KR101187347B1 - Anode of lithium secondary battery and manufacturing method thereof - Google Patents

Abstract

According to one aspect of the invention, forming a silicon layer on a substrate, supplying a pretreatment gas to the surface of the silicon layer, etching the silicon layer to form a plurality of silicon rods spaced apart from each other, conductive A method of forming a negative electrode of a lithium secondary battery is provided, the method including filling a spaced space between the silicon rods with a solution and drying the conductive solution to form a current collector in the spaced space.
According to another aspect of the invention, there is provided a negative electrode of a lithium secondary battery comprising a substrate, a plurality of silicon rods formed spaced apart from each other on one surface of the substrate and a current collector to fill the separation space between the silicon rods.

Description

Anode of lithium secondary battery and method of forming the same {Anode of lithium secondary battery and manufacturing method

The present invention relates to a negative electrode (anode) and a manufacturing method used for a lithium secondary battery, and more particularly to a negative electrode for a lithium secondary battery having a high capacity and excellent cycle life characteristics by using silicon as a negative electrode active material will be.

The lithium secondary battery includes a cathode and an anode in which recalation and deintercalation of lithium ions moving through a separator are interposed between electrolytes. Lithium ions move between the positive electrode and the negative electrode through an electrolyte consisting of an organic electrolyte or a solid electrolyte, and the charge and discharge of electrical energy occurs as the lithium ions are inserted into and separated from the positive electrode and the negative electrode.

Such lithium secondary batteries have recently been accompanied by the development of small portable electronic products such as wireless mobile communication devices, notebook computers, etc., and the demand for such power sources is increasing. Lithium secondary batteries used in such applications require high storage capacity and excellent cycle characteristics due to charge and discharge.

Conventionally, as an active material used for a positive electrode, a chalcogenide-based composite oxide containing cobalt (Co), manganese (Mn), and nickel (Ni) having excellent cycle characteristics is mainly used.

Moreover, metal lithium was initially used as an active material of a negative electrode. However, metal lithium is inferior in reversibility during charging and discharging, and when charging, lithium grows into resin and penetrates a separator and contacts an anode, thereby causing an internal short circuit or an explosion of a battery.

Due to these problems, the most widely used negative electrode active material is a carbon-based material. Carbonaceous materials have the advantage of low volume change and excellent reversibility when lithium is inserted. Representative carbon-based negative electrode active materials react with lithium as graphite to form LiC ₆ .

However, the theoretical specific capacity of such carbon-based materials is not high, and for graphite, for example, the maximum theoretical theoretical capacity is only 372 Ah / kg. Therefore, in order to manufacture a battery having a higher capacity, it is necessary to develop a negative active material having a higher specific capacity.

Under these technical backgrounds, silicon (Si), tin (Sn), bismuth (Bi) and the like have been proposed as new anode active materials. All of these materials have higher maximum capacities than carbonaceous materials. As an example, silicon reacts with lithium to form Li ₂ 1Si ₅ , and the theoretical maximum capacity is 4010 Ah / kg, which is 10 times higher than graphite. Therefore, these materials are highly applicable to the negative electrode active material of a high capacity battery.

However, all these materials involve high volume expansion upon reaction with lithium. That is, in the filling process, more lithium ions are inserted into the material than in the conventional carbon-based material, and the increase in lithium content causes significant volume expansion compared to the carbon-based material.

 The extreme volume change during the insertion / extraction of lithium causes high stress on the electrode itself when the battery is driven. Therefore, there is a problem that not only the cycle characteristics of the battery is deteriorated but also the life is significantly shortened as the battery itself is damaged.

An object of the present invention is to provide a method for forming a negative electrode of a lithium secondary battery having a stable cycle characteristics even after repeated charge and discharge by relieving the stress caused by the reaction with lithium and the negative electrode produced by the method.

In addition, another object of the present invention is to provide a lithium secondary battery having such a negative electrode structure.

The object of the present invention is not limited to those mentioned above, and other objects not mentioned will be clearly understood by those skilled in the art from the following description.

According to an aspect of the present invention for solving the above problems, forming a silicon layer on a substrate, supplying a pretreatment gas to the surface of the silicon layer, a plurality of silicon spaced apart from each other by etching the silicon layer A method of forming a negative electrode of a lithium secondary battery is provided, comprising: forming a rod, filling a space between the silicon rods with a conductive solution, and drying the conductive solution to form a current collector in the space.

In this case, the separation space may be partially embedded by the conductive solution.

In addition, the forming of the silicon layer may include stacking a single crystal silicon wafer.

As another example, the forming of the silicon layer may include depositing polycrystalline silicon or amorphous silicon by physical vapor deposition or plasma chemical vapor deposition.

On the other hand, the pretreatment gas may be a fluorocarbon gas, for example CF _4, C ₂ F ₆ or At least one of C ₃ F ₈ .

According to another aspect of the invention, there is provided a negative electrode of a lithium secondary battery comprising a substrate, a plurality of silicon rods formed spaced apart from each other on one surface of the substrate and a current collector to fill the separation space between the silicon rods.

In this case, the current collector may fill a part of the separation space and may include copper.

Meanwhile, the substrate may include a polymer material or a metal in a thin plate form.

According to another aspect of the present invention, a lithium secondary battery including a positive electrode, a negative electrode, an ion permeable membrane, the negative electrode is a substrate, a plurality of silicon rods formed on one surface of the substrate spaced apart from each other and a space for filling the space between the silicon rods A lithium secondary battery including the whole may be provided.

In the case of the lithium secondary battery using the negative electrode structure according to the present invention, the stress caused by the volume change during charge and discharge generated by using the silicon as the negative electrode active material is remarkably alleviated, so that the charge and discharge cycle characteristics with high storage capacity and stable Will be displayed. Therefore, a lithium secondary battery having a high capacity and a long lifespan can be manufactured.

The effects of the present invention are not limited to those mentioned above, and other effects, which are not mentioned above, will be clearly understood by those skilled in the art from the following description.

1 to 5 show step by step a method of manufacturing a negative electrode according to an embodiment of the present invention.
6 is a plan view of the cathode structure of FIG.
7 to 8 illustrate the insertion process of lithium ions in the negative electrode according to an embodiment of the present invention during charging.
9 is a plan view of a cathode structure in which lithium ions are inserted.
10 is a result of observing the silicon rod formed by the method according to an embodiment of the present invention.
11 to 12 are the results of observing the structure of the silicon rod and the current collector manufactured according to an embodiment of the present invention.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention. In the following description of the present invention, detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

1 to 5 illustrate a method of manufacturing a negative electrode according to an embodiment of the present invention.

Referring to FIG. 1, a substrate 101 for forming a cathode is provided. In this case, the substrate 101 may be a substrate having a flexible material having elasticity and may be a polymer material. For example, any one of polyphenylene, polyimide, polydimethylsiloxane, and polyphenylene sulfide may be used.

As another example, the substrate 101 may be a metal in a thin plate form, and as an example, an electrolytic copper foil may be used.

Next, as shown in FIG. 1, the silicon layer 102 is formed on one surface of the substrate 101. In this case, the silicon layer 102 may be monocrystalline silicon, polycrystalline silicon, or amorphous silicon.

In the case where the silicon layer 102 is single crystal silicon, it can be formed by directly stacking a single crystal silicon wafer on one surface of the substrate 101. In this case, one surface of the single crystal silicon wafer may be polished to reduce its thickness.

When the silicon layer 102 is polycrystalline silicon or amorphous silicon, it may be formed by physical vapor deposition such as sputtering or plasma enhanced chemical vapor deposition.

Next, as shown in FIG. 2, a gas supply step of supplying a predetermined gas 103 to the surface of the silicon layer 102 is performed. In this case, the predetermined gas 103 supplied to the surface of the silicon layer 102 may be referred to as a pretreatment gas. Such a pretreatment gas may physically or chemically modify the surface of the silicon layer 102 to form an unetched region that is not etched for a particular etching gas in an etching process subsequent to a portion of the surface of the silicon layer 102.

In this case, the non-etched region may include a region in which the non-etched material 104 derived from the pretreatment gas 103 supplied to the surface of the silicon layer 102 is formed on the surface of the silicon layer 102, or the pretreatment gas 103 supplied thereto. The surface of the silicon layer 102 may be a physically or chemically modified region so that the silicon layer 102 may not be etched during the etching process.

In this case, the non-etched regions formed by the surface modification may be distributed on the surface of the silicon layer 102 at random intervals of minute regions having an average diameter of several hundred nanometers.

In this case, the pretreatment gas may be a fluorocarbon gas, for example CF ₄ C ₂ F _{6 ,} or At least one of C ₃ F ₈ . For example, in the step of blowing CF ₄ , which is a fluorocarbon gas, directly onto the silicon layer 102 for a predetermined time on the surface of the silicon layer 102, fine particles containing a material derived from the CF ₄ gas are formed. It may be formed on the surface of the silicon layer 102. In this case, the particle 104 is a material that is not etched in the subsequent etching of the silicon layer 102 and is a carbon particle or a compound particle including carbon formed by reduction of the fluorocarbon gas on the surface of the silicon layer 102. Can be.

Alternatively, the surface of the silicon layer 102 may react with the CF ₄ gas while the CF ₄ gas is supplied, thereby modifying a partial region of the surface of the silicon layer 102 into an unetched region.

After the step of supplying the pretreatment gas 103 over the silicon layer 102 is completed, the silicon layer 102 is etched in the subsequent etching process. As a result of the etching process, only a part of the silicon layer 102 is etched, as shown in FIG. 3. As shown, a rod-shaped silicon rod 105 is formed.

That is, the non-etched region, for example, the region in which the non-etched material 104 is formed is not etched in the etching process and thus serves as a mask in the etching process. Accordingly, as shown in FIG. 3, as the non-etched region is not etched and the silicon layer 102 is etched in other regions, a rod-shaped silicon rod 105 may be formed.

In this case, the etching gas may be a fluorocarbon gas, for example CF ₄ C ₂ F _6, or At least one of C ₃ F ₈ .

10 shows the observation result of the silicon rod 105 formed using CF ₄ gas as a pretreatment gas and an etching gas on a single crystal silicon wafer. At this time, the pressure of the pretreatment gas was 30mTorr, and the etching process was performed for 120 minutes by applying a plasma acceleration voltage of -600V.

The silicon rods 105 are formed by transferring the non-etched regions formed on the surface of the silicon layer 102 to the silicon layer 102, and are formed in plural with the spaces D1 spaced apart from each other as shown in FIG. 3. Therefore, when appropriately adjusting the distribution of the non-etched region on the surface of the silicon layer 102, the size of the cross-sectional area of the silicon rod 105 or the distance D1 between the silicon rods 105 may be controlled.

In this case, the type of pretreatment gas, flow rate, pressure, and temperature of the silicon layer 102 may be appropriately selected to adjust the distribution of the non-etched region 104.

On the other hand, supplying the pretreatment gas to the surface of the silicon layer 102 and etching the silicon layer 102 may be performed in-situ in the same etching chamber.

That is, the gas supply step of introducing the substrate 101 on which the silicon layer 102 is formed into an etching chamber having a predetermined vacuum degree and then blowing a pretreatment gas having a predetermined pressure onto the surface of the silicon layer 102 for a suitable time is performed. To perform.

Next, when the gas supply step is completed, the plasma is immediately generated in the etching chamber to perform the etching process of the silicon layer 102.

As the pretreatment gas and the etching gas, both fluorocarbon-based gas may be used, and the same gas may be used, but the present invention is not limited thereto, and a heterogeneous gas may be used.

The space D1 between the silicon rods 105 may use a space for accommodating volume expansion generated when the silicon rod 105 as a negative electrode active material reacts with lithium ions to form a lithium-silicon compound. This will be described in more detail in the section describing the reaction mode in the charging process of the negative electrode.

When the formation of the silicon rod 105 is completed, the spaced space of the silicon rod 105 is filled using the conductive solution 106 as shown in FIG. 4.

In this case, the conductive solution 106 may be, for example, a dispersible ink in which a conductor of minute size is dispersed in a solvent. As another example, it may be a solution ink in which the organometallic complex compound is completely dissolved in a solvent.

The conductor included in the conductive solution 106 forms a current collector in a subsequent drying process, wherein the conductor may be a metal that does not react with lithium, for example, copper (Cu) or silver (Ag).

In the case of a dispersible ink, the conductor may include conductor particles. Such conductor particles may include metal particles, for example copper or silver particles. In this case, the particles may be in the form of powder, plate, beads, fibers, balls, for example, and may also be nanoparticles having a diameter in the range of 10 to 100 nm.

The solution ink includes an organometallic complex compound present in the form of an organometallic in a solvent, wherein the metal may include copper or silver.

In this case, as the solvent of the above-described inks, water, an organic solvent, or water may include one or more organic solvents.

The method of filling the space D1 using the conductive solution 106 may be variously selected according to the physical properties of the ink or the shape of the substrate. For example, inkjet spraying, spin coating, dip coating, or the like can be used.

For example, in the case of using the inkjet injection method, the space between the silicon rods 105 may be filled by spraying the conductive solution 106 onto the structure on which the silicon rods 105 are formed as shown in FIG. 3 using an inkjet injector.

The conductive solution 106 is buried between the silicon rods 105 and then dried by heat treatment to remove the solvent of the conductive solution 106 by scattering and removing the current collector 108 made of a solid conductor as shown in FIG. 5. ).

For example, when the conductive solution 106 contains copper particles or a copper complex compound, when the solvent is completely scattered in the drying process, the current collector 108 is formed in a form in which the copper particles or the copper complex compound are aggregated with each other.

In this case, a method such as annealing or rapid thermal annealing in the heat treatment furnace may be used.

In this case, the current collector 108 may fill a part of the separation space D1 between the silicon rods 105. That is, only a portion of the current collector 108 may be embedded in the separation space D1 in the extending direction of the silicon rod 105 from the substrate 101 and the upper space may be left as an empty space.

In this case, the current collector 108 filling the lower space serves as a support for supporting the silicon rod 105 to stably stand, as well as providing a path of movement of electrons as a conductor.

The upper space where the current collector 108 is not embedded may be used as a space to accommodate the volume expansion generated by the reaction of lithium ions and the silicon rod 105. That is, as the lithium ions moved through the electrolyte during charging of the lithium secondary battery react with the silicon rod 105 to form a lithium-silicon intermetallic compound (Li ₂₁ Si ₅ ), volume expansion occurs. At this time, since the volume expansion in the lateral direction of the silicon rod 105 (that is, the vertical direction of the extension direction of the silicon rod 105) is the volume expansion into the empty space, the possibility of occurrence of stress due to the reaction force that prevents such volume expansion Will be significantly lowered.

FIG. 6 is a plan view of the cathode structure shown in FIG. 5. 5 and 6, the cathode 100 according to the exemplary embodiment of the present invention may be spaced apart from a substrate 101, a plurality of silicon rods 105 and silicon rods 105 spaced apart from each other on one surface of the substrate. It can be seen that the current collector 108 to fill the space (D1).

7 and 8 illustrate the reaction pattern of the negative electrode active material during charging in the lithium secondary battery having the negative electrode according to the present invention.

Referring to FIG. 7, lithium ions 701 detached from a positive electrode (not shown) during charging of a lithium secondary battery having a negative electrode according to the present invention pass through a separator 702 through an electrolyte (not shown) as a negative electrode. To the side.

The lithium ions 701 which have moved to the negative electrode react with the silicon rod 105 as the negative electrode active material to form the lithium-silicon intermetallic compound 105a as shown in FIG. 8. In this case, since the current collector 108 is made of a material that does not react with lithium, for example, copper, only the upper region of the silicon rod 105, not the region buried by the current collector 108, reacts with the lithium ion 701. Done.

Due to this reaction, volume expansion occurs in the upper region of the silicon rod 105 as shown in FIG. 8. 9 is a plan view of this volume expanded cathode structure. 8 and 9, the space D2 between the lithium-silicon intermetallic compounds 105a formed by the reaction is reduced compared to the space D1 between the silicon rods 105 before the reaction.

In this case, as shown in FIG. 9, when the separation space D2 has a value greater than 0, it corresponds to a case in which there is no contact between the lithium-silicon intermetallic compound 105a. Practically not happening.

In some cases, the contact between the lithium-silicon intermetallic compound 105a is generated by the above-described volume expansion, so that the space D2 may be zero. However, even in such a case, as the expanded volume is accommodated corresponding to the separation space D1, the stress due to the volume expansion is reduced by that amount.

According to the negative electrode structure according to the present invention, even if a sudden expansion of the silicon, the negative electrode active material generated during charging, the stress is significantly reduced accordingly, and thus has a stable cycle characteristics even by repeated charging and discharging .

Hereinafter, experimental examples are provided to help the understanding of the present invention. It should be understood, however, that the following examples are for the purpose of promoting understanding of the present invention and are not intended to limit the scope of the present invention.

Experimental Example 1

FIG. 11A is a result of observing a silicon rod 105 formed on a single crystal silicon wafer by a method according to an embodiment of the present invention, and FIG. 11B shows a current collector containing silver in a space between the silicon rods 105. 108) is the result of observation after embedding. At this time, CF ₄ gas was used for both the pretreatment gas and the etching gas.

The current collector 108 of FIG. 11B was formed by using a spin coating method of a conductive solution containing silver. After the spin coating was completed, the current collector 108 was cured by rapid heat treatment.

As shown in FIG. 11A, the silicon rods 105 formed on the single crystal silicon wafer have a height of about 490 nm and are randomly spaced apart from each other. Meanwhile, as shown in FIG. 11B, the space between the silicon rods 105 may be almost filled by the current collector 108 including silver.

Experimental Example 2

FIG. 12A is a result of observing a silicon rod 105 formed using CF ₄ as a pretreatment gas and an etching gas on a single crystal silicon wafer as in Experimental Example 1, and FIG. 12B illustrates an inkjet spray method of a conductive solution containing silver. This is the result of observing the current collector 108 formed by annealing in a heat treatment furnace after spraying on.

As in Experimental Example 1, it can be seen that the gap between the minutely formed silicon rods 105 is almost filled by the current collector 108.

The foregoing description of specific embodiments of the invention has been presented for purposes of illustration and description. Therefore, the present invention is not limited to the above embodiments, and various modifications and changes can be made by those skilled in the art within the technical spirit of the present invention in combination with the above embodiments. Do.

101: substrate 102: silicon layer
103: pretreatment gas 201: non-etched material
105: silicon rod 106: conductive solution
108: whole house

Claims (11)

Forming a silicon layer on the substrate;
Supplying a pretreatment gas to the silicon layer surface;
Etching the silicon layer to form a plurality of silicon rods spaced apart from each other;
Filling gaps between the silicon rods with a conductive solution; And
Drying the conductive solution to form a current collector in the separation space;
A method of forming a negative electrode of a lithium secondary battery comprising a. The method of claim 1, wherein a portion of the separation space is buried. The method of claim 1, wherein the forming of the silicon layer comprises stacking a single crystal silicon wafer. The method of claim 2, wherein the forming of the silicon layer comprises depositing polycrystalline silicon or amorphous silicon by physical vapor deposition or plasma chemical vapor deposition. The method of claim 1, wherein the pretreatment gas comprises a fluorocarbon gas. The method of claim 5, wherein the fluorocarbon gas is CF ₄ C ₂ F _6, or A method of forming a negative electrode of a lithium secondary battery, comprising any one or more of C ₃ F ₈ . Board;
A plurality of silicon rods formed spaced apart from each other on one surface of the substrate; And
A current collector filling a space between the silicon rods;
A negative electrode of the lithium secondary battery comprising a. The method of claim 7, wherein the current collector fills a portion of the separation space. The negative electrode of claim 7, wherein the current collector comprises copper (Cu) or silver (Ag). The method of claim 7, wherein the substrate comprises a polymer material or a metal in a thin plate form. In a lithium secondary battery comprising a positive electrode, a negative electrode, an ion permeable membrane, the negative electrode is
Board;
A plurality of silicon rods formed spaced apart from each other on one surface of the substrate; And
A current collector filling a space between the silicon rods;
Lithium secondary battery comprising a.

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