CN112713260B - Flexible lithium metal battery cathode, preparation method thereof and lithium metal battery - Google Patents

Abstract

The invention discloses a flexible lithium metal battery cathode, which comprises a current collector, a lithium-philic substance and lithium metal, wherein the lithium-philic substance and the lithium metal are loaded on the current collector; the lithium-philic substance is a substance that can lower the nucleation barrier of lithium. The invention loads the substance capable of reducing the nucleation barrier of the lithium on the current collector, on one hand, the nucleation barrier of the lithium can be reduced, the uniform composition of the lithium metal and the current collector is realized, on the other hand, the invention can enhance the bonding force of the lithium metal and the current collector as the effect similar to a rivet, and the preparation of the flexible lithium metal electrode is realized. The invention also provides a preparation method of the flexible lithium metal battery cathode. The method can enable the lithium-philic substance to play the effects of inhibiting the growth of lithium dendrites and the effect of a rivet in the negative electrode of the flexible lithium metal battery. The invention also discloses a lithium metal battery. The lithium metal battery disclosed by the invention has the advantages that the short circuit hidden danger is reduced, the coulomb efficiency is improved, and the service life of the battery is prolonged.

Description

A kind of flexible lithium metal battery negative electrode and its preparation method and lithium metal battery

technical field

The invention relates to a lithium metal electrode, in particular to a flexible lithium metal battery negative electrode, a preparation method thereof, and a lithium metal battery.

Background technique

Lithium metal batteries have the potential of ultra-high energy density and are considered to be the ultimate goal in the development of secondary batteries. The development of flexible lithium metal batteries can not only provide a choice of high-performance secondary batteries for traditional electronic products such as mobile phones, computers, and electric vehicles, but also provide a basis for secondary batteries to be used in new wearable electronic products such as monitoring bracelets and smart watches. applications are possible. The key to the development of flexible lithium metal batteries lies in the design and preparation of high-performance flexible lithium metal anodes. At present, there are the following technical difficulties in the development of lithium metal negative electrodes. First, the electrochemical performance of lithium metal negative electrodes is poor, and dendrites are easily generated during charging and discharging, causing problems such as battery short circuit, low Coulombic efficiency, and short cycle life; Second, in the electrode preparation process, the recombination methods of lithium metal and current collectors are limited, mostly based on mechanical pressing, which makes it difficult to achieve uniform and effective recombination, and is limited by the metal material of traditional current collectors, making it difficult to achieve flexible functions. Improving the electrochemical performance of lithium metal anodes and solving the difficulties in the preparation of lithium metal anodes are the key to the development of flexible lithium metal batteries.

The invention patent with the publication number CN105789559A "A Flexible Lithium Metal Battery Negative Electrode and Its Preparation Method" discloses a method for preparing a flexible lithium metal negative electrode. The gaseous lithium metal is fused to obtain a flexible lithium metal anode with improved safety performance and cycle life.

Although the preparation of flexible lithium metal electrodes has been realized, the above-mentioned technical solutions have certain defects in improving the electrochemical performance of lithium metal negative electrodes: 1. The conductivity of the framework material has a decisive influence on the deposition behavior of lithium metal. When the framework material is When used as an insulating material, it will inevitably cause uneven distribution of current density in the electrode, which will make the growth of lithium dendrites more serious; 2. The improvement of the electrochemical performance of lithium negative electrodes depends on the regulation of current density, nucleation barrier, etc. , and the framework material selected in the above patent is a single substance, which is difficult to achieve multifunctionality. In addition, the above-mentioned technical solution uses thermal fusion to realize the compounding of metal lithium and the skeleton material. Although the operation is simple, it relies on the solidification of liquid lithium or gaseous lithium, and the process controllability is poor, and it is difficult to obtain a smooth surface. Uniform lithium metal anode.

Contents of the invention

The object of the present invention is to overcome the shortcomings of the prior art and provide a flexible lithium metal battery negative electrode, a preparation method thereof and a lithium metal battery.

In order to achieve the above object, the technical solution adopted by the present invention is: a negative electrode of a flexible lithium metal battery, including a current collector, a lithium-philic substance and lithium metal, and the lithium-philic substance and lithium metal are loaded on the current collector; Lithophilic substances are substances that lower the nucleation barrier of lithium.

The substance that can reduce the nucleation barrier of lithium is a substance that has an affinity with lithium metal, such as an electrode material that can store lithium. Lithophilic substances can be granular on the current collector, but are not limited to particles Shape, also can be flake.

The negative electrode of the flexible lithium metal battery of the present invention loads the substance that can reduce the nucleation barrier of lithium on the current collector, on the one hand, it can reduce the nucleation barrier of lithium, and realizes the uniformity of lithium metal and the current collector. Recombination, on the other hand, acts like a "rivet", which can enhance the bonding force between lithium metal and current collectors, and realize the preparation of flexible lithium metal electrodes.

The lithium metal negative electrode described in the present invention has the characteristics of light weight and flexibility. When used as the negative electrode, the hidden danger of short circuit of the battery is reduced, the safety is improved, the Coulombic efficiency is improved, and the service life of the battery is prolonged. At the same time, the preparation method described in the invention is simple and easy to operate, has strong controllability, and is easy to realize large-scale preparation.

Preferably, the current collector is a flexible conductive frame. The flexible conductive framework is selected as the current collector. The flexible conductive framework has a three-dimensional microstructure. As the current collector of the lithium metal electrode, it can disperse the current density to the greatest extent, inhibit the growth of lithium dendrites, and improve the electrochemical performance of the lithium metal electrode. More preferably, the current collector is a carbon-based flexible conductive framework. The carbon-based flexible conductive skeleton has certain mechanical strength and can be self-supporting.

More preferably, the current collector is at least one of carbon fiber cloth, carbon nanotube film and graphene paper, but not limited thereto; more preferably, the flexible conductive skeleton is carbon fiber cloth, and the carbon fiber cloth has a multi-level three-dimensional Microstructure, and the preparation process is mature.

Preferably, the lithium-philic substance is at least one of tin, silicon, copper oxide, cobalt oxide and nickel oxide. The lithium-loving substance can be a metal oxide, such as copper oxide, cobalt oxide and nickel oxide, or it can be a metal (such as tin) or a non-metal simple substance (such as simple silicon), when it has the ability to reduce the nucleation barrier of lithium When the oxide is in the form of particles, it can be evenly dispersed on the current collector, and the uniform recombination of lithium metal and the current collector can be realized.

Preferably, the weight ratio of the lithium-philic substance to the lithium metal is: lithium-philic substance:lithium metal=1:1-5. The loading amount of the lithium metal on the current collector can be selected according to the actual energy density requirement.

Preferably, the particle size of the lithium-philic substance is 10 nm˜1 μm. The inventors have found that when the particle size of the metal oxide is too large, it will lead to serious growth of dendrites in the lithium metal electrode, which poses a safety hazard.

The object of the present invention is also to provide a method for preparing the negative electrode of the flexible lithium metal battery, comprising the following steps:

(1) Lithophilic substances are loaded on the current collector;

(2) Lithium metal is loaded on the current collector loaded with the lithium-philic substance, and the negative electrode of the flexible lithium metal battery is obtained.

The method enables the lithium-philic substance to play the effect of inhibiting the growth of lithium dendrites and the role of a "rivet" in the negative electrode of the flexible lithium metal battery.

Preferably, in step (1), the lithium-philic substance is supported on the current collector by electroplating, evaporation, CVD or PVD. By adopting the above method, the lithium-philic substance can be effectively dispersed on the current collector evenly, and the lithium-philic substance with different particle sizes can be prepared by controlling the preparation process conditions.

Preferably, in step (1), the current collector is used as the working electrode, the metal is used as the counter electrode, and the platinum carbon electrode is used as the reference electrode, and the electroplating is performed in the electrolyte, the electroplating current is 1-10mA/cm ² , and the electroplating time is 1 to 10 minutes to obtain a current collector loaded with metal particles, and then oxidize the metal particles to obtain a current collector loaded with metal oxides. The oxidation of the metal particles can be realized by drying the current collector loaded with the metal particles at a temperature of 90-120°C.

Preferably, in step (2), the lithium metal is loaded on the current collector by electroplating or PVD. The lithium metal can be uniformly wrapped on the current collector loaded with the lithium-philic substance by using the above method, which has conformality.

Lithophilic substances are loaded first, and then lithium metal is loaded. The introduction of the lithium-philic substances prepared by the above method into the current collector can make the surface of the prepared lithium metal electrodes smooth and evenly distributed.

Preferably, the current collector loaded with lithium-philic substances is placed under an inert atmosphere, the current collector loaded with lithium-philic substances is used as the working electrode, and lithium metal is used as the counter electrode, and deposited in the electrolyte for 40 to 60 minutes, and the current is 1-10mA/cm ² to obtain the negative electrode of the flexible lithium metal battery. The electrolyte may be a mixture of lithium trifluoromethanesulfonimide, 3-dioxolane and methyl ether, or other lithium-containing electrolytes.

Preferably, step (1a) is further included before step (1): performing hydrophilic treatment on the current collector. Hydrophilic treatment is conducive to the enrichment of lithium-philic substances. The hydrophilic treatment method can be a common treatment method in the field, preferably using a mixed acid of sulfuric acid and nitric acid for treatment, and soaking the current collector in a mixed solution of nitric acid and sulfuric acid . The molar ratio of nitric acid to sulfuric acid is: nitric acid: sulfuric acid = 3:1, soaking time can be 1min-10h, after soaking, wash in pure water and dry to complete the treatment.

The object of the present invention is also to provide a lithium metal battery, the lithium metal battery comprises a positive pole, a negative pole, a separator and an electrolyte placed between the positive pole and the negative pole, the negative pole is the above-mentioned flexible lithium metal battery negative electrode. The negative pole of the flexible lithium metal battery provides a lithium source for the lithium metal battery. As an independent negative pole, it matches with a lithium-free positive pole such as sulfur, and is assembled into a secondary battery for use.

The beneficial effect of the present invention is that: the present invention provides a flexible lithium metal battery negative electrode, the present invention loads the substance that can reduce the nucleation barrier of lithium on the current collector, on the one hand, it can reduce the nucleation barrier of lithium , to realize the uniform recombination of lithium metal and current collector, on the other hand, as a role similar to "rivets", it can enhance the bonding force between lithium metal and current collector, and realize the preparation of flexible lithium metal electrodes. The invention also provides a preparation method of the negative electrode of the flexible lithium metal battery. The method enables the lithium-philic substance to play the effect of inhibiting the growth of lithium dendrites and the role of a "rivet" in the negative electrode of the flexible lithium metal battery. The invention provides a lithium metal battery comprising the negative electrode of the flexible lithium metal battery. The lithium metal negative electrode described in the present invention has the characteristics of light weight and flexibility. When used as the negative electrode, the hidden danger of short circuit of the battery is reduced, the safety is improved, the Coulombic efficiency is improved, and the service life of the battery is extended. At the same time, the preparation method described in the invention is simple and easy to operate, has strong controllability, and is easy to realize large-scale preparation.

Description of drawings

Fig. 1 is the structural representation of current collector described in embodiment 1;

2 is a schematic structural view of a current collector loaded with a lithium-philic substance as described in Example 1;

3 is a schematic structural view of the flexible lithium metal negative electrode described in Example 1; wherein, 1 is a current collector, 2 is a lithium-philic material, and 3 is lithium metal;

Fig. 4 is the microscopic morphology figure of carbon fiber cloth in embodiment 1;

Fig. 5 is the microscopic topography figure of carbon fiber cloth supporting copper oxide in embodiment 1;

FIG. 6 shows the Coulombic efficiency of lithium metal negative electrodes in Example 1 and Comparative Example 1.

detailed description

In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific examples.

Example 1

The schematic diagrams of the structure of the negative electrode of the flexible lithium metal battery in this embodiment are shown in Figures 1 to 3. The negative electrode of the flexible lithium metal battery includes a current collector 1, a lithium-friendly material 2, and a lithium metal 3. The current collector 1 is carbon fiber cloth, which is lithium-friendly. The substance 2 is granular copper oxide, which is evenly loaded on the carbon fiber cloth, and the lithium metal 3 is evenly wrapped on the current collector loaded with the lithium-philic substance 2 .

Fig. 4 is the microscopic topography of the carbon fiber cloth described in this example. The carbon fiber cloth has a thickness of 320 μm, a density of 115 g/m ² , and an electrical conductivity of 1.89 mΩ/cm ² . Fig. 5 is a microscopic topography of copper oxide distribution , the particle size of the copper oxide particles is in the range of 10nm-1μm, uniformly dispersed on the carbon fiber cloth, lithium metal is deposited on the carbon fiber cloth loaded with copper oxide particles, and the deposition amount of lithium is 10mAh/cm ² .

The preparation method of the flexible lithium metal battery negative electrode described in this embodiment comprises the following steps:

(1) Hydrophilic treatment of carbon fiber cloth:

Prepare 30 mL of mixed solution of nitric acid and sulfuric acid, wherein the molar ratio of nitric acid and sulfuric acid is: nitric acid: sulfuric acid = 3:1, select a 3*5cm carbon cloth, soak it in the above mixed solution for 20 minutes, and then ultrasonically clean it in pure water for 30 minutes , vacuum drying;

(2) Loading of copper oxide:

Use the carbon fiber cloth treated in step (1) as the working electrode, the copper foil as the counter electrode, the platinum carbon electrode as the reference electrode, and 1M copper ^sulfate as the electrolyte for electroplating. After the electroplating is completed, the obtained carbon fibers loaded with copper particles are placed in an oven to dry for 1 h at a temperature of 90°C. After the drying is completed, the metal particles are oxidized and transformed into corresponding metal oxides, that is, copper oxide loaded Granular carbon fiber cloth;

(3) Lithium deposition:

The carbon fiber cloth loaded with copper oxide obtained in step (2) is transferred to a glove box, and the glove box is an argon atmosphere, and lithium is deposited, and lithium is a counter electrode. Lithium trifluoromethanesulfonyl imide, 3-bis The mixed solution of oxycyclopentane and methyl ether is the electrolyte (purchased from Dodochem, product model LP-001), the current is 10mA/cm ² , the deposition time is 60min, and after the deposition is completed, it is cleaned in 3-dioxolane , and dried to obtain the negative electrode of the flexible lithium metal battery.

Comparative example 1

The structure of the negative electrode of the flexible lithium metal battery described in this comparative example differs from that of Example 1 only in that it does not contain lithium-loving substances, and that lithium metal is directly loaded on the carbon fiber cloth. The difference between the preparation method of the negative electrode of the flexible lithium metal battery and that of Example 1 is that step (2) is not included.

Test the electrochemical performance of the negative electrode of the flexible lithium metal battery described in this example: use the negative electrode of the flexible lithium metal battery described in Example 1 and Comparative Example 1 as the electrode, use the polypropylene microporous membrane as the separator, and use 1mol/L of three The lithium fluoromethanesulfonimide (LITFSI) solution is the electrolyte, and the solvent is a mixed system of 3-dioxolane (DOL) and methyl ether (DME) (volume ratio 1:1), assembled into a symmetrical button battery. Use the blue electric charge and discharge test cabinet to conduct constant capacity charge and discharge tests. Accompanying drawing 6 is the Coulombic efficiency of the battery described in Example 1 and Comparative Example 1. The Coulombic efficiency of the negative electrode of the flexible lithium metal battery described in Example 1 is as high as 99%, indicating that the growth of lithium dendrites is inhibited, while the Coulombic efficiency of Comparative Example 1 Lower than Example 1, and there is a sharp downward trend.

Example 2

An embodiment of the negative electrode of the flexible lithium metal battery described in the present invention, the negative electrode of the flexible lithium metal battery described in this embodiment includes a current collector, a lithium-friendly material and lithium metal, the lithium-friendly material is cobalt oxide, and the current collector is carbon fiber cloth , Cobalt oxide is uniformly loaded on carbon fiber cloth in granular form, the particle size of cobalt oxide particles is in the range of 10nm to 1μm, and lithium metal is evenly wrapped on the current collector loaded with lithium-friendly substances. The carbon fiber cloth has a thickness of 320 μm, a density of 115 g/m ² , and an electrical conductivity of 1.89 mΩ/cm ² . The deposited amount of lithium metal was 10 mAh/cm ² .

The preparation method of the flexible lithium metal battery negative electrode described in this embodiment comprises the following steps:

(1) Hydrophilic treatment of carbon fiber cloth: with embodiment 1;

(2) Loading of cobalt oxide:

The carbon fiber cloth treated in step (1) is used as the working electrode, the cobalt sheet is used as the counter electrode, the platinum carbon electrode is used as the reference electrode, and 1M cobalt sulfate is used as the electrolyte for electroplating. The electroplating current is 1mA/cm ² and the electroplating time is 1min. After the electroplating is completed, the obtained carbon fibers loaded with cobalt particles are placed in an oven to dry for 1 h at a temperature of 90°C. After the drying is completed, the metal particles are oxidized and transformed into corresponding metal oxides, that is, cobalt oxide-loaded carbon fibers are obtained. Granular carbon fiber cloth;

(3) Lithium deposition: Same as in Example 1, to obtain the negative electrode of the flexible lithium metal battery.

According to the same test method as in Example 1 and Comparative Example 1, the Coulombic efficiency of the negative electrode of the flexible lithium metal battery described in this example was tested in this example, and it was found that the Coulombic efficiency of the negative electrode of the flexible lithium metal battery described in this example was also as high as 99%.

Example 3

An embodiment of the negative electrode of the flexible lithium metal battery described in the present invention, the negative electrode of the flexible lithium metal battery described in this embodiment includes a current collector, a lithium-friendly material and lithium metal, the lithium-friendly material is nickel oxide, and the current collector is carbon fiber cloth , Nickel oxide is uniformly loaded on carbon fiber cloth in granular form, the particle size of nickel oxide particles is in the range of 10nm to 1μm, and lithium metal is evenly wrapped on the current collector loaded with lithium-friendly substances. The carbon fiber cloth has a thickness of 320 μm, a density of 115 g/m ² , and an electrical conductivity of 1.89 mΩ/cm ² . The deposition amount of lithium metal is 10mAh/cm ²

The preparation method of the flexible lithium metal battery negative electrode described in this embodiment comprises the following steps:

(1) Hydrophilic treatment of carbon fiber cloth: with embodiment 1;

(2) Loading of nickel oxide:

The carbon fiber cloth treated in step (1) is used as the working electrode, the nickel sheet is used as the counter electrode, the platinum carbon electrode is used as the reference electrode, and 1M nickel sulfate is used as the electrolyte, and the electroplating is carried out at a current of 1mA/cm ² , and the electroplating time is 2min After the electroplating is completed, the obtained carbon fibers loaded with nickel particles are placed in an oven to dry for 1 h at a temperature of 90°C. After the drying is completed, the metal particles are oxidized and transformed into corresponding metal oxides, that is, nickel oxide loaded Granular carbon fiber cloth;

(3) Lithium deposition: Same as in Example 1, to obtain the negative electrode of the flexible lithium metal battery.

According to the same test method as in Example 1 and Comparative Example 1, the Coulombic efficiency of the negative electrode of the flexible lithium metal battery described in this example was tested in this example, and it was found that the Coulombic efficiency of the negative electrode of the flexible lithium metal battery described in this example was also as high as 99%.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that The technical solution of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solution of the present invention.

Claims (2)

1. The flexible lithium metal battery negative electrode is characterized by comprising a current collector, a lithium-philic substance and lithium metal, wherein the lithium-philic substance and the lithium metal are loaded on the current collector; the current collector is carbon fiber cloth, the thickness of the carbon fiber cloth is 320 mu m, and the density of the carbon fiber cloth is 115g/m ² The conductivity is 1.89m omega/cm ² The lithium-philic substance is at least one of copper oxide, cobalt oxide and nickel oxide;

the preparation method of the flexible lithium metal battery negative electrode comprises the following steps:

(1) Soaking the current collector in a mixed solution of nitric acid and sulfuric acid for 1 min-1 h, then cleaning in pure water, and drying, wherein the molar ratio of the nitric acid to the sulfuric acid is nitric acid: sulfuric acid = 3;

(2) Electroplating in electrolyte by taking the current collector treated in the step (1) as a working electrode, a metal as a counter electrode and a platinum-carbon electrode as a reference electrode, wherein the electroplating current is 1-10 mA/cm ² Electroplating ofThe time is 1-10 min, so as to obtain a current collector loaded with metal particles, and then the metal particles are oxidized, so as to obtain a current collector loaded with metal oxides, namely the current collector loaded with the lithium-philic substance;

(3) Putting the current collector loaded with the lithium-philic substance in an inert atmosphere, taking the current collector loaded with the lithium-philic substance as a working electrode and lithium metal as a counter electrode, depositing in an electrolyte for 1-60 min, wherein the current is 1-10 mA/cm ² Obtaining the flexible lithium metal battery cathode;

the weight ratio of the lithium-philic substance to the lithium metal is as follows: lithium metal =1 to 5;

the particle size of the lithium-philic substance is 10 nm-1 mu m.

2. A lithium metal battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, the negative electrode being the flexible lithium metal battery negative electrode of claim 1.

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