POSITIVE ELECTRODE ACTIVE MATERIAL, ELECTRODE, BATTERY AND METHOD OF PRODUCING POSITIVE ELECTRODE ACTIVE MATERIAL

[0001] This application claims priority to Japanese Patent Application No. 2024-214280 filed on Dec. 9, 2024. The disclosure of the above-identified application, including the specification, drawings, and claims, is incorporated by reference herein in its entirety.

[0002] The present disclosure relates to a positive electrode active material, an electrode, a battery, and a method of producing a positive electrode active material.

[0003] Japanese Unexamined Patent Application Publication No. 2023-039365 (JP2023-039365A) discloses a positive electrode active material represented by LiMn_zM2_bFe_1−z−bPO₄ (M2 is at least one selected from the group consisting of Ni, Co, Ti, Cu, Zn, Mg, Zr, Ca, Y, Mo, Ba, Pb, Bi, La, Ce, Nd, Gd, Al, Ga, and Sr).

[0004] Olivine lithium manganese iron phosphate (LMFP) is examined as a positive electrode active material. LMFP has room for improvement of cycle durability.

[0005] The present disclosure relates to a positive electrode active material that improves the cycle durability of LMFP, an electrode, a battery, and a method of producing the positive electrode active material.

[0006] Hereinafter, the technical constitution and the operation and effect of the present disclosure will be described. However, the operation mechanism includes presumptions. The operation mechanism does not limit the technical scope of the present disclosure.

[0007] The first aspect of the present disclosure is a positive electrode active material. The positive electrode active material includes olivine lithium manganese iron phosphate. The olivine lithium manganese iron phosphate includes a first dopant at a manganese-iron site. The first dopant is at least one selected from the group consisting of tungsten and molybdenum. A first site occupancy of the first dopant is 1% to 10% at the manganese-iron site.

[0008] With respect to the improvement of the performance of LMFP, for example, the introduction of various dopants into the MnFe site has conventionally been attempted. However, it is considered that the first dopant (W, Mo) has not conventionally been introduced such that the site occupancy at the MnFe site is 1% or more. Even in the case where 1% or more of the first dopant seems to have been successfully doped in terms of composition, it is considered that, in reality, the greater part of the first dopant is not introduced into the MnFe site and is present outside the crystal structure in the form of an oxide or the like. This is considered due to a significantly high melting point of the dopant source of the first dopant.

[0009] According to the novel findings of the present disclosure, when a specific dopant source (Li₂WO₃, Li₂MoO₄) is used and firing is conducted at a high temperature of about 1200° C. in an oxygen atmosphere, the MnFe site is doped with 1% or more of the first dopant. Further, when the MnFe site is doped with 1% or more of the first dopant, the cycle durability of LMFP is expected to be significantly improved. However, when the site occupancy of the first dopant is more than 10%, initial capacity may be reduced. Therefore, the site occupancy is 1% or more and 10% or less.

[0010] Since Fe is usually oxidized at a high temperature of about 1200° C. in an oxygen atmosphere, the dopant is considered to be hardly introduced into the MnFe site. However, it is considered that, when the specific dopant source (Li₂WO₃, Li₂MoO₄) is used, the dopant source is oxidized more preferentially than Fe, which enables the introduction into the MnFe site.

[0011] Although the details of the mechanism of improvement of cycle durability are unclear, one of the reasons is presumed to be a high valence of the first dopant (W, Mo). However, it is difficult to introduce Os, Re, and the like having a high valence like the first dopant into the MnFe site under the same conditions as the first dopant. This is considered due to that Os, Re, and the like have no valence appropriate to the MnFe site.

[0012] In the positive electrode active material according to the first aspect of the present disclosure, the olivine lithium manganese iron phosphate may include a second dopant at a phosphorus site, and the second dopant may be at least one selected from the group consisting of aluminum and gallium.

[0013] The first dopant (W, Mo) has two excess valence electrons relative to surrounding Mn and Fe at the MnFe site. When excess electrons reduce Mn and Fe, the potential may be reduced. The reduction of the potential may reduce energy density.

[0014] The second dopant (Al, Ga) lacks two valence electrons relative to surrounding P at the P site (the phosphorus site). When the second dopant is introduced into the P site, charge compensation may occur. That is, the improvement of valence balance is expected. By improving valence balance, the improvement of cycle durability is expected. Further, by improving valence balance, the reduction of initial capacity along with the introduction of the first dopant is expected to be moderated. It is considered that the higher the amount of the first dopant added is, the more charge compensation is needed.

[0015] In the positive electrode active material according to the first aspect of the present disclosure, the second dopant may include a second site occupancy at the phosphorus site, and a ratio of the second site occupancy to the first site occupancy may be 0.8 to 1.2.

[0016] Charge compensation is considered to easily occur because the abundance of the second dopant (Al, Ga) is approximate to the abundance of the first dopant (W, Mo).

[0017] In the positive electrode active material according to the first aspect of the present disclosure, the olivine lithium manganese iron phosphate may include a composition represented by the general formula “Li_1+a[(Mn_1−bFe_b)_1−cX_c][P_1−dY_d]O₄”, and in the general formula, “X” may represent the first dopant, “Y” may represent the second dopant, and the relationships of “−0.5≤a≤0.5”, “0.1≤b≤0.9”, “0.01≤c≤0.10”, and “0.8≤d/c≤1.2” may be satisfied.

[0018] In the positive electrode active material according to the first aspect of the present disclosure, the first site occupancy may be 2% to 6%.

[0019] When the site occupancy of the first dopant is 2% to 6%, the improvement of cycle durability is expected.

[0020] The electrode according to the second aspect of the present disclosure may include a positive electrode layer, and the positive electrode layer may include the positive electrode active material according to the first aspect of the present disclosure.

[0021] The positive electrode layer may be referred to as “a positive electrode active material layer”, “a positive electrode composite layer”, and the like. The “electrode” may be “a monopolar electrode (positive electrode)” or “a bipolar electrode”, as long as the electrode includes the positive electrode layer.

[0022] The battery according to the third aspect of the present disclosure may include the electrode according to the second aspect of the present disclosure.

[0023] In the battery according to the third aspect of the present disclosure, the battery may include a bipolar structure.

[0024] The method of producing a positive electrode active material according to the fourth aspect of the present disclosure includes stirring and mixing manganese carbonate, ferric phosphate, and lithium dihydrogen phosphate at a predetermined composition ratio in water to form a slurry, spray-drying the slurry to form a first precursor, mixing the first precursor and a first dopant source, firing the mixture of the first precursor and the first dopant source in an oxygen atmosphere at 1200° C. to form a second precursor, mixing the second precursor, lithium hydroxide, and a second dopant source, and firing the mixture of the second precursor, the lithium hydroxide, and the second dopant source in a nitrogen atmosphere at 650° C.

[0025] In the method of producing a positive electrode active material according to the fourth aspect of the present disclosure, the first dopant source may include at least one of compounds including a composition represented by the chemical formula: Li₂WO₃ or Li₂MoO₄.

[0026] In the method of producing a positive electrode active material according to the fourth aspect of the present disclosure, the second dopant source may be a hydroxide or carbonate salt including aluminum and gallium as elements.

[0027] The bipolar structure may be formed by laminating bipolar electrodes. The bipolar structure is expected to improve, for example, output characteristics.

[0028] Hereinafter, an embodiment of the present disclosure (hereinafter, optionally abbreviated as “the present embodiment”), and an example of the present disclosure (hereinafter, optionally abbreviated as “the present example”) will be described. However, the present embodiment and the present example do not limit the technical scope of the present disclosure. The present embodiment and the present example are exemplary only in all respects. The present embodiment and the present example are non-limiting. The technical scope of the present disclosure encompasses all modifications within the meanings and scope equivalent to the description of claims. For example, it is also anticipated from the beginning that any structures may be extracted from the present embodiment and are arbitrarily combined.

[0035] The terms “comprise”, “include”, “have”, and variations thereof are open-ended expressions. The structure represented by an open-ended expression may further include or may not include additional elements in addition to essential elements. The description “consist of” is a closed-ended expression. However, even a structure represented by a closed-ended expression may include additional elements that are usually accompanying impurities or irrelevant to the target technique. The description of “substantially consist of . . . ” is a semi-closed-ended expression. In the structure represented by a semi-closed-ended expression, addition of the elements that substantially do not affect basic and novel characteristics of the target technique is acceptable.

[0036] The expressions such as “may” and “can” do not mean “must” that signifies requisiteness, and are used as “be likely to” that signifies acceptability.

[0037] Geometric terms should not be interpreted in a strict sense. Examples of geometric terms include “parallel”, “perpendicular”, and “orthogonal”. For example, the direction, angle, and distance may be relatively displaced, within a range capable of obtaining substantially the same or similar functions. Geometric terms may include, for example, a tolerance and an error in design, work, and manufacture. The dimensional relationships in each drawing sometimes do not correspond to actual dimensional relationships. To help the understanding of the readers, the dimensional relationships in each drawing are sometimes changed. For example, the length, width, thickness, and the like are changed in some cases. Some structures are omitted in some cases.

[0038] An element described by “a singular form” may include a plural form, unless otherwise specified. For example, a particle may refer to a plurality of particles, an aggregation of particles, and a powder and granular material, in some cases. Note that, “a plurality of particles” may be referred to as “a particle group”.

[0039] Unless otherwise specified, a numerical range such as “m to n%” includes an upper limit value and a lower limit value. That is, the term “m to n%” refers to a numerical range of “m% or more and n% or less”. The term “m% or more and n% or less” includes “more than m% and less than n%”. The terms “or more” and “or less” are represented by a less-than-or-equal-to sign and a greater-than-or-equal-to sign “≤,≥”. The terms “more than” and “less than” are represented by a less-than sign and a greater-than sign “<, >”. A numerical value arbitrarily selected from the numerical range may be determined as a new upper limit value or lower limit value. For example, a new numerical range may be set by arbitrarily combining a numerical value in the numerical range with a numerical value described in another part, table, drawing, or the like in the present specification.

[0040] All numerical values are modified by the term “about”. The term “about” may mean, for example, ±5%, ±3%, or ±1%. All numerical values may be appropriate values that may be changed depending on the mode of use of the target technique. All numerical values may be expressed in significant figures. A measured value may be an average value in measurement performed multiple times, unless otherwise specified. The number of times of measurement may be three times or more, five times or more, or 10 times or more. In general, the larger the number of times of measurement is, the more the reliability of the average value is expected to be improved. The measured value may be rounded off to the nearest unit based on the number of digits of the significant figure. The measured value may include, for example, an error due to the detection limit of the measurement apparatus.

[0041] The apparatuses, software, and the like used in measurement of various values are merely examples. An apparatus equivalent to the exemplified apparatus or the like may be used. When an equivalent is used, measurement conditions may be regulated according to the apparatus.

[0042] The term “D50” refers to a particle size at a cumulative value of 50% in a volume-based particle size distribution (cumulative distribution). The volume-based particle size distribution is measured by a laser diffraction particle size distribution analyzer.

[0043] The term “maximum Feret diameter” refers to the length of the long side of the minimum bounding rectangle (MBR) of a particle in an scanning electron microscope (SEM) image or transmission electron microscope (TEM) image of the particle. Note that, various dimension measurements and shape analyses in the SEM image and the like may be conducted by using, for example, image analysis software “Image”.

[0044] The chemical composition of a compound may be measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES). A sample solution is prepared by dissolving 0.1 g of a sample (e.g., a positive electrode active material) in mixed acid of hydrochloric acid and sulfuric acid (10 ml). The sample solution is diluted to an appropriate concentration using a volumetric flask. After dilution, composition analysis is conducted using an ICP-AES apparatus. For example, the product name “PS3520UVDDII (manufactured by Hitachi High-Tech Corporation)” may be used.

[0045] A stoichiometric composition formula represents a representative example of a compound. The compound may have a non-stoichiometric composition. For example, “Al₂O₃” is not limited to the compound having an amount-of-substance ratio (molar ratio) of “Al/O=2/3”. “Al₂O₃” represents a compound that contains Al and O at any amount-of-substance ratio, unless otherwise specified. For example, the compound may be doped with a trace amount of elements. Some Al and O may be substituted with another element.

[0046] The introduction site and site occupancy of each dopant may be determined by the following procedures. When the powder X-ray diffraction (XRD) measurement of the positive electrode active material is conducted, an XRD pattern is obtained. For example, the measurement conditions of XRD are as follows.

• • [0047] Analysis method: wide-angle method
  • [0048] Measurement apparatus: SmartLabII (manufactured by Rigaku Corporation)
  • [0049] Measurement angle: 10 to 120°
  • [0050] Tube: CuKα
  • [0051] Tube voltage: 45 kV
  • [0052] Tube current: 200 mA
  • [0053] Measurement mode: continuous mode
  • [0054] Step: 0.02
  • [0055] IS: 1/2
  • [0056] Speed: 2°/min
  • [0057] RS: 20 mm
  • [0058] Detection mode: one-dimensional

[0059] The XRD pattern is subjected to Rietveld refinement using software “GSAS-II”. The structure model is the space group Pnma. The XRD pattern is subjected to background treatment and structure refinement. A variable is set to the composition of w. At this time, setting is generally conducted in the range of “0≤w≤1”. Thereafter, when lattice constant refinement is conducted by determining the balance of the amount of addition as the first dopant (W, Mo) of the MnFe site and the second dopant (Al, Ga) of the P site, “Rwp” that is one of refinement indices is calculated. A quadratic function “Rwp=aw²+bw+c” is fitted to the values of Rwp and w. FIG. 1 is a graph of an example of the fitting results. In the obtained approximate curve, the percentage of w at which Rwp is minimum is considered as the site occupancy of each dopant.

[0060] The term “derivative” refers to a compound in which a part of the compound as a matrix is modified by at least one selected from the group consisting of the introduction of a functional group, the substitution of an atom, oxidation, reduction, and other chemical reactions. The site of modification may be one or a plurality of sites. For example, the term “substituent” may include at least one selected from the group consisting of an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an unsaturated cycloalkyl group, an aromatic group, a heterocyclic ring group, a halogen atom (such as F, Cl, Br, or I), an OH group, an SH group, a CN group, an SCN group, an OCN group, a nitro group, an alkoxy group, an unsaturated alkoxy group, an amino group, an alkylamino group, a dialkylamino group, an aryloxy group, an acyl group, an alkoxycarbonyl group, an acyloxy group, an aryloxycarbonyl group, an acylamino group, an alkoxycarbonylamino group, an aryloxycarbonylamino group, a sulfonylamino group, a sulfamoyl group, a carbamoyl group, an alkylthio group, an arylthio group, a sulfonyl group, a sulfinyl group, a ureide group, an amide phosphate group, a sulfo group, a carboxy group, a hydroxamic acid group, a sulfino group, a hydrazino group, an imino group, and a silyl group. These substituents may be further substituted. When there are two or more substituents, the substituents may be the same or different from one another. A plurality of substituents may be bonded to one another to form a ring.

[0061] FIG. 2 is a conceptual diagram of a crystal structure. The positive electrode active material contains olivine lithium manganese iron phosphate (LMFP). LMFP has a crystal structure that belongs to the space group Pnma. The crystal structure can be specified by the XRD pattern. LMFP may contain, for example, a crystal phase, a crystallized glass phase, and a glass phase. LMFP contains a Li site, a MnFe site, a P site, and an O site.

[0062] LMFP contains a first dopant “X” at the MnFe site. The first dopant is at least one selected from the group consisting of W and Mo. The first dopant may be an interstitial dopant or a substitutional dopant. In the case of the substitutional dopant, the first dopant may substitute Mn or Fe.

[0063] A first site occupancy of the first dopant is 1% to 10% at the MnFe site. When the first site occupancy is 1% or more, the improvement of cycle durability is expected. The first site occupancy may be, for example, 1.5% or more, 2% or more, 3% or more, 4% or more, 5% or more, 6% or more, 7% or more, 8% or more, or 9% or more. The first site occupancy may be, for example, 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, 4% or less, 3% or less, 2% or less, or 1.5% or less. The first site occupancy may be, for example, 2% to 6%.

[0064] LMFP may contain a second dopant “Y” at the P site, in addition to the first dopant “X” at the MnFe site. The second dopant is at least one selected from the group consisting of Al and Ga. When the second dopant is introduced into the P site, the improvement of cycle durability is expected. The second dopant may be an interstitial dopant or a substitutional dopant.

[0065] The second dopant has a second site occupancy at the P site. When the ratio of the second site occupancy “d” to the first site occupancy “c”, “d/c” is, for example, 0.8 to 1.2, the improvement of cycle durability is expected. The ratio “d/c” may be, for example, 0.85 or more, 0.90 or more, 0.95 or more, 0.96 or more, 0.97 or more, 0.98 or more, 0.99 or more, 1.00 or more, 1.01 or more, 1.02 or more, 1.03 or more, 1.04 or more, 1.05 or more, 1.10 or more, or 1.15 or more. The ratio “d/c” may be, for example, 1.15 or less, 1.10 or less, 1.05 or less, 1.04 or less, 1.03 or less, 1.02 or less, 1.01 or less, 1.00 or less, 0.99 or less, 0.98 or less, 0.97 or less, 0.96 or less, 0.95 or less, 0.90 or less, or 0.85 or less.

[0066] LMFP may have, for example, a composition represented by the general formula “Li_1+a[(Mn_1−bFe_b)_1−cX_c][P_1−dY_d]O₄”. In the general formula, for the Li composition ratio “1+a”, for example, the relationship of “−0.5≤a≤0.5” may be satisfied. “a” may be, for example, −0.4 or more, −0.3 or more, −0.2 or more, −0.1 or more, 0 or more, 0.1 or more, 0.2 or more, 0.3 or more, or 0.4 or more. “a” may be, for example, 0.4 or less, 0.3 or less, 0.2 or less, 0.1 or less, 0 or less, −0.1 or less, −0.2 or less, −0.3 or less, or −0.2 or less.

[0067] In the above general formula, for the Fe composition ratio “b”, for example, the relationship of “0.1≤b≤0.9” may be satisfied. The Fe composition ratio “b” may be, for example, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, or 0.8 or more. The Fe composition ratio “b” may be, for example, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, or 0.2 or less.

[0068] In the above general formula, “X” represents the first dopant. That is, “X” is at least one selected from the group consisting of W and Mo. In the above general formula, for the composition ratio “c” of the first dopant, for example, the relationship of “0.01≤c≤0.10” may be satisfied. The composition ratio “c” of the first dopant may be, for example, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, or 0.09 or more. The composition ratio “c” of the first dopant may be, for example, 0.09 or less, 0.08 or less, 0.07 or less, 0.06 or less, 0.05 or less, 0.04 or less, 0.03 or less, or 0.02 or less.

[0069] In the above general formula, “Y” represents the second dopant. That is, “Y” is at least one selected from the group consisting of Al and Ga. For the composition ratio “c” of the first dopant and the composition ratio “d” of the second dopant, the relationship of “0.8≤d/c≤1.2” may be satisfied. For example, the relationship such as “0.90≤d/c≤1.10” or “0.95≤d/c≤1.05” may be satisfied. The composition ratio “d” of the second dopant may be, for example, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, or 0.09 or more. The composition ratio “d” of the second dopant may be, for example, 0.09 or less, 0.08 or less, 0.07 or less, 0.06 or less, 0.05 or less, 0.04 or less, 0.03 or less, or 0.02 or less.

[0070] LMFP may have, for example, a powder form. D50 of LMFP may be, for example, 5 μm or more, 10 μm or more, 15 μm or more, or 20 μm or more. D50 of LMFP may be, for example, 30 μm or less, 25 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less.

[0071] LMFP may form secondary particles. A secondary particle is an aggregate of primary particles. The term “primary particle” refers to particles having apparently no grain boundaries on a two-dimensional image. The two-dimensional image may be, for example, a TEM image or an SEM image. The magnification of the image may be, for example, 10000 times to 30000 times. The secondary particle may have any shape. The secondary particle may be, for example, spherical, rodlike, or angular. When the secondary particle is spherical, for example, the improvement of packability is expected. The sphericity of the secondary particle may be, for example, 0.85 or more, 0.90 or more, or 0.95 or more. The sphericity of the secondary particle may be, for example, 1 or less, 0.95, or 0.90 or less. The term “sphericity” refers to circularity in the SEM image. The sphericity (circularity) is determined by the following equation. As the value of sphericity, an arithmetic mean of 30 secondary particles is adopted.

• • [0072] ψ=4 πS/L²
  • [0073] ψ: Sphericity (circularity)
  • [0074] π: Circumference ratio
  • [0075] S: Cross-sectional area of a particle (the area of the region surrounded by the outline of the particle)
  • [0076] L: Circumference of a particle (the length of the outline of the particle)

[0077] The primary particle may have any shape. The primary particle may be, for example, spherical, rodlike, or angular. The primary particle may be a nanoparticle. The maximum Feret diameter of the primary particle may be, for example, 10 nm to 300 nm. The maximum Feret diameter of the primary particle may be, for example, 15 nm or more, 20 nm or more, 25 nm or more, 50 nm or more, 75 nm or more, 100 nm or more, 150 nm or more, 200 nm or more, or 250 nm or more. The maximum Feret diameter of the primary particle may be, for example, 250 nm or less, 200 nm or less, 150 nm or less, 100 nm or less, 75 nm or less, 50 nm or less, or 25 nm or less. The maximum Feret diameter of the primary particle represents an arithmetic mean of 30 primary particles.

[0078] The surface of the primary particle may be coated with carbon. That is, a carbon layer or a carbon coating may be formed on the surface of the primary particle. A part of the surface of the primary particle or the entire surface of the primary particle may be coated with carbon. Carbon may be derived from a saccharide or the like. The amount of carbon attached may be, for example, 0.1% or more, 0.5% or more, 1% or more, 2% or more, 3% or more, or 4% or more by the mass fraction with respect to the secondary particle. The amount of carbon attached may be, for example, 5% or less, 4% or less, or 3% or less by the mass fraction with respect to the secondary particle.

[0079] The positive electrode active material may further contain other components, as long as containing LMFP. The mixing ratio of LMFP to other components (mass ratio) may be, for example, “LMFP/other components=9/1 to 1/9”, “LMFP/other components=8/2 to 2/8”, “LMFP/other components=7/3 to 3/7”, or “LMFP/other components=6/4 to 4/6”. The positive electrode active material may be, for example, a mixture of the powder of LMFP and the powder of other components. Other components may include, for example, at least one selected from the group consisting of Li[NiCoMn]O₂ (layered structure), Li[NiCoAl]O₂ (layered structure), LiMnO₂ (rock-salt structure), and Li[NiMn]₂O₄ (spinel structure). Note that the description such as [NiCoMn] represents that the sum of the composition ratio in [] is one. As long as the sum is one, components in [] may have any composition ratio.

[0080] In some present embodiments, the battery may be a liquid battery. The term “liquid battery” refers to a battery including an electrolyte. For example, since a polymer battery includes an electrolyte, the polymer battery belongs to the liquid battery. In some present embodiments, the battery has a monopolar structure. In the monopolar structure, a power generation element may be a wound type or a laminated type. In some present embodiments, the battery has a bipolar structure. As an example, a battery (bipolar battery) having a bipolar structure will be described.

[0081] FIG. 3 is a schematic perspective view of the battery in the present embodiment. FIG. 4 is a schematic cross-sectional view along the line IV-IV in FIG. 3. Hereinafter, the term “perpendicular direction” refers to the normal direction to the surface of a sheet member (e.g., a foil or an electrode). The term “in-plane direction” refers to any direction orthogonally intersects the perpendicular direction. In the drawing of the present embodiment, the Z axis direction corresponds to the perpendicular direction. Each of the X axis direction and the Y axis direction is an example of the in-plane direction.

[0082] A battery 100 includes an outer packaging 90 and a power generation element. The outer packaging 90 stores the power generation element. The outer packaging 90 may include, for example, a first current-collector plate 91, a first laminate film 92, a second laminate film 93, and a second current-collector plate 94. The first laminate film 92 and the second laminate film 93 are joined with each other at an end part in the in-plane direction. At the joint part of the first laminate film 92 and the second laminate film 93, a sealing material (not shown) may be interposed between the first laminate film 92 and the second laminate film 93.

[0083] The first current-collector plate 91 and the second current-collector plate 94 are joined to the power generation element at the end part in the lamination direction (the Z axis direction). The first laminate film 92 is joined to the first current-collector plate 91. The second laminate film 93 is joined to the second current-collector plate 94. At the joint part of the current-collector plate and the laminate film, a sealing material (not shown) may be interposed between the current-collector plate and the laminate film.

[0084] The power generation element includes a plurality of bipolar electrodes. The plurality of bipolar electrodes is laminated in the perpendicular direction (the Z axis direction). Each of the bipolar electrodes includes a positive electrode layer 11, a collector foil 13, and a negative electrode layer 12 in the perpendicular direction in the order presented. In the in-plane direction (e.g., the X axis direction), the collector foil 13 is extended to the outside as compared with the positive electrode layer 11 and the negative electrode layer 12. For example, the collector foil 13 may be extended to the outside as compared with the positive electrode layer 11 and the negative electrode layer 12 over the whole circumference in the in-plane direction.

[0085] The collector foil 13 is a conductor. The collector foil 13 may contain, for example, a metal foil or a conductive resin layer. For example, the collector foil 13 may be formed by sticking an Al foil and a Cu foil together. A carbon material may be applied to the surface of the collector foil 13. The carbon material may contain, for example, carbon black.

[0086] The power generation element includes a sealing material 30. The sealing material 30 is joined to the collector foil 13 at the end part in the in-plane direction. The sealing material 30 may be heat-welded to, for example, the collector foil 13. For example, the sealing material 30 may be arranged over the whole circumference in the in-plane direction. The sealing material may contain, for example, a resin material. The sealing material 30 seals the space between the collector foils 13 adjacent to each other in the perpendicular direction. The sealing material 30 seals the space between the collector foils 13, so that cells are divided. The cell is the minimum unit of the power generation element. Since the battery 100 includes a plurality of cells, the cell may also be referred to as “a bipolar module”. Each of the cells is sealed. Each of the cells is isolated from one another. Each of the cells includes the positive electrode layer 11, a separator 20, the negative electrode layer 12, and an electrolyte.

[0087] The positive electrode layer 11 is attached to a surface of the collector foil 13. For example, a groove may be formed on the positive electrode layer 11. The positive electrode layer 11 may be formed, for example, in a stripe form. The positive electrode layer 11 contains a positive electrode active material. That is, the battery 100 contains the positive electrode active material. The details of the positive electrode active material are as described above.

[0088] The positive electrode layer 11 may further contain, for example, a conductive material and a binder, in addition to the positive electrode active material. The amount of the conductive material formulated may be, for example, 0.1 to 10 parts by mass based on 100 parts by mass of the positive electrode active material. The conductive material may contain any component. The conductive material may contain, for example, at least one selected from the group consisting of graphite, acetylene black (AB), ketjen black (R), vapor grown carbon fiber (VGCF), carbon nanotube (CNT), and graphene flake (GF).

[0089] The amount of the binder formulated may be, for example, 0.1 to 10 parts by mass based on 100 parts by mass of the positive electrode active material. The binder may contain any component. The binder may contain, for example, at least one selected from the group consisting of polyvinylidene fluoride (PVdF), a vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyoxyethylene alkyl ether, and derivatives thereof.

[0090] The positive electrode layer 11 may contain, for example, an inorganic filler, an organic filler, a solid electrolyte, a surface modifier, a dispersant, a lubricant, a flame retardant, a protective agent, a flux, a coupling agent, or an adsorbent. The positive electrode layer may contain, for example, polyoxyethylene allyl phenyl ether phosphate, zeolite, a silane coupling agent, MoS₂, or WO₃.

[0091] The negative electrode layer 12 is attached to a surface of the collector foil 13. The negative electrode layer 12 is arranged on the back of the positive electrode layer 11. The negative electrode layer 12 may have a larger area than the area of the positive electrode layer 11. The negative electrode layer 12 contains a negative electrode active material.

[0092] The negative electrode active material may be, for example, in a particle form or a sheet form. D50 of the negative electrode active material may be, for example, 1 μm or more, 5 μm or more, or 10 μm or more. D50 of the negative electrode active material may be, for example, 30 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less.

[0093] The negative electrode active material may contain any component. The negative electrode active material may contain, for example, at least one selected from the group consisting of a carbon-based active material, an alloy-based active material, a Si—C composite material, a Li metal, a Li base alloy, and lithium titanate. In some present embodiments, the battery may be a Li metal negative electrode battery.

[0094] The carbon active material may contain, for example, at least one selected from the group consisting of graphite, soft carbon, and hard carbon. The term “graphite” is a generic term for natural graphite and artificial graphite. Graphite may be a mixture of natural graphite and artificial graphite. The mixing ratio (mass ratio) may be, for example, “natural graphite/artificial graphite=1/9 to 9/1”, “natural graphite/artificial graphite=2/8 to 8/2” or “natural graphite/artificial graphite=3/7 to 7/3”.

[0095] The surface of graphite may be coated with, for example, amorphous carbon. The surface of graphite may be coated with, for example, a different material. The different material may contain, for example, at least one selected from the group consisting of P, W, Al, and O. The different material may contain, for example, at least one selected from the group consisting of Al(OH)₃, AlOOH, Al₂O₃, WO₃, Li₂CO₃, LiHCO₃, and Li₃PO₄.

[0096] The alloy-based active material may contain, for example, at least one selected from the group consisting of Si, Li silicate, SiO, a Si base alloy, tin (Sn), SnO, and a Sn base alloy.

[0097] For example, SiO may have a composition represented by the general formula “SiO_x”. In the general formula, for example, the relationship of “0<x<2”, “0.5≤x≤1.5” or “0.8≤x≤1.2” may be satisfied.

[0098] The term “Si—C composite material” refers to a composite material of a carbon-based active material (such as graphite) and an alloy-based active material (such as Si). For example, Si fine particles may be dispersed in carbon particles. For example, Si fine particles may be dispersed in graphite particles. For example, Li silicate particles may be coated with a carbon material (such as amorphous carbon).

[0099] The separator 20 may separate the positive electrode layer 11 from the negative electrode layer 12. The separator 20 has electrical insulating properties. The separator 20 may include, for example, at least one selected from the group consisting of a resin film (polymer film), an inorganic particle layer, and an organic particle layer. The separator 20 may include, for example, a resin film and an inorganic particle layer.

[0100] The resin film is porous. The resin film may include, for example, a microporous film and non-woven fabric. The resin film contains a resin backbone. The resin backbone may be, for example, continuously present in a mesh form. Pores are formed in the gaps of the resin backbone. The resin film allows the electrolyte to be transmitted. The resin film may have, for example, an average pore diameter of 1 μm or less. The average pore diameter of the resin film may be, for example, 0.01 to 1 μm or 0.1 to 0.5 μm. The “average pore diameter” may be measured by mercury porosimetry. The Gurley value of the resin film may be, for example, 50 to 250 s/100 cm³. The “Gurley value” may be measured by the Gurley method.

[0101] The resin film may contain, for example, at least one selected from the group consisting of an olefin-based resin, a polyurethane-based resin, a polyamide-based resin, a cellulose-based resin, a polyether-based resin, an acrylic resin, and a polyester-based resin. The resin film may contain, for example, at least one selected from the group consisting of polyethylene (PE), polypropylene (PP), polyamide (PA), polyamideimide (PAI), polyimide (PI), aromatic polyamide (aramid), polyphenylene ether (PPE), and derivatives thereof. The resin film may be formed by, for example, a drawing method or a phase separation method. The thickness of the resin film may be, for example, 5 to 50 μm or 10 to 25 μm.

[0102] The resin film may have, for example, a single layer structure. The resin film may be formed of, for example, a PE layer. The backbone of the PE layer is formed of PE. The PE layer may have a shutdown function. The resin film may have, for example, a multilayer structure. The resin film may include, for example, a PP layer and a PE layer. The backbone of the PP layer is formed of PP. The resin film may have, for example, a three-layer structure. For example, the resin film may be formed by laminating the PP layer, the PE layer, and the PP layer in the order presented. The thickness of the PE layer may be, for example, 5 to 20 μm. The thickness of the PP layer may be, for example, 3 to 10 μm.

[0103] The inorganic particle layer may be formed on the surface of the resin film. The inorganic particle layer may be formed only on a surface or on both surfaces of the resin film. The inorganic particle layer may be formed on a surface facing the positive electrode layer 11 or a surface facing the negative electrode layer 12. Note that, the inorganic particle layer may be formed on the surface of the positive electrode layer 11 or the surface of the negative electrode layer 12.

[0104] The inorganic particle layer is porous. The inorganic particle layer contains inorganic particles. The inorganic particle may also be referred to as an “inorganic filler”. Pores are formed in the gaps between inorganic particles. The thickness of the inorganic particle layer may be, for example, 0.5 to 10 μm or 1 to 5 μm. The inorganic particle may contain, for example, a heat-resistant material. The inorganic particle layer containing the heat-resistant material may also be referred to as a “heat resistance layer (HRL)”. The inorganic particle may contain at least one selected from the group consisting of boehmite, alumina, zirconia, titania, magnesia, and silica. The inorganic particle may have any shape. The inorganic particle may be, for example, spherical, rodlike, platy, or fibrous. D50 of the inorganic particle may be, for example, 0.1 to 10 μm or 0.5 to 3 μm. The inorganic particle layer may further contain a binder. The binder may contain, for example, at least one selected from the group consisting of an acrylic resin, a polyamide-based resin, a fluorine-based resin, an aromatic polyether-based resin, and a liquid crystal polyester-based resin.

[0105] The separator 20 may include, for example, an organic particle layer. For example, the separator 20 may include the organic particle layer instead of the resin film. For example, the separator 20 may include the organic particle layer instead of the inorganic particle layer. The separator 20 may include both the resin film and the organic particle layer. The separator 20 may include both the inorganic particle layer and the organic particle layer. The separator 20 may include the resin film, the inorganic particle layer, and the organic particle layer.

[0106] The thickness of the organic particle layer may be, for example, 0.1 to 50 μm, 0.5 to 20 μm, 0.5 to 10 μm, or 1 to 5 μm. The organic particle layer contains organic particles. The organic particle may also be referred to as an “organic filler”. The organic particle may contain a heat-resistant material. The organic particle may contain, for example, at least one selected from the group consisting of PE, PP, PTFE, PI, PAI, PA, and aramid. The organic particle may be, for example, spherical, rodlike, platy, or fibrous. D50 of the organic particle may be, for example, 0.1 to 10 μm or 0.5 to 3 μm.

[0107] The separator 20 may include, for example, a mix layer. The mix layer contains both the inorganic particle and the organic particle.

[0108] The electrolyte is a liquid electrolyte. The electrolyte contains a solute and a solvent. The concentration of the solute may be, for example, 0.5 to 1 mol/L, 1 to 1.5 mol/L, 1.5 to 2 mol/L, 2 to 2.5 mol/L, or 2.5 to 3 mol/L. The term “mol/L” may sometimes be described as “M”. The solute contains a supporting salt (Li salt). The solute may include, for example, an inorganic acid salt, an imide salt, an oxalate complex, and a halide. The solute may include, for example, at least one selected from the group consisting of LiPF₆, LiBF₄, LiClO₄, LiAsF₆, LiSbF₆, LiN(SO₂F)₂ “LiFSI”, LiN(SO₂CF₃)₂ “LiTFSI”, LiB(C₂O₄)₂ “LiBOB”, LiBF₂(C₂O₄) “LiDFOB”, LiPF₂(C₂O₄)₂ “LiDFOP”, LiPO₂F₂, FSO₃Li, LiI, LiBr and derivatives thereof.

[0109] The electrolyte may contain, for example, a carbonate-based solvent (carbonic ester-based solvent). The solvent may contain, for example, cyclic carbonate, chain carbonate, and fluorinated carbonate. The solvent may contain, for example, at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), monofluoroethylene carbonate (FEC), difluoroethylene carbonate, 4,4-difluoroethylene carbonate, trifluoroethylene carbonate, perfluoroethylene carbonate, fluoropropylene carbonate, difluoropropylene carbonate, and derivatives thereof.

[0110] The solvent may contain cyclic carbonate (such as EC, PC, or FEC) and chain carbonate (such as EMC, DMC, or DEC). The mixing ratio (volume ratio) of cyclic carbonate to chain carbonate may be, for example, “cyclic carbonate/chain carbonate=1/9 to 4/6”, “cyclic carbonate/chain carbonate=2/8 to 3/7”, or “cyclic carbonate/chain carbonate=3/7 to 4/6”.

[0111] The solvent may contain cyclic carbonate (such as EC or PC) and fluorinated cyclic carbonate (such as FEC). The mixing ratio (volume ratio) of cyclic carbonate to fluorinated cyclic carbonate may be, for example, “cyclic carbonate/fluorinated cyclic carbonate=99/1 to 90/10”, “cyclic carbonate/fluorinated cyclic carbonate=9/1 to 1/9”, “cyclic carbonate/fluorinated cyclic carbonate=9/1 to 7/3” or “cyclic carbonate/fluorinated cyclic carbonate=3/7 to 1/9”.

[0112] The solvent may contain, for example, EC, FEC, EMC, DMC, and DEC. The volume ratio of each component may satisfy, for example, the relationship represented by the relational equation “V_EC+V_FEC+V_EMC+V_DMC+V_DEC=10”. In the relational equation, “V_EC, V_FEC, V_EMC, V_DMC, and V_DEC” represent the volume ratio of EC, FEC, EMC, DMC, and DEC, respectively. The relationships of “1≤V_EC≤4”, “0≤V_FEC≤3”, “V_EC+V_FEC≤4”, “0≤V_EMC≤9”, “0≤V_DMC≤9”, “0≤V_DEC≤9”, and “6≤V_EMC+V_DMC+V_DEC≤9” are satisfied. For example, the relationship of “1≤V_EC≤2” or “2≤V_EC≤3” may be satisfied. For example, the relationship of “1≤V_FEC≤2” or “2≤V_FEC≤4” may be satisfied. For example, the relationship of “3≤V_EMC≤4” or “6≤V_EMC≤8” may be satisfied. For example, the relationship of “3≤V_DMC≤4” or “6≤V_DMC≤8” may be satisfied. For example, the relationship of “3≤V_DEC≤4” or “6≤V_DEC≤8” may be satisfied.

[0113] The solvent may have a composition of, for example, “EC/EMC=3/7”, “EC/DMC=3/7”, “EC/FEC/DEC=1/2/7”, “EC/DMC/EMC=3/4/3”, “EC/DMC/EMC=3/3/4”, “EC/FEC/DMC/EMC=2/1/4/3”, “EC/FEC/DMC/EMC=1/2/4/3”, “EC/FEC/DMC/EMC=2/1/3/4”, or “EC/FEC/DMC/EMC=1/2/3/4”, in the volume ratio.

[0114] The electrolyte may contain an ether-based solvent. The electrolyte may contain, for example, at least one selected from the group consisting of tetrahydrofuran (THF), 1,4-dioxane (DOX), 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), hydrofluoroether (HFE), ethylglyme, triglyme, tetraglyme, and derivatives thereof.

[0115] The electrolyte may contain any additive. The amount of addition (mass fraction with respect to the whole electrolyte) may be, for example, 0.01 to 5%, 0.05 to 3%, or 0.1 to 1%. The additive may include, for example, a solid electrolyte interphase (SEI) formation promoter, an SEI formation inhibitor, a gas generating agent, an overcharging inhibitor, a flame retardant, an antioxidant, an electrode protective agent, and a surfactant.

[0116] The additive may contain, for example, at least one selected from the group consisting of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), 1,3-propanesultone (PS), tert-amylbenzene, 1,4-di-tert-butylbenzene, biphenyl (BP), cyclohexylbenzene (CHB), ethylene sulfite(ES), ethylene sulfate (DTD), γ-butyrolactone, a phosphazene compound, carboxylate ester [e.g., methyl formate (MF), methyl acetate (MA), methyl propionate (MP), or diethyl malonate (DEM)], fluorobenzene [e.g., monofluorobenzene (FB), 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, 1,3,5-trifluorobenzene, 1,2,3,4-tetrafluorobenzene, 1,2,3,5-tetrafluorobenzene, 1,2,4,5-tetrafluorobenzene, pentafluorobenzene, and hexafluorobenzene), fluorotoluene (e.g., 2-fluorotoluene, 3-fluorotoluene, 4-fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,6-difluorotoluene, 3,4-difluorotoluene, and octafluorotoluene), benzotrifluoride (e.g., benzotrifluoride, 2-fluorobenzotrifluoride, 3-fluorobenzotrifluoride, 4-fluorobenzotrifluoride, 2-methylbenzotrifluoride, 3-methylbenzotrifluoride, and 4-methylbenzotrifluoride), fluoroxylene (e.g., 3-fluoro-o-xylene, 4-fluoro-o-xylene, 2-fluoro-m-xylene, and 5-fluoro-m-xylene), a sulfur-containing heterocyclic compound (e.g., benzothiazole, 2-methylbenzothiazole, and tetrathiafulvalene), a nitrile compound (e.g., adiponitrile and succinonitrile), phosphate ester (e.g., trimethyl phosphate and triethyl phosphate), carboxylic anhydride (e.g., acetic anhydride, propionic anhydride, oxalic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, and benzoic anhydride), alcohol (e.g., methanol, ethanol, n-propyl alcohol, ethylene glycol, and diethylene glycol monomethyl ether), and derivatives thereof.

[0117] The components described above as the solute and the solvent may be used as trace components (additives). The additive may contain, for example, at least one selected from the group consisting of LiBF₄, LiFSI, LiTFSI, LiBOB, LiDFOB, LiDFOP, LiPO₂F₂, FSO₃Li, LiI, LiBr, HFE, DOX, PC, FEC, and derivatives thereof.

[0118] The electrolyte may contain an ionic liquid. The ionic liquid may contain, for example, at least one selected from the group consisting of a sulfonium salt, an ammonium salt, a pyridinium salt, a piperidinium salt, a pyrrolidinium salt, a morpholinium salt, a phosphonium salt, an imidazolium salt, and derivatives thereof.

[0119] In some present embodiments, the battery may include a gel electrolyte. That is, the battery may be a polymer battery. The gel electrolyte may contain an electrolyte and a polymer material. The polymer material may form a polymer matrix. The polymer material may contain, for example, at least one selected from the group consisting of PVdF, PVdF-HFP, polyacrylonitrile (PAN), PVdF-PAN, polyethylene oxide (PEO), polyethylene glycol (PEG), and derivatives thereof.

[0120] In some present embodiments, the battery may be a solid-state battery. The solid-state battery may have a bipolar structure. The solid-state battery includes a solid electrolyte instead of the electrolyte and the separator 20. The solid electrolyte may be included in the positive electrode layer 11 and the negative electrode layer 12. Instead of the separator 20, a solid electrolyte layer separates the negative electrode layer 12 from the positive electrode layer 11. For example, the solid electrolyte layer contains the solid electrolyte and the binder.

[0121] For example, the solid electrolyte may be powder. D50 of the solid electrolyte may be, for example, 0.1 μm or more, 0.2 μm or more, 0.3 μm or more, 0.4 μm or more, 0.5 μm or more, 0.6 μm or more, 0.7 μm or more, 0.8 μm or more, 0.9 μm or more, or 1 μm or more. D50 of the solid electrolyte may be, for example, 5 μm or less, 4 μm or less, 3 μm or less, 2 μm or less, or 1 μm or less.

[0122] The solid electrolyte may contain, for example, at least one selected from the group consisting of a sulfide solid electrolyte, a halide solid electrolyte, an oxide solid electrolyte, a hydride solid electrolyte, and a nitride solid electrolyte.

[0123] The sulfide solid electrolyte may contain at least one selected from the group consisting of an amorphous phase, a crystalline phase, and a glass-ceramic (crystallized glass) phase. The crystalline phase may be, for example, argyrodite or LGPS. The sulfide solid electrolyte contains Li and sulfur(S). The sulfide solid electrolyte may further contain any component in addition to Li and S.

[0124] The sulfide solid electrolyte may contain, for example, at least one selected from the group consisting of LiI—LiBr—Li₃PS₄, Li₂S—SiS₂, LiI—Li₂S—SiS₂, LiI—Li₂S—P₂S₅, LiI—Li₂O—Li₂S—P₂S₅, LiI—Li₂S—P₂O₅, LiI—Li₃PO₄—P₂S₅, Li₂S—GeS₂—P₂S₅, Li₂S—P₂S₅, Li₁₀GeP₂S₁₂, Li₄P₂S₆, Li₇P₃S₁₁, Li₃PS₄, and Li₇PS₆.

[0125] For example, “LiI—LiBr—Li₃PS₄” represents a sulfide solid electrolyte produced by mixing LiI, LiBr, and Li₃PS₄ at any amount-of-substance ratio. For example, the sulfide solid electrolyte may be produced by a mechanochemical method. The mixing ratio may be specified by adding a number in front of each raw material. For example, “10LiI—15LiBr—75Li₃PS₄” indicates that the mixing ratio is “LiI/LiBr/Li₃PS₄=10/15/75 (amount-of-substance ratio)”.

[0126] For example, the sulfide solid electrolyte may have a composition represented by the general formula “xLi₂S—(1−x)P₂S₅”. In the general formula, “x” may be, for example, more than 0, 0.1 or more, 0.2 or more, 0.25 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.75 or more, 0.8 or more, or 0.9 or more. “x” may be, for example, 1 or less, 0.9 or less, 0.8 or less, 0.7 or less, 0.75 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less. For example, when “x=0.75”, “xLi₂S—(1−x)P₂S₅” may have a composition of Li₃PS₄.

[0127] For example, the sulfide solid electrolyte may have a composition represented by the general formula “yLiI—zLiBr—(100−y−z)[xLi₂S—(1−x)P₂S₅]”. In the general formula, “x” may be, for example, 0.5 or more, 0.6 or more, 0.7 or more, 0.75 or more, 0.8 or more, or 0.9 or more. “x” may be, for example, 1 or less, 0.9 or less, 0.8 or less, 0.75 or less, 0.7 or less, or 0.6 or less. “y” may be, for example, 0 or more, 5 or more, 10 or more, 15 or more, 20 or more, or 25 or more. “y” may be, for example, 30 or less, 25 or less, 20 or less, 15 or less, 10 or less, or 5 or less. “z” may be, for example, 0 or more, 5 or more, 10 or more, 15 or more, 20 or more, or 25 or more. “z” may be, for example, 30 or less, 25 or less, 20 or less, 15 or less, 10 or less, or 5 or less.

[0128] For example, the sulfide solid electrolyte may have a composition represented by the general formula “Li_7−x−2yPS_6−x−yX_y”. In the general formula, the relationships of “0<7−x−2y”, “0<6−x−y”, “0≤x” and “0≤y” are satisfied. “X” may include, for example, at least one selected from the group consisting of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).

[0129] For example, the sulfide solid electrolyte may have a composition represented by the general formula “Li_4−xM_1−xP_xS₄”. In the general formula, “x” may be, for example, more than 0, 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more. “x” may be, for example, less than 1, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less. “M” may include, for example, at least one selected from the group consisting of Al, Zn, In, Ge, Si, Sn, Sb, Ga, and Bi.

[0130] For example, the sulfide solid electrolyte may have a composition represented by the general formula “Li_10+xGe_1+xP_2−xS₁₂”. In the general formula, “x” may be, for example, 0 or more, 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, or 0.6 or more. “x” may be, for example, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less. The sulfide solid electrolyte represented by the above general formula may contain, for example, an LGPS crystal phase.

[0131] For example, the halide solid electrolyte may have a composition represented by the general formula “Li_6−naM_aX₆”. In the general formula, “n” represents the oxidation number of “M”. For example, “M” may include an atom having an oxidation number of +3. For example, “M” may include an atom having an oxidation number of +4. For example, “M” may include at least one selected from the group consisting of Y, Al, Ti, Zr, Ca, and Mg. For example, “0<a<2” may be satisfied. “X” may include, for example, at least one selected from the group consisting of F, Cl, Br, and I.

[0132] For example, the halide solid electrolyte may have a composition represented by the general formula “Li_3−aTi_aAl_1−aF₆”. In the general formula, “a” may be, for example, 0 or more, 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more. “a” may be, for example, 1 or less, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less.

[0133] For example, the halide solid electrolyte may have a composition represented by the general formula “Li₃YCl_aBr_bI_6−a−b”. In the general formula, for example, the relationship of “0≤a+b≤6” may be satisfied. “a” may be, for example, 0 or more, 1 or more, 2 or more, 3 or more, 4 or more, or 5 or more. “a” may be, for example, 6 or less, 5 or less, 4 or less, 3 or less, 2 or less, or 1 or less. “b” may be, for example, 0 or more, 1 or more, 2 or more, 3 or more, 4 or more, or 5 or more. “b” may be, for example, 6 or less, 5 or less, 4 or less, 3 or less, 2 or less, or 1 or less.

[0134] For example, the oxide solid electrolyte may contain, for example, at least one selected from the group consisting of LiNbO₃, Li_1.5Al_0.5Ge_1.5(PO₄)₃, La_2/3−xLi_3xTiO₃, and Li₇La₃Zr₂O₁₂. For example, the hydride solid electrolyte may contain LiBH₄. For example, the nitride solid electrolyte may contain Li₃N or Li₃BN₂.

[0135] Various LMFP are produced by the following procedures. Manganese carbonate, ferric phosphate, and lithium dihydrogen phosphate are weighed such that Mn, Fe, and P achieve a desired composition ratio. Manganese carbonate, ferric phosphate, and lithium dihydrogen phosphate are stirred and mixed in water to form a slurry. The slurry is spray dried to form a first precursor (powder). A mixture of the first precursor and a first dopant source (Li₂WO₃, Li₂MoO₄) is fired in an oxygen atmosphere at 1200° C., to form a second precursor. That is, the first dopant source contains at least one compound having a composition represented by the chemical formula “Li₂WO₃” or “Li₂MoO₄”. The second precursor is pulverized by a planetary ball mill. A mixture of the second precursor, lithium hydroxide, and a second dopant source is fired in a nitrogen atmosphere at 650° C. to synthesize LMFP. The second dopant source is a hydroxide or carbonate salt of the second dopant (Al, Ga). That is, the second dopant source is a hydroxide or carbonate salt containing aluminum and gallium as elements. LMFP is pulverized by a planetary ball mill. That is, the above procedure includes stirring and mixing manganese carbonate, ferric phosphate, and lithium dihydrogen phosphate at a predetermined composition ratio in water to form a slurry, spray drying the slurry to form a first precursor, mixing the first precursor and a first dopant source, firing the mixture of the first precursor and the first dopant source in an oxygen atmosphere at 1200° C. to form a second precursor, mixing the second precursor, lithium hydroxide, and a second dopant source, and firing the mixture of the second precursor, the lithium hydroxide, and the second dopant source in a nitrogen atmosphere at 650° C.

[0136] An evaluation cell that contains LMFP as the positive electrode active material is produced. In the evaluation cell, a charge and discharge cycle test is conducted.

[0137] FIG. 5 is a graph of the results of the charge and discharge cycle test. The abscissa indicates the cycle number. The ordinate indicates capacity retention. The higher the capacity retention, the better the cycle durability. In the undoped sample and the sample in which 0.1% of W is doped, the final capacity retention is about 6%. In the sample in which 1% or more of W is doped, cycle durability tends to be significantly improved. In the sample in which 6% or more of W is doped, the final capacity retention is 65.7%.