KR20150040227A - Secondary Battery - Google Patents

Abstract

Provided is a secondary battery comprising: (i) a positive electrode active material comprising compounds of chemical formula 1 and 2: Li_2Ni_(1-a)MaO_2 (1), Li[Li_a′Ni_xMn_yCo_zM_w]O_(2-t)A_t (2). In the chemical formula, 0<=a<1, 0<=a′<=0.2, 0<=x<=0.9, 0<=y<=0.9, 0<=z<=1, 0<=w<=0.9, a′+x+y+z+w=1, 0<=t<0.2; M is a positive ion of one or more metals or transition metals having +2 to +4 valent oxidation number; A is a -1 or -2 valent negative ion, the content is A_(2t) when A is -1, and the content is A_t when A is -2; and (ii) a negative electrode active material including a carbon-based material and a silicon (Si)-based compound. According to the present invention, the secondary battery can show excellent capacity properties and battery efficiency.

Description

Secondary Battery

The present invention relates to a secondary battery exhibiting excellent capacity characteristics and high energy efficiency.

As technology development and demand for mobile devices are increasing, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life and low self- It has been commercialized and widely used.

In a conventional lithium secondary battery, a layered lithium cobalt composite oxide is used for the anode and a graphite based material is used for the cathode. However, in the case of the lithium cobalt composite oxide, the main component cobalt is very expensive, It is disadvantageous in that it is not suitable for an electric automobile from the side and it is difficult to exert a high capacity due to an increase in energy density.

The use of lithium-containing manganese oxides such as LiMnO _{2 having a} layered crystal structure and LiMn ₂ O _{4 having a} spinel crystal structure and lithium-containing nickel oxide (LiNiO ₂ ) is considered as a cathode active material, and as a negative electrode active material, Is mixed with a carbon-based material.

However, in the case of the carbonaceous anode active material, an irreversible capacity of about 10 to 20% is generated during the initial charge / discharge including the initial charge. Therefore, when a material having an efficiency of 80 to 90% or more is used as the cathode active material, There is a problem that waste of the electrode material is caused by the irreversible capacity of about 1%. In addition, in the case of using a negative electrode active material having a relatively low efficiency, the amount of the negative electrode to be used must be increased in accordance with the high efficiency anode, resulting in an increase in manufacturing cost.

Therefore, there is a high need for a technique for controlling the efficiency of the cathode active material to exhibit a high capacity while reducing the amount of the active material.

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.

The inventors of the present application have conducted intensive research and various experiments. As described later, when a secondary battery including a predetermined positive electrode active material and a negative electrode active material is manufactured, the capacity and energy density of the battery are maximized, The inventors of the present invention have found that the desired characteristics can be attained by increasing the overall characteristics, and the present invention has been accomplished.

Therefore,

(i) a cathode active material comprising a compound of the following formulas (1) and (2):

Li ₂ Ni _1-a M _a O ₂ (1)

Li [Li _{a '} Ni _x Mn _y Co _z M _w ] O _{2 -te t} (2)

In this formula,

0? A <? 1, 0? A?? 0.2, 0? X? 0.9, 0? Y? 0.9, 0? Z? 1, 0? W? 0.9, a '+ x + y + z + w = 0? T <0.2; M is at least one metal or transition metal cation of +2 to +4 oxidation numbers; A is an anion of -1 or -2 valence, the content being -1 when A _2t and -2 being A _t ; And

(ii) a negative electrode active material containing a carbon-based material and a silicon (Si) -based compound;

The secondary battery includes a secondary battery.

The secondary battery according to the present invention can provide a high energy density by using a carbon-based material and a silicon-based compound as a negative electrode active material.

Also, in order to compensate for the low efficiency occurring when the negative electrode active material is used, the operation efficiency of the positive electrode active material can be relatively lowered by including the compound of Formula 1 as the positive electrode active material. Accordingly, even when the anode active material having a relatively low operating efficiency is used, the operating efficiency of the cathode active material can be leveled by adjusting the operating efficiency to a proper level to the cathode.

Therefore, waste of the electrode material can be minimized, manufacturing cost can be greatly reduced, desired battery efficiency, capacity and the like can be obtained, which is highly desirable in view of the manufacturing process. In addition, the problem due to the irreversible capacity of the negative electrode active material can be solved, and the range of selection of the negative electrode active material corresponding to the positive electrode active material can be widened in terms of the efficiency of the battery.

In the present invention, the compounds of formulas (1) and (2) may be represented by the following formulas (3) and (4), respectively.

Li ₂ NiO ₂ (3)

LiNi _{1- (y '+ z')} Mn _{y '} Co _z' O ₂ (4)

In this formula,

0? Y? 0.7, 0 <z? 1, 0 <y '+ z'?

More specifically, the compound of Formula 4 may be LiCoO ₂ .

The compounds of formulas (1) and (2) may be used in a weight ratio of 3: 1 to 6: 1. In particular, the compounds of formula (1) and (2) may be used in a weight ratio of 4: 1 to 5: 1.

When the amount of the compound of the formula (2) is too small, the operation efficiency of the cathode active material can not be appropriately controlled, and when it is too large, the energy density can not be maximized.

In the present invention, the carbon-based material may be, 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, These may be used alone or in combination of two or more, and may be graphite in detail.

The silicon-based compound may be at least one selected from the group consisting of, for example, chlorosilane, alkoxysilane, aminosilane, fluoroalkylsilane, silicon, silicon chloride and silicon oxide (SiO 2) Silicon (SiO). Such silicon oxide (SiO ₂ ) is a material in which silicon dioxide (SiO ₂ ) and amorphous silicon are mixed at a mixing ratio of 1: 1 based on the weight ratio.

The carbon-based material and the silicon (Si) -based compound may be present in a weight ratio of 80:20 to 99: 1, and more specifically, the carbon-based material and the silicon- 5 &lt; / RTI &gt;

When the amount of the silicon (Si) -based compound is too small, it is difficult to increase the energy density of the battery, and if it is too large, the operation efficiency of the negative electrode active material becomes too low and the degree of volume expansion becomes large.

The secondary battery may be a lithium secondary battery.

Hereinafter, the configuration of such a lithium secondary battery will be described.

The lithium secondary battery includes a cathode prepared by coating a mixture of a cathode active material, a conductive material and a binder on the anode current collector, followed by drying and pressing, and a cathode manufactured using the same method. In this case, A filler is further added to the mixture.

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, and various copolymers.

The filler is optionally used as a component for suppressing 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-based polymerizers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are 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.

Such a lithium secondary battery may have a structure in which a lithium salt-containing electrolyte is impregnated in an electrode assembly having a separator interposed between a cathode and an anode.

The separation membrane is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The electrolyte solution containing the lithium salt is composed of an electrolyte solution and a lithium salt. The electrolyte solution may be a non-aqueous organic solvent, an organic solid electrolyte, or an inorganic solid electrolyte, but is not limited thereto.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , Acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Nonionic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymer containing an ionic dissociation group and the like may be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides 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.

The battery pack including at least one lithium secondary battery may be used as a power source for devices requiring high temperature stability, long cycle characteristics, and high rate characteristics.

Examples of the device may be an electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV) But is not limited thereto.

As described above, the secondary battery according to the present invention can appropriately adjust the operation efficiency of the cathode active material to a cathode by using a predetermined compound as the cathode active material, thereby minimizing the waste of the electrode material, thereby greatly reducing the manufacturing cost And the desired cell efficiency, capacity, and the like can be obtained. In addition, by using a predetermined compound as the negative electrode active material, it is possible to maximize the energy density and capacity increase effect.

&Lt; Example 1 >

The negative electrode active material was prepared by mixing graphite, silicon oxide (97: 3 by weight), conductive material (Denka black) and aqueous binder (SBR / CMC) in distilled water at a weight ratio of 97: 0.5: 2.5, Coated on a copper foil, rolled and dried to prepare a negative electrode.

LiCoO ₂ and Li ₂ NiO ₂ (4: 1 by weight), a conductive material (Denka black) and a binder (PVdF) were mixed in NMP at a weight ratio of 96: 2.0: 2.0 respectively as cathode active materials and mixed. Was coated on an aluminum foil, rolled and dried to prepare a positive electrode.

A polyethylene electrolyte membrane was interposed between the thus prepared negative electrode and the positive electrode, and an electrolytic solution containing 1 M of LiPF ₆ in a solvent of EC: EMC: DEC = 3: 2: 5 based on the volume ratio was used to prepare a 2100 mA secondary battery .

&Lt; Comparative Example 1 &

A secondary battery was fabricated in the same manner as in Example 1, except that LiCoO ₂ alone was used as the cathode active material.

<Experimental Example>

The efficiency (%) and the required amount of active material were measured at 0.5 C charging, 0.5 C discharge condition,

Square 2100 mA design basis Comparative Example 1 Example 1 LiCoO ₂ SiO and graphite LiCoO ₂ and Li ₂ NiO ₂ SiO and graphite efficiency (%) 97.6 91.5 93.9 91.5 Amount of active material required (g) 13.5 6.2 13.0 5.9

According to Table 1, the working efficiency of the positive electrode active material of Example 1 is low as the working efficiency level of the negative electrode active material, so that the battery of Example 1 uses a small amount of the positive electrode active material as compared with the battery of Comparative Example 1 It can be confirmed that excellent capacity characteristics can be exhibited.

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)

(i) a cathode active material comprising a compound of the following formulas (1) and (2):
Li ₂ Ni _1-a M _a O ₂ (1)
Li [Li _{a '} Ni _x Mn _y Co _z M _w ] O _{2 -te t} (2)
In this formula,
0? A <? 1, 0? A?? 0.2, 0? X? 0.9, 0? Y? 0.9, 0? Z? 1, 0? W? 0.9, a '+ x + y + z + w = 0? T <0.2; M is at least one metal or transition metal cation of +2 to +4 oxidation numbers; A is an anion of -1 or -2 valence, the content being -1 when A _2t and -2 being A _t ; And
(ii) a negative electrode active material containing a carbon-based material and a silicon (Si) -based compound;
And a secondary battery. 2. The secondary battery according to claim 1, wherein the compounds of the general formulas (1) and (2) are compounds of the following general formulas (3) and (4)
Li ₂ NiO ₂ (3)
LiNi _{1- (y '+ z')} Mn _{y '} Co _z' O ₂ (4)
In this formula,
0? Y? 0.7, 0 <z? 1, 0 <y '+ z'? The secondary battery according to claim 2, wherein the compound of Formula 4 is LiCoO ₂ . The secondary battery according to claim 1, wherein the compound of Formula 1 or 2 is used in a weight ratio of 3: 1 to 6: 1. The secondary battery according to claim 1, wherein the compounds of the general formulas (1) and (2) are in a weight ratio of 4: 1 to 5: 1. The secondary battery according to claim 1, wherein the carbon-based material is graphite. The method according to claim 1, wherein the silicon-based compound is at least one selected from the group consisting of chlorosilane, alkoxysilane, aminosilane, fluoroalkylsilane, silicon, silicon chloride and silicon oxide (SiO 2) battery. The secondary battery according to claim 1, wherein the silicon (Si) based compound is silicon oxide (SiO). The secondary battery according to claim 8, wherein the silicon oxide (SiO ₂ ) comprises silicon dioxide (SiO ₂ ) and amorphous silicon in a mixing ratio of 1: 1 based on the weight ratio. The secondary battery according to claim 1, wherein the carbon-based material and the silicon (Si) -based compound are in a weight ratio of 80:20 to 99: 1. The secondary battery according to claim 1, wherein the carbon-based material and the silicon (Si) -based compound are in a weight ratio of 85:15 to 95: 5. The secondary battery according to claim 1, wherein the secondary battery is a lithium secondary battery. A device comprising at least one secondary battery according to claim 1.