JP2017084788A - Lithium titanium composite oxide powder and active substance material for power storage device electrode, and electrode sheet and power storage device which are arranged by use thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: lithium titanium composite oxide powder which is superior in high-temperature charge and discharge cycle characteristics, and enables the suppression of gas generation at a high temperature; an active substance material; and a power storage device arranged by use thereof.SOLUTION: Powder of a lithium titanium composite oxide has a crystal structure belonging to the space group Fd-3 m and is expressed by LiM1M2M3M4TiO(where M1 represents at least one of Mg, Ca, Sr, Ba and Ni, M2 represents at least one of Cr, Al, Ga, Co and Y, M3 represents at least one of Zr and Ge, M4 represents at least one of V, Nb, Sb and Ta, 0.9≤x≤1.1, 0≤y1≤1.1, 0≤y2≤1.1, 0≤y3≤1.1, 0≤y4≤1.10≤(y1+y2+y3+y4)≤1.1, 2.9≤{(2y1+3y2+4y3+5y4)/(y1+y2+y3+y4)}≤3.1). The lithium titanium composite oxide powder has a specific surface area of 1-50 m/g, and a crystallite diameter of 80 nm or larger.SELECTED DRAWING: None

Description

  The present invention relates to a lithium-titanium composite oxide powder suitable as an electrode material for an electricity storage device, an active material containing the lithium-titanium composite oxide powder, an electrode sheet using the active material, and an electricity storage device It is.

  In recent years, various materials have been studied as electrode materials for power storage devices. Among them, lithium-titanium composite oxides can provide an electricity storage device with excellent input / output characteristics when used as an active material for a negative electrode, and thus are attracting attention as an active material material for electricity storage devices for electric vehicles such as HEV, PHEV, and BEV. ing. Among them, lithium titanate having a spinel structure has almost no volume change associated with charge / discharge and can move three-dimensional Li ions, and is particularly excellent in charge / discharge cycle characteristics and input / output characteristics. It is promising as an active material for electricity storage devices.

However, in lithium titanate having a spinel structure (Li ₄ Ti ₅ O ₁₂ ), the lithium occlusion and release reaction proceeds at a high potential of about 1.55 V, so the operating voltage of the electricity storage device to which it is applied is low. , Energy density becomes smaller.

Therefore, as an electrode material having a relatively high lithium occlusion-release reaction, LiTi ₂ O ₄ having a crystal structure belonging to the space group Fd-3m, and a part of the Li site or Ti site of LiTi ₂ O ₄ are other elements. Substituted lithium titanium composite oxides have attracted attention, and various studies have been made as electrode materials.

For example, Patent Document 1 discloses Li _x Ti _y O ₄ (where 0 <x ≦ 2, 0 <y ≦ 3) or Li _a Ti _{b McO 4} (where 0 <a ≦ 2, 0 <B ≦ 3, 0 <c ≦ 3, where M is at least one element selected from Mn, Fe, Cr, Ni, Co, Mg, and B), and LiTi ₂ A lithium titanium composite oxide such as O ₄ and LiTi _0.9 Mn _1.1 O ₄ is specifically disclosed.

Patent Document 2 describes that high-purity LiTi ₂ O ₄ can be produced by reacting a lithium compound, TiO ₂ and Ti ₃ O ₅ , and Li ₂ TiO ₃ and Ti ₃ O ₅ are combined with each other. It is specifically disclosed that high purity LiTi ₂ O ₄ was obtained by mixing and heating the obtained mixed powder at 800 ° C. for 16 hours and cooling over 12 hours.

Patent Document 3 _discloses lithium iron titanium having a crystal structure represented by Li _{(1 + x) / 2} Fe _{(5-3x) / 2} Ti _x O ₄ (0 ≦ x <1) and belonging to the space group Fd-3m. An oxide is described, and lithium iron titanium oxide such as Li _0.9375 Fe _1.1875 Ti _0.875 O ₄ has a larger initial discharge capacity in a charge / discharge cycle test (25 ° C.) than LiFeTiO ₄ or the like. Is specifically disclosed. Further, in the composition represented by the composition formula, it is specifically disclosed that although the initial discharge capacity becomes smaller as the composition of x increases, the capacity retention rate in the charge / discharge cycle test (25 ° C.) becomes larger. Yes.

JP-A-8-180874 JP 2003-238156 A JP 2014-78442 A

However, LiTi ₂ O ₄ having a crystal structure belonging to the space group Fd-3m as described above, and a lithium titanium composite oxide in which a part of the Li site or Ti site of LiTi ₂ O ₄ is substituted with another element Has a poor charge / discharge cycle characteristic at high temperatures, and is an important subject for application to an electric storage device for an electric vehicle that is required to have excellent charge / discharge cycle characteristics even in a high temperature environment. It is also an important issue to suppress gas generation in a high temperature environment.

  Therefore, the present invention is a lithium-titanium composite oxide powder that is excellent in charge / discharge cycle characteristics under a high-temperature environment and that suppresses gas generation after the charge-discharge cycle under a high-temperature environment, and an active material, and the same. It aims at providing an electrode sheet and an electrical storage device.

As a result of examining the above problems, the present inventors have found that a lithium titanium composite oxide represented by LiTi ₂ O ₄ having a crystal structure belonging to the space group Fd-3m and a part of the Ti site of LiTi ₂ O _4. Is substituted with a specific element, and when there are two or more elements that replace the Ti site, a specific specific surface area and a specific crystallite diameter in a lithium-titanium composite oxide having a specific relationship in their proportion. It was found that the lithium titanium composite oxide had a long charge / discharge cycle life at a high temperature and a small amount of gas was generated after the charge / discharge cycle in a high temperature environment, thereby completing the present invention. That is, the present invention relates to the following matters.

(1) has a crystal structure belonging to the space group Fd-3m, the general _{formula: Li x M1 y1 M2 y2 M3} y3 M4 y4 Ti 2-y1-y2-y3-y4 O 4 ( provided that, M1 is Mg, Ca, Sr , Ba and Ni, M2 is at least one element selected from Cr, Al, Ga, Co and Y, and M3 is at least one element selected from Zr and Ge M4 is at least one element selected from V, Nb, Sb and Ta, x is 0.9 ≦ x ≦ 1.1, y1 is 0 ≦ y1 ≦ 1.1, and y2 Is 0 ≦ y2 ≦ 1.1, y3 is 0 ≦ y3 ≦ 1.1, y4 is 0 ≦ y4 ≦ 1.1, y1 + y2 + y3 + y4 is 0 ≦ (y1 + y2 + y3 + y4) ≦ 1.1, 2y + 3y2 + 4y3 + 5y4) / (y1 + y2 + y3 + y4) is a lithium-titanium composite oxide powder having a lithium-titanium composite oxide represented by 2.9 ≦ {(2y1 + 3y2 + 4y3 + 5y4) / (y1 + y2 + y3 + y4)} ≦ 3.1. , specific surface area determined by the BET method is ^{1m 2} / ^g~50m 2 / g, the X-ray diffraction peak corresponding to (111) plane of LiTi ₂ O ₄ having a crystal structure belonging to the space group Fd-3m half the crystallite size calculated from the Scherrer formula from the width is taken as D _X, the electrode active material for a lithium-titanium composite oxide powder of the power storage device, wherein the D _X is 80nm or more.

(2) The electrode of the electricity storage device according to (1), wherein the ratio D _BET / D _X (μm / μm) of D _BET and D _X is 4 or less when the specific surface area equivalent diameter is D _BET Lithium titanium composite oxide powder for active materials.

  (3) The lithium-titanium composite oxide powder for an electrode active material for an electricity storage device according to (1) or (2), wherein the total pore volume is 0.001 ml / g to 0.5 ml / g.

  (4) The lithium titanium composite oxide powder for an electrode active material for an electricity storage device according to any one of (1) to (3), wherein y2 is y2> 0 in the general formula.

  (5) The electrode active material for an electricity storage device according to any one of (1) to (4), wherein at least two of y1, y2, y3, and y4 in the general formula are greater than 0. Lithium titanium composite oxide powder.

  (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 electrode sheet for an electricity storage device, comprising the active material of (6), at least one conductive agent selected from graphites, carbon blacks, and carbon nanotubes, and a binder.

  (8) The electrode sheet for an electricity storage device according to (7), wherein the conductive agent contains at least carbon nanotubes.

  (9) The conductive agent contains at least one conductive agent selected from graphites and carbon blacks in addition to carbon nanotubes, and the proportion of carbon nanotubes in the total conductive agent is 1% by mass or more and 49% by mass. The electrode sheet for an electricity storage device according to (8), characterized in that:

  (10) The carbon nanotubes are formed by stacking 2 to 30 bell-shaped structural units having a top portion having a closed graphite mesh surface and a trunk portion having an open lower portion, sharing a central axis. A plurality of bell-shaped structural unit aggregates, and the carbon nanotubes are formed by connecting a plurality of bell-shaped structural unit aggregates at intervals in a head-to-tail manner to form fibers. The electrode sheet for an electricity storage device according to any one of (7) to (9).

  (11) An electricity storage device using the electrode sheet according to any one of (7) to (10).

  (12) An electricity storage device including a positive electrode including a material capable of inserting and extracting lithium as an active material, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. And the said negative electrode contains the electrode sheet in any one of (7)-(10), The electrical storage device characterized by the above-mentioned.

  (13) The nonaqueous electrolytic solution is obtained by dissolving an electrolyte salt in a nonaqueous solvent, and ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, and 2,3-butylene are dissolved in the nonaqueous solvent. A ratio of cyclic carbonate having at least one alkylene chain selected from propylene carbonate, 1,2-butylene carbonate and 2,3-butylene carbonate in all cyclic carbonates, including at least one cyclic carbonate selected from carbonates (55) is 55 volume% or more and 100 volume% or less.

  (14) The non-aqueous electrolyte is obtained by dissolving an electrolyte salt in a non-aqueous solvent, and dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, It contains a chain ester having at least one methyl group selected from methyl propionate, methyl acetate and ethyl acetate, and the content of all chain esters in the non-aqueous solvent is 60% by volume or more and 90% by volume or less. The electric storage device according to (12) or (13),

(15) The non-aqueous electrolyte is obtained by dissolving an electrolyte salt in a non-aqueous solvent, and includes at least LiPF ₆ as the electrolyte salt in the non-aqueous electrolyte, and further includes LiBF ₄ , LiPO ₂ F ₂ and The electrical storage device according to (12) to (14), wherein at least one lithium salt selected from LiN (SO ₂ F) ₂ is contained in the nonaqueous electrolytic solution at a concentration of 0.001M to 1M.

  (16) The power storage device according to any one of (11) to (15) is a lithium ion secondary battery, and a charging potential in a fully charged state of a negative electrode of the lithium ion secondary battery is 1.15 V with respect to a lithium reference electrode. A lithium ion secondary battery characterized by the above.

  (17) The lithium ion secondary battery according to (16), wherein a discharge potential of the negative electrode in a completely discharged state is 1.8 V or less with respect to a lithium reference electrode.

  (18) The lithium ion secondary battery according to (16) or (17), wherein the active material contained in the positive electrode is a composite metal oxide having a spinel structure.

  (19) The lithium ion secondary battery according to (18), wherein the composite metal oxide having a spinel structure contains manganese.

(20) The lithium ion secondary battery according to (19), wherein the composite metal oxide having a spinel structure is LiMn ₂ O ₄ or LiNi _0.5 Mn _1.5 O ₄ .

(21) The lithium ion secondary battery according to (19), wherein the composite metal oxide having a spinel structure is LiMn ₂ O ₄ .

  According to the present invention, when applied as an electrode material for an electricity storage device, the charge / discharge cycle life at high temperatures is long, that is, the discharge capacity retention rate after charge / discharge cycles at high temperatures is large, and the gas after charge / discharge cycles A lithium-titanium composite oxide powder with a small amount of generation, an active material containing the same, an electrode sheet using the active material, and an electricity storage device can be provided.

(Lithium titanium composite oxide powder)
The lithium titanium composite oxide powder of the present invention has a crystal structure belonging to the space group Fd-3m, and has a general formula: Li _x M1 _y1 M2 _y2 M3 _y3 M4 _y4 Ti _{2-y1-y2-y3-y4} O ₄ , M1 is at least one element selected from Mg, Ca, Sr, Ba and Ni, M2 is at least one element selected from Cr, Al, Ga, Co and Y, and M3 is Zr and Ge M4 is at least one element selected from V, Nb, Sb and Ta, x is 0.9 ≦ x ≦ 1.1, and y1 is 0 ≦ y1 ≦ 1.1, y2 is 0 ≦ y2 ≦ 1.1, y3 is 0 ≦ y3 ≦ 1.1, y4 is 0 ≦ y4 ≦ 1.1, and y1 + y2 + y3 + y4 is 0 ≦ (y1 + y2 + 3 + y4) ≦ 1.1, and (2y1 + 3y2 + 4y3 + 5y4) / (y1 + y2 + y3 + y4) is 2.9 ≦ {(2y1 + 3y2 + 4y3 + 5y4) / (y1 + y2 + y3 + y4)} ≦ 3.1.) a lithium-titanium composite oxide powder with a specific surface area determined by the BET method is that ^{1m 2 / g~50m 2 / g,} Li x M1 having a crystal structure belonging to the space group Fd-3m y1 _M2 y2 _{M3 y3} M4 _y4 Ti _{2-y1-y2-y3-y4} O ₄ (where M1 is at least one element selected from Mg, Ca, Sr, Ba and Ni, and M2 is Cr, Al, Ga, Co and Y) At least one element selected from: M3 is at least selected from Zr and Ge Is also a kind of element, M4 is at least one element selected from V, Nb, Sb and Ta, x is 0.9 ≦ x ≦ 1.1, and y1 is 0 ≦ y1 ≦ 1.1. Y2 is 0 ≦ y2 ≦ 1.1, y3 is 0 ≦ y3 ≦ 1.1, y4 is 0 ≦ y4 ≦ 1.1, and y1 + y2 + y3 + y4 is 0 ≦ (y1 + y2 + y3 + y4) ≦ 1.1 (2y1 + 3y2 + 4y3 + 5y4) / (y1 + y2 + y3 + y4) is 2.9 ≦ {(2y1 + 3y2 + 4y3 + 5y4) / (y1 + y2 + y3 + y4)} ≦ 3.1)) belonging to the space group Fd-3m, which belongs to the space group Fd-3m. When the crystallite diameter calculated from the Scherrer equation from the half-value width of the X-ray diffraction peak corresponding to the (111) plane of LiTi ₂ O ₄ having a structure is D _X An electrode active material for lithium-titanium composite oxide powder of the power storage device, wherein the D _X is 80nm or more.

Here, the general formula Li _x M1 _y1 M2 _y2 M3 _y3 M4 _y4 Ti _{2-y1-y2-y3-y4} O ₄ (where M1 is Mg, Ca, Sr) having a crystal structure belonging to the space group Fd-3m. , Ba and Ni, M2 is at least one element selected from Cr, Al, Ga, Co and Y, and M3 is at least one element selected from Zr and Ge M4 is at least one element selected from V, Nb, Sb and Ta, x is 0.9 ≦ x ≦ 1.1, y1 is 0 ≦ y1 ≦ 1.1, and y2 Is 0 ≦ y2 ≦ 1.1, y3 is 0 ≦ y3 ≦ 1.1, y4 is 0 ≦ y4 ≦ 1.1, y1 + y2 + y3 + y4 is 0 ≦ (y1 + y2 + y3 + y4) ≦ 1.1, 2 1 + 3y2 + 4y3 + 5y4) / (y1 + y2 + y3 + y4) is 2.9 ≦ {(2y1 + 3y2 + 4y3 + 5y4) / (y1 + y2 + y3 + y4)} ≦ 3.1.) The main phase is measured by the X-ray diffraction method. Among the diffraction peaks, the main peak of LiTi ₂ O ₄ in the PDF card 00-040-0407 of ICDD (PDF 2010), that is, the (111) plane of LiTi ₂ O ₄ having a crystal structure belonging to the space group Fd-3m ( When the peak intensity of the peak corresponding to the diffraction peak belonging to 2θ = 18.1 to 18.5 ° is defined as 100, the total peak intensity of the main peaks of other phases detected is 5 or less. Say.

Other phases detected when the lithium titanium composite oxide represented by the above general formula is synthesized usually include anatase type titanium dioxide, rutile type titanium dioxide and Li ₂ TiO _3, and the lithium of the present invention. As the titanium composite oxide, among the diffraction peaks measured by the X-ray diffraction method, the main peak of LiTi ₂ O ₄ in PDF card 00-040-0407 of ICDD (PDF2010), that is, a crystal belonging to the space group Fd-3m. When the peak intensity of a peak corresponding to the diffraction peak attributed to the (111) plane (2θ = 18.1 to 18.5 °) of LiTi ₂ O ₄ having a structure is 100, PDF card 01-070-6826 The main peak of anatase-type titanium dioxide at, ie, (101) plane (2θ = 24.7 to 25.7) ), The intensity of the peak corresponding to the diffraction peak attributed to), the main peak of rutile titanium dioxide in PDF card 01-070-7347, ie the diffraction attributed to the (110) plane (2θ = 27.2 to 27.6 °). The intensity of the peak corresponding to the peak, the peak corresponding to the diffraction peak attributed to the (−133) plane (2θ = 2θ = 43.5 to 43.8 °) of Li ₂ TiO ₃ in PDF card 00-033-0831 The total peak intensity corresponding to the (002) plane, which is the main peak of Li ₂ TiO ₃ , calculated by multiplying the peak intensity by 100/80, is preferably 5 or less. For Li ₂ TiO _3, a main peak of Li 2 TiO ₃ (002) plane attributed to place the peak _was calculated by multiplying the 100/80 to the intensity of the peak of Li 2 TiO ₃ of (-133) plane attributed The value is used, and this is the intensity of the peak corresponding to the (002) plane, which is the main peak of Li ₂ TiO ₃ . A main peak of Li ₂ TiO ₃ (002) plane whereas it may be necessary to peak separation peak attributions overlap with skirt of the peak of attribution (111) plane of LiTi ₂ O _4, Li ₂ This is because the peak corresponding to the (−133) plane of TiO ₃ does not overlap with the peaks attributed to other constituent phases, and the intensity corresponding to the main peak of Li ₂ TiO ₃ can be calculated more easily. Also, multiplying by 100/80 is based on these peak intensity ratios. Note that “ICDD” is an abbreviation for International Center for Diffraction Data, and “PDF” is an abbreviation for Powder Diffraction File.

_{Li x M1 y1 M2 y2 M3 y3} M4 y4 Ti 2-y1-y2-y3-y4 O 4 having a crystal structure belonging to the space group Fd-3m (although, M1 is selected from Mg, Ca, Sr, Ba and Ni M2 is at least one element selected from Cr, Al, Ga, Co and Y, M3 is at least one element selected from Zr and Ge, M4 is V, And at least one element selected from Nb, Sb and Ta, x is 0.9 ≦ x ≦ 1.1, y1 is 0 ≦ y1 ≦ 1.1, and y2 is 0 ≦ y2 ≦ 1. 1, y3 is 0 ≦ y3 ≦ 1.1, y4 is 0 ≦ y4 ≦ 1.1, y1 + y2 + y3 + y4 is 0 ≦ (y1 + y2 + y3 + y4) ≦ 1.1, and (2y1 + 3y2 + 4y + 5y4) / (y1 + y2 + y3 + y4) is 2.9 ≦ {(2y1 + 3y2 + 4y3 + 5y4) / (y1 + y2 + y3 + y4)} ≦ 3.1.) The smaller the components, the higher the initial discharge capacity of the electricity storage device. The number of other phases is preferably small, and the total peak intensity of main peaks of other phases to be detected is particularly preferably 3 or less.

  M1 in the general formula is at least one element selected from Mg, Ca, Sr, Ba, and Ni. When M1 is at least one of these elements, the discharge capacity retention rate after the charge / discharge cycle in a high temperature environment is increased. As M1, Mg or Ni is preferable and Mg is particularly preferable from the viewpoint of further improving the discharge capacity retention rate after the charge / discharge cycle in a high temperature environment.

  M2 in the general formula is at least one element selected from Cr, Al, Ga, Co, and Y. When M2 is at least one of these elements, the discharge capacity retention rate after the charge / discharge cycle in a high temperature environment is increased. As M2, Al or Cr is preferable, and Cr is particularly preferable from the viewpoint of further improving the discharge capacity retention rate after the charge / discharge cycle in a high temperature environment.

  M3 in the general formula is at least one element selected from Zr and Ge. When M3 is at least one of these elements, the discharge capacity retention rate after the charge / discharge cycle under a high temperature environment is increased. As M3, Ge is preferable from the viewpoint of improving the discharge capacity retention rate after the charge / discharge cycle in a high temperature environment.

  M4 in the general formula is at least one element selected from V, Nb, Sb, and Ta. When M4 is at least one of these elements, the discharge capacity retention rate after a charge / discharge cycle in a high temperature environment increases. M4 is preferably V or Nb, particularly preferably Nb, from the viewpoint of improving the discharge capacity retention rate after the charge / discharge cycle in a high temperature environment.

  The upper limit of x in the general formula is 1.1. When x is 1.1 or less, the discharge capacity retention rate after the charge / discharge cycle in a high temperature environment increases. The upper limit of x is preferably 1.08, more preferably 1.06 from the viewpoint of maximizing the utilization efficiency of lithium ions and improving the discharge capacity retention rate after a charge / discharge cycle in a high temperature environment. And particularly preferably 1.04. The lower limit of x in the general formula is 0.9. When x is 0.9 or more, the discharge capacity retention rate after the charge / discharge cycle in a high temperature environment increases. The lower limit of x is preferably 0.92, more preferably 0.94, and particularly preferably 0.96 or more.

  The upper limit of y1 in the general formula is 1.1. When y1 is 1.1 or less, the discharge capacity retention rate after the charge / discharge cycle in a high temperature environment increases. The upper limit of y1 is preferably 1.08, more preferably 1.06, and particularly preferably 1 from the viewpoint of strengthening the crystal structure and improving the discharge capacity retention rate after the charge / discharge cycle in a high temperature environment. .04. The lower limit of y1 in the general formula is 0. The lower limit of y1 is preferably 0.01, more preferably 0.05, and particularly preferably 0.1.

  The upper limit of y2 in the general formula is 1.1. When y2 is 1.1 or less, the discharge capacity maintenance rate after the charge / discharge cycle in a high temperature environment increases. The upper limit of y2 is preferably 1.08, more preferably 1.06, and particularly preferably 1 from the viewpoint of strengthening the crystal structure and improving the discharge capacity retention rate after the charge / discharge cycle in a high temperature environment. .04. The lower limit of y2 in the general formula is 0. y2 is preferably y2> 0. The lower limit of y2 is preferably 0.01, more preferably 0.05, and particularly preferably 0.1.

  The upper limit of y3 in the general formula is 1.1. When y3 is 1.1 or less, the discharge capacity maintenance rate after the charge / discharge cycle in a high temperature environment increases. The upper limit of y3 is preferably 1.08, more preferably 1.06, and particularly preferably 1 from the viewpoint of strengthening the crystal structure and improving the discharge capacity retention rate after the charge / discharge cycle in a high temperature environment. .04. The lower limit of y3 in the general formula is 0. The lower limit of y3 is preferably 0.01, more preferably 0.05, and particularly preferably 0.1.

  The upper limit of y4 in the general formula is 1.1. When y4 is 1.1 or less, the discharge capacity maintenance rate after the charge / discharge cycle in a high temperature environment increases. The upper limit of y4 is preferably 1.08, more preferably 1.06, and particularly preferably 1 from the viewpoint of strengthening the crystal structure and improving the discharge capacity retention rate after the charge / discharge cycle in a high temperature environment. .04. The lower limit of y4 in the general formula is 0. The lower limit of y4 is preferably 0.01, more preferably 0.05, and particularly preferably 0.1.

  The upper limit of y1 + y2 + y3 + y4 in the general formula is 1.1. When y1 + y2 + y3 + y4 is 1.1 or less, the discharge capacity retention rate after the charge / discharge cycle in a high-temperature environment increases. The upper limit of y1 + y2 + y3 + y4 is preferably 1.08, more preferably 1.06, and particularly preferably 1.04 from the viewpoint of strengthening the crystal structure and improving the discharge capacity retention rate. The lower limit of y1 + y2 + y3 + y4 in the general formula is 0. The lower limit of y1 + y2 + y3 + y4 is preferably 0.01, more preferably 0.05, and particularly preferably 0.1.

  In the above general formula, the lithium titanium composite oxide powder of the present invention has (2y1 + 3y2 + 4y3 + 5y4) / (y1 + y2 + y3 + y4) satisfying 2.9 ≦ {(2y1 + 3y2 + 4y3 + 5y4) / (y1 + y2 + y3 + y4)} ≦ 3.1. When (2y1 + 3y2 + 4y3 + 5y4) / (y1 + y2 + y3 + y4) is within this range, the discharge capacity retention rate after the charge / discharge cycle in a high-temperature environment increases. The upper limit of (2y1 + 3y2 + 4y3 + 5y4) / (y1 + y2 + y3 + y4) is preferably 3.08, more preferably 3.06, and particularly preferably 3.04. The lower limit of (2y1 + 3y2 + 4y3 + 5y4) / (y1 + y2 + y3 + y4) is preferably 2.92, more preferably 2.94, and particularly preferably 2.96 or more.

  In the general formula, at least two of y1, y2, y3, and y4 are preferably larger than zero. This is because, in particular, the charge / discharge cycle characteristics under a high temperature environment are excellent, and gas generation after the charge / discharge cycle under a high temperature environment is suppressed.

<Specific surface area>
The specific surface area of the lithium-titanium composite oxide powder of the present invention as determined by the BET method is ^{1m 2} / ^g~50m 2 / g. If the specific surface area is in this range, high input / output characteristics can be realized without impairing the handling of the powder. Preferably ^{2m 2} / ^g~45m 2 / g from the above ^viewpoints, 3m ² / ^g~40m 2 / g is particularly preferred.

<Specific surface area equivalent diameter D _BET >
The specific surface area equivalent diameter D _BET of the lithium titanium composite oxide powder of the present invention is a specific surface area equivalent diameter calculated from the specific surface area determined by the BET method. The specific surface area equivalent diameter D _BET of the lithium titanium composite oxide of the present invention is preferably 0.03 μm to 0.6 μm. When D _BET is 0.03 μm to 0.6 μm, the charge / discharge capacity of the electricity storage device can be increased. Moreover, it is especially preferable that D _BET is 0.03 to 0.4 μm, and if it is within this range, the input characteristics of the electricity storage device are also improved.

<Crystallite diameter D _X >
In the present invention, the crystallite diameter calculated from the Scherrer equation from the half-value width of the diffraction peak corresponding to the (111) plane of LiTi ₂ O ₄ having a crystal structure belonging to the space group Fd-3m is represented by D _X. Here, the diffraction peak corresponding to the (111) plane of LiTi ₂ O ₄ having a crystal structure belonging to the space group Fd-3m is a PDF of ICDD (PDF2010) among diffraction peaks measured by the X-ray diffraction method. In Card 00-040-0407, it refers to a peak corresponding to the diffraction peak attributed to the (111) plane (2θ = 18.1 to 18.5 °) of LiTi ₂ O ₄ . _{D X} of the lithium-titanium composite oxide powder of the present invention is 80nm or more. Suppression and D _X is larger than 80 nm, lithium ions can minimize the effects of resistance when moving the grain boundary, deterioration in battery performance due to polarization increases caused by the grain boundaries lithium ion moves it can. The _{D X} is preferably at 500nm or less. D _X it is possible to minimize the influence of diffusion resistance inside the particles as long as 500nm or less, it is possible to suppress the deterioration of the cell performance due to polarization increases caused by the internal particles of lithium ions to move. A method for measuring the D _X, described in detail in Example.

<D _BET / D _X (μm / μm)>
The ratio D _BET / D _X (μm / μm) of D _BET and D _X of the lithium titanium composite oxide powder of the present invention is preferably 4 or less, more preferably 3 or less, and 2.5 or less. It is more preferable that it is 2 or less. The smaller the D _BET / D _X is, the larger the discharge capacity maintenance rate after a charge / discharge cycle in a high temperature environment of the electricity storage device to which the lithium titanium composite oxide powder of the present invention is applied as an electrode material.

<Total pore volume>
The total pore volume of the lithium titanium composite oxide powder of the present invention is preferably 0.001 to 0.5 ml / g. When the total pore volume is within this range, an electricity storage device having a high discharge capacity retention rate after a charge / discharge cycle in a high temperature environment can be obtained by applying to the electricity storage device. The total pore volume is preferably 0.005 ml / g or more and more preferably 0.01 ml / g or more from the viewpoint of further improving the discharge capacity maintenance rate after the charge / discharge cycle in a high temperature environment. More preferably, it is particularly preferably 0.015 ml / g or more. Further, it is preferably 0.45 ml / g or less, more preferably 0.4 ml / g or less, and particularly preferably 0.35 ml / g or less. The total pore volume of the lithium titanium composite oxide powder of the present invention is the total pore volume measured by a gas adsorption method.

<Volume median particle size>
The volume median particle size (average particle size, hereinafter referred to as D50) of the lithium titanium composite oxide powder of the present invention is preferably 0.01 to 30 μm. In order to suppress the aggregation of the lithium titanium composite oxide powder and improve the handleability when producing the electrode, the upper limit of D50 of the lithium titanium composite oxide powder of the present invention is preferably 20 μm or less, Preferably it is 15 micrometers or less, Most preferably, it is 10 micrometers or less. The lower limit of D50 is preferably 0.1 μm or more, and more preferably 0.5 μm or more. Here, D50 means a particle size in which the cumulative volume frequency calculated by the volume fraction is 50% when integrated from the smaller particle size. The measurement method is described in [5. Particle size distribution].

(Method for producing lithium titanium composite oxide powder)
Hereinafter, an example of the method for producing the lithium titanium composite oxide powder of the present invention will be described by dividing it into a raw material preparation process, a drying / granulation process, and a firing process. The manufacturing method is not limited to this.

<Raw material preparation process>
As a raw material of the lithium titanium composite oxide powder of the present invention, a titanium raw material and a lithium raw material are used. When obtaining a lithium-titanium composite oxide powder having a composition containing a metal element (M1, M2, M3 and M4 in the above general formula) substituting a part of the titanium site, in addition to these raw materials, one or more titanium sites Substitute element materials are used. As the titanium raw material, titanium compounds such as anatase type titanium dioxide, rutile type titanium dioxide, Ti ₂ O ₃ , H ₂ TiO ₃ and Ti metal are used. Two or more kinds of titanium raw materials may be used. As a titanium raw material, it is preferable that it reacts easily with a lithium raw material in a short time, and the anatase type titanium dioxide is preferable from the viewpoint. In particular, when titanium oxide is used for the anatase type, complete anatase type titanium dioxide having a rutile ratio of 0% is preferable.

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

  Examples of the raw material of the element that substitutes a part of the titanium site include M oxide, hydroxide, nitride, phosphide, sulfide, fluoride, chloride, bromide, iodide, or carbonate, sulfate, Inorganic salts such as nitrates, borates and phosphates, and organic salts such as acetates are used. From the viewpoint of ease of synthesis, oxides, fluorides, sulfates, and acetates are 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 4 μm or less. It is preferable to prepare. The D95 is to increase the _{D x,} to reduce the _{D BET / D X (μm /} μm), from the viewpoint of increasing the total pore volume, more preferably 3μm or less, more preferably at 2.5μm or less Yes, particularly preferably 2 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 4 μm or less, and is preferably a granulated powder obtained by granulating a mixed powder having a D95 of 4 μm or less.

  In the case of the composition containing the titanium raw material, the lithium raw material, and the metal element that substitutes a part of the titanium site, the raw material of the titanium site substitution element is mixed in addition to these. As a method for preparing a mixture of a titanium raw material, a lithium raw material, and a titanium site-substitution element raw material to be added as necessary, 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 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.

[Baking process]
The resulting mixture is then fired. From the viewpoint of reducing the particle size of the powder obtained by firing and increasing the crystallite size, firing is preferably performed at a high temperature for a short time. From such a viewpoint, the maximum temperature during firing is preferably 820 to 990 ° C, more preferably 840 to 970 ° C, and particularly preferably 860 to 950 ° C. Similarly, from the above viewpoint, the holding time at the maximum temperature during firing is preferably 8 hours or less, more preferably 7 hours or less, and even more preferably 6 hours or less. When the maximum temperature during firing is high, a shorter holding time is selected. Similarly, from the viewpoint of reducing the particle size of the powder obtained by firing and increasing the crystallite size, it is preferable to particularly shorten the residence time from 700 ° C. to the highest temperature in the temperature rising process during firing, It is preferable that the heating rate is 200 ° C./h or more.

  The firing method is not particularly limited as long as it can be fired under such conditions. Examples of calcining furnaces that can be used include box-shaped and tubular fixed-bed calcining furnaces, roller hearth calcining furnaces, mesh belt calcining furnaces, fluidized-bed calcining furnaces, and rotary kiln calcining furnaces. However, when using a roller hearth firing furnace or a mesh belt firing furnace that contains the granulated powder in a sagger and fires, in order to keep the quality of the resulting lithium titanium composite oxide powder constant, It is preferable to make the temperature distribution of the mixed powder uniform, and it is preferable to reduce the amount of the mixed powder contained in the mortar.

  The atmosphere at the time of firing is not particularly limited, but when the titanium raw material is only a titanium raw material having a valence of titanium of 4, the atmosphere containing oxygen is preferable, and the titanium raw material has a valence of titanium of 4 When a titanium raw material other than the valence is included, an inert atmosphere such as argon gas or nitrogen gas is preferable.

(Active material)
The active material of the present invention contains the lithium titanium composite oxide powder of the present invention. One or more substances other than the lithium titanium composite oxide powder of the present invention may be contained. Examples of other substances include carbon materials (pyrolytic carbons, cokes, graphites (artificial graphite, natural graphite, etc.), organic polymer compound combustion bodies, carbon fibers), tin and tin compounds, silicon and silicon compounds. Is used.

(Electrode sheet)
The electrode sheet of the present invention comprises, as an electrode mixture layer on one or both sides of a current collector, an active material of the present invention, and at least one conductive agent selected from graphites, carbon blacks, and carbon nanotubes. The electrode sheet for an electricity storage device including a binder, and is cut according to the design shape of the electricity storage device and used as a negative electrode. Examples of graphites include natural graphite (such as flake graphite), artificial graphite, and the like. Examples of carbon blacks include acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and the like. Carbon nanotubes include single-phase carbon nanotubes, multi-wall carbon nanotubes (graphite layers are multi-layer concentric cylinders) (non-fishbones), cup-stacked carbon nanotubes (fishbones), and nodal carbon nanofibers (Non-fishbone structure), platelet-type carbon nanofibers (like a playing card), and the like. These graphites, carbon blacks, and carbon nanotubes can 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. The specific surface area of the graphite is preferably 30 to 600 m ² / g, more preferably 50 to 500 m ² / g. The aspect ratio of the carbon nanotubes is preferably 10 to 1000. With such a conductive agent, the electrode density is particularly likely to increase, and the capacity can be easily increased. The addition amount of the conductive agent is optimized depending on the specific surface area of the active material and the type and combination of the conductive agent, but is preferably 10% by mass or less, more preferably 8% by mass with respect to the entire electrode mixture layer. Or less, more preferably 6% by mass or less.

  The electrode sheet of the present invention preferably contains carbon nanotubes as the conductive agent. If carbon nanotubes are included as a conductive agent, the discharge capacity retention rate after a charge / discharge cycle at a high temperature is further increased. Among the carbon nanotubes, multi-walled carbon nanotubes (graphite layers are multi-layer concentric cylinders) (non-fish-bone-like) are preferable. In particular, a head with a closed graphite network surface described in JP 2012-46864 A or the like is used. A bell-shaped structural unit having a top portion and a body portion having an open bottom includes a plurality of bell-shaped structural unit assemblies formed by stacking 2 to 30 layers sharing a central axis, and a plurality of the bell-shaped structural units. Particularly preferred is fibrous carbon in which bell-shaped structural unit aggregates are connected in a head-to-tail manner at intervals to form fibers. If this fibrous carbon is contained as a conductive agent, the discharge capacity maintenance rate after a charge / discharge cycle at a high temperature is particularly increased.

  Furthermore, the electrode sheet of the present invention preferably contains at least one conductive agent selected from graphites and carbon blacks in addition to containing carbon nanotubes as the conductive agent. The proportion of the carbon nanotubes in it is preferably 1% by mass or more and 49% by mass or less, and more preferably 5% by mass or more and 40% by mass or less.

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), a copolymer of styrene and butadiene (SBR), and a copolymer of acrylonitrile and butadiene (NBR). ), Carboxymethylcellulose (CMC) and the like. 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 electrode 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, 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 amount of the binder added is optimized depending on the specific surface area of the active material and the type and combination of the conductive agent, but is usually 0.2 to 15% by mass with respect to the entire electrode mixture layer. . From the viewpoint of enhancing the binding property and increasing the strength of the mixture layer, the content is more preferably 0.5% by mass or more, further preferably 1% by mass or more, and particularly preferably 2% by mass or more. From the viewpoint of increasing the active material ratio in the mixture layer and increasing the discharge capacity of the electricity storage device per unit mass and unit volume of the mixture layer, the addition amount of the binder is preferably 10% by mass or less, More preferably, it is 5 mass% or less.

  Examples of the current collector include aluminum, stainless steel, nickel, copper, titanium, baked carbon, and those whose surfaces are coated with carbon, nickel, titanium, and silver. Moreover, the surface of these materials may be oxidized, and unevenness | corrugation may be given to the collector surface 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.

  The electrode sheet is prepared by adding a solvent to the active material, conductive agent and binder of the present invention, mixing and kneading them, adjusting the viscosity while adding the solvent, and forming a paint. It can be obtained by coating on top, drying and compressing.

  A method for mixing the active material of the present invention, the conductive agent, and the binder in the solvent is not particularly limited, but the active material of the present invention, the conductive agent, and the binder are simultaneously mixed in the solvent. The method of mixing in the method, the method of mixing the conductive material and the binder in a solvent in advance, and then the additional mixing of the active material of the present invention, the slurry of the active material of the present invention, the conductive agent slurry and the binder solution in advance The method of producing and mixing each is mentioned. In order to make these electrode mixture layer constituent materials uniformly disperse in the mixture layer, a method in which the conductive material and the binder are previously mixed in a solvent and then the active material is additionally mixed, and the negative electrode active material slurry, A method of preparing a conductive agent slurry and a binder solution in advance and mixing them 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, the binder is preferably added at the stage of finally adjusting to a desired viscosity in order not to cause the binder to aggregate. When aluminum is used as the negative electrode current collector, it is preferable to adjust pH by adding an acidic compound in order to suppress corrosion of aluminum. 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. Further, as a method for preventing corrosion of aluminum, it is preferable to use an aluminum current collector in which the surface of the aluminum current collector is coated with an alkali-resistant material such as carbon. In the case of using an organic solvent as the solvent, it is preferable to use the binder by dissolving it in an organic solvent in advance.

As an apparatus for mixing and kneading by adding a solvent to the active material, the conductive agent and the binder of the present invention, for example, a kneader of a type in which a stirring bar rotates while rotating in a kneading container such as a planetary mixer In addition, a twin-screw extrusion 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. In addition, it is preferable to start mixing and kneading in a state where the solid content concentration is high, and adjust the viscosity of the coating material by gradually reducing the solid content concentration. It is preferable to use the mixing / kneading apparatus properly. The solid content concentration at the stage of starting mixing and kneading is preferably 60 to 90% by mass, and more preferably 70 to 90% by mass.
If the solid content concentration is 60% by mass or more, sufficient shearing force can be obtained to uniformly disperse the active material of the present invention, the binder, and the conductive agent, and if it is 90% by mass or less, It is possible to avoid applying an extremely large load to the device.

(Electric storage device)
The power storage device of the present invention is a power storage device using the electrode sheet of the present invention, and stores and releases energy using intercalation and deintercalation of lithium ions to the electrode containing the active material. For example, it is a hybrid capacitor or a lithium battery.

[Hybrid capacitor]
As the hybrid capacitor, 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, intercalation, deintercalation, etc., such as graphite. In this device, an active material in which a capacity is formed by an active material having a capacity formed by redox, such as a conductive polymer, and the active material is used for a negative electrode.

[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 includes a positive electrode, a negative electrode, a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a non-aqueous solvent, and the like. Below, the structure of the positive electrode which comprises the lithium battery of this invention, a non-aqueous electrolyte, and a lithium battery is demonstrated.

<Non-aqueous 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 (lithium) And a lithium salt having an anion of an oxalate complex such as lithium (mubisoxalate borate) or difluoro [oxalate-O, O ′] lithium borate. 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. As the preferred combination of these electrolyte salts include LiPF _6, further LiBF _4, LiPO ₂ F _2, and LiN _(SO 2 _F) at least one lithium salt selected from ₂ nonaqueous solution Is preferable.

  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.

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

  Examples of the cyclic carbonate include one or more selected from ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, and 2,3-butylene carbonate. Ethylene carbonate, propylene carbonate, 1, One or more selected from 2-butylene carbonate and 2,3-butylene carbonate are more preferable from the viewpoint of improving the 50C charge rate characteristics and reducing the amount of gas generated during high-temperature storage. Propylene carbonate, 1,2- One or more cyclic carbonates having an alkylene chain selected from butylene carbonate and 2,3-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.

Therefore, as the non-aqueous electrolyte, a non-aqueous solvent containing one or more cyclic carbonates selected from ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, and 2,3-butylene carbonate, LiPF ₆ , LiBF ₄ , It is preferable to use a nonaqueous electrolytic solution in which an electrolyte salt containing at least one lithium salt selected from LiPO ₂ F ₂ and LiN (SO ₂ F) ₂ is used. As the cyclic carbonate, propylene carbonate, 1, One or more cyclic carbonates having an alkylene chain selected from 2-butylene carbonate and 2,3-butylene carbonate are more preferred.

In particular, the concentration of the total electrolyte salt is 0.5 M or more and 2.0 M or less, and the electrolyte salt includes at least LiPF ₆ and further 0.001 M or more and 1 M or less of LiBF ₄ , LiPO ₂ F ₂ , and LiN. It is preferable to use a nonaqueous electrolytic solution containing at least one lithium salt selected from (SO ₂ F) ₂ . When the proportion of the lithium salt other than LiPF _{6 in the} non-aqueous solvent is 0.001 M or more, the effect of improving the charge / discharge cycle characteristics of the electricity storage device in a high-temperature environment and the reduction of gas generation after the charge / discharge cycle It is preferable that the effect is easily exhibited, and that it is 1.0 M or less because there is little concern that the effect of improving the charge / discharge cycle characteristics under a high temperature environment and the effect of reducing the amount of gas generated after the charge / discharge cycle are reduced. The proportion of the lithium salt other than LiPF _{6 in the} non-aqueous solvent is preferably 0.01 M or more, particularly preferably 0.03 M or more, and most preferably 0.04 M or more. The upper limit is preferably 0.8M or less, more preferably 0.6M or less, and particularly preferably 0.4M or less.

  The non-aqueous solvent is preferably 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.

  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. When the content is 60% by volume or more, the viscosity of the non-aqueous electrolyte does not become too high, and when the content 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 effect of improving the discharge cycle characteristics and the effect of reducing the amount of gas generated after the charge / discharge cycle will be 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 improving the charge / discharge cycle characteristics under a higher temperature environment and the effect of reducing the amount of gas generated after the charge / discharge cycle are improved.

  The ratio of cyclic carbonate and chain ester is cyclic carbonate: chain ester (volume ratio) from the viewpoint of improving the effect of improving charge / discharge cycle characteristics in a high temperature environment and the effect of reducing the amount of gas generated after the charge / discharge cycle. Is preferably 10:90 to 45:55, more preferably 15:85 to 40:60, and particularly preferably 20:80 to 35:65.

<Structure of lithium battery>
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, and is, 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.

[Lithium ion secondary battery]
A lithium ion secondary battery of the present invention includes a positive electrode containing a material capable of inserting and extracting lithium as an active material, a negative electrode, a separator disposed between the positive electrode and the negative electrode, a non-aqueous electrolyte, It is preferable that the negative electrode includes the electrode sheet of the present invention, and a charging potential of the negative electrode in a fully charged state is 1.15 V or more with respect to a lithium reference electrode. . This is because, in the lithium ion secondary battery of the present invention, when the charge potential in the fully charged state of the negative electrode is in this range, the discharge capacity maintenance rate after the charge / discharge cycle in a high temperature environment is further increased. The charging potential of the negative electrode in a fully charged state is more preferably 1.2 V or more, and particularly preferably 1.25 V or more with respect to the lithium reference electrode. By setting it as the above range, the discharge capacity maintenance rate after the charge / discharge cycle especially in a high temperature environment becomes large. In the lithium ion secondary battery, in addition to the charge potential in the fully charged state of the negative electrode being in the above range, the discharge potential in the fully discharged state of the negative electrode is 1.8 V or less with respect to the lithium reference electrode. More preferably. In the lithium ion secondary battery of the present invention, when the charge potential in the complete discharge state of the negative electrode is within this range, the discharge capacity retention rate after the charge / discharge cycle in a high temperature environment is further increased. This is because if the discharge potential in the complete discharge state of the negative electrode is within this range, the discharge capacity retention rate after the charge / discharge cycle in a higher temperature environment is further increased. The discharge potential in the complete discharge state of the negative electrode is more preferably 1.7 V or less, and particularly preferably 1.6 V or less with respect to the lithium reference electrode. By setting it as the above range, the discharge capacity maintenance factor after the charging / discharging cycle especially in a high temperature environment becomes large, and the gas generation in a high temperature environment is also suppressed.

The active material contained in the positive electrode of the lithium ion secondary battery of the present invention is preferably a composite metal oxide having a spinel structure. This is because the discharge capacity retention rate after the charge / discharge cycle in a high temperature environment is increased. Here, as the composite metal oxide having a spinel structure, specifically, LiMn ₂ O ₄ , LiNi _0.5 Mn _1.5 O ₄ , LiMg _0.5 Mn _1.5 O ₄ , LiNi _0.5 Ge _1.5 O ₄ , LiNiVO ₄ , LiMnVO ₄ , LiMnVO ₄ , and the like. Among these composite metal oxides having a spinel structure, a composite metal oxide containing manganese is preferable, LiMn ₂ O ₄ or LiNi _0.5 Mn _1.5 O ₄ is more preferable, and LiMn ₂ O ₄ is Particularly preferred. In these two types, the discharge capacity maintenance rate after the charge / discharge cycle in a high temperature environment is particularly large. Note that the composite metal oxide having the spinel structure may be a composition in which a part of the constituent elements is replaced with another element.

  Next, the details of 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 can be easily inferred from the gist of the invention. Including any combination. In particular, it is not limited to the combination of the solvent which comprises the non-aqueous electrolyte of an Example. Details of the physical property values given in the following examples and comparative examples are described.

(Various physical property measurement methods)
[1. XRD]
As a measuring device, an X-ray diffractometer using CuKα ray (Rigaku Corporation, RINT-TTR-III type) was used. The measurement conditions of the X-ray diffraction measurement 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.

From the obtained X-ray diffraction measurement results, the main peak of LiTi ₂ O ₄ in the PDF card 00-040-0407 of ICDD (PDF2010), that is, (111) of LiTi ₂ O ₄ having a crystal structure belonging to the space group Fd-3m. ) The diffraction intensity of the peak corresponding to the diffraction peak attributed to the plane (2θ = 18.1 to 18.5 °), the main peak of anatase-type titanium dioxide in PDF card 01-070-6826 of ICDD (PDF2010), ie ( 101) the intensity of the peak corresponding to the diffraction peak attributed to the plane (2θ = 24.7 to 25.7 °), the main peak of rutile titanium dioxide in PDF card 01-070-7347 of ICDD (PDF2010), that is, ( 110) diffraction peak attributed to the plane (2θ = 27.2 to 27.6 °) Intensity of a peak equivalent to the peak corresponding to the diffraction peak assigned to _Li 2 TiO ₃ of (-133) plane (2 [Theta] = 43.5-43.8 °) in the PDF card 00-033-0831 of ICDD (PDF2010) The strength of was measured. Further, _the, Li 2 TiO ₃ of (-133) plane by multiplying the 100/80 to the intensity of the peak corresponding to the diffraction peak attributable to (2 [Theta] = from 43.5 to 43.8 °) of _Li 2 TiO ₃ The main peak intensity (the intensity of the peak corresponding to the (002) plane) was calculated. The main peak intensities of the rutile titanium dioxide, anatase titanium dioxide, and Li ₂ TiO _{3 when} the main peak intensity of LiTi ₂ O ₄ having a crystal structure belonging to the space group Fd-3m is 100 are shown. Relative values were calculated.

[2. Crystallite diameter (D _X )]
The crystallite diameter (D _X ) of the lithium titanium composite oxide powder of the present invention was measured using an X-ray diffractometer (RINT-TTR-III, manufactured by Rigaku Corporation) using CuKα rays. Measurement conditions were as follows: 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: Main peak of LiTi ₂ O ₄ in PDF card 00-040-0407 of ICDD (PDF2010) obtained as 300 mA, that is, (111) plane of LiTi ₂ O ₄ having a crystal structure belonging to space group Fd-3m From the peak half-value width of (2θ = 18.1 to 18.5 °), it was obtained 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. Specific surface area (m ² / g)]
About the lithium titanium composite oxide powder of the present invention, a BET specific surface area is measured by a one-point method using liquid nitrogen using a fully automatic BET specific surface area measuring device, trade name “Macsorb HM model-1208” manufactured by Mountec Co., Ltd. did.

[4. BET diameter (D _BET )]
The BET diameter (D _BET ) was calculated from the following formula (2) on the assumption that all particles constituting the powder were spheres having the same diameter. Here, D _BET is the BET diameter (μm), ρ _S is the true density (g / cc) of the lithium titanium composite oxide, and S is [3. Specific surface area (m ² / g) measured by the method described in “Specific surface area (m ² / g)”.
D _BET = 6 / (ρ _S × S) (2)

[5. Particle size distribution)
For the measurement of the particle size distribution of the lithium titanium composite oxide of the present invention, a laser diffraction / scattering type particle size distribution analyzer (Nikkiso Co., Ltd., Microtrac MT3300EXII) was used. For the preparation of the measurement sample, ion exchange water was used as a measurement solvent. About 50 mg of a sample was put into 50 ml of a measurement solvent, and 1 cc of 0.2% sodium hexametaphosphate aqueous solution as a surfactant was added, and the obtained measurement slurry was processed with an ultrasonic disperser. 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.

[6. Measurement of total pore volume (gas adsorption method)]
The total pore volume of the lithium sodium titanium composite oxide of the present invention was measured by a gas adsorption method using a fully automatic gas adsorption amount measuring apparatus AC1-iQ (manufactured by QUANTACHROME) as follows. 1 g of lithium sodium titanium composite oxide powder was accommodated in a measuring cell (large cell) having a stem diameter of 6 mm, stored in the measuring device, and deaerated under vacuum at 200 ° C. for 15 hours. With the measurement apparatus, nitrogen gas was used as the adsorption gas, and a fully automatic gas adsorption amount measurement was performed by a constant volume method to measure the total pore volume.

(Example 1-1)
<Preparation of raw materials>
LiOH.H ₂ O (manufactured by Alfa Aesar (AFA), product number: A15519), Ti ₂ O ₃ (manufactured by Wako Pure Chemical Industries, product number: 207-18941) and anatase TiO ₂ (average particle size 0.6 μm), The composition was weighed so that the composition shown in Table 1 was obtained and the ratio of Ti ₂ O ₃ and TiO ₂ was 0.45 / 1.1 (Ti ₂ O ₃ / TiO ₂ ) in terms of molar ratio. The weighed powder was put in a container together with ZrO ₂ balls (diameter 2 mm), and mixed and pulverized with a ball mill until D95 of the obtained mixed powder became 1.0 μm.

<Baking>
The obtained mixed powder was filled in a high-purity alumina sagger and fired at 890 ° C. for 6 hours in an Ar atmosphere using a fixed-bed tubular furnace. The heating rate was 200 ° C./h. Thereafter, the fired product obtained was collected, sieved (mesh roughness: 45 μm), and the powder that passed through the sieve was collected to obtain a lithium titanium composite oxide powder.

  The physical properties of the obtained lithium titanium composite oxide powder were measured by the methods described in [Methods for measuring various physical properties]. The production conditions of Example 1 and the physical properties of the lithium titanium composite oxide powder are shown in Tables 1 and 2 together with other examples and comparative examples.

(Electrochemical evaluation)
<Preparation of non-aqueous electrolyte for characteristic evaluation>
The non-aqueous electrolyte used for the battery for evaluating the characteristics was prepared as follows. A nonaqueous solvent of ethylene carbonate (EC): propylene carbonate (PC): methyl ethyl carbonate (MEC): dimethyl carbonate (DMC) (volume ratio) = 10: 20: 20: 50 was prepared, and LiPF was used as an electrolyte salt thereof. ₆ was dissolved to a concentration of 1M and LiPO ₂ F ₂ to a concentration of 0.05M to prepare a non-aqueous electrolyte.

<Preparation of multi-walled carbon nanotube for conductive agent>
{Synthesis of multi-walled carbon nanotubes}
In ion-exchanged water, cobalt nitrate [Co (NO ₃ ) ₂ .6H ₂ O: molecular weight 291.03], magnesium nitrate [so that the molar ratio of metal elements is Co: Mg: Al = 8: 66: 26 Mg (NO ₃ ) 2 · 6H ₂ O: molecular weight 256.41] and aluminum nitrate [Al (NO ₃ ) ₃ · 9H ₂ O: molecular weight 375.13] were dissolved and mixed under stirring under basic conditions. Thereafter, the produced precipitate was filtered, washed and dried. After heating this to 500 degreeC and baking for 1 hour, it grind | pulverized in the mortar and the catalyst with the spinel structure by substitution solid solution was acquired. Next, a quartz wool support was provided in the quartz reaction tube, and a catalyst was sprayed thereon. After heating the temperature in the tube to 550 ° C. in a He atmosphere, a mixed gas composed of CO and H ₂ (volume ratio: CO / H ₂ = 99.0 / 1.0) is used as a raw material gas from the bottom of the reaction tube. A multi-walled carbon nanotube was obtained by flowing at a flow rate of 28 L / min for 7 hours. The obtained multi-walled carbon nanotubes had a yield of 15 times the mass of the catalyst.

{Preparation of multi-walled carbon nanotube slurry}
The obtained multi-walled carbon nanotube, carboxymethylcellulose (CMC) and ion-exchanged water were prepared and stirred so as to have a mass ratio of 1.0: 0.8: 98.2 to prepare a slurry. Using this slurry, beads made of zirconia (outer diameter: 1.0 mm) are vesseld using a bead mill (made by Iwata Tekko Co., Ltd., model: PICOMILL PCM-LR type, agitator material: silicon nitride, vessel inner surface material: zirconia). The mixture was pulverized while controlling the internal pressure of the vessel to be 0.06 MPa or less at an agitator peripheral speed of 8 m / sec and a slurry feed speed of 30 to 50 ml / min.

<Preparation of negative electrode sheet>
90% by mass of the lithium titanium composite oxide powder of Example 1 as an active material, 4.5% by mass of acetylene black, 0.5% by mass of multi-walled carbon nanotubes, and 5% by mass of polyvinylidene fluoride (binder) A paint containing a proportion was prepared as follows. After mixing polyvinylidene fluoride, acetylene black, the above-mentioned multi-walled carbon nanotube slurry and 1-methyl-2-pyrrolidone solvent previously dissolved in 1-methyl-2-pyrrolidone solvent with a planetary stirring deaerator, lithium titanium composite Oxide powder was added, and the total solid content concentration was adjusted to 64% by mass and mixed with a planetary stirring deaerator. Further, a 1-methyl-2-pyrrolidone solvent was added to prepare a total solid content concentration of 56% by mass, and the mixture was mixed with a planetary stirring and deaerator to prepare a coating material. The obtained paint was applied onto an aluminum foil and dried to prepare an evaluation electrode single-sided sheet. Moreover, the obtained coating material was apply | coated on both surfaces of the aluminum foil, it was made to dry and the evaluation electrode double-sided sheet was produced.

<Preparation of positive electrode sheet>
In the same production method as in <Preparation of negative electrode sheet>, as an active material, 90% by mass of lithium manganate (LiMn ₂ O ₄ ) powder, 5% by mass of acetylene black (conductive auxiliary agent), polyvinylidene fluoride (condensation) A coating material containing 5% by mass of the adhesive was prepared, applied onto an aluminum foil and dried, and then coated on the opposite side and dried to prepare a counter electrode double-sided sheet.

<Production of laminated battery>
The negative electrode double-sided sheet was pressed to obtain a predetermined electrode density, punched out, and a negative electrode having a mixture layer having a lead wire connecting portion of 4.2 cm in length and 5.2 cm in width was produced. At this time, the thickness of the mixture layer on one side was 28 μm, and the amount of the mixture was 56 g / m ² . After pressing the positive electrode double-sided sheet, a positive electrode having a mixture layer having a length of 4 cm and a width of 5 cm and having a lead wire connecting portion was produced. At this time, the thickness of the mixture layer on one side was 40 μm, and the amount of the mixture was 140 g / m ² . The prepared negative electrode and positive electrode, and a 1 mm thick Li metal foil punched out to 14 mmφ as a lithium reference electrode are opposed to each other through a separator made of a microporous polyethylene film, and the aluminum foil lead wire is used as a positive and negative electrode. Connect the nickel foil lead wire to the lithium reference electrode, add the non-aqueous electrolyte for characteristic evaluation to each other, and vacuum seal it with an aluminum laminate. A laminated battery for gas generation evaluation was produced. The capacity of this laminated battery was 200 mAh.

<Charge / discharge cycle test and measurement of gas generation amount>
Charge the laminated battery produced by the method described in <Preparation of Laminated Battery> in a constant temperature bath at 25 ° C. with a current of 40 mA until the negative electrode potential becomes 1.2 V with respect to the lithium reference electrode. In addition, after carrying out constant-current constant-voltage charging in which the charging current is 10 mA in a state where the potential of the negative electrode is 1.2 V with respect to the lithium reference electrode, 3 cycles of constant current discharge for discharging until the potential became 1.8 V with respect to the lithium reference electrode (however, charging is performed when current flows so that Li is occluded in the negative electrode. Current was set to flow between the positive and negative electrodes.) The laminate battery was taken out from the thermostat and the volume of the laminate battery (volume of the laminate battery before the cycle test) was measured by Archimedes method. Thereafter, the temperature of the thermostatic chamber is set to 45 ° C., and charging is performed at a current of 200 mA until the potential of the negative electrode becomes 1.2 V with respect to the lithium reference electrode. After performing constant current and constant voltage charging in which the charging current reaches 10 mA in a state of 2 V, discharging is performed until the negative electrode potential becomes 1.8 V with respect to the lithium reference electrode at a current of 200 mA. 500 cycles of constant current discharge were performed. The discharge capacity at the first cycle was divided by the discharge capacity at the 500th cycle, and a discharge capacity retention rate after a 500 cycle charge / discharge test at 45 ° C., that is, a 500 cyc discharge capacity retention rate (45 ° C.) was calculated. Then, the temperature of the thermostat was set to 25 ° C. and stored for 1 hour. Next, the laminate battery was taken out from the thermostat, and the volume of the laminate battery (the volume of the laminate battery after storage) was measured by the Archimedes method. The volume of the laminate battery before the cycle test was subtracted from the volume of the laminate battery after the cycle test, and the amount of gas generated after the 500-cycle charge / discharge test at 45 ° C. was calculated. The gas generation amount shown in Table 1 was a relative amount when the gas generation amount in Comparative Example 1 described later was 100%.

  The characteristics evaluation results of the laminate type battery using the lithium-titanium composite oxide powder of Example 1 as an electrode sheet are described above, and the laminate using the lithium-titanium composite oxide powder of other examples and comparative examples as a negative electrode active material. It shows in Table 1 together with the characteristic evaluation result of the type battery. In Table 1, acetylene black and multi-walled carbon nanotubes used as conductive agents in this example are abbreviated as AB and CNT.

(Example 1-2)
In the same manner as in Example 1-1, except that a powder having an average particle diameter of 0.1 μm was used for TiO ₂ as a titanium raw material and that the holding time at the maximum temperature during firing was 2 hours, Example A lithium titanium composite oxide powder of 1-2 was produced. The physical properties of the obtained lithium titanium composite oxide powder were measured by the same method as in Example 1-1. Moreover, the laminated battery was produced by the method similar to Example 1-1, the charge / discharge cycle test and the gas generation amount measurement after a charge / discharge cycle were performed by the method similar to Example 1-1. The results are shown in Table 1 together with other examples and comparative examples.

(Example 1-3)
The ratio of Ti ₂ O ₃ and TiO ₂ was set to a molar ratio of 0.45 / 1.1 (Ti ₂ O ₃ / TiO ₂ ), and each raw material was weighed so as to have the composition shown in Table 1 and mixed and pulverized. Except for this, the lithium titanium composite oxide powder of Example 1-3 was produced in the same manner as in Example 1-1. The physical properties of the obtained lithium titanium composite oxide powder were measured by the same method as in Example 1-1. Moreover, the laminated battery was produced by the method similar to Example 1-1, the charge / discharge cycle test and the gas generation amount measurement after a charge / discharge cycle were performed by the method similar to Example 1-1. The results are shown in Table 1 together with other examples and comparative examples.

(Example 1-4)
The ratio of Ti ₂ O ₃ and TiO ₂ was set to 0.475 / 1.05 (Ti ₂ O ₃ / TiO ₂ ) in molar ratio, and each raw material was weighed so as to have the composition shown in Table 1 and mixed and pulverized. Except for this, the lithium titanium composite oxide powder of Example 1-4 was produced in the same manner as in Example 1-1. The physical properties of the obtained lithium titanium composite oxide powder were measured by the same method as in Example 1-1. Moreover, the laminated battery was produced by the method similar to Example 1-1, the charge / discharge cycle test and the gas generation amount measurement after a charge / discharge cycle were performed by the method similar to Example 1-1. The results are shown in Table 1 together with other examples and comparative examples.

(Example 1-5)
The ratio of Ti ₂ O ₃ and TiO ₂ was 0.525 / 0.95 (Ti ₂ O ₃ / TiO ₂ ) in terms of molar ratio, and each raw material was weighed so as to have the composition shown in Table 1 and mixed and pulverized. Except for this, the lithium titanium composite oxide powder of Example 1-5 was produced in the same manner as in Example 1-1. The physical properties of the obtained lithium titanium composite oxide powder were measured by the same method as in Example 1-1. Moreover, the laminated battery was produced by the method similar to Example 1-1, the charge / discharge cycle test and the gas generation amount measurement after a charge / discharge cycle were performed by the method similar to Example 1-1. The results are shown in Table 1 together with other examples and comparative examples.

(Example 1-6)
The ratio of Ti ₂ O ₃ and TiO ₂ was set to 0.55 / 0.9 (Ti ₂ O ₃ / TiO ₂ ) in molar ratio, and each raw material was weighed so as to have the composition shown in Table 1 and mixed and pulverized. Except for this, the lithium titanium composite oxide powder of Example 1-6 was produced in the same manner as in Example 1-1. The physical properties of the obtained lithium titanium composite oxide powder were measured by the same method as in Example 1-1. Moreover, the laminated battery was produced by the method similar to Example 1-1, the charge / discharge cycle test and the gas generation amount measurement after a charge / discharge cycle were performed by the method similar to Example 1-1. The results are shown in Table 1 together with other examples and comparative examples.

(Example 1-7)
Cr ₂ O ₃ (product number: 93-2438 manufactured by Strem Chemicals, Inc.) is added as a raw material for the titanium site substitution element, and the molar ratio of Ti ₂ O ₃ and TiO ₂ is 0.475 / 1.0 ( Ti ₂ O ₃ / TiO ₂ ), each raw material was weighed, mixed and pulverized so as to have the composition shown in Table 1, and heated to 900 ° C. at a heating rate of 300 ° C./h. The lithium-titanium composite oxide powder of Example 1-7 was produced in the same manner as in Example 1-1 except that it was calcined for 6 hours. The physical properties of the obtained lithium titanium composite oxide powder were measured by the same method as in Example 1-1. Moreover, the laminated battery was produced by the method similar to Example 1-1, the charge / discharge cycle test and the gas generation amount measurement after a charge / discharge cycle were performed by the method similar to Example 1-1. The results are shown in Table 1 together with other examples and comparative examples.

(Examples 1-8, 1-9)
The composition shown in Table 1 is obtained using Li ₂ CO ₃ (product number: 034418 manufactured by Wako Pure Chemical Industries) as the lithium raw material and using only anatase TiO ₂ (average particle size 0.6 μm) as the titanium raw material. The lithium titanium composite oxide powders of Examples 1-8 and 1-9 were produced in the same manner as in Example 1-7, except that each raw material was weighed, mixed, pulverized, and fired in the air. The physical properties of the obtained lithium titanium composite oxide powder were measured by the same method as in Example 1-1. Moreover, the laminated battery was produced by the method similar to Example 1-1, the charge / discharge cycle test and the gas generation amount measurement after a charge / discharge cycle were performed by the method similar to Example 1-1. The results are shown in Table 1 together with other examples and comparative examples.

(Example 1-10)
Al ₂ O ₃ (product number: 015-13001, manufactured by Wako Pure Chemical Industries, Ltd.) is added as a raw material for the titanium site substitution element, and each raw material is weighed, mixed and pulverized so as to have the composition shown in Table 1, and then in the atmosphere. A lithium-titanium composite oxide powder of Example 1-10 was produced in the same manner as in Example 1-7, except that it was fired. The physical properties of the obtained lithium titanium composite oxide powder were measured by the same method as in Example 1-1. Moreover, the laminated battery was produced by the method similar to Example 1-1, the charge / discharge cycle test and the gas generation amount measurement after a charge / discharge cycle were performed by the method similar to Example 1-1. The results are shown in Table 1 together with other examples and comparative examples.

(Example 1-11)
CoO (Alfa Aesar (ALF) product number: 0231141) was added as a raw material for the substitution element of the titanium site, and each raw material was weighed, mixed, pulverized, and fired in the atmosphere so as to have the composition shown in Table 1. Except for this, the lithium titanium composite oxide powder of Example 1-11 was produced in the same manner as in Example 1-7. The physical properties of the obtained lithium titanium composite oxide powder were measured by the same method as in Example 1-1. Moreover, the laminated battery was produced by the method similar to Example 1-1, the charge / discharge cycle test and the gas generation amount measurement after a charge / discharge cycle were performed by the method similar to Example 1-1. The results are shown in Table 1 together with other examples and comparative examples.

(Example 1-12)
As raw materials for the substitution element of the titanium site, Cr ₂ O ₃ (Strem Chemicals, Inc. product number: 93-2438) and Ga ₂ O ₃ (Strem Chemicals, Inc. product number: 93-3106) are added, and titanium raw material is added. In the same manner as in Example 1-7, except that each raw material was weighed, mixed and pulverized so as to have the composition shown in Table 1 using only TiO ₂ , and fired in the air, Example 1-7 12 lithium titanium composite oxide powders were produced. The physical properties of the obtained lithium titanium composite oxide powder were measured by the same method as in Example 1-1. Moreover, the laminated battery was produced by the method similar to Example 1-1, the charge / discharge cycle test and the gas generation amount measurement after a charge / discharge cycle were performed by the method similar to Example 1-1. The results are shown in Table 1 together with other examples and comparative examples.

(Example 1-13)
Al ₂ O ₃ (manufactured by Wako Pure Chemical Industries, product number: 015-13001) and Ga ₂ O ₃ (manufactured by Strem Chemicals, Inc., product number: 93-3106) were added as raw materials for the substitution element of the titanium site, and the titanium raw material was added. Example 1-7, except that only the anatase TiO ₂ (average particle size 0.6 μm) was used, and each raw material was weighed, mixed and pulverized so as to have the composition shown in Table 1, and fired in the air. In the same manner as in Example 1, a lithium titanium composite oxide powder of Example 1-13 was produced. The physical properties of the obtained lithium titanium composite oxide powder were measured by the same method as in Example 1-1. Moreover, the laminated battery was produced by the method similar to Example 1-1, the charge / discharge cycle test and the gas generation amount measurement after a charge / discharge cycle were performed by the method similar to Example 1-1. The results are shown in Table 1 together with other examples and comparative examples.

(Example 1-14)
LiOH · H ₂ O (Alfa Aesar (AFA) product number: A15519) is used as the lithium source, and MgO (Alfa Aesar (ALF) product number: 036388) and GeO ₂ (Alfa Aesar) are used as the raw material for the titanium site substitution element. (ALF) product number: 0111155) is added, and the ratio of Ti ₂ O ₃ and TiO ₂ is 0.45 / 1.0 (Ti ₂ O ₃ / TiO ₂ ) in terms of molar ratio, resulting in the composition shown in Table 1. Thus, the lithium titanium composite oxide powder of Example 1-14 was produced in the same manner as in Example 1-7, except that each raw material was weighed, mixed and pulverized. The physical properties of the obtained lithium titanium composite oxide powder were measured by the same method as in Example 1-1. Moreover, the laminated battery was produced by the method similar to Example 1-1, the charge / discharge cycle test and the gas generation amount measurement after a charge / discharge cycle were performed by the method similar to Example 1-1. The results are shown in Table 1 together with other examples and comparative examples.

(Example 1-15)
Nb ₂ O ₅ (Alfa Aesar (ALF) product number: 011366) and MgO (Alfa Aesar (ALF) product number: 036388) were added as raw materials for the titanium site substitution element, and the ratio of Ti ₂ O ₃ and TiO ₂ was added. Example 1-7 except that each raw material was weighed, mixed and pulverized so that the composition shown in Table 1 was obtained with a molar ratio of 0.45 / 1.0 (Ti ₂ O ₃ / TiO ₂ ). In the same manner as in Example 1, the lithium titanium composite oxide powder of Example 1-15 was produced. The physical properties of the obtained lithium titanium composite oxide powder were measured by the same method as in Example 1-1. Moreover, the laminated battery was produced by the method similar to Example 1-1, the charge / discharge cycle test and the gas generation amount measurement after a charge / discharge cycle were performed by the method similar to Example 1-1. The results are shown in Table 1 together with other examples and comparative examples.

(Comparative Example 1)
A lithium titanium composite oxide powder of Comparative Example 1 was produced in the same manner as in Example 1-1 except that the maximum temperature during firing was 750 ° C. The physical properties of the obtained lithium titanium composite oxide powder were measured by the same method as in Example 1-1. Moreover, the laminated battery was produced by the method similar to Example 1-1, the charge / discharge cycle test and the gas generation amount measurement after a charge / discharge cycle were performed by the method similar to Example 1-1. The results are shown in Table 1 together with other examples and comparative examples.

(Comparative Example 2)
A lithium titanium composite oxide powder of Comparative Example 2 was produced in the same manner as in Example 1-1, except that the maximum temperature during firing was 1000 ° C. The physical properties of the obtained lithium titanium composite oxide powder were measured by the same method as in Example 1-1. Moreover, the laminated battery was produced by the method similar to Example 1-1, the charge / discharge cycle test and the gas generation amount measurement after a charge / discharge cycle were performed by the method similar to Example 1-1. The results are shown in Table 1 together with other examples and comparative examples. As a result of X-ray diffraction, the lithium-titanium composite oxide powder of Comparative Example 2 has a main peak of Li ₂ Ti ₃ O ₇ in PDF card 00-034-0393 of ICDD (PDF2010), that is, Li ₂ Ti ₃ O ₇ ( The diffraction intensity of the peak corresponding to the diffraction peak attributed to the (110) plane (2θ = 19.8 to 20.2 °) showed the maximum intensity. LiTi ₂ O ₄ to become so weighed each raw material are mixed and pulverized, but was calcined by firing temperature is high, once decomposed generated _{LiTi 2 O 4, Li 2 Ti} 3 O 7 was produced It seems to be.

(Comparative Example 3)
A lithium titanium composite oxide powder of Comparative Example 3 was produced in the same manner as in Example 1-1 except that the holding time at the maximum temperature during firing was 12 hours. The physical properties of the obtained lithium titanium composite oxide powder were measured by the same method as in Example 1-1. Moreover, the laminated battery was produced by the method similar to Example 1-1, the charge / discharge cycle test and the gas generation amount measurement after a charge / discharge cycle were performed by the method similar to Example 1-1. The results are shown in Table 1 together with other examples and comparative examples.

(Comparative Example 4)
The raw material of the substitution element of the titanium site is La ₂ O ₃ (product number: 93-5716, manufactured by Strem Chemicals, Inc.), each raw material is weighed so as to have the composition shown in Table 1, and mixed and pulverized. A lithium-titanium composite oxide powder of Comparative Example 4 was produced in the same manner as in Example 1-8, except that it was fired. The physical properties of the obtained lithium titanium composite oxide powder were measured by the same method as in Example 1-1. Moreover, the laminated battery was produced by the method similar to Example 1-1, the charge / discharge cycle test and the gas generation amount measurement after a charge / discharge cycle were performed by the method similar to Example 1-1. The results are shown in Table 1 together with other examples and comparative examples.

(Comparative Example 5)
NiO (product number: 93-2832 manufactured by Strem Chemicals, Inc.) and Nb ₂ O ₅ (product number: 011366 manufactured by Alfa Aesar (ALF)) were added as raw materials for the substitution element of the titanium site, and Ti ₂ O ₃ and TiO ₂ were added. Example 1 except that the raw material was adjusted to a molar ratio of 0.4265 / 1.0 (Ti ₂ O ₃ / TiO ₂ ), and each raw material was weighed, mixed and pulverized to have the composition shown in Table 1. 8 was used to produce a lithium titanium composite oxide powder of Comparative Example 5. The physical properties of the obtained lithium titanium composite oxide powder were measured by the same method as in Example 1-1. Moreover, the laminated battery was produced by the method similar to Example 1-1, the charge / discharge cycle test and the gas generation amount measurement after a charge / discharge cycle were performed by the method similar to Example 1-1. The results are shown in Table 1 together with other examples and comparative examples.

(Comparative Example 6)
MgO (Alfa Aesar (ALF) product number: 036388) and GeO ₂ (Alfa Aesar (ALF) product number: 011155) are added as raw materials for the titanium site substitution element, and the ratio of Ti ₂ O ₃ and TiO ₂ is mol. The ratio was 0.4265 / 1.0 (Ti ₂ O ₃ / TiO ₂ ) in the same manner as in Example 1-1 except that each raw material was weighed, mixed and pulverized so as to have the composition shown in Table 1. The lithium titanium composite oxide powder of Comparative Example 6 was produced by the method. The physical properties of the obtained lithium titanium composite oxide powder were measured by the same method as in Example 1-1. Moreover, the laminated battery was produced by the method similar to Example 1-1, the charge / discharge cycle test and the gas generation amount measurement after a charge / discharge cycle were performed by the method similar to Example 1-1. The results are shown in Table 1 together with other examples and comparative examples.

(Comparative Example 7)
Iron oxyhydroxide α-FeOOH (manufactured by Alfa Aesar (ALF), product number: 019496) was added as a raw material for the substitution element of the titanium site, and each raw material was weighed so as to have the composition shown in Table 1, as in Example 1. The mixed powder was prepared by mixing and pulverizing. The mixed powder was fired in the same manner as in Example 1-1 except that the maximum temperature during firing was 750 ° C., the atmosphere during firing was air, and the holding time during firing was 12 hours, to obtain a fired product. The collected fired product was sieved in the same manner as in Example 1-1 to obtain a lithium titanium composite oxide powder. The physical properties of the obtained lithium titanium composite oxide powder were measured by the same method as in Example 1-1. Moreover, the laminated battery was produced by the method similar to Example 1-1, the charge / discharge cycle test and the gas generation amount measurement after a charge / discharge cycle were performed by the method similar to Example 1-1. The results are shown in Table 1 together with other examples and comparative examples.

(Examples 2-1 to 2-3)
Using the lithium titanium composite oxide powder of Example 1-1, a laminate battery was produced in the same manner as in Example 1-1. Example 1-1, except that the charge potential and discharge potential with respect to the lithium reference electrode of each example were changed as shown in Table 1 in the charge / discharge cycle test and the gas generation amount measurement after the charge / discharge cycle. In the same manner as above, the characteristics of the laminate type batteries of each example were evaluated. The results are shown in Table 2.

(Examples 2-4 to 2-6)
The lithium-titanium composite oxide powder of Example 1-1 was used as the negative electrode active material except that the positive electrode active material shown in Table 1 was used instead of lithium manganate as the positive electrode active material. In the same manner as in Example 1-1, laminated batteries of Examples 2-4 to 2-6 were produced. The characteristics of the laminate type battery of each example were evaluated in the same manner as in Example 1-1. The results are shown in Table 2.

(Examples 2-7 to 2-9)
The proportion of the conductive agent used in the preparation of the negative electrode sheet and the conductive agent in the paint was 5% by mass of acetylene black in Example 2-7, and 3.0% by mass of acetylene black in Example 2-8. Example 1 was used as the active material for the negative electrode except that the carbon nanotube was 2.0% by mass, and in Example 2-9, acetylene black was 2.0% by mass and the multi-walled carbon nanotube was 3.0% by mass. Laminated batteries of Examples 2-7 to 2-9 were produced in the same manner as in Example 1-1, including the use of the lithium titanium composite oxide powder of -1. The characteristics of the laminate type battery of each example were evaluated in the same manner as in Example 1-1. The results are shown in Table 2.

(Examples 2-10 to 2-14)
The lithium sodium titanium composite oxide powder of Example 1-1 is used as an active material for the negative electrode, except that the nonaqueous solvent of the nonaqueous electrolyte used in the battery for evaluating characteristics is changed as follows. In addition, a laminated battery was produced in the same manner as in Example 1-1, and the characteristics of the laminated battery were evaluated in the same manner as in Example 1-1. The results are shown in Table 2.
Example 2-10; ethylene carbonate (EC): methyl ethyl carbonate (MEC): dimethyl carbonate (DMC) (volume ratio) = 30: 20: 50
Example 2-11; ethylene carbonate (EC): propylene carbonate (PC): methyl ethyl carbonate (MEC): dimethyl carbonate (DMC) (volume ratio) = 15: 15: 20: 50
Example 2-12; Propylene carbonate (PC): Methyl ethyl carbonate (MEC): Dimethyl carbonate (DMC) (volume ratio) = 30: 20: 50
Example 2-13; ethylene carbonate (EC): propylene carbonate (PC): diethyl carbonate (DEC) (volume ratio) = 10: 20: 70
Example 2-14; ethylene carbonate (EC): propylene carbonate (PC): diethyl carbonate (DEC) (volume ratio) = 17: 33: 50
(Examples 2-15 to 2-19)

  Lithium sodium titanium of Example 1-1, except that the type of electrolyte salt of the non-aqueous electrolyte used in the battery for evaluating characteristics and the concentration of each electrolyte salt in the non-aqueous electrolyte were changed as follows: A laminated battery was produced in the same manner as in Example 1-1 including using the composite oxide powder as the negative electrode active material, and the characteristics of the laminated battery were evaluated in the same manner as in Example 1-1. The results are shown in Table 2.

Example 2-15; LiPF _{6 at a} concentration of 1M
Example 2-16; LiPF _{6 at a} concentration of 1M and LiBF _{4 at a} concentration of 0.05M
Example 2-17; LiPF _{6 at a} concentration of 1M and LiN (SO ₂ F) _{2 at a} concentration of 0.05M (lithium bisfluorosulfonylimide, hereinafter sometimes abbreviated as LiFSI)
Example 2-18; LiPF _{6 at a} concentration of 1 M and LiB (C ₂ O ₄ ) _{2 at a} concentration of 0.05 M (lithium bisoxalate borate, hereinafter sometimes abbreviated as LiBOB)
Example 2-19; concentration 1M LiPF ₆ and concentration 0.5M LiBF ₄

  From the results shown in Table 1, it was found that the lithium titanium composite oxide powder of the present invention had a large discharge capacity retention rate after a high temperature cycle and a small amount of gas generation at a high temperature. Moreover, the following was found from the results shown in Table 2.

  In the lithium ion secondary battery using the lithium-titanium composite oxide powder of the present invention as the negative electrode active material, the non-aqueous electrolyte is obtained by dissolving an electrolyte salt in a non-aqueous solvent, Includes at least one cyclic carbonate selected from ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, and 2,3-butylene carbonate, and propylene carbonate, 1,2-butylene carbonate, and When the ratio of the cyclic carbonate having at least one alkylene chain selected from 2,3-butylene carbonate is 55% by volume or more and 100% by volume or less, the discharge capacity maintenance rate after the high-temperature cycle is further large, and at a higher temperature. There was little gas generation amount.

  Further, in the lithium ion secondary battery using the lithium titanium composite oxide powder of the present invention as an active material for a negative electrode, the non-aqueous electrolytic solution is obtained by dissolving an electrolyte salt in a non-aqueous solvent, Non-aqueous solvent containing a chain ester having at least one 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 in the solvent In the case where the content of all the chain esters was 60% by volume or more and 90% by volume or less, the discharge capacity retention rate after the high-temperature cycle was further large, and the gas generation amount at a high temperature was small.

Further, in the lithium ion secondary battery using the lithium titanium composite oxide powder of the present invention as an active material for a negative electrode, the nonaqueous electrolytic solution is obtained by dissolving an electrolyte salt in a nonaqueous solvent, and the electrolyte salt And at least LiPF ₆ in the non-aqueous electrolyte, and at least one lithium salt selected from LiBF ₄ , LiPO ₂ F ₂ and LiN (SO ₂ F) ₂ at a concentration of 0.001 M to 1 M in nonaqueous electrolysis When it was contained in the liquid, the discharge capacity retention rate after the high-temperature cycle was further large, and the amount of gas generated at a high temperature was small.

  Further, in the lithium ion secondary battery using the lithium titanium composite oxide powder of the present invention as the negative electrode active material, the negative electrode conductive agent contains at least one conductive agent selected from graphites and carbon blacks, When the ratio of the carbon nanotubes in the conductive agent was 1% by mass or more and 49% by mass or less, the discharge capacity retention rate after the high-temperature cycle was further large, and the amount of gas generated at a high temperature was small.

  When the lithium titanium composite oxide powder of the present invention is used, an electricity storage device having a large energy density, excellent charge / discharge cycle characteristics in a high temperature environment, and a small amount of gas generated after the charge / discharge cycle can be obtained. Accordingly, the lithium-titanium composite oxide powder of the present invention is suitable as an electrode material for an electricity storage device that is particularly required to be mounted on HEV, PHEV, BEV, etc., and that performance is not deteriorated over a long period of time.

Claims (21)

Having the crystal structure belonging to the space group Fd-3m, the general formula: Li _x M1 _y1 M2 _y2 M3 _y3 M4 _y4 Ti _{2-y1-y2-y3-y4} O ₄ (where M1 is Mg, Ca, Sr, Ba and At least one element selected from Ni, M2 is at least one element selected from Cr, Al, Ga, Co and Y, M3 is at least one element selected from Zr and Ge; M4 is at least one element selected from V, Nb, Sb and Ta, x is 0.9 ≦ x ≦ 1.1, y1 is 0 ≦ y1 ≦ 1.1, and y2 is 0 ≦ y2 ≦ 1.1, y3 is 0 ≦ y3 ≦ 1.1, y4 is 0 ≦ y4 ≦ 1.1, y1 + y2 + y3 + y4 is 0 ≦ (y1 + y2 + y3 + y4) ≦ 1.1, and (2y1 + 3 2 + 4y3 + 5y4) / (y1 + y2 + y3 + y4) is a lithium-titanium composite oxide powder whose main phase is a lithium-titanium composite oxide represented by 2.9 ≦ {(2y1 + 3y2 + 4y3 + 5y4) / (y1 + y2 + y3 + y4)} ≦ 3.1. ,
Specific surface area determined by the BET method is ^{1m 2} / ^g~50m 2 / g,
When the crystallite diameter calculated from the Scherrer equation from the half width of the X-ray diffraction peak corresponding to the (111) plane of LiTi ₂ O ₄ having a crystal structure belonging to the space group Fd-3m is D _x , D _x is 80 nm or more, The lithium titanium complex oxide powder for electrode active materials of an electrical storage device characterized by the above-mentioned. 2. The electrode active material for an electricity storage device according to claim 1, wherein a ratio D _BET / D _X (μm / μm) of D _BET and D _X is 4 or less when a specific surface area equivalent diameter is D _BET. Lithium titanium composite oxide powder.   3. The lithium-titanium composite oxide powder for an electrode active material for an electricity storage device according to claim 1, wherein the total pore volume is 0.001 ml / g to 0.5 ml / g.   The lithium-titanium composite oxide powder for an electrode active material for an electricity storage device according to any one of claims 1 to 3, wherein y2 in the general formula is y2> 0.   5. The lithium titanium for electrode active material of an electricity storage device according to claim 1, wherein in the general formula, at least two of y1, y2, y3, and y4 have a coefficient larger than 0. Composite oxide powder.   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 electrode sheet for an electricity storage device, comprising the active material according to claim 6, at least one conductive agent selected from graphites, carbon blacks, and carbon nanotubes, and a binder.   The electrode sheet for an electricity storage device according to claim 7, wherein the conductive agent contains at least carbon nanotubes.   The conductive agent includes at least one conductive agent selected from graphites and carbon blacks in addition to carbon nanotubes, and the ratio of carbon nanotubes in the total conductive agent is 1% by mass or more and 49% by mass or less. The electrode sheet for an electricity storage device according to claim 8. A bell formed by stacking 2 to 30 bell-shaped structural units, each having the top of the carbon nanotubes having a closed graphite mesh surface and a trunk having an open lower portion, sharing a central axis. A plurality of structural unit assemblies,
The carbon nanotubes are configured by forming a plurality of bell-shaped structural unit assemblies connected at intervals in a head-to-tail manner to form fibers. An electrode sheet for an electricity storage device according to claim 1.   The electrical storage device characterized by using the electrode sheet as described in any one of Claims 7-10. A positive electrode including a material capable of inserting and extracting lithium as an active material, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a nonaqueous electrolytic solution,
The said negative electrode contains the electrode sheet as described in any one of Claims 7-10, The electrical storage device characterized by the above-mentioned.   The non-aqueous electrolyte solution is obtained by dissolving an electrolyte salt in a non-aqueous solvent, and selected from ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, and 2,3-butylene carbonate in the non-aqueous solvent. The ratio of the cyclic carbonate having at least one alkylene chain selected from propylene carbonate, 1,2-butylene carbonate and 2,3-butylene carbonate in the total cyclic carbonate is 55 volumes. The electrical storage device according to claim 12, wherein the electrical storage device is not less than 100% and not more than 100% by volume.   The non-aqueous electrolyte is obtained by dissolving an electrolyte salt in a non-aqueous solvent, and dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, methyl propionate in the non-aqueous solvent. Including a chain ester having at least one methyl group selected from methyl acetate and ethyl acetate, and the content of all chain esters in the non-aqueous solvent is 60% by volume or more and 90% by volume or less. The electricity storage device according to claim 12 or 13. The non-aqueous electrolyte solution is obtained by dissolving an electrolyte salt in a non-aqueous solvent, and includes at least LiPF ₆ as the electrolyte salt in the non-aqueous electrolyte solution. Further, LiBF ₄ , LiPO ₂ F ₂ and LiN (SO _{2 F)} storage device as claimed in any one claims 12 to 14, characterized in that it comprises at least one lithium salt selected from ₂ in the nonaqueous electrolytic solution in 1M concentrations below or 0.001 M. The electricity storage device according to any one of claims 11 to 15 is a lithium ion secondary battery,
The lithium ion secondary battery is characterized in that a charging potential in a fully charged state of the negative electrode of the lithium ion secondary battery is 1.15 V or more with respect to a lithium reference electrode.   The lithium ion secondary battery according to claim 16, wherein a discharge potential of the negative electrode in a fully discharged state is 1.8 V or less with respect to a lithium reference electrode.   The lithium ion secondary battery according to claim 16 or 17, wherein the active material contained in the positive electrode is a composite metal oxide having a spinel structure.   The lithium ion secondary battery according to claim 18, wherein the composite metal oxide having a spinel structure contains manganese. 20. The lithium ion secondary battery according to claim 19, wherein the composite metal oxide having a spinel structure is LiMn ₂ O ₄ or LiNi _0.5 Mn _1.5 O ₄ . The lithium ion secondary battery according to claim 19, wherein the composite metal oxide having a spinel structure is LiMn ₂ O ₄ .