JP2018139172A - Nonaqueous electrolyte power storage element, electrical equipment, and method of using nonaqueous electrolyte power storage element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte power storage element high in energy density, electrical equipment including such a nonaqueous electrolyte power storage element, and a method of using such a nonaqueous electrolyte power storage element.SOLUTION: An embodiment of the present invention is a nonaqueous electrolyte power storage element which has a positive electrode containing a composite oxide containing lithium, bismuth and a metal element (M). The metal element (M) includes at least one of aluminum, vanadium, iron, cobalt, and nickel, and the discharge end potential of the positive electrode during normal use is 0.8 V(vs.Li/Li) or more and 1.4 V(vs.Li/Li) or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a nonaqueous electrolyte storage element, an electrical device, and a method of using the nonaqueous electrolyte storage element.

  Nonaqueous electrolyte secondary batteries typified by lithium ion secondary batteries are widely used in electronic devices such as personal computers and communication terminals, automobiles and the like because of their high energy density. The nonaqueous electrolyte secondary battery generally has a pair of electrodes electrically isolated by a separator and a nonaqueous electrolyte interposed between the electrodes, and transfers ions between the electrodes. It is comprised so that it may charge / discharge. In addition, capacitors such as lithium ion capacitors and electric double layer capacitors are widely used as nonaqueous electrolyte storage elements other than nonaqueous electrolyte secondary batteries.

  Lithium-containing transition metal oxides are widely used as active materials contained in the positive electrode of the nonaqueous electrolyte storage element. Under such circumstances, various positive electrode active materials have been developed for increasing the capacity of the nonaqueous electrolyte storage element. As one of the techniques, a technique using a composite oxide containing lithium and bismuth as a positive electrode active material of a non-aqueous electrolyte secondary battery has been proposed (see Patent Documents 1 and 2 and Non-Patent Document 1).

JP 2013-62114 A JP 2007-242570 A

W. L. Schmidt, “Synthesis and Investigation of Layered Oxides with Honeycomb Ordering,” (Ph. D. diss., Oregon State University, 2014), p 88-113.

  In the future, energy storage devices will be required to have higher energy density as a power source for electric vehicles (EV). However, the non-aqueous electrolyte storage element in which the above-described conventional composite oxide is used as the positive electrode active material does not have a high energy density that can sufficiently meet such a requirement.

  The present invention has been made based on the circumstances as described above, and an object thereof is a non-aqueous electrolyte storage element having a high energy density, an electric device including such a non-aqueous electrolyte storage element, and such a device. It is providing the usage method of a non-aqueous electrolyte electrical storage element.

One embodiment of the present invention made to solve the above problems has a positive electrode containing a composite oxide containing lithium, bismuth, and a metal element (M), and the metal element (M) contains aluminum, vanadium, Including at least one of iron, cobalt, and nickel, the discharge end potential of the positive electrode during normal use is 0.8 V (vs. Li ^/ Li ⁺ ) or more and 1.4 V (vs. Li ^/ Li ⁺ ) or less. This is a non-aqueous electrolyte electricity storage device.

  Another embodiment of the present invention is an electric device including the nonaqueous electrolyte storage element.

Another embodiment of the present invention includes a positive electrode containing a composite oxide containing lithium, bismuth, and a metal element (M), and the metal element (M) is selected from aluminum, vanadium, iron, cobalt, and nickel. performing a non-aqueous electrolyte energy storage device to the discharge in the range cutoff potential of the positive electrode is 0.8V (vs.Li/Li ⁺⁾ or 1.4V (vs.Li/Li ⁺⁾ or less containing at least one This is a method of using a non-aqueous electrolyte electricity storage device.

  ADVANTAGE OF THE INVENTION According to this invention, the nonaqueous electrolyte electrical storage element which has a high energy density, the electric equipment provided with such a nonaqueous electrolyte electrical storage element, and the usage method of such a nonaqueous electrolyte electrical storage element can be provided.

FIG. 1 is an external perspective view showing a nonaqueous electrolyte storage element according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing a power storage device configured by assembling a plurality of nonaqueous electrolyte power storage elements according to an embodiment of the present invention. FIG. 3 is an X-ray diffraction pattern of the composite oxides obtained in Synthesis Examples 1 to 7 and Comparative Synthesis Example 1. FIG. 4 is an X-ray diffraction pattern of the composite oxide obtained in Synthesis Examples 8-10. FIG. 5 is an X-ray diffraction pattern of the composite oxide obtained in Synthesis Examples 4, 11, and 12. 6A is an X-ray diffraction pattern of the composite oxide obtained in Synthesis Example 13, and FIG. 6B is an X-ray diffraction pattern of the composite oxide obtained in Synthesis Example 14. (C) is an X-ray diffraction pattern of the composite oxide obtained in Synthesis Example 15, and FIG. 6 (d) is an X-ray diffraction pattern of the composite oxide obtained in Comparative Synthesis Example 2. FIG. 7 is a charge / discharge curve of Example 4. FIG. 8 is a charge / discharge curve of Example 20.

A nonaqueous electrolyte storage element according to an embodiment of the present invention has a positive electrode containing a composite oxide containing lithium, bismuth and a metal element (M), and the metal element (M) is aluminum, vanadium, iron , Including at least one of cobalt and nickel, and the discharge end potential of the positive electrode during normal use is 0.8 V (vs. Li ^/ Li ⁺ ) or more and 1.4 V (vs. Li ^/ Li ⁺ ) or less. This is a non-aqueous electrolyte storage element.

The nonaqueous electrolyte electricity storage element has a high energy density. Although this reason is not certain, the following reason is guessed. Lowering the discharge cutoff potential of the positive electrode containing a composite oxide having the above composition to below 0.8V (vs.Li/Li ⁺⁾ or 1.4V (vs.Li/Li ^+), carried out to a low potential range of discharge At this time, it is presumed that the conversion reaction proceeds in the composite oxide. Therefore, it is considered that this makes it possible to utilize a discharge reaction that has not been used in the past, increasing the discharge capacity and, as a result, increasing the energy density.

Here, “during normal use” refers to a case where the nonaqueous electrolyte storage element is used under the recommended discharge conditions and charge conditions for the nonaqueous electrolyte storage element. For example, the discharge conditions are determined by the setting of the electrical equipment that uses the nonaqueous electrolyte storage element. As for charging conditions, when a charger for the non-aqueous electrolyte storage element is prepared, the charging means is used when the non-aqueous electrolyte storage element is used.

The charge termination potential of the positive electrode during normal use of the nonaqueous electrolyte storage element is preferably 2.5 V (vs. Li ^/ Li ⁺ ) or more and 3.5 V (vs. Li ^/ Li ⁺ ) or less. By doing in this way, in addition to an energy density, the capacity maintenance rate in a charging / discharging cycle can also be raised. The reason for this is not clear, but lithium intercalation occurs mainly in the region of potential higher than 3.5 V (vs. Li ^/ Li ⁺ ), and this causes a decrease in capacity retention rate. Guessed. Therefore, the charge end potential of the positive electrode is 2.5 V (vs. Li ^/ Li ⁺ ) or more and 3.5 V (vs. Li ^/ Li ⁺ ) or less, and the discharge end potential is 0.8 V (vs. Li ^/ Li ⁺ ) or more. By setting it to 1.4 V (vs. Li ^/ Li ⁺ ) or less, it is presumed that charge and discharge can be performed mainly by a conversion reaction, and the capacity maintenance rate can be increased while maintaining a high energy density. Compared to intercalation reactions in which the recombination of lithium causes only expansion and contraction of the lattice volume and the crystal structure (atomic arrangement) does not change significantly, the conversion reaction in which recombination of the bonds occurs is generally a capacity. It is said that the maintenance rate is likely to decrease. However, in the non-aqueous electrolyte storage element, it is surprisingly possible to increase the capacity maintenance rate of the charge / discharge cycle by using mainly the conversion reaction without using the intercalation reaction.

  The metal element (M) is a combination of at least one of aluminum, vanadium, iron, cobalt and nickel, or at least one of aluminum, vanadium, iron, cobalt and nickel and at least one of copper and zinc. It is preferable that By using a composite oxide containing such a metal element, the energy density can be further increased.

  The metal element (M) preferably contains nickel, and the nickel content in the metal element (M) is preferably 50 mol% or more. Thus, the energy density can be further increased by using a composite oxide having a high nickel content.

  The content of the metal element (M) with respect to the total content of bismuth and the metal element (M) in the composite oxide is preferably 30 mol% or more and 75 mol% or less. By using the composite oxide having such a composition, the energy density can be further increased.

The composite oxide is preferably represented by the following formula (1). By using the composite oxide having such a composition, the energy density can be further increased.
Li ₃ M _3x Bi _{3 (1-x)} O ₆ (1)
(In the formula (1), M is a metal element containing at least one of Al, V, Fe, Co, and Ni. 0 <x <1.)

  An electrical device according to an embodiment of the present invention is an electrical device including the nonaqueous electrolyte storage element. Since the electrical device includes the non-aqueous electrolyte storage element having a high energy density, the electrical device can be downsized or increased in capacity, and the charging frequency can be reduced to improve convenience.

A method for using a non-aqueous electrolyte electricity storage device according to an embodiment of the present invention includes a positive electrode containing a composite oxide containing lithium, bismuth and a metal element (M), wherein the metal element (M) is aluminum, For a non-aqueous electrolyte storage element containing at least one of vanadium, iron, cobalt, and nickel, the terminal potential of the positive electrode is 0.8 V (vs. Li ^/ Li ⁺ ) or more and 1.4 V (vs. Li ^/ Li) ⁺ ) A method of using a non-aqueous electrolyte electricity storage device having discharge in the following range. According to the method of using the nonaqueous electrolyte storage element, the nonaqueous electrolyte storage element can be used with a high energy density.

  Hereinafter, a nonaqueous electrolyte storage element, an electrical device, and a method of using the nonaqueous electrolyte storage element according to an embodiment of the present invention will be described in detail.

<Nonaqueous electrolyte storage element>
A nonaqueous electrolyte storage element according to an embodiment of the present invention includes a positive electrode, a negative electrode, and a nonaqueous electrolyte. Hereinafter, a nonaqueous electrolyte secondary battery will be described as an example of a nonaqueous electrolyte storage element. The positive electrode and the negative electrode usually form an electrode body that is alternately superposed by stacking or winding via a separator. This electrode body is housed in a case, and the case is filled with a nonaqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. Moreover, as said case, the well-known aluminum case, resin case, etc. which are normally used as a case of a nonaqueous electrolyte secondary battery can be used.

(Positive electrode)
The positive electrode has a positive electrode base material and a positive electrode mixture layer disposed on the positive electrode base material directly or via an intermediate layer.

The positive electrode base material has conductivity. As the material of the substrate, metals such as aluminum, copper, titanium, tantalum, stainless steel, or alloys thereof are used. Among these, aluminum, copper, and alloys thereof are preferable, and copper and copper alloys may be more preferable from the viewpoint of potential resistance, high conductivity, and cost. For example, when the charge end potential is 3 V (vs. Li ^/ Li ⁺ ) or less, copper or a copper alloy can be used. On the other hand, when the charge end potential is more than 3 V (vs. Li ^/ Li ⁺ ), it is preferable to use aluminum or an aluminum alloy. Moreover, foil, a vapor deposition film, etc. are mentioned as a formation form of a positive electrode base material, and foil is preferable from the surface of cost. That is, the positive electrode base material is preferably an aluminum foil or a copper foil.

The said intermediate | middle layer is a coating layer of the surface of a positive electrode base material, and reduces the contact resistance of a positive electrode base material and a positive electrode compound material layer by including electroconductive particles, such as a carbon particle. The configuration of the intermediate layer is not particularly limited, and can be formed of a composition containing a resin binder and conductive particles, for example. “Conductive” means that the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 ⁷ Ω · cm or less, and “nonconductive” Means that the volume resistivity is more than 10 ⁷ Ω · cm.

  The positive electrode mixture layer is a layer formed from a so-called positive electrode mixture containing a specific composite oxide. The composite oxide functions as a positive electrode active material. This positive electrode mixture can contain optional components such as other positive electrode active materials, conductive agents, binders, thickeners, fillers and the like as necessary.

  The composite oxide includes lithium (Li), bismuth (Bi), and a metal element (M). The metal element (M) is a metal element other than Li and Bi, and includes at least one of aluminum (Al), vanadium (V), iron (Fe), cobalt (Co), and nickel (Ni). .

  The content ratio of lithium (Li) in the composite oxide is not particularly limited. From the fact that the composition ratio of lithium greatly varies due to charge and discharge, and that the lithium raw material is generally added in excess of the theoretical composition ratio during synthesis, the lithium content in the composite oxide is, It does not significantly affect the performance as the positive electrode active material. The lithium content in the composite oxide is, for example, 30 mol% (0.3 times as the atomic ratio) as the lithium content (Li / (Bi + M)) with respect to the total content of bismuth and the metal element (M). ) To 300 mol% (three times) or less. The lower limit of the content ratio (Li / (Bi + M)) is preferably 50 mol% (0.5 times), and the upper limit is preferably 200 mol% (2 times). Moreover, it is more preferable that the content ratio (Li / (Bi + M)) is substantially 100 mol% (1 time).

  The lower limit of the content (M / (Bi + M)) of the metal element (M) with respect to the total content of bismuth (Bi) and the metal element (M) in the composite oxide is, for example, 10 mol% as the atomic ratio. However, 30 mol% is preferable, 40 mol% is more preferable, 50 mol% is further more preferable, and 60 mol% is still more preferable. By setting the content of the metal element (M) to be equal to or higher than the above lower limit, the energy density is further increased and the capacity retention rate is also increased. In addition, the content (M / (Bi + M)) of the metal element (M) with respect to the total content of bismuth (Bi) and the metal element (M) may be 66.7 mol%, that is, 2/3. it can.

  On the other hand, the upper limit of the content (M / (Bi + M)) of the metal element (M) with respect to the total content of bismuth (Bi) and the metal element (M) in the composite oxide is, for example, 95 mol% as the atomic ratio However, 90 mol% is preferable, 80 mol% is more preferable, 75 mol% is further more preferable, and 70 mol% is still more preferable. By setting the content of the metal element (M) to be equal to or lower than the above upper limit, the energy density is further increased and the capacity maintenance rate is also increased.

  The metal element (M) includes at least one of Al, V, Fe, Co, and Ni. The metal element (M) may be composed of only one element or may be composed of two or more elements. This metal element (M) may contain other metal elements other than Al, V, Fe, Co, and Ni. Other metal elements include magnesium (Mg), calcium (Ca), titanium (Ti), chromium (Cr), manganese (Mn), copper (Cu), zinc (Zn), zirconium (Zr), niobium (Nb ), Molybdenum (Mo), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), and the like. Among these, the fourth periodic element (Ca, Ti, Cr, Mn, Cu, Zn, etc.) is preferable. Further, Group 9-12 elements (Rh, Pd, Cu, Ag, Zn, Cd, etc.) are also preferred, and Group 11-12 elements (Cu, Ag, Zn, etc.) are more preferred. As other elements, Cu and Zn are particularly preferable. When these metal elements are contained, the energy density and capacity retention rate may be further increased.

  Further, the lower limit of the total content of Al, V, Fe, Co, Ni, Cu and Zn in the metal element (M) is preferably 50 mol%, preferably 90 mol%, and 99 mol% More preferably. Furthermore, the total content of Al, V, Fe, Co, Ni, Cu and Zn in the metal element (M) is particularly preferably substantially 100 mol%. That is, the metal element (M) is at least one of Al, V, Fe, Co and Ni, or at least one of Al, V, Fe, Co and Ni and at least one of Cu and Zn. It is preferable that it is the combination of these. By using the composite oxide containing the metal element (M) having such a composition, the energy density can be further increased.

  The metal element (M) preferably contains Ni or Co, and more preferably contains Ni. The lower limit of the Ni content in the metal element (M) is not particularly limited and may be 30 mol%, but is preferably 50 mol%, sometimes 70 mol%, and preferably 90 mol%. In some cases. It is also preferable that the metal element (M) is only Ni. Thus, the energy density can be further increased by preferably including a predetermined amount of Ni as the metal element (M). The upper limit of the Ni content in the metal element (M) may be 100 mol%, but 80 mol% may be preferable, and 60 mol% may be preferable.

  The oxygen (O) content in the composite oxide is not particularly limited, and is usually determined from the composition ratio of the metal elements, the valence of the metal elements, and the like. However, since it may be an oxygen-deficient or oxygen-rich oxide, it is not determined only by the composition and valence of the metal element. The oxygen content in the composite oxide is, for example, 60 mol% (0.6 times) in terms of the atomic ratio as the oxygen content (O / (Bi + M)) with respect to the total content of bismuth and the metal element (M). ) To 600 mol% (6 times) or less. The lower limit of the content ratio (O / (Bi + M)) is preferably 100 mol% (1 time), and the upper limit is preferably 400 mol% (4 times). Further, it is more preferable that the content ratio (O / (Bi + M)) is substantially 200 mol% (twice).

  The complex oxide may contain other elements other than lithium, bismuth, metal element (M) and oxygen in a range that does not affect the operational effects of the present invention. Examples of such other optional elements include non-metallic elements such as halogen, carbon, and nitrogen. The upper limit of the content of these optional elements is preferably 50 mol%, more preferably 20 mol%, more preferably 10 mol%, based on the total content (100 mol%) of bismuth and the metal element (M). More preferably, 1 mol% is still more preferable, and 0.1 mol% is especially preferable. This optional element may not be substantially contained.

As the complex oxide, a compound represented by the following formula (2) can be preferably used.
Li _{3 + a} M _3x Bi _{3 (1-x)} O _{6 + δ} (2)
(In Formula (2), M is a metal element containing at least one of Al, V, Fe, Co, and Ni. 0 <x <1, 0 ≦ a ≦ 3.5, −0.6 ≦ δ ≦ 0.6.)
Especially, it is preferable to employ | adopt the compound represented by following formula (1).
Li ₃ M _3x Bi _{3 (1-x)} O ₆ (1)
(In Formula (1), M is a metal element containing at least one of Al, V, Fe, Co, and Ni. 0 <x <1.)

  X in the above formulas (1) and (2) represents the content (M / (Bi + M)) of the metal element (M) with respect to the total content of bismuth (Bi) and the metal element (M). The lower limit of x may be 0.1, but 0.3 is preferable, 0.4 is more preferable, 0.5 is more preferable, and 0.6 is still more preferable. Moreover, 0.95 may be sufficient as the upper limit of x, However, 0.9 is preferable, 0.8 is more preferable, 0.75 is further more preferable, 0.7 is still more preferable. x may be 2/3.

  M in the above formulas (1) and (2) is not particularly limited as long as it is a metal element containing at least one of Al, V, Fe, Co, and Ni, and is composed of only one metal element. It may be composed of two or more metal elements. A preferable composite oxide can be represented by the following formula (1 ′).

Li ₃ M ¹ _3xy M ² _{3x (1-y)} Bi _{3 (1-x)} O ₆ (1 ′)
(In Formula (1 ′), M ¹ is Al, V, Fe, Co, Ni, or a combination thereof. M ² is Cu, Zn, or a combination thereof. 0 <x <1. 0 <y ≦ 1.)

In the formula (1 ′), for example, when M ¹ = Ni, M ² = Cu, x = 2/3, and y = 0.5, the composite oxide is represented by Li ₃ NiCuBiO ₆ .

A more preferable range of x in the formula (1 ′) is the same as x in the formula (1). Y in the above formula (1 ′) represents the content ratio of Al, V, Fe, Co, and Ni in the metal element (M). For example, y may be 0.1 or more, but is preferably 0.5 or more, more preferably 0.7 or more, still more preferably 0.9 or more, and even more preferably 1. Moreover, y can be set to 0.5 or 1. M ¹ preferably contains Ni or Co, more preferably Ni, and even more preferably Ni.

  The composite oxide may be crystalline, amorphous, or a mixture thereof. When the composite oxide is crystalline, the crystal structure of the composite oxide is not particularly limited, but in the X-ray diffraction diagram, a peak that can be assigned to the space group C2 / m, Fm-3m, C2 / c, or Ibam. Having a peak that can be assigned to the space group C2 / m is more preferable. That is, the composite oxide preferably has a space group C2 / m, Fm-3m, C2 / c, or Ibam crystal structure, and more preferably has a space group C2 / m crystal structure. However, the crystal structure may not be maintained by repeated charge and discharge. Therefore, it is preferable that the crystal structure before charging / discharging belongs to the space group. X-ray diffraction measurement of the composite oxide is performed by powder X-ray diffraction measurement using an X-ray diffractometer (“MiniFlex II” manufactured by Rigaku), with the source being CuKα ray, the tube voltage being 30 kV and the tube current being 15 mA. be able to. At this time, the diffracted X-rays are detected by a high-speed one-dimensional detector (D / teX Ultra 2) through a Kβ filter having a thickness of 30 μm. The sampling width is 0.01 °, the scanning speed is 5 ° / min, the divergence slit width is 0.625 °, the light receiving slit width is 13 mm (OPEN), and the scattering slit width is 8 mm. Based on the obtained X-ray diffraction data, the crystal structure can be analyzed by Rietveld analysis using the “Rietan 2000” program (F. Izumi and T. Ikeda, Mater. Sci. Forum, 198 (2000)). it can. The same results can be obtained for the space group and the lattice constant even when using the comprehensive powder X-ray analysis software “PDXL” (manufactured by Rigaku).

When the metal element (M) contains Ni, the composite oxide has 0.4 to 0.6 V (vs. Li ^/ V) in a dQ / dV plot when reducing to 0 V (vs. Li / Li ⁺ ). Li ⁺ ) preferably has a peak. By using a complex oxide having a peak at such a position in the dQ / dV plot as the positive electrode active material, the energy density can be further increased. The lower limit of this peak position can be 0.44 V (vs. Li ^/ Li ⁺ ) and 0.48 V (vs. Li ^/ Li ⁺ ). On the other hand, the upper limit may be a 0.56V (vs.Li/Li ^+), it can be 0.52V (vs.Li/Li ^+).

In addition, the electric current value at the time of the measurement of a dQ / dV plot shall be 50 mA / g with respect to the mass of complex oxide. This peak can be specified by fitting by the least square method using the Lorentz function shown in the following formula (3). The background of the dQ / dV plot is approximated by a linear function.
y = A / (1+ (x−x ₀ ) ² / w ² ) (3)
In the formula (3), A represents the peak height, x ₀ represents the peak position, and w represents the half width at half maximum of the peak.
In the composite oxide represented by the above formula (1), when x ≧ 0.67, the function used for fitting is “background + peak 1 (a linear function and a function represented by the above formula (3)”. In the case of x <0.67, the function used for fitting is “background + peak 1 + peak 2 + peak 3 (primary function, respectively expressed by the above formula (3)”. The function can be expressed as the sum of the three functions.

The method for producing the composite oxide is not particularly limited. The composite oxide can be obtained, for example, by a solid phase method in which a Li compound (carbonate or the like), a Bi compound (oxide or the like), and a metal element (M) compound (oxide or the like) are mixed and fired. . Note that mechanochemical treatment may be performed after synthesis by a solid phase method. Examples of the Li compound include Li ₂ CO ₃ . Examples of Bi compounds include Bi ₂ O _{3 and the} like. NiO, CoO, CuO, ZnO etc. can be mentioned as a compound containing a metal element (M).

Further, the composite oxide can be synthesized by mechanochemical treatment of LiBiO ₂ and LiMO ₂ (M = Al, V, Co, etc.). LiBiO ₂ can be synthesized, for example, by a solid phase method using a Li compound such as Li ₂ CO ₃ and a Bi compound such as Bi ₂ O ₃ as raw materials. LiMO ₂ (M = Al, V, Co, etc.) is also synthesized by a solid phase method using a Li compound such as Li ₂ CO ₃ and a compound of a metal element M (V ₂ O ₃ etc.) as raw materials. Can do.

  The compounding ratio of the compounds as the raw materials can be appropriately adjusted according to the composition ratio of the target composite oxide.

  The positive electrode active material containing the composite oxide can be previously doped with lithium using a reducing agent. As such a reducing agent, in addition to lithium metal, for example, literature (DW Murphy, and PA Christian, “Solid State Electrodes for High Energy Batteries”, Science, 205, 651-656 (1979). )), Alkyl lithium such as propyl lithium and butyl lithium, and the like.

  The lower limit of the content of the composite oxide in the positive electrode mixture (positive electrode mixture layer) is preferably, for example, 50% by mass, and more preferably 60% by mass. On the other hand, the upper limit of the content is, for example, 95% by mass, 90% by mass, or 80% by mass. By setting the content of the composite oxide in the above range, the energy density can be further increased.

Other positive electrode active materials are, for example, complex oxides represented by Li _x MO _y (M represents at least one transition metal) (Li _x CoO ₂ , Li _x NiO having a layered α-NaFeO ₂ type crystal structure). _{2, Li x MnO 3, Li} x Ni α Co (1-α) O 2, Li x Ni α Mn β Co (1-α-β) O 2 , etc., _Li x _Mn 2 _{O 4} having a spinel type crystal structure , Li _x Ni _α Mn _(2-α) O ₄ ), Li _w Me _x (XO _y ) _z (Me represents at least one transition metal, X represents P, Si, B, V, etc.) And a polyanion compound represented by the formula (LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , Li ₂ CoPO ₄ F, etc.). The elements or polyanions in these compounds may be partially substituted with other elements or anion species.

  The conductive agent is not particularly limited as long as it is a conductive material that does not adversely affect the performance of the storage element. Examples of such a conductive agent include natural or artificial graphite, furnace black, acetylene black, carbon black such as ketjen black, metal, conductive ceramics, and the like, and acetylene black is preferable. Examples of the shape of the conductive agent include powder and fiber.

  Examples of the binder (binder) include fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), thermoplastic resins such as polyethylene, polypropylene, polyimide; ethylene-propylene-diene rubber (EPDM), Examples thereof include elastomers such as sulfonated EPDM, styrene butadiene rubber (SBR) and fluororubber; polysaccharide polymers and the like.

  Examples of the thickener include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. When the thickener has a functional group that reacts with lithium, it is preferable to deactivate this functional group in advance by methylation or the like.

  The filler is not particularly limited as long as it does not adversely affect the performance of the storage element. Examples of the main component of the filler include polyolefins such as polypropylene and polyethylene, silica, alumina, zeolite, and glass.

(Negative electrode)
The negative electrode includes a negative electrode base material and a negative electrode mixture layer disposed on the negative electrode base material directly or via an intermediate layer. The intermediate layer can have the same configuration as the positive electrode intermediate layer.

  The negative electrode base material can have the same configuration as the positive electrode base material, but as a material, a metal such as copper, nickel, stainless steel, nickel-plated steel, or an alloy thereof is used. preferable. That is, copper foil is preferable as the negative electrode substrate. Examples of the copper foil include rolled copper foil and electrolytic copper foil.

  The negative electrode mixture layer is formed from a so-called negative electrode mixture containing a negative electrode active material. Moreover, the negative electrode composite material which forms a negative electrode composite material layer contains arbitrary components, such as a electrically conductive agent, a binder, a thickener, and a filler, as needed. Arbitrary components such as a conductive agent, a binder, a thickener, and a filler can be the same as those for the positive electrode mixture layer.

  As the negative electrode active material, a material that can occlude and release lithium ions is usually used. Specific negative electrode active materials include, for example, metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide and Sn oxide; polyphosphate compounds; graphite (graphite) and amorphous Examples thereof include carbon materials such as carbon (easily graphitizable carbon or non-graphitizable carbon). Among these, a carbon material is preferable, and graphite is more preferable.

  Further, the negative electrode mixture (negative electrode mixture layer) includes typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, Li, Na, Mg, Al, K, Ca, Zn, Ga, and Ge. Typical metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W may be contained.

(Separator)
As the material of the separator, for example, a woven fabric, a nonwoven fabric, a porous resin film, or the like is used. Among these, a porous resin film is preferable from the viewpoint of strength, and a nonwoven fabric is preferable from the viewpoint of liquid retention of the nonaqueous electrolyte. The main component of the separator is preferably a polyolefin such as polyethylene or polypropylene from the viewpoint of strength, and is preferably polyimide or aramid from the viewpoint of resistance to oxidative degradation. These resins may be combined.

  An inorganic layer may be provided between the separator and the electrode (usually a positive electrode). This inorganic layer is a porous layer also called a heat-resistant layer. Moreover, the separator by which the inorganic layer was formed in one surface of the porous resin film can also be used. The inorganic layer is usually composed of inorganic particles and a binder, and may contain other components.

(Nonaqueous electrolyte)
As said nonaqueous electrolyte, the well-known electrolyte normally used for a nonaqueous electrolyte electrical storage element (secondary battery) can be used. The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

  Examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and the like. A chain carbonate etc. can be mentioned.

Examples of the electrolyte salt include lithium salt, sodium salt, potassium salt, magnesium salt, onium salt, and the like, but lithium salt is preferable. Examples of the lithium salt include inorganic lithium salts such as LiPF ₆ , LiPO ₂ F ₂ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ F) ₂ , LiSO ₃ CF ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO Fluorohydrocarbon groups such as ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), LiC (SO ₂ CF ₃ ) ₃ , LiC (SO ₂ C ₂ F ₅ ) ₃ A lithium salt having

  As the non-aqueous electrolyte, a room temperature molten salt, an ionic liquid, a polymer solid electrolyte, or the like can be used.

(Discharge end potential, charge end potential, etc.)
The upper limit of the discharge cutoff potential of the positive electrode at the time of normal use in the non-aqueous electrolyte energy storage device is a 1.4V (vs.Li/Li ^+), preferably 1.3V (vs.Li/Li ^+), 1 .2V (vs. Li / Li ⁺ ) is more preferable. By setting the discharge end potential to be equal to or lower than the above upper limit, the conversion reaction can be sufficiently utilized as described above, and the nonaqueous electrolyte storage element can exhibit a high energy density.

On the other hand, the lower limit of the discharge end potential is 0.8 V (vs. Li ^/ Li ⁺ ), preferably 0.9 V (vs. Li ^/ Li ⁺ ), and 1.0 V (vs. Li ^/ Li ⁺ ). More preferred. By setting the discharge end potential to the above lower limit or more, the conversion reaction of the positive electrode active material can be used to increase the energy density and the capacity retention rate. In addition, by setting the discharge end potential to the above lower limit or more, a sufficient potential can be maintained and it can be effectively used as a positive electrode.

The upper limit of the charge termination potential of the positive electrode during normal use in the non-aqueous electrolyte storage element may be, for example, 5 V (vs. Li ^/ Li ⁺ ) or 4 V (vs. Li ^/ Li ⁺ ). but preferably 3.5V (vs.Li/Li ^+), more preferably ^{3.2V (vs.Li/Li +), 3.0V (} vs.Li/Li +) is more preferred. The capacity maintenance rate can be increased by setting the charge end potential to the upper limit or less. Here, as shown in FIG. 8, the charge / discharge curve of the nonaqueous electrolyte storage element has a potential flat portion in the vicinity of 3.7 V (vs. Li ^/ Li ⁺ ). From this result, it is estimated that an intercalation reaction occurs in a region of 3.7 V (vs. Li ^/ Li ⁺ ) or higher, and a conversion reaction occurs in a region of 3.7 V (vs. Li ^/ Li ⁺ ) or lower. Is done. In general, the reaction with lithium causes only expansion and contraction of the lattice volume, and the conversion reaction, in which the recombination of the bond occurs, is maintained compared to the intercalation reaction in which the crystal structure (atomic arrangement) does not change significantly. The rate is likely to drop. However, in the non-aqueous electrolyte storage element, it is surprisingly possible to increase the capacity maintenance rate of the charge / discharge cycle by using mainly the conversion reaction without using the intercalation reaction.

On the other hand, the lower limit of the charge end potential is preferably 2.5 V (vs. Li ^/ Li ⁺ ), more preferably 2.8 V (vs. Li ^/ Li ⁺ ), and 3.0 V (vs. Li ^/ Li ⁺ ). Is more preferable. By setting the charging end potential to be equal to or higher than the lower limit, the nonaqueous electrolyte storage element can exhibit a higher energy density.

  Further, the lower limit of the potential difference between the charge end potential and the discharge end potential is preferably 1V, more preferably 1.5V, still more preferably 2V, and may be 2.5V. By setting the potential difference to be equal to or higher than the lower limit, the energy density can be increased.

  On the other hand, the upper limit of this potential difference is preferably 4V, more preferably 3V, even more preferably 2.5V, and even more preferably 2.0V. The capacity maintenance rate can be increased by setting the potential difference to be equal to or less than the upper limit.

  The current value during charging and discharging during normal use in the nonaqueous electrolyte storage element is not particularly limited, but the lower limit is, for example, 1 mA / g with respect to the mass of the composite oxide contained in the positive electrode. It may be 5 mA / g, 10 mA / g, or 30 mA / g. On the other hand, the upper limit may be, for example, 10 A / g, 5 A / g, or 1 A / g.

  The non-aqueous electrolyte storage element can be manufactured by using a positive electrode containing the composite oxide. The manufacturing method includes, for example, a step of producing a positive electrode, a step of producing a negative electrode, a step of preparing a nonaqueous electrolyte, and an electrode body in which the positive electrode and the negative electrode are alternately superposed by being stacked or wound via a separator. Forming a positive electrode and a negative electrode (electrode body) in a case, and injecting the nonaqueous electrolyte into the case. After the injection, the nonaqueous electrolyte storage element can be obtained by sealing the injection port. The details of each element constituting the nonaqueous electrolyte storage element (secondary battery) obtained by the manufacturing method are as described above.

<Electrical equipment>
An electric apparatus according to an embodiment of the present invention includes the nonaqueous electrolyte storage element described above. The electric device is not particularly limited, such as an electronic device such as a personal computer or a communication terminal, a home appliance, an electric vehicle, and other industrial electric devices.

The electrical equipment, in use, the discharge cutoff potential of the positive electrode of the nonaqueous electrolyte battery element becomes 0.8V (vs.Li/Li ⁺⁾ or 1.4V (vs.Li/Li ⁺⁾ the range It is preferable to set as follows. That is, it is preferable to set the positive electrode so that it can be used as there is a remaining amount of electricity until the potential of the positive electrode reaches 1.4 V (vs. Li ^/ Li ⁺ ). Moreover, when the electric potential of a positive electrode reaches to 0.8V (vs.Li/Li ^<+> ), it is preferable to set so that it may not be used any more substantially. By setting in this way, the nonaqueous electrolyte electricity storage element provided in the electric device can exhibit a high energy density. The preferred range of the discharge end potential is the same as that described above as the preferred range of the discharge end potential of the positive electrode during normal use of the nonaqueous electrolyte storage element.

When the electric device includes a charger (charging function), the charge end potential of the positive electrode of the nonaqueous electrolyte storage element is 2.5 V (vs. Li ^/ Li ⁺ ) or more and 3.5 V (vs. Li ^/ Li ⁺ ). ) It is preferably set to be in the following range. By setting in this way, the non-aqueous electrolyte electricity storage element provided in the electric device can exhibit a good capacity maintenance rate. The further preferable range of the charge end potential is the same as that described above as the preferable range of the charge end potential of the positive electrode during normal use of the nonaqueous electrolyte storage element.

<Usage method of nonaqueous electrolyte storage element>
A method for using a nonaqueous electrolyte storage element according to an embodiment of the present invention includes a positive electrode containing a composite oxide containing Li, Bi, and a metal element (M), wherein the metal element (M) is Al, For a non-aqueous electrolyte storage element containing at least one of V, Fe, Co, and Ni, the terminal potential of the positive electrode is 0.8 V (vs. Li ^/ Li ⁺ ) or more and 1.4 V (vs. Li ^/ Li). ⁺ ) A method of using a non-aqueous electrolyte electricity storage device having discharge in the following range.

  In the usage method, the above-described non-aqueous electrolyte electricity storage device according to one embodiment of the present invention can be suitably used. Moreover, the suitable range of the said termination potential in the said usage method is the same as what was mentioned above as the discharge termination potential of the positive electrode at the time of the normal use of the said nonaqueous electrolyte electrical storage element. Moreover, in the said usage method, the electric equipment which concerns on one Embodiment of this invention mentioned above can be used conveniently. According to the method of use, the nonaqueous electrolyte storage element can be used with a high energy density.

Further, the usage method is such that the non-aqueous electrolyte storage element is charged in a range where the terminal potential of the positive electrode is 2.5 V (vs. Li ^/ Li ⁺ ) or more and 3.5 V (vs. Li ^/ Li ⁺ ) or less. It is preferable to further perform. By doing in this way, the capacity | capacitance maintenance factor of the said nonaqueous electrolyte electrical storage element can be raised. The preferred range of the end potential at the time of charging is the same as that described above as the charge end potential of the positive electrode during normal use of the nonaqueous electrolyte storage element.

<Other embodiments>
The present invention is not limited to the above-described embodiment, and can be implemented in a mode in which various changes and improvements are made in addition to the above-described mode. For example, in the positive electrode, the intermediate layer may not be provided, and the positive electrode mixture may not form a clear layer. For example, the positive electrode may have a structure in which a positive electrode mixture is supported on a mesh-like positive electrode base material. Further, in the above embodiment, the description has been made centering on the form in which the nonaqueous electrolyte storage element is a secondary battery, but other nonaqueous electrolyte storage elements may be used. Examples of other nonaqueous electrolyte storage elements include capacitors (electric double layer capacitors, lithium ion capacitors) and the like.

  FIG. 1 shows a schematic diagram of a rectangular nonaqueous electrolyte storage element (secondary battery) 1 which is an embodiment of the nonaqueous electrolyte storage element. In the figure, the inside of the container is seen through. In the nonaqueous electrolyte storage element 1 shown in FIG. 1, an electrode body 2 is housed in a container (case) 3. The electrode body 2 is formed by winding a positive electrode including a positive electrode active material and a negative electrode including a negative electrode active material via a separator. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 4 ′, and the negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 5 ′.

  The configuration of the nonaqueous electrolyte storage element (secondary battery) is not particularly limited, and examples thereof include a cylindrical battery, a square battery (rectangular battery), a flat battery, and the like. The present invention can also be realized as a power storage device including a plurality of the above nonaqueous electrolyte power storage elements. One embodiment of a power storage device is shown in FIG. In FIG. 2, the power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of nonaqueous electrolyte power storage elements 1. The power storage device 30 can be mounted as a power source for vehicles such as an electric vehicle (EV), a hybrid vehicle (HEV), a plug-in hybrid vehicle (PHEV), and the like.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

[Synthesis Example 1]
A composite oxide was obtained by the following solid phase method (SSR). Lithium carbonate (Li ₂ CO ₃ ), nickel oxide (NiO), and bismuth oxide (Bi ₂ O ₃ ) were mixed at a molar ratio of Li: Ni: Bi = 10: 3: 7. Specifically, these were put into a zirconia pot containing zirconia balls together with ethanol as an auxiliary agent, and the lid was capped. This was set in a planetary ball mill ("Pulverisete 5" manufactured by FRITSCH) and wet-mixed for 1 hour at a revolution speed of 300 rpm. This mixture was dried in a dryer at 75 ° C. for 3 hours or more to prepare a precursor. Next, this precursor was placed on an alumina crucible, and this crucible was placed in a tabletop vacuum / gas displacement furnace (“KDF75” manufactured by Denken Haydental). Subsequently, the temperature was raised from normal temperature to 700 ° C. in an air stream under normal pressure for 10 hours, and kept at this temperature for 4 hours, and then naturally cooled to room temperature. In this way, a composite oxide (Li ₃ Ni _0.9 Bi _2.1 O ₆ : M = Ni, x = 0.30) was obtained.

[Synthesis Examples 2 to 7, Comparative Synthesis Example 1]
Li ₂ CO ₃ , NiO and Bi ₂ O ₃ were mixed in Li: Ni: Bi (molar ratio), and the same operation as in Synthesis Example 1 was performed except that the mixing ratio was as follows. Negative electrode active materials of certain synthesis examples 2 to 7 and comparative synthesis example 1 were obtained.
Synthesis Example 2 Li: Ni: Bi = 5: 2: 3
(Li ₃ Ni _1.2 Bi _1.8 O ₆ : M = Ni, x = 0.40)
Synthesis Example 3 Li: Ni: Bi = 2: 1: 1
(Li ₃ Ni _1.5 Bi _1.5 O ₆ : M = Ni, x = 0.50)
Synthesis Example 4 Li: Ni: Bi = 3: 2: 1
(Li ₃ Ni ₂ BiO ₆ : M = Ni, x = 0.67)
Synthesis Example 5 Li: Ni: Bi = 4: 3: 1
(Li ₃ Ni _2.25 Bi _0.75 O ₆ : M = Ni, x = 0.75)
Synthesis Example 6 Li: Ni: Bi = 6: 5: 1
(Li ₃ Ni _2.5 Bi _0.5 O ₆ : M = Ni, x = 0.83)
Synthesis Example 7 Li: Ni: Bi = 10: 9: 1
(Li ₃ Ni _2.7 Bi _0.3 O ₆ : M = Ni, x = 0.90)
Comparative Synthesis Example 1 Li: Ni: Bi = 1: 1: 0
(Li ₃ Ni ₃ O ₆ : M = Ni, x = 1.00)

[Synthesis Example 8]
The following mechanochemical (MC) treatment was performed on the composite oxide (Li ₃ Ni _1.2 Bi _1.8 O ₆ ) obtained by the solid phase method of Synthesis Example 2 above. The composite oxide was put into a tungsten carbide pot containing tungsten carbide balls and covered in a glove box maintained in an argon atmosphere. This was set in a planetary ball mill and mixed at a revolution speed of 400 rpm for 4 hours. Thus, a composite oxide (Li ₃ Ni _1.2 Bi _1.8 O ₆ : M = Ni, x = 0.40) subjected to MC treatment was obtained.

[Synthesis Examples 9 and 10]
The composite oxide (Li ₃ Ni ₂ BiO ₆ ) obtained by the solid phase method of Synthesis Example 4 or the composite oxide (Li ₃ Ni _2.7 Bi _0.3 O) obtained by the solid phase method of Synthesis Example 7 ₆ ) The composite oxide (Li ₃ Ni ₂ BiO ₆ : M = Ni, x = 0.67: Synthesis example 9) and composite oxide subjected to MC treatment was used in the same manner as in Synthesis Example 8 except that ₆ ) was used. (Li ₃ Ni _2.7 Bi _0.3 O ₆ : M = Ni, x = 0.90: Synthesis Example 10) were obtained.

[Synthesis Example 11]
Complex oxidation was performed in the same manner as in Synthesis Example 1 except that Li ₂ CO ₃ , NiO, CuO, and Bi ₂ O ₃ were mixed at a molar ratio of Li: Ni: Cu: Bi = 3: 1: 1: 1. things _{(Li 3 NiCuBiO 6: M =} Ni 0.5 Cu 0.5, x = 0.67) was obtained.

[Synthesis Example 12]
Complex oxidation was performed in the same manner as in Synthesis Example 1 except that Li ₂ CO ₃ , NiO, ZnO, and Bi ₂ O ₃ were mixed at a molar ratio of Li: Ni: Zn: Bi = 3: 1: 1: 1. things _{(Li 3 NiZnBiO 6: M =} Ni 0.5 Zn 0.5, x = 0.67) was obtained.

[Synthesis Example 13]
Lithium carbonate (Li ₂ CO ₃ ) and bismuth oxide (Bi ₂ O ₃ ) were mixed at a molar ratio of Li: Bi = 1: 1. Specifically, these were put into a zirconia pot containing zirconia balls together with ethanol as an auxiliary agent, and the lid was capped. This was set in a planetary ball mill and wet-mixed for 1 hour at a revolution speed of 300 rpm. This mixture was dried in a dryer at 75 ° C. for 3 hours or more to prepare a precursor. Next, this precursor was placed on an alumina crucible, and this crucible was placed in a tabletop vacuum / gas replacement furnace. Subsequently, the temperature was raised from normal temperature to 750 ° C. in an air stream under normal pressure for 10 hours, and kept at this temperature for 4 hours, and then allowed to cool naturally to room temperature. In this way, LiBiO ₂ was obtained.

Lithium carbonate (Li ₂ CO ₃ ) and cobalt oxide (Co ₃ O ₄ ) were mixed at a molar ratio of Li: Co = 1: 1. Specifically, these were put into a zirconia pot containing zirconia balls together with ethanol as an auxiliary agent, and the lid was capped. This was set in a planetary ball mill and wet-mixed for 1 hour at a revolution speed of 300 rpm. This mixture was dried in a dryer at 75 ° C. for 3 hours or more to prepare a precursor. Next, this precursor was placed on an alumina crucible, and this crucible was placed in a tabletop vacuum / gas replacement furnace. Subsequently, the temperature was raised from room temperature to 650 ° C. in an air stream under normal pressure for 10 hours, and kept at this temperature for 4 hours, and then allowed to cool naturally to room temperature. In this way, LiCoO ₂ was obtained.

The obtained LiCoO ₂ and LiBiO ₂ were put in a tungsten carbide pot containing tungsten carbide balls at a molar ratio of 1: 1, and the lid was covered in a glove box maintained in an argon atmosphere. This was set in a planetary ball mill and mixed at a revolution speed of 400 rpm for 4 hours. Thus, a composite oxide (Li ₃ Co _1.5 Bi _1.5 O ₆ : M = Co, x = 0.50) subjected to MC treatment was obtained.

[Synthesis Example 14]
LiOH.H ₂ O and Al ₂ O ₃ were mixed at a molar ratio of Li: Al = 1: 1. Specifically, these were put into a zirconia pot containing zirconia balls together with acetone as an auxiliary agent and covered. This was set in a planetary ball mill and wet-mixed for 1 hour at a revolution speed of 300 rpm. This mixture was dried in a dryer at 75 ° C. for 3 hours or more to prepare a precursor. Next, this precursor was placed on an alumina crucible, and this crucible was placed in a tabletop vacuum / gas replacement furnace. Subsequently, the temperature was raised from normal temperature to 750 ° C. in an air stream under normal pressure for 10 hours, and kept at this temperature for 4 hours, and then allowed to cool naturally to room temperature. In this way, LiAlO ₂ was obtained.
In the same manner as in Synthesis Example 13, LiBiO ₂ was obtained. The obtained LiBiO ₂ and LiAlO ₂ were used at a molar ratio of 1: 1, and the same MC treatment as in Synthesis Example 13 was performed to obtain a composite oxide (Li ₃ Al _1.5 Bi _1.5 O ₆ : M = Al, x = 0.50).

[Synthesis Example 15]
Lithium carbonate (Li ₂ CO ₃ ) and vanadium oxide (V ₂ O ₃ ) were mixed at a molar ratio of Li: V = 1.03: 1. Specifically, these were put into a zirconia pot containing zirconia balls together with acetone as an auxiliary agent and covered. This was set in a planetary ball mill and wet-mixed for 1 hour at a revolution speed of 300 rpm. This mixture was dried in a dryer at 75 ° C. for 3 hours or more to prepare a precursor. Next, this precursor was placed on an alumina crucible, and this crucible was placed in a tabletop vacuum / gas replacement furnace. Next, the temperature was raised from normal temperature to 1050 ° C. in a nitrogen flow under normal pressure in 100 minutes, and kept at this temperature for 10 minutes, and then allowed to cool naturally to room temperature. In this way, LiVO ₂ was obtained.
In the same manner as in Synthesis Example 13, LiBiO ₂ was obtained. The obtained LiBiO ₂ and LiVO ₂ were used at a molar ratio of 1: 1, and the same MC treatment as in Synthesis Example 13 was performed to obtain a composite oxide (Li ₃ V _1.5 Bi _1.5 O ₆ : M = V, x = 0.50).

[Synthesis Example 16]
Lithium carbonate (Li ₂ CO ₃ ) and iron oxide (Fe ₂ O ₃ ) were mixed at a molar ratio of 1: 1. Specifically, these were put into a zirconia pot containing zirconia balls together with ethanol as an auxiliary agent, and the lid was capped. This was set in a planetary ball mill and wet-mixed for 1 hour at a revolution speed of 300 rpm. This mixture was dried in a dryer at 75 ° C. for 3 hours or more to prepare a precursor. Next, this precursor was placed on an alumina crucible, and this crucible was placed in a tabletop vacuum / gas replacement furnace. Subsequently, the temperature was raised from room temperature to 950 ° C. in an air stream under normal pressure for 10 hours, and kept at this temperature for 4 hours, and then allowed to cool naturally to room temperature. In this way, LiFeO ₂ was obtained.
In the same manner as in Synthesis Example 13, LiBiO ₂ was obtained. The resulting a LiBiO ₂ and LiFeO ₂ 1: Use 1 molar ratio, subjected to the same MC processing as in Synthesis Example 13, a composite oxide _{(Li 3 Fe 1.5 Bi 1.5 O} 6: M = Fe, x = 0.50) was obtained.

[Comparative Synthesis Example 2]
In the same manner as in Synthesis Example 13, LiBiO ₂ was obtained. Using only the obtained LiBiO ₂ , the same MC treatment as in Synthesis Example 13 was performed to obtain a composite oxide (LiBiO ₂ : x = 0) subjected to the MC treatment.

[Analysis of complex oxides]
About the complex oxide obtained by the said synthesis example and the comparative synthesis example, the powder X-ray-diffraction measurement was performed with the following method. An X-ray diffractometer (“MiniFlex II” manufactured by Rigaku) was used, the source was CuKα ray, the tube voltage was 30 kV, and the tube current was 15 mA. Diffraction X-rays were detected by a high-speed one-dimensional detector (model number: D / teX Ultra 2) through a Kβ filter having a thickness of 30 μm. The sampling width was 0.01 °, the scanning speed was 5 ° / min, the divergence slit width was 0.625 °, the light receiving slit width was 13 mm (OPEN), and the scattering slit width was 8 mm. The X-ray diffraction data obtained from Synthesis Example 4 was subjected to Rietveld analysis using the “RIETA 2000” program.

FIG. 3 shows X-ray diffraction patterns of the composite oxides obtained in Synthesis Examples 1 to 7 and Comparative Synthesis Example 1. The complex oxide obtained in Synthesis Example 4 was found to have a crystal structure that can be assigned to the space group C2 / m by Rietveld analysis. From the Rietveld analysis results, the lattice constants of the composite oxide of Synthesis Example 4 (x = 0.67) are a = 5.2629 ｂ, b = 9.1293 Å, c = 5.2203 Å, and β = 109.346 °. there were. In addition, it turns out that the synthesis example 7 (x = 0.90) with much Ni content, etc. contain the peak which can be assigned to space group Fm-3m and C2 / c other than space group C2 / m. This can be attributed to Li _0.3 Ni _0.7 O and Li ₂ CO ₃ (PDF cards, numbers 01-075-0543 and 01-083-1454) by analysis using “PDXL”, respectively. I understood. Moreover, it turns out that the synthesis example 3 (x = 0.50) with much Bi content contains the peak which can be attributed to space group Ibam other than space group C2 / m. This was found to be attributable to LiBiO ₂ (PDF card, number 00-001-1067) by analysis using the above “PDXL”.

  FIG. 4 shows an X-ray diffraction pattern of the composite oxide obtained in Synthesis Examples 8-10. By applying mechanochemical treatment to the complex oxide obtained by the solid phase method, the peak that can be attributed to the space group C2 / m before the treatment disappears, and the peak that can be attributed to the space group Fm-3m is observed. It was done.

FIG. 5 shows X-ray diffraction patterns of the composite oxides obtained in Synthesis Examples 4, 11, and 12. It was found that Li ₃ NiCuBiO ₆ and Li ₃ NiZnBiO ₆ are also attributed to the space group C2 / m, like Li ₃ Ni ₂ BiO ₆ .

6A to 6D show X-ray diffraction patterns of the composite oxides obtained in Synthesis Examples 13 to 15 and Comparative Synthesis Example 2. FIG. In addition, in Fig.6 (a)-(d), it shows together with the X-ray-diffraction figure of the raw material before MC process. From FIG. 6A, LiCoO ₂ and an amorphous phase could be confirmed in the composite oxide (Li ₃ Co _1.5 Bi _1.5 O ₆ ) treated with MC in Synthesis Example 13. From FIG. 6B, an amorphous phase was confirmed in the composite oxide (Li ₃ Al _1.5 Bi _1.5 O ₆ ) treated with MC in Synthesis Example 14. In the composite oxide (Li ₃ V _1.5 Bi _1.5 O ₆ ) treated with MC in Synthesis Example 15, Bi and amorphous phases could be confirmed. In the composite oxide (LiBiO ₂ ) treated with MC in Comparative Synthesis Example 2, it was confirmed that the reaction did not proceed, the powder was pulverized, and the orientation was changed.

[Example 1] Production of secondary battery (test battery) Using the composite oxide obtained in Synthesis Example 1 as a positive electrode active material, a nonaqueous electrolyte secondary battery (electric storage element) was produced in the following manner. 2.275 g of the synthesized composite oxide powder and 0.700 g of acetylene black (AB) were weighed. These were put into a zirconia pot having an internal volume of 80 mL containing 90 g (about 250 pieces) of zirconia balls having a diameter of 5 mm. Further, 10 mL of ethanol was added to the pot as an auxiliary agent, and the pot was covered. This was set in a planetary ball mill and mixed for 1 hour at a revolution speed of 300 rpm. This mixture was dried in a dryer at 75 ° C. for 3 hours or more to prepare a mixed powder. 2.55 g of this mixed powder, a 12% by mass N-methylpyrrolidone (NMP) solution of PVDF, and NMP were placed in a predetermined plastic container and covered with air. In addition, the 12 mass% N-methylpyrrolidone (NMP) solution and NMP of the PVDF contain 0.45 g of PVDF and 4.3 g of NMP. This was set in a stirring defoaming device (“Shintaro Awatori” manufactured by Shinky) and kneaded at 2000 rpm for 5 minutes. Further, 0.5 g of NMP was added, and the operation of kneading for 5 minutes at a rotational speed of 2000 rpm using a stirring deaerator was repeated 6 times in total to prepare a slurry using N-methylpyrrolidone (NMP) as a dispersion medium. The mass ratio of the positive electrode active material, AB and PVDF in the slurry is 65:20:15. This slurry was applied to one side of a 20 μm thick copper foil current collector. This was dried on an 80 ° C. hot plate for 60 minutes to evaporate the dispersion medium, and then subjected to roll press to obtain a positive electrode.

A secondary battery (test battery) was assembled using the positive electrode. Metallic lithium was used for the counter electrode (negative electrode). Further, LiPF ₆ is dissolved as an electrolyte in a mixed solvent in which ethylene carbonate (EC): dimethyl carbonate (DMC): ethyl methyl carbonate (EMC) has a volume ratio of 30:35:35 so that the concentration becomes 1 mol / L. Solution was used. As the separator, a polypropylene microporous film whose surface was modified with polyacrylate was used. A metal resin composite film made of polyethylene terephthalate (15 μm) / aluminum foil (50 μm) / metal-adhesive polypropylene film (50 μm) is used for the exterior body, and the electrodes are exposed so that the open ends of the positive electrode terminal and the negative electrode terminal are exposed to the outside. Stowed. Subsequently, the fusion allowance in which the inner surfaces of the metal resin composite film face each other was hermetically sealed except for a portion serving as a liquid injection hole, and after pouring the electrolyte, the liquid injection hole was sealed.

[Charge / discharge test]
The obtained secondary battery was charged and discharged in a thermostat set at 25 ° C. First, as an initial discharge, a constant current (CC) discharge with a discharge end potential of 1.0 V (vs. Li ^/ Li ⁺ ) was performed. Next, a charge / discharge cycle was performed under the following conditions. Charging was constant current constant voltage (CCCV) charging, and the charge end potential was 3.0 V (vs. Li ^/ Li ⁺ ). The charge termination condition was the time when the charging current was attenuated to 2 mA / g, or the time when 15 hours had passed since the charge upper limit potential was reached. The discharge was a constant current (CC) discharge, and the discharge end potential was 1.0 V (vs. Li ^/ Li ⁺ ). The constant current value for charging and discharging was 50 mA / g with respect to the mass of the positive electrode active material contained in the positive electrode. A 10 minute rest period was set after each charge and after discharge. This charge / discharge cycle was carried out 10 times.

[Examples 2-9, 11-20, Comparative Examples 1, 3-7]
Examples 2 to 9, 11 to 11 were the same as Example 1 except that the positive electrode active material, the positive electrode base material, and the current density and potential range in the charge / discharge test were as shown in Tables 1 to 4. 20 and Comparative Examples 1 and 3 to 7 were performed. In addition, about the Example and comparative example whose charge end voltage is 4.2V (vs.Li/Li ^<+> ) or more, the charging / discharging cycle was started, without performing initial discharge. In Tables 3 and 4, some of the examples or comparative examples described in Tables 1 and 2 are shown for comparison.

[Example 10] Production of secondary battery (test battery) Using the composite oxide obtained in Synthesis Example 13 as a positive electrode active material, a nonaqueous electrolyte secondary battery (electric storage element) was produced in the following manner. 2.275 g of the synthesized composite oxide powder and 0.700 g of acetylene black (AB) were weighed. These were put into a zirconia pot having an internal volume of 80 mL containing 90 g (about 250 pieces) of zirconia balls having a diameter of 5 mm. To this pot, 10 mL of acetone was added as an auxiliary agent, and the pot was covered in a glove box maintained in an argon atmosphere. This was set in a planetary ball mill and mixed for 1 hour at a revolution speed of 300 rpm. This mixture was dried in a dryer at 75 ° C. for 3 hours or more to prepare a mixed powder. 2.55 g of this mixed powder, 12% by mass N-methylpyrrolidone (NMP) solution of PVDF and NMP were put in a predetermined plastic container, and the lid was put in a glove box maintained in an argon atmosphere. The 12% by mass N-methylpyrrolidone (NMP) solution of PVDF and NMP contain 0.45 g of PVDF and 6.6 g of NMP. This was set in a stirring defoaming device (“Shintaro Nawataro” manufactured by Shinky Corporation) and kneaded at 2000 rpm for 5 minutes to prepare a slurry using N-methylpyrrolidone (NMP) as a dispersion medium. The mass ratio of the positive electrode active material, AB and PVDF in the slurry is 65:20:15. This slurry was applied to one side of an aluminum foil current collector having a thickness of 20 μm. This was dried on an 80 ° C. hot plate for 60 minutes to evaporate the dispersion medium, and then subjected to roll press to obtain a positive electrode.

A secondary battery (test battery) was assembled using the positive electrode. Metallic lithium was used for the counter electrode (negative electrode). Further, LiPF ₆ is dissolved as an electrolyte in a mixed solvent in which ethylene carbonate (EC): dimethyl carbonate (DMC): ethyl methyl carbonate (EMC) has a volume ratio of 30:35:35 so that the concentration becomes 1 mol / L. Solution was used. As the separator, a polypropylene microporous film whose surface was modified with polyacrylate was used. A metal resin composite film made of polyethylene terephthalate (15 μm) / aluminum foil (50 μm) / metal-adhesive polypropylene film (50 μm) is used for the exterior body, and the electrodes are exposed so that the open ends of the positive electrode terminal and the negative electrode terminal are exposed to the outside. Stowed. Subsequently, the fusion allowance in which the inner surfaces of the metal resin composite film face each other was hermetically sealed except for a portion serving as a liquid injection hole, and after pouring the electrolyte, the liquid injection hole was sealed.

[Charge / discharge test]
The obtained secondary battery was charged and discharged in a thermostat set at 25 ° C. First, as an initial discharge, a constant current (CC) discharge with a discharge end potential of 1.0 V (vs. Li ^/ Li ⁺ ) was performed. Next, a charge / discharge cycle was performed under the following conditions. Charging was constant current constant voltage (CCCV) charging, and the charge end potential was 3.0 V (vs. Li ^/ Li ⁺ ). The charge termination condition was the time when the charging current was attenuated to 2 mA / g, or the time when 15 hours had passed since the charge upper limit potential was reached. The discharge was a constant current (CC) discharge, and the discharge end potential was 1.0 V (vs. Li ^/ Li ⁺ ). The constant current value for charging and discharging was 20 mA / g with respect to the mass of the positive electrode active material contained in the positive electrode. A 10 minute rest period was set after each charge and after discharge. This charge / discharge cycle was carried out 10 times.

[Examples 21 to 29, Comparative Example 2]
Examples 21 to 29 and Example 21 except that the positive electrode active material used, the base material of the positive electrode, and the current density and potential range in the charge / discharge test were as shown in Tables 1, 3, and 4. Comparative Example 2 was performed. In addition, about the Example and comparative example whose charge end voltage is 4.2V (vs.Li/Li ^<+> ) or more, the charging / discharging cycle was started, without performing initial discharge. In Tables 3 and 4, some of the examples or comparative examples described in Tables 1 and 2 are shown for comparison.

  Tables 1 to 4 show the discharge capacity, energy density, and capacity retention ratio (discharge capacity at the 10th cycle / discharge capacity at the 1st cycle) in the charge / discharge cycle tests of Examples 1 to 29 and Comparative Examples 1 to 7. Shown in

Here, the energy density indicates the energy density per volume of the positive electrode active material (composite oxide). The energy density was calculated by the product of the discharge capacity at the first cycle, the average discharge potential, and the true density. For M = Ni, when x ≧ 0.67, (Li _0.3 Ni _0.7 O + Li ₂ CO ₃ ) -Li ₃ Ni ₂ BiO ₆ system, when x <0.67, Li as ₃ Ni ₂ BiO ₆ -LiBiO ₂ system was calculated by taking the weighted average. _{Further, M =} Ni 0.5 _{Cu 0.5,} about or _Ni 0.5 as _Zn is _0.5 was calculated from the lattice constant of the non-patent document 1. M = Al, V, about what is Fe or Co _was calculated by taking the weighted average as LiBiO ₂ -LiMO 2 system. Tables 1 to 4 also show the true density values of the calculated compounds (positive electrode active materials). FIG. 7 shows the charge / discharge curve of Example 4, and FIG. 8 shows the charge / discharge curve of Example 20.

  In the potential ranges of 1.0 to 3.0 V and 1.0 to 2.5 V, the discharge starts, but the first discharge is not included in the number of cycles.

As shown in Tables 1 to 4, it has a positive electrode containing a composite oxide containing Li, Bi and a metal element (M), and the metal element (M) is made of Al, V, Fe, Co and Ni. In the nonaqueous electrolyte storage element containing at least one of them, it is understood that the energy density is increased by setting the discharge end potential to 0.8 to 1.4 V (vs. Li / Li ⁺ ). Furthermore, as shown in Table 3, it is understood that the capacity retention rate is also increased by setting the charge end potential to 2.5 to 3.5 V (vs. Li / Li ⁺ ). On the other hand, even when the nonaqueous electrolyte storage element has the composite oxide, it can be seen that the energy density is low when the discharge end potential is higher than 1.4 V (vs. Li ^/ Li ⁺ ) (Comparative Examples 4 to 7). . Further, as shown in Table 1, when the potential range is 1.0 to 3.0 V (vs. Li / Li ⁺ ), x in formulas (1) and (2) is 0.30 to 0.00. By setting it as the range of 75, it turns out that an energy density exceeds 3000 mWhcm < ^-3 > and an energy density is high.

[DQ / dV plot]
After the charge and discharge cycles of Examples 1 to 7, reduction to 0 V (vs. Li ^/ Li ⁺ ) was performed, and dQ / dV plots at that time were obtained. The peaks were fitted by the least square method using the Lorentz function. The background was approximated by a linear function. In the above formula (1), when x ≧ 0.67, the function used for fitting is “background + peak 1”, and when x <0.67, the function used for fitting is “background + Peak 1 + peak 2 + peak 3 ”. Table 5 shows peak positions in dQ / dV plots of the electricity storage devices of Examples 1 to 7.

In any of the electricity storage devices of Examples 1 to 7, the range is 0.4 to 0.6 V (vs. Li / Li ⁺ ), and is unique to the composite oxide containing any one of Li, Bi, and Ni. A reduction peak was confirmed.

  The present invention can be applied to electronic devices such as personal computers and communication terminals, nonaqueous electrolyte storage elements used as power sources for automobiles, and the like.

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte electrical storage element 2 Electrode body 3 Container 4 Positive electrode terminal 4 'Positive electrode lead 5 Negative electrode terminal 5' Negative electrode lead 20 The electrical storage unit 30 The electrical storage apparatus

Claims (8)

A positive electrode containing a composite oxide containing lithium, bismuth and a metal element (M);
The metal element (M) includes at least one of aluminum, vanadium, iron, cobalt and nickel,
Discharge cutoff potential of the positive electrode at the time of normal use, 0.8V (vs.Li/Li ⁺⁾ or 1.4V (vs.Li/Li ⁺⁾ or less is the non-aqueous electrolyte energy storage device. The nonaqueous electrolyte storage element according to claim 1, wherein a charge end potential of the positive electrode during normal use is 2.5 V (vs. Li ^/ Li ⁺ ) or more and 3.5 V (vs. Li ^/ Li ⁺ ) or less. The metal element (M) is
The combination of at least one of aluminum, vanadium, iron, cobalt and nickel, or at least one of aluminum, vanadium, iron, cobalt and nickel and at least one of copper and zinc. 2. A nonaqueous electrolyte storage element.   The non-aqueous electrolyte storage element according to claim 1, wherein the metal element (M) contains nickel, and the content of nickel in the metal element (M) is 50 mol% or more.   The content of the metal element (M) with respect to the total content of bismuth and the metal element (M) in the composite oxide is 30 mol% or more and 75 mol% or less. The nonaqueous electrolyte electricity storage element of a term. The non-aqueous electrolyte electricity storage element according to claim 1, wherein the composite oxide is represented by the following formula (1).
Li ₃ M _3x Bi _{3 (1-x)} O ₆ (1)
(In the formula (1), M is a metal element containing at least one of Al, V, Fe, Co, and Ni. 0 <x <1.)   An electric device comprising the nonaqueous electrolyte storage element according to any one of claims 1 to 6. A positive electrode containing a composite oxide containing lithium, bismuth and a metal element (M);
For the non-aqueous electrolyte electricity storage element in which the metal element (M) contains at least one of aluminum, vanadium, iron, cobalt and nickel,
Using the non-aqueous electrolyte energy storage device having to perform a discharge in the range cutoff potential of the positive electrode is 0.8V (vs.Li/Li ⁺⁾ or 1.4V (vs.Li/Li ⁺⁾ following.

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