KR20130116806A - Anode for secondary battery - Google Patents

Abstract

PURPOSE: An anode for a secondary battery is provided to be excellent in the electrolyte impregnation, the ion conductivity and the electron conductivity by having a specific porosity. CONSTITUTION: An anode is coated with an anode formulation on one side or both sides of an anode current collector. The porosity of the anode formulation layer is 10-60% range. The anode uses a lithium metal oxide represented by Chemical formula 1: L1_aM'_bO_(4-c)A_c as an anode active material, wherein M' is selected from Ti, Sn, Cu, Pb, Sb, Zn, Fe, In, Al or Zr, a and b are determined according to the oxidation number of M' in the range of 0.1<=a<=4 and 0.2<=b<=4, c is determined according to the oxidation number in the range of 0<=c<0.2, and A is at least one anion of -1 or -2 valence.

Description

Anode for Secondary Battery

The present invention relates to a negative electrode for a secondary battery in which a negative electrode mixture is coated on one or both surfaces of a negative electrode current collector, wherein the porosity of the negative electrode mixture layer is in a range of 10% to 60%.

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.

In general, in order to manufacture a negative electrode for a secondary battery, a method of applying a slurry mixture in the form of a slurry to a negative electrode current collector, drying, and pressing is used.

When the cathode has a high porosity, the electrolyte impregnation may be excellent and thus the ion conductivity may be excellent, but the capacity per unit volume may be lowered and the electronic conductivity may be lowered. In addition, when the porosity of the negative electrode is low, the electronic conductivity may be excellent, but the electrolyte impregnation may be degraded and the negative electrode may be broken because it does not escape well when the internal gas is generated.

Therefore, there is a very high need for a secondary battery negative electrode capable of satisfying both ion conductivity and electronic conductivity.

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 the desired effect can be achieved when the negative electrode mixture layer has a specific porosity, as described later. Reached.

Accordingly, the present invention provides a negative electrode for a secondary battery having a negative electrode mixture coated on one or both surfaces of a negative electrode current collector, and has a porosity of the negative electrode mixture layer in a range of 10% to 60%.

As described above, when the porosity is too low, it may be excellent in electronic conductivity, but it is not preferable because the impregnation with the electrolyte solution and ionic conductivity is lowered. On the contrary, when the porosity is too large, the electrolyte impregnation and the ionic conductivity may be relatively excellent, but the electron conductivity and the capacity are reduced, which is not preferable. Therefore, such porosity range is preferable.

For this reason, the porosity of the negative electrode mixture layer may be in the range of 20% to 50%, and more specifically in the range of 25% to 45%, based on the total volume of the negative electrode mixture layer.

The negative electrode for a secondary battery is prepared by applying a mixture of a negative electrode active material, a conductive material, and a binder on a negative electrode current collector, followed by drying and pressing. If necessary, a filler may be further added to the mixture.

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 example, the negative electrode active material may be a lithium metal oxide represented by the following Chemical Formula 1.

Li _a M ' _b O _4-c A _c (1)

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 negative electrode active material may be lithium titanium oxide (LTO) represented by the following Chemical Formula 2, which is easy to fast charge, and 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, and the like, but are not limited thereto. More specifically, the Li _1.33 Ti _{1.67 having a} spinel structure with little change in crystal structure and excellent reversibility during charge and discharge. O ₄ or LiTi ₂ O ₄ .

Li _a Ti _b O ₄ (2)

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

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.

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

The positive electrode is manufactured by coating, drying, and pressing a positive electrode active material on a positive electrode current collector, and optionally, the conductive material, binder, filler, and the like as described above may be further included.

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 example, a lithium manganese composite oxide having a spinel structure, which is a high potential oxide, may be used as a cathode active material corresponding to the high potential of the lithium titanium oxide, and the lithium manganese composite oxide may be represented by the following Chemical Formula 3.

Li _x M _y Mn _2-y O _4-z A _z (3)

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.

Specifically, the lithium manganese composite oxide may be lithium nickel manganese complex oxide (LNMO) represented by Formula 4 below, and more specifically, LiNi _0.5 Mn _1.5 O ₄ or LiNi _0.4 Mn _1.6 O Can be _four .

Li _x Ni _y Mn _2-y O ₄ (4)

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

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, sulfates, and the like of Li, such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , and the like, may 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 secondary battery negative electrode according to the present invention has a specific porosity, and thus, an electrolyte solution impregnation property, an ion conductivity, an electron conductivity, and the like are all good.

1 is a graph showing experimental results of capacity retention and resistance increase according to Experimental Example 1. FIG.

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 >

Cathode manufacturing

A negative active material (Li _1.33 Ti _1.67 O ₄ ), a conductive material (Denka black), and a binder (PVdF) having an average particle diameter (D50) of 8.66 μm and a specific surface area (BET) of 4.01 m ² / g were 91: 3: 6 The negative electrode mixture was prepared by mixing into NMP at a weight ratio of and preparing a negative electrode mixture. The negative electrode mixture was prepared by coating a 20 μm thick copper foil, followed by rolling and drying. At this time, the pressing pressure was adjusted so that the negative electrode mixture layer had a 38% porosity.

Manufacture of lithium secondary battery

The positive electrode was prepared by mixing LiNi _0.5 Mn _1.5 O ₄ as a positive electrode active material and mixing a conductive material (Denka black) and a binder (PVdF) in NMP at a weight ratio of 88.5: 8.5: 3, respectively, to prepare a positive electrode mixture, and then 20 μm thick. It was prepared by coating on aluminum foil, rolling and drying.

After manufacturing the electrode assembly through a separator (thickness: 20 ㎛) between the positive electrode and the negative electrode prepared in this way, the electrode assembly is housed in a pouch-type battery case, 1M LiPF ₆ composite of carbonate-based composite The solution was injected into the electrolyte and then sealed to prepare a lithium secondary battery.

<Examples 2 and 3>

In Example 1, a negative electrode and a lithium secondary battery were manufactured in the same manner as in Example 1 except that the pressing pressure was adjusted so that the negative electrode mixture layer had a porosity of 43% and 48%.

<Experimental Example 1>

After charging and discharging the secondary batteries according to Examples 1 to 3 at 1 C in a section of 2 V to 3.35 V to measure capacity and discharge resistance, and storing the batteries as SOC 100% at 60 ° C. for 4 weeks. , The capacity and the discharge resistance were measured again, and the results are shown in Table 1 and FIG. 1.

1 ^st discharge 60 ℃, 4week, SOC 100% Volume
increase(%) resistance
increase(%) 1C capacity (mAh) Discharge resistance
(mΩ) 1C capacity (mAh) Discharge resistance
(mΩ) Example 1 20.42 2.01 17.49 2.85 85.66 141.94 Example 2 18.54 1.87 16.92 2.35 91.25 125.74 Example 3 20.75 2.08 16.64 3.53 80.20 169.33

* The discharge resistance is the equivalent area (13 bicell) equivalent resistance value.

Referring to Table 1 and FIG. 1, if the battery performance deteriorates little by little when it is out of the range based on a specific range of porosity, it is very important for the electrode to have a proper porosity in order to have improved battery performance in various aspects. It can be seen.

The inventors of the present application, in addition to the above experiment, when the porosity exceeds 60%, it is difficult to form a smooth contact path between the active material and the conductive material, the resistance increases as the conductivity decreases, the initial output is lowered, and the active material Inadequate adhesion between the current collector and the current collector further increased the electrode contact resistance between the high temperature storage and the deterioration phenomenon. Further, when the porosity was lowered to a very low level of less than 10% by increasing the press pressure, it occurred during press. It was confirmed that a large force to break the shape of the active material secondary particles causes a bad contact with the conductive material, thereby increasing the resistance.

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 (12)

A negative electrode for a secondary battery, wherein a negative electrode mixture is coated on one or both surfaces of a negative electrode current collector, wherein a porosity of the negative electrode mixture layer is in a range of 10% to 60%. The negative electrode of claim 1, wherein the porosity of the negative electrode mixture layer is in a range of 20% to 50%. The negative electrode of claim 1, wherein the porosity of the negative electrode mixture layer is in a range of 25% to 45%. The method of claim 1, wherein the negative electrode is a negative electrode for a secondary battery, characterized in that using a lithium metal oxide represented by the formula (1) as a negative electrode active material:
Li _a M ' _b O _4-c A _c (1)
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 negative electrode for a secondary battery of claim 4, wherein the lithium metal oxide of Chemical Formula 1 is lithium titanium oxide (LTO) represented by Chemical Formula 2.
Li _a Ti _b O ₄ (2)
In the above formula, 0.5? A? 3, 1? B? 2.5. The anode of claim 5, wherein the lithium titanium oxide is Li _1.33 Ti _1.67 O ₄ or LiTi ₂ O ₄ . A secondary battery comprising the negative electrode according to any one of claims 1 to 6. The secondary battery according to claim 7, wherein the secondary battery is a lithium secondary battery. A battery module comprising a secondary battery according to claim 7 as a unit cell. A battery pack comprising the battery module according to claim 9. A device comprising a battery pack according to claim 10. The device of claim 11, wherein the device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a system for power storage.

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