A cellulose-based battery separator and a preparation method and application thereof

Abstract

The present application relates to the technical field of battery separator, and especially relates to a cellulose-based battery separator, a preparation method and application thereof. The present application provides a cellulose-based battery separator, which comprises a separator base film and second nanoscale cellulose fibers coated on the surface of the separator base film; the preparation raw material of the separator base film comprises conventional cellulose fibers, microscale cellulose fibers, first nanoscale cellulose fibers and defibrated ultrafine polyester sea-island fibers; the diameter distribution range of the conventional cellulose fibers is 10-50 mu m, the diameter distribution range of the microscale cellulose fibers is 1-10 mu m, and the fineness of the defibrated ultrafine polyester sea-island fibers is 0.02-0.05D, and the length is 3-6 mm. The cellulose-based battery separator has excellent mechanical strength and electrolyte wetting performance, and can effectively improve the cycle life and rate performance of the battery, and improve the safety of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery separator, in particular to a cellulose-based battery separator and a preparation method and application thereof. BACKGROUND

[0002] New energy technology is the main way to implement the "double carbon" strategic goal. The booming new energy technologies such as wind energy, solar energy and even future nuclear fusion need advanced and efficient new energy battery energy storage technology. Lithium ion batteries have become the mainstream power supply for current new energy vehicles due to their high specific energy characteristics, but the scarcity of lithium resources limits their application in large-scale energy storage systems. Sodium is a homolog of lithium and has similar chemical properties, and is abundant and low in price. Therefore, in recent years, both sodium ion batteries and lithium ion batteries have received extensive attention and in-depth research.

[0003] Currently, the commercial lithium ion battery separator is mainly polyolefin separator, such as: PP dry process microporous membrane, PE wet process microporous membrane or composite separator of the two. However, these separators generally have poor thermal stability and weak affinity for electrolyte, which affects the performance of lithium ion batteries. At the same time, since sodium battery technology is closely related to lithium battery technology, the conventional lithium battery separator is basically used for sodium battery. Under the above premise, the lithium ion battery separator will also have the problem of low sodium ion transmission speed when applied to sodium ion battery, which affects the cycle performance of the battery. In addition, due to the more active nature of sodium, more sodium dendrites will grow on the sodium ion battery separator and the negative electrode, causing the separator to be penetrated, reducing the energy density of the battery, and even causing short circuit of the battery. Therefore, it is crucial to develop a battery separator that can improve the electrochemical performance of both lithium ion batteries and sodium ion batteries. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a cellulose-based battery separator and a preparation method and application thereof, which has excellent mechanical strength and electrolyte wettability, and can effectively improve the cycle life and rate performance of the battery, and improve the safety of the battery.

[0005] In order to achieve the above-mentioned purpose of the application, the present application provides the following technical solutions:

[0006] The present application provides a cellulose-based battery separator, comprising a separator base film and second nanoscale cellulose fibers coated on the surface of the separator base film;

[0007] The preparation raw materials of the separator base film include conventional cellulose fibers, micron-scale cellulose fibers, first nanoscale cellulose fibers and ultra-fine polyester island fibers after defibration;

[0008] The diameter of the conventional cellulose fibers is distributed in the range of 10-50 pm;

[0009] The diameter distribution range of the microcellulose fiber is 1-10 um;

[0010] The fineness distribution range of the defibrated ultrafine polyester sea-island fiber is 0.02-0.05D, and the length distribution range is 3-6 mm.

[0011] Preferably, the preparation raw material of the diaphragm base film includes 20-30 parts of conventional cellulose fiber, 40-60 parts of microcellulose fiber, 1-5 parts of first nanocellulose fiber and 5-30 parts of defibrated ultrafine polyester sea-island fiber in terms of mass fraction.

[0012] Preferably, the diameter distribution range of the first nanocellulose fiber and the second nanocellulose fiber is independently 3-5 nm, and the length distribution range is independently 500-1000 nm.

[0013] Preferably, the type of the conventional cellulose fiber includes natural cellulose fiber and / or regenerated cellulose fiber;

[0014] The type of the microcellulose fiber includes natural cellulose fiber;

[0015] The natural cellulose fiber includes one or more of wood pulp cellulose fiber, cotton pulp cellulose fiber and bamboo pulp cellulose fiber;

[0016] The regenerated cellulose fiber includes viscose cellulose fiber and / or tencel cellulose fiber.

[0017] The application further provides a preparation method of the cellulose-based battery diaphragm.

[0018] The conventional cellulose fiber, the microcellulose fiber, the first nanocellulose fiber, the defibrated ultrafine polyester sea-island fiber, the dispersant and water are mixed to obtain a dispersion slurry;

[0019] The dispersion slurry is dried after being made into paper to obtain a diaphragm base film;

[0020] The second nanocellulose fiber and water are mixed to obtain a sol;

[0021] The sol is coated on the surface of the diaphragm base film, and then heat-pressed and shaped to obtain the cellulose-based battery diaphragm.

[0022] Preferably, the dispersant includes polyacrylamide and / or polyoxyethylene;

[0023] The total mass concentration of the conventional cellulose fiber, the microcellulose fiber, the first nanocellulose fiber and the defibrated ultrafine polyester sea-island fiber in the dispersion slurry is 3 / 10,000 to 8 / 10,000.

[0024] Preferably, the mass percentage of the second nanoscale cellulose fiber in the sol is 0.2-1%.

[0025] Preferably, the coating amount of the coating is 1±0.2 g / m 2 .

[0026] Preferably, the temperature of the hot-pressing shaping is 120-160℃, and the time is 20-40 s.

[0027] The application also provides the application of the cellulose-based battery separator in a secondary battery.

[0028] The application provides a cellulose-based battery separator, which comprises a separator base film and second nanoscale cellulose fibers coated on the surface of the separator base film; the preparation raw material of the separator base film comprises conventional cellulose fibers, micrometer-scale cellulose fibers, first nanoscale cellulose fibers and defibrated ultrafine polyester sea-island fibers; the diameter distribution range of the conventional cellulose fibers is 10-50 μm; the diameter distribution range of the micrometer-scale cellulose fibers is 1-10 μm; the fineness distribution range of the defibrated ultrafine polyester sea-island fibers is 0.02-0.05 D, and the length distribution range is 3-6 mm. The separator base film prepared by using cellulose fibers has the advantages of biodegradability, environmental protection, non-toxicity, large aspect ratio, high strength, high temperature resistance, strong adsorption capacity, rich hydroxyl groups on the surface and easy interweaving into a reticular structure, etc. The surface has a large number of hydroxyl groups, and hydrogen bonds are easily generated, so that the wettability of the cellulose is better, and the thermal stability is also excellent. Compared with the polyolefin film, inorganic particle film and other synthetic fiber non-woven film commonly used in the prior art, the cellulose-based battery separator is particularly prominent. By adding cellulose fibers (conventional cellulose fibers, micrometer-scale cellulose fibers, first nanoscale cellulose fibers) and defibrated ultrafine polyester sea-island fibers of different sizes, the porosity and pore size of the cellulose-based battery separator can be adjusted, the barrier performance of the separator can be effectively improved, the dendrite piercing of the separator can be prevented, the cycle life and rate performance of the battery can be effectively improved, the formation of sodium dendrites can be inhibited, and the safety of the battery can be improved. At the same time, the affinity of the cellulose fibers to the electrolyte is excellent, which is beneficial to the wettability of the electrolyte and the diffusion and migration of ions. The addition of the micrometer-scale cellulose fibers is beneficial to obtaining a uniformly distributed cellulose suspension in the preparation process, and thus the uniform distribution of the pore structure of the separator can be realized. The nanoscale cellulose fibers have extremely high mechanical strength and are rich in hydroxyl groups, can form more hydrogen bonds between fibers, and play a "bridging" role. The addition of the nanoscale cellulose fibers can greatly improve the mechanical strength of the cellulose-based battery separator. DETAILED DESCRIPTION

[0029] The present application provides a cellulose-based battery separator, comprising a separator base film and second nanoscale cellulose fibers coated on the surface of the separator base film;

[0030] The preparation raw material of the separator base film comprises conventional cellulose fibers, microscale cellulose fibers, first nanoscale cellulose fibers and defibrated ultrafine polyester island fibers;

[0031] The diameter of the conventional cellulose fibers is distributed in the range of 10-50 μm;

[0032] The diameter of the microscale cellulose fibers is distributed in the range of 1-10 μm;

[0033] The fineness of the defibrated ultrafine polyester island fibers is distributed in the range of 0.02-0.05D, and the length is distributed in the range of 3-6 mm.

[0034] In the present application, all the preparation raw materials are commercially available products well known to those skilled in the art, unless otherwise specified.

[0035] In the present application, the diameter of the conventional cellulose fibers is distributed in the range of 10-50 μm, preferably 20-50 μm.

[0036] In the present application, the type of the conventional cellulose fibers is preferably natural cellulose fibers and / or regenerated cellulose fibers; the natural cellulose fibers preferably comprise one or more of wood pulp cellulose fibers, cotton pulp cellulose fibers and bamboo pulp cellulose fibers. When the natural cellulose fibers are two or more of the above-mentioned specific choices, the present application does not have any special limitation on the ratio of the above-mentioned specific substances, and they can be mixed in any ratio. The regenerated cellulose fibers preferably comprise viscose cellulose fibers and / or lyocell cellulose fibers. When the regenerated cellulose fibers comprise viscose cellulose fibers and lyocell cellulose fibers, the present application does not have any special limitation on the ratio of the viscose cellulose fibers and lyocell cellulose fibers, and they can be mixed in any ratio. When the type of the conventional cellulose fibers is two or more of the above-mentioned specific choices, the present application does not have any special limitation on the ratio of the above-mentioned specific substances, and they can be mixed in any ratio.

[0037] In the present application, the preparation method of the conventional cellulose fibers preferably comprises the following steps:

[0038] The cellulose fibers and water are mixed and then defibrated and beaten in sequence to obtain the conventional cellulose fibers.

[0039] In the present application, the cellulose fibers preferably include natural cellulose fibers and / or regenerated cellulose fibers; the natural cellulose fibers preferably include one or more of wood pulp cellulose fibers, cotton pulp cellulose fibers and bamboo pulp cellulose fibers; the regenerated cellulose fibers preferably include viscose cellulose fibers and / or lyocell cellulose fibers; when the cellulose fibers are two or more of the above specific choices, the present application does not have any special limitation on the ratio of the above specific substances, and they can be mixed in any ratio.

[0040] In the present application, the water is preferably deionized water.

[0041] The present application does not have any special limitation on the mixing process, and any process known to those skilled in the art can be used.

[0042] In the present application, the mass concentration of cellulose fibers in the slurry obtained after mixing is preferably 2% to 3%, and more preferably 2.2% to 2.6%.

[0043] In the present application, the time for defibrillation is preferably 20 to 30 minutes, and more preferably 23 to 25 minutes; the present application does not have any special limitation on the defibrillation process, and any process known to those skilled in the art can be used.

[0044] In the present application, the time for beating is preferably 40 to 60 minutes, and more preferably 45 to 55 minutes; the present application does not have any special limitation on the beating process, and any process known to those skilled in the art can be used as long as it can ensure that the cellulose fibers are completely dispersed and have no beating points within the above beating time.

[0045] In the present application, the diameter distribution range of the micron-level cellulose fibers is preferably 1 to 10 μm, and more preferably 2 to 8 μm.

[0046] In the present application, the preparation process of the micron-level cellulose fibers preferably includes the following steps:

[0047] The natural cellulose pulp is irradiated to obtain irradiated cellulose pulp;

[0048] The irradiated cellulose pulp and water are mixed, the pH value is adjusted to be alkaline, and the pulp is beaten to obtain the micron-level cellulose fibers.

[0049] In the present application, the natural cellulose pulp preferably includes one or more of wood cellulose pulp, cotton cellulose pulp and bamboo cellulose pulp; when the natural cellulose pulp is two or more of the above specific choices, the present application does not have any special limitation on the ratio of the above specific substances, and they can be mixed in any ratio.

[0050] In the present application, the irradiation dose adopted in the irradiation is preferably 30-100 kGy, and more preferably 50-80 kGy. In the present application, the irradiation is preferably performed by using an electron beam irradiation accelerator.

[0051] After obtaining the irradiated cellulose pulp, the present application mixes the irradiated cellulose pulp with water, adjusts the pH value to be alkaline, and grinds to obtain the micron-sized cellulose fibers.

[0052] In the present application, the mass ratio of the irradiated cellulose pulp to water is preferably (3-5):100, and more preferably (3.5-4.5):100.

[0053] In the present application, the mixing is preferably performed under stirring, and the present application does not have any special limitation on the process of the stirring, which can be performed by using the process well known to those skilled in the art.

[0054] In the present application, the adjusting agent adopted in the adjusting of the pH value is preferably a sodium hydroxide solution with a mass concentration of 10%, and the adjusted pH value is preferably 11-12.

[0055] In the present application, the grinding is preferably performed by using a grinder, and the present application does not have any special limitation on the process of the grinding, which can be performed by using the process well known to those skilled in the art and ensuring that the beating degree of the pulp obtained after the grinding is 65-80°SR.

[0056] After the grinding is completed, the present application further preferably includes sequentially performed washing, separation and purification, and the present application does not have any special limitation on the process of the washing, separation and purification, which can be performed by using the process well known to those skilled in the art.

[0057] In the present application, the diameter distribution range of the first and second nanoscale cellulose fibers is independently preferably 3-5 nm. In the present application, the length distribution range of the first and second nanoscale cellulose fibers is independently preferably 500-1000 nm.

[0058] In the present application, the preparation method of the first and second nanoscale cellulose fibers is independently preferably includes the following steps:

[0059] After mixing the micron-sized cellulose fibers with water, high-pressure homogenization treatment or ultrasonic treatment is performed to obtain the first or second nanoscale cellulose fibers.

[0060] In the present application, the micron-sized cellulose fibers are preferably the micron-sized cellulose fibers described in the above technical solutions.

[0061] In the present application, the mass ratio of the microscale cellulose fiber and water is preferably (1-3):100, and more preferably (1.8-2.2):100.

[0062] The present application does not have any special limitation on the mixing process, and the process known to those skilled in the art can be used.

[0063] In the present application, when high-pressure homogenization treatment is used, the pressure of the high-pressure homogenization treatment is preferably 60-80 MPa, and the flow rate of the high-pressure homogenization treatment is preferably 5-15 mL / min; when ultrasonic treatment is used, the power of the ultrasonic treatment is preferably 4000-5000 W, and the time of the ultrasonic treatment is preferably 60-90 min.

[0064] In the present application, the fineness distribution range of the defibrated ultrafine polyester sea-island fiber is 0.02-0.05D, and preferably 0.03-0.04D. In the present application, the length distribution range of the defibrated ultrafine polyester sea-island fiber is 3-6 mm, and preferably 3-5 mm.

[0065] In the present application, the preparation method of the defibrated ultrafine polyester sea-island fiber preferably comprises the following steps:

[0066] The ultrafine polyester sea-island fiber is subjected to alkali treatment in an alkali liquor to obtain the defibrated ultrafine polyester sea-island fiber.

[0067] In the present application, the mass concentration of the alkali liquor is preferably 0.5-1.5%, and more preferably 0.8-1.2%.

[0068] In the present application, the mass ratio of the ultrafine polyester sea-island fiber and the alkali liquor is preferably 1:(5-8), and more preferably 1:(6-7).

[0069] In the present application, the temperature of the alkali treatment is preferably 90-100°C, and more preferably 93-96°C; and the time of the alkali treatment is preferably 30-40 min, and more preferably 33-36 min.

[0070] After the alkali treatment is completed, the present application further preferably comprises the processes of sequentially filtering the alkali liquor, washing to neutral and drying, and the present application does not have any special limitation on the processes of filtering the alkali liquor, washing to neutral and drying, and the processes known to those skilled in the art can be used.

[0071] In the present application, the preparation raw material of the separator base film preferably comprises 20-30 parts of conventional cellulose fiber, 40-60 parts of microscale cellulose fiber, 1-5 parts of first nanoscale cellulose fiber and 5-30 parts of defibrated ultrafine polyester sea-island fiber in terms of mass fraction.

[0072] The preparation raw material of the diaphragm base film in the application preferably comprises 20-30 parts of conventional cellulose fibers, more preferably 23-26 parts.

[0073] In the application, the conventional cellulose fibers serve to build the diaphragm skeleton structure.

[0074] The preparation raw material of the diaphragm base film in the application preferably comprises 40-60 parts of micron cellulose fibers, more preferably 45-55 parts, in terms of the mass fraction of the conventional cellulose fibers.

[0075] In the application, the micron cellulose fibers serve to reduce the diaphragm pore size, increase the porosity, and build the micron pore structure.

[0076] The preparation raw material of the diaphragm base film in the application preferably comprises 1-5 parts of first nanometer cellulose fibers, more preferably 2-4 parts, in terms of the mass fraction of the conventional cellulose fibers.

[0077] In the application, the first nanometer cellulose fibers serve to regulate the porosity and pore distribution of the diaphragm, build the micro-nano multi-level pore structure, facilitate the absorption of electrolyte and the migration of ions, and prevent dendrite from piercing the diaphragm. The addition of nanometer cellulose can obtain uniformly distributed fiber suspension and realize uniform distribution of the diaphragm pore structure.

[0078] The preparation raw material of the diaphragm base film in the application preferably comprises 5-30 parts of defibrated ultrafine polyester island fibers, more preferably 15-25 parts, in terms of the mass fraction of the conventional cellulose fibers.

[0079] In the application, the defibrated ultrafine polyester island fibers serve to improve the temperature resistance and safety performance of the diaphragm.

[0080] The application further provides a preparation method of the cellulose-based battery diaphragm.

[0081] The conventional cellulose fibers, micron cellulose fibers, first nanometer cellulose fibers, defibrated ultrafine polyester island fibers, dispersant, and water are mixed to obtain a dispersion slurry;

[0082] The dispersion slurry is subjected to papermaking and drying to obtain a diaphragm base film.

[0083] The second nanometer cellulose fibers and water are mixed to obtain a sol;

[0084] The sol is coated on the surface of the diaphragm base film, and then heat-pressed and shaped to obtain the cellulose-based battery diaphragm.

[0085] The present application mixes conventional cellulose fiber, micron cellulose fiber, first nanometer cellulose fiber, ultrafine polyester sea-island fiber after defibration, dispersant and water to obtain dispersion slurry.

[0086] In the present application, the dispersant preferably includes polyacrylamide and / or polyoxyethylene, and when the dispersant is polyacrylamide and polyoxyethylene, the present application does not have any special limitation on the ratio of the polyacrylamide and polyoxyethylene, and they can be mixed in any ratio.

[0087] In the present application, the mass concentration of the dispersant in the dispersion slurry is preferably 0.1 to 0.5 parts per million, and more preferably 0.2 to 0.3 parts per million.

[0088] In the present application, the water is preferably deionized water.

[0089] In the present application, the total mass concentration of the conventional cellulose fiber, micron cellulose fiber, first nanometer cellulose fiber and ultrafine polyester sea-island fiber after defibration in the dispersion slurry is preferably 3 to 8 parts per million, and more preferably 4 to 6 parts per million.

[0090] In the present application, the mixing is preferably placing the conventional cellulose fiber, micron cellulose fiber, first nanometer cellulose fiber and ultrafine polyester sea-island fiber after defibration in a fiber defibrator drum, adding part of the water, defibrating through a fiber standard defibrator, then adding the remaining water and dispersant, and stirring. In the present application, the mass ratio of the part of the water to the remaining water is preferably 1: (10-60), and more preferably 1: (20-50). The present application does not have any special limitation on the process of stirring, and it can be performed using a process well known to those skilled in the art.

[0091] After obtaining the dispersion slurry, the present application performs papermaking on the dispersion slurry, dries it, and obtains the separator base film.

[0092] In the present application, the process of papermaking is preferably transporting the dispersion slurry through a pipeline to a headbox, forming a wet film through an inclined wire or a cylinder former, and drying to obtain the separator base film through vacuum dewatering, an oven and a dryer. In the present application, the vacuum dewatering is preferably forming a wet film through an inclined wire or a cylinder former, and removing part of the water in the wet film through a vacuum dewatering box attached to the wire belt.

[0093] The preparation method of the present application further preferably includes mixing second nanometer cellulose fiber and water to obtain sol.

[0094] In the present application, the water is preferably deionized water. The present application does not have any special limitation on the process of mixing, and it can be performed using a process well known to those skilled in the art.

[0095] In the present application, the mass concentration of the second nanocellulose fiber in the sol is preferably 0.2-1%, more preferably 0.5-0.8%.

[0096] After obtaining the separator base film and the sol, the present application coats the sol on the surface of the separator base film, and then performs heat press setting to obtain the cellulose-based battery separator.

[0097] In the present application, the coating amount of the coating is preferably 1±0.2 g / m 2 The present application does not have any special limitation on the process of the coating, and a process well known to those skilled in the art can be used.

[0098] After the coating is completed, the present application also preferably includes drying, and the present application does not have any special limitation on the process of the drying, and a process well known to those skilled in the art can be used.

[0099] In the present application, the temperature of the heat press setting is preferably 120-160°C, more preferably 130-150°C; the time is preferably 20-40 s, more preferably 25-35 s; and the pressure is preferably 1-6 MPa, more preferably 2-4 MPa.

[0100] The present application also provides the application of the cellulose-based battery separator described in the above technical solution or the cellulose-based battery separator prepared by the preparation method described in the above technical solution in a secondary battery. In the present application, the secondary battery is preferably a lithium ion battery or a sodium ion battery. The present application does not have any special limitation on the method of the application, and a method well known to those skilled in the art can be used.

[0101] The technical solutions in the present application will be described clearly and completely in combination with the embodiments in the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0102] Example 1

[0103] Preparation of conventional cellulose fiber (CF): 10 g of natural cellulose fiber (specific type: wood pulp cellulose fiber) and 15 g of regenerated cellulose fiber (specific type: Tencel cellulose fiber) and 975 g of water were mixed, and then defibrated in a beater for 25 min, and then lightly beaten for 50 min until the cellulose fiber was completely dispersed without pulp point. The knife was raised, and pulp was obtained (the solid content of the pulp was 2.5 wt%, and the diameter distribution range of the cellulose fiber in the pulp was 20-50 μm);

[0104] Preparation of microcellulose fibers: 30 g of natural cellulose fiber pulp (specific type of wood cellulose pulp) was irradiated by an electron beam irradiator (the dose of the irradiation was 50 kGy), then the irradiated natural cellulose fiber pulp and water were mixed in a mass ratio of 4:96 and stirred, 10% sodium hydroxide solution was added to adjust the pH value to 11, and the pulp was treated by a pulp mill until the beating degree of the pulp was 70°SR, then the pulp was taken out, washed, separated, and purified to obtain microcellulose fiber pulp (the solid content of the pulp was 4 wt%, and the diameter distribution range of the microcellulose fiber was 1-10 μm);

[0105] Preparation of nanocellulose fibers: 200 g of the microcellulose fiber pulp and water were mixed to obtain a microcellulose fiber dispersion liquid with a mass concentration of 2%; the microcellulose fiber dispersion liquid was treated by high-pressure homogenization (the treatment conditions were a homogenization pressure of 70 MPa and a flow rate of 10 mL / min) to obtain a nanocellulose fiber hydrogel (the solid content of the nanocellulose fiber hydrogel was 2 wt%, the diameter distribution range of the nanocellulose fiber was 3-5 nm, and the length distribution range was 500-1000 nm);

[0106] Superfine polyester island fibers after defibration: 50 g of superfine polyester island fibers were treated with alkali in 250 g of 1% sodium hydroxide solution at a mass ratio of 1:6 for 35 min (the temperature of the alkali treatment was 95°C), the superfine polyester island fibers were taken out, the alkali solution was filtered out, washed with water until neutral, and dried to obtain superfine polyester island fibers after defibration;

[0107] According to the mass ratio of 20:50:3:27 of the absolute dry fibers, 2 g of conventional cellulose fibers (80 g of the above pulp), 5 g of microcellulose fibers (125 g of the above microcellulose fiber pulp), 0.3 g of nanocellulose fibers (15 g of the above nanocellulose hydrogel), and 2.7 g of superfine polyester island fibers after defibration were added to the cylinder of a fiber defibrator, deionized water was added to a total weight of 1000 g, and then defibration was performed by a standard fiber defibrator, 24000 g of deionized water and 0.5 g of a dispersant (the type of the dispersant was polyacrylamide) were continuously added, and stirring was performed (the stirring conditions were mechanical stirring for 3 min at a stirring speed of 2000 rpm) to obtain a dispersion slurry with a mass percentage concentration of 0.04%;

[0108] The dispersion slurry was transported to a headbox by a pipeline, and then wet membranes were formed by an inclined wire or a cylinder former, vacuum dewatering was performed, drying was performed in an oven and a drying cylinder, and a separator base film was obtained, the surface density of the base film was 9.98 g / m 2 ;

[0109] 80 g of the nanoscale cellulose fiber hydrogel and 120 g of deionized water were mixed to obtain a sol with a mass concentration of 0.8%, which was coated on the surface of the above-mentioned separator base film using a coater (coating amount: 1.03 g / m 2 ), and then placed in a drying oven for drying, followed by heat pressing and setting on a hot calender (heat pressing temperature: 140°C) to obtain a cellulose-based battery separator (areal density: 11.01 g / m 2 , separator thickness: 22.92 μm, porosity: 71%, liquid absorption rate: 324%);

[0110] The cellulose-based battery separator was applied to a sodium-ion battery (CR2025 button cell), which had a discharge specific capacity of 100.5 mA·h·g -1 at a 5C rate, and a discharge specific capacity of 99.2 mA·h·g -1 after 200 cycles of charge and discharge, which was 98.7% of the initial discharge specific capacity, showing good cycle stability. At a 10C rate, the discharge specific capacity was 94.01 mA·h·g -1 after 200 cycles of charge and discharge, showing good rate performance.

[0111] Example 2

[0112] The conventional cellulose fiber, microscale cellulose fiber, nanoscale cellulose fiber, and defiberized ultrafine polyester island fiber were prepared according to Reference Example 1.

[0113] According to a mass ratio of 25:55:4:16 of the absolute dry fiber, 5 g of conventional cellulose fiber (200 g of the above-mentioned pulp), 11 g of microscale cellulose fiber (275 g of the above-mentioned pulp), 0.8 g of nanoscale cellulose fiber (40 g of the above-mentioned nanocellulose hydrogel), and 3.2 g of defiberized ultrafine polyester island fiber were added to the fiber defibrator drum, deionized water was added to a total weight of 1000 g, and then defiberized by a fiber standard defibrator, 39000 g of deionized water and 1.2 g of a dispersant (the type of the dispersant was polyoxyethylene) were continuously added, and stirred (the stirring conditions were mechanical stirring for 3 min at a stirring speed of 2000 rpm) to obtain a dispersion slurry with a mass percentage concentration of 0.05%;

[0114] The dispersion slurry was transported to a headbox through a pipeline, and then formed into a wet film by a sloping wire or a cylinder former, vacuum dewatered, dried in an oven and a dryer, and a separator base film was obtained, with a base film areal density of 19.93 g / m 2; 40 g of the nanoscale cellulose fibers and 120 g of deionized water were mixed to obtain a sol with a mass concentration of 0.5%, and the sol was coated on the surface of the separator base film by a coater (coating amount: 0.8 g / m 2 ), and then dried in a drying oven, and then heat-pressed and shaped by a hot calender (heat-pressing temperature: 160°C) to obtain a cellulose-based battery separator (areal density: 20.73 g / m 2 , separator thickness: 43.17 μm, porosity: 79.96%, and liquid absorption rate: 351%);

[0115] The cellulose-based battery separator was applied to a sodium-ion battery (CR2025 button cell), and the discharge specific capacity thereof could reach 100.1 mA·h·g -1 at a rate of 5C, and the discharge specific capacity thereof was 97.87 mA·h·g -1 after 200 cycles of charge-discharge, which was 97.77% of the initial discharge specific capacity, showing good cycle stability. The discharge specific capacity was 95.51 mA·h·g -1 after 200 cycles of charge-discharge at a rate of 10C, showing good rate performance.

[0116] Example 3.

[0117] The conventional cellulose fibers, the microscale cellulose fibers, the nanoscale cellulose fibers, and the defiberized ultrafine polyester island fibers were prepared according to Reference Example 1.

[0118] According to a mass ratio of 25:45:5:25 of the absolute dry fibers, 3.75 g of the conventional cellulose fibers (the above 150 g of slurry), 6.75 g of the microscale cellulose fibers (the above 168.75 g of slurry), 0.75 g of the nanoscale cellulose fibers (the above 37.5 g of nanocellulose hydrogel), and 3.75 g of the defiberized ultrafine polyester island fibers were added into a fiber defiberizer drum, deionized water was added to a total weight of 1000 g, and then defiberization was performed by a fiber standard defiberizer, 24000 g of deionized water and 0.75 g of a dispersant (the type of the dispersant was polyacrylamide) were continuously added, and stirring was performed (the stirring conditions were mechanical stirring for 3 min, and the stirring speed was 2000 rpm) to obtain a dispersion slurry with a mass percentage concentration of 0.06%;

[0119] The dispersion slurry was transported to a headbox by a pipeline, and then wetting was performed by an inclined wire or a cylinder former to obtain a wet film, vacuum dewatering was performed, drying was performed in an oven and a drying cylinder, and a separator base film was obtained, and the areal density of the base film was 14.97 g / m 2; 50 g of the nanoscale cellulose fibers and 75 g of deionized water were mixed to obtain a sol with a mass concentration of 0.8%, and the sol was coated on the surface of the separator base film by a coater (coating amount: 0.9 g / m 2 ), and then dried in a drying oven, and then heat-pressed and shaped by a hot calender (heat-pressing temperature: 140°C) to obtain a cellulose-based battery separator (areal density: 15.87 g / m 2 , separator thickness: 29.2 μm, porosity: 74%, liquid absorption rate: 336%);

[0120] The cellulose-based battery separator was applied to a sodium-ion battery (CR2025 button cell), and the discharge specific capacity thereof could reach 101.7 mA·h·g -1 at a 5C rate, and the discharge specific capacity thereof was 98.3 mA·h·g -1 after 200 cycles of charge and discharge, which was 96.6% of the initial discharge specific capacity, showing good cycle stability. The discharge specific capacity was 94.27 mA·h·g -1 after 200 cycles of charge and discharge at a 10C rate, showing good rate performance.

[0121] Comparative Example 1

[0122] The conventional cellulose fibers, microscale cellulose fibers, nanoscale cellulose fibers and defibrated ultrafine polyester island fibers were prepared according to Reference Example 1.

[0123] According to a mass ratio of 25:50:25 of the absolute dry fibers, 3.75 g of the conventional cellulose fibers (from 150 g of the slurry), 7.5 g of the microscale cellulose fibers (from 187.5 g of the slurry) and 3.75 g of the defibrated ultrafine polyester island fibers were added into a fiber defibrator drum, deionized water was added to a total weight of 1000 g, and then defibrated by a fiber standard defibrator, 24000 g of deionized water and 0.75 g of a dispersant (the type of the dispersant was polyacrylamide) were continuously added, and stirred (the stirring conditions were mechanical stirring for 3 min, stirring speed: 2000 rpm) to obtain a dispersion slurry with a mass percentage concentration of 0.06%;

[0124] The dispersion slurry was transported to a headbox by a pipeline, and then formed into a wet film by a inclined wire or a cylinder mold former, vacuum dewatered, dried in an oven and a dryer cylinder to obtain a separator base film, and the areal density of the base film was 14.92 g / m 2 ; 50 g of the nanoscale cellulose fibers and 50 g of deionized water were mixed to obtain a sol with a mass concentration of 1%, and the sol was coated on the surface of the separator base film by a coater (coating amount: 0.95 g / m 2), and then placed in a drying oven for drying, and then heat-pressed and shaped by a hot rolling machine (the temperature of heat-pressing was 140 DEG C), to obtain a cellulose-based battery separator (the surface density was 15.87 g / m 2 , the thickness of the separator was 32.1 pm, the porosity was 67.8%, and the liquid absorption rate was 307%);

[0125] The cellulose-based battery separator was applied to a sodium ion battery (a CR2025 button cell), and the discharge specific capacity thereof could reach 100.1 mA.h.g -1 after 200 cycles of charge and discharge, the discharge specific capacity was 91.3 mA.h.g -1 , which was 91.21% of the initial discharge specific capacity, and after 200 cycles of charge and discharge at a rate of 10C, the discharge specific capacity was 89.96 mA.h.g -1 .

[0126] The above only describes the preferred implementation method of the present application, and does not limit the present application in any form. It should be noted that, for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A cellulose-based battery separator, characterized by, The second nanoscale cellulose fibers are coated on the surface of the diaphragm base film. The raw materials for preparing the diaphragm base film include conventional cellulose fibers, microscale cellulose fibers, first nanoscale cellulose fibers and defibrated ultrafine polyester island fibers. The diameter of the conventional cellulose fibers is distributed in the range of 10-50 μm. The diameter of the microscale cellulose fibers is distributed in the range of 1-10 μm. The fineness of the defibrated ultrafine polyester island fibers is distributed in the range of 0.02-0.05D, and the length is distributed in the range of 3-6 mm. The conventional cellulose fibers include natural cellulose fibers and / or regenerated cellulose fibers. The microscale cellulose fibers include natural cellulose fibers. The natural cellulose fibers include one or more of wood pulp cellulose fibers, cotton pulp cellulose fibers and bamboo pulp cellulose fibers. The regenerated cellulose fibers include viscose cellulose fibers and / or tencel cellulose fibers.

2. The cellulose-based battery separator of claim 1, wherein, The raw materials for preparing the diaphragm base film include 20-30 parts of conventional cellulose fibers, 40-60 parts of microscale cellulose fibers, 1-5 parts of first nanoscale cellulose fibers and 5-30 parts of defibrated ultrafine polyester island fibers, in terms of mass fraction.

3. The cellulose-based battery separator of claim 2, wherein, The diameter of the first nanoscale cellulose fibers and the second nanoscale cellulose fibers is independently distributed in the range of 3-5 nm, and the length is independently distributed in the range of 500-1000 nm.

4. The process for the production of a cellulose-based battery separator according to any one of claims 1 to 3, characterized in that, The method comprises the following steps: The conventional cellulose fibers, the microscale cellulose fibers, the first nanoscale cellulose fibers, the defibrated ultrafine polyester island fibers, a dispersing agent and water are mixed to obtain a dispersion slurry; The diaphragm base film is obtained by drying the dispersion slurry after the dispersion slurry is papermaking; The second nanoscale cellulose fibers and water are mixed to obtain a sol; The sol is coated on the surface of the diaphragm base film, and then heat-pressed to obtain the cellulose-based battery diaphragm.

5. The production method according to claim 4, wherein The dispersing agent includes polyacrylamide and / or polyoxyethylene; The total mass concentration of the conventional cellulose fibers, the microscale cellulose fibers, the first nanoscale cellulose fibers and the defibrated ultrafine polyester island fibers in the dispersion slurry is 3-8 parts per million.

6. The production method according to claim 4, wherein The mass percentage of the second nanoscale cellulose fibers in the sol is 0.2-1%.

7. The production method according to claim 4, wherein The coated coated amount is 1 ± 0.2 g / m 2 .

8. The production method according to claim 4, wherein The temperature of the heat-pressing is 120-160℃, and the time is 20-40 s.

9. The cellulose-based battery diaphragm of any one of claims 1-3 or prepared by the method of any one of claims 4-8 is applied in a secondary battery.