KR102111479B1 - Negative electrode and secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a negative electrode and a secondary battery including the same, specifically, a current collector, a graphene layer formed on the current collector, a graphite-based active material layer formed on the graphene layer, and on the graphite-based active material layer A cathode comprising a formed silicon layer is provided.
The negative electrode according to the present invention, including a graphene layer on the current collector, can improve the adhesion and electrical conductivity between the graphite-based active material layer on the graphene layer and the current collector. Furthermore, since a silicon layer is formed on the surface of the graphite-based active material layer, battery capacity may be improved.

Description

A negative electrode and a secondary battery comprising the same {NEGATIVE ELECTRODE AND SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to a negative electrode and a secondary battery comprising the same.

Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative or clean energy is increasing, and as a part, the most actively researched field is the field of power generation and electricity storage using electrochemical reactions.

At present, a representative example of an electrochemical device using such electrochemical energy is a secondary battery, and its use area is gradually expanding. Recently, as technology development and demand for portable devices such as portable computers, portable telephones, and cameras have increased, the demand for secondary batteries as an energy source has rapidly increased, and among such secondary batteries, high energy density and operating potential are exhibited, and cycle life Many studies have been conducted on this long and low self-discharge lithium secondary battery, and it has been commercialized and widely used.

In general, a secondary battery is composed of a positive electrode, a negative electrode, and an electrolyte, and transfers energy while reciprocating both electrodes, such as lithium ions from the positive electrode active material inserted into the negative electrode active material such as carbon particles and desorpted again during discharge by first charging. Because it plays a role, charging and discharging becomes possible.

For example, a lithium secondary battery has a structure in which a lithium electrolyte is impregnated in an electrode assembly composed of a positive electrode comprising a lithium transition metal oxide as an electrode active material, a negative electrode containing a carbon-based active material, and a porous separator. The positive electrode is prepared by coating a positive electrode mixture containing a lithium transition metal oxide on an aluminum foil, and the negative electrode is prepared by coating a negative electrode mixture containing a carbon-based active material on a copper foil.

On the other hand, the negative electrode active material based on silicon has a high capacity of 3570 mAh / g, and exhibits very good storage characteristics, but there is a problem in that the battery performance deteriorates due to repeated expansion and contraction of the material during the continuous charge and discharge process.

Accordingly, development of a cathode having excellent safety and storage capacity is required.

Republic of Korea Registered Patent No. 10-0994181

The first technical problem to be solved of the present invention is to provide a cathode having excellent adhesion between a current collector and an active material layer, and excellent storage capacity and storage efficiency characteristics.

The second technical problem to be solved of the present invention is to provide a method for manufacturing the negative electrode and a secondary battery including the negative electrode.

In order to solve the above problems, the present invention is a negative electrode comprising a current collector and a graphene layer formed on the current collector, a graphite-based active material layer formed on the graphene layer, and a silicon layer formed on the graphite-based active material layer Gives

In addition, the present invention is a step of depositing a graphene layer on the copper current collector by LPCVD (step 1); Coating a slurry containing a graphite-based active material on the graphene layer to form a graphite-based active material layer (step 2); Depositing silicon on the graphite-based active material layer by sputtering and rolling (step 3); And forming a silicon layer by re-depositing silicon on the rolled silicon in a sputtering method (step 4).

Furthermore, the present invention provides a secondary battery including the negative electrode, the positive electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte.

The negative electrode according to the present invention, including a graphene layer on the current collector, can improve the adhesion and electrical conductivity between the graphite-based active material layer on the graphene layer and the current collector. Furthermore, since a silicon layer is formed on the surface of the graphite-based active material layer, lithium precipitation is effectively prevented through active Faradaic reaction at the interface between the electrode and the separator, thereby improving charging and discharging efficiency and improving battery capacity. Can be.

1 is a schematic view showing a cross section of a cathode according to an embodiment of the present invention.

Hereinafter, the present invention will be described in more detail to aid understanding of the present invention.

The terms or words used in the present specification and claims should not be interpreted as being limited to ordinary or lexical meanings, and the inventor can appropriately define the concept of terms in order to best describe his or her invention. Based on the principle that it should be interpreted as meanings and concepts consistent with the technical spirit of the present invention.

The terminology used herein is only used to describe exemplary embodiments, and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

In this specification, the terms "comprises", "haves" or "have" are intended to indicate the presence of implemented features, numbers, steps, elements or combinations thereof, one or more other features or It should be understood that the existence or addition possibilities of numbers, steps, elements, or combinations thereof are not excluded in advance.

The negative electrode according to the present invention provides a negative electrode including a current collector, a graphene layer formed on the current collector, a graphite active material layer formed on the graphene layer, and a silicon layer formed on the graphite active material layer. .

The negative electrode may include a graphene layer on the current collector, and improve adhesion and electrical conductivity between the graphite-based active material layer on the graphene layer and the current collector. Furthermore, since a silicon layer is formed on the surface of the graphite-based active material layer, battery capacity may be improved.

1 shows an embodiment of a negative electrode according to the present invention, the present invention will be described in detail with reference to FIG. 1 below.

The current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or the surface of aluminum or stainless steel. The surface treatment with carbon, nickel, titanium, silver, or the like may be used.

Specifically, a transition metal that adsorbs carbon such as copper and nickel well can be used as a current collector. When the metal is used as a current collector, since the current collector itself can be used as a catalyst layer for graphene production, the process of transferring the manufactured graphene back to the current collector is unnecessary, thereby saving cost and time in the process. It has the advantage of being able to obtain a higher quality graphene layer.

The current collector may have a thickness of 6 μm to 20 μm, but the thickness of the current collector is not limited thereto.

The graphene layer is positioned between the current collector and the graphite-based active material layer, and may improve adhesion between the current collector and the graphite-based active material layer, and may serve to improve electrical conductivity.

The graphene layer may include graphene. The graphene may be in the form of a sheet, and the sheet is a thin film composed of one carbon atom, and the thickness of one sheet may be about 0.35 nm. The graphene layer may be stacked in the form of several sheets of graphene in the form of an overlapping layer. At this time, the surface of the sheet may be arranged parallel to the surface of the current collector. The gap between the sheet-like graphene and the closest another sheet-like graphene may be 0.3 nm to 0.4 nm.

The graphene of the graphene layer may be composed of graphene, graphene oxide, reduced graphene oxide, or a mixture thereof. Since graphene, graphene oxide, reduced graphene oxide, or a mixture thereof has high surface energy, it provides a property of significantly increasing the bonding strength with the graphite-based active material layer coated thereon. Therefore, since the adhesive strength between the current collector and the graphite-based active material layer is strong, desorption of the graphite-based active material particles can be reduced.

The thickness of the graphene layer may be 1 nm to 5 nm. If the thickness of the graphene layer is less than 1 nm, the effect of improving the adhesion strength may be insignificant, and if it is more than 5 nm, a problem of insufficient electrical conductivity may occur.

The graphite-based active material layer may include a graphite-based active material that plays a role of intercalation and deintercalation of lithium ions, so as to serve as a negative electrode.

In this case, the graphite-based active material layer may include a graphite-based active material, a conductive material, and a binder. Specifically, the graphite-based active material layer may be prepared by applying a slurry made by mixing a negative electrode mixture containing the graphite-based active material particles, a conductive material, and a binder in an organic solvent or distilled water onto a negative electrode current collector, followed by drying and rolling. Can be.

As the graphite-based active material, one or more selected from the group consisting of natural graphite, artificial graphite, soft carbon, and hard carbon may be used, but in particular, when using natural graphite or artificial graphite, battery efficiency may be increased. Since natural graphite is cheaper than other types of graphite and has a relatively large specific surface area, when using natural graphite, the output characteristics of the battery may be excellent. Artificial graphite has better solid diffusion than natural graphite, so it can be excellent in battery efficiency when using artificial graphite. In addition, when the graphene layer is used together with artificial graphite, mechanical and chemical properties of the electrode may be improved by improving the adhesion between the artificial graphite and the current collector.

The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon blacks such as carbon black, acetylene black, ketjen black, channel black, panes black, lamp black, and thermal black; Conductive fibers such as carbon fibers and metal fibers; Conductive tubes such as carbon nanotubes; Metal powders such as fluorocarbon, aluminum, and nickel powders; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

The binder includes polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride, polyacrylonitrile, polymethylmethacrylate, Polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropyl cellulose, recycled cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), Various types of binder polymers such as sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, poly acrylic acid, and polymers substituted with hydrogen, Li, Na, or Ca, or various copolymers can be used. Can be.

The thickness of the graphite-based active material layer may be 40 μm to 100 μm. If the thickness of the graphite-based active material layer is less than 40 μm, a problem in which the capacity of the battery is not sufficient may occur, and when the thickness of the graphite-based active material layer is greater than 100 μm, a thickness of the battery may become too thick.

The silicon layer, as a high-capacity anode material, is used together with a graphite-based active material layer to increase the capacity of the anode, and can be prevented from being precipitated by lithium by being located on the outermost surface of the anode. In addition, when the cycle of the secondary battery is repeated to fulfill its role, the lithium-silicon alloy is present, and the graphite-based active material layer existing at the bottom of the silicon layer can serve as a negative electrode.

The silicon layer may be formed by a sputtering method, and accordingly, silicon in the silicon layer may have an amorphous structure. Since the amorphous silicon has higher elasticity than crystalline silicon, loss due to volume expansion of silicon may be reduced.

On the other hand, as an example of the manufacturing process of the silicon layer, after the first sputtering to prepare some silicon layer, rolling may be applied, and accordingly, some silicon of the silicon layer may penetrate to the top of the graphite-based active material layer. Therefore, the graphite-based active material layer and the silicon layer may exist in an overlapped state.

In this way, by penetrating silicon to the top of the graphite-based active material layer, a part of the graphite-based active material of the graphite-based active material layer may exist in a form surrounding the silicon. There is an effect in that the movement of electrons is more easy, and thus the output characteristics and the capacity characteristics are excellent.

The thickness of the silicon layer may be 1 μm to 20 μm. If the thickness of the silicon layer is less than 1 μm, lithium may be deposited on the surface of the negative electrode, and when the thickness of the silicon layer is greater than 20 μm, excessive capacity loss due to volume expansion due to charge and discharge may occur.

 The cathode manufacturing method according to the present invention comprises the steps of depositing a graphene layer on a copper current collector by a LPCVD (Low-Pressure Chemical Vapor Deposition) method (step 1); Coating a slurry containing a graphite-based active material on the graphene layer to form a graphite-based active material layer (step 2); Depositing silicon on the graphite-based active material layer by sputtering and rolling (step 3); And

It includes; re-depositing silicon on the rolled silicon by sputtering to form a silicon layer (step 4).

Hereinafter, the cathode manufacturing method according to the present invention will be described in detail for each step.

In the cathode manufacturing method according to the present invention, step 1 is a step of depositing a graphene layer on the copper current collector by LPCVD. Through the above steps, a graphene layer may be formed on the current collector, and adhesion and electrical conductivity between the graphite-based active material layer and the current collector on the graphene layer to be formed in a subsequent process may be improved.

The copper metal can be utilized as a catalyst layer for graphene production as a transition metal that adsorbs carbon well, so the process of transferring the prepared graphene back to the current collector is unnecessary, thereby saving cost and time in the process. It has the advantage of obtaining a higher quality graphene layer.

Specifically, the LPCVD deposition conditions in step 1 may be as follows. That is, LPCVD uses a mixed gas of hydrogen and methane on the current collector, but H2 / CH4 satisfies a flow rate ratio of 1/7 to 1/15, and a current collector temperature of 700 ° C to 1000 ° C, 0.5 hour to It can be performed under the condition of a growth time of 2 hours and a pressure of 500 mTorr.

In general, the CVD method using plasma is performed at a lower temperature and a higher pressure than the LPCVD method, so the quality of crystallinity, efficiency, etc. of the formed graphene layer is not good. The present invention can provide an improved graphene layer using LPCVD rather than PECVD.

In the negative electrode manufacturing method according to the present invention, step 2 is a step of forming a graphite-based active material layer by coating a slurry containing a graphite-based active material on the graphene layer. Through the above step, by forming a layer of a graphite-based active material that performs the role of insertion and desorption of lithium ions, it is possible to perform the role of a negative electrode.

At this time, the slurry of step 2 may include a conductive material and a binder in addition to the graphite-based active material. Specifically, the graphite-based active material layer may be prepared by applying a slurry made by mixing a negative electrode mixture containing the graphite-based active material particles, a conductive material, and a binder with an organic solvent on a negative electrode current collector, followed by drying and rolling. . Specifically, the weight ratio of the graphite-based active material, the conductive material, and the binder in the slurry may be 93 to 97: 1 to 3: 2 to 4.

In the cathode manufacturing method according to the present invention, step 3 is a step of depositing and rolling silicon on the slurry coating layer by sputtering. Through the above steps, a silicon layer capable of exhibiting high-capacity negative electrode properties can be formed on the graphite-based active material layer, and some silicon in the silicon layer penetrates to the top of the graphite-based active material layer by performing rolling, and the graphite-based active material Since the portion in contact with the graphite-based active material of the layer and the silicon becomes wider, it is easier to transfer lithium ions and electrons, thereby exhibiting excellent output characteristics and capacity characteristics.

Specifically, the sputtering condition in step 3 may be as follows. That is, sputtering may be performed under argon gas atmosphere, a substrate temperature of 50 ° C. to 100 ° C. (current collector performed up to step 2), and a pressure of 5 mTorr at 200 W power.

The rolling of step 3 may be carried out at a pressure of 0.1 MPa to 100 MPa, and some silicon may penetrate to the top of the graphite-based active material layer by the rolling. Accordingly, since the portion in contact with the graphite-based active material and the silicon becomes wider, the transfer of lithium ions and electrons is easier, so that output characteristics and capacity characteristics can be excellent.

If, when the rolling of the step 3 is performed at a pressure of less than 0.1 MPa, there may be a problem that the contact area between the silicon and the graphite-based active material is not sufficiently secured, and when performed at a pressure greater than 100 MPa, the graphite-based A problem in which the active material is destroyed may occur.

In the cathode manufacturing method according to the present invention, step 4 is a step of forming a silicon layer by re-depositing silicon on the rolled silicon by sputtering. In this step, it is a step of re-depositing silicon on the rolled silicon to prepare a silicon layer including the silicon rolled in step 3 and the silicon deposited in step 4.

Through the above steps, a silicon layer capable of exhibiting high-capacity cathode characteristics may be formed on the graphite-based active material layer, wherein the sputtering in step 4 is a substrate of 50 ° C to 100 ° C in an argon gas atmosphere, 200W power ( Current collector performed up to step 3) temperature, may be performed under a pressure condition of 5mTorr.

The silicon layer according to steps 3 and 4 may be formed by performing the above process once, but is not limited thereto, and is repeated several times to achieve overlap between a specific thickness and a silicon layer and a graphite-based active material layer. It may be.

The present invention provides a secondary battery including the negative electrode, the positive electrode and a separator interposed between the negative electrode and the positive electrode, and an electrolyte. The negative electrode, including a graphene layer on the current collector, has excellent adhesion and electrical conductivity between the graphite-based active material layer on the graphene layer and the current collector, and is a high capacity including a silicon layer, so the secondary containing the negative electrode The battery is of high capacity, high power and high safety.

Meanwhile, the positive electrode may be prepared by applying a slurry made by mixing a positive electrode mixture containing positive electrode active material particles, a conductive material, and a binder in an organic solvent, onto a positive electrode current collector, followed by drying and rolling.

The positive electrode active material is not particularly limited, and specifically, a lithium transition metal oxide may be used. As the lithium transition metal oxide, for example, Li · Co-based composite oxide such as LiCoO ₂ , Li · Ni · Co • Mn-based composite oxide such as LiNi _x Co _y Mn _z O ₂ , Li · such as LiNiO ₂ And Li-Mn-based composite oxides such as Ni-based composite oxides and LiMn ₂ O _4. These may be used alone or in combination of a plurality of them.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surfaces treated with carbon, nickel, titanium, silver, or the like may be used.

The binder includes polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride, polyacrylonitrile, polymethylmethacrylate, Polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), Various types of binder polymers such as sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, poly acrylic acid, and polymers substituted with hydrogen, Li, Na, or Ca, or various copolymers can be used. Can be.

The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon blacks such as carbon black, acetylene black, ketjen black, channel black, panes black, lamp black, and thermal black; Conductive fibers such as carbon fibers and metal fibers; Conductive tubes such as carbon nanotubes; Metal powders such as fluorocarbon, aluminum, and nickel powders; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

As the separator, a conventional porous polymer film conventionally used as a separator, such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer, etc. A porous polymer film made of a polymer may be used alone or by laminating them, or a conventional porous nonwoven fabric, for example, a high melting point glass fiber, a polyethylene terephthalate fiber, or the like, may be used, but is not limited thereto. no.

The electrolyte may include a non-aqueous organic solvent and a metal salt.

As the non-aqueous organic solvent, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyl lactone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxorun, formamide, dimethylformamide, dioxol , Acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxy methane, dioxone derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbohydrate Aprotic organic solvents such as nate derivatives, tetrahydrofuran derivatives, ethers, methyl pyropionate and ethyl propionate can be used.

The metal salt may be a lithium salt, the lithium salt is a material that is soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF _{3 SO 3, LiCF 3 CO 2,} LiAsF 6, LiSbF 6, LiAlCl 4, CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, 4-phenyl Lithium borate, imide and the like can be used.

According to another embodiment of the present invention, a battery module including the secondary battery as a unit cell and a battery pack including the same are provided. Since the battery module and the battery pack include the secondary battery having excellent capacity characteristics and stability, it can be used as a power source for devices such as mobile electronic devices, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles or power storage devices. Can be.

Claims (16)

delete delete delete delete delete delete delete delete Depositing a graphene layer on the copper current collector by LPCVD (step 1);
Coating a slurry containing a graphite-based active material on the graphene layer to form a graphite-based active material layer (step 2);
Depositing silicon on the graphite-based active material layer by sputtering and rolling (step 3); And
And forming a silicon layer by re-depositing silicon on the rolled silicon by sputtering (step 4);
The method of claim 9,
The LPCVD method of step 1 is performed under conditions of a flow rate of 1/7 to 1/15 under H2 / CH4, a current collector temperature of 700 ° C to 1000 ° C, a growth time of 0.5 to 2 hours, and a pressure of 500 mTorr. Cathode manufacturing method characterized by.
The method of claim 9,
The slurry of step 2 includes a conductive material and a binder in addition to the graphite-based active material, and the weight ratio of the graphite-based active material, the conductive material, and the binder is 93 to 97: 1 to 3: 2 to 4.
The method of claim 9,
The rolling of step 3 is a negative electrode manufacturing method characterized in that proceeds at a pressure of 0.1 MPa to 100 MPa. delete delete delete delete

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