Patent Description:
Conventionally, an all-solid-state battery which is nonpolar and has no distinction between a positive electrode and a negative electrode (hereinafter, sometimes referred to as a "nonpolar all-solid-state battery") has been known (for example, <CIT>). Specifically, <CIT> describes a nonpolar all-solid-state battery in which both first and second electrode layers include Li<NUM>MnO<NUM> as an active material.

When Li<NUM>MnO<NUM> is used as an active material, it is difficult to achieve a high-capacity all-solid-state battery. To achieve a high-capacity all-solid-state battery, it is conceivable to use an active material having a specific capacity higher than Li<NUM>MnO<NUM> (capacity per active material weight, amount of electricity (Ah/g) according to the number of lithium ions desorbed from the active material). Examples of the active material having a specific capacity higher than Li<NUM>MnO<NUM> includes, for example, Li<NUM>V<NUM>(PO<NUM>)<NUM>.

<CIT> describes an all-solid-state battery in which Li<NUM>V<NUM>(PO<NUM>)<NUM> having a NASICON-type structure is commonly used as a positive electrode active material and a negative electrode active material. However, Li<NUM>V<NUM>(PO<NUM>)<NUM> has a large difference in specific capacity when functioning as the positive electrode active material and when functioning as the negative electrode active material. Therefore, when only Li<NUM>V<NUM>(PO<NUM>)<NUM> is commonly used as the positive electrode active material and the negative electrode active material, it is difficult to achieve a nonpolar all-solid-state battery having no distinction between the positive electrode and the negative electrode.

<CIT> discloses an all-solid battery having a high output power, exhibiting high safety, and capable of being produced at a low cost. The all-solid battery includes an internal electrode body having a cathode comprising a cathode material, an anode comprising an anode material, and a solid electrolyte layer comprising a solid electrolyte, the cathode material, the anode material, and the solid electrolyte being phosphoric acid compounds, the internal electrode body being integrated by firing the cathode, anode, and solid electrolyte layer, and the internal electrode body containing water.

<CIT> discloses that a lithium ion secondary battery includes a pair of electrodes and a solid electrolyte layer. The solid electrolyte layer is provided between the pair of electrodes and includes titanium aluminum lithium phosphate. At least one of the pair of electrodes includes vanadium lithium phosphate. At least one of the pair of electrodes includes at least one constituent of titanium and aluminum. The amount of the at least one constituent existing on a side opposite to the solid electrolyte layer is smaller than the amount of the at least one constituent existing on the solid electrolyte layer side.

<CIT> discloses that a solid-state rechargeable battery includes a pair of electrode layers and a solid electrolyte layer interposed between the pair of electrode layers. The pair of electrode layers each include a phosphate having an olivine crystal structure. The phosphate contains a transition metal and lithium.

We have appreciated that it would be desirable to provide a high-capacity nonpolar all-solid-state battery.

A nonpolar all-solid-state battery according to the present invention includes a first electrode, a second electrode, and a solid electrolyte layer. The solid electrolyte layer is provided between the first electrode and the second electrode. Each of the first electrode and the second electrode includes a first active material and at least one kind of negative electrode active material. The first active material functions as both a positive electrode active material and a negative electrode active material. The first active material is an active material having a larger specific capacity when functioning as the positive electrode active material than a specific capacity when functioning as the negative electrode active material. In each of the first electrode and the second electrode, a ratio of the first active material to a total amount of active materials is more than <NUM>% by mass and less than <NUM>% by mass. A mass of each of the active materials is equal between the first electrode and the second electrode.

<FIG> is a schematic cross-sectional view of a nonpolar all-solid-state battery according to one embodiment of the present invention.

Hereinafter, an example of a preferred embodiment of the present invention will be described. However, the following embodiment is merely an example. The present invention is not at all limited to the following embodiments.

<FIG> is a schematic cross-sectional view of a nonpolar all-solid-state battery <NUM> according to the present embodiment. The nonpolar all-solid-state battery <NUM> includes a first electrode <NUM>, a second electrode <NUM>, and a solid electrolyte layer <NUM>. The solid electrolyte layer <NUM> is provided between the first electrode <NUM> and the second electrode <NUM>. Specifically, one main surface of the solid electrolyte layer <NUM> is in contact with the first electrode <NUM>, and the other main surface is in contact with the second electrode <NUM>. Each of the first electrode <NUM> and the second electrode <NUM> is joined to the solid electrolyte layer <NUM> by sintering. That is, the first electrode <NUM>, the solid electrolyte layer <NUM>, and the second electrode <NUM> are an integrated sintered body.

The nonpolar all-solid-state battery <NUM> is a nonpolar all-solid-state battery that functions as a battery when the first electrode <NUM> is connected to a positive electrode and the second electrode <NUM> is connected to a negative electrode, and also when the first electrode <NUM> is connected to the negative electrode and the second electrode <NUM> is connected to the positive electrode.

Each of the first electrode <NUM> and the second electrode <NUM> includes a first active material and at least one kind of negative electrode active material.

The first active material is an active material that functions as both a positive electrode active material and a negative electrode active material. However, the specific capacity when the first active material functions as a positive electrode active material is larger than the specific capacity when the first active material functions as a negative electrode active material. Examples of such a first active material include, for example, Li(<NUM>-x)V(<NUM>-y)My(PO<NUM>)<NUM> (where M is at least one kind of element selected from the group consisting of Al, Ge, Ti, Zr, Mg, Fe, Nb, and Sn, <NUM> ≤ x ≤ <NUM>, and <NUM> ≤ y ≤ <NUM>). Specific examples of Li(<NUM>-x)V(<NUM>-y)My(PO<NUM>)<NUM> include NASICON-type Li<NUM>V<NUM>(PO<NUM>)<NUM>, Li<NUM>Al<NUM>V<NUM>(PO<NUM>)<NUM>, Li<NUM>Fe<NUM>V<NUM>(PO<NUM>)<NUM>, Li<NUM>Ti<NUM>V<NUM>(PO<NUM>)<NUM>, and Li<NUM>Ti<NUM>Mg<NUM>V<NUM>(PO<NUM>)<NUM>. Among them, NASICON-type Li<NUM>V<NUM>(PO<NUM>)<NUM> is more preferably used as the first active material.

Each of the first electrode <NUM> and the second electrode <NUM> may include one kind of first active material, or may include a plurality of kinds of first active material.

Each of the first electrode <NUM> and the second electrode <NUM> includes at least one kind of negative electrode active material in addition to the first active material. In the present invention, the "negative electrode active material" refers to an active material that functions as a negative electrode active material but does not substantially function as a positive electrode active material. Here, the phrase "does not substantially function as a positive electrode active material" means that it is an active material that functions only from lithium insertion reaction, that is, no lithium detrimental reaction can occur during charging.

The first electrode <NUM> and the second electrode <NUM> may each include, in addition to the first active material and the negative electrode active material, for example, a conductive material having electronic conductivity, a solid electrolyte, a structure holding material, a positive electrode active material, and the like. Specific examples of the conductive material preferably used include, for example, metals, carbons, conductive oxides, conductive organic substances. The structure holding material is not particularly limited as long as it does not deteriorate the functions of the active material, the solid electrolyte, and the conductive material by reacting with the solid electrolyte and the conductive material. Specific examples of the structure holding material preferably used include Al<NUM>O<NUM>, SiO<NUM>, ZrO<NUM>, and GeO<NUM>. The solid electrolyte included in each of the first electrode <NUM> and the second electrode <NUM> preferably has the same crystal structure as that of the solid electrolyte included in the solid electrolyte layer <NUM>, and more preferably is the same solid electrolyte as the solid electrolyte included in the solid electrolyte layer <NUM>. Specific examples of the positive electrode active material preferably used include, for example, LiVOPO<NUM>, and LiVP<NUM>O<NUM>.

In the nonpolar all-solid-state battery <NUM> according to the present embodiment, each of the first electrode <NUM> and the second electrode <NUM> includes the negative electrode active material in addition to the first active material having the larger specific capacity when functioning as a positive electrode active material than the specific capacity when functioning as a negative electrode active material. Therefore, for example, when the first electrode <NUM> is a positive electrode and the second electrode <NUM> is a negative electrode, the negative electrode active material included in the first electrode <NUM> does not function as an active material, and the negative electrode active material included in the second electrode <NUM> functions as an active material. When the first electrode <NUM> is a negative electrode and the second electrode <NUM> is a positive electrode, the negative electrode active material included in the first electrode <NUM> functions as an active material, and the negative electrode included in the second electrode <NUM> does not function as an active material. For this reason, the capacity difference of the nonpolar all-solid-state battery <NUM> between the case where the first electrode <NUM> is a positive electrode and the case where the first electrode <NUM> is a negative electrode can be reduced. Thus, for example, an active material such as NASICON-type Li<NUM>V<NUM>(PO<NUM>)<NUM>, which has a large specific capacity but has the larger specific capacity when functioning as a positive electrode active material than the specific capacity when functioning as a negative electrode active material can be used in the nonpolar all-solid-state battery <NUM>. Therefore, a high-capacity nonpolar all-solid-state battery <NUM> can be achieved.

However, when the content of the first active material having a large specific capacity is small, the capacity of the nonpolar all-solid-state battery <NUM> cannot be sufficiently increased. Therefore, in each of the first electrode <NUM> and the second electrode <NUM>, the ratio of the first active material to the total amount of the active materials needs to be more than <NUM>% by mass and less than <NUM>% by mass.

From the viewpoint of achieving a nonpolar all-solid-state battery <NUM> having a larger capacity, in each of the first electrode <NUM> and the second electrode <NUM>, the ratio of the first active material to the total amount of the active materials is more than <NUM>% by mass, preferably more than <NUM>% by mass, and more preferably <NUM>% by mass or more. In each of the first electrode <NUM> and the second electrode <NUM>, the ratio of the first active material to the total amount of the active materials is less than <NUM>% by mass, preferably <NUM>% by mass or less, and more preferably <NUM>% by mass or less.

From the same viewpoint, it is preferable to use the first active material having a large specific capacity. Specifically, it is preferable to use, as the first active material, for example, Li(<NUM>-x)V(<NUM>-y)My(PO<NUM>)<NUM> (where M is at least one kind of element selected from the group consisting of Al, Ge, Ti, Zr, Mg, Fe, Nb, and Sn, <NUM> ≤ x ≤ <NUM>, and <NUM> ≤ y ≤ <NUM>), and among them, it is more preferable to use NASICON-type Li<NUM>V<NUM>(PO<NUM>)<NUM>.

Further, from the viewpoint of achieving the nonpolar all-solid-state battery <NUM>, the mass of each active material needs to be substantially equal between the first electrode <NUM> and the second electrode <NUM>.

From the viewpoint of achieving a nonpolar all-solid-state battery <NUM> having a smaller polarity, it is preferable that the total amount of the specific capacity of the active material included in the first electrode <NUM> when the first electrode <NUM> is a positive electrode is substantially equal to the total amount of the specific capacity of the active material included in the second electrode <NUM> when the second electrode <NUM> is a positive electrode. It is preferable that the total amount of the specific capacity of the active material included in the first electrode <NUM> when the first electrode <NUM> is a negative electrode is substantially equal to the total amount of the specific capacity of the active material included in the second electrode <NUM> when the second electrode <NUM> is a negative electrode.

The negative electrode active material included in the first electrode <NUM> and the second electrode <NUM> is not particularly limited. Examples of the negative electrode active material preferably used when Li(<NUM>-x)V(<NUM>-y)My(PO<NUM>)<NUM> (where M is at least one kind of element selected from the group consisting of Al, Ge, Ti, Zr, Mg, Fe, Nb, and Sn, <NUM> ≤ x ≤ <NUM>, and <NUM> ≤ y ≤ <NUM>) is used as the first active material include, for example, MOx (M is at least one kind of element selected from the group consisting of Ti, Nb, Mo and P, and <NUM> ≤ x ≤ <NUM>). Among them, TiO<NUM>, PNb<NUM>O<NUM>, TiNb<NUM>O<NUM>, Ti<NUM>Nb<NUM>O<NUM>, and the like are preferably used as the negative electrode active material, and anatase-type TiO<NUM> is more preferably used. This is because the negative electrode active material is difficult to react with Li(<NUM>-x)V(<NUM>-y)My(PO<NUM>)<NUM> (where M is at least one kind of element selected from the group consisting of Al, Ge, Ti, Zr, Mg, Fe, Nb, and Sn, <NUM> ≤ x ≤ <NUM>, and <NUM> ≤ y ≤ <NUM>).

In the present invention, MOx includes those in which part of M is substituted with Si, Zr, Y, or the like, and those in which part of oxygen is lost (for example, TiO<NUM> or the like).

Since the first electrode <NUM> and the second electrode <NUM> include the first active material that functions as both a positive electrode active material and a negative electrode active material, the nonpolar all-solid-state battery <NUM> can be charged and discharged even at a voltage higher than zero volt, and can be charged and discharged at a voltage lower than zero volt.

The solid electrolyte included in the solid electrolyte layer <NUM> is not particularly limited. From the viewpoint of increasing the close-contact property between the solid electrolyte layer <NUM> and the first electrode <NUM> or the second electrode <NUM>, a solid electrolyte having the same crystal structure as the first electrolyte included in the first electrode <NUM> and the second electrode <NUM> is preferably used. For example, when the first electrolyte is a NASICON type, it is preferable to use a NASICON-type solid electrolyte. Specific examples of the NASICON-type solid electrolyte include, for example, Li<NUM>Al<NUM>Ge<NUM>(PO<NUM>)<NUM> and Li<NUM>Al<NUM>Ti<NUM>(PO<NUM>)<NUM>, Li<NUM>Na<NUM>Al<NUM>Ge<NUM>(PO<NUM>)<NUM>.

As described above, since the nonpolar all-solid-state battery <NUM> of the present embodiment has a high capacity, a high-performance electronic device can be achieved by using the nonpolar all-solid-state battery <NUM>.

Hereinafter, the present invention will be described in more detail with reference to specific examples. However, the present invention is not limited to the following examples, and can be appropriately changed and carried out without departing from the gist thereof.

In order to produce an all-solid-state battery, respective main materials were prepared as starting materials for the electrode layers <NUM> and <NUM> and the solid electrolyte layer <NUM> as follows. A slurry was produced from each of the prepared main materials, and a green sheet was produced using the slurry.

Powder obtained by mixing powder having a NASICON-type structure crystal phase having a composition of Li<NUM>V<NUM>(PO<NUM>)<NUM> as the active material <NUM> which is a positive electrode active material, glass powder having a composition of Li<NUM>Al<NUM>Ge<NUM>(PO<NUM>)<NUM> as a solid electrolyte, and carbon powder as a conductive material at a mass ratio of <NUM> : <NUM> : <NUM> was used as a main material.

Glass powder having a composition of Li<NUM>Al<NUM>Ge<NUM>(PO<NUM>)<NUM> was used as a main material.

Each of the main materials prepared above, polyacetal resin, and alcohol were mixed at a mass ratio of <NUM> : <NUM> : <NUM> to produce an electrode slurry and a solid electrolyte slurry.

Each of the slurries produced above was coated on a polyethylene terephthalate (PET) film using a doctor blade method, and dried on a hot plate heated to a temperature of <NUM>, and a sheet was formed to have a thickness of <NUM>. The sheet was cut so as to have a plane size of <NUM> × <NUM> to produce an electrode layer sheet to be the electrode layer <NUM>, an electrode layer sheet to be the electrode layer <NUM>, and a solid electrolyte layer sheet to be the solid electrolyte layer <NUM>.

A laminate was produced, in which the electrode layer sheet to be the electrode layer <NUM> was laminated on one surface of the solid electrolyte sheet obtained as described above, and the electrode layer sheet to be the electrode layer <NUM> was laminated on the other surface. This laminate was cut so as to have a plane size of <NUM> × <NUM>. Thereafter, each laminate was sandwiched between two porous ceramic plates and fired at a temperature of <NUM> in an air atmosphere to remove the polyacetal resin. Thereafter, by firing the resultant at a temperature of <NUM> in a nitrogen gas atmosphere, an all-solid-state battery element body of Comparative Example <NUM> was produced.

Thereafter, the resultant was dried at a temperature of <NUM> to remove moisture, and then sealed with a <NUM> type coin cell to produce an all-solid-state battery of Comparative Example <NUM>.

The all-solid-state battery of Comparative Example <NUM> was charged to a voltage of <NUM> V at a current of <NUM> mA (held at <NUM> V for <NUM> hours after reaching <NUM> V), and then discharged to <NUM> V at a discharge current of <NUM> mA. This charge/discharge was repeated <NUM> cycles.

The initial charge capacity or discharge capacity per unit weight of the active material and the initial charge capacity or discharge capacity per total active material weight included in the electrode layer <NUM> or <NUM> are values shown in Table <NUM>, respectively.

The initial charge/discharge efficiency, which is the ratio between the initial discharge capacity and the initial charge capacity, and the capacity retention ratio after <NUM> cycles, which is the ratio between the initial discharge capacity and the discharge capacity at the 10th cycle are values shown in Table <NUM>, respectively.

An all-solid-state battery was produced and evaluated in the same manner as in Comparative Example <NUM> except that, in the electrode layers <NUM> and <NUM>, powder obtained by mixing powder having a NASICON-type structure crystal phase having a composition of Li<NUM>V<NUM>(PO<NUM>)<NUM> as the active material <NUM> which is a positive electrode active material, powder having a composition of Li<NUM>Ti<NUM>O<NUM> as an active material <NUM> which is a negative electrode active material, glass powder having a composition of Li<NUM>Al<NUM>Ge<NUM>(PO<NUM>)<NUM> as a solid electrolyte, and carbon powder as a conductive material at a mass ratio of <NUM> : <NUM> : <NUM> : <NUM> was used as a main material.

An all-solid-state battery was produced and evaluated in the same manner as in Comparative Example <NUM> except that, in the electrode layers <NUM> and <NUM>, powder obtained by mixing powder having a NASICON-type structure crystal phase having a composition of Li<NUM>V<NUM>(PO<NUM>)<NUM> as the active material <NUM> which is a positive electrode active material, powder of anatase-type TiO<NUM> as an active material <NUM> which is a negative electrode active material, glass powder having a composition of Li<NUM>Al<NUM>Ge<NUM>(PO<NUM>)<NUM> as a solid electrolyte, and carbon powder as a conductive material at a mass ratio of <NUM> : <NUM> : <NUM> : <NUM> was used as a main material.

An all-solid-state battery was produced and evaluated in the same manner as in Comparative Example <NUM> except that, in the electrode layers <NUM> and <NUM>, powder obtained by mixing powder having a composition of Li<NUM>MnO<NUM> as the active material <NUM> which is a positive electrode active material, glass powder having a composition of Li<NUM>Al<NUM>Ge<NUM>(PO<NUM>)<NUM> as a solid electrolyte, and carbon powder as a conductive material at a mass ratio of <NUM> : <NUM> : <NUM> was used as a main material.

An all-solid-state battery was produced and evaluated in the same manner as in Comparative Example <NUM> except that, in the electrode layers <NUM> and <NUM>, powder obtained by mixing powder having a composition of Li<NUM>Al<NUM>Ti<NUM>(PO<NUM>)<NUM> as the active material <NUM> which is a negative electrode active material, LiFePO<NUM> as an active material <NUM> which is a positive electrode active material that does not function as a negative electrode active material, glass powder having a composition of Li<NUM>Al<NUM>Ge<NUM>(PO<NUM>)<NUM> as a solid electrolyte, and Ag-Pd powder as a conductive material at a mass ratio of <NUM> : <NUM> : <NUM> : <NUM> was used as a main material.

An all-solid-state battery was produced and evaluated in the same manner as in Comparative Example <NUM> except that, in the electrode layers <NUM> and <NUM>, powder obtained by mixing powder having a NASICON-type structure crystal phase having a composition of Li<NUM>V<NUM>(PO<NUM>)<NUM> as the active material <NUM> which is a positive electrode active material, powder of anatase-type TiO<NUM> as the negative electrode active material <NUM>, glass powder having a composition of Li<NUM>Al<NUM>Ge<NUM>(PO<NUM>)<NUM> as a solid electrolyte, and carbon powder as a conductive material at a mass ratio of <NUM> : <NUM> : <NUM> : <NUM> was used as a main material.

An all-solid-state battery was produced and evaluated in the same manner as in Example <NUM> except that powder of rutile-type TiO<NUM> was used as the active material <NUM> which is a negative electrode active material.

An all-solid-state battery was produced and evaluated in the same manner as in Example <NUM> except that powder of Nb<NUM>O<NUM> was used as the active material <NUM> which is a negative electrode active material.

An all-solid-state battery was produced and evaluated in the same manner as in Example <NUM> except that powder of PNb<NUM>O<NUM> was used as the active material <NUM> which is a negative electrode active material.

An all-solid-state battery was produced and evaluated in the same manner as in Example <NUM> except that powder of TiNb<NUM>O<NUM> was used as the active material <NUM> which is a negative electrode active material.

An all-solid-state battery was produced and evaluated in the same manner as in Example <NUM> except that powder of Ti<NUM>Nb<NUM>O<NUM> was used as the active material <NUM> which is a negative electrode active material.

An all-solid-state battery was produced and evaluated in the same manner as in Comparative Example <NUM> except that, in the electrode layers <NUM> and <NUM>, powder obtained by mixing powder having a NASICON-type structure crystal phase having a composition of Li<NUM>V<NUM>(PO<NUM>)<NUM> as the active material <NUM> which is a positive electrode active material, powder of anatase-type TiO<NUM> as the active material <NUM> which is a negative electrode active material, powder of Ti<NUM>Nb<NUM>O<NUM> as the active material <NUM> which is a negative electrode active material, glass powder having a composition of Li<NUM>Al<NUM>Ge<NUM>(PO<NUM>)<NUM> as a solid electrolyte, and carbon powder as a conductive material at a mass ratio of <NUM> : <NUM> : <NUM> : <NUM> : <NUM> was used as a main material.

An all-solid-state battery was produced and evaluated in the same manner as in Example <NUM> except that powder obtained by mixing the active material <NUM>, the active material <NUM>, the solid electrolyte, and the conductive material at a mass ratio of <NUM> : <NUM> : <NUM> : <NUM> was used as a main material.

An all-solid-state battery was produced and evaluated in the same manner as in Comparative Example <NUM> except that, in the electrode layers <NUM> and <NUM>, powder obtained by mixing powder having a NASICON-type structure crystal phase having a composition of Li<NUM>V<NUM>(PO<NUM>)<NUM> as the active material <NUM> which is a positive electrode active material, powder of TiNb<NUM>O<NUM> as the active material <NUM> which is a negative electrode active material, powder of LiVOPO<NUM> as the active material <NUM> which is a positive electrode active material, glass powder having a composition of Li<NUM>Na<NUM>Ti<NUM>Al<NUM>(PO<NUM>)<NUM> as a solid electrolyte, and carbon powder as a conductive material at a mass ratio of <NUM> : <NUM> : <NUM> : <NUM> : <NUM> was used as a main material, and further, after polyacetal resin was removed, the resultant was fired at a temperature of <NUM> in a nitrogen gas atmosphere.

An all-solid-state battery was produced and evaluated in the same manner as in Comparative Example <NUM> except that, in the electrode layers <NUM> and <NUM>, powder obtained by mixing powder having a NASICON-type structure crystal phase having a composition of Li<NUM>V<NUM>(PO<NUM>)<NUM> as the active material <NUM> which is a positive electrode active material, powder of TiNb<NUM>O<NUM> as the active material <NUM> which is a negative electrode active material, powder of LiVOPO<NUM> as the active material <NUM> which is a positive electrode active material, powder of rutile-type TiO<NUM> as an active material <NUM> which is a negative electrode active material, glass powder having a composition of Li<NUM>Ti<NUM>Al<NUM>(PO<NUM>)<NUM> as a solid electrolyte, and carbon powder as a conductive material at a mass ratio of <NUM> : <NUM> : <NUM> : <NUM> : <NUM> : <NUM> was used as a main material, and further, after polyacetal resin was removed, the resultant was fired at a temperature of <NUM> in a nitrogen gas atmosphere.

An all-solid-state battery was produced and evaluated in the same manner as in Comparative Example <NUM> except that, in the electrode layers <NUM> and <NUM>, powder obtained by mixing powder having a NASICON-type structure crystal phase having a composition of Li<NUM>V<NUM>(PO<NUM>)<NUM> as the active material <NUM> which is a positive electrode active material, powder of TiNb<NUM>O<NUM> as a negative electrode active material of the active material <NUM>, powder of PNb<NUM>O<NUM> as a negative electrode active material of the active material <NUM>, powder of rutile-type TiO<NUM> as a negative electrode active material of the active material <NUM>, glass powder having a composition of Li<NUM>Al<NUM>Ge<NUM>Ti<NUM>(PO<NUM>)<NUM> as a solid electrolyte, and carbon powder as a conductive material at a mass ratio of <NUM> : <NUM> : <NUM> : <NUM> : <NUM> : <NUM> was used as a main material, and further, after polyacetal resin was removed, the resultant was fired at a temperature of <NUM> in a nitrogen gas atmosphere.

An all-solid-state battery was produced and evaluated in the same manner as in Comparative Example <NUM> except that, in the electrode layers <NUM> and <NUM>, powder obtained by mixing powder having a NASICON-type structure crystal phase having a composition of Li<NUM>V<NUM>(PO<NUM>)<NUM> as the active material <NUM> which is a positive electrode active material, powder of PNb<NUM>O<NUM> as the active material <NUM> which is a negative electrode active material, glass powder having a composition of Li<NUM>Na<NUM>Ca<NUM>Zr<NUM>(PO<NUM>)<NUM> as a solid electrolyte, and carbon powder as a conductive material at a mass ratio of <NUM> : <NUM> : <NUM> : <NUM> was used as a main material, and further, after polyacetal resin was removed, the resultant was fired at a temperature of <NUM> in a nitrogen gas atmosphere.

An all-solid-state battery was produced and evaluated in the same manner as in Comparative Example <NUM> except that, in the electrode layers <NUM> and <NUM>, powder obtained by mixing powder having a NASICON-type structure crystal phase having a composition of Li<NUM>Al<NUM>V<NUM>(PO<NUM>)<NUM> as the active material <NUM> which is a positive electrode active material, powder of anatase-type TiO<NUM> as the active material <NUM> which is a negative electrode active material, glass powder having a composition of Li<NUM>Al<NUM>Ge<NUM>(PO<NUM>)<NUM> as a solid electrolyte, and carbon powder as a conductive material at a mass ratio of <NUM> : <NUM> : <NUM> : <NUM> was used as a main material, and further, after polyacetal resin was removed, the resultant was fired at a temperature of <NUM> in a nitrogen gas atmosphere.

An all-solid-state battery was produced and evaluated in the same manner as in Example <NUM> except that powder having a NASICON-type structure crystal phase having a composition of Li<NUM>Ge<NUM>V<NUM>(PO<NUM>)<NUM> as the active material <NUM> which is a positive electrode active material was used.

An all-solid-state battery was produced and evaluated in the same manner as in Example <NUM> except that powder having a NASICON-type structure crystal phase having a composition of Li<NUM>Ti<NUM>V<NUM>(PO<NUM>)<NUM> as the active material <NUM> which is a positive electrode active material was used.

An all-solid-state battery was produced and evaluated in the same manner as in Example <NUM> except that powder having a NASICON-type structure crystal phase having a composition of Li<NUM>Zr<NUM>V<NUM>(PO<NUM>)<NUM> as the active material <NUM> which is a positive electrode active material was used.

An all-solid-state battery was produced and evaluated in the same manner as in Example <NUM> except that powder having a NASICON-type structure crystal phase having a composition of Li<NUM>Ti<NUM>Mg<NUM>V<NUM>(PO<NUM>)<NUM> as the active material <NUM> which is a positive electrode active material was used.

An all-solid-state battery was produced and evaluated in the same manner as in Example <NUM> except that powder having a NASICON-type structure crystal phase having a composition of Li<NUM>Ti<NUM>Fe<NUM>V<NUM>(PO<NUM>)<NUM> as the active material <NUM> which is a positive electrode active material was used.

From the results of Comparative Example <NUM>, Comparative Example <NUM>, Example <NUM>, and Examples <NUM> to <NUM>, it is found that a large initial discharge capacity and a high capacity retention ratio can be achieved when the first active material that functions as both the positive electrode active material and the negative electrode active material and has the larger specific capacity when functioning as the positive electrode active material than the specific capacity when functioning as the negative electrode active material, and at least one kind of negative electrode active material are used, and when the ratio of the first active material to the total amount of the active materials is more than <NUM>% by mass and less than <NUM>% by mass in each of the first electrode and the second electrode.

Further, from the results of Example <NUM> and Examples <NUM> to <NUM>, it is found that, from the viewpoint of achieving a larger initial discharge capacity, a higher charge/discharge efficiency, and a high capacity retention ratio, in each of the first electrode and the second electrode, the ratio of the first active material to the total amount of the active materials is more than <NUM>% by mass, preferably <NUM>% by mass or less, more preferably <NUM>% by mass or more, and more preferably <NUM>% by mass or less.

From the results of Examples <NUM> to <NUM>, it is found that a large initial discharge capacity, a high charge/discharge efficiency, and a high capacity retention rate can be realized even when various negative electrode active materials represented by the general formula MOx (M is at least one kind of element selected from the group consisting of Ti, Nb, Mo, and P, and <NUM> ≤ x ≤ <NUM>) are used.

From the results of Example <NUM>, Example <NUM>, and Example <NUM>, it is found that a large initial discharge capacity, a high charge/discharge efficiency, and a high capacity retention rate can be achieved even when two or more kinds of negative electrode active materials are used.

The nonpolar all-solid-state battery according to the present embodiment includes the first electrode, the second electrode, and the solid electrolyte layer. The solid electrolyte layer is provided between the first electrode and the second electrode. Each of the first electrode and the second electrode includes a first active material and at least one kind of negative electrode active material. The first active material functions as both a positive electrode active material and a negative electrode active material. The first active material is an active material having a larger specific capacity when functioning as the positive electrode active material than a specific capacity when functioning as the negative electrode active material. In each of the first electrode and the second electrode, a ratio of the first active material to a total amount of active materials is more than <NUM>% by mass and less than <NUM>% by mass. A mass of each of the active materials is equal between the first electrode and the second electrode.

In the nonpolar all-solid-state battery according to the present embodiment, it is preferable that the total amount of the specific capacities of all the active materials included in the first electrode (capacity per total active material weight included in the first electrode) when the first electrode is a positive material is equal to the total amount of the specific capacities of all the active materials included in the second electrode (capacity per total active material weight included in the second electrode) when the second electrode is a positive electrode. It is preferable that the total amount of the specific capacities of all the active materials included in the first electrode when the first electrode is a negative electrode is substantially equal to the total amount of the specific capacities of all the active materials included in the second electrode when the second electrode is a negative electrode.

In the nonpolar all-solid-state battery according to the present embodiment, it is preferable that each of the first electrode and the second electrode includes, as the first active material, a NASICON-type active material Li(<NUM>-x)V(<NUM>-y)My(PO<NUM>)<NUM> (where M is at least one kind of element selected from the group consisting of Al, Ge, Ti, Zr, Mg, Fe, Nb, and Sn, <NUM> ≤ x ≤ <NUM>, and <NUM> ≤ y ≤ <NUM>).

In the nonpolar all-solid-state battery according to the present embodiment, it is preferable that each of the first electrode and the second electrode includes, as the negative electrode active material, MOx (M is at least one kind of element selected from the group consisting of Ti, Nb, Mo, and P, and <NUM> ≤ x ≤ <NUM>).

In the nonpolar all-solid-state battery according to the present embodiment, it is preferable that each of the first electrode and the second electrode includes, as the negative electrode active material, at least one kind of active material selected from the group consisting of TiO<NUM>, PNb<NUM>O<NUM>, TiNb<NUM>O<NUM>, and Ti<NUM>Nb<NUM>O<NUM>.

In the nonpolar all-solid-state battery according to the present embodiment, it is preferable that each of the first electrode and the second electrode includes anatase-type TiO<NUM> as the negative electrode active material.

In the nonpolar all-solid-state battery according to the present embodiment, it is preferable that, in each of the first electrode and the second electrode, the ratio of the first active material to the total amount of the active materials is more than <NUM>% by mass and <NUM>% by mass or less.

In the nonpolar all-solid-state battery according to the present embodiment, it is preferable that, in each of the first electrode and the second electrode, the ratio of the first active material to the total amount of the active materials is <NUM>% by mass or more and <NUM>% by mass or less.

Claim 1:
A nonpolar all-solid-state battery (<NUM>) comprising:
a first electrode (<NUM>);
a second electrode (<NUM>); and
a solid electrolyte layer (<NUM>) provided between the first electrode (<NUM>) and the second electrode (<NUM>),
wherein each of the first electrode (<NUM>) and the second electrode (<NUM>) includes:
a first active material that functions as both a positive electrode active material and a negative electrode active material, and has a larger specific capacity when functioning as the positive electrode active material than a specific capacity when functioning as the negative electrode active material; and
at least one kind of negative electrode active material, and
in each of the first electrode (<NUM>) and the second electrode (<NUM>), a ratio of the first active material to a total amount of active materials is more than <NUM>% by mass and less than <NUM>% by mass, and a mass of each of the active materials is equal between the first electrode (<NUM>) and the second electrode (<NUM>).