KR101792750B1 - Cathode comprising double layer of cathode active material and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention provides a lithium secondary battery comprising a cathode active material layer comprising a first cathode active material layer containing at least one lithium metal oxide selected from the group consisting of a compound represented by the following formula 1 and a compound represented by the following formula 2, A positive electrode comprising a second positive electrode active material layer containing lithium iron phosphate represented by the general formula (3), and a lithium secondary battery comprising such a positive electrode.
[Chemical Formula 1]
Li _x M _y Mn _{2 - y} O _{4 - z} A _z
In this formula,
0.9? X? 1.2, 0 <y <2, 0? Z <0.2;
M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, ;
A is one or more of an anion of -1 or -2.
(2)
(1-x) LiM'O _{2 - y} A _y -xLi ₂ MnO _{3 -y '} A _{y '}
In this formula,
M 'is Mn _a M _b ;
M is one or more selected from the group consisting of Ni, Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr, Zn and two period transition metals;
A is at least one selected from the group consisting of PO ₄ , BO ₃ , CO ₃ , F and NO ₃ anions,
0 &lt; x &lt;1; 0 &lt; y? 0.02; 0 &lt; y &apos; 0.5? A? 1.0; 0? B? 0.5; a + b = 1.
(3)
Li _{1 + a} Fe _{1 -x} M " _x (PO _{4 -b} ) X _b
In this formula,
M &quot; is at least one selected from Al, Mg and Ti,
X is at least one selected from F, S and N,
-0.5? A? + 0.5, 0? X? 0.5, and 0? B?

Description

[0001] The present invention relates to a positive electrode comprising a dual positive electrode active material layer and a lithium secondary battery comprising the positive electrode active material layer,

[0001] The present invention relates to a positive electrode comprising a dual positive electrode active material layer and a lithium secondary battery comprising the same, and more particularly to a lithium secondary battery comprising a lithium iron phosphate on a first positive electrode active material layer containing a Mn- By coating or laminating the second positive electrode active material layer including the second positive electrode active material layer, it is possible to prevent the deterioration of the battery performance caused by the structural change of the Mn-rich positive electrode active material, Capacity reduction can be prevented. Thereby improving battery life and performance.

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.

Such a lithium secondary battery has mainly lithium-containing cobalt oxide (LiCoO ₂₎ is used, and that in addition to the layered crystal structure of LiMnO _2, lithium-containing manganese oxide, lithium-containing nickel oxides such as LiMn ₂ O ₄ of spinel crystal structure (LiNiO ₂ ) is also considered.

LiCoO ₂ has excellent properties such as excellent cycle characteristics and is widely used at present. However, LiCoO ₂ is low in safety, is expensive due to the resource limit of cobalt as a raw material, and has a limitation in mass use as a power source for fields such as electric vehicles. LiNiO ₂ is difficult to apply to actual mass production process at a reasonable cost due to its characteristics depending on its manufacturing method.

Mn-rich cathode active materials such as LiMnO ₂ , LiMn ₂ O ₄ , xLi ₂ MnO _3. (1-x) LiMO ₂ (M = Mn, Ni, Co, Fe and Cr) are rich in resources and environmentally friendly Has a merit of using manganese as a cathode active material, and thus attracts much attention as a cathode active material that can replace LiCoO ₂ . These Mn-rich cathode active materials exhibit a high capacity due to the change in structure due to the exiting of Li ₂ O from the Li ₂ MnO ₃ portion through the activation of high voltage. However, due to Mn deposition, cathodic degeneration occurs due to the change of the structure, There is also a problem that it gets worse. In order to solve these technical problems, the performance was improved by coating the Mn-rich active material or the Mn-rich electrode by atomic layer deposition, but this atomic layer has a disadvantage that it can not contribute to the lithium capacity expression.

On the other hand, lithium iron phosphate is excellent in safety due to its crystal structure characteristic, and has a high price competitiveness by using iron (Fe) at a low price. However, since the discharge voltage is low as 3.5 V as compared with the layered and spinel type cathode materials, the output characteristics are lowered and the energy density per unit volume is low, so commercialization is delayed and research for solving the problem of low output continues have.

The present invention provides a positive electrode which is effective in preventing capacity deterioration degraded by Mn dissolution generated during charging / discharging due to a change in Mn-rich cathode active material structure and also in capacity development.

In one embodiment of the present invention, the positive electrode contains a first positive electrode active material layer containing at least one lithium metal oxide selected from a compound represented by the following formula (1) and a compound represented by the following formula (2) And a second cathode active material layer containing lithium iron phosphate represented by the following Chemical Formula 3 on the cathode active material layer.

[Chemical Formula 1]

Li _x M _y Mn _{2 - y} O _{4 - z} A _z

In this formula,

0.9? X? 1.2, 0 <y <2, 0? Z <0.2;

M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, ;

A is one or more of an anion of -1 or -2.

(2)

(1-x) LiM'O _{2 - y} A _y -xLi ₂ MnO _{3 -y '} A _{y '}

In this formula,

M 'is Mn _a M _b ;

M is one or more selected from the group consisting of Ni, Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr, Zn and two period transition metals;

A is at least one selected from the group consisting of anions of PO ₄ , BO ₃ , CO ₃ , F and NO ₃ ;

0 &lt; x &lt;1; 0 < y? 0.02; 0 < y &apos; 0.5? A? 1.0; 0? B? 0.5; a + b = 1.

(3)

Li _{1 + a} Fe _{1 -x} M " _x (PO _{4 -b} ) X _b

In this formula,

M &quot; is at least one selected from Al, Mg and Ti,

X is at least one selected from F, S and N,

-0.5? A? + 0.5, 0? X? 0.5, and 0? B?

The first cathode active material layer may have a thickness ranging from 30 [mu] m to 300 [mu] m.

The second cathode active material layer may have a thickness ranging from 1 um to 300 um.

Another aspect of the present invention is a lithium secondary battery comprising the positive electrode.

The lithium secondary battery may include a carbon-based material and / or Si as a negative electrode active material.

The lithium secondary battery may be one selected from the group consisting of a lithium ion battery, a lithium ion polymer battery, and a lithium polymer battery.

Another aspect of the present invention can provide a battery pack including the lithium secondary battery.

Further, it is possible to provide a device using the battery pack as an energy source.

The positive electrode for a lithium secondary battery according to the present invention includes a second positive electrode active material layer containing lithium iron phosphate on a first positive electrode active material layer containing a Mn-rich positive electrode active material, It has an effect of increasing capacity expression due to lithium iron phosphate compared with other inorganic metal coatings while preventing performance deterioration. Therefore, the lithium secondary battery including the positive electrode has improved battery performance and lifetime.

The positive electrode according to the present invention includes a first positive electrode active material layer containing at least one lithium metal oxide selected from a compound represented by the following formula 1 and a compound represented by the following formula 2 on a positive electrode collector, And a second cathode active material layer containing lithium iron phosphate expressed by the following Chemical Formula 3 on the layer.

[Chemical Formula 1]

Li _x M _y Mn _{2 - y} O _{4 - z} A _z

In this formula,

0.9? X? 1.2, 0 <y <2, 0? Z <0.2;

M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, ;

A is one or more of an anion of -1 or -2.

(2)

(1-x) LiM'O _{2 - y} A _y -xLi ₂ MnO _{3 -y '} A _{y '}

In this formula,

M 'is Mn _a M _b ;

M is one or more selected from the group consisting of Ni, Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr, Zn and two period transition metals;

A is at least one selected from the group consisting of PO ₄ , BO ₃ , CO ₃ , F and NO ₃ anions,

0 &lt; x &lt;1; 0 < y? 0.02; 0 < y &apos; 0.5? A? 1.0; 0? B? 0.5; a + b = 1.

(3)

Li _{1 + a} Fe _{1 -x} M " _x (PO _{4 -b} ) X _b

In this formula,

M &quot; is at least one selected from Al, Mg and Ti,

X is at least one selected from F, S and N,

-0.5? A? + 0.5, 0? X? 0.5, and 0? B?

The positive electrode is formed by applying an electrode mixture, which is a mixture of a positive electrode active material used in a first positive electrode active material, a conductive material and a binder, to a positive electrode collector, drying the positive electrode collector as needed, And a binder may be coated on the first cathode active material layer and then dried. Alternatively, it can be manufactured by applying and drying a first cathode active material layer on a cathode current collector, and then separately laminating a second cathode active material layer dried in a sheet form to the first cathode active material layer.

The positive electrode active material contained in the first positive electrode active material layer may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ) or one or more transition metals Substituted compounds; Lithium manganese oxides such as Li _{1 + x} Mn _{2 -x} O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ and the like; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; A Ni-site type lithium nickel oxide expressed by the formula LiNi _1-x M _x O ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3); Formula _{LiMn 2 - x M x O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, x = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); A lithium manganese composite oxide having a spinel structure represented by LiNi _x Mn _{2 - x} O ₄ ; LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like, but is not limited thereto.

The first cathode active material layer is not particularly limited to an amount formed on the current collector, and may be formed and dried in an amount commonly used in the art. May be applied on the current collector so as to have a thickness in the range of 30 [mu] m to 300 [mu] m, and dried and formed.

The second cathode active material layer may be coated or laminated on the first cathode active material layer to have a thickness of 1 [mu] m to 300 [mu] m.

The positive electrode current collector is generally made to have a thickness of 3 to 500 μm. 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 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 first and second cathode active material layers may include a conductive material. The conductive material is usually added in an amount of 1 to 50 wt% 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 polymer used for the first and second positive electrode active material layers is a component that assists in bonding between the active material and the conductive material and bonding to the current collector and is usually 1 to 50 wt% based on the total weight of the mixture including the positive electrode active material %. Examples of such a binder polymer include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, Polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

The filler which can be used for the first and second positive electrode active material layers is selectively used as a component for suppressing the expansion of the positive electrode and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery, Olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The present invention also provides a secondary battery comprising the positive electrode, wherein the secondary battery may be a lithium ion battery, a lithium ion polymer battery, or a lithium polymer battery.

The lithium secondary batteries are generally composed of a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte containing a lithium salt. Other components of the lithium secondary battery will be described below.

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.

Examples of the negative electrode active material include carbon such as non-graphitized carbon and 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 &lt; 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, and Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials; Titanium oxide; Lithium titanium oxide and the like can be used, and in particular, a carbon-based material and / or Si can be included.

The anode current collector is generally made to have a thickness of 3 to 500 μm. 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.

The separator is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene, or the like may be used, and a composite separator having a porous coating layer containing inorganic particles / organic particles on the sheet or the nonwoven fabric may be 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 nonaqueous electrolyte containing a lithium salt is composed of a nonaqueous electrolyte and a lithium salt. Nonaqueous 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, But are not limited to, butylolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, But are not limited to, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxy methane, dioxolane derivatives, sulfolane, methyl sulfolane, Derivatives, tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used.

The organic solid electrolyte includes, for example, 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 acid 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 , Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS _2, and the like can be used.

The lithium salt is a substance which is easily 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 ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic carboxylate lithium, lithium tetraphenylborate, and imide.

The lithium salt-containing non-aqueous electrolyte may further contain, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, May be added. 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 one specific _{example, 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 present invention provides a battery module including the secondary battery as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source.

At this time, specific examples of the device include a power tool that is powered by an electric motor and moves; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like; An electric motorcycle including an electric bike (E-bike) and an electric scooter (E-scooter); An electric golf cart; And a power storage system, but the present invention is not limited thereto.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (8)

A lithium secondary battery comprising a cathode active material layer comprising a cathode active material layer containing at least one lithium metal oxide selected from the group consisting of a compound represented by the following general formula (1) and a compound represented by the following general formula (2) And a second cathode active material layer comprising lithium iron phosphate represented by the formula
Wherein the first cathode active material layer has a thickness in the range of 30 to 300 mu m and the second cathode active material layer has a thickness in the range of 1 to 300 mu m.
[Chemical Formula 1]
Li _x M _y Mn _2-y O _{4-za z}
In this formula,
0.9? X? 1.2, 0 <y <2, 0? Z <0.2;
M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, ;
A is one or more of an anion of -1 or -2.

(2)
(1-x) LiM'O _2-y A _y -xLi ₂ MnO _{3-y '} A _y'
In this formula,
M 'is Mn _a M _b ;
M is one or more selected from the group consisting of Ni, Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr, Zn and two period transition metals;
A is at least one selected from the group consisting of PO ₄ , BO ₃ , CO ₃ , F and NO ₃ anions,
0 < x &lt;1; 0 &lt; y? 0.02; 0 &lt; y ' 0.5? A? 1.0; 0? B? 0.5; a + b = 1.

(3)
Li _{1 + a} Fe _1-x M " _x (PO _4-b ) X _b
In this formula,
M &quot; is at least one selected from Al, Mg and Ti,
X is at least one selected from F, S and N,
-0.5? A? + 0.5, 0? X? 0.5, and 0? B?
The method according to claim 1,
And a second cathode active material layer is coated on the first cathode active material layer.
The method according to claim 1,
Wherein the second cathode active material layer is adhered and laminated on the first cathode active material layer in a thickness ranging from 1 [mu] m to 300 [mu] m.
A lithium secondary battery comprising a positive electrode according to any one of claims 1 to 3.
5. The method of claim 4,
A carbon-based material, and / or a negative electrode containing Si as a negative electrode active material.
6. The method of claim 5,
Wherein the lithium secondary battery is one selected from the group consisting of a lithium ion battery, a lithium ion polymer battery, and a lithium polymer battery.
A battery pack comprising the lithium secondary battery according to claim 6.
A device according to claim 7, wherein the battery pack is used as an energy source.