KR101348547B1 - Surface coated lithium titanate powder and fabricating method thereof - Google Patents

Abstract

(a) providing a fine powder of lithium titanium oxide; And (b) atomically depositing a conductive material on the surface of the fine powder to form a coating layer.

Description

Surface coated lithium titanate powder and fabricating method

The present invention relates to a surface-coated lithium titanium oxide powder and a manufacturing method thereof, and more particularly to a surface-coated lithium titanium oxide powder used as an active material for secondary batteries having high electrical conductivity and excellent rate characteristics and a method for producing the same. .

Recently, the demand for secondary batteries is increasing due to the rapid increase in demand for portable devices such as mobile phones, notebook computers, camcorders, and the commercialization of hybrid electric vehicles and the development of pure electric vehicles. In particular, high power secondary batteries are required for automotive applications. Metallic lithium, carbon, etc. are used as a negative electrode material of a secondary battery. In the case of using metal lithium, dendritic crystals are formed on the surface of the anode material when charging and discharging are repeated, which is likely to cause a short circuit. Therefore, various types of carbon including artificial, natural graphite, and hard carbon capable of intercalating and deintercalating lithium can be used. System materials are commercially available. However, such a carbon-based negative electrode material has a low energy density per unit volume and a large irreversible capacity, resulting in a low initial charge and discharge efficiency and a decrease in capacity. In addition, lithium is deposited on the surface of the carbon during overcharging, and there is a risk of ignition due to the reaction of lithium with the electrolyte.

On the other hand, there is an attempt to use lithium titanium oxide of Li ₄ Ti ₅ O ₁₂ having a spinel structure as a negative electrode material. Lithium titanium oxide has a voltage of 1.5V on the basis of lithium metal, good cycle characteristics, and because the operating voltage is higher than the reduction potential of lithium, there is an advantage that can prevent the problem of lithium precipitated on the surface of the negative electrode during overcharging. Lithium titanium oxide of Li ₄ Ti ₅ O ₁₂ is promising as a large lithium secondary battery anode material because the change of crystal structure is very small even when repeated insertion and desorption reaction of lithium can ignore the expansion and contraction during charging and discharging. However, there is a problem in that the reaction resistance is high when the lithium insertion and desorption reaction is low due to the low electron conductivity, and thus, the characteristic of the rapid charging / discharging is significantly reduced, and there is a difficulty in application to a battery requiring high power. In order to overcome this problem, conventionally, an attempt has been made to coat carbon mainly on the surface of lithium titanium oxide particles as an active material by using a solution method (Korean Patent No. 1023354). At this time, since the active material is an oxide and the carbon is coated to coat the high temperature heat treatment, the coated carbon on the surface is oxidized to reduce the electrical conductivity contribution effect of the carbon layer coated on the surface of the active material.

According to one aspect of the invention, (a) providing a fine powder of lithium titanium oxide; And (b) atomically depositing a conductive material on the surface of the fine powder to form a coating layer.

According to another aspect of the invention, (a) mixing, heat treatment and grinding the lithium titanium oxide particles and metal particles to provide a fine mixed powder; And (b) forming a coating layer by atomically depositing a conductive material on the surface of the mixed fine powder.

According to another aspect of the invention, the lithium titanium oxide represented by the composition formula of Li _x Ti _y O ₄ (0.5≤x≤3, 1≤y≤2.5) or Li element site, Ti element site and O element in the above formula Fine powder of lithium titanium oxide in which at least one of the sites is substituted with a dissimilar element; A first coating layer having conductivity applied to the surface of the fine powder; And a second coating layer having conductivity applied to the first coating layer, wherein the first coating layer and the second coating layer each include any one of a metal or a non-metal conductive inorganic material. Powder is provided.

According to another aspect of the invention, the lithium titanium oxide represented by the composition formula of Li _x Ti _y O ₄ (0.5≤x≤3, 1≤y≤2.5) or Li element site, Ti element site and O element in the above formula Particles of lithium titanium oxide in which at least one of the sites is substituted with a heterogeneous element; And a coating layer having conductivity applied to the particle surface, wherein the fine powder is at least one selected from the group consisting of Cu, Ag, Zn, Fe, Co, Ni, Mn, Al, Mg, Cr, and Mo. Metal is alloyed, and the coating layer is provided with a surface-coated lithium titanium oxide powder containing either a metal or a non-metal conductive inorganic material.

According to another aspect of the present invention, there is provided an electrode including the lithium titanium oxide powder as an active material, and a secondary battery comprising the electrode.

1 is a cross-sectional view of a surface-coated lithium titanium oxide powder according to a first embodiment of the present invention.
2 shows a cross section of a surface coated lithium titanium oxide powder according to a second embodiment of the present invention.
Figure 3 shows a cross section of the surface-coated lithium titanium oxide powder according to a third embodiment of the present invention.

Hereinafter, the present invention will be described in detail.

According to one embodiment of the present invention, the surface-coated lithium titanium oxide may be prepared by the following process. That is, (a) providing a fine powder of lithium titanium oxide; And (b) forming a coating layer by atomically depositing a conductive material on the surface of the fine powder.

Lithium titanium oxide in the present invention may be represented by the composition formula of Li _x Ti _y O ₄ (0.5≤x≤3, 1≤y≤2.5). And the like, with specific examples _{Li 4/3 Ti 5/3} O 4, LiTi 2 O 4, Li 8/7 Ti 12/7 O 4, Li 4/5 Ti 11/5 O 4, ease of manufacturing and chemical stability In view of the charge and discharge capacity, the composition of Li ₄ Ti ₅ O ₁₂ is most preferable as the electrode active material.

However, lithium titanium oxide Li ₄ Ti ₅ O ₁₂ has a problem that the rate performance (rate performance) is not good for use as a negative electrode material of a battery that requires a high output due to high electrical resistance. The cause of lowering the rate characteristic of the battery seems to be caused by the polarization of the electrode material due to the high current and the increase of the internal resistance of the electrode. In order to reduce the internal resistance of the electrode, Li ₄ Ti ₅ O ₁₂ may be doped with other heterogeneous elements or uniformly coated with a highly conductive material on the surface of the negative electrode active material.

In order to increase battery capacity and improve rate characteristics, the lithium titanium oxide may be doped with at least one or more sites, preferably at least two or more sites of Li element sites, Ti element sites, and O element sites. As a specific example, Li _{(4-x) / 3} Ti _{(5-2x) / 3} A _x O _4-y C _y based on the spinel oxide of Li ₄ Ti ₅ O ₁₂ (0 ≦ x ≦ 0.9, ≦ y Lithium titanium oxide which has a composition formula of (= 0.5) is mentioned. Where there is a seat ^{3 +} Cr, Al ^{+ 3,} Ni ^{+ 3,} attempt to achieve an enhanced increase in the capacity and rate characteristics by addition of a variety of one kinds of elements such as Mn ^{+ 3} in the A. However, lithium titanium is improved when two or more elements are replaced at the same time in various composition ranges, or two or more elements are replaced at the same time with Br ^- or F ^- in place of C. Oxide capacity and electrical conductivity will be expected.

Other examples include _{Li 4 Ti 5 - x B x} O 12 - y C y include lithium titanium oxide having the formula (0 ≤ x ≤ 0.9, ≤ y ≤ 0.5). The Again substitution on the different composition range of La, Mo, Zr, Ta, V the element position of B, and at the same time, in place of the C Br ^- or F ^- for the Li ₄ Ti ₅ O ₁₂ spinel oxide based even if the substituted An improvement in electrochemical properties can be expected.

The fine powder of lithium titanium oxide can be produced by various known methods. For example, the raw material precursors constituting the final lithium titanium oxide to be prepared can be mixed in a quantitative ratio, and then pulverized in a solvent by a mechanical grinding method such as ball milling to obtain fine powder. Alternatively, the raw material precursor may be absorbed into the activated cellulose treated with nitric acid, then dried and heat treated, and then ground to obtain fine powder. In some embodiments, a mixed fine powder in which metal particles, such as Al and Cu, are mixed with annealing and then pulverized to lithium titanium oxide particles formed as a single phase obtained in one of the above manners, and then pulverized to integrally mix metal particles with lithium titanium oxide. You can also get

The size of the lithium titanium oxide fine powder of the present invention may have an average particle diameter of 0.1 μm to 100 μm, and preferably 1 μm to 20 μm. When the lithium titanium oxide of the present invention is used as the active material particles of the secondary battery, when the particle size is smaller than the above range, it may be difficult to mix the carbon black, the binder, and the like, in the preparation of the electrode slurry. The electrode surface may become uneven after electrode application.

In order to obtain higher conductivity after obtaining the fine powder of lithium titanium oxide in the above-described manner, it is necessary to coat a highly conductive uniform material on the surface of the powder thus prepared. Conventionally, the carbon precursor is coated on the surface of the active material using a solution method, and then heat-treated at a high temperature of 600 to 900 ° C. At this time, an uncoated area is not generated due to the reduction in coating uniformity. .

In the present invention, in order to overcome such disadvantages, a coating layer is formed by uniformly depositing a conductive material on the surface of lithium titanium oxide particles using atomic layer deposition without using a solution method. The use of an atomic layer evaporator enables the deposition of highly crystalline inorganic thin films on the surface of lithium titanium oxide particles at a low temperature and has the advantage of being very finely controlled in thickness.

Atomic layer evaporator is a device using nano thin film deposition technology that uses the phenomenon of chemically adhering monoatomic layer, and has a method of alternately adsorbing and replacing molecules. Since it has the characteristics of a chemical vapor deposition (CVD) at the same time, the oxide and the metal thin film can be uniformly deposited at a low temperature even in a minute gap. Therefore, it is possible to uniformly coat each surface of the powder particles on the substrate.

The conductive material may be any one selected from the group consisting of metals and nonmetal conductive inorganics. Non-limiting examples of the metal used as the conductive material include Cu, Ag, Zn, Fe, Co, Ni, Mn, Al, Mg, Cr, Mo, etc., Al or Cu, preferably a ductile metal Can be. On the other hand, the non-metal conductive inorganic material used as the conductive material is not particularly limited as long as it is a material capable of forming an inorganic thin film of high conductivity, and may include Al substituted ZnO, RuAlO, TiC _x and the like.

The coating layer formed through atomic layer deposition may be a single coating layer including a metal. When Al or Cu is uniformly deposited on the surface, Al and Cu may contribute to the improvement of conductivity. However, when the anode material is pasted on the current collector using a ductile feature, it is a good link between particles. Also do.

More preferably, the coating layer may be a double coating layer of the non-metal conductive inorganic layer and the metal layer. The atomic layer deposition may include depositing a first coating layer comprising a nonmetallic conductive inorganic material to form a double coating layer; And depositing a second coating layer including a metal on the first coating layer. For example, by using an atomic layer evaporator, a highly conductive inorganic thin film such as ZnO, RuAlO, TiC _x, etc., in which Al is substituted, is uniformly coated on the surface of the lithium titanium oxide anode particle, and then coated with Al or Cu to form a coating with a double layer. This significantly improves the electrical conductivity.

According to another embodiment of the present invention, the method for producing a surface-coated lithium titanium oxide powder comprises the steps of: (a) mixing, heat treating and grinding lithium titanium oxide particles and metal particles to provide a fine mixed powder; And (b) forming a coating layer by atomically depositing a conductive material on the surface of the mixed fine powder.

The metal particles may be at least one selected from the group consisting of Cu, Ag, Zn, Fe, Co, Ni, Mn, Al, Mg, Cr, and Mo. Preferably it may be Al or Cu with good ductility.

For example, a lithium titanium oxide active material formed of a single phase and Al particles or Cu particles are mixed and heat treated, followed by ball milling to synthesize particles in which Al particles or Cu particles and a lithium titanium oxide active material are mixed in one mass. The formed particles have an advantage in that the conductive network is well formed by Al or Cu internally. If a single coating layer or a double coating layer is formed on the surface of the active material formed as above using an atomic layer deposition machine, better electrical conductivity can be expected.

In some embodiments, the thickness of the conductive material coated on the surface of the lithium titanium oxide particles may be in the range of 1 nm to 100 nm, preferably in the range of 1 nm to 40 nm. In this case, the coated conductive material layer is very uniformly covered on the surface of the lithium titanium oxide particles, and is effective in showing excellent conductive properties. The surface coating method of lithium titanium oxide using a general carbon precursor additionally requires a high temperature heat treatment of 400 ° C. or higher, but does not require an additional heat treatment process because the coating is completed at a low temperature using an atomic layer deposition machine.

According to the first embodiment of the present invention, the lithium titanium oxide represented by the composition formula of Li _x Ti _y O ₄ (0.5≤x≤3, 1≤y≤2.5) or Li element site, Ti element site and O in the above formula There is provided a surface coated lithium titanium oxide powder based on particles of lithium titanium oxide in which at least one of the element sites is replaced by a heterogeneous element. And a coating layer having conductivity applied to the particle surface. Here, the fine powder may be alloyed with another metal, and Al or Cu having good ductility is preferably alloyed. In addition, the coating layer includes any one of a metal and a nonmetal conductive inorganic material.

1 is a cross-sectional view of a surface-coated lithium titanium oxide powder according to a first embodiment of the present invention. In the figure, LTO represents doped or undoped lithium titanium oxide.

Further, according to the second embodiment of the present invention, lithium titanium oxide represented by the composition formula of Li _x Ti _y O ₄ (0.5≤x≤3, 1≤y≤2.5) as in the above-described embodiment or the element Li in the composition formula At least one or more of the sites, Ti element sites and O element sites is provided based on a fine powder of lithium titanium oxide substituted with a heterogeneous element, and a lithium titanium oxide powder having a double layer coated surface is provided. That is, a conductive first coating layer exists on the surface of the fine powder. In addition, the second coating layer having a conductivity in the first coating layer constitutes a double layer coating. Wherein the first coating layer and the second coating layer each comprise any one of a metal or a non-metal conductive inorganic material.

2 shows a cross section of a surface coated lithium titanium oxide powder according to a second embodiment of the present invention. The double layer of the first coating layer and the second coating layer may be in the form of a metal layer / non-metal conductive inorganic layer or in the form of a non-metal conductive inorganic layer / metal layer. Preferably, the first coating layer may include a non-metal conductive inorganic material, and the second coating layer may include a metal.

According to the third embodiment of the present invention, the lithium titanium oxide fine powder of the second embodiment may be alloyed with another metal. That is, the fine powder may be alloyed with at least one metal selected from the group consisting of Cu, Ag, Zn, Fe, Co, Ni, Mn, Al, Mg, Cr, and Mo. 3 shows a cross section of a surface coated lithium titanium oxide powder according to a second embodiment of the present invention.

According to the present invention, lithium titanium oxides such as Li ₄ Ti ₅ O ₁₂ or doped lithium titanium oxides (eg, Li element sites, Ti element sites, O element sites, or two or all three sites at the same time are heterogeneous. Element-substituted material), and then using ZnO, RuAlO, TiC _x thin film substituted with Al, which is a conductive ceramic, using the atomic layer deposition machine, which is a physical method, to precisely control the thickness and uniformity of the surface of the negative electrode active material body Coating can maximize the effect of improving electrical conductivity. Therefore, the rate performance of a lithium secondary battery can be improved. In addition, capacity increase can be expected by multi-element substitution.

Hereinafter, the present invention will be described in more detail with reference to specific examples, which are only intended to help the understanding of the present invention, but the present invention is not limited thereto.

[Example]

Example   One

The precursors constituting the final lithium titanium oxide based composition to be prepared are mixed quantitatively. For example, _{Li 1 .3 Ti 1 .6 Cr 0} .1 O 3 .9 when trying to produce a negative electrode active material of _{Br 0 .1 Li 2 CO 3,} TiO 2, Cr (NO 3) 3 -9H 2 O, Precursors of LiBr-H ₂ O are mixed to the stoichiometric ratio of the final composition. Then, ball milling is performed for 24 hours by mixing alcohol or acetone with Zr balls as a solvent. The ball milled precursor powder is dried and then calcined in air or in a reducing atmosphere for 12 hours, and then crushed to form a fine powder by ball milling. The powder is spread thinly on a glass substrate, and finally, an atomic layer deposition machine is used to uniformly coat a desired Al or Cu metal conductive layer at a temperature of 250 ° C. or lower to prepare a final negative electrode material. More preferably, a highly conductive inorganic thin film such as ZnO, RuAlO, TiC _x, etc., in which Al is substituted, is coated on the surface of the lithium titanium oxide active material, and then Al or Cu metal is uniformly coated on the surface to form a coating layer in duplicate. To prepare a secondary battery negative electrode active material.

Example  2

Various precursors are dissolved in a solvent such as an aqueous solution and glycine is added according to the stoichiometric ratio of the final composition to be prepared by preparing activated cellulose treated with nitric acid. The mixed solution is slowly absorbed into the activated cellulose. After drying at 80 ° C. for several hours, burning at 250 ° C., pulverizing to powder, and finally calcining at 900 ° C. or lower. The calcined material is pulverized again and then uniformly distributed on the glass substrate, and then the Al or Cu metal conductive layer is homogeneously conductive coated on the surface of the negative electrode active material particles using an atomic layer deposition machine. More preferably, a highly conductive inorganic thin film such as ZnO, RuAlO, TiC _x, etc., in which Al is substituted, is coated on the surface of the lithium titanium oxide active material, and then Al or Cu metal is uniformly coated on the surface to form a coating layer. Finally, a secondary battery negative electrode active material is prepared.

Example  3

The precursors constituting the final lithium titanium oxide based composition to be prepared are mixed quantitatively. For example, _{Li 1 .3 Ti 1 .6 Cr 0} .1 O 3 .9 when trying to produce a negative electrode active material of _{Br 0 .1 Li 2 CO 3,} TiO 2, Cr (NO 3) 3 -9H 2 O, Precursors of LiBr-H ₂ O are mixed to the stoichiometric ratio of the final composition. Then, ball milling is performed for 24 hours by mixing alcohol or acetone with Zr balls as a solvent. The ball milled precursor powder is dried and then calcined in air or in a reducing atmosphere for 12 hours, and then crushed to form a fine powder by ball milling. The lithium titanium oxide active material formed in a single phase and Al particles or Cu particles are mixed and heat treated, followed by ball milling to synthesize particles in which Al particles or Cu particles and a lithium titanium oxide active material are mixed in one mass. A single layer coating film or a double layer coating film is formed on the surface of the formed particles using the atomic layer deposition machine as in the examples of Examples 1 and 2.

The formed powder is spread thinly on a glass substrate, and finally a uniform Al or Cu metal conductive layer is uniformly coated at a temperature of 250 ° C. or lower using an atomic layer deposition machine to prepare a final negative electrode material. More preferably, a highly conductive inorganic thin film such as ZnO, RuAlO, TiC _x, etc., in which Al is substituted, is coated on the surface of the lithium titanium oxide active material, and then Al or Cu metal is uniformly coated on the surface to form a coating layer in duplicate. To prepare a secondary battery negative electrode active material.

Example  4

Various precursors are dissolved in a solvent such as an aqueous solution and glycine is added according to the stoichiometric ratio of the final composition to be prepared by preparing activated cellulose treated with nitric acid. The mixed solution is slowly absorbed into the activated cellulose. After drying at 80 DEG C for several hours, burning at 250 DEG C, pulverizing to powder, and finally calcining at 900 DEG C or lower. The calcined material is again mixed with Al particles or Cu particles, heat treated, and then pulverized to synthesize Al particles or Cu particles and particles in which a lithium titanium oxide active material is mixed in one mass.

The pulverized particles are evenly distributed on the glass substrate, and then an Al or Cu metal conductive layer is uniformly coated on the surface of the negative electrode active material particles using an atomic layer deposition machine. More preferably, a highly conductive inorganic thin film such as ZnO, RuAlO, TiC _x, etc., in which Al is substituted, is coated on the surface of the lithium titanium oxide active material, and then Al or Cu metal is uniformly coated on the surface to form a coating layer in duplicate. To prepare a secondary battery negative electrode active material.

As described above, the present invention provides a method for producing lithium titanium oxide based particles in which a conductive material is uniformly coated so as to be suitable for a lithium secondary battery negative electrode material capable of high speed charging and discharging. Conventional spinel oxides of pure Li ₄ Ti ₅ O ₁₂ have low electrical conductivity and poor rate characteristics of secondary batteries, but dopants of various elements in place of Li, Ti, O, or alloy ductile metals and at the same time Forming a highly conductive uniform conductive material coating layer using a vapor deposition machine can overcome low electrical conductivity, which is very useful for power tools and hybrid electric vehicles requiring high power. Considering the very small volume expansion and shrinkage characteristics of the charge-discharge characteristic of this material, it is useful for large secondary battery applications, which will contribute to the improvement of efficiency of the large battery.

Claims (14)

(a) providing a fine powder of lithium titanium oxide; And
(b) atomically depositing a conductive material on the surface of the fine powder to form a coating layer,
The step (a) is a method for producing a surface-coated lithium titanium oxide powder, characterized in that to provide a mixed fine powder by mixing, heat treatment and grinding the lithium titanium oxide particles and metal particles. The method according to claim 1,
The lithium titanium oxide is Li _x Ti _y O ₄ (0.5≤x≤3, 1≤y≤2.5) A method for producing a surface-coated lithium titanium oxide powder represented by the formula. The method according to claim 1,
The lithium titanium oxide is a method for producing a surface-coated lithium titanium oxide powder in which at least one or more of the Li element site, Ti element site and O element site is substituted with a heterogeneous element. The method according to claim 1,
Wherein the conductive material is any one selected from the group consisting of metals and non-metal conductive inorganics. The method according to claim 1,
The coating layer is a method of producing a surface-coated lithium titanium oxide powder is a single coating layer containing a metal. The method according to claim 1,
The atomic layer deposition of step (b)
(b-1) depositing a first coating layer comprising a non-metal conductive inorganic material; And
(b-2) Method of manufacturing a surface-coated lithium titanium oxide powder comprising the step of forming a double coating layer by depositing a second coating layer containing a metal on the first coating layer. delete The method according to claim 1,
The metal particles are Cu, Ag, Zn, Fe, Co, Ni, Mn, Al, Mg, Cr and Mo one or more selected from the group consisting of surface-coated lithium titanium oxide powder manufacturing method. Lithium titanium oxide represented by the composition formula of Li _x Ti _y O ₄ (0.5≤x≤3, 1≤y≤2.5) or at least one of Li element site, Ti element site and O element site in the composition formula is heterogeneous Fine powder of lithium titanium oxide substituted with;
A first coating layer having conductivity applied to the surface of the fine powder; And
Including a second coating layer having a conductivity applied to the first coating layer,
The first coating layer and the second coating layer each comprise any one of a metal or a non-metal conductive inorganic material,
The fine powder is a surface coated lithium titanium oxide powder, characterized in that the alloy of one or more metals selected from the group consisting of Cu, Ag, Zn, Fe, Co, Ni, Mn, Al, Mg, Cr and Mo. 10. The method of claim 9,
Wherein said first coating layer comprises a non-metal conductive inorganic material, and said second coating layer comprises a metal. delete Lithium titanium oxide represented by the composition formula of Li _x Ti _y O ₄ (0.5≤x≤3, 1≤y≤2.5) or at least one of Li element site, Ti element site and O element site in the composition formula is heterogeneous Fine powder of lithium titanium oxide particles substituted with; And
Including a coating layer having a conductivity applied to the surface of the fine powder,
The fine powder is the lithium titanium oxide particles are alloyed with Al or Cu,
The coating layer is a surface-coated lithium titanium oxide powder containing any one of metal or non-metal conductive inorganic. An electrode comprising the surface-coated lithium titanium oxide powder according to any one of claims 9, 10, or 12 as an active material. A secondary battery comprising the electrode of claim 13.

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