JP2021136215A - Lithium ion secondary battery - Google Patents

Abstract

To provide means for preventing the occurrence of an internal short circuit caused by an electrodeposition of metallic lithium while effectively utilizing a high capacity that metallic lithium has in a lithium ion secondary battery.SOLUTION: A lithium ion secondary battery comprises a power-generating element having a positive electrode containing a positive electrode active material capable of occluding and releasing lithium ions, a solid electrolyte layer containing a solid electrolyte and a negative electrode including a conductive porous body holding metallic lithium, which are laminated in this order, provided that the metallic lithium precipitates when the battery is charged. In the lithium ion secondary battery, the negative electrode has a porosity-gradually-decreasing region having a smaller porosity farther from the solid electrolyte layer along a laminating direction of the power-generating element; in at least a part of a portion where the negative electrode and the solid electrolyte layer are closest to each other, a porosity of the negative electrode becomes larger than a porosity of the solid electrolyte layer.SELECTED DRAWING: Figure 3

Description

The present invention relates to a lithium ion secondary battery.

In recent years, there is an urgent need to reduce the amount of carbon dioxide in order to cope with global warming. In the automobile industry, expectations are high for the reduction of carbon dioxide emissions by introducing 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, the lithium-ion secondary battery, which has the highest theoretical energy among all realistic batteries, is attracting attention and is currently being rapidly developed.

Here, the lithium ion secondary battery currently widely used uses a flammable organic electrolyte as an 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-ion secondary batteries using oxide-based or sulfide-based solid electrolytes as electrolytes have been actively carried out. The solid electrolyte is a material composed mainly of an ionic conductor capable of conducting ions in a solid. Therefore, in the all-solid-state lithium ion 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. An all-solid-state lithium-ion secondary battery using sulfur alone (S) or a sulfide-based material as the positive electrode active material is a promising candidate.

By the way, in a lithium ion 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, causing 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 uses a mixture of granular metallic lithium and carbon black as a negative electrode active material, and sets the mixing ratio thereof within a specific range. The technology to control is disclosed.

Japanese Unexamined Patent Publication No. 2009-218005

Here, in the technique disclosed in Patent Document 1, the characteristics of metallic lithium having an extremely high capacity are sacrificed by using carbon black in combination. Therefore, there is a problem that the high capacity originally possessed by metallic lithium cannot be effectively utilized, and the irreversible capacity is large, so that the energy density of the battery cannot be sufficiently improved.

Therefore, the present invention provides a means capable of effectively utilizing the high capacity of metallic lithium in a lithium ion secondary battery and preventing the occurrence of an internal short circuit due to electrodeposition of metallic lithium. The purpose.

According to one embodiment of the present invention, a positive electrode containing a positive electrode active material capable of occluding and releasing lithium ions, a solid electrolyte layer containing a solid electrolyte, and a conductive porous body holding metallic lithium precipitated by charging are included. A lithium ion secondary battery including a power generation element in which negative electrodes are laminated in this order is provided. In the battery, the negative electrode has a void ratio gradual decrease region in which the void ratio decreases as the distance from the solid electrolyte layer increases along the stacking direction of the power generation element, and the negative electrode and the solid electrolyte layer are the most. It is characterized in that the void ratio of the negative electrode is larger than the void ratio of the solid electrolyte layer in at least a part of the adjacent portions.

According to the present invention, in a lithium ion secondary battery, it is possible to prevent the occurrence of an internal short circuit due to the electrodeposition of metallic lithium while effectively utilizing the high capacity of metallic lithium.

FIG. 1 is a perspective view showing the appearance of a flat laminated all-solid-state lithium ion secondary battery according to an embodiment of the lithium ion secondary 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 an embodiment of a single battery layer constituting a power generation element of the laminated battery shown in FIGS. 1 and 2. FIG. 4 is a cross-sectional view of another embodiment of the cell cell layer constituting the power generation element of the laminated battery shown in FIGS. 1 and 2. FIG. 5 is a cross-sectional view schematically showing a bipolar type (bipolar type) all-solid-state lithium ion secondary battery which is an embodiment of the lithium ion secondary battery according to the present invention. FIG. 6 is a discharge curve acquired when a charge / discharge test was performed using the test cells produced in Examples 1 and 2 described later. FIG. 7 is a photomicrograph showing the results of performing a charge / discharge test using the test cell prepared in Example 1 described later, disassembling the cell, and observing it with an optical microscope. FIG. 8 is a photomicrograph showing the results of performing a charge / discharge test using the test cell prepared in Example 1 described later, disassembling the cell, and observing it with an optical microscope.

《Lithium-ion secondary battery》
One embodiment of the present invention includes a positive electrode containing a positive electrode active material capable of storing and releasing lithium ions, a solid electrolyte layer containing a solid electrolyte, and a negative electrode including a conductive porous body that retains metallic lithium precipitated by charging. The negative electrode has a void ratio gradual decrease region in which the void ratio decreases as the distance from the solid electrolyte layer increases along the stacking direction of the power generation elements, and the negative electrode and the negative electrode A lithium ion secondary battery in which the void ratio of the negative electrode is larger than the void ratio of the solid electrolyte layer at least in a part of the portion closest to the solid electrolyte layer.

Hereinafter, embodiments of the present embodiment described above 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 lithium ion secondary battery according to an embodiment of the lithium ion 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 non-bipolar lithium ion secondary battery (hereinafter, also simply referred to as “laminated 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 lithium-ion secondary battery according to this embodiment, either a non-bipolar type (internal parallel connection type) battery or a bipolar type (internal series connection type) battery It can also be applied to.

As shown in FIG. 1, 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 side portions thereof. There is. The power generation element 21 is wrapped with a battery exterior material (laminate 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 outside. It is sealed in the state of being pulled out.

The lithium ion secondary battery according to this embodiment is not limited to a laminated flat battery. The wound lithium-ion secondary battery may have a cylindrical shape, or may be deformed into a rectangular flat shape. There are no particular restrictions. The cylindrical shape is not particularly limited, for example, a laminated film may be used for the exterior material, or a conventional cylindrical can (metal can) may be used. 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 each and taken out from each side. It is not limited to what is shown in FIG. 1, such as good. Further, in the winding type lithium ion 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. The positive electrode has a structure in which the positive electrode active material layers 15 containing the positive electrode active material are arranged on both sides of the positive electrode current collector 11 ″. The negative electrode is a negative electrode containing the negative electrode active material on both sides of the negative electrode current collector 11 ′. It has a structure in which the active material layer 13 is arranged. Specifically, one positive electrode active material layer 15 and a negative electrode active material layer 13 adjacent thereto are opposed to each other via the solid electrolyte layer 17. The positive electrode, the solid electrolyte layer, and the negative electrode are laminated in this order. Therefore, the adjacent positive electrode, the solid electrolyte layer, and the negative electrode form one cell cell layer 19. Therefore, the laminated battery 10a shown in FIG. 1 is It can be said that a plurality of cell cell layers 19 are laminated so as to have a configuration in which they are electrically connected in parallel.

As shown in FIG. 2, in each of the outermost layer positive electrode current collectors located in both outermost layers of the power generation element 21, the positive electrode active material layer 15 is arranged on only one side, but the active material layers are provided on both sides. May be done. That is, instead of using a current collector dedicated to the outermost layer in which the active material layer is provided on only one side, a current collector having active material layers on both sides may be used as it is as the current collector in the outermost layer. Further, in some cases, the negative electrode active material layer 13 and the positive electrode active material layer 15 may be used as the negative electrode and the positive electrode, respectively, without using the current collectors (11', 11 ").

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

FIG. 3 is a 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 positive electrode (positive electrode current collector 11 ”and positive electrode active material layer 15) constituting the cell cell layer 19, the solid electrolyte layer 17, and the negative electrode (negative electrode active material layer 13 and negative electrode current collector 11 ′) , Are laminated in this order. In the embodiment shown in FIG. 3, the negative electrode active material layer 13 is made of stainless steel (here, SUS316L), which is a conductive porous body (conductive porous body). The shape of the negative electrode active material layer 13 is defined by the body. More specifically, the negative electrode active material layer 13 is a first conductive porous portion located in the central portion of the solid electrolyte layer 17 side when the negative electrode active material layer is viewed in a plan view. The body 13a, the outer peripheral edge of the first conductive porous body 13a, and the second conductive porous body 13b located on the side opposite to the solid electrolyte layer 17 with respect to the first conductive porous body 13a. The void ratio of the first conductive porous body 13a is larger than the void ratio of the second conductive porous body 13b and the solid electrolyte layer 17, for example. The void ratio of the first conductive porous body 13a is 70%, the void ratio of the second conductive porous body is 5%, and the void ratio of the solid electrolyte layer 17 is 4%. The value of the void ratio of the conductive porous body is a value measured using only the conductive porous body itself (in other words, in a state where no other component is held in the void). In the present embodiment, the negative electrode active material layer 13 is composed of a plurality of layers in which the void ratio gradually decreases as the distance from the solid electrolyte layer 17 increases along the stacking direction of the power generation element 21. As described above, the negative electrode active material layer 13. By constructing the negative electrode using a plurality of layers in which the void ratio changes discretely, instead of continuously changing the void ratio of the conductive porous body constituting the layer 13, the present embodiment can be obtained by a simple method. In other words, the negative electrode (negative electrode active material layer 13) of the present embodiment has a smaller void ratio as it moves away from the solid electrolyte layer 17 along the stacking direction of the power generation element 21. It can be said that it has a region (a region where the void ratio is gradually reduced).

The negative electrode active material layer 13 having such a configuration has a function of receiving lithium ions diffused from the positive electrode active material layer 15 via the solid electrolyte layer 17 at the time of charging and holding the lithium ions as metallic lithium. That is, when the laminated battery 10a according to the present embodiment is charged, metallic lithium is deposited on the negative electrode active material layer 13 to bring the battery into a charged state. Therefore, in the state of complete discharge (SOC = 0%), the negative electrode active material may not be present in the negative electrode active material layer 13.

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 negative electrode active material layer 13 and the solid electrolyte layer 17. In a conventional lithium ion secondary battery, this dendrite may grow toward the positive electrode active material layer 15 side, which causes an internal short circuit. On the other hand, in the present embodiment, the void ratio of the negative electrode active material layer 13 is higher than the void ratio of the solid electrolyte layer 17 at the portion where the negative electrode active material layer 13 and the solid electrolyte layer 17 are closest to each other. It is configured to be large. Therefore, the dendrite generated by electrodeposition at the interface between the negative electrode active material layer 13 and the solid electrolyte layer 17 has a larger void ratio than the solid electrolyte layer 17 side (that is, the positive electrode active material layer 15 side). Easy to grow to the 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. As described above, in the lithium ion secondary battery according to the present embodiment, it is not necessary to use a negative electrode active material having a capacity lower than that of metallic lithium as in the technique described in Patent Document 1. Therefore, according to the battery according to the present embodiment, the high capacity potentially possessed by metallic lithium can be fully utilized, which also contributes to the improvement of the energy density of the lithium ion secondary battery. Further, according to the present embodiment, there is an advantage that the current density can be improved by the presence of the second conductive porous body having a small porosity. Further, since the electric resistance in the stacking direction of the power generation elements can be reduced, the internal resistance of the battery is reduced, and further improvement of the rate characteristics can be expected.

In the embodiment shown in FIG. 3, when the portion of the negative electrode (conductive porous body) closest to the solid electrolyte layer 17 is viewed in a plan view, the void in the central portion (conductive porous body 13a) of the negative electrode is viewed. The ratio is configured to be larger than the void ratio of the outer peripheral edge portion (conductive porous body 13b) of the negative electrode. As a result, there is an advantage that the generation of dendrites due to electrodeposition at the end of the negative electrode is suppressed, and an internal short circuit at the end can be further prevented. However, the present invention is not limited to such an embodiment, and for example, as shown in FIG. 4, the porosity of the conductive porous body 13a arranged on the solid electrolyte layer 17 side is set between the central portion and the outer peripheral portion. Of course, it may be in the same (uniform) form.

Hereinafter, the main components of the lithium ion secondary 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 viewpoints of electron conductivity, battery operating potential, adhesion of the negative electrode active material by sputtering to the current collector, 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), Polyethyleneimide (PAI), Polyethylene (PA), Polytetrafluoroethylene (PTFE), Styrene-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 can have excellent potential resistance 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 cell layers, a metal layer may be provided as a part of the current collector. Further, in the lithium ion secondary battery according to the present embodiment, the shape of the negative electrode active material layer 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 (negative electrode active material layer)]
In the lithium ion secondary battery according to this embodiment, the negative electrode (negative electrode active material layer 13) contains a conductive porous body. When the conductive porous body itself has a function as a negative electrode current collector without using a negative electrode current collector separately, the negative electrode active material layer becomes the negative electrode as it is.

(Conductive porous material)
The 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. As an example, from the viewpoint of excellent conductivity and potential resistance, metal materials such as stainless steel (SUS304, SUS316L, etc.), nickel, aluminum, manganese, and zinc can be mentioned.

In a preferred embodiment, the conductive porous body contains an element that can be alloyed with lithium. Examples of elements that can be alloyed with lithium include Al, Mg, Zn, Bi, Sn, Pb, In, Ru, Rh, Ir, Pd, Pt, Ag, Au, Cd, Ga, Tl, Si, Ge and the like. Can be mentioned. Among these, from the viewpoint of being able to construct a battery having excellent capacity and energy density, the material that can be alloyed with lithium is at least one selected from the group consisting of Si, Au, In, Ge, Sn, Pb, Al and Zn. It preferably contains a seed element, more preferably Si, Au or In. These elements 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 the conductive porous body made of a material that does not alloy with lithium. It may be used. However, it is preferably used 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.

Since the conductive porous body contains an element that can be alloyed with lithium as described above, the lithium ions that have moved from the positive electrode to the negative electrode during charging of the lithium ion secondary battery are present in the form of the lithium ion-containing alloy. As a result, the interfacial resistance between the negative electrode active material layer and the solid electrolyte layer is reduced as compared with the case where it exists in the form of metallic lithium, and a larger current density can be realized. That is, it is possible to provide a battery that can sufficiently support charging at a high rate during quick charging.

As described above, the conductive porous body has a porous structure inside, but the value of the void ratio is such that the void ratio gradually decreases region where the void ratio decreases as the distance from the solid electrolyte layer increases along the stacking direction of the power generation elements. The negative electrode (conductive porous body) is present in at least a part of the negative electrode (conductive porous body), and at least a part of the portion where the negative electrode (conductive porous body) and the solid electrolyte layer are closest to each other. As long as the void ratio of the solid electrolyte layer is configured to be larger than the void ratio of the solid electrolyte layer, there is no particular limitation. The porosity of the conductive porous body is preferably 2 to 95%. In the porosity gradual decrease region, the porosity of the portion having the largest porosity is preferably 70% or more, more preferably 75% or more, still more preferably 80% or more, and most preferably 85. % Or more. Since the portion having the largest porosity in the porosity gradual decrease region has such a porosity, lithium ions diffused from the positive electrode during charging can be precipitated as metallic lithium and sufficiently retained. In the porosity gradual decrease region, the porosity of the portion having the smallest porosity is preferably 30% or less, more preferably 20% or less, still more preferably 10% or less, and most preferably 5. % Or less. The value of the porosity of the conductive porous body can be controlled by appropriately adopting a conventionally known method. As an example, when the conductive porous body is composed of the conductive porous body having a mesh shape, the porosity can be controlled by appropriately adjusting the size and distribution of the mesh.

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. Further, when the porosity gradual decrease region of the negative electrode is formed by laminating two conductive porous bodies having different porosities, the first conductive porous body having a large porosity (arranged on the solid electrolyte layer side). It is preferable to increase the thickness of the body. As an example, the thickness of the first conductive porous body having a large porosity is preferably 15 to 250 μm, more preferably 20 to 200 μm. On the other hand, the thickness of the second conductive porous body having a small porosity is preferably 5 to 50 μm, more preferably 10 to 50 μm.

The conductive porous body constituting the negative electrode may hold negative electrode active material particles made of metallic lithium or a lithium-containing alloy. The type of the negative electrode active material constituting such negative electrode active material particles is not particularly limited, and examples of the lithium-containing alloy include an alloy of lithium and at least one of materials that can be alloyed with lithium. .. Here, as the material that can be alloyed with lithium, the above-mentioned materials can be similarly used. In some cases, two or more kinds of negative electrode active materials may be used in combination. Of course, particles made of a negative electrode active material (for example, carbon material, silicon-containing alloy, etc.) other than the above may be used as long as metallic lithium or a lithium-containing alloy is essentially contained. However, from the viewpoint of improving the energy density of the battery, the content ratio of the metallic lithium or the lithium-containing alloy in the constituent materials of the negative electrode active material particles is preferably 50 to 100% by mass, more preferably 80 to 100% by mass. %, More preferably 90 to 100% by mass, even more preferably 95 to 100% by mass, particularly preferably 98 to 100% by mass, and most preferably 100% by mass.

The shape of the negative electrode active material particles may be particulate (spherical, fibrous). The average particle size (D50) of the negative electrode active material particles is, for example, preferably in the range of 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 to 20 μm. , Especially preferably in the range of 1 to 20 μm. In the present specification, the value of the average particle size (D50) of the active material can be measured by the laser diffraction / scattering method.

The content of the negative electrode active material particles held in the voids of the conductive porous body in the negative electrode active material layer (negative electrode) is not particularly limited and can be appropriately determined in consideration of the capacity or energy density of the battery. Further, in the negative electrode active material layer, the voids of the conductive porous body contain components other than the negative electrode active material particles (for example, binder and solid electrolyte) within a range that does not adversely affect the action and effect of the present invention. You may. However, the content ratio of the negative electrode active material particles in the components contained in the voids of the conductive porous body is preferably 50 to 100% by mass, more preferably 80 to 100% by mass, and further preferably 90 to 90 to 100% by mass. It is 100% by mass, more preferably 95 to 100% by mass, particularly preferably 98 to 100% by mass, and most preferably 100% by mass.

[Solid electrolyte layer]
In the lithium ion 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 active material layer and the negative electrode active material layer 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. Examples of the solid electrolyte include a sulfide solid electrolyte and an oxide solid electrolyte, and a sulfide solid electrolyte is preferable.

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 SP 2} S ₅ , _{LiI-Li 3 PS 4, LiI} -LiBr-Li 3 PS 4, Li 3 PS 4, Li 2 S-P 2 S 5, Li 2 S-P 2 S 5 -LiI, Li 2 S-P 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 S _n (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 , Examples thereof include Li ₂ S-SiS _{2 -Li x} MO _y (where x and y are positive numbers, and M is any of P, Si, Ge, B, Al, Ga and In). .. The description of "Li ₂ SP ₂ S ₅ " means a sulfide solid electrolyte made by 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 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 is preferably a sulfide solid electrolyte containing a P element, and the sulfide solid electrolyte is more preferably a material containing Li ₂ SP ₂ S ₅ as a main component. Further, the sulfide solid electrolyte may contain halogen (F, Cl, Br, 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 a molar ratio of Li ₂ S: P ₂ S ₅ = 50: 50 to 100. 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 ion 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 ionic conductivity of the 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 NASICON 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).} In addition, as other examples 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 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, and further 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.

The solid electrolyte layer may further contain a binder in addition to the solid electrolyte described above. 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 by 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 , Thermoplastic polymers such as styrene / isoprene / styrene block copolymers and their hydrogenated additives, tetrafluoroethylene / hexafluoropropylene copolymers (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymers (PFA) , Fluorine resins such as ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE), polyvinylfluoride (PVF), vinylidene fluoride- Hexafluoropropylene-based fluorine rubber (VDF-HFP-based fluorine rubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluorine rubber (VDF-HFP-TFE-based fluorine rubber), vinylidene fluoride-pentafluoropropylene-based fluorine rubber (VDF-PFP-based fluorine rubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluorine rubber (VDF-PFP-TFE-based fluorine rubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene-based fluorine rubber (VDF-PFP-TFE-based fluorine rubber) Examples thereof include vinylidene fluoride-based fluororubber, epoxy resin and the like, such as VDF-PFMVE-TFE-based fluororubber) and vinylidene fluoride-chlorotrifluoroethylene-based fluororubber (VDF-CTFE-based fluororubber). Of these, polyimide, styrene-butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide are more preferable.

The value of the void ratio of the solid electrolyte layer is configured so that the void ratio of the negative electrode is larger than the void ratio of the solid electrolyte layer at least in a part of the portion where the negative electrode and the solid electrolyte layer are closest to each other. As long as it is, there are no particular restrictions. 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 15% or less, more preferably 10% or less, still more preferably 5% or less, and particularly preferably 4% or less. When the solid electrolyte layer is a laminate of a plurality of sub-solid electrolyte layers having different void ratios as described later, the value of the void ratio of the solid electrolyte layer is the average void ratio of the entire solid electrolyte layer as the laminate. It shall point. Further, 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 forming a hybrid form with the organic solid electrolyte, the density of the solid electrolyte can be improved, and as a result, the void ratio can be lowered.

The solid electrolyte layer may be composed of a single layer having a uniform composition and density (porosity), or may be a laminate of a plurality of layers having different compositions and densities (porosity). In a preferred embodiment, the solid electrolyte layer has a gradient of void ratio in the stacking direction of the power generation elements, and the void ratio of the region of the solid electrolyte layer facing the negative electrode is smaller than the average void ratio of the solid electrolyte layer. It has become. According to such an embodiment, the void ratio of the entire solid electrolyte layer is secured to some extent to suppress an increase in the diffusion resistance of lithium ions, and the dendrite generated at the interface between the solid electrolyte layer and the negative electrode is on the solid electrolyte layer side. It is possible to surely prevent the growth to. As an example of such an embodiment, a solid electrolyte layer is formed by laminating a plurality of sub-solid electrolyte layers having different void ratios, and at this time, the void ratio becomes smaller from the positive electrode side to the negative electrode side. The form in which the sub-solid electrolyte layer is arranged is exemplified. However, the present invention is not limited to such a form, and if possible, the porosity may be continuously changed.

The thickness of the solid electrolyte layer varies depending on the configuration of the target lithium ion secondary battery, but is preferably 600 μm or less, more preferably 500 μm or less, from the viewpoint of improving the volumetric energy density of the battery. , More preferably 400 μm or less. On the other hand, the lower limit of the thickness of the solid electrolyte layer is not particularly limited, but is preferably 10 μm or more, more preferably 50 μm or more, and further preferably 100 μm or more. When the solid electrolyte layer is a laminate of a plurality of sub-solid electrolyte layers having different layers, the value of the thickness of the solid electrolyte layer is the total value of the child thicknesses of all the sub-solid electrolyte layers.

[Positive electrode active material layer]
The positive electrode active material layer preferably contains a positive electrode active material containing sulfur. The type of positive electrode active material containing sulfur is not particularly limited, and examples thereof include particles or thin films of an organic sulfur compound or an inorganic sulfur compound in addition to sulfur alone (S), and charging is performed by utilizing the oxidation-reduction reaction of sulfur. Any substance may be used as long as it can release lithium ions at times and occlude lithium ions at the time of discharge. 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, rubianic acid (dithiooxamide), and polycarbon sulfide. Of these, disulfide compounds, sulfur-modified polyacrylonitrile, and rubianic acid are preferable, and sulfur-modified polyacrylonitrile is particularly preferable. As the disulfide compound, those having a dithiobiurea derivative, a thiourea group, a thioisocyanate, or a thioamide group are 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 in the Raman spectrum, there is a strong peak signal in the vicinity of 1330 cm ^-1 and 1560 cm ^{-1, further, 307cm -1, 379cm -1, 472cm} -1, there is a peak around 929 cm ^-1 do. On the other hand, inorganic sulfur compounds are preferable because they have excellent stability. Specifically, sulfur simple substance (S), S-carbon composite, TiS ₂ , TiS ₃ , TiS ₄ , NiS, NiS ₂ , CuS, FeS ₂ , Li. ₂ S, 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 and pores of the carbon material, 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.

The positive electrode active material layer may contain a positive electrode active material containing no sulfur instead of the positive electrode active material containing sulfur. Examples of the sulfur-free positive electrode active material include layered rock salt type active materials _{such as LiCoO 2} , LiMnO ₂ , LiNiO ₂ , LiVO ₂ , and Li (Ni-Mn-Co) O _{2 , LiMn 2} O ₄ , LiNi _0. Examples thereof include spinel-type active materials such as ₅ Mn _1.5 O ₄ , olivine-type active materials such as _{LiFePO 4} and LiMnPO ₄ , and Si-containing active materials such as _{Li 2} FeSiO ₄ and Li _{2 MnSiO 4.} Examples of the oxide active material other than the above include Li ₄ Ti ₅ O ₁₂ .

In some cases, two or more kinds of positive electrode active materials may be used in combination. Needless to say, 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, 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 ~ 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, preferably in the range of 50 to 90% by mass, for example. 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 a known highly conductive material conventionally used as a current collector plate for a secondary battery 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 or different materials may be used for the positive electrode current collector plate 27 and the negative electrode current collector plate 25.

[Positive lead and negative electrode lead]
Further, although not shown, the current collector (11, 12) and the current collector plate (25, 27) may be electrically connected via a positive electrode lead or a negative electrode lead. As a constituent material of the positive electrode and the negative electrode lead, a material used in a known lithium ion secondary battery can be similarly adopted. The part taken out from the exterior is heat-shrinkable with heat-resistant insulation so that it does not come into contact with peripheral devices or wiring and cause an electric leakage and affect the product (for example, automobile parts, especially electronic devices). It is preferable to cover with a tube or the like.

[Battery exterior material]
As the battery exterior material, a known metal can case can be used, and as shown in FIGS. 1 and 2, a bag-shaped case using a laminated film 29 containing aluminum, which can cover the power generation element, is used. Can be done. As the laminate film, for example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order can be used, but the laminate film is not limited thereto. A laminated film is desirable from the viewpoint of high output and excellent cooling performance, and can be suitably used for batteries for large devices 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 laminated battery according to this embodiment has a configuration in which a plurality of cell cell layers are connected in parallel, so that it has a high capacity and excellent cycle durability. Therefore, the laminated battery according to this embodiment is suitably used as a power source for driving EVs and HEVs.

Although one embodiment of the lithium ion secondary battery has been described above, the present invention is not limited to the configuration described in the above-described embodiment, and may be appropriately modified based on the description of the claims. It is possible.

For example, as the type of battery to which the lithium ion secondary battery according to the present invention is applied, a positive electrode active material layer electrically bonded to one surface of a current collector and an electrical electrode to the opposite surface of the current collector are used. A bipolar type battery including a bipolar type electrode having a negative electrode active material layer bonded to the negative electrode can also be mentioned.

FIG. 5 schematically shows a bipolar type (bipolar type) lithium ion secondary battery (hereinafter, also simply referred to as “bipolar type secondary battery”) which is an embodiment of the lithium ion secondary battery according to the present invention. It is a cross-sectional view. The bipolar secondary battery 10b shown in FIG. 5 has a structure in which a 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.

As shown in FIG. 5, in the power generation element 21 of the bipolar secondary battery 10b of the present embodiment, a positive electrode active material layer 15 electrically bonded to one surface of the current collector 11 is formed, and the current collector 11 has a positive electrode active material layer 15. It has a plurality of bipolar electrodes 23 in which a negative electrode active material layer 13 electrically bonded is formed on the opposite surface. Each bipolar electrode 23 is laminated via a solid electrolyte layer 17 to form a power generation element 21. The solid electrolyte layer 17 has a structure in which the solid electrolyte is formed into layers. As shown in FIG. 5, the solid electrolyte layer 17 is between the positive electrode active material layer 15 of the one bipolar electrode 23 and the negative electrode active material layer 13 of the other bipolar electrode 23 adjacent to the one bipolar electrode 23. Are sandwiched between them.

The adjacent positive electrode active material layer 15, the solid electrolyte layer 17, and the negative electrode active material layer 13 constitute one cell cell layer 19. Therefore, it can be said that the bipolar secondary battery 10b has a configuration in which the single battery layers 19 are laminated. The positive electrode active material layer 15 is formed on only one side of the outermost layer current collector 11a on the positive electrode side located in the outermost layer of the power generation element 21. Further, the negative electrode active material layer 13 is formed on only one side of the outermost layer current collector 11b on the negative electrode side located in the outermost layer of the power generation element 21.

Further, in the bipolar secondary battery 10b shown in FIG. 5, a positive electrode current collector plate (positive electrode tab) 25 is arranged so as to be adjacent to the outermost layer current collector 11a on the positive electrode side, and this is extended to form a battery exterior. It is derived from the laminated film 29. On the other hand, the negative electrode current collector plate (negative electrode tab) 27 is arranged so as to be adjacent to the outermost layer current collector 11b on the negative electrode side, and is similarly extended and led out from the laminate film 29.

The number of times the cell cell layer 19 is laminated is adjusted according to a desired voltage. Further, in the bipolar secondary battery 10b, the number of times the cell cell layer 19 is laminated may be reduced as long as a sufficient output can be secured even if the thickness of the battery is made as thin as possible. Even in the bipolar secondary battery 10b, in order to prevent external impact and environmental deterioration during use, the power generation element 21 is vacuum-sealed in the laminated film 29 which is the battery exterior, and the positive electrode current collector plate 27 and the negative electrode current collector are collected. It is preferable to have a structure in which the electric plate 25 is taken out from the laminated film 29.

Further, the lithium ion secondary battery according to this embodiment does not have to be an all-solid-state type. 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. When calculating the value of the void ratio of the solid electrolyte layer containing the liquid electrolyte (electrolyte solution), it is assumed that the liquid electrolyte (electrolyte solution) does not exist (in other words, based on the amount of solid content). It shall be.

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 charging 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} ) ₂ N (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-vinylethylene carbonate, 1-methyl-2-vinylethylene carbonate, 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. In addition, the amount used when the additive is used in the electrolytic solution can be appropriately adjusted.

[Battery set]
An assembled battery is formed 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, the capacitance and voltage can be adjusted freely.

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 driving 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 having an output (battery module, battery pack, etc.). 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 installed. It may be decided according to the output.

[vehicle]
A battery or an assembled battery formed by combining a plurality of these batteries can be mounted on the vehicle. In the present invention, since a long-life battery having excellent long-term reliability can be configured, a plug-in hybrid electric vehicle having a long EV mileage and an electric vehicle having a long one-charge mileage can be configured by mounting such a battery. In addition to hybrid vehicles, fuel cell vehicles, electric vehicles (all four-wheeled vehicles (commercial vehicles such as passenger cars, trucks, 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 with reference to Examples. However, the technical scope of the present invention is not limited to the following examples.

<< Production example of test cell >>
[Example 1]
_{A predetermined amount of LPS (Li 2 SP 2} S ₅ (mixing ratio 80:20 (mol%))), which is a lithium ion conductive solid electrolyte, was weighed. Next, this was placed in a jig (Macol tube) and powder-molded at a molding pressure of 400 [MPa] to prepare a solid electrolyte layer (disk shape with a diameter of 10 mm and a thickness of 600 μm, a void ratio of 4%). ..

On the other hand, LiNi _0.5 Mn _0.3 Co _0.2 O ₂ is 60% by mass, the solid electrolyte (LPS) is 30% by mass, acetylene black which is a conductive auxiliary agent is 5% by mass, and polyvinylidene fluoride which is a binder. A mixture containing (PVdF) in an amount of 5% by mass was prepared and used as a positive mixture.

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, a circular conductive porous body 1 (made of SUS316L, thickness 100 μm, porosity 70%) having a diameter of 10 mm was placed on the other surface of the solid electrolyte layer. Further, another circular conductive porous body 2 having a diameter of 10 mm (manufactured by SUS316L, thickness 10 μm, porosity 5%) was further placed on the conductive porous body 1. Then, a molding pressure of 100 [MPa] was applied by fastening the jig, and a lead for taking out a current was connected to each electrode to prepare a test cell of this example.

[Example 2]
Instead of the conductive porous body 1, a circular conductive porous body 3 (made of SUS316L, thickness 100 μm, porosity 70%) having a diameter of 8 mm and an outer diameter (diameter) having a circular hole with a diameter of 8 mm in the center. ) A test cell of this example was prepared by the same method as in Example 1 described above, except that a 10 mm donut-shaped conductive porous body 4 (made of SUS316L, thickness 100 μm, porosity 5%) was used. bottom. At this time, the conductive porous body 3 was arranged so as to fit exactly into the hole in the central portion of the conductive porous body 4.

[Comparative Example 1]
The test cell of this example was produced by the same method as in Example 1 described above, except that the arrangement order of the conductive porous body 1 and the conductive porous body 2 was reversed.

[Comparative Example 2]
This implementation was carried out by the same method as in Comparative Example 1 described above, except that the conductive porous body 5 having a diameter of 10 mm (manufactured by SUS316L, thickness 100 μm, porosity 5%) was used instead of the conductive porous body 1. An example test cell was made.

<< Test example of test cell (charge / discharge test) >>
Charge / discharge evaluation was performed at room temperature for each of the test cells prepared in the above-mentioned Examples and Comparative Examples. Specifically, CC-CV charging was performed at a 0.1 C rate, and then CC discharge was performed at a 0.1 C rate. The range of cell voltage was 2.5 to 4.3 [V].

As a result, in the test cells of Comparative Example 1 and Comparative Example 2, almost no discharge could be performed. On the other hand, as shown in FIG. 6, in the test cell of Example 1, discharge could be performed up to a capacity of about 10 [mAh / g]. Further, in the test cell of Example 2, discharge could be performed up to a capacity of about 30 [mAh / g] without lowering the cell voltage.

When the test cell was disassembled after the above-mentioned charging treatment and the inside of the cell was observed using an optical microscope, in the test cells of Comparative Example 1 and Comparative Example 2, the metallic lithium precipitated on the negative electrode was solid. It grew like a dendrite toward the inside of the electrolyte layer, causing an internal short circuit. On the other hand, in the test cell of Example 1, as shown in FIG. 7, metallic lithium is precipitated in the pores of the conductive porous body in both the central portion and the outer peripheral portion of the test cell. Was observed. Further, in the test cell of Example 2, as shown in FIG. 8, although it was observed that metallic lithium was precipitated in the pores of the conductive porous body in the central portion of the test cell, it was outside. No precipitation of metallic lithium was observed at the peripheral edge.

10a stacked battery,
10b bipolar battery,
11 current collector,
11'Negative current collector,
11 ”Positive current collector,
13 Negative electrode active material layer,
13a First conductive porous body,
13b Second conductive porous body,
15 Positive electrode active material layer,
17 solid electrolyte layer,
19 Single battery layer,
21 Power generation element,
25 Negative current collector plate,
27 Positive electrode current collector plate,
29 Laminated film.

Claims (7)

A positive electrode containing a positive electrode active material that can occlude and release lithium ions,
A solid electrolyte layer containing a solid electrolyte and
A negative electrode containing a conductive porous body that retains metallic lithium deposited by charging,
Is equipped with power generation elements that are stacked in this order,
The negative electrode has a porosity gradual decrease region in which the porosity decreases as the distance from the solid electrolyte layer increases along the stacking direction of the power generation elements.
A lithium ion secondary battery in which the void ratio of the negative electrode is larger than the void ratio of the solid electrolyte layer at least in a part of the portion where the negative electrode and the solid electrolyte layer are closest to each other. The lithium ion secondary battery according to claim 1, wherein the void ratio gradual decrease region is composed of a plurality of layers in which the void ratio gradually decreases as the distance from the solid electrolyte layer increases along the stacking direction of the power generation elements. The lithium ion secondary battery according to claim 1 or 2, wherein in the porosity gradual decrease region, the porosity of the portion having the largest porosity is 70% or more. 3. The lithium ion secondary battery according to item 1. The lithium ion secondary battery according to any one of claims 1 to 4, wherein the constituent material of the conductive porous body is stainless steel, nickel, aluminum, manganese or zinc. The solid electrolyte layer has a gradient of void ratio in the stacking direction of the power generation element, and the void ratio of the portion of the solid electrolyte layer closest to the negative electrode is smaller than the average void ratio of the solid electrolyte layer. , The lithium ion secondary battery according to any one of claims 1 to 5. The lithium ion secondary battery according to any one of claims 1 to 6, wherein the solid electrolyte layer has a thickness of 600 μm or less.

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