JP2011241100A - Titanium dioxide, method of producing the same, lithium ion battery, and electrode for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide TiO(B) having excellent initial discharge capacity and initial charge/discharge efficiency when used as an electrode material of a lithium ion battery, to provide a method of producing TiO(B), and to provide a lithium ion battery using the production method.SOLUTION: The titanium dioxide includes bronze-type crystal structure, where a specific surface area is 6-100 m/g, an average aspect ratio expressed by a ratio (S/L) of the long diameter L to the short diameter S of a primary particle is within 0.37≤S/L≤1 in an SEM photograph image, and a ratio (I/I) of peak intensity of a (002) plane to the peak intensity of a (401) plane in an X-ray diffraction pattern is not less than 0.7.

Description

  The present invention relates to titanium dioxide suitable as an electrode active material of a lithium ion battery, a method for producing titanium dioxide, a lithium ion battery using titanium dioxide, and an electrode for a lithium ion battery.

In power storage devices such as lithium primary batteries and lithium secondary batteries that have been widely used in recent years, charging and discharging are performed by movement of lithium ions.
Accompanying the miniaturization and high performance of portable devices in which these electricity storage devices are used, energy storage devices are required to have higher energy density and higher output.

Currently, there are many positive electrode active materials for lithium secondary batteries, but the most commonly known one is a lithium cobalt oxide whose operating voltage is around 4 V (vs. Li / Li ⁺ ). It is a lithium-containing transition metal oxide based on (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide having a spinel structure (LiMn ₂ O ₄ ), or the like. Widely adopted as a positive electrode active material because of its excellent charge / discharge characteristics and energy density.
As the negative electrode active material, carbon materials such as hard carbon, soft carbon, and graphite are widely used, and an electrolytic solution in which LiPF ₆ is dissolved in cyclic and chain carbonates is used.

  However, considering the future development of medium-sized and large-sized batteries, especially the installation in HEVs (Hybrid Electric Vehicles), which are expected to have a large demand, the current small-sized specifications require the safety required for HEV applications and Long life cannot be satisfied.

  Under such circumstances, studies have been made on using a titanium oxide-based active material as an electrode active material. The titanium oxide active material has a voltage of about 1 to 2 V when lithium metal is used for the counter electrode. Therefore, titanium oxide-based active materials having various crystal structures or particle shapes have been studied as electrode active materials.

Among these, bronze-type titanium oxide (hereinafter referred to as a bronze-type crystal structure, which can have a higher capacity than spinel-type lithium titanate represented by Li _{4 + x} Ti ₅ O ₁₂ (0 ≦ x ≦ 3)). Titanium oxide is abbreviated as “TiO ₂ (B)” has attracted attention as an electrode active material for lithium ion batteries.

For example, TiO ₂ (B) active materials having nanoscale shapes such as nanowires and nanotubes have attracted attention as electrode materials that can have an initial discharge capacity exceeding 300 mAh / g (for example, non-patent literature). 1).

However, in TiO ₂ (B) such as nanowires and nanotubes, a part of the lithium ions inserted by the initial insertion reaction is not desorbed, so that the irreversible capacity increases due to the presence of lithium ions that are not released. As a result, the initial charge / discharge efficiency (= charge capacity (lithium desorption amount) ÷ discharge capacity (lithium insertion amount)) of TiO ₂ (B) such as nanowires and nanotubes is about 73%, and a high capacity lithium ion battery There has been a problem in application as an electrode material.

Here, for example, a method of obtaining TiO ₂ (B) from K ₂ Ti ₄ O ₉ polycrystalline powder produced by high-temperature firing is disclosed (for example, see Patent Document 1). In addition, TiO ₂ (B) obtained using Na ₂ Ti ₃ O ₇ as a starting material has been reported to have a high initial charge / discharge efficiency of 99% (see, for example, Patent Document 2).

JP 2008-34368 A JP 2008-117625 A

A. R. Armstrong, G. Armstrong, J. Canales, R. Garcia, P. G. Bruce, Advanced Materials, 17, 862-865 (2005)

According to the study by the present inventors, TiO ₂ (B) disclosed in the above-mentioned Patent Document 1 shows a high initial discharge capacity of 200 mAh / g, but the capacity decrease at a high current density is remarkably large. It became clear. Further, it has been clarified that TiO ₂ (B) disclosed in the above-mentioned Patent Document 2 cannot obtain a sufficient initial discharge capacity and initial charge / discharge efficiency.

An object of the present invention, the initial discharge capacity and TiO 2 having excellent initial charge-discharge efficiency _(B), a method of manufacturing a lithium-ion battery and a lithium ion battery using it when used as an electrode material for lithium ion batteries It is to provide an electrode.

As a result of intensive studies to solve the above-mentioned problems, the present inventors, as TiO ₂ (B), have a BET specific surface area in the range of 6 to 100 m ² / g, and the major axis L and minor axis of the primary particles. The average aspect ratio expressed by the S ratio (S / L) is in the range of 0.37 ≦ S / L ≦ 1, and the (002) plane peak intensity relative to the (401) plane peak intensity in the X-ray diffraction pattern. It was found that when the ratio of (I ₍₀₀₂₎ / I ₍₄₀₁₎ ) is 0.7 or more, the initial discharge capacity and the initial charge / discharge efficiency are excellent.
That is, the present invention is as follows.

<1> The BET specific surface area is 6 to 100 m ² / g, and the average aspect ratio represented by the ratio of the major axis L to the minor axis S (S / L) of the primary particles is 0.37 ≦ S in the SEM photographic image. / L ≦ 1, and the ratio of the peak intensity of the (002) plane to the peak intensity of the (401) plane in the X-ray diffraction pattern (I ₍₀₀₂₎ / I ₍₄₀₁₎ ) is 0.7 or more Titanium dioxide having a type crystal structure.

  <2> Titanium dioxide having a bronze-type crystal structure according to <1>, wherein the average major axis of primary particles observed by SEM is 1 μm or less.

  <3> The titanium dioxide according to <1> or <2>, wherein the average particle size (median particle size) is 0.3 μm to 50 μm.

  <4> An electrode for a lithium ion battery comprising the titanium dioxide according to any one of <1> to <3>.

<5> A positive electrode, a negative electrode, and an electrolyte,
A lithium ion battery comprising the electrode for a lithium ion battery according to <4> as the positive electrode or the negative electrode.

  <6> The lithium ion battery according to <5>, which contains γ-butyrolactone as a solvent for the electrolyte.

<7> A step of baking a mixture of a titanium compound and a sodium compound or a potassium compound to prepare a sodium titanate powder or a potassium titanate powder;
A step of impregnating the sodium titanate powder or potassium titanate powder with an aqueous hydrochloric acid solution and firing at 250 ° C. to 400 ° C .;
The manufacturing method of the titanium dioxide of any one of said <1>-<3> which has these.

<8> BET specific surface area of the potassium titanate or sodium titanate ^powder, method for producing titanium dioxide according to the a ^{3m 2 / g~50m 2 / g <} 7>.

<9> BET specific surface area of the potassium titanate or sodium titanate ^powder, method for producing titanium dioxide according to the an ^{5m 2 / g~30m 2 / g <} 7> or <8>.

According to the present invention, it is possible to provide TiO ₂ (B) that exhibits excellent initial discharge capacity and initial charge / discharge efficiency when used as an electrode material of a lithium ion battery.

_{2 is} an X-ray powder diffraction pattern of TiO ₂ (B) of the present invention obtained in Example 1. FIG. ₂ is an SEM observation image of TiO ₂ (B) of the present invention obtained in Example 1. ₂ is a SEM observation image of TiO ₂ (B) of the present invention obtained in Comparative Example 1.

<Titanium dioxide having a bronze crystal structure [TiO ₂ (B)]>
The titanium dioxide [TiO ₂ (B)] having a bronze type crystal structure of the present invention has an average aspect ratio represented by the ratio of the major axis L to the minor axis S (S / L) of the primary particles in the SEM photographic image. The range of 0.37 ≦ S / L ≦ 1, the BET specific surface area is 6 to 100 m ² / g, and the (002) plane peak intensity relative to the (401) plane peak intensity in the X-ray diffraction pattern Ratio (I ₍₀₀₂₎ / I ₍₄₀₁₎ ) is 0.7 or more.
TiO ₂ (B), which is the target substance of the present invention, exhibits excellent initial discharge capacity and initial charge / discharge efficiency when used as an active material for a lithium ion battery electrode. Incidentally, TiO 2 _(B) of the present invention can be used in any of the positive electrode active material and the negative electrode active material of a lithium ion battery.

(Average aspect ratio)
In the TiO ₂ (B) of the present invention, the average aspect ratio represented by the ratio (S / L) of the minor axis S to the major axis L of the primary particles measured by the SEM photographic image is 0.37 ≦ S / L ≦. 1 is more preferable, and 0.4 ≦ S / L ≦ 1 is more preferable, and 0.5 ≦ S / L ≦ 1 is still more preferable. When the average aspect ratio is less than 0.37, the initial discharge capacity and the initial charge / discharge efficiency are lowered when used as an active material of an electrode for a lithium ion battery.

The “aspect ratio” in the present invention means a ratio of short diameter (minimum diameter) / long diameter (maximum diameter) for spherical particles, and hexagonal plate-like or disc-like particles are observed from the thickness direction, respectively. In the projected image of the particles, it means the ratio of minor axis (minimum diameter or minimum diagonal length) / major axis (maximum diameter or maximum diagonal length).
The average aspect ratio is calculated as the number average of the aspect ratios of 300 or more particles measured by the above method.

  In the present invention, “primary particles” represent the smallest particles that can exist alone, and “secondary particles” are the smallest in normal behavior formed by agglomeration of a plurality of primary particles. Means particles.

(Average major axis of primary particles)
In the TiO ₂ (B) of the present invention, the average major axis of primary particles observed with a scanning electron microscope (SEM) is preferably 1 μm or less, and more preferably 10 nm to 0.8 μm. When the average major axis of the primary particles is 1 μm or less, the discharge capacity tends to be excellent.

The “major diameter of primary particles” in the present invention means the maximum diameter of primary particles for spherical particles, and the maximum in projected images of particles observed from the thickness direction for hexagonal or disk-like particles, respectively. Mean diameter or maximum diagonal length.
The average major axis is calculated as the number average of the major axis of 300 or more particles measured by the above method.

In order to set the average major axis of the primary particles of TiO ₂ (B) within the above range, a method of selecting the particle size of titanium dioxide used as a raw material, a method of adjusting pulverization conditions, or granulation by spray drying. Can adopt methods such as adjusting the spraying conditions.

(BET specific surface area)
BET specific surface area of _TiO 2 (B) of the present invention ^is a 6m ² / g~100m 2 / ^g, is preferably 10m ² / g~50m 2 / g. When the BET specific surface area is 6 m ² / g or more, a sufficient discharge capacity can be obtained, and when the BET specific surface area is 100 m ² / g or less, the handleability during electrode production is excellent.
The BET specific surface area is calculated from an adsorption isotherm of nitrogen at −196 ° C.
A method of setting the BET specific surface area of TiO ₂ (B) within the above range will be described in detail in the manufacturing method described later.

(Peak intensity of powder X-ray diffraction pattern)
TiO ₂ (B) of the present invention is a ratio of peak intensity of (002) plane to peak intensity of (401) plane in a powder X-ray diffraction (XRD) pattern using Cu—Kα as a radiation source (I ₍₀₀₂₎ / I ₍₄₀₁₎ ) is preferably 0.7 or more, and more preferably 0.8 or more. Although the detailed mechanism is unknown, when the ratio of peak intensities (I ₍₀₀₂₎ / I ₍₄₀₁₎ ) is 0.7 or more, the initial discharge capacity is obtained when used as an active material of a lithium ion battery electrode. And excellent initial charge / discharge efficiency.
A method in which the ratio (I ₍₀₀₂₎ / I ₍₄₀₁₎ ) of the (002) plane peak intensity to the (401) plane peak intensity in the powder X-ray diffraction (XRD) pattern of TiO ₂ (B) is within the above range. Will be described in detail in the manufacturing method described later.

(Average particle diameter (median particle diameter))
The average particle diameter (median particle diameter) of TiO ₂ (B) of the present invention is preferably 0.3 μm to 50 μm, more preferably 1 μm to 40 μm, and still more preferably 2 μm to 20 μm. When the median particle diameter is 50 μm or less, it is easy to apply a thin film to the electrode, and it is easy to produce a low-resistance battery. Moreover, in the case of 0.3 micrometer or more, it is excellent in the handleability at the time of electrode preparation.
The average particle diameter (median particle diameter) is measured by a laser diffraction method.

In order to keep the average particle diameter (median particle diameter) of TiO ₂ (B) within the above range, a method of adjusting the pulverizing conditions, or a method of adjusting the spraying conditions when granulating by spray drying is used. Can be adopted.

<Method for producing TiO ₂ (B)>
Titanium dioxide [TiO ₂ (B)] having a bronze type crystal structure of the present invention is obtained by using sodium titanate (Na ₂ Ti ₃ O ₇ ) or potassium titanate (K ₂ Ti ₄ O ₉ ) powder as an acidic solution. It is obtained by a method in which a proton exchange reaction is performed to form H ₂ Ti ₃ O ₇ or H ₂ Ti ₄ O ₉ and then firing, or a water-soluble titanium complex emulsion is prepared by an emulsion method and this is heat-treated. .

(First manufacturing method)
The first method of titanium dioxide [TiO ₂ (B)] having a bronze type crystal structure of the present invention includes the following steps.

(1) A step of firing a mixture of a titanium compound and a sodium compound or a potassium compound to prepare a powder of sodium titanate (Na ₂ Ti ₃ O ₇ ) or potassium titanate (K ₂ Ti ₄ O ₉ ).
(2) A step of impregnating the sodium titanate powder or potassium titanate powder in an acidic solution to form H ₂ Ti ₃ O ₇ by a proton exchange reaction.
(3) the _H 2 _Ti 3 _{O 7} and calcining at 250 ° C. to 800 ° C..

  Hereinafter, the production method using a sodium compound will be described, but the word “sodium” can be read as “potassium”.

(1) Step of synthesizing Na ₂ Ti ₃ O ₇ Sodium titanate (Na ₂ Ti ₃ O ₇ ) is composed of at least one sodium compound and at least one titanium compound, and the chemistry of Na ₂ Ti ₃ O ₇ . It can be manufactured by weighing and mixing so as to have a composition and heating in an atmosphere in which oxygen exists, such as in air. The mixing method may be either dry mixing or wet mixing. Among these, wet mixing is preferable. When mixing, pulverization may be performed simultaneously.

  As the solvent in the wet mixing, water or an organic solvent can be used, and it is preferable to use water or alcohol from the viewpoint of easy handling. As a mixing method, a mortar, a ball mill, a bead mill, a jet mill, a vibration mill, a mixer, or the like can be adopted.

  The sodium compound used as a raw material may be any of a salt, an oxide, or a hydroxide. For example, sodium carbonate, sodium hydroxide, sodium nitrate, sodium oxide, sodium oxalate, sodium acetate, or sodium fluoride can be used. A sodium compound may be used individually by 1 type, or may use 2 or more types together.

These sodium compounds used as a raw material preferably have a high purity, and it is usually desirable that the purity is 99.0% by mass or more. For example, in the case of using sodium carbonate as the sodium compound, preferably contains _Na 2 CO ₃ 99.0% by mass, and more preferably contains more than 99.5 wt%. Further, the sodium compound is desirably one from which water has been sufficiently removed, and the water content is desirably 1% by mass or less.
Furthermore, the average particle size of the sodium compound is desirably 0.01 μm to 100 μm. In the case of using a sodium compound having an average particle diameter of 100 μm or more, it is preferable that the pulverization step be performed together with pulverization in advance or when mixed with titanium oxide.

  The titanium compound used as the raw material may be any of oxide, hydroxide, chloride, or alkoxide. Examples thereof include titanium oxide, titanium hydroxide, titanium chloride, metatitanic acid, orthotitanic acid, titanium alkoxide, and a titanium complex compound. A titanium compound may be used individually by 1 type, or may use 2 or more types together.

In the case of using titanium oxide (TiO ₂₎ as the titanium compound, it is preferable that a BET specific surface area titanium oxide over ^2m 2 / g, BET specific surface area of the titanium oxide ^{2m 2} / ^g~100m 2 / g it is more preferable to ^use, it is more preferable to use a titanium oxide 4m ² / g~50m 2 / g. When a titanium oxide having a BET specific surface area of less than 2 m ² / g is used, the primary particle diameter of TiO ₂ (B) finally obtained is obtained unless the intermediate product Na ₂ Ti ₃ O ₇ is ground. Tends to be large and the BET specific surface area tends to be small. When it exceeds 50 m < ² > / g, there exists a tendency for handling property to be inferior.

The crystal form of titanium oxide is not particularly limited and may be any of a rutile type, anatase type, or brookite type, preferably a rutile type or anatase type, and more preferably a rutile type. By using rutile type titanium oxide, it is easy to obtain sodium titanate having a high aspect ratio, and finally, TiO ₂ (B) having a high aspect ratio is likely to be obtained.

The mixture of the sodium compound and titanium oxide obtained as described above is heat-treated (fired) at 600 ° C. or higher in the presence of oxygen to synthesize Na ₂ Ti ₃ O ₇ .
The firing temperature at this time can be appropriately set depending on the raw material, but is usually about 600 to 1200 ° C., preferably 700 to 1000 ° C., more preferably 750 to 900 ° C. The firing time can also be appropriately set depending on the raw materials, but is usually about 1 hour to 30 hours, preferably 5 hours to 20 hours. The rate of temperature increase is preferably 0.5 ° C./min to 3.0 ° C./min, and preferably 1.0 ° C./min to 2.0 ° C./min.

In addition, the higher the firing temperature, the smaller the BET specific surface area of the finally obtained TiO ₂ (B), and the smaller the peak intensity ratio (I ₍₀₀₂₎ / I ₍₄₀₁₎ ) in the X-ray diffraction pattern. The average major axis and the average particle diameter (median particle diameter) of the primary particles tend to increase.

  The firing atmosphere is not particularly limited, and the firing is performed in an oxidizing atmosphere or an atmosphere in which oxygen exists, such as in the air.

Further, a slurry-like mixture containing a titanium compound and a sodium compound is granulated by spray drying or the like, and the granulated product is fired to produce sodium titanate (Na ₂ Ti ₃ O ₇ ) particles. May be. In this method, the granulation step (2) can be omitted because it is approximately granulated to a desired particle size by the spray drying step.

In the method of spray drying and granulating the mixture, it is preferable to use a titanic acid compound, titanium oxide, or a mixture thereof as a raw material titanium compound. Examples of the titanate compound, TiO _{(OH) 2} or _TiO 2 · _{H 2} metatitanic acid represented by O; Ti _{(OH) 4} or orthotitanate represented by _{TiO 2} · 2H 2 O; or mixtures thereof Etc. can be used.

  In the method of spray drying and granulating the slurry, there is no particular limitation on the sodium compound used as a raw material, but when slurried using an aqueous medium, a water solution such as sodium hydroxide, sodium carbonate, sodium nitrate, or sodium sulfate is used. It is preferable to use a reactive sodium compound, and it is particularly preferable to use sodium hydroxide having high reactivity.

  The slurry containing the titanic acid compound and sodium compound thus prepared is spray-dried and granulated into secondary particles of about 0.5 to 100 μm. The spray dryer used for spray drying can be appropriately selected according to the properties and processing capacity of the slurry, such as a disk type, a pressure nozzle type, and a two-fluid nozzle type.

  The control of the secondary particle size is, for example, when the disk type spray dryer is used, the rotational speed of the disk, and when using a spray dryer such as a pressure nozzle type or a two-fluid nozzle type, the spray pressure or nozzle diameter is controlled. Can be adjusted to control the size of the sprayed droplets.

It is desirable to appropriately set the properties such as the concentration and viscosity of the slurry to be used according to the ability of the spray dryer. When the slurry is low in viscosity and difficult to granulate, or to make it easier to control the particle size, binders such as polyvinyl alcohol, methylcellulose and gelatin, and nonionic, anionic, amphoteric and nonionic surfactants Various additives such as may be added to the slurry. As the additive, an organic compound that does not contain a metal component is desirable because it is difficult to decompose and volatilize and remain in the subsequent heating and baking step.
As the drying temperature of the spray dryer, an inlet temperature of 200 to 450 ° C. and an outlet temperature of 80 to 120 ° C. are preferable.

The obtained granulated dried product is heated and fired to produce sodium titanate.
The heating and firing temperature varies depending on the composition of the granulated dried product, the firing atmosphere, etc., but since the granulated powder is almost granulated to the desired particle size by the spray drying process, the titanate compound reacts with the sodium compound to react with titanate. The temperature for becoming sodium may be approximately 600 ° C. or higher, and is preferably 1100 ° C. or lower in order to prevent sintering between secondary particles. A more preferable heating and baking temperature is 600 to 1000 ° C, and more preferably 600 to 800 ° C. The firing time is about 700 to 1000 hours, preferably 1 to 20 hours. The rate of temperature increase is preferably 0.5 ° C./min to 3.0 ° C./min, and preferably 1.0 ° C./min to 2.0 ° C./min.

  The firing atmosphere is not particularly limited, and firing is performed in an inert atmosphere such as a nitrogen atmosphere or an argon atmosphere, an oxygen atmosphere, or an air atmosphere.

(2) Step of producing sodium titanate (Na ₂ Ti ₃ O ₇ ) powder After firing, sodium titanate (Na ₂ Ti ₃ O ₇ ), which is a fired product, is pulverized to obtain Na ₂ Ti ₃ O ₇ powder. It is preferable. By pulverizing after firing, the final particle size of TiO ₂ (B) can be reduced. As a pulverization method, an alumina mortar, a ball mill, a bead mill, a jet mill, a vibration mill, a mixer, or the like can be employed.

In addition, compared with the pulverization method using an alumina mortar and a zirconia ball mill, pulverization with zirconia balls tends to increase the BET specific surface area of the finally obtained TiO ₂ (B), and it is easy to reduce the average particle size. The aspect ratio tends to increase, and the peak intensity ratio (I ₍₀₀₂₎ / I ₍₄₀₁₎ ) in the X-ray diffraction pattern tends to increase.

When pulverization with a bead mill is performed for 2 hours or more, crystal distortion tends to increase, and the peak intensity ratio (I ₍₀₀₂₎ / I ₍₄₀₁₎ ) tends to decrease. Further, when heat treatment is performed after the pulverization treatment, crystal distortion increases, and the peak intensity ratio (I ₍₀₀₂₎ / I ₍₄₀₁₎ ) tends to decrease. From these, when pulverizing with a bead mill, it is preferable to use 0.5 to 2 mm beads and to set the pulverizing ability low.

In the case where the pulverization treatment of Na ₂ Ti ₃ O ₇ is not performed, it is preferable to employ a material having a small particle diameter as the raw material titanium compound. By using a titanium compound having a small particle diameter, Na ₂ Ti ₃ O ₇ having a small primary particle diameter can be easily obtained.
Further, as described above, in the method of obtaining a Na ₂ Ti ₃ O ₇ powder after spray-drying and granulating a slurry-like mixture containing a titanium compound and a sodium compound, this pulverization step can be omitted. is there.

Furthermore, the above baking process may be repeated, or the above series of baking, cooling, and pulverization processes may be repeated twice or more. It is preferable to carry out repeatedly in this manner from the viewpoint of reducing the ratio of unreacted TiO ₂ as much as possible and obtaining TiO ₂ (B) having a uniform primary particle size.

The series of steps is preferably repeatedly performed 2 times or more and 5 times or less, and more preferably 3 times or more and 4 times or less.
From the viewpoint of making the particle growth of the sodium titanate having a reduced particle size as small as possible, it is preferable that the firing temperature of the last firing step to be performed is lower than the firing temperature of the firing step performed before that. Specifically, the firing temperature in the final firing step is preferably 300 ° C to 800 ° C, more preferably 350 ° C to 700 ° C, and still more preferably 400 ° C to 600 ° C. If it is lower than 300 ° C., it is difficult to sufficiently obtain an effect of reducing distortion of crystals produced by pulverization, and battery characteristics tend to be deteriorated.

After heating and firing, if the obtained secondary particles of sodium titanate (Na ₂ Ti ₃ O ₇ ) are sintered and agglomerated, they can be crushed using a flake crusher, hammer mill, pin mill, etc. as necessary. May be.

The resulting BET specific surface area of _Na 2 _Ti 3 _{O 7} ^is preferably 2m ² / g~50m 2 / ^g, and more preferably 3m ² / g~50m 2 / g. When the BET specific surface area is 2 m ² / g or more, excellent discharge capacity is exhibited.

(3) Step of producing H ₂ Ti ₃ O ₇ Next, Na ₂ Ti ₃ O ₇ obtained as described above is obtained by applying a proton exchange reaction using an acidic solution so that part or all of sodium is protonated. And replaced with H ₂ Ti ₃ O ₇ .

Here, it is preferable to disperse Na ₂ Ti ₃ O ₇ in an acidic solution, hold it for a certain period of time, and then dry it. As the acid, hydrochloric acid, sulfuric acid, nitric acid or the like having any concentration can be used, and an aqueous solution containing any one or more of these is preferable. In particular, it is preferable to use dilute hydrochloric acid having a concentration of 0.1N to 1.0N.
The treatment time is 10 hours to 10 days, preferably 1 day to 7 days, at room temperature (20 ° C. to 25 ° C.). Moreover, in order to shorten processing time, it is preferable to replace | exchange an acidic solution for a new thing suitably. By optimizing the conditions for the exchange treatment, it is possible to reduce the amount of sodium remaining from the starting material in H ₂ Ti ₃ O ₇ to be below the detection limit of chemical analysis by a wet method.

  A known drying method can be applied to the drying after the treatment with the acidic solution, and vacuum drying or the like is preferable.

(4) Step of firing H ₂ Ti ₃ O ₇ to obtain TiO ₂ (B) The H ₂ Ti ₃ O ₇ obtained as described above is heat treated in air to obtain TiO ₂ (B).
The heat treatment temperature is preferably in the range of 280 ° C to 750 ° C, more preferably in the range of 280 ° C to 400 ° C, and still more preferably in the range of 280 ° C to 380 ° C. The treatment time is usually 0.5 to 100 hours, preferably 1 to 30 hours, and the treatment time can be shortened as the treatment temperature is higher.

(5) Other steps When TiO ₂ (B) synthesized from a raw material with low purity is used, it may be used in a method for producing an electrode for a lithium ion battery described later after washing with ion-exchanged water or distilled water. Good.

Firing obtained was _TiO 2 (B) may be pulverized. As a pulverization method, a ball mill, a bead mill, a jet mill, a vibration mill, a mixer or the like can be adopted. Further, a part of the bronze type crystal phase may be transferred to an anatase type crystal structure by pulverization.
Furthermore, after mixing, granulation may be performed by spray drying or the like.

(Second manufacturing method)
TiO ₂ (B) nanoparticles can also be synthesized by an emulsion method using a water-soluble titanium complex.
Specifically, first, titanium metal is reacted with hydrogen peroxide water and ammonia water to form a peroxotitanium titanium complex. Glycolic acid is added as a complexing agent to this complex to prepare a titanium glycolate complex solution.

To the obtained titanium glycolate complex solution, decanol, octanol, nonanol and the like are mixed and stirred to produce an emulsion in which the aqueous phase is the titanium glycolate complex solution and the oil phase is decanol or the like.
Furthermore, sulfuric acid is added as an additive to the emulsion, and TiO ₂ (B) nanoparticles are synthesized using an autoclave under strongly acidic conditions.

<Method for producing electrode for lithium ion battery>
The obtained TiO ₂ (B) of the present invention is used for an electrode for a lithium ion battery. The electrode for lithium ion batteries containing TiO ₂ (B) of the present invention exhibits excellent initial discharge capacity and initial charge / discharge efficiency.

TiO ₂ (B) can also be used as an electrode active material after granulation. Specifically, the slurry containing TiO ₂ (B) is spray-dried and granulated into secondary particles of about 0.5 μm to 100 μm.
The spray dryer used for spray drying can be appropriately selected according to the properties and processing capacity of the slurry, such as a disk type, a pressure nozzle type, and a two-fluid nozzle type.
The control of the secondary particle size is, for example, by adjusting the number of rotations of the disk in the case of the above-mentioned disk type, and adjusting the spray pressure and the nozzle diameter in the case of a pressure nozzle type or a two-fluid nozzle type, etc. This can be done by controlling.
As the drying temperature, the inlet temperature is preferably 200 ° C to 450 ° C, and the outlet temperature is preferably 80 ° C to 120 ° C.

Properties such as concentration and viscosity of the slurry to be used can be appropriately set according to the ability of the spray dryer. When the slurry is low in viscosity and difficult to granulate, or to make it easier to control the particle size, binders such as polyvinyl alcohol, methyl cellulose, polyacrylic acid, gelatin, nonionic, anionic, amphoteric, nonionic, etc. Various additives such as a surfactant may be used.
In consideration of decomposition and volatilization in the subsequent heating and baking heat step, these additives are desirably organic and do not contain a metal component.
Among the binders, methylcellulose and polyacrylic acid are preferably used. In this case, the heating and baking process can be omitted. Although the detailed mechanism is unknown, when these binders are not decomposed and volatilized by heating and firing and used as a battery active material, battery characteristics at high temperatures tend to be improved.

<Lithium ion battery>
The lithium ion battery of the present invention includes a positive electrode, a negative electrode, and an electrolyte, and includes an electrode containing the above-described TiO ₂ (B) of the present invention as the positive electrode or the negative electrode.

  The basic structure of a lithium ion battery is one in which a positive electrode and a negative electrode are opposed to each other with a separator interposed between them and impregnated with an electrolytic solution. The lithium ion battery of the present invention can be applied as a lithium secondary battery or a lithium primary battery.

When TiO ₂ (B) of the present invention is used for the negative electrode of a lithium secondary battery, the positive electrode active material contained in the positive electrode is LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNi _0.5 Mn _1. Composite oxides of lithium and transition metals such as ₅ O ₄ , transition metal oxides such as MnO ₂ and V ₂ O ₅ , transition metal sulfides such as MoS ₂ and TiS, polyacetylene, polyacene, polyaniline, polypyrrole, polythiophene, etc. Or a disulfide compound such as poly (2,5-dimercapto-1,3,4-thiadiazole).

Further, TiO 2 _(B) of the present invention can be suitably used as a positive electrode of a lithium primary battery.

  The electrolytic solution is not particularly limited, and a known one can be used. For example, a non-aqueous lithium ion secondary battery can be manufactured by using a solution in which an electrolyte is dissolved in an organic solvent as the electrolytic solution.

Examples of the organic solvent include carbonates (propylene carbonate, ethylene carbonate, diethyl carbonate, etc.), lactones (γ-butyrolactone, etc.), chain ethers (1,2-dimethoxyethane, dimethyl ether, diethyl ether, etc.), Cyclic ethers (tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, 4-methyldioxolane, etc.), sulfolanes (sulfolane, etc.), sulfoxides (dimethylsulfoxide, etc.), nitriles (acetonitrile, propionitrile, benzonitrile, etc.), amides Aprotic solvents such as polyoxyalkylene glycols (diethylene glycol, etc.), and the like (N, N-dimethylformamide, N, N-dimethylacetamide, etc.). Can.
An organic solvent may be used independently and may be used as a 2 or more types of mixed solvent.

  The organic solvent preferably contains γ-butyrolactone. The mass ratio A of γ-butyrolactone contained in the organic solvent is preferably 0.05 ≦ A ≦ 1, more preferably 0.1 ≦ A ≦ 0.8, and 0.2 ≦ A ≦. More preferably, it is 0.5.

As the electrolyte, for _{example, LiPF 6, LiClO 4, LiBF} 4, LiClF 4, LiAsF 6, LiSbF 6, LiAlO 4, LiAlCl 4, LiN (CF 3 SO 2) 2, LiN (C 2 F 5 SO 2) 2, Examples thereof include lithium salts that generate anions that are difficult to solvate, such as LiC (CF ₃ SO ₂ ) ₃ , LiCl, and LiI.

  The electrolyte concentration is, for example, about 0.3 to 5 mol, preferably 0.5 to 3 mol, and more preferably about 0.8 to 1.5 mol with respect to 1 L of the electrolyte.

Examples of the conductive auxiliary used when producing an electrode using an electrode active material include carbon black such as acetylene black and ketjen black, natural graphite, thermally expanded graphite, carbon fiber, ruthenium oxide, non-stoichiometric titanium oxide. Titanium black, aluminum, nickel, etc. are used. Among these, acetylene black and ketjen black that can ensure desired conductivity with a small amount of blend are preferable.
In addition, about 1 mass%-20 mass% are normally mix | blended with a conductive support agent with respect to an electrode active material, and it is more preferable to mix | blend 5 mass%-10 mass%.

Various known binders can be used as the binder used together with the conductive assistant. For example, polytetrafluoroethylene, polyvinylidene fluoride, carboxymethyl cellulose, fluoroolefin copolymer crosslinked polymer, styrene-butadiene copolymer, polyacrylonitrile, polyvinyl alcohol, polyacrylic acid, polyimide, phenol resin and the like can be mentioned.
In addition, it is preferable to mix | blend a binder with about 3 mass parts-20 mass parts with respect to 100 mass parts of total amounts of an electrode active material, a conductive support agent, and a binder, and mix | blending 5 mass%-10 mass%. More preferred. When the amount is 3 parts by mass or more, the binding property, which is a role of the binder, is sufficiently imparted.

  As the separator, various known separators can be used. Specific examples include paper, polypropylene, polyethylene, glass fiber separators, and the like.

In the TiO ₂ (B) of the present invention, one of the positive and negative electrodes is a polarizable electrode used in an electric double layer capacitor, and the other is an active material that can insert and desorb lithium ions used in a lithium ion battery. The present invention can also be applied to an active material of a hybrid power storage device used as a material electrode.

  EXAMPLES Hereinafter, although a synthesis example, an Example, and a comparative example are given and this invention is demonstrated more concretely, this invention is not restrict | limited to the following Example.

[Example 1]
(Synthesis Example 1)
20.0 g of titanium oxide (manufactured by Wako Pure Chemical Industries, Ltd., purity 99.9% by mass or more, BET specific surface area 8 m ² / g, rutile titanium oxide, purity of titanium oxide is SII NanoTechnology Corporation ) And 9.1 g of sodium carbonate (manufactured by Wako Pure Chemical Industries, Ltd., purity 99% by mass or more, special grade) was put in a ball mill, and 25 g of pure water was added, After mixing for 10 minutes in an agate mortar, it was dried at 130 ° C. This was crushed in an alumina mortar, transferred to a crucible, and baked at 800 ° C. for 20 hours. The temperature was raised at a rate of 1.7 ° C./min.
After firing, it was allowed to cool and then taken out, 25 g of pure water was added, put into a ball mill, 10 mm and 5 mm zirconia balls were added, and the mixture was pulverized for 20 hours. Subsequently, it dried and the baking process at 800 degreeC was performed on the same conditions once again. After grinding again with a ball mill, it was dried and baked at 500 ° C. for 2 hours. The temperature was raised at a rate of 1.7 ° C./min.

The fired product thus obtained was crushed with an alumina mortar to obtain Na ₂ Ti ₃ O ₇ . The crystal phase was identified using a powder X-ray diffractometer manufactured by Rigaku Corporation. The obtained Na ₂ Ti ₃ O _{7 had} an average particle diameter of 1.0 μm and a BET specific surface area of 6 m ² / g.

Subsequently, it was dispersed in 1 mol / L hydrochloric acid and kept at room temperature for 5 days. At this time, the aqueous hydrochloric acid solution was changed every 12 hours. Thereafter, it was repeatedly washed with water and vacuum-dried at 120 ° C. for 1 hour to obtain H ₂ Ti ₃ O ₇ .
The obtained H ₂ Ti ₃ O ₇ was fired at 320 ° C. for 20 hours in air to obtain TiO ₂ (B). The temperature was raised at a rate of 1.7 ° C./min. An SEM observation image of the obtained TiO ₂ (B) is shown in FIG. The crystal phase was identified by the following powder X-ray diffraction pattern.

<Powder X-ray diffraction>
FIG. 1 shows a powder X-ray diffraction pattern of the obtained TiO ₂ (B). It was confirmed that it was a single phase of TiO ₂ (B). The peak intensity ratio (I ₍₀₀₂₎ / I ₍₄₀₁₎ ) of the (002) plane at 2θ = 29 ° and the (401) plane at 2θ = 30 ° was 1.3.

<Average particle diameter (median particle diameter)>
The average particle diameter (median particle diameter) was measured using a laser diffraction particle size measuring instrument “SALD3000J” manufactured by Shimadzu Corporation. The average particle diameter (median particle diameter) of TiO ₂ (B) obtained above was 0.6 μm.

<BET specific surface area>
The BET specific surface area was calculated from an adsorption isotherm of nitrogen at −196 ° C. using an autosorb-1 manufactured by QUANTACHROME INSTRUMENTS. Table 1 shows the BET specific surface area of TiO ₂ (B) obtained above.

<Average aspect ratio>
The average aspect ratio was calculated by the following method using SEM photographic images.
For spherical particles, the ratio of minor axis (minimum diameter) / major axis (maximum diameter) is used, and for hexagonal or disk-shaped particles, the minor diameter (minimum diameter or The ratio of minimum diagonal length) / long diameter (maximum diameter or maximum diagonal length) was measured. And the aspect-ratio of 300 or more particle | grains was measured by the said method, and the number average was computed. Table 1 shows the average aspect ratio of TiO ₂ (B) obtained above.

<Average major axis of primary particles>
The major axis was measured for 300 primary particles of TiO ₂ (B) by the same method as the average aspect ratio, and the number average was calculated. Table 1 shows the average aspect ratio of the obtained TiO ₂ (B).

(Preparation of TiO ₂ (B) electrode)
TiO ₂ (B) as an electrode active material, carbon black (manufactured by Denki Kagaku Kogyo Co., Ltd., trade name: HS-100) as a conductive additive, and N-methylpyrrolidone of polyvinylidene fluoride (PVDF) as a binder resin (NMP) solution (manufactured by Kureha Corporation, trade name: KF polymer # 1120, content of polyvinylidene fluoride: 12% by mass), active material: conductive auxiliary agent: PVDF = 85: 5: 10 (mass ratio) The electrode composition was prepared by mixing at a ratio of 5 to a paste.
This paste-like electrode composition was applied to an aluminum current collector foil (“20CB” manufactured by Nippon Electric Power Storage Co., Ltd.) and dried at 80 ° C. for 4 hours to obtain an electrode having an electrode mixture layer.

(Production of lithium battery)
In the 2016 type coin cell (made by Hosen Co., Ltd.), the above-prepared TiO ₂ (B) electrode and metal lithium as the counter electrode were used. As the electrolytic solution, EC (ethylene carbonate) / PC (propylene carbonate) / GBL (γ-butyrolactone) (1/1/1 volume ratio) in which LiPF ₆ was dissolved at a concentration of 1M was used.

(Evaluation of initial discharge capacity)
The counter electrode (lithium electrode) was charged to 1.2 V with a current corresponding to 0.1 C, and then charged at a constant voltage of 1.2 V until the current dropped to 0.01 C. Here, 1 / xC means flowing at a current value at which charging / discharging is completed in x hours. Discharge was performed up to 2.5 V with a current corresponding to 0.1 C with respect to the lithium electrode, and the initial (initial) discharge capacity was measured. At this time, the capacity was converted per mass of titanium oxide used.

(Evaluation of initial charge / discharge efficiency)
A value obtained by dividing the initial discharge capacity by the initial charge capacity was calculated as the initial charge / discharge efficiency (%). The results are shown in Table 2.

(Evaluation of capacity maintenance rate)
Charge to 1.2V with a current equivalent to 0.1C, then charge until the current drops to 0.01C at a constant voltage of 1.2V, then discharge to 2.5V with a current value equivalent to 30C The discharge capacity was measured, and a value obtained by multiplying the value obtained by dividing the discharge capacity at 30 C by the discharge capacity at 0.1 C by 100 was calculated as the capacity retention rate.

[Example 2]
(Synthesis Example 2)
Instead of the titanium oxide (manufactured by Wako Pure Chemical Industries, Ltd., purity 99.9% by mass or more, BET specific surface area 8 m ² / g, rutile titanium oxide) used in Example 1, titanium oxide (Toho Titanium Co., Ltd.) ), Purity 99.99% by mass, BET specific surface area 2 m ² / g, rutile type titanium oxide). The obtained Na ₂ Ti ₃ O _{7 had} an average particle size of 1.3 μm and a BET specific surface area of 6 m ² / g. Table 1 shows the characteristics of the synthesized TiO ₂ (B).

The battery characteristics of TiO ₂ (B) obtained in Synthesis Example 2 were evaluated. The electrode and battery fabrication conditions were the same as in Example 1. The results are shown in Table 2.

[Example 3]
(Synthesis Example 3)
20.0 g of titanium oxide (manufactured by Wako Pure Chemical Industries, Ltd., purity 99.9% by mass or more, BET specific surface area 8 m ² / g, rutile titanium oxide) and 9.1 g of sodium carbonate (Wako Pure Chemical Industries ( Co., Ltd., purity 99% by mass or more, special grade) was placed in a ball mill, 25 g of pure water was added, mixed for 10 minutes in an agate mortar, and then dried at 130 ° C. This was crushed in an alumina mortar, transferred to a crucible, and baked at 800 ° C. for 20 hours. The temperature was raised at a rate of 1.7 ° C./min.
After firing, the mixture was allowed to cool and then taken out. After pulverizing this with an alumina mortar, the baking process at 800 ° C. was performed again under the same conditions. This was crushed in an alumina mortar and then fired at 500 ° C.
The fired product thus obtained was crushed with an alumina mortar to obtain Na ₂ Ti ₃ O ₇ . The obtained Na ₂ Ti ₃ O _{7 had} an average particle diameter of 10 μm and a BET specific surface area of 2 m ² / g.

Subsequently, it was dispersed in a 1 mol / L hydrochloric acid aqueous solution and kept at room temperature for 5 days. At this time, the aqueous hydrochloric acid solution was changed every 12 hours. Thereafter, it was repeatedly washed with water and vacuum-dried at 120 ° C. for 1 hour to obtain H ₂ Ti ₃ O ₇ .
Next, the obtained H ₂ Ti ₃ O ₇ was fired at 320 ° C. for 20 hours in the air to obtain TiO ₂ (B). The temperature was raised at a rate of 1.7 ° C./min. This was put into a ball mill pot and pulverized for 2 hours using 5 mm and 10 mm balls. Table 1 shows the characteristics of the synthesized TiO ₂ (B). The electrode and battery fabrication conditions were the same as in Example 1. The results are shown in Table 2.

[Example 4]
The same procedure as in Example 1 was performed except that a γ-butyrolactone (GBL) solution containing LiPF ₆ at a concentration of 1 M was used as the electrolytic solution. The results are shown in Table 2.

[Example 5]
The same procedure as in Example 1 was performed except that a propylene carbonate (PC) / γ-butyrolactone (GBL) (1/1 volume ratio) solution containing LiPF ₆ at a concentration of 1 M was used as the electrolytic solution. The results are shown in Table 2.

[Comparative Example 1]
(Synthesis Example 4)
20.0 g of titanium oxide (manufactured by Wako Pure Chemical Industries, Ltd., purity 99.9% by mass or more, BET specific surface area 8 m ² / g, rutile titanium oxide) and 9.1 g of sodium carbonate (Wako Pure Chemical Industries ( Co., Ltd., purity 99% by mass or more, special grade) was placed in a ball mill, 25 g of pure water was added, mixed for 10 minutes in an agate mortar, and then dried at 130 ° C. This was crushed in an alumina mortar, transferred to a crucible, and baked at 800 ° C. for 20 hours. The temperature was raised at a rate of 1.7 ° C./min.
After firing, the mixture was allowed to cool and then taken out. After pulverizing this with an alumina mortar, the baking process at 800 ° C. was performed again under the same conditions. This was crushed in an alumina mortar and then fired at 500 ° C.
The fired product thus obtained was crushed with an alumina mortar to obtain Na ₂ Ti ₃ O ₇ . The obtained Na ₂ Ti ₃ O _{7 had} an average particle diameter of 10 μm and a BET specific surface area of 2 m ² / g.

Subsequently, it was dispersed in a 1 mol / L hydrochloric acid aqueous solution and kept at room temperature for 5 days. At this time, the aqueous hydrochloric acid solution was changed every 12 hours. Thereafter, it was repeatedly washed with water and vacuum-dried at 120 ° C. for 1 hour to obtain H ₂ Ti ₃ O ₇ .
The obtained H ₂ Ti ₃ O ₇ was fired at 320 ° C. for 20 hours in air to obtain TiO ₂ (B). The temperature was raised at a rate of 1.7 ° C./min. Table 1 shows the characteristics of the synthesized TiO ₂ (B). Furthermore, Figure 3 shows the SEM image of _TiO 2 obtained (B).

The battery characteristics of TiO ₂ (B) obtained in Synthesis Example 4 were evaluated. The electrode and battery fabrication conditions were the same as in Example 1. The results are shown in Table 2.

[Comparative Example 2]
(Synthesis Example 5)
Instead of titanium oxide (manufactured by Wako Pure Chemical Industries, Ltd., purity 99.9% by mass or more, BET specific surface area 8 m ² / g, rutile type titanium oxide) used in Comparative Example 1, titanium oxide (Taika Co., Ltd.) Comparative Example 1 was performed except that “JR” (BET specific surface area 12 m ² / g, rutile type titanium oxide) was used. The obtained Na ₂ Ti ₃ O _{7 had} an average particle diameter of 4 μm and a BET specific surface area of 1 m ² / g. Table 1 shows the characteristics of the synthesized TiO ₂ (B).

The battery characteristics of TiO ₂ (B) obtained in Synthesis Example 5 were evaluated. The electrode and battery fabrication conditions were the same as in Example 1. The results are shown in Table 2.

[Comparative Example 3]
(Synthesis Example 6)
20.0 g of titanium oxide (“A120” manufactured by Sakai Chemical Co., Ltd., BET specific surface area 12 m ² / g, anatase type titanium oxide) and 9.1 g of sodium carbonate (manufactured by Wako Pure Chemical Industries, Ltd., purity 99 mass) % Or more, special grade) was put in a ball mill, 25 g of pure water was added, mixed for 10 minutes in an agate mortar, and then dried at 130 ° C. This was crushed in an alumina mortar, transferred to a crucible, and baked at 900 ° C. for 20 hours. The temperature was raised at a rate of 1.7 ° C./min.
After firing, the mixture was allowed to cool and then taken out. After this was crushed in an alumina mortar, the firing step at 900 ° C. was performed again under the same conditions.
The fired product thus obtained was crushed with an alumina mortar to obtain Na ₂ Ti ₃ O ₇ . The obtained Na ₂ Ti ₃ O _{7 had} an average particle diameter of 15 μm and a BET specific surface area of 1 m ² / g. Subsequently, it was dispersed in a 1 mol / L hydrochloric acid aqueous solution and kept at room temperature for 5 days. At this time, the aqueous hydrochloric acid solution was changed every 12 hours. Thereafter, it was repeatedly washed with water and vacuum-dried at 120 ° C. for 1 hour to obtain H ₂ Ti ₃ O ₇ .
Next, the obtained H ₂ Ti ₃ O ₇ was fired at 320 ° C. for 20 hours in the air to obtain TiO ₂ (B). The temperature was raised at a rate of 1.7 ° C./min. Table 1 shows the characteristics of the synthesized TiO ₂ (B).

The battery characteristics of TiO ₂ (B) obtained in Synthesis Example 6 were evaluated. The electrode and battery fabrication conditions were the same as in Example 1. The results are shown in Table 2.

[Comparative Example 4]
(Synthesis Example 7)
The same procedure as in Synthesis Example 2 was performed except that pulverization was performed with a bead mill instead of pulverization with a ball mill. A 0.3 mm zirconia bead was used as the bead, and a bead mill LMZ-015 manufactured by Ashizawa Finetech was used as the bead mill. The bead filling amount was 85% by mass, the liquid amount was 250 mL / min, and the rotation speed was 12 m / sec. After pulverization with a bead mill and heat treatment at 500 ° C. for 2 hours, the average particle size of sodium titanate was 1.0 μm and the BET specific surface area was 31 m ² / g. Table 1 shows the characteristics of the synthesized TiO ₂ (B).

As shown in Table 2, TiO ₂ (B) having a BET specific surface area, I ₍₀₀₂₎ / I ₍₄₀₁₎ in an X-ray diffraction diagram, and an aspect ratio within the range defined in the present invention is used as an electrode active material. The lithium secondary battery of the used example has high initial discharge capacity and initial charge / discharge efficiency, and excellent initial battery characteristics.
On the other hand, it can be seen that Comparative Example 1 using TiO ₂ (B) of Synthesis Example 4 having a low aspect ratio has a low initial discharge capacity, initial charge / discharge efficiency, and a capacity retention rate at 30C. Further, TiO ₂ (B) of Synthesis Example 5 has a low initial discharge capacity because the value of I ₍₀₀₂₎ / I ₍₄₀₁₎ is not sufficiently high. Further, TiO ₂ (B) of Synthesis Example 6 has a very low initial discharge capacity because I ₍₀₀₂₎ / I ₍₄₀₁₎ is small. In addition, although TiO ₂ (B) of Synthesis Example 7 has a high aspect ratio and a small average major axis of primary particles, the initial discharge capacity is inferior because I ₍₀₀₂₎ / I ₍₄₀₁₎ is small.

Claims (9)

The BET specific surface area is 6 to 100 m ² / g, and the average aspect ratio represented by the ratio of the major axis L to the minor axis S (S / L) of the primary particles is 0.37 ≦ S / L ≦ in the SEM photographic image. A bronze type crystal having a ratio (I ₍₀₀₂₎ / I ₍₄₀₁₎ ) of the peak intensity of the (002) plane to the peak intensity of the (401) plane in the X-ray diffraction pattern is 0.7 or more Titanium dioxide having a structure.   The titanium dioxide having a bronze type crystal structure according to claim 1, wherein the average major axis of primary particles observed by SEM is 1 μm or less.   3. The titanium dioxide according to claim 1, wherein an average particle diameter (median particle diameter) is 0.3 μm to 50 μm.   The electrode for lithium ion batteries containing the titanium dioxide of any one of Claims 1-3. A positive electrode, a negative electrode, and an electrolyte;
A lithium ion battery comprising the lithium ion battery electrode according to claim 4 as the positive electrode or the negative electrode.   The lithium ion battery according to claim 5, which contains γ-butyrolactone as a solvent for the electrolyte. Firing a mixture of a titanium compound and a sodium or potassium compound to prepare a sodium titanate powder or a potassium titanate powder;
A step of impregnating the sodium titanate powder or potassium titanate powder with an aqueous hydrochloric acid solution and firing at 250 ° C. to 400 ° C .;
The manufacturing method of the titanium dioxide of any one of Claims 1-3 which has these. The BET specific surface area of titanium sodium or potassium titanate ^powder, method for producing titanium dioxide according to claim 7 is 3m ² / g~50m 2 / g. The BET specific surface area of titanium sodium or potassium titanate ^powder, method for producing titanium dioxide according to claim 7 or claim 8 which is 5m ² / g~30m 2 / g.