JP2017091810A - Method for manufacturing positive electrode mixture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a positive electrode mixture which enables the increase in a charge/discharge capacity of a sulfur battery.SOLUTION: The above problem is solved by providing a method for manufacturing a positive electrode mixture used for a sulfur battery in the present invention. The method comprises: a preparation step for preparing a sulfide solid electrolyte including an ion conductor having Li, P and S, and LiBr; and an amorphization step for performing the amorphization of a mixture including the sulfide solid electrolyte, a positive electrode active material which is an elemental sulfur, and a conductive assistant which is a carbon material, thereby to obtain the positive electrode mixture increased in LiS content.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a positive electrode mixture used for a sulfur battery.

  With the rapid spread of information-related equipment and communication equipment such as personal computers, video cameras, and mobile phones in recent years, development of batteries that are used as power sources has been regarded as important. Also in the automobile industry and the like, development of high-power and high-capacity batteries for electric vehicles or hybrid vehicles is being promoted.

Development of sulfur batteries using sulfur as a positive electrode active material is underway. Sulfur is characterized by a very high theoretical capacity of about 1672 mAh / g. Patent Document 1 discloses a positive electrode mixture containing a Li ₂ S—P ₂ S ₅ -based solid electrolyte, a positive electrode active material that is elemental sulfur, and a conductive material that is a carbon material. Cited Document 1 describes that LiI may be further contained in the Li ₂ S—P ₂ S ₅ based solid electrolyte. Patent document 1 aims at providing the lithium sulfur battery which has the outstanding charging / discharging capacity | capacitance.

Although not related to sulfur battery, Patent Document _2, LiI to Li 2 _S-P 2 _{S 5} based solid electrolyte, LiBr or the addition of LiCl technique, is disclosed. Patent Document 2 aims to suppress an increase in interface resistance and a decrease in bulk resistance (decrease in ionic conductivity).

International Publication No. 2014/203575 Pamphlet JP 2012-048771 A

  In recent years, a further increase in capacity has been demanded for sulfur batteries. This invention is made | formed in view of the said situation, and it aims at providing the manufacturing method of the positive electrode compound material which can enlarge the charging / discharging capacity | capacitance of a sulfur battery.

In order to achieve the above-described object, in the present invention, a method for producing a positive electrode mixture used in a sulfur battery, which is a sulfide solid composed of an ion conductor having Li, P, and S and LiBr The mixture of the preparation step for preparing the electrolyte, the sulfide solid electrolyte, the positive electrode active material that is elemental sulfur, and the conductive additive that is the carbon material is amorphized, and the Li ₂ S content is reduced. There is provided an amorphization step for obtaining the increased positive electrode mixture, and a method for producing the positive electrode mixture.

According to the present invention, by making the mixture amorphous, it is possible to obtain a positive electrode mixture in which the content of Li ₂ S is increased, so that the charge / discharge capacity of the sulfur battery can be increased. A positive electrode mixture can be produced.

  The present invention has an effect that a positive electrode mixture capable of increasing the charge / discharge capacity of a sulfur battery can be produced.

It is a result of the initial stage charge-and-discharge capacity | capacitance measurement of the sulfur battery of Examples 1, 2 and Comparative Examples 1, 2. It is a result of the structural analysis by XPS of the positive electrode compound material of Example 1 and Comparative Examples 1 and 2.

Hereinafter, the detail of the manufacturing method of the positive electrode compound material of this invention is demonstrated.
The method for producing a positive electrode mixture of the present invention is a method for producing a positive electrode mixture used for a sulfur battery, and prepares a sulfide solid electrolyte composed of an ion conductor having Li, P and S and LiBr. The content of Li ₂ S was increased by amorphizing a mixture containing a preparatory step, a sulfide solid electrolyte, a positive electrode active material that is elemental sulfur, and a conductive additive that is a carbon material. And an amorphization step for obtaining the positive electrode mixture.

According to the present invention, by making the mixture amorphous, it is possible to obtain a positive electrode mixture in which the content of Li ₂ S is increased, so that the charge / discharge capacity of the sulfur battery can be increased. A positive electrode mixture can be produced.

In the present invention, the reason why the charge / discharge capacity of the sulfur battery can be increased by making the mixture amorphous is presumed as follows.
The elemental positive electrode active material contains elemental sulfur in an inactive state. In the present invention, it is presumed that what has not contributed to the discharge capacity in the inactive state as it is simple sulfur is activated by becoming Li ₂ S ₂ and has contributed to the discharge capacity.
In the amorphous process, it is estimated that the following phenomenon will occur by amorphizing (for example, ball milling) a mixture containing elemental sulfur, sulfide solid electrolyte, and conductive additive (carbon material). Is done. That is, when the mixture is made amorphous, the conductive additive (carbon material) functions as a reducing agent that reduces elemental sulfur. Therefore, elemental sulfur is reduced by the conductive auxiliary agent (carbon material) by amorphization. It is presumed that the reduced sulfur reacts with a sulfide solid electrolyte containing LiBr, thereby becoming Li ₂ S _{2 and} being activated. As a result, it is presumed that the discharge capacity is increased by increasing the ratio of sulfur in the active state in the positive electrode mixture. Along with this, it is estimated that the charging capacity also increases.
Moreover, in the positive electrode active material obtained by the present invention, the reason why the content of Li ₂ S is increased is that Li ₂ S having a sulfur valence of −2 due to the progress of a partial reduction reaction of elemental sulfur. It is presumed that a lot was generated.

“Increasing the content of Li ₂ S” in the positive electrode active material obtained according to the present invention is one index indicating that the percentage of sulfur in the active state in the positive electrode mixture has increased. Since Li ₂ S is the final product in the reduction reaction of sulfur, there is an advantage that the progress of the reduction reaction is less affected and easier to use as an index than the content of Li ₂ S ₂ . The increase in the content of Li ₂ S can be confirmed, for example, using structural analysis by XPS.

In general, it is considered that a reaction in which S becomes Li ₂ S via Li ₂ S ₂ proceeds during discharge in the positive electrode active material of simple sulfur.

As shown in Examples 1 and 2 and Comparative Example 1 to be described later, Li ₂ S—P ₂ S ₅ —LiBr solid electrolyte or Li ₂ S—P ₂ S ₅ —LiI solid electrolyte is replaced with elemental sulfur and conductive assistant. The phenomenon that Li ₂ S increases (generates) by making it amorphous together with the agent and the effect that the charge / discharge capacity can be increased have been confirmed for the first time.

In paragraph [0023] of Patent Document 1, it is described that LiI may be further contained in the Li ₂ S—P ₂ S ₅ based solid electrolyte. However, Patent Document 1 does not describe an example in which LiI is added to a Li ₂ S—P ₂ S ₅ based solid electrolyte. Moreover, there is no disclosure or suggestion regarding the phenomenon that Li ₂ S is increased by using the Li ₂ S—P ₂ S ₅ —LiI-based solid electrolyte, and the effect that the charge / discharge capacity can be increased. It has not been. Patent Document 2 is not an invention relating to a sulfur battery, and does not describe an example of a sulfide solid electrolyte material containing LiBr.

That is, by making the Li ₂ S—P ₂ S ₅ —LiBr solid electrolyte, elemental sulfur and the conductive additive amorphous, the phenomenon that Li ₂ S increases and the charge / discharge capacity can be increased. These effects are unexpected phenomena and effects from Patent Documents 1 and 2, which are conventional techniques.

  Hereafter, each process in the manufacturing method of this invention is demonstrated.

1. Preparatory process The preparatory process in this invention is a process of preparing the sulfide solid electrolyte comprised from the ion conductor which has Li, P, and S, and LiBr.

(I) Sulfide solid electrolyte A sulfide solid electrolyte is comprised from the ion conductor which has Li, P, and S, and LiBr. The sulfide solid electrolyte usually has Li ion conductivity. At least a part of LiBr is usually present in a state of being incorporated into the structure of the ionic conductor as a LiBr component. The sulfide solid electrolyte may or may not have a LiBr peak in X-ray diffraction measurement, but the latter is preferred. This is because ionic conductivity is high.

The ionic conductor has Li, P, and S. The ionic conductor is not particularly limited as long as it has Li, P, and S, but among them, it is preferable to have an ortho composition. This is because a sulfide solid electrolyte having high chemical stability can be obtained. Here, ortho generally refers to one having the highest degree of hydration among oxo acids obtained by hydrating the same oxide. In the present invention, the crystal composition in which Li ₂ S is added most in the sulfide is called the ortho composition. For example, in the Li ₂ S—P ₂ S ₅ system, Li ₃ PS ₄ corresponds to the ortho composition.

In the present invention, “having an ortho composition” includes not only a strict ortho composition but also a composition in the vicinity thereof. Specifically, the main component is an anion structure (PS ₄ ^3- structure) having an ortho composition. The ratio of the anion structure of the ortho composition is preferably 60 mol% or more, more preferably 70 mol% or more, still more preferably 80 mol% or more, based on the total anion structure in the ion conductor, 90 mol % Or more is particularly preferable. The ratio of the anion structure of the ortho composition can be determined by Raman spectroscopy, NMR, XPS, or the like.

The sulfide solid electrolyte may or may not contain Li ₂ S, but the latter is more preferable. This is because when Li ₂ S is not contained, a sulfide solid electrolyte having high chemical stability can be obtained. “Not containing Li ₂ S” can be confirmed by X-ray diffraction. Specifically, when it does not have a Li ₂ S peak (2θ = 27.0 °, 31.2 °, 44.8 °, 53.1 °), it can be determined that it does not contain Li ₂ S. it can.

The sulfide solid electrolyte may or may not contain bridging sulfur, but the latter is more preferable. This is because when no cross-linking sulfur is contained, a sulfide solid electrolyte with high chemical stability can be obtained. “Bridged sulfur” refers to bridged sulfur in a compound formed by reaction of Li ₂ S and P ₂ S ₅ . For example, Li ₂ S and _P 2 _{S 5} is bridging sulfur reactions to become _{S 3} PS-PS 3 structure corresponds. It can confirm that "it does not contain bridge | crosslinking sulfur" by the measurement of a Raman spectrum. For example, in the case of a Li ₂ S—P ₂ S ₅ -based sulfide solid electrolyte, the peak of the S ₃ P—S—PS ₃ structure usually appears at 402 cm ⁻¹ . Therefore, it is preferable that this peak is not detected.

In the case of a Li ₂ S—P ₂ S ₅ -based sulfide solid electrolyte, the ratio of Li ₂ S and P ₂ S ₅ to obtain the ortho composition is Li ₂ S: P ₂ S ₅ = 75: on a molar basis. 25. The ratio of Li ₂ S to the sum of Li ₂ S and P ₂ S ₅ is preferably in the range of 70 mol% to 80 mol%, more preferably in the range of 72 mol% to 78 mol%, and 74 mol% to More preferably, it is in the range of 76 mol%.

Further, the ratio of LiBr in the sulfide solid electrolyte is not particularly limited as long as it is a ratio capable of obtaining a desired sulfide solid electrolyte, but is preferably in the range of, for example, 10 mol% to 30 mol%. More preferably, it is in the range of 15 mol% to 25 mol%. When the sulfide solid electrolyte has a composition of aLiBr · (1-a) (bLi ₂ S · (1-b) P ₂ S ₅ ), a corresponds to the ratio of LiBr, and b is the Li ₂ corresponds to the proportion of S.

Examples of the shape of the sulfide solid electrolyte include a particulate shape. The average particle diameter (D ₅₀ ) of the particulate sulfide solid electrolyte is preferably in the range of 0.1 μm to ₅₀ μm, for example. Also, the sulfide solid electrolyte is preferably higher Li ion conductivity, Li ion conductivity at room temperature is preferably for example 1 × ¹⁰ -4 S / cm or more, 1 × ¹⁰ -3 S / More preferably, it is cm or more.

The sulfide solid electrolyte may be, for example, sulfide glass or glass ceramics. The sulfide solid electrolyte may contain, for example, at least one of Li ₂ S, P ₂ S ₅ and LiBr which are raw materials.

(Ii) Preparation Step In the preparation step, a sulfide solid electrolyte may be prepared, or a commercially available sulfide solid electrolyte may be prepared. Examples of the method for producing a sulfide solid electrolyte include a method of obtaining a sulfide solid electrolyte by amorphizing a raw material composition containing Li ₂ S, P ₂ S ₅ and LiBr. Therefore, the preparation step may be a sulfide solid electrolyte preparation step in which a raw material composition containing Li ₂ S, P ₂ S ₅ and LiBr is made amorphous to produce a sulfide solid electrolyte. Incidentally, Li 2 _S in the raw material _composition, the content of each component of the P ₂ S ₅ and LiBr is tailored to the content of each component of the sulfide solid electrolyte described above.

  Examples of a method for amorphizing the raw material composition include mechanical milling. The mechanical milling may be dry mechanical milling or wet mechanical milling, but the latter is preferred. Examples of mechanical milling include a ball mill, and a planetary ball mill is more preferable.

  Various conditions of mechanical milling are set so that a desired sulfide solid electrolyte can be obtained. The number of platen rotations when performing the planetary ball mill is preferably in the range of 200 rpm to 500 rpm, for example. Moreover, it is preferable that the processing time at the time of performing a planetary ball mill exists in the range of 1 hour-100 hours, for example. Mechanical milling is preferably performed in an inert gas atmosphere (for example, an Ar gas atmosphere).

  The liquid used for wet mechanical milling preferably has an aprotic property such that hydrogen sulfide is not generated. Specifically, a polar aprotic liquid, a nonpolar aprotic liquid, etc. Mention may be made of aprotic liquids.

  By making the raw material composition amorphous, an amorphous sulfide solid electrolyte (sulfide glass) is usually obtained. In the method for producing a sulfide solid electrolyte, the sulfide glass may be heat-treated as necessary. As heat processing temperature, it is preferable to exist in the range of 100 to 300 degreeC, for example. The heat treatment time is preferably in the range of 1 minute to 24 hours, for example. The heat treatment is preferably performed in an inert gas atmosphere (for example, an Ar gas atmosphere). Examples of the heat treatment method include a method using a firing furnace.

2. Amorphization step The amorphization step in the present invention is performed by amorphizing a mixture containing a sulfide solid electrolyte, a positive electrode active material that is elemental sulfur, and a conductive additive that is a carbon material, ₂ is a step of obtaining a positive electrode mixture in which the content of S is increased. In the amorphization process, usually, than the content of Li 2 _S in the mixture, increasing the content of Li 2 _S in the positive electrode material.

The positive electrode mixture obtained in the amorphization step is usually a positive electrode mixture in which the content of sulfur in the active state is increased. Usually, the content of Li ₂ S and the content of Li ₂ S ₂ Is a positive electrode composite in which As described above, in the present invention, the content of Li ₂ S is used as an index for activating sulfur, but if there is no particular problem, the content of Li ₂ S ₂ is used as the index. Also good. That is, the amorphization step amorphizes a mixture containing a sulfide solid electrolyte, a positive electrode active material that is elemental sulfur, and a conductive additive that is a carbon material, and the content of Li ₂ S ₂ It may be a step of obtaining a positive electrode mixture with an increased amount.

As the content of Li ₂ S in the positive electrode mixture obtained in the amorphization step, it is sufficient that the content of sulfur in the active state in the positive electrode mixture can be increased. The content is preferably less than the content of Li ₂ S ₂ . Specifically, the intensity ratio (B / B) of the intensity (160 eV) (A) of the binding energy corresponding to Li ₂ S in the XPS spectrum and the intensity (161 eV) (B) of the binding energy corresponding to Li ₂ S ₂ A) is preferably 4 or more. Moreover, B / A is 10 or less, for example.

(I) Mixture The mixture used in the amorphization step includes a sulfide solid electrolyte, a positive electrode active material that is elemental sulfur, and a conductive additive that is a carbon material.

The sulfide solid electrolyte is prepared in the preparation process.
As the content of the sulfide solid electrolyte in the mixture, for example, the sulfide solid electrolyte is preferably in the range of 20 to 400 parts by weight with respect to 100 parts by weight of the positive electrode active material (single sulfur), More preferably, it is in the range of 150 to 300 parts by weight. This is because if the content of the sulfide solid electrolyte is small, it may be difficult to make the ion conductivity of the positive electrode mixture obtained by the present invention sufficient.

The positive electrode active material in the present invention is usually elemental sulfur.
The elemental sulfur, for example, S ₈ sulfur. Specific examples include α sulfur (rhombic sulfur), β sulfur (monoclinic sulfur), and γ sulfur (monoclinic sulfur).

  As content of the positive electrode active material in a mixture, it is preferable that it is 20 weight% or more, for example, and it is more preferable that it is 25 weight% or more. Moreover, as content of the positive electrode active material in a mixture, it is preferable that it is 40 weight% or less, for example, and it is more preferable that it is 35 weight% or less. This is because if the content of the positive electrode active material is small, it may be difficult to ensure a sufficient charge / discharge capacity.

  The conductive aid used in the amorphization process is a carbon material. The conductive auxiliary agent has a function of improving the electronic conductivity of the positive electrode mixture. In addition, it is presumed that the conductive auxiliary agent functions as a reducing agent that reduces elemental sulfur when the mixture is made amorphous.

  The conductive auxiliary agent may be a carbon material, and examples thereof include acetylene black, activated carbon, furnace black, carbon nanotube, and graphene.

  As content of the conductive support agent in a mixture, it is preferable to exist in the range of 20 weight part-200 weight part with respect to 100 weight part of positive electrode active materials (single sulfur), for example, 100 weight part-150 weight part. More preferably within the range of parts.

(Ii) Amorphization step In the amorphization step, the mixture is amorphized to obtain a positive electrode mixture in which the content of Li ₂ S is increased.
The method for making the mixture amorphous is not particularly limited as long as it is a method capable of obtaining a positive electrode mixture in which the content of Li ₂ S is increased. Examples of the amorphization method include mechanical milling. Further, for example, dry mechanical milling or wet mechanical milling may be used.

  The mechanical milling is not particularly limited as long as it mixes the positive electrode mixture while applying mechanical energy, and examples thereof include a ball mill, a vibration mill, a turbo mill, a mechanofusion, and a disk mill. Among these, a ball mill is preferable, and a planetary ball mill is particularly preferable.

Various conditions of mechanical milling are set so that the content of Li ₂ S in the positive electrode mixture increases. For example, when a planetary ball mill is used, a positive electrode mixture and a grinding ball are added to a container, and processing is performed at a predetermined rotation speed and time. The rotation speed of the base plate when performing the planetary ball mill is preferably in the range of 200 rpm to 700 rpm, for example, and more preferably in the range of 300 rpm to 500 rpm. Further, the treatment time when performing the planetary ball mill is preferably in the range of 30 minutes to 30 hours, for example, and more preferably in the range of 5 hours to 20 hours. Examples of the material for the container and ball for grinding used in the ball mill include ZrO ₂ and Al ₂ O ₃ . Moreover, the diameter of the ball for grinding | pulverization exists in the range of 1 mm-20 mm, for example. Mechanical milling is preferably performed in an inert gas atmosphere (for example, an Ar gas atmosphere).

3. Positive electrode mixture for sulfur battery The positive electrode mixture obtained by this invention is normally used for the positive electrode layer of a sulfur battery. Therefore, in this invention, it has a positive electrode layer, a negative electrode layer, and the electrolyte layer formed between the said positive electrode layer and the said negative electrode layer, and forms the said positive electrode layer using the positive electrode compound material mentioned above. A method for manufacturing a sulfur battery having a positive electrode layer forming step can also be provided. Here, the sulfur battery refers to a battery using elemental sulfur as a positive electrode active material. As the electrolyte used for the electrolyte layer, for example, a solid electrolyte is preferably used. It does not specifically limit as a solid electrolyte, For example, the sulfide solid electrolyte mentioned above can be used. The negative electrode active material is not particularly limited, and examples thereof include metal lithium and a lithium alloy (for example, a Li—In alloy). The sulfur battery usually has a positive electrode current collector that collects current from the positive electrode layer and a negative electrode current collector that collects current from the negative electrode layer.

  The sulfur battery may be a primary battery or a secondary battery, but is preferably a secondary battery. This is because it can be repeatedly charged and discharged and is useful, for example, as an in-vehicle battery. Note that the primary battery includes primary battery use (use for the purpose of discharging only once after charging). In particular, the sulfur battery is preferably a lithium sulfur battery.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

  Hereinafter, the present invention will be described in more detail with reference to examples. Unless otherwise specified, each operation such as weighing, synthesis, and drying was performed in an Ar atmosphere.

[Example 1]
(Production of solid electrolyte)
Li ₂ S (manufactured by Nippon Kagaku Kogyo Co., Ltd.), P ₂ S ₅ (manufactured by Aldrich) and LiBr (manufactured by Niho Chemical) were used as starting materials. The materials were mixed in an agate mortar for 5 minutes so that the molar ratio of LiBr: Li ₂ S: P ₂ S ₅ was 20:60:20. 2 g of the mixture is put into a planetary ball mill container (45 cc, made of ZrO ₂ ), dehydrated heptane (moisture content of 30 ppm or less, 4 g) is added, and ZrO ₂ balls (φ = 5 mm, 53 g) are further charged. Was completely sealed. This container was attached to a planetary ball mill (P7 made by Fritsch), and mechanical milling was performed for 2 hours at a base plate rotation speed of 500 rpm. Then, the heptane was removed by drying at 110 degreeC for 1 hour, and sulfide glass was obtained. The composition was 20 LiBr · 80 (0.75 Li ₂ S · 0.25P ₂ S ₅ ) in terms of mole. Next, the obtained sulfide glass was vacuum-sealed in a quartz tube and heat-treated at 170 ° C. Specifically, the sample was put into a furnace previously maintained at 170 ° C. and heat-treated for 3 hours to obtain a solid electrolyte that was glass ceramic.

(Preparation of positive electrode mixture)
Sulfur powder (manufactured by Aldrich) and acetylene black (conductive aid) were prepared. It was weighed so that sulfur: conducting aid: solid electrolyte was 100: 100: 200 by weight ratio. Each of these materials was put into a planetary ball mill container (45 cc, made of ZrO ₂ ), and further ZrO ₂ balls (φ = 5 mm, 53 g) were put in, and the container was completely sealed. This container was attached to a planetary ball mill machine (P7 made by Fritsch), and mechanical milling was performed at a base plate rotation speed of 400 rpm for 5 hours. Thus, a positive electrode mixture was obtained.

(Battery assembly)
A Li—In alloy was prepared as a negative electrode layer.
100 mg of the solid electrolyte was put into a 1 cm ² ceramic mold and pressed at 1 ton / cm ² to compact the solid electrolyte layer. On one side, 10 mg of the positive electrode mixture was put and pressed at 1 ton / cm ² to prepare a positive electrode layer. On the opposite side, a Li—In alloy as a negative electrode layer was arranged and pressed at 4 ton / cm ² to obtain a power generation element. Al foil (positive electrode current collector) was disposed on the positive electrode layer side, and Cu foil (negative electrode current collector) was disposed on the negative electrode layer side. A battery was produced by the above procedure.

[Example 2]
Same as Example 1 except that each material was weighed so that LiBr: Li ₂ S: P ₂ S ₅ was 30: 52.5: 17.5 in the molar ratio during the production of the solid electrolyte. A battery was obtained. The composition of the solid electrolyte was 30LiBr · 70 (0.75Li ₂ S · 0.25P ₂ S ₅ ) in terms of mole.

[Comparative Example 1]
The battery was fabricated in the same manner as in Example 1 except that each material was weighed so that the molar ratio of LiI: Li ₂ S: P ₂ S ₅ was 20:60:20 during the production of the solid electrolyte. Obtained. The composition of the solid electrolyte was 20LiI · 80 (0.75Li ₂ S · 0.25P ₂ S ₅ ) in terms of mole.

[Comparative Example 2]
A battery was obtained in the same manner as in Example 1 except that each material was weighed so that the molar ratio of Li ₂ S: P ₂ S ₅ was 75:25 when the solid electrolyte was produced. The composition of the solid electrolyte was 75Li ₂ S · 25P ₂ S ₅ in terms of mole.

[Evaluation]
(Initial charge / discharge capacity measurement)
Current values of 400 mA / cm ² (CC-CV 200 mA / cm ² cut), 0.5 V to 2.5 V (counter electrode Li-In) for all solid state batteries obtained in Examples 1 and 2 and Comparative Examples 1 and ² ), And charging / discharging was performed at a temperature of 25 ° C. The measurement results are shown in FIG.

The results of the initial charge / discharge capacity measurement in Examples 1 and 2 and Comparative Examples 1 and 2 are shown in FIG. From FIG. 1, it was confirmed that Examples 1 and 2 and Comparative Example 1 had a larger charge / discharge capacity than Comparative Example 2. From this result, it was confirmed that the charge / discharge capacity can be increased by using a positive electrode mixture using a solid electrolyte containing LiBr or LiI halogenated Li in the composition.
In addition, it was confirmed that the charge / discharge capacity of Example 1 was larger than that of Comparative Example 1. From this result, when the positive electrode mixture using the solid electrolyte containing LiBr is used, the charge / discharge capacity can be increased as compared with the case where the positive electrode mixture using the solid electrolyte containing LiI is used. confirmed.

From FIG. 1, it was confirmed that Examples 1 and 2 and Comparative Example 1 had an increase in the first stage charge / discharge plateau compared to Comparative Example 2. Here, from the potential, it is presumed that the first-stage charging plateau (in Example 1, around 100 mAh / g to 1000 mAh / g) is attributed to Li ₂ S. From this result, it was suggested that the amount of Li ₂ S generated at the time of discharge increases by using a positive electrode mixture using a solid electrolyte containing LiBr or LiI halogenated Li in the composition.
In addition, it was confirmed that the charge / discharge plateau in the first stage increased in Example 1 as compared with Comparative Example 1. From this result, when the positive electrode mixture using the solid electrolyte containing LiBr is used, the amount of Li ₂ S generated at the time of discharge is larger than when the positive electrode mixture using the solid electrolyte containing LiI is used. Was suggested to increase.
On the other hand, in Example 1, the amount of the first stage charge / discharge plateau was similar to that in Example 2, but it was confirmed that the amount of the second stage charge / discharge plateau decreased. From this result, when there is too much LiBr in the solid electrolyte, there is a possibility that the amount of Li ₂ S generated during discharge does not increase.

The reason why the charge / discharge capacity is increased and the reason why the amount of Li ₂ S generated during discharge is increased is presumed as follows.
By mechanically milling a solid electrolyte containing LiBr or LiI halogenated Li in the composition, elemental sulfur and a conductive additive, heat and pressure are applied to the entire area of the positive electrode mixture, and Li halide and elemental sulfur are applied. It is presumed that the inactive elemental sulfur became Li ₂ S ₂ and activated by the reaction. Moreover, since LiBr has softer powder than LiI, LiBr is likely to react with elemental sulfur and Li ₂ S ₂ is likely to be generated.

(Structural analysis by XPS)
Structural analysis by XPS was performed on the solid electrolyte and the positive electrode mixture of Example 1 and Comparative Examples 1 and 2. The results are shown in FIG. In FIG. 2, the spectrum of elemental sulfur (S ⁰ ) is also shown as a reference.
In the spectra of the solid electrolytes of Example 1 and Comparative Examples 1 and 2, the spectral intensity of the binding energy (about 160 eV) corresponding to Li ₂ S was not confirmed. On the other hand, in the spectra of the positive electrode composites of Example 1 and Comparative Examples 1 and ₂ , the spectral intensity of Li ₂ S was confirmed in Example 1 and Comparative Example 1, whereas in Li ₂ S in Comparative Example 2, The spectral intensity was not confirmed. From this result, it was confirmed that Li ₂ S was generated by mechanically milling a solid electrolyte containing LiBr or LiI halogenated Li in the composition, elemental sulfur, and a conductive additive.
Regarding the spectrum at the binding energy (about 164 eV) corresponding to S ⁰ of the positive electrode composite material, it was confirmed that the slope of the spectrum of Example 1 and Comparative Example 1 was larger than the slope of the spectrum of Comparative Example 2. It was. From this result, it is presumed that elemental sulfur and halogenated Li reacted to generate Li ₂ S.

Further, regarding the spectrum of the positive electrode composite material, it was confirmed that in Example 1, the spectrum area from about 161 eV (binding energy corresponding to Li ₂ S ₂ ) to about 160 eV increased compared to Comparative Example 1. From this result, it was confirmed that when LiBr was used, Li ₂ S ₂ was more easily generated than when LiI was used.
The reason why Li ₂ S ₂ is likely to be generated is presumed that LiBr was more flexible than LiI, so that it easily reacted with elemental sulfur when the positive electrode mixture was amorphized. .

Claims (1)

A method for producing a positive electrode mixture used in a sulfur battery,
A preparatory step of preparing a sulfide solid electrolyte composed of an ion conductor having Li, P and S and LiBr;
The positive electrode mixture in which the content of Li ₂ S is increased by amorphizing a mixture containing the sulfide solid electrolyte, a positive electrode active material that is elemental sulfur, and a conductive additive that is a carbon material. Obtaining an amorphization step;
The manufacturing method of the positive electrode compound material characterized by having.