A coated separator comprising a biomass carbon material, and a method of preparing and use thereof

Abstract

The present application relates to the field of lithium battery separator, discloses a kind of coating separator comprising biomass carbon material and its preparation method and application, preparation steps include: straw is added in chlorinated salt solution and soaked, obtain activated straw;A portion of activated straw is calcined under inert atmosphere, obtain biomass porous carbon;Another portion of activated straw is mixed with nano iron powder, then calcined under inert atmosphere, obtain biomass carbon nanotube;Biomass porous carbon and biomass carbon nanotube are mixed according to mass ratio 1:3~5, obtain mixed biomass carbon material;Mixed biomass carbon material is mixed with adhesive, dispersing agent and water, obtain coating slurry;It is coated on the surface of base film, and after drying, coating separator is obtained.The present application is made into porous carbon and carbon nanotube by straw, which is applied to the coating material of separator, and can significantly improve the ion transmission efficiency and mechanical properties of separator.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery separator, in particular to a coated separator containing biomass carbon material and a preparation method and application thereof. BACKGROUND

[0002] Plant straw is a common waste during the processing of agricultural products. The common treatment methods are local incineration and centralized treatment. Local incineration is easy to cause random emission of carbon dioxide, and centralized treatment, whether simple incineration or fertilizer making, only achieves centralized emission but does not realize additional value. Straw contains N and P elements, and if it is converted into biomass carbon by reasonable means, the utilization rate can be greatly improved and the use value can be improved.

[0003] At present, there are studies on using biomass carbon in battery separators. For example, a composite separator and a preparation method thereof disclosed in patent CN116864917A include a separator substrate and a modified coating layer. The modified coating layer is arranged on the surface of the separator substrate, and the modified coating layer includes a biomass carbon / metal oxide composite material. The biomass carbon / metal oxide composite material includes biomass carbon and metal oxide in a porous structure. However, the pore structure of the biomass carbon in the prior art is uncontrollable and the electrical conductivity is insufficient. The proportion of micropores in some materials is too high, which will hinder the transmission of lithium ions when used in separators and reduce the rate performance of the battery. SUMMARY

[0004] The present application is to overcome the above-mentioned problems of the biomass carbon coated separator in the prior art, and to provide a coated separator containing biomass carbon material and a preparation method and application thereof. The straw is made into porous carbon and carbon nanotubes, which are applied to the coating material of the separator, which can significantly improve the ion transmission efficiency and mechanical properties of the separator.

[0005] In order to achieve the above-mentioned purpose, the present application adopts the following technical scheme:

[0006] In a first aspect, the present application provides a preparation method of a coated separator containing biomass carbon material, comprising the following steps:

[0007] (1) washing, drying and crushing the straw, and then soaking it in a chloride salt solution to obtain activated straw;

[0008] (2) calcining a part of the activated straw in an inert atmosphere to obtain biomass porous carbon;

[0009] (3) mixing another part of the activated straw with nano-iron powder, and then calcining in an inert atmosphere to obtain biomass carbon nanotubes;

[0010] (4) mixing the biomass porous carbon and the biomass carbon nanotubes in a mass ratio of 1:3-5 to obtain a mixed biomass carbon material;

[0011] (5) mixing the mixed biomass carbon material with the adhesive, the dispersant and water to obtain a coating slurry;

[0012] (6) coating the coating slurry on the surface of the base film to obtain the coated separator after drying.

[0013] The present application uses straw as a raw material to prepare biomass porous carbon and biomass carbon nanotubes, which are used as coating particles in the separator, and can maximize the utilization of agricultural and sideline products. The straw contains N and P elements. In the present application, the straw is crushed and soaked in a chloride salt solution, and then calcined in an inert atmosphere to obtain N and P doped biomass porous carbon. Because of the introduction of nitrogen and phosphorus elements, the spatial structure of the carbon material has defects, which can promote the transfer of ions inside the battery. At the same time, the doping of heteroatoms can make the material have better wettability, which can have more sufficient contact with the electrolyte, promote the free transmission of ions, and thus improve the ionic conductivity of the separator. Furthermore, the present application uses chloride salt as a hard template pore-forming agent, which can provide basic support during calcination, resulting in uniform and evenly distributed pores, which can provide a good three-dimensional structure. This three-dimensional structure can make the biomass porous carbon maintain good stability during related charge and discharge tests, reduce the collapse of the material at the micro level, and provide basic mechanical stability. As a conductive material, the porous carbon can effectively improve the conductivity of the composite separator, promote the lithium ion transport process inside the battery, and the uniformly distributed pores can promote the transmission of ions, which can shorten the transmission path of ions, which greatly promotes the transport efficiency of ions inside the battery.

[0014] At the same time, the present application mixes another part of activated straw with nano iron powder and calcines them. The gas released during pyrolysis can form carbon nanotubes under the catalysis of iron powder. The electrochemical performance of carbon nanotubes is greatly improved compared with that of porous carbon. The present application mixes the obtained biomass porous carbon and biomass carbon nanotubes as coating particles. Carbon nanotubes can construct a long-range conductive network, while porous carbon can provide local conductive points. Through the rigid skeleton of biomass porous carbon and the flexible winding of carbon nanotubes, a "rigid and flexible" structure is formed, which can significantly improve the ionic conductivity of the separator, inhibit the deformation of the separator during the cycle process, and thus improve the rate performance and cycle stability of the battery.

[0015] As preferred, the chlorinated salt solution in step (1) is one or more of cobalt chloride solution, ferric chloride solution, copper chloride solution, nickel chloride solution; the concentration of the chlorinated salt solution is 0.5-2 mol / L; the soaking time of the straw in the chlorinated salt solution is 12-24 h. The activation time of the straw in the chlorinated salt solution should not be too long, and the soaking time that is too long will lead to over-activation, introduction of more ions, and structural collapse of the carbon material in the calcination process. The structural collapse of the carbon material has a great influence on the electrochemical performance of the carbon material, and at the same time, due to the structural collapse, the porous structure will be significantly damaged, which will greatly affect the liquid absorption rate of the material.

[0016] As preferred, the calcination temperature in step (2) is 600-1200℃, and the calcination time is 3-5 h.

[0017] As preferred, the mass of the nano-iron powder added in step (3) is 5-10% of the mass of the activated straw. The addition of iron powder can promote the nucleation and growth of carbon nanotubes to a certain extent. However, too high an iron powder content may cause defects in the structure of carbon nanotubes. Because too much iron powder may cause the reaction to be too violent, leading to the loss of order of carbon atom deposition and arrangement, destroying the regular tubular structure of carbon nanotubes, and affecting the crystallinity and graphitization degree. At the same time, due to the presence of water in the biomass pyrolysis process, part of the iron powder will be oxidized to Fe3O4. Continuing to increase the iron powder content may increase the generation amount of impurities such as Fe3O4, which may adhere to the surface of carbon nanotubes or be embedded in the structure, not only affecting the purity of carbon nanotubes, but also possibly having a negative impact on its physical and chemical properties, such as electrical conductivity, mechanical properties, etc. In addition, the increase of the iron powder content may change the path and selectivity of the pyrolysis reaction, in addition to promoting the formation of carbon nanotubes, it may also trigger other side reactions, consume more carbon sources, reduce the amount of carbon sources for the growth of carbon nanotubes, and reduce the yield of carbon nanotubes, thereby affecting the performance of the separator.

[0018] As preferred, the calcination temperature in step (3) is 700-900℃, and the calcination time is 3-5 h.

[0019] As preferred, in step (5), 15-25 parts of the mixed biomass carbon material are mixed with 1-3 parts of the adhesive, 10-15 parts of the dispersing agent, and 60-70 parts of water to obtain a coating slurry.

[0020] As preferred, in step (6), the thickness of the base film is 12-20 μm, and the thickness of the coating after coating is 3-5 μm.

[0021] As preferred, the base film in step (6) is a polypropylene separator.

[0022] In a second aspect, the present application provides a coated separator comprising biomass carbon material prepared by the above preparation method.

[0023] In a third aspect, the present application provides an application of the coated separator comprising biomass carbon material prepared by the above preparation method in a lithium battery.

[0024] Therefore, the present application has the following beneficial effects:

[0025] (1) The biomass porous carbon and biomass carbon nanotube prepared by using straw as raw material are used as coating particles in the separator, which can maximize the utilization of agricultural and sideline products;

[0026] (2) The porous carbon material prepared by using straw as raw material has defects in the spatial structure due to the doping of heteroatoms, which promotes the ion transfer in the battery. The introduction of nitrogen and phosphorus elements improves the wettability of the porous carbon, and the wettability of the electrolyte is improved, which promotes the free transmission of ions;

[0027] (3) In the present application, another part of the activated straw is mixed with nano-iron powder and calcined. The gas released in the pyrolysis process can form carbon nanotubes under the catalysis of iron powder. The electrochemical performance of the carbon nanotube is greatly improved compared with that of the porous carbon;

[0028] (4) The biomass porous carbon and biomass carbon nanotube obtained in the present application are mixed as coating particles. The carbon nanotube can construct a long-range conductive network, and the porous carbon can provide local conductive points. Through the "rigidity and flexibility" structure formed by the rigid skeleton of the biomass porous carbon and the flexible winding of the carbon nanotube, the ion conductivity of the separator can be significantly improved, the deformation of the separator in the cycle process can be inhibited, and the rate performance and cycle stability of the battery can be improved. DETAILED DESCRIPTION

[0029] The present application will be further described in combination with the specific embodiments.

[0030] In the present application, all the equipment and raw materials can be purchased from the market or commonly used in the industry, unless otherwise specified. The methods in the following examples are conventional methods in the art, unless otherwise specified.

[0031] General example:

[0032] A preparation method of a coated separator comprising biomass carbon material, comprising the following steps:

[0033] (1) After washing, drying and crushing the straw, it is soaked in a ferric chloride solution to obtain activated straw;

[0034] (2) A part of the activated straw is calcined under an inert atmosphere to obtain biomass porous carbon;

[0035] (3) mixing another part of the activated straw with nano-iron powder, and then calcining under inert atmosphere to obtain biomass carbon nanotubes;

[0036] (4) mixing the biomass porous carbon and the biomass carbon nanotubes at a mass ratio of 1:3-5 to obtain a mixed biomass carbon material;

[0037] (5) mixing the mixed biomass carbon material with a binder, a dispersant and water to obtain a coating slurry;

[0038] (6) coating the coating slurry on the surface of a base film, and drying to obtain the coated separator.

[0039] As a specific embodiment, the chlorinated salt solution in step (1) is one or more of a cobalt chloride solution, an iron chloride solution, a copper chloride solution and a nickel chloride solution; the concentration of the chlorinated salt solution is 0.5-2 mol / L; and the soaking time of the straw in the chlorinated salt solution is 12-24 h.

[0040] As a specific embodiment, the calcination temperature in step (2) is 600-1200℃, and the calcination time is 3-5 h.

[0041] As a specific embodiment, the mass of the nano-iron powder added in step (3) is 5-10% of the mass of the activated straw.

[0042] As a specific embodiment, the calcination temperature in step (3) is 700-900℃, and the calcination time is 3-5 h.

[0043] As a specific embodiment, in step (5), 15-25 parts of the mixed biomass carbon material is mixed with 1-3 parts of a binder, 10-15 parts of a dispersant and 60-70 parts of water to obtain the coating slurry.

[0044] As a specific embodiment, the binder in step (5) is selected from one or more of polytetrafluoroethylene, polyvinylidene fluoride, epoxy resin, polyimide, polyurethane and polyvinyl acetal.

[0045] As a specific embodiment, the dispersant in step (5) is selected from one or more of triethylhexyl phosphoric acid, sodium dodecyl sulfate, methyl amyl alcohol, sodium carboxymethyl cellulose, polyacrylamide, gum gur, and fatty acid polyethylene glycol ester.

[0046] As a specific embodiment, in step (6), the thickness of the base film is 12-20 μm, and the thickness of the coating layer after coating is 3-5 μm.

[0047] As a specific embodiment, the base film in step (6) is a polypropylene separator.

[0048] Example 1:

[0049] A method for preparing a coated separator comprising biomass carbon material, steps are:

[0050] (1) After washing, drying and crushing rice straw, it is soaked in 1 mol / L ferric chloride solution for 12 h to obtain activated straw;

[0051] (2) Two porcelain boats are placed in a high-temperature tube furnace under argon protection, activated straw is placed in the front porcelain boat, and a mixture of activated straw and nano-iron powder is placed in the rear porcelain boat, the mass of nano-iron powder is 5% of the mass of activated straw; under argon protection, the temperature is raised to 700°C at a rate of 5°C / min, and the temperature is kept for 4 h;

[0052] (3) The product in the front porcelain boat is washed with dilute sulfuric acid (10wt%), deionized water and ethanol alternately for five times, and dried to obtain biomass porous carbon; the product in the rear porcelain boat is washed with dilute sulfuric acid (10wt%), deionized water and ethanol alternately for five times, and dried to obtain biomass carbon nanotubes;

[0053] (4) Biomass porous carbon and biomass carbon nanotubes are mixed in a mass ratio of 1:4 to obtain a mixed biomass carbon material;

[0054] (5) The mixed biomass carbon material is uniformly mixed with epoxy resin adhesive (3M DP100NS), dispersant carboxymethyl cellulose sodium and deionized water in a mass ratio of 20:2:13:65 to obtain a coating slurry;

[0055] (6) The coating slurry is coated on the surface of a 12 μm polypropylene separator (Hefei Changyang New Energy Technology Co., Ltd.), and the coating thickness is 4 μm. After drying in a 60°C oven for 10 min, the coated separator is obtained.

[0056] Example 2:

[0057] A method for preparing a coated separator comprising biomass carbon material, steps are:

[0058] (1) After washing, drying and crushing rice straw, it is soaked in 1 mol / L cobalt chloride solution for 24 h to obtain activated straw;

[0059] (2) Two porcelain boats are placed in a high-temperature tube furnace under argon protection, activated straw is placed in the front porcelain boat, and a mixture of activated straw and nano-iron powder is placed in the rear porcelain boat, the mass of nano-iron powder is 10% of the mass of activated straw; under argon protection, the temperature is raised to 700°C at a rate of 5°C / min, and the temperature is kept for 4 h;

[0060] (3) The product in the front porcelain boat is washed with dilute sulfuric acid (10wt%), deionized water and ethanol alternately for five times, and after drying, biomass porous carbon is obtained; the product in the rear porcelain boat is washed with dilute sulfuric acid (10wt%), deionized water and ethanol alternately for five times, and after drying, biomass carbon nanotubes are obtained;

[0061] (4) Biomass porous carbon and biomass carbon nanotubes are mixed in a mass ratio of 1:3 to obtain a mixed biomass carbon material;

[0062] (5) The mixed biomass carbon material is uniformly mixed with an epoxy resin adhesive (3M DP100NS), a dispersing agent carboxymethyl cellulose sodium and deionized water in a mass ratio of 20:2:13:65 to obtain a coating slurry;

[0063] (6) The coating slurry is coated on the surface of a 12μm polypropylene separator (Hefei Changyang New Energy Technology Co., Ltd.), and the coating thickness is 4μm. After drying in a 60℃ oven for 10min, the coated separator is obtained.

[0064] Example 3:

[0065] A preparation method of a coated separator containing a biomass carbon material, the steps are:

[0066] (1) After washing, drying and crushing, the rice straw is soaked in a 1mol / L ferric chloride solution for 24h to obtain activated straw;

[0067] (2) Two porcelain boats are placed in a high-temperature tube furnace under argon protection. Activated straw is placed in the front porcelain boat, and a mixture of activated straw and nano-iron powder is placed in the rear porcelain boat. The mass of the nano-iron powder is 10% of the mass of the activated straw. Under argon protection, the temperature is raised to 700℃ at a rate of 5℃ / min, and the temperature is maintained for 4h;

[0068] (3) The product in the front porcelain boat is washed with dilute sulfuric acid (10wt%), deionized water and ethanol alternately for five times, and after drying, biomass porous carbon is obtained; the product in the rear porcelain boat is washed with dilute sulfuric acid (10wt%), deionized water and ethanol alternately for five times, and after drying, biomass carbon nanotubes are obtained;

[0069] (4) Biomass porous carbon and biomass carbon nanotubes are mixed in a mass ratio of 1:5 to obtain a mixed biomass carbon material;

[0070] (5) The mixed biomass carbon material is uniformly mixed with an epoxy resin adhesive (3M DP100NS), a dispersing agent carboxymethyl cellulose sodium and deionized water in a mass ratio of 20:2:13:65 to obtain a coating slurry;

[0071] (6) The coating slurry is coated on the surface of a 12 μm polypropylene separator (Hefei Changyang New Energy Technology Co., Ltd.), with a coating thickness of 4 μm, and the coated separator is obtained after drying in a 60°C oven for 10 min.

[0072] Comparative Example 1 (excessive activation time):

[0073] A method for preparing a coated separator containing a biomass carbon material, the steps being:

[0074] (1) After washing, drying and crushing rice straw, the rice straw is soaked in a 1 mol / L ferric chloride solution for 36 h to obtain activated straw;

[0075] (2) Two porcelain boats are placed in a high-temperature tube furnace under argon protection, activated straw is placed in the front porcelain boat, and a mixture of activated straw and nano-iron powder is placed in the rear porcelain boat, the mass of the nano-iron powder being 5% of the mass of the activated straw; the temperature is raised to 700°C at a rate of 5°C / min under argon protection, and the temperature is maintained for 4 h;

[0076] (3) The product in the front porcelain boat is washed with dilute sulfuric acid (10 wt%), deionized water and ethanol alternately five times, and biomass porous carbon is obtained after drying; the product in the rear porcelain boat is washed with dilute sulfuric acid (10 wt%), deionized water and ethanol alternately five times, and biomass carbon nanotubes are obtained after drying;

[0077] (4) The biomass porous carbon and the biomass carbon nanotubes are mixed in a mass ratio of 1:4 to obtain a mixed biomass carbon material;

[0078] (5) The mixed biomass carbon material is uniformly mixed with an epoxy resin adhesive (3M DP100NS), a dispersant carboxymethyl cellulose sodium and deionized water in a mass ratio of 20:2:13:65 to obtain a coating slurry;

[0079] (6) The coating slurry is coated on the surface of a 12 μm polypropylene separator (Hefei Changyang New Energy Technology Co., Ltd.), with a coating thickness of 4 μm, and the coated separator is obtained after drying in a 60°C oven for 10 min.

[0080] Comparative Example 2 (excessive addition of iron powder):

[0081] A method for preparing a coated separator containing a biomass carbon material, the steps being:

[0082] (1) After washing, drying and crushing rice straw, the rice straw is soaked in a 1 mol / L ferric chloride solution for 12 h to obtain activated straw;

[0083] (2) Put two porcelain boats in a high-temperature tube furnace under argon protection, put the activated straw into the front porcelain boat, and put the mixture of activated straw and nano-iron powder into the rear porcelain boat, the mass of nano-iron powder is 15% of the mass of activated straw; under argon protection, heat at a rate of 5℃ / min to 700℃, and keep for 4h;

[0084] (3) Wash the product in the front porcelain boat with dilute sulfuric acid (10wt%), deionized water and ethanol alternately for five times, and get biomass porous carbon after drying; wash the product in the rear porcelain boat with dilute sulfuric acid (10wt%), deionized water and ethanol alternately for five times, and get biomass carbon nanotube after drying;

[0085] (4) Mix the biomass porous carbon and biomass carbon nanotube according to the mass ratio of 1:4 to get mixed biomass carbon material;

[0086] (5) Mix the mixed biomass carbon material, epoxy resin adhesive (3M DP100NS), dispersant carboxymethyl cellulose sodium and deionized water according to the mass ratio of 20:2:13:65 to get coating slurry;

[0087] (6) Coating the coating slurry on the surface of 12μm polypropylene separator (Hefei Changyang New Energy Technology Co., Ltd.), the coating thickness is 4μm, and get the coated separator after drying in 60℃ oven for 10min.

[0088] Comparative Example 3 (only using biomass porous carbon):

[0089] A preparation method of a coated separator containing biomass carbon material, the steps are:

[0090] (1) After washing, drying and crushing the rice straw, immerse it in 1mol / L ferric chloride solution for 12h to get activated straw;

[0091] (2) Put a porcelain boat in a high-temperature tube furnace under argon protection, put the activated straw into the porcelain boat, and heat at a rate of 5℃ / min to 700℃ under argon protection, and keep for 4h;

[0092] (3) Wash the product in the porcelain boat with dilute sulfuric acid (10wt%), deionized water and ethanol alternately for five times, and get biomass porous carbon after drying;

[0093] (4) Mix the biomass porous carbon, epoxy resin adhesive (3M DP100NS), dispersant carboxymethyl cellulose sodium and deionized water according to the mass ratio of 20:2:13:65 to get coating slurry;

[0094] (5) The coating slurry is coated on the surface of a 12 μm polypropylene separator (Hefei Changyang New Energy Technology Co., Ltd.), with a coating thickness of 4 μm, and the coated separator is obtained after drying in a 60°C oven for 10 min.

[0095] Comparative Example 4 (using only carbon nanotubes):

[0096] A method for preparing a coated separator comprising a biomass carbon material, comprising the following steps:

[0097] (1) After washing, drying and crushing rice straw, the rice straw is soaked in a 1 mol / L ferric chloride solution for 12 h to obtain activated straw;

[0098] (2) A porcelain boat is placed in a high-temperature tube furnace under argon protection, and the mixture of activated straw and nano-iron powder is placed in the porcelain boat, with the mass of nano-iron powder being 5% of the mass of activated straw; the temperature is raised to 700°C at a rate of 5°C / min under argon protection, and the temperature is maintained for 4 h;

[0099] (3) The product in the porcelain boat is washed with dilute sulfuric acid (10 wt%), deionized water and ethanol alternately for five times, and dried to obtain biomass carbon nanotubes;

[0100] (4) The biomass carbon nanotubes, epoxy resin adhesive (3M DP100NS), dispersant carboxymethyl cellulose sodium and deionized water are mixed uniformly at a mass ratio of 20:2:13:65 to obtain a coating slurry;

[0101] (5) The coating slurry is coated on the surface of a 12 μm polypropylene separator (Hefei Changyang New Energy Technology Co., Ltd.), with a coating thickness of 4 μm, and the coated separator is obtained after drying in a 60°C oven for 10 min.

[0102] The performance of the coated separators prepared in the above examples and comparative examples is tested, and the results are shown in Table 1.

[0103] The test items and methods are as follows:

[0104] (1) Tensile strength: tested by using a CTM universal testing machine from Xieqiang, including the test of the longitudinal and transverse tensile strength of the separator, 5 samples in each direction, and the average value is calculated;

[0105] (2) Puncture strength: tested by using a CTM universal testing machine from Xieqiang, 5 samples are tested, and the average value is calculated;

[0106] (3) Film breaking temperature: measured by using the resistance mutation method, and the point of sudden increase in resistance is the film breaking temperature;

[0107] (4) Liquid absorption rate: the liquid absorption rate of the coated separator was tested by weighing method. First, the mass of the completely dried separator was recorded, then the completely dried separator was soaked in electrolyte for 24 h, the surface electrolyte was wiped dry, and the mass of the separator was recorded again. The difference between the two records was the liquid absorption rate of the separator. Five samples were tested, and the average value was calculated;

[0108] (5) Ion conductivity: the bulk resistance was tested by using the electrochemical impedance spectroscopy (EIS) mode of the VMP3B-10 electrochemical workstation (Bio-Logic Science Instruments) with the steel sheet / separator / steel sheet assembly, wherein the perturbation voltage amplitude was 5 mV, and the frequency was 10 mHz~1 MHz. The relationship between the bulk resistance and the ion conductivity was that the ion conductivity was equal to the ratio of the thickness of the separator to the product of the resistance of the separator and the effective contact area.

[0109] Table 1: Performance test results of coated separators

[0110]

[0111] From the data in Table 1, it can be seen that the coated separators prepared in Examples 1~3 using the method in the application have high tensile strength, puncture strength and membrane breaking temperature, and also have high liquid absorption rate and ion conductivity.

[0112] In Comparative Example 1, the activation time of the straw in the ferric chloride solution was too long, and the membrane breaking temperature was not greatly affected. However, due to excessive activation, more ions were introduced, and during the calcination process, the structure of the carbon material collapsed. The structure collapse of the carbon material had a great influence on the electrochemical performance of the carbon material. At the same time, due to the structure collapse, the porous structure was significantly damaged, which significantly reduced the liquid absorption rate of the separator compared with Example 1.

[0113] The performance of the separator in Comparative Example 2 is also decreased compared with that in Example 1, because the excessive nano-iron powder added during calcination can promote the nucleation and growth of carbon nanotubes to some extent. However, excessive iron powder content can cause defects in the structure of carbon nanotubes. Because excessive iron powder can make the reaction too violent, causing the deposition and arrangement of carbon atoms to lose order, destroying the regular tubular structure of carbon nanotubes, and affecting the crystallinity and graphitization degree. At the same time, in the biomass pyrolysis process, due to the presence of water, part of the iron powder will be oxidized to Fe3O4, and the increase of iron powder content can increase the generation amount of impurities such as Fe3O4; these impurities can adhere to the surface of carbon nanotubes or be embedded in their structure, not only affecting the purity of carbon nanotubes, but also possibly having a negative impact on their physical and chemical properties, such as electrical conductivity, mechanical properties, etc. In addition, the increase of iron powder content can change the path and selectivity of the pyrolysis reaction, in addition to promoting the formation of carbon nanotubes, it can also trigger other side reactions, consume more carbon sources, and reduce the amount of carbon sources for carbon nanotube growth, thereby reducing the yield of carbon nanotubes.

[0114] In Comparative Example 3, only biomass porous carbon is used as coated particles, and no biomass carbon nanotubes are added, which lacks the high electrical conductivity of carbon nanotubes, and the liquid absorption rate and ionic conductivity of the separator are both decreased compared with Example 1.

[0115] In Comparative Example 4, only biomass carbon nanotubes are used as coated particles, and no biomass porous carbon is added, and the puncture strength and liquid absorption rate and ionic conductivity of the separator are all decreased. This is mainly because when biomass carbon nanotubes and biomass porous carbon are used together, a continuous conductive network can be constructed, with carbon nanotubes constructing a long-range conductive network and porous carbon providing local conductive points, thereby optimizing lithium ion transmission; when carbon nanotubes are used alone, carbon nanotubes are prone to accumulation, and local fracture can lead to a decrease in ion transmission performance.

[0116] The above-described examples only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as limiting the scope of the patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application. Therefore, the protection scope of the present application patent should be subject to the appended claims.

Claims

1. Use of a coated separator comprising a biomass carbon material in a lithium battery, characterized in that, The preparation method of the coated separator containing biomass carbon material comprises the following steps: (1) washing, drying and crushing the straw, and then soaking in a chlorinated salt solution to obtain activated straw; the concentration of the chlorinated salt solution is 0.5-2 mol / L, and the soaking time of the straw in the chlorinated salt solution is 12-24 h; (2) calcining a part of the activated straw in an inert atmosphere to obtain biomass porous carbon with uniform and evenly distributed pores; (3) mixing another part of the activated straw with nano-iron powder, and then calcining in an inert atmosphere to obtain biomass carbon nanotubes; the mass of the nano-iron powder is 5-10% of the mass of the activated straw; (4) mixing the biomass porous carbon and the biomass carbon nanotubes in a mass ratio of 1:3-5 to obtain a mixed biomass carbon material; (5) mixing the mixed biomass carbon material with an adhesive, a dispersant and water to obtain a coating slurry; (6) coating the coating slurry on the surface of a base film, and drying to obtain the coated separator.

2. Use of a coated separator comprising a biomass carbon material in a lithium battery according to claim 1, characterized in that, The chlorinated salt solution in step (1) is one or more of cobalt chloride solution, iron chloride solution, copper chloride solution and nickel chloride solution.

3. Use of the coated separator comprising biomass carbon material according to claim 1 in lithium batteries, characterized in that, The calcination temperature in step (2) is 600-1200°C, and the calcination time is 3-5 h.

4. Use of the coated separator comprising biomass carbon material according to claim 1 in lithium batteries, characterized in that, The calcination temperature in step (3) is 700-900°C, and the calcination time is 3-5 h.

5. Use of the coated separator comprising biomass carbon material according to claim 1 in lithium batteries, characterized in that, In step (5), 15-25 parts of the mixed biomass carbon material is mixed with 1-3 parts of an adhesive, 10-15 parts of a dispersant and 60-70 parts of water to obtain a coating slurry.

6. Use of the coated separator comprising biomass carbon material according to claim 1 in lithium batteries, characterized in that, In step (6), the thickness of the base film is 12-20 μm, and the thickness of the coating after coating is 3-5 μm.

7. Use of the coated separator comprising biomass carbon material according to claim 1 or 6 in a lithium battery, characterized in that, The base film in step (6) is a polypropylene separator.

8. A coated separator comprising a biomass carbon material, characterized by, The preparation method is prepared by using any one of claims 1-7.

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