Lithium titanate powder, electrodes using the same, and electricity storage devices

Abstract

To provide lithium titanate powder, which is used as an electrode material for an electric storage device and is excellent in maintaining electrode density, volumetric energy density, rate characteristics, initial low-temperature input characteristics, and charge rate characteristics after storage at a high temperature in a balanced manner, and provide an electrode using the same and an electric storage device.SOLUTION: Lithium titanate powder consists mainly of Li4Ti5O12, wherein aluminum (Al) is locally present on the surface of primary particles of the lithium titanate powder, the aluminum content of the lithium titanate powder is 0.2 mass%, and the following formula (I) is satisfied: log10(D90)-log10(D10)<0.8 (I) (D90 denotes a particle size at the point where the cumulative volume distribution of particle size is 90% in the particle size distribution, and D10 denotes a particle size at the point where the cumulative volume distribution of particle size is 10% in the particle size distribution).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a lithium titanate powder suitable as an electrode material for an electricity storage device, an electrode using the same, and an electricity storage device. [Background technology]

[0002] In recent years, various materials have been studied as electrode materials for energy storage devices. Among these, lithium titanate has attracted attention as an active material for energy storage devices in electric vehicles (HEVs, PHEVs, and BEVs) due to its excellent input / output characteristics.

[0003] Energy storage devices for electric vehicles require high energy density to improve fuel economy and power consumption. In addition, stability over a wide temperature range, from high to low, is also important. For example, in cold winter regions, guaranteed operational performance is required down to temperatures below -20°C. Lithium titanate, with its excellent initial input / output characteristics, is a promising candidate electrode material for these applications. However, since temperatures inside automobiles can reach 60°C or higher in summer, it is essential that the device remains safe and maintains its performance even at high temperatures. Energy storage devices containing lithium titanate are known to have storage stability issues, such as gas generation, when used for long periods at temperatures above 60°C, leading to an increase in battery resistance and changes in long-term input / output characteristics. Therefore, there is a need for lithium titanate that can increase the energy density of energy storage devices while maintaining its excellent initial input / output characteristics and suppressing gas generation and resistance increases after long-term high-temperature operation.

[0004] Patent Document 1 describes the specific surface area equivalent diameter DBET and crystallite diameter D calculated from the specific surface area obtained by the BET method. Xis specified within a certain range, and contains at least one localized element selected from M (M is at least one metal element selected from Mg, Zn, Al, Ga, or In), the element being localized near the surface of the lithium titanate particles. Patent Document 1 discloses a lithium titanate powder that, when used as an electrode material for an electricity storage device, not only has a large initial charge / discharge capacity and excellent input / output characteristics, but also exhibits an extremely high charge / discharge capacity at an extremely low temperature of -30°C.

[0005] Patent Document 2 describes lithium titanate using anatase-type titanium dioxide with a purity of 95% by mass or more as a raw material, Li4Ti5O 12 Patent Document 2 discloses a lithium titanate powder for electrodes, which is mainly composed of , has an average particle size of 0.5 to 1.5 μm, a maximum particle size of 25 μm or less, and an SD value ((D84%-D16%) / 2) shown by particle size distribution of 0.5 μm or less. Patent Document 2 discloses an electricity storage device that can increase the discharge capacity during large current discharge by controlling the particle size and particle size distribution.

[0006] Patent Document 3 discloses a lithium-titanium composite oxide containing primary particles coated with aluminum. According to Patent Document 3, the decomposition of the electrolyte and the residual lithium It is disclosed that this has the effect of suppressing gas generation. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 5790894 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-137547 [Patent Document 3] Special Publication No. 2021-516208 Summary of the Invention [Problem to be solved by the invention]

[0008] However, while Patent Document 1 discloses that the energy storage device using lithium titanate as the anode material exhibits excellent initial input / output characteristics, it does not disclose any information regarding electrode density, nor does it provide any insight into achieving both initial input / output characteristics and volumetric energy density. The benefits of increasing electrode density include making the battery itself lighter and smaller, thereby reducing the proportion of the battery in electronic devices and vehicle components, significantly increasing the design flexibility of electronic devices. In the case of large battery applications, this eliminates the need for battery space, leading to improved energy density per unit volume, which can extend the driving range of electric vehicles and secure storage battery installation space, as well as reducing electrode contact resistance within the battery. Additionally, it was found that further suppression of gas generation after high-temperature storage and suppression of resistance increases after cycle testing are necessary.

[0009] The lithium titanate powder in Patent Document 2, in which the particle size and particle size distribution are specified within a certain range, does not include any description of suppressing gas generation or resistance increase during high-temperature operation, nor of input / output characteristics at low temperatures. It was also found that there are issues with achieving a balance with volumetric energy density.

[0010] Furthermore, although Patent Document 3 describes rate characteristics and the amount of gas generated after high-temperature storage, it does not describe an increase in resistance after high-temperature storage or battery performance at low temperatures, and does not disclose any knowledge regarding compatibility with improved electrode density.

[0011] For the reasons described above, the electricity storage devices using the negative electrode active materials and electrodes of Patent Documents 1 to 3 cannot simultaneously improve the electrode density of the negative electrode, which is directly linked to the energy density, while maintaining the initial excellent input / output characteristics and suppressing gas generation and resistance increase during high-temperature operation.

[0012] Therefore, in the present invention, the present invention is used as an electrode material for an electricity storage device, and is excellent in maintaining a good balance of electrode density, volumetric energy density, rate characteristics, initial low-temperature input characteristics, and charge rate characteristics after high-temperature storage. For example, the present invention provides an electrode material having an electrode density of 1.98 g / cm 3 The objective of the present invention is to provide a lithium titanate powder having battery characteristics such as a volumetric energy density of 334 mAh / g or more, a 50C rate characteristic of 74% or more, an initial low-temperature input characteristic of 46% or more, and a charge rate characteristic after high-temperature storage of 93% or more, an electrode using the same, and an electricity storage device. [Means for solving the problem]

[0013] As a result of extensive investigations to achieve the above-mentioned object, the inventors have discovered a lithium titanate powder in which Al is locally present on the primary particle surface at a content of 0.2 mass% or more and which has a specific particle size distribution, by controlling the calcination temperature of the lithium titanate powder, the crushing process in the post-treatment step after calcination, the amount of aluminum (Al) added in the surface treatment step, etc. Electricity storage devices in which this lithium titanate powder is used as an electrode material are excellent in maintaining a good balance of electrode density, volumetric energy density, rate characteristics, initial low-temperature input characteristics, and charge rate characteristics after high-temperature storage, and for example, an electrode density of 1.98 g / cm 3 As described above, the inventors have found that the battery has battery characteristics such as a volumetric energy density of 334 mAh / g or more, a 50C rate characteristic of 74% or more, an initial low-temperature input characteristic of 46% or more, and a charge rate characteristic after high-temperature storage of 93% or more, and have completed the present invention.

[0014] (1) Li4Ti5O 12 a lithium titanate powder having as its main component aluminum (Al) locally present on the surfaces of primary particles of the lithium titanate powder, an aluminum content of the lithium titanate powder being 0.2 mass% or more, and satisfying the following formula (I): log 10 (D 90 )-log 10 (D 10) < 0.8 (I) (Note: D 90 D indicates the particle size at which the cumulative volume distribution of the particle size of primary particles is 90% in the particle size distribution. 10 indicates the particle size at which the cumulative volume distribution of the particle size of primary particles is 10% in the particle size distribution.

[0015] (2) The lithium titanate powder according to (1) above, which satisfies the following formula (II): log 10 (D 90 )-log 10 (D 10 ) < 0.7 (II) (Note: D 90 D indicates the particle size at which the cumulative volume distribution of the particle size of primary particles is 90% in the particle size distribution. 10 indicates the particle size at which the cumulative volume distribution of the particle size of primary particles is 10% in the particle size distribution.

[0016] (3) The particle size D of the primary particles that corresponds to 50% of the cumulative volume in the particle size distribution 50 The lithium titanate powder according to (1) or (2) above, characterized in that the particle size is 0.5 μm or more.

[0017] (4) The lithium titanate powder according to (3) above, which contains primary particles and secondary particles of lithium titanate and satisfies the following formula (III): D of primary particles 50 / D of secondary particles 50 ≦ 0.05 (III)

[0018] (5) The lithium titanate powder has a specific surface area of ​​6 m 2 / g or more.

[0019] (6) An electrode comprising the lithium titanate powder according to any one of (1) to (5).

[0020] (7) An electricity storage device comprising the electrode according to (6) above. [Effects of the Invention]

[0021] According to the present invention, it is possible to maintain a good balance among electrode density, volumetric energy density, rate characteristics, initial low-temperature input characteristics, and charge rate characteristics after high-temperature storage. For example, when the electrode density is 1.98 g / cm 3 As described above, it is possible to provide a lithium titanate powder suitable as an electrode material for an electricity storage device having battery characteristics of a volumetric energy density of 334 mAh / g or more, a 50C rate characteristic of 74% or more, an initial low-temperature input characteristic of 46% or more, and a charge rate characteristic after high-temperature storage of 93% or more, as well as an electrode and an electricity storage device using the same. DETAILED DESCRIPTION OF THE INVENTION

[0022] [Lithium titanate powder of the present invention] The lithium titanate powder of the present invention is Li4Ti5O 12 a lithium titanate powder having as its main component aluminum (Al) locally present on the surfaces of primary particles of the lithium titanate powder, an aluminum content of the lithium titanate powder being 0.2 mass% or more, and satisfying the following formula (I): log 10 (D 90 )-log 10 (D 10 ) < 0.8 (I) (Note: D 90 D indicates the particle size at which the cumulative volume distribution of particle size reaches 90% in the particle size distribution. 10 indicates the particle size at which the cumulative volume distribution of particle size is 10% in the particle size distribution.)

[0023] <Li4Ti5O 12 Lithium titanate powder containing The lithium titanate powder of the present invention is Li4Ti5O 12 The main component is Li4Ti5O within the range in which the effects of the present invention can be obtained. 12The main component is a crystalline component and / or amorphous component other than Li4Ti5O among the diffraction peaks measured by X-ray diffraction. 12 The lithium titanate powder of the present invention has a diffraction peak intensity ratio of 90% or more of the main peak of Li4Ti5O among the diffraction peaks measured by X-ray diffraction. 12 The ratio of the intensity of the main peak of Li4Ti5O is more preferably 92% or more, and even more preferably 95% or more. 12 The other components are the sum of the intensity of the main peak due to the crystalline component and the maximum intensity of the halo pattern due to the amorphous component. In particular, the lithium titanate powder of the present invention contains anatase-type titanium dioxide, rutile-type titanium dioxide, and lithium titanate with a different chemical formula, Li2TiO, due to the raw materials and synthesis conditions used during synthesis. 3、 Li 0.6 Ti 3.4 O 8、 The lithium titanate powder of the present invention may contain these Li4Ti5O 12 Crystalline components other than Li 0.6 Ti 3.4 The lower the rate of O8 generation, the more improved the charging characteristics and charge / discharge capacity of the energy storage device. 12 When the intensity of the main peak of anatase titanium dioxide is taken as 100, it is particularly preferable that the sum of the intensity of the main peak of anatase titanium dioxide, the intensity of the main peak of rutile titanium dioxide, and the intensity corresponding to the main peak of Li2TiO3 calculated by multiplying the peak intensity corresponding to the (-133) plane of Li2TiO3 by 100 / 80 is 5 or less. 12 The main peak of Li4Ti5O in ICDD (PDF2010) PDF card 00-049-0207 is 12The main peak of anatase titanium dioxide is a peak corresponding to the diffraction peak attributable to the (111) plane (2θ=18.33) of PDF card 01-070-6826. The main peak of rutile titanium dioxide is a peak corresponding to the diffraction peak attributable to the (110) plane (2θ=27.44) of PDF card 01-070-7347. The peak corresponding to the (-133) plane of Li2TiO3 is a peak corresponding to the diffraction peak attributable to the (-133) plane of Li2TiO3 (2θ=43.58) of PDF card 00-033-0831. Li 0.6 Ti 3.4 The main peak of O8 corresponds to the diffraction peak attributable to the (101) plane (2θ = 19.98) on PDF card 01-070-2732. Note that "ICDD" stands for International Centre for Diffraction Data, and "PDF" stands for Powder Diffraction File.

[0024] <Aluminum (Al) content> The lithium titanate powder of the present invention contains Al on the surfaces of its primary particles. The term "containing Al" means that Al is detected by inductively coupled plasma atomic emission spectroscopy (ICP-AES) or X-ray fluorescence spectroscopy (XRF) of the niobium oxide powder of the present invention. The lower limit of the detectable amount by inductively coupled plasma atomic emission spectroscopy is typically 0.001% by mass, and the lower limit of the detectable amount by X-ray fluorescence spectroscopy is typically 0.001% by mass.

[0025] <Aluminum (Al) content> The Al content of the lithium titanate powder of the present invention, as determined by X-ray fluorescence analysis (XRF), may be 0.2% by mass or more. The upper limit is preferably 3% by mass or less, since a higher Al content leads to a decrease in initial capacity. A content within this range results in an electricity storage device that is excellent in electrode density, volumetric energy density, rate characteristics, initial low-temperature input characteristics, and suppression of gas generation during high-temperature storage. The Al content is more preferably 0.25% by mass or more and 2% by mass or less, even more preferably 0.27% by mass or more and 1% by mass or less, and particularly preferably 0.27% by mass or more and 0.4% by mass or less. The Al content refers to the mass ratio of Al to the total mass of the lithium titanate powder.

[0026] <Inclusion of additional heterogeneous elements> The lithium titanate powder of the present invention may contain further heterogeneous elements other than the aluminum (Al), and preferably contains at least one element selected from the group consisting of B, Mo, and W. Of these, Mo is particularly preferred. It is believed that the lithium titanate powder of the present invention contains such heterogeneous elements together with aluminum (Al), which leads to more advanced powder surface modification than when aluminum (Al) is contained alone, thereby suppressing the amount of gas generated after high-temperature storage.

[0027] <Mass ratio of molybdenum (Mo) to aluminum (Al) (Mo (mass%) / Al (mass%)> In the case of the lithium titanate powder, it is preferable that Mo and Al are contained on the surfaces of the primary particles, and that the mass ratio (Mo (mass%) / Al (mass%)) is 0.01 or more and 80 or less. If the mass ratio is within this range, an electricity storage device excellent in rate characteristics, initial low-temperature input characteristics, and suppression of gas generation after high-temperature storage can be obtained. The mass ratio is more preferably 0.2 or more and 6 or less, even more preferably 0.3 or more and 4 or less, and particularly preferably 0.5 or more and 1.5 or less.

[0028] Furthermore, the lithium titanate powder of the present invention contains more Al on the surface than in the interior of the lithium titanate primary particles. In cross-sectional analysis of lithium titanate primary particles using a scanning transmission electron microscope, energy dispersive X-ray spectroscopy (EDX) measurements reveal that Al is present in a high concentration in the so-called near-surface region extending from the surface of the lithium titanate primary particles to a depth of approximately 20 nm. Preferably, no Al is detected at a depth of approximately 100 nm. Preferably, Al is chemically bonded to and fixed on the primary particle surface. When Al is present in this state, an energy storage device can be obtained that exhibits excellent electrode density, volumetric energy density, rate characteristics, initial low-temperature input characteristics, and reduced gas generation during high-temperature storage. The lower limit of the detectable amount in EDX measurements varies depending on the element and state being measured, but is typically 0.5 atm%. Therefore, at a depth of approximately 100 nm, Al may be detected at a range of 0.5 atm% or less.

[0029] The reasons for the excellent electrode density, volumetric energy density, rate characteristics, initial low-temperature input characteristics, and suppression of gas generation after high-temperature storage are not clear, but it is thought that the local presence of Al at the interface between the lithium titanate particle surface and the non-aqueous electrolyte (including solid electrolyte) efficiently converts decomposition products generated on the particle surface into other substances, thereby suppressing the overall amount of gas generation and an increase in resistance components.

[0030] The lithium titanate powder of the present invention may further contain at least one element selected from Mg, Zn, Ga, sulfur (S), or In as a different element. This is because the lithium titanate powder of the present invention further improves the efficiency and rate characteristics during high-temperature charge / discharge by containing these different elements together with Al (or together with Mo and / or Al). Of these, sulfur (S) is preferred. It is presumed that this is because the lithium titanate powder of the present invention contains the element S together with Al (or together with Mo and / or Al), which adjusts the electronic conductivity of the surface of the primary particles of the lithium titanate powder and reduces the electrical resistance.

[0031] <Molybdenum (Mo) valence> Regarding the valence of molybdenum (Mo), X-ray photoelectron spectroscopy (XPS) of the lithium titanate primary particles contained in the lithium titanate powder of the present invention preferably shows that the ratio of the peak area of ​​Mo (pentavalent and tetravalent) to the total peak area of ​​Mo (hexavalent, pentavalent, and tetravalent) is 30% or less, more preferably 20% or less. If the ratio of the peak area of ​​Mo (pentavalent and tetravalent) is 30% or less, side reactions of Mo are suppressed during the initial charge / discharge, resulting in an electricity storage device with excellent initial discharge capacity, rate characteristics, and suppressed gas generation after high-temperature storage. Furthermore, regarding Mo, it is preferable that the lithium titanate powder of the present invention has a configuration in which more Mo is contained on the surface than inside the primary particles of the lithium titanate contained in the powder.

[0032] <1-methyl-2-pyrrolidone oil absorption> The 1-methyl-2-pyrrolidone (hereinafter sometimes referred to as NMP) oil absorption of the lithium titanate powder of the present invention is preferably 80 ml / 100 g or less. This range of NMP oil absorption allows for the production of an electricity storage device with excellent electrode density, volumetric energy density, rate characteristics, and suppressed gas generation during high-temperature storage. A more preferable range is 75 ml / 100 g or less, and even more preferable is 71 ml / 100 g or less. Here, the unit ml / 100 g represents the amount of NMP absorbed per 100 g of the lithium titanate powder of the present invention (unit: ml). While the reason for this effect is not entirely clear, it is presumed that NMP is a solvent used in electrode production, and appropriate control of the NMP oil absorption of the lithium titanate powder contributes to efficient adhesion between the negative electrode active material, conductive additive, and binder, thereby enabling the fabrication of high-density electrodes.

[0033] <Specific surface area> The specific surface area of ​​the lithium titanate powder of the present invention refers to the adsorption area per unit mass when nitrogen is used as the adsorption gas. The measurement method will be explained in the examples below.

[0034] The lithium titanate constituting the lithium titanate powder of the present invention has a specific surface area of ​​4.0 m 2 / g or more, which allows for the production of an electricity storage device with excellent initial discharge capacity and rate characteristics. 2 / g or more, and 6.0m 2 On the other hand, the specific surface area of ​​lithium titanate powder is 9.0 m 2 / g or less is more preferable, and 7.0m 2 / g or less is more preferable.

[0035] <D 50 > D of the lithium titanate powder of the present invention 50 is an index of the volume median particle size. It means the particle size at which the cumulative volume frequency calculated from the volume fraction determined by laser diffraction / scattering particle size distribution measurement reaches 50% when calculated from the smallest particle size. The measurement method will be explained in the examples below.

[0036] <Primary particles and secondary particles> The lithium titanate powder of the present invention comprises primary particles of lithium titanate and secondary particles formed by aggregation of the primary particles. The primary particles refer to individual particles that constitute the lithium titanate powder and cannot be further divided by a crushing treatment.

[0037] D of the secondary particles of the lithium titanate powder of the present invention 50 From the viewpoint of improving the rate characteristics and initial low-temperature input characteristics, 50 is 11 μm or more, preferably 12 μm or more, and more preferably 12.4 μm or more. 50 is 20 μm or less, preferably 18 μm or less, and more preferably 14 μm or less. 50 is the D before crushing process (ultrasonic irradiation with an ultrasonic irradiator). 50 Represents.

[0038] D of the primary particles of the lithium titanate powder of the present invention 50From the viewpoint of improving the electrode density and volumetric energy density, the D of the primary particles 50 is 0.5 μm or more, and more preferably 0.6 μm or more. 50 is 3 μm or less, preferably 2 μm or less, and more preferably 1.5 μm or less. 50 is the D after disintegration treatment using an ultrasonic irradiator. 50 The lithium titanate powder may contain primary particles having a primary particle diameter of less than 0.5 μm at a cumulative volume frequency of 10% to 50%, and may contain primary particles having a primary particle diameter of less than 0.6 μm at a cumulative volume frequency of 15% to 55%. Furthermore, the lithium titanate powder may contain primary particles having a primary particle diameter of more than 3 μm at a cumulative volume frequency of 50% to 90%, and may contain primary particles having a primary particle diameter of more than 2 μm at a cumulative volume frequency of 50% to 90%.

[0039] The logarithm of the primary particles of the lithium titanate powder of the present invention 10 (D 90 )-log 10 (D 10 ) is less than 0.8, preferably less than 0.7, more preferably less than 0.6, and even more preferably less than 0.5, from the viewpoint of improving the electrode density, volumetric energy density, initial low-temperature input characteristics, and charge rate characteristics after high-temperature storage. The lower limit is preferably greater than 0.3, more preferably greater than 0.4. This is because a small value may result in a decrease in battery performance.

[0040] D 90 D indicates the particle size at which the cumulative volume distribution of the particle size of primary particles is 90% in the particle size distribution. 10 D indicates the particle size at which the cumulative volume distribution of the particle size of primary particles in the particle size distribution is 10%. More specifically, for the primary particles of lithium titanate powder, the particle size at which the cumulative volume frequency calculated from the volume fraction obtained by laser diffraction / scattering particle size distribution measurement is 10% when calculated from the smallest particle size is D. 10 The particle size that is 90% of the total particle size is D 90 Here, D 90is the D of the primary particle 90 and D after disintegration treatment using an ultrasonic irradiator. 90 represents D 10 is the D of the primary particle 10 and D after disintegration treatment using an ultrasonic irradiator. 10 Represents.

[0041] Also, log 10 (D 90 ) is the D of the primary particle 90 It is a logarithmic value in the logarithmic value with the base 10, and its unit is μm. 90 = 10 μm, log 10 (D 90 ) is 1, and D 90 = 1 μm, log10(D 90 ) has a value of 0. Similarly, log 10 (D 10 ) is the D of the primary particle 10 It is a logarithmic value in the logarithmic value with the base 10, and its unit is μm.

[0042] D of the primary particles of the lithium titanate powder described above 10 is D 10 is 0.3 μm or more, and more preferably 0.4 μm or more. 90 is 4 μm or less, and more preferably 3 μm or less.

[0043] From the above-mentioned points, the D of the primary particles and secondary particles of the lithium titanate powder 50 Ratio of primary particles (D 50 / D of secondary particles 50 ) is preferably 0.06 or less, more preferably 0.05 or less. If it exceeds 0.06, there is a risk that any one of the performances such as electrode density, initial low-temperature input characteristics, and volumetric energy density may be reduced.

[0044] <Moisture content> The moisture content (25°C to 350°C) of the lithium titanate powder of the present invention measured by the Karl Fischer method (hereinafter sometimes referred to as the moisture content at 25°C to 350°C) is preferably 5000 ppm or less. Here, the moisture content (25°C to 350°C) of the lithium titanate powder of the present invention measured by the Karl Fischer method refers to the total moisture content obtained by heating the lithium titanate powder of the present invention from 25°C to 200°C under nitrogen flow and maintaining it at 200°C for one hour, followed by heating it from 200°C to 350°C under nitrogen flow and maintaining it at 350°C for one hour. A moisture content of 5000 ppm or less is preferred because it provides good handleability during electrode coating when used as an electrode material for an electrical storage device. The moisture content (25°C to 350°C) measured by the Karl Fischer method includes both physically adsorbed moisture and chemically adsorbed moisture on the lithium titanate powder of the present invention. Generally, in lithium titanate powder, it is difficult to measure moisture by the Karl Fischer method in the range above 350°C, and moisture is hardly detected by other methods (for example, pyrolysis gas chromatography mass spectrometry). From the viewpoint of further suppressing the amount of gas generated during high-temperature operation of the electricity storage device, the moisture content measured by the Karl Fischer method (25°C to 350°C) is more preferably 1000 ppm or less, and particularly preferably 600 ppm or less.

[0045] Here, the moisture content (200°C to 350°C) of the lithium titanate powder of the present invention measured by the Karl Fischer method refers to the amount of moisture obtained from the start of heating at 200°C to the end of holding at 350°C, out of the moisture content (25°C to 350°C). The moisture contained in lithium titanate includes physically adsorbed moisture and chemically adsorbed moisture, as described above. It is presumed that most of the moisture present on the surface of the lithium titanate powder is likely desorbed by 200°C and included in the moisture content (25°C to 200°C) measured by the Karl Fischer method. Here, the moisture content (25°C to 200°C) of the lithium titanate powder of the present invention measured by the Karl Fischer method refers to the amount of moisture released from the lithium titanate powder of the present invention when the lithium titanate powder of the present invention is heated from 25°C to 200°C under a nitrogen flow and held at 200°C for 1 hour, measured by the Karl Fischer method. Furthermore, since the fabrication of a typical electricity storage device involves a step of drying the electrodes, the moisture content (25°C to 200°C) measured by the Karl Fischer method is almost entirely released during this drying step. Therefore, it is believed that the moisture that affects the electricity storage device is not present on the surface of the lithium titanate particles, but is present mainly inside the particles, where it is difficult to remove during this drying step. Therefore, it is believed that the moisture present inside the particles and that substantially affects the electricity storage device is mostly included in the moisture content (200°C to 350°C) measured by the Karl Fischer method. From the above perspective, the moisture content (200°C to 350°C) measured by the Karl Fischer method is more preferably 300 ppm or less, and particularly preferably 150 ppm or less. The lower limit of the moisture content (200°C to 350°C) measured by the Karl Fischer method is not particularly limited, and in some cases, it may be below the detection limit of the measuring device (i.e., it can be determined to be essentially 0 ppm).

[0046] [Method of manufacturing lithium titanate powder of the present invention] An example of the method for producing the lithium titanate powder of the present invention will be explained below, divided into a raw material preparation step, a firing step, and a surface treatment step, but the method for producing the lithium titanate powder of the present invention is not limited to this.

[0047] <Raw material preparation process> The raw materials for the lithium titanate powder of the present invention are titanium raw materials and lithium raw materials. As the titanium raw material, titanium compounds such as anatase type titanium dioxide and rutile type titanium dioxide are used.

[0048] As the lithium raw material, lithium compounds such as lithium hydroxide monohydrate, lithium oxide, lithium hydrogen carbonate, and lithium carbonate are used.

[0049] In the preparation step, the above raw materials are mixed to obtain a mixture. As a method for preparing the mixture, a method in which the raw materials are mixed and then pulverized at the same time can be mentioned.

[0050] <Firing process> The resulting mixture is then fired. From the viewpoints of increasing the specific surface area of ​​the powder obtained by firing, increasing the crystallite size and primary particle size of the powder, and reducing the amount of impurities from furnace materials, etc., firing at a high temperature for a short time is preferred. From these viewpoints, the maximum temperature during firing is preferably 1100°C or less, more preferably 1000°C or less, and even more preferably 960°C or less. From the viewpoints of reducing the proportion of impurities and increasing the crystallinity of lithium titanate, the maximum temperature during firing is preferably 800°C or more, more preferably 840°C or more, and even more preferably 860°C or more. Similarly, from the above viewpoints, the holding time at the maximum temperature during firing is preferably 2 minutes to 60 minutes, more preferably 5 minutes to 45 minutes, and even more preferably 5 minutes to 30 minutes. When the maximum temperature during firing is high, it is preferable to select a shorter holding time. Similarly, from the viewpoint of increasing the crystallite size obtained by firing, it is preferable to particularly shorten the residence time at 700°C to 800°C during the temperature rise process during firing, for example, preferably within 15 minutes.

[0051] The calcination method is not particularly limited as long as it can be performed under the above conditions. Usable calcination methods include fixed-bed calcination furnaces, roller hearth calcination furnaces, mesh belt calcination furnaces, fluidized bed calcination furnaces, and rotary kiln calcination furnaces. However, for efficient calcination in a short time, roller hearth calcination furnaces, mesh belt calcination furnaces, and rotary kiln calcination furnaces are preferred. When using a roller hearth calcination furnace or mesh belt calcination furnace in which the mixture is placed in a sagger and calcined, it is preferable to limit the amount of mixture placed in the sagger to ensure uniformity in the temperature distribution of the mixture during calcination and to ensure consistent quality of the resulting lithium titanate.

[0052] <Crushing process> The lithium titanate powder after calcination must be crushed. Methods for crushing the calcined product recovered from the calcined product recovery side include a hammer mill, a ball mill, a jet mill, a vibration mill, a bead mill, etc., with a bead mill being particularly preferred. When a bead mill is used, any of the following methods can be used for crushing: wet-crushing circulation treatment, wet-crushing batch treatment, dry-crushing circulation treatment, and dry-crushing batch treatment. However, it is preferable to perform crushing uniformly, and in this respect, wet-crushing circulation treatment is preferred. The circulation conditions may be determined taking into consideration the calcination temperature in the calcination step, etc., and, for example, by adjusting the circulation conditions, the log of the primary particles of the lithium titanate powder can be reduced. 10 (D 90 )-log 10 (D 10 ) value can be suitably controlled. In wet crushing, the calcined lithium titanate powder is introduced into a water or alcohol solvent and mixed in a slurry state. As the alcohol solvent, those with a boiling point of 100°C or less, such as methanol, ethanol, and isopropyl alcohol, are preferred because they are easy to remove. Furthermore, from an industrial perspective, water solvents are preferred because of the ease of recovery and disposal.

[0053] The amount of solvent is preferably such that the lithium titanate powder after firing is uniformly dispersed in the solvent, and for this purpose the slurry viscosity is preferably 8000 cP or less, more preferably 5000 cP or less, and even more preferably 3000 cP or less.

[0054] The circulation treatment time of the wet crushing (the number of crushing passes by the circulation treatment) is not particularly limited as long as the crystallinity of the lithium titanate does not decrease and the battery performance is not adversely affected. 10 (D 90 )-log 10 (D 10 It is desirable to determine this based on the value of

[0055] <Surface treatment process> The lithium titanate powder of the present invention is a lithium titanate powder containing aluminum, and when used as an electrode material for an electricity storage device, it can provide excellent effects in terms of electrode density, volumetric energy density, rate characteristics, initial low-temperature input characteristics, and suppression of gas generation during high-temperature storage. The lithium titanate powder of the present invention can be produced by adding a compound containing a different element such as aluminum (hereinafter sometimes referred to as a treating agent) in the firing step, but more preferably, the lithium titanate powder of the present invention can be produced by the following surface treatment step or the like.

[0056] The lithium titanate powder before surface treatment obtained by the above steps (hereinafter, this may be referred to as the base lithium titanate powder. Also, hereinafter, the lithium titanate particles constituting the base lithium titanate powder may be referred to as the base lithium titanate particles) is mixed with a treatment agent and preferably heat-treated.

[0057] The aluminum-containing compound (treatment agent) is not particularly limited, but examples thereof include aluminum oxides, hydroxides, sulfate compounds, nitrate compounds, fluorides, organic compounds, and aluminum-containing metal salt compounds. Specific examples of Al-containing compounds include aluminum acetate, aluminum fluoride, and aluminum sulfate. Of these, aluminum sulfate, its hydrate, and aluminum fluoride are preferred.

[0058] The amount of aluminum-containing compound (treatment agent) added may be any amount as long as the aluminum content in the lithium titanate powder falls within the range of the present invention. For example, when aluminum sulfate 14-18 hydrate (Al(SO)·14-18H0) is used, the treatment agent should be added in a ratio of 0.16 mmol / 100g of LTO to 63.5 mmol / 100g of LTO, more preferably 3.2 mmol / 100g of LTO to 31.7 mmol / 100g of LTO, and most preferably 4.0 mmol / 100g of LTO to 15.9 mmol / 100g of LTO. Note that 1.0 mmol of aluminum sulfate 14-18 hydrate corresponds to 0.34 g, depending on the hydrate ratio. Here, "mmol / 100g of LTO" is the amount (mmol) of the treatment agent per 100g of lithium titanate powder as the base material (the same applies hereinafter).

[0059] Furthermore, when Mo, in addition to Al, is to be localized on the surface of the primary particles of the lithium titanate powder, it is desirable to use a compound containing molybdenum in addition to a compound containing aluminum in the surface treatment step. The molybdenum-containing compound (Mo-containing treatment agent) is not particularly limited, and examples thereof include molybdenum oxides, hydroxides, sulfates, nitrates, fluorides, organic compounds, and molybdenum-containing metal salt compounds. Specific examples include molybdenum oxide, molybdenum trioxide, molybdenum trioxide hydrate, molybdenum boride, molybdophosphoric acid, molybdenum disilicide, molybdenum chloride, molybdenum sulfide, molybdenum silicic acid hydrate, sodium molybdenum oxide, molybdenum carbide, molybdenum acetate dimer, lithium molybdate, sodium molybdate, potassium molybdate, calcium molybdate, magnesium molybdate, manganese molybdate, and ammonium molybdate. To uniformly diffuse molybdenum over the particle surfaces of lithium titanate powder, it is suitable to use the wet method described below. In this case, it is preferable to dissolve a molybdenum-containing compound soluble in a solvent in the solvent and mix it with the lithium titanate powder as the base material. Lithium molybdate containing molybdenum is preferred in terms of suppressing gas generation. Regarding the valence of molybdenum, even if it is added as a raw material in a hexavalent state, it is expected that dangling bonds will exist when chemical bonds are formed on the LTO surface or inside the crystal, resulting in partial tetravalent or pentavalent states.

[0060] The amount of molybdenum-containing compound (Mo-containing treatment agent) added may be any amount as long as the molybdenum content in the lithium titanate powder falls within the range of the present invention. For example, when lithium molybdate (Li2MoO4) is used as the Mo-containing treatment agent, the ratio of the Mo-containing treatment agent to the lithium titanate powder substrate should be 0.12 mmol / 100g LTO to 28.8 mmol / 100g LTO, more preferably 0.5 mmol / 100g LTO to 15.5 mmol / 100g LTO, and most preferably 1.0 mmol / 100g LTO to 10.0 mmol / 100g LTO. Note that 1.0 mmol of lithium molybdate corresponds to 0.17 g.

[0061] In the surface treatment step, a compound containing B or a compound containing W may be used as needed. There are no particular limitations on the method for mixing the lithium titanate powder as the base material with the aluminum-containing compound, and the molybdenum-containing compound, which is used as needed, and further with the B-containing compound and the W-containing compound, and either wet mixing or dry mixing can be used. However, it is preferable to uniformly disperse the aluminum-containing compound and further the molybdenum-containing compound on the surface of the lithium titanate particles as the base material, and in this respect, wet mixing is preferred.

[0062] After mixing the lithium titanate powder of the substrate with the treatment agent, it is preferable to perform a heat treatment. The heat treatment temperature is a temperature at which aluminum or other elements diffuse into at least the surface region of the lithium titanate particles of the substrate, and at which a significant decrease in the specific surface area due to sintering of the lithium titanate of the substrate does not occur. The upper limit of the heat treatment temperature is preferably 700°C or less, more preferably 600°C or less. The lower limit of the heat treatment temperature is preferably 300°C or more, more preferably 400°C or more. The heat treatment time is preferably 0.1 to 8 hours, more preferably 1 to 5 hours. The temperature and time at which element M diffuses into at least the surface region of the lithium titanate particles of the substrate should be appropriately set, as the reactivity varies depending on the compound containing element M.

[0063] The heating method for the heat treatment is not particularly limited. Usable heat treatment furnaces include fixed-bed calciners, roller hearth calciners, mesh belt calciners, fluidized-bed calciners, and rotary kiln calciners. The atmosphere during the heat treatment may be either air or an inert atmosphere such as a nitrogen atmosphere. When a metal salt compound containing molybdenum or other elements is used as the compound (treatment agent) containing aluminum or other elements, an air atmosphere is preferred, as it facilitates the removal of anion species from the particle surface.

[0064] The lithium titanate powder of the present invention may be mixed with a treatment agent in a surface treatment step, granulated, and then heat-treated to form a powder containing secondary particles formed by aggregation of primary particles. Any method for granulation may be used as long as it can produce secondary particles, but a spray dryer is preferred because it can process large quantities.

[0065] Dew point control may be performed during the heat treatment process to reduce the moisture content of the lithium titanate powder of the present invention. Since the moisture content of the heat-treated powder increases if exposed to the atmosphere, it is preferable to handle the powder in a dew point-controlled environment during cooling in the heat treatment furnace and after heat treatment. The heat-treated powder may be classified as needed to adjust the particles to the desired maximum particle size range. When dew point control is performed during the heat treatment process, it is preferable to seal the lithium titanate powder of the present invention in an aluminum-laminated bag or the like and then place it in an environment outside of dew point control. Even under dew point control, pulverizing the heat-treated lithium titanate powder makes it more likely to absorb moisture from the crushed surfaces, increasing the moisture content of the powder. Therefore, it is preferable not to pulverize the powder after heat treatment. Regarding heat treatment conditions, the temperature and holding time within specific ranges significantly affect the secondary particle morphology and surface treatment process. The heat treatment temperature is preferably 450°C or higher, but less than 550°C. This is because a heat treatment temperature above 550°C significantly reduces the specific surface area, significantly degrading battery performance, particularly rate characteristics. Furthermore, the holding time is preferably 11 hours or more, because if the heating time is short, the amount of moisture contained in the powder will increase and it is thought that this will also affect the particle surface condition and the interfacial reaction with the electrolyte or solid electrolyte.

[0066] [Active material] The active material used in the electrode of the present invention contains the lithium titanate powder of the present invention. It may contain one or more substances other than the lithium titanate powder of the present invention. Examples of other substances include carbon materials (pyrolytic carbons, cokes, graphites (artificial graphite, natural graphite, etc.), organic polymer compound combustion products, and carbon fibers), tin and tin compounds, silicon and silicon compounds.

[0067] [Energy storage devices] The electricity storage device of the present invention is a device that includes an electrode containing the active substance material of the present invention and stores and releases energy by utilizing the intercalation and deintercalation of lithium ions into such an electrode, and examples thereof include a hybrid capacitor and a lithium battery.

[0068] The lithium battery is composed of a positive electrode, a negative electrode, and a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a non-aqueous solvent, or a solid electrolyte, and 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 of the lithium battery. This active material may be used as either a positive electrode active material or a negative electrode active material, but the following description will be given of the case where it is used as a negative electrode active material.

[0069] <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 or both sides of a negative electrode current collector. This mixture layer is usually in the form of an electrode. In the case of a negative electrode current collector that is porous or the like and has pores, the mixture layer contains the negative electrode active material (the active material of the present invention), a conductive agent, and a binder in the pores. When this mixture layer is used in an all-solid-state battery, the mixture layer may further contain a solid electrolyte material.

[0070] <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 a positive electrode current collector.

[0071] As the positive electrode active material, a material capable of absorbing and releasing lithium is used, and examples of the active material include composite metal oxides containing cobalt, manganese, and nickel with lithium, and lithium-containing olivine-type phosphates. These positive electrode active materials can be used alone or in combination of two or more. Examples of such composite metal oxides include LiCoO2, LiMn2O4, LiNiO2, and LiCo 1-x Ni x O2(0.01 <x<1)、LiCo1 / 3 Ni 1 / 3 Mn 1 / 3 O2, LiNi 1 / 2 Mn 3 / 2 O4, etc., and these lithium composite oxides may be partially substituted with other elements, such as partially substituting cobalt, manganese, and nickel with at least one element such as B, Nb, Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, Cu, Bi, Mo, and La, partially substituting O with S or F, or coating with a compound containing these other elements. Examples of lithium-containing olivine-type phosphates include LiFePO4, LiCoPO4, LiNiPO4, LiMnPO4, and LiFe 1-x Examples include MxPO4 (M is at least one selected from Co, Ni, Mn, Cu, Zn, and Cd, and x is 0≦x≦0.5).

[0072] The conductive agent and binder for the positive electrode may be the same as those for the negative electrode. Examples of the positive electrode current collector include aluminum, stainless steel, nickel, titanium, baked carbon, and aluminum or stainless steel surfaces treated with carbon, nickel, titanium, or silver. The surface of these materials may be oxidized, or the positive electrode current collector surface may be roughened by surface treatment. Examples of the current collector form include a sheet, net, foil, film, punched material, lath, porous material, foam, fiber group, and nonwoven fabric molded body.

[0073] <Nonaqueous electrolyte> The non-aqueous electrolyte is a non-aqueous solvent in which an electrolyte salt is dissolved. There are no particular limitations on the non-aqueous electrolyte, and various types can be used.

[0074] The electrolyte salt used is one that dissolves in a non-aqueous electrolyte. Examples of the electrolyte salt include inorganic lithium salts such as LiPF, LiBF, LiPO, LiN(SOF), and LiClO; lithium salts containing a chain-like fluorinated alkyl group such as LiN(SOCF), LiN(SOCF) , LiCFSO, LiC(SOCF), LiPF(CF), LiPF(CF) , LiPF(CF) , LiPF(CF) , LiPF(iso-CF) , and LiPF(iso-CF); lithium salts containing a cyclic fluorinated alkylene chain such as (CF)(SO)NLi and (CF)(SO)NLi; and lithium salts having an oxalate complex as the anion, such as lithium bis[oxalate-O,O']borate and lithium difluoro[oxalate-O,O']borate. Among these, particularly preferred electrolyte salts are LiPF6, LiBF4, LiPO2F2, and LiN(SO2F)2, with LiPF6 being the most preferred. These electrolyte salts can be used alone or in combination of two or more. A preferred combination of these electrolyte salts is one in which the non-aqueous electrolyte solution contains LiPF6 and at least one lithium salt selected from LiBF4, LiPO2F2, and LiN(SO2F)2.

[0075] On the other hand, examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, chain esters, ethers, amides, phosphate esters, sulfones, lactones, nitriles, and S=O bond-containing compounds, and the non-aqueous solvent preferably contains a cyclic carbonate. Note that the term "chain ester" is used as a concept including chain carbonates and chain carboxylic acid esters.

[0076] Examples of cyclic carbonates include one or more selected from 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, both are collectively referred to as "DFEC"), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and 4-ethynyl-1,3-dioxolan-2-one (EEC); One 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-dioxolan-2-one (EEC) are more preferred from the viewpoint of improving the charge rate characteristics of the power storage device and suppressing the amount of gas generated during high-temperature operation, and one or more cyclic carbonates having an alkylene chain selected from propylene carbonate, 1,2-butylene carbonate, and 2,3-butylene carbonate are even more preferred. The proportion of the cyclic carbonate having an alkylene chain in all cyclic carbonates is preferably 55% to 100% by volume, and more preferably 60% to 90% by volume.

[0077] Suitable examples of the chain ester include 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 symmetric chain carbonates selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, and dibutyl carbonate; pivalic acid esters such as methyl pivalate, ethyl pivalate, and propyl pivalate; and one or more chain carboxylic acid esters selected from methyl propionate, ethyl propionate, propyl propionate, methyl acetate, and ethyl acetate (EA).

[0078] <Lithium battery structure> The structure of the lithium battery of the present invention is not particularly limited, and examples include a coin battery having a positive electrode, a negative electrode, and a single-layer or multi-layer separator, and further, a cylindrical battery or a prismatic battery having a positive electrode, a negative electrode, and a roll-shaped separator.

[0079] The separator is an insulating thin film having high ion permeability and a predetermined mechanical strength. Examples include polyethylene, polypropylene, cellulose paper, glass fiber paper, polyethylene terephthalate, and polyimide microporous membranes. Multilayer membranes formed by combining two or more of these materials can also be used. The surface of these separators can also be coated with resins such as PVDF, silicone resins, and rubber-based resins, or particles of metal oxides such as aluminum oxide, silicon dioxide, and magnesium oxide. The pore size of the separator may be within a range generally useful for batteries, for example, 0.01 μm to 10 μm. The thickness of the separator may be within a range generally used for batteries, for example, 5 μm to 300 μm.

[0080] <Solid electrolyte> A solid electrolyte is a solid electrolyte capable of ion migration. In particular, inorganic solid electrolytes are solid in a steady state and are not typically dissociated or liberated into cations and anions. Inorganic solid electrolytes are not particularly limited as long as they have the conductivity of metal ions belonging to Group 1 of the periodic table, but generally have almost no electronic conductivity. Representative examples of inorganic solid electrolytes include sulfide inorganic solid electrolytes and oxide inorganic solid electrolytes. Sulfide solid electrolytes are particularly preferred because they have high ionic conductivity and can be formed into dense compacts with few grain boundaries simply by applying pressure at room temperature. The periodic table in this specification refers to the long-period periodic table of elements based on the IUPAC (International Union of Pure and Applied Chemistry) standard.

[0081] The sulfide inorganic solid electrolyte may be amorphous glass, crystallized glass, or a crystalline material. Specific examples of the sulfide inorganic solid electrolyte include, but are not limited to, the following combinations: Li2S-P2S5, Li2S-P2S5-Al2S3, Li2S-GeS2, Li2S-Ga2S3, Li2S-GeS2-Ga2S3, Li2S-GeS2-P2S5, Li2S -GeS2-Sb2S5, Li2S-GeS2-Al2S3, Li2S-SiS2, Li2S-Al2S3, Li2S-SiS2-Al2S3, Li2S-SiS2-P2S5, Li 10 GeP2S 12 .

[0082] Among the above combinations, LPS glass produced by combining Li2S-P2S5 Preferred examples of sulfide inorganic solid electrolytes other than those mentioned above include argerodite-type solid electrolytes such as Li6PS5Cl and Li6PS5Br.

[0083] Oxide-based inorganic solid electrolytes contain oxygen atoms and are made of metals belonging to Group 1 of the periodic table. Preferably, the material has both ionic conductivity and electronic insulation.

[0084] Examples of oxide inorganic solid electrolytes include Lithium super ionic conductor (LISICON) type crystal structures. 3.5 Zn 0.25 GeO4, La with perovskite crystal structure 0.55 Li 0.35 TiO3, LiTi2P3O with NASICON (sodium super ionic conductor) type crystal structure 12 , Li7La3Zr2O with a garnet-type crystal structure 12(LLZ), lithium phosphate (Li3PO4), lithium phosphate in which some of the oxygen is replaced with nitrogen, such as LiPON, Li3BO3-Li2SO4, Li2O-B2O3-P2O5, Li2O-SiO2, or Li6BaLa2Ta2O 12 Suitable examples include:

[0085] The volume average particle size of the inorganic solid electrolyte is not particularly limited, but is preferably 0.01 μm or more, more preferably 0.1 μm or more, and the upper limit is preferably 100 μm or less, more preferably 50 μm or less. [Example]

[0086] Next, the present invention will be explained in more detail with reference to examples and comparative examples, but 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.

[0087] [Example 1-1] <Raw material preparation process> Li2CO3 (average particle size 4.6 μm) and anatase TiO2 (specific surface area 10 m) were mixed so that the atomic ratio of Li to Ti (Li / Ti) was 0.83. 2 The raw material powder was weighed out (100g / g), and ion-exchanged water was added to the resulting raw material powder to a solids concentration of 41% by mass. The mixture was then stirred to produce a raw material mixed slurry. The raw material mixed slurry was then wet-mixed and milled using a bead mill (Willi & Bachofen, Model: Dynomill KD-20BC, agitator material: polyurethane, vessel inner surface material: zirconia) with a vessel filled to 80% by volume with zirconia beads (outer diameter: 0.65 mm). The agitator peripheral speed was 13 m / s, the slurry feed rate was 55 kg / hr, and the vessel inner pressure was controlled to 0.02-0.03 MPa.

[0088] <Firing process> The resulting mixed slurry was introduced into a rotary kiln-type firing furnace (furnace tube length: 4 m, furnace tube diameter: 30 cm, external heating type) equipped with an adhesion prevention mechanism. The furnace tube was inclined from the raw material supply side of the firing furnace, rotated at 20 rpm, and introduced into the furnace tube from the sintered product recovery side at a nitrogen atmosphere with a 2.5° inclination angle from the horizontal. The furnace tube rotation speed was 20 rpm. The nitrogen flow rate introduced into the furnace tube from the sintered product recovery side was 20 L / min. The heating temperatures of the furnace tube were 600°C on the raw material supply side, 900°C in the center, and 900°C on the sintered product recovery side. The sintered product was held at 900°C for 30 minutes.

[0089] <Post-processing process> The sintered material collected from the sintered material collection side of the furnace tube was crushed using a bead mill (Imex, NVM-1.5 model) at a flow rate of 5 L / min and a rotation speed of 2143 rpm. The processing time, calculated by dividing the total amount of slurry by the flow rate, was defined as the unit time for one pass, and the number of passes was set to 9 to strengthen the crushing of the sintered material.

[0090] <Surface treatment process> The crushed calcined powder was mixed with ion-exchanged water to a solids concentration of 40% by mass, and the mixture was stirred. Aluminum sulfate hexahydrate (Al2(SO4)3·16H2O) was added as a treatment agent at 3.2% by mass per 100 g of crushed calcined powder to produce a mixed slurry. This mixed slurry was spray-dried and granulated using a spray dryer (Okawara Kakoki Co., Ltd., L-8i) at an atomizer rotation speed of 25,000 rpm and a drying temperature of 235°C. The powder that passed through a sieve was then placed in an alumina sagger and heat-treated at 500°C for 1 hour in a continuous furnace with a mesh belt conveyor and equipped with a collection box at the outlet, where the dew point was controlled to 25°C and below -20°C. The heat-treated powder was cooled in the recovery box and classified using a sieve (screen opening: 53 μm). The powder that passed through the sieve was collected in an aluminum laminated bag, sealed, and then removed from the recovery box to produce lithium titanate powder.

[0091] [Example 1-2] Lithium titanate powder was produced in the same manner as in Example 1-1, except that 0.48 mass% of lithium molybdate (Li2MoO4) and 3.2 mass% of aluminum sulfate hexahydrate (Al2(SO4)3·16H2O) were added as treatment agents in the surface treatment step. Details are shown in Table 1.

[0092] [Examples 1-3] Lithium titanate powder was produced in the same manner as in Example 1-1, except that in the firing step, the heating temperatures of the furnace tube were 600°C on the raw material supply side, 920°C in the center, and 920°C on the fired product recovery side, the firing product was held at 920°C for 30 minutes, and the number of crushing passes in the post-treatment step was 3. Details are shown in Table 1.

[0093] [Comparative Example 1-1] Lithium titanate powder was produced in the same manner as in Example 1-1, except that in the sintering process, the heating temperatures of the furnace tube were 840°C in the center and 840°C on the sintered product recovery side, the sintered product was held at 840°C for 30 minutes, the number of crushing passes in the post-treatment process was 3, and in the surface treatment process, aluminum sulfate hexahydrate (Al2(SO4)3·16H2O) was added as a treatment agent in the amount shown in Table 1.

[0094] [Comparative Example 1-2] Lithium titanate powder was produced in the same manner as in Comparative Example 1-1, except that in the surface treatment step, 0.48 mass% of lithium molybdate (Li2MoO4) was further added as a treatment agent, and aluminum sulfate hexahydrate (Al2(SO4)3·16H2O) was added in the amounts shown in Table 1.

[0095] [Comparative Example 1-3] In the firing process, the heating temperature of the furnace tube was set to 920°C in the center and 920°C on the fired product recovery side, the holding time of the fired product at 920°C was set to 30 minutes, and 0.48 mass% of lithium molybdate (Li2MoO4) was further added as a processing agent. Except for this, lithium titanate powder was produced in the same manner as in Comparative Example 1-1.

[0096] [Comparative Example 1-4] In the firing step, the heating temperature of the furnace tube was set to 920°C in the center and 920°C on the fired product recovery side, the holding time of the fired product at 920°C was set to 30 minutes, and in the surface treatment step, no treatment agent was added. Except for this, lithium titanate powder was produced in the same manner as in Comparative Example 1-1.

[0097] [Comparative Example 1-5] A lithium titanate powder was produced in the same manner as in Comparative Example 1-1, except that no treatment agent was added in the surface treatment step.

[0098] [Measuring the content of metal elements] The contents of metal elements contained in the lithium titanate powders of Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-5 (hereinafter sometimes referred to as the lithium titanate powders of the respective Examples and Comparative Examples) were measured as follows.

[0099] <X-ray fluorescence analysis (XRF): Identification of molybdenum, aluminum, and impurity content> The elements contained in the lithium titanate powders of each example and comparative example were quantitatively analyzed using an X-ray fluorescence analyzer (manufactured by SII Technology Inc., product name "SPS5100"). The lithium titanate powder itself was used as the measurement sample, and the mass ratio of the element content was calculated. The amount of metal impurities was the total content of iron (Fe), chromium (Cr), and nickel (Ni).

[0100] [Measurement of powder properties] The various physical properties of the lithium titanate powders of the Examples and Comparative Examples were measured as follows.

[0101] <Measurement of specific surface area> The specific surface area (m 2 / g) was measured using a fully automatic BET specific surface area measurement device (manufactured by Mountec Co., Ltd., product name "Macsorb HM model-1208"), with nitrogen gas as the adsorption gas. 0.5 g of the measurement sample powder was weighed out and placed in a φ12 standard cell (HM1201-031), and after degassing for 0.5 hours under vacuum at 100°C, measurement was performed using the BET single-point method. In addition, the specific surface area equivalent diameter (DBET) calculated from the specific surface area determined by the BET method was measured using the method described in Patent Document 1.

[0102] <D of primary particles and secondary particles 50 Calculation: Dry laser diffraction scattering method D of lithium titanate powder in each example and comparative example 50 was calculated from the particle size distribution curve measured using a laser diffraction / scattering particle size distribution analyzer (Microtrac MT3300EXII, manufactured by Nikkiso Co., Ltd.). 50 mg of sample was placed in a container containing 50 ml of ion-exchanged water as the measurement solvent, and the container was shaken by hand until it was visually apparent that the powder was uniformly dispersed in the measurement solvent. The container was then placed in the measurement cell and measured. The crushing process was carried out by applying ultrasound (30 W, 3 s) using an ultrasonicator inside the device. Further, the measurement solvent was added until the transmittance of the slurry was within the appropriate range (the range displayed by the green bar on the device), and particle size distribution measurement was carried out. From the obtained particle size distribution curve, the D of the mixed powder before and after crushing was calculated. 50 Before crushing, D 50 is the secondary particle D 50 , after crushing D 50 is the D of the primary particle 50 is equivalent to

[0103] <D of primary particles 90 , D 10 , log 10 (D 90 )-log 10 (D 10 ) Calculation: Dry laser diffraction scattering method D of lithium titanate powder in each example and comparative example 90 , D 10was calculated from the particle size distribution curve measured using a laser diffraction / scattering particle size distribution analyzer (Microtrac MT3300EXII, manufactured by Nikkiso Co., Ltd.). 50 mg of sample was placed in a container containing 50 ml of ion-exchanged water as the measurement solvent, and the container was shaken by hand until the powder was visually uniformly dispersed in the measurement solvent. The container was then placed in the measurement cell and measured. The crushing process was performed by applying ultrasound (30 W, 3 s) using the ultrasonicator inside the device. Further, the measurement solvent was added until the transmittance of the slurry was within the appropriate range (the range displayed by the green bar on the device), and particle size distribution measurement was performed. From the obtained particle size distribution curve, the particle size at the point where the cumulative volume distribution was 90% and the particle size at the point where the cumulative volume distribution was 10% were determined, and the D of the mixed powder after crushing was calculated. 90 , D 10 of the primary particles, 90 , D 10 The D of the obtained primary particles was calculated as 90 , D 10 From log 10 (D 90 )-log 10 (D 10 ) values ​​were calculated.

[0104] [Evaluation of battery characteristics] Coin-type batteries were fabricated using the lithium titanate powders of each Example and Comparative Example, and their battery characteristics were evaluated. The evaluation results are shown in Tables 1 and 2.

[0105] <Preparation of negative electrode sheet> The negative electrode sheet was prepared as follows in a room controlled at a room temperature of 25°C and a dew point of -20°C or less. The lithium titanate powder of each example was removed from an aluminum laminate bag in a room controlled at a temperature of 25°C and a dew point of -20°C or less. The removed lithium titanate powder of each example was mixed in the following proportions as an active material: 90% by mass of the active material, acetylene black: 5% by mass of a conductive agent, and polyvinylidene fluoride: 5% by mass of a binder. A coating material was prepared by mixing the following proportions: Polyvinylidene fluoride, acetylene black, and 1-methyl-2-pyrrolidone, which had been previously dissolved in 1-methyl-2-pyrrolidone, were mixed in a planetary agitator / defoamer, and then the lithium titanate powder was added. The total solids concentration was adjusted to 64% by mass, and the mixture was mixed in a planetary agitator / defoamer. Then, 1-methyl-2-pyrrolidone was added, and the total solids concentration was adjusted to 50% by mass, and the mixture was mixed in a planetary agitator / defoamer to prepare a coating material. The resulting coating material was applied to aluminum foil and dried to prepare a single-sided negative electrode sheet for use in a coin battery (described later) and a double-sided negative electrode sheet for use in a laminate battery (described later). The target coating weight was 7.5 mg / cm. 2 It was decided.

[0106] <Measurement of electrode density> The negative electrode single-sided sheet coated in the above manner was pressed with a roll press (roll φ60 × 150 mm, press pressure equivalent to 40 MPa), and the density of the active material layer was measured as "electrode density." The evaluation results are shown in Table 1. A high electrode density is desirable because it allows more active material to be packed into a given volume, resulting in an increase in the capacity that can be used as a battery.

[0107] <Preparation of positive electrode sheet> A single-sided positive electrode sheet was produced in the same manner as described above in <Production of Negative Electrode Sheet>, including the ratios of the active material, conductive agent, and binder, except that lithium nickel cobalt manganese oxide powder was used as the active material.

[0108] <Preparation of electrolyte> The electrolyte used in the battery for characteristic evaluation was prepared as follows. In an argon glove box controlled at a temperature of 25°C and a dew point of -70°C or less, a nonaqueous solvent of ethylene carbonate (EC):dimethyl carbonate (DMC) = 1:2 (volume ratio) was prepared, and LiPF6 was dissolved in this as an electrolyte salt to a concentration of 1 M to prepare the electrolyte for the coin battery described below. Similarly, a nonaqueous solvent of propylene carbonate (PC):diethyl carbonate (DEC) = 1:2 (volume ratio) was prepared, and LiPF6 was dissolved in this as an electrolyte salt to a concentration of 1.3 M to prepare the electrolyte for the laminate battery described below.

[0109] <Creating a coin battery> The negative electrode single-sided sheet prepared by the above method was punched into a circle with a diameter of 14 mm and cut into 2 t / cm 2 An electrode for evaluation was prepared by pressing the electrode at a pressure of 1000 kJ / cm2 and then vacuum drying at 120°C for 5 hours. The electrode for evaluation and metallic lithium (formed into a circle with a thickness of 0.5 mm and a diameter of 16 mm) were placed opposite each other via glass filters (one each of ADVANTEC GA-100 and Whatman GF / C), and the nonaqueous electrolyte prepared by the method described above in <Preparation of electrolyte> was added and sealed to prepare a 2032-type coin battery.

[0110] <Making a laminated battery> The laminate battery was fabricated in a room controlled at a room temperature of 25°C and a dew point of -40°C or less as follows. 2 After pressing at a pressure of 2 t / cm, a negative electrode having a lead wire connection portion was fabricated. 2After pressing at a pressure of 1000 kJ / cm², a positive electrode with a lead wire connection was fabricated. The fabricated negative and positive electrodes were vacuum dried at 150°C for 12 hours. After vacuum drying, the positive and negative electrodes were stacked facing each other with a separator (UPZ210, manufactured by Ube Industries) in between. Aluminum foil lead wires were connected to the positive and negative electrodes, respectively. The laminated battery electrolyte prepared as described in the "Preparation of Electrolyte" section above was added, and the laminate was vacuum sealed with an aluminum laminate to fabricate a laminated battery for evaluation. The battery capacity was 30 mAh, and the ratio of the negative and positive electrode capacities (negative electrode capacity / positive electrode capacity) was 1.2. Next, as an aging step, the laminate battery prepared by the method described above in <Preparation of Laminated Battery> was charged to 2.75 V at a current of 0.2 C in a constant temperature bath at 25°C, and then subjected to constant current / constant voltage charging at 2.75 V until the charging current became 0.05 C, followed by three cycles of constant current discharge at a current of 0.2 C to 1.4 V. The volume of the laminate battery was then measured by Archimedes' method, and this was defined as the initial volume of the laminate battery (hereinafter sometimes referred to as the initial volume).

[0111] <Coin battery: Measurement of initial discharge capacity, volumetric energy density, and 50-rate characteristics> The coin battery fabricated by the method described in the above <Coin Battery Fabrication> was placed in a thermostatic chamber at 25°C and charged at 0.2 mA / cm in the direction in which Li was absorbed into the evaluation electrode. 2 The battery was charged to 1 V at a current density of 0.05 mA / cm at 1 V. 2 After constant current and constant voltage charging, the current density was increased to 0.2 mA / cm. 2Three cycles of constant-current discharge were performed, with the battery discharging to 2 V at a current density of 1000 kJ / g. The discharge capacity (mAh) at the third cycle was divided by the mass of lithium titanate to determine the initial discharge capacity (mAh / g). This initial discharge capacity was multiplied by the electrode density calculated above to determine the volumetric energy density. A high volumetric energy density increases the capacity available per unit volume of the battery, which is desirable for miniaturization. Next, the battery was charged to 1 V at a current equivalent to 1 C of the initial discharge capacity, and then discharged to 2 V at a current of 50 C to determine the 5 C discharge capacity. The rate capability (%) was calculated by dividing the 50 C discharge capacity by the initial discharge capacity. A high 50 C rate capacity percentage of lithium titanate powder is expected to improve the charge rate capability of energy storage devices when used as an electrode material. The evaluation results are shown in Table 1. Note that the "C" in 1 C represents the current value during charging and discharging. For example, 1C refers to the current value that can fully discharge (or fully charge) the theoretical capacity in 1 / 1 hour, and 0.1C refers to the current value that can fully discharge (or fully charge) the theoretical capacity in 1 / 0.1 hour.

[0112] <Laminated battery: Initial IMP (impedance) measurement> A symmetrical cell with both electrodes negative was created by removing the negative electrode sheet from the laminated battery fabricated by the method described above in <Fabrication of Laminated Battery>. Using this cell, IMP (impedance) measurements were performed at -20°C and from 0.01 to 10 MHz to determine the IMP value (Ω) from a specific frequency (1 Hz) to -20°C.

[0113] <Laminated battery: Measurement of initial low-temperature input characteristics at -30°C> Using the laminated battery fabricated by the method described above in <Fabrication of Laminated Battery>, the charge capacity was measured when charging to 2.75 V at a constant current (CC) equivalent to 1 C at 25°C and -30°C. The low-temperature input characteristics at -30°C were calculated by inserting this value into the following equation.

number

[0114] <Laminated battery: Measurement of low-temperature input characteristics at -30°C after 400 cycles at 55°C> Using a laminated battery prepared by the method described above in <Preparation of Laminated Battery>, the battery was charged at a current of 1 C up to 2.75 V in a thermostatic chamber at 55°C, and then subjected to constant-current, constant-voltage charging in which the battery was further charged at 2.75 V until the charging current became 0.05 C, and then constant-current discharging in which the battery was discharged at a current of 1 C down to 1.4 V was repeated 400 cycles.

[0115] After 400 cycles, the charge capacity was measured at -30°C when the battery was charged to 2.75 V at a constant current (CC) equivalent to 1 C. This value was used in the above (Equation 1) to calculate the low-temperature input characteristics at -30°C.

[0116] <Laminated battery: Amount of gas generated after high-temperature storage at 60°C and charge rate characteristics> A laminate battery fabricated by the method described above in <Fabrication of Laminated Battery> was charged to 2.75 V at a current of 0.2 C in a 25°C thermostatic chamber, and then subjected to a 30-day storage test in a 60°C thermostatic chamber. After the storage test, the volume of the laminate battery was measured using the Archimedes method to determine the post-storage volume (hereinafter sometimes referred to as "post-storage volume"). The amount of gas generated (ml) was calculated by subtracting the initial volume from the post-storage volume. Table 1 shows the relative value, with the amount of gas generated in Comparative Example 1-1 set to 100%. Furthermore, the battery after the storage test was used to determine the charge capacity when charged at currents of 0.5 C and 0.2 C, and the charge rate characteristics were calculated from the ratio. The results are shown in Table 1.

[0117] [Table 1]

[0118] <Evaluation results> The electrodes using the lithium titanate powders of Examples 1-1 to 1-3 were excellent in maintaining a good balance of electrode density, volumetric energy density, rate characteristics, initial low-temperature input characteristics, and charge rate characteristics after high-temperature storage. On the other hand, when lithium titanate powders produced at firing temperatures, post-treatment processes, or surface treatment processes different from those of Examples 1-1 to 1-3 were used (Comparative Examples 1-1 to 1-5), the volumetric energy density decreased due to a decrease in electrode density, or the low-temperature characteristics decreased, and the amount of gas generated and resistance increased during high-temperature operation. In particular, the log of primary particles containing aluminum on the surface but produced at firing temperatures and post-treatment processes different from those of Example 1-1 10 (D 90 )-log 10 (D 10 When a lithium titanate powder having a value of 0.8 or more was used (Comparative Example 1-1), the value of the diameter equivalent to the specific surface area (DBET) calculated from the specific surface area determined by the BET method was almost the same as in Example 1-1, but the electrode density was reduced, resulting in a lower volumetric energy density and an increased amount of gas generated after storage. Furthermore, a comparison of Example 1-1 and Example 1-3 revealed that the rate characteristics and low-temperature input characteristics could be further improved by adjusting the firing temperature and the number of crushing passes in the post-treatment process.

[0119] [Influence of manufacturing process conditions for lithium titanate powder] [Examples 2-1 to 2-3] A lithium titanate powder was produced in the same manner as in Example 1-2 except that the firing step and post-treatment step were carried out under the conditions shown in Table 2, and evaluations were carried out using coin batteries and laminate batteries.

[0120] [Table 2]

[0121] <Evaluation results> It was found that the electrodes using the lithium titanate powders of Examples 2-1 to 2-3 tend to be excellent in maintaining a good balance of electrode density, volumetric energy density, rate characteristics, and initial low-temperature input characteristics. In particular, it was found that the electrode density and initial low-temperature input characteristics can be further improved by adjusting the number of crushing passes in the post-treatment process.

[0122] (All-solid-state secondary battery) [Example 3-1] In a glove box under an argon atmosphere, the lithium titanate powder from Example 1-2 and a sulfide solid electrolyte powder, Li6PS5Cl (volume average particle size: 6 μm, measured using a laser diffraction / scattering particle size distribution analyzer), were weighed out to a mass ratio of 60:40, and mixed in an agate mortar. Next, zirconia balls (3 mm diameter, 20 g) were placed in an 80 mL zirconia pot, and the mixed powder was added. The pot was then placed in a planetary ball mill, and stirring was continued at 200 rpm for 15 minutes, yielding the negative electrode active material composition of Example 2-1. The resulting negative electrode active material composition was pressed (360 MPa) at room temperature for 10 minutes to produce a pellet (molded body) with a diameter of 10 mm and a thickness of approximately 0.7 mm. A pellet-shaped electrode containing this negative electrode active material composition, a pellet-shaped solid electrolyte layer (LPS glass with a molar ratio of Li2S:P2S5 = 75:25) as a separator layer, and a lithium-indium alloy foil as a counter electrode were laminated in this order, and the laminate was sandwiched between stainless steel current collectors to fabricate an all-solid-state secondary battery. The battery characteristics were evaluated by charging and discharging at 0.05 C and 0.5-2.0 V. As a result, a discharge capacity of 133 mAh / g was confirmed initially, confirming that the composition also functions effectively as an active material for all-solid-state secondary batteries.

[0123] [Comparative Example 3-1] An all-solid-state secondary battery was fabricated and its battery characteristics were evaluated in the same manner as in Example 3-1, except that the lithium titanate powder was changed to the lithium titanate powder of Comparative Example 1-5. As a result, a discharge capacity of 118 mAh / g was confirmed initially, which was inferior to that of Example 3-1. [Industrial Applicability]

[0124] The lithium titanate powder obtained by the present invention is excellent in maintaining a good balance of electrode density, volumetric energy density, rate characteristics, initial low-temperature input characteristics, and charge rate characteristics after high-temperature storage. For example, the lithium titanate powder can have an electrode density of 1.98 g / cm. 3 As described above, the lithium titanate has battery properties such as a volumetric energy density of 334 mAh / g or more, a 50C rate characteristic of 74% or more, an initial low-temperature input characteristic of 46% or more, and a charge rate characteristic after high-temperature storage of 93% or more, making it useful as an electrode active material for lithium ion secondary batteries.Furthermore, lithium ion secondary batteries using this lithium titanate as an electrode active material are capable of stable, high-speed charging and discharging, making them useful as energy storage devices such as secondary batteries for driving or backing up various devices such as automobiles and electronic devices, and for storing power at night in homes and offices.

Claims

1. Li ４ Ti ５ O １２ a lithium titanate powder having as a main component thereof aluminum (Al) locally present on the surfaces of primary particles of the lithium titanate powder, an aluminum content of the lithium titanate powder being 0.2 mass% or more and 0.4 mass% or less, and satisfying the following formula (I): log １０ (D ９０ )-log １０ (D １０ ) < 0.8 (I) (Note: D ９０ indicates the particle size at which the cumulative volume distribution of the particle size of primary particles is 90% in the particle size distribution, and D １０ indicates the particle size at the point where the cumulative volume distribution of particle sizes of primary particles is 10% in the particle size distribution.

2. 2. The lithium titanate powder according to claim 1, wherein the lithium titanate powder satisfies the following formula (II): log １０ (D ９０ )-log １０ (D １０ ) < 0.7 (II) (Note: D ９０ indicates the particle size at which the cumulative volume distribution of the particle size of primary particles is 90% in the particle size distribution, and D １０ indicates the particle size at the point where the cumulative volume distribution of particle sizes of primary particles is 10% in the particle size distribution.

3. The particle size D of the primary particles corresponding to 50% cumulative volume in the particle size distribution ５０ 3. The lithium titanate powder according to claim 1, wherein the particle size is 0.5 μm or more.

4. 4. The lithium titanate powder according to claim 3, wherein the lithium titanate powder contains primary particles and secondary particles of lithium titanate and satisfies the following formula (III): Primary particle D ５０ / Secondary particle D ５０ ≦ 0.05 (III)

5. In the lithium titanate powder, the specific surface area is 6 m ２ 5. The lithium titanate powder according to claim 4, wherein the SiO 2 content is 1 / g or more.

6. An electrode comprising the lithium titanate powder according to any one of claims 1 to 5.

7. An electricity storage device comprising the electrode according to claim 6.

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