JP6609217B2 - Composite oxide, positive electrode active material for non-aqueous electrolyte secondary battery, positive electrode for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery, and method for producing composite oxide - Google Patents

Description

  The present invention relates to a composite oxide, a positive electrode active material for a nonaqueous electrolyte secondary battery, a positive electrode for a nonaqueous electrolyte secondary battery, a nonaqueous electrolyte secondary battery, a method for producing the composite oxide, and a nonaqueous electrolyte secondary battery. It relates to a manufacturing method.

  Nonaqueous electrolyte secondary batteries represented by lithium ion secondary batteries are frequently used in electronic devices such as personal computers and communication terminals, automobiles and the like because of their high energy density. For example, the non-aqueous electrolyte secondary battery generally has a pair of electrodes electrically separated by a separator and a non-aqueous electrolyte interposed between the electrodes, and transfers ions between the electrodes. It is comprised so that it may charge / discharge by performing.

Various composite oxides are used for the active material contained in the positive electrode of the nonaqueous electrolyte secondary battery. Table Such composite oxide is _represented by _{Li 1 + x Mo 2x Cr 1-3x} O 2, complex oxide which changes the crystal structure during charge and discharge (see Patent Document _1), in Li _x M y Mo _z O And a composite oxide having a crystal structure of Li ₅ ReO ₆ type (space group c2 / m), Li ₄ MoO ₅ type (space group P-1) or Li ₂ MnO ₃ type (space group C2 / m) (patent A composite oxide containing lithium and molybdenum such as LiMoO ₂ (see Non-Patent Document 1) having a crystal structure belonging to the space group R-3m or C2 / m has been developed.

However, there is room for improvement in secondary batteries using these composite oxides as the positive electrode active material, such as a further increase in capacity. In addition, since the composite oxide represented by Li _{1 + x} Mo _2x Cr _1-3x O ₂ contains chromium and can be oxidized to highly toxic hexavalent chromium, from the viewpoint of safety and environmental impact, Industrial use is limited.

Special table 2015-535801 gazette Japanese Patent Laying-Open No. 2015-166291

K. Ben-Kamel, N.A. Amdouni, H.M. Grout, A.M. Mauger, K.M. Zaghib, C.I. M.M. Julien, J .; Power Sources 202 (2012) 314-321.

  The present invention has been made based on the circumstances as described above, and its purpose is that there are few industrial restrictions on the use, and when used as an active material for a positive electrode provided in a nonaqueous electrolyte secondary battery, Composite oxide capable of increasing discharge capacity of secondary battery, method for producing such composite oxide, positive electrode active material for non-aqueous electrolyte secondary battery containing the composite oxide, active for non-aqueous electrolyte secondary battery It is providing the positive electrode for nonaqueous electrolyte secondary batteries containing a substance, the nonaqueous electrolyte secondary battery provided with this positive electrode for nonaqueous electrolyte secondary batteries, and the manufacturing method of this nonaqueous electrolyte secondary battery.

  A composite oxide according to one embodiment of the present invention, which has been made to solve the above problems, has a crystal structure that can be assigned to the space group Fm-3m, includes lithium and molybdenum, and does not substantially include chromium. It is an oxide.

  A positive electrode active material for a non-aqueous electrolyte secondary battery according to another embodiment of the present invention includes the composite oxide.

  A positive electrode for a nonaqueous electrolyte secondary battery according to another embodiment of the present invention contains the positive electrode active material for a nonaqueous electrolyte secondary battery.

  A non-aqueous electrolyte secondary battery according to another embodiment of the present invention is a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode is the positive electrode for the non-aqueous electrolyte secondary battery. It is characterized by being.

  The manufacturing method of the composite oxide which concerns on the other one aspect | mode of this invention has processing the material for active materials containing the composite oxide which contains lithium and molybdenum and does not contain chromium substantially by a mechanochemical method. , A method for producing a complex oxide having a crystal structure that can be assigned to the space group Fm-3m.

  A method for producing a nonaqueous electrolyte secondary battery according to another aspect of the present invention is a method for producing a nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a nonaqueous electrolyte, wherein the composite oxide is used as the positive electrode. A positive electrode containing a positive electrode active material containing is used.

  According to the present invention, there are few restrictions on industrial use, and a composite oxide that can increase the discharge capacity of a secondary battery when used as an active material for a positive electrode provided in a nonaqueous electrolyte secondary battery, Manufacturing method of composite oxide, positive electrode active material for nonaqueous electrolyte secondary battery containing the composite oxide, positive electrode for nonaqueous electrolyte secondary battery containing the positive electrode active material for nonaqueous electrolyte secondary battery, A nonaqueous electrolyte secondary battery including a positive electrode for a water electrolyte secondary battery, and a method for producing the nonaqueous electrolyte secondary battery can be provided.

FIG. 1 is a graph showing calculated values, measured values, and differences between them in Rietveld analysis for the complex oxide of Example 2. FIG. 2 is a discharge curve of the secondary batteries of Examples 1 to 3 and Comparative Example 1. 3 is an X-ray diffraction pattern of the composite oxide of Example 2. FIG. 4A to 4C are charge / discharge curves of the secondary battery of Example 5. FIG. 5A to 5B are charge / discharge curves of the secondary battery of Example 6. FIG. FIG. 6 is an external perspective view showing an embodiment of the nonaqueous electrolyte secondary battery according to the present invention. FIG. 7 is a schematic diagram showing a power storage device configured by assembling a plurality of nonaqueous electrolyte secondary batteries according to the present invention.

  Hereinafter, a composite oxide according to an embodiment of the present invention, a manufacturing method thereof, a positive electrode active material for a nonaqueous electrolyte secondary battery, a positive electrode for a nonaqueous electrolyte secondary battery, a nonaqueous electrolyte secondary battery, and a manufacturing method thereof Will be described in order.

<Composite oxide>
The composite oxide according to one embodiment of the present invention is a composite oxide having a crystal structure that can be assigned to the space group Fm-3m, containing lithium and molybdenum, and substantially free of chromium.

  Since this complex oxide does not substantially contain chromium, there are few industrial restrictions on this point. Further, since the complex oxide does not substantially contain chromium, it is safer than those containing chromium. In addition, since the composite oxide includes lithium and molybdenum and has a crystal structure that can be assigned to the space group Fm-3m, the composite oxide is used as an active material for a positive electrode included in a nonaqueous electrolyte secondary battery. In addition, the discharge capacity of the secondary battery can be increased. The reason for this is not clear, but a complex oxide containing lithium and molybdenum formed by a general firing method or the like is formed in a stable phase, whereas the crystal structure belonging to the space group Fm-3m is quasi It is a stable phase, and it is assumed that such a difference in crystal structure affects the discharge capacity and the like. In addition, a secondary battery using the composite oxide as a positive electrode active material also has a good discharge capacity maintenance rate in a charge / discharge cycle.

  Here, “substantially not containing chromium” means that chromium is not intentionally added. That is, it is within the scope of the present invention that chromium is inevitably contained within a range that does not affect the operational effects of the present invention. Regarding the fact that chromium is not substantially contained, the content of chromium in the composite oxide may be 1,000 ppm (0.1% by mass) or less. Further, the chromium content relative to all metal elements other than lithium may be 0.1 mol% or less. The content of each element in the complex oxide is a value measured by an ICP emission spectroscopic analyzer.

  In addition, the crystal structure that can be assigned to the space group Fm-3m means that it has a peak that can be assigned to the space group Fm-3m in the X-ray diffraction pattern. The complex oxide may have a crystal structure belonging to the space group Fm-3m. Note that “−3” in the space group “Fm−3m” represents the target element of the three-fold anti-axis, and should be described by adding a bar “−” above “3”. 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 crystal lattice constant of the composite oxide is not particularly limited, but the lower limit is preferably 4.1 and more preferably 4.15. Moreover, as this upper limit, 4.2? Is preferable, 4.18? Is more preferable, and 4.16? Is more preferable. When the crystal lattice constant is in the above range, the discharge capacity of a secondary battery using the composite oxide as a positive electrode active material can be further increased.

  The valence of molybdenum contained in the composite oxide is usually +3. However, other valences (for example, +6 etc.) may be included, and other valences may be used.

  The lower limit of the molybdenum content relative to all metal elements other than lithium in the composite oxide may be, for example, 10 mol%, but is preferably 40 mol%, and more preferably 60 mol%. By setting the molybdenum content to the above lower limit or more, the discharge capacity of the secondary battery can be further increased. From the viewpoint of further increasing the discharge capacity, the lower limit of the molybdenum content is more preferably 80 mol%, and still more preferably 90 mol%. On the other hand, the upper limit of the content may be 100%, but may be 99 mol%, or less. This is because the retention rate of the discharge capacity of the secondary battery can be increased by containing a specific metal element other than lithium and molybdenum as will be described later.

  The composite oxide preferably further contains a metal element (α) made of aluminum, silicon, scandium, titanium, zinc, germanium, zirconium, niobium, tin, tellurium, tantalum, rhenium, or a combination thereof. Among these metal elements (α), titanium and niobium are preferable, and niobium is more preferable. By containing these metal elements (α), the discharge capacity maintenance rate of a secondary battery using the composite oxide as a positive electrode active material can be increased. The reason why such an effect occurs is assumed as follows, for example. These metal elements (α) are metals in which oxidation-reduction reaction hardly occurs in a normal potential range when used as a positive electrode. For this reason, when this metal element (α) is contained in the composite oxide, the load on the crystal structure is reduced during the detachment and insertion of lithium atoms associated with charge and discharge, and the decrease in capacity retention rate is suppressed. It is inferred that

  From the viewpoint of further increasing the capacity retention rate of the secondary battery, the lower limit of the molybdenum content relative to the total content of molybdenum and the metal element (α) is preferably 30 mol%, more preferably 40 mol%, 50 mol% is more preferable. From the same viewpoint, the upper limit of the molybdenum content relative to the total content of molybdenum and the metal element (α) is preferably 90 mol%, more preferably 80 mol%, and even more preferably 70 mol%. A secondary battery when used as a positive electrode active material by setting the molybdenum content to the total content of molybdenum and the metal element (α), that is, the content ratio of molybdenum and the metal element (α) in the above range. The capacity maintenance rate can be further increased.

  The lithium content in the composite oxide is not particularly limited. Lithium composition ratio greatly fluctuates due to charge and discharge, lithium composition ratio may be larger than at the end of the synthesis at the end of discharge, and lithium raw material is added in excess of the theoretical composition ratio during synthesis Therefore, the lithium content in the composite oxide does not significantly affect the performance as the positive electrode active material. The lithium content in the composite oxide is, for example, as an atomic ratio, for example, 1 time (100 mol%) to 5 times (500 mol%) with respect to the content of all metal elements other than lithium (100 mol%). ) Or less, and may be less than 3 times (300 mol%). Moreover, it can be 1 time (100 mol%) or more and 5 times (500 mol%) or less to 3 times (300 mol%) with respect to the total content (100 mol%) of molybdenum and the said metal element ((alpha)). Mol%).

  The oxygen content in the composite oxide is not particularly limited, and is usually determined from the composition ratio of metal elements, the valence of 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, as the atomic ratio, 1 time (100 mol%) to 8 times (800 mol%) with respect to the content of all metal elements other than lithium (100 mol%). 2 times (200 mol%) or more, or less than 4 times (400 mol%). Moreover, it can be 1 time (100 mol%) or more and less than 8 times (800 mol%) to 2 times (200 mol%) with respect to the total content (100 mol%) of molybdenum and the metal element (α). Mol%) or more, or less than 4 times (400 mol%).

  In the composite oxide, elements other than lithium, molybdenum, metal element (α), and oxygen may be contained in a range that does not affect the operational effects of the present invention. Examples of such other optional elements include metal elements such as sodium, potassium, magnesium, calcium, and indium, and nonmetallic elements such as halogen. The upper limit of the content of these optional elements is preferably 50 mol% with respect to the content of all metal elements other than lithium or the total content (100 mol%) of molybdenum and the metal element (α). 20 mol% is more preferable, 10 mol% is further more preferable, 1 mol% is further more preferable, and 0.1 mol% is especially preferable. This optional element may not be substantially contained.

The complex oxide can be represented by the following formula (1).
Li _{1 + x} Mo _y Me _{1-y Ap} O _z (1)
(In the formula (1), Me is Al, Si, Sc, Ti, Zn, Ge, Zr, Nb, Sn, Te, Ta, Re, or a combination thereof. A is Li, Mo, Me, and O. Elements other than 0 ≦ x, 0 <y ≦ 1, 0 <z, 0 ≦ p ≦ 0.2.)

The formula (1) is the composite oxide, and LiMoO _2, based on the case of a solid solution of a compound represented by _Li 3 MeO ₄ such as Li 3 NbO ₄ (including the case of only LiMoO ₂₎ The following can be derived.

A solid solution of LiMoO ₂ : Li ₃ MeO ₄ = a: 1-a (including only LiMoO ₂ ) is represented by the following formula.
aLiMoO _2. (1-a) Li ₃ MeO ₄ (0 <a ≦ 1)

By transforming this, the following formula is obtained.
Li _{1 + 2 (1-a)} Mo _a Me _1-a O _4-2a (0 <a ≦ 1) (i)

By adding arbitrary element A to this, the said solid solution can be represented by following formula (1).
Li _{1 + x} Mo _y Me _{1-y Ap} O _z (1)

Here, when the solid solution satisfies the relationship of the above formula (i), (x + 2y) / 2 = 1 is derived from 2 (1-a) = x and a = y. Further, (2y + z) / 4 = 1 is derived from a = y and 4-2a = z. Therefore, if 0.9 ≦ (x + 2y) /2≦1.1 and / or 0.9 ≦ (2y + z) /4≦1.1, an oxide represented by LiMoO ₂ and Li ₃ MeO ₄ is used. Thus, it is possible to efficiently produce a composite oxide that can exhibit a higher discharge capacity and capacity retention rate.

  X in the above formula (1) is a coefficient related to the composition ratio of lithium. When the solid solution satisfies the relationship of the above formula (i), 2 (1-a) = x. Therefore, theoretically, 0 ≦ x <2. However, as described above, since lithium has a variation factor, it is preferable that 0 ≦ x <4 in practice.

  In the above formula (1), y is a coefficient representing the ratio between Mo and Me (the metal element (α)). Therefore, the lower limit of y may be 0.1 or 0.4, but from the viewpoint of discharge capacity in the secondary battery, 0.6 is preferable, 0.8 is more preferable, and 0.9 is further preferable. In addition, the upper limit of y may be 0.99 from the viewpoint of the discharge capacity in the secondary battery. Moreover, from the viewpoint of the capacity retention rate in the secondary battery, the lower limit of y is preferably 0.3, more preferably 0.4, and even more preferably 0.5. On the other hand, from the viewpoint of the capacity retention rate in the secondary battery, the upper limit of y is preferably 0.9, more preferably 0.8, and even more preferably 0.7.

  Z in the above formula (1) is a coefficient representing the composition ratio of oxygen. When the solid solution satisfies the relationship of the above formula (i), 4-2a = z. Therefore, theoretically, 2 ≦ z <4. However, as described above, since oxygen also has a variation factor, it is preferable that 1 ≦ z <8 in practice.

  P in the above formula (1) is a coefficient representing the composition ratio of the arbitrary element A. The upper limit of p is preferably 0.1, more preferably 0.01, and still more preferably 0.001. p may be substantially zero. In addition, the specific example of the arbitrary element A contained in the complex oxide is as described above.

<Production method of composite oxide>
Although the manufacturing method of the said complex oxide is not specifically limited, The following manufacturing methods are preferable. That is, the method for producing a composite oxide according to an embodiment of the present invention includes treating a material for an active material containing a composite oxide containing lithium and molybdenum and substantially not containing chromium by a mechanochemical method. It is a manufacturing method of the complex oxide which has a crystal structure which can be assigned to space group Fm-3m.

  According to the manufacturing method, a composite oxide having a crystal structure that can be assigned to the space group Fm-3m can be obtained by processing the material for active material by processing by a mechanochemical method. This is because, in the case of conventional methods such as high-temperature firing, sufficient reaction proceeds and a stable phase is formed, whereas in the case of mechanochemical method, the reaction is insufficient and a metastable phase is likely to be formed. Inferred.

  The mechanochemical method (also referred to as mechanochemical treatment) refers to a synthesis method utilizing a mechanochemical reaction. The mechanochemical reaction refers to a chemical reaction such as a crystallization reaction, a solid solution reaction, or a phase transition reaction that uses high energy locally generated by mechanical energy such as friction and compression in the crushing process of a solid substance. Examples of the apparatus for performing the mechanochemical method include ball mills, bead mills, vibration mills, turbo mills, mechano fusions, and disk mills. Among these, a ball mill is preferable.

As a composite oxide used as a material, in addition to an oxide containing lithium and molybdenum, a mixture of the oxide and the oxide of the metal element (α) can be given. Further, it may be a mixture of an oxide containing lithium, an oxide containing molybdenum, and, if necessary, other metal oxides. Specific examples of the oxide include LiMoO ₂ , Li ₄ MoO ₅ , Li ₃ NbO ₄ , and Li ₂ TiO ₃ . The crystal structure of these composite oxides is not particularly limited. For example, in the case of LiMoO ₂ , those having a crystal structure belonging to a space group such as R-3m and C2 / m can be mentioned. The composite oxide used as a material may be only one kind, or two or more kinds may be used. When using 2 or more types, the composite oxide of a desired composition ratio can be obtained by adjusting the ratio of the materials. Preferred materials include LiMoO ₂ alone and combinations of LiMoO ₂ and Li ₃ NbO ₄ .

  These composite oxides as materials are usually in the form of powder, and the powdered composite oxide is subjected to a process by a mechanochemical method. This treatment can be performed under an inert gas atmosphere such as argon or an active gas atmosphere, but is preferably performed under an inert gas atmosphere. The composite oxide obtained through such treatment is usually in the form of a powder.

<Positive electrode active material for non-aqueous electrolyte secondary battery>
A positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention (hereinafter also simply referred to as “active material”) includes the composite oxide. Since the active material includes the composite oxide, there are few industrial restrictions on use, and the discharge capacity of the secondary battery can be increased by using the active material as an active material for the positive electrode.

The active material may be formed only from the composite oxide, but may contain other active materials other than the composite oxide. As another active material as the positive electrode active material, for example, a composite oxide (layered α-NaFeO ₂ type crystal structure represented by Li _x MO _y (M represents at least one transition metal other than Mo) is used. _{Li x CoO 2, Li x NiO} 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 , and the like having, spinel crystalline Li _x Mn ₂ O ₄ having a structure, Li _x Ni _α Mn _(2-α) O _4, etc.), Li _w M ′ _x (XO _y ) _z (M ′ represents at least one transition metal other than Mo) , X is for example P, Si, B, polyanionic compound represented by the representative of the V or the _{like) (LiFePO 4, LiMnPO 4,} LiNiPO 4, LiCoPO 4, Li 3 V 2 (PO 4) 3, Li 2 MnSiO 4, L ₂ CoPO ₄ F, etc.).

  The content ratio of the composite oxide in the active material (a composite oxide having a crystal structure that can be assigned to the space group Fm-3m, including lithium and molybdenum, and substantially free of chromium) is 50% by mass. The above is preferable, 70 mass% or more is more preferable, and 90 mass% or more is further preferable. By increasing the content rate of the composite oxide, the discharge capacity and capacity retention rate of the secondary battery can be sufficiently increased.

<Positive electrode for non-aqueous electrolyte secondary battery>
A positive electrode for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention (hereinafter also simply referred to as “positive electrode”) contains the above active material. Since the positive electrode contains the active material, there are few industrial usage restrictions, and the discharge capacity and the like of the secondary battery can be increased.

  The positive electrode has a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector directly or through an intermediate layer.

  The positive electrode current collector has conductivity. As the material of the current collector, metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof are used. Among these, aluminum and aluminum alloys are preferable from the balance of potential resistance, high conductivity and cost. Moreover, as a formation form of a positive electrode electrical power collector, foil, a vapor deposition film, etc. are mentioned, A foil is preferable from the surface of cost. That is, an aluminum foil is preferable as the positive electrode current collector. Examples of aluminum or aluminum alloy include A1085P and A3003P defined in JIS-H-4000 (2014).

The intermediate layer is a coating layer on the surface of the positive electrode current collector, and reduces the contact resistance between the positive electrode current collector and the positive electrode active material layer by containing conductive particles such as carbon particles. The structure of an intermediate | middle layer is not specifically limited, For example, it can form with the composition containing a resin binder and electroconductive particle. “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 active material layer is formed from a so-called positive electrode mixture containing a positive electrode active material. In addition, the positive electrode mixture for forming the positive electrode active material layer contains optional components such as a conductive agent, a binder (binder), a thickener, and a filler as necessary.

  As the positive electrode active material, an active material having a crystal structure that can be assigned to the above-described space group Fm-3m, including a composite oxide containing lithium and molybdenum and substantially not containing chromium is used.

  The conductive agent is not particularly limited as long as it is a conductive material that does not adversely affect battery performance. Examples of such a conductive agent include carbon black such as natural or artificial graphite, furnace black, acetylene black, and ketjen black, metals, and conductive ceramics. 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.

  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 battery performance. Examples of the main component of the filler include polyolefins such as polypropylene and polyethylene, silica, alumina, zeolite, glass, and carbon.

<Nonaqueous electrolyte secondary battery>
A non-aqueous electrolyte secondary battery according to an embodiment of the present invention (hereinafter also simply referred to as “secondary battery”) is a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, and the positive electrode Is the positive electrode for a non-aqueous electrolyte secondary battery. Since the secondary battery includes the positive electrode containing the active material, there are few industrial usage restrictions, and the discharge capacity and the like are high. Further, the secondary battery can have a good discharge capacity maintenance rate.

  The positive electrode and the negative electrode in the secondary battery usually form power generation elements that are alternately superimposed by stacking or winding via a separator. This power generation element 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. In addition, as the case, a known aluminum case that is usually used as a case of a nonaqueous electrolyte secondary battery can be used.

  As described above, the positive electrode according to an embodiment of the present invention is usually used as the positive electrode. The details of the positive electrode are as described above.

  The negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector directly or via an intermediate layer. The intermediate layer can have the same configuration as the positive electrode intermediate layer.

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

  The negative electrode active material 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 active material layer contains arbitrary components, such as a electrically conductive agent, a binder (binder), a thickener, and a filler as needed. The same components as those for the positive electrode active material layer can be used as optional components such as a conductive agent, a binder, a thickener, and a filler.

  As the negative electrode active material, conventionally known negative electrode active materials for non-aqueous electrolytic secondary batteries are 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 graphitized carbon or non-graphitizable carbon).

  Furthermore, the negative electrode mixture (negative electrode active material 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.

  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. The main component of the porous resin film is preferably a polyolefin such as polyethylene or polypropylene from the viewpoint of strength. Moreover, you may use the porous resin film which compounded these resins and resin, such as an aramid and a polyimide.

  As said non-aqueous electrolyte, the well-known electrolyte normally used for a non-aqueous electrolyte secondary battery can be used, and what dissolved electrolyte salt in the non-aqueous solvent can be used.

  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 nonaqueous electrolyte, a room temperature molten salt, an ionic liquid, a polymer solid electrolyte, or the like can be used.

  FIG. 6 shows a schematic diagram of a rectangular nonaqueous electrolyte secondary battery 1 which is an embodiment of the nonaqueous electrolyte secondary battery. In the figure, the inside of the container is seen through. In the nonaqueous electrolyte secondary battery 1 shown in FIG. 6, the electrode group 2 is housed in a battery container 3. The electrode group 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 non-aqueous electrolyte 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 non-aqueous electrolyte secondary batteries. One embodiment of a power storage device is shown in FIG. In FIG. 7, the power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of nonaqueous electrolyte secondary batteries 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), and a plug-in hybrid vehicle (PHEV).

<Method for producing non-aqueous electrolyte secondary battery>
Although the manufacturing method of the said nonaqueous electrolyte secondary battery is not specifically limited, The following manufacturing methods are preferable. That is, a method for manufacturing a nonaqueous electrolyte secondary battery according to an embodiment of the present invention is a method for manufacturing a nonaqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a nonaqueous electrolyte. The positive electrode containing the positive electrode active material containing the complex oxide which concerns on one Embodiment is used, It is characterized by the above-mentioned.

  According to the manufacturing method, a positive electrode including a positive electrode active material having a crystal structure that can be assigned to the space group Fm-3m, including a composite oxide containing lithium and molybdenum and substantially not containing chromium is used. Thus, it is possible to obtain a secondary battery with less industrial restrictions and excellent discharge capacity.

The manufacturing method includes, for example, a step of housing a positive electrode and a negative electrode (power generation element) in a case, and a step of injecting the nonaqueous electrolyte into the case. As the positive electrode, a positive electrode having a crystal structure that can be assigned to the space group Fm-3m, a positive electrode active material including a composite oxide containing lithium and molybdenum and substantially not containing chromium is used. In the secondary battery thus obtained, the composite oxide usually has a crystal structure that can be assigned to the space group Fm-3m even before the start of charge / discharge and after repeated charge / discharge.

  Each said process can be performed by a well-known method. After the injection, the non-aqueous electrolyte secondary battery can be obtained by sealing the injection port. The details of each element constituting the nonaqueous electrolyte secondary battery obtained by the manufacturing method are as described above.

<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.

  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] (Synthesis of lithium molybdenum composite oxide)
Lithium carbonate (Li ₂ CO ₃ ) (manufactured by Nacalai Tesque), molybdenum trioxide (MoO ₃ ) (manufactured by High-Purity Chemical Co., Ltd.), and acetylene black as a reducing agent were mixed at a molar ratio of Li: Mo: C of 4: Weighed out to be 4: 3. 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, and the lid was capped. This was set on a planetary ball mill ("Pulverisete 5" manufactured by FRITSCH), mixed for 9 minutes at a revolution speed of 120 rpm, and then put into a rest for 1 minute for a total of 6 times. Then, the lid was opened, the mixture in the pot was stirred with a spoon, and again the operation of mixing for 9 minutes at a revolution speed of 120 rpm and then resting for 1 minute was repeated a total of 2 times. Next, this mixed powder was placed in an alumina crucible (model number: 1-7745-07) with a capacity of 30 mL, and this crucible was placed in a tabletop vacuum / gas displacement furnace (“KDF75” from Denken Hydental). . Next, the temperature was raised from room temperature to 1000 ° C. in a nitrogen 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, a lithium molybdenum composite oxide represented by the composition formula LiMoO ₂ was produced.

[Synthesis Example 2] (Synthesis of lithium niobium composite oxide)
Lithium carbonate (Li ₂ CO ₃ ) (manufactured by Nacalai Tesque) and niobium pentoxide (Nb ₂ O ₅ ) (manufactured by High Purity Chemical Co., Ltd.) were weighed so that the molar ratio of Li: Nb was 3: 1. 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. An additional 10 mL of ethanol was added to the pot and the lid was covered. This was set on a planetary ball mill ("Pulverisete 5" manufactured by FRITSCH), mixed for 9 minutes at a revolution speed of 300 rpm, and then put into a pause for 1 minute, a total of 6 times. Subsequently, this mixture was dried at 80 ° C. for 3 hours or more with a dryer to obtain a mixed powder. This mixed powder was placed in an alumina crucible (model number: 1-7745-07) having a capacity of 30 mL, 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 950 ° 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 lithium niobium composite oxide represented by the composition formula Li ₃ NbO ₄ was produced.

[Examples 1 to 4] (Production of lithium molybdenum composite oxide or lithium molybdenum niobium composite oxide)
The lithium molybdenum composite oxide and the lithium niobium composite oxide obtained by the above method have Mo: Nb molar ratios of 100: 0 (Example 1), 80:20 (Example 2), and 60:40 (Examples). 3) and 40:60 (Example 4), and the total mass of these oxides was weighed to be about 4.5 g. These were put into a tungsten carbide pot having an internal volume of 80 mL containing 250 g (about 250 pieces) of tungsten carbide balls having a diameter of 5 mm, and were covered in a glove box maintained in an argon atmosphere. This operation was set on a planetary ball mill ("Pulverisete 5" manufactured by FRITSCH), mixed for 12 minutes at a revolution speed of 400 rpm, and then put into a rest for 3 minutes for a total of 8 times. In this manner, a lithium molybdenum composite oxide or a lithium molybdenum niobium composite oxide represented by a composition formula aLiMoO ₂ — (1-a) Li ₃ NbO ₄ was produced.

[Analysis of complex oxides]
The lithium molybdenum composite oxide obtained in Synthesis Example 1 and the lithium molybdenum composite oxide and lithium molybdenum niobium composite oxide obtained in Examples 1 to 4 were analyzed by the following method. Powder X-ray diffraction measurement was carried out using an X-ray diffractometer (“MiniFlex II” from Rigaku). The radiation source was CuKα ray, the tube voltage was 30 kV, the tube current was 15 mA, and the diffracted X-ray was 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 obtained X-ray diffraction data was subjected to Rietveld analysis using the “Rietan 2000” program.

  In the Rietveld analysis, a Pearson VII function was used as a function representing a profile, and a NaCl-type crystal structure model as shown in Table 1 was used. As an example, as a result of Rietveld analysis of the lithium niobium molybdenum oxide according to Example 2, a refined crystal structure model is shown in Table 1, and a calculated value, an actual measurement value, and a graph representing the difference therebetween are shown in FIG. . According to the crystal structure model shown in Table 1, the difference between the calculated value and the actually measured value was sufficiently small as shown in FIG. The reliability factors were Rwp = 4.46%, RI = 0.79%, and RF = 0.51%, respectively, indicating that the difference between the calculated value and the actual measurement value was sufficiently small. From these results, it was judged that the crystal structure model shown in Table 1 was appropriate. For the lithium-molybdenum composite oxide according to Example 1 and the lithium-niobium-molybdenum composite oxides according to Example 3 and Example 4, Rietveld analysis was performed in the same manner as described above, and the difference between the calculated value and the actually measured value was similarly It was judged that the NaCl-type crystal structure model was appropriate because it was sufficiently small.

  Table 2 shows the space group to which the crystal structure of each composite oxide obtained by the Rietveld analysis belongs, the lattice constant, and the Li content (molar ratio) with respect to the total content of Mo and Nb.

[Production of secondary battery (test battery)]
The lithium-molybdenum composite oxide obtained in Synthesis Example 1 (Comparative Example 1), and the lithium-molybdenum composite oxide and lithium-molybdenum niobium composite oxide obtained in Examples 1 to 4 were used as positive electrode active materials. A non-aqueous electrolyte secondary battery was produced. 2.275 g of each synthesized composite oxide powder and 0.525 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. A further 10 mL of acetone was added to the pot, and the pot was covered in a glove box maintained in an argon atmosphere. This was set in a planetary ball mill ("Pulverisete 5" manufactured by FRITSCH), mixed for 12 minutes at a revolution speed of 240 rpm, and then put into a rest for 3 minutes, 48 times in total. This mixture was dried with a dryer at 75 ° C. for 3 hours or more to prepare a mixed powder. 1.6 g of the mixed powder, 0.1 g of AB, 12% by mass N-methylpyrrolidone (NMP) solution of PVDF and NMP were put in a predetermined plastic container, and the lid was covered in a glove box maintaining an argon atmosphere. The 12 mass% N-methylpyrrolidone (NMP) solution and NMP of PVDF contain 0.3 g of PVDF and 4.4 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 active material, AB and PVDF in the slurry is 65:20:15. This slurry was applied to one side of a 20 μm thick aluminum foil current collector. This was dried on a hot plate at 80 ° C. for 60 minutes to evaporate the dispersion medium, and then subjected to roll press to obtain a positive electrode plate.

A test battery was assembled using the positive electrode as a working electrode, and the behavior as a positive electrode was evaluated. For the purpose of accurately observing the single behavior, a counter electrode in which metallic lithium was adhered to a nickel foil current collector was used. Here, a sufficient amount of metallic lithium was arranged so that the capacity of the test battery was not limited by the counter electrode. A solution obtained by dissolving LiPF ₆ as an electrolyte in a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / dimethyl carbonate (DMC) in a volume ratio of 6: 7: 7 so that the concentration becomes 1 mol / L. 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 the liquid injection hole was sealed after pouring the electrolytic solution.

[Charge / discharge test]
The obtained nonaqueous electrolyte secondary battery was charged / discharged in a thermostat set at 25 ° C. Charging was constant current constant voltage (CCCV) charging, and discharging was constant current (CC) discharging. 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 plate. The charge upper limit voltage and the discharge end voltage were 4.4 V and 1.2 V, respectively. The charge termination conditions were the time when the charging current was attenuated to 2 mA / g or the time when 3 hours had passed since the charging upper limit voltage was reached. In each cycle, a pause time of 10 minutes was set after charging and discharging. This cycle was performed for 4 cycles. In this test, voltage control was performed between the working electrode and the counter electrode. However, since the dissolution / deposition reaction resistance of metallic lithium at the counter electrode was extremely low, metal lithium was used as the voltage between terminals during charging and discharging. It can be regarded as being equal to the potential of the working electrode with respect to the reference electrode. Table 2 shows the discharge capacity at the first cycle in this charge / discharge cycle test. Further, the ratio of the discharge capacity at the fourth cycle to the discharge capacity at the second cycle was determined as “capacity maintenance ratio (%)”. This capacity retention rate is also shown in Table 2. Moreover, the discharge curve of the 1st cycle of Examples 1-3 and the comparative example 1 is shown in FIG.

  As shown in Table 2 and FIG. 2, it can be seen that the secondary batteries of Examples 1 to 4 have a high discharge capacity and a high capacity retention rate.

Moreover, about each composite oxide of Examples 1-4, the X-ray-diffraction measurement was performed before and after the charging / discharging test. Before the charge / discharge test, the produced complex oxide in the powder state was measured under the same conditions as described above. After the charge / discharge test, the secondary battery using each composite oxide as the positive electrode active material was charged / discharged for 10 cycles according to the above method, then the positive electrode plate was taken out and washed with dimethyl carbonate, The measurement was performed under the same conditions as described above except that the positive electrode plate was placed in a dedicated device (general-purpose atmospheric separator) (manufactured by Rigaku) for maintaining an argon atmosphere and the scan speed was set to 2 ° / min. As a result, it was confirmed that the crystal structure belonging to the space group Fm-3m was maintained before and after the charge / discharge cycle test. As a representative, an X-ray diffraction diagram of the composite oxide of Example 2 (Li _1.4 Mo _0.8 Nb _0.2 O _2.4 ) is shown in FIG. The lower diffraction pattern in FIG. 3 is an X-ray diffraction pattern before the charge / discharge test. The upper diffraction pattern in FIG. 3 is an X-ray diffraction pattern after charging and discharging.

[Example 5]
An appropriate amount of LiMoO ₂ and Li ₄ MoO ₅ were weighed so that the molar ratio was 2: 1, a zirconia container having an internal volume of 45 mL, and zirconia balls having a diameter of 10 mm, 5 mm, and 1 mm were used in appropriate amounts. And a planetary ball mill (FRISTSCH “pulverisette 7”), and mixing for 15 minutes at a revolution speed of 600 rpm followed by a 3-minute rest was repeated 120 times. Li _4/3 Mo (III) _4/9 Mo (VI) _2/9 O ₂ (Li ₂ Mo (III) _2/3 Mo (VI) _1/3 O _1/3 ) A composite oxide was obtained. Also, weighed appropriate amounts of complex oxide and AB, used zirconia containers with an internal volume of 45 mL, zirconia balls with diameters of 10 mm, 5 mm and 1 mm, and used dry balls without adding acetone. Except for milling, setting on a planetary ball mill (FRITSCH "pulverisete 7"), mixing for 15 minutes at revolution speed of 300 rpm and then putting in a pause for 3 minutes for a total of 40 times. In the same manner as in Examples 1 to 4, secondary batteries using this composite oxide as a positive electrode active material were obtained. The charge / discharge curves measured using this secondary battery are shown in FIGS. FIG. 4A is a charge / discharge curve when 27 cycles of constant current charge and constant current discharge are performed in a voltage range of 1.0 to 4.4 V, and FIG. FIG. 4C is a charge / discharge curve when 30 cycles of constant current charge and constant current discharge are performed in a voltage range of .4V, and FIG. 4C is a constant current charge and constant current in a voltage range of 1.0-4.8V. It is a charging / discharging curve when discharging is performed 2 cycles. As the charging current and the discharging current, current values corresponding to a current density of 30 mA / g per active material mass were adopted.

[Example 6]
Except that LiMoO ₂ and Li ₂ TiO ₃ were used in a molar ratio of 1: 1, the same procedure as in Example 5 was performed, and Li _6/5 Mo _2/5 MoTi _2/5 O ₂ ( Li _3/2 Mo _1/2 Ti _1/2 O _5/2 ) composite oxide and a secondary battery using this composite oxide as a positive electrode active material were obtained. The charge / discharge curves measured using this secondary battery are shown in FIGS. Fig.5 (a) is a charging / discharging curve when 30 cycles of constant current charge and constant current discharge are performed in the voltage range of 1.0-4.4V, FIG.5 (b) is 1.0-4. It is a charging / discharging curve when a constant current charge and a constant current discharge are performed 2 cycles in the voltage range of .8V. As the charging current and the discharging current, a current value corresponding to 30 mA / g was adopted as the current density per mass of the active material.

  Since the conditions are different, these Examples 5 to 6 cannot be directly compared with Comparative Example 1 and Examples 1 to 4, but also in Examples 5 to 6, the obtained secondary battery has a sufficient discharge capacity. Can be confirmed. Further, from the results of FIG. 4A and FIG. 5A, from the case of having a crystal structure that can be assigned to the space group Fm-3m and containing only lithium and molybdenum as metal elements (FIG. 4A). In addition, it can be seen that the capacity retention rate after the charge / discharge cycle is higher when lithium, molybdenum, and titanium are included as the metal elements (FIG. 5A).

  Moreover, about the complex oxide of the powder state of Examples 5-6, the X-ray-diffraction measurement was performed on the same conditions as the above. As a result, it was confirmed that all X-ray diffraction patterns had diffraction peaks belonging to the space group Fm-3m.

  The present invention can be applied to electronic devices such as personal computers and communication terminals, nonaqueous electrolyte secondary batteries used as a power source for automobiles, electrodes provided in the secondary battery, active materials, and the like.

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 2 Electrode group 3 Battery container 4 Positive electrode terminal 4 'Positive electrode lead 5 Negative electrode terminal 5' Negative electrode lead 20 Power storage unit 30 Power storage device

Claims (10)

Composite oxide having a crystal structure that can be assigned to space group Fm-3m, including lithium and molybdenum, substantially free of chromium, and having a molybdenum content of 10 mol% or more with respect to all metal elements other than lithium (However, Li _1.2 Mn _0.6 Mo _0.2 O ₂ and Li _{1 + a / 100} (NiTi) _{1 / 2-a / 120} Mo _{a / 150} O ₂ (5 ≦ a ≦ 20) Except the ones) . Composite oxide having a crystal structure that can be assigned to space group Fm-3m, including lithium and molybdenum, substantially free of chromium, and having a molybdenum content of 40 mol% or more with respect to all metal elements other than lithium . The composite oxide according to claim 1 or 2 , wherein the content of molybdenum with respect to all metal elements other than lithium is 60 mol% or more. The metal element (α) made of aluminum, silicon, scandium, titanium, zinc, germanium, zirconium, niobium, tin, tellurium, tantalum, rhenium, or a combination thereof further includes any one of claims 1 to 3. The composite oxide described. Having a crystal structure that can be assigned to space group Fm-3m, including lithium and molybdenum, substantially free of chromium,
A metal element (α) further comprising aluminum, silicon, scandium, titanium, zinc, germanium, zirconium, niobium, tin, tellurium, tantalum, rhenium, or a combination thereof;
Molybdenum and the metal element (alpha) and the total content double focus oxide content Ru der 30 mol% to 90 mol% or less of molybdenum to the. The composite oxide according to any one of claims 1 to 5 , which is represented by the following formula (1).
Li _{1 + x} Mo _y Me _{1-y Ap} O _z (1)
(In the formula (1), Me is Al, Si, Sc, Ti, Zn, Ge, Zr, Nb, Sn, Te, Ta, Re, or a combination thereof. A is Li, Mo, Me, and O. Elements other than 0 ≦ x, 0.1 ≦ y ≦ 1, 0 <z, 0 ≦ p ≦ 0.2.) The positive electrode active material for nonaqueous electrolyte secondary batteries containing the complex oxide of any one of Claims 1-6 . The positive electrode for nonaqueous electrolyte secondary batteries containing the positive electrode active material for nonaqueous electrolyte secondary batteries of Claim 7 . Cathode, a non-aqueous electrolyte secondary battery comprising a negative electrode and a nonaqueous electrolyte, the positive electrode, a non-aqueous electrolyte secondary battery positive electrode der Ru non-aqueous electrolyte secondary battery according to claim 8. A method for producing the composite oxide according to any one of claims 1 to 6,
Includes lithium and molybdenum, the production method of the chromium double focus oxide that have a treating an active material for material containing a complex oxide which is substantially free by mechanochemical method.

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