Aramid diaphragm for lithium battery without negative electrode structure

Abstract

The invention relates to the technical field of lithium battery diaphragms, and particularly discloses an aramid diaphragm for a lithium battery without a negative electrode structure. The aramid diaphragm comprises a base material layer and coating layers, the coating layers are coated on the front and back surfaces of the base material layer, the coating layers are formed by curing aramid slurry, and the aramid slurry comprises the following components in parts by weight: 14-18% of aromatic polyester, 2-3% of kapok fiber powder, 3.2-3.6% of an adhesive, 3-5% of a reinforcing agent, 0.7-1.4% of a pore forming agent, 4.8-6.8% of filler and the balance of a solvent. A lithium battery without a negative electrode structure is a novel lithium ion battery, foamy copper is generally used as a negative electrode current collector, and lithium ions are directly deposited on the surface of the foamy copper during charging to form a lithium metal elementary substance. The aramid diaphragm disclosed by the invention has good electrolyte wettability, so that the polarization degree can be reduced, the phenomena of internal short circuit and battery failure caused by lithium dendrite growth can be relieved, and the service life of the negative-electrode-free lithium battery can be effectively prolonged.

Description

Technical Field

[0001] The present application relates to the technical field of lithium battery separators, and more specifically, to an aramid separator for a lithium battery without a negative electrode structure. Background Art

[0002] Lithium-ion batteries are secondary batteries that are charged and discharged mainly by the insertion and extraction of lithium ions between the positive and negative electrodes. Taking LiCoO2 / C as an example, when this type of lithium-ion battery is charged, lithium ions are extracted from the lattice of the positive electrode LiCoO2 and transformed into an ionic state, and then directed to move to the graphite negative electrode in the diaphragm rich in organic electrolyte and embedded in the graphite lattice. At this time, the positive electrode changes from a lithium-rich state to a lithium-poor state, and the negative electrode changes from a lithium-poor state to a lithium-rich state; when discharging, lithium ions are extracted from the lithium-rich graphite negative electrode into the electrolyte, and then directed to move to the LiCoO2 positive electrode in the diaphragm and insert into the LiCoO2 lattice. At this time, the positive electrode changes from a lithium-poor state to a lithium-rich state again. Lithium batteries without negative electrode structures are a new type of lithium-ion battery, which usually uses copper foam as the negative electrode current collector. When charging, lithium ions are directly deposited on the surface of copper foam to form lithium metal single substance. During this process, if the separator has good electrolyte wettability, it can reduce the degree of polarization and alleviate the internal short circuit and battery failure caused by the growth of lithium dendrites, which can effectively improve the service life of the negative electrode-free lithium battery.

[0003] In the structure of lithium batteries, the diaphragm is one of the key internal components. The performance of the diaphragm determines the interface structure and internal resistance of the battery, directly affecting the battery's capacity, cycle and safety performance. A diaphragm with excellent performance plays an important role in improving the overall performance of the battery. The main function of the diaphragm is to separate the positive and negative electrodes of the battery to prevent the two electrodes from contacting and short-circuiting. In addition, it also has the function of allowing electrolyte ions to pass through. The diaphragm material is non-conductive, and its physical and chemical properties have a great influence on the performance of the battery. Generally speaking, different types of batteries use different diaphragms. For lithium battery series, since the electrolyte is an organic solvent system, a diaphragm material resistant to organic solvents is required, and a high-strength thin-film polyolefin porous membrane is generally used. At present, polyolefin materials such as polyethylene (PE) and polypropylene (PP) are the main raw materials for commercial diaphragms.

[0004] Regarding the above-mentioned related technologies, the inventors believe that the microporous diaphragm prepared by polyolefin materials has poor wettability and limited liquid absorption rate, and cannot fully contact with the electrolyte, which not only limits the performance of the lithium battery, but also easily brings some safety hazards. Summary of the invention

[0005] In the related art, the microporous diaphragm prepared by polyolefin materials has poor wettability, limited liquid absorption rate, and cannot fully contact with the electrolyte, which not only limits the performance of lithium batteries, but also easily brings some safety hazards. In order to improve this defect, the present application provides an aramid diaphragm for a lithium battery without a negative electrode structure.

[0006] The present application provides an aramid diaphragm for a lithium battery without a negative electrode structure, which adopts the following technical solution: An aramid diaphragm for a lithium battery without a negative electrode structure, the aramid diaphragm comprising a substrate layer and a coating layer, the coating layer being coated on both sides of the substrate layer, the coating layer being formed by curing aramid slurry, the aramid slurry comprising the following components in parts by weight: 14-18% aromatic polyester, 2-3% kapok fiber powder, 3.2-3.6% adhesive, 3-5% reinforcing agent, 0.7-1.4% pore former, 4.8-6.8% filler, the remainder being supplemented to 100% by a solvent; the aromatic polyester comprising meta-aramid resin and para-aramid resin, the filler comprising titanium dioxide powder.

[0007] By adopting the above technical scheme, the present application selects meta-aramid resin and para-aramid resin as the main components of aramid slurry, and the coating layer prepared with these two aromatic polyesters as the substrate has good wettability, which helps the diaphragm to fully contact with the electrolyte. During the curing process of the aramid slurry, the two aromatic polyesters form pores as the solvent evaporates. In this process, the pore-forming agent can effectively promote the generation of pores, thereby obtaining a coating layer with a relatively dense pore distribution. These pore structures reduce the barrier effect of the diaphragm on the electrolyte and provide sufficient space inside the diaphragm so that the diaphragm can effectively accommodate the electrolyte. Kapok fiber powder has good oil absorption, and the titanium dioxide powder in the filler has good lyophilicity. These components can effectively transmit lithium battery electrolyte with organic solvent as the medium. Through the combination of the above components, the aramid diaphragm of the present application fully overcomes the defect of poor liquid absorption of traditional polyolefin diaphragms, can fully contact with the electrolyte, has a high liquid absorption rate in the electrolyte, and is suitable for application in lithium batteries without negative electrode structure. The aramid diaphragm of the present application has good electrolyte wettability, and thus can reduce the degree of polarization, and alleviate the internal short circuit and battery failure caused by the growth of lithium dendrites, and can effectively increase the service life of the negative electrode-free lithium battery.

[0008] Preferably, the meta-aramid resin is prepared according to the following method: (1) adding m-phenylenediamine to a solvent under nitrogen protection, stirring and dissolving, and then freezing and storing to obtain a m-phenylenediamine solution for standby use; (2) adding isophthaloyl chloride to the m-phenylenediamine solution, cleaning the inner wall of the reaction container with a solvent, first reacting under freezing conditions, then heating the reaction, and finally adding an acid-binding agent, calcium hydroxide, to react until the reaction is complete, thereby obtaining a m-aramid resin.

[0009] By adopting the above technical scheme, the present application adopts a low-temperature polycondensation method to synthesize meta-aramid resin using meta-phenylenediamine and isophthaloyl chloride as monomers.

[0010] Preferably, the adhesive comprises PVDF.

[0011] By adopting the above technical solution, during the curing process of the aramid slurry, PVDF and aromatic polyester gradually separate, cross-linking occurs between the chain segments, and the PVDF chain segments accumulate to form microspheres. Larger pore structures will be generated near the PVDF microspheres, which can enable the diaphragm to absorb and retain more electrolyte, thereby improving the liquid absorption of the diaphragm.

[0012] Preferably, the filler further comprises boehmite powder.

[0013] By adopting the above technical solution, the boehmite powder has a certain supporting effect, which can reduce the filling of the pores of the substrate layer by the aramid slurry and help improve the liquid absorption of the diaphragm.

[0014] Preferably, the substrate layer is a PE-based film with polydopamine on the surface.

[0015] By adopting the above technical scheme, polydopamine can be fully adhered to the surface of the PE base film through the synergistic effect of amino groups and phenolic hydroxyl groups. At the same time, the abundant amino groups and hydroxyl groups on the surface of polydopamine can improve the poor lyophilicity of the PE base film. After coating with aramid slurry, an aramid diaphragm with better liquid absorption performance can be obtained.

[0016] Preferably, the substrate layer is prepared according to the following method: (1) adding dopamine hydrochloride to a Tris solution to dissolve it, obtaining a dopamine solution for later use; adding a PE base film to ethanol for washing, and then removing it for later use; (2) The PE base film is immersed in a dopamine solution and then oscillated at a constant temperature to obtain a base material layer.

[0017] By adopting the above technical scheme, the present application first uses Tris solution and dopamine hydrochloride to prepare a dopamine solution, and pretreats the PE base film, and then loads the dopamine in the dopamine solution onto the surface of the PE base film by immersion modification to obtain a substrate layer.

[0018] Preferably, the filler also includes nano-alumina.

[0019] By adopting the above technical scheme, nano-alumina can promote heterogeneous nucleation during the solidification of aramid slurry, reduce the free energy barrier required to overcome for pore nucleation, increase the probability of pore formation during phase separation, increase the porosity of the coating layer, and improve the liquid absorption performance of the aramid diaphragm.

[0020] Preferably, the pore-forming agent is a mixture of lithium bromide and glycerol.

[0021] By adopting the above technical solution and selecting the above pore-forming agent, the pore-forming effect can be fully achieved, thereby improving the liquid absorption performance of the aramid diaphragm.

[0022] Preferably, the filler also includes at least one of nanocellulose and graphene oxide.

[0023] By adopting the above technical solution, nanocellulose and graphene oxide can be assembled on the surface of the coating layer to form a multilayer structure, which can assist in the absorption and storage of electrolyte and help improve the liquid absorption performance of the aramid diaphragm.

[0024] In summary, this application has the following beneficial effects: 1. The aramid diaphragm of the present application fully overcomes the defect of poor liquid absorption of traditional polyolefin diaphragms, can fully contact with the electrolyte, has a high liquid absorption rate in the electrolyte, and is suitable for use in lithium batteries without negative electrode structure.

[0025] 2. In this application, PVDF is preferably used as an adhesive. During the curing process of the aramid slurry, PVDF and aromatic polyester gradually separate, cross-linking occurs between the segments, and the PVDF segments accumulate to form microspheres. The PVDF microspheres have larger pore structures near them, which enable the diaphragm to absorb and retain more electrolyte, thereby improving the liquid absorption of the diaphragm.

[0026] 3. The present application defines the substrate layer and its preparation method. The polydopamine on the surface of the substrate layer can be fully adhered to the surface of the PE base film through the synergistic effect of amino groups and phenolic hydroxyl groups. At the same time, the abundant amino groups and hydroxyl groups on the surface of the polydopamine can improve the defect of poor lyophilicity of the PE base film. After coating with aramid slurry, an aramid diaphragm with better liquid absorption performance can be obtained. DETAILED DESCRIPTION

[0027] The present application is further described in detail below in conjunction with embodiments, preparation examples and comparative examples. The raw materials involved in the present application can all be obtained commercially.

[0028] Preparation Example of Meta-aramid Resin The following is an explanation using Preparation Example 1.

[0029] Preparation Example 1 In this preparation example, the molar ratio of m-phenylenediamine to isophthaloyl chloride is 1.05:1.

[0030] In this preparation example, the meta-aramid resin was prepared according to the following method: (1) adding m-phenylenediamine to N,N-dimethylacetamide solvent under nitrogen protection, stirring to dissolve, and freezing and storing at -15°C for 5 minutes to obtain a m-phenylenediamine solution for later use; (2) adding isophthaloyl chloride to the m-phenylenediamine solution in a ratio of 1:4 twice, reacting at low temperature for 5 minutes after the first addition, and then adding the second time. After the addition of isophthaloyl chloride, the inner wall of the reaction container is cleaned with a solvent N,N-dimethylacetamide, first reacting at -10°C for 15 minutes, then heating to 70°C at a uniform speed for 1 hour, and continuing to react for 1 hour. Finally, an acid-binding agent, calcium hydroxide, is added to react for 30 minutes to obtain a m-aramid resin.

[0031] Preparation Example of Base Material Layer The following is an explanation using Preparation Example 2.

[0032] Preparation Example 2 In this preparation example, the porosity of the PE-based membrane is 60%, the average pore diameter is 65 nm, and the thickness is 35 μm.

[0033] In this preparation example, the substrate layer was prepared according to the following method: (1) adding dopamine hydrochloride to a 0.1 mol / L Tris solution (pH=8.5) at a concentration of 10 mg / L to dissolve the solution to obtain a dopamine solution for later use; washing the PE base film in ethanol, and then removing the solution for later use; (2) The PE base film is immersed in a dopamine solution and then oscillated at a constant temperature for 5 hours to obtain a base material layer.

[0034] Preparation Example of Para-aramid Resin The following is an explanation using Preparation Example 3.

[0035] Preparation Example 3 In this preparation example, the para-aramid resin was prepared according to the following method: Add 84 kg of N,N-dimethylacetamide solvent and 5.45 kg of anhydrous calcium chloride to the reactor, heat to 50°C under nitrogen atmosphere, stir for 4 hours to completely dissolve the calcium chloride, then add 2.658 kg of p-phenylenediamine, and continue stirring until the solid is completely dissolved. Use chilled water to lower the temperature of the solution to 10°C, add 4.940 kg of terephthaloyl chloride, and react for 1 hour to obtain para-aramid resin. Example

[0036] Examples 1-5 The following description is given by taking Example 1 as an example.

[0037] Example 1 In this embodiment, the aromatic polyester is prepared by mixing meta-aramid resin and para-aramid resin in a weight ratio of 3:2, the meta-aramid resin is prepared according to the method of Preparation Example 1, and the para-aramid resin is prepared according to the method of Preparation Example 3. The filler is titanium dioxide powder (average particle size 1.7 μm), the average particle size of kapok fiber powder is 260 nm, the adhesive is PVDF (Arkema, France), the reinforcing agent is polyimide (model P84@NT2), the pore-forming agent is mixed with lithium bromide and propylene glycol in a weight ratio of 1:30, and the solvent is N,N-dimethylacetamide.

[0038] This embodiment provides an aramid diaphragm for a lithium battery without a negative electrode structure, the aramid diaphragm comprising a substrate layer and a coating layer, the substrate layer is prepared according to the method of Preparation Example 2, the coating layer is coated on both sides of the substrate layer, and the thickness of the coating layer is 5 μm. The coating layer is formed by curing aramid slurry, and the aramid slurry comprises the following components by weight: 14% aromatic polyester, 2% kapok fiber powder, 3.2% adhesive, 3% reinforcing agent, 0.7% pore former, 4.8% filler, and the balance is supplemented to 100% by solvent.

[0039] The method for preparing an aramid diaphragm for a lithium battery without a negative electrode structure comprises the following steps: (1) mixing aromatic polyester, kapok fiber powder, adhesive, reinforcing agent, pore-forming agent, filler and solvent, stirring to obtain aramid slurry, and setting aside; performing corona pretreatment on the base film, and setting aside; (2) The aramid slurry is coated on both sides of the base film by gravure coating at a coating rate of 5 m / min to obtain a coating layer; (3) The coating layer is preheated with water vapor for 15 s in an environment with 95% humidity, and then hot air dried to solidify the coating layer into a 5 μm thick coating, thereby obtaining an aramid diaphragm for a lithium battery without a negative electrode structure.

[0040] As shown in Table 1, the main difference between Examples 1-5 is that the raw material ratios of the aramid slurry are different.

[0041] Table 1 Ratio of raw materials for aramid slurry Example 6 The difference between this embodiment and embodiment 5 is that the filler further includes boehmite powder, the average particle size of the boehmite powder is 1 μm, and the amount of the boehmite powder accounts for 20% of the total weight of the filler.

[0042] Example 7 The difference between this embodiment and embodiment 6 is that the filler further comprises nano-alumina, the amount of the nano-alumina accounts for 8% of the total weight of the filler, and the average particle size of the nano-alumina is 50 nm.

[0043] Example 8 The difference between this embodiment and embodiment 7 is that the filler further comprises nanocellulose, and the amount of nanocellulose accounts for 5% of the total weight of the filler.

[0044] Example 9 The difference between this embodiment and embodiment 7 is that the filler further includes graphene oxide, and the amount of graphene oxide used accounts for 1% of the total weight of the filler.

[0045] Example 10 The difference between this embodiment and embodiment 7 is that the filler further includes nanocellulose and graphene oxide, and the amounts of nanocellulose and graphene oxide are 5% and 1% of the total weight of the filler, respectively.

[0046] Comparative Example Comparative Example 1 The difference between this comparative example and Example 1 is that a PE-based membrane is directly selected as the diaphragm, and the porosity of the PE-based membrane is 60%, the average pore diameter is 65 nm, and the thickness is 35 μm.

[0047] Comparative Example 2 The difference between this comparative example and Example 1 is that the meta-aramid resin is replaced with the same weight of para-aramid resin.

[0048] Comparative Example 3 The difference between this comparative example and Example 1 is that the para-aramid resin is replaced with the meta-aramid resin of the same weight.

[0049] Comparative Example 4 The difference between this comparative example and Example 1 is that the components of the aramid slurry do not include kapok fiber powder.

[0050] Comparative Example 5 The difference between this comparative example and Example 1 is that the components of the aramid slurry do not include fillers.

[0051] Comparative Example 6 The difference between this comparative example and Example 1 is that the components of the aramid slurry do not include a pore former.

[0052] Comparative Example 7 The difference between this comparative example and Example 1 is that the substrate layer is a PE base film having no polydopamine on the surface.

[0053] Comparative Example 8 The difference between this comparative example and Example 1 is that the amount of adhesive used is adjusted to half of that in Example 1.

[0054] Performance testing methods The liquid absorption rate of the diaphragm was detected using electrolyte, and the electrolyte parameters were: 1 mol / LLiPF6 / EC∶DMC∶EMC (volume ratio 1∶1∶1) / 1%VC.

[0055] Before testing, the prepared aramid diaphragm (Comparative Example 1 uses a PE base film) was cut into a circular diaphragm with a diameter of 16 mm as a sample. The entire testing process was carried out in a glove box, and the sample was immersed in the above electrolyte. After immersion for 30 minutes, it was taken out and weighed, and the liquid absorption rate was calculated. The calculation method was the weight increased after immersion / the weight of the dry film before immersion × 100%. After completing the test and calculation, the liquid absorption rate of Comparative Example 1 was used as a reference, and the ratio between the liquid absorption rate of each embodiment and comparative example and the liquid absorption rate of Comparative Example 1 was calculated, and the ratio was recorded as the relative liquid absorption rate. The results are shown in Table 2.

[0056] Table 2 Relative liquid absorption rate sample Relative liquid absorption rate / % sample Relative liquid absorption rate / % Example 1 139.6 Example 10 146.9 Example 2 141.1 Comparative Example 1 100.0 Example 3 141.4 Comparative Example 2 124.7 Example 4 142.2 Comparative Example 3 120.6 Example 5 142.6 Comparative Example 4 132.6 Example 6 143.7 Comparative Example 5 128.4 Example 7 145.5 Comparative Example 6 119.5 Example 8 145.8 Comparative Example 7 123.2 Example 9 145.6 Comparative Example 8 115.4 It can be seen from Examples 1-5 and Comparative Example 1 and Table 2 that the relative liquid absorption rates measured in Examples 1-5 are all higher than those in Comparative Example 1, indicating that through the coordinated cooperation of various components, the aramid diaphragm of the present application fully overcomes the defect of poor liquid absorption of traditional polyolefin diaphragms, can fully contact with the electrolyte, and has a high liquid absorption rate in the electrolyte, and is suitable for application in lithium batteries without a negative electrode structure.

[0057] Combining Example 1 and Comparative Example 2 and Table 2, it can be seen that the relative liquid absorption rate measured in Example 1 is higher than that in Comparative Example 2. This is because Comparative Example 2 lacks meta-aramid resin and cannot achieve the synergistic combination of the two aramid resins. The para-aramid resin alone cannot effectively improve the wettability of the aramid diaphragm to the electrolyte.

[0058] Combining Example 1 and Comparative Example 3 and Table 2, it can be seen that the relative liquid absorption rate measured in Example 1 is higher than that in Comparative Example 3. This is because Comparative Example 3 lacks para-aramid resin and cannot achieve the synergistic combination of the two aramid resins. The meta-aramid resin alone cannot effectively improve the wettability of the aramid diaphragm to the electrolyte.

[0059] Combining Example 1 and Comparative Example 4 and Table 2, it can be seen that the relative liquid absorption rate measured in Example 1 is higher than that in Comparative Example 4. This is because Comparative Example 4 lacks kapok fiber powder and cannot utilize the good liquid absorption of kapok fiber powder to promote the absorption of electrolyte by the aramid membrane, resulting in poor liquid absorption of the membrane.

[0060] Combining Example 1 and Comparative Example 5 and Table 2, it can be seen that the relative liquid absorption rate measured in Example 1 is higher than that in Comparative Example 5. This is because Comparative Example 5 lacks titanium dioxide powder and cannot utilize the good lyophilicity of titanium dioxide powder to promote the absorption of electrolyte by the aramid diaphragm, resulting in poor liquid absorption of the diaphragm.

[0061] Combining Example 1 and Comparative Example 6 and Table 2, it can be seen that the relative liquid absorption rate measured in Example 1 is higher than that in Comparative Example 6. This is because Comparative Example 6 lacks a pore-forming agent and cannot utilize the pore-forming agent to promote the formation of pores. Since the formation of pores is affected, the aramid diaphragm cannot fully absorb and accommodate the electrolyte and has poor liquid absorption.

[0062] Combining Example 1 and Comparative Example 7 and Table 2, it can be seen that the relative liquid absorption rate measured in Example 1 is higher than that in Comparative Example 7. This is because the substrate layer of Comparative Example 7 lacks polydopamine, and the rich amino and hydroxyl groups on the surface of polydopamine cannot be used to improve the poor lyophilicity of the PE-based membrane, resulting in poor liquid absorption of the diaphragm.

[0063] Combining Example 1 and Comparative Example 8 and Table 2, it can be seen that the relative liquid absorption rate measured in Example 1 is higher than that in Comparative Example 8. This is because the amount of PVDF used in Comparative Example 8 is small, and PVDF cannot be used to promote the formation of pores, resulting in poor liquid absorption of the diaphragm.

[0064] Combining Example 5 and Example 6 and Table 2, it can be seen that the relative liquid absorption rate measured in Example 6 is higher than that in Example 5. This is because the boehmite powder has a certain supporting effect, which can reduce the filling of the pores of the substrate layer by the aramid slurry, and help to improve the liquid absorption of the diaphragm.

[0065] Combining Example 6 and Example 7 with Table 2, it can be seen that the relative liquid absorption rate measured in Example 7 is higher than that in Example 6. This is because the nano-alumina can promote heterogeneous nucleation during the solidification of the aramid slurry, reduce the free energy barrier required to overcome for pore nucleation, increase the probability of pore formation during the phase separation process, increase the porosity of the coating layer, and improve the liquid absorption performance of the aramid diaphragm.

[0066] It can be seen from Example 7, Examples 8-10 and Table 2 that the relative liquid absorption rate measured in Example 10 is higher than that in Examples 7-9. This is because nanocellulose and graphene oxide can be assembled on the surface of the coating layer to form a multilayer structure, which can assist in the absorption and storage of the electrolyte and help improve the liquid absorption performance of the aramid diaphragm.

[0067] The above embodiments are merely explanations of the present application and are not limitations of the present application. After reading this specification, those skilled in the art may make modifications to the embodiments of the present application without any creative contribution as needed. However, as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. An aramid diaphragm for a lithium battery without a negative electrode structure, characterized in that: The aramid membrane includes a substrate layer and a coating layer, wherein the coating layer is coated on both sides of the substrate layer, and the coating layer is solidified by aramid slurry, wherein the aramid slurry includes the following components in parts by weight: 14-18% aromatic polyester, 2-3% kapok fiber powder, 3.2-3.6% adhesive, 3-5% reinforcing agent, 0.7-1.4% pore former, 4.8-6.8% filler, and the remainder is supplemented to 100% by solvent; the aromatic polyester includes meta-aramid resin and para-aramid resin, and the filler includes titanium dioxide powder.

2. The aramid diaphragm for a lithium battery without a negative electrode structure according to claim 1, characterized in that: The meta-aramid resin is prepared according to the following method: (1) adding m-phenylenediamine to a solvent under nitrogen protection, stirring to dissolve, and then freezing and storing to obtain a m-phenylenediamine solution for standby use; (2) Add isophthaloyl chloride to the m-phenylenediamine solution, clean the inner wall of the reaction container with a solvent, first react under freezing conditions, then heat the reaction, and finally add an acid-binding agent, calcium hydroxide, to react until the reaction is complete, thereby obtaining a m-aramid resin.

3. The aramid diaphragm for a lithium battery without a negative electrode structure according to claim 2, characterized in that: The adhesive includes PVDF.

4. The aramid diaphragm for a lithium battery without a negative electrode structure according to claim 3, characterized in that: The filler also includes boehmite powder.

5. The aramid diaphragm for a lithium battery without a negative electrode structure according to claim 1, characterized in that: The substrate layer is a PE base film with polydopamine on the surface.

6. The aramid diaphragm for a lithium battery without a negative electrode structure according to claim 5, characterized in that: The substrate layer is prepared according to the following method: (1) adding dopamine hydrochloride to a Tris solution to dissolve it, obtaining a dopamine solution for later use; adding a PE base film to ethanol for washing, and then removing it for later use; (2) The PE base film is immersed in a dopamine solution and then oscillated at a constant temperature to obtain a base material layer.

7. The aramid diaphragm for a lithium battery without a negative electrode structure according to claim 1, characterized in that: The filler also includes nano-alumina.

8. The aramid diaphragm for a lithium battery without a negative electrode structure according to claim 7, characterized in that: The pore-forming agent is a mixture of lithium bromide and glycerol.

9. The aramid diaphragm for a lithium battery without a negative electrode structure according to claim 7, characterized in that: The filler also includes at least one of nanocellulose and graphene oxide.

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