Zn-mof material containing lithium element and solid-state electrolyte and battery using same

Abstract

The application provides a Zn-MOF material containing lithium elements, which is prepared from a zinc source material, a first ligand, a second ligand and a lithium source material, wherein the first ligand is trimesic acid, and the molecular structure of the second ligand satisfies general formula I: R1-R8 are independently selected from hydrogen, methyl, methoxy and ethyl, and 0<=n<3. The Zn-MOF material containing lithium elements is prepared by a specific preparation method, has high lithium ion conductivity and large lithium ion transference number, and can widen the electrochemical stability window of a battery using the Zn-MOF material containing lithium elements and improve the cycle stability of the battery.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lithium ion battery electrolytes, in particular to a Zn-MOF material containing lithium elements and a solid-state electrolyte and a battery using the Zn-MOF material. BACKGROUND

[0002] Energy, as the driving force for industrial development, plays a very important role in social development. With the introduction of a series of policies such as carbon emission and carbon standard, it is imperative to develop clean energy. Compared with traditional energy, clean energy has the great advantage of environmental friendliness, which is conducive to sustainable development. Among many new energy devices, lithium batteries have been industrialized and widely used in various industries due to their long cycle life, no memory effect and high energy density, but the reserves of lithium resources on earth are limited. In order to reduce costs, sodium batteries, potassium batteries, magnesium batteries, calcium batteries, zinc batteries, aluminum batteries and other new energy devices have also attracted attention. At the same time, supercapacitors, as new energy not inferior to lithium batteries, also play an important role in energy storage materials and clean energy. Among the above-mentioned many new energy devices, lithium batteries are the most mature, and other secondary batteries and supercapacitors are also developing rapidly. Taking lithium batteries as an example, the safety performance of current commercial lithium batteries is not high, and the internal short circuit of the battery is easily caused by the growth of lithium dendrites. The use of liquid electrolyte is prone to leakage, which can easily cause fire, which greatly limits the further application of lithium batteries. As a substitute for lithium batteries, other secondary batteries also have the problem of dendrite growth, so it is necessary to develop a solid-state electrolyte that has high efficient ion transmission capacity and does not leak electrolyte.

[0003] Although the common inorganic solid-state electrolyte has high ionic conductivity, its interface contact efficiency is low, and it is unstable in water and air, which greatly limits its practicability. The polymer electrolyte usually has good flexibility and mechanical properties, but the problems of low conductivity and narrow electrochemical working window still exist. Therefore, metal-organic frameworks (MOFs) mainly composed of metal ions and organic linkers are considered to be ideal materials for constructing solid-state lithium ion conductors due to their structural stability, low electronic conductivity and low interface impedance.

[0004] However, the lithium ion conduction performance of commercially available metal-organic framework materials still needs to be improved to better apply them to solid-state lithium ion conductive materials. Therefore, it is necessary to design a metal-organic framework material with high lithium ion conduction performance. SUMMARY

[0005] The application aims to provide a Zn-MOF material containing lithium elements, and a solid-state electrolyte and a battery using the Zn-MOF material, the Zn-MOF material containing lithium elements has high lithium ion conductivity and large lithium ion transference number, and the electrochemical stability window of the battery using the Zn-MOF material containing lithium elements is widened and the cycle stability is improved.

[0006] According to one aspect of the application, a Zn-MOF material containing lithium elements is prepared by the following steps: S1. preparing a Zn-MOF material with a polycarboxylic acid structure: uniformly mixing a zinc source material, a first ligand, a second ligand and a first solvent to prepare a first reaction solution, and reacting the first reaction solution at 100-120 DEG C for 30-40 hours, and then cooling to 25-35 DEG C to prepare the Zn-MOF material with a polycarboxylic acid structure; wherein the first ligand is trimesic acid, the pH value of the first reaction solution is 1-2, and the molecular structure of the second ligand satisfies general formula I: R1-R8 are independently selected from hydrogen, methyl, methoxy, ethyl, and 0<=n<3; S2. uniformly mixing the Zn-MOF material with a polycarboxylic acid structure, a lithium source material and a second solvent to prepare a second reaction solution, and stirring the second reaction solution at 25-35 DEG C for 40-50 hours to prepare the Zn-MOF material containing lithium elements.

[0007] The Zn-MOF material with a polycarboxylic acid structure (Zn-MOF@COOH) is prepared by a hydrothermal method, and the lithium ions in the lithium source material replace the uncoordinated free carboxyl groups in the ligand in the reaction in S2, thereby preparing the Zn-MOF material containing lithium elements (Zn-MOF@COOLi). The Zn-MOF@COOLi changes the chemical composition and crystal structure of the Zn-MOF material without affecting the main framework of the Zn-MOF material, so that a large number of lithium ions are loaded in the pore channel of the Zn-MOF material. The Zn-MOF@COOLi prepared by the application has excellent mechanical stability and electrochemical stability as an electrolyte, and can improve the lithium ion conductivity. As known, the movement speed of electrons and ions is not matched. The lithium ions released from the positive electrode need to diffuse to gradually migrate to the negative electrode, while the electrons released from the positive electrode at the same time reach the negative electrode almost instantaneously, so that there needs to be enough lithium ions near the negative electrode to complete the ion cycle. Therefore, since the Zn-MOF@COOLi itself contains a large number of lithium ions, the Zn-MOF@COOLi can provide enough lithium ions for battery cycle when used as an electrolyte, thereby improving the lithium ion conductivity of the electrolyte and further improving the cycle performance of the battery using the Zn-MOF@COOLi as an electrolyte.

[0008] Secondly, the second ligand satisfying the general formula I is more conducive to the reaction. Firstly, both ends of the second ligand need to have coordination sites N. The N in the pyridine structure has an uncoordinated lone pair of electrons, and the binding force of the electron is weaker than other electrons, which is easy to coordinate with zinc ions in the reaction. Moreover, the second ligand is linear, which helps to reduce the steric hindrance in the reaction process, so that the coordination reaction can proceed smoothly.

[0009] Preferably, in S1, the molar ratio of zinc element in the zinc source material: the first ligand: the second ligand is 1:0.35-0.45:1.05-1.15.

[0010] The first ligand and the second ligand are both coordinated with zinc ions. In the preparation of Zn-MOF@COOLi, the sum of the amount of the first ligand and the second ligand is greater than the amount of zinc ions in the zinc source material, which is conducive to the full reaction of the ligand. Moreover, when the molar ratio of zinc element in the zinc source material: the first ligand: the second ligand is 1:0.35-0.45:1.05-1.15, the prepared Zn-MOF material has a stable structure, and by adjusting the amount of the first ligand, the carboxylic acid content in the prepared Zn-MOF@COOH can be moderate, so that the prepared Zn-MOF@COOLi meets the experimental expectations. When the feeding ratio in S1 meets the above conditions, the prepared Zn-MOF@COOLi has a large amount of lithium ions, which can further improve the lithium ion transmission rate, and the mechanical structure is stable.

[0011] Preferably, in S2, the molar ratio of zinc element in the Zn-MOF material with a polycarboxylic acid structure: lithium element in the lithium source material is 1:1.2-1.4.

[0012] When the feeding amount in S2 meets the above conditions, the amount of lithium ions is slightly greater than the amount of Zn-MOF@COOH, which is more conducive to the preparation of Zn-MOF@COOLi rich in lithium ions, promotes lithium ion conduction, and reduces the activation energy of the Zn-MOF material containing lithium elements.

[0013] Preferably, in S2, the pH value of the second reaction solution is 11-12.

[0014] The pH value of the second reaction solvent is controlled to be 11-12, which not only removes the residual free carboxyl groups in the Zn-MOF@COOH, but also promotes the acid-base neutralization reaction between the Zn-MOF@COOH and the lithium source material in S2. Thus, the concentration of lithium ions in the prepared Zn-MOF@COOLi is increased, the lithium ion conduction in the battery charging and discharging process is promoted, the activation energy is reduced, and the electrochemical stability window is widened. The smaller the activation energy of the Zn-MOF@COOLi, the stronger the ability of ions to jump under the action of an electric field, and the higher the conductivity, so that the cycle performance of the battery using Zn-MOF@COOLi as the electrolyte is better.

[0015] Preferably, the lithium source material is selected from lithium oxide and lithium hydroxide.

[0016] Preferably, in the chemical structure of the second ligand, n is 0 or 1.

[0017] When the number of benzene rings contained in the second ligand is 0 or 1, the steric hindrance of the second ligand is small, and the second ligand is more likely to coordinate with the first ligand and zinc ions.

[0018] Preferably, in the chemical structure of the second ligand, at least one of R1, R4, R6, and R7 is a methoxy group.

[0019] The methoxy group belongs to an electron-rich group and can play an electron-donating role, which can make the large π bond in the pyridine structure more stable. When at least one of R1, R4, R6, and R7 is a methoxy group, the reactivity of the N atom in the pyridine structure can be improved, which is helpful for the coordination reaction to generate Zn-MOF@COOH.

[0020] Preferably, the second ligand is 2,2'-dimethoxy-4,4'-bipyridine.

[0021] When 2,2'-dimethoxy-4,4'-bipyridine is used as the second ligand, the prepared Zn-MOF@COOLi has a stable structure and good lithium ion transport performance. The battery using the Zn-MOF@COOLi as the electrolyte has excellent cycle performance and a wide electrochemical stability window.

[0022] Preferably, in S1, the first solvent is selected from at least one of tetrahydrofuran, cyclohexane, and N,N-dimethylformamide.

[0023] According to a second aspect of the present application, a solid-state electrolyte is provided, which comprises the above-mentioned Zn-MOF material containing lithium elements, and the Zn-MOF material containing lithium elements accounts for not less than 80% in the solid-state electrolyte film in terms of mass percentage.

[0024] The solid-state electrolyte prepared by using the Zn-MOF material containing lithium element can improve the lithium ion conductivity and lithium ion transference number of the solid-state electrolyte film, so that the battery using the solid-state electrolyte film has excellent cycle performance.

[0025] According to a third aspect of the present application, a battery is provided, comprising the solid-state electrolyte film, a positive electrode sheet and a negative electrode sheet, wherein the solid-state electrolyte film is arranged between the positive electrode sheet and the negative electrode sheet.

[0026] The battery provided by the present application has the advantages of strong cycle stability, long cycle life and wide electrochemical stability window. DETAILED DESCRIPTION

[0027] In order to make the personnel in the technical field better understand the technical solutions in the present application, the technical solutions of the present application will be described clearly and completely in combination with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should belong to the scope of protection of the present application.

[0028] Embodiment 1

[0029] The present embodiment provides a Zn-MOF material containing lithium element, and the raw materials used include: zinc source material, first ligand, second ligand, first solvent, lithium source material, and second solvent. In the present embodiment, Zn(NO3)2·6H2O is selected as the zinc source material, trimesic acid is selected as the first ligand, tetrahydrofuran is selected as the first solvent, and 2,2'-dimethoxy-4,4'-bipyridine is selected as the second ligand, wherein the CAS number of 2,2'-dimethoxy-4,4'-bipyridine is 142929-11-1, and the chemical structure is LiOH is selected as the lithium source material, and deionized water is selected as the second solvent.

[0030] The Zn-MOF material containing lithium element is prepared by the following operation steps:

[0031] S1. Preparation of Zn-MOF material with polycarboxylic acid structure (Zn-MOF@COOH): 1.0 mmol of zinc source material, 0.4 mmol of the first ligand, 1.1 mmol of the second ligand and 10 ml of the first solvent were ultrasonically mixed for 15 minutes to prepare a first reaction solution, and the pH value of the first reaction solution was adjusted to 1 by adding 0.1 mol / L HCl solution. The first reaction solution was reacted at 110°C for 36 hours, and then cooled to 30°C at a cooling rate of 5°C / hour. The product was washed with deionized water and acetone, and then vacuum dried to prepare the Zn-MOF material with polycarboxylic acid structure (Zn-MOF@COOH).

[0032] S2. Preparation of Zn-MOF material containing lithium element (Zn-MOF@COOLi): 1.0 mmol of Zn-MOF@COOH and 1.3 mmol of lithium source material were uniformly mixed with 250 ml of the second solvent to prepare a second reaction solution, and the pH value of the second reaction solution was adjusted to 11-12. The second reaction solution was stirred at 30°C for 48 hours, and the precipitate was collected by centrifugation. The precipitate was washed with deionized water and vacuum dried at 60°C for 24 hours to prepare the Zn-MOF material containing lithium element (Zn-MOF@COOLi).

[0033] Example 2

[0034] In this example, a Zn-MOF material containing lithium element was prepared by referring to the preparation method provided in Example 1. The difference between this example and Example 1 is that in S1, the molar ratio of zinc element in the zinc source material: the first ligand: the second ligand is 1:0.3:1.0. The remaining raw materials and preparation methods are strictly consistent with those of Example 1.

[0035] Example 3

[0036] In this example, a Zn-MOF material containing lithium element was prepared by referring to the preparation method provided in Example 1. The difference between this example and Example 1 is that in S1, the molar ratio of zinc element in the zinc source material: the first ligand: the second ligand is 1:0.5:1.2. The remaining raw materials and preparation methods are strictly consistent with those of Example 1.

[0037] Example 4

[0038] This embodiment refers to the preparation method provided in Embodiment 1 to prepare a Zn-MOF material containing lithium element. The difference between this embodiment and Embodiment 1 is that in S2, the molar ratio of zinc element in the Zn-MOF material of polycarboxylic acid structure: lithium element in the lithium source material = 1:1.2. The remaining raw materials and preparation method are strictly consistent with Embodiment 1.

[0039] Embodiment 5

[0040] This embodiment refers to the preparation method provided in Embodiment 1 to prepare a Zn-MOF material containing lithium element. The difference between this embodiment and Embodiment 1 is that in S2, the molar ratio of zinc element in the Zn-MOF material of polycarboxylic acid structure: lithium element in the lithium source material = 1:1.2. The remaining raw materials and preparation method are strictly consistent with Embodiment 1.

[0041] Embodiment 6

[0042] This embodiment refers to the preparation method provided in Embodiment 1 to prepare a Zn-MOF material containing lithium element. The difference between this embodiment and Embodiment 1 is that in S2, the molar ratio of zinc element in the Zn-MOF material of polycarboxylic acid structure: lithium element in the lithium source material = 1:1.4. The remaining raw materials and preparation method are strictly consistent with Embodiment 1.

[0043] Embodiment 7

[0044] This embodiment refers to the preparation method provided in Embodiment 1 to prepare a Zn-MOF material containing lithium element. The difference between this embodiment and Embodiment 1 is that in S2, the molar ratio of zinc element in the Zn-MOF material of polycarboxylic acid structure: lithium element in the lithium source material = 1:1.6. The remaining raw materials and preparation method are strictly consistent with Embodiment 1.

[0045] Embodiment 8

[0046] This embodiment refers to the preparation method provided in Embodiment 1 to prepare a Zn-MOF material containing lithium element. The difference between this embodiment and Embodiment 1 is that in S2, the pH of the second reaction solution is greater than 12. The remaining raw materials and preparation method are strictly consistent with Embodiment 1.

[0047] Embodiment 9

[0048] This embodiment refers to the preparation method provided in Embodiment 1 to prepare a Zn-MOF material containing lithium element. The difference between this embodiment and Embodiment 1 is that in S1, equimolar amount of 4,4'-dipyridyl is selected instead of 2,2'-dimethoxy-4,4'-dipyridyl selected in Embodiment 1. The CAS number of 4,4'-dipyridyl is 553-26-4, and the chemical structure of 4,4'-dipyridyl is The remaining raw materials and preparation methods are strictly consistent with those of Example 1.

[0049] Example 10

[0050] This example refers to the preparation method provided in Example 1 to prepare a Zn-MOF material containing lithium element. The difference between this example and Example 1 is that in S1, an equal molar amount of 1,4-bis(pyrilidinyl) benzene is selected instead of 2,2'-dimethoxy-4,4'-bipyridine selected in Example 1. Among them, the CAS number of 1,4-bis(pyrilidinyl) benzene is 113682-56-7, and the chemical structure of 1,4-bis(pyrilidinyl) benzene is The remaining raw materials and preparation methods are strictly consistent with those of Example 1.

[0051] Example 11

[0052] This example refers to the preparation method provided in Example 1 to prepare a Zn-MOF material containing lithium element. The difference between this example and Example 1 is that in S1, an equal molar amount of 4,4'-bis(4-pyrilidinyl) biphenyl is selected instead of 2,2'-dimethoxy-4,4'-bipyridine selected in Example 1. Among them, the CAS number of 4,4'-bis(4-pyrilidinyl) biphenyl is 319430-87-0, and the chemical structure of 4,4'-bis(4-pyrilidinyl) biphenyl is The remaining raw materials and preparation methods are strictly consistent with those of Example 1.

[0053] Example 12

[0054] This example refers to the preparation method provided in Example 1 to prepare a Zn-MOF material containing lithium element. The difference between this example and Example 1 is that in S1, an equal molar amount of 3-methoxy-4,4'-bipyridine is selected instead of 2,2'-dimethoxy-4,4'-bipyridine selected in Example 1. Among them, the CAS number of 3-methoxy-4,4'-bipyridine is 1214325-92-4, and the chemical structure of 3-methoxy-4,4'-bipyridine is The remaining raw materials and preparation methods are strictly consistent with those of Example 1.

[0055] Comparative Example 1

[0056] This comparative example refers to the preparation method provided in Example 1 to prepare a Zn-MOF material. The difference between this comparative example and Example 1 is that in S1, the pH value of the first reaction solution is less than 1. The remaining raw materials and preparation methods are strictly consistent with those of Example 1.

[0057] Comparative Example 2

[0058] A Zn-MOF material was prepared according to the preparation method provided in Example 1. The difference between this comparative example and Example 1 is that in S1, the pH value of the first reaction solution is greater than 2. The remaining raw materials and preparation methods are strictly consistent with Example 1.

[0059] Comparative Example 3

[0060] A Zn-MOF material was prepared according to the preparation method provided in Example 1. The difference between this comparative example and Example 1 is that in S1, equimolar amount of p-toluic acid was selected instead of trimesic acid selected in Example 1. The remaining raw materials and preparation methods are strictly consistent with Example 1.

[0061] Comparative Example 4

[0062] A Zn-MOF material was prepared according to the preparation method provided in Example 1. The difference between this comparative example and Example 1 is that in S1, equimolar amount of 2-methoxy-4-phenylpyridine was selected instead of 2,2'-dimethoxy-4,4'-bipyridine selected in Example 1. The CAS number of 2-methoxy-4-phenylpyridine is 53698-46-7, and the chemical structure of 2-methoxy-4-phenylpyridine is The remaining raw materials and preparation methods are strictly consistent with Example 1.

[0063] Comparative Example 5

[0064] A Zn-MOF material was prepared according to the preparation method provided in Example 1. The difference between this comparative example and Example 1 is that in S1, equimolar amount of m-bis(4-pyridyl)benzene was selected instead of 2,2'-dimethoxy-4,4'-bipyridine selected in Example 1. The CAS number of m-bis(4-pyridyl)benzene is 170165-79-4, and the chemical structure of m-bis(4-pyridyl)benzene is The remaining raw materials and preparation methods are strictly consistent with Example 1.

[0065] Comparative Example 6

[0066] A Zn-MOF material was prepared according to the preparation method provided in Example 1. The difference between this comparative example and Example 1 is that in the preparation of the Zn-MOF material, the preparation step of S2 is omitted. The remaining raw materials and preparation methods are strictly consistent with Example 1.

[0067] Comparative Example 7

[0068] A Zn-MOF material was prepared according to the preparation method provided in Example 1. The difference between the present comparative example and Example 1 is that the commercially available Zn-MOF material was directly used instead of the Zn-MOF@COOLi prepared in Example 1. The remaining raw materials and preparation method were strictly consistent with Example 1.

[0069] Test Example 1

[0070] 1. Test objects: The solid-state electrolyte membranes prepared from the Zn-MOF materials provided in Examples 1-12 and Comparative Examples 1-7 were used as test objects. The specific preparation method was as follows:

[0071] The Zn-MOF materials provided in Examples 1-12 and Comparative Examples 1-7 were respectively dispersed in an amount of isopropanol with 60% polytetrafluoroethylene emulsion (wt%=9:1), and then sufficiently ground into a mud-like substance. The mud-like substance was rolled into a thin film with a thickness of 200 um on a copper foil, punched into a circular sheet with a diameter of 16 mm, and placed in a vacuum drying box for drying for 24 h. Then, the circular sheet was soaked in 1 mol / L LiPF6 electrolyte for 24 h. The prepared circular sheet after soaking was used as a solid-state electrolyte membrane.

[0072] 2. Test items and test methods:

[0073] (1) Lithium ion conductivity σ:

[0074] A stainless steel sheet was used as the positive electrode, and a lithium sheet was used as the negative electrode. Each test object was used as a solid-state electrolyte membrane, and was assembled in an inert gas atmosphere with a water and oxygen content of less than 0.5 ppm to obtain a (stainless steel SS | solid-state electrolyte | lithium sheet) CR2032 type asymmetric button cell. The lithium ion conductivity was tested at 25±5°C using an electrochemical workstation, and the test frequency was 1-10 6 Hz.

[0075] The calculation formula of the lithium ion conductivity is σ=L / (R*S). L is the thickness, R is the resistance, and S is the contact area.

[0076] (2) Lithium ion transference number t Li+ :

[0077] A lithium sheet was used as the positive electrode and the negative electrode. Each test object was used as a solid-state electrolyte membrane, and was assembled in an inert gas atmosphere with a water and oxygen content of less than 0.5 ppm to obtain a (stainless steel SS | solid-state electrolyte | lithium sheet) CR2032 type symmetric button cell. The lithium ion transference number was tested at 25±5°C using the Bruce-Vincent-Evans method, and the polarization voltage was 10 mV, and the impedance test frequency was 1 Hz-1 MHz.

[0078] The calculation formula of the lithium ion transference number is: tLi+ = (IS (AV - I0R0) ) / (I (AV - IsRs) ). I0 and I S are the initial and steady currents, R0 and R S are the interface resistances before and after polarization, and AV is the polarization voltage.

[0079] (3) Electrochemical window:

[0080] Stainless steel sheet was selected as the positive electrode, lithium sheet as the negative electrode, and each test object as the solid-state electrolyte membrane. The (stainless steel SS | solid-state electrolyte | lithium sheet) CR2032 type asymmetric button cell was assembled in an inert gas atmosphere with water and oxygen content less than 0.5 ppm. The button cell was evaluated at 25 ± 5°C using linear sweep voltammetry (LSV). The scan rate was 10 mV / s, and the voltage range was 0-7 V. The decomposition voltage was recorded.

[0081] (4) Cycle performance:

[0082] LiFePO4 was selected as the positive electrode, lithium sheet as the negative electrode, and each test object as the solid-state electrolyte membrane. The (LiFePO4 | solid-state electrolyte | lithium sheet) CR2032 type asymmetric button cell was assembled in an inert gas atmosphere with water and oxygen content less than 0.5 ppm. The battery was subjected to 50 charge-discharge cycles at 25 ± 5°C, with a voltage range of 2.5-4.2 V. The capacity retention rate was recorded.

[0083] 3. Test results: The reaction conditions and raw material compositions of each test object are shown in Table 1, the chemical structural formulas of the second ligands selected by each test object are shown in Table 2, and the test results are shown in Table 3.

[0084] Table 1. Reaction conditions and raw material compositions of each test object

[0085]

[0086]

[0087] Table 2. Chemical structural formulas of the second ligands selected by each test object

[0088]

[0089]

[0090] Table 3. Test results summary table

[0091]

[0092]

[0093] Results analysis:

[0094] Comparing the reaction conditions and raw material compositions of Examples 1-12 and Comparative Examples 1-5 in Table 1, it can be seen that the Zn-MOF materials provided by Examples 1-12 are prepared by a specific reaction pH value, a specific first ligand and a second ligand satisfying the general formula I. Among all the above test objects, the solid electrolyte membrane provided by Example 1 exhibits the best ion transmission efficiency, so that the battery using the solid electrolyte membrane has excellent cycle capacity retention rate and a wide chemical window.

[0095] Firstly, the main components in the solid electrolyte membrane are explored. In Examples 1, Comparative Example 6 and Comparative Example 7, different types of Zn-MOF materials are used to prepare solid electrolyte membranes. Example 1 is to prepare a solid electrolyte membrane by using a Zn-MOF material containing lithium element (i.e. Zn-MOF@COOLi), Comparative Example 6 is to prepare a solid electrolyte membrane by using a Zn-MOF material with polycarboxylic acid structure, and Comparative Example 7 is to prepare a solid electrolyte membrane by using a conventional commercially available Zn-MOF material. The batteries provided by Examples 1, Comparative Example 6 and Comparative Example 7 are tested, and by comparing the test data of the three test objects in Table 3, it can be seen that the battery of Example 1 exhibits better ion transmission rate and cycle performance than the batteries provided by Comparative Example 6 and Comparative Example 7, which indicates that the Zn-MOF@COOLi in Example 1 changes the chemical composition and crystal structure of the Zn-MOF material without affecting the main framework of the Zn-MOF material, so that a large number of lithium ions are loaded in the pore channel of the Zn-MOF material. The Zn-MOF@COOLi prepared by the present application as an electrolyte not only retains the excellent mechanical stability and electrochemical stability of the Zn-MOF material, but also can improve the conduction performance of lithium ions, thereby improving the cycle performance of the battery using the Zn-MOF@COOLi as an electrolyte.

[0096] Secondly, before preparing Zn-MOF@COOLi, it is necessary to prepare Zn-MOF material with polycarboxylic acid structure (Zn-MOF@COOH) first. In the process of preparing Zn-MOF material with polycarboxylic acid structure in Example 1, the pH value of the first reaction solution is 1-2, in Comparative Example 1, the pH value of the first reaction solution is less than 1; in Comparative Example 2, the pH value of the first reaction solution is greater than 2; and in Comparative Example 3, p-benzoic acid is selected as the first ligand, both carboxyl groups in the structure of p-benzoic acid are coordinated with zinc ions, so that there is no free carboxyl group structure in the pore channel of the prepared Zn-MOF, and the pore channel of the Zn-MOF cannot be further enriched with lithium ions. The test performance of the solid electrolyte membrane provided by Example 1 and Comparative Examples 1-3 is compared. It can be seen that, compared with the batteries provided by Comparative Examples 1-3, the battery provided by Example 1 has a higher cycle retention rate and a wider electrochemical window. Moreover, with the increase of the pH value of the first reaction solution for preparing Zn-MOF@COOH, the ion transmission performance and stability of the prepared Zn-MOF material show a trend of first rising and then falling. When the pH value of the first reaction solution is 1-2, the prepared Zn-MOF@COOH has excellent ionic conductivity, and the measured ion transference number is higher, which is beneficial to improve the cycle stability of the battery using the Zn-MOF@COOH. Therefore, it is indicated that, in the process of preparing Zn-MOF material with polycarboxylic acid structure, the first reaction solution is adjusted to be acidic, the pH value is in the range of 1-2, and the first ligand of trimesic acid rich in carboxyl structure is introduced at the same time, so that Zn-MOF@COOH with a large number of free carboxyl groups can be prepared. By using the free carboxyl group of Zn-MOF@COOH, lithium element can be further introduced into the Zn-MOF material to prepare Zn-MOF@COOLi.

[0097] Based on the above analysis of the pH value of the first reaction solution in the process of preparing Zn-MOF@COOH, the types of the second ligand are further explored. As shown in Table 2, the molecular structure of the second ligand selected in Example 1 and Examples 9-12 satisfies the general formula I: 0 ≤ n < 3. The second ligand used in Comparative Example 4 had only one coordination site N on one side, while the second ligand used in Comparative Example 5 had a nonlinear structure. By comparing the test data of Examples 1, 9-12, and Comparative Examples 4-5 in Table 3, it can be found that the Zn-MOFs provided in Examples 1 and 9-12 have better chemical stability than the Zn-MOF prepared in Comparative Example 4. This indicates that a second ligand satisfying General Formula I is more conducive to the reaction, and the coordination reaction can proceed more smoothly when coordination sites N exist at both ends of the second ligand. This is because N in the pyridine structure has an uncoordinated lone pair of electrons, and the binding force of this lone pair of electrons is weaker than that of other electrons, making it easier to coordinate this lone pair of electrons with zinc ions in the reaction. Comparing the performance measured by the batteries prepared in Comparative Example 5 with those in Examples 1 and 9-12, the batteries provided in Examples 1 and 9-12 exhibited higher cycle performance and ion transport performance than the battery in Comparative Example 5, and had a wider electrochemical window and better cycle capacity retention. This demonstrates that when the second ligand has a linear structure, it helps to reduce steric hindrance during the coordination reaction, allowing the coordination reaction to proceed smoothly.

[0098] Furthermore, the raw materials used in the preparation of Zn-MOF@COOLi in Examples 9-11 were compared. Example 9 used 4,4'-bipyridine with n=0 in the molecular structure of general formula I; Example 10 used 1,4-bis(p-pyridyl)benzene with n=1 in the molecular structure of general formula I; and Example 11 used 2,2'-dimethoxy-4,4'-bipyridine with n=2 in the molecular structure of general formula I. Comparing the electrochemical performance measured for the three test subjects in Table 3, it can be seen that the cycle stability measured for the battery in Example 9 is higher than that measured for the batteries in Examples 10 and 11; while the cycle stability and electrochemical window of the battery in Example 10 are better than those of the battery in Example 11. This indicates that as the value of n in the molecular structure of general formula I increases, the chemical stability of the prepared Zn-MOF@COOLi shows a trend of first increasing and then decreasing. In other words, when the second ligand has fewer benzene ring structures, it experiences less steric hindrance and is more likely to undergo coordination reactions with the first ligand and zinc ions.

[0099] The batteries provided by Example 1, Example 9 and Example 12 are compared, which are different in the type and position of the groups in the selected second ligand. The second ligand in Example 1 comprises two methoxy groups, which are located at R1 and R7 respectively, and the remaining positions are hydrogen; the second ligand in Example 9 comprises hydrogen at R1-R8; and the second ligand in Example 10 comprises one methoxy group at R2. In the test data shown in Table 3, compared with the Zn-MOF@COOLi prepared by Example 9, the Zn-MOF@COOLi provided by Example 1 and Example 12 has better chemical stability and can provide better cycle performance in the process of battery charging and discharging. This shows that the Zn-MOF@COOLi prepared by using the second ligand comprising the methoxy group in Example 1 and Example 12 can make the Zn-MOF have better electrochemical performance, because the methoxy group belongs to an electron-rich group and can play an electron-donating role, which can make the large π bond in the pyridine structure more stable. Among them, compared with the battery of Example 12, the battery provided by Example 1 has higher ionic conductivity, more ion transference number, wider electrochemical window and higher cycle capacity retention rate. This shows that when at least one of R1, R4, R6 and R7 of the second ligand is a methoxy group, the reactivity of the N atom in the pyridine structure of the second ligand can be improved, which is helpful for the coordination reaction to generate Zn-MOF@COOH, thereby improving the structural stability and lithium ion transmission performance of Zn-MOF@COOLi.

[0100] Next, the amount of zinc source material, the first ligand and the second ligand in the preparation of Zn-MOF@COOH is explored. In the Zn-MOF@COOLi provided by Example 1-3, according to the molar ratio, the zinc element in the zinc source material: the first ligand: the second ligand in Example 1 is 1:0.4:1.1, the zinc element in the zinc source material: the first ligand: the second ligand in Example 2 is 1:0.3:1, and the zinc element in the zinc source material: the first ligand: the second ligand in Example 3 is 1:0.5:1.2. Compared with the batteries provided by Example 2 and Example 3, the battery provided by Example 1 has higher cycle stability and longer cycle life, and the electrochemical stability window is wider. This shows that when the zinc element in the zinc source material: the first ligand: the second ligand is 1:0.35-0.45:1.05-1.15, not only the prepared Zn-MOF material has a stable structure, but also the carboxylic acid content in the prepared Zn-MOF@COOH is moderate, so that the prepared Zn-MOF@COOLi has a large amount of lithium ions, which can further improve the lithium ion transmission rate and the mechanical structure is stable.

[0101] In the reaction conditions and raw material compositions of Example 1, Examples 4-7, the difference lies in the different amounts of the material of Zn-MOF@COOH and lithium source. By comparing the test data of the above five examples in Table 3, it can be found that, compared with the test performance of Example 4 and Example 7, the ion conductivity of the battery in Example 1 and Examples 5-6 is higher, and the ion migration number is more. Therefore, in the process of preparing Zn-MOF@COOLi, when the molar ratio of zinc element in Zn-MOF@COOH to lithium element in lithium source material is 1:1.2-1.4, it is more conducive to prepare Zn-MOF@COOLi rich in lithium ions, promote lithium ion conduction, and reduce the activation energy of Zn-MOF material containing lithium element.

[0102] Comparing the batteries provided by Example 1 and Example 8, the difference lies in the pH value of the second reaction solution in the process of preparing Zn-MOF@COOLi. In Example 1, the pH value of the second reaction solution is in the range of 11-12, and the pH value of the second reaction solution in Example 8 is greater than 12. Comparing the electrochemical performance of the batteries of the two examples in Table 2, it can be seen that the battery of Example 1 has higher ion conduction performance than the battery provided by Example 8, and also has higher cycle stability. This shows that controlling the pH value of the second reaction solvent to be 11-12 can not only remove the residual free carboxyl groups in Zn-MOF@COOH, but also promote the acid-base neutralization reaction between Zn-MOF@COOH and lithium source material in S2. Therefore, the concentration of lithium ions in the pore channel of the prepared Zn-MOF@COOLi is increased, the lithium ion conduction in the battery charging and discharging process is promoted, the activation energy is reduced, and the electrochemical stability window is widened. The smaller the activation energy of Zn-MOF@COOLi, the stronger the ability of ions to jump under the action of an electric field, and the higher the conductivity, so that the cycle performance of the battery using Zn-MOF@COOLi as electrolyte is better.

[0103] The above examples are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A lithium-containing Zn-MOF material, characterized in that, It is prepared by the following steps: S1. Preparation of Zn-MOF material with polycarboxylic acid structure: A zinc source material, a first ligand, a second ligand, and a first solvent are mixed uniformly to obtain a first reaction solution. The first reaction solution is reacted at 100-120℃ for 30-40 hours, and then cooled to 25-35℃ to obtain the Zn-MOF material with the polycarboxylic acid structure; wherein the first ligand is trimesic acid, the pH value of the first reaction solution is 1-2, and the molecular structure of the second ligand satisfies general formula I: R1 to R8 are independently selected from hydrogen, methyl, methoxy, and ethyl, 0 ≤ n < 3, and the zinc element in the zinc source material is calculated according to the molar ratio: first ligand: second ligand = 1: 0.35~0.45: 1.05~1.15; S2. The Zn-MOF material with the polycarboxylic acid structure, the lithium source material, and the second solvent are mixed evenly to obtain a second reaction solution. The second reaction solution is stirred at 25~35℃ for 40~50 hours to obtain the Zn-MOF material containing lithium element. The pH of the second reaction solution is 11~12.

2. The lithium-containing Zn-MOF material as described in claim 1, characterized in that, In S2, the ratio of zinc in the polycarboxylic acid structure Zn-MOF material to lithium in the lithium source material is calculated as 1:1.2~1.

4.

3. The lithium-containing Zn-MOF material as described in claim 1, characterized in that, The lithium source material is selected from at least one of lithium oxide and lithium hydroxide.

4. The lithium-containing Zn-MOF material as described in claim 1, characterized in that, In the chemical structure of the second ligand, n is 0 or 1.

5. The lithium-containing Zn-MOF material as described in claim 4, characterized in that, In the chemical structure of the second ligand, at least one of R1, R4, R6, and R7 is a methoxy group.

6. The lithium-containing Zn-MOF material as described in claim 5, characterized in that, The second ligand is 2,2'-dimethoxy-4,4'-bipyridine.

7. A solid electrolyte membrane, characterized in that, The lithium-containing Zn-MOF material as described in any one of claims 1 to 6, wherein the lithium-containing Zn-MOF material comprises not less than 80% of the solid electrolyte membrane by mass percentage.

8. A battery, characterized in that: It includes the solid electrolyte membrane, positive electrode, and negative electrode as described in claim 7, wherein the solid electrolyte membrane is disposed between the positive electrode and the negative electrode.

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