Positive electrode material, and positive electrode mixture and lithium secondary battery using same

Abstract

The present invention addresses the problem of providing a means which is capable of reducing the cell resistance of a lithium secondary battery. The problem addressed by the present invention is solved by a positive electrode material which is obtained by filling pores of a porous carbon with sulfur and a phosphorus-containing sulfide solid electrolyte, wherein in a spectrum obtained by 31P solid-state nuclear magnetic resonance spectroscopy, the ratio (B / A) of the sum B of integral values of signals that are present in chemical shifts other than 85.0 ± 10 ppm to the integral value A of a signal that is present at 85.0 ± 10 ppm is less than 0.32.

Description

Positive electrode material, positive electrode mixture using the same, and lithium secondary battery

[0001] The present invention relates to a positive electrode material, a positive electrode mixture using the same, and a lithium secondary battery.

[0002] In recent years, research and development into lithium secondary batteries that use oxide-based or sulfide-based solid electrolytes has been actively conducted. Solid electrolytes are materials that are mainly composed of ion conductors that can conduct ions in a solid state. Therefore, in principle, all-solid-state lithium secondary batteries do not encounter the various problems that arise from flammable organic electrolytes, as in conventional liquid-based lithium secondary batteries. In addition, generally, the use of high-potential, large-capacity positive electrode materials and large-capacity negative electrode materials can significantly improve the output density and energy density of the battery. For example, elemental sulfur (S ８ ) has an extremely large theoretical capacity of about 1670 mAh / g, and has the advantages of being low cost and abundant in resources.

[0003] On the other hand, due to the low electronic conductivity of sulfur, the high capacity characteristic of sulfur-containing positive electrode active materials has not yet been fully utilized.

[0004] International Publication No. 2022 / 090757 (corresponding to U.S. Patent Application Publication No. 2023 / 0395788) discloses a positive electrode material for an electric device, the positive electrode material comprising a composite material including a conductive material having pores, a solid electrolyte, and a positive electrode active material containing sulfur, wherein at least a portion of the solid electrolyte and at least a portion of the positive electrode active material are disposed on the inner surfaces of the pores so as to be in contact with each other. By applying the positive electrode material described in this document to an electric device, the capacity characteristics and charge / discharge rate characteristics of the electric device can be improved.

[0005] The document also describes that the composite material having the above-described structure may be used as a positive electrode material as it is, and that a solid electrolyte may be further added to and mixed with the composite material, and the resultant may be processed as needed using an apparatus such as a ball mill, before being used as a positive electrode material.

[0006] In lithium secondary batteries, there is a demand for a reduction in cell resistance.

[0007] Therefore, an object of the present invention is to provide a means for reducing the cell resistance of a lithium secondary battery.

[0008] The present inventors have conducted extensive research in light of the above problems and have found that ３１ The present inventors have found that the above-mentioned problems can be solved by using a positive electrode material that exhibits a predetermined profile in a spectrum determined by P solid-state nuclear magnetic resonance spectroscopy, and have thus completed the present invention.

[0009] That is, one aspect of the present invention relates to a positive electrode material in which a sulfur- and phosphorus-containing sulfide solid electrolyte is filled into the pores of porous carbon. ３１ In a spectrum obtained by P solid-state nuclear magnetic resonance spectroscopy, the ratio (B / A) of the integral value A of the signal present at 85.0±10 ppm to the sum B of the integral values ​​of signals present at chemical shifts other than 85.0±10 ppm is less than 0.32.

[0010] FIG. 1 is a cross-sectional view showing a schematic overall structure of a stacked-type (internal parallel connection type) lithium secondary battery (hereinafter also simply referred to as a "stacked-type secondary battery") according to one embodiment of the present invention.

[0011] Hereinafter, embodiments of the present invention will be described, but the technical scope of the present invention should be determined based on the claims and is not limited to the following embodiments. Note that the range "X to Y" means "X or more and Y or less."

[0012] <Positive Electrode Material> One embodiment of the present invention is a positive electrode material comprising a sulfur- and phosphorus-containing sulfide solid electrolyte filled in pores of porous carbon, ３１ In a spectrum obtained by P solid-state nuclear magnetic resonance spectroscopy (NMR), the ratio (B / A) of the sum B of the integrals of signals present at chemical shifts other than 85.0±10 ppm to the integral A of the signal present at 85.0±10 ppm is less than 0.32. The positive electrode material according to this embodiment makes it possible to reduce the cell resistance in a lithium secondary battery.

[0013] In an investigation to solve the above problem, the inventors performed a predetermined mechanical milling on a composite material in which a sulfur- and phosphorus-containing sulfide solid electrolyte was filled into the pores of porous carbon, and then added a solid electrolyte to prepare a positive electrode mixture. A lithium secondary battery was fabricated using this positive electrode mixture, and the cell resistance was measured. It was found that the resistance was significantly reduced compared to when the technology described in the above document was used. The composite material after mechanical milling was then ３１ When analyzed using P solid state NMR, it was found that the NMR spectrum had a predetermined profile, leading to the completion of the present invention.

[0014] The mechanism by which the positive electrode material according to the present embodiment exhibits the above-described effects has not been fully elucidated, and although the present invention is not bound by any theory, the following mechanism is presumed. ３１ In the spectrum obtained by P solid-state NMR, the ratio (B / A) of the integral value A of the signal present at 85.0±10 ppm to the sum B of the integral values ​​of the signals present at chemical shifts other than 85.0±10 ppm is less than 0.32. ４ ３－ Therefore, the signal is attributed to Li ３ P.S. ４ On the other hand, signals present at chemical shifts other than 85.0±10 ppm include, for example, POS ３ ３－ , P.O. ２ S ２ ３－ , P.O. ３ S ３－ , P.O. ４ ３－ Therefore, these signals are attributed to Li ３ POS ３ , Li ３ P.O. ２ S ２ , Li ３ P.O. ３ S., Li. ３ P.O. ４Therefore, the ratio (B / A) of less than 0.32 indicates the presence of oxides such as Li. ３ P.S. ４ This means that the amount of oxide is small compared to the amount of Li. ３ P.S. ４ has high lithium ion conductivity, whereas the lithium ion conductivity of the oxide is low. Therefore, it is presumed that by applying the positive electrode material according to the present embodiment to a lithium secondary battery, the lithium ion conductivity in the battery is improved, and as a result, the cell resistance is reduced.

[0015] A positive electrode material having a ratio (B / A) of less than 0.32 can be prepared by preparing a composite material (referred to as "composite material 2" in the method for producing a positive electrode material described below) in which sulfur and a phosphorus-containing sulfide solid electrolyte are filled into the pores of porous carbon, and then subjecting the composite material alone to mechanical milling. Conventionally, in preparing composite materials, a method for filling the pores with the phosphorus-containing sulfide solid electrolyte has been employed in which porous carbon is dispersed in a solution in which the phosphorus-containing sulfide solid electrolyte is dissolved in a dehydrated solvent, and the solvent is then removed. Another method for filling the pores with sulfur has been to mix sulfur with porous carbon, then heat the mixture to melt the sulfur, thereby impregnating the pores with sulfur. Although these methods are performed in an inert atmosphere, the inclusion of trace amounts of moisture or oxygen can oxidize a portion of the phosphorus-containing sulfide solid electrolyte, inevitably resulting in the aforementioned oxides. It is believed that mechanical milling of only the composite material containing such oxides causes the following mechanochemical reaction:

[0016]

[0017] The mechanochemical reaction described above converts the oxide into Li, which has high lithium ion conductivity. ３ P.S. ４ is regenerated, and the ratio (B / A) is less than 0.32 (i.e., Li ３ P.S. ４ It is thought that a positive electrode material with a high proportion of

[0018] Incidentally, the above-mentioned International Publication No. 2022 / 090757 also discloses a composite material in which a sulfur- and phosphorus-containing sulfide solid electrolyte is filled into the pores of porous carbon (see FIG. 3B and Example 1, etc.). However, in the above-mentioned document, the composite material does not contain Li. ６ P.S. ５ All-solid-state lithium secondary batteries have been produced using a material that has been mechanically milled using a ball mill after adding Cl as a positive electrode material (Example 1, etc.), but there is no mention of mechanically milling only the composite material. According to the inventors' investigations, as described in the above document, if mechanical milling is performed after mixing the composite material with other materials, the above-mentioned effects cannot be obtained. This is because the probability of contact between oxides is reduced, and Li due to a mechanochemical reaction is reduced. ３ P.S. ４ This is thought to be because regeneration of the

[0019] [Sulfur] Sulfur (elemental sulfur) can function as a positive electrode active material. The sulfur preferably has an S8 structure and is preferably at least one selected from α-sulfur, β-sulfur, and γ-sulfur. The sulfur content is not particularly limited, but is preferably 50 to 90 mass%, more preferably 55 to 85 mass%, and even more preferably 60 to 80 mass%, relative to 100 mass% of the total mass of the positive electrode material. When the sulfur content is within the above range, a good balance between capacity and output characteristics can be achieved in the lithium secondary battery.

[0020] [Phosphorus-containing sulfide solid electrolyte] The phosphorus-containing sulfide solid electrolyte is a solid electrolyte containing at least lithium atoms, phosphorus atoms, and sulfur atoms. Examples of such phosphorus-containing sulfide solid electrolytes include Li ２ S-P ２ S ５ , Li ２ S-P ２ S ５ , Li ２ S-P ２ S ５ - LiI, Li ２ S-P ２ S５ -Li ２ O-LiI, Li ２ S-SiS ２ -P ２ S ５ - LiI, Li ２ S-P ２ S ５ -Z ｍ S ｎ (where m and n are positive numbers, and Z is Ge, Zn, or Ga). ２ S-P ２ S ５ " is written by Li ２ S and P ２ S ５ The same applies to other descriptions.

[0021] The phosphorus-containing sulfide solid electrolyte may be, for example, Li ３ P.S. ４ It may have a Li framework. ４ P ２ S ７ It may have a Li framework. ４ P ２ S ６ It may have a Li skeleton. ３ P.S. ４ Examples of the phosphorus-containing sulfide solid electrolyte having a skeleton include LiI-Li ３ P.S. ４ , LiI-LiBr-Li ３ P.S. ４ , Li ３ P.S. ４ Li ４ P ２ S ７ Examples of the phosphorus-containing sulfide solid electrolyte having a skeleton include Li-P-S solid electrolytes called LPS (e.g., Li ７ P ３ S １１ Furthermore, examples of the phosphorus-containing sulfide solid electrolyte include a solid electrolyte having an LGPS-type crystal structure (Li （４－ｘ） Ge （１－ｘ） P ｘ S ４(where x satisfies 0<x<1)), and a solid electrolyte having an argyrodite-type crystal structure (Li ６ P.S. ５ X (X is Cl, Br, or I) is also preferably used. These phosphorus-containing sulfide solid electrolytes have high ionic conductivity and can effectively contribute to reducing internal resistance. Among them, the phosphorus-containing sulfide solid electrolyte is preferably one having an LPS, LGPS, or argyrodite-type crystal structure, and more preferably one having an argyrodite-type crystal structure.

[0022] The content of the phosphorus-containing sulfide solid electrolyte is not particularly limited, but is preferably 5 to 35 mass %, more preferably 7 to 30 mass %, and even more preferably 10 to 25 mass %, relative to 100 mass % of the total mass of the positive electrode material. When the content of the phosphorus-containing sulfide solid electrolyte is within the above range, the lithium secondary battery can have a good balance between capacity and output characteristics.

[0023] [Porous Carbon] In this specification, porous carbon refers to a carbon material that has pores and is composed primarily of carbon. Here, "composed primarily of carbon" refers to containing carbon atoms as the main component, and is a concept that encompasses both "consisting solely of carbon atoms" and "consisting essentially of carbon atoms." "Consisting essentially of carbon atoms" means that the inclusion of impurities in an amount of about 2 to 3 mass % or less is acceptable.

[0024] The shape of the porous carbon is not particularly limited, but particulate is preferred. Examples of porous carbon particles include activated carbon, carbon black (e.g., Ketjen Black®), (oil) furnace black, channel black, acetylene black, thermal black, and lamp black; carbon particles (carbon supports) made of coke, natural graphite, artificial graphite, and the like. Alternatively, a ceramic or other mold may be mixed with a carbon raw material (e.g., resin), fired under an inert atmosphere, and then the mold may be dissolved with acid to synthesize a carbon material having a porous structure in which the shape of the mold has been transferred. This carbon material may then be used as the porous carbon particles. In this case, the pore size and pore volume of the resulting carbon material can be changed by appropriately adjusting the particle size of the mold and the compounding ratio of the carbon raw material.

[0025] The content of the porous carbon is not particularly limited, but is preferably 3 to 25 mass %, more preferably 5 to 20 mass %, and even more preferably 7 to 15 mass %, relative to 100 mass % of the total mass of the positive electrode material. When the content of the porous carbon is within the above range, the lithium secondary battery can have a good balance between capacity and output characteristics.

[0026] The positive electrode material according to this embodiment is ３１ In a spectrum obtained by P solid-state nuclear magnetic resonance spectroscopy (NMR), the ratio (B / A) of the integral value A of the signal present at 85.0±10 ppm to the sum B of the integral values ​​of the signals present at chemical shifts other than 85.0±10 ppm is less than 0.32. The ratio (B / A) is determined by the method described in the Examples below. As described above, the ratio (B / A) is determined by the method described in the Examples below. ３ P.S. ４The ratio (B / A) is an index of the ratio of the amount of oxide to the amount of sintered material, and the smaller this value, the more improved the lithium ion conductivity of the positive electrode material. From the viewpoint of further reducing cell resistance, the ratio (B / A) is preferably 0.30 or less, more preferably 0.25 or less, even more preferably 0.23 or less, and most preferably 0.225 or less. While a smaller ratio (B / A) is preferable for reducing cell resistance, it is usually 0.05 or more because it is difficult to completely eliminate the oxides that inevitably form. The ratio (B / A) can be controlled by the processing conditions when mechanically milling the composite material 2 in the manufacturing method of the positive electrode material described below. Specifically, the ratio (B / A) can be reduced by increasing the load of mechanical milling (e.g., when using a ball mill, increasing the centrifugal acceleration and / or lengthening the processing time).

[0027] The positive electrode material according to this embodiment preferably has a molar ratio (P / C) of phosphorus (P) to carbon (C) of 0.025 or more, as determined by surface analysis using X-ray photoelectron spectroscopy. The molar ratio (P / C) is determined by the method described in the Examples below. The molar ratio (P / C) is an index indicating the amount of phosphorus-containing sulfide solid electrolyte present on the surface of the positive electrode material. A larger value indicates a larger amount of phosphorus-containing sulfide solid electrolyte present on the surface of the positive electrode material. Therefore, by setting the molar ratio (P / C) to 0.025 or more, the formation of an interface between the positive electrode material and the sulfide solid electrolyte in the positive electrode mixture described below can be promoted, thereby further improving lithium ion conductivity. From the viewpoint of further reducing cell resistance, the molar ratio (P / C) is preferably 0.030 or more, more preferably 0.035 or more, and even more preferably 0.036 or more. Note that, although a larger molar ratio (P / C) value is preferable for reducing cell resistance, it is usually a value of 0.100 or less. The molar ratio (P / C) value can be controlled by the processing conditions when subjecting the composite material 2 to mechanical milling, similar to the value of the ratio (B / A) described above. Specifically, the molar ratio (P / C) value can be increased by increasing the load of mechanical milling (for example, when using a ball mill, increasing the centrifugal acceleration and / or lengthening the processing time).

[0028] The positive electrode material according to the present embodiment has a PS ratio relative to carbon (C) determined by surface analysis using X-ray photoelectron spectroscopy. ４ Mass ratio of unit (PS ４ It is preferable that the mass ratio (PS / C) is 0.32 or more. ４ / C) can be determined by the method described in the Examples below. ４ / C) is an index showing the amount of phosphorus-containing sulfide solid electrolyte present on the surface of the positive electrode material, and the larger this value, the more phosphorus-containing sulfide solid electrolyte is present on the surface of the positive electrode material. ４By setting the mass ratio (PS / C) to 0.32 or more, the formation of an interface between the positive electrode material and the sulfide solid electrolyte in the positive electrode mixture described later is promoted, and the lithium ion conductivity can be further improved. ４ From the viewpoint of further reducing the cell resistance, the mass ratio (PS / C) is preferably 0.35 or more, more preferably 0.40 or more, even more preferably 0.45 or more, particularly preferably 0.46 or more, and most preferably 0.48 or more. ４ The mass ratio (PS / C) is preferably large in order to reduce the cell resistance, but is usually 1.00 or less. ４ The value of the mass ratio (PS / C) can be controlled by the processing conditions when subjecting the composite material 2 to mechanical milling, similar to the value of the ratio (B / A). Specifically, the mass ratio (PS ４ / C) can be increased.

[0029] <Method for Producing Cathode Material> The cathode material according to this embodiment can be produced by the following method. That is, another embodiment of the present invention is a method for producing a cathode material, comprising: impregnating porous carbon with a solution containing a phosphorus-containing sulfide solid electrolyte and a solvent, and then removing the solvent to obtain a composite material 1 (hereinafter also referred to as "step (1)"); impregnating the composite material 1 with a sulfur melt to obtain a composite material 2 (hereinafter also referred to as "step (2)"); and mechanically milling the composite material 2 (hereinafter also referred to as "step (3)"). Each step of the production method will be described below.

[0030] In step (1), porous carbon is impregnated with a solution containing a phosphorus-containing sulfide solid electrolyte and a solvent, and then the solvent is removed, thereby obtaining a composite material 1 in which the phosphorus-containing sulfide solid electrolyte is filled in the pores of the porous carbon.

[0031] The phosphorus-containing sulfide solid electrolyte solution is prepared by dissolving the phosphorus-containing sulfide solid electrolyte in a solvent. The solvent used in this case is not particularly limited, but from the viewpoints of solubility, operability, safety, etc., it is preferably a lower alcohol, and more preferably an alcohol having 1 to 4 carbon atoms. Examples of alcohols having 1 to 4 carbon atoms include methanol, ethanol, 1-propanol, 2-propanol, n-butanol, 2-butanol, and tert-butanol. Among these, from the viewpoints of solubility, operability, safety, etc., methanol, ethanol, 1-propanol, and 2-propanol are preferred, methanol and ethanol are more preferred, and ethanol is even more preferred.

[0032] The solvent preferably has a low water content, specifically, the water content of the solvent is preferably less than 0.2% by mass. More preferably, the water content of the solvent is 0.1% by mass or less, even more preferably 0.05% by mass or less, even more preferably 0.02% by mass or less, even more preferably 0.01% by mass or less, even more preferably 0.005% by mass or less, and particularly preferably 0.002% by mass or less. The water content of the solvent can be measured, for example, by Karl Fischer coulometric titration.

[0033] The content of the phosphorus-containing sulfide solid electrolyte in the phosphorus-containing sulfide solid electrolyte solution is preferably 3 to 30 mass %, more preferably 5 to 20 mass %. When the content of the phosphorus-containing sulfide solid electrolyte is within the above range, a desired amount of the phosphorus-containing sulfide solid electrolyte can be filled into the pores of the porous carbon.

[0034] The porous carbon can be impregnated with the phosphorus-containing sulfide solid electrolyte solution by adding the porous carbon to the phosphorus-containing sulfide solid electrolyte solution and dispersing the porous carbon in the solution. The solvent is then removed while stirring the dispersion. The solvent removal is preferably carried out under reduced pressure at a temperature of 70°C or less. This prevents decomposition of the phosphorus-containing sulfide solid electrolyte and an increase in cell resistance.

[0035] In step (2), the sulfur melt is impregnated into the composite material 1. This results in a composite material 2 in which the pores of the porous carbon are filled with the sulfur- and phosphorus-containing sulfide solid electrolyte.

[0036] In the step (2), an example of a method for impregnating the composite material 1 with the sulfur melt is a method in which sulfur and porous carbon are mixed in advance, the mixture is then heat-treated to melt the sulfur, and the porous carbon is then impregnated with the sulfur melt.

[0037] In step (3), the composite material 2 is subjected to mechanical milling, thereby obtaining a positive electrode material.

[0038] Mechanical milling can be performed using a ball mill such as a planetary ball mill or an agitation ball mill. For example, in the examples described below, a planetary ball mill is used, and milling balls and the composite material 2 are placed in a milling pot, and mechanical milling is performed at a predetermined rotation speed and time. As described above, mechanical milling applies forces such as shear stress, friction, shear, impact, and compression to the composite material 2, causing a mechanochemical reaction, and converting oxides that are inevitably produced in the process of producing the composite material 2 into Li ions with high lithium ion conductivity. ３ P.S. ４ As mentioned above, when the composite material 2 is mixed with other materials and then mechanical milling is performed, Li ３ P.S. ４ It is preferable to perform mechanical milling only on the composite material 2, since this makes it difficult for regeneration of the composite material 2 to occur.

[0039] In mechanical milling, the load (centrifugal acceleration [G] × processing time [min]) applied to the composite material 2 is preferably 1000 to 7000 [G·min], and more preferably 2000 to 5000 [G·min]. When the load applied to the composite material 2 is within the above range, the cell resistance of the lithium secondary battery can be further reduced. The centrifugal acceleration [G] is preferably 10 to 100 [G], and more preferably 20 to 50 [G]. The processing time is preferably 10 to 600 [min], and more preferably 30 to 300 [min].

[0040] <Positive Electrode Mixture> The positive electrode material may be used as it is as a material for the positive electrode active material layer. However, it is preferable to add a solid electrolyte to the positive electrode material to form a positive electrode mix and then use the positive electrode active material layer as a material. In order to further reduce the cell resistance in a lithium secondary battery, it is more preferable to use a sulfide solid electrolyte as the solid electrolyte used in the positive electrode mix, and to control the crystallite diameters of sulfur in the positive electrode mix and the sulfide solid electrolyte within predetermined ranges. That is, according to one embodiment of the present invention, there is provided a positive electrode mix comprising the positive electrode material and a sulfide solid electrolyte, wherein the crystallite diameter X of the sulfide solid electrolyte calculated from the half-width of the peak at 2θ = 29.9° ± 0.5° in an X-ray diffraction spectrum is 25 nm or more, and the crystallite diameter Y of the sulfur calculated from the half-width of the peak at 2θ = 23.0° ± 0.5° is less than 66.0 nm.

[0041] The positive electrode mixture according to this embodiment essentially contains the positive electrode material and a sulfide solid electrolyte. The sulfide solid electrolyte may be the same as or different from the phosphorus-containing sulfide solid electrolyte contained in the positive electrode material, but is preferably the same.

[0042] The sulfide solid electrolyte essentially contains the S element, preferably contains the Li element, the M element (wherein M 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 the S element, and more preferably contains the S element, the Li element, and the P element.

[0043] The sulfide solid electrolyte is Li ３ P.S. ４ It may have a Li framework. ４ P ２ S ７ It may have a Li framework. ４ P ２ S ６ It may have a Li skeleton. ３ P.S. ４ Examples of sulfide solid electrolytes having a skeleton include LiI-Li ３ P.S. ４, LiI-LiBr-Li ３ P.S. ４ , Li ３ P.S. ４ In addition, Li ４ P ２ S ７ Examples of sulfide solid electrolytes having a skeleton include Li-P-S solid electrolytes called LPS. （４－ｘ） Ge （１－ｘ） P ｘ S ４ (x satisfies 0<x<1) or the like. 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 P.S. ５ X (wherein X is Cl, Br or I). ２ S-P ２ S ５ " is written by Li ２ S and P ２ S ５ The same applies to other descriptions. Among them, the sulfide solid electrolyte is preferably LPS (Li ２ S-P ２ S ５ ), Li ６ P.S. ５ X (wherein X is Cl, Br or I), Li ７ P ３ S １１ , Li ３．２ P ０．９６ S and Li３ P.S. ４ In particular, the sulfide solid electrolyte is preferably one having an argyrodite-type crystal structure, and Li having an argyrodite-type crystal structure is preferably one having an argyrodite-type crystal structure. ６ P.S. ５ X (wherein X is Cl, Br or I) is more preferred.

[0044] The sulfide solid electrolyte preferably has a particulate shape such as a perfect sphere or an oval sphere.

[0045] In the positive electrode mixture according to this embodiment, the content of the positive electrode material is preferably 88% by mass or less, and more preferably 85% by mass or less. When the content of the positive electrode material is within the above range, the cell resistance of the lithium secondary battery can be further reduced. Furthermore, from the viewpoint of increasing the capacity of the lithium secondary battery, the content of the positive electrode material is preferably more than 50% by mass, more preferably 60% by mass or more, and even more preferably 70% by mass or more.

[0046] The positive electrode mixture according to this embodiment is characterized in that the crystallite diameter X of the sulfide solid electrolyte calculated from the half-width of the peak at 2θ = 29.9 ° ± 0.5 ° in the X-ray diffraction spectrum is 25 nm or more, and the crystallite diameter Y of sulfur calculated from the half-width of the peak at 2θ = 23.0 ° ± 0.5 ° is less than 66.0 nm. The crystallite diameter X and crystallite diameter Y are determined by the method described in the Examples below. The crystallite diameter X of the sulfide solid electrolyte is more preferably 25 nm or more, even more preferably 29 nm or more, and even more preferably 30 nm or more. The crystallite diameter Y of sulfur is more preferably less than 60 nm, even more preferably less than 56.9 nm, and particularly preferably less than 50 nm. When the crystallite diameter X and crystallite diameter Y are within the above ranges, the lithium ion conductivity of the positive electrode mixture is further improved, and as a result, the cell resistance of the lithium secondary battery can be further reduced. In order to make the crystallite diameter X of the sulfide solid electrolyte 25 nm or more, it is preferable not to perform mechanical milling on the sulfide solid electrolyte in the process of producing the positive electrode mixture. On the other hand, by performing mechanical milling on only the composite 2 in the method of producing the positive electrode material, the crystallite diameter Y of sulfur can be made less than 60 nm.

[0047] <Lithium Secondary Battery> By applying the above-mentioned positive electrode mixture to a positive electrode active material layer of a lithium secondary battery, it is possible to reduce the cell resistance of the lithium secondary battery. That is, according to one embodiment of the present invention, there is also provided a lithium secondary battery including a power generating element including a positive electrode having a positive electrode active material layer containing the above-mentioned positive electrode mixture, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte.

[0048] Hereinafter, an embodiment of a lithium secondary battery according to one aspect of the present invention will be described with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicated explanations will be omitted. Furthermore, the dimensional proportions in the drawings are exaggerated for the sake of explanation and may differ from the actual proportions.

[0049] FIG. 1 is a cross-sectional view schematically illustrating the overall structure of a stacked-type (internal parallel connection type) all-solid-state lithium secondary battery (hereinafter also simply referred to as a "stacked-type secondary battery") according to one embodiment of the present invention. The stacked-type secondary battery 10a shown in FIG. 1 has a structure in which a substantially rectangular power generating element 21, in which charge and discharge reactions actually proceed, is sealed inside a laminate film 29, which is a battery outer casing. Here, the power generating element 21 has a structure in which a negative electrode, a solid electrolyte layer 17, and a positive electrode are stacked. The negative electrode has a structure in which a negative electrode current collector 11' and a negative electrode active material layer 13 are disposed on the surface of the negative electrode current collector 11'. The positive electrode has a structure in which a positive electrode active material layer 15 are disposed on the surface of a positive electrode current collector 11". As a result, the negative electrode current collector 11', the negative electrode active material layer 13, the solid electrolyte layer 17, the positive electrode active material layer 15, and the positive electrode current collector 11" constitute one unit cell layer 19. Therefore, the stacked secondary battery 10a shown in FIG. 1 can be said to have a configuration in which a plurality of unit cell layers 19 are stacked and electrically connected in parallel. A negative electrode current collector 25 and a positive electrode current collector 27, which are electrically connected to the respective electrodes (negative and positive electrodes), are attached to the negative electrode current collector 11' and the positive electrode current collector 11", respectively, and are configured to be sandwiched between the ends of the laminate film 29 and extended to the outside of the laminate film 29. A restraining pressure is applied to the stacked secondary battery 10a in the stacking direction of the power generation element 21 by a pressure member (not shown). Therefore, the volume of the power generation element 21 is kept constant.

[0050] The main components of the lithium secondary battery according to this embodiment will be described below.

[0051] [Current Collector] The current collector (negative electrode current collector, positive electrode current collector) has the function of mediating the movement of electrons from the electrode active material layer (negative electrode active material layer, positive electrode active material layer). There are no particular restrictions on the material that constitutes the current collector. Examples of materials that can be used for the current collector include metals such as aluminum, nickel, iron, stainless steel, titanium, and copper, as well as conductive resins. There are also no particular restrictions on the thickness of the current collector, but an example is 10 to 100 μm.

[0052] [Negative Electrode Active Material Layer] The negative electrode active material layer contains a negative electrode active material. The type of negative electrode active material is not particularly limited, but includes carbon materials, metal oxides, and metal active materials. Alternatively, a lithium-containing active material such as lithium metal or a lithium-containing alloy may be used as the negative electrode active material. Examples of lithium-containing alloys include alloys of Li with at least one of In, Al, Si, Sn, Mg, Au, Ag, and Zn. When using lithium metal or a lithium-containing alloy as the negative electrode active material, the lithium secondary battery is preferably 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 charging. The layer of lithium metal deposited on the negative electrode current collector during charging constitutes the negative electrode active material layer. Therefore, 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 full discharge, but in some cases, a negative electrode active material layer made of a certain amount of lithium metal may be present during full discharge.

[0053] The thickness of the negative electrode active material layer (in the case of a lithium deposition type, the thickness at full charge) differs depending on the configuration of the intended lithium secondary battery, but is preferably within the range of, for example, 0.1 to 1000 μm.

[0054] [Solid Electrolyte Layer] The solid electrolyte layer is interposed between the negative electrode and the positive electrode and contains a solid electrolyte (usually as a main component). The solid electrolyte contained in the solid electrolyte layer is not particularly limited, and any solid electrolyte known in the art can be appropriately used, for example, a sulfide solid electrolyte or an oxide solid electrolyte.

[0055] The content of the solid electrolyte in the solid electrolyte layer is preferably 50% by mass or more and 100% by mass or less, and more preferably 90% by mass or more and 99% by mass or less.

[0056] The solid electrolyte layer may further contain a binder in addition to the solid electrolyte. The type of binder that can be used in the solid electrolyte layer is not particularly limited, and binders known in the art can be appropriately adopted. Examples include styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are substituted with other halogen elements), and carboxymethyl cellulose (CMC). Among these, styrene-butadiene rubber, tetrafluoroethylene, and polyvinylidene fluoride are preferred, and tetrafluoroethylene and polyvinylidene fluoride are more preferred. These binders may be used alone or in combination of two or more.

[0057] The thickness of the solid electrolyte layer varies depending on the intended configuration of the lithium secondary battery, but is usually 0.1 to 1000 μm, preferably 10 to 40 μm.

[0058] [Positive Electrode Active Material Layer] The positive electrode active material layer essentially contains the positive electrode mixture and may contain a binder and / or a conductive additive as necessary. The positive electrode active material layer is typically disposed on the surface of a positive electrode current collector as shown in Figure 1. However, if the positive electrode active material layer 15 itself has a certain degree of conductivity, it may also constitute a positive electrode without using a positive electrode current collector.

[0059] The content of the positive electrode mixture contained in the positive electrode active material layer is not particularly limited, but from the viewpoint of energy density, it is, for example, 50 to 100 mass %, preferably 70 to 99 mass % or less, and more preferably 80 to 99 mass % or less, relative to the total mass of the positive electrode active material layer.

[0060] The binder that can be used in the positive electrode active material layer is the same as that described above for the solid electrolyte layer.

[0061] Examples of conductive additives that can be used in the positive electrode active material layer include, but are not limited to, metals such as aluminum, stainless steel (SUS), silver, gold, copper, and titanium, alloys or metal oxides containing these metals, carbon fibers (specifically, vapor-grown carbon fibers (VGCF), polyacrylonitrile-based carbon fibers, pitch-based carbon fibers, rayon-based carbon fibers, activated carbon fibers, etc.), carbon nanotubes (CNT), and carbon black (specifically, acetylene black, Ketjen Black (registered trademark), furnace black, channel black, thermal lamp black, etc.). Furthermore, particulate ceramic materials or resin materials coated with the above-mentioned metal materials by plating or the like can also be used as conductive additives. These conductive additives may be used alone or in combination of two or more. The concept of a conductive additive does not include those having pores but retaining sulfur or a solid electrolyte inside the pores.

[0062] The thickness of the positive electrode active material layer varies depending on the configuration of the intended lithium secondary battery, but is, for example, 0.1 to 1000 μm, preferably 30 to 300 μm, more preferably 50 to 200 μm, and even more preferably 70 to 150 μm.

[0063] [Positive current collector plate and negative current collector plate] The material constituting the current collector plate (25, 27) is not particularly limited, and known highly conductive materials conventionally used as current collector plates for secondary batteries can be used. Metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferred as constituent materials of the current collector plate. From the viewpoints of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferred, and aluminum is particularly preferred. The positive current collector plate 27 and the negative current collector plate 25 may be made of the same material or different materials.

[0064] [Positive Electrode Lead and Negative Electrode Lead] Although not shown in the drawings, the current collectors (11", 11') and the current collector plates (27, 25) may be electrically connected via a positive electrode lead or a negative electrode lead. As the constituent materials of the positive electrode and the negative electrode lead, materials used in known lithium ion secondary batteries can be similarly adopted. Note that the portion removed from the exterior is preferably covered with a heat-resistant, insulating heat-shrinkable tube or the like so as to prevent contact with peripheral devices or wiring, etc., causing electrical leakage and affecting products (for example, automobile parts, particularly electronic devices, etc.).

[0065] [Battery Exterior Material] As the battery exterior material, a known metal can case can be used. Alternatively, a bag-shaped case using an aluminum-containing laminate film 29 that can cover the power generating element as shown in FIG. 1 can be used. The laminate film can be, for example, a three-layer laminate film formed by laminating PP, aluminum, and nylon in this order, but is not limited thereto. A laminate film is desirable from the viewpoint of achieving high output and excellent cooling performance, making it suitable for use in batteries for large equipment such as EVs and HEVs. Furthermore, an aluminum-containing laminate film is more preferable as the exterior material because it allows for easy adjustment of the collective pressure applied to the power generating element from the outside.

[0066] The lithium secondary battery according to the present embodiment has a configuration in which a plurality of unit cell layers are connected in parallel, and therefore has high capacity and excellent cycle durability, and is therefore suitable for use as a driving power source for EVs and HEVs.

[0067] The above describes an embodiment of the present invention, but the present invention is not limited to the configurations described in the above embodiment, and can be modified as appropriate based on the claims.

[0068] For example, the type of battery to which the positive electrode mixture according to the present invention is applied includes a bipolar battery including a bipolar electrode having a positive electrode active material layer electrically bonded to one surface of a current collector and a negative electrode active material layer electrically bonded to the opposite surface of the current collector.

[0069] Furthermore, the lithium secondary battery according to the present embodiment does not have to be an all-solid-state type. That is, the solid electrolyte layer may further contain a conventionally known liquid electrolyte (electrolytic solution). There is no particular limitation on the amount of liquid electrolyte (electrolytic solution) that can be contained in the solid electrolyte layer, but it is preferably an amount that allows the shape of the solid electrolyte layer formed by the solid electrolyte to be maintained and prevents leakage of the liquid electrolyte (electrolytic solution).

[0070] The following items are also included in the scope of the present invention: Item 1: A sulfur- and phosphorus-containing sulfide solid electrolyte is filled into the pores of porous carbon, ３１ Item 2: A positive electrode material in which, in a spectrum obtained by P solid-state nuclear magnetic resonance spectroscopy, the ratio (B / A) of the sum B of integral values ​​of signals present at chemical shifts other than 85.0±10 ppm to the integral value A of a signal present at 85.0±10 ppm is less than 0.32; Item 3: A positive electrode material in which the molar ratio (P / C) of phosphorus (P) to carbon (C) obtained by surface analysis using X-ray photoelectron spectroscopy is 0.025 or more; Item 4: A positive electrode material in which the molar ratio (P / C) of phosphorus (P) to carbon (C) obtained by surface analysis using X-ray photoelectron spectroscopy is 0.025 or more; ４ Mass ratio of unit (PS ４Item 4: A cathode mixture comprising the cathode material according to any one of Items 1 to 3 and a sulfide solid electrolyte, wherein, in an X-ray diffraction spectrum, the sulfide solid electrolyte has a crystallite diameter X of 25 nm or more, calculated from the half-width of a peak at 2θ = 29.9° ± 0.5°, and the sulfur has a crystallite diameter Y of less than 66.0 nm, calculated from the half-width of a peak at 2θ = 23.0° ± 0.5°; Item 5: The cathode mixture according to Item 4, wherein the sulfide solid electrolyte has a crystallite diameter X of 30 nm or more, and a crystallite diameter Y of less than 56.9 nm; Item 6: The cathode mixture according to Item 4 or 5, wherein the sulfide solid electrolyte has an argyrodite-type crystal structure; Item 7: The cathode mixture according to any one of Items 4 to 6, wherein the content of the cathode material is 88 mass % or less; Item 8: A lithium secondary battery comprising a power generating element having a positive electrode having a positive electrode active material layer containing the positive electrode mixture according to any one of items 4 to 7, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte.

[0071] Item 9: A method for producing a positive electrode material, comprising: impregnating porous carbon with a solution containing a phosphorus-containing sulfide solid electrolyte and a solvent, and then removing the solvent to obtain a composite material 1; impregnating the composite material 1 with a sulfur melt to obtain a composite material 2; and mechanically milling the composite material 2.

[0072] 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. In the following, the instruments and devices used in the glove box were thoroughly dried beforehand.

[0073] <Examples of Preparation of Positive Electrode Material and Positive Electrode Mixture> [Example 1] (Preparation of Composite Material 1) In a glove box with an argon atmosphere having a dew point of −68° C. or less, 1 g of granular porous carbon (Knobel (registered trademark) P(3)010, manufactured by Toyo Tanso Co., Ltd.) and 1 g of an argyrodite-type phosphorus-containing sulfide solid electrolyte (Li ６ P.S. ５1.5 g of ethanol (Cl) was placed in a flask. 18 mL of ultra-dehydrated ethanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to the flask, and while the dispersion in the flask was stirred with a magnetic stirrer, the flask was reduced in pressure to 1 Pa or less using an oil rotary pump. Since the solvent ethanol volatilizes under reduced pressure, the ethanol was removed over time. This resulted in a composite material 1 (phosphorus-containing sulfide solid electrolyte-carbon composite material) in which the pores were filled with the phosphorus-containing sulfide solid electrolyte.

[0074] (Preparation of Composite Material 2) 0.3 g of the composite material 1 obtained above and 0.7 g of elemental sulfur (manufactured by Aldrich), which is the positive electrode active material, were thoroughly mixed in an agate mortar, and the mixed powder was then placed in a sealed pressure-resistant autoclave and heated at 185°C for 8 hours to melt the sulfur, thereby impregnating the composite material 1 with sulfur. In this way, composite material 2 (sulfur-phosphorus-containing sulfide solid electrolyte-carbon composite material) was obtained.

[0075] (Preparation of Positive Electrode Material) In a glove box with an argon atmosphere having a dew point of −68° C. or less, 40 g of 5 mm diameter zirconia balls and 1 g of the composite material 2 prepared above were placed in a 45 mL zirconia container. This container was attached to a planetary ball mill (Fritsch, Premium Line P-7), and mechanical milling was performed at a centrifugal acceleration of 20 G for 120 minutes to obtain the positive electrode material of this example.

[0076] (Preparation of Positive Electrode Mixture) In a glove box in an argon atmosphere with a dew point of −68° C. or less, 1.48 g (74 parts by mass) of the positive electrode material prepared above and a solid electrolyte, an argyrodite-type phosphorus-containing sulfide solid electrolyte (manufactured by Ampcera, Li ６ P.S. ５ The mixture was mixed in a mortar with 0.52 g (26 parts by mass) of ammonium hydroxide (C1), to obtain a positive electrode mixture of this example.

[0077] Example 2 A positive electrode material and a positive electrode mixture of this example were obtained in the same manner as in Example 1 above, except that in the above (preparation of positive electrode material), mechanical milling was performed at a centrifugal acceleration of 20 G for 180 minutes.

[0078] [Example 3] The cathode material and cathode mixture of this example were obtained in the same manner as in Example 1 above, except that in the above (preparation of cathode material), mechanical milling was performed for 240 minutes at a centrifugal acceleration of 20 G; and in the above (preparation of cathode mixture), 1.68 g (84 parts by mass) of the cathode material and 0.32 g (16 parts by mass) of the solid electrolyte were mixed in a mortar.

[0079] Comparative Example 1 A positive electrode mixture of this comparative example was obtained in the same manner as in Example 1, except that the above (Preparation of a positive electrode material) was not performed, and in the above (Preparation of a positive electrode mixture), the composite material 2 obtained in the above (Preparation of a composite material 2) was used instead of the positive electrode material.

[0080] [Comparative Example 2] In the above (preparation of the positive electrode mixture), before mixing the materials, the solid electrolyte was subjected to mechanical milling in advance using a planetary ball mill. The mechanical milling was performed by first placing 40 g of 5 mm diameter zirconia balls and 2 g of solid electrolyte in a 45 mL zirconia container, attaching the container to the planetary ball mill, and processing at a centrifugal acceleration of 20 G for 180 minutes. A positive electrode mixture of this comparative example was obtained using the same method as in Comparative Example 1.

[0081] < ３１ Analysis of Positive Electrode Materials by P Solid-State Nuclear Magnetic Resonance Spectroscopy (NMR)> In a glove box with an argon atmosphere having a dew point of −68° C. or less, the positive electrode materials prepared in the above Examples and Composite Material 2 used in the above Comparative Examples were each sealed in a solid-state NMR sample tube and analyzed under the following conditions: ３１ Analysis was carried out by P solid state NMR.

[0082] Apparatus: Agilent NMR System 400WB Probe: 4.0 mm MAS spinning speed: 15 kHz Measurement range: -100 to 200 ppm Measurement temperature: room temperature (25°C).

[0083] obtained ３１ In the P solid-state NMR spectrum, the ratio (B / A) of the integral value A of the signal present at 85.0±10 ppm to the sum B of the integral values ​​of signals present at chemical shifts other than 85.0±10 ppm was calculated. The values ​​are shown in Table 1 below.

[0084] <Analysis of Positive Electrode Material by X-ray Photoelectron Spectroscopy (XPS)> The positive electrode material prepared in the above example and the composite material 2 used in the above comparative example were subjected to surface analysis by XPS under the following conditions.

[0085] Apparatus: VersaProbeIII manufactured by ULVAC-PHI X-ray source: Monochromated Al Kα ray (1486.6 eV) 50 W Photoelectron take-off angle: 45° (measurement depth: approximately 4 nm) Measurement area: 200 μm φ Sample: In a glove box in an argon atmosphere with a dew point of −68° C. or lower, the positive electrode material or composite material 2 was fixed to a sample holder and introduced into the apparatus using a transfer vessel without being exposed to the atmosphere.

[0086] From the obtained XPS spectrum, the element content was quantified using the relative sensitivity factor method from the peak area, and the molar ratio (P / C) of phosphorus (P) with a binding energy of 132 eV to carbon (C) with a binding energy of 284 eV on the surface was calculated. In addition, from the obtained XPS spectrum, the molar ratio of sulfur (S) with a binding energy of 132 eV, which is the same as the quantified carbon (C) and phosphorus (P), was used to calculate the ratio of PS to carbon (C) from the molar mass. ４ Mass ratio of unit (PS ４ / C) were calculated. These values ​​are shown in Table 1 below.

[0087] <Analysis of Positive Electrode Mixture by X-ray Diffraction (XRD)> In a glove box in an argon atmosphere with a dew point of −68° C. or lower, the positive electrode mixtures prepared in the above Examples and Comparative Examples were each sealed in a transparent glass, and analyzed by XRD under the following conditions.

[0088] Apparatus: Rigaku MiniFlex600-C X-ray tube: Cu Measurement temperature: room temperature (25°C) Scan range: 2θ, 3-90° From the obtained XRD spectrum, the half width of the peak at 2θ = 29.9° ± 0.5° was determined, and the crystallite diameter X of the sulfide solid electrolyte was calculated using Scherrer's formula. Furthermore, from the XRD spectrum, the half width of the peak at 2θ = 23.0° ± 0.5° was determined, and the crystallite diameter Y of sulfur was calculated using Scherrer's formula. These values ​​are shown in Table 1 below.

[0089] <Preparation of Evaluation Cell> Evaluation cells were prepared using the positive electrode mixtures prepared in the above Examples and Comparative Examples. The cell was prepared in a glove box in an argon atmosphere with a dew point of −68° C. or less. A stainless steel cylindrical convex punch (10 mm diameter) was inserted into one side of a cylindrical tube jig (manufactured by Macor Corporation) (tube inner diameter 10 mm, outer diameter 23 mm, height 20 mm), and a solid electrolyte (manufactured by Apcera Corporation, Li ６ P.S. ５ 80 mg of HCl was placed inside the cylindrical tube jig. Then, another stainless steel cylindrical convex punch was inserted to sandwich the solid electrolyte, and the solid electrolyte was pressed for 3 minutes at a pressure of 75 MPa using a hydraulic press to form a solid electrolyte layer with a diameter of 10 mm and a thickness of approximately 0.6 mm in the cylindrical tube jig. Next, the cylindrical convex punch inserted from above was temporarily removed, and 5.4 mg of the positive electrode mixture prepared above was placed on one side of the solid electrolyte layer inside the cylindrical tube. A cylindrical convex punch (also serving as a positive electrode current collector) was inserted again from above, and the solid electrolyte layer was pressed for 3 minutes at a pressure of 300 MPa to form a positive electrode active material layer with a diameter of 10 mm and a thickness of approximately 0.06 mm on one side of the solid electrolyte layer. Next, the lower cylindrical convex punch was removed, and a lithium foil (manufactured by Honjo Metals, thickness 0.20 mm) punched to a diameter of 8 mm as the negative electrode and an indium foil (manufactured by Nilaco Corporation, thickness 0.30 mm) punched to a diameter of 9 mm were stacked together, and the cylindrical tube jig was inserted from the bottom so that the indium foil was positioned on the solid electrolyte layer side. A cylindrical convex punch (also serving as the negative electrode current collector) was then inserted again, and pressed at a pressure of 75 MPa for 3 minutes to form a lithium-indium negative electrode. In this way, an evaluation cell (all-solid-state lithium secondary battery) was produced in which the negative electrode current collector (punch), lithium-indium negative electrode, solid electrolyte layer, positive electrode active material layer, and positive electrode current collector (punch) were stacked in this order.

[0090] <Resistance Measurement> A charge-discharge test was performed on the evaluation cell using a charge-discharge tester (HJ-SD8, manufactured by Hokuto Denko Corporation) in a thermostatic chamber set at 25° C. The cell was placed in the thermostatic chamber, and after the cell temperature became constant, constant-current constant-voltage charging at 2.5 V was performed at a current density of 1 C with a cutoff current of 0.01 mA / cm. ２The battery was then set to a constant current of 0.5 V, followed by constant current discharge to 0.5 V at the same current density. The capacity value per mass of the positive electrode active material (mAh / g) was calculated from the charge / discharge capacity value at this time and the mass of the positive electrode active material (sulfur) contained in the positive electrode. Next, the battery was discharged for 10 seconds at 0.03 C, 0.05 C, and 0.1 C at a 50% state of charge (SOC 50%) relative to the capacity value calculated in this way (100%). The direct current resistance (DCR) value was calculated according to Ohm's law from the voltage drop and current value at this time. The results are shown in Table 1 below. In Table 1, the values ​​are expressed as relative values ​​when the DCR value in Comparative Example 1 is set to 100.

[0091]

[0092] As shown in Table 1, according to the present invention, it is possible to reduce the cell resistance of a lithium secondary battery.

[0093] 10a: laminated battery, 11': negative electrode current collector, 11'': positive electrode current collector, 13: negative electrode active material layer, 15: positive electrode active material layer, 17: solid electrolyte layer, 19: single cell layer, 21: power generating element, 25: negative electrode current collector, 27: positive electrode current collector, 29: laminate film.

Claims

1. A sulfur- and phosphorus-containing sulfide solid electrolyte is filled into the pores of porous carbon, ３１ a ratio (B / A) of the integral value A of a signal present at 85.0±10 ppm to the sum B of integral values ​​of signals present at chemical shifts other than 85.0±10 ppm in a spectrum obtained by P solid-state nuclear magnetic resonance spectroscopy is less than 0.

32.

2. The positive electrode material according to claim 1, wherein the molar ratio of phosphorus (P) to carbon (C) (P / C) determined by surface analysis using X-ray photoelectron spectroscopy is 0.025 or more.

3. PS relative to carbon (C) determined by surface analysis using X-ray photoelectron spectroscopy ４ Mass ratio of unit (PS ４ 2. The positive electrode material according to claim 1, wherein the Cr content of the positive electrode material is 0.32 or more.

4. A positive electrode mixture comprising the positive electrode material according to claim 1 and a sulfide solid electrolyte, wherein the crystallite diameter X of the sulfide solid electrolyte calculated from the half-width of the peak at 2θ = 29.9° ± 0.5° in an X-ray diffraction spectrum is 25 nm or more, and the crystallite diameter Y of the sulfur calculated from the half-width of the peak at 2θ = 23.0° ± 0.5° is less than 66.0 nm.

5. The positive electrode mixture according to claim 4, wherein the sulfide solid electrolyte has a crystallite diameter X of 30 nm or more, and the sulfur has a crystallite diameter Y of less than 56.9 nm.

6. The positive electrode mixture according to claim 4, wherein the sulfide solid electrolyte has an argyrodite-type crystal structure.

7. The positive electrode mixture according to claim 4, wherein the content of the positive electrode material is 88 mass % or less.

8. A lithium secondary battery comprising a power generating element including: a positive electrode having a positive electrode active material layer containing the positive electrode mixture according to claim 4; a negative electrode; and a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte.

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