JP6099407B2 - All-solid-state energy storage device - Google Patents

Description

  The present invention relates to an all-solid-state energy storage device using a solid electrolyte having lithium ion conductivity, such as a lithium ion capacitor and a lithium ion secondary battery.

  In recent years, lithium ion secondary batteries have attracted attention from the viewpoint of high energy density. However, since lithium ion secondary batteries currently widely used are mainly organic electrolytes in which lithium salts are dissolved in flammable organic solvents, it is important to ensure safety against liquid leakage and the like. Yes. On the other hand, an all-solid battery using a solid electrolyte instead of an electrolytic solution has been proposed as a highly safe battery that does not require the use of a flammable organic solvent.

As such an all solid state battery, an all solid state battery using a Ni—Co—Al based positive electrode active material film has been proposed. For example, Patent Document 1 (Japanese Patent No. 4745463) discloses a general formula: Li _p (Ni _x , Co _y , Al _z ) O ₂ (where 0.9 ≦ p ≦ 1.3, 0.6 < x ≦ 0.9, 0.1 <y ≦ 0.3, 0 ≦ z ≦ 0.2, x + y + z = 1), and an active material film having a layered rock salt structure is disclosed, and (003) plane Is oriented so as to intersect the plate surface of the particles, so that high capacity and high rate characteristics can be realized simultaneously when used as a positive electrode material of a solid-state lithium secondary battery. In the battery having such a configuration, since the conductivity of lithium ions and electrons is improved by the orientation, the electrode can be constituted only by the positive electrode active material in the form of a ceramic plate without using a conductive auxiliary agent, a binder, or the like. And a high capacity density can be realized. In addition, since the lithium entrance / exit surface of the positive electrode active material forms an interface with the solid electrolyte, it is possible to provide a solid battery that can be charged and discharged with a small loss.

  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. For such a problem, in Patent Document 2 (Japanese Patent Application Laid-Open No. 2011-146202), the battery cell is arranged so that the positive electrode of one battery cell and the negative electrode of another 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.

On the other hand, as a solid electrolyte having lithium ion conductivity, a garnet-type ceramic material having a Li ₇ La ₃ Zr ₂ O ₁₂ (hereinafter referred to as LLZ) -based composition has attracted attention. For example, Patent Document 3 (Japanese Patent Application Laid-Open No. 2011-051800) discloses that the addition of Al in addition to Li, La and Zr, which are basic elements of LLZ, can improve the density and lithium ion conductivity. ing. Patent Document 4 (Japanese Patent Laid-Open No. 2011-073962) discloses that lithium ion conductivity can be further improved by adding Nb and / or Ta in addition to Li, La, and Zr, which are basic elements of LLZ. ing. Patent Document 5 (Japanese Patent Application Laid-Open No. 2011-073963) includes Li, La, Zr, and Al, and the density can be further improved by setting the molar ratio of Li to La to 2.0 to 2.5. Is disclosed.

Japanese Patent No. 4745463 JP 2011-146202 A JP 2011-051800 A JP 2011-073962 A JP 2011-073963 A

  In general, the present inventors have a configuration in which a solid electrolyte having lithium ion conductivity is sandwiched between two electrodes made of a lithium-transition metal composite oxide capable of inserting and extracting lithium ions, The inventor has obtained knowledge that it is possible to provide a non-polar power storage element that can be charged / discharged in both directions with little loss, while having an extremely simple configuration that does not require polarity identification.

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

According to one aspect of the invention,
A first electrode and a second electrode made of a lithium-transition metal composite oxide capable of absorbing and desorbing lithium ions;
A solid electrolyte interposed between the first electrode and the second electrode and having lithium ion conductivity;
An all-solid-state energy storage device is provided.

It is a schematic cross section which shows the structure of the all-solid-state electrical storage element by this invention. A change in lithium ion content and oxidation-reduction equilibrium potential in a series of processes from charging (I) to discharging (II) to reverse charging (III) of the all-solid-state energy storage device according to the present invention and vice versa will be described. FIG. In the figure, E represents the potential difference of the power storage elements, E _max represents the maximum value of the equilibrium potential, E _min represents the minimum value of the equilibrium potential, and E _eq represents the equilibrium potential at the completion of discharge. It is a figure which shows the relationship between the oxidation reduction potential in a 1st electrode and a 2nd electrode, and the amount of lithium ions. 1 is a schematic cross-sectional view showing an example of a stack-type all-solid-state energy storage device according to the present invention.

All-solid-state electricity storage device FIG. 1 schematically shows the configuration of an all-solid-state electricity storage device according to the present invention. The all-solid-state energy storage device 10 shown in FIG. 1 includes a first electrode 12, a second electrode 14, and a solid electrolyte 16. Both the first electrode 12 and the second electrode 14 are composed of a lithium-transition metal composite oxide capable of absorbing and desorbing lithium ions. The solid electrolyte 16 is interposed between the first electrode 12 and the second electrode 14 and has lithium ion conductivity. 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, by using the electrodes 12 and 14 capable of occluding and desorbing lithium ions as non-polar electrodes and combining with the lithium ion conductive solid electrolyte 16, both lithium ions are transferred between the electrodes 12 and 14 in accordance with the potential difference between the electrodes. It becomes possible to move in the direction. This is because the lithium-transition metal composite oxide constituting the first electrode 12 and the second electrode 14 has a reduced redox potential due to occlusion of lithium ions and an increased redox potential due to lithium ion desorption. This is because it generally has the property of As described above, charging / discharging can be performed by changing the oxidation-reduction potential in accordance with insertion and extraction of lithium ions. Therefore, by interposing the solid 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 as a nonpolar storage element Function is secured. That is, in charging, when a voltage is applied between the first electrode 12 and the second electrode 14 that are initially set so that the amounts of lithium ions are equal, a low potential electrode passes from the high potential side electrode through the solid electrolyte. As a result of the movement of lithium ions, the 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, the composition of the first electrode is represented by Li _x-α MO _y (wherein M is a constituent element other than Li and O, x and y are arbitrary numbers, and 0 <α <x). When the composition of the second electrode is expressed as Li _{x + α} MO _y and the composition of the first electrode is expressed as Li _{x + α} MO _y , the composition of the second electrode may be expressed as Li _x-α MO _y. it can. A diagram for explaining the above-described charging / discharging using this expression is shown in FIG. First, as shown in “II discharge” in FIG. 2, the potential difference E of the electric storage element 10 at the completion of discharge is 0 (that is, both electrodes have equal equilibrium potential E _eq ). The coefficient x indicating the amount of lithium is Both the first electrode 12 and the second electrode 14 have the same value. When the storage element 10 is charged, as shown in “I charge” in FIG. 2, the equilibrium potential of the first electrode 12 is reduced to E _min and the lithium amount is increased to x + α by supplying and inserting lithium ions. On the other hand, the equilibrium potential of the second electrode 14 increases to E _max and the amount of lithium decreases to x−α due to desorption and release of lithium ions. As a result, the potential difference E = E _max −E _min > 0 results. When charging is performed in the opposite direction to this charging, as shown in “III reverse charging” in FIG. 2, the potential and lithium in the case of “I charging” and the first electrode 12 and the second electrode 14 The relationship between the quantities is reversed, and an opposite potential difference E = E _min −E _max <0 is generated in the electric storage element 10. 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 addition, since it is not necessary to adopt a configuration in which the positive and negative electrodes are short-circuited as disclosed in Japanese Patent Application Laid-Open No. 2011-146202, charging and discharging can be performed with little loss. In addition, since it is not necessary to identify the polarity in mounting, the manufacturing cost and workload can be reduced.

In particular, in order to obtain desirable characteristics as a lithium ion capacitor, as illustrated in FIG. 3 to be described later, the oxidation-reduction equilibrium potential is increased to a maximum value E _max (or a minimum value) in accordance with insertion and extraction of lithium ions. A characteristic that continuously changes from E _min ) to the minimum value E _min (or the maximum value E _max ) is desired. Such characteristics are the characteristics of many lithium-transition metal composite oxides with a layered rock salt structure, but even lithium-transition metal composite oxides with other structures have this characteristic. As long as it is, it can be suitably used for a lithium ion capacitor. FIG. 3 shows redox potentials and lithium ions in the first electrode and the second electrode in a power storage device using the first electrode and the second electrode having a composition represented by Li _x (Ni, Co, Al) O _2. The relationship with quantity is shown. As is clear from FIG. 3, the behavior of the first electrode and the behavior of the second electrode are completely symmetrical in a series of processes of charging, discharging and reverse charging. It can function as an electrical storage element.

The first electrode and the second electrode The first electrode 12 and the second electrode 14 are composed of a lithium-transition metal-based composite oxide capable of inserting and extracting lithium ions, and are typically ceramic sintered bodies. . In order to make it possible to occlude and desorb lithium ions with certainty, the lithium-transition metal-based composite oxide is preferably one in which a desired amount of lithium has been desorbed by electrochemical treatment or the like. The lithium-transition metal-based composite oxide preferably has a layered rock salt structure or a spinel structure, and more preferably has a layered rock salt structure. The layered rock salt structure has the property that the oxidation-reduction potential decreases due to occlusion of lithium ions, and the oxidation-reduction potential increases due to the elimination of lithium ions. Since many insertions can be removed, it is particularly preferable in that cycle deterioration due to volume change accompanying crystal phase transition can be suppressed. Here, the layered rock salt structure is a crystal structure in which transition metal layers other than lithium and lithium layers are alternately stacked with an oxygen atom layer interposed therebetween, that is, an ion layer and lithium ions of transition metals other than lithium. Crystal structure in which layers are alternately stacked with oxide ions in between (typically α-NaFeO ₂ type structure: structure in which transition metal and lithium are regularly arranged in the [111] axis direction of cubic rock salt type structure ). Typical examples of the lithium-transition metal composite oxide having a layered rock salt structure include lithium nickelate, lithium manganate, nickel / lithium manganate, nickel / lithium cobaltate, cobalt / nickel / lithium manganate, cobalt / manganese. Examples of these materials include Mg, Al, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, Ag, Sn, and the like. One or more elements such as Sb, Te, Ba, Bi and the like may be further included.

That is, the lithium-transition metal composite oxide is Li _z M1O ₂ or Li _z (M1, M2) O ₂ (where 0 <z <1, M1 is selected from the group consisting of Ni, Mn, and Co). At least one transition metal element, M2 is Mg, Al, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, Ag, Sn, Sb, Te , Ba and Bi, which is at least one element selected from the group consisting of, and more preferably Li _z (M1, M2) O ₂ , where M1 is Ni and Co. M2 is a composition that is at least one selected from the group consisting of Mg, Al, and Zr, more preferably Li _z (M1, M2) O ₂ , M1 is Ni and Co, and M2 Is Al . Any of such compositions can take a layered rock salt structure. The atomic ratio of Ni in the total amount of M1 and M2 is preferably 0.6 or more. Although the coefficient z of Li can vary depending on the charge states of the first electrode and the second electrode, the above composition means a composition in an uncharged state (a state in which no charge is accumulated in the storage element). Typically, z is in a range of 0.4 to 0.7 in an uncharged state, and z can be varied in a range of 0.2 to 1.0 during charge accumulation. Note that a ceramic having a Li _z (Ni, Co, Al) O ₂ -based composition in which M1 is Ni and Co and M2 is Al may be referred to as NCA ceramics. Particularly preferred NCA ceramics have a general formula: Li _z (Ni _a , Co _b , Al _c ) O ₂ (where 0 <z <1, 0.6 <a ≦ 0.9, 0. 1 <b ≦ 0.3, 0 ≦ c ≦ 0.2, a + b + c = 1), and has a layered rock salt structure.

  Typically, the lithium-transition metal composite oxide is a polycrystalline body composed of a plurality of crystal particles, and the plurality of crystal particles are preferably oriented. This orientation is preferably such that the (003) plane of the layered rock salt structure intersects the plate surface (principal surface) of the electrode, more preferably a plane other than (003) (for example, ( 104) surface) is preferably oriented parallel to the plate surface of the electrode. This facilitates insertion / removal of lithium ions, and improves the rate characteristics when a power storage element is configured. The degree of orientation in such an electrode is evaluated by the ratio [003] / [104] of the diffraction intensity (peak intensity) by the (003) plane to the diffraction intensity by the (104) plane in X-ray diffraction from the plate surface of the electrode. The preferred [003] / [104] ratio is 2 or less, more preferably 1 or less, and even more preferably 0.5 or less. Note that such a low [003] / [104] ratio means that the ratio of appearance of the (003) plane parallel to the plate surface on the plate surface or inside of the electrode is reduced.

  The first electrode 12 and the second electrode 14 are made of a lithium-transition metal complex oxide. The first electrode and the second electrode may contain optional components such as a conductive additive and a binder in addition to the lithium-transition metal-based composite oxide, but the configuration does not substantially include such optional components. It is also possible. For example, in the case of using a lithium-transition metal composite oxide in which crystal grains are oriented, ion mobility can be improved without using a conductive auxiliary agent, etc., so that the active material filling rate can be maximized. Can be increased. Therefore, it is preferable that the electrodes 12 and 14 consist essentially of only the lithium-transition metal composite oxide, and more preferably consist only of the lithium-transition metal composite oxide.

The first electrode 12 and the second electrode 14 preferably have pores. The presence of pores in the electrode can relieve stress that may be caused by expansion or contraction associated with insertion and removal of lithium ions due to charge and discharge. Moreover, the difference in thermal expansion coefficient caused during bonding (e.g., 8.0 × ¹⁰ -6 at NCA ceramics, the LLZ ceramic 4.0 × ^{10 -6)} suppressing generation of cracks and cracks due to. As a result, it is possible to effectively prevent peeling at the interface that may occur when the dense plates are joined together. The first and second electrodes preferably have a porosity of 3 to 30%, more preferably 5 to 25%, and still more preferably 10 to 20%. The voidage is the volume ratio of pores (including open pores and closed pores) in the first and second electrodes, and is sometimes referred to as porosity, and the bulk density and true density of the electrodes. And can be calculated from The volume ratio (open pore ratio) of open pores to all pores is preferably 70% or more, more preferably 80% or more, and further preferably 95% or more. The open pores mean pores communicating with the outside of the electrode, and if the electrolyte can be filled in the open pores, further improvement in rate characteristics is expected. This open pore ratio can be calculated from, for example, the total of open pores and closed pores obtained from the bulk density and the closed pores obtained from the apparent density. The parameter used for calculation of the open pore ratio can be measured using Archimedes method or the like.

The lithium-transition metal composite oxide having such pores is preferably produced from electrode active material precursor particles prepared in advance. The electrode active material precursor particles are preferably precursor particles that can become an electrode active material containing a lithium-transition metal composite oxide having a layered rock salt structure by introducing lithium. Particularly preferred electrode active material precursor particles are formed in a substantially spherical shape, and a large number of voids are provided almost uniformly therein, the average particle diameter D50 (volume basis) is 0.5 to 5 μm, and the specific surface area is 3 ~25m a ² / g, relative tap density is a value obtained by dividing the tap density by the theoretical density of 0.25 to 0.4. When such conditions are satisfied, when the electrode active material is generated through the subsequent molding step and firing step (lithium introduction step), the firing environment is stabilized and the lithium introduction (diffusion) state is made uniform, Thereby, the internal fine structure is made as uniform as possible. Further, the shape stability and crystallographic synthesis degree of the electrode active material which is the final object are improved.

  Preferably, the lithium-transition metal composite oxide includes (a) a large number of transition metal hydroxide plate-like particles constituting the main raw material of the lithium composite oxide, and a large number of voids are provided substantially uniformly therein. A granulation step for forming the granulated body, (b) a heat treatment step for forming electrode active material precursor particles by heat-treating the granulation body, and (c) a number of electrode active material precursor particles. It is manufactured by a method having a molding step of obtaining a molded body by molding the material into a predetermined shape and (d) a firing step of producing a lithium composite oxide by firing the molded body. The granulation step (a) is preferably a step of forming a granulated body by spray drying a slurry prepared by mixing raw material powder containing a transition metal hydroxide while being pulverized wet. In particular, spray drying using a two-fluid nozzle system can be suitably used. The raw material powder may contain nickel and cobalt hydroxides as transition metal hydroxides. The raw material powder may contain a metal compound other than a transition metal such as an aluminum oxide hydrate or an aluminum hydroxide. The lithium compound can be added at the time of molding or before firing after molding. That is, for example, the lithium compound can be added to the above-described molding slurry together with the electrode active material precursor particles at the time of molding. Alternatively, a compact that does not contain a lithium compound is temporarily calcined (molded calcined), and then a mixture of the calcined compact and the lithium compound is calcined (main calcining) in two stages (lithium Step) may be performed.

  The first electrode 12 and the second electrode 14 typically have a plate shape and the dimensions thereof are not particularly limited, but the thickness is 0.1 to 300 μm from the viewpoint of the active material capacity per unit area. It is preferably 10 to 200 μm, more preferably 50 to 100 μm, and the size of the plate surface is preferably 0.2 mm × 0.2 mm to 10 mm × 10 mm, more preferably from the viewpoint of ease of electrode production. It is 0.5 mm x 0.5 mm to 2 mm x 2 mm.

  According to a preferred embodiment of the present invention, a plurality of first electrodes 12 and a plurality of second electrodes 14 are prepared, and the plurality of first electrodes 12 are arranged in a tile shape on one surface of the plate-like solid electrolyte 16, A plurality of second electrodes 14 are arranged in a tile shape on the other surface of the plate-like solid electrolyte 16. Accordingly, there is an advantage that the active material can be filled in the electrode with higher density.

  The first electrode 12 and the second electrode 14 may be further provided with a current collector on the side opposite to the solid electrolyte 16. The current collector may be a film or foil formed of gold, silver, copper, aluminum, nickel or the like, and is formed by, for example, a sputtering method.

The solid electrolyte 16 is an inorganic solid electrolyte having lithium ion conductivity. Preferable examples of the lithium ion conductive inorganic solid electrolyte include at least one selected from the group consisting of garnet-based ceramic materials, nitride-based ceramic materials, perovskite-based ceramic materials, and phosphate-based ceramic materials. 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 ) can be used, and those described in JP 2011-051800 A, JP 2011-073962 A, and JP 2011-073963 A 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 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 known methods as described in JP 2011-051800 A, JP 2011-073962 A and JP 2011-073963, or appropriately modified. Can be performed.

  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.

Stacked all-solid-state energy storage device The all-solid-state energy storage device 10 shown in FIG. 1 is an example of a unit cell-type all-solid-state energy storage device having a pair of first electrode 12 and second electrode 14, but as shown in FIG. In addition, a plurality of all-solid-state energy storage devices may be stacked as a stack type all-solid-state energy storage device. The stack type all-solid-state energy storage device 20 shown in FIG. 4 has a configuration similar to that of the all-solid-state energy storage device 10 shown in FIG. 1 and includes a plurality of unit cell type all-solid-state energy storage devices 10a, 10b, 10c, 10d. It is laminated via electric bodies 22a, 22b and 22c. 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 first electrodes 12a, 12b, 12c and the second electrodes 14b, 14c, 14d adjacent to each other are ionically insulated by the current collectors 22a, 22b, 22c, that is, the passage of lithium ions is blocked. It is preferable to be configured so as to be isolated, and this configuration can be realized by forming a current collector that is thick enough to eliminate defects such as pinholes. 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. Of course, in the stack type all-solid-state energy storage device 20, an external current collector may be further provided outside the first electrode 12d at the upper end and the second electrode 14a at the lower end.

  According to a preferred aspect of the present invention, the current collectors 22a, 22b, and 22c are internal current collectors embedded in each of the active material plates 24a, 24b, and 24c made of a lithium-transition metal composite oxide. One side of the active material plates 24a, 24b, and 24c constitutes the first electrodes 12a, 12b, and 12c, and the other side constitutes the second electrodes 14a, 14b, and 14c. In this case, the active material plates 24a, 24b, and 24c are more preferably in the form of an integrated sintered body that is integrally fired together with the internal current collectors 22a, 22b, and 22c. At this time, the active material plates 24a, 24b, and 24c are a combination of the first electrode 12a and the second electrode 14b, a combination of the first electrode 12b and the second electrode 14c, and a combination of the first electrode 12c and the second electrode 14d. Corresponding to each other, each combination can function substantially as one electrode. In this case, the electrode works effectively as the total thickness of the lithium-transition metal-based composite oxide disposed on both main surfaces of the current collector, so that the charge / discharge capacity of the storage element does not decrease. Moreover, since the thickness of the electrode (lithium one transition metal-based composite oxide) that works effectively can be reduced, the charge / discharge rate can be improved. In addition, even if the lithium-transition metal-based composite oxide layer becomes thin, the mechanical strength as an electrode can be improved because it is held by the internal current collector and disposed on both main surfaces of the current collector. . The electrode according to such an embodiment is, for example, a sintered body electrode obtained by laminating, pressing, and firing so as to sandwich a green body of a current collector with a precursor of a lithium monotransition metal-based composite oxide (green sheet or the like). Alternatively, a layer of lithium-transition metal composite oxide is formed on both sides of the current collector foil by aerosol deposition, powder jet deposition, thermal spraying, etc., and then heat treatment or firing is performed. You may produce by doing.

Manufacturing Method The power storage device according to the present invention may be manufactured by any method. According to a preferred embodiment of the present invention, the production of the electricity storage device includes (a) a step of obtaining a laminate by laminating a first electrode, a solid electrolyte and a second electrode, both of which are made of a ceramic sintered body, and (b) ) By a method comprising heating and pressurizing the laminate simultaneously and integrating them by solid phase reaction; and (c) optionally desorbing a desired amount of lithium from the first electrode and the second electrode. It can be carried out. As described above, since the electrode and the solid electrolyte used in this embodiment are both formed 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, the solid electrolyte, and the second electrode are integrated by a solid-phase reaction by simultaneously heating and pressing the electrode / solid electrolyte / electrode laminate comprising the ceramic sintered body. Can be made. 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.

  In order to reduce the interfacial resistance between the plate-like positive electrode active material and the plate-like solid electrolyte, the plate-like positive electrode active material and the plate-like solid electrolyte are subjected to a solid phase reaction on the plate-like positive electrode active material or on the plate-like solid electrolyte. A layer made of an element (for example, a thin film made of NbO having a thickness of several tens of nanometers or less) may be formed so as to reduce the resistance of the reaction layer formed at the time of integration.

The electrode / solid electrolyte / electrode composite thus obtained is preferably subjected to a lithium desorption process. Lithium desorption is a process for initially setting the lithium-transition metal composite oxide constituting the first electrode and the second electrode to a state in which both of lithium ion occlusion and desorption are possible. This can be done according to electrochemical techniques. The following procedure is mentioned as a preferable example of the lithium desorption technique. That is, the first electrode and the second electrode are sealed in the cell together with the electrolytic solution in an inert atmosphere such as Ar in a state where the first electrode and the second electrode are respectively wired to the external terminals. At this time, the electrolytic solution may be obtained by dissolving a desired amount of LiPF ₆ in an organic solvent. Then, a metal lithium electrode is separately wired in the electrolytic solution. Then, by applying a voltage between the metal lithium electrode and each of the first electrode and the second electrode, the composition of the first electrode and the second electrode is a composition in which the same Li is reduced in both electrodes (for example, Li _A desired amount of lithium is desorbed by performing a charging process so as to be _0.6 (Ni, Co, Al) O ₂ ). The power storage element after the charging process is taken out of the cell and preferably dried appropriately in a vacuum.

  As described above, the first electrode and the second electrode, which are initially set to the same composition by desorbing an appropriate amount of lithium, can both occlude and desorb lithium ions. As a result, these electrodes The storage element provided with can function as a nonpolar storage element that can be charged and discharged in both directions.

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

Example 1 Production of NCA Ceramic Plate NCA ceramic plates used as the first electrode and the second electrode in the present invention were produced by the following procedure.

(1) Slurry preparation 81.6 parts by weight of Ni (OH) ₂ powder (manufactured by Kojundo Chemical Laboratory Co., Ltd.), 15.0 parts by weight of Co (OH) ₂ powder (manufactured by Wako Pure Chemical Industries, Ltd.), and Al _A raw material powder was prepared by weighing 3.4 parts by weight of ₂ O ₃ .H ₂ O powder (manufactured by SASOL). Next, 97.3 parts by weight of pure water, 0.4 part by weight of a dispersant (manufactured by NOF Corporation: Part No. AKM-0521), 0.2 weight of 1-octanol (made by Katayama Chemical Co., Ltd.) as an antifoaming agent Part and a binder (Nippon Vinegar Poval Co., Ltd. product: PV3) 2.0 parts by weight was produced. The vehicle and raw material powder thus obtained were mixed and pulverized in a wet manner to prepare a slurry. This mixing and pulverization was performed by treating for 24 hours with a ball mill using zirconia balls having a diameter of 2 mm and then treating with a bead mill using zirconia beads having a diameter of 0.1 mm for 40 minutes.

(2) Granulation The obtained slurry was put into a two-fluid nozzle type spray dryer to form a granulated body. By appropriately adjusting parameters such as the spray pressure of the spray dryer, the nozzle diameter, and the circulating air volume, it is possible to form granulated bodies of various sizes.

(3) Heat treatment (temporary firing)
The obtained granule was heat-treated at 1100 ° C. for 3 hours (atmospheric atmosphere) to form a composite oxide of nickel, cobalt, and aluminum ((Ni _0.8 , Co _0.15 , Al _0.05 ) O). Electrode active material precursor particles, which are particles, were obtained. When the obtained electrode active material precursor particles were analyzed as shown below, the average particle diameter D50 (volume basis) was 2.3 μm, the specific surface area was 12 m ² / g, and the relative tap density was 0.3. Met.
<Average particle diameter D50>
By dispersing a powder sample of electrode active material precursor particles using water as a dispersion medium into a laser diffraction / scattering particle size distribution analyzer (model number “LA-700” manufactured by Horiba, Ltd.), the average The particle size D50 (volume basis) was measured.
<Relative tap density>
After tapping a graduated cylinder containing a powder sample of electrode active material precursor particles 200 times using a commercially available tap density measuring device, the tap density is calculated by calculating (powder weight) / (powder bulk volume). Asked. Thereafter, the relative tap density [dimensional value] was calculated by dividing the obtained tap density by the theoretical density.

(4) Molding 100 parts by weight of the obtained electrode active material precursor particle powder, 50 parts by weight of a dispersion medium (xylene: butanol = 1: 1), polyvinyl butyral as a binder (manufactured by Sekisui Chemical Co., Ltd .: product number BM-2) )) 10 parts by weight, DOP (Di (2-ethylhexyl) phthalate: manufactured by Kurokin Kasei Co., Ltd.) 4.5 parts by weight as a plasticizer, and a dispersant (product name “Reodol SPO-30” manufactured by Kao Corporation) 3 parts by weight are weighed, pre-kneaded in a mortar, and then kneaded using a tri-roll to measure a molding slurry having a viscosity of 2000 to 3000 cP (measured using a Brookfield LVT viscometer). Prepared. A sheet having a thickness of 50 μm was formed by the doctor blade method using the molding slurry thus obtained. By punching the dried sheet, a 1 mm square green sheet molded body was obtained.

(5) Firing (Lithium introduction)
The 1 mm square green sheet molded body obtained as described above was heat-treated at 900 ° C. in an air atmosphere, whereby the molded body was degreased and pre-fired. The temperature of the green body preliminary firing is lower than the above-described heat treatment (granulated body preliminary firing) temperature. This is because lithium is uniformly diffused and reacted during the subsequent main firing by suppressing the progress of sintering between the internal particles during the temporary firing of the molded body.

On the other hand, an ethanol dispersion of lithium hydroxide was prepared as follows. First, LiOH.H ₂ O powder (manufactured by Wako Pure Chemical Industries, Ltd.) was pulverized using a jet mill so as to have a visual particle diameter of 1 to 5 μm by observation with an electron microscope. What added this powder in the ratio of 1 weight part with respect to 100 weight part of ethanol (made by Katayama Chemical Co., Ltd.) was disperse | distributed until it became impossible to confirm powder visually by an ultrasonic wave.

A solution obtained by spraying a predetermined amount of the ethanol dispersion of lithium hydroxide with an airbrush onto both surfaces of the calcined molded body is heat-treated at 750 ° C. for 10 hours (oxygen atmosphere), whereby Li (Ni _0.8 , An NCA ceramic plate having a composition of Co _0.15 , Al _0.05 ) O ₂ was obtained as an electrode. When the obtained electrode was analyzed by the procedure shown below, the porosity was 15%, the open pore ratio was 95%, and the diffraction intensity (peak intensity) ratio [003] / [104] was 0.5. .
<Porosity>
The porosity is a value calculated from the relative density (porosity = 1−relative density). The relative density is a value obtained by dividing the bulk density obtained by the Archimedes method by the true density obtained using a pycnometer. In the measurement of the bulk density, the sample was boiled in water in order to sufficiently expel the air present in the voids.
<Open pore ratio>
The open pore ratio is a value obtained by calculation from the closed porosity and the total porosity (open pore ratio = open pores / total pores = open pores / (open pores + closed pores)). The closed porosity is obtained from the apparent density measured by the Archimedes method. The total porosity is determined from the bulk density measured by the Archimedes method.
<Diffraction intensity (peak intensity) ratio>
The diffraction intensity (peak intensity) ratio is measured by placing a ceramic plate for an electrode active material layer processed to a size of about φ5 to 10 mm in a sample folder for XRD measurement, and an XRD apparatus (product name “RINT, manufactured by Rigaku Corporation”). -TTRIII ") was used to measure the XRD profile when the surface of the electrode was irradiated with X-rays, and the diffraction intensity (peak height) from the (003) plane relative to the diffraction intensity (peak height) from the (104) plane This was done by determining the ratio of According to this measuring method, a diffraction profile can be obtained from a crystal plane parallel to the crystal plane of the plate plane, that is, a crystal plane oriented in the plate plane direction.

Example 2: Production of LLZ ceramic plate An LLZ ceramic plate used as a solid electrolyte in the present invention was produced by the following procedure.

Lithium hydroxide (Kanto Chemical Co., Inc.), 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. Place the obtained pellets on a magnesia setter, place the setter in a magnesia sheath as shown in Table 1, raise the temperature at 200 ° C./hour in an Ar atmosphere, and hold at 1000 ° C. for 36 hours. Thus, a sintered body having a size of 35 mm × 18 mm and a thickness of 11 mm was obtained, and an LLZ ceramic plate having a size of 1.5 mm × 1.5 mm and a thickness of 0.2 mm was obtained therefrom 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, an X-ray diffraction file No. of CSD (Cambridge Structural Database) was obtained. 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.

Example 3: Production and evaluation of NCA / LLZ / NCA all-solid-state electricity storage element and coin cell A 1 mm thick LLZ ceramic plate processed to 1.5 mm square was sandwiched between two 1 mm square NCA ceramic plates. The upper and lower surfaces of this laminate are sandwiched between Pt foils for preventing adhesion to a firing jig, and fired by hot pressing at a pressure of 2000 kgf / cm ² at a firing condition of 700 ° C. for 5 hours to obtain an NCA / LLZ / NCA composite. It was.

Next, the obtained NCA / LLZ / NCA composite was subjected to lithium desorption treatment. Specifically, the NCA / LLZ / NCA composite was encapsulated in a beaker cell together with the electrolyte in an Ar atmosphere with each NCA electrode wired to an external terminal. In addition, the electrolyte solution used here was prepared by dissolving LiPF ₆ in an organic solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at an equal volume ratio so as to have a concentration of 1 mol / L. Is. Furthermore, by separately wiring a metal lithium electrode in the electrolyte and applying a voltage between the metal lithium electrode and each NCA electrode, the composition of the NCA electrode is Li _0.6 (Ni, Co, Al) O for both electrodes. _The charging process was performed to be ₂ . The NCA / LLZ / NCA complex after the charge treatment was taken out from the beaker cell and dried at 80 ° C. in a vacuum.

  An Au film having a thickness of 500 mm was formed on both sides of the NCA / LLZ / NCA composite thus obtained by sputtering to obtain a current collector. Next, this Au / NCA / LLZ / NCA / Au composite was incorporated into a stainless steel CR2032 case to form a coin cell.

  When this coin cell was charged and discharged at a charge voltage of 0.7 V and a discharge voltage of -0.7 V, it was confirmed that both charge and discharge in the forward direction and the reverse direction were normally performed. As described above, according to the present invention, it is possible to provide a non-polar storage element that can be charged / discharged bidirectionally with a small loss, while having a very simple configuration that does not require polarity identification.

Claims (19)

A first electrode and a second electrode made of a lithium-transition metal composite oxide capable of absorbing and desorbing lithium ions;
A solid electrolyte interposed between the first electrode and the second electrode and having lithium ion conductivity;
Wherein the lithium-transition metal-based composite oxide is Li _z M1O ₂ or Li _z (M1, M2) O ₂ (where 0 <z <1, M1 represents Ni, Mn and Co in an uncharged state ) At least one transition metal element selected from the group consisting of M2, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, A nonpolar all solid state storage element having a composition represented by (at least one element selected from the group consisting of Ag, Sn, Sb, Te, Ba and Bi) .   The all-solid-state electricity storage according to claim 1, wherein the lithium-transition metal-based composite oxide has a property that a redox potential decreases due to occlusion of lithium ions and a redox potential increases due to elimination of lithium ions. element. The all-solid-state electricity storage element as described in any one of Claim 1 or 2 with which the said lithium- transition metal type complex oxide has a layered rock salt structure or a spinel structure. The all-solid-state electrical storage element as described in any one of Claims 1-3 with which the said lithium- transition metal type complex oxide has a layered rock salt structure. Z is in the range of 0.4 to 0.7 in the uncharged state, z can be varied in the range of 0.2 to 1.0 at the time of charge accumulation, in any one of claims 1 to 4 The all-solid-state electricity storage element of description. The composition of the lithium-transition metal composite oxide is represented by Li _z (M1, M2) O ₂ , M1 is Ni and Co, and M2 is at least one selected from the group consisting of Mg, Al, and Zr. The all-solid-state electrical storage element as described in any one of Claims 1-5 . The lithium - composition of the transition metal based composite oxide is represented by _{Li z (M1, M2) O} 2, M1 is Ni and Co, M2 is Al, in any one of claims 1 to 6, The all-solid-state electricity storage element of description. Ratio of Ni to the total amount of M1 and M2 is less than 0.6 in atomic ratio, all-solid battery element according to any one of claims 1 to 7. The all-solid-state energy storage device according to any one of claims 1 to 8 , wherein the lithium-transition metal composite oxide is a polycrystal formed of a plurality of crystal particles, and the plurality of crystal particles are oriented. . Said first electrode and said having a second electrode pores, all-solid battery element according to any one of claims 1-9. The all-solid-state energy storage device according to claim 10 , wherein the first electrode and the second electrode have a porosity of 3 to 30%. The all-solid-state energy storage device according to claim 10 or 11 , wherein the volume ratio of open pores to all pores is 70% or more. Wherein the solid electrolyte is a garnet ceramic material, all-solid battery element according to any one of claims 1 to 12. The all-solid-state electric storage element according to claim 13 , wherein the garnet-based ceramic material is an oxide sintered body having a garnet-type or garnet-like crystal structure including at least Li, La, Zr, and O. . The all-solid-state electric storage element according to claim 14 , wherein the garnet-type or garnet-like crystal structure further includes Nb and / or Ta. The all-solid-state electric storage element according to claim 14 or 15 , wherein the oxide sintered body further contains Al and / or Mg. A plurality of the first electrode and the second electrode are prepared, and the solid electrolyte has a plate shape, and the plurality of first electrodes are arranged in a tile shape on one surface of the plate solid electrolyte. The all-solid-state energy storage device according to any one of claims 1 to 16 , wherein the plurality of second electrodes are arranged in a tile shape on the other surface of the plate-like solid electrolyte. A stack type all-solid-state energy storage device, wherein a plurality of all-solid-state energy storage devices according to any one of claims 1 to 17 are stacked via a current collector. Wherein the first electrode of the all-solid battery element of adjacent ones of the all-solid battery element, constitutes an active material plate with the second electrode and the current collector, the current collector is embedded in the interior of the active material plate 19. The stacked all-solid body according to claim 18 , wherein the stack is configured as an internal current collector, wherein one side of the active material plate constitutes the first electrode, and the other side of the active material plate constitutes the second electrode. Power storage element.