CN109004276B - Lithium negative electrode protective film, preparation method and lithium metal secondary battery - Google Patents
Lithium negative electrode protective film, preparation method and lithium metal secondary battery Download PDFInfo
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Abstract
本发明涉及一种锂负极保护膜、制备方法及锂金属二次电池，属于锂金属二次电池领域。所述锂负极保护膜由锂盐、离子液体、无机物纳米颗粒和锂化处理的Nafion聚合物组成；含锂盐的离子液体吸附在无机物纳米颗粒表面并均匀分散在锂化处理的Nafion聚合物中。通过配置锂盐与离子液体的混合溶液；将混合溶液及无机物纳米颗粒密封球磨混合得到准固态电解质；将准固态电解质与锂化处理的Nafion聚合物溶液混合后涂覆于锂或铜箔表面，溶剂挥发完全后制得所述保护膜。所述锂负极保护膜可抑制锂枝晶产生，具有良好机械性能和化学稳定性、高锂离子电导率以及良好成膜性能；具备所述锂负极保护膜的锂金属二次电池具有优异的电化学性能。
The invention relates to a lithium negative electrode protective film, a preparation method and a lithium metal secondary battery, and belongs to the field of lithium metal secondary batteries. The lithium anode protective film is composed of lithium salt, ionic liquid, inorganic nanoparticles and lithiated Nafion polymer; the ionic liquid containing lithium salt is adsorbed on the surface of the inorganic nanoparticles and uniformly dispersed in the lithiated Nafion polymer thing. A quasi-solid electrolyte is obtained by configuring a mixed solution of lithium salt and ionic liquid; mixing the mixed solution and inorganic nanoparticles by sealing ball milling; mixing the quasi-solid electrolyte with the lithiated Nafion polymer solution and coating it on the surface of lithium or copper foil , the protective film is prepared after the solvent is completely evaporated. The lithium anode protective film can inhibit the generation of lithium dendrites, has good mechanical properties and chemical stability, high lithium ion conductivity and good film-forming performance; the lithium metal secondary battery provided with the lithium anode protective film has excellent electrical properties. chemical properties.
Description
Technical Field
The invention relates to a lithium cathode protective film, a preparation method and a lithium metal secondary battery, and belongs to the technical field of lithium metal secondary batteries.
Background
Along with social progress, energy sources utilized by human beings are increasing day by day. Efficient energy storage and conversion is a driving force for social progress, and the appearance and use of batteries enable people to utilize energy more efficiently and conveniently. Currently, lead-acid batteries, cadmium-nickel batteries, nickel-hydrogen batteries, and lithium ion batteries have achieved commercial applications. Especially lithium ion batteries, change people's communication and traffic ways. As the actual energy density of lithium ion batteries (especially graphite cathodes) is gradually approaching its theoretical limit, more efficient electrode materials are urgently needed to meet the requirements of the development of emerging high-end energy storage devices. The metallic lithium negative electrode is an ideal negative electrode material of the next-generation lithium secondary battery due to the extremely high capacity density (3680mAh/g) and the low standard electrode potential (-3.04V). Lithium metal batteries using metallic lithium as a negative electrode, including lithium sulfur batteries, lithium air batteries, and lithium oxide batteries, all exhibit extremely high theoretical energy densities.
However, the direct use of metallic lithium as a negative electrode material still has many problems: the lithium metal has active chemical property and can react with air and water to cause the difficulty in assembling the battery; during charging, the deposited lithium reacts with the electrolyte, resulting in low coulombic efficiency; the uneven surface shape of the lithium metal causes uneven surface charge distribution, and dendrites are easy to pierce the diaphragm to cause short circuit of the battery, thereby causing potential safety hazards. These problems hinder the commercial application of lithium metal secondary batteries. In the last decade, researchers have developed various novel methods for inhibiting dendrite generation of metallic lithium negative electrodes to improve the safety and service life of batteries, which mainly include: 1) alloying to reduce the reaction activity of the metallic lithium; 2) modifying a negative electrode Solid Electrolyte Interface (SEI) film; 3) a solid electrolyte having a high mechanical modulus that impedes lithium dendrite growth; 4) reasonable battery structure design. Because the electrochemical property of the surface of the metal lithium is mainly determined by an SEI film, the construction of the long-acting stable SEI film has important significance for improving the electrochemical performance of the metal lithium cathode. It is a common method to add additives to the electrolyte, such as LiNO, which contribute to the formation of a stable SEI film3The lithium-sulfur battery can be widely applied to lithium-sulfur batteries. However, as the cycle progresses, the additives are consumed, the battery impedance gradually increases, and the performance decreases. Scientific researchers form a layer of artificial SEI film on the surface of the lithium cathode in a pretreatment mode, so that the problem can be avoided, the generation of lithium dendrites is effectively inhibited, and the service life of the battery is prolonged. Cui and the like deposit two-dimensional material h-BN and graphene atomic layers on the copper foil, and because of the high mechanical strength of the h-BN and the graphene, the generation of dendritic crystals during the deposition of the metal lithium is effectively inhibited; guo et al introduce Li on the surface of lithium negative electrode by pretreatment3PO4Improving the diffusion rate of lithium ions at the interface of the metal lithium and the electrolyte,thereby suppressing generation of dendrites; in CN106935800A, poplar and the like forms a protective layer on the surface of the lithium negative electrode by soaking or electroplating.
Although the above-mentioned method inhibits the generation of metallic lithium dendrites to some extent, it has many limitations in the application process, for example, the method of Cui et al is expensive, Guo et al produces Li3PO4The requirements on environmental conditions are strict, and the modified SEI film formed by the poplar and other methods has poor mechanical properties and is not beneficial to prolonging the cycle life of the battery. Therefore, how to introduce the SEI film having high mechanical strength and high ionic conductivity in a simple and effective manner is of great significance in suppressing the generation of metallic lithium dendrites and improving the safety of the battery.
Disclosure of Invention
In view of the above, an object of the present invention is to provide a lithium negative electrode protective film; the lithium negative electrode protective film can inhibit the generation of lithium dendrites, and has good mechanical property and chemical stability, high lithium ion conductivity and good film-forming property.
The second purpose of the invention is to provide a preparation method of the lithium negative electrode protective film.
It is a further object of the present invention to provide a lithium metal secondary battery having a lithium negative electrode protective film according to the present invention, which has excellent electrochemical properties.
The purpose of the invention is realized by the following technical scheme.
A lithium negative electrode protective film is composed of lithium salt, ionic liquid, inorganic nanoparticles and a lithiated Nafion polymer; wherein, the ionic liquid containing lithium salt is absorbed on the surface of inorganic nano-particles and is uniformly dispersed in the Nafion polymer after lithiation treatment.
The lithium salt is a lithium salt used in a lithium battery conventional in the art, and is preferably lithium bis (oxalato) borate (LiB (C)2O4)2LiBOB), lithium difluorooxalato borate (LiBF)2(C2O4) LiODFB), lithium trifluoromethanesulfonate (LiCF)3SO3) Lithium bistrifluoromethanesulfonylimide (Li (CF)3SO2)2N, LiTFSI), lithium bis (fluorosulfonylimide) (Li (FSO)2)2N, LiFSI), lithium perfluoroethylsulfonimide (Li (C)2F5SO2)2N) and perfluoroalkyl sulfonyl methyllithium (LiC (CF)3SO2)3) More than one of them.
The ionic liquid is an ionic liquid used for a lithium battery in the prior art, and is preferably 1-ethyl-3-methylimidazole bistrifluoromethylsulfonyl imide salt, 1-propyl-3-methylimidazole bistrifluoromethylsulfonyl imide salt, 1-butyl-3-methylimidazole bistrifluoromethylsulfonyl imide salt, 1-ethyl-3-methylimidazole bistrifluoromethylsulfonyl imide salt, 1-propyl-3-methylimidazole bistrifluoromethylsulfonyl imide salt, 1-butyl-3-methylimidazole bisfluoromethanesulfonylimide salt, N-methyl, propylpyrrole bistrifluoromethanesulfonimide salt, N-methyl, butylpyrrole bistrifluoromethanesulfonimide salt, N-methyl, propylpyrrole bisfluoromethanesulfonylimide salt and N-methyl, butylpyrrole bisfluoromethanesulfonylimide salt.
The inorganic nanoparticles are inorganic oxide nanoparticles, preferably silicon dioxide nanoparticles, zirconium dioxide nanoparticles, titanium dioxide nanoparticles or aluminum oxide nanoparticles.
The thickness of the protective film is preferably 0.1 to 100. mu.m.
The invention relates to a preparation method of a lithium negative electrode protective film, which comprises the following steps:
(1) preparing a mixed solution of lithium salt and ionic liquid in an oxygen-free environment with the moisture content of less than or equal to 0.1 ppm;
(2) placing the mixed solution prepared in the step (1) and inorganic nano particles in a ball milling tank, sealing, and performing ball milling and mixing uniformly to obtain a quasi-solid electrolyte;
(3) mixing and stirring the quasi-solid electrolyte prepared in the step (2) and a Nafion polymer solution subjected to lithiation treatment, and carrying out the following operation on the material obtained by mixing and stirring in an oxygen-free environment with the moisture content of less than or equal to 0.1 ppm:
1) coating the metal lithium on the surface of the metal lithium, standing, and volatilizing the solvent completely to obtain the metal lithium covered with a film, wherein the film is the lithium cathode protective film; or
2) Coating the film on the surface of a copper foil, standing, obtaining a metal copper foil covered with a film after the solvent is completely volatilized, and stripping the film formed on the surface of the copper foil, wherein the film is the lithium negative electrode protective film; when the protective film is used, the protective film is used as an interlayer between the metal lithium negative electrode and the diaphragm, and has the function of protecting the metal lithium negative electrode.
In the step (1):
the concentration of the lithium salt in the ionic liquid is preferably 0.5mol/L to 2 mol/L.
In the step (2):
the mass ratio of the mixed solution to the inorganic nanoparticles is preferably 0.5-1.5: 1.
The ball milling time is preferably 20min to 200min, the ball milling speed is preferably 300r/min to 600r/min, and the ball-to-material ratio is preferably 25-30: 1.
In the step (3):
the mass ratio of the quasi-solid electrolyte to the lithiated Nafion polymer is preferably 0.2-5: 1.
Wherein, the lithiation-treated Nafion polymer solution is obtained by dissolving lithiation-treated Nafion polymer powder in an organic solvent, and the organic solvent is dimethyl sulfoxide or N-methylpyrrolidone; the mass fraction of the lithiated Nafion polymer powder in the lithiated Nafion polymer solution is preferably 5% to 30%.
Lithiated Nafion polymer powders can be prepared by methods known in the literature, for example:
adding lithium hydroxide solution into the Nafion solution, carrying out lithiation treatment until the pH value is 8, and drying in vacuum at 40-120 ℃ to obtain lithiated Nafion polymer powder.
In the steps (1) and (3):
the oxygen-free environment with the moisture content of less than or equal to 0.1ppm can be realized by adopting a glove box which is filled with inert gas and has the moisture content of less than or equal to 0.1 ppm.
A lithium metal secondary battery having a lithium negative electrode protective film according to the present invention.
Advantageous effects
1. The invention provides a lithium cathode protective film which can inhibit the growth of lithium dendrite, the Nafion polymer subjected to lithiation treatment enables the protective film to have high elastic modulus, and the inorganic nanoparticles improve the mechanical strength of the protective film, so that the growth of the lithium dendrite is hindered, and the cycle life of a lithium metal secondary battery is prolonged;
2. the invention provides a lithium cathode protective film, wherein lithium salt is dissolved in ionic liquid and uniformly coated on the surface of inorganic nanoparticles, so that the protective film has high ionic conductivity, and is beneficial to uniform deposition and falling of lithium ions, thereby inhibiting the generation of lithium dendrites; in addition, the lithiated Nafion polymer has single permeability to lithium ions, can inhibit other ions in the electrolyte from permeating through the protective film and generating side reactions with metal lithium, and is favorable for keeping lower internal resistance of the battery;
3. the invention provides a lithium cathode protective film which is good in thermal stability and can be applied to a high-temperature lithium metal secondary battery;
4. the invention provides a lithium cathode protective film which is simple in preparation method, green and environment-friendly and easy for mass production.
Drawings
Fig. 1 is a scanning electron microscope photograph of a lithium metal negative electrode with a protective film prepared in example 1.
Fig. 2 is a plot of Li | Li versus battery cycle performance as prepared in example 1.
Detailed Description
The invention is described in further detail below with reference to the figures and examples. However, the present invention is not limited to the following examples.
In the following examples, the analytical test methods used are as follows:
scanning Electron Microscope (SEM) testing: type HITACHI S-4800, Japan;
and (3) electrochemical performance testing: land, Wuhan.
Example 1
(1) In a glove box filled with Ar gas and with the moisture content of less than or equal to 0.1ppm, 1.4354g of lithium bistrifluoromethanesulfonimide are dissolved in 10ml of 1-ethyl-3-methylimidazole bistrifluoromethanesulfonimide salt, and are mixed and dissolved to obtain a mixed solution, wherein the concentration of the lithium bistrifluoromethanesulfonimide salt in the 1-ethyl-3-methylimidazole bistrifluoromethanesulfonimide salt is 0.5 mol/L;
(2) placing 0.5g of the mixed solution prepared in the step (1) and 1g of zirconium dioxide with the average particle size of 50nm into a ball milling tank, placing 37.5g of ceramic balls, mixing and ball milling by using a planetary ball mill, wherein the ball milling speed is 300r/min, the ball milling time is 30min, uniformly mixing, and then taking out to obtain a quasi-solid electrolyte;
(3) weighing 20g of Nafion solution, dissolving 0.1g of lithium hydroxide in 20g of deionized water to obtain a lithium hydroxide solution, dropwise adding the lithium hydroxide solution into the Nafion solution to carry out lithiation treatment until the pH value is 8, and then carrying out vacuum drying at 80 ℃ to obtain lithiated Nafion polymer powder; dissolving 100mg of lithiated Nafion polymer powder in 2ml of dimethyl sulfoxide, stirring for 2 hours, and uniformly mixing to obtain a lithiated Nafion polymer solution with the mass fraction of 5%;
adding 500mg of quasi-solid electrolyte into the lithiated Nafion polymer solution, and mixing and stirring at room temperature at 300r/min for 30 min; and then coating the mixed and stirred material on the surface of the lithium metal in a glove box which is filled with Ar gas and has the water content of less than or equal to 0.1ppm, standing for 48 hours at room temperature, and obtaining the lithium metal covered with a film after the dimethyl sulfoxide is completely volatilized, wherein the film is the lithium cathode protective film.
Li | Li pair batteries were assembled using the lithium metal with and without protective film prepared in this example as the negative electrodes, respectively, and the electrolytes were lithium bistrifluoromethanesulfonylimide (LiTFSI) and LiNO3Dissolving in a mixed solution of 1, 3-Dioxolane (DOL) and ethylene glycol dimethyl ether (DME) at a volume ratio of 1:1, a LiTFSI concentration of 0.6M, and LiNO3The concentration of (3) was 0.4M.
A lithium metal with a protective film prepared in this example was tested and the results were as follows:
(1) scanning Electron Microscope (SEM) testing:
as shown in fig. 1, SEM test showed that the protective film was uniformly dense, and the zirconium dioxide nanoparticles were uniformly dispersed in the lithiated Nafion polymer without agglomeration.
(2) Li | Li test for electrochemical performance of battery:
FIG. 2 shows blue data of Li | Li vs. battery under the test condition of 1mA/cm of charging and discharging current2And the charge-discharge capacity is 1mAh/cm2. As can be seen from fig. 2, after the comparative experiment of pure lithium metal is cycled for 120 hours, the overpotential for deposition and peeling of lithium metal is gradually increased, and the internal resistance is increased, because the electrolyte and the negative electrode of lithium metal are continuously reacted during the cycle, and the SEI film is continuously generated and gradually thickened, so that the internal resistance of the battery is increased. After 140h, the overpotential exceeds 200mV, and the internal resistance of the battery is overlarge. And the overpotential of the metal lithium with the protective film is still stabilized at 50mV after cycling for 260h, so that the battery is cycled stably.
Example 2
(1) In a glove box filled with Ar gas and with the moisture content of less than or equal to 0.1ppm, 3.7414 lithium bis (fluorosulfonyl) imide is dissolved in 10ml of N-methyl propyl pyrrole bis (trifluoromethanesulfonyl) imide salt, and the mixture is mixed and dissolved to obtain a mixed solution, wherein the concentration of the lithium bis (trifluoromethanesulfonyl) imide in the N-methyl propyl pyrrole bis (trifluoromethanesulfonyl) imide salt is 2 mol/L;
(2) placing 0.5g of the mixed solution prepared in the step (1) and 1g of silicon dioxide with the average particle size of 100nm into a ball milling tank, placing 37.5g of ceramic balls, mixing and ball milling by using a planetary ball mill, wherein the ball milling speed is 300r/min, the ball milling time is 30min, uniformly mixing, and then taking out to obtain a quasi-solid electrolyte;
(3) weighing 20g of Nafion solution, dissolving 0.1g of lithium hydroxide in 20g of deionized water to obtain a lithium hydroxide solution, dropwise adding the lithium hydroxide solution into the Nafion solution to carry out lithiation treatment until the pH value is 8, and then carrying out vacuum drying at 80 ℃ to obtain lithiated Nafion polymer powder; dissolving 600mg of lithiated Nafion polymer powder in 2ml of N-methyl pyrrolidone, stirring for 2 hours, and uniformly mixing to obtain a lithiated Nafion polymer solution with the mass fraction of 30%;
adding 120mg of quasi-solid electrolyte into the lithiated Nafion polymer solution, and mixing and stirring at room temperature at 300r/min for 30 min; and then coating the mixed and stirred material on the surface of the lithium metal in a glove box which is filled with Ar gas and has the water content of less than or equal to 0.1ppm, standing for 48 hours at room temperature, and obtaining the lithium metal covered with a film after the N-methylpyrrolidone is completely volatilized, wherein the film is the lithium cathode protective film.
Li | Li pair batteries were assembled using the lithium metal with and without protective film prepared in this example as the negative electrodes, respectively, and the electrolytes were lithium bistrifluoromethanesulfonylimide (LiTFSI) and LiNO3Dissolving in a mixed solution of 1, 3-Dioxolane (DOL) and ethylene glycol dimethyl ether (DME) at a volume ratio of 1:1, a LiTFSI concentration of 0.6M, and LiNO3The concentration of (3) was 0.4M.
A lithium metal with a protective film prepared in this example was tested and the results were as follows:
(1) scanning Electron Microscope (SEM) testing:
similar to fig. 1, SEM tests showed that the protective film was dense and flat, and the silica nanoparticles were uniformly dispersed in the lithiated Nafion polymer without agglomeration.
(2) Li | Li test for electrochemical performance of battery:
similar to FIG. 2, the blue test condition of Li | Li for the battery is a charge-discharge current of 1mA/cm2And the charge-discharge capacity is 1mAh/cm2. According to the test results, after the pure metal lithium comparative experiment is cycled for 100 hours, the overpotential is suddenly increased to 200mV, the internal resistance is overlarge, and the metal lithium with the protective film is still stable after being cycled for 250 hours, which shows that the reaction of the metal lithium and the electrolyte is avoided due to the protective film, the SEI film is stable, and the internal resistance of the battery is unchanged.
Example 3
(1) In a glove box filled with Ar gas and with the moisture content of less than or equal to 0.1ppm, 2.8708g of lithium bis (trifluoromethanesulfonyl) imide are dissolved in 10ml of N-methyl propyl pyrrole bis (trifluoromethanesulfonyl) imide salt, and the mixture is mixed and dissolved to obtain a mixed solution, wherein the concentration of the lithium bis (trifluoromethanesulfonyl) imide in the N-methyl propyl pyrrole bis (trifluoromethanesulfonyl) imide salt is 1 mol/L;
(2) placing 0.5g of the mixed solution prepared in the step (1) and 1g of titanium dioxide with the average particle size of 50nm into a ball milling tank, placing 37.5g of ceramic balls, mixing and ball milling by using a planetary ball mill, wherein the ball milling speed is 300r/min, the ball milling time is 200min, uniformly mixing, and then taking out to obtain a quasi-solid electrolyte;
(3) weighing 20g of Nafion solution, dissolving 0.1g of lithium hydroxide in 20g of deionized water to obtain a lithium hydroxide solution, dropwise adding the lithium hydroxide solution into the Nafion solution to carry out lithiation treatment until the pH value is 8, and then carrying out vacuum drying at 80 ℃ to obtain lithiated Nafion polymer powder; dissolving 100mg of lithiated Nafion polymer powder in 2ml of N-methylpyrrolidone, stirring for 2 hours, and uniformly mixing to obtain a lithiated Nafion polymer solution with the mass fraction of 5%;
adding 400mg of quasi-solid electrolyte into the lithiated Nafion polymer solution, and mixing and stirring at room temperature at 300r/min for 30 min; and then coating the mixed and stirred material on the surface of copper foil in a glove box filled with Ar gas and having the water content of less than or equal to 0.1ppm, standing for 48 hours at room temperature, obtaining the copper foil covered with a film after N-methylpyrrolidone is completely volatilized, and stripping the film formed on the copper foil, wherein the film is the lithium cathode protective film and is used as an interlayer between a metal lithium cathode and a diaphragm when in use.
The lithium sulfur battery is assembled by using the metal lithium with the protective film and the metal lithium without the protective film prepared in the embodiment as negative electrodes respectively, a protective film interlayer is arranged between the metal lithium and a diaphragm, the positive electrode is an active carbon/S composite material electrode piece, the diaphragm is Celgard 2325, and the electrolyte is lithium bis (trifluoromethane) sulfonimide (LiTFSI) and LiNO3Dissolving in a mixed solution of 1, 3-Dioxolane (DOL) and ethylene glycol dimethyl ether (DME) at a volume ratio of 1:1, a LiTFSI concentration of 0.6M, and LiNO3The concentration of (3) was 0.4M.
A lithium metal with a protective film prepared in this example was tested and the results were as follows:
(1) scanning Electron Microscope (SEM) testing:
similar to fig. 1, SEM tests showed that the protective film was dense and flat, and the titanium dioxide nanoparticles were uniformly dispersed in the lithiated Nafion polymer without agglomeration.
(2) Testing the electrochemical performance of the lithium-sulfur battery:
the blue test conditions of the lithium-sulfur battery are that the charge-discharge voltage is 1.7V-3V, and the charge-discharge multiplying power is as follows: 2C, charge-discharge temperature: at 30 ℃. According to the cycle performance curve of the lithium-sulfur battery, the capacity of the lithium-sulfur battery with the protective film is 715mAh/g after the lithium-sulfur battery is cycled for 300 weeks at the room temperature under the 2C multiplying power, and the capacity of the lithium-sulfur battery without the protective film is 619mAh/g after the lithium-sulfur battery is cycled for 50 circles.
Example 4
(1) In a glove box filled with Ar gas and with the moisture content of less than or equal to 0.1ppm, 2.8708g of lithium bis (trifluoromethanesulfonyl) imide are dissolved in 10ml of N-methyl propyl pyrrole bis (trifluoromethanesulfonyl) imide salt, and the mixture is mixed and dissolved to obtain a mixed solution, wherein the concentration of the lithium bis (trifluoromethanesulfonyl) imide in the N-methyl propyl pyrrole bis (trifluoromethanesulfonyl) imide salt is 1 mol/L;
(2) placing 0.5g of the mixed solution prepared in the step (1) and 1g of aluminum oxide with the average particle size of 100nm into a ball milling tank, placing 37.5g of ceramic balls, mixing and ball milling by using a planetary ball mill, wherein the ball milling speed is 300r/min, the ball milling time is 200min, uniformly mixing, and then taking out to obtain a quasi-solid electrolyte;
(3) weighing 20g of Nafion solution, dissolving 0.1g of lithium hydroxide in 20g of deionized water to obtain a lithium hydroxide solution, dropwise adding the lithium hydroxide solution into the Nafion solution to carry out lithiation treatment until the pH value is 8, and then carrying out vacuum drying at 80 ℃ to obtain lithiated Nafion polymer powder; dissolving 100mg of lithiated Nafion polymer powder in 2ml of N-methylpyrrolidone, stirring for 2 hours, and uniformly mixing to obtain a lithiated Nafion polymer solution with the mass fraction of 5%;
adding 400mg of quasi-solid electrolyte into the lithiated Nafion polymer solution, and mixing and stirring at room temperature at 300r/min for 30 min; and then coating the mixed and stirred material on the surface of a copper foil, standing for 48h at room temperature, obtaining the copper foil covered with a film after N-methylpyrrolidone is completely volatilized, and stripping the film formed on the copper foil, wherein the film is the lithium cathode protective film and is used as an interlayer between a metal lithium cathode and a diaphragm when in use.
The lithium-air battery is assembled by taking the metal lithium with the protective film and the metal lithium without the protective film prepared in the embodiment as negative electrodes respectively, a protective film interlayer is arranged between the metal lithium and a diaphragm, the positive electrode is an active carbon material electrode piece loaded by ruthenium dioxide, the diaphragm is Glass fiber, the electrolyte is prepared by dissolving bis (trifluoromethane) sulfonyl imide Lithium (LiTFSI) in triethylene glycol dimethyl ether (TEGDME), and the concentration of the LiTFSI is 1M.
A lithium metal with a protective film prepared in this example was tested and the results were as follows:
(1) scanning Electron Microscope (SEM) testing:
similar to fig. 1, SEM tests showed that the protective film was dense and flat, and the alumina nanoparticles were uniformly dispersed in the lithiated Nafion polymer without agglomeration.
(2) Testing the electrochemical performance of the lithium-air battery:
the blue test conditions of the lithium-sulfur battery are capacity-limited charging and discharging: 1000mAh/g, charge-discharge voltage of 2.2V-4.5V, charge-discharge current: 0.5mA/cm2The charge and discharge temperature: at 30 ℃. From the cycle performance curve of the lithium air battery, the lithium air battery with the protective film is cycled for more than 200 weeks and the capacity is kept stable, while the lithium air battery without the protective film is cycled for 90 circles and then the charge-discharge capacity is lower than 1000 mAh/g. When the battery is disassembled, the pulverization of the lithium cathode without the protective film is found to be serious, so that the capacity of the battery is reduced, because the lithium cathode without the protective film is easy to react with water and oxygen in the electrolyte to generate lithium hydroxide and lithium oxide, and the lithium cathode with the protective film still keeps blocky and has no pulverization phenomenon.
Although the invention has been described in detail hereinabove with respect to a general description and specific embodiments thereof, it will be apparent to those skilled in the art that modifications or improvements may be made thereto based on the invention. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.
Claims (2)
1. A lithium negative electrode protective film characterized in that: the protective film is composed of lithium salt, ionic liquid, inorganic nanoparticles and a Nafion polymer subjected to lithiation treatment; the lithium salt-containing ionic liquid is adsorbed on the surface of the inorganic nano-particles and is uniformly dispersed in the lithiated Nafion polymer; the inorganic nanoparticles are inorganic oxide nanoparticles;
the lithium salt is more than one of lithium bis (oxalate) borate, lithium difluoro (oxalate) borate, lithium trifluoromethanesulfonate, lithium bis (trifluoromethanesulfonyl) imide, lithium bis (fluorosulfonyl) imide, lithium perfluoroethylsulfonyl imide and lithium perfluoroalkyl sulfonyl methide;
the ionic liquid is more than one of 1-ethyl-3-methylimidazole bistrifluoromethylsulfonyl imide salt, 1-propyl-3-methylimidazole bistrifluoromethylsulfonyl imide salt, 1-butyl-3-methylimidazole bistrifluoromethylsulfonyl imide salt, N-methyl, propyl pyrrole bistrifluoromethylsulfonyl imide salt, N-methyl, butyl pyrrole bistrifluoromethylsulfonyl imide salt, N-methyl, propyl pyrrole bistrifluoromethylsulfonyl imide salt and N-methyl, butyl pyrrole bistrifluoromethylsulfonyl imide salt;
the inorganic nanoparticles are silicon dioxide nanoparticles, zirconium dioxide nanoparticles, titanium dioxide nanoparticles or aluminum oxide nanoparticles;
the thickness of the protective film is 0.1-100 mu m;
the preparation method of the lithium negative electrode protective film comprises the following steps:
(1) preparing a mixed solution of lithium salt and ionic liquid in an oxygen-free environment with the moisture content of less than or equal to 0.1 ppm;
(2) placing the mixed solution and inorganic nanoparticles in a ball milling tank, sealing, and performing ball milling and uniform mixing to obtain a quasi-solid electrolyte;
(3) mixing and stirring a quasi-solid electrolyte and a Nafion polymer solution subjected to lithiation treatment, and carrying out the following operation on a material obtained by mixing and stirring in an oxygen-free environment with the moisture content of less than or equal to 0.1 ppm:
1) coating the lithium metal surface with the solution, standing, and volatilizing the solvent completely to obtain the lithium metal covered with a film, wherein the film is the lithium cathode protective film; or
2) Coating the film on the surface of a copper foil, standing, obtaining a metal copper foil covered with a film after the solvent is completely volatilized, and stripping the film formed on the surface of the copper foil, wherein the film is the lithium negative electrode protective film;
the concentration of the lithium salt in the ionic liquid is 0.5-2 mol/L;
the mass ratio of the mixed solution to the inorganic nanoparticles is 0.5-1.5: 1;
the mass ratio of the quasi-solid electrolyte to the lithiated Nafion polymer is 0.2-5: 1;
the mass fraction of the Nafion polymer powder subjected to lithiation treatment in the Nafion polymer solution subjected to lithiation treatment is 5-30%;
the ball milling time is 20-200 min, the ball milling speed is 300-600 r/min, and the ball material ratio is 25-30: 1;
the lithiation-treated Nafion polymer solution is obtained by dissolving lithiation-treated Nafion polymer powder in dimethyl sulfoxide or N-methylpyrrolidone;
lithiated Nafion polymer powder was prepared by the following method:
adding a lithium hydroxide solution into the Nafion solution, carrying out lithiation treatment until the pH value is 8, and carrying out vacuum drying at 40-120 ℃ to obtain lithiated Nafion polymer powder;
the oxygen-free environment with the moisture content of less than or equal to 0.1ppm is realized by adopting a glove box which is filled with inert gas and has the moisture content of less than or equal to 0.1 ppm.
2. A lithium metal secondary battery characterized in that: the lithium metal secondary battery has the lithium negative electrode protective film according to claim 1.
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