KR101443500B1 - Lithium-metal oxide and lithium secondary battery having the same - Google Patents

Abstract

More particularly, the present invention relates to a lithium metal oxide represented by the following formula (1) and a lithium secondary battery comprising the same. The lithium metal oxide according to the present invention can be applied to a cathode active material, and can provide a lithium secondary battery which exhibits a high battery capacity while improving the capacity reduction by repeated charge and discharge.
[Chemical Formula 1]
Li _{1 + x} Ni _a M _{1 -2? X} Mn _b O _{2 + x}
(Wherein x, a and b are as defined in claim 1).

Description

FIELD OF THE INVENTION [0001] The present invention relates to a lithium metal oxide, and a lithium secondary battery comprising the lithium metal oxide.

The present invention relates to a lithium metal oxide, a cathode active material containing the same, and a lithium secondary battery.

Lithium ion secondary batteries are increasingly being used in electric vehicles for existing IT applications, and the need for high-capacity materials is emerging. For example, when the capacity of an anode material and an anode material is increased at the same weight, studies are being conducted in such a direction as to express a high capacity in a small amount. Particularly, the lithium ion secondary battery is used while moving from the anode to the cathode when charging and from the cathode to the anode when discharging. Therefore, it can be said that the relationship between the amount of lithium and the capacity is very close to that of the lithium ion secondary battery. Existing materials include LiMn ₂ O ₄ , LiMnO ₂ , _{LiNixCoyMnzO 2 (x + y + z} = 1), LiCoO 2 These materials need to be improved in price competitiveness, charge / discharge capacity, and thermal stability. Particularly, in recent years, a layered Li ₂ MnO ₃ Research on materials is underway. However, when Li ₂ MnO ₃ alone is used, Mn ^{4 +} is very stable and high voltage is required for oxidation-reduction reaction, and there is a problem that the de-insertion of Li ions is not desired. In order to solve this problem, a layered lithium metal oxide, LigNixCoyMnzO ₂ (in the above formula, g> 1.0, 0 <x <1, 0 <y <1, 0 <z <1, g + x + y + z = 2). However, the lithium metal oxide is used in charge and discharge in the range of 3.0 to 4.2 V, and in order to increase the capacity, the Li layer is excessively desorbed when the voltage is higher than 4.2 V, especially above 4.5 V, and the crystal structure collapses abruptly, This is difficult. Therefore, there is a need for a high capacity battery in electric vehicles and smart devices. Therefore, it is necessary to improve stability such as capacity and deterioration in order to enable stable lithium insertion at a wide range of 2.0V to 4.7V.

Layered LiMO ₂ and Li ₂ M? ₃ composite. However, in the case of the composition proposed in the present invention, since the Ni content is higher than the Mn content, the production of Li ₂ MnO ₃ is not performed well. Therefore, in the high- There is a problem in that the capacity is reduced when charging / discharging the battery.

Accordingly, it is an object of the present invention to provide a positive electrode active material capable of containing an excessive amount of Li contributing to charging and discharging and capable of stably carrying out charging and discharging up to a high voltage region.

DISCLOSURE OF THE INVENTION In order to solve the above problems, the present invention provides a lithium metal oxide capable of exhibiting improved charging / discharging capacity with less deterioration in life span even when charging / discharging is repeated in a wide range of 2.0 to 4.7V.

The present invention also provides a cathode active material comprising the lithium metal oxide.

The present invention also relates to a lithium secondary battery including the positive electrode active material.

Aspects of the present invention,

The present invention relates to a lithium metal oxide represented by the following general formula (1).

[Chemical Formula 1]

Li _{1 + x} Ni _a M _{1 -2? X} Mn _b O _{2 + x}

b is a + x (provided that a + x is less than 1), M is at least one element selected from the group consisting of Ti, Cr, Fe, Co, and Ge (where x is 0.01? x? 0.8, a is 0.07? a < to be.)

Yet another aspect of the present invention relates to a cathode active material comprising the lithium metal oxide.

Another aspect of the present invention relates to a lithium secondary battery comprising the cathode active material.

The present invention can provide a lithium metal oxide having a high capacity in various charge and discharge regions and improved structural stability and lifetime characteristics. Further, the present invention can provide a lithium secondary battery in which the phenomenon of reduction in capacity due to repetitive charging and discharging is improved.

Hereinafter, the present invention will be described in more detail.

The present invention provides a lithium metal oxide represented by the following Chemical Formula 1, wherein the lithium metal oxide is a layered compound in which an excess amount of Li is contained in a transition metal layer of a crystal lattice, &Lt; / RTI &gt; More specifically, the lithium metal oxide according to the present invention has a high Mn content relative to Ni, and thus has a layered structure of a layered LiMO ₂ structure at a ratio of Ni: Mn = 1: 1. Wherein Li bonded to Mn is dissolved in the transition metal layer.

The lithium metal oxide can be realized in a high capacity in various charging and discharging voltage ranges, and in particular, it is possible to prevent deterioration of capacity and lifetime characteristics even if charge and discharge are repeated up to a high voltage region. In this case, when the charge / discharge voltage rises to the high voltage region, a part of Li dissolved in the transition metal layer is activated and contributes to charge / discharge to provide a high capacity. Inert lithium which does not contribute to charge / Thereby contributing to maintenance of the life characteristic.

[Chemical Formula 1]

Li _{1 + x} Ni _a M _{1 -2? X} Mn _b O _{2 + x}

b is a + x (provided that a + x is less than 1), M is at least one element selected from the group consisting of Ti, Cr, Fe, Co, and Ge (where x is 0.01? x? 0.8, a is 0.07? a < to be.)

The excess equivalent ratio (x) of lithium is 0.01 to 0.8, preferably 0.01 to 0.6, and more preferably 0.1 to 0.6. If x is less than 0.01, the effect of realizing a large amount of the layered compound due to excessive lithium can not be obtained. If x is more than 0.8, irreversible capacity may increase.

The molar ratio (a) of the nickel is 0.07 or more and less than 0.5, preferably 0.1 or more and less than 0.5, and more preferably 0.15 to 0.4. If (a) is less than 0.07, if Li is excessively contained in the transition metal layer, charge and discharge can be performed only in the 4.5 to 4.7 V region, and capacity is difficult to realize in the region of 4.5 V or less, It is difficult to realize a high capacity. If it is 0.5 or more, excessive Li is hardly dissolved in the transition metal layer by inhibiting the bonding of Mn and Li, and unreacted Li is LiO ₂ , Li ₂ CO ₃ Or the like may be formed, and battery capacity and output characteristics may be deteriorated.

The molar ratio (a + x) of manganese in the lithium metal oxide is the sum of an excess molar ratio (x) of lithium and a molar ratio (a) of nickel. When the molar ratio is within the range shown in the above formula (1) It can be moved to the metal layer to form a stable lithium metal oxide. On the other hand, if the value is less than the value of a + x, excess lithium is not dissolved in the crystal lattice of the lithium metal oxide, and Li ₂ O, Li ₂ CO ₃ And can be simply adsorbed on the surface of the oxide. As a result, when the lithium metal oxide is used as the cathode active material, the charging capacity is high at the time of one charge, but the actual discharge capacity is low and the initial efficiency may be lowered.

The M may be at least one element selected from Ti, Cr, Fe, Co, and Ge, and is preferably Co.

The present invention can provide a process for producing the lithium metal oxide represented by the above formula (1). The manufacturing method may include a lithium metal precursor mixing step and a firing step.

The step of mixing the lithium metal precursor is a step of mixing lithium (A) and a metal (B) to form lithium and metal according to the compositional formula 1 of the present invention.

The mixing step may be performed by mixing the compounds in a powder state or in a solution state. Or coprecipitate them in solution to form precipitates such as metal precursor complex carbonate salts, hydroxide salts, and the like.

According to an embodiment of the present invention, a metal hydroxide salt is prepared by adjusting the pH of a mixed aqueous solution of the metal-containing compound (B) to 9.5 or more, preferably 10 to 11.5, After separating the side salt, the lithium metal precursor mixture can be prepared by mixing the metal hydroxide salt and the compound (A) containing lithium.

The lithium-containing compound (A) may be at least one selected from the group consisting of lithium, ammonium, sulfate, alkoxide, oxalate, phosphate, halide ), Oxyhalide, sulfide, oxide, peroxide, acetate, nitrate, (S), carbonate, citrate, phthalate, perchlorate, acetylacetonate, acrylate, formate, oxalate compounds and their hydrates , But the present invention is not limited thereto.

The metal-containing compound (B) may be at least one of hydroxide, ammonium, sulfate, alkoxide ), Oxalate, phosphate, halide, oxyhalide, sulfide, oxide, peroxide, acetate, nitrate, Carbonate, citrate, phthalate, perchlorate, acetylacetonate, acrylate, formate, oxalate compounds and their derivatives, such as, for example, And may be at least one of hydrates, but the present invention is not limited thereto.

The calcination step may calcine the lithium metal precursor mixture at 600 to 1000 ° C, preferably 800 to 950 ° C. The firing time in the firing step is 10 to 30 hours, and the firing atmosphere may be atmospheric or oxygen atmosphere, but is not limited thereto.

After the firing step, a post-treatment process according to a conventional solid-phase method may be further performed. For example, a grinding step and a powder step may be performed to control particle size and remove impurities. The grinding step may be a ball mill, a vibration mill, a satellite ball mill, a tube mill, a rod mill, a jet mill, a hammer mill, or the like.

The present invention provides a lithium secondary battery comprising the lithium metal oxide according to the present invention.

The lithium secondary battery may further include a nonaqueous electrolyte containing a positive electrode containing a positive electrode active material, a negative electrode, a separator, and a lithium salt. The structure and the manufacturing method of the secondary battery are known in the technical field of the present invention and can be appropriately selected without departing from the scope of the present invention.

For example, the positive electrode may be prepared by applying a composition for forming a positive electrode active material containing a positive electrode active material and a binder to a positive electrode collector, drying and then rolling.

The cathode active material may use the lithium metal oxide according to the present invention alone or may mix the cathode active material and the lithium metal oxide that are conventionally used.

The binder serves to bind the positive electrode active materials and to fix them to the current collector. Any binders used in the technical field can be used without limitation, and preferable examples include polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl Tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, vinylidene fluoride-hexafluoropropylene copolymer , Vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene - chlorotrifluoroethylene copolymer, vinylidene fluoride-hex Vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, polyvinylpyrrolidone, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydrolyzed vinylidene fluoride, Polyethylene, polypropylene, styrene-butylene rubber, and fluorine rubber.

The composition for forming a positive electrode active material may further include a solvent such as NMP (N-methyl-2-pyrrolidone) and an oligomer such as polyethylene or polypropylene to the positive electrode active material and the binder; A filler made of a fibrous material such as a glass fiber, a carbon fiber, or the like, and may further include a conductive material known in the art.

The conductive material may be graphite; Carbon blacks such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber, metal powders such as carbon fluoride, aluminum and nickel powder; Zinc oxide, potassium titanate, titanium oxide, polyphenylene derivatives, and the like, but the present invention is not limited thereto.

The positive electrode collector may be made of copper, stainless steel, aluminum, nickel, titanium, sintered carbon; Surfaces of copper and stainless steel surface treated with carbon, nickel, titanium or silver; Aluminum-cadmium alloy, and the like, and various shapes such as a film, a sheet, a foil, a net, a porous body, a foaming agent, and a nonwoven fabric can be used.

The negative electrode may be prepared by applying a composition for forming an anode active material containing a negative electrode active material on a negative electrode collector and drying the same, or may be a lithium metal. The composition for forming the negative electrode active material may further include a binder, a conductive material, and the like known in the art.

The negative electrode active material may be selected from the group consisting of carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers and amorphous carbon, lithium, Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, , alloying is possible metallic compounds such as Al alloys and composites containing the metallic compound and the carbonaceous material, GeO, GeO _2, SnO, SnO _2, PbO, PbO _2, Pb ₂ O _3, Pb ₃ O _4, But are not limited to, metal oxides such as Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , Bi ₂ O ₃ , Bi ₂ O ₄ , and Bi ₂ O ₅ .

The negative electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, sintered carbon; Surfaces of copper and stainless steel surface treated with carbon, nickel, titanium or silver; Aluminum-cadmium alloy, and the like, and various shapes such as a film, a sheet, a foil, a net, a porous body, a foaming agent, and a nonwoven fabric can be used.

The separation membrane is disposed between the cathode and the anode, and includes an olefin-based polymer such as polypropylene; A sheet or a nonwoven fabric made of glass fiber, polyethylene, or the like. For example, a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator, a polyethylene / polypropylene double-layer separator, And the like, but the present invention is not limited thereto.

The lithium salt wherein the non-aqueous electrolyte comprises a non-aqueous electrolyte and a lithium salt is _{LiCl, LiBr, LiI, LiClO 4} , LiBF 4, LiB 10 OCl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, But are not limited to, LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, lithium tetraphenylborate and imide.

The non-aqueous electrolyte may include non-aqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, and the like. Examples of the non-aqueous organic solvent include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate Methyl ethyl ketone, diethyl carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate,? -Butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, Examples of the solvent include 1,2-dioxane, 2-methyltetrahydrofuran, acetonitrile, formamide, dimethylformamide, N-methyl-2-pyrrolidinone, dimethylsulfoxide, , Sulfolane, methylsulfolane, dioxolane, dioxolane derivative, methyl nitromethaneacetate, phosphoric acid triester, trimethoxymethane, sulfolane, methylsulfolane, 3-methyl-2-oxazolidinone, propylene Viterbo carbonate but are the derivative, diethyl ether and the like, not to limit it.

The organic solid electrolyte may be a gel polymer electrolyte obtained by impregnating a polymer electrolyte such as polyethylene oxide or polyacrylonitrile with an electrolytic solution, a polyethylene derivative, a polyethylene oxide derivative or a polymer containing the same, a polypropylene oxide derivative or a polymer containing the same, But are not limited to, polymers containing an ionic dissociation group such as phosphoric acid ester polymer, polyphosphazene, polyaziridine, polyethylene sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polyhexafluoropropylene .

Wherein the inorganic solid electrolyte is selected from the group consisting of Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, Li ₂ SO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ -LiI- _{Li 3 PO 4 -Li 2 S-} SiS 2, Li 2 SP 2 S 5, Li 2 S-SiS 2, Li 2 S-GeS 2, Li 2 nitride, halides of Li, such as S, oxygen acid salts, sulfides, etc. But is not limited thereto.

The lithium secondary battery can be separated into a coin type, a prismatic type, a cylindrical type, a pouch type, and the like. Since the structure and manufacturing method of these batteries are known in the art, detailed description thereof will be omitted.

Hereinafter, the present invention will be described in more detail with reference to the following examples and comparative examples. The following examples are only illustrative of the present invention and do not limit the scope of protection of the present invention.

[ Example  1 to 7]

Lithium metal oxide manufacturing

Ni (SO ₄ ) ₂ , Co (SO ₄ ) ₂ and Mn (SO ₄ ) ₂ were weighed in the molar ratios shown in Table 1 below to dissolve the three raw materials in distilled water, and then, using NaOH and NH ₄ OH at pH 11, Lt; / RTI &gt; Afterwards, Na 2 ⁺ , NH ₄ ⁺ and SO ₄ ^{2 -} ions were removed by using distilled water to improve the purity, and after drying at 150 ° C. for 12 hours or more, Li ₂ CO ₃ was weighed at a molar ratio of the following Table 1, Followed by heat treatment at 950 ° C for 10 hours to synthesize a lithium metal oxide.

Lithium secondary battery  Produce

Lithium secondary batteries were fabricated and characterized according to methods customary in the art. More specifically, the lithium metal oxide of Example 1 was used as a positive electrode active material, and the positive electrode active material and a conductive material such as Denka Black and PVDF binder were mixed at a ratio of 94: 3: 3 (w / w) Electrode plate was produced. A coin cell was fabricated by using lithium metal as a cathode and a 1.3M LiPF6 EC / DMC / EC = 5: 3: 2 solution as an electrolyte, and then a battery capacity and an output characteristic were measured. The results are shown in Table 1.

[ Comparative Example  1 to 5]

The lithium metal oxide and the battery were prepared in the same manner as in Example 1 except that the chemical equivalent ratio to lithium and metal was set forth in the following Table 1, and the battery capacity and output characteristics were measured. The results are shown in Table 1.

Mole ratio Li
(1 + x) Ni
(a) Co
(1-2a-x) Mn
(a + x) O
(2 + x) 1 time
Charging capacity
(0.1 C, 4.7 V) 1 time
Discharge capacity
(0.1 C, 2.5 V) After 50 rounds discharge
Volume
(0.1 C) Example 1 1.1 0.18 0.54 0.28 2.1 289 266 218 Example 2 1.6 0.08 0.24 0.68 2.6 312 259 220 Example 3 1.1 0.36 0.18 0.46 2.1 292 269 236 Example 4 1.6 0.16 0.08 0.76 2.6 334 277 249 Example 5 1.01 0.1 0.79 0.11 2.01 261 248 206 Example 6 1.4 0.3 0 0.7 2.4 280 258 240 Example 7 1.8 0.07 0.06 0.87 2.8 325 254 215 Comparative Example 1 One 0.5 0.2 0.3 2 220 187 105 Comparative Example 2 1.1 0.54 0.18 0.28 2.1 242 225 162 Comparative Example 3 1.2 0.48 0.16 0.36 2.2 267 254 137 Comparative Example 4 1.9 0.04 0.02 0.94 2.9 250 205 170 Comparative Example 5 1.6 0.05 0.3 0.65 2.06 287 212 172

As shown in Table 1, the examples including the chemical equivalent ratios for lithium and metal shown in the formula 1 of the present invention show excellent charge / discharge capacities in the high voltage range as compared with the comparative examples, . This is because, when the chemical equivalent ratio of the metal according to the present invention is applied, excess lithium is transferred to the transition metal layer to form a structurally stable lithium metal oxide, and as a result, an improved charge / discharge capacity can be exhibited. In addition, it can be confirmed that the charge / discharge capacity is drastically reduced when the value of the chemical equivalent ratio of the metal is out of the range of the chemical equivalence ratio of the present invention as in Comparative Examples 1 to 5.

Claims (6)

A lithium metal oxide represented by the following formula (1)
[Chemical Formula 1]
Li _{1 + x} Ni _a Mn _b M _c O _{2 + x}
(where x is 0.01? x? 0.8, a is 0.07? a <0.5, b = a + x where a + x is less than 1, c = 1-2a-x, 1.01? x + a + b + c &amp;le; 1.8, and M is at least one element selected from the group consisting of Ti, Cr, Fe, Co and Ge.
The method according to claim 1,
Wherein M is Co in the above formula (1).
The method according to claim 1,
Wherein x is 0.01? X? 0.6 in the formula (1).
The method according to claim 1,
Wherein a in the formula (1) is 0.1? A <0.5.
A positive electrode active material comprising the lithium metal oxide of claim 1.
A cathode comprising the cathode active material of claim 5;
A negative electrode comprising a negative electrode active material;
A separator existing between the anode and the cathode, and
A lithium secondary battery comprising a non-aqueous electrolyte.