KR20090008078A - Anode mix containing anode additive for improving efficiency of electrode - Google Patents

Abstract

An anode mix for a secondary battery is provided to maximize the efficiency and capacity of an electrode active material and to reduce the manufacturing costs by minimizing the waste of material. An anode mix for a secondary battery comprises a first anode active material of high efficiency and a second anode active material causing the irreversible reaction in the operating potential of the first anode active material, in the amount that the operational efficiency of the first anodal active material is leveled to the level of a cathode active material.

Description

Anode Mix Containing Anode Additive for Improving Efficiency of Electrode

The present invention relates to a negative electrode mixture including a negative electrode additive for improving electrode efficiency, and more particularly, to a negative electrode mixture for a secondary battery including a high efficiency negative electrode active material, the operating efficiency of the negative electrode active material level of the positive electrode active material The present invention relates to a negative electrode mixture further comprising another negative electrode active material that causes an irreversible reaction at an operating potential of the negative electrode active material, and a lithium secondary battery including the same, in an amount capable of leveling.

As the development and demand for mobile devices increases, the demand for secondary batteries as energy sources is rapidly increasing. Among them, lithium secondary batteries with high energy density and voltage, long cycle life, and low self discharge rate It is commercially used and widely used.

Lithium-containing cobalt oxide (LiCoO ₂ ) is mainly used as a positive electrode active material of the lithium secondary battery. In addition, lithium-containing manganese oxide such as spinel crystal structure LiMn ₂ O ₄ , lithium-containing nickel oxide (LiNiO ₂ ), and the like are also used. have. Carbon materials are mainly used as the negative electrode active material, and use of lithium metal, sulfur compounds and the like is also contemplated.

In these electrodes, by controlling the efficiency of the positive electrode and the negative electrode to a similar level it is possible to minimize the waste of inefficient electrodes. For example, if a positive electrode having 100% efficiency is used for a negative electrode having approximately 100% efficiency, the cell may exhibit 100% efficiency while 90% for a negative electrode having 100% efficiency. When using a positive electrode having efficiency, the battery can exhibit only 90% efficiency. As a result, there is a problem that 10% of the cathode is unnecessarily wasted.

In this regard, when a carbon-based negative electrode active material is generally used and lithium oxide is used as the positive electrode active material, an irreversible capacity of about 10 to 20% occurs during initial charge and discharge including an initial charge, and 80 to 90% Only degree can be used reversibly. Therefore, using an electrode active material having an irreversible capacity causes a problem that waste of electrode material by the irreversible capacity is caused.

On the contrary, in order to exhibit 100% battery efficiency while using a negative electrode having an efficiency of 100%, a positive electrode having an efficiency close to 100% should be used, but in this case, there is a problem in that the selection of the positive electrode active material becomes very narrow. . In a specific example, when lithium titanium oxide having high efficiency is used as the negative electrode active material, it is preferable to use manganese having a spinel structure or the like as the positive electrode active material having similar efficiency in terms of battery efficiency. However, in this case, there exists a problem that a high temperature characteristic and a lifetime characteristic become worse. On the other hand, in the case of using a positive electrode active material having a relatively low efficiency but excellent in the high temperature characteristics or life characteristics, the amount of use of the positive electrode should be increased in accordance with the high efficiency negative electrode, there is a problem that the manufacturing cost increases.

However, there is no technology presenting a method of controlling the efficiency of the electrode active material. Accordingly, the inventors of the present application, as will be described in detail later, another negative electrode active material, that is, the second negative electrode active material causing an irreversible reaction at the operating potential of the high efficiency negative electrode active material in order to equalize the efficiency of the positive electrode active material and the efficiency of the negative electrode active material It suggests ways to include it.

In this regard, some techniques for adding metal materials to existing carbon-based negative electrode active materials are known. These prior arts have a disadvantage in that the irreversible capacity is large when a metal material having a large volume capacity is used as the negative electrode active material, and thus, a carbon-based negative active material having a relatively low irreversible capacity is mixed to compensate for this, thereby improving cycle characteristics. It is aimed at.

For example, Japanese Patent Application Laid-Open No. 2002-251992 consists of a metal material and a capacitive carbon material capable of occluding and releasing lithium, and a fine conductive material powder mixture, if necessary, Disclosed is an electrode material comprising 5 to 60% by weight of material and 40 to 95% by weight of the carbon material.

In addition, Korean Patent Application No. 2003-0029159 discloses a technique of doping lithium to graphite or coating a predetermined metal oxide on the graphite surface, and Korean Patent Application No. 2003-0057928 discloses the insertion and desorption of lithium ions. A carbonaceous compound and an oxide film or hydroxide film of at least one element selected from the group consisting of Al, Ag, B, Cu, Mg, Si, Ti, Zn and Zr formed on the surface of the carbon-based compound, wherein the oxide or hydroxide Disclosed is an electrode active material having 80 to 100% by weight of a compound containing an element having a coordination number with heavy oxygen of 4 coordination and 6 coordination.

However, these techniques are to reduce power characteristics and initial irreversibility of the carbon-based negative electrode active material having high reactivity with the organic electrolyte and exhibiting low wettability, and controlling the efficiency of the negative electrode active material in consideration of the efficiency of the positive electrode active material. There is a remarkable difference from the present invention.

Moreover, according to the above techniques, the process of coating the metal material on the carbon-based negative electrode active material is difficult and complicated, and the capacity of the carbon material itself can be reduced due to the high irreversible capacity of the metal material in the non-uniform coating of the metal material. There is such a problem.

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

The inventors of the present application, after extensive research and various experiments, add a negative electrode active material that causes an irreversible reaction at an operating potential of the high efficiency negative electrode active material in an amount capable of leveling it to the level of the positive electrode active material. It was found that it is possible to minimize the waste, and ultimately maximize the efficiency and capacity of the electrode and the battery, and came to complete the present invention.

Accordingly, the negative electrode mixture according to the present invention is a negative electrode mixture for a secondary battery including a high efficiency negative electrode active material ('first negative electrode active material'), and the operating efficiency of the first negative electrode active material can be leveled to the level of the positive electrode active material. It is comprised by the quantity which further contains the 2nd negative electrode active material which produces an irreversible reaction in the operating potential of a 1st negative electrode active material.

In the negative electrode mixture according to the present invention, since the second negative electrode active material is an active material that causes an irreversible reaction at the operating potential of the first negative electrode active material, when the second negative electrode active material is added in an amount corresponding to the irreversible capacity of the positive electrode active material, the first negative electrode The operating efficiency of the active material can be leveled to the level of the positive electrode active material.

Accordingly, the waste of the electrode material can be minimized, thereby greatly reducing the manufacturing cost, and the battery efficiency and capacity desired to be additionally included together with the first negative electrode active material without having to go through a separate coating process or the like. Since it can obtain etc., it is very preferable from a manufacturing process viewpoint. In addition, there is an advantage in that the selection range of the positive electrode active material corresponding to the negative electrode active material in terms of efficiency of the battery can be widened.

The high-efficiency first negative electrode active material means a material having a relatively higher efficiency than the positive electrode active material, not only when the efficiency of the negative electrode active material itself is high, but also when the theoretical capacity is similar to or lower than that of the positive electrode active material, including the initial charge. It is a concept that includes a negative electrode active material in the case where the irreversible capacity is generated in the positive electrode active material during the initial charge and discharge becomes lower than the capacity of the negative electrode active material.

Considering that the efficiency of the general cathode active material is about 80 to 93%, the efficiency of the first anode active may be 90% or more, more preferably 94% or more.

Lithium titanium oxide (LTO) is mentioned as a preferable example of a high efficiency itself negative electrode active material (1st negative electrode active material). Since the LTO has an operating potential of about 1.5 V and no decomposition reaction of the electrolyte at this potential, the efficiency of itself reaches almost 99%. Therefore, in the case of using a nickel-based positive electrode active material, a nickel-cobalt-manganese composite positive electrode active material (three-component positive electrode active material), etc., which are relatively low in efficiency as the positive electrode active material, many electrodes have a reversible capacity similar to that of LTO. Since a material is needed, manufacturing cost rises, and there exists a problem. In addition, due to the low efficiency of the positive electrode active material, the irreversible capacity generated during the initial charge and discharge process also causes a problem such as reducing the operating capacity of the entire battery. On the other hand, by adding a second negative electrode active material exhibiting irreversibility at the operating potential of the LTO negative electrode active material according to the present invention, when leveling to have an efficiency almost equal to that of the positive electrode active material, the waste of the negative electrode active material is minimized, Can solve the problems caused by irreversible capacity.

Even if the efficiency itself is not high, examples of the negative electrode active material (first negative electrode active material) in which the efficiency is relatively high with respect to the positive electrode active material or the relative efficiency increases due to the reaction during initial charge and discharge are non-graphitizable carbon and black. Carbon such as linked carbon; Li _y Fe ₂ O ₃ (0 ≦ _y ≦ 1), Li _y WO ₂ (0 ≦ _y ≦ 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 ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8); Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; 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 metal oxides such as Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni system material etc. are mentioned. However, it is determined whether they can be used as the first negative electrode active material of the present invention according to the type of the positive electrode active material.

In the present invention, the second negative electrode active material is a material causing an irreversible reaction at the operating potential of the first negative electrode active material, as defined above.

Specifically, since the first negative electrode active material is a high efficiency material and has a small irreversible capacity at an operating potential, a difference in efficiency with a relatively low efficiency positive electrode active material occurs, so that the operating efficiency of the first negative electrode active material may be leveled to the level of the positive electrode active material. When the second negative electrode active material is added, an irreversible capacity is generated at the operating potential of the first negative electrode active material, so that the efficiency is adjusted to the level of the positive electrode active material.

The second negative electrode active material may vary depending on the type of the first negative electrode active material and the positive electrode active material, and may be preferably a metal or a nonmetal oxide. The metal or nonmetal oxide is, for example, one, two or more elements selected from Cu, Co, Fe, Ni, Mn, Al, B, Ga, Nb, Sn, Ti, Zr, Zn, Si, and V. An oxide consisting of, but is not limited to these. Such a method for producing or obtaining a metal or nonmetal oxide is well known in the art, and thus detailed description thereof will be omitted.

The second negative electrode active material should be added in an amount capable of leveling the operating efficiency of the first negative electrode active material to the level of the positive electrode active material, and if too much is added, the irreversible capacity is increased, causing material waste of the second negative electrode active material. Since the efficiency and capacity of the entire battery may be reduced, there is a problem. On the contrary, when too little is added, the desired first negative electrode active material may not be leveled. It may be included in an amount of 1 to 10% by weight based on the total content.

In addition to the first negative electrode active material and the second negative electrode active material, the negative electrode mixture of the present invention may optionally include a conductive material, a binder, a filler, and the like.

The conductive material is typically added in an amount of 1 to 50% 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 conductivity without causing chemical change in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder 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 the active material and the conductive material to the current collector, and is generally added in an amount of 1 to 50 wt% based on the total weight of the mixture including the negative electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, 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 inhibiting 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 fiber and carbon fiber, are used.

The present invention also provides a negative electrode for a secondary battery in which the negative electrode mixture is coated on a current collector.

The negative electrode for a secondary battery may be prepared by, for example, applying a slurry made by mixing the negative electrode mixture with a solvent such as NMP onto a negative electrode current collector, followed by drying and rolling.

The negative electrode current collector is generally made to a thickness of 3 to 500 ㎛. Such a negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver, and the like, aluminum-cadmium alloy, and the like can be used. In addition, like the positive electrode current collector, fine concavities and convexities may be formed on the surface to enhance the bonding strength of the negative electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The present invention also provides a lithium secondary battery comprising the negative electrode, a positive electrode, a separator, and a lithium salt-containing nonaqueous electrolyte. The lithium secondary battery according to the present invention may be secured during overdischarge due to the lithium-containing composite nitride contained in a predetermined amount in the negative electrode mixture.

For example, the positive electrode is manufactured by applying a positive electrode mixture including a positive electrode active material on a positive electrode current collector and then drying the positive electrode mixture. The positive electrode mixture may include components as described above, if necessary.

The positive electrode current collector is generally made to a thickness of 3 to 500 μm. 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 form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The positive electrode 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; Li _{1 + y} Mn _{2 - y} O ₄ (Where y is 0 to 0.33), lithium manganese oxide such as LiMnO ₃ , LiMn ₂ O ₃ , LiMnO _2, etc .; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , Cu ₂ V ₂ O ₇ and the like; Ni-site-type lithium nickel oxide represented by the formula LiNi _1-y M _y O ₂ , wherein M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and y = 0.01 to 0.3; Formula LiMn _2-y M _y O ₂ , wherein M = Co, Ni, Fe, Cr, Zn or Ta and y = 0.01 to 0.1, or Li ₂ Mn ₃ MO ₈ , where M = Fe, Co, Lithium manganese composite oxide represented by Ni, Cu or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ and the like, but are not limited to these.

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 from 0.01 to 10 ㎛ ㎛, thickness is generally 5 ~ 300 ㎛. As such a separator, for example, olefin polymers such as chemical resistance and hydrophobic polypropylene; Sheets or non-woven fabrics made of glass fibers or polyethylene are used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The lithium salt-containing non-aqueous electrolyte is composed of an electrolyte and a lithium salt, and the electrolyte is a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, or the like.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and gamma Butyl lactone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxorone, formamide, dimethylformamide, dioxolon , Acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxy methane, dioxorone derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbo Aprotic organic solvents such as nate derivatives, tetrahydrofuran derivatives, ethers, methyl pyroionate and ethyl propionate can be used.

Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyedgetion lysine, polyester sulfides, polyvinyl alcohols, polyvinylidene fluorides, Polymerizers containing ionic dissociating groups and the like can 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 good material to be dissolved 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, in the electrolyte solution, for the purpose of improving the charge and discharge characteristics, flame retardancy, etc., for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitro Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxy ethanol, aluminum trichloride and the like may be added. . In some cases, in order to impart nonflammability, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high temperature storage characteristics.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are provided to illustrate the present invention, and the scope of the present invention is not limited thereto.

Example 1

90% by weight of Li _4/3 Ti _5/3 O ₄ as the first negative electrode active material, 5% by weight of CoO as the second negative electrode active material, 2.5% by weight of Super-P (conductor) and 2.5% by weight of PVdF (binder) Was added to prepare a negative electrode mixture slurry. It was coated on one surface of the copper foil, dried and pressed to prepare a negative electrode.

Of a positive electrode active material a lithium nickel cobalt manganese composite oxide _{(LiNi 1/3 Co 1/} 3 Mn 1/3 O 2) 95 % by weight, Super-P (conductive material) of 2.5% by weight of PVdF (binder) 2.5% by weight of solvent A positive electrode mixture slurry was prepared by adding to N-methyl-2-pyrrolidone (NMP), and coated, dried, and pressed on one surface of aluminum foil to prepare a positive electrode.

After the electrode assembly was prepared by laminating the positive electrode and the negative electrode using Celgard ^TM as a separator, a lithium non-aqueous electrolyte solution containing 1M LiPF ₆ was added to a cyclic and linear carbonate mixed solvent to prepare a battery.

Comparative Example 1

A negative electrode mixture slurry was prepared in the same manner as in Example 1 except that 95 wt% of Li _4/3 Ti _5/3 O ₄ was mixed as a negative electrode active material and no second negative electrode active material was added, and the same was carried out using the same. A battery was prepared in the same manner as in Example 5.

Experimental Example 1

The efficiency and capacity of the batteries prepared in Example 1 and Comparative Example 1 were measured, and the results are shown in Table 1 below.

TABLE 1

According to Table 1, the battery of Example 1 and Comparative Example 1 was the same efficiency, but the battery of Example 1 was higher in terms of capacity. That is, since the efficiency of the battery is substantially determined by the low-efficiency positive electrode active material, it does not increase in the battery of Comparative Example 1 in which only high-efficiency LTO is used as the negative electrode active material. On the contrary, in the battery of Comparative Example 1, due to the low efficiency of the positive electrode active material, irreversible lithium ions that cannot be occluded back into the positive electrode in the discharge process are limited even to the expression capacity of the negative electrode. Compared with the battery of 1, a capacity reduction of about 15% was caused.

On the other hand, in the battery of Example 1, the irreversible capacity of the positive electrode was irreversibly consumed during the initial charging and discharging process by CoO of the negative electrode, which did not cause a capacity reduction as in Comparative Example 1.

In addition, in the case of the battery according to Example 1, despite the relatively low addition of the first negative electrode active material, by exhibiting the same efficiency and relatively high capacity as the battery of Comparative Example 1, ultimately reduce the manufacturing cost of the battery It can be seen that.

Those skilled in the art to which the present invention pertains will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

As described above, the present invention adds a second negative electrode active material irreversible to the high efficiency of the negative electrode active material in an amount capable of leveling the operation efficiency to the level of the positive electrode active material, thereby minimizing the waste of the electrode and reducing the battery manufacturing cost It is possible to maximize the use efficiency of the electrode and the battery.

Claims (10)

A negative electrode mixture for a secondary battery including a high-efficiency negative electrode active material ('first negative electrode active material'), the operation of the first negative electrode active material in an amount capable of leveling the operation efficiency of the first negative electrode active material to the level of the positive electrode active material A negative electrode mixture, further comprising a second negative electrode active material causing an irreversible reaction at a potential. The negative electrode mixture according to claim 1, wherein the first negative electrode active material is an active material having high efficiency in itself. The negative electrode mixture of claim 1, wherein the first negative electrode active material has a capacity similar to that of the positive electrode active material, but an irreversible capacity is generated in the positive electrode active material during initial charging and discharging, thereby lowering the reversible capacity of the negative electrode active material. The negative electrode mixture of claim 2, wherein the first negative electrode active material is lithium titanium oxide (LTO). The negative electrode mixture of claim 1, wherein the first negative electrode active material has an efficiency of 90% or more. The negative electrode mixture according to claim 1, wherein the second negative electrode active material is a metal or a nonmetal oxide. According to claim 6, wherein the metal or non-metal oxide is one, two or more selected from Cu, Co, Fe, Ni, Mn, Al, B, Ga, Nb, Sn, Ti, Zr, Zn, Si and V A negative electrode mixture, characterized in that the oxide consisting of an element. The negative electrode mixture of claim 1, wherein the second negative electrode active material is included in an amount of 1 to 10% by weight based on the total content of the negative electrode active material. The negative electrode for secondary batteries in which the negative electrode mixture in any one of Claims 1-8 is apply | coated on an electrical power collector. A lithium secondary battery comprising the negative electrode according to claim 9.