JP5632794B2 - Lithium titanate and method for producing the same, electrode active material containing the lithium titanate, and power storage device using the electrode active material - Google Patents

Description

  The present invention relates to a novel lithium titanate and a method for producing the same. The present invention also relates to an electrode active material containing the lithium lithium titanate and an electricity storage device using the electrode active material.

Lithium secondary batteries have been rapidly spreading in recent years because of their excellent cycle characteristics. As an electrode active material of a lithium secondary battery, in particular, a negative electrode active material, a lithium-titanium composite oxide having a high energy density and excellent rate characteristics is widespread, while a discharge potential is high and safety is excellent. Titanate compounds are also attracting attention. For example, a spinel type represented by Li ₄ Ti ₅ O ₁₂ (patent document 1), a ramsdelite type (patent document 2) lithium titanate represented by Li ₂ Ti ₃ O ₇ , and H ₂ Ti ₁₂ O _25. A technique using a titanic acid compound represented by the formula (Patent Document 3) as an electrode active material is known. A technique using lithium titanate (Patent Document 4) represented by Li ₂ Ti ₁₂ O _{25 as} an electrode active material has also been proposed. Alternatively, a technique for reducing the decomposition of the electrolyte and suppressing the generation of gas by coating the surface of the spinel-type or Ramsdelite-type lithium titanate with a copper oxide such as copper oxide is also known. (Patent Document 5).

JP 2002-270175 A Japanese Patent Laid-Open No. 11-283624 International Publication WO2008 / 111465 Pamphlet JP 2011-26188 A JP 2009-245929 A

  The present invention provides lithium titanate that is further excellent in battery characteristics, in particular, high temperature cycle characteristics.

As a result of intensive research, the present inventors have made copper and / or tin into lithium titanate having a chemical composition of (formula 1) Li ₂ Ti _x O _{2x + 1} (x is an even number of 4 or more) as a general formula. It was found that when this lithium titanate was used as an active material, excellent battery characteristics, particularly high-temperature cycle characteristics were obtained, and the present invention was completed.

That is, the present invention
(1) Lithium titanate containing copper and / or tin in a compound having a chemical composition of (Formula 1) Li ₂ Ti _x O _{2x + 1} (x is an even number of 4 or more) as a general formula.
(2) Electrode active material for an electricity storage device containing lithium titanate containing copper and / or tin in a compound having a chemical composition of (Formula 1) Li ₂ Ti _x O _{2x + 1} (x is an even number of 4 or more) as a general formula .
(3) An electricity storage device including a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode or the negative electrode contains the electrode active material according to (2) above,
It is.

  When the lithium titanate of the present invention is used as an electrode active material, an electricity storage device having excellent battery characteristics, particularly high-temperature cycle characteristics, can be obtained.

Is a powder X-ray diffraction pattern measured using CuKα ray of _Li 1.4 _Ti 18 _{O 37} containing copper reference object (Reference Example 1). Is a powder X-ray diffraction pattern measured using CuKα ray of _Li 2 _Ti 18 _{O 37} containing tin of the present invention (Example 1). There the powder X-ray diffraction pattern was measured using a CuKα line as the compared copper or _Li 1.7 _Ti 18 _{O 37} containing no tin (Comparative Example 2). Li ₂ Ti ₁₈ O ₃₇ (Example 1) containing tin of the present invention, Li _1.4 Ti ₁₈ O ₃₇ (Reference Example 1) containing copper as a reference object, H ₂ Ti ₁₂ O ₂₅ (Comparison) as a comparison object It is a figure which shows the high temperature cycling characteristic of Example 1).

In the lithium titanate of the present invention, copper and / or tin is contained in a compound having a chemical composition of (formula 1) Li ₂ Ti _x O _{2x + 1} (x is an even number of 4 or more) as a general formula.
The compound represented by (Formula 1), in particular, the compound in which x in Formula 1 is 4, 6, 8, 12, 18, or 24 is presumed that the crystal structure has a one-dimensional tunnel structure. Therefore, it is possible to occlude a large amount of lithium ions in the tunnel, and since a one-dimensional conduction path is secured, it is considered that ions can be easily moved in the tunnel direction. Furthermore, by including copper and / or tin, these lithium titanates are modified to give excellent high-temperature cycle characteristics.
For this reason, the lithium titanate of this invention is suitable as an electrode active material of the electrode material for electrical storage devices.
Among the compounds represented by (Formula 1), as a general formula, (Formula 1 ′) Li ₂ Ti ₁₈ O ₃₇ (x in Formula 1 is 18), (Formula 1 ″) Li ₂ Ti ₁₂ O ₂₅ (Formula 1 Among them, those in which x has a chemical composition of 12) are preferred, and those of formula 1 ′ are more preferred.

  Copper or tin may be contained in the compound of (Formula 1) as a compound such as an oxide or hydroxide, or may be contained as a metal, an alloy, or the like. Among them, it is preferable that copper and tin are contained in a state of being supported on the particle surface of the compound of (Formula 1). The supporting mode may be a continuous layer having a uniform thickness, a supporting layer having a non-uniform thickness, or a discontinuous supporting layer that exists in an island shape. The content of copper and / or tin is preferably within a range of 0.001 / 1 to 0.1 / 1 as copper, tin, or a total amount thereof with respect to titanium contained in the compound of (Formula 1). The range of 005/1 to 0.05 / 1 is more preferable.

The average particle diameter (median diameter by laser scattering method) of the compound of (Formula 1) is not particularly limited, but is usually in the range of 0.05 to 10 μm and in the range of 0.1 to 2 μm. Further preferred. The particle shape is not particularly limited, for example, isotropic shapes such as spherical and polyhedral shapes, anisotropic shapes such as rod shapes and plate shapes, and irregular shapes. When the primary particles are aggregated into secondary particles, powder characteristics such as fluidity, adhesion, and filling properties are improved, and battery characteristics such as cycle characteristics are improved when used as an electrode active material. Therefore, it is preferable. The secondary particles in the present invention are in a state in which the primary particles are firmly bonded to each other, and are not easily disintegrated by industrial operations such as normal mixing, pulverization, filtration, washing, transport, weighing, bagging, and deposition. Most of them remain as secondary particles. The average particle diameter (median diameter by laser scattering method) of the secondary particles is preferably in the range of 0.1 to 20 μm. Although the specific surface area _{(N 2} BET method by adsorption) is not particularly limited, preferably in the range of 0.1 to 100 m ² / g, more preferably in the range of 1 to 100 m ² / g. The particle shape is not limited as in the case of the primary particle, and various shapes can be used.

  In addition to copper and tin, the surface of the primary particles or secondary particles of the compound of formula (1) is selected from inorganic compounds such as carbon, silica and alumina, and organic compounds such as surfactants and coupling agents. It may have at least one kind of coating. Alternatively, different elements other than titanium and lithium can be contained in the crystal lattice by doping, etc., as long as the crystal form is not inhibited.

  The lithium titanate of this invention is obtained by the manufacturing method including the process of including copper and / or tin in the particle | grain surface of the compound of (Formula 1). To include copper and tin, there are various methods such as dry coating methods such as CVD methods and sputtering methods, wet coating methods such as sol-gel methods and electroless plating, mixed and pulverized compound processing methods such as ball mill methods and jet mill methods. These methods can be appropriately selected depending on the coating type. For example, if copper and / or tin oxide is supported on the particle surface of the compound of the formula (1), a water-soluble compound of copper or tin is added to the aqueous slurry in which the compound of the formula 1 is dispersed, This can be done by neutralization.

Alternatively, (1) as a general formula (Formula 2) H ₂ Ti _xy O _{2 (xy) +1} (0 ≦ y <x, xy> 2, y is an integer, where x is The compound having the chemical composition of (the same numerical value as x) and the copper compound and / or the tin compound are 0.001 / 1 to 0 as copper, tin, or the total amount thereof with respect to titanium contained in the compound of formula 1 A step of obtaining a reaction product (A) by reacting to a range of 1/1 (first step), (2) a reaction product (A) and a lithium compound are reacted with the reaction product (A). Step (second step) for obtaining a reaction product (B) by reacting in a liquid phase so that lithium is equal to or more than the equivalent amount of copper, tin or the total amount thereof contained in (3) reaction product A method including a step (third step) of heat-dehydrating after solid-liquid separation of (B) is also included.
Also by this method, a coating containing copper and / or tin is formed, or a coating containing most of copper and tin is formed, and a part thereof is considered to be included in the crystal lattice of the compound of (Formula 1). It is done. If the compound has a one-dimensional tunnel structure, in the above-described known method, cations such as hydrogen ions and alkali metal ions derived from the neutralizing agent are easily inserted into the tunnel structure. Especially for the production of compounds where x in formula 1 is 4, 6, 8, 12, 18 or 24, especially for the production of compounds of formula (1 ′) or (formula 1 ″) containing copper and / or tin. More suitable for the production of compounds of formula (1 ′) comprising copper and / or tin.

In the first step, in order to react the compound of (Formula 2) with the copper compound or the tin compound, a method of contacting them by mixing them in a liquid phase may be used. It may be contacted and heated. When the reaction is performed in the liquid phase, the reaction is preferably performed in a slurry, and more preferably in a slurry using an aqueous medium. When an aqueous medium is used, it is preferable to use a water-soluble compound such as copper chloride or copper ammonium chloride as the copper compound, and as the tin compound, tin chloride, sodium stannate or the like is preferable. When obtaining a compound of formula 1 ′ (x in formula 1 is 18), the compound of (formula 2) is represented by the general formula (formula 2 ′) H ₂ Ti ₁₂ O ₂₅ (x in formula 2). It is preferable to use a compound having a chemical composition in which y is 18 and y is 6). In order to obtain the compound of (Formula 1 ″), it is preferable to use the compound of (Formula 2 ′). The compound of (Formula 2 ′) has a tunnel structure in which hydrogen ions are inserted into the tunnel. When a compound of (Formula 2 ′) is reacted with a copper compound, tin compound, etc. within the above range, it is presumed that some of the hydrogen ions in the tunnel structure are replaced with copper ions, tin ions, etc. .

The reaction and reaction of the reaction product (A) in the second step and the lithium compound are preferably performed in a slurry, and more preferably in a slurry using an aqueous medium. When an aqueous medium is used, it is preferable to use a water-soluble lithium compound such as lithium hydroxide or lithium carbonate as the lithium compound. The reaction temperature is preferably 80 ° C. or higher, more preferably 300 ° C. or lower, and further preferably 80 to 200 ° C. When making it react at 100 degreeC or more, it is preferable to use pressure-resistant containers, such as an autoclave. The reaction between the reaction product (A) and the lithium compound is carried out by adjusting the reaction amount so that the amount of lithium is greater than the equivalent amount with respect to the total amount of copper, tin, or their contained in the reaction product (A). It is preferable to adjust so that all of copper ions and / or tin ions and a part of hydrogen ions are replaced with lithium ions.
For example, when obtaining the compound of (Formula 1 ′), the reaction product is adjusted so that the molar ratio of hydrogen to lithium contained in the reaction product (B) is 0.5 / 1 to 1.5 / 1. It is preferable to react (A) with a lithium compound. By the reaction between the reaction product (A) and the lithium compound, copper ions, tin ions and the like in the tunnel structure of the reaction product (A) are replaced with lithium ions.
Copper desorbed from within the tunnel structure It is considered that these ions generate copper hydroxide, tin hydroxide and the like. In this second step, the reaction product (B) is supported by the produced copper hydroxide, tin hydroxide, etc. on the surface of particles mainly composed of a compound in which hydrogen ions and lithium ions are inserted into the tunnel structure. Or a state in which a part of the produced copper hydroxide, tin hydroxide, etc. is supported on the particle surface, and an unsupported copper hydroxide, tin hydroxide, etc. are present in the liquid phase, Or it is estimated that all of the produced | generated copper hydroxide, tin hydroxide, etc. exist in any state in a liquid phase.
Part or all of copper hydroxide, tin hydroxide and the like in the liquid phase is presumed to be supported on the surface of the particles when solid-liquid separation is performed in a third step described later.

  In the third step, the obtained reaction product is solid-liquid separated and dehydrated by heating. You may perform washing | cleaning, drying, etc. as needed. Next, heat dehydration is preferably performed at a temperature in the range of 300 to 600 ° C. By heat dehydration, the remaining hydrogen ions in the reaction product are removed together with oxygen to form lithium titanate. At the same time, from copper hydroxide and tin hydroxide supported on the particle surface of the reaction product, copper oxide, It is considered that tin oxide, metal copper, metal tin, or the like is generated to form a support layer containing copper and / or tin. When the heating temperature is lower than 300 ° C., dehydration is insufficient and it is difficult to obtain lithium titanate having a desired composition. When the heating temperature is higher than 600 ° C., titanium dioxide such as bronze type or anatase type is partially generated. . Or you may grind | pulverize in the range which does not impair the effect of this invention using a well-known apparatus according to the grade of aggregation of particle | grains.

Since the compound represented by (Formula 2) is obtained by a well-known method, a manufacturing method is suitably selected according to a desired composition. For example, if it is a compound of (Formula 2 '), it can be obtained by the method disclosed in Patent Document 3. That is, a step of calcining a mixture of a sodium compound and titanium oxide at a temperature of 600 ° C. or higher to obtain a compound having the general formula (formula 3) Na ₂ Ti ₃ O ₇ , a compound of formula 3 and an acidic solution To obtain a compound having the chemical formula of (Formula 4) H ₂ Ti ₃ O ₇ as a general formula, the compound of (Formula 4) in the range of 150 ° C. or more and less than 280 ° C. in air or in vacuum It can be obtained by a method including a step of heat dehydration at a temperature.

In this production method, secondary particles of the compound of (Formula 1) can also be obtained. In the method described in paragraph (0014), for example, (1) in the first step, the secondary particles of the compound of formula (2) are reacted with a copper compound and / or a tin compound, (2) second In the step, the primary particles of the reaction product (A) obtained in the first step are granulated into secondary particles, and then reacted with a lithium compound. (3) In the third step, the reaction product (B) A method of granulating primary particles into secondary particles, followed by heat dehydration; (4) secondary particles of a compound of formula (1) containing copper and / or tin obtained by the third step; Examples thereof include a method of granulating particles.
In the method of (1), when the compound of (Formula 2 ′) is used as the compound of (Formula 2), the secondary particles of the compound of (Formula 2 ′) obtain primary particles of the compound of (Formula 2 ′). Then, it may be granulated into secondary particles, or after granulating sodium compound and titanium oxide into secondary particles, calcined, reacted with an acidic solution, and heated to dehydrate; compound of (Formula 3) After obtaining the primary particles, the particles are granulated into secondary particles, reacted with an acidic compound, and dehydrated by heating; after obtaining the primary particles of the compound of formula (4), the particles are granulated into secondary particles and dehydrated by heating. It can also be obtained by such a method. Examples of granulation include dry granulation, stirring granulation, compaction granulation, and the like, and dry granulation is preferable because the particle diameter and shape of secondary particles can be easily adjusted. In dry granulation, the slurry containing the compounds of (Formula 1) to (Formula 4), reaction products (A) and (B), sodium compounds, titanium oxide and the like is dehydrated, dried and pulverized; After the slurry is dehydrated, it is molded and dried; a method such as spray drying of the slurry is mentioned, and spray drying is industrially preferable.

  If spray drying is performed, the spray dryer to be used can be appropriately selected according to the properties of the slurry and the processing capability, such as a disk type, a pressure nozzle type, a two-fluid nozzle type, and a four-fluid nozzle type. The control of the secondary particle size is, for example, adjusting the solid content concentration in the slurry, or if the above disk type, the rotational speed of the disk, if it is a pressure nozzle type, two fluid nozzle type, four fluid nozzle type, etc. This can be done by controlling the size of droplets to be sprayed by adjusting the spray pressure or nozzle diameter. As the drying temperature, the inlet temperature is preferably in the range of 150 to 250 ° C, and the outlet temperature is preferably in the range of 70 to 120 ° C. An organic binder may be used when the slurry has a low viscosity and is difficult to granulate, or for easier control of the particle size. Examples of the organic binder to be used include (1) vinyl compounds (polyvinyl alcohol, polyvinyl pyrrolidone, etc.), (2) cellulose compounds (hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose, ethyl cellulose, etc.), (3) protein compounds ( Gelatin, gum arabic, casein, sodium caseinate, ammonium caseinate, etc.), (4) acrylic acid compounds (sodium polyacrylate, ammonium polyacrylate, etc.), (5) natural polymer compounds (starch, dextrin, agar) , Sodium alginate, etc.), (6) synthetic polymer compounds (polyethylene glycol, etc.), etc., and at least one selected from these can be used. Especially, what does not contain inorganic components, such as soda, is more preferable because it is easily decomposed and volatilized by heat treatment.

  In addition, an electricity storage device using an electrode containing the compound of Formula (1) containing copper and / or tin of the present invention as an electrode active material has a high capacity, excellent high-temperature cycle characteristics, and reversible. It is an electricity storage device that can perform lithium insertion / extraction reactions and can be expected to have high reliability.

Specific examples of the electricity storage device include a lithium battery, a capacitor, and the like. These include a positive electrode, a negative electrode, a separator, and an electrolyte. The electrode includes a conductive material such as carbon black and a fluorine resin as the electrode active material. It can be obtained by adding a binder such as In the case of a lithium battery, the electrode active material can be used for a positive electrode, and metallic lithium, a lithium alloy, or a carbon-based material such as graphite can be used as a counter electrode. Alternatively, the electrode active material is used as a negative electrode, and a lithium / transition metal composite oxide such as a lithium / manganese composite oxide, a lithium / cobalt composite oxide, a lithium / nickel composite oxide, a lithium / vanadine composite oxide, Olivine type compounds such as lithium, iron, and complex phosphate compounds can be used. Further, the electrode active material of the present invention may be mixed with a known active material to produce an electrode. In the case of a capacitor, an asymmetric capacitor using the electrode active material and graphite can be used. For the separator, a porous polyethylene film or the like is used for each of the separators, and for the electrolyte, LiPF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₃₎ are used in a solvent such as propylene carbonate, ethylene carbonate, or dimethyl carbonate. ₂ ) A conventional material such as a solution in which a lithium salt such as ₂ or LiBF ₄ is dissolved can be used.

  Examples of the present invention are shown below, but these do not limit the present invention.

Reference Example 1: Lithium titanate containing copper (first step)
To 1000 g of commercially available rutile type high-purity titanium dioxide (PT-301: manufactured by Ishihara Sangyo) and 451.1 g of sodium carbonate, 1284 g of pure water was added and stirred to form a slurry. This slurry was spray-dried under conditions of an inlet temperature of 200 ° C. and an outlet temperature of 70 to 90 ° C. using a spray dryer (MDL-050C type: manufactured by Fujisaki Electric). The obtained spray-dried product was heated and calcined in the atmosphere at a temperature of 800 ° C. for 10 hours using an electric furnace to obtain a compound of formula (3): Na ₂ Ti ₃ O ₇ .

4310 g of pure water was added to 1077 g of the obtained Na ₂ Ti ₃ O ₇ to obtain a dispersed slurry. 711 g of 64% sulfuric acid was added to 4848 g of this slurry, and the mixture was reacted for 5 hours at 50 ° C. with stirring, followed by washing with filtered water. After adding pure water to the filter cake to make 3370 g, redispersed, adding 31.3 g of 64% sulfuric acid, reacting at 70 ° C. for 5 hours with stirring, washing with filtered water and drying (compound of formula 4) : was obtained _H 2 _Ti 3 _{O 7.}

300 g of the obtained H ₂ Ti ₃ O ₇ was dehydrated by heating at 260 ° C. for 10 hours in the atmosphere using an electric furnace to obtain a compound of formula 2 ′: H ₂ Ti ₁₂ O ₂₅ (sample a). The validity of the chemical composition, where the heat loss in the temperature range of 250 to 600 ° C. samples were measured using a differential thermal balance, heat loss was calculated on the assumption that corresponding to structural water, H ₂ Ti ₁₂ O ₂₅ chemical compositions were confirmed to be reasonable.

After 258.3 g of the obtained H ₂ Ti ₁₂ O ₂₅ was dispersed in 1 liter of pure water, 13.29 g of copper chloride ammonium dihydrate (Cu (NH ₄ ) ₂ Cl ₂ · 2H ₂ O) was purified. An aqueous solution dissolved in 200 ml was added (Cu / Ti = 0.015), and the mixture was stirred for 30 minutes for reaction to obtain a reaction product (A)-(1).

(Second step)
An aqueous solution in which 35.18 g of lithium hydroxide monohydrate (LiOH.H ₂ O) was dissolved in 300 ml of pure water was added to the resulting slurry of the reaction product (A)-(1), and then the autoclave The reaction product (B)-(1) was obtained by stirring at 120 ° C. for 5 hours while stirring. A portion of the sample was collected and analyzed for Cu, Li, and Ti contents, and heating loss in the temperature range of 250 to 600 ° C. was measured using a differential thermal balance. As a result, it was confirmed that Cu / Ti was 0.015 / 1, H / Ti was 0.074 / 1, and Li / Ti was 0.078 / 1 in molar ratio.

(Third process)
The obtained reaction product (B)-(1) was washed with filtered water, dried and then heat-treated at a temperature of 400 ° C. for 10 hours to obtain copper-containing lithium titanate. (Sample A)

Example 1: Tin titanate containing tin (first step)
Compound (Formula 2) obtained in the first step of Reference Example 1 10.2 g of H ₂ Ti ₁₂ O ₂₅ was dispersed in 80 ml of pure water, and then sodium stannate trihydrate (Na ₂ SnO) ₃ · _3H 2 O) was added 0.50g (Sn / Ti = 0.00054) , and reacted with stirring for 30 min, the reaction product (a) - to obtain a (2).

(Second step)
Lithium hydroxide monohydrate (LiOH.H ₂ O) 1.39 g was added to the resulting reaction product (A)-(2) slurry, then charged into an autoclave and stirred at 120 ° C. for 5 hours. Reaction was carried out for a time to obtain a reaction product (B)-(2). It is assumed that the Sn, Li, Ti content is analyzed by ICP emission spectroscopy, and the heating loss in the temperature range of 250 to 600 ° C. is measured using a differential thermal balance, and the heating loss corresponds to structural water. It was confirmed that Sn / Ti was 0.00054 / 1, H / Ti was 0.071 / 1, and Li / Ti was 0.1126 / 1 in molar ratio.

(Third process)
The obtained reaction product (B)-(2) was washed with filtered water, dried and then heat-treated at a temperature of 400 ° C. for 10 hours to obtain a compound of (formula 1 ′) containing a tin compound. (Sample B)

Comparative Example 1
The compound of (Formula 2 ′) obtained in the first step of Reference Example 1 was used as a comparative compound. (Sample a)

Comparative Example 2

To 258.3 g of the compound of the formula (2 ′) obtained in the first step of Reference Example 1, 1 liter of pure water and 35.18 g of lithium hydroxide monohydrate (LiOH.H ₂ O) were added to 500 ml of pure water. The aqueous solution dissolved in was added to an autoclave and reacted at 120 ° C. for 5 hours with stirring to obtain a reaction product. The obtained reaction product was washed with filtered water, dried and then heat-treated at 400 ° C. for 10 hours to obtain lithium titanate containing no copper, tin or the like. (Sample C)

Evaluation 1: Confirmation of crystallinity With respect to the compounds (samples A to C) obtained in Reference Example 1, Example 1, and Comparative Example 2, X-ray diffraction data were measured by a powder X-ray diffractometer. It was found to be monoclinic with good crystallinity. In addition, since the X-ray diffraction patterns of Samples A to C are almost the same, copper ions are not present in the crystal structure of Sample A, and tin ions are present in the crystal structure of Sample B. I guess it is not. Each X-ray diffraction pattern is shown in FIGS.

Evaluation 2: Confirmation of composition The compounds (samples A to C) obtained in Reference Example 1, Example 1 and Comparative Example 2 were dissolved in hydrofluoric acid, and contained titanium, lithium, copper and tin by ICP emission spectrometry. The amount was measured. Moreover, the heating loss of these samples in a temperature range of 250 to 600 ° C. is measured using a differential thermobalance, and assuming that the heating loss corresponds to structural water, the heating loss of samples A to C is 0.00. Since it was% by weight, it was considered that all of the structural water had been removed and converted to oxides. And the molar ratio of oxygen and titanium was identified as a thing without the defect | deletion of a titanium ion, and the chemical composition was determined from this and the analysis value of said titanium and lithium. The results are shown in Table 1. Example 1 confirmed that the desired compound was obtained.

Evaluation 3: Evaluation of high-temperature cycle characteristics Using the compounds (samples A, B, and a) obtained in Reference Example 1, Example 1, and Comparative Example 1 as electrode active materials, lithium secondary batteries were prepared. The charge / discharge characteristics were evaluated. The battery configuration and measurement conditions will be described.

  Each of the above samples, acetylene black powder as a conductive agent, and polytetrafluoroethylene resin as a binder were mixed at a weight ratio of 50:40:10, kneaded in a mortar, and stretched to form a sheet. This sheet was cut into a circle with a diameter of 10 mm and a weight of 10 mg, sandwiched between two aluminum meshes cut into a circle with a diameter of 10 mm, and pressed at 9 MPa to produce a positive electrode.

This positive electrode was vacuum-dried at a temperature of 220 ° C. for 4 hours, and then incorporated in a sealable coin cell in a glove box having a dew point of −70 ° C. or less. A coin type cell made of stainless steel (SUS316), having an outer diameter of 20 mm and a height of 3.2 mm was used. As the negative electrode, a metal lithium having a thickness of 0.5 mm formed into a circle having a diameter of 12 mm was used by being pressed onto a copper foil. As the non-aqueous electrolyte, a mixed solution of ethylene carbonate and dimethyl carbonate (mixed in a volume ratio of 1: 2) in which LiPF ₆ was dissolved at a concentration of 1 mol / liter was used.

  The positive electrode was placed in a lower can of a coin-type cell, a porous polypropylene film was placed thereon as a separator, and a nonaqueous electrolyte was dropped from above. Further, a negative electrode, a 0.5 mm-thickness spacer for adjusting the thickness, and a spring (both made of SUS316) were placed thereon, and an upper can with a polypropylene gasket was put on the outer peripheral edge portion and sealed.

  The prepared lithium secondary battery was charged and discharged for 50 cycles at a charge / discharge current of 0.25 mA and a cut-off potential of 1.0 V to 2.5 V in a high-temperature bath at 60 ° C. Regarding the discharge capacity at the second cycle and the 50th cycle, (discharge capacity at the 50th cycle / discharge capacity at the second cycle) × 100 was defined as the high temperature cycle characteristic. The results are shown in Table 2. Moreover, transition of each capacity maintenance rate is shown in FIG. It can be seen that the present invention is excellent in high-temperature cycle characteristics.

  An electricity storage device using the lithium titanate of the present invention as an electrode active material as an electrode material is capable of reversible lithium insertion / extraction reaction, and can be used for a long-term charge / discharge cycle at a high temperature. In addition, it is an electricity storage device that can be expected to have a high capacity.

  Also, the manufacturing method does not require a special apparatus, and the raw material to be used is low in price, so that a high value-added material can be manufactured at a low cost.

Claims (13)

Lithium titanate containing copper and / or tin in a compound having a chemical composition of the general formula (Formula 1) Li ₂ Ti _x O _{2x + 1} (x is an even number of 4 or more). The lithium titanate according to claim 1, wherein x in formula 1 is 4, 6, 8, 12, 18 or 24. Lithium titanate according to any one of claims 1 and 2 compound takes the chemical composition of _Li 2 _Ti 18 _{O 37} (Formula 1). The lithium titanate according to claim 1, which is a secondary particle in which primary particles are aggregated. An electrode active material for an electricity storage device containing lithium titanate containing copper and / or tin in a compound having a chemical composition of the general formula (Formula 1) Li ₂ Ti _x O _{2x + 1} (x is an even number of 4 or more). The manufacturing method of lithium titanate of any one of Claims 1-4 including the process of including copper and / or tin in the compound of Formula 1. It is a method of including copper and / or tin in the compound of formula 1, wherein (1) H ₂ Ti _xy O _{2 (xy) +1} (0 ≦ y <x, x− y> 2, y is an integer, where x is the same numerical value as x in formula 1) and a copper compound and / or a tin compound, with respect to titanium contained in the compound of formula 1 , Reacting tin or a total amount thereof in a range of 0.001 / 1 to 0.1 / 1 to obtain a reaction product (A), (2) reaction product (A) and lithium compound A reaction product (B) to obtain a reaction product (B) by reacting in a liquid phase such that lithium is equal to or more than an equivalent amount of copper, tin or a total amount thereof contained in the reaction product (A), (3 The process according to claim 6, comprising a step of subjecting the reaction product (B) to solid-liquid separation followed by heat dehydration. The production method according to claim 7, wherein in the second step, the reaction in the liquid phase is performed at a temperature of 80 ° C. or higher. The manufacturing method according to claim 7, wherein the heat dehydration temperature is in the range of 300 to 600 ° C in the third step. The production method according to claim 7, wherein secondary particles of the compound of formula 1 are obtained. 8. The production method according to claim 7, wherein x in formula 1 is 18 and y in formula 2 is 6. In the second step, the reaction product (A) and the lithium compound so that the molar ratio of hydrogen and lithium contained in the reaction product (B) is in the range of 0.5 / 1 to 1.5 / 1. The manufacturing method of Claim 11 made to react. The electrical storage device containing a positive electrode, a negative electrode, a separator, and an electrolyte, The electrical storage device in which the said positive electrode or negative electrode contains the electrode active material of Claim 5 .

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