CN108400316A - Selfreparing oxidation film coats Na-K liquid alloy electrodes and its preparation method and application - Google Patents

Abstract

The invention discloses a high-efficiency self-repairing oxide film-coated Na-K liquid alloy electrode and its preparation method and application as a negative electrode. Under the protection of an inert gas, the K metal and the Na metal are heated separately until they melt, and then the conductive The carrier is in contact with the metal, the molten metal slowly wets the conductive carrier, and the conductive carrier loaded with K metal and Na metal is respectively obtained after cooling to room temperature; through the method of physical stacking and alloying, a self-healing oxide film coated Na with a stable structure is prepared at room temperature. ‑K liquid alloy electrodes. The electrode includes a conductive carrier, Na-K liquid alloy adsorbed on the carrier and a self-repairing oxide film on the surface. The electrode of the present invention has the characteristics of high Coulombic efficiency, no dendrite growth and stable structure, and can be used as a potassium metal negative electrode and a sodium metal negative electrode at the same time. When matched with positive electrode materials such as sulfur and Prussian blue, the energy density and cycle stability of the full battery are significantly improved. sex.

Description

Self-healing oxide film coated Na-K liquid alloy electrode and its preparation method and application

technical field

The invention relates to the technical field of negative electrode materials for alkali metal secondary batteries, in particular to a self-repairing oxide film-coated Na-K liquid alloy electrode, a preparation method thereof, and an application as negative electrode materials for alkali metal secondary batteries.

Background technique

With the popularity of new energy vehicles and mobile electronic devices, there is an urgent need to develop batteries with high specific capacity, high safety, long cycle life, and low cost. As a new type of energy storage device, alkali metal secondary batteries have the characteristics of large reserves, low preparation cost, and wide electrochemical window, and have broad application prospects in the fields of mobile communications, electric vehicles, and energy storage. Among them, the alkali metal negative electrode has a higher specific capacity than carbon materials, metal oxides, etc., but the alkali metal negative electrode is prone to dendrites during use, which leads to a short circuit of the battery and poses a safety hazard. Liquid alloys represented by Na-K alloys can completely inhibit the growth of dendrites and become an emerging research direction for dendrite-free electrode materials. However, the high surface tension of Na-K liquid alloy makes it difficult to wet on the surface of the current collector, which seriously hinders its commercial application. Therefore, the study of liquid metal electrodes with stable structure at room temperature is of great significance for the application and development of alkali metal secondary batteries.

Studies have shown that Na-K liquid alloy is a high-performance dendrite-free electrode material with great development potential. It has the characteristics of low toxicity and wide stable temperature (it exists in liquid form at room temperature even at -12.6 °C). In order to obtain a Na-K liquid alloy electrode with a stable structure, the following problems need to be solved (as shown in Figure 1): 1) Na-K liquid alloy is difficult to form, and the Na-K alloy has a large surface tension and is difficult to wet on the surface of the current collector. And because of its liquid form, it has a certain fluidity and is difficult to form a fixed form; 2) The interface between the Na-K liquid alloy electrode and the electrolyte is unstable, and the Na-K liquid alloy is easy to fall off from the electrode surface and form in the electrolyte. The free liquid metal makes it difficult to maintain a stable interface between the Na-K liquid alloy electrode and the electrolyte, resulting in voltage fluctuations during the battery cycle.

Studies have shown that high temperature treatment (>420°C) can improve the wettability of Na-K liquid alloy on carbon paper, and at the same time, the porous structure substrate can capture more Na-K liquid alloy, which solves the problem of Na-K liquid alloy fluidity. question. However, at room temperature, due to the recovery of the surface tension of the Na-K liquid alloy, the exposed Na-K liquid alloy on the surface of the composite electrode fell off, indicating that the simple carbon carrier loaded Na-K liquid alloy cannot essentially solve the problem of interface stability. .

At present, there is no research on stable Na-K liquid alloy electrode and electrolyte interface at home and abroad, and there is no solution to the Na-K liquid alloy shuttle problem at home and abroad. Therefore, constructing a stable electrode-electrolyte interface is a key issue for the large-scale application of Na-K liquid alloy anodes.

Contents of the invention

For the problems in the background technology, the object of the present invention is to provide a kind of high-efficiency self-repairing oxide film coating Na-K liquid alloy electrode and its preparation method and the application as alkali metal secondary battery negative electrode material, and this method can be directly in each A self-healing oxide film coated Na-K liquid alloy is constructed on a conductive support with various structures and types to prepare a dendrite-free alkali metal battery negative electrode with strong stability.

A method for preparing an efficient self-repairing oxide film-coated Na-K liquid alloy electrode, comprising the following steps:

1) Under the protection of an inert gas, heat the K metal until it melts, and then contact the conductive carrier with the molten K metal. The molten K metal slowly wets the conductive carrier. After it is completely absorbed, it is cooled to obtain a conductive carrier loaded with K metal ;

Under the protection of an inert gas, the Na metal is heated until it melts, and then the conductive carrier is contacted with the molten Na metal, and the molten Na metal slowly wets the conductive carrier, and after being completely absorbed, the conductive carrier for loading the Na metal is obtained after cooling;

2) Under the protection of an inert gas, the conductive carrier loaded with K metal and the conductive carrier loaded with Na metal prepared in step 1) are physically stacked, the alloying reaction of K metal and Na metal occurs, and an oxide film is formed at the same time to obtain self-repairing oxidation Membrane-coated Na-K liquid alloy electrode;

Alternatively, the conductive carrier loaded with K metal and the conductive carrier loaded with Na metal prepared in step 1) are soaked in the electrolyte, and stacked, an alloying reaction occurs, and a self-repairing oxide film is formed at the same time to obtain a self-repairing oxide film coating Na-K liquid alloy electrode.

In step 1), the conductive carrier can be a conductive carrier of various dimensions, and can be a film, block, powder, etc. from a structural point of view, and can be a polymer, metal, metal oxide, or metal organic framework from a material point of view. , carbon materials, etc. It is preferably a two-dimensional thin film conductive carrier with a certain thickness, and most preferably a two-dimensional thin film carbon material with a certain thickness and area.

The carbon material can be quantum dots, carbon tubes, multi-walled carbon tubes, carbon fibers, graphene, graphene rolls, carbon arrays, vertical graphene, carbon cloth, mesoporous carbon, hollow spheres, multilayer hollow spheres, nano Flowers, biomass carbon materials, etc. The conductive carrier material may be a composite of various materials. The carbon material can be hard carbon or soft carbon.

Further preferably, the conductive carrier is carbon cloth.

The thickness of the conductive carrier is 0.1mm-10mm, more preferably 0.5mm-5mm, most preferably 1mm-2mm.

The conductive carrier has an area of 0.1 cm ² to 10 cm ² , more preferably 0.2 cm ² to 2 cm ² , most preferably 0.5 cm ² to 1.5 cm ² , wherein the length, width, and shape are not limited, and are preferably square or circular.

In step 1), the K metal is calculated according to the area of the conductive carrier to be 0.001gcm ^-2 ~ 10gcm ^-2 , more preferably 0.01gcm ^-2 ~ 5gcm ^-2 , most preferably 0.05gcm ^-2 ~ 0.2gcm ^-2 , A certain mass of Na metal is calculated according to a certain ratio relative to K metal.

The Na metal is 0.00028gcm ^-2 to 2.8gcm ^-2 calculated according to the area of the conductive carrier, more preferably 0.0028gcm ^-2 to 1.4gcm ^-2 , most preferably 0.014gcm ^-2 to 0.056gcm ^-2 .

The amounts of K and Na are in a certain ratio, and the ratio of the mass of K metal to Na metal is 70-86:14-30, more preferably 75-81:19-25, and even more preferably 77-79: 21-23.

The K metal and Na metal are pure K and pure Na.

The K metal and Na metal need to be cut to remove surface oxides before use.

In step 1), the K metal is heated to a temperature of 300°C to 500°C, most preferably 350°C to 450°C;

The Na metal is heated to a temperature of 300°C to 500°C, most preferably 350°C to 450°C.

In step 2), the obtained composite electrode can be soaked in the electrolyte to obtain a self-healing oxide film containing new components.

The self-healing oxide film is mainly wrapped on the surface of the electrode in the form of a film.

The electrolyte solute is one or more mixed electrolytes such as KPF ₆ , KClO ₄ , KTFSI, NaPF ₆ , NaClO ₄ , NaTFSI, etc.; the solvent is ethylene carbonate (EC), DEC, dimethyl carbonate (DMC ), DIGLYM, PC, etc., one or more mixed solutions, and various additives, such as F-containing additives, etc. Further preferably, the solute in the electrolyte is KPF ₆ and NaPF ₆ with a molar ratio of 1:1, and the solute solvent in the electrolyte is ethylene carbonate (EC) and dimethyl carbonate ( DMC), the concentrations of KPF ₆ and NaPF ₆ in the electrolyte are both 0.5 mol/L to 3 mol/L, more preferably 1 mol/L.

The new components are high ion conductivity KF and NaF.

In step 2), the Na-K alloy will be completely adsorbed in the conductive carrier.

The self-repairing oxide film will repair itself after being mechanically damaged.

The mechanical damage mainly refers to the removal of the film, the generation of cracks, and the crushing caused by extrusion.

In step 1) and step 2), the content of nitrogen or oxygen in the inert gas can be adjusted to obtain self-healing oxide films with different compositions.

The inert gas is argon, preferably high-purity argon. In an inert gas environment, the water content is less than 0.1ppm.

The nitrogen or oxygen content is 0.1ppm-100ppm, more preferably 0.1ppm-10ppm, most preferably 0.1ppm-0.5ppm, wherein the nitrogen and oxygen contents are adjusted independently and do not need to be in a fixed ratio.

The Na-K alloy inside the obtained Na-K alloy composite electrode is liquid at normal temperature, the surface oxide film is solid, and there is no dendrite growth, and can be used as the negative electrode material of K ion battery and Na ion battery at the same time.

The described self-healing oxide film-coated Na-K liquid alloy electrode includes a conductive carrier, a Na-K liquid alloy deposited on the conductive carrier, and a self-repairing oxide film formed on the surface, that is, the conductive carrier, the conductive carrier adsorbed Na-K Liquid Alloy and Self-healing Oxide Film on Surface

The application of the self-repairing oxide film-coated Na-K liquid alloy electrode as the negative electrode material of the alkali metal secondary battery.

Compared with the prior art, the present invention has the following advantages and outstanding effects:

The invention is aimed at preparing a dendrite-free liquid alloy negative electrode with a stable structure. The present invention has the following two advantages: the conventional electrode structure is mainly composed of a current collector and Na-K liquid alloy, and the Na-K liquid alloy is easy to fall off, resulting in an unstable electrode structure. The present invention proposes a new electrode structure, wherein Na-K The alloy composite electrode includes a conductive substrate, a Na-K alloy deposited on a conductive carrier, and a self-healing oxide film formed on the surface. This structure can increase the structural stability of the electrode structure, enhance electrical conductivity, and improve high-rate performance and Coulombic efficiency; The preparation method is convenient, and the conventional preparation method requires high-temperature heating of Na-K liquid alloy, which has certain risks. The present invention obtains a self-repairing oxide film-coated Na-K liquid alloy electrode at normal temperature through a simple physical superposition method. The composite negative electrode improves the safety performance and cycle performance of the alkali metal, and helps to promote the development of high energy density and high stability alkali metal secondary batteries.

The high-efficiency self-healing oxide film-coated Na-K liquid alloy electrode of the present invention has the characteristics of high coulombic efficiency, no dendrite growth and stable structure, and can be used as potassium metal negative electrode and sodium metal negative electrode at the same time, matching with positive electrode materials such as sulfur and Prussian blue. , significantly improving the energy density and cycle stability of the full battery.

Description of drawings

Fig. 1 is a research train of thought diagram of the present invention;

Figure 2 is a schematic diagram of the preparation of carbon cloth loaded Na-K alloy/oxide film composite electrode;

Fig. 3 is the XRD diffractogram of the self-repairing oxide film coating Na-K liquid alloy electrode surface that makes in embodiment 1;

Fig. 4 is a graph under different magnifications after the self-healing oxide film-coated Na-K liquid alloy electrode prepared in Example 1 is assembled into a symmetrical electrode.

Detailed ways

The present invention will be described in detail below in conjunction with the examples, but the present invention is not limited thereto.

Example 1

Heat 0.1g of K metal and 0.028g of Na metal in a glove box to 450°C to melt, and then use tweezers to contact the two kinds of molten metal with a carbon cloth (thickness 2mm) with a length of 1cm and a thickness of 2mm. Cool to room temperature 25°C. Stack the carbon cloth loaded with K metal and Na metal respectively, and the alloying reaction of the two metals occurs on the surface of the carbon cloth, and a self-healing oxide film is formed on the surface. After a period of reaction, a self-healing oxide film is formed to cover Na-K Liquid alloy electrodes.

The XRD diffraction pattern of the self-healing oxide film coated Na-K liquid alloy electrode surface prepared in Example 1 is shown in FIG. 3 . As shown in the figure, the prepared electrode has no characteristic peaks of Na metal and K metal, indicating that the formed alloy is a liquid Na-K alloy. At the same time, weak peaks of KO ₂ and K ₂ O were found, indicating that a solid oxide film was formed on the surface of Na-K alloy, and the main components were KO ₂ and K ₂ O.

Example 2

Adjust the oxygen content in the glove box to 0.2ppm, and the nitrogen content to 0.1ppm. Heat 0.2g of K metal and 0.056g of Na metal in a glove box to 400°C to melt respectively, and then use tweezers to contact the two kinds of molten metal with a carbon cloth (thickness 2mm) of 1cm in length and width. Cool to room temperature 25°C. Stack the carbon cloth loaded with K metal and Na metal respectively, and the alloying reaction of the two metals occurs on the surface of the carbon cloth, and a self-healing oxide film is formed on the surface. After a period of reaction, a self-healing oxide film is formed to cover Na-K Liquid alloy electrodes.

The obtained XRD diffraction pattern of the electrode is similar to Example 1, and a small amount of KN ₃ peaks are found.

Example 3

Heat 0.2g of K metal and 0.056g of Na metal in a glove box to 400°C to melt respectively, and then use tweezers to contact the two kinds of molten metal with a carbon cloth (thickness 2mm) of 1cm in length and width. Cool to room temperature 25°C. Immerse the carbon cloth loaded with K metal and Na metal respectively in the electrolyte (the solute is KPF ₆ and NaPF ₆ with a molar ratio of 1:1; the organic solvent is ethylene carbonate (EC) and dimethyl carbonate with a volume ratio of 1:1 (DMC), the concentrations of KPF ₆ and NaPF ₆ in the electrolyte are both 1mol/L), and stacked, the two metals undergo an alloying reaction on the surface of the carbon cloth, and a self-healing structure with a new composition is formed on the surface The oxide film, after a period of reaction, forms a self-healing oxide film to cover the Na-K liquid alloy electrode.

The obtained XRD diffraction pattern of the electrode is similar to that of Example 1, and a small amount of KF peaks are found.

Performance Testing

The N self-healing oxide film-coated Na-K liquid alloy electrodes prepared in the above-mentioned Examples 1-3 were respectively used as the counter electrode and the working electrode of the coin cell, and the electrolyte was in 1M KPF ₆ (or 1M NaPF ₆ ) electrolyte, The current density is 1mA cm ^-2 , the cycle capacity is 1mAh cm ^-2 , and the overpotential of the K (or Na) metal negative electrode in the symmetrical electrode system is measured in an environment of 25±1°C.

The performance test results are as follows:

The Na-K alloy composite electrodes of embodiment 1, embodiment 2 and embodiment 3 are cycled 200 times under the current density of 1mAcm ^- 2, and the overvoltage can be stabilized respectively within 22mV, 19mV and 17mV, and the voltage platform is stable without obvious fluctuation. However, the potential of the Na-K liquid alloy composite electrode without oxide film fluctuates violently. In addition, the coulombic efficiencies of the electrodes cycled for 100 cycles can be maintained above 97.9%, 98.5% and 99.2%, respectively. It can be seen that the Na-K alloy composite electrode prepared above has low overvoltage, good cycle stability and high Coulombic efficiency. The curves at different magnifications after the self-healing oxide film-coated Na-K liquid alloy electrode prepared in Example 1 is assembled into a symmetrical electrode are shown in FIG. 4 .

This is because the existence of the self-healing oxide film provides a stable interface for the Na-K alloy, and the Na-K alloy in liquid form at room temperature avoids the generation of dendrites and ensures the stability of the electrode structure.

Therefore, the high-efficiency self-healing oxide film-coated Na-K liquid alloy electrode of the present invention has the characteristics of high Coulombic efficiency, significant inhibition of dendrite growth and stable interface structure, and has a good effect on the metal negative electrode modification of alkali metal secondary batteries. Instructive, this method is conducive to the large-scale application of dendrite-free alkali metal anodes.

Claims (10)

1. a kind of preparation method of selfreparing oxidation film cladding Na-K liquid alloy electrodes, which is characterized in that include the following steps：

1) under inert gas protection, karat gold is belonged to and being heated, until fusing, then conductive carrier is contacted with the karat gold category of fusing, it melts The karat gold of change belongs to slowly moistening conductive carrier, and after all absorbing, the conductive carrier that load karat gold belongs to is obtained after cooling；

Under inert gas protection, by Na METAL HEATING PROCESSs, until melting, then conductive carrier is contacted with the Na metals of fusing, is melted The Na metals of change slowly moisten conductive carrier, and after all absorbing, the conductive carrier of load Na metals is obtained after cooling；

2) under inert gas protection, the conductive carrier that load karat gold prepared by step 1) belongs to is carried with the conductive of load Na metals Body physics stacks, and karat gold category and the metallic alloying reactions of Na occurs, and generate oxidation film simultaneously, obtains selfreparing oxidation film cladding Na-K liquid alloy electrodes；

Alternatively, infiltrating the conductive carrier of conductive carrier and load Na metals that load karat gold prepared by step 1) belongs in electrolyte In, and stack, alloying reaction occurs, and generate selfreparing oxidation film simultaneously, obtains selfreparing oxidation film and coat Na-K liquid Alloy electrode.

2. preparation method according to claim 1, which is characterized in that in step 1), karat gold category is heated to 300 DEG C of temperature ~500 DEG C；

By Na METAL HEATING PROCESSs to 300 DEG C~500 DEG C of temperature.

3. preparation method according to claim 1, which is characterized in that in step 1), the conductive carrier is carbon cloth.

4. preparation method according to claim 1, which is characterized in that in step 1), the thickness of the conductive carrier is 0.5mm~5mm；

The area of the conductive carrier is 0.2cm²~2cm²。

5. preparation method according to claim 1, which is characterized in that in step 1), the karat gold category is according to conductive carrier Areal calculation is 0.01gcm^-2~5gcm^-2；

The Na metals are 0.0028gcm according to conductive carrier areal calculation^-2~1.4gcm^-2。

6. preparation method according to claim 1, which is characterized in that in step 1), the quality and Na that the karat gold belongs to are golden The mass ratio of category is 70~86：14~30.

7. preparation method according to claim 1, which is characterized in that in step 2), solute is to rub in the electrolyte That ratio 1：1 KPF₆And NaPF₆, solvents are by volume ratio 1 in the electrolyte：1 ethylene carbonate and dimethyl carbonate The solution of composition, KPF₆And NaPF₆Concentration in the electrolytic solution is 0.5mol/L~3mol/L.

8. coating Na-K liquid alloys according to selfreparing oxidation film prepared by claim 1~7 any one of them preparation method Electrode.

9. selfreparing oxidation film according to claim 8 coats Na-K liquid alloy electrodes, which is characterized in that including conduction Carrier, the Na-K liquid alloys deposited on conductive carrier and the selfreparing oxidation film formed on surface.

10. selfreparing oxidation film according to claim 8 coats Na-K liquid alloy electrodes as alkali metal secondary battery The application of negative material.