A composite battery separator, its preparation method and application

Abstract

This invention provides a composite battery separator, its preparation method, and its application, relating to the field of lithium-ion battery technology. Specifically, the composite battery separator includes a base film and a coating loaded on at least one side of the base film; the coating includes organic components, inorganic components, and functional components; wherein the organic component includes polyethylene oxide (PEO), and the inorganic component includes scandium oxide and titanium dioxide. This invention improves the thermal stability, electrolyte affinity, and ionic conductivity of the separator by coating a mixture of inorganic metal materials and the organic component PEO onto the base film. Simultaneously, the nanoparticles formed by the mixed doping of scandium oxide and titanium dioxide effectively improve the uneven pore distribution on the surface of the polyolefin separator, reducing the formation of lithium dendrites.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to a composite battery separator, its preparation method, and its application. Background Technology

[0002] Currently, rechargeable lithium-ion batteries (LIBs) are widely used in wearable devices, electric vehicles, and industrial energy storage. However, the rapid development of electric vehicles has placed higher demands on battery safety and energy density. In this regard, the separator, as a key component of the battery, plays a crucial role. The most common lithium-ion battery separators are made of polyolefin materials, such as polypropylene (PP), polyethylene (PE), and their blends. Although conventional lithium-ion battery separators have excellent chemical stability and high mechanical strength, they suffer from defects such as poor electrolyte wettability, low ionic conductivity, and poor thermal stability, which severely limit the electrochemical performance and safety of lithium-ion batteries.

[0003] Specifically, the preparation methods of polyolefin separators are mainly divided into two processes: dry process and wet process. The dry process, also known as the melt stretching method, first requires heating the polyolefin resin to a molten state, then extruding it to form a crystalline film, followed by annealing to form a highly oriented multilayer non-porous structure, and finally hot stretching under high temperature and low stretching rate conditions to separate the regularly arranged wafers and form small, uniformly distributed slit-like micropores. The wet process, also known as the thermally induced phase separation method, first heats the polyolefin resin and other additives to a molten state, mixes them evenly, and then extrudes them to form a non-porous film. This is followed by casting, cooling, and biaxial stretching, using volatile solvents to extract the additives and form micropores, and finally heat setting. Although polyolefin separators are relatively mature in development and application, the low melting points of polypropylene and polyethylene (PE melting point 110℃, PP melting point 150℃) and non-polar surfaces result in poor thermal stability and wettability of polyolefin separators, which limits their application in high-performance lithium-ion batteries.

[0004] Taking polyolefin separators as an example, these separators are widely used in the field of secondary lithium-ion batteries, but they have at least the following defects: 1) Poor thermal stability: polyolefin separators are prone to shrinkage or melting at high temperatures, which may lead to thermal runaway or short circuits inside the battery, affecting battery safety; 2) Poor wettability: the polarity of polyolefin separators does not match the polarity of organic electrolytes, resulting in poor wettability of the electrolyte on the separator, which seriously affects the cycle performance of lithium-ion batteries; 3) Low ionic conductivity: the battery internal resistance is relatively high, which cannot meet the high-rate charging and discharging requirements of power cells.

[0005] To address the above issues, current solutions mainly include: 1) Organic coating: applying a water-based PVDF or PMMA adhesive layer to one or both sides of the polyolefin separator base membrane. This adhesive layer effectively improves the wettability of the separator and also enhances the adhesion between the separator and the electrode. 2) Inorganic coating: coating both sides of the polyolefin separator with treated inorganic nanoparticles. The use of inorganic ceramic particles with high specific surface area and good heat resistance can give the separator better hydrophilicity and higher thermal stability. However, inorganic coatings are prone to peeling off after heating, while separators with organic polymer coatings have poor mechanical properties.

[0006] In view of this, there is an urgent need to develop a novel diaphragm with good thermal stability, high electrolyte affinity, and high ionic conductivity, and this invention is proposed. Summary of the Invention

[0007] The primary objective of this invention is to provide a composite battery separator that uses an organic-inorganic composite modified material as a coating layer to solve the technical problems existing in existing inorganic or organic coatings. This is mainly to address the technical problems of low affinity between lithium-ion battery polyolefin separators and electrolytes, poor thermal stability, and easy formation of lithium dendrites on the surface, which affect battery cycle safety. Thus, a novel separator that combines the advantages of both inorganic and organic coatings is provided.

[0008] The second objective of this invention is to provide a method for preparing the composite battery separator described above, which is simple and easy to implement and can be mass-produced.

[0009] A third objective of this invention is to provide a secondary battery.

[0010] The fourth objective of this invention is to provide an electrical device.

[0011] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0012] A composite battery separator includes a base membrane and a coating loaded on at least one side of the base membrane; the coating includes an organic component, an inorganic component, and a functional component; wherein the organic component includes polyethylene oxide, and the inorganic component includes scandium oxide and titanium dioxide.

[0013] A method for preparing the composite battery separator includes the following steps:

[0014] A mixed dispersion of scandium oxide and titanium dioxide was prepared and then subjected to heating treatment to obtain a doped inorganic powder; the doped inorganic powder and polyethylene oxide were thoroughly mixed in an organic solvent to obtain a composite material.

[0015] The composite material and functional components are thoroughly mixed in water to obtain a composite slurry; the composite slurry is coated on at least one side of the base membrane and then vacuum dried to obtain a composite battery separator.

[0016] A secondary battery, comprising the aforementioned composite battery separator.

[0017] An electrical device includes the aforementioned secondary battery.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] In this invention, the polar polymer polyethylene oxide of the organic component can effectively improve the wettability, thermal stability, and mechanical properties of conventional polyolefins. Titanium dioxide, with its advantages of being non-toxic, stable, and easy to prepare, can improve the thermal stability and electrolyte wettability of the separator, and can absorb some impurity electrolytes, helping to reduce the interfacial impedance between the separator and the electrode. Simultaneously, titanium dioxide has good compatibility with the electrolyte, promoting lithium-ion transport and improving the ionic conductivity of the separator, making it an ideal organic polymer separator modification material. Furthermore, the introduction of titanium dioxide into the separator in this invention can reduce interparticle stress and improve the internal stability of the battery. Further, in this invention, doping scandium oxide with titanium dioxide forms oxygen vacancies, which can effectively adsorb lithium ions and ensure uniform lithium-ion deposition, effectively reducing the formation of lithium dendrites on the separator surface. Furthermore, this invention coats a base film with a mixture of nanoscale inorganic metal materials and organic component PEO. This improves the thermal stability, electrolyte affinity, and ionic conductivity of the separator. At the same time, the nanoparticles formed by the mixed doping of scandium oxide and titanium dioxide can effectively improve the uneven distribution of pores on the surface of the PP separator and reduce the formation of lithium dendrites. Detailed Implementation

[0020] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. 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. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially. In addition, the terms "a", "b", and "c" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0021] The first objective of this invention is to provide a composite battery separator, comprising a base film and a coating loaded on at least one side of the base film; the coating comprises an organic component, an inorganic component and a functional component; wherein the organic component comprises polyethylene oxide (PEO) and the inorganic component comprises scandium oxide (Sc2O3) and titanium dioxide (TiO2).

[0022] In a preferred embodiment, the base film comprises a polyimide (PI)-polypropylene (PP) composite film; it is understood that the composite film used is prepared by combining microsphere polyimide and polypropylene.

[0023] In a preferred embodiment, the porosity of the base film is 48% to 55%; in some more preferred embodiments, the porosity is 51%.

[0024] In a more preferred embodiment, the polyimide-polypropylene composite film is prepared with a polyimide to polypropylene ratio of (1-1.5):2.

[0025] In a more preferred embodiment, the thickness of the polyimide-polypropylene composite film is 12 μm to 24 μm.

[0026] In a preferred embodiment, the ratio of the organic component to the inorganic component by mass is (3-10):(10-20).

[0027] In a preferred embodiment, the thickness of the coating is 2μm to 6μm; it is understood that when the coating is applied on both sides, the thickness of each layer of the coating is independently 2μm to 6μm.

[0028] In a preferred embodiment, the molecular weight of the polyethylene oxide is 2*10. 6 ~6*10 6 In some preferred embodiments, the molecular weight is selected as 4*10. 6 .

[0029] In a preferred embodiment, the ratio of scandium oxide to titanium dioxide by mass is (2-5):(20-30).

[0030] In a preferred embodiment, the functional component includes at least one of a dispersant, a thickener, a wetting agent, and a binder. In some more preferred embodiments, the functional component includes a dispersant, a thickener, a wetting agent, and a binder simultaneously.

[0031] In a more preferred embodiment, the functional components include the following components by weight: 0.55 to 2.5 parts of dispersant, 2.5 to 12 parts of thickener, 0.2 to 0.8 parts of wetting agent, and 2 to 5 parts of binder.

[0032] In a more preferred embodiment, the mass ratio of the sum of the organic components and the inorganic components to the mass of the functional components is (25-40):(5.25-20.3).

[0033] In a more preferred embodiment, the dispersant includes at least one of polyvinylpyrrolidone (PVP), polyacrylate (PAA), polyacrylamide (PAM), and polyacrylic acid.

[0034] In a more preferred embodiment, the thickener includes at least one of hydroxymethyl cellulose (CMC), sodium hydroxymethyl cellulose (CMCNa), hydroxypropyl methylcellulose (HPMC), and methylcellulose (MC).

[0035] In a more preferred embodiment, the wetting agent includes at least one of sodium butylnaphthalenesulfonate or sodium alkyl sulfate.

[0036] In a more preferred embodiment, the adhesive comprises at least one of polyacrylic acid or polyacrylonitrile.

[0037] The second objective of this invention is to provide a method for preparing the composite battery separator, which mainly includes the following four steps (1) to (4).

[0038] (1) A mixed dispersion of scandium oxide and titanium dioxide was prepared and then heated to obtain doped inorganic powder.

[0039] In a preferred embodiment, a dispersion of scandium oxide is first prepared, and then titanium dioxide is added to it and mixed thoroughly to obtain the mixed dispersion.

[0040] In a preferred embodiment, the solvent of the mixed dispersion is water; in some optional embodiments, the solid content of the mixed dispersion is 0.08 g / mL to 0.2 g / mL.

[0041] In a preferred embodiment, the preparation of the mixed dispersion includes a thorough mixing step, which includes, but is not limited to, shaking, stirring, centrifugation, and sonication.

[0042] As an optional implementation, scandium oxide is added to a solvent, stirred for 30 to 60 minutes, and then sonicated to obtain a dispersion of scandium oxide; titanium dioxide is added to the scandium oxide dispersion and stirred for 40 to 60 minutes to obtain the mixed dispersion.

[0043] In a preferred embodiment, the temperature of the heating treatment is 160℃~200℃, including but not limited to any one or any two of the following values: 160, 165, 170, 175, 180, 185, 190, 195, 200 (℃). The holding time of the heating treatment is 2h~4h, including but not limited to any one or any two of the following values: 2, 2.2, 2.4, 2.5, 2.6, 2.8, 3, 3.2, 3.4, 3.5, 3.6, 3.8, 4 (h).

[0044] In a preferred embodiment, the heating process further includes washing, solid-liquid separation, and drying.

[0045] (2) The doped inorganic powder and polyethylene oxide are thoroughly mixed in an organic solvent to obtain a composite material.

[0046] In a preferred embodiment, the process further includes washing, solid-liquid separation, and drying after thorough mixing. In some optional embodiments, the washing medium is acetone.

[0047] In a preferred embodiment, the doped inorganic powder is first fully dispersed in a first organic solvent to obtain a first dispersion; then the polyethylene oxide is fully dispersed in a second organic solvent to obtain a second dispersion; the first dispersion and the second dispersion are then fully mixed to obtain a composite material.

[0048] In a more preferred embodiment, the first solvent comprises N-methylpyrrolidone (NMP) and the second solvent comprises acetone.

[0049] As a more preferred embodiment, similar to step (1), any of the thorough mixing involved in this step includes, but is not limited to, oscillation, stirring, centrifugation, ultrasonication, heat treatment, bubbling, etc.

[0050] In a more preferred embodiment, the mass ratio of the doped inorganic powder to the first organic solvent is (1-2):(6-10).

[0051] In a more preferred embodiment, the mass ratio of the polyethylene oxide to the second organic solvent is (3-10):(45-80).

[0052] As an optional implementation, the doped inorganic powder is first fully dispersed in a first organic solvent and ultrasonically treated for 0.5 h to 3 h to obtain a first dispersion; then the polyethylene oxide is fully dispersed in a second organic solvent, and stirred in a sealed container at 50 °C to 80 °C for 5 h to 8 h, followed by ultrasonic treatment to obtain a second dispersion; the first dispersion and the second dispersion are fully mixed and stirred for 5 h to 8 h to obtain a composite material.

[0053] (3) The composite material and functional components are thoroughly mixed in water to obtain a composite slurry.

[0054] In a preferred embodiment, the thorough mixing is achieved by high-speed stirring and dispersion, wherein the high-speed stirring and dispersion speed is 300 rpm to 500 rpm.

[0055] In a preferred embodiment, the thorough mixing process further includes one or more of the following steps: sieving, iron removal, and defoaming.

[0056] In a preferred embodiment, the water content in the composite slurry is 40% to 70% by mass. Those skilled in the art can adjust the solid content of the coating slurry according to the actual functional requirements of the coating process.

[0057] (4) The composite slurry is coated on at least one side of the base film and then vacuum dried to obtain a composite battery separator.

[0058] In a preferred embodiment, the coating is performed using either gravure coating or slot extrusion coating.

[0059] In a preferred embodiment, the vacuum drying temperature is 65℃~75℃, and the vacuum drying time is 6h~8h.

[0060] A third objective of this invention is to provide a secondary battery, including the aforementioned composite battery separator. It is understood that, apart from the composite battery separator, the secondary battery should include positive and negative electrodes, electrolyte, and other necessary or non-essential functional components or packaging assemblies, which can be arbitrarily selected and combined by those skilled in the art. When the secondary battery includes the composite battery separator described in this invention, regardless of whether other separator functional components are used in the secondary battery, it can be considered an embodiment of this invention.

[0061] A fourth objective of this invention is to provide an electrical device including the aforementioned secondary battery. The electrical device can be any device or apparatus that relies on electrical energy for operation, including but not limited to new energy vehicles, building electrical equipment, industrial electrical appliances, household and agricultural electrical appliances, etc.; when the secondary battery is included, any electrical device equipped with the aforementioned secondary battery can be considered an embodiment of this invention.

[0062] Example 1

[0063] S1: Add 25g of nano-TiO2 particle powder to 250mL of pure water, stir for 45min, and then ultrasonically disperse for 65min to obtain TiO2 dispersion; then slowly add 3g of Sc2O3 to it, stir for 50min, then heat to 180℃ and keep it at that temperature for 3h; after the reaction, wash, centrifuge and dry the reaction product to obtain Sc2O3-doped TiO2 particle powder.

[0064] S2: Add 15g of the nanopowder obtained in S1 to 100g of N-methylpyrrolidone, stir and then sonicate for 3h to obtain a dispersion of modified nanomaterials in a dispersed state; then slowly add 3g of PEO powder to 80g of acetone, seal and stir at 70℃ for 8h and sonicate to obtain PEO slurry; slowly add the PEO slurry to the modified nanomaterial dispersion, stir for 8h, and then wash, centrifuge and dry the obtained dispersion to obtain the organic-inorganic mixed material.

[0065] S3: Add 25g of the organic-inorganic mixture obtained in S2 and 0.5g of the dispersant (PVP) to pure water and mix. Then add 5g of the thickener (CMC), 0.5g of the wetting agent (sodium butylnaphthalene sulfonate), and 2.4g of the binder (polyacrylic acid). Then, perform high-speed dispersion, sieving, iron removal, and defoaming treatment in sequence to obtain the mixed coating slurry.

[0066] S4: The mixed coating slurry obtained in S3 is coated on one side of a PI-PP composite base film with a thickness of 14μm using a slit extrusion coating method, with a coating thickness of 4μm. The film is then vacuum dried at 70℃ for 8h to obtain a composite material coated diaphragm with a thickness of 18μm.

[0067] Example 2

[0068] It is basically the same as Example 1, except that:

[0069] In step S1: the amount of nano TiO2 particle powder used is 20g, and the amount of Sc2O3 used is 2g.

[0070] Example 3

[0071] It is basically the same as Example 1, except that:

[0072] In step S1: the amount of nano TiO2 particle powder used is 30g, and the amount of Sc2O3 used is 5g.

[0073] Example 4

[0074] It is basically the same as Example 1, except that:

[0075] In step S2: the amount of nanopowder used is 10g, and the mass of PEO powder is 5g.

[0076] Example 5

[0077] It is basically the same as Example 1, except that:

[0078] In step S2: the amount of nanopowder used is 20g, and the mass of PEO powder is 10g.

[0079] Example 6

[0080] It is basically the same as Example 1, except that:

[0081] In step S3: the type of dispersant is replaced with PAA, the type of thickener is replaced with HPMC, the type of wetting agent is replaced with sodium alkyl sulfate, and the type of binder is replaced with polyacrylonitrile.

[0082] Example 7

[0083] It is basically the same as Example 1, except that:

[0084] In step S4: the mixed coating slurry obtained in S3 is coated on both sides of the PI-PP composite base film; wherein the coating thickness on each side is 4μm, and a composite material coated diaphragm with a thickness of 22μm is finally obtained.

[0085] Comparative Example 1

[0086] It is basically the same as Example 1, except that:

[0087] In step S4: the PI-PP composite base film is replaced with a PP film of the same thickness.

[0088] Comparative Example 2

[0089] It is basically the same as Example 1, except that:

[0090] Step S1 is cancelled, and only operations related to PEO powder are retained in step S2; that is, only organic components are used in the coating slurry, and the inorganic components of Sc2O3-doped TiO2 particles are cancelled.

[0091] Test case

[0092] (1) Air permeability: Cut three diaphragms at 150mm intervals along the longitudinal direction on the membrane roll. The sample size of each piece is 100mm×100mm. Place the diaphragm in the test head of the air permeability tester to test the air permeability. Take the average value of the three test results as the air permeability value of the diaphragm.

[0093] (2) Heat shrinkage rate: Cut three 100mm×100mm square diaphragms from the longitudinal direction of the membrane roll. When cutting the diaphragms, one edge of the membrane roll should be parallel to at least one edge of the diaphragm, and the maximum deviation angle should not exceed 5°. Place the stainless steel plate and two pieces of quantitative filter paper in the middle of the oven, and control the temperature to (105±1)℃. Mark the longitudinal and transverse directions of the test diaphragm, and then place the diaphragm flat on the quantitative filter paper on the stainless steel plate in the middle of the blower-type constant temperature chamber. After that, press it down with another piece of quantitative filter paper, close the constant temperature chamber door, and start the timer. Maintain the temperature at 105℃ for 1h±5min. After the heating is completed, take out the diaphragm and wait for it to return to room temperature. Then measure the longitudinal and transverse marking lengths again. Calculate the longitudinal and transverse shrinkage rates of the diaphragm respectively, and take the average of the three test results as the heat shrinkage rate of the diaphragm.

[0094] (3) Liquid absorption rate: Three 100mm×100mm square diaphragms were cut from the longitudinal direction of the membrane roll. The samples were baked in a drying oven at 105±2℃ until constant weight, and then cooled to room temperature. The mass m1 was recorded. The samples were placed in a container with a sufficient amount of electrolyte, ensuring that the samples were completely immersed, and soaked at a constant temperature of 23℃ for 24 hours. The soaked samples were taken out, the surface moisture was gently wiped off, and the samples were weighed immediately and the mass m2 was recorded. The liquid absorption rate was calculated as (m2-m1) / m1×100%.

[0095] Table 1

[0096]

[0097] As can be seen from Table 1, the thermal shrinkage rate and liquid absorption rate of the membrane samples in the examples are significantly higher than those in the comparative examples, indicating that the PEO@TiO2 composite material coated membrane of the present invention can effectively improve the problems of poor thermal stability and insufficient electrolyte affinity of polyolefin membranes, and ensure the performance and safety of battery cell products.

[0098] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A composite battery separator, characterized in that, The composite battery separator includes a base film and a coating loaded on at least one side of the base film; The coating comprises organic components, inorganic components, and functional components; wherein the organic components include polyethylene oxide, and the inorganic components include doped inorganic powder formed from scandium oxide and titanium dioxide.

2. The composite battery separator according to claim 1, characterized in that, The base film includes a polyimide-polypropylene composite film.

3. The composite battery separator according to claim 1, characterized in that, The mass ratio of the organic component to the inorganic component is (3~10):(10~20); And / or, the mass ratio of scandium oxide to titanium dioxide is (2~5):(20~30); And / or, the mass ratio of the sum of the organic components and the inorganic components to the mass of the functional components is (25~40):(5.25~20.3).

4. The composite battery separator according to claim 1, characterized in that, The functional components include at least one of dispersants, thickeners, wetting agents, and binders.

5. The composite battery separator according to claim 4, characterized in that, The dispersant includes at least one of polyvinylpyrrolidone, polyacrylate, polyacrylamide, and polyacrylic acid; The thickener includes at least one of hydroxymethylcellulose, sodium hydroxymethylcellulose, hydroxypropyl methylcellulose, and methylcellulose; The wetting agent includes at least one of sodium butylnaphthalene sulfonate or sodium alkyl sulfate; The adhesive includes at least one of polyacrylic acid or polyacrylonitrile.

6. The composite battery separator according to claim 4, characterized in that, The functional components include the following components by weight: 0.55-2.5 parts of dispersant, 2.5-12 parts of thickener, 0.2-0.8 parts of wetting agent, and 2-5 parts of binder.

7. The method for preparing the composite battery separator according to any one of claims 1 to 6, characterized in that, The preparation method includes the following steps: A mixed dispersion of scandium oxide and titanium dioxide was prepared and then subjected to heating treatment to obtain a doped inorganic powder; the doped inorganic powder and polyethylene oxide were thoroughly mixed in an organic solvent to obtain a composite material. The composite material and functional components are thoroughly mixed in water to obtain a composite slurry; the composite slurry is coated on at least one side of the base membrane and then vacuum dried to obtain a composite battery separator.

8. The method for preparing the composite battery separator according to claim 7, characterized in that, In the composite slurry, the mass percentage of water is 40% to 70%.

9. The method for preparing the composite battery separator according to claim 7, characterized in that, The temperature of the heating treatment is 160℃~200℃, and the holding time of the heating treatment is 2h~4h; And / or, the vacuum drying temperature is 65℃~75℃, and the vacuum drying time is 6h~8h.

10. A secondary battery, characterized in that, Including the composite battery separator as described in any one of claims 1 to 6.

11. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 10.

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