KR101503433B1 - Manufacturing method of lithium-titanium composite comprising carbon in crystal, lithium-titanium composite comprising carbon in crystal made by the same, and the use of the same - Google Patents

Abstract

The present invention relates to a method for producing a lithium-titanium composite oxide containing carbon in a crystal, and a lithium secondary battery exhibiting excellent capacity characteristics by using a lithium-titanium composite oxide containing carbon in the crystal produced thereby.
More particularly, the present invention relates to a method for producing a lithium-titanium composite oxide containing carbon in a crystal by a wet pulverization and spray drying method and a lithium-titanium composite oxide containing carbon in the crystal produced by the method and a lithium ion The present invention relates to a secondary battery.
The method for producing a lithium-titanium composite oxide containing carbon in the crystal according to the present invention provides a lithium-manganese composite oxide for lithium ion batteries excellent in electrochemical characteristics.

Description

TECHNICAL FIELD The present invention relates to a method for producing a lithium-titanium composite oxide containing carbon in a crystal, a lithium-titanium composite oxide containing carbon in the crystal thus produced, and a use thereof. BACKGROUND OF THE INVENTION 1. Field of the Invention COMPRISING CARBON IN CRYSTAL MADE BY THE SAME, AND THE USE OF THE SAME}

The present invention relates to a method for producing a lithium-titanium composite oxide containing carbon in a crystal, a lithium-titanium composite oxide containing carbon in the crystal produced thereby, and a lithium-titanium composite oxide containing carbon in the crystal, As a positive electrode or a negative electrode active material.

The lithium-titanium composite oxide includes lithium titanate represented by the general formula Li _{(1 + x)} Ti _(2-x) O _y (x = -0.2 to 1.0, y = 3 to 4) a _{4/3 Ti 5/3 O4} , LiTi 2 O 4 , and Li ₂ TiO _3. They have a voltage of 1.5 V on a lithium basis and have a long lifetime. Further, it is a material that has been successfully used as an active material in a lithium ion battery for a watch, and it can neglect the expansion and shrinkage during charging-discharging. This material has been conventionally used as a positive electrode active material and can also be utilized as a negative electrode active material, and its future as a positive electrode and negative electrode active material of a battery is expected.

The following methods have been proposed for lithium titanate or a method for producing the same.

In JPA No. 320784/95, anatase-type titanium dioxide and lithium hydroxide were mixed at a ratio of 5: 4 in atomic ratio and the mixture was calcined at 900 ° C for 15 hours to obtain Li _4/3 Ti _{5/3 O} 4 , And a method of obtaining LiTi ₂ O ₄ by calcining titanium dioxide and lithium carbonate in a hydrogen stream at 800 to 950 ° C. However, the lithium titanate obtained by such a production method has poor fluidity due to non-uniform formation. This leads to handling problems during mixing with a conducting agent or a binder at the time of preparing the electrode, and it becomes difficult to uniformly mix. In addition, since the absorption / holding of the electrolyte is insufficient, it is difficult to coat the product on a collector, and a battery having excellent cycling characteristics can not be produced.

JPA No. 309726/97 discloses a process for producing a lithium titanate hydrate comprising the steps of reacting a titanium compound and an ammonia compound in water to obtain a titanic acid compound and a step of reacting the titanic acid compound with a lithium compound in water to obtain lithium titanate hydrate A manufacturing method is described. However, the lithium titanate obtained by this method contains water because it is a hydrate. As the electrolyte, LiPF ₆ Or LiBF ₄ is used, water and electrolyte react to liberate hydrogen fluoride, which in turn reacts with lithium or counter electrode active materials to undesirably reduce capacity or cycling.

Korean Patent Application No. 10-2006-0039137 discloses a lithium secondary battery comprising a lithium titanate containing a predetermined amount of lithium titanate as a negative electrode active material for a lithium secondary battery including a carbonaceous anode active material and having excellent output characteristics at a low temperature, , Attempts have been made to use lithium secondary batteries which can be used as a power source for hybrid electric vehicles. However, in this case, since the carbon-based anode active material and the lithium titanium compound are simply mixed, the capacity increase and the low-temperature stability can not be obtained as desired.

Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a method for producing a lithium-titanium composite oxide containing carbon in a crystal.

Another object of the present invention is to provide a use of the lithium-titanium composite oxide produced by the above-described method for producing a lithium-titanium composite oxide as a positive electrode and a negative electrode active material of a lithium secondary battery.

In order to achieve the above object,

i) solid-phase mixing the carbon compound, the lithium-containing compound, and the titanium oxide in a stoichiometric ratio;

ii) dispersing the solid phase mixture of i) in a solvent and wet milling the slurry until it contains particles having an average particle diameter of less than about 0.5 占 퐉;

iii) spray-drying the slurry of ii); and

and iv) calcining the spray-dried slurry of iii). The present invention also provides a process for producing a lithium-titanium composite oxide comprising carbon in a crystal.

In the production method of the present invention, the carbon compound is at least one selected from the group consisting of pyrocarbon, coke, glassy carbon, sintered organic polymer compound, and carbon fiber.

In the production method of the present invention, the titanium oxide is anatase type, rutile type titanium dioxide having a purity of 95% or more, or hydrous titanium oxide having a purity of 90% or more.

In the production method of the present invention, the lithium-containing compound is lithium hydroxide or lithium carbonate.

In the production method of the present invention, the atomic ratio of titanium to carbon in the lithium-titanium composite oxide is 1: 0.01 to 1: 0.1.

In the production method of the present invention, the wet grinding in the step (ii) is characterized by using water as a solvent and wet pulverizing at 3000 to 4000 rpm using zirconia beads.

In the manufacturing method of the present invention, in the step of spray drying the slurry of ii) in the step iii), the hot air is heated to a temperature of 250 to 300 ° C and the hot air temperature of the exhaust is 100 to 150 ° C.

In the manufacturing method of the present invention, the firing step in the step iv) is characterized in that the spray dried body in the step iii) is fired at 700 to 800 ° C for 5 hours to 10 hours under a reducing atmosphere.

The present invention also provides a lithium-titanium composite oxide comprising carbon in a crystal prepared by the production method of the present invention and formed of spherical secondary particles having a particle diameter of 1 to 50 mu m formed by aggregation of primary particles.

The present invention also provides a negative electrode used as a positive electrode or negative electrode active material using a lithium-titanium composite oxide containing carbon as a positive electrode active material, and a lithium secondary battery containing the positive electrode or the negative electrode.

Hereinafter, the present invention will be described in more detail.

In the production method of the present invention, a lithium titanium compound in which carbon is contained in a crystal structure is produced by simultaneously mixing a lithium compound, a titanium compound and a carbon compound from the beginning using solid phase mixing, wet pulverization and spray drying. do.

The starting material of the titanium oxide used as the starting material may be chloride, sulfate or organic salt. The crystal structure may be any of anatase, rutile or amorphous. However, in order to produce a lithium-titanium composite oxide having excellent discharge capacity or cell characteristics as in the present invention, It is preferable to use titanium oxide. The anatase-type titanium dioxide needs to have a purity of 95% or more, preferably 98% or more. If the purity is less than 95%, the capacity per weight of active material decreases, which is not preferable. High purity, for example, 99.99% purity may be used, but in this case the cost is high. From the viewpoint of the electrode active material, when the purity is 98% or more, the influence of the particle diameter and the shape becomes greater than the effect of high purity. The hydrous titanium oxide should have a purity of 90% or more before firing in order to obtain anatase-type titanium dioxide having the above range of purity after firing, because the above-described anatase type is the same as titanium oxide

In the production method of the present invention, the carbon compound used as the starting material is one capable of reversibly doping and undoping lithium, for example, pyrocarbon, coke (pitchcoke, needlecoke, petroleum coke, etc. ), Graphite, glassy carbon, organic polymer compound sintered body (carbonized phenol resin or furan resin calcined at a suitable temperature), carbon fiber, activated carbon and other carbon materials or metallic lithium, lithium alloy and polyacene, polypyrrole And the like can be used.

The carbon compound according to the present invention can be solid-state carbon or liquid-state carbon which is generally used, and is not particularly limited in the present invention. Typically, the solid carbon is obtained by heat-treating a phenol resin, a naphthalene resin, a polyvinyl alcohol resin, a urethane resin, a polyimide resin, a furan resin, a furfuryl alcohol, a cellulose resin, an epoxy resin, a polystyrene resin, have. It is also possible to heat treat the petroleum-based, coal-based carbon raw material or the resin-based carbon at 600 to 1500 ° C after the mesophase pitch, the raw cokes and the carbon raw material heat-treated at 300 to 600 ° C are not subjected to the infusibilization treatment, Amorphous carbon such as a mesophase pitch carbide and a calcined coke can be used. The liquid carbon may be one selected from the group consisting of coal-based pitch, petroleum pitch, tar, and pitch produced by heat treating low-molecular weight heavy oil at about 1000 캜.

In the production method of the present invention, the lithium compound to be used as a starting material is lithium hydroxide such as lithium hydroxide, lithium hydroxide monohydrate, lithium oxide, lithium hydrogen carbonate or lithium carbonate.

The method for producing a carbon-containing lithium-titanium composite oxide in a crystal according to the present invention is characterized in that a lithium compound, a titanium compound, and a carbon compound are mixed as a starting material in a stoichiometric ratio, and the solid mixture is dispersed in a liquid medium and wet pulverized A granulated powder obtained by spray-drying and assembling a slurry by a known method can be used.

In the production method of the present invention, it is preferable to use a method in which the simultaneously mixed lithium compound, titanium compound, and carbon compound are dispersed in a dispersion medium, followed by wet grinding using a medium agitation type pulverizer or the like. As the dispersion medium used for the wet pulverization of the slurry, various organic solvents and aqueous solvents can be used, but water is preferred. The ratio of the total weight of the raw material compound to the weight of the whole slurry is preferably 50 wt% or more and 60 wt% or less. When the weight ratio is less than the above range, spherical particles produced by spray drying tend to be smaller or more likely to break due to the extremely low slurry concentration. If the weight ratio exceeds the above range, it is difficult to maintain the uniformity of the slurry.

It is preferable that the wet grinding is performed at 3000 to 4000 rpm so that the average particle diameter of the solid matter in the slurry is usually 2 탆 or less, particularly 1 탆 or less, particularly 0.5 탆 or less. If the average particle diameter of the solid in the slurry is too large, the reactivity in the firing step is lowered and the sphericity is lowered, and the final powder filling density tends to be lowered. However, since pulverization more than necessary leads to an increase in the cost of pulverization, the average particle diameter of the pulverized product is usually 0.5 탆 or less.

Air, nitrogen, or the like can be used as the gas to be supplied during spray drying of the slurry, but air is usually used. These are preferably used under pressure. The particle size (D50) of particles produced by spray drying of the lithium manganese composite oxide powder of the present invention is 1 to 50 mu m.

The means for atomizing is not particularly critical and is not limited to pressurizing nozzles with a specified pore size, in fact, any known spray-drying apparatus can be used. Sprayers are generally divided into two types, rotating-type and nozzle-type. The nozzle type is divided into a pressure nozzle and a two-fluid nozzle. In addition, any means known in the art can be used, such as rotary atomizers, pressure nozzles, pneumatic nozzles, sonic nozzles, and the like. The feed rate, feed viscosity, the desired particle size of the spray-dried product, the dispersion, the water droplet size of the water-in-oil emulsion or the water-in-water microemulsion are typically considered factors in the selection of the atomizing means.

In the step of spray drying the slurry of ii) in the step iii), it is preferable to spray-dry the supplied hot air at 250 to 300 ° C and the hot air temperature at 100 to 150 ° C in order to increase the shape, size and crystallinity of the particles .

The mixed powder thus obtained is then subjected to a firing treatment. At this time, the firing conditions depend on the composition of the raw material. However, if the firing temperature is too high, the primary particles excessively grow, while if too low, the bulk density becomes small and the specific surface area becomes excessively large. The firing temperature is usually 600 占 폚 or higher, preferably 700 占 폚 or higher, and usually 900 占 폚 or lower, preferably 600 占 폚 or higher, although it depends on the kind of the lithium compound, titanium oxide, Lt; / RTI >

The firing time varies depending on the temperature, but is usually 30 minutes or more, preferably 5 hours or more, and usually 20 hours or less, preferably 10 hours or less, in the above-mentioned temperature range. When the firing time is too short, it is difficult to obtain a lithium-titanium composite oxide powder having good crystallinity, and it is not very practical that the firing time is too long. If the baking time is too long, it is preferably not more than 10 hours, since pulverization may be required afterwards or cracking may become difficult.

The atmosphere at the time of firing may be an inert gas atmosphere such as nitrogen or argon depending on the composition and structure of the compound to be produced.

The composition of each component of the lithium-titanium composite oxide in which carbon is contained in the synthesized crystals in the present invention can be adjusted by the introduction (mixing ratio) of each compound at the time of mixing. The particle size distribution, BET specific surface area, tap density and green compact density, which are powder characteristics, can be adjusted by a mixing method and an oxidation treatment.

In the present invention, the weight ratio of titanium to carbon in the lithium-titanium composite oxide is preferably 1: 0.08 to 1: 0.1. When the content of carbon is less than 0.08, the effect of improving the safety of the battery is insignificant. When the content of carbon is less than 0.1, the conductivity of the negative electrode is remarkably lowered, resulting in deterioration of the battery performance.

In the lithium-titanium composite oxide containing carbon in the crystal of the present invention, the particle size is 1 to 50 탆.

According to the production method of the present invention, carbon is contained in the lithium-titanium composite oxide crystal, and the lithium secondary battery using the lithium-titanium composite oxide containing carbon in such a crystal structure exhibits high-rate characteristics.

Fig. 1 shows an analysis photograph (Example 1A, Comparative Example 1B) of a cut surface of a cathode active material according to Examples of the present invention and Comparative Example and SEM photograph (Fig. 1C) of a cathode active material of the Example.
FIG. 2 is a graph showing a result of measuring the capacitance while charging a coin battery manufactured by using a lithium-titanium composite oxide containing carbon in the crystal of the present invention as a cathode active material and then varying the current density.
FIG. 3 is a graph showing a result of measuring the capacity while charging a coin battery manufactured using a conventional lithium-titanium composite oxide as a cathode active material and then varying the current density.

≪ Example 1 > Preparation of cathode active material

1 mol of lithium hydroxide, 1 mol of anatase type titanium oxide and 1 mol of graphite as a starting material were mixed in a solid phase and dissolved in water with stirring. Zirconia beads at 3000 rpm and then spray-dried at a hot air temperature of 270 ° C and an exhaust hot air temperature of 120 ° C and heat-treated at 700 ° C for 10 hours in an oxygen atmosphere to obtain a lithium-titanium composite Oxide.

<Comparative Example>

1 mol of lithium hydroxide as a starting material was dissolved in 451 g of water with stirring. Anatase-type titanium oxide (2.453 mol as TiO2) having a purity of 98% was added to the solution and stirred. The atomic ratio of Li to Ti is 4: 5. The volume of the mixed slurry was 0.502 L, and the slurry concentrations of Li source and Ti source before drying were 3.91 mol / L and 4.89 mol / L, respectively. The mixture was spray-dried at 110 DEG C, and then the dried mixture was heat-treated at 800 DEG C for 6 hours in an N2 gas atmosphere to prepare a lithium-titanium composite oxide.

<SEM photograph measurement>

The cut surfaces of the lithium-titanium composite oxide containing carbon and the lithium-titanium composite oxide of the comparative example were observed by SEM EDAX to determine whether or not each metal element was detected in each cross section. And FIG. 1B. In the case of LTO according to the embodiment of the present invention, a carbon element was detected in the cross section, and it was confirmed that carbon according to the present invention is a structure including carbon in the crystal. On the other hand, in the case of LTO according to the comparative example, it was confirmed that only oxygen and titanium elements were detected in the cross section.

A scanning electron micrograph of the secondary particles of the lithium-titanium composite oxide according to the embodiment of the present invention is shown in FIG. 1C. In the case of the lithium-titanium composite oxide according to the embodiment of the present invention, the primary particles are composed of aggregated secondary particles, and the secondary particles have a diameter of 1 to 50 탆.

&Lt; Example 2 > Preparation of coin battery

The lithium-titanium composite oxide containing carbon was used as the cathode active material, the lithium foil was used as the counter electrode, and a porous polyethylene film (Celgard 2300, thickness: 25 Mu m) as a separator, and a liquid electrolyte in which LiPF ₆ was dissolved in a concentration of 1 mol in a solvent in which ethylene carbonate and dimethyl carbonate were mixed at a ratio of 1: 2 by volume, was used to prepare a coin battery . In the case of the comparative example, a coin battery was similarly manufactured.

&Lt; Evaluation of electrochemical characteristics &

An electrochemical analyzer (TOSCAT 3100, manufactured by Toyo Co., Ltd.) was used to evaluate the electrochemical characteristics of the test cell made of the cathode active materials of the examples and comparative examples. The electrochemical analysis was carried out at a current density of 0.2 mA / And discharge experiments were carried out. The results are shown in Fig. 2 (Example) and Fig. 3 (Comparative Example).

Claims (13)

i) solid-phase mixing the carbon compound, the lithium-containing compound, and the titanium oxide in a stoichiometric ratio;
ii) dispersing the solid mixture of i) in a solvent and wet-milling the slurry until it contains particles having an average particle diameter of less than 0.5 mu m;
iii) spray-drying the slurry of ii); and
iv) calcining the spray-dried slurry of iii)
Wherein the weight ratio of titanium to carbon is from 1: 0.01 to 1: 0.1.
Titanium composite oxide containing carbon in the crystal.
The method according to claim 1,
Wherein the carbon compound is at least one material selected from the group consisting of pyrocarbon, cokes, glassy carbon, organic polymer compound sintered body, and carbon fiber. Gt;
The method according to claim 1,
Wherein the titanium oxide is anatase type, rutile type titanium dioxide having a purity of 95% or more, or titanium oxide hydrate having a purity of 90% or more.
The method of claim 1, wherein
Wherein the lithium-containing compound is lithium hydroxide or lithium carbonate.
delete The method according to claim 1,
Wherein the wet grinding in the step ii) includes carbon in a crystal including wet grinding at 3000 to 4000 rpm using water as a solvent and zirconia beads as a solvent.
The method according to claim 1,
In the step of spray drying the slurry of ii) in the step iii), the step of spray drying the slurry of ii) may include spray-drying the hot air stream at a temperature of 250 to 300 ° C and the hot air stream temperature at 100 to 150 ° C, Oxide.
The method according to claim 1,
The firing step in the step iv) is a step of firing the spray dried product in the step iii) at 700 to 800 DEG C for 5 hours to 10 hours under a reducing atmosphere. The lithium-titanium composite oxide containing carbon Gt;
9. A process for producing a polyurethane foam according to any one of claims 1 to 4, 6 to 8,
A lithium-titanium composite oxide comprising carbon in a crystal formed by spherical secondary particles having a particle diameter of 1 to 50 mu m formed by aggregation of primary particles.
A positive electrode for a lithium secondary battery using a lithium-titanium composite oxide containing carbon as a positive electrode active material in the crystal of claim 9
A lithium secondary battery cathode using a lithium-titanium composite oxide containing carbon as a negative electrode active material in the crystal of claim 9
A lithium secondary battery containing the positive electrode of claim 10.
12. A lithium secondary battery comprising the negative electrode of claim 11.

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