JP2016066405A - Solid electrolyte for all-solid type secondary battery, method for manufacturing the same, and all-solid type secondary battery including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a Mg-S based solid electrolyte having high conductivity, which enables the manufacturing of an all-solid type secondary battery of a high capacity; and a method for manufacturing such a Mg-S based solid electrolyte.SOLUTION: A solid electrolyte for an all-solid type secondary battery is expressed by the compositional formula (I), MgS-MgX(where X is a halogen atom selected from F, Cl, Br and I) or MgX. A method for manufacturing the solid electrolyte for an all-solid type secondary battery comprises the steps of: performing a mechanical milling process on a raw material mixture including MgS and MgXin a given proportion, or a raw material mixture including MgXin a given proportion, thereby obtaining a processed product; and performing a thermal treatment on the processed product at a temperature of 200°C or higher, thereby obtaining MgS-MgX.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a solid electrolyte for an all-solid-state secondary battery, a method for producing the same, and an all-solid-state secondary battery including the same. More specifically, the present invention relates to a solid electrolyte having high conductivity that can provide an all-solid-state secondary battery at low cost, a method for producing the same, and an all-solid-state secondary battery including the same.

Lithium secondary batteries have high voltage and high capacity, and are therefore widely used as power sources for mobile phones, digital cameras, video cameras, notebook computers, electric vehicles and the like. A lithium secondary battery that is generally distributed is a lithium ion secondary battery that uses a liquid electrolyte in which an electrolytic salt is dissolved in a non-aqueous solvent as an electrolyte. Since non-aqueous solvents contain a lot of flammable solvents, it is desired to ensure safety.
In order to ensure safety, an electrolyte is formed from Li ₂ S—P ₂ S _5, which is a solid material made of glass ceramics, without using a non-aqueous solvent. A solid secondary battery has been proposed (Non-Patent Document 1).

In recent years, demand for lithium secondary batteries has been increasing in order to store electric power in automobiles such as electric vehicles and hybrid vehicles, power generation devices such as solar cells and wind power generation. However, since the lithium secondary battery uses lithium that has a small reserve and is unevenly distributed, there are concerns that supply cannot catch up with demand, and there is a problem of high cost.
From the viewpoint of the above problem, an all-solid-state secondary battery that uses Mg with abundant resources instead of Li has been proposed (Non-Patent Document 2). In addition to the abundance of resources, when each metal is used for the negative electrode, divalent Mg has the advantage that the theoretical capacity of charge / discharge per unit volume can be larger than monovalent Li. In this document, the physical properties of a magnesium-sulfur solid electrolyte made of glass ceramics made of MgS—P ₂ S ₅ —MgI ₂ are reported based on the knowledge of a lithium solid electrolyte.

M. Tatsumisago et.al., Funct. Mater. Lett., 1 (2008) 31 T. Yamanaka et.al., Solid State Ionics 262 (2014) 601-603

In Non-Patent Document 2, a relatively high conductivity of the order of 10 ⁻⁷ Scm ⁻¹ is obtained at 200 ° C. However, this conductivity is not sufficient, and further improvement in conductivity is desired.

Li ₂ S—P ₂ S ₅ made of glass ceramics, which is a lithium-sulfur based solid electrolyte in Non-Patent Document 1, has a relatively high conductivity. Based on this knowledge, Non-Patent Document 2 attempts to achieve high electrical conductivity by adding P ₂ S ₅ to MgS and then heat-treating it into a glass ceramic state. By the way, since the magnesium-sulfur-based solid electrolyte for an all-solid-state secondary battery is a new material that has recently been studied, it is unclear whether or not it is appropriate to apply the knowledge of Non-Patent Document 1. Currently.
Therefore, the inventors of the present invention reviewed the material for the magnesium-sulfur solid electrolyte from the beginning, and in the absence of P ₂ S ₅ , combined the MgS and the magnesium halide in the non-patent literature. Surprisingly, a high conductivity of the order of 10 ⁻⁶ Scm ⁻¹ exceeding the 10 ⁻⁷ Scm ⁻¹ order reported in 2 was obtained, and the present invention was achieved.

Thus, according to the present invention, the solid electrolyte for an all-solid-state secondary battery represented by the general formula (I): MgS—MgX ₂ (X is a halogen atom selected from F, Cl, Br and I) or MgX ₂ Is provided.
Furthermore, according to the present invention, there is provided a method for producing the solid electrolyte for an all-solid secondary battery,
A step of subjecting the general formula (I): MgS-MgX ₂ MgS and MgX ₂ in a predetermined ratio or a raw material mixture containing MgX ₂ in a predetermined ratio to mechanical milling to obtain a processed product; And a step of obtaining the general formula (I): MgS—MgX ₂ by heat-treating the treated product at a temperature of 200 ° C. or higher. The
Further, according to the present invention, at least a positive electrode, a negative electrode, and a solid electrolyte layer positioned between the positive electrode and the negative electrode are provided, and the solid electrolyte layer includes the solid electrolyte for an all-solid secondary battery. An all-solid-state secondary battery is provided.

According to the present invention, it is possible to provide a solid electrolyte that can provide a high-capacity all-solid-state secondary battery without depending on the amount of lithium resources.
Further, MgX ₂ is the case of MgBr _2, it can provide an all-solid secondary battery solid electrolyte having a higher conductivity.
Further, MgX ₂ If the contained 50-60 mol%, can provide an all-solid secondary battery solid electrolyte having a higher conductivity.
According to the method for producing a solid electrolyte for an all-solid-state secondary battery of the present invention, it is possible to provide a solid electrolyte having high conductivity that does not depend on the amount of lithium resources by a simple method of mechanical milling and heat treatment.
Since the all-solid-state secondary battery of the present invention uses a solid electrolyte layer containing magnesium having high electrical conductivity, it is possible to achieve a high capacity without depending on the amount of lithium resources.

It is an XRD pattern before the heat treatment of 50MgS-50MgBr ₂ of Example 1. It is an XRD pattern before the heat treatment of MgBr ₂ in Example 1. Is a Raman spectrum before the heat treatment 50MgS-50MgBr ₂ of Example 1. It is an XRD pattern after heat treatment 50MgS-50MgBr ₂ of Example 1. ₂ is an impedance plot after heat treatment of 50MgS-50MgBr ₂ and MgBr ₂ in Example 1. FIG. Is a graph showing the heating and conductivity in the cooling cycle of 50MgS-50MgBr ₂ and MgBr ₂ of Example 1. 4 is a plot of current values during direct current polarization after heat treatment of 50MgS-50MgBr ₂ and MgBr ₂ in Example 1. FIG. It is an XRD pattern before the heat treatment of MgS-MgBr ₂ and MgBr ₂ of Example 2. It is a Raman spectrum before the heat treatment of MgS-MgBr ₂ of Example 2. 4 is an XRD pattern after heat treatment of MgS—MgBr ₂ of Example 2. It is a Raman spectrum after heat treatment of MgS-MgBr ₂ of Example 2. 6 is a graph showing the relationship between the molar ratio of MgS—MgBr ₂ and the conductivity in Example 2.

(Solid electrolyte for all-solid-state secondary battery)
The solid electrolyte of the present invention is represented by the general formula (I): MgS—MgX ₂ (X is a halogen atom selected from F, Cl, Br and I) or MgX ₂ . _{Specifically, MgF 2, MgCl 2, MgBr} 2, MgI 2, MgS-MgF 2, MgS-MgCl 2, MgS-MgBr 2, MgS-MgI 2 and the like. Of these, MgS—MgBr ₂ is particularly preferable. Further, other magnesium salts such as Mg (CF ₃ SO ₃ ) ₂ and Mg [N (SO ₂ CF ₃ ) ₂ ] and ion conductive materials may be added.

MgS-MgX ₂ is the total of MgS and MgX _2, greater than 40 mole%, including MgX ₂ of less than 100 mol%. If it is this range, electrical conductivity can be improved more. Further, MgX ₂ may be contained in less than 50 mol%, 60 mol%, 70 mol%, 80 mol%, 90 mol%, and 100 mol%.

The solid electrolyte preferably has a broad peak in the XRD pattern derived from MgBr ₂ after mechanical milling. The cause of the broad is unknown, but since these peaks of the solid electrolyte with improved conductivity are broad, it is expected that some component contributing to the improvement is generated. As for the degree of broadness, for example, the peaks of the (001) plane near 14 ° represented by 2θ, the (002) plane near 28 °, and the (110) plane near 48 ° are 0.7 ° to 7 °. It is preferable that the half value width is about 0 °. A more preferable half width is 1.2 ° to 4.5 °. The sample after the mechanical milling treatment is heat-treated to obtain a final product, and the half width of the XRD peak of the solid electrolyte obtained at that time is 0.2 ° to 1.0 °.

Furthermore, the ratio A / B of the peak intensity A on the (002) plane and the peak intensity B on the (110) plane is preferably 0.5 to 2.5. The reason why the ratio A / B falls within this range is unknown, but it is expected that some component that contributes to the improvement of the conductivity is generated as in the case of the half width. Since the ratio A / B of the raw material MgBr ₂ is about 25, it is estimated that the ratio A / B in the solid electrolyte can be used as an index for improving the electrical conductivity. A more preferable ratio A / B is 0.9 to 2.0.

(Method for producing solid electrolyte)
The manufacturing method of the solid electrolyte is:
(I) General formula (I): A step of obtaining a processed product by subjecting a raw material mixture containing MgS and MgX ₂ giving MgS—MgX ₂ at a predetermined ratio or a raw material mixture containing MgX ₂ at a predetermined ratio to a mechanical milling process. (Ii) A step of obtaining a general formula (I): MgS—MgX ₂ by heat-treating the treated product at a temperature of 200 ° C. or higher.

(1) Step (i)
The mechanical milling process in the step (i) is not particularly limited to the processing apparatus and the processing conditions as long as the raw materials can be sufficiently mixed.
As a processing apparatus, a ball mill can be used normally. A ball mill is preferable because large mechanical energy can be obtained. Among the ball mills, the planetary ball mill is preferable because the pot rotates and the base plate revolves and high impact energy can be generated efficiently.

  The processing conditions can be appropriately set according to the processing apparatus to be used. For example, when a ball mill is used, the raw materials can be mixed and reacted more uniformly as the rotational speed is higher and / or the treatment time is longer. Note that “and / or” means A, B, or A and B when expressed as A and / or B. Specifically, when a planetary ball mill is used, conditions of a rotation speed of 50 to 700 revolutions / minute, a treatment time of 0.1 to 50 hours, and 1 to 100 kWh / kg of a raw material mixture are exemplified. More preferable processing conditions include a rotation speed of 200 to 600 rotations / minute, a processing time of 1 to 20 hours, and 6 to 50 kWh / kg of a raw material mixture.

(2) Step (ii)
A solid electrolyte is obtained by subjecting the treated product obtained in the step (i) to a heat treatment. This heat treatment is performed at a temperature of 200 ° C. or higher. If it is performed at a temperature higher than this, there is an advantage that a solid electrolyte having good conductivity can be easily obtained. It is preferable that the temperature of heat processing is the range of 200-500 degreeC. Note that the temperature of the heat treatment can be determined in consideration of the existence state of the crystal phase in XRD.
The heat treatment time is sufficient for improving the electrical conductivity, and is short when the heat treatment temperature is high and long when the heat treatment temperature is low. The heat treatment time is usually in the range of 0.1 to 10 hours.

(All-solid secondary battery)
The all solid state secondary battery is not particularly limited, but usually includes at least a positive electrode, a negative electrode, and a solid electrolyte layer located between the positive electrode and the negative electrode.
(1) The solid electrolyte layer a solid electrolyte layer includes the solid electrolyte (MgS-MgX ₂₎ is. The thickness of the solid electrolyte layer is preferably 1 to 1000 μm, and more preferably 1 to 200 μm. The solid electrolyte layer can be obtained as a pellet by pressing the raw material, for example.

(2) Positive electrode A positive electrode is not specifically limited. The negative electrode may be composed of only the negative electrode active material, and may be mixed with a binder, a conductive agent, an electrolyte, and the like.
Examples of the positive electrode active material include various transition metal compounds such as V ₂ O ₅ , MnO ₂ , MgFeSiO ₄ , MgCo ₂ O ₄ , Mo ₆ S ₈ , and NiS.
Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyvinyl acetate, polymethyl methacrylate, and polyethylene.

Examples of the conductive agent include natural graphite, artificial graphite, acetylene black, ketjen black, Denka black, carbon black, vapor grown carbon fiber (VGCF) and the like.
Examples of the electrolyte include an electrolyte used for a solid electrolyte layer.
The positive electrode can be obtained as a pellet by, for example, mixing a positive electrode active material and optionally a binder, a conductive agent, an electrolyte, and the like, and pressing the obtained mixture.
The positive electrode may be formed on a current collector such as aluminum or copper.

(3) Negative electrode A negative electrode is not specifically limited. The negative electrode may be composed of only the negative electrode active material, and may be mixed with a binder, a conductive agent, an electrolyte, and the like.
Examples of the negative electrode active material include metals such as Mg, In, and Sn, various transition metal oxides such as Mg alloy, hard carbon, TiO ₂ , and SnO.
As the binder, the conductive agent, and the electrolyte, any of those mentioned in the column of the positive electrode can be used.

The negative electrode can be obtained in the form of pellets by, for example, mixing a negative electrode active material and optionally a binder, a conductive agent, an electrolyte, and the like, and pressing the obtained mixture. Moreover, when using the metal sheet (foil) which consists of a metal or its alloy as a negative electrode active material, can be used as it is.
The negative electrode may be formed on a current collector such as aluminum or copper.
(4) Manufacturing method of all-solid-state secondary battery An all-solid-state secondary battery can be obtained by, for example, laminating and pressing a positive electrode, an electrolyte layer, and a negative electrode.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.
Example 1
Step (i): Mechanical milling treatment MgS (purity 99% manufactured by Aldrich) and MgBr ₂ (purity 99% manufactured by Aldrich) were charged into a planetary ball mill at a molar ratio of 50:50. After the addition, 50MgS-50MgBr ₂ was obtained by mechanical milling. Three samples were prepared with mechanical milling time of 5 hours, 10 hours and 20 hours. In addition, MgS and MgBr ₂ were mixed in a mortar to prepare a sample that was not subjected to mechanical milling.

In addition, a sample was prepared in which only MgBr ₂ was subjected to mechanical milling treatment for 20 hours under the same conditions as 50MgS-50MgBr ₂ . For MgBr ₂ alone, a sample not subjected to mechanical milling was prepared.
As the planetary ball mill, Pulverisette P-7 manufactured by Fritsch was used, and the pot and balls were made of ZrO ₂ , and a mill containing 500 balls of 4 mm in diameter in a 45 ml pot was used. The mechanical milling process was performed in a rotation speed of 510 rpm, room temperature, and a dry nitrogen glove box.

Note that the mechanical milling process is performed according to Akitoshi Hayashi et al. , Journal of Non-Crystalline Solids 356 (2010) 2670-2673.
The above six samples were pressed (pressure 370 MPa / cm ² ) to form pellets having a diameter of 10 mm and a thickness of about 1 mm.

The four samples of the XRD patterns of 50MgS-50MgBr ₂ in FIG. 1, showing the two samples of the XRD patterns of only MgBr ₂ in FIG. 1 and 2, MM0h, MM5h, MM10h, and MM20h mean that 5 hours, 10 hours, and 20 hours, which are not attached to the mechanical milling process, are applied. The XRD pattern of MgS and MgBr ₂ is described in the lower part of FIG. 1, and the XRD pattern of MgBr ₂ is described in the lower part of FIG. 1 and 2, ◯ means a peak corresponding to MgS, ▲ means a peak corresponding to MgBr ₂ , and ◇ means a peak whose correspondence is unknown.

From FIG. 1, it can be seen that the XRD pattern without mechanical milling is simply the sum of MgS and MgBr ₂ , but the peak corresponding to MgBr ₂ is broadened by applying mechanical milling. This broadening can also be seen from FIG. 2, which shows the XRD pattern of MgBr ₂ .
FIG. 3 shows the Raman spectrum of a sample subjected to mechanical milling for 20 hours. In FIG. 3, peaks derived from the spectrum of MgS and MgBr ₂ alone shown at the bottom are observed.

Step (ii): From a heat treatment above six samples, the two samples of the mechanical milling process only 20 hours 50MgS-50MgBr ₂ and MgBr ₂ was performed, and heated towards 400 ° C. from room temperature (25 ° C.), further, After reaching 400 ° C., it was cooled to room temperature. Figure 4 shows the front and rear of the XRD patterns heat treatment for the samples of 50MgS-50MgBr _2. The XRD pattern of MgO, MgS, and MgBr ₂ is shown in the lower part of FIG. In FIG. 4, the peak corresponding to ● MgO, the circle represents the peak corresponding to MgS, the triangle represents the peak corresponding to MgBr ₂ , and the triangle represents an unknown peak.

FIG. 4 shows that the intensity of the peak attributed to MgBr ₂ is increased by the heat treatment. This is presumably because the MgBr ₂ component in the sample partially amorphized by the mechanical milling process was recrystallized by the heat treatment. The full widths at half maximum of the peaks near 14 °, 28 ° and 48 ° are 0.50 °, 0.92 ° and 0.44 °, and the peak intensity A near 28 ° is about 48 °. The ratio A / B with the peak intensity B was 0.95.

In 2 samples after the heat treatment, FIGS. 5 (a) to the 50MgS-50MgBr ₂ of 325 ° C. during shows AC impedance plots at the time of heating of 360 ° C. during the MgBr ₂ in Figure 5 (b). The measurement of AC impedance was performed on a cell in which the sample was sandwiched between stainless steel plates, and the measurement conditions were an applied voltage of 50 mV and a frequency of 0.01 Hz to 1 MHz. In these figures, spikes derived from the ion blocking behavior are seen on the low frequency side. Therefore, it is inferred that both samples are ionic conductors.

  Further, for the above two samples, the conductivity of the sample is measured about every 15 ° C. during the heating and cooling cycle in which the sample is heated from room temperature to 400 ° C. and then cooled to room temperature after reaching 400 ° C. did. The measurement results are shown in FIGS. 6 (a) and (b). In the figure, ● is a plot during heating, and ○ is a plot during cooling.

Figures 6 (a), 50MgS-50MgBr 2 the conductivity at the time of cooling, show different behavior from that during heating. The difference in behavior is, for example, that the conductivity at 200 ° C. is 7.3 × 10 ⁻⁷ Scm ⁻¹ during heating and 9.0 × 10 ⁻⁶ Scm ⁻¹ during cooling. You can see from On the other hand, from FIG. 6 (b), MgBr ₂ shows a behavior with substantially the same conductivity during cooling and heating. The results for the sample of 50MgS-50MgBr _2, irreversible changes in the structure capable of improving the conductivity by heating is presumed to have occurred. Note that two samples, was subjected to re-heating and cooling cycles, samples 50MgS-50MgBr _2, the heating time and cooling time both showed the same behavior as when cooling of FIG. 6 (a), a sample of MgBr ₂ is The same behavior as in FIG. 6B was exhibited during heating and cooling. This result also for samples of 50MgS-50MgBr _2, irreversible changes in the structure capable of improving the conductivity by heating is presumed to have occurred.

In two samples after the heat treatment, FIG. 7A shows the current value during direct current polarization of the heat-treated 50MgS-50MgBr ₂ when heated at 330 ° C. and FIG. 7B shows the heat-treated MgBr ₂ when heated at 365 ° C. A plot of is shown. The current value was measured under the condition that two samples were sandwiched between a pair of stainless steel electrodes, the applied voltage was 0.1 V, and the application time was 3600 seconds for 50MgS-50MgBr ₂ and 3000 seconds for MgBr ₂ . In both samples, rapid polarization occurred in the initial stage of voltage application. From the steady-state current value (2.7 × 10 ⁻⁶ A) of 50MgS-50MgBr ₂ obtained from FIG. 7A and the AC impedance method, the total electric conductivity is 2.9 × 10 ⁻⁵ Scm ^−1. The electron conductivity was calculated to be 2.5 × 10 ⁻⁶ Scm ^−1, and as a result, the ionic conductivity was 2.5 × 10 ⁻⁵ Scm ⁻¹ . The proportion of the ionic conductivity to the total conductivity (electrical conductivity) of 50MgS-50MgBr ₂ rose to about 90%, is found to be useful as a solid electrolyte. Similarly to FIG. 7 (a), the ionic conductivity of the total conductivity is calculated from the steady-state current value (9.0 × 10 ⁻⁶ A) of MgBr ₂ obtained from FIG. 7 (b) and the AC impedance method. When the ratio is calculated, it is about 40%, which shows that the ratio of electron conductivity is large.

Example 2
Step (i): the mechanical milling MgS and MgBr ₂ 60: 40,40: 60 and three subjected to mechanical milling process similarly 20 hours as in Example 1 except that the molar ratio of 30:70 A sample (pellet) of MgS-MgBr ₂ was obtained.

The XRD patterns of the three types of samples are shown in FIG. FIG. 8 also shows the 10-hour and 20-hour XRD patterns of 50MgS-50MgBr ₂ of FIG. 1 and the 20-hour XRD pattern of mechanical milling treatment of only MgBr ₂ . In FIG. 8, x means the molar ratio of MgBr ₂ , and MM10h means that the mechanical milling process was performed for 10 hours. The XRD pattern of MgS and MgBr ₂ is shown in the lower part of FIG. In FIG. 8, ◯ means a peak corresponding to MgS, ▲ means a peak corresponding to MgBr ₂ , and ◇ means a peak whose correspondence is unknown.

From FIG. 8, it can be seen that the peak corresponding to MgBr ₂ is broadened at any molar ratio by being subjected to the mechanical milling treatment. The molar ratio of 50: 50 to 30: in the range of 70 peaks not attributable to the spectrum of MgS and MgBr ₂ alone are shown in the lower part is seen.
FIG. 9 shows the Raman spectra of the three samples. FIG. 9 also shows the Raman spectrum of 50MgS-50MgBr ₂ in FIG. In FIG. 9, peaks derived from the spectra of MgS and MgBr ₂ alone shown at the bottom are observed.

Step (ii): Heat treatment The three types of samples were subjected to heat treatment in the same manner as in Example 1. FIG. 10 shows the XRD pattern of the sample after the heat treatment. FIG. 10 also shows the XRD pattern of 50MgS-50MgBr ₂ in FIG. The XRD pattern of MgS and MgBr ₂ is shown at the bottom of FIG. In FIG. 10, ● represents a peak corresponding to MgO, ◯ represents a peak corresponding to MgS, ▲ represents a peak corresponding to MgBr ₂ , and ◇ represents an unknown peak.

FIG. 10 shows that the intensity of the peak attributed to MgBr ₂ is increased by the heat treatment. This is presumably because the MgBr ₂ component in the sample partially amorphized by the mechanical milling process was recrystallized by the heat treatment. For the molar ratio of 60:40, the half-widths of the peaks near 14 °, 28 ° and 48 ° are 0.36 °, 1.28 ° and 0.44 °, and the peaks near 28 ° The ratio A / B between the intensity A and the intensity B of the peak around 48 ° was 1.06. For the molar ratio 40:60, the full widths at half maximum of the peaks near 14 °, 28 ° and 48 ° are 0.36 °, 0.55 ° and 0.36 °, and the peak intensity A around 28 ° The ratio A / B with the intensity B of the peak in the vicinity of 48 ° was 1.03. For the molar ratio 30:70, the full widths at half maximum of the peaks near 14 °, 28 ° and 48 ° are 0.30 °, 0.55 ° and 0.30 °, and the intensity A of the peak near 28 ° And the ratio A / B of the intensity B of the peak in the vicinity of 48 ° was 1.04. In addition, it can be seen that the intensity of the ◇ peak, which is unknown, has increased due to the heat treatment. This peak of ◇ is located on the lower angle side of the peak of MgS (◯) having a cubic structure, and is due to a cubic crystal having a larger lattice constant than MgS in which a part of S of MgS is replaced with Br. Presumed to be.

Raman spectra of the samples and 50MgS-50MgBr ₂ of the three shown in Figure 11. The Raman spectra of MgS and MgBr ₂ are shown at the bottom of FIG. It is confirmed that the peak around 220 cm ⁻¹ that existed before the heat treatment disappeared. No peaks other than those derived from MgS and MgBr ₂ are observed.

Also for the above three types of samples, as in Example 1, the impedance plot and the change in the conductivity of the sample during the heating and cooling cycle were confirmed. As a result, the 50 MgS − in FIG. 5A and FIG. it was confirmed that shows the same tendency as 50MgBr _2.
FIG. 12 shows the relationship between the molar ratio and the electrical conductivity. In the figure, ● is a plot during heating, and ○ is a plot during cooling. From FIG. 12, it can be seen that the conductivity is maximum when MgBr ₂ is around 50 mol%.

Claims (5)

A solid electrolyte for an all-solid-state secondary battery represented by the general formula (I): MgS—MgX ₂ (X is a halogen atom selected from F, Cl, Br and I) or MgX ₂ . The solid electrolyte for an all-solid-state secondary battery according to claim 1, wherein the MgX ₂ is MgBr ₂ . The solid electrolyte for an all-solid-state secondary battery according to claim 1, wherein the MgX ₂ is contained in an amount of 50 to 60 mol%. A method for producing a solid electrolyte for an all-solid-state secondary battery according to any one of claims 1 to 3,
A step of subjecting the general formula (I): MgS-MgX ₂ MgS and MgX ₂ in a predetermined ratio or a raw material mixture containing MgX ₂ in a predetermined ratio to mechanical milling to obtain a processed product; And a step of obtaining the general formula (I): MgS—MgX ₂ by heat-treating the treated product at a temperature of 200 ° C. or higher.   It comprises at least a positive electrode, a negative electrode, and a solid electrolyte layer positioned between the positive electrode and the negative electrode, and the solid electrolyte layer comprises the solid electrolyte for an all-solid-state secondary battery according to any one of claims 1 to 3. All-solid-state secondary battery characterized by including.