Positive electrode material and secondary battery using same

Abstract

[Problem] The present invention addresses the problem of providing a means which is capable of improving the charge and discharge characteristics of a secondary battery that uses a positive electrode material which contains sulfur. [Solution] The present invention provides a positive electrode material which is characterized by containing a phosphorus-containing component that is composed of phosphorus sulfide and / or a discharge product thereof, and a conductive material that has pores, and which is also characterized in that: the phosphorus-containing component covers at least a part of the surface of the conductive material so as to be arranged inside the pores, thereby forming a cover layer; and the mass ratio (P / S) of elemental phosphorus to elemental sulfur in the positive electrode material is more than 0 but not more than 0.38.

Description

Positive electrode material and secondary battery using the same

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

[0002] In recent years, research and development into all-solid-state lithium secondary batteries using 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. In general, 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 the advantages of extremely large theoretical capacity, low cost and abundant resources.

[0003] On the other hand, elemental sulfur has high resistance, so it is difficult to ensure sufficient charge / discharge capacity when used as a positive electrode material at a practical current. To address this problem, Japanese Patent Application Laid-Open No. 2010-95390 proposes a technology for using a mesoporous carbon composite material containing at least mesoporous carbon and sulfur disposed in the mesopores of the mesoporous carbon as a positive electrode material for an all-solid-state lithium secondary battery. According to Japanese Patent Application Laid-Open No. 2010-95390, by using a positive electrode material having such a configuration, the electron conductivity can be improved by the fine particle formation of sulfur and the formation of a composite with the mesoporous carbon, thereby improving the battery characteristics.

[0004] However, the inventors have conducted studies and found that even when the positive electrode material described in JP-A-2010-95390 is used, sufficient charge / discharge characteristics are still not obtained.

[0005] Therefore, an object of the present invention is to provide a means for improving the charge-discharge characteristics of a secondary battery using a cathode material containing sulfur.

[0006] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found that the above-mentioned problems can be solved by disposing phosphorus sulfide and / or its discharge products on the surface of a conductive material having micropores and inside the micropores, thereby forming a positive electrode material having a specific P / S mass ratio, and have thus completed the present invention.

[0007] One aspect of the present invention is a positive electrode material comprising: a phosphorus-containing component made of phosphorus sulfide and / or a discharge product thereof; and a conductive material having pores, wherein the phosphorus-containing component coats at least a portion of a surface of the conductive material and is disposed inside the pores to form a coating layer; and wherein a mass ratio (P / S) of elemental phosphorus to elemental sulfur contained in the positive electrode material is greater than 0 and not greater than 0.38.

[0008] Fig. 1 is a schematic cross-sectional view of a flat laminate-type all-solid-state lithium secondary battery according to one embodiment of the present invention. Fig. 2 shows Raman spectra obtained by microscopic Raman spectroscopy of the positive electrode materials produced in Examples 3 and 12.

[0009] The above-mentioned embodiments of the present invention will be described below with reference to the drawings. However, the technical scope of the present invention should be defined based on the claims and is not limited to the following embodiments. Note that the dimensional ratios in the drawings are exaggerated for the convenience of explanation and may differ from the actual ratios. The present invention will be described below using a stacked-type (internal parallel connection type) all-solid-state lithium secondary battery, which is one type of secondary battery, as an example.

[0010] One aspect of the present invention is a positive electrode material comprising: a phosphorus-containing component comprising phosphorus sulfide and / or a discharge product thereof; and a conductive material having pores, wherein the phosphorus-containing component coats at least a portion of the surface of the conductive material and is disposed inside the pores to form a coating layer, and the mass ratio of phosphorus to sulfur contained in the positive electrode material (P / S) is greater than 0 and not greater than 0.38. According to the present invention, the charge-discharge characteristics of a secondary battery using a sulfur-containing positive electrode material can be improved.

[0011] FIG. 1 is a schematic cross-sectional view of a flat-layered all-solid-state lithium secondary battery according to one embodiment of the present invention. The layered structure allows the battery to be compact and have a high capacity. In this specification, the flat-layered non-bipolar lithium secondary battery shown in FIG. 1 (hereinafter also simply referred to as a "layered battery") will be used as an example for detailed explanation. However, in terms of the internal electrical connection configuration (electrode structure) of the lithium secondary battery according to this embodiment, it can be applied to both non-bipolar (internal parallel connection type) batteries and bipolar (internal series connection type) batteries.

[0012] In one embodiment, the stacked battery 10a has a flat, rectangular shape. The power generating element 21 is wrapped in a battery exterior material (a laminate film 29) of the stacked battery 10a, and the periphery of the battery exterior material is heat-sealed. The power generating element 21 is sealed with the negative electrode current collector 25 and the positive electrode current collector 27 extended to the outside.

[0013] 1, the stacked battery 10a of this embodiment has a structure in which a flat, generally rectangular power generating element 21, where charge and discharge reactions actually proceed, is sealed inside a laminate film 29, which is a battery exterior material. Here, the power generating element 21 has a structure in which a positive electrode, a solid electrolyte layer 17, and a negative electrode are stacked. The positive electrode has a structure in which positive electrode active material layers 15 containing the positive electrode material according to one embodiment of the present invention are disposed on both sides of a positive electrode current collector 11". This can improve the charge / discharge characteristics of the stacked battery 10a. The negative electrode has a structure in which negative electrode active material layers 13 containing a negative electrode active material are disposed on both sides of a negative electrode current collector 11'. Specifically, the positive electrode, solid electrolyte layer, and negative electrode are laminated in this order such that one positive electrode active material layer 15 faces the adjacent negative electrode active material layer 13 with the solid electrolyte layer 17 interposed therebetween. As a result, the adjacent positive electrode, solid electrolyte layer, and negative electrode constitute one unit cell layer 19. Therefore, the stacked battery 10a shown in FIG. 1 can also be said to have a structure in which a plurality of unit cell layers 19 are laminated and electrically connected in parallel.

[0014] Negative electrode current collector 11′ and positive electrode current collector 11″ are respectively attached with a negative electrode current collector (tab) 25 and a positive electrode current collector (tab) 27 that are electrically connected to the respective electrodes (positive and negative electrodes), and are structured so as to be sandwiched between the ends of laminate film 29, which is the battery outer casing material, and extended to the outside of laminate film 29. Positive electrode current collector 27 and negative electrode current collector 25 may be attached to positive electrode current collector 11″ and negative electrode current collector 11′ of the respective electrodes by ultrasonic welding, resistance welding, or the like, via positive electrode leads and negative electrode leads (not shown) as necessary.

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

[0016] [Current Collector] The current collector has a function of mediating the transfer of electrons from the electrode active material layer. The constituent material of the current collector is not particularly limited, but for example, a metal or a conductive resin can be used.

[0017] [Negative Electrode (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. Furthermore, silicon-based or tin-based negative electrode active materials may be used as the negative electrode active material, and metallic lithium or lithium-containing alloys may also be used. Examples of lithium-containing alloys include alloys of Li with at least one of In, Al, Si, and Sn. In some cases, two or more negative electrode active materials may be used in combination. When the negative electrode active material is metallic lithium or a lithium-containing alloy, the lithium secondary battery 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 charging.

[0018] The content of the negative electrode active material in the negative electrode active material layer is not particularly limited, but is preferably within the range of 40 to 99 mass %, and more preferably within the range of 50 to 90 mass %, for example.

[0019] The negative electrode active material layer preferably further contains a solid electrolyte. By including the 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, and the sulfide solid electrolyte is preferred.

[0020] Examples of sulfide solid electrolytes include LiI-Li ２ S-SiS ２ , LiI-Li ２ S-P ２ O ５ , LiI-Li ３ P.O. ４ -P ２ S ５ , Li ２ S-P ２ S ５ , LiI-Li ３ P.S. ４ , LiI-LiBr-Li ３ P.S. ４ , Li ３ P.S. ４ , Li ２ S-P ２ S ５ - LiI, Li ２ S-P ２ S ５ -Li ２ O, Li ２ S-P ２ S ５ -Li ２ O-LiI, Li ２ S-SiS ２ , Li ２ S-SiS ２ - LiI, Li ２ S-SiS ２ - LiBr, Li ２ S-SiS ２ -LiCl, Li ２ S-SiS ２ -B ２ S ３ - LiI, Li ２ S-SiS ２ -P ２ S ５ - LiI, Li ２ S-B ２ S ３ , Li２ S-P ２ S ５ -Z ｍ S ｎ (where m and n are positive numbers, and Z is Ge, Zn, or Ga), Li ２ S-GeS ２ , Li ２ S-SiS ２ -Li ３ P.O. ４ , Li ２ S-SiS ２ -Li ｘ MO ｙ (where x and y are positive numbers, and M is any of P, Si, Ge, B, Al, Ga, and In). 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 sulfide solid electrolyte is, 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 sulfide solid electrolytes having a framework 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 the sulfide solid electrolyte having a skeleton include Li ７ P ３ S １１ Examples of sulfide solid electrolytes include Li （４−ｘ） Ge （１−ｘ） Pｘ S ４ (x satisfies 0<x<1), or the like may be used. Among them, a sulfide solid electrolyte containing a P element is preferable. Furthermore, the sulfide solid electrolyte may contain a halogen (F, Cl, Br, I). In a preferred embodiment, the sulfide solid electrolyte is Li ６ P.S. ５ X, where X is Cl, Br or I, preferably Cl.

[0022] The ionic conductivity (e.g., Li ion conductivity) of the solid electrolyte at room temperature (25°C) is, for example, 1 × 10 −５ S / cm or more, and preferably 1×10 −４ The ionic conductivity of the solid electrolyte can be measured by an AC impedance method.

[0023] The content of the solid electrolyte in the negative electrode active material layer is, for example, preferably in the range of 1 to 60 mass %, and more preferably in the range of 10 to 50 mass %.

[0024] The negative electrode active material layer may further contain at least one of a conductive additive and a binder in addition to the above-mentioned negative electrode active material and solid electrolyte.

[0025] The thickness of the negative electrode active material layer varies depending on the intended configuration of the secondary battery, but is preferably within the range of 0.1 to 1000 μm, for example.

[0026] [Solid Electrolyte Layer] The solid electrolyte layer is interposed between the positive electrode active material layer and the negative electrode active material layer and contains a solid electrolyte. There are no particular restrictions on the specific form of the solid electrolyte contained in the solid electrolyte layer, and the solid electrolytes exemplified in the section on the negative electrode active material layer and their preferred forms can be similarly adopted. In addition to the solid electrolyte, the solid electrolyte layer may further contain a known binder.

[0027] The thickness of the solid electrolyte layer varies depending on the configuration of the intended lithium secondary battery, but from the viewpoint of improving the volumetric energy density of the battery, it is preferably 1000 μm or less, more preferably 800 μm or less, and even more preferably 600 μm or less. On the other hand, there is no particular restriction on the lower limit of the thickness of the solid electrolyte layer, but it is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more.

[0028] [Positive Electrode Active Material Layer] (Positive Electrode Material) In the stacked battery according to the embodiment shown in Fig. 1, the positive electrode active material layer includes a positive electrode material according to one embodiment of the present invention. The positive electrode material includes a phosphorus-containing component made of phosphorus sulfide and / or a discharge product thereof, and a conductive material having pores, wherein the phosphorus-containing component coats at least a portion of the surface of the conductive material and is disposed inside the pores to form a coating layer, and the mass ratio (P / S) of phosphorus to sulfur contained in the positive electrode material is greater than 0 and not greater than 0.38.

[0029] As mentioned above, Japanese Patent Application Laid-Open No. 2010-95390 proposes a technique of using a mesoporous carbon composite material containing at least mesoporous carbon and sulfur arranged in the mesopores of the mesoporous carbon as a positive electrode material for an all-solid-state battery. However, when an electrode is produced using such a positive electrode material, the reaction resistance of the electrode reaction is high. This is because sulfur has low electrical conductivity and also because sulfur, which has low ionic conductivity, is easily dissolved near the interface between the positive electrode material and the solid electrolyte during the electrode reaction. ２ This is thought to be because S is generated, which increases the resistance to the diffusion of lithium ions in the positive electrode material.

[0030] In contrast, the positive electrode material of the present invention contains a phosphorus-containing component consisting of phosphorus sulfide and / or its discharge products on the surface of a porous conductive material and inside the pores. Both sulfur and phosphorus contained in the phosphorus-containing component can function as a positive electrode active material. Furthermore, although phosphorus sulfide has extremely low lithium ion conductivity, it can in situ form a lithium phosphorus sulfur compound (LPS) that can function as a solid electrolyte upon discharge. This reduces the diffusion resistance of lithium ions. Furthermore, an ion conduction path favorable for lithium ion migration can be established in the positive electrode active material, such as sulfur, allowing lithium ions to be efficiently introduced into the pores of the conductive material via the LPS. Furthermore, on the surface of the positive electrode active material located deep within the pores, not only can electrons be transferred via the conductive material, but also lithium ions can be transferred from the solid electrolyte via the LPS. Therefore, in the positive electrode material of the present invention, a reaction region where the positive electrode active material, LPS, and conductive material coexist is formed not only on the surface of the conductive material but also inside the pores, allowing the electrode reaction to proceed sufficiently. As a result, the positive electrode active material present inside the pores can also be utilized as an active material in the electrode reaction, which is believed to sufficiently reduce the internal resistance of the battery. As a result, it is believed that the charge / discharge characteristics of the battery are improved. According to a preferred embodiment of the present invention, the phosphorus-containing component includes both phosphorus sulfide and its discharge product. Preferably, the phosphorus-containing component consists of both phosphorus sulfide and its discharge product. This makes it possible to obtain the effects of the present invention more significantly. According to another embodiment of the present invention, the phosphorus-containing component consists of phosphorus sulfide.

[0031] Here, whether or not phosphorus sulfide and / or its discharge products are disposed on the surface and inside the pores of the conductive material can be confirmed using various conventionally known methods. For example, an image of a cross section of the conductive material observed with a transmission electron microscope (TEM) is subjected to element mapping of each material using energy dispersive X-ray spectroscopy (EDX), and the arrangement of each material can be confirmed using the obtained element map and the count number of elements derived from each material relative to the count number of all elements as indicators.

[0032] Furthermore, the positive electrode material of this embodiment has a mass ratio (P / S) of phosphorus to sulfur contained in the positive electrode material of greater than 0 and not greater than 0.38. If the P / S ratio is 0, LPS formation during discharge is not achieved, and the effects of the present invention cannot be obtained. On the other hand, if the P / S ratio exceeds 0.38, the amount of sulfur that can act as a positive electrode active material is reduced, and the effects of the present invention cannot be obtained.

[0033] (Phosphorus-containing component consisting of phosphorus sulfide and / or its discharge product) Phosphorus sulfide is P ｘ S ｙ Here, x and y are positive numbers. ２ S ３ , P ２ S ５ (P ４ S １０ ), P ４ S ３ , P ４ S ５ , P ４ S ７ , P ４ S ９ These may be used in combination of two or more kinds.

[0034] The discharge product of phosphorus sulfide is not particularly limited, but for example, Li ３ P.S. ４ , Li ４ P ２ S ７ , Li ４ P ２ S ６ , Li ７ P ３ S １１ Examples of LPS include:

[0035] (Elemental sulfur and / or its discharge products) The positive electrode material of the present invention preferably further contains, as a coating layer, elemental sulfur and / or its discharge products in addition to the phosphorus-containing component consisting of phosphorus sulfide and / or its discharge products. Elemental sulfur is a positive electrode active material with an extremely high capacity. Therefore, this form can provide a positive electrode material with a higher capacity. In addition, the in-situ formation reaction of LPS can proceed more efficiently. Therefore, a more significant resistance reduction effect can be obtained. Preferably, the positive electrode material further contains both elemental sulfur and its discharge products. This can provide a more significant effect of the present invention. In a preferred embodiment of the present invention, the phosphorus sulfide and elemental sulfur contained in the positive electrode material are, as a whole, P Ｘ S Ｙ In this case, X and Y are positive numbers. X and Y can take any positive value depending on the composition of the mixture, regardless of the stoichiometric ratio.

[0036] Here, elemental sulfur acts as a high-capacity positive electrode active material, and due to the oxidation-reduction reaction of sulfur, it can release lithium ions during charging and absorb lithium ions during discharging. In addition, by melting it, it can be easily supported on a conductive material. As elemental sulfur, S ８ α-sulfur, β-sulfur, or γ-sulfur having the structure can be used. Elemental sulfur can absorb lithium ions during discharge and exist in the positive electrode material in the form of lithium (poly)sulfides. That is, the discharge product of elemental sulfur is Li ２ Examples of the discharge product include lithium (poly)sulfides such as S. The discharge product of phosphorus sulfide and the discharge product of elemental sulfur may be the same as each other.

[0037] In a preferred embodiment of the present invention, the positive electrode material contains phosphorus sulfide, elemental sulfur, and their discharge products. By including phosphorus sulfide and elemental sulfur, LPS is effectively generated upon discharge, and the excess sulfur can contribute to the charge / discharge reactions of the battery as a positive electrode active material. As a result, a positive electrode material with higher capacity and reduced reaction resistance can be obtained. The estimated charge / discharge reaction formula when elemental sulfur and diphosphorus pentasulfide as the phosphorus sulfide are used is shown below.

[0038]

[0039] Although the positive electrode material of this embodiment can achieve high charge / discharge capacity and low resistance without using a solid electrolyte as a raw material, a solid electrolyte may be used in addition to phosphorus sulfide or elemental sulfur as a raw material. As described below, the positive electrode material of this embodiment can be produced by melt-impregnating phosphorus sulfide together with a positive electrode active material such as sulfur into a conductive material. If a solid electrolyte is used as a raw material, the solid electrolyte is not melt-impregnated and is therefore less likely to be located in the surface recesses or pores of the conductive material. As a result, the resistance reduction effect of adding a solid electrolyte may not be fully achieved. While increasing the amount of solid electrolyte added tends to reduce resistance, a high solid electrolyte content relatively reduces the proportion of positive electrode active material, which can reduce energy density. Therefore, from the perspective of energy density, it is preferable that the positive electrode material of this embodiment does not contain any solid electrolyte other than the discharge product. In one embodiment, the positive electrode material contains, in addition to the discharge product, a material having a lithium ion conductivity of 1×10 at room temperature (25°C). −５ It does not contain a solid electrolyte having a conductivity of 0.25 S / cm or more.

[0040] The positive electrode material of this embodiment has a coating layer on the surface of the conductive material and inside the pores thereof, the coating layer having a phosphorus-containing component consisting of phosphorus sulfide and / or its discharge products. Preferably, the positive electrode material of this embodiment has a coating layer on the surface of the conductive material and inside the pores thereof, the coating layer having a phosphorus-containing component and elemental sulfur and / or its discharge products. In one embodiment, the positive electrode material has a coating layer on the surface of the conductive material and inside the pores thereof, the coating layer having a phosphorus-containing component consisting of phosphorus sulfide and its discharge products, and elemental sulfur and its discharge products. In another embodiment, the positive electrode material has a coating layer on the surface of the conductive material and inside the pores thereof, the coating layer having phosphorus sulfide and elemental sulfur.

[0041] The coating layer is preferably substantially composed of a phosphorus-containing component and elemental sulfur and / or its discharge products, but is not limited thereto. For example, it may contain elemental phosphorus or its discharge products. It may also contain a component containing an element other than lithium, sulfur, or phosphorus. Examples of such components include organic sulfur compounds or inorganic sulfur compounds as positive electrode active materials containing sulfur other than elemental sulfur. Examples of organic sulfur compounds include disulfide compounds, sulfur-modified polyacrylonitrile, sulfur-modified polyisoprene, rubeanic acid (dithiooxamide), polycarbonate, etc. Examples of inorganic sulfur compounds include TiS ２ and FeS ２ Examples include: phosphorus oxide, lithium halides (e.g., LiCl, LiBr, LiI), and the like may be included as components containing elements other than lithium, sulfur, or phosphorus. Furthermore, these discharge products may be included. In this case, the proportion of the phosphorus-containing component and elemental sulfur and / or its discharge products in the total amount (100% by mass) of the coating layer is preferably more than 50% by mass, more preferably 70% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, particularly preferably 98% by mass or more, and most preferably 100% by mass.

[0042] In a preferred embodiment of the present invention, the components constituting the coating layer do not contain any halogen element, and in a preferred embodiment of the present invention, the components constituting the coating layer do not contain any elements other than lithium, sulfur, and phosphorus.

[0043] Furthermore, the mass ratio (P / S) of phosphorus to sulfur contained in the positive electrode material of this embodiment may be greater than 0 and less than or equal to 0.38, preferably less than or equal to 0.24. Within this range, excess phosphorus sulfide is reduced during the in-situ LPS generation reaction accompanying discharge. Because phosphorus sulfide has neither ionic nor electronic conductivity, the amount of remaining phosphorus sulfide is prevented from becoming too large, resulting in a more significant resistance reduction effect. More preferably, the P / S ratio is 0.20 or less, even more preferably 0.14 or less, and even more preferably 0.10 or less. While the P / S ratio is not particularly limited as long as it is greater than 0, a ratio of 0.03 or more is preferred because sufficient LPS can be generated, and the P / S ratio is more preferably 0.05 or more, even more preferably 0.07 or more, and even more preferably 0.08 or more. The P / S ratio can be controlled by adjusting the types and mixing ratios of phosphorus sulfide and elemental sulfur.

[0044] (Conductive material having micropores) The positive electrode material according to this embodiment includes a conductive material having micropores. The conductive material having micropores is not particularly limited, but is preferably a conductive porous body. By using a conductive porous body, a phosphorus-containing component is filled into the pores, which can further improve the conductivity of the positive electrode material. In particular, if elemental sulfur and / or its discharge products are further introduced into the pores, a positive electrode material with even higher capacity can be obtained. The material constituting the conductive material is also not particularly limited, and materials such as metals, conductive polymers, and carbon materials can be appropriately adopted. Among these, from the viewpoints of excellent conductivity and ease of processing, it is preferable that the conductive material be made of a carbon material. More preferably, the conductive material is a conductive porous body made of a carbon material.

[0045] Examples of conductive porous bodies made of carbon materials include activated carbon, Ketjen Black (registered trademark) (highly conductive carbon black), (oil) furnace black, channel black, acetylene black, thermal black, and lamp black, as well as carbon particles (carbon supports) made of coke, natural graphite, and artificial graphite. Commercially available porous carbons, such as Knobel (registered trademark) manufactured by Toyo Tanso Co., Ltd., which have numerous mesopores and interconnected pores, can also be used. Alternatively, a ceramic or other mold and a carbon raw material, such as a resin, can be mixed and fired in an inert atmosphere. The mold can then be dissolved with acid to synthesize a conductive porous body having a porous structure in which the shape of the mold is transferred. The pore size and pore volume of the resulting conductive porous body can be controlled by appropriately adjusting the particle size of the mold and the blending ratio of the carbon raw materials. Among these, activated carbon or porous carbon having interconnected pores, in which mesopores are interconnected, is preferably used.

[0046] It is preferable that the carbon material is mainly composed of carbon. Here, "mainly composed of carbon" refers to containing carbon atoms as the main component, and is a concept that includes both consisting of only carbon atoms and consisting essentially of carbon atoms. "Substantially consisting of carbon atoms" means that the inclusion of impurities of about 2 to 3 mass % or less is acceptable. In this specification, particulate carbon materials consisting mainly of carbon are referred to as porous carbon particles.

[0047] The BET specific surface area of ​​the conductive material is 500 m ２ / g or more, and ２ / g or more, and 1200m ２ / g or more, and more preferably 1500m ２ / g or more is particularly preferred. The pore volume of the conductive material is preferably 1.0 mL / g or more, more preferably 1.3 mL / g or more, and even more preferably 1.5 mL / g or more. If the BET specific surface area and pore volume of the conductive material are within such ranges, a sufficient amount of pores can be maintained, and therefore a sufficient amount of phosphorus-containing components, and, if contained, elemental sulfur and / or its discharge products, can be maintained. In addition, since the average thickness of the coating layer coating the conductive material does not become too thick, sufficient conductivity can be easily ensured, which is preferable. In addition, the BET specific surface area of ​​the conductive material is not particularly limited, but is preferably 3100 m ２ / g or less, and ２ / g or less is more preferable, and 2500m ２ / g or less is more preferable, and 2000m ２ / g or less is particularly preferred. Within the above range, the coating layer can be formed more uniformly, allowing the battery reaction to proceed more efficiently. The BET specific surface area and pore volume of the conductive material can be measured by nitrogen adsorption / desorption measurement. This nitrogen adsorption / desorption measurement is performed using a BELSORP mini manufactured by Microtrac-Bell Corporation, at a temperature of -196°C, using a multipoint method. 0.01<P / P ０ The BET specific surface area is determined from the adsorption isotherm in the range of relative pressure <0.05. The pore volume is determined from the adsorption N at a relative pressure of 0.96. ２ Calculate from the volume.

[0048] The average pore diameter of the conductive material is not particularly limited, but is preferably 1 to 50 nm, and more preferably 1 to 30 nm. If the average pore diameter of the conductive material is within these ranges, electrons can be sufficiently supplied to phosphorus-containing components, elemental sulfur, and / or their discharge products present inside the pores at positions distant from the pore walls. The average pore diameter of the conductive material can be calculated by nitrogen adsorption / desorption measurement, similar to the case of determining the BET specific surface area and pore volume. In this specification, the pore distribution of the conductive material obtained using the BJH method is used.

[0049] The conductive material is not particularly limited, but it is preferable that the percentage of the pore volume of pores having a pore diameter in the range of 1 to 4 nm relative to the pore volume of pores having a pore diameter in the range of 1 to 100 nm is 20% or less. This allows the phosphorus-containing component and elemental sulfur as the positive electrode active material and / or its discharge products to be easily retained inside the pores. As a result, it is believed that the internal resistance of the battery is further reduced. The percentage value is more preferably 18% or less, even more preferably 15% or less, even more preferably 12% or less, and particularly preferably 9%. Meanwhile, there is no particular limit on the lower limit of the percentage, but it is, for example, 3% or more.

[0050] The average particle diameter (primary particle diameter) of the conductive material is not particularly limited, but is preferably 0.05 to 50 μm, more preferably 0.1 to 20 μm, and even more preferably 0.5 to 10 μm. In this specification, the term "particle diameter of the conductive material" refers to the longest distance L between any two points on the contour line of the conductive material. The value of the "average particle diameter of the conductive material" is calculated as the arithmetic mean value of particle diameters observed within several to several tens of fields of view using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0051] The amount of the porous conductive material is not particularly limited, but is preferably 0.05 to 10, more preferably 0.1 to 5, even more preferably 0.15 to 2, and even more preferably 0.2 to 2, in mass ratio relative to phosphorus sulfide (or the total amount of phosphorus sulfide and elemental sulfur when elemental sulfur is further used). As long as the amount of the conductive material is within the above range, a cathode material with sufficient conductivity can be obtained. In the cathode material of this embodiment, discharge products are formed from at least a portion of the phosphorus sulfide (or phosphorus sulfide and elemental sulfur when elemental sulfur is included) during discharge. It is preferable that the above range is satisfied both before and after discharge and before and after charge. In a preferred embodiment, the amount of the conductive material is, in terms of a charging ratio, for example, 10 to 20 mass%, preferably 11 to 19 mass%, relative to the total amount of phosphorus sulfide, elemental sulfur, and conductive material.

[0052] In the positive electrode material of the present invention, the average thickness of the coating layer covering the surface of the conductive material is preferably 5 nm or less. This configuration can further enhance the effects of the present invention. Although phosphorus sulfide does not have electronic conductivity, it is believed that if the average thickness of the coating layer is 5 nm or less, electrons are supplied to the conductive material by the tunneling effect, thereby maintaining low reaction resistance. The average thickness of the coating layer is preferably 4 nm or less, more preferably 3 nm or less, and even more preferably 2 nm or less. The average thickness of the coating layer is not particularly limited, but is, for example, 0.1 nm or more, preferably 0.5 nm or more, more preferably 0.8 nm or more, and even more preferably 1.0 nm or more. Within the above range, the coating layer can be formed more uniformly, thereby allowing the battery reaction to proceed more efficiently and improving charge / discharge characteristics. The average thickness can be determined by the method described in the examples. The average thickness can be controlled by adjusting the types and mixing ratios of components such as the conductive material, phosphorus sulfide, and elemental sulfur. Furthermore, in the positive electrode material of this embodiment, discharge products are formed from at least a portion of the phosphorus sulfide and elemental sulfur as the material is discharged, and it is preferable that the above range be satisfied both before and after discharge and before and after charge.

[0053] (Manufacturing method by collective heating impregnation) The positive electrode material according to the present embodiment can be manufactured by a manufacturing method (manufacturing method by collective heating impregnation) including a step of heat-treating a mixture containing a porous conductive material, phosphorus sulfide, and elemental sulfur.

[0054] In this case, the specific forms of the porous conductive material, phosphorus sulfide, and elemental sulfur are as described above. The mixing ratio of the porous conductive material, phosphorus sulfide, and elemental sulfur is not particularly limited, but can be adjusted so that the mass ratio of phosphorus to sulfur (P / S) in the resulting positive electrode material is more than 0 and 0.38 or less.

[0055] For example, the ratio of elemental sulfur to phosphorus sulfide may be 17.25:1 to 0.75:1, preferably 6:1 to 2:1. ２ S ５Converted to S:P ２ S ５ = 69:1 to 3:1.

[0056] The specific means for mixing the porous conductive material, phosphorus sulfide, and elemental sulfur is not particularly limited, and conventionally known knowledge may be referred to as appropriate. Examples include a mixing treatment using a mixing means such as a mortar, and a milling treatment using a pulverizing means such as a planetary ball mill.

[0057] The step of mixing the components is preferably carried out in an inert gas atmosphere with a controlled dew point, for example, an inert gas atmosphere with a dew point of −60° C. or lower.

[0058] The heat treatment temperature is not particularly limited, but is preferably a temperature equal to or higher than the melting point of the material used. For example, it is above 170°C, preferably 200°C or higher, more preferably 250°C or higher, even more preferably 290°C or higher, and even more preferably 300°C or higher. On the other hand, the upper limit of the heat treatment temperature is not particularly limited, but is, for example, 500°C or lower, preferably 400°C or lower. Furthermore, the heat treatment time is not particularly limited, but is, for example, 0.5 to 20 hours, preferably 1 to 10 hours. In this way, phosphorus sulfide and elemental sulfur are melted and mixed to form the phosphorus polysulfide composition P. Ｘ S Ｙ It is believed that the phosphorus sulfide and the elemental sulfur are not in separate states, but are combined with the conductive material in the molten state. Ｘ S Ｙ It is believed that the conductive material can be introduced into the surface and pores of the conductive material in a homogeneous state, resulting in a reduced reaction resistance and a positive electrode material with excellent charge-discharge characteristics.

[0059] The heat treatment is preferably carried out under reduced pressure, since this allows for degassing of residual gas in the pores of the conductive material. The heat treatment is not particularly limited, but can be carried out under reduced pressure of, for example, 100 Pa or less, preferably 10 Pa or less.

[0060] The positive electrode material thus obtained is discharged to form a phosphorus polysulfide composition PＸ S Ｙ LPS can be generated as a discharge product from at least a portion of the above. The specific procedure for discharging is not particularly limited, and can be carried out by a general method.

[0061] (Manufacturing Method by Sequential Heating Impregnation) The positive electrode material according to the present embodiment can be manufactured by a manufacturing method (manufacturing method by sequential heat impregnation) including the steps of: heat-treating a porous conductive material and elemental sulfur to cause the elemental sulfur to be supported in a gas phase on the conductive material; and mixing phosphorus sulfide with the conductive material on which the elemental sulfur is supported in a gas phase, followed by further heat treatment.

[0062] In this method, elemental sulfur is first supported on the conductive material by vapor phase support in a sublimated state. This allows for a uniform coating on the surface and inside the pores of the conductive material. This allows for a good electron conduction path to be established for the sulfur. Then, phosphorus sulfide is mixed with the sulfur-supported conductive material, and the material is further heat-treated. This melts the phosphorus sulfide, which diffuses into the already supported sulfur, forming a uniform P Ｘ S Ｙ It is believed that a composition is formed. Here, elemental sulfur has a lower sublimation point than a mixture in which elemental sulfur and phosphorus sulfide are mixed in advance, and therefore can be supported in the gas phase. It is believed that supporting elemental sulfur in the gas phase enables more uniform coating and increases the reaction interface area. Therefore, even if the amounts of elemental sulfur and phosphorus sulfide used are similar, it is believed that the reaction resistance can be further reduced and the charge / discharge characteristics can be further improved.

[0063] The heat treatment temperature in the step of supporting elemental sulfur in a gas phase on a porous conductive material is not particularly limited, but is, for example, 150 to 250°C, more preferably 150 to 200°C, and even more preferably 150 to 180°C. The heat treatment time is also not particularly limited, but is, for example, 1 to 5 hours. Other than the above, the heat treatment can be carried out under the same conditions as those for the heat treatment in the production method by collective thermal impregnation.

[0064] The heat treatment conditions in the step of mixing phosphorus sulfide with the conductive material carrying elemental sulfur in a gas phase and further heat treating the material can be the same as those in the heat treatment in the manufacturing method by collective heating impregnation. The specific means for mixing phosphorus sulfide with the conductive material carrying elemental sulfur in a gas phase are also the same as those described above.

[0065] Note that, as a specific embodiment, the same embodiment as in the production method by collective thermal impregnation can be preferably adopted, except that elemental sulfur is supported on the conductive material by thermal impregnation and then phosphorus sulfide is supported by thermal impregnation.

[0066] However, simply mechanically mixing the above-mentioned components such as phosphorus sulfide and elemental sulfur with a conductive material having pores in a solid state does not allow the components such as phosphorus sulfide and elemental sulfur to be arranged inside the pores of the conductive material. In this case, the components such as phosphorus sulfide and elemental sulfur only adhere to the surface of the conductive material particles. Therefore, these discharge products are not arranged inside the pores of the conductive material, but only adhere to the surface of the conductive material particles.

[0067] The manufacturing method of this embodiment can be carried out without using a solid electrolyte as a raw material, and in a preferred embodiment, a solid electrolyte is not used as a raw material. In a positive electrode material in which a solid electrolyte is used as a raw material and is supported on a conductive material together with a positive electrode active material, for example, a Raman spectrum obtained by microscopic Raman spectroscopy using a laser with a wavelength of 532 nm shows a peak at 420 cm −１ Nearby is PS derived from solid electrolyte ４ ３− In particular, when a process of dissolving and re-precipitating the solid electrolyte using a solvent is performed, a peak corresponding to 1300 to 1700 cm −１ PS in the range ｘ O ｙ ｎ− On the other hand, in the case of the positive electrode material of this embodiment, which does not use a solid electrolyte as a raw material, a peak corresponding to a decomposition product of the solid electrolyte (a by-reaction product of the solid electrolyte and the solvent) such as 420 cm −１ PS derived from nearby solid electrolyte ４ ３−In addition, since no solvent is used, a strong peak corresponding to 1300-1700 cm −１ In addition, the positive electrode material of this embodiment does not produce a peak corresponding to the decomposition product of the solid electrolyte in the range of 1300 to 1700 cm even after discharge. −１ No peaks corresponding to decomposition products of the solid electrolyte are observed in the range of 1000 to 10000.

[0068] The content of the positive electrode material of this embodiment in the positive electrode active material layer is not particularly limited, but is preferably in the range of 35 to 99 mass%, more preferably in the range of 40 to 90 mass%. The positive electrode active material layer may further contain a known positive electrode material (positive electrode active material) in addition to the positive electrode material of this embodiment, as long as the effects of the present invention are not impaired. The content of the positive electrode material of this embodiment in the positive electrode material contained in the positive electrode active material layer is preferably 90 mass% or more, more preferably 95 mass% or more.

[0069] The positive electrode active material layer may further contain a solid electrolyte, which may be contained in the negative electrode active material layer, if necessary. The content of the solid electrolyte in the positive electrode active material layer is, for example, preferably in the range of 1 to 65 mass %, more preferably in the range of 10 to 50 mass %. The positive electrode active material layer may further contain a conductive additive and / or a binder.

[0070] The thickness of the positive electrode active material layer varies depending on the intended configuration of the secondary battery, but is preferably within the range of 0.1 to 1000 μm.

[0071] Furthermore, the 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).

[0072] The following embodiments are also included within the scope of the present invention: a cathode material according to claim 1 having the features of claim 2; a cathode material according to claim 1 having the features of claim 3; a cathode material according to any one of claims 1 to 3 having the features of claim 4; a cathode material according to any one of claims 1 to 4 having the features of claim 5; a cathode material according to any one of claims 1 to 5 having the features of claim 6; a cathode material according to any one of claims 1 to 6 having the features of claim 7; and a secondary battery comprising a cathode material according to any one of claims 1 to 7.

[0073] The present invention will be described in more detail below with reference to examples, although the technical scope of the present invention is not limited to the following examples.

[0074] [Example 1] (Preparation of Positive Electrode Material) In a glove box with an argon atmosphere having a dew point of -68°C or less, 0.100 g of porous carbon (Carbon 1, Knobel (registered trademark) P(3)010 manufactured by Toyo Tanso Co., Ltd., BET specific surface area 1640 m) as a conductive material was added. ２ / g) with 0.440 g of sulfur (α sulfur, S ８ , manufactured by Tsurumi Chemical Industry Co., Ltd.) and 0.06 g of diphosphorus pentasulfide (manufactured by Kojundo Chemical Laboratory Co., Ltd.). Here, the molar ratio of sulfur to diphosphorus pentasulfide was S:P ２ S ５ Converted to S:P ２ S ５ The ratio was 51:1. After thorough mixing in an agate mortar, the mixed powder was placed in a quartz container and sealed under reduced pressure of about 4 mbar. The container was then placed in a tubular furnace and heated at 350°C for 6 hours to melt the sulfur and diphosphorus pentasulfide, thereby impregnating the porous carbon. In the positive electrode material of this example, the ratio of (total mass of sulfur and diphosphorus pentasulfide):(mass of porous carbon) was 5:1.

[0075] [Examples 2 to 8] (Preparation of Positive Electrode Material) In Example 1, the molar ratio of sulfur to diphosphorus pentasulfide was changed as shown in Table 1 below. In each example, the ratio of (total mass of sulfur and diphosphorus pentasulfide):(mass of porous carbon) was set to 5:1. Furthermore, in Examples 7 and 8, carbon 2 (MSC-30 manufactured by Kansai Thermal Chemical Co., Ltd., BET specific surface area 3040 m) was used instead of carbon 1. ２ / g) and carbon 3 (Merck xGnP graphene nanoplatelets-grade C-500, BET specific surface area 500 m ２ A positive electrode material was prepared in the same manner as in Example 1 except for the above.

[0076] [Example 9] (Preparation of Positive Electrode Material) In a glove box with an argon atmosphere having a dew point of -68°C or less, 0.100 g of porous carbon (Carbon 1, Knobel (registered trademark) P(3)010 manufactured by Toyo Tanso Co., Ltd., BET specific surface area 1640 m) as a conductive material was added. ２ / g) with 0.454 g of sulfur (α sulfur, S ８ , manufactured by Tsurumi Chemical Industry Co., Ltd.) was added and thoroughly mixed in an agate mortar, and the mixed powder was then placed in a sealed pressure-resistant autoclave and heated at 170°C for 3 hours to melt the sulfur and impregnate the porous carbon with the sulfur, thereby obtaining a sulfur-impregnated porous carbon.

[0077] In a glove box under an argon atmosphere with a dew point of −68° C. or less, 0.554 g of the sulfur-impregnated porous carbon prepared above was added with 0.046 g of diphosphorus pentasulfide (manufactured by Kojundo Chemical Laboratory Co., Ltd.). Here, the molar ratio of sulfur to diphosphorus pentasulfide was S:P. ２ S ５ The ratio was 69:1. After thoroughly mixing these in an agate mortar, the mixed powder was placed in a quartz container and sealed under a reduced pressure of about 4 mbar. The container was then placed in a tubular furnace and heated at 350°C for 6 hours, whereby the diphosphorus pentasulfide was melted and combined with the sulfur-impregnated porous carbon to obtain a positive electrode material.

[0078] [Examples 10 to 14] In Example 9 (preparation of positive electrode material), the molar ratio of sulfur to diphosphorus pentasulfide was changed as shown in Table 1 below. In each example, the ratio of (total mass of sulfur and diphosphorus pentasulfide):(mass of porous carbon) was set to 5:1. Other than the above, positive electrode materials were prepared in the same manner as in Example 9.

[0079] Comparative Example 1 A positive electrode material was prepared in the same manner as in Example 1 (preparation of positive electrode material), except that the amount of sulfur was changed to 0.500 g and diphosphorus pentasulfide was not added.

[0080] Comparative Example 2 A positive electrode material was prepared in the same manner as in Example 1 (preparation of positive electrode material), except that the amount of diphosphorus pentasulfide was changed to 0.500 g and no sulfur was added.

[0081] Comparative Example 3 Preparation of Positive Electrode Material In a glove box with an argon atmosphere having a dew point of −68° C. or less, porous carbon (Carbon 1, Knobel® P(3)010 manufactured by Toyo Tanso Co., Ltd., BET specific surface area 1640 m) was prepared. ２ / g) and sulfur (α sulfur, S ８ (manufactured by Tsurumi Chemical Industry Co., Ltd.) and diphosphorus pentasulfide (manufactured by Kojundo Chemical Laboratory Co., Ltd.) were mixed in a molar ratio of sulfur to diphosphorus pentasulfide of S:P. ２ S ５ The weight ratio of sulfur and diphosphorus pentasulfide to porous carbon was 18:1, and the total weight of sulfur and diphosphorus pentasulfide to porous carbon was 5:1. Each component was placed in a 45 mL zirconia container and treated at 370 rpm for 6 hours in a planetary ball mill (Premium line P-7, manufactured by Fritsch) to obtain a positive electrode material.

[0082] (Average Thickness of Coating Layer) The average thickness of the coating layer coating the conductive material was estimated for the positive electrode materials prepared in each Example and Comparative Example. Here, "coating" refers to the adhesion of the phosphorus-containing component and elemental sulfur and / or its discharge product (if present) as components constituting the coating layer to the portion where nitrogen gas is adsorbed when measuring the specific surface area of ​​the conductive material by the BET method. The average thickness was calculated using the following formula.

[0083]

[0084] The BET specific surface area of ​​the conductive material was measured by nitrogen adsorption / desorption measurement. The input volume of the components constituting the coating layer is the total volume of the components constituting the coating layer input per unit mass of the conductive material, and the density of sulfur (α sulfur) is 2.07 g / cm ３ and the density of diphosphorus pentasulfide is 2.05 g / cm ３ The results are shown in Table 1 below.

[0085] (Microscopic Raman Spectroscopic Analysis of Positive Electrode Material) In a glove box with an argon atmosphere having a dew point of -68°C or less, the powder sample of the positive electrode material obtained above was placed on a glass plate, the surface was flattened, and Raman point measurement was performed at an excitation wavelength of 532 nm using a confocal microspectrophotometer (WITec, α300). The Raman spectra of the positive electrode materials of Examples 3 and 12 obtained in this manner are shown in Figure 2. As shown in Figure 2, the Raman spectrum of the positive electrode material obtained in this example was measured at 470-475 cm. −１ Range: 220-230cm −１ Around 155-165cm −１ In the presence of a large amount of solid electrolyte, the decomposition product PS ４ ３− Corresponding to 420 cm −１ Around (for example, 385-430 cm −１ Although it is expected that a peak due to the P-S bond would be observed in the range of 1300 to 1700 cm, no significant peak was observed in the positive electrode material of this example. When a positive electrode material is prepared by a method including a step of dissolving and re-precipitating a solid electrolyte using a solvent, the Raman spectrum of the positive electrode material shows a peak in the range of 1300 to 1700 cm. −１ In the range of 0.1 to 1.0, a peak corresponding to the decomposition product of the solid electrolyte (a by-reaction product of the solid electrolyte and the solvent) is observed, but no such peak was observed in the positive electrode material of this example (not shown).

[0086] Separately, the Raman spectrum of the positive electrode material of this example after discharge was measured. −１Around (for example, 385-430 cm −１ No significant peak was observed in the 1300-1700 cm range. −１ No peaks corresponding to decomposition products of the solid electrolyte were observed in the range of 1000 to 10000.

[0087] <<Example of Test Cell Preparation>> (Preparation of Positive Electrode Mixture) In a glove box in an argon atmosphere with a dew point of −68° C. or less, 40 g of zirconia balls with a diameter of 5 mm, 0.375 g of the positive electrode material prepared in each Example and Comparative Example, and a solid electrolyte (Li, manufactured by Ampcera Corporation) were mixed. ６ P.S. ５ The resulting mixture and 0.125 g of ammonium hydroxide (CaO) were placed in a 45 ml zirconia container and processed at 370 rpm for 6 hours in a planetary ball mill (Premium line P-7, manufactured by Fritsch GmbH), to obtain a powder of a positive electrode mixture. The composition of the positive electrode mixture was positive electrode material:solid electrolyte=75:25 (mass ratio).

[0088] (Fabrication of Test Cell (All-Solid-State Lithium Secondary Battery)) The battery was fabricated in a glove box in an argon atmosphere with a dew point of −68° C. or less. A SUS cylindrical convex punch (10 mm diameter) was inserted into one side of a cylindrical tube jig (inner diameter 10 mm, outer diameter 23 mm, height 20 mm) manufactured by Macor, and a sulfide solid electrolyte (manufactured by Apcera, Li ６ P.S. ５80 mg of SUS304 (C1) was placed inside the cylindrical tube jig. Then, another SUS cylindrical convex punch was inserted to sandwich the solid electrolyte, and the tube 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 7.5 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 tube 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 (which also serves as the negative electrode current collector) was removed, and a lithium foil (manufactured by Nilaco Corporation, thickness 0.20 mm) punched to a diameter of 8 mm and an indium foil (manufactured by Nilaco Corporation, thickness 0.30 mm) punched to a diameter of 9 mm were stacked as the negative electrode, and the cylindrical tube jig was inserted from the bottom so that the indium foil was positioned on the solid electrolyte layer side.The cylindrical convex punch 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, a test 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.

[0089] Evaluation of Test Cells The capacity characteristics of the test cells prepared in the above examples and comparative examples were evaluated by the following method. All of the following measurements were carried out using a charge / discharge tester (HJ-SD8, manufactured by Hokuto Denko Corporation) in a constant temperature bath set at 25°C.

[0090] (Evaluation of capacity characteristics) A test cell was placed in a thermostatic chamber, and after the cell temperature became constant, a current of 0.2 mA / cm was applied as cell conditioning. ２ A constant current discharge was performed at a current density of 0.5 V to a cell voltage of 0.5 V, followed by a constant current / constant voltage charge at the same current density to 2.5 V with a cut-off current of 0.01 mA / cm ２This conditioning charge-discharge cycle was repeated three times, and the discharge capacity in the third cycle was taken as the rated capacity. The capacity value per mass of sulfur (S) (mAh / g-S) was calculated from the value of this third discharge capacity and the mass of sulfur (S) contained in the positive electrode active material layer. In addition, the capacity value per mass of the positive electrode mixture (mAh / g-positive electrode) was calculated from the value of the third discharge capacity and the mass of the positive electrode active material layer. The results are shown in Table 1 below.

[0091] (Evaluation of Resistance Value) A test cell was placed in a thermostatic chamber, and the SOC (state of charge) of the cell was adjusted to 50%, and the current density was adjusted to 0.2, 0.4, and 0.8 mA / cm. ２ The resistance was calculated from the IV curve obtained by varying the current and discharging for 10 seconds. Before applying the voltage at each current value, the voltage was adjusted to 0.2 mA / cm so that the SOC was 50%. ２ The results are shown in Table 1 below.

[0092]

[0093] The results shown in Table 1 demonstrate that the present invention can improve the charge-discharge characteristics of secondary batteries using sulfur-containing cathode materials. In contrast, the cathode material of Comparative Example 1, which does not contain a component containing phosphorus sulfide, and the cathode material of Comparative Example 2, which has a P / S mass ratio of more than 0.38, have high reaction resistance and do not provide good charge-discharge characteristics. Furthermore, the cathode material of Comparative Example 3, which was produced by ball milling, does not provide a sufficient resistance reduction effect because it is not possible to dispose a layer containing phosphorus sulfide inside the pores of the conductive material.

[0094] Furthermore, a comparison of Examples 1 to 8 with Examples 9 to 14 revealed that the positive electrode materials of Examples 9 to 14, in which sulfur and phosphorus sulfide were successively impregnated by heating, provided superior charge / discharge characteristics.

[0095] 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 phosphorus-containing component composed of phosphorus sulfide and / or its discharge product, and a conductive material having pores, wherein the phosphorus-containing component covers at least a part of the surface of the conductive material and is disposed inside the pores to form a coating layer, the mass ratio (P / S) of the phosphorus element to the sulfur element contained in the positive electrode material is more than 0 and 0.38 or less, The conductive material is a conductive porous body with a BET specific surface area of 800 to 3000 m ２ / g, and the average thickness of the coating layer is 1.0 nm or more and 4 nm or less. The positive electrode material is characterized by this.

2. The positive electrode material according to claim 1, wherein the phosphorus-containing component is composed of phosphorus sulfide and its discharge product.

3. The positive electrode material according to claim 1, wherein the phosphorus-containing component is composed of phosphorus sulfide.

4. The positive electrode material according to claim 1 or 2, wherein the coating layer further contains elemental sulfur and / or its discharge product.

5. The BET specific surface area of the conductive material is 1,200 to 2,500 m ２ / g, and the positive electrode material according to claim 1 or 2.

6. The positive electrode material according to claim 1 or 2, wherein the mass ratio (P / S) of the phosphorus element to the sulfur element contained in the positive electrode material is 0.03 or more and 0.38 or less.

7. The positive electrode material according to claim 1 or 2, wherein the mass ratio (P / S) of the phosphorus element to the sulfur element contained in the positive electrode material is 0.03 or more and 0.24 or less.

8. A method for manufacturing a positive electrode material, comprising: a step of heat-treating a conductive material having pores and elemental sulfur to vapor-phase support the elemental sulfur on the conductive material; and a step of mixing phosphorus sulfide with the conductive material on which the elemental sulfur is vapor-phase supported and further heat-treating.

9. In the step of heat-treating a conductive material having pores and elemental sulfur to vapor-phase support the elemental sulfur on the conductive material, the heat treatment temperature is 150 to 250°C, and in the step of mixing phosphorus sulfide with the conductive material on which the elemental sulfur is vapor-phase supported and further heat-treating, the heat treatment temperature is more than 170°C and 500°C or less. The method for manufacturing a positive electrode material according to claim 8.

10. A secondary battery including the positive electrode material according to claim 1 or 2.