CN113943012A - Ultra-long lithium fluoride nanofiber and preparation method and application thereof - Google Patents

Ultra-long lithium fluoride nanofiber and preparation method and application thereof Download PDF

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CN113943012A
CN113943012A CN202111110708.9A CN202111110708A CN113943012A CN 113943012 A CN113943012 A CN 113943012A CN 202111110708 A CN202111110708 A CN 202111110708A CN 113943012 A CN113943012 A CN 113943012A
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lithium fluoride
lithium
nanofiber
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long
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安琴友
谭双双
麦立强
王昊
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Wuhan University of Technology WUT
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    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
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Abstract

The invention provides an ultralong lithium fluoride nanofiber and a preparation method and application thereof, wherein the ultralong lithium fluoride nanofiber comprises a plurality of nanofibers, the structure of the nanofiber is at least one of a linear type, a sawtooth type and a branch type, the diameter of the nanofiber is within the range of 0.3-1 mu m, and the length of the nanofiber is within the range of 0.5-1 mm. When the ultra-long lithium fluoride nanofiber prepared by the invention is used as the intermediate layer of the lithium metal battery, the lithium fluoride content of the lithium metal electrolyte interface can be improved, and the lithium-lithium fluoride interface with high lithium ion adsorption energy and large migration barrier is formed, so that the lithium metal is uniformly and compactly deposited and dissolved, the formation of dendritic crystals is avoided, and the cycle life, rate capability and safety of the lithium metal battery are greatly improved.

Description

Ultra-long lithium fluoride nanofiber and preparation method and application thereof
Technical Field
The invention relates to the technical field of nano materials and electrochemistry, in particular to an ultralong lithium fluoride nanofiber and a preparation method and application thereof.
Background
The increasing consumption of fossil energy and the increasing weight of environmental pollution place ever higher demands on the development and storage of renewable energy. The traditional lithium ion secondary battery has been widely used in the aspect of renewable energy storage due to the advantages of high capacity, long service life, no memory effect and the like. However, the energy density of the lithium ion battery still cannot meet the use requirements of emerging industrial equipment such as electric automobiles and unmanned aerial vehicles in the future. The lithium metal battery used has the highest theoretical capacity (3861mAh g) compared to the lithium ion battery-1) And lowest redox potential (-3.04V vs Li)+Li) lithium metal negative electrode instead of conventional graphite negative electrode (372mAh g)-1) The energy density of the lithium battery can be greatly improved. The lithium metal negative electrode mainly undergoes metal deposition/dissolution reaction during charge and discharge, and an uneven current collector surface electric field and an interfacial ion field under a large current cause uneven nucleation of lithium and induce further lithium dendrite growth. Lithium dendrites easily pierce the separator, causing short circuits and thermal runaway of the battery, and further causing combustion and even explosion. Therefore, there is still a great safety risk in the commercial application of the lithium metal battery. At the same time, the presence of lithium dendrites also leads to the formation of "dead lithium" in the battery cycle, which continues to decrease the coulombic efficiency and the cycle life is not high.
Lithium fluoride as a material which is stable in air, light in weight and high in ionic conductivity has wide application prospects in the aspects of lithium metal battery interlayers, organic-inorganic solid electrolytes, all-inorganic solid electrolytes and the like. They can effectively limit the growth of lithium dendrites and improve the cycle life and safety of lithium metal batteries. However, the crystal structure of lithium fluoride is cubic, and the appearance of a conventional powder sample is square block-shaped, so that the lithium fluoride is difficult to prepare into a lithium metal battery interlayer film; meanwhile, the lithium fluoride square block cannot form a continuous ion-conducting interface with a polymer when used as a framework material of an organic-inorganic solid electrolyte, resulting in low electrical conductivity.
In contrast, lithium fluoride nanowires have a high aspect ratio, continuous ion conduction path, and are advantageous structures as an interlayer and a framework of an organic-inorganic solid electrolyte. Lithium fluoride nanowire materials have not been reported at present.
Disclosure of Invention
In view of the above, the invention provides an ultralong lithium fluoride nanofiber, and a preparation method and an application thereof, so as to solve the problems of low conductivity and poor electrochemical performance caused by a blocky structure when the existing lithium fluoride is applied to the field of lithium metal batteries.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
the super-long lithium fluoride nanofiber comprises a plurality of nanofibers, and the structure of the nanofibers is at least one of linear type, sawtooth type and branch type.
Optionally, the diameter of the nanofibers is in the range of 0.3 to 1 μm, and the length of the nanofibers is in the range of 0.5 to 1 mm.
The second purpose of the invention is to provide a preparation method of the ultralong lithium fluoride nanofiber, which comprises the following steps:
s1, preparing a lithium fluoride solution;
and S2, freezing the lithium fluoride solution into a solid, placing the solid in a freeze dryer, and drying in vacuum until ice is completely sublimated to obtain the ultralong lithium fluoride nanofiber material.
Alternatively, in step S1, the preparing lithium fluoride solution includes the steps of: dissolving lithium hydroxide monohydrate powder in deionized water, stirring uniformly, and then dropwise adding hydrofluoric acid to form the lithium fluoride solution, or dissolving anhydrous lithium fluoride powder in deionized water, and stirring uniformly to form the lithium fluoride solution.
Optionally, when the lithium fluoride solution is formed by dissolving or dissolving the lithium hydroxide monohydrate powder in deionized water, and dropping hydrofluoric acid after uniform stirring, the mass ratio of the deionized water to the lithium hydroxide monohydrate powder is greater than 228, and the molar ratio of the hydrofluoric acid to the lithium hydroxide monohydrate powder is in a range from 1 to 5.
Optionally, when the anhydrous lithium fluoride powder is dissolved in deionized water and uniformly stirred to form the lithium fluoride solution, the mass ratio of the deionized water to the lithium fluoride powder is greater than 371.
Optionally, in step S2, the frozen temperature is less than or equal to-40 ℃.
Optionally, in step S2, the vacuum degree of the vacuum drying is in the range of 5Pa to 10 Pa.
The third purpose of the invention is to provide an application of the ultra-long lithium fluoride nano-fiber in the field of lithium metal batteries.
Optionally, the ultra-long lithium fluoride nanofiber is applied to a diaphragm modification layer, an intermediate layer, an electrode electrolyte interface layer, a polymer-inorganic solid electrolyte and an all-inorganic solid electrolyte of the lithium metal battery.
Compared with the prior art, the ultralong lithium fluoride nanofiber and the preparation method and application thereof provided by the invention have the following advantages:
(1) when the ultra-long lithium fluoride nanofiber provided by the invention is used as the intermediate layer of the lithium metal battery, the lithium fluoride content of a lithium metal electrolyte interface can be improved, a lithium-lithium fluoride interface with high lithium ion adsorption energy and a large migration barrier is formed, lithium metal is uniformly and compactly deposited and dissolved, dendritic crystals are avoided, and the cycle life, rate capability and safety of the lithium metal battery are greatly improved.
(2) The single crystal ultra-long lithium fluoride nanofiber material prepared by the simple freeze drying method has the advantages of low raw material cost, simple and environment-friendly process, high purity of the prepared material, good dispersibility and large-scale application potential.
Drawings
In order to more clearly illustrate the technical solutions of the present invention or the prior art, the drawings needed for the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and those skilled in the art can also obtain other drawings according to the drawings without creative efforts.
FIG. 1 is an X-ray diffraction pattern of an ultralong lithium fluoride nanofiber according to an embodiment of the present invention;
FIG. 2 is a scanning electron micrograph and an optical photograph of an ultra-long lithium fluoride nanofiber according to an embodiment of the present invention;
FIG. 3 is a transmission electron micrograph and a selected area electron diffraction of the ultra-long lithium fluoride nanofiber according to the embodiment of the present invention;
FIG. 4 is a schematic diagram of the formation of an ultra-long lithium fluoride nanofiber according to an embodiment of the present invention;
FIG. 5 is a thermogravimetric curve, an optical photograph and a scanning electron microscope image of an intermediate layer of ultralong lithium fluoride nanofibers according to an embodiment of the present invention;
FIG. 6 is a graph of rate performance of an ultra-long lithium fluoride nanofiber interlayer as applied to a symmetric lithium metal battery in accordance with an embodiment of the present invention;
FIG. 7 shows that the ultra-long lithium fluoride nanofiber interlayer of the embodiment of the invention is applied to a symmetric lithium metal battery at 4mA cm-2And 4mAh cm-2Cycle life plot under conditions;
FIG. 8 shows that the ultra-long lithium fluoride nanofiber interlayer of the embodiment of the invention is applied to a symmetric lithium metal battery at 4mA cm-2In-situ optical photographs at current density;
FIG. 9 is a cycle life diagram of a ternary lithium metal battery with the ultra-long lithium fluoride nanofiber interlayer applied thereto at a magnification of 0.5C, according to an embodiment of the present invention;
FIG. 10 is a graph of rate performance of an ultra-long lithium fluoride nanofiber interlayer as applied to a ternary lithium metal battery in accordance with an embodiment of the present invention;
FIG. 11 is a graph of cycle life at 0.1C rate for an ultra-long lithium fluoride nanofiber interlayer as described in an embodiment of the present invention applied to a lithium sulfur battery;
FIG. 12 is a graph of rate performance of an ultra-long lithium fluoride nanofiber interlayer as applied to a lithium sulfur battery in accordance with an embodiment of the present invention;
FIG. 13 is a scanning electron microscope image of a polyoxyethylene solid electrolyte with ultra-long lithium fluoride nano-fibers as inorganic frameworks according to an embodiment of the invention;
fig. 14 is a temperature-varying impedance graph and an arrhenius curve of a symmetrical solid-state battery assembled by a polyoxyethylene solid-state electrolyte with ultra-long lithium fluoride nanofibers as inorganic frameworks according to an embodiment of the present invention.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.
It should be noted that in the description of the embodiments herein, the description of the term "some specific embodiments" means that a specific feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. Throughout this specification, the schematic representations of the terms used above do not necessarily refer to the same implementation or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
The term "in.
The embodiment of the invention provides an ultralong lithium fluoride nanofiber material which comprises a plurality of nanofibers, wherein the structure of the nanofibers is at least one of linear type, sawtooth type and branch type.
Further, the diameter of the nanofibers is in the range of 0.3 to 1 μm, and the length of the nanofibers is in the range of 0.5 to 1 mm.
The ultra-long lithium fluoride nanofiber provided by the invention is in a cotton shape, has a high aspect ratio and a continuous ion conduction path, and can improve the lithium fluoride content of a lithium metal electrolyte interface when being used as a lithium metal battery interlayer, so that a lithium-lithium fluoride interface with high lithium ion adsorption energy and a large migration barrier is formed, lithium metal is uniformly and compactly deposited and dissolved, dendritic crystals are prevented from being formed, and the cycle life, rate capability and safety of the lithium metal battery are greatly improved.
Referring to fig. 4, another embodiment of the present invention provides a method for preparing the ultra-long lithium fluoride nanofiber, including the following steps:
s1, preparing a lithium fluoride solution;
and S2, freezing the lithium fluoride solution into a solid, placing the solid in a freeze dryer, and drying in vacuum until ice is completely sublimated to obtain the ultralong lithium fluoride nanofiber material.
Fig. 4 is a schematic diagram of the formation of the ultra-long lithium fluoride nanofiber, and the formation mechanism mainly comprises: in the early stage of freeze-drying, sublimation of ice induces nucleation of a large amount of lithium fluoride; then, lithium fluoride continuously grows at the crystal nucleus along the ice sublimation direction, and a nanofiber structure is gradually formed.
Specifically, in step S1, there are various preparation methods for the lithium fluoride solution, and in the present embodiment, the following 2 preparation methods are preferred:
the method comprises the following steps: dissolving monohydrate lithium hydroxide powder into deionized water, stirring uniformly, and then dropwise adding hydrofluoric acid to form a lithium fluoride solution. Wherein the mass ratio of the deionized water to the lithium hydroxide monohydrate powder is more than 228, and the molar ratio of the hydrofluoric acid to the lithium hydroxide monohydrate powder is in the range of 1 to 5.
The second method comprises the following steps: dissolving anhydrous lithium fluoride powder in deionized water, and uniformly stirring to form a lithium fluoride solution; wherein the mass ratio of the deionized water to the lithium fluoride powder is more than 371.
The single crystal ultra-long lithium fluoride nanofiber material is prepared by a simple freeze-drying method, the raw materials are low in price, the process is simple and environment-friendly, the adopted freeze-drying method has low requirements on equipment, and the prepared material is high in purity and good in dispersity and has the potential of large-scale application.
Specifically, in step S2, the lithium fluoride solution is frozen at a temperature of-40 ℃ or lower, and the degree of vacuum drying in the freeze dryer is in the range of 5Pa to 10 Pa.
The invention further provides an application of the ultra-long lithium fluoride nanofiber in the field of lithium metal batteries.
In particular, the ultra-long lithium fluoride nanofibers can be applied to separator modification layers, intermediate layers, electrode electrolyte interface layers, polymer-inorganic solid electrolytes, and all-inorganic solid electrolytes of lithium metal batteries.
The lithium fluoride nanofiber is filtered into a flexible film which can be used as a middle layer of a lithium metal battery, so that the growth of lithium dendrites is inhibited, and the safety of the battery is improved; meanwhile, the lithium fluoride nano-fiber can be used as a framework material of a polymer-electrodeless solid electrolyte and an all-inorganic solid electrolyte, so that high ionic conductivity can be obtained, and the rate capability of the solid battery can be improved.
On the basis of the above embodiments, the present invention is further illustrated by the following specific examples of the preparation method and application of the ultra-long lithium fluoride nanofiber. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. The following examples are examples of experimental procedures not specified under specific conditions, generally according to the conditions recommended by the manufacturer. Unless otherwise specified, percentages and parts are by mass.
Example 1
The embodiment provides a preparation method of an ultralong lithium fluoride nanofiber, which comprises the following steps:
1) weighing 503.56mg of monohydrate lithium hydroxide powder, dissolving in 200mL of deionized water, and stirring at normal temperature for 15 minutes; then slowly dripping 600 mu L of hydrofluoric acid (the concentration is more than or equal to 40 percent), stirring at normal temperature until the solution is clear, and obtaining a lithium fluoride solution;
2) and (3) freezing the lithium fluoride solution into a solid, quickly transferring the solid into a freeze dryer, keeping the vacuum degree at 5-10Pa, and drying until ice is completely sublimated to obtain the ultralong lithium fluoride nanofiber material.
The ultra-long lithium fluoride nanofibers prepared in example 1 were characterized by an X-ray diffractometer (XRD), a Scanning Electron Microscope (SEM), a Transmission Electron Microscope (TEM), etc., and the result graphs shown in fig. 1 to 3 were obtained.
As can be seen from the X-ray diffraction pattern shown in FIG. 1, the ultralong lithium fluoride nanofiber material is orthorhombic cubic phase (JCPDS card number 01-089-3610).
As can be seen from the scanning electron microscope image and the optical photograph shown in FIG. 2, the overall appearance of the ultra-long lithium fluoride nanofiber is cotton-shaped, the nanofiber material is uniformly dispersed, the appearance is uniform, and the length is 0.5-5 mm.
As can be seen from the transmission electron microscope image and the selected area electron diffraction pattern (SAED) shown in FIG. 3, the growth directions of the "sawtooth" and "branched" lithium fluoride fibers are the [111] crystal direction, and the nanometer "branches" are formed by the growth of the "sawtooth" along the [1] crystal direction; the growth direction of the common linear lithium fluoride nano fiber is the [220] crystal direction, and the lithium fluoride nano fibers with various shapes are all single crystal materials.
The ultralong lithium fluoride nanofiber material prepared in example 1 is used as an interlayer of a lithium metal battery, and the preparation method is as follows: weighing ultralong lithium fluoride nano fibers with different masses, dispersing the ultralong lithium fluoride nano fibers in 20mL of alcohol, and stirring the mixture for 20min at normal temperature to form a uniform mixed solution; and then placing the mixed solution on a glass fiber diaphragm with the diameter of 4cm for vacuum filtration to obtain lithium fluoride nanofiber interlayers with different thicknesses. The lithium fluoride nanofiber interlayers were tested and the results are shown in figure 5.
As shown in fig. 5, thermogravimetric analysis (TG) shows that the lithium fluoride nanofiber interlayer has good thermal stability, does not undergo thermal decomposition below 800 ℃ and in an air environment, and can meet the use requirements of a high-temperature lithium metal battery; meanwhile, under the suction filtration quantity of 10mg, 30mg and 50mg, the thickness is respectively 40 μm, 120 μm and 200 μm, namely the size is controllable.
The lithium fluoride nanofiber interlayer is applied to various lithium metal batteries, wherein the specific assembling method of the symmetric lithium metal battery is as follows: the positive electrode and the negative electrode of the symmetric lithium metal battery are lithium metal foils with the diameter of 16cm, 1M lithium bistrifluoromethanesulfonimide (LiTFSI) serving as electrolyte is dissolved in 1, 3-Dioxolane (DOL) and ethylene glycol dimethyl ether (DME) in a volume ratio of 1:1, and 0.2M lithium nitrate serving as an additive is added; and the intermediate layer of the ultralong lithium fluoride nano fiber with the diameter of 17cm is used as a diaphragm, and CR 2025 type stainless steel is used as a battery shell to assemble the button cell.
The assembly method of the ternary lithium metal battery is as follows: the positive plate of the ternary lithium metal battery is made of 94.5 wt% of nickel-rich layered ternary material (LiNi)0.8Co0.1Mn0.1O2) Active material, 5.5 wt% polyvinylidene fluoride (PVDF) binder and conductive additive, and the area load is 8.3mg cm-2(ii) a LiPF with electrolyte of 1M6Dissolving in 1:1 volume ratio of Ethylene Carbonate (EC) and diethyl carbonate (DEC), and adding 5% of fluoroethylene carbonate (FEC) as additive; the diaphragm is a polypropylene diaphragm. During assembly, the ultra-long lithium fluoride nanofiber interlayer is placed between the polypropylene diaphragm and the lithium metal negative electrode.
The lithium sulfur battery is assembled as follows: the positive electrode of the lithium-sulfur battery is a reduced graphene oxide composite sulfur positive electrode, does not contain a bonding agent and a conductive additive, has the sulfur content of 70wt percent and the area load of 10.7mg cm-2(ii) a The electrolyte is consistent with the symmetric lithium metal battery; the diaphragm is a polypropylene diaphragm. During assembly, the intermediate layer of the ultralong lithium fluoride nanofiber is placed between the polypropylene diaphragm and the lithium metal negative electrode.
Electrochemical performance tests were performed on the assembled symmetric lithium metal batteries, ternary lithium metal batteries, and lithium sulfur batteries, and the test results are shown in fig. 6 to 14.
FIG. 6 is a graph of rate capability of a symmetric lithium metal battery, and it can be seen from FIG. 6 that the symmetric lithium metal battery assembled by the ultra-long lithium fluoride nanofiber interlayer is at 4mAh cm-2Can be 12mA cm at the specific capacity of-2The charge and discharge were stable at the current density of (1), no short circuit occurred, and the polarization voltage was 125 mV.
FIG. 7 shows a symmetric lithium metal battery at 4mA cm-2And 4mAh cm-2Cycle life under the conditions, as can be seen from FIG. 7, the symmetric lithium metal battery is at 4mA cm-2Current density of 4mAh cm-2Can stably circulate for 800 hours under the specific capacity of (1), and the polarization voltage is kept at 60 mV.
FIG. 8 shows a symmetric lithium metal cell at 4mA cm-2In-situ optical photographs under current density, as can be seen from fig. 8, the lithium metal negative electrode covered by the lithium fluoride nanofiber interlayer has uniform and compact lithium deposition behavior, and no obvious dendritic crystal growth phenomenon exists.
FIG. 9 is a cycle life diagram of a ternary lithium metal battery at 0.5C rate, and from FIG. 9, it can be seen that lithium fluoride nano-scaleThe first discharge specific capacity of the ternary lithium metal battery assembled by the fiber interlayer is 180mAh g under the multiplying power of 0.5C-1And after 200 times of circulation, the capacity retention rate is 85 percent.
FIG. 10 is a graph of rate performance of a ternary lithium metal battery, and as can be seen from FIG. 10, the ternary lithium metal battery was operated at 5C rate (7.8mA cm)-2) Under the action of the slow release, 98.6mAh g can be released-1The specific capacity of (A).
FIG. 11 is a cycle life diagram of a lithium-sulfur battery at a rate of 0.1C, and it can be seen from FIG. 11 that the specific first discharge capacity is 828.5mAh g-1And the capacity retention rate is 83.8 percent after the circulation for 120 times.
FIG. 12 is a graph of rate performance of a lithium sulfur battery, and as can be seen from FIG. 12, the lithium sulfur battery has a 1C rate (17.9mA cm)-2) At last, 528mAh g can still be released-1High specific capacity of (2).
The test result shows that the lithium fluoride nanofiber interlayer can enable lithium metal to deposit and grow uniformly and compactly, the formation of dendrites is avoided, the cycle life and the rate capability of the lithium battery are greatly improved, and the lithium fluoride nanofiber interlayer is a potential application material of the lithium battery interlayer.
The lithium fluoride nanofiber prepared in example 1 was used as an organic-inorganic solid electrolyte of a solid lithium battery, and the preparation method was as follows: weighing 80mg of ultralong lithium fluoride nanofiber material, dispersing in 20mL of acetonitrile, stirring for 20min to uniformly disperse the lithium fluoride nanofibers, then adding 400mg of polyethylene oxide (PEO) and 320mg of LiTFSI salt into the solution, placing the solution in an argon glove box, stirring for 6h at 55 ℃, standing the mixed solution in a watch glass, and drying in vacuum for 12h at 80 ℃ to obtain the film inorganic solid electrolyte. The inorganic solid electrolyte was characterized to obtain a result graph as shown in fig. 13.
Fig. 13 is a scanning electron microscope image of a polyethylene oxide solid electrolyte with ultra-long lithium fluoride nanofibers as an inorganic skeleton, and it can be seen from fig. 13 that the lithium fluoride nanofibers are uniformly dispersed in a PEO matrix, and the thickness of the solid electrolyte is 148 μm.
A symmetrical solid state battery was assembled by using stainless steel sheets having a diameter of 16.2mm as positive and negative electrodes and a polyethylene oxide solid state electrolyte, and the symmetrical solid state battery was tested to obtain a result graph as shown in fig. 14.
As can be seen from fig. 14, the impedance spectrum (EIS) of the symmetric solid-state battery showed an impedance value of 12.3 Ω at 20 ℃ and an ionic conductivity of 5.8 × 10-4S cm-1。
The above results show that: the ultra-long lithium fluoride nanofiber serving as an inorganic framework of the polymer solid electrolyte can greatly improve the ionic conductivity, and is a potential inorganic framework material of the polymer solid electrolyte of the lithium battery.
Example 2
This example provides a method for preparing a super-long lithium fluoride nanofiber, which is different from example 1 in that:
in the step 1), 877.19mg of monohydrate lithium hydroxide powder is weighed and dissolved in 200mL of deionized water, and the mixture is stirred for 15min at normal temperature; slowly adding 930 mu L of hydrofluoric acid (the concentration is more than or equal to 40 percent) dropwise, and stirring at normal temperature until the solution is clear to obtain a lithium fluoride solution;
the remaining steps and parameters were the same as in example 1.
The ultra-long lithium fluoride nanofiber material prepared in example 2 was characterized and found to be composed of ordinary linear, "saw-tooth" and "branched" nanofibers, with a diameter of 0.3-1 μm and a length of 0.5-5 mm.
The lithium fluoride nano-fiber material prepared in example 2 is used as a lithium battery intermediate layer, and the assembled symmetrical lithium metal battery is 1mA cm-2Current density of 1mAh cm-2The specific capacity of the composite material can be stably circulated for 1600 hours, and the polarization voltage is kept at 30 mV.
Example 3
This example provides a method for preparing a super-long lithium fluoride nanofiber, which is different from example 1 in that:
in the step 1), 877.19mg of monohydrate lithium hydroxide powder is weighed and dissolved in 400mL of deionized water, and the mixture is stirred for 15min at normal temperature; then slowly dropwise adding 4.6mL of hydrofluoric acid (the concentration is more than or equal to 40%), stirring at normal temperature until the solution is clear, and obtaining a lithium fluoride solution;
the remaining steps and parameters were the same as in example 1.
The ultralong lithium fluoride nanofiber material prepared in example 3 was characterized and found to be composed of ordinary straight, "saw-tooth" and "branched" nanofibers, with a diameter of 0.3-1 μm and a length of 0.5-5 mm.
The ultra-long lithium fluoride nanofiber material prepared in example 3 is used as a lithium battery interlayer, and the first discharge specific capacity of the assembled ternary lithium metal battery is 179mAh g under the multiplying power of 0.5C-1After 200 cycles, the capacity retention rate was 84.3%.
Example 4
This example provides a method for preparing a super-long lithium fluoride nanofiber, which is different from example 1 in that:
in the step 1), 500mg of anhydrous lithium fluoride powder is weighed and dissolved in 185.5mL of deionized water, and the solution is stirred at normal temperature until the solution is clear, so that a lithium fluoride solution is obtained;
the remaining steps and parameters were the same as in example 1.
The ultra-long lithium fluoride nanofiber material prepared in example 4 was characterized and found to be composed of ordinary straight, "saw-tooth" and "branched" nanofibers, with a diameter of 0.3-1 μm and a length of 0.5-5 mm.
The ultra-long lithium fluoride nanofiber material prepared in example 4 is used as a lithium battery middle layer, and the first discharge specific capacity of the assembled lithium-sulfur battery is 815.5mAh g at the multiplying power of 0.1C-1And after 100 times of circulation, the capacity retention rate is 85 percent.
Example 5
This example provides a method for preparing a super-long lithium fluoride nanofiber, which is different from example 1 in that:
in the step 1), 1g of anhydrous lithium fluoride powder is weighed and dissolved in 500mL of deionized water, and the solution is stirred at normal temperature until the solution is clear, so that a lithium fluoride solution is obtained;
the remaining steps and parameters were the same as in example 1.
The ultra-long lithium fluoride nanofiber material prepared in example 5 was characterized and found to be composed of ordinary straight, "saw-tooth" and "branched" nanofibers, with a diameter of 0.3-1 μm and a length of 0.5-5 mm.
The ultra-long lithium fluoride nanofiber material prepared in example 5 was used as an inorganic skeleton of a PEO solid electrolyte, and the impedance spectrum of the assembled solid-state battery was 13 Ω at 20 ℃ and the ionic conductivity was 5.5 × 10-4S cm-1。
In conclusion, the first specific discharge capacity of the ternary lithium metal battery assembled by the ultralong lithium fluoride nanofibers prepared by the invention is 180mAh g at the multiplying power of 0.5C-1After 200 times of circulation, the capacity retention rate is 85%; and at 5C magnification (7.8mA cm)-2) Under the condition of no pollution, the product can still release 98.6mAh g-1The specific capacity of (A). The first discharge specific capacity of the assembled lithium-sulfur battery is 828.5mAh g under the multiplying power of 0.1C-1After 120 times of circulation, the capacity retention rate is 83.8%; at 1C magnification (17.9mA cm)-2) At the same time, 528mAh g can be released-1High specific capacity of (2). When the material is used as an inorganic framework material of an organic-inorganic solid electrolyte, the ionic conductivity of the electrolyte can be greatly improved, and the rate capability of a solid battery is improved. The ionic conductivity of the prepared polyoxyethylene composite lithium fluoride nanofiber solid electrolyte is 5.8 multiplied by 10 at the temperature of 20 DEG C-4S cm-1。
Although the present disclosure has been described above, the scope of the present disclosure is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present disclosure, and such changes and modifications will fall within the scope of the present disclosure.

Claims (10)

1. The super-long lithium fluoride nanofiber is characterized by comprising a plurality of nanofibers, wherein the structure of each nanofiber is at least one of a linear type, a sawtooth type and a branch type.
2. The ultralong lithium fluoride nanofiber according to claim 1, wherein the diameter of the nanofiber is in the range of 0.3 μm to 1 μm, and the length of the nanofiber is in the range of 0.5 mm to 1 mm.
3. A method for preparing the ultra-long lithium fluoride nanofiber as claimed in claim 1 or 2, comprising the steps of:
s1, preparing a lithium fluoride solution;
and S2, freezing the lithium fluoride solution into a solid, placing the solid in a freeze dryer, and drying in vacuum until ice is completely sublimated to obtain the ultralong lithium fluoride nanofiber.
4. The method according to claim 3, wherein in step S1, the step of preparing the lithium fluoride solution comprises the steps of:
dissolving monohydrate lithium hydroxide powder in deionized water, stirring uniformly, and then dropwise adding hydrofluoric acid to form the lithium fluoride solution, or dissolving anhydrous lithium fluoride powder in deionized water, and stirring uniformly to form the lithium fluoride solution.
5. The method according to claim 4, wherein when the lithium fluoride solution is formed by dissolving or dissolving the lithium hydroxide monohydrate powder in deionized water, stirring the solution uniformly and then adding hydrofluoric acid dropwise, the mass ratio of the deionized water to the lithium hydroxide monohydrate powder is greater than 228, and the molar ratio of the hydrofluoric acid to the lithium hydroxide monohydrate powder is in a range of 1 to 5.
6. The preparation method according to claim 4, wherein when the anhydrous lithium fluoride powder is dissolved in deionized water and stirred uniformly to form the lithium fluoride solution, the mass ratio of the deionized water to the lithium fluoride powder is greater than 371.
7. The method according to any one of claims 3 to 6, wherein the temperature of the freezing is-40 ℃ or lower in step S2.
8. The method according to claim 7, wherein in step S2, a degree of vacuum of the vacuum drying is in a range of 5Pa to 10 Pa.
9. Use of the ultra-long lithium fluoride nanofibres according to claims 1-2 in the field of lithium metal batteries.
10. The use of claim 9, wherein the ultra-long lithium fluoride nanofibers are applied on separator modification layers, intermediate layers, electrode electrolyte interface layers, polymer-inorganic solid state electrolytes, all-inorganic solid state electrolytes of the lithium metal batteries.
CN202111110708.9A 2021-09-18 2021-09-18 Ultra-long lithium fluoride nanofiber and preparation method and application thereof Pending CN113943012A (en)

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WO2019148913A1 (en) * 2018-01-31 2019-08-08 华南理工大学 Lithium anode surface modification method for lithium metal battery and lithium metal battery
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Application publication date: 20220118