Additive for PVDF-based composite solid electrolyte and preparation method thereof

Abstract

The invention belongs to the technical field of electrolyte additives, and particularly relates to an additive for a PVDF-based composite solid electrolyte and a preparation method. The lithium ion liquid is absorbed by the MOF (UIO-66-F4) with a three-dimensional structure, and then the MOF (UIO-66-F4) is added into PVDF (Polyvinylidene Fluoride) to improve the performance of the lithium metal battery. The process has the advantages of cost saving, simplicity in operation, high universality, excellent performance and the like. The additive prepared by the invention has an effect of improving the ionic conductivity, the battery capacity and the cycle life of the PVDF-based composite solid-state electrolyte, and meanwhile, compared with UIO-66 without a branched chain F, the additive has a more obvious improvement effect, and a new research path is provided for improving the performance of a lithium metal solid-state battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrolyte additives, and particularly relates to an additive for PVDF-based composite solid electrolytes and a preparation method thereof. Background Art

[0002] With the growing global demand for clean energy and efficient energy storage technologies, lithium metal batteries, as a high-energy-density energy storage technology, have received extensive attention. Lithium metal batteries are considered an important development direction for next-generation battery technologies due to their high theoretical specific capacity (3860 mAh / g) and low electrochemical potential (-3.04 V vs. standard hydrogen electrode). However, the practical application of lithium metal batteries has long been limited by two core problems: uncontrollable growth of lithium dendrites and insufficient electrolyte interface stability. To solve these problems, researchers have begun to explore new electrolyte materials and additives to improve the ionic conductivity and interface stability of electrolytes.

[0003] In traditional liquid electrolyte systems, the uneven deposition of lithium ions can trigger the growth of lithium dendrites, leading to battery short circuits and even thermal runaway. At the same time, the high reactivity of lithium metal will continuously undergo side reactions with the liquid electrolyte, forming a loose and porous solid electrolyte interface (SEI), which exacerbates the irreversible consumption of lithium and the electrolyte, reducing the Coulomb efficiency and cycle life. Although solid electrolytes (such as inorganic ceramics or sulfide electrolytes) can physically inhibit dendrites, their rigid contact interface with the electrode results in high interface impedance, and mechanical brittleness and low ionic conductivity limit their practical performance.

[0004] In recent years, polymer-based composite electrolytes have become a research hotspot due to their flexibility, interface compatibility, and adjustable ion transport characteristics. By introducing functional additives (such as inorganic fillers, lithium salt derivatives) into a polymer matrix (such as PEO, PVDF-HFP, PVDF), the mechanical strength, ion transference number, and electrochemical stability of the electrolyte can be synergistically improved.

[0005] PVDF electrolytes have become an important research direction for lithium metal battery electrolytes due to their good mechanical properties and processability. However, the ionic conductivity of PVDF electrolytes is usually low, and an uneven SEI layer is easily formed when in contact with the lithium metal anode, leading to the growth of lithium dendrites and an increase in interface impedance.

[0006] Based on the problems existing in the above technologies, the current modification of PVDF electrolytes is mainly carried out by introducing active fillers. The current active fillers are mainly inorganic substances, such as LLZO, etc. These inorganic substances can conduct lithium ions themselves, thereby improving the ionic conductivity of PVDF electrolytes. However, due to the poor compatibility between inorganic substances and PVDF, agglomeration will occur after the inorganic substances are added to PVDF. Summary of the Invention

[0007] In view of this, the present invention discloses an additive for a PVDF-based composite solid electrolyte and a preparation method thereof.

[0008] It should be noted that using a metal-organic framework (MOF) loaded with lithiated ionic liquid as an active filler can improve the ionic conductivity while avoiding agglomeration. Therefore, the present invention has developed an additive that can improve the ionic conductivity of PVDF, inhibit the growth of lithium dendrites, and reduce the interfacial impedance to better solve the defects existing in PVDF electrolytes.

[0009] In addition, in previous studies on solid electrolytes, many active fillers have played a role in improving performance. Among them, the metal-organic framework (MOF) solves the problems of low ionic conductivity and poor interfacial stability of traditional polymer electrolytes through its unique porous structure advantages and adjustable functionalized side chain groups. At the same time, it has high safety and long cycle life, and its adjustable functionalized side chain groups provide broad space for the modification direction.

[0010] Among many MOFs, UIO-66 has a three-dimensional porous structure. Its porous structure can absorb ionic liquid and can be introduced into the solid electrolyte as an additive with excellent performance. With the deeper research on space charge by scientific researchers in recent years, it has been found that F atoms with strong electron-withdrawing effects may be beneficial to the dissociation of lithium salts and the improvement of the SEI film. Therefore, introducing F branches into the solid electrolyte has become a major direction.

[0011] To achieve the above object, the present invention adopts the following technical solutions:

[0012] The first technical object of the present invention is to provide an additive for a PVDF-based composite solid electrolyte, and the additive is formed by mixing UIO-66-F4 and lithiated ionic liquid in a ratio of 1 g: 0.8 ml;

[0013] The UIO-66-F4 is the main body of the additive;

[0014] The lithiated ionic liquid is a solution formed by dissolving a lithium salt in an ionic liquid to assist in improving the performance of the main body.

[0015] It should be noted that the additive disclosed in the present invention is UIO-66-F4 absorbing lithiated ionic liquid. The F branches are beneficial to the dissociation of lithium salts in the electrolyte, and the inside can absorb lithiated ionic liquid and provide a fast lithium ion channel to improve the ionic conductivity, which has a better improvement effect compared with ordinary UIO-66 without F branches.

[0016] The second technical object of the present invention is to provide a preparation method of an additive for a PVDF-based composite solid electrolyte as described above. The specific operations of the method are as follows:

[0017] Step 1: Prepare UIO-66-F4

[0018] Add 1.162 g of ZrCl4 to a mixed solution of 30 ml of H2O and 20 ml of acetic acid. After stirring for half an hour, add 1 g of tetrafluoro terephthalic acid. Transfer the mixed solution into a high-pressure reactor and seal it for heating at 100 °C for 24 hours. Centrifuge the product at 8000 revolutions for 10 minutes, wash it with ethanol and centrifuge again to obtain UIO-66-F4. Put it into a vacuum drying oven and dry it overnight at 100 °C, then transfer it to an argon glove box for storage until use.

[0019] It should be noted that the purity of the raw materials used in the above operations should reach more than 99%.

[0020] Step 2: Preparation of lithiated ionic liquid

[0021] In an argon glove box, add LiTFSI to EMIMTFSI and stir evenly to obtain a lithiated ionic liquid.

[0022] Step 3: Preparation of the additive

[0023] Mix and grind the synthesized UIO-66-F4 with the lithiated ionic liquid to prepare an additive suitable for PVDF-based composite solid electrolytes.

[0024] Optionally, the concentration of the lithiated ionic liquid is 0.5 mol / kg - 1.5 mol / kg.

[0025] Optionally, the mass-to-volume ratio of the UIO-66-F4 to the lithiated ionic liquid is 1 g: 0.1 - 0.8 mL.

[0026] It is worth noting that the greater the concentration of the lithiated ionic liquid in Step 2, the greater the final improvement in electrochemical performance. The closer the mixing ratio in Step 3 is to 1:0.8, the greater the improvement in electrochemical performance, but when it exceeds 1:0.8, there may be a risk of leakage of the lithiated ionic liquid.

[0027] In summary, the present invention discloses an additive for a PVDF-based composite solid electrolyte and a preparation method thereof. The additive is UIO-66-F4 absorbing lithiated ionic liquid, and UIO-66-F4 is a derivative with the highest F atom content in the UIO-66 family. The F-containing branched chain is beneficial to the dissociation of lithium salts in the electrolyte, and the internal part can absorb lithiated ionic liquid and provide a fast lithium ion channel to improve the ionic conductivity. Its internal lithium ion conduction ability is stronger than that in PVDF, so that when the electrolyte conducts lithium ions, it preferentially conducts through the constructed fast channel to improve the ionic conductivity and battery capacity. From the experimental results, the improvement effect is better than that of ordinary UIO-66 without F-containing branched chain. It has a large specific surface area and is uniformly dispersed in the electrolyte, which is beneficial to enhancing the contact with the electrode and improving the battery cycle life. The capacity of the lithium metal battery is improved by increasing the ionic conductivity of the electrolyte and enhancing the contact between the electrolyte and the electrode. The present invention not only effectively improves the performance of the composite electrolyte, but also has a simple synthesis process and low cost, showing certain innovation and practicality.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] (1) Strong stability: Both UIO-66-F4 and lithiated ionic liquid have stable chemical properties. The lithiated ionic liquid itself is not easy to volatilize, and the lithiated ionic liquid is adsorbed inside UIO-66-F4, making the safety and stability stronger.

[0030] (2) Obvious improvement in ionic conductivity: Compared with the case without additive and UIO-66 without F-containing branched chain, only a small amount of this additive needs to be added to reduce the impedance, improve the ionic conductivity and battery capacity.

[0031] (3) Lower attenuation of cycle capacity: After using the additive of the present invention, as the number of cycles increases, the attenuation degree of the battery capacity is lower than that without additive, improving the service life. Description of the Drawings

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0033] Figure 1 is the impedance change of 10% additive compared with no additive.

[0034] Figure 2 is the comparison of the cycle performance of lithium metal batteries with 10% additive compared with no additive.

[0035] Figure 3 It is the impedance change of 30% additive compared with no additive.

[0036] Figure 4 It is the comparison of the cycling performance of lithium metal batteries with 30% additive and no additive.

[0037] Figure 5 It is the X-ray diffractometer test of unloaded lithiated ionic liquid UIO-66-F4 and UIO-66-F4@Li-IL after loading lithiated ionic liquid.

[0038] Figure 6 It is the infrared spectrum test of unloaded lithiated ionic liquid UIO-66-F4 and UIO-66-F4@Li-IL after loading lithiated ionic liquid.

[0039] Figure 7 It is the comparison of ionic conductivity changes of no additive, 10% additive, and 30% additive.

[0040] Figure 8 It is the scanning electron microscope photo of UIO-66-F4 without loaded lithiated ionic liquid.

[0041] Figure 9 It is the impedance comparison of UIO-66-F4@Li-IL and UIO-66@Li-IL with the same addition amount. Detailed implementation manners

[0042] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0043] Here, the special term "embodiment" means that any embodiment described as "exemplary" does not have to be interpreted as superior to or better than other embodiments. For the performance index tests in the embodiments of this application, unless otherwise specified, the conventional test methods in the art are used. It should be understood that the terms described in this application are only used to describe specific embodiments and are not used to limit the content disclosed in this application.

[0044] Unless otherwise specified, the technical and scientific terms used herein have the same meanings as those commonly understood by those of ordinary skill in the technical field to which this application belongs; other test methods and technical means not specifically noted in this application refer to the experimental methods and technical means commonly used by those of ordinary skill in the art.

[0045] To better illustrate the content of this application, numerous specific details are given in the following specific embodiments. Those skilled in the art should understand that this application can still be implemented without certain specific details. In the embodiments, some methods, means, instruments, equipment, etc. that are well-known to those skilled in the art are not described in detail in order to highlight the gist of this application.

[0046] On the premise of no conflict, the technical features disclosed in the embodiments of this application can be combined arbitrarily, and the obtained technical solutions belong to the content disclosed in the embodiments of this application.

[0047] The present invention discloses an additive for a PVDF-based composite solid electrolyte and a preparation method thereof.

[0048] To better understand the present invention, the following embodiments are used to further specifically elaborate on the present invention, but it should not be understood as a limitation to the present invention. For some non-essential improvements and adjustments made by those skilled in the art based on the above-mentioned invention content, they are also considered to fall within the protection scope of the present invention.

[0049] Example 1:

[0050] A preparation method of an additive for a PVDF-based composite solid electrolyte, and the specific operations of the method are as follows:

[0051] Step 1: Prepare UIO-66-F4

[0052] Add 1.162 g of ZrCl4 to a mixed solution of 30 ml of H2O and 20 ml of acetic acid, stir for half an hour, then add 1 g of tetrafluoroterephthalic acid, transfer the mixed solution into a high-pressure reaction kettle, seal and heat it at 100 °C for 24 hours; centrifuge the product at 8000 revolutions for 10 minutes, wash and centrifuge it with ethanol to obtain UIO-66-F4, put it into a vacuum drying oven, dry it overnight at 100 °C, and then transfer it to an argon glove box for storage for later use;

[0053] It should be noted that the purity of the raw materials used in the above operations needs to reach more than 99%.

[0054] Step 2: Preparation of lithiated ionic liquid

[0055] In an argon glove box, add 4 g of LiTFSI to 7 ml of EMIMTFSI and stir well to obtain a lithiated ionic liquid;

[0056] Step 3: Preparation of the additive

[0057] In an argon glove box, use 1 g of UIO-66-F4 and 0.8 ml of lithiated ionic liquid to mix and grind evenly with an agate mortar to finally obtain an additive suitable for a PVDF-based composite solid electrolyte.

[0058] Examples 2 - 3:

[0059] The operations of Examples 2 and 3 are only different from those of Example 1 in that: in Step 3, the volumes of the lithiated ionic liquid used are 0.4 ml and 0.6 ml respectively.

[0060] It should be noted that the ratio of LiTFSI to EMIMTFSI used in Step 2 is close to its maximum solubility. If the ratio continues to increase, LiTFSI may precipitate. When the ratio of UIO - F4 to the ionic liquid in Step 3 is greater than 1:0.8, it will change from a solid powder to a gel state. In order to achieve the best additive effect, the optimal ratio is 1:0.8.

[0061] Application experimental example:

[0062] It should be noted that the additives used in the following application experimental examples are all prepared from Example 1 above.

[0063] Experimental Example 1:

[0064] In this experimental example, 10% of the additive is added to the PVDF electrolyte to form a composite electrolyte membrane and its performance is tested:

[0065] Step 1: Preparation of PVDF electrolyte membrane without additive

[0066] 0.3 g of PVDF, 0.1 g of LiTFSI, and 5 ml of NMP are added to a reagent bottle and stirred for 24 hours. The mixture is dropped into a tetrafluoroethylene mold and dried at 60°C for 48 hours and then at 70°C for 5 hours to obtain the composite electrolyte membrane.

[0067] Step 2: Preparation of PVDF electrolyte membrane containing 10% additive

[0068] 0.3 g of PVDF, 0.1 g of LiTFSI, 5 ml of NMP, and 0.03 g of the additive are added to a reagent bottle and stirred for 24 hours. The mixture is dropped into a tetrafluoroethylene mold and dried at 60°C for 48 hours and then at 70°C for 5 hours to obtain the composite electrolyte membrane.

[0069] After testing, Figure 1 、 Figure 7 it shows that the ionic conductivity is significantly increased after adding 10% of the additive compared with that without the additive; Figure 2 After assembling into a lithium - metal battery, the capacity decay rate decreases and the battery capacity retention rate increases.

[0070] Experimental Example 2:

[0071] In this experimental example, 30% of the additive is added to the PVDF electrolyte to form a composite electrolyte membrane and its performance is tested:

[0072] Step 1: Preparation of PVDF electrolyte membrane without additives

[0073] Add 0.3 g of PVDF, 0.1 g of LiTFSI, and 5 ml of NMP into a reagent bottle and stir for 24 hours. Drop the mixture into a tetrafluoroethylene mold, dry it at 60 °C for 48 hours, and then dry it at 70 °C for 5 hours to obtain a composite electrolyte membrane.

[0074] Step 2: Preparation of PVDF electrolyte membrane containing 30% additives

[0075] Add 0.3 g of PVDF, 0.1 g of LiTFSI, 5 ml of NMP, and 0.09 g of additives into a reagent bottle and stir for 24 hours. Drop the mixture into a tetrafluoroethylene mold, dry it at 60 °C for 48 hours, and then dry it at 70 °C for 5 hours to obtain a composite electrolyte membrane.

[0076] After testing, Figure 3 、 Figure 7 it shows that after adding 30% additives, its ionic conductivity increases significantly compared to that without additives; Figure 4 After assembling into a lithium metal battery, the capacity decay rate decreases and its capacity retention rate increases.

[0077] Experimental Example 3:

[0078] In this experimental example, UIO-66 without F-branches was prepared and compared with UIO-66-F4 containing F-branches after absorbing lithiated ionic liquid. The synthesis method of UIO-66 is as follows:

[0079] Add 0.3 g of ZrCl4 into 75 ml of DMF, then add 2.21 ml of acetic acid. After stirring for half an hour, add 0.2138 g of terephthalic acid. Transfer the mixture into a high-pressure reaction kettle and seal it for heating at 120 °C for 24 hours; Centrifuge the product at 8000 rpm for 10 minutes, wash the centrifuged product with DMF twice and with ethanol once. The final product obtained is UIO-66. Place it in a vacuum drying oven and dry it at 100 °C overnight, then transfer it to an argon glove box for storage until use. After absorbing lithiated ionic liquid, the synthesized UIO-66 is stored in the glove box for use.

[0080] Step 1: Preparation of electrolyte membrane by adding 30% UIO-66 additive without F-branches to PVDF

[0081] [[ID=

[0082] Step 2: Preparation of PVDF electrolyte membrane containing 30% additive

[0083] Add 0.3 g of PVDF, 0.1 g of LiTFSI, 5 ml of NMP and 0.09 g of additive into a reagent bottle and stir for 24 hours. Drop the mixture into a tetrafluoroethylene mold, dry at 60 °C for 48 hours, and dry at 70 °C for 5 hours to obtain the composite electrolyte membrane.

[0084] After testing, Figure 8 it shows that the impedance is significantly reduced compared with UIO-66 without F-branches with the same 30% addition amount.

[0085] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An additive for PVDF-based composite solid electrolytes, characterized in that, The additive is prepared by mixing UIO-66-F4 and lithiated ionic liquid in a ratio of 1 g: 0.8 ml; The UIO-66-F4 is the main body of the additive; The lithiated ionic liquid is a solution formed by dissolving a lithium salt in an ionic liquid, which helps to improve the performance of the main body.

2. A preparation method of an additive for a PVDF-based composite solid electrolyte as described in claim 1, characterized in that, The specific operation of the method is as follows: Step 1: Preparation of UIO-66-F4 Add 1.162 g of ZrCl4 to a mixed solution of 30 ml of H2O and 20 ml of acetic acid. After stirring for half an hour, add 1 g of tetrafluoroterephthalic acid. Transfer the mixed solution into a high-pressure reaction kettle and seal it for heating at 100 °C for 24 hours; Centrifuge the product at 8000 revolutions for 10 minutes, wash it with ethanol and centrifuge to obtain UIO-66-F4; Step 2: Preparation of lithiated ionic liquid In an argon glove box, add LiTFSI (lithium salt) to EMIMTFSI (ionic liquid) and stir evenly to obtain a lithiated ionic liquid; Step 3: Preparation of the additive Mix and grind the synthesized UIO-66-F4 and the lithiated ionic liquid to prepare an additive suitable for PVDF-based composite solid electrolytes.

3. The preparation method according to claim 2, characterized in that, The concentration of the lithiated ionic liquid is 0.5 mol / kg - 1.5 mol / kg.

4. The preparation method according to claim 2, characterized in that, The mass-volume ratio of the UIO-66-F4 to the lithiated ionic liquid is 1 g: 0.1 - 0.8 mL.

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