A multifunctional additive, a solid electrolyte, and preparation methods and applications thereof

Abstract

The present invention relates to the field of battery technologies, and provides a multifunctional additive, a solid electrolyte, and their preparation methods and applications. The additive includes fluoroaniline and its derivatives, and the structural general formula thereof is: #imgabs0# wherein, R1 includes a fluorine atom, R2 is a single bond or an alkyl group, and x is an integer from 1 to 5. In the present invention, fluoroaniline and its homologues are used as additives for solid electrolytes. Due to the presence of amino groups, the additive can have strong interactions with the anion groups of various lithium salts, promoting the dissociation of lithium salts, thereby increasing the ionic conductivity of the solid electrolyte to above 10 ‑4 S / cm; at the same time, the antioxidant performance of the solid electrolyte is also improved, providing a practical research solution for the development of high-performance solid-state lithium-ion batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a multifunctional additive, a solid electrolyte, and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries have been widely used in energy storage fields, electric vehicles, consumer electronic products such as laptop computers and mobile phones. However, the electrolytes used in commercial lithium-ion batteries have flammability, volatility and fluidity, which hinder the reliability and safety of lithium-ion batteries. Solid electrolytes have intrinsic safety and show good application potential. Polymer solid electrolytes, as an important branch in the field of solid electrolytes, have become a research hotspot in solid-state batteries due to their good flexibility and easy processability, high compatibility with current battery manufacturing processes, and the ability to effectively adapt to various anode and cathode material interfaces. However, the main challenge faced by polymer solid electrolytes in practical applications is their low ionic conductivity, which is caused by the low dissociation efficiency of lithium salts in the polymer matrix.

[0003] To address the problem of low ionic conductivity, various strategies have been developed. Among them, introducing inorganic additives such as Li7La3Zr2O 12 and other solid electrolytes aims to promote the dissociation of lithium salts and construct efficient lithium-ion transport channels. Although this method can effectively improve the ionic conductivity, the high cost of inorganic additives and the problem of difficult control of uniformity in the preparation process limit its application in large-scale production. On the other hand, attempting to incorporate organic additives into polymers can bring certain performance improvements, such as succinonitrile (Energy Chem. 2022, 74:18) and methyl propionate (Adv. Energy Mater. 2022, 12, 2102932). However, these additives often face the challenge of insufficient electrochemical stability and are prone to degradation during battery operation, affecting the long-term stability and function of the electrolyte. Therefore, developing a new type of functional additive with excellent electrochemical stability, capable of withstanding adverse factors in the environment and showing high dissociation ability for lithium salts, can significantly improve the ionic conductivity and electrochemical window of polymer solid electrolytes.

[0004] CN 115020818 A discloses a polymer electrolyte additive of 2,3,4,5,6-pentafluorobenzeneboronic acid. The ionic conductivity of the solid electrolyte introduced with this additive is 3.06×10 -5 Scm -1 , and the voltage window is 5V. The ionic conductivity performance of this electrolyte does not reach the average value of current electrolytes (10 -4 Scm -1) This indicates that the additive has limited effect on improving the electrochemical performance of the solid electrolyte. The possible reason is that the additive contains hydroxyl functional groups, and its electrochemical instability will cause side reactions with lithium metal. In addition, the additive does not really play an effective role in the dissociation of lithium salts, resulting in limited effect on improving the ionic conductivity. Therefore, a solid electrolyte additive with an ionic conductivity reaching 10 -4 Scm -1 order of magnitude is needed. Summary of the Invention

[0005] In view of this, the present invention provides a solid electrolyte additive with an ionic conductivity reaching 10 -4 Scm -1 order of magnitude and an electrochemical window reaching 5.2V, a solid electrolyte containing the additive, and its preparation method and application.

[0006] The technical solution of the present invention is realized as follows: In the first aspect, the present invention provides a multifunctional additive, and the additive includes fluoroaniline and its derivatives, and its structural general formula is:

[0007]

[0008] Among them, R1 includes a fluorine atom, R2 is a single bond or an alkyl group, and x is an integer from 1 to 5.

[0009] Specifically, the amino group (NH2) has strong polarity and nucleophilicity. Since the additive of the present invention contains an amino group, it can have a strong interaction with the anion group of the lithium salt (such as PF6 - , BF4 - etc.). This interaction helps the dissociation of lithium salts, generating more free lithium ions (Li + ), thereby improving the ionic conductivity of the solid electrolyte.

[0010] Fluorine atoms have high electronegativity and small atomic radius, and can enhance the stability of molecules. Introducing fluorine atoms into the benzene ring can improve the antioxidant performance of the molecules, reduce the decomposition and degradation of the electrolyte under high voltage, and thus improve the cycle life and safety of solid-state batteries.

[0011] Since the fluoroaniline and its derivative additives have both amino groups and fluorine atoms, they show multifunctionality in solid electrolytes: improving ionic conductivity and enhancing stability, thereby improving the overall performance and safety of the battery.

[0012] Based on the above technical solutions, preferably, R1 further includes one or more of a chlorine atom, an alkoxy group, a phenyl group, a nitrile group, and an alkyl group.

[0013] Specifically, chlorine has a high electronegativity, which can enhance the polarity of the molecule; this polarity helps the interaction with the lithium salt anion, promotes the dissociation of the lithium salt, and improves the ionic conductivity; the chlorine atom can also improve the chemical stability of the molecule and reduce the decomposition of the electrolyte at high voltages. The alkoxy group (such as ethoxy) has a strong electron-donating ability, which can stabilize the anion of the lithium salt and promote the migration of lithium ions; in addition, the introduction of the alkoxy group increases the flexibility of the molecule, which helps to improve the mechanical properties and interfacial contact of the electrolyte and increases the cycle life. The phenyl group can stabilize the anion of the lithium salt through π-π interaction and improve the ionic conductivity; in addition, the introduction of the phenyl group also increases the rigidity of the molecule and improves the thermal stability and antioxidant performance of the electrolyte. The nitrile group has strong polarity and coordination ability, which can form a stable complex with the lithium salt anion, promote the dissociation and migration of lithium ions; the introduction of the nitrile group also improves the antioxidant performance of the molecule and extends the cycle life of the battery.

[0014] In the present invention, by introducing a chlorine atom, an alkoxy group, a phenyl group or a nitrile group on the basis of a fluorine atom, the physical and chemical properties of the electrolyte can be regulated at the molecular level, thereby further improving the ionic conductivity, cycle life and antioxidant performance of the solid electrolyte. This diverse substituent design provides more possibilities and flexibility for the performance optimization of solid-state batteries.

[0015] On the basis of the above technical solutions, preferably, when x≥3, the additive is a solid powder at room temperature and is easily soluble in common electrolyte solvents: fluoroethylene carbonate (FEC), 1,3-dioxolane (DOL), diethyl carbonate (DEC), etc. or common solvents for preparing solid electrolytes by the casting method: dimethylformamide (DMF), N-methylpyrrolidone (NMP), acetonitrile, etc.; when x≤2, the additive is a liquid at room temperature.

[0016] In a second aspect, the present invention provides a solid electrolyte, comprising a lithium salt, a polymer matrix and the above additive.

[0017] On the basis of the above technical solutions, preferably, the dosage of the additive is 0.5%-10% of the total mass of the lithium salt and the polymer matrix.

[0018] On the basis of the above technical solutions, preferably, the polymer matrix is one or more combinations of polyethers, polyvinylidene fluoride and its homologues or cyclic ethers, acrylates and their homologues; the lithium salt is one or more combinations of lithium hexafluorophosphate, lithium difluorooxalate borate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

[0019] In a third aspect, the present invention provides a method for preparing a solid electrolyte, comprising the following steps:

[0020] S1. Under the argon protection atmosphere in the glove box, uniformly mix the additive and the polymer matrix to obtain the mixed solution Ⅰ.

[0021] S2. Mix the mixed solution Ⅰ with the lithium salt to obtain a precursor solution, and heat it until the solvent volatilizes to obtain a solid electrolyte.

[0022] On the basis of the above technical solutions, preferably, in step S1, when the polymer matrix is polyether, polyvinylidene fluoride and its homologues, first dissolve it with an organic solvent and then mix it with the additive; the mass ratio of the polymer matrix to the organic solvent is (5 - 20)∶100, and the organic solvent is dimethylformamide or acetonitrile.

[0023] On the basis of the above technical solutions, preferably, in step S2, the concentration of the lithium salt is 1 - 3 mol / L.

[0024] On the basis of the above technical solutions, preferably, when the polymer matrix is cyclic ether, acrylate and its homologues, in step S2, after mixing the mixed solution Ⅰ with the lithium salt, add an initiator to obtain a precursor solution.

[0025] On the basis of the above technical solutions, preferably, the initiator is one or a combination of aluminum trifluoromethanesulfonate, stannous trifluoromethanesulfonate and azobisisobutyronitrile, and the dosage of the initiator is 0.1% - 0.5% of the total mass of the mixed solution Ⅰ and the lithium salt.

[0026] Fourthly, the present invention also provides the application of the solid electrolyte in the preparation of a lithium battery.

[0027] A multifunctional additive, a solid electrolyte and its preparation method and application of the present invention have the following beneficial effects compared with the prior art:

[0028] (1) The additive of the present invention includes fluoroaniline and its homologues. Due to having an amino group and fluorine atoms, this multifunctional electrolyte additive can have a strong interaction with the anion groups of various lithium salts, promote the dissociation of the lithium salt, and thus improve the ionic conductivity of the solid electrolyte (above 10 -4 S / cm). In addition, the introduction of fluorine atoms improves the antioxidant performance of the molecule, reduces the decomposition and degradation of the electrolyte at high voltages, and thus improves the cycle life and safety of the solid-state battery.

[0029] (2) By further introducing halogen atoms, alkoxy groups, hydrogen atoms, phenyl groups, nitrile groups or alkyl groups on the basis of fluorine atoms, the present invention further improves the ionic conductivity, cycle life and antioxidant performance of the solid electrolyte by regulating the physical and chemical properties of the electrolyte at the molecular level, providing more possibilities and flexibility for the performance optimization of the solid-state battery.

[0030] (3) This multifunctional electrolyte additive has wide application value and can be applied to various lithium-ion solid electrolyte polymer systems, specifically including polymers and their derivatives such as polyethers, cyclic ethers, acrylates, polyvinylidene fluoride, etc., providing a practical research solution for the development of high-performance solid-state lithium-ion batteries.

[0031] (4) The fluoroaniline derivative additive provided by the present invention is easily soluble in a variety of common electrolyte solvents and the solvents used for preparing solid electrolytes. Through a solution method with simple process and easy implementation, the fluoroaniline derivative additive can be introduced into the solid electrolyte, which is beneficial to industrial application. Brief 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 some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0033] Figure 1 is the electrochemical impedance spectroscopy diagram of the polymer electrolytes prepared in Example 1 and Comparative Example 1 of the present invention;

[0034] Figure 2 is the linear sweep voltammetry curve diagram of the polymer electrolytes prepared in Example 1 and Comparative Example 1 of the present invention;

[0035] Figure 3 is the voltage-time curve diagram of the Li / / Li symmetric battery assembled with the polymer electrolytes prepared in Example 1 and Comparative Example 1 at 0.5 mA cm -2 、0.5 mAh cm -2 ;

[0036] Figure 4 is the scanning electron microscope photograph of the Li / / Li symmetric battery assembled with the polymer electrolytes prepared in Example 1 and Comparative Example 1 after 20 cycles;

[0037] Figure 5 is the cycling performance diagram of the lithium battery assembled with the polymer electrolytes prepared in Example 1 and Comparative Example 1 at a rate of 0.5C in the voltage range of 2.5V to 4V; among them, Figure a is Example 1 and Figure b is Comparative Example 1. Detailed Embodiments

[0038] Next, in combination with the embodiments of the present invention, 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 of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0039] Example 1

[0040] The solid electrolyte and solid battery of the multifunctional additive of fluorinated aniline derivative in this example are prepared by the following steps:

[0041] S1, under the argon protection atmosphere in the glove box, weigh 1 mL of DOL (cyclic ether) and 0.1 g of 2,4-difluoroaniline and mix them evenly. Add 0.287 g of LiTFSI (lithium bis(trifluoromethanesulfonyl)imide, 1 mol / L) thereto and stir evenly. The stirring speed is 600 r / min -1 , and stir for 1 h.

[0042] S2, add 0.1 wt% of the initiator aluminum trifluoromethanesulfonate to the mixed solution and stir at a stirring speed of 600 r / min -1 for 0.5 h. After stirring evenly, a precursor solution is obtained.

[0043] S3, according to the assembly method of the button battery, use lithium iron phosphate (LiFePO4) as the positive electrode and lithium metal as the negative electrode. Drop the prepared precursor liquid onto a polypropylene (PP) separator and assemble the button battery. Let the button battery stand for 2 h, and then place it at 60 °C and heat for 12 h. The monomer is completely polymerized, and finally a polymer electrolyte lithium battery is obtained.

[0044] Example 2

[0045] The solid electrolyte and solid battery of the multifunctional additive of fluorinated aniline derivative in this example are prepared by the following steps:

[0046] S1, under the argon protection atmosphere in the glove box, weigh 1 mL of methacrylate and 0.1 g of 2,4-difluoroaniline and mix them evenly. Add 0.144 g of LiDFOB (lithium difluorooxalate borate, 1 mol / L) thereto and stir evenly. The stirring speed is 600 r / min -1 , and stir for 1 h.

[0047] S2, add 0.1 wt% of the initiator azobisisobutyronitrile to the mixed solution and stir at a stirring speed of 600 r / min -1 for 0.5 h. After stirring evenly, a precursor solution is obtained.

[0048] S3. According to the assembly method of the button battery, using lithium iron phosphate (LiFePO4) as the positive electrode and lithium metal as the negative electrode, the prepared precursor liquid is dropped into a polypropylene (PP) separator, and the button battery is assembled. The button battery is left standing for 2 h, and then heated at 60 °C for 12 h. The monomers are completely polymerized, and finally a polymer electrolyte lithium battery is obtained.

[0049] Example 3

[0050] The solid electrolyte and solid battery with the fluorinated aniline derivative multifunctional additive of this example are prepared through the following steps:

[0051] S1. Under the argon protection atmosphere in the glove box, weigh 1 g of PEO (polyether) and 10 g of acetonitrile and mix them evenly. Add 0.1 g of 2,4-difluoroaniline and 0.374 g of LiFSI (lithium bis(fluorosulfonyl)imide, 2 mol / L) thereto, stir evenly, and the stirring speed is 600 r / min -1 , stir for 1 h to obtain a precursor solution.

[0052] S2. Pour the precursor liquid into a polytetrafluoroethylene mold and dry it at 60 °C for 24 hours to obtain a solid electrolyte with a fluorinated aniline derivative multifunctional additive.

[0053] S3. According to the assembly method of the button battery, using lithium iron phosphate (LiFePO4) as the positive electrode and lithium metal as the negative electrode, the prepared precursor liquid is dropped into a polypropylene (PP) separator, and the button battery is assembled. The button battery is left standing for 2 h, and then heated at 60 °C for 12 h. The monomers are completely polymerized, and finally a polymer electrolyte lithium battery is obtained.

[0054] Example 4

[0055] The solid electrolyte and solid battery with the fluorinated aniline derivative multifunctional additive of this example are prepared through the following steps:

[0056] S1. Under the argon protection atmosphere in the glove box, weigh 1 g of PVDF (polyvinylidene fluoride) and 10 g of DMF (dimethylformamide) and mix them evenly. Add 0.08 g of 2,4-difluoroaniline and 0.456 g of LiFSI (lithium hexafluorophosphate, 3 mol / L) thereto, stir evenly, and the stirring speed is 600 r / min -1 , stir for 1 h to obtain a precursor solution.

[0057] S2. Pour the precursor liquid into a polytetrafluoroethylene mold and dry it at 60 °C for 24 hours to obtain a solid electrolyte with a fluorinated aniline derivative multifunctional additive.

[0058] S3. According to the assembly method of the button battery, using lithium iron phosphate (LiFePO4) as the positive electrode and lithium metal as the negative electrode, the prepared precursor solution was dropped into a polypropylene (PP) separator, and the button battery was assembled. The button battery was left standing for 2 h and then heated at 60 °C for 12 h. The monomers were completely polymerized, and finally a polymer electrolyte lithium battery was obtained.

[0059] Example 5

[0060] The solid electrolyte and solid battery of the fluorinated aniline derivative multifunctional additive in this example were prepared through the following steps:

[0061] S1. Under the argon protection atmosphere in the glove box, 1 mL of methoxypolyethylene glycol acrylate (acrylate homolog) and 0.05 g of 2,4-difluoroaniline were weighed and uniformly mixed. 0.861 g of LiTFSI (lithium bis(trifluoromethanesulfonyl)imide, 3 mol / L) was added thereto, and the stirring speed was 600 r / min -1 , and stirred for 1 h until evenly mixed.

[0062] S2. 0.2 wt% of the initiator stannous trifluoromethanesulfonate was added to the mixed solution, and stirred at a stirring speed of 600 r / min -1 for 0.5 h. After stirring evenly, a precursor solution was obtained.

[0063] S3. According to the assembly method of the button battery, using lithium iron phosphate (LiFePO4) as the positive electrode and lithium metal as the negative electrode, the prepared precursor solution was dropped into a polypropylene (PP) separator, and the button battery was assembled. The button battery was left standing for 2 h and then heated at 60 °C for 12 h. The monomers were completely polymerized, and finally a polymer electrolyte lithium battery was obtained.

[0064] Example 6

[0065] The difference between this example and Example 1 is that the additive is 2,4-dichloro-5-fluoroaniline, and the rest is the same as in Example 1.

[0066] Example 7

[0067] The difference between this example and Example 1 is that the additive is p-fluorobenzylamine, and the rest is the same as in Example 1.

[0068] Example 8

[0069] The difference between this example and Example 1 is that the additive is 2,3,4,5,6-pentafluoroaniline, and the rest is the same as in Example 1.

[0070] Example 9

[0071] The difference between this example and Example 1 is that the additive is 2-(4-fluorophenyl)-2-propanamine, and the rest is the same as in Example 1.

[0072] Example 10

[0073] The difference between this example and Example 1 is that the additive is 4-ethoxy-2-fluoroaniline, and the rest is the same as in Example 1.

[0074] Example 11

[0075] The difference between this example and Example 1 is that the additive is 5-benzyloxy-2-fluoroaniline, and the rest is the same.

[0076] Example 12

[0077] The difference between this example and Example 1 is that the additive is 2-amino-6-fluorobenzonitrile, and the rest is the same.

[0078] Comparative Example 1

[0079] Compared with Example 1, Comparative Example 1 lacks an additive. The specific scheme is as follows:

[0080] The solid electrolyte and solid battery of the fluorinated aniline derivative multifunctional additive in this comparative example are prepared by the following steps:

[0081] S1. Under the argon protection atmosphere in the glove box, weigh 1 mL of DOL (cyclic ether), add 0.287 g of LiTFSI (lithium bis(trifluoromethanesulfonyl)imide 1 mol / L) thereto, stir evenly, and the stirring speed is 600 r / min -1 , and stir for 1 h.

[0082] S2. Add 0.1 wt% of the initiator aluminum trifluoromethanesulfonate to the mixed solution, and stir at a stirring speed of 600 r / min -1 for 0.5 h. After stirring evenly, a precursor solution is obtained.

[0083] S3. According to the assembly method of the button battery, using lithium iron phosphate (LiFePO4) as the positive electrode and lithium metal as the negative electrode, the prepared precursor solution is dropped into a polypropylene (PP) separator, and the button battery is assembled. The button battery is left standing for 2 h, and then placed in an oven at 60 °C for 12 h. The monomer is completely polymerized, and finally a polymer electrolyte lithium battery is obtained.

[0084] Comparative Example 2

[0085] Compared with Example 1, in Comparative Example 2, the dosage of the additive exceeds the scope defined in this application. The specific scheme is as follows:

[0086] The solid electrolyte and solid battery of the fluorinated aniline derivative multifunctional additive in this comparative example are prepared by the following steps:

[0087] S1. Under the argon protection atmosphere in the glove box, weigh 1 mL of DO (cyclic ether) L and 0.5 g of 2,4-difluoroaniline, mix them evenly, add 0.287 g of LiTFSI (lithium bis(trifluoromethanesulfonyl)imide, 1 mol / L) thereto, stir evenly, and the stirring speed is 600 r / min -1 , and stir for 1 h.

[0088] S2. Add 0.1 wt% of the initiator aluminum trifluoromethanesulfonate to the mixed solution, and stir at a stirring speed of 600 r / min -1 for 0.5 h. After stirring evenly, a precursor solution is obtained.

[0089] S3. According to the assembly method of the coin cell, use lithium iron phosphate (LiFePO4) as the positive electrode and lithium metal as the negative electrode, drop the prepared precursor solution onto the polypropylene (PP) separator, and assemble the coin cell. Let the coin cell stand for 2 h, and then place it at 60 °C and heat for 12 h. The monomer is completely polymerized, and finally a polymer electrolyte lithium battery is obtained.

[0090] Perform performance tests on the polymer electrolytes containing aniline derivatives prepared in the examples and comparative examples, including ion conductivity test (test frequency is 10 6 -1 Hz, amplitude is 5 mV), antioxidant test (electrochemical window), and lithium stability test. The results are shown in Table 1 and Figures 1-5 as follows.

[0091] Lithium stability test method: The Li / / Li symmetric battery prepared with the polymer electrolyte is tested for the voltage-time curve at 0.5 mA / cm -2 2 and 0.5 mAh / cm -2 .

[0092] Table 1 Comparison of polymer electrolyte performance

[0093]

[0094] The results in Table 1 show that when the addition amount range of the additive is between 1-10 wt%, it is beneficial to improve the performance of the polymer electrolyte. Beyond this range, the effect is not obvious. For example, under the same test conditions as in Example 1, for Comparative Example 1, the ion conductivity of the polymer electrolyte with an additive addition amount of 0 is significantly reduced, the electrochemical window is significantly reduced, and the polarization voltage is significantly increased; for Comparative Example 2, under the same test conditions as in Example 1, the electrochemical performance of the polymer electrolyte with an additive addition amount of 50 wt% also shows an obvious decline. When the addition content is too low, the dissociation effect on the lithium salt is not obvious, and it is difficult to improve the solvation structure of lithium ions; while excessive additives will destroy the network structure of the polymer and reduce the lithium ion transport.

[0095] It can be seen from Examples 1-5 that, based on the same additives, due to the differences in the polymer matrix and the additive content, the performance of the polymer electrolyte varies greatly, and the effect of Example 1 is the best. It can be seen from Examples 6-12 that, based on fluorine atoms, after adding chlorine atoms, alkoxy groups, phenyl groups or nitrile groups, the ionic conductivity, cycle life and antioxidant performance of the solid electrolyte are further improved. Among them, the effect of Example 12 is the best, indicating that the introduction of nitrile groups helps the dissociation of lithium salts, promotes the migration of lithium ions, and prolongs the cycle life of the battery.

[0096] Electrochemical impedance spectroscopy tests were performed on the polymer electrolytes prepared in Example 1 and Comparative Example 1. The results are as Figure 1 shown. The impedance of the polymer electrolyte prepared in Example 1 is 2.4 ohms. By calculation, its ionic conductivity is 8.56×10 -4 S cm -1 . The fluorine atoms of the additive can improve the solvation structure of lithium ions, and its weak solvation ability can enhance the interaction ability between lithium ions and anions. The amino group can interact with the lithium salt, promote the dissociation of the lithium salt, and improve the ionic conductivity. The impedance of the polymer electrolyte prepared in Comparative Example 1 is 14 ohms. By calculation, its ionic conductivity is 1.72×10 -4 S cm -1 , and its ionic conductivity is relatively low, and the ability to transport lithium ions is weak.

[0097] Linear sweep voltammetry tests were performed on the polymer electrolytes prepared in Example 1 and Comparative Example 1. The results are as Figure 2 shown. The electrochemical window of the polymer electrolyte prepared in Example 1 is 5.2 V, and the electrochemical window of the polymer electrolyte prepared in Comparative Example 1 is 4.5 V. It shows that the addition of additives can significantly improve the electrochemical window of the electrolyte, increase the oxidation potential of the electrolyte, and improve its antioxidant ability.

[0098] The compatibility between the polymer electrolytes prepared in Example 1 and Comparative Example 1 and the lithium negative electrode was detected. The results are as Figure 3 shown. It shows that the polymer electrolyte of Example 1 can stably cycle for more than 300 h, and the overpotential is about 60 mV. It can be seen that this polymer electrolyte has good compatibility with the lithium negative electrode. The polarization voltage of the polymer electrolyte of Comparative Example 1 is relatively large. After cycling for 200 h, the polarization voltage increases significantly, and the compatibility with lithium is poor.

[0099] Scanning electron microscopy tests were performed on the lithium sheets after cycling 20 times of the Li / / Li symmetric batteries assembled with the polymer electrolytes prepared in Example 1 and Comparative Example 1. The results are as Figure 4As shown, Figure a shows the surface morphology of the lithium metal after cycling in Example 1. It can be seen that the lithium deposition is relatively dense and the surface is relatively flat. However, the morphology of the lithium metal after cycling in Comparative Example 1 (Figure b) is relatively loose, moss-like, and the surface is uneven. It can be seen that the addition of the additive can significantly improve the compatibility between the polymer electrolyte and the lithium metal, promote the uniform deposition of lithium, and inhibit the growth of lithium dendrites.

[0100] The cycling performance of the composite solid polymer electrolytes prepared in Example 1 and Comparative Example 1 was tested. The testing method was as follows: The prepared coin cells were tested for cycling performance at a rate of 0.5C (1C = 170 mAh g-1) in the voltage range of 2.5V to 4V. The results are as Figure 5 shown. It shows that for the polymer electrolyte prepared in Example 1, the initial discharge specific capacity is 153.5 mAh g -1 . After 30 cycles, the battery capacity retention rate is 95.3%, and the cycling performance is relatively stable. For the polymer electrolyte prepared in Comparative Example 1, the initial discharge specific capacity is 142.6 mAh g -1 . After 30 cycles, the battery capacity retention rate is 78.9%, and the cycling performance is poor. It can be seen that the addition of the additive can significantly improve the stability of the battery cycling performance.

[0101] The above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A solid electrolyte, characterized in that: It is composed of lithium salt, polymer matrix and additives, wherein the additives are fluoroaniline and its derivatives, and its general structural formula is: ， Wherein, R1 is one or more of a fluorine atom, a chlorine atom and a nitrile group; R2 is a single bond, and x is an integer of 1 to 5; The amount of the additive is 0.5%-10% of the total mass of the lithium salt and the polymer matrix; The polymer matrix is ​​polyvinylidene fluoride; the lithium salt is one or more combinations of lithium hexafluorophosphate, lithium difluorooxalatoborate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluorosulfonyl)imide.

2. The method for preparing a solid electrolyte according to claim 1, wherein: The steps include: S1, in an argon protective atmosphere of a glove box, uniformly mixing the additive and the polymer matrix to obtain a mixed solution I; S2, mixing the mixed solution I with a lithium salt to obtain a precursor solution, and heating the solution until the solvent evaporates to obtain a solid electrolyte.

3. The method for preparing a solid electrolyte according to claim 2, characterized in that: In step S1, the polymer matrix is ​​first dissolved in an organic solvent and then mixed with the additive; The mass ratio of polymer matrix to organic solvent is (5-20):100, and the organic solvent is dimethylformamide or acetonitrile.

4. The method for preparing a solid electrolyte according to claim 2, characterized in that: In step S2, the concentration of the lithium salt is 1-3 mol / L.

5. Use of the solid electrolyte as claimed in claim 1 in the preparation of lithium batteries.

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