KR101338299B1 - Secondary Battery for High Voltage - Google Patents

Abstract

The present invention, the positive electrode active material is a lithium transition metal oxide of the formula (1), the negative electrode active material is natural graphite, the natural graphite has a BET of 2.5 to 2.6 m ² / g, the positive electrode loading amount is 2.3 to 2.4 mAh / cm ² And, the negative electrode loading amount provides a secondary battery, characterized in that 2.5 to 2.7 mAh / cm ² . The secondary battery has an advantage of excellent high voltage characteristics.
Li (Ni _x Mn _y Co _z ) O ₂ (1)
In the above formula, 0.2 ≦ x ≦ 0.3, 0.6 ≦ y ≦ 0.7, 0 <z ≦ 0.2, and x + y + z = 1.

Description

Secondary Battery for High Voltage

The present invention relates to a secondary battery for high voltage, more specifically, the positive electrode active material is a lithium transition metal oxide of a specific composition, the negative electrode active material is natural graphite, the natural graphite has a BET of 2.5 to 2.6 m ² / g, The positive electrode loading amount is 2.3 to 2.4 mAh / cm ² , the negative electrode loading amount relates to a secondary battery consisting of 2.5 to 2.7 mAh / cm ² .

As technology development and demand for mobile devices have increased, there has been a rapid increase in demand for secondary batteries as energy sources. Among such secondary batteries, lithium secondary batteries, which exhibit high energy density and operational potential, long cycle life, Batteries have been commercialized and widely used.

In recent years, there has been a growing interest in environmental issues, and as a result, electric vehicles (EVs) and hybrid electric vehicles (HEVs), which can replace fossil-fueled vehicles such as gasoline vehicles and diesel vehicles, And the like. Although a nickel metal hydride (Ni-MH) secondary battery is mainly used as a power source for such an electric vehicle (EV) and a hybrid electric vehicle (HEV), a lithium secondary battery having a high energy density, a high discharge voltage, Research is being actively carried out, and some are commercialized.

The lithium secondary battery has a structure in which a non-aqueous electrolyte containing a lithium salt is impregnated in an electrode assembly having a porous separator interposed between a positive electrode and a negative electrode coated with an active material on a current collector.

Lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium composite oxide, etc. are used as a positive electrode active material of such a lithium secondary battery, and a carbon material is mainly used as a negative electrode active material, and a silicon compound, a sulfur compound, etc. Use is also considered.

However, there is a situation in which a combination of a positive electrode and a negative electrode material that satisfies the high voltage characteristics required by the electric vehicle is not found.

Therefore, there is a very high need for a technology that can fundamentally solve the above problems.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

The inventors of the present application after extensive research and various experiments, as described later, the positive electrode active material is a lithium transition metal oxide of a specific composition, the negative electrode active material is natural graphite, the natural graphite has a BET of 2.5 to 2.6 m ² / g, the positive electrode loading amount is 2.3 to 2.4 mAh / cm ² , the negative electrode loading amount is 2.5 to 2.7 mAh / cm ² , the secondary battery is surprisingly confirmed that the high voltage characteristics are excellent, the present invention Came to complete.

Therefore, the secondary battery according to the present invention,

The positive electrode active material is a lithium transition metal oxide of Formula 1, the negative electrode active material is natural graphite, the natural graphite has a BET of 2.5 to 2.6 m ² / g, the positive electrode loading amount is 2.3 to 2.4 mAh / cm ² , the negative electrode loading The amount is comprised of 2.5-2.7 mAh / cm <^2> .

Li (Ni _x Mn _y Co _z ) O ₂ (1)

In the above formula, 0.2 ≦ x ≦ 0.3, 0.6 ≦ y ≦ 0.7, 0 <z ≦ 0.2, and x + y + z = 1.

The natural graphite may be surface treatment, and the surface treatment may be at least one selected from the group consisting of chemical surface treatment and heat treatment.

The secondary battery may use a potential region of 2.5 to 4.55V.

Preferably, the active material of formula (1) may be a Li (Ni Mn _{0 .28 0 .60 0 .12} Co) O _2.

The present invention may also provide a battery module including the secondary battery as a unit cell, and provide a battery pack including the battery module.

The battery pack may be used as a power source for a medium and large device, and the medium and large device may be an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a system for power storage.

As described above, in the secondary battery according to the present invention, the positive electrode active material is a lithium transition metal oxide having a specific composition, the negative electrode active material is natural graphite, and the natural graphite has a BET of 2.5 to 2.6 m ² / g, and a positive electrode loading amount. Is 2.3 to 2.4 mAh / cm ² , and the negative electrode loading amount is 2.5 to 2.7 mAh / cm ² , thereby improving the high voltage characteristics of the secondary battery.

Hereinafter, the present invention will be described in more detail.

As described above, the secondary battery according to the present invention, the positive electrode active material is a lithium transition metal oxide of a specific composition, the negative electrode active material is natural graphite, the natural graphite has a BET of 2.5 to 2.6 m ² / g, the positive electrode loading amount Is 2.3 to 2.4 mAh / cm ² , and the negative electrode loading amount is 2.5 to 2.7 mAh / cm ² .

Li (Ni _x Mn _y Co _z ) O ₂ (1)

In the above formula, 0.2 ≦ x ≦ 0.3, 0.6 ≦ y ≦ 0.7, 0 <z ≦ 0.2, and x + y + z = 1.

Recently, a lithium composite transition metal oxide is generally used as the cathode active material.

Although studies have been conducted to develop high voltage secondary batteries used in electric vehicles (EVs) and hybrid electric vehicles (HEVs), the results showing the desired high voltage characteristics have been difficult to find.

In general, lithium composite transition metal oxide has been studied a lot of cases of the same amount of nickel, manganese, cobalt, or some excess nickel, and part of the lithium composite transition metal oxide, but the conventional composition for the excessive amount of manganese Not much is known.

However, the inventors of the present application, as described above, the positive electrode active material is a lithium transition metal oxide of a specific composition, the negative electrode active material is natural graphite, the natural graphite has a BET of 2.5 to 2.6 m ² / g, the positive electrode loading amount is 2.3 To 2.4 mAh / cm ² and the negative electrode loading amount is 2.5 to 2.7 mAh / cm ² , when the secondary battery is configured, the high voltage characteristic of the secondary battery is improved and the present invention has been completed.

The natural graphite has a layered structure, whereby lithium ions are inserted / desorbed into the layered structure to perform charge and discharge. When the lithium ions are inserted / desorbed into the layered structure of natural graphite, the layered structure is opened and narrowed. Therefore, as the cycle increases, collapse of the layered structure may occur due to repetitive insertion / desorption of lithium ions, which is a major cause of deterioration of life characteristics of the secondary battery.

As an example for preventing the collapse of the layered structure, surface treatment may be applied to the natural graphite. The surface treatment is not limited in kind as long as it can prevent the collapse of the layered structure, a preferred example, may be one or more selected from the group consisting of chemical surface treatment and heat treatment.

The chemical treatment may be treatment with an acidic or basic solution, and may be any one that changes the surface modification using other chemical substances.

The heat treatment may vary the conditions according to the properties and properties of the natural graphite, which can be selected by the person skilled in the art through repeated experiments, the detailed description is omitted herein.

The secondary battery may preferably use a potential region of 2.5 to 4.55V. If it exceeds 4.55V, the performance of the battery may be degraded due to manganese elution from the positive electrode active material, which is not preferable in terms of battery safety.

Preferred in one embodiment, the active material of Formula 1 may be a Li (Ni Mn _{0 .28 0 .60 0 .12} Co) O _2.

Preferably, the secondary battery according to the present invention may be a lithium secondary battery. The lithium secondary battery has a structure in which a lithium salt-containing non-aqueous electrolyte is impregnated in an electrode assembly having a separator interposed between the positive electrode and the negative electrode. have.

For example, the positive electrode may be manufactured by coating and drying the positive electrode active material on a positive electrode current collector, and optionally further include a binder, a conductive material, a filler, a viscosity regulator, an adhesion promoter, and the like.

The positive electrode current collector is generally made to a thickness of 120 to 160 ㎛. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with carbon, nickel, titanium, silver, or the like can be used. The positive electrode current collector may have fine unevenness formed on the surface thereof to increase the adhesive force of the positive electrode active material as in the case of the negative electrode current collector. Alternatively, the positive electrode current collector may have various properties such as a film, sheet, foil, net, porous body, Form is possible.

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), cellulose, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluorine rubber, various copolymers, high molecular weight polyolefins such as polyolefin, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, Vinyl alcohol, and the like.

The conductive material is not particularly limited as long as it has electrical conductivity without causing any chemical change in the battery, for example, graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used. Concrete examples of commercially available conductive materials include acetylene black series such as Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, etc.), Ketjenblack, EC (Armak Company), Vulcan XC-72 (Cabot Company), and Super P (Timcal).

In some cases, a filler may be optionally added as a component to suppress the expansion of the negative electrode. Such a filler is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery, and examples thereof include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

In addition, other components such as a viscosity adjusting agent, an adhesion promoter and the like may be further included as a selective or a combination of two or more.

The viscosity modifier may be added up to 30% by weight based on the total weight of the negative electrode mixture as a component for adjusting the viscosity of the electrode mixture so that the mixing process of the electrode mixture and the coating process on the current collector may be easy. Examples of such viscosity modifiers include carboxymethylcellulose, polyvinylidene fluoride and the like, but are not limited thereto. In some cases, the above-described solvent may play a role as a viscosity adjusting agent.

The adhesion promoter may be added in an amount of 10% by weight or less based on the binder, for example, oxalic acid, adipic acid, Formic acid, acrylic acid derivatives, itaconic acid derivatives, and the like.

For example, the negative electrode may be manufactured by coating and drying the negative electrode active material on a negative electrode current collector, and optionally further include other components described above with respect to the structure of the positive electrode, such as a binder and a conductive material.

The negative electrode current collector is generally made to a thickness of 100 to 150 ㎛. Such an anode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the negative electrode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The binder, the conductive material and the components added as necessary are the same as those described for the positive electrode.

The separator is an insulating thin film interposed between the anode and the cathode and having high ion permeability and mechanical strength. The pore diameter of the separator is generally 0.01 to 10 ㎛ ㎛, thickness is generally 10 ~ 20 ㎛. As such a separation membrane, for example, a sheet or a nonwoven fabric made of an olefin-based polymer such as polypropylene which is chemically resistant and hydrophobic, glass fiber, polyethylene or the like is used.

In some cases, a gel polymer electrolyte may be coated on the separator to increase battery stability. Representative of such gel polymers are polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile and the like. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The lithium salt-containing non-aqueous electrolyte is composed of an organic solvent electrolyte and a lithium salt.

Examples of the electrolytic solution include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, 4 Methyl-1,3-dioxane, diethyl ether, formamide, dimethyl formamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivative An aprotic organic solvent such as sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl pyrophosphate and ethyl propionate can be used have.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymer containing an ionic dissociation group and the like may be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The lithium salt is a material that is readily 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, LiSCN, LiC (CF 3 SO 2) 3, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, 4-phenylborate, imide, and the like can be used.

For the purpose of improving the charge / discharge characteristics and the flame retardancy, the electrolytic solution is preferably mixed with an organic solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (Fluoro-Ethylene Carbonate, PRS (Propene sultone), and the like.

In a preferred _{embodiment, LiPF 6, LiClO 4, LiBF} 4, LiN (SO 2 CF 3) 2 , such as a lithium salt, a highly dielectric solvent of DEC, DMC or EMC Fig solvent cyclic carbonate and a low viscosity of the EC or PC of And then adding it to a mixed solvent of linear carbonate to prepare a lithium salt-containing non-aqueous electrolyte.

The present invention also provides a battery module including the secondary battery as a unit cell and a battery pack including the battery module.

The battery pack may be used as a power source for medium and large devices requiring high temperature safety, long cycle characteristics, high rate characteristics, and the like.

Preferred examples of the medium-to-large device include a power tool driven by a battery-based motor; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like; An electric motorcycle including an electric bike (E-bike) and an electric scooter (E-scooter); Electric golf cart; And a power storage system, but the present invention is not limited thereto.

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (9)

The positive electrode active material is a lithium transition metal oxide of Formula 1, the negative electrode active material is natural graphite, the natural graphite has a BET of 2.5 to 2.6 m ² / g, the positive electrode loading amount is 2.3 to 2.4 mAh / cm ² , the negative electrode loading A secondary battery, characterized in that the amount is 2.5 to 2.7 mAh / cm ² :
Li (Ni _x Mn _y Co _z ) O ₂ (1)
In the above formula, 0.2 ≦ x ≦ 0.3, 0.6 ≦ y ≦ 0.7, 0 <z ≦ 0.2, and x + y + z = 1. The secondary battery according to claim 1, wherein the natural graphite is surface treated. The secondary battery of claim 2, wherein the surface treatment is at least one selected from the group consisting of chemical surface treatment and heat treatment. The secondary battery of claim 1, wherein the secondary battery uses a potential region of 2.5 to 4.55V. The method of claim 1, wherein the active material of formula (I) is a secondary battery characterized in that Li (Ni Mn _{0 .28 0 .60 0 .12} Co) O ₂ in. A battery module comprising the secondary battery according to any one of claims 1 to 5 as a unit cell. A battery pack comprising the battery module according to claim 6. The battery pack as claimed in claim 7, wherein the battery pack is used as a power source for medium and large devices. The battery pack according to claim 8, wherein the medium-large device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a system for storing power.