JP7707928B2 - Solid electrolyte member and method for producing the same - Google Patents

Description

The present invention relates to a solid electrolyte member and a method for manufacturing a solid electrolyte member.

Sulfide-based solid electrolytes are known as solid electrolytes for lithium batteries. Patent Document 1 describes a sulfide solid electrolyte material made of glass ceramics composed of an ion conductor containing lithium, phosphorus, and sulfur and a lithium halide, and containing at least one of Al ₂ O ₃ , ZrO ₃ , TiO ₂ , and SiO _2. Patent Document 2 describes a solid electrolyte containing 100 ppm to 1000 ppm of aluminum by mass and having lithium ion conductivity.

JP 2015-76316 A International Publication No. 2020/105604

Solid electrolyte materials containing lithium, phosphorus, and sulfur are required to suppress deterioration of battery performance.

The present invention has been made in view of the above, and aims to provide a solid electrolyte member and a method for manufacturing a solid electrolyte member that can suppress deterioration of battery performance.

The present invention provides a solid electrolyte member and a method for manufacturing a solid electrolyte member that satisfy the following conditions:

<1> A solid electrolyte member containing Li, P, and S, in which the Li content measured by ICP atomic emission spectroscopy (ICP-AES) is 8.1% by mass or more and 17.9% by mass or less based on the total content of elements contained in the solid electrolyte member, and the Li content measured by X-ray fluorescence spectroscopy (XRF) is 8.1% by mass or more and 17.9% by mass or less based on the total content of elements contained in the solid electrolyte member. A solid electrolyte member in which the total content of Al, Zr, Ti, Si, and W measured by X-ray fluorescence spectroscopy is less than 100 ppm by mass relative to the total content of elements contained in the solid electrolyte member, and when the solid electrolyte member is classified into particle sizes of less than 5 μm, particle sizes of 5 μm or more and less than 100 μm, and particle sizes of 100 μm or more, the total content of Al, Zr, Ti, Si, and W measured by X-ray fluorescence spectroscopy is less than 100 ppm by mass relative to the total content of elements contained in the solid electrolyte member.

<2> A solid electrolyte member containing Li, Si, P, and S, in which the Li content measured by ICP atomic emission spectroscopy (ICP-AES) is 8.1% by mass or more and 17.9% by mass or less based on the total content of elements contained in the solid electrolyte member, and the Li content measured by X-ray fluorescence spectroscopy (XRF) is 8.1% by mass or more and 17.9% by mass or less based on the total content of elements contained in the solid electrolyte member. A solid electrolyte member in which the total content of Al, Zr, Ti, and W measured by X-ray fluorescence spectroscopy is less than 100 ppm by mass relative to the total content of elements contained in the solid electrolyte member, and when the solid electrolyte member is classified into particle sizes of less than 5 μm, particle sizes of 5 μm or more and less than 100 μm, and particle sizes of 100 μm or more, the total content of Al, Zr, Ti, and W measured by X-ray fluorescence spectroscopy is less than 100 ppm by mass relative to the total content of elements contained in the solid electrolyte member.

<3> Preferably, the solid electrolyte member has an average crystallite diameter of 50 nm or more and a conductivity of 4 mS/cm or more.

<4> Preferably, a solid electrolyte member has a crystal structure of space group _P42nmc , and when measured by X-ray diffraction measurement using CuKα radiation, peaks of the following formulas (A) to (E) are detected as crystal peaks, and a peak of formula (F) is not detected as a crystal peak on the higher angle side of the peak of formula (D), or a peak of formula (F) is detected such that, when the diffraction intensity of the peak of formula ( _E ) is _IA and the diffraction intensity of the peak of formula (F) is IB, the ratio _IB / _IA is less than 0.50.
2θ=17.38°±0.50°...(A)
2θ=20.18°±0.50°...(B)
2θ=20.44°±0.50°...(C)
2θ=26.96°±0.50°...(D)
2θ=29.58°±0.50°...(E)
2θ=27.33°±0.50°...(F)

<5> Preferably, the solid electrolyte member has an Argyrodite-type crystal structure.

<6> A method for manufacturing a solid electrolyte member according to the present disclosure, comprising a preparation step of preparing an assembly of manufacturing raw materials for the solid electrolyte member, and a production step of heating the assembly of starting raw materials to produce the solid electrolyte member, in which in the preparation step, the starting raw materials are mixed to produce the assembly of starting raw materials such that a crystal peak of a crystalline substance can be detected when the produced assembly of starting raw materials is measured by X-ray diffraction.

The present invention can suppress the deterioration of battery performance.

FIG. 1 is a flowchart showing a method for manufacturing a solid electrolyte member according to the present embodiment. FIG. 2 is a schematic diagram of a facility for producing a solid electrolyte member. FIG. 3 is a graph showing the XRD spectrum of each example. FIG. 4 is a graph showing the results of measuring the cycle life.

The present invention will be described in detail below with reference to the drawings. Note that the present invention is not limited to the following modes for carrying out the invention (hereinafter referred to as embodiments). Furthermore, the components in the following embodiments include those that a person skilled in the art can easily imagine, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the components disclosed in the following embodiments can be combined as appropriate.

First Embodiment
(Solid electrolyte member)
The solid electrolyte member according to the first embodiment is a sulfide-based solid electrolyte. The solid electrolyte member according to the first embodiment is a lithium ion conductor containing Li, P, and S, and is used in, for example, lithium batteries. More specifically, the solid electrolyte member according to the first embodiment has a so-called LGPS-type crystal structure. Specifically, the solid electrolyte member according to the first embodiment is represented by the chemical formula Li _a M _b P _c S _d . Here, a, b, c, and d are numbers greater than 0. The element M is at least one element of Group 13, Group 14, and Group 15 except Al and Si. In this embodiment, the element M is preferably at least one of Ge and Sn. The solid electrolyte member according to the first embodiment includes one type of element M, but may include multiple types of elements M.
Thus, the solid electrolyte member according to the first embodiment is a solid electrolyte containing lithium, element M, phosphorus, and sulfur, but is not limited thereto, and may be a sulfide-based solid electrolyte containing components other than lithium, element M, and phosphorus. The solid electrolyte member is not limited to one having an LGPS-type crystal structure, and is not limited to Li _a M _b P _c S _d . Other examples of the composition of the solid electrolyte member will be described later.

In the solid electrolyte member according to the first embodiment, the Li content is, by mass, 8.1% by mass or more and 17.9% by mass or less, more preferably 10.0% by mass or more and 15.0% by mass or less, and even more preferably 10.7% by mass or more and 12.8% by mass or less, based on the total content of elements contained in the solid electrolyte member. By setting the total Li content within this range, appropriate conductivity can be imparted. The Li content can be measured by ICP atomic emission spectroscopy (ICP-AES).

When the Li content is measured using ICP emission spectrometry, the following conditions may be applied.
Measurement device: SPS3100 (manufactured by SII Nano Technology)
Wavelength range: 160 nm to 770 nm
RF output: 1.4 kW

In the solid electrolyte member according to the first embodiment, the total content of Al, Zr, Ti, Si, and W is 100 ppm or less, preferably 80 ppm or less, and more preferably 50 ppm or less, based on the total content of the elements contained in the solid electrolyte member, on a mass basis. That is, the total value of the content of the Al element, the content of the Zr element, the content of the Ti element, the content of the Si element, and the content of the W element is preferably within the above numerical range with respect to the total content of all elements contained in the solid electrolyte member. By having the total content of Al, Zr, Ti, Si, and W within this range, the solid electrolyte member has a high purity with few impurities, and the amount of by-products generated by the reaction of the impurities is suppressed, so that the deterioration of the battery performance can be appropriately suppressed. The contents of Al, Zr, Ti, Si, and W can be measured by X-ray fluorescence spectroscopy (XRF). Battery performance here refers, for example, to cycle life.

More specifically, when X-ray fluorescence analysis is used, the content of the target element may be calculated based on the peak intensity in the intensity spectrum of fluorescent X-rays measured by X-ray fluorescence analysis. Specifically, the content of the target element relative to the total content of all elements contained in the solid electrolyte member excluding Li is calculated based on the peak intensity of the target element in the intensity spectrum of fluorescent X-rays. Then, the content of the target element relative to the total content of elements contained in the solid electrolyte member (the total content of all elements including Li) is calculated using the following formula (1).

A=A ₀・(100-A _Li )...(1)

Here, A is the content (mass%) of the target element relative to the total content of the elements contained in the solid electrolyte member. A ₀ is the content (mass%) of the target element relative to the total content of all elements contained in the solid electrolyte member excluding Li, calculated based on the peak intensity in the fluorescent X-ray intensity spectrum. A _Li is the content (mass%) of Li calculated using ICP atomic emission spectroscopy. The total content of Al, Zr, Ti, Si, and W relative to the total content of the elements contained in the solid electrolyte member is calculated by calculating A for each of Al, Zr, Ti, Si, and W, and adding up the respective A's.

When fluorescent X-ray analysis is used, the following conditions may be applied.
Measurement device: M4 TORNADO (manufactured by Bruker)
Excitation X-ray: Polycapillary X-ray optical system Rh tube Output: 50 kV, 200 μA
・X-ray diameter: 20 μm

In addition, when the solid electrolyte member according to the first embodiment is classified into a particle size of less than 5 μm, a particle size of 5 μm or more and less than 100 μm, and a particle size of 100 μm or more, the total content of Al, Zr, Ti, Si, and W measured by X-ray fluorescence analysis in each classified solid electrolyte member is less than 100 ppm, preferably 80 ppm or less, and more preferably 50 ppm or less, based on the total content of elements contained in the solid electrolyte member, by mass. That is, if the solid electrolyte member according to the present embodiment has a particle size of less than 5 μm, the first solid electrolyte member has a total content of Al, Zr, Ti, Si, and W measured by X-ray fluorescence analysis in the first solid electrolyte member, less than 100 ppm, preferably 80 ppm or less, and more preferably 50 ppm or less, based on the total content of elements contained in the first solid electrolyte member, by mass. Similarly, if the second solid electrolyte member has a particle diameter of 5 μm or more and less than 100 μm, the total content of Al, Zr, Ti, Si, and W measured by X-ray fluorescence analysis in the second solid electrolyte member is less than 100 ppm, preferably 80 ppm or less, and more preferably 50 ppm or less, based on the total content of elements contained in the second solid electrolyte member, based on mass. Also, if the third solid electrolyte member has a particle diameter of 100 μm or more in the solid electrolyte member according to the present embodiment, the total content of Al, Zr, Ti, Si, and W measured by X-ray fluorescence analysis in the third solid electrolyte member is less than 100 ppm, preferably 80 ppm or less, and more preferably 50 ppm or less, based on mass. By ensuring that the total content of Al, Zr, Ti, Si, and W in each of the classified solid electrolyte components falls within this range, the solid electrolyte components have a high purity and few impurities, and the amount of by-products generated by the reaction of the impurities is reduced, making it possible to appropriately suppress deterioration of battery performance.

Classification into particle diameters of less than 5 μm, 5 μm to less than 100 μm, and 100 μm or more may be performed using a sieve made of SUS or nylon mesh. For example, particles with a particle diameter of less than 5 μm may be classified using a nylon mesh (Tantore #508/585-5, mesh size 5 μm). Particles with a particle diameter of 5 μm to less than 100 μm may be classified using a SUS sieve with a nominal mesh size of 100 μm that conforms to the JIS standard (JIS Z8801-1). Particles that remain unclassified as particles with a particle diameter of less than 5 μm and particles with a particle diameter of 5 μm to less than 100 μm may be treated as particles with a particle diameter of 100 μm or more. Particle diameters may be measured using a particle diameter distribution measuring device, for example, a laser diffraction scattering type particle diameter distribution measuring device LA-960 (manufactured by Horiba, Ltd.).

In addition, the solid electrolyte member according to the first embodiment preferably has an average crystallite diameter of 50 nm or more, more preferably 60 nm or more and 500 nm or less, and even more preferably 70 nm or more and 500 nm or less. When the average crystallite diameter of the solid electrolyte member is in this range, the solid electrolyte member becomes a material in which crystal growth has progressed, and the battery performance can be improved. Furthermore, in a state in which crystal growth has progressed in this way, the solid electrolyte member is prone to by-products being generated by reaction of impurities, but since the amount of impurities is small as described above, the battery performance can be improved while suppressing deterioration of the battery performance. The average crystallite diameter can be measured by X-ray diffraction method, and more specifically, it can be measured by powder X-ray diffraction measurement using CuKα as a radiation source and with a measurement range of the diffraction angle 2θ of 10° to 60°. As a result of the powder X-ray diffraction measurement, an X-ray diffraction spectrum is obtained, in which the horizontal axis is 2θ and the vertical axis is the relative intensity when the maximum peak intensity of all peaks in the measurement range is set to 1. The average crystallite diameter can be measured by substituting the diffraction angle of the peak and the half-width obtained in the X-ray diffraction spectrum into the following formula (2), which is the Scherrer formula, where D is the crystallite size (average crystallite diameter), K is the Scherrer constant, and B is the half-width of the peak.

D=Kλ/Bcosθ...(2)

The solid electrolyte member according to the first embodiment preferably has a conductivity of 1 mS/cm or more, more preferably 3 mS/cm or more, and even more preferably 4 mS/cm or more. By having the conductivity in this range, the battery performance of the solid electrolyte member can be appropriately maintained.

(Method for manufacturing solid electrolyte member)
Next, a method for producing the solid electrolyte member according to the present embodiment will be described. However, the following method is merely an example, and the present embodiment may be produced by any method without being limited to the following description.

1 is a flowchart showing a method for producing a solid electrolyte member according to the present embodiment. As shown in FIG 1, in the production method of the present embodiment, first, in a preparation step, an aggregate of starting materials A of the solid electrolyte member is prepared (step S10; preparation step).
The starting material A is each of the raw materials containing the elements constituting the solid electrolyte member, and the aggregate of the starting material A here refers to a mixture (stirring) of the powders of each raw material without chemical changes of each raw material (each starting raw material A). Here, it is preferable that each raw material is mixed to be homogeneous. Thus, the starting material A refers to one type of raw material, and the aggregate of the starting material A refers to an aggregate of each starting raw material A mixed together. In addition, the aggregate of the starting material A refers to an aggregate of raw materials in a state before the process of producing the solid electrolyte member is started, not an intermediate product produced during the process of producing the solid electrolyte member. Furthermore, the aggregate of the starting material A here refers to raw materials in a state before being stored in the furnace 10 described below.
In this production method, a raw material containing elemental sulfur and any one of Li, P, and M is used as a starting material.

(elemental sulfur)
Elemental sulfur refers to sulfur that does not contain any elements other than sulfur, except for inevitable impurities. Hereinafter, unless otherwise specified, each raw material may contain inevitable impurities.

(S raw material, Li raw material, P raw material, M raw material)
The starting material A is a material containing elements constituting the solid electrolyte member, and therefore in this embodiment, it can be said to contain an S material containing sulfur, a Li material containing lithium, a P material containing phosphorus, and an M material containing the element M.

(S raw material)
The S raw material is elemental sulfur, as described above.

(Li raw material)
The Li raw material is at least one of elemental lithium, a compound of lithium and element M, a compound of lithium and phosphorus, a compound of lithium, element M and phosphorus, a compound of lithium and sulfur (lithium sulfide), a compound of lithium, element M and sulfur (e.g. _Li4GeS4 , _Li4SnS4 , etc.), a compound of lithium, phosphorus and sulfur (e.g. _Li3PS4 ), _and a compound _of lithium, element M, phosphorus and sulfur. When _the Li raw material is a compound of lithium and another element, the Li raw material also serves as the raw material of the other element. For example, when the Li raw material is a compound of lithium and phosphorus, the compound of lithium and phosphorus can be said to be the Li raw material and the P raw material.

(P raw material)
The P raw material is at least one of phosphorus, a compound of lithium and phosphorus, a compound of element M and phosphorus, a compound of lithium, element M and phosphorus, a compound of phosphorus and sulfur (phosphorus sulfide), a compound of lithium, phosphorus and sulfur (e.g., _Li3PS4 ), a compound of element M, phosphorus and sulfur, and a compound _of lithium, element M, phosphorus and sulfur.

(M raw material)
The M raw material is at least one of the following: a simple substance of element M, a compound of lithium and element M, a compound of element M and phosphorus, a compound of lithium, element M and phosphorus, a compound of element M and sulfur (e.g., GeS, _GeS2 , SnS, _SnS2 , etc.), a compound of lithium, element M and sulfur, a compound of element M and phosphorus and sulfur (e.g., GeP, _Sn3P4 , _etc. ), and a compound of lithium, element M, phosphorus and sulfur.

(Mixing method)
Next, a method for mixing the raw materials will be described. In the preparation step, the raw materials (elemental sulfur, Li raw material, P raw material, and M raw material) are weighed out in a weight ratio that will be the composition of the solid electrolyte member to be manufactured, and are used as starting raw materials A. The starting raw materials A are mixed together to form an aggregate of the starting raw materials A.
In this embodiment, the elemental sulfur, the Li raw material, the P raw material, and the M raw material are weighed and mixed in a glove box in an argon atmosphere, but the present invention is not limited thereto, and the elements may be mixed in an inert gas atmosphere such as nitrogen. In addition, in this embodiment, the mixed elemental sulfur, the Li raw material, the P raw material, and the M raw material are pressed and molded into a pellet shape, but the present invention is not limited thereto.

In the preparation step, the raw materials (elemental sulfur, Li raw material, P raw material, M raw material) weighed as starting material A are mixed to form an aggregate of starting material A. The mixing here refers to stirring to the extent that each raw material is uniformly dispersed, and does not involve mechanical or chemical changes of each raw material as in the mechanical milling method. Therefore, when the aggregate of starting material A produced by this manufacturing method is measured by X-ray diffraction using CuKα radiation, the crystal peak of the crystalline substance constituting starting material A is detected, and no other crystal peaks are detected.
In addition, when elemental sulfur, Li raw material, P raw material, and M raw material are, for example, Li ₂ S, elemental P, and metal Sn (elemental Sn), when the aggregate of starting material A produced by this production method is measured by X-ray diffraction using CuKα radiation, the peaks of the following formulas (3) to (11) are detected as crystal peaks. Note that the crystal peak here refers to a peak whose intensity is equal to or greater than a threshold value, and the threshold value here is, for example, a relative intensity of 0.05 when the maximum peak intensity of the measurement result is set to 1.

2θ=23.06±0.50...(3)
2θ=25.83±0.50...(4)
2θ=27.00±0.50...(5)
2θ=27.71±0.50...(6)
2θ=30.63±0.50...(7)
2θ=32.01±0.50...(9)
2θ=44.81±0.50...(10)
2θ=44.89±0.50...(11)

In the preparation step, the mixing conditions for each raw material are set to a mixing time of 10 minutes or less and an upper limit of the load per unit area applied in the shear direction of 0.1 N/ ^mm2 or less, thereby enabling the crystal peaks of each raw material to be properly detected in the generated starting material A.

1 , after preparing an assembly of starting material A in the preparation step, a production step is performed in which the assembly of starting material A is heated to produce a solid electrolyte member (step S12; production step). That is, before the production step, elemental sulfur, Li raw material, P raw material, and M raw material contained in starting material A are not bonded to each other by chemical reaction, but in the production step, they are bonded to each other by chemical reaction to produce a solid electrolyte member represented by the chemical formula Li _a M _b P _c S _d .
Specifically, in the production step, the starting material A is heated to a temperature T1 and is maintained at the temperature T1 for a predetermined period of time to produce the solid electrolyte member.
The temperature T1 is preferably 400° C. or more and 1000° C. or less, more preferably 500° C. or more and 600° C. or less, and even more preferably 500° C. or more and 560° C. or less. By setting the temperature T1 within this numerical range, the liquefied elemental sulfur is bonded with raw materials other than S through a chemical reaction, and the solid electrolyte member can be appropriately produced.
The holding time at temperature T1 is preferably 1 hour or more and 72 hours or less, more preferably 1 hour or more and 24 hours or less, and even more preferably 1 hour or more and 12 hours or less. By setting the holding time within this range, the raw materials can be appropriately reacted to appropriately produce the solid electrolyte member.

Figure 2 is a schematic diagram of equipment for producing a solid electrolyte member. As shown in Figure 2, a furnace 10 is a furnace for heating starting material A to produce a solid electrolyte member. The furnace 10 is provided with a heating section 12. The heating section 12 is a heat source for heating the inside of the furnace 10. Note that the structure in Figure 2 is an example, and the equipment for producing a solid electrolyte member is not limited to the structure in Figure 2.

In the generation step, the starting material A is stored in the furnace 10 in a predetermined gas atmosphere, and the furnace 10 is sealed. Then, the inside of the furnace 10 in which the starting material A is stored is heated by the heating unit 12 to reach a temperature T1, and the temperature is maintained at T1 for a predetermined holding time. The gas filled in the furnace 10 may be any gas, and may be an inert gas (rare gas) such as argon, or hydrogen sulfide. It is not essential to seal the furnace, and for example, the furnace may be heated while supplying a predetermined gas without sealing it. For example, the furnace may be heated while supplying argon at 100 mL/min.
The elemental sulfur in the starting material A melts and liquefies before the temperature reaches T1, and a solid electrolyte member is produced by a solid-liquid reaction between the liquefied sulfur and the other raw materials.

In this way, in this manufacturing method, once the starting material A is stored in the furnace 10, the solid electrolyte member is generated without removing the starting material A from the furnace 10. In other words, in this manufacturing method, the sulfides (intermediate products) of Li, P, and element M generated from the starting material A are generated while being kept in the furnace 10, i.e., without being removed from the furnace 10 to the outside. That is, the sulfides (intermediate products) of Li, P, and element M generated from the starting material A react while being sealed in the furnace 10 in a predetermined gas atmosphere without being exposed to the air, to become the solid electrolyte member.

In this embodiment, only one stage of heating at temperature T1 is performed in the production step, but multiple stages of heating may be performed. In this case, for example, a process of heating at temperature T2 for a predetermined time to melt the elemental sulfur may be performed before heating at temperature T1. By providing a process of heating at temperature T2, it is possible to perform firing at temperature T1 in a state in which the elemental sulfur is reliably liquefied, and the solid electrolyte member can be appropriately produced. Temperature T2 here is lower than temperature T1 and higher than the melting point of elemental sulfur, for example, 115°C or higher and 150°C or lower.

(effect)
Here, when the solid electrolyte member contains impurities such as Al, Zr, Ti, Si, and W in addition to the composition of Li, P, and S, these impurities may react to generate by-products. When by-products are formed, the battery characteristics of the solid electrolyte member may deteriorate. Note that the battery performance here is, for example, cycle life, as described above. In contrast, the solid electrolyte member according to the present embodiment contains Li, P, and S, and the content of Li measured by ICP emission spectroscopy is 8.1 mass% or more and 17.9 mass% or less based on the total content of the elements contained in the solid electrolyte member. In addition, the solid electrolyte member according to the present embodiment has a total content of Al, Zr, Ti, Si, and W measured by fluorescent X-ray analysis that is less than 100 ppm based on the total content of the elements contained in the solid electrolyte member. In addition, when the solid electrolyte member according to the present embodiment is classified into a particle size of less than 5 μm, a particle size of 5 μm or more and less than 100 μm, and a particle size of 100 μm or more, the total content of Al, Zr, Ti, Si, and W in each classified solid electrolyte member measured by fluorescent X-ray analysis is less than 100 ppm by mass with respect to the total content of elements contained in the solid electrolyte member. Therefore, the solid electrolyte member according to the present embodiment can reduce the content of impurities regardless of the whole and particle size, and can suitably suppress deterioration of battery performance. Furthermore, the more reactive the impurities are near the surface, but the solid electrolyte member according to the present embodiment has a reduced amount of impurities even for a solid electrolyte member with a small particle size in which the ratio of impurities near the surface tends to be high, and therefore can suitably suppress deterioration of battery performance.

In addition, the solid electrolyte member according to this embodiment preferably has an average crystallite diameter of 50 nm or more and a conductivity of 4 mS/cm or more. The solid electrolyte member according to this embodiment can appropriately improve battery performance by having an average crystallite diameter of 50 nm or more. Furthermore, in such a state where crystal growth has progressed, by-products are likely to be generated by reactions of impurities, but the solid electrolyte member according to this embodiment has a small amount of impurities as described above, and therefore can improve battery performance while suppressing deterioration of battery performance.

In addition, the solid electrolyte member according to this embodiment preferably has an LGPS-type crystal structure. Being an LGPS-type, it can be suitably used in lithium batteries, etc.

In addition, the solid electrolyte member according to the present embodiment has a crystal structure of space group P4 ₂ nmc, and when measured by an X-ray diffraction method using CuKα radiation, it is preferable that the peaks of the following formulas (12) to (16) are detected. In addition, when the solid electrolyte member according to the present embodiment is measured by an X-ray diffraction method using CuKα radiation, it is preferable that the peak of formula (17) is not detected as a crystal peak on the high-angle side of the peak of formula (15), or that the peak of formula (17) is detected such that I _B /I _A is less than 0.50 when the diffraction intensity of the peak of formula (16) is I _A and the diffraction intensity of the peak of formula (17) is _I B. That is, the solid electrolyte member according to the present embodiment is preferably Li _a M _b P _c S _d (more preferably Li ₁₀ GeP ₂ S ₁₂ ) of the so-called LGPS type. The diffraction intensity refers to the peak height of the waveform measured by the X-ray diffraction method.

2θ=17.38°±0.50°...(12)
2θ=20.18°±0.50°...(13)
2θ=20.44°±0.50°...(14)
2θ=26.96°±0.50°...(15)
2θ=29.58°±0.50°...(16)
2θ=27.33°±0.50°...(17)

In addition, the method for producing a solid electrolyte member according to this embodiment preferably includes a preparation step of preparing an assembly of starting materials containing Li, P, and S, and a production step of heating the assembly of starting materials to produce a solid electrolyte member. In the preparation step, it is preferable to mix the starting materials to produce an assembly of starting materials so that a crystal peak of a crystalline substance can be detected when the produced assembly of starting materials is measured by X-ray diffraction. According to this production method, since the solid electrolyte member is produced by a solid-liquid reaction, the solid electrolyte member can be appropriately produced by mixing to the extent that crystals remain. Therefore, according to this production method, the mixing process is simplified, making it possible to produce many solid electrolyte members in a short time, while eliminating the need for mechanical milling, suppressing the inclusion of impurities during the production process, and suppressing deterioration of battery performance.

Second Embodiment
Next, a second embodiment will be described. The solid electrolyte member according to the first embodiment is mainly composed of Li, P, and S and does not substantially contain Si, whereas the solid electrolyte member according to the second embodiment is different from the first embodiment in that it also contains Si. Descriptions of the configurations of the second embodiment common to the first embodiment will be omitted.

The solid electrolyte member according to the second embodiment contains Li, Si, P, and S, in other words, contains at least Si as element M. In the second embodiment, element M may contain only Si, or may contain, in addition to Si, at least one element of Group 13, Group 14, and Group 15 excluding Al and Si. Furthermore, in the second embodiment, element M may contain, in addition to Si, at least one of Ge and Sn.

In the solid electrolyte member according to the second embodiment, the total content of Al, Zr, Ti, and W is 100 ppm or less, preferably 80 ppm or less, and more preferably 50 ppm or less, based on the total content of the elements contained in the solid electrolyte member, on a mass basis. In other words, the total value of the content of Al, the content of Zr, the content of Ti, and the content of W is preferably within the above numerical range relative to the total content of all elements contained in the solid electrolyte member. By having the total content of Al, Zr, Ti, and W within this range, the solid electrolyte member has a high purity with few impurities, and the amount of by-products generated by the reaction of the impurities is suppressed, thereby appropriately suppressing deterioration of the battery performance. The contents of Al, Zr, Ti, and W can be measured by fluorescent X-ray analysis.

In addition, when the solid electrolyte member according to the second embodiment is classified into a particle size of less than 5 μm, a particle size of 5 μm or more and less than 100 μm, and a particle size of 100 μm or more, the total content of Al, Zr, Ti, and W measured by X-ray fluorescence analysis in each classified solid electrolyte member is less than 100 ppm, preferably 80 ppm or less, and more preferably 50 ppm or less, based on the total content of elements contained in the solid electrolyte member, based on mass. That is, if the solid electrolyte member according to the present embodiment has a particle size of less than 5 μm as the first solid electrolyte member, the total content of Al, Zr, Ti, and W measured by X-ray fluorescence analysis in the first solid electrolyte member is less than 100 ppm, preferably 80 ppm or less, and more preferably 50 ppm or less, based on mass, based on the total content of elements contained in the first solid electrolyte member. Similarly, if the second solid electrolyte member has a particle diameter of 5 μm or more and less than 100 μm, the total content of Al, Zr, Ti, and W measured by X-ray fluorescence analysis in the second solid electrolyte member is less than 100 ppm, preferably 80 ppm or less, and more preferably 50 ppm or less, based on the total content of elements contained in the second solid electrolyte member, based on mass. Also, if the third solid electrolyte member has a particle diameter of 100 μm or more in the solid electrolyte member according to this embodiment, the total content of Al, Zr, Ti, and W measured by X-ray fluorescence analysis in the third solid electrolyte member is less than 100 ppm, preferably 80 ppm or less, and more preferably 50 ppm or less, based on mass.

As described above, the solid electrolyte member according to the second embodiment contains Li, Si, P, and S, and the Li content measured by ICP atomic emission spectroscopy is 8.1% by mass or more and 17.9% by mass or less with respect to the total content of the elements contained in the solid electrolyte member. In addition, the solid electrolyte member according to the second embodiment has a total content of Al, Zr, Ti, and W measured by X-ray fluorescence analysis, which is less than 100 ppm by mass with respect to the total content of the elements contained in the solid electrolyte member. In addition, when the solid electrolyte member according to the second embodiment is classified into a particle diameter of less than 5 μm, a particle diameter of 5 μm or more and less than 100 μm, and a particle diameter of 100 μm or more, in each classified solid electrolyte member, the total content of Al, Zr, Ti, and W measured by X-ray fluorescence analysis is less than 100 ppm by mass with respect to the total content of the elements contained in the solid electrolyte member. Therefore, the solid electrolyte member according to the second embodiment can reduce the impurity content, regardless of the overall and particle size, and can effectively suppress deterioration of battery performance.

The manufacturing method for the solid electrolyte member of the second embodiment is the same as that of the first embodiment, except that a raw material containing Si is used as the M raw material, so a description thereof will be omitted.

(Other examples)
In the above description, the solid electrolyte member has a chemical formula of Li _a M _b P _c S _d , but the composition is not limited thereto. Modifications of the solid electrolyte member will be described below. The modifications described below are applicable to both the solid electrolyte member of the first embodiment and the solid electrolyte member of the second embodiment.

(First Modification)
As described in the first modified example, the solid electrolyte member may have a chemical formula represented by Li _a M _b P _c S _d Ha _e , where a, b, c, d, and e are numbers greater than 0. The element Ha is a halogen element, and more preferably at least one element selected from the group consisting of F, Cl, Br, and I.

When the solid electrolyte member of the first modified example is measured by an X-ray diffraction method using CuKα radiation, it is preferable that a peak is detected at the position of the following formula (18) to formula (19).

2θ=26.96°±0.50°...(18)
2θ=29.58°±0.50°...(19)

In addition, when the solid electrolyte member of the first modified example is measured by an X-ray diffraction method using CuKα radiation, a peak may or may not be detected at the position of the following formula (20) on the higher angle side of the peak of formula (18). That is, in the first modified example, a solid electrolyte member may be manufactured in which a peak is detected at the position of formula (20), or a solid electrolyte member may be manufactured in which a peak is not detected at the position of formula (20).

2θ=27.33°±0.50°...(20)

Here, when the diffraction intensity of the peak at the position of formula (19) in X-ray diffraction measurement using CuKα radiation of the solid electrolyte member of the first modified example is I _A and the diffraction intensity at the position of formula (20) in X-ray diffraction measurement using CuKα radiation is I _B , it is preferable that the value of I _B /I _A is less than 0.50.

(Second Modification)
As described in the second modified example, _the solid electrolyte member has a chemical formula represented by _{LiaMbPcXdSeHaf} , where a, _b , _c , d, _e , and _f are numbers greater than 0.
The element Ha is a halogen element, and more preferably at least one of F, Cl, Br, and I.
The element X is a Group 16 element other than S, and more preferably at least one element selected from the group consisting of O, Se, and Te.

In the solid electrolyte member of the second modification, a peak is preferably detected at the position of formula (14) as in the solid electrolyte member of the first modification. In addition, in the solid electrolyte member manufactured in the second modification, a peak may or may not be detected at the position of formula (19) as in the solid electrolyte member of the first modification. In the solid electrolyte member of the second modification, a value of I _B /I _A is preferably less than 0.50 as in the solid electrolyte member of the second embodiment.

In the second modification, the element Ha and the element X are introduced into the solid electrolyte member of the present embodiment, but the element X may be introduced without the element Ha being introduced. That is, the solid electrolyte member may be expressed as Li _a M _b P _c X _d S _e . In this case, a, b, c, d, and e are numbers greater than 0.

(Third Modification)
The solid electrolyte member of the third modification has a crystal phase of an Argyrodite crystal structure. The solid electrolyte member of the third modification has a chemical formula represented by Li _a P _b S _c Ha _d , where a, b, c, and d are numbers greater than 0.
The element Ha is a halogen element, and more preferably at least one of F, Cl, Br, and I.

(Fourth Modification)
The solid electrolyte member of the fourth modification has a crystal phase of an Argyrodite crystal structure. The solid electrolyte member of the fourth modification has a chemical formula represented by Li _a P _b X _c S _d Ha _e , where a, b, c, d, and e are numbers greater than 0.
The element Ha is a halogen element, and more preferably at least one of F, Cl, Br, and I.
The element X is a Group 16 element other than S, and more preferably at least one element selected from the group consisting of O, Se, and Te.

(Fifth Modification)
The solid electrolyte member of the fifth modification has a chemical formula represented by Li _a M _{b Sc} , where a, b, and c are numbers greater than 0.

In the fifth modification, P is removed from the solid electrolyte member of the present embodiment, but an element X may be introduced therein. That is, the solid electrolyte member may be expressed as Li _a M _b X _c S _d . In this case, a, b, c, and d are numbers greater than 0, and the element X is an element of Group 16 other than S, and more preferably at least one element selected from O, Se, and Te.

(Example)
Next, examples will be described. Table 1 shows the amounts of raw materials used in each example.

Example 1
In Example 1, elemental sulfur was used as the starting material, lithium sulfide was used as the Li raw material, elemental phosphorus was used as the P raw material, and metal tin was used as the M raw material. In a glove box with an argon atmosphere and a dew point of -70°C or less, elemental sulfur, lithium sulfide, elemental phosphorus, and metal tin were weighed to obtain a desired composition, and mixed in a SUS mortar for 5 minutes to a degree that the color was uniform, and formed into a pellet shape. Here, 0.71 g of elemental sulfur, 0.72 g of lithium sulfide, 0.20 g of elemental phosphorus, and 0.37 g of metal tin were mixed. Then, the pellets placed in a carbon sintering container were placed in a furnace, and the inside of the furnace was heated and held at 560°C in an argon atmosphere. The holding time here was 6 hours. After that, the solid electrolyte member was obtained by cooling at 1°C/min.

Example 2
In Example 2, elemental sulfur was used as the starting material, lithium sulfide was used as the Li raw material, elemental phosphorus was used as the P raw material, and metal silicon was used as the M raw material. In a glove box with an argon atmosphere and a dew point of -70°C or less, elemental sulfur, lithium sulfide, elemental phosphorus, and metal tin were weighed to obtain a desired composition, mixed in a SUS mortar for 5 minutes to a degree that the color was uniform, and formed into a pellet shape. Here, 0.83 g of elemental sulfur, 0.84 g of lithium sulfide, 0.23 g of elemental phosphorus, and 0.10 g of metal silicon were mixed. Then, the pellets placed in a carbon sintering container were placed in a furnace, and the inside of the furnace was heated and held at 560°C in an argon atmosphere. The holding time here was 6 hours. After that, the mixture was cooled at 1°C/min to obtain a solid electrolyte member.

Example 3
In Example 3, elemental sulfur was used as the starting material, lithium sulfide and lithium chloride were used as the Li raw material, and elemental phosphorus was used as the P raw material. In an argon atmosphere, in a glove box with a dew point of -70°C or less, elemental sulfur, lithium sulfide, lithium chloride, and elemental phosphorus were weighed to obtain a desired composition, mixed in a SUS mortar for 5 minutes to a degree that the color was uniform, and formed into a pellet shape. Here, 0.60 g of elemental sulfur, 0.92 g of lithium sulfide, 0.28 g of lithium chloride, and 0.23 g of elemental phosphorus were mixed. Then, the pellets placed in a carbon sintering container were placed in a furnace, and the inside of the furnace was heated and held at 500°C in an argon atmosphere. The holding time here was 6 hours. After that, the mixture was cooled at 1°C/min to obtain a solid electrolyte member.

(Comparative Example 1)
In Comparative Example 1, lithium sulfide was used as the Li raw material, phosphorus sulfide was used as the P raw material, and tin sulfide was used as the M raw material. Here, 0.72 g of lithium sulfide, 0.70 g of phosphorus sulfide, and 0.58 g of tin sulfide were mixed. In addition, a ball mill using tungsten carbide media of 10 mmφ was used as the mixing condition, and the mixture was mixed for 24 hours at 360 rpm, and then formed into pellets. Then, the pellets placed in an alumina firing container were placed in a furnace, and the inside of the furnace was heated and held at 560 ° C. in an argon atmosphere. The holding time here was 6 hours. After that, the mixture was cooled at 1 ° C./min to obtain a solid electrolyte member.

(Measurement of Li Content)
The Li content was measured for each example using ICP emission spectrometry. As a pretreatment, a solution was decomposed under pressure using aqua regia hydrofluoric acid, and then treated with sulfuric acid to produce white smoke. Hydrochloric acid and water were added to the solution to obtain a measurement solution. The device used was an inductively coupled plasma emission spectrometer SPS3100 manufactured by SII Nanotechnology.

(Measurement of Content of Elements Other Than Li)
For each example, the contents of elements other than Li were measured by fluorescent X-ray analysis under the following measurement conditions.
Measurement device: M4 TORNADO (manufactured by Bruker)
Excitation X-ray: Polycapillary X-ray optical system Rh tube Output: 50 kV, 200 μA
・X-ray diameter: 20 μm

In addition, each example was classified into a first solid electrolyte member having a particle diameter of less than 5 μm, a second solid electrolyte member having a particle diameter of 5 μm or more and less than 100 μm, and a third solid electrolyte member having a particle diameter of 100 μm or more, and the content of elements other than Li was measured under the above conditions for each of the first solid electrolyte member, the second solid electrolyte member, and the third solid electrolyte member using fluorescent X-ray analysis.

(Measurement results of the content of each element)
Table 2 shows the measurement results of the content of each element.

In Table 2, the ICP result is the Li content (mass%) relative to the total content of elements contained in the solid electrolyte member, measured using ICP atomic emission spectroscopy. The XRF result is the content (mass%) of the target element relative to the total content of all elements contained in the solid electrolyte member, excluding Li, measured using X-ray fluorescence spectroscopy. The mass ratio is the Li content (mass%) relative to the total content of elements contained in the solid electrolyte member, measured using ICP atomic emission spectroscopy, for Li, and is the value calculated using formula (1) in the above embodiment for elements other than Li.

As shown in Table 2, in Example 1, in the unclassified solid electrolyte member (the entire solid electrolyte member), the Al content was 40 ppm, the Si content was 19 ppm, and Zr, Ti, and W were not detected, so the total content of Al, Zr, Ti, Si, and W was less than 100 ppm.
Similarly, in Example 2, in the unclassified solid electrolyte member (the entire solid electrolyte member), the Al content was 44 ppm, and Zr, Ti, and W were not detected, so the total content of Al, Zr, Ti, and W was less than 100 ppm.
Similarly, in Example 3, in the unclassified solid electrolyte member (the entire solid electrolyte member), the Al content was 52 ppm, the Si content was 25 ppm, and Zr, Ti, and W were not detected, so the total content of Al, Zr, Ti, Si, and W was less than 100 ppm.
On the other hand, in Comparative Example 1, in the unclassified solid electrolyte member (the entire solid electrolyte member), the Al content was 978 ppm, the Si content was 459 ppm, and the W content was 214 ppm, and Zr and Ti were not detected, so that the total content of Al, Zr, Ti, Si and W was outside the range of less than 100 ppm.

Also, as shown in Table 2, in Example 1, the total content of Al, Zr, Ti, and W for each of the classified first solid electrolyte member, second solid electrolyte member, and third solid electrolyte member was less than 100 ppm, and in Comparative Example 1, the total content of Al, Zr, Ti, and W for each of the classified first solid electrolyte member, second solid electrolyte member, and third solid electrolyte member was outside the range of less than 100 ppm.

(Average crystallite size)
The average crystallite diameter (nm) of each solid electrolyte member was measured using the method described in this embodiment. The measurement results are shown in Table 2.

(conductivity)
Furthermore, the solid electrolyte member of each example was pulverized in an agate mortar in a glove box in an argon atmosphere, and an AC impedance measurement was carried out with a Biologic Corp. potentio/galvanostat SP-300 using a SUS conductivity measurement cell to measure the conductivity. The measurement conditions were 25° C. and a measurement range of 1 Hz to 1 MHz. The measurement results of each conductivity are shown in Table 2.

(Crystal Structure)
In addition, the X-ray diffraction spectrum of each solid electrolyte member was measured using CuKα radiation to confirm the crystal structure. FIG. 3 is a graph showing the XRD spectrum of each example. Table 3 shows the diffraction angle and relative intensity of the crystal peak confirmed at 2θ=15° to 55°, and the space group of the estimated crystal structure. The crystal peak is a peak having an intensity equal to or greater than a threshold value, and the threshold value here is, for example, a relative intensity of 0.05 when the maximum peak intensity of the measurement result is 1.
Table 3 shows that Examples 1 and 2 have an LGPS structure. The LGPS structure in Table 3 means a structure having a crystal structure of space group P4 ₂ nmc, in which, when measured by X-ray diffraction measurement using CuKα radiation, peaks of the following formulas (A) to (E) are detected as crystal peaks, and when the diffraction intensity of the peak of formula (E) is I _A and the diffraction intensity of the peak of formula (F) is I _B , I _B /I _A is less than 0.50.
2θ=17.38°±0.50°...(A)
2θ=20.18°±0.50°...(B)
2θ=20.44°±0.50°...(C)
2θ=26.96°±0.50°...(D)
2θ=29.58°±0.50°...(E)
2θ=27.33°±0.50°...(F)
Table 3 also shows that Example 3 has an Argyrodite type crystal structure.

(evaluation)
The solid electrolyte member obtained as described above was molded into a pellet having a diameter of 10 mm at a molding pressure of 600 MPa, and the pellet was used as a separator. A lithium cobalt oxide coated with lithium niobate was used as a cathode, and a lithium-indium alloy was used as an anode to prepare an all-solid-state lithium battery.
In addition, a constant current test was performed on the prepared all-solid-state lithium battery at a current of 1/10C (=15mA/g). The results up to 100 cycles when the initial discharge current capacity was 100% are shown in FIG. 4. As shown in FIG. 4, in Example 1, Example 2, and Example 3, it is possible to suppress the deterioration after the charge/discharge cycle compared to Comparative Example 1, and it is possible to suitably suppress the deterioration of the battery performance. This is because the amount of impurities such as Al, Zr, Ti, Si, and W is small, so the amount of by-products derived from the impurities is suppressed, and the deterioration of the battery performance is suppressed. Although Si is included in Example 2, in this case, since Si constitutes the solid electrolyte crystal, it is considered that it does not generate by-products and does not contribute to the deterioration of the battery performance.

Although the embodiment of the present invention has been described above, the embodiment is not limited to the contents of this embodiment. The above-mentioned components include those that a person skilled in the art can easily imagine, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the above-mentioned components can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the components can be made without departing from the spirit of the above-mentioned embodiment.

A starting material

Claims (6)

A solid electrolyte member containing Li, P, and S, wherein the Li content measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) is 8.1 mass% or more and 17.9 mass% or less based on the total content of elements contained in the solid electrolyte member, and the Li content measured by X-ray fluorescence spectroscopy (XRF) is 8.1 mass% or more and 17.9 mass% or less based on the total content of elements contained in the solid electrolyte member. a total content of Al, Zr, Ti, Si, and W measured by X-ray fluorescence spectroscopy is less than 100 ppm by mass with respect to a total content of elements contained in the solid electrolyte member, and when the solid electrolyte member is classified into a particle size of less than 5 μm, a particle size of 5 μm or more and less than 100 μm, and a particle size of 100 μm or more, a total content of Al, Zr, Ti, Si, and W measured by X-ray fluorescence spectroscopy is less than 100 ppm by mass with respect to a total content of elements contained in the solid electrolyte member.
Solid electrolyte material. A solid electrolyte member containing Li, Si, P, and S, wherein the Li content measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) is 8.1 mass% or more and 17.9 mass% or less based on the total content of elements contained in the solid electrolyte member, and the Li content measured by X-ray fluorescence spectroscopy (XRF) is 8.1 mass% or more and 17.9 mass% or less based on the total content of elements contained in the solid electrolyte member. a total content of Al, Zr, Ti, and W measured by X-ray fluorescence spectroscopy is less than 100 ppm by mass with respect to a total content of elements contained in the solid electrolyte member, and when the solid electrolyte member is classified into a particle size of less than 5 μm, a particle size of 5 μm or more and less than 100 μm, and a particle size of 100 μm or more, a total content of Al, Zr, Ti, and W measured by X-ray fluorescence spectroscopy is less than 100 ppm by mass with respect to a total content of elements contained in the solid electrolyte member.
Solid electrolyte material. The solid electrolyte member according to claim 1 or 2, having an average crystallite size of 50 nm or more and an electrical conductivity of 4 mS/cm or more. 4. The solid electrolyte member according to claim 1, wherein the solid electrolyte member has a crystal structure of space group _P42nmc , and when measured by X-ray diffraction measurement using CuKα radiation, peaks of the following formulas (A) to (E) are detected as crystal peaks, and a peak of formula (F) is not detected as a crystal peak on the higher angle side than the peak of formula (D ₎ , or a _peak of formula (F) is detected such that _IB / _IA is less than 0.50, where IA is the diffraction intensity of the peak of formula (E) and IB is the diffraction intensity of the peak of formula (F).
2θ=17.38°±0.50°...(A)
2θ=20.18°±0.50°...(B)
2θ=20.44°±0.50°...(C)
2θ=26.96°±0.50°...(D)
2θ=29.58°±0.50°...(E)
2θ=27.33°±0.50°...(F) A solid electrolyte member according to any one of claims 1 to 3, having an Argyrodite-type crystal structure. 6. A method for producing a solid electrolyte member according to claim 1, comprising: a preparation step of preparing an assembly of starting materials containing Li, P, and elemental sulfur; and a production step of heating the assembly of starting materials to produce the solid electrolyte member, wherein in the preparation step, the starting materials are mixed to produce the assembly of starting materials such that a crystal peak of a crystalline substance can be detected when the produced assembly of starting materials is measured by an X-ray diffraction method.
A method for producing a solid electrolyte member.