KR101684338B1 - Electrode Material for Secondary Battery and Lithium Secondary Battery Comprising the Same - Google Patents

Abstract

The present invention provides a lithium secondary battery comprising at least one first lithium metal oxide selected from compounds represented by the following formula (1), wherein the first lithium metal oxide is composed of primary particles and has an average particle diameter (D50) Of the total weight of the electrode active material.
(1-x) LiM'O _2-y A _y -xLi ₂ MnO _{3 -y '} A _y' (1)
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 < x &lt;1; 0 &lt; y? 0.02; 0 &lt; y &apos; 0.5? A? 1.0; 0? B? 0.5; a + b = 1.

Description

TECHNICAL FIELD [0001] The present invention relates to an electrode active material for a secondary battery, and a lithium secondary battery including the electrode active material.

The present invention relates to an electrode active material for a secondary battery and a lithium secondary battery including the electrode active material.

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, but its safety is low and it is expensive due to the resource limit of cobalt as a raw material, and there is a limit to 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.

On the other hand, lithium manganese oxides such as LiMnO ₂ and LiMn ₂ O ₄ have the advantage of using manganese which is rich in resources and environment-friendly as a raw material, and thus attracts much attention as a cathode active material capable of replacing LiCoO ₂ . However, these lithium manganese oxides also have a disadvantage of poor cycle characteristics and the like.

First, LiMnO ₂ has a disadvantage in that the initial capacity is small, and in particular, several tens of charge / discharge cycles are required until a certain capacity is reached. In addition, LiMn ₂ O ₄ has a disadvantage in that the capacity deteriorates as the cycle continues, and in particular, at a high temperature of 50 ° C or higher, the cycle characteristics are drastically lowered due to decomposition of the electrolytic solution and elution of manganese.

On the other hand, among the lithium-containing manganese oxides, there are Li ₂ MnO _{3 in} addition to LiMnO ₂ and LiMn ₂ O ₄ . Li ₂ MnO ₃ has excellent structural stability but is not electrochemically inert and thus can not be used as a cathode active material of a secondary battery. Therefore, among some prior arts, there is proposed a technique of using Li ₂ MnO ₃ as a cathode active material by forming a solid solution with LiMO ₂ (M = Co, Ni, Ni _0.5 Mn _0.5 , Mn). Such a solid solution cathode active material has a high possibility of decomposition of electrolyte and gas generation at a high voltage, and the LiMO ₂ (M = Co, Ni, Ni _0.5 Mn &lt; / RTI &gt; _0.5 , Mn).

In addition, the lithium-containing manganese oxide has a low conductivity and thus has a large resistance difference depending on the particle size. When the activation is progressed at a high voltage of 4.4 V or more in order to exhibit a high capacity, Li₂MnO₃in Li₂O may be detached to cause a change in structure. Due to the crystal structure, it is difficult to secure a desired degree of stability, and there is a limit to expect improvement of energy density.

Therefore, a need exists for a technique capable of solving such a problem.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the prior art and the technical problems required from the past.

An object of the present invention is to provide an electrode active material and a lithium secondary battery including the electrode active material, which have improved capacity and lifetime characteristics by delaying the structural change by changing the activation voltage according to the particle size of the electrode active material.

Accordingly, in a non-limiting example of the present invention, the electrode active material comprises at least one first lithium metal oxide selected from compounds represented by the following formula (1), wherein the first lithium metal oxide is composed of primary particles, And a secondary particle having a particle diameter (D50) within a range of 1 mu m or more and 15 mu m or less.

(1-x) LiM'O _2-y A _y -xLi ₂ MnO _{3 -y '} A _y' (1)

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 <1; 0? Y? 0.02; 0? Y? 0.02; 0.5? A? 1.0; 0? B? 0.5; a + b = 1.

As described above, the lithium-containing manganese oxide, when the conductivity activation is in progress on more than 4.4 V high voltage in order according to the magnitude of the low particle large and the difference in resistance, and to develop the high volume, Li ₂ O is separated from the Li ₂ MnO ₃ Thereby causing a change in the structure.

On the other hand, in the case of using the electrode active material according to the present invention, the activation process is lower than the existing activation voltage by using the electrode active material having a small secondary particle size, thereby delaying the structural change as described above.

The average particle diameter (D50) of the secondary particles may be in the range of 3 mu m or more and 11 mu m or less.

The average particle size (D50) of the secondary particles may be in the range of 3 mu m or more and 8 mu m or less.

If the average particle diameter of the secondary particles is too small, the manufacturing process becomes complicated and the surface area is widened. Therefore, even when the same amount of binder is used, the adhesive force may be lowered. There is a problem that the resistance increases. When the average particle diameter of the secondary particles is too large, the electric conductivity is lowered, which is not preferable.

Wherein the electrode active material further comprises at least one second lithium metal oxide selected from compounds represented by the formula (1), and the second lithium metal oxide is composed of primary particles and has an average particle diameter (D50) Lt; / RTI &gt; to 15 &lt; RTI ID = 0.0 &gt; urn &lt; / RTI &gt;

The average particle diameter (D50) of the secondary particles may be in the range of 3 mu m or more and 11 mu m or less.

The average particle size (D50) of the secondary particles may be in the range of 3 mu m or more and 8 mu m or less.

The present invention can also provide a lithium secondary battery comprising the electrode active material as a cathode active material.

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.

Generally, the positive electrode is prepared by applying an electrode mixture, which is a mixture of a positive electrode active material, a conductive material and a binder, on a positive electrode collector, followed by drying. If necessary, a filler may be further added to the mixture.

The positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ) or lithium nickel oxide (LiNiO ₂ ) or a compound substituted with one or more transition metals, in addition to the electrode active material represented by the formula (1). 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 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.

On the other hand, the graphite based material having elasticity may be used as a conductive material, and may be used together with the materials.

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, various copolymers and the like.

The filler is optionally used as a component for suppressing the 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 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 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 generally include an anode, a cathode, a separator interposed between the anode and the cathode, and a non-aqueous electrolyte containing a lithium salt. Other components of the lithium secondary battery will be described below.

The negative electrode is manufactured 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 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 &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 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.

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 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 -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.

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, etc. 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 can also provide a battery pack including the lithium secondary battery.

A device using the battery pack as an energy source can be provided.

As described above, the electrode active material according to the present invention can provide an electrode active material having improved capacity and lifetime characteristics by delaying the structural change by changing the activation voltage according to the particle size of the electrode active material, and a lithium secondary battery comprising the electrode active material have.

1 is a graph showing lifetime characteristics according to Experimental Example 1;
2 is a graph showing XRD equipment analysis information according to Experimental Example 2. FIG.

Hereinafter, the present invention will be described in further detail with reference to the following examples. However, the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

&Lt; Example 1 >

A lithium manganese-based oxide as an essential transition metal including Mn and having a layered crystal _{structure, 0.5Li 2 MnO 3 · 0.5Li (} Ni 0.45 Mn 0.35 Ni 0.20) O 2 1 and average particle size of primary particles in the formula consisting of (D50 ) Was used as a cathode active material, and the cathode active material was slurried at a ratio of active material, a conductive agent and a binder of 90: 5: 5, and a thickness of 20 탆 Of Al-foil, followed by rolling and drying to prepare a positive electrode.

Lithium metal was used as the cathode, coated on a copper foil with a thickness of 20 ㎛ to a thickness of 80 ㎛, rolled and dried to prepare a negative electrode.

An electrode assembly was manufactured through a separator (CELLGUARD ^TM , thickness: 20 mu m) between the cathode and the anode. The electrode assembly was housed in a pouch-shaped battery case. Ethyl carbonate, dimethyl carbonate and ethyl methyl carbonate A pouch-type battery was prepared by adding a lithium non-aqueous electrolyte containing 1 M LiPF ₆ as a lithium salt in a volume ratio of 1: 1: 1.

&Lt; Example 2 >

A pouch-shaped battery was fabricated in the same manner as in Example 1, except that artificial graphite was used instead of Li metal as a negative electrode.

&Lt; Comparative Example 1 &

A pouch-shaped battery was fabricated in the same manner as in Example 1, except that the average particle diameter (D50) of the secondary particles in the cathode active material was 15 mu m in size.

&Lt; Comparative Example 2 &

A pouch-shaped battery was fabricated in the same manner as in Example 2, except that the average particle diameter (D50) of the secondary particles in the cathode active material was 15 mu m in size.

<Experimental Example 1>

The coin-type battery manufactured in Example 1 had a resistance lower than that of the battery manufactured in Comparative Example 1, so that activation was carried out at a voltage range of 2.75 to 4.55 V, and a current of 0.1 C-rate was passed for one cycle. As the size of the cathode active material is high, the battery has a high resistance and an overvoltage is applied. Therefore, the activation of the Li ₂ MnO ₃ portion was performed in the voltage range of 2.75 to 4.65 V to activate. The charging and discharging characteristics at this time are shown in Fig.

<Experimental Example 2>

The structural change according to the activation voltage of the coin-type battery manufactured in Example 1 was analyzed using XRD equipment. Coin-type batteries filled with bare electrodes and charged to 4.65 V with a current of 0.1 C-rate, Coin-type batteries discharged from 4.65 V to 2.75 V, Coin-type batteries charged to 4.4 V, Discharges from 4.4 V to 2.75 V The results of analyzing the structure change of the Li ₂ MnO ₃ part using the XRD equipment are shown in FIG.

Figures 1 and Li ₂ to FIG forward low activation process according to the second, lower Plateou interval voltage appearing to exit the Li ₂ O from Li ₂ MnO ₃ with a small electrode active material size of the secondary particles than the conventional activation voltage MnO ₃ is activated to enable the capacity to be expressed and the activation voltage to be lowered to delay the structural change of the active material, thereby contributing to enhancement of output and lifetime improvement.

<Experimental Example 3>

The coin-type battery manufactured in Example 2 was subjected to 1 cycle activation by flowing a current of 0.1 C-rate in a voltage range of 2.5 to 4.5 V, and the coin-type battery manufactured in Comparative Example 2 was operated at 0.1 C- 1 cycle activation was performed. The activated coin type battery was charged to a charging end voltage of 4.4 V with a charging current of 0.1 C and then discharged at a discharging rate of 0.1 C, 0.5 C and 1 C to discharge end voltage of 2.5 V. Table 1 below shows discharge capacities of 0.1C, 0.5C and 1C.

0.1C capacity (2.5-4.4V)
(mAh / g) 0.5C capacity (2.5-4.4V)
(mAh / g) 1C capacity (2.5-4.4V)
(mAh / g) Example 2 211.5 190 176 Comparative Example 2 206.8 179 153

<Experimental Example 4>

The coin-type battery manufactured in Example 2 and Comparative Example 2 was subjected to a life characteristic test by flowing a current of 25 / 0.5 / 1.0 C-rate in a voltage range of 2.5 to 4.4 V. At this time, The results are shown in Table 2 below.

Life characteristics
(Capacity in 100 cycles compared to initial capacity,%) Example 2 79 Comparative Example 2 15

According to Table 1, in the case of the batteries of Examples 1 and 2 using a compound having a small secondary particle size in the compound of Chemical Formula 1, the C-Rate characteristic Is excellent.

Further, according to the above Table 2, in the case of the battery of Example 2 using a compound having a small secondary particle size in the compound of Chemical Formula 1, life characteristics were remarkably higher than those in the case of using a compound having a large secondary particle .

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 (11)

At least one first lithium metal oxide selected from a compound represented by the following formula (1) and at least one second lithium metal oxide selected from a compound represented by the following formula (1)
Wherein the first lithium metal oxide and the second lithium metal oxide each comprise an electrode active material composed of primary particles and containing secondary particles having an average particle diameter (D50) in a range of 3 mu m or more to 8 mu m or less as a cathode active material And is activated in a voltage range from 2.5 V to 4.55 V. A lithium secondary battery comprising:

(1-x) LiM'O ₂ -xLi ₂ MnO ₃ (1)
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;

0 &lt; x &lt;1; 0.5? A? 1.0; 0? B? 0.5; a + b = 1. delete delete delete delete delete delete The lithium secondary battery according to claim 1, wherein the lithium secondary battery comprises a carbon-based material, Si, or a carbon-based material and Si as a negative electrode active material. The lithium secondary battery according to claim 1, 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 1. A device using the battery pack according to claim 10 as an energy source.

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