KR101812269B1 - Mn-rich cathode active material with surface treatment for high-voltage and high-capacity lithium secondary battery and High-voltage and high-capacity lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a surface-coated Mn-rich cathode active material for a high-capacity high-voltage lithium secondary battery with reduced phenomenon of being cracked or broken even after the rolling process, and a high-capacity high-voltage lithium secondary battery comprising the same.

Description

TECHNICAL FIELD The present invention relates to a surface-coated Mn-rich cathode active material for a high-capacity high-voltage lithium secondary battery, and a high-capacity high-voltage lithium secondary battery including the same, capacity lithium secondary battery comprising the same}

The present invention relates to a surface-coated Mn-rich cathode active material for a high-capacity high-voltage lithium secondary battery and a high-capacity high-voltage lithium secondary battery comprising the same. More particularly, the present invention relates to a lithium- And a high-capacity high-voltage lithium secondary battery including the Mn-rich cathode active material.

As technology development and demand for mobile devices have increased, there has been a rapid increase in demand for secondary batteries as energy sources. Among such secondary batteries, lithium secondary batteries, which exhibit high energy density and operating potential, long cycle life, Batteries have been commercialized and widely used.

In recent years, as interest in environmental issues has increased, there has been a growing demand for electric vehicles (EVs) and hybrid electric vehicles (HEVs) that can replace fossil-fueled vehicles such as gasoline vehicles and diesel vehicles, Much research is underway. Although a nickel metal hydride (Ni-MH) secondary battery is mainly used as a power source for such an electric vehicle (EV) and a hybrid electric vehicle (HEV), a lithium secondary battery having a high energy density, a high discharge voltage, Research is being actively carried out, and some are commercialized.

The lithium secondary battery has a structure in which a non-aqueous electrolyte containing a lithium salt is impregnated in an electrode assembly in which a porous separator is interposed between a positive electrode and a negative electrode each coated with an active material on a current collector. The positive electrode active material constituting the positive electrode is mainly composed of a lithium cobalt oxide, a lithium manganese oxide, a lithium nickel oxide, a lithium composite oxide, etc. The negative electrode active material constituting the negative electrode is mainly a carbon-based material.

As a cathode active material is LiCoO was ₂ are mainly used, the current in addition to a different positive electrode active material is the Ni-based (Li (Ni-Co-Al ) O 2), Ni-Co-Mn -based (Li (Ni-Co-Mn ) O 2 ) And a high-stability spinel-type Mn-based (LiMn ₂ O ₄ ).

In particular, although spinel-type manganese batteries have been applied to mobile phones, they have not been able to take advantage of the low price due to the aging of the energy density in the face of the high-priority mobile phone market. Recently, There is a growing demand for Mn-rich cathode active material, which is a high-capacity active material.

The Mn-rich cathode active material must be activated at a high voltage and operated at a high voltage for high capacity expression. However, when activated and operated at such a high voltage, the Mn-rich cathode active material generates a large amount of gas at the interface with the electrolyte.

A technique of coating the surface of a Mn-rich cathode active material (lithium composite oxide) to reduce such gas generation is known. However, since the cathode active material is liable to be cracked or broken while being subjected to a pressing process for rolling, a lithium composite oxide, There is a problem that the surface is exposed and the surface coating effect disappears.

Therefore, when the Mn-rich cathode active material for a high-capacity high-voltage lithium secondary battery is coated on the surface, a surface-coated Mn-rich cathode active material that does not crack or break even after the rolling process is required.

In the present invention, the surface coated Mn-rich cathode active material for a high-capacity high-voltage lithium secondary battery is cracked or broken while being subjected to the rolling process, thereby solving the problem of exposing the bare surface.

According to one aspect of the present invention, there is provided a lithium composite oxide represented by the following general formula (1) or (2); And a metal oxide coating layer coating the surface of the lithium composite oxide.

[Chemical Formula 1]

Li _{1 + x} Mn _2-y A _y O _{4-za z}

Wherein 0? X? 0.1; 0? Y? 0.2; 0? Z? 0.5; A is one or two or more selected from the group consisting of Al, Mg, Ni, Co, Fe, Ti, V, Zr and Zn; A 'is one or two or more selected from the group consisting of F, Cl, Br, I, S, chalcogenide compounds, and nitrogen.

(2)

Li ₂ M _x Mn _(1-x) O ₃

Wherein 0? X? 0.2; M is at least one selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Or more.

The lithium composite oxide may have a compressive fracture strength in the range of 50 to 300 MPa.

The metal oxide is _{Al 2 O 3, ZrO 2,} ZnO, MgO, SnO 2, TiO 2, B 2 O 3, SiO 2, CeO 2, SnPO 4 and Al (OH) 1 kind or two selected from the group consisting of ₃ It can be more than a species.

The coating layer may have a thickness of 0.1 to 10.0 nm.

The metal oxide may be surface-coated by a wet coating method, a dry coating method, a plasma coating method or an ALD (Atomic Layer Deposition) method.

According to another aspect of the present invention, there is provided a positive electrode comprising the above-mentioned positive electrode active material.

The anode may have a porosity of 20-30%.

The pellet formed of the positive electrode active material in the positive electrode ⁽² ton / cm 2 basis) before and after an average particle size retention (delta D50 D50 = _{pellet after molding} / D50 _{pellet before molding)} may be 95 to 100%.

According to still another aspect of the present invention, there is provided a lithium secondary battery including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the positive electrode may be the above-described positive electrode.

The operating voltage range of the lithium secondary battery may be 2.5V to 5V.

The surface-coated Mn-rich cathode active material according to an embodiment of the present invention does not cause cracking or breakage of the cathode active material even when subjected to a rolling process for producing a cathode having a porosity ranging from 20 to 30% .

As a result, the effect of the surface coating of the cathode active material can be maintained.

Hereinafter, the present invention will be described in detail. Prior to this, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms, and the inventor should appropriately interpret the concepts of the terms appropriately It should be interpreted in accordance with the meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined. Accordingly, the drawings described in the present specification or the constitutions described in the embodiments are merely the most preferred embodiments of the present invention and are not intended to represent all of the technical ideas of the present invention. Therefore, various equivalents It should be understood that water and variations may be present.

The high-capacity high-voltage Mn-rich cathode active material usable in the present invention is composed of a Mn-rich lithium composite oxide having a high strength and a metal oxide coated on the surface thereof. Even if the cathode active material is subjected to a rolling process for producing an electrode, Or destruction of the lithium composite oxide does not occur at all or very little, so that the bare surface exposure of the lithium composite oxide is minimized or minimized. The lithium composite oxide satisfying these requirements can be represented by the following formula 1 or 2:

[Chemical Formula 1]

Li _{1 + x} Mn _2-y A _y O _{4-za z}

Wherein 0? X? 0.1; 0? Y? 0.2; 0? Z? 0.5; A is one or two or more selected from the group consisting of Al, Mg, Ni, Co, Fe, Ti, V, Zr and Zn; A 'is one or two or more selected from the group consisting of F, Cl, Br, I, S, chalcogenide compounds, and nitrogen.

(2)

Li ₂ M _x Mn _(1-x) O ₃

Wherein 0? X? 0.2; M is at least one selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Or more.

The lithium composite oxide represented by the formula (1) or (2) is characterized in that it has high strength such that it does not crack or break even when it is subjected to a rolling process, for example, a pressing process.

As used herein, the term "rolling" refers to a step in a battery manufacturing process for increasing the density and increasing the crystallinity of the active material, for example, a step of pressing the active material layer at least once at a predetermined pressure.

In the present specification, 'pellet forming' is an experimental method that can replace active material breakage caused by rolling. The degree of cracking of the active material by applying a certain pressure is determined by maintaining the average particle size (D50) retention rate (delta D50 = D50 _pellet / D50 _{before pellet molding} ).

Although the process conditions for rolling are not particularly limited, it is preferable to carry out the rolling process so that a cathode porosity of 20 to 30% is formed in terms of ensuring that the final produced cell has optimum conductivity.

In this respect, the lithium composite oxide according to one aspect of the present invention may have a compressive fracture strength in the range of 50 MPa or more, or 50 to 300 MPa.

Alternatively, the cathode active material according to one aspect of the present invention after coating the surface of pellet molding (2ton / cm ² basis) before and after an average particle size retention (delta D50 = D50 _{pellet after molding} / D50 _{pellet before molding)} of approximately 95 to 100 %. ≪ / RTI >

Herein, the term "bare surface" refers to a surface of a lithium composite oxide which is exposed due to cracking or fracture of the cathode active material.

The coating layer may be formed on the surface of the lithium composite oxide to exhibit a specific effect, for example, an effect of improving output and lifetime characteristics.

Non-limiting examples of the metal oxide constituting the coating layer is _{Al 2 O 3, ZrO 2,} ZnO, MgO, SnO 2, TiO 2, B 2 O 3, SiO 2, CeO 2, SnPO 4, Al (OH) 3 , etc. , And the like, but the present invention is not limited thereto.

Although the coating layer is not particularly limited in terms of its thickness, it is possible to prevent the surface resistance from excessively increasing and the rate characteristic from remarkably lowering when the thickness is in the range of 0.1 to 10.0 nm or 0.2 to 5.0 nm, It can exhibit an effect of preventing generation of gas

In order to coat the metal oxide with the lithium composite oxide, a method commonly known in the art may be used. For example, a wet coating method, a dry coating method, a plasma coating method, or an ALD (Atomic Layer Deposition) have.

The positive electrode active material constitutes a positive electrode, and forms a lithium secondary battery together with a negative electrode, a separator, and a nonaqueous electrolyte containing a lithium salt.

The positive electrode is prepared, for example, by coating a mixture of the positive electrode active material, the conductive material and the binder on the positive electrode current collector, followed by drying, and if necessary, a filler may be further added.

The cathode current collector generally has a thickness of 3 to 500 mu m. The 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 positive electrode current collector may be made of stainless steel, aluminum, nickel, titanium, sintered carbon or a surface of aluminum or stainless steel Coated 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 30% 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 which 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 30% by weight 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 butadiene rubber, fluorine rubber, various copolymers and the like.

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, and examples thereof include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The negative electrode is prepared by applying, drying and pressing an anode active material on an anode current collector, and may optionally further include a conductive material, a binder, a filler, and the like as described above.

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 Nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like may 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 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 &lt; 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, Bi ₂ O ₅ and the like; Conductive polymers such as polyacetylene; Li-Co-Ni-based material, and the like.

The separator is interposed between the anode and the cathode. A separator commonly used in the art can be used without limitation, for example, an insulating thin film having high ion permeability and mechanical strength can be used. The pore diameter of the separator is generally 0.01 to 10 mu m, and the thickness is generally 5 to 30 mu m. As such a separator, for example, an olefin-based polymer such as polypropylene having chemical resistance and hydrophobicity; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like; Kraft paper and the like are used. Representative examples currently on the market include Celgard R2400, 2300 (from Hoechest Celanese Corp.), polypropylene separator (from Ube Industries Ltd. or Pall RAI), and polyethylene series (from Tonen or Entek).

In some cases, a gel polymer electrolyte may be coated on the separator to improve the safety of the battery. Representative examples of such a gel polymer include polyethylene oxide, polyvinylidene fluoride, and polyacrylonitrile. 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 nonaqueous electrolyte is composed of a nonaqueous electrolyte and lithium. Nonaqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, and the like are used as the nonaqueous electrolyte, but the present invention 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-butylolactone, Tetrahydrofuran, tetrahydrofuran, tetrahydrofuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, Examples of the organic solvent include methyl acetate, phosphoric acid triester, trimethoxy methane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, Propylenic organic solvents such as methylmethyl, ethylpropionate 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.

Claims (10)

A lithium complex oxide represented by the following general formula (1) or (2); And a positive electrode active material composed of a metal oxide coating layer coating the surface of the lithium composite oxide,
The lithium composite oxide has a compressive fracture strength in the range of 50 to 300 MPa,
The metal oxide is _{Al 2 O 3, ZrO 2,} ZnO, MgO, SnO 2, TiO 2, B 2 O 3, SiO 2, CeO 2, SnPO 4 and Al (OH) 1 kind or two selected from the group consisting of ₃ More than species,
The metal oxide coating layer has a thickness of 0.1 to 10 nm,
The pellet formed from the positive electrode active material (2ton / cm ² based) around a mean particle size retention (delta D50 = D50 _{before and after the pellet} / _pellet D50 _{molding molded)} and after 95 to 100%, and
A positive electrode for a lithium secondary battery having a porosity of 20 to 30%
[Chemical Formula 1]
Li _{1 + x} Mn _2-y A _y O _{4-za z}
Wherein 0? X? 0.1; 0 &lt; y &lt;0.2; 0? Z? 0.5; A is one or two or more selected from the group consisting of Al, Mg, Ni, Co, Fe, Ti, V, Zr and Zn; A 'is one or two or more selected from the group consisting of F, Cl, Br, I, S, chalcogenide compounds, and nitrogen.

(2)
Li ₂ M _x Mn _(1-x) O ₃
Wherein 0 < x &lt; = 0.2; M is at least one selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Or more.
delete delete delete The method according to claim 1,
Wherein the metal oxide is surface-coated by a wet coating method, a dry coating method, a plasma coating method or an ALD (Atomic Layer Deposition) method.
delete delete delete A lithium secondary battery comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode,
The lithium secondary battery according to claim 1, wherein the positive electrode is the positive electrode according to claim 1.
10. The method of claim 9,
And an operating voltage range of 2.5 V to 5 V.