KR20190016904A - Cathode mixture and method for producing the same - Google Patents

Abstract

An object of the present disclosure to manufacture an anode mixture capable of increasing the charging/discharging capacity of a sulfur battery. In the anode mixture used in the sulfur battery and the manufacturing method thereof of the present disclosure, the object is achieved by providing an anode mixture and a manufacturing method thereof characterized by subjecting a raw material mixture, which comprises Li_2S and M_xS_y (M is selected from P, Si, Ge, B, Al, or Sn, x and y are integers which give electrical neutrality to S depending on the type of M), an anode active material containing single sulfur, and a conductive auxiliary agent containing a carbon material, to a mechanical milling process.

Description

[0001] CATHODE MIXTURE AND METHOD FOR PRODUCING THE SAME [0002]

The present disclosure discloses a positive electrode material used in a sulfur battery and a method of manufacturing the same.

BACKGROUND ART In recent years, with the rapid spread of information-related devices such as personal computers, video cameras, mobile phones, and communication devices, development of batteries to be used as power sources has become important. In addition, in the automotive industry and the like, development of a high-output and high-capacity battery for an electric vehicle or a hybrid vehicle is progressing.

Development of a sulfur battery using sulfur as a positive electrode active material has been progressing. The sulfur has a characteristic that the theoretical capacity is very high at 1675 mAh / g. Further, in the field of sulfur batteries, attempts have been made to improve the utilization ratio of sulfur and increase the charge / discharge capacity of sulfur batteries. Patent Document 1 discloses a positive electrode composite material including a Li ₂ SP ₂ S ₅ solid electrolyte, a positive electrode active material that is a single sulfur, and a conductive material that is a carbon material. Patent Document 1 discloses a method of producing a solid electrolyte comprising (a) a Li ₂ SP ₂ S ₅ sulphide solid electrolyte previously prepared by an oil-based ball milling treatment, or Li ₂ S and red sulfur as starting materials as a solid electrolyte, (A) - (c) were mixed by a planetary ball mill, using the sulfide solid electrolyte thus prepared, (b) sulfur as the positive electrode active material, and (c) Ketjen black as the conductive additive, A lithium-sulfur battery is disclosed.

Patent Document 2 discloses a manufacturing method of producing a positive electrode material by mechanical milling using sulfur, acetylene black, and 80Li ₂ S-20P ₂ S ₅ sulfide solid electrolyte prepared using a planetary ball mill as a starting material have.

In Patent Document 3, (A) sulfur or its discharge product, (B) Li ₂ S and P ₂ S ₅ are used as a starting material (Li ₂ S: P ₂ S ₅ = composition ratio (molar ratio) of 65:35) (C) a step of mixing the conductive material (1), an 80Li ₂ S-20P ₂ S ₅ sulphide solid electrolyte prepared by using a planetary ball mill in advance, and a step (2) of mixing the mixture obtained in the step (1).

Japanese Patent No. 5445809 Japanese Patent Application Laid-Open No. 2011-181260 Japanese Unexamined Patent Application Publication No. 2014-160572

Also in the prior art, the utilization ratio of sulfur is not sufficiently improved, and it is further demanded to increase the charge-discharge capacity of the sulfur battery. SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a positive electrode material capable of improving the utilization ratio of sulfur and increasing the charge / discharge capacity of a sulfur battery, and a method for producing the same.

In order to achieve the above-mentioned object, in the present disclosure, in a method of manufacturing a positive electrode material used in a sulfur battery, Li ₂ S and M _x S _y (M is P, Si, Ge, B, And x and y are constants which give electrical neutrality to S in accordance with the type of M), a positive electrode active material containing a simple sulfur, and a conductive auxiliary agent containing a carbon material are subjected to a mechanical milling treatment The present invention also provides a method for producing a positive electrode material.

Li ₂ S and M _x S _{y wherein} M is selected from P, Si, Ge, B, Al or Sn, x and y are constants which give electrical neutrality to S depending on the type of M, And a conductive auxiliary agent containing a carbon material are mechanically milled to produce a positive electrode composite material in which a good interface between sulfur and a solid electrolyte, sulfur and a conductive auxiliary agent is formed.

The present disclosure has an effect that it is possible to manufacture a positive electrode material capable of improving the utilization ratio of sulfur and increasing the charge-discharge capacity of a sulfur battery.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a view for explaining the flow of the manufacturing method of the first embodiment in the present disclosure; FIG.
Fig. 2 is a view for explaining the flow of the manufacturing method of the comparative example in the present disclosure. Fig.
3 (a) is an XRD pattern in the vicinity of 2? = 23 占 of the positive electrode mixture powder produced by the process of Example 1 and the comparative example.
3 (b) is an XRD pattern in the vicinity of 2? = 27 占 of the positive electrode composite material powder produced by the process of Example 1 and the comparative example.
4 is a reversible capacitance density at the time of charging / discharging at C / 10 (456 占 / / cm2) in Example 1 and Comparative Example.
5 is a ratio of the reversible capacity density at charging and discharging to a) C / 3, b) 1C, c) 2C for C / 10 (456 / / cm2) of Example 1 and Comparative Example.
6 is a view for explaining the flow of the manufacturing method of the second to seventh embodiments in this disclosure.
7 is a graph showing discharge capacities of C / 10, 1C and 2C of the battery using the positive electrode mixture obtained in Examples 2 to 7 and Reference Example.
8 is a graph showing the ratio (high-rate discharge characteristics) of the discharge capacity to 2C with respect to the discharge capacity to C / 10 of the battery using the positive electrode mixture obtained in Examples 2 to 7 and Reference Example.
9 is an XRD pattern of the positive electrode mixture obtained in Examples 2 to 7 and Reference Example.
10 is a graph showing the Li ₂ S (111) / GeS ₂ (111) intensity ratios of the positive electrode mixture obtained in Examples 2 to 7 and Reference Example.

Hereinafter, the positive electrode mixture of the present disclosure and the production method thereof will be described in detail.

The positive electrode mixture of the present disclosure and its production method are characterized in that Li ₂ S and M _x S _y (M is selected from P, Si, Ge, B, Al, or Sn, x and y are constants which give electrical neutrality to S in accordance with the type of M), a positive electrode active material containing a simple sulfur, and a conductive auxiliary agent containing a carbon material by mechanical milling .

Li ₂ S and M _x S _{y wherein} M is selected from P, Si, Ge, B, Al or Sn, x and y are constants which give electrical neutrality to S depending on the type of M, And a conductive auxiliary agent containing a carbon material are mechanically milled to produce a positive electrode composite in which a good interface between sulfur and a solid electrolyte, sulfur and a conductive auxiliary agent is formed.

The reason why the charge / discharge capacity of the sulfur battery can be increased by manufacturing the positive electrode material of the sulfur battery by the above production method is presumed as follows.

In the case of using sulfur as a positive electrode active material for all solid-state batteries, a charge-discharge reaction proceeds only at a three-phase interface where a solid electrolyte that becomes a Li ion pass and a conductive auxiliary agent that is an electron path coexist on the surface of sulfur as an active material.

In the present disclosure, Li ₂ S and M _x S _y (where M is selected from P, Si, Ge, B, Al or Sn, x and y are constants which give electrical neutrality to S depending on the kind of M) Since the positive electrode material is produced by mechanically milling the raw material mixture containing the positive electrode active material containing the sulfur and the conductive auxiliary agent containing the carbon material, the good three-phase interface between the solid electrolyte and the conductive auxiliary agent .

As a result, the charging / discharging reaction can be promoted at the time of charging / discharging, the utilization ratio of sulfur can be improved, and the charge / discharge capacity of the sulfur battery can be increased.

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

As shown in the following examples, Li ₂ S and M _x S _y (M is selected from P, Si, Ge, B, Al or Sn, and x and y are given electrical neutrality with S Discharge capacity) of the positive electrode material produced by subjecting the raw material mixture containing the positive electrode active material containing the sulfur and the conductive auxiliary agent containing the carbon material to mechanical milling can exhibit a large charge / .

Patent Documents 1 to 3 disclose that mixing a sulfide solid electrolyte prepared by using a planetary ball mill in advance, a basic sulfur as a positive electrode active material, a discharge product thereof, and a conductive auxiliary agent by mechanical milling, such as a ball mill, However, Li ₂ S and M _x S _y (M is selected from P, Si, Ge, B, Al, or Sn, and x and y are constants giving electrical neutrality to S ), A positive electrode active material containing a base sulfur, and a conductive auxiliary agent containing a carbon material are mechanically milled to produce a positive electrode composite material.

Li ₂ S and M _x S _{y wherein} M is selected from P, Si, Ge, B, Al or Sn, x and y are constants which give electrical neutrality to S depending on the type of M, And a conductive auxiliary agent containing a carbon material are subjected to a mechanical milling treatment to improve the utilization ratio of sulfur in the positive electrode composite material and to increase the charge and discharge capacity And unexpected phenomena and effects in the conventional patent documents 1-3.

The reason why the present disclosure shows unexpected phenomena and effects in the conventional patent documents 1-3 is presumed as follows.

Li ₂ S and M _x S _{y wherein} M is selected from P, Si, Ge, B, Al or Sn, x and y are constants which give electrical neutrality to S depending on the type of M, And a conductive auxiliary agent containing a carbon material are mechanically milled to synthesize a solid electrolyte, and a part of a single sulfur or a combination of sulfur and Li ₂ S is generated in the process of synthesizing the solid electrolyte It is believed that lithium sulfide (Li _x S) is incorporated into the structure of the solid electrolyte. Thereafter, a single sulfur or lithium polysulfide in the solid electrolyte becomes a solute limit, and a single sulfur or Li ₂ S re-precipitates on the surface of the solid electrolyte, and the solid electrolyte, the simple sulfur, and the solid electrolyte and Li ₂ S is improved, it is estimated that the utilization ratio of sulfur in the positive electrode composite material is improved and the charge-discharge capacity is increased.

On the other hand, in the prior art, since the positive electrode material is produced by mixing the sulfide solid electrolyte prepared by using the planetary ball mill in advance, the basic sulfur as the positive electrode active material, the discharge product thereof, and the conductive auxiliary agent by mechanical milling, such as a ball mill, It is presumed that a phenomenon such as the above-mentioned phenomenon does not occur.

Further, the raw material mixture in the present disclosure, as M _x S _y, including M ¹ _x S _y, and M ² _x S _y (M ¹ and M ² are different elements), and further M ¹ _x S _y is P ₂ S ₅ , it is possible to suppress the capacitance drop at high current density. Specifically, it is as follows. First, in the present disclosure, as described above, by mechanically milling a raw material mixture containing Li ₂ S and M _x S _y , a positive electrode active material containing a simple sulfur, and a conductive auxiliary containing a carbon material, The dispersibility of sulfur is improved and the utilization ratio of sulfur in the positive electrode composite material is improved. And Li ₂ S and M _x S _y, when the positive electrode active material containing sulfur, hayeoteul mixing a conductive additive containing a carbon material, a portion of the elemental sulfur, or sulfur and Li ₂ S as described above is The lithium polysulfide (Li _x S) produced by the reaction is taken into the structure of the solid electrolyte. At this time, if the sulfur is rich, the sulfur may be saturated and precipitate on the surface of the solid electrolyte in some cases. Then, the sulfur introduced into the solid electrolyte structure functions as a solid electrolyte, while the precipitated sulfur functions as a positive electrode active material. As a result, it is considered that the utilization ratio of sulfur is improved as a result.

In the present disclosure, in particular, sulfur has high reactivity with P ₂ S ₅ and is easy to form a network. It is considered that this is due to the fact that, in the steric structure possessed by P ₂ S ₅ , the crosslinked sulfur among the steric structure has high reactivity and is chemically easy to react with sulfur by mixing with sulfur. Further, in the conventional method of producing a positive electrode composite material, since the solid electrolyte and the basic sulfur are mechanically mixed, the reaction between the solid electrolyte and the basic sulfur is not usually caused. This is presumably because P ₂ S ₅ and Li ₂ S, which are the starting materials of the solid electrolyte, react in advance, and even if they are mixed with a unitary sulfur thereafter, the reaction of P ₂ S ₅ and sulfur does not occur.

On the other hand, in the present disclosure, the present inventors have found a new problem that the capacity of the positive electrode current density is improved and the utilization ratio of sulfur is improved, thereby increasing the charge / discharge capacity, but discharging at a high current density. More specifically, M _x S _y is P ₂ S ₅ in the case, constituting the ion conductor Li ₂ S and P ₂ S ₅ wherein the results are part of a P ₂ S ₅ which is incorporated into the active material layer to react with the active material of sulfur, There is a case where Li ₂ S becomes excessive in the constitution of the ion conductor and the ion conductivity is lowered (resistance is increased) in some cases. As described above, in the present disclosure, a part of P ₂ S ₅ reacts with sulfur to become an active material, so that the capacity can be increased at a low current density while the capacity is remarkably lowered when the load is increased (high current density) I found a new task. In addition, the above-mentioned problem in the present disclosure that the capacity is lowered extremely when the discharge is carried out at the low current density and the capacity is remarkably lowered at the high current density can not be easily overcome. With respect to the above-mentioned problems, in the present disclosure, the raw material mixture is, as a M _x S _y, M ¹ _x S _y, and M ² _x S _y including the (M ¹ and M ² are different elements), and further M ¹ _x and S _y is P ₂ S _5, the M ² of the M ² _x S _y Si, Ge, B, being selected from Al and Sn, with the excess in the configuration of the ion conductor Li ₂ S wherein M ² _x S _y , it is possible to suppress a reduction in capacity at a high current density.

Hereinafter, the positive electrode mixture and its manufacturing method will be described.

1) Raw material mixture

The raw material mixture is a mixture containing a starting material of a sulfide solid electrolyte, a positive electrode active material containing a sulfur atom, and a conductive auxiliary agent containing a carbon material. That is, the raw material mixture is selected from Li ₂ S and M _x S _y (M is selected from P, Si, Ge, B, Al or Sn, and x and y are constants which give electrical neutrality to S depending on the type of M) , A positive electrode active material including a base sulfur, and a conductive auxiliary agent containing a carbon material.

(I) the starting material of the sulfide solid electrolyte

The sulfide solid electrolyte prepared as the starting material of the sulfide solid electrolyte is composed of an ion conductor containing at least Li and S, and includes Li ₂ S and M _x S _y . M is selected from P, Si, Ge, B, Al, or Sn, and x and y are constants that give electrical neutrality to S depending on the kind of M. M may be one species selected from P, Si, Ge, B, Al, or Sn, or two or more species selected from P, Si, Ge, B, Al, or Sn. Specific examples of M _x S _y include P ₂ S ₅ , SiS ₂ , GeS ₂ , B ₂ S ₃ , Al ₂ S ₃ and SnS _2. Examples of the combination of Li ₂ S and M _x S _y include Li ₂ SP ₂ S ₅ , Li ₂ S-SiS ₂ , Li ₂ S-GeS ₂ , Li ₂ SB ₂ S ₃ , Li ₂ S-Al ₂ S ₃ and Li ₂ S-SnS ₂ .

Also, M _x S _y (where M is selected from P, Si, Ge, B, Al, or Sn, and x and y are constants that give electrical neutrality to S depending on the type of M) , A plurality of M _x S _y may be used. Specific examples thereof include Li ₂ SP ₂ S ₅ -GeS ₂ , Li ₂ SP ₂ S ₅ -SiS ₂ and Li ₂ S-SiS ₂ -Al ₂ S ₃ .

In the present disclosure, the raw material mixture may contain a plurality of M _x S _y . That is, M _x S _{y may} include M ¹ _x S _y and M ² _x S _y (M ¹ and M ² are other elements). Here, M ¹ is selected from P, Si, Ge, B, Al, or Sn, and x and y are integers that give electrical neutrality to S depending on the kind of M ¹ and M ² . M ¹ is preferably the P. That is, M ¹ _x S _y is preferably P ₂ S ₅ . M ¹ may be one species selected from P, Si, Ge, B, Al, or Sn, or two or more species selected from P, Si, Ge, B, Al, or Sn. Specific examples of M ¹ _x S _y include P ₂ S ₅ , SiS ₂ , GeS ₂ , B ₂ S ₃ , Al ₂ S ₃ and SnS ₂ . On the other hand, M ² is selected from P, Si, Ge, B, Al, or Sn, and x and y are constants that give electrical neutrality to S depending on the kind of M ¹ and M ² . M ² is preferably selected from Si, Ge, B, Al or Sn. That is, it is preferable that M ² _x S _y is, for example, SiS ₂ , GeS ₂ , B ₂ S ₃ , Al ₂ S ₃ or SnS ₂ , and GeS ₂ is particularly preferable.

The raw material mixture is a mixture of Li ₂ S and P ₂ S when M ¹ _x S _y is P ₂ S ₅ and M ² _x S _y is SiS ₂ , GeS ₂ , B ₂ S ₃ , Al ₂ S ₃ or SnS _{2 5} at a predetermined ratio. The raw material mixture preferably contains Li ₂ S and P ₂ S ₅ in a ratio of 60:40 to 90:10 (molar ratio), and is preferably provided in a ratio of 70:30 to 90:10 (molar ratio) desirable. Among them, it is preferable to provide Li ₂ S and P ₂ S ₅ at a ratio of 84:16 (molar ratio). Specifically, the ratio of Li ₂ S to the total of Li ₂ S and P ₂ S ₅ is, for example, 70 mol% or more, 75 mol% or more, 80 mol% or more, 84 mol% or more Or may be 90 mol% or more. The molar ratio (Li / P) of Li to P is, for example, 2 or more, 4 or more, or 5 or more. On the other hand, the molar ratio (Li / P) of Li to P is, for example, 10 or less, 8 or less, or 6 or less. Li ₂ S and P ₂ S ₅ are included at the above ratios, so that Li ₂ S becomes excessive in the constitution of the ion conductor, and the capacity at a high current density is lowered. In the present disclosure, however, When the raw material mixture contains M ¹ _x S _y (P ₂ S ₅ ) and M ² _x S _y (M ² is an element selected from Si, Ge, B, Al or Sn) ₂ S and M ² _x S _y can be reacted with each other to suppress the capacity drop at high current density.

When the raw material mixture contains M ¹ _x S _y (P ₂ S ₅ ) and M ² _x S _y (M ² is an element selected from Si, Ge, B, Al or Sn) ² (M ² / P) is preferably 0.08 or more and 1.23 or less. This is because it is possible to effectively suppress the capacity drop at high current density. M ² / P is, for example, not less than 0.34 and not less than 0.54. On the other hand, M ² / P is, for example, not more than 1.00 and not more than 0.79. In the present disclosure, it is preferable to determine the input weights of P ₂ S ₅ and M ² _x S _y contained in the raw material mixture so that M ² (M ² / P) with respect to P in the positive electrode mixture is within the above range Do.

When the raw material mixture contains M ¹ _x S _y (P ₂ S ₅ ) and M ² _x S _y (M ² is an element selected from Si, Ge, B, Al or Sn) , The intensity ratio of the diffraction peak of the Li ₂ S (111) face to the diffraction peak of the M ² _x S _y (111) plane is preferably 0.9 or more and 10.4 or less. The intensity ratio is, for example, 1.0 or more and 2.0 or more. On the other hand, the intensity ratio is, for example, 7.0 or less, or 5.0 or less. Here, the intensity ratio can be obtained by the following formula.

Intensity ratio = diffraction peak intensity of Li ₂ S (111) plane / diffraction peak intensity of M ² _x S _y (111) plane

Specifically, when M ² _x S _y is GeS ₂ ,

Intensity ratio = I (27) -I (26) / I (15.5) -I (14.5)

The intensity ratio can be obtained. The diffraction peak (I (27 DEG), etc.) used in the above formula can be an average value of the peak intensities within a range of +/- 0.05 DEG.

Further, a lithium salt such as LiCl, LiI, or LiBr, or other electrolyte such as Li ₃ PO ₄ may be added to the starting material of the sulfide solid electrolyte.

The sulfide solid electrolyte usually has Li ion conductivity.

The ionic conductor contains at least Li and S. The ionic conductor is not particularly limited as long as it has at least Li and S, and for example, an ion conductor having an ortho-composition can be mentioned. Here, orthorrh implies generally the highest degree of hydration among the oxoacids obtained by hydrating the same oxide. In the present disclosure, the crystal composition in which Li ₂ S is most added in the sulfide is referred to as ortho composition. For example, in a Li ₂ SP ₂ S ₅ system, Li ₃ PS ₄ corresponds to an ortho composition.

The term " having an ortho-composition " includes not only a strict ortho-composition but also a composition in the vicinity thereof. Specifically, it means that an anion structure (PS ₄ ³ -structure) is mainly used. The proportion of the anion structure in the ortho composition is preferably 60 mol% or more, more preferably 70 mol% or more, further preferably 80 mol% or more, and further preferably 90 mol% or more, relative to the total anion structure in the ion conductor. % Or more. The ratio of the anion structure of the ortho composition can be determined by Raman spectroscopy, NMR, XPS and the like.

For example, in the case of a Li ₂ SP ₂ S ₅ system sulfide solid electrolyte, the ratio of Li ₂ S and P ₂ S ₅ to obtain an ortho composition is Li ₂ S: P ₂ S ₅ = 75: 25 to be. The raw material mixture in the present disclosure preferably contains Li ₂ S and P ₂ S ₅ at a ratio of 60:40 to 90:10 (molar ratio). Specifically, the ratio of Li ₂ S to the total of Li ₂ S and P ₂ S ₅ is, for example, in the range of 60 mol% to 90 mol% and in the range of 70 mol% to 80 mol% , More preferably within a range of 72 mol% to 78 mol%, and still more preferably within a range of 74 mol% to 76 mol%.

The shape of the sulfide solid electrolyte is, for example, a particle shape. The average particle diameter (D ₅₀ ) of the particle-shaped sulfide solid electrolyte is preferably in the range of, for example, 0.1 탆 to ₅₀ 탆. It is preferable that the sulfide solid electrolyte has a high Li ion conductivity. The Li ion conductivity at room temperature is preferably 1 x 10 ^-4 S / cm or more, more preferably 1 x 10 ^-3 S / Cm or more. The average particle size can be a value calculated by a particle size distribution analyzer of laser diffraction type or a value measured based on image analysis using an electron microscope such as SEM.

The sulfide solid electrolyte may be, for example, a crystal, a sulfide glass, or a glass ceramic. The sulfide solid electrolyte may contain at least one of Li ₂ S and P ₂ S ₅ as raw materials, for example.

As the content of the sulfide solid electrolyte in the raw material mixture, for example, the sulfide solid electrolyte is preferably in the range of 20 parts by weight to 400 parts by weight, more preferably 30 parts by weight to 250 parts by weight, per 100 parts by weight of the positive electrode active material Is more preferable. When the content of the sulfide solid electrolyte is small, there is a possibility that it becomes difficult to make the ionic conductivity of the positive electrode mixture obtained by the present disclosure sufficient. Further, if the content of the sulfide solid electrolyte is large, the content of the positive electrode active material becomes small, and it may become difficult to secure a sufficient charge-discharge capacity.

(Ii) positive electrode active material

The positive electrode active material is usually a single sulfur. It is preferable to use as high a purity as possible for the group sulfur. As the group sulfur, for example, S ₈ sulfur can be mentioned. Specific examples thereof include? Sulfur (alluvial sulfur),? Sulfur (monosulfur sulfur), and? Sulfur (monosulfur sulfur).

The content of the positive electrode active material in the raw material mixture is, for example, preferably 20% by weight or more, more preferably 25% by weight or more. The content of the positive electrode active material in the mixture is, for example, preferably 70% by weight or less, and more preferably 60% by weight or less. If the content of the positive electrode active material is small, there is a possibility that it becomes difficult to secure a sufficient charge-discharge capacity.

(Iii)

The conductive additive is a carbon material used in a mixing process. The conductive additive has a function of improving the electronic conductivity of the positive electrode composite material. It is also presumed that the conductive auxiliary functions as a reducing agent for reducing the elemental sulfur when the mixture is mixed.

The conductive auxiliary may be a carbon material, and examples thereof include vapor grown carbon fiber (VGCF), acetylene black, activated carbon, furnace black, carbon nanotubes, ketjen black and graphene.

The content of the conductive auxiliary agent in the mixture is preferably in the range of 10 parts by weight to 200 parts by weight, more preferably in the range of 15 parts by weight to 100 parts by weight, relative to 100 parts by weight of the positive electrode active material (unitary sulfur) .

2) Mixing process

The mixing step is a step of mixing the starting material of the sulfide solid electrolyte, the positive electrode active material including the sulfur, and the raw material mixture containing the conductive auxiliary containing the carbon material to obtain a positive electrode mixture. As a mixing method of the raw material mixture, for example, mechanical milling can be mentioned. The mechanical milling may be a dry mechanical milling or a wet mechanical milling.

The mechanical milling is not particularly limited as long as it is a method of mixing the positive electrode material while imparting mechanical energy. Examples of the mechanical milling include a ball mill, a vibration mill, a turbo mill, a mechanofusion, a disc mill, Is preferable, and a planetary ball mill is particularly preferable.

The liquid used for the wet mechanical milling preferably has an aprotic property to the extent that hydrogen sulfide is not generated. Specifically, it is preferable to use an aprotic liquid such as a polar aprotic liquid or a non-polar aprotic liquid .

When the planetary ball mill is used, the positive electrode mixture and the ball for grinding are added to the vessel, and the treatment is performed at a predetermined number of revolutions and for a predetermined time. The rotational speed of the base plate when the planetary ball mill is performed is preferably within a range of, for example, 200 rpm to 800 rpm, and more preferably, in a range of 300 rpm to 600 rpm. It is preferable that the treatment time for the planetary ball mill is within a range of, for example, 30 minutes to 100 hours, more preferably 5 hours to 60 hours. Examples of the container used for the ball mill and the ball material for grinding include ZrO ₂ and Al ₂ O ₃ . The diameter of the grinding balls is, for example, in the range of 1 mm to 20 mm. The mechanical milling is preferably performed in an inert gas atmosphere (for example, an Ar gas atmosphere).

3) Positive electrode for sulfur battery

The positive electrode material in the present disclosure is a material obtained by using the above-described materials and methods. Specifically, the positive electrode material in this disclosure is used in a sulfur battery, and Li ₂ S and M _x S _y (where M is selected from P, Si, Ge, B, Al, or Sn, And a conductive auxiliary agent containing a carbon material, and a composite obtained by a mechanical milling treatment. The present invention is also directed to a composite material obtained by mechanical milling a raw material mixture containing a positive electrode active material containing a simple sulfur and a conductive auxiliary agent.

In the positive electrode composite material of the present disclosure, the diffraction intensity at a peak of 2? = 23 ° .05 ± 1.00 ° in the X-ray diffraction measurement using a CuK? Ray is I _A , When the diffraction intensity at a peak of 1.00 is I _B , it is preferable that the value of I _B is larger than the value of I _A.

In addition, the positive electrode laminated material according to the present disclosure, the raw material mixture, as the M _x S _y, comprising a M ¹ _x S _y, and M ² _x S _y (M ¹ and M ² are different elements), the M ¹ _x S _y is the P ₂ S _5, the M ² _x wherein M ² in the S _y is is selected from Si, Ge, B, Al or Sn, wherein M ² _x S _y (111) surface The intensity ratio of the diffraction peak of the Li ₂ S (111) face to the diffraction peak is preferably 0.9 or more and 10.4 or less.

The positive electrode material is usually used for a positive electrode layer of a sulfur battery. Therefore, a sulfur battery cell having a positive electrode layer, a negative electrode layer, and an electrolyte layer formed between the positive electrode layer and the negative electrode layer and having a positive electrode layer forming step of forming the positive electrode layer using the above- May also be provided. Here, the sulfur battery refers to a battery using a single sulfur as a positive electrode active material. As the electrolyte used for the electrolyte layer, for example, a solid electrolyte is preferably used. The solid electrolyte is not particularly limited, and for example, the above-described sulfide solid electrolyte can be used. The negative electrode active material is not particularly limited, and examples thereof include metal lithium, a lithium alloy (for example, Li-In alloy), and the like. The sulfur battery usually has a positive electrode collector for collecting the positive electrode layer and a negative electrode collector for collecting the negative electrode layer.

The sulfur battery may be a primary battery or a secondary battery, but is preferably a secondary battery. And can be repeatedly charged and discharged, for example, as a vehicle-mounted battery. The primary battery also includes a primary battery (use for discharging only once after charging) of the secondary battery. The sulfur battery is preferably a lithium sulfur battery.

(X-ray diffraction measurement)

When the X-ray diffraction (XRD) measurement was performed on the positive electrode composite material, the powder sample was subjected to CuK? Ray under an inert atmosphere. Powder samples using the XRD measurement, the voltage to the positive electrode laminated material, the opening of the manufactured battery 2.2V (vs Li / Li ⁺⁾ or more, less than 2.5V (vs Li / Li ⁺⁾ produced by the production method of the base material ( OCV), or a positive electrode mixture in which the battery is charged.

The present disclosure is not limited to the above-described embodiments. The above-described embodiments are examples, and any of those having substantially the same structure as the technical idea described in the claims of the present disclosure and having similar operational effects are included in the technical scope of the present disclosure.

[Example]

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

[Example 1 (1step)]

(Production of positive electrode mixture)

Li ₂ S (made of a locked lithium), P ₂ S ₅ (an aldrich), a unit sulfur powder (a high purity chemical) and VGCF (a conductive additive) as starting materials for a sulfide solid electrolyte were prepared. Starting materials of these raw material mixtures were weighed to the weight ratio shown in Table 1, and the respective materials were kneaded in agate for 15 minutes. These raw material mixtures were put into a vessel (45 cc, made of ZrO ₂ ) of a planetary ball mill, and further a ZrO ₂ ball (Ø = 4 mm, 96 g) was further added, and the vessel was completely sealed. The container was attached to a planetary ball mill (pleats P7), mechanical milling was performed for a total of 48 hours by repeating the cycle of one hour mechanical milling and stopping for 15 minutes at 500 revolutions per minute. Thus, a positive electrode mixture was obtained.

The production method (synthesis flow) of the positive electrode composite material according to Example 1 is referred to as 1step, and the flow of the production method is shown in Fig.

Table 1 shows the weight of various materials used as starting materials and the open circuit voltage (OCV) of the produced cell.

(Assembly of battery)

A Li metal foil was prepared as a negative electrode layer.

100 mg of a solid electrolyte was put into a 1 cm 2 ceramic mold, and pressed at 1 ton / cm 2 to compact the solid electrolyte layer. 7.8 mg of the positive electrode composite material was placed on one side thereof and pressed at 6 ton / cm 2 to prepare a positive electrode layer. On the opposite side, a lithium metal foil serving as a negative electrode layer was disposed and pressed at 1 ton / cm 2 to obtain a power generation element. An Al foil (positive electrode collector) was disposed on the positive electrode layer side, and a Cu foil (negative electrode collector) was disposed on the negative electrode layer side. A battery was produced by the above procedure.

[Comparative Example (2 step)]

(Preparation of Solid Electrolyte)

Li ₂ S (made of locked lithium) and P ₂ S ₅ (made of aldrich) were used as starting materials. And the weight ratio of Li ₂ S: P ₂ S ₅ was 75:25 in terms of molar ratio, and each material was mixed in agate for 15 minutes. The mixture was put into a container (45 cc, made of ZrO ₂ ) of a planetary ball mill, and further a ZrO ₂ ball (Ø = 4 mm, 96 g) was further added, and the vessel was completely closed. The container was attached to a planetary ball mill (pleats P7) and subjected to a mechanical milling for a total of 24 hours by repeating the cycle of the one-hour mechanical milling and the fifteen minute stopping at a rotational speed of 500 rpm for one hour. Thus, a solid electrolyte was obtained.

(Production of positive electrode mixture)

(High purity chemical) and VGCF (conductive additive) were prepared. These starting materials were weighed to the weight ratio shown in Table 1, put into a planetary ball mill container in which the solid electrolyte was produced, and the vessel was completely closed. The container was attached to a planetary ball mill (pleats P7) and subjected to a mechanical milling for a total of 24 hours by repeating the cycle of the one-hour mechanical milling and the fifteen minute stopping at a rotational speed of 500 rpm for one hour. Thus, a positive electrode mixture was obtained.

The production method (synthesis flow) of the positive electrode material according to the comparative example is referred to as 2 step, and the flow of the production method is shown in Fig.

(Assembly of battery)

The battery was assembled in the same manner as in Example 1 to obtain a battery.

[evaluation]

(Open circuit voltage measurement)

The produced battery was measured for an open circuit voltage (OCV) of the battery after one minute or more had elapsed. The OCV values of the cells of Example 1 and Comparative Example are shown in Table 1.

(X-ray diffraction measurement)

X-ray diffraction (XRD) measurement was carried out by using each positive electrode material prepared in Example 1 and Comparative Example. XRD measurement was carried out on powder samples under an inert atmosphere using CuK alpha radiation. As a powder sample used for the XRD measurement, the positive electrode material prepared by the manufacturing method described in Example 1 and Comparative Example was used.

As shown in Fig. 3 (a), in Example 1, no diffraction peak assigned to the (222) plane of sulfur was observed in the vicinity of 23 ° 0.05, while in the comparative example, A diffraction peak was observed. It can be presumed that the application of the synthetic flow (1 step) according to Example 1 to the production process of the positive electrode mixture of the sulfur battery resulted in highly dispersed sulfur molecules in the positive electrode mixture, resulting in a decrease in the crystallinity of sulfur.

3 (a) and 3 (b), the diffraction intensity of the peak near 2θ = 23 ° 0.05 in the X-ray diffraction measurement using the CuKα line is denoted by I _A and 2θ = 27 ° 0.05 If the diffraction intensity of a diffraction peak attributed to the (111) plane of the Li ₂ S at hayeoteul that I _B, in example 1, the by the diffraction peak value (Fig. 3 (b) described in the I _B, example 1 I _B = 1364) is larger than the value of I _A (I _A = 1273 in Example 1 due to the diffraction peak described in FIG. 3 (a)). On the other hand, in the comparative example, it was confirmed that the value of I _B was smaller than the value of I _A , unlike in Example 1. From this, it was confirmed that the crystallinity of Li ₂ S in the positive electrode composite material was also different in Example 1 and Comparative Example. Therefore, it is presumed that, by applying the synthesis flow (1 step) according to Example 1 to the production process of the positive electrode mixture of the sulfur battery, the base sulfur and Li ₂ S are re-precipitated on the surface of the solid electrolyte.

(Reversible capacity density measurement)

(Vs. Li / Li ⁺ ) at a constant current value (C / 10: 456 占 / / cm2) in the first cycle and 3.1V Li / Li ^< ^{+ &} gt ^; ), and then discharged to 1.5V (vs Li / Li ⁺ ) in the second cycle. Fig. 4 shows the value of the capacity density (reversible capacity density: mAh / g) when discharged to 1.5 V in the second cycle. Charging and discharging were performed at a temperature of 25 占 폚. The term "Crate" refers to a current value for discharging the capacity of the battery in one hour, and the current value at 1 C of the battery manufactured in the present disclosure is 4.56 mA / cm 2.

The values of the reversible capacity density of Example 1 and Comparative Example are shown in Fig. 4, it was confirmed that the reversible capacity density of Example 1 was larger than that of Comparative Example. As a result, in Example 1, a good three-phase interface in which a solid electrolyte which becomes a Li ion pass and a conductive auxiliary which is an electron path coexist is formed on the surface of sulfur which is an active material, and a charge- It is assumed that the charge / discharge capacity of the sulfur battery can be increased.

(Measurement of reversible capacity at the time of charging / discharging at different C rate)

The entire solid battery obtained in Example 1 and Comparative Example was discharged at a different C rate (current values of C / 3, 1C and 2C) after the current value was charged to C / 10. FIG. 5 is a graph showing the relationship between the discharge capacity at the time of discharging at the other C rate of the substrate as a numerator and the discharge capacity at the second cycle in measuring the reversible capacity density (discharging to 1.5 V with a current value C / 10) Discharge characteristic (high rate discharge characteristic:%).

Charging and discharging were carried out at a potential of 1.5 V to 3.1 V (vs Li / Li ⁺ ) at a temperature of 25 캜.

The values of the high rate discharge characteristics of Example 1 and Comparative Example are shown in Fig. From FIG. 5, it was confirmed in Example 1 that discharge characteristics were higher in the respective C rates (current values of C / 3, 1C and 2C) as compared with the comparative example.

The reason why the discharge characteristics of Example 1 is high is presumed as follows.

It is recognized from the result of XRD measurement that the synthesis process (1 step) according to Example 1 is applied to the production process of the positive electrode mixture of a sulfur battery, whereby the sulfur particles are highly dispersed in the positive electrode mixture and the crystallinity of the sulfur is lowered. Therefore, lithium sulfosilicate (Li _x S) in which some sulfur or sulfur reacts with Li ₂ S is incorporated into the solid electrolyte structure when the solid electrolyte is synthesized at the time of preparing the positive electrode mixture according to Embodiment 1, It is presumed that the contact between the solid electrolyte and the active material is increased due to redeposition of sulfur or Li ₂ S on the solid electrolyte.

[Examples 2 to 7]

(Production of positive electrode mixture)

Li ₂ S (manufactured by Lockwood Lithium) and P ₂ S ₅ (Aldrich), a sulfur powder (high purity chemical), GeS ₂ and VGCF (conductive additive) as starting materials for the sulfide solid electrolyte were prepared. The starting materials of these raw material mixtures were weighed to the weight ratio shown in Table 2, and the respective materials were kneaded in agate for 15 minutes. These raw material mixtures were charged into a vessel (45 cc, made of ZrO ₂ ) in which the mixture was previously dried under reduced pressure at 150 ° C. overnight, and a ZrO ₂ ball (Ø = 4 mm, 96 g, 500 ) Was further added, and the container was completely sealed. The container was attached to a planetary ball mill (pleats P7), mechanical milling was performed for a total of 48 hours by repeating the cycle of one hour mechanical milling and stopping for 15 minutes at 500 revolutions per minute. After mechanical milling, the vessel was moved into the glove box and the sample was recovered. In addition, the sample attached to the ZrO ₂ ball was collected by shaking it into a sieve, and the sample adhered to the container was scraped off with a spoon to be recovered. Thus, a positive electrode mixture was obtained.

The production method (synthesis flow) of the positive electrode mixture according to Examples 2 to 7 is referred to as 1step, and the flow of the production method is shown in Fig.

(Assembly of battery)

A battery was produced in the same manner as in Example 1, using the obtained positive electrode material.

[Reference Example]

(Production of positive electrode mixture)

A positive electrode mixture was obtained in the same manner as in Examples 2 to 7 except that the raw material mixture did not contain GeS ₂ .

(Assembly of battery)

A battery was produced in the same manner as in Example 1, using the obtained positive electrode material.

Table 2 shows the weight of various materials used as starting materials in Examples 2 to 7 and Reference Examples, the molar ratio of Li to P (Li / P) in the raw material mixture, and the molar ratio of Ge to P in the raw material mixture (Ge / P).

[evaluation]

(Characteristic evaluation of positive electrode composite material)

The properties of the positive electrode composite material were evaluated for the batteries obtained in Examples 2 to 7 and Reference Example. The characteristic evaluation flow is as follows.

(1) OCV measurement (1 minute)

(2) Discharge to C / 10 to 1.5V, then pause for 10 minutes.

(3) A cycle of charging to 3.1 V with C / 10, stopping for 10 minutes, then discharging to 1.5 V with C / 10, and stopping for 10 minutes are repeated five times in total.

(4) Charge to 3.1 V with C / 10, and stop for 10 minutes. Subsequently, discharge to 1.5 V with C / 3, stopping for 10 minutes, discharging to 1.5 V with C / 10, and stopping for 10 minutes.

(5) After charging to 3.1V with C / 1C, stop for 10 minutes. Subsequently, discharge is performed up to 1.5 V at 1 C, and the discharge is stopped for 10 minutes. Thereafter, discharge is performed at C / 10 to 1.5 V, and the discharge is stopped for 10 minutes.

(6) Charge to 3.1 V with C / 10, then stop for 10 minutes. Thereafter, discharge is performed up to 1.5 V at 2 C, and the discharge is stopped for 10 minutes. Thereafter, discharge is performed at C / 10 to 1.5 V, and the discharge is stopped for 10 minutes.

(7) Charge to 3.1 V with C / 10, stop for 10 minutes, then discharge to 1.5 V with C / 10, then stop for 10 minutes.

In addition, the current value at 1 C of the battery produced in this disclosure is 4.56 mA / cm 2.

(Corresponding to the fifth cycle, (5), (6) of the characteristic evaluation flow (3)) of C / 10, 1C and 2C of the battery using the positive electrode material obtained in Examples 2 to 7 and Reference Example, The high rate discharge characteristics (the ratio of the discharge capacity to 2 C to the discharge capacity at 0.1 C) are shown in Tables 3, 7, and 8.

As shown in FIG. 3 and FIG. 7, at the low current density (C / 10), the discharge capacity slightly decreased by the addition of GeS ₂ , but there was no significant difference in the reference example and the examples 2 to 7. On the other hand, as shown in Table 3 and Fig. 8, when the discharge was carried out at a high current density (1C), there were differences in Reference Examples and Examples 2 to 7. Specifically, by using GeS ₂ , it is possible to suppress the capacity decrease at high current density, and particularly, by using the positive electrode mixture of Examples 4 and 5 having Ge / P of not less than 0.54 and not more than 0.79, . The battery using the positive electrode material having such an effect is preferably used under a use environment where the output (load) fluctuation is great as in a vehicle mounted use, and has an advantage that the capacity change is small.

(Structural analysis of positive electrode material)

Structural analysis was performed on the positive electrode materials obtained in Examples 2 to 7 and Reference Example using an XRD diffraction measurement apparatus made by RIGAKU. The measurement was carried out using a CuK? Ray by three times of integration at 2? = 10 to 80 and at a scan rate of 10 占 min. Examples 2 to 7 and Reference indicates the XRD pattern of the positive electrode laminated material obtained in Example 9, it is shown in _{Li 2 S (111) / GeS} 2 (111) the intensity ratio of Table 3 and Fig. The method of calculating the intensity ratio can be carried out in the same manner as described in the item of "1) raw material mixture", so the description thereof is omitted here.

The positive electrode composite material obtained in Examples 2 to 7 contains Li ₂ S, P ₂ S ₅ , a single sulfur powder, GeS ₂ and VGCF as raw material mixture. As shown in Fig. 9, in Examples 2 to 7, the raw material mixture contains GeS ₂ , so that the excess Li ₂ S bonds with GeS ₂ to lower the Li ₂ S strength, while the amount of retained GeS ₂ increases thereby, since the GeS ₂ of the US (未) response increase, it is the strength of the steel is GeS _2. It is also presumed that excess Li ₂ S has no ionic conductivity and is a resistor, while excess GeS ₂ functions as an active material with a low capacity. As a result, it is presumed that the addition of GeS ₂ to the raw material mixture does not contribute to the increase in resistance at a low rate and the capacity is lowered. However, since the resistance is low at a high rate, it is presumed that the decrease in capacity can be suppressed.

Claims (13)

A method of manufacturing a positive electrode material used in a sulfur battery,
Li ₂ S and M _x S _y where M is selected from P, Si, Ge, B, Al or Sn, x and y are constants which give electrical neutrality to S depending on the type of M,
A positive electrode active material including a basic sulfur,
A method for producing a positive electrode mixture, wherein a raw material mixture containing a conductive auxiliary containing a carbon material is produced by a mechanical milling process. The method according to claim 1,
And M _x S _y is P ₂ S ₅ . 3. The method of claim 2,
Wherein the raw material mixture comprises the Li ₂ S and P ₂ S ₅ in a ratio of 60:40 to 90:10 (molar ratio). The method according to claim 1,
The raw material mixture, as the ^{_{M x S y, M 1 x}} S y S _{y x,} and M ² (M ¹ and M ² are different elements), manufacturing method of the positive electrode laminated material comprising a. 5. The method of claim 4,
Wherein M ¹ _x S _y is P ₂ S ₅ ,
Wherein M ^2, the method of producing a positive electrode laminated material selected from Si, Ge, B, Al or Sn in the above M ² S _{x y.} 6. The method of claim 5,
Wherein the raw material mixture comprises Li ₂ S and P ₂ S ₅ in a ratio of 70:30 to 90:10 (molar ratio). The method according to claim 5 or 6,
And M ² _x S _y is GeS ₂ . 8. The method according to any one of claims 5 to 7,
Wherein the molar ratio of M ^{2 to} P is 0.08 or more and 1.23 or less. 9. The method according to any one of claims 5 to 8,
Wherein the positive electrode mixture has an intensity ratio of a diffraction peak of the Li ₂ S (111) face to a diffraction peak of the M ² _x S _y (111) plane of 0.9 or more and 10.4 or less. 10. The method according to any one of claims 1 to 9,
Wherein the mechanical milling process is performed using a planetary ball mill. In the positive electrode material used for a sulfur battery,
Li ₂ S and M _x S _y where M is selected from P, Si, Ge, B, Al or Sn, x and y are constants which give electrical neutrality to S depending on the type of M,
A positive electrode active material including a basic sulfur,
Characterized in that the raw material mixture containing the conductive auxiliary agent containing the carbon material is composed of a composite obtained by mechanical milling treatment. 12. The method of claim 11,
The diffraction intensity at a peak at 2? = 23 ° .05 ± 1.00 ° in the X-ray diffraction measurement using a CuK? Ray is I _A and the diffraction intensity at the peak at 2? = 27 ° .05 ± 1.00 ° is I _B , The value of I _B is larger than the value of I _A. 13. The method according to claim 11 or 12,
The raw material mixture, as the M _x S _{y, x} S _y ¹ includes M, and M ² _x S _y (M ¹ and M ² are different elements),
Wherein M ¹ _x S _y is P ₂ S ₅ ,
Wherein M ² in the above M ² S _{x y} is is selected from Si, Ge, B, Al or Sn,
And the intensity ratio of the diffraction peak of the Li ₂ S (111) face to the diffraction peak of the M ² _x S _y (111) face is not less than 0.9 and not more than 10.4.

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