WO2012141503A2 - Positive electrode active material, method for preparing same, and positive electrode and lithium battery using same - Google Patents

Abstract

Provided is a positive electrode active material, comprising: a core containing a material having an olivine structure; and a carbon-based coating layer formed on at least a portion of the surface of the core, wherein the carbon-based coating layer contains one or more selected from a group consisting of a conductive metal material and the non-metal heterogeneous elements of groups 15 to 17 of the periodic table of the elements. Also provided are a method for preparing the positive electrode active material, and an active electrode and a lithium battery using the positive electrode active material.

Description

Cathode active material, method for manufacturing the same, cathode and lithium battery employing the same

A positive electrode active material, a manufacturing method thereof, and a positive electrode and a lithium battery employing the same.

In order to meet miniaturization and high performance of various devices, miniaturization and weight reduction of lithium batteries have become important. In addition, the cycle characteristics of the lithium battery at room temperature and high temperature are also important for application in fields such as electric vehicles.

Various positive electrode active materials have been studied to implement lithium batteries that meet the above applications.

The olivine positive electrode active material is excellent in high temperature stability as LiCoO ₂ as a phosphate.

Among the olivine-based positive electrode active materials, LiFePO ₄ is structurally stable without structural change during charge and discharge, and does not have side reactions such as oxygen generation and is inexpensive. However, LiFePO ₄ has low conductivity and low energy capacity .

Therefore, there is a need for a method capable of improving the conductivity of the olivine-based positive electrode active material.

One aspect is to provide a positive electrode active material having improved conductivity.

Another aspect is to provide a method for producing the cathode active material.

Another aspect is to provide a positive electrode including the positive electrode active material.

Another aspect is to provide a lithium battery employing the positive electrode.

According to one side

A core comprising a material having an olivine structure; And

It includes a carbon-based coating layer formed on at least a portion of the core surface,

Provided is a cathode active material including one or more carbon-based coating layers selected from the group consisting of conductive metal materials and nonmetallic hetero elements belonging to Groups 15 to 17 of the Periodic Table of the Elements.

According to the other side

Preparing a mixture by mixing a material having an olivine structure, a carbon precursor, and optionally one or more precursors selected from the group consisting of nonmetallic hetero elements and conductive metal materials belonging to Groups 15-17 of the Periodic Table of Elements; And

It is provided with a method for producing a positive electrode active material comprising a; firing the mixture in an inert atmosphere.

According to another aspect, a cathode including the cathode active material is provided.

According to another aspect, there is provided a lithium battery employing the positive electrode.

According to one aspect, by including a cathode active material with improved conductivity, high rate characteristics of a lithium battery may be improved.

1 is a transmission electron microscope (TEM) image of a cathode active material prepared in Example 3. FIG.

2 is a scanning electron microscope (SEM) image of the cathode active material prepared in Example 3. FIG.

3 is an EDAX spectrum of the cathode active material prepared in Example 3. FIG.

4 is a Nyquist plot of the impedance measurement results of the cathode active materials prepared in Examples 1 and 3. FIG.

5 is a schematic diagram of a lithium battery according to an exemplary embodiment.

Hereinafter, a cathode active material, a method of manufacturing the same, and a cathode and a lithium battery including the same according to exemplary embodiments will be described in more detail.

In one embodiment, a cathode active material includes a core including a material having an olivine structure; And a carbon-based coating layer formed on at least a portion of the core surface, wherein the carbon-based coating layer includes at least one selected from the group consisting of a conductive metal material and a nonmetallic hetero element belonging to Groups 15 to 17 of the Periodic Table of the Elements. The cathode active material may have improved conductivity.

The reason why the positive electrode active material has improved conductivity will be described in more detail below, but the following description is provided to assist the understanding of the present invention, and is not intended to limit the scope of the present invention in any intention.

For example, the carbon-based coating layer formed on the surface of the core including the material having the olivine structure may have high conductivity, robustness, and excellent thermal stability by additionally including a conductive metal material and / or a nonmetallic dissimilar element. . Therefore, the surface conductivity of the material core having the olivine structure can be improved.

In the positive electrode active material, the nonmetallic dissimilar element may be at least one selected from the group consisting of P, S, F, Cl, Br, I, and O. For example, the carbon-based coating layer may include one or more substituents and / or ions selected from the group consisting of PO ₄ , SO ₄ , F, Cl, Br, and I, but are not necessarily limited thereto. As the non-metallic dissimilar elements other than carbon and metal, any one capable of improving the conductivity of the carbon-based coating layer is possible.

In addition, the material having the olivine structure may also include at least one of the conductive metal material and the nonmetallic dissimilar element.

In the positive electrode active material, the content of the nonmetallic dissimilar element may be 0.05 to 5% by weight based on the total weight of the positive electrode active material. For example, the content of the nonmetallic dissimilar element may be 5 to 50000 ppm based on the total weight of the positive electrode active material. If the content of the non-metallic dissimilar element is too low, high rate characteristics may be lowered. If the content of the non-metallic dissimilar element is too high, discharge capacity may be reduced.

In the cathode active material, the conductive metal material may be at least one selected from the group consisting of alkali metals, alkaline earth metals, transition metals, metalloids, and metals belonging to groups 13 to 15 of the periodic table of the elements. For example, the conductive metal material may be at least one selected from the group consisting of Ni, Co, Fe, Mo, Cr, B, Al, Ga, Si, Sn, Na, K, Mg, and Ca, but is not limited thereto. Also, any metal material capable of improving conductivity of the cathode active material is possible.

The content of the conductive metal material in the positive electrode active material may be 0.1 to 10% by weight of the total weight of the positive electrode active material. If the content of the conductive metal material is too low, the conductivity of the positive electrode active material may be lowered. If the content of the conductive metal material is too high, the discharge capacity may be reduced.

In the cathode active material, an average particle diameter of the conductive metal material may be 0.1 nm to 100 nm. For example, the average particle diameter of the conductive metal material may be 0.5 nm to 50 nm. For example, the average particle diameter of the conductive metal material may be 1 nm to 10 nm. The conductive metal material may be a particulate powder. If the average particle diameter of the conductive metal material is too small, an increase in electrode volume may occur due to the lower density of the metal material during electrode production, and thus the capacity per volume may be reduced. If the average particle diameter of the conductive metal material is too large, the electrode is homogeneous. One slurry can be difficult to form.

The carbon-based coating layer covering the conductive metal material in the cathode active material may be a carbon film that is a fired product of a carbon source such as glucose. The carbon source is not particularly limited as long as it can provide a carbon film by firing in the art. For example, the carbon source may be a monomer, oligomer, natural polymer, synthetic polymer, or the like. For example, the carbon source may be glucose, sucrose, starch, oligosaccharide, polyoligosaccharide, fructose, cellulose, polymer of furfuryl alcohol, block copolymer of ethylene and ethylene oxide, vinyl resin, cellulose resin, phenolic It may be at least one selected from the group consisting of resin, pitch resin and tar resin. In addition, various natural materials may also be used. For example, cotton wool, paper, textiles, wood, pollen, sugar beet, grass, insect wings, egg shells, hair, squid bones, chitin, algae, sea urchins and the like can also be used.

In the cathode active material, the carbon-based coating layer including the conductive metal material and / or the nonmetallic heterogeneous element belonging to Groups 15 to 17 of the Periodic Table of the Elements may have a crystal spacing d ₀₀₂ of 3.45 Å or more or amorphous. In addition, the gap d ₀₀₂ between the crystal planes of the carbon-based coating layer may be composed of low crystalline carbon or amorphous carbon of 3.45 kPa to 3.70 kPa.

When the carbon-based coating layer has a high crystallinity, it may act as a kind of graphite and may react with the electrolyte at the surface. The low crystalline or amorphous carbon film can achieve high charge and discharge efficiency because the carbon film does not react with the electrolyte during charging and discharging, thereby preventing decomposition of the electrolyte.

In addition, the carbon-based coating layer is so close that it blocks the contact between the core and the electrolyte solution can prevent the reaction between the electrolyte and the core. That is, the carbon film may act as a reaction prevention layer to block contact between the electrolyte and the material having the olivine structure. The average thickness of the carbon-based coating layer in the positive electrode active material may be 1 nm to 5 ㎛. For example, the thickness of the carbon-based coating layer may be 2 nm to 100 nm. If the average thickness is less than 1 nm, conductivity may decrease. If the average thickness is more than 20 μm, the density of the positive electrode active material may decrease. The thickness of the carbon-based coating layer is best maintained uniformly over the entire area around the core, but there may be a dispersion of the thickness or may be coated only on a portion of the core.

In the cathode active material, an average particle diameter of the core including the material having the olivine structure may be 10 nm to 20 μm. For example, the average particle diameter of the core may be 50 nm to 10 μm. For example, the average particle diameter of the core may be 50 nm to 1000 nm. The core may be a particulate powder. If the average particle diameter of the core is less than 10 nm, a problem may occur in the capacity implementation, and if the average particle diameter of the core is more than 20 μm, a problem may occur in the diffusion of lithium.

In the positive electrode active material, a material having the olivine structure may be represented by Formula 1 below:

<Formula 1>

Li _x Me _y M _z PO _4-d X _d

Wherein 0.9 ≦ x ≦ 1.1, 0.9 ≦ y ≦ 1.1, 0 ≦ z ≦ 0.2, 0 ≦ d ≦ 0.2; Me is at least one selected from the group consisting of Fe, Mn, Ni and Co; M is one or more selected from the group consisting of Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al and Si; X is at least one selected from the group consisting of S and F.

For example, the material having the olivine structure may be at least one selected from the group consisting of LiFePO ₄ , LiFe _1-a Mn _a PO ₄ (0 <a <1) and LiMnPO ₄ .

According to another exemplary embodiment, a method of manufacturing a cathode active material is performed by mixing one or more precursors selected from the group consisting of a material having an olivine structure, a carbon precursor, and optionally a nonmetallic hetero element and a conductive metal material belonging to Groups 15 to 17 of the Periodic Table Preparing a mixture; And calcining the mixture in an inert atmosphere. By the firing, a carbon-based coating layer is formed on part or all of the surface of the material having the olivine structure.

The carbon precursor may be a complex of a hydrocarbon and a metal salt. For example, it may include one or more selected from the group consisting of glucophosphate disodium salt, glucophosphate magnesium salt, and glucophosphate iron salt. That is, the carbon precursor includes functional groups having ion conductivity and / or conductivity in precursor molecules. Therefore, by firing the carbon precursor, the carbon-based coating layer may include a component having ion conductivity and / or conductivity, thereby improving conductivity.

In the production method, the carbon precursor may further include a conventional general carbon precursor. In conventional general carbon precursors, for example, the carbon source may be a monomer, oligomer, natural polymer, synthetic polymer, or the like. For example, the carbon source may be glucose, sucrose, starch, oligosaccharide, polyoligosaccharide, fructose, cellulose, polymer of furfuryl alcohol, block copolymer of ethylene and ethylene oxide, vinyl resin, cellulose resin, phenolic It may be at least one selected from the group consisting of resin, pitch resin and tar resin. In addition, various natural materials may also be used. For example, cotton wool, paper, textiles, wood, pollen, sugar beet, grass, insect wings, egg shells, hair, squid bones, chitin, algae, sea urchins and the like can also be used.

In the preparation method, the precursor of the nonmetallic heterogeneous element belonging to Groups 15 to 17 of the periodic table of the elements is phosphoric acid (H ₃ PO ₄ ), ammonium chloride (NH ₄ Cl) and sulfuric acid (H ₂ SO ₄ ) It may be one or more selected from, but is not limited to these, any precursor that can leave the ion conductive and / or conductive components in the carbon-based coating layer by firing in the art.

In the manufacturing method, the precursor of the conductive metal material may be one or more selected from the group consisting of FeCl ₂ , MgCl ₂ , NiCl _2, and CoCl ₂ , but is not limited thereto, and forms a conductive metal material by firing in the art. Any precursor that can be made is possible.

In the cathode active material manufacturing method, the material having the olivine structure may be represented by the following formula (1):

<Formula 1>

Li _x Me _y M _z PO _4-d X _d

Wherein 0.9 ≦ x ≦ 1.1, 0.9 ≦ y ≦ 1.1, 0 ≦ z ≦ 0.2, 0 ≦ d ≦ 0.2; Me is at least one selected from the group consisting of Fe, Mn, Ni and Co; M is one or more selected from the group consisting of Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al and Si; X is at least one selected from the group consisting of S and F.

For example, the material having the olivine structure may be at least one selected from the group consisting of LiFePO ₄ , LiFe _1-a Mn _a PO ₄ (0 <a <1) and LiMnPO ₄ .

In the manufacturing method, the firing temperature may be 500 to 1000 ° C., but is not necessarily limited to the above temperature range, and may be appropriately selected within a range capable of achieving the object of the present invention. For example, the temperature may be 500 ~ 800 ℃. For example, the temperature may be 600 to 750 ° C. If the firing temperature is too low, the crystallinity of the fired product may be insufficient or the specific surface area may be large, and the tap density may be low. In addition, the improvement of crystallinity may not be sufficient and the material may not be sufficiently stabilized, such that discharge capacity, life characteristics, and the like may be lowered. If the firing temperature is too high, phase decomposition may occur. Therefore, the cathode active material having further improved physical properties at a firing temperature of a predetermined range in the cathode active material manufacturing method may be manufactured.

The firing time may be 1 to 10 hours. For example, the firing time may be 1 to 20 hours. For example, the firing time may be 3 to 15 hours. If the firing time is too short, the crystallinity of the fired product may be insufficient or the specific surface area may be large, and the tap density may be low. In addition, the improvement of crystallinity may not be sufficient and the material may not be sufficiently stabilized, such that discharge capacity, life characteristics, and the like may be lowered. If the firing time is too long, manufacturing efficiency may decrease. Therefore, the cathode active material may be manufactured having more improved physical properties in a predetermined range of firing time in the cathode active material manufacturing method.

According to another embodiment, the positive electrode includes the positive electrode active material described above. For example, the positive electrode may be manufactured by a method in which a positive electrode active material composition including the positive electrode active material and a binder is molded into a predetermined shape or the positive electrode active material composition is applied to a current collector such as copper foil or aluminum foil. Can be.

Specifically, a cathode active material composition in which the cathode active material, the conductive material, the binder, and the solvent are mixed is prepared. The positive electrode active material composition is directly coated on a metal current collector to prepare a positive electrode plate. Alternatively, the cathode active material composition may be cast on a separate support, and then a film peeled from the support may be laminated on a metal current collector to prepare a cathode plate. The anode is not limited to the above enumerated forms and may be in any form other than the foregoing.

Carbon black, graphite fine particles and the like may be used as the conductive material, but is not limited thereto, and any conductive material may be used as long as it can be used as a conductive material in the art. For example, graphite, such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder and nickel powder; Conductive whiskeys 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 may be vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene and mixtures thereof, or styrene butadiene rubber polymers. It may be used, but is not limited to these may be used as long as it can be used as a binder in the art.

As the solvent, N-methylpyrrolidone, acetone, or water may be used, but is not limited thereto, and any solvent may be used as long as it can be used in the art.

The content of the positive electrode active material, the conductive material, the binder, and the solvent is at a level commonly used in lithium batteries. At least one of the conductive material, the binder, and the solvent may be omitted according to the use and configuration of the lithium battery.

According to another embodiment, a lithium battery employs a cathode including the cathode active material. The lithium battery may be manufactured by the following method.

First, a positive electrode is manufactured according to the above positive electrode manufacturing method.

Next, a negative electrode active material composition is prepared by mixing a negative electrode active material, a conductive material, a binder, and a solvent. The negative electrode active material composition is directly coated and dried on a metal current collector to prepare a negative electrode plate. Alternatively, the negative electrode active material composition may be cast on a separate support, and then a film peeled from the support may be laminated on a metal current collector to prepare a negative electrode plate.

The negative electrode active material is generally used in this field, and is not particularly limited. More specifically, lithium metal, a metal alloyable with lithium, a transition metal oxide, a transition metal sulfide, a material capable of doping and undoping lithium, Materials capable of reversibly inserting and detaching lithium ions, conductive polymers, and the like may be used.

The transition metal oxide may be, for example, tungsten oxide, molybdenum oxide, titanium oxide, lithium titanium oxide, vanadium oxide, lithium vanadium oxide, or the like. For example, Group I metal compounds such as CuO, Cu ₂ O, Ag ₂ O, CuS, CuSO ₄ , Group IV metal compounds such as TiS ₂ , SnO, V ₂ O ₅ , V ₆ O ₁₂ , VO _x (0 <x <6), Group V metal compounds such as Nb ₂ O ₅ , Bi ₂ O ₃ , Sb ₂ O ₃ , Group VI such as CrO ₃ , Cr ₂ O ₃ , MoO ₃ , MoS ₂ , WO ₃ , SeO ₂ Group VII metal compounds such as metal compounds, MnO ₂ , Mn ₂ O ₃ , Fe ₂ O ₃ , FeO, Fe ₃ O ₄ , Ni ₂ O ₃ , Group VIII metal compounds such as NiO, CoO ₃ , CoO, and general formula Li _x MN _y X ₂ (M, N is a metal of Groups I to VIII, X is oxygen, sulfur, 0.1≤x≤2, 0≤y≤1) and the like, for example, Li _y TiO ₂ ( Lithium titanate such as 0 ≦ _y ≦ 1), Li _{4 + y} Ti ₅ O ₁₂ (0 ≦ _y ≦ 1), Li _{4 + y} Ti ₁₁ O ₂₀ (0 ≦ _y ≦ 1), or the like.

Materials capable of doping and undoping lithium include, for example, Si, SiO _x (0 <x <2), Si-Y alloys (wherein Y is an alkali metal, an alkaline earth metal, an element of Group 13, an element of Group 14, and a transition). Metals, rare earth elements or combinations thereof, not Si), Sn, SnO ₂ , Sn-Y (wherein Y is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, or a combination thereof) Combination element, not Sn), and at least one of them and SiO ₂ may be mixed and used. As the element Y, Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, or a combination thereof.

As a material capable of reversibly inserting and detaching lithium ions, a carbon-based material may be used as long as it is a carbon-based negative electrode active material generally used in lithium batteries. For example, crystalline carbon, amorphous carbon or mixtures thereof. The crystalline carbon is, for example, amorphous, plate-like, flake, spherical or fibrous natural graphite; Or artificial graphite, and the amorphous carbon may be, for example, soft carbon (low temperature calcined carbon) or hard carbon, mesophase pitch carbide, calcined coke, or the like.

The conductive polymer may be a disulfide-based, polyethlyenedioxythiophene (PEDOT), polypyrrole, polyaniline, polyparaphenylene, polyacetylene, polyacene-based material, or the like.

In the negative electrode active material composition, the same conductive material, binder, and solvent may be used as the positive electrode active material composition. Meanwhile, a plasticizer may be further added to the cathode active material composition and / or the anode active material composition to form pores inside the electrode plate.

The amount of the negative electrode active material, the conductive material, the binder, and the solvent is at a level commonly used in lithium batteries. At least one of the conductive material, the binder, and the solvent may be omitted according to the use and configuration of the lithium battery.

Next, a separator to be inserted between the positive electrode and the negative electrode is prepared. The separator may be used as long as it is commonly used in lithium batteries. A low resistance to the ion migration of the electrolyte and excellent in the ability to hydrate the electrolyte can be used. For example, it is selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE) or a combination thereof, and may be in a nonwoven or woven form. For example, a rollable separator such as polyethylene or polypropylene may be used for a lithium ion battery, and a separator having excellent organic electrolyte impregnation ability may be used for a lithium ion polymer battery. For example, the separator may be manufactured according to the following method.

A separator composition is prepared by mixing a polymer resin, a filler, and a solvent. The separator composition may be directly coated and dried on the electrode to form a separator. Alternatively, after the separator composition is cast and dried on a support, a separator film separated from the support may be laminated on the electrode to form a separator.

The polymer resin used to manufacture the separator is not particularly limited, and any materials used for the binder of the electrode plate may be used. For example, vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate or mixtures thereof and the like can be used.

Next, the electrolyte is prepared.

For example, the electrolyte may be an organic electrolyte. The organic electrolyte may be prepared by dissolving lithium salt in an organic solvent.

The organic solvent may be used as long as it can be used as an organic solvent in the art. For example, propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate , Benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N, N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide , Dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether or a mixture thereof.

Any lithium salt may be used as long as it can be used as a lithium salt in the art. For example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₂ , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ) (where x and y are natural numbers), LiCl, LiI, or a mixture thereof.

In addition, the electrolyte may be a solid electrolyte such as an organic solid electrolyte or an inorganic solid electrolyte. When a solid electrolyte is used, the solid electrolyte may also serve as a separator.

Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyedgetion lysine, polyester sulfides, polyvinyl alcohols, polyvinylidene fluorides, Polymers containing ionic dissociating groups and the like can be used.

The inorganic solid electrolyte may be, for example, boron oxide, lithium oxynitride, and the like, but is not limited thereto. Any inorganic solid electrolyte may be used as the solid electrolyte in the art. The solid electrolyte may be formed on the negative electrode by sputtering or the like. For example, 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- Nitrides, halides, sulfates, and the like of Li, such as LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ , may be used.

As shown in FIG. 1, the lithium battery 1 includes a positive electrode 3, a negative electrode 2, and a separator 4. The positive electrode 3, the negative electrode 2, and the separator 4 described above are wound or folded to be accommodated in the battery case 5. Subsequently, an organic electrolyte is injected into the battery case 5 and sealed with a cap assembly 6 to complete the lithium battery 1. The battery case may be cylindrical, rectangular, thin film, or the like. For example, the lithium battery may be a thin film battery. The lithium battery may be a lithium ion battery.

A separator may be disposed between the positive electrode and the negative electrode to form a battery structure. The battery structure is stacked in a bi-cell structure, and then impregnated in an organic electrolyte, and the resultant is accommodated in a pouch and sealed to complete a lithium ion polymer battery.

In addition, a plurality of battery structures are stacked to form a battery pack connected in series, and the battery pack may be used in any device requiring high capacity and high power. For example, it can be used in notebooks, smartphones, power tools, electric vehicles and the like.

In particular, the lithium battery has excellent high temperature cycling characteristics and high temperature stability, and thus is suitable for medium and large energy storage devices. For example, it is suitable as a power source of an electric vehicle (EV). For example, it is suitable as a power source of a hybrid electric vehicle such as a plug-in hybrid electric vehicle (PHEV).

The present invention is described in more detail through the following examples and comparative examples. However, the examples are provided to illustrate the present invention, and the scope of the present invention is not limited only to these examples.

(Manufacture of Olivine-Based Materials)

Preparation Example 1

After 1 mol H ₃ PO ₄ and 1 mol FeSO ₄ were stirred in distilled water, 1 mol NH ₃ and 0.5 mol H ₂ O ₂ were added to form amorphous FePO ₄ · 2H ₂ O.

(Manufacture of Anode Active Material)

Example 1

21.994 g of FePO ₄ .2H ₂ O, 5.199 g of LiOH.H ₂ O, and 1.275 g of glucose-6-phosphate magnesium salt were prepared in 45 g of ethylene glycol at room temperature. After addition and mixing, the cathode active material was prepared by sintering at 600 ° C. for 4 hours in an argon gas atmosphere.

Example 2

21.994 g of FePO ₄ .2H ₂ O, 5.199 g of LiOH.H ₂ O, 0.067 g of phosphoric acid (H ₃ PO ₄ ) and 0.882 g of glucose were added and mixed to 45 g of ethylene glycol at room temperature. After sintering at 600 ° C. for 4 hours in an argon gas atmosphere, a cathode active material was prepared.

Example 3

21.994 g of FePO ₄ .2H ₂ O prepared in Preparation Example 1, 5.199 g of LiOH.H ₂ O, 0.629 g of NH ₄ Cl and 0.882 g of glucose were added and mixed with ethylene glycol at room temperature, followed by 4 at 600 ° C. The cathode active material was prepared by sintering in an argon gas atmosphere for an hour.

Example 4

21.994 g of FePO ₄ .2H ₂ O, 5.199 g of LiOH.H ₂ O, 0.061 g of H ₂ SO ₄ and 0.882 g of glucose were added and mixed with ethylene glycol at room temperature at 600 ° C. The cathode active material was prepared by sintering in an argon gas atmosphere for 4 hours.

Example 5

21.994 g of FePO ₄ .2H ₂ O prepared in Preparation Example 1, 5.199 g of LiOH.H ₂ O, 0.067 g of phosphoric acid (H ₃ PO ₄ ), 0.056 g of MgCl ₂ and 0.882 g of glucose were added to ethylene glycol at room temperature. After addition and mixing, the cathode active material was prepared by sintering at 600 ° C. for 4 hours in an argon gas atmosphere.

Example 6

21.994 g of FePO ₄ .2H ₂ O prepared in Preparation Example 1, 5.199 g of LiOH.H ₂ O, 0.067 g of phosphoric acid (H ₃ PO ₄ ), 0.074 g of FeCl ₂ , and 0.882 g of glucose were added to ethylene glycol at room temperature. After addition and mixing, the cathode active material was prepared by sintering at 600 ° C. for 4 hours in an argon gas atmosphere.

Example 7

21.994 g of FePO ₄ .2H ₂ O prepared in Preparation Example 1, 5.199 g of LiOH.H ₂ O, 0.056 g of MgCl ₂ and 0.882 g of glucose were added to ethylene glycol at room temperature, followed by mixing for 4 hours at 600 ° C. Sintered in an argon gas atmosphere to prepare a positive electrode active material.

Example 8

21.994 g of FePO ₄ .2H ₂ O prepared in Preparation Example 1, 5.199 g of LiOH.H ₂ O, 0.074 g of FeCl ₂ and 0.882 g of glucose were added to ethylene glycol at room temperature, followed by mixing for 4 hours at 600 ° C. Sintered in an argon gas atmosphere to prepare a positive electrode active material.

Comparative Example 1

21.994 g of FePO ₄ .2H ₂ O prepared in Preparation Example 1, 5.199 g of LiOH.H ₂ O, and 0.882 g of glucose were added to ethylene glycol at room temperature, followed by mixing and argon gas atmosphere at 600 ° C. for 4 hours. The cathode active material was prepared by sintering at.

(Manufacture of Anode and Lithium Battery)

Example 9

The positive electrode active material powder synthesized in Example 1 and the carbon conductive material (Super P) were uniformly mixed at a weight ratio of 82:10, and then PVDF (polyvinylidene fluoride) binder solution was added to the active material: carbon conductive agent: binder = 82: 10 The slurry was prepared to have a weight ratio of 8: 8. The slurry was applied using a doctor blade to a 100 μm gap on an aluminum current collector and dried at 120 ° C. to prepare a positive electrode plate.

Using the positive electrode plate, a lithium metal is used as a counter electrode, and a solution in which a PE separator and 1.3 M LiPF ₆ are dissolved in EC (ethylene carbonate) + DEC (diethylene carbonate) (3: 7 volume ratio) is used as an electrolyte. 2032 standard coin cell was used.

Examples 10-16

Except for using the positive electrode active material prepared in Examples 2 to 8 instead of the positive electrode active material prepared in Example 1 was prepared in the same manner as in Example 9.

Comparative Example 2

Except for using the positive electrode active material of Comparative Example 1 in place of the positive electrode active material prepared in Example 1 was prepared in the same manner as in Example 10.

Evaluation Example 1 SEM, TEM and EDAX Evaluation

SEM images, TEM images, and energy-dispersive X-ray (EDAX) spectra of the cathode active materials prepared in Example 3 were measured.

As shown in the TEM image of FIG. 1, a carbon-based coating layer was formed on the olivine core. The thickness of the coating layer was about 5 nm.

As shown in the SEM image of FIG. 2, the particle size of the cathode active material was about 200 nm.

The presence of carbon and chlorine atoms was detected as shown in the EDAX spectrum of FIG. 3. That is, the carbon-based coating layer is formed on the surface of the cathode active material particles, it is determined that Cl atoms are present in the carbon-based coating layer.

Evaluation Example 2: XRD Experiment

The lattice size of LiFePO ₄ was calculated from XRD diffraction patterns for the positive electrode active material powders prepared in Examples 1 to 8 and Comparative Example 1.

As shown in Table 1 below, the cathode active material of Examples reduced the lattice size compared to Comparative Example 1. That is, since the lattice size is reduced by the addition of the conductive metal material and / or the nonmetallic dissimilar element, it is determined that the conductive metal material and / or the nonmetallic dissimilar element also exist in the olivine core of the cathode active material.

Table 1 a [Å] b [Å] c [Å] V [Å ³ ] Example 1 10.301 5.991 4.684 289.065 Example 2 10.305 5.992 4.686 289.349 Example 3 10.315 5.995 4.690 290.022 Example 4 10.320 5.998 4.692 290.432 Example 5 10.298 5.989 4.684 288.884 Example 6 10.299 5.991 4.683 288.947 Example 7 10.325 6.004 4.693 290.925 Example 8 10.326 6.005 4.693 291.002 Comparative Example 1 10.336 6.006 4.695 291.456

In Table 1, a, b, and c are the lengths of each axis in an orthorhombic system lattice structure, and V = a × b × c.

Evaluation Example 3: Impedance Measurement

Impedance was measured for the cathode active materials prepared in Example 1 and Comparative Example 1, and the results are shown in FIG. 4.

The coin cell to which the cathode active materials prepared in Example 1 and Comparative Example 1 were applied was measured by a 2-probe method using PARSTAT 2273 for impedance analysis. The frequency range was 10 ⁴ Hz to 10 MHz. The Nyquist plot obtained from the impedance measurement is shown in FIG. 4.

As shown in FIG. 4, the cathode active material of Example 1 has improved impedance compared to the cathode active material of Comparative Example 1, thereby improving conductivity.

Evaluation Example 4: High Rate Charge / Discharge Experiment

After charging and discharging the coin cells prepared in Examples 9 to 16 and Comparative Example 2 with a constant current of 0.1 C-rate in a voltage range of 2.0 to 4.0 V relative to lithium metal at room temperature, 0.1 C- in the 10th cycle. After charging with a constant current of rate, the discharge capacity when the discharge at the constant current of 0.1 C-rate, 1.0 C-rate, 5.0 C-rate and 10.0 C-rate, respectively, are shown in Table 2 below.

TABLE 2 Discharge Capacity at 0.1 C-rate [mAh / g] Discharge Capacity at 1.0 C-rate [mAh / g] Discharge Capacity at 5 C-rate [mAh / g] Discharge Capacity at 10 C-rate [mAh / g] Example 9 162 156 135 120 Example 10 165 159 130 116 Example 11 163 150 120 100 Example 12 163 149 115 90 Example 13 167 160 137 125 Example 14 165 156 133 121 Example 15 162 152 95 80 Example 16 163 151 90 75 Comparative Example 2 160 140 70 40

As shown in Table 2, the lithium batteries of Examples 9 to 16 significantly improved high rate characteristics compared to the lithium batteries of Comparative Example 2.

Evaluation Example 5: Lifespan Characteristic Experiment

The coin cell prepared in Examples 9 to 16 and Comparative Example 2 was charged and discharged at a constant current of 1.0 C-rate up to 100 cycles in a voltage range of 2.0 to 4.0 V relative to lithium metal at room temperature, and then the discharge capacity was measured. Capacity retention rate was calculated from Equation 1 and the results are shown in Table 3 below.

<Equation 1>

Capacity retention rate [%] = [100th cycle discharge capacity / 1st cycle discharge capacity] × 100

TABLE 3 Capacity retention rate [%] Example 9 99 Example 10 98 Example 11 97 Example 12 90 Example 13 99 Example 14 99 Example 15 90 Example 16 89 Comparative Example 1 80

As shown in Table 2, the lithium batteries of Examples 9 to 16 at high rates have improved life characteristics compared to the lithium batteries of Comparative Example 2.

Claims (20)

A core comprising a material having an olivine structure; And It includes a carbon-based coating layer formed on at least a portion of the core surface, The carbon-based coating layer comprises a conductive metal material and at least one selected from the group consisting of non-metallic heterogeneous elements belonging to Groups 15 to 17 of the Periodic Table of the Elements. The cathode active material of claim 1, wherein the nonmetallic dissimilar element is at least one selected from the group consisting of P, S, F, Cl, Br, I, and O. 3. The cathode active material of claim 1, wherein the carbon-based coating layer comprises at least one selected from the group consisting of PO ₄ , SO ₄ , F, Cl, Br, and I. 3. The cathode active material of claim 1, wherein the content of the nonmetallic dissimilar element is 0.05 to 5 wt% of the total weight of the active material. The cathode active material of claim 1, wherein the conductive metal material is at least one selected from the group consisting of alkali metals, alkaline earth metals, transition metals, metalloids, and metals belonging to groups 13 to 15 of the periodic table. The cathode active material of claim 1, wherein the conductive metal material is at least one selected from the group consisting of Ni, Co, Fe, Mo, Cr, B, Al, Ga, Si, Sn, Na, K, Mg, and Ca. The cathode active material of claim 1, wherein the content of the conductive metal material is 0.1 to 10 wt% of the total weight of the active material. The cathode active material according to claim 1, wherein the carbon-based coating layer is made of low crystalline carbon or amorphous carbon having an inter-crystal spacing d ₀₀₂ of 3.45 kPa or more. The cathode active material of claim 1, wherein the carbonaceous coating layer has an average thickness of 1 nm to 5 μm. The cathode active material of claim 1, wherein the core has an average particle diameter of 10 nm to 20 μm. The cathode active material of claim 1, wherein the material having the olivine structure is represented by Formula 1 below: <Formula 1> Li _x Me _y M _z PO _4-d X _d Wherein 0.9 ≦ x ≦ 1.1, 0.9 ≦ y ≦ 1.1, 0 ≦ z ≦ 0.2, 0 ≦ d ≦ 0.2; Me is at least one selected from the group consisting of Fe, Mn, Ni and Co; M is one or more selected from the group consisting of Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al and Si; X is at least one selected from the group consisting of S and F. The cathode active material according to claim 1, wherein the material having an olivine structure is at least one selected from the group consisting of LiFePO ₄ , LiFe _1-a Mn _a PO ₄ (0 <a <1) and LiMnPO ₄ . Preparing a mixture by mixing a material having an olivine structure, a carbon precursor, and optionally one or more precursors selected from the group consisting of nonmetallic hetero elements and conductive metal materials belonging to Groups 15-17 of the Periodic Table of Elements; And Calcining the mixture in an inert atmosphere. The method of claim 13, wherein the carbon precursor comprises at least one selected from the group consisting of glucophosphate disodium salt, glucophosphate magnesium salt, and glucophosphate iron salt. The method of claim 13, wherein the precursor of the non-metallic heterogeneous element belonging to Group 15 to 17 of the periodic table of the elements is phosphoric acid (H ₃ PO ₄ ), ammonium chloride (NH ₄ Cl), sulfuric acid (H ₂ SO ₄ ) Cathode active material manufacturing method comprising one or more selected from the group consisting of. The method of claim 13, wherein the precursor of the conductive metal material comprises at least one selected from the group consisting of FeCl ₂ , MgCl ₂ , NiCl _2, and CoCl ₂ . The method of claim 13, wherein the material having the olivine structure is represented by Formula 1 below: <Formula 1> Li _x Me _y M _z PO _4-d X _d Wherein 0.9 ≦ x ≦ 1.1, 0.9 ≦ y ≦ 1.1, 0 ≦ z ≦ 0.2, 0 ≦ d ≦ 0.2; Me is at least one selected from the group consisting of Fe, Mn, Ni and Co; M is one or more selected from the group consisting of Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al and Si; X is at least one selected from the group consisting of S and F. The method of claim 13, wherein the firing temperature is 500 ° C. to 800 ° C., and the firing time is 1 to 10 hours. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 12. A lithium battery employing the positive electrode according to claim 19.

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