Asymmetric composite solid electrolyte and method for preparing the same

Abstract

The application discloses an asymmetric composite solid electrolyte and a preparation method thereof. The asymmetric composite solid electrolyte comprises a first electrolyte layer and a second electrolyte layer, and the second electrolyte layer is arranged on the first electrolyte layer. The first electrolyte layer comprises 75-85 wt% Li-IL@Cu-BTC and 15-25 wt% PVDF-HFP, and the second electrolyte layer comprises 15-25 wt% Li-IL@Cu-BTC and 75-85 wt% PVDF-HFP. Li-IL is encapsulated in the Cu-BTC channel. The room temperature ionic liquid exhibits high ionic conductivity, high thermal stability and environmental friendliness. The MOF channel is modified to form a Li-IL@Cu-BTC ionic conductor. The high content of the Li-IL@Cu-BTC ionic conductor shortens the lithium ion transmission distance, and the lithium ions are densely stacked on the cathode side, thereby establishing a continuous lithium ion transport path.

Description

TECHNICAL FIELD

[0001] The present application belongs to electrolyte and its preparation method, specifically to asymmetric composite solid-state electrolyte and its preparation method. BACKGROUND

[0002] Traditional lithium-ion batteries are widely used in computer, mobile phone, electric vehicle and energy storage power station due to their inherent advantages such as high energy density, long cycle life, no memory effect and convenient carrying. However, the energy density of commercial lithium-ion batteries has reached the limit, and the leakage of organic electrolyte can easily lead to short circuit and explosion of the battery, causing safety problems such as fire. Therefore, solid-state lithium metal batteries using solid-state electrolyte are considered as an effective strategy to meet the increasing demand for high safety and high energy density energy storage devices. However, solid-state electrolyte faces problems such as low ionic conductivity, poor flexibility and low mechanical strength, which hinder the practical application of solid-state electrolyte.

[0003] Solid-state electrolyte can be divided into inorganic solid-state electrolyte, organic solid-state electrolyte and composite solid-state electrolyte. Inorganic solid-state electrolyte has high ionic conductivity, but it has insufficient contact with the electrode and large interface impedance. Organic solid-state electrolyte has good flexibility, low cost and easy processing, but its ionic conductivity is relatively low. Composite solid-state electrolyte combines the advantages of inorganic and organic solid-state electrolyte, effectively solving the problems of the two types of electrolyte. The ionic conductivity of pure polymer electrolyte is very low (usually <10 -6 S cm -1 ), by using imidazole type ionic liquid (Li-IL) and other surface chemical modification of MOF as functional filler, the ionic conductivity and electrochemical performance of polymer electrolyte can be improved. The introduction of MOF can reduce the crystallinity of polymer, and its porous structure can also be used as an ion transmission channel, but the improvement of ionic conductivity by doping a small amount of MOF particles is limited. In addition, a small amount of MOF filler added in the polymer matrix can improve the mechanical strength of the composite electrolyte. In general, the excellent mechanical strength and flexibility of the composite electrolyte can physically suppress lithium dendrites. However, there is a negative correlation between the ionic conductivity and the mechanical strength of most polymer-based composite solid-state electrolytes, which makes it challenging to simultaneously improve the mechanical properties and ionic conductivity.

[0004] Therefore, it is urgent to construct a new type of microstructure polymer composite electrolyte to precisely control the ionic conductivity and improve the lithium dendrite suppression ability respectively. SUMMARY

[0005] The purpose of the present application is to overcome the deficiencies in the prior art, and the purpose of the present application is to provide an asymmetric composite solid-state electrolyte with flexibility and high ionic conductivity, and the purpose of the present application is to provide an environmentally friendly and convenient preparation method for the asymmetric composite solid-state electrolyte.

[0006] Technical solution: The asymmetric composite solid electrolyte comprises a first electrolyte layer and a second electrolyte layer, and the second electrolyte layer is arranged on the first electrolyte layer; the first electrolyte layer comprises 75-85wt% Li-IL@Cu-BTC and 15-25wt% PVDF-HFP, and the second electrolyte layer comprises 15-25wt% Li-IL@Cu-BTC and 75-85wt% PVDF-HFP; the Li-IL in the Li-IL@Cu-BTC is encapsulated in the Cu-BTC channel.

[0007] Further, the Li-IL@Cu-BTC in the first electrolyte layer and the second electrolyte layer is uniformly dispersed in the PVDF-HFP.

[0008] Further, the thickness of the first electrolyte layer is 28-32μm, and the thickness of the second electrolyte layer is 7-10μm.

[0009] The preparation method of the asymmetric composite solid electrolyte comprises the following steps:

[0010] Step one, respectively configure methanol solutions of 1,3,5-benzene tricarboxylic acid, copper nitrate trihydrate and polyvinylpyrrolidone, mix uniformly, stand for aging, then collect the sample by centrifugation, and wash with methanol for several times, vacuum dry the Cu-BTC, and grind into powder;

[0011] Step two, in an argon glove box, prepare Li-IL by dissolving LiTFSI in 1-ethyl-3-methylimidazole bis(trifluoromethylsulfonyl) imide ([EMIM][TFSI]), stir uniformly, mix Li-IL and Cu-BTC uniformly, and heat under vacuum conditions, so that Li-IL enters into the Cu-BTC channel, and form Li-IL@Cu-BTC powder;

[0012] Step three, disperse the Li-IL@Cu-BTC powder in N-methylpyrrolidone solvent, stir to form a suspension, then respectively add LiTFSI and PVDF-HFP particles, and perform uniform magnetic stirring, to obtain a first electrolyte layer slurry and a second electrolyte layer slurry respectively;

[0013] Step four, coat the first electrolyte layer slurry on a glass plate, vacuum dry to obtain the first electrolyte layer, then coat the second electrolyte layer slurry on the first electrolyte layer, vacuum dry to obtain the asymmetric composite solid electrolyte film.

[0014] Further, in step one, the concentration of 1,3,5-benzenetricarboxylic acid in the methanol solution is 0.04-0.1 mol / L, the concentration of copper nitrate trihydrate in the methanol solution is 0.06-0.1 mol / L, and the mass ratio of copper nitrate trihydrate to PVP is 1:0.2-0.5. The temperature for standing and aging is 25-30 DEG C, and the time is 24-36 hours.

[0015] Further, in step two, the mass ratio of LiTFSI to 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide is 1:4-6, and the mass ratio of Li-IL to Cu-BTC is 1-2:1. The Li-IL is vacuum dried at 110-120 DEG C for 12-24 hours before use, and the Cu-BTC is vacuum dried at 150-160 DEG C for 8-12 hours before use.

[0016] Further, in step three, the mass ratio of PVDF-HFP to LiTFSI is 1-5:1.

[0017] Further, in step four, the vacuum drying is performed by using a stepwise temperature rise within 30-60 DEG C.

[0018] Preparation principle: the ion liquid is encapsulated in the pore structure of Cu-BTC to obtain functional filler Li-IL@Cu-BTC, which is added into a PVDF-HFP-based solid electrolyte, and different mass ratios of Li-IL@Cu-BTC polymer solid electrolyte are coated layer by layer. The double-layer structure makes the composite solid electrolyte have excellent mechanical properties and good ionic conductivity, and the Li-IL@Cu-BTC ion conductor can also uniformly guide the deposition / exfoliation of lithium ions. The double-layer coating design can adapt to the cathode and anode according to the different characteristics of the content of Li-IL@Cu-BTC ion conductor in the matrix. The high content of Li-IL@Cu-BTC ion conductor on the cathode side is densely packed, which shortens the lithium ion transmission distance, establishes a continuous lithium ion transport path, and shows good ionic conductivity, which can improve the cathode activity and stability. The low content of Li-IL@Cu-BTC polymer matrix thin layer on the anode side is only 8.1 microns thick, which reduces the adverse effect on the overall ionic conductivity of the membrane, shows excellent mechanical properties, and effectively hinders the growth of lithium dendrites, reducing the risk of short circuit of the battery. The two sides of the asymmetric ion conductor content double-layer structure have the same transmission mechanism and synergistic complementary effect, so that the composite solid lithium metal battery has good cycle stability and high reversible capacity.

[0019] Beneficial effects: compared with the prior art, the present application has the following remarkable features:

[0020] 1. Room temperature ionic liquid shows high ionic conductivity, high thermal stability and environmental friendliness, modifying MOF channels to form Li-IL@Cu-BTC ionic conductor;

[0021] 2. High content of Li-IL@Cu-BTC ionic conductor shortens the transmission distance of lithium ions, and densely accumulates on the cathode side, establishing a continuous lithium ion transport path;

[0022] 3. High content of Li-IL@Cu-BTC layer shows good ionic conductivity, which can improve the activity and stability of the cathode;

[0023] 4. The low content of Li-IL@Cu-BTC polymer matrix thin layer on the anode side, with a thickness of only 8.1 μm, reduces the adverse effects on the overall ionic conductivity of the membrane, and shows excellent mechanical properties, which effectively hinders the growth of lithium dendrites and reduces the risk of short circuit of the battery;

[0024] 5. The asymmetric structure makes the composite solid-state electrolyte flexible and has high ionic conductivity, with a total thickness of only 38.4 μm. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 FIG. 1 is the surface morphology and cross-sectional SEM images of the 20% Li-IL@Cu-BTC side and the 80% Li-IL@Cu-BTC side of the asymmetric composite solid-state electrolyte of Example 1, wherein a) is the SEM image of the second electrolyte layer, b) is the SEM image of the first electrolyte layer, c) is the SEM image of the cross section of the first electrolyte layer, and d) is the SEM image of the cross section of the second electrolyte layer;

[0026] Figure 2 FIG. 3 is a tensile strength and Young's modulus column chart of Example 1, Comparative Example 2, and Comparative Example 4;

[0027] Figure 3 FIG. 4 is a stress-strain curve of Example 1, Comparative Example 2, and Comparative Example 4;

[0028] Figure 4 FIG. 5 is an ionic conductivity chart of Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4;

[0029] Figure 5 FIG. 6 is a cycle performance chart of Example 1, Comparative Example 2, and Comparative Example 4 at room temperature 0.1 mA cm -2 under the condition of lithium symmetric battery;

[0030] Figure 6 FIG. 7 is a long cycle performance chart of Example 1, Comparative Example 2, and Comparative Example 4 at room temperature 0.5 C under the condition of lithium metal battery. DETAILED DESCRIPTION

[0031] The materials, reagents, instruments, etc. used in the following examples, unless otherwise specified, can be obtained commercially. The experimental methods in the examples not marked with specific conditions are usually carried out according to the conventional conditions or the conditions recommended by the manufacturer. 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMIM TFSI, 99%), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, 99.9%), 1-methyl-2-pyrrolidinone (NMP, 99.9%), trimesic acid, polyvinylpyrrolidone, copper nitrate, poly(vinylidene-co-hexafluoropropylene) (PVDF-HFP) were purchased from Macklin.

[0032] Example 1

[0033] A method for preparing an asymmetric composite solid-state electrolyte, comprising the following steps:

[0034] (1) A 125 mL, 0.066 mol / L methanol solution of copper nitrate trihydrate was prepared, 1 g of PVP was dispersed in the above solution, and the solution was marked as solution A. A 125 mL, 0.042 mol / L methanol solution of 1,3,5-benzene tricarboxylic acid was prepared, and the solution was marked as solution B. Solution B was added dropwise to solution A, and the mixture was placed at 25°C for 24 h. The blue product was collected by centrifugation, washed with methanol for 3 times, dried at 80°C for 12 h, and ground into powder to prepare Cu-BTC.

[0035] (2) Li-IL was dried at 120°C under vacuum for 12 hours to remove water. In an argon glove box, 1 g of LiTFSI was dissolved in 5.46 g of [EMIM][TFSI] to prepare Li-IL, which was stirred uniformly at a temperature of 30°C.

[0036] (3) 1 g of Cu-BTC powder was vacuum activated at 160°C for 8 hours. 2 g of Li-IL was added dropwise to the activated Cu-BTC powder, which was ground and mixed uniformly, and then heated at 120°C under vacuum for 12 h to make Li-IL enter the Cu-BTC channels to form Li-IL@Cu-BTC powder. Cu-BTC has a multi-level microporous structure, and the pore size is mainly distributed between 0.5-0.8 nm, which ensures that EMIM + and TFSI - can enter the inside of the channel, while the micropores smaller than 0.7 nm hinder the migration of EMIM + and TFSI - , while allowing the free movement of Li + (0.076 nm), so that the composite solid-state electrolyte film has a higher lithium ion migration number.

[0037] (4) The Li-IL@Cu-BTC powder is dispersed in NMP solvent to form a suspension, then LiTFSI and PVDF-HFP particles with a mass ratio of 1:4 are added respectively, and uniform magnetic stirring is performed for 24 h to obtain a first electrolyte layer slurry and a second electrolyte layer slurry respectively.

[0038] (5) The first electrolyte layer slurry is uniformly coated on a glass plate by using a doctor blade, and then placed in a vacuum drying oven for temperature increase at 40°C and 50°C for 2 h respectively, and then vacuum dried at 60°C for 24 h to obtain the first electrolyte layer. Then the second electrolyte layer slurry is uniformly coated on the first electrolyte layer by using a doctor blade, and then placed in a vacuum drying oven for temperature increase at 40°C and 50°C for 2 h respectively, and then vacuum dried at 60°C for 24 h to obtain the second electrolyte layer, thereby obtaining an asymmetric composite solid-state electrolyte membrane.

[0039] The first electrolyte layer of the obtained composite solid-state electrolyte membrane comprises 80wt% Li-IL@Cu-BTC and 20wt% PVDF-HFP, and the thickness is 30.3μm. The second electrolyte layer comprises 20wt% Li-IL@Cu-BTC and 80wt% PVDF-HFP, and the thickness is 8.1μm. Li-IL@Cu-BTC is uniformly dispersed in PVDF-HFP.

[0040] Comparative Example 1

[0041] LiTFSI and PVDF-HFP particles are added in NMP solvent, and uniform magnetic stirring is performed for 24 h, wherein the mass ratio of PVDF-HFP to LiTFSI is 4:1. The above slurry is uniformly coated on a glass plate by using a doctor blade, and then placed in a vacuum drying oven for temperature increase at 40°C and 50°C for 2 h respectively, and then vacuum dried at 60°C for 24 h to obtain a composite solid-state electrolyte membrane.

[0042] Comparative Example 2

[0043] Step (1), 125mL of 0.066mol / L copper nitrate trihydrate methanol solution is prepared, 1g of PVP is dispersed in the above solution, and is recorded as solution A. 125mL of 0.042mol / L benzene tricarboxylic acid methanol solution is prepared, and is recorded as solution B. B liquid is added dropwise into A liquid, and is placed at room temperature for 24h, and then centrifuged to collect the blue product, which is washed with methanol for 3 times, dried at 80°C for 12h, and ground into powder to prepare Cu-BTC.

[0044] Step (2), 1g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is weighed in an argon glove box, dissolved in 5.46g of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide salt (EMIMTFSI) ionic liquid to prepare Li-IL, and stirred uniformly at 30°C, and dried at 120°C under vacuum before use to remove water.

[0045] Step (3), 1 g of Cu-BTC powder was vacuum activated at 160°C for 8h, 2 g of Li-IL was added dropwise to the activated MOFs, and the mixture was ground and mixed uniformly, and then heated at 120°C under vacuum for 12h to make Li-IL@Cu-BTC powder.

[0046] Step (4), Li-IL@Cu-BTC was dispersed in NMP solvent to form a suspension, then LiTFSI and PVDF-HFP were added respectively, and uniform magnetic stirring was carried out for 24h, wherein the mass ratio of PVDF-HFP and LiTFSI in the above process was 4:1. The above slurry was uniformly coated on a glass plate with a doctor blade, and then placed in a vacuum drying oven with temperature increasing steps of 40, 50°C for 2h, and then vacuum dried at 60°C for 24h to obtain a composite solid electrolyte membrane. The mass ratio of Li-IL@Cu-BTC in the solid electrolyte was 20%.

[0047] Comparative Example 3

[0048] Step (1), 125 mL of 0.066 mol / L copper nitrate trihydrate methanol solution was prepared, 1 g of PVP was dispersed in the above solution, and was recorded as solution A. 125 mL of 0.042 mol / L benzene tricarboxylic acid methanol solution was prepared and was recorded as solution B. B solution was added dropwise to A solution, and was placed at room temperature for 24h, and then the blue product was collected by centrifugation, washed with methanol for 3 times, dried at 80°C for 12h, and ground into powder to prepare Cu-BTC.

[0049] Step (2), 1 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was weighed in an argon glove box, dissolved in 5.46 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMIMTFSI) ionic liquid to prepare Li-IL, and then stirred uniformly at 30°C. Before use, it was dried at 120°C under vacuum to remove water.

[0050] Step (3), 1 g of Cu-BTC powder was vacuum activated at 160°C for 8h, 2 g of Li-IL was added dropwise to the activated MOFs, and the mixture was ground and mixed uniformly, and then heated at 120°C under vacuum for 12h to make Li-IL@Cu-BTC powder.

[0051] Step (4), Li-IL@Cu-BTC was dispersed in NMP solvent, stirred to form a suspension, then LiTFSI and PVDF-HFP were added respectively, and uniform magnetic stirring was carried out for 24 h, wherein the mass ratio of PVDF-HFP and LiTFSI in the above process was 4:1. The above slurry was uniformly coated on a glass plate with a scraper, and was placed in a vacuum drying oven and heated at 40, 50°C for 2 h, and then vacuum dried at 60°C for 24 h to obtain a composite solid electrolyte film. The mass ratio of Li-IL@Cu-BTC in the solid electrolyte was 50%.

[0052] Comparative Example 4

[0053] Step (1), 125 mL of 0.066 mol / L copper nitrate trihydrate methanol solution was prepared, 1 g of PVP was dispersed in the above solution, and was recorded as solution A. 125 mL of 0.042 mol / L benzene tricarboxylic acid methanol solution was prepared and was recorded as solution B. B liquid was added dropwise to A liquid, and was placed at room temperature for 24 h, and the blue product was collected by centrifugation, washed with methanol for 3 times, dried at 80°C for 12 h, and ground into powder to prepare Cu-BTC.

[0054] Step (2), 1 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was weighed in an argon glove box, dissolved in 5.46 g of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTFSI) ionic liquid to prepare Li-IL, and was stirred uniformly at 30°C. Before use, it was vacuum dried at 120°C to remove water.

[0055] Step (3), 1 g of Cu-BTC powder was vacuum activated at 160°C for 8 h, 2 g of Li-IL was added dropwise to the activated MOFs, and was ground and mixed uniformly, and was heated at 120°C for 12 h under vacuum conditions, so that Li-IL fully entered the pores of Cu-BTC, to prepare Li-IL@Cu-BTC powder.

[0056] Step (4), Li-IL@Cu-BTC was dispersed in NMP solvent, stirred to form a suspension, then LiTFSI and PVDF-HFP were added respectively, and uniform magnetic stirring was carried out for 24 h, wherein the mass ratio of PVDF-HFP and LiTFSI in the above process was 4:1. The above slurry was uniformly coated on a glass plate with a scraper, and was placed in a vacuum drying oven and heated at 40, 50°C for 2 h, and then vacuum dried at 60°C for 24 h to obtain a composite solid electrolyte film. The mass ratio of Li-IL@Cu-BTC in the solid electrolyte was 50%.

[0057] Comparative Example 5

[0058] Step (1), 125 mL of 0.066 mol / L copper nitrate trihydrate methanol solution was prepared, 1 g of PVP was dispersed in the above solution, and the solution was recorded as solution A. 125 mL of 0.042 mol / L benzene tricarboxylic acid methanol solution was prepared and recorded as solution B. B solution was added dropwise to A solution, and the mixture was left at room temperature for 24 h. The blue product was collected by centrifugation, washed with methanol for 3 times, dried at 80℃ for 12 h, and ground into powder to prepare Cu-BTC.

[0059] Step (2), 1 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was weighed in an argon glove box and dissolved in 5.46 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMIMTFSI) ionic liquid to prepare Li-IL. The mixture was stirred at 30℃ until uniform, and then vacuum dried at 120℃ to remove water before use.

[0060] Step (3), 1 g of Cu-BTC powder was activated at 160℃ for 8 h under vacuum. After activation, 2 g of Li-IL was added dropwise to the MOFs, and the mixture was ground until uniform. The mixture was heated at 120℃ for 12 h under vacuum to allow the Li-IL to fully enter the pores of the Cu-BTC, and Li-IL@Cu-BTC powder was prepared.

[0061] Step (4), Li-IL@Cu-BTC was dispersed in NMP solvent to form a suspension, and then LiTFSI and PVDF-HFP were added respectively. The mixture was stirred at a constant speed for 24 h. The mass ratio of PVDF-HFP to LiTFSI in the above process was 4:1. The slurry was uniformly coated on a glass plate using a doctor blade, and then the glass plate was placed in a vacuum drying oven and heated at 40℃ and 50℃ for 2 h respectively, and then vacuum dried at 60℃ for 24 h to obtain a composite solid electrolyte membrane. The mass ratio of Li-IL@Cu-BTC in the solid electrolyte was 65%.

[0062] The solid electrolytes obtained in Example 1, Comparative Example 2, and Comparative Example 4 were assembled into stainless steel symmetric batteries in an argon glove box to measure their ionic conductivities. In addition, lithium deposition performance was measured by assembling lithium symmetric batteries. The solid electrolytes obtained in Example 1, Comparative Example 2, and Comparative Example 3 were assembled into full batteries with LFP as the positive electrode and Li as the negative electrode to test their performance. The side of the Li-IL@Cu-BTC with a mass ratio of 20% was in contact with the lithium metal negative electrode, and the side of the Li-IL@Cu-BTC with a mass ratio of 80% was in contact with the LFP positive electrode.

[0063] As Figure 1The morphology and thickness of the asymmetric composite solid electrolyte Li-IL@Cu-BTC ion conductor on the side with different contents of Li-IL@Cu-BTC. When the mass ratio is 20%, a small amount of Li-IL@Cu-BTC filler improves the crystallinity of the pure PVDF-HFP polymer matrix, and the surface is smooth and uniform. When the mass ratio of Li-IL@Cu-BTC is 80%, a large number of MOF particles are densely packed, forming a continuous ion transmission channel.

[0064] As Figures 2-3 In the ion conductivity test, the counterexample 2 showed an ion conductivity of 1.77 x 10 -4 S cm -1 at room temperature, which was significantly lower than the ion conductivity of 4.08 x 10 -4 S cm -1 of the counterexample 4. In addition, the example 1 has a higher ion conductivity of 3.51 x 10 -4 S cm -1 , which ensures the rapid transmission of lithium ions in the solid-state electrolyte.

[0065] As Figure 4 The mechanical properties of the counterexample 2 are excellent, while the mechanical properties of the counterexample 4 are very poor. In addition, the mechanical properties of the example 1 are greatly improved and better than those of the counterexample 4.

[0066] As Figure 5 The counterexample 2 has the highest overpotential in lithium deposition, relies on better mechanical strength to suppress dendrite penetration into the electrolyte, and the voltage increases until the battery dies. The overpotential of the counterexample 4 is the lowest, but it is very easy to short circuit. The overpotential of the example 1 is lower and stable, and can be stably cycled for 500h.

[0067] As Figure 6 The initial specific capacity of the counterexample 2 is the lowest and decays quickly. The initial specific capacity of the counterexample 4 is higher, but also decays quickly. The initial specific capacity of the example 1 is 140mAh g -1 , and after 100 cycles of long cycle, it still can reach a discharge specific capacity of 138.4mAh g -1 and a cycle efficiency of 99.58%, and the capacity retention rate reaches 98.9%. This shows that the asymmetric double-layer structure design well balances the ion conductivity and mechanical strength of the composite solid electrolyte, and exhibits good performance of the lithium metal battery.

[0068] Example 2

[0069] A preparation method of an asymmetric composite solid electrolyte, comprising the following steps:

[0070] (1) A 125 mL, 0.06 mol / L copper nitrate trihydrate methanol solution was prepared, 0.8 g of PVP was dispersed in the solution, and the solution was recorded as solution A. A 125 mL, 0.04 mol / L 1,3,5-benzene tricarboxylic acid methanol solution was prepared, and the solution was recorded as solution B. Solution B was added dropwise to solution A, and the mixture was left to stand at 25°C for 36 h. The blue product was collected by centrifugation, washed with methanol three times, dried at 80°C for 12 h, and ground into a powder to prepare Cu-BTC.

[0071] (2) Li-IL was dried at 110°C under vacuum for 24 h to remove water. In an argon glove box, 1 g of LiTFSI was dissolved in 4 g of [EMIM][TFSI] to prepare Li-IL, which was stirred uniformly at a temperature of 30°C.

[0072] (3) 1 g of Cu-BTC powder was vacuum activated at 150°C for 12 h. 1 g of Li-IL was added dropwise to the activated Cu-BTC powder, which was ground and mixed uniformly, and then heated at 120°C under vacuum for 12 h to allow the Li-IL to enter the pores of the Cu-BTC, forming Li-IL@Cu-BTC powder.

[0073] (4) The Li-IL@Cu-BTC powder was dispersed in NMP solvent, stirred to form a suspension, and then 1:1 mass ratio of LiTFSI and PVDF-HFP particles were added, respectively, and uniform magnetic stirring was performed for 24 h to obtain a first electrolyte layer slurry and a second electrolyte layer slurry, respectively.

[0074] (5) The first electrolyte layer slurry was uniformly coated on a glass plate using a doctor blade, and then placed in a vacuum drying oven and subjected to temperature gradient heating at 30°C and 40°C for 2 h, respectively, and then vacuum dried at 60°C for 24 h to obtain the first electrolyte layer. The second electrolyte layer slurry was uniformly coated on the first electrolyte layer using a doctor blade, and then placed in a vacuum drying oven and subjected to temperature gradient heating at 30°C and 40°C for 2 h, respectively, and then vacuum dried at 60°C for 24 h to obtain the second electrolyte layer, i.e., an asymmetric composite solid-state electrolyte membrane.

[0075] The first electrolyte layer of the obtained composite solid-state electrolyte membrane comprises 75 wt% Li-IL@Cu-BTC and 25 wt% PVDF-HFP, and has a thickness of 28 μm. The second electrolyte layer comprises 25 wt% Li-IL@Cu-BTC and 75 wt% PVDF-HFP, and has a thickness of 7 μm. Li-IL@Cu-BTC is uniformly dispersed in PVDF-HFP.

[0076] Example 3

[0077] A method for preparing an asymmetric composite solid-state electrolyte, comprising the following steps:

[0078] (1) A 125 mL, 0.1 mol / L copper nitrate trihydrate methanol solution was prepared, 0.9 g of PVP was dispersed in the solution, and the solution was recorded as solution A. A 125 mL, 0.1 mol / L 1,3,5-benzenetricarboxylic acid methanol solution was prepared, and the solution was recorded as solution B. Solution B was added dropwise to solution A, and the mixture was placed at 30°C for 24 h. The blue product was collected by centrifugation, washed with methanol three times, dried at 80°C for 12 h, and ground into a powder to prepare Cu-BTC.

[0079] (2) Li-IL was dried at 120°C under vacuum for 12 h to remove water. In an argon glove box, 1 g of LiTFSI was dissolved in 5 g of [EMIM][TFSI] to prepare Li-IL, which was stirred uniformly at a temperature of 30°C.

[0080] (3) 1 g of Cu-BTC powder was vacuum activated at 160°C for 8 h. 2 g of Li-IL was added dropwise to the activated Cu-BTC powder, which was ground and mixed uniformly, and then heated at 120°C under vacuum for 12 h to allow the Li-IL to enter the Cu-BTC channels to form Li-IL@Cu-BTC powder.

[0081] (4) The Li-IL@Cu-BTC powder was dispersed in NMP solvent to form a suspension, and then 1:5 mass ratio of LiTFSI and PVDF-HFP particles were added, respectively, and stirred at a constant speed for 24 h to obtain a first electrolyte layer slurry and a second electrolyte layer slurry, respectively.

[0082] (5) The first electrolyte layer slurry was uniformly coated on a glass plate using a doctor blade, and then placed in a vacuum drying oven and heated at 40°C and 50°C for 2 h, respectively, and then dried at 60°C under vacuum for 24 h to obtain the first electrolyte layer. The second electrolyte layer slurry was uniformly coated on the first electrolyte layer using a doctor blade, and then placed in a vacuum drying oven and heated at 40°C and 50°C for 2 h, respectively, and then dried at 60°C under vacuum for 24 h to obtain the second electrolyte layer, i.e., an asymmetric composite solid-state electrolyte membrane.

[0083] The first electrolyte layer of the obtained composite solid-state electrolyte membrane comprises 85 wt% Li-IL@Cu-BTC and 15 wt% PVDF-HFP, and has a thickness of 32 μm. The second electrolyte layer comprises 15 wt% Li-IL@Cu-BTC and 85 wt% PVDF-HFP, and has a thickness of 10 μm. Li-IL@Cu-BTC is uniformly dispersed in PVDF-HFP.

[0084] Example 4

[0085] A preparation method of an asymmetric composite solid-state electrolyte, comprising the following steps:

[0086] (1) A 125 mL, 0.08 mol / L copper nitrate trihydrate methanol solution was prepared, 0.9 g of PVP was dispersed in the solution, and the solution was recorded as solution A. A 125 mL, 0.07 mol / L 1,3,5-benzene tricarboxylic acid methanol solution was prepared, and the solution was recorded as solution B. Solution B was added dropwise to solution A, and the mixture was placed at 28°C for 30 h. The blue product was collected by centrifugation, washed with methanol three times, dried at 80°C for 12 h, and ground into a powder to prepare Cu-BTC.

[0087] (2) Li-IL was vacuum dried at 115°C for 18 h to remove water. In an argon glove box, 1 g of LiTFSI was dissolved in 5 g of [EMIM][TFSI] to prepare Li-IL, which was stirred uniformly at a temperature of 30°C.

[0088] (3) 1 g of Cu-BTC powder was vacuum activated at 155°C for 10 h. 1.5 g of Li-IL was added dropwise to the activated Cu-BTC powder, which was ground and mixed uniformly, and then heated at 120°C under vacuum for 12 h to allow the Li-IL to enter the Cu-BTC channels to form Li-IL@Cu-BTC powder.

[0089] (4) The Li-IL@Cu-BTC powder was dispersed in NMP solvent to form a suspension, and then 1:3 mass ratio of LiTFSI and PVDF-HFP particles were added, respectively, and uniform magnetic stirring was performed for 24 h to obtain a first electrolyte layer slurry and a second electrolyte layer slurry, respectively.

[0090] (5) The first electrolyte layer slurry was uniformly coated on a glass plate using a doctor blade, and then placed in a vacuum drying oven and subjected to temperature gradient heating at 35°C and 45°C for 2 h, respectively, and then vacuum dried at 60°C for 24 h to obtain the first electrolyte layer. The second electrolyte layer slurry was uniformly coated on the first electrolyte layer using a doctor blade, and then placed in a vacuum drying oven and subjected to temperature gradient heating at 35°C and 45°C for 2 h, respectively, and then vacuum dried at 60°C for 24 h to obtain the second electrolyte layer, i.e., an asymmetric composite solid-state electrolyte membrane.

[0091] The first electrolyte layer of the obtained composite solid-state electrolyte membrane comprises 78 wt% Li-IL@Cu-BTC and 22 wt% PVDF-HFP, and has a thickness of 30 μm. The second electrolyte layer comprises 22 wt% Li-IL@Cu-BTC and 78 wt% PVDF-HFP, and has a thickness of 8 μm. Li-IL@Cu-BTC is uniformly dispersed in PVDF-HFP.

[0092] Example 5

[0093] A preparation method of an asymmetric composite solid-state electrolyte, comprising the following steps:

[0094] (1) A 125 mL, 0.07 mol / L copper nitrate trihydrate methanol solution was prepared, 1 g of PVP was dispersed in the solution, and the solution was recorded as solution A. A 125 mL, 0.08 mol / L 1,3,5-benzene tricarboxylic acid methanol solution was prepared, and the solution was recorded as solution B. Solution B was added dropwise to solution A, and the mixture was left to stand at 28°C for 26 h. The blue product was collected by centrifugation, washed with methanol three times, dried at 80°C for 12 h, and ground into a powder to prepare Cu-BTC.

[0095] (2) Li-IL was vacuum dried at 112°C for 20 h to remove water. In an argon glove box, 1 g of LiTFSI was dissolved in 5 g of [EMIM][TFSI] to prepare Li-IL, which was stirred uniformly at a temperature of 30°C.

[0096] (3) 1 g of Cu-BTC powder was vacuum activated at 158°C for 9 h. 1 g of Li-IL was added dropwise to the activated Cu-BTC powder, which was ground and mixed uniformly, and then heated at 120°C under vacuum for 12 h to allow the Li-IL to enter the Cu-BTC channels, forming Li-IL@Cu-BTC powder.

[0097] (4) The Li-IL@Cu-BTC powder was dispersed in NMP solvent to form a suspension, and then 1:4 mass ratio of LiTFSI and PVDF-HFP particles were added, respectively, and uniform magnetic stirring was performed for 24 h to obtain a first electrolyte layer slurry and a second electrolyte layer slurry, respectively.

[0098] (5) The first electrolyte layer slurry was uniformly coated on a glass plate using a doctor blade, and then placed in a vacuum drying oven and subjected to stepwise temperature increase at 36°C and 47°C for 2 h, respectively, and then vacuum dried at 60°C for 24 h to obtain the first electrolyte layer. The second electrolyte layer slurry was uniformly coated on the first electrolyte layer using a doctor blade, and then placed in a vacuum drying oven and subjected to stepwise temperature increase at 36°C and 47°C for 2 h, respectively, and then vacuum dried at 60°C for 24 h to obtain the second electrolyte layer, i.e., an asymmetric composite solid-state electrolyte membrane.

[0099] The first electrolyte layer of the obtained composite solid-state electrolyte membrane comprises 81 wt% Li-IL@Cu-BTC and 19 wt% PVDF-HFP, and has a thickness of 31 μm. The second electrolyte layer comprises 19 wt% Li-IL@Cu-BTC and 81 wt% PVDF-HFP, and has a thickness of 9 μm. Li-IL@Cu-BTC is uniformly dispersed in PVDF-HFP.

Claims

1. An asymmetric composite solid electrolyte, characterized in that: The invention comprises a first electrolyte layer and a second electrolyte layer, wherein the second electrolyte layer is arranged on the first electrolyte layer; the first electrolyte layer comprises 75-85wt% Li-IL@Cu-BTC and 15-25wt% PVDF-HFP, and the second electrolyte layer comprises 15-25wt% Li-IL@Cu-BTC and 75-85wt% PVDF-HFP; the Li-IL in the Li-IL@Cu-BTC is encapsulated in the pores of the Cu-BTC.

2. An asymmetric composite solid electrolyte according to claim 1, characterized in that: The Li-IL@Cu-BTC in the first electrolyte layer and the second electrolyte layer is uniformly dispersed in PVDF-HFP.

3. The asymmetric composite solid electrolyte according to claim 1, characterized in that: The thickness of the first electrolyte layer is 28 to 32 μm, and the thickness of the second electrolyte layer is 7 to 10 μm.

4. A method for preparing an asymmetric composite solid electrolyte according to claim 1, characterized in that: The following steps are involved: Step 1: Prepare methanol solutions of 1,3,5-benzenetricarboxylic acid, copper nitrate trihydrate, and polyvinylpyrrolidone, mix them evenly, let them stand for aging, collect the samples by centrifugation, wash them multiple times with methanol, vacuum dry the Cu-BTC, and grind them into powder; Step 2: In an argon glove box, LiTFSI was dissolved in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide to prepare Li-IL. The mixture was stirred evenly, and the Li-IL and Cu-BTC were ground and mixed evenly. The mixture was then heated under vacuum to allow the Li-IL to enter the pores of the Cu-BTC to form Li-IL@Cu-BTC powder. Step 3: Disperse the Li-IL@Cu-BTC powder in N-methylpyrrolidone solvent and stir to form a suspension. Then, add LiTFSI and PVDF-HFP particles respectively and perform uniform magnetic stirring to obtain the first electrolyte layer slurry and the second electrolyte layer slurry respectively. Step 4: coating the first electrolyte layer slurry on a glass plate and vacuum drying to obtain a first electrolyte layer, and then coating the second electrolyte layer slurry on the first electrolyte layer and vacuum drying to obtain an asymmetric composite solid electrolyte membrane.

5. The method for preparing the asymmetric composite solid electrolyte according to claim 4, characterized in that: In the step 1, the concentration of 1,3,5-benzenetricarboxylic acid in the methanol solution of 1,3,5-benzenetricarboxylic acid is 0.04-0.1 mol / L, the concentration of copper nitrate trihydrate in the methanol solution of copper nitrate trihydrate is 0.06-0.1 mol / L, and the mass ratio of copper nitrate trihydrate to PVP is 1:0.2-0.

5.

6. The method for preparing an asymmetric composite solid electrolyte according to claim 4, wherein: In the step 1, the temperature for static aging is 25-30° C., and the time is 24-36 hours.

7. The method for preparing an asymmetric composite solid electrolyte according to claim 4, wherein: In the step 2, the mass ratio of LiTFSI to 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide is 1:4-6, and the mass ratio of Li-IL to Cu-BTC is 1-2:

1.

8. The method for preparing an asymmetric composite solid electrolyte according to claim 4, wherein: In the step 2, the Li-IL is vacuum dried at 110-120° C. for 12-24 hours before use, and the Cu-BTC is vacuum dried at 150-160° C. for 8-12 hours before use.

9. The method for preparing an asymmetric composite solid electrolyte according to claim 4, wherein: In the step 3, the mass ratio of PVDF-HFP to LiTFSI is 1 to 5:

1.

10. The method for preparing an asymmetric composite solid electrolyte according to claim 4, wherein: In the step 4, vacuum drying is performed by stepwise heating within a range of 30 to 60°C.

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