Composite filtering membrane, preparation method thereof and filtering device

Abstract

The invention discloses a composite filtering membrane, a preparation method thereof and a filtering device. The composite filtration membrane comprises: a base membrane; the film layer is arranged on at least one side of the base film; the membrane layer comprises molecular sieve particles; the hydrophilic diaphragm is arranged on the side, away from the base membrane, of the membrane layer, and the hydrophilic diaphragm comprises a hydrophilic polymer. The membrane layer of the composite filter membrane provided by the embodiment of the invention contains the molecular sieve particles, so that the falling and pulverization of the molecular sieve particles during use are reduced, the influence of the falling and pulverization of the molecular sieve particles on the quality of the ionic liquid is reduced, the service life of the composite filter membrane is also prolonged, and the removal effect on the water content in the ionic liquid is improved. The filter device comprising the composite filter membrane also has corresponding advantages.

Description

Technical Field

[0001] The present application belongs to the technical field of battery electrolyte treatment, and in particular relates to a composite filter membrane, a preparation method thereof, and a filter device. Background Art

[0002] Ionic liquids are a special type of ionic compounds, which are mainly characterized by being liquid at room temperature or lower temperatures. The water content in ionic liquids can affect the chemical reactions, product purity, material stability, and electrochemical applications in ionic liquids.

[0003] When ionic liquids are used in battery electrolytes, the water present in the ionic liquids will cause serious side reactions during the use of the battery, thereby adversely affecting the stability, reliability and service life of the battery.

[0004] Therefore, how to efficiently and reliably remove trace water from ionic liquids is a problem that still needs to be solved. Summary of the invention

[0005] The present application provides a composite filter membrane and a preparation method and a filter device. The membrane layer of the composite filter membrane of the embodiment of the present application contains molecular sieve particles, which reduces the shedding and powdering of the molecular sieve particles during use, reduces the impact of the shedding and powdering of the molecular sieve particles on the quality of the ionic liquid, and also increases the service life of the composite filter membrane and improves the removal effect of the water content in the ionic liquid. The filter device containing the composite filter membrane also has corresponding advantages.

[0006] In a first aspect, the present application provides a composite filtration membrane, the composite filtration membrane comprising:

[0007] Basement membrane,

[0008] The membrane layer is disposed on at least one side of the base membrane; the membrane layer includes molecular sieve particles;

[0009] The hydrophilic membrane is arranged on the side of the membrane layer away from the base membrane; the hydrophilic membrane contains a hydrophilic polymer.

[0010] According to the embodiments of the present application, the base membrane is a porous base membrane known in the art. Molecular sieve particles refer to solid particles from a microscopic perspective. Molecular sieve particles are the main component of the membrane layer. Molecular sieve particles (abbreviated as molecular sieves or zeolites) are a porous material with a highly regular pore structure, which can selectively adsorb molecules or ions and has good thermal stability. Molecular sieves are usually made of silicon oxides or aluminum oxides and have different crystal structures and pore sizes. In the embodiments of the present application, different types of molecular sieves can be selected as needed,

[0011] According to the embodiments of the present application, a hydrophilic polymer is a type of polymer material with hydrophilic properties. Hydrophilicity means that it has hydrophilic groups, that is, it can attract and interact with water molecules. This property enables the hydrophilic polymer to be compatible with water molecules in a liquid environment and usually has excellent water absorption. The hydrophilic diaphragm also has good hydrophilicity in a liquid environment, and water molecules can pass through the hydrophilic diaphragm, and it has a good adsorption effect on water molecules.

[0012] The composite filtration membrane of the embodiments of the present application includes three layers, namely a base membrane, a membrane layer, and a hydrophilic diaphragm. The membrane layer containing molecular sieve particles is disposed between the base membrane and the hydrophilic diaphragm. Such a setting can inhibit the shedding of the molecular sieve particles in the membrane layer during use, reduce the pulverization of the molecular sieve particles and affect the quality of the ionic liquid, and also improve the service life of the composite filtration membrane.

[0013] The hydrophilic diaphragm is disposed on the surface of the molecular sieve particles. When using the composite filtration membrane to remove trace water in the ionic liquid, due to the good affinity of the hydrophilic polymer therein for the trace water, it is beneficial to adsorb the trace water in the ionic liquid and improve the effect of removing trace water.

[0014] In any embodiment of the present application, the thickness of the membrane layer is 0.1 mm to 2 mm.

[0015] According to the embodiments of the present application, the membrane layer with the above thickness is beneficial to reducing the overall thickness of the composite filtration membrane on the basis of providing a certain mechanical strength; when the composite filtration membrane with the above thickness filters the ionic liquid, it can reduce the probability of the membrane layer breaking and reduce the influence of the composite filtration membrane on the components of the ionic liquid; the thickness of the membrane layer within a suitable range ensures that it has a certain filtration efficiency.

[0016] In any embodiment of the present application, the ratio of the thickness of the base membrane to the thickness of the membrane layer is 1:(0.01 - 1), and can be selected as 1:(0.2 - 0.8).

[0017] According to the embodiments of the present application, controlling the ratio of the thickness of the base membrane to the thickness of the membrane layer within the above range can avoid the pulverization of the molecular sieve particles in the membrane layer on the basis of ensuring a certain mechanical strength of the composite filtration membrane and improve the service life of the composite filtration membrane.

[0018] In any embodiment of the present application, the molar ratio of silicon to aluminum in the molecular sieve particles is W:1, and W satisfies: 1 < W ≤ 3.5.

[0019] According to the embodiments of the present application, the molar ratio of silicon to aluminum can be understood as the molar ratio of silicon element to aluminum element. The molar ratio of silicon to aluminum in the molecular sieve particles within the above range makes it have a suitable pore size, which is convenient for removing trace water in the ionic liquid, especially the trace moisture contained in the electrolyte.

[0020] In any embodiment of the present application, the molecular sieve particles are attached with a soluble organic lithium salt.

[0021] According to an embodiment of the present application, the molecular sieve particles are attached with a soluble organic lithium salt, so the soluble organic lithium salt is included in the membrane layer. When the composite filtration membrane is in use, especially when used in the electrolyte of a lithium battery, the soluble organic lithium salt can have a strong coordination effect with the molecular sieve particles or the high-valent impurity metal ions in the electrolyte. The organic functional groups in the soluble organic lithium salt bind to the high-valent metal ions and simultaneously ionize lithium ions, thereby realizing the lithium supplement effect on the electrolyte.

[0022] In any embodiment of the present application, the soluble organic lithium salt includes one or more of lithium acrylate, lithium methacrylate, lithium 2-ethylacrylate, lithium 3-(4-fluorophenyl)-2-methylacrylate, and lithium 3-(3-hydroxyphenyl)-2-methylacrylate.

[0023] According to an embodiment of the present application, on the one hand, the soluble organic lithium salts of the above types have a certain bonding effect, which can enhance the bonding force between the molecular sieve particles. On the other hand, the functional group -COO- in the soluble organic lithium salts of the above types can have a strong coordination effect with the high-valent metal ions, with a strong binding force. When binding to the high-valent metal ions, lithium ions are simultaneously ionized to play a lithium supplement role.

[0024] When the composite filtration membrane is used, when the heavy metal ions in the electrolyte contact the soluble organic lithium salt in the molecular sieve particles, the heavy metal ions will undergo ion exchange with the lithium ions on the surface of the molecular sieve, thereby achieving the effect of the molecular sieve capturing the heavy metal ions. At the same time, the pores of the molecular sieve particles can also adsorb a certain amount of heavy metal ions.

[0025] In any embodiment of the present application, based on the total mass of the membrane layer, the membrane layer includes 0.1% to 1% of lithium element.

[0026] According to an embodiment of the present application, the membrane layer containing the lithium element with the above mass content is beneficial for providing lithium ions when removing trace water from the electrolyte of a lithium battery, increasing the lithium ion content in the electrolyte or reducing the influence of the composite filtration membrane on the lithium ion content in the electrolyte.

[0027] In any embodiment of the present application, the ratio of the thickness of the membrane layer to that of the hydrophilic separator is 1:(0.00005 - 0.001).

[0028] According to an embodiment of the present application, the ratio of the thickness of the membrane layer to that of the hydrophilic separator within the above range is beneficial for realizing the adsorption of water in the ionic liquid by utilizing the water adsorption effect of the hydrophilic separator, so that water molecules pass through the thinner hydrophilic separator and reach the membrane layer, improving the contact degree between the molecular sieve particles in the membrane layer and the ionic liquid, and reducing the water content in the ionic liquid.

[0029] In any embodiment of the present application, the thickness of the hydrophilic diaphragm is 0.01 to 0.1 μm.

[0030] According to the embodiments of the present application, when the thickness ratio of the membrane layer to the hydrophilic diaphragm is within the above range, it is beneficial to utilize the water adsorption effect of the hydrophilic diaphragm to adsorb the water in the ionic liquid, so that water molecules can pass through the thinner hydrophilic diaphragm to reach the bottom membrane layer, reducing the water content in the ionic liquid.

[0031] In any embodiment of the present application, the hydrophilic polymer includes hydrophilic groups; optionally, the hydrophilic groups include one or more of hydroxyl, carboxyl, and imino groups.

[0032] According to the embodiments of the present application, the hydrophilic polymer of the hydrophilic diaphragm includes hydrophilic groups. Having hydrophilic groups of the above types can improve the affinity between the hydrophilic diaphragm and the water in the electrolyte, thereby adsorbing trace water in the electrolyte by means of the hydrophilic groups and improving the removal effect of trace water in the electrolyte.

[0033] In any embodiment of the present application, the hydrophilic polymer of the hydrophilic diaphragm comprises one or more of natural cellulose, microcrystalline cellulose, ethyl cellulose, hydroxymethyl cellulose, carboxymethyl cellulose, and amino cellulose.

[0034] According to the embodiments of the present application, for the hydrophilic diaphragm composed of the above types, having hydrophilic groups of the above types can improve the affinity between the hydrophilic diaphragm and the water in the electrolyte, thereby adsorbing trace water in the electrolyte by means of the hydrophilic groups and improving the removal effect of trace water in the electrolyte.

[0035] In any embodiment of the present application, the thickness of the composite filter membrane is 1.1 mm to 12 mm.

[0036] According to the embodiments of the present application, controlling the thickness of the composite filter membrane within a suitable range is beneficial to improving the water adsorption rate of the composite filter membrane, and can further reduce the water content in the ionic liquid when using the composite filter membrane to treat the ionic liquid, improving the effect of removing water.

[0037] In any embodiment of the present application, the specific surface area of the composite filter membrane is 259 m 2 / g to 780 m 2 / g, and can be optionally 275 m 2 / g to 615 m 2 / g.

[0038] According to the embodiments of the present application, controlling the specific surface area of the composite filter membrane within a suitable range is beneficial to improving the water adsorption rate of the composite filter membrane, and can further reduce the water content in the ionic liquid when using the composite filter membrane to treat the ionic liquid, improving the effect of removing water.

[0039] In a second aspect, an embodiment of the present application provides a method for preparing a composite filtration membrane, the method comprising:

[0040] providing a slurry comprising molecular sieve particles;

[0041] The slurry forms a film layer on the surface of the base film;

[0042] The hydrophilic polymer is formed into a hydrophilic membrane on the side of the membrane layer away from the base membrane to obtain the composite filtration membrane of the first aspect.

[0043] According to the method of the embodiment of the present application, a composite filter membrane comprising a base membrane, a membrane layer, and a hydrophilic membrane is prepared. The membrane layer comprising molecular sieve particles is arranged between the base membrane and the hydrophilic membrane. Such an arrangement can inhibit the molecular sieve particles in the membrane layer from falling off during use, reduce the impact of molecular sieve particle pulverization on the quality of the ionic liquid, and also increase the service life of the composite filter membrane.

[0044] The hydrophilic membrane is arranged on the surface of the molecular sieve particles. When the composite filtration membrane is used to remove trace water in the ionic liquid, the hydrophilic polymer therein has good affinity for the trace water therein, which is conducive to adsorbing the trace water in the ionic liquid and improving the effect of removing trace water.

[0045] In any embodiment of the present application, the slurry includes a soluble organic lithium salt or a soluble organic lithium salt attached to molecular sieve particles.

[0046] According to an embodiment of the present application, a soluble organic lithium salt can be added to the slurry as a raw material alone. The soluble organic lithium salt can be added to the slurry together with the molecular sieve particles as a raw material as a part of the attachment of the molecular sieve particles. The slurry includes a soluble organic lithium salt, which is convenient for the composite filter membrane when it is used, especially when it is used in the electrolyte of a lithium battery. The soluble organic lithium salt can have a strong coordination effect with the molecular sieve particles or the high-valent impurity metal ions in the electrolyte. The organic functional groups in the soluble organic lithium salt bind to the high-valent metal ions and ionize the lithium ions at the same time, thereby achieving the lithium replenishment effect on the electrolyte. In addition, the soluble organic lithium salt has a certain bonding effect, which can improve the bonding force between the molecular sieve particles.

[0047] In any embodiment of the present application, forming a film layer on the surface of the base film by making the slurry include: forming a raw film layer on the surface of the base film by making the slurry; immersing the raw film layer in a solution containing a soluble lithium salt, forming a film layer after drying, and the mass fraction of the molecular sieve particles in the film layer is ≥97%.

[0048] According to the embodiments of the present application, immersing the raw material film layer into a solution containing a soluble lithium salt can cause the soluble lithium salt to adhere to the surface of the raw material film layer, facilitating the subsequent preferential strong coordination with the impurity metal ions in the high valence state in the ionic liquid, thereby better ionizing lithium ions and realizing the lithium supplementation effect on the electrolyte.

[0049] In any embodiment of the present application, the volume average particle size Dv50 of the molecular sieve particles is 0.5 to 10 μm.

[0050] According to the embodiments of the present application, when the volume average particle size Dv50 of the molecular sieve particles is within the above range, it is beneficial to form a uniform film layer, improve the effect of removing trace water in the ionic liquid, and reduce the trace water in the ionic liquid to a lower level.

[0051] In any embodiment of the present application, the specific surface area of the molecular sieve particles is 50 m 2 / g to 950 m 2 / g, and can be optionally 325 m 2 / g to 675 m 2 / g.

[0052] According to the embodiments of the present application, when the specific surface area of the molecular sieve particles is within the above range, it is beneficial to form a uniform film layer, improve the effect of removing trace water in the ionic liquid, and reduce the trace water in the ionic liquid to a lower level.

[0053] In any embodiment of the present application, the average pore diameter of the molecular sieve particles is 0.1 nm to 2 nm.

[0054] According to the embodiments of the present application, when the pore diameter of the molecular sieve particles is within the above range, on the basis of taking into account the filtration efficiency, it is beneficial to remove trace water in the ionic liquid.

[0055] In a third aspect, the embodiments of the present application provide a filtration device, including the composite filtration membrane of the first aspect or the composite filtration membrane prepared by the preparation method of the second aspect.

[0056] The filtration device of the embodiments of the present application includes a composite filtration membrane, thereby being able to inhibit the shedding of the molecular sieve particles during use, reduce the pulverization of the molecular sieve particles from affecting the quality of the ionic liquid, also improve the service life of the composite filtration membrane, improve the filtration efficiency and save costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 The structural schematic diagram of the composite filtration membrane of the embodiments of the present application is shown.

[0058] 1. Composite filtration membrane; 10. Base film; 20. Film layer; 30. Hydrophilic separator.

[0059] The drawings of the present application are not necessarily drawn to scale. Detailed implementation manners

[0060] In order to make the invention object, technical solution and beneficial technical effects of the present application clearer, the present application will be described in detail below in conjunction with specific embodiments. It should be understood that the embodiments described in this specification are only for explaining the present application and not for limiting the present application.

[0061] For simplicity, only some numerical ranges are explicitly disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, although not explicitly recited, each point or single value between the range endpoints is included in the range. Thus, each point or single value can be used as its own lower or upper limit and combined with any other point or single value or combined with other lower or upper limits to form a range not explicitly recited.

[0062] In the description herein, it should be noted that unless otherwise specified, "above" and "below" include this number, and the meaning of "several" in "one or several" is two or more.

[0063] The above-mentioned inventive content of the present application does not intend to describe every disclosed embodiment or every implementation manner in the present application. The following description more specifically exemplifies exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments, which can be used in various combinations. In each embodiment, the enumeration is only as a representative group and should not be construed as exhaustive.

[0064] Ionic Liquids are a special type of ionic compound, and their main feature is that they are in a liquid state at room temperature or lower temperatures. An electrolyte is an ionic liquid state.

[0065] Taking a battery as an example, the battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator disposed between the positive electrode plate and the negative electrode plate. The electrolyte usually contains ions, and these ions can be cations and anions. In a battery, the movement of positive and negative ions in the electrolyte generates an electric current, thereby generating electrical energy. Therefore, the performance of the electrolyte has an important impact on improving the stability, reliability, and service life of the battery cell.

[0066] The water content in the electrolyte has a great influence on the performance of the electrolyte. In addition, during the electrolysis process, the electrolyte allows ions to migrate between the electrodes, thereby promoting the electrochemical reaction of chemical substances to occur.

[0067] Trace water generally refers to a very small amount of water, usually measured in micrograms (μg) or nanograms (ng). Trace water in the electrolyte needs to be removed because trace water may have an adverse effect on the electrolysis process, especially in high-purity or high-sensitivity electrochemical reactions, and can improve the reliability of the battery containing the electrolyte. For example, the presence of trace water can increase the conductivity of the electrolyte, which may make the electric field in the electrolyte uneven and affect the rate of the electrode reaction.

[0068] In the related art, the molecular sieve method is generally used to remove trace water in the electrolyte. When the molecular sieve method is used to remove trace water in the ionic liquid, there are a series of problems. For example, the granular aluminosilicate molecular sieve has the risk of pulverization during use. The micron-sized aluminosilicate powder is easily introduced into the ionic liquid, causing contamination. At the same time, the molecular sieve will also ionize impure metal ions, affecting the ion content in the ionic liquid. For example, it can bind lithium ions and consume lithium ions in the electrolyte.

[0069] In view of this, an embodiment of the present application provides a composite filtration membrane to improve at least one of the above-mentioned problems.

[0070] Composite filtration membrane

[0071] In a first aspect, the present application provides a composite filtration membrane, the composite filtration membrane comprising:

[0072] Basement membrane,

[0073] The membrane layer is disposed on at least one side of the base membrane; the membrane layer includes molecular sieve particles;

[0074] The hydrophilic membrane is arranged on the side of the membrane layer away from the base membrane; the hydrophilic membrane contains a hydrophilic polymer.

[0075] According to an embodiment of the present application, the basement membrane is a porous film known in the art. The basement membrane can be used to support the membrane layer and the hydrophilic diaphragm, providing the necessary mechanical strength and structural stability for the composite filtration membrane. The porous basement membrane allows the liquid to be filtered (e.g., a battery electrolyte containing an ionic liquid) to pass through its pores from one side to the other side of the membrane, while preventing larger foreign matter from passing through the basement membrane.

[0076] The base membrane has a certain mechanical strength, can support the membrane layer and the hydrophilic diaphragm, and can also reduce the shedding of molecular sieve particles during use, reduce the pulverization of molecular sieve particles, avoid affecting the quality of the ionic liquid, and also increase the service life of the composite filter membrane. The present application does not impose obvious restrictions on the type of base membrane, and any base membrane that can achieve the purpose of the present application can be used.

[0077] According to the embodiments of the present application, a molecular sieve particle refers to a solid particle from a microscopic perspective. The molecular sieve particle is the main component of the membrane layer. A molecular sieve particle (abbreviated as molecular sieve or zeolite) is a porous material with a highly regular pore structure, which can selectively adsorb molecules or ions and has good thermal stability. Molecular sieves usually include silicon oxides or aluminum oxides and have different crystal structures and pore sizes. In the embodiments of the present application, different types of molecular sieves can be selected according to needs. For example, in some embodiments, the surface of the molecular sieve particle has hydroxyl groups.

[0078] According to the embodiments of the present application, a hydrophilic polymer is a type of polymer material with hydrophilic properties. Hydrophilicity means that it has hydrophilic groups, that is, it can attract and interact with water molecules. This property makes the hydrophilic polymer compatible with water molecules in a liquid environment and usually has excellent water absorption. The hydrophilic diaphragm also has good hydrophilicity in a liquid environment and has a good adsorption effect on water molecules.

[0079] The composite filtration membrane of the embodiments of the present application includes three layers, namely a base membrane, a membrane layer, and a hydrophilic diaphragm. The membrane layer containing molecular sieve particles is disposed between the base membrane and the hydrophilic diaphragm. Such an arrangement can inhibit the shedding of the molecular sieve particles in the membrane layer during use, reduce the pulverization of the molecular sieve particles and affect the quality of the ionic liquid, and also improve the service life of the composite filtration membrane.

[0080] The hydrophilic diaphragm is disposed on the surface of the molecular sieve particle. When using the composite filtration membrane to remove trace water in the ionic liquid, due to the good affinity of the hydrophilic polymer therein for the trace water, it is beneficial to adsorb the trace water in the ionic liquid and improve the effect of removing trace water.

[0081] The present application does not impose obvious restrictions on the type of the base membrane, and any base membrane that can achieve the purpose of the present application can be used. In some optional embodiments, the base membrane includes one or several of a ceramic membrane and an organic polymer membrane.

[0082] For example, the polymer in the organic polymer membrane can be cellulose, polyolefin, etc. For example, a base membrane obtained with a polyethylene-based polymer as the main polymer component can have good strength and toughness, thereby improving the reliability of the composite filtration membrane.

[0083] The present application does not impose obvious restrictions on the thickness of the base membrane, and any base membrane that can achieve the purpose of the present application can be used. In some optional embodiments, the thickness of the base membrane is 1 to 10 mm. Optionally, the thickness of the base membrane can be any value among 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm or a range composed of them.

[0084] On the basis of providing a certain mechanical strength, the base film with the above thickness is beneficial to reducing the overall thickness of the composite filtration membrane; when filtering ionic liquids, it avoids the influence on the components of ionic liquids caused by the breakage of the base film with a small thickness.

[0085] This application does not impose obvious restrictions on the average pore size of the base film, and any base film that can achieve the purpose of this application can be used. In some optional embodiments, the average pore size of the base film is 1 nm to 50 nm.

[0086] Optionally, the average pore size of the base film can be any value among 1 nm, 3 nm, 5 nm, 7 nm, 9 nm, 11 nm, 13 nm, 15 nm, 17 nm, 19 nm, 21 nm, 23 nm, 25 nm, 27 nm, 29 nm, 31 nm, 33 nm, 35 nm, 37 nm, 39 nm, 41 nm, 43 nm, 45 nm, 47 nm, 49 nm, 50 nm or the range composed of them.

[0087] According to the embodiments of this application, the base film with the above pore size can enable ionic liquids to pass through its pores smoothly, and at the same time can reduce the possibility that the pulverized molecular sieve particles in the film layer pass through the base film from one side of the base film and mix into the filtered ionic liquids, reducing the influence of the composite filtration membrane on the quality of ionic liquids.

[0088] In some optional embodiments, the thickness of the film layer is 0.1 to 2 mm. Optionally, the thickness of the film layer can be any value among 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, 1.5 mm, 2.0 mm or the range composed of them.

[0089] According to the embodiments of this application, the film layer with the above thickness is beneficial to reducing the overall thickness of the composite filtration membrane on the basis of providing a certain mechanical strength; when filtering ionic liquids, the film layer with the above thickness of the composite filtration membrane can reduce the probability of film layer rupture and reduce the influence of the composite filtration membrane on the components of ionic liquids; the thickness of the film layer within a suitable range ensures a certain filtration efficiency.

[0090] In some alternative embodiments, the ratio of the thickness of the base film to that of the film layer is 1:(0.01 - 1), and may be 1:(0.2 - 0.8). The ratio of the thickness of the base film to that of the film layer may be any value in the range of 1:0.01, 1:0.03, 1:0.05, 1:0.07, 1:0.09, 1:0.11, 1:0.13, 1:0.15, 1:0.17, 1:0.19, 1:0.21, 1:0.23, 1:0.25, 1:0.27, 1:0.29, 1:0.31, 1:0.33, 1:0.35, 1:0.50, 1:0.60, 1:0.70, 1:0.80, 1:0.90, 1:1 or any range composed of these values.

[0091] According to the embodiments of the present application, controlling the ratio of the thickness of the base film to that of the film layer within the above range can avoid the pulverization of the molecular sieve particles in the film layer while ensuring a certain mechanical strength of the composite filtration membrane, thereby improving the service life of the composite filtration membrane.

[0092] In some alternative embodiments, the chemical general formula of the molecular sieve particles is aM′ 2 O·bMO·Al 2 O 3 ·xSiO 2 ·yH 2 O. Optionally, M′ includes one or more of K and Na; optionally, M includes one or more of Ca and Ba; the value of a ranges from 1 / 3 to 1; the value of b ranges from 1 / 3 to 1; the value of x ranges from 3 to 7; the value of y ranges from 1 to 9.

[0093] According to the embodiments of the present application, the molecular sieve particles can be synthetic hydrated aluminosilicates (zeolites) or natural zeolites with the function of screening molecules. Molecular sieves with different pore sizes separate molecules of different sizes and shapes. Different pore-sized molecular sieves are obtained according to different molecular ratios of SiO 2 and Al 2 O 3 . Their models include: 3A (potassium A-type), 4A (sodium A-type), 5A (calcium A-type), 10Z (calcium Z-type), 13Z (sodium Z-type), Y (sodium Y-type), sodium mordenite type, etc. They have the characteristics of high adsorption capacity, strong selectivity, and high temperature resistance.

[0094] The structural general formula of the molecular sieve particles can be detected by commonly used methods in the art, such as using XRD or XPF to confirm the various oxides M’ 2 O, MO, SiO 2 and Al 2 O 3The content of water molecules. The content of water molecules can be obtained by TG test. XRD is the abbreviation of X-Ray Diffraction. It uses the diffraction phenomenon of X-rays in crystals to obtain the characteristics of the X-ray signal after diffraction, and the diffraction pattern is obtained after processing.

[0095] Thermogravimetry Analysis (abbreviated as TG or TGA) is to control the sample under a certain temperature program (heating / cooling / constant temperature), and observe the change process of the sample's mass with temperature or time.

[0096] In some alternative embodiments, the silicon-aluminum molar ratio of the molecular sieve particles is W:1, where W satisfies: 1 < W ≤ 3.5.

[0097] According to the embodiments of the present application, the silicon-aluminum molar ratio can be understood as the molar ratio of silicon element to aluminum element. When the silicon-aluminum molar ratio of the molecular sieve particles is within the above range, it has a suitable pore size, which is convenient for removing trace water in the ionic liquid, especially the trace moisture contained in the electrolyte.

[0098] The silicon-aluminum molar ratio of the molecular sieve particles can be detected by commonly used methods in the art, such as using XRD or XPF to confirm the molar content of each oxide SiO 2 and Al 2 O 3 in the molecular sieve.

[0099] In some alternative embodiments, the molecular sieve particles are attached with a soluble organic lithium salt.

[0100] According to the embodiments of the present application, when the composite filtration membrane is in use, especially when used in the electrolyte of a lithium battery, the soluble organic lithium salt can have a strong coordination effect with the molecular sieve particles or the high-valent impurity metal ions in the electrolyte. The organic functional groups in the soluble organic lithium salt bind the high-valent metal ions, and at the same time ionize lithium ions, thereby realizing the lithium supplement effect on the electrolyte.

[0101] In some alternative embodiments, the soluble organic lithium salt includes one or more of lithium acrylate, lithium methacrylate, lithium 2-ethylacrylate, lithium 3-(4-fluorophenyl)-2-methylacrylate, and lithium 3-(3-hydroxyphenyl)-2-methylacrylate.

[0102] According to the embodiments of the present application, on the one hand, the above-mentioned types of soluble organic lithium salts have a certain bonding effect, which can enhance the bonding force between the molecular sieve particles. On the other hand, the functional group -COO- in the above-mentioned types of soluble organic lithium salts can have a strong coordination effect with high-valent metal ions, with a strong binding force. When binding high-valent metal ions, lithium ions are ionized at the same time to play a lithium supplement role.

[0103] When using a composite filtration membrane, the heavy metal ions in the electrolyte come into contact with the soluble organic lithium salt in the molecular sieve particles. The heavy metal ions will undergo ion exchange with the lithium ions on the surface of the molecular sieve, thereby achieving the effect of the molecular sieve capturing heavy metal ions. At the same time, the pores of the molecular sieve particles can also absorb a certain amount of heavy metal ions, such as divalent iron ions, etc.

[0104] In some alternative embodiments, based on the total mass of the film layer, the film layer contains 0.1% to 1% of lithium element. Optionally, the film layer contains any value or a range composed thereof among 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0% of lithium element.

[0105] According to the embodiments of the present application, the film layer containing the lithium element in the above mass content is beneficial to providing lithium ions when removing trace water from the electrolyte for lithium batteries, increasing the lithium ion content in the electrolyte or reducing the influence of the composite filtration membrane on the lithium ion content in the electrolyte.

[0106] In some alternative embodiments, the film layer includes a binder. This binder helps the molecular sieve particles to form a film layer. In some embodiments, based on the total weight of the film layer, the film layer contains 0.01% to 1% by mass of the binder.

[0107] Optionally, based on the total weight of the film layer, the film layer contains any value or a range composed thereof among 0.01%, 0.06%, 0.11%, 0.16%, 0.21%, 0.26%, 0.31%, 0.36%, 0.41%, 0.46%, 0.51%, 0.56%, 0.61%, 0.66%, 0.71%, 0.76%, 0.81%, 0.86%, 0.91%, 0.96%, 1% by mass of the binder.

[0108] According to the embodiments of the present application, the inclusion of the binder in the film layer is beneficial to improving the adhesion between the molecular sieve particles in the film layer, reducing the pulverization of the molecular sieve particles, increasing the service life of the composite separator membrane, and reducing its influence on the quality of the ionic liquid.

[0109] In addition, controlling the mass content of the binder in the film layer within the above range is beneficial to improving the adhesion between the molecular sieve particles in the film layer, reducing the pulverization of the molecular sieve particles; and can also ensure the filtration efficiency of the ionic liquid.

[0110] In some alternative embodiments, in some embodiments, the negative electrode film layer may further optionally include a negative electrode binder. There is no particular limitation on the type of the binder in the embodiments of the present application. As an example, the negative electrode binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, aqueous acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0111] The binder may also include one or several of lithium acrylate, lithium methacrylate, lithium 2-ethylacrylate, lithium 3-(4-fluorophenyl)-2-methylacrylate, and lithium 3-(3-hydroxyphenyl)-2-methylacrylate. According to the embodiments of the present application, the binders of the above types have a certain bonding force, which can improve the bonding effect between molecular sieve particles.

[0112] In some alternative embodiments, the ratio of the thickness of the film layer to that of the hydrophilic separator is 1:(0.00005 - 0.001).

[0113] According to the embodiments of the present application, when the ratio of the thickness of the film layer to that of the hydrophilic separator is within the above range, it is beneficial to utilize the water adsorption effect of the hydrophilic separator to achieve the adsorption of water in the ionic liquid, so that water molecules can pass through the thinner hydrophilic separator and reach the film layer, improving the contact degree between the molecular sieve particles in the film layer and the ionic liquid, and reducing the water content in the ionic liquid.

[0114] According to the embodiments of the present application, the hydrophilic separator can be used to cover and fix the molecular sieve particles in the film layer. At the same time, the hydrophilic separator has good water affinity, which is beneficial to assisting the molecular sieve particles to adsorb trace water. It provides the necessary mechanical stability for the composite filtration membrane. In addition, the hydrophilic separator is a porous membrane, allowing the liquid to be filtered (e.g., the battery electrolyte containing ionic liquid) to pass through its pores from one side to the other side of the membrane, while preventing larger foreign objects from passing through the hydrophilic separator.

[0115] The present application does not impose obvious limitations on the composition type and thickness of the hydrophilic separator, and any base film that can achieve the purpose of the present application can be used.

[0116] In some alternative embodiments, the thickness of the hydrophilic separator is 0.01 - 0.1 μm. Optionally, the thickness of the hydrophilic separator can be any value among 0.01 μm, 0.02 μm, 0.03 μm, 0.04 μm, 0.05 μm, 0.06 μm, 0.07 μm, 0.08 μm, 0.09 μm, 0.1 μm or the range composed of them.

[0117] According to the embodiments of the present application, the thickness ratio of the film layer to the hydrophilic separator within the above range is beneficial to realizing the adsorption of water in the ionic liquid by utilizing the water adsorption effect of the hydrophilic separator, so that water molecules can pass through the relatively thin hydrophilic separator to reach the bottom film layer, reducing the water content in the ionic liquid.

[0118] In some alternative embodiments, the hydrophilic polymer of the hydrophilic separator includes hydrophilic groups; optionally, the hydrophilic groups include one or more of hydroxyl, carboxyl, and imino groups.

[0119] According to the embodiments of the present application, the hydrophilic polymer of the hydrophilic separator includes hydrophilic groups, and having hydrophilic groups of the above types can improve the affinity between the hydrophilic separator and water in the electrolyte, thereby adsorbing trace water in the electrolyte by using the hydrophilic groups and improving the removal effect of trace water in the electrolyte.

[0120] In some alternative embodiments, the hydrophilic polymer of the hydrophilic separator comprises one or more of natural cellulose, microcrystalline cellulose, ethyl cellulose, hydroxymethyl cellulose, carboxymethyl cellulose, and amino cellulose.

[0121] In some alternative embodiments, the thickness of the composite filter membrane is 1.1 mm to 12 mm. Optionally, the thickness of the composite filter membrane can be any value among 1.1 mm, 1.6 mm, 2.1 mm, 2.6 mm, 3.1 mm, 3.6 mm, 4.1 mm, 4.6 mm, 5.6 mm, 6.6 mm, 7.6 mm, 8.6 mm, 9.6 mm, 10.6 mm, 11.6 mm, 12 mm or the range composed thereof.

[0122] In some alternative embodiments, the specific surface area of the composite filter membrane is 259 m 2 / g to 780 m 2 / g, and can be optionally 275 m 2 / g to 615 m 2 / g.

[0123] Optionally, the specific surface area of the composite filter membrane can be 259 m 2 / g, 269 m 2 / g, 280 m 2 / g, 300 m 2 / g, 320 m 2 / g, 340 m 2 / g, 360 m 2 / g, 380 m 2 / g, 400 m 2 / g, 420 m 2 / g, 440 m 2 / g, 460 m 2 / g, 480 m 2 / g, 500 m 2 / g, 520 m 2 / g, 540 m 2 / g, 560 m 2 / g, 580 m 2 / g, 600 m 2 / g, 620 m 2 / g, 640 m 2 / g, 660 m 2 / g, 680 m 2 / g, 700 m 2 / g, 720 m 2 / g, 740 m 2 / g, 760 m 2 / g, 780 m 2 Any value in / g or the range composed of them.

[0124] According to the embodiments of the present application, controlling the thickness and specific surface area of the composite filtration membrane within a suitable range is beneficial to improving the water adsorption rate of the composite filtration membrane, and can further reduce the moisture in the ionic liquid when using the composite filtration membrane to treat the ionic liquid, and improve the effect of removing moisture.

[0125] The specific surface area of the composite filtration membrane can be measured by the gas adsorption method using a fully automatic specific surface area and micropore size analyzer of PMI Instruments in the United States. As an example, an appropriate amount of the separator membrane sample (about 100 mg) can be taken. The sample is placed in a sample tube, and its mass is recorded as m1 mg. The sample tube is installed on the degassing station, and the sample is heated and vacuum degassed to remove the gas adsorbed on the surface of the separator membrane. Subsequently, after the sample is cooled to room temperature, helium gas is backfilled to atmospheric pressure. The mass of the sample tube is weighed and recorded as m2 mg, and (m2 - m1) is the weight of the sample after degassing. Referring to the test standard GB / T 19587-2017, the sample tube is placed in a liquid nitrogen environment. After the sample tube is evacuated, helium gas is introduced into the sample tube and then evacuated, and the adsorption amount, adsorption-desorption isotherm, and BET surface area A of the sample at each partial pressure point are measured. Based on the adsorption-desorption isotherm, the capillary radius rk corresponding to capillary condensation at the abscissa P / P0 is calculated by the Kelvin formula. Under this P / P0 condition, all pores smaller than the rk value are filled with the adsorbate of capillary condensation. Therefore, the adsorption volume Vr corresponding to this relative pressure P / P0 on the adsorption isotherm is the total volume of all pores with a radius less than or equal to rk. The Vr-rk relationship curve is plotted, which is the integral distribution curve of pore volume versus pore radius. On the integral distribution curve, the volume ΔVr of the increase in adsorption amount when the pore radius increases by Δr is obtained by the graphical method, and ΔVr / Δr is calculated. Plotting ΔVr / Δr against rk gives the differential distribution curve of pore radius. The pore size value corresponding to the maximum point on the abscissa of the differential distribution curve is the maximum pore size of the separator membrane. Using the multi-molecular layer adsorption theory (BET theory), the average pore size of the separator membrane can be calculated by the formula d = 4V / A, where d represents the average pore size, V represents the total pore volume (the volume of the adsorbed gas converted into liquid), and A represents the BET surface area of the sample. [WZ1] National standard GB / T 19587-2017 Determination of specific surface area of solid substances by gas adsorption BET method.

[0126] In some alternative embodiments, the water adsorption rate of the composite filtration membrane is 97.5% to 99.8%.

[0127] Optionally, the water adsorption rate of the composite filtration membrane can be any value or a range composed of 97.5%, 97.7%, 97.9%, 98.1%, 98.3%, 98.5%, 98.7%, 98.9%, 99.1%, 99.3%, 99.5%, 99.7%.

[0128] According to the embodiments of the present application, the water adsorption rate of the composite filtration membrane is within the above range, indicating that the composite filtration membrane has good quality and is convenient for popularization and application.

[0129] In some optional embodiments, according to the weightlessness method, when the use period is 2 months, the wear rate of the composite filter membrane to the electrolyte is 0.01% to 0.1%. Optionally, the wear rate of the composite filter membrane to the electrolyte can be any value or a range of its composition among 0.01%, 0.06%, 0.11%, 0.16%, 0.21%, 0.26%, 0.31%, 0.36%, 0.41%, 0.46%, 0.51%, 0.56%, 0.61%, 0.66%, 0.71%, 0.76%, 0.81%, 0.86%, 0.91%, 0.96%, 1%.

[0130] According to the embodiments of the present application, the adsorption rate of water by the composite filtration membrane is within the above range, which indicates that the composite filtration membrane has good quality and is easy to promote and apply.

[0131] According to the embodiment of the present application, when the test is performed according to the weightlessness method, the test period of the composite filter membrane can be maintained for 1 to 3 months. When the adsorption rate is tested, the test is performed in an environment of 25-35°C. The electrolyte containing trace water is filtered through the multi-stage composite filter membrane at a flow rate of 5L / min.

[0132] Figure 1 The embodiment of the composite filtration membrane according to the present application is shown as an example. The composite filtration membrane 1 includes a base membrane 10, a membrane layer 20 laminated on any surface of the base membrane 10, and a hydrophilic membrane 30 disposed on the surface of the membrane layer. The base membrane 10, the membrane layer 20, and the hydrophilic membrane 30 can be the base membrane, the membrane layer, and the hydrophilic membrane described in any of the above embodiments. Figure 1 Only an example of providing the membrane layer 20 and the hydrophilic membrane 30 on one surface of the base membrane 10 is shown, but as another example, the composite filtration membrane may provide the above-mentioned membrane layer and hydrophilic membrane on the surfaces of opposite sides of the base membrane.

[0133] Preparation method of composite filtration membrane

[0134] In a second aspect, an embodiment of the present application provides a method for preparing a composite filtration membrane, the method comprising:

[0135] providing a slurry comprising molecular sieve particles;

[0136] The slurry forms a film layer on the surface of the base film;

[0137] The hydrophilic polymer is formed into a hydrophilic membrane on the side of the membrane layer away from the base membrane to obtain the composite filtration membrane of the first aspect.

[0138] According to the method of the embodiments of the present application, a composite filtration membrane including a base film, a film layer, and a hydrophilic separator is prepared. The film layer containing molecular sieve particles is disposed between the base film and the hydrophilic separator. Such an arrangement can inhibit the shedding of the molecular sieve particles in the film layer during use, reduce the pulverization of the molecular sieve particles and affect the quality of the ionic liquid, and also improve the service life of the composite filtration membrane.

[0139] The hydrophilic separator is disposed on the surface of the molecular sieve particles. When using the composite filtration membrane to remove trace water in the ionic liquid, due to the good affinity of the hydrophilic polymer therein for the trace water, it is beneficial to adsorb the trace water in the ionic liquid and improve the effect of removing trace water.

[0140] The base film, the film layer, and the hydrophilic separator of the embodiments of the present application and their constituent components can be the base film, the film layer, and the hydrophilic separator and their constituent components described in any of the above embodiments.

[0141] In some alternative embodiments, the slurry includes a soluble organic lithium salt or a molecular sieve particle-attached soluble organic lithium salt.

[0142] According to the embodiments of the present application, the soluble organic lithium salt can be added as a raw material alone to the slurry. The soluble organic lithium salt can be added to the slurry together with the molecular sieve particles as a part of the attachment of the molecular sieve particles. The slurry includes a soluble organic lithium salt, which facilitates the soluble organic lithium salt to have a strong coordination effect with the molecular sieve particles or the high-valent impurity metal ions in the electrolyte when the composite filtration membrane is used, especially when used in the electrolyte of a lithium battery. The organic functional groups in the soluble organic lithium salt bind to the high-valent metal ions and simultaneously ionize lithium ions, thereby realizing the lithium supplementation effect on the electrolyte. In addition, the soluble organic lithium salt has a certain bonding effect and can improve the bonding force between the molecular sieve particles.

[0143] In some alternative embodiments, forming a film layer of the slurry on the surface of the base film includes: forming a raw material film layer of the slurry on the surface of the base film; immersing the raw material film layer in a solution containing a soluble lithium salt and drying to form a film layer, and the mass fraction of the molecular sieve particles in the film layer ≥ 97%. Optionally, the mass fraction of the molecular sieve particles in the film layer can be any value or a range composed thereof among 97%, 97.5%, 98.0%, 98.5%, 99.0%, and 99.5%.

[0144] According to the embodiments of the present application, immersing the raw material film layer in a solution containing a soluble lithium salt can make the soluble lithium salt adhere to the surface of the raw material film layer, which is convenient for preferentially having a strong coordination effect with the high-valent impurity metal ions in the ionic liquid during subsequent use, thereby better ionizing lithium ions and realizing the lithium supplementation effect on the electrolyte.

[0145] In some embodiments, based on the total mass of the membrane layer, the membrane layer comprises a soluble lithium salt with a mass content of 0 to 3%.

[0146] According to the embodiments of the present application, the mass content of the soluble lithium salt in the membrane layer can be determined by sampling the membrane layer and then detecting the compounds contained therein by nuclear magnetic resonance.

[0147] In some alternative embodiments, the average particle size Dv50 of the molecular sieve particles is 0.5 to 10 μm. Optionally, the average particle size Dv50 of the molecular sieve particles can be any value among 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or a range composed thereof.

[0148] According to the embodiments of the present application, when the average particle size Dv50 of the molecular sieve particles is within the above range, it is beneficial to form a uniform membrane layer, improve the effect of removing trace water in the ionic liquid, and reduce the trace water in the ionic liquid to a lower level.

[0149] The particle size distribution D v 50 has the meaning well-known in the art and can be measured by instruments and methods well-known in the art. For example, it can be measured by a laser particle size analyzer, such as the Mastersizer 3000 type laser particle size analyzer of Malvern Instruments Limited in the UK.

[0150] In some alternative embodiments, the specific surface area of the molecular sieve particles is 50m 2 / g to 950m 2 / g, and can be optionally 325m 2 / g to 675m 2 / g.

[0151] According to the embodiments of the present application, when the specific surface area of the molecular sieve particles is within the above range, it is beneficial to form a uniform membrane layer, improve the effect of removing trace water in the ionic liquid, and reduce the trace water in the ionic liquid to a lower level.

[0152] The specific surface area of the molecular sieve particles has the meaning well-known in the art and can be measured by instruments and methods well-known in the art. For example, it can be measured with reference to the standard for the determination of the specific surface area of solid substances by the gas adsorption BET method in GB / T 19587-2004, tested by the nitrogen adsorption specific surface area analysis test method, and calculated by the BET (Brunauer Emmett Teller) method. Among them, the nitrogen adsorption specific surface area analysis test can be carried out by the Tri StarII 3020 type specific surface area and pore analyzer of Micromeritics Company in the United States.

[0153] In some alternative embodiments, the pore size of the molecular sieve particles is from 0.1 nm to 2 nm, and may be optionally from 0.35 nm to 0.42 nm.

[0154] According to the embodiments of the present application, when the pore size of the molecular sieve particles is within the above range, it is beneficial to remove trace water in the ionic liquid while taking into account the filtration efficiency.

[0155] In some alternative embodiments, when forming a membrane layer on the surface of the base membrane with the slurry, the drying temperature is 100 °C to 150 °C, and the time is 1 h to 3 h.

[0156] According to the embodiments of the present application, the molecular sieve in the membrane layer can be dried at the above drying temperature and time. While taking into account the production efficiency, the surface flatness of the base membrane and the molecular sieve particles is maintained to achieve drying.

[0157] In some alternative embodiments, when forming a nanocrystalline cellulose membrane on the side of the membrane layer facing away from the base membrane with the cellulose solution, the cellulose solution includes one or more of natural cellulose and microcrystalline cellulose; optionally, the mass concentration of the cellulose solution is 50% to 75%; optionally, the cellulose solution includes one or more of water, acetone, and N-methylpyrrolidone.

[0158] According to the embodiments of the present application, using the above types of hydrophilic polymers, hydrophilic polymer concentrations, and solvents of the above types to prepare the nanocrystalline cellulose membrane, the nanocrystalline cellulose of the nanocrystalline cellulose membrane is hydrophilic, so it helps the molecular sieve particles interact with water. It can be prepared into an extremely thin membrane with a nanoscale pore structure, which can provide more surface area for the adsorption and fixation of molecular sieve particles, thereby improving the adsorption capacity and efficiency of the molecular sieve; it can also achieve precise control of the pore size and pore distribution; it has excellent mechanical strength and can maintain the structural stability and durability in various applications.

[0159] In some alternative embodiments, when forming a hydrophilic separator on the side of the membrane layer facing away from the base membrane, the drying temperature is 100 °C to 150 °C, and the drying time is 1 h to 3 h.

[0160] According to the embodiments of the present application, the hydrophilic polymer can be dried at the above drying temperature and time. While taking into account the production efficiency, the surface flatness of the hydrophilic separator and the stability of the related pore distribution are maintained to achieve drying.

[0161] Filter device

[0162] In a third aspect, the embodiments of the present application provide a filter device, including the composite filter membrane of the first aspect or the composite filter membrane prepared by the preparation method of the second aspect.

[0163] For example, in the pipeline filtration device of the commercially available Chris Filtration Technology Co., Ltd., the pipeline through which the electrolyte passes is provided with multiple-stage filtration composite membranes of the embodiments of the present application, so as to industrially remove trace water in the electrolyte.

[0164] The filtration device in the embodiments of the present application can use the composite filtration membrane of the embodiments of the present application to replace the existing filtration membrane for use.

[0165] The filtration device of the embodiments of the present application includes a composite filtration membrane, which can inhibit the shedding of molecular sieve particles during use, reduce the pulverization of molecular sieve particles and affect the quality of ionic liquids, and also improve the service life of the composite filtration membrane, improve the filtration efficiency and save costs.

[0166] The filtration device of the embodiments of the present application includes a composite filtration membrane, which can achieve multi-stage filtration of the electrolyte, and the multi-stage filtration can be 2 to 5 stages of filtration.

[0167] When the electrolyte passes through the composite filtration membrane of the first stage of the embodiments of the present application, the filtration device includes a real-time monitoring component that can real-time monitor the water content in the electrolyte. If the water content is qualified, it directly flows to the next process for use. If the detected water content in the electrolyte is unqualified, it passes through the composite filtration membrane of the next stage, the second stage of the embodiments of the present application, and real-time monitors the water content. It can also pass through the composite filtration membrane of the next stage, the third stage of the embodiments of the present application, until the water content is qualified and then directly flows to the next process for use.

[0168] When the composite filtration membrane of the present application is in use, there is no clear limitation on the type of ionic liquid. The ionic liquid can be an electrolyte solution. There is no specific limitation on the type of electrolyte solution, and it can be selected according to requirements. The electrolyte solution includes an electrolyte salt and a solvent. Among them, the specific types of the electrolyte salt and the solvent are not specifically limited and can be selected according to actual needs.

[0169] When the battery cell of the present application is a lithium-ion battery, preferably, the electrolyte salt can be selected from LiPF 6 (lithium hexafluorophosphate), LiBF 4 (lithium tetrafluoroborate), LiClO 4 (lithium perchlorate), LiAsF 6 (lithium hexafluoroarsenate), LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiBOB (lithium bis(oxalato)borate), LiPO 2 F 2 (lithium difluorophosphate), LiDFOP (lithium difluoro bis(oxalato)phosphate) and LiTFOP (lithium tetrafluoro bis(oxalato)phosphate), or one or more of them.

[0170] When the battery cell of the present application is a sodium-ion battery, preferably, the electrolyte salt can be selected from NaPF 6 , NaClO 4 , NaBCl 4 , NaSO 3 CF 3 and Na(CH 3 )C 6 H 4 SO 3 , or one or more of them.

[0171] In the battery cell of the present application, preferably, the solvent can be one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE).

[0172] The electrolyte may also optionally include additives, and there is no specific limitation on the types of additives, which can be selected according to requirements. For example, the additives can include negative electrode film-forming additives, or can include positive electrode film-forming additives, or can also include additives that can improve certain battery performances, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature performance of the battery, additives for improving the low-temperature performance of the battery, etc.

[0173] Examples

[0174] The following examples more specifically describe the content disclosed in the present application. These examples are only for illustrative purposes, because various modifications and changes within the scope of the content disclosed in the present application are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the examples are all commercially available. The cellulose-based film and ceramic-based film in the base film in the examples of the present application are respectively from products of Beijing Huaxia Yuanyang Technology Co., Ltd. and Shandong Guoci Company.

[0175] Example 1

[0176] Preparation of the composite filtration membrane:

[0177] (1) Mix 100 g of molecular sieve particles containing SiO 2 :Al 2 O 3 . In the molecular sieve, the molar ratio of SiO 2 :Al 2 O 3 is 5:1, the average particle size DV50 of the molecular sieve is 1 μm, the average pore diameter of the molecular sieve is 0.35 nm, and the specific surface area of the molecular sieve particles is 595 m 2 / g.

[0178] (2) Mix the molecular sieve particles with a mixed solution of water and ethanol, where water and ethanol are mixed at a volume ratio of 4:1 to make a slurry with a solid content of 40%. Then directly coat it on the surface of a ceramic-based membrane from Shandong Guoci Company. The main component of the ceramic-based membrane is zirconia. Then dry it at a temperature of 100 °C for 2 h to obtain a porous ceramic molecular sieve;

[0179] (3) Spray an aqueous solution with a mass concentration of 55% of the cellulose solution on the surface of the porous ceramic molecular sieve and dry it at 110 °C for 3 h to obtain a composite filtration membrane.

[0180] The usage method of the composite filtration membrane includes: passing an electrolyte containing trace water through the composite filtration membrane prepared in the embodiment of the present application along the thickness direction of the composite filtration membrane at a flow rate of 5 L / min for filtration.

[0181] Example 2-1

[0182] Preparation of the composite filtration membrane:

[0183] (1) Mix 100 g of molecular sieve containing SiO 2 :Al 2 O 3 in a lithium acrylate solution. In the molecular sieve, the molar ratio of SiO 2 :Al 2 O 3 is 5:1, the average particle size DV50 of the molecular sieve is 1 μm, the concentration of lithium acrylate in the lithium acrylate solution is 3%, and the solvent in the lithium acrylate solution is acetone. Put the above 100 g of molecular sieve into a lithium acrylate solution with a total mass of 150 g, and obtain pre-lithiated high-aluminum-silica-ratio molecular sieve through drying;

[0184] (2) Mix the pre-lithiated high-aluminum-silica-ratio molecular sieve obtained in step (1) with a mixed solution of water and ethanol with a mass ratio of 4:1 to make a slurry with a solid content of 40%. Then directly coat it on the surface of a ceramic-based membrane from Shandong Guoci Company, and then dry it at a temperature of 100 °C for 2 h;

[0185] (3) Spray an aqueous cellulose solution with a solids content of 10% on the surface of the porous ceramic sheet molecular sieve, and dry it at 110 °C for 3 hours to obtain a composite filtration membrane.

[0186] Examples 2-2 to 2-8

[0187] Different from Example 2-1, the types of soluble organic lithium salts in Examples 2-2 to 2-5 are different, and the mass content of soluble lithium salts in the membrane layer in Examples 2-6 to 2-7 is different.

[0188] Examples 3-1 to 3-3

[0189] Different from Example 2-1, the volume average particle size Dv50 of the molecular sieve particles is different.

[0190] Example 3a

[0191] Different from Example 2-1, the type of the base membrane is different.

[0192] Examples 4-1 to 4-2

[0193] Different from Example 3a, the type of the hydrophilic separator is different, and the thickness of the base membrane is different.

[0194] Examples 4-3 to 4-6

[0195] Different from Example 2-1, the thickness of the membrane layer in Examples 4-3 to 4-4 is different; the thickness of the hydrophilic separator in Examples 4-5 to 4-6 is different.

[0196] Examples 5-1 to 5-3

[0197] Different from Example 2-1, by adjusting the type of the molecular sieve particles, the specific surface area and thickness of the composite filtration membrane are different. In Example 5-1, the molar ratio of SiO 2 : Al 2 O 3 in the molecular sieve particles is 6:1; in Example 5-2, the molar ratio of SiO 2 : Al 2 O 3 in the molecular sieve particles is 4.5:1; in Example 5-3, the molar ratio of SiO 2 : Al 2 O 3 in the molecular sieve particles is 3.5:1. The membrane layer in Examples 5-1 to 5-5 does not contain soluble organic lithium salts.

[0198] Comparative Example 1

[0199] A commercially available filtration product composed only of molecular sieve particles is adopted. It is from Guangzhou Xinci Environmental Protection Materials Co., Ltd. The average pore size of the molecular sieve product is 0.5 nm. The particle size of the molecular sieve particles is 10 microns.

[0200] Comparative Example 2

[0201] Different from Example 1, this composite filtration membrane does not contain a hydrophilic diaphragm. It is only composed of two layers.

[0202] Test section

[0203] The molecular sieve particles and the composite filtration membrane are tested by the test method described above.

[0204] 1. Electrolyte water removal test:

[0205] The composite filtration membranes prepared by the examples and comparative examples of this application are used to carry out water removal performance tests on the electrolyte for lithium-ion batteries. The initial water content of the electrolyte is 20 ppm. The components of the electrolyte include: dimethyl carbonate (DMC) and diethyl carbonate (DEC), and their volume ratio is 5:1. The lithium salt therein is lithium hexafluorophosphate, and the concentration is 10 g / L. Using the composite filtration membranes prepared by the examples and Comparative Example 2 of this application, the electrolyte containing trace water is filtered through the prepared composite filtration membranes in multiple stages at a flow rate of 5 L / min. The multiple stages of this test method refer to three-stage filtration. Using a commercially available pipeline filtration device, when the electrolyte passes through the composite filtration membrane prepared in the first stage of this application and then through the composite filtration membrane of the next stage, the second stage of the example of this application, the water content is monitored in real time. It can also pass through the composite filtration membrane of the third stage of the next stage of the example of this application until the water content is qualified and directly flow to the next process for use.

[0206] The molecular sieve particles in Comparative Example 1 are placed in the electrolyte, and then the electrolyte is filtered, and then the trace water content in the electrolyte is detected.

[0207] The detection method of water content adopts the Karl Fischer moisture test. The specific detection method is:

[0208] 1). Solvent ratio:

[0209] 30 ml of anhydrous methanol and formamide are configured in a ratio of 2:1 and added to the reaction cup.

[0210] 2). Sample treatment:

[0211] Use a 1 ml syringe without a needle to take about 0.5 ml of the sample to be tested.

[0212] 3). Measurement and result calculation:

[0213] ① Use the "blanking" function in the instrument to react the water in the solvent.

[0214] ② Use a 10 μL syringe to take 10 μL of pure water and calibrate the Karl Fischer reagent in the "Calibration" function of the instrument. Repeat 3 - 5 times, and the instrument will automatically calculate the average value of the calibration.

[0215] ③ Enter the measurement interface. Weigh the prepared sample on the balance and inject it into the reaction cup. Then weigh the syringe again after injecting the sample on the balance. Enter the sample weight to start the measurement. The measurement will end in about 2 minutes. After the measurement ends, the instrument will automatically calculate the result and save it. Repeat this process 3 - 5 times.

[0216] 2. Wear rate detection: Calculate its loss rate by the weighing method and observe whether the surface of the composite filter membrane is damaged by using a CCD: For wear rate detection, weigh the composite filter membrane with a weight of m1. Use it for a certain period of time. In this embodiment of the present application, it is used for 2 months. Take it out, wash it with NMP solvent for 1 h, then dry it at 125 °C for 2 h, and after cooling to room temperature, weigh its weight as m2;

[0217] Wear rate = (m1 - m2) / m1 * 100%

[0218] CCD-assisted test, directly take photos with the CCD to detect the surface flatness of the composite membrane

[0219] 3. Detection method for heavy metal ion content: The electrolyte may contain iron ions, copper ions, zinc ions, and lithium ions; Use the composite filter membranes prepared in this embodiment and the comparative example for filtration. After the filtration and detection are completed, detect the mass content of iron ions, copper ions, zinc ions, and lithium ions in the electrolyte. In this detection method, the components of the electrolyte include: dimethyl carbonate (DMC) and diethyl carbonate (DEC), and their volume ratio is 5:1. The lithium salt therein is lithium hexafluorophosphate with a concentration of 10 g / L. The electrolyte contains 15 ppm of divalent iron ion content. After filtration, the test method for the divalent iron ion content is directly detected by ICP.

[0220]

[0221]

[0222] The data in Table 1 show that the composite filter membrane in the embodiment has a good effect on removing trace water in the electrolyte, and it is wear-resistant. After using the composite filter membrane of this embodiment of the present application, the content of divalent iron ions therein is relatively low, and it has a good effect on adsorbing heavy metal ions.

[0223] Compared with Comparative Example 1 and Comparative Example 2, the examples all have good effects on removing trace water in the electrolyte. In Comparative Example 1, the molecular sieve particles were added in a blocky form, and its effect on removing trace water was relatively low, and its adsorption effect on heavy metal ions was also relatively low. In Comparative Example 2, there was only a base film and a film layer, and its effect on removing trace water was limited, and there was a certain risk of powdering.

[0224] The data in Table 2 show that the composite filter membrane in the examples controls the type of molecular sieve particles and their content (film layer thickness) in the film layer, making the composite filter membrane have different film thicknesses and specific surface areas, and also realizes the removal of water in the electrolyte, has a better wear rate, is relatively durable, and is convenient for industrial application.

[0225] The above is only the specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present application can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A composite filtration membrane, characterized in that, it comprises: a base membrane, a membrane layer disposed on at least one side of the base membrane; the membrane layer comprises molecular sieve particles; a hydrophilic separator disposed on the side of the membrane layer facing away from the base membrane, the hydrophilic separator comprising a hydrophilic polymer.

2. The composite filtration membrane according to claim 1, characterized in that, the molar ratio of silicon to aluminum in the molecular sieve particles is W:1, where W satisfies: 1 < W ≤ 3.

5.

3. The composite filtration membrane according to claim 1 or 2, characterized in that, the molecular sieve particles are attached with a soluble organic lithium salt; optionally, the soluble organic lithium salt comprises one or more of lithium acrylate, lithium methacrylate, lithium 2-ethylacrylate, lithium 3-(4-fluorophenyl)-2-methylacrylate, lithium 3-(3-hydroxyphenyl)-2-methylacrylate.

4. The composite filtration membrane according to any one of claims 1 to 3, characterized in that, based on the total mass of the membrane layer, the membrane layer comprises 0.1% to 1% of lithium element.

5. The composite filtration membrane according to any one of claims 1 to 4, characterized in that, the hydrophilic polymer comprises hydrophilic groups; optionally, the hydrophilic groups comprise one or more of hydroxyl groups, carboxyl groups, and imino groups.

6. The composite filtration membrane according to any one of claims 1 to 5, characterized in that, the hydrophilic polymer comprises one or more of natural cellulose, microcrystalline cellulose, ethyl cellulose, hydroxymethyl cellulose, carboxymethyl cellulose, and amino cellulose.

7. The composite filtration membrane according to any one of claims 1 to 6, characterized in that, the membrane layer satisfies at least one of the following conditions: 1) The ratio of the thickness of the base membrane to the thickness of the membrane layer is 1:(0.01 - 1), optionally 1:(0.2 - 0.8); 2) The thickness of the membrane layer is 0.1 mm to 2 mm; 3) The ratio of the thickness of the membrane layer to the thickness of the hydrophilic separator is 1:(0.00005 - 0.001).

8. The composite filtration membrane according to any one of claims 1 to 7, wherein, the composite filtration membrane satisfies at least one of the following conditions: 1) The specific surface area of the composite filtration membrane is 259 m 2 / g to 780 m 2 / g, and it can be optionally 275 m 2 / g to 615 m 2 / g; 2) The average thickness of the composite filtration membrane is 1.1 mm to 12 mm.

9. A method for preparing a composite filtration membrane, characterized in that, the method comprises: providing a slurry containing molecular sieve particles; forming a membrane layer from the slurry on the surface of the base membrane; forming a hydrophilic separator from the hydrophilic polymer on the side of the membrane layer facing away from the base membrane to obtain the composite filtration membrane.

10. The preparation method according to claim 9, characterized in that, the slurry comprises a soluble organic lithium salt or the molecular sieve particles are attached with a soluble organic lithium salt.

11. The preparation method according to claim 10, characterized in that, forming a membrane layer from the slurry on the surface of the base membrane comprises: coating the slurry on the surface of the base membrane to form a raw material membrane layer; immersing the raw material membrane layer into a solution containing a soluble lithium salt and drying to form the membrane layer, and the mass fraction of the molecular sieve particles in the membrane layer ≥ 97%.

12. The preparation method according to claim 10 or 11, wherein, The molecular sieve particles satisfy at least one of the following conditions: 1) The volume average particle size Dv50 of the molecular sieve particles is 0.5 to 10 μm. 2) The specific surface area of the molecular sieve particles is 50 m 2 / g to 950 m 2 / g, and can be optionally 325 m 2 / g to 675 m 2 / g; 3) The average pore size of the molecular sieve particles is from 0.1 nm to 2 nm.

13. A filtration device comprising the composite filtration membrane according to any one of claims 1-5 or the composite filtration membrane prepared by the preparation method according to any one of claims 9-12.

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