Preparation method of single lithium ion conductor slow release membrane for lithium metal battery

Abstract

The invention relates to a preparation method of a single lithium ion conductor slow-release membrane for a lithium metal battery, belongs to the technical field of lithium metal batteries, and aims to solve the problems that a battery diaphragm in the prior art is low in ionic conductivity and cannot participate in formation and modification of a solid electrolyte interface membrane on the surface of lithium metal, and the lithium metal battery is low in coulombic efficiency, short in cycle life and the like. The lithiated single-ion conductor adopted by the single-lithium-ion conductor slow-release membrane for the lithium metal battery prepared by the method can reduce concentration polarization in the battery, so that self-discharge and degradation on the surface of an electrode are reduced, the interface impedance, charge transfer impedance and nucleation overpotential of the lithium metal battery are reduced, and the comprehensive performance of the battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium metal batteries, and particularly to a preparation method of a single lithium ion conductor slow-release film for lithium metal batteries. Background Art

[0002] The lithium metal anode has a high theoretical specific capacity and a low electrochemical potential, making lithium metal batteries the most promising choice for achieving high energy density batteries. However, the practical application of lithium metal anodes is still limited by their inherent problems. When lithium metal comes into contact with the electrolyte, a reaction occurs, resulting in the formation of a heterogeneous and unstable solid electrolyte interface film on the surface of the lithium metal. In addition, during the repeated plating / stripping process of the lithium metal, the anode undergoes infinite volume changes, and the stress changes on the anode surface cause cracks to form in the solid electrolyte interface film. At the cracks, the Li + flux is higher, which not only exacerbates the reaction consumption of the electrolyte and the lithium metal, but also causes the solid electrolyte interface film to continuously repair and thicken, increasing the interfacial impedance of the lithium metal battery. Worse still, lithium dendrites are easily formed at the cracks in the solid electrolyte interface film, accumulating "dead lithium", causing the anode to powder and the structure to collapse. The lithium metal anode is severely corroded, the coulombic efficiency of the battery is reduced, the life is terminated, and even the safety problems of the battery are triggered.

[0003] To solve the above problems of the lithium metal anode, the interface of the lithium metal can be modified. By adjusting the electrolyte components, the solid electrolyte interface film can be enhanced in situ, stabilizing the interface between the lithium metal anode and the electrolyte and guiding the uniform deposition of lithium ions. However, limited by the chemical compatibility between the additive and the original components of the electrolyte, it is difficult to obtain an ideal in-situ modified solid electrolyte interface film, and the additive reacts uncontrollably with the lithium metal during the cycling process and is continuously consumed, eventually losing its protective effect. The function of the artificial solid electrolyte interface film is similar to that of the in-situ solid electrolyte interface film, and it is prepared on the surface of the lithium metal before battery assembly. The inorganic component has a high Young's modulus, which can mechanically inhibit the growth of lithium dendrites, and the inorganic particles can break the long-range order of the solid electrolyte interface film, improving the ionic conductivity of the modified solid electrolyte interface film. The organic component can enhance the flexibility and mechanical stability of the modified solid electrolyte interface film. However, the artificial solid electrolyte interface film is usually thick, increasing the interfacial impedance of the lithium metal battery. Therefore, there are still some problems in directly modifying the lithium metal interface.

[0004] The separator is a key component that directly contacts the lithium metal anode. Commercial separators are mainly made of polyethylene or polypropylene, with a porosity of about 40%. They have no restrictive effect on the distribution of lithium ions and cannot effectively block the growth of lithium dendrites through the separator. The electrolyte wettability of commercial separators is poor, resulting in uneven distribution of lithium ions and an increase in the internal resistance of the battery. To optimize the separator characteristics, a functional coating is usually added to the separator surface. However, most of the current separator functional coating materials are chemically inert materials, such as functional carbon materials, conductive polymers, inorganic ceramics, etc. Although they can indirectly protect the lithium metal anode to a certain extent, they cannot directly participate in the formation and modification of the solid electrolyte interface film on the lithium metal surface, and the introduction of non-active substances also reduces the mass energy density and volume energy density of the battery. Another way to optimize the separator characteristics is to develop a self-supporting film to replace the commercial separator. The self-supporting film can avoid the additional increase of non-active substances. However, the current self-supporting film has a single function and a relatively complex preparation process. Summary of the Invention

[0005] In view of the above analysis, the present invention provides a preparation method of a single lithium ion conductor slow-release film for a lithium metal battery, so as to solve at least one of the problems such as the battery separator prepared by the prior art having no restrictive effect on the distribution of lithium ions, no promoting effect on the transmission of lithium ions, and inability to participate in the formation and modification of the solid electrolyte interface film on the lithium metal surface.

[0006] In the first aspect, the present invention provides a preparation method of a single lithium ion conductor slow-release film for a lithium metal battery, including the following steps:

[0007] (1) Polymerize 4,4-difluorobis(phenylsulfonyl)imide and 4,4-dihydroxybis(phenylsulfonyl)imide, and then perform lithiation modification to obtain a lithiated single lithium ion conductor. Dissolve the lithiated single lithium ion conductor and an anchoring matrix polymer in an organic solvent and stir to obtain a preliminary slurry.

[0008] (2) Stir and disperse a chemically active substance into the preliminary slurry to obtain a uniform slurry.

[0009] (3) Prepare the uniform slurry into a film, dry it, and peel it off to obtain the single lithium ion conductor slow-release film for the lithium metal battery.

[0010] Further, in step (1), the molar ratio of 4,4-difluorobis(phenylsulfonyl)imide to 4,4-dihydroxybis(phenylsulfonyl)imide is 1:1 to 5, the polymerization temperature is 150 to 180 °C, and the polymerization time is 12 to 24 h.

[0011] Further, in step (1), the anchoring matrix polymer is one or more of polyethylene oxide, polyethylene glycol bis(propylene oxide) ether, polyacrylonitrile, polyvinyl acetate, polylactic acid, polydimethylsiloxane, or polyacrylate.

[0012] Further, in step (1), the organic solvent is one or more of dimethylformamide, triethylamine, acetonitrile, chloroform, methanol, ethylene glycol dimethyl ether, dimethyl sulfoxide, or N-methylpyrrolidone.

[0013] Further, in step (1), the mass concentration of the lithiated single lithium ion conductor in the organic solution is 0.05 - 0.5 g / mL, the mass ratio of the lithiated single lithium ion conductor to the anchored matrix polymer is 0.5 - 5:1, and the mixing and dissolution stirring time is 6 - 48 h.

[0014] Further, in step (2), the chemically active substance is one or more of silicon fluoride, stannous fluoride, tin tetrafluoride, antimony pentafluoride, magnesium fluoride, aluminum fluoride, germanium tetrafluoride, lead fluoride, zinc fluoride, bismuth trifluoride, or indium fluoride.

[0015] Further, in step (2), the mass ratio of the chemically active substance to the lithiated single lithium ion conductor is 1:1 - 20, and the stirring and dispersion time is 3 - 12 h.

[0016] Further, in step (3), the method for forming the film is the coating method, casting method, casting method, or electrospinning method, and the film thickness is 100 - 1000 μm.

[0017] Further, in step (3), the film drying temperature is 30 - 80 °C, and the drying time is 6 - 72 h.

[0018] In the second aspect, the present invention provides a single lithium ion conductor slow-release film for a lithium metal battery prepared by the above method.

[0019] In the third aspect, the present invention provides a lithium metal battery including the single lithium ion conductor slow-release film for a lithium metal battery.

[0020] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0021] (1) The single lithium ion conductor slow-release film for a lithium metal battery prepared by the method of the present invention has good electrolyte wettability, promotes the rapid and uniform distribution of lithium ions, and reduces the local current density on the lithium metal surface;

[0022] (2) The single lithium ion conductor slow-release film prepared by the method of the present invention can slowly release chemically active substances during the electrochemical reaction process. The modified components generated in situ on the lithium metal surface participate in the formation of the solid electrolyte interface film on the lithium metal surface, improving the ionic conductivity and electronic conductivity on the lithium metal surface and promoting the uniform deposition of lithium metal;

[0023] (3) The slow-release process of the chemical active substance by the single lithium-ion conductor slow-release film prepared by the method of the present invention is continuously controllable and continuously functions during the deposition / stripping process of lithium metal, improving the uniformity and stability of the solid electrolyte interface film;

[0024] (4) The single lithium-ion conductor slow-release film prepared by the method of the present invention uses a single lithium-ion conductor as the matrix, has good mechanical properties and high ionic conductivity. By introducing various chain segments, the movement of molecular chain segments can be increased to construct an ion transport channel; by restricting the migration of anions in the copolymer, the transport of lithium ions in the lithium battery system is improved, and the formation and growth of lithium dendrites are inhibited;

[0025] (5) The lithiated single-ion conductor used in the single lithium-ion conductor slow-release film prepared by the method of the present invention can reduce the concentration polarization inside the battery, thereby reducing self-discharge and degradation on the electrode surface, reducing the interfacial impedance, charge transfer impedance and nucleation overpotential of the lithium metal battery, and improving the comprehensive performance of the battery;

[0026] (6) The preparation method of the single lithium-ion conductor slow-release film for lithium metal batteries of the present invention is simple, can promote the uniform deposition of lithium metal, improve the cycle stability of lithium metal batteries, is green and environmentally friendly and is easy to scale up production.

[0027] In the present invention, the above technical solutions can also be combined with each other to achieve more preferred combination schemes. Other features and advantages of the present invention will be described in the following specification, and some advantages can be made obvious from the specification or understood by implementing the present invention. The objectives and other advantages of the present invention can be realized and obtained from the content specifically pointed out in the specification and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings are only for the purpose of showing specific embodiments and are not considered as limiting the present invention. Throughout the drawings, the same reference signs represent the same components.

[0029] Figure 1 It is a scanning electron microscope image of the polypropylene separator provided by the present invention;

[0030] Figure 2 It is a scanning electron microscope image of the single lithium-ion conductor slow-release film prepared in Example 1 provided by the present invention;

[0031] Figure 3 It is the change of the contact angle of the electrolyte provided by the present invention on the polypropylene separator;

[0032] Figure 4 It is the change of the contact angle of the electrolyte provided by the present invention on the single lithium-ion conductor slow-release film prepared in Example 1;

[0033] Figure 5Stable cycling performance graphs of two groups of lithium symmetric batteries, namely test sample 1 and control sample 1, provided by the present invention;

[0034] Figure 6 AC impedance test graph of the lithium symmetric battery assembled with control sample 1 provided by the present invention;

[0035] Figure 7 AC impedance test graph of the lithium symmetric battery assembled with test sample 1 provided by the present invention;

[0036] Figure 8 SEM graph of the deposition morphology of the lithium metal negative electrode after 50 h of cycling of the lithium symmetric battery assembled with control sample 1 provided by the present invention;

[0037] Figure 9 SEM graph of the deposition morphology of the lithium metal negative electrode after 50 h of cycling of the lithium symmetric battery assembled with test sample 1 provided by the present invention. Detailed implementation manners

[0038] The following will specifically describe the preferred embodiments of the present invention in conjunction with the accompanying drawings. Among them, the accompanying drawings constitute a part of the present invention and are used together with the embodiments of the present invention to explain the principle of the present invention, rather than to limit the scope of the present invention.

[0039] A specific embodiment of the present invention discloses a preparation method of a single lithium ion conductor slow-release film for a lithium metal battery, including the following steps:

[0040] (1) Polymerize 4,4-difluorobis(phenylsulfonyl)imide and 4,4-dihydroxybis(phenylsulfonyl)imide, and then perform lithiation modification to obtain a lithiated single lithium ion conductor. Dissolve the obtained lithiated single lithium ion conductor and an anchoring matrix polymer in an organic solvent and stir to obtain a preliminary slurry;

[0041] (2) Stir and disperse a chemically active substance into the preliminary slurry to obtain a uniform slurry;

[0042] (3) Prepare the uniform slurry into a film, dry it, and peel it off to obtain the single lithium ion conductor slow-release film for the lithium metal battery.

[0043] Compared with the prior art, the single lithium-ion conductor slow-release film for lithium metal batteries prepared by the method of the present invention has good electrolyte wettability, which promotes the rapid and uniform distribution of lithium ions and reduces the local current density on the lithium metal surface; the single lithium-ion conductor slow-release film can slowly release chemical active substances during the electrochemical reaction process, and the modified components generated in situ on the lithium metal surface participate in the formation of the solid electrolyte interface film on the lithium metal surface, improving the ionic conductivity and electronic conductivity on the lithium metal surface and promoting the uniform deposition of lithium metal; the slow-release process of the chemical active substances by the single lithium-ion conductor slow-release film is continuously controllable and continuously plays a role during the deposition / stripping process of lithium metal, improving the uniformity and stability of the solid electrolyte interface film; the single lithium-ion conductor slow-release film uses a lithiated single lithium-ion conductor as the matrix, has good mechanical properties and high ionic conductivity, and can increase the movement of molecular chain segments and construct ion transport channels by introducing various chain segments; by restricting the migration of anions in the copolymer, the transport of lithium ions in the lithium battery system is improved, and the formation and growth of lithium dendrites are inhibited; the lithiated single ion conductor used in the single lithium-ion conductor slow-release film can reduce the concentration polarization inside the battery, thereby reducing self-discharge and degradation on the electrode surface, reducing the interface impedance, charge transfer impedance and nucleation overpotential of the lithium metal battery, and improving the comprehensive performance of the battery.

[0044] In a specific embodiment, in step (1), the molar ratio of 4,4-difluorobis(phenylsulfonyl)imide to 4,4-dihydroxybis(phenylsulfonyl)imide is 1:1 to 5, for example, the molar ratio is 1:1, 1:2, 1:3, 1:4, 1:5, the polymerization temperature is 150 to 180 °C, for example, the temperature is 150 °C, 160 °C, 170 °C, 180 °C, and the polymerization time is 12 to 24 h, for example, the polymerization time is 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 24 h.

[0045] Among them, the reaction equation for the polymerization of 4,4-difluorobis(phenylsulfonyl)imide and 4,4-dihydroxybis(phenylsulfonyl)imide is as follows:

[0046]

[0047] In a specific embodiment, in step (1), the anchoring matrix polymer is one or more of polyethylene oxide, polyethylene glycol bis(propylene oxide) ether, polyacrylonitrile, polyvinyl acetate, polylactic acid, polydimethylsiloxane or polyacrylate.

[0048] In a specific embodiment, in step (1), the organic solvent is one or more of dimethylformamide, triethylamine, acetonitrile, chloroform, methanol, ethylene glycol dimethyl ether, dimethyl sulfoxide or N-methylpyrrolidone.

[0049] In a specific embodiment, in step (1), the mass concentration of the lithiated single lithium ion conductor in the organic solution is 0.05 - 0.5 g / mL. For example, the mass concentrations are 0.05 g / mL, 0.1 g / mL, 0.2 g / mL, 0.3 g / mL, 0.4 g / mL, 0.5 g / mL. The mass ratio of the lithiated single lithium ion conductor to the anchored matrix polymer is 0.5 - 5:1. For example, the mass ratios are 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1. The mixing and dissolution stirring time is 6 - 48 h. For example, the stirring times are 6 h, 12 h, 18 h, 24 h, 30 h, 36 h, 48 h.

[0050] In a specific embodiment, in step (2), the chemical active substance is one or several of silicon fluoride, stannous fluoride, tin tetrafluoride, antimony pentafluoride, magnesium fluoride, aluminum fluoride, germanium tetrafluoride, lead fluoride, zinc fluoride, bismuth trifluoride or indium fluoride.

[0051] In a specific embodiment, in step (2), the mass ratio of the chemical active substance to the lithiated single lithium ion conductor is 1:1 - 20. For example, the mass ratios are 1:1, 1:5, 1:10, 1:15, 1:20. The stirring and dispersion time is 3 - 12 h. For example, the stirring times are 3 h, 6 h, 9 h, 12 h.

[0052] In a specific embodiment, in step (3), the method for film formation is coating method, casting method, casting film method or electrospinning method. The film formation thickness is 100 - 1000 μm. For example, the thicknesses are 100 μm, 150 μm, 200 μm, 250 μm, 500 μm, 750 μm, 1000 μm.

[0053] In a specific embodiment, in step (3), the film formation drying temperature is 30 - 80 °C. For example, the temperatures are 30 °C, 40 °C, 50 °C, 60 °C, 70 °C, 80 °C. The drying time is 6 - 72 h. For example, the drying times are 6 h, 12 h, 24 h, 36 h, 48 h, 60 h, 72 h.

[0054] Another embodiment of the present invention discloses a single lithium ion conductor slow-release film for a lithium metal battery prepared by the said method.

[0055] Specifically, the single lithium ion conductor slow-release film is a thin film formed with an anchored matrix polymer as the skeleton, anchoring the lithiated single lithium ion conductor, and uniformly filling the chemical active substance between the skeletons.

[0056] Among them, the anchored lithiated single lithium-ion conductor is formed by dissolving the lithiated single lithium-ion conductor and the anchored matrix polymer together in an organic solvent. The lithiated single lithium-ion conductor is obtained by polymerizing 4,4'-difluorobis(phenylsulfonyl)imide and 4,4'-dihydroxybis(phenylsulfonyl)imide followed by lithiation modification.

[0057] In a specific embodiment, the contact angle between the single lithium-ion conductor slow-release film and the electrolyte is 7.0° to 7.4°. For example, the contact angle is 7.4°, 7.3°, 7.2°, 7.1°, 7.0°.

[0058] The third embodiment of the present invention discloses a lithium metal battery, including the single lithium-ion conductor slow-release film for the lithium metal battery.

[0059] In a specific embodiment, the polarization voltage of the lithium metal battery after stable cycling for 1000 h is 13 mV to 17 mV. For example, the polarization voltage is 13 mV, 14 mV, 15 mV, 16 mV, 17 mV.

[0060] In a specific embodiment, the charge transfer impedance of the lithium metal battery is 39.4 to 44.2 Ω. For example, the charge transfer impedance is 39.4 Ω, 39.6 Ω, 39.8 Ω, 44.0 Ω, 44.2 Ω.

[0061] In a specific embodiment, the nucleation overpotential of the lithium metal battery is 30 to 34 mV. For example, the nucleation overpotential is 30 mV, 31 mV, 32 mV, 33 mV, 34 mV.

[0062] It should be noted that the single lithium-ion conductor slow-release film for the lithium metal battery of the present invention has a self-supporting function and replaces the separator of a conventional battery. At the same time, the single lithium-ion conductor slow-release film of the present invention is a single layer of film with firm bonding and better safety performance.

[0063] Example 1

[0064] A preparation method of a single lithium-ion conductor slow-release film for a lithium metal battery includes the following steps:

[0065] (1) Add 10 mmol of 4,4-difluorobis(phenylsulfonyl)imide, 30 mmol of 4,4-dihydroxybis(phenylsulfonyl)imide, and 30 mmol of potassium carbonate into a round-bottom flask, and react at 150 °C for 24 h. After the reaction is completed, precipitate it in hydrochloric acid solution. After lithiation with lithium hydroxide, poly(lithium 4,4-difluorobis(phenylsulfonyl)imide-alt-4,4-dihydroxybis(phenylsulfonyl)imide) (i.e., lithiated single-ion conductor) is obtained. Dissolve the above product in an organic solvent methanol with a mass concentration of 0.05 g / mL, and at the same time dissolve the anchoring matrix polymer polyethylene oxide. The mass ratio of poly(lithium 4,4-difluorobis(phenylsulfonyl)imide-alt-4,4-dihydroxybis(phenylsulfonyl)imide) to polyethylene oxide is 0.5:1, and the mixing and dissolution stirring time is 6 h to obtain a preliminary slurry by stirring.

[0066] (2) Stir and disperse the chemically active substance stannous fluoride into the preliminary slurry prepared above to obtain a uniform slurry. The mass ratio of stannous fluoride to poly(lithium 4,4-difluorobis(phenylsulfonyl)imide-alt-4,4-dihydroxybis(phenylsulfonyl)imide) is 1:1, and the stirring and dispersion time is 3 h.

[0067] (3) Coat the above uniform slurry into a film, dry it at 30 °C for 6 h, and the film thickness after peeling is 100 μm to obtain the single-ion conductor slow-release film for lithium metal batteries.

[0068] Example 2

[0069] (1) Add 10 mmol of 4,4-difluorobis(phenylsulfonyl)imide, 50 mmol of 4,4-dihydroxybis(phenylsulfonyl)imide, and 30 mmol of potassium carbonate into a round-bottom flask, and react at 180 °C for 18 h. After the reaction is completed, precipitate it in hydrochloric acid solution. After lithiation with lithium hydroxide, poly(lithium 4,4-difluorobis(phenylsulfonyl)imide-alt-4,4-dihydroxybis(phenylsulfonyl)imide) is obtained. Dissolve the above product and the anchoring matrix polymer polyacrylonitrile in N,N-dimethylformamide according to a mass ratio of 1:1. The mass concentration of poly(lithium 4,4-difluorobis(phenylsulfonyl)imide-alt-4,4-dihydroxybis(phenylsulfonyl)imide) is 0.1 g / mL, and the mixing and dissolution stirring time is 12 h to obtain a preliminary slurry by stirring.

[0070] (2) Stir and disperse the chemically active substance aluminum fluoride into the preliminary slurry prepared above to obtain a uniform slurry. The mass ratio of aluminum fluoride to poly(lithium 4,4-difluorobis(phenylsulfonyl)imide-alt-4,4-dihydroxybis(phenylsulfonyl)imide) is 1:5, and the stirring and dispersion time is 6 h.

[0071] (3) Cast the above uniform slurry into a film, dry it at 50 °C for 12 h, and the film thickness after peeling is 250 μm to obtain the single-ion conductor slow-release film for lithium metal batteries.

[0072] Example 3

[0073] (1) 10 mmol of 4,4-difluorobis(phenylsulfonyl)imide, 20 mmol of 4,4-dihydroxybis(phenylsulfonyl)imide and 30 mmol of potassium carbonate were added to a round-bottom flask and reacted at 165 °C for 15 h. After the reaction was completed, it was precipitated in hydrochloric acid solution. After lithiation with lithium hydroxide, poly(4,4-difluorobis(phenylsulfonyl)imide)(4,4-dihydroxybis(phenylsulfonyl)imide)lithium was obtained. 0.2 g of the above product and 0.1 g of the anchored matrix polymer polyvinyl acetate were dissolved in 3 mL of chloroform, and the mixture was stirred for 12 h to obtain a preliminary slurry.

[0074] (2) The chemically active substance germanium tetrafluoride was stirred and dispersed into the preliminary slurry prepared above to obtain a uniform slurry. The mass ratio of germanium tetrafluoride to poly(4,4-difluorobis(phenylsulfonyl)imide)(4,4-dihydroxybis(phenylsulfonyl)imide)lithium was 1:10, and the stirring and dispersing time was 12 h.

[0075] (3) The above-mentioned uniform slurry was cast into a film and dried at 60 °C for 24 h. After peeling, the film thickness was 200 μm to obtain the single lithium-ion conductor sustained-release film for lithium metal batteries.

[0076] Example 4

[0077] (1) 10 mmol of 4,4-difluorobis(phenylsulfonyl)imide, 10 mmol of 4,4-dihydroxybis(phenylsulfonyl)imide and 30 mmol of potassium carbonate were added to a round-bottom flask and reacted at 180 °C for 12 h. After the reaction was completed, it was precipitated in hydrochloric acid solution. After lithiation with lithium hydroxide, poly(4,4-difluorobis(phenylsulfonyl)imide)(4,4-dihydroxybis(phenylsulfonyl)imide)lithium was obtained. 1.5 g of the above product and 0.3 g of the anchored matrix polymer polyacrylate were dissolved in 3 mL of chloroform, and the mixture was stirred for 48 h to obtain a preliminary slurry.

[0078] (2) The chemically active substance zinc fluoride was stirred and dispersed into the preliminary slurry prepared above to obtain a uniform slurry. The mass ratio of zinc fluoride to poly(4,4-difluorobis(phenylsulfonyl)imide)(4,4-dihydroxybis(phenylsulfonyl)imide)lithium was 1:20, and the stirring and dispersing time was 12 h.

[0079] (3) The above-mentioned uniform slurry was cast into a film and dried at 80 °C for 72 h. After peeling, the film thickness was 1000 μm to obtain the single lithium-ion conductor sustained-release film for lithium metal batteries.

[0080] Test Example 1

[0081] 1. Sample preparation

[0082] Test sample 1

[0083] Assemble a lithium symmetric battery

[0084] The electrolyte in the battery uses a mixed solvent of ethylene glycol dimethyl ether and 1,3-dioxolane with a volume ratio of 1:1, and the lithium salt is lithium bis(trifluoromethylsulfonyl)imide with a concentration of 1 mol / L. Both electrodes of the battery use metallic lithium. The single lithium-ion conductor slow-release membrane prepared in Example 1 is cut into a disc with a diameter of 19 mm as the battery separator, and it is assembled into a CR2025-type lithium symmetric battery in a glove box filled with argon (H 2 O < 1 ppm, O 2 < 1 ppm).

[0085] Control sample 1

[0086] This control sample assembles a lithium symmetric battery using the same method as test sample 1. The difference is that the battery separator uses a polypropylene separator (a commercially available product).

[0087] 2. Observe the surface morphologies of the single lithium-ion conductor slow-release membrane for the lithium metal battery prepared in Example 1 and the polypropylene separator respectively, as shown in Figure 1 and 2 .

[0088] From Figure 1 's scanning electron microscope image, it can be seen that the polypropylene separator has obvious pores and the pore size distribution is uneven, which is likely to cause uneven deposition of metallic lithium. In addition, lithium dendrites are likely to penetrate through the polypropylene separator and continue to grow, resulting in a short circuit of the lithium metal battery.

[0089] In contrast, from Figure 2 's scanning electron microscope image, it can be seen that the surface of the single lithium-ion conductor slow-release membrane is flat and dense, and the chemically active substances are evenly dispersed in the chemically inert substances, and the modified components generated by subsequent reactions on the surface of metallic lithium are also more uniform.

[0090] 3. Test the contact angle changes of the electrolytes in control sample 1 and test sample 1 on the polypropylene separator and the single lithium-ion conductor slow-release membrane prepared in Example 1. The change in the contact angle can quantitatively analyze the wettability of the electrolyte. The test results are shown in Figure 3 and Figure 4 respectively.

[0091] As shown in Figure 3 , when the electrolyte drops on the polypropylene separator, the contact angle of the surface electrolyte is 37.3°. The electrolyte is in an aggregated state. After 3 seconds, the contact angle is 36.5°. The electrolyte disperses slowly. Even after 15 seconds, the contact angle still remains at 33.9°. Only a small amount of electrolyte is dispersed by the polypropylene separator, indicating that its wettability to the electrolyte is poor.

[0092] In contrast, as shown in Figure 4As shown, the contact angle of the electrolyte on the surface of the single lithium-ion conductor slow-release membrane prepared in Example 1 was 23.5° at the beginning, indicating that a part of the electrolyte was instantaneously dispersed. After 3 seconds, the contact angle decreased to 18.2°, and after 15 seconds, the contact angle was only 7.4°, with almost no obvious electrolyte suspension, indicating that the single lithium-ion conductor slow-release membrane improved the wettability of the separator to the electrolyte, which was more conducive to the + uniform distribution of Li

[0093] 4. The assembled lithium symmetric battery test sample 1 and control sample 1 were tested for electrochemical performance at room temperature using a Blue-Energy test system.

[0094] Test conditions: Deposition / stripping capacity of 2 mAh cm -2 of lithium metal at a current density of 4 mA cm -2 , and the results are as Figure 5 shown.

[0095] According to Figure 5 , it can be seen that the polarization voltage of the lithium symmetric battery of test sample 1 was only 13 mV after 1000 h of stable cycling, while the polarization voltage of the lithium symmetric battery of control sample 1 exceeded 500 mV in the initial stage of cycling.

[0096] This is because the single lithium-ion conductor slow-release membrane of the present invention can slowly release chemically active substances during the electrochemical reaction process. The modified components generated in situ on the lithium metal surface participate in the formation of the solid electrolyte interface membrane on the lithium metal surface, improving the ionic conductivity and electronic conductivity on the lithium metal surface, and promoting the uniform deposition of lithium metal. The lithiated single ion conductor used in the single lithium-ion conductor slow-release membrane can reduce the concentration polarization inside the battery, thereby reducing self-discharge and degradation on the electrode surface, reducing the interfacial impedance, charge transfer impedance and nucleation overpotential of the lithium metal battery, and improving the cycle life of the battery.

[0097] The AC impedance of the lithium symmetric batteries assembled based on control sample 1 and test sample 1 was tested, and the test results are respectively as Figure 6 and Figure 7 shown.

[0098] The charge transfer impedance of the lithium symmetric battery based on control sample 1 was 84.6 Ω, and the charge transfer impedance of the lithium symmetric battery based on test sample 1 was 44.2 Ω. The single lithium-ion conductor slow-release membrane described in the present invention reduced the charge transfer impedance of the battery.

[0099] 5. After the lithium symmetric batteries assembled with control sample 1 and test sample 1 were cycled for 50 h, disassembled and the electrolyte on the electrode surface was cleaned, the deposition morphology of lithium metal was observed using a scanning electron microscope, and the characterization results are respectively as Figure 8 and 9 shown.

[0100] It can be seen from Figure 8 that after cycling the battery based on the polypropylene separator, the surface of the lithium metal is loose and porous, with obvious cracks and a large number of dendritic lithium, resulting in an increase in the specific surface area of the lithium metal interface, an intensification of the side reaction with the electrolyte, and a reduction in the cycle life of the lithium metal battery.

[0101] In contrast, it can be seen from Figure 9 that after cycling the lithium symmetric battery using the single lithium ion conductor slow-release membrane, the lithium metal interface is flat and dense. The chemically active substances that are continuously slow-released during the electrochemical reaction react with the lithium metal, in-situ modifying the SEI film, and the in-situ generated modified components promote the diffusion of Li + , serving as the nucleation sites for lithium, promoting the uniform and dense deposition of lithium metal, thereby improving the cycle stability of the lithium metal battery.

[0102] The present inventors also conducted the above tests on the single lithium ion conductor slow-release membranes prepared in other embodiments, and the results were basically the same. Due to limited space, they will not be listed one by one.

[0103] As mentioned above, the above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a single lithium ion conductor sustained-release membrane for a lithium metal battery, characterized in that: The steps include: (1) polymerizing 4,4-difluorobisbenzenesulfonyl imide and 4,4-dihydroxybisbenzenesulfonyl imide, and then performing lithium modification to obtain a lithiated single lithium ion conductor, and dissolving the lithiated single lithium ion conductor and the anchoring matrix polymer in an organic solvent, stirring, and obtaining a preliminary slurry; (2) stirring and dispersing the chemically active substance into the preliminary slurry to obtain a uniform slurry; (3) Forming the uniform slurry into a film, drying it, and peeling it off to obtain the single lithium ion conductor sustained-release film for lithium metal batteries.

2. The method for preparing a single lithium ion conductor sustained-release membrane for a lithium metal battery according to claim 1, characterized in that: In step (1), the molar ratio of 4,4-difluorobisbenzenesulfonyl imide to 4,4-dihydroxybisbenzenesulfonyl imide is 1:1-5, the polymerization temperature is 150-180° C., and the polymerization time is 12-24 hours.

3. The method for preparing a single lithium ion conductor sustained-release membrane for a lithium metal battery according to claim 1, characterized in that: In step (1), the anchoring matrix polymer is one or more of polyethylene oxide, polyethylene glycol dipropylene oxide, polyacrylonitrile, polyvinyl acetate, polylactic acid, polydimethylsiloxane or polyacrylate.

4. The method for preparing a single lithium ion conductor sustained-release membrane for a lithium metal battery according to claim 1, characterized in that: In step (1), the organic solvent is one or more of dimethylformamide, triethylamine, acetonitrile, chloroform, methanol, ethylene glycol dimethyl ether, dimethyl sulfoxide or N-methylpyrrolidone.

5. The method for preparing a single lithium ion conductor sustained-release membrane for a lithium metal battery according to any one of claims 1 to 4, characterized in that: In step (1), the mass concentration of the lithiated single lithium ion conductor in the organic solution is 0.05-0.5 g / mL, the mass ratio of the lithiated single lithium ion conductor to the anchoring matrix polymer is 0.5-5:1, and the mixed dissolution stirring time is 6-48 hours.

6. The method for preparing a single lithium ion conductor sustained-release membrane for a lithium metal battery according to claim 1, characterized in that: In step (2), the chemically active substance is one or more of silicon fluoride, stannous fluoride, tin tetrafluoride, antimony pentafluoride, magnesium fluoride, aluminum fluoride, germanium tetrafluoride, lead fluoride, zinc fluoride, bismuth trifluoride or indium fluoride.

7. The method for preparing a single lithium ion conductor sustained-release membrane for a lithium metal battery according to claim 1, characterized in that: In step (2), the mass ratio of the chemically active substance to the lithiated single lithium ion conductor is 1:1-20, and the stirring and dispersing time is 3-12 hours.

8. The method for preparing a single lithium ion conductor sustained-release membrane for a lithium metal battery according to claim 1, characterized in that: In step (3), the method for preparing the film is coating, casting, tape casting or electrospinning, and the film thickness is 100 to 1000 μm.

9. The method for preparing a single lithium ion conductor sustained-release membrane for a lithium metal battery according to claim 1, characterized in that: In step (3), the film forming and drying temperature is 30 to 80° C., and the drying time is 6 to 72 hours.

10. A single lithium ion conductor sustained-release membrane for a lithium metal battery prepared by the method of any one of claims 1 to 9.

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