KR101283342B1 - Active Material For Anode of Lithium Secondary Battery - Google Patents

Abstract

The present invention provides a negative electrode active material as a negative electrode active material for a lithium secondary battery, characterized in that it has a multi-stage charging profile that can solve the over-potential of the negative electrode in the initial state of charge, the negative electrode active material is the amount of current in the initial state of charge By suppressing Li-plating by an increase, Li-plating by a side reaction, etc., the secondary battery excellent in a fast charge and a long-term cycle can be manufactured.

Description

Negative active material for lithium secondary battery {Active Material For Anode of Lithium Secondary Battery}

The present invention relates to a negative electrode active material for a lithium secondary battery, and relates to a negative electrode active material having a multi-stage charging profile capable of solving an over-potential of a negative electrode in an initial state of charge.

Due to the rapid increase in the use of fossil fuels, there is an increasing demand for the use of alternative energy and clean energy, and the most actively researched areas are electricity generation and electricity storage methods. At present, a representative example of a system using such electrochemical energy is a lithium secondary battery, and its area is gradually expanding.

In other words, as the development and demand for mobile devices increases, the demand for secondary batteries is rapidly increasing as an energy source. Among them, lithium has high energy density and operating potential, has a long cycle life, and has a low self-discharge rate. Secondary batteries have been widely used.

In addition, as interest in environmental problems grows, researches on electric vehicles and hybrid electric vehicles that 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. have. Although nickel-metal hydride secondary batteries are mainly used as power sources for such electric vehicles and hybrid electric vehicles, researches using lithium secondary batteries having high energy density and discharge voltage are being actively carried out, and they are in the commercialization stage.

In response to this, as part of research on materials, a cathode active material based on lithium transition metal oxide and a cathode active material based on carbon have been utilized.

However, in the case of a negative electrode active material using carbon, the potential is very low, similar to Li, and has a problem in that Li precipitates in the negative electrode due to an increase in resistance or an increase in current.

Such lithium deposition is a situation that causes a big problem in performance and safety, such as reducing the cycle, causing micro-short due to lithium dendrites.

The present invention aims to solve these problems of the prior art and technical problems that have been requested from the past.

The present inventors have conducted extensive research on the over-potential phenomenon of the negative electrode that causes Li-plating, and then developed a negative active material capable of controlling the initial state of charge. As described above, the anode active material was confirmed to solve the problems of the above-described problems of the prior art, such as the reduction of cycles and the occurrence of fine short circuits due to lithium dendrites, and thus, the present invention was completed.

Accordingly, the present invention provides a negative electrode active material having a multi-stage charging profile that can solve the over-potential of the negative electrode in an initial state of charge as a negative electrode active material for a lithium secondary battery.

Precipitation of lithium, i.e. Li-plating, results in over-potential, where the over-potential at the negative electrode is mainly due to the initial state of charge and the terminal state of charge. Among them, the problem of the terminal charge state can be solved by a method of adjusting the cathode / anode ratio, and the like. In the terminal charge state, the amount of the cathode, for example, the loading amount is adjusted to be larger than that of the positive electrode. Over-potential problem can be solved.

However, in the case of the initial charging state, there is a part that is difficult to solve by electrode design, such as using a special charger to control this.

On the other hand, in the present invention, based on the electrode active material having a multi-stage charge profile, Li-plating by increasing the amount of current in the initial state of charge, Li-plating by side reactions, etc. are suppressed, so that fast charging and long-term cycles are reduced. It provides an excellent secondary battery negative electrode.

Specifically, in the case of the negative electrode, charging is performed from a region existing in a high voltage section during charging, and it is possible to control Li-plating generated by over-potential in this initial charging section.

Thus, the multistage charging profile is a charging profile having at least two or more charging steps, wherein the potential difference of each charging step may preferably be 0.1 to 2.0V.

In one preferred example, the multi-stage charging profile may be a configuration comprising two to five charging steps with a potential difference of at least 0.2 to 1.5 V in each charging step. Such a multi-stage charging profile may be implemented by one type of negative electrode active material exhibiting such characteristics, and may be a combination of two or more types of negative electrode active materials having different charging potentials within the above ranges.

As described above, according to the present invention, since the negative electrode active material is made of a material having a multi-stage charge profile that can solve the over-potential in the initial state of charge, Li-plating, side reaction by increasing the amount of current in the initial state of charge By suppressing Li-plating and the like, a secondary battery excellent in fast charging and a long-term cycle can be produced.

The present invention also provides a negative electrode comprising a negative electrode active material as described above, and a lithium secondary battery comprising such a negative electrode. Hereinafter, the negative electrode will be abbreviated as a negative electrode.

The lithium secondary battery is generally composed of a positive electrode, a negative electrode, a separator and a lithium salt-containing nonaqueous electrolyte. Therefore, hereinafter, other components constituting the lithium secondary battery in addition to the negative electrode active material according to the present invention described above will be described.

The negative electrode is manufactured by applying and drying a negative electrode active material, a conductive material, a binder, and the like on a negative electrode current collector, and if necessary, other components such as a filler may be further included.

The negative electrode 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 conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, 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 binder is a component that assists the bonding of the active material and the conductive material to the current collector, and is generally added in an amount of 1 to 20 wt% based on the total weight of the mixture including the negative electrode 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 conductive material is typically added in an amount of 1 to 20% by weight based on the total weight of the mixture including the negative electrode 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 filler is optionally used as a component for inhibiting the expansion of the negative electrode, and is not particularly limited as long as it is a fibrous material without causing chemical change in the battery. Examples of the filler include olefinic polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The positive electrode is produced by, for example, applying a mixture of a positive electrode active material, a conductive material, and a binder onto a positive electrode current collector and then drying it.

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. For example, the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with carbon, nickel, titanium, silver or the like can 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.

Examples of the positive electrode active material include a layered compound such as lithium cobalt oxide (LiCoO ₂ ) and 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); 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.

The separator 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 non-aqueous electrolyte consists of a non-aqueous electrolyte and a lithium salt. As the non-aqueous electrolyte, a liquid solvent, a solid electrolyte, an inorganic solid electrolyte, and the like are used.

As said liquid solvent, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, fluoro ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylo lactone, 1, 2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolon, formamide, dimethylformamide, dioxoron, acetonitrile, nitromethane, Methyl formate, methyl acetate, phosphate triester, trimethoxy methane, dioxoron derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether Aprotic organic solvents such as methyl pyroionate and ethyl propionate 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, Polymers containing ionic dissociation groups, and the like can be used.

As the inorganic solid electrolyte, for example, 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 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

In addition, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., the non-aqueous electrolyte solution includes, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, and hexaphosphate triamide. Nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxy ethanol, aluminum trichloride, etc. It may be. In some cases, in order to impart nonflammability, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included, or carbon dioxide gas may be further included to improve high temperature storage characteristics.

Lithium secondary battery according to the present invention can be used regardless of the appearance, such as cylindrical, square, pouch-type battery.

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 (6)

As a negative electrode active material for a lithium secondary battery, a combination of two or more types of negative electrode active materials having different charging potentials, so that the over-potential of the negative electrode can be solved in an initial state of charge, A negative electrode active material having a multi-stage charge profile with a potential difference of 0.1 to 2.0 V. delete The negative active material of claim 1, wherein the charging profile comprises two to five charging steps having a potential difference of 0.2 to 1.5 V in each charging step. delete A negative electrode comprising the negative electrode active material according to claim 1. A lithium secondary battery comprising the negative electrode according to claim 5.