Preparation method of composite ion conductor and lithium battery

Abstract

The invention discloses a preparation method of a composite ion conductor, and belongs to the field of lithium battery solid electrolyte materials. The composite ion conductor is obtained by loading ionic liquid through MOFs pore channels. The preparation method comprises the following steps: S1, preparing an Al-based MOFs material MIL-101; s2, the MIL-101 is modified, and NH2 (at) MIL-101 is prepared; s3, preparing a lithium ion liquid Li-IL; and S4, preparing a composite ion conductor NH2 (at) MIL-101 / Li-IL. The prepared composite ion conductor is used as a solid electrolyte, carbon-coated lithium iron phosphate is used as a positive electrode, a lithium battery is assembled by matching, the electrochemical performance of the lithium battery is tested, and the test finds that the solid electrolyte shows excellent rate capability and cycle performance at room temperature and has wide application potential.

Description

Technical Field

[0001] The invention relates to the field of lithium battery solid electrolyte materials, and in particular to a method for preparing a composite ion conductor. Background Art

[0002] In the field of new energy, in addition to industries such as solar energy and wind energy that focus on energy generation, the lithium battery industry, as a key energy storage link, also occupies a pivotal position. At present, the electrolyte system commonly used in lithium batteries is mainly composed of organic solvents. However, this type of electrolyte faces a significant challenge, that is, its electrochemical stability window is relatively limited. This means that when the battery is charged to a higher voltage level, the electrolyte is prone to oxidative decomposition reactions accompanied by heat release, which may trigger thermal runaway of the battery. What is more noteworthy is that due to the high flammability of the organic electrolyte itself, as the heat in the battery system continues to accumulate and rise, it is very easy to ignite the electrolyte, causing a fire in the battery system, and even causing an explosion in extreme cases.

[0003] Solid electrolytes are the key to achieving solid-state batteries with high electrochemical performance and high safety performance. Compared with traditional liquid electrolytes, solid electrolytes have better thermal stability and can effectively solve the safety problems of lithium batteries.

[0004] However, there are still some difficulties and challenges in the practical application of solid-state electrolytes. For example, the low ionic conductivity at room temperature leads to poor rate performance, which limits the development of lithium batteries. Summary of the invention

[0005] In order to overcome the deficiencies of the prior art, the purpose of the present invention is to provide a method for preparing a composite ion conductor, to prepare the composite ion conductor as a solid electrolyte for a lithium battery, and to solve the problem of poor rate performance of the solid electrolyte of a lithium battery.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] The method for preparing a composite ion conductor comprises the following steps:

[0008] S1. Preparation of Al-based MOFs material MIL-101;

[0009] S2, MIL-101 modification to prepare NH2@MIL-101;

[0010] S3, preparing lithium ion liquid Li-IL;

[0011] S4. Preparation of composite ion conductor NH2@MIL-101 / Li-IL.

[0012] Furthermore, the steps for preparing the Al-based MOFs material MIL-101 described in S1 are:

[0013] Aluminum chloride hexahydrate and an organic ligand are added to DMF and subjected to ultrasonic treatment for 15-20 minutes to obtain a dispersion; the dispersion is heated to 120-130° C. for reaction for 70-72 hours, and the product is collected by centrifugation. The product is washed with DMF and anhydrous ethanol and dried at 60-70° C. for 10-12 hours to obtain MIL-101.

[0014] Further, the organic ligand is one of 1,3,5-trimethylbenzene dicarboxylic acid, terephthalic acid or 2-aminoterephthalic acid;

[0015] The molar ratio of aluminum chloride hexahydrate to the organic ligand is 1:1-3.

[0016] Furthermore, the steps of modifying MIL-101 in S2 to prepare NH2@MIL-101 are:

[0017] MIL-101, H2O and 3-aminopropyltriethoxysilane (APTES) were mixed into a solution, the solution was ultrasonically treated for 30-40 min, then centrifuged, washed with DMF and anhydrous ethanol, and dried at 60-70°C for 10-12 h to obtain NH2@MIL-101.

[0018] Furthermore, the usage ratio of MIL-101, H2O and APTES is 3g:5mL:3-5mL.

[0019] Furthermore, the steps of preparing the lithium ion liquid Li-IL in S3 are:

[0020] The lithium salt lithium bis(trifluoromethanesulfonyl imide) (LiTFSI) was dissolved in the ionic liquid 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl imide) ([EMIM][TFSI]) and stirred for 2-3 h to obtain the lithium ion liquid Li-IL.

[0021] Furthermore, the usage ratio of LiTFSI and [EMIM][TFSI] is 2-3g:3-4g.

[0022] Furthermore, the steps of preparing the composite ion conductor NH2@MIL-101 / Li-IL described in S4 are:

[0023] Activate NH2@MIL-101 at 110-120°C for 20-24h; fully mix the activated NH2@MIL-101 and Li-IL, centrifuge, wash with DMF and anhydrous ethanol, dry at 60-70°C for 10-12h, and press into tablets to obtain the composite ion conductor NH2@MIL-101 / Li-IL.

[0024] Furthermore, the usage ratio of the activated NH2@MIL-101 to Li-IL is 1g:0.8-1g.

[0025] A lithium battery comprises a composite ion conductor prepared by the above preparation method and carbon-coated lithium iron phosphate.

[0026] Beneficial effects of the present invention:

[0027] (1) The composite ion conductor NH2@MIL-101 / Li-IL prepared in the present invention has excellent rate performance as a solid electrolyte for lithium batteries.

[0028] (2) The present invention prepares the composite ion conductor NH2@MIL-101 / Li-IL by loading ionic liquid into MOFs pores; MOFs material, as a porous material, has open metal sites, porous characteristics and ordered pore structure; ionic liquids have high ionic conductivity, negligible volatility, non-flammability and high thermal stability and electrochemical stability; when the prepared composite ion conductor NH2@MIL-101 / Li-IL is used as a solid electrolyte for lithium batteries, on the one hand, it retains the high ion transport characteristics of ionic liquids and avoids leakage; on the other hand, the loaded ionic liquid can improve the contact between MOFs particles / interfaces, reduce the interfacial resistance inside the electrolyte, and facilitate the migration of lithium ions inside, thereby improving the rate performance of the solid electrolyte.

[0029] (3) The present invention introduces amino groups on the surface of MIL-101 to modify it. The amino groups can react with the anion TFSI of the lithium ion liquid. - Form hydrogen bonds, thereby enhancing the affinity of MIL-101 to TFSI - The adsorption and fixation ability of solid electrolytes can promote the dissociation of lithium ions, enhance the transmission performance of lithium ions in the electrolyte, and improve the rate performance of solid electrolytes. DETAILED DESCRIPTION

[0030] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] Example 1

[0032] This embodiment provides a method for preparing a composite ion conductor, comprising the following steps:

[0033] S1. Preparation of Al-based MOFs material MIL-101:

[0034] 2.17 g of aluminum chloride hexahydrate and 2.49 g of 2-aminoterephthalic acid were added to DMF and ultrasonicated for 15-20 min to obtain a dispersion; the dispersion was heated to 130° C. and reacted for 72 h, and the product was collected by centrifugation. The product was washed with DMF and anhydrous ethanol and dried at 70° C. for 10 h to obtain MIL-101.

[0035] S2. Preparation of NH2@MIL-101 by modification of MIL-101:

[0036] 3 g of MIL-101, 5 mL of H2O and 3 mL of APTES were mixed into a solution. The solution was ultrasonically treated for 40 min, centrifuged, washed with DMF and anhydrous ethanol, and dried at 70°C for 10 h to obtain NH2@MIL-101.

[0037] S3. Preparation of lithium ion liquid Li-IL:

[0038] 3 g of LiTFSI was dissolved in 4 g of [EMIM][TFSI] and stirred for 3 h to obtain lithium ion liquid Li-IL.

[0039] S4. Preparation of composite ion conductor NH2@MIL-101 / Li-IL:

[0040] 1 g of NH2@MIL-101 was activated at 120°C for 24 h; the activated NH2@MIL-101 was fully mixed with 0.8 g of Li-IL, centrifuged, washed with DMF and anhydrous ethanol, dried at 60-70°C for 10-12 h, and pressed into tablets to obtain the composite ion conductor NH2@MIL-101 / Li-IL.

[0041] Example 2

[0042] The difference between this embodiment and embodiment 1 is that the "2.49 g of 2-aminoterephthalic acid" in S1 is changed to "2.98 g of terephthalic acid"; the other raw materials and preparation process remain the same as those in embodiment 1.

[0043] Example 3

[0044] The difference between this embodiment and embodiment 1 is that the "2.49 g of 2-aminoterephthalic acid" in S1 is changed to "3.78 g of 1,3,5-trimethylbenzenecarboxylic acid"; the other raw materials and preparation process remain the same as those in embodiment 1.

[0045] Example 4

[0046] The difference between this embodiment and embodiment 1 is that "3 mL of APTES" in S2 is changed to "4 mL of APTES"; the other raw materials and preparation process remain the same as those in embodiment 1.

[0047] Example 5

[0048] The difference between this embodiment and embodiment 1 is that "3 mL of APTES" in S2 is changed to "5 mL of APTES"; the other raw materials and preparation process remain the same as those in embodiment 1.

[0049] Comparative Example 1

[0050] Compared with Example 1, this comparative example differs in that step S2 is not performed to modify MIL-101 to prepare NH2@MIL-101, that is, APTES is not used to modify MIL-101; the remaining raw materials and preparation process remain the same as in Example 1.

[0051] The composite ion conductors prepared in the above-mentioned Examples 1 to 5 and Comparative Example 1 were used as solid electrolytes, carbon-coated lithium iron phosphate was used as the positive electrode, and graphite was used as the negative electrode, and matched and assembled into lithium batteries for electrochemical performance tests such as rate and cycle tests; the discharge capacity of the lithium battery at different rates was tested, and the results are shown in Table 1; the discharge capacity of the lithium battery at different times of charge and discharge cycles at a current density of 0.5C was tested, and the test results are shown in Table 2:

[0052] Table 1

[0053] Discharge capacity (mAh / g) 0.5C 1C 2C 5C 10C Example 1 158.1 156.4 154.3 151.2 147.5 Example 2 155.2 153.3 151.6 148.4 144.6 Example 3 150.3 148.1 146.5 143.2 139.3 Example 4 163.2 161.3 159.6 156.5 152.1 Example 5 157.5 155.4 153.3 150.4 146.1 Comparative Example 1 156.3 154.1 152.4 149.2 145.1

[0054] Table 2

[0055] Discharge capacity (mAh / g) 20 times 50 times 100 times Example 1 158.0 156.8 155.4 Example 2 155.1 153.9 152.5 Example 3 150.2 149.0 147.5 Example 4 163.1 162.0 160.6 Example 5 157.3 156.2 154.7 Comparative Example 1 156.1 154.8 153.4

[0056] It can be seen from Table 1 that the composite ion conductors in Examples 1 to 5 can still maintain a high discharge capacity at a high current density when used as solid electrolytes for lithium batteries, and have excellent rate performance; compared with Example 3, Examples 1 and 2 have more excellent rate performance, which may be because the organic ligands used in the composite ion conductor NH2@MIL-101 / Li-IL are different. The organic ligand used in Example 1 is 2-aminoterephthalic acid, the organic ligand used in Example 2 is terephthalic acid, and the organic ligand used in Example 3 is 1,3,5-trimethylbenzene; the pore size of MIL-101 obtained from 2-aminoterephthalic acid and terephthalic acid is larger, and the anion TFSI of the lithium ion liquid is -They can move and diffuse freely inside MIL-101, so they are stronger in fixing TFSI- than MIL-101 obtained by 1,3,5-triphenyltricarboxylic acid, and can better promote the dissociation of lithium ions, enhance the transmission performance of lithium ions in the electrolyte, and thus show better rate performance; compared with Example 2, Example 1 shows better rate performance, because 2-aminoterephthalic acid has more amino functional groups than terephthalic acid, and the amino group can form hydrogen bonds with the anion TFSI- of the lithium ion liquid, thereby enhancing the adsorption and fixation ability of MIL-101 for TFSI-, and can promote the dissociation of lithium ions, enhance the transmission performance of lithium ions in the electrolyte, and improve the rate performance of the solid electrolyte.

[0057] Compared with Example 1, Example 4 and Example 5, Example 4 has better rate performance. Therefore, when modifying MIL-101, the amount of APTES should not be too little or too much; because when the amount is too little, the effect is not obvious, and when the amount is too much, the excess APTES will hydrolyze in water to produce intermediates, and the intermediates may prevent APTES from further reacting or combining with the surface of MIL-101 through self-polymerization. Therefore, the amino groups on the surface of MIL-101 will decrease with the excess of APTES, thereby weakening the lithium ion transmission performance in the solid electrolyte and reducing the rate performance of the solid electrolyte.

[0058] Comparison between Comparative Example 1 and Example 1 shows that introducing amino groups on the surface of MIL-101 to modify it can improve the rate performance of the solid electrolyte, because the amino groups can form hydrogen bonds with the anion TFSI- of the lithium ion liquid, thereby enhancing the adsorption and fixation ability of MIL-101 for TFSI-, which can further promote the dissociation of lithium ions, enhance the transmission performance of lithium ions in the electrolyte, and improve the rate performance of the solid electrolyte.

[0059] It can be seen from Table 2 that the composite ion conductors of Examples 1 to 5 and Comparative Example 1 have excellent cycle performance when used as solid electrolytes for lithium batteries, because the ionic liquid in the solid electrolyte has excellent electrochemical stability, and the properties of the ionic liquid can be well retained by loading the ionic liquid through the MOFs pores.

[0060] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0061] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a composite ion conductor, characterized in that: The steps include: S1. Preparation of Al-based MOFs material MIL-101; S2, MIL-101 modification to prepare NH2@MIL-101; S3, preparing lithium ion liquid Li-IL; S4. Preparation of composite ion conductor NH2@MIL-101 / Li-IL.

2. The method for preparing a composite ion conductor according to claim 1, characterized in that: The steps for preparing the Al-based MOFs material MIL-101 described in S1 are: Aluminum chloride hexahydrate and an organic ligand are added to DMF and subjected to ultrasonic treatment for 15-20 minutes to obtain a dispersion; the dispersion is heated to 120-130° C. for reaction for 70-72 hours, and the product is collected by centrifugation. The product is washed with DMF and anhydrous ethanol and dried at 60-70° C. for 10-12 hours to obtain MIL-101.

3. The method for preparing a composite ion conductor according to claim 2, characterized in that: The organic ligand is one of 1,3,5-trimethylenediamine, terephthalic acid or 2-aminoterephthalic acid; The molar ratio of aluminum chloride hexahydrate to the organic ligand is 1:1-3.

4. The method for preparing a composite ion conductor according to claim 1, characterized in that: The steps of modifying MIL-101 to prepare NH2@MIL-101 described in S2 are: MIL-101, H2O and 3-aminopropyltriethoxysilane were mixed into a solution, the solution was ultrasonically treated for 30-40 minutes, centrifuged, washed with DMF and anhydrous ethanol, and dried at 60-70°C for 10-12 hours to obtain NH2@MIL-101.

5. The method for preparing a composite ion conductor according to claim 4, characterized in that: The usage ratio of the MIL-101, H2O and 3-aminopropyltriethoxysilane is 3g:5mL:3-5mL.

6. The method for preparing a composite ion conductor according to claim 1, characterized in that: The steps for preparing lithium ion liquid Li-IL described in S3 are: The lithium salt lithium bis(trifluoromethanesulfonyl imide) was dissolved in the ionic liquid 1-ethyl-3-methylimidazoline bis(trifluoromethanesulfonyl imide) and stirred for 2-3 hours to obtain the lithium ion liquid Li-IL.

7. The method for preparing a composite ion conductor according to claim 6, characterized in that: The usage ratio of the lithium salt and the ionic liquid is 2-3g:3-4g.

8. The method for preparing a composite ion conductor according to claim 1, characterized in that: The steps for preparing the composite ion conductor NH2@MIL-101 / Li-IL described in S4 are: Activate NH2@MIL-101 at 110-120°C for 20-24h; fully mix the activated NH2@MIL-101 and Li-IL, centrifuge, wash with DMF and anhydrous ethanol, dry at 60-70°C for 10-12h, and press into tablets to obtain the composite ion conductor NH2@MIL-101 / Li-IL.

9. The method for preparing a composite ion conductor according to claim 8, characterized in that: The usage ratio of the activated NH2@MIL-101 to Li-IL is 1g:0.8-1g.

10. A lithium battery, characterized in that: The invention comprises a composite ion conductor prepared by the preparation method according to any one of claims 1 to 9 and carbon-coated lithium iron phosphate.