Single lithium ion conductor slow release membrane for lithium metal battery and battery

Abstract

The invention relates to a single lithium ion conductor slow-release membrane for a lithium metal battery and the battery, and aims to solve the problems that a battery diaphragm in the prior art has no limiting effect on lithium ion distribution, has no promoting effect on lithium ion transmission, and cannot participate in formation and modification of a solid electrolyte interface membrane on the surface of lithium metal. The single lithium ion conductor slow-release film can slowly release chemical active substances in the electrochemical reaction process, modified components generated through in-situ reaction on the surface of lithium metal participate in formation of a solid electrolyte interface film on the surface of the lithium metal, ionic conductivity and electronic conductivity of the surface of the lithium metal are improved, and uniform deposition of the lithium metal is promoted; concentration polarization in the battery can be reduced, so that self-discharge and degradation of 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 batteries, and particularly to a single lithium ion conductor slow-release film and a battery for a lithium metal battery. Background Art

[0002] The lithium metal anode has a high theoretical specific capacity and a low electrochemical potential, making the lithium metal battery the most promising choice for achieving high energy density batteries. However, the practical application of the lithium metal anode is still limited by its inherent problems. When the 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 change on the anode surface causes cracks to form in the solid electrolyte interface film. At the crack, 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 rupture of 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 problem of the battery is 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, the interface between the lithium metal anode and the electrolyte can be stabilized, and the uniform deposition of lithium ions can be guided. 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 in direct contact with 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 lithium ion distribution 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 films have a single function and a relatively complex preparation process. Summary of the Invention

[0005] In view of the above analysis, the present invention aims to provide a single lithium ion conductor slow-release film and a battery for lithium metal batteries, so as to solve at least one of the problems in the prior art that the battery separator has no restrictive effect on the distribution of lithium ions, no promoting effect on the transmission of lithium ions, and cannot 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 single lithium ion conductor slow-release film for a lithium metal battery. The single lithium ion conductor slow-release film is a thin film formed by using an anchored matrix polymer as a skeleton, anchoring a lithiated single lithium ion conductor, and uniformly filling a chemically active substance between the skeletons.

[0007] Among them, the anchored lithiated single lithium ion conductor is obtained by co-dissolving the lithiated single lithium ion conductor and the anchored matrix polymer 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 and then performing lithiation modification.

[0008] Further, the contact angle between the single lithium ion conductor slow-release film and the electrolyte is 7.0° to 7.4°.

[0009] Further, the anchored matrix polymer is one or more of polyethylene oxide, polyethylene glycol bis(propylene oxide) ether, polyacrylonitrile, polyvinyl acetate, polylactic acid, polydimethylsiloxane, or polyacrylate.

[0010] Further, the organic solvent is one or more of dimethylformamide, triethylamine, acetonitrile, chloroform, methanol, ethylene glycol dimethyl ether, dimethyl sulfoxide, or N-methylpyrrolidone.

[0011] Further, 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.

[0012] Further, the chemical 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.

[0013] Further, the mass ratio of the chemical active substance to the lithiated single lithium ion conductor is 1:1 - 20, and the stirring and dispersion time is 3 - 12 h.

[0014] Further, the molar ratio of 4,4-difluorobis(phenylsulfonyl)imide to 4,4-dihydroxybis(phenylsulfonyl)imide is 1:1 - 5, the polymerization temperature is 150 - 180 °C, and the polymerization time is 12 - 24 h.

[0015] In a second aspect, the present invention provides a lithium metal battery including the single lithium ion conductor slow-release film for the lithium metal battery.

[0016] Further, after the lithium metal battery is stably cycled for 1000 h, the polarization voltage is 13 mV - 17 mV, the charge transfer impedance of the lithium metal battery is 39.4 - 44.2 Ω, and the nucleation overpotential of the lithium metal battery is 30 - 34 mV.

[0017] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0018] (1) The single lithium ion conductor slow-release film for the lithium metal battery 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;

[0019] (2) The single lithium ion conductor slow-release film of the present invention 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;

[0020] (3) The slow-release process of the chemical active substances by the single lithium ion conductor slow-release film of the present invention 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;

[0021] (4) The single lithium-ion conductor slow-release film described in the present invention uses a single lithium-ion conductor as the matrix, has good mechanical properties and high ionic conductivity, can increase the movement of molecular chain segments by introducing various segments, and 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;

[0022] (5) The lithiated single-ion conductor used in the single lithium-ion conductor slow-release film described in 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;

[0023] (6) The preparation method of the single lithium-ion conductor slow-release film for lithium metal batteries described in 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.

[0024] 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. Description of the Drawings

[0025] The drawings are only for the purpose of showing specific embodiments, and are not considered to be a limitation of the present invention. Throughout the drawings, the same reference signs represent the same components.

[0026] Figure 1 It is a scanning electron microscope image of the polypropylene separator provided by the present invention;

[0027] 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;

[0028] Figure 3 It is the change of the contact angle of the electrolyte provided by the present invention on the polypropylene separator;

[0029] 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;

[0030] Figure 5 It is the stable cycle performance diagram of two groups of lithium symmetric batteries of test sample 1 and control sample 1 provided by the present invention;

[0031] Figure 6 It is the AC impedance test diagram of the lithium symmetric battery assembled with control sample 1 provided by the present invention;

[0032] Figure 7 AC impedance test diagram of the lithium symmetric battery assembled with Test Sample 1 provided by the present invention;

[0033] Figure 8 SEM image of the deposition morphology of the lithium metal anode after 50 h of cycling of the lithium symmetric battery assembled with Control Sample 1 provided by the present invention;

[0034] Figure 9 SEM image of the deposition morphology of the lithium metal anode after 50 h of cycling of the lithium symmetric battery assembled with Test Sample 1 provided by the present invention. Detailed implementation manners

[0035] The following will specifically describe the preferred embodiments of the present invention with reference to the accompanying drawings. The accompanying drawings form 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.

[0036] A specific embodiment of the present invention discloses a single lithium ion conductor slow-release film for a lithium metal battery. The single lithium ion conductor slow-release film is a thin film formed by using an anchored matrix polymer as a skeleton, anchoring a lithiated single lithium ion conductor, and uniformly filling a chemically active substance between the skeletons;

[0037] Among them, the anchored lithiated single lithium ion conductor is obtained by co-dissolving the lithiated single lithium ion conductor and the anchored matrix polymer 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 and then performing lithiation modification.

[0038] Compared with the prior art, the single lithium-ion conductor slow-release film for lithium metal batteries described in 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 plays a continuous 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 interfacial impedance, charge transfer impedance and nucleation overpotential of the lithium metal battery, and improving the comprehensive performance of the battery.

[0039] Among them, the reaction equation for the polymerization of 4,4-difluorobis(phenylsulfonyl)imide and 4,4-dihydroxybis(phenylsulfonyl)imide is as follows:

[0040]

[0041] 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°.

[0042] In a specific embodiment, 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.

[0043] In a specific embodiment, the organic solvent is one or more of dimethylformamide, triethylamine, acetonitrile, chloroform, methanol, ethylene glycol dimethyl ether, dimethyl sulfoxide or N-methylpyrrolidone.

[0044] In a specific embodiment, 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.

[0045] In a specific embodiment, 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.

[0046] In a specific embodiment, 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.

[0047] In a specific embodiment, the molar ratio of 4,4 - difluorobis(phenylsulfonyl)imide to 4,4 - dihydroxybis(phenylsulfonyl)imide is 1:1 - 5. For example, the molar ratios are 1:1, 1:2, 1:3, 1:4, 1:5. The polymerization temperature is 150 - 180 °C. For example, the temperatures are 150 °C, 160 °C, 170 °C, 180 °C. The polymerization time is 12 - 24 h. For example, the polymerization times are 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 24 h.

[0048] In a specific embodiment, the preparation method of the thin film is the coating method, casting method, casting film method or electrospinning method. The film - forming thickness is 100 - 1000 μm. For example, the thicknesses are 100 μm, 150 μm, 200 μm, 250 μm, 500 μm, 750 μm, 1000 μm.

[0049] In a specific embodiment, after film - forming, drying treatment and peeling are carried out to obtain the single lithium ion conductor sustained - release film for the lithium metal battery.

[0050] In a specific embodiment, the 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.

[0051] Another specific embodiment of the present invention discloses a lithium metal battery, including the single lithium-ion conductor slow-release film for the lithium metal battery described above.

[0052] In a specific embodiment, the polarization voltage of the lithium metal battery is 13 mV to 17 mV after stable cycling for 1000 h. For example, the polarization voltage is 13 mV, 14 mV, 15 mV, 16 mV, 17 mV.

[0053] 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.

[0054] 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.

[0055] It should be noted that the single lithium-ion conductor slow-release film for the lithium metal battery described in the present invention has a self-supporting effect 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 strong adhesion and better safety performance.

[0056] Example 1

[0057] A preparation method of a single lithium-ion conductor slow-release film for a lithium metal battery includes the following steps:

[0058] (1) Add 10 mmol of 4,4-difluorobis(phenylsulfonyl)imide, 30 mmol of 4,4-dihydroxybis(phenylsulfonyl)imide, and 30 mmol of potassium carbonate to a round-bottom flask, and react at 150 °C for 24 h. After the reaction is completed, precipitate in a 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.

[0059] (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 dispersing time is 3 h.

[0060] (3) Coating the above-mentioned uniform slurry into a film, drying at 30 °C for 6 h, and after peeling, the film thickness is 100 μm to obtain the single lithium-ion conductor slow-release film for lithium metal batteries.

[0061] Example 2

[0062] (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, it is precipitated in hydrochloric acid solution. After lithium hydroxide lithiation, poly(lithium bis(phenylsulfonyl)imide)(lithium bis(dihydroxyphenylsulfonyl)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 bis(phenylsulfonyl)imide)(lithium bis(dihydroxyphenylsulfonyl)imide) is 0.1 g / mL, and the mixing and dissolution stirring time is 12 h to obtain a preliminary slurry by stirring.

[0063] (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 bis(phenylsulfonyl)imide)(lithium bis(dihydroxyphenylsulfonyl)imide) is 1:5, and the stirring and dispersing time is 6 h.

[0064] (3) Cast the above-mentioned uniform slurry into a film, dry at 50 °C for 12 h, and after peeling, the film thickness is 250 μm to obtain the single lithium-ion conductor slow-release film for lithium metal batteries.

[0065] Example 3

[0066] (1) Add 10 mmol of 4,4-difluorobis(phenylsulfonyl)imide, 20 mmol of 4,4-dihydroxybis(phenylsulfonyl)imide, and 30 mmol of potassium carbonate into a round-bottom flask, and react at 165 °C for 15 h. After the reaction is completed, it is precipitated in hydrochloric acid solution. After lithium hydroxide lithiation, poly(lithium bis(phenylsulfonyl)imide)(lithium bis(dihydroxyphenylsulfonyl)imide) is obtained. Dissolve 0.2 g of the above product and 0.1 g of the anchoring matrix polymer polyvinyl acetate in 3 mL of chloroform, and the mixing and dissolution stirring time is 12 h to obtain a preliminary slurry by stirring.

[0067] (2) Stir and disperse the chemically active substance germanium tetrafluoride into the preliminary slurry prepared above to obtain a uniform slurry. The mass ratio of germanium tetrafluoride to poly(lithium bis(phenylsulfonyl)imide)(lithium bis(dihydroxyphenylsulfonyl)imide) is 1:10, and the stirring and dispersing time is 12 h.

[0068] (3) Cast the above-mentioned uniform slurry into a film by casting, dry at 60 °C for 24 h, and after peeling, the film thickness is 200 μm to obtain the single lithium-ion conductor slow-release film for lithium metal batteries.

[0069] Example 4

[0070] (1) Add 10 mmol of 4,4-difluorobis(phenylsulfonyl)imide, 10 mmol of 4,4-dihydroxybis(phenylsulfonyl)imide, and 30 mmol of potassium carbonate to a round-bottom flask and react at 180 °C for 12 h. After the reaction is completed, precipitate in hydrochloric acid solution. After lithiation with lithium hydroxide, poly(4,4-difluorobis(phenylsulfonyl)imide)(4,4-dihydroxybis(phenylsulfonyl)imide) lithium is obtained. Dissolve 1.5 g of the above product and 0.3 g of the anchored matrix polymer polyacrylate in 3 mL of chloroform, and mix and dissolve for 48 h with stirring to obtain a preliminary slurry.

[0071] (2) Stir and disperse the chemically active substance zinc fluoride 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 is 1:20, and the stirring and dispersion time is 12 h.

[0072] (3) Cast the uniform slurry into a film, dry it at 80 °C for 72 h, and the film thickness after peeling is 1000 μm to obtain the single lithium ion conductor slow-release film for lithium metal batteries.

[0073] Test Example 1

[0074] 1. Sample preparation

[0075] Test sample 1

[0076] Assemble a lithium symmetric battery

[0077] 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. Cut the single lithium ion conductor slow-release film for lithium metal batteries prepared in Example 1 into a disc with a diameter of 19 mm as the battery separator, and assemble it into a CR2025 type lithium symmetric battery in a glove box filled with argon (H 2 O < 1 ppm, O 2 < 1 ppm).

[0078] Control sample 1

[0079] This control sample assembles a lithium symmetric battery using the same method as test sample 1, except that the battery separator uses a polypropylene separator (a commercially available product).

[0080] 2. Observe the surface morphologies of the single lithium ion conductor slow-release film for lithium metal batteries prepared in Example 1 and the polypropylene separator respectively, as Figure 1 and 2 shown.

[0081] From Figure 1As can be seen from the scanning electron microscope images, the polypropylene separator has obvious pores and the pore size distribution is uneven, which easily leads to uneven deposition of lithium metal. In addition, lithium dendrites easily penetrate through the polypropylene separator and continue to grow, causing short circuits in lithium metal batteries.

[0082] In contrast, as can be seen from Figure 2 the scanning electron microscope images, the surface of the single lithium-ion conductor slow-release film is flat and dense, and the chemically active substances are evenly dispersed in the chemically inert substances. The modified components formed by subsequent reactions on the lithium metal surface are also more uniform.

[0083] 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 film 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.

[0084] As Figure 3 shown, when the electrolyte is dropped on the polypropylene separator, the contact angle of the electrolyte on the surface 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 remains at 33.9°, and only a small amount of electrolyte is dispersed by the polypropylene separator, indicating that its wettability to the electrolyte is poor.

[0085] In contrast, as Figure 4 shown, the contact angle of the electrolyte on the surface of the single lithium-ion conductor slow-release film prepared in Example 1 is 23.5° at the beginning, indicating that a part of the electrolyte is instantaneously dispersed. After 3 seconds, the contact angle drops to 18.2°, and after 15 seconds, the contact angle is only 7.4°. There is almost no obvious electrolyte suspension, indicating that the single lithium-ion conductor slow-release film improves the wettability of the separator to the electrolyte, which is more conducive to the + uniform distribution of Li

[0086] 4. Use a Blue Power test system to perform electrochemical performance tests on the assembled lithium symmetric battery test sample 1 and control sample 1 at room temperature.

[0087] Test conditions: Deposit / strip a capacity of 2 mAh cm -2 of lithium metal at a current density of 4 mA cm -2 . The results are shown in Figure 5 respectively.

[0088] According to Figure 5 it can be seen that the polarization voltage of the lithium symmetric battery of test sample 1 is only 13 mV after stable cycling for 1000 h, while the polarization voltage of the lithium symmetric battery of control sample 1 exceeds 500 mV in the initial stage of cycling.

[0089] This is because the single lithium-ion conductor slow-release film of the present invention can slowly release chemically 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 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 interfacial impedance, charge transfer impedance and nucleation overpotential of the lithium metal battery, and improving the cycle life of the battery.

[0090] The AC impedance of the lithium symmetric battery assembled based on Control Sample 1 and Test Sample 1 was tested, and the test results are shown in Figure 6 and Figure 7 respectively.

[0091] The charge transfer impedance of the lithium symmetric battery based on Control Sample 1 is 84.6 Ω, and the charge transfer impedance of the lithium symmetric battery based on Test Sample 1 is 44.2 Ω. The single lithium-ion conductor slow-release film described in the present invention reduces the charge transfer impedance of the battery.

[0092] 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 by scanning electron microscopy, and the characterization results are shown in Figure 8 and 9 respectively.

[0093] It can be seen from Figure 8 that after cycling, the lithium metal surface of the battery based on the polypropylene separator 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.

[0094] In contrast, it can be seen from Figure 9 that after cycling, the lithium metal interface of the lithium symmetric battery using the single lithium-ion conductor slow-release film is flat and dense. The chemically active substances continuously released during the electrochemical reaction react with the lithium metal, in-situ modify 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.

[0095] The inventors of the present invention also conducted the above tests on the single lithium-ion conductor slow-release films prepared in other embodiments, and the results were basically the same. Due to limited space, they will not be listed one by one.

[0096] As described above, it is only the preferred specific embodiment 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 within the protection scope of the present invention.

Claims

1. A single lithium ion conductor sustained-release membrane for a lithium metal battery, characterized in that: The single lithium ion conductor sustained-release membrane is a thin film formed by using an anchoring matrix polymer as a skeleton, anchoring a lithiated single lithium ion conductor, and uniformly filling chemically active substances between the skeletons; The anchored lithiated single lithium ion conductor is a lithiated single lithium ion conductor and an anchoring matrix polymer dissolved together in an organic solvent, and the lithiated single lithium ion conductor is obtained by polymerizing 4,4-difluorobisbenzenesulfonimide and 4,4-dihydroxybisbenzenesulfonimide and then performing lithiation modification.

2. The single lithium ion conductor sustained-release membrane for lithium metal batteries according to claim 1, characterized in that: The contact angle between the single lithium ion conductor sustained-release membrane and the electrolyte is 7.0° to 7.4°.

3. A single lithium ion conductor sustained-release membrane for a lithium metal battery according to claim 1 or 2, characterized in that: The anchoring matrix polymer is one or more of polyethylene oxide, polyethylene glycol dipropylene oxide ether, polyacrylonitrile, polyvinyl acetate, polylactic acid, polydimethylsiloxane or polyacrylate.

4. A single lithium ion conductor sustained-release membrane for a lithium metal battery according to claim 1 or 2, characterized in that: The organic solvent is one or more of dimethylformamide, triethylamine, acetonitrile, chloroform, methanol, ethylene glycol dimethyl ether, dimethyl sulfoxide or N-methylpyrrolidone.

5. The single lithium ion conductor sustained-release membrane for lithium metal batteries according to claim 1, characterized in that: 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 single lithium ion conductor sustained-release membrane for lithium metal batteries according to claim 1, characterized in that: 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. A single lithium ion conductor sustained-release membrane for a lithium metal battery according to claim 1 or 6, characterized in that: 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 single lithium ion conductor sustained-release membrane for lithium metal batteries according to claim 1, characterized in that: 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.

9. A lithium metal battery, characterized in that: The invention comprises a single lithium ion conductor sustained-release membrane for a lithium metal battery as described in any one of claims 1 to 8.

10. The lithium metal battery according to claim 9, characterized in that After the lithium metal battery is stably cycled for 1000 hours, the polarization voltage is 13mV to 17mV, the charge transfer impedance of the lithium metal battery is 39.4 to 44.2Ω, and the nucleation overpotential of the lithium metal battery is 30 to 34mV.

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