KR20080100152A - Positive active material for lithium secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

A positive active material for lithium secondary battery and a lithium secondary battery comprising the same are provided to improve high effective charging/discharging characteristic and lifetime property of the lithium secondary battery. A positive active material for lithium secondary battery has a nanowire shape and contains a lithium composite metal oxide capable of performing intercalation and deintercalation of the lithium. The lithium composite metal oxide is a lithium metal phosphate which is shown in the following chemical formula (LixMyM'zPO4-wBw), wherein M and M' are an element selected from a group consisting of Fe, Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Mo, Ti, Zn, Al, Ga, Mg, B and their combination; B is the element selected from the group consisting of F, and S and their combination; and 0<x<=1, 0<y<=1, 0<z<=1, 0<x+y+z<=2 and 0<=w<=0.5.

Description

A positive electrode active material for a lithium secondary battery and a lithium secondary battery including the same {POSITIVE ACTIVE MATERIAL FOR LITHIUM SECONDARY BATTERY AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to a cathode active material for a lithium secondary battery and a lithium secondary battery including the same, and more particularly, to a cathode active material for a lithium secondary battery and a lithium secondary battery including the same, which improves high rate charge and discharge characteristics and lifespan characteristics of a lithium secondary battery. It is about.

Recently, the demand for a battery that is repeatedly charged and discharged using a portable electronic device such as a mobile phone, a portable personal digital assistant (PDA), a notebook computer, a digital camera, a camcorder, an electric bicycle, an electric vehicle, and the like is exponential. Is increasing. Commercially available lithium batteries mainly use LiCoO ₂ for the positive electrode and carbon for the negative electrode.

However, cobalt, which is a starting material of the positive electrode active material, has a low reserve and high cost, and there is a demand for development of an alternative positive electrode material due to toxicity and environmental pollution problems. LiNiO ₂ , LiCo _x Ni _1-x O ₂ , LiMn ₂ O ₄ , and the like are currently being actively researched and developed as positive electrode active materials. However, LiNiO ₂ having a layered structure such as LiCoO ₂ has difficulty in synthesizing materials at a stoichiometric ratio, and has not been commercialized due to problems in thermal stability.

LiMn ₂ O ₄ , a 4V class spinel cathode active material, has the advantage of using manganese as a starting material, and some of them are commercialized in low-cost products. However, there is a problem that the life characteristics are not good because of the structural variation called Jahn-Teller distortion due to manganese ³⁺ .

Therefore, development of a positive electrode active material which is more economical, stable, high capacity, and has good cycle characteristics is desired. Li _x M _y PO ₄ , where x is 0 <x ≦ 2, y is 0.8 ≦ y ≦ 1.2, and M is a periodic table Group 3d transition metal, may be mentioned as a positive electrode active material of a lithium battery.

The use of LiFePO ₄ as a positive electrode of a lithium ion battery among the compounds represented by Li _x M _y PO ₄ is disclosed in Japanese Patent Laid-Open No. 9-171827. LiFePO ₄ is environmentally friendly, rich in reserves and very low in raw material prices. In addition, it is possible to implement low power and low voltage more easily than the existing cathode active material, and the theoretical capacity is 170mAh / g, which is also excellent in battery capacity. However, the LiFePO ₄ has a problem that the high rate discharge characteristic of 2C or more is poor due to low electron conductivity (10 ⁻⁶ S / cm).

One embodiment of the present invention is to provide a cathode active material for a lithium secondary battery that can improve the high rate charge and discharge characteristics and life characteristics of the lithium secondary battery.

Another embodiment of the present invention is to provide a lithium secondary battery including the positive electrode active material.

However, technical problems to be achieved by the present invention are not limited to the above-mentioned problems, and other technical problems will be clearly understood by those skilled in the art from the following description.

One embodiment of the present invention provides a cathode active material for a lithium secondary battery having a nanowire shape and including a lithium composite metal oxide capable of intercalation and deintercalation of lithium.

Another embodiment of the present invention provides a cathode active material for a lithium secondary battery having a hollow spherical particle shape and including a lithium composite metal oxide capable of intercalation and deintercalation of lithium.

Another embodiment of the present invention provides a lithium secondary battery including the cathode active material.

Other specific details of embodiments of the present invention are included in the following detailed description.

The positive electrode active material according to the embodiment of the present invention includes a lithium composite metal oxide having a nanowire shape or a hollow spherical shape, thereby improving high rate charge / discharge characteristics and lifespan characteristics of a battery using the same.

By using the method of manufacturing a cathode active material according to an embodiment of the present invention, a cathode active material including a lithium composite metal oxide having the nanowire shape or a hollow spherical shape may be manufactured.

Lithium secondary battery according to an embodiment of the present invention by including the positive electrode active material, high rate charge and discharge characteristics and life characteristics are improved.

Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, by which the present invention is not limited and the present invention is defined only by the scope of the claims to be described later.

According to an embodiment of the present invention, there is provided a cathode active material for a lithium secondary battery having a nanowire shape and including a lithium composite metal oxide capable of intercalation and deintercalation of lithium. The positive electrode active material for a lithium secondary battery includes a lithium composite metal oxide having a nanowire shape, thereby improving high rate discharge characteristics.

The lithium composite metal oxide having the nanowire shape preferably has a particle size of 1 to 50 nm, more preferably 1 to 10 nm. When the particle size of the lithium composite metal oxide having the nanowire shape is less than 1 nm, there is a problem in that synthesis is difficult, and when it exceeds 50 nm, the battery high rate characteristics are not greatly improved, which is not preferable.

It is preferable that it is 1-100 micrometers or less, and, as for the length of the lithium composite metal oxide which has the said nanowire shape, it is more preferable that it is 1-10 micrometers. When the length of the lithium composite metal oxide having the nanowire shape is less than 1 μm, there is a problem in that synthesis is difficult.

According to another embodiment of the present invention, there is provided a cathode active material for a lithium secondary battery having a hollow spherical particle shape and including a lithium composite metal oxide capable of intercalation and deintercalation of lithium. The positive electrode active material for a lithium secondary battery includes a lithium composite metal oxide having a hollow spherical particle shape, thereby improving high rate discharge characteristics.

The particle size of the lithium composite metal oxide having an empty spherical particle shape is preferably 200 nm to 1 μm, and preferably 300 nm to 500 nm. When the particle size of the lithium composite metal oxide having an empty spherical particle shape is less than 200 nm, synthesis is difficult. If the particle size exceeds 1 μm, battery high rate characteristics are not greatly improved, which is not preferable.

It is preferable that it is 10-200 nm, and, as for the thickness of the lithium composite metal oxide which has an empty spherical particle shape inside, it is preferable that it is 50-150 nm. If the thickness of the lithium composite metal oxide having an empty spherical particle shape is less than 10 nm, there is a problem in that the synthesis is difficult, and if it exceeds 200 nm, the battery high rate characteristic is not improved significantly, which is not preferable.

The lithium composite metal oxide is preferably lithium metal phosphate represented by the following formula (1).

[Formula 1]

Li _x M _y M ' _z PO _4-w B _w

Wherein M and M 'are independently of each other consisting of Fe, Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Mo, Ti, Zn, Al, Ga, Mg, B, and combinations thereof An element selected from the group, B is an element selected from the group consisting of F, S, and combinations thereof, 0 <x≤1, 0 <y≤1, 0 <z≤1, 0 <x + y + z ≦ 2 and 0 ≦ w ≦ 0.5)

The lithium metal phosphate is more preferably lithium iron phosphate, and more preferably a compound selected from the group consisting of the following Chemical Formulas 2 to 5, and combinations thereof.

[Formula 2]

LiFe _1-a A _a PO ₄

[Formula 3]

Li _1-a A _a FePO ₄

[Formula 4]

LiFe _1-a A _a PO _4-z B _z

[Formula 5]

Li _1-a A _a FePO _4-z B _z

(In Formulas 2 to 5, A is selected from the group consisting of Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Mo, Ti, Zn, Al, Ga, Mg, B, and combinations thereof. Element, B is an element selected from the group consisting of F, S, and combinations thereof, wherein 0 ≦ a <1, 0.01 ≦ z ≦ 0.5)

The positive electrode active material for a lithium secondary battery according to an embodiment of the present invention is to prepare a porous silica skeleton, to dissolve the precursor of the lithium composite metal oxide in a solvent to prepare a precursor solution of the lithium composite metal oxide, the precursor of the lithium composite metal oxide After adding the porous silica backbone to the solution, the first heat treatment to prepare a lithium composite metal oxide-silica composite, remove the silica from the lithium composite metal oxide-silica composite, it can be prepared by a second heat treatment.

The preparation of the porous silica skeleton can be made using any conventional method for producing the porous silica skeleton. The preparation of the porous silica skeleton can be prepared by mainly reacting a silica source with a surfactant, followed by calcining to remove the surfactant. In the manufacturing process of the porous silica skeleton, the structure and size of the pores may be controlled by varying the synthesis conditions such as the synthesis temperature, the carbon chain size of the surfactant, the molar ratio of Si and the surfactant.

For example, the porous silica backbone is a hexadecyltrimethyl ammonium bromide (C ₁₆ H ₃₃ N (CH ₃ ) ₃ Br; CTABr) and polyoxyethylene lauryl ether (C ₁₂ H 25 _O (C ₂ H ₄₀ ) ₄ ) as a surfactant H; Brij 30), and can be synthesized using colloidal silica or waterglass as silica source. After the mixture of the surfactant and the silica source was stirred, the mixture was reacted at 80 to 120 ° C. for 36 to 54 hours, cooled to room temperature, and then the pH of the reaction mixture was adjusted to 9 to 11 using acetic acid or the like. Again, it is maintained at 80 to 120 ℃ for 36 to 48 hours. The precipitate in the reaction mixture is filtered, washed with excess water and dried to produce a porous silica backbone.

In another example, the porous silica backbone is a terpolymer of tetraethoxysilane (TEOS) or water glass, and poly (ethylene oxide) -poly (propylene oxide) -poly (ethylene oxide) (EO20-PO70-EO20; P123 ) And the reaction mixture is stirred at a temperature of 35 to 100 ° C. for 15 to 25 hours to obtain a reaction mixture in a gel state, which is left without stirring at the same temperature for 24 hours, and then in a solid state produced in the reaction mixture. The porous silica backbone may be filtered and then dried.

A precursor solution of a lithium composite metal oxide was prepared by dissolving a precursor of a lithium composite metal oxide in a solvent, adding the porous silica skeleton to the precursor solution of the lithium composite metal oxide, and performing a first heat treatment to form a lithium composite metal oxide-silica composite. Can be prepared.

The precursor of the lithium composite metal oxide may be variously adjusted according to the composition of the lithium composite metal oxide to be prepared, and the molar ratio. Any precursor of the lithium composite metal oxide can be preferably used as long as it is a precursor used for producing a conventional lithium composite metal oxide.

However, when the lithium composite metal oxide is lithium metal phosphate, the precursor of the lithium composite metal oxide preferably includes lithium salt, metal salt, and phosphate salt.

The lithium salt may be preferably used as long as it is conventionally used for producing lithium metal phosphate, and is composed of lithium hydroxide, lithium fluoride, lithium nitrate, lithium carbonate, lithium acetate, hydrates thereof, and combinations thereof. What is chosen from the group can be used preferably.

The metal salt may be preferably used as long as it is conventionally used to manufacture lithium metal phosphate, and may be Fe, Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Mo, Ti, Zn, Al, Ga It may be preferably used selected from the group consisting of nitrates, chlorides, sulfates, carbonates, acetates, hydrates thereof, and combinations thereof including metals selected from the group consisting of Mg, B, and combinations thereof.

The phosphate salt may be preferably used as long as it is conventionally used to prepare lithium metal phosphate, and may include first ammonium phosphate (NH ₄ H ₂ PO ₄ ), second ammonium phosphate ((NH ₄ ) ₂ HPO ₄ ), What is selected from the group consisting of phosphoric acid (H ₃ PO ₄ ), hydrates thereof, and combinations thereof can be preferably used.

The solvent for dissolving the precursor of the lithium composite metal oxide may be preferably selected from the group consisting of water, methanol, ethanol, isopropyl alcohol, and combinations thereof.

The primary heat treatment is preferably carried out at a temperature of 100 to 400 ℃, more preferably at a temperature of 200 to 300 ℃. If the temperature of the first heat treatment is less than 100 ℃, there is a problem that some of the lithium composite metal oxide-silica composite prepared in the process of removing silica, there is a problem that, if it exceeds 400 ℃, the lithium composite metal oxide-silica composite In addition to being manufactured, there is a problem in that the precursor of some lithium composite metal oxides and silica react.

The primary heat treatment is preferably performed for 1 to 3 hours. If the time of the first heat treatment is less than 1 hour, there is a problem that a part of the lithium composite metal oxide-silica composite prepared in the process of removing silica is also removed, and if more than 3 hours, the lithium composite metal oxide-silica composite is In addition to being prepared, there is a problem in that precursors of some composite metal oxides and silica react.

The method of manufacturing a cathode active material according to another exemplary embodiment of the present invention may further include adding the porous silica skeleton to the precursor solution of the lithium composite metal oxide, followed by drying before primary heat treatment.

After removing the silica from the lithium composite metal oxide-silica composite and performing a second heat treatment, a nanowire-shaped lithium composite metal oxide may be manufactured.

The lithium composite metal oxide-silica composite may be added to HF aqueous solution, NaOH aqueous solution, or KOH aqueous solution, and then stirred to remove silica. It is more preferable to remove the silica using 1 to 2 M NaOH aqueous solution.

The secondary heat treatment is preferably carried out at a temperature of 600 to 700 ℃. If the secondary heat treatment temperature is less than 600 ℃, there is a problem that some of the lithium composite metal oxide produced does not have a nano-wire shape or the hollow spherical particle shape therein, when the secondary heat treatment temperature exceeds 700 ℃, by-products other than the lithium composite metal oxide It is not desirable because it is generated.

The secondary heat treatment is preferably performed for 3 to 5 hours. If the secondary heat treatment temperature is less than 3 hours, there is a problem that some of the lithium composite metal oxide produced does not have a nanowire shape or an empty spherical particle shape therein, and when more than 5 hours, the nano of some lithium composite metal oxide There is a problem that the wire shape or the hollow spherical particle shape is collapsed.

The first heat treatment or the second heat treatment is preferably made in an atmosphere containing hydrogen and nitrogen in a volume ratio of 10:90.

According to another embodiment of the present invention, before adding the porous silica skeleton to the precursor solution of the lithium composite metal oxide, leaving the precursor solution of the lithium composite metal oxide to prepare a precursor solution of the lithium composite metal oxide having a viscosity It provides a method for producing a cathode active material for a lithium secondary battery further comprising the step of.

When the precursor solution of the lithium composite metal oxide having the viscosity is used, a lithium composite metal oxide having an empty spherical particle shape can be produced.

The viscosity of the precursor solution of the lithium composite metal oxide having the viscosity is preferably 50 to 4000 cps, more preferably 200 to 2000 cps. When the viscosity of the precursor solution of the lithium composite metal oxide is less than 50 cps, there is a problem that the precursor solution of the lithium composite metal oxide is not coated on silica, and when it exceeds 4000 cps, there is a problem that it is difficult to uniformly mix with the silica.

The viscosity of the precursor solution of the lithium composite metal oxide can be adjusted by changing the temperature and time of the standing. The temperature and time of the standing may be variously adjusted according to the type of lithium composite metal oxide to be prepared, the type of precursor of the lithium composite metal oxide, the molar ratio of the precursors of the lithium composite metal oxide, and the like, and is made at 20 to 100 ° C. desirable.

According to an embodiment of the present invention, a lithium secondary battery including the cathode active material is provided.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

1 is an exploded perspective view of a rechargeable lithium battery according to one embodiment of the present invention. Referring to FIG. 1, the lithium secondary battery 1 according to the exemplary embodiment of the present invention has a negative electrode 2 and a positive electrode 3, and a separator disposed between the negative electrode 2 and the positive electrode 3. (4), an electrolyte (not shown) impregnated in the negative electrode 2, the positive electrode 3, and the separator 4, the battery container 5, and the sealing member 6 for enclosing the battery container 5 It is composed of main parts.

The positive electrode 3 is manufactured using a positive electrode active material according to an embodiment of the present invention. The positive electrode 3 is prepared by mixing a positive electrode active material, a conductive agent, and a binder to prepare a composition for forming a positive electrode active material, and then applying the composition to a positive electrode current collector such as aluminum foil and rolling.

As the binder, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropylene cellulose, diacetylene cellulose, polyvinyl chloride, polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, or polypropylene may be used. It may be, but is not limited thereto.

In addition, as the conductive agent, any battery may be used as long as it does not cause chemical change and has an electronic conductivity. Examples thereof include natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, or copper. , Metal powders such as nickel, aluminum, silver, metal fibers and the like can be used, and conductive materials such as polyphenylene derivatives can be mixed and used.

The negative electrode 2 includes a negative electrode active material, and a compound capable of reversible intercalation and deintercalation of lithium may be used as the negative electrode active material. Specific examples of the negative electrode active material may be a carbonaceous material such as artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, and the like. In addition to the carbonaceous material, a metallic compound capable of alloying with lithium, or a composite including a metallic compound and a carbonaceous material may also be used as the negative electrode active material. Examples of the metal that can be alloyed with lithium include Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, Al alloys, and the like. Moreover, a metal lithium thin film can also be used as a negative electrode active material.

Like the positive electrode 3, the negative electrode 2 may be prepared by mixing a negative electrode active material, a binder, and optionally a conductive agent to prepare a composition for forming a negative electrode active material, and then applying the same to a negative electrode current collector such as copper foil. .

As the electrolyte charged in the lithium secondary battery, a non-aqueous electrolyte or a known solid electrolyte may be used.

The non-aqueous electrolyte serves as a medium through which ions involved in the electrochemical reaction of the battery can move. The non-aqueous electrolyte may be a carbonate, ester, ether or ketone solvent. As the carbonate solvent, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. may be used. Examples of the ester solvent include n-methyl acetate, n-ethyl acetate, n-propyl acetate, and the like. Can be used.

The separator 4 may exist between the positive electrode 3 and the negative electrode 2 according to the type of the lithium secondary battery. As the separator 4, polyethylene, polypropylene, polyvinylidene fluoride or two or more multilayer films thereof may be used, and polyethylene / polypropylene two-layer separator, polyethylene / polypropylene / polyethylene three-layer separator, polypropylene / polyethylene Of course, a mixed multilayer film such as a polypropylene three-layer separator can be used.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following embodiments are only preferred embodiments of the present invention, and the present invention is not limited to the following embodiments.

(Manufacture of Anode Active Material)

(Example 1)

3.5 g of EO20-PO70-EO20 (Pluronic P123 ^® , manufactured by Aldrich) was dissolved in 25 g of distilled water and 6 g of HCl (40%). 7.8 g of TEOS (manufactured by Aldrich) was added thereto, stirred at room temperature for 24 hours, and then sealed in a Teflon bottle. It was left at 100 ° C. for 24 hours to prepare a porous silica skeleton. The porous silica backbone was calcined at 500 ° C. for 5 hours.

12.8 g Fe (NO ₃ ) ₃ H ₂ O (99%, manufactured by Junsei), 3.23 g LiC ₂ H ₃ O ₂ · 2H ₂ O (99.9%, manufactured by Aldrich), and 3.10 g H ₃ PO ₄ (99%, available from Aldrich) was completely dissolved in 20 ml of ethanol to prepare a precursor solution. 1.7 g of the prepared porous silica skeleton was added to the precursor solution, dried at 120 ° C., and then heated at 300 ° C. for 3 hours in a kiln in which a composite gas containing H ₂ and N ₂ in a volume ratio of 10:90 was injected. Heat treatment. The heat treatment was repeated two more times to obtain a LiFePO ₄ -SiO ₂ composite. The LiFePO ₄ -SiO ₂ composite was placed in 1 M NaOH and left for 5 minutes to completely remove silica. Removing the silica, and the rest of LiFePO _4, H ₂ and N ₂ 10: In the firing furnace for injecting a compound gas containing a volume ratio of 90 at a temperature of 700 ℃ by heating for 5 hours, preparing the LiFePO ₄ has a nanowire shape It was.

(Example 2)

LiFePO ₄ having a nanowire shape was prepared in the same manner as in Example 1 except that the first heat treatment was performed at a temperature of 100 ° C. for 3 hours.

(Example 3)

LiFePO ₄ having a nanowire shape was prepared in the same manner as in Example 1 except that the first heat treatment was performed at a temperature of 200 ° C. for 2 hours.

(Example 4)

LiFePO ₄ having a nanowire shape was prepared in the same manner as in Example 1 except that the first heat treatment was performed at a temperature of 300 ° C. for 2 hours.

(Example 5)

LiFePO ₄ having a nanowire shape was prepared in the same manner as in Example 1 except that the first heat treatment was performed at a temperature of 400 ° C. for 1 hour.

(Example 6)

LiFePO ₄ having a nanowire shape was prepared in the same manner as in Example 1 except that the second heat treatment was performed at a temperature of 700 ° C. for 3 hours.

(Example 7)

LiFePO ₄ having a nanowire shape was prepared in the same manner as in Example 1 except that the second heat treatment was performed at a temperature of 700 ° C. for 4 hours.

(Example 8)

LiFePO ₄ having a nanowire shape was prepared in the same manner as in Example 1 except that the second heat treatment was performed at a temperature of 600 ° C. for 5 hours.

(Example 9)

LiFePO ₄ having a nanowire shape was prepared in the same manner as in Example 1 except that the second heat treatment was performed at a temperature of 600 ° C. for 3 hours.

(Example 10)

LiFePO ₄ having a nanowire shape was prepared in the same manner as in Example 1 except that the second heat treatment was performed at a temperature of 600 ° C. for 4 hours.

(Example 11)

Before adding the porous silica backbone to the precursor solution in Example 1, the precursor solution was maintained at 50 ° C for 30 minutes to have a viscosity of 1000 cps, except that the porous silica backbone was added, Example 1 LiFePO ₄ having the shape of a hollow spherical particle was prepared in the same manner as the above.

(Example 12)

The precursor solution was maintained at 50 ° C. for 40 minutes to have a viscosity of 2000 cps, followed by the same procedure as in Example 11 except for adding a porous silica skeleton to form LiFePO ₄ having a hollow spherical particle shape. Prepared.

(Example 13)

The precursor solution was maintained at 50 ° C. for 50 minutes to have a viscosity of 3000 cps, followed by the same procedure as in Example 11 except for adding a porous silica skeleton to form LiFePO ₄ having a hollow spherical particle shape. Prepared.

(Example 14)

After maintaining the precursor solution at 50 ° C. for 10 minutes to have a viscosity of 400 cps, LiFePO ₄ having an empty spherical particle shape was performed in the same manner as in Example 11 except for adding a porous silica skeleton. Prepared.

(Example 15)

After maintaining the precursor solution at 50 ° C. for 1 hour to have a viscosity of 4000 cps, LiFePO ₄ having an empty spherical particle shape was performed in the same manner as in Example 11 except for adding a porous silica skeleton. Prepared.

(Comparative Example 1)

12.8 g of Fe (NO ₃ ) ₃ H ₂ O (99%, manufactured by Junsei), 3.23 g of LiC ₂ H ₃ O ₂ .2H ₂ O (99.9%, manufactured by Aldrich), and 3.10 g of H ₃ After dissolving PO ₄ (99%, Aldrich) completely in 20 ml of ethanol, drying at 120 ° C., 10 hours at a temperature of 700 ° C. in a firing furnace injecting a complex gas containing H ₂ and N ₂ in a volume ratio of 10:90. It was calcined during to prepare a LiFePO ₄ powder.

(Observation of transmission electron microscope (TEM) and electron diffraction photo of the positive electrode active material)

The cathode active materials prepared in Examples 1 to 15 were observed with a transmission electron microscope, and transmission electron micrographs of the cathode active material of Example 1 are shown in FIGS. 2A and 2B, and transmission electron micrographs of the cathode active material of Example 11 3A and 3B, transmission electron micrographs of the positive electrode active material of Example 15 are shown in FIGS. 4A to 4C.

In addition, the positive electrode active material of Example 15 was subjected to electron diffraction analysis, and the results are shown in FIG. 5.

Referring to FIG. 2A, it can be seen that LiFePO ₄ having a nanowire shape is present in a bundle form. Referring to FIG. 2B, the nanowire-shaped LiFePO ₄ may have a particle diameter of about 4 nm and a length of 3 μm. In addition, a LiFePO ₄ (111) lattice fringe image can be observed.

In addition, in the case of the positive electrode active material prepared in Examples 2 to 10, the nanowire-shaped LiFePO ₄ was prepared, and the nanowire-shaped LiFePO ₄ had a particle diameter of 1 to 50 nm and a length of 1 to 100 μm. Could.

Referring to FIG. 3A, it can be seen that the cathode active material prepared in Example 11 has an empty spherical shape. Referring to FIG. 3B, the cathode active material prepared in Example 11 has a thickness of about 60 nm and a size of about 200 nm.

4A and 4B, the thickness of the LiFePO ₄ powder having an empty spherical shape is about 120 nm, and the size is about 500 nm. This is considered to be a result of the increase in the viscosity of the precursor solution. 4C and 5, it can be seen that the manufactured LiFePO ₄ having a hollow spherical shape is a single crystal.

Also, in the case of the positive electrode active materials prepared in Examples 12 to 14, LiFePO ₄ having a hollow spherical shape was also produced, and the size of LiFePO ₄ having a hollow spherical shape was 200 nm to 1 μm, and the thickness thereof. Was confirmed to be 10nm to 200nm.

(Energy dispersive x-ray analysis)

FIG. 6 illustrates EDX analysis of regions 1 and 2 in FIG. 3B. Referring to FIG. 6, it can be seen that impurities such as Na and Si cannot be observed. This means that after the first heat treatment at 300 ° C., the silica was completely removed during the removal of silica from NaOH, and the positive electrode composite metal oxide did not react with NaOH.

(Measurement of high rate characteristics and life characteristics of batteries)

In each of the positive electrode active material and the conductive agent prepared in Examples 1 to 15, and Comparative Example 1 Polyvinylidene fluoride (PVdF) was mixed with acetylene black and a binder so as to have a weight ratio of 85: 7.5: 7.5 to prepare a slurry for the positive electrode. The slurry for the positive electrode was uniformly coated on a 20 μm thick aluminum foil, dried at 110 ° C., and rolled by roll press. The rolled formed product was cut out to 50 mm × 30 mm, and dried under reduced pressure at 120 ° C. for 24 hours to prepare a positive electrode.

As the negative electrode, mesocarbon microbeads (MCMB) and PVdF were mixed in a weight ratio of 96: 4 to prepare a negative electrode slurry, and the negative electrode slurry was uniformly coated on a copper foil. The separator is in the first, and of ethylene carbonate and dimethyl carbonate, using a porous polyethylene film (Celgard ^® 2300, Cell garde El elssi claim) 25㎛ thickness: adding a solution of 1M LiPF ₆ in a mixed solvent in a volume ratio of 1 A test cell having a bicell structure was prepared using one solution as an electrolyte.

An electrochemical analyzer (Toscat 3000U ^® , manufactured by Toyo Corporation) was used to evaluate the characteristics of the test cell.

The results of the high rate characteristics and the life characteristics of the battery using the positive electrode active material of Example 1 and Example 15 are shown in FIG.

In addition, the high rate characteristics and the life characteristics of the battery using the positive electrode active material of Example 1, Example 15, and Comparative Example 1 were compared in Table 1 below.

TABLE 1

0.5C 1C 3C 6C 10C 15C Example 1 156 mAh / g 155 mAh / g 155 mAh / g 148 mAh / g 144 mAh / g 137 mAh / g Example 15 165 mAh / g 164 mAh / g 164 mAh / g 157 mAh / g 154 mAh / g 150 mAh / g Comparative Example 1 150 mAh / g 140 mAh / g 110 mAh / g 90 mAh / g 60 mAh / g 40 mAh / g

Referring to FIG. 7 and Table 1, it can be seen that the high rate property of 5C or higher of the batteries using the positive electrode active materials of Example 1 and Example 15 was improved by 70% or more than the battery using the positive electrode active material of Comparative Example 1.

In the case of the battery using the positive electrode active material of Examples 2 to 14 also showed a high rate and life characteristics similar to the battery using the positive electrode active material of Example 1 or Example 15.

The present invention is not limited to the above embodiments, but may be manufactured in various forms, and a person skilled in the art to which the present invention pertains has another specific form without changing the technical spirit or essential features of the present invention. It will be appreciated that the present invention may be practiced as. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

1 is a cross-sectional view of a lithium secondary battery according to an embodiment of the present invention.

2A and 2B are transmission electron microscope (TEM) photographs of the positive electrode active material of Example 1 according to the present invention.

3A and 3B are transmission electron micrographs of the positive electrode active material of Example 11 according to the present invention.

4A to 4C are transmission electron micrographs of the positive electrode active material of Example 15 according to the present invention.

5 is an electron diffraction photo of the positive electrode active material of Example 15 according to the present invention.

Figure 6 is a graph showing the results of energy dispersive x-ray (EDX) analysis of region 1 and region 2 of Figure 3b.

Figure 7 is a graph showing the high rate characteristics and life characteristics of the battery using the positive electrode active material of Example 1 and Example 15 according to the present invention.

<Explanation of symbols for the main parts of the drawings>

1: lithium secondary battery 2: negative electrode

3: anode 4: separator

5: battery container 6: sealing member

Claims (13)

A cathode active material for a lithium secondary battery having a nanowire shape and comprising a lithium composite metal oxide capable of intercalation and deintercalation of lithium. The method of claim 1, The lithium composite metal oxide is a lithium metal phosphate represented by the following formula (1) positive electrode active material for a lithium secondary battery. [Formula 1] Li _x M _y M ' _z PO _4-w B _w Wherein M and M 'are independently of each other consisting of Fe, Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Mo, Ti, Zn, Al, Ga, Mg, B, and combinations thereof An element selected from the group, B is an element selected from the group consisting of F, S, and combinations thereof, 0 <x≤1, 0 <y≤1, 0 <z≤1, 0 <x + y + z ≦ 2 and 0 ≦ w ≦ 0.5) The method of claim 2, The lithium metal phosphate is a lithium iron phosphate positive active material for a lithium secondary battery. The method of claim 3, The lithium iron phosphate is a positive electrode active material for a lithium secondary battery that is a compound selected from the group consisting of the following formulas 2 to 5, and combinations thereof. [Formula 2] LiFe _1-a A _a PO ₄ [Formula 3] Li _1-a A _a FePO ₄ [Formula 4] LiFe _1-a A _a PO _4-z B _z [Formula 5] Li _1-a A _a FePO _4-z B _z (In Formulas 2 to 5, A is selected from the group consisting of Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Mo, Ti, Zn, Al, Ga, Mg, B, and combinations thereof. Element, B is an element selected from the group consisting of F, S, and combinations thereof, wherein 0 ≦ a <1, 0.01 ≦ z ≦ 0.5) The method of claim 1, The lithium composite metal oxide having the nanowire shape has a diameter of 1 to 50nm positive electrode active material for a lithium secondary battery. The method of claim 1, The average length of the lithium composite metal oxide having a nanowire shape is 1 to 100㎛ positive electrode active material for a lithium secondary battery. A cathode active material for a lithium secondary battery having a hollow spherical particle shape and containing a lithium composite metal oxide capable of intercalation and deintercalation of lithium. The method of claim 7, wherein The lithium composite metal oxide is a lithium metal phosphate represented by the following formula (1) positive electrode active material for a lithium secondary battery. [Formula 1] Li _x M _y M ' _z PO _4-w B _w Wherein M and M 'are independently of each other consisting of Fe, Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Mo, Ti, Zn, Al, Ga, Mg, B, and combinations thereof An element selected from the group, B is an element selected from the group consisting of F, S, and combinations thereof, 0 <x≤1, 0 <y≤1, 0 <z≤1, 0 <x + y + z ≦ 2 and 0 ≦ w ≦ 0.5) The method of claim 8, The lithium metal phosphate is a lithium iron phosphate positive active material for a lithium secondary battery. The method of claim 9, The lithium iron phosphate is a positive electrode active material for a lithium secondary battery that is a compound selected from the group consisting of the following formulas 2 to 5, and combinations thereof. [Formula 2] LiFe _1-a A _a PO ₄ [Formula 3] Li _1-a A _a FePO ₄ [Formula 4] LiFe _1-a A _a PO _4-z B _z [Formula 5] Li _1-a A _a FePO _4-z B _z (In Formulas 2 to 5, A is selected from the group consisting of Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Mo, Ti, Zn, Al, Ga, Mg, B, and combinations thereof. Element, B is an element selected from the group consisting of F, S, and combinations thereof, wherein 0 ≦ a <1, 0.01 ≦ z ≦ 0.5) The method of claim 7, wherein The particle size of the lithium composite metal oxide having a hollow spherical particle shape therein is 200nm to 1㎛ positive electrode active material for a lithium secondary battery. The method of claim 7, wherein Wherein the difference between the outer diameter and the inner diameter of the lithium composite metal oxide having a hollow spherical particle shape is 10 to 200nm positive electrode active material for a lithium secondary battery. A lithium secondary battery comprising the positive electrode active material according to any one of claims 1 to 12.

Images