JP2019145360A - Positive electrode active material, method for producing positive electrode active material, positive electrode, nonaqueous electrolyte power storage element, method for manufacturing nonaqueous electrolyte power storage element, and method for using nonaqueous electrolyte power storage element - Google Patents

Abstract

To provide: a positive electrode active material high in energy density and a method for producing the same; a positive electrode including the positive electrode active material and a nonaqueous electrolyte power storage element; and a method for manufacturing and using the nonaqueous electrolyte power storage element.SOLUTION: One embodiment of the present invention is a positive electrode active material for a nonaqueous electrolyte power storage element. The positive electrode active material contains an oxide including lithium, chromium and an element A, the element A being a Group 4 element, a Group 5 element, a Group 13 element, a Group 14 element, a Group 15 element, a Group 16 element other than oxygen, or a combination thereof. In an X-ray diffraction pattern of the oxide, a ratio (Is/Ib) of an intensity Ia of a peak appearing in a range where 2θ is 13-23° to an intensity Ib of a peak appearing in a range where 2θ is 39-49° is 0.7 or less.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a positive electrode active material, a method for producing a positive electrode active material, a positive electrode, a nonaqueous electrolyte electricity storage element, a method for producing a nonaqueous electrolyte electricity storage element, and a method for using the nonaqueous electrolyte electricity storage element.

  Nonaqueous electrolyte secondary batteries represented by lithium ion secondary batteries are widely used in electronic devices such as personal computers and communication terminals, automobiles, and the like. The non-aqueous electrolyte secondary battery generally has a pair of electrodes electrically isolated by a separator and a non-aqueous electrolyte interposed between the electrodes. In the non-aqueous electrolyte secondary battery, the active material contained in each electrode occludes and releases ions, and the ions can be transferred between the electrodes to be charged / discharged. 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.

  Various composite oxides and the like are used for the positive electrode active material of the nonaqueous electrolyte electricity storage device. As complex oxides, Li—Cr—Mn—O compounds (see Patent Document 1), Li—Cr—Mo—O compounds (see Patent Document 2), and layered rock salt type Li—Cr—Ti—O systems An oxide containing lithium and chromium such as a compound (see Non-Patent Document 1) has been synthesized, and its use as a positive electrode active material has been studied.

JP 2003-002653 A Special table 2015-535801 gazette

J. et al. Electrochem. Soc. , 150 (5), A601-A607, 2003

  Chromium can be in an oxidation state with an oxidation number of up to +6. For this reason, for example, an oxide containing chromium having an oxidation number of +2 or +3 is expected to be used as a positive electrode active material having a high energy density. However, a conventional oxide containing lithium and chromium does not have a sufficiently high energy density as a positive electrode active material.

  The present invention has been made based on the circumstances as described above, and the object thereof is a positive electrode active material having a high energy density and a method for producing the same, a positive electrode including the positive electrode active material, a nonaqueous electrolyte storage element, and the above It is providing the manufacturing method and usage method of a nonaqueous electrolyte electrical storage element.

  One embodiment of the present invention made to solve the above problems includes an oxide containing lithium, chromium, and an element A, and the element A is a group 4 element, a group 5 element, a group 13 element, or a group 14 element. , Group 15 elements, group 16 elements other than oxygen, or a combination thereof, and in the X-ray diffraction pattern of the oxide, the peak intensity Ia that appears in the range of 2θ of 13 to 23 ° and 2θ of 39 to 49 ° The ratio (Ia / Ib) with the peak intensity Ib appearing in the range is 0.7 or less.

  Another embodiment of the present invention includes treating one or more oxides by a mechanochemical method, and the one or more oxides include lithium, chromium, and an element A. In the method for producing a positive electrode active material, the element A is a group 4 element, a group 5 element, a group 13 element, a group 14 element, a group 15 element, a group 16 element other than oxygen, or a combination thereof.

  Another embodiment of the present invention is a positive electrode for a non-aqueous electrolyte storage element having the positive electrode active material.

  Another embodiment of the present invention is a nonaqueous electrolyte electricity storage element including the positive electrode.

  Another embodiment of the present invention is a method for manufacturing a non-aqueous electrolyte electricity storage element including preparing a positive electrode using the positive electrode active material.

  Another embodiment of the present invention is a method for using the nonaqueous electrolyte electricity storage element, comprising charging and discharging within a range in which the oxidation number of the element A does not change.

  According to the present invention, it is possible to provide a positive electrode active material having a high energy density and a method for producing the same, a positive electrode including the positive electrode active material and a nonaqueous electrolyte electricity storage device, and a method for producing and using the nonaqueous electrolyte electricity storage device. it can.

FIG. 1 is an external perspective view showing an embodiment of a nonaqueous electrolyte electricity storage device according to 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 the present invention. FIG. 3 is an X-ray diffraction pattern of each oxide obtained in Examples 1-4 and Comparative Examples 1-3. FIG. 4 is a charge / discharge curve of Example 2.

  The positive electrode active material according to an embodiment of the present invention contains an oxide containing lithium, chromium, and an element A, and the element A includes a group 4 element, a group 5 element, a group 13 element, a group 14 element, and a group 15 Element, a group 16 element other than oxygen, or a combination thereof, and in the X-ray diffraction pattern of the oxide, the peak intensity Ia that appears in the range of 2θ in the range of 13 to 23 ° and the range of 2θ in the range of 39 to 49 ° It is a positive electrode active material for a non-aqueous electrolyte electricity storage device having a ratio (Ia / Ib) with the peak intensity Ib that appears is 0.7 or less.

  The positive electrode active material has a high energy density. The reason for this is not clear, but the following reason is presumed. Conventional Li-Cr-Mo-O-based compounds and Li-Cr-Mn-O-based compounds include Mo that is a Group 6 element and Mn that is a Group 7 element, and oxidation and reduction of Mo and Mn during charge and discharge. A reaction occurs. Accordingly, in the Li-Cr-Mo-O-based compound and the Li-Cr-Mn-O-based compound, the discharge potential is lowered due to the occurrence of the redox reaction of Mo and Mn together with the redox reaction of Cr. It is estimated that the energy density is low. On the other hand, the element A contained together with Cr in the oxide of the positive electrode active material is an element that hardly undergoes a redox reaction during charge / discharge. Therefore, since the positive electrode active material can substantially use only the redox reaction of Cr, the discharge potential is increased, and as a result, the energy density is estimated to increase. In the oxide of the positive electrode active material, the peak intensity ratio (Ia / Ib) in the X-ray diffraction pattern is 0.7 or less. When the oxide has such a peak intensity ratio, it is presumed that the crystal structure is an irregular rock salt type, and such a crystal structure also contributes to an improvement in energy density for the following reasons. Guessed. In the case of an irregular rock salt type crystal structure, there are various combinations of atoms coordinated to oxygen. For this reason, in the case of an irregular rock salt type, a coordination state in which Li and electrons are weakly bound, that is, a site where insertion and desorption are easy can be formed, and a coordination state in which an oxygen redox reaction can occur can be formed. Therefore, it is estimated that the charge / discharge electricity amount can be increased.

  Note that the X-ray diffraction pattern of the oxide of the positive electrode active material in this specification is measured with respect to an oxide that has not been charged or discharged or an oxide taken out from a non-aqueous electrolyte storage element in a discharged state. Say. In addition, the composition ratio of the oxide of the positive electrode active material, which will be described later, and the maximum oxidation number and oxidation number of each element of the oxide are also taken out from the oxide that has not been charged or discharged, or from the nonaqueous electrolyte storage element in the discharged state. The value in the oxide.

Specifically, if the sample used for measurement such as X-ray diffraction measurement is a positive electrode active material (oxide) powder before the positive electrode preparation, it is used for measurement as it is. When collecting a sample from the positive electrode taken out by disassembling the nonaqueous electrolyte storage element, the nonaqueous electrolyte storage element is brought into a discharged state by the following procedure before disassembling the nonaqueous electrolyte storage element. First, constant current charging is performed at a current of 0.1 C to a voltage at which the potential of the positive electrode becomes 4.3 V (vs. Li ^/ Li ⁺ ), and the current is constant at the same voltage until the current value decreases to 0.01 C. Charge the battery voltage to the end-of-charge state. After a pause of 30 minutes, constant current discharge is performed at a current of 0.1 C until the potential of the positive electrode reaches 2.0 V (vs. Li ^/ Li ⁺ ), and a discharge end state is obtained. In the case of a non-aqueous electrolyte storage element using a metal lithium electrode as a negative electrode, the non-aqueous electrolyte storage element may be disassembled after the non-aqueous electrolyte storage element has been discharged, and the positive electrode may be taken out. If it is not the non-aqueous electrolyte storage element used for the negative electrode, in order to accurately control the positive electrode potential, after disassembling the non-aqueous electrolyte storage element and taking out the positive electrode, a non-aqueous electrolyte storage element using a metal lithium electrode as a counter electrode After assembly, adjust to the end-of-discharge state according to the above procedure. The work from disassembly of the nonaqueous electrolyte storage element to measurement is performed in an argon atmosphere with a dew point of −60 ° C. or lower. The extracted positive electrode is sufficiently washed with dimethyl carbonate. After sufficiently drying at room temperature, the positive electrode active material (oxide) is taken out and used for measurement.

  X-ray diffraction measurement of the 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. At this time, the diffracted X-ray passes through a Kβ filter having a thickness of 30 μm and is detected by a high-speed one-dimensional detector (D / teX Ultra 2). The sampling width is 0.02 °, the scan 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.

The oxide is preferably represented by the following formula (1).
Li _a Cr _{b AcO 2} (1)
(In Formula (1), A is the said element A. a, b, and c are respectively independent positive numbers.)
When the oxide has such a composition, the energy density can be further increased.

  The element A is preferably titanium, niobium or tellurium. Since these elements are presumed to be particularly difficult to cause oxidation-reduction reactions during charge and discharge, the energy density can be further increased by using these elements.

  It is preferable that the element A is present in the state of the maximum oxidation number. In such a case, since the redox reaction of the element A does not substantially occur during charge / discharge, the energy density can be further increased.

  A method for producing a positive electrode active material according to an embodiment of the present invention comprises treating one or more oxides by a mechanochemical method, wherein the one or more oxides are lithium, A method for producing a positive electrode active material comprising chromium and element A, wherein element A is a group 4 element, group 5 element, group 13 element, group 14 element, group 15 element, group 16 element other than oxygen, or a combination thereof It is. According to the manufacturing method, a positive electrode active material having a high energy density can be manufactured.

  The positive electrode which concerns on one Embodiment of this invention is a positive electrode for nonaqueous electrolyte electrical storage elements which has the said positive electrode active material. Since the said positive electrode has the said positive electrode active material, the energy density of a nonaqueous electrolyte electrical storage element can be raised.

  A nonaqueous electrolyte storage element according to an embodiment of the present invention is a nonaqueous electrolyte storage element (hereinafter, also simply referred to as “storage element”) provided with the positive electrode. The power storage element has a high energy density.

  The manufacturing method of the nonaqueous electrolyte electrical storage element which concerns on one Embodiment of this invention is a manufacturing method of a nonaqueous electrolyte electrical storage element provided with producing a positive electrode using the said positive electrode active material. According to the manufacturing method, an energy storage device having a high energy density can be manufactured.

  The usage method of the nonaqueous electrolyte electricity storage element which concerns on one Embodiment of this invention is a usage method of the said nonaqueous electrolyte electricity storage element provided with performing charging / discharging in the range in which the oxidation number of the said element A does not change. According to this method of use, since the redox reaction of element A is not caused in the positive electrode and the redox reaction of only chromium is used, charging / discharging can be performed at a higher energy density. .

  Hereinafter, a positive electrode active material according to an embodiment of the present invention, a method for manufacturing a positive electrode active material, a positive electrode, a nonaqueous electrolyte storage element, a method for manufacturing a nonaqueous electrolyte storage element, and a method for using a nonaqueous electrolyte storage element in order explain.

<Positive electrode active material>
The positive electrode active material according to an embodiment of the present invention contains an oxide containing Li (lithium), Cr (chromium), and the element A.

  The oxidation number of Cr in the oxide may be +2, +3 or +4, but is preferably +2 or +3. In such a case, Cr may cause an oxidation-reduction reaction (charge / discharge reaction) between +2 and +6, or between +3 and +6. That is, in this case, since the redox reaction of 3 electrons or 4 electrons occurs by Cr, the energy density can be further increased.

  In the positive electrode active material, a redox reaction of Cr mainly occurs, but a redox reaction of other elements may occur.

  The element A is a group 4 element, a group 5 element, a group 13 element, a group 14 element, a group 15 element, a group 16 element other than oxygen, or a combination thereof.

  Examples of the group 4 element include Ti (titanium), Zr (zirconium), Hf (hafnium), and the like, and Ti is preferable.

  Examples of the group 5 element include V (vanadium), Nb (niobium), Ta (tantalum), and Nb is preferable.

  Examples of the group 13 element include B (boron), Al (aluminum), Ga (gallium), In (indium), and Tl (thallium).

  Examples of the group 14 element include C (carbon), Si (silicon), Ge (germanium), Sn (tin), and Pb (lead).

  Examples of the group 15 element include N (nitrogen), P (phosphorus), As (arsenic), Sb (antimony), Bi (bismuth), and the like.

  Examples of Group 16 elements other than O (oxygen) include S (sulfur), Se (selenium), Te (tellurium), Po (polonium), and Te is preferred.

  The element A is preferably a metal element. The element A is preferably a group 4 element, a group 5 element, a group 16 element, or a combination thereof, and more preferably a group 4 element. The element A is preferably a third to fifth periodic element, more preferably a fourth to fifth periodic element, and more preferably a fourth periodic element. More specifically, the element A is preferably titanium, niobium or tellurium, and more preferably titanium.

The element A in the oxide is preferably present in a state in which the oxidation number hardly changes during charge / discharge. For example, it is preferable that the redox potential of the element A in the final discharge state does not exist in the potential range of 2.0 to 4.8 V (vs. Li / Li ⁺ ).

  As a suitable state of the element A in the oxide, for example, the state of the maximum oxidation number can be mentioned. If the element A is in the state of the maximum oxidation number at the end of the discharge, the element A is not oxidized any more during charging, so that it can be said that the oxidation number of the element A does not change with charge / discharge.

  When the element A is a group 4 element, the maximum oxidation number of this element is +4. When element A is a group 5 element, the maximum oxidation number of this element is +5. When element A is a group 13 element, the maximum oxidation number of this element is 3. When the element A is a group 14 element other than Fl (fullerobium), the maximum oxidation number of this element is 4. When the element A is Fl, the maximum oxidation number of this element is 2. When the element A is a group 15 element other than Mc (moscobium), the maximum oxidation number of this element is 5. When element A is a group 16 element other than O and Lv (livermorium), the maximum oxidation number of this element is 6. When the element A is Lv, the maximum oxidation number of this element is 4.

  The oxide may further contain elements other than Li, Cr, O, and element A. However, the upper limit of the content ratio of the other elements in the oxide is preferably 10 atm%, more preferably 1 atm%, and more preferably 0.1 atm%. Thus, when the oxide is substantially composed only of Li, Cr, O and element A, an oxidation-reduction reaction of only Cr is more likely to occur, and the energy density can be further increased.

The oxide is preferably represented by the following formula (1).
Li _a Cr _{b AcO 2} (1)
In the formula (1), A is the element A. a, b and c are each an independent positive number.

  As a lower limit of a, 1 is preferable, 1.1 is more preferable, and 1.2 is more preferable. Also, a is preferably more than 1. The upper limit of a is preferably 2, more preferably 1.7, and even more preferably 1.5.

  As a minimum of b, 0.1 is preferred, 0.3 is more preferred, and 0.4 is still more preferred. As an upper limit of b, 1 is preferable, 0.8 is more preferable, 0.6 is more preferable, and 0.5 is still more preferable.

  The lower limit of c is preferably 0.01, more preferably 0.1, and still more preferably 0.2. As an upper limit of c, 1 is preferable, 0.7 is more preferable, and 0.5 is more preferable.

  In the formula (1), it is preferable that the relationship of a / (b + c)> 1 holds. In this case, a so-called lithium-excess type oxide is obtained, and the multi-electron reaction of Cr can be used more effectively. The lower limit of a / (b + c) is preferably 1.2, and more preferably 1.4. On the other hand, the upper limit of a / (b + c) is 3, for example, may be 2.25, or may be 2.

  In Formula (1), the relationship of a <= 3b may be materialized. In this case, all the charge compensation accompanying the insertion and desorption of lithium can be provided by the multi-electron reaction of Cr. However, a> 3b may be sufficient. For example, when using the oxidation-reduction reaction of oxygen in the oxide, a> 3b may be preferable.

  As a minimum of a + b + c, 1.5 is preferable, 1.8 is preferable and 1.9 is more preferable. Moreover, as an upper limit of a + b + c, 2.5 is preferable, 2.2 is more preferable, 2.1 is further more preferable. a + b + c may be substantially 2. In such a case, a good irregular rock salt type crystal structure can be obtained. However, since there may be a case where a defect portion or an excess portion of oxygen is generated, even if a + b + c is deviated from 2, the effect of the present invention can be produced.

  When the oxidation number of Cr is +3 and the oxidation number of element A is + x, the relationship of a + 3b + xc = 4 is usually satisfied. Similarly, when the oxidation number of Cr is +2 and the oxidation number of element A is + x, the relationship of a + 2b + xc = 4 is usually satisfied. At this time, the oxidation number of element A is preferably the maximum oxidation number described above.

  In the X-ray diffraction pattern of the oxide, the peak intensity Ia that appears in the range of 2θ of 13 to 23 ° (preferably in the range of 16 to 20 °) and the range of 2θ in the range of 39 to 49 ° (preferably 42 The upper limit of the ratio (Ia / Ib) to the peak intensity Ib appearing in the range of ˜46 ° is 0.7, preferably 0.2, and more preferably 0.1. Thus, the oxide having a small ratio (a / Ib) has an irregular rock salt type crystal structure and a high energy density. The lower limit of this ratio (Ia / Ib) may be zero.

  The positive electrode active material may contain a component other than the oxide. However, the lower limit of the content of the oxide in the positive electrode active material is preferably 70% by mass, more preferably 90% by mass, and even more preferably 99% by mass. The upper limit of the oxide content may be 100% by mass. The positive electrode active material may consist essentially of the oxide. Thus, energy density can be raised more because the said positive electrode active material most is comprised from the said oxide.

<Method for producing positive electrode active material>
The positive electrode active material can be produced, for example, by the following method. That is, the method for producing a positive electrode active material according to an embodiment of the present invention includes:
Treating one or more oxides by a mechanochemical method,
The one or more oxides include lithium, chromium and element A,
In the method for producing a positive electrode active material, the element A is a group 4 element, a group 5 element, a group 13 element, a group 14 element, a group 15 element, a group 16 element other than oxygen, or a combination thereof.

  According to the production method, a positive electrode active material having a high energy density can be obtained by treating one or more oxides containing a predetermined element by a mechanochemical method. 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. In the manufacturing method, it is considered that an oxide having an irregular rock salt type crystal structure containing Li, Cr, and element A is synthesized by a process by a mechanochemical method. In addition, when an oxide containing Li, Cr, and element A as a raw material and having a crystal structure other than the irregular rock salt type is used, the crystal structure is considered to be transferred to the irregular rock salt type by the treatment by the mechanochemical method. It is done.

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. No particular limitation is imposed on the ball, made of tungsten carbide (WC) or the like can be suitably used as those made of zirconium oxide (ZrO _2).

  When processing by a ball mill, the number of rotations of the ball at the time of processing can be, for example, 100 rpm or more and 1,000 rpm or less. Moreover, as processing time, it can be set as 0.1 hours or more and 10 hours or less, for example. This treatment can be performed in an inert gas atmosphere such as argon or an active gas atmosphere, but is preferably performed in an inert gas atmosphere.

  The oxide used for the process by the mechanochemical method should just contain Li, Cr, and the element A with the 1 type, or 2 or more types of whole oxide. That is, one kind of oxide containing Li, Cr, and element A may be used, or a plurality of kinds of oxides containing at least one of Li, Cr, and element A may be used in combination. In the case of using a plurality of types of oxides, for example, it is preferable to use an oxide containing Li and Cr and an oxide containing Li and the element A. Moreover, when using multiple types of oxides, the mixing ratio of each raw material oxide is adjusted so that it may become the composition of the target oxide.

Examples of the oxide containing Li and Cr include LiCrO ₂ . LiCrO ₂ usually has a layered rock salt type crystal structure.

Examples of the oxide containing Li and the element A include Li ₂ TiO ₃ , Li ₂ ZrO ₃ , Li ₃ VO ₄ , Li ₃ NbO ₄ , Li ₃ BO ₃ , Li ₅ AlO ₄ , Li ₅ GaO ₄ , and Li ₅ InO _4. , Li ₂ SiO ₃ , Li ₄ SiO ₄ , Li ₂ GeO ₃ , Li ₄ GeO ₄ , Li ₂ SnO ₃ , Li ₄ SnO ₄ , Li ₃ PO ₄ , Li ₃ SbO ₄ , Li ₅ SbO ₅ , Li ₅ BiO ₅ , Li ₄ TeO _{5 and the} like. The oxide containing Li and the element A preferably has a rock salt type crystal structure including a layered rock salt type, an irregular rock salt type, and the like. By using an oxide having a rock salt type crystal structure as a raw material, a target oxide having an irregular rock salt type crystal structure can be effectively obtained by treatment by a mechanochemical method.

The oxide containing Li, Cr, and element A is represented by Li _a Cr _{b AcO 2} (A is element A. a, b, and c are each an independent positive number). And an oxide having a layered rock salt type crystal structure. Such an oxide can be obtained by, for example, a solid phase reaction method using lithium carbonate, chromium oxide, and an oxide of element A as raw materials.

Other oxides used for the mechanochemical process include lithium oxide (Li ₂ O), chromium oxide (CrO, Cr ₂ O ₃ etc.), element A oxide (TiO ₂ , Nb ₂ O ₅ , Al ₂ O). ₃ , TeO _3, etc.) may be used.

<Positive electrode>
The positive electrode which concerns on one Embodiment of this invention is a positive electrode for nonaqueous electrolyte electrical storage elements which has the said positive electrode active material mentioned above. The positive electrode has a positive electrode base material and a positive electrode active material 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, titanium, tantalum, 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, 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, an aluminum foil is preferable as the positive electrode base material. Examples of aluminum or aluminum alloy include A1085P and A3003P defined in JIS-H-4000 (2014).

An 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 active material layer by including electroconductive particles, such as a carbon particle. 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.

  The positive electrode active material includes the positive electrode active material described above. As said positive electrode active material, well-known positive electrode active materials other than the said positive electrode active material may be contained. As a content rate of the said positive electrode active material which occupies for all the positive electrode active materials, 50 mass% or more is preferable, 70 mass% or more is more preferable, 90 mass% or more is further more preferable, 99 mass% or more is further more preferable. By increasing the content ratio of the positive electrode active material, the energy density can be sufficiently increased. The content rate of the said positive electrode active material in the said positive electrode active material layer can be 50 mass% or more and 95 mass% or less, for example.

  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 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.

<Nonaqueous electrolyte storage element>
The electrical storage element which concerns on one Embodiment of this invention has a positive electrode, a negative electrode, and a nonaqueous electrolyte. Hereinafter, a non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as “secondary battery”) will be described as an example of a 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. The electrode body is housed in a container, and the container is filled with a nonaqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. Moreover, as said container, the well-known metal container normally used as a container of a secondary battery, a resin container, etc. can be used.

(Positive electrode)
The positive electrode provided in the secondary battery is as described above.

(Negative electrode)
The negative electrode includes a negative electrode base material and a negative electrode active material 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, and copper or a copper alloy 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 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, 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), non-graphitic Examples thereof include carbon materials such as carbon (easily graphitizable 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.

(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 the non-aqueous electrolyte, a known non-aqueous electrolyte that is usually used in a general non-aqueous electrolyte secondary battery can be used. The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

  As said non-aqueous solvent, the well-known non-aqueous solvent normally used as a non-aqueous solvent of the general non-aqueous electrolyte for secondary batteries can be used. Examples of the non-aqueous solvent include cyclic carbonate, chain carbonate, ester, ether, amide, sulfone, lactone, and nitrile. Among these, it is preferable to use at least cyclic carbonate or chain carbonate, and it is more preferable to use cyclic carbonate and chain carbonate in combination.

  Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), and difluoroethylene. Examples include carbonate (DFEC), styrene carbonate, catechol carbonate, 1-phenyl vinylene carbonate, 1,2-diphenyl vinylene carbonate, and among these, EC is preferable.

  Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diphenyl carbonate. Among these, DMC and EMC are preferable.

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 , LiPF ₂ (C ₂ O ₄ ) ₂ , LiClO ₄ , LiN (SO ₂ F) ₂ , LiSO ₃ CF ₃ , LiN ( _{SO 2 CF 3) 2, LiN} (SO 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 ) A lithium salt having a fluorinated hydrocarbon group such as ₃ can be mentioned.

  Other additives may be added to the non-aqueous electrolyte. Moreover, room temperature molten salt, ionic liquid, polymer solid electrolyte, etc. can also be used as the non-aqueous electrolyte.

  The electrical storage element which concerns on one Embodiment of this invention has a high energy density. The discharge capacity of the electricity storage element is preferably equal to or greater than the amount of discharge electricity corresponding to 1.45 electron reaction of Cr, and more preferably equal to or greater than the amount of discharge electricity corresponding to 1.5 electron reaction of Cr. Thus, the energy density can be further increased by utilizing the multi-electron reaction of Cr. It should be noted that the discharge capacity of the electricity storage element is usually equal to or less than the amount of discharge electricity corresponding to the 4-electron reaction of Cr, and may be equal to or less than the amount of discharge electricity corresponding to the 3-electron reaction of Cr.

<Method for Manufacturing Nonaqueous Electrolyte Storage Element>
The power storage element can be manufactured by using the positive electrode active material. For example, in the method of manufacturing the electricity storage element, the step of producing a positive electrode, the step of producing a negative electrode, the step of preparing a nonaqueous electrolyte, and laminating or winding the positive electrode and the negative electrode through a separator are alternately superimposed. A step of forming an electrode body, a step of accommodating a positive electrode and a negative electrode (electrode body) in a container, and a step of injecting the nonaqueous electrolyte into the container. After the injection, the storage element can be obtained by sealing the injection port.

  In the step of manufacturing the positive electrode, the positive electrode active material is used. The positive electrode can be produced, for example, by applying a positive electrode mixture paste directly or via an intermediate layer to a positive electrode substrate and drying it. The positive electrode mixture paste includes each component constituting the positive electrode mixture, such as a positive electrode active material, and a dispersion medium. As the dispersion medium, a known dispersion medium such as N-methyl-2-pyrrolidone (NMP) can be used.

<Usage method of nonaqueous electrolyte storage element>
The nonaqueous electrolyte storage element can be used by charging and discharging in the same manner as a conventionally known nonaqueous electrolyte storage element. The nonaqueous electrolyte storage element is preferably charged and discharged within a range where the oxidation number of the element A does not change. By using the non-aqueous electrolyte in this manner, the redox reaction of the element A is not caused in the positive electrode, and the redox reaction of only Cr is used. Therefore, charging / discharging at a high energy density is performed. It can be performed.

As a method for performing charge / discharge within a range in which the oxidation number of element A does not change, charge / discharge may be performed in a potential range in which the positive electrode potential does not include the oxidation-reduction potential of element A in the final state of discharge. For example, when the element A is present in the state of the maximum oxidation number at the end of discharge, the positive electrode potential is charged and discharged in the range of 2.0 to 4.8 V (vs. Li / Li ⁺ ). The oxidation number does not change.

<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 of the nonaqueous electrolyte storage element, the positive electrode mixture does not have to 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.

  In the above embodiment, the non-aqueous electrolyte storage element is mainly described as a non-aqueous electrolyte secondary battery. However, other non-aqueous 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 1 (nonaqueous electrolyte secondary battery) which is an embodiment of the nonaqueous electrolyte storage element according to the present invention. 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 battery container 3. The electrode body 2 is formed by winding a positive electrode including a positive electrode mixture containing 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 ′. As the positive electrode active material, the positive electrode active material according to an embodiment of the present invention is used. In addition, a non-aqueous electrolyte is injected into the battery container 3.

  The configuration of the nonaqueous electrolyte storage element according to the present invention 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.

Comparative Example 1 Synthesis of Li _6/5 Cr _2/5 Ti _2/5 O ₂ (Layered Rock Salt Type) Li ₂ CO ₃ (2.0540 g), Cr ₂ O ₃ (1.6659 g) and TiO ₂ (Anatase) After mixing the mold, 1.801 g), the mixture was heated at 10 ° C./min in an argon atmosphere and baked at 1100 ° C. for 8 hours. Thereby, Li _6/5 Cr _2/5 Ti _2/5 O ₂ (layered rock salt type) was obtained as the positive electrode active material of Comparative Example 1.

Example 1 Synthesis of Li _6/5 Cr _2/5 Ti _2/5 O ₂ (Random Rock Salt Type) Li _6/5 Cr _2/5 Ti _2/5 O ₂ (Layered) Obtained in Comparative Example 1 The rock salt mold (2.0000 g) was put into a WC pot having an internal volume of 80 mL containing 250 g of a WC ball having a diameter of 5 mm under an argon atmosphere, and the lid was capped. This was set in a planetary ball mill ("Pulverisete 5" manufactured by FRITSCH) and treated at a revolution speed of 400 rpm for 30 minutes. As a result of such a mechanochemical process, Li _6/5 Cr _2/5 Ti _2/5 O ₂ (irregular rock salt type) was obtained as the positive electrode active material of Example 1.

[Example 2] Synthesis of Li _6/5 Cr _2/5 Ti _2/5 O ₂ (irregular rock salt type) LiCrO ₂ (layered rock salt type, 0.9063 g) and Li ₂ TiO ₃ (1.0937 g) were mixed. Then, in an argon atmosphere, it was put into a WC pot having an internal volume of 80 mL containing 250 g of a WC ball having a diameter of 5 mm, and the lid was capped. This was set in a planetary ball mill ("Pulverisete 5" manufactured by FRITSCH) and treated at a revolution speed of 400 rpm for 30 minutes. As a result of such a mechanochemical process, Li _6/5 Cr _2/5 Ti _2/5 O ₂ (irregular rock salt type) was obtained as the positive electrode active material of Example 2.

[Example 3] Synthesis of Li _9/7 Cr _3/7 Nb _2/7 O ₂ (irregular rock salt type) LiCrO ₂ (layered rock salt type, 0.8685 g) and Li ₃ NbO ₄ (1.1315 g) were mixed. Then, in an argon atmosphere, it was put into a WC pot having an internal volume of 80 mL containing 250 g of a WC ball having a diameter of 5 mm, and the lid was capped. This was set in a planetary ball mill ("Pulverisete 5" manufactured by FRITSCH) and treated at a revolution speed of 400 rpm for 40 minutes. By such a mechanochemical process, Li _9/7 Cr _3/7 Nb _2/7 O ₂ (irregular rock salt type) was obtained as the positive electrode active material of Example 3.

[Example 4] Synthesis of Li _12/9 Cr _4/9 Te _2/9 O ₂ (irregular rock salt type) LiCrO ₂ (layered rock salt type, 0.8718 g) and Li ₄ TeO ₅ (1.1282 g) were mixed. Then, in an argon atmosphere, it was put into a WC pot having an internal volume of 80 mL containing 250 g of a WC ball having a diameter of 5 mm, and the lid was capped. This was set in a planetary ball mill ("Pulverisete 5" manufactured by FRITSCH) and treated at a revolution speed of 400 rpm for 40 minutes. By the treatment by such a mechanochemical method, Li _12/9 Cr _4/9 Te _2/9 O ₂ (irregular rock salt type) was obtained as the positive electrode active material of Example 4.

The synthesis of Comparative Example _{2] Li 9/7 Cr 3/7 Nb 2/7} O 2 Synthesis of (layered _{rock-salt) Li 9/7 Cr 3/7 Nb 2/7 O} 2 ( layered rock-salt type) For the purpose, Li ₂ CO ₃ (1.9251 g), Cr ₂ O ₃ (1.9990 g) and Nb ₂ O ₅ (1.0759 g) were mixed, and then heated at 10 ° C./min in an argon atmosphere, Firing was performed at 1100 ° C. for 8 hours.

[Comparative Example 3] Synthesis of Li _12/9 Cr _4/9 Mo _2/9 O ₂ (irregular rock salt type) LiCrO ₂ (layered rock salt type, 0.9434 g) and Li ₄ MoO ₅ (1.0566 g) were mixed. Then, in an argon atmosphere, it was put into a WC pot having an internal volume of 80 mL containing 250 g of a WC ball having a diameter of 5 mm, and the lid was capped. This was set in a planetary ball mill ("Pulverisete 5" manufactured by FRITSCH) and treated at a revolution speed of 400 rpm for 120 minutes. By the treatment by such a mechanochemical method, Li _12/9 Cr _4/9 Mo _2/9 O ₂ (irregular rock salt type) was obtained as the positive electrode active material of Comparative Example 3.

(X-ray diffraction measurement)
The positive electrode active materials (oxides) obtained in the above examples and comparative examples were subjected to X-ray diffraction measurement by the following method. Using an airtight X-ray diffraction measurement sample holder, the powder sample was filled in an argon atmosphere. 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 scanning range 2θ is 10 to 80 °, the sampling width is 0.02 °, 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. . Each X-ray diffraction pattern is shown in FIG.

As shown in FIG. 3, the positive electrode active materials (oxides) of Examples 1 to 4 and Comparative Example 3 obtained by performing the ball mill treatment have a peak intensity (Ib) in the vicinity of 44 ° (b). Thus, the intensity (Ia) of the peak in the vicinity of 18 ° (a) is small. Specifically, the peak intensity ratio (Ia / Ib) is 0.7 or less, and it can be confirmed that an irregular rock salt type oxide is obtained. On the other hand, the positive electrode active materials (oxides) of Comparative Examples 1 and 2 subjected to the solid-phase reaction method have a large peak intensity (Ia) near 18 ° (a) and can be confirmed to be a layered rock salt type. In Comparative Example 2, the phase of LiCrO _{2 and} the phase of Li ₃ NbO ₄ could be confirmed, and the intended Li _9/7 Cr _3/7 Nb _2/7 O ₂ was not synthesized. Therefore, the following evaluation was not performed for the positive electrode active material of Comparative Example 2.

(Preparation of positive electrode)
A total of 2 g of the positive electrode active material and acetylene black obtained in each Example and Comparative Example were weighed at a mass ratio of 85:15. Under an argon atmosphere, the mixture was put into a ZrO ₂ pot having an internal volume of 80 mL containing 90 g of a ZrO ₂ ball having a diameter of 5 mm and capped. This was set in a planetary ball mill ("Premium Line P-7" manufactured by FRITSCH), and dry pulverized at a revolution speed of 300 rpm for 30 minutes to prepare a mixed powder of a positive electrode active material and acetylene black. In this process, it has been confirmed that no phase transition from lamellar rock salt type to irregular rock salt type occurs.

  Using the obtained mixed powder of the positive electrode active material and acetylene black, NMP as a dispersion medium, and the positive electrode active material, acetylene black, and PVDF in a mass ratio of 76.5: 13.5: 10 (solid content conversion) The positive electrode mixture paste contained in was prepared in an argon atmosphere. This positive electrode mixture paste was applied to an aluminum substrate and vacuum dried at 120 ° C. to obtain a positive electrode.

(Preparation of nonaqueous electrolyte storage element (evaluation cell))
LiPF ₆ was dissolved at a concentration of 1 mol / dm ³ in a non-aqueous solvent in which EC, EMC, and DMC were mixed at a volume ratio of 30:35:35 to prepare a non-aqueous electrolyte. A tripolar beaker cell as an evaluation cell (storage element) was produced using the positive electrode and the nonaqueous electrolyte, and the negative electrode and reference electrode as lithium metal. The evaluation cell was produced under an argon atmosphere.

(Charge / discharge test)
About the evaluation cell obtained using each positive electrode active material of Examples 1-4 and Comparative Examples 1 and 3, the charging / discharging test was done in 25 degreeC environment in the glove box of argon atmosphere. The current density was 10 mA / g, and constant current (CC) charge / discharge was performed. Charging was started, and charging was terminated when the upper limit potential of 4.8 V (vs. Li ^/ Li ⁺ ) was reached. The discharge was terminated when the lower limit potential of 2.0 V (vs. Li ^/ Li ⁺ ) was reached. This charge / discharge was carried out for 3 cycles. Note that a pause process of 10 min was provided from the end of charging to the start of discharging, and from the end of discharging to the start of charging, respectively. As a representative, the charge / discharge curve of Example 2 is shown in FIG. Table 1 shows the amount of discharge electricity, the average discharge potential, and the discharge energy density in the first cycle in the charge / discharge test.

  As shown in Table 1, Examples 1 to 4, which contain a predetermined element A and have a peak intensity ratio (Ia / Ib) of 0.7 or less, have a large discharge electricity amount and a high average discharge potential. It can be seen that it has a high discharge energy density. On the other hand, Comparative Example 1 having a peak intensity ratio (Ia / Ib) exceeding 0.7 and having a layered rock salt type crystal structure has a small amount of discharge electricity and a low discharge energy density. Moreover, the comparative example 3 containing Mo which is a group 6 element instead of the element A has a low average discharge potential and a low discharge energy density. In Comparative Example 3, it is presumed that the working potential is lowered due to the occurrence of the redox reaction of Mo together with Cr. On the other hand, in Examples 1 to 4 including the element A which is a group 4 element, a group 5 element, a group 13 element, a group 14 element, a group 15 element, a group 16 element other than oxygen, or a combination thereof, In addition, since the redox reaction of element A does not occur and only the redox reaction of Cr can be used, it is presumed that the operating potential is high. Further, when the amount of discharge electricity at the first cycle is converted to the number of reaction electrons of Cr, Example 1 is 2.0, Example 2 is 1.9, Example 3 is 1.5, and Example 4 is 1.6. Comparative Example 1 was 1.4. Thus, in Examples 1-4, it can confirm that there are many reaction electrons of Cr.

  The present invention can be applied to electronic devices such as personal computers and communication terminals, nonaqueous electrolyte storage elements used as a power source for automobiles, electrodes provided therein, positive electrode active materials, and the like.

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte electrical storage element 2 Electrode body 3 Battery 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 (9)

Containing an oxide containing lithium, chromium and element A;
The element A is a group 4 element, a group 5 element, a group 13 element, a group 14 element, a group 15 element, a group 16 element other than oxygen, or a combination thereof,
In the X-ray diffraction pattern of the oxide, the ratio (Ia / Ib) between the peak intensity Ia that appears in the range of 2θ in the range of 13 to 23 ° and the peak intensity Ib that appears in the range of 2θ in the range of 39 to 49 ° is: The positive electrode active material for nonaqueous electrolyte electrical storage elements which is 0.7 or less. The positive electrode active material according to claim 1, wherein the oxide is represented by the following formula (1).
Li _a Cr _{b AcO 2} (1)
(In Formula (1), A is the said element A. a, b, and c are respectively independent positive numbers.)   The positive electrode active material according to claim 1, wherein the element A is titanium, niobium, or tellurium.   The positive electrode active material according to claim 1, wherein the element A is present in a state of maximum oxidation number. Treating one or more oxides by a mechanochemical method,
The one or more oxides include lithium, chromium and element A,
A method for producing a positive electrode active material, wherein the element A is a group 4 element, a group 5 element, a group 13 element, a group 14 element, a group 15 element, a group 16 element other than oxygen, or a combination thereof.   The positive electrode for nonaqueous electrolyte electrical storage elements which has a positive electrode active material of any one of Claims 1-4.   A non-aqueous electrolyte electricity storage device having the positive electrode according to claim 6.   A manufacturing method of a nonaqueous electrolyte electrical storage element provided with producing a positive electrode using the positive electrode active material of any one of Claims 1-4. The use method of the nonaqueous electrolyte electricity storage element of Claim 7 provided with performing charging / discharging in the range in which the oxidation number of the said element A does not change.

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