Separator, secondary battery including the same, and electrical device

Abstract

The present invention provides a separator, comprising a base film having a plurality of pores, wherein a part of the pores are filled with support particles, and the support particles include first inorganic particles with a melting point greater than or equal to 200 °C. Compared with the prior art, for the separator provided by the present invention, support particles are filled in a part of the pores of the base film, and inorganic particles with a melting point greater than or equal to 200 °C are used for filling, so that the inorganic particles are dispersed in each region of the base film. Thus, by reconstructing the base film system, the supporting effect of the inorganic particles can effectively reduce the problem that the base film is prone to shrinkage at high temperatures, effectively improve the heat shrinkage resistance of the separator at high temperatures, and further improve the safety performance of the battery. In addition, the present invention also provides a secondary battery and an electrical device containing the separator.

Description

Technical Field

[0001] The present invention relates to the field of secondary batteries, and particularly to a separator, a secondary battery containing the separator, and an electrical device. Background Art

[0002] With the continuous progress of technology, people have an increasing demand for safer and more environmentally friendly lithium-ion batteries. Common lithium-ion batteries mainly include a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The separator is disposed between the positive electrode sheet and the negative electrode sheet, providing a path for the smooth movement of ions and also being an important component to prevent battery short circuit.

[0003] Currently, the mainstream separators used in lithium-ion batteries are all made of polyolefin materials. However, polyolefin will severely shrink at high temperatures and is prone to heat accumulation in the case of short circuit or local overheating, which may even lead to explosion. Based on this, there are also related solutions that record the modification of polyolefin separators to improve the safety of the battery. However, the current modification solutions mainly modify the surface of polyolefin, such as coating a mixture layer of polymethyl methacrylate, alumina, or polyvinylidene fluoride and alumina on the surface. Although these modifications improve the safety of the battery to a certain extent compared with pure polyolefin separators, they still shrink to a large extent at high temperatures and there are still relatively large potential safety hazards.

[0004] In view of this, it is necessary to provide a technical solution to solve the above problems. Summary of the Invention

[0005] One of the purposes of the present invention is to provide a separator to improve the problem that the current polyolefin separators are prone to shrink at high temperatures, resulting in poor safety performance of the battery, in view of the deficiencies of the prior art.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions:

[0007] A separator includes a base film containing a plurality of pores, and a part of the pores are filled with support particles. The support particles include first inorganic particles with a melting point greater than or equal to 200°C.

[0008] Preferably, the base film is a polyolefin base film modified by polydopamine.

[0009] Preferably, the method for modifying the polyolefin base film with polydopamine is: immersing the polyolefin base film in a polydopamine solution, taking it out after standing, and drying to obtain the modified polyolefin base film; the method for filling the support particles is: immersing the polyolefin base film modified by polydopamine in a solution containing support particles, taking it out and drying to obtain a base film with a part of the pores filled with support particles.

[0010] Preferably, the support particles further include a binder, and the mass ratio of the binder to the first inorganic particles is (1-5):(5-9).

[0011] Preferably, the binder is at least one of polyethylene oxide, polyvinyl alcohol, polyvinylpyrrolidone, and polyvinyl acetal; the first inorganic particles are at least one of alumina, titanium dioxide, and silica.

[0012] Preferably, a composite layer is further included and is coated on at least one surface of the base film.

[0013] Preferably, the composite layer includes second inorganic particles, polyethylene oxide, and cellulose, and the weight ratio of the second inorganic particles, polyethylene oxide, and cellulose is (4-8):(1-5):(1-5).

[0014] Preferably, the second inorganic particles are at least one of alumina, titanium dioxide, and silica; the molecular weight of the polyethylene oxide is 500,000-600,000; the cellulose includes at least one of softwood lignocellulose, hardwood lignocellulose, and herbaceous lignocellulose; preferably, the preparation method of the composite layer is: first, a liquid is prepared by mixing the second inorganic particles with a polyethylene oxide mixed solution, and b liquid is prepared by dissolving cellulose; then, a liquid and b liquid are stirred and mixed to obtain a composite layer slurry; the composite layer slurry is coated on at least one surface of the base film and dried.

[0015] A second object of the present invention is to provide a secondary battery, including a positive electrode plate, a negative electrode plate, and a separator disposed between the positive electrode plate and the negative electrode plate, and the separator is the separator described in any one of the above.

[0016] A third object of the present invention is to provide an electrical device, including the secondary battery described above.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: for the separator provided by the present invention, support particles are filled in a part of the pores of the base film, and inorganic particles with a melting point greater than or equal to 200 °C are used for filling, so that the inorganic particles are dispersed in each region of the base film. Thus, by reconstructing the base film system, the supporting effect of the inorganic particles can effectively reduce the problem that the base film is prone to shrinkage at high temperatures, effectively improve the heat shrinkage resistance of the separator at high temperatures, and further improve the safety performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the separator structure of the present invention.

[0019] Figure 2 It is a second schematic diagram of the separator structure of the present invention.

[0020] Figure 3 This is a comparative test chart of the thermal shrinkage rate for Example 7 of the present invention and Comparative Example 2.

[0021] Figure 4 This is a cyclic performance test chart of the batteries made from Example 7 of the present invention and Comparative Example 2.

[0022] In the figure: 1 - base film; 2 - composite layer. Detailed implementation manners

[0023] To make the technical solutions and advantages of the present invention clearer, the present invention and its beneficial effects will be further described in detail below in conjunction with the detailed implementation manners and the accompanying drawings of the specification. However, the implementation manners of the present invention are not limited thereto.

[0024] The terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality of" means two or more unless otherwise specifically defined.

[0025] The standard parts used in the present invention can all be purchased from the market. The special-shaped parts can be customized according to the records in the specification and the drawings. The specific connection manners of each part all adopt conventional means such as bolts, rivets, welding, etc. that are mature in the prior art. The machines, parts, and equipment all adopt conventional models in the prior art. In addition, the circuit connection adopts the conventional connection manner in the prior art, which will not be elaborated here.

[0026] In a battery, a temperature greater than 100 °C is regarded as high temperature. Under high temperature conditions, all performances of the battery face great challenges, especially the safety performance. Currently, the mainstream polyolefin-based separator used will undergo severe shrinkage at 130 °C, presenting a relatively large potential safety hazard.

[0027] Based on this, the first aspect of the present invention aims to provide a separator, as Figure 1 shown, including a base film 1 containing a number of pores, and a part of the pores are filled with support particles, and the support particles include first inorganic particles with a melting point greater than or equal to 200 °C.

[0028] The base film 1 described in the present invention preferably refers to a base film based on polyolefin materials. The polyolefin materials include, but are not limited to, polyethylene and / or polypropylene base films. By reconstructing the structure of this material and filling inorganic particles with a melting point ≥200 °C into a part of the pores, with the assistance of the inorganic particles for support, the thermal shrinkage performance of the polyolefin-based base film can be better improved, thereby ensuring the safety performance of the battery.

[0029] Preferably, the melting point of the first inorganic particles is greater than or equal to 500 °C. More preferably, the melting point of the first inorganic particles is greater than or equal to 1000 °C. Relatively speaking, using inorganic particles with a higher melting point as a support can more significantly improve the thermal shrinkage performance of the separator. Preferably, the first inorganic particles are at least one of alumina, titanium dioxide, and silicon dioxide. Further preferably, the first inorganic particles are alumina. Alumina is usually a white crystalline powder, easy to absorb moisture but not deliquescent, with a melting point of 2050 °C, a boiling point of 2980 °C, a relative density of 3.965, a Mohs hardness of 8.8, and is an electrical insulator. The volume resistivity at 300 °C is 1.2×10 13 Q·cm. In addition, alumina is almost insoluble in water and non-polar organic solvents such as ethanol and ether, and has a very low solubility in weak acids or weak bases. It can have good stability when applied in the battery. As a component of the support particles, it can better support the structure of the separator and ensure the thermal stability of the separator at high temperatures.

[0030] Even more preferably, the present invention selects α-phase nano-alumina. This crystal structure is spherical-like, has a low specific surface area, and is more inert to high temperatures.

[0031] In addition, since only a part of the pores are filled with support particles, there are still many remaining pores for ions to pass through, which basically does not affect the cycling performance of the battery. Preferably, the present invention uses a base film 1 with a higher porosity as the basis. In this way, on the basis of ensuring the filling of support particles, it still has a porosity similar to that of currently commonly used separators, thereby better ensuring the cycling performance of the battery.

[0032] In some embodiments, the base film 1 is a polyolefin base film modified with polydopamine.

[0033] Polydopamine (PDA) is a highly cross-linked polymer formed by the oxidative polymerization of dopamine, and has many similarities with naturally occurring biopolymers, melanin, and eumelanin. Modifying the polyolefin base film with PDA, on the one hand, PDA has biocompatibility, can resist many reagents, and has strong adhesion to various materials and surfaces. Therefore, it can grow well on the surface of the base film 1, thereby improving the compatibility of the base film 1 with other substances, such as improving the hydrophilicity of the base film 1; on the other hand, the PDA structural fragment is a conjugated system containing rich π electron clouds, which can generate π-π interaction forces with other molecules containing π systems and then adsorb. In addition, the PDA structure also contains active double bonds, which can react with multiple groups, such as amino groups (-NH 2 ), mercapto groups (-SH), etc. Through the reaction between groups, the purpose of compounding other substances with the polyolefin base film can also be achieved.

[0034] Specifically, the method for modifying a polyolefin-based membrane with polydopamine is as follows: Immerse the polyolefin-based membrane in a polydopamine solution, take it out after standing still, and dry it to obtain the modified polyolefin-based membrane.

[0035] More specifically, the method for modifying a polyolefin-based membrane with polydopamine is as follows:

[0036] 1) Dissolve ammonium persulfate to prepare an ammonium persulfate solution, stir it evenly and then let it stand for later use, denoted as solution A;

[0037] 2) Dissolve dopamine hydrochloride to prepare a dopamine hydrochloride solution, stir it evenly and then let it stand for later use, denoted as solution B;

[0038] 3) Mix solution A and solution B in a weight ratio of 1:1, stir it evenly and pour it into a petri dish, add dilute hydrochloric acid to adjust the pH to 4, stir it evenly again for later use, denoted as solution C;

[0039] 4) Completely immerse the polyolefin-based membrane in solution C, take it out after standing at room temperature for 36h to 60h, wash the surface of the membrane with deionized water to remove the excess ions, and prepare a polyolefin-based membrane modified with polydopamine with good hydrophilicity, which is stored in vacuum drying for later use.

[0040] Among them, the growth of polydopamine on the surface of the polyolefin-based membrane can be regulated by adjusting the standing time. Specifically, the standing time can be 36h - 40h, 40h - 44h, 44h - 48h, 48h - 52h, 52h - 56h or 56h - 60h. Preferably, the standing time is 44h - 52h.

[0041] For the polyolefin-based membrane modified with polydopamine first, then a part of its pores are filled with support particles. Thanks to the hydrophilicity of the polyolefin-based membrane and the action of the surface polydopamine, the support particles can better fill the pores.

[0042] Specifically, the method for filling the support particles is as follows: Immerse the polyolefin-based membrane modified with polydopamine in a solution containing support particles, take it out and dry it to obtain a base membrane 1 with support particles filled in a part of its pores.

[0043] Among them, the immersion time of the modified polyolefin-based membrane in the solution containing support particles is 18 - 30h. The specific immersion time is 18h - 20h, 20h - 22h, 22h - 24h, 24h - 26h, 26h - 28h or 28h - 30h. Preferably, the immersion time is 22h - 26h. Within the preferred immersion time, it can ensure that more support particles are dispersed and filled in the pores of the polyolefin-based membrane, thereby improving the subsequent thermal shrinkage performance of the separator.

[0044] Preferably, the support particles further include a binder, and the binder is at least one of polyethylene oxide, polyvinyl alcohol, polyvinylpyrrolidone, and polyvinyl acetal. Increasing the use of the binder and compounding it with inorganic particles, on the one hand, the binder has a certain viscosity, which can ensure to a certain extent that the inorganic particles are stably filled in the pores without falling off; on the other hand, the binder also contains a π system, and the π-bond adsorption with polydopamine further ensures the reconstruction of the base film 1. Preferably, the binder is polyethylene oxide. Polyethylene oxide has thermoplasticity, and its melting point is between 87 and 140 °C. When the battery is in a high-temperature state, polyethylene oxide will turn into a molten state and adhere the inorganic particles to the pores, and the inorganic particles are not likely to fall off at high temperatures, better ensuring the stability of the base film 1.

[0045] In some embodiments, the mass ratio of the binder to the first inorganic particles is (1-5):(5-9). Specifically, the mass ratio of the binder to the first inorganic particles can be 1:9, 2:8, 3:7, 4:6, or 5:5. Preferably, the mass ratio of the binder to the first inorganic particles is (1-4):(6-9). The combination of the above mass ratios can, on the one hand, avoid the situation where the content of the binder is too small to ensure the stable filling of inorganic particles; on the other hand, it can also avoid the situation where the binder content is too large and the heat shrinkage resistance of the base film 1 is weakened. Among them, it is preferred that the mass proportion of the binder is lower than that of the inorganic particles, with the inorganic particles as the main support. On the basis of ensuring the stable filling of inorganic particles, the improvement effect on the heat shrinkage performance of the base film 1 is better.

[0046] In some embodiments, the separator further includes a composite layer 2, which is coated on at least one surface of the base film 1. Specifically, it can be coated on one surface of the base film 1, or coated on two opposite surfaces of the base film 1. Preferably, the composite layer 2 is coated on two opposite surfaces of the base film 1, that is, the structure of composite layer 2 + base film 1 + composite layer 2.

[0047] Increasing the setting of the composite layer 2 can further stabilize the inorganic particles in the pores, and the construction of the multi-layer structure can also improve the mechanical properties of the separator, and the thermal stability of the separator is higher. Especially for the sandwich structure of composite layer 2 + base film 1 + composite layer 2, the thermal stability of the separator is more excellent.

[0048] In some embodiments, the composite layer 2 includes second inorganic particles, polyethylene oxide, and cellulose.

[0049] Among them, polyethylene oxide is a crystalline and thermoplastic polymer, and its main functional group is an ether bond. In the infrared spectrum, at 1100 cm -1There are obvious characteristic peaks at [the relevant position]. In addition, a large number of hydroxyl groups are contained at the end of PEO, while the surface of the cellulose used in the present invention contains a large number of carboxyl groups, which can form hydrogen bonds with the hydroxyl groups of PEO. When used in combination, a tightly structured cross-linked structure can be formed. This cross-linked structure can not only lock the second inorganic particles on the surface of the base film 1, further reducing the thermal shrinkage performance of the base film 1; but also form a gel state in the electrolyte with good stability, which can keep Li + on both sides of the separator. Experiments have also proved that the separator with the composite layer 2 of the present invention has a high liquid absorption rate and liquid retention rate.

[0050] Specifically, the polyethylene oxide used is a high-molecular polyethylene oxide with a molecular weight of 500,000 to 600,000. The cellulose used is lignocellulose, which is an organic fiber material obtained by chemically treating and mechanically processing natural renewable wood, and is non-toxic, odorless, pollution-free, and non-radioactive. Among them, the lignocellulose includes at least one of softwood lignocellulose, hardwood lignocellulose, and herbaceous lignocellulose.

[0051] Preferably, the lignocellulose used is softwood lignocellulose, which has the characteristics of long fibers, a tight organizational structure, and a low content of miscellaneous cells (most of the miscellaneous cells in chemical pulp are lost during washing). Therefore, the pulp quality is good, and the mechanical properties of the formed finished product are strong. The softwood lignocellulose used in the present invention is used after ball milling. After ball milling, the fiber diameter can reach 1 nm, and the length is 0.5 - 1 μm. The surface of the ball-milled softwood lignocellulose has abundant hydroxyl functional groups, which are extremely easy to form hydrogen bonds and are more likely to form a cross-linked structure with PEO. In addition, the present invention preferably uses softwood lignocellulose in combination with PEO and inorganic particles, which can not only improve the liquid absorption rate, liquid retention rate, and thermal shrinkage resistance of the separator, but also use the softwood lignocellulose as the support layer of the separator, which can better ensure the integrity of the separator structure. Preferably, the mass ratio of cellulose in the composite layer 2 can be 10 - 50%, and the proportion within this range has a good effect on simultaneously improving the liquid absorption rate and liquid retention rate of the separator and serving as a support layer.

[0052] Preferably, the second inorganic particle is at least one of alumina, titanium dioxide, and silicon dioxide. The second inorganic particle can be the same substance as the first inorganic particle, and preferably both are alumina.

[0053] In some embodiments, the weight ratio of the second inorganic particles, polyethylene oxide, and cellulose is (4-8):(1-5):(1-5). By regulating the proportion of the three, the liquid absorption rate and liquid retention rate of the separator can be effectively improved, and the stability of the cross-linked structure can be avoided from being affected by too much or too little content of cellulose and polyethylene oxide. Experiments show that the separator still has a high liquid retention rate after 48 h. After being applied to the battery, the cycle performance of the battery is also greatly improved. Specifically, the weight ratio of the three includes but is not limited to 4:5:1, 5:4:1, 6:3:1, 7:2:1, 8:1:1, 4:4:2, 5:3:2, 6:2:2, 7:1:2, 4:3:3, 5:2:3, 6:1:3, 4:2:4, 5:1:4, or 5:5:5. Preferably, the weight ratio of the three is (4-7):(2-5):1. More preferably, the weight ratio of the three is 4:5:1, 5:4:1, 6:3:1, 7:2:1.

[0054] The preparation method of the above-mentioned separator includes the following steps:

[0055] S1. Modify the polyolefin-based membrane with polydopamine to obtain a modified polyolefin-based membrane;

[0056] S2. Immerse the modified polyolefin-based membrane in a solution containing support particles, take it out and dry it to obtain a polyolefin-based membrane with support particles filled in part of the pores, wherein the support particles include first inorganic particles with a melting point greater than or equal to 200 °C, and the preparation of the separator is completed.

[0057] In some embodiments, it further includes step S3: First, mix the second inorganic particles with a polyethylene oxide mixed solution to make solution a, and dissolve cellulose to make solution b; then stir and mix solution a and solution b to obtain a composite layer slurry; coat the composite layer slurry on at least one surface of the base membrane and dry it to complete the preparation of the separator. Separately preparing solutions of polyethylene oxide and cellulose and then mixing them results in a more uniform and stable cross-linked structure, which is more conducive to retaining Li + on both sides of the separator.

[0058] In addition, when the first inorganic particles and the second inorganic particles are both the same substance, and the binder is polyethylene oxide, solution a can also be used as the solution containing support particles, that is, the modified polyolefin-based membrane can be immersed in solution a, taken out and dried, and a polyolefin-based membrane with support particles filled in part of the pores can also be obtained. Preferably, the first inorganic particles and the second inorganic particles are both alumina, and the binder is polyethylene oxide. Such a combination has better compatibility between the base membrane and the composite layer, and is more conducive to stabilizing the overall structure of the separator.

[0059] A second aspect of the present invention aims to provide a secondary battery, comprising a positive electrode plate, a negative electrode plate, and a separator disposed between the positive electrode plate and the negative electrode plate, wherein the separator is the separator described in any one of the above.

[0060] In some embodiments, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer coated on at least one surface of the positive electrode current collector. The positive electrode active material may be one or more combinations of compounds represented by, but not limited to, the chemical formula such as Li x Ni h Co y M z O 2-d N d (where 0.95 ≤ x ≤ 1.2, h > 0, y ≥ 0, z ≥ 0, and h + y + z = 1, 0 ≤ d ≤ 1, M is selected from one or more combinations of Mn and Al, and N is selected from one or more combinations of F, P, and S), and the positive electrode active material may also be one or more combinations of, but not limited to, LiCoO 2 , LiNiO 2 , LiVO 2 , LiCrO 2 , LiMn 2 O 4 , LiCoMnO 4 , Li 2 NiMn 3 O 8 , LiNi 0.5 Mn 1.5 O 4 , LiCoPO 4 , LiMnPO 4 , LiFePO 4 , LiNiPO 4 , LiCoFSO 4 , CuS 2 , FeS 2 , MoS 2 , NiS, TiS 2 etc. The positive electrode active material may also be subjected to modification treatment. The methods for modifying the positive electrode active material should be known to those skilled in the art. For example, methods such as coating and doping can be used to modify the positive electrode active material, and the materials used for the modification treatment may be one or more combinations of, but not limited to, Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, W, etc. The positive electrode current collector can be various materials suitable for use as the positive electrode current collector of a lithium-ion battery in the art. For example, the positive electrode current collector may be, but not limited to, a metal foil, and more specifically, may be, but not limited to, an aluminum foil, etc.

[0061] The negative electrode plate includes a negative current collector and a negative active material layer coated on at least one surface of the negative current collector. The negative active material layer can be one or several of, including but not limited to, graphite, soft carbon, hard carbon, carbon fiber, mesocarbon microbeads, silicon-based materials, tin-based materials, lithium titanate, or other metals that can form alloys with lithium. Among them, the graphite can be selected from one or several of artificial graphite, natural graphite, and modified graphite; the silicon-based materials can be selected from one or several of elemental silicon, silicon oxides, silicon-carbon composites, and silicon alloys; the tin-based materials can be selected from one or several of elemental tin, tin oxides, and tin alloys. The negative current collector is usually a structure or part for collecting current, and the negative current collector can be various materials in the art suitable for use as the negative current collector of a lithium-ion battery. For example, the negative current collector can be, including but not limited to, metal foils, and more specifically can be, including but not limited to, copper foils, etc.

[0062] The secondary battery further includes an electrolyte, which includes an organic solvent, an electrolyte lithium salt, and an additive. Among them, the electrolyte lithium salt can be LiPF used in high-temperature electrolytes 6 and / or LiBOB; it can also be at least one of LiBF used in low-temperature electrolytes 4 , LiBOB, LiPF 6 ; it can also be at least one of LiBF used in overcharge-preventing electrolytes 4 , LiBOB, LiPF 6 , LiTFSI; it can also be at least one of LiClO 4 , LiAsF 6 , LiCF 3 SO 3 , LiN(CF 3 SO 2 ) 2 . The organic solvent can be cyclic carbonates, including PC and EC; it can also be chain carbonates, including DFC, DMC, or EMC; it can also be carboxylic acid esters, including MF, MA, EA, MP, etc. The additives include at least one of, including but not limited to, film-forming additives, conductive additives, flame retardant additives, overcharge-preventing additives, additives for controlling the content of H 2 O and HF in the electrolyte, additives for improving low-temperature performance, and multifunctional additives.

[0063] 3. Electrical device

[0064] A third aspect of the present invention aims to provide an electrical device, including the secondary battery described above.

[0065] The electrical device can be a vehicle, mobile phone, portable device, laptop computer, ship, spacecraft, electric toy, electric tool, etc. The vehicle can be a fuel vehicle, gas vehicle or new energy vehicle, and the new energy vehicle can be a pure electric vehicle, hybrid vehicle or range-extended vehicle, etc.; the spacecraft includes airplanes, rockets, space shuttles, spaceships, etc.; the electric toy includes fixed or mobile electric toys, such as game consoles, electric vehicle toys, electric ship toys, electric airplane toys, etc.; the electric tool includes metal cutting electric tools, grinding electric tools, assembly electric tools and railway electric tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact electric drills, concrete vibrators and electric planers, etc.

[0066] To make the technical solutions and advantages of the present invention clearer, the present invention and its beneficial effects will be further described in detail below in conjunction with specific embodiments and the accompanying drawings of the specification, but the embodiments of the present invention are not limited thereto.

[0067] Example 1

[0068] A separator includes a base film containing a number of pores, and a part of the pores are filled with support particles, and the support particles include first inorganic particles with a melting point greater than or equal to 200 °C.

[0069] Specifically, the base film in this embodiment is a polyolefin base film modified by polydopamine; the support particles are polyethylene oxide and alumina.

[0070] The method for modifying the polyolefin base film with polydopamine is as follows:

[0071] 1) Weigh 57 g of ammonium persulfate and place it in a 500 mL beaker to prepare a 0.5 mol / L ammonium persulfate solution. After stirring evenly, let it stand for use, denoted as solution A;

[0072] 2) Weigh 47.4 g of dopamine hydrochloride and place it in a 500 mL beaker to prepare a 0.5 mol / L dopamine solution. After stirring evenly, let it stand for use, denoted as solution B;

[0073] 3) Use syringes to suck 200 mL of each of solution A and solution B respectively, stir evenly and pour them into a petri dish, add dilute hydrochloric acid to adjust the pH = 4, stir evenly again and let it stand for use, denoted as solution C;

[0074] 4) Cut a polyethylene base film of a certain size of 20*20 cm, clamp it with a dovetail clip and completely immerse it in solution C. After standing at room temperature for 48 h, take it out, wash the surface with deionized water to remove the excess ions, and prepare a polyolefin base film modified by polydopamine with good hydrophilicity, and store it in a vacuum drying at 45 °C for standby.

[0075] The preparation method of the separator is as follows:

[0076] S1. Preparation of the solution containing support particles: First, weigh 0.6 g of polyethylene oxide (PEO) and pour it into a beaker. Then weigh 1.4 g of Al 2 O 3 powder, and add 100 mL of deionized water to prepare a 20 mg / mL PEO / Al 2 O 3 slurry, denoted as solution a;

[0077] S2. Take a petri dish with a diameter of 20 cm, suck 20 mL of solution a with a syringe and pour it into the petri dish. Immerse the polyolefin-based membrane modified with polydopamine in solution a. The modified polyolefin-based membrane has good hydrophilic properties and good compatibility with the PEO / Al 2 O 3 slurry. After immersing for 24 h, the PEO / Al 2 O 3 can fill a part of the pores of the polyolefin-based membrane. Take it out, wipe off the floating liquid on the surface, and dry it in a vacuum drying oven at 45 °C for standby to complete the preparation of the separator.

[0078] Example 2

[0079] The difference from Example 1 is the composition of the support particles. The mass ratio of PEO to Al 2 O 3 is 1:9.

[0080] The rest is the same as Example 1 and will not be elaborated here.

[0081] Example 3

[0082] The difference from Example 1 is the composition of the support particles. The mass ratio of PEO to Al 2 O 3 is 5:5.

[0083] The rest is the same as Example 1 and will not be elaborated here.

[0084] Example 4

[0085] The difference from Example 1 is the composition of the support particles. The support particles in this example are PEO and SiO 2 .

[0086] The rest is the same as Example 1 and will not be elaborated here.

[0087] Example 5

[0088] The difference from Example 1 is the composition of the support particles. The support particles in this example are PEO and TiO 2 .

[0089] The rest is the same as Example 1 and will not be elaborated here.

[0090] Example 6

[0091] Different from Example 1, the separator of this example further includes a composite layer, which is coated on one surface of the base film. The composite layer includes alumina, polyethylene oxide, and needle wood cellulose.

[0092] The preparation method of the separator is as follows:

[0093] S1. Preparation of the solution containing support particles: First, weigh 0.6 g of polyethylene oxide (PEO) and pour it into a beaker. Then weigh 1.4 g of Al 2 O 3 powder, and add 100 mL of deionized water to prepare a 20 mg / mL PEO / Al 2 O 3 slurry, denoted as solution a;

[0094] S2. Take a petri dish with a diameter of 20 cm, suck 20 mL of solution a with a syringe and pour it into the petri dish. Immerse the polyolefin-based film modified with polydopamine in solution a. The modified polyolefin-based film has good hydrophilic properties and good compatibility with the PEO / Al 2 O 3 slurry. After immersing for 24 h, the PEO / Al 2 O 3 can fill a part of the pores of the polyolefin-based film. Take it out, wipe off the floating liquid on the surface, and dry it in a vacuum drying oven at 45 °C for later use;

[0095] S3. Preparation of cellulose slurry: First, weigh 2 g of cellulose and place it in a ball milling tank, add 100 mL of deionized water, and ball mill it at a ball-to-material ratio of 50:1 at a rotation speed of 1032 r / min for 1 h, and then collect it for later use, denoted as solution b;

[0096] S4. Preparation of the composite layer slurry: Use a syringe to suck 2 mL of solution b and 18 mL of solution a, and stir them evenly in a 100 mL beaker to obtain the composite layer slurry;

[0097] S5. Coat the composite layer slurry on one surface of the base film prepared in step S2, with a coating thickness of 1 - 2 μm, and dry it at 60 °C to obtain the separator of this example.

[0098] The rest is the same as Example 1 and will not be elaborated here.

[0099] Example 7

[0100] Different from Example 6, the composite layer of this example is coated on the two opposite surfaces of the base film, that is, the structure of composite layer + base film + composite layer.

[0101] The rest is the same as Example 6 and will not be elaborated here.

[0102] Example 8

[0103] Differing from Example 7 is the composition of the composite layer.

[0104] In the composite layer of this example, the weight parts of alumina, polyethylene oxide, and softwood cellulose are 8 parts, 1 part, and 1 part respectively.

[0105] The rest is the same as in Example 7 and will not be elaborated here.

[0106] Example 9

[0107] Differing from Example 7 is the composition of the composite layer.

[0108] In the composite layer of this example, the weight parts of alumina, polyethylene oxide, and softwood cellulose are 7 parts, 2 parts, and 1 part respectively.

[0109] The rest is the same as in Example 7 and will not be elaborated here.

[0110] Example 10

[0111] Differing from Example 7 is the composition of the composite layer.

[0112] In the composite layer of this example, the weight parts of alumina, polyethylene oxide, and softwood cellulose are 5 parts, 4 parts, and 1 part respectively.

[0113] The rest is the same as in Example 7 and will not be elaborated here.

[0114] Example 11

[0115] Differing from Example 7 is the composition of the composite layer.

[0116] In the composite layer of this example, the weight parts of alumina, polyethylene oxide, and softwood cellulose are 4 parts, 5 parts, and 1 part respectively.

[0117] The rest is the same as in Example 7 and will not be elaborated here.

[0118] Example 12

[0119] Differing from Example 7 is the composition of the composite layer.

[0120] The composition of the composite layer in this example is silica, polyethylene oxide, and softwood cellulose.

[0121] The rest is the same as in Example 7 and will not be elaborated here.

[0122] Example 13

[0123] Differing from Example 7 is the composition of the composite layer.

[0124] The composition of the composite layer in this embodiment is titanium dioxide, polyethylene oxide and softwood cellulose.

[0125] The rest is the same as in Example 7 and will not be elaborated here.

[0126] Example 14

[0127] Differing from Example 7 is the composition of the composite layer.

[0128] The composition of the composite layer in this embodiment is alumina and polyethylene oxide, where the weight fraction of alumina is 7 parts and the weight fraction of polyethylene oxide is 3 parts.

[0129] Differing from Example 7 is the composition of the composite layer.

[0130] Example 15

[0131] Differing from Example 7 is the composition of the composite layer.

[0132] The composition of the composite layer in this embodiment is alumina and softwood cellulose, where the weight fraction of alumina is 7 parts and the weight fraction of softwood cellulose is 1 part.

[0133] Differing from Example 7 is the composition of the composite layer.

[0134] Example 16

[0135] Differing from Example 7 is the composition of the composite layer.

[0136] The composition of the composite layer in this embodiment is polyethylene oxide and softwood cellulose, where the weight fraction of polyethylene oxide is 3 parts and the weight fraction of softwood cellulose is 1 part.

[0137] Differing from Example 7 is the composition of the composite layer.

[0138] Comparative Example 1

[0139] This comparative example is an ordinary untreated polyethylene film.

[0140] Comparative Example 2

[0141] A separator, comprising a base film and composite layers coated on two opposite surfaces of the base film, wherein the base film is an untreated polyethylene film and the composite layer is a conventional PVDF / Al 2 O 3 ceramic coating.

[0142] The separators obtained from the above Examples 1 to 16 and Comparative Examples 1 to 2 were tested for the thermal shrinkage rate and liquid retention rate at 130 °C.

[0143] Liquid holding rate detection: Cut circular pieces of the same size, weigh them once, soak them in the electrolyte for 0.5 h, wipe off the floating liquid on the surface and then weigh them again to obtain the liquid absorption rate data. Then, let them stand at room temperature for 1 h, 2 h, 4 h, 8 h, 24 h, and 48 h respectively, and test their liquid holding rate data. The liquid absorption rate data is not listed in Table 1, and the 1 h liquid holding rate data can be referred to, and the two are similar.

[0144] The test results are shown in Table 1 below and Figure 3 as follows.

[0145] Table 1

[0146]

[0147]

[0148] From the result comparison of the above Examples 1-5 and Comparative Examples 1-2, it can be seen that by reconstructing the polyolefin separator and introducing inorganic particles into a part of the pores of the polyolefin separator, the thermal shrinkage of the polyolefin separator at 130 °C is effectively reduced. At the same time, from the comparison of Examples 1-5, it can also be seen that different mass ratios of the coupling agent to the inorganic particles also have a certain difference in the improvement of thermal shrinkage. This is mainly because relatively speaking, if the content of the coupling agent is relatively small, the inorganic particles are relatively easy to fall off and cannot better support the stability of the separator at high temperature; on the contrary, if the content of the coupling agent is relatively high, the proportion of inorganic particles will decrease, and of course, it cannot better support the stability of the separator at high temperature.

[0149] In addition, from the result comparison of Examples 1-5 and Examples 6-14, it can also be seen that by adding the composite layer of the present invention on the surface of the base film, the liquid absorption rate and liquid holding rate of the separator can be effectively enhanced. This is mainly because the cross-linked structure formed in the composite layer can intercept Li + on both sides of the separator, improving the liquid absorption rate and liquid holding rate of the separator and ensuring the cycle performance of the battery.

[0150] In addition, from the result comparison of Examples 7-14, it can also be seen that different compositions and contents in the composite layer also have a certain influence on the thermal shrinkage, liquid absorption rate and liquid holding rate of the separator. In particular, in Example 7, when alumina, polyethylene oxide and cellulose are simultaneously adjusted to the preferred ratio, compared with the conventional PVDF / Al 2 O 3 ceramic separator in Comparative Example 2, the thermal shrinkage, liquid absorption rate and liquid holding rate of the separator can be simultaneously greatly improved.

[0151] Continue to cut the separators obtained in Example 7 and Comparative Example 2 into 19 mm circular pieces with a slicing machine and apply them to button batteries. Refer to the conventional preparation method, which will not be elaborated here.

[0152] Cycling performance test of the button battery: At 25 °C, the button battery was charged at 1C and discharged at a rate of 1C, and a full charge and discharge cycling test was carried out. The test results are as Figure 4 shown.

[0153] It can be seen from Figure 4 that compared with the conventional PVDF / Al 2 O 3 ceramic separator in Comparative Example 2, the button battery in Example 7 of the present invention still has a high cycling capacity retention rate of up to 93% after 600 cycles. It can be seen that the present invention also effectively improves the cycling stability of the battery.

[0154] In summary, by reconstructing the base film structure and cooperating with the setting of the composite layer, the present invention can effectively improve the thermal shrinkage, liquid absorption rate and liquid retention rate of the separator, not only ensuring the safety of the battery, but also improving the cycling stability of the battery.

[0155] Based on the disclosure and teachings of the above specification, those skilled in the art to which the present invention pertains can also make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the above specific embodiments, and any obvious improvements, substitutions or variations made by those skilled in the art on the basis of the present invention fall within the protection scope of the present invention. In addition, although some specific terms are used in this specification, these terms are only for convenience of description and do not constitute any limitation to the present invention.

Claims

1. A separator, characterized in that, it comprises a base film having a plurality of pores, and a part of the pores are filled with support particles, and the support particles include first inorganic particles with a melting point greater than or equal to 200 °C; the base film is a polyolefin base film modified by polydopamine; the support particles further include a binder, and the mass ratio of the binder to the first inorganic particles is (1~5):(5~9); the binder is at least one of polyethylene oxide, polyvinyl alcohol, and polyvinylpyrrolidone; the first inorganic particles are at least one of alumina, titanium dioxide, and silica; it further includes a composite layer coated on at least one surface of the base film; the composite layer includes second inorganic particles, polyethylene oxide, and cellulose, and the weight ratio of the second inorganic particles, polyethylene oxide, and cellulose is (4~8):(1~5):(1~5); The method for modifying the polyolefin base film with polydopamine is as follows: 1) Dissolve ammonium persulfate to prepare an ammonium persulfate solution, stir evenly and then stand by, denoted as solution A; 2) Dissolve dopamine hydrochloride to prepare a dopamine hydrochloride solution, stir evenly and then stand by, denoted as solution B; 3) Mix solution A and solution B in a weight ratio of 1:1, stir evenly, pour into a petri dish, add dilute hydrochloric acid to adjust the pH to 4, stir evenly again and stand by, denoted as solution C; 4) Immerse the polyolefin base film completely in solution C, take it out after standing at room temperature for 36h~60h, wash the surface with deionized water to remove excess ions, and prepare a polyolefin base film modified by polydopamine with good hydrophilicity, and store it in vacuum drying for later use.

2. The separator according to claim 1, characterized in that, the second inorganic particles are at least one of alumina, titanium dioxide, and silica; the molecular weight of the polyethylene oxide is 500,000~600,000; the cellulose includes at least one of softwood lignocellulose, hardwood lignocellulose, and herbaceous lignocellulose.

3. The separator according to claim 1, characterized in that, The preparation method of the composite layer is as follows: first, mix and dissolve the second inorganic particles and polyethylene oxide to make solution a, and dissolve cellulose to make solution b; then stir and mix solution a and solution b to obtain a composite layer slurry; coat the composite layer slurry on at least one surface of the base film and dry it.

4. A secondary battery, comprising a positive electrode plate, a negative electrode plate, and a separator disposed between the positive electrode plate and the negative electrode plate, characterized in that, the separator is the separator according to any one of claims 1~3.

5. An electrical device, characterized in that, it includes the secondary battery according to claim 4.

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