Positive electrode material for secondary battery and secondary battery using same

Abstract

[Problem] To provide, for a secondary battery in which a solid electrolyte is used, a means for preventing a decrease in discharge capacity when the secondary battery is repeatedly charged and discharged. [Solution] A positive electrode material for a secondary battery, the positive electrode comprising: positive electrode active material particles; an organic solid electrolyte covering at least a portion of the surface of each positive electrode active material particle; and an inorganic solid electrolyte. The organic solid electrolyte is a composite of an electrolyte salt and a polyether-based polymer compound having a weight average molecular weight (Mw) of from greater than 1,000 to less than 1,000,000, and the content of the organic solid electrolyte is 0.40 mass% or greater relative to 100 mass% of the total amount of the positive electrode active material particles.

Description

Positive electrode material for secondary batteries and secondary batteries using the same

[0001] This invention relates to a positive electrode material for secondary batteries and a secondary battery using the same.

[0002] In recent years, research and development on all-solid-state batteries using oxide-based or sulfide-based solid electrolytes has been actively pursued. Solid electrolytes are materials mainly composed of ion conductors capable of ion conduction in a solid state. Therefore, all-solid-state batteries have the advantage of not, in principle, occurring in the way that conventional liquid-based batteries using non-aqueous electrolytes are caused by flammable organic electrolytes.

[0003] In such all-solid-state batteries, it is desirable that the charge and discharge capacity does not decrease as much as possible even when repeated charging and discharging is performed, similar to conventional non-aqueous electrolyte secondary batteries. As a means of solving this problem, for example, Japanese Patent Application Publication No. 2016-197590 discloses a technique in which positive electrode active material particles are thinly coated with an organic solid electrolyte, which is a composite of a polyether polymer compound and an electrolyte salt. According to this document, by coating the surface of the positive or negative electrode active material particles with the above-mentioned composite with an average thickness of 20 nm or less, it is possible to suppress the decrease in charge and discharge capacity when repeated charging and discharging is performed.

[0004] However, our investigations have revealed that even when using the technology described in Japanese Patent Publication No. 2016-197590, the discharge capacity may still decrease when repeated charging and discharging is performed (for example, when the restraining pressure on the cell (power generation element) is small).

[0005] Therefore, the present invention aims to provide a means for preventing a decrease in discharge capacity when repeated charging and discharging is performed in a secondary battery using a solid electrolyte.

[0006] The inventors diligently conducted research to solve the above problems. As a result, they discovered that the above problems can be solved by using a cathode active material particle coated with a predetermined amount of an organic solid electrolyte, which is a composite of a polyether polymer compound having a predetermined weight-average molecular weight and an electrolyte salt, and an inorganic solid electrolyte to create a cathode material for a secondary battery, and thus completed the present invention.

[0007] One embodiment of the present invention is a positive electrode material for a secondary battery, comprising positive electrode active material particles, an organic solid electrolyte coating at least a portion of the surface of the positive electrode active material particles, and an inorganic solid electrolyte, wherein the organic solid electrolyte is a composite of a polyether polymer compound having a weight-average molecular weight (Mw) greater than 1,000 and less than 1,000,000 and an electrolyte salt, and the content of the organic solid electrolyte is 0.40% by mass or more relative to 100% by mass of the total amount of the positive electrode active material particles.

[0008] Figure 1 is a schematic cross-sectional view showing the overall structure of a stacked (internal parallel connection type) all-solid-state lithium secondary battery (stacked secondary battery) according to one embodiment of the present invention. Figure 2 is a perspective view of a stacked secondary battery according to one embodiment of the present invention. Figure 3 is a side view taken from direction A shown in Figure 2.

[0009] One embodiment of the present invention is a positive electrode material for a secondary battery, comprising positive electrode active material particles, an organic solid electrolyte coating at least a portion of the surface of the positive electrode active material particles, and an inorganic solid electrolyte, wherein the organic solid electrolyte is a composite of a polyether polymer compound having a weight-average molecular weight (Mw) greater than 1,000 and less than 1,000,000 and an electrolyte salt, and the content of the organic solid electrolyte is 0.40% by mass or more relative to 100% by mass of the total amount of the positive electrode active material particles. With such a positive electrode material for a secondary battery, it is possible to prevent a decrease in discharge capacity when repeated charging and discharging is performed in a secondary battery using a solid electrolyte.

[0010] Embodiments of the present invention will be described below with reference to the attached drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant explanations are omitted. Also, the dimensional ratios in the drawings are exaggerated for illustrative purposes and may differ from the actual ratios.

[0011] Figure 1 is a schematic cross-sectional view showing the overall structure of a stacked (internal parallel connection type) all-solid-state lithium secondary battery (hereinafter also simply referred to as "stacked secondary battery"), which is one embodiment of the present invention. Figure 1 shows a cross-section of the stacked secondary battery during charging. The stacked secondary battery 10a shown in Figure 1 has a structure in which a substantially rectangular power generation element 21, where the charge and discharge reaction actually proceeds, is sealed inside a laminate film 29, which is the battery casing. Here, the power generation element 21 has a configuration in which a negative electrode, a solid electrolyte layer 17 containing a solid electrolyte, and a positive electrode are stacked.

[0012] The negative electrode has a structure in which a negative electrode current collector 11' and a negative electrode active material layer 13 made of lithium metal deposited on the surface of the negative electrode current collector 11' are stacked. Furthermore, a negative electrode intermediate layer 14 is arranged so as to be in contact with the negative electrode active material layer 13 and the solid electrolyte layer 17, respectively.

[0013] The positive electrode has a structure in which a positive electrode active material layer 15 is arranged on the surface of the positive electrode current collector 11''. As a result, the negative electrode current collector 11'', the negative electrode active material layer 13, the negative electrode intermediate layer 14, the solid electrolyte layer 17, the positive electrode active material layer 15, and the positive electrode current collector 11'' constitute a single cell layer 19. Therefore, the stacked secondary battery 10a shown in Figure 1 can also be said to have a configuration in which multiple single cell layers 19 are stacked and electrically connected in parallel.

[0014] The negative electrode current collector 11' and the positive electrode current collector 11'' are each fitted with a negative electrode current collector plate 25 and a positive electrode current collector plate 27, which are electrically connected to the respective electrodes (negative and positive electrodes), and are structured to be sandwiched between the edges of the laminate film 29 and led out to the outside of the laminate film 29. In the stacked secondary battery 10a, a restraining pressure is applied in the stacking direction of the power generation elements 21 by a pressurizing member. As a result, the volume of the power generation elements 21 is kept constant.

[0015] The main components of the secondary battery according to this embodiment will be described below.

[0016] [Current Collector] The current collector has the function of mediating the movement of electrons from the electrode active material layer. There are no particular restrictions on the materials that make up the current collector. For example, metals or conductive resins can be used as the constituent materials of the current collector.

[0017] The current collector may be a single-layer structure made of a single material, or it may be a laminated structure in which layers made of these materials are appropriately combined. From the viewpoint of reducing the weight of the current collector, it is preferable to include at least a conductive resin layer made of a conductive resin. Furthermore, from the viewpoint of blocking the movement of lithium ions between single cell layers, a metal layer may be provided on a part of the current collector. Moreover, if the negative electrode active material layer and positive electrode active material layer described later are conductive and can perform the current collecting function on their own, it is not necessary to use a current collector as a separate component from these electrode active material layers. In such a configuration, the negative electrode active material layer described later will directly constitute the negative electrode, and the positive electrode active material layer described later will directly constitute the positive electrode.

[0018] [Negative Electrode Active Material Layer] The negative electrode active material layer 13 contains a negative electrode active material. The type of negative electrode active material is not particularly limited, but examples include carbon materials, metal oxides, and metal active materials. In addition, a lithium-containing metal may be used as the negative electrode active material. Such a negative electrode active material is not particularly limited as long as it is a lithium-containing active material, and examples include lithium metal and lithium-containing alloys. Examples of lithium-containing alloys include alloys of Li and at least one of In, Al, Si, Sn, Mg, Au, Ag, and Zn. The negative electrode active material preferably contains lithium metal or a lithium-containing alloy, a silicon-based negative electrode active material, or a tin-based negative electrode active material, and is particularly preferably lithium metal or a lithium-containing alloy.

[0019] Furthermore, when lithium metal or a lithium-containing alloy is used as the negative electrode active material, the secondary battery according to this embodiment may be a so-called lithium deposition type, in which lithium metal as the negative electrode active material is deposited on the negative electrode current collector during the charging process. Therefore, in such an embodiment, the thickness of the negative electrode active material layer increases as the charging process progresses, and decreases as the discharging process progresses. The negative electrode active material layer does not need to be present during complete discharge, but in some cases, a negative electrode active material layer consisting of a certain amount of lithium metal may be present during complete discharge.

[0020] The content of the negative electrode active material in the negative electrode active material layer is not particularly limited, but for example, it is preferably in the range of 40 to 100% by mass, and more preferably in the range of 50 to 90% by mass.

[0021] The negative electrode active material layer may further contain a solid electrolyte as needed. By including a solid electrolyte in the negative electrode active material layer, the ionic conductivity of the negative electrode active material layer can be improved. Examples of the solid electrolyte include sulfide solid electrolytes and oxide solid electrolytes. In this specification, the solid electrolyte refers to a material mainly composed of an ion conductor capable of ionic conduction in a solid, and in particular, the lithium ion conductivity at room temperature (25 °C) is 1 × 10 －５ S / cm or more, and this lithium ion conductivity is preferably 1 × 10 －４ S / cm or more. Here, the value of the ionic conductivity can be measured by the alternating current impedance method.

[0022] The solid electrolyte preferably is a sulfide solid electrolyte containing S element from the viewpoint that it exhibits excellent lithium ion conductivity and can better follow the volume change of the electrode active material accompanying charge and discharge. More preferably, it is a sulfide solid electrolyte containing Li element, M element and S element, and the M element is at least one element selected from the group consisting of P, Si, Ge, Sn, Ti, Zr, Nb, Al, Sb, Br, Cl and I, and even more preferably, it is a sulfide solid electrolyte containing S element, Li element and P element.

[0023] The sulfide solid electrolyte may have a Li ３ PS ４ skeleton, and may have a Li ４ P ２ S ７ skeleton, and may have a Li ４ P ２ S ６ skeleton. Examples of the sulfide solid electrolyte having a Li ３ PS ４ skeleton include, for example, LiI - Li ３ PS ４ , LiI - LiBr - Li ３ PS ４ , Li３ PS ４ This can be cited. Also, Li ４ P ２ S ７ Examples of sulfide solid electrolytes having a framework include Li-P-S system solid electrolytes called LPS. Also, as sulfide solid electrolytes, for example, Li （４－ｘ） Ge （１－ｘ） P ｘ S ４ You may also use LGPS, etc., which is represented as (where x satisfies 0 < x < 1). More specifically, for example, LPS(Li ２ S-P ２ S ５ ), Li ７ P ３ S １１ Li ３．２ P ０．９６ S, Li ３．２５ Ge ０．２５ P ０．７５ S ４ Li １０ GeP ２ S １２ , or Li ６ PS ５ Examples include X (where X is Cl, Br, or I). ２ S-P ２ S ５ The description of " is Li ２ S and P ２ S ５ This refers to a sulfide solid electrolyte made using a raw material composition containing the above, and the same applies to other descriptions. In particular, the sulfide solid electrolyte is preferably LPS (Li) because it has high ionic conductivity and a low bulk modulus, and can therefore follow the volume change of the electrode active material associated with charging and discharging. ２ S-P ２ S ５ ), Li ６ PS ５ X (where X is Cl, Br, or I), Li ７ P ３ S １１ Li ３．２ P ０．９６ S and Li ３ PS ４ It is selected from the group consisting of the following.

[0024] Examples of solid electrolyte shapes include spherical, ellipsoidal, and other particulate forms, as well as thin films. When the solid electrolyte is particulate, its average particle size (D50) is not particularly limited, but is preferably 40 μm or less, more preferably 20 μm or less, and even more preferably 10 μm or less. On the other hand, the average particle size (D50) is preferably 0.01 μm or more, and more preferably 0.1 μm or more. The solid electrolyte content in the negative electrode active material layer is preferably in the range of 1 to 60% by mass, and more preferably in the range of 10 to 50% by mass.

[0025] The negative electrode active material layer may further contain, in addition to the negative electrode active material and solid electrolyte described above, at least one of a binder and a conductive additive. Examples of binders include polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are substituted with other halogen elements), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), and carboxymethylcellulose (CMC). Examples of conductive additives include fibrous conductive additives and particulate conductive additives. Examples of fibrous conductive additives include carbon fibers such as carbon nanotubes, carbon nanohorns, carbon nanofibers, carbon nanofilaments, carbon fibrils, and vapor-grown carbon fibers. Examples of particulate conductive additives are not particularly limited and include carbon powders such as acetylene black, Ketjen black (furnace black), channel black, and thermal black.

[0026] The thickness of the negative electrode active material layer varies depending on the intended configuration of the secondary battery, but is preferably in the range of 0.1 to 1,000 μm, and more preferably 40 to 100 μm.

[0027] [Negative Electrode Intermediate Layer] In the case of a secondary battery according to this embodiment that is of the lithium deposition type in which lithium metal or lithium-containing alloy as a negative electrode active material is deposited on the negative electrode current collector 11' during the charging process, it is preferable that the power generation element includes a negative electrode intermediate layer containing a lithium-reactive material between the negative electrode active material layer and the solid electrolyte layer. Examples of lithium-reactive materials include materials that can intercept and deintercept lithium ions during charging and metals that can alloy with lithium during charging. The presence of such a negative electrode intermediate layer suppresses the growth of dendrites from the lithium metal layer (negative electrode active material layer) when lithium metal is deposited between the negative electrode intermediate layer and the negative electrode current collector during charging, thereby preventing short circuits in the battery and the resulting decrease in capacity.

[0028] While there are no particular limitations on the material capable of intercalating and deintercalating lithium ions, carbon materials are preferred. Specific examples of carbon materials include carbon black (specifically, acetylene black, Ketjenblack®, furnace black, channel black, thermal lamp black, etc.), carbon nanotubes (CNTs), graphite, and hard carbon. Among these, carbon black is preferred, and it is more preferable that it be at least one selected from the group consisting of acetylene black, Ketjenblack®, furnace black, channel black, and thermal lamp black.

[0029] Examples of metals that can be alloyed with lithium include In, Al, Si, Sn, Mg, Au, Ag, and Zn. Among these, In, Si, Sn, and Ag are preferred, with Ag being more preferred.

[0030] The lithium-reactive material may be used alone or in combination of two or more types. As a form of using two or more types in combination, a preferred embodiment is to use a material capable of intercalating and deintercalating lithium ions in combination with a metal capable of alloying with lithium. This ensures sufficient strength and lithium-ion conductivity of the negative electrode intermediate layer. More specifically, it is preferable to use nanoparticles made of In, Si, Sn, and Ag in combination with carbon black, and more preferably to use nanoparticles made of Ag in combination with carbon black. When using a material capable of intercalating and deintercalating lithium ions in combination with a metal capable of alloying with lithium, the mixing ratio (mass ratio) of these materials is not particularly limited, but the ratio of material capable of intercalating and deintercalating lithium ions to metal capable of alloying with lithium is preferably 10:1 to 1:1, and more preferably 5:1 to 2:1.

[0031] The content of lithium-reactive material in the negative electrode intermediate layer (referring to the total content of two or more materials when used in combination; the same applies hereinafter) is not particularly limited, but is preferably in the range of 50 to 100% by mass, more preferably in the range of 70 to 100% by mass, even more preferably in the range of 85 to 100% by mass, and particularly preferably in the range of 90 to 99% by mass.

[0032] The negative electrode intermediate layer may consist solely of lithium-reactive material if a self-supporting film can be fabricated using only lithium-reactive material, but may also contain a binder as needed. The type of binder is not particularly limited, and any known binder in the art can be used as appropriate; one example is described above.

[0033] The binder content in the negative electrode intermediate layer is not particularly limited, but is preferably in the range of 1 to 15% by mass, and more preferably in the range of 5 to 10% by mass. If the binder content is 1% by mass or more, a negative electrode intermediate layer with sufficient strength can be formed. If the binder content is 15% by mass or less, a negative electrode intermediate layer with sufficient lithium ion conductivity can be formed.

[0034] The thickness of the negative electrode intermediate layer is not particularly limited, but is preferably 1 to 50 μm, more preferably 5 to 40 μm, and even more preferably 10 to 30 μm. When the thickness of the negative electrode intermediate layer is 1 μm or more, the functions of the negative electrode intermediate layer can be fully exhibited. When the thickness of the negative electrode intermediate layer is 50 μm or less, the decrease in energy density can be suppressed.

[0035] [Solid Electrolyte Layer] The solid electrolyte layer 17 is interposed between the positive electrode active material layer 15 and the negative electrode active material layer 13 and contains a solid electrolyte (usually as the main component). There are no particular restrictions on the specific form of the solid electrolyte contained in the solid electrolyte layer, and the solid electrolytes and their preferred forms exemplified in the section on the negative electrode active material layer can be used in the same way. In some cases, solid electrolytes other than those described above may be used in combination.

[0036] The solid electrolyte content in the solid electrolyte layer is preferably in the range of 10 to 100% by mass, more preferably in the range of 50 to 100% by mass, and even more preferably in the range of 90 to 100% by mass, relative to the total mass of the solid electrolyte layer.

[0037] The solid electrolyte layer may further contain a binder in addition to the solid electrolyte described above. The thickness of the solid electrolyte layer varies depending on the configuration of the secondary battery, but is preferably in the range of 0.1 to 1,000 μm, and more preferably 10 to 100 μm.

[0038] [Positive Electrode Active Material Layer] In the secondary battery according to the embodiment shown in Figure 1, the positive electrode active material layer is composed of a positive electrode material for secondary batteries according to one embodiment of the present invention. That is, the material constituting the positive electrode active material layer is the positive electrode material. The positive electrode material for secondary batteries essentially includes positive electrode active material particles, an organic solid electrolyte that covers at least a portion of the surface of the positive electrode active material particles, and an inorganic solid electrolyte.

[0039] (Positive Electrode Active Material Particles) Positive electrode active material particles are particles made of positive electrode active material. The positive electrode active material is not particularly limited as long as it is a material that can release lithium ions during the charging process of a secondary battery and absorb lithium ions during the discharging process. An example of such a positive electrode active material is one that contains an M1 element and an O element, and the M1 element contains at least one element selected from the group consisting of Li, Mn, Ni, Co, Cr, Fe, and P. An example of such a positive electrode active material is LiCoO ２ LiMnO ２ LiNiO ２ , Li(Ni-Mn-Co)O ２ Layered rock salt type active materials such as LiMn ２ O ４ LiNi ０．５ Mn １．５ O ４ spinel-type active materials such as LiFePO ４ LiMnPO ４ Olivine-type active materials such as Li ２ FeSiO ４ Li ２ MnSiO ４ Examples of Si-containing active materials include the above. Other oxide active materials include, for example, Li ４ Ti ５ O １２ LiVO ２ These are some examples.

[0040] In particular, the positive electrode active material, in a fully discharged state, is given by the following general formula (1): Li ｘ Ni ａ M ｂ N ｃ O ２(1) It is preferable to include a lithium transition metal composite oxide having a composition represented by the formula (wherein x, a, b, and c satisfy 0.8 ≤ x ≤ 1.1, a + b + c = 1, 0.80 ≤ a ≤ 1.00, 0 ≤ b ≤ 0.20, and 0 ≤ c ≤ 0.20. M is one or more elements selected from the group consisting of Mn and Co, and N is one or more elements selected from the group consisting of Al, Sn, Nb, Ti, Zr, and Mg). This positive electrode active material is a so-called high-nickel positive electrode active material, which has a high proportion of nickel atoms in its composition, and is known to exhibit significant expansion and contraction during charging and discharging. Therefore, it is preferable for the positive electrode material to contain positive electrode active material particles containing this positive electrode active material, as this can lead to a more pronounced effect of the present invention.

[0041] Furthermore, the positive electrode active material may contain sulfur. The positive electrode active material containing sulfur is not particularly limited, but examples include elemental sulfur (S), organic sulfur compounds, or particles or thin films of inorganic sulfur compounds. Any material that can release lithium ions during charging and absorb lithium ions during discharge by utilizing the oxidation-reduction reaction of sulfur is acceptable. Examples of organic sulfur compounds include disulfide compounds, sulfur-modified polyacrylonitriles represented by the compounds described in International Publication No. 2010 / 044437, sulfur-modified polyisoprene, rubeanoic acid (dithiooxamide), and polysulfurized carbon. Among these, disulfide compounds, sulfur-modified polyacrylonitriles, and rubeanoic acid are preferred, and sulfur-modified polyacrylonitriles are particularly preferred. As disulfide compounds, those having dithiobiurea derivatives, thiourea groups, thioisocyanates, or thioamide groups are more preferred. Here, sulfur-modified polyacrylonitrile is a modified polyacrylonitrile containing sulfur atoms, obtained by mixing sulfur powder and polyacrylonitrile and heating it under an inert gas or reduced pressure. Its presumed structure is, for example, shown in Chem. Mater. 2011, 23, 5024-5028, a structure in which the polyacrylonitrile is ring-closed to become polycyclic, and at least some of the sulfur atoms are bonded to carbon atoms. The compound described in this document shows a Raman spectrum at 1330 cm⁻¹.－１ and 1560 cm －１ There is a strong peak signal in the vicinity, and further, 307 cm －１ , 379 cm －１ , 472 cm －１ , 929 cm －１ There is a peak in the vicinity. On the other hand, inorganic sulfur compounds are preferable because of their excellent stability. Specifically, elemental sulfur (S), Li ２ S, TiS ２ , TiS ３ , TiS ４ , NiS, NiS ２ , CuS, FeS ２ , MoS ２ , MoS ３ etc. can be mentioned. Among them, elemental sulfur (S), Li ２ S, S-carbon composite, TiS ２ , TiS ３ , TiS ４ , FeS ２ and MoS ２ are preferable, and elemental sulfur (S), Li ２ S, TiS ２ and FeS ２ are more preferable. From the viewpoint of high capacity, elemental sulfur (S) or Li ２ S is particularly preferable. Note that as elemental sulfur (S), α-sulfur, β-sulfur, or γ-sulfur having an S ８ structure can be used. These elemental sulfur (S) exist in the positive electrode active material layer in the form of (poly) sulfide of lithium by occluding lithium ions during discharge.

[0042] In some cases, two or more positive electrode active materials may be used in combination. Of course, positive electrode active materials other than those described above may also be used.

[0043] The positive electrode active material has a particle shape. The average particle diameter of the positive electrode active material (positive electrode active material particles) is preferably in the range of 1 nm to 100 μm, more preferably in the range of 10 nm to 50 μm, even more preferably in the range of 100 nm to 20 μm, and particularly preferably in the range of 1 to 20 μm. Here, the "average particle diameter" of the positive electrode active material particles is defined as the 50% cumulative diameter (D50) measured by a laser diffraction / scattering particle size distribution device.

[0044] The content of the positive electrode active material in the positive electrode material is not particularly limited, but it is preferably more than 50% by mass, more preferably in the range of 50% to 98% by mass, even more preferably in the range of 60% to 95% by mass, and particularly preferably in the range of 70% to 90% by mass, based on 100% by mass of the total amount of the positive electrode material.

[0045] (Organic Solid Electrolyte) The organic solid electrolyte is a solid electrolyte made of organic material, and in the positive electrode material according to this embodiment, it coats at least a portion of the surface of the positive electrode active material particles. Here, the organic solid electrolyte is a composite of a polyether polymer compound having a weight-average molecular weight (Mw) greater than 1,000 and less than 1,000,000 and an electrolyte salt.

[0046] Polyether polymer compounds have an ether bond "-R". １ -O-R ２ It is a polymer compound that contains the ether bond "-R" within its structure. １ -O-R ２ -" in R １ and R ２ R is a hydrocarbon group. Specifically, １ and R ２ These include methylene groups, ethylene groups, and propylene groups. １ and R ２ These may be the same hydrocarbon group. Alternatively, R １ and R ２ These may be different hydrocarbon groups.

[0047] Such polyether polymer compounds may be those in which ether bonds are linked in a linear fashion. Furthermore, polymer compounds with hydroxyl groups, carboxyl groups, amino groups, etc., crosslinked into them may also be used.

[0048] In particular, as a polyether polymer compound, R 1 and R 2 It is preferable to use a polymer compound having a linear polyoxyethylene structure composed of ethylene groups. This polymer compound is suitable because it has high ionic conductivity and can rapidly transport ions to the coated positive electrode active material particles. In addition, this polymer compound has the advantage of being more flexible and deformable compared to other polymer compounds. Examples of polymer compounds having an ethylene oxide structure include polyethylene oxide (PEO), polyethylene glycol dimethyl ester (PEGDME), and polyethylene carbonate (PEC), and among these, polyethylene oxide is preferred. The weight-average molecular weight (Mw) of the polyether polymer compound is greater than 1,000 and less than 1,000,000 as described above, but if the Mw value is 1,000 or less or 1,000,000 or more, the polyether polymer compound (and by extension the organic solid electrolyte) cannot adequately follow the expansion and contraction of the positive electrode active material during battery charging and discharging. As a result, a problem may arise in which sufficient discharge capacity cannot be obtained after repeated charging and discharging of the battery. The weight-average molecular weight (Mw) of the polyether polymer compound is preferably 2,000 to 800,000, more preferably 3,000 to 700,000, even more preferably 4,000 to 600,000, and particularly preferably 5,000 to 500,000. A value above these lower limits has the advantage of preventing the polymer compound from becoming too fluid, while a value below these upper limits prevents the polymer compound from becoming too rigid. The polyether polymer compound may be used alone or in combination of two or more types. The weight-average molecular weight (Mw) values ​​of the polyether polymer compound described here shall be calculated using the method described in the examples below.

[0049] As the electrolyte salt, conventionally known electrolyte salts in this art can be used in the same way. In particular, the electrolyte salt is given by the following general formula (2): ((C ｍ F ２ｍ＋１ ) SO ２ ) ((C ｎ F ２ｎ＋１ ) SO ２ ) N － (2) Preferably, the electrolyte salt contains a fluorine-containing sulfonyliimide anion represented by (2) (wherein m and n are each independent integers from 0 to 4). Examples of such electrolyte salts include lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and by constructing an organic solid electrolyte using an electrolyte salt containing a fluorine-containing sulfonyliimide anion represented by general formula (2), the effects of the present invention can be expressed more significantly compared to when other electrolyte salts are used. However, other electrolyte salts may also be used, and examples of other electrolyte salts include LiClO4, LiBF4, LiPF6, LiAlCl4, LiSbF6, LiSCN, LiCl, LiCF3SO3, LiCF3CO2, LiAsF6, LiB 10 Cl 10 Examples include LiCl, LiBr, and LiI. The electrolyte salt may be used alone or in combination of two or more types.

[0050] Furthermore, the organic solid electrolyte may contain nanofillers of metal oxides such as SiO2, TiO2, and ZrO2 in order to further improve its ionic conductivity.

[0051] The content of the organic solid electrolyte in the positive electrode material is 0.40% by mass or more, relative to 100% by mass of the total amount of positive electrode active material particles. If this content is less than 0.40% by mass, the polyether polymer compound (and thus the organic solid electrolyte) cannot adequately follow the expansion and contraction of the positive electrode active material during battery charging and discharging. As a result, a problem may arise in which sufficient discharge capacity cannot be obtained after repeated charging and discharging of the battery. The value of this content is preferably 0.45 to 3.66% by mass, more preferably 0.45 to 3.50% by mass, particularly preferably 0.49 to 3.50% by mass, and most preferably 0.70 to 2.00% by mass. Values ​​below these upper limits are preferable because they can suppress the increase in resistance and decrease in capacity that occur with an increase in the amount of organic solid electrolyte. The value of the percentage of organic solid electrolyte content in the positive electrode material described here shall be calculated using the method described in the examples below.

[0052] (Inorganic Solid Electrolyte) The positive electrode material according to this embodiment must include an inorganic solid electrolyte. There are no particular restrictions on the specific form of the inorganic solid electrolyte included in the positive electrode material according to this embodiment, and the solid electrolytes and their preferred forms exemplified in the negative electrode active material layer section may be used in the same manner. In some cases, inorganic solid electrolytes other than those described above may be used in combination.

[0053] The inorganic solid electrolyte content in the positive electrode material is preferably in the range of 5 to 20% by mass, more preferably in the range of 10 to 17% by mass, and even more preferably in the range of 12 to 15% by mass, based on 100% by mass of the total amount of the positive electrode material.

[0054] The positive electrode material preferably contains a conductive additive or a binder in addition to the components described above. In particular, since the conductivity of the positive electrode active material is not high, it is more preferable for the positive electrode material to contain a conductive additive. The types of conductive additives and binders are not particularly limited, and those known in the art can be used as appropriate, and some examples of them are described above.

[0055] The thickness of the positive electrode active material layer varies depending on the intended configuration of the secondary battery, but is preferably in the range of 0.1 to 1000 μm, and more preferably 40 to 100 μm.

[0056] [Positive electrode current collector plate and negative electrode current collector plate] The material constituting the current collector plates (25, 27) is not particularly limited, and known highly conductive materials conventionally used as current collector plates for secondary batteries can be used. Preferred materials for the current collector plates are metallic materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof. From the viewpoint of lightness, corrosion resistance, and high conductivity, aluminum and copper are more preferred, and aluminum is particularly preferred. The positive electrode current collector plate 27 and the negative electrode current collector plate 25 may be made of the same material, or different materials may be used.

[0057] [Positive and Negative Leads] Although not shown in the diagram, the current collectors (11', 11") and the current collector plates (25, 27) may be electrically connected via positive and negative leads. The materials used for the positive and negative leads may be the same as those used in known secondary batteries. It is preferable to cover the parts that are removed from the casing with heat-resistant insulating heat shrink tubing or the like to prevent leakage current from coming into contact with peripheral equipment or wiring and affecting the product (for example, automotive parts, especially electronic equipment).

[0058] [Battery casing material] As the battery casing material, known metal can cases can be used, or, as shown in Figure 1, a bag-shaped case made of aluminum-containing laminate film 29 that can cover the power generation elements can be used. For example, a three-layer laminate film made by laminating PP, aluminum, and nylon in that order can be used, but there are no limitations to these. Laminate film is preferable from the viewpoint of being able to increase output power and have excellent cooling performance, and can be suitably used for batteries in large equipment for EVs and HEVs. Furthermore, since the group pressure applied to the power generation elements from the outside can be easily adjusted, an aluminum-containing laminate film is more preferable for the casing.

[0059] The stacked secondary battery according to this embodiment has a configuration in which multiple single cell layers are connected in parallel, resulting in high capacity and excellent cycle durability. Therefore, the stacked secondary battery according to this embodiment is suitable for use as a power source for EVs and HEVs.

[0060] Although one embodiment of a secondary battery has been described above, the present invention is not limited to the configuration described in the above-described embodiment, and can be modified as appropriate based on the description of the claims.

[0061] For example, one type of battery to which the secondary battery according to the present invention is applied is a bipolar battery, which includes a bipolar electrode having a positive electrode active material layer electrically coupled to one side of a current collector and a negative electrode active material layer electrically coupled to the opposite side of the current collector.

[0062] Furthermore, the secondary battery according to this embodiment does not have to be all-solid type. That is, the solid electrolyte layer may further contain a conventionally known liquid electrolyte (electrolyte solution). There are no particular restrictions on the amount of liquid electrolyte (electrolyte solution) that can be contained in the solid electrolyte layer, but it is preferable that the amount is such that the shape of the solid electrolyte layer formed by the solid electrolyte is maintained and leakage of the liquid electrolyte (electrolyte solution) does not occur. As the liquid electrolyte (electrolyte solution), a solution having the form of a conventionally known lithium salt dissolved in a conventionally known organic solvent is used. The liquid electrolyte (electrolyte solution) may further contain additives other than the organic solvent and lithium salt. These additives may be used individually or in combination of two or more. Also, the amount of additives used in the electrolyte can be adjusted as appropriate.

[0063] [Pressurizing Member] As described above, in the secondary battery according to this embodiment, a restraining pressure is applied to the stacking direction of the power generation elements by a pressurizing member. Figure 2 is a perspective view of a stacked secondary battery according to one embodiment of the present invention. Figure 3 is a side view taken from direction A shown in Figure 2.

[0064] As shown in Figures 2 and 3, the stacked secondary battery 100 according to this embodiment includes a power generation element 21 sealed in a laminate film 29 as shown in Figure 1, two metal plates 200 that sandwich the power generation element 21 sealed in the laminate film 29, and a bolt 300 and a nut 400 as fastening members. These fastening members (bolt 300 and nut 400) have the function of fixing the metal plates 200 in a state where they are sandwiching the power generation element 21 sealed in the laminate film 29. As a result, the metal plates 200 and the fastening members (bolt 300 and nut 400) function as pressurizing members that pressurize (restrain) the power generation element 21 in its stacking direction. Note that the pressurizing members are not particularly limited as long as they are members that can pressurize the power generation element 21 in its stacking direction. Typically, a combination of a plate made of a rigid material such as the metal plate 200 and the fastening members described above is used as the pressurizing members. Furthermore, regarding the fastening members, not only bolts 300 and nuts 400 may be used, but also tension plates that fix the ends of the metal plates 200 so as to restrain the power generation element 21 in its stacking direction.

[0065] In this embodiment, the load applied to the power generation element 21 (restraining pressure in the stacking direction of the power generation element) is preferably 10 MPa or less. That is, the secondary battery according to this embodiment is preferably operated with the positive electrode active material layer pressurized with a restraining pressure of 10 MPa or less in the stacking direction of the power generation element. The restraining pressure is more preferably 5 MPa or less, even more preferably 3 MPa or less, and particularly preferably 1 MPa or less. On the other hand, there is no particular limit to the lower limit of the restraining pressure, but it is preferably 0.11 MPa or more.

[0066] In addition to the positive electrode material for secondary batteries and secondary batteries according to the above-described embodiment, the present invention also provides a method for producing a precursor for a positive electrode material for secondary batteries and a method for producing a positive electrode material for secondary batteries.

[0067] That is, a method for producing a positive electrode material precursor for a secondary battery according to another embodiment of the present invention includes: obtaining an organic solid electrolyte by compounding a polyether polymer compound having a weight-average molecular weight (Mw) greater than 1,000 and less than 1,000,000 with an electrolyte salt; and obtaining a mixture by mixing the organic solid electrolyte with positive electrode active material particles in a ratio such that the content of the organic solid electrolyte is 0.40% by mass or more relative to 100% by mass of the total amount of the positive electrode active material particles. Furthermore, a method for producing a positive electrode material for a secondary battery according to yet another embodiment of the present invention includes: obtaining an organic solid electrolyte by compounding a polyether polymer compound having a weight-average molecular weight (Mw) greater than 1,000 and less than 1,000,000 with an electrolyte salt; obtaining a mixture by mixing the organic solid electrolyte with positive electrode active material particles in a ratio such that the content of the organic solid electrolyte is 0.40% by mass or more relative to 100% by mass of the total amount of the positive electrode active material particles; and obtaining a positive electrode material by mixing the mixture with an inorganic solid electrolyte. These manufacturing methods have the advantage that, by going through a process of mixing an organic solid electrolyte, which is a composite of a polyether polymer compound and an electrolyte salt, with positive electrode active material particles, a sufficient amount of organic solid electrolyte can be present on the surface of the positive electrode active material particles contained in the positive electrode material.

[0068] Furthermore, the following items are also included in the scope of the present invention: Item 1: A positive electrode material for a secondary battery comprising: positive electrode active material particles; an organic solid electrolyte coating at least a portion of the surface of the positive electrode active material particles; and an inorganic solid electrolyte, wherein the organic solid electrolyte is a composite of a polyether polymer compound having a weight-average molecular weight (Mw) greater than 1,000 and less than 1,000,000 and an electrolyte salt, and the content of the organic solid electrolyte relative to 100% by mass of the total amount of the positive electrode active material particles is 0.40% by mass or more; Item 2: The positive electrode material for a secondary battery according to Item 1, wherein the content of the organic solid electrolyte is 0.45 to 3.50% by mass; Item 3: The positive electrode material for a secondary battery according to Item 1 or 2, wherein the content of the organic solid electrolyte is 0.70 to 2.00% by mass; Item 4: The positive electrode material for a secondary battery according to any one of Items 1 to 3, wherein the weight-average molecular weight (Mw) of the organic solid electrolyte is 5,000 to 500,000; Item 5: When the positive electrode active material particles are in a complete discharge state, the following general formula (1): Li ｘ Ni ａ M ｂ N ｃ O ２ (1) A positive electrode material for a secondary battery according to any one of items 1 to 4, comprising a lithium transition metal composite oxide having a composition represented by the following formula: (wherein x, a, b, and c satisfy 0.8 ≤ x ≤ 1.1, a + b + c = 1, 0.80 ≤ a ≤ 1.00, 0 ≤ b ≤ 0.20, and 0 ≤ c ≤ 0.20, M is one or more elements selected from the group consisting of Mn and Co, and N is one or more elements selected from the group consisting of Al, Sn, Nb, Ti, Zr, and Mg); Item 6: The electrolyte salt is the following general formula (2): ((C ｍ F ２ｍ＋１ ) SO ２ ) ((C ｎ F ２ｎ＋１ ) SO ２ ) N －(2) A positive electrode material for a secondary battery according to any one of items 1 to 5, comprising a fluorine-containing sulfonyliimide anion represented by the formula (wherein m and n are each independently integers from 0 to 4); Item 7: A positive electrode material for a secondary battery according to any one of items 1 to 6, wherein the inorganic solid electrolyte comprises a sulfide solid electrolyte; Item 8: A positive electrode for a secondary battery comprising a positive electrode active material layer comprising the positive electrode material for a secondary battery according to any one of items 1 to 7; Item 9: A secondary battery comprising the positive electrode for a secondary battery according to item 8; Item 10: A secondary battery according to item 9, wherein the positive electrode active material layer is operated under a constraining pressure of 10 MPa or less in the stacking direction of the power generation element; Item 11: Obtaining an organic solid electrolyte by compounding a polyether polymer compound having a weight-average molecular weight (Mw) greater than 1,000 and less than 1,000,000 with an electrolyte salt, A method for producing a positive electrode material precursor for a secondary battery, comprising: mixing the organic solid electrolyte and positive electrode active material particles in a ratio such that the content of the organic solid electrolyte relative to 100% by mass of the total amount of the positive electrode active material particles is 0.40% by mass or more to obtain a mixture; Item 12: A method for producing a positive electrode material for a secondary battery, comprising: compounding a polyether polymer compound having a weight-average molecular weight (Mw) greater than 1,000 and less than 1,000,000 with an electrolyte salt to obtain an organic solid electrolyte; mixing the organic solid electrolyte and positive electrode active material particles in a ratio such that the content of the organic solid electrolyte relative to 100% by mass of the total amount of the positive electrode active material particles is 0.40% by mass or more to obtain a mixture; and mixing the mixture with an inorganic solid electrolyte to obtain a positive electrode material.

[0069] The present invention will be described in more detail below with reference to examples. However, the technical scope of the present invention is not limited to the following examples.

[0070] 《Method for Measuring the Weight-Average Molecular Weight (Mw) of Polyether Polymer Compounds》 The weight-average molecular weight (Mw) of the polyether polymer compounds used in the following examples and comparative examples was measured using gel permeation chromatography (GPC) under the following measurement conditions.

[0071] (GPC measurement conditions) Measurement device: HLC-8320GPC (manufactured by Tosoh Corporation) Sample concentration: 0.01% by mass Column: TSKgel GMPWXL Detector: Differential refractometer Eluent: Solution of 10 mM lithium bromide dissolved in N,N-dimethylformamide Flow rate: 1 mL / min Measurement temperature: 40°C Molecular weight conversion: Polyethylene glycol equivalent Sample injection volume: 200 μL.

[0072] 《Preparation of Test Cells》 [Example 1] (Preparation of Organic Solid Electrolyte / Cathode Active Material Composite) 0.0917 g of polyethylene oxide (manufactured by Thermo Fisher Scientific, weight-average molecular weight (Mw) 100,000) as a polyether polymer compound and 0.299 g of lithium bis(trifluoromethanesulfonyl)imide (manufactured by Kishida Chemical Co., Ltd., LiTFSI) as an electrolyte salt were weighed out. These were added to 30.9 g of N-methyl-2-pyrrolidone. This was stirred at 60°C overnight to prepare an organic solid electrolyte-containing solution.

[0073] Next, to the organic solid electrolyte solution prepared above, 0.500 g of positive electrode active material (LiNi, manufactured by MSE Corporation) is added. ０．８２ Mn ０．０７ Co ０．１１ O ２ (NMC811; D50 = 4 μm) was added, and the mixture was heated and stirred overnight before being allowed to cool to room temperature. Next, the solution was transferred to a centrifuge tube and centrifuged at 13,000 rpm for 10 minutes, after which the supernatant solution was removed by decantation. Subsequently, the mixture was vacuum dried at 60°C for 24 hours to obtain an organic solid electrolyte / cathode active material composite. In this process, a portion of the organic solid electrolyte contained in the organic solid electrolyte-containing solution coats the cathode active material. The amount of coating of the cathode active material by the organic solid electrolyte was controlled by adjusting the amount of N-methyl-2-pyrrolidone added as a solvent.

[0074] Furthermore, the fluorine content of the organic solid electrolyte / cathode active material composite obtained above was quantified using combustion ion chromatography, and the carbon content was quantified using a carbon-sulfur analyzer. Then, by referring to the following formula, the content of the organic solid electrolyte in the organic solid electrolyte / cathode active material composite (total mass of polyether polymer compound and electrolyte salt) was calculated, and the ratio (mass%) of the organic solid electrolyte content relative to 100% of the total mass of cathode active material particles was calculated. The results are shown in Table 1 below.

[0075]

[0076] Furthermore, for the organic solid electrolyte / cathode active material composite obtained above, the total volume of the organic solid electrolyte was calculated from the quantified mass of the organic solid electrolyte based on the specific gravities of the polyether polymer compound and electrolyte salt, which are constituent components of the organic solid electrolyte (assuming a simple mixed system and no density change due to interaction). Next, the specific surface area of ​​the cathode active material particles was calculated by assuming that they are perfect spheres with a particle size corresponding to the average particle diameter (D50). Then, the theoretical value of the coating thickness of the cathode active material particles by the organic solid electrolyte was calculated by dividing the total volume of the organic solid electrolyte by the specific surface area of ​​the cathode active material particles. The results are shown in Table 1 below.

[0077] (Preparation of Cathode Compound) In a glove box with an argon atmosphere and a dew point of -68°C or lower, 0.1648 g of the organic solid electrolyte / cathode active material composite prepared above and an inorganic solid electrolyte, a sulfide solid electrolyte (manufactured by Ampcera, Li) ６ PS ５ A positive electrode mixture powder was obtained by mixing 0.0292 g of Cl and 0.0060 g of conductive additive (VGCF, manufactured by Resonaq Co., Ltd.) in an agate mortar for 30 minutes.

[0078] (Preparation of test cells) Test cells were prepared in a glove box under an argon atmosphere with a dew point of -68°C or lower.

[0079] First, insert a SUS cylindrical convex punch (10 mm diameter, also serving as a negative electrode current collector) into one side of a Macol cylindrical tube jig (10 mm inner diameter, 23 mm outer diameter, 20 mm height), and then insert a sulfide solid electrolyte (Ampcera, Li) from the top of the cylindrical tube jig. ６ PS ５ 80 mg of Cl was added. Then, another SUS cylindrical convex punch (10 mm in diameter, also serving as the positive electrode current collector) was inserted to sandwich the solid electrolyte, and a hydraulic press was used to press it at a pressure of 75 MPa for 3 minutes, thereby forming a solid electrolyte layer with a diameter of 10 mm and a thickness of approximately 0.6 mm inside the cylindrical tube jig.

[0080] Next, the cylindrical convex punch inserted from the top was temporarily removed, and 20.4 mg of the cathode composite powder obtained above was placed on one side of the solid electrolyte layer inside the cylindrical tube, and the cylindrical convex punch was inserted again from the top. Subsequently, the cylindrical convex punch inserted from the bottom was temporarily removed, and indium foil (manufactured by Nilaco, 0.02 mm thick, 10 mm in diameter) was placed on the other side of the solid electrolyte layer inside the cylindrical tube, and the cylindrical convex punch was inserted again from the bottom. The cathode composite layer and indium foil were pressed against the solid electrolyte layer by pressing at a pressure of 300 MPa for 3 minutes. The lower cylindrical convex punch was removed again, and lithium foil (manufactured by Nilaco, 0.20 mm thick, 8 mm diameter) and indium foil (manufactured by Nilaco, 0.30 mm thick, 9 mm diameter) were placed on top of the indium foil. The cylindrical convex punch was then inserted again, and the indium-lithium-indium anode was formed by pressing at a pressure of 100 MPa for 3 minutes. The cell restraint pressure was set to 0.5 MPa.

[0081] As described above, a test cell (all-solid-state lithium secondary battery) was fabricated in which a positive electrode current collector, a positive electrode composite layer, a solid electrolyte layer, a lithium-indium negative electrode, and a negative electrode current collector were stacked.

[0082] [Example 2] Polyether polymer compound (polyethylene oxide) and inorganic solid electrolyte (Li) in cathode mixture ６ PS ５The test cell (all-solid-state lithium secondary battery) of this example was prepared using the same method as in Example 1 described above, except that the amount of Cl) was changed.

[0083] [Example 3] Polyether polymer compound (polyethylene oxide) and inorganic solid electrolyte (Li) in cathode mixture ６ PS ５ The test cell (all-solid-state lithium secondary battery) of this example was prepared using the same method as in Example 1 described above, except that the amount of Cl) was changed.

[0084] [Example 4] A test cell (all-solid-state lithium secondary battery) for this example was prepared using the same method as in Example 1 described above, except that polyethylene oxide (manufactured by Merck) with a weight-average molecular weight (Mw) of 10,000 was used as the polyether polymer compound.

[0085] [Example 5] As an inorganic solid electrolyte in the positive electrode mixture, Li ６ PS ５ Replace Cl with Li ２ S-P ２ S ５ The test cell (all-solid-state lithium secondary battery) of this embodiment was fabricated using the same method as in Example 1 described above, except for the use of [specific material].

[0086] [Example 6] As an inorganic solid electrolyte in the positive electrode mixture, Li ６ PS ５ Replace Cl with Li ３ YCl ６ The test cell (all-solid-state lithium secondary battery) of this embodiment was fabricated using the same method as in Example 1 described above, except for the use of [specific material].

[0087] [Example 7] In the cathode mixture, LiPF was used as the electrolyte salt of the organic solid electrolyte instead of LiTFSI. ６ The test cell (all-solid-state lithium secondary battery) of this embodiment was fabricated using the same method as in Example 1 described above, except for the use of [specific material].

[0088] [Example 8] LiNi as the positive electrode active material ０．８２ Mn ０．０７ Co ０．１１ O２ Instead, LiNi ０．６７ Mn ０．２８ Co ０．０５ O ２ The test cell (all-solid-state lithium secondary battery) for this example was fabricated using the same method as in Example 1 described above, except that it used NMC721 (manufactured by MSE Corporation; D50 = 4 μm).

[0089] [Comparative Example 1] A test cell (all-solid-state lithium secondary battery) for this comparative example was prepared using the same method as in Example 1 described above, except that an organic solid electrolyte (a composite of a polyether polymer compound and an electrolyte salt) was not incorporated into the cathode mixture.

[0090] [Comparative Example 2] A test cell (all-solid-state lithium secondary battery) for this comparative example was prepared using the same method as in Example 8 described above, except that an organic solid electrolyte (a composite of a polyether polymer compound and an electrolyte salt) was not incorporated into the cathode mixture.

[0091] [Comparative Example 3] A test cell (all-solid-state lithium secondary battery) for this comparative example was prepared using the same method as in Example 1 described above, except that polyethylene oxide (manufactured by Thermo Fisher Scientific) with a weight-average molecular weight (Mw) of 1,000,000 was used as the polyether polymer compound.

[0092] [Comparative Example 4] A test cell (all-solid-state lithium secondary battery) for this comparative example was prepared using the same method as in Example 1 described above, except that polyethylene oxide (manufactured by Merck) with a weight-average molecular weight (Mw) of 1,000 was used as the polyether polymer compound.

[0093] [Comparative Example 5] Polyether polymer compound (polyethylene oxide) and inorganic solid electrolyte (Li) in cathode mixture ６ PS ５ The test cell (all-solid-state lithium secondary battery) of this comparative example was prepared using the same method as in Example 1 described above, except that the amount of Cl) was changed.

[0094] 《Evaluation of Test Cells》 The test cells prepared in the above examples and comparative examples were subjected to charge-discharge tests using a charge-discharge test apparatus (Hokuto Denko Co., Ltd., HJ-SD8) in a constant temperature chamber set to 60°C. Specifically, the test cells were placed in the constant temperature chamber, and after the cell temperature stabilized, a charge of 0.2 mA / cm² was applied. ２ With a current density equivalent to 0.1C, constant current constant voltage charging (upper voltage 3.68V) is performed with a cutoff current of 0.04mA / cm². ２ The test was performed with the following settings. Subsequently, constant current discharge was performed at the same current density until the cell voltage reached 1.88V. This charge-discharge cycle was repeated 10 times, and the discharge capacity value at the 10th cycle was measured. The results are shown in Table 1 below. Here, the discharge capacity ratio values ​​shown in Table 1 are relative values ​​with the discharge capacity value in Comparative Example 1 set to 1. Note that for Comparative Example 4, a short circuit occurred during the charge-discharge test, so the discharge capacity ratio could not be measured.

[0095]

[0096] The results shown in Table 1 indicate that the all-solid-state lithium secondary batteries of Examples 1 to 8, using the predetermined positive electrode material according to the present invention, exhibit high discharge capacity even after repeated charging and discharging.

[0097] In contrast, in Comparative Examples 1 and 2, which did not use an organic solid electrolyte, and in Comparative Examples 3 to 5, which did use an organic solid electrolyte but either the weight-average molecular weight (Mw) of the polyether polymer compound was outside the specified range or the amount of organic solid electrolyte used relative to the positive electrode active material particles was small, sufficient discharge capacity could not be obtained after repeated charging and discharging.

[0098] 10a, 100 stacked secondary battery, 11' negative electrode current collector, 11" positive electrode current collector, 13 negative electrode active material layer, 14 negative electrode intermediate layer, 15 positive electrode active material layer, 17 solid electrolyte layer, 19 single cell layer, 21 power generation element, 25 negative electrode current collector plate, 27 positive electrode current collector plate, 29 laminate film. 200 metal plate, 300 bolt, 400 nut.

Claims

1. A positive electrode material for a secondary battery comprising: positive electrode active material particles; an organic solid electrolyte coating at least a portion of the surface of the positive electrode active material particles; and an inorganic solid electrolyte, wherein the organic solid electrolyte is a composite of a polyether polymer compound having a weight-average molecular weight (Mw) greater than 1,000 and less than 1,000,000 and an electrolyte salt, and the content of the organic solid electrolyte relative to 100% by mass of the total amount of the positive electrode active material particles is 0.40% by mass or more.

2. The positive electrode material for a secondary battery according to claim 1, wherein the content of the organic solid electrolyte is 0.45 to 3.50% by mass.

3. The positive electrode material for a secondary battery according to claim 1, wherein the content of the organic solid electrolyte is 0.70 to 2.00% by mass.

4. The positive electrode material for a secondary battery according to claim 1, wherein the weight-average molecular weight (Mw) of the organic solid electrolyte is 5,000 to 500,000.

5. When the positive electrode active material particles are in a complete discharge state, the following general formula (1): Li ｘ Ni ａ M ｂ N ｃ O ２ (1) A positive electrode material for a secondary battery according to claim 1, comprising a lithium transition metal composite oxide having a composition represented by the formula: (wherein x, a, b, and c satisfy 0.8 ≤ x ≤ 1.1, a + b + c = 1, 0.80 ≤ a ≤ 1.00, 0 ≤ b ≤ 0.20, and 0 ≤ c ≤ 0.20, M is one or more elements selected from the group consisting of Mn and Co, and N is one or more elements selected from the group consisting of Al, Sn, Nb, Ti, Zr, and Mg).

6. The electrolyte salt is represented by the following general formula (2): ((C ｍ F ２ｍ＋１ )(SO ２ ))((C ｎ F ２ｎ＋１ )(SO ２ ))N － (2) (wherein m and n are each independently an integer of 0 to 4), and the positive electrode material for a secondary battery according to claim 1, which contains a fluorine-containing sulfonylimide anion represented by the formula.

7. The positive electrode material for a secondary battery according to claim 1, wherein the inorganic solid electrolyte includes a sulfide solid electrolyte.

8. A positive electrode for a secondary battery comprising a positive electrode active material layer containing the positive electrode material for a secondary battery described in any one of claims 1 to 7.

9. A secondary battery comprising the positive electrode for a secondary battery as described in claim 8.

10. The secondary battery according to claim 9, wherein the positive electrode active material layer is operated under a constraining pressure of 10 MPa or less in the stacking direction of the power generation element.

11. A method for producing a positive electrode material precursor for a secondary battery, comprising: compounding a polyether polymer compound having a weight-average molecular weight (Mw) greater than 1,000 and less than 1,000,000 with an electrolyte salt to obtain an organic solid electrolyte; and mixing the organic solid electrolyte with positive electrode active material particles in a ratio such that the content of the organic solid electrolyte is 0.40% by mass or more relative to 100% by mass of the total amount of the positive electrode active material particles to obtain a mixture.

12. A method for producing a positive electrode material for a secondary battery, comprising: compounding a polyether polymer compound having a weight-average molecular weight (Mw) greater than 1,000 and less than 1,000,000 with an electrolyte salt to obtain an organic solid electrolyte; mixing the organic solid electrolyte with positive electrode active material particles in a ratio such that the content of the organic solid electrolyte is 0.40% by mass or more relative to 100% by mass of the total amount of the positive electrode active material particles to obtain a mixture; and mixing the mixture with an inorganic solid electrolyte to obtain a positive electrode material.

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