KR20150047274A - Negative electrode active material for rechargeable lithium battery, method for preparing the same and rechargeable lithium battery using the same - Google Patents

Abstract

The present invention relates to an anode active material for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery comprising the same. Provided is an anode active material for a carbon-metal complex type lithium secondary battery, which comprises: a core containing a flake graphite particle and a metal-based active material; and a ceramic coating layer placed on the surface of the core.

Description

TECHNICAL FIELD The present invention relates to a negative electrode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery including the same. BACKGROUND OF THE INVENTION [0001] The present invention relates to a negative active material for a lithium secondary battery,

A negative electrode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery comprising the same.

Recently, a lithium secondary battery, which is attracting attention as a power source for portable electronic devices, has a discharge voltage twice as high as that of a conventional battery using an alkaline aqueous solution, resulting in a high energy density.

The positive electrode active material of the lithium secondary battery is preferably made of lithium and a transition metal having a structure capable of intercalating lithium ions such as LiCoO ₂ , LiMn ₂ O ₄ , and LiNi _{1 -x} Co _x O ₂ (0 <x <1) Oxide is mainly used.

As the anode active material, various types of carbon-based materials including artificial graphite, natural graphite, and hard carbon capable of lithium insertion / desorption have been applied. Graphite among the carbon series is currently the most widely used.

However, recently, as the functions of portable electronic devices have been diversified and miniaturization and weight have been progressed, there has been a demand for higher capacity of lithium secondary batteries. Accordingly, the theoretical capacity of graphite used as a negative electrode active material of lithium secondary batteries is 372 mAh / g There is a growing interest in metal-based anode active material materials having a higher theoretical capacity.

Particularly, the silicon-based metal material is an active material having a theoretical capacity 10 times or more higher than that of graphite, and researches thereof are actively under way. However, due to the volume change caused by the volume expansion of the silicon particles generated during the charging process, cracks are generated and the life characteristics of the lithium secondary battery are deteriorated due to the decrease in conductivity between the active materials, the desorption from the electrode plate, and the continuous reaction with the electrolyte. Which is not yet commercialized.

A negative electrode active material for a lithium rechargeable battery of high capacity which has excellent lifetime characteristics by suppressing volume expansion and a method of manufacturing the same.

Further, there is a need to provide a lithium secondary battery having improved characteristics using such an anode active material.

In one embodiment of the present invention, a core comprising scaly graphite particles and a metal-based active material; And a ceramic coating layer disposed on the surface of the core. The present invention also provides a negative electrode active material for a lithium secondary battery, which is in the form of a carbon-metal composite.

The core may further comprise low-crystalline carbon.

The low crystalline carbon may be at least one selected from the group consisting of petroleum pitch, coal pitch, mesophase pitch, heavy oil, light oil, polyvinyl alcohol (PVA), polyvinyl chloride (PVC), sucrose, phenol resin, A furan resin, a furfuryl alcohol, a polyacrylonitrile, a cellulose, a styrene, a polyimide, an epoxy resin, a glucose, Or a combination thereof.

The content of the low-crystalline carbon may be 0.1 to 50% based on 100% by weight of the total active material.

The metal-based active material may be at least one selected from the group consisting of silicon, tin, aluminum, vanadium, magnesium, and antimony; An alloy of one or more of these; A compound selected from oxides, nitrides, carbides, or combinations of these metals; Or a combination thereof.

The scratched graphite particles may be natural graphite, artificial graphite, or a combination thereof.

The ceramic may be a metal oxide, a non-metal oxide, a composite metal oxide, a rare earth oxide, a compound containing a halogen group, an oxide produced from a ceramic precursor, or a combination thereof.

The ceramic precursor may be zirconia, aluminum, polycarbosilane, polysiloxane, polysilazane, or a combination thereof.

Said ceramic is _{SiO 2, Al 2 O 3,} Li 2 Ti 5 O 12, TiO 2, CeO 2, ZrO 2, BaTiO 3, Y 2 O 3, MgO, CuO, ZnO, AlPO 4, AlF, Si 3 N 4 , AlN, TiN, may be WC, SiC, TiC, MoSi _2, Fe ₂ O _3, GeO _2, Li ₂ O, MnO, NiO, zeolite, or a combination thereof.

The average particle size of the scratched graphite particles may be 3 to 100 탆.

The average particle size of the metal-based active material may be 0.03 to 20 탆.

The ceramic coating layer may include ceramic particles, and the average particle size of the ceramic particles may be 10 to 1000 nm.

The weight ratio of the flake graphite particles to the metal-based active material may be 60/40 to 99/1.

In another embodiment of the present invention, there is provided a method for producing a graphite core material, comprising the steps of: preparing a core material comprising scaly graphite particles and a metal-based active material; Mixing the prepared core material and assembling it into a spherical shape to prepare a core; And forming a ceramic coating layer on the surface of the core. The present invention also provides a method of manufacturing a negative electrode active material for a lithium secondary battery.

Preparing the core material comprising the flaky graphite particles and the metal-based active material, and preparing a core material including flake graphite particles, a metal-based active material, and low-crystalline carbon.

The step of preparing the core by mixing the prepared core materials into a spherical shape may be a mechanical mixing method.

The mechanical mixing method may be selected from the group consisting of rotor blade milling, mechanofusion milling, planetary milling, shape milling, vertical shape milling, Millimeter milling, high speed mixing, or a combination thereof.

The mechanical mixing method may be performed at a rotational speed of 500 to 20000 rpm.

The step of preparing the core by mixing the prepared core material and then assembling into a spherical shape may be a method of performing heat treatment in hydrogen, nitrogen, argon, or a mixed gas atmosphere thereof.

The step of mixing the prepared core material and assembling into a spherical shape to prepare a core may be performed at 600 to 1500 ° C.

The step of forming a ceramic coating layer on the surface of the core may be performed by a method of mechanically mixing the prepared core and ceramic particles.

The mechanical mixing method may be selected from the group consisting of rotor blade milling, ball milling, mechanofusion milling, shaker milling, planetary milling, such as attritor milling, disk milling, shape milling, vertical shape milling, nauta milling, nobilta milling, high speed mixing, Or a combination thereof.

The mechanical mixing method may be performed at a rotational speed of 500 to 7,000 rpm.

According to another embodiment of the present invention, there is provided a negative electrode comprising a negative electrode active material for a lithium secondary battery according to an embodiment of the present invention; anode; And an electrolyte.

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

It is possible to realize a high capacity lithium secondary battery having excellent lifetime characteristics by suppressing the volume expansion of the negative electrode active material.

1 is an exploded perspective view of a lithium secondary battery according to one embodiment.
FIG. 2 is a schematic cross-sectional view of a negative electrode active material for a lithium secondary battery in the form of a carbon-metal composite including a ceramic coating layer produced according to an embodiment.
3 is a scanning electron microscope (SEM) image of a negative electrode active material prepared according to Comparative Example 2. FIG.
FIG. 4 is a scanning electron microscope (SEM) image of a negative electrode active material prepared according to Example 1. FIG.
5 is a graph showing charge / discharge curves of the initial three cycles of the lithium secondary battery produced according to Example 1 and Comparative Example 2. FIG.
6 is a graph showing the capacity retention rate of the lithium secondary battery manufactured according to Example 1, Example 2, Comparative Example 1, and Comparative Example 2 according to charge / discharge life span.
7 is a graph showing swelling evaluation of a lithium secondary battery manufactured according to Example 1, Example 2, Comparative Example 1, and Comparative Example 2. FIG.

Hereinafter, embodiments of the present invention will be described in detail. However, it should be understood that the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

In the present specification, the average particle diameter means the particle diameter of D50. D50 is the particle size when the cumulative volume of the particles becomes 50% by volume in the small particle order.

In one embodiment of the present invention, a core comprising scaly graphite particles and a metal-based active material; And a ceramic coating layer disposed on the surface of the core. The present invention also provides a negative electrode active material for a lithium secondary battery, which is in the form of a carbon-metal composite.

Low-crystalline carbon may be additionally contained in the core including the scratched graphite particles and the metal-based active material.

FIG. 2 is a schematic cross-sectional view of a negative electrode active material for a lithium secondary battery according to an embodiment of the present invention.

Referring to FIG. 2, the anode active material according to an embodiment of the present invention may be in the state where the graphite particles and the low-crystallinity carbon are spheroidized. And the metal active material may be dispersed between the scratched graphite particles and the low-definition carbon. In addition, a ceramic coating layer may be placed on the surface of the spheroidized composite. However, the present invention is not limited thereto.

The weight ratio of the flake graphite particles to the metal-based active material may be 60/40 to 99/1. When such a range is satisfied, it is possible to realize the high capacity and long life of the lithium secondary battery by minimizing the particle damage and maintaining the electric conductivity at the time of charging and discharging.

The metal-based active material may be one selected from the group consisting of silicon, tin, aluminum, vanadium, magnesium, and antimony; An alloy of one or more of these; A compound selected from oxides, nitrides, carbides, or combinations of these metals; Or a combination thereof. Specifically, x may be an integer in the range of 0 < x < 2, and Q may be an alkali metal, an alkaline earth metal, a group 13 to 16 Group element, a transition metal, a rare earth element, or a combination thereof, and is not Si. Specific examples of the above-mentioned Q include Ti, V, Al, Sn, or a combination thereof. The most specific metal-based active material may be Si or an oxide thereof SiOx (0.1? X? 2).

The scratched graphite particles may be natural graphite, artificial graphite, or a combination thereof.

Low-crystalline carbon may be additionally contained in the core including the scaly graphite particles and the metal-based active material. In this case, the graphite particles and the metal-based active material can be bound to each other, . In addition, the irreversible reaction can be reduced during charging and discharging of the battery. Further, the electrical conductivity between the active material particles and the electrochemical characteristics with respect to the electrolyte can be improved by the low-crystalline carbon material. In addition, the volume expansion of the active material can be alleviated.

The low crystalline carbon material may be selected from the group consisting of petroleum pitch, coal pitch, mesophase pitch, heavy oil, light oil, polyvinyl alcohol (PVA), polyvinyl chloride (PVC), sucrose, phenol resin, furan resin, furfuryl alcohol, polyacrylonitrile, cellulose, styrene, polyimide, epoxy resin, glucose, or a mixture thereof. Lt; / RTI &gt;

Specifically, it may be a petroleum pitch, a coal pitch, a phenol resin, a heavy oil, a light oil, or a combination thereof. More specifically, it may be a petroleum pitch, a coal pitch or a combination thereof.

The content of the low-crystalline carbon may be 0.1 to 50% based on 100% by weight of the total active material. When this range is satisfied, the graphite particles and the metal-based active material can be easily bound and the side reaction can be reduced. In addition, the conductivity of the active material can be improved. In addition, the lifetime characteristics of the lithium secondary battery can be improved.

By forming a ceramic coating layer on the surface of the carbon-metal composite (carbon-metal composite), it is possible to improve lifetime characteristics while maintaining a high capacity of the lithium secondary battery.

The ceramic coating layer is uniformly coated on the surface of the active material to form a hard coating film. This coating film inhibits the expansion and contraction of the active material generated during charging and discharging of the carbon-metal composite, have.

Further, since the ceramic coating layer has a surface roughness, the lifetime characteristics of the active material can be maintained by improving the interfacial contact ability even when expansion and contraction occur during charging and discharging.

Further, when the ceramic coating layer is formed on the surface of the carbon-metal composite, exposure of the metal active material is prevented to suppress side reactions with the electrolyte, thereby improving not only the lifetime characteristics but also the safety problem.

The ceramic may be a metal oxide, a non-metal oxide, a composite metal oxide, a rare earth oxide, a compound containing a halogen group, an oxide produced from a ceramic precursor, or a combination thereof.

The ceramic precursor may be zirconia, aluminum, polycarbosilane, polysiloxane, polysilazane, or a combination thereof.

Said ceramic is _{SiO 2, Al 2 O 3,} Li 2 Ti 5 O 12, TiO 2, CeO 2, ZrO 2, BaTiO 3, Y 2 O 3, MgO, CuO, ZnO, AlPO 4, AlF, Si 3 N 4 , AlN, TiN, may be WC, SiC, TiC, MoSi _2, Fe ₂ O _3, GeO _2, Li ₂ O, MnO, NiO, zeolite, or a combination thereof.

The content of the ceramics may be 0.1 to 10 parts by weight based on 100 parts by weight of the carbon-metal composite. When the ceramic is contained within the above range, a uniform coating layer can be formed, volume expansion can be effectively maintained, and lifetime characteristics can be improved. If the ceramic is out of the above range, Can be degraded.

The average particle size of the scratched graphite particles may be 3 to 100 탆.

The average particle size of the metal-based active material may be 0.03 to 20 탆. However, the present invention is not limited thereto.

Also, the ceramic coating layer may include ceramic particles, and the average particle size of the ceramic particles may be 10 to 1000 nm.

In another embodiment of the present invention, there is provided a method for producing a graphite core material, comprising the steps of: preparing a core material comprising scaly graphite particles and a metal-based active material; Mixing the prepared core material and assembling it into a spherical shape to prepare a core; And forming a ceramic coating layer on the surface of the core. The present invention also provides a method of manufacturing a negative electrode active material for a lithium secondary battery.

Preparing the core material comprising the flaky graphite particles and the metal-based active material, mixing the flake graphite particles and the metal-based active material, and mechanically mixing them at a rotation speed of 100 to 1000 rpm to prepare the core material .

More specifically, the step of preparing the core material comprising the scaly graphite particles and the metal-based active material may include the steps of preparing a core material comprising graphite particles, a metal-based active material, and low-crystalline carbon . That is, it may optionally further comprise the low crystalline carbon.

The step of preparing the core by mixing the prepared core materials into a spherical shape may be a mechanical mixing method.

The mechanical mixing method may be selected from the group consisting of rotor blade milling, mechanofusion milling, planetary milling, shape milling, vertical shape milling, Or may be performed by any of the following methods: milling (nobilta milling), high speed mixing, or a combination thereof.

The mechanical mixing method may be a mechanical mixing method at a rotating speed of 500 to 20000 rpm.

The step of preparing the core by mixing the prepared core material and then assembling into a spherical shape may be a method of performing heat treatment in hydrogen, nitrogen, argon, or a mixed gas atmosphere thereof.

The step of preparing the core by mixing the prepared core material and assembling into a spherical shape may be a method of heat treatment at 600 to 1500 ° C. The range may be for effective manufacture of an assembled composite of scaly graphite particles and a metal-based active material comprising a low crystalline carbon material.

The step of forming a ceramic coating layer on the surface of the core may be performed by a method of mechanically mixing the prepared core and ceramic particles.

The mechanical mixing method may be selected from the group consisting of rotor blade milling, ball milling, mechanofusion milling, shaker milling, planetary milling, attritor milling, disk milling, shape milling, vertical shape milling, nauta milling, nobilta milling, high speed mixing, or the like. Or a combination of these.

The mechanical mixing method may be performed at a rotational speed of 500 to 7,000 rpm.

The range may be a suitable range for the formation of an effective ceramic coating layer.

According to another embodiment of the present invention, there is provided a negative electrode comprising a negative electrode active material prepared according to the method for manufacturing the negative electrode active material for a lithium secondary battery; A cathode comprising a cathode active material; A separator existing between the cathode and the anode; And a lithium secondary battery comprising the electrolyte.

The lithium secondary battery can be classified into a lithium ion battery, a lithium ion polymer battery, and a lithium polymer battery depending on the type of the separator and electrolyte used. The lithium secondary battery can be classified into a cylindrical shape, a square shape, a coin shape, Depending on the size, it can be divided into bulk type and thin type. The structure and the manufacturing method of these cells are well known in the art, and detailed description thereof will be omitted.

1 is an exploded perspective view of a lithium secondary battery according to one embodiment. 1, the lithium secondary battery 100 has a cylindrical shape and includes a cathode 112, a cathode 114, a separator 113 disposed between the cathode 112 and the anode 114, An electrolyte 114 (not shown), an electrolyte (not shown) impregnated into the separator 113, a battery container 120, and a sealing member 140 for sealing the battery container 120. The lithium secondary battery 100 is constructed by laminating a cathode 112, a separator 113 and an anode 114 in this order and then winding them in a spiral wound state in the battery container 120.

The negative electrode includes a current collector and a negative active material layer formed on the current collector, and the negative active material layer includes a negative active material.

The negative electrode active material is as described above.

The negative electrode active material layer also includes a binder, and may further include a conductive material.

The binder serves to adhere the anode active material particles to each other and to adhere the anode active material to the current collector. Typical examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, Such as polyvinyl chloride, polyvinyl fluoride, polymers comprising ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, Styrene-butadiene rubber, epoxy resin, nylon, and the like may be used, but the present invention is not limited thereto.

The conductive material is used for imparting conductivity to the electrode. Any material can be used as long as it does not cause any chemical change in the battery. Examples of the conductive material include natural graphite, artificial graphite, carbon black, acetylene black, , Carbon-based materials such as carbon fibers; Metal powders such as copper, nickel, aluminum, and silver, or metal-based materials such as metal fibers; Conductive polymers such as polyphenylene derivatives; Or a mixture thereof may be used.

The current collector may be a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foil, a copper foil, a polymer substrate coated with a conductive metal, or a combination thereof.

The anode includes a current collector and a cathode active material layer formed on the current collector.

As the cathode active material, a compound capable of reversibly intercalating and deintercalating lithium (a lithiated intercalation compound) can be used. Concretely, it is possible to use at least one of complex oxides of cobalt, manganese, nickel or a combination of metals and lithium, and specific examples thereof include compounds represented by any one of the following formulas. Li _a A _{1 - b} R _b D ₂ wherein, in the formula, 0.90? A? 1.8 and 0? B? 0.5; Li _a E _{1 - b} R _b O _{2 - c} D _c , wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.05; LiE _{2 - b} R _b O _{4 - c} D _{c where} 0? B? 0.5, 0? C? 0.05; Li _a Ni _{1 -b- c} Co _b R _c D _{α where} 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, and 0 <α ≦ 2; Li _a Ni _{1 - b - c} Co _b R _c O _{2 - ?} Z _{? Wherein} 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05 and 0 <? Li _a Ni _{1 -b- c} Co _b R _c O _{2 - ?} Z ₂ wherein 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05 and 0 <? Li _a Ni _1-bc Mn _b R _c D _? Wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05 and 0 <? Li _a Ni _{1 -b- c} Mn _b R _c O _{2 - ?} Z _{? Where the} 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05 and 0 <? Li _a Ni _{1 -b- c} Mn _b R _c O _{2 - ?} Z ₂ wherein 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05 and 0 <? Li _a Ni _b E _c G _d O ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, and 0.001 ≤ d ≤ 0.1; Li _a Ni _b Co _c Mn _d GeO ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, and 0.001 ≤ e ≤ 0.1; Li _a NiG _b O ₂ (in the above formula, 0.90? A? 1.8 and 0.001? B? 0.1); Li _a CoG _b O ₂ (in the above formula, 0.90? A? 1.8 and 0.001? B? 0.1); Li _a MnG _b O ₂ wherein, in the above formula, 0.90? A? 1.8 and 0.001? B? 0.1; Li _a Mn ₂ G _b O ₄ (in the above formula, 0.90? A? 1.8 and 0.001? B? 0.1); QO _2; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiTO ₂ ; LiNiVO _4; Li _(3-f) J ₂ (PO ₄ ) ₃ (0? F? 2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0? F? 2); And LiFePO _4.

In the above formula, A is Ni, Co, Mn or a combination thereof; R is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof; D is O, F, S, P or a combination thereof; E is Co, Mn or a combination thereof; Z is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof; T is Cr, V, Fe, Sc, Y or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu or a combination thereof.

Of course, a compound having a coating layer on the surface of the compound may be used, or a compound having a coating layer may be mixed with the compound. The coating layer may comprise, as a coating element compound, an oxide, a hydroxide of a coating element, an oxyhydroxide of a coating element, an oxycarbonate of a coating element, or a hydroxycarbonate of a coating element. The compound constituting these coating layers may be amorphous or crystalline. The coating layer may contain Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr or a mixture thereof. The coating layer forming step may be any coating method as long as it can coat the above compound by a method that does not adversely affect physical properties of the cathode active material (for example, spray coating, dipping, etc.) by using these elements, It will be understood by those skilled in the art that a detailed description will be omitted.

The cathode active material layer also includes a binder and a conductive material.

The binder serves to adhere the positive electrode active material particles to each other and to adhere the positive electrode active material to the current collector. Typical examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl Polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-acrylonitrile, styrene-butadiene rubber, Butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like, but not limited thereto.

The conductive material is used for imparting conductivity to the electrode. Any conductive material can be used without causing any chemical change in the battery. Examples of the conductive material include natural graphite, artificial graphite, carbon black, acetylene black, Metal powders such as black, carbon fiber, copper, nickel, aluminum, and silver, metal fibers, and the like, and conductive materials such as polyphenylene derivatives may be used alone or in combination.

As the current collector, Al may be used, but the present invention is not limited thereto.

The negative electrode and the positive electrode are prepared by mixing an active material, a conductive material and a binder in a solvent to prepare an active material composition, and applying the composition to a current collector. The method of manufacturing the electrode is well known in the art, and therefore, a detailed description thereof will be omitted herein. As the solvent, N-methylpyrrolidone or the like can be used, but it is not limited thereto.

The electrolyte includes a non-aqueous organic solvent and a lithium salt.

The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

As the non-aqueous organic solvent, a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based or aprotic solvent may be used. Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC) EC), propylene carbonate (PC), and butylene carbonate (BC) may be used. As the ester solvent, methyl acetate, ethyl acetate, n-propyl acetate, 1,1-dimethyl ethyl acetate, methyl propionate , Ethyl propionate,? -Butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone and the like can be used. Examples of the ether solvent include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran. As the ketone solvent, cyclohexanone may be used have. As the alcoholic solvent, ethyl alcohol, isopropyl alcohol and the like can be used. As the aprotic solvent, R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, An amide such as nitriles such as dimethylformamide, and dioxolanes such as 1,3-dioxolane, sulfolanes, and the like can be used.

The non-aqueous organic solvent may be used alone or in admixture of one or more. If the non-aqueous organic solvent is used in combination, the mixing ratio may be appropriately adjusted according to the desired cell performance. .

In the case of the carbonate-based solvent, it is preferable to use a mixture of a cyclic carbonate and a chain carbonate. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1: 1 to about 1: 9, the performance of the electrolytic solution may be excellent.

The non-aqueous organic solvent may further include the aromatic hydrocarbon-based organic solvent in the carbonate-based solvent. In this case, the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent may be mixed in a volume ratio of about 1: 1 to about 30: 1.

The aromatic hydrocarbon-based organic solvent may be an aromatic hydrocarbon-based compound represented by the following formula (1).

[Chemical Formula 1]

In Formula 1, R ₁ to R ₆ are each independently hydrogen, halogen, a C1 to C10 alkyl group, a C1 to C10 haloalkyl group, or a combination thereof.

The aromatic hydrocarbon-based organic solvent is selected from the group consisting of benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3- , 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4 - triiodobenzene, toluene, fluorotoluene, 1,2-difluorotoluene, 1,3-difluorotoluene, 1,4-difluorotoluene, 1,2,3-trifluorotoluene, 1,2,4-trifluorotoluene, chlorotoluene, 1,2-dichlorotoluene, 1,3-dichlorotoluene, 1,4-dichlorotoluene, 1,2,3-trichlorotoluene, 1,2,4 - trichlorotoluene, iodotoluene, 1,2-diiodotoluene, 1,3-diiodotoluene, 1,4-diiodotol Ene, 1,2,3-tree-iodo toluene, 1,2,4-iodo toluene, xylene, or may be a combination thereof.

The non-aqueous electrolyte may further include vinylene carbonate or an ethylene carbonate-based compound represented by the following formula (2) to improve battery life.

(2)

Wherein R ₇ and R ₈ are each independently hydrogen, a halogen group, a cyano group (CN), a nitro group (NO ₂ ) or a C1 to C5 fluoroalkyl group, and at least one of R ₇ and R ₈ Is a halogen group, a cyano group (CN), a nitro group (NO ₂ ) or a C1 to C5 fluoroalkyl group.

Representative examples of the ethylene carbonate-based compound include, for example, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, fluoroethylene carbonate, . When the vinylene carbonate or the ethylene carbonate compound is further used, the amount of the vinylene carbonate or the ethylene carbonate compound can be appropriately controlled to improve the life.

The lithium salt is dissolved in the non-aqueous organic solvent to act as a source of lithium ions in the battery to enable operation of a basic lithium secondary battery, and a material capable of promoting the movement of lithium ions between the positive electrode and the negative electrode to be. The lithium salt Representative examples are _{LiPF 6, LiBF 4, LiSbF 6} , LiAsF 6, LiC 4 F 9 SO 3, LiClO 4, 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, LiB ( C 2 O 4) 2 ( lithium bis oxalate reyito borate (lithium bis (oxalato) borate; LiBOB) , or in a combination thereof The concentration of the lithium salt is preferably within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity Can exhibit excellent electrolyte performance, and lithium ions can effectively migrate.

The separator 113 separates the cathode 112 and the anode 114 and provides a passage for lithium ions. Any separator 113 may be used as long as it is commonly used in a lithium battery. That is, it is possible to use an electrolyte having a low resistance to ion movement and an excellent ability to impregnate an electrolyte. For example, selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and may be nonwoven fabric or woven fabric. For example, a polyolefin-based polymer separator such as polyethylene, polypropylene and the like is mainly used for a lithium ion battery, and a coated separator containing a ceramic component or a polymer substance may be used for heat resistance or mechanical strength, Structure.

Hereinafter, examples and comparative examples of the present invention will be described. The following embodiments are only examples of the present invention and the present invention is not limited to the following embodiments.

Example  One

(Preparation of negative electrode active material for lithium secondary battery)

(Average particle size (D50): 54 mu m), a metal-based active material, nanosilicon (average particle size (D50): 30 nm) and a petroleum pitch as a low crystalline carbon precursor were mixed at a weight ratio of 60:10:30 Then, the mixture was spherically granulated by rotating at a rotor blade milling speed of 15,000 rpm for 5 minutes and then heat-treated at a temperature of 1,100 ° C. under a nitrogen atmosphere and classified to prepare a carbon-metal granulated composite containing low-crystalline carbon.

Then, a carbon-metal composite and a TiO ₂ ceramic (average particle size (D50): 30 nm) were mixed at a weight ratio of 100: 2 and mechanically mixed at 2000 rpm for 20 minutes in a high- To prepare an active material.

(Preparation of negative electrode)

Styrene-butadiene rubber (SBR) as a binder and carboxymethyl cellulose (CMC) as a thickener were mixed at a mass ratio of 96: 2: 2 and dispersed in deionized water to prepare an anode active material layer composition Respectively.

The composition was coated on a Cu-foil current collector, dried and rolled to prepare a cathode having an electrode density of 1.50 +/- 0.05 g / cm &lt; 3 &gt;.

(Production of lithium secondary battery)

A coin type 2032 half cell was fabricated by using the negative electrode as the working electrode and the lithium metal as the counter electrode. At this time, a separator made of a porous polypropylene film was inserted between the working electrode and the counter electrode, and a mixed volume ratio of ethylene carbonate (EC), diethyl carbonate (DEC) and fluoroethylene carbonate (FEC) 25 in which 1.5 M LiPF ₆ was dissolved was used.

Example  2

A negative electrode active material and a negative electrode were prepared in the same manner as in Example 1 except that an SiO ₂ ceramic (average particle diameter (D ₅₀ ): 10 nm) was used in place of TiO ₂ to prepare a lithium secondary battery.

Comparative Example  One

(Average particle size (D50): 54 占 퐉), a metal-based active material, nano silicon (average particle size (D50): 30 nm) and a petroleum pitch as a low crystalline carbon precursor were mixed at a weight ratio of 60:10:30 Next, the carbon-metal composite was heat-treated at a temperature of 1,100 ° C under a nitrogen atmosphere and classified to prepare a ceramic-uncoated carbon-metal composite.

A negative electrode was prepared in the same manner as in Example 1 except for the production process of the negative electrode active material composition, and a lithium secondary battery was produced.

Comparative Example  2

(Average particle size (D50): 54 占 퐉), a metal-based active material, nano silicon (average particle size (D50): 30 nm) and a petroleum pitch as a low crystalline carbon precursor were mixed at a weight ratio of 60:10:30 Then, the mixture was spherically granulated by rotating at a rotor blade milling speed of 15,000 rpm for 5 minutes, and then heat-treated at a temperature of 1,100 ° C under a nitrogen atmosphere and classified to prepare a carbon-metal granulated composite.

A negative electrode was prepared in the same manner as in Example 1 except for the production process of the negative electrode active material composition, and a lithium secondary battery was produced.

Experimental Example

Evaluation 1: Scanning electron microscope ( Scanning Electron Microscope , SEM ) Picture

3 is an SEM photograph showing the surface state of the negative electrode active material according to Comparative Example 2. Fig.

4 is a SEM photograph showing the surface state of the negative electrode active material according to Example 1. Fig.

Referring to FIGS. 3 and 4, it can be seen that the negative active material according to Example 1 has a uniform coating of ceramic on its surface.

Evaluation 2: Initial of lithium secondary battery Charging and discharging  Character rating

The lithium secondary batteries fabricated according to Example 1 and Comparative Example 2 were set to a cut-off voltage of 0.005 V (0.01 C), charged in a CC-CV mode at 0.1 C rate, The battery was discharged at 0.1 C rate up to 1.5 V in the CC mode, and the charge and discharge were repeated to measure the capacity and efficiency after three cycles. The results are shown in Fig.

Specifically, FIG. 5 is a graph showing charge / discharge curves of the initial three cycles of the lithium secondary battery manufactured according to Example 1 and Comparative Example 2. FIG. Referring to FIG. 5, it can be seen that the capacity maintenance according to Example 1 is improved as compared with the battery according to Comparative Example 2.

Evaluation 3: Lithium secondary battery Charging and discharging  Evaluation of life characteristics

The lithium secondary batteries fabricated according to Examples 1, 2, and 1 and Comparative Example 2 were set to a cut-off voltage of 0.005 V (0.01 C) After the battery was charged at 0.5C rate, the battery was discharged at 0.5C rate up to 1.5V in the CC mode, and the capacity retention rate was measured after 50 cycles of charging and discharging. The results are shown in Table 1 and FIG.

6 is a graph showing the capacity retention rate of the lithium secondary battery manufactured according to Example 1, Example 2, Comparative Example 1, and Comparative Example 2 according to charge / discharge life span.

Referring to Table 1 and FIG. 6, it can be seen that the capacity retention ratio of the lithium secondary battery according to Example 1 and Example 2 is higher than that of the lithium secondary battery according to Comparative Example 1 and Comparative Example 2 have.

50 times charge / discharge capacity retention rate (%) Example 1 91.6 Example 2 87.8 Comparative Example 1 38.6 Comparative Example 2 63.1

Evaluation 4: Evaluation of Thickness Expansion Characteristics of Cathode

A coin type 2032 half-cell was fabricated using the negative electrode active material prepared in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 as the working electrode. The prepared battery was charged and discharged three times at 0.1 C, and then charged again to decompose the fully charged battery. After washing with DEC (diethyl carbonate) to measure the thickness of the charged cathode and the initial electrode, swelling was evaluated according to the following equation (1).

[Equation 1]

Swelling (%) = (thickness of charged cathode electrode - fo foil thickness) / (thickness of initial cathode electrode - fo foil thickness) * 100

The results are shown in Table 2 and Fig.

Cathode Thickness Expansion (%) Example 1 73.1 Example 2 74.5 Comparative Example 1 91.9 Comparative Example 2 109.3

7 is a graph showing swelling evaluation of a lithium secondary battery manufactured according to Example 1, Example 2, Comparative Example 1, and Comparative Example 2. FIG.

Referring to Table 2 and FIG. 7, it can be seen that the change in the thickness of the negative electrode according to Examples 1 and 2 is reduced compared to the negative electrode according to Comparative Example 1 and Comparative Example 2.

That is, when the anode active material according to one embodiment is applied, the design of the pouch cell is not only easy, but also the lifetime characteristics during charging and discharging can be improved.

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 present invention as defined by the following claims. As will be understood by those skilled in the art. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

100: lithium secondary battery 112: cathode
113: separator 114: positive electrode
120: battery container 140: sealing member

Claims (24)

A core comprising flaky graphite particles and a metal-based active material; And
A ceramic coating layer positioned on the core surface;
And a negative electrode active material for a lithium secondary battery.
The method according to claim 1,
Wherein the core further comprises low-crystallinity carbon.
3. The method of claim 2,
The low-crystallinity carbon may be, for example,
(PU), petroleum pitch, coal pitch, mesophase pitch, heavy oil, light oil, polyvinyl alcohol (PVA), polyvinyl chloride (PVC), sucrose, phenol resin, furan resin, Lithium secondary, which is a furfuryl alcohol, polyacrylonitrile, cellulose, styrene, polyimide, epoxy resin, glucose, or a combination thereof. Anode active material for batteries.
3. The method of claim 2,
Wherein the low crystalline carbon content is 0.1 to 50% based on 100% by weight of the total active material.
The method according to claim 1,
The metal-
Silicon, tin, aluminum, vanadium, magnesium, or antimony; An alloy of one or more of these; A compound selected from oxides, nitrides, carbides, or combinations of these metals; Or a combination thereof.
The method according to claim 1,
Wherein the scratched graphite particles are natural graphite, artificial graphite, or a combination thereof.
The method according to claim 1,
Wherein the ceramic is a metal oxide, a non-metal oxide, a composite metal oxide, a rare earth oxide, a compound containing a halogen group, an oxide produced from a ceramic precursor, or a combination thereof.
8. The method of claim 7,
Wherein the ceramic precursor is zirconia, aluminum, polycarbosilane, polysiloxane, polysilazane, or a combination thereof.
The method according to claim 1,
Said ceramic is _{SiO 2, Al 2 O 3,} Li 2 Ti 5 O 12, TiO 2, CeO 2, ZrO 2, BaTiO 3, Y 2 O 3, MgO, CuO, ZnO, AlPO 4, AlF, Si 3 N 4 , AlN, TiN, WC, SiC, TiC, MoSi _2, Fe ₂ O _3, GeO _2, Li ₂ O, MnO, NiO, zeolite, or a combination thereof that would negative active material.
The method according to claim 1,
And the average particle size of the scratched graphite particles is 3 to 100 탆.
The method according to claim 1,
Wherein the metal-based active material has an average particle diameter of 0.03 to 20 占 퐉.
The method according to claim 1,
Wherein the ceramic coating layer comprises ceramic particles, and the average particle diameter of the ceramic particles is 10 to 1000 nm.
The method according to claim 1,
The weight ratio of the flaky graphite particles to the metal-
60/40 to 99/1. &Lt; / RTI &gt;
Preparing a core material comprising flake graphite particles and a metal-based active material;
Mixing the prepared core material and assembling it into a spherical shape to prepare a core; And
Forming a ceramic coating layer on the core surface;
Wherein the negative electrode active material is a carbon-metal composite material.
15. The method of claim 14,
Preparing a core material comprising the scaly graphite particles and the metal-based active material,
Preparing a core material containing scaly graphite particles, a metal-based active material, and low-crystalline carbon.
15. The method of claim 14,
And mixing the prepared core material and then assembling into a spherical shape to prepare a core, wherein a mechanical mixing method is used.
17. The method of claim 16,
In the mechanical mixing method,
But are not limited to, rotor blade milling, mechanofusion milling, planetary milling, shape milling, vertical shape milling, nobilta milling, High speed mixing, or a combination thereof. The method for producing a negative electrode active material for a lithium secondary battery according to claim 1,
17. The method of claim 16,
Wherein the mechanical mixing method is performed at a rotating speed of 500 to 20000 rpm.
15. The method of claim 14,
Mixing the prepared core material and assembling the core material into a sphere to prepare a core,
And a heat treatment is performed in a hydrogen, nitrogen, argon, or mixed gas atmosphere thereof.
20. The method of claim 19,
Wherein the core material is mixed with the core material and assembled into a spherical shape to produce a core, the method being performed at a temperature of 600 to 1500 占 폚.
15. The method of claim 14,
Forming a ceramic coating layer on the core surface,
And then mechanically mixing the prepared core and ceramic particles. The method for manufacturing a negative electrode active material for a lithium secondary battery according to claim 1,
22. The method of claim 21,
In the mechanical mixing method,
Such as rotor blade milling, ball milling, mechanofusion milling, shaker milling, planetary milling, attritor milling disc milling, or any combination thereof, such as disk milling, shape milling, vertical shape milling, nauta milling, nobilta milling, high speed mixing, Wherein the negative electrode active material is one method.
22. The method of claim 21,
Wherein the mechanical mixing method is performed at a rotating speed of 500 to 7,000 rpm.
A negative electrode comprising the negative electrode active material for a lithium secondary battery according to claim 1;
anode; And
A lithium secondary battery comprising: an electrolyte;

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