JP5968712B2 - Method for producing lithium titanate powder, lithium ion secondary battery and lithium ion capacitor using the lithium titanate powder - Google Patents

Description

  The present invention relates to a method for producing a lithium titanate powder suitable for an electrode of a lithium ion secondary battery, and a lithium ion secondary battery and a lithium ion capacitor using the lithium titanate powder.

  Lithium ion secondary batteries are rapidly spreading in recent years because of their excellent cycle characteristics. Electrode active materials of lithium secondary batteries, particularly negative electrode active materials, have a high discharge potential and are highly safe, such as an alkali metal titanate compound, for example, a lithium titanium compound having a spinel structure or a ramsdellite structure. Titanium compounds are attracting attention. In particular, spinel type lithium titanate has a theoretical capacity of 175 mAh / g, and is excellent in cycle characteristics because of a small volume change during charge and discharge.

  As a method for producing spinel type lithium titanate powder, a titanium compound is neutralized with an ammonium compound to form a precursor, which is further reacted with a lithium compound at 100 ° C. to 250 ° C. to form lithium titanate hydrate. Furthermore, a method of firing this lithium titanate hydrate at 700 ° C. to 1300 ° C. has been proposed (see, for example, Patent Document 1).

  In the solid phase method, a predetermined amount of a lithium compound and titanium oxide are mixed and mixed with a vibration mill, a ball mill, or the like, and then 600 ° C. to 800 ° C. (30 minutes to 4 hours, temperature increase rate 0.5 to 10 ° C./min. ) And calcining at 800 ° C. to 950 ° C. (for example, refer to Patent Document 2), lithium compound and titanium oxide, lithium compound 0.48 to 4.8 mol / L, titanium oxide 0 A method in which the slurry concentration is adjusted so as to be in the range of .60 to 6.0 mol / L and wet mixing is performed, followed by firing at 700 ° C. to 1000 ° C. as spherical particles by spray drying, fluidized bed drying, etc. Reference 3), a method in which a predetermined amount of a lithium compound and titanium oxide are mixed and fired in a reducing atmosphere such as hydrogen, hydrocarbon, carbon monoxide, etc. under conditions of 500 ° C. to 925 ° C. for 30 minutes to 180 minutes (for example, Patent Literature Reference) has been proposed.

  Furthermore, by solid phase method, lithium carbonate and titanium oxide are pulverized in a ball mill for 24 hours and then calcined at 700 ° C. to 900 ° C. for 3 hours. A method (for example, see Non-Patent Document 1) has been proposed.

JP-A-9-309728 JP 2000-302547 A JP 2001-192208 A Special table 2011-520752 gazette

C. H. Hong et al. , Ceramics International 38 (2012) 301-310.

  The production method obtained by the production method described in Patent Document 1 can produce spinel type lithium titanate powder having a small particle size of the lithium titanate primary crystal and a large specific surface area. However, the obtained spinel type lithium titanate has low crystallinity, and when it is used for the negative electrode of a lithium secondary battery, it is desired that the electric capacity at the time of rapid charge / discharge is not sufficient but higher.

  In addition, none of the lithium titanate powders obtained by the methods of Patent Documents 2 to 4 and Non-Patent Document 1 have been substantially improved, and the improvement of the discharge characteristics of the lithium secondary battery characteristics is insufficient. It was something.

  This invention is made | formed in view of such a subject, and it aims at providing the lithium titanate powder active material which can maintain the electrical capacity at the time of rapid charge / discharge.

  Under such circumstances, as a result of intensive studies, the present inventors have found that when lithium titanate produced using a specific lithium carbonate is used as a lithium source, the lithium ion secondary battery is rapidly charged and discharged. It has been found that the electric capacity and cycle characteristics of the lithium ion capacitor and the rapid charge / discharge characteristics of the lithium ion capacitor can be further improved, and the present invention has been completed.

That is, the present invention includes a titanium raw material having a BET specific surface area of 5 m ² / g or more selected from titanium oxide, metatitanic acid, orthotitanic acid, or a mixture thereof, and lithium hydroxide and lithium carbonate. When the total Li amount of lithium hydroxide and lithium carbonate is 100, the mixing ratio of lithium is mixed with a lithium raw material having a lithium molar ratio of lithium hydroxide: lithium carbonate = 95: 5 to 10:90, A method for producing a lithium titanate powder to be fired, wherein an average particle size of lithium carbonate before firing is 1.0 μm or less.

Further , according to the present invention , a positive electrode having a positive electrode active material capable of inserting and extracting lithium, and a negative electrode for a lithium ion secondary battery using the lithium titanate powder obtained by the production method as a negative electrode active material, There is obtained a lithium ion secondary battery comprising an ion conductive medium that is interposed between the positive electrode and the negative electrode for a lithium ion secondary battery and conducts lithium ions.

Furthermore, according to the present invention , the negative electrode electrode body provided with the negative electrode active material layer containing the lithium titanate powder obtained by the above production method on the negative electrode current collector, and the positive electrode current collector provided with the positive electrode active material layer A lithium ion capacitor provided with a positive electrode body and a non-aqueous electrolyte containing an electrolyte containing lithium ions interposed between the positive electrode and the negative electrode is obtained .

  By using lithium titanate obtained by the production method of the present invention for a lithium secondary battery, the charge / discharge capacity at the time of rapid charge / discharge can be maintained, and in the lithium ion capacitor, the rapid charge / discharge characteristics can be improved. Can do.

  The reason why such an effect is obtained is not clear, but is presumed as follows. For example, the lithium titanate powder obtained by the production method of the present invention has a high single-phase ratio, a large specific surface area, and high crystallinity, so that it has a particularly low resistance when inserting and extracting Li ions. It is thought to be due to showing. Furthermore, since the lithium titanate powder obtained by the production method of the present invention has a high affinity with the conductive additive (carbon material) constituting the negative electrode, there is a possibility of reducing the contact resistance.

It is sectional drawing which shows the structure of the coin cell used for evaluation of the lithium secondary battery characteristic evaluation method of an Example.

The titanium raw material of the method for producing lithium titanate powder according to the present invention is selected from titanium oxide, metatitanic acid, orthotitanic acid, or a mixture thereof, and has a BET specific surface area of 5 m ² / g or more. Since the specific surface area of the lithium titanate powder is determined depending on the specific surface area of the titanium raw material, a lithium titanate powder having a large specific surface area can be obtained by using this range. The specific surface area of the titanium raw material is preferably 5 m ² / g or more and 50 m ² / g or less, more preferably 10 m ² / g or more and 40 m ² / g or less.

  Titanium oxide is titanium oxide having an anatase type, rutile type or brookite type crystal structure. In the present invention, the X-ray diffraction pattern has a plurality of crystal structures such as a crystalline titanium oxide having only a diffraction peak from a single crystal structure, as well as an anatase type diffraction peak and a rutile type diffraction peak. It may have a diffraction peak from. Moreover, a part of the amorphous material that does not appear in the X-ray diffraction pattern may be included.

Metatitanic acid is represented by TiO (OH) ₂ or TiO ₂ .H ₂ O, and orthotitanic acid is represented by Ti (OH) ₄ or TiO ₂ .2H ₂ O. Metatitanic acid and orthotitanic acid are obtained by heat hydrolysis or neutralization hydrolysis of a titanium compound. For example, metatitanic acid is obtained by heating hydrolysis of titanyl sulfate (TiOSO ₄ ), neutralization hydrolysis of titanium chloride at a high temperature, etc., and orthotitanic acid is obtained from titanium sulfate (Ti (SO ₄ ) ₂ ), titanium chloride. The mixture of metatitanic acid and orthotitanic acid can be obtained by appropriately controlling the neutralization hydrolysis temperature of titanium chloride by neutralization hydrolysis at a low temperature.

  As a neutralizing agent used for neutralization hydrolysis, ammonium compounds such as ammonia, ammonium carbonate, ammonium sulfate, and ammonium nitrate can be used. These ammonium compounds can be decomposed and volatilized during firing. As the titanium compound, in addition to the inorganic compounds such as titanium sulfate, titanyl sulfate, and titanium chloride, organic compounds such as titanium alkoxide can be used. In particular, the titanium raw material is preferably titanium oxide from the viewpoint of improving the crystallinity of lithium titanate.

  Further, the titanium raw material is desirably highly pure, specifically, a purity of 99.0% by weight or more, preferably 99.5% by weight or more, and Fe, Al, Si and Na contained as impurities are included. Desirably, each is less than 20 ppm and Cl is less than 500 ppm. Desirably, Fe, Al, Si and Na are each less than 10 ppm, and Cl is less than 100 ppm, more desirably less than 50 ppm.

  The lithium raw material of the method for producing lithium titanate powder according to the present invention includes lithium hydroxide and lithium carbonate, and the mixing ratio of lithium hydroxide and lithium carbonate to lithium hydroxide and lithium carbonate is such that lithium hydroxide and lithium carbonate are mixed. When the total amount of Li is 100, the lithium raw material is Li hydroxide: lithium carbonate = 95: 5 to 10:90 in terms of Li molar ratio.

  The lithium carbonate used as the lithium raw material is preferably highly pure, and usually has a purity of 99.0% by weight or more. Further, it is desirable that the water contained in the lithium carbonate is sufficiently removed, and the content is desirably 0.1% by weight or less. Further, the average particle size is desirably 0.01 to 100 μm, and in particular, in the case of lithium carbonate, it is 50 μm or less, preferably 5 μm or less, more preferably 0.01 μm or more.

  Further, the preferred purity, moisture content, and average particle size of lithium hydroxide used as the lithium raw material are the same as those of lithium carbonate. The mixing ratio of lithium hydroxide and lithium carbonate is Li hydroxide: lithium carbonate = 95: 5 to 10:90, preferably 95: 5 to 50:50 in terms of Li molar ratio, assuming that the required amount of Li is 100. Adjust to be within the range. By setting it within this range, characteristics (rapid charge / discharge characteristics) sufficient as an active material for a lithium ion battery can be obtained.

  In the method for producing lithium titanate powder according to the present invention, the lithium raw material and the titanium raw material are separated from a target value of Li / Ti ratio (atomic ratio) of lithium titanate, for example, in the range of 0.68 to 0.82. In accordance with the selected value, both raw materials are weighed and then mixed with an organic solvent such as water or alcohol, or a mixture thereof to make a slurry of 10 to 50% by weight of lithium raw material and titanium raw material in total. Then, it grind | pulverizes as needed and the average particle diameter of lithium carbonate after mixing with a titanium raw material is 1.0 micrometer or less, Preferably it is 0.8 micrometer or less, More preferably, it is 0.01 micrometer or more and 0.5 micrometer or less. By setting the average particle size of the lithium carbonate in this range, a lithium titanate powder having a high single phase ratio and a large specific surface area can be obtained. The average particle size of lithium carbonate is obtained from the particle size distribution measured in ethanol using a laser diffraction / scattering method.

  For mixing both raw materials, a mixer with a stirrer, a rotary mixer or the like is appropriately used. The mixing may be performed simultaneously with pulverization, and a pulverizing mixer such as a ball mill and a bead mill can also be used. For example, pulverization conditions of the ball mill are zirconia balls as the pulverization media, and the pulverization time is 20 to 40 hours. In addition, in order to increase the pulverization efficiency of lithium carbonate, a procedure of preparing a slurry of an organic solvent such as water or alcohol containing only lithium carbonate and pulverizing to a predetermined particle size in advance and then adding and mixing a titanium raw material is used. May be. The particle size of the lithium carbonate after pulverization can be adjusted by pulverization conditions such as pulverization time.

  The slurry after mixing is preferably granulated and dried. The drying method is not limited, and examples thereof include a method of spray-drying the slurry and granulating into secondary particles. In particular, the method using spray drying is preferable because the particle diameter can be easily controlled and spherical secondary particles can be easily obtained. 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, a two-fluid nozzle type, and a four-fluid nozzle type. The secondary particle size can be controlled by adjusting the number of revolutions of the disc for the above-described disc type, and adjusting the spray pressure and nozzle diameter for the pressure nozzle type, two-fluid nozzle type, four-fluid nozzle type, etc. This can be done by controlling the drop size. In order to make it easier to control the particle size, various additives such as binders such as polyvinyl alcohol, methylcellulose, and gelatin, and nonionic, anionic, amphoteric, and nonionic surfactants 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 heating and firing step. As the drying temperature, the inlet temperature is preferably in the range of 200 to 450 ° C, and the outlet temperature is preferably in the range of 80 to 120 ° C.

  Even when the raw material powder after mixing is in a dry state, the powder may be slurry-dried and then spray-dried in order to improve the handleability of the powder. The medium used for slurrying is not particularly limited, but it is preferable to use water industrially.

  The average particle size of the secondary particles after granulation is 1 μm or more and 100 μm or less, preferably 1 μm or more and 50 μm or less, and more preferably 1 μm or more and 10 μm or less.

The firing conditions of the method for producing a lithium titanate powder according to the present invention are not particularly limited as long as a lithium titanate powder having a single phase conversion ratio of 90% or more and a specific surface area of 4.0 m ² / g or more is obtained. For example, the firing temperature is 700 to 950 ° C., preferably 720 to 950 ° C. and fired. In the first stage, calcining is performed at a slightly low temperature of 600 to 700 ° C. for about 30 minutes to 5 hours, and then in the second stage, the temperature is increased to 700 to 950 ° C., preferably 720 to 950 ° C. May be adopted. When titanium oxide is used as the titanium raw material, when the primary particle diameter of titanium oxide is 0.01 to 0.5 μm, the firing temperature is 700 to 850 ° C., and the primary particle diameter is 0.5 to 1.0 μm. In this case, the firing temperature is preferably 800 to 950 ° C. from the viewpoint of the primary particle diameter and purity (referred to as single phase degree) of lithium titanate, which is the object, and battery characteristics and capacitor characteristics. The heating rate during firing is preferably 1 ° C./min or less, preferably 0.5 ° C./min or less. Cycle characteristics during rapid charge / discharge of a large current (0.875 A / g: current value with respect to negative electrode active material weight (g)) can be further enhanced. In addition, since the temperature increase rate affects the firing time, it is necessary to set it in consideration of the balance between production efficiency and characteristics. If the obtained lithium titanate secondary particles are sintered and agglomerated after heating and firing, they may be pulverized using a hammer mill, a pin mill or the like, if necessary.

The lithium titanate powder obtained by the production method according to the present invention is represented by the general formula Li _X Ti _Y O ₁₂ , for example, Li _{4 + x} Ti ₅ O ₁₂ (0 ≦ x ≦ 3) having a spinel structure, ram, Examples include Li _{2 + y} Ti ₃ O ₇ (0 ≦ y ≦ 3) having a steride structure. The preferred if a single phase, some of the titanium oxide within a range not to impair the effects of the present invention, may be mixed different phase of Li ₂ TiO ₃ equality. In particular, Li _{4 + x} Ti ₅ O ₁₂ (0 ≦ x ≦ 3) having a spinel structure, particularly Li ₄ Ti ₅ O ₁₂ is preferable, and a single phase conversion rate of 90% or more (partially Li ₂ TiO ₃ or TiO _2). May be mixed).

Note that the single phase conversion rate refers to the diffraction result measured using the X-ray diffractometer of the lithium titanate powder according to the present invention, and the analysis software X'Part-HighScore Plus Ver. 2 based on the semi-quantitative value analyzed using the quasi-quantitative software (manufactured by PANalytical) and analyzed for three components of Li ₄ Ti ₅ O ₁₂ , TiO ₂ (rutile phase), and Li ₂ TiO _3. This is the calculated value. The quasi-quantification is a method of performing quantification using a quasi-quantitative value (RIR = Reference Intensity Ratio: intensity ratio of the strongest line of the card diffraction line to the strongest line of Al ₂ O ₃ (corundum)) described in the ICDD card. .
Single phase conversion rate = I _A / (I _A + I _B + I _C )
Li ₄ Ti ₅ O ₁₂ semiquantitative value I _A of semi-quantitative value I _B of TiO ₂ (rutile phase),
Semiquantitative value I _C for li ₂ TiO ₃

  The lithium titanate powder obtained by the production method of the present invention can be used as a negative electrode active material of a lithium ion secondary battery and an active material of a negative electrode current collector of a lithium ion capacitor.

  The lithium ion secondary battery of the present invention includes a positive electrode having a positive electrode active material capable of inserting and extracting lithium, a negative electrode for a lithium ion secondary battery using the above lithium titanate powder as a negative electrode active material, and the positive electrode And an ion conductive medium that conducts lithium ions and is interposed between the negative electrode for a lithium ion secondary battery.

  The positive electrode of the lithium ion secondary battery of the present invention is prepared by, for example, mixing a positive electrode active material, a conductive material, a binder, and a solvent into a paste and applying and drying on the surface of the positive electrode current collector (if necessary, the electrode Can be compressed) to increase density.

As the positive electrode active material, an oxide containing lithium and a transition metal element or a polyanionic compound can be used. Specifically, for example, lithium cobalt composite oxide (Li _(1-n) CoO ₂ or the like (0 <n <1, the same applies hereinafter)), lithium nickel composite oxide (Li _(1-n) NiO ₂ or the like) , Lithium manganese composite oxide (Li _(1-n) MnO ₂ , Li _(1-n) Mn ₂ O ₄ etc.), lithium iron composite phosphate (LiFePO ₄ etc.), lithium vanadium composite oxide (LiV ₂ O ₃ ) and the like.

  The positive electrode current collector is not particularly limited as long as it is formed of a conductive material. For example, a foil or mesh formed of a metal such as aluminum, copper, stainless steel, or nickel-plated steel can be used. .

  The binder plays a role of connecting the active material particles and the conductive material particles. For example, a fluorine-containing resin such as polytetrafluoroethylene, polyvinylidene fluoride, or fluororubber, or a thermoplastic resin such as polypropylene or polyethylene can be used.

  The conductive material is for ensuring the electrical conductivity of the positive electrode. For example, one or more of carbon powder materials such as carbon black, acetylene black, natural graphite, artificial graphite, and cokes are mixed. Things can be used.

  As the solvent for dispersing the positive electrode active material, the conductive material, and the binder, for example, an organic solvent such as N-methyl-2-pyrrolidone can be used.

  The negative electrode for lithium ion secondary batteries of this invention is equipped with the negative electrode active material containing the above-mentioned lithium titanate powder. The negative electrode of the lithium ion secondary battery of the present invention is prepared by, for example, mixing a negative electrode active material, a conductive material, and a binder, and adding a suitable solvent to form a paste-like negative electrode material on the surface of the current collector. It can be dried and compressed to increase the electrode density as needed.

  Moreover, what was illustrated by the positive electrode can respectively be used for the electrically conductive material, binder, solvent, etc. which are used for the negative electrode for lithium ion secondary batteries of this invention.

  The negative electrode current collector includes copper, nickel, stainless steel, titanium, aluminum, calcined carbon, conductive polymer, conductive glass, Al-Cd alloy, etc., as well as improved adhesion, conductivity and reduction resistance. For the purpose, for example, a copper surface treated with carbon, nickel, titanium, silver or the like can be used. The shape of the current collector can be the same as that of the positive electrode.

In the lithium ion secondary battery of the present invention, the ion conduction medium may be a non-aqueous electrolyte solution, an ionic liquid, a gel electrolyte, a solid electrolyte, or the like in which a supporting salt is dissolved in an organic solvent. Of these, a non-aqueous electrolyte is preferable. As the supporting salt, for example, LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , Li (CF ₃ SO ₂ ) ₂ N, Li (CF ₃ SO ₃ ), LiN (C ₂ F ₅ SO ₂ ) _{2 and the} like are known. The supporting salt can be used. The concentration of the supporting salt is preferably 0.1 to 2.0M, and more preferably 0.8 to 1.2M.

  Examples of the organic solvent include ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (γ-BL), diethyl carbonate (DEC), dimethyl carbonate (DMC), butylene carbonate (BC), ethyl methyl carbonate ( EMC) and other organic solvents used in conventional secondary batteries and capacitors. These may be used alone or in combination.

  Further, the ionic liquid is not particularly limited, but 1-methyl-3-propylimidazolium bis (trifluorosulfonyl) imide, 1-ethyl-3-butylimidazolium tetrafluoroborate, N -Methyl-N-propylpyrrolidinium bis (fluorosulfonyl) imide and the like can be used.

  The gel electrolyte is not particularly limited, but for example, a polymer such as polyvinylidene fluoride, polyethylene glycol, or polyacrylonitrile, or a saccharide such as an amino acid derivative or sorbitol derivative is added with an electrolyte containing a supporting salt. And a gel electrolyte.

Examples of the solid electrolyte include inorganic solid electrolytes and organic solid electrolytes. Well-known inorganic solid electrolytes include, for example, Li nitrides, halides, oxyacid salts, and the like. Among _{them, Li 4 SiO 4, Li 4} SiO 4 -LiI-LiOH, xLi 3 PO 4 - (1-x) Li 4 SiO 4, Li 2 SiS 3, Li 3 PO 4 -Li 2 S-SiS 2, sulfide Examples thereof include phosphorus compounds. These may be used alone or in combination.

  Examples of the organic solid electrolyte include polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyvinylidene fluoride, polyphosphazene, polyethylene sulfide, polyhexafluoropropylene, and derivatives thereof. These may be used alone or in combination.

  The lithium ion secondary battery of the present invention may include a separator between the negative electrode and the positive electrode. The separator is not particularly limited as long as the composition can withstand the use range of the lithium ion secondary battery. For example, a polymer nonwoven fabric such as a polypropylene nonwoven fabric or a polyphenylene sulfide nonwoven fabric, or a thin olefin resin such as polyethylene or polypropylene is used. A microporous membrane is mentioned. These may be used alone or in combination.

  The shape of the lithium ion secondary battery of the present invention is not particularly limited, and examples thereof include a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, and a square type. Moreover, you may apply to the large sized thing used for an electric vehicle etc.

  A lithium ion capacitor of the present invention includes a negative electrode body including a layer made of the above-described lithium titanate powder as a negative electrode active material in a negative electrode current collector, a positive electrode body in which a positive electrode current collector is provided with a positive electrode active material layer, and A lithium ion capacitor comprising a non-aqueous electrolyte solution containing an electrolyte containing lithium ions interposed between a positive electrode and the negative electrode.

  A lithium ion capacitor is a storage element that uses a non-aqueous electrolyte containing an electrolyte containing lithium ions. In the positive electrode, the non-Faraday reaction by adsorption / desorption of anions is the same as in an electric double layer capacitor. It is a power storage element that charges and discharges by a Faraday reaction by insertion and extraction of lithium ions similar to a lithium ion battery. A lithium ion capacitor can achieve both excellent output characteristics and high energy density by performing charge and discharge by a non-Faraday reaction at the positive electrode and a Faraday reaction at the negative electrode.

  The positive electrode of the lithium ion capacitor of the present invention is prepared by, for example, mixing a positive electrode active material, a conductive material and a binder as necessary, and adding a suitable solvent to form a paste, which is applied to the surface of the positive electrode current collector and dried. If necessary, it can be compressed and formed.

  The positive electrode active material is preferably a porous carbon material, specifically activated carbon. As the binder in the positive electrode active material layer, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), fluororubber, styrene-butadiene copolymer, and the like can be used.

  The conductive agent can be mixed with a conductive filler made of a conductive carbon material. As such a conductive filler, ketjen black, acetylene black, vapor grown carbon fiber, graphite, a mixture thereof and the like are preferable.

  On the positive electrode current collector, a conductive layer containing a conductive filler and a binder can be provided in advance before applying the positive electrode active material layer, thereby reducing the resistance of the positive electrode body itself. As the conductive filler, acetylene black, ketjen black, vapor-grown carbon fiber, and a mixture thereof are preferable. Examples of the coating method include a bar coating method, a transfer roll method, a T-die method, a screen printing method, and the like, and a coating method according to the physical properties and coating thickness of the paste can be appropriately selected.

  The negative electrode of the lithium ion capacitor of the present invention is obtained, for example, by mixing the lithium titanate of the present invention as a negative electrode active material, a conductive material and a binder as necessary, and adding a suitable solvent to form a paste, It can be applied to the surface of the body, dried and compressed as necessary.

  As the binder, PVdF, PTFE, fluororubber, styrene-butadiene copolymer and the like can be used as in the positive electrode. If necessary, a conductive material made of a carbonaceous material having higher conductivity than the negative electrode active material can be mixed. Examples of the conductive material include acetylene black, ketjen black, vapor grown carbon fiber, and mixtures thereof. Before applying the negative electrode active material layer, a conductive layer containing a conductive filler and a binder may be provided on the negative electrode current collector in advance. As the conductive filler, acetylene black, ketjen black, vapor-grown carbon fiber, and a mixture thereof are preferable.

  The molded positive electrode body and negative electrode body are laminated or wound as needed via a separator and inserted into an outer package formed from a metal can or a laminated film. As the separator, a polyethylene microporous film or a polypropylene microporous film used in a lithium ion secondary battery, or a cellulose non-woven paper used in an electric double layer capacitor can be used.

  A metal can or a laminate film can be used for the exterior body. The metal can is made of aluminum, and the laminate film used for the exterior body is a film in which a metal foil and a resin film are laminated (for example, a three-layer structure comprising an outer layer resin film / metal foil / interior resin film). Are). The outer layer resin film is for preventing the metal foil from being damaged by contact or the like, and a resin such as nylon or polyester can be suitably used. The metal foil is for preventing the permeation of moisture and gas, and foils of copper, aluminum, stainless steel, etc. can be suitably used. The interior resin film protects the metal foil from the electrolyte contained therein and melts and seals it at the time of heat sealing, and polyolefin and acid-modified polyolefin can be preferably used.

In the lithium ion capacitor of the present invention, examples of the electrolyte include LiN (SO ₂ C ₂ F ₅ ) ₂ , LiBF ₄ , and LiPF ₆ . Solvents for non-aqueous electrolytes that dissolve these electrolytic chambers include cyclic carbonates represented by ethylene carbonate (EC) and propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate. A chain carbonate represented by (MEC), lactones such as γ-butyrolactone (γBL), and a mixed solvent thereof can be used.

(Particle shape observation)
The particle shape was observed using an electron microscope S-4700 manufactured by Hitachi High-Technology Co., Ltd. under conditions of an accelerating voltage: 5 kV and a working distance: 7.5 mm. The observation magnification was 5000 times at which the size and shape of the sample aggregates can be observed, and the magnification at which the primary particle surface of the sample can be clearly observed, and was observed in the range of 10,000 to 100,000 times.

(Single phase rate)
Under the following conditions, the lithium titanate powder obtained by the production method of the present invention was measured using an X-ray diffractometer (product number: X′Part-ProMPD) manufactured by Panalical.
Measurement conditions X-ray tube: Cu
Acceleration voltage: 45 kV, current value: 40 mA
Scanning speed: 0.104 ° / sec Optical system (incident side)
Filter: Ni
Mask: 15mm
Divergent slit: 0.5 °
Anti-scattering slit: 1 °
Attenuation plate: None Optical system (receiving side)
Filter: Ni
Solar slit: 0.04 rad
Anti-scattering slit: 5.5mm
Attenuator plate: None Receiving slit: None Detector: X'Celerator
The diffraction results were analyzed using the semi-quantitative software (manufactured by Panalical) of analysis software “X'Part-HighScore Plus Ver. 2”, and Li ₃ Ti ₅ O ₁₂ , TiO ₂ (rutile phase), and Li ₂ TiO ₃ 3 Based on the quasi-quantitative values analyzed for the two components, the value is obtained from the following formula. The quasi-quantification is a method of performing quantification using a quasi-quantitative value (RIR = Reference Intensity Ratio: intensity ratio of the strongest line of the card diffraction line to the strongest line of Al ₂ O ₃ (corundum)) described in the ICDD card. .
Single phase conversion rate = I _A / (I _A + I _B + I _C )
Quasi-quantitative value of Li ₄ Ti ₅ O ₁₂ : I _A , Quasi-quantitative value of TiO ₂ (rutile phase): I _B ,
Semi-quantitative value of Li ₂ TiO ₃ : I _C

(Measurement method of specific surface area)
It was measured by the BET method. The degassing conditions for the pretreatment were 110 ° C. and 30 minutes.

(Particle size measurement)
The particle size distribution of the lithium titanate powder was measured from the SEM observation image (magnification: 10,000 to 100,000 times). The particle size distribution of lithium carbonate (average particle size D50 (50% particle size in the cumulative particle size distribution) is measured with 100% ethanol using a particle size distribution analyzer LA-920 (manufactured by Horiba, Ltd.). Was measured using an ultrasonic dispersion apparatus (output 30 W—range 5) with built-in LA-920 for 3 minutes.

Evaluation method of lithium secondary battery characteristics (coin cell fabrication)
After mixing 95 parts by weight of lithium titanate aggregates, 5 parts by weight of ketjen black and 5 parts by weight of polyvinylidene fluoride, N-methyl-2-pyrrolidone was added to a solid content concentration of 45%, and 10 times with a handy mixer. A paste was prepared by kneading for a minute. Next, the obtained paste was applied to the surface of the aluminum foil by a doctor blade method. This coating film was vacuum-dried overnight at 80 ° C., and then punched into a 1.5 cm ² circle. The punched coating film was pressed at a pressure of 64 MPa.

A coin cell 10 shown in FIG. 1 was produced. The electrode 1 is a pressed product of the above lithium titanate powder, the counter electrode 2 is a metal Li plate, and the electrolyte 3 is 1 mol of LiPF ₆ in a 1: 1 (volume ratio) mixture of ethylene carbonate and dimethyl carbonate. Celgard # 2400 manufactured by Celgard was used for the separator 4 dissolved at a ratio of / L. After the electrode 1, the counter electrode 2, the electrolyte 3, and the separator 4 were installed in the coin can 5, the gasket 6 was attached to the outer periphery of the coin can, the can lid portion 7 was placed, the outer periphery was caulked and sealed to form a coin cell 10. All the assembly operations of the coin cell 10 were performed in a glove box in an argon atmosphere in which the dew point was controlled to −80 ° C. or lower.

(Evaluation method of charge / discharge characteristics)
The charge / discharge characteristics were evaluated using a charge / discharge device HJ1001SD manufactured by Hokuto Denko Corporation with the coin cell 10 set in a holder installed in a thermostat at 30 ° C. First, a current (0.1 C) of 17.5 mA per 1 g of lithium titanate aggregate is supplied and discharged until the voltage reaches 1.0 V, and further maintained by holding at 1.0 V for 6 hours to sufficiently discharge ( Initial discharge).

  Next, after charging to 2.0 V with a current of 0.1 C, the battery is discharged again to 1.0 V at 0.1 C. At this time, the amount of current flowing at the time of discharging is integrated, and the value converted to the amount of electricity per 1 g of lithium titanate is defined as the electric capacity at 0.1 C. After repeating the capacitance measurement with a current value of 0.1 C three times, the battery was charged with current values of 175 mA (1 C), 350 mA (2 C), 875 mA (5 C), and 1.75 A (10 C) per gram of lithium titanate aggregate. The discharge is repeated 5 times, and the electric capacity at that time is measured. Five measured values of 10 C electric capacity were averaged and evaluated as representative values. In Tables 1 to 4, the measurement value of Comparative Example 1 was set to 100, and each measurement value was measured.

[Example 1]
194 g of lithium carbonate powder with a purity of 99.5% (manufactured by Kanto Chemical Co., Ltd.) (Li molar ratio 90 when the number of Li moles of the raw material is 100) and lithium hydroxide monohydrate with a purity of 99.0% 24.4 g (manufactured by Kanto Chemical Co., Ltd.) (the same Li molar ratio: 10) was weighed and put into a nylon 10 L ball mill. After adding 4.8 kg of 3 mm diameter zirconia balls, 3.2 kg of 1.5 mm diameter zirconia balls and 2 kg of pure water, they were mixed and pulverized by a ball mill for 20 hours. The average particle size of the lithium carbonate after pulverization was 1.1 μm. To this slurry was added 582 g of a titanium oxide powder having a purity of 99.9% (manufactured by Toho Titanium Co., Ltd., specific surface area 30 m ² / g), 40 g of a dispersant (manufactured by Kao Corporation, Poaz 532A), and 1.2 kg of pure water. The slurry was recovered after adding and further grinding and mixing for 8 hours. The particle size distribution of the resulting slurry was a double peak of lithium carbonate and titanium oxide, but the average particle size of the peak attributed to lithium carbonate was 0.89 μm. The obtained slurry was spray-granulated with hot air at 220 ° C. using a spray dryer (manufactured by Yamato Scientific Co., Ltd., GB210-B) to obtain a spherical granulated mixed powder. Next, the mixed powder is put in an alumina sheath, heated to 800 ° C. at a temperature rising rate of 0.5 ° C./min, fired at 800 ° C. for 4 hours, cooled to room temperature at a temperature decreasing rate of 1 ° C./min, Lithium titanate aggregates were obtained.

As a result of X-ray diffraction measurement, the obtained lithium titanate aggregate was mainly composed of Li ₄ Ti ₅ O ₁₂ , and the specific surface area by the BET method using nitrogen adsorption was 6.1 m ² / g, and was made into a single phase. The rate was 95%.

[Comparative Example 1]
216 g of 99.5% pure lithium carbonate powder (manufactured by Kanto Chemical Co., Ltd.), 584 g of titanium oxide powder (99.9% pure, manufactured by Toho Titanium Co., Ltd., specific surface area 30 m ² / g) and a dispersant (Kao ( Co., Ltd., Poise 532A) 40 g and pure water 3.2 kg were added simultaneously and mixed for 8 hours by a ball mill, the same method as in Example 1 except that the firing temperature was 850 ° C. and the firing time was 4 hours. Thus, lithium titanate powder was prepared.

After mixing, the average particle size of lithium carbonate in the slurry was 2.7 μm, the specific surface area of the obtained lithium titanate was 4.5 m ² / g, and the single phase conversion rate was 92%.

[Example 2]
Lithium carbonate powder with a purity of 99.5% (manufactured by Kanto Chemical Co., Ltd.) 10.6 g (Li molar ratio 5), lithium hydroxide monohydrate with a purity of 99.0% (manufactured by Kanto Chemical Co., Ltd.) 225 g (Li molar ratio 95) was weighed and put into a nylon 10L ball mill. After adding 4.8 kg of 3 mm diameter zirconia balls, 3.2 kg of 1.5 mm diameter zirconia balls and 2 kg of pure water, they were mixed and pulverized by a ball mill for 20 hours. The average particle size of the lithium carbonate after pulverization was 0.65 μm. To this slurry, 565 g of 99.9% pure titanium oxide powder (manufactured by Toho Titanium Co., Ltd., specific surface area 30 m ² / g), 40 g of a dispersant (Kao Co., Ltd., Poaz 532A), and 1.2 kg of pure water were added. The slurry was recovered after adding and further grinding and mixing for 8 hours. The particle size distribution of the resulting slurry was a double peak of lithium carbonate and titanium oxide, but the average particle size of the peak attributed to lithium carbonate was 0.48 μm. The obtained slurry was spray-granulated with hot air at 220 ° C. using a spray dryer (manufactured by Yamato Scientific Co., Ltd., GB210-B) to obtain a spherical granulated mixed powder. Next, the mixed powder is put in an alumina sheath, heated to 800 ° C. at a temperature rising rate of 0.5 ° C./min, fired at 800 ° C. for 4 hours, cooled to room temperature at a temperature decreasing rate of 1 ° C./min, Lithium titanate aggregates were obtained.

As a result of X-ray diffraction measurement, the obtained lithium titanate aggregate is mainly composed of Li ₄ Ti ₅ O _{12 and} has a specific surface area of 6.5 m ² / g by BET method using nitrogen adsorption. The rate was 93%.

[Example 3]
Titanium oxide powder with a purity of 99.9% (manufactured by Toho Titanium Co., Ltd., specific surface area 30 m ^{2 /} g) 12.26 kg, lithium carbonate powder with a purity of 99.5% (manufactured by Kanto Chemical Co., Inc.) 2.28 kg (Li Molar ratio 50), purity 99.0% lithium hydroxide monohydrate (Kanto Chemical Co., Ltd.) 2.57 kg (Li molar ratio 50), dispersant (Kao Co., Ltd., Poaz 532A) 800 g Were weighed and put into an alumina-lined 200 L ball mill. After adding 120 kg of zirconia balls having a diameter of 3 mm, 80 kg of zirconia balls having a diameter of 1.5 mm and 80 kg of pure water, they were mixed and pulverized by a ball mill for 25 hours. The particle size distribution of the obtained slurry was a double peak of lithium carbonate and titanium oxide, but the average particle size of the peak attributed to lithium carbonate was 0.23 μm. The obtained slurry was spray-granulated with hot air at 220 ° C. using a spray dryer (manufactured by Fujisaki Electric Co., Ltd., MDP-050) to obtain a spherical granulated mixed powder. Next, this mixed powder is put in an alumina sheath, heated to 800 ° C. at a heating rate of 0.8 ° C./min, fired at 800 ° C. for 5 hours, cooled to room temperature at a cooling rate of 1 ° C./min, Lithium titanate aggregates were obtained.

As a result of X-ray diffraction measurement, the obtained lithium titanate aggregate is mainly composed of Li ₄ Ti ₅ O _{12 and} has a specific surface area of 5.8 m ² / g by BET method using nitrogen adsorption. The rate was 94%.

[Example 4]
93.5% purity lithium carbonate powder (Kanto Chemical Co., Ltd.) 13.5 g (Li molar ratio 51), purity 99.0% lithium hydroxide monohydrate (Kanto Chemical Co., Ltd.) 14 0.8 g (Li molar ratio 49) was weighed and placed in a nylon 1 L ball mill. After adding 600 g of zirconia balls having a diameter of 3 mm, 400 g of zirconia balls having a diameter of 1.5 mm and 250 g of pure water, they were mixed and pulverized by a ball mill for 20 hours. The average particle size of the lithium carbonate after pulverization was 0.89 μm. To this slurry, 71.7 g of 99.9% pure titanium oxide powder (manufactured by Toho Titanium Co., Ltd., specific surface area 5 m ² / g), 5 g of a dispersant (manufactured by Kao Corporation, Poaz 532A), and 150 g of pure water were added. The slurry was recovered after adding and further grinding and mixing for 8 hours. The particle size distribution of the obtained slurry was a double peak of lithium carbonate and titanium oxide, but the average particle size of the peak attributed to lithium carbonate was 0.75 μm. The obtained slurry was spray-granulated with hot air at 220 ° C. using a spray dryer (manufactured by Yamato Scientific Co., Ltd., GB210-B) to obtain a spherical granulated mixed powder. Next, this mixed powder is put in an alumina sheath, heated to 850 ° C. at a heating rate of 0.5 ° C./min, fired at 850 ° C. for 4 hours, cooled to room temperature at a cooling rate of 1 ° C./min, Lithium titanate aggregates were obtained.

As a result of X-ray diffraction measurement, the obtained lithium titanate aggregate is mainly composed of Li ₄ Ti ₅ O _{12 and} has a specific surface area of 4.0 m ² / g according to the BET method using nitrogen adsorption. The rate was 94%.

[Comparative Example 2]
Titanium oxide powder with a purity of 99.9% (manufactured by Toho Titanium Co., Ltd., specific surface area 5 m ² / g), 73 g of lithium carbonate powder with a purity of 99.5% (manufactured by Kanto Chemical Co., Ltd.), dispersant (Kao ( Co., Ltd., Poaz 532A) 5 g was weighed and placed in a nylon 1 L ball mill. After adding 1 kg of zirconia balls and 400 g of pure water, the mixture was mixed by a ball mill for 8 hours, and then the slurry was collected. The particle size distribution of the resulting slurry was a double peak of lithium carbonate and titanium oxide, but the average particle size of the peak attributed to lithium carbonate was 1.4 μm. The obtained slurry was dried by vat drying in a dryer at 110 ° C., and then crushed and sieved with a 200 μm mesh sieve to obtain a mixed powder. Next, this mixed powder is put in an alumina sheath, heated to 900 ° C. at a heating rate of 0.5 ° C./min, then fired at 900 ° C. for 4 hours, cooled to room temperature at a cooling rate of 1 ° C./min, Lithium titanate aggregates were obtained.

As a result of X-ray diffraction measurement, the obtained lithium titanate aggregate is mainly composed of Li ₄ Ti ₅ O _{12 and} has a specific surface area of 2.4 m ² / g according to the BET method using nitrogen adsorption. The rate was 91%.

[Example 5]
A slurry of a titanium oxide lithium compound was produced in the same manner as in Example 4 except that titanium oxide powder having a specific surface area of 40 m ² / g was used in Example 4. The particle size distribution of the resulting slurry was a double peak of lithium carbonate and titanium oxide, but the average particle size of the peak attributed to lithium carbonate was 0.68 μm. The obtained slurry was spray-granulated with hot air at 220 ° C. using a spray dryer (manufactured by Yamato Scientific Co., Ltd., GB210-B) to obtain a spherical granulated mixed powder. Next, this mixed powder is put in an alumina-made sheath, heated to 800 ° C. at a heating rate of 0.5 ° C./min, then fired at 800 ° C. for 5 hours, cooled to room temperature at a cooling rate of 1 ° C./min, Lithium titanate aggregates were obtained. The obtained lithium titanate aggregate had a specific surface area of 6.5 m ² / g and a single phase conversion rate of 94%.

[Comparative Example 3]
According to the same method as in Example 5, except that lithium carbonate, lithium hydroxide and titanium oxide of Example 5 were simultaneously added and mixed for 8 hours by a ball mill, the firing temperature was 850 ° C., and the firing time was 4 hours. A lithium titanate powder was prepared.

The average particle diameter of lithium carbonate in the slurry after mixing and pulverization was 2.3 μm, and the obtained lithium titanate had a specific surface area of 3.7 m ² / g and a single phase conversion rate of 92%.

[Comparative Example 4]
Titanium oxide powder with a purity of 99.9% (manufactured by Toho Titanium Co., Ltd., specific surface area 40 m ^{2 /} g) 70.4 g, lithium hydroxide monohydrate with a purity of 99.0% (manufactured by Kanto Chemical Co., Inc.) 29.6 g and 5 g of a dispersant (manufactured by Kao Corporation, Poaz 532A) were weighed and put into a 1 L ball mill made of nylon. After adding 600 g of zirconia balls having a diameter of 3 mm, 400 g of zirconia balls having a diameter of 1.5 mm and 400 g of pure water, the slurry was collected after mixing for 28 hours by a ball mill. The particle size distribution of the lithium compound slurry of the obtained titanium oxide powder was only the peak of titanium oxide. The obtained slurry was spray-granulated with hot air at 220 ° C. using a spray dryer (manufactured by Yamato Scientific Co., Ltd., GB210-B) to obtain a spherical granulated mixed powder. Next, this mixed powder is put in an alumina-made sheath, heated to 800 ° C. at a heating rate of 0.5 ° C./min, then fired at 800 ° C. for 5 hours, cooled to room temperature at a cooling rate of 1 ° C./min, Lithium titanate aggregates were obtained. The obtained lithium titanate aggregate had a specific surface area of 2.1 m ² / g and a single phase conversion rate of 90%.

[Comparative Example 5]
A lithium titanate powder was produced in the same manner as in Example 4 except that titanium oxide powder having a specific surface area of 2 m ² / g was used in Example 4 and the firing conditions were 900 ° C. and 6 hours.

The average particle diameter of the peak due to lithium carbonate after the slurry was recovered was 0.95 μm. The specific surface area of the obtained lithium titanate powder was 1.7 m ² / g, and the single phase conversion rate was 93%.

[Comparative Example 6]
A lithium titanate powder was produced in the same manner as in Example 1 except that 216 g of lithium carbonate powder with a purity of 99.5% (manufactured by Kanto Chemical Co., Inc.) and lithium hydroxide monohydrate were not added. .

After mixing, the average particle size of lithium carbonate in the slurry was 0.86 μm, the specific surface area of the obtained lithium titanate was 5.5 m ² / g, and the single phase conversion rate was 94%.

  Table 1 also shows the ratios of the electric capacities of the examples and the comparative examples when a coin cell is manufactured using the lithium titanate powder of Comparative Example 1 and the electric capacity when measured at a current density of 10 C is 100. It is written together.

  As shown in Table 1, Examples 1 to 5 within the scope of the present invention showed good results that the single phase conversion ratio was 93% or more and the capacitance ratio was 110 or more. On the other hand, Comparative Examples 1 and 2 having no lithium hydroxide and a large lithium carbonate particle size, Comparative Example 3 having a large lithium carbonate particle size, Comparative Example 4 not containing lithium carbonate, a large lithium carbonate particle size and a titanium raw material specific surface area The small comparative example 5 and the comparative example 6 which does not contain lithium hydroxide resulted in a small electric capacity ratio.

  It is promising for the production of lithium ion secondary batteries and lithium ion capacitors that can maintain the electric capacity during rapid charge and discharge.

DESCRIPTION OF SYMBOLS 1 ... Electrode 2 ... Counter electrode 3 ... Electrolytic solution 4 ... Separator 5 ... Coin can 6 ... Gasket 7 ... Can lid part 10 ... Coin cell

Claims (3)

A titanium raw material having a BET specific surface area of 5 m ² / g or more selected from titanium oxide, metatitanic acid, orthotitanic acid, or a mixture thereof, and lithium hydroxide and lithium carbonate, wherein the mixing ratio of the lithium hydroxide and lithium carbonate is When the total amount of Li of lithium hydroxide and lithium carbonate is 100, lithium titanium oxide to be fired after mixing with a lithium raw material having a lithium molar ratio of lithium hydroxide: lithium carbonate = 95: 5 to 10:90 A method for producing a lithium titanate powder, wherein the lithium carbonate has an average particle size of 1.0 μm or less before firing.   The method for producing a lithium titanate powder according to claim 1, wherein the titanium raw material and the lithium raw material are mixed with water, and then pulverized and granulated and dried.   The method for producing a lithium titanate powder according to claim 1 or 2, wherein the titanium raw material is titanium oxide.

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