A composite diaphragm for semi-solid lithium battery and its preparation method and application

Abstract

The present invention provides a composite diaphragm for a semi-solid lithium battery, a preparation method thereof, and an application thereof. The composite diaphragm comprises a base layer and a PEO layer located on one or both sides of the base layer; the base layer comprises a base film and a coating layer located on one side of the base film; the coating layer comprises aramid and h-BN-LATP; the h-BN-LATP is obtained by hydroxyl-modifying a hexagonal boron nitride layer coated on the surface of LATP. The composite diaphragm can effectively prevent LATP from directly contacting a metallic lithium negative electrode through the cooperation between the layers, while improving the binding force between LATP and aramid. At the same time, the diaphragm's liquid absorption and retention capacity, heat resistance, and ionic conductivity are improved, and the interface impedance between the coating and the electrode is reduced, which helps to improve the battery cycle performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery separators, and in particular relates to a composite separator for semi-solid lithium batteries, a preparation method thereof, and an application thereof. Background Art

[0002] The core of a traditional liquid lithium-ion battery consists of a positive electrode, a negative electrode, an electrolyte (a lithium-containing electrolyte dissolved in an organic compound), and a separator. The separator separates the positive and negative electrodes in a lithium-ion battery, allowing lithium ions to pass freely while blocking electron conduction and preventing short circuits between the positive and negative electrodes. Simultaneously, the porous separator absorbs the electrolyte to form ion channels. Ionic conduction is one of the primary functions of a lithium-ion battery separator, specifically enabling lithium ion conduction within the battery through lithium salt dissociation and lithium ion solvation. However, solvents pose risks such as flammability, volatility, and leakage at high temperatures. Furthermore, lithium hexafluorophosphate, one of the most commonly used electrolytes in commercial lithium-ion batteries, has drawbacks such as poor thermal stability and susceptibility to deliquesce and hydrolysis. The PF5 produced by thermal decomposition at high temperatures can lead to fluorination of solvent impurities. Furthermore, lithium hexafluorophosphate can react with water, alcohols, phenols, aldehydes, and active hydrogen to produce HF, all of which can lead to reduced battery capacity, shortened cycle life, and even safety concerns such as fire or explosion.

[0003] Compared to all-liquid lithium-ion batteries, semi-solid lithium battery separators significantly reduce the amount of liquid electrolyte required, thereby significantly reducing the risk of battery fire or explosion and improving the safety performance of lithium-ion batteries. Currently, most traditional semi-solid lithium-ion batteries are constructed by coating the separator with a solid electrolyte. The solid electrolyte is the core component of the semi-solid lithium-ion battery separator and is also the focus of semi-solid lithium-ion battery research. The performance parameters of semi-solid lithium-ion batteries, such as power density, cycling stability, safety, high- and low-temperature performance, and service life, are largely dependent on the solid electrolyte material coated on the separator. Among them, oxide-based solid electrolytes (such as the NASICON system, LISICON system, and perovskite structure with the general formula ABO3) have been widely studied and have good stability in air, but their interfacial compatibility with electrode materials is poor. Polymer-based electrolytes offer advantages such as excellent machinability, light weight, and low electrode / electrolyte interface impedance, but their ionic conductivity is lower than that of oxide-based solid electrolytes.

[0004] In response to the above problems, the prior art uses a mixture of heat-resistant materials, high molecular polymers and solid electrolytes to form a coating layer on the surface of the base film. The coating layer formed on the surface of the base film by this functional diaphragm has good adhesion to the battery electrode, and has high ionic conductivity, while having good insulation and heat resistance. The battery assembled using this functional diaphragm is not easy to deform and has low internal resistance, good rate and power performance, as well as high needle puncture and high-temperature hot box safety performance and good cycle performance. However, the lithium aluminum titanium phosphate LATP used in this solution is easily reduced and rendered ineffective when in direct contact with the metal lithium negative electrode, resulting in a short battery life. In addition, the poor dispersion of inorganic heat-resistant materials and LATP with high molecular polymers can easily cause powdering problems on the coating surface, affecting the physical properties of the diaphragm. Summary of the Invention

[0005] Based on the technical problems existing in the prior art and the direction of improvement, the present invention provides a composite separator for a semi-solid lithium battery, which is used to solve the problems in the prior art of LATP being reduced due to direct contact with the metal lithium negative electrode and powder falling in the coating due to weak bonding between LATP and aramid.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A composite diaphragm for a semi-solid lithium battery, comprising a base layer and a PEO (polyethylene oxide) layer located on one side or both sides of the base layer;

[0008] The base layer includes a base film and a coating layer located on one side of the base film; the coating layer includes aramid and h-BN-LATP (modified lithium aluminum titanium phosphate); when the PEO layer is located on one side of the base film, the PEO layer is located on one side of the coating layer;

[0009] The h-BN-LATP is obtained by modifying the hexagonal boron nitride layer coated on the surface of LATP with hydroxyl groups.

[0010] The composite separator for semi-solid lithium batteries provided by the present invention comprises a base layer formed by coating a layer comprising aramid and h-BN-LATP on one side of a base membrane, and further comprising a PEO layer on one side (the coating layer side) or both sides of the base layer. The layers work together to effectively prevent direct contact between the LATP and the lithium metal anode, while also improving the bonding strength between the LATP and the aramid. Specifically, the use of chemically inert hexagonal boron nitride as the LATP coating effectively inhibits its reduction reaction with the lithium metal anode. Hydroxylated hexagonal boron nitride forms hydrogen bonds with amino groups in aramid molecules, stabilizing LATP while improving the bonding between h-BN-LATP and aramid. The resulting coating exhibits better dispersibility of h-BN-LATP and a high degree of bonding with aramid, preventing the coating from powdering. Furthermore, the three-dimensional fibrous network structure of aramid can serve as a carrier for h-BN-LATP, while also improving the membrane's ability to absorb and retain liquid and its heat resistance. h-BN-LATP is filled within the three-dimensional aramid structure, reducing the air permeability of the coating and benefiting the improvement of the ionic conductivity of the diaphragm. Combined with a single- or double-sided PEO layer, it can reduce the interfacial impedance between the coating and the electrode, contributing to improved battery cycle performance.

[0011] Optionally, in the coating layer, the mass ratio of the aramid to the h-BN-LATP is (1-10):(1-5).

[0012] Optionally, the base film is a polyolefin base film with a microporous structure; preferably, the base film is made of polyethylene, or a copolymer of ethylene and propylene; more preferably, the base film has a thickness of 5-13.5 μm.

[0013] Optionally, the aramid is selected from poly(m-phenylene isophthalamide) (aramid 1313) and / or poly(p-phenylene terephthalamide) (aramid 1414, aramid II).

[0014] Optionally, the thickness of the composite membrane is less than 20 μm, the thickness of the coating layer is 2-4 μm, and the thickness of the PEO layer is 0.5-2.5 μm.

[0015] The semi-solid lithium battery composite diaphragm provided by the present invention cooperates with each other between each layer to prevent the surface of the composite diaphragm from falling off, thereby significantly improving the ionic conductivity, air permeability and cyclic stability of the composite diaphragm. Among them, the PEO layer and h-BN modification synergistically stabilize LATP, especially when using metallic lithium as the negative electrode, LATP can be avoided from reacting with lithium, and PEO is distributed in particles on the surface of the composite diaphragm. Compared with the unilateral coating of the PEO layer on the base, the PEO layer is coated on both sides of the base, which affects the air permeability of the composite diaphragm, but the impact is not great, and the ionic conductivity will be correspondingly lower. Aramid, as a heat-resistant skeleton material, can cooperate with h-BN-LATP. h-BN-LATP has a pore-forming effect in aramid, thereby improving the ionic conductivity and air permeability of the composite diaphragm.

[0016] The present invention also provides a method for preparing the composite diaphragm for the semi-solid lithium battery, comprising the following steps:

[0017] h-BN-LATP: A hexagonal boron nitride coating is formed on the surface of LATP by chemical vapor deposition, and then the boron nitride coating is modified by hydroxylation to obtain h-BN-LATP;

[0018] Aramid glue: dissolve aramid in a solvent and control the solid content of aramid to be 1.8%-2.2% to obtain aramid glue;

[0019] h-BN-LATP suspension: Disperse h-BN-LATP and solvent evenly to form a suspension, thereby obtaining h-BN-LATP suspension;

[0020] Coating slurry: after the aramid glue solution and the h-BN-LATP suspension are mixed and dispersed evenly, the mixture is filtered and degassed to obtain the coating slurry;

[0021] PEO glue: Mix PEO and solvent evenly to obtain PEO glue;

[0022] Composite diaphragm: The coating slurry is coated on one side of the base film, and is sequentially treated with water vapor and deionized water to obtain a base layer; the PEO glue is then coated on one or both sides of the base layer and dried to obtain a composite diaphragm for a semi-solid lithium battery.

[0023] Optionally, the steps for forming a hexagonal boron nitride coating on the surface of LATP by chemical vapor deposition are as follows:

[0024] At 750-1200° C., chemical vapor deposition reaction is carried out on the surface of LATP using BH3-NH3 as boron source and nitrogen source in a pure N2 atmosphere to obtain LATP with a surface coated with a hexagonal boron nitride layer; preferably, the thickness of the hexagonal boron nitride coating layer is 5-10 nm.

[0025] By adopting the chemical vapor deposition method, chemically inert hexagonal boron nitride with a certain thickness and more defects can be obtained at a lower deposition temperature, thereby ensuring that the deposited layer has a higher lithium ion pass rate.

[0026] Optionally, the method for hydroxylation modification of the boron nitride coating is not specifically limited, and conventional physical methods or chemical methods in the industry can be used. For example, the physical method can be ball milling, and the chemical method can be molten hydroxide or hydrogen peroxide. The steps recommended by the present invention for hydroxylation modification of the boron nitride coating are as follows:

[0027] The LATP coated with a hexagonal boron nitride layer is placed in a 1-10 mol / L alkali solution (conventional inorganic alkali solutions such as potassium hydroxide and sodium hydroxide can be used without specific limitation), heated to 80-150° C. under stirring and maintained for 12-24 hours, and then separated. The obtained solid is washed with deionized water until the pH of the filtrate is neutral, and then dried to obtain h-BN-LATP.

[0028] Optionally, the aramid adhesive further contains a cosolvent, and the mass content of the cosolvent in the aramid adhesive is ≤10%; preferably, the cosolvent is selected from at least one of CaCl2, KOH, LiCl and pyridine;

[0029] In the h-BN-LATP suspension, the mass ratio of the h-BN-LATP to the solvent is 1:5-12.

[0030] Optionally, the solvent is selected from an organic solvent and / or water, and the organic solvent is selected from at least one of NMP, DMSO, DMF and DMAc;

[0031] The coating method is not particularly limited and can be any conventional method in the industry, such as blade coating, roller coating, wire rod coating, and dip coating.

[0032] The present invention also provides a semi-solid lithium-ion battery, comprising the above-mentioned composite diaphragm for a semi-solid lithium battery or the composite diaphragm for a semi-solid lithium battery prepared by the above-mentioned method for preparing the composite diaphragm for a semi-solid lithium battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a scanning electron microscope image of the composite diaphragm for semi-solid lithium batteries prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0034] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0035] The thickness of the boron nitride coating involved in the following examples and comparative examples was calculated based on the deposition rate and time, and the thickness values ​​related to other diaphragms were measured using a Mahr thickness gauge.

[0036] Example 1

[0037] This embodiment provides a composite diaphragm for a semi-solid lithium battery, and the preparation method thereof is as follows:

[0038] Preparation of h-BN-LATP: Using BH3-NH3 as a boron nitride precursor, chemical vapor deposition (CVD) was performed on the LATP surface at 900°C, atmospheric pressure (101.325 kPa), and a pure N2 atmosphere to obtain LATP with a 10 nm thick hexagonal boron nitride coating. This LATP was then added to a 5 mol / L potassium hydroxide solution and heated in an oil bath at 150°C for 24 hours under continuous mechanical stirring. The resulting mixture was filtered and washed multiple times with deionized water until the filtrate had a pH of 7. Finally, the mixture was dried to obtain LATP with a hydroxylated hexagonal boron nitride coating, i.e., h-BN-LATP.

[0039] Preparation of h-BN-LATP suspension: 2 parts by weight of h-BN-LATP was added to 12 parts by weight of N-methylpyrrolidone (NMP) and dispersed at high speed for 20 minutes to obtain a h-BN-LATP suspension;

[0040] Preparation of aramid glue: Take 8 parts of calcium chloride and 90 parts of N-methylpyrrolidone NMP and fully dissolve them under high-speed dispersion conditions, then add 2 parts of aramid 1414 to the above mixed solvent, and then disperse it at high speed for 5 hours to obtain aramid glue.

[0041] Preparation of coating slurry: 50 parts by weight of the above aramid glue was mixed with the above h-BN-LATP suspension, and then dispersed at high speed for 30 minutes. Then, the mixture was filtered through a 400-mesh filter and vacuum-debubbled for 5 minutes to obtain a coating slurry.

[0042] Preparation of PEO glue: 0.5 parts by weight of PEO was mixed with 200 parts by weight of deionized water and subjected to high-speed dispersion treatment for 120 minutes to obtain PEO glue;

[0043] Preparation of composite diaphragm: The above-mentioned coating slurry is evenly coated on one side of a 13.5μm thick polyethylene porous substrate using a wire rod, and the coated wet film is retained in a water vapor atmosphere at 65°C and 85% RH for 60s, then transferred to a pure water tank for washing for 5min, and then transferred to the above-mentioned PEO glue solution for 5s and taken out, and finally dried in an oven at 65°C for 15min to obtain a composite diaphragm for semi-solid lithium batteries with a total thickness of about 3μm for the double-sided PEO layer and the coating layer.

[0044] The composite membrane was subjected to electron microscope scanning. Figure 1 As shown. Figure 1 It can be seen that the h-BN-LATP solid electrolyte is evenly wrapped by aramid fibers inside the coating, with no obvious exposed particles on the surface, and the surface of the obtained coated diaphragm is not easy to fall off.

[0045] Example 2

[0046] This embodiment provides a composite diaphragm for a semi-solid lithium battery, and the preparation method thereof is as follows:

[0047] The preparation of h-BN-LATP, h-BN-LATP suspension, aramid glue and coating slurry are the same as the preparation method in Example 1.

[0048] Preparation of PEO glue: 1 part by weight of PEO was mixed with 200 parts by weight of deionized water and subjected to high-speed dispersion treatment for 120 minutes to obtain PEO glue;

[0049] Preparation of composite diaphragm: The above-mentioned coating slurry is evenly coated on one side of a 7μm thick polyethylene porous substrate using a wire rod, and the coated wet film is retained in a water vapor atmosphere at 65°C and 85% RH for 60s, then transferred to a pure water tank for washing for 5min, and then transferred to the above-mentioned PEO glue solution for 5s and then taken out, and finally dried in an oven at 65°C for 15min to obtain a composite diaphragm for semi-solid lithium batteries with a total thickness of about 3μm for the double-sided PEO layer and the coating layer.

[0050] Example 3

[0051] This embodiment provides a composite diaphragm for a semi-solid lithium battery, and the preparation method thereof is as follows:

[0052] Preparation of h-BN-LATP: Using BH3-NH3 as a boron nitride precursor, chemical vapor deposition (CVD) was performed on the LATP surface at 1100°C, atmospheric pressure (101.325 kPa), and a pure N2 atmosphere to obtain LATP with a 5nm hexagonal boron nitride coating. This LATP was then added to a 5 mol / L sodium hydroxide solution and heated in an oil bath at 150°C for 24 hours under continuous mechanical stirring. The resulting mixture was filtered and washed multiple times with deionized water until the filtrate had a pH of 7. Finally, the mixture was dried to obtain LATP with a hydroxylated hexagonal boron nitride coating, i.e., h-BN-LATP.

[0053] The preparation methods of aramid glue and PEO glue are the same as those in Example 1. The preparation methods of h-BN-LATP suspension and coating slurry are similar to those in Example 1. The only difference is that h-BN-LATP in this example is used in the preparation of h-BN-LATP suspension, and h-BN-LATP suspension in this example is used in the preparation of coating slurry.

[0054] Preparation of composite diaphragm: The above-mentioned coating slurry is evenly coated on one side of a 9μm thick polyethylene porous substrate using a wire rod, and the coated wet film is retained in a water vapor atmosphere at 65°C and 85% RH for 60s, then transferred to a pure water tank for washing for 5min, and then transferred to the above-mentioned PEO glue solution for 5s and taken out, and finally dried in an oven at 65°C for 15min to obtain a composite diaphragm for semi-solid lithium batteries with a total thickness of about 3μm for the double-sided PEO layer and the coating layer.

[0055] Example 4

[0056] This embodiment provides a composite diaphragm for a semi-solid lithium battery, and the preparation method thereof is as follows:

[0057] The preparation methods of h-BN-LATP, aramid glue and PEO glue are the same as those in Example 1. The preparation method of the coating slurry is similar to that in Example 1, with the only difference being that the h-BN-LATP suspension in this example is used in the preparation of the coating slurry.

[0058] Preparation of h-BN-LATP suspension: 1 part by weight of h-BN-LATP was added to 12 parts by weight of N-methylpyrrolidone (NMP) and dispersed at high speed for 20 minutes to obtain a h-BN-LATP suspension;

[0059] Preparation of composite diaphragm: The above-mentioned coating slurry is evenly coated on one side of a 12μm thick polyethylene porous substrate using a wire rod, and the coated wet film is retained in a water vapor atmosphere of 65°C and 85% RH for 60s, then transferred to a pure water tank for washing for 5min, and then transferred to the above-mentioned PEO glue solution for 5s and taken out, and finally dried in an oven at 65°C for 15min to obtain a composite diaphragm for semi-solid lithium batteries with a total thickness of about 3μm for the double-sided PEO layer and the coating layer.

[0060] Example 5

[0061] This embodiment provides a composite diaphragm for a semi-solid lithium battery, and the preparation method thereof is as follows:

[0062] The preparation methods of h-BN-LATP, h-BN-LATP suspension, aramid adhesive, coating slurry and PEO adhesive are the same as those in Example 1.

[0063] Composite membrane preparation: The coating slurry was evenly applied to one side of a 13.5 μm thick polyethylene porous substrate using a wire rod. The coated wet membrane was held in a water vapor atmosphere at 65°C and 85% RH for 60 seconds, then rinsed in a pure water tank for 5 minutes. The PEO glue was then evenly applied to one side of the coating layer using a wire rod. Finally, the membrane was dried in an oven at 65°C for 15 minutes, resulting in a semi-solid lithium battery composite membrane with a combined thickness of approximately 3 μm for the PEO layer and coating layer on one side.

[0064] Example 6

[0065] This embodiment provides a composite diaphragm for a semi-solid lithium battery, and the preparation method thereof is as follows:

[0066] The preparation methods of h-BN-LATP, aramid adhesive and PEO adhesive are the same as those in Example 1. Preparation of h-BN-LATP suspension:

[0067] 0.2 parts by weight of h-BN-LATP was added to 1.2 parts by weight of N-methylpyrrolidone (NMP) and dispersed at high speed for 20 minutes to obtain a suspension of h-BN-LATP;

[0068] The preparation method of the coating slurry is similar to that of Example 1, except that the h-BN-LATP suspension in this example is used.

[0069] Composite membrane preparation: The coating slurry was evenly applied to one side of a 13.5 μm thick polyethylene porous substrate using a wire rod. The coated wet membrane was held in a water vapor atmosphere at 65°C and 85% RH for 60 seconds, then rinsed in a pure water tank for 5 minutes. The PEO glue was then evenly applied to one side of the coating layer using a wire rod. Finally, the membrane was dried in an oven at 65°C for 15 minutes, resulting in a semi-solid lithium battery composite membrane with a combined thickness of approximately 3 μm for the PEO layer and coating layer on one side.

[0070] Comparative Example 1

[0071] This comparative example provides a composite diaphragm for a semi-solid lithium battery, and its preparation method is as follows:

[0072] Preparation of LATP suspension: 2 parts by weight of LATP was added to 12 parts by weight of N-methylpyrrolidone (NMP) and dispersed at high speed for 20 minutes to obtain a LATP suspension;

[0073] The preparation method of the aramid glue is the same as that of Example 1, and the preparation method of the coating slurry is similar to that of Example 1, except that the LATP suspension in this comparative example is used instead of the h-BN-LATP suspension in Example 1.

[0074] Preparation of composite diaphragm: The preparation method is similar to that of Example 6, except that the coating slurry in this comparative example is used.

[0075] Comparative Example 2

[0076] This embodiment provides a composite diaphragm for a semi-solid lithium battery, and the preparation method thereof is as follows:

[0077] Preparation of LATP suspension: 2 parts by weight of LATP was added to 12 parts by weight of N-methylpyrrolidone (NMP) and dispersed at high speed for 20 minutes to obtain a LATP suspension;

[0078] Preparation of aramid glue and PEO glue: the same as the preparation method in Example 1.

[0079] Preparation of coating slurry: 50 parts by weight of the above aramid glue solution was mixed with the above LATP suspension, and then dispersed at high speed for 30 minutes, and then filtered through a 400-mesh filter and vacuum-debubbled for 5 minutes to obtain a coating slurry;

[0080] Preparation of composite diaphragm: The preparation method is similar to that of Example 1, except that the coating slurry in this comparative example is used.

[0081] Comparative Example 3

[0082] This comparative example provides a composite diaphragm for a semi-solid lithium battery, and its preparation method is as follows:

[0083] Preparation of aramid glue: the same as the preparation method in Example 1.

[0084] Preparation of coating slurry: 50 parts by weight of the above aramid glue was mixed with 12 parts by weight of N-methylpyrrolidone (NMP), and then dispersed at high speed for 20 minutes. The mixture was filtered through a 400-mesh filter, and vacuum-debubbled for 5 minutes to obtain coating slurry.

[0085] Preparation of PEO glue: the same as the preparation method in Example 1.

[0086] Preparation of composite diaphragm: The preparation method is similar to that of Example 6, except that the coating slurry in this comparative example is used.

[0087] Comparative Example 4

[0088] This comparative example provides a composite diaphragm for a semi-solid lithium battery, and its preparation method is as follows:

[0089] Preparation of aramid glue: the same as the preparation method in Example 1.

[0090] Preparation of coating slurry: the same preparation method as that of Comparative Example 3.

[0091] Preparation of PEO glue: the same as the preparation method in Example 1.

[0092] Preparation of composite membrane: the preparation method is the same as that in Example 1.

[0093] Comparative Example 5

[0094] This comparative example provides a composite diaphragm for a semi-solid lithium battery, and its preparation method is as follows:

[0095] Preparation of h-BN-LATP: The preparation method is the same as that in Example 1.

[0096] Preparation of h-BN-LATP suspension: 2 parts by weight of h-BN-LATP was added to 12 parts by weight of N,N-dimethylacetamide (DMAc) and dispersed at high speed for 20 minutes to obtain a h-BN-LATP suspension;

[0097] Preparation of aramid adhesive: Take 8 parts of calcium chloride and 90 parts of N,N-dimethylacetamide (DMAc) and fully dissolve them under high-speed dispersion conditions, then add 2 parts of aramid 1414 to the above mixed solvent, and then disperse it at high speed for 5 hours to obtain aramid adhesive.

[0098] Preparation of coating slurry: 0.5 parts by weight of PEO, 200 parts by weight of N,N-dimethylacetamide (DMAc), and 50 parts by weight of the above-mentioned aramid glue were mixed with the above-mentioned h-BN-LATP suspension, and then dispersed at high speed for 120 minutes. Then, the mixture was filtered through a 400-mesh filter and vacuum-debubbled for 5 minutes to obtain a coating slurry.

[0099] Preparation of composite diaphragm: The above-mentioned coating slurry is evenly coated on one side of a 13.5 μm thick polyethylene porous substrate using a wire rod. The coated wet film is retained in a water vapor atmosphere at 65°C and 85% RH for 60 seconds, then transferred to a pure water tank for washing for 5 minutes, and finally dried in an oven at 65°C for 15 minutes to obtain a composite diaphragm for semi-solid lithium batteries with a single-side coating layer thickness of about 3 μm.

[0100] The composite membranes prepared in the above examples and comparative examples were assembled into stainless steel|composite membrane|stainless steel symmetrical cells, and the impedance values ​​of each cell were tested and the ionic conductivity values ​​of the membranes were calculated. 0.33 Mn 0.33 Co 0.33 The electrochemical performance of the O2(NMC) / composite separator / Li full cell was tested. The specific test data are shown in Table 1.

[0101] Table 1

[0102]

[0103] Note: The more ☆ in the battery cycle stability, the better the cycle stability.

[0104] As can be seen from the data in the above table, the composite membrane for semi-solid lithium batteries provided by the present invention has layers that cooperate with each other to prevent powdering from the surface of the composite membrane and significantly improve the ionic conductivity, air permeability, and cyclic stability of the composite membrane. Specifically, in Examples 1-4, PEO layers were coated on both sides of the base layer, and the surfaces of the resulting composite membranes did not shed powder. In Example 1, LATP had high stability and the highest ionic conductivity. Compared with Example 1, the PEO concentration in the PEO glue of Example 2 was higher, and the ionic conductivity of the resulting composite membrane was slightly lower; in Example 3, the chemical vapor deposition temperature was increased during the preparation of h-BN-LATP, and the final LATP stability and ionic conductivity of the composite membrane were both lower than those of Example 1; in Example 4, the amount of h-BN-LATP was reduced, and the final LATP stability was high, but the ionic conductivity was low. In Examples 5 and 6, a PEO layer was coated on one side of the coating layer, and the resulting composite membranes had high LATP stability and no powdering, but the ionic conductivity was slightly lower than that of Examples 1-4.

[0105] Compared with the above-described embodiment, the surface of the composite membrane obtained in the comparative example all loses powder. Specifically, in comparative example 1, comparative example 3 and comparative example 5, a PEO layer is applied on one side of the coating layer, and in comparative example 2 and comparative example 4, a PEO layer is applied on both sides of the base layer. In comparative example 1 and comparative example 2, LATP is not modified, and the stability of the composite membrane finally obtained is poor, powdering, and the ionic conductivity is low. In comparative example 3 and comparative example 4, no LATP is added, and the ionic conductivity of the composite membrane finally obtained is low, the permeability is poor, and the cyclic stability is poor. In comparative example 5, a mixed coating method of PEO and h-BN-LATP is adopted. During the mixed coating process, PEO particles are filled into the aramid fiber pores, and the porosity in the coating is reduced, which leads to an increase in permeability (poor permeability) and a reduction in ionic conductivity.

[0106] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the specific technical features in any suitable manner. To avoid unnecessary repetition, the present invention will not further describe various possible combinations. However, these simple variations and combinations should also be considered as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A composite diaphragm for a semi-solid lithium battery, characterized in that: The composite diaphragm includes a base layer and a PEO layer located on one side or both sides of the base layer; The base layer includes a base film and a coating layer located on one side of the base film; the coating layer includes aramid and h-BN-LATP, and when the PEO layer is located on one side of the base film, the PEO layer is located on one side of the coating layer; The h-BN-LATP is obtained by performing hydroxyl modification on a hexagonal boron nitride layer coated on the surface of LATP, wherein the thickness of the hexagonal boron nitride layer is 5-10 nm.

2. The composite separator for a semi-solid lithium battery according to claim 1, wherein In the coating layer, the mass ratio of the aramid to the h-BN-LATP is (1-10):(1-5).

3. The composite separator for a semi-solid lithium battery according to claim 1, wherein The base film is a polyolefin base film with a microporous structure; the material of the base film is polyethylene or ethylene-propylene copolymer.

4. The composite separator for a semi-solid lithium battery according to claim 3, wherein The base film has a thickness of 5-13.5 μm.

5. The composite separator for a semi-solid lithium battery according to claim 1, wherein The aramid is selected from poly(m-phenylene isophthalamide) and / or poly(p-phenylene terephthalamide).

6. The composite separator for a semi-solid lithium battery according to claim 1, wherein The thickness of the composite membrane is less than 20 μm, the thickness of the coating layer is 2-4 μm, and the thickness of the PEO layer is 0.5-2.5 μm.

7. A method for preparing a composite separator for a semi-solid lithium battery according to any one of claims 1 to 6, characterized in that: The steps include: h-BN-LATP: A hexagonal boron nitride coating is formed on the surface of LATP by chemical vapor deposition, and then the boron nitride coating is modified by hydroxylation to obtain h-BN-LATP; Aramid glue: dissolve aramid in a solvent and control the solid content of aramid to be 1.8%-2.2% to obtain aramid glue; h-BN-LATP suspension: Disperse h-BN-LATP and solvent evenly to form a suspension, thereby obtaining h-BN-LATP suspension; Coating slurry: after the aramid glue solution and the h-BN-LATP suspension are mixed and dispersed evenly, the mixture is filtered and degassed to obtain the coating slurry; PEO glue: Mix PEO and solvent evenly to obtain PEO glue; Composite diaphragm: The coating slurry is coated on one side of the base film, and is sequentially treated with water vapor and deionized water to obtain a base layer; the PEO glue is then coated on one or both sides of the base layer and dried to obtain a composite diaphragm for a semi-solid lithium battery.

8. The method for preparing a composite separator for a semi-solid lithium battery according to claim 7, wherein: The steps for forming a hexagonal boron nitride coating on the surface of LATP by chemical vapor deposition are as follows: At 750-1200°C, chemical vapor deposition reaction is carried out on the surface of LATP using BH3-NH3 as boron source and nitrogen source in a pure N2 atmosphere to obtain LATP with a surface coated with a hexagonal boron nitride layer; the thickness of the hexagonal boron nitride coating is 5-10nm.

9. The method for preparing a composite separator for a semi-solid lithium battery according to claim 7, wherein: The steps of hydroxylating and modifying the boron nitride coating are as follows: The LATP coated with a hexagonal boron nitride layer is placed in a 1-10 mol / L alkali solution, heated to 80-150° C. under stirring and maintained for 12-24 hours, then separated. The obtained solid is washed with deionized water until the pH of the filtrate is neutral, and then dried to obtain h-BN-LATP.

10. The method for preparing a composite separator for a semi-solid lithium battery according to claim 7, wherein: In the h-BN-LATP suspension, the mass ratio of the h-BN-LATP to the solvent is 1:5-12.

11. The method for preparing a composite separator for a semi-solid lithium battery according to claim 7, wherein the aramid glue further contains a co-solvent, and the mass content of the co-solvent is ≤10%; The co-solvent is selected from at least one of CaCl2, KOH, LiCl and pyridine.

12. The method for preparing a composite separator for a semi-solid lithium battery according to claim 7, wherein: The solvent is selected from an organic solvent and / or water, and the organic solvent is selected from at least one of NMP, DMSO, DMF and DMAc; and / or The coating can be performed by any one of blade coating, roller coating, wire rod coating and dip coating.

13. A semi-solid lithium-ion battery, characterized in that: A composite diaphragm for a semi-solid lithium battery comprising the composite diaphragm for a semi-solid lithium battery according to any one of claims 1 to 6 or a composite diaphragm for a semi-solid lithium battery prepared by the preparation method of the composite diaphragm for a semi-solid lithium battery according to any one of claims 7 to 12.

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