KR20140008956A - A method of preparing anode for lithium secondary battery and lithium secondary battery comprising anode prepared by the method - Google Patents

Abstract

The present invention relates to a production method of a negative electrode for a lithium secondary battery and the lithium secondary battery comprising the negative electrode produced by the method, more specifically to: a production method of a negative electrode for a lithium secondary battery which includes a step of producing an aluminum current collector with the surface roughness of 0.5-5 um for improving binding power of an electrode active material and a current collector; and the lithium secondary battery comprising the negative electrode produced by the method.

Description

A method of preparing Anode for Lithium Secondary Battery and Lithium Secondary Battery Comprising Anode Prepared by the Method}

The present invention relates to a method for manufacturing a negative electrode for a lithium secondary battery and a lithium secondary battery including a negative electrode prepared by the method, more specifically, to improve the binding force between the electrode active material and the current collector, about 0.5 to 5 ㎛ size A method of manufacturing a negative electrode for a lithium secondary battery, the method comprising surface treating a surface of a metal current collector to have _a surface roughness (roughness, [R _a ]) of _a , and a lithium secondary battery comprising an electrode manufactured by the method will be.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among secondary batteries, lithium secondary batteries that exhibit high energy density and operating potential, have a long cycle life, and have a low self-discharge rate are commercially used.

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

In the lithium secondary battery, charging and discharging proceed while repeating a process of inserting and detaching lithium ions of a positive electrode into a negative electrode. In this case, the electrode is separated between an electrode active material and a current collector by a volume change of the electrode generated during charging and discharging. Since the active material does not perform a function, there is a problem that the charge and discharge capacity and life characteristics of the battery is also reduced.

In order to prevent separation between the electrode active material and the current collector, when the amount of the binder is increased during manufacturing of the electrode, the amount of the electrode active material and the conductive material is relatively decreased, so that the conductivity of the electrode is lowered or the battery capacity is decreased. Another problem arises.

In order to improve such a problem, secondary batteries using lithium metal oxide having a low volume expansion as a negative electrode material in the fast charge and discharge characteristics and charge and discharge process has emerged.

In the prior art, while using lithium metal oxide as a negative electrode material, using a copper current collector in the same weight ratio, there was a disadvantage that it is difficult to secure a proper adhesion between the negative electrode material and the copper current collector.

Accordingly, in recent years, an example in which an aluminum current collector is applied in manufacturing an electrode using lithium metal oxide as a negative electrode material is increasing. This is because when the lithium metal oxide is charged, the voltage at which lithium is inserted is around 1.5V, and thus aluminum can be used. However, if the lithium insertion potential of the virtual active material A, which is not coated on the copper current collector, is near 0V relative to lithium, the lithium current reacts with aluminum at near 0V relative to lithium, and the aluminum current collector is oxidized. An oxide is shaped. As a result, the electrical conductivity between the aluminum current collector and the negative electrode active material layer decreases, thereby affecting electrical characteristics such as deterioration in charge and discharge efficiency of the battery.

Therefore, there is a very high need for a technology capable of improving the performance of a secondary battery by improving the conductivity between the electrode active material and the metal current collector and at the same time the conductivity.

The present invention provides a method for producing a negative electrode for a lithium secondary battery and a lithium secondary battery including the negative electrode produced by the method.

The present invention

As a method of manufacturing a negative electrode for a secondary battery,

Surface treating the surface of the negative electrode current collector; And

It provides a method of manufacturing a negative electrode for a secondary battery comprising the step of forming a negative electrode active material layer on the surface-treated negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel, or a surface thereof. Surface treated with carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

Specifically, in the method of the present invention, a current collector made of aluminum foil having a thickness of about 10 to 30 μm may be used.

In the method of the present invention, the surface treatment of the surface of the negative electrode current collector may be performed by a chemical or electrical etching method by a wet method. In the practice of the chemical etching method using a wet process, an etching agent to be used may include FeCl ₃ / HCl / H ₂ O mixtures. In addition, the etching time may vary depending on various factors such as the type of the negative electrode current collector and the type of the etchant.

Specifically, when the metal current collector is made of aluminum foil, surface treatment may be performed by immersing the aluminum foil current collector in the etchant.

The method for surface treatment throughout the anode current collector surface from 0.5 to 5 ㎛ over by, and can be specifically formed with a 0.5 to 3 ㎛ size of the surface roughness (R _a).

As described above, in the present invention, by forming fine unevenness on the surface of the negative electrode current collector to increase the surface area, the binding force between the electrode active material and the current collector can be strengthened, thereby improving overall performance of the secondary battery, such as improvement of charge and discharge cycle characteristics. Can be. At this time, if the surface roughness value is too small, it is difficult to form fine concavities and convexities, it is difficult to distribute the stress during the volume expansion of the electrode active material, on the contrary, if the surface roughness value is too large, the stress dispersion of the electrode active material in the large irregularities formed And the problem that the mitigation effect is lowered may occur.

In the method of the present invention, the negative electrode active material layer formed on the surface-treated negative electrode current collector surface is prepared by applying a slurry containing a negative electrode active material, a conductive material and a binder to the negative electrode current collector surface, followed by drying and pressing, Optionally, the conductive material, binder, filler, and the like as described above may be further included. In this case, the conductive material and the binder used are not particularly limited as long as they are materials used for manufacturing a negative electrode active material.

Specifically, the negative electrode active material is a lithium metal oxide represented by the following formula (1).

[Formula 1]

Li _x M _y O _z

Wherein M are each independently Ti, Sn, Cu, Pb, Sb, Zn, Fe, In, Al or Zr; x, y, and z are determined according to the oxidation number of M.

Specifically, the internal porosity of the lithium metal oxide is 5 to 15%, the particle size is 3 to 8 ㎛, specific surface area (BET) may be 1 to 15 m ² / g.

The lithium metal oxide may be agglomerated two or more primary particles, wherein the average particle diameter of the primary particles may be 100 to 400 nm.

The lithium metal oxide is Li ₄ Ti ₅ O ₁₂ , LiTi ₂ O ₄ , Li ₂ TiO ₃ And at least one lithium titanium oxide (LTO) selected from the group consisting of Li ₂ Ti ₃ O ₇ .

The method of the present invention may further include forming a conductive layer on the surface-treated negative electrode current collector before coating the negative electrode active material.

In addition, the present invention provides a secondary battery, preferably a lithium secondary battery comprising a secondary battery negative electrode, a positive electrode, a separator and an electrolyte prepared by the above manufacturing method.

In this case, the positive electrode is prepared by applying a mixture of a positive electrode active material, a conductive material and a binder on a positive electrode current collector, followed by drying and pressing, and optionally a filler is further added to the mixture.

The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, sintered carbon or aluminum or stainless steel Surface-treated with carbon, nickel, titanium, silver, or the like may be used. The current collector may form fine irregularities on its surface to increase the binding power of the positive electrode active material, and may be in various forms such as film, sheet, foil, net, porous body, foam, and nonwoven fabric, and generally have a thickness of 3 to 500 μm. Has a thickness.

The cathode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + x} Mn _{2 -x} O _{4 (} where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO _2, and the like; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; Ni-site-type lithium nickel oxide represented by the formula LiNi _{1- x} M _x O ₂ , wherein M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3; Formula LiMn _{2 -x} M _x O ₂ (wherein M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (wherein M = Fe, Co, Lithium manganese composite oxide represented by Ni, Cu or Zn); Spinel-structure lithium manganese composite oxides represented by LiNi _x Mn _{2 - x} O ₄ (x = 0.01 to 0.6); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ and the like, but not limited to these, in the case of using lithium titanium oxide (LTO) as the negative electrode active material, LiNi _x Mn having a relatively high potential due to the high potential of LTO _{2 - x O 4 (x =} 0.01 to 0.6 Im), can be specifically used LiNi _{0 .5} Mn _{1 .5} O ₄ or LiNi _0.4 Mn _1.6 O _4.

The conductive material is usually added in an amount of 1 to 50% by weight based on the total weight of the mixture including the cathode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial 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.

The binder is a component that assists in bonding of the active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 50 wt% based on the total weight of the mixture containing the cathode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

The filler is optionally used as a component for suppressing the expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

In addition, the present invention provides a secondary battery having a structure in which a lithium salt-containing electrolyte is impregnated into an electrode assembly having a structure in which a separator is interposed between a positive electrode and a negative electrode manufactured by the method of the present invention.

The separation membrane is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m, and the thickness is generally 5 to 300 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The electrolyte solution containing the lithium salt is composed of an electrolyte solution and a lithium salt. The electrolyte solution may be a non-aqueous organic solvent, an organic solid electrolyte, or an inorganic solid electrolyte, but is not limited thereto.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , Acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Nonionic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used.

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 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide.

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.

Also, the present invention provides a battery module including the secondary battery as a unit battery, a battery pack including the battery module, and a device including the battery pack.

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

The device may be an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a system for power storage.

Preferred examples of the above medium to large devices include a power tool that is powered by an electric motor and moves; 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); An electric golf cart; And a power storage system, but the present invention is not limited thereto.

As described above, in the present invention, before the negative electrode active material is coated, the negative electrode current collector is surface treated, thereby increasing the surface area of the negative electrode current collector due to the fine roughness formed on the surface, thereby improving the binding force between the electrode active material and the current collector. As a result, the electrode binding properties and high rate characteristics can be secured, thereby improving the overall performance of the secondary battery, such as improving charge / discharge cycle characteristics.

The foregoing is merely illustrative of the technical idea of the present invention, and those skilled in the art to which the present invention pertains various modifications, modifications, and substitutions without departing from the essential characteristics of the present invention. And addition would be possible. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical matters of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. It should be interpreted by the claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

Example

Preparation Example 1 .

An aluminum current collector having a thickness of 20 μm was immersed at room temperature for 30 seconds in an etchant composed of a FeCl ₃ / HCl / H ₂ O mixture, and then dried to prepare an aluminum current collector having a roughness [Ra] 2 μm.

Example  One

84g of lithium titanium oxide (LTO), 6g of conductive material, and 10g of binder were mixed as a negative electrode active material to prepare a slurry for negative electrode active material (100g). The slurry for the negative electrode active material was applied onto the surface-treated aluminum current collector of Preparation Example 1, followed by drying and pressing to prepare a negative electrode. The half battery was manufactured by the conventional method using the said negative electrode. Using the obtained negative electrode and the battery, the binding force between the negative electrode active material and the aluminum current collector (180 degree peel test and rate capability) (Toyo cycler, Japan, Japan) was measured using a conventional measuring method, The results are shown in Table 1. In this case, the high rate characteristic is expressed as a percentage value of the capacity at 0.1C by measuring the capacity at 10C.

Comparative Example  One

A negative electrode and a half cell were manufactured in the same manner as in Example 1, except that an aluminum current collector having an untreated roughness [Ra] 0.5 μm was used instead of the surface-treated aluminum current collector. The binding force between the whole and high rate characteristics were measured, and the results are shown in Table 1.

division Binding [gf] High rate characteristic [%, 10C / 0.1C capacity] Example 1 40.6 80 Comparative Example 1 7.6 63

As described above, in the case of the electrode to which the aluminum foil without surface treatment was applied, the binding force between the negative electrode active material and the current collector was decreased, and in the case of the electrode using the surface-etched aluminum foil, the binding force and the high rate characteristic were improved. .

Claims (19)

As a method of manufacturing a negative electrode for a secondary battery,
Surface treating the surface of the negative electrode current collector; And
Method of manufacturing a negative electrode for a secondary battery comprising coating a negative electrode active material layer on the surface-treated negative electrode current collector. The method according to claim 1,
The negative electrode current collector is a method of manufacturing a negative electrode for a secondary battery, characterized in that the negative electrode current collector made of aluminum. The method according to claim 1,
The surface treatment step is a method of manufacturing a negative electrode for a secondary battery, characterized in that performed by a chemical or electrical etching method by a wet method. The method according to claim 1 or 3,
Chemical etching by the wet method is a method for producing a negative electrode for a secondary battery, characterized in that performed using an etchant consisting of FeCl ₃ / HCl / H ₂ O. The method according to claim 1,
The surface-treated negative electrode current collector has a surface roughness (R _a ) of 0.5 to 5 ㎛ size over the entire surface, the method of manufacturing a negative electrode for a secondary battery. The method according to claim 5,
The surface-treated negative electrode current collector has a surface roughness (R _a ) of 0.5 to 3 ㎛ size over the entire surface, the method of manufacturing a negative electrode for a secondary battery. The method according to claim 1,
The negative electrode active material layer is formed by applying a slurry containing a negative electrode active material, a conductive material and a binder to the surface of the negative electrode current collector, followed by drying and pressing. The method of claim 7,
The negative electrode active material is a method for producing a negative electrode for a secondary battery, characterized in that the lithium metal oxide represented by the formula (1):
[Chemical Formula 1]
Li _x M _y O _z
(Wherein M are each independently Ti, Sn, Cu, Pb, Sb, Zn, Fe, In, Al or Zr; x, y, and z are determined according to the oxidation number of M). The method according to claim 8,
The internal porosity of the lithium metal oxide is 5 to 15%, the particle size is 3 to 8 ㎛, specific surface area (BET) is a method for producing a negative electrode for a secondary battery, characterized in that 1 to 15 m ² / g. The method according to claim 8,
The lithium metal oxide is a method of manufacturing a negative electrode for a secondary battery, characterized in that the aggregate of two or more primary particles. The method of claim 10,
The average particle diameter of the primary particles of the lithium metal oxide is 100 to 400 nm manufacturing method of the negative electrode for a secondary battery. The method according to claim 8,
The lithium metal oxide is Li ₄ Ti ₅ O ₁₂ , LiTi ₂ O ₄ , Li ₂ TiO ₃ And at least one lithium titanium oxide selected from the group consisting of Li ₂ Ti ₃ O ₇ . A negative electrode for a secondary battery, which is prepared according to the method of claim 1. A secondary battery comprising a positive electrode, a separator, a negative electrode according to claim 13 and an electrolyte solution. The method according to claim 14,
The secondary battery is a secondary battery, characterized in that the lithium secondary battery. A battery module comprising the secondary battery according to claim 15 as a unit cell. Battery pack comprising a battery module according to claim 16. A device comprising a battery pack according to claim 17. 19. The method of claim 18,
The device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a system for power storage.