KR20140009625A - Electrode for secondary battery and manufacturing method thereof - Google Patents

Abstract

The present invention relates to an electrode for a secondary battery and a manufacturing method thereof. An electrode coupling agent is coated on the surface of a conductor. The electrode coupling agent comprises, besides electrode active material, a compound containing sulfur (S) and/or Phosphorus (P). The content of sulfur ingredient and/or phosphorus ingredient is 500-4000 ppm to the total amount of the electrode coupling agent. The conductor has an improved bonding ability to the electrode coupling agent because the interface with the electrode coupling agent is corroded due to the compound containing sulfur and/or phosphorus.

Description

Electrode for secondary battery and manufacturing method thereof {Electrode for Secondary Battery and Manufacturing Method etc}

The present invention relates to a secondary battery electrode and a method of manufacturing the same, and more particularly, an electrode mixture is an electrode coated on the surface of the current collector, the electrode mixture in addition to the electrode active material sulfur (S) and / or phosphorus (P) And a sulfur component and / or a phosphorus component in a content of 500 to 4000 ppm in the total amount of the electrode mixture, and the current collector is formed of the electrode by the compound containing sulfur and / or phosphorus in the electrode mixture. It relates to an electrode and a method for producing the same, characterized in that the interface with the mixture is corroded to have an improved bonding strength to the electrode mixture.

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 interest in environmental issues grows, researches on electric vehicles and hybrid electric vehicles, which can replace vehicles using fossil fuel, such as gasoline and diesel vehicles, which are one of the main causes of air pollution, are being conducted. . 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 uses a lithium salt such as LiPF ₆ in an electrode assembly including a positive electrode including a lithium transition metal oxide and a negative electrode including a carbon-based active material as an electrode active material, and a polyolefin-based porous separator interposed between the positive electrode and the negative electrode. It consists of a structure impregnated with a nonaqueous electrolyte solution.

A typical lithium secondary battery is discharged while lithium ions of the positive electrode active material are released and inserted into the carbon layer of the negative electrode, and lithium ions of the carbon layer are released and inserted into the positive electrode active material.

However, since the contraction and expansion of the electrode mixture are repeated by lithium ions during charging and discharging of the lithium secondary battery, the bonding force between the electrode mixture and the current collector is lowered, thereby increasing the resistance of the electrode in the portion, and in the portion of which the resistance is high. Side reactions occur and the life of the battery is deteriorated, and resistance causes a problem that the output characteristics of the battery are degraded.

In addition, when the bonding force between the electrode mixture and the current collector is too low, the electrode mixture may be detached from the current collector and electrically short-circuited, thereby causing a fatal risk to the stability of the battery.

In order to solve this problem, increasing the content of the binder not only increases the resistance of the battery due to the electrically nonconductive binder, but also decreases the capacity of the active material, thereby lowering the capacity of the battery. In addition, when the electrolyte is injected during battery manufacturing, the binder contained in the electrode expands while lowering the binding force between the current collector and the active material, thereby increasing the content of the binder.

Therefore, there is a high demand for a technology capable of improving the bonding force between the electrode mixture and the current collector so as to improve battery life characteristics, output characteristics, and electrode stability.

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 include a compound containing sulfur (S) and / or phosphorus (P) in the electrode mixture so that the content of the sulfur component and / or phosphorus component is in a specific range. When it had, it confirmed that the bonding force of an electrode mixture and an electrical power collector improves, and came to complete this invention.

An electrode according to the present invention for achieving this object is an electrode in which the electrode mixture is applied to the surface of the current collector, the electrode mixture containing sulfur (S) and / or phosphorus (P) in addition to the electrode active material And a content of sulfur and / or phosphorus in the total amount of the electrode mixture is 500 to 4000 ppm, and the current collector has an interface with the electrode mixture by the sulfur- and / or phosphorus-containing compound in the electrode mixture. It is corroded and has improved bonding to the electrode mixture.

In one specific example, the compound containing sulfur or phosphorus may be derived from impurities contained in the electrode active material in the electrode mixture. For example, in the case of a lithium transition metal oxide forming an electrode active material, precursors for preparing the same are prepared by mixing transition metal salts. In this case, since the transition metal salt preferably has an anion that is easily decomposed and volatilized upon firing, the transition metal salt may be sulfate or phosphate. Therefore, when the precursor is synthesized using the same and calcined together with the lithium-containing material to form a lithium transition metal oxide, a compound containing sulfur or a compound containing phosphorus may be included in the electrode active material.

In one specific example, the electrode mixture according to the present invention may further comprise at least one selected from the group consisting of a conductive material, a binder and a filler, and thus, the compound containing sulfur or phosphorus may be a conductive material in the electrode mixture. It may also be derived from impurities contained in. For example, when manufacturing carbon, which is a main raw material of the conductive material, a compound containing sulfur or phosphorus may be included as an impurity during carbonization.

In another specific example, the content of sulfur and / or phosphorus in the electrode mixture is desired by the compounds containing sulfur or phosphorus derived from impurities of the electrode active material or conductive material in the preparation of the electrode mixture as mentioned above. When not included in the range, in order to improve the bonding strength between the electrode mixture and the current collector, the compound containing sulfur or phosphorus may be artificially added in the preparation of the electrode mixture to obtain a desired effect.

In this regard, the inventors of the present application when the electrode is prepared using an electrode mixture having a specific range of sulfur and / or phosphorus component due to the sulfur or phosphorus-containing compound included in the electrode mixture, When the interface with the electrode mixture of the current collector is corroded by a compound containing sulfur or phosphorus to improve the bonding strength of the electrode mixture and the current collector, in addition to manufacturing a lithium secondary battery based on this, the electrode from the current collector It was confirmed that not only the stability was excellent but also the life characteristics and the output characteristics were prevented because the mixture was prevented from being detached and the electrical short was prevented.

In one specific example, the content of the sulfur component or phosphorus component, as described above, may be 500 to 4000 ppm based on the total amount of the electrode mixture, in detail, may be 1000 to 3500 ppm. If the content of sulfur or phosphorus is too high, the current collector may be excessively corroded to increase resistance, but rather, the performance of the battery may be degraded by lowering the performance of the active material. If the content is too low, the electrode mixture and the current collector may be deteriorated. Can not achieve the desired effect of improving the cohesion of.

The content of the sulfur component or phosphorus component ranges from the content of sulfur or phosphorus in the electrode mixture when only sulfur-containing compounds or phosphorus-containing compounds are present. In the case where one compound and a compound containing phosphorus are present together, a value obtained by adding the content of the sulfur component and the content of the phosphorus component may satisfy the above range.

The present invention also provides a method for producing an electrode having the sulfur or phosphorus component of the specific content.

Specifically, the electrode according to the present invention comprises the steps of (i) calibrating sulfur and / or phosphorus in the electrode active material and the conductive material; (ii) preparing an electrode mixture including an electrode active material; (iii) adjusting the content of the sulfur component and / or the phosphorus component within the above range when the content of the sulfur component and / or the phosphorus component is not 500 to 4000 ppm relative to the total amount of the electrode mixture; And (iv) applying the electrode mixture onto a current collector and then drying the electrode mixture.

In one specific example, in the process (iii), when the content of the sulfur component and / or phosphorus component is 500 ppm or less based on the total amount of the electrode mixture, the compound artificially containing sulfur and / or phosphorus is added to the mixture. It can be added to increase the amount, and if it is 4000 ppm or more, the mixture can be washed to reduce the amount.

In the process (ii), the method of measuring the content of the sulfur- or phosphorus-containing compound in the electrode mixture may vary, and methods for measuring the content of specific materials are well known in the art, and thus detailed description thereof is omitted. do.

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

As described above, the electrode according to the present invention includes a compound containing sulfur and / or phosphorus in the electrode mixture, whereby the compound and electrode mixture due to the compound when the content of the sulfur component and / or phosphorus component has a specific range By making the whole interface corrode, the bonding force between the electrode mixture and the current collector can be improved.

In addition, the lithium secondary battery based on this has the effect of having excellent life characteristics, output characteristics and stability.

As described above, the present invention is an electrode, the electrode mixture is applied to the surface of the current collector, the electrode mixture contains a compound containing sulfur (S) and / or phosphorus (P) in addition to the electrode active material, The content of sulfur and / or phosphorus is 500 to 4000 ppm in the total amount of the electrode mixture, and the current collector corrodes the interface with the electrode mixture by the sulfur- and / or phosphorus-containing compound in the electrode mixture, thereby causing It provides an electrode and a method for manufacturing the same, characterized in that having an improved bonding force.

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 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 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 (12)

As the electrode mixture is applied to the surface of the current collector,
In addition to the electrode active material, the electrode mixture contains a compound containing sulfur (S) and / or phosphorus (P), and the content of sulfur and / or phosphorus is 500 to 4000 ppm in the total amount of the electrode mixture. The whole has an improved bonding strength to the electrode mixture due to corrosion of the interface with the electrode mixture by the sulfur- and / or phosphorus-containing compound in the electrode mixture. The electrode according to claim 1, wherein the compound containing sulfur and / or phosphorus is derived from impurities contained in an electrode active material. The electrode of claim 2, wherein the impurity contained in the electrode active material is derived from a transition metal salt for preparing a precursor of the electrode active material. The electrode according to claim 3, wherein the transition metal salt is sulfate or phosphate. The electrode according to claim 1, wherein the electrode mixture further comprises a conductive material, and the sulfur- and / or phosphorus-containing compound is derived from impurities contained in the conductive material. The electrode as claimed in claim 1, wherein the sulfur- and / or phosphorus-containing compound is artificially added when preparing the electrode mixture. The electrode according to claim 1, wherein the sulfur and / or phosphorus content is included in an amount of 1000 to 3500 ppm based on the total amount of the electrode mixture. 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 or 5,
(i) calibrating the sulfur component and / or phosphorus component in the electrode active material and the conductive material;
(ii) preparing an electrode mixture including an electrode active material;
(iii) adjusting the content of the sulfur component and / or the phosphorus component within the above range when the content of the sulfur component and / or phosphorus component is out of 500 to 4000 ppm relative to the total amount of the electrode mixture; And
(iv) applying and drying the electrode mixture on a current collector;
Method for producing an electrode comprising a. 10. The compound according to claim 9, wherein in the process (iii), the sulfur and / or phosphorus content is 500 ppm or less based on the total amount of the electrode mixture. A method for producing an electrode, characterized in that the addition further.  10. The method according to claim 9, wherein in the process (iii), when the content of the sulfur component and / or phosphorus component is 4000 ppm or more based on the total amount of the electrode mixture, the mixture is washed. Lithium secondary battery comprising an electrode according to claim 1.