JP5450284B2 - Lithium titanate particles and manufacturing method thereof, negative electrode for lithium ion battery, and lithium battery - Google Patents

Description

  The present invention relates to lithium titanate particles and a method for producing the same, a negative electrode for a lithium ion battery, and a lithium battery.

  In a power storage device such as a lithium ion primary battery and a lithium ion secondary battery that have been widely used in recent years, discharging and charging are performed by movement of lithium ions.

Currently, many positive electrode active materials for lithium ion secondary batteries have been proposed, but the most commonly known one is cobalt acid that operates near 4 V (vs. Li ^/ Li ⁺ ). It is a lithium-containing transition metal oxide based on lithium (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate having a spinel structure (LiMn ₂ O ₄ ), or the like. These are widely employed as positive electrode active materials because of their excellent charge / discharge characteristics and energy density.
On the other hand, carbon materials such as hard carbon, soft carbon, and graphite are widely used as the negative electrode active material. In addition, an electrolytic solution in which LiPF ₆ is dissolved in a cyclic or chain carbonate compound is used.

  However, when considering installation in HEV (Hybrid Electric Vehicle), which is expected to have a large demand in the future, the specifications adopted for the current small lithium-ion secondary batteries as described above are required for HEV applications. May fail to satisfy the safety and input / output characteristics.

  Titanium oxide-based active materials exhibit a voltage of about 1 to 2 V when lithium metal is used for the counter electrode. Therefore, as materials for negative electrodes of lithium ion batteries, materials having various crystal structures or particle shapes. The possibility as an electrode active material has been studied.

Among them, the spinel type lithium titanate represented by Li _{4 + x} Ti ₅ O ₁₂ (0 ≦ x ≦ 3) has a voltage of 1.5 V on the basis of lithium, and changes in crystal structure accompanying charging / discharging are hardly seen. Therefore, it has been attracting attention as an electrode material with excellent safety and longevity.

  For example, it has been reported that a lithium ion battery having a crystallite size of 70 nm to 80 nm and using a highly crystalline lithium titanate exhibits a high initial discharge capacity (see, for example, Patent Document 1).

  Further, it has been reported that the lithium ion diffusion rate can be improved by using lithium titanate having a small crystallite size and a small impurity phase, and a method for producing lithium titanate having a small crystallite size and a small impurity phase. As described above, a method of suppressing crystal growth by adding Na or K and synthesizing is disclosed (for example, see Patent Document 2).

  Furthermore, lithium titanate synthesized using titanium oxide having a primary particle size of 1.0 μm or less and a rutile ratio of 15 to 100% as a raw material has higher charge / discharge capacity, higher coulomb efficiency, and cycle life. Have been reported to be excellent (see, for example, Patent Document 3).

Japanese Patent Laid-Open No. 2001-240498 JP 2006-318797 A JP 2002-289194 A

  However, an electrode active material for a lithium ion secondary battery used in an automobile or the like is required to have good characteristics in a wide temperature range. On the other hand, the conventionally known lithium titanate is insufficient to satisfy the discharge capacity particularly in a low temperature environment.

  The present invention relates to lithium titanate particles as an electrode active material capable of constituting a lithium ion secondary battery excellent in discharge capacity in a low temperature environment, a method for producing the same, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery It is an issue to provide.

As a result of intensive studies to solve the above problems, the present inventors have appropriately controlled the average primary particle size and the distribution of the primary particle size even if the crystallite size is about the same for lithium titanate particles. As a result, it was found that the discharge capacity at low temperature was improved, and the present invention was completed.
That is, specific means for solving the above-described problems are as follows.
<1> Lithium titanate particles having an average primary particle size of 0.1 μm to 1.0 μm, a crystallite size of 10 nm to 60 nm , and an SD value represented by the following formula (I) of 0.80 μm or less It is.

(In the formula (I), D90% indicates a primary particle diameter corresponding to 90% accumulation in the volume cumulative distribution of primary particle diameters, and D10% is a primary particle diameter corresponding to 10% accumulation in the volume cumulative distribution of primary particle diameters. Indicate)

<2> The lithium titanate particles according to the BET specific surface area of ^{1.5m 2 / g~100m 2 / g <} 1>.
< 3 > The lithium titanate particles according to <1> or <2>, wherein the volume average secondary particle diameter is 1 μm to 30 μm.
< 4 > The lithium titanate particle according to any one of <1> to < 3 >, which is an electrode active material for a lithium ion battery.

< 5 > A negative electrode for a lithium ion secondary battery comprising the lithium titanate particles according to any one of <1> to < 4 >.
< 6 > A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to < 5 >.
< 7 > A step of mixing a titanium compound and a lithium compound to obtain a raw material mixture, a step of heat-treating the raw material mixture to obtain lithium titanate, a step of pulverizing the lithium titanate to obtain a pulverized product, The production of lithium titanate particles according to any one of <1> to < 4 >, comprising a step of granulating a pulverized product to obtain a granulated product, and a step of heat-treating the granulated product. Is the method.

  According to the present invention, lithium titanate particles as an electrode active material capable of constituting a lithium ion secondary battery excellent in discharge capacity under a low temperature environment, a method for producing the same, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery A secondary battery can be provided.

It is an example of the scanning electron micrograph of the lithium titanate particle concerning the Example of this invention. It is a figure which shows an example of the primary particle diameter distribution of the lithium titanate particle concerning the Example of this invention.

In the present invention, the term “process” is not limited to an independent process, and is included in the term if the intended action of the process is achieved even when it cannot be clearly distinguished from other processes.
In the present specification, numerical ranges indicated using “to” indicate ranges including the numerical values described before and after “to” as the minimum value and the maximum value, respectively.

<Lithium titanate particles>
The lithium titanate particles of the present invention (hereinafter sometimes simply referred to as “lithium titanate”) have an average primary particle size of 0.1 μm to 1.0 μm, a crystallite size of 10 nm to 60 nm , and The SD value represented by the following formula (I) is 0.80 μm or less.
By constructing a lithium ion battery electrode (preferably a negative electrode) using lithium titanate particles having such a small average primary particle size and a small SD value, that is, a narrow primary particle size distribution, as an electrode active material, a low temperature A lithium ion secondary battery excellent in discharge capacity under the environment can be configured.

  In the formula (I), D90% represents the primary particle diameter corresponding to 90% cumulative when the volume cumulative distribution curve is drawn from the small particle diameter side with respect to the primary particle diameter of the lithium titanate particles, About the primary particle diameter of lithium titanate particle | grains, the primary particle diameter corresponding to 10% of accumulation when a volume cumulative distribution curve is drawn from the small particle diameter side is shown.

The lithium titanate in the present invention is basically represented by the general formula Li _X Ti _Y O ₁₂ , the Li / Ti atomic ratio is 0.68 to 0.82, X is 3 to 5, and Y is 4 to 6 It is a compound in the range of. Specifically, for example, the main component is preferably a single-phase lithium titanate having a spinel type crystal structure represented by Li ₄ Ti ₅ O ₁₂ . In the lithium titanate of the present invention, as long as it does not inhibit the effect of the present invention, partially Li ₂ TiO ₃ and TiO ₂ is may coexist.

The lithium titanate particles of the present invention have an average primary particle size of 0.1 μm to 1.0 μm, and preferably 0.1 μm to 0.8 μm from the viewpoint of discharge capacity in a low temperature environment. More preferably, it is 1 μm to 0.5 μm.
When the average primary particle diameter exceeds 1.0 μm, the diffusion distance of lithium ions in the lithium titanate particles is extended, and it tends to be difficult to obtain a good discharge capacity in a low temperature environment. If the thickness is less than 0.1 μm, even if a heat treatment step is performed on the pulverized lithium titanate, crystal distortion tends to remain, and the discharge capacity in a low-temperature environment tends to be insufficient.

  The average primary particle diameter in the present invention is obtained as an arithmetic average by measuring the long diameter of 100 randomly selected primary particles using a scanning electron microscope (magnification 10,000 ×). . The primary particles referred to here are individual particles that can form secondary particles, and mean the smallest unit particles that can be identified as individual particles even when they are bonded to each other.

The lithium titanate of the present invention has an SD value represented by the above formula (I) of 0.80 μm or less, preferably from 0.60 μm or less from the viewpoint of discharge capacity in a low temperature environment. More preferably, it is 40 μm or less.
If the SD value exceeds 0.80 μm, good charge / discharge characteristics may not be exhibited in a low temperature environment when used as an electrode.
The lower limit of the SD value is not particularly limited, but from the viewpoint of production, the SD value is preferably 0.10 μm or more.

The SD value is an index relating to the width of the primary particle size distribution calculated from the values of D90% and D10%, and a small SD value means a narrow primary particle size distribution.
D90% and D10% are specifically determined as follows. In a volume-based primary particle size distribution measured by a laser diffraction / scattering method in a state where lithium titanate is dispersed in water, a particle corresponding to 90% cumulative when a volume cumulative distribution curve is drawn from the small particle size side D90% is obtained as the diameter, and D10% is obtained as the particle diameter corresponding to a cumulative 10%.

In the present invention, an aqueous dispersion of lithium titanate for measuring D90% and D10% is obtained by dispersing for 1 hour or more using an ultrasonic disperser. The maximum amplitude for ultrasonic dispersion is 20 μm or more. If the maximum amplitude is less than 20 μm, the aggregation of primary particles cannot be sufficiently solved, so that an appropriate primary particle size distribution may not be examined.
The output of the ultrasonic disperser is appropriately selected according to the amount of measurement sample to be prepared, and is, for example, 100 W or more. Furthermore, the content rate of lithium titanate in the aqueous dispersion of lithium titanate is appropriately selected according to the apparatus for measuring the particle size distribution, and is, for example, 1 to 5% by mass.

  In the present invention, the method for setting the average primary particle size and the SD value in the above ranges is, for example, a method for selecting a primary particle size of titanium dioxide used as a raw material, a method for producing lithium titanate described later, and a method after firing treatment. A method for adjusting the pulverization conditions, a method for adjusting the heat treatment conditions after the granulation treatment, and the like can be appropriately employed.

The crystallite size in the lithium titanate of the present invention is preferably 10 nm to 60 nm, and more preferably 30 nm to 50 nm, from the viewpoint of output characteristics when a lithium ion battery is configured. When the crystallite size is 10 nm or more and 60 nm or less, it is possible to smoothly diffuse lithium ions in the crystallite, and the output characteristics are further improved.

The crystallite size can be measured by a conventional method. For example, the crystallite size can be calculated by applying the Scherrer equation to the half-width of the X-ray diffraction peak.
The method for adjusting the crystallite size to the above range includes, for example, a method of selecting titanium dioxide used as a raw material, a method of adjusting pulverization conditions after baking treatment, and a method of adjusting heat treatment conditions after granulation treatment Etc. can be adopted as appropriate.

The BET specific surface area in the lithium titanate of the present invention is not particularly limited, it is preferable from the viewpoint of the energy density in the case of forming the output characteristics and lithium ion batteries, which is 1.5m 2 ^/ g~100m 2 ^{/ g} , more preferably ^{2m 2} / ^g~100m 2 / ^g, further preferably 3m ² / g~80m 2 / g.
When the BET specific surface area is 1.5 m ² / g or more, the electrolytic solution contributing to the electrode reaction can sufficiently come into contact with lithium titanate, and the output characteristics are further improved. Moreover, the binder etc. which are required when producing an electrode as an electrode active material as it is 100 m < ² > / g or less can be reduced, and the energy density of a battery improves more.

The BET specific surface area can be measured by a conventional method. For example, it can be calculated from an adsorption isotherm of nitrogen at −196 ° C.
The method for adjusting the BET specific surface area to the above range includes, for example, a method of selecting titanium dioxide used as a raw material, a method of adjusting pulverization conditions after baking treatment, and a method of adjusting heat treatment conditions after granulation treatment Etc. can be adopted as appropriate.

Furthermore, the volume average secondary particle diameter in the lithium titanate of the present invention is not particularly limited, but is preferably 1 μm to 30 μm, more preferably 3 μm to 25 μm, more preferably 4 μm to 4 μm from the viewpoint of output characteristics and electrode density. More preferably, it is 15 μm.
When the volume average secondary particle diameter is 1 μm or more, an electrode density can be further improved when an electrode is configured as an electrode active material. Moreover, the BET specific surface area of the lithium titanate obtained as it is 30 micrometers or less tends to become larger than 1.5 m < ² > / g, and an output characteristic improves more.

The volume average secondary particle diameter can be measured by a conventional method. For example, it can be measured by a laser diffraction / scattering method.
Examples of a method for adjusting the volume average secondary particle diameter to the above range include, for example, a method for adjusting the pulverization conditions after the baking treatment, a method for adjusting the granulation treatment conditions, and a heat treatment condition after the granulation treatment. The method of performing etc. can be employ | adopted suitably.

The lithium titanate of the present invention may be coated with a carbonaceous material as necessary, or may be a composite with a carbonaceous material.
Examples of the carbon coating or composite method include, for example, mixing a titanium compound (preferably titanium oxide) that is a raw material, a lithium compound, and a precursor of a carbonaceous material, followed by heat treatment, thereby carbon-coated lithium titanate. Alternatively, a material in which lithium titanate and a carbonaceous material are combined can be obtained. The atmosphere for performing the heat treatment is preferably a vacuum atmosphere or an inert gas atmosphere.

  In addition, a material in which lithium titanate and a carbonaceous material are combined can also be obtained by heat treatment after mixing lithium titanate and a carbonaceous material precursor. The atmosphere for the heat treatment is preferably a vacuum atmosphere or an inert gas atmosphere.

  Examples of the precursor of the carbonaceous material include coal-based pitch materials, petroleum-based pitch materials, synthetic pitches, tar-based materials, thermoplastic resins, thermosetting resins, vinyl-based resins, cellulose-based resins, and phenol-based resins. Is mentioned.

The weight ratio of the lithium titanate and the carbonaceous material is not particularly limited, but is preferably 99.9 / 0.1 to 90/10 (lithium titanate / carbonaceous material), particularly 99.5 / 0.5 to 93/7 is preferred.
Although the electron conductivity improves as the carbonaceous material increases, the discharge capacity tends to decrease.

The heat treatment temperature is preferably 400 to 1000 ° C, particularly 450 to 950 ° C, and more preferably 450 to 900 ° C.
When the heat treatment temperature is 400 ° C. or higher, the carbonaceous material precursor is sufficiently carbonized and the conductivity is further improved. On the other hand, when the heat treatment temperature is 1000 ° C. or lower, the sintering of lithium titanate can be suppressed, and the crystal size and primary particle diameter of the lithium titanate can be suppressed from increasing.

  In the lithium titanate of the present invention, any of Li (lithium atom), Ti (titanium atom), and O (oxygen atom) is partially substituted with another atom unless the effects of the present invention are impaired. May be.

Examples of atoms that can be substituted for the Li atom include H (hydrogen atom), Na (sodium atom), K (potassium atom), Rb (rubidium atom), Cs (cesium atom), and the like.
The lithium titanate in which a part of the Li atom is substituted with a hydrogen atom or the like can be obtained, for example, by an ion exchange method.

As atoms that can be substituted for Ti atoms, Sc (scandium atoms), V (vanadium atoms), Cr (chromium atoms), Mn (manganese atoms), Fe (iron atoms), Co (cobalt atoms), Ni (nickel atoms) ), Cu (copper atom), Zn (zinc atom), Al (aluminum atom), Si (silicon atom), Ga (gallium atom), Ge (germanium atom), Y (yttrium atom), Zr (zirconium atom), Nb (niobium atom), Mo (molybdenum atom), Sn (tin atom), Ce (cerium atom), Eu (europium atom), La (lanthanum atom), W (tungsten atom), etc. are mentioned.
As a method for substituting a part of Ti atoms, for example, when a titanium compound (preferably titanium oxide) and a lithium compound are mixed, a metal exemplified above or a metal salt thereof is simultaneously mixed and fired. Can be mentioned.

N (nitrogen atom) and F (fluorine atom) are mentioned as an atom which can be substituted with an oxygen atom.
The lithium titanate in which a part of the oxygen atom is substituted with a fluorine atom can be produced, for example, by mixing a titanium compound (preferably titanium oxide), a lithium compound, and lithium fluoride and baking.
The lithium titanate in which part of the oxygen atoms is substituted with nitrogen atoms can be produced by, for example, firing in a ammonia atmosphere when firing a mixture of a titanium compound (preferably titanium oxide) and a lithium compound. It is.

  The lithium titanate of this invention can be used suitably as an electrode active material of a lithium ion battery. The lithium titanate can be used as either a positive electrode active material or a negative electrode active material of a lithium ion battery, but is preferably used as a negative electrode active material.

The lithium titanate of the present invention can also be used as a positive electrode active material for a lithium primary battery.
Furthermore, the lithium titanate of the present invention has a positive electrode and a negative electrode as a polarizable electrode used in an electric double layer capacitor, and the other as a material capable of inserting / extracting lithium ions used in a lithium ion secondary battery. The present invention can also be applied to an active material for a hybrid type electricity storage device.

<Method for producing lithium titanate particles>
The method for producing lithium titanate particles of the present invention is a method for producing lithium titanate particles having the specific structure described above, and a step of obtaining a raw material mixture by mixing a titanium compound and a lithium compound; A step of obtaining a lithium titanate by heat treatment, a step of pulverizing the lithium titanate to obtain a pulverized product, a step of granulating the pulverized product to obtain a granulated product, and a heat treatment of the granulated product And a step of performing.
By being this aspect, lithium titanate particles having desired characteristics can be produced efficiently.

In the step of obtaining the raw material mixture in the present invention, a titanium compound such as titanium oxide and a lithium compound are mixed.
The lithium compound is not particularly limited as long as it is a compound containing lithium, and may be any of lithium salt, lithium oxide, and lithium hydroxide. Specific examples include lithium carbonate, lithium hydroxide, lithium nitrate, lithium oxide, lithium oxalate, lithium acetate, and lithium fluoride, and it is preferable to use at least one selected from these.
Further, the lithium compounds may be used alone or as a mixture of two or more.

The purity of these lithium compounds used as a raw material is not particularly limited, but is preferably high purity, and more preferably 99.0% by mass or more. Specifically, for example, when lithium carbonate is used as the lithium compound, the content of Li ₂ CO ₃ is preferably 99.0% by mass or more, more preferably 99.5% by mass or more. Further, it is desirable that the moisture is sufficiently removed, and the content is preferably 1% by mass or less with respect to the lithium compound.
Further, the average particle size of the lithium compound is not particularly limited, but is preferably 0.01 μm to 100 μm from the viewpoint of production efficiency. However, when a lithium compound having an average particle diameter of 100 μm or more is used as a raw material, for example, the pulverization treatment may be performed at the same time as pulverization or mixing with titanium oxide.

As the titanium compound, titanium oxide can be preferably used. The crystal phase of titanium oxide is not particularly limited, and may be any of rutile type, anatase type, and brookite type. Further, amorphous titanium oxide may be used. From the viewpoint of production cost, it is preferable to use at least one of a rutile type and an anatase type.
As the titanium compound, hydrous titanium oxide such as orthotitanic acid or metatitanic acid may be used instead of titanium oxide.
Further, titanium oxide or hydrous titanium oxide having different crystal phases may be mixed and used.

  In the production of the lithium titanate compound, the lithium compound and the titanium compound are selected from the target value of the Li / Ti ratio (atomic ratio) in the target lithium titanate, for example, in the range of 0.68 to 0.82. The lithium compound and the titanium compound are weighed and mixed in accordance with the value to be determined.

  The method of mixing is not particularly limited as long as a uniform mixture is obtained, and may be a method of mixing in powder form or a method using a solvent, but it is a method of obtaining a raw material mixture using a solvent. It is preferable.

  Known mixing means can be applied without particular limitation to the method of mixing the powder as it is. In addition, known mixing and pulverizing means such as a vibration mill and a ball mill can be appropriately used.

Further, as another mixing means, a raw material mixture may be obtained by adding a solvent to a lithium compound and a titanium compound (for example, titanium oxide) and stirring sufficiently, and then drying the slurry by heat drying or spray drying. .
The stirring means is not particularly limited, and may be a simple stirring means that is usually used, or a mixing / pulverizing means using a ball mill, a bead mill, or the like.

  There is no restriction | limiting in particular as a solvent used for mixing, Although water and an organic solvent can be mentioned, From the ease of handleability, it is preferable that they are water and alcohol. Moreover, the density | concentration of a slurry is not specifically limited, For example, it can be 10-50 mass%.

  Or when the said lithium compound is a lithium compound which is easy to melt | dissolve in water, after making a lithium compound into aqueous solution and impregnating this with a titanium compound (for example, titanium oxide), it can dry and obtain a raw material mixture Good.

The raw material mixture obtained by mixing the lithium compound and the titanium compound can be used in the next step as a molded body obtained in a bulk state or compressed at a pressure of about 0.5 t / cm ² .

  The raw material mixture obtained as described above is heat-treated to obtain lithium titanate. The heat treatment (firing) conditions are not particularly limited, but may be performed at 600 ° C. to 1200 ° C. for about 1 hour to 24 hours. Preferably, they are 700 degreeC or more and 1000 degrees C or less for 5 hours or more and 20 hours or less.

By baking at 600 ° C. or higher, the reaction between the titanium compound (preferably titanium oxide) and the lithium compound is sufficiently performed, and an impurity phase such as anatase type titanium oxide, rutile type titanium oxide, Li ₂ TiO ₃ increases. It is possible to suppress the decrease in electric capacity. Further, by firing at 1200 ° C. or lower, the transition of spinel type lithium titanate to titanium oxide or the like can be suppressed.

The firing may be performed under an inert gas atmosphere such as nitrogen or argon, an oxygen atmosphere, or an air atmosphere.
The lithium titanate thus obtained may be taken out of the firing furnace, cooled, crushed as necessary, and further fired once or more as necessary. When baking is performed twice or more, each heat treatment condition may be the same or different. In the present invention, firing is preferably performed at least twice, and it is more preferable to perform the second firing at a firing temperature higher than the first firing temperature. By firing by such a method, it becomes possible to synthesize lithium titanate having a small impurity phase, and an effect of exhibiting a higher charge / discharge capacity can be obtained.

In the present invention, the lithium titanate obtained by the heat treatment is pulverized to obtain a pulverized product. However, if necessary, pulverization may be performed in advance.
By performing the pulverization treatment, lithium titanate particles having a desired average primary particle size and SD value can be obtained.

  For the pulverization treatment, a jet mill, a vibration mill, a ball mill, a bead mill or the like can be employed. Among these, it is preferable to pulverize using a bead mill, and wet pulverization using a bead mill is more preferable. By grinding with a bead mill, lithium titanate having a small primary particle size and a narrow primary particle size distribution can be obtained.

  As materials for the pulverization container, beads, balls and the like used for the pulverization treatment, it is preferable to select materials having little influence on the charge / discharge reaction. Specifically, for example, alumina, partially stabilized zirconia, or the like can be used.

  In the present invention, the solvent used for wet pulverization is not particularly limited, and examples thereof include water and organic solvents. Specific examples include water, ethanol, ethylene glycol, benzene, hexane, and the like. A grinding aid (dispersant) such as polyol may be further used as necessary.

  The processing conditions for the pulverization treatment can be appropriately selected according to the pulverization method so that the desired average primary particle diameter and SD value are obtained.

In the present invention, the pulverized product obtained by the pulverization treatment is granulated to obtain the granulated product. The method for the granulation treatment is not particularly limited, and a known granulation method can be appropriately selected. Among these, it is preferable to perform granulation treatment by a spray drying method from the viewpoint that it is possible to synthesize lithium titanate having a narrow production efficiency and volume cumulative distribution.
Specifically, a slurry containing a pulverized lithium titanate and a solvent can be prepared, spray-dried, and granulated into desired large particles, that is, secondary particles of about 0.5 μm to 100 μm.

The spray dryer used for spray drying is not particularly limited, and can be appropriately selected from, for example, a disk type, a pressure nozzle type, a two-fluid nozzle type, and the like according to the properties of the slurry and the processing capacity.
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. The properties such as the concentration and viscosity of the slurry to be used can be appropriately set according to the ability of the spray dryer.

  When the viscosity of the slurry is low and granulation is difficult, or to make it easier to control the particle size, binders such as polyvinyl alcohol, methyl cellulose, gelatin, and surfactants such as cationic, nonionic, anionic, and amphoteric surfactants Various additives may be used. These additives are desirable if they are organic and do not contain a metal component, because they are decomposed and volatilized in a later heat treatment step.

  As the drying temperature, the inlet temperature is preferably 180 ° C to 400 ° C, and the outlet temperature is preferably 70 ° C to 120 ° C. The spray pressure can be set to, for example, 0.1 MPa to 1.5 MPa, and the sample supply rate can be set to, for example, 1.0 kg / h to 5.0 kg / h.

The manufacturing method of this invention includes the process of heat-processing the lithium titanate granulated as mentioned above. As the heat treatment conditions, for example, baking is preferably performed at 250 ° C. or higher and 900 ° C. or lower for 1 minute or longer and 10 hours or shorter.
When the heat treatment temperature is 250 ° C. or more, the distortion of the crystallite is effectively relieved, and it is possible to suppress a decrease in capacity when used as a battery. Moreover, it can suppress that a particle | grain grows and a primary particle diameter becomes large because it is 900 degrees C or less.
The heat treatment may be performed in an inert gas atmosphere such as nitrogen or argon, an oxygen atmosphere, or an air atmosphere.

(Lithium ion secondary battery)
The lithium ion secondary battery according to the present invention includes an electrode containing the above-described lithium titanate as an electrode active material.
The basic structure of a lithium ion secondary battery is such that a positive electrode and a negative electrode are arranged opposite to each other with a separator interposed between them and impregnated with a non-aqueous electrolyte. In the present invention, the above-described lithium titanate of the present invention is used as the electrode active material constituting the positive electrode or the negative electrode.
In the present invention, the lithium titanate is used as an electrode active material constituting a positive electrode or a negative electrode, but is used as an electrode active material constituting a negative electrode from the viewpoint of excellent long-life and input / output characteristics in a wide temperature range. It is preferable.

In the lithium ion secondary battery of the present invention, when the lithium titanate is used as a negative electrode active material, examples of the positive electrode active material included in the positive electrode include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , and LiNi _{0. .5} Composite oxides of lithium and transition metals such as Mn _1.5 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 , Conductive polymer compounds such as polypyrrole and polythiophene, disulfide compounds such as poly (2,5-dimercapto-1,3,4-thiadiazole), and the like are used.

The electrode containing lithium titanate as an electrode active material can be configured to include a conductive additive, a binder, and the like in addition to the electrode active material.
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, although a conductive support agent is normally mix | blended about 1-20 mass% with respect to an electrode active material, it is more preferable to mix | blend 5-10 mass%.

Moreover, as a binder used with a conductive support agent, well-known various binders can be used. 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, although a binder is normally mix | blended about 1-20 mass% with respect to an electrode active material, it is more preferable to mix | blend 5-15 mass%.

  The electrolyte solution used for the lithium ion secondary battery of the present invention 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 obtained by dissolving an electrolyte in an organic solvent as the electrolytic solution.

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.

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 2 or more types of mixed solvents.

  The electrolyte concentration in the electrolytic solution 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 electrolytic solution.

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

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, “part” and “%” are based on mass.

<Example 1>
(Synthesis of lithium titanate)
100 g of titanium oxide (“A120” manufactured by Sakai Chemical Industry Co., Ltd.) having a BET specific surface area of 11 m ² / g and an average particle size (D50%) of 0.5 μm and 38.1 g of lithium carbonate (manufactured by Wako Pure Chemical Industries, Ltd.) In a ball mill, 300 g of pure water and 200 g of 10 mm zirconia balls were added and mixed for 5 hours, after which the zirconia balls were removed and dried at 130 ° C. This was crushed in an alumina mortar and then calcined in air at 800 ° C. for 20 hours. The temperature was raised at a rate of 1.7 ° C./min. After firing, the product was allowed to cool and then taken out, mixed again with a ball mill, and then fired at 900 ° C. for 20 hours.

  The fired product thus obtained was pulverized with an alumina mortar and then pulverized using a bead mill. The bead mill used was a star mill “LMZ015” manufactured by Ashizawa Finetech Co., Ltd., and 0.3 mm stabilized zirconia beads were used for the beads. Further, using water as a solvent, 1% by mass of “POLYTY A550” manufactured by Lion Corporation as a dispersant was added to the lithium titanate and pulverized. When the particle size distribution of the crushed slurry was measured, the volume average primary particle size (D50%) was 0.21 μm.

  This slurry was spray-dried using a spray dryer “NL-5” manufactured by Okawahara Koki Co., Ltd. under the conditions of an inlet temperature of 200 ° C., an outlet temperature of 90 ° C., a spray pressure of 0.2 MPa, and a sample supply rate of 3.0 kg / h. . The granulated powder thus obtained was air baked at 700 ° C. for 5 hours to obtain the target lithium titanate.

When the crystal phase was identified using a powder X-ray diffractometer manufactured by Rigaku Corporation, it was a single phase of Li ₄ Ti ₅ O ₁₂ and the crystallite size was 42 nm. The BET specific surface area was 5.8 m ² / g, and the volume average secondary particle size (D50%) was 5.7 μm.
The BET specific surface area was calculated from an adsorption isotherm of nitrogen at −196 ° C. using an autosorb-1 manufactured by QUANTACHROME INSTRUMENTS. The volume average particle size was measured using a laser diffraction particle size analyzer “SALD3000J” manufactured by Shimadzu Corporation.
The crystallite size was determined by measuring the half width of the X-ray diffraction peak and using the Scherrer equation. At this time, metallic silicon (manufactured by Kojundo Chemical Laboratory Co., Ltd., high purity silicon, purity: 99.999%) was used as an internal standard sample, and the (111) plane of lithium titanate and the (111) plane of metallic silicon. The peak of was used. The diverging slit and scattering slit were 1/2 °, the light receiving slit was 0.15 mm, and measurement was performed at a scanning speed of 0.1 ° / min.

  In order to observe the shape of the particles, a desktop microscope, Miniscope (TM-1000, manufactured by Hitachi High-Tech) was used and observed at a magnification of 10,000 ×. An example of the observed particle shape is shown in FIG. The observed primary particles were measured for 100 major axes, and the average primary particle size determined as the arithmetic average was 0.2 μm.

5 g of the lithium titanate obtained above was dispersed in 95 g of water, and this was subjected to a dispersion treatment for 1 hour at a maximum amplitude of 25 μm using an ultrasonic disperser (Homomixer manufactured by Nippon Seiki Co., Ltd.). When the primary particle size distribution of the slurry thus obtained was measured using a laser diffraction particle size measuring device “SALD3000J” manufactured by Shimadzu Corporation, the particle sizes of D10%, D50%, and D90% were 0.00. They were 37 μm, 0.62 μm, and 1.1 μm. An outline of the primary particle size distribution is shown in FIG.
The SD value calculated from these was 0.37 μm.

(Production of lithium titanate electrode)
Lithium titanate obtained above as an electrode active material, carbon black (trade name: HS-100, manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive additive, and N- of polyvinylidene fluoride (PVDF) as a binder resin Methylpyrrolidone (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) The electrode composition was prepared by mixing at a ratio of (ratio) to a paste. This paste-like electrode composition was applied to the glossy surface of the electrolytic copper foil and dried at 80 ° C. for 1 hour. Subsequently, it vacuum-dried at 120 degreeC for 1 hour, and the electrode which has an electrode composition layer was obtained.

(Production of lithium ion secondary battery)
A lithium ion secondary battery was produced as follows using the electrode obtained above as a negative electrode and metallic lithium as a counter electrode. EC (ethylene carbonate) / PC (propylene carbonate) / GBL (γ-butyrolactone) (1/1/1 volume ratio) in which LiPF ₆ is dissolved at a concentration of 1M is used as an electrolyte, and a 2016 type coin cell (Hosen stock) Coin-type battery was produced by a conventional method.

(Evaluation)
-Initial discharge capacity-
First, the battery was evaluated at 25 ° C. The counter electrode (lithium electrode) was charged to 1.2 V with a current corresponding to 0.1 C. 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 weight of the lithium titanate used.

−Discharge capacity maintenance rate−
Next, the lithium electrode is charged to 1.2 V with a current corresponding to 0.1 C, and discharged to 2.5 V with a current corresponding to 10 C to the lithium electrode, and the discharge capacity at 10 C is measured. The discharge capacity retention ratio was calculated as the ratio of the discharge capacity at 0.1 C to the discharge capacity at 0.1 C, and the rate characteristics were evaluated.
Here, xC refers to a current value at which charging or discharging is completed in 1 / x time, that is, a discharge rate of 10 C means a current value at which discharging is completed in (1/10) time.

-Discharge capacity (-10 ° C)-
Next, the lithium electrode was charged to 1.2 V with a current corresponding to 0.2 C, and the test was performed in an environment of −10 ° C. for discharging the lithium electrode to 2.5 V with a current corresponding to 10 C. The discharge capacity at −10 ° C. was measured.
The results are shown in Table 1.

<Example 2>
In Example 1, lithium titanate particles were obtained in the same manner as in Example 1 except that the heat treatment temperature after pulverization was changed to 600 ° C. for 5 hours.
The BET specific surface area was 17.5 m ² / g, the volume average secondary particle diameter (D50%) was 6.0 μm, and the crystallite size was 47 nm.
The average primary particle size was 0.2 μm.
The particle diameters corresponding to D10%, D50%, and D90% of the slurry obtained by treating with an ultrasonic disperser for 1 hour were 0.35 μm, 0.60 μm, and 1.0 μm, respectively. The SD value was 0.33 μm.
An electrode and a lithium ion secondary battery were prepared and evaluated in the same manner as in Example 1 except that the obtained lithium titanate particles were used. The results are shown in Table 1.

<Comparative Example 1>
In Example 1, lithium titanate particles were obtained in the same manner as in Example 1 except that the pulverization process was replaced with a pulverization process with a ball mill instead of the pulverization process with a bead mill. Incidentally, 5 mm and 10 mm stabilized zirconia balls were used for pulverization with a ball mill.
The BET specific surface area was 2.2 m ² / g, the volume average secondary particle diameter (D50%) was 5.7 μm, and the crystallite size was 44 nm.
The average primary particle size was 1.2 μm.
The particle diameters corresponding to D10%, D50%, and D90% of the slurry obtained by treating with an ultrasonic disperser for 1 hour were 0.34 μm, 1.1 μm, and 2.1 μm, respectively. The SD value was 0.88 μm. The outline of the primary particle size distribution is shown in FIG. 2. An electrode and a lithium ion secondary battery were prepared and evaluated in the same manner as in Example 1 except that the obtained lithium titanate particles were used. . The results are shown in Table 1.

  As shown in Table 1, it can be seen that the lithium secondary batteries of the examples are excellent in battery characteristics at a low temperature, particularly in discharge capacity.

Claims (7)

Lithium titanate particles having an average primary particle diameter of 0.1 μm to 1.0 μm, a crystallite size of 10 nm to 60 nm , and an SD value represented by the following formula (I) of 0.80 μm or less.


(In the formula (I), D90% indicates a primary particle diameter corresponding to 90% accumulation in the volume cumulative distribution of primary particle diameters, and D10% is a primary particle diameter corresponding to 10% accumulation in the volume cumulative distribution of primary particle diameters. Indicate) Lithium titanate particles according to claim 1 BET specific surface area of 1.5m ² / g~100m ² / g. Lithium titanate particles according to claim 1 or claim 2 volume average secondary particle size of 1 to 30 [mu] m. It is an electrode active material for lithium ion batteries, The lithium titanate particle of any one of Claims 1-3 . The negative electrode for lithium ion secondary batteries containing the lithium titanate particle of any one of Claims 1-4 . A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to claim 5 . A step of mixing a titanium compound and a lithium compound to obtain a raw material mixture;
Heat treating the raw material mixture to obtain lithium titanate;
Pulverizing the lithium titanate to obtain a pulverized product;
A step of granulating the pulverized product to obtain a granulated product;
Heat-treating the granulated product,
The manufacturing method of the lithium titanate particle of any one of Claims 1-4 containing this.