Positive electrode material for electric device, and positive electrode for electric device and electric device using the same

Abstract

[Problem] To provide a means for improving capacity characteristics and charge / discharge rate characteristics in an electrical device using a positive electrode active material including sulfur. [Solution] A positive electrode material for an electrical device including a sulfur-containing positive electrode active material and a sulfur-containing solid electrolyte, the positive electrode material showing a peak in the range of 1400-1450 cm-1 of a Raman spectrum of microscopic Raman spectrometry using a laser with a wavelength of 532 nm.

Description

[Technical Field]

[0001] The present invention relates to a positive electrode material for an electric device, and a positive electrode for an electric device and an electric device using the same. [Background technology]

[0002] Metallic lithium, which is a negative electrode active material that supplies lithium ions to the positive electrode, is known as a high-capacity negative electrode material that can be used in all-solid-state batteries. However, in all-solid-state batteries that use metallic lithium as the negative electrode active material and a sulfide solid electrolyte as the solid electrolyte, the lithium metal and the sulfide solid electrolyte may react with each other, resulting in a deterioration in battery performance.

[0003] To address this problem, International Publication No. 2012 / 102037 proposes a technology for using a composite material containing a conductive agent and an alkali metal sulfide integrated on the surface of the conductive agent as a positive electrode material for an all-solid-state battery. According to Patent Document 1, by using a positive electrode material having such a configuration, a positive electrode material and a lithium-ion battery are provided that have a high theoretical capacity and can also use a negative electrode active material that does not supply lithium ions to the positive electrode. Summary of the Invention [Problem to be solved by the invention]

[0004] However, as described in Table 1 of International Publication No. 2012 / 102037, even when the above-mentioned technology is adopted, the discharge capacity that can be extracted is not necessarily sufficient, and there is a problem that the large theoretical capacity of the sulfur active material is not fully utilized. Furthermore, depending on the application of the secondary battery, it is not enough to simply have a large extractable capacity; it is also required that sufficient capacity can be extracted during charging and discharging at a high charge and discharge rate (i.e., so-called sufficient charge and discharge rate characteristics). For example, a secondary battery with insufficient charge and discharge rate characteristics cannot utilize sufficient capacity in response to rapid charging and discharging.

[0005] Therefore, an object of the present invention is to provide a means for improving the capacity characteristics and charge / discharge rate characteristics of an electric device using a positive electrode active material containing sulfur. [Means for solving the problem]

[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 using a positive electrode material for an electric device that includes a sulfur-containing positive electrode active material and a sulfur-containing solid electrolyte, and that exhibits a peak in a predetermined wavenumber region in a Raman spectrum, thereby completing the present invention. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a perspective view showing the appearance of a flat laminated type all-solid-state lithium secondary battery according to one embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view taken along line 2-2 shown in FIG. [Figure 3A] FIG. 3A is a cross-sectional schematic diagram of a prior art positive electrode material. [Figure 3B] FIG. 3B is a cross-sectional schematic diagram of a positive electrode material according to one embodiment of the present invention. [Figure 4A] FIG. 4A is a graph showing a Raman spectrum obtained by performing microscopic Raman spectroscopy using a laser with a wavelength of 532 nm on powder particles of the positive electrode material for an electric device prepared in Example 1. [Figure 4B] FIG. 4B is a graph showing a Raman spectrum obtained by performing microscopic Raman spectroscopy using a laser with a wavelength of 532 nm on the powder particles of the positive electrode material for an electric device prepared in Comparative Example 1. [Figure 5] FIG. 5 is a graph showing the change in charge capacity value when the positive electrode materials obtained in Example 1 and Comparative Example 1 were subjected to charging treatment at different charge rates. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, the above-mentioned embodiment of the present invention will be described with reference to the drawings. One embodiment of the present invention includes a cathode active material containing sulfur and a solid electrolyte containing sulfur, and in a Raman spectrum measured by microscopic Raman spectroscopy using a laser with a wavelength of 532 nm, the cathode active material has a peak intensity of 1400 to 1450 cm. -1 The positive electrode material for an electric device according to this embodiment can improve the capacity characteristics and charge / discharge rate characteristics of an electric device that uses a positive electrode active material containing sulfur.

[0009] Fig. 1 is a perspective view showing the appearance of a flat laminated type all-solid-state lithium secondary battery according to one embodiment of the present invention. Fig. 2 is a cross-sectional view taken along line 2-2 shown in Fig. 1. In this specification, the flat laminated type non-bipolar lithium ion secondary battery shown in Figs. 1 and 2 (hereinafter also simply referred to as a "laminated battery") will be described in detail as an example.

[0010] 1, the stacked battery 10a has a flat, rectangular shape, with a negative electrode current collector 25 and a positive electrode current collector 27 extending from both sides for extracting power. The power generating element 21 is wrapped in the battery exterior material (laminate film 29) of the stacked battery 10a, and the periphery is heat-sealed, with the negative electrode current collector 25 and positive electrode current collector 27 extending to the outside.

[0011] As shown in FIG. 2, the stacked battery 10a of this embodiment has a structure in which a flat, approximately 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 configuration in which a positive electrode, a solid electrolyte layer 17, and a negative electrode are laminated. The positive electrode has a structure in which positive electrode active material layers 15 containing a positive electrode active material are disposed on both sides of a positive electrode current collector 11". 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'. As a result, the adjacent positive electrode, solid electrolyte layer, and negative electrode constitute one single cell layer 19.

[0012] 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 have a structure in which they are sandwiched between the ends of laminate film 29, which is the battery exterior material, and are led out of laminate film 29. Below, the main components of the lithium ion secondary battery according to this embodiment will be described.

[0013] [Current collector] The current collector has a function of mediating the transfer of electrons from the electrode active material layer. There are no particular limitations on the material that constitutes the current collector. Note that, if the negative electrode active material layer and the positive electrode active material layer described below are themselves conductive and can exhibit a current collecting function, it is not necessary to use a current collector as a member separate from these electrode active material layers.

[0014] [Negative electrode (negative electrode active material layer)] In the stacked battery according to the embodiment shown in FIGS. 1 and 2, the negative electrode active material layer 13 contains a negative electrode active material. The type of negative electrode active material is not particularly limited, but examples include carbon materials, metal oxides, and metal active materials. Furthermore, a lithium-containing metal may be used as the negative electrode active material. Such a negative electrode active material is not particularly limited as long as it is a lithium-containing active material, and examples thereof include metallic lithium and lithium-containing alloys. Examples of lithium-containing alloys include alloys of Li with at least one of In, Al, Si, and Sn. The negative electrode active material preferably contains metallic lithium or a lithium-containing alloy, a silicon-based negative electrode active material, or a tin-based negative electrode active material, and more preferably contains metallic lithium or a lithium-containing alloy. When metallic lithium or a lithium-containing alloy is used as the negative electrode active material, the lithium secondary battery as an electric device 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. Therefore, in this configuration, the thickness of the negative electrode active material layer increases as the charging process progresses and decreases as the discharging process progresses. The negative electrode active material layer does not need to be present during full discharge, but in some cases, a negative electrode active material layer made of a certain amount of lithium metal may be present during full discharge.

[0015] 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.

[0016] 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.

[0017] 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 (where m and n are positive numbers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (where x and y are positive numbers, and M is any of P, Si, Ge, B, Al, Ga, and In).

[0018] The sulfide solid electrolyte may have, for example, a Li3PS4 skeleton, a Li4P2S7 skeleton, or a Li4P2S6 skeleton. Examples of sulfide solid electrolytes having a Li3PS4 skeleton include LiI-Li3PS4, LiI-LiBr-Li3PS4, and Li3PS4. Examples of sulfide solid electrolytes having a Li4P2S7 skeleton include Li-PS-based solid electrolytes known as LPS (for example, Li7P3S 11 ) can be mentioned. In addition, examples of sulfide solid electrolytes include Li (4-x) Ge (1-x) P xAn LGPS or the like represented by S4 (where 0 < x < 1) may be used. Among these, the sulfide solid electrolyte contained in the active material layer is preferably a sulfide solid electrolyte containing P element, and more preferably, the sulfide solid electrolyte is a material mainly composed of Li2S - P2S5. 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).

[0019] The ionic conductivity (e.g., Li ion conductivity) of the sulfide solid electrolyte at room temperature (25 °C) is, for example, 1×10 -5 S / cm or more, preferably, 1×10 -4 S / cm or more. The value of the ionic conductivity of the solid electrolyte can be measured by the AC impedance method.

[0020] Examples of the oxide solid electrolyte include compounds having a NASICON-type structure. Further examples of the oxide solid electrolyte include LiLaTiO (e.g., Li 0.34 La 0.51 TiO3), LiPON (e.g., Li 2.9 PO 3.3 N 0.46 ), LiLaZrO (e.g., Li7La3Zr2O 12 ), etc.

[0021] The content of the solid electrolyte 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.

[0022] In addition to the above-described negative electrode active material and solid electrolyte, the negative electrode active material layer may further contain at least one of a conductive assistant and a binder.

[0023] The thickness of the negative electrode active material layer varies depending on the configuration of the target secondary battery, but is preferably in the range of 0.1 to 1000 μm, for example.

[0024] [Solid electrolyte layer] In the stacked battery according to the embodiment shown in Figures 1 and 2, the solid electrolyte layer is a layer interposed between the above-described positive electrode active material layer and negative electrode active material layer, and essentially 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 employed. The solid electrolyte layer may further contain a binder in addition to the above-described predetermined solid electrolyte.

[0025] The thickness of the solid electrolyte layer varies depending on the configuration of the intended lithium ion secondary battery, but from the viewpoint of improving the volumetric energy density of the battery, it is preferably 600 μm or less, more preferably 500 μm or less, and even more preferably 400 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.

[0026] [Cathode active material layer] 1 and 2, the positive electrode active material layer contains a positive electrode material for an electric device according to one embodiment of the present invention. The positive electrode material for an electric device essentially contains a positive electrode active material containing sulfur and a solid electrolyte containing sulfur, and preferably further contains a conductive material.

[0027] (Cathode active material containing sulfur) The type of sulfur-containing cathode active material is not particularly limited, but includes elemental sulfur (S), lithium sulfide (LiS), and particles or thin films of organic or inorganic sulfur compounds. Any material can be used as long as it utilizes the sulfur redox reaction to release lithium ions during charging and absorb lithium ions during discharging. Inorganic sulfur compounds are particularly preferred due to their excellent stability. Specific examples include elemental sulfur (S), TiS, TiS, TiS, NiS, NiS, CuS, FeS, LiS, MoS, MoS, MnS, MnS, CoS, and CoS. Of these, S, S-carbon composite, TiS, TiS, TiS, TiS, FeS, and MoS are preferred. Elemental sulfur (S), lithium sulfide (LiS), TiS, and FeS are more preferred. Elemental sulfur (S) and lithium sulfide (LiS) are particularly preferred due to their high capacity.

[0028] The positive electrode material according to this embodiment may further contain a sulfur-free positive electrode active material in addition to the sulfur-containing positive electrode active material, provided that the proportion of the sulfur-containing positive electrode active material in the total amount (100% by mass) of the positive electrode active material is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, still more preferably 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 100% by mass.

[0029] (Sulfur-containing solid electrolyte) The cathode material according to the present embodiment essentially contains a sulfur-containing solid electrolyte. The specific form of the sulfur-containing solid electrolyte contained in the cathode material according to the present embodiment is not particularly limited, and the sulfur-containing solid electrolytes exemplified in the section on the negative electrode active material layer and their preferred forms may be similarly employed.

[0030] In particular, the solid electrolyte contained in the positive electrode material according to this embodiment is preferably a sulfide solid electrolyte. In another preferred embodiment, the sulfur-containing solid electrolyte contained in the solid electrolyte layer contains alkali metal atoms. Here, examples of alkali metal atoms that can be contained in the sulfur-containing solid electrolyte include lithium atoms, sodium atoms, and potassium atoms. Among these, lithium atoms are preferred because of their excellent ionic conductivity. In yet another preferred embodiment, the solid electrolyte contained in the solid electrolyte layer contains alkali metal atoms (e.g., lithium atoms, sodium atoms, or potassium atoms; preferably lithium atoms) and phosphorus atoms and / or boron atoms. In a preferred embodiment, the sulfide solid electrolyte contains Li6PS5X (where X is Cl, Br, or I, preferably Cl). These solid electrolytes have high ionic conductivity and can therefore effectively contribute to the development of the effects of the present invention.

[0031] (Conductive materials) The positive electrode material according to this embodiment preferably further contains a conductive material. The specific form of the conductive material contained in the positive electrode material according to this embodiment is not particularly limited, and conventionally known materials can be appropriately adopted. In particular, when the positive electrode material according to this embodiment contains a conductive material, it is more preferable that the conductive material has pores. The use of a conductive material having pores allows the positive electrode active material and solid electrolyte to be filled into the pores, which has the advantage of forming a three-phase interface consisting of these three materials, making the positive electrode reaction more likely to proceed. Furthermore, from the viewpoints of excellent conductivity, ease of processing, and ease of designing a desired pore distribution, the conductive material having pores is preferably a carbon material.

[0032] Examples of carbon materials having pores include carbon particles (carbon carriers) such as activated carbon, Ketjenblack (registered trademark) (highly conductive carbon black), (oil) furnace black, channel black, acetylene black, thermal black, lamp black, etc., coke, natural graphite, artificial graphite, etc. The carbon material preferably has carbon as its main component. Here, "having carbon as the main component" means containing carbon atoms as the main component, and includes both the concept of consisting only of carbon atoms and substantially consisting of carbon atoms. "Substantially consisting of carbon atoms" means that the inclusion of impurities of about 2 to 3 mass% or less is allowable.

[0033] The BET specific surface area of the conductive material (preferably a carbon material) having pores is preferably 200 m 2 / g or more, more preferably 500 m 2 / g or more, even more preferably 800 m 2 / g or more, particularly preferably 1200 m 2 / g or more, and most preferably 1500 m 2 / g or more. Also, 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 the positive electrode active material can be retained. The values of 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 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. Also, the pore volume is determined from the volume of adsorbed N2 at a relative pressure of 0.96.

[0034] The average pore diameter of the conductive material is not particularly limited, but is preferably 50 nm or less, and particularly preferably 30 nm or less. If the average pore diameter is within this range, electrons can be sufficiently supplied to the active material located far from the pore wall among the sulfur-containing positive electrode active materials arranged inside the pores. The average pore diameter of the conductive material can be calculated by nitrogen adsorption / desorption measurement as described above.

[0035] When the conductive material is particulate, the average particle size (primary particle size) 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 "particle size 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 size of the conductive material" is calculated as the average particle size of particles observed in 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).

[0036] As described above, the cathode material according to this embodiment includes a cathode active material containing sulfur and a solid electrolyte containing sulfur. When the cathode material further includes a conductive material having pores, it is preferable that at least a portion of the solid electrolyte and at least a portion of the cathode active material are disposed on the inner surfaces of the pores of the conductive material so as to be in contact with each other. Hereinafter, a preferred embodiment of this embodiment will be described with reference to the drawings.

[0037] FIG. 3A is a cross-sectional view of a cathode material 100′ according to the prior art. FIG. 3B is a cross-sectional view of a cathode material 100 according to one embodiment of the present invention. In FIGS. 3A and 3B, a conductive carbon material (e.g., activated carbon) 110 has numerous pores 110a. The pores 110a are filled with sulfur 120, a cathode active material. The cathode active material (sulfur) 120 is also disposed on the surface of the carbon material (activated carbon) 110. In the cathode material 100′ according to the prior art shown in FIG. 3A, the solid electrolyte 130 is disposed only on the surface of the carbon material (activated carbon) 110. In contrast, in the cathode material 100 according to one embodiment of the present invention shown in FIG. 3B, the solid electrolyte 130 is present in a highly dispersed state within the cathode active material (sulfur) 120, which is disposed on the surface of the carbon material (activated carbon) 110 and the inner surfaces of the pores of the carbon material (activated carbon) 110. More specifically, a continuous phase consisting of a positive electrode active material (sulfur) 120 fills the pores 110a and is also present on the surface of the carbon material (activated carbon) 110, and a solid electrolyte 130 is disposed as a dispersed phase within the continuous phase. This allows at least a portion of the solid electrolyte disposed on the surface of the conductive material (activated carbon) to be in contact with at least a portion of the positive electrode active material (sulfur) also disposed on the surface of the conductive material (activated carbon). This configuration allows for the formation of particularly large numbers of reaction sites (three-phase interfaces), effectively contributing to improved performance of electrical devices. Whether or not the positive electrode active material or solid electrolyte is disposed within the pores of the conductive material can be confirmed using various conventionally known techniques. For example, elemental mapping of each material can be performed using energy dispersive X-ray spectroscopy (EDX) on a transmission electron microscope (TEM) image of a cross section of the conductive material contained in the positive electrode material. The resulting elemental map and the counts of elements from each material relative to the counts of all elements can be used as indicators to confirm the arrangement of each material. For example, in the positive electrode material according to the present embodiment, if the sulfur-containing solid electrolyte essentially contains phosphorus atoms and there is no possibility that the phosphorus atoms are derived from other materials, it is possible to obtain the above-mentioned element map for phosphorus and confirm the arrangement form of the solid electrolyte from its distribution.The arrangement of the solid electrolyte can also be confirmed from the ratio of the number of phosphorus counts to the number of all elements counted in EDX. When the arrangement of the solid electrolyte is confirmed using the number of counts of elements derived only from the solid electrolyte as an index in EDX, if the ratio of the number of counts of elements derived only from the solid electrolyte to the number of all elements counted in EDX is 0.10 or more, it can be determined that the solid electrolyte is arranged inside the pores of the conductive material. The value of this ratio is preferably 0.15 or more, more preferably 0.20 or more, even more preferably 0.26 or more, and particularly preferably 0.35 or more. A larger value indicates that more solid electrolyte is arranged on the inner surface of the pores of the conductive material. Therefore, when the value of this ratio is within this range, the effects of the present invention can be more significantly exhibited. While there is no particular limitation on the preferred upper limit of this ratio, a preferred upper limit is, for example, 0.50 or less, more preferably 0.45 or less.

[0038] The positive electrode material for an electric device according to the present embodiment has a peak intensity of 1400 to 1450 cm in a Raman spectrum obtained by microscopic Raman spectroscopy using a laser with a wavelength of 532 nm on powder particles of the positive electrode material. -1 It is characterized by showing a peak in the range.

[0039] 4A is a graph showing the Raman spectrum obtained by performing microscopic Raman spectroscopy using a laser with a wavelength of 532 nm on the powder particles of the positive electrode material for an electric device prepared in Example 1 described later. As shown in FIG. 4A, the Raman spectrum of the positive electrode material for an electric device according to this embodiment first exhibits a peak at 600 cm -1 The Raman spectrum of the positive electrode material for an electric device according to the present invention shows peaks at 1430 cm in addition to the above-mentioned peaks. -1 A characteristic of this is that peaks are also observed in the vicinity.

[0040] According to the study by the present inventors, a cathode active material containing sulfur and a solid electrolyte containing sulfur exhibit a Raman spectrum of 1400 to 1450 cm in a micro-Raman spectrum using a laser with a wavelength of 532 nm. -1 It has been found that when an electric device such as an all-solid-state lithium secondary battery is constructed using a cathode material that exhibits a peak in the range of 1400 to 1450 cm, the capacity characteristics and charge / discharge rate characteristics can be significantly improved. Although the mechanism behind this is not completely clear, the following mechanism is presumed. That is, the cathode material having the above-mentioned predetermined peak according to this embodiment can be produced, for example, by mixing a cathode active material containing sulfur with a solid electrolyte containing sulfur to obtain a mixture, as described below, and then heating this mixture at a relatively high temperature (185°C in Example 1). On the other hand, in Comparative Example 1, which was not subjected to this heat treatment, the peak was 1400 to 1450 cm, as shown in FIG. 4B. -1 Therefore, it is thought that an intermediate layer consisting of some component with excellent ionic conductivity is formed at the interface where the sulfur-containing cathode active material and the sulfur-containing solid electrolyte come into contact during the heat treatment at a relatively high temperature as described above. The nature of this component is also unknown, but for example, at the contact interface between elemental sulfur (S) and a phosphorus-containing sulfide solid electrolyte, a sulfur (S)-rich ion-conducting layer (Li6PS 5+n Cl, Li3PS 4+n The Raman band corresponding to the double bond in the compound is the 1400-1450 cm -1 It is estimated that a peak in the range of

[0000] will be observed. Of course, it is thought that the composition of the compound formed at the contact interface will change depending on the type of active material and solid electrolyte, so it is not essential to form a compound having the above-mentioned composition. As a result of the intermediate layer having excellent ionic conductivity being interposed between the positive electrode active material and the solid electrolyte, the charge-discharge reaction can proceed sufficiently even when charge-discharge cycles are advanced, and it is thought that the capacity characteristics and cycle durability are significantly improved.

[0041] An example of a method for producing the cathode material according to the present embodiment having the above-described configuration will be described. As described above, the excellent capacity characteristics and charge / discharge rate characteristics of the cathode material according to the present embodiment are presumably due to the presence of an ion-conductive compound present at the contact interface between the sulfur-containing cathode active material and the sulfur-containing solid electrolyte. It is believed that this ion-conductive compound is generated by heat treatment at a relatively high temperature. Therefore, the cathode material according to the present embodiment is presumably obtained by heat-treating a mixture of a sulfur-containing cathode active material and a sulfur-containing solid electrolyte at a high temperature. The heat treatment temperature is not particularly limited, but is preferably above 170°C, more preferably 175°C or higher, even more preferably 180°C or higher, and particularly preferably 185°C or higher. The upper limit of the heat treatment temperature is also not particularly limited, but is, for example, 250°C or lower, preferably 200°C or lower. The heat treatment time is also not particularly limited, but may be approximately 1 to 5 hours. When performing this heat treatment, it is sufficient that the sulfur-containing cathode active material and the sulfur-containing solid electrolyte are present in a mixed state. It is preferable that the mixture further contains a conductive material. When the mixture contains a porous conductive material, the heat treatment described above can fill the pores of the conductive material with the sulfur-containing cathode active material and the sulfur-containing solid electrolyte, resulting in a preferred cathode material with numerous three-phase interfaces. The means for obtaining the mixture containing the three components are not particularly limited, but examples include mixing using a mixing means such as a mortar or milling using a pulverizing means such as a planetary ball mill. From the perspective of achieving a larger initial capacity and better charge / discharge rate characteristics, it is preferable to subject the mixture obtained by milling to the heat treatment described above. Alternatively, instead of the three-component mixture described above, a mixture of the sulfur-containing cathode active material and the sulfur-containing solid electrolyte may first be obtained by mixing or milling, and then the heat treatment described above can be applied to the mixture. Subsequently, an additional conductive material can be added, followed by a mixing process such as mixing or milling to obtain a cathode material containing the three components according to one embodiment of the present invention.

[0042] Another manufacturing method may involve preparing a mixture of a conductive material and a sulfur-containing solid electrolyte by mixing or milling, adding a sulfur-containing cathode active material to the mixture, and then subjecting the mixture to the heat treatment described above. This method allows the cathode active material and the solid electrolyte to penetrate into the pores of the porous conductive material through the heat treatment, resulting in a preferred cathode material in which multiple three-phase interfaces are formed. The mixture of the porous conductive material and the sulfur-containing cathode active material may also be prepared by a wet method rather than the dry method described above. For example, a solution of the solid electrolyte in a suitable solvent capable of dissolving the solid electrolyte is first prepared, and then the porous conductive material is impregnated therein. If necessary, the solution is heated to a temperature of approximately 100 to 180°C for approximately 1 to 5 hours to obtain a solid electrolyte / conductive material composite. In this composite, the solid electrolyte typically penetrates and adheres to the pores of the conductive material. Next, by adding a sulfur-containing cathode active material to this composite and then subjecting it to the heat treatment described above, the cathode active material is melted and penetrates into the pores of the conductive material, resulting in a cathode material with a favorable form in which numerous three-phase interfaces are formed. This manufacturing method using a wet process can produce a cathode material that is particularly excellent in initial capacity characteristics and charge / discharge rate characteristics.

[0043] The content of the positive electrode active material 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 %, for example. Note that this content value is calculated based on the mass of only the positive electrode active material excluding the conductive material and solid electrolyte.

[0044] The positive electrode active material layer may further contain a conductive additive (one that does not hold the positive electrode active material or solid electrolyte inside the pores) and / or a binder. Similarly, the positive electrode active material layer preferably further contains a solid electrolyte in addition to the above-mentioned positive electrode material.

[0045] The above describes one embodiment of a lithium secondary battery to which the positive electrode material according to the present invention can be applied. However, the present invention is not limited to the configuration described in the above embodiment and can be modified as appropriate based on the claims. For example, a bipolar battery can also be used as a type of battery to which the lithium secondary battery can be applied. The solid electrolyte layer of the lithium secondary battery may further contain a conventionally known liquid electrolyte (electrolytic solution). In this case, the amount of the liquid electrolyte (electrolytic solution) is preferably an amount that maintains the shape of the solid electrolyte layer formed by the solid electrolyte and prevents leakage of the liquid electrolyte (electrolytic solution). [Example]

[0046] 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.

[0047] <<Example of test cell production>> [Example 1] (Preparation of sulfur-containing cathode materials) In a glove box with an argon atmosphere at a dew point of -68°C or less, sulfur (manufactured by Aldrich), a sulfide solid electrolyte (manufactured by Ampcera, Li6PS5Cl), and carbon (manufactured by Kansai Coke and Chemicals Co., Ltd., activated carbon, MSC-30) were weighed out. The components were weighed out so that the mass ratio of sulfur:sulfide solid electrolyte:carbon was 50:40:10. The components were then thoroughly mixed in an agate mortar, and the mixed powder was placed in a sealed pressure-resistant autoclave and heated at 185°C for 3 hours. This melted the sulfur, allowing it to impregnate the carbon, yielding a powder of sulfur-containing positive electrode material.

[0048] (Microscopic Raman spectroscopy of sulfur-containing cathode materials) Microscopic Raman spectroscopy was performed on the powder particles of the sulfur-containing positive electrode material to obtain a Raman spectrum. Here, the Raman analyzer used was an HR manufactured by HORIBA. The measurement conditions were a 100x objective lens, a 532 nm wavelength laser as incident light, and a 0.1 mm slit width. The measurement range was 0 to 2000 cm. -1 The measurement time was 10 seconds, and the number of accumulations was 24. The Raman spectrum thus obtained is shown in FIG. 4A. As shown in FIG. 4A, the Raman spectrum of the sulfur-containing positive electrode material obtained in this example first shows a peak at 600 cm -1 The following regions show peaks that are thought to be derived from the sulfur active material and the sulfide solid electrolyte. In addition to the above peaks, the Raman spectrum of the sulfur-containing positive electrode material obtained in this example also shows a peak at 1430 cm -1 A peak was also observed nearby.

[0049] (Production of test cells (all-solid-state lithium secondary batteries)) The battery was fabricated in a glove box with an argon atmosphere at a dew point of -68°C or below. A 10mm diameter stainless steel cylindrical punch was inserted into one side of a Macor cylindrical tube jig (inner diameter 10mm, outer diameter 23mm, height 20mm), and 80mg of sulfide solid electrolyte (Li6PS5Cl, manufactured by Ampcera) was placed from the top of the cylindrical tube jig. The other 10mm diameter stainless steel cylindrical punch was then inserted to sandwich the solid electrolyte. The tube was then pressed at 75MPa for 3 minutes using a hydraulic press to form a 10mm diameter, approximately 0.6mm thick solid electrolyte layer in the cylindrical tube jig. Next, the cylindrical convex punch inserted from above was removed, and 7.5 mg of the sulfur-containing positive electrode material 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 from above and pressed at 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 (also serving as a 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 negative electrodes. The cylindrical tube was inserted from the bottom so that the indium foil was positioned next to the solid electrolyte layer. The cylindrical convex punch was inserted again and pressed at 75 MPa for 3 minutes to form a lithium-indium negative electrode. In this manner, a test cell (all-solid-state lithium secondary battery) was produced in which a negative electrode current collector (punch), a lithium-indium negative electrode, a solid electrolyte layer, a positive electrode active material layer, and a positive electrode current collector (punch) were stacked in this order.

[0050] [Example 2] A test cell was prepared in the same manner as in Example 1, except that the components of the positive electrode material were mixed using a planetary ball mill instead of an agate mortar. The components were mixed in a 45 mL zirconia container and milled for 6 hours at 370 rpm using a planetary ball mill (Fritsch, Premium line P-7). The sulfur-containing positive electrode material prepared in this example was subjected to microscopic Raman spectroscopy in the same manner as above to obtain a Raman spectrum. As a result, similar to Example 1 (FIG. 4A), a Raman spectrum was obtained from the 1400-1450 cm -1 A peak was observed in the region of

[0051] [Example 3] In a glove box with an argon atmosphere and a dew point of −68°C or lower, a predetermined amount of sulfur (manufactured by Aldrich) and a predetermined amount of sulfide solid electrolyte (manufactured by Ampcera, Li6PS5Cl) were weighed out. The weighed components were then thoroughly mixed in an agate mortar, and the mixed powder was placed in a sealed pressure-resistant autoclave and heated at 185°C for 3 hours. This melted the sulfur, yielding a sulfur active material / sulfide solid electrolyte composite. A predetermined amount of carbon (activated carbon, MSC-30, manufactured by Kansai Coke and Chemicals Co., Ltd.) was then weighed out and thoroughly mixed with the sulfur active material / sulfide solid electrolyte composite in the agate mortar to obtain a powder of sulfur-containing positive electrode material. The components were weighed out so that the mass ratio of sulfur:sulfide solid electrolyte:carbon was 50:40:10. A test cell was fabricated in the same manner as in Example 1, except that the sulfur-containing positive electrode material thus obtained was used. The sulfur-containing positive electrode material prepared in this example was subjected to microscopic Raman spectroscopy in the same manner as described above to obtain a Raman spectrum. As a result, similar to Example 1 (FIG. 4A), a peak at 1400 to 1450 cm -1 A peak was observed in the region of

[0052] [Example 4] First, in a glove box with an argon atmosphere below -68°C, 2.00 g of sulfide solid electrolyte (Li6PS5Cl, manufactured by Ampcera) was added to 100 ml of ultra-dehydrated ethanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and stirred until the solution became clear, dissolving the solid electrolyte in the ethanol. 1.00 g of carbon (MSC-30, activated carbon, manufactured by Kansai Thermal Chemicals Co., Ltd.) was added to the resulting solid electrolyte ethanol solution and stirred thoroughly to fully disperse the carbon in the solution. The container containing this carbon dispersion was connected to a vacuum device, and the pressure in the container was reduced to below 1 Pa using an oil-sealed rotary pump while stirring the carbon dispersion in the container with a magnetic stirrer. Because the solvent ethanol volatilizes under reduced pressure, the ethanol was removed over time, leaving the carbon impregnated with the solid electrolyte in the container. After removing the ethanol under reduced pressure, the container was heated to 150°C under reduced pressure and heat-treated for 3 hours to obtain a sulfide solid electrolyte / carbon composite. Next, a predetermined amount of sulfur (manufactured by Aldrich) was weighed and thoroughly mixed with the sulfide solid electrolyte / carbon composite obtained above in an agate mortar. The mixed powder was then placed in a sealed pressure-resistant autoclave and heated at 185°C for 3 hours. This melted the sulfur, allowing it to impregnate the carbon, resulting in a sulfur active material / sulfide solid electrolyte / carbon composite. Next, the sulfur active material / sulfide solid electrolyte / carbon composite and a separately weighed predetermined amount of sulfide solid electrolyte were placed in a 45 mL zirconia container and milled in a planetary ball mill (Fritsch, Premium line P-7) at 370 rpm for 6 hours to obtain a powder of sulfur-containing positive electrode material. Note that each component was weighed so that the mass ratio of sulfur:(sulfide solid electrolyte in the sulfide solid electrolyte / carbon composite):remaining sulfide solid electrolyte:carbon = 50:20:20:10. A test cell was fabricated using the same method as in Example 1 described above, except for using the sulfur-containing positive electrode material obtained in this manner. The sulfur-containing positive electrode material prepared in this example was subjected to microscopic Raman spectroscopy in the same manner as described above to obtain a Raman spectrum. As a result, similar to Example 1 (FIG. 4A), a peak at 1400 to 1450 cm -1 A peak was observed in the region of

[0053] [Comparative Example 1] A test cell was prepared in the same manner as in Example 1, except that the heat treatment at 185°C for 3 hours in a sealed pressure-resistant autoclave was not performed in the preparation of the sulfur-containing positive electrode material. The Raman spectrum of the sulfur-containing positive electrode material prepared in this comparative example was obtained by microscopic Raman spectroscopy in the same manner as above. The Raman spectrum thus obtained is shown in FIG. 4B. As shown in FIG. 4B, the Raman spectrum of the sulfur-containing positive electrode material obtained in this comparative example was first obtained at 600 cm, similar to FIG. 4A. -1 The Raman spectrum of the sulfur-containing positive electrode material obtained in this comparative example showed peaks in the range of 1400 to 1450 cm , which are thought to be derived from the sulfur active material and the sulfide solid electrolyte, respectively. -1 No peak was observed in the region.

[0054] Comparative Example 2 A test cell was fabricated in the same manner as in Example 2, except that the heat treatment at 185°C for 3 hours in a sealed pressure-resistant autoclave was not performed in the preparation of the sulfur-containing positive electrode material. The Raman spectrum of the sulfur-containing positive electrode material prepared in this comparative example was obtained by microscopic Raman spectroscopy in the same manner as above. As a result, as shown in FIG. 4B, a Raman spectrum of 600 cm -1 Although several peaks were observed in the region of 1400–1450 cm -1 No peak was observed in the region.

[0055] <Test cell evaluation example> The test cells prepared in the above comparative examples and examples were evaluated for capacity characteristics and charge / discharge rate characteristics by the following methods. 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.

[0056] (Evaluation of capacity characteristics and charge rate characteristics) The test cell was placed in a thermostatic chamber, and after the cell temperature had stabilized, a current of 0.2 mA / cm was applied as cell conditioning. 2 The cell was discharged to a cell voltage of 0.5 V at a current density of 0.01 mA / cm. The cell was then subsequently charged to 2.5 V at a constant current and constant voltage with a cut-off current of 0.01 mA / cm. 2 The charging / discharging cycle was repeated 10 times. After full discharge at 0.05C with a cutoff voltage of 0.5V, the battery was charged at a constant current of 0.05C with a cutoff voltage of 2.5V, and the charge capacity at 0.05C was measured. Similarly, a separate constant current charge at 0.2C with a cutoff voltage of 2.5V was performed, and the charge capacity at 0.2C was also measured. The percentage of the charge capacity obtained by constant current charging at 0.2C relative to the charge capacity obtained by constant current charging at 0.05C (charge capacity retention) was calculated. The results are shown in Table 1 below, along with the charge capacity values at each rate.

[0057] [Table 1]

[0058] Furthermore, the charge capacity values of the positive electrode materials obtained in Example 1 and Comparative Example 1 were measured in the same manner as above at charge rates of 0.1 C, 0.5 C, and 1.0 C, and the results are shown in Figure 5 together with the results shown in Table 1. From the results shown in Table 1 and Figure 5, it can be seen that according to the present invention, improvements in capacity characteristics and charge / discharge rate characteristics can be achieved in all-solid-state lithium secondary batteries using a positive electrode active material containing sulfur. [Explanation of symbols]

[0059] 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, 100, 100' positive electrode material, 110 carbon material (activated carbon), 110a pores, 120 positive electrode active material (sulfur), 130 solid electrolyte.

Claims

1. a cathode active material containing sulfur and a solid electrolyte containing sulfur, further comprising a conductive material; The pore volume of the conductive material is 1.0 mL / g or more; the solid electrolyte / conductive material composite is obtained by removing the solvent from a solution containing the conductive material and the sulfur-containing solid electrolyte, and then the sulfur-containing cathode active material is added to the solid electrolyte / conductive material composite, and the composite is subjected to a heat treatment at a temperature higher than 170°C and not higher than 250°C; In the Raman spectrum of microscopic Raman spectroscopy using a laser with a wavelength of 532 nm, －１ This positive electrode material for electrical devices exhibits a peak in the range

2. 2. The positive electrode material for an electric device according to claim 1, wherein the positive electrode active material is elemental sulfur or lithium sulfide.

3. 3. The positive electrode material for an electric device according to claim 1, wherein the solid electrolyte is a sulfide solid electrolyte containing alkali metal atoms and phosphorus atoms and / or boron atoms.

4. 4. The positive electrode material for an electrical device according to claim 3, wherein the alkali metal is lithium.

5. 5. The positive electrode material for an electrical device according to claim 1, wherein the conductive material has an average pore size of 50 nm or less.

6. 6. The positive electrode material for an electrical device according to claim 1, wherein the conductive material is a carbon material.

7. 7. The positive electrode material for an electric device according to claim 1, wherein in a TEM-EDX observation image of a cross section of the conductive material contained in the positive electrode material, the ratio of the count number of elements derived only from the solid electrolyte to the count number of all elements is 0.10 or more.

8. 8. The positive electrode material for an electric device according to claim 1, wherein at least a portion of the solid electrolyte and at least a portion of the positive electrode active material are disposed on inner surfaces of the pores so as to be in contact with each other.

9. 9. The positive electrode material for an electric device according to claim 8, wherein a continuous phase made of the positive electrode active material fills the inside of the pores, and the solid electrolyte is disposed as a dispersed phase in the continuous phase.

10. A positive electrode for an electric device, comprising the positive electrode material for an electric device according to any one of claims 1 to 9.

11. An electric device comprising the positive electrode for an electric device according to claim 10.

12. The electrical device according to claim 11, which is an all-solid-state lithium secondary battery.

13. A method for producing a positive electrode material for an electric device, comprising: removing a solvent from a solution containing a conductive material having a pore volume of 1.0 mL / g or more and a solid electrolyte containing sulfur, to obtain a solid electrolyte / conductive material composite; and then adding a positive electrode active material containing sulfur to the solid electrolyte / conductive material composite, and subjecting the solid electrolyte / conductive material composite to a heat treatment at a temperature higher than 170°C and not higher than 250°C.

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