width of the base film (120mm) minus the width of the upper and lower coatings 2 (8mm×2), which is 104mm.

[0034] 4. Preparation method: (1) Preparation of the first coating 10 slurry: Alumina ceramic particles, PVDF binder and NMP solvent are mixed in proportion, and 0.2% (mass fraction) of wetting agent is added. The mixture is dispersed at high speed for 25 min at a dispersion speed of 2800 r / min to obtain the first coating 10 slurry with a solid content of 38%.

[0035] (2) Preparation of coating 2 slurry: LATP fast ion conductor material, alumina ceramic particles, PVDF binder and NMP solvent are mixed in proportion, 0.8% (mass fraction) of dispersant is added, and high-speed dispersion is carried out for 35 min at a dispersion speed of 3200 r / min to obtain coating 2 slurry with a solid content of 32%.

[0036] (3) Partition coating: Using the comma scraper coating technique, the first coating 10 slurry and the coating 2 slurry are coated on the corresponding areas of the base film respectively. The coating speed is 4m / min to ensure uniform coating thickness.

[0037] (4) Drying and curing: The coated diaphragm is placed in an oven and dried at 90°C for 15 min and at 110°C for 25 min to complete the curing and obtain a partitioned coated diaphragm.

[0038] 5. Performance testing: The separator, positive electrode (LFP), and negative electrode (graphite) were stacked together to form a core, and assembled into a soft-pack lithium-ion battery. The performance test results are as follows: after 1000 cycles, the capacity retention rate is 86%, the battery internal resistance is 48mΩ, there is no thermal runaway after 2 hours of storage at 130℃, and the electrolyte wetting time is ≤25s. Example 3

[0039] This embodiment provides a partitioned coated diaphragm, with the following specific parameters: 1. Base membrane: PP dry process membrane is selected, with a thickness of 15μm, porosity of 40%, pore size of 0.3~0.8μm, longitudinal tensile strength of 170MPa, transverse tensile strength of 120MPa, and heat shrinkage rate of 4.8% (1h) at 130℃.

[0040] 2. Coating: Coated on both sides of the base film, the coating on both sides has the same partitioning method, composition and parameters, as detailed below: (1) First coating 10 (central area): The composition includes titanium oxide and zirconium oxide composite ceramic particles (mass ratio 1:0.7) and polyacrylate binder. The ceramic particles have a mass fraction of 85% and the binder has a mass fraction of 15%. The ceramic particles have a particle size of 0.3~0.5μm. The thickness of the first coating 10 is T1=2μm, the surface contact angle is 25°, and the porosity is 38%.

[0041] (2) Second coating 2 (first region and second region): The composition includes LZTP fast ion conductor material, titanium dioxide ceramic particles, and polyacrylate binder. The mass fraction of fast ion conductor material is 25%, the mass fraction of ceramic particles is 60%, and the mass fraction of binder is 15%. The particle size of ceramic particles is 2~5μm. The thickness of coating 2 is T2=6μm (satisfying T2-T1>1~5μm), the porosity is 55%, and the ionic conductivity is 1.5×10 -3 S / cm (25℃), electrochemical stability window 4.9V (vs Li⁺ / Li).

[0042] 3. Partition size: The width of the second coating 20 is 15mm, which is equal to the thinning width of the electrode (15mm); the width of the first coating 10 is the total width of the base film (140mm) minus the width of the second coating 20 in the first and second regions (15mm×2), which is 110mm.

[0043] 4. Preparation method: (1) Preparation of the first coating 10 slurry: ceramic particles, polyacrylate binder and deionized water are mixed in proportion, 0.4% (mass fraction) of wetting agent is added, and the mixture is dispersed at high speed for 35 min at a dispersion speed of 3200 r / min to obtain the first coating 10 slurry with a solid content of 42%.

[0044] (2) Preparation of coating 2 slurry: LZTP fast ion conductor material, ceramic particles, polyacrylate binder and deionized water are mixed in proportion, 1.2% (mass fraction) of dispersant is added, and high-speed dispersion is carried out for 45 min at a dispersion speed of 3800 r / min to obtain the second coating 20 slurry with a solid content of 36%.

[0045] (3) Partition coating: The first coating 10 slurry and the second coating 20 slurry are simultaneously coated on the corresponding areas of the base film using slit coating technology. The coating speed is 6m / min to ensure that the coating is free of bubbles and pinholes.

[0046] (4) Drying and curing: The coated diaphragm is placed in an oven and dried at 85°C for 12 min and at 125°C for 18 min to complete the curing and obtain a partitioned coated diaphragm.

[0047] 5. Performance Testing: The separator, positive electrode (NCM622), and negative electrode (silicon-carbon negative electrode) were wound together to form a core and assembled into a cylindrical lithium-ion battery. The performance test results are as follows: after 1000 cycles, the capacity retention rate is 87%, the battery internal resistance is 45mΩ, there is no thermal runaway after 2 hours of storage at 130℃, and the electrolyte wetting time is ≤35s.

[0048] Comparative Example

[0049] A single-coated separator was used, with the base membrane identical to that of Example 1. The coating consisted of alumina ceramic particles and styrene-butadiene rubber binder (mass ratio 8:2), with a thickness of 3 μm, a porosity of 35%, a surface contact angle of 28°, and a non-partitioned design. This separator was assembled into a battery using the same positive and negative electrodes as in Example 1, and performance tests were conducted. The results are as follows: after 1000 cycles, the capacity retention was 72%, the battery internal resistance was 68 mΩ, slight thermal shrinkage occurred after 2 hours of storage at 130°C, and the electrolyte wetting time was 60 seconds.

[0050] Based on the structural analysis of Examples 1-3 and the comparative examples, it can be seen that the present invention provides two different coating materials with different thicknesses on the separator. The second coating can completely cover the thinned area of ​​the electrode, effectively filling the interfacial gap caused by the thinning of the electrode, improving the interfacial contact performance, reducing the interfacial impedance, and avoiding puncture damage to the separator by the electrode edge, further improving the safety and cycle life of the battery. The first coating can quickly absorb the electrolyte and maintain the electrolyte wettability, solving the problem of insufficient electrolyte wettability in the center area of ​​the core. With the dual-layer design, the present invention is significantly superior to the existing single-coated separator in terms of cycle life, internal resistance, high-temperature safety, and electrolyte wettability, fully demonstrating the technical advantages of the present invention.

Claims

1. A diaphragm, characterized in that, include: The base film includes a central region and a peripheral region adjacent to the central region, the peripheral region including a first region located above the central region and a second region located below the central region; The first coating is applied to the central region of the base film; The second coating is applied to the first and second regions of the base film; the first coating includes first ceramic particles, a first binder, and a wetting agent; the second coating includes a fast ion conductor material, second ceramic particles, and a second binder; wherein the ceramic particles in the first coating have a mass fraction of 80% to 95% in the second coating, the fast ion conductor material in the second coating has a mass fraction of 10% to 30% in the second coating, and the thickness T2 of the second coating is greater than the thickness T1 of the first coating.

2. The diaphragm as described in claim 1, characterized in that, The first ceramic particle is one or more of zirconium oxide, aluminum oxide, and titanium oxide.

3. The diaphragm as described in claim 2, characterized in that, The first adhesive is a compound adhesive of styrene-butadiene rubber and polyacrylic acid, wherein the mass ratio of styrene-butadiene rubber to polyacrylic acid is 1:0.5~1.

2.

4. The diaphragm as described in claim 3, characterized in that, The thickness T1 of the first coating is 0.5~3μm.

5. The diaphragm as described in claim 1, characterized in that, The fast ion conductor material is one or more of LATP, LZTP, and MXNE materials.

6. The diaphragm as described in claim 1, characterized in that, The thickness T2 of the second coating is 2.5~8μm.

7. The diaphragm as described in claim 1, characterized in that, The porosity of the second coating is 45% to 60%.

8. The diaphragm as claimed in claim 1, characterized in that, The width of the second coating is 8-15 mm.

9. A battery cell, characterized in that, It includes a diaphragm as described in any one of claims 1-8.

10. An electrical device, characterized in that, It includes a diaphragm as described in any one of claims 1-8.

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