KR20220073525A - Resistance Gradient Three Dimensional Current Collector, Lithium Anode and Manufacturing Method For The Same - Google Patents

Abstract

SUMMARY OF THE INVENTION The present invention is to solve the above problems, and an object of the present invention is to provide a current collector having a porous three-dimensional structure and having a gradient of electrical resistance in the thickness direction. In order to achieve the above object, a first aspect of the present invention includes a substrate having a three-dimensional porous structure and a metal layer coated on the surface of the substrate, wherein the metal layer has a predetermined depth inside from at least one surface of the substrate To provide a negative electrode current collector for a secondary battery having a structure in which the thickness increases continuously or intermittently from the surface to the inside, and the electrical resistance decreases from the surface to the inside.

Description

Resistance Gradient Three Dimensional Current Collector, Lithium Anode and Manufacturing Method For The Same}

The present invention relates to a resistance gradient-type three-dimensional current collector used for a negative electrode of a secondary battery, a lithium negative electrode using the current collector, and a manufacturing method thereof. In more detail, the current collector having a three-dimensional porous structure has a structure in which electrical resistance is continuously or intermittently decreased as it goes inside from at least one surface, and the lithium negative electrode has a structure in which lithium is electrodeposited on the current collector. Through this, when applied to a lithium secondary battery, it relates to a volume change that occurs during the electrodeposition/desorption process of lithium, a safety problem caused by dendrite growth, and a problem of limiting the charging speed caused by this.

Graphite-based anodes have excellent cycle life, stability and low electrochemical reactivity, which are required for anodes, so graphite is mainly used as anode materials for currently commercialized lithium-ion batteries. However, the graphite anode has a limitation in that the capacity is small and the charging and discharging efficiency is lowered.

Lithium metal has the highest energy density among anode materials known to date, and has a very low oxidation-reduction potential, so it has great potential as the most suitable material for secondary batteries that require light weight and large capacity. , lithium all-solid-state batteries, lithium-sulfur batteries, lithium-air batteries, etc. are being considered for use in negative electrode materials.

In general, a lithium metal secondary battery has a structure in which an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode is embedded in a battery case, and an electrolyte solution is injected therein. However, the negative electrode containing lithium metal is prone to damage to the negative electrode due to the large volume change that occurs during the electrodeposition/desorption process of lithium, and dendrite growth occurs during high-speed charging, resulting in safety issues and deterioration of cycle characteristics and charging speed limiting problem arises.

To solve this problem, attempts have been made to use a three-dimensional mesh as a current collector, but when lithium metal is electrodeposited on a current collector having such a three-dimensional structure, a lithium metal layer is formed only on the surface, and the plating solution is caused by the lithium metal layer formed on the surface inside. There is a problem in that the lithium metal layer cannot be formed because this does not penetrate.

Therefore, in order to apply a lithium negative electrode using a three-dimensional current collector to a lithium secondary battery, the above-described problem must be solved.

Republic of Korea Patent Publication No. 2019-0112707

SUMMARY OF THE INVENTION The present invention is to solve the above problems, and an object of the present invention is to provide a current collector having a porous three-dimensional structure and having a gradient of electrical resistance in the thickness direction.

Another object of the present invention is to provide a lithium negative electrode in which lithium is electrodeposited on the surface of the current collector.

Another object of the present invention is to provide a method for manufacturing the current collector and the lithium negative electrode.

A first aspect of the present invention for achieving the above object includes a substrate having a three-dimensional porous structure and a metal layer coated on the surface of the substrate, wherein the metal layer extends from at least one surface of the substrate to a predetermined depth inside It is to provide a negative electrode current collector for a secondary battery having a structure in which the thickness increases continuously or intermittently from the surface to the inside, and the electrical resistance decreases from the surface to the inside.

A second aspect of the present invention includes the negative electrode current collector for a lithium secondary battery, and a lithium metal layer coated on the surface of the negative electrode current collector, wherein the lithium metal layer on the surface of the substrate is thinner than the lithium metal layer inside the substrate To provide a lithium negative electrode for a secondary battery, which is formed or not formed.

A third aspect of the present invention comprises the steps of: modifying the surface of a three-dimensional porous structure substrate; Irradiating and activating the UV-irradiated three-dimensional porous substrate; and performing electroless plating on the activated three-dimensional porous structure substrate to form a metal plating layer.

In the current collector according to the present invention, when lithium is coated by a plating method for use as a lithium negative electrode, lithium plating is performed smoothly from the surface layer having a large electrical resistance to the inside, so lithium plating is not performed well on the surface layer It is possible to solve the problem that lithium plating is not formed inside due to clogging of holes in the surface layer during the plating process.

The lithium negative electrode obtained by performing lithium plating on the current collector according to the present invention can not only secure sufficient energy density, but also suppress the volume change and dendrite growth that occur during the electrodeposition/desorption process of lithium, thereby improving cycle characteristics. can be improved

In addition, according to the method for manufacturing a current collector and a lithium negative electrode according to the present invention, a lithium negative electrode having excellent performance can be manufactured through a simple process.

1 shows a current collector manufacturing process according to an embodiment of the present invention.
2 is an image of a three-dimensional porous substrate made of fibers used in an embodiment of the present invention.
3 is a surface image of a lithium anode manufactured according to an embodiment of the present invention.
4 is a surface image of a lithium negative electrode prepared according to Comparative Example.
5 is a surface image after performing a charge/discharge test 30 times using a lithium negative electrode prepared according to an embodiment of the present invention.
6 is a surface image after performing a charge/discharge test 30 times using the lithium negative electrode prepared according to Comparative Example.

Hereinafter, the configuration and operation of the embodiment of the present invention will be described with reference to the accompanying drawings. In the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. In addition, when a part 'includes' a certain component, this means that other components may be further included, rather than excluding other components, unless otherwise stated.

As described above, the negative electrode made of lithium metal is limited in its active application due to low cycle characteristics, safety problems, and charging rate limitations despite its high energy density. In order to solve this problem, by forming a lithium metal layer on the conductive current collector of a porous three-dimensional structure, damage to the electrode due to contraction/expansion during charging and discharging, safety problems due to dendrite formation, and charging/discharging rate limitation problems are solved However, for this purpose, it is necessary to form a uniform lithium metal layer on the conductive current collector having a three-dimensional structure.

The present invention proposes a three-dimensional structure anode current collector for forming such a uniform lithium metal layer and a lithium anode for a secondary battery made therefrom.

First, the anode current collector for a secondary battery that can be provided in the present invention includes a substrate having a three-dimensional porous structure and a metal layer coated on the surface of the substrate, and the metal layer extends from at least one surface of the substrate to a predetermined depth inside. It is characterized in that it has a structure in which the thickness increases continuously or intermittently from the surface to the inside, so that the electrical resistance gradually decreases from the surface to a predetermined thickness inside.

Meanwhile, in the present invention, 'the predetermined depth' refers to a depth of at least 1/50 of the total thickness from the surface.

When a lithium metal layer is formed on a three-dimensional porous substrate through electroplating, a lithium metal layer is first formed on the outermost surface in contact with the plating solution. formation is not smooth. For this reason, the lithium metal layer is not uniformly formed on the entire current collector but thickly formed only on the surface, so it is difficult to obtain a negative electrode having a desired energy density, and the volume contraction/expansion may be severely damaged.

In order to solve this problem, in the present invention, the electric resistance decreases from at least one surface of the substrate having a three-dimensional porous structure toward the inside, thereby increasing the resistance at the surface to the highest, thereby suppressing the rate of formation of the lithium metal layer on the surface. First, the lithium metal layer is formed, and the lithium metal layer is formed last on the surface in direct contact with the plating solution, so that the plating solution penetrates into the inside during the plating process and a uniform lithium metal layer is formed in the thickness direction of the substrate.

In the secondary battery negative electrode current collector having such a three-dimensional porous structure, the metal layer may be a copper metal layer. Copper is a metal with high conductivity and is the most suitable metal as a current collector of a negative electrode considering the operating voltage range of a lithium secondary battery.

In addition, the base material of the three-dimensional porous structure may be in the form of a nonwoven fabric, a woven form, or a mesh form in which elastic polymer fibers are irregularly entangled. The polymer may be, for example, polypropylene (PP), poly (methyl metacrylate) (PMMA), polyethylene (PE), or polyethylene terephthalate (PET), but the present invention is not limited thereto.

By using a flexible polymer, it is possible to cope with the volume change caused by the contraction/expansion of the negative electrode and to control the size and shape of the pores in various ways. In addition, it may be advantageous in terms of manufacturing cost of the negative electrode compared to a substrate such as a metal.

In addition, the thickness of the substrate is It is preferably in the range of 1 to 500 μm. If it is too thin, it may not be possible to manufacture an anode of sufficient capacity, and if it is too thick, it may be difficult to form a uniform lithium metal layer to the inside. More preferably, the thickness of the substrate is 5 μm or more in consideration of an appropriate negative electrode capacity, and is preferably 200 μm or less in consideration of the internal penetration depth of the plating solution, and more preferably in the range of 10 to 100 μm.

As described above, the method proposed in the present invention for making a negative electrode current collector having a three-dimensional porous structure in which electrical resistance is lowered from the surface to the inside as described above includes the steps of modifying the surface of the three-dimensional porous substrate, the surface of which is modified. Treating a substrate with Sn sensitization, irradiating UV to at least one surface of the Sn-sensitized substrate, activating the UV-irradiated 3D porous substrate, and the activation-treated 3D porous substrate It may include the step of performing electroless plating to form a metal plating layer.

In general, in order to form a metal layer on the surface of a polymer by electroless plating, the fiber surface is pretreated in an alkali solution, sensitized using a solution containing Sn ²⁺ ions, and then activated using a palladium catalyst solution. A metal layer is formed by forming a Pd ⁰ seed and then performing electroless plating.

The present invention further includes the step of irradiating UV between the sensitization treatment and the activation treatment as described above. When UV is irradiated, Sn ²⁺ ions positioned for sensitization are oxidized to Sn ⁴⁺ , so that Pd ⁰ in the subsequent activation treatment. The seed is not smoothly formed, and plating is suppressed in the electroless plating step for forming the final metal layer.

The substrate having a three-dimensional porous structure irradiated with UV after sensitization treatment according to the present invention has the greatest amount of UV radiation from the surface and the radiation amount decreases as it goes inside ^. becomes more and more Accordingly, in the final electroless plating step, the thickness of the metal layer inside is the thickest and the thickness of the metal layer on the surface is the thinnest.

When a lithium metal layer is formed through electroplating on the anode current collector, which has the greatest electrical resistance on the surface through this method, the lithium metal layer formation occurs the fastest on the inside and the latest on the surface of the lithium metal layer plating solution formed on the surface. It is possible to form a lithium metal layer uniformly in the thickness direction of the substrate without interfering with the penetration into the current collector.

On the other hand, the lithium electroplating is preferably made by disposing the lithium plating electrode, which is the lithium source, so as to be closest to the surface of the substrate having the metal plating layer formed thereon with the highest electrical resistance. It is located closest to the lithium plated electrode, which is the lithium source, so that the surface with the highest electrical resistance is located where the movement distance of lithium is short, so that the lithium metal layer is formed last on the surface where lithium ions can reach first It can be made so as not to interfere with the formation of the lithium metal layer.

[Example]

1 shows a current collector manufacturing process according to an embodiment of the present invention.

As shown in Figure 1, the current collector manufacturing process according to the present invention, the step of modifying the surface of the three-dimensional porous structure substrate, the step of performing Sn sensitization treatment on the surface of the modified substrate, Sn sensitized The steps of irradiating UV to at least one surface of the substrate, activating the UV-irradiated three-dimensional porous substrate, and performing electroless plating on the UV-irradiated three-dimensional porous substrate to form a metal plating layer include

The base material of the three-dimensional porous structure is preferably made of a non-conductive material, and in an embodiment of the present invention, as shown in FIG. A nonwoven fabric, a three-dimensional porous body with many irregular pores, was used. Specifically, the three-dimensional porous structure substrate was immersed in a mixed solution of 1M KOH and 0.9M EDA at 50° C. for 5 minutes, followed by immersion in 0.2M HCl solution for 5 minutes to perform neutralization treatment.

The step of performing the Sn sensitization treatment on the surface-modified substrate is a process of treating for 4 minutes at room temperature using SnCl ₂ as a pre-step for electroless.

In the step of irradiating UV, a copper plating layer is not formed or thinly formed on the surface irradiated with UV during subsequent electroless plating by irradiating UV to one surface of the three-dimensional substrate treated with Sn sensitization, It is a process to make a structure in which the electrical resistance increases from the inside to the surface. For UV irradiation, UV of a wavelength of 280 to 350 nm was treated at about 30 mW/cm ² for 5 to 10 minutes.

After activation treatment using a palladium catalyst solution, electroless copper plating was performed. The electroless copper plating process is a process of forming a copper plating layer on the surface of a three-dimensional substrate irradiated with UV using an electroless copper plating solution. At this time, since copper is not plated or plated very thinly from one surface of the three-dimensional substrate subjected to UV irradiation to a predetermined depth, the surface includes a region where a copper plating layer is not formed. As such, during electroless plating, since the plating layer is not well formed in the surface layer in contact with the plating solution, plating is formed only on the surface of the three-dimensional porous structure by the plating layer formed at the beginning of the plating process, and plating is not formed inside. be able to prevent

Accordingly, in the current collector manufactured according to the embodiment of the present invention, the copper plating layer is sufficiently formed therein and the copper plating layer is not formed as it goes to the surface layer, so it has a gradient structure in which the electrical resistance increases toward the surface.

The manufacturing process of the lithium negative electrode according to the present invention uses the current collector manufactured by the above process as the negative electrode and lithium metal as the positive electrode, and a method of electrodepositing lithium metal of the positive electrode on the current collector. .

Since the electrodeposition state of lithium varies depending on the electrical conductivity of the negative electrode, the lithium plating layer is formed from the inside of the current collector in which the copper plating layer is sufficiently formed, and the lithium plating layer is thin or there is a region where the lithium plating layer is not formed toward the surface.

3 is a surface image of a lithium anode manufactured through the above process. As can be seen in FIG. 3 , it can be seen that a lithium plating layer is not formed in a significant area of the exposed fibers on the surface.

[Comparative example]

In Comparative Example, a current collector and a lithium negative electrode were manufactured in the same manner as in Examples, except that a UV irradiation process was not performed among the manufacturing processes of the current collector and the lithium negative electrode according to the Example.

4 is a surface image of a lithium negative electrode prepared according to Comparative Example. As can be seen in FIG. 4 , a thick lithium plating layer is formed on the fibers on the surface. Meanwhile, although not shown in FIG. 4 , a lithium plating layer was not sufficiently formed therein.

Cycle Characteristics Test

A charge/discharge test was performed to compare the battery characteristics of the lithium negative electrode according to the embodiment of the present invention and the lithium negative electrode according to the comparative example.

The three-dimensional lithium electrode prepared according to the example was put in both the negative electrode and the positive electrode, and a symmetric cell evaluation was performed using a 2032 coin cell composed of a PE-based 20um-thick separator between them, and in this case, the charge/discharge test was 5mA/cm ² , It was carried out under the condition of 2mAh/cm ² .

5 is a surface image after performing a charge/discharge test 30 times using a lithium negative electrode prepared according to an embodiment of the present invention, FIG. 6 is a lithium negative electrode prepared according to a comparative example 30 times charge and discharge test This is the surface image after performing.

As can be seen in FIG. 5 , in the lithium negative electrode according to the embodiment of the present invention, the growth of dendrites was hardly observed even after 30 cycles, and a state similar to the initial state was maintained. In contrast, as shown in FIG. 6 , it is observed that the surface of the lithium negative electrode according to the comparative example is changed to a dendrite structure after 30 cycles.

As described above, the lithium negative electrode according to the embodiment of the present invention is excellent in energy density as well as cycle characteristics compared to the comparative example.

Claims (7)

A substrate having a three-dimensional porous structure, and
A metal layer coated on the surface of the substrate,
The metal layer has a structure in which the thickness increases continuously or intermittently from the surface to a predetermined depth inside the substrate from at least one surface of the substrate, so that the electrical resistance decreases from the surface to the inside. Anode current collector for secondary battery. The method of claim 1,
The metal layer is a metal layer comprising copper, a negative electrode current collector for a secondary battery. The method of claim 1,
The base material of the three-dimensional porous structure is made of one or more selected from a nonwoven fabric shape, a woven shape, or a mesh shape in which elastic polymer fibers are irregularly entangled, a negative electrode current collector for a secondary battery. The method of claim 1,
The thickness of the substrate is 1-500 μm, a negative electrode current collector for a secondary battery. A negative electrode current collector for a secondary battery according to any one of claims 1 to 4;
A lithium metal layer coated on the surface of the negative electrode current collector,
The lithium metal layer on the surface of the substrate is formed thinner or not formed compared to the lithium metal layer inside the substrate, a lithium negative electrode for a secondary battery. modifying the surface of the three-dimensional porous structure substrate;
performing Sn sensitization treatment on the surface-modified substrate;
irradiating UV to at least one surface of the Sn-sensitized substrate;
Activating the UV-irradiated three-dimensional porous substrate; and
A method of manufacturing an anode current collector for a secondary battery, comprising: forming a metal plating layer by performing electroless plating on the activated three-dimensional porous structure substrate. A method of manufacturing a lithium negative electrode for a secondary battery, comprising the step of performing lithium electroplating on the negative electrode current collector for a secondary battery according to claim 6 .

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