KR20140033934A - Electrode which have improved ion conductivity and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to an electrode having improved ion conductivity and a lithium secondary battery comprising the same, and more specifically, to an electrode in which an electrode mixture is coated on the surface of a current collector and the electrode mixture additionally contains an additive with a solid electrolyte function as well as an electrode active material; and a secondary battery comprising the same. The electrode of the present invention has improved ion conductivity, thereby improving the output of a secondary battery.

Description

Electrode with improved ion conductivity and secondary battery comprising same {Electrode Which Have Improved Ion Conductivity and Lithium Secondary Battery Comprising the Same}

The present invention relates to an electrode having improved ion conductivity and a secondary battery including the same, and more particularly, an electrode mixture is coated on a surface of a current collector, and the electrode mixture includes an additive having a solid electrolyte function in addition to the electrode active material. It relates to an electrode and a secondary battery comprising the same further comprises.

Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy or clean energy is increasing. As a part of this, the most active field of research is electric power generation and storage.

A representative example of an electrochemical device using such electrochemical energy is a secondary battery, and its use area is gradually increasing.

Recently, as the development and demand for portable devices such as portable computers, portable telephones, cameras, and the like, the demand for secondary batteries is rapidly increasing, and these secondary batteries exhibit high energy density and operating potential, and have a cycle life. Many studies have been conducted on this long, low self-discharge rate lithium battery and are commercially available and widely used.

In addition, as the interest in environmental problems grows, researches on electric vehicles and hybrid electric vehicles that can replace fossil fuel-based vehicles such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, . As a power source of such electric vehicles and hybrid electric vehicles, nickel-metal hydride secondary batteries are mainly used, but researches using lithium secondary batteries with high energy density and discharge voltage have been actively conducted and some commercialization stages are in progress.

In general, a lithium secondary battery has a structure in which a lithium electrolyte is impregnated into an electrode assembly including a cathode including a lithium transition metal oxide, a cathode including a carbon-based active material, and a separator.

The secondary battery is a non-aqueous composition, the electrode is generally manufactured by coating an electrode slurry on a metal foil, the electrode slurry is an electrode active material for storing energy, a conductive material for imparting electrical conductivity, and It is prepared by mixing an electrode mixture composed of a binder for adhering to the electrode foil in an organic solvent such as NMP (N-methyl pyrrolidone). In this case, a lithium cobalt oxide, a lithium manganese oxide, a lithium nickel oxide, or a lithium composite oxide is mainly used as the positive electrode active material, and the negative electrode active material is mainly a carbon-based material or an alloy composed of silicon, tin, these oxides or alloys, and the like. Type active materials are used.

As the lithium secondary battery expands in use, a high output, high temperature safety, excellent rate characteristics, and lifetime characteristics are required in consideration of capacity, electrical conductivity, and ionic conductivity.

Therefore, researches to satisfy the above conditions are actively underway, and the use of a positive electrode active material is mixed to maximize the capacity or a conductive material is coated on the surface of the positive electrode and negative electrode active material to improve the output characteristics of the conventional electrons. Techniques for facilitating and the like have been proposed. However, the composition of the electrode slurry including such an electrode active material is designed to focus only on the resistance portion from the viewpoint of the battery capacity and electrical as described above, and there is no consideration of ion conductivity.

Accordingly, there is a high demand for a technology capable of improving output characteristics by increasing the capacity and battery resistance of the battery as well as ion conductivity in the electrode.

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 further includes an additive having a solid electrolyte function in addition to the electrode active material, ion conductivity in the electrode is improved to improve output characteristics. The present invention has been completed.

The electrode according to the present invention for achieving this object is an electrode, the electrode mixture is applied to the surface of the current collector, the electrode mixture is characterized in that it further comprises an additive having a solid electrolyte function in addition to the electrode active material.

In general, the electrode mixture is prepared by mixing a conductive material and a binder in addition to the electrode active material, and is prepared by further adding a filler as necessary. The electrode mixture according to the present invention may further include an additive having a solid electrolyte function in addition to the above materials. In one specific example, the additive may be a solid electrolyte which does not cause side reactions at an operating voltage of 3.5 V or more.

In one specific example, the solid electrolyte may be an inorganic solid electrolyte, the inorganic solid electrolyte may be, for example, zirconium oxide, β-alumina, LISICON (Lithium Super Ionic Conductor) compound, LIPON (Li _{3+ y} PO _4-x N _x ) compound, Thio-LISICON (Li _4-x Ge _1-y P _y S ₄ ) compound, Li ₂ SP ₂ S ₅ compound, 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 , Li ₄ SiO ₄ -LiI-LiOH, Li ₂ S, Li ₂ S-SiS ₂ , Li ₂ S-GeS ₂ , Li ₂ SB ₂ S ₅ , Li ₂ S-Al ₂ S ₂ , Li ₂ O-Al ₂ O ₃ -TiO ₂ -P ₂ O ₅ (LATP), CaF ₂ , AgI and RbAg ₄ I _It may be any one or more selected from the group consisting of ₅ , specifically, zirconium oxide, β-alumina, and Thio-LISICON (Li _4-x Ge _1-y P _y S ₄ ) -based compound selected from the group consisting of It may be any one or more.

Since the inorganic solid electrolyte as described above has a particulate structure similar to the conductive material included in the electrode mixture, it may be mixed with other materials and added to the electrode mixture.

In one specific example, the solid electrolyte may be a polymer-based solid electrolyte, the polymer-based solid electrolyte, in detail, polytetrafluoroethylene (Nafion), a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative having a sulfonic acid group , At least one selected from the group consisting of a phosphate ester polymer, a poly agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, and an ionic dissociation group, and more specifically, May be any one or more selected from the group consisting of polytetrafluoroethylene having a sulfonic acid group, a polyethylene oxide derivative, and a polypropylene oxide derivative.

If the polymer-based solid electrolyte as described above can be applied in the same way as the solvent of the electrode mixture is not difficult to apply. Therefore, in one specific example, the polymer-based solid electrolyte may be a material having dissolution characteristics in the solvent of the electrode mixture slurry for applying the current collector. In this case, since the solvent is variously applied according to the electrode mixture, the polymer-based solid electrolyte included therein may also vary accordingly. In general, the solvent used for the positive electrode mixture may be an organic solvent such as NMP, and the solvent used for the negative electrode mixture may be water or the like.

In this regard, the inventors of the present application further include an additive having a solid electrolyte function in the electrode mixture to increase the reaction rate during charging and discharging because the additive facilitates movement of ions in the electrode. It was confirmed that the output characteristics can be improved by reducing the resistance caused by lithium ions.

 In one specific example, the additive may be included in 0.01 to 20 wt% based on the total weight of the electrode mixture. When the content of the additive is less than 0.01 wt%, it is difficult to expect the effect according to the present invention. On the contrary, when the content of the additive is more than 20 wt%, the amount of the active material in the total electrode mixture is relatively decreased, which may reduce the capacity of the battery. In particular, an electrical insulator such as zirconium oxide in the inorganic solid electrolyte may increase the electrical resistance, which is not preferable.

Only the inorganic solid electrolyte or the polymer solid electrolyte may be added to the electrode mixture, and the inorganic solid electrolyte and the polymer solid electrolyte may be added together, and the range may be the sum of all the solid electrolytes added. have.

The present invention also provides a method of manufacturing an electrode comprising an additive having a solid electrolyte function.

Specifically, the electrode according to the present invention comprises the steps of: (i) preparing an electrode mixture slurry by adding an electrode mixture containing an electrode active material to a solvent; (ii) adding an additive having a solid electrolyte function to the electrode mixture slurry; And (iii) applying the electrode mixture slurry onto a current collector and drying to remove the solvent.

The present invention also provides a secondary battery comprising the electrode.

In one specific example, the electrode may be a positive electrode or a negative electrode, and the secondary battery is a lithium secondary battery, and may include an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode and a non-aqueous electrolyte. have.

As described above, the electrode according to the present invention further includes an additive having a solid electrolyte function in addition to the electrode active material in the electrode mixture to improve the ion conductivity in the electrode, thereby increasing the reaction rate during charging and discharging and increasing the resistance by lithium ions. Since it can be reduced, there is an effect that can improve the output characteristics of the secondary battery based on this.

As described above, the present invention provides an electrode and a method for producing the electrode, characterized in that the electrode mixture is applied to the surface of the current collector, the electrode mixture further comprises an additive having a solid electrolyte function in addition to the electrode active material. do.

In this case, the electrode may be applied to both the positive electrode and the negative electrode.

The positive electrode is prepared by, for example, applying a mixture of a positive electrode active material, a conductive material, and a binder onto a positive electrode current collector, followed by drying. If necessary, a filler may be further added to the mixture.

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.

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 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 whiskey 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, 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 adjusting agent may be added up to 30% by weight based on the total weight of the electrode mixture, so as to control the viscosity of the electrode mixture so that the mixing process of the electrode mixture and the coating process on the 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.

The negative electrode is manufactured by coating, drying, and pressing a negative electrode active material on a negative electrode current collector, and optionally, the conductive material, binder, filler, etc. may be further included as necessary.

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 < x < 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.

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 present invention also provides a lithium secondary battery comprising the electrode.

The lithium secondary battery includes a positive electrode, a negative electrode, a separator, and a lithium salt-containing nonaqueous electrolyte.

Other components of the secondary battery according to the present invention will be described below.

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 lithium salt-containing nonaqueous electrolyte is composed of a nonaqueous electrolyte and lithium. A nonaqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte and the like are used as the nonaqueous electrolyte, but are 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.

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 (13)

As the electrode mixture is applied to the surface of the current collector,
The electrode mixture is characterized in that it further comprises an additive having a solid electrolyte function in addition to the electrode active material. The electrode of claim 1, wherein the additive is included in an amount of 0.01 to 20 wt% based on the total weight of the electrode mixture. The electrode according to claim 1, wherein the additive is a solid electrolyte which does not cause side reactions at an operating voltage of 3.5V or higher. 4. The electrode according to claim 3, wherein the solid electrolyte is an inorganic solid electrolyte or a polymer solid electrolyte. The method of claim 4, wherein the inorganic solid electrolyte is zirconium oxide, β-alumina, LISICON (Lithium Super Ionic Conductor) compound, LIPON (Li _{3 + y} PO _4-x N _x ) compound, Thio-LISICON (Li _4-x Ge _1-y P _y S ₄ ) -based compound, Li ₂ SP ₂ S ₅ -based compound, 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 , Li ₄ SiO ₄ -LiI-LiOH, Li ₂ S, Li ₂ S-SiS ₂ , Li ₂ S-GeS ₂ , Li ₂ SB ₂ S ₅ , Li ₂ S At least one selected from the group consisting of -Al ₂ S ₂ , Li ₂ O-Al ₂ O ₃ -TiO ₂ -P ₂ O ₅ (LATP), CaF ₂ , AgI and RbAg ₄ I ₅ . The method of claim 5, wherein the inorganic solid electrolyte is one or more selected from the group consisting of zirconium oxide, β-alumina, and Thio-LISICON (Li _4-x Ge _1-y P _y S ₄ ) -based compound. Electrode. The method of claim 4, wherein the polymer-based solid electrolyte is polytetrafluoroethylene (Nafion), a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, a poly etchation lysine, a polyester having a sulfonic acid group And at least one selected from the group consisting of sulfides, polyvinyl alcohols, polyvinylidene fluorides, and polymers containing ionic dissociation groups. 8. The electrode according to claim 7, wherein the polymer solid electrolyte is at least one selected from the group consisting of polytetrafluoroethylene having a sulfonic acid group, a polyethylene oxide derivative, and a polypropylene oxide derivative. The electrode according to claim 4, wherein the polymer-based solid electrolyte has dissolution characteristics in a solvent of an electrode mixture slurry for applying a current collector. The electrode of claim 1, wherein the electrode mixture further comprises at least one selected from the group consisting of a conductive material, a binder, and a filler. A method of manufacturing an electrode according to claim 1,
(i) preparing an electrode mixture slurry by adding an electrode mixture containing an electrode active material to a solvent;
(ii) adding an additive having a solid electrolyte function to the electrode mixture slurry; And
(iii) applying the electrode mixture slurry on a current collector and drying to remove the solvent;
Method for producing an electrode comprising a. A secondary battery comprising an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode and a non-aqueous electrolyte,
At least one electrode of the positive electrode and the negative electrode is an electrode according to any one of claims 1 to 10. The secondary battery of claim 12, wherein the secondary battery is a lithium secondary battery.