KR20130118243A - Electrode for secondary battery - Google Patents

Abstract

PURPOSE: An electrode for a secondary battery has a specific thickness or a loading amount, thereby having excellent electrolyte solution impregnation, ion conductivity, and electron conductivity. CONSTITUTION: In an electrode, one side or both sides of an electrode current collector is coated with an electrode mixture. Each layer of the electrode mixture has a thickness of 100 micron or less. The electrode is a positive electrode or a negative electrode. The positive electrode includes a lithium manganese composite oxide in a spinel structure represented by chemical formula 1: Li_xM_yMn_(2-y)O_(4-z)A_z where 0.9<=x<=1.2, 0<y<2, 0<=z<0.2; M is at least one element selected from Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Ti, and Bi; and A is an anion with a valence of -1 or -2.

Description

Secondary Battery Electrode {Electrode for Secondary Battery}

The present invention relates to a secondary battery electrode having an electrode mixture applied to one or both surfaces of an electrode current collector, wherein the electrode mixture has a thickness of 100 μm or less per surface.

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 an electrode current collector.

Generally, in order to manufacture an electrode for a secondary battery, a slurry-type electrode mixture is applied to an electrode current collector, followed by drying and pressing.

The higher the loading amount of the electrode mixture is, the thicker the electrode thickness, the pressure is not evenly transmitted in the thickness direction during the press. That is, while the electrode surface is under greater pressure, the pressure decreases toward the electrode core. For this reason, the bonding force between an electrode collector and an electrode becomes low, peeling phenomenon arises, the contact resistance between an electrical power collector and an electrode mixture increases, and the output performance falls.

In addition, since the density of the electrode surface is greater than the density of the electrode core, the electron conductivity at the core portion that requires higher electron conductivity is lower than that of the electrode surface, and the surface where the electrolyte solution impregnation property is required is higher due to the electrolyte density. When the internal gas is deteriorated and the gas is not easily released, the electrode may be broken.

Therefore, there is a very high need for a technology that can 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.

After extensive research and various experiments, the inventors of the present application have confirmed that, when the electrode mixture is below a certain thickness or loading amount, as described later, the pressure is uniformly transmitted in the thickness direction during pressing, and the present invention Came to complete.

Accordingly, the present invention provides a secondary battery electrode having an electrode mixture applied to one or both surfaces of an electrode current collector, wherein the electrode mixture has a thickness of 100 μm or less per surface.

As described above, when the thickness of the electrode mixture is too thick, a pressure gradient occurs in the thickness direction during pressing after drying, resulting in a problem that the pressure transmitted to the core portion decreases.

According to the inventors of the present invention, it was confirmed that the above pressure gradient occurs when the thickness of the electrode mixture is more than 100 µm for each surface.

The thickness is in proportion to the loading amount of the electrode. Therefore, the secondary battery electrode may have an electrode mixture having a loading amount of 11 mg / cm ² or less. When the loading amount is exceeded, the thickness may exceed 100 μm, which is not preferable.

The electrode mixture having the thickness or the loading amount may be delivered with a uniform pressure from the surface to the core at the time of pressing after drying. For this reason, it is possible to reduce the electrode peeling phenomenon, to strengthen the adhesive strength of the electrode, to enhance the productivity of the electrode, and to reduce the contact resistance between the electrode active material and the current collector, thereby preventing output degradation.

The secondary battery electrode may be a cathode including a cathode active material or an anode active material.

The positive electrode for a secondary battery 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. If necessary, a filler may be further added to the mixture.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a 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, aluminum or stainless steel A surface treated with carbon, nickel, titanium, silver or the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode 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 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 ; A Ni-site type lithium nickel oxide expressed by the formula LiNi _1-x M _x O ₂ (where 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} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, x = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); A lithium manganese composite oxide having a spinel structure represented by LiNi _x Mn _2-x O ₄ ; 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. However, the present invention is not limited to these.

In one specific example, the cathode active material may be a lithium manganese composite oxide having a spinel structure, which is a high potential oxide represented by Chemical Formula 1.

Li _x M _y Mn _{2 - y} O _{4 - z z} (1)

Wherein 0 < y < 2, 0 z < 0.2,

M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, ;

A is one or more of an anion of -1 or -2.

In detail, the lithium manganese composite oxide may be a lithium nickel manganese composite oxide represented by the following Chemical Formula 2, and more specifically, LiNi _0.5 Mn _1.5 O ₄ or LiNi _0.4 Mn _1.6 O ₄ .

Li _x Ni _y Mn _2-y O ₄ (2)

In the above formula, 0.9? X? 1.2 and 0.4? Y? 0.5.

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.

On the other hand, the negative electrode is manufactured by applying, drying and pressing an anode active material on an anode current collector, and may optionally further include a conductive material, a binder, a filler, and the like as described above.

The negative electrode current collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, and examples of the anode current collector include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, a 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. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

The negative electrode active material may include, for example, carbon such as non-graphitized carbon or graphite carbon; _{Li x Fe 2 O 3 (0≤x≤1} ), Li x WO 2 (0≤x≤1), Sn x Me 1-x Me 'y O z (Me: Mn, Fe, Pb, Ge; Me' : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 &lt; x &lt; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, and Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials; Titanium oxide; Lithium titanium oxide and the like can be used.

In one specific example, the negative electrode active material may be a lithium metal oxide represented by the following Chemical Formula 3.

Li _a M ' _b O _{4-ca c} (3)

In the above formula, M 'is at least one element selected from the group consisting of Ti, Sn, Cu, Pb, Sb, Zn, Fe, In, Al and Zr;

a and b are 0.1? a? 4; Is determined according to the oxidation number of M 'in the range of 0.2? B? 4;

c is determined according to the oxidation number in the range of 0? c <0.2;

A is one or more of an anion of -1 or -2.

Specifically, the lithium metal oxide of Formula 3 may be lithium titanium oxide (LTO) represented by the following formula (4), specifically Li _0.8 Ti _2.2 O ₄ , Li _2.67 Ti _1.33 O ₄ , LiTi ₂ O ₄ , Li _1.33 Ti _1.67 O ₄ , Li _1.14 Ti _1.71 O _4, etc., but if the lithium ions can be occluded / released there is no restriction in the composition and type, and more specifically, the crystal structure of the charge and discharge It may be Li _1.33 Ti _1.67 O ₄ or LiTi ₂ O ₄ of the spinel structure with little change and excellent reversibility.

Li _a Ti _b O ₄ (4)

In the above formula, 0.5? A? 3, 1? B? 2.5.

In this case, it is preferable to use a spinel lithium manganese oxide of Li _x Ni _y Mn _2-y O ₄ represented by Formula 2 having a relatively high potential due to the high potential of LTO as the positive electrode active material.

The present invention provides a secondary battery including the electrode, and more specifically, a lithium secondary battery having a structure in which a lithium salt-containing electrolyte is impregnated in an electrode assembly having a separator interposed between the cathode and the anode.

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 an electrolyte, the solid electrolyte may also serve as a separation membrane.

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 one specific example, lithium salts such as LiPF ₆ , LiClO ₄ , LiBF ₄ , LiN (SO ₂ CF ₃ ) _2, and the like, may be prepared by cyclic carbonate of EC or PC, which is a highly dielectric solvent, and DEC, DMC, or EMC, which are low viscosity solvents. Lithium salt-containing non-aqueous electrolyte can be prepared by adding to a mixed solvent of linear carbonate.

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 devices requiring high temperature stability, long cycle characteristics, high rate characteristics, and the like.

Specific examples of the device include a power tool moving by being driven by an electric 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); An electric golf cart; And a power storage system, but the present invention is not limited thereto.

As described above, the electrode for secondary batteries according to the present invention has the effect that the electrolyte mixture impregnation, ionic conductivity, electron conductivity, etc., all have a good thickness or loading amount.

Hereinafter, although described in more detail with reference to embodiments according to the present invention, the scope of the present invention is not limited thereto.

&Lt; Example 1 >

LiNi _0.5 Mn _1.5 O ₄ was used as a positive electrode active material, and a conductive material (Denka black) and a binder (PVdF) were added to NMP at a weight ratio of 90: 6.5: 3.5, respectively, mixed to prepare a positive electrode mixture, and 20 μm thick aluminum foil was prepared. Coated, rolled and dried to prepare a positive electrode.

The negative electrode active material (Li _1.33 Ti _1.67 O ₄ ), the conductive material (Denka black), and the binder (PVdF) having an average particle diameter (D50) of 6.9 μm and a specific surface area (BET) of 10.9 m ² / g were 85: 5: 10. The negative electrode mixture was prepared by mixing in NMP at a weight ratio of, and coating the negative electrode mixture with a thickness of 100 μm on a copper foil having a thickness of 20 μm, and then rolling and drying the mixture so that the total porosity of the negative electrode mixture was 40%. At this time, the loading capacity of the negative electrode was 0.585 mAh / cm ^2, and the thickness of the negative electrode mixture was 80 μm.

After preparing an electrode assembly with a separator (thickness: 20 μm) between the cathode and the anode thus prepared, the electrode assembly was housed in a pouch-type battery case, and a carbonate-based composite including 1 M LiPF ₆ was present. The solution was injected into the electrolyte and then sealed to prepare a lithium secondary battery.

&Lt; Comparative Example 1 &

In Example 1, a lithium secondary battery was manufactured in the same manner as in Example 1 except that the negative electrode mixture was coated with a thickness of 140 μm, followed by rolling and drying. At this time, the loading capacity of the negative electrode was 0.684 mAh / cm ^2, and the thickness of the negative electrode mixture was 120 μm.

Comparative Example 2

In Example 1, a lithium secondary battery was manufactured in the same manner as in Example 1 except that the negative electrode mixture was coated with a thickness of 200 μm, followed by rolling and drying. At this time, the loading capacity of the negative electrode was 0.81 mAh / cm ^2, and the thickness of the negative electrode mixture was 180 μm.

<Experimental Example 1>

After cutting the negative electrode according to Example 1 and Comparative Examples 1 to 2 to a fixed size and fixed to the slide glass, the current collector was peeled off, and the peel strength was measured 180 degrees. The results are shown in Table 1 below.

In addition, the secondary batteries of Example 1 and Comparative Examples 1 and 2 were charged and discharged at 1C in a section of 2 V to 3.35 V to measure whether the electrodes were peeled, capacity and discharge resistance, and the results are shown in Table 1 below.

Adhesion (gf / cm) Whether the electrode is peeled off 1C capacity (mAh) Discharge resistance (mΩ) Example 1 15.30 X 6.27 1.80 Comparative Example 1 8.64 ? 7.44 2.11 Comparative Example 2 2.78 O 8.45 2.34

As the negative electrode loading capacity increases, the capacity of the battery also increases, so that the discharge resistance value is a resistance value converted into the same capacity (5Ah).

In general, the minimum adhesion of the electrode required for battery assembly work is 10 gf / cm. Referring to Table 1, the adhesion of the negative electrode of Example 1 was 15.30 gf / cm, which is greater than the minimum adhesion, whereas the adhesion of the negative electrodes of Comparative Examples 1 and 2 was 8.64 gf / cm and 2.78, respectively, despite the high content of the binder. gf / cm, less than minimum adhesion Therefore, the secondary batteries of Comparative Examples 1 and 2 are easily peeled off the electrode, thereby increasing the discharge resistance due to an increase in the contact resistance, while the secondary battery of Example 1 was confirmed that the electrode was not peeled off and the discharge resistance was 2.0 mΩ or less. Can be.

That is, the negative electrode of Example 1 has a high bonding force between the electrode current collector and the electrode as the pressure is uniformly transmitted in the thickness direction, so that no peeling phenomenon occurs. Therefore, the output performance is improved by preventing an increase in contact resistance between the electrode current collector and the electrode mixture, and as the pores of the electrode are evenly formed over the entire electrode, the degradation of the electrolyte impregnation can also be prevented.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (16)

A secondary battery electrode in which an electrode mixture is coated on one or both surfaces of an electrode current collector, wherein the electrode mixture has a thickness of 100 μm or less per each surface. The method of claim 1, wherein the electrode mixture is a secondary battery electrode, characterized in that the loading amount of 11 mg / cm ² or less. The method of claim 1, wherein the electrode mixture is a secondary battery electrode, characterized in that the uniform pressure is transmitted from the surface to the core portion during pressing. According to claim 1, wherein the electrode is a secondary battery electrode, characterized in that the positive electrode or the negative electrode. The electrode of claim 4, wherein the cathode comprises a lithium manganese composite oxide having a spinel structure represented by Chemical Formula 1 as a cathode active material:
Li _x M _y Mn _{2 - y} O _{4 - z z} (1)
Wherein 0 < y < 2, 0 z < 0.2,
M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, ;
A is one or more of an anion of -1 or -2. The method of claim 5, wherein the lithium manganese composite oxide of Formula 1 is a lithium nickel manganese complex oxide (Lithium Nickel Manganese complex oxide: LNMO) represented by the formula (2):
Li _x Ni _y Mn _2-y O ₄ (2)
In the above formula, 0.9? X? 1.2 and 0.4? Y? 0.5. The electrode of claim 6, wherein the lithium nickel manganese composite oxide of Formula 2 is LiNi _0.5 Mn _1.5 O ₄ or LiNi _0.4 Mn _1.6 O ₄ . The electrode for secondary batteries of claim 4, wherein the negative electrode comprises a lithium metal oxide represented by the following Chemical Formula 3 as a negative electrode active material:
Li _a M ' _b O _{4-ca c} (3)
In the above formula, M 'is at least one element selected from the group consisting of Ti, Sn, Cu, Pb, Sb, Zn, Fe, In, Al and Zr;
a and b are 0.1? a? 4; Is determined according to the oxidation number of M 'in the range of 0.2? B? 4;
c is determined according to the oxidation number in the range of 0? c <0.2;
A is one or more of an anion of -1 or -2. The method of claim 8, wherein the lithium metal oxide of Formula 3 is a lithium titanium oxide (Lithium Titanium Oxide: LTO) represented by the following formula (4):
Li _a Ti _b O ₄ (4)
In the above formula, 0.5? A? 3, 1? B? 2.5. The electrode of claim 9, wherein the lithium titanium oxide of Formula 4 is Li _1.33 Ti _1.67 O ₄ or LiTi ₂ O ₄ . A secondary battery comprising the electrode according to any one of claims 1 to 10. 12. The secondary battery according to claim 11, wherein the secondary battery is a lithium secondary battery. A battery module comprising the secondary battery according to claim 11 as a unit cell. A battery pack comprising the battery module according to claim 13. A device comprising a battery pack according to claim 14. The device of claim 15, wherein the device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a system for power storage.