JP2018006164A - Lithium titanate powder for power storage device electrode, active substance material, and power storage device using the active substance material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: lithium titanate powder for a power storage device electrode, containing LiTiOas a main constituent and excellent in effects of suppressing resistance change before and after storage at high temperature in a charged state for a long term, when applied, as an electrode material, for the power storage device; an active substance material; and a power storage device using the active substance material.SOLUTION: There is provided lithium titanate powder for a power storage device electrode, which is lithium titanate powder containing LiTiOas a main constituent and has a surface layer at least at a part of a particle surface, the surface layer containing a sulfonic acid lithium salt compound represented by the following general formula (I) (In the formula, R represents a 1-5C alkyl group or a 6-12C aryl group.)SELECTED DRAWING: None

Description

  The present invention relates to a lithium titanate powder for an electrode capable of suppressing a change in resistance before and after long-term high-temperature charge storage of an electricity storage device, and an active material using the lithium titanate powder. The present invention also relates to an electricity storage device using this active material as an electrode.

  In recent years, various materials have been studied as electrode materials for power storage devices. Among them, lithium titanate is attracting attention as an active material for electric storage devices for electric vehicles such as HEV, PHEV, and BEV because it has excellent input / output characteristics when used as an active material.

  Since it is not uncommon for the temperature inside a vehicle to exceed 60 ° C. in summer, an electric storage device for an electric vehicle is required to have no safety problem or performance degradation even at high temperatures. However, it is known that problems such as a large change in resistance before and after high-temperature charge storage occur in an electricity storage device using lithium titanate as an active material. Therefore, development of lithium titanate that can suppress a resistance change before and after high temperature charge storage of an electricity storage device is desired.

  In Patent Document 1, a secondary battery in which lithium phosphate or a lithium titanate powder having a surface layer of lithium phosphate and lithium sulfate is applied to an electrode on a particle surface is a lithium titanate having no surface layer. It is disclosed that the resistance change after a high temperature storage test at 60 ° C. for 4 weeks is reduced in a charged state of 2.55 V compared to a secondary battery in which the powder is applied to the electrode.

JP 2010-27377 A

  However, even if it is spinel type lithium titanium complex oxide which has a surface layer of lithium phosphate or lithium phosphate and lithium sulfate like patent documents 1, an electrical storage device which applied it to an electrode in a charge state It was found that, when stored at a high temperature for a long period of time, the resistance change suppressing effect before and after storage is reduced, and in some cases, the resistance change is larger than when applying lithium titanate powder without a surface layer. . Therefore, when applied as an electrode material to an electricity storage device, lithium titanate is required which has a large effect of suppressing resistance change before and after long-term high-temperature charge storage.

Therefore, the present invention is an electricity storage device mainly composed of Li ₄ Ti ₅ O ₁₂ which is excellent in the effect of suppressing resistance change before and after long-term high-temperature charge storage when applied as an electrode material to an electricity storage device. An object of the present invention is to provide a lithium titanate powder for an electrode, an active material, and an electricity storage device using the same.

  As a result of various studies to achieve the above object, the present inventors have found a lithium titanate powder containing a specific lithium salt compound on at least a part of the particle surface, and the lithium titanate powder is applied as an electrode material. The present invention was completed by finding that the electricity storage device has an extremely large effect of suppressing the resistance change before and after long-term storage at high temperature. That is, the present invention relates to the following matters.

(1) A lithium titanate powder containing Li ₄ Ti ₅ O ₁₂ as a main component, and a surface layer containing a lithium sulfonate compound represented by the following general formula (I) on at least a part of the particle surface: A lithium titanate powder for an electrode of an electricity storage device, comprising:

(In the formula, R represents an alkyl group having 1 to 5 carbon atoms or an aryl group having 6 to 12 carbon atoms.)

  (2) The lithium titanate powder for an electrode of an electricity storage device according to (1), wherein a content ratio of the lithium sulfonate compound in the lithium titanate powder is 0.1% by mass to 10% by mass.

  (3) The electricity storage according to (1) or (2), wherein the total pore volume in a state where the surface layer is removed from the lithium titanate powder is 0.03 to 0.5 ml / g. Lithium titanate powder for device electrodes.

(4) The specific surface area equivalent diameter calculated from the specific surface area in a state where the surface layer is removed from the lithium titanate powder is D _{BET. In the} lithium titanate powder, Li ₄ Ti ₅ O ₁₂ (111) When the crystallite diameter calculated from the Scherrer equation from the peak half-width of the surface is D _X , D _BET is 0.1 to 0.6 μm, D _X is larger than 80 nm, and D _BET and D _X The ratio D _BET / D _X (μm / μm) is 3 or less, the lithium titanate powder for an electrode of an electricity storage device according to any one of (1) to (3).

(5) In the peak intensity obtained by X-ray diffraction measurement of the lithium titanate powder, when the intensity of the peak derived from the (111) plane of Li ₄ Ti ₅ O ₁₂ is 100, (101 ) The value calculated by multiplying the intensity of the peak derived from the plane, the intensity of the peak derived from the (110) plane of rutile titanium dioxide, and the intensity of the peak derived from the (−133) plane of Li ₂ TiO ₃ by 100/80. The lithium titanate powder for an electrode of an electricity storage device according to any one of (1) to (4), wherein the total is 1 or less.

  (6) An active material containing the lithium titanate powder for an electrode of the electricity storage device according to any one of (1) to (5).

  (7) An electricity storage device comprising an electrode, a non-aqueous electrolyte, and a separator, wherein the electrode includes the active material according to (6).

(8) The non-aqueous electrolyte contains LiPF ₆ and further contains one or more selected from the group consisting of LiBF ₄ , LiPO ₂ F ₂ , and LiN (SO ₂ F) _2. The electrical storage device as described in (7).

  (9) The electricity storage device according to (7) or (8), wherein the electricity storage device is a lithium ion secondary battery.

  (10) The power storage device according to claim 7 or 8, wherein the power storage device is a hybrid capacitor.

  According to the present invention, a lithium titanate powder and an active material for an electrode of an electricity storage device having an extremely large effect of suppressing resistance change before and after long-term high-temperature charge storage, and resistance change before and after long-term high-temperature charge storage Can be provided.

(Lithium titanate powder)
The lithium titanate powder of the present invention is a lithium titanate powder mainly composed of Li ₄ Ti ₅ O ₁₂ , and a lithium sulfonate salt represented by the following general formula (I) on at least a part of the particle surface. A lithium titanate powder for an electrode of an electricity storage device, comprising a surface layer containing a compound.

(In the formula, R represents an alkyl group having 1 to 5 carbon atoms or an aryl group having 6 to 12 carbon atoms.)

Here, Li ₄ Ti ₅ O ₁₂ as a main component means that the peak intensity derived from the (111) plane of Li ₄ Ti ₅ O ₁₂ in the X-ray diffraction diagram obtained by X-ray diffraction measurement of the lithium titanate powder. Is 100, the peak intensity derived from the (101) plane of anatase-type titanium dioxide is 5 or less, the peak intensity derived from the (110) plane of rutile-type titanium dioxide is 5 or less, and Li ₂ TiO ₃ The value calculated by multiplying the peak intensity derived from the (-133) plane by 100/80 is 5 or less. However, it is preferably less components other than these _Li 4 _Ti 5 _{O 12,} the intensity of the peak derived from (101) plane of anatase type titanium dioxide, the intensity of the peak derived from (110) plane of rutile titanium dioxide, and The sum of values calculated by multiplying the intensity of the peak derived from the (−133) plane of Li ₂ TiO ₃ by 100/80 is preferably 1 or less. The X-ray diffraction measurement method will be described in (1) XRD of [Various physical property measurement methods] described later.

In the lithium titanate powder of the present invention, the atomic ratio Li / Ti of Li to Ti is preferably 0.79 to 0.85. Within this range, the proportion of Li ₄ Ti ₅ O ₁₂ in the lithium titanate powder increases, and the initial charge / discharge capacity of the electricity storage device to which the lithium titanate powder of the present invention is applied as an electrode material increases. In this respect, the atomic ratio Li / Ti is more preferably 0.80 to 0.85, and still more preferably 0.81 to 0.85.

<Surface layer>
The lithium titanate powder of the present invention has a surface layer containing a lithium sulfonate compound represented by the following general formula (I) on at least a part of the particle surface of the particles constituting the lithium titanate powder. The surface layer is preferably present on the entire particle surface, but if present on at least a part of the particle surface, the effects of the present invention can be obtained.

(In the formula, R represents an alkyl group having 1 to 5 carbon atoms or an aryl group having 6 to 12 carbon atoms.)

  The surface layer is preferably substantially composed of the lithium sulfonate compound, but the effect of the present invention can be obtained if the lithium sulfonate compound is included. In addition, substantially consisting of the said sulfonic-acid lithium salt compound means that it is accept | permitted that components other than the said sulfonic-acid lithium salt compound are contained to such an extent that the effect of this invention does not fall remarkably.

  Examples of the lithium sulfonate compound include lithium methanesulfonate, lithium ethanesulfonate, lithium propane-1-sulfonate, lithium propane-2-sulfonate, lithium butane-1-sulfonate, and butane-2-sulfone. Lithium acid, lithium 2-methylpropane-1-sulfonate, lithium 2-methylpropane-2-sulfonate, lithium pentane-1-sulfonate, lithium 3-methylbutane-1-sulfonate, 2-methylbutane-1-sulfone Lithium acid, lithium pentane-2-sulfonate, lithium 3-methylbutane-2-sulfonate, lithium pentane-3-sulfonate, lithium benzenesulfonate, lithium 2-methylbenzenesulfonate, lithium 3-methylbenzenesulfonate, 4-methylben Lithium sulfonate, lithium 4-ethylbenzenesulfonate, lithium 2,3-dimethylbenzenesulfonate, lithium 2,4-dimethylbenzenesulfonate, lithium 2,5-dimethylbenzenesulfonate, lithium 2,6-dimethylbenzenesulfonate Lithium 3,4-dimethylbenzenesulfonate, lithium 3,5-dimethylbenzenesulfonate, lithium 2-cyclohexylbenzenesulfonate, lithium 3-cyclohexylbenzenesulfonate, lithium 4-cyclohexylbenzenesulfonate, 1,1'- Preferred examples include lithium biphenylyl-2-sulfonate, lithium 1,1′-biphenylyl-3-sulfonate, lithium 1,1′-biphenylyl-4-sulfonate, and among them, lithiated methanesulfonate , Lithium ethanesulfonate, lithium propane-1-sulfonate, lithium 2-propanesulfonate, lithium benzenesulfonate, or lithium 4-methylbenzenesulfonate, lithium methanesulfonate, lithium ethanesulfonate, or propane Particularly preferred is lithium -1-sulfonate.

  Moreover, it is preferable that the content rate of the said sulfonic-acid lithium salt compound in the lithium titanate powder of this invention is 0.1 mass%-10 mass%. As a minimum of the above-mentioned content rate, 0.3 mass% or more is still more preferred, and 0.5 mass% or more is especially preferred. Moreover, as an upper limit of the said content rate, 5 mass% or less is further more preferable, and 2 mass% or less is especially preferable.

  The lithium titanate powder of the present invention preferably has a total pore volume of 0.03 to 0.5 ml / g in a state where the surface layer is removed from the lithium titanate powder of the present invention. If the total pore volume is within this range, by applying the lithium titanate powder of the present invention to an electricity storage device, the charge / discharge capacity is large and the input / output characteristics are excellent, and in addition, before and after long-term storage at high temperature. An electricity storage device in which an increase in resistance is suppressed is obtained. From the viewpoint of further improving the effect of suppressing the increase in resistance before and after long-term storage at high temperature, the lower limit of the total pore volume is more preferably 0.1 ml / g or more, and more preferably 0.15 ml / g or more. Is more preferably 0.2 ml / g or more. From the same viewpoint, the upper limit of the total pore volume is more preferably 0.45 ml / g or less, further preferably 0.4 ml / g or less, and 0.35 ml / g or less. Particularly preferred. The total pore volume of the lithium titanate powder of the present invention is the total pore volume measured by a gas adsorption method. Here, the state in which the surface layer is removed from the lithium titanate powder of the present invention means that the endothermic reaction accompanying melting and evaporation of lithium methanesulfonate is observed from the measurement results of TG-DTA from room temperature to 600 ° C. The surface layer removing means will be described later.

In the present invention, the crystallite diameter calculated from the Scherrer equation from the peak half-value width of the (111) plane of Li ₄ Ti ₅ O ₁₂ of the lithium titanate powder of the present invention is D _X. And in the present invention, it is preferred that _{D X} is larger than 80 nm. The method for measuring the D _X, will be described in later [lithium titanate powder physical properties measurement method] (2) crystallite diameter (D _X).

In the present invention, the specific surface area equivalent diameter calculated from the specific surface area obtained by measuring the specific surface area by the BET method for the lithium titanate powder from which the surface layer has been removed from the lithium titanate powder of the present invention. _Is D _BET . In the present invention, the D _BET is preferably 0.1 to 0.6 μm. In the present invention, The method for measuring D _BET will be described in (4) BET diameter (D _BET ) in [Methods for measuring various physical properties of lithium titanate powder] described later.

In the present invention, the ratio D _BET / D _X (μm / μm) of D _BET and D _X is preferably 3 or less, more preferably 2 or less, still more preferably 1.5 or less, and particularly preferably 1.1 or less. The lower limit of D _BET / D _X (μm / μm) is not particularly limited, but is usually 0.6.

(Method for producing lithium titanate powder)
Next, although an example of the manufacturing method of the lithium titanate powder of this invention is demonstrated, the manufacturing method of the lithium titanate powder of this invention is not limited to the following description. The lithium titanate powder of the present invention can be obtained by a step of mixing a Ti source and a Li source, a step of firing, and a post-treatment step such as crushing / classification / magnetic separation performed as necessary.

<Raw material preparation process>
The raw material of the lithium titanate powder of the present invention comprises a titanium raw material and a lithium raw material. As the titanium raw material, titanium compounds such as anatase type titanium dioxide and rutile type titanium dioxide are used. It is preferable that it reacts easily with a lithium raw material in a short time, and anatase type titanium dioxide is preferable from this viewpoint. The volume median particle size (average particle size, D50) of the titanium raw material is preferably 2 μm or less in order to sufficiently react the raw material by short-time firing. As the lithium raw material, lithium compounds such as lithium hydroxide monohydrate, lithium oxide, lithium hydrogen carbonate, and lithium carbonate are used. In terms of firing at a high temperature, a lithium compound having a high melting point is preferable, and lithium carbonate is particularly preferable.

  In the present invention, before firing the mixture composed of the above raw materials, the particle size distribution curve measured by a laser diffraction / scattering type particle size distribution measuring machine of the mixed powder constituting the mixture is such that D95 is 5 μm or less. It is preferable to prepare. From the viewpoint of increasing the total pore volume, it is more preferably 1 μm or less, still more preferably 0.7 μm or less, and particularly preferably 0.5 μm or less. Here, D95 is a particle size in which the cumulative volume frequency calculated by the volume fraction is 95% when integrated from the smaller particle size. The mixture may be a mixed powder prepared as described above, or a granulated powder obtained by granulating the mixed powder prepared as described above. Moreover, it is good also considering the state of the mixture used for baking as the slurry form containing the above mixed powder or granulated powder. When the mixture is a granulated powder, the D95 of the granulated powder is not necessarily 5 μm or less, and is preferably a granulated powder obtained by granulating a mixed powder having a D95 of 5 μm or less.

  As a method for preparing the mixture, the following methods can be employed. The first method is a method in which the raw materials are mixed and then pulverized simultaneously with mixing. The second method is a method in which each raw material is pulverized until D95 after mixing becomes 5 μm or less, and then mixed or mixed while lightly pulverizing. The third method is a method in which powders made of fine particles are produced from each raw material by a method such as crystallization, classified as necessary, and mixed while mixing or lightly pulverizing. Among them, in the first method, the method of pulverizing simultaneously with the mixing of the raw materials is an industrially advantageous method because it involves fewer steps. Moreover, you may add a conductive support agent simultaneously.

  When the obtained mixture is a mixed powder, it can be directly used for the next firing step. In the case of a mixed slurry made of a mixed powder, the mixed slurry can be granulated and dried with a spray dryer or the like and then subjected to the next firing step. When baking is performed using a rotary kiln furnace, it can use in a furnace with a mixed slurry.

<Baking process>
The resulting mixture is then fired. From the viewpoint of reducing the equivalent surface area diameter of the powder obtained by firing and increasing the crystallite diameter, firing is preferably performed at a high temperature for a short time. From such a viewpoint, the maximum temperature during firing is preferably 800 to 1100 ° C, more preferably 850 to 1100 ° C, and further preferably 900 to 1000 ° C. Similarly, from the above viewpoint, the holding time at the maximum temperature during firing is preferably 2 to 90 minutes, more preferably 5 to 60 minutes, and further preferably 5 to 45 minutes. When the maximum temperature during firing is high, it is preferable to select a shorter holding time. Likewise, from the viewpoint of reducing the specific surface area equivalent diameter of the powder obtained by firing and increasing the crystallite diameter, it is preferable to particularly shorten the residence time at 700 to 800 ° C. in the heating process during firing. For example, it is preferably within 15 minutes.

  The firing method is not particularly limited as long as it can be fired under such conditions. Examples of the firing furnace that can be used include a fixed bed type firing furnace, a roller hearth type firing furnace, a mesh belt type firing furnace, a fluidized bed type, and a rotary kiln type firing furnace. However, when performing efficient firing in a short time, a roller hearth firing furnace, a mesh belt firing furnace, and a rotary kiln firing furnace are preferable. When using a roller hearth type baking furnace or a mesh belt type baking furnace in which the mixture is stored and fired in a mortar, the quality of the lithium titanate obtained by ensuring the uniformity of the temperature distribution of the mixture during baking is constant. In order to make it small, it is preferable to make the accommodation amount of the mixture into a mortar small.

  The rotary kiln-type firing furnace does not require a container to contain the mixture, can be fired while continuously charging the mixture, has a uniform heat history on the material to be fired, and can obtain homogeneous lithium titanate From this, it is a particularly preferable firing furnace for producing the lithium titanate powder of the present invention.

  The atmosphere at the time of firing is not particularly limited regardless of the firing furnace, as long as the desorbed moisture and carbon dioxide gas can be removed. Usually, an air atmosphere using compressed air is used, but an oxygen, nitrogen, or hydrogen atmosphere may be used.

<Disintegration / classification process>
The fired lithium titanate powder obtained as described above can be crushed or classified to the extent that it can be agglomerated as necessary.

<Surface treatment process>
A treatment is performed to form a surface layer containing a lithium sulfonate salt on the surface of the particles of the obtained lithium titanate powder after firing or the lithium titanate powder that has been crushed or classified thereafter. The method is not particularly limited, but surface treatment by a wet method is suitable for uniformly and uniformly forming a surface layer on the surface of the particles constituting the lithium titanate powder of the present invention. Mixing in which lithium titanate powder and lithium sulfonate are put into a solvent in which lithium sulfonate is completely dissolved, and lithium titanate powder can be uniformly dispersed in a solution in which lithium sulfonate is dissolved Mixing is performed using an apparatus such as a Henschel mixer, an ultrasonic dispersion apparatus, a homomixer, a ball mill, a centrifugal ball mill, a planetary ball mill, a vibrating ball mill, an attritor type high-speed ball mill, a bead mill, a roll mill, or the like. The solvent is not particularly limited as long as it is a liquid that can dissolve the lithium sulfonate, but it is preferable to use water such as ion-exchanged water from the viewpoints of economy, ease of disposal after use, and environmental burden. Next, by drying the obtained lithium sulfonate solution in which the lithium titanate powder is uniformly dispersed, a lithium titanate powder having a surface layer of lithium sulfonate on the particle surface can be obtained. The drying method is not particularly limited, but a spray drying method using a spray dryer or the like is efficient and preferable. Further, when the surface treatment method as described above is adopted, the ratio of the mass of the lithium sulfonate salt to the total mass of the lithium titanate powder and the lithium sulfonate salt added to the solvent is the sulfone in the lithium titanate powder of the present invention. Since it becomes the content rate of an acid lithium salt compound, the content rate of the said sulfonic-acid lithium salt compound can be adjusted easily.

(Active material)
The active material of the present invention contains the lithium titanate powder of the present invention, and may contain one or more substances other than the lithium titanate powder of the present invention. Examples of substances other than the lithium titanate powder of the present invention include carbon materials (pyrolytic carbons, cokes, graphites (artificial graphite, natural graphite, etc.), organic polymer compound combustion bodies, carbon fibers), tin, and the like. Tin compounds, silicon and silicon compounds are used.

(Electric storage device)
The electricity storage device of the present invention is an electricity storage device composed of electrodes, that is, a positive electrode and a negative electrode, a nonaqueous electrolytic solution, and a separator, and the electrode includes the active material of the present invention. The active material of the present invention may be contained in either the positive electrode or the negative electrode, but is preferably contained in the negative electrode. The active material is usually used in the form of an electrode sheet. Specifically, the electricity storage device of the present invention is a device for storing and releasing energy using intercalation and deintercalation of lithium ions to an electrode containing the active material, for example, a hybrid capacitor And lithium batteries.

(Hybrid capacitor)
As the hybrid capacitor of the present invention, an active material having a capacity formed by physical adsorption similar to the electrode material of an electric double layer capacitor such as activated carbon, or physical adsorption and intercalation such as graphite, deintercalation, etc. This is a device that uses an active material whose capacity is formed by redox, such as a conductive polymer, and an active material of the present invention for the negative electrode. The active material is usually used in the form of an electrode sheet.

(Lithium battery)
The lithium battery of the present invention is a generic term for a lithium primary battery and a lithium secondary battery. In this specification, the term lithium secondary battery is used as a concept including a so-called lithium ion secondary battery.

  The lithium battery is composed of a positive electrode, a negative electrode, a nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a nonaqueous solvent, and the like, but the active material of the present invention can be used as an electrode material. The active material of the present invention is usually used in the form of an electrode sheet. The active material of the present invention may be used as either a positive electrode active material or a negative electrode active material, but the case where it is used as a negative electrode active material will be described below.

(Negative electrode)
The negative electrode has a mixture layer containing a negative electrode active material (the active material of the present invention), a conductive agent, and a binder on one surface or both surfaces of the negative electrode current collector. This mixture layer is usually in the form of an electrode sheet.

The conductive agent for the negative electrode is not particularly limited as long as it is an electron conductive material that does not cause a chemical change. For example, natural graphite (flaky graphite, etc.), graphite such as artificial graphite, carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, single-phase carbon nanotube, multi-walled carbon nanotube (Graphite layer is multi-layer concentric cylinder) (non-fishbone), cup-stacked carbon nanotube (fishbone) (fishbone), nodal carbon nanofiber (non-fishbone structure), platelet-type carbon nanofiber ( And carbon nanotubes such as a playing card). Further, graphites, carbon blacks, and carbon nanotubes may be appropriately mixed and used. There is no particular limitation, specific surface area of the carbon blacks is preferably 30~3000m ² / g, more preferably from 50~2000m ² / g. When the specific surface area is less than 30 m ² / g, the contact area with the active material decreases, so that the electrical conductivity cannot be obtained and the internal resistance increases. When the specific surface area exceeds 3000 m ² / g, the amount of solvent required for coating increases, so it becomes more difficult to improve the electrode density, and it is not suitable for increasing the capacity of the mixture layer. The specific surface area of the graphite is preferably 30 to 600 m ² / g, more preferably 50 to 500 m ² / g. When the specific surface area is less than 30 m ² / g, the contact area with the active material decreases, so that the electrical conductivity cannot be obtained and the internal resistance increases. When the specific surface area exceeds 600 m ² / g, the amount of solvent required for coating increases, so it becomes more difficult to improve the electrode density, and it is not suitable for increasing the capacity of the mixture layer. Moreover, the aspect ratio of carbon nanotubes is 2-150, Preferably it is 2-50, More preferably, it is 2-30, More preferably, it is 2-20. When the aspect ratio is large, the structure of the formed fiber approaches a cylindrical tube shape, and the conductivity in the fiber axis direction of one fiber is improved. However, the open end of the graphite network surface constituting the structural unit body is a fiber. Since the frequency of exposure to the outer peripheral surface is reduced, the conductivity between adjacent fibers is deteriorated. On the other hand, when the aspect ratio is small, the open end of the graphite mesh surface constituting the structural unit body portion is more frequently exposed to the outer peripheral surface of the fiber, so that the conductivity between adjacent fibers is improved. Since many short graphite mesh surfaces are connected in the axial direction, conductivity in the fiber axial direction of one fiber is impaired.

  Since the addition amount of the conductive auxiliary agent varies depending on the specific surface area of the active material and the type and combination of the conductive auxiliary agent, it should be optimized, but preferably 0.1 to 10% by mass in the mixture layer. More preferably, it is 0.5-5 mass%. If it is less than 0.1% by mass, the conductivity of the mixture layer cannot be ensured, and if it exceeds 10% by mass, the active material ratio decreases, and the unit mass of the mixture layer and the discharge capacity of the electricity storage device per unit volume are inadequate. It is not suitable for high capacity because it is sufficient.

Examples of the binder for the negative electrode include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinylpyrosidone (PVP), a copolymer of styrene and butadiene (SBR), and a copolymer of acrylonitrile and butadiene. Examples thereof include a polymer (NBR) and carboxymethyl cellulose (CMC). Although not particularly limited, the molecular weight of polyvinylidene fluoride is preferably 20,000 to 200,000. From the viewpoint of securing the binding property of the mixture layer, it is preferably 25,000 or more, more preferably 30,000 or more, and further preferably 50,000 or more. From the viewpoint of ensuring conductivity without hindering contact between the active material and the conductive agent, it is preferably 150,000 or less. In particular, when the specific surface area of the active material is 10 m ² / g or more, the molecular weight is preferably 100,000 or more.

  The addition amount of the binder varies depending on the specific surface area of the active material and the type and combination of the conductive aids, and therefore should be optimized. In the mixture layer, preferably 0.2 to 15% by mass. is there. From the viewpoint of enhancing the binding property and securing the strength of the mixture layer, it is preferably 0.5% by mass or more, more preferably 1% by mass or more, and further preferably 2% by mass or more. From the viewpoint of reducing the active material ratio and not reducing the unit mass of the mixture layer and the discharge capacity of the electricity storage device per unit volume, it is preferably 10% by mass or less, and more preferably 5% by mass or less.

  Examples of the negative electrode current collector include aluminum, stainless steel, nickel, copper, titanium, calcined carbon, and copper or stainless steel having a surface treated with carbon, nickel, titanium, or silver. Moreover, the surface of these materials may be oxidized, and an unevenness | corrugation may be given to the negative electrode collector surface by surface treatment. Examples of the form of the negative electrode current collector include a sheet, a net, a foil, a film, a punched one, a lath body, a porous body, a foamed body, a fiber group, and a nonwoven fabric molded body.

  The negative electrode is prepared by uniformly mixing a negative electrode active material (the active material of the present invention), a conductive agent and a binder in a solvent to form a paint, and then applying the mixture onto the negative electrode current collector, followed by drying and compression. Can be obtained by:

  As a method of uniformly mixing a negative electrode active material (active material of the present invention), a conductive agent and a binder in a solvent to form a paint, for example, while a stirring bar rotates in a kneading container such as a planetary mixer A revolving type kneader, a twin-screw extrusion type kneader, a planetary stirring and defoaming device, a bead mill, a high-speed swirling mixer, a powder suction continuous dissolution and dispersion device, and the like can be used. Moreover, as a manufacturing process, you may divide a process according to solid content concentration and use these apparatuses properly.

  In order to uniformly mix the negative electrode active material (the active material of the present invention), the conductive agent and the binder in the solvent, the specific surface area of the active material, the type of conductive auxiliary agent, the type of binder, and combinations thereof However, optimization should be performed, but a kneader of a type in which a stirring bar revolves in a kneading container such as a planetary mixer, a twin-screw extrusion kneader, a planetary stirring deaerator, etc. When used, it is preferable to divide the process according to the solid content concentration as a manufacturing process, knead in a state where the solid content concentration is high, and then gradually reduce the solid content concentration to adjust the viscosity of the paint. The state where the solid content concentration is high is preferably 60 to 90% by mass, and more preferably 70 to 90% by mass. If it is less than 60% by mass, a shearing force cannot be obtained, and if it exceeds 90% by mass, the load on the apparatus becomes large.

  The mixing procedure is not particularly limited, but a method in which the negative electrode active material, the conductive agent and the binder are mixed in the solvent at the same time, the conductive agent and the binder are mixed in advance in the solvent, and then the negative electrode active material And a method in which the negative electrode active material slurry, the conductive agent slurry, and the binder solution are prepared in advance and mixed together. Among these, in order to disperse uniformly, a method of additionally mixing the negative electrode active material after previously mixing the conductive agent and the binder in a solvent and the negative electrode active material slurry, the conductive agent slurry and the binder solution are prepared in advance, The method of mixing each is preferable.

  As the solvent, water or an organic solvent can be used. Examples of the organic solvent include aprotic organic solvents such as N-methylpyrrolidone, dimethylacetamide, and dimethylformamide, or a mixture of two or more kinds, preferably N-methylpyrrolidone.

  When water is used as the solvent, it is preferably added in the final viscosity adjustment step as a production step in order not to cause the binder to aggregate. In addition, when aluminum is used as the negative electrode current collector when the pH of the coating is high, corrosion of aluminum occurs. Therefore, it is preferable to add an acidic compound to lower the pH at which corrosion does not occur. As the acidic compound, either an inorganic acid or an organic acid can be used. As the inorganic acid, phosphoric acid, boric acid and oxalic acid are preferable, and oxalic acid is more preferable. The organic acid is preferably an organic carboxylic acid. When an organic solvent is used as the solvent, it is preferable to use the binder by dissolving it in an organic solvent in advance.

(Positive electrode)
The positive electrode has a mixture layer containing a positive electrode active material, a conductive agent, and a binder on one or both surfaces of the positive electrode current collector.

As the positive electrode active material, a material capable of inserting and extracting lithium is used. For example, as the active material, a composite metal oxide with lithium containing cobalt, manganese, nickel, lithium-containing olivine-type phosphate, or the like These positive electrode active materials can be used singly or in combination of two or more. Examples of such composite metal oxides include LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiCo _1-x Ni _x O ₂ (0.01 <x <1), LiCo _1/3 Ni _1/3 Mn. _1/3 O ₂ , LiNi _1/2 Mn _3/2 O _{4 and the} like. A part of these lithium composite oxides may be substituted with other elements, and a part of cobalt, manganese, nickel may be replaced with Sn. , Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, Cu, Bi, Mo, La, etc., or a part of O is replaced with S or F Alternatively, a compound containing these other elements can be coated. Examples of the lithium-containing olivine-type phosphate include LiFePO ₄ , LiCoPO ₄ , LiNiPO ₄ , LiMnPO ₄ , LiFe _1-x M _x PO ₄ (M is selected from Co, Ni, Mn, Cu, Zn, and Cd). At least one, and x is 0 ≦ x ≦ 0.5.

  Examples of the conductive agent and binder for the positive electrode include the same as those for the negative electrode. Examples of the positive electrode current collector include aluminum, stainless steel, nickel, titanium, calcined carbon, and aluminum or stainless steel having a surface treated with carbon, nickel, titanium, or silver. The surface of these materials may be oxidized, and the surface of the positive electrode current collector may be uneven by surface treatment. Examples of the shape of the current collector include a sheet, a net, a foil, a film, a punched one, a lath body, a porous body, a foamed body, a fiber group, and a nonwoven fabric molded body.

(Nonaqueous electrolyte)
The nonaqueous electrolytic solution is obtained by dissolving an electrolyte salt in a nonaqueous solvent. There is no restriction | limiting in particular in this non-aqueous electrolyte, A various thing can be used.

As the electrolyte salt, one that dissolves in a non-aqueous electrolyte is used. For example, an inorganic lithium salt such as LiPF ₆ , LiBF ₄ , LiPO ₂ F ₂ , LiN (SO ₂ F) ₂ , LiClO _4, or LiN (SO _{2). CF 3) 2, LiN (SO} 2 C 2 F 5) 2, LiCF 3 SO 3, LiC (SO 2 CF 3) 3, LiPF 4 (CF 3) 2, LiPF 3 (C 2 F 5) 3, LiPF 3 Lithium salts containing a chain-like fluorinated alkyl group such as (CF ₃ ) ₃ , LiPF ₃ (iso-C ₃ F ₇ ) ₃ , LiPF ₅ (iso-C ₃ F ₇ ), and (CF ₂ ) ₂ ( SO ₂ ) ₂ NLi, (CF ₂ ) ₃ (SO ₂ ) ₂ NLi and other lithium salts containing cyclic fluorinated alkylene chains, bis [oxalate-O, O ′] lithium borate and diflu Examples thereof include lithium salts using an oxalate complex such as oro [oxalate-O, O ′] lithium borate as an anion. Among these, particularly preferable electrolyte salts are LiPF ₆ , LiBF ₄ , LiPO ₂ F ₂ , and LiN (SO ₂ F) ₂ , and the most preferable electrolyte salt is LiPF ₆ . These electrolyte salts can be used singly or in combination of two or more.

  The concentration used by dissolving all the electrolyte salts is usually preferably 0.3 M or more, more preferably 0.5 M or more, and even more preferably 0.7 M or more with respect to the non-aqueous solvent. Moreover, the upper limit is preferably 2.5 M or less, more preferably 2.0 M or less, and even more preferably 1.5 M or less.

In addition, as a preferable combination of these electrolyte salts, LiPF ₆ is included, and one or more lithium salts selected from LiBF ₄ , LiPO ₂ F ₂ , and LiN (SO ₂ F) ₂ are non-aqueous electrolysis. This is the case when it is contained in the liquid. In the case of this combination, the effect of suppressing the resistance change before and after long-term storage at high temperature of the electricity storage device of the present invention is particularly great. Further, when the proportion of the lithium salt other than LiPF _{6 in the} non-aqueous solvent is 0.001M or more, the effect of suppressing the resistance change of the electricity storage device before and after long-term high-temperature charge storage is easily exhibited, and 1.0M The following is preferable because there is little concern that the effect of suppressing resistance change before and after long-term high-temperature charge storage is reduced. Preferably it is 0.01M or more, Especially preferably, it is 0.03M or more, Most preferably, it is 0.04M or more. The upper limit is preferably 0.8M or less, more preferably 0.6M or less, and particularly preferably 0.4M or less.

  Examples of the non-aqueous solvent include cyclic carbonates, chain esters, ethers, amides, phosphate esters, sulfones, lactones, nitriles, and S═O bond-containing compounds. The term “chain ester” is used as a concept including a chain carbonate and a chain carboxylic acid ester.

  The non-aqueous solvent is usually used as a mixture in order to achieve appropriate physical properties. The combination includes, for example, a combination of a cyclic carbonate and a chain carbonate, a combination of a cyclic carbonate, a chain carbonate and a lactone, a combination of a cyclic carbonate, a chain carbonate and an ether, a cyclic carbonate, a chain carbonate and a chain ester. Combinations, combinations of cyclic carbonates, chain carbonates, and nitriles, combinations of cyclic carbonates, chain carbonates, and S═O bond-containing compounds are included.

  Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 4-fluoro-1,3-dioxolan-2-one (FEC), trans or Cis-4,5-difluoro-1,3-dioxolan-2-one (hereinafter collectively referred to as “DFEC”), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and 4-ethynyl-1 , 3-dioxolan-2-one (EEC) or two or more selected from ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 4-fluoro-1,3 -Dioxolan-2-one and 4-ethynyl-1,3- One or more selected from oxolan-2-one (EEC) is more preferable from the viewpoint of enhancing the effect of suppressing resistance change before and after long-term high-temperature charge storage. Propylene carbonate, 1,2-butylene carbonate and 2 One or more cyclic carbonates having a branched alkylene group selected from 1,3-butylene carbonate are more preferred.

  The ratio of the cyclic carbonate having an alkylene chain in the total cyclic carbonate is preferably 55% by volume to 100% by volume, and more preferably 60% by volume to 90% by volume.

  As the chain ester, one or more asymmetric chain carbonates selected from methyl ethyl carbonate (MEC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC), methyl butyl carbonate, and ethyl propyl carbonate, One or more symmetrical linear carbonates selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, and dibutyl carbonate, pivalate esters such as methyl pivalate, ethyl pivalate, and propyl pivalate Preferable examples include one or more chain carboxylic acid esters selected from methyl propionate, ethyl propionate, propyl propionate, methyl acetate, and ethyl acetate (EA).

  Among the chain esters, chain esters having a methyl group selected from dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, methyl propionate, methyl acetate and ethyl acetate (EA) are preferable. In particular, a chain carbonate having a methyl group is preferred.

  Moreover, when using chain carbonate, it is preferable to use 2 or more types. Further, it is more preferable that both a symmetric chain carbonate and an asymmetric chain carbonate are contained, and it is further more preferable that the content of the symmetric chain carbonate is more than that of the asymmetric chain carbonate.

  The content of the chain ester is not particularly limited, but it is preferably used in the range of 60 to 90% by volume with respect to the total volume of the nonaqueous solvent. If the content is 60% by volume or more, the viscosity of the non-aqueous electrolyte does not become too high, and if it is 90% by volume or less, the electrical conductivity of the non-aqueous electrolyte is decreased, The above range is preferable because there is little possibility that the resistance change suppressing effect is reduced.

  The volume ratio of the symmetric chain carbonate in the chain carbonate is preferably 51% by volume or more, and more preferably 55% by volume or more. The upper limit is more preferably 95% by volume or less, and still more preferably 85% by volume or less. It is particularly preferred that the symmetric chain carbonate contains dimethyl carbonate. The asymmetric chain carbonate preferably has a methyl group, and methyl ethyl carbonate is particularly preferable. In the above case, it is preferable because the effect of suppressing the resistance change before and after long-term high-temperature charge storage is improved.

  The ratio between the cyclic carbonate and the chain ester is preferably 10:90 to 45:55 in terms of the cyclic carbonate: chain ester (volume ratio) from the viewpoint of enhancing the effect of suppressing resistance change before and after long-term storage at high temperature. 85-40: 60 is more preferable, and 20: 80-35: 65 is particularly preferable.

(Lithium battery structure)
The structure of the lithium battery of the present invention is not particularly limited, and a coin-type battery having a positive electrode, a negative electrode, and a single-layer or multi-layer separator, and a cylindrical battery and a corner having a positive electrode, a negative electrode, and a roll separator. An example is a type battery.

  As the separator, an insulating thin film having a large ion permeability and a predetermined mechanical strength is used. For example, polyethylene, polypropylene, cellulose paper, glass fiber paper, polyethylene terephthalate, polyimide microporous film and the like can be mentioned, and a multilayer film constituted by combining two or more kinds can also be used. In addition, the surfaces of these separators can be coated with resin such as PVDF, silicon resin, rubber-based resin, particles of metal oxide such as aluminum oxide, silicon dioxide, and magnesium oxide. The pore diameter of the separator may be in a range generally useful for batteries, for example, 0.01 to 10 μm. The thickness of the separator may be in a general battery range, and is, for example, 5 to 300 μm.

  Next, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the following examples, and includes various combinations that can be easily inferred from the gist of the invention. In particular, it is not limited to the solvent combinations of the examples.

(Various physical property measurement methods)
(1) XRD
In the present invention, X-ray diffraction measurement was performed on the powder in which the surface layer was removed from the lithium titanate powder of the present invention. The surface layer was removed as follows. The lithium titanate powder of the present invention is put into a container containing ion-exchanged water having a mass 10 times that of the lithium titanate powder of the present invention having the surface layer on the particle surface, and sufficient using an ultrasonic dispersing device. The mixture was stirred and filtered using a filter having a pore size of 0.1 μm. This process was repeated 5 times. The fact that the lithium titanate powder after 5 times of treatment does not contain lithium methanesulfonate indicates that no endothermic reaction accompanying melting and evaporation of lithium methanesulfonate is observed from the measurement results of TG-DTA from room temperature to 600 ° C. Confirmed by that. X-ray diffraction measurement of the lithium titanate powder obtained as described above was performed using an X-ray diffraction apparatus (RINT-TTR-III, manufactured by Rigaku Corporation) using CuKα rays as a measurement apparatus. . The measurement conditions are: measurement angle range (2θ): 10 ° to 90 °, step interval: 0.02 °, measurement time: 0.25 seconds / step, radiation source: CuKα ray, tube voltage: 50 kV, current : 300 mA.

The main peak intensity of Li ₄ Ti ₅ O ₁₂ (peak intensity derived from the (111) plane (diffraction angle 2θ = 18.1 to 18.5 °)), the main peak intensity of rutile titanium dioxide (diffraction angle 2θ) = 27.2-27.6 ° peak intensity), and main peak intensity of anatase titanium dioxide (from (110) plane (diffraction angle 2θ = 24.7-25.7 ° range)) Peak intensity) was measured. Also the calculation of _Li 2 TiO ₃ and (-133) main peak intensity of _Li 2 TiO ₃ is multiplied by 100/80 on surface derived peak intensity ((002) intensity of the peak of the corresponding surface). The peak intensity derived from the (−133) plane of Li ₂ TiO ₃ (diffraction angle 2θ = in the range of 43.5 to 43.8 °) was measured.

Then, the calculation of when the main peak intensity of the lithium titanate and 100, the rutile type titanium dioxide, anatase titanium dioxide, and the relative value of the peak intensity of Li ₂ TiO _3.

(2) Crystallite diameter (D _X )
The crystallite diameter (D _X ) of the lithium titanate powder of the present invention was measured using the same X-ray diffraction measurement apparatus as that of the above-mentioned XRD, and the measurement conditions were the measurement angle range (2θ): 15.8 ° to 21.0. °, step interval: 0.01 °, measurement time: 1 second / step, radiation source: CuKα ray, tube voltage: 50 kV, current: 300 mA peak width at half maximum of (111) plane of lithium titanate From the Scherrer equation, that is, the following equation (1). In calculating the half width, it is necessary to correct the line width by the optical system of the diffractometer, and silicon powder was used for this correction.
D _X = K · λ / (FW (S) · cos θ _c ) (1)
FW (S) ^ D = FWHM ^ D-FW (I) ^ D
FW (I) = f0 + f1 × (2θ) + f2 × (2θ) ²
θ _c = (t0 + t1 × (2θ) + t2 (2θ) ² ) / 2
K: Scherrer constant (0.94)
λ: wavelength of CuKα ₁ line (1.54059 mm)
FW (S): Sample-specific half-width (FWHM)
FW (I): Device-specific half-width (FWHM)
D: Deconvolution parameter (1.3)
f0 = 5.108673E-02
f1 = 1.058424E-04
f2 = 6.871481E-06
θ _c : Bragg angle correction value t0 = −3,000E-03
t1 = 5.119E-04
t2 = −3.599E-06

(3) BET specific surface area (m ² / g)
In the present invention, the specific surface area was also measured in the state where the surface layer was removed from the lithium titanate powder of the present invention, as in the case of the X-ray diffraction measurement described above. The obtained BET specific surface area with the surface layer removed from the lithium titanate powder of the present invention uses a fully automatic BET specific surface area measuring device manufactured by Mountec Co., Ltd., trade name “Macsorb HM model-1208”. Then, it was measured by a one-point method using liquid nitrogen.

(4) BET diameter (D _BET )
The BET diameter (D _BET ) in a state where the surface layer is removed from the lithium titanate powder of the present invention is obtained from the following formula (2) assuming that all particles constituting the powder are spheres having the same diameter. It was.
D _BET = 6 / (ρ _S × S) (2)

Here, D _BET is the BET diameter (μm), ρ _S is the true density of lithium titanate (g / cc), and S is measured by the method described in (3) BET specific surface area (m ² / g). BET specific surface area (m ² / g) in a state where the surface layer is removed from the lithium titanate powder of the present invention obtained.

(5) Total pore volume In the present invention, the total pore volume in a state where the surface layer is removed from the lithium titanate powder of the present invention is used as a measuring device, and a high performance fully automatic gas adsorption measuring device AC1-iQ. (Manufactured by QUANTACHROME) was measured by a gas adsorption method using nitrogen gas as an adsorption gas as follows. 1 g of lithium titanate powder was weighed and placed in a measurement cell (large cell with a stem diameter of 6 mmφ), and deaerated under vacuum at 200 ° C. for 15 hours as a pretreatment. Then, using the said apparatus, the fully automatic gas adsorption amount measurement by the constant volume method was performed, and the total pore volume was measured. The method for removing the surface layer is the same as the method for removing the surface layer described in (3) BET specific surface area (m ² / g).

(6) Particle size distribution For measurement of the particle size distribution of the powder according to the present invention, a laser diffraction / scattering particle size distribution measuring machine (Nikkiso Co., Ltd., Microtrac MT3300EXII) was used. For adjustment of the measurement sample, ethanol was used as a measurement solvent in the case of mixed powder, and ion-exchanged water was used in the case of lithium titanate powder. When the measurement sample is in powder form, about 50 mg of the sample is put into 50 ml of the measurement solvent, and further 1 cc of 0.2% sodium hexametaphosphate aqueous solution as a surfactant is added, and the obtained measurement slurry is ultrasonicated. Processed with a disperser. In the case where the measurement sample was a mixed slurry made of mixed powder, the method was the same as that in the case where the measurement sample was powdery, except that about 50 mg of the sample in terms of powder was added. Subsequent operations were the same regardless of the measurement sample. The measurement slurry subjected to the dispersion treatment was accommodated in a measurement cell, and a measurement solvent was added to adjust the slurry concentration. The particle size distribution was measured when the transmittance of the slurry was within an appropriate range. D95 of the mixed powder was calculated from the obtained particle size distribution curve.

Example 1
<Manufacture of lithium titanate powder>
Raw material obtained by weighing Li ₂ CO ₃ (average particle diameter 4.6 μm) and anatase TiO ₂ (average particle diameter 0.6 μm) so that the atomic ratio Li / Ti of Ti to Ti is 0.81. Ion exchange water was added to the powder and stirred so that the solid content concentration of the slurry was 41% by mass to prepare a raw material slurry. Using this raw material slurry, beads beads (outer diameter: 0.65 mm) using a bead mill (manufactured by Willy et Bacofen, model: dyno mill KD-20BC type, agitator material: polyurethane, vessel inner surface material: zirconia). ) In 80% by volume of the vessel, the agitator peripheral speed is 13 m / s, the slurry feed speed is 55 kg / hr, and the vessel internal pressure is controlled so as to be 0.02 to 0.03 MPa or less. Wet mixing and pulverization were performed to prepare a raw material mixed slurry. D95 of the obtained raw material mixed slurry was 0.75 μm.

  Using the rotary kiln type firing furnace (furnace core tube length: 4 m, furnace core tube diameter: 30 cm, external heating type) equipped with an adhesion prevention mechanism, the obtained raw material mixed slurry is put into the core tube from the raw material supply side of the firing furnace. It was introduced, dried in a nitrogen atmosphere, and fired. At this time, assuming that the inclination angle from the horizontal direction of the core tube is 2 degrees, the rotation speed of the core tube is 20 rpm, the flow rate of nitrogen introduced into the core tube from the fired product collection side is 20 L / min, and the heating temperature of the core tube is The raw material supply side: 600 ° C., the central part: 900 ° C., the fired product recovery side: 900 ° C., and the holding time of the fired product at 900 ° C. was 26 minutes. Using a hammer mill (Dalton, AIIW-5 type), the fired product collected from the fired product collection side of the furnace core tube was screen-opened: 0.5 mm, rotation speed: 8,000 rpm, powder feed speed: Crushing was performed at 25 kg / hr to obtain a fired powder (lithium titanate powder before surface treatment).

  Next, the obtained fired powder and lithium methanesulfonate were mixed as follows. A solvent prepared by dissolving lithium methanesulfonate in an amount such that lithium methanesulfonate / calcined powder becomes 1/99 by mass ratio in ion exchange water in an amount such that water / calcined powder becomes 40/60 by mass ratio. The whole amount of the obtained fired powder was added and stirred. Using this slurry, beads beads (outer diameter: 0.65 mm) are made using a bead mill (made by Willy et Bacofen, model: dyno mill KD-20BC type, agitator material: polyurethane, vessel inner surface material: zirconia). In a vessel at a volume of 13 m / s, a slurry feed speed of 55 kg / hr, and controlled so that the internal pressure of the vessel is 0.02 to 0.03 MPa or less. A mixed slurry was prepared by wet mixing with lithium sulfonate.

  The obtained mixed slurry was sprayed and dried using a spray dryer (L-8i, manufactured by Okawara Chemical Co., Ltd.) at an atomizer rotational speed of 25000 rpm and an inlet temperature of 210 ° C., and the lithium methanesulfonate of Example 1 A lithium titanate powder having a content ratio of 1% by mass was obtained.

  The obtained lithium titanate powder was subjected to cross-sectional TOF-SIMS analysis and cross-sectional EDX analysis. As a result, it was confirmed that a surface layer containing sulfur was formed on the entire surface of the lithium titanate powder. Moreover, the component of the surface layer containing sulfur was identified as lithium methanesulfonate from the results of TOF-SIMS and XPS. The obtained lithium titanate powder was measured for various physical properties by the method described in [Methods for measuring various physical properties]. The results are as shown in Table 1.

<Production of battery and evaluation of its characteristics>
Using the lithium titanate powder of Example 1, a laminate-type lithium ion secondary battery (hereinafter sometimes referred to as a laminate-type battery) was produced as follows, and the battery characteristics were evaluated.

[Production of evaluation electrode sheet]
The coating composition was prepared by mixing 90% by mass of the lithium titanate powder of Example 1 as an active material, 5% by mass of acetylene black as a conductive agent, and 5% by mass of polyvinylidene fluoride as a binder as follows. Produced. Polyvinylidene fluoride, acetylene black and 1-methyl-2-pyrrolidone solvent previously dissolved in a 1-methyl-2-pyrrolidone solvent are mixed with a planetary stirring deaerator, then lithium titanate powder is added, and the whole solid It prepared so that a partial concentration might be 64 mass%, and it mixed with the planetary stirring deaerator. Thereafter, a 1-methyl-2-pyrrolidone solvent was added to prepare a total solid content concentration of 56% by mass and mixed with a planetary stirring deaerator to prepare a paint. The obtained coating material was applied onto an aluminum foil and dried, and then subjected to pressure treatment and cut into a predetermined size to produce an evaluation electrode sheet. The following lithium ion secondary battery (lithium ion secondary battery of the present invention) ) Negative electrode. The density of the portion excluding the current collector of the evaluation electrode (negative electrode) sheet was 2.0 g / cm ³ .

[Production of lithium ion secondary battery]
94% by mass of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ powder as an active material, 3% by mass of acetylene black as a conductive agent, and 3% by mass of polyvinylidene fluoride as a binder, The paint was prepared by mixing as described above. Polyvinylidene fluoride, acetylene black, and 1-methyl-2-pyrrolidone solvent previously dissolved in a 1-methyl-2-pyrrolidone solvent were mixed with a planetary stirring deaerator, and then LiNi _1/3 Mn _1/3 Co _1/3 O ₂ powder was added to prepare a total solid content concentration of 64% by mass, and the mixture was mixed in a planetary stirring deaerator. Thereafter, a 1-methyl-2-pyrrolidone solvent was added to prepare a total solid content concentration of 56% by mass and mixed with a planetary stirring deaerator to prepare a paint. This positive electrode mixture paste was applied to one side of an aluminum foil (current collector), dried and pressurized, and cut into a predetermined size to produce a belt-like positive electrode sheet. The density of the portion excluding the current collector of the positive electrode was 3.6 g / cm ³ . LiPF ₆ was dissolved in a solvent in which propylene carbonate (PC), methyl ethyl carbonate (MEC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 30:30:40 so as to be 1.1 mol / L, and non-aqueous. An electrolyte was used. Then, a positive electrode sheet, a microporous polyethylene film separator, and the negative electrode sheet were laminated in this order, and a non-aqueous electrolyte was added to produce a laminate type battery.

[Evaluation of long-term high-temperature storage characteristics]
Using the laminate type battery, the long-term high-temperature storage characteristics were evaluated as follows.

<Measurement of initial impedance>
Using the laminate battery, the battery was charged with a constant current and a constant voltage of 0.2 C for 3 hours to a final voltage of 2.55 V in a constant temperature bath at 25 ° C., and the impedance was measured at 1 kHz in the charged state.

<Measurement of impedance increase rate after long-term storage at high temperature>
After the initial impedance measurement, the battery was charged in a constant temperature bath at 60 ° C. with a constant current and constant voltage of 0.2 C for 3 hours to a final voltage of 2.7 V, and stored for 8 weeks (1344 hours) in that charged state. went. After storage, the battery was discharged at a constant current of 0.2 C to a final voltage of 1.0 V, then charged at a constant current of 0.2 C and a constant voltage to a final voltage of 2.0 V for 3 hours, and the impedance was measured at 1 kHz in the charged state. . After the measurement, the rate of increase in impedance (%) due to storage was determined by the following equation (3). The results are shown in Table 1.
Impedance increase rate (%) = [(impedance after 8 weeks storage−initial impedance) ÷ impedance after 8 weeks storage] × 100 (3)

(Example 2)
In a solvent in which propylene carbonate (PC), methyl ethyl carbonate (MEC), and dimethyl carbonate (DMC) are mixed at a volume ratio of 30:30:40, LiPF ₆ is 1.0 mol / L, and LiPO ₂ F ₂ is 0.00. A laminate type battery was prepared in the same manner as in Example 1 except that it was dissolved to 1 mol / L to obtain a non-aqueous electrolyte, and its long-term high-temperature storage characteristics were evaluated. The results are shown in Table 1.

(Example 3)
Example 1 except that lithium methanesulfonate and calcined powder (lithium titanate powder before surface treatment) were mixed so that the mass ratio of lithium methanesulfonate / calcined powder was 1/99. Similarly, lithium titanate powder having a lithium methanesulfonate content of 0.1% by mass was obtained. It was confirmed in the same manner as in Example 1 that the obtained lithium titanate powder had a surface layer of lithium methanesulfonate on the particle surface. In the same manner as in Example 1, a battery was produced and its long-term high-temperature storage characteristics were evaluated. The results are shown in Table 1.

Example 4
Example 1 except that lithium methanesulfonate and calcined powder (lithium titanate powder before surface treatment) were mixed so that the lithium methanesulfonate / calcined powder had a mass ratio of 5/95. Similarly, a lithium titanate powder having a lithium methanesulfonate content of 5% by mass was obtained. It was confirmed in the same manner as in Example 1 that the obtained lithium titanate powder had a surface layer of lithium methanesulfonate on the particle surface. In the same manner as in Example 1, a battery was produced and its long-term high-temperature storage characteristics were evaluated. The results are shown in Table 1.

(Example 5)
Example 1 except that lithium methanesulfonate and calcined powder (lithium titanate powder before surface treatment) were mixed so that the mass ratio of lithium methanesulfonate / calcined powder was 12/88. Similarly, a lithium titanate powder having a lithium methanesulfonate content of 12% by mass was obtained. The obtained lithium titanate powder had a surface layer of lithium methanesulfonate on the particle surface, and the content ratio of lithium methanesulfonate in the lithium titanate powder was confirmed in the same manner as in Example 1. In the same manner as in Example 1, a battery was produced and its long-term high-temperature storage characteristics were evaluated. The results are shown in Table 1.

(Example 6)
Example 1 except that the heating temperature of the core tube of the rotary kiln-type firing furnace was set to 600 ° C. on the raw material supply side, 780 ° C. in the center, and 780 ° C. on the fired product recovery side, and the raw material mixed slurry was dried and fired. In the same manner as above, a lithium titanate powder having a lithium methanesulfonate content of 1% by mass was obtained. It was confirmed in the same manner as in Example 1 that the obtained lithium titanate powder had lithium methanesulfonate on the particle surface. In the same manner as in Example 1, a battery was produced and its long-term high-temperature storage characteristics were evaluated. The results are shown in Table 1.

(Example 7)
The raw material mixture to be baked is Li ₂ CO ₃ (average particle size 2.1 μm) and anatase TiO ₂ (average particle size 0.6 μm, rutile ratio 1% by mass), the atomic ratio of Li to Ti Li / Ti : Weighed to 0.83 and mixed for 20 minutes with a Henschel mixer type mixer to prepare a raw material mixed powder with D95 of 8.02 μm, and this raw material mixed powder was made of high-purity alumina. Except that it was filled in a made sagger and heated in an air atmosphere with a residence time at 700 to 900 ° C. as 60 minutes and held at 900 ° C. for 3 hours and then fired in a muffle-type electric furnace. In the same manner as in Example 1, a lithium titanate powder having a lithium methanesulfonate content of 1% by mass was obtained. It was confirmed in the same manner as in Example 1 that the obtained lithium titanate powder had lithium methanesulfonate on the particle surface. In the same manner as in Example 1, a battery was produced and its long-term high-temperature storage characteristics were evaluated. The results are shown in Table 1.

(Comparative Example 1)
Except that the fired powder obtained in Example 1 (lithium titanate powder before surface treatment) was not mixed with lithium methanesulfonate as it was as an active material for the negative electrode, but a laminate type battery was produced. In the same manner as in Example 1, a battery was produced and its long-term high-temperature storage characteristics were evaluated. The results are shown in Table 1.

(Comparative Example 2)
Lithium sulfate was obtained in the same manner as in Example 1 except that the calcined powder obtained in Example 1 (lithium titanate powder before surface treatment) was mixed with lithium sulfate instead of lithium methanesulfonate. A lithium titanate powder having a content ratio of 1% by mass was obtained. It was confirmed in the same manner as in Example 1 that the obtained lithium titanate powder had lithium sulfate on the particle surface. In the same manner as in Example 1, a battery was produced and its long-term high-temperature storage characteristics were evaluated. The results are shown in Table 1.

(Comparative Example 3)
Lithium sulfate was obtained in the same manner as in Example 1 except that the calcined powder obtained in Example 7 (lithium titanate powder before surface treatment) was mixed with lithium sulfate instead of lithium methanesulfonate. A lithium titanate powder having a content ratio of 1% by mass was obtained. It was confirmed in the same manner as in Example 1 that the obtained lithium titanate powder had lithium sulfate on the particle surface. In the same manner as in Example 1, a battery was produced and its long-term high-temperature storage characteristics were evaluated. The results are shown in Table 1.

(Comparative Example 4)
Phosphorous powder obtained in Example 1 (lithium titanate powder before surface treatment) was mixed with lithium phosphate instead of lithium methanesulfonate in the same manner as in Example 1, except that A lithium titanate powder having a lithium acid content of 1% by mass was obtained. It was confirmed in the same manner as in Example 1 that the obtained lithium titanate powder had lithium phosphate on the particle surface. In the same manner as in Example 1, a battery was produced and its long-term high-temperature storage characteristics were evaluated. The results are shown in Table 1.

(Comparative Example 5)
The calcined powder obtained in Example 1 (lithium titanate powder before surface treatment) was replaced with lithium methanesulfonate, and a mixture of lithium sulfate and lithium phosphate was used. The content ratio of lithium sulfate and lithium phosphate was the same as in Example 1 except that the mixture was mixed so that the lithium sulfate / lithium phosphate / calcined powder was 0.5 / 0.5 / 99 by mass ratio. 0.5% by mass of lithium titanate powder was obtained. It was confirmed in the same manner as in Example 1 that the obtained lithium titanate powder had lithium sulfate and lithium phosphate on the particle surface. In the same manner as in Example 1, a battery was produced and its long-term high-temperature storage characteristics were evaluated. The results are shown in Table 1.
(Comparative Example 6)
Except that the fired powder obtained in Example 1 (lithium titanate powder before surface treatment) was not mixed with lithium methanesulfonate as it was as an active material for the negative electrode, but a laminate type battery was produced. In the same manner as in Example 2, a battery was produced and its long-term high-temperature storage characteristics were evaluated. The results are shown in Table 1.

  From the results of Examples and Comparative Examples, lithium titanate powder having a surface layer of lithium methanesulfonate on at least a part of the particle surface is obtained by using lithium titanate powder having no surface layer, lithium sulfate and / or phosphorus. It was found that the rate of increase in impedance after storage at 60 ° C. for a long period (8 weeks) was extremely small as compared with lithium titanate powder having a lithium oxide surface layer.

  When the lithium titanate powder of the present invention is used as an active material for an electrode of a power storage device, the power storage device of the present invention can be provided that has an extremely excellent effect of suppressing resistance change before and after long-term storage at high temperature. The electricity storage device of the present invention is particularly suitable as an electricity storage device such as a lithium secondary battery mounted in a hybrid electric vehicle, a plug-in hybrid electric vehicle, a battery electric vehicle or the like.

Claims (10)

Lithium titanate powder containing Li ₄ Ti ₅ O ₁₂ as a main component, and having a surface layer containing a lithium sulfonate compound represented by the following general formula (I) on at least a part of the particle surface A lithium titanate powder for an electrode of an electricity storage device, which is characterized.
(In the formula, R represents an alkyl group having 1 to 5 carbon atoms or an aryl group having 6 to 12 carbon atoms.)   The lithium titanate powder for an electrode of an electricity storage device according to claim 1, wherein a content ratio of the lithium sulfonate compound in the lithium titanate powder is 0.1 mass% to 10 mass%.   3. The titanium for electrodes of an electricity storage device according to claim 1, wherein the total pore volume in a state where the surface layer is removed from the lithium titanate powder is 0.03 to 0.5 ml / g. Lithium acid powder. The specific surface area equivalent diameter calculated from the specific surface area of the lithium titanate powder from which the surface layer has been removed is defined as D _{BET. In the} lithium titanate powder, the peak of the (111) plane of Li ₄ Ti ₅ O ₁₂ When the crystallite diameter calculated from Scherrer's formula from the half width is D _X , D _BET is 0.1 to 0.6 μm, D _X is larger than 80 nm, and the ratio D _BET between D _BET and D _X 4. The lithium titanate powder for an electrode of an electricity storage device according to claim 1, wherein / D _X (μm / μm) is 3 or less. In the peak intensity obtained by X-ray diffraction measurement of the lithium titanate powder, when the intensity of the peak derived from the (111) plane of Li ₄ Ti ₅ O ₁₂ is taken as 100, it is derived from the (101) plane of anatase titanium dioxide. The sum of the values calculated by multiplying 100/80 by the intensity of the peak, the intensity of the peak derived from the (110) plane of rutile titanium dioxide, and the intensity of the peak derived from the (-133) plane of Li ₂ TiO ₃ is It is 1 or less, The lithium titanate powder for electrodes of the electrical storage device as described in any one of Claims 1-4 characterized by the above-mentioned.   The active material material containing the lithium titanate powder for electrodes of the electrical storage device as described in any one of Claims 1-5.   An electricity storage device comprising an electrode, a non-aqueous electrolyte, and a separator, wherein the electrode includes the active material according to claim 6. The non-aqueous electrolyte contains LiPF ₆ and further contains one or more selected from the group consisting of LiBF ₄ , LiPO ₂ F ₂ , and LiN (SO ₂ F) _2. The electricity storage device described in 1.   The power storage device according to claim 7 or 8, wherein the power storage device is a lithium ion secondary battery.   The power storage device according to claim 7 or 8, wherein the power storage device is a hybrid capacitor.