JP2022092896A - Lithium secondary battery - Google Patents

Abstract

To provide means capable of improving charge/discharge rate characteristics in a lithium secondary battery having a solid electrolyte layer containing a lithium ion conductive solid electrolyte.SOLUTION: A lithium secondary battery includes a power generation element including: a positive electrode; a negative electrode; and a solid electrolyte layer interposed between the positive electrode and the negative electrode, and having a first lithium ion conductive solid electrolyte. Therein, the negative electrode includes a lithium ion/electron conductive structure including a conductive porous body and a second lithium ion conductive solid electrolyte that covers at least a part of an inner surface of the porous body, and a porosity of the lithium ion/electron conductive structure is configured to be larger than a porosity of the solid electrolyte layer.SELECTED DRAWING: Figure 3

Description

The present invention relates to a lithium secondary battery.

In recent years, in order to cope with global warming, it is urgently desired to reduce the amount of carbon dioxide. In the automobile industry, expectations are high for the reduction of carbon dioxide emissions through the introduction of electric vehicles (EVs) and hybrid electric vehicles (HEVs), and non-water batteries such as secondary batteries for driving motors, which hold the key to their practical application. The development of secondary electrolyte batteries is being actively carried out.

The secondary battery for driving a motor is required to have extremely high output characteristics and high energy as compared with a consumer lithium ion secondary battery used in mobile phones, notebook computers and the like. Therefore, lithium-ion secondary batteries, which have the highest theoretical energy among all realistic batteries, are attracting attention and are currently being rapidly developed.

Here, the lithium ion secondary battery currently widely used uses a flammable organic electrolytic solution as the electrolyte. In such a liquid-based lithium-ion secondary battery, safety measures against liquid leakage, short circuit, overcharge, etc. are required more strictly than other batteries.

Therefore, in recent years, research and development on all-solid-state batteries such as all-solid-state lithium secondary batteries using oxide-based or sulfide-based solid electrolytes as the electrolyte have been actively carried out. The solid electrolyte is a material composed mainly of an ionic conductor capable of ionic conduction in a solid. Therefore, in the all-solid-state lithium secondary battery, various problems caused by the flammable organic electrolytic solution do not occur in principle unlike the conventional liquid-based lithium ion secondary battery. Further, in general, when a high potential / large capacity positive electrode material and a large capacity negative electrode material are used, the output density and energy density of the battery can be significantly improved. A positive electrode active material made of sulfur alone (S) or a sulfide-based material, and an all-solid-state lithium secondary battery using a solid electrolyte containing sulfur are promising candidates.

By the way, in a lithium secondary battery, the negative electrode potential decreases as the charging progresses. When the negative electrode potential drops below 0 V (vs. Li / Li ⁺ ), metallic lithium precipitates at the negative electrode and dendrite (dendritic) crystals precipitate (this phenomenon is also referred to as electrodeposition of metallic lithium). When the electrodeposition of metallic lithium occurs, there is a problem that the deposited dendrite penetrates the electrolyte layer, which causes an internal short circuit of the battery. This problem of internal short circuit becomes particularly remarkable when the solid electrolyte layer is thinned from the viewpoint of improving the energy density of the battery.

For the purpose of preventing such electrodeposition of metallic lithium, for example, Patent Document 1 describes granular metallic lithium as a negative electrode active material in a secondary battery having a solid electrolyte layer containing a lithium ion conductive inorganic solid electrolyte. Disclosed is a technique of using a mixture of and carbon black to control the mixing ratio of these to a specific range.

Japanese Unexamined Patent Publication No. 2009-21005

According to the study by the present inventors, if an attempt is made to prevent the electrodeposition of metallic lithium by using the technique described in Patent Document 1, a sufficient capacity cannot be taken out during charging / discharging at a high charge / discharge rate (that is,). , So-called charge / discharge rate characteristics are not sufficient). As described above, the secondary battery having insufficient charge / discharge rate characteristics cannot utilize sufficient capacity for rapid charge / discharge.

Therefore, an object of the present invention is to provide a means capable of improving charge / discharge rate characteristics in a lithium secondary battery having a solid electrolyte layer containing a lithium ion conductive solid electrolyte.

According to one embodiment of the present invention, a lithium secondary battery including a positive electrode, a negative electrode, and a power generation element interposed between the positive electrode and the negative electrode and having a solid electrolyte layer containing a lithium ion conductive solid electrolyte is provided. Provided. Then, in the lithium secondary battery, the negative electrode contains a porous body having conductivity and a lithium ion conductive solid electrolyte that covers at least a part of the inner surface of the porous body, and lithium ion / electron conduction. It is characterized in that it contains a sexual structure and the void ratio of the lithium ion / electron conductive structure is larger than the void ratio of the solid electrolyte layer.

Another embodiment of the present invention also relates to a lithium secondary battery comprising a power generation element interposed between the positive electrode, the negative electrode, and the positive electrode and the negative electrode, and having a solid electrolyte layer containing a lithium ion conductive solid electrolyte. It is a thing. In the lithium secondary battery according to this embodiment, the negative electrode contains a lithium ion / electron containing a porous body having conductivity and a lithium ion conductive solid electrolyte that covers at least a part of the inner surface of the porous body. The void ratio of the lithium ion / electron conductive structure including the conductive structure is larger than the void ratio of the solid electrolyte layer, and metallic lithium is retained in the voids of the lithium ion / electron conductive structure. The feature is that it is done.

In the lithium secondary battery according to the present invention, due to the presence of the lithium ion / electron conductive structure in which the conductive porous body is coated with the solid electrolyte, both the lithium ion conduction path and the electron conduction path in the negative electrode are sufficient. Is secured in. As a result, according to the present invention, it is possible to improve the charge / discharge rate characteristics in a lithium secondary battery having a solid electrolyte layer containing a lithium ion conductive solid electrolyte.

FIG. 1 is a perspective view showing the appearance of a flat laminated battery according to an embodiment of the all-solid-state battery according to the present invention. FIG. 2 is a cross-sectional view taken along the line 2-2 shown in FIG. FIG. 3 is a cross-sectional view of a single battery layer constituting a power generation element of the laminated battery shown in FIGS. 1 and 2.

One embodiment (first embodiment) of the present invention is a power generation element having a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a first lithium ion conductive solid electrolyte. The negative electrode comprises a lithium ion / electron conductive structure containing a porous body having conductivity and a second lithium ion conductive solid electrolyte covering at least a part of the inner surface of the porous body. It is a lithium secondary battery including, and the void ratio of the lithium ion / electron conductive structure is larger than the void ratio of the solid electrolyte layer. When the lithium secondary battery according to the first embodiment is in a completely discharged state, the negative electrode (specifically, the voids of the lithium ion / electron conductive structure) does not contain metallic lithium. On the other hand, when the lithium secondary battery according to the first embodiment is charged, the negative electrode contains metallic lithium.

Another embodiment (second embodiment) of the present invention is a power generation having a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a first lithium ion conductive solid electrolyte. The negative electrode comprises a lithium ion / electron conductive structure comprising a porous body having conductivity and a second lithium ion conductive solid electrolyte covering at least a part of the inner surface of the porous body. The void ratio of the lithium ion / electron conductive structure is larger than the void ratio of the solid electrolyte layer, and metallic lithium is held in the voids of the lithium ion / electron conductive structure. It is a lithium secondary battery. That is, the lithium secondary battery according to the second embodiment is in a charged state.

Hereinafter, embodiments of the present embodiment will be described with reference to the drawings, but the technical scope of the present invention should be determined based on the description of the scope of claims, and is not limited to the following embodiments. The dimensional ratios in the drawings are exaggerated for convenience of explanation and may differ from the actual ratios.

FIG. 1 is a perspective view showing the appearance of a flat laminated all-solid-state battery according to an embodiment of the secondary battery according to the present invention. FIG. 2 is a cross-sectional view taken along the line 2-2 shown in FIG. By making it a laminated type, the battery can be made compact and has a high capacity. In this specification, the flat laminated type non-bipolar all-solid-state lithium secondary battery (hereinafter, also simply referred to as “laminated type battery”) shown in FIGS. 1 and 2 will be described in detail. However, when viewed in terms of the electrical connection form (electrode structure) inside the all-solid-state battery according to this embodiment, it can be used for both non-bipolar type (internal parallel connection type) batteries and bipolar type (internal series connection type) batteries. It is applicable.

As shown in FIG. 2, the laminated battery 10a has a rectangular flat shape, and a negative electrode current collector plate 25 and a positive electrode current collector plate 27 for extracting electric power are pulled out from both sides thereof. There is. The power generation element 21 is wrapped with a battery exterior material (laminated film 29) of the laminated battery 10a, and the periphery thereof is heat-sealed. The power generation element 21 has a negative electrode current collector plate 25 and a positive electrode current collector plate 27 external to the power generation element 21. It is sealed in the state of being pulled out.

The all-solid-state battery according to this embodiment is not limited to a laminated flat battery. The winding type all-solid-state battery may have a cylindrical shape, or may be deformed into a rectangular flat shape by deforming such a cylindrical shape. There are no particular restrictions. In the case of the cylindrical shape, a laminated film may be used for the exterior material, or a conventional cylindrical can (metal can) may be used, and the present invention is not particularly limited. Preferably, the power generation element is housed inside a laminated film containing aluminum. By this form, weight reduction can be achieved.

Further, the removal of the current collector plates (25, 27) shown in FIG. 1 is not particularly limited. The negative electrode current collector plate 25 and the positive electrode current collector plate 27 may be pulled out from the same side, or the negative electrode current collector plate 25 and the positive electrode current collector plate 27 may be divided into a plurality of parts and taken out from each side. It is not limited to what is shown in FIGS. 1 and 2, such as good. Further, in the winding type lithium secondary battery, the terminal may be formed by using, for example, a cylindrical can (metal can) instead of the tab.

As shown in FIG. 2, the laminated battery 10a of the present embodiment has a structure in which a flat, substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a laminated film 29 which is a battery exterior material. Has. Here, the power generation element 21 has a configuration in which a positive electrode, a solid electrolyte layer 17, and a negative electrode are laminated. In the present embodiment, the solid electrolyte layer 17 contains an argylodite-type sulfide solid electrolyte (Li ₆ PS ₅ Cl), which is one of the sulfide solid electrolytes. The negative electrode has a structure in which the lithium ion / electron conductive structure 13 is arranged on both sides of the negative electrode current collector 11'. Here, the lithium ion / electron conductive structure 13 contains a porous body having conductivity and a lithium ion conductive solid electrolyte that covers at least a part of the inner surface of the porous body (lithium ion / Details of the electron conductive structure 13 will be described later). When the laminated battery 10a is in a completely discharged state, metallic lithium does not exist in the negative electrode. On the other hand, when the laminated battery 10a is charged, lithium ions reach the lithium ion / electron conductive structure 13 of the negative electrode from the positive electrode active material layer 15 through the solid electrolyte layer 17, and enter the voids of the structure 13. Precipitates as metallic lithium or lithium-containing alloys. The positive electrode has a structure in which a positive electrode active material layer 15 containing a positive electrode active material is arranged on both sides of a positive electrode current collector 11 ”.Specifically, one lithium ion / electron conductive structure 13 and the positive electrode thereof. The negative electrode, the solid electrolyte layer, and the positive electrode are laminated in this order so that the adjacent positive electrode active material layer 15 faces each other via the solid electrolyte layer 17, whereby the adjacent negative electrode, the solid electrolyte layer, and the positive electrode are laminated in this order. Consists of one cell cell layer 19. Therefore, it can be said that the laminated battery 10a shown in FIG. 2 has a configuration in which a plurality of cell cell layers 19 are stacked and electrically connected in parallel. ..

As shown in FIG. 2, in each of the outermost layer negative electrode current collectors located in both outermost layers of the power generation element 21, the lithium ion / electron conductive structure 13 is arranged on only one side, but lithium is arranged on both sides. An ion / electron conductive structure may be provided. That is, instead of using the current collector dedicated to the outermost layer having the structure on only one side, the current collector having the structure on both sides may be used as it is as the current collector of the outermost layer.

A negative electrode current collector plate (tab) 25 and a positive electrode current collector plate (tab) 27 that are conductive to each electrode (positive electrode and negative electrode) are attached to the negative electrode current collector 11'and the positive electrode current collector 11', respectively, and a battery is provided. It has a structure that is led out to the outside of the laminated film 29 so as to be sandwiched between the ends of the laminated film 29 that is an exterior material. The negative electrode current collector plate 25 and the positive electrode current collector plate 27, respectively, are required. It may be attached to the negative electrode current collector 11'and the positive electrode current collector 11' of each electrode by ultrasonic welding, resistance welding, or the like via the negative electrode lead and the positive electrode lead (not shown).

FIG. 3 is an enlarged cross-sectional view of a single battery layer 19 constituting the power generation element 21 of the laminated battery 10a shown in FIGS. 1 and 2. In FIG. 3, the negative electrode current collector 11'constituting the cellar layer 19, the lithium ion / electron conductive structure 13, the solid electrolyte layer 17, the positive electrode active material layer 15, and the positive electrode current collector 11' , Are laminated in this order. And, in the embodiment shown in FIG. 3, the lithium ion / electron conductive structure 13 is a stainless steel (here, SUS304) which is a porous body having conductivity (conductive porous body). The inner surface of the conductive porous body (stainless porous body) is defined by the porous body made of). It is coated with an electrolyte (Li ₆ PS ₅ Cl). Here, the void ratio of the lithium ion / electron conductive structure 13 having the above configuration is, for example, 60%, and the void ratio of the solid electrolyte layer (Li 6 PS 5 Cl). For example, it is configured to have a value larger than 5%). Further, when the laminated battery 10a is charged, metallic lithium is contained in the voids of the conductive porous body (stainless porous body). The value of the void ratio of the above-mentioned conductive porous body is a value measured in a state where metallic lithium is not retained in the voids.

In a preferred embodiment, the negative electrode further comprises a metal that can be alloyed with lithium. Specifically, for example, silver (Ag) particles, which are metals that can be alloyed with lithium, are attached in a dispersed state on the surface of the solid electrolyte that coats the inner surface of the conductive porous body. According to such a configuration, the lithium ions that reach the negative electrode during charging of the laminated battery 10a are alloyed with silver (Ag) and held as a lithium ion / electron conductive structure 13 in the voids of the lithium ion / electron conductive structure 13. It will be. Since the precipitation energy is smaller in the case of precipitating as a lithium-containing alloy than in the case of precipitating metallic lithium alone, it is possible to precipitate metallic lithium more uniformly by adopting the above configuration. It will be possible. In addition, the interfacial resistance between the lithium ion / electron conductive structure and the solid electrolyte layer is also reduced, and a larger current density can be realized. As a result, the rate characteristics can be further improved. In the present specification, the concept of "metal lithium is held in the voids of the lithium ion / electron conductive structure" includes the lithium ion / electron conductive structure 13 in which metallic lithium is used as a lithium-containing alloy. The form held in the void is also included.

In the embodiment shown in FIG. 3, for example, when the laminated battery 10a is charged, dendrites made of metallic lithium may be generated by electrodeposition at the interface between the lithium ion / electron conductive structure 13 and the solid electrolyte layer 17. This dendrite grows toward the positive electrode active material layer 15. In the present embodiment, since the porosity of the conductive porous body constituting the lithium ion / electron conductive structure 13 is larger than the porosity of the solid electrolyte layer 17, the generated dendrite is on the solid electrolyte layer 17 side (that is, the positive electrode). It is more likely to grow on the conductive porous body side than on the active material layer 15 side). Therefore, in the embodiment shown in FIG. 3, the growth of dendrites on the solid electrolyte layer 17 side (that is, the positive electrode active material layer 15 side) can be suppressed, and the occurrence of an internal short circuit can be prevented.

Further, it is important from the viewpoint of input / output characteristics that the conduction of lithium ions and electrons in each electrode is smooth when the laminated battery 10a is charged and discharged. Here, in the embodiment shown in FIG. 3, among the lithium ion / electron conductive structures 13 constituting the negative electrode, the conductive porous body (stainless porous body) functions as an electron conduction path. Further, among the lithium ion / electron conductive structures 13 constituting the negative electrode, the solid electrolyte (algirodite type sulfide solid electrolyte) covering the inner surface of the conductive porous body functions as a conduction path for lithium ions. As described above, in the lithium secondary battery according to the present embodiment, both the electron and lithium ion conduction paths in the negative electrode are sufficiently secured. As a result, according to the lithium secondary battery according to the present embodiment, it is possible to improve the charge / discharge rate characteristics in the lithium secondary battery having the solid electrolyte layer containing the lithium ion conductive solid electrolyte.

Hereinafter, the main components of the all-solid-state battery according to this embodiment will be described.

[Current collector]
The current collector has a function of mediating the movement of electrons from the electrode active material layer. There are no particular restrictions on the materials that make up the current collector. As a constituent material of the current collector, for example, a metal or a resin having conductivity can be adopted.

Specific examples of the metal include aluminum, nickel, iron, stainless steel, titanium, and copper. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, and the like may be used. Further, the foil may be a metal surface coated with aluminum. Of these, aluminum, stainless steel, copper, and nickel are preferable from the viewpoint of electron conductivity, battery operating potential, and the like.

Further, as the latter resin having conductivity, a resin in which a conductive filler is added to a non-conductive polymer material as needed can be mentioned.

Examples of the non-conductive polymer material include polyethylene (PE; high density polyethylene (HDPE), low density polyethylene (LDPE), etc.), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), and polyimide. (PI), Polypropyleneimide (PAI), Polypropylene (PA), Polytetrafluoroethylene (PTFE), Polystyrene-butadiene rubber (SBR), Polyacrylonitrile (PAN), Polymethylacrylate (PMA), Polymethylmethacrylate (PMMA) , Polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), polystyrene (PS) and the like. Such non-conductive polymer materials may have excellent potential or solvent resistance.

A conductive filler may be added to the above-mentioned conductive polymer material or non-conductive polymer material, if necessary. In particular, when the resin used as the base material of the current collector is composed of only a non-conductive polymer, a conductive filler is inevitably indispensable in order to impart conductivity to the resin.

The conductive filler can be used without particular limitation as long as it is a conductive substance. For example, materials having excellent conductivity, potential resistance, or lithium ion blocking property include metals and conductive carbon. The metal is not particularly limited, and includes at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, and Sb, or at least one of these metals. It preferably contains an alloy or metal oxide. Further, the conductive carbon is not particularly limited. Preferably, it is selected from the group consisting of acetylene black, vulcan (registered trademark), black pearl (registered trademark), carbon nanofiber, Ketjen black (registered trademark), carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene. It contains at least one species.

The amount of the conductive filler added is not particularly limited as long as it can impart sufficient conductivity to the current collector, and is generally 5 to 80% by mass with respect to 100% by mass of the total mass of the current collector. Is.

The current collector may have a single-layer structure made of a single material, or may have a laminated structure in which layers made of these materials are appropriately combined. From the viewpoint of reducing the weight of the current collector, it is preferable to include a conductive resin layer made of at least a conductive resin. Further, from the viewpoint of blocking the movement of lithium ions between the cells of the cell, a metal layer may be provided on a part of the current collector. Further, in the all-solid-state lithium secondary battery according to the present embodiment, the shape of the negative electrode is defined by the conductive porous body. Therefore, in some cases, it is possible to make the conductive porous body take on the function as the negative electrode current collector without separately providing the negative electrode current collector. In this case, the negative electrode lead described later may be directly connected to the conductive porous body.

[Negative electrode]
In the lithium secondary battery according to the present invention, the negative electrode has a lithium ion / electron conductive structure containing a porous body having conductivity and a lithium ion conductive solid electrolyte covering at least a part of the inner surface of the porous body. It is characterized by including the body. Further, as described above, when the lithium secondary battery according to the present invention is in a completely discharged state, the negative electrode does not contain metallic lithium. On the other hand, when the lithium secondary battery according to the present invention is in a charged state, the negative electrode contains metallic lithium in the form of a simple substance or a lithium-containing alloy. When the conductive porous body itself has a function as a negative electrode current collector without using a negative electrode current collector separately, the lithium ion / electron conductive structure becomes the negative electrode as it is.

(Porous medium with conductivity)
A porous body having conductivity (conductive porous body) is a member having a porous structure (a large number of voids) inside and having conductivity. The material constituting the conductive porous body may be any material having conductivity, and the above-mentioned material can be similarly adopted as the constituent material of the current collector. Among them, the conductive porous body preferably contains a metal material or a carbon material from the viewpoint of being inexpensive and easily available and having excellent action and effect of the present invention. Here, examples of the metal material include aluminum, nickel, iron, stainless steel (SUS304, SUS316L, etc.), titanium, copper, and the like. As carbon materials, hard carbon, acetylene black, vulcan (registered trademark), black pearl (registered trademark), carbon nanofiber, Ketjen black (registered trademark), carbon nanotube, carbon nanohorn, carbon nanoballoon, fullerene, etc. Examples include mesoporous carbon or activated carbon. Among them, the conductive porous body more preferably contains stainless steel, nickel, carbon black, hard carbon, mesoporous carbon or activated carbon.

The shape of the conductive porous body is not particularly limited, but for example, if it is composed of a metal material, the shape of a mesh, an expanded grid (expanded metal), a punched metal, a foam, or the like is preferably exemplified. Further, a molded body obtained by molding a powder of a metal material or a carbon material by a method such as powder compaction may be used as the conductive porous body.

As described above, the conductive porous body has a porous structure (a large number of voids) inside, but the value of the porosity is not particularly limited as long as it is larger than the porosity of the solid electrolyte layer. The porosity of the conductive porous body is preferably 5 to 95%, more preferably 30 to 90%, still more preferably 50 to 70%. The value of the porosity of the conductive porous body can be controlled by appropriately adopting a conventionally known method.

The thickness of the conductive porous body is also not particularly limited, but is preferably 20 to 300 μm, more preferably 30 to 250 μm, and even more preferably 50 to 200 μm.

(Lithium ion conductive solid electrolyte)
Examples of the lithium ion conductive solid electrolyte include a sulfide solid electrolyte and an oxide solid electrolyte, and the sulfide solid electrolyte is preferable from the viewpoint of excellent lithium ion conductivity and durability. In the present specification, the lithium ion conductive solid electrolyte contained in the solid electrolyte layer 17 is also referred to as a "first lithium ion conductive solid electrolyte", and the lithium ion conduction constituting the lithium ion / electron conductive structure is used. The sex solid electrolyte may also be referred to as a "second lithium ion conductive solid electrolyte". These names are intended only to distinguish the sites where the solid electrolytes are located, and the ordinal numbers 1 and 2 themselves have no substantial meaning. That is, in the present invention, it is preferable that both the first lithium ion conductive solid electrolyte and the second lithium ion conductive solid electrolyte are sulfide solid electrolytes.

Examples of the sulfide solid electrolyte include LiI-Li ₂ S-SiS ₂ , LiI-Li ₂ S-P ₂ O ₅ , LiI-Li ₃ PO ₄ -P ₂ S ₅ , Li ₂ S-P ₂ S ₅ (Li 2 S-P 2 S 5). LPS), LiI-Li ₃ PS ₄ , LiI-LiBr-Li ₃ PS _4, Li ₃ PS _4, Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ -LiI, Li ₂ SP ₂ S ₅ -Li ₂ O, Li ₂ S-P ₂ S ₅ -Li ₂ O-LiI, Li ₂ S-SiS ₂ , Li ₂ S-SiS ₂ -LiI, Li ₂ S-SiS ₂ -LiBr, Li ₂ S -SiS ₂ -LiCl, Li ₂ S-SiS ₂ -B ₂ S ₃ -LiI, Li ₂ S-SiS ₂ -P ₂ S ₅ -LiI, Li ₂ SB ₂ S ₃ , Li ₂ SP ₂ S ₅ -Z _m Sn (where m and _n are positive numbers and Z is one of Ge, Zn or Ga), Li ₂ S-GeS ₂ , Li ₂ S-SiS ₂ -Li ₃ PO ₄ , Li ₂ S-SiS ₂ -Li _x MO _y (where x, y are positive numbers, M is any of P, Si, Ge, B, Al, Ga, In), etc. Can be mentioned. The description of "Li ₂ SP _{2 S 5" means a sulfide solid electrolyte using a raw material composition containing Li 2 S and P 2 S 5 , and} the same applies to other descriptions.

The sulfide solid electrolyte may have, for example, a Li ₃ PS ₄ skeleton, a Li ₄ P ₂ S ₇ skeleton, or a Li ₄ P ₂ S ₆ skeleton. .. Examples of the sulfide solid electrolyte having a Li ₃ PS ₄ skeleton include LiI-Li ₃ PS ₄ , LiI-LiBr-Li ₃ PS _{4, and} Li ₃ PS ₄ . Examples of the sulfide solid electrolyte having a Li ₄ P ₂ S ₇ skeleton include a Li-PS-based solid electrolyte called LPS (for example, Li ₇ P ₃ S ₁₁ ). Further, as the sulfide solid electrolyte, for example, LGPS represented by Li _(4-x) Ge _(1-x) P _x S ₄ (x satisfies 0 <x <1) may be used. Among them, the sulfide solid electrolyte contained in the active material layer is preferably a sulfide solid electrolyte containing P element. Further, the sulfide solid electrolyte may contain halogen (F, Cl, Br, I). From the viewpoint of excellent ionic conductivity, in a preferred embodiment, the lithium ion conductive solid electrolyte is Li ₂ SP ₂ S ₅ , Li ₇ P ₃ S ₁₁ , Li _3.2 P _0.96 S, Li ₂ S-SiS ₂ , Li ₂ SB ₂ S ₃ , Li ₂ S-GeS ₂ , Li _3.25 Ge _0.25 P _0.75 S ₄ , Li ₁₀ GeP ₂ S ₁₂ and Li ₆ PS ₅ X Contains a sulfide solid electrolyte selected from the group consisting of (where X is Cl, Br or I).

When the sulfide solid electrolyte is a Li ₂ SP ₂ S ₅ system, the ratio of Li ₂ S and P ₂ S ₅ is Li ₂ S: P ₂ S ₅ = 50: 50 to 100 in terms of molar ratio. It is preferably in the range of: 0, and in particular, Li ₂ S: P ₂ S ₅ = 70: 30 to 80:20.

Further, the sulfide solid electrolyte may be sulfide glass, crystallized sulfide glass, or a crystalline material obtained by the solid phase method. The sulfide glass can be obtained, for example, by performing mechanical milling (ball mill or the like) on the raw material composition. Further, the crystallized sulfide glass can be obtained, for example, by heat-treating the sulfide glass at a temperature equal to or higher than the crystallization temperature. The ionic conductivity (for example, Li ionic conductivity) of the sulfide solid electrolyte at room temperature (25 ° C.) is preferably 1 × 10 ^-5 S / cm or more, for example, 1 × 10 ^-4 S / cm. It is more preferably cm or more. The value of the ion conductivity of the lithium ion conductive solid electrolyte can be measured by the AC impedance method.

Examples of the oxide solid electrolyte include compounds having a NASICON type structure and the like. As an example of a compound having a NASION type structure, a compound (LAGP) represented by the general formula Li _{1 + x} Al _x Ge _2-x (PO ₄ ) ₃ (0 ≦ x ≦ 2), a general formula Li _{1 + x} Al _x Ti ₂ Examples thereof include a compound (LATP) represented by _−x (PO ₄ ) ₃ (0 ≦ x ≦ 2). Further, as another example of the oxide solid electrolyte, LiLaTIO (for example, Li _0.34 La _0.51 TiO ₃ ), LiPON (for example, Li _2.9 PO _3.3 N _0.46 ), LiLaZrO (for example, LiLaZrO). , Li ₇ La ₃ Zr ₂ O ₁₂ ) and the like.

Examples of the shape of the lithium ion conductive solid electrolyte include a particle shape such as a true spherical shape and an elliptical spherical shape, and a thin film shape. When the solid electrolyte has a particle shape, its average particle size (D ₅₀ ) is not particularly limited, but is preferably 40 μm or less, more preferably 20 μm or less, still more preferably 10 μm or less. On the other hand, the average particle size (D ₅₀ ) is preferably 0.01 μm or more, and more preferably 0.1 μm or more.

In the lithium secondary battery according to the present invention, the lithium ion / electron conductive structure constituting the negative electrode has a structure in which the inner surface of the conductive porous body is coated with a lithium ion conductive solid electrolyte. Here, the coating thickness of the lithium ion conductive solid electrolyte on the inner surface of the conductive porous body is not particularly limited, but is preferably about 1 to 100 μm, and more preferably 10 to 80 μm.

In a preferred embodiment of the lithium secondary battery according to the present invention, the negative electrode contains a metal that can be alloyed with lithium. Elements that can be alloyed with lithium include, for example, aluminum, magnesium, zinc, bismuth, tin, lead, indium, ruthenium, rhodium, iridium, palladium, platinum, silver, gold, cadmium, gallium, tarium, silicon, germanium and the like. Can be mentioned. Among these, the material that can be alloyed with lithium is selected from the group consisting of silver, silicon, gold, indium, germanium, tin, lead, aluminum and zinc from the viewpoint of being able to construct a battery having excellent capacity and energy density. It is preferable to contain at least one metal, and more preferably silver, silicon, gold or indium. These metals that can be alloyed with lithium may be used in the form of a conductive porous body made of itself, or in the form of a coating formed on the surface of a conductive porous body made of a material that does not alloy with lithium. It may be used. At this time, the metal that can be alloyed with lithium may be present so that the solid electrolyte is exposed on the coating layer formed by coating the inner surface of the conductive porous body, or the conductive porous body may be present. It may exist between the coating layer and the covering layer, but the former form is more preferable.

According to the above configuration, the lithium ions that reach the negative electrode during charging of the lithium secondary battery are alloyed with a metal that can be alloyed with lithium. Then, it is held in the voids of the lithium ion / electron conductive structure 13 as a lithium-containing alloy. Since the precipitation energy is smaller in the case of precipitating as a lithium-containing alloy than in the case of precipitating metallic lithium alone, it is possible to precipitate metallic lithium more uniformly by adopting the above configuration. It will be possible. In addition, the interfacial resistance between the lithium ion / electron conductive structure and the solid electrolyte layer is also reduced, and a larger current density can be realized. As a result, the rate characteristics can be further improved.

[Solid electrolyte layer]
In the lithium secondary battery according to the present embodiment, the solid electrolyte layer contains the solid electrolyte as a main component and is a layer interposed between the positive electrode and the negative electrode described above. The specific form of the solid electrolyte contained in the solid electrolyte layer is not particularly limited, and conventionally known findings can be appropriately referred to. Here, since the specific form and preferable examples of the solid electrolyte are as described above, the description thereof will be omitted here.

The solid electrolyte layer may further contain a binder in addition to the above-mentioned solid electrolyte. The binder that can be contained in the solid electrolyte layer is not particularly limited, and examples thereof include the following materials.

Polybutylene terephthalate, polyethylene terephthalate, polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are replaced with other halogen elements), polyethylene, polypropylene, polymethylpentene, polybutene, polyethernitrile, polytetrafluoroethylene, Polyacrylonitrile, polyimide, polyamide, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), ethylene-propylene-diene copolymer, styrene-butadiene-styrene block copolymer and its hydrogenated products , Polymeric polymers such as styrene / isoprene / styrene block copolymers and their hydrogenated additives, tetrafluoroethylene / hexafluoropropylene copolymers (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymers (PFA). , Fluororesin such as ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE), polyvinylfluoride (PVF), vinylidene fluoride- Hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP-TFE-based fluororubber), vinylidene fluoride-pentafluoropropylene-based fluororubber (VDF-PFP-based fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber), vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber) Examples thereof include vinylidene fluoride-based fluororubbers such as VDF-PFMVE-TFE-based fluororubbers and vinylidene fluoride-chlorotrifluoroethylene-based fluororubbers (VDF-CTFE-based fluororubbers), epoxy resins and the like. Of these, polyimide, styrene-butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide are more preferable.

The value of the porosity of the solid electrolyte layer is not particularly limited as long as it is smaller than the porosity of the lithium ion / electron conductive structure constituting the negative electrode. Ideally, the porosity of the solid electrolyte layer is preferably close to 0%. On the other hand, the upper limit of the porosity of the solid electrolyte layer is preferably 25% or less, more preferably 20% or less, still more preferably 15% or less, and particularly preferably 10% or less. The value of the porosity of the solid electrolyte layer can be controlled by appropriately adopting a conventionally known method. As an example, when a solid electrolyte layer is produced by powder molding of a solid electrolyte powder, the void ratio of the solid electrolyte layer is controlled by adjusting the pressure applied during the powder molding. Can be done. Further, by making the solid electrolyte amorphous or in the form of a hybrid with the organic solid electrolyte, the density of the solid electrolyte can be improved, and as a result, the void ratio can be lowered. Here, the solid electrolyte layer may be composed of a single layer having a uniform composition, density (porosity), etc., or may be a laminated body of a plurality of layers having different compositions, densities (porosity), and the like. good.

The thickness of the solid electrolyte layer varies depending on the configuration of the target lithium secondary battery, but is preferably in the range of 0.1 to 1000 μm, more preferably in the range of 0.1 to 500 μm, for example. preferable.

[Positive electrode]
The positive electrode contains a positive electrode active material that can occlude and release lithium ions. Here, when a battery in a completely discharged state is manufactured at the time of manufacturing the battery, metallic lithium is not held in the negative electrode. Therefore, the positive electrode needs to contain a positive electrode active material capable of releasing lithium ions during charging. Examples of such positive electrode active materials include layered rock salt type active materials such as LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiVO ₂ , Li (Ni—Mn—Co) O ₂ , LiMn ₂ O ₄ , LiNi _0.5 . Spinel-type active materials such as Mn _1.5 O ₄ , Libin-type active materials such as LiFePO ₄ , LiMnPO ₄ , Si-containing active materials such as Li ₂ FeSiO ₄ , Li ₂ MnSiO ₄ , Li ₄ Ti ₅ O ₁₂ and the like. Be done. Further, a reduction product of sulfur ₍ S) (for example, pumped lithium (Li 2S ₈ )) may be used as the positive electrode active material.

On the other hand, when a fully charged battery is manufactured at the time of manufacturing the battery, metallic lithium is held in the negative electrode (for example, the voids of the lithium ion / electron conductive structure are filled with metallic lithium). .. Therefore, the positive electrode needs to contain a positive electrode active material that can occlude lithium ions at the time of discharge. Examples of such a positive electrode active material include elementary sulfur (S) and particles or thin films of an organic sulfur compound or an inorganic sulfur compound. These positive electrode active materials can store lithium ions at the time of discharge and release lithium ions at the time of charging by utilizing the redox reaction of sulfur. Examples of the organic sulfur compound include disulfide compounds, sulfur-modified polyacrylonitrile represented by the compounds described in International Publication No. 2010/0444437, sulfur-modified polyisoprene, rubian acid (dithiooxamide), and polysulfide carbon. Of these, disulfide compounds, sulfur-modified polyacrylonitrile, and rubianic acid are preferable, and sulfur-modified polyacrylonitrile is particularly preferable. As the disulfide compound, a compound having a dithiobiurea derivative, a thiourea group, a thioisocyanate, or a thioamide group is more preferable. Here, the sulfur-modified polyacrylonitrile is a modified polyacrylonitrile containing a sulfur atom, which is obtained by mixing sulfur powder and polyacrylonitrile and heating them under an inert gas or under reduced pressure. The estimated structure is, for example, Chem. Mater. As shown in 2011, 23, 5024-5028, the polyacrylonitrile is ring-closed to form a polycyclic structure, and at least a part of S is bound to C. The compounds described in this document have strong peak signals near 1330 cm ^-1 and 1560 cm ^-1 in Raman spectra, and peaks near 307 cm ^-1 , 379 cm ^-1 , 472 cm ^-1 , and 929 cm ^-1 . do. On the other hand, inorganic sulfur compounds are preferable because they are excellent in stability, and specifically, sulfur simple substance (S), S-carbon composite, TiS ₂ , TiS ₃ , TiS ₄ , NiS, NiS ₂ , CuS, FeS ₂ , Li. 2S, MoS _{2 , MoS 3 and} the like can be mentioned. Among them, S, S-carbon composite, TiS ₂ , TiS ₃ , TiS ₄ , FeS ₂ and MoS ₂ are preferable, sulfur simple substance (S), S-carbon composite, TiS ₂ and FeS ₂ are more preferable, and sulfur simple substance (S) is preferable. S) is particularly preferable. Here, the S-carbon composite contains sulfur powder and a carbon material, and is in a state of being composited by subjecting them to heat treatment or mechanical mixing. More specifically, the state where sulfur is distributed on the surface of the carbon material and in the pores, the state where sulfur and the carbon material are uniformly dispersed at the nano level, and they are aggregated into particles, fine sulfur. The carbon material is distributed on the surface or inside of the powder, or a combination of these states.

In some cases, two or more kinds of positive electrode active materials may be used in combination. Of course, a positive electrode active material other than the above may be used.

Examples of the shape of the positive electrode active material include particulate (spherical and fibrous) and thin film. When the positive electrode active material has a particle shape, its average particle size (D ₅₀ ) is preferably in the range of, for example, 1 nm to 100 μm, more preferably in the range of 10 nm to 50 μm, and further preferably in the range of 100 nm. It is in the range of about 20 μm, and particularly preferably in the range of 1 to 20 μm. In the present specification, the value of the average particle size (D ₅₀ ) of the active material can be measured by the laser diffraction / scattering method.

The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but is preferably in the range of 40 to 99% by mass, and preferably in the range of 50 to 90% by mass. More preferred. The positive electrode active material layer may further contain a conductive auxiliary agent and / or a binder.

[Positive current collector plate and negative electrode current collector plate]
The material constituting the current collector plates (25, 27) is not particularly limited, and known highly conductive materials conventionally used as current collector plates for secondary batteries can be used. As the constituent material of the current collector plate, for example, metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable. From the viewpoint of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferable, and aluminum is particularly preferable. The same material may be used for the positive electrode current collector plate 27 and the negative electrode current collector plate 25, or different materials may be used.

[Positive lead and negative electrode lead]
Further, although not shown, the current collector (11', 11 ") and the current collector plate (25, 27) may be electrically connected via a positive electrode lead or a negative electrode lead. As the constituent material of the negative electrode lead, a material used in a known lithium secondary battery can be similarly adopted. In addition, the portion taken out from the exterior may come into contact with peripheral devices, wiring, etc. and leak electricity to the product. It is preferable to cover it with a heat-resistant and insulating heat-shrinkable tube so as not to affect (for example, automobile parts, particularly electronic devices, etc.).

[Battery exterior material]
As the battery exterior material, a known metal can case can be used, and a bag-shaped case using a laminated film 29 containing aluminum, which can cover the power generation element as shown in FIGS. 1 and 2, is used. Can be done. As the laminated film, for example, a laminated film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order can be used, but the laminated film is not limited thereto. A laminated film is desirable from the viewpoint of high output, excellent cooling performance, and suitable use for batteries for large equipment for EVs and HEVs. Further, since the group pressure applied to the power generation element from the outside can be easily adjusted, a laminated film containing aluminum is more preferable for the exterior body.

The lithium secondary battery according to the present invention has a configuration in which a plurality of single battery layers are connected in parallel, so that it has a high capacity and is excellent in cycle durability and charge / discharge rate characteristics. Therefore, the lithium secondary battery according to the present invention is suitably used as a driving power source for EVs and HEVs.

Although one embodiment of the all-solid-state battery has been described above, the present invention is not limited to the configuration described in the above-described embodiment, and can be appropriately changed based on the description of the claims. be.

For example, the lithium secondary battery according to this embodiment does not have to be an all-solid-state battery. That is, the solid electrolyte layer may further contain a conventionally known liquid electrolyte (electrolyte solution). The amount of the liquid electrolyte (electrolyte solution) that can be contained in the solid electrolyte layer is not particularly limited, but the shape of the solid electrolyte layer formed by the solid electrolyte is maintained and the liquid electrolyte (electrolyte solution) does not leak. Is preferably the amount of.

The liquid electrolyte (electrolyte solution) that can be used has a form in which a lithium salt is dissolved in an organic solvent. Examples of the organic solvent used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propionate (MP), methyl acetate (MA), and methyl formate. (MF), 4-methyldioxolane (4MeDOL), dioxolane (DOL), 2-methyltetrahydrofuran (2MeTHF), tetrahydrofuran (THF), dimethoxyethane (DME), propylene carbonate (PC), butylene carbonate (BC), dimethyl sulfoxide (DMSO), γ-butylolactone (GBL) and the like. Among them, the organic solvent is preferably a chain carbonate, more preferably diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) from the viewpoint of further improving the quick charge property and the output property. It is at least one selected from the group consisting of, and more preferably selected from ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC).

Lithium salts include Li (FSO ₂ ) ₂ N (lithium bis (fluorosulfonyl) imide; LiFSI), Li (C ₂ F ₅ SO ₂ ) ₂ N, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ and the like can be mentioned. Among them, the lithium salt is preferably Li (FSO ₂ ) 2N ₍ LiFSI) from the viewpoint of battery output and charge / discharge cycle characteristics.

The liquid electrolyte (electrolyte solution) may further contain additives other than the above-mentioned components. Specific examples of such compounds include, for example, ethylene carbonate, vinylene carbonate, methylvinylene carbonate, dimethylvinylene carbonate, phenylvinylene carbonate, diphenylvinylene carbonate, ethylvinylene carbonate, diethylvinylene carbonate, vinylethylene carbonate, 1,2-. Divinylethylene carbonate, 1-methyl-1-vinylethylenecarbonate, 1-methyl-2-vinylethylenecarbonate, 1-ethyl-1-vinylethylenecarbonate, 1-ethyl-2-vinylethylenecarbonate, vinylvinylene carbonate, allylethylene Carbonate, vinyloxymethylethylene carbonate, allyloxymethylethylene carbonate, acrylicoxymethylethylene carbonate, methacryloxymethylethylene carbonate, ethynylethylene carbonate, propargylethylene carbonate, ethynyloxymethylethylene carbonate, propargyloxyethylene carbonate, methyleneethylene carbonate, 1 , 1-Dimethyl-2-methyleneethylene carbonate and the like. Only one of these additives may be used alone, or two or more of these additives may be used in combination. Further, when the additive is used in the electrolytic solution, the amount used can be appropriately adjusted.

[Battery set]
An assembled battery is configured by connecting a plurality of batteries. More specifically, it is composed of serialization, parallelization, or both by using at least two or more. By serializing and parallelizing, it becomes possible to freely adjust the capacity and voltage.

It is also possible to connect a plurality of batteries in series or in parallel to form a small assembled battery that can be attached / detached. Then, by connecting a plurality of small detachable batteries in series or in parallel, a large capacity and a large capacity suitable for a vehicle drive power source or an auxiliary power source that require a high volume energy density and a high volume output density. It is also possible to form an assembled battery with an output. How many batteries are connected to make an assembled battery, and how many stages of small assembled batteries are stacked to make a large-capacity assembled battery depends on the battery capacity of the vehicle (electric vehicle) to be mounted. It may be decided according to the output.

[vehicle]
The lithium secondary battery according to the present invention maintains a discharge capacity even after long-term use, and has good cycle characteristics and charge / discharge rate characteristics. In addition, the volumetric energy density is high. In vehicle applications such as electric vehicles, hybrid electric vehicles, fuel cell vehicles, and hybrid fuel cell vehicles, higher capacity and larger size are required and longer life is required compared to electric and portable electronic device applications. .. Therefore, the non-aqueous electrolyte secondary battery can be suitably used as a power source for a vehicle, for example, a vehicle drive power source or an auxiliary power source.

Specifically, a battery or a combined battery formed by combining a plurality of batteries can be mounted on the vehicle. In the present invention, a long-life battery having excellent long-term reliability and output characteristics can be configured. Therefore, when such a battery is installed, a plug-in hybrid electric vehicle having a long EV mileage or an electric vehicle having a long one-charge mileage can be configured. .. In addition to hybrid vehicles, fuel cell vehicles, electric vehicles (all four-wheeled vehicles (passenger cars, trucks, commercial vehicles such as buses, light vehicles, etc.)) This is because it becomes a highly reliable automobile with a long life by using it for two-wheeled vehicles (including motorcycles) and three-wheeled vehicles. However, the application is not limited to automobiles, and can be applied to various power sources of other vehicles, for example, moving objects such as trains, and power supplies for mounting such as uninterruptible power supplies. It is also possible to use it as.

Hereinafter, the present invention will be described in more detail by way of examples. However, the technical scope of the present invention is not limited to the following examples.

<< Production example of test cell >>
[Example 1-1]
(Manufacturing of negative electrode)
A predetermined amount of the argylodite-type sulfide solid electrolyte (Li ₆ PS ₅ Cl), which is a lithium ion conductive solid electrolyte, was weighed. This was then dispersed in an appropriate amount of dehydrated ethanol to prepare solution A.

On the other hand, as a porous body having conductivity, a mesh made of stainless steel (SUS304) was prepared, and this was immersed in the solution A for a sufficient time. Then, this was taken out from the solution A and dried in a constant temperature bath at 150 ° C. for a sufficient time to prepare a negative electrode made of an electrolyte-coated stainless steel mesh (lithium ion / electron conductive structure).

(Preparation of test cell)
As the positive electrode active material, a lithium-containing composite oxide having a uniform composition of LiNi _0.8 Mn _0.1 Co _0.1 O ₂ and having the form of secondary particles which are aggregates of primary particles was prepared. The average particle size (D50) of the lithium-containing composite oxide (secondary particles) was measured by a laser diffraction / scattering method and found to be 11.5 μm. Further, as the solid electrolyte for the positive electrode mixture, the same algyrodite-type sulfide solid electrolyte as described above was prepared. Further, acetylene black was prepared as a conductive auxiliary agent for the positive electrode mixture.

60 parts by mass of the positive electrode active material, 6 parts by mass of the conductive auxiliary agent, and 34 parts by mass of the argylodite-type sulfide solid electrolyte prepared above were weighed and mixed using a table mill to prepare a positive electrode mixture.

Subsequently, the same argilodite-type sulfide solid electrolyte as described above is placed in a jig (Macol tube) and powder-molded at a molding pressure of 400 [MPa] to form a solid electrolyte layer (a disk having a diameter of 10 mm and a thickness of 600 μm). Shape) was produced.

Next, the positive electrode mixture prepared above was placed on one surface of the solid electrolyte layer prepared above, and powder molding was performed at a molding pressure of 200 [MPa] to obtain a positive electrode active material layer (diameter 10 mm and thickness 70 μm). (Disc shape) was produced.

Then, the (lithium ion / electron conductive structure) prepared above was placed on the other surface of the solid electrolyte layer prepared above. Next, after fastening the jig with a restraining pressure of 100 [MPa], a lead for taking out a current was connected to each electrode to prepare a test cell of this example. The porosities of the solid electrolyte layer and the negative electrode (lithium ion / electron conductive structure) in the test cell thus produced were 5% and 60%, respectively.

[Example 1-2]
A predetermined amount of silver (Ag) powder was weighed as a metal that could be alloyed with lithium. This was then dispersed in an appropriate amount of dehydrated ethanol to prepare solution B. Then, before the production of the test cell, the solution B was uniformly sprayed on the negative electrode made of an electrolyte-coated stainless mesh (lithium ion / electron conductive structure) and naturally dried.

The test cell of this example was produced by the same method as in Example 1-1 described above except that the negative electrode subjected to the above treatment was used. The porosities of the solid electrolyte layer and the negative electrode (lithium ion / electron conductive structure) in the test cell thus produced were 5% and 60%, respectively.

[Comparative Example 1-1]
In Example 1-1 described above, when arranging the negative electrode of the test cell, instead of the negative electrode (lithium ion / electron conductive structure) produced above, a stainless steel mesh not coated with a solid electrolyte was used. , 7 mg of argilodite-type sulfide solid electrolyte (Li ₆ PS ₅ Cl) was simply encapsulated at the same time, and a confining pressure was applied under the same conditions as described above. Except for this, the test cell of this comparative example was prepared by the same method as in Example 1-1 described above. The porosities of the solid electrolyte layer and the negative electrode in the test cell thus produced were 5% and 60%, respectively.

[Comparative Example 1-2]
In Comparative Example 1-1 described above, the comparison described above was performed except that when the negative electrode of the test cell was arranged, only the stainless steel mesh not coated with the solid electrolyte was arranged and the solid electrolyte was not enclosed at the same time. The test cell of this comparative example was prepared by the same method as in Example 1-1. The porosities of the solid electrolyte layer and the negative electrode in the test cell thus produced were 5% and 60%, respectively.

[Example 2-1]
As a constituent material of the conductive porous body, Ketjen Black (registered trademark) (manufactured by Ketjen Black International Co., Ltd.) EC300, which is a carbon material, was prepared. The carbon material was then immersed in the solution A prepared above for a sufficient period of time. Then, this was taken out from the solution A and dried in a constant temperature bath at 150 ° C. for a sufficient time to prepare an electrolyte-coated carbon material.

Subsequently, a laminate of the solid electrolyte layer and the positive electrode active material layer was prepared by the same method as in Example 1-1 described above.

Next, the electrolyte-coated carbon material prepared above is placed on the other surface of the solid electrolyte layer prepared above, and powder molding is performed at a molding pressure of 100 [MPa] to obtain a negative electrode (lithium ion / electron conductive structure). A body) (a disk shape having a diameter of 10 mm and a thickness of 70 μm) was produced. Then, a lead for taking out a current was connected to each electrode to prepare a test cell of this example. The porosities of the solid electrolyte layer and the negative electrode (lithium ion / electron conductive structure) in the test cell thus produced were 5% and 60%, respectively.

[Example 2-2]
Prior to preparation of the test cell, the solution B prepared above was uniformly sprayed onto the electrolyte-coated carbon material and air-dried.

For the test of this example by the same method as in Example 2-1 described above, except that the negative electrode (lithium ion / electron conductive structure) was prepared using the electrolyte-coated carbon material subjected to the above treatment. A cell was prepared. The porosities of the solid electrolyte layer and the negative electrode (lithium ion / electron conductive structure) in the test cell thus produced were 5% and 60%, respectively.

[Comparative Example 2]
In Example 2-1 described above, instead of the electrolyte-coated carbon material, a mixture obtained by mixing 1 mg of a carbon material (Ketjen Black EC300) and 5.6 mg of an algyrodite-type sulfide solid electrolyte with a roll mill was used. A negative electrode was prepared. Except for this, the test cell of this comparative example was prepared by the same method as in Example 2-1 described above. The porosities of the solid electrolyte layer and the negative electrode in the test cell thus produced were 5% and 60%, respectively.

[Example 3-1]
This Example is carried out by the same method as in Example 2-1 described above, except that hard carbon, which is another carbon material, is used as a constituent material of the conductive porous body in place of Ketjen Black (registered trademark). The test cell of was prepared. The porosities of the solid electrolyte layer and the negative electrode (lithium ion / electron conductive structure) in the test cell thus produced were 5% and 60%, respectively.

[Example 3-2]
Prior to preparation of the test cell, the solution B prepared above was uniformly sprayed onto the electrolyte-coated carbon material and air-dried.

For the test of this example by the same method as in Example 3-1 described above, except that the negative electrode (lithium ion / electron conductive structure) was prepared using the electrolyte-coated carbon material subjected to the above treatment. A cell was prepared. The porosities of the solid electrolyte layer and the negative electrode (lithium ion / electron conductive structure) in the test cell thus produced were 5% and 60%, respectively.

[Comparative Example 3]
In Example 3-1 described above, instead of the electrolyte-coated carbon material, a negative electrode was prepared by using a mixture obtained by mixing 1 mg of a carbon material (hard carbon) and 5.6 mg of an argylodite-type sulfide solid electrolyte with a roll mill. Made. Except for this, the test cell of this comparative example was prepared by the same method as in Example 3-1 described above. The porosities of the solid electrolyte layer and the negative electrode in the test cell thus produced were 5% and 60%, respectively.

<< Test example of test cell (evaluation of charge / discharge rate characteristics) >>
The charge / discharge rate characteristics of the test cells produced in the above-mentioned Examples and Comparative Examples were evaluated.

In the charge / discharge test, charging in the constant current / low voltage (CCCV) mode and discharging in the constant current (CC) mode are performed at 0.2 C (CCCV) in the voltage range of 4.3 V / 2.5 V with respect to Li, respectively. Low rate condition) and 2C (high rate condition) rate condition respectively. The evaluation temperature was 298 K (25 ° C.), and there was a 30-minute rest between charging and discharging. In addition, "1C" is a current value which makes the battery fully charged (100% charged) when it is charged with the current value for 1 hour.

From the discharge capacities at 0.2C and 2C measured in this way, the discharge capacity retention rate (= 2C discharge capacity / 0.2C discharge capacity × 100) was calculated and used as an index of the charge / discharge rate characteristics (this). The larger the value, the better the charge / discharge rate characteristics). The results are shown in Table 1 below.

From the results shown in Table 1, when the examples and comparative examples in which the constituent materials of the conductive porous body are the same are compared, it can be seen that the charge / discharge rate characteristics can be significantly improved by providing the configuration of the present invention. It can also be seen that the charge / discharge rate characteristics are further improved when the negative electrode contains a metal (Ag) that can be alloyed with lithium.

10a laminated battery,
11'Negative current collector,
11 ”Positive current collector,
13 Lithium-ion / electron conductive structure,
15 Positive electrode active material layer,
17 Electrolyte layer,
19 Single battery layer,
21 Power generation element,
25 Negative electrode current collector plate (negative electrode tab),
27 Positive electrode current collector plate (positive electrode tab),
29 Laminated film.

Claims (7)

With the positive electrode
With the negative electrode
A solid electrolyte layer, which is interposed between the positive electrode and the negative electrode and contains a first lithium ion conductive solid electrolyte,
Equipped with a power generation element that has
The negative electrode comprises a lithium ion / electron conductive structure comprising a porous body having conductivity and a second lithium ion conductive solid electrolyte covering at least a part of the inner surface of the porous body.
A lithium secondary battery in which the void ratio of the lithium ion / electron conductive structure is larger than the void ratio of the solid electrolyte layer. With the positive electrode
With the negative electrode
A solid electrolyte layer, which is interposed between the positive electrode and the negative electrode and contains a first lithium ion conductive solid electrolyte,
Equipped with a power generation element that has
The negative electrode comprises a lithium ion / electron conductive structure comprising a porous body having conductivity and a second lithium ion conductive solid electrolyte covering at least a part of the inner surface of the porous body.
The porosity of the lithium ion / electron conductive structure is larger than the porosity of the solid electrolyte layer, and
A lithium secondary battery in which metallic lithium is held in the voids of the lithium ion / electron conductive structure. The lithium secondary battery according to claim 1 or 2, wherein the conductive porous body contains a metal material or a carbon material. The lithium secondary battery according to claim 3, wherein the conductive porous body contains stainless steel, nickel, carbon black, hard carbon, mesoporous carbon or activated carbon. The lithium secondary battery according to any one of claims 1 to 4, wherein the negative electrode contains a metal that can be alloyed with lithium. The lithium secondary battery according to any one of claims 1 to 5, wherein the first lithium ion conductive solid electrolyte and the second lithium ion conductive solid electrolyte contain a sulfide solid electrolyte. The lithium secondary battery according to any one of claims 1 to 6, which is an all-solid-state lithium secondary battery.

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