Diaphragm and lithium ion battery

Abstract

The invention provides a diaphragm and a lithium ion battery. The diaphragm comprises a first coating, a polymer matrix membrane and a second coating which are sequentially stacked, wherein the first coating contains a modified or unmodified molecular sieve; and the second coating contains a modified or unmodified lithium supplement agent. The first coating contains a modified or unmodified molecular sieve, and the pore structure and the large specific surface area of the molecular sieve provide more adsorption sites for the electrolyte, so that the electrolyte can be more uniformly and stably distributed on the diaphragm, thereby being beneficial to optimizing the conduction path of lithium ions, improving the electrochemical performance of the battery, and prolonging the service life of the battery. Particularly, the performance under a high-rate charge-discharge condition is realized. And the second coating contains the modified or unmodified lithium supplement agent, so that the effect of lossless lithium supplement for the battery can be achieved, and the charge-discharge capacity of the battery can be improved. The diaphragm provided by the invention maintains the original mechanical strength and thermal stability of the polymer matrix membrane while improving the wettability of an electrolyte and providing a lossless lithium supplement function.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and more particularly, to a separator and a lithium-ion battery. Background Art

[0002] The separator, as an important component of a lithium-ion battery, mainly functions to prevent direct contact between the positive and negative electrodes to ensure the safety of the battery, and to allow and promote the conduction of lithium ions to ensure the efficient operation of the battery. Therefore, both the electrical performance and safety performance of lithium-ion batteries are strongly related to the performance of the separator.

[0003] Currently, common lithium-ion separators are mostly polyolefin separators based on polyethylene (PE) or polypropylene (PP). Such separators have the advantages of low cost, good flexibility, high mechanical strength, etc. In addition, their self-insulation and rich pore structure endow them with the property of conducting ions but not electrons. However, due to the relatively low melting point of polyolefin materials, the separator is prone to thermal shrinkage, resulting in short circuit between the positive and negative electrodes, thus triggering thermal safety problems. In addition, the hydrophobic property of polyolefin materials also leads to poor wetting performance of the electrolyte on the separator, thereby affecting the conduction of lithium ions on it and further affecting the electrical performance of the battery.

[0004] To address the above problems, it is usually adopted to coat inorganic particles such as alumina and boehmite on the surface of polyolefin separators to improve the thermal stability, hydrophilicity and liquid absorption rate of the separator. However, the improvement of such materials on performance still needs to be enhanced. For example, the Chinese patent application with the patent application number 202111664559.0 provides a preparation of a coating film containing lithium salt and molecular sieve coated on the polyolefin surface. The molecular sieve has a specific surface area and pore volume far exceeding those of alumina and boehmite. Coating it on the separator can improve the wettability and liquid retention ability of the separator to the electrolyte, thereby enhancing the cycle performance of the battery. However, this separator has a single function and limited improvement on battery performance. The Chinese patent application with the patent application number 202210446299.8 provides a non-destructive lithium compensation composite separator, which can reduce the decomposition potential of organic lithium compensation materials such as lithium oxalate and lithium carbonate to about 4.2V. However, the de-lithiation potential is still very high, resulting in a low de-lithiation capacity. In addition, in lithium iron phosphate manganese batteries, due to the Jahn-Teller effect, manganese in the cathode material continuously dissolves and deposits on the anode surface, causing the continuous decomposition and regeneration of the SEI film on the anode surface and continuously consuming active lithium, thereby reducing the battery cycle performance. In summary, in order to meet the growing energy demand, it is particularly important to develop separator materials with multiple functions for improving the cycle life and energy density of lithium-ion batteries. Summary of the Invention

[0005] The main object of the present invention is to provide a separator and a lithium-ion battery to solve the problems in the prior art that the separator has a relatively low liquid retention rate and limited improvement in the rate performance and cycle performance of the battery.

[0006] To achieve the above object, according to one aspect of the present invention, a separator is provided, which includes a first coating, a polymer matrix film, and a second coating stacked in sequence; wherein, the first coating contains modified or unmodified molecular sieve; the second coating contains modified or unmodified lithium supplement agent.

[0007] Further, the mass ratio of the modified or unmodified molecular sieve in the first coating is 50-96%; and / or, the mass ratio of the modified or unmodified lithium supplement agent in the second coating is 68-94%.

[0008] Further, the specific surface area of the modified or unmodified molecular sieve is not less than 500m 2 / g; and / or, the D50 particle size of the modified or unmodified lithium supplement agent is 0.8-1.3μm.

[0009] Further, the modified molecular sieve is a molecular sieve loaded with a metal chelating agent; preferably, the mass ratio of the metal chelating agent in the molecular sieve loaded with the metal chelating agent is 10-40%; and / or, the modified lithium supplement agent is a lithium supplement agent coated with a carbon material; preferably, the mass ratio of the carbon material in the lithium supplement agent coated with the carbon material is 2-6%.

[0010] Further, the metal chelating agent is an amino carboxylic acid-based metal chelating agent and / or a hydroxy carboxylic acid-based metal chelating agent; preferably, the amino carboxylic acid-based metal chelating agent is selected from any one or more of ethylenediaminetetraacetic acid, nitrilotriacetic acid, and nitrilotriacetate; and / or, the hydroxy carboxylic acid-based metal chelating agent is selected from any one or more of citric acid, tartaric acid, gluconic acid, N-(2-hydroxyethyl)ethylenediamine-N,N',N'-triacetic acid, and bis(2-hydroxyethyl)glycine; further preferably, the metal chelating agent is ethylenediaminetetraacetic acid; and / or, the carbon material is selected from any one or more of carbon nanotubes, carbon nanofibers, graphene, and conductive carbon black; preferably, the carbon material is carbon nanotubes, and the average diameter of the carbon nanotubes is 1-3nm, and the average length is 5-10μm.

[0011] Further, the thicknesses of the first coating and the second coating are each independently 1-5μm, preferably 2-4μm.

[0012] Further, the molecular sieve is selected from any one or more of MCM series molecular sieves, SBA series molecular sieves, Y molecular sieves, and Beta molecular sieves; preferably, the MCM series molecular sieves are selected from any one or more of MCM-49 molecular sieve, MCM-41 molecular sieve, and MCM-22 molecular sieve; and / or, the SBA series molecular sieves are SBA-15 molecular sieve and / or SBA-16 molecular sieve; further preferably, the molecular sieve is MCM-41 molecular sieve; and / or, the lithium supplement agent is selected from Li 2 C 2O 4 、 Li 2 C 4 O 4 、 Li 2 C 3 O 5 and Li 2 C 4 O 6 any one or more of; preferably, the lithium supplement agent is Li 2 C 2 O 4 ; and / or, the polymer matrix film is a polyolefin matrix film; preferably, the material of the polyolefin matrix film is selected from any one or more of polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, poly-1-hexene, poly-1-octene, and polymethyl methacrylate.

[0013] Furthermore, the first coating further contains a first binder and a dispersant, and the mass ratio of the modified or unmodified molecular sieve, the first binder, and the dispersant is (15-40):(1-10):(1-5), preferably (30-40):(3-6):(1-3); and / or, the second coating further contains a second binder and a conductive agent, and the mass ratio of the modified or unmodified lithium supplement agent, the second binder, and the conductive agent is (30-60):(2-7):(2-7), preferably (50-60):(3-6):(3-6).

[0014] Furthermore, the first binder is an aqueous binder; preferably, the aqueous binder is selected from any one or more of polyacrylate and its derivatives, styrene-butadiene rubber, polyvinyl alcohol and its derivatives, polyvinyl acetate, polyacrylic acid, and carboxymethyl cellulose; and / or, the dispersant is a water-soluble surfactant; preferably, the water-soluble surfactant is selected from any one or more of sodium α-allyl sulfonate, sodium dodecyl sulfate, sodium lauryl polyoxyethylene ether sulfate, coconut diethanolamide, sodium dodecylbenzenesulfonate, ethoxylated alkyl sulfate, and dodecyl dimethyl betaine; and / or, the second binder is selected from any one or more of polyvinylidene fluoride, polyvinylidene difluoride, polyacrylic acid, polyvinyl alcohol, polyimide, carboxymethyl cellulose, sodium carboxymethyl cellulose, sodium alginate, and styrene-butadiene rubber; and / or, the conductive agent is selected from any one or more of conductive carbon black, conductive graphite, acetylene black, carbon nanotubes, carbon nanofibers, and graphene.

[0015] According to another aspect of the present invention, a lithium-ion battery is provided, including a positive electrode sheet, a separator, an electrolyte, and a negative electrode sheet, and the separator is the aforementioned separator.

[0016] Applying the technical solution of the present invention, the first coating contains modified or unmodified molecular sieve. Due to its ultra-high specific surface area and pore volume, it can significantly improve the wettability of the separator to the electrolyte and the liquid retention capacity. The pore structure and large specific surface area of the molecular sieve provide more adsorption sites for the electrolyte, enabling the electrolyte to be more evenly and stably distributed on the separator, which helps to optimize the lithium-ion conduction path and improve the electrochemical performance of the battery, especially its performance under high-rate charge and discharge conditions. The second coating contains modified or unmodified lithium supplement agent, which can achieve the effect of non-destructively supplementing lithium for the battery, thus helping to improve the charge and discharge capacity of the battery. Through the above design, while improving the wettability of the electrolyte and providing the function of non-destructive lithium supplementation, the separator of the present application also maintains the original mechanical strength and thermal stability of the polymer matrix membrane. Therefore, using the separator of the present application to assemble the battery core can effectively improve the cycle performance and rate performance of the battery core. Description of the Drawings

[0017] The specification drawings forming a part of the present application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0018] Figure 1 Shows the charge and discharge curves of the batteries assembled in Example 1 and Comparative Example 2 of the present application at 0.33C. Detailed Embodiments

[0019] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the drawings and in conjunction with the embodiments.

[0020] As analyzed in the background art of the present application, there are problems in the prior art that the separator has a relatively low liquid retention rate and is relatively limited in improving the rate performance and cycle performance of the battery. To solve the above problems, the present application provides a separator and a lithium-ion battery.

[0021] In a typical embodiment of the present application, a separator is provided. The separator includes a first coating, a polymer matrix membrane, and a second coating stacked in sequence; wherein, the first coating contains modified or unmodified molecular sieve; the second coating contains modified or unmodified lithium supplement agent.

[0022] The first coating contains modified or unmodified molecular sieves. Due to their ultra-high specific surface area and pore volume, they can significantly improve the wettability of the separator to the electrolyte and the liquid retention ability. The pore structure and large specific surface area of the molecular sieve provide more adsorption sites for the electrolyte, enabling the electrolyte to be more evenly and stably distributed on the separator, which helps to optimize the conduction path of lithium ions and improve the electrochemical performance of the battery, especially under high-rate charge and discharge conditions. The second coating contains modified or unmodified lithium supplement agents, which can achieve the effect of non-destructively supplementing lithium for the battery, thus helping to improve the charge and discharge capacity of the battery. Through the above design, the separator of the present application not only improves the wettability of the electrolyte and provides the function of non-destructive lithium supplementation, but also maintains the original mechanical strength and thermal stability of the polymer matrix film. Therefore, using the separator of the present application to assemble the battery cell can effectively improve the cycle performance and rate performance of the battery cell.

[0023] In one embodiment of the present application, the mass ratio of the modified or unmodified molecular sieve in the first coating is 50-96%, specifically it can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 96% and the range values between any two values; and / or, the mass ratio of the modified or unmodified lithium supplement agent in the second coating is 68-94%, specifically it can be 68%, 75%, 80%, 85%, 90%, 94% and the range values between any two values.

[0024] Controlling the mass ratio of the modified or unmodified molecular sieve in the first coating within the above range helps to provide more adsorption sites, enhance the wettability of the electrolyte, improve the ionic conductivity of the battery, and at the same time helps to improve the stability of the first coating. Controlling the mass ratio of the modified or unmodified lithium supplement agent in the second coating within the above range helps to provide more lithium ions. Especially during the first charge, it can compensate for the lithium loss in the first cycle of the positive electrode material, help to improve the first efficiency of the battery, and at the same time can also provide supplementation for the lithium ions consumed during subsequent cycle processes, help to further improve the cycle performance of the battery, and at the same time helps to improve the stability of the second coating.

[0025] In one embodiment of the present application, the specific surface area of the modified or unmodified molecular sieve is not less than 500m 2 / g, preferably 520-910m 2 / g; and / or, the D50 particle size of the modified or unmodified lithium supplement agent is 0.8-1.3μm, specifically it can be 0.8μm, 0.9μm, 1.0μm, 1.1μm, 1.2μm, 1.3μm and the range values between any two values.

[0026] Molecular sieves with a high specific surface area can provide more adsorption sites, which enables the separator to more effectively adsorb and retain the electrolyte, thereby improving the wettability and liquid retention rate of the electrolyte. This enhanced adsorption capacity helps to improve the lithium-ion transport efficiency, especially under high-rate charge and discharge conditions, and can maintain the stability and efficiency of the battery. Controlling the D50 particle size of the modified or unmodified lithium supplement agent within the above range helps to increase its surface activity and improve the contact area with the electrolyte and active materials, thus promoting the lithium-ion replenishment process. Especially during the first charge, this highly efficient lithium supplementation can effectively compensate for the first-cycle lithium loss of the cathode material and improve the first charge-discharge efficiency of the battery.

[0027] In one embodiment of the present application, the above-mentioned modified molecular sieve is a molecular sieve loaded with a metal chelating agent; preferably, the mass ratio of the metal chelating agent in the molecular sieve loaded with the metal chelating agent is 10-40%, specifically it can be 10%, 15%, 20%, 25%, 30%, 35%, 40% and the range values between any two values; and / or, the modified lithium supplement agent is a lithium supplement agent coated with a carbon material; preferably, the mass ratio of the carbon material in the lithium supplement agent coated with the carbon material is 2-6%, specifically it can be 2%, 3%, 4%, 5%, 6% and the range values between any two values.

[0028] The metal chelating agent on the molecular sieve loaded with the metal chelating agent can capture metal ions dissolved from the cathode, especially manganese ions, which can effectively improve the problem that manganese ions continuously dissolve and deposit on the surface of the anode, reducing the battery cycle performance. Controlling the mass ratio of the metal chelating agent in the molecular sieve loaded with the metal chelating agent within the above range helps to optimize the binding strength between the metal chelating agent and the molecular sieve, improve the stability of the metal chelating agent in the pore channels of the molecular sieve, and thus helps to improve the capture stability and efficiency of metal ions. Using a lithium supplement agent coated with a carbon material helps to lower the decomposition potential of the lithium supplement agent. Controlling the mass ratio of the carbon material in the lithium supplement agent coated with the carbon material within the above range helps to enable the composite of the carbon material and the lithium supplement agent to form a good conductive network, reduce the electron insulation, and enable the lithium supplement agent to start decomposing at a lower potential, releasing lithium ions, thereby achieving lossless lithium supplementation and improving the battery cycle performance.

[0029] In an embodiment of the present application, the above metal chelating agent is an amino carboxylic acid-based metal chelating agent and / or a hydroxy carboxylic acid-based metal chelating agent; preferably, the amino carboxylic acid-based metal chelating agent is selected from any one or more of ethylenediaminetetraacetic acid, nitrilotriacetic acid, and nitrilotriacetate; and / or, the hydroxy carboxylic acid-based metal chelating agent is selected from any one or more of citric acid, tartaric acid, gluconic acid, hydroxyethyl ethylenediaminetriacetic acid, and dihydroxyethylglycine; further preferably, the metal chelating agent is ethylenediaminetetraacetic acid; and / or, the carbon material is selected from any one or more of carbon nanotubes, carbon nanofibers, graphene, and conductive carbon black; preferably, the carbon material is carbon nanotubes, and the average diameter of the carbon nanotubes is 1-3 nm, and the average length is 5-10 μm.

[0030] Preferably, an amino carboxylic acid-based metal chelating agent is used, especially ethylenediaminetetraacetic acid, which has a strong metal ion capture ability and can effectively capture the metal ions dissolved in the positive electrode material, especially manganese ions, reduce their deposition on the negative electrode surface, and reduce the instability of the SEI film and the consumption of active lithium, thereby improving the cycle performance of the battery. Selecting an amino carboxylic acid-based or hydroxy carboxylic acid-based metal chelating agent, especially EDTA, can form a stable bond inside the molecular sieve. The multi-functional group characteristics of EDTA enable it to form multi-point chelation with the active sites on the surface of the molecular sieve, which not only enhances the stability of the chelating agent but also improves the capture efficiency of metal ions. The hydrophilic groups contained in the above types of metal chelating agents help to improve the affinity of the molecular sieve coating for the electrolyte, thereby improving the wetting and retention ability of the electrolyte and enhancing the electrochemical performance of the battery. Using a carbon material, especially carbon nanotubes (CNT), to modify the lithium supplement agent, the conductivity of CNT can significantly reduce the decomposition potential and the initial activation energy barrier of the lithium supplement agent, improve its charging capacity, and further enhance the overall performance of the battery. Controlling the average diameter and average length of the carbon nanotubes within the above ranges, such dimensions can provide a larger specific surface area, enhance the interaction between the carbon nanotubes and the lithium supplement agent, and thus help to promote electron transfer and improve the lithium supplement effect.

[0031] In an embodiment of the present application, the thicknesses of the above first coating and second coating are each independently 1-5 μm, preferably 2-4 μm.

[0032] If the coating is too thick, it will increase the lithium ion transport resistance and reduce the rate performance and energy density of the battery; while if the coating is too thin, it may not provide sufficient electrolyte retention ability and lithium supplement ability. Controlling the thickness of the first coating within the above range helps the separator to better adsorb and retain the electrolyte, improve the liquid retention rate of the battery, and further improve the cycle performance and overall stability of the battery. Controlling the thickness of the second coating within the above range helps to efficiently release lithium ions, supplement the lithium loss in the first cycle of the positive electrode material, and improve the first charge-discharge efficiency and cycle stability of the battery.

[0033] In one embodiment of the present application, the above-mentioned molecular sieve is selected from any one or more of MCM series molecular sieves, SBA series molecular sieves, Y molecular sieves and Beta molecular sieves; preferably, the MCM series molecular sieve is selected from any one or more of MCM-49 molecular sieve, MCM-41 molecular sieve and MCM-22 molecular sieve; and / or, the SBA series molecular sieve is SBA-15 molecular sieve and / or SBA-16 molecular sieve; further preferably, the molecular sieve is MCM-41 molecular sieve; and / or, the lithium supplement agent is selected from Li 2 C 2 O 4 、Li 2 C 4 O 4 、Li 2 C 3 O 5 and Li 2 C 4 O 6 and any one or more of the following; preferably, the lithium supplement agent is Li 2 C 2 O 4 ; and / or, the polymer matrix film is a polyolefin matrix film; preferably, the material of the polyolefin matrix film is selected from any one or more of polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, poly-1-hexene, poly-1-octene and polymethyl methacrylate.

[0034] MCM series molecular sieves, SBA series molecular sieves, Y molecular sieves and Beta molecular sieves have unique mesoporous structures and high specific surface areas, which can provide more pores and adsorption sites to adsorb and retain the electrolyte, thereby improving the wettability and liquid retention ability of the electrolyte. MCM-41 molecular sieve is particularly preferred because of its uniform pore size distribution, moderate pore size, which can more effectively promote the transport of lithium ions, and its high thermal stability and chemical stability enable the separator to maintain stable functions during battery operation. Its high pore structure and specific surface area provide more binding sites for metal chelating agents, thereby enhancing the ability of the separator to capture metal ions (such as manganese ions) dissolved from the positive electrode material. The preferred lithium supplement agent is Li 2 C 2 O 4 , compared with other lithium supplement agents, it can release more lithium ions during the decomposition process, and its decomposition potential is lower, so it can start releasing lithium ions earlier, achieving a more efficient lithium supplement effect. Controlling the type of the polymer matrix film within the above range helps to enrich the material selectivity.

[0035] In an embodiment of the present application, the first coating further contains a first binder and a dispersant, and the mass ratio of the modified or unmodified molecular sieve, the first binder and the dispersant is (15-40):(1-10):(1-5), preferably (30-40):(3-6):(1-3); and / or, the second coating further contains a second binder and a conductive agent, and the mass ratio of the modified or unmodified lithium supplementing agent, the second binder and the conductive agent is (30-60):(2-7):(2-7), preferably (50-60):(3-6):(3-6).

[0036] Controlling the mass ratio of the modified or unmodified molecular sieve, the first binder and the dispersant within the above range helps to form a uniform and stable first coating and improve the bonding strength between the first coating and the polymer matrix film. Controlling the mass ratio of the modified or unmodified lithium supplementing agent, the second binder and the conductive agent within the above range helps to construct a stable conductive network, reduce the decomposition potential of the lithium supplementing agent, and improve the lithium supplementing capacity and battery cycling performance.

[0037] To improve the lithium ion transport ability and stability of the separator, in an embodiment of the present application, it is preferred that the first binder is an aqueous binder; preferably, the aqueous binder is selected from any one or more of polyacrylate and its derivatives, styrene-butadiene rubber, polyvinyl alcohol and its derivatives, polyvinyl acetate, polyacrylic acid, and carboxymethyl cellulose; and / or, the dispersant is a water-soluble surfactant; preferably, the water-soluble surfactant is selected from any one or more of sodium α-allylsulfonate, sodium dodecyl sulfate, sodium lauryl polyoxyethylene ether sulfate, coconut diethanolamide, sodium dodecylbenzenesulfonate, ethoxylated alkyl sodium sulfate, and dodecyl dimethyl betaine; and / or, the second binder is selected from any one or more of polyvinylidene fluoride, polyvinylidene difluoride, polyacrylic acid, polyvinyl alcohol, polyimide, carboxymethyl cellulose, sodium carboxymethyl cellulose, sodium alginate, and styrene-butadiene rubber; and / or, the conductive agent is selected from any one or more of conductive carbon black, conductive graphite, acetylene black, carbon nanotubes, carbon nanofibers, and graphene.

[0038] In a typical embodiment of the present application, a method for preparing a molecular sieve loaded with a metal chelating agent is provided: by the equal-volume impregnation method, a certain amount of metal chelating agent is dispersed in a solvent to prepare a solution with a certain concentration, stirred magnetically for 30 min after dissolution, and then the molecular sieve with the liquid absorption measured is impregnated in the solution, left overnight at room temperature, and dried at 100 °C for 12 h to obtain a molecular sieve loaded with a metal chelating agent.

[0039] The method for measuring the liquid absorption capacity of the molecular sieve is as follows: Put the molecular sieve into an oven and dry it at 110 °C for 2 h. Then weigh a certain amount of the dried molecular sieve and place it in a beaker. Gradually add distilled water drop by drop with a burette until the carrier just reaches saturation. At this time, stop adding distilled water and weigh it. The mass difference between the two weighings is the liquid absorption capacity of the molecular sieve.

[0040] In a typical embodiment of the present application, a method for preparing a lithium supplement agent coated with a carbon material is provided: Dissolve an organic acid and lithium carbonate in an equimolar ratio in deionized water. Stir the resulting mixture at room temperature for 1 - 3 h, preferably 2 h, to obtain a lithium supplement agent solution. Subsequently, add a certain amount of carbon material to the solution and continue stirring for 1 h. Then pour the solution into a spray dryer and prepare a lithium supplement agent coated with a carbon material with a smaller particle size under the equipment conditions of a certain temperature and speed. The equipment conditions for pouring the solution into the spray dryer to prepare the lithium supplement agent particles coated with a carbon material are: the temperature is 100 - 300 °C, and the feeding speed is 1 - 30 mL / min. More preferably, the temperature is 150 - 250 °C; the speed is 5 - 25 mL / min. Most preferably, the temperature is 200 °C and the speed is 20 mL / min. The lithium supplement agent coated with a carbon material prepared under these conditions has the best sphericity and the smallest and uniform particle size and distribution.

[0041] In a typical embodiment of the present application, a method for preparing a separator is provided: Disperse the modified or unmodified molecular sieve, the first binder, and the dispersant in water to form a coating slurry A; Disperse the modified or unmodified lithium supplement agent, the second binder, and the conductive agent in an organic solvent to form a coating slurry B; Uniformly coat the above coating slurry A on the A side of the polymer matrix film, and then uniformly coat the above coating slurry B on the B side of the polymer matrix film. After drying, a separator is obtained.

[0042] In another typical embodiment of the present application, a lithium-ion battery is provided, which includes a positive electrode sheet, a separator, an electrolyte, and a negative electrode sheet. The separator is the aforementioned separator.

[0043] Since the above lithium-ion battery contains the separator of the present application, therefore, the lithium-ion battery has high rate performance and cycle stability.

[0044] In yet another typical embodiment of the present application, a method for preparing a lithium-ion battery is provided: disposing the above-mentioned separator between the positive electrode material and the negative electrode material (for example, assembling in the order of positive electrode material-separator-negative electrode material or negative electrode material-separator-positive electrode material); laminating the layered component including the positive electrode material, the separator, and the negative electrode material to obtain a dry battery cell; placing the dry battery cell into a battery casing; injecting an electrolyte. Through processes such as encapsulation, baking, liquid injection, and formation, a finished lithium-ion battery can be manufactured. The prepared battery has a capacity of 10 Ah and an operating voltage of 2.75 - 4.3 V. Among them, the positive electrode material can be obtained in the following manner: mixing lithium iron phosphate manganese as the active positive electrode material, a conductive agent, a dispersant, and a binder in a mass ratio of 95.3:2.5:0.2:2 in a solvent (N-methylpyrrolidone) to form a positive electrode slurry; uniformly coating the positive electrode slurry on both sides of an aluminum foil through a coating device; drying the positive electrode slurry on the plate through an oven to remove the solvent; rolling and slicing the positive electrode material on the plate for standby; the negative electrode material can be obtained in the following manner: mixing the negative active material, conductive agent SP, thickening agent (carboxymethyl cellulose), and adhesive (styrene-butadiene rubber) in a mass ratio of 96.5:0.5:1.8:1.2 in a solvent (deionized water) to form a negative electrode slurry; uniformly coating the negative electrode slurry on both sides of a plate (such as a copper foil) through a coating device; drying the negative electrode slurry on the plate through an oven to remove the solvent; cold pressing and slicing the negative electrode material on the plate for standby. The electrolyte is a special type of electrolyte matching the above system.

[0045] The beneficial effects of the present application will be further described below in conjunction with embodiments.

[0046] Example 1

[0047] Preparation method of molecular sieve loaded with metal chelating agent (EDTA / MCM-41): After dissolving the metal chelating agent in water, add the molecular sieve and stir at 25 °C for 12 h, and finally dry at 100 °C for 12 h to obtain the molecular sieve loaded with the metal chelating agent. Among them, the molecular sieve is MCM-41 molecular sieve, the specific surface area is 910 m 2 / g, the metal chelating agent is ethylenediaminetetraacetic acid, and the mass proportion of the metal chelating agent in EDTA / MCM-41 is 30%.

[0048] Li 2 C 2 O 4 -CNT preparation method: Dissolve H 2 C 2 O 4 and lithium carbonate in equimolar ratio in deionized water, and stir the obtained mixture at room temperature for 2 h to obtain Li 2 C 2 O4 solution, and then CNT (carbon nanotube) was added to Li 2 C 2 O 4 solution and stirred continuously for 1 h. Subsequently, the solution was poured into a spray dryer, and under the equipment conditions of 200 °C and a speed of 20 mL / min, Li 2 C 2 O 4 -CNT with a D50 particle size of 1 μm was prepared. The mass ratio of CNT in Li 2 C 2 O 4 -CNT was 4%, the average diameter of CNT was 2 nm, and the average length of CNT was 7 μm.

[0049] 3 parts by weight of sodium dodecyl sulfate, 12 parts by weight of polyacrylic acid, and 105 parts by weight of EDTA / MCM-41 were weighed and successively added to 180 parts by weight of deionized water, and dispersed by high-speed stirring to obtain coating slurry 1A; 15 parts by weight of polyvinylidene fluoride, 15 parts by weight of conductive carbon black, and 165 parts by weight of Li 2 C 2 O 4 -CNT were successively added to 135 parts by weight of NMP, and dispersed by high-speed stirring to obtain coating slurry 1B. Coating slurry 1A was respectively coated on the A side of a 9-μm wet-process PE substrate film, and coating slurry 1B was coated on the B side of the 9-μm wet-process PE substrate film. After drying, it was wound up to obtain a separator with a first coating on the A side and a second coating on the B side, and the thicknesses of both the first coating and the second coating were 3 μm.

[0050] Example 2

[0051] The difference from Example 1 was that 1 part by weight of ethoxylated alkyl sulfate, 4 parts by weight of polyacrylic acid, and 35 parts by weight of MCM-41 were weighed and successively added to 60 parts by weight of deionized water, and dispersed by high-speed stirring to obtain coating slurry 2A; 5 parts by weight of polyvinylidene fluoride, 5 parts by weight of conductive carbon black, and 55 parts by weight of Li 2 C 2 O 4 -CNT were successively added to 45 parts by weight of NMP, and dispersed by high-speed stirring to obtain coating slurry 2B. Coating slurry 2A was respectively coated on the A side of a 9-μm wet-process PE substrate film, and coating slurry 2B was coated on the B side of the 9-μm wet-process PE substrate film. After drying, it was wound up to obtain a separator with a first coating on the A side and a second coating on the B side, and the thicknesses of both the first coating and the second coating were 3 μm.

[0052] Example 3

[0053] The difference from Example 1 is that 4 parts by weight of ethoxylated alkyl sulfate, 16 parts by weight of polyacrylic acid, and 140 parts by weight of EDTA / MCM-41 are successively added to 240 parts by weight of deionized water, and dispersed by high-speed stirring to obtain coating slurry 3A; 20 parts by weight of polyvinylidene fluoride, 20 parts by weight of acetylene black, and 220 parts by weight of Li 2 C 2 O 4 are successively added to 180 parts by weight of NMP, and dispersed by high-speed stirring to obtain coating slurry 3B. Coating slurry 3A is respectively coated on the A side of a 9-μm wet-process PE substrate film, and coating slurry 3B is coated on the B side of the 9-μm wet-process PE substrate film. After drying, it is wound up to obtain a separator with a first coating on the A side and a second coating on the B side, and the thicknesses of both the first coating and the second coating are 3 μm.

[0054] Example 4

[0055] The difference from Example 1 is that the temperature of the spray dryer is 250 °C and the feeding rate is 5 mL / min to obtain Li with a D50 particle size of 0.8 μm 2 C 2 O 4 -CNT, and finally a separator is obtained.

[0056] Example 5

[0057] The difference from Example 1 is that the temperature of the spray dryer is 150 °C and the feeding rate is 25 mL / min to obtain Li with a D50 particle size of 1.3 μm 2 C 2 O 4 -CNT, and finally a separator is obtained.

[0058] Example 6

[0059] The difference from Example 1 is that the temperature of the spray dryer is 100 °C and the feeding rate is 30 mL / min to obtain Li with a D50 particle size of 1.8 μm 2 C 2 O 4 -CNT, and finally a separator is obtained.

[0060] Example 7

[0061] The difference from Example 1 is that the mass ratio of the metal chelating agent in EDTA / MCM-41 is 10%, and finally a separator is obtained.

[0062] Example 8

[0063] The difference from Example 1 is that the mass ratio of the metal chelating agent in EDTA / MCM-41 is 40%, and finally a separator is obtained.

[0064] Example 9

[0065] The difference from Example 1 is that the mass ratio of CNT in Li 2 C 2 O 4 -CNT is 2%, the average diameter of CNT is 1 nm, the average length of CNT is 5 μm, and finally a separator is obtained.

[0066] Example 10

[0067] The difference from Example 1 is that the mass ratio of CNT in Li 2 C 2 O 4 -CNT is 6%, the average diameter of CNT is 3 nm, the average length of CNT is 10 μm, and finally a separator is obtained.

[0068] Example 11

[0069] The difference from Example 1 is that the metal chelating agent is citric acid, and finally a separator is obtained.

[0070] Example 12

[0071] The difference from Example 1 is that conductive carbon black is used to replace carbon nanotubes, and finally a separator is obtained.

[0072] Example 13

[0073] The difference from Example 1 is that Li 2 C 4 O 4 is used to replace Li 2 C 2 O 4 , and finally a separator is obtained.

[0074] Example 14

[0075] The difference from Example 1 is that SBA-15 molecular sieve is used to replace MCM-41 molecular sieve, and the specific surface area of SBA-15 molecular sieve is 690 m 2 / g, and finally a separator is obtained.

[0076] Example 15

[0077] Preparation method of molecular sieve loaded with metal chelating agent: After dissolving the metal chelating agent in water, add the molecular sieve and stir at 25 °C for 12 h, and finally dry at 100 °C for 12 h to obtain the molecular sieve loaded with metal chelating agent, where the molecular sieve is MCM-49 molecular sieve, the specific surface area is 520 m 2 / g, the metal chelating agent is nitrilotriacetic acid, and the mass ratio of the metal chelating agent in the molecular sieve loaded with metal chelating agent is 20%.

[0078] Li 2 C 3 O 5 Preparation method of Li-CNT: Dissolve H 2 C 3 O 5 in deionized water in an equimolar ratio with lithium carbonate, stir the resulting mixture at room temperature for 2 h to obtain a Li 2 C 3 O 5 solution. Subsequently, add CNT (carbon nanotube) to the Li 2 C 3 O 5 solution and continue stirring for 1 h. Then pour the solution into a spray dryer, and under the equipment conditions of 200 °C and a speed of 20 mL / min, prepare Li 2 C 3 O 5 -CNT. The mass percentage of CNT in Li 2 C 3 O 5 -CNT is 4%, the average diameter of CNT is 2 nm, and the average length of CNT is 7 μm.

[0079] Weigh 20 parts by weight of ethoxylated alkyl sulfate, 40 parts by weight of carboxymethyl cellulose, and 60 parts by weight of molecular sieve loaded with metal chelator, and add them to 180 parts by weight of deionized water in sequence, and disperse them by high-speed stirring to obtain coating slurry 4A; Weigh 31 parts by weight of sodium alginate, 31 parts by weight of carbon nanofiber, and 133 parts by weight of Li 2 C 3 O 5 -CNT and add them to 135 parts by weight of NMP in sequence, and disperse them by high-speed stirring to obtain coating slurry 4B. Coat slurry 4A on the A side of a 9-μm wet PE substrate film and coat slurry 4B on the B side of the 9-μm wet PE substrate film respectively, dry and wind up to obtain a separator with a first coating on the A side and a second coating on the B side, and the thicknesses of the first coating and the second coating are both 2 μm.

[0080] Example 16

[0081] Preparation method of molecular sieve loaded with metal chelator: Dissolve the metal chelator in water, add the molecular sieve and stir at 25 °C for 12 h, and finally dry at 100 °C for 12 h to obtain the molecular sieve loaded with metal chelator. Among them, the molecular sieve is Y molecular sieve, the specific surface area is 550 m 2 / g, the metal chelator is hydroxyethyl ethylenediamine triacetic acid, and the mass percentage of the metal chelator in the molecular sieve loaded with metal chelator is 25%.

[0082] Li 2 C 4 O 6 Preparation method of Li-CNT: Dissolve H 2 C 4 O 6 and lithium carbonate in equimolar ratio in deionized water, stir the obtained mixture at room temperature for 2 h to obtain a Li 2 C 4 O 6 solution. Subsequently, add CNT (carbon nanotube) to the Li 2 C 4 O 6 solution and continue to stir for 1 h. Then pour the solution into a spray dryer, and under the equipment conditions of 200 °C and a speed of 20 mL / min, prepare Li 2 C 4 O 6 -CNT. The mass ratio of CNT in Li 2 C 4 O 6 -CNT is 4%, the average diameter of CNT is 2 nm, and the average length of CNT is 7 μm.

[0083] Weigh 3 parts by weight of dodecyldimethylbetaine, 3 parts by weight of styrene-butadiene rubber, and 114 parts by weight of molecular sieve loaded with metal chelating agent, and add them to 180 parts by weight of deionized water in sequence, and stir and disperse at high speed to obtain coating slurry 5A; Weigh 6 parts by weight of polyimide, 6 parts by weight of graphene, and 183 parts by weight of Li 2 C 4 O 6 -CNT and add them to 135 parts by weight of NMP in sequence, and stir and disperse at high speed to obtain coating slurry 5B. Coat slurry 5A on the A side of a 9-μm wet-process PE substrate film and coat slurry 5B on the B side of the 9-μm wet-process PE substrate film, dry and wind up to obtain a separator with a first coating on the A side and a second coating on the B side, and the thicknesses of the first coating and the second coating are both 4 μm.

[0084] Comparative Example 1

[0085] The difference from Example 1 is that weigh 3 parts by weight of sodium dodecyl sulfate, 6 parts by weight of CMC (carboxymethyl cellulose), 6 parts by weight of SBR, and 105 parts by weight of EDTA / MCM-41, and add them to 60 parts by weight of deionized water in sequence, and stir and disperse at high speed to obtain coating slurry 6A; Coat 6A on both sides AB of a 9-μm wet-process PE substrate film, dry and wind up to obtain a separator with a first coating on the A side and a second coating on the B side, and the thicknesses of the first coating and the second coating are both 3 μm.

[0086] Comparative Example 2

[0087] The difference from Example 1 is that Al 2 O 3 coating is applied to both sides AB of a 9-μm wet-process PE substrate film, dried and then wound up to obtain a separator with a first coating on side A and a second coating on side B, and the thicknesses of both the first coating and the second coating are 3 μm.

[0088] Comparative Example 3

[0089] The difference from Example 1 is that 15 parts by weight of polyvinylidene fluoride, 15 parts by weight of conductive carbon black, and 165 parts by weight of Li 2 C 2 O 4 -CNT are successively added to 135 parts by weight of NMP (N-methylpyrrolidone), and dispersed by high-speed stirring to obtain coating slurry 6B. Coating slurry 6B is applied to both sides AB of a 9-μm wet-process PE substrate film, dried and then wound up to obtain a separator with a first coating on side A and a second coating on side B, and the thicknesses of both the first coating and the second coating are 3 μm.

[0090] Contact angle test

[0091] The contact angle of the separator is tested using a contact angle measuring instrument (JC2000C) produced by Shanghai Zhongchen Digital Technology Equipment Co., Ltd. The titrant is LiPF6 solution, the solvent of the LiPF6 solution is ethylene carbonate and dimethyl carbonate, the volume ratio of ethylene carbonate to dimethyl carbonate is 1:1, and the concentration of LiPF6 in the LiPF6 solution is 1 mol / L.

[0092] Liquid absorption rate test

[0093] A separator to be tested with a mass of W0 is immersed in LiPF6 solution (the solvent of the LiPF6 solution is ethylene carbonate and dimethyl carbonate, the volume ratio of ethylene carbonate to dimethyl carbonate is 1:1, and the concentration of LiPF6 in the LiPF6 solution is 1 mol / L) for 30 minutes, and the excess solution on the surface of the separator is blotted with filter paper. The mass after immersion is weighed as Wi, and the liquid absorption rate is calculated: Liquid absorption rate = (Wi - W0) / W0 × 100%.

[0094] The separators prepared in the examples and comparative examples are subjected to contact angle test and liquid absorption rate test, and the test results are shown in Table 1.

[0095] Electrical property test

[0096] The separators prepared in the examples and comparative examples are assembled into batteries. The coating with the lithium supplement material is the positive electrode facing side A, and the coating with the molecular sieve material is the negative electrode facing side B. The batteries are subjected to rate discharge, normal temperature, and high temperature cycle performance tests.

[0097] The conditions for the multiple-rate discharge test are as follows: under the test conditions where the test voltage range is 2.75V to 4.3V, the battery is charged to full charge with constant current and constant voltage, and then discharged to 2.75V at current densities of 0.33C, 1C, 2C, and 3C respectively. Using the discharge capacity at 0.33C as a reference, the discharge capacity retention rates of the battery cells at 1C, 2C, and 3C are calculated. The test results are shown in Table 2.

[0098] The conditions for the normal temperature cycle test are as follows: under the test conditions where the test voltage range is 2.75V to 4.3V, the battery is charged and discharged at a current density of 1C / 1C until the discharge capacity of the battery drops below 80% of the initial discharge capacity and then stops. Record the number of cycles. The test results are shown in Table 3.

[0099] The conditions for the high temperature cycle test are as follows: in an environment of 45°C and under the test conditions where the test voltage range is 2.75V to 4.3V, the battery is charged and discharged at a current density of 1C / 1C until the discharge capacity of the battery drops below 80% of the initial discharge capacity and then stops. Record the number of cycles. The test results are shown in Table 3.

[0100] Table 1

[0101]

[0102]

[0103] Table 2

[0104]

[0105]

[0106] Table 3

[0107]

[0108]

[0109] Figure 1 This is the charge and discharge curve diagram of the assembled batteries in Example 1 and Comparative Example 2 of this application at 0.33C. From Figure 1 it can be seen that using the separator of this application has higher charge and discharge capacities.

[0110] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0111] The first coating contains modified or unmodified molecular sieves. Due to its ultra-high specific surface area and pore volume, it can significantly improve the wettability of the separator to the electrolyte and the liquid retention capacity. The pore structure and large specific surface area of the molecular sieve provide more adsorption sites for the electrolyte, enabling the electrolyte to be more evenly and stably distributed on the separator, which helps to optimize the conduction path of lithium ions and improve the electrochemical performance of the battery, especially its performance under high-rate charge and discharge conditions. The second coating contains modified or unmodified lithium supplement agents, which can achieve the effect of non-destructively supplementing lithium for the battery, thus helping to improve the charge and discharge capacity of the battery. Through the above design, while improving the electrolyte wettability and providing the non-destructive lithium supplement function, the separator of this application also maintains the original mechanical strength and thermal stability of the polymer matrix membrane. Therefore, using the separator of this application to assemble the battery cell can effectively improve the cycle performance and rate performance of the battery cell.

[0112] The above are only the embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A diaphragm, characterized in that: The separator comprises a first coating layer, a polymer matrix film and a second coating layer stacked in sequence; wherein the first coating layer contains a modified or unmodified molecular sieve; and the second coating layer contains a modified or unmodified lithium supplement agent.

2. The diaphragm according to claim 1, characterized in that The mass proportion of the modified or unmodified molecular sieve in the first coating layer is 50-96%; and / or the mass proportion of the modified or unmodified lithium supplement agent in the second coating layer is 68-94%.

3. The diaphragm according to claim 1 or 2, characterized in that: The specific surface area of ​​the modified or unmodified molecular sieve is not less than 500m 2 / g; and / or, the D50 particle size of the modified or unmodified lithium supplement agent is 0.8-1.3 μm.

4. The diaphragm according to any one of claims 1 to 3, characterized in that The modified molecular sieve is a molecular sieve loaded with a metal chelating agent; preferably, the mass proportion of the metal chelating agent in the molecular sieve loaded with a metal chelating agent is 10 to 40%; And / or, the modified lithium supplement agent is a lithium supplement agent coated with a carbon material; preferably, the mass proportion of the carbon material in the lithium supplement agent coated with a carbon material is 2-6%.

5. The diaphragm according to claim 4, characterized in that The metal chelating agent is an aminocarboxylic acid metal chelating agent and / or a hydroxycarboxylic acid metal chelating agent; Preferably, the aminocarboxylic acid metal chelator is selected from any one or more of ethylenediaminetetraacetic acid, aminotriacetic acid and aminotriacetate; and / or, the hydroxycarboxylic acid metal chelator is selected from any one or more of citric acid, tartaric acid, gluconic acid, hydroxyethylethylenediaminetriacetic acid and dihydroxyethylglycine; further preferably, the metal chelator is ethylenediaminetetraacetic acid; And / or, the carbon material is selected from any one or more of carbon nanotubes, carbon nanofibers, graphene and conductive carbon black; preferably, the carbon material is carbon nanotubes, and the average diameter of the carbon nanotubes is 1 to 3 nm and the average length is 5 to 10 μm.

6. The diaphragm according to any one of claims 1 to 5, characterized in that The thickness of the first coating layer and the second coating layer is independently 1 to 5 μm, preferably 2 to 4 μm.

7. The diaphragm according to any one of claims 1 to 6, characterized in that The molecular sieve is selected from any one or more of the MCM series molecular sieves, SBA series molecular sieves, Y molecular sieves and Beta molecular sieves; preferably, the MCM series molecular sieve is selected from any one or more of the MCM-49 molecular sieves, MCM-41 molecular sieves and MCM-22 molecular sieves; and / or, the SBA series molecular sieves are SBA-15 molecular sieves and / or SBA-16 molecular sieves; further preferably, the molecular sieve is MCM-41 molecular sieve; And / or, the lithium supplement agent is selected from any one or more of Li2C2O4, Li2C4O4, Li2C3O5 and Li2C4O6; preferably, the lithium supplement agent is Li2C2O4; And / or, the polymer matrix film is a polyolefin matrix film; preferably, the material of the polyolefin matrix film is selected from any one or more of polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, poly-1-hexene, poly-1-octene and polymethyl methacrylate.

8. The diaphragm according to any one of claims 1 to 7, characterized in that The first coating layer further contains a first binder and a dispersant, and the mass ratio of the modified or unmodified molecular sieve, the first binder and the dispersant is (15-40):(1-10):(1-5), preferably (30-40):(3-6):(1-3); And / or, the second coating layer further contains a second binder and a conductive agent, and the mass ratio of the modified or unmodified lithium supplement agent, the second binder and the conductive agent is (30-60):(2-7):(2-7), preferably (50-60): (3～6):(3～6)。 9. The diaphragm according to claim 8, characterized in that The first binder is an aqueous binder; preferably, the aqueous binder is selected from any one or more of polyacrylate and its derivatives, styrene-butadiene rubber, polyvinyl alcohol and its derivatives, polyvinyl acetate, polyacrylic acid and carboxymethyl cellulose; And / or, the dispersant is a water-soluble surfactant; preferably, the water-soluble surfactant is selected from any one or more of sodium α-allyl sulfonate, sodium lauryl sulfate, sodium fatty alcohol polyoxyethylene ether sulfate, coconut acid diethanolamide, sodium dodecylbenzene sulfonate, sodium ethoxylated alkyl sulfate and dodecyl dimethyl betaine; and / or, the second binder is selected from any one or more of polyvinylidene fluoride, polyvinylidene fluoride, polyacrylic acid, polyvinyl alcohol, polyimide, carboxymethyl cellulose, sodium carboxymethyl cellulose, sodium alginate and styrene-butadiene rubber; And / or, the conductive agent is selected from any one or more of conductive carbon black, conductive graphite, acetylene black, carbon nanotubes, carbon nanofibers and graphene.

10. A lithium ion battery comprising a positive electrode, a separator, an electrolyte and a negative electrode, characterized in that: The separator is the separator according to any one of claims 1 to 9.

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