WO2012153561A1

WO2012153561A1 - Lithium titanate particles, active material, and method for producing lithium titanate particles

Info

Publication number: WO2012153561A1
Application number: PCT/JP2012/054798
Authority: WO
Inventors: 和生橋本; 博文竹本; 寛之藤野; 吉積田中; 秀哉吉武
Original assignee: 宇部興産株式会社
Priority date: 2011-05-12
Filing date: 2012-02-27
Publication date: 2012-11-15
Also published as: JP5892161B2; TW201300323A; JPWO2012153561A1

Abstract

Provided are: lithium titanate particles having high rate characteristics; an active material; and a method for producing lithium titanate particles. The lithium titanate particles contain a metal-substituted lithium titanate which is doped with Cr, Fe and Ni. The lithium titanate particles has a main peak intensity of anatase titanium dioxide of 5 or less, a main peak intensity of rutile titanium dioxide of 5 or less and a peak intensity corresponding to the main peak of Li₂TiO₃ of 3 or less when the peak intensity corresponding to the main peak of Li₄Ti₅O₁₂ is taken as 100 among the peaks as determined by an x-ray diffraction method. The lithium titanate particles has a volume-based median diameter (D50) of 0.1-1 μm.

Description

Lithium titanate particles, active material, and method for producing lithium titanate particles

The present invention relates to a lithium titanate particle suitable as an electrode material of an electricity storage device, a method for producing the same, and an active material using the lithium titanate particle.

In recent years, various materials have been studied as electrode materials for lithium secondary batteries. Among them, lithium titanate is attracting attention because it has a large theoretical capacity. As lithium titanate, Li ₄ Ti ₅ O ₁₂ , LiTi ₂ O ₄ , Li ₂ TiO _{3 and the} like are known. Among these, Li ₄ Ti ₅ O ₁₂ is attracting attention because of its particularly large capacity (theoretical value: 175 mAh / g).
In Patent Document 1, Li _4/3 Ti _5/3 O ₄ (Li ₄ Ti ₅ O ₁₂ ) is the main component, and the main peak intensity of Li _4/3 Ti _5/3 O ₄ by the X-ray diffraction method is 100. The main peak intensity of anatase-type titanium dioxide, rutile-type titanium dioxide, and Li ₂ TiO ₃ is all lithium titanate of 5 or less, and the crystallite diameter is 700 to 800 mm. Crystalline lithium titanate is disclosed. According to Patent Document 1, since this lithium titanate has a small amount of components other than Li ₄ Ti ₅ O ₁₂ , the initial charge / discharge capacity can be set to 165 mAh / g or more.
Patent Document 2 _discloses at least one selected from the group consisting of Mg, Nb, Al, Zr, Ni and Co at the Ti site of Li _4/3 Ti _5/3 O ₄ (Li ₄ Ti ₅ O ₁₂ ). Including lithium titanate is disclosed. According to Patent Document 2, it is said that a high capacity can be obtained in high rate charge / discharge.
Patent Document 3 _discloses that Be, B, C, Mg, Al, Si, P, Ca, Sc, V, and Ti at a Ti site of Li _4/3 Ti _5/3 O ₄ (Li ₄ Ti ₅ O ₁₂ ). Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Sr, Y, Zr, Nb, Mo, Pd, Ag, Cd, In, Sn, Sb, Te, Ba, La, A lithium titanate substituted with Ta, W, Au, Hg, Pb or the like is disclosed. By replacing a part of titanium with a different element, this bulkiness can be suppressed, and there is a function of smoothly transferring ions and electrons between particles, thereby improving electrode performance.
In Patent Document 4, Li sites of lithium titanate represented by the general formula Li _X _MY Ti _Z O ₄ are represented by cobalt, nickel, manganese, vanadium, iron, boron, aluminum having a valence of 2 or more. Lithium titanate substituted with at least one metal selected from the group consisting of silicon, zirconium, strontium, magnesium and tin is disclosed. By substituting a part of Li, doping and undoping of lithium ions are facilitated, and characteristics such as battery capacity can be improved when used as an electrode for a lithium battery. However, if the Li site is replaced with another element, it is considered that the capacity decreases.

Japanese Patent Laid-Open No. 2001-240498 JP 2010-135237 A Japanese Patent Laid-Open No. 2001-196061 JP-A-10-251020

Lithium titanate mainly composed of Li ₄ Ti ₅ O ₁₂ as in Patent Documents 1 to 4 has a high capacity value and excellent rate characteristics, but further improvement of the rate characteristics is desired.
Here, the rate characteristics refer to the relationship between charge / discharge current and dynamic capacity. It is said that the rate characteristic is high when the capacity decreases little even when charging / discharging with a large current. When the rate characteristic is high, the output density (the power (current × voltage) that can be taken out from the battery divided by the total weight or the total volume of the battery) increases, and it is excellent as an electrode material.
An object of the present invention is to provide a lithium titanate particle, an active material, and a method for producing a lithium titanate particle having high rate characteristics.

As a result of various studies to achieve the above-mentioned object, the present inventor has found that rate characteristics can be improved by using a metal-substituted lithium titanate containing Cr, Fe, and Ni, thereby completing the present invention. did.
That is, the present invention provides the following (1) to (3).

(1) Lithium titanate particles containing metal-substituted lithium titanate doped with Cr, Fe, and Ni.
(2) An active material containing the lithium titanate particles.
(3) The lithium titanate particles including a firing step of heating a mixture containing Cr, Fe, and Ni, a titanium compound, and a lithium compound at a firing temperature of 600 to 1000 ° C. for a firing time of 10 to 120 minutes. Production method.

According to the present invention, it is possible to provide lithium titanate particles having high rate characteristics and suitable as an electrode material for an electricity storage device, a method for producing the same, and an active material.

It is a graph which shows the charge rate characteristic of an Example and a comparative example. It is a graph which shows the charge capacity maintenance factor of an Example and a comparative example.

[Lithium titanate particles]
The lithium titanate particles of the present invention contain metal-substituted lithium titanate doped with Cr, Fe, and Ni. Thus, the metal-substituted lithium titanate doped with Cr, Fe, and Ni has high rate characteristics.

<Metal-substituted lithium titanate>
Metal-substituted lithium titanate of the present invention is Cr, Fe, and Ni doped into Li ₄ Ti ₅ O _12. The metal-substituted lithium titanate is preferably represented by the following general formula (1).
Li _{4 + x} Ti _5- _{y My} O ₁₂ (1)
However, M must contain at least Cr, Fe, and Ni, and may further contain one or two of Zr and Al as optional components.
The metal-substituted lithium titanate represented by the general formula (1) has a spinel structure like Li ₄ Ti ₅ O ₁₂ and has a large charge capacity and discharge capacity. In addition, the metal-substituted lithium titanate represented by the general formula (1) is excellent in rate characteristics as compared with Li ₄ Ti ₅ O ₁₂ that is not metal-substituted as described later.

In the above general formula (1), the values of x and y are preferably −0.05 ≦ x ≦ 0.25 and 0 <y ≦ 0.2. Within this range, the rate characteristics, charge capacity, and discharge capacity are good. From these viewpoints, the range of x is more preferably 0 ≦ x ≦ 0.25, still more preferably 0 ≦ x ≦ 0.2, and the range of y is more preferably 0.01 ≦ y ≦ 0. .2, more preferably 0.05 ≦ y ≦ 0.2, and still more preferably 0.08 to 0.15.

<Other phases>
In addition to the metal-substituted lithium titanate, anatase-type titanium dioxide, rutile-type titanium dioxide, and Li ₂ TiO ₃ may be present in the lithium titanate particles. However, if these phases are present, the content of the metal-substituted lithium titanate is relatively lowered and the rate characteristics, charge capacity, and discharge capacity are lowered. Therefore, it is preferable that these phases be small.
From this viewpoint, when the peak intensity corresponding to the main peak of Li ₄ Ti ₅ O ₁₂ among the peaks measured by the X-ray diffraction method is 100, the main peak intensity of the anatase-type titanium dioxide is preferably 5 Or less, more preferably 3 or less, still more preferably less than 1, and still more preferably 0.
Here, “the peak intensity corresponding to the main peak of Li ₄ Ti ₅ O ₁₂ ” means the main peak existing at a position that approximates the main peak of Li ₄ Ti ₅ O _{12 in} the metal-substituted lithium titanate. It means peak intensity.

Moreover, when the peak intensity corresponding to the main peak of Li ₄ Ti ₅ O ₁₂ among the peaks measured by the X-ray diffraction method is 100, the main peak intensity of rutile titanium dioxide is preferably 5 or less. , More preferably 3 or less, even more preferably 2 or less, still more preferably 1 or less, and even more preferably 0.
Of the peaks measured by the X-ray diffraction method, when the peak intensity corresponding to the main peak of Li ₄ Ti ₅ O ₁₂ is 100, the main peak intensity of the peak corresponding to Li ₂ TiO ₃ is preferably 3 or less. More preferably, it is 2 or less, More preferably, it is 1 or less, More preferably, it is 0.
Here, the "peak intensity corresponding to the main peak of Li ₂ TiO _3", among the peaks of the compound obtained by doping the metal M with respect to Li ₂ TiO _3, a main peak of Li ₂ TiO ₃ approximation It means the peak intensity of the main peak existing at the position. The peak intensity refers to the height from the baseline to the peak top.

<Cr, Fe, and Ni>
The Fe content relative to the entire lithium titanate particles is preferably 5 to 300 ppm by mass. If it is 5 ppm by mass or more, the rate characteristics will be good. The fall of charge capacity and discharge capacity is suppressed as it is 300 mass ppm or less. From these viewpoints, the Fe content is more preferably 10 to 250 ppm by mass, still more preferably 50 to 200 ppm by mass, and still more preferably 100 to 200 ppm by mass.
The content of Cr with respect to the entire lithium titanate particles is preferably 5 to 200 ppm by mass. If it is 5 ppm by mass or more, the rate characteristics will be good. The fall of charge capacity and discharge capacity is controlled as it is 200 mass ppm or less. From these viewpoints, the Cr content is more preferably 10 to 150 ppm by mass, still more preferably 10 to 120 ppm by mass, and still more preferably 10 to 100 ppm by mass.
The content of Ni with respect to the entire lithium titanate particles is preferably 5 to 200 ppm by mass. If it is 5 ppm by mass or more, the rate characteristics will be good. The fall of charge capacity and discharge capacity is controlled as it is 200 mass ppm or less. From these viewpoints, the Ni content is more preferably 5 to 150 ppm by mass, still more preferably 5 to 120 ppm by mass, and still more preferably 5 to 100 ppm by mass.

<Li and Ti>
In the lithium titanate particles, the atomic ratio Li / Ti of Li to Ti is preferably 0.79 to 0.87. Within this range, the proportion of spinel-structured metal-substituted lithium titanate Li ₄ Ti ₅ O _{12 in} the lithium titanate particles increases, and the charge capacity and discharge capacity increase. In this respect, the atomic ratio Li / Ti is more preferably 0.79 to 0.85, further preferably 0.80 to 0.85, and still more preferably 0.81 to 0.85. More preferably, it is 0.82 to 0.85.

<Zr>
The lithium titanate particles may further contain Zr. The content of Zr with respect to the entire lithium titanate particles is preferably 5 to 1000 ppm by mass. If it is 5 ppm by mass or more, the rate characteristics will be good. The fall of charge capacity and discharge capacity is controlled as it is 1000 mass ppm or less. From these viewpoints, the Zr content is more preferably 5 to 800 ppm by mass, further preferably 5 to 600 ppm by mass, still more preferably 50 to 150 ppm by mass, and still more preferably 80 ppm. ~ 120 ppm.

<Al>
The lithium titanate particles may further contain Al. The content of Al with respect to the entire lithium titanate particles is preferably 0.03 to 5% by mass. A rate characteristic becomes it favorable that it is 0.03 mass% or more. When the content is 5% by mass or less, a decrease in charge capacity and discharge capacity is suppressed. From these viewpoints, the Al content is more preferably 0.1 to 5% by mass, still more preferably 1 to 5% by mass, still more preferably 1 to 3% by mass, and still more preferably. Is 1 to 2% by mass.

<Particle size>
The volume median particle size (D50) of the lithium titanate particles is preferably 0.1 to 1 μm. When it is 0.1 μm or more, aggregation and the like are suppressed when an electrode is prepared using the lithium titanate particles, and the handleability is excellent. When it is 1 μm or less, charge / discharge characteristics are improved. From these viewpoints, D50 is more preferably 0.2 to 0.9 μm, still more preferably 0.4 to 0.8 μm, still more preferably 0.5 to 0.7 μm, and still more. Preferably, it is 0.6 to 0.7 μm.
Here, “volume median particle size (D50)” means a particle size at which the cumulative volume frequency calculated by the volume fraction is 50% when calculated from the smaller particle size. The measuring method is as described later.

<BET specific surface area>
The BET specific surface area (hereinafter also simply referred to as “specific surface area”) of lithium titanate particles by the nitrogen adsorption method is preferably 3 m ² / g or more, more preferably 5 m ² / g, from the viewpoint of improving rate characteristics. Or more, more preferably 7 m ² / g or more. Also, from the viewpoint of reducing the amount of solvent when the lithium titanate particles are dispersed in a solvent in the process of producing an electrode to make a slurry, it is preferably 100 m ² / g or less, more preferably 20 m ² / g or less. More preferably, it is 10 m ² / g or less. Therefore, the numerical range of the BRT specific surface area is preferably 3 to 100 m ² / g, more preferably 5 to 20 m ² / g, and further preferably 7 to 10 m ² / g.

<Bulk density and tap density>
From the viewpoint of increasing the capacity, the bulk density and tap density of the lithium titanate particles are preferably large.
The bulk density is preferably 0.1 g / ml or more, more preferably 0.2 g / ml or more, still more preferably 0.3 g / ml or more, still more preferably 0.4 g / ml or more. is there.
The tap density is preferably 0.5 g / ml or more, more preferably 0.6 g / ml or more, still more preferably 0.7 g / ml or more, and even more preferably 0.8 g / ml or more. And more preferably 1 g / ml or more.

<PH>
The pH of the lithium titanate particles is preferably 10-12. When it is 10 or more, there is an advantage that the dispersibility is good, and when it is 12 or less, there is an advantage that when the electrode slurry is produced, the slurry is gelled and cannot be slurried. From this viewpoint, it is more preferably 10.5 to 12, still more preferably 10.5 to 11.8, and still more preferably 11 to 11.8.
Here, the pH of the lithium titanate particles means the pH of the dispersion when 10 g of lithium titanate particles are dispersed in 90 g of water.

[Method for producing lithium titanate particles]
The lithium titanate particles can be obtained by mixing and refining the raw materials, firing, and then performing post-treatment such as crushing.
<Raw material>
As the Ti component, one or more of titanium compounds such as anatase type titanium dioxide and rutile type titanium dioxide are used. The volume median particle size (D50) of this Ti component is preferably 0.2 to 5 μm. When it is 0.2 μm or more, aggregation is suppressed, and the particle diameter of the lithium titanate particles after firing becomes small. If the particle size is 5 μm or less, the particle size of the Ti titanate particles after firing is small because the particle size of the Ti component is small.
As the Li component, lithium compounds such as lithium hydroxide monohydrate, lithium oxide, lithium hydrogen carbonate, and lithium carbonate are used. This Li component melts during firing.
As Al, Cr, Fe, Ni, and Zr, in addition to these metals and alloys, metal salts such as oxides, hydroxides, and carbonates are used.

<Mixing / miniaturization>
Mixing / miniaturization can be performed by a conventional method, and either wet or dry process may be performed. The device for efficiently obtaining the mixing is not particularly limited, but for example, a stirring device having stirring blades, an ultrasonic dispersion device, a homomixer, a mortar, a ball mill, a centrifugal ball mill, a planetary ball mill, a vibrating ball mill, an attritor type A high-speed ball mill, bead mill, roll mill, or other device that generates shearing force or impact force can be used. For example, a slurry in which a predetermined amount of the above raw material is mixed with water is stirred and mixed in a mixed layer, and then mixed and refined by a ball mill or a bead mill. There is no restriction | limiting in particular in the material of the ball | bowl with which a mill is filled, For example, iron, stainless steel, zirconia, titania, silicon carbide etc. are mentioned.
Moreover, it is preferable that the solid content concentration of the obtained mixture is 10 mass% or more. When the solid content concentration is 10% by mass or more, the load during drying is reduced, and the production efficiency of lithium titanate is improved.
After mixing and miniaturization in this way, the next firing is performed after drying as necessary.

<Baking>
Next, the mixture is fired. From the viewpoint of reducing the particle size of the particles obtained by firing, firing at a low temperature and in a short time is preferable. On the other hand, from the viewpoint of generating a larger amount of the compound represented by the general formula (1), it is preferable to perform baking at a high temperature for a long time. From these viewpoints, the firing temperature is preferably 600 to 1000 ° C., more preferably 650 to 900 ° C., and further preferably 700 to 900 ° C. Similarly, from the above viewpoint, the firing time is preferably 10 to 120 minutes, more preferably 15 to 120 minutes, still more preferably 20 to 120 minutes, and still more preferably 30 to 120 minutes.
The firing method is not particularly limited as long as it can be fired under the above conditions. As a firing method that can be used, a fixed bed type firing furnace, a roller hearth type firing furnace, a mesh belt type firing furnace, a fluidized bed type, or a rotary kiln type firing furnace can be considered. However, when efficient baking is performed in a short time, a rotary kiln type baking furnace, a roller hearth type baking furnace, or a mesh belt type baking furnace is preferable. In particular, rotary kiln-type firing furnaces do not require containers for raw materials, can be fired by continuously charging raw materials, and in addition, the heat history of the fired product is uniform, so a homogeneous product can be obtained. I can do it. Among them, the rotary kiln of the type provided with a stirring blade in the rotating cylinder is characterized in that the stirring blade rotates by rotating the rotating cylinder, and the raw material is scraped, fluidized, and floated. It is particularly preferable for synthesizing lithium titanate. In addition, raw materials mixed in a dry process can be used as raw materials. However, slurry prepared by a wet method in which raw material powder is mixed with a predetermined amount of water and mixed while being refined using a media such as a bead mill, is added as it is. Therefore, the rotary kiln-type firing method is particularly preferable for producing the lithium titanate of the present invention.
The atmosphere during firing is not particularly limited as long as the desorbed moisture and carbon dioxide gas can be removed. Usually, the lithium titanate particles of the present invention can be synthesized by using compressed air, but oxygen, nitrogen, hydrogen or the like may be used.
Next, firing using a rotating cylinder will be described in more detail.

(Baking using a rotating cylinder)
[Details of rotating cylinder]
In the case of using a rotary kiln of the type provided with a stirring blade in the rotating cylinder, the stirring blade has a plurality of blade pieces radially at equal intervals, and at least one tip of the blade pieces is the inner surface of the cylinder. It is preferable that the stirring blades are also rotated by the rotation of the cylindrical body. By rotating the stirring blade, the mixture in the cylindrical body is stirred and lifted by the blades of the stirring blade, the adhesion growth of the mixture on the inner surface of the cylindrical body is suppressed, and the contact between the mixture and the gas in the rotating cylindrical body and Heat transfer is kept good.

The rotating cylinder is preferably inclined with respect to the horizontal plane. Thereby, the mixture in the cylindrical body is sequentially sent from the raw material supply side to the recovery side, and during that time, drying and baking are performed. Here, the “raw material supply side” and the “recovery side” refer to the upper side and the lower side in the axial direction of the inclined rotating cylindrical body, respectively.
The inclination angle with respect to the horizontal plane is preferably 1 to 10 degrees. When the tilt angle is equal to or greater than the lower limit, the product can be easily discharged and can be recovered constantly. When the tilt angle is less than or equal to the upper limit value, the residence time of the raw materials in the rotating cylinder is prevented from becoming too short, and the mixture is sufficiently dried and fired. From this viewpoint, the inclination angle is more preferably 1 to 5 degrees.
The rotation speed of the rotating cylinder is preferably 5 to 40 rpm. When it is at least the lower limit value, the residence time of the mixture is prevented from becoming too short, drying becomes sufficient, and adhesion of the mixture to the inner surface of the rotating cylinder is prevented or suppressed. If it is less than or equal to the upper limit value, the rotational speed becomes too fast and the stirring effect is prevented from being reduced, and the stirring effect becomes sufficient. From this viewpoint, the rotation speed is more preferably 5 to 20 rpm, and further preferably 5 to 15 rpm.

The material of the blades of the stirring blade and the rotating cylinder is not particularly limited, but it is preferable to use austenitic heat resistant steel.
The rotating cylinder is preferably one that can control the internal temperature to a predetermined temperature. As the heating method, either an external heating source or an internal heating source of the rotating cylindrical body may be used, but an external heating source is preferable from the viewpoint of controlling the firing atmosphere.

[Baking]
When the mixture is fired using the rotating cylinder, first, the mixture is supplied to the raw material supply side of the rotating cylinder. The mixture may be supplied in either a slurry state or a dry state, but is preferably supplied directly in a slurry state. When supplying, a raw material supply means for quantitatively supplying the mixture to the rotating cylindrical body may be used. When the fluidity of the mixture is low, it may be supplied using a screw.
When the supplied mixture is in a slurry state, this mixture is swept into droplets by a stirring blade in a heated rotating cylinder, and rapidly dried and solidified on the surface of the rotating cylinder and gas while flowing and floating. And dehydrated.

This dried and solidified mixture is heated in a rotating cylinder, stirred and baked while being swirled. Similarly, the mixture supplied in the rotating cylinder in a dry state is also heated in the rotating cylinder, stirred, and baked while being swirled. The fired product thus obtained is recovered from the recovery side of the rotating cylinder.
In the process of drying and firing the mixture, the use of a stirring blade prevents or suppresses the mixture from adhering to the inner surface of the rotating cylindrical body, uniformly mixes the mixture, and shortens the heating time. Is played.

The heating temperature in the rotating cylinder is the same as that when a furnace other than the rotating cylinder is used.
On the other hand, the firing time in the case of using the rotating cylinder can be shortened compared to the case of using a furnace other than the rotating cylinder, and is preferably 10 to 90 minutes. When it is at least the lower limit, the mixture can be sufficiently fired, and when it is at most the upper limit, the operating cost can be reduced. From this viewpoint, the firing time is more preferably 15 to 60 minutes, further preferably 20 to 40 minutes, and still more preferably 20 to 30 minutes.

<Post-processing>
The above-mentioned lithium titanate particles can be obtained by subjecting the lump of the particles after firing to treatments such as crushing, classification, and magnetic separation by a conventional method.

[Active material]
The active material of the present invention contains the lithium titanate particles. One or more substances other than the lithium titanate particles may be included. Examples of other substances include carbon materials (pyrolytic carbons, cokes, graphites (artificial graphite, natural graphite, etc.), organic polymer compound combustion bodies, carbon fibers), tin and tin compounds, silicon and silicon compounds. Is used.

[Power storage device]
An electricity storage device such as a lithium secondary battery includes a positive electrode, a negative electrode, an electrolyte, and the like. The above active material can be suitably used as an active material for these positive electrode and negative electrode.
Next, regarding the constituent elements of these power storage devices, an electrolyte, a negative electrode active material when the active material is used as a positive electrode active material, and a positive electrode active when the active material is used as a negative electrode active material. Material materials will be described in this order.

<Electrolyte>
As the form of the electrolyte, there are a gel electrolyte and a solid electrolyte in addition to the electrolyte solution. These will be described in order.
(Electrolyte solution)
The electrolyte solution is obtained by dissolving a solute that exhibits ionic conductivity in a solvent.
[Solute]
The solute is not particularly limited as long as it exhibits ionic conductivity, and LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) _{3 and the} like. Is mentioned.
〔solvent〕
The solvent is not particularly limited as long as it dissolves and retains a solute and does not decompose during charge / discharge or storage of the battery, and an organic solvent is preferably used. Examples of organic solvents include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and vinylene carbonate (VC); chain carbonates such as dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), and diethyl carbonate (DEC). Cyclic ethers such as tetrahydrofuran (THF), 2-methyltetrahydrofuran (2MeTHF); chain ethers such as dimethoxyethane (DME); γ-butyrolactone (BL); acetonitrile (AN); sulfolane (SL); 1,3-propane And sultone such as sultone and 1,3-propene sultone. These organic solvents can be used alone or in a mixture of two or more.
(Gel electrolyte and solid electrolyte)
As the gel electrolyte, a gel polymer electrolyte obtained by impregnating a polymer electrolyte such as polyethylene oxide or polyacrylonitrile with an electrolytic solution can be preferably used.
As the solid electrolyte, an inorganic solid electrolyte such as LiI can be suitably used.

<Negative electrode active material when the above active material is used as a positive electrode active material>
When the active material of the present invention is used as a positive electrode active material, a Li metal such as Li metal, Li / Al alloy, Li / In alloy, Li / Al / Mn alloy, or the like is preferably used as the negative electrode active material. be able to.

<Positive electrode active material when the above active material is used as a negative electrode active material>
On the other hand, when the active material of the present invention is used as the negative electrode active material, examples of the positive electrode active material include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO ₂ , LiCo _0.5 Ni _0.5 O ₂ , LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiNi _0.7 Co _0.2 Mn _0.1 O ₂ , LiCo _0.9 Ti _0.1 O ₂ , LiCo _0.5 Ni _0.4 Zr _0.1 O ₂ , LiFePO ₄ , LiFe _1-x Co _x PO ₄ , LiMnPO ₄ , Lithium-containing transition metal composite oxides such as LiVPO ₄ ; carbon materials such as graphite, coke, and activated carbon can be used. When a lithium-containing transition metal composite oxide is used as the positive electrode active material, a lithium ion secondary battery that requires high load characteristics is used. When a carbon material is used, an electrochemical that requires high load characteristics is used. It can be suitably used for a capacitor.

<Structure of power storage device>
The structure of the electricity storage device is not particularly limited, and a coin-type battery having a positive electrode, a negative electrode, and a single-layer or multi-layer separator, and a cylindrical battery and a square battery having a positive electrode, a negative electrode, and a roll separator, etc. Is given as an example. As the separator, a known polyolefin microporous film, woven fabric, non-woven fabric, glass filter, paper (cellulose) or the like is used.

Further, the separator may have any structure of a single layer porous film and a laminated porous film. Although the separator varies depending on the production conditions, the air permeability is preferably 50 to 1000 seconds / 100 cc, more preferably 100 to 800 seconds / 100 cc, and even more preferably 300 to 500 seconds / 100 cc. When the air permeability is less than or equal to the upper limit, the function as a separator is sufficiently exhibited because of high ionic conductivity, and when the air permeability is greater than or equal to the lower limit, the mechanical strength is improved.
Further, the porosity of the separator is preferably 30 to 60%, more preferably 35 to 55%, and still more preferably 40 to 50%. In particular, it is preferable to set the porosity within this range because the capacity characteristics of the battery are improved.
Furthermore, the thickness of the separator is preferably as thin as possible because the energy density can be increased. However, it is preferably 5 to 50 μm, more preferably 10 to 40 μm, and still more preferably 15 to 25 μm from both aspects of mechanical strength and performance.

Next, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the following examples, and includes various combinations that can be easily inferred from the gist of the invention. In particular, it is not limited to the solvent combinations of the examples.
[Various measurement methods]

(1) XRD
The main peak intensity of the metal-substituted lithium titanate represented by the general formula (1) (diffraction angle 2θ = 18.1 to 18.5 ° in the range of peak intensity) by X-ray diffraction using CuKα rays, Main peak intensity of rutile titanium dioxide (diffraction angle 2θ = 27.0 to 27.6 °), main peak intensity of anatase titanium dioxide (diffraction angle 2θ = 24.7 to 25.7 °) And the main peak intensity of the metal-substituted Li ₂ TiO ₃ (with other metal M substituted at the Ti site) (peak intensity within the range of diffraction angle 2θ = 18.2 to 18.7 °) Was measured.
Then, the general formula (1) of the metal-substituted lithium titanate represented by the time of the main peak intensity is 100, the above-mentioned rutile titanium dioxide, anatase titanium dioxide, and the main peak intensity of the metal-substituted Li ₂ TiO ₃ The relative value of was calculated.
(2) Volume-median particle size (D50)
As a measuring device, a laser diffraction / scattering particle size distribution measuring machine (Nikkiso Co., Ltd., Microtrack MT3300EXII) was used. About 50 mg of a sample was placed in 50 ml of ion-exchanged water, and 3 drops of 0.2% sodium hexametaphosphate aqueous solution as a surfactant was added with a dropper, and this was treated with an ultrasonic disperser. The obtained solution was put into a measurement cell, distilled water was added, and the volume median particle diameter (D50) was measured when the transmittance of the apparatus was within an appropriate range.
(3) BET specific surface area (m ³ / g)
The BET specific surface area was measured by a one-point method using liquid nitrogen using a fully automatic BET specific surface area measuring device manufactured by Mountec Co., Ltd., trade name “Macsorb HM model-1208”.

(4) Bulk density (g / ml)
A sample was placed in a 10 ml graduated cylinder up to a 10 ml memory, the sample weight at that time was measured, and the value divided by the volume of the graduated cylinder was taken as the bulk density.
(5) Tap density (g / ml)
A 10-ml graduated cylinder subjected to bulk density measurement was tapped 300 times using a powder density measuring device (Powder Tester PT-E manufactured by Hosokawa Micron Corporation), and the density was calculated from the volume at that time and the weight of the sample.
(6) pH
The pH of the dispersion when 10 g of lithium titanate particles were dispersed in 90 g of water was measured.

(7) Charging rate characteristics At room temperature (25 ° C.), the coin battery is subjected to constant current charging for a predetermined time at 1.0 V and a predetermined C rate (charging rate) Y, and the charging capacity _BY is measured. did.
(8) the charging capacity retention ratio C _Y at each C-rate Y charge capacity maintenance rate was calculated by the following equation.
Charging capacity maintenance rate C _Y = B _Y / B _0.1

[material]
The following were used as raw materials for the lithium titanate particles.
(titanium dioxide)
Ti-1: anatase type titanium dioxide (manufactured by Kojundo Chemical Laboratory Co., Ltd. 2N, D50 = 0.5 μm)
Ti-2: Rutile type titanium dioxide (4N, D50 = 0.5 μm, Al ₂ O ₃ content 1.7 wt%, manufactured by Kojundo Chemical Laboratory Co., Ltd.)
Ti-3: Anatase type titanium dioxide (manufactured by Sakai Chemical Co., Ltd. Grade name: SA-1, D50 = 0.46 μm)
(Lithium carbonate)
Li-1: “Product name: Anhydrous lithium carbonate 4N” manufactured by Kojundo Chemical Laboratory
(Al)
Al-1: “Purchased product: α-alumina 4N” manufactured by Kojundo Chemical Laboratory Co., Ltd.
(Cr)
Cr-1: “Product name: Chromium (III) oxide 3N” manufactured by High Purity Chemical Research Co., Ltd.
(Fe)
Fe-1: “Product name: Ferric oxide 4N” manufactured by High Purity Chemical Research Co., Ltd.
(Ni)
Ni-1: “Product name: Nickel monoxide 3N” manufactured by High Purity Chemical Laboratory Co., Ltd.
(Zr)
Zr-1: “Product name: Zirconium oxide 98%” manufactured by Kojundo Chemical Laboratory Co., Ltd.

[Example 1]
<Production and measurement of lithium titanate particles>
The raw materials and water in the blending amounts shown in Table 1 were put in a mortar and mixed and refined with a pestle to obtain a slurry. This slurry was dehydrated with a rotary evaporator and then dried with a dryer at 105 ° C. for 12 hours. This dry powder was put into an electric furnace and fired at a firing temperature of 900 ° C. and a firing time of 120 minutes. Thereafter, the fired product was collected and crushed with a mortar and pestle, and then sieved (mesh roughness: 25 μm), and the particles passed through the sieve were collected to obtain lithium titanate particles. The lithium titanate particles were measured for XRD, D50 (μm), BET specific surface area (m ³ / g), bulk density (g / ml), tap density (g / ml), and pH. The results are shown in Table 1.
Moreover, the value of x and y in General formula (1) was computed from content of a raw material supposing that all the raw materials became a metal substituted lithium titanate represented by General formula (1). The results are also shown in Table 1.

<Manufacture and measurement of batteries>
A positive electrode plate was produced using the obtained lithium titanate particles as a positive electrode active material. That is, this positive electrode active material, acetylene black (“trade name: DENKA BLACK” manufactured by Denki Kagaku Kogyo Co., Ltd.) and polyvinylidene fluoride (PVDF) (“trade name: KF polymer” manufactured by Kureha Co., Ltd.) 90: 5: These were weighed to a mass ratio of 5, and kneaded with a kneader using N-methylpyrrolidone as a solvent to prepare an electrode slurry. The electrode slurry was applied to an aluminum substrate and dried, then punched out to 14 mmφ, further pressed, and then vacuum dried at 120 ° C. to prepare a positive electrode plate.
An electrolyte solution was prepared by dissolving LiPF ₆ at a concentration of 1 mol / L in a solvent having a ratio of ethylene carbonate (EC) to dimethyl carbonate (DMC) of 1: 2.
The positive electrode plate and the negative electrode plate made of Li metal were laminated through a separator made of a glass filter (two laminates of Whatman GA-100 and GF / C), and the laminate was impregnated with the electrolytic solution. Thereafter, a coin-type battery (diameter 20 mm, thickness 3.2 mm) was produced by sealing with a stainless steel exterior material.

Measurement Using this battery, battery characteristics (charge rate characteristics, charge capacity retention rate) were measured. The results are shown in Tables 2 and 3, and FIGS.

[Comparative Example 1]
The same operation as in Example 1 was performed except that the raw materials and the blending ratio thereof were as shown in Table 1. The results are shown in Table 1, Table 2, Table 3, and FIGS.

[Examples 2 to 3]
The same operation as in Example 1 was performed except that the raw materials and the blending ratio thereof were as shown in Table 1. The results are shown in Table 1, Table 2, Table 3, and FIGS.

[Example 4]
The raw materials and water in the blending amounts shown in Table 1 were pulverized and mixed using a bead mill to prepare a mixture as a raw material. About the mixture, a rotating cylinder (furnace core tube length: 4 m, furnace core tube diameter: 30 cm, stirring blade: 14 cm from the center, 10 sheets, external heating type) with a tilt angle of 2 degrees and a rotation speed of 10 rpm was used. Drying and calcination were performed while flowing the minute from the collection side. The heating temperature of the cylindrical rotating body was 700 ° C. on the raw material supply side, 900 ° C. at the center, and 900 ° C. on the recovery side, and the residence time of the heated portion was 26 minutes. Thereafter, the fired product was collected and crushed with a mortar and pestle, and then sieved (mesh roughness: 25 μm), and the particles passed through the sieve were collected to obtain lithium titanate particles. The obtained powder was analyzed in the same manner as in Example 1. The results are shown in Table 1, Table 2, Table 3, and FIGS.

[result]
As shown in FIGS. 1 to 2, Tables 1, 2 and 3, lithium titanate particles containing metal-substituted lithium titanate doped with Cr, Fe and Ni (Examples 1 to 4). ) Was excellent in rate characteristics as compared with lithium titanate particles not containing these metals (Comparative Example 1).
Further, in Examples 2 and 3 containing α-alumina in the raw material, the volume median particle size (D50) of the obtained lithium titanate particles was smaller than that in Example 1 not containing α-alumina, The rate characteristics were even better.

Claims

Lithium titanate particles containing metal-substituted lithium titanate doped with Cr, Fe, and Ni.
Of the peaks measured by the X-ray diffraction method, when the peak intensity corresponding to the main peak of Li 4 Ti 5 O 12 is 100, the main peak intensity of anatase-type titanium dioxide is 5 or less, and rutile-type titanium dioxide. And the peak intensity corresponding to the main peak of Li 2 TiO 3 is 3 or less,
The lithium titanate particles according to claim 1, having a volume median particle size (D50) of 0.1 to 1 µm.
The atomic ratio Li / Ti to Ti is 0.79 to 0.87, the Fe content is 5 to 300 ppm by mass, the Cr content is 5 to 200 ppm by mass, and the Ni content is 5 to 300 ppm. The lithium titanate particles according to claim 1 or 2, wherein the content is 200 ppm by mass.
The lithium titanate particles according to any one of claims 1 to 3, further comprising Zr.
The lithium titanate particles according to any one of claims 1 to 4, further comprising Al.
The metal-substituted lithium titanate has the general formula Li 4 + x Ti 5-y M y O 12 ( although, M is, Al, Cr, Fe, 3 or four selected Ni, and from the group consisting of Zr It is a metal that is at least Cr, Fe, and Ni, and is represented by −0.05 ≦ x ≦ 0.25 and 0 <y ≦ 0.2. The lithium titanate particles according to any one of claims 1 to 5.
The lithium titanate particles according to any one of claims 1 to 6, produced using anatase-type titanium dioxide and / or rutile-type titanium dioxide as a raw material.
An active material containing the lithium titanate particles according to any one of claims 1 to 7.
8. The firing process according to claim 1, further comprising a firing step of heating a mixture containing Cr, Fe, and Ni, a titanium compound, and a lithium compound at a firing temperature of 600 to 1000 ° C. and a firing time of 10 to 120 minutes. The method for producing lithium titanate particles according to Item.