JP2018041677A - Positive electrode active material, positive electrode, and nonaqueous electrolyte power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a positive electrode active material which enables the increase in the discharge capacity of a nonaqueous electrolyte power storage device; a positive electrode having the positive electrode active material; and a nonaqueous electrolyte power storage device.SOLUTION: An embodiment of the present invention is a positive electrode active material (a) for a nonaqueous electrolyte power storage device, which comprises an oxide including lithium and cobalt, and having an antifluorite type crystal structure; the average crystallite size of the oxide calculated from peaks originating from (201)- and (222)-planes is 240 Å or less according to X-ray diffraction. Another embodiment of the invention is a positive electrode active material (b) for a nonaqueous electrolyte power storage device, which comprises LiCoOof which the average crystallite size calculated from peaks originating from (201)- and (222)-planes is 240 Å or less according to X-ray diffraction.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a positive electrode active material, a positive electrode, and a nonaqueous electrolyte storage element.

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

Various active materials are employed for the positive electrode and the negative electrode of the nonaqueous electrolyte storage element, and composite oxides are generally widely used as the positive electrode active material. Li ₆ CoO ₄ having a reverse fluorite type crystal structure has a large theoretical capacity of 977 mAh / g. Therefore, Li ₆ CoO ₄ is expected as one of the positive electrode active materials that can increase the capacity of the nonaqueous electrolyte storage element.

However, in the non-aqueous electrolyte storage element using this Li ₆ CoO ₄ , no report showing a discharge capacity of 200 mAh / g or more has been confirmed (see Patent Documents 1 and 2 and Non-Patent Documents 1 and 2). ). Regarding the nonaqueous electrolyte storage element using Li ₆ CoO ₄ , Patent Document 1 discloses that the initial discharge capacity is about 140 mAh / g, while Patent Document 2 does not describe the initial discharge capacity. The non-patent document 1 shows that the discharge capacity at the 10th cycle is 88 mAh / g, the non-patent document 1 shows that the initial discharge capacity is about 150 mAh / g, and the non-patent document 2 shows that the initial discharge capacity is 13 mAh / g. It is described that it is about g. Thus, although Li ₆ CoO ₄ has a large theoretical capacity itself, the discharge capacity of the nonaqueous electrolyte storage element using this Li ₆ CoO ₄ is not large at all.

JP-A-4-332480 JP 2003-68302 A

S. Narukawa, Y .; Takeda, M .; Nishijima, N .; Imanishi, O .; Yamamoto, M .; Tabuchi, Solid State Ionics, 122, 59-64 (1999). M.M. Noh, J. et al. Cho, J. et al. Electrochem. Soc. , 159, A1329-A1334 (2012).

  The present invention has been made based on the circumstances as described above, and an object of the present invention is to provide a positive electrode active material capable of increasing the discharge capacity of the nonaqueous electrolyte storage element, and a positive electrode and a non-electrode having the positive electrode active material. It is to provide a water electrolyte storage element.

  One embodiment of the present invention, which has been made to solve the above problems, is an oxide containing lithium and cobalt and having an inverted fluorite-type crystal structure, and has (201) plane and (222) plane in X-ray diffraction. It is the positive electrode active material (a) for nonaqueous electrolyte electricity storage elements whose average crystallite size of the said oxide calculated from the peak derived from is 240 or less.

Another aspect of the present invention is for a non-aqueous electrolyte energy storage device in which the average crystallite size calculated from peaks derived from the (201) plane and the (222) plane in X-ray diffraction is Li ₆ CoO ₄ of 240 Å or less. The positive electrode active material (b).

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

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

  ADVANTAGE OF THE INVENTION According to this invention, the positive electrode active material which can enlarge the discharge capacity of a nonaqueous electrolyte electrical storage element, the positive electrode which has this positive electrode active material, and a nonaqueous electrolyte electrical storage element can be provided.

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. 3 is an X-ray diffraction (XRD) spectrum of the positive electrode active materials of Examples 1 to 4 and Comparative Example 1. FIG.

  The positive electrode active material according to an embodiment of the present invention is an oxide containing lithium and cobalt and having an inverted fluorite-type crystal structure, and peaks derived from the (201) plane and the (222) plane in X-ray diffraction. This is a positive electrode active material (a) for a non-aqueous electrolyte electricity storage device in which the average crystallite size A of the above oxide calculated from the formula is 240 or less.

  By using the positive electrode active material (a), the discharge capacity of the nonaqueous electrolyte storage element can be increased. Although this reason is not certain, the following reason is guessed. In an oxide containing lithium and cobalt and having an inverted fluorite type crystal structure, ions such as lithium ions easily move at the interface between the crystallites. On the other hand, in the positive electrode active material (a), since the average crystallite size A is as small as 240 mm or less, there are many interfaces between crystallites. Thereby, in the said positive electrode active material (a), the electrical conductivity of ion increases and it is estimated that discharge capacity becomes large. In addition, according to the positive electrode active material (a), the charge / discharge cycle capacity retention rate of the nonaqueous electrolyte storage element (hereinafter also simply referred to as “capacity retention rate”), particularly the capacity when operating at a high voltage. A decrease in maintenance rate can be suppressed.

The “average crystallite size” is a value obtained by the Scherrer method using an XRD spectrum obtained by powder X-ray diffraction (XRD) measurement. The Scherrer method is a method of calculating the crystallite size by the following Scherrer equation.
D = Kλ / βcos θ
In the above formula, D is the crystallite size (Å), K is the Scherrer constant, λ is the wavelength of the X-ray used, β is the half width (rad), and θ is the Bragg angle (rad).

  Specifically, it is determined by the following method. A sample (oxide) powder is placed on a sealed sample plate in an argon atmosphere. The powder may be a mixture with other components that do not affect the measurement (for example, acetylene black). Next, an XRD spectrum of the oxide is obtained with an XRD apparatus (“Miniflex II” manufactured by Rigaku Corporation) equipped with an X-ray tube made of Cu (copper) and a high sensitivity detector DteX. Note that the source CuKα line, scanning range 2θ = 10−80 °, scanning speed 2 ° / min, and step width 0.02 °. The crystallite size is derived from the obtained XRD spectrum using analysis software (“PDXL” manufactured by Rigaku Corporation). The procedure for deriving the crystallite size is performed in accordance with the PDXL manual. In the analysis software, the crystallite size is calculated by the following method. K (Scherrer constant) is set to 0.94. λ (the wavelength of the used X-ray) is 1.54015 mm. β (half width) is derived by the peak top method. That is, the background intensity (cps) is subtracted from the intensity (cps) of each diffraction line, and the value (rad) obtained by converting the diffraction line spread (degree) of the portion where the intensity is ½ into a radian angle. θ (Bragg angle) is a value (rad) obtained by performing a radian transform on the Bragg angle (degree) corresponding to hkl = 201 and 222 described in the ICDD PDF. These values are introduced into the Scherrer equation, and the calculated value is defined as a crystallite size D (Å). An average value of two crystallite sizes corresponding to each Bragg angle ((201) plane and (222) plane) is defined as an average crystallite size A (Å).

The oxide is preferably Li ₆ CoO ₄ . By using Li ₆ CoO ₄ as an oxide containing lithium and cobalt and having an inverted fluorite-type crystal structure, the discharge capacity of the nonaqueous electrolyte storage element can be further increased.

The positive electrode active material according to another embodiment of the present invention is Li ₆ CoO ₄ having an average crystallite size A calculated from peaks derived from the (201) plane and the (222) plane in X-ray diffraction of 240 Å or less. It is a positive electrode active material (b) for a certain nonaqueous electrolyte electricity storage element.

By using the positive electrode active material (b), the discharge capacity of the non-aqueous electrolyte storage element can be increased, and a decrease in capacity retention rate can be suppressed. The reason why the above effect occurs is that, like the positive electrode active material (a), the average crystallite size A of Li ₆ CoO ₄ is reduced, and the presence of many interfaces between crystallites reduces the ion conductivity. Presumably due to the increase.

  The average crystallite size B calculated from the peaks derived from the (110) plane, (201) plane and (222) plane in the X-ray diffraction of the positive electrode active material (a) and the positive electrode active material (b) is 270 mm or less. Preferably there is. Thereby, the discharge capacity of the nonaqueous electrolyte storage element can be further increased. This average crystallite size B can be determined according to the method described above. That is, as the θ (Bragg angle), Bragg angles corresponding to hkl = 110, 201, and 222 are adopted, and three crystals corresponding to the Bragg angles ((111) plane, (201) plane, and (222) plane) are used. The average crystallite size B can be obtained by taking the average of the child sizes.

  The positive electrode which concerns on other one Embodiment of this invention is a positive electrode for nonaqueous electrolyte electrical storage elements which has the said positive electrode active material (a) or the said positive electrode active material (b). According to the positive electrode, the discharge capacity of the nonaqueous electrolyte storage element can be increased, and a decrease in capacity retention rate can be suppressed.

  A non-aqueous electrolyte storage element according to another embodiment of the present invention is a non-aqueous electrolyte storage element (hereinafter sometimes simply referred to as “storage element”) including the positive electrode. The power storage element has a large discharge capacity and can suppress a decrease in capacity maintenance rate.

In the non-aqueous electrolyte electricity storage device, the charge termination potential of the positive electrode during normal use is preferably 3.2 V (vs. Li / Li ⁺ ) or more and 4.5 V (vs. Li ^/ Li ⁺ ) or less. The power storage element can have a particularly large discharge capacity in the charge end potential range, and can suppress a decrease in capacity maintenance rate. Here, “during normal use” is a case where the nonaqueous electrolyte storage element is used under the recommended charging conditions or specified for the nonaqueous electrolyte storage element. When the charger for the battery is prepared, it refers to the case where the charger is used and the nonaqueous electrolyte storage element is used. For example, in a nonaqueous electrolyte storage element using graphite as a negative electrode active material, the positive electrode potential is about 4.1 V (vs. Li ^/ Li ⁺ ) when the end-of-charge voltage is 4.0 V, depending on the design. is there.

  Hereinafter, the positive electrode active material (a), the positive electrode active material (b), the positive electrode, and the nonaqueous electrolyte storage element according to an embodiment of the present invention will be described in order.

<Positive electrode active material (a)>
The positive electrode active material (a) is an oxide containing lithium and cobalt and having an inverted fluorite crystal structure. Note that the crystal structure of the oxide can be specified by a known analysis method based on the XRD spectrum.

  The oxide can contain elements other than lithium, cobalt, and oxygen. Examples of other elements include transition metal elements other than cobalt such as manganese, iron, nickel, and copper, metal elements other than transition metal elements such as magnesium and aluminum, and halogens such as fluorine. The transition metal element refers to an element that exists between the Group 3 element and the Group 11 element in the periodic table.

  In the oxide, the content ratio (atomic ratio) of cobalt in the total transition metal elements is preferably 50 mol% or more, more preferably 70 mol% or more, further preferably 90 mol% or more, and 99 mol%. There may be. On the other hand, the upper limit is preferably 100 mol%.

  In the above oxide, the content ratio (atomic ratio) of the transition metal element including lithium and cobalt and the other elements other than oxygen in the total element may be preferably 20 mol% or less, and may be 10 mol%. The following may be preferable, and 1 mol% or less may be preferable.

Specific examples of the oxide include Li ₆ Co _α M _1-α O ₄ (0 <α ≦ 1, M represents a transition metal element other than cobalt), Li ₅ Co _β Fe _1-β O ₄ (0 <Β <1), Li ₆ Co _γ Mn _1-γ O ₄ (0 <γ <1), and the like. Among these, Li ₆ Co _α M _1-α O ₄ is preferable. α is preferably 0.5 or more, more preferably 0.9 or more, and even more preferably 1. That is, as the oxide, Li ₆ CoO ₄ is most preferable.

  The upper limit of the average crystallite size A of the oxide calculated from the peaks derived from the (201) plane and the (222) plane in X-ray diffraction is 240Å, preferably 150Å, more preferably 120Å, 115% may be more preferred. By setting the average crystal size A to the above upper limit or less, the discharge capacity of the nonaqueous electrolyte storage element can be further increased, and a sufficient capacity retention rate can be exhibited.

  On the other hand, the lower limit of the average crystallite size A is not particularly limited, but is, for example, 10 、, preferably 30 、, more preferably 50 、, and still more preferably 100 Å. Further, the lower limit may be preferably 120 、, and may be preferably 150 Å. According to the end-of-charge potential or the like, the discharge capacity retention rate may be higher when the average crystallite size A is relatively large.

  The upper limit of the average crystallite size B of the oxide calculated from the peaks derived from the (110) plane, (201) plane and (222) plane in X-ray diffraction is preferably 270、２, more preferably 240Å, and 210Å. More preferably, 190 Å is even more preferable, and 150 Å is even more preferable. By setting the average crystal size B to be equal to or less than the above upper limit, the discharge capacity of the nonaqueous electrolyte storage element can be further increased, and a sufficient capacity retention rate can be exhibited.

  On the other hand, the lower limit of the average crystallite size B is not particularly limited, but is, for example, 10 、, preferably 30 、, more preferably 50 、, and still more preferably 100 Å. In addition, the lower limit may be preferably 140 、 or 180 Å. According to the end-of-charge potential or the like, the discharge capacity retention rate may be higher when the average crystallite size B is relatively large.

The positive electrode active material can be produced by a known method. For example, Li ₆ CoO ₄ can be synthesized by mixing Li ₂ O and CoO in a molar ratio of 3: 1 and firing in an inert gas atmosphere. The average crystallite size (average crystallite size A and average crystallite size B) can be adjusted by, for example, pulverizing after firing. This pulverization treatment can be performed using a known device such as a mortar or a ball mill. By such a pulverization process, it is presumed that at least a part of the crystallites is destroyed and refined, and the average crystallite size is reduced.

<Positive electrode active material (b)>
The positive electrode active material (b) is Li ₆ CoO ₄ having an average crystallite size A calculated from peaks derived from the (201) plane and the (222) plane in X-ray diffraction of 240 Å or less. The positive electrode active material (b) is as described above as the positive electrode active material (a) whose oxide is Li ₆ CoO ₄ . However, the crystal structure of the positive electrode active material (b) is not limited to the inverted fluorite type, and may have any crystal structure. Moreover, the crystal structure of the positive electrode active material (b) may change with repeated charge and discharge.

<Positive electrode>
The said positive electrode is a positive electrode for nonaqueous electrolyte electrical storage elements which has the said positive electrode active material (a) or the said positive electrode active material (b) 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 (a) or the positive electrode active material (b) described above. As said positive electrode active material, well-known positive electrode active materials other than the said positive electrode active material (a) and positive electrode active material (b) may be contained. The content ratio of the positive electrode active material (a) and the positive electrode active material (b) in the total positive electrode active material is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 90% by mass or more, 99 A mass% or more is even more preferable. By increasing the content ratios of the positive electrode active material (a) and the positive electrode active material (b), the discharge capacity and capacity retention rate of the nonaqueous electrolyte storage element can be sufficiently increased. The content rate of the said positive electrode active material in the said positive electrode active material layer can be 30 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 battery performance. 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 nonaqueous electrolyte secondary battery will be described as an example of a nonaqueous electrolyte storage element. The positive electrode and the negative electrode usually form an electrode body that is alternately superposed by stacking or winding via a separator. This electrode body is housed in a case, and the case is filled with a nonaqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. Moreover, as said case, the well-known aluminum case, resin case, etc. which are normally used as a case of a nonaqueous electrolyte secondary battery can be used.

(Positive electrode)
The positive electrode included in the power storage element 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) and amorphous 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, EMC is 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.

(Charge end potential)
The nonaqueous electrolyte secondary battery (storage element) can be used at a relatively high operating voltage. For example, the positive electrode potential at the charge voltage at the time of normal use (charging end potential) may be a noble than 3.2V (vs.Li/Li ^+), from 3.4V (vs.Li/Li ⁺⁾ It can also be noble, can be noble from 3.6 V (vs. Li ^/ Li ⁺ ), and can be noble from 4.0 V (vs. Li ^/ Li ⁺ ). On the other hand, the upper limit of the positive electrode potential in the end-of-charge voltage during normal use is, for example, 5.0 V (vs. Li ^/ Li ⁺ ), and may be 4.5 V (vs. Li ^/ Li ⁺ ). .0V may be a (vs.Li/Li ^+), it may be a 3.6V (vs.Li/Li ^+).

  The power storage element can be manufactured by a known method. 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 battery container, and a step of injecting the nonaqueous electrolyte into the battery container. After the injection, the storage element can be obtained by sealing the injection port.

<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, the intermediate layer may not be provided in the positive electrode or the negative electrode. Moreover, 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 accommodated in a battery container 3 (case). 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 (a) or the positive electrode active material (b) 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.

[Examples 1 to 4 and Comparative Example 1]
(Synthesis of Li ₆ CoO ₄ )
Li ₂ O and CoO were mixed at a molar ratio of 3: 1 and baked at 700 ° C. for 12 hours in an N ₂ atmosphere to synthesize Li ₆ CoO ₄ . Under an argon atmosphere, Li ₆ CoO ₄ and acetylene black were mixed at a mass ratio of 1: 1, put into a pot made of tungsten carbide having an inner volume of 80 mL containing 250 g of tungsten carbide balls having a diameter of 5 mm, and capped. . This was set in a planetary ball mill ("Pulversette 5" manufactured by FRITSCH), and dry pulverized at a revolution speed of 200 rpm for 20 minutes to prepare a mixture of the positive electrode active material of Example 1 and acetylene black. For Examples 2, 3 and 4, the grinding time was 1 hour, 2 hours and 3 hours, respectively. For Comparative Example 1, Li ₆ CoO ₄ and acetylene black were mixed at a mass ratio of 1: 1 in an argon atmosphere, and pulverized in an agate mortar, whereby the positive electrode active material of Comparative Example 1 and acetylene black were A mixture of was prepared.

(Measurement of average crystallite size)
About the obtained positive electrode active material, XRD measurement was performed by said method in the mixed state with acetylene black, and the average crystallite size was calculated | required. The obtained XRD spectrum is shown in FIG. From the XRD spectrum, it was confirmed that the obtained positive electrode active material had a reverse fluorite type crystal structure. In addition, Table 1 shows the obtained average crystallite size. The average crystallite size A is an average value of two crystallite sizes calculated from peaks derived from the (201) plane and the (222) plane. The average crystallite size B is an average value of three crystallite sizes calculated from peaks derived from the (110) plane, the (201) plane, and the (222) plane.

(Production of electricity storage element (evaluation cell))
A solution in which PVDF powder was dissolved in an NMP solvent was added to the mixture of each of the positive electrode active materials obtained in Examples 1 to 4 and Comparative Example 1 and acetylene black to prepare a positive electrode mixture paste. In this positive electrode mixture paste, the mass ratio of the positive electrode active material, acetylene black, and PVDF was 40:40:20. The positive electrode mixture paste was applied to a mesh-like aluminum substrate and dried to obtain a positive electrode.
In addition, LiPF ₆ was dissolved at a concentration of 1M in a non-aqueous solvent in which EC, DMC, and EMC 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.

(Charge / discharge cycle test)
The obtained evaluation cell was subjected to a charge / discharge cycle test of 9 cycles in an environment of 20 ° C. Charging ^{potential, 3.2V (vs.Li/Li +), 3.4V} (vs.Li/Li +), 3.6V (vs.Li/Li +) or 4.5V (vs.Li/Li ⁺ ). The discharge potential was 1.0 V (vs. Li ^/ Li ⁺ ). The current density was 50 mA / g, and constant current (CC) charge / discharge was performed. Table 1 shows the measured discharge capacity (initial discharge capacity) of the first cycle and the ratio of the discharge capacity of the ninth cycle to the initial discharge capacity (capacity maintenance ratio) in the charge / discharge cycle test corresponding to each charge potential.

  As shown in Table 1, it can be seen that the storage elements of Examples 1 to 4 have a large discharge capacity at the first cycle and a high capacity retention rate. In particular, it can be seen that the discharge capacity tends to increase as the average crystallite size decreases. In addition, regarding the capacity maintenance rate, in Comparative Example 1, the capacity maintenance rate was greatly reduced particularly in the charge / discharge cycle test at 4.5 V, whereas in each example, the decrease in the capacity maintenance rate was suppressed. You can see that

  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 (7)

An oxide containing lithium and cobalt and having an inverted fluorite-type crystal structure;
The positive electrode active material for nonaqueous electrolyte electrical storage elements whose average crystallite size of the said oxide computed from the peak originating in the (201) plane and (222) plane in X-ray diffraction is 240 or less. The positive electrode active material according to claim 1, wherein the oxide is Li ₆ CoO ₄ . A positive electrode active material for a non-aqueous electrolyte storage element, in which an average crystallite size calculated from peaks derived from the (201) plane and the (222) plane in X-ray diffraction is Li ₆ CoO ₄ of 240Å or less.   4. The positive electrode active material according to claim 1, wherein an average crystallite size calculated from peaks derived from the (110) plane, the (201) plane, and the (222) plane in X-ray diffraction is 270 μm or less. 5. material.   The positive electrode for nonaqueous electrolyte electrical storage elements which has a positive electrode active material of any one of Claims 1-4.   A nonaqueous electrolyte storage element comprising the positive electrode according to claim 5. The nonaqueous electrolyte storage element according to claim 6, wherein the charge termination potential of the positive electrode during normal use is 3.2 V (vs. Li / Li ⁺ ) or more and 4.5 (vs. Li ^/ Li ⁺ ) or less.

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