KR20140026806A - Negative-electrode and lithium secondary battery with high capacity comprising the same - Google Patents

Abstract

The present invention relates to a negative electrode and a lithium secondary battery with high capacity comprising the same, more specifically to: a negative electrode capable of maximizing the capacity of a battery by preventing the loss of irreversible capacity from the formation of an SEI layer during an initial formation by connecting lithium metal encapsulated with a polymer material to the negative electrode; and a lithium secondary battery with high capacity comprising the same. [Reference numerals] (AA) Laser welding unit for connecting a cathode tap; (BB) Lithium metal encapsulated with a polymer film

Description

A negative electrode and a high capacity lithium secondary battery including the same {NEGATIVE-ELECTRODE AND LITHIUM SECONDARY BATTERY WITH HIGH CAPACITY COMPRISING THE SAME}

The present invention relates to a negative electrode and a high capacity lithium secondary battery including the same.

Recently, interest in energy storage technology is increasing. As the field of application extends to the energy of mobile phones, camcorders, notebook PCs, and even electric vehicles, efforts for research and development of electrochemical devices are becoming more concrete. The electrochemical device is the field that attracts the most attention in this respect, and among them, the development of a secondary battery capable of charging and discharging has become a focus of attention. Recently, in the development of such secondary batteries, research and development on the design of new electrodes and batteries have been conducted in order to improve capacity density and specific energy.

Among the secondary batteries currently applied, lithium secondary batteries developed in the early 1990s have a higher operating voltage and a higher energy density than conventional batteries such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries that use an aqueous electrolyte solution. I am in the spotlight.

In general, a method of manufacturing a lithium secondary battery is to apply a slurry containing a positive electrode active material and a negative electrode active material to each current collector, and then wound or laminated together with a separator, which is an insulator, to prepare and prepare an electrode assembly, and to prepare the electrode assembly in a battery case. And inserting and injecting electrolyte into the battery case to seal the battery case, and performing degassing to remove gas generated during initial formation.

Here, lithium ions are transferred to a carbon-based negative electrode, such as graphite, from the lithium metal oxide used as the positive electrode during the initial charging, and intercalated between the layers of the graphite electrode. At this time, since lithium is highly reactive, lithium reacts with an electrolyte solution (non-aqueous organic solvent) on the graphite negative electrode surface, thereby producing compounds such as Li ₂ CO ₃ , Li ₂ O, and LiOH. These compounds form a kind of passivation layer on the surface of the graphite cathode, which is called a solid electrolyte interface (SEI) layer.

Once formed, the SEI layer acts as an ion tunnel to pass only lithium ions. The ion tunnel solvates lithium ions and moves organic solvents of a large molecular weight electrolyte that move together. Co-intercalated together in the cathode prevents the structure of the carbon anode from collapsing. In addition, the SEI layer suppresses side reactions between lithium ions and graphite anodes or other materials during charge and discharge after formation, thereby allowing the amount of lithium ions to be reversibly maintained.

That is, the SEI layer serves to prevent side reactions between the negative electrode and the electrolyte to prevent further decomposition of the electrolyte and to maintain a stable charge and discharge by maintaining the amount of lithium ions in the electrolyte reversibly. Once formed, the battery's life and cycle characteristics are also improved. Therefore, to improve the performance of the lithium secondary battery, a solid SEI layer must be formed on the negative electrode of the lithium secondary battery.

However, since a certain amount of lithium is essentially consumed in forming the SEI layer, the amount of reversible lithium is inevitably reduced than originally designed. Lithium consumed to form the SEI layer acts as an irreversible capacity to reduce the capacity of the battery.

Thus, the development of a technology that can maximize the capacity of the battery by preventing lithium consumption (ie, irreversible capacity loss) due to the formation of the SEI layer on the negative electrode surface during the initial formation is an urgent time.

Korean Patent Publication No. 10-2010-0128276

The present invention has been made to solve the above-mentioned demands and conventional problems, and to provide a lithium secondary battery capable of maximizing the capacity of the battery by preventing irreversible capacity loss due to the SEI layer formation during the initial formation.

In order to achieve the above technical problem, the present invention provides a negative electrode comprising a negative electrode current collector and a negative electrode active material, characterized in that the lithium metal encapsulated with a polymer material is connected to the negative electrode.

In another aspect, the present invention provides an electrode assembly comprising a positive electrode, a negative electrode as described above, and a separator interposed between the positive electrode and the negative electrode.

In addition, another aspect of the present invention provides a lithium secondary battery comprising the electrode assembly.

The negative electrode according to the present invention is connected to a lithium metal encapsulated in a polymer material, it is possible to maximize the capacity of the battery by preventing irreversible capacity loss due to the SEI layer formation during the initial formation.

1 illustrates a structure in which a lithium metal encapsulated in a polymer material is connected to a negative electrode according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail.

cathode

The present invention is characterized in that in a negative electrode including a negative electrode current collector and a negative electrode active material, lithium metal encapsulated with a polymer material is connected to the negative electrode.

The present invention can maximize the capacity of the battery by connecting the lithium metal to the negative electrode, preventing the irreversible capacity loss caused by the SEI layer formation during the initial formation. Specifically, in the negative electrode of the present invention, the lithium metal serves as a lithium source for providing lithium ions irreversibly consumed in forming the SEI layer during initial formation or supplementing the amount of lithium ions already consumed in forming the SEI layer. Or by performing both of these roles, to prevent the irreversible capacity loss of the battery inevitably accompanying the formation of the SEI layer.

In addition, the present invention encapsulates the lithium metal in a polymer material, thereby preventing the lithium metal from being oxidized in the air. In detail, the lithium metal is encapsulated in a form entirely wrapped by the polymer material, thereby preventing the oxidation of lithium metal in the air.

The form of the lithium metal is not particularly limited. In detail, a sheet may be used.

The method of connecting the lithium metal with the negative electrode is not particularly limited. In detail, the lithium metal may be placed on the negative electrode current collector to be in flat contact so that one surface of the lithium metal is entirely connected to the negative electrode.

The negative electrode current collector is platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS), copper (Cu ), Molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In doped SnO ₂ ), FTO (F doped SnO ₂ ), and alloys thereof The surface of carbon (C), nickel (Ni), titanium (Ti), or silver (Ag) may be used on the surface of copper (Cu) or stainless steel, but is not limited thereto. The shape of the negative electrode current collector is not particularly limited, and may be, for example, in the form of a foil, a film, a sheet, a punched material, a porous body, a foam, or the like.

Specifically, a copper material is used as the negative electrode current collector, and more specifically, a perforated copper foil (porous copper foil) is used.

In one embodiment, the polymer material is an insulating material that can move lithium ions but block outside air. That is, the polymer material is used to compensate for the loss of irreversible capacity due to the formation of the SEI layer. Lithium ions must be free to move, and the lithium metal encapsulated therein is prevented from being oxidized / degraded by contact with air. It is recommended to have an insulating material to prevent unwanted side reactions caused by the direct contact between the lithium metal and the negative electrode current collector.

The form of the polymer material is not particularly limited as long as it can encapsulate lithium metal. For example, it may have a form corresponding to that of lithium metal, and in detail, may be in the form of a sheet or a film.

The method of forming the negative electrode of the present invention by connecting lithium metal encapsulated with a polymer material is not particularly limited. For example, a negative electrode active material (for example, graphite), a conductive material, a binder, a filler (if necessary), and the like are dispersed and mixed in a dispersion medium (solvent) to form a slurry, which is coated on a current collector, and then dried and rolled. To prepare a negative electrode such as. In addition, the sheet-shaped lithium metal may be separately wrapped and sealed with a polymer film of the same material as the separator, and then placed on a porous copper foil, which is a negative electrode current collector, to make planar contact with each other to manufacture the negative electrode of the present invention (see FIG. 1). ).

Electrode assembly and Lithium secondary battery

According to another aspect of the present invention, an electrode assembly comprising a negative electrode, a positive electrode, and a separator interposed between the positive electrode and the negative electrode of the present invention as described above; and a lithium secondary battery comprising the electrode assembly Is provided.

In general, an electrode assembly includes a unit cell based on a cathode composed of a cathode material and a current collector, a cathode composed of an anode material and a current collector, and a separator that blocks electrical contact between the cathode and the cathode and moves lithium ions. One or more are included (eg, a structure in which a plurality of unit cells are overlapped).

The shape of the electrode assembly of the present invention is not particularly limited, and may be, for example, jelly-roll type, stacked type or stack-folded type (including stack-Z-folded type).

In the jelly-roll type electrode assembly, an electrode active material or the like is coated on a metal foil used as a current collector, dried and pressed, cut into a band shape having a desired width and length, and a cathode and an anode are diaphragm- . Although the jelly-roll type electrode assembly is suitable for a cylindrical battery, when applied to a square or pouch type battery, it has disadvantages such as separation of electrode active material and low space utilization.

On the other hand, the stacked electrode assembly is a structure in which a plurality of anode and cathode unit cells are sequentially stacked, and there is an advantage that it is easy to obtain a rectangular shape, but when the manufacturing process is complicated and an impact is applied, the electrode is pushed and a short circuit occurs. There is a disadvantage that is caused.

In order to solve this problem, the electrode assembly of the advanced structure of the jelly-roll-type and stack-type mixed form, the full unit and / or bicell of a certain unit size of continuous separation film of long length A stack-foldable electrode assembly of a folding structure has been proposed. That is, in one embodiment of the present invention, the electrode assembly is a unit cell in a stacked manner to make a bi-cell and / or a full cell and placed a plurality of them on a long separation film (membrane sheet) and then folded sequentially folded It may be a stack-foldable electrode assembly of the structure.

The positive electrode and the negative electrode included in the electrode assembly may be prepared according to conventional methods known in the art. For example, an active material, a conductive material, a binder, a filler (if necessary), and the like are dispersed and mixed in a dispersion medium (solvent) to form a slurry, which is coated on a current collector (for example, aluminum), followed by drying and rolling to form a positive electrode. It can manufacture. The manufacturing of the negative electrode included in the electrode assembly has been described above.

As the active material, conventional ones known in the art may be used. For example, as the positive electrode active material, various kinds of lithium transition metal oxides commonly used in lithium secondary batteries may be used alone or in combination of two or more thereof. In addition, the negative electrode active material may be lithium metal, a lithium alloy (for example, lithium and an alloy of a metal such as aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium), amorphous carbon, crystalline carbon, carbon composite material And SnO ₂ may be used, but the type thereof is not necessarily limited, but the formation of the SEI layer during formation is mainly related to the use of a carbon-based negative electrode. The electrode assembly of the present invention is a carbon-based material (eg, Graphite graphite cathode).

The electrode material (ie, the cathode material and the anode material) including the active material may further include a conductive material to improve electrical conductivity. The conductive material is not particularly limited as long as the conductive material has excellent electrical conductivity without causing side reactions in the internal environment of the lithium secondary battery and without causing chemical changes to the battery. Typically, graphite or conductive carbon may be used.

In addition, the electrode material may further include a binder as a component to assist in the bonding of the active material and the conductive material and the bonding to the current collector. As the binder, polyvinylidene fluoride (PVdF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVdF / HFP), polyvinylacetate, polyvinyl alcohol, polyvinyl ether, etc. may be used. It is not limited.

In addition, a filler may be selectively added to the electrode material as a component that suppresses the expansion of the electrode.

The dispersant may be N-methyl-2-pyrrolidone (NMP), dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), ethanol, isopropanol, water, and mixtures thereof, but is not limited thereto.

The separator included in the electrode assembly is interposed between the positive electrode and the negative electrode to prevent a short circuit therebetween and serve to provide a passage for moving lithium ions.

As the separator, an olefin polymer such as polyethylene or polypropylene, glass fiber, or the like may be used in the form of a sheet, a multilayer, a microporous film, a woven fabric, and a nonwoven fabric, but is not limited thereto. On the other hand, when a solid electrolyte such as a polymer (eg, an organic solid electrolyte, an inorganic solid electrolyte, etc.) is used as the electrolyte, the solid electrolyte may also serve as a separator. Specifically, an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 ~ 10㎛, the thickness may generally range from 5 ~ 300㎛.

In one embodiment, the polymer material and the separator used in the encapsulation of the lithium metal may be made of the same material. For example, polyethylene film containing fine pores; Polypropylene film; Multilayer films made by a combination of these films; And at least one selected from the group consisting of a polymer film for polymer electrolyte of polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, or polyvinylidene fluoride hexafluoropropylene copolymer. The same can be used for encapsulation.

The lithium secondary battery of the present invention can be prepared according to a conventional method in the art, including the electrode assembly as described above. For example, accommodating the electrode assembly provided as described above in a battery case; Injecting an electrolyte into the battery case and then sealing the battery case; Initial charging (forming) to activate the cell; And degassing.

The battery case may be one or more selected from pouch type, cylindrical type and square type, but is not limited thereto. Specifically, a pouch type case is used.

The electrolyte may be used alone or as a mixture of two or more kinds of carbonate, ester, ether or ketone as a non-aqueous electrolyte (non-aqueous organic solvent), but is not limited thereto.

For example, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, methylethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butylolactone, n-methyl acetate, n- Such as ethyl acetate, n-propyl acetate, phosphoric acid triesters, dibutyl ether, N-methyl-2-pyrrolidinone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran Tetrahydrofuran derivatives, dimethyl sulfoxide, formamide, dimethylformamide, dioxolon and derivatives thereof, acetonitrile, nitromethane, methyl formate, methyl acetate, trimethoxy methane, sulfolane, methyl sulfolane, 1,3 Aprotic organic solvents such as dimethyl-2-imidazolidinone, methyl propionate and ethyl propionate may be used, but are not limited thereto. It is not.

Lithium salt may be further added to the electrolyte solution (so-called lithium salt-containing non-aqueous electrolyte solution), and the lithium salt may be well-known in the non-aqueous electrolyte solution, for example, LiCl, LiBr, LiI, and LiClO _4. , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiPF ₃ (CF ₂ CF ₃ ) _3, LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, lithium chloroborane, lower aliphatic lithium carbonate, lithium 4-phenylborate, imide, and the like, but are not necessarily limited thereto.

In the (non-aqueous) electrolyte, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, for the purpose of improving charge and discharge characteristics, flame retardancy, and the like. Nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxy ethanol, aluminum trichloride, etc. It may be. In some cases, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included to impart nonflammability, and carbon dioxide gas may be further included to improve high temperature storage characteristics.

The lithium secondary battery of the present invention can maximize the capacity of the battery by preventing the irreversible capacity loss due to the SEI layer formation during the initial formation by connecting the lithium metal encapsulated with a polymer material to the negative electrode.

Therefore, the lithium secondary battery of the present invention can be suitably used as a power source for medium and large devices in which high capacity and high output characteristics are particularly important, as well as small devices in which irreversible capacity loss due to SEI layer formation is relatively large.

In this aspect, the present invention also provides a battery module including two or more lithium secondary batteries are connected in series or in parallel. The number of lithium secondary batteries included in the battery module may be variously adjusted in consideration of the purpose and capacity of the battery module. Furthermore, the present invention provides a battery pack in which the battery module is electrically connected according to a conventional technique in the art.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. The scope of the present invention should be interpreted based on the scope of the following claims, and all technical ideas within the scope of equivalents thereof should be interpreted in accordance with the following claims: It is to be understood that the invention is not limited thereto.

Claims (13)

In the negative electrode comprising a negative electrode current collector and a negative electrode active material,
An anode characterized in that lithium metal encapsulated with a polymer material is connected to the cathode.
The method of claim 1,
The lithium metal is a negative electrode, characterized in that the sheet (sheet) form.
The method of claim 1,
The lithium metal is a negative electrode, characterized in that encapsulated in a form entirely wrapped by the polymer material.
The method of claim 1,
The lithium metal is located on the negative electrode current collector, the negative electrode, characterized in that connected entirely to the negative electrode by plane contact.
The method of claim 1,
The negative electrode current collector is characterized in that the copper material.
6. The method of claim 5,
The negative electrode current collector is characterized in that the perforated copper foil.
The method of claim 1,
The polymer material is a negative electrode, characterized in that the insulating material that can move the lithium ions but can block the outside air.
The method of claim 1,
The polymer material is a negative electrode, characterized in that the sheet (sheet) or film (film) form.
An electrode assembly comprising an anode, a cathode according to any one of claims 1 to 8, and a separator interposed between the anode and the cathode.
10. The method of claim 9,
The electrode assembly, characterized in that the lithium metal is encapsulated with a polymer material of the same material as the separator is connected.
11. The method of claim 10,
The polymer material may be a polyethylene film including fine pores; Polypropylene film; Multilayer films made by a combination of these films; And a polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, or polyvinylidene fluoride hexafluoropropylene copolymer polymer film for polymer electrolyte.
10. The method of claim 9,
The electrode assembly is an electrode assembly, characterized in that the stack-folding type.
A lithium secondary battery comprising the electrode assembly according to claim 9.

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