Positive electrode material and secondary battery using the 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

[Technical Field]

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

[0002] In recent years, research and development on all-solid-state lithium secondary batteries using oxide-based or sulfide-based solid electrolytes has been actively pursued. Solid electrolytes are materials mainly composed of ionic conductors capable of ion conduction in a solid state. Generally, using high-potential, high-capacity positive electrode materials and high-capacity negative electrode materials can significantly improve the power density and energy density of the battery. For example, elemental sulfur (S8) has an extremely large theoretical capacity and has the advantages of being low-cost and abundant in resources.

[0003] On the other hand, since elemental sulfur has high resistance, it is difficult to secure sufficient charge and discharge capacity when used as a positive electrode material with practical currents. To address this problem, Japanese Patent Publication No. 2010-95390 proposes a technology for using a mesoporous carbon composite material, which contains at least mesoporous carbon and sulfur disposed within the mesopores of the mesoporous carbon, as a positive electrode material for an all-solid-state lithium secondary battery. According to Japanese Patent Publication No. 2010-95390, by using a positive electrode material with such a configuration, the electron conductivity can be improved by the micronization of sulfur and its composite with mesoporous carbon, thereby improving battery characteristics. [Overview of the project]

[0004] However, the inventors' investigation revealed that even using the positive electrode material described in Japanese Patent Publication No. 2010-95390, sufficient charge-discharge characteristics could still not be obtained.

[0005] Therefore, the present invention aims to provide a means for improving the charge-discharge characteristics of a secondary battery using a positive electrode material containing sulfur.

[0006] The inventors have conducted intensive studies to solve the above problems. As a result, by disposing phosphorus sulfide and / or its discharge product on the surface and inside the pores of a conductive material having pores and using a cathode material having a P / S mass ratio with a specific value, it has been found that the above problems can be solved, and the present invention has been completed.

[0007] One embodiment of the present invention includes 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, and the mass ratio (P / S) of the phosphorus element to the sulfur element contained in the cathode material is more than 0 and 0.38 or less. It is a cathode material characterized by the above.

Brief Description of Drawings

[0008] [Figure 1] 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. [Figure 2] FIG. 2 is a Raman spectrum obtained by microscopic Raman spectroscopic analysis of the cathode materials manufactured in Example 3 and Example 12.

Embodiments for Carrying Out the Invention

[0009] Hereinafter, while referring to the drawings, the above-described embodiments of the present invention will be described. However, the technical scope of the present invention should be determined based on the description in the claims and is not limited only to the following embodiments. The dimensional ratios in the drawings are exaggerated for the convenience of explanation and may be different from the actual ratios. Hereinafter, the present invention will be described by taking a laminated type (internally parallel-connected type) all-solid-state lithium secondary battery, which is one form of a secondary battery, as an example.

[0010] One embodiment of the present invention is a positive electrode material comprising a phosphorus-containing component consisting of phosphorus sulfide and / or its discharge products, and a conductive material having pores, wherein the phosphorus-containing component covers at least a portion of the surface of the conductive material and is arranged inside the pores to form a coating layer, and the mass ratio (P / S) of the phosphorus element to the sulfur element contained in the positive electrode material is greater than 0 and less than or equal to 0.38. According to the present invention, the charge-discharge characteristics can be improved in a secondary battery using a positive electrode material containing sulfur.

[0011] Figure 1 is a schematic cross-sectional view of a flat-stacked all-solid-state lithium secondary battery, which is one embodiment of the present invention. By using a stacked design, the battery can be made compact and have a high capacity. In this specification, the flat-stacked non-bipolar lithium secondary battery shown in Figure 1 (hereinafter also simply referred to as "stacked battery") will be used as an example for detailed explanation. However, in terms of the electrical connection configuration (electrode structure) inside 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 rectangular, flattened shape. The power generation element 21 is encased in the battery casing material (laminate film 29) of the stacked battery 10a, and its periphery is heat-sealed, so that the power generation element 21 is sealed with the negative electrode current collector plate 25 and the positive electrode current collector plate 27 exposed to the outside.

[0013] As shown in Figure 1, the stacked battery 10a of this embodiment has a structure in which a flattened, roughly rectangular power generation element 21, in which the charge and discharge reaction actually takes place, is sealed inside a laminate film 29, which is the battery's outer casing material. Here, the power generation element 21 has a configuration in which a positive electrode, a solid electrolyte layer 17, and a negative electrode are stacked. The positive electrode has a structure in which a positive electrode active material layer 15 containing a positive electrode material according to one embodiment of the present invention is arranged on both sides of a positive electrode current collector 11''. This can improve the charge and discharge characteristics of the stacked battery 10a. The negative electrode has a structure in which a negative electrode active material layer 13 containing a negative electrode active material is arranged on both sides of a negative electrode current collector 11'. Specifically, the positive electrode, solid electrolyte layer, and negative electrode are stacked in this order such that one positive electrode active material layer 15 and an adjacent negative electrode active material layer 13 face each other via a solid electrolyte layer 17. As a result, adjacent positive electrodes, solid electrolyte layers, and negative electrodes constitute one single cell layer 19. Therefore, the stacked battery 10a shown in Figure 1 can also be said to have a configuration in which multiple single cell layers 19 are stacked and electrically connected in parallel.

[0014] The negative electrode current collector 11' and the positive electrode current collector 11'' are each attached to a negative electrode current collector plate (tab) 25 and a positive electrode current collector plate (tab) 27, which are electrically connected to the respective electrodes (positive and negative electrodes), and are structured to be led out of the laminate film 29, which is the battery casing material, by being sandwiched between the edges of the laminate film 29. The positive electrode current collector plate 27 and the negative electrode current collector plate 25 may be attached to the positive electrode current collector 11'' and the negative electrode current collector 11' of each electrode via positive electrode leads and negative electrode leads (not shown) as needed, by ultrasonic welding, resistance welding, or the like.

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

[0016] [Current collector] The current collector has the function of mediating the movement of electrons from the electrode active material layer. While there are no particular limitations on the materials used for the current collector, for example, metals or conductive resins may be employed.

[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 examples include carbon materials, metal oxides, and metallic active materials. Furthermore, silicon-based or tin-based negative electrode active materials may be used, or metallic lithium or lithium-containing alloys may 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 the charging process.

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

[0019] The negative electrode active material layer preferably further contains a solid electrolyte. The inclusion of a solid electrolyte in the negative electrode active material layer improves its ionic conductivity. Examples of solid electrolytes include sulfide solid electrolytes and oxide solid electrolytes, but a sulfide solid electrolyte is preferred.

[0020] Examples of sulfide solid electrolytes include LiI-Li2S-SiS2, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-P2S5, LiI-Li3PS4, LiI-LiBr-Li3PS4, Li3PS4, Li2S-P2S5-LiI, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z. m S n(However, m and n are positive numbers, and Z is any one of Ge, Zn, and Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (However, x and y are positive numbers, and M is any one of P, Si, Ge, B, Al, Ga, and In), etc. are mentioned. Note that the description of "Li2S-P2S5" means a sulfide solid electrolyte formed using a raw material composition containing Li2S and P2S5, and the same applies to other descriptions.

[0021] The sulfide solid electrolyte may, for example, have a Li3PS4 skeleton, a Li4P2S7 skeleton, or a Li4P2S6 skeleton. Examples of the sulfide solid electrolyte having a Li3PS4 skeleton include LiI-Li3PS4, LiI-LiBr-Li3PS4, and Li3PS4. Further, examples of the sulfide solid electrolyte having a Li4P2S7 skeleton include, for example, Li7P3S 11 and the like. Also, as the sulfide solid electrolyte, for example, Li (4-x) Ge (1-x) P x S4 (where x satisfies 0 < x < 1), such as LGPS, may be used. Among them, it is preferable that the sulfide solid electrolyte contains a P element. Further, the sulfide solid electrolyte may contain a halogen (F, Cl, Br, I). In a preferred embodiment, the sulfide solid electrolyte contains Li6PS5X (where X is Cl, Br, or I, preferably Cl).

[0022] Note that the ionic conductivity (for example, Li ion conductivity) of the solid electrolyte at room temperature (25 °C) is preferably, for example, 1 × 10 -5 S / cm or more, and more preferably 1 × 10 -4 S / cm or more. Note that the value of the ionic conductivity of the solid electrolyte can be measured by the alternating current impedance method.

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

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

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

[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; the solid electrolytes and their preferred forms exemplified in the section on the negative electrode active material layer can be similarly employed. 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 intended configuration of the 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 limit 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] [Cathode active material layer] (Positive electrode material) In the stacked battery according to the embodiment shown in Figure 1, the positive electrode active material layer includes a positive electrode material according to one embodiment of the present invention. The positive electrode material comprises a phosphorus-containing component consisting of phosphorus sulfide and / or its discharge products, and a conductive material having pores, wherein the phosphorus-containing component covers at least a portion of the surface of the conductive material and is arranged inside the pores to form a covering layer, and the mass ratio (P / S) of the phosphorus element to the sulfur element contained in the positive electrode material is greater than 0 and 0.38 or less.

[0029] As mentioned above, Japanese Patent Publication No. 2010-95390 proposes a technique for using a mesoporous carbon composite material, which includes at least mesoporous carbon and sulfur disposed within the mesopores of the mesoporous carbon, as a positive electrode material for an all-solid-state battery. However, when electrodes are fabricated using such a positive electrode material, the reaction resistance of the electrode reaction is high. This is thought to be because sulfur has low conductivity, and during the electrode reaction, it generates Li2S with low ionic conductivity near the interface between the positive electrode material and the solid electrolyte, increasing the resistance to the diffusion of lithium ions within the positive electrode material.

[0030] In contrast, the positive electrode material of the present invention has a phosphorus-containing component consisting of phosphorus sulfide and / or its discharge products on the surface and inside the pores of a conductive material having pores. Both sulfur and phosphorus contained in the phosphorus-containing component can act as positive electrode active material. Although phosphorus sulfide is a material with extremely low lithium ion conductivity, it can form lithium phosphorus sulfur compounds (LPS) in-situ, which can function as a solid electrolyte, upon discharge. This reduces the diffusion resistance of lithium ions. As a result, ion conduction pathways favorable to the movement of lithium ions can be constructed in the positive electrode active material such as sulfur, and lithium ions can be efficiently introduced into the pores of the conductive material via LPS. Furthermore, at the surface of the positive electrode active material located deep within the pores, not only can electrons enter and exit via the conductive material, but lithium ions can also enter and exit from the solid electrolyte via LPS smoothly. Therefore, in the positive electrode material of the present invention, reaction regions where the positive electrode active material, LPS, and conductive material coexist are 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 used as an active material in the electrode reaction, and the internal resistance of the battery is thought to be sufficiently reduced. As a result, the charge and discharge characteristics of the battery are thought to be improved. According to a preferred embodiment of the present invention, the phosphorus-containing component includes both phosphorus sulfide and its discharge products. Preferably, the phosphorus-containing component consists of both phosphorus sulfide and its discharge products. This can make the effects of the present invention more pronounced. Furthermore, according to another embodiment of the present invention, the phosphorus-containing component consists of phosphorus sulfide.

[0031] Here, it is possible to confirm whether or not phosphorus sulfide and / or its discharge products are present on the surface and inside the pores of the conductive material using various conventionally known methods. For example, by performing elemental mapping of each material using energy-dispersive X-ray spectroscopy (EDX) on cross-sectional images of the conductive material obtained by transmission electron microscopy (TEM), it is possible to confirm the arrangement of each material using the resulting elemental map and the count of elements from each material relative to the total count as indicators.

[0032] Furthermore, in this embodiment of the positive electrode material, the mass ratio (P / S) of phosphorus to sulfur contained in the positive electrode material is greater than 0 and less than or equal to 0.38. If the P / S ratio is 0, LPS formation does not occur during discharge, and therefore 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 decreases, and therefore the effects of the present invention cannot be obtained.

[0033] (Phosphorus-containing components consisting of phosphorus sulfide and / or its discharge products) Phosphorus sulfide is P x S y It is preferable that the phosphorus sulfide is represented by the formula P2S3, P2S5, (P4S 10 Examples include, but are not limited to, P4S3, P4S5, P4S7, and P4S9. Two or more of these may be used in combination.

[0034] The discharge products of phosphorus sulfide are not particularly limited, but examples include Li3PS4, Li4P2S7, Li4P2S6, and Li7P3S 11 Examples of LPS include the following.

[0035] (Elemental sulfur and / or its discharge products) The positive electrode material of the present invention preferably further contains, as a coating layer, a phosphorus-containing component consisting of phosphorus sulfide and / or its discharge products, as well as elemental sulfur and / or its discharge products. Elemental sulfur is an extremely high-capacity positive electrode active material. Therefore, this configuration allows for the acquisition of a higher-capacity positive electrode material. Furthermore, the in-situ formation reaction of LPS can proceed more efficiently. Consequently, a more significant resistance reduction effect can be obtained. Preferably, the positive electrode material further contains both elemental sulfur and its discharge products. This allows for a more significant acquisition of the effects of the present invention. In a preferred embodiment of the present invention, the phosphorus sulfide and elemental sulfur contained in the positive electrode material, as a whole, are P X S YA mixture having the following composition can be formed. In this case, X and Y are each 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, releasing lithium ions during charging and intercalating lithium ions during discharge through sulfur oxidation-reduction reactions. Furthermore, it can be easily supported on conductive materials by melting. As elemental sulfur, α-sulfur, β-sulfur, or γ-sulfur having an S8 structure can be used. During discharge, elemental sulfur can intercalate lithium ions and exist in the positive electrode material in the form of lithium (poly)sulfides. Specifically, discharge products of elemental sulfur include lithium (poly)sulfides such as Li2S. Note that the discharge products of phosphorus sulfide and elemental sulfur may be identical.

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

[0038] [ka]

[0039] 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, but a solid electrolyte may be further used in addition to phosphorus sulfide and elemental sulfur as raw materials. As will be described later, the positive electrode material of this embodiment can be manufactured by melt-impregnating phosphorus sulfide with a positive electrode active material such as sulfur into a conductive material. In this case, if a solid electrolyte is used as a raw material, the solid electrolyte is not melt-impregnated and is therefore difficult to place in surface depressions and pores of the conductive material. Therefore, the resistance reduction effect by adding a solid electrolyte may not be sufficiently obtained. Increasing the amount of solid electrolyte tends to reduce resistance, but if the solid electrolyte content is high, the proportion of positive electrode active material relatively decreases, and the energy density may decrease. Therefore, from the viewpoint of energy density, it is preferable that the positive electrode material of this embodiment does not contain solid electrolytes other than discharge products. In one embodiment, the positive electrode material has a lithium ion conductivity of 1 × 10⁻¹⁶ at room temperature (25°C) in addition to discharge products. -5 It does not contain solid electrolytes with a concentration of S / cm or higher.

[0040] The positive electrode material of this embodiment has a coating layer on the surface and inside the pores of the conductive material that contains 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 and inside the pores of the conductive material that contains 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 and inside the pores of the conductive material that contains 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 and inside the pores of the conductive material that consists of phosphorus sulfide and elemental sulfur.

[0041] The coating layer described above 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 components containing elements 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, rubeanoic acid (dithiooxamide), and polysulfide carbon. Examples of inorganic sulfur compounds include TiS2 and FeS2. Furthermore, components containing elements other than lithium, sulfur, or phosphorus may include phosphorus oxide and lithium halides (e.g., LiCl, LiBr, LiI). In addition, their discharge products may be included. In this case, the proportion of phosphorus-containing components and elemental sulfur and / or its discharge products in the total amount of the coating layer (100% by mass) 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 halogen elements. In a preferred embodiment of the present invention, the components constituting the coating layer do not contain elements other than lithium, sulfur, and phosphorus.

[0043] Furthermore, the positive electrode material in this embodiment may have a mass ratio (P / S) of phosphorus to sulfur (P / S) greater than 0 and 0.38 or less, but preferably 0.24 or less. Within this range, there is less excess phosphorus sulfide in the in-situ LPS generation reaction accompanying discharge. Since phosphorus sulfide has neither ionic nor electronic conductivity, the resistance reduction effect can be more pronounced by not having too much residual phosphorus sulfide. 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. The P / S ratio is not particularly limited as long as it is greater than 0, but it is preferable to have a P / S ratio of 0.03 or more so that sufficient LPS can be generated, 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 type and mixing ratio of phosphorus sulfide and elemental sulfur.

[0044] (Conductive material with pores) The positive electrode material according to this embodiment includes a conductive material having pores. The conductive material having pores is not particularly limited, but it is preferably a conductive porous body. By using a conductive porous body, phosphorus-containing components are 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 not particularly limited, and materials such as metals, conductive polymers, and carbon materials can be used as appropriate. Among these, from the viewpoint of excellent conductivity and ease of processing, it is preferable that the conductive material be made of carbon material. More preferably, the conductive material is a conductive porous body made of carbon material.

[0045] Examples of conductive porous materials made of carbon include activated carbon, carbon blacks such as Ketjenblack (registered trademark) (highly conductive carbon black), (oil) furnace black, channel black, acetylene black, thermal black, and lamp black, as well as carbon particles (carbon carriers) made of coke, natural graphite, and artificial graphite. Commercially available porous carbon materials such as Knobel (registered trademark) manufactured by Toyo Tanso Co., Ltd., which have many mesopores and interconnected mesopores, can also be used. Alternatively, a conductive porous material with a porous structure, in which the shape of the mold is transferred by mixing a mold such as ceramics with a carbon raw material such as resin, firing it in an inert atmosphere, and then dissolving the mold with acid, may be synthesized and used. In this case, the pore diameter and pore volume of the resulting conductive porous material can be changed by appropriately adjusting the particle size of the mold and the mixing ratio of the carbon raw material. Among these, activated carbon or porous carbon with interconnected mesopores is preferably used.

[0046] Furthermore, it is preferable that the carbon material's main component is carbon. Here, "main component is carbon" means that it contains carbon atoms as its main component, and is a concept that includes both being composed solely of carbon atoms and being substantially composed of carbon atoms. "Substantially composed of carbon atoms" means that the inclusion of impurities of about 2-3% by mass or less is permissible. In this specification, particulate carbon material whose main component is carbon is referred to as porous carbon particles.

[0047] The BET specific surface area of ​​the conductive material is 500 m². 2 It is preferable that it be 1 / g or more, and 800m 2 It is more preferable that it be 1200m or more per gram. 2 It is even more preferable that it be 1500m or more per gram. 2It is particularly preferable that it is / g or more. Further, 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 retained, and thus a sufficient amount of phosphorus-containing components and, when contained, elemental sulfur and / or its discharge products can be retained. Further, since the average thickness of the coating layer covering the conductive material does not become too thick, sufficient conductivity can be easily ensured, which is preferable. Further, the BET specific surface area of the conductive material is not particularly limited, but is preferably 3100 m 2 / g or less, more preferably 3000 m 2 / g or less, even more preferably 2500 m 2 / g or less, and particularly preferably 2000 m 2 / g or less. When it is within the above range, the coating layer can be formed more uniformly, so that the battery reaction can proceed more efficiently. The values of the BET specific surface area and pore volume of the conductive material can be measured by nitrogen adsorption and desorption measurement. This nitrogen adsorption and desorption measurement is performed using BELSORP mini manufactured by MicrotracBEL Corporation at a temperature of -196°C by the multi-point method. The BET specific surface area is determined from the adsorption isotherm in the relative pressure range of 0.01 < P / P0 < 0.05. Further, the pore volume is determined from the volume of adsorbed N2 at a relative pressure of 0.96.

[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 the phosphorus-containing components, elemental sulfur and / or its discharge products present at positions away from the pore walls inside the pores. The value of the average pore diameter of the conductive material can be calculated by nitrogen adsorption and desorption measurement in the same manner as when obtaining the values of the BET specific surface area and pore volume. In this specification, the pore distribution of the conductive material is adopted as that obtained using the BJH method.

[0049] The conductive material described above is not particularly limited, but it is preferable that the percentage of the pore volume of pores with a diameter in the range of 1 to 4 nm relative to the pore volume of pores with a diameter in the range of 1 to 100 nm is 20% or less. This allows phosphorus-containing components, elemental sulfur as a positive electrode active material, and / or their discharge products to be easily retained inside the pores. As a result, the internal resistance of the battery is thought to be 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%. On the other hand, there is no particular limit to the lower limit of the percentage, but for example, it is 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, "particle diameter of the conductive material" means the maximum distance L between any two points on the contour line of the conductive material. The value of "average particle diameter of the conductive material" shall be the value calculated as the arithmetic mean of the particle diameters of particles observed in several to tens of fields of view using observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0051] The amount of conductive material having pores 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 terms of mass ratio to phosphorus sulfide (or the total amount of phosphorus sulfide and elemental sulfur if elemental sulfur is further used). If the amount of conductive material is within the above range, a positive electrode material with sufficient conductivity can be obtained. In the positive electrode material of this embodiment, discharge products are formed from at least a portion of phosphorus sulfide (or phosphorus sulfide and elemental sulfur if elemental sulfur is included) during discharge, but it is preferable that the above range is satisfied in both the pre- and post-discharge and pre- and post-charge states. In a preferred embodiment, the amount of conductive material is, for example, 10 to 20% by mass, and preferably 11 to 19% by mass, in terms of charging ratio, with respect to the total amount of phosphorus sulfide, elemental sulfur, and conductive material.

[0052] In the positive electrode material of the present invention, it is preferable that the average thickness of the coating layer covering the surface of the conductive material is 5 nm or less. With this configuration, the effects of the present invention can be obtained even more significantly. Although phosphorus sulfide does not have electron conductivity, if the average thickness of the coating layer is 5 nm or less, it is thought that electrons can be supplied to the conductive material by the tunnel effect, and low reaction resistance can be maintained. 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. Furthermore, the average thickness of the coating layer is not particularly limited, but for example, it is 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, so that the battery reaction proceeds more efficiently and the charge / discharge characteristics can be further improved. The above average thickness can be determined by the method described in the examples. The above average thickness can be controlled by adjusting the type and mixing ratio 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 phosphorus sulfide and elemental sulfur during discharge, and it is preferable that the above range is satisfied in both the pre- and post-discharge and pre- and post-charge states.

[0053] (Manufacturing method by batch heating and impregnation) The positive electrode material according to this embodiment can be manufactured by a manufacturing method (a manufacturing method by batch heating and impregnation) that includes 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 it can be adjusted so that the mass ratio of phosphorus to sulfur (P / S) in the resulting cathode material is greater than 0 and less than or equal to 0.38.

[0055] For example, the charging ratio of elemental sulfur to phosphorus sulfide may be 17.25:1 to 0.75:1, and preferably 6:1 to 2:1. In one embodiment, the above charging ratio can be converted to S:P2S5, resulting in S:P2S5 = 69:1 to 3:1.

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

[0057] Furthermore, the process of mixing the above components is preferably carried out under an inert gas atmosphere with a controlled dew point. For example, it can be carried out under an inert gas atmosphere with a dew point of -60°C or lower.

[0058] There are no particular restrictions on the heat treatment temperature, but it is preferable that it be above 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, there are no particular restrictions on the upper limit of the heat treatment temperature, but for example, it is 500°C or lower, preferably 400°C or lower. There are also no particular restrictions on the heat treatment time, but for example, it is 0.5 to 20 hours, preferably 1 to 10 hours. In this way, phosphorus sulfide and elemental sulfur melt and mix to form the phosphorus polysulfide composition P X S Y It is thought that a compound is formed and composite formation with the conductive material proceeds in the molten state. As a result, phosphorus sulfide and elemental sulfur are not in separate states but P X S Y It is believed that this material can be introduced into the surface and pores of the conductive material in a state having a homogeneous composition. Therefore, a positive electrode material with reduced reaction resistance and excellent charge-discharge characteristics can be obtained.

[0059] The above heat treatment is preferably carried out under reduced pressure. This is preferable because it allows for the degassing of residual gases within the pores of the conductive material. The above heat treatment is not particularly limited, but for example, it can be carried out under reduced pressure of 100 Pa or less, preferably 10 Pa or less.

[0060] The positive electrode material obtained in this way contains a phosphorus polysulfide composition P inside the positive electrode material due to discharge. X S Y LPS can be generated as a discharge product from at least a portion of it. The specific discharge procedure is not particularly limited and can be carried out using general methods.

[0061] (Manufacturing method by sequential heating and impregnation) The positive electrode material according to this embodiment can be manufactured by a manufacturing method (manufacturing method by sequential heating and impregnation) which includes the steps of: heat-treating a porous conductive material and elemental sulfur to support the elemental sulfur in the gas phase on the conductive material; and mixing phosphorus sulfide with the conductive material on which the elemental sulfur is supported in the gas phase, and then heat-treating it further.

[0062] In this method, elemental sulfur is first supported on the conductive material by gas-phase support in a sublimation state. This allows for a homogeneous coating on the surface and within the pores of the conductive material. Therefore, a good electron conduction path can be established for the sulfur. Subsequently, phosphorus sulfide is mixed with the sulfur-supported conductive material and further heat-treated. This causes the phosphorus sulfide to melt and diffuse into the already supported sulfur, forming a homogeneous phosphorus (P) X S Y It is believed that a composition is formed. Here, elemental sulfur has a lower sublimation point compared to a mixture of elemental sulfur and phosphorus sulfide that has been pre-mixed, and can be supported in the gas phase. By supporting elemental sulfur in the gas phase, it is thought that a more uniform coating can be achieved, and the reaction interface area can be increased. Therefore, even if the amount of elemental sulfur and phosphorus sulfide used is about the same, it is thought that the reaction resistance can be reduced even further, and the charge-discharge characteristics can be further improved.

[0063] The heat treatment temperature in the process of supporting elemental sulfur in the 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. Except as described above, the process can be carried out under the same conditions as the heat treatment in the manufacturing method by batch heating and impregnation.

[0064] The heat treatment conditions in the process of mixing phosphorus sulfide with a conductive material on which elemental sulfur is supported in the gas phase, followed by heat treatment, can be the same as those used in the heat treatment in the manufacturing method using batch heating and impregnation. The specific method for mixing phosphorus sulfide with the conductive material on which elemental sulfur is supported in the gas phase is also the same as described above.

[0065] Aside from supporting elemental sulfur on the conductive material by heat impregnation, and then supporting phosphorus sulfide by heat impregnation, the specific form may preferably be the same as that used in the manufacturing method by simultaneous heat impregnation.

[0066] Furthermore, simply mechanically mixing the above-mentioned components such as phosphorus sulfide and elemental sulfur with a porous conductive material in a solid state will not allow the components to be placed inside the pores of the conductive material. In this case, the components such as phosphorus sulfide and elemental sulfur will only adhere to the surface of the conductive material particles. Consequently, these discharge products will not be placed inside the pores of the conductive material, but will 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, for example, a positive electrode active material, the Raman spectrum measured by micro-Raman spectroscopy using a laser with a wavelength of 532 nm shows 420 cm⁻¹. -1 PS4 derived from solid electrolytes is found nearby. 3-In some cases, a prominent peak corresponding to this may be observed. This is especially true when there is a step of dissolving and reprecipitation of a solid electrolyte using a solvent, at 1300-1700 cm⁻¹. -1 PS x O y n- In some cases, a prominent peak corresponding to the decomposition products of the solid electrolyte (by-reaction products between the solid electrolyte and the solvent) may be observed. On the other hand, in the cathode material of this embodiment, which does not use a solid electrolyte as a raw material, 420 cm² -1 PS4 originating from nearby solid electrolytes 3- Strong peaks corresponding to this are unlikely to occur. Also, since no solvent is used, 1300-1700 cm -1 No peaks corresponding to the decomposition products of the solid electrolyte in the range are produced. Furthermore, even after discharge, the positive electrode material of this embodiment does not produce peaks corresponding to 1300-1700 cm⁻¹. -1 No peaks corresponding to the decomposition products of solid electrolytes in this range are observed.

[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% by mass, and more preferably in the range of 40 to 90% by mass. In addition, the positive electrode active material layer may further contain known positive electrode materials (positive electrode active materials) in addition to the positive electrode material of this embodiment, to the extent that it does not impede the effects of the present invention. The content of the positive electrode material of this embodiment in the positive electrode active material layer is preferably 90% by mass or more, and more preferably 95% by mass or more.

[0069] Furthermore, the positive electrode active material layer may further contain a solid electrolyte that may be contained in the negative electrode active material layer, if necessary. The solid electrolyte content in the positive electrode active material layer is preferably in the range of 1 to 65% by mass, and more preferably in the range of 10 to 50% by 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 it is preferably in the range of 0.1 to 1000 μm.

[0071] Furthermore, the secondary battery according to this embodiment does not have to be all-solid type. That is, the solid electrolyte layer may further contain a conventionally known liquid electrolyte (electrolyte). There are no particular restrictions on the amount of liquid electrolyte (electrolyte) that can be contained in the solid electrolyte layer, but it is preferable that the amount is such that the shape of the solid electrolyte layer formed by the solid electrolyte is maintained and leakage of the liquid electrolyte (electrolyte) does not occur.

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

[0073] 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.

[0074] [Example 1] (Preparation of positive electrode material) In a glove box with an argon atmosphere and a dew point of -68°C or lower, 0.100g of porous carbon (Carbon 1, manufactured by Toyo Tanso Co., Ltd., Knobel® P(3)010, BET specific surface area 1640m²) was used as a conductive material. 20.440 g of sulfur (α-sulfur, S8, manufactured by Tsurumi Chemical Industries, Ltd.) and 0.06 g of diphosphorus pentasulfide (manufactured by Kojun Chemical Laboratory Co., Ltd.) were added to the ( / g) mixture. Here, the molar ratio of sulfur to diphosphorus pentasulfide was converted to S:P2S5, resulting in S:P2S5 = 51:1. After thoroughly mixing this in an agate mortar, the mixed powder was placed in a quartz container and sealed under reduced pressure of ~4 mbar. This container was then placed in a tubular furnace and heated at 350°C for 6 hours to melt the sulfur and diphosphorus pentasulfide and impregnate the porous carbon. In this example, the ratio of (total mass of sulfur and diphosphorus pentasulfide) to (mass of porous carbon) was set to 5:1.

[0075] [Examples 2-8] (Preparation of positive electrode material) In Example 1, the molar ratio of sulfur to phosphorus pentasulfide was changed as shown in Table 1 below. In each example, the ratio of (total mass of sulfur and phosphorus pentasulfide) to (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., with a BET specific surface area of ​​3040 m²) was used instead of carbon 1. 2 ( / g) and carbon 3 (Merck xGnP graphene nanoplatelets - grade C-500, BET specific surface area 500m²) 2 / g) was used. The cathode material was prepared using the same method as in Example 1, except for the above.

[0076] [Example 9] (Preparation of positive electrode material) In a glove box with an argon atmosphere and a dew point of -68°C or lower, 0.100g of porous carbon (Carbon 1, manufactured by Toyo Tanso Co., Ltd., Knobel® P(3)010, BET specific surface area 1640m²) was used as a conductive material. 2 0.454 g of sulfur (α-sulfur, S8, manufactured by Tsurumi Chemical Industry Co., Ltd.) was added to the mixture ( / g) and thoroughly mixed in an agate mortar. The mixed powder was then placed in a sealed pressure-resistant autoclave container and heated at 170°C for 3 hours to melt the sulfur, impregnate the porous carbon with sulfur, and obtain sulfur-impregnated porous carbon.

[0077] In a glove box with an argon atmosphere and a dew point of -68°C or lower, 0.046 g of phosphorus pentasulfide (manufactured by Kojun Chemical Laboratory Co., Ltd.) was added to 0.554 g of the sulfur-impregnated porous carbon prepared above. Here, the molar ratio of sulfur to phosphorus pentasulfide was S:P2S5 = 69:1. After thoroughly mixing this in an agate mortar, the mixed powder was placed in a quartz container and sealed under reduced pressure of ~4 mbar. This container was then placed in a tubular furnace and heated at 350°C for 6 hours to melt the phosphorus pentasulfide and compound it with the sulfur-impregnated porous carbon, thereby obtaining the cathode material.

[0078] [Examples 10-14] In Example 9 (Preparation of Cathode Material), the molar ratio of sulfur to phosphorus pentasulfide was changed as shown in Table 1 below. In each example, the ratio of (total mass of sulfur and phosphorus pentasulfide) to (mass of porous carbon) was set to 5:1. The cathode material was prepared using the same method as in Example 9, except for the above.

[0079] [Comparative Example 1] In Example 1 (Preparation of Cathode Material), the cathode material was prepared using the same method as in Example 1, except that the amount of sulfur was changed to 0.500 g and phosphorus pentasulfide was not added.

[0080] [Comparative Example 2] In Example 1 (Preparation of Cathode Material), the cathode material was prepared using the same method as in Example 1, except that the amount of phosphorus 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 and a dew point of -68°C or lower, porous carbon (Carbon 1, Knobel® P(3)010 manufactured by Toyo Tanso Co., Ltd., BET specific surface area 1640 m²) 2The following components were weighed: sulfur (α-sulfur, S8, manufactured by Tsurumi Chemical Industries, Ltd.), phosphorus pentasulfide (manufactured by Kojun Chemical Laboratory Co., Ltd.), with a molar ratio of sulfur to phosphorus pentasulfide of 18:1 when converted to S:P2S5, and (total mass of sulfur and phosphorus pentasulfide) : (mass of porous carbon) = 5:1. Each component was placed in a 45 mL zirconia container and processed at 370 rpm for 6 hours using a planetary ball mill (Fritsch, Premium line P-7) to obtain the cathode material.

[0082] (Average thickness of the coating layer) For each example and comparative example, the average thickness of the coating layer covering the conductive material was estimated. Here, "coating" means that when measuring the specific surface area of ​​the conductive material by the BET method, phosphorus-containing components and elemental sulfur and / or their discharge products (if present) as components of the coating layer adhere to the areas where nitrogen gas is adsorbed. The average thickness was calculated using the following formula.

[0083]

number

[0084] The BET specific surface area of ​​the conductive material was measured by nitrogen adsorption / desorption measurement. The volume of components constituting the coating layer is the total volume of components constituting the coating layer added per unit mass of the conductive material, with a sulfur (α-sulfur) density of 2.07 g / cm³. 3 The density of phosphorus pentasulfide is 2.05 g / cm³. 3 The amount of each component was estimated based on the amount used. The results are shown in Table 1 below.

[0085] (Micro-Raman spectroscopy analysis of cathode materials) In a glove box with an argon atmosphere and a dew point of -68°C or lower, the powder samples of the cathode material obtained above were placed on a glass plate, the surface was flattened, and Raman point measurements were performed at an excitation wavelength of 532 nm using a confocal microspectroscopy analyzer (WITec, α300). The Raman spectra of the cathode materials of Examples 3 and 12 obtained in this way are shown in Figure 2. As shown in Figure 2, the Raman spectra of the cathode materials obtained in this example are 470-475 cm⁻¹. -1 The range is 220-230cm -1 Approximately 155-165cm -1 A peak is observed nearby, which is thought to originate from SS bonds. Here, if there is a large amount of solid electrolyte present, it is the decomposition product PS4. 3- Corresponding to 420cm -1 Nearby (for example, 385-430cm) -1 A peak originating from PS bonding is expected to be observed in the range of 1300-1700 cm⁻¹, but no significant peak was observed in the cathode material of this example. Furthermore, when the cathode material is prepared by a method including the step of dissolving and reprecipitation of a solid electrolyte using a solvent, the Raman spectrum of the cathode material shows a peak in the range of 1300-1700 cm⁻¹. -1 A peak corresponding to the decomposition products of the solid electrolyte (by-reaction products between the solid electrolyte and the solvent) is observed in the range shown, but no such peak was observed in the cathode material of this example (not shown).

[0086] Furthermore, when the Raman spectrum of the positive electrode material of this embodiment was measured separately after discharge, it was found to be 420 cm⁻¹. -1 Nearby (for example, 385-430cm) -1 No significant peaks were observed in the range of 1300-1700 cm. -1 No peaks corresponding to the decomposition products of solid electrolytes in this range were observed.

[0087] Examples of test cell preparations (Preparation of positive electrode mixture) In a glove box under an argon atmosphere with a dew point of -68°C or lower, 40 g of 5 mm diameter zirconia balls, 0.375 g of the cathode material prepared in each example and comparative example, and 0.125 g of solid electrolyte (Ampcera, Li6PS5Cl) were placed in a 45 ml zirconia container and processed at 370 rpm for 6 hours using a planetary ball mill (Fritsch, Premium line P-7) to obtain a cathode mixture powder. The composition of the cathode mixture was cathode material:solid electrolyte = 75:25 (mass ratio).

[0088] (Fabrication of test cells (all-solid-state lithium secondary batteries)) The battery was fabricated in a glove box under an argon atmosphere with a dew point of -68°C or lower. A cylindrical convex punch (10 mm in diameter) made of stainless steel was inserted into one side of a cylindrical tube jig made by Macol (10 mm inner diameter, 23 mm outer diameter, 20 mm height), and 80 mg of sulfide solid electrolyte (Ampcera, Li6PS5Cl) was placed in from the top of the cylindrical tube jig. Then, another cylindrical convex punch made of stainless steel was inserted to sandwich the solid electrolyte, and a solid electrolyte layer with a diameter of 10 mm and a thickness of approximately 0.6 mm was formed inside the cylindrical tube jig by pressing with a hydraulic press at a pressure of 75 MPa for 3 minutes. Next, the cylindrical convex punch inserted from the top was temporarily removed, 7.5 mg of the positive electrode mixture prepared above was placed on one side of the solid electrolyte layer inside the cylindrical tube, the cylindrical convex punch (which also serves as the positive electrode current collector) was inserted again from the top, and pressed at a pressure of 300 MPa for 3 minutes 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 punched to a diameter of 8 mm (manufactured by Nilaco, thickness 0.20 mm) and an indium foil punched to a diameter of 9 mm (manufactured by Nilaco, thickness 0.30 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, and the cylindrical convex punch was inserted again and pressed at a pressure of 75 MPa for 3 minutes to form a lithium-indium negative electrode. As described above, a test cell (all-solid-state lithium secondary battery) was fabricated 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 each of the above examples and comparative examples were evaluated using the following methods. All of the following measurements were performed using a charge / discharge test apparatus (Hokuto Denko Co., Ltd., HJ-SD8) in a constant temperature chamber set to 25°C.

[0090] (Evaluation of capacity characteristics) The test cell is placed in a constant temperature bath, and after the cell temperature stabilizes, 0.2 mA / cm² is used for cell conditioning.2 Constant current discharge is performed at a current density down to a cell voltage of 0.5V, followed by constant current constant voltage charging at 2.5V with the same current density and a cutoff current of 0.01mA / cm². 2 The test was performed with the following settings. This conditioning charge-discharge cycle was repeated three times, and the discharge capacity of the third cycle was taken as the rated capacity. The capacity value per unit mass of sulfur (S) (mAh / gS) 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 unit 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 constant temperature bath, the cell's SOC (state of charge) was adjusted to 50%, and the current density was set to 0.2, 0.4, and 0.8 mA / cm². 2 The resistance value was calculated from the IV curve obtained by varying the current and discharging for 10 seconds. Before applying voltage at each current value, 0.2 mA / cm was used to achieve a SOC of 50%. 2 The device was charged using the following method. The results are shown in Table 1 below.

[0092] [Table 1]

[0093] The results shown in Table 1 indicate that, according to the present invention, the charge-discharge characteristics of a secondary battery using a positive electrode material containing sulfur can be improved. In contrast, the positive electrode material of Comparative Example 1, which does not use a component containing phosphorus sulfide, and the positive electrode material of Comparative Example 2, which has a P / S mass ratio greater than 0.38, have high reaction resistance and do not yield good charge-discharge characteristics. Furthermore, in the positive electrode material of Comparative Example 3, which is manufactured by a ball mill, it is not possible to place a layer containing phosphorus sulfide inside the pores of the conductive material, and therefore a sufficient resistance reduction effect cannot be obtained.

[0094] Furthermore, a comparison of Examples 1-8 and Examples 9-14 revealed that the cathode materials of Examples 9-14, in which sulfur and phosphorus sulfide were sequentially heated and impregnated, yielded superior charge-discharge characteristics. [Explanation of symbols]

[0095] 10A stacked 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 layers, 21 Power generation elements, 25 Negative electrode current collector plate, 27 Positive electrode current collector plate, 29. Laminating film.

Claims

1. A phosphorus-containing component comprising phosphorus sulfide and / or its discharge products, and a conductive material having pores, The phosphorus-containing component coats at least a portion of the surface of the conductive material and is arranged inside the pores to form a coating layer. The mass ratio (P / S) of phosphorus to sulfur in the positive electrode material is greater than 0 and less than or equal to 0.

38. The positive electrode material is characterized in that the conductive material is a conductive porous body with a BET specific surface area of ​​1200 to 2500 m² / g, and the average thickness of the coating layer is 1.0 nm or more and 4 nm or less.

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

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

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

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

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

7. A method for producing a positive electrode material, comprising the steps of: heat-treating a porous conductive material and elemental sulfur to support the elemental sulfur in the gas phase on the conductive material; and mixing phosphorus sulfide with the conductive material on which the elemental sulfur is supported in the gas phase, and further heat-treating the mixture.

8. A method for manufacturing a positive electrode material according to claim 7, wherein the heat treatment temperature in the step of heat-treating the conductive material having pores and elemental sulfur to support the elemental sulfur in the gas phase on the conductive material is 150 to 250°C, and the heat treatment temperature in the step of mixing phosphorus sulfide with the conductive material on which the elemental sulfur is supported in the gas phase and further heat-treating the material is greater than 170°C and less than or equal to 500°C.

9. A secondary battery comprising the positive electrode material according to claim 1 or 2.

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