KR102242271B1 - Method for manufacturing pre-lithiated carbon, electrode materials for secondary battery manufactured thereby and secondary battery including the same - Google Patents

Abstract

The present invention, (a) preparing a mixed powder of lithium (Li) and carbon (C); And (b) applying mechanical energy to the mixed powder to use a non-electrochemical pre-lithiation reaction to prepare pre-lithiated carbon. As for a method for producing pre-lithiated carbon, according to the method for producing pre-lithiated carbon according to the present invention, a simple solid synthesis without going through a complicated and inefficient process such as a chemical method It is possible to simply and efficiently manufacture pre-lithiated carbon by using ball milling, and also, pre-lithiated carbon produced by the above method is used in the secondary battery. When used as an electrode active material, problems such as low initial efficiency, low lifespan, and low reversible capacity, which are disadvantages of conventional electrode materials for lithium ion secondary batteries, can be solved, and high capacity and excellent cycle life due to excellent initial efficiency while maintaining high capacity It is possible to implement a secondary battery system having a.

Description

Manufacturing method of pre-lithiated carbon, electrode material for secondary battery manufactured thereby, and secondary battery including the same TECHNICAL FIELD [METHOD FOR MANUFACTURING PRE-LITHIATED CARBON]

The present invention is a method for producing pre-lithiated carbon using a non-electrochemical pre-lithiation reaction of lithium (Li) metal and carbon (C), and all lithium produced thereby It relates to an electrode material for a secondary battery containing carbonized carbon, and to a secondary battery containing the same.

Lithium-ion secondary batteries, the most widely used representative energy storage devices in the world, are researched in various areas such as high-capacity and high-speed charging to be applied to small portable electronic devices, mid-to-large electric and hybrid vehicles, and energy storage systems (ESS). In progress. Silicon (Si), a negative electrode material using lithium, which has the highest energy density, has a theoretical capacity of 3860 mAh/g, which has higher energy density than any other material. However, despite the superiority of the high capacity of lithium-ion secondary batteries, lithium metal In the case of using as a negative electrode material for a secondary battery, a safety problem occurs due to dendritic growth during charging of the secondary battery.

As an alternative to this problem, carbon materials used as negative active materials for secondary batteries, in particular, graphite materials have a smaller theoretical capacity (372mAh/g) than lithium metal, but have little change in volume, excellent reversibility, and advantageous in terms of price. However, as the scope of application of the lithium secondary battery is expanded, research on a high-capacity and high-performance negative electrode active material is continuously required than that of a secondary battery using a graphite-based negative electrode that is currently commercially available.

Currently, a method using a lithium alloy-based metal that can be electrochemically alloyed with lithium is being studied for the high-capacity negative active material. Among them, a group IV element, namely silicon (Si, theoretical capacity: 4197mAh/g), tin (Sn) , Theoretical capacity: 993mAh/g), Germanium (Ge, theoretical capacity: 1383mAh/g) are actively being studied to apply as high-capacity alloy-based negative electrode active materials. The lithium alloy-based negative electrode material has the advantage that it can implement a higher charge and discharge capacity per weight/volume than the limited capacity of the carbon negative electrode material, and can be used even at a high charge and discharge current.

However, the lithium alloy-based negative electrode material causes a change in volume due to the phase change that occurs during charging and discharging, and the resulting stress causes the destruction of the active material, causing a big problem that causes a decrease in capacity according to the cycle, which is a lithium alloy. There is a difficulty in commercialization of the cathode material.

In addition, currently commercially available cathode materials, metal oxides containing lithium (LiMO2, M=Co, Ni, Mn, etc.) must use a limited capacity for reversible lithium insertion/desorption without structural collapse during charging/discharging. Therefore, the negative electrode material requires high initial efficiency during initial charging/discharging.

Korean Patent Publication No. 10-1998-0019243 (Publication date: 1998.05.27.) Korean Patent Publication No. 10-2016-0121565 (Publication date: 2016.10.19.) Korean Patent Publication No. 10-2015-0014877 (Publication date: 2015.02.09.)

The present invention is to solve the above problems, and an object of the present invention is to use a simple and efficient method without going through a complicated and inefficient process such as an existing chemical method, and charging/discharging characteristics superior to conventional commercialized graphite. And it is to provide a method for non-electrochemically manufacturing a new electrode active material for a lithium ion secondary battery exhibiting initial efficiency.

Another object of the present invention is to provide a novel electrode active material for a secondary battery manufactured by the above method, and further, to provide a secondary battery including the same.

The present invention for solving the above problems, (a) preparing a mixed powder of lithium (Li) and carbon (C); And (b) applying mechanical energy to the mixed powder to cause a pre-lithiation reaction to produce pre-lithiated carbon. Provides a way.

In addition, the carbon is one or more selected from the group consisting of graphite-based carbon, carbon black-based carbon, activated carbon-based carbon, hard carbon, soft carbon, and carbon nanostructures. It provides a method for producing all-lithiated carbon.

In addition, in the step (b), a high-energy spex mill, a vibrotary-mill, a Z-mill, a planetary ball-mill, or an attraction mill ( It provides a method for producing prelithiated carbon, characterized in that mechanical energy is applied by means of attrition-mill).

In addition, there is provided a method for producing prelithiated carbon, characterized in that pre-lithiated carbon represented by LixC (X=0.01 to 1) is prepared in step (b).

In addition, there is provided a method for producing pre-lithiated carbon, characterized in that in step (b), pre-lithiated carbon powder having an average diameter of 1 nm or more and 500 μm or less is prepared.

In another aspect of the present invention, the present invention provides an electrode active material for a secondary battery including pre-lithiated carbon manufactured by the above manufacturing method.

Further, the present invention provides a secondary battery including the electrode active material for a secondary battery in another aspect of the present invention.

According to the method for producing pre-lithiated carbon according to the present invention, the pre-lithiated carbon is simply and efficiently pre-lithiated using ball milling, a simple solid synthesis method, without going through a complicated and inefficient process such as a chemical method. Carbon (pre-lithiated carbon) can be produced.

In addition, when pre-lithiated carbon prepared by the above method is used as an electrode active material for a secondary battery, the problem of low capacity and initial efficiency, which is a disadvantage of graphite, an electrode material for a lithium ion secondary battery, is solved. By overcoming it, it is possible to implement a secondary battery system having an excellent cycle life while maintaining a higher capacity and higher initial efficiency than graphite.

1 is a process flow diagram sequentially describing each step of the method for producing pre-lithiated carbon according to the present invention.
2 is a conceptual diagram illustrating a method of manufacturing pre-lithiated carbon according to an embodiment of the present invention.
3 is a schematic diagram of a lithium secondary battery including pre-lithiated carbon according to the present invention as an electrode active material.
4 is a schematic diagram of a secondary battery negative electrode including pre-lithiated carbon according to the present invention as an electrode active material.
5 is a graph showing a result of X-ray diffraction analysis of pre-lithiated carbon according to an embodiment of the present invention.
6 is a high-resolution transmission electron microscope (HRTEM) analysis result of pre-lithiated carbon according to an embodiment of the present invention.
7 is a graph showing a result of an experiment for charging and discharging a lithium secondary battery of pre-lithiated carbon according to an embodiment of the present invention.
8 is a graph showing results of a cycle life test of a lithium secondary battery of pre-lithiated carbon.

In describing the present invention, when it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, a detailed description thereof will be omitted.

Since the embodiments according to the concept of the present invention can apply various changes and have various forms, specific embodiments are illustrated in the drawings and will be described in detail in the present specification or application. However, this is not intended to limit the embodiments according to the concept of the present invention to a specific form of disclosure, it should be understood to include all changes, equivalents, or substitutes included in the spirit and scope of the present invention.

The terms used in the present specification are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present specification, terms such as "comprise" or "have" are intended to designate the presence of a set feature, number, step, action, component, part, or combination thereof, and one or more other features or numbers. It is to be understood that the possibility of addition or presence of, steps, actions, components, parts, or combinations thereof is not preliminarily excluded.

Hereinafter, the present invention will be described in detail.

The method for preparing pre-lithiated carbon according to the present invention includes the steps of: (a) preparing a mixed powder of lithium (Li) and carbon (C); And (b) applying mechanical energy to the mixed powder to prepare pre-lithiated carbon using a pre-lithiation reaction.

The step (a) is a step of preparing a mixed powder by mixing lithium (Li) and carbon (C) powder, which are starting raw materials for compound production, and the method used for preparing the mixed powder in this step is lithium ( It is not particularly limited as long as it is a method capable of uniformly mixing Li) and carbon (C) powder.

The lithium (Li) used in manufacturing the mixed powder in this step may be lithium obtained by pulverizing metal lithium in the form of a foil, agglomerate, etc., as well as metal lithium in powder form. For example, in the case of using a lithium foil, it is preferable to cut a piece of less than ^{1 cm 2 and mix it with the carbon powder.}

In addition, the carbon-based material constituting the carbon powder to be introduced in step (a) is not particularly limited in its kind, but natural graphite, artificial graphite, expanded graphite, graphene, Super P, and super Graphite-based carbon such as Super C; Acetylene black, Denka black, Ketjen black, Channel black, Furnace black, Thermal black, Contact black, lamp Carbon black-based carbon such as Lamp black; Active carbon-based carbon; Carbon nanostructures such as carbon fiber, carbon nanotube (CNT), and fullerene; Hard carbon; And it may be one or a combination of two or more selected from soft carbon and the like.

In this step (a), the carbon powder is preferably added in an amount of 99.5 wt% to 63.5 wt% based on the total weight of the mixed powder. When the carbon powder is contained in an amount of less than 63.5 wt%, the amount of lithium metal becomes excessive in the total weight, which is not preferable for producing pre-lithiated carbon in step (b) to be described later.

Next, in step (b), the mechanical energy obtained in the previous step is applied to cause a pre-lithiation reaction between lithium (Li) and carbon (C), thereby pre-lithiated carbon. It is a step of manufacturing.

2 is a conceptual diagram illustrating a method of manufacturing pre-lithiated carbon in this step (b).

Referring to FIG. 2, mechanical energy is applied to a mixed powder including lithium (Li) and carbon (C) powder by high energy mechanical milling (HEMM), and lithium (Li) and carbon (C) are applied. ), a partial pre-lithiation reaction is caused to obtain pre-lithiated carbon, and this process can be expressed by the following reaction equation.

<Reaction Scheme>

xLi + C → Li _x C (X=0.01 ~ 1)

Referring to the above reaction equation, by the solid synthesis method using ball milling, lithium (Li) metal and carbon are added to induce a prelithiation reaction to prepare prelithiated carbon. In particular, by using a ball milling method of a simple process in order to induce a prelithiation reaction, a composite can be manufactured simply and efficiently without performing a conventional chemical synthesis method.

The pre-lithiated carbon contains some lithium before it is applied to the secondary battery, so when it is applied to a secondary battery, especially when used in a lithium secondary battery, it has high initial efficiency in the initial charging and discharging process. The initial efficiency problem, which is the biggest problem of amorphous, that is, amorphous carbon, can be solved, and furthermore, it is possible to solve the limitation of the negative electrode capacity of a lithium secondary battery with a higher reversible capacity than the currently commercially available graphite.

In this step (b), the method of applying mechanical energy to the pre-lithiated carbon powder is not particularly limited, but it is preferable to use high-energy ball milling for the pre-lithiation reaction. desirable.

For reference, high-energy ball milling can induce a chemical reaction to the reactant through the maximized diffusion force between the powder particles as well as to atomize the powder by applying high energy through high rotational power to the reactant.

The high-energy ball milling includes a high-energy spex mill, a vibrotary-mill, a Z-mill, a planetary ball-mill, and an attraction mill. mill) can be performed by all known ball milling devices used for high energy ball milling. For reference, in a typical high-energy ball milling process, the temperature may rise to 200°C during ball milling, and the pressure may also be on the order of 6 GPa.

When the solid-phase synthesis method using a high-energy ball ring is used as described above, pre-lithiated carbon can be prepared simply and efficiently without performing a conventional chemical synthesis method. Meanwhile, a more specific method of manufacturing pre-lithiated carbon according to the present invention through a solid-phase synthesis method using high-energy ball milling is as follows.

First, uniformly mixed pieces of lithium foil and carbon component powder are charged into a cylindrical vial together with a ball, mounted on a high-energy ball mill, and then mechanically synthesized at a rotational speed of 500-2000 times per minute to obtain prelithiated carbon. To manufacture. The ball milling may be performed for 1-24 hours. Here, the weight ratio of the ball and the mixture is maintained at, for example, 10:1 to 30:1, and mechanical synthesis is prepared in a glove box in an argon gas atmosphere in order to minimize the influence of oxygen and moisture.

Pre-lithiated carbon prepared by the above-described manufacturing method, particularly, pre-lithiated carbon including amorphous carbon, has improved initial efficiency and charging and discharging characteristics. Therefore, it is suitable for use as an electrode active material for secondary batteries, especially lithium secondary batteries. In particular, the cycle life of the secondary battery including the pre-lithiated carbon is very excellent.

On the other hand, the prelithiated carbon contains 99.5 wt% to 63.5 wt% of carbon, preferably has a powder form having an average diameter of 1 nm or more and less than 500 μm, and is preferably amorphous carbon particles.

In another aspect of the present invention, the present invention provides an electrode active material for a secondary battery including pre-lithiated carbon manufactured by the above manufacturing method.

Further, the present invention provides a secondary battery including the electrode active material for a secondary battery in another aspect of the present invention.

3 is a schematic diagram of a lithium secondary battery including pre-lithiated carbon according to the present invention as an electrode active material.

The secondary battery 1 may include a positive electrode 12, a negative electrode 11, and a separator 13 disposed between the positive electrode 12 and the negative electrode 11. The secondary battery 1 may further include an electrolyte (not shown), a battery container 14, and a sealing member 15 for sealing the battery container 14. The secondary battery 1 may be manufactured by sequentially stacking the positive electrode 12, the negative electrode 11, and the separator 13, and then receiving them in the battery container 14 in a wound state.

4 is a schematic diagram of a secondary battery negative electrode including pre-lithiated carbon according to the present invention as an electrode active material.

The negative electrode 11 may include a current collector 111 and an active material layer 112 formed on the current collector 111. The active material layer 112 includes a metal-tellurium compound and a carbon-containing composite according to the present invention. The cathode 11 is a water-insoluble binder such as polyvinylidene fluoride (PVdF) or polyethyleneimine, polyaniline, polythiophene, polyacrylic acid (PAA), carboxymethylcellulose (CMC), styrene-butadiene lever (SBR) It may further include a water-soluble binder such as.

Hereinafter, examples of the present invention will be described. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided so that the disclosed contents may be thorough and complete, and the spirit of the present invention may be sufficiently conveyed to those skilled in the art.

<Example> Preparation of pre-lithiated carbon and secondary battery containing the same

(1) Preparation of pre-lithiated carbon through pre-lithiation of lithium metal and carbon

Commercially available lithium metal foil ^{is cut into pieces of 1 cm 2} , mixed with carbon (Super P) powder in a molar ratio of 0.3: 1, and then placed in a cylindrical vial made of SKD11 material with a diameter of 5.5 cm and a height of 9 cm. It was charged with a /8 inch ball and mounted on a vibrating mill (spex 8000), and then mechanical synthesis was performed at a rotational speed of 900 times per minute.

At this time, the weight ratio between the balls and the powder was kept at 20:1, and mechanical synthesis was prepared in a glove box in an argon gas atmosphere in order to suppress the effects of oxygen and moisture as much as possible. The mechanical synthesis was performed for 3 hours to prepare pre-lithiated carbon.

5 is a graph showing the results of X-ray diffraction analysis of pre-lithiated carbon. The prepared pre-lithiated carbon _{can be synthesized as Li x} C (X=0.01 ~ 1) by the molar ratio of lithium, and its form is an amorphous form when prepared using the mechanical synthesis method described above. When pre-lithiated carbon is used as an electrode material for a lithium secondary battery, the problem of low capacity and initial efficiency, which is a disadvantage of the currently commercially available carbon-based negative electrode (graphite). By overcoming the graphite, it is possible to realize higher capacity and initial efficiency than graphite. The material used in an embodiment of the present study is prepared by using lithium metal and carbon powder together in an appropriate molar ratio in order to prepare pre-lithiated carbon containing lithium and carbon components.

6 is a high-resolution transmission electron microscope (HRTEM) photograph of the prepared pre-lithiated carbon. Referring to FIG. 6, it can be seen that amorphous pre-lithiated carbon was produced through the above manufacturing method, and pre-lithiated carbon prepared through an Energy Dispersive Spectrometer (EDS) mapping photograph. lithiated carbon) is uniformly distributed with lithium and carbon components.

(2) Evaluation of initial efficiency characteristics and cycle characteristics of secondary batteries containing manufactured pre-lithiated carbon

7 is a graph showing results of a charge/discharge experiment when pre-lithiated carbon is used as an electrode for a lithium secondary battery. The blue graph of FIG. 7 is a result of charging and discharging carbon (amorphous carbon) subjected to ball milling only under the same conditions as pre-lithiated carbon, which is an exemplary embodiment of the present invention. The red graph of FIG. 7 is a graph showing charging and discharging behaviors for the first cycle when pre-lithiated carbon is used. The charging and discharging capacities of the first cycle were 482 mAh/g and 640 mAh/g, and the efficiency of the initial cycle was about 133%. This showed an improved result compared to the charging and discharging capacity of 563 mAh/g and 916 mAh/g of the amorphous carbon prepared by the same method, the efficiency of the initial cycle of 61.5%, and the prepared pre-lithiated carbon (pre-lithiated carbon). carbon) showed significantly higher capacity and initial efficiency values compared to the existing carbon-based negative electrode (372mAh/g).

FIG. 8 is a graph showing cycle characteristic data when pre-lithiated carbon is used as a negative active material in a lithium secondary battery. In the case of a lithium secondary battery used as a material for a negative electrode active material, it exhibits excellent life characteristics without change in capacity even for several cycles at a reaction potential of 0V to 2V.

As described above, in the present invention, pre-lithiated carbon is used as a negative electrode material for a secondary battery, especially a lithium secondary battery, and in this case, it occurs at the negative electrode during charging and discharging of a secondary battery, especially a lithium secondary battery. The large initial irreversible capacity of the negative electrode material can be improved by controlling the amount of lithium in the manufacturing step.

Accordingly, it is possible to secure initial efficiency, which is most important in secondary batteries, especially lithium secondary battery electrodes, and improve capacity and cycle life. Further, the secondary battery in which the pre-lithiated carbon is used, in particular, the lithium secondary battery exhibits higher capacity, initial efficiency, and excellent cycle characteristics than commercialized graphite.

In the above, embodiments of the present invention have been described with reference to the accompanying drawings, but those of ordinary skill in the art to which the present invention pertains can be implemented in other specific forms without changing the technical spirit or essential features. You can understand that there is. Therefore, it should be understood that the embodiments described above are illustrative in all respects and are not limiting.

1: lithium or sodium secondary battery 11: negative electrode
12: anode 13: separator
14: battery container 15: sealing member
111: current collector 112: active material layer

Claims (7)

(a) preparing a mixed powder of lithium (Li) and carbon (C); And
(b) applying mechanical energy to the mixed powder to cause a pre-lithiation reaction to produce pre-lithiated amorphous carbon. The method of claim 1,
The carbon is at least one selected from the group consisting of carbon black-based carbon, hard carbon, and soft carbon. The method of claim 1,
In the step (b), a high-energy spex mill, a vibrotary-mill, a Z-mill, a planetary ball-mill, or an attraction mill. A method for producing all-lithiated carbon, characterized in that mechanical energy is applied with a mill). The method of claim 1,
In the step (b), a method for producing prelithiated carbon, characterized in that pre-lithiated amorphous carbon represented by LixC (X = 0.01 to 1) is prepared. The method of claim 1,
In the step (b), a method for producing prelithiated carbon, characterized in that pre-lithiated amorphous carbon powder having an average diameter of 1 nm or more and 500 μm or less is prepared. An electrode active material for a secondary battery comprising pre-lithiated carbon prepared by the manufacturing method of any one of claims 1 to 5. A secondary battery comprising the electrode active material for secondary batteries of claim 6.

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