JP2017157473A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery with an increased discharge capacity.SOLUTION: A lithium ion secondary battery 1 comprises: a positive electrode layer 10 including at least a halogen-added sulfide kasolite 100 arranged by adding haloid to a sulfide kasolite, and a conductive assistant 102; a solid electrolyte layer 30; and a negative electrode layer 20. The halogen-added sulfide kasolite 100 shows a redox capacity in the positive electrode layer 10.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a lithium ion secondary battery.

  In recent years, an all-solid-state lithium ion secondary battery using a sulfide-based solid electrolyte having lithium ion conductivity has attracted attention. In an all-solid-state lithium ion secondary battery, in order to improve battery characteristics, it is considered to mix a sulfide-based solid electrolyte not only in an electrolyte layer but also in an electrode layer.

For example, in Patent Document 1 below, in order to prevent a reaction that adversely affects a secondary battery from occurring between an anode made of an active metal and an environment outside the anode such as ambient moisture and organic liquid electrolyte. Discloses a technique using a sulfide having lithium ion conductivity as a protective film of an anode. Non-Patent Document 1 below discloses an all-solid-state lithium ion secondary battery using Li ₃ PS ₄ that is a sulfide-based solid electrolyte as a positive electrode active material in order to increase energy density.

Special table 2009-505355

Journal of Power Sources, 2015, vol. 293, p. 721-725

  However, since the all-solid-state lithium ion secondary battery described in Non-Patent Document 1 uses a solid electrolyte as a positive electrode active material, the battery capacity can be increased, but the solid electrolyte used as the positive electrode active material The problem was that the capacity of the battery was low.

  Therefore, the present invention has been made in view of the above problems, and a new and improved lithium ion secondary battery that has improved charge / discharge capacity by adopting a positive electrode active material that can cope with higher capacity. To provide a battery.

  In order to solve the above problems, the present invention comprises a halogen-added sulfide catholyte obtained by adding a halide to sulfide catholyte, a positive electrode layer containing at least a conductive additive, a solid electrolyte layer, and a negative electrode layer, The halogen-added sulfide catholyte provides a lithium ion secondary battery that exhibits redox capacity in the positive electrode layer.

  According to the present invention, since the halogen-added sulfide catholyte exhibiting a high redox capacity can be functioned as the positive electrode active material, the charge / discharge capacity of the lithium ion secondary battery can be increased.

  The positive electrode layer further includes a positive electrode active material different from the halogen-added sulfide catholyte, and the halogen-added sulfide catholyte is reversible redox in a partial range or the entire range of the reversible redox potential of the positive electrode active material. Potential may be indicated. According to this aspect, since the oxidation-reduction reaction occurs in both the halogen-added sulfide catholyte and the positive electrode active material in the positive electrode layer during charge / discharge, the charge / discharge capacity of the positive electrode active material can be improved.

The positive electrode active material may be an active material in which a partial range of the reversible redox potential overlaps with a range of at least 1.0 V to 3.5 V (vs. Li / Li ⁺ ). According to this viewpoint, the charge / discharge capacity of the lithium ion secondary battery can be further improved.

The positive electrode active material may be S (sulfur), Li ₂ S (lithium sulfide), or V ₂ O ₅ (vanadium dioxide). According to this viewpoint, the charge / discharge capacity of the lithium ion secondary battery can be further improved.

The composition of the sulfide catholyte may be 0.75Li ₂ S-0.25P ₂ S ₅ and the halide added to the sulfide catholyte is LiX (X is Cl, Br or I) Also good. According to this, the charge / discharge capacity of the lithium ion secondary battery can be further improved, and the Li ion conductivity in the electrolyte layer can be increased.

The composition of the halogen-added sulfide catholyte is aLiX- (100-a) (0.75Li ₂ S-0.25P ₂ S ₅ ) (where 0 <a <50, X is Cl, Br or I) The halide added to the sulfide catholyte may be LiI, and the composition of the halogen-added sulfide catholyte is 35LiI-65 (0.75 Li ₂ S-0.25P ₂ S ₅ ) Also good. According to this, the charge / discharge capacity of the lithium ion secondary battery can be further improved, and the Li ion conductivity in the electrolyte layer can be increased.

  As described above, according to the present invention, the charge / discharge capacity of the lithium ion secondary battery can be further improved.

It is sectional drawing which shows typically the laminated constitution of the lithium ion secondary battery which concerns on one Embodiment of this invention. 2 is a graph showing a charge / discharge curve of a lithium ion secondary battery according to Example 1. FIG. 4 is a graph showing cycle characteristics of the lithium ion secondary battery according to Example 1. FIG. 4 is a graph showing a charge / discharge curve of a lithium ion secondary battery according to Example 2. FIG. 6 is a graph showing cycle characteristics of a lithium ion secondary battery according to Example 2. FIG. 5 is a graph showing a charge / discharge curve of a lithium ion secondary battery according to Comparative Example 1. FIG. 5 is a graph showing cycle characteristics of a lithium ion secondary battery according to Comparative Example 1. FIG. It is a graph which shows the charging / discharging curve of the lithium ion secondary battery which concerns on Example 3 and Comparative Example 2. FIG.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

<1. Overview of lithium-ion secondary battery>
First, with reference to FIG. 1, the outline | summary of the lithium ion secondary battery which concerns on one Embodiment of this invention is demonstrated. FIG. 1 is a cross-sectional view schematically showing a layer configuration of a lithium ion secondary battery 1 according to this embodiment.

  As shown in FIG. 1, a lithium ion secondary battery 1 according to an embodiment of the present invention is an all-solid lithium ion secondary battery using a solid electrolyte as an electrolyte.

  Specifically, the lithium ion secondary battery 1 according to this embodiment includes a positive electrode layer 10 including at least a halogen-added sulfide catholyte 100 obtained by adding a halide to sulfide catholyte, and a positive electrode layer conductive additive 102. Here, the halogen-added sulfide catholyte 100 exhibits a redox capacity in the positive electrode layer 10. By charging and discharging such a lithium ion secondary battery 1 at the reversible redox potential of the halogen-added sulfide catholyte 100, the halogen-added sulfide catholyte 100 exhibiting a high redox capacity is allowed to function as a positive electrode active material. Can do. According to this, the discharge capacity of the lithium ion secondary battery 1 according to the present embodiment can be increased.

  In the lithium ion secondary battery 1 according to this embodiment, the positive electrode layer 10 may further include a positive electrode active material 101 different from the halogen-added sulfide catholyte 100. Here, the halogen-added sulfide catholyte 100 may exhibit a reversible redox potential in a partial range or a full range of the reversible redox potential of the positive electrode active material 101. According to this configuration, it is possible to cause a redox reaction in both the halogen-added sulfide catholyte 100 and the positive electrode active material 101 in the positive electrode layer 10 at the time of charge and discharge. Can be improved.

<2. Configuration of lithium ion secondary battery>
Next, a specific configuration of the lithium ion secondary battery according to the present embodiment will be described.

  As shown in FIG. 1, the lithium ion secondary battery 1 includes a positive electrode layer 10, a negative electrode layer 20, and a solid electrolyte layer 30, and the solid electrolyte layer 30 is disposed between the positive electrode layer 10 and the negative electrode layer 20. With a structure.

[Positive electrode layer]
The positive electrode layer 10 includes a halogen-added sulfide catholyte 100, a positive electrode active material 101, and a positive electrode layer conductive additive 102 for supplementing electron conductivity.

(Halogen-added sulfide catholyte)
The halogen-added sulfide catholyte 100 is formed of a sulfide catholyte material to which a halide is added. In the present embodiment, catholyte is a solid-state battery that functions as a positive electrode active material by exhibiting redox capacity in the positive electrode layer 10 when the lithium ion secondary battery 1 is operated, that is, when a charge / discharge potential is applied. The compound which shows Li ion conductivity in the electrolyte layer 30 is represented.

Specifically, examples of the halide include lithium halide (LiX), sodium halide (NaX), and alkyl halide. Note that X represents, for example, chlorine (Cl), bromine (Br), or iodine (I). Further, as the sulfide catholyte material to which halogen is added, a sulfide solid electrolyte material can be used, for example, Li ₂ S—P ₂ S ₅ , Li ₂ S—P ₂ S ₅ —Li ₂ O. _{, Li 2 S-SiS 2,} Li 2 S-SiS 2 -B 2 S 3, Li 2 S-B 2 S 3, Li 2 S-P 2 S 5 -Z m S n (m, n is a positive number , Z is Ge, either Zn or _{Ga), Li 2 S-GeS} 2, Li 2 S-SiS 2 -Li 3 PO 4, Li 2 S-SiS 2 -Li p MO q (p, q are positive The number M can be P, Si, Ge, B, Al, Ga, or In).

In addition, the halogen-added sulfide catholyte 100 preferably uses a material containing at least sulfur (S), phosphorus (P), and lithium (Li) as constituent elements among the above-described sulfide solid electrolyte materials, and at least Li _2. It is more preferable to use one containing S—P ₂ S ₅ . The halogen-added sulfide catholyte 100 may be any of a crystalline material, an amorphous material, and a glass material, and a material suitable for battery characteristics can be selected as appropriate.

Here, the case of using those containing _Li 2 _S-P 2 _{S 5} as a sulfide solid electrolyte material to form a halogen-containing sulfide catholyte 100, the mixing molar ratio of Li ₂ S and _P 2 _{S 5,} for example, Li ₂ S: P ₂ S ₅ = selected in the range of 50:50 to 90:10. In addition, the halogen-added sulfide catholyte 100 preferably uses amorphous 0.75Li ₂ S-0.25P ₂ S ₅ as a sulfide solid electrolyte material, and the added halide includes LiX (X is Preference is given to using Cl, Br or I). Thereby, the charge / discharge capacity of the lithium ion secondary battery 1 can be further improved, and the Li ion conductivity in the positive electrode layer 10 can be further increased.

Preferably, the composition of the halogenated sulfide catholyte 100 is aLiX- (100-a) (0.75Li ₂ S-0.25P ₂ S ₅ ) (where 0 <a <50, X is Cl, Br or I More preferably, the added halide may be LiI, and more preferably, the composition of the halogenated sulfide catholyte 100 is 35LiI-65 (0.75 Li ₂ S-0). .25P ₂ S ₅ ). When the composition of the halogen-added sulfide catholyte 100 is as described above, the charge / discharge capacity of the lithium ion secondary battery 1 can be further improved, and the Li ion conductivity in the positive electrode layer 10 can be further increased.

  Examples of the shape of the halogen-added sulfide catholyte 100 include a particle shape such as a true sphere or an oval sphere. The particle diameter of the halogen-added sulfide catholyte 100 is not particularly limited, but the average particle diameter of the halogen-added sulfide catholyte 100 is preferably 0.01 μm or more and 30 μm or less, and preferably 0.1 μm or more and 20 μm or less. More preferred. The “average particle diameter” refers to the number average diameter in the particle size distribution of particles determined by a scattering method or the like, and can be measured by a particle size distribution meter or the like.

  In addition, the content of the halogen-added sulfide catholyte 100 in the positive electrode layer 10 is preferably 10% by mass or more and 95% by mass or less, and preferably 20% by mass or more and 90% by mass or less, with respect to the total mass of the positive electrode layer 10, for example. It is more preferable that

(Positive electrode active material)
The positive electrode active material 101 has a higher charge / discharge potential than the negative electrode active material 201 included in the negative electrode layer 20 described later, and is formed of an active material capable of reversibly inserting and extracting lithium ions.

Specifically, the positive electrode active material 101 is preferably an active material in which at least a partial range of the reversible redox potential overlaps with a range of 1.0 V to 3.5 V (vs. Li / Li ⁺ ). Examples of the positive electrode active material 101 include LiFePO ₄ , Li _4/3 Ti _5/3 O ₄ , S, Li ₂ S, and V ₂ O ₅ . In the lithium ion secondary battery 1 according to the present embodiment, S (sulfur), Li ₂ S (lithium sulfide), or V ₂ O ₅ (vanadium oxide) is preferably used as the positive electrode active material 101, and S is used. It is more preferable.

  Examples of the shape of the positive electrode active material 101 include particle shapes such as a true sphere or an oval sphere. The average particle diameter of the positive electrode active material 101 is preferably, for example, from 0.1 μm to 50 μm. The “average particle diameter” represents the number average diameter in the particle size distribution of particles obtained by a scattering method or the like, and can be measured by a particle size distribution meter or the like.

  In addition, the content of the positive electrode active material 101 in the positive electrode layer 10 is preferably 10% by mass or more and 99% by mass or less, and preferably 20% by mass or more and 90% by mass or less, with respect to the total mass of the positive electrode layer 10, for example. It is more preferable.

(Positive layer conductive aid)
The positive electrode layer conductive additive 102 has a role of imparting electron conductivity to the halogen-added sulfide catholyte 100 and the positive electrode active material 101. As the positive electrode layer conductive additive 102, for example, activated carbon, graphite, carbon black, acetylene black, ketjen black, carbon fiber, or metal powder can be used. The content of the positive electrode layer conductive additive 102 in the positive electrode layer 10 is, for example, preferably 1% by mass or more and 50% by mass or less with respect to the total mass of the positive electrode layer 10 and is 5% by mass or more and 20% by mass or less. It is more preferable.

  In addition to the halogen-added sulfide catholyte 100, the positive electrode active material 101, and the positive electrode layer conductive additive 102 described above, the positive electrode layer 10 includes, for example, a binder, a filler, a dispersant, and ionic conductivity. An additive such as an agent may be appropriately blended.

  Examples of the binder that can be blended in the positive electrode layer 10 include polytetrafluoroethylene, polyvinylidene fluoride, and polyethylene. Furthermore, as a filler, a dispersing agent, an ionic conductive agent, and the like that can be blended in the positive electrode layer 10, known materials that are generally used for electrodes of lithium ion secondary batteries can be used.

[Negative electrode layer]
As shown in FIG. 1, the negative electrode layer 20 includes a negative electrode active material 201, a halogen-added sulfide catholyte 100, and a negative electrode layer conductive additive 202. Note that the negative electrode layer conductive auxiliary agent 202 can be the same conductive auxiliary agent as the positive electrode layer conductive auxiliary agent 102. As the halogen-added sulfide catholyte 100, the same compound as the halogen-added sulfide catholyte 100 contained in the positive electrode layer 10 can be used. Therefore, description of these configurations is omitted here.

  The negative electrode active material 201 has a lower charge / discharge potential than the positive electrode active material 101 included in the positive electrode layer 10, and is composed of an active material capable of being alloyed with lithium or reversibly occluding and releasing lithium. Is done.

  For example, as the negative electrode active material 201, a metal active material, a carbon active material, or the like can be used. As the metal active material, for example, metals such as lithium (Li), indium (In), aluminum (Al), tin (Sn), and silicon (Si), and alloys thereof can be used. Examples of the carbon active material include artificial graphite, graphite carbon fiber, resin-fired carbon, pyrolytic vapor-grown carbon, coke, mesocarbon microbeads (MCMB), and furfuryl alcohol (furfuryl alcohol) resin. Carbon, polyacene, pitch-based carbon fiber, vapor-grown carbon fiber, natural graphite, non-graphitizable carbon, and the like can be used. In addition, these negative electrode active materials may be used independently and may be used in combination of 2 or more type.

  In addition, the content of the negative electrode active material 201 in the negative electrode layer 20 is preferably, for example, 20% by mass or more and 95% by mass or less with respect to the total mass of the negative electrode layer 20, and is 50% by mass or more and 90% by mass or less. It is more preferable. Further, the content of the halogen-added sulfide catholyte 100 in the negative electrode layer 20 is preferably 10% by mass or more and 95% by mass or less, and preferably 20% by mass or more and 90% by mass or less, with respect to the total mass of the negative electrode layer 20, for example. It is more preferable that Furthermore, the content of the negative electrode layer conductive additive 202 in the negative electrode layer 20 is preferably 1% by mass or more and 50% by mass or less, for example, with respect to the total mass of the negative electrode layer 20, and is 5% by mass or more and 20% by mass or less. It is more preferable that

  In addition to the negative electrode active material 201, the halogen-added sulfide catholyte 100, and the negative electrode layer conductive additive 202, the negative electrode layer 20 includes, for example, a binder, a filler, a dispersant, and an ionic conductive agent. Additives may be appropriately blended.

  In addition, as an additive mix | blended with the negative electrode layer 20, the thing similar to the additive mix | blended with the positive electrode layer 10 mentioned above can be used.

[Solid electrolyte layer]
Solid electrolyte layer 30 is formed between positive electrode layer 10 and negative electrode layer 20 and includes halogen-added sulfide catholyte 100. As the halogen-added sulfide catholyte 100, the same compound as the halogen-added sulfide catholyte 100 contained in the positive electrode layer 10 can be used. Therefore, description of the configuration here is omitted.

  The configuration of the lithium ion secondary battery 1 according to this embodiment has been described in detail above.

<3. Manufacturing method of lithium ion secondary battery>
Then, the manufacturing method of the lithium ion secondary battery 1 which concerns on this embodiment is demonstrated. The lithium ion secondary battery 1 according to this embodiment can be manufactured by stacking the above layers after manufacturing the positive electrode layer 10, the negative electrode layer 20, and the solid electrolyte layer 30, respectively.

[Production of solid electrolyte layer]
The solid electrolyte layer 30 can be produced by the halogen-added sulfide catholyte 100 obtained by adding a halide to the sulfide catholyte material.

  First, a halogen-added sulfide catholyte material to which a halide is added is produced using a melt quenching method or a mechanical milling method.

For example, when the melt quenching method is used, a predetermined amount of a halide, Li ₂ S, and P ₂ S ₅ are mixed, and the pellets are reacted in a vacuum at a predetermined reaction temperature, and then rapidly cooled. A halogen-added sulfide catholyte material can be produced. Incidentally, the reaction temperature of the mixture and a halide, a Li ₂ S and _P 2 _{S 5} is, for example, 400 ° C. to 1000 ° C., preferably from 800 ° C. to 900 ° C.. Moreover, reaction time is 0.1 to 12 hours, for example, Preferably it is 1 to 12 hours. Furthermore, the quenching temperature of the reaction product is, for example, 10 ° C. or less, preferably 0 ° C. or less. The rapid cooling rate is, for example, about 1 ° C./sec to about 10,000 ° C./sec, and preferably about 1 ° C./sec to about 1000 ° C./sec.

In addition, when using the mechanical milling method, a predetermined amount of halide, Li ₂ S and P ₂ S ₅ are mixed, and stirred and reacted using a ball mill or the like to produce a halogen-added sulfide catholyte material. Can do. In addition, although the stirring speed and stirring time in a mechanical milling method are not specifically limited, The production speed of a halogen addition sulfide catholyte material can be made quick, so that stirring speed is high. Further, the longer the stirring time, the higher the conversion rate of the raw material to the halogen-added sulfide catholyte material.

  Thereafter, the halogen-added sulfide catholyte material obtained by the melt quenching method or the mechanical milling method is heat-treated at a predetermined temperature and then pulverized to produce the particulate halogen-added sulfide catholyte 100.

  Subsequently, the halogen-added sulfide catholyte 100 obtained by the above method is, for example, a blast method, an aerosol deposition method, a cold spray method, a sputtering method, a CVD method, and The solid electrolyte layer 30 can be produced by forming a film using a known film forming method such as a thermal spraying method. The solid electrolyte layer 30 may be produced by pressing the halogen-added sulfide catholyte 100 alone. The solid electrolyte layer 30 may be formed by mixing and pressurizing the halogen-added sulfide catholyte 100, a solvent, and a binder or a support. Here, the binder or the support is added for the purpose of reinforcing the strength of the solid electrolyte layer 30 or preventing a short circuit of the halogen-added sulfide catholyte 100.

[Preparation of positive electrode layer]
The positive electrode layer 10 can be produced by the following method. First, the positive electrode active material 101, the halogen-added sulfide catholyte 100 produced above, the positive electrode layer conductive additive 102, and various additives are mixed and added to a solvent such as water or an organic solvent to form a slurry ( Slurry or paste is formed. Subsequently, the obtained slurry or paste is applied to a current collector, dried, and then rolled, whereby the positive electrode layer 10 can be obtained. Alternatively, the positive electrode layer 10 may be produced by pressing and rolling a mixture of the halogen-added sulfide catholyte 100, the positive electrode active material 101, and the positive electrode layer conductive additive 102.

[Preparation of negative electrode layer]
The negative electrode layer 20 can be produced by the same method as the positive electrode layer. Specifically, first, the negative electrode active material 201, the halogen-added sulfide catholyte 100, the negative electrode layer conductive additive 202, and various additives are mixed and added to a solvent such as water or an organic solvent. Or form a paste. Furthermore, the obtained slurry or paste is applied to a current collector, dried, and then rolled, whereby the negative electrode layer 20 can be obtained. A metal foil or a metal foil that forms an alloy with Li ions may be used as the negative electrode layer 20.

  Here, as the current collector used in the positive electrode layer 10 and the negative electrode layer 20, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), A plate or foil made of cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge) and lithium (Li), and alloys thereof can be used. Note that the positive electrode layer 10 or the negative electrode layer 20 is formed by compacting a mixture of the positive electrode active material 101 or the negative electrode active material 201 and various additives into a pellet shape without using a current collector. Also good.

[Manufacture of lithium ion secondary batteries]
Furthermore, the lithium ion secondary battery 1 according to this embodiment can be manufactured by laminating the solid electrolyte layer 30, the positive electrode layer 10, and the negative electrode layer 20 produced by the above method. Specifically, the lithium ion secondary battery 1 according to this embodiment can be manufactured by laminating the positive electrode layer 10 and the negative electrode layer 20 so as to sandwich the solid electrolyte layer 30 and applying pressure.

  Hereinafter, the lithium ion secondary battery according to the present embodiment will be specifically described with reference to Examples and Comparative Examples. In addition, the Example shown below is an example to the last, and the lithium ion secondary battery which concerns on this embodiment is not limited to the following example.

Example 1
It was first synthesized _LiI-Li 3 PS ₄ as the halogen-containing sulfide catholyte 100. Specifically, as the composition ratio of _{35LiI-65 (0.75Li 2 S-} 0.25P 2 S 5), 0.64g of Li _{2 S,} 1.03 g of P 2 _{S 5,} the LiI 1 .33 g were weighed and mixed in a mortar. The mixed powder is sealed in a 45 ml ZrO ₂ pot together with ZrO ₂ balls (φ10 mm × φ7.5 mm × 20) in an Ar (argon) atmosphere, and a mechanical milling reaction is performed by rotating at 380 rpm for 10 minutes × 20 times. was synthesized _LiI-Li 3 PS ₄ is a halogen-containing sulfide catholyte 100.

Subsequently, LiI-Li ₃ PS ₄ synthesized as the halogen-added sulfide catholyte 100 and activated carbon as the positive electrode layer conductive additive 102 were mixed in a mortar at a mass ratio of 80:20. Next, the mixed powder is sealed in a 45 ml ZrO ₂ pot together with ZrO ₂ balls (φ10 mm × φ7.5 mm × 20) in an Ar atmosphere, mixed by rotating at 380 rpm for 10 minutes × 20 times, and mixed with the positive electrode. An agent was used. Furthermore, the positive electrode layer 10 was produced by uniformly spreading 3.6 mg of the generated positive electrode mixture.

Further, LiI-Li ₃ PS ₄ synthesized as the halogen-added sulfide catholyte 100 was pressed and solidified in a 200 mg polypropylene cylinder to produce a solid electrolyte layer 30. Further, a metal lithium foil having a thickness of 30 μm was prepared as the negative electrode layer 20.

Subsequently, the positive electrode layer 10, the solid electrolyte layer 30, and the negative electrode layer 20 are stacked in a cell container, and pressed from a uniaxial direction at a pressure of 4 t / cm ² to produce a pellet. (Cell) was produced.

(Example 2)
A test cell according to Example 2 was produced in the same manner as in Example 1 except that sulfur was added as the positive electrode active material 101 to the positive electrode mixture. Specifically, first, sulfur as the positive electrode active material 101 and activated carbon as the positive electrode layer conductive additive 102 were mixed in a mortar at a mass ratio of 74:26. The mixed powder is sealed in a 45 ml ZrO ₂ pot together with ZrO ₂ balls (φ10 mm × φ7.5 mm × 20) in an Ar atmosphere, mixed by rotating at 380 rpm for 10 minutes × 20 times, and combined with sulfur and activated carbon The body was made. Subsequently, the obtained composite of sulfur and activated carbon and the same amount of LiI-Li ₃ PS ₄ were mixed in a mortar and put into a 45 ml ZrO ₂ pot with ZrO ₂ balls (φ10 mm × φ7.5 mm × 20). After encapsulating in an Ar atmosphere, the mixture was mixed by rotating at 380 rpm for 10 minutes × 20 times to obtain a positive electrode mixture. The molar composition ratio of the obtained positive electrode mixture was sulfur: activated carbon: LiI-Li ₃ PS ₄ = 37: 13: 50.

(Example 3)
A test cell according to Example 3 was produced in the same manner as in Example 1 except that the positive electrode layer 10 was produced as follows. Specifically, V ₂ O ₅ that is the positive electrode active material 101, LiI-Li ₃ PS ₄ synthesized as the halogen-added sulfide catholyte 100, and activated carbon that is the positive electrode layer conductive additive 102 are in a mass ratio of 44:49. : 7 in a mortar. Next, the mixed powder is sealed in a 45 ml ZrO ₂ pot together with ZrO ₂ balls (φ10 mm × φ7.5 mm × 20) in an Ar atmosphere, mixed by rotating at 380 rpm for 10 minutes × 20 times, and mixed with the positive electrode. An agent was used. Furthermore, the positive electrode layer 10 was produced by uniformly spreading 10 mg of the produced positive electrode mixture.

(Comparative Example 1)
NCA (LiNi _0.8 Co _0.15 Al _0.05 O ₂ ) coated with Li ₂ ZrO ₃ , LiI-Li ₃ PS ₄ synthesized as halogen-added sulfide catholyte 100, and positive electrode layer conductive additive 102 A test cell according to Comparative Example 1 was produced in the same manner as in Example 1 except that a positive electrode mixture in which the activated carbon was mixed in a mortar at a mass ratio of 60: 35: 5 was used.

(Comparative Example 2)
A test cell according to Comparative Example 2 was produced in the same manner as in Example 3 except that Li ₃ PS ₄ was used instead of LiI-Li ₃ PS ₄ synthesized as the halogen-added sulfide catholyte 100.

(Evaluation)
The charge / discharge characteristics of the test cell prepared above were evaluated. Specifically, at 25 ° C., the test cell according to Examples 1 and 2 was charged to the upper limit voltage of 3.1 V with a constant current of 0.25 mA / cm ² and then discharged to the lower limit voltage of 1.3 V. Each discharge cycle was performed 50 times, and the charge / discharge characteristics were evaluated. Further, the discharge capacity and Coulomb efficiency from the first cycle to the 50th cycle were calculated and evaluated as cycle characteristics. The charge / discharge cycle was measured in a state of being sealed in an Ar atmosphere while applying an external pressure of 3 Nm to the test cell.

  The graph which shows the charging / discharging curve of the lithium ion secondary battery which concerns on Example 1 is shown in FIG. 2, and the graph which shows cycling characteristics is shown in FIG. Moreover, the graph which shows the charging / discharging curve of the lithium ion secondary battery which concerns on Example 2 is shown in FIG. 4, and the graph which shows cycling characteristics is shown in FIG.

Referring to the results of FIG. 2 and FIG. 3, in Example 1, the discharge capacity (about 150 mAh / g) of Li ₃ PS ₄ of the all-solid-state lithium ion secondary battery described in Non-Patent Document 1 is It was found that the discharge capacity was greatly increased, and the deterioration of the cycle characteristics was suppressed. This is because Li ₃ PS ₄ and LiI show a reversible redox potential in the range of 1.3 V-3.1 V (vs. Li / Li ⁺ ), and therefore, halogenated sulfides are charged and discharged in this range. This is because the redox capacity of LiI-Li ₃ PS ₄ which is the catholyte 100 changes. Thus, LiI-Li ₃ PS _4, since it is possible to function as a positive electrode active material, it was found that the capacity of the lithium ion secondary battery is increasing.

Referring to the results of FIGS. 4 and 5, in Example 2, the charge / discharge capacity of the lithium ion secondary battery is greatly increased from the theoretical capacity of sulfur (about 1600 mAh / g), and the cycle characteristics are also deteriorated. It was found that the battery was reversibly charged and discharged. This is because Li ₃ PS ₄ and LiI show a reversible redox potential in the range of 1.3V-3.1V (vs. Li / Li ⁺ ), and therefore, LiI by adding -Li ₃ PS _4, because that can function both S and _LiI-Li 3 PS ₄ as a cathode active material. Thereby, in the lithium ion secondary battery (so-called sulfur battery) according to Example 2, an effect of increasing the charge / discharge capacity could be obtained. In FIG. 4, another plateau is observed in the charging curve of 2.5 V to 2.8 V, which is presumed to be a change in charging capacity derived from LiI—Li ₃ PS ₄ .

Next, the test cell according to Comparative Example 1 was charged at 25 ° C. with a constant current of 0.05 mA / cm ^{2 to} an upper limit voltage of 4.0 V, and then charged with a constant current to a lower limit voltage of 2.5 V. The discharge cycle was performed 100 times, and charge / discharge characteristics were evaluated. In addition, the discharge capacity and Coulomb efficiency from the first cycle to 100 cycles were calculated and evaluated as cycle characteristics. The charge / discharge cycle was measured with an external pressure of 3 Nm applied to the test cell and sealed in an Ar atmosphere.

  A graph showing a charge / discharge curve of the lithium ion secondary battery of Comparative Example 1 is shown in FIG. 6, and a graph showing cycle characteristics is shown in FIG.

Referring to the results of FIGS. 6 and 7, in Comparative Example 1, only the positive electrode capacity of NCA (132 mAh / g) was observed, and the cycle characteristics were not good. This is the average discharge potential of NCA is 3.6V-3.7V, because it does not overlap with the range of charge and discharge potentials of _{LiI-Li 3 PS 4, LiI} -Li 3 PS 4 functions as a cathode active material It is because it is not.

Next, after charging the test cells according to Example 3 and Comparative Example 2 at a constant current of 0.70 mA / cm ^{2 to} an upper limit voltage of 4.0 V at 25 ° C., then to a lower limit voltage of 1.5 V at a constant current. The charging / discharging cycle which discharges was performed 100 times, and the charging / discharging characteristic was evaluated. In addition, the discharge capacity and Coulomb efficiency from the first cycle to 100 cycles were calculated and evaluated as cycle characteristics. The charge / discharge cycle was measured with an external pressure of 3 Nm applied to the test cell and sealed in an Ar atmosphere.

The graph which shows the charging / discharging curve of the lithium ion secondary battery which concerns on Example 3 and Comparative Example 2 is shown in FIG. Referring to the results of FIG. 8, it can be seen that Example 3 shows a higher charge / discharge capacity than Comparative Example 2. From this result, when charged and discharged at 1.3V-3.1V (vs.Li/Li ^+), it is possible towards the _LiI-Li 3 PS ₄ is a high capacity as a positive electrode active material than _Li 3 PS ₄ Recognize.

As can be seen from the above evaluation results, the lithium ion secondary battery 1 according to the present embodiment includes the halogen-added sulfide catholyte 100 and the positive electrode layer conductive additive 102 in the positive electrode layer 10. By indicating the redox capacity, the discharge capacity can be increased. Specifically, by operating the lithium ion secondary battery 1 at a charge / discharge potential of 1.3 V to 3.1 V (vs. Li ^/ Li ⁺ ), LiI that is a halogen-added sulfide catholyte 100 in the positive electrode layer 10. it is possible to exhibit a high oxidation-reduction capacity -Li ₃ PS _4. Therefore, the lithium ion secondary battery 1 according to the present embodiment can increase the discharge capacity.

In particular, as shown in Example 2, the lithium ion secondary battery 1 according to the present embodiment is a sulfur battery in which the positive electrode layer 10 includes a halogen-added sulfide catholyte 100 and sulfur as the positive electrode active material 101. May be. Since sulfur has a reversible oxidation-reduction potential of 1.3 V-3.1 V (vs. Li ^/ Li ⁺ ), the sulfur battery exhibits a charge / discharge plateau in the above range. Therefore, since LiI-Li ₃ PS ₄ having a reversible oxidation potential overlapping with sulfur can be used as the halogen-added sulfide catholyte 100, LiI-Li ₃ PS ₄ can also function as a positive electrode active material. The charge / discharge capacity of the sulfur battery can be further increased.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

  In the above embodiment, the example in which the negative electrode layer 20 and the solid electrolyte layer 30 also contain the halogen-added sulfide catholyte 100 has been shown, but the present invention is not limited to such illustration. For example, the negative electrode layer 20 and the solid electrolyte layer 30 may not include the halogen-added sulfide catholyte 100, and may include a known sulfide solid electrolyte.

DESCRIPTION OF SYMBOLS 1 Lithium ion secondary battery 10 Positive electrode layer 20 Negative electrode layer 30 Solid electrolyte layer 100 Halogen addition sulfide catholyte 101 Positive electrode active material 102 Positive electrode layer conductive support agent 201 Negative electrode active material 202 Negative electrode layer conductive support agent

Claims (9)

A halogen-added sulfide catholyte obtained by adding a halide to sulfide catholyte, and a positive electrode layer including at least a conductive additive;
A solid electrolyte layer;
A negative electrode layer;
With
The halogen-added sulfide catholyte exhibits a redox capacity in the positive electrode layer, and is a lithium ion secondary battery. The positive electrode layer further includes a positive electrode active material different from the halogen-added sulfide catholyte,
2. The lithium ion secondary battery according to claim 1, wherein the halogen-added sulfide catholyte exhibits a reversible redox potential in a partial range or the entire range of the reversible redox potential of the positive electrode active material. 3. The lithium ion secondary material according to claim 2, wherein the positive electrode active material is an active material in which at least a partial range of the reversible redox potential overlaps with a range of 1.0 V to 3.5 V (vs. Li / Li ⁺ ). Next battery. The lithium ion secondary battery according to claim ₂ , wherein the positive electrode active material is S, Li ₂ S, or V ₂ O ₅ . 5. The lithium ion secondary battery according to claim 1, wherein a composition of the sulfide catholyte is 0.75Li ₂ S-0.25P ₂ S ₅ .   The lithium ion secondary battery according to any one of claims 1 to 5, wherein a halide added to the sulfide catholyte is LiX (where X is Cl, Br or I). The composition of the halogen-added sulfide catholyte is aLiX- (100-a) (0.75Li ₂ S-0.25P ₂ S ₅ ) (where 0 <a <50, X is Cl, Br or I). The lithium ion secondary battery as described in any one of Claims 1-6.   The lithium ion secondary battery according to any one of claims 1 to 7, wherein a halide added to the sulfide catholyte is LiI. The halogen-containing sulfide catholyte composition is _{35LiI-65 (0.75Li 2 S-} 0.25P 2 S 5), the lithium ion secondary battery according to any one of claims 1-8.

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