Patent Application
20240347723
The present invention relates to a positive electrode material for an electric device, a positive electrode for an electric device and an electric device using the positive electrode material for an electric device.
A known large-capacity negative electrode material to be used in an all-solid battery is metallic lithium, i.e., a negative electrode active material which supplies lithium ions to a positive electrode. However, in an all-solid battery which uses metallic lithium as a negative electrode active material and a sulfide solid electrolyte as a solid electrolyte, the metallic lithium reacts with the sulfide solid electrolyte, and thus the battery characteristics may be deteriorated.
Here, for the purpose of addressing such a problem, WO 2012/102037 proposes a technique in which a composite material containing a conductive agent and an alkali metal sulfide integrated with the surface of the conductive agent is used as a positive electrode material for an all-solid battery. According to WO 2012/102037, use of a positive electrode material having such a configuration makes it possible to provide a positive electrode material as well as a lithium-ion battery which have a high theoretical capacity and can use a negative electrode active material which does not supply lithium ions to the positive electrode.
However, as described in Table 1 of WO 2012/102037, even when the above technique is adopted, it cannot be necessarily said that the discharge capacity to be taken out is sufficient, and there is a problem that a sulfur active material having large theoretical capacity cannot be fully utilized. Further, depending on the application of the secondary battery, it is insufficient that the capacity to be taken out is large, and it is also required that a sufficient capacity can be taken out during discharging and charging at a high charge-discharge rate (i.e., so-called charge-discharge rate capability is required to be sufficient). For example, a secondary battery having insufficient charge-discharge rate capability cannot utilize a sufficient capacity in response to rapid discharging and charging.
Therefore, an object of the present invention is to provide a means for enhancing capacity performance and charge-discharge rate capability of an electric device which uses a positive electrode active material containing sulfur.
The present inventors have carried out a diligent study in order to solve the problem described above. As a result, it has been found that the problem described above can be solved by using a positive electrode material for an electric device showing a peak in a predetermined wave number region of a Raman spectrum among positive electrode materials for an electric device containing a sulfur-containing positive electrode active material and a sulfur-containing solid electrolyte, and the present invention has been completed.
Hereinafter, the embodiments of the present invention described above will be described with reference to drawings. One aspect of the present invention is a positive electrode material for an electric device that contains a sulfur-containing positive electrode active material and a sulfur-containing solid electrolyte, and shows a peak in a range of 1400 to 1450 cm−1 in a Raman spectrum of microscopic Raman spectrometry using a laser with a wavelength of 532 nm. With the positive electrode material for an electric device according to the present aspect, capacity characteristics and charge-discharge rate characteristics can be improved in an electric device using a sulfur-containing positive electrode active material.
As illustrated in
As illustrated in
The negative electrode has a structure in which a negative electrode active material layer 13 containing a negative electrode active material is disposed on both surfaces of a negative electrode current collector 11′. Thus, the positive electrode, solid electrolyte layer, and negative electrode that are adjacent constitute one single battery layer 19.
The negative electrode current collector 11′ and the positive electrode current collector 11″ have a structure in which a negative electrode current collecting plate (tab) 25 and a positive electrode current collecting plate (tab) 27 which are electrically connected to the respective electrodes (the positive electrode and the negative electrode) are respectively attached to the negative electrode current collector 11′ and the positive electrode current collector 11″ and are led to an outside of the laminate film 29 so as to be sandwiched between ends of the laminate film 29 as the outer casing material. Hereinafter, main constituent members of the lithium-ion secondary battery according to the present aspect is applied will be described.
A current collector has a function of mediating transfer of electrons from electrode active material layers. Further, as long as a negative electrode active material layer and a positive electrode active material layer to be described later have conductivity by themselves and can have a current collecting function, a current collector as a member different from these electrode active material layers is not necessarily used.
In a laminate type battery according to the embodiment illustrated in
The content of the negative electrode active material in the negative electrode active material layer is not particularly limited, but for example, is preferably within a range of 40 to 99 mass %, and more preferably within a range of 50 to 90 mass %.
Preferably, the negative electrode active material layer further contains a solid electrolyte. When the negative electrode active material layer contains the solid electrolyte, the ion conductivity of the negative electrode active material layer can be improved. Examples of the solid electrolyte include a sulfide solid electrolyte and an oxide solid electrolyte, and a sulfide solid electrolyte is preferred.
Examples of the sulfide solid electrolyte 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, Li2S—P2S5—ZmSn (where m and n are positive numbers, and Z is any of Ge, Zn, and Ga), Li2S—GeS2, Li2S—SiS2—Li3PO4, Li2S—SiS2—LixMOy (where x and y are positive numbers, and M is any of P, Si, Ge, B, Al, Ga, and In), and the like.
The sulfide solid electrolyte may have, for example, 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. Examples of the sulfide solid electrolyte having a Li4P2S7 skeleton include a Li—P—S-based solid electrolyte called LPS (e.g., Li7P3S11). As the sulfide solid electrolyte, for example, LGPS expressed by Li(4−x)Ge(1−x)PxS4 (x satisfies 0<x<1) or the like may be used. Above all, the sulfide solid electrolyte contained in the active material layer is preferably a sulfide solid electrolyte containing a P element, and the sulfide solid electrolyte is more preferably a material containing Li2S—P2S5 as a main component. Furthermore, the sulfide solid electrolyte may contain halogen (F, Cl, Br, I). In one preferred embodiment, the sulfide solid electrolyte contains Li6PS5X (where X is Cl, Br, or I, preferably Cl).
Ion conductivity (e.g., Li ion conductivity) of the sulfide solid electrolyte at a normal temperature (25° C.) is, for example, preferably 1×10−5 S/cm or more, and more preferably 1×10−4 S/cm or more. A value of the ion conductivity of the solid electrolyte can be measured by an AC impedance method.
Examples of the oxide solid electrolyte include a compound having a NASICON-type structure, and the like. Other examples of the oxide solid electrolyte include LiLaTiO (e.g., Li0.34La0.51TiO3), LiPON (e.g., Li2.9PO3.3N0.46), LiLaZrO (e.g., Li7La3Zr2O12), and the like.
The content of the solid electrolyte in the negative electrode active material layer is, for example, preferably within a range of 1 to 60 mass %, and more preferably within a range of 10 to 50 mass %.
The negative electrode active material layer may further contain at least one of a conductive aid and a binder in addition to the negative electrode active material and the solid electrolyte described above.
The thickness of the negative electrode active material layer varies depending on the configuration of the intended secondary battery, but is preferably, for example, within a range of 0.1 to 1000 m.
In the laminate type battery according to the embodiment as shown in
The thickness of the solid electrolyte layer varies depending on the configuration of the intended lithium-ion secondary battery, but is preferably 600 μm or less, more preferably 500 μm or less, and still more preferably 400 μm or less from the viewpoint that the volume energy density of the battery can be improved. Meanwhile, the lower limit of the thickness of the solid electrolyte layer is not particularly limited, but is preferably 1 μm or more, more preferably 5 μm or more, and still more preferably 10 μm or more.
In the laminate type battery according to the embodiment illustrated in
The type of the sulfur-containing positive electrode active material is not particularly limited, but examples thereof include a particle or a thin film of an organic sulfur compound or an inorganic sulfur compound in addition to a sulfur simple substance (S) and lithium sulfide (Li2S), and any material may be used as long as the material can release lithium ions during charge and occlude the lithium ions during discharge by utilizing an oxidation-reduction reaction of the sulfur. In particular, the inorganic sulfur compound is preferable for being excellent in stability, and specific examples thereof include the sulfur simple substance (S), TiS2, TiS3, TiS4, NiS, NiS2, CuS, FeS2, Li2S, MoS2, MoS3, MnS, MnS2, CoS, CoS2, or the like. Among the compounds, the S, an S-carbon composite, TiS2, TiS3, TiS4, FeS2, and MoS2 are preferable, the sulfur simple substance (S) and the lithium sulfide (Li2S), TiS2, and FeS2 are more preferable, and the sulfur simple substance (S) and the lithium sulfide (Li2S) are particularly preferable from a viewpoint of high capacity.
The positive electrode material according to the present aspect may further contain a sulfur-free positive electrode active material, in addition to the positive electrode active material containing sulfur. Here, a ratio of a content of the positive electrode active material containing sulfur to a total amount of 100 mass % of the positive electrode active material is preferably 50 mass % or more, more preferably 70 mass % or more, still more preferably 80 mass % or more, yet still more preferably 90 mass % or more, particularly preferably 95 mass % or more, and most preferably 100 mass %.
The positive electrode material according to the present aspect essentially contains a sulfur-containing solid electrolyte. A specific form of the sulfur-containing solid electrolyte contained in the positive electrode material according to the present aspect is not particularly limited, and the sulfur-containing solid electrolyte exemplified in the section of the negative electrode active material layer and a preferred form thereof can be similarly employed.
Among the forms, the solid electrolyte contained in the positive electrode material according to the present aspect is preferably a sulfide solid electrolyte. In another preferred embodiment, the sulfur-containing solid electrolyte contained in a solid electrolyte layer contains an alkali metal atom. Here, examples of the alkali metal atom that can be contained in the sulfur-containing solid electrolyte include a lithium atom, a sodium atom, or a potassium atom, and among the atoms, the lithium atom is preferable from the viewpoint of excellent ionic conductivity. In still another preferred embodiment, the solid electrolyte contained in the solid electrolyte layer contains an alkali metal atom (for example, lithium atom, sodium atom or potassium atom; preferably lithium atom) as well as a phosphorus atom and/or a boron atom. In one preferred embodiment, the sulfide solid electrolyte includes Li6PS5X (wherein X is Cl, Br or I, and preferably Cl). These solid electrolytes can also effectively contribute to expression of the effect of the present invention for having a high ionic conductivity.
The positive electrode material according to the present aspect preferably further contains a conductive material. The specific form of the conductive material contained in the positive electrode material according to the present aspect is not particularly limited, and conventionally known materials can be appropriately adopted. Among the forms, in a case where the positive electrode material according to the present aspect contains a conductive material, the conductive material more preferably has pores. By using the conductive material having pores, there is an advantage that the positive electrode active material and the solid electrolyte can be filled in inner portions of the pores, and a three-phase interface containing these three materials is formed and the positive electrode reaction is more likely to proceed. Furthermore, the conductive material having pores is preferably a carbon material from the viewpoint of excellent conductivity, ease of processing, and ease of designing a desired pore distribution.
Examples of the carbon material having pores include carbon black, such as activated carbon, ketjen black (registered trademark) (highly conductive carbon black), (oil) furnace black, channel black, acetylene black, thermal black, and lamp black; and carbon particles (carbon carriers) made of coke, natural graphite, artificial graphite, and the like. The main component of the carbon material is preferably carbon. Here, the phrase “the main component is carbon” means that carbon atoms are contained as a main component, and includes the concept of consisting only of carbon atoms and the concept of consisting substantially of carbon atoms. The phrase “consisting substantially of carbon atoms” means that the mixing of approximately 2 to 3 mass % or less of impurities may be allowable.
The BET specific surface area of the conductive material having pores (preferably, a carbon material) is preferably 200 m2/g or more, more preferably 500 m2/g or more, still more preferably 800 m2/g or more, particularly preferably 1200 m2/g or more, and most preferably 1500 m2/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 still more preferably 1.5 mL/g or more. When the BET specific surface area and pore volume of the conductive material are values within such ranges, a sufficient number of pores can be held, and thus a sufficient amount of the positive electrode active material can be held. The BET specific surface area and pore volume of the conductive material can be measured based on adsorption and desorption of nitrogen. The measurement based on adsorption and desorption of nitrogen at a temperature of −196° C. is performed using BELSORP mini, manufactured by MicrotracBEL Corp., and analysis is conducted by a multipoint method. The BET specific surface area is determined from the adsorption isotherm in a relative pressure range of 0.01<P/P0<0.05. Further, the pore volume is determined from the volume of the adsorbed N2 at a relative pressure of 0.96.
An average pore size of the conductive material is not particularly limited, but is preferably 50 nm or less, and particularly preferably 30 nm or less. When the average pore size is a value within these ranges, electrons can be sufficiently supplied to the active material present at a position away from the pore wall, among the positive electrode active materials containing sulfur placed in the pores. Note that the average pore size of the conductive material can be calculated by the measurement based on adsorption and desorption of nitrogen, in the same manner as above.
An average particle diameter (primary particle diameter) in a case where the conductive material is in particle form is not particularly limited, but is preferably in a range of 0.05 to 50 m, more preferably in a range of 0.1 to 20 m, and still more preferably in a range of 0.5 to 10 m. Note that, in the present description, “a particle diameter of the conductive material” means a maximum distance L among distances between any two points on a contour line of the conductive material. As a value of “an average particle diameter of the conductive material”, a value is adopted that is calculated as an average value of particle diameters of particles observed in several to several tens of fields of view by using an observation means such as a scanning electron microscope (SEM), a transmission electron microscope (TEM), or the like.
As described above, the positive electrode material according to the present aspect contains a sulfur-containing positive electrode active material and a sulfur-containing solid electrolyte, but in a case where the positive electrode material further includes a conductive material having pores, it is preferable that at least a part of the solid electrolyte and at least a part of the positive electrode active material are disposed on inner surfaces of the pores of the conductive material described above to be in contact with each other. Hereinafter, one preferred embodiment of such form will be described with reference to the drawings.
The positive electrode material for an electric device according to the present aspect is characterized in that a peak is shown in a range of 1400 to 1450 cm1 in the Raman spectrum of the microscopic Raman spectrometry using the laser with the wavelength of 532 nm for the powder particles of the positive electrode material.
Here,
Then, according to the study of the present inventors, it has been determined that when the electric device such as an all-solid-state lithium secondary battery or the like is configured by using a positive electrode material that contains a sulfur-containing positive electrode active material and a sulfur-containing solid electrolyte, and shows the peak in the range of 1400 to 1450 cm−1 in a Raman spectrum of the microscopic Raman spectroscopy using the laser with the wavelength of 532 nm, the capacity characteristics and the charge-discharge rate characteristics can be significantly improved. Although such mechanism is not completely clear, the mechanism below is presumed. That is, the positive electrode material having the peak determined above according to the present aspect can be produced, for example, by mixing the sulfur-containing positive electrode active material and the sulfur-containing solid electrolyte to obtain a mixture, and then heating the mixture at a relatively high temperature (185° C. in Example 1) as described later. On the other hand, in Comparative Example 1 in which such heating treatment is not performed, the peak in the range of 1400 to 1450 cm−1 is not observed as illustrated in
One example of a method for producing the positive electrode material having the configuration described above according to the present aspect will be described. As described above, it is presumed that the positive electrode material according to the present aspect contributes to excellent capacity characteristics and charge-discharge rate characteristics due to presence of an ion conductive compound present at the contact interface between the sulfur-containing positive electrode active material and the sulfur-containing solid electrolyte. Then, it is considered that the ion conductive compound is generated by the heating treatment at the relatively high temperature. Therefore, it is considered that the positive electrode material according to the present aspect is obtained by heat-treating the mixture of the sulfur-containing positive electrode active material and the sulfur-containing solid electrolyte at a high temperature. At this time, the temperature of the heating treatment is not particularly limited, but is preferably higher than 170° C., more preferably 175° C. or higher, still more preferably 180° C. or higher, and particularly preferably 185° C. or higher.
On the other hand, an upper limit value of the temperature of the heating treatment is also not particularly limited, but is, for example, 250° C. or lower, and preferably 200° C. or lower. Furthermore, heating treatment time is not particularly limited, and may be about 1 to 5 hours. When the heating treatment is performed, the sulfur-containing positive electrode active material and the sulfur-containing solid electrolyte may be present in a mixture state, but the mixture preferably further contains a conductive material. In a case where the mixture contains the conductive material having pores, the sulfur-containing positive electrode active material and the sulfur-containing solid electrolyte are filled up to the inner portions of the pores of the conductive material by the heating treatment described above, and a positive electrode material having a preferred form in which a large number of the three-phase interfaces are formed can be obtained. At this time, the means for obtaining a mixture containing the three components described above is also not particularly limited, and examples thereof include mixing treatment using a mixing means such as a mortar or the like, milling treatment using a grinding means such as a planetary ball mill or the like, etc. Among the treatment, from the viewpoint of obtaining a larger initial capacity and more excellent charge-discharge rate characteristics, it is preferable to subject a mixture obtained by the milling treatment to the heating treatment described above. On the other hand, instead of the mixture of the three components described above, the mixture of the sulfur-containing positive electrode active material and the sulfur-containing solid electrolyte may be first obtained by the mixing treatment or the milling treatment, and then the mixture may be subjected to the heating treatment described above. Subsequently, by additionally adding the conductive material, and performing mix treatment such as the mixing treatment, the milling treatment, or the like, the positive electrode material according to one aspect of the present invention containing the three components described above can also be obtained.
As still another production method, a method may be employed in which a mixture of the conductive material and the sulfur-containing solid electrolyte is obtained by the mixing treatment or the milling treatment, and then the heating treatment described above is performed in a state where the sulfur-containing positive electrode active material is additionally added to the mixture. According to such a method, the positive electrode active material and the solid electrolyte enter into the inner portions of the pores of the conductive material having the pores by the heating treatment, and the positive electrode material in the preferred form in which the large number of the three-phase interfaces are formed is obtained. Note that, the mixture of the conductive material having pores and the sulfur-containing positive electrode active material may be prepared by a wet method instead of a dry method as described above. For example, a solution in which the solid electrolyte is dissolved in an appropriate solvent capable of dissolving the solid electrolyte is first prepared, impregnated with the conductive material having pores, and heated to a temperature of about 100 to 180° C. for about 1 to 5 hours as necessary, and therefore, a solid electrolyte/conductive material composite can be obtained. In the composite, the solid electrolyte usually enters into and adheres to the inner portions of the pores of the conductive material. Next, by subjecting the composite to the heating treatment described above in the state where the sulfur-containing positive electrode active material is additionally added, the positive electrode active material is melted to allow the positive electrode active material to enter into the inner portions of the pores of the conductive material, and the positive electrode material in the preferred form in which the large number of the three-phase interfaces are formed can be obtained. According to the production method in which the wet method is adopted, a positive electrode material particularly excellent in initial capacity characteristics and charge-discharge rate characteristics can be obtained.
The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but for example, is preferably within a range of 35 to 99 mass %, and more preferably within a range of 40 to 90 mass %. The value of the content is calculated based on the mass of only the positive electrode active material excluding the conductive material and the solid electrolyte.
Furthermore, the positive electrode active material layer may further contain a conductive aid (in which the positive electrode active material and the solid electrolyte are not held inside the pores) and/or a binder. Similarly, the positive electrode active material layer preferably further contains a solid electrolyte separately from the positive electrode material described above.
One embodiment of the lithium secondary battery to which the positive electrode material according to the present aspect is applicable has been described above. Further, the present invention is not limited to only the configuration described in the embodiments described above, and can be appropriately changed based on descriptions of the claims. For example, as a type of a battery to which the lithium secondary battery is applied, a bipolar battery is also exemplified. Furthermore, the solid electrolyte layer of the lithium secondary battery may further contain a conventionally known liquid electrolyte (an electrolyte solution). An amount of the liquid electrolyte (the electrolyte solution) at this time is preferably such an amount that a shape of the solid electrolyte layer formed by the solid electrolyte is maintained and liquid leakage of the liquid electrolyte (the electrolyte solution) does not occur.
Hereinbelow, the present invention will be described in more detail with reference to Examples. However, the technical scope of the present invention is not limited to the following Examples.
In a glove box under an argon atmosphere having a dew point of −68° C. or lower, sulfur (manufactured by Sigma-Aldrich Co., LLC), a sulfide solid electrolyte (Li6PS5Cl manufactured by Ampcera Inc.), and carbon (activated carbon MSC-30 manufactured by Kansai Coke & Chemicals Co., Ltd.) were respectively weighed. At this time, respective components were weighed to make a mass ratio of the sulfur:the sulfide solid electrolyte:the carbon=50:40:10. Next, the respective components weighed above were sufficiently mixed in an agate mortar, and then mixed powder was placed in a sealed pressure-resistant autoclave vessel and heated at 185° C. for 3 hours. Accordingly, the sulfur was melted, the carbon was impregnated with the sulfur, and powder of the sulfur-containing positive electrode material was obtained.
The microscopic Raman spectrometry is performed on the powder particles of the sulfur-containing positive electrode material to obtain a Raman spectrum. Here, HR manufactured by HORIBA, Ltd. was used as a Raman analyzer. As measurement conditions, an objective lens of 100 times was used, a laser having a wavelength of 532 nm was used as incident light, and a slit width was set to 0.1 mm. A measurement range was set to 0 to 2000 cm−1, measurement time was set to 10 seconds, and a number of times of integrations was set to 24. The Raman spectrum thus obtained is illustrated in
A battery was produced in a glove box in an argon atmosphere with a dew point of −68° C. or lower. A cylindrical recessed punch (10 mm diameter) made of SUS was inserted into one side of a cylindrical tube jig (tube inner diameter: 10 mm, outer diameter: 23 mm, height: 20 mm) made of Macor, and 80 mg of sulfide solid electrolyte (Li6PS5Cl, manufactured by Ampcera Inc.) was inserted from the upper side of the cylindrical tube jig. Thereafter, another cylindrical recessed punch made of SUS was inserted into the jig to sandwich the solid electrolyte. The solid electrolyte was pressed using an oil hydraulic press at a pressure of 75 MPa for 3 minutes to form a solid electrolyte layer having a diameter of 10 mm and a thickness of about 0.6 mm in the cylindrical tube jig. Next, the cylindrical recessed punch inserted from the upper side was once removed, 7.5 mg of the sulfur-containing positive electrode material prepared above was added to one side surface of the solid electrolyte layer in the cylindrical tube. The cylindrical recessed punch (also serving as a positive electrode current collector) was inserted again from the upper side and pressed at a pressure of 300 MPa for 3 minutes to form a positive electrode active material layer having a diameter of 10 mm and a thickness of about 0.06 mm on one side surface of the solid electrolyte layer. Then, the lower side of the cylindrical recessed punch (also serving as a negative electrode current collector) was removed. Negative electrodes: a lithium foil (manufactured by The Nilaco Corporation, thickness: 0.20 mm) punched to a diameter of 8 mm and an indium foil (manufactured by The Nilaco Corporation, thickness: 0.30 mm) punched to a diameter of 9 mm were overlapped. The overlapped foil was put in from the lower side of the cylindrical tube jig such that the indium foil was located on the solid electrolyte layer side. Then, the cylindrical recessed 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 lithium secondary battery) including 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) laminated in this order was produced.
A test cell was produced by the same method as in Example 1 described above except that mixing using the planetary ball mill was adopted instead of the mixing using the agate mortar as a method of mixing the respective components of the positive electrode material. Note that, the respective components were mixed by being placed in a zirconia container having a volume of 45 mL and treated with the planetary ball mill (a premium line P-7 manufactured by Fritsch Japan Co., Ltd.) at 370 rpm for 6 hours. Furthermore, for the sulfur-containing positive electrode material prepared in the present Example, the Raman spectrum was acquired by performing the microscopic Raman spectrometry in the same manner as described above. As a result, similarly to Example 1 (
In the glove box under the argon atmosphere having the dew point of −68° C. or lower, a predetermined amount of the sulfur (manufactured by Sigma-Aldrich Co., LLC) and a predetermined amount of the sulfide solid electrolyte (Li6PS5Cl manufactured by Ampcera Inc.) were respectively weighed. Next, the respective components weighed above were sufficiently mixed in an agate mortar, and then mixed powder was placed in a sealed pressure-resistant autoclave vessel and heated at 185° C. for 3 hours. Accordingly, the sulfur was melted to obtain a sulfur active material/sulfide solid electrolyte composite. Subsequently, a predetermined amount of the carbon (the activated carbon MSC-30 manufactured by Kansai Coke & Chemicals Co., Ltd.) was further weighed, and sufficiently mixed with the sulfur active material/sulfide solid electrolyte composite obtained above in the agate mortar to obtain the powder of the sulfur-containing positive electrode material. Note that, the respective components were weighed to make the mass ratio of the sulfur:the sulfide solid electrolyte:the carbon=50:40:10. The test cell was produced by the same method as in Example 1 described above except that the sulfur-containing positive electrode material thus obtained was used. Note that, for the sulfur-containing positive electrode material prepared in the present Example, the Raman spectrum was acquired by performing the microscopic Raman spectrometry in the same manner as described above. As a result, similarly to Example 1 (
First, in the glove box under the argon atmosphere having the dew point of −68° C. or lower, 2.00 g of the sulfide solid electrolyte (Li6PS5Cl manufactured by Ampcera Inc.) was added to 100 ml of super dehydrated ethanol (manufactured by FUJIFILM Wako Pure Chemical Corporation), and stirred to dissolve the solid electrolyte in the ethanol until a solution became transparent. 1.00 g of the carbon (the activated carbon MSC-30 manufactured by Kansai Coke & Chemicals Co., Ltd.) was added to the solid electrolyte ethanol solution obtained, and well stirred to sufficiently disperse the carbon in the solution. A container containing the solution with the carbon dispersed was connected to a vacuum apparatus, and the container was brought into a depressurized state inside to 1 Pa or less by an oil rotary pump while the solution with the carbon dispersed in the container was stirred with a magnetic stirrer. Since the ethanol as the solvent was volatilized under reduced pressure, the ethanol was removed with a lapse of time, and the carbon impregnated with the solid electrolyte remained in the container. In this way, the ethanol was removed under the reduced pressure, then the heating treatment was performed to 150° C. under the reduced pressure, and heat-treated for 3 hours to obtain a sulfide solid electrolyte/carbon composite. Next, a predetermined amount of sulfur (manufactured by Sigma-Aldrich Co., LLC) was weighed, and sufficiently mixed with the sulfide solid electrolyte/carbon composite obtained above in the agate mortar. Subsequently, the mixed powder was placed in the sealed pressure-resistant autoclave container and heated at 185° C. for 3 hours. Accordingly, the sulfur was melted, the carbon was impregnated with the sulfur to obtain a sulfur active material/sulfide solid electrolyte/carbon composite. Next, the sulfur active material/sulfide solid electrolyte/carbon composite and further a predetermined amount of the sulfide solid electrolyte separately weighed were placed in the zirconia container having a capacity of 45 mL, and treated with the planetary ball mill (premium line P-7 manufactured by Fritsch Japan Co., Ltd.) at 370 rpm for 6 hours to obtain the powder of the sulfur-containing positive electrode material. Note that, the respective components were weighed to make a mass ratio of the sulfur:(the sulfide solid electrolyte/the sulfide solid electrolyte in the carbon composite):balance sulfide solid electrolyte:the carbon=50:20:20:10. The test cell was produced by the same method as in Example 1 described above except that the sulfur-containing positive electrode material thus obtained was used. Note that, for the sulfur-containing positive electrode material prepared in the present Example, the Raman spectrum was acquired by performing the microscopic Raman spectrometry in the same manner as described above. As a result, similarly to Example 1 (
The test cell was produced by the same method as in Example 1 described above except that the heating treatment was not performed at 185° C. for 3 hours in the sealed pressure-resistant autoclave container in the preparation of the sulfur-containing positive electrode material. Note that, for the sulfur-containing positive electrode material prepared in the present Comparative Example, the Raman spectrum was acquired by performing the microscopic Raman spectrometry in the same manner as described above. The Raman spectrum thus obtained is illustrated in
The test cell was produced by the same method as in Example 2 described above except that the heating treatment was not performed at 185° C. for 3 hours in the sealed pressure-resistant autoclave container in the preparation of the sulfur-containing positive electrode material. Note that, for the sulfur-containing positive electrode material prepared in the present Comparative Example, the Raman spectrum was acquired by performing the microscopic Raman spectrometry in the same manner as described above. As a result, as illustrated in
The capacity performance and charge-discharge rate capability of each of the test cells produced in the Comparative Examples and Examples described above were evaluated by the methods below. All the following measurements were performed in a constant temperature thermostat bath set at 25° C. using a charge-discharge test device (HJ-SD8, manufactured by HOKUTO DENKO CORPORATION).
The test cell was placed in a thermostatic bath, and after a cell temperature became constant, discharge was performed up to a cell voltage of 0.5 V at a current density of 0.2 mA/cm2, and then constant current constant voltage charge at 2.5 V was performed at the same current density by setting a cutoff current to 0.01 mA/cm2 as cell conditioning. Then, such conditioning charge-discharge cycle was repeated for 10 times. Next, after full discharge was performed by 0.05 C discharge at a cutoff voltage of 0.5 V, constant current charge at 0.05 C was performed at a cutoff voltage of 2.5 V, and a charge capacity value in the charge at 0.05 C was measured. Similarly, constant current charge at 0.2 C was separately performed at a cutoff voltage of 2.5 V, and a charge capacity value in the charge at 0.2 C was also measured. Then, a percentage (a charge capacity retention rate) of the charge capacity value obtained by the constant current charge at 0.2 C to the charge capacity value obtained by the constant current charge at 0.05 C was calculated. Results are shown in Table 1 below together with a value of the charge capacity value at each rate.
Furthermore, for the positive electrode materials obtained in Example 1 and Comparative Example 1, the results of the charge capacity values that were measured at charge rates of 0.1 C, 0.5 C and 1.0 C in the same manner as described above are further illustrated in
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/017154 | 4/30/2021 | WO |
