JP6153802B2 - Electricity storage element - Google Patents

Description

  The present invention relates to a storage element that is charged and discharged by insertion and extraction of lithium ions, such as a lithium ion secondary battery and a lithium ion capacitor.

  In recent years, lithium ion secondary batteries have attracted attention from the viewpoint of high energy density. By the way, in the lithium ion battery, different active materials are used for the positive electrode and the negative electrode. That is, a material having a noble oxidation-reduction potential associated with lithium insertion is used as a positive electrode, and a base material is used as a negative electrode. Thus, since the terminal electrode of a battery has polarity, in mounting of a battery, it is necessary to identify and perform polarity. In particular, in the case of a small battery having a side of 5 mm or less, the manufacturing cost and work load in mounting are large. With respect to such a problem, in Patent Document 1 (Japanese Patent Laid-Open No. 2011-146202), the battery cell is arranged so that the positive electrode of one battery cell and the negative electrode of the other battery cell are connected to the same terminal electrode. Nonpolar battery cells, that is, battery cells that do not require identification of polarity in mounting, are disclosed. However, in such a configuration, since the positive electrode of one battery cell and the negative electrode of another battery cell are short-circuited, it is considered that the loss increases.

By the way, spinel type lithium manganate (LiMn ₂ O ₄ ) (hereinafter sometimes abbreviated as LMO) can release lithium ions out of the structure or take them into the structure depending on the applied voltage. (See, for example, Non-Patent Document 1 (J. Electrochem. Soc. 1995, Volume 142, Issue 6, P1742-1746)). Therefore, a lithium ion secondary battery can be constituted by sandwiching an electrolyte between two electrodes made of this compound. For example, Patent Document 2 (Japanese Patent Application Laid-Open No. 2011-129474) discloses lithium in which first electrode layers and second electrode layers each including the same active material are alternately stacked via an electrolyte region. An ion secondary battery is disclosed, which describes that spinel lithium manganate can be used as an active material. In this document, an electrode layer is produced by simultaneously firing an Ag / Pd current collector and lithium manganate, but stable cycle characteristics are not obtained.

  On the other hand, Patent Document 3 (Japanese Patent Application Laid-Open No. 2010-212260) discloses a positive electrode active material containing a large number of crystal particles including primary particles made of spinel lithium manganate and a bismuth compound containing bismuth. It is preferable to further include secondary particles in which a plurality of primary particles are connected in a plane. On the other hand, a lithium metal plate is used as the negative electrode.

JP 2011-146202 A JP 2011-129474 A JP 2010-212260 A JP 2011-051800 A JP 2011-073962 A JP 2011-073963 A

J. Electrochem. Soc. 1995, Volume142, Issue 6, P1742-1746

  The present inventors are now able to identify polarity by using an electrode including an active material plate mainly composed of a plurality of spinel type lithium manganate single crystal particles that are two-dimensionally connected to each other. It was found that a non-polar storage element capable of bidirectional charge and discharge with improved cycle characteristics can be provided while having an unnecessary and extremely simple configuration.

  Accordingly, an object of the present invention is to provide a non-polar storage element that can be charged and discharged bidirectionally with improved cycle characteristics, while having a very simple configuration that does not require polarity identification.

According to one aspect of the invention,
A first electrode comprising: a current collecting layer; and an active material plate comprising a plurality of spinel type lithium manganate single crystal particles provided on at least one side of the current collecting layer and mainly connected two-dimensionally And a second electrode;
An electrolyte provided between the first electrode and the second electrode so as to be in contact with the active material plate and having lithium ion conductivity;
Is provided.

It is a schematic cross section which shows the structure of the electrical storage element by this invention. 1 is a schematic cross-sectional view showing an example of a stacked storage element according to the present invention. 3 is a SEM photograph of the LMO ceramic plate produced in Example 1.

Storage Element FIG. 1 schematically shows the configuration of a storage element according to the present invention. A power storage device 10 shown in FIG. 1 includes a first electrode 12, a second electrode 14, and an electrolyte 16. The first electrode 12 includes a current collecting layer 12a and an active material plate 12b provided on at least one surface of the current collecting layer. Similarly, the second electrode 14 includes a current collecting layer 14a and an active material plate 14b provided on at least one surface of the current collecting layer. The active material plates 12b and 14b are mainly composed of a plurality of spinel type lithium manganate single crystal particles S that are two-dimensionally connected. The electrolyte 16 is provided between the first electrode 12 and the second electrode 14 so as to be in contact with the active material plates 12b and 14b, and has lithium ion conductivity. The electrolyte 16 shown in FIG. 1 is a solid electrolyte, but may be in the form of an electrolytic solution.

  Thus, the first electrode 12 and the second electrode 14 have no difference in configuration, and are nonpolar electrodes that can function as either a positive electrode or a negative electrode depending on the charged state or applied voltage. That is, when the electrodes 12 and 14 capable of inserting and extracting lithium ions are used as nonpolar electrodes and combined with the lithium ion conductive electrolyte 16, the lithium ions are bidirectional between the electrodes 12 and 14 according to the potential difference between the electrodes. It becomes possible to move to. This is because the spinel type lithium manganate constituting the active material plates 12b and 14b in the first electrode 12 and the second electrode 14 has a reduction in redox potential due to occlusion of lithium ions and oxidation due to desorption of lithium ions. This is because the reduction potential increases. As described above, charging / discharging can be performed by changing the oxidation-reduction potential in accordance with insertion and extraction of lithium ions. Accordingly, by interposing the electrolyte 16 having lithium ion conductivity between the electrodes 12 and 14 having such properties, bidirectional charge / discharge can be performed regardless of the positive and negative electrodes, and the function as a nonpolar storage element is achieved. Is secured. That is, in charging, when a voltage is applied between the first electrode 12 and the second electrode 14 that are initially derived from the basic composition of the active material and have the same lithium ion content, the voltage is reduced from the high potential side electrode through the solid electrolyte. As a result of the movement of lithium ions to the potential electrode, charge is accumulated. On the other hand, in the discharge, lithium ions move from the low potential side electrode to the high potential electrode through the solid electrolyte. As a result, both electrodes become equipotential and the potential difference becomes zero. Since the first electrode 12 and the second electrode 14 have no difference in configuration, charges are accumulated and discharged according to the same principle even when charged in the opposite direction.

Therefore, assuming the active material basic composition of LiMn ₂ O _{4, the} composition of the active material plate 12b of the first electrode is represented by Li _1−α Mn ₂ O ₄ (where 0 <α ≦ 1). The composition of the active material plate 14b of the second electrode is expressed as Li _{1 + α} Mn ₂ O ₄ and the composition of the first electrode is expressed as Li _{1 + α} Mn ₂ O ₄ (where 0 <α ≦ 1). Sometimes the composition of the second electrode can be expressed as Li _1-α Mn ₂ O ₄ . The above-described charging / discharging will be described using this expression. First, the potential difference E of the electric storage element 10 at the time of completion of discharge is 0 (that is, both electrodes have the same equilibrium potential E _eq ). Are the same 0 for both the first electrode 12 and the second electrode 14. When the storage element 10 is charged, the equilibrium potential of the first electrode 12 decreases to E _min and the amount of lithium increases to 1 + α by the supply and insertion of lithium ions, while the equilibrium potential of the second electrode 14 increases to E _{As a result} of increasing to _max and decreasing the amount of lithium to 1−α due to desorption and release of lithium ions, a potential difference E = E _max −E _min > 0 is generated in the power storage element 10. When charging is performed in the opposite direction to this charging, the relationship between the potential and the amount of lithium in the first electrode 12 and the second electrode 14 is reversed from that in the previous charging, and is opposite to the power storage element 10. A potential difference E = E _min −E _max <0 occurs. As described above, the power storage device 10 according to the present invention can be charged and discharged bidirectionally while having a very simple configuration with no polarity. In particular, lithium manganate (LiMn ₂ O ₄ ) is bi-directional in that it can occlude lithium until it has a composition of Li ₂ Mn ₂ O ₄ , while it can release Li until it has a composition of Mn ₂ O _4. It can be said that it is extremely suitable for charging and discharging. In addition, since it is not necessary to adopt a configuration in which the positive and negative electrodes are short-circuited as disclosed in Patent Document 1, it is possible to charge and discharge with little loss. In addition, since it is not necessary to identify the polarity in mounting, the manufacturing cost and workload can be reduced.

Here, when lithium manganate (LiMn ₂ O ₄ ) takes in Li and changes to Li _{1 + α} Mn ₂ O ₄ and releases Li and changes to Li _1−α Mn ₂ O ₄ , the lattice volume It has the characteristic that the amount of change of is large. In particular, the change in the lattice volume when taking in Li and changing to Li _{1 + α} Mn ₂ O ₄ is particularly large because it involves a change in crystal structure from cubic to tetragonal. For this reason, in a conventional electrode having a structure in which lithium manganate powder is mixed with a conductive additive, the contact failure between the active material powder and the conductive additive (that is, the active material and the conductive additive are reduced) by repeated charge / discharge cycles. There is a problem that the discharge capacity is greatly reduced. In this regard, the active material plates 12b and 14b used in the electricity storage device of the present invention are mainly composed of a plurality of spinel type lithium manganate single crystal particles S that are two-dimensionally connected as shown in FIG. ing. In this configuration, each single crystal particle S formed by bonding to the current collecting layers 12a and 14a at one end contacts the electrolyte 16 at the other end. That is, the current collecting layers 12a, 14a and the electrolyte 16 are connected through the single crystal particles S arranged in a single layer so that lithium ion conduction is possible. That is, the thicknesses of the active material plates 12b and 14b substantially coincide with the grain sizes in the thickness direction of the single crystal particles S. In that sense, it can be said that the active material plates 12b and 14b composed of such a plurality or a large number of single crystal particles S have a structure in which there is substantially or almost no grain boundary due to the overlapping of particles in the thickness direction. In this structure, lithium ion conduction is not easily inhibited by grain boundaries. In addition, in the configuration of the present invention, since almost all the single crystal particles S constituting the active material plates 12b and 14b are bonded to the current collecting layers 12a and 14a (preferably by sintering), the volume changes. Even if it does not peel. In addition, since a grain boundary that easily breaks due to the volume change exists only in a direction substantially perpendicular to the electrode, even if it breaks, the lithium ion conduction path between the current collecting layers 12a and 14a and the electrolyte 16 Is not divided at the grain boundaries, and therefore has no effect on current collection. Due to these various factors, the power storage device of the present invention can greatly improve the cycle characteristics while having a very simple configuration that does not require polarity identification.

The first electrode and the second electrode first electrode 12 include a current collecting layer 12a and an active material plate 12b provided on at least one surface of the current collecting layer. Similarly, the second electrode 14 includes a current collecting layer 14a and an active material plate 14b provided on at least one surface of the current collecting layer. The active material plates 12b and 14b are preferably configured to be surely prevented from being peeled off due to volume changes by being bonded to the current collecting layers 12a and 14a by sintering.

  The current collection layers 12a and 14a are current collector layers mainly made of a conductor, and may be in the form of a plate, foil, or film. The material of the current collecting layer is a conductor such as stainless steel, gold, platinum, palladium, copper, nickel, silver, and alloys thereof, and can be integrally fired at the same time as the active material plates 12b and 14b. However, a metal foil may be processed. The material of the current collecting layer is not limited to metal, and may be a composite of lithium ion conductor and electron conductor. The dimensions of the current collecting layers 12a and 14a are not particularly limited, but the thickness is preferably 0.1 to 20 μm, more preferably 0.2 to 10 μm, and still more preferably 1 to 1 in terms of the current collecting capacity per unit area. 5 μm.

  The active material plates 12b and 14b are mainly composed of a plurality of spinel type lithium manganate single crystal particles S that are two-dimensionally connected. In this active material plate, there is a grain growth of crystal particles that does not reach the thickness of the active material plate during grain growth. Is included. That is, the thicknesses of the active material plates 12b and 14b substantially coincide with the grain sizes in the thickness direction of the single crystal particles S. In that sense, it can be said that the active material plates 12b and 14b have a structure in which there is substantially or almost no grain boundary due to particle overlap in the thickness direction. In this active material plate, the portion containing only one crystal particle is preferably 70% or more, more preferably 80% or more, and more preferably 90% or more in terms of the area ratio of the active material plate. Preferably, it is about 100% ideally.

  The spinel type lithium manganate single crystal particle S is a particle made of a spinel structure lithium manganate compound containing lithium and manganese as constituent elements, and a plurality of single crystal particles S are mainly connected two-dimensionally. Thus, one active material plate 12b, 14b is formed. The active material in such a form is known as a positive electrode active material, and is disclosed as a positive electrode active material in, for example, Patent Document 3 described above. However, in the present invention, the active material plates 12b and 14b constitute nonpolar electrodes that can function as either positive or negative electrodes according to the charged state or applied voltage.

The single crystal particles S constituting the active material plates 12b and 14b are made of a lithium manganate compound. In the present invention, the lithium manganate-based compound may be a compound having a basic composition LiMn ₂ O _{4 of} lithium manganate or a similar composition as long as it has a spinel structure. Specifically, the single crystal particle S has a general formula:
LiM _x Mn _2-x O ₄ (1)
(Wherein, M is at least one selected from the group consisting of Li, Fe, Ni, Mg, Zn, Al, Co, Cr, Si, Sn, P, V, Sb, Nb, Ta, Mo and W. It is a substitution element, and may contain at least one selected from the group consisting of Ti, Zr and Ce together with the at least one element, and 0 ≦ x <0.55, preferably 0 <x <0.4. More preferably 0.05 <x <0.15)
It is preferable to have a composition represented by: This is because Li is +1 valence, Fe, Mn, Ni, Mg and Zn are +2 valence, B, Al, Co and Cr are +3 valence, Si, Ti, Sn, Zr and Ce are +4 valence, P, V, Sb This is because Nb and Ta become +5 valence, and Mo and W become +6 valent ions, and both elements are theoretically dissolved in LiMn ₂ O ₄ . In addition, Co and Sn may be +2 valence, Fe, Sb and Ti may be +3 valence, Mn may be +3 or +4 valence, and Cr may be +4 or +6 valence. Therefore, the substitution element M may exist in a state having a mixed valence. In addition, oxygen is not necessarily represented by the above chemical formula, and may be deficient or excessive in the range for maintaining the crystal structure.

When Mn is substituted with Li in the general formula (1) (when Li is excessive), the chemical formula of the lithium manganate compound is Li _{(1 + x)} Mn _(2-x) O ₄ . Note that the value of x is preferably 0.05 to 0.15. When the value of x is 0.05 or more, the effect of improving the cycle characteristics due to the replacement of Mn with Li is sufficiently obtained. Moreover, even if the value of the lattice strain (η) is small, the deterioration of the cycle characteristics can be avoided. On the other hand, when the value of x is 0.15 or less, the initial capacity can be increased to, for example, 100 mAh / g or more.

On the other hand, when Mn is substituted with a substitution element M other than Li in the general formula (1), the Li / Mn ratio is 1 / (2-X) (that is, the Li / Mn ratio> 0.5). . When lithium manganate satisfying the relationship of Li / Mn> 0.5 is used, the crystal structure is further stabilized as compared with the case where lithium manganate having a chemical formula represented by LiMn ₂ O ₄ is used. A lithium secondary battery having excellent cycle characteristics at high temperatures can be produced.

The single crystal particle S is composed of a lithium manganate compound (for example, LiNi _0.5 Mn _1.5 O ₄ ) in which 25 to 55 mol% of the total Mn is substituted with Ni, Co, Fe, Cu, Cr, or the like. It may be a particle. By using such a lithium manganate compound, the obtained positive electrode active material is not only a positive electrode active material capable of producing a lithium secondary battery with improved high-temperature cycle characteristics, but also has a high charge / discharge potential. Since the energy density can be increased, a lithium secondary battery having a so-called 5V class electromotive force can be manufactured.

The active material plates 12b and 14b may contain a bismuth compound. The content ratio of bismuth contained in the bismuth compound is 0.005 to 0.5 mol%, preferably 0.01 to 0.2 mol%, based on manganese contained in the lithium manganate compound. More preferably, it is 0.01-0.1 mol%. When it is 0.005 mol% or more, the cycle characteristics at high temperatures are excellent. On the other hand, when it is 0.5 mol% or less, a decrease in the initial capacity can be avoided. The content ratio of bismuth is calculated based on the result of quantitative determination of lithium, manganese, and bismuth using an ICP (inductively coupled plasma) emission spectrometer (trade name “ULTIMA2”, manufactured by HORIBA, Ltd.). can do. Examples of the bismuth compound include bismuth oxide and a compound of bismuth and manganese, and a compound of bismuth and manganese is preferable. Examples of bismuth and manganese compounds include compounds represented by the chemical formulas of Bi ₂ Mn ₄ O ₁₀ and Bi ₁₂ MnO ₂₀ . Among these, a compound represented by the chemical formula of Bi ₂ Mn ₄ O ₁₀ is particularly preferable. The bismuth compound can be identified by X-ray diffraction measurement (hereinafter also referred to as “XRD measurement”) or electron beam microanalysis (hereinafter also referred to as “EPMA measurement”). It is speculated that bismuth compounds, especially bismuth and manganese compounds, have the effect of improving the cycle characteristics by suppressing the elution of Mn from the surface of single crystal particles or from grain boundaries where a plurality of single crystal particles are interconnected. The Therefore, it is preferable that the bismuth compound exists in either the surface of the single crystal particle and the grain boundary part where the plurality of single crystal particles are connected to each other. The presence of the bismuth compound can be confirmed using, for example, an electron microscope (trade name “JSM-6390”, manufactured by JEOL Ltd.).

  The active material plates 12b and 14b typically have a plate shape and the dimensions thereof are not particularly limited, but the thickness is preferably 0.1 to 300 μm from the viewpoint of the active material capacity per unit area. More preferably, it is 10-200 micrometers, More preferably, it is 20-100 micrometers.

  According to a preferred embodiment of the present invention, as shown in FIG. 1, the active material plates 12b and 14b are provided only on one side of the current collecting layers 12a and 14a, whereby the current collecting layer is configured as an external current collecting layer. It becomes. Such an electrode with an external current collecting layer is suitable as an electrode located on the outer surface of a unit cell type power storage element 10 as shown in FIG. 1 or a stacked type power storage element 20 as shown in FIG. 2 described later.

  According to another preferred embodiment of the present invention, active material plates are provided on both sides of the current collecting layer of at least one of the first electrode and the second electrode, whereby the current collecting layer is configured as an internal current collecting layer. May be. For example, as shown in a power storage element 20 of FIG. 2 to be described later, two active material plates 12b ′ and 12b ′ are provided on both sides of the current collecting layer 12a ′, and 2 on both sides of the current collecting layer 14a ′. One active material plate 14b ′, 14b ′ may be provided, whereby each of the current collecting layers 12a ′, 14a ′ may be configured as an internal current collecting layer. Such electrodes 12 ′ and 14 ′ with an internal current collecting layer are suitable as electrodes positioned inside the stacked storage element 20 as shown in FIG. 2.

  The internal current collecting layer may have at least one opening, and the opening may be filled with spinel type lithium manganate single crystal particles, whereby the single crystal particles are bonded through the opening. Therefore, the adhesiveness with the current collecting layer can be further improved. Therefore, it is preferable that a plurality or a plurality of openings are scattered throughout the current collecting layer. In addition, the electrode with the internal current collecting layer provided with the opening is configured so that lithium ions can move between both surfaces via the single crystal particles filled in the opening. Regardless of the type of storage element, it can also be used as an electrode located on the outer surface of the storage element. The shape of such an opening is not particularly limited, and may be a lattice shape, a mesh shape, a structure having innumerable fine holes, or the like, but is preferably a lattice shape. Where the openings need to be filled with an active material, the grid shape makes it easy to fill the active material, as well as ensuring the flatness of the current collector, making the distance between the electrodes constant, Electric field concentration is less likely to occur.

The electrolyte electrolyte 16 is an electrolyte having lithium ion conductivity, and may be a solid electrolyte as shown in FIG. 1 or an electrolyte solution in which the electrolyte is dissolved. For example, a non-aqueous solvent based electrolyte in which an electrolyte salt such as a lithium salt is dissolved in a non-aqueous solvent such as an organic solvent is preferably used because of its electrical characteristics and ease of handling. However, a polymer electrolyte, a gel electrolyte, an organic solid electrolyte, or an inorganic solid electrolyte can also be used without any problem as an electrolyte. For example, by using an inorganic solid electrolyte, it is possible to configure an all-solid power storage element that does not leak and has high safety. When the electromotive force is 1.2 V or less, an aqueous electrolyte can also be used.

  The solvent for the non-aqueous electrolyte is not particularly limited, but for example, chain esters such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and methyl propion carbonate; dielectric constants such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate High cyclic esters; mixed solvents of chain esters and cyclic esters; and the like, and mixed solvents with cyclic esters having chain esters as the main solvent are particularly suitable.

As the electrolyte salt to be dissolved in the solvent described above when the preparation of the non-aqueous electrolyte, for _{example, LiClO 4, LiPF 6, LiBF} 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiCF 3 CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN (RfSO ₂ ) (Rf′SO ₂ ), LiC (RfSO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (n ≧ 2), LiN (RfOSO ₂ ) ₂ (wherein Rf and Rf ′ are fluoroalkyl groups) and the like can be used. These may be used alone or in combination of two or more. Among the above electrolyte salts, a fluorine-containing organic lithium salt having 2 or more carbon atoms is particularly preferable. This is because the fluorine-containing organic lithium salt is highly anionic and easily separates ions, and thus is easily dissolved in the above-mentioned solvent. The concentration of the electrolyte salt in the nonaqueous electrolytic solution is not particularly limited, but is preferably 0.3 mol / l or more, more preferably 0.4 mol / l or more, and more preferably 1.7 mol / l or less. Is 1.5 mol / l or less.

Preferred examples of the inorganic solid electrolyte include at least one selected from the group consisting of garnet ceramic materials, nitride ceramic materials, perovskite ceramic materials, sulfide ceramic materials, phosphate ceramic materials, and zeolite materials. Can be mentioned. Examples of garnet ceramic material, Li-La-Zr-O-based material _{(specifically,} such as _{Li 7 La 3 Zr 2 O 12} ), the Li-La-Ta-O-based material (specifically, Li ₇ La ₃ Ta ₂ O ₁₂ etc.) can be used, and those described in Patent Documents 4 to 6 can also be used. Examples of nitride ceramic materials include Li ₃ N, LiPON, and the like. Examples of the perovskite-based ceramic material include Li-La-Zr-O-based materials (specifically, LiLa _1-x Ti _x O ₃ (0.04 ≦ x ≦ 0.14) and the like). Examples of sulfide-based ceramic materials include Li ₂ S—P ₂ S ₅ , Li ₂ S—P ₂ S ₃ , Li ₂ S—P ₂ S ₃ —P ₂ S ₅ , Li ₂ S—SiS ₂ , LiI. _{-Li 2 S-P 2 S 5} , LiI-Li 2 S-SiS 2 -P 2 S 5, Li 2 S-SiS 2 -Li 4 SiO 4, Li 2 S-SiS 2 -Li 3 PO 4, Li 3 _{PS 4 -Li 4 GeS 4, Li} 3.4 P 0.6 Si 0.4 S 4, Li 3.25 P 0.25 Ge 0.76 S 4, Li 4-x Ge 1-x P x S 4 , Li ₇ P ₃ S _{11 and the} like. Examples of phosphoric acid-based ceramic materials include Li-Al-Ti-PO, Li-Al-Ge-PO, and Li-Al-Ti-Si-PO (specifically, Li _{1 + x + y al x Ti 2-x Si y} P 3-y O 12 (0 ≦ x ≦ 0.4,0 <y ≦ 0.6) , and the like).

A particularly preferable lithium ion conductive inorganic solid electrolyte is a garnet-based ceramic material. In particular, an oxide sintered body having a garnet type or a garnet type-like crystal structure containing Li, La, Zr and O is excellent in sinterability and easily densified, and has high ionic conductivity. Therefore, it is preferable. A garnet-type or garnet-like crystal structure of this type of composition is called an LLZ crystal structure, and is referred to as an X-ray diffraction file No. of CSD (Cambridge Structural Database). It has an XRD pattern similar to 422259 (Li ₇ La ₃ Zr ₂ O ₁₂ ). In addition, No. Compared to 422259, the constituent elements are different and the Li concentration in the ceramics may be different, so the diffraction angle and the diffraction intensity ratio may be different. The molar ratio Li / La of Li to La is preferably 2.0 or more and 2.5 or less, and the molar ratio Zr / La to La is preferably 0.5 or more and 0.67 or less. This garnet-type or garnet-like crystal structure may further comprise Nb and / or Ta. That is, by replacing a part of Zr of LLZ with one or both of Nb and Ta, the conductivity can be improved as compared with that before the substitution. The substitution amount (molar ratio) of Zr with Nb and / or Ta is preferably set such that the molar ratio of (Nb + Ta) / La is 0.03 or more and 0.20 or less. The garnet-based oxide sintered body preferably further contains Al and / or Mg, and these elements may exist in the crystal lattice or may exist in other than the crystal lattice. The addition amount of Al is preferably 0.01 to 1% by mass of the sintered body, and the molar ratio Al / La to La is preferably 0.008 to 0.12. The addition amount of Mg is preferably 0.01 to 1% by mass or more, and more preferably 0.05 to 0.30% by mass. It is preferable that the molar ratio Mg / La of Mg to La is 0.0016 to 0.07. Such LLZ-based ceramics can be manufactured according to a known technique as described in Patent Documents 4 to 6, or by appropriately modifying it.

  The solid electrolyte 16 typically has a plate-like shape, and its dimensions are not particularly limited, but the thickness is preferably 0.005 to 5 mm, more preferably from the viewpoint of charge / discharge rate characteristics and mechanical strength. 0.01 to 2 mm, more preferably 0.05 to 1 mm, and the size of the plate surface is preferably 0.2 mm × 0.2 mm to 500 mm × 500 mm, more preferably from the viewpoint of charge / discharge capacity and mechanical strength. Is 0.5 mm × 0.5 mm to 200 mm × 200 mm.

Power storage device 10 shown in stacked battery device Figure 1 shows an example of a storage element of the unit cell type having a first electrode 12 and the second electrode 14 of the pair, a plurality of the storage element via the collector You may be comprised as a laminated | stacked electrical storage element in which two or more were laminated | stacked. For example, as shown in FIG. 2, a plurality of at least one of the first electrode 12 and the second electrode 14 (both in FIG. 2) are provided, and the first electrode 12, 12 ′ and the second electrode 14, 14 are provided. 'Are alternately stacked via the electrolyte 16, and at least the electrodes 12 ′ and 14 ′ located inside the electricity storage device 20 have active material plates 12 b ′ and 14 b ′ on both surfaces of the current collecting layers 12 a ′ and 14 a ′. It is preferable that the current collecting layers 12a ′ and 14a ′ are configured as internal current collecting layers. In this case, the internal current collecting layers 12a ′ and 14a ′ may have at least one opening, and the opening may be filled with spinel type lithium manganate single crystal particles. In the electricity storage element 20, the electrodes 12 and 14 located on the outer surface are provided with the active material plates 12b and 14b only on one side of the current collecting layers 12a and 14a, whereby the current collecting layers 12a and 14a serve as external current collecting layers. Although configured, an electrode with an internal current collecting layer having an opening can also be used as an electrode positioned on the outer surface of the stacked power storage element 20. This is because lithium ions can move between both surfaces via single crystal particles (active material) filled in the opening.

  With such a stacked structure, a stacked cell in which a plurality of unit cells are connected in series or in parallel can be constructed. When connected in series, the active material plates 12b ′ and 12b ′ facing each other with the current collector 12a ′ interposed therebetween and the active material plates 14b ′ and 14b ′ facing each other across the current collector 14a ′ are respectively connected to the current collector 12a. It is preferable that the insulating layer is ionically insulated by ', 14a', that is, isolated so as to block the passage of lithium ions, and this configuration has a current collecting layer that is thick enough to eliminate defects such as pinholes. It can be realized by forming. As described above, a power storage element capable of extracting a high voltage can be obtained by wiring a plurality or many unit cells in series. On the other hand, when connected in parallel, the combination of active material plate 12b ′ / current collecting layer 12a ′ / active material plate 12b ′ and active material plate 14b ′ / current collecting layer 14a ′ / active material plate 14b ′ Each can function as substantially one first electrode 12 ′ and second electrode 14 ′. In this case, since the electrode works effectively as the total thickness of the active material plates disposed on both main surfaces of the current collecting layer, the charge / discharge capacity of the power storage element does not decrease. Moreover, since the thickness of the electrode (active material plate) that works effectively can be reduced, the charge / discharge rate can be improved. Moreover, even if the active material plate is thinned, the mechanical strength as an electrode can be improved because it is held by the internal current collecting layer and disposed on both main surfaces of the current collecting layer.

Manufacturing Method The power storage device according to the present invention may be manufactured by any method. For example, the manufacture of an all-solid-state electricity storage device using an inorganic solid electrolyte includes: (a) a current collecting layer 12a, an active material plate 12b, a solid electrolyte 16, an active material plate 14b, and a current collecting layer, all made of a ceramic sintered body. It can be performed by a method including a step of laminating 14a to obtain a laminated body, and (b) a step of simultaneously applying heat and pressure to the laminated body and integrating them by solid phase reaction. As described above, since the active material plate and the solid electrolyte used in this embodiment are both composed of a ceramic sintered body, they are not a green compact, a green sheet, and a vapor-phase synthetic thin film. In the method of this aspect, the first electrode 12, the solid electrolyte 16, and the first electrode 12, the solid electrolyte 16, and the second electrode 14 made of the ceramic sintered body are simultaneously heated and pressurized. The two electrodes 14 can be integrated by a solid phase reaction. The bonding between the sintered ceramics does not require the sintering of the powders as required for the lamination of the green sheets, and can be performed at a relatively low temperature under pressure. It is possible to suppress the formation of a high-resistance reaction layer that can occur between different types of highly active powders in an extremely high temperature range such as a sintering temperature. Moreover, the adhesion of the composite interface obtained by simultaneous heating and pressing is surprisingly high. As described above, according to the method of this aspect, bonding at a relatively low temperature is enabled to suppress the formation of a high-resistance reaction layer at the interface, and the adhesion between the electrode and the solid electrolyte at the interface is increased to increase the bonding area. Can be maximized. By using the electrode / solid electrolyte / electrode composite having such characteristics, it is possible to provide an all-solid-state energy storage device having an extremely high capacity while being thin.

  The heating and pressurization according to this aspect are performed simultaneously, and it is sufficient that the step of pressurizing while heating is included, and there may be a deviation in the timing of heating and pressurization. Examples of methods for performing heating and pressurization simultaneously include hot press method (HP), hot isostatic press method (HIP), and discharge plasma sintering method (SPS). Is preferable because the hot pressing method (HP) is preferable.

Heating is preferably performed at a temperature of 600 to 800 ° C, more preferably 650 to 750 ° C, and even more preferably 675 to 725 ° C. Pressurization is preferably carried out at a pressure of 5~3000kgf / cm ^2, more preferably 500~2500kgf / cm ^2, more preferably 1000~2000kgf / cm ^2. Further, the time to reach the target pressure is preferably 0.1 to 10 hours, more preferably 1 to 7 hours, and further preferably 3 to 5 hours. Furthermore, it is preferable that the timing of the pressurization start is after the end of the temperature raising process in the firing profile. Heating and pressing are preferably performed for 0.05 to 10 hours, more preferably 1 to 8 hours, and further preferably 2 to 5 hours. Within such a range, the formation of a high-resistance reaction layer at the interface can be more reliably suppressed, and the adhesion between the electrode and the solid electrolyte at the interface can be further enhanced.

  For the purpose of reducing the interface resistance between the active material plate and the solid electrolyte, the reaction layer formed when the active material plate and the solid electrolyte are integrated on the active material plate or the solid electrolyte by solid phase reaction. A layer made of an element that makes the resistance smaller (for example, a thin film made of NbO having a thickness of several tens of nm or less) may be formed.

  The present invention is more specifically described by the following examples.

Example 1
(1) Production of LMO ceramic plate In the present invention, an LMO ceramic plate used as an active material plate for the first electrode and the second electrode was produced by the following procedure. First, Li ₂ CO ₃ powder (made by Honjo Chemical Co., fine grade, average particle size 3 μm), MnO ₂ powder (made by Tosoh Corporation) so as to have a chemical formula of Li _1.08 Mn _1.83 Al _0.09 O ₄ , Electrolytic manganese dioxide, FM grade, average particle size 5 μm, purity 95%), and Al (OH) ₃ powder (Showa Denko H-43M, average particle size 0.8 μm) were weighed, and Bi ₂ O _Three powders (average particle size 0.3 μm, manufactured by Taiyo Mining Co., Ltd.) were weighed so that the amount of Bi added to Mn contained in the MnO ₂ raw material was 0.4 mol%. 100 parts by weight of this weighed product and 100 parts by weight of an organic solvent (mixed liquid in which equal amounts of toluene and isopropyl alcohol are mixed) as a dispersion medium are put in a cylindrical wide-mouth bottle made of synthetic resin, and a ball mill (zirconia having a diameter of 5 mm) is placed. Ball) for 16 hours to obtain a mixed powder.

  For 100 parts by mass of the mixed powder, 10 parts by mass of polyvinyl butyral (ESREC BM-2, manufactured by Sekisui Chemical Co., Ltd.) as a binder, 4 parts by mass of a plasticizer (DOP, manufactured by Kurokin Kasei Co., Ltd.), and a dispersant ( A slurry-like forming raw material was obtained by adding and mixing 2 parts by mass of Rheodor SP-O30 (manufactured by Kao Corporation). The resulting slurry-like forming raw material was stirred and degassed under reduced pressure, whereby the viscosity of the slurry was adjusted to 4000 mPa · s. The slurry-like forming raw material with adjusted viscosity was formed on a PET film by a doctor blade method to obtain a sheet-like formed body. In addition, the thickness of the sheet-like molded object after drying was 20 micrometers.

  The sheet-like molded body peeled off from the PET film was cut into a 12 mm square with a cutter, and placed in the center of a zirconia setter (dimension 90 mm square, height 1 mm) with an embossed projection of 300 μm in size. Degreasing was performed at 600 ° C. for 2 hours in the air, and then calcined at 900 ° C. for 5 hours. As a result, a ceramic plate in which single crystals were connected in a plane was obtained as in the SEM photograph shown in FIG.

(2) Production of LLZ ceramic plate A LLZ ceramic plate used as a solid electrolyte in the present invention was produced by the following procedure. First, lithium hydroxide (Kanto Chemical Co., Ltd.), lanthanum hydroxide (Shin-Etsu Chemical Co., Ltd.), zirconium oxide (Tosoh Corp.), and tantalum oxide were prepared as raw material components for preparing the raw material for firing. These powders are weighed and blended so as to be LiOH: La (OH) ₃ : ZrO ₂ : Ta ₂ O ₅ = 7: 3: 1.625: 0.1875, and mixed by a laika machine to be a raw material for firing. Got.

  As the first firing step, the firing raw material was placed in an alumina crucible, heated at 600 ° C./hour in the air atmosphere, and held at 900 ° C. for 6 hours.

As a second firing step, γ-Al ₂ O ₃ is added to the powder obtained in the first firing step so that the Al concentration is 0.08 wt%, and this powder and cobblestone are mixed to form a vibration mill. And milled for 3 hours. After pulverizing this pulverized powder, the obtained powder was press-molded at about 100 MPa using a mold into pellets. The obtained pellets are placed on a magnesia setter, and the whole setter is placed in a magnesia sheath, heated at 200 ° C./hour in an Ar atmosphere, and held at 1000 ° C. for 36 hours to obtain 35 mm × 18 mm. A sintered body having a size of 11 mm and a thickness of 11 mm was obtained, from which a LLZ ceramic plate having a size of 1.5 mm × 1.5 mm and a thickness of 0.2 mm was obtained as a solid electrolyte. As the Ar atmosphere, the inside of the furnace having a capacity of about 3 L was evacuated in advance, and then Ar gas having a purity of 99.99% or more was flowed into the electric furnace at 2 L / min.

After polishing the upper and lower surfaces of the obtained sintered body sample, various evaluations and measurements shown below were performed. When the X-ray diffraction measurement of the sintered body sample was performed, the X-ray diffraction file No. of CSD (Cambridge Structural Database). A crystal structure similar to 422259 (Li ₇ La ₃ Zr ₂ O ₁₂ ) was obtained. From this, it was confirmed that the obtained sample has the characteristics of the LLZ crystal structure. Further, in order to grasp the Al and Mg contents of the sintered body sample, when chemical analysis was performed by inductively coupled plasma emission analysis (ICP analysis), the Al content was 0.08 wt% and the Mg content was 0.07 wt. %Met.

(3) Production and evaluation of all-solid-state electricity storage element and coin cell On the LMO ceramic plate obtained in (1) above, an Au foil (thickness 20 μm) serving as a current collecting layer is stacked, and on the opposite side in (2) above The obtained LLZ ceramic plates were stacked. On the LLZ ceramic plate of the obtained laminate, an LMO ceramic plate and an Au foil are further stacked to form an Au / LMO / LLZ / LMO / Au laminate, which is fired under conditions of 700 ° C. for 5 hours and 2000 kgf / cm ² . Hot press firing was performed under pressure. The Au / LMO / LLZ / LMO / Au composite thus obtained was incorporated into a stainless steel CR2032 case to obtain a coin cell. This coin cell was repeatedly charged and discharged at a current density of 0.1 C between 0V and 1.2V.
At this time, the maintenance ratio of the 50th discharge capacity with respect to the first discharge capacity was 75%. The battery after the 50th charge / discharge cycle was disassembled, and the cross section of the electrode on the low potential side of the Au / LMO / LLZ / LMO / Au composite was observed with SEM. No cracks were observed in the in-plane direction that disrupted the lithium ion conduction path.

Example 2 (Comparison)
A battery was fabricated in the same manner as in Example 1 except that Bi ₂ O ₃ was not added in the LMO ceramic plate raw material adjustment step. The thickness of the fired LMO ceramic plate obtained at this time was about 10 μm, and the primary particle size of the LMO-based single crystal particles was about 2 μm, which was caused by the overlap of the single crystal particles in the thickness direction. It was in a state that included many grain boundaries. The maintenance ratio of the 50th discharge capacity to the first discharge capacity in this battery was 45%. The battery after 50 charge / discharge cycles was disassembled and the cross section of the low potential side electrode of the Au / LMO / LLZ / LMO / Au composite was observed by SEM. A large number of cracks occurred, and it was observed that cracks were running in the in-plane direction so as to break the lithium ion conduction path between Au and LLZ.

Claims (9)

An active material composed of a current collector layer and a plurality of spinel-type lithium manganate single crystal particles provided on at least one surface of the current collector layer and mainly connected two-dimensionally and composed of a ceramic sintered body A first electrode and a second electrode comprising a plate;
An electrolyte provided between the first electrode and the second electrode so as to be in contact with the active material plate and having lithium ion conductivity;
A power storage device comprising: The single crystal particles have the general formula:
LiM _x Mn _2-x O ₄ (1)
(Wherein, M is at least one selected from the group consisting of Li, Fe, Ni, Mg, Zn, Al, Co, Cr, Si, Sn, P, V, Sb, Nb, Ta, Mo and W. A substitution element, and at least one selected from the group consisting of Ti, Zr and Ce may be further contained together with the at least one element, and 0 ≦ x <0.55)
The electrical storage element of Claim 1 which has a composition represented by these. The power storage device according to claim 1 or 2 , wherein the active material plate is provided only on one side of the current collecting layer, whereby the current collecting layer is configured as an external current collecting layer. Wherein the active material plate on both sides of at least one of the collector layer of the first electrode and the second electrode is provided, the current collector layer are configured as an internal collector layer thereby to claim 1, wherein 2. The electricity storage device according to 2 . The electric storage element according to claim 4 , wherein the internal current collecting layer has at least one opening, and the opening is filled with the spinel type lithium manganate single crystal particles. A plurality of at least one of the first electrode and the second electrode are provided, and the first electrode and the second electrode are alternately stacked via the electrolyte,
The electrode located within at least the electric storage device, the active material sheet is provided on both surfaces of the current collector layer, the collector layer are configured as an internal collector layer thereby, according to claim 1 to 5 The electrical storage element as described in any one. The electrical storage element according to claim 6 , wherein the internal current collecting layer has at least one opening, and the opening is filled with the spinel type lithium manganate single crystal particles. Electrodes located on the outer surface of the electric storage device, the only one surface of the collector layer active material plate is provided, the current collector layer are configured as an external collector layer thereby, claim 6 or 7 The electrical storage element as described in. The electrical storage element as described in any one of Claims 1-8 whose said electrolyte is an inorganic solid electrolyte which has lithium ion conductivity.