JP2012214362A - Lithium titanate particulate powder and production method for the same, negative electrode active material particulate powder for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide lithium titanate particle powder in which battery characteristics with balance can be obtained among initial electric discharge capacity, an output characteristic (high electric discharge capacity maintenance rate), and gas generation control, when using the powder as active material for a non-aqueous electrolyte secondary battery.SOLUTION: In the impurities phase of TiOand LiTiOcontained in LiTiO, the lithium titanate particle powder is controlled of the BET specific surface area in the specific range, while making a specific quantity of LiTiOpresent therein. The lithium titanate particle powder concerned can be obtained by firing at least a mixture of LiTiOand TiOat 650°C or higher and lower than 800°C.

Description

  The present invention relates to a lithium titanate particle powder having excellent initial discharge capacity and high output characteristics (high rate discharge capacity retention rate) as a negative electrode active material for a nonaqueous electrolyte secondary battery, a method for producing the same, and the negative electrode A nonaqueous electrolyte secondary battery using an active material is provided.

  In recent years, electronic devices such as AV devices and personal computers are rapidly becoming portable and cordless, and there is an increasing demand for secondary batteries having a small size, light weight, and high energy density as power sources for driving these devices. Under such circumstances, a lithium ion secondary battery having advantages such as a high charge / discharge voltage and a large charge / discharge capacity has attracted attention.

  In this lithium ion secondary battery, in recent years, it is known to use lithium titanate as a negative electrode active material.

Lithium titanate: Li ₄ Ti ₅ O ₁₂ is known as a highly reliable negative electrode active material with high structural stability because the crystal structure change in the lithium ion insertion / extraction reaction due to charge / discharge is very small. .

Conventionally, as a manufacturing method for obtaining lithium titanate (Li ₄ Ti ₅ O ₁₂ ), a mixed powder in which a lithium salt and a titanium oxide are dry or wet mixed so that a Li / Ti ratio is approximately 0.80. There is known a so-called solid phase reaction method (dry method) in which Li ₄ Ti ₅ O ₁₂ is obtained by heating and firing (these are simply a mixture of a lithium salt and a titanium oxide) (Patent Documents 1 and 2). ).

On the other hand, a liquid phase reaction + solid phase reaction method (wet method) is known in which a mixture of titanium and lithium is hydrothermally treated and then heated and fired to obtain Li ₄ Ti ₅ O ₁₂ (Patent Documents 3 and 4). ).

In Patent Document 5, in the XRD of lithium titanate, the peak intensity ratios of TiO ₂ and Li ₂ TiO ₃ are both 7 or less, preferably 3 or less, relative to the peak intensity ratio with Li ₄ Ti ₅ O ₁₂ . More preferably, it is set to 1 or less, and it is disclosed that the smaller the impurity phase, the higher the lithium ion diffusion rate, and the better the ion conductivity and large current characteristics (high rate discharge capacity retention rate).

JP 2001-192208 A JP 2001-213622 A JP-A-9-309727 JP 2010-228980 A JP 2006-318797 A

Previous reports have aimed to further increase the purity of the final composition Li ₄ Ti ₅ O ₁₂ , and it is known that the higher the purity, the better the battery characteristics.

However, as in Patent Document 5, the lithium titanate particle powder made of Li ₄ Ti ₅ O ₁₂ having a high purity by reducing the impurity phase as much as possible has a high initial discharge capacity and high output characteristics (at a high rate). The negative electrode active material that has an excellent discharge capacity maintenance rate and can suppress gas generation has not yet been obtained.

The inventors of the present invention focused on the abundance of TiO ₂ and Li ₂ TiO ₃ contained in the target product Li ₄ Ti ₅ O _12, and as a result of earnest and examination, as a result of the conventional knowledge, that is, Li ₄ Ti Rather than increasing the purity of ₅ O ₁₂ , Li ₂ TiO ₃ is present in a specific range, and the specific surface area by the BET method is adjusted to a specific range, whereby the initial discharge capacity and output characteristics (high-rate discharge capacity) The present inventors have found that battery characteristics excellent in both the maintenance ratio and gas generation suppression can be obtained.

  The technical problem can be achieved by the present invention as follows.

That is, according to the present invention, when lithium titanate particles having a spinel structure are indexed with Fd-3m by XRD, the amount of TiO ₂ by Rietveld analysis is 1.5% or less, and the amount of Li ₂ TiO ₃ is 1 % Titanic acid characterized in that the amount of Li ₄ Ti ₅ O ₁₂ is in the range of 94% to 99% and the specific surface area by the BET method is in the range of 7 to 15 m ² / g. Lithium particle powder. (Invention 1)

  Moreover, this invention is a lithium titanate particle powder of this invention 1 whose Li / Ti ratio (molar ratio) is 0.805-0.83. (Invention 2)

Further, the present invention is at least _Li 2 TiO ₃ and the present invention 1 or 2 method for producing a lithium titanate particles as described in the mixture, characterized by baking below 800 ° C. 650 ° C. or more and TiO ₂ ( Invention 3).

  Moreover, this invention is negative electrode active material particle powder which consists of lithium titanate particle powder as described in this invention 1 or 2 (this invention 4).

  The present invention also provides a cell in which the negative electrode active material is used and the counter electrode is made of lithium metal, and the initial discharge capacity is 165 mAh / g or more when the direction in which lithium is released is charged. When the C-rate in the measurement is 0.1 C, the output characteristics (high rate discharge capacity maintenance ratio) corresponding to the ratio of 10 C and 0.1 C are 80% or more, and the negative electrode active for a non-aqueous electrolyte secondary battery according to the present invention 4 Substance particle powder (Invention 5)

  Further, the present invention is a non-aqueous electrolyte secondary battery using the negative electrode active material particle powder according to the present invention 4 or 5 (Invention 6).

  The lithium titanate particle powder according to the present invention has an excellent initial discharge capacity and high output characteristics when used as a negative electrode active material particle powder in a non-aqueous electrolyte secondary battery, and a balance in which gas generation is suppressed. Therefore, it is suitable as an active material particle powder for a non-aqueous electrolyte secondary battery.

2 is an XRD pattern of lithium titanate particle powder obtained in Example 1. FIG. It is an XRD pattern of the lithium titanate particle powder obtained in Example 6. It is an XRD pattern of the lithium titanate particle powder obtained in Comparative Example 2. 2 is a scanning electron micrograph of lithium titanate particle powder obtained in Example 2. FIG.

  The configuration of the present invention will be described in more detail as follows.

The lithium titanate particle powder according to the present invention has at least a spinel structure, is a compound that can be expressed as Li ₄ Ti ₅ O _{12 in} a general chemical formula, and contains at least Li ₂ TiO ₃ .

The presence state of Li ₂ TiO ₃ in the lithium titanate particle powder according to the present invention may be in a state of being coated on the particle surface or in an island shape as long as it is in an amount specified by the present invention, Any shape may be present in the grains.

In the lithium titanate particle powder according to the present invention, diffraction between 10 and 90 degrees (2θ / θ) can be indexed with Fd-3m in XRD. By performing Rietveld analysis from the XRD pattern, the amount of residual TiO _{2 and the} amount of Li ₂ TiO ₃ can be quantified. In the present invention, the abundance of TiO ₂ is 1.5% or less, and the abundance of Li ₂ TiO ₃ is in the range of 1.0 to 6.0%. When the abundance of TiO ₂ exceeds 1.5%, the output characteristics (high rate discharge capacity maintenance rate) are deteriorated. When the abundance of Li ₂ TiO ₃ is less than 1.0%, the initial discharge capacity and output characteristics (high rate discharge capacity retention rate) of a secondary battery produced using this lithium titanate particle powder as the negative electrode active material particle powder ) Is good, but gas generation increases as shown in a comparative example described later. When the abundance of Li ₂ TiO ₃ exceeds 6.0%, the initial discharge capacity of a secondary battery produced using this lithium titanate particle powder as the negative electrode active material particle powder becomes low, and a high value of 165 mAh / g or more is obtained. The capacity cannot be filled. Preferably, the abundance of TiO ₂ is 1.0% or less, the abundance of Li ₂ TiO ₃ is 1.5 to 5.0%, more preferably the abundance of TiO ₂ is 0.5% or less. And the abundance of Li ₂ TiO ₃ is 2.0-4.0%.

In the present invention, it is important that Li ₂ TiO ₃ exists by Rietveld analysis of lithium titanate particle powder. The presence of Li ₂ TiO ₃ in the particles or in the particle surface layer within a specific range is considered to produce mainly three effects.

The first point is considered that the lattice distortion in high-speed charge / discharge is reduced by the presence of Li ₂ TiO _{3 in the} lithium titanate particles or in the surface layer. Therefore, it is considered that the output characteristics (high rate discharge capacity maintenance rate) described in the present invention are good.

Second, it is considered that Li ₂ TiO ₃ is present in the lithium titanate particles or on the surface layer according to the present invention, so that a kind of defects (point defects, surface defects, etc.) are generated. For this reason, Li ₄ Ti _The point where the valence balance of ₅ O ₁₂ as a whole is shifted is generated, and the lithium titanate particle powder according to the present invention is considered to have higher conductivity than the pure lithium titanate particle powder. It is considered that the capacity maintenance ratio is improved.

The third point is that Li ₂ TiO ₃ is present in the lithium titanate particles or in the surface layer, and when the lithium titanate becomes Li ₇ Ti ₅ O ₁₂ by full charge, not the entire particles but Li ₂ TiO _3. It is considered that the existence point of the gas remains, and as a result, gas generation becomes small.

  The primary particle size of the lithium titanate particle powder according to the present invention is preferably 0.1 to 0.4 μm. In the present invention, it has been found that the primary particle size greatly affects the output characteristics. When it is smaller than the range of the present invention, the crystal structure is not stable, and the initial charge characteristics are deteriorated. If it is large, the required output characteristics (high rate discharge capacity maintaining characteristics) cannot be obtained. A more preferable range is 0.1 to 0.3 μm.

The specific surface area by the BET method of the lithium titanate particle powder according to the present invention is in the range of 7 to 15 m ² / g. When the specific surface area is smaller than this range, the output characteristics (high rate discharge capacity retention rate) are deteriorated. When the specific surface area is larger than this range, swelling of the battery becomes remarkable due to gas generation. A preferable specific surface area is 8 to 13 m ² / g.

  Next, the manufacturing method of the lithium titanate particle powder concerning this invention is described.

That is, the lithium titanate particle powder according to the present invention can be obtained by firing at 650 ° C. or more and less than 800 ° C. using at least a mixture of Li ₂ TiO ₃ and TiO ₂ .

_Li 2 TiO ₃ to be used in the preparation of lithium titanate particles according to the present invention, if a particular _Li 2 TiO ₃ is in indexing in the JCPDS, or have structural defects in the crystal structure, there is an oxygen deficiency / oxygen excess It doesn't matter.

Li ₂ TiO ₃ used in the present invention can be obtained by reacting a lithium compound and a titanium compound such as titanium oxide by a wet reaction or a solid phase method.

  The Li compound that can be used in the present invention is not particularly limited, and various lithium salts can be used. In the wet method, lithium hydroxide is particularly preferable, and in the dry method, lithium carbonate is particularly preferable.

TiO ₂ that can be used in the present invention has an anatase type, a rutile type, and a mixed phase thereof, and an anatase type is preferable.
In the case of performing a mixing reaction, it is advantageous to use fine particles in order to improve the reactivity.

Moreover, if the state of Li ₂ TiO ₃ and TiO ₂ is a uniformly mixed state, it may be a dry-type mixing, a wet-coated state, or a mixed phase state It may be.

This mixture can be adjusted by controlling temperature and time in the wet method. Further, in _advance, by generating a Li 2 TiO _3, can also be adjusted by mixing with TiO _2, it is necessary to increase the sintering temperature, Li / Ti ratio, it is necessary to consider the control of the BET.

In addition, the mixture of Li ₂ TiO ₃ and TiO ₂ is not particularly limited in the production conditions, and titanium oxide and lithium hydroxide are in a molar ratio of Li / Ti ratio exceeding 1.0 and less than 1.5. It can also be obtained by heating the reaction suspension adjusted to 80 ° C. to less than 100 ° C., stirring and aging for 5 hours to less than 15 hours, and then filtering and drying the reaction suspension.

_Li 2 TiO ₃ and TiO ₂ used in the production of the lithium titanate particles according to the present invention is preferably adjusted to be 0.805 to 0.83 in Li / Ti ratio after firing. To adjust the range, it can be carried out to adjust the mixing ratio of the Li ₂ TiO ₃ and TiO _2, by and add lithium compound. The reason why Li / Ti is made larger than 0.80 is that Li ₂ TiO ₃ remains after firing. When the amount is larger than the above range, the initial discharge capacity is reduced, and when the Li ₂ TiO ₃ residue is further increased, the residual alkali of the obtained lithium titanate particle powder increases, and the coating gels.

The prepared mixture of Li ₂ TiO ₃ and TiO ₂ is fired at 650 ° C. or higher and lower than 800 ° C. If the firing temperature is less than 650 ° C., a large amount of TiO ₂ remains. If the firing temperature is too high, the BET becomes too small due to grain growth, and as a result, the output characteristics (high rate discharge capacity retention rate) are impaired. The firing temperature is preferably 680 to 780 ° C.

  The atmosphere in firing may be an oxidizing atmosphere or a reducing atmosphere. The obtained lithium titanate particle powder may have oxygen deficiency or oxygen excess in the present invention within the scope of known techniques.

  The lithium titanate particle powder obtained by firing can be pulverized to adjust the particle size distribution. The shape of the particle size distribution may be sharp, broad, or bimodal.

  The lithium titanate particle powder according to the present invention can be used as a negative electrode active material particle powder for a non-aqueous electrolyte secondary battery.

  Next, the negative electrode containing the negative electrode active material particle powder and the nonaqueous electrolyte secondary battery according to the present invention will be described.

  When manufacturing the negative electrode containing the negative electrode active material particle powder according to the present invention, a conductive agent and a binder are added and mixed according to a conventional method. As the conductive agent, acetylene black, carbon black, graphite and the like are preferable, and as the binder, polytetrafluoroethylene, polyvinylidene fluoride and the like are preferable.

  The secondary battery manufactured using the negative electrode containing the active material particle powder for negative electrodes which concerns on this invention is comprised from a positive electrode, a negative electrode, and electrolyte.

  As the positive electrode active material, lithium cobaltate, lithium manganate, lithium nickelate, etc., which are common positive electrode materials for non-aqueous secondary batteries, can be used.

  In addition to the combination of ethylene carbonate and diethyl carbonate, an organic solvent containing at least one of carbonates such as propylene carbonate and dimethyl carbonate and ethers such as dimethoxyethane can be used as the solvent for the electrolytic solution.

  Further, as the electrolyte, in addition to lithium hexafluorophosphate, at least one lithium salt such as lithium perchlorate and lithium tetrafluoroborate can be dissolved in the above solvent and used.

  The non-aqueous electrolyte secondary battery manufactured using the electrode containing the negative electrode active material particle powder according to the present invention has a capacity of 1.0 V or more is 165 mAh / g or more and 10 C / 0.00. The output characteristic (high rate discharge capacity retention rate) taking the ratio of 1C is 80% or more.

Li ₂ TiO ₃ having a specific amount remaining in lithium titanate, which is the negative electrode active material particle, is considered to have a buffering effect on the expansion and contraction of the lattice in a load test using a secondary battery. In addition, the presence of Li ₂ TiO ₃ in the particles is thought to cause distortion of the crystal structure (point defects, surface defects, etc.), so that it is considered that the electronic conductivity and ionic conductivity of the powder are improved. As a result, it is considered that the negative electrode active material particle powder according to the present invention can have high output characteristics (high rate discharge capacity retention rate).

  In addition, the lithium titanate particle powder according to the present invention can be used as a positive electrode active material.

  When the lithium titanate particle powder according to the present invention is used as a positive electrode active material, the non-aqueous electrolyte secondary battery is composed of the above electrode, counter electrode and electrolyte, and the counter electrode (negative electrode) is metallic lithium, lithium alloy, or graphite. Carbonaceous materials such as coke are used.

<Action>
The most important point in the present invention is that by using the lithium titanate particle powder in which a specific amount of Li ₂ TiO ₃ is present according to the present invention, excellent initial discharge capacity and high output characteristics (high rate discharge) as a secondary battery. (Capacity maintenance ratio) and a non-aqueous electrolyte secondary battery in which gas generation is suppressed can be obtained.

Conventionally, as in Patent Document 5 described above, lithium titanate particle powder composed of Li ₄ Ti ₅ O ₁₂ having a high purity is obtained by reducing the impurity phase with reference to the peak intensity ratio by X-ray diffraction. I have been. However, simply by making it high purity, the initial discharge capacity is high, the output characteristics (maintenance rate of the discharge capacity at a high rate) are excellent, and the characteristics that gas generation can be suppressed can be sufficiently satisfied. There wasn't.

The present inventors have quantified the impurity phase by Rietveld analysis that can be quantified more accurately than quantification by the peak intensity ratio of X-ray diffraction, and a very small amount of Li ₂ TiO ₃ is present, and the BET specific surface area. By controlling the above, it has become possible to obtain a negative electrode active material exhibiting high battery characteristics.

  A typical embodiment of the present invention is as follows.

  The average primary particle diameter was observed using a scanning electron microscope SEM-EDX with an energy dispersive X-ray analyzer [manufactured by Hitachi High-Technologies Corporation], and the average value was read from the SEM image.

  The BET specific surface area was measured by drying and deaerating the sample under nitrogen gas at 120 ° C. for 45 minutes, and then using a Macsorb HM Model-1208 manufactured by Mountec Co., Ltd.

  The composition and the amount of impurities were prepared by preparing adjustment liquids, and ICP measurements were determined by quantifying each element using iCAP6500 manufactured by Thermo Fisher Scientific Co., Ltd.

The X-ray diffraction of the sample was measured using RAD-IIA manufactured by Rigaku Corporation. The amount of TiO _{2 and the} amount of Li ₂ TiO ₃ were quantified by performing Rietveld analysis using X-ray diffraction data. Rietan2000 was used for Rietveld analysis.

  About the negative electrode active material particle powder which concerns on this invention, battery evaluation was performed using the 2032 type | mold coin cell.

For coin cells related to battery evaluation, lithium titanate, which is an active material particle powder for a negative electrode according to the present invention, is used as a positive electrode, the amount of active material is 90% by weight, acetylene black is 2.5% by weight as a conductive material, and graphite is 2%. Then, 5% by weight and 5% by weight of polyvinylidene fluoride dissolved in N-methylpyrrolidone as a binder were mixed, applied to an Al metal foil, and dried at 120 ° C. The sheet was punched out to 16 mmΦ, and then pressure-bonded at 3.0 t / cm ² was used for the positive electrode. The counter electrode was made of metallic lithium having a thickness of 500 μm punched to 16 mmΦ, and the electrolyte was a 2032 type coin cell using a solution in which EC and DMC in which 1 mol / L LiPF ₆ was dissolved were mixed at a volume ratio of 1: 2. .

  The charge / discharge characteristics are as follows. When charging is performed in the direction in which Li is released (in the direction in which the voltage increases as a battery) in an environment of 25 ° C. in a thermostatic chamber, the discharge is performed at a current density of 0.1 C up to 1.0 V. (CC-CC operation), charging was performed at a current density of 0.1 C up to 3.0 V (CC-CC operation). The first discharge capacity of this operation was measured.

  The output characteristics (high rate discharge capacity maintenance rate) are as follows. Discharge was performed at a current density of 0.1 C up to 1.0 V (CC-CC operation) in an environment set to 25 ° C. in a thermostatic chamber, and then charged 3. It was performed at a current density of 0.1 C up to 0 V (CC-CC operation). Let the discharge capacity at this time be a. Next, after discharging was performed at a current density of 10 C up to 1.0 V (CC-CC operation), charging was performed at a current density of 0.1 C up to 3.0 V (CC-CC operation). When the discharge capacity at this time is b, the output characteristic is (b / a × 100 (%)).

  The gas generation amount was evaluated by producing a laminate cell by the following method.

90% by weight of lithium titanate, which is an active material particle powder for negative electrodes according to the present invention, 2.5% by weight of acetylene black as a conductive material, 2.5% by weight of graphite, and polyfluoride dissolved in N-methylpyrrolidone as a binder After mixing with 5% by weight of vinylidene, it was applied to an Al metal foil and dried at 120 ° C. This sheet was cut into a 40 mm × 100 mm square, and then consolidated at 3.0 t / cm ² to be used as a negative electrode.

The counter electrode was mixed with 92% by weight of LiMn ₂ O ₄ , 2.5% by weight of acetylene black as a conductive material, 2.5% by weight of graphite, and 3% by weight of polyvinylidene fluoride dissolved in N-methylpyrrolidone as a binder. After that, it was applied to an Al metal foil and dried at 120 ° C., and this sheet was cut into a 40 mm × 100 mm square and then consolidated at 3.0 t / cm ² .

  A laminate cell was prepared by combining two sets of these electrodes so as to face each other.

  In the laminate cell, first, initial charge / discharge was performed at room temperature, and then charged to 2.7 V, and the volume of the laminate cell at this voltage was measured. Next, after storing the cell after measurement for 24 hours in an environment of 85 ° C., the volume of the laminate cell was measured again, and the amount of gas generated was evaluated from the volume change before and after high-temperature storage.

Example 1
<Manufacture of lithium titanate particle powder>
A reaction suspension prepared by adjusting titanium oxide and lithium hydroxide having a specific surface area of 10 m ² / g and a primary particle diameter of 180 nm to a Li / Ti molar ratio of 1.4 is heated to 85 ° C. and stirred for 12 hours. Thereafter, the reaction suspension was filtered and dried at 120 ° C. When the obtained dry powder was subjected to X-ray diffraction, it was at least a mixture of Li ₂ TiO ₃ and TiO ₂ .
The dried powder was put in an alumina crucible and baked in a muffle furnace at a temperature of 760 ° C. for 4 hours in an air atmosphere to obtain lithium titanate particle powder.

Examples 2-5, Comparative Examples 1-5
Except having changed the kind of titanium oxide, Li / Ti molar ratio, reaction temperature, reaction time, and calcination temperature, it processed similarly to Example 1 and obtained lithium titanate particle powder.

Example 6
A reaction suspension prepared by adjusting titanium oxide and lithium hydroxide having a specific surface area of 10 m ² / g and a primary particle diameter of 180 nm to a molar ratio of Li / Ti of 2.5 was charged in an autoclave and heated to 175 ° C., 8 Stir for hours. Thereafter, the reaction suspension was filtered and dried at 120 ° C.
When the obtained dry powder was subjected to X-ray diffraction, it was a Li ₂ TiO ₃ single phase.

This Li ₂ TiO ₃ powder and titanium oxide having a specific surface area of 344 m ² / g and a primary particle diameter of 5 nm were adjusted and mixed to a molar ratio of Li / Ti ratio of 0.84, and the mixed powder was put into an alumina crucible, and a muffle furnace Then, baking was performed in an air atmosphere at a temperature of 780 ° C. for 4 hours to obtain lithium titanate particle powder.

Comparative Example 6
Titanium oxide having a specific surface area of 10 m ² / g and a primary particle size of 180 nm and lithium carbonate were adjusted and mixed at a molar ratio of Li / Ti ratio of 0.90, and the mixed powder was put in an alumina crucible and heated at a temperature of 850 in a muffle furnace. Firing was performed in an air atmosphere at 4 ° C. for 4 hours to obtain lithium titanate particle powder.

Comparative Example 7
A suspension of titanium oxide having a specific surface area of 299 m ² / g and a primary particle diameter of 5 nm and lithium hydroxide adjusted to 0.9 in terms of a molar ratio of Li / Ti ratio is stirred at room temperature for 2 hours. Thereafter, the mixed suspension was evaporated to dryness at 120 ° C. The dried powder was placed in an alumina crucible and baked in a muffle furnace at a temperature of 650 ° C. for 4 hours and then at 800 ° C. for 4 hours in an air atmosphere to obtain lithium titanate particle powder.

  Tables 1 and 2 show the characteristics and conditions of the lithium titanates obtained in the examples and comparative examples.

  As shown in the examples, the lithium titanate particles according to the present invention have high initial discharge capacity of 165 mAh / g or more, output characteristics (discharge capacity maintenance rate at a high rate) of 80% or more, and gas generation. Is suppressed to less than 4.0 cc / g, it is suitable as an active material for a non-aqueous electrolyte secondary battery.

In addition, in the said Example, although the example which used the lithium titanate particle powder which concerns on this invention as a positive electrode active material is shown, also when the lithium titanate particle powder which concerns on this invention is used as a negative electrode active material, As an active material of a nonaqueous electrolyte secondary battery, it can exhibit excellent characteristics.

Claims (6)

In the lithium titanate particles having a spinel structure, when indexed with Fd-3m in XRD, Ried weight TiO2 by the belt analysis 1.5% or _less, Li 2 TiO ₃ amount less than 6% 1% Lithium titanate particle powder, wherein the amount of Li ₄ Ti ₅ O ₁₂ is in the range of 94% to 99% and the specific surface area by the BET method is in the range of 7 to 15 m ² / g. The lithium titanate particle powder according to claim 1, wherein the Li / Ti ratio (molar ratio) is 0.805 to 0.83. The method for producing lithium titanate particle powder according to claim 1 or 2, wherein a mixture of at least Li ₂ TiO ₃ and TiO ₂ is fired at 650 ° C or higher and lower than 800 ° C. A negative electrode active material particle powder comprising the lithium titanate particle powder according to claim 1. In the cell using the negative electrode active material particle powder according to claim 4 and having a counter electrode made of lithium metal, the initial discharge capacity is 165 mAh / g or more when the direction in which lithium is released is charged. The negative electrode active material particle powder for a non-aqueous electrolyte secondary battery according to claim 4, wherein when the C-rate in the measurement is 0.1C, the output characteristic corresponding to the ratio of 10C to 0.1C is 80% or more. A nonaqueous electrolyte secondary battery using the negative electrode active material particle powder according to claim 4.