Solid electrolyte material, electrode, battery, and method for producing solid electrolyte material

Abstract

A solid electrolyte material 10 according to the present disclosure comprises amorphous solid electrolyte particles 11 and a carbon material 12 that covers a portion of the outer surface 11s of the solid electrolyte particles 11. The solid electrolyte includes a lithium-containing phosphoric acid compound. The ratio ID / IG of the D band peak intensity ID to the G band peak intensity IG in a Raman spectrum of the carbon material 12 is 0.5 or more and less than 1.2.

Description

Solid electrolyte material, electrode, battery, and method for manufacturing solid electrolyte material

[0001] This disclosure relates to solid electrolyte materials, electrodes, batteries, and methods for manufacturing solid electrolyte materials.

[0002] Research and development of solid-state batteries are actively underway as a next-generation battery. One of the challenges of solid-state batteries is that the high resistance of the electrodes prevents the full utilization of the battery capacity. Therefore, there is a need to reduce the resistance of the electrodes. To reduce the resistance of the electrodes, it is important to form a good interface between the solid electrolyte and the electrode active material. For example, a sintered body of a solid electrolyte and an electrode active material easily forms a good interface between the solid electrolyte and the electrode active material, making it suitable for electrodes in solid-state batteries.

[0003] Patent Document 1 describes how to achieve densification and low resistance of sintered electrodes by using a mixture of amorphous primary inorganic solid electrolyte powder and crystalline secondary solid electrolyte powder, which soften at low temperatures, as the solid electrolyte.

[0004] Japanese Patent Publication No. 2012-209256

[0005] In conventional technology, there is room for improvement in terms of improving the ionic and electronic conductivity of the electrodes while maintaining the sinterability of the electrodes.

[0006] This disclosure comprises amorphous solid electrolyte particles containing a lithium-containing phosphate compound, and a carbon material covering a portion of the outer surface of the solid electrolyte particles, wherein the peak intensity of the G band in the Raman spectrum of the carbon material is I G D-band peak intensity I D Ratio I D / I G The present invention provides a solid electrolyte material having a value of 0.5 or more and less than 1.2.

[0007] From another perspective, the present disclosure provides an electrode comprising an electrode active material and a solid electrolyte material of the present disclosure, wherein in the electrode, the particles of the electrode active material are bound together by a sintered phase of the solid electrolyte material, and the sintered phase of the solid electrolyte material includes a crystalline phase and an amorphous phase.

[0008] In another aspect, the present disclosure provides a battery comprising: a positive electrode; a negative electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode, wherein at least one selected from the group consisting of the positive electrode and the negative electrode includes the electrode of the present disclosure.

[0009] From yet another perspective, the disclosure includes: attaching a liquid component as a carbon source to a portion of the outer surface of particles of an amorphous solid electrolyte containing a lithium-containing phosphate compound; and heating the solid electrolyte particles with the liquid component attached at a temperature higher than the carbonization temperature of the carbon source and lower than the crystallization temperature of the solid electrolyte to coat a portion of the outer surface of the solid electrolyte particles with a carbon material, wherein the carbon source carbonizes at a temperature lower than the crystallization temperature of the solid electrolyte, and the peak intensity of the G band in the Raman spectrum of the carbon material is I G D-band peak intensity I D Ratio I D / I G The present invention provides a method for producing a solid electrolyte material, wherein the ratio is 0.5 or greater and less than 1.2.

[0010] According to this disclosure, it is possible to improve the ionic conductivity and electronic conductivity of the electrode while maintaining the sinterability of the electrode.

[0011] Figure 1 is a cross-sectional view showing the schematic configuration of the solid electrolyte material in the first embodiment. Figure 2 is a process diagram showing the manufacturing method of the solid electrolyte material in the first embodiment. Figure 3 is a cross-sectional view showing the schematic configuration of the electrode in the second embodiment. Figure 4 is a process diagram showing the manufacturing method of the electrode in the second embodiment. Figure 5 is a cross-sectional view showing the schematic configuration of the battery in the third embodiment. Figure 6 is a process diagram showing the manufacturing method of the battery in the third embodiment. Figure 7 is the X-ray diffraction pattern of the solid electrolyte particles used in Example 1. Figure 8 is the X-ray diffraction pattern of the solid electrolyte particles used in Comparative Example 1. Figure 9 is the X-ray diffraction pattern of the solid electrolyte particles used in Comparative Example 2. Figure 10 is the X-ray diffraction pattern of the solid electrolyte particles used in Comparative Example 3.

[0012] (Knowledge underlying the present disclosure) In Patent Document 1, as a solid electrolyte, a mixture of an amorphous first inorganic solid electrolyte powder that softens at low temperatures and a crystalline second solid electrolyte powder is adopted to achieve densification and low resistance of the sintered electrode. However, the amorphous component that softens at low temperatures has low ionic conductivity, leading to an increase in resistance in the sintered electrode.

[0013] The present inventors have intensively studied a solid electrolyte material suitable for improving the ionic conductivity and electronic conductivity of an electrode while maintaining the sinterability of the electrode, and arrived at the present invention.

[0014] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0015] (First Embodiment) [Solid Electrolyte Material] FIG. 1 is a cross-sectional view showing a schematic configuration of a solid electrolyte material 10 in the first embodiment. The solid electrolyte material 10 includes particles 11 of an amorphous solid electrolyte containing a lithium-containing phosphate compound, and a carbon material 12 that covers a part of the outer surface 11s of the particles 11 of the solid electrolyte. The ratio I G of the peak intensity I D of the D band to the peak intensity I D of the G band in the Raman spectrum of the carbon material 12 G is 0.5 or more and less than 1.2.

[0016] The ratio I D / I G represents the graphitization degree, that is, the crystallinity, of the carbon material 12 included in the solid electrolyte material 10. The smaller the ratio I D / I G , the higher the crystallinity of the carbon material 12. The present inventors have found that according to the solid electrolyte material 10 in which a part of the outer surface 11s of the particles 11 of the amorphous solid electrolyte containing a lithium-containing phosphate compound is covered with the carbon material 12 having the ratio I D / I G within the above numerical range, it is possible to improve the ionic conductivity and electronic conductivity of the electrode while maintaining the sinterability of the electrode.

[0017] In this specification, "sintering" refers to the phenomenon in which bonding occurs between particles when a molded body of powder material is heated, resulting in densification of the molded body accompanied by volume shrinkage. "Firing" refers to the heat treatment for sintering.

[0018] In this specification, the "G band" in Raman spectra refers to the 1580 cm⁻¹ band originating from graphite. -1 The Raman bands in the vicinity are shown. In Raman spectra, the "D band" is the 1360 cm band, which originates from structural disorder and defects in graphite. -1 This shows the nearby Raman bands.

[0019] As described above, the solid electrolyte particles 11 contain a lithium-containing phosphate compound. The solid electrolyte particles 11 may also contain a lithium-containing phosphate compound. When a lithium-containing phosphate compound is used for the solid electrolyte particles 11 and a titanium-containing oxide is used for the electrode active material, the effects of the configuration of this embodiment can be fully realized.

[0020] In this embodiment, the carbon material 12 covers only a portion of the outer surface 11s of the solid electrolyte particles 11. In other words, a portion of the outer surface 11s of the solid electrolyte particles 11 is exposed. Carbon is known to be an inhibitor of sinterability. Therefore, the fact that the carbon material 12 does not cover the entire outer surface 11s of the solid electrolyte particles 11 is advantageous in suppressing a decrease in the sinterability of the electrode.

[0021] The solid electrolyte particles 11 may be of the NASICON type. In this specification, "NASICON (Natrium superionic conductor) type solid electrolyte" refers to a solid electrolyte having a structure derived from an orthophosphate represented by the general formula LiM2(PO4)3. The M site is occupied by a tetravalent transition metal or a main group element. The occupying metal is not limited to one type. Examples of tetravalent transition metals include Ti and Zr. Examples of tetravalent main group elements include Ge. In some cases, the tetravalent transition metal or tetravalent main group element may be substituted with a trivalent transition metal or a trivalent main group element, respectively. In that case, charge compensation is provided by Li. Examples of such materials include Li 1+x Alx Ge 2-x (PO4)3 (0≦x≦2), Li 1+x Al x Ti 2-x (PO4)3 (0≦x≦2), Li 1+y Al y Ti z Ge 2-y-z (PO4)3 (0 < y < 1, 0 < z < 1) is one example. Below, Li 1+x Al x Ge 2-x The solid electrolyte represented by (PO4)3 (0 ≤ x ≤ 2) is sometimes called lithium aluminum germanium phosphate (LAGP). 1+x Al x Ti 2-x The solid electrolyte represented by (PO4)3 (0 ≤ x ≤ 2) is sometimes called lithium aluminum titanium phosphate (LATP). 1+y Al y Ti z Ge 2-y-z A solid electrolyte represented by (PO4)3 (0 < y < 1, 0 < z < 1) is sometimes called lithium aluminum germanium titanium phosphate (LAGTP).

[0022] The solid electrolyte particles 11 can be an electrolyte suitable for electrode formation. Examples of such electrolytes include oxide solid electrolytes. The solid electrolyte particles 11 may contain an oxide solid electrolyte. The solid electrolyte particles 11 may also be an oxide solid electrolyte. Among these, NASICON-type oxide solid electrolytes are suitable for electrodes.

[0023] NASICON-type oxide solid electrolytes are materials that can be sintered at low temperatures compared to other oxide solid electrolytes, such as those with a perovskite structure or a garnet structure. Being able to sinter at low temperatures is advantageous for suppressing reactions between the solid electrolyte and the electrode active material. Furthermore, low-temperature sintering also avoids the phase transition from anatase-type titanium oxide to rutile-type titanium oxide.

[0024] The solid electrolyte particles 11 may contain at least one selected from the group consisting of LAGP, LATP, and LAGTP.

[0025] The solid electrolyte particles 11 are Li 1+x Al x Ge 2-x (PO4)3 (0≦x≦2), Li 1+x Al x Ti 2-x (PO4)3 (0≦x≦2), and Li 1+y Al y Ti z Ge 2-y-z It may have at least one composition selected from the group consisting of (PO4)3 (0 < y < 1, 0 < z < 1).

[0026] The solid electrolyte particles 11 are Li 1+x Al x Ge 2-x LAGP having the composition (PO4)3 (0 ≤ x ≤ 2) may also be used. When a compound with such a composition is used for the solid electrolyte particles 11 and a titanium-containing oxide is used for the electrode active material, the effects of the configuration of this embodiment are more fully realized.

[0027] The solid electrolyte particles 11 are Li 1+x Al x Ti 2-x LATP may have a composition of (PO4)3 (0 ≤ x ≤ 2).

[0028] The solid electrolyte particles 11 are Li 1+y Al y Ti z Ge 2-y-z LAGTP having the composition (PO4)3 (0 < y < 1, 0 < z < 1). Furthermore, the solid electrolyte particles 11 are Li 1.5 Al 0.5 (Ge 1.5-x Ti xThe LAGTP may have a composition of PO4)3 (0.015 ≤ x ≤ 0.04). With the latter LAGTP composition, side reactions caused by the reductive decomposition of LAGTP can be suppressed, and the decrease in charge-discharge efficiency can be suppressed. This can, for example, suppress the decrease in the initial discharge capacity of the battery.

[0029] LAGP is more suitable for electrodes. That is, because LAGP does not contain Ti, it has a wider potential window on the negative side compared to LATP. In this case, it is possible to select a negative electrode active material with a lower potential. This is advantageous for providing high-voltage and high-capacity batteries. One example of this effect is the combination of LAGP and titanium(IV) oxide. Furthermore, LAGP is an electrolyte that can be sintered at a lower temperature than LATP. Being able to sinter at a lower temperature is advantageous because it suppresses reactions between the electrode active material and the solid electrolyte.

[0030] The crystallinity of solid electrolytes can be determined by X-ray diffraction (XRD) or differential scanning calorimeter (DSC). When using X-ray diffraction, if only a halo pattern is observed in the X-ray diffraction pattern of the solid electrolyte, it can be determined that the solid electrolyte is amorphous.

[0031] Specific ratio I of carbon material 12 D / I G This can be determined based on the Raman spectrum of the solid electrolyte material 10 obtained by Raman spectroscopy. Specifically, for example, the peak intensity I in the Raman spectrum obtained using a micro-laser Raman spectrometer (NRS-5100, manufactured by JASCO Corporation) can be determined. G and peak intensity I D Based on this, ratio I D / I G It is possible to calculate this.

[0032] Specific ratio I of carbon material 12 D / I G The lower limit may be 0.6 or higher, and may be even more than 0.7 or higher. Specific ratio I of carbon material 12 D / I GThe upper limit may be 1.1 or less, and may also be 1.0 or less. Ratio I of carbon material 12 D / I G It may be between 0.5 and 1.0, or between 0.6 and 1.1.

[0033] In the solid electrolyte material 10, the carbon content (Ratm) present on the outer surface 11s of the solid electrolyte particles 11 may be 12 atomic% or more and less than 35 atomic%. Keeping the carbon content (Ratm), which is known to be an inhibitor of sinterability, within the above numerical range is advantageous in suppressing a decrease in the sinterability of the electrode.

[0034] As described above, in the solid electrolyte material 10, the carbon material 12 covers only a portion of the outer surface 11s of the solid electrolyte particles 11. For example, in the solid electrolyte material 10, if the thickness of the carbon material 12 is 4 nm or more, and the carbon content (Ratm) present on the outer surface 11s of the solid electrolyte particles 11 is 12 atomic percent or more and less than 35 atomic percent, then the carbon material 12 can be considered to cover only a portion of the outer surface 11s of the solid electrolyte particles 11. The fact that the thickness of the carbon material 12 is 4 nm or more can be considered to reflect the coating state of the carbon material 12 on the outer surface 11s of the solid electrolyte particles 11 from the viewpoint of XPS detection depth. In addition, the fact that the carbon content (Ratm) present on the outer surface 11s of the solid electrolyte particles 11 is 12 atomic percent or more and less than 35 atomic percent means that it is less than 100 atomic percent, so it can be determined that the carbon material 12 is in a partially coating state. Also, for example, LAGP appears white, and the carbon material appears black. Therefore, if the solid electrolyte particles 11 are LAGP, it is possible to consider that the carbon material 12 has coated only a portion of the outer surface 11s of the solid electrolyte particles 11, since the solid electrolyte material 10 after coating with the carbon material 12 is still observed as a white powder.

[0035] The carbon content (Ratm) present on the outer surface 11s of the solid electrolyte particles 11 can be determined, for example, by X-ray photoelectron spectroscopy (XPS). Specifically, by filling a powder cell with the solid electrolyte material 10 and performing XPS analysis, the XPS spectra of major elements, including carbon, can be obtained. The proportion (atomic %) of each element is calculated using the peak area intensity and the sensitivity factor of each element in each XPS spectrum. The calculated proportion (atomic %) of carbon can be considered as the carbon content (Ratm) (atomic %).

[0036] The lower limit of the carbon content Ratm may be 14 atomic% or more, 17 atomic% or more, 19 atomic% or more, 22 atomic% or more, 24 atomic% or more, 27 atomic% or more, and even 29 atomic% or more. The upper limit of the carbon content Ratm may be 32 atomic% or less, and even 30 atomic% or less. The carbon content Ratm may be 15 atomic% or more and 30 atomic% or less, and 20 atomic% or more and 30 atomic% or less. By setting the carbon content Ratm within the above numerical range, the influence of the carbon material 12, which is an inhibitor of sinterability, can be reduced. Furthermore, when the solid electrolyte particles 11 are LAGP, localized heat generation is more likely to occur due to the reaction of a portion of the carbon material 12 with oxygen in the amorphous LAGP, which is the solid electrolyte particle 11, making it easier to obtain the effect of promoting sintering between the solid electrolyte particles 11.

[0037] The thickness T12 of the carbon material 12 on the outer surface 11s of the solid electrolyte particles 11 may be 1 nm or more and less than 10 nm. Keeping the thickness T12 of the carbon material 12 within the above numerical range is advantageous in suppressing a decrease in the sinterability of the electrode. This is because it can reduce the influence of the carbon material 12, which is an inhibitor of sinterability.

[0038] The method for determining the thickness T12 of the carbon material 12 on the outer surface 11s of the solid electrolyte particles 11 is not particularly limited. For example, the thickness T12 of the carbon material 12 on the outer surface 11s of the solid electrolyte particles 11 can be determined by the following method. First, a sample is prepared by embedding powder of the solid electrolyte material 10 in epoxy resin. A thin section is prepared by cross-sectional processing of the sample using a focused ion beam (FIB) device. The thickness of the carbon material 12 is measured at multiple locations (e.g., five locations) for each of the multiple (e.g., three) solid electrolyte materials 10 contained in the thin section using a transmission electron microscope (TEM) or the like, and the average of these measured values ​​can be considered as the thickness T12 of the carbon material 12.

[0039] The lower limit of the thickness T12 of the carbon material 12 on the outer surface 11s of the solid electrolyte particles 11 may be 2 nm or more, 3 nm or more, 4 nm or more, or even 5 nm or more. The upper limit of the thickness T12 of the carbon material 12 may be 9 nm or less, 8 nm or less, 7 nm or less, or even 6 nm or less. The thickness T12 of the carbon material 12 may be 2 nm or more and 8 nm or less, or 4 nm or more and 7 nm or less. By setting the thickness T12 of the carbon material 12 within the above numerical range, the influence of the carbon material 12, which is an inhibitor of sinterability, can be reduced. Furthermore, when the solid electrolyte particles 11 are LAGP, localized heat generation is more likely to occur due to the reaction of a portion of the carbon material 12 with oxygen in the amorphous LAGP, which is the solid electrolyte particle 11, making it easier to obtain the effect of promoting sintering between the solid electrolyte particles 11.

[0040] The median diameter of the solid electrolyte particles 11 may be between 0.1 μm and 3 μm. By setting the median diameter of the solid electrolyte particles 11 within the above numerical range, the geometric contact between the solid electrolyte material 10 and the electrode active material can be improved in the electrode, making it easier to form a good interface at the stage of the unsintered electrode.

[0041] In this disclosure, median diameter means the particle size (D50) when the cumulative volume in the volume-based particle size distribution is equal to 50%. The volume-based particle size distribution is measured, for example, by a laser diffraction measuring device or an image analysis device.

[0042] The lower limit of the median diameter of the solid electrolyte particles 11 may be 0.2 μm or more, 0.3 μm or more, 0.4 μm or more, or even 0.5 μm or more. The upper limit of the median diameter of the solid electrolyte particles 11 may be 2.5 μm or less, 2.0 μm or less, or even 1.5 μm or less. The median diameter of the solid electrolyte particles 11 may be 0.2 μm or more and 2.5 μm or less, or 0.4 μm or more and 2.0 μm or less. By setting the median diameter of the solid electrolyte particles 11 within the above numerical range, the geometric contact between the solid electrolyte material 10 and the electrode active material 20 (described later) in the electrode can be further improved, and a good interface can be easily formed at the stage of the unsintered electrode.

[0043] The BET specific surface area of ​​the solid electrolyte material 10 is 1 m². 2 / g or more 10m 2 It may be less than or equal to / g. The BET specific surface area of ​​the solid electrolyte material 10 is 3m². 2 / g or more 9m 2 It may be less than or equal to / g. Furthermore, the BET specific surface area of ​​the solid electrolyte material 10 is 5m². 2 / g or more 8m 2 The value may be less than or equal to / g. By setting the value within this range, good contact with other electrode components can be maintained, thereby effectively forming a good interface. In addition, it becomes easier to suppress the reaction with the electrode active material 20, which will be described later, during the firing stage.

[0044] The BET specific surface area of ​​the solid electrolyte material 10 can be determined, for example, by converting the data of adsorption isotherms obtained by a gas adsorption method using nitrogen gas using the BET (Brunauer-Emmett-Teller) method. Specifically, a predetermined amount of solid electrolyte material 10 is placed in a test tube for measurement, and the test tube is connected to a specific surface area / pore distribution measuring device (manufactured by Quantachrome). Then, a nitrogen gas adsorption test is performed under the conditions of an adsorption temperature of 77 K and an upper limit of adsorption relative pressure of 0.99 (P / P0). Using the analysis software ASiQWin, the BET method analysis can be performed in the linear region of the adsorption isotherm to calculate the BET specific surface area of ​​the solid electrolyte material 10.

[0045] [Method for Manufacturing Solid Electrolyte Material] Next, the method for manufacturing the solid electrolyte material 10 described above will be explained. Figure 2 is a process diagram showing the method for manufacturing the solid electrolyte material 10.

[0046] A method for producing the solid electrolyte material 10 includes, for example, attaching a liquid component as a carbon source to a part of the outer surface 11s of amorphous solid electrolyte particles 11 containing a lithium-containing phosphate compound (step S1), and heating the solid electrolyte particles 11 with the liquid component attached at a temperature higher than the carbonization temperature of the carbon source and lower than the crystallization temperature of the solid electrolyte particles 11 to coat a part of the outer surface 11s of the solid electrolyte particles 11 with a carbon material 12 (step S2). The carbon source carbonizes at a temperature lower than the crystallization temperature of the solid electrolyte particles 11. The peak intensity of the G band in the Raman spectrum of the carbon material 12 is I G D-band peak intensity I D Ratio I D / I G However, it is between 0.5 and less than 1.2.

[0047] According to this manufacturing method, a portion of the outer surface 11s of the amorphous solid electrolyte particles 11 containing a lithium-containing phosphate compound is divided into parts I D / I G A solid electrolyte material 10 can be obtained that is coated with a carbon material 12 whose values ​​fall within the above numerical range.

[0048] For example, it has been confirmed that the crystallization temperature of amorphous LAGP (D50 = 1 μm) is in the range of 590°C to 600°C. Therefore, when the solid electrolyte particles 11 are amorphous LAGP (D50 = 1 μm), a carbon source that carbonizes at a temperature lower than 590°C is used. Examples of such liquid components as carbon sources include protic solvents. The liquid component as a carbon source may also be a protic solvent.

[0049] Examples of protic solvents include alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, 2-butanol, isobutanol, tert-butanol, ethylene glycol (EG), 1,2-propylene glycol, 1,3-propylene glycol, polyethylene glycol, glycerin, and polyglycerin. The liquid component as a carbon source may also be an alcohol. Alcohols are desirable because they carbonize at a temperature lower than the crystallization temperature of amorphous LAGP. For example, the carbonization of ethanol is known to begin in the temperature range of 250°C to 300°C. The liquid component as a carbon source may also be ethanol. Ethanol is more desirable because it is non-toxic like methanol and is a solvent that carbonizes at a particularly low temperature among alcohols. In addition, ethanol is desirable as a carbon source for forming a coating layer because of its low viscosity.

[0050] If the solid electrolyte particles 11 are amorphous LAGP, in step S1, ethanol as a liquid component may be attached to a portion of the outer surface 11s of the solid electrolyte particles 11.

[0051] The water content in the liquid component is, for example, 100 ppm or less. The water content in the liquid component may also be 50 ppm or less. When the water content is within the above numerical range, the degradation of the solid electrolyte particles 11 can be suppressed. If the water content deviates from the above numerical range, microcracks may form during the sintering stage, potentially hindering sintering.

[0052] In step S1, the method for attaching the liquid component as a carbon source to a portion of the outer surface 11s of the solid electrolyte particles 11 is not particularly limited. For example, a method of immersing the solid electrolyte particles 11 in the liquid component, or a method of coating or spraying the liquid component onto the outer surface 11s of the solid electrolyte particles 11 can be employed. Alternatively, after bringing the liquid component into contact with the solid electrolyte particles 11, a process to remove excess liquid component (e.g., drying) may be performed.

[0053] In step S1, by selecting a low-boiling point solvent as the liquid component for the carbon source, and by appropriately controlling the temperature, time, and atmosphere of the processing step for removing the carbon source attached to the solid electrolyte particles 11, the liquid component for the carbon source can be attached only to a portion of the outer surface 11s of the solid electrolyte particles 11. Examples of processing steps for removing the carbon source attached to the solid electrolyte particles 11 include drying steps.

[0054] If the solid electrolyte particles 11 are amorphous LAGP, in step S2, the solid electrolyte particles 11 to which the liquid component is attached may be heated at a temperature lower than 590°C to coat a portion of the outer surface 11s of the solid electrolyte particles 11 with the carbon material 12.

[0055] The lower limit of the heating temperature in step S2 can be appropriately set depending on the solid electrolyte particles 11 and the carbon source. For example, if the solid electrolyte particles 11 are amorphous LAGP (D50 = 1 μm) and the liquid component as the carbon source is ethanol, the lower limit of the heating temperature may be 250°C. From the viewpoint of appropriately controlling the degree of graphitization of the carbon material 12, 300°C or higher is desirable, and 400°C or higher is more desirable.

[0056] The upper limit of the heating temperature in step S2 can be appropriately set depending on the solid electrolyte particles 11 and the carbon source. For example, if the solid electrolyte particles 11 are amorphous LAGP (D50 = 1 μm) and the liquid component as the carbon source is ethanol, then, from the viewpoint of appropriately controlling the degree of graphitization of the carbon material 12, the upper limit of the heating temperature is preferably less than 600°C, and more preferably 500°C or less.

[0057] The heating time in step S2 is not particularly limited, as long as the carbon material 12 can coat a portion of the outer surface 11s of the solid electrolyte particles 11. The heating time can be, for example, in the range of 30 minutes to 60 hours. The heating time may also be in the range of 1 hour to 24 hours. Whether or not carbonization is occurring can be confirmed, for example, by Raman spectroscopy.

[0058] The heating atmosphere in step S2 is not particularly limited, as long as it is an atmosphere that can carbonize the liquid components. The heating atmosphere may be a vacuum or an inert gas atmosphere. When the heating atmosphere is a vacuum or an inert gas atmosphere, oxidation of the liquid components is suppressed. In addition, the oxidative decomposition of carbon formed after carbonization can be suppressed. Therefore, the upper limit of the heating temperature can be extended, and it becomes possible to select a solvent that carbonizes at a higher temperature, thereby expanding the range of solvents that can be selected.

[0059] (Second Embodiment) [Electrode] Figure 3 is a cross-sectional view showing the schematic configuration of the electrode 100 in the second embodiment. The electrode 100 comprises an electrode active material 20 and the solid electrolyte material 10 of the first embodiment. The particles of the electrode active material 20 are bound together by the sintered phase of the solid electrolyte material 10.

[0060] According to electrode 100, ionic conductivity and electronic conductivity can be improved while maintaining sinterability.

[0061] The electrode 100 is a sintered electrode manufactured by firing an unsintered electrode, formed from an electrode-forming material containing an electrode active material 20 and a solid electrolyte material 10, at a temperature above the crystallization temperature of the solid electrolyte particles 11. The electrode 100 is used, for example, as the positive or negative electrode of a solid-state battery.

[0062] In the electrode 100, the solid electrolyte material 10 forms a mesh-like sintered phase. For example, in the cross-section of the electrode 100, the length of the interface where the particles of the electrode active material 20 and the sintered phase of the solid electrolyte material 10 particles are in contact without gaps is on the order of micrometers, and the sintered phase of the solid electrolyte material 10 particles forms a good interface with the particles of the electrode active material 20. The presence of such a contact interface contributes to reducing the resistance of the electrode 100.

[0063] The sintered phase of the solid electrolyte material 10 particles may be a phase in which the particles of the solid electrolyte material 10 bond together and grain boundaries are lost. A sintered phase without grain boundaries exhibits excellent ionic conductivity and can form a good contact interface with the particles of the electrode active material 20. Such a structure can be formed by using amorphous solid electrolyte particles 11 as the raw material for the electrode 100. For example, the structure of the sintered phase can be confirmed by observing a cross-section of the electrode 100 at a magnification of 10,000 times using a scanning electron microscope.

[0064] In electrode 100, the sintered phase of the solid electrolyte material 10 includes a crystalline phase and an amorphous phase. When the sintered phase of the solid electrolyte material 10 includes a crystalline phase, electrode 100 exhibits higher ionic conductivity. The crystalline phase can be formed by appropriately adjusting the firing temperature. For example, if firing is performed at a temperature higher than the crystallization temperature of the solid electrolyte particles 11 contained in the solid electrolyte material 10, an electrode 100 containing crystalline solid electrolyte particles 11 can be obtained. However, the amorphous phase may also be included in the solid electrolyte particles 11. When an amorphous phase is included, the flexibility of the solid electrolyte material 10 increases, so that volume changes due to expansion and contraction of the electrode active material 20 are more easily absorbed by the solid electrolyte material 10, and structural damage to electrode 100 is more easily suppressed.

[0065] The electrode active material 20 is a material that has the ability to intercept and release metal ions such as lithium ions. In this embodiment, the electrode active material 20 includes an oxide that contains titanium and does not contain lithium.

[0066] In electrode 100, the electrode active material 20 may exist in the form of particles having a median diameter greater than 2 μm and less than 7 μm. The median diameter of the electrode active material 20 may be greater than 3 μm and less than 7 μm, or greater than 3.4 μm and less than 6 μm.

[0067] In electrode 100, the oxide as the electrode active material 20 may exist in the form of particles having a median diameter greater than 2 μm and less than 7 μm. The oxide particles are bound together by the sintered phase of the solid electrolyte material 10. The median diameter of the oxide particles may be greater than 3 μm and less than 7 μm, or greater than 3.4 μm and less than 6 μm.

[0068] The electrode 100 may have oxide particles of the order of micrometers in size as the electrode active material 20. Although oxide particles of this size may exist between the particles of the solid electrolyte material 10 during the molding of the powder material, the total contact area between the oxide particles and the particles of the solid electrolyte material 10 can be reduced compared to the case where oxide particles of the order of nanometers in size are used. Therefore, the influence of oxide particles of the order of micrometers as an inhibitor of sinterability can be reduced, and the sinterability of the electrode 100 can be improved. In other words, it becomes possible to form a good contact interface between the oxide particles and the particles of the solid electrolyte material 10. As a result, the resistance of the electrode 100 is reduced. The quality of the sinterability of the electrode 100 can be determined, for example, by the porosity of the electrode 100.

[0069] The median diameter of the oxide particles used as the electrode active material 20 may be a value calculated from an electron microscope image of the cross-section of the electrode 100. Specifically, the cross-section of the electrode 100 is observed with a scanning electron microscope (SEM). The magnification is, for example, 3000x. Image analysis software is used to measure the ferret diameter of the oxide particles present in two different observation fields. The "ferret diameter" is the length of the perpendicular line formed when a particle is sandwiched between two parallel lines in a certain direction. The number of particles to be measured is, for example, 185 or more. That is, the width of the observation fields is adjusted so that 185 or more particles are included in two different observation fields. If coarse particles are present due to the aggregation of secondary particles, it is difficult to say that such coarse particles accurately represent the structure of the electrode 100. Therefore, such coarse particles are excluded from the measurement. Coarse particles are, for example, particles with a ferret diameter of 16.5 μm or more. Next, the volume of each particle is calculated by considering it as a sphere with the measured ferret diameter. A particle size distribution is created by plotting particle size (= Ferret diameter, in 0.1 μm increments) on the horizontal axis and the volume of the group of particles with that particle size in the total volume on the vertical axis. The particle size at which the cumulative volume in this particle size distribution is 50% is considered to be the median diameter of the oxide particles contained in electrode 100.

[0070] The above median diameter may be the median diameter of secondary particles. Primary particles having a size on the order of nanometers may be granulated to produce secondary particles. Further, primary particles on the order of micrometers can be produced by a hydrothermal synthesis method.

[0071] The BET specific surface area of the oxide particles as the electrode active material 20 may be 1 m 2 / g or more and 10 m 2 / g or less. The BET specific surface area of the oxide particles as the electrode active material 20 may be 3 m 2 / g or more and 8 m 2 / g or less. Further, the BET specific surface area of the oxide particles as the electrode active material 20 may be 4 m 2 / g or more and 7 m 2 / g or less. By setting this numerical range, contact with other electrode constituent members can be maintained well, which is effective for forming a good interface. Further, in the firing stage, it becomes easier to suppress the reaction with the solid electrolyte material 10.

[0072] The BET specific surface area of the oxide particles can be determined by the same method as the method described above for the BET specific surface area of the solid electrolyte material 10.

[0073] Examples of the oxide containing titanium include titanium(IV) oxide and composite oxides containing titanium and transition metals other than titanium. Since these materials have the ability to occlude and release metal ions such as lithium ions, they are suitable for the electrode 100 of the present embodiment.

[0074] It is desirable that the oxide as the electrode active material 20 is co-sinterable with the particles 11 of the solid electrolyte. Specifically, it is desirable that the oxide is less likely to react with the particles 11 of the solid electrolyte and the crystal structure of the oxide is maintained after sintering. For example, titanium(IV) oxide is less likely to react with NASICON-type oxide solid electrolytes, which are typical oxide solid electrolytes, and thus is suitable for the electrode 100 of the present embodiment.

[0075] Examples of titanium(IV) oxide include anatase-type (tetragonal) titanium oxide, rutile-type (tetragonal) titanium oxide, and brookite-type (orthorhombic) titanium oxide.

[0076] Titanium dioxide may contain anatase-type titanium dioxide. The main component of titanium dioxide may be anatase-type titanium dioxide. Anatase-type titanium dioxide is suitable, for example, as an active material for lithium-ion secondary batteries. Furthermore, using anatase-type titanium dioxide improves the sinterability of electrode 100. As can be seen from the fact that the true density of anatase-type titanium dioxide is lower than that of rutile-type titanium dioxide, oxygen diffusion is easy, and mass transfer during the sintering process is smooth. Therefore, with anatase-type titanium dioxide, sintering can proceed at a lower temperature. "Main component" means the component that is present in the largest amount by mass. 90% or more by mass of titanium dioxide may be anatase-type titanium dioxide. The titanium dioxide may contain substantially only anatase-type titanium dioxide.

[0077] The structure of titanium dioxide can be investigated by X-ray diffraction or Raman spectroscopy. The ratio of components contained in titanium dioxide can be confirmed by analyzing the results of X-ray diffraction measurements using the Rietveld method.

[0078] Examples of composite oxides suitable for the electrode active material 20 include composite oxides containing titanium and niobium. Since composite oxides containing titanium and niobium also have the ability to intercept and release metal ions such as lithium ions, they are suitable for the electrode 100 of this embodiment. A composite oxide containing titanium and niobium has, for example, the composition TiNb2O7.

[0079] The oxide particles used as the electrode active material 20 may also contain secondary particles. The secondary particles have multiple voids inside. When the oxide particles used as the electrode active material 20 absorb metal ions such as lithium ions, the voids absorb the volume change of the particles. As a result, good contact between the electrode active material 20 and the solid electrolyte material 10 is maintained even when the battery is repeatedly charged and discharged. Furthermore, one of the causes of degradation in sintered oxide all-solid-state batteries is that cracks occur in the electrodes with charging and discharging, worsening the contact between the electrode active material 20 and the solid electrolyte material 10. By using secondary particles as the active material, it is possible to mitigate such degradation.

[0080] The electrode active material 20 may comprise oxide particles and a carbon material. This carbon material may have the same composition as the carbon material present on the outer surface 11s of the solid electrolyte particles 11, or it may have a different composition. Although titanium-containing oxide particles have poor electronic conductivity, as in this embodiment, by compounding titanium-containing oxide particles with a carbon material, an electrode active material 20 with improved electronic conductivity can be obtained. As a result, the electronic conductivity of the electrode 100 containing the electrode active material 20 can be improved. The electrode active material 20 is also suitable for use in combination with the solid electrolyte material 10.

[0081] In the electrode active material 20, the carbon material is present, for example, inside the pores of oxide particles. With this configuration, many electron conduction paths are formed between the oxide particles and the carbon material. As a result, electrons can be transported into the pores of the oxide particles, improving the electron conductivity of the electrode active material 20. Consequently, the electron conductivity of the electrode 100 containing the electrode active material 20 is improved. Furthermore, because the carbon material is placed inside the pores of the oxide particles, the amount of conductive additive mixed with the electrode active material 20 during the electrode 100 molding stage can be reduced. Therefore, the conductive additive is less likely to penetrate between the particles of the solid electrolyte material 10 and is less likely to become a factor that inhibits the interparticle sinterability of the solid electrolyte material 10. In other words, the electrode active material 20 in this embodiment can improve the interparticle sinterability of the solid electrolyte material 10 and improve the sinterability of the electrode 100. Therefore, a good contact interface is easily formed between the electrode active material 20 and the solid electrolyte material 10.

[0082] On the other hand, if carbon material is present inside the pores of the oxide particles, the shrinkage of the pores due to sintering during the firing process in the manufacture of the electrode 100 can be suppressed. When shrinkage is suppressed, even after sintering, a longer diffusion distance for the Ti atoms contained in the electrode active material 20 into the solid electrolyte material 10 can be ensured.

[0083] The fact that oxide particles have multiple pores, and that carbon material is present inside the pores in the electrode active material 20, can be confirmed, for example, by observing a cross-section of the electrode active material 20 with a scanning electron microscope (SEM).

[0084] The carbon material does not need to be present inside all of the multiple pores. Some of the multiple pores may not contain any carbon material.

[0085] The oxide particles may have multiple pores with an average pore diameter S of 50 nm to 200 nm. When using sintered electrodes, such as in oxide solid-state batteries, structural damage to the sintered electrodes due to expansion and contraction of the electrode active material becomes a problem. However, by using the electrode active material 20 in this embodiment as the electrode active material, the above-mentioned structural damage can be mitigated.

[0086] The fact that the oxide particles have an average pore diameter S within the above numerical range means that the diffusion distance of Ti atoms contained in the oxide particles increases. In this case, for example, the diffusion of Ti atoms from the oxide particles to the LAGP contained in the solid electrolyte material 10 is suppressed, and the deviation of the composition of LAGP near the interface between the electrode active material 20 and the solid electrolyte material 10, that is, the increase in the Ti atom concentration in LAGP, can be suppressed. As a result, side reactions caused by the reductive decomposition of LAGP formed at the interface accompanying the insertion of lithium ions into the electrode active material 20 can be suppressed, and the decrease in charge-discharge efficiency can be suppressed. This can, for example, suppress the decrease in the initial discharge capacity of the battery.

[0087] The average pore diameter S of the oxide particles may be between 60 nm and 190 nm, or between 70 nm and 180 nm. With this configuration, structural damage to the sintered electrode due to expansion and contraction of the electrode active material 20 is easily mitigated.

[0088] The lower limit of the average pore diameter S of the oxide particles may be 80 nm, 90 nm, or even 100 nm. With this configuration, structural damage to the sintered electrode due to the expansion and contraction of the electrode active material 20 is easily mitigated.

[0089] The upper limit of the average pore diameter S of the oxide particles may be 170 nm, 160 nm, or even 150 nm. With this configuration, the decrease in the volume ratio of the electrode active material 20 in the battery is suppressed, and therefore the decrease in battery capacity is easily suppressed.

[0090] The average pore diameter S of oxide particles can be determined, for example, by the mercury intrusion method. In the mercury intrusion method, high-pressure mercury is first injected into a sample having pores. The pore distribution can be determined from the relationship between the pressure applied to the mercury and the amount of mercury injected into the sample. The pore distribution can be measured, for example, using a mercury porosimeter. In detail, the diameter D of the pores into which mercury has been injected in the sample can be determined from the following relation (I). In relation (I), γ is the surface tension of mercury. θ is the contact angle between the mercury and the wall of the sample. P is the pressure applied to the mercury.

[0091] D=-4γcosθ÷P...(I)

[0092] The pressure P is changed in steps, and the amount of mercury injected is measured for each pressure P. The amount of mercury injected can be considered as the cumulative value of the pore volume up to a diameter D corresponding to a specific pressure P. This allows us to obtain a pore distribution in which the pore volume is specified for each diameter D. The pore distribution is, for example, a graph showing the relationship between the pore diameter D and the log differential pore volume.

[0093] From the pore distribution obtained for the electrode active material 20, the average pore diameter S (median diameter) of multiple pores in the electrode active material 20 can be calculated. At this time, pores observed other than intraparticle voids in the electrode active material 20, i.e., pores associated with interparticle voids, are excluded. Intraparticle voids and interparticle voids can be confirmed by cross-sectional SEM observation of the particles of the electrode active material 20.

[0094] The carbon material may coat a portion of the outer surface of the oxide particles. The oxide particles may have an outer surface coated with the carbon material and an outer surface that is not coated with the carbon material.

[0095] In oxide particles, multiple pores may include pores that communicate with the outside. Oxide particles do not necessarily have to contain completely closed voids that do not communicate with the outside. With such a configuration, it is easier to arrange carbon material inside the pores during the manufacturing process of the electrode active material 20. The presence of multiple pores that communicate with the outside can be confirmed, for example, in an SEM image of a cross-section of the electrode active material 20.

[0096] The oxide particles may be secondary particles containing multiple primary particles. With such a configuration, the average pore diameter S of the electrode active material 20 is more likely to satisfy the above numerical range.

[0097] The shape of the primary particles is not particularly limited. The shape of the primary particles may be, for example, plate-like, flake-like, needle-like, spherical, ellipsoidal, or the like.

[0098] For example, a pore may be formed between two primary particles among a plurality of primary particles. The plurality of pores may be formed continuously in three dimensions.

[0099] When the oxide particles are secondary particles, they may be sintered bodies of multiple primary particles. With this configuration, the primary particles bond together and densify, forming good ion conduction paths within the oxide particles. As a result, the ion conductivity inside the electrode active material 20 is further improved, and the ion conductivity of the electrode 100 containing the electrode active material 20 is further improved. In the case of a solid-state battery that does not use a liquid electrolyte, it is desirable that the secondary particles be sintered bodies of multiple primary particles.

[0100] The shape of the oxide particles is not particularly limited. For example, the shape of the oxide particles may be spherical or ellipsoidal. The shape of the oxide particles may also be needle-shaped or plate-shaped. If the oxide particles are secondary particles, the oxide particles may have an uneven surface on their outer surface, which is caused by primary particles such as spheres. When the outer surface of the oxide particles has an uneven surface, it is easier to form a good interface between the solid electrolyte material 10 and the electrode active material 20.

[0101] When the oxide particles are secondary particles, the median diameter of the multiple primary particles in the electrode active material 20 may be between 50 nm and 500 nm. With such a configuration, the average pore diameter S of the electrode active material 20 is more likely to satisfy the above numerical range.

[0102] The median diameter of the multiple primary particles in the electrode active material 20 may be 60 nm to 400 nm, or 70 nm to 300 nm.

[0103] The lower limit of the median diameter of the multiple primary particles in the electrode active material 20 may be 80 nm or 90 nm. A larger median diameter of the primary particles reduces the number of grain boundaries. Therefore, from the viewpoint of ion conduction paths, it is desirable that the lower limit of the median diameter of the primary particles be within the above numerical range.

[0104] The upper limit of the median diameter of the multiple primary particles in the electrode active material 20 may be 250 nm, 200 nm, or even 150 nm. A smaller median diameter of the primary particles makes it easier to control the pore structure.

[0105] The pore volume of the oxide particles before the carbon material 12 is placed is defined as V. The pore volume V may be 0.01 mL / g or more and 0.5 mL / g or less. With this configuration, the electronic conductivity of the electrode active material 20 is further improved. As a result, the electronic conductivity of the electrode 100 containing the electrode active material 20 is further improved. The electrode active material 20 may be a composite particle containing oxide particles and carbon material, or it may be oxide particles that do not contain carbon material.

[0106] The pore volume V of oxide particles can be determined, for example, from the pore distribution obtained by the mercury intrusion method described above. Alternatively, the pore volume V can be determined by calcining the oxide particles after the carbon material has been placed, decomposing and removing the carbon material 12, and then using the mercury intrusion method. The pore volume V can also be calculated from the pore distribution obtained for oxide particles before the carbon material is placed. In this case, voids observed in addition to intraparticle voids, i.e., pores associated with interparticle voids, are excluded. Intraparticle voids and interparticle voids can be confirmed by cross-sectional SEM observation of the oxide particles.

[0107] The pore volume V may be 0.015 mL / g or more and 0.5 mL / g or less, or 0.02 mL / g or more and 0.5 mL / g or less.

[0108] The lower limit of the pore volume V may be 0.03 mL / g or more, and may be even more than 0.04 mL / g. The upper limit of the pore volume V is not particularly limited. For example, the upper limit of the pore volume V may be 0.3 mL / g or less, and may be even more than 0.2 mL / g or less. With this configuration, it is possible to suppress a decrease in the volume ratio of the electrode active material 20 in the battery and the resulting decrease in the battery capacity due to the pore volume V becoming too large. In addition, it is possible to avoid the collapse of the electrode active material 20 in processes in which pressure is applied to the electrode active material 20 during the manufacturing of the battery, such as the pressing process.

[0109] The electrode 100 may further contain a conductive additive 30. Examples of the conductive additive 30 include carbon materials such as graphite, carbon black, carbon fiber, and carbon nanotubes. The conductive additive 30 may be a carbon material. The graphite may be natural graphite or artificial graphite. Examples of carbon black include acetylene black and Ketjen black. The carbon material may be crystalline or amorphous. The conductive additive 30 typically has a particle shape on the order of nanometers or micrometers. Examples of particle shapes include spherical, ellipsoidal, flaky, and fibrous.

[0110] [Method for manufacturing an electrode] Next, the method for manufacturing the above-described electrode 100 will be described. FIG. 4 is a process diagram showing the method for manufacturing the electrode 100.

[0111] The method for manufacturing the electrode 100 includes, for example, preparing an electrode-forming material including solid electrolyte particles 11 of an amorphous solid electrolyte containing a lithium-containing phosphate compound and a carbon material 12 covering a part of the outer surface 11s of the solid electrolyte particles 11, and an electrode active material 20 (step ST1), forming the electrode-forming material to produce an unsintered body electrode (step ST2), and firing the unsintered body electrode at a temperature not lower than the crystallization temperature of the solid electrolyte particles 11 (step ST3). In the electrode-forming material, the peak intensity I G of the G band in the Raman spectrum of the carbon material 12 with respect to the peak intensity I D of the D band is such that the ratio I D / I G is not less than 0.5 and less than 1.2. In step ST1, particles having a median diameter exceeding 2.5 μm and less than 9 μm are used as the electrode active material 20.

[0112] According to this manufacturing method, an electrode 100 having improved ionic conductivity and electronic conductivity while maintaining sinterability can be obtained.

[0113] In step ST1, a raw material including the solid electrolyte material 10 and the electrode active material 20 is mixed to prepare a slurry-like electrode-forming material. The raw material may include, for example, a conductive assistant 30, a binder, and a solvent in addition to the solid electrolyte material 10 and the electrode active material 20. The electrode-forming material may be prepared by previously mixing the binder and the solvent to prepare a binder solution and mixing the solid electrolyte material 10, the electrode active material 20, and the conductive assistant 30 in the binder solution.

[0114] The binder is decomposed and removed by firing. Thermoplastic resins such as polyvinyl butyral, polyvinylidene fluoride, cellulose, acrylic, urethane, and polyvinyl alcohol can be used as the binder. The solvent is typically an organic solvent such as anhydrous alcohol (e.g., anhydrous ethanol), toluene, butyl acetate, or NMP. The slurry may also contain a plasticizer. The type of plasticizer is not particularly limited, and phthalate esters such as dioctyl phthalate and diisononyl phthalate can be used.

[0115] Step ST1 may include the method for producing the solid electrolyte material 10 described in the first embodiment as a substep.

[0116] In step ST2, the electrode-forming material is applied to a substrate to form a coating film. The substrate can be a resin substrate, a glass substrate, a ceramic substrate, or a metal substrate. After forming the coating film, the solvent is removed from the coating film. This yields an unsintered electrode. To remove the solvent from the coating film, the coating film may be heated or allowed to air dry. If necessary, the coating film may be press-formed or hot-pressed. An unsintered electrode may also be produced by molding and drying the electrode-forming material without using a substrate. Alternatively, after applying the electrode-forming material to a substrate to form a coating film, the coating film may be pulverized, and the raw material powder obtained by pulverization may be press-formed or hot-pressed to produce an unsintered electrode.

[0117] In step ST3, the unsintered electrode is fired at a temperature above the crystallization temperature of the solid electrolyte particles 11. As described in the method for manufacturing the solid electrolyte material in the first embodiment, for example, it has been confirmed that the crystallization temperature of amorphous LAGP (D50 = 1 μm) is in the range of 590°C to 600°C. Therefore, if the solid electrolyte particles 11 are amorphous LAGP, the firing temperature (ambient temperature) in step ST3 is 590°C or higher. The upper limit of the firing temperature in step ST3 is, for example, 900°C or lower.

[0118] Step ST3 is carried out, for example, under air or an inert atmosphere. The inert atmosphere is, for example, a nitrogen gas atmosphere or a noble gas atmosphere. A small amount of oxygen may also be mixed into the inert atmosphere. The firing time for step ST3 is, for example, 1 to 15 hours.

[0119] In step ST3, the particles of the solid electrolyte material 10 bond together to form a sintered phase without grain boundaries. As the crystallinity of the solid electrolyte material 10 improves, the ionic conductivity of the electrode 100 improves.

[0120] The manufacturing method may include a substep of calcining the unsintered electrode between step ST2 and step ST3. Calcination is carried out, for example, under air or an inert atmosphere. The inert atmosphere is, for example, a nitrogen gas atmosphere or a noble gas atmosphere. A small amount of oxygen may also be mixed into the inert atmosphere. The calcination temperature (ambient temperature) is, for example, 250°C to 600°C. The calcination time is, for example, 1 hour to 60 hours. It is desirable to carry out the calcination in a temperature range in which the binder is sufficiently removed, the solid electrolyte particles 11 soften beyond the glass transition temperature, and the crystallization of the solid electrolyte particles 11 does not proceed. In this way, a good interface is formed between the electrode active material 20 and the solid electrolyte material 10 as the binder is removed and the solid electrolyte particles 11 are vitrified.

[0121] (Third Embodiment) [Battery] Figure 5 is a cross-sectional view showing the schematic configuration of the battery 1000 in the third embodiment. The battery 1000 comprises a positive electrode 101, a negative electrode 102, and an electrolyte layer 103. The electrolyte layer 103 is disposed between the positive electrode 101 and the negative electrode 102. At least one electrode selected from the group consisting of the positive electrode 101 and the negative electrode 102 uses the electrode 100 described in the second embodiment. By using the electrode 100 in at least one electrode selected from the group consisting of the positive electrode 101 and the negative electrode 102, the effect of reducing resistance is obtained in at least one electrode selected from the group consisting of the positive electrode 101 and the negative electrode 102.

[0122] The electrode 100 described in the second embodiment is preferably used as a negative electrode 102. In this case, a titanium-containing oxide acts as the negative electrode active material. Since a titanium-containing oxide is suitable as a negative electrode active material, the electrode 100 is suitable as a negative electrode 102.

[0123] When electrode 100 is used as the negative electrode 102, the titanium-containing oxide does not contain lithium when the battery 1000 has not been charged or discharged after assembly. In other words, the battery 1000 is in a completely discharged state.

[0124] However, it is also possible to use electrode 100 as the positive electrode. In this case, a material less noble than a titanium-containing oxide, such as lithium metal, is used as the negative electrode active material.

[0125] The positive electrode 101 contains a positive electrode active material. The positive electrode active material is a material that has the ability to intercept and release metal ions such as lithium ions. Examples of positive electrode active materials include lithium-containing transition metal oxides and lithium-containing transition metal phosphates. Among these, lithium-containing transition metal phosphates are suitable for electrode 100. Examples of lithium-containing transition metal phosphates include lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, and lithium nickel phosphate. In addition to the positive electrode active material, the positive electrode 101 may also contain a solid electrolyte, a conductive additive, and the like.

[0126] The electrolyte layer 103 contains a solid electrolyte. The solid electrolyte is, for example, a sulfide solid electrolyte, a halide solid electrolyte, a complex hydride solid electrolyte, a porous oxide solid electrolyte impregnated with an electrolyte solution, or an oxide solid electrolyte. The composition of the solid electrolyte contained in the electrolyte layer 103 may be the same as or different from the composition of the solid electrolyte contained in the positive electrode 101. The composition of the solid electrolyte contained in the electrolyte layer 103 may be the same as or different from the composition of the solid electrolyte contained in the negative electrode 102. The positive electrode 101, the electrolyte layer 103, and the negative electrode 102 may all contain solid electrolytes of the same composition.

[0127] In the battery 1000, the positive electrode 101, the negative electrode 102, and the electrolyte layer 103 may be composed of sintered bodies. In this case, the positive electrode 101, the negative electrode 102, and the electrolyte layer 103 can be integrally formed by simultaneous firing. Integrating the positive electrode 101, the negative electrode 102, and the electrolyte layer 103 by simultaneous firing ensures reliable contact between the positive electrode 101, the negative electrode 102, and the electrolyte layer 103, thereby improving the conductivity of metal ions such as lithium ions. However, if the solid electrolyte contained in the electrolyte layer 103 is, for example, a sulfide solid electrolyte, a halide solid electrolyte, a complex hydride solid electrolyte, a porous oxide solid electrolyte impregnated with an electrolyte solution, or an oxide solid electrolyte that does not require sintering due to firing at high temperatures, simultaneous firing is not necessarily required. For example, the positive electrode 101 and the negative electrode 102 may be fired individually and then integrated.

[0128] [Battery Manufacturing Method] Next, the manufacturing method of the battery 1000 described above will be explained. Figure 6 is a process diagram showing the manufacturing method of the battery 1000.

[0129] A method for manufacturing a battery 1000 includes, for example, forming an electrode forming material (step STP1) that includes a solid electrolyte material 10 comprising amorphous solid electrolyte particles 11 containing a lithium-containing phosphate compound and a carbon material 12 covering a part of the outer surface 11s of the solid electrolyte particles 11, and an electrode active material 20 to produce an unsintered electrode; forming an electrolyte layer forming material (step STP2) to produce an unsintered electrolyte layer; stacking the unsintered electrode and the unsintered electrolyte layer to produce a laminate (step STP3); and firing the laminate at a temperature above the crystallization temperature of the solid electrolyte particles 11 (step STP4). For example, if the negative electrode 102 is lithium metal, a laminate can be made by stacking the positive electrode 101 and the electrolyte layer 103, firing the laminate to produce a sintered body, and then pressing, sputtering, or depositing lithium metal onto the sintered body to form the negative electrode 102. In the electrode formation material, the peak intensity of the G band in the Raman spectrum of the carbon material 12 is I G D-band peak intensity I D Ratio I D / IG However, it is between 0.5 and less than 1.2. As the electrode active material 20, particles having a median diameter greater than 2.5 μm and less than 9 μm are used.

[0130] In step STP1, an unsintered electrode is produced by molding the electrode-forming material. Step STP1 corresponds to step ST2 in the manufacturing method of the electrode 100 of the second embodiment.

[0131] Step STP1 may include step ST1 in the manufacturing method of the electrode 100 of the second embodiment as a substep.

[0132] In step STP2, first, raw materials are mixed to prepare a slurry-like material for forming the electrolyte layer. The raw materials include a solid electrolyte. Examples of solid electrolytes include sulfide solid electrolytes, halide solid electrolytes, complex hydride solid electrolytes, porous oxide solid electrolytes impregnated with electrolyte, and oxide solid electrolytes. The composition of the solid electrolyte may be the same as or different from the composition of the solid electrolyte particles 11. In addition to the solid electrolyte, the raw materials may include, for example, a binder and a solvent. The binder and solvent may be mixed in advance to prepare a binder solution, and the material for forming the electrolyte layer may be prepared by mixing the solid electrolyte into the binder solution.

[0133] In step STP2, the electrolyte layer forming material is applied to the substrate to form a coating film. The substrate can be a resin substrate, a glass substrate, a ceramic substrate, or a metal substrate. After forming the coating film, the solvent is removed from the coating film. This yields an unsintered electrolyte layer. To remove the solvent from the coating film, the coating film may be heated or allowed to air dry. If necessary, the coating film may be press-formed or hot-pressed. An unsintered electrolyte layer may also be produced by molding and drying the electrolyte layer forming material without using a substrate. After applying the electrolyte layer forming material to the substrate to form a coating film, the coating film may be pulverized, and the raw material powder obtained by pulverization may be press-formed or hot-pressed to produce an unsintered electrolyte layer.

[0134] In step STP3, a laminate is fabricated by stacking an unsintered electrode and an unsintered electrolyte layer. Specifically, an unsintered positive electrode, an unsintered electrolyte layer, and an unsintered negative electrode are stacked in this order and pressed together. This results in a laminate containing an unsintered positive electrode, an unsintered electrolyte layer, and an unsintered negative electrode. For example, if the negative electrode 102 is lithium metal, a laminate containing an unsintered positive electrode and an unsintered electrolyte layer is obtained, excluding the unsintered negative electrode.

[0135] In step STP4, the laminate is fired. Step STP4 corresponds to step ST3 in the manufacturing method of the electrode 100 of the second embodiment. That is, when the solid electrolyte particles 11 are amorphous LAGP (D50 = 1 μm), the firing temperature (ambient temperature) in step STP4 is 590°C or higher. The upper limit of the firing temperature in step STP4 is, for example, 900°C or lower. For example, when the negative electrode 102 is lithium metal, in step STP4, the laminate including the unsintered positive electrode and unsintered electrolyte layer is fired, excluding the unsintered negative electrode. The lithium metal as the negative electrode 102 is formed by pressing, sputtering, or vapor deposition after firing. Furthermore, if a sulfide solid electrolyte, halide solid electrolyte, complex hydride solid electrolyte, porous oxide solid electrolyte impregnated with electrolyte, or oxide electrolyte is selected as the solid electrolyte contained in the electrolyte layer 103, which does not require sintering due to firing at high temperatures, the unsintered negative electrode and unsintered positive electrode, excluding the unsintered electrolyte layer, are fired individually before being laminated with the unsintered electrolyte layer.

[0136] Similar to the method for manufacturing the electrode 100 described in the second embodiment, the manufacturing method may include a substep of calcining the laminate between step STP3 and step STP4. The substep of calcining the laminate corresponds to the substep of calcining the unsintered electrode in the manufacturing method of the electrode 100 of the second embodiment.

[0137] (Other Embodiments) (Note) The above description of embodiments discloses the following technologies.

[0138] (Technology 1) A solid electrolyte comprising amorphous solid electrolyte particles containing a lithium-containing phosphate compound, and a carbon material covering a portion of the outer surface of the solid electrolyte particles, wherein the peak intensity of the G band in the Raman spectrum of the carbon material is G D-band peak intensity I D Ratio I D / I G However, a solid electrolyte material whose value is between 0.5 and less than 1.2.

[0139] According to the solid electrolyte material of Technology 1, it is possible to improve the ionic conductivity and electronic conductivity of the electrode while maintaining the sinterability of the electrode.

[0140] (Technology 2) The solid electrolyte material according to Technology 1, wherein the carbon content present on the outer surface of the particles of the solid electrolyte is 12 atomic percent or more and less than 35 atomic percent. A solid electrolyte material having such a configuration is advantageous in suppressing a decrease in the sinterability of the electrode.

[0141] (Technology 3) The solid electrolyte material according to Technology 1 or 2, wherein the thickness of the carbon material on the outer surface of the particles of the solid electrolyte is 1 nm or more and less than 10 nm. A solid electrolyte material having such a configuration can reduce the influence of the carbon material, which is an inhibitor of sinterability, and is advantageous in suppressing a decrease in the sinterability of the electrode.

[0142] (Technology 4) A solid electrolyte material according to any one of the technologies 1 to 3, wherein the median diameter of the particles of the solid electrolyte is 0.1 μm or more and 3 μm or less. With such a configuration, a good interface between the solid electrolyte material and the electrode active material is easily formed in the electrode.

[0143] (Technical 5) The solid electrolyte is Li 1+x Al x Ge 2-x (PO4)3 (0≦x≦2), Li 1+x Al x Ti 2-x (PO4)3 (0≦x≦2), and Li 1+y Al y Ti z Ge 2-y-zA solid electrolyte material according to any one of the techniques 1 to 4, having at least one composition selected from the group consisting of (PO4)3 (0 < y < 1, 0 < z < 1). When a compound of such composition is used as solid electrolyte particles and a titanium-containing oxide is used as the electrode active material, the effects of the present invention are easily fully realized.

[0144] (Technical 6) An electrode comprising an electrode active material and a solid electrolyte material described in any one of Technical 1 to 5, wherein in the electrode, the particles of the electrode active material are bound together by the sintered phase of the solid electrolyte material, and the sintered phase of the solid electrolyte material includes a crystalline phase and an amorphous phase.

[0145] According to the electrode of Technology 6, it is possible to improve ionic conductivity and electronic conductivity while maintaining sinterability. Furthermore, because the flexibility of the solid electrolyte material is increased, volume changes due to the expansion and contraction of the electrode active material are more easily absorbed by the solid electrolyte material, thereby suppressing structural damage to the electrode.

[0146] (Technical 7) The electrode according to Technical 6, wherein the electrode active material contains an oxide that contains titanium and does not contain lithium. With this configuration, a good contact interface is formed between the electrode active material and the solid electrolyte material. As a result, the sinterability of the electrode is improved.

[0147] (Technical 8) The electrode according to Technical 7, wherein 90% by mass or more of the oxide is anatase-type titanium oxide. Anatase-type titanium oxide is suitable, for example, as an active material for lithium-ion secondary batteries. Furthermore, the sinterability of the electrode is improved by using anatase-type titanium oxide.

[0148] (Technical 9) The electrode according to Technical 7 or 8, wherein the oxide exists in the form of particles having a median diameter greater than 2 μm and less than 7 μm. Particles of oxide having such a size can reduce the total contact area between the electrode active material and the solid electrolyte, which is advantageous in suppressing the decrease in the initial discharge capacity of the battery due to the reductive decomposition of the solid electrolyte.

[0149] (Technical 10) The electrode according to any one of Technical 7 to 9, wherein the oxide has a plurality of pores having an average pore diameter of 50 nm to 200 nm. Particles of oxide having such a configuration are advantageous in mitigating structural damage to the sintered electrode due to the expansion and contraction of the electrode active material.

[0150] (Technical 11) The electrode according to any one of Technical 7 to 10, wherein the electrode contains oxide particles as the electrode active material, the oxide particles have a plurality of pores, and a carbon material is present inside the plurality of pores. With such a configuration, many electron conduction paths are formed between the oxide particles and the carbon material. As a result, electrons can be transported to the inside of the pores of the oxide particles, improving the electron conductivity of the electrode active material. Consequently, the electron conductivity of the electrode containing the electrode active material is improved.

[0151] (Technical 12) A battery comprising: a positive electrode; a negative electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode, wherein at least one selected from the group consisting of the positive electrode and the negative electrode includes an electrode as described in any one of Technical 6 to 11.

[0152] In the battery of Technology 12, the sinterability of the electrodes is maintained while the ionic conductivity and electronic conductivity of the electrodes are improved.

[0153] (Technology 13) The method includes: attaching a liquid component as a carbon source to a portion of the outer surface of amorphous solid electrolyte particles containing a lithium-containing phosphate compound; and heating the solid electrolyte particles with the liquid component attached at a temperature higher than the carbonization temperature of the carbon source and lower than the crystallization temperature of the solid electrolyte to coat a portion of the outer surface of the solid electrolyte particles with a carbon material, wherein the carbon source carbonizes at a temperature lower than the crystallization temperature of the solid electrolyte, and the peak intensity of the G band in the Raman spectrum of the carbon material is I G D-band peak intensity I D Ratio I D / I G A method for producing a solid electrolyte material, wherein the ratio is 0.5 or more and less than 1.2.

[0154] According to the method for manufacturing solid electrolyte materials of Technology 13, a portion of the outer surface of the particles of an amorphous solid electrolyte containing a lithium-containing phosphate compound is divided into two parts. D / I G A solid electrolyte material can be obtained by coating it with a carbon material within the above numerical range.

[0155] Details of this disclosure will be explained below using examples and comparative examples.

[0156] [Preparation of Solid Electrolyte Material] <<Example 1>> Amorphous LAGP (D50 = 1 μm) powder was prepared as the solid electrolyte particles. Ethanol (concentration 99.5 wt%) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Ethanol (super dehydrated)) was prepared as the liquid component to serve as the carbon source. The LAGP powder was placed in a container and ethanol was added and stirred so that the mass ratio of LAGP:ethanol was 100:155. The mixture was stirred using a rotary-orbit mixer (manufactured by Shinki Co., Ltd., Rentaro) at 2000 rpm for 10 minutes. At this time, in order to remove excess carbon source, a drying treatment was performed under atmospheric conditions at 150°C for 1 hour, thereby attaching a minute amount of ethanol to a part of the outer surface of the LAGP particles. Next, the LAGP powder with the ethanol attached was heated under atmospheric conditions at 400°C for 2 hours. This coated a part of the outer surface of the LAGP particles with carbon material. In this way, the solid electrolyte material of Example 1 was obtained. The solid electrolyte material of Example 1 had a white appearance.

[0157] ≪Comparative Example 1≫ The amorphous LAGP powder used as the solid electrolyte particles in Example 1 was used as the solid electrolyte material in Comparative Example 1. That is, the solid electrolyte material of Comparative Example 1 did not have a carbon material coating layer. The appearance of the solid electrolyte material of Comparative Example 1 was white.

[0158] <<Comparative Example 2>> Amorphous LAGP coated with ethanol was heated in air at 500°C for 2 hours. This coated a portion of the outer surface of the amorphous LAGP particles with a carbon material in a different state. The solid electrolyte material of Comparative Example 2 was obtained by the same method as in Example 1, except for this coating. The solid electrolyte material of Comparative Example 2 was white in appearance.

[0159] <<Comparative Example 3>> Amorphous LAGP coated with ethanol was heated in air at 600°C for 2 hours. This coated a portion of the outer surface of the amorphous LAGP particles with a carbon material in a different state. The solid electrolyte material of Comparative Example 3 was obtained by the same method as in Example 1, excluding this coating. The solid electrolyte material of Comparative Example 3 was white in appearance.

[0160] [Evaluation of the Crystal Structure of Solid Electrolyte Particles] Before the liquid component was attached to the solid electrolyte particles, X-ray diffraction patterns were acquired using an X-ray diffraction analyzer (MiniFlex600, Rigaku Corporation) to evaluate the crystal structure of the solid electrolyte particles. If only a halo pattern was observed in the X-ray diffraction pattern, it was determined that the solid electrolyte particles were amorphous. The results are shown in Table 1. Figures 7 to 10 show the X-ray diffraction patterns of the solid electrolyte particles used in Example 1 and Comparative Examples 1 to 3.

[0161] [Measurement of Median Diameter of Solid Electrolyte Particles] The median diameter of solid electrolyte particles before the liquid component was attached was measured using a laser diffraction particle size distribution analyzer (Malvern Panalytical). The results are shown in Table 1.

[0162] [Measurement of Carbon Material Thickness] Based on the method described above, the thickness of the carbon material in the solid electrolyte material was determined using a transmission electron microscope (TEM). Specifically, a sample was prepared by embedding powder of the solid electrolyte material in epoxy resin. A thin section was prepared by cross-sectional processing of the sample using a FIB (Fibrillation-Injection Bomb) device. Using TEM, the thickness of the carbon material in each of the three solid electrolyte materials contained in the thin section was measured at five locations, and the average of these measurements was considered to be the thickness of the carbon material. The results are shown in Table 1.

[0163] [Ratio I D / I G [Measurement] For solid electrolyte materials, the peak intensity of the G band in the Raman spectrum is measured. G D-band peak intensity I D Ratio I D / I GWe sought to obtain the following. Specifically, we used a micro-laser Raman spectroscopy analyzer (JASCO Corporation, NRS-5100) to obtain the Raman spectrum of the sample under the following analytical conditions. The peak intensity I obtained from the Raman spectrum G and peak intensity I D Based on this, ratio I D / I G The result was calculated. The results are shown in Table 1.

[0164] <Analysis Conditions> Measurement Method: Microscopic measurement (x100) Laser Wavelength: 532 nm, Output 4.8 mW Slit: 100 μm x 1000 μm Aperture: Diameter 4000 μm Exposure: 1 second x 2 times (equivalent to 100 points) Measurement Wavenumber Range: 950 cm -1 From 1900cm -1

[0165] [Measurement of Carbon Content on the Outer Surface of Solid Electrolyte Particles] For solid electrolyte materials, the carbon content (atomic %) on the outer surface of the solid electrolyte particles was determined. Specifically, using an XPS instrument (ULVAC-PHI, PHI Quantera SXM), the sample was packed into a powder cell, and XPS analysis was performed under the following analytical conditions to obtain XPS spectra for carbon, lithium, aluminum, germanium, and phosphorus. The proportion (atomic %) of each element was calculated using the peak area intensity in each XPS spectrum and the sensitivity factor of each element. The calculated proportion (atomic %) of carbon was considered as the content (atomic %). The results are shown in Table 1.

[0166] <Analysis Conditions> X-ray source: Monochromatic Al-Kα (1486.6 eV), 15 kV / 25 W Analysis area: 300 nm × 800 nm (scanning microfocus, 100 mm f) Photoelectron extraction angle: 45° <Neutralization Conditions> Neutralization of electrons + floating ions <Measurement Conditions> Step (eV): 1.0 (wide), 0.05 (narrow) Pass energy (eV): 280.0 (wide), 55.0 (narrow) Measurement time (ms): 60 (narrow)

[0167] [Measurement of BET specific surface area of ​​solid electrolyte materials] The BET specific surface area of ​​solid electrolyte materials was measured. Specifically, a nitrogen gas adsorption test was performed on the samples. Using analysis software (ASiQWin), the BET method was used to analyze the linear region of the adsorption isotherm, and the BET specific surface area was calculated. The results are shown in Table 1.

[0168]

[0169] [Electrode Fabrication] <Example 2> Using the solid electrolyte material and electrode active material A from Example 1, the electrode of Example 2 was fabricated by the following method. The electrode was composed of a sintered body.

[0170] As electrode active material A, anatase-type TiO2 powder was prepared. The TiO2 particles were secondary particles. 20 parts by mass of TiO2 powder, 75 parts by mass of solid electrolyte material, 5 parts by mass of acetylene black (Denka Co., Ltd., Li-400), and 155 parts by mass of binder solution were added to a 58 mL container and stirred. The binder solution was prepared by mixing 15 parts by mass of polyvinyl butyral (Sekisui Chemical Co., Ltd., BM-1) and 140 parts by mass of super-dehydrated ethanol. Stirring was performed using a rotation-orbit mixer (Thinky Co., Ltd., Rentaro) at 2000 rpm for 30 minutes. In this way, a slurry-like electrode-forming material was prepared.

[0171] Next, a 58 mL container was placed on a hot plate set to 80°C to dry the slurry. After confirming that the ethanol had been sufficiently removed from the slurry, the dried film was coarsely ground and vacuum-dried at 80°C for 2 hours. The coarsely ground product after vacuum drying was placed in a mortar and manually ground for 15 minutes to obtain powder for preparing the unsintered electrode. Next, 122 mg of the powder for preparing the unsintered electrode was formed using a 10.5 mm diameter press molding machine by uniaxial pressing. In this way, the unsintered electrode of Example 1 was obtained. The pressurizing conditions were 276 MPa for 1 minute.

[0172] Next, the unsintered electrode was pre-sintered in an electric furnace to remove the binder. The pre-sintering conditions were 500°C (ambient temperature), under air, for 2 hours, with no gas flow, and a heating rate of 100°C / hour. Finally, the pre-sintered unsintered electrode was fully fired in an electric furnace. The conditions for the final firing were 700°C (ambient temperature), under a nitrogen atmosphere, for 2 hours, with a gas flow of 1 L / min and a heating rate of 100°C / hour. This yielded the electrode of Example 2, which is composed of a sintered body. The dimensions of the electrode of Example 2 were a diameter of 9.71 mm, a thickness of 0.6425 mm, and a mass of 104.0 mg.

[0173] <<Comparative Example 4>> The solid electrolyte material of Comparative Example 1 was used as the solid electrolyte material. Except for this, the electrode of Comparative Example 4 was obtained by the same method as in Example 2. The dimensions of the electrode of Comparative Example 4 were a diameter of 9.73 mm, a thickness of 0.6520 mm, and a mass of 103.225 mg.

[0174] <<Comparative Example 5>> The solid electrolyte material of Comparative Example 2 was used as the solid electrolyte material. Except for this, the electrode of Comparative Example 5 was obtained by the same method as in Example 2. The dimensions of the electrode of Comparative Example 5 were a diameter of 9.97 mm, a thickness of 0.6596 mm, and a mass of 103.9 mg.

[0175] <<Comparative Example 6>> The solid electrolyte material of Comparative Example 3 was used as the solid electrolyte material. Except for this, the electrode of Comparative Example 6 was obtained by the same method as in Example 2. The dimensions of the electrode of Comparative Example 6 were a diameter of 10.57 mm, a thickness of 0.6568 mm, and a mass of 104.0 mg.

[0176] [Measurement of Median Diameter of Electrode Active Material] The median diameter of the electrode active material before preparation of the electrode formation material was measured using a laser diffraction particle size distribution analyzer (Malvern Panalytical, Mastersizer 3000). RO water with added surfactant was used as the solvent. After ultrasonic dispersion in the solvent for 1 minute, the median diameter was measured using the laser diffraction particle size distribution analyzer. The results are shown in Table 2.

[0177] [Measurement of BET specific surface area of ​​electrode active material] The BET specific surface area of ​​the electrode active material was measured before preparation of the electrode formation material. Specifically, a nitrogen gas adsorption test was performed on the sample. Using analysis software (ASiQWin), the BET method was performed in the linear region of the adsorption isotherm, and the BET specific surface area was calculated. The results are shown in Table 2.

[0178] [Measurement of Average Pore Diameter S of Electrode Active Material] The average pore diameter S (nm) of the electrode active material before preparation of the electrode forming material was determined. Specifically, the pore distribution was measured using a mercury porosimeter (Micromeristics, Autopore V 9620) under the following analytical conditions. From the obtained pore distribution, the average pore diameter S (median diameter) was determined. The results are shown in Table 2.

[0179] <Analysis Conditions> Sample: Approximately 0.2 g (taken into a standard 5 cc powder cell) Measurement range: Equivalent pore diameter D in the range of approximately 0.003 μm to 100 μm Initial pressure P: 3.5 psia (equivalent to a pore diameter of approximately 50 μm) Contact angle θ between mercury and the sample wall: 130° Surface tension γ of mercury: 485 dynes / cm

[0180] [Measurement of Pore Volume V of Electrode Active Material] The pore volume V of the electrode active material was measured before the preparation of the electrode forming material. Specifically, the pore distribution was measured using a mercury porosimeter (Micromeristics, Autopore V 9620 model) under the analytical conditions described above. The pore volume was calculated from the pore distribution. The results are shown in Table 2.

[0181]

[0182] [Measurement of electrode porosity] The true density of each material used in the manufacture of the electrodes was measured in advance. The porosity of the electrodes was calculated using the electrode dimensions, the measured true density, and the content of each material. However, the electrodes were assumed to contain only TiO2, LAGP, and acetylene black. The true density was measured using a pycnometer (Anton Paar, Ultrapyc 5000) by the He substitution method. For LAGP, since amorphous material is used as the starting material, it is difficult to evaluate the density after sintering. Therefore, the theoretical density was used for the true density of LAGP. The results are shown in Table 3.

[0183] [Measurement of Electrode Ionic Conductivity] The ionic conductivity of the electrode was measured by the following method. First, the electrode was placed in a vacuum dryer and dried at 80°C for 1 hour. Next, Li metal foil, solid polymer electrolyte membrane, electrode, solid polymer electrolyte membrane, and Li metal foil were stacked in this order and placed inside a sealed two-electrode cell (manufactured by Hosen Co., Ltd.). A LiTFSI-PEO membrane was used as the solid polymer electrolyte membrane. The weight-average molecular weight Mw of PEO contained in the LiTFSI-PEO membrane was 600,000. In the LiTFSI-PEO membrane, the ratio of PEO to LiTFSI was PEO:LiTFSI = 18:1 in molar ratio. Subsequently, chronoamperometry measurements were performed at measurement voltages of 0.1V, 0.25V, 0.5V, and 0.75V. The current value used was the value 70 seconds after the voltage was applied. The ambient temperature during measurement was 60°C. Resistance was calculated from the relationship between voltage and current. Ionic conductivity was calculated using the electrode dimensions. The results are shown in Table 3.

[0184] [Measurement of Electrode Electronic Conductivity] The electronic conductivity of the electrodes was measured using the following method. First, the electrodes were placed in a vacuum dryer and dried at 80°C for 1 hour. Next, a 290 nm thick Au thin film was formed on both sides of the electrodes by sputtering. The electrodes were placed inside a sealed two-electrode cell (manufactured by Hosen Co., Ltd.). Then, chronoamperometry measurements were performed at measurement voltages of 0.1 V, 0.25 V, 0.5 V, and 0.75 V. The current value used was the value 70 seconds after the voltage was applied. The ambient temperature during measurement was 25°C. The resistance value was calculated from the relationship between voltage and current. The electronic conductivity was calculated using the dimensions of the electrodes. The results are shown in Table 3.

[0185]

[0186] ≪Discussion≫ As shown in Table 3, the electrode of Example 2 had a smaller porosity compared to the electrode of Comparative Example 4, which used solid electrolyte particles before carbon coating. No decrease in sinterability due to the coating of carbon material, which is a sintering inhibitor, was observed, and sinterability was maintained. Furthermore, the electrode of Example 2 showed improved ionic conductivity and electronic conductivity compared to the electrodes of Comparative Examples 4 to 6. This is thought to be because, in the electrode of Example 2, by using the solid electrolyte material of Example 1 as the solid electrolyte, improvements in ionic conductivity and electronic conductivity were achieved without causing a decrease in sinterability between solid electrolyte particles, despite the coating of carbon material, which is a sintering inhibitor. Regarding electronic conductivity, it is thought that during the firing process (step ST3) in the manufacture of the electrode, a portion of the carbon material coating a part of the outer surface of the solid electrolyte particles burned with oxygen in the electrode active material TiO2, promoting the introduction of oxygen vacancies into the electrode active material TiO2, thereby improving the electronic conductivity of the electrode. Despite using the solid electrolyte material of Example 1, in which a portion of the outer surface of the solid electrolyte particles was coated with a carbon material known to inhibit sintering, the decrease in sintering performance of the electrode in Example 2 was suppressed. This is thought to be because, during the firing process (step ST3) in the manufacture of the electrode, a portion of the carbon material reacted with oxygen in the amorphous LAGP, which is the solid electrolyte particle, causing localized heat generation, which promoted sintering between the solid electrolyte particles. In the solid electrolyte material of Comparative Example 2, although a portion of the outer surface of the solid electrolyte particles was coated with a carbon material known to inhibit sintering, similar to the solid electrolyte material of Example 1, the effect observed in the electrode of Comparative Example 5 was not confirmed. This is thought to be because the degree of graphitization of the carbon material coating a portion of the outer surface of the solid electrolyte particles is involved in the reactivity with amorphous LAGP and the reactivity with TiO2, the electrode active material, and it is important to coat a portion of the outer surface of the solid electrolyte particles with a carbon material of an appropriate degree of graphitization.

[0187] The solid electrolyte material of this disclosure can be used, for example, in automotive lithium-ion secondary batteries.

Claims

1. A solid electrolyte comprising amorphous solid electrolyte particles containing a lithium-containing phosphate compound, and a carbon material covering a portion of the outer surface of the solid electrolyte particles, wherein the peak intensity of the G band in the Raman spectrum of the carbon material is I G D-band peak intensity I D Ratio I D / I G However, a solid electrolyte material whose value is between 0.5 and less than 1.

2.

2. The solid electrolyte material according to claim 1, wherein the carbon content present on the outer surface of the particles of the solid electrolyte is 12 atomic percent or more and less than 35 atomic percent.

3. The solid electrolyte material according to claim 1, wherein the thickness of the carbon material on the outer surface of the particles of the solid electrolyte is 1 nm or more and less than 10 nm.

4. The solid electrolyte material according to claim 1, wherein the median diameter of the particles of the solid electrolyte is 0.1 μm or more and 3 μm or less.

5. The solid electrolyte is Li 1+x Al x Ge 2-x (PO4)3 (0 ≤ x ≤ 2), Li 1+x Al x Ti 2-x (PO4)3 (0 ≤ x ≤ 2), and Li 1+y Al y Ti z Ge 2-y-z (PO4)3 (0 < y < 1, 0 < z < 1), and the solid electrolyte material according to claim 1 having at least one composition selected from the group consisting of 6. An electrode comprising an electrode active material and a solid electrolyte material according to claim 1, wherein in the electrode, the particles of the electrode active material are bound together by the sintered phase of the solid electrolyte material, and the sintered phase of the solid electrolyte material includes a crystalline phase and an amorphous phase.

7. The electrode according to claim 6, wherein the electrode active material includes an oxide that contains titanium and does not contain lithium.

8. The electrode according to claim 7, wherein 90% by mass or more of the oxide is anatase-type titanium oxide.

9. The electrode according to claim 7, wherein the oxide exists in the form of particles having a median diameter greater than 2 μm and less than 7 μm.

10. The electrode according to claim 7, wherein the oxide has a plurality of pores having an average pore diameter of 50 nm or more and 200 nm or less.

11. The electrode according to claim 7, wherein the electrode contains oxide particles as the electrode active material, the oxide particles have a plurality of pores, and a carbon material is present inside the plurality of pores.

12. A battery comprising: a positive electrode; a negative electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode, wherein at least one selected from the group consisting of the positive electrode and the negative electrode is an electrode as described in claim 6.

13. The method comprises: attaching a liquid component as a carbon source to a portion of the outer surface of amorphous solid electrolyte particles containing a lithium-containing phosphate compound; and heating the solid electrolyte particles with the liquid component attached at a temperature higher than the carbonization temperature of the carbon source and lower than the crystallization temperature of the solid electrolyte to coat a portion of the outer surface of the solid electrolyte particles with a carbon material, wherein the carbon source carbonizes at a temperature lower than the crystallization temperature of the solid electrolyte, and the peak intensity of the G band in the Raman spectrum of the carbon material is I G D-band peak intensity I D Ratio I D / I G A method for producing a solid electrolyte material, wherein the ratio is 0.5 or more and less than 1.2.

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