Positive electrode material and secondary battery using the same

Abstract

To provide means for improving charge / discharge capacity in a secondary battery using a positive electrode active material containing sulfur.SOLUTION: In a positive electrode material that includes a compound containing elemental sulfur and elemental phosphorus, and a conductive material, a ratio (A / B) of the intensity of a peak A in a range of 385-430 cm-1 and a peak B in a range of 470-475 cm-1 in a Raman spectrum of microscopic Raman spectrometry using a laser with a wavelength of 532 nm, and a ratio (α / β) of the intensity of a peak α in a range of 161 to 162 eV and a peak β in a range of 163 to 164 eV in an X-ray photoelectron spectroscopy spectrum satisfies a relation of (A / B)<0.1(α / β).SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] In recent years, reducing carbon dioxide emissions has become a pressing need to address global warming. The automotive industry is hoping that the introduction of electric vehicles (EVs) and hybrid electric vehicles (HEVs) will reduce carbon dioxide emissions, and development of non-aqueous electrolyte secondary batteries, such as motor drive batteries, which are key to the practical application of these vehicles, is actively underway.

[0003] For motor-driven secondary batteries, there is a demand for extremely high output characteristics and high energy compared to consumer lithium secondary batteries used in mobile phones, laptops, and other devices. Therefore, lithium secondary batteries, which possess the highest theoretical energy among all practical batteries, are attracting attention and are currently undergoing rapid development.

[0004] Currently, lithium-ion secondary batteries commonly used in Japan utilize flammable organic electrolytes. Such liquid-based lithium-ion secondary batteries require stricter safety measures against leakage, short circuits, and overcharging compared to other types of batteries.

[0005] Therefore, in recent years, research and development on all-solid-state lithium secondary batteries using oxide-based or sulfide-based solid electrolytes has been actively pursued. Solid electrolytes are materials mainly composed of ionic conductors that can conduct ions in a solid state. For this reason, all-solid-state lithium secondary batteries do not, in principle, suffer from the various problems caused by flammable organic electrolytes that occur in conventional liquid-based lithium secondary batteries. In addition, generally, using high-potential, high-capacity positive electrode materials and high-capacity negative electrode materials can significantly improve the power density and energy density of the battery. For example, elemental sulfur (S8) has an extremely large theoretical capacity of about 1670 mAh / g and has the advantages of being low-cost and abundant in resources.

[0006] On the other hand, it is difficult to maintain the contact between sulfur, which is a solid, and the solid electrolyte, and the current situation is that the characteristic of the high capacity of the sulfur positive electrode active material cannot be fully utilized.

[0007] Here, Patent Document 1 discloses a positive electrode material including a carbon replica having a three-dimensional honeycomb structure and a specific pore diameter, sulfur encapsulated in the pores, and a solid electrolyte, and the volume of the pores in the state of encapsulating sulfur and the solid electrolyte is 0.5 to 2.5 cm 3 / g. According to Patent Document 1, by applying a positive electrode material having such a configuration to a lithium-sulfur solid battery, it is said that it is possible to suppress a decrease in the contact area between sulfur and the solid electrolyte and a decrease in the capacity retention rate as the cycles are repeated.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] However, as a result of the study by the present inventors, it was found that sufficient charge and discharge capacity still cannot be obtained even when using the positive electrode material described in Patent Document 1.

[0010] [[ID=ssID=34]]Therefore, an object of the present invention is to provide means for improving the charge and discharge capacity in a secondary battery using a positive electrode active material containing sulfur.

Means for Solving the Problems

[0011] The inventors diligently conducted research to solve the above problems. As a result, they found that the above problems could be solved by using a cathode material manufactured by impregnating a conductive material into a solution in which a solid electrolyte containing sulfur and phosphorus elements and sulfur were sequentially dissolved in a solvent, and then removing the solvent. Further research by the inventors revealed that this cathode material exhibits a specific decrease in the peak intensity of the peak originating from SP bonding in the Raman spectrum, thus completing the present invention.

[0012] A positive electrode material according to one embodiment of the present invention comprises a compound containing sulfur and phosphorus elements and a conductive material. The positive electrode material is measured using micro-Raman spectroscopy with a 532 nm wavelength laser, and the Raman spectrum is 385-430 cm⁻¹. -1 Peak A and 470-475cm in the range -1 The ratio of the intensities of peak B in the range (A / B) and the ratio of the intensities of peak α in the range of 161-162 eV and peak β in the range of 163-164 eV in the X-ray photoelectron spectroscopy spectrum (α / β) satisfy the relationship (A / B) < 0.1(α / β). [Effects of the Invention]

[0013] According to the present invention, a means is provided for improving the charge and discharge capacity of a secondary battery using a positive electrode active material containing sulfur. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a magnified view of the Raman spectrum obtained by micro-Raman spectroscopy analysis of the cathode material manufactured in Comparative Example 1, which will be described later. [Figure 2] Figure 2 is an enlarged view of the XPS spectrum obtained by XPS analysis of the cathode material manufactured in Comparative Example 1, which will be described later. [Figure 3] Figure 3 is a magnified view of the Raman spectrum obtained by micro-Raman spectroscopy analysis of the cathode material manufactured in Example 1, which will be described later. [Figure 4]Figure 4 is an enlarged view of the XPS spectrum obtained by XPS analysis of the cathode material manufactured in Example 1, which will be described later. [Figure 5] Figure 5 is a perspective view showing the external appearance of a flat-stacked, all-solid-state lithium secondary battery, which is one embodiment of the present invention. [Figure 6] Figure 6 is a cross-sectional view along the line 2-2 shown in Figure 5. [Modes for carrying out the invention]

[0015] The embodiments of the present invention described above will be explained below with reference to the drawings, but the technical scope of the present invention should be determined based on the claims and is not limited to the following forms.

[0016] <Positive electrode material> One embodiment of the present invention relates to a cathode material comprising a compound containing sulfur and phosphorus elements and a conductive material. The cathode material exhibits a Raman spectrum of 385-430 cm⁻¹ measured using a 532 nm wavelength laser. -1 Peak A and 470-475cm in the range -1 The positive electrode material according to this embodiment is characterized in that the ratio of the intensities of peak B in the range (A / B) and the ratio of the intensities of peak α in the range of 161-162 eV and peak β in the range of 163-164 eV in the X-ray photoelectron spectroscopy (XPS) spectrum (α / β) satisfy the relationship (A / B) < 0.1(α / β). According to this embodiment, the charge and discharge capacity can be improved in secondary batteries using a positive electrode active material containing sulfur. For the sake of explanation, the manufacturing method of the positive electrode material according to this embodiment will be described first, followed by a description of the material characteristics of the positive electrode material according to this embodiment.

[0017] The positive electrode material according to this embodiment can be manufactured by a manufacturing method that includes the steps of sequentially dissolving a solid electrolyte containing sulfur and phosphorus elements and sulfur in a solvent (hereinafter also referred to as "Step 1"), and impregnating the resulting solution with a conductive material and then removing the solvent (hereinafter also referred to as "Step 2"). Each step will be described below.

[0018] (1) Process 1 In step 1, a solid electrolyte containing sulfur and phosphorus elements, and sulfur are sequentially dissolved in the solvent.

[0019] The solvent is not particularly limited, but from the viewpoint of solubility, operability, and safety, alcohols are preferred, and C1-C4 alcohols are preferred. Examples of C1-C4 alcohols include methanol, ethanol, 1-propanol, 2-propanol, n-butanol, 2-butanol, isobutanol, and tert-butanol. Among these, methanol, ethanol, 1-propanol, and 2-propanol are preferred, methanol and ethanol are more preferred, and ethanol is particularly preferred.

[0020] The solvent preferably has a low water content, specifically less than 0.2% by mass. A water content of less than 0.2% by mass suppresses the decomposition of the solid electrolyte by water in the solvent. More preferably, the water content of the solvent is 0.1% by mass or less, even more preferably 0.05% by mass or less, even more preferably 0.02% by mass or less, even more preferably 0.01% by mass or less, even more preferably 0.005% by mass or less, and particularly preferably 0.002% by mass or less. The water content of the solvent can be measured, for example, by Karl Fischer coulometric titration.

[0021] There are no particular restrictions on the solid electrolyte containing sulfur and phosphorus elements, but examples include 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-P2S5-LiI, and Li2S-P2S5-Z m S n (where m and n are positive numbers, and Z is one of Ge, Zn, or Ga), Li2S-SiS2-Li3PO4 is an example. Among these, Li3PS4 and Li7P3S11 , Li (4-x) , Ge (1-x) , P x S4 (where 0 < x < 1), Li6PS5X (where X is Cl, Br, or I) are preferred, and Li3PS4 and Li6PS5Cl are more preferred. These solid electrolytes may be used alone or in combination of two or more.

[0022] First, dissolve a solid electrolyte containing sulfur and phosphorus elements in a solvent. The ratio of the solvent to the solid electrolyte containing sulfur and phosphorus elements at this time is not particularly limited, but per 100 mL of the solvent, the solid electrolyte is preferably 0.1 - 20 g, and more preferably 1 - 10 g.

[0023] Next, dissolve sulfur (sulfur monomer (S)) in the solution obtained by dissolving the solid electrolyte containing sulfur and phosphorus elements in the solvent. As the sulfur monomer (S), α-sulfur, β-sulfur, or γ-sulfur having an S8 structure can be used. The ratio of the solution to sulfur at this time is not particularly limited, but per 100 mL of the solution, sulfur is preferably 0.1 - 20 g, and more preferably 1 - 10 g.

[0024] Also, the ratio of the mass of the solid electrolyte containing sulfur and phosphorus elements to the mass of sulfur (solid electrolyte / sulfur) is preferably 0.5 - 2, more preferably 0.8 - 1.2, and even more preferably 0.9 - 1.1.

[0025] Normally, sulfur is unnecessary in solvents such as alcohols, but the inventors of the present invention surprisingly found that after dissolving the solid electrolyte containing sulfur and phosphorus elements in the solvent and then dissolving sulfur, it is possible to prepare a solution containing both the solid electrolyte and sulfur. According to the speculation of the inventors, it is considered that the solid electrolyte and sulfur form polysulfide ions as shown in the following formula (where l, m, and n each independently represent an integer of 0 or more) in the solution. And it is considered that the polysulfide ions precipitate as a lithium salt by solvent removal in step 2 described below.

[0026] [ka]

[0027] As shown in the examples described later, since it is possible to carry out the charge-discharge reaction in a secondary battery by arranging a positive electrode active material layer containing the deposited lithium salt, it is presumed that the lithium salt is a substance (lithium-conducting polysulfide) that combines the function of a lithium-conducting solid electrolyte with the function of a positive electrode active material. The presumed reaction equation of the lithium-conducting polysulfide during discharge is shown below.

[0028] [ka]

[0029] Furthermore, as shown in the examples described later, secondary batteries using the positive electrode material according to this embodiment have superior charge and discharge capacity compared to secondary batteries using conventional positive electrode materials. Conventional positive electrode materials ensure lithium conductivity by bringing solid electrolytes and sulfur into contact with each other, but in the positive electrode material according to this embodiment, the lithium-conducting polysulfide itself, which has lithium conductivity, functions as the active material, thus improving lithium conductivity, and as a result, it is thought that the charge and discharge reaction can proceed more efficiently.

[0030] (2) Process 2 In step 2, the conductive material is impregnated into the solution obtained in step 1, and then the solvent is removed.

[0031] The conductive material is not particularly limited, but it is preferably a conductive porous body having pores. By using a conductive porous body having pores, lithium conductive polysulfides are filled into the pores, which can further improve the conductivity of the positive electrode material. The materials constituting the conductive material are also not particularly limited, and materials such as metals, conductive polymers, and carbon materials can be used as appropriate. Among these, from the viewpoint of excellent conductivity and ease of processing, it is preferable that the conductive material be made of carbon material. More preferably, the conductive material is a conductive porous body made of carbon material.

[0032] Examples of conductive porous materials made of carbon include activated carbon, carbon black such as Ketjenblack (registered trademark) (highly conductive carbon black), (oil) furnace black, channel black, acetylene black, thermal black, and lamp black, as well as carbon particles (carbon carriers) made of coke, natural graphite, and artificial graphite. Alternatively, a conductive porous material having a porous structure in which the shape of the mold is transferred can be synthesized by mixing a mold such as ceramics with a carbon raw material such as resin, firing it in an inert atmosphere, and then dissolving the mold with acid, and this can be used. In this case, the pore size and pore volume of the resulting conductive porous material can be changed by appropriately adjusting the particle size of the mold and the mixing ratio of the carbon raw material.

[0033] Furthermore, it is preferable that the carbon material's main component is carbon. Here, "main component is carbon" means that it contains carbon atoms as its main component, and this concept includes both being composed solely of carbon atoms and being substantially composed of carbon atoms. "Substantially composed of carbon atoms" means that the inclusion of impurities of approximately 2-3% by mass or less is permissible.

[0034] The BET specific surface area of ​​a conductive porous material (preferably porous carbon) is 200 m². 2 It is preferable that it be 1 / g or more, and 500m 2 It is more preferable that it be 800m or more per gram. 2 It is even more preferable that it be 1200m or more per gram. 2 It is particularly preferable that the amount be 1 / g or more, and 1500m2 It is most preferable that it is 1.0 mL / g or more. Further, the pore volume of the conductive porous body 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 porous body are within such ranges, a sufficient amount of pores can be retained, and as a result, a sufficient amount of the positive electrode active material (lithium conductive polysulfide) can be retained. Note that the values of the BET specific surface area and pore volume of the conductive porous body can be measured by nitrogen adsorption and desorption measurement. This nitrogen adsorption and desorption measurement is performed using BELSORP mini manufactured by MicrotracBEL Corporation at a temperature of -196 °C by the multi-point method. The BET specific surface area is determined from the adsorption isotherm in the relative pressure range of 0.01 < P / P0 < 0.05. Further, the pore volume is determined from the volume of adsorbed N2 at a relative pressure of 0.96.

[0035] The average pore diameter of the conductive porous body (preferably porous carbon) is not particularly limited, but is preferably 1 to 50 nm, and particularly preferably 1 to 30 nm. If the average pore diameter of the conductive porous body is within these ranges, electrons can be sufficiently supplied to the positive electrode active material (lithium conductive polysulfide) existing at a position away from the pore wall among the positive electrode active materials containing sulfur disposed inside the pores. Note that the value of the average pore diameter of the conductive porous body can be calculated by nitrogen adsorption and desorption measurement in the same manner as when obtaining the values of the BET specific surface area and pore volume.

[0036] The average particle diameter (primary particle diameter) of the conductive porous material (preferably porous carbon) is not particularly limited, but is preferably 0.05 to 50 μm, more preferably 0.1 to 20 μm, and even more preferably 0.5 to 10 μm. In this specification, "particle diameter of the conductive porous material (preferably porous carbon)" means the maximum distance L between any two points on the contour line of the conductive porous material (preferably porous carbon). The value of "average particle diameter of the conductive porous material (preferably porous carbon)" shall be the value calculated as the arithmetic mean of the particle diameters of particles observed in several to tens of fields of view using observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0037] The amount of conductive material is not particularly limited, but is preferably 0.1 to 10, more preferably 0.2 to 5, and even more preferably 0.5 to 2, in terms of its mass ratio to the amount of sulfur. If the amount of conductive material is within the above range, a positive electrode material with sufficient conductivity can be obtained.

[0038] The method for removing the solvent after impregnating the solution obtained in step 1 with the conductive material is not particularly limited, but it is preferable to impregnate the solution with the conductive material and then remove the solvent while stirring the dispersion. The removal of the solvent is preferably carried out under reduced pressure at a temperature of 100°C or lower. This can suppress the decomposition of lithium conductive polysulfides.

[0039] Through the above steps, a solid containing lithium-conducting polysulfide and a conductive material is obtained. This solid may be used as is as a positive electrode material, but by stirring the solid, the agglomeration is broken down and a more homogeneous positive electrode material can be obtained. Therefore, a preferred embodiment of the method for producing a positive electrode material further includes a step of stirring the obtained solid after steps 1 and 2.

[0040] Various known methods can be used for the stirring process. For example, stirring processes using a mortar and pestle, ball mill, planetary ball mill, dynamic mill, bead mill, jet mill, hammer mill, disc mill, and pin mill are possible. Among these, stirring using a mill is preferred, stirring using a ball mill is more preferred, and stirring using a planetary ball mill is even more preferred. By using a planetary ball mill, the charge and discharge capacity of the resulting positive electrode active material can be further improved.

[0041] (Positive electrode material) Next, the physical characteristics of the positive electrode material according to this embodiment will be described. This embodiment includes a compound containing sulfur and phosphorus elements and a conductive material. Here, the "compound containing sulfur and phosphorus elements" is a compound (presumably a lithium-conducting polysulfide) obtained by dissolving and reprecipitation a solid electrolyte containing sulfur and phosphorus elements and sulfur in the aforementioned manufacturing method. Although the chemical structure of the "compound containing sulfur and phosphorus elements" is unknown, for convenience in this specification it will also be referred to as a "lithium-conducting polysulfide." If the conductive material is a conductive porous body, the positive electrode material may have a structure in which the compound containing sulfur and phosphorus elements (presumably a lithium-conducting polysulfide) is arranged within the pores of the conductive porous body. Having such a structure can further improve the conductivity of the positive electrode material.

[0042] The cathode material in this embodiment exhibits a Raman spectrum of 385-430 cm⁻¹ in micro-Raman spectroscopy measurements using a 532 nm wavelength laser. -1 Peak A and 470-475cm in the range -1The positive electrode material has the characteristic that the ratio of the intensities of peak B in the range (A / B) and the ratio of the intensities of peak α in the range of 161-162 eV and peak β in the range of 163-164 eV in the X-ray photoelectron spectroscopy (XPS) spectrum (α / β) satisfy the relationship (A / B) < 0.1(α / β). By applying such a positive electrode material to a secondary battery, the charge and discharge capacity of the secondary battery can be improved. In this specification, the specific measurement methods for micro-Raman spectroscopy and XPS measurements will be those described in the examples below. This relationship will be explained in detail below with reference to the Raman and XPS spectra.

[0043] Figure 1 is a magnified view of the Raman spectrum obtained by micro-Raman spectroscopy of the cathode material produced in Comparative Example 1, which will be described later. Figure 2 is a magnified view of the XPS spectrum obtained by XPS analysis of the cathode material produced in Comparative Example 1, which will be described later. In Comparative Example 1, similar to the method described in Patent Document 1, sulfur-impregnated carbon is prepared by thermally impregnating porous carbon with sulfur, and then the sulfur-impregnated carbon is dispersed in an ethanol solution of a solid electrolyte (Li6PS5Cl) and the solvent is removed to produce the cathode material. According to this manufacturing method, a large amount of sulfur is arranged in the deep pores of the porous carbon, and the solid electrolyte (Li6PS5Cl) is arranged in the shallow pores. In the Raman spectrum shown in Figure 1, at 425 cm⁻¹ -1 A peak A, thought to originate from the PS bond of the solid electrolyte (Li6PS5Cl), was observed at 472 cm⁻¹. -1A peak B, thought to originate from the SS bond of sulfur (S8), is observed. The ratio of the intensity of peak A to the intensity of peak B (A / B) is calculated to be 0.80. Furthermore, while quantitative analysis of each element is possible based on peak intensity according to the XPS spectrum, as shown in Figure 2, a peak α, thought to originate from the P-"S" bond of the solid electrolyte (Li6PS5Cl), is observed at 161.7 eV, and a peak β, thought to originate from the S-"S"-S and P-"S"-S bonds of sulfur (S8), is observed at 163.8 eV. The ratio of the intensity of peak α to the intensity of peak β (α / β) is calculated to be 0.46. Therefore, the relationship (A / B) < 0.1(α / β) is not satisfied. In other words, the value of the ratio of the intensity of peak A to the intensity of peak B (A / B) and the value of the ratio of the intensity of peak α to the intensity of peak β (α / β) are of the same order.

[0044] On the other hand, Figure 3 is a magnified view of the Raman spectrum obtained by micro-Raman spectroscopy analysis of the cathode material manufactured in Example 1, which will be described later. Figure 4 is a magnified view of the XPS spectrum obtained by XPS analysis of the cathode material manufactured in Example 1, which will be described later. In Example 1, the cathode material is manufactured by the manufacturing method according to the present embodiment described above. According to this manufacturing method, a compound containing sulfur and phosphorus elements (presumably the lithium-conducting polysulfide shown in the above formula) is filled inside the pores of porous carbon. In the Raman spectrum shown in Figure 3, at 425 cm⁻¹, -1 While the intensity of peak A, which is thought to originate from the PS bond of the solid electrolyte (Li6PS5Cl), decreases significantly, at 472 cm⁻¹ -1Peak B, which is thought to originate from the SS bond of sulfur (S8), is observed to the same extent as in Figure 1. The ratio of the intensity of peak A to the intensity of peak B (A / B) is calculated to be less than 0.04. The inventors speculate as follows about the reason for this significant decrease in peak A. That is, as shown in the following formula, the Li3PS4 unit in the solid electrolyte has tetrahedral (point group: Td) symmetry, and therefore the PS symmetric stretching vibration has Raman activity. On the other hand, according to the manufacturing method of this embodiment, lithium conductive polysulfide precipitates after dissolving both the solid electrolyte and sulfur in a solvent and then removing the solvent. In this lithium conductive polysulfide after dissolution and reprecipitation, the tetrahedral (point group: Td) symmetry is broken, and it is thought that the Raman activity of the PS bond is lost. For this reason, peak A decreases significantly after dissolution and reprecipitation. In the lithium conductive polysulfide after dissolution and reprecipitation, new SS bonds are formed, but since these SS bonds have Raman activity, the intensity of peak B does not change significantly.

[0045] [ka]

[0046] On the other hand, in the XPS spectrum shown in Figure 4, peaks α and β are observed at approximately the same intensity as in the XPS spectrum for Comparative Example 1 shown in Figure 2, and the ratio of the intensity of peak α to the intensity of peak β (α / β) is calculated to be 0.46. This is because the XPS spectrum can quantify each atom, and the raw material mixing ratio is the same for Comparative Example 1 and Example 1. Thus, according to the Raman spectrum and XPS spectrum of the cathode material of Example 1, peak A decreases significantly, but peaks B, α, and β remain unchanged. Therefore, the relationship (A / B) < 0.1(α / β) is satisfied.

[0047] Furthermore, in the Raman spectrum obtained by micro-Raman spectroscopy using a 532 nm wavelength laser, the range was 385-430 cm⁻¹. -1 Multiple peaks within this range may be observed. For example, PS4 3-The peak originating from the PS bond is at 425 cm. -1 Observed in P2S7 4- The peak originating from the PS bond is at 410 cm. -1 Observed in P2S6 4- The peak originating from the PS bond is at 390 cm. -1 This can be observed. When multiple peaks are observed in this way, the range is 385-430 cm. -1 Peak A is defined as the peak with the highest peak intensity within the specified range.

[0048] <All-solid-state lithium secondary battery> As described above, by applying the positive electrode material according to this embodiment to a secondary battery, the charge and discharge capacity can be improved. Therefore, according to a preferred embodiment of the present invention, a secondary battery including a positive electrode material is provided. The embodiment will be described below with reference to the drawings, but the dimensional ratios in the drawings are exaggerated for illustrative purposes and may differ from the actual ratios. In the following, the present invention will be described using a stacked (internal parallel connection type) all-solid-state lithium secondary battery, which is one form of secondary battery, as an example.

[0049] Figure 5 is a perspective view showing the external appearance of a flat-stacked all-solid-state lithium secondary battery, which is one embodiment of the present invention. Figure 6 is a cross-sectional view along the line 2-2 shown in Figure 5. By using a stacked design, the battery can be made compact and have a high capacity. In this specification, the flat-stacked non-bipolar lithium secondary battery shown in Figures 5 and 6 (hereinafter also simply referred to as "stacked battery") will be used as an example for detailed explanation. However, in terms of the electrical connection configuration (electrode structure) inside the lithium secondary battery according to this embodiment, it can be applied to both non-bipolar (internal parallel connection type) batteries and bipolar (internal series connection type) batteries.

[0050] As shown in Figure 5, the stacked battery 10a has a rectangular, flattened shape, with a negative electrode current collector plate 25 and a positive electrode current collector plate 27 extending from both sides for extracting power. The power generation element 21 is encased in the battery casing material (laminate film 29) of the stacked battery 10a, and its periphery is heat-sealed, so that the power generation element 21 is sealed with the negative electrode current collector plate 25 and the positive electrode current collector plate 27 extended to the outside.

[0051] Furthermore, the lithium secondary battery according to this embodiment is not limited to a stacked, flat shape. In the case of a wound lithium secondary battery, it may be cylindrical, or a cylindrical shape may be deformed into a rectangular, flat shape, and there are no particular limitations. In the case of the cylindrical shape described above, the outer material may be a laminate film or a conventional cylindrical can (metal can), and there are no particular limitations. Preferably, the power generation element is housed inside a laminate film containing aluminum. This embodiment can achieve weight reduction.

[0052] Furthermore, there are no particular restrictions on how the current collector plates (25, 27) shown in Figure 5 are removed. The negative electrode current collector plate 25 and the positive electrode current collector plate 27 may be removed from the same side, or the negative electrode current collector plate 25 and the positive electrode current collector plate 27 may each be divided into multiple parts and removed from each side. In addition, in wound lithium batteries, instead of tabs, for example, cylindrical cans (metal cans) may be used to form the terminals.

[0053] As shown in Figure 6, the stacked battery 10a of this embodiment has a structure in which a flattened, roughly rectangular power generation element 21, in which the charge-discharge reaction actually takes place, is sealed inside a laminate film 29, which is the battery's outer casing material. Here, the power generation element 21 has a configuration in which a positive electrode, a solid electrolyte layer 17, and a negative electrode are stacked. The positive electrode has a structure in which a positive electrode active material layer 15 containing a positive electrode material according to one embodiment of the present invention is arranged on both sides of a positive electrode current collector 11''. This can improve the charge and discharge capacity of the stacked battery 10a. The negative electrode has a structure in which a negative electrode active material layer 13 containing a negative electrode active material is arranged on both sides of a negative electrode current collector 11'. Specifically, the positive electrode, solid electrolyte layer, and negative electrode are stacked in this order such that one positive electrode active material layer 15 and an adjacent negative electrode active material layer 13 face each other via a solid electrolyte layer 17. As a result, adjacent positive electrodes, solid electrolyte layers, and negative electrodes constitute one single cell layer 19. Therefore, the stacked battery 10a shown in Figure 6 can also be said to have a configuration in which multiple single cell layers 19 are stacked and electrically connected in parallel.

[0054] As shown in Figure 6, the outermost negative electrode current collectors located on both outermost layers of the power generation element 21 each have a negative electrode active material layer 13 on only one side, but active material layers may be provided on both sides. That is, instead of using a current collector specifically for the outermost layer with an active material layer on only one side, a current collector with active material layers on both sides may be used as the outermost current collector. In addition, in some cases, the negative electrode active material layer 13 and the positive electrode active material layer 15 may be used as the negative electrode and positive electrode, respectively, without using current collectors (11',11”).

[0055] The negative electrode current collector 11' and the positive electrode current collector 11'' are each attached to a negative electrode current collector plate (tab) 25 and a positive electrode current collector plate (tab) 27, which are electrically connected to the respective electrodes (positive and negative electrodes), and are structured to be led out of the laminate film 29, which is the battery casing material, by being sandwiched between the edges of the laminate film 29. The positive electrode current collector plate 27 and the negative electrode current collector plate 25 may be attached to the positive electrode current collector 11'' and the negative electrode current collector 11' of each electrode via positive electrode leads and negative electrode leads (not shown) as needed, by ultrasonic welding, resistance welding, or the like.

[0056] The main components of the secondary battery according to this embodiment will be described below.

[0057] [Current collector] The current collector has the function of mediating the movement of electrons from the electrode active material layer. There are no particular restrictions on the materials that make up the current collector. For example, metals or conductive resins can be used as the constituent materials of the current collector.

[0058] Specifically, examples of metals include aluminum, nickel, iron, stainless steel, titanium, and copper. In addition to these, clad materials of nickel and aluminum, or copper and aluminum may also be used. Alternatively, a foil in which aluminum is coated on a metal surface may also be used. Among these, aluminum, stainless steel, copper, and nickel are preferred from the viewpoint of electronic conductivity, battery operating potential, and adhesion of the negative electrode active material to the current collector by sputtering.

[0059] Furthermore, examples of conductive resins include resins in which conductive fillers are added to non-conductive polymer materials.

[0060] The current collector may be a single-layer structure made of a single material, or it may be a laminated structure in which layers made of these materials are appropriately combined. From the viewpoint of reducing the weight of the current collector, it is preferable to include at least a conductive resin layer made of a conductive resin. Furthermore, from the viewpoint of blocking the movement of lithium ions between single cell layers, a metal layer may be provided on a part of the current collector. Moreover, if the negative electrode active material layer and positive electrode active material layer described later are conductive and can perform the current collecting function on their own, it is not necessary to use a current collector as a separate component from these electrode active material layers. In such a configuration, the negative electrode active material layer described later will directly constitute the negative electrode, and the positive electrode active material layer described later will directly constitute the positive electrode.

[0061] [Negative electrode (negative electrode active material layer)] The negative electrode active material layer contains a negative electrode active material. The type of negative electrode active material is not particularly limited, but examples include carbon materials, metal oxides, and metallic active materials. Furthermore, a lithium-containing metal may be used as the negative electrode active material. Such negative electrode active materials include metallic lithium as well as lithium-containing alloys. Examples of lithium-containing alloys include alloys of Li with at least one of In, Al, Si, and Sn. In some cases, two or more negative electrode active materials may be used in combination. Of course, other negative electrode active materials may also be used. 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 is particularly preferably 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 electrical 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 the charging process. 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 complete discharge, but in some cases, a negative electrode active material layer made of a certain amount of lithium metal may be present during complete discharge.

[0062] The content of the negative electrode active material in the negative electrode active material layer is not particularly limited, but is preferably in the range of 40 to 99% by mass, and more preferably in the range of 50 to 90% by mass.

[0063] The negative electrode active material layer preferably further contains a solid electrolyte. The inclusion of a solid electrolyte in the negative electrode active material layer improves its ionic conductivity. Examples of solid electrolytes include sulfide solid electrolytes and oxide solid electrolytes, but a sulfide solid electrolyte is preferred.

[0064] 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 one of Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (wherein x and y are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, or In) are some examples. The notation "Li2S-P2S5" refers to a sulfide solid electrolyte made using a raw material composition containing Li2S and P2S5, and the same applies to other notations.

[0065] 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 called LPS (e.g., Li7P3S 11 ) are examples. Also, as a sulfide solid electrolyte, for example, Li (4-x) Ge (1-x) P xAn LGPS or the like represented by S4 (where 0 < x < 1) may be used. Among them, it is preferably a sulfide solid electrolyte containing a P element, and more preferably a material mainly composed of Li2S - P2S5. Furthermore, 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).

[0066] Also, when the sulfide solid electrolyte is a Li2S - P2S5 system, the ratio of Li2S and P2S5 is preferably within the range of Li2S:P2S5 = 50:50 to 100:0 in terms of molar ratio, and more preferably Li2S:P2S5 = 70:30 to 80:20.

[0067] Also, the sulfide solid electrolyte may be a sulfide glass, a crystallized sulfide glass, or a crystalline material obtained by a solid-phase method. The sulfide glass can be obtained, for example, by performing mechanical milling (such as a ball mill) on a raw material composition. Also, the crystallized sulfide glass can be obtained, for example, by performing heat treatment on the sulfide glass at a temperature above the crystallization temperature. Also, the ionic conductivity (for example, 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 an alternating current impedance method.

[0068] Examples of the oxide solid electrolyte include compounds having a NASICON-type structure. As an example of a compound having a NASICON-type structure, a compound represented by the general formula Li 1+x Al x Ge 2-x (PO4)3 (0 ≤ x ≤ 2) (LAGP), and a compound represented by the general formula Li 1+x Al x Ti 2-xExamples include compounds represented by (PO4)3 (0≦x≦2), such as (LATP). Other examples of oxide solid electrolytes include LiLaTiO (for example, Li 0.34 La 0.51 TiO3), LiPON (for example, Li 2.9 PO 3.3 N 0.46 ), LiLaZrO (for example, Li7La3Zr2O) 12 Examples include:

[0069] The solid electrolyte content in the negative electrode active material layer is preferably in the range of 1 to 60% by mass, and more preferably in the range of 10 to 50% by mass.

[0070] The negative electrode active material layer may further contain at least one of a conductive additive and a binder, in addition to the negative electrode active material and solid electrolyte described above.

[0071] The thickness of the negative electrode active material layer varies depending on the intended configuration of the secondary battery, but it is preferably in the range of 0.1 to 1000 μm.

[0072] [Solid electrolyte layer] The solid electrolyte layer is interposed between the positive electrode active material layer and the negative electrode active material layer and contains a solid electrolyte.

[0073] There are no particular restrictions on the specific form of the solid electrolyte contained in the solid electrolyte layer; the solid electrolytes and their preferred forms exemplified in the section on the negative electrode active material layer can be used in the same manner. In some cases, solid electrolytes other than those described above may be used in combination.

[0074] The solid electrolyte layer may further contain a binder in addition to the predetermined solid electrolyte described above.

[0075] The thickness of the solid electrolyte layer varies depending on the intended configuration of the lithium secondary battery, but from the viewpoint of improving the volumetric energy density of the battery, it is preferably 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 limit on the lower limit of the thickness of the solid electrolyte layer, but it is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more.

[0076] [Cathode active material layer] The positive electrode active material layer includes a positive electrode material according to one embodiment of the present invention.

[0077] The positive electrode active material layer may, in addition to the positive electrode material, further contain a solid electrolyte that may be contained in the negative electrode active material layer, if necessary. The solid electrolyte content in the positive electrode active material layer is preferably in the range of 1 to 60% by mass, and more preferably in the range of 10 to 50% by mass.

[0078] Furthermore, the positive electrode active material layer may further contain a conductive additive (one that does not retain the positive electrode active material or solid electrolyte inside the pores) and / or a binder.

[0079] The thickness of the positive electrode active material layer varies depending on the intended configuration of the secondary battery, but it is preferably in the range of 0.1 to 1000 μm.

[0080] [Positive electrode current collector plate and negative electrode current collector plate] The materials constituting the current collector plates (25, 27) are not particularly limited, and known highly conductive materials conventionally used as current collector plates for secondary batteries can be used. Preferred materials for the current collector plates are metallic materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof. From the viewpoint of lightness, corrosion resistance, and high conductivity, aluminum and copper are more preferred, and aluminum is particularly preferred. The positive electrode current collector plate 27 and the negative electrode current collector plate 25 may be made of the same material or different materials.

[0081] [Positive lead and negative lead] Although not shown in the diagram, the current collector and the current collector plate may be electrically connected via positive and negative leads. The materials used for the positive and negative leads can be the same as those used in known lithium-ion batteries. Furthermore, it is preferable to cover the parts exposed from the casing with heat-resistant, heat-shrinkable tubing or the like to prevent leakage current from contacting peripheral equipment or wiring and affecting the product (e.g., automotive parts, especially electronic equipment).

[0082] [Battery casing material] As the battery casing material, known metal can cases can be used, or, as shown in Figures 5 and 6, a bag-shaped case made of aluminum-containing laminate film 29 that can cover the power generation elements can be used. For example, a three-layer laminate film made by laminating PP, aluminum, and nylon in that order can be used, but there are no limitations to these. Laminate film is desirable from the viewpoint of high output and excellent cooling performance, and can be suitably used for batteries in large equipment for EVs and HEVs. Furthermore, since the group pressure applied to the power generation elements from the outside can be easily adjusted, an aluminum-containing laminate film is more preferable for the casing.

[0083] The stacked battery according to this embodiment has a configuration in which multiple single cell layers are connected in parallel, resulting in high capacity and excellent cycle durability. Therefore, the stacked battery according to this embodiment is suitable for use as a power source for EVs and HEVs.

[0084] Although one embodiment of a lithium secondary battery has been described above, the present invention is not limited to the configuration described in the above-described embodiment, and can be modified as appropriate based on the description of the claims.

[0085] For example, one type of battery to which the lithium secondary battery according to this embodiment should be applied is a bipolar battery, which includes a bipolar electrode having a positive electrode active material layer electrically coupled to one side of the current collector and a negative electrode active material layer electrically coupled to the opposite side of the current collector.

[0086] Furthermore, the secondary battery according to this embodiment does not have to be all-solid type. That is, the solid electrolyte layer may further contain a conventionally known liquid electrolyte (electrolyte). There are no particular restrictions on the amount of liquid electrolyte (electrolyte) that can be contained in the solid electrolyte layer, but it is preferable that the amount is such that the shape of the solid electrolyte layer formed by the solid electrolyte is maintained and leakage of the liquid electrolyte (electrolyte) does not occur. [Examples]

[0087] The present invention will be described in more detail below with reference to examples. However, the technical scope of the present invention is not limited to the following examples.

[0088] Examples of test cell preparations [Example 1] (Preparation of positive electrode material) In a glove box under an argon atmosphere with a dew point of -68°C or lower, 2,000 g of sulfide solid electrolyte (Ampcera, Li6PS5Cl) was added to 100 ml of super-dehydrated ethanol (Fujifilm Wako Pure Chemical Industries, Ltd.), and the mixture was stirred until no solid matter was visible, dissolving the solid electrolyte in the ethanol. 2,000 g of sulfur (Aldrich) was added to the resulting solid electrolyte ethanol solution, and the mixture was stirred until no solid matter was visible, dissolving the sulfur in the solid electrolyte ethanol solution. 1.00 g of porous carbon (Kansai Thermal Chemical Co., Ltd., MSC-30) was added to the resulting sulfur-solid electrolyte ethanol solution, and the mixture was stirred thoroughly to sufficiently disperse the porous carbon in the solution. The container holding this porous carbon dispersion was connected to a vacuum apparatus, and the carbon dispersion in the container was stirred using a magnetic stirrer while the pressure inside the container was reduced to 1 Pa or less using an oil rotary pump. Under reduced pressure, the solvent ethanol evaporates, and over time, the ethanol is removed, leaving porous carbon impregnated with a solid electrolyte and sulfur-derived compounds (presumably ion-conducting polysulfides) in the container. After removing the ethanol under reduced pressure, the material was heated to 80°C under reduced pressure for 3 hours to obtain ion-conducting polysulfide-impregnated carbon.

[0089] Next, in a glove box with an argon atmosphere and a dew point of -68°C or lower, 40 g of 2 mm diameter zirconia balls and 0.200 g of ion-conducting polysulfide-impregnated carbon were placed in a 45 ml zirconia container and processed at 370 rpm for 6 hours using a planetary ball mill (Fritsch, Premium line P-7) to obtain a powdered cathode material.

[0090] (Micro-Raman spectroscopy analysis of cathode materials) In a glove box with an argon atmosphere and a dew point of -68°C or lower, a powder sample of the cathode material was placed on a glass plate, its surface flattened, and a Raman point measurement was performed at an excitation wavelength of 532 nm using a confocal microspectroscopy analyzer (WITec, α300). The resulting Raman spectrum is shown in Figure 3. As shown in Figure 3, the Raman spectrum of the cathode material obtained in this example first shows 470-475 cm⁻¹.-1 A peak (peak B) is shown in the range of 385-430 cm, which is thought to originate from SS bonds. -1 No peaks (peak A) that appear to originate from PS binding were observed within this range. Therefore, it was confirmed that the ratio of the intensity of peak A to the intensity of peak B (A / B) is less than 0.04.

[0091] (X-ray photoelectron spectroscopy analysis of cathode materials) In a glove box under an argon atmosphere with a dew point of -68°C or lower, a powder sample of the cathode material was fixed to a sample holder using indium foil and introduced into a combined electron spectrometer (PHI, ESCA-5800) using a transfer vessel without exposure to air, and X-ray photoelectron spectroscopy analysis was performed. The XPS spectrum obtained in this manner is shown in Figure 4. As shown in Figure 4, the XPS spectrum of the cathode material obtained in this example first shows a peak (peak β) in the 163-164 eV range that is thought to originate from SS bonds. In addition, no peak (peak α) that is thought to originate from PS bonds was observed in the 161-162 eV range. The ratio of the intensity of peak α to the intensity of peak β (α / β) was calculated to be 0.46.

[0092] Therefore, it was confirmed that the positive electrode material obtained in this embodiment satisfies the relationship (A / B) < 0.1(α / β).

[0093] (Fabrication of test cells (all-solid-state lithium secondary batteries)) The battery was fabricated in a glove box under an argon atmosphere with a dew point of -68°C or lower. A cylindrical convex punch (10 mm in diameter) made of stainless steel was inserted into one side of a cylindrical tube jig made by Macol (10 mm inner diameter, 23 mm outer diameter, 20 mm height), and 80 mg of sulfide solid electrolyte (Ampcera, Li6PS5Cl) was placed in from the top of the cylindrical tube jig. Then, another cylindrical convex punch made of stainless steel was inserted to sandwich the solid electrolyte, and a solid electrolyte layer with a diameter of 10 mm and a thickness of approximately 0.6 mm was formed inside the cylindrical tube jig by pressing with a hydraulic press at a pressure of 75 MPa for 3 minutes. Next, the cylindrical convex punch inserted from above was temporarily removed, 7.5 mg of the positive electrode material prepared above was placed on one side of the solid electrolyte layer inside the cylindrical tube, and the cylindrical convex punch (which also serves as the positive electrode current collector) was inserted again from above. By pressing at a pressure of 300 MPa for 3 minutes, a positive electrode active material layer with a diameter of 10 mm and a thickness of approximately 0.06 mm was formed on one side of the solid electrolyte layer. Next, the lower cylindrical convex punch (which also serves as the negative electrode current collector) was removed, and a lithium foil punched to a diameter of 8 mm (manufactured by Nilaco, thickness 0.20 mm) and an indium foil punched to a diameter of 9 mm (manufactured by Nilaco, thickness 0.30 mm) were stacked as the negative electrode. The cylindrical tube jig was inserted from below so that the indium foil was positioned on the solid electrolyte layer side, and the cylindrical convex punch was inserted again. By pressing at a pressure of 75 MPa for 3 minutes, a lithium-indium negative electrode was formed. As described above, a test cell (all-solid-state lithium secondary battery) was fabricated in which the negative electrode current collector (punch), lithium-indium negative electrode, solid electrolyte layer, positive electrode active material layer, and positive electrode current collector (punch) were stacked in this order.

[0094] [Example 2] In the preparation of the positive electrode material described above, a test cell was prepared using the same method as in Example 1, except that Li3PS4 was used instead of Li6PS5Cl as the sulfide solid electrolyte.

[0095] From the Raman spectrum of the cathode material obtained in this embodiment, it was confirmed that the ratio of the intensity of peak A to the intensity of peak B (A / B) was less than 0.06. Furthermore, from the XPS spectrum of the cathode material obtained in this embodiment, the ratio of the intensity of peak α to the intensity of peak β (α / β) was calculated to be 0.68. Therefore, it was confirmed that the cathode material obtained in this embodiment satisfies the relationship (A / B) < 0.1(α / β).

[0096] [Example 3] In the preparation of the positive electrode material described above, the test cell was prepared using the same method as in Example 1, except that the planetary ball mill treatment was replaced with a mortar treatment for 10 minutes.

[0097] From the Raman spectrum of the cathode material obtained in this embodiment, it was confirmed that the ratio of the intensity of peak A to the intensity of peak B (A / B) was less than 0.05. Furthermore, from the XPS spectrum of the cathode material obtained in this embodiment, the ratio of the intensity of peak α to the intensity of peak β (α / β) was calculated to be 0.51. Therefore, it was confirmed that the cathode material obtained in this embodiment satisfies the relationship (A / B) < 0.1(α / β).

[0098] [Comparative Example 1] A test cell was prepared using the same method as in Example 1, except that the cathode material was prepared using the method described below instead of the method described above (preparation of cathode material).

[0099] (Preparation of positive electrode material) In a glove box with an argon atmosphere and a dew point of -68°C or lower, 2,000 g of sulfur (Aldrich) and 1.00 g of porous carbon (Kansai Thermal Chemical Co., Ltd., MSC-30) were thoroughly mixed in an agate mortar. The mixed powder was then placed in a sealed, pressure-resistant autoclave container and heated at 185°C for 8 hours to melt the sulfur and prepare sulfur-impregnated carbon.

[0100] Next, in a glove box under an argon atmosphere with a dew point of -68°C or lower, 2,000 g of sulfide solid electrolyte (Ampcera, Li6PS5Cl) was added to 100 ml of super-dehydrated ethanol (Fujifilm Wako Pure Chemical Industries, Ltd.), and the mixture was stirred until the solution became clear to dissolve the solid electrolyte in the ethanol. To the resulting solution, 3,000 g of sulfur-impregnated carbon prepared above was added and stirred well to thoroughly disperse the sulfur-impregnated carbon in the solution. The container holding this dispersion was connected to a vacuum apparatus, and while stirring the dispersion in the container with a magnetic stirrer, the pressure inside the container was reduced to 1 Pa or less using an oil rotary pump. Under reduced pressure, the solvent, ethanol, evaporates, and over time the ethanol is removed, leaving porous carbon with sulfur and solid electrolyte filling the pores in the container. After removing the ethanol under reduced pressure in this way, the mixture was heated to 70°C under reduced pressure for 3 hours to prepare sulfur / solid electrolyte-impregnated carbon.

[0101] Next, in a glove box with an argon atmosphere and a dew point of -68°C or lower, 40 g of 2 mm diameter zirconia balls and 0.200 g of sulfur / solid electrolyte-impregnated carbon were placed in a 45 ml zirconia container and processed at 370 rpm for 6 hours using a planetary ball mill (Fritsch, Premium line P-7) to obtain a powdered cathode material.

[0102] From the Raman spectrum of the positive electrode material obtained in this comparative example, the ratio of the intensity of peak A to the intensity of peak B (A / B) was calculated to be 0.80. Furthermore, from the XPS spectrum of the positive electrode material obtained in this example, the ratio of the intensity of peak α to the intensity of peak β (α / β) was calculated to be 0.46. Therefore, it was confirmed that the positive electrode material obtained in this comparative example does not satisfy the relationship (A / B) < 0.1(α / β).

[0103] [Comparative Example 2] In the preparation of the positive electrode material described above, a test cell was prepared using the same method as in Example 1, except that Li2S was used instead of Li6PS5Cl as the sulfide solid electrolyte.

[0104] From the Raman spectrum of the positive electrode material obtained in this comparative example, it was confirmed that the ratio of the intensity of peak A to the intensity of peak B (A / B) was less than 0.04. Furthermore, from the XPS spectrum of the positive electrode material obtained in this example, the ratio of the intensity of peak α to the intensity of peak β (α / β) was calculated to be 0.42. Therefore, it was confirmed that the positive electrode material obtained in this example satisfies the relationship (A / B) < 0.1(α / β).

[0105] [Comparative Example 3] In the preparation of the positive electrode material described above, the test cell was prepared using the same method as in Comparative Example 1, except that the planetary ball mill treatment was replaced with a mortar treatment for 10 minutes.

[0106] From the Raman spectrum of the positive electrode material obtained in this comparative example, the ratio of the intensity of peak A to the intensity of peak B (A / B) was calculated to be 0.89. Furthermore, from the XPS spectrum of the positive electrode material obtained in this example, the ratio of the intensity of peak α to the intensity of peak β (α / β) was calculated to be 0.53. Therefore, it was confirmed that the positive electrode material obtained in this comparative example does not satisfy the relationship (A / B) < 0.1(α / β).

[0107] [Comparative Example 4] A test cell was prepared using the same method as in Example 1, except that the cathode material was prepared using the method described below instead of the method described above (preparation of cathode material).

[0108] (Preparation of positive electrode material) In a glove box under an argon atmosphere with a dew point of -68°C or lower, 2,000 g of sulfur (Aldrich), 2,000 g of sulfide solid electrolyte (Ampcera, Li6PS5Cl), 100 ml of super-dehydrated ethanol (Fujifilm Wako Pure Chemical Industries, Ltd.), and 1.00 g of porous carbon (Kansai Thermal Chemical Co., Ltd., MSC-30) were stirred in an agate mortar for 10 minutes to obtain a powdered cathode material.

[0109] From the Raman spectrum of the positive electrode material obtained in this comparative example, the ratio of the intensity of peak A to the intensity of peak B (A / B) was calculated to be 0.91. Furthermore, from the XPS spectrum of the positive electrode material obtained in this example, the ratio of the intensity of peak α to the intensity of peak β (α / β) was calculated to be 0.55. Therefore, it was confirmed that the positive electrode material obtained in this comparative example does not satisfy the relationship (A / B) < 0.1(α / β).

[0110] Evaluation of test cells The capacity characteristics of the test cells prepared in each of the above examples and comparative examples were evaluated using the following methods. All of the following measurements were performed using a charge / discharge test apparatus (Hokuto Denko Co., Ltd., HJ-SD8) in a constant temperature chamber set to 25°C.

[0111] (Evaluation of capacity characteristics) The test cell is placed in a constant temperature bath, and after the cell temperature stabilizes, 0.2 mA / cm² is used for cell conditioning. 2 The cell voltage is discharged to 0.5V at a current density, followed by constant current / voltage charging at 2.5V with the same current density and a cutoff current of 0.01mA / cm². 2 The test was performed with the following settings. After repeating this conditioning charge-discharge cycle 10 times, the charge-discharge capacity values ​​obtained and the mass of the positive electrode active material contained in the positive electrode were used to calculate the capacity value per unit mass (mAh / gS) of the positive electrode active material (sulfur). The results are shown in Table 1 below.

[0112] [Table 1]

[0113] The results shown in Table 1 demonstrate that, according to the present invention, the charge and discharge capacity can be improved in a secondary battery using a positive electrode active material containing sulfur.

[0114] Furthermore, a comparison between Example 1 and Example 3, and between Comparative Example 1 and Comparative Example 3, showed that the charge and discharge capacity increased more significantly by applying a stirring treatment using a planetary ball mill. [Explanation of Symbols]

[0115] 10A stacked battery, 11' negative electrode current collector, 11” positive electrode current collector, 13 negative electrode active material layer, 15 positive electrode active material layer, 17 solid electrolyte layer, 19 single cell layers, 21 Power generation elements, 25 Negative electrode current collector plate, 27 Positive electrode current collector plate, 29. Laminating film.

Claims

1. A step of sequentially dissolving a solid electrolyte containing sulfur and phosphorus elements, and sulfur, in a solvent, The process involves impregnating the resulting solution with a conductive material, then removing the solvent to precipitate lithium-conducting polysulfide. A method for manufacturing a positive electrode material, including [the specified component].

2. The manufacturing method according to claim 1, wherein the solvent is an alcohol.

3. The manufacturing method according to claim 1 or 2, wherein the solid electrolyte comprises Li 6 PS 5 Cl.

4. The manufacturing method according to claim 1 or 2, further comprising the step of removing the solvent to precipitate a lithium-conducting polysulfide, followed by the step of stirring the obtained solid using a mill.

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