Porous lithium metal organic framework composite lithium supplement agent as well as preparation method and application thereof

Abstract

The invention relates to the technical field of lithium ion battery electrolyte additives, in particular to a porous lithium metal organic framework composite lithium supplement agent and a preparation method and application thereof. A porous lithium metal organic framework composite lithium supplementing agent comprises a lithium metal organic framework (Li-MOF), a three-dimensional porous structure is formed by Li and a biphenyldicarboxylic acid (BPDC) ligand through a coordinate bond, the pore diameter is 2-5 nm, and the specific surface area is larger than or equal to 500 m / g; the LiF nano-particles are loaded in the pore channels of the Li-MOF, the particle size is less than or equal to 5 nm, and the LiF nano-particles are uniformly distributed in the pore channels of the Li-MOF. According to the porous lithium metal organic framework composite lithium supplement agent and the preparation method thereof, the problems of an existing lithium supplement agent in the aspects of lithium supplement efficiency, interface stability, safety and the like can be effectively solved, and meanwhile the porous lithium metal organic framework composite lithium supplement agent has wide adaptability and remarkable commercial potential.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion battery electrolyte additives, and in particular to a porous lithium metal organic framework composite lithium supplement and a preparation method and application thereof. Background Art

[0002] As the core technology of modern energy storage, the improvement of energy density of lithium-ion batteries has always been the research focus of academia and industry. According to the forecast of the International Energy Agency (IEA), by 2030, the number of electric vehicles in the world will exceed 300 million, and the demand for power batteries will exceed 3TWh, which puts higher requirements on the energy density (target ≥400Wh / kg) and cycle life (>1500 times) of batteries. To achieve this goal, the battery material system is undergoing the following changes: 1) High nickelization of positive electrode materials: ternary materials with a nickel content of more than 90% (such as NCM90, NCA) can provide a specific capacity of >220mAh / g, but high voltage (>4.3V) operation aggravates the oxidation and decomposition of the electrolyte, resulting in active lithium loss. 2) Siliconization of negative electrode materials: The theoretical capacity of silicon-based negative electrode (SiOx / C) (≈4200mAh / g) far exceeds that of graphite (372mAh / g), but its huge volume expansion (>300%) during charging and discharging causes repeated rupture of SEI film and continuous consumption of lithium ions. 3) Solid-state battery technology: Solid-state electrolytes (such as sulfides and oxides) are compatible with lithium metal negative electrodes, but problems such as poor interface contact and lithium dendrite growth have not been completely solved.

[0003] In the above system, low first coulombic efficiency (ICE) and cycle life decay have become two core issues restricting the commercialization of high energy density batteries. Taking silicon-based negative electrodes as an example, the irreversible lithium loss caused by SEI film formation and silicon volume expansion in the first cycle can reach 20-30%, while ICE is only 70-85%; and the electrolyte side reactions of high nickel positive electrodes under high pressure further aggravate the consumption of lithium stocks. If the active lithium cannot be effectively compensated and the electrode interface cannot be stabilized, the actual capacity and life of the battery will be far lower than the theoretical value.

[0004] Lithium replenishment technology introduces additional lithium sources into the battery system to offset irreversible lithium loss. It is mainly divided into the following three categories: (1) Positive electrode lithium supplement: By adding lithium-rich compounds (such as Li2O2, Li5FeO4) to the positive electrode, it decomposes and releases Li during the first charge + It has strong process compatibility and does not require changes to the existing battery structure. However, due to its high decomposition voltage (>4.5V), it needs to be used with a high-voltage electrolyte, which causes gas production (O2) and oxidation side reactions, and its lithium replenishment capacity is limited (Li2O2 theoretical capacity ≈1168mAh / g, actual utilization rate <50%).

[0005] (2) Anode prelithiation technology: Lithium metal powder, lithium alloy or chemical lithiation reagent is directly used to supplement lithium to the anode. Its lithium supplementation efficiency is high, and it can significantly improve the ICE (the ICE of silicon-based anodes can be increased to >90%). However, lithium metal powder is prone to react with the electrolyte to generate by-products such as LiOH and Li2CO3, resulting in rapid capacity decay of the battery during cycling. In addition, the operation of chemical lithiation reagents is highly dangerous and difficult to apply on a large scale.

[0006] (3) Electrolyte lithium supplement: The lithium supplement is directly added to the electrolyte, and Li is continuously released through electrochemical decomposition. + , with simple process, adaptable to existing production lines, and capable of realizing dynamic lithium supplementation.

[0007] Although the electrolyte lithium supplement has unique advantages, its industrialization still faces the following technical bottlenecks: 1) Chemical stability: Most inorganic lithium compounds (such as Li3N and Li2O2) undergo hydrolysis or reduction reactions in carbonate solvents (EC, DEC). For example: Li3N + 3EC → 3Li+ + NH3↑ + 3EC- (gas generation and solvent consumption) Li3N + 3EC → 3Li+ + NH3↑ + 3EC- (gas generation and solvent consumption). 2) Electrochemical stability: Organic lithium salts (such as LiDFOB) are oxidized and decomposed under high voltage (>4.5V) to generate fluorine-containing acidic substances (HF), which corrode the cathode material (such as patent EP3252864B1). 3) Insufficient improvement in the first efficiency: If the lithium supplement decomposes prematurely (such as Li3N completely decomposes during the first charge cycle), although the ICE can be improved, there is no continuous lithium source supply during cycling, and the capacity decay accelerates; if the decomposition potential of the lithium supplement is too high (such as Li2O2 requires >4.5V), the improvement in the first efficiency is limited, and the subsequent lithium release cannot cover the electrode demand. 4) Lack of dynamic repair of the SEI film: Existing lithium supplements only focus on lithium compensation and cannot repair the rupture of the SEI film during cycling, resulting in continuous lithium consumption (such as patent CN112467214A).

[0008] According to the report of Benchmark Mineral Intelligence, the global demand for lithium supplements in power batteries will exceed 150,000 tons in 2025, and the market scale will reach $8 billion. However, due to the above technical defects, the market penetration rate of existing lithium supplement products is less than 10%. The market urgently needs a new type of electrolyte lithium supplement to solve the above problems. Summary of the Invention

[0009] Aiming at the problems that existing lithium supplements cannot balance lithium supplementation efficiency, interface stability, and safety due to material limitations, the present application provides a porous lithium metal-organic framework composite lithium supplement, its preparation method, and application. The porous lithium metal-organic framework composite lithium supplement prepared in the present application uses Li+ as the metal node and biphenyl dicarboxylic acid (BPDC) as the organic ligand to construct a three-dimensional porous framework (pore diameter 2 - 3nm, specific surface area >500m2 / g), inhibiting the growth of lithium dendrites through the pore confinement effect, and controllably releasing Li through the breaking of coordination bonds + (release potential ≈ 3.8 - 4.2 V vs. Li / Li + ). And loading LiF nanoparticles into the pores of Li-MOF to generate LiF particles with a size < 5 nm. During the release of Li + , synchronously providing F - , which participates in the formation of a LiF-rich SEI film with a high ionic conductivity (> 10 - ⁻³ S / cm), repairing the cracks in the SEI film during cycling and reducing the interfacial impedance. The technical advantage of this application is that it can achieve the synergistic effect of dynamic lithium supplementation and self-repair. The Li-MOF framework releases Li during the first charge + , thereby improving the first Coulombic efficiency of the battery; at the same time, the LiF released during cycling continuously repairs the SEI film, thereby extending the cycle life of the battery. In addition, the prepared porous structure can limit the uneven deposition of lithium, thereby improving the safety performance of the battery, and has wide adaptability, compatible with existing commercial liquid electrolytes (such as EC / DMC + FEC) and solid electrolytes (sulfides, polymers), and applicable to silicon-based anodes, high-nickel cathodes and lithium metal battery systems. This application realizes the combination of dynamic lithium supplementation and SEI film self-repair function by designing a porous lithium metal-organic framework composite lithium supplement (Li-MOF@LiF), providing a new solution for breaking through the battery performance bottleneck. This technology not only meets the market demand, but also lays the foundation for the next generation of technologies such as solid-state batteries and lithium metal batteries, with significant commercial potential and social and economic value.

[0010] In the first aspect, this application provides a porous lithium metal-organic framework composite lithium supplement, adopting the following technical solution: A porous lithium metal-organic framework composite lithium supplement, comprising: a lithium metal-organic framework (Li-MOF), formed by Li + and biphenyldicarboxylic acid (BPDC) ligands through coordination bonds to form a three-dimensional porous structure with a pore size of 2 - 5 nm and a specific surface area ≥ 500 m 2 / g; LiF nanoparticles, loaded in the pores of Li-MOF, with a particle size ≤ 5 nm and evenly distributed in the Li-MOF pores.

[0011] By adopting the above technical solution, by releasing Li during the first charge through the Li-MOF framework + , it is possible to compensate for the capacity decline caused by irreversible lithium loss during the first cycle of the battery, thereby improving the first Coulombic efficiency of the battery. The three-dimensional porous framework structure effectively inhibits the growth of lithium dendrites through the pore confinement effect, reducing the threat of lithium dendrites to the battery safety. During the battery cycling process, the Li-MOF framework continuously releases Li +Meanwhile, LiF nanoparticles simultaneously provide F - , participate in the formation of a LiF-rich SEI film with high ionic conductivity, repair the cracks in the SEI film during cycling, reduce the interfacial impedance, and improve the cycle life of the battery. The porous structure restricts the uneven deposition of lithium, thereby improving the safety performance of the battery. This lithium supplement agent is compatible with existing commercial liquid electrolytes and solid electrolytes and is applicable to various battery systems, such as silicon-based anodes, high-nickel cathodes, and lithium metal battery systems. The synergistic effect is mainly reflected in the combined action of Li-MOF and LiF nanoparticles. Li-MOF provides a three-dimensional porous structure that not only helps with the storage and release of Li + , but also inhibits the growth of lithium dendrites through the pore confinement effect. LiF nanoparticles, on the other hand, participate in the formation of an SEI film with high ionic conductivity by providing F - , repair the cracks in the SEI film, and reduce the interfacial impedance. This synergistic effect enables the battery to continuously repair the SEI film during cycling, improving the cycle life and safety of the battery.

[0012] Preferably, the pore diameter of the Li-MOF is 2 - 3 nm, and the specific surface area is 550 - 600 m 2 / g.

[0013] In a second aspect, the present application provides a method for preparing a porous lithium metal-organic framework composite lithium supplement agent, adopting the following technical solution: As a general technical concept, the present application also provides a method for preparing the above-mentioned porous lithium metal-organic framework composite lithium supplement agent, including the following steps: S31. Mix lithium nitrate (LiNO3) and biphenyldicarboxylic acid (BPDC) evenly to obtain a mixed solution A; mix N,N-dimethylformamide (DMF) and cetyltrimethylammonium bromide (CTAB) evenly to obtain a mixed solution B; then mix the mixed solution A and the mixed solution B, and perform ultrasonic treatment for 30 min until completely dissolved to obtain a mixed solution C; S32. Transfer the mixed solution C to a high-pressure reaction kettle, seal it, and place it in an oven. Heat it to 80 - 120 °C at a rate of 2 °C / min and keep it warm for 6 - 24 h; S33. Naturally cool the high-pressure reaction kettle to room temperature, take out the solution, filter and collect the white precipitate, and wash it 1 - 3 times with N,N-dimethylformamide DMF and methanol respectively to obtain a Li-MOF precursor; S34. Vacuum-dry the Li-MOF precursor at 40 - 120 °C for 2 - 12 h to obtain Li-MOF crystals; S35. Activate the Li-MOF crystals in a nitrogen atmosphere to remove the template agent cetyltrimethylammonium bromide CTAB and obtain porous Li-MOF powder; S36. Immerse the porous Li-MOF powder in a 0.5 M lithium hexafluorophosphate LiPF6 ethanol solution, and after drying and high-temperature annealing, a porous lithium metal-organic framework composite lithium supplement agent is obtained, denoted as the LiF@Li-MOF composite material.

[0014] By adopting the above technical solution, the preparation of the mixed solution: First, prepare the mixed solution A by mixing lithium nitrate and biphenyl dicarboxylic acid, and at the same time prepare the mixed solution B by mixing N,N-dimethylformamide and cetyltrimethylammonium bromide. This step is mainly to form the precursor of Li-MOF. Treatment of the mixed solution: Mix the mixed solution A and B and perform ultrasonic treatment to ensure that the two solutions are fully mixed and form a uniform solution C. Ultrasonic treatment helps to improve the mixing efficiency and uniformity. High-temperature reaction: Transfer the mixed solution C to a high-pressure reactor and perform high-temperature treatment in an oven. This step is the key step in forming the Li-MOF precursor, and high temperature helps the formation of coordination bonds and pore channels. Washing and drying: Obtain the Li-MOF precursor by washing and drying the white precipitate. This step is mainly to remove impurities and ensure the purity and stability of Li-MOF. Activation and drying: Perform vacuum drying and activation treatment on the Li-MOF precursor to obtain Li-MOF crystals. This step helps to remove the template agent and ensure that the pore size and specific surface area of Li-MOF meet the expected requirements. Loading of LiF nanoparticles: Immerse the Li-MOF powder in the LiPF6 ethanol solution and perform drying and high-temperature annealing treatment. This step is mainly to load LiF nanoparticles in the Li-MOF pore channels, thereby forming the LiF@Li-MOF composite material. The result of the synergistic effect of these steps is to form a Li-MOF composite material with a three-dimensional porous structure, in which LiF nanoparticles are uniformly distributed in the pore channels of Li-MOF. This structure not only helps to improve the lithium supplement efficiency and the cycle life of the battery, but also can inhibit the growth of lithium dendrites through the pore confinement effect and improve the safety performance of the battery. At the same time, LiF nanoparticles synchronously provide F + when released - , which participates in the formation of a LiF-rich SEI film with high ionic conductivity, helps to repair the cracks in the SEI film during cycling and reduce the interfacial impedance. In addition, the concentration of the template agent CTAB has an important influence on the specific surface area and pore size distribution of Li-MOF. An appropriate CTAB concentration helps to form a larger specific surface area and a smaller pore size distribution, while an excessive CTAB concentration will block the Li-MOF pore channels. Therefore, selecting an appropriate CTAB concentration is crucial for the preparation of high-performance Li-MOF composite materials.

[0015] Preferably, in step S31, the molar ratio of lithium nitrate (LiNO3) to biphenyldicarboxylic acid (BPDC) is 1-50:1-50; the mass ratio of N,N-dimethylformamide (DMF) to cetyltrimethylammonium bromide (CTAB) is 1-1000:1-100.

[0016] Preferably, in step S35, the process parameters for activation are: the activation temperature is 150-300 °C, and the activation time is 2-4 h.

[0017] Preferably, in step S36, the specific operation of impregnating the porous Li-MOF powder in a 0.5 M lithium hexafluorophosphate LiPF6 ethanol solution is as follows: mixing the porous Li-MOF powder and the 0.5 M lithium hexafluorophosphate LiPF6 ethanol solution evenly at a mass ratio of 1-50:1-50, and then maintaining it at 0.05 kPa for 2 h to ensure that the pores are fully infiltrated.

[0018] Preferably, in step S36, the process conditions for drying are: drying at 60 °C for 6-8 h to remove the ethanol solvent.

[0019] Preferably, in step S36, the process conditions for high-temperature annealing are: heating to 200-600 °C at a rate of 5 °C / min in an argon atmosphere, holding for 2-4 h, and then cooling to room temperature.

[0020] In a third aspect, the present application provides a lithium supplement electrolyte for a lithium battery, adopting the following technical solution: As a general technical concept, the present application also provides the above-mentioned porous lithium metal-organic framework composite lithium supplement agent as a lithium supplement electrolyte for a lithium battery. Mix LiF@Li-MOF composite material, carbon nanotubes (CNT) and N,N-dimethylformamide DMC at a mass ratio of 10:1:100, and then stir at 500 rpm for 1-5 h to form a pre-dispersed liquid; then mix the pre-dispersed liquid and a commercial electrolyte at a mass ratio of 1:25, stir for 4 h, and let stand for 12 h to obtain a lithium supplement electrolyte for a lithium battery.

[0021] In a fourth aspect, the present application provides an application of a porous lithium metal-organic framework composite lithium supplement agent, adopting the following technical solution: As a general technical concept, the present application also provides the above-mentioned application of the porous lithium metal-organic framework composite lithium supplement agent in a silicon-based anode battery, a high-nickel cathode battery or a lithium metal battery.

[0022] In summary, the present application includes at least one of the following beneficial technical effects: 1. Improve the lithium supplement efficiency: Through the pore confinement effect of the Li-MOF framework and the controllable fracture mechanism of the coordination bond, the growth of lithium dendrites can be effectively inhibited and the release of lithium ions can be precisely controlled, thereby improving the lithium supplement efficiency.

[0023] 2. Improvement in interfacial stability: The introduction of LiF nanoparticles can participate in the formation of a LiF-rich SEI film with high ionic conductivity. This film has a self-healing function, can repair the cracks in the SEI film during cycling, reduce the interfacial impedance, and thus improve the interfacial stability of the battery.

[0024] 3. Enhancement of safety: The design of the porous structure helps to limit the uneven deposition of lithium, reduce the risk of the formation of lithium dendrites in lithium metal batteries, and thus improve the safety performance of the battery.

[0025] 4. Wide adaptability: This lithium supplement agent is applicable not only to existing commercial liquid electrolytes and solid electrolytes, but also to silicon-based anodes, high-nickel cathodes, and lithium metal battery systems, showing wide adaptability.

[0026] 5. Improvement of battery performance: The Li-MOF framework releases Li during the first charge + , which can improve the first Coulombic efficiency of the battery. Meanwhile, the LiF released during cycling can continuously repair the SEI film and improve the cycle life of the battery.

[0027] 6. Commercialization potential and social and economic value: The technology of this application not only meets the market demand, but also lays a foundation for the development of next-generation battery technologies such as solid-state batteries and lithium metal batteries, showing significant commercialization potential and social and economic value. Description of the Drawings

[0028] In order to more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the embodiments are briefly introduced below: Figure 1 It is a graph of the battery cycle stability obtained by preparing a porous lithium metal-organic framework composite lithium supplement agent prepared in Example 1, Comparative Example 1, and Comparative Example 2 into a lithium supplement electrolyte and adding it to a lithium battery. Detailed Embodiments

[0029] The embodiments of this application will be described in detail below in conjunction with the embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate this application and should not be regarded as limiting the scope of this application. For those conditions not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0030] Step 1 of Example 1: Dissolve LiNO3 (4 mmol) and BPDC (2 mmol) in 40 g of DMF, add CTAB (0.01 g), and ultrasonically treat for 30 min until completely dissolved.

[0031] Step 2: Transfer the mixed solution to a high-pressure reactor, seal it, and place it in an oven. Heat it to 120 °C at a rate of 2 °C / min and keep it at this temperature for 24 h; Step 3: Naturally cool it to room temperature, centrifuge (8000 rpm, 10 min) to collect the white precipitate, and wash it 3 times with DMF and methanol respectively; Step 4: Dry the precipitate in vacuum at 80 °C for 12 h to obtain Li-MOF crystals; Step 5: Activate it in a nitrogen atmosphere at 300 °C for 2 h to remove the template agent CTAB and obtain porous Li-MOF powder.

[0032] Step 6: Immerse the Li-MOF powder (5 g) in 0.5 M LiPF6 / ethanol solution (50 g), keep it under vacuum conditions (0.05 kPa) for 2 h to ensure that the pores are fully infiltrated, and then dry it at 60 °C for 6 h to remove the ethanol solvent.

[0033] Step 7: Place the impregnated and dried Li-MOF in a tubular furnace, heat it to 300 °C at a rate of 5 °C / min in an argon atmosphere, keep it at this temperature for 2 h, and cool it to room temperature to obtain a porous lithium metal-organic framework lithium supplement agent, labeled as LiF@Li-MOF composite material.

[0034] Step 1 of Example 2: Dissolve LiNO3 (1 mmol) and BPDC (50 mmol) in 50 g of DMF, add CTAB (0.01 g), and ultrasonically treat it for 30 min until it is completely dissolved.

[0035] Step 2: Transfer the mixed solution to a high-pressure reactor, seal it, and place it in an oven. Heat it to 120 °C at a rate of 2 °C / min and keep it at this temperature for 24 h; Step 3: Naturally cool it to room temperature, centrifuge (8000 rpm, 10 min) to collect the white precipitate, and wash it 3 times with DMF and methanol respectively; Step 4: Dry the precipitate in vacuum at 80 °C for 12 h to obtain Li-MOF crystals; Step 5: Activate it in a nitrogen atmosphere at 150 °C for 4 h to remove the template agent CTAB and obtain porous Li-MOF powder.

[0036] Step 6: Immerse the Li-MOF powder (5 g) in 0.5 M LiPF6 / ethanol solution (250 g), keep it under vacuum conditions (0.05 kPa) for 2 h to ensure that the pores are fully infiltrated, and then dry it at 60 °C for 8 h to remove the ethanol solvent.

[0037] Step 7: Place the impregnated and dried Li-MOF in a tubular furnace, heat it to 600 °C at a rate of 5 °C / min under an argon atmosphere, hold for 3 h, and then cool to room temperature to obtain a porous lithium metal-organic framework composite lithium supplement agent, labeled as LiF@Li-MOF composite material.

[0038] Example 3 Step 1: Dissolve LiNO3 (4 mmol) and BPDC (100 mmol) in 50 g of DMF, add CTAB (0.01 g), and ultrasonically treat for 30 min until completely dissolved.

[0039] Step 2: Transfer the mixed solution to a high-pressure reaction kettle, seal it and place it in an oven, heat it to 120 °C at a rate of 2 °C / min, and hold for 24 h. Step 3: Naturally cool to room temperature, centrifuge (8000 rpm, 10 min) to collect the white precipitate, and wash it 3 times with DMF and methanol respectively. Step 4: Vacuum dry the precipitate at 80 °C for 12 h to obtain Li-MOF crystals. Step 5: Activate for 3 h in a nitrogen atmosphere at 200 °C to remove the template agent CTAB and obtain porous Li-MOF powder.

[0040] Step 6: Immerse the Li-MOF powder (5 g) in a 0.5 M LiPF6 / ethanol solution (100 g), keep it under vacuum conditions (0.05 kPa) for 2 h to ensure that the pores are fully infiltrated, and then dry it at 60 °C for 7 h to remove the ethanol solvent.

[0041] Step 7: Place the impregnated and dried Li-MOF in a tubular furnace, heat it to 400 °C at a rate of 5 °C / min under an argon atmosphere, hold for 3 h, and then cool to room temperature to obtain a porous lithium metal-organic framework composite lithium supplement agent, labeled as LiF@Li-MOF composite material.

[0042] Comparative Example 1: Step 1: Dissolve LiNO3 (4 mmol) and BPDC (2 mmol) in 40 g of DMF, add CTAB (0.1 g), and ultrasonically treat for 30 min until completely dissolved.

[0043] Step 2: Transfer the mixed solution to a high-pressure reaction kettle, seal it and place it in an oven, heat it to 120 °C at a rate of 2 °C / min, and hold for 24 h. Step 3: Naturally cool to room temperature, centrifuge (8000 rpm, 10 min) to collect the white precipitate, and wash it 3 times with DMF and methanol respectively. Step 4: Vacuum dry the precipitate at 80 °C for 12 h to obtain Li-MOF crystals. Step 5: Activate in a nitrogen atmosphere at 300 °C for 2 h to remove the template agent CTAB and obtain porous Li-MOF powder.

[0044] Step 6: Immerse the Li-MOF powder (5 g) in a 0.5 M LiPF6 / ethanol solution (50 g) and keep it under vacuum conditions (0.05 kPa) for 2 h to ensure that the pores are fully infiltrated, and then dry it at 60 °C for 6 h to remove the ethanol solvent.

[0045] Step 7: Place the impregnated and dried Li-MOF in a tube furnace, heat it to 300 °C at a rate of 5 °C / min under an argon atmosphere, hold for 2 h, and cool to room temperature to obtain a porous lithium metal-organic framework composite lithium supplement agent, labeled as LiF@Li-MOF composite material.

[0046] Comparative Example 2: Step 1: Dissolve LiNO3 (4 mmol) and BPDC (2 mmol) in 40 g of DMF and ultrasonically treat for 30 min until completely dissolved.

[0047] Step 2: Transfer the mixed solution to a high-pressure reactor, seal it and place it in an oven, heat it to 120 °C at a rate of 2 °C / min, and hold for 24 h; Step 3: Naturally cool to room temperature, centrifuge (8000 rpm, 10 min) to collect the white precipitate, and wash it 3 times with DMF and methanol respectively; Step 4: Vacuum dry the precipitate at 80 °C for 12 h to obtain Li-MOF crystals; Step 5: Activate in a nitrogen atmosphere at 300 °C for 2 h to remove the template agent CTAB and obtain porous Li-MOF powder.

[0048] Step 6: Immerse the Li-MOF powder (5 g) in a 0.5 M LiPF6 / ethanol solution (50 g) and keep it under vacuum conditions (0.05 kPa) for 2 h to ensure that the pores are fully infiltrated, and then dry it at 60 °C for 6 h to remove the ethanol solvent.

[0049] Step 7: Place the impregnated and dried Li-MOF in a tube furnace, heat it to 300 °C at a rate of 5 °C / min under an argon atmosphere, hold for 2 h, and cool to room temperature to obtain a porous lithium metal-organic framework composite lithium supplement agent, labeled as LiF@Li-MOF composite material.

[0050] Performance Detection Test 1. Use the BET specific surface area tester BSD-BET400 of the full-automatic nitrogen adsorption instrument of Beishide Instrument to test the specific surface area and pore size distribution of the LiF@Li-MOF powders prepared in Example 1 to Example 3 and Comparative Example 1 and Comparative Example 2 respectively. The test results are shown in Table 1.

[0051] 2. Preparation and Testing of Button Batteries Preparation of Lithium-Supplementing Electrolyte (1) The prepared porous lithium metal-organic framework composite lithium-supplementing agents of Example 1, Comparative Example 1, and Comparative Example 2 were respectively mixed with carbon nanotubes (CNT) and N,N-dimethylformamide DMC at a mass ratio of 10:1:100, and then stirred at 500 rpm for 3 h to form a pre-dispersion; then the pre-dispersion was mixed with a commercial electrolyte at a mass ratio of 1:25, stirred for 4 h, and left standing for 12 h to obtain the lithium-supplementing electrolyte for lithium batteries. Among them, the formula of the commercial electrolyte was 1M LiPF6 / EC + DMC (3:7, volume ratio), containing 2% FEC (fluoroethylene carbonate).

[0052] (2) Assemble a button battery. The assembly order of the battery is the positive electrode case, LiNi 0.5 Co 0.2 Mn 0.3 O2 (523 positive electrode material), PE separator, silicon-oxygen negative electrode, gasket, and negative electrode case. The entire assembly process is carried out in a glove box under an argon atmosphere; the button battery is kept warm in a constant-temperature oven at 60 °C for 12 hours and then tested. Charge and discharge are carried out at a constant current of 50 mAh to detect the cycle stability of the button battery. The test results are as shown in Figure 1 shown.

[0053] Table 1 Specific Surface Area and Pore Size Distribution Project Specific surface area Material pore size distribution Example 1 <![CDATA[550m 2 / g]]> 3 - 5nm Example 2 <![CDATA[530m 2 / g]]> 2 - 5nm Example 3 <![CDATA[500m 2 / g]]> 2 - 5nm Comparative Example 1 <![CDATA[100m 2 / g]]> >100nm Comparative Example 2 <![CDATA[23m 2 / g]]> >1000nm It can be seen from Table 1 that when preparing porous Li-MOF, the template concentration is a key parameter affecting the specific surface area and pore size distribution of Li-MOF. When the concentration of the template CTAB is appropriate, a larger specific surface area and a smaller pore size distribution can be formed. When the template concentration is too large, the pores of Li-MOF will be blocked (BET specific surface area < 400 m 2 / g). When no template is added, Li-MOF cannot form a uniform pore structure, so its specific surface area is also the smallest. Having an appropriate template concentration has a significant impact on the specific surface area and pore size distribution of the prepared LiF@Li-MOF.

[0054] Figure 1 The battery cycle stability curve graphs were obtained by preparing the porous lithium metal-organic framework composite lithium-supplementing agents prepared in Example 1, Comparative Example 1, and Comparative Example 2 into lithium-supplementing electrolytes and adding them to lithium batteries. From Figure 1 it can be seen that when different contents of the template CTAB were added during the preparation of Example 1, Comparative Example 1, and Comparative Example 2, the prepared Li-MOF materials had different pore size distributions, resulting in different amounts of loaded LiF nanoparticles. Therefore, during the battery cycle, the Li in the lithium-supplementing agent +The amount of F- synchronously provided during release is also different, and the degree of participation in the formation of the LiF-rich SEI film with high ionic conductivity (>10 -3 S / cm) is also inconsistent, and the degree of crack repair of the SEI film during electrode cycling is also different, thus resulting in significant differences in the cycling performance of the battery. Having an appropriate template concentration has a significant impact on the specific surface area and pore size distribution of LiF@Li-MOF and promotes the cycling performance of the battery.

[0055] The above embodiments are only used to explain the technical solutions of the present application and are not intended to limit them. Although the above embodiments have specifically described the present application, those skilled in the art should understand that the specific implementation manners of the present application can still be modified or equivalently replaced. Any modification and equivalent replacement without departing from the spirit and scope of the present application shall be covered by the protection scope of the present application.

Claims

1. A porous lithium metal organic framework composite lithium supplement, characterized in that: include: Lithium metal organic framework (Li-MOF) is a three-dimensional porous structure formed by Li⁺ and biphenyl dicarboxylic acid (BPDC) ligands through coordination bonds. The pore size is 2-5 nm and the specific surface area is ≥500 m² / g. LiF nanoparticles are loaded in the pores of Li-MOF, with a particle size of ≤5 nm and are evenly distributed in the pores of Li-MOF.

2. A porous lithium metal organic framework composite lithium supplement according to claim 1, characterized in that: The pore size of the Li-MOF is 2-3 nm and the specific surface area is 550-600 m² / g.

3. A method for preparing a porous lithium metal organic framework composite lithium supplement agent as claimed in claim 1 or 2, characterized in that: The following steps are involved: S31, lithium nitrate (LiNO3) and biphenyl dicarboxylic acid (BPDC) are mixed evenly to obtain a mixed solution A; N, N-dimethylformamide (DMF) and hexadecyl trimethyl ammonium bromide (CTAB) are mixed evenly to obtain a mixed solution B; the mixed solution A is then mixed with the mixed solution B, and ultrasonic treatment is performed for 30 min until the mixture is completely dissolved to obtain a mixed solution C; S32, transferring the mixed solution C to a high pressure reactor, sealing it and placing it in an oven, heating it to 80-120°C at a rate of 2°C / min, and keeping it warm for 6-24 h; S33, cooling the autoclave to room temperature naturally, taking out the solution, filtering and collecting the white precipitate, and washing with N,N-dimethylformamide DMF and methanol 1-3 times each, to obtain a Li-MOF precursor; S34, vacuum drying the Li-MOF precursor at 40-120° C. for 2-12 h to obtain Li-MOF crystals; S35, activating the Li-MOF crystal in a nitrogen atmosphere, removing the template agent hexadecyltrimethylammonium bromide (CTAB), and obtaining a porous Li-MOF powder; S36. The porous Li-MOF powder is immersed in a 0.5 M lithium hexafluorophosphate LiPF6 ethanol solution, and after drying and high-temperature annealing, a porous lithium metal organic framework composite lithium supplement is obtained, which is marked as LiF@Li-MOF composite material.

4. The method for preparing a porous lithium metal organic framework composite lithium supplement according to claim 3, characterized in that: In step S31, the molar ratio of lithium nitrate (LiNO3) to biphenyl dicarboxylic acid (BPDC) is 1-50:1-50; the mass ratio of N,N-dimethylformamide (DMF) to hexadecyltrimethylammonium bromide (CTAB) is 1-1000:1-100.

5. The method for preparing a porous lithium metal organic framework composite lithium supplement according to claim 3, characterized in that: In step S35, the activation process parameters are: activation temperature is 150-300°C, and activation time is 2-4 h.

6. The method for preparing a porous lithium metal organic framework composite lithium supplement according to claim 3, characterized in that: In step S36, the porous Li-MOF powder is immersed in a 0.5 M lithium hexafluorophosphate LiPF6 ethanol solution. The specific operation is: the porous Li-MOF powder and the 0.5 M lithium hexafluorophosphate LiPF6 ethanol solution are evenly mixed in a mass ratio of 1-50:1-50, and then maintained at 0.05 kPa for 2 h to ensure that the pores are fully infiltrated.

7. The method for preparing a porous lithium metal organic framework composite lithium supplement according to claim 3, characterized in that: In step S36, the drying process conditions are: drying at 60° C. for 6-8 h to remove the ethanol solvent.

8. The method for preparing a porous lithium metal organic framework composite lithium supplement according to claim 3, characterized in that: In step S36, the process conditions of the high temperature annealing are: heating to 200-600° C. at 5° C. / min in an argon atmosphere, keeping the temperature for 2-4 h, and cooling to room temperature.

9. A lithium-supplementing electrolyte for a lithium battery, characterized in that: The porous lithium metal organic framework composite lithium replenisher comprises the following steps: mixing the LiF@Li-MOF composite material, carbon nanotubes (CNT) and N,N-dimethylformamide DMC at a mass ratio of 10:1:100, and then stirring at 500 rpm for 1-5 hours to form a pre-dispersion liquid; and then mixing the pre-dispersion liquid with a commercial electrolyte at a mass ratio of 1:25, stirring for 4 hours, and standing for 12 hours to obtain a lithium replenishment electrolyte for a lithium battery.

10. An application of the porous lithium metal organic framework composite lithium supplement agent as claimed in claim 1 or 2, characterized in that: The porous lithium metal organic framework composite lithium supplement is used in silicon-based negative electrode batteries, high-nickel positive electrode batteries or lithium metal batteries.

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