Preparation method of high-conductivity solid electrolyte and application of high-conductivity solid electrolyte in lithium metal battery

Abstract

The invention discloses a preparation method of a high-conductivity solid electrolyte and application of the high-conductivity solid electrolyte in a lithium metal battery, and belongs to the technical field of lithium batteries. Kevlar fibrils are dissolved in a potassium hydroxide / dimethyl sulfoxide mixed system, aramid nanofiber dispersion liquid is obtained through deprotonation and serves as a polymer additive, then lithium salt serves as filler and is added into a polymer electrolyte, and the high-conductivity solid electrolyte is obtained through stirring. The aramid nanofiber dispersion liquid is used as a functional additive of a polymer, so that the problem of volume expansion of the lithium metal negative electrode in the charging and discharging process can be relieved, and Li < + > preferential transmission can be realized. The conductivity of the solid electrolyte can be further improved by adding the lithium salt as a filler into the polymer. The solid electrolyte is applied to assembly of a solid-state lithium metal battery, and the electrochemical performance of the battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a method for preparing a high-conductivity solid electrolyte and application of the same in lithium metal batteries. Background Art

[0002] As an important device for energy storage, lithium (Li) ion batteries have high energy and power density, excellent recyclability and reliability, and have been widely used in people's daily life, such as mobile phones, computers, cameras, cars and other fields. The current lithium ion battery energy density is relatively low and cannot meet the needs of high energy density systems such as long-distance vehicles. Lithium metal has an ultra-high theoretical capacity (3860mAh g -1 ) and the lowest electrochemical reduction potential (-3.04V vs. standard hydrogen electrode), as a negative electrode material for lithium metal batteries, it has attracted much attention in the research of secondary batteries. However, lithium metal is very sensitive to traditional commercial liquid organic electrolytes, that is, it will inevitably react with the electrolyte to form lithium dendrites during the cycle process, resulting in safety problems such as combustion or explosion, which seriously limits the development of lithium metal batteries.

[0003] In recent years, solid-state lithium metal batteries have higher safety and energy density than liquid lithium-ion batteries, and are an important development direction of energy storage technology in the future. With the continuous increase in demand for high-power equipment, it is particularly important to develop long-life and fast charging technologies. This requires solid electrolytes to have high ionic conductivity, excellent interfacial stability and strong mechanical properties. Among them, polymer electrolytes with excellent flexibility and good interfacial contact properties are regarded as ideal material choices for practical applications. So far, solid electrolytes based on polyethylene (PEO), polyacrylonitrile (PAN), poly(propylene carbonate) (PPC) and polyvinylidene fluoride (PVDF) have been developed. However, the low ionic conductivity of the electrolyte limits their large-scale application, resulting in the battery being able to only be charged and discharged at a lower current density. Therefore, it is urgent to improve the ionic conductivity of polymer solid electrolytes.

[0004] Solid electrolytes are the core components of solid-state batteries, and designing high ionic conductivity polymer electrolytes is a promising strategy to improve the performance of solid-state lithium metal batteries. Although the preparation routes of typical polymer electrolytes are mature and have good development prospects, the room temperature ionic conductivity of currently available solid electrolytes is not ideal, which has delayed the commercialization of lithium metal batteries. Specifically, low ionic conductivity means that the solid-solid interface energy barrier inside the solid-state battery is high, which makes lithium ion transmission difficult, which in turn leads to slow charge and discharge rates and poor rate performance of the finished solid-state battery, which has become a major obstacle to the widespread practical application of all-solid-state batteries.

[0005] In the research reported so far, polymer-based solid electrolytes are usually composed of a polymer matrix, an inorganic filler, a lithium salt, and an ionic liquid additive. In some new composite solid electrolyte structures, polymer-based electrolytes can be prepared by the composite of two or more polymers. This can not only improve the ionic conductivity, but also provide additional transfer pathways for lithium ions and increase the transfer number of lithium. It provides a new theoretical basis and technical route for the practical application of polymer electrolytes, and establishes a new idea for the development of all-solid-state lithium metal batteries with high specific capacity, good rate performance and excellent stability. However, the current preparation technology of existing polymer solid electrolytes is not only expensive, but also cumbersome. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing a high-conductivity solid electrolyte and its application in a lithium metal battery, so as to solve the problems in the background technology.

[0007] To achieve the above objectives, the present invention provides a method for preparing a high-conductivity solid electrolyte, wherein Kevlar fibrils are dissolved in a potassium hydroxide / dimethyl sulfoxide mixed system, an aramid nanofiber dispersion is obtained by deprotonation and used as a polymer additive, and then lithium salt is added as a filler to the polymer electrolyte and stirred to obtain a high-conductivity solid electrolyte.

[0008] Preferably, by mass percentage, the added content of the aramid nanofiber dispersion is 1%-10%; the added content of the lithium salt is 40%-50%, and the rest is polymer electrolyte.

[0009] Preferably, the concentration of the aramid nanofiber dispersion is 1-10 mg mL -1 .

[0010] Preferably, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium perchlorate (LiClO 4 ), lithium hexafluorophosphate (LiPF 6 ), lithium trifluoromethanesulfonate (LiCF 3 SO 3 ) one or more of the following.

[0011] Preferably, the polymer electrolyte is one or more of polyethylene (PEO), polyacrylonitrile (PAN), poly(propylene carbonate) (PPC), and polyvinylidene fluoride (PVDF).

[0012] Preferably, the stirring speed is 400-800 rpm.

[0013] The present invention also provides a high-conductivity solid electrolyte prepared by the above preparation method.

[0014] The invention also provides the application of the above-mentioned high-conductivity solid electrolyte in a solid-state lithium metal battery system.

[0015] Therefore, the present invention provides a method for preparing a high-conductivity solid electrolyte and its application in a lithium metal battery, wherein an aramid nanofiber dispersion is used as a functional additive for a polymer, and the fiber has a unique porous structure and can be used as a lithium metal battery. + It provides abundant fast transmission channels and storage space, which can effectively alleviate the volume expansion problem of lithium metal anode during charging and discharging. Because it carries negative charge, the electrostatic interaction in the fiber network channel shows cation selectivity, which can realize Li + Prioritized transport, the introduction of lithium salts further improves the lithium conductivity of solid electrolytes. Adding lithium salts as fillers to polymers can simultaneously improve the conductivity of solid electrolytes.

[0016] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Nyquist plots of button cells assembled with solid electrolytes prepared in this embodiment at different temperatures; Figure 2 The activation energy diagram of button batteries assembled in the embodiments of the present invention and the comparative examples. DETAILED DESCRIPTION

[0018] The technical solution of the present invention is further described below by means of the accompanying drawings and embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. Any other changes, modifications, substitutions, combinations, simplifications made without violating the spirit and principle of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention. In addition, it should be understood that after reading the content of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application and belong to the scope of protection of the present invention.

[0019] Reference to "embodiment" herein means that the specific features, structures or characteristics described in conjunction with the embodiment may be included in at least one embodiment of the present application. The term "embodiment" appearing in various places in the specification does not necessarily refer to the same embodiment, nor does it particularly limit its independence or association with other embodiments. In principle, in the present application, as long as there is no technical contradiction or conflict, the various technical features mentioned in the embodiments can be combined in any way to form a corresponding implementable technical solution.

[0020] Unless otherwise defined, the technical terms used in this document have the same meanings as those generally understood by those skilled in the art to which this application belongs; the use of relevant terms in this document is only for describing specific embodiments and is not intended to limit this application.

[0021] Unless otherwise specified in the present invention, the reagents, instruments, and equipment used are those commonly used by technicians in this field.

[0022] Example The present embodiment provides a method for preparing a high-conductivity solid electrolyte, and the specific steps are as follows: dissolving Kevlar fibrils in a potassium hydroxide / dimethyl sulfoxide mixed system, obtaining an aramid nanofiber dispersion with a concentration of 2 mg / mL by a deprotonation method, taking 15 mL of the aramid nanofiber dispersion as a polymer additive, and then taking 2 g of lithium bistrifluoromethanesulfonyl imide as a filler and adding it to 2 g of polyacrylonitrile, uniformly stirring and coating to form a film, and then drying to obtain a high-conductivity solid electrolyte.

[0023] The polymer electrolyte prepared in this embodiment and compounded with aramid nanofibers was used, and pure polymer polyacrylonitrile was used as the electrolyte as a comparative example, and button batteries were assembled and the battery performance was tested. The specific method is as follows: a) Li||Li symmetric cell: Two identical lithium sheets (~450 μm) were placed in an argon-filled glove box (H 2 O<0.1ppm, O 2 <0.1ppm) coupling. The electrodes were separated by a solid electrolyte as a separator and electrolyte. Then, the electrochemical performance was evaluated by cycling at different current densities and capacities.

[0024] b) Coin cell: The lithium iron phosphate cathode is then paired with a ~450 μm lithium sheet anode to assemble the full cell. The lithium iron phosphate-based full cell is cycled in the voltage range of 2.5 to 4.0 V (vs. Li / Li + ), and the cycle current density was 0.1 C. Each button cell was activated for 5 cycles at a current density of 0.05 C before testing.

[0025] c) Ionic conductivity: Two stainless steel discs with a diameter of 15.8 mm were sandwiched on both sides of the solid electrolyte to assemble into a button cell. The ionic conductivity was tested using a Swiss Metrohm electrochemical workstation with a frequency range of 0.1~100000 Hz.

[0026] The Nyquist plots of the button cells assembled with the solid electrolyte prepared in this embodiment at different temperatures are as follows: Figure 1 As shown. Figure 1 Calculations show that the composite solid electrolyte prepared in this embodiment has good ionic conductivity in a wide temperature range.

[0027] The activation energy diagram of the button cells assembled in the embodiments and comparative examples is shown in FIG. Figure 2 As shown. Figure 2 It can be seen that under the same conditions, the polymer electrolyte with 4% ANF additive has a lower activation energy.

[0028] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing a high conductivity solid electrolyte, characterized in that: Kevlar fibrils are dissolved in a potassium hydroxide / dimethyl sulfoxide mixed system, and aramid nanofiber dispersion is obtained by deprotonation and used as a polymer additive. Then lithium salt is added as a filler into the polymer electrolyte and stirred to obtain a high-conductivity solid electrolyte.

2. The method for preparing a high conductivity solid electrolyte according to claim 1, characterized in that: Calculated by mass percentage, the added content of aramid nanofiber dispersion is 1%-10%; the added content of lithium salt is 40%-50%, and the rest is polymer electrolyte.

3. The method for preparing a high conductivity solid electrolyte according to claim 1, characterized in that: The concentration of aramid nanofiber dispersion is 1~10mg mL -1 .

4. The method for preparing a high conductivity solid electrolyte according to claim 1, characterized in that: The lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, lithium hexafluorophosphate and lithium trifluoromethanesulfonate.

5. The method for preparing a high conductivity solid electrolyte according to claim 1, characterized in that: The polymer electrolyte is one or more of polyethylene, polyacrylonitrile, poly(propylene carbonate) and polyvinylidene fluoride.

6. The method for preparing a high conductivity solid electrolyte according to claim 1, characterized in that: The stirring speed is 400-800rpm.

7. A high conductivity solid electrolyte, characterized in that: The high-conductivity solid electrolyte is prepared by the preparation method described in any one of claims 1 to 6.

8. The use of a high conductivity solid electrolyte as claimed in claim 7, characterized in that: The high-conductivity solid electrolyte is applied in solid-state lithium metal batteries.

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