Lithium secondary battery

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

Technical Field

[0001] The present invention relates to a lithium secondary battery.

Background Art

[0002] In recent years, in order to address global warming, it has been urgently desired to reduce the amount of carbon dioxide. In the automotive industry, expectations are gathering for the reduction of carbon dioxide emissions by introducing electric vehicles (EVs) and hybrid electric vehicles (HEVs), and the development of non-aqueous electrolyte secondary batteries such as secondary batteries for motor drive, which hold the key to their practical use, has been actively carried out.

[0003] As a secondary battery for motor drive, it is required to have extremely high output characteristics and high energy compared to consumer lithium-ion secondary batteries used in mobile phones, notebook computers, etc. Therefore, lithium-ion secondary batteries, which have the highest theoretical energy among all realistic batteries, have attracted attention and are currently being rapidly developed.

[0004] Here, currently widely used lithium-ion secondary batteries use a flammable organic electrolyte as the electrolyte. In such liquid-based lithium-ion secondary batteries, safety measures against liquid leakage, short circuit, overcharging, etc. are more strictly required than in other batteries.

[0005] 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. A solid electrolyte is a material mainly composed of an ion conductor capable of ion conduction in a solid. For this reason, in all-solid-state lithium secondary batteries, various problems caused by the flammable organic electrolyte in conventional liquid-based lithium-ion secondary batteries do not occur in principle. Also, generally, when using a high-potential and large-capacity positive electrode material and a large-capacity negative electrode material, a significant improvement in the output density and energy density of the battery can be achieved. All-solid-state lithium secondary batteries using a sulfur single substance (S) or a positive electrode active material made of a sulfide-based material and a solid electrolyte containing sulfur are promising candidates.

[0006] Incidentally, in a lithium secondary battery, the negative electrode potential decreases as charging progresses. When the negative electrode potential decreases and falls below 0 V (vs. Li / Li + ), metallic lithium precipitates at the negative electrode and dendrite (tree-like) crystals precipitate (this phenomenon is also referred to as the electrodeposition of metallic lithium). When the electrodeposition of metallic lithium occurs, there is a problem that the precipitated dendrites penetrate the electrolyte layer, causing an internal short circuit of the battery. This problem of internal short circuit becomes particularly prominent when the solid electrolyte layer is made thinner from the viewpoint of improving the energy density of the battery.

[0007] For the purpose of preventing such electrodeposition of metallic lithium, for example, Patent Document 1 discloses a technique in a secondary battery having a solid electrolyte layer containing a lithium ion conductive inorganic solid electrolyte, using a mixture of granular metallic lithium and carbon black as a negative electrode active material, and controlling the mixing ratio thereof within a specific range.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] According to the study by the present inventors, when attempting to prevent the electrodeposition of metallic lithium using the technique described in Patent Document 1, there is a problem that sufficient capacity cannot be extracted during charge and discharge at a high charge-discharge rate (that is, the so-called charge-discharge rate characteristics are not sufficient). A secondary battery with insufficient charge-discharge rate characteristics like this cannot utilize sufficient capacity in response to rapid charge and discharge.

[0010] Accordingly, an object of the present invention is to provide a means for improving charge / discharge rate characteristics in a lithium secondary battery having a solid electrolyte layer containing a lithium ion conductive solid electrolyte. **Means for Solving the Problems**

[0011] According to one embodiment of the present invention, there is provided a lithium secondary battery including 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 lithium ion conductive solid electrolyte. In the lithium secondary battery, the negative electrode includes a lithium ion / electron conductive structure including 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, and the porosity of the lithium ion / electron conductive structure is larger than the porosity of the solid electrolyte layer.

[0012] Another embodiment of the present invention also relates to a lithium secondary battery including 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 lithium ion conductive solid electrolyte. In the lithium secondary battery according to this embodiment, the negative electrode includes a lithium ion / electron conductive structure including 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, the porosity of the lithium ion / electron conductive structure is larger than the porosity of the solid electrolyte layer, and metallic lithium is retained in the pores of the lithium ion / electron conductive structure. **Advantages of the Invention**

[0013] In the lithium secondary battery according to the present invention, the presence of the lithium ion / electron conductive structure in which the conductive porous body is covered with the solid electrolyte ensures both the conduction path of lithium ions and the conduction path of electrons in the negative electrode. 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. **Brief Description of the Drawings**

[0014]

Figure 1

Figure 2

Figure 3

MODE FOR CARRYING OUT THE INVENTION

[0015] One embodiment (first embodiment) of the present invention includes 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 includes 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, and includes a lithium ion / electron conductive structure. The porosity of the lithium ion / electron conductive structure is larger than the porosity of the solid electrolyte layer, and it is a lithium secondary battery. When the lithium secondary battery according to the first embodiment is in a fully 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.

[0016] Another embodiment (second embodiment) of the present invention includes 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 includes 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, and includes a lithium ion / electron conductive structure. The porosity of the lithium ion / electron conductive structure is larger than the porosity of the solid electrolyte layer, and metallic lithium is retained in the voids of the lithium ion / electron conductive structure, and it is a lithium secondary battery. That is, the lithium secondary battery according to the second embodiment is in a charged state.

[0017] Hereinafter, embodiments of the above-described main form will be described with reference to the drawings. However, the technical scope of the present invention should be determined based on the description in the claims and is not limited only to the following forms. Note that the dimensional ratios in the drawings are exaggerated for convenience of explanation and may be different from the actual ratios.

[0018] FIG. 1 is a perspective view showing the appearance of a flat laminated all-solid-state battery which is an embodiment of a secondary battery according to the present invention. FIG. 2 is a cross-sectional view taken along line 2-2 shown in FIG. 1. By adopting a laminated type, the battery can be made compact and have a high capacity. In this specification, a non-bipolar all-solid-state lithium secondary battery of the flat laminated type shown in FIGS. 1 and 2 (hereinafter, also simply referred to as a "laminated battery") will be described in detail as an example. However, when viewed from the electrical connection form (electrode structure) inside the all-solid-state battery according to this embodiment, it can be applied to both non-bipolar (internal parallel connection type) batteries and bipolar (internal series connection type) batteries.

[0019] As shown in FIG. 2, the laminated battery 10a has a rectangular flat shape, and a negative electrode current collector 25 and a positive electrode current collector 27 for extracting electric power are drawn out from both side portions thereof. The power generation element 21 is wrapped by a battery exterior material (laminate film 29) of the laminated battery 10a, and the periphery thereof is heat-sealed. The power generation element 21 is sealed in a state where the negative electrode current collector 25 and the positive electrode current collector 27 are drawn out to the outside.

[0020] Note that the all-solid-state battery according to this embodiment is not limited to a flat laminated shape. In the case of a wound all-solid-state battery, it may have a cylindrical shape, or may be a deformed cylindrical shape, such as a rectangular flat shape, and is not particularly limited. In the case of the above cylindrical shape, a laminate film may be used for the exterior material, or a conventional cylindrical can (metal can) may be used, and is not particularly limited. Preferably, the power generation element is housed inside a laminate film containing aluminum. By this embodiment, weight reduction can be achieved.

[0021] Also, regarding the extraction of the current collectors (25, 27) shown in FIG. 1, there are no particular restrictions. The negative electrode current collector 25 and the positive electrode current collector 27 may be drawn out from the same side, or the negative electrode current collector 25 and the positive electrode current collector 27 may be divided into a plurality of parts and drawn out from each side, etc., and it is not limited to those shown in FIGS. 1 and 2. Further, in a wound lithium secondary battery, instead of tabs, for example, a cylindrical can (metal can) may be used to form the terminals.

[0022] As shown in Fig. 2, the laminated battery 10a of the present embodiment has a structure where a flat and substantially rectangular power generation element 21 in which charge and discharge reactions actually proceed is sealed inside a laminate film 29 which is a battery exterior material. 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 argyrodite-type sulfide solid electrolyte (Li6PS5Cl), which is one type of sulfide solid electrolyte. The negative electrode has a structure in which lithium ion / electron conductive structures 13 are disposed on both surfaces of a 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 covering at least a part of the inner surface of the porous body (details of the lithium ion / electron conductive structure 13 will be described later). When the laminated battery 10a is in a fully 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 precipitate as metallic lithium or a lithium-containing alloy in the voids of the structure 13. The positive electrode has a structure in which a positive electrode active material layer 15 containing a positive electrode active material is disposed on both surfaces of a positive electrode current collector 11". Specifically, one lithium ion / electron conductive structure 13 and the positive electrode active material layer 15 adjacent thereto face each other through the solid electrolyte layer 17, and the negative electrode, the solid electrolyte layer, and the positive electrode are laminated in this order. Thereby, the adjacent negative electrode, solid electrolyte layer, and positive electrode constitute one single 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 single cell layers 19 are laminated and electrically connected in parallel.

[0023] As shown in Fig. 2, on the outermost negative electrode current collectors located on both outermost layers of the power generation element 21, the lithium ion / electron conductive structures 13 are disposed on only one side of each, but the lithium ion / electron conductive structures may be provided on both sides. That is, instead of using a current collector dedicated to the outermost layer with the structure provided on only one side, a current collector having the structure on both sides may be used as the outermost layer current collector as it is.

[0024] Negative current collectors 11' and positive current collectors 11" are respectively attached with negative current collector plates (tabs) 25 and positive current collector plates (tabs) 27 that are electrically connected to the respective electrodes (positive electrode and negative electrode), and have a structure that is led out to the outside of the laminate film 29 so as to be sandwiched between the ends of the laminate film 29 which is the battery exterior material. The negative current collector plate 25 and the positive current collector plate 27 may each be attached to the negative current collector 11' and the positive current collector 11" of the respective electrodes by ultrasonic welding, resistance welding, etc. via negative leads and positive leads (not shown) as necessary.

[0025] Figure 3 is an enlarged cross-sectional view of a single cell layer 19 that constitutes the power generation element 21 of the laminated battery 10a shown in FIGS. 1 and 2. In FIG. 3, a negative current collector 11', a lithium ion / electron conductive structure 13, a solid electrolyte layer 17, a positive electrode active material layer 15, and a positive current collector 11" that constitute the single cell layer 19 are laminated in this order. And in the embodiment shown in FIG. 3, the shape of the lithium ion / electron conductive structure 13 is defined by a porous body (conductive porous body) made of stainless steel (here, SUS304) having conductivity. The inner surface of the conductive porous body (stainless steel porous body) is coated with an argyrodite type sulfide solid electrolyte (Li6PS5Cl) which is the same sulfide solid electrolyte that constitutes the solid electrolyte layer 17. Here, the porosity of the lithium ion / electron conductive structure 13 having the above configuration is, for example, 60%, and is configured to have a value larger than the porosity of the solid electrolyte layer (for example, 5%). Also, when the laminated battery 10a is in a charged state, metallic lithium is held in the voids of the above conductive porous body (stainless steel porous body). Note that the value of the porosity of the above conductive porous body described above is a value measured in a state where metallic lithium is not held in the voids.

[0026] In a preferred embodiment, the negative electrode further contains a metal capable of alloying with lithium. Specifically, for example, particles of silver (Ag), which is a metal capable of alloying with lithium, are adhered in a dispersed state on the surface of a solid electrolyte that coats the inner surface of a conductive porous body. According to such a configuration, lithium ions that reach the negative electrode during charging of the laminated battery 10a alloy with silver (Ag) and are retained as a lithium-containing alloy in the voids of the lithium ion / electron conductive structure 13. Since the precipitation energy is smaller when the lithium-containing alloy is precipitated compared to the case where metallic lithium is precipitated alone, by adopting the above-described configuration, it is possible to precipitate metallic lithium more uniformly. In addition, the interfacial resistance between the lithium ion / electron conductive structure and the solid electrolyte layer can be reduced, making it possible to achieve a larger current density. As a result, the rate characteristics can be further improved. In the present specification, the concept of "metallic lithium is retained in the voids of the lithium ion / electron conductive structure" shall also include the form in which metallic lithium is retained as a lithium-containing alloy in the voids of the lithium ion / electron conductive structure 13.

[0027] In the embodiment shown in FIG. 3, for example, during charging of the laminated battery 10a, 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. These dendrites grow toward the positive electrode active material layer 15 side. 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 dendrites are more likely to grow toward the conductive porous body side rather than the solid electrolyte layer 17 side (i.e., the positive electrode active material layer 15 side). Therefore, in the embodiment shown in FIG. 3, the growth of dendrites toward the solid electrolyte layer 17 side (i.e., the positive electrode active material layer 15 side) is suppressed, and the occurrence of an internal short circuit can be prevented.

[0028] Also, during charge and discharge of the laminated battery 10a, it is important from the perspective of input / output characteristics that the conduction of lithium ions and electrons in each electrode is made smooth. 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 (al-didrite type sulfide solid electrolyte) covering the inner surface of the conductive porous body functions as a lithium ion conduction path. Thus, in the lithium secondary battery according to this embodiment, both the electron and lithium ion conduction paths in the negative electrode are sufficiently ensured. As a result, according to the lithium secondary battery according to this embodiment, in a lithium secondary battery having a solid electrolyte layer containing a lithium ion conductive solid electrolyte, it is possible to improve the charge / discharge rate characteristics.

[0029] Hereinafter, the main constituent members of the all-solid battery according to this embodiment will be described.

[0030] [Current collector] The current collector has a function of mediating the movement of electrons from the electrode active material layer. There is no particular limitation on the material constituting the current collector. As the constituent material of the current collector, for example, a metal or a conductive resin can be adopted.

[0031] Specifically, examples of the metal include aluminum, nickel, iron, stainless steel, titanium, copper, etc. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, etc. may be used. Also, a foil in which the metal surface is coated with aluminum may be used. Among them, from the viewpoints of electron conductivity, battery operating potential, etc., aluminum, stainless steel, copper, and nickel are preferable.

[0032] Also, examples of the latter conductive resin include a resin in which a conductive filler is added to a non-conductive polymer material as necessary.

[0033] Examples of non-conductive polymer materials include polyethylene (PE; such as high-density polyethylene (HDPE) and low-density polyethylene (LDPE)), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyimide (PI), polyamideimide (PAI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), or polystyrene (PS), etc. Such non-conductive polymer materials can have excellent potential resistance or solvent resistance.

[0034] To the above conductive polymer materials or non-conductive polymer materials, conductive fillers can be added as necessary. In particular, when the resin serving as the base material of the current collector consists only of non-conductive polymers, conductive fillers are necessarily essential to impart conductivity to the resin.

[0035] The conductive filler can be used without particular limitation as long as it is a conductive substance. For example, as materials excellent in conductivity, potential resistance, or lithium ion blocking property, metals and conductive carbon, etc. can be mentioned. There is no particular limitation on the metal, but it preferably contains at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, and Sb, or an alloy or metal oxide containing these metals. Also, there is no particular limitation on the conductive carbon. Preferably, it contains at least one 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.

[0036] The addition amount of the conductive filler is not particularly limited as long as it can impart sufficient conductivity to the current collector. Generally, it is 5 to 80% by mass based on 100% by mass of the total mass of the current collector.

[0037] Note that the current collector may have a single-layer structure composed 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 resin having conductivity. Further, from the viewpoint of blocking the movement of lithium ions between the single battery layers, a metal layer may be provided on a part of the current collector. In the all-solid-state lithium secondary battery according to this embodiment, the shape of the negative electrode is defined by a conductive porous body. Therefore, in some cases, it is possible to cause the conductive porous body to function as a negative electrode current collector without separately providing a negative electrode current collector. In this case, a negative electrode lead described later may be directly connected to the conductive porous body.

[0038] [Negative electrode] In the lithium secondary battery according to the present invention, the negative electrode is characterized by including a lithium ion / electron conductive structure including 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. Further, as described above, when the lithium secondary battery according to the present invention is in a fully 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 charged, the negative electrode contains metallic lithium in the form of a single substance or a lithium-containing alloy. When the conductive porous body itself functions as a negative electrode current collector without separately using a negative electrode current collector, the lithium ion / electron conductive structure directly becomes the negative electrode.

[0039] (Porous body having 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 materials described above can be similarly adopted as the constituent materials of the current collector. Among them, from the viewpoint of being easily available at low cost and excellent in the effects of the present invention, it is preferable that the conductive porous body contains a metal material or a carbon material. Here, examples of the metal material include aluminum, nickel, iron, stainless steel (such as SUS304 and SUS316L), titanium, and copper. Examples of the carbon material include hard carbon, acetylene black, Vulcan (registered trademark), Black Pearl (registered trademark), carbon nanofiber, Ketjen black (registered trademark), carbon nanotube, carbon nanohorn, carbon nanoballon, fullerene, mesoporous carbon, or activated carbon. Among them, it is more preferable that the conductive porous body contains stainless steel, nickel, carbon black, hard carbon, mesoporous carbon, or activated carbon.

[0040] There is no particular limitation on the shape of the conductive porous body. However, for example, if it is made of a metal material, shapes such as mesh, expanded grid (expanded metal), punched metal, and foam are preferably exemplified. Further, a molded body formed by molding a powder of a metal material or a carbon material by a method such as powder compacting may be used as the conductive porous body.

[0041] As described above, the conductive porous body has a porous structure (a large number of voids) inside, but the value of its 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%, and even more preferably 50 to 70%. It should be noted that the value of the porosity of the conductive porous body can be controlled by appropriately adopting conventionally known methods.

[0042] There is no particular limitation on the thickness of the conductive porous body, but it is preferably 20 to 300 μm, more preferably 30 to 250 μm, and even more preferably 50 to 200 μm.

[0043] (Lithium ion conductive solid electrolyte) Examples of the lithium ion conductive solid electrolyte include sulfide solid electrolytes and oxide solid electrolytes. From the viewpoint of excellent lithium ion conductivity and durability, a sulfide solid electrolyte is preferable. In the present specification, the lithium ion conductive solid electrolyte contained in the solid electrolyte layer 17 may also be referred to as the "first lithium ion conductive solid electrolyte", and the lithium ion conductive solid electrolyte constituting the lithium ion / electron conductive structure may also be referred to as the "second lithium ion conductive solid electrolyte". These names are only for the purpose of distinguishing the sites where the solid electrolyte is disposed, and the ordinal numbers 1st and 2nd 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.

[0044] Examples of the sulfide solid electrolyte include LiI-Li2S-SiS2, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-P2S5 (LPS), LiI-Li3PS4, LiI-LiBr-Li3PS 4、 Li3PS 4、 Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (However, m and n are positive numbers, and Z is any one of Ge, Zn, and Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y(However, x and y are positive numbers, and M is any one of P, Si, Ge, B, Al, Ga, In, etc.). Examples include. Note that the description "Li2S-P2S5" means a sulfide solid electrolyte formed using a raw material composition containing Li2S and P2S5, and the same applies to other descriptions.

[0045] The sulfide solid electrolyte may, for example, have a Li3PS4 skeleton, a Li4P2S7 skeleton, or a Li4P2S6 skeleton. Examples of the sulfide solid electrolyte having a Li3PS4 skeleton include, for example, LiI-Li3PS4, LiI-LiBr-Li3PS 4、 Li3PS4. Examples of the sulfide solid electrolyte having a Li4P2S7 skeleton include, for example, the Li-P-S-based solid electrolyte called LPS (e.g., Li7P3S 11 ). Also, as the sulfide solid electrolyte, for example, Li (4-x) Ge (1-x) P x S4 (where x satisfies 0 < x < 1), such as LGPS, may be used. Among them, the sulfide solid electrolyte contained in the active material layer is preferably a sulfide solid electrolyte containing the P element. Furthermore, the sulfide solid electrolyte may contain a halogen (F, Cl, Br, I). From the viewpoint of excellent ion conductivity, in a preferred embodiment, the lithium ion conductive solid electrolyte is Li2S-P2S5, Li7P3S 11 , Li 3.2 P 0.96 S, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, Li 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12 and includes a sulfide solid electrolyte selected from the group consisting of Li6PS5X (X is Cl, Br, or I).

[0046] In addition, when the sulfide solid electrolyte is of the Li2S-P2S5 system, the ratio of Li2S and P2S5 is preferably in the range of 50:50 to 100:0 in terms of molar ratio, and more preferably Li2S:P2S5 = 70:30 to 80:20.

[0047] Further, the sulfide solid electrolyte may be a sulfide glass, a crystallized sulfide glass, or a crystalline material obtained by a solid-phase method. The sulfide glass can be obtained, for example, by performing mechanical milling (such as a ball mill) on a raw material composition. The crystallized sulfide glass can be obtained, for example, by performing heat treatment on the sulfide glass at a temperature equal to or higher than the crystallization temperature. The ionic conductivity (e.g., Li ion conductivity) of the sulfide solid electrolyte at room temperature (25 °C) is, for example, preferably 1×10 -5 S / cm or more, and more preferably 1×10 -4 S / cm or more. The value of the ionic conductivity of the lithium-ion conductive solid electrolyte can be measured by an alternating current impedance method.

[0048] Examples of the oxide solid electrolyte include compounds having a NASICON-type structure. An example of a compound having a NASICON-type structure is a compound represented by the general formula Li 1+x Al x Ge 2-x (PO4)3 (0 ≦ x ≦ 2) (LAGP), a compound represented by the general formula Li 1+x Al x Ti 2-x (PO4)3 (0 ≦ x ≦ 2) (LATP), etc. Further, other examples of the oxide solid electrolyte include LiLaTiO (e.g., Li 0.34 La 0.51 TiO3), LiPON (e.g., Li 2.9 PO 3.3 N 0.46 ), LiLaZrO (e.g., Li7La3Zr2O 12 ), etc.

[0049] Examples of the shape of the lithium ion conductive solid electrolyte include particle shapes such as true spherical and elliptical spherical shapes, and thin film shapes. When the solid electrolyte is in a particle shape, its average particle diameter (D 50 ) is not particularly limited, but is preferably 40 μm or less, more preferably 20 μm or less, and even more preferably 10 μm or less. On the other hand, the average particle diameter (D 50 ) is preferably 0.01 μm or more, and more preferably 0.1 μm or more.

[0050] 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, there is no particular limitation on the coating thickness of the lithium ion conductive solid electrolyte on the inner surface of the conductive porous body, but it is preferably about 1 to 100 μm, and more preferably 10 to 80 μm.

[0051] In a preferred embodiment of the lithium secondary battery according to the present invention, the negative electrode contains a metal that can alloy with lithium. Examples of elements that can alloy with lithium include aluminum, magnesium, zinc, bismuth, tin, lead, indium, ruthenium, rhodium, iridium, palladium, platinum, silver, gold, cadmium, gallium, thallium, silicon, germanium, and the like. Among these, from the viewpoint of being able to construct a battery excellent in capacity and energy density, the material that can alloy with lithium preferably contains at least one metal selected from the group consisting of silver, silicon, gold, indium, germanium, tin, lead, aluminum, and zinc, and more preferably contains silver, silicon, gold, or indium. These metals that can alloy with lithium may be used in the form of a conductive porous body composed of themselves, or may be used in the form of a coating formed on the surface of a conductive porous body composed of a material that does not alloy with lithium. At this time, the metal that can alloy with lithium may be present so as to be exposed on the coating layer formed by the solid electrolyte covering the inner surface of the conductive porous body, or may be present between the conductive porous body and the coating layer, but the former form is more preferable.

[0052] According to the above configuration, lithium ions reaching the negative electrode during charging of the lithium secondary battery alloy with the metal that can alloy with lithium. Then, they are retained in the voids of the lithium ion / electron conductive structure 13 as a lithium-containing alloy. Since the precipitation energy is smaller when precipitating as a lithium-containing alloy compared to the case where metallic lithium precipitates alone, by adopting the above configuration, it becomes possible to precipitate metallic lithium more uniformly. In addition, the interfacial resistance between the lithium ion / electron conductive structure and the solid electrolyte layer can also be reduced, making it possible to achieve a larger current density. As a result, the rate characteristics can be further improved.

[0053] [Solid electrolyte layer] In the lithium secondary battery according to this embodiment, the solid electrolyte layer contains a solid electrolyte as a main component and is a layer interposed between the above-described positive electrode and negative electrode. There is no particular limitation on the specific form of the solid electrolyte contained in the solid electrolyte layer, and conventionally known knowledge can be appropriately referred to. Here, since the specific form and preferred examples of the solid electrolyte are as described above, the description is omitted here.

[0054] In addition to the above-described solid electrolyte, the solid electrolyte layer may further contain a binder. The binder that can be contained in the solid electrolyte layer is not particularly limited, and examples thereof include the following materials.

[0055] Thermoplastic polymers such as polybutylene terephthalate, polyethylene terephthalate, polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are substituted with other halogen elements), polyethylene, polypropylene, polymethylpentene, polybutene, polyether nitrile, 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 product, styrene-isoprene-styrene block copolymer and its hydrogenated product, etc.; fluororesins such as tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF), etc.; vinylidene fluoride-based fluororubbers such as 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-perfluoromethyl vinyl ether-tetrafluoroethylene-based fluororubber (VDF-PFMVE-TFE-based fluororubber), vinylidene fluoride-chlorotrifluoroethylene-based fluororubber (VDF-CTFE-based fluororubber), etc.; epoxy resins, etc. Among them, polyimide, styrene-butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, polyamide are more preferable.

[0056] 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 as close to 0% as possible. On the other hand, the upper limit value 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 conventionally known methods. As an example, when producing a solid electrolyte layer by compacting a powder of the solid electrolyte, the porosity of the solid electrolyte layer can be controlled by adjusting the pressure applied during the compacting. Also, by making the solid electrolyte amorphous (non-crystalline) or in the form of a hybrid with an organic solid electrolyte, the density of the solid electrolyte can be improved, and as a result, the porosity can be reduced. Here, the solid electrolyte layer may be composed of a single layer with uniform composition, density (porosity), etc., or may be a laminate of a plurality of layers with different compositions, density (porosity), etc.

[0057] The thickness of the solid electrolyte layer varies depending on the configuration of the target lithium secondary battery. For example, it is preferably in the range of 0.1 to 1000 μm, and more preferably in the range of 0.1 to 500 μm.

[0058] [Positive Electrode] The positive electrode contains a positive electrode active material capable of occluding and releasing lithium ions. Here, when a battery in a fully discharged state is produced during the production of the battery, the negative electrode does not hold metallic lithium. For this reason, 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 LiCoO2, LiMnO2, LiNiO2, LiVO2, Li(Ni-Mn-Co)O2, spinel type active materials such as LiMn2O4, LiNi 0.5 Mn 1.5 O4, olivine type active materials such as LiFePO4, LiMnPO4, Si-containing active materials such as Li2FeSiO4, Li2MnSiO4, Li4Ti5O 12Examples include the above. In addition, a reduction product of sulfur (S) (for example, added lithium (Li2S8)) may be used as the positive electrode active material.

[0059] On the other hand, when a fully charged battery is manufactured during the production of the battery, metallic lithium is retained in the negative electrode (for example, metallic lithium is filled in the voids of the lithium ion / electron conductive structure). Therefore, the positive electrode needs to contain a positive electrode active material capable of occluding lithium ions during discharge. Examples of such positive electrode active materials include, in addition to elemental sulfur (S), particles or thin films of organic sulfur compounds or inorganic sulfur compounds. These positive electrode active materials can occlude lithium ions during discharge and release lithium ions during charging by utilizing the redox reaction of sulfur. Examples of organic sulfur compounds include disulfide compounds, sulfur-modified polyacrylonitrile represented by the compounds described in WO 2010 / 044437 pamphlet, sulfur-modified polyisoprene, rubane acid (dithiooxamide), polysulfurized carbon, and the like. Among them, disulfide compounds, sulfur-modified polyacrylonitrile, and rubane 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, sulfur-modified polyacrylonitrile is a modified polyacrylonitrile containing sulfur atoms obtained by mixing sulfur powder and polyacrylonitrile and heating under an inert gas or reduced pressure. Its presumed structure is, for example, as shown in Chem. Mater. 2011, 23, 5024-5028, a structure in which polyacrylonitrile is cyclized into a polycyclic form and at least a part of S is bonded to C. The compounds described in this document have strong peak signals at around 1330 cm -1 and 1560 cm -1 In addition, there are strong peak signals at around 307 cm -1 379 cm -1 472 cm -1 929 cm -1There is a peak in the vicinity. On the other hand, inorganic sulfur compounds are preferable because of their excellent stability. Specifically, elemental sulfur (S), S-carbon composite, TiS2, TiS3, TiS4, NiS, NiS2, CuS, FeS2, Li2S, MoS2, MoS3, etc. can be mentioned. Among them, S, S-carbon composite, TiS2, TiS3, TiS4, FeS2 and MoS2 are preferable, elemental sulfur (S), S-carbon composite, TiS2 and FeS2 are more preferable, and elemental sulfur (S) is particularly preferable. Here, the S-carbon composite contains sulfur powder and a carbon material, and is in a state of being compounded by subjecting these to heat treatment or mechanical mixing. More specifically, it is a state in which sulfur is distributed on the surface or in the pores of the carbon material, a state in which sulfur and the carbon material are uniformly dispersed at the nanolevel and aggregated into particles, a state in which the carbon material is distributed on the surface or inside of fine sulfur powder, or a state in which a plurality of these states are combined.

[0060] In some cases, two or more cathode active materials may be used in combination. Needless to say, cathode active materials other than the above may also be used.

[0061] Examples of the shape of the cathode active material include particulate (spherical, fibrous), thin film, etc. When the cathode active material is in a particulate 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, still more preferably in the range of 100 nm to 20 μm, and particularly preferably in the range of 1 to 20 μm. In this specification, the value of the average particle size (D 50 ) of the active material can be measured by the laser diffraction scattering method.

[0062] The content of the cathode active material in the cathode active material layer is not particularly limited, but is preferably in the range of, for example, 40 to 99% by mass, and more preferably in the range of 50 to 90% by mass. The cathode active material layer may further contain a conductive assistant and / or a binder.

[0063] [Positive current collector plate and negative 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 viewpoints of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferable, and aluminum is particularly preferable. Note that the same material may be used for the positive current collector plate 27 and the negative current collector plate 25, or different materials may be used.

[0064] [Positive electrode lead and negative electrode lead] Although not shown in the figure, the current collector (11’, 11”) and the current collector plates (25, 27) may be electrically connected via a positive electrode lead or a negative electrode lead. As the constituent material of the positive and negative electrode leads, materials used in known lithium secondary batteries can be similarly adopted. Note that the portion taken out from the exterior should be covered with a heat shrinkable tube having heat and insulation properties, etc., so as not to affect the product (for example, automotive parts, particularly electronic devices, etc.) due to leakage caused by contact with peripheral devices, wiring, etc.

[0065] [Battery exterior material] As the battery exterior material, a known metal can case can be used, or a bag-shaped case using a laminate film 29 containing aluminum, which can cover the power generation element as shown in FIGS. 1 and 2, can be used. For the laminate film, for example, a laminate film having a three-layer structure formed by laminating PP, aluminum, and nylon in this order can be used, but it is not limited thereto. From the viewpoints of high output and excellent cooling performance, and being suitably applicable to large-sized device batteries for EV and HEV, the laminate film is desirable. Further, since the external pressure applied to the power generation element can be easily adjusted, the exterior body is more preferably a laminate film containing aluminum.

[0066] The lithium secondary battery according to the present invention has a configuration in which a plurality of single battery layers are connected in parallel, and thus has a high capacity and excellent 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.

[0067] As described above, one embodiment of the all-solid-state battery has been described. However, 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.

[0068] For example, the lithium 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). There is no particular limitation on the amount of the liquid electrolyte (electrolyte solution) that can be contained in the solid electrolyte layer, but it is preferably an amount such that the shape of the solid electrolyte layer formed by the solid electrolyte is maintained and no liquid leakage of the liquid electrolyte (electrolyte solution) occurs.

[0069] The liquid electrolyte 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), methyl formate (MF), 4-methyldioxolane (4MeDOL), dioxolane (DOL), 2-methyltetrahydrofuran (2MeTHF), tetrahydrofuran (THF), dimethoxyethane (DME), propylene carbonate (PC), butylene carbonate (BC), dimethyl sulfoxide (DMSO), and γ-butyrolactone (GBL). Among them, from the viewpoint of being able to further improve the rapid charging characteristics and output characteristics, the organic solvent is preferably a chain carbonate, more preferably at least one selected from the group consisting of diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC), and more preferably selected from ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC).

[0070] Examples of the lithium salt include Li(FSO2)2N (lithium bis(fluorosulfonyl)imide; LiFSI), Li(C2F5SO2)2N, LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, etc. Among them, from the viewpoint of battery output and charge-discharge cycle characteristics, the lithium salt is preferably Li(FSO2)2N (LiFSI).

[0071] The liquid electrolyte may further contain additives other than the above-described components. Specific examples of such compounds include, for example, ethylene carbonate, vinylene carbonate, methyl vinylene carbonate, dimethyl vinylene carbonate, phenyl vinylene carbonate, diphenyl vinylene carbonate, ethyl vinylene carbonate, diethyl vinylene carbonate, vinyl ethylene carbonate, 1,2-divinyl ethylene carbonate, 1-methyl-1-vinyl ethylene carbonate, 1-methyl-2-vinyl ethylene carbonate, 1-ethyl-1-vinyl ethylene carbonate, 1-ethyl-2-vinyl ethylene carbonate, vinyl vinylene carbonate, allyl ethylene carbonate, vinyloxy methyl ethylene carbonate, allyloxy methyl ethylene carbonate, acryloxy methyl ethylene carbonate, methacryloxy methyl ethylene carbonate, ethynyl ethylene carbonate, propargyl ethylene carbonate, ethynyloxy methyl ethylene carbonate, propargyloxy ethylene carbonate, methylene ethylene carbonate, 1,1-dimethyl-2-methylene ethylene carbonate, and the like. These additives may be used alone or in combination of two or more. Also, the amount of the additive used when it is used in the electrolyte can be adjusted as appropriate.

[0072] [Battery pack] A battery pack is an assembly formed by connecting a plurality of batteries. Specifically, it is composed of at least two or more batteries connected in series, in parallel, or both. By connecting them in series or parallel, it becomes possible to freely adjust the capacity and voltage.

[0073] A plurality of batteries can also be connected in series or in parallel to form a small-sized assembled battery that can be detachably attached. Then, a plurality of such small-sized assembled batteries that can be detachably attached are further connected in series or in parallel to form an assembled battery with a large capacity and a large output, which is suitable for a vehicle drive power source or an auxiliary power source that requires a high volumetric energy density and a high volumetric output density. The number of batteries to be connected to fabricate the assembled battery and the number of stages of small-sized assembled batteries to be stacked to fabricate a large-capacity assembled battery may be determined according to the battery capacity and output of the vehicle (electric vehicle) to be mounted.

[0074] [Vehicle] The lithium secondary battery according to the present invention maintains a discharge capacity even after long-term use, has good cycle characteristics and charge-discharge rate characteristics. Furthermore, it has a high volumetric energy density. In vehicle applications such as electric vehicles, hybrid electric vehicles, fuel cell vehicles, and hybrid fuel cell vehicles, compared with electric and portable electronic device applications, a high capacity and a large size are required, and a long service life is also necessary. Therefore, the non-aqueous electrolyte secondary battery can be suitably used as a power source for vehicles, for example, as a vehicle drive power source or an auxiliary power source.

[0075] Specifically, a battery or an assembled battery formed by combining a plurality of these can be mounted on a vehicle. In the present invention, since a high-life battery with excellent long-term reliability and output characteristics can be configured, mounting such a battery can configure a plug-in hybrid electric vehicle with a long EV driving range or an electric vehicle with a long single-charge driving range. A battery or an assembled battery formed by combining a plurality of these can be used, for example, in an automobile such as a hybrid vehicle, a fuel cell vehicle, or an electric vehicle (any of which is a four-wheeled vehicle (commercial vehicles such as passenger cars, trucks, buses, and light automobiles) and also includes two-wheeled vehicles (motorcycles) and three-wheeled vehicles), resulting in a high-life and highly reliable automobile. However, the application is not limited to automobiles. For example, it can also be applied to various power sources of other vehicles, such as trains, and can also be used as a mounting power source for an uninterruptible power supply device or the like.

Examples

[0076] 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 only to the following examples.

[0077] <<Example of Preparation of Test Cell>> [Example 1-1] (Preparation of Negative Electrode) A predetermined amount of an argyrodite-type sulfide solid electrolyte (Li6PS5Cl), which is a lithium-ion conductive solid electrolyte, was weighed. Then, this was dispersed in an appropriate amount of dehydrated ethanol to prepare Solution A.

[0078] On the other hand, as a porous body having conductivity, a mesh made of stainless steel (SUS304) was prepared and immersed in Solution A for a sufficient time. Then, this was taken out of Solution A and dried in an internal thermostat at 150°C for a sufficient time to produce a negative electrode composed of an electrolyte-coated stainless steel mesh (lithium-ion / electron conductive structure).

[0079] (Preparation of Test Cell) As a positive electrode active material, a lithium-containing composite oxide having a uniform composition of LiNi 0.8 Mn 0.1 Co 0.1 O2 and having a form of secondary particles that are aggregates of primary particles was prepared. When the average particle diameter (D50) of this lithium-containing composite oxide (secondary particles) was measured by the laser diffraction scattering method, it was 11.5 μm. Also, as a solid electrolyte for the positive electrode binder, the same argyrodite-type sulfide solid electrolyte as above was prepared. Further, acetylene black was prepared as a conductive aid for the positive electrode binder.

[0080] 60 parts by mass of the positive electrode active material prepared above, 6 parts by mass of the conductive aid, and 34 parts by mass of the argyrodite-type sulfide solid electrolyte were each weighed and mixed using a table mill to prepare a positive electrode binder.

[0081] Subsequently, the same argyrodite-type sulfide solid electrolyte as described above was placed in a jig (Macor tube) and compacted by pressing at a molding pressure of 400 [MPa] to produce a solid electrolyte layer (disk shape with a diameter of 10 mm and a thickness of 600 μm).

[0082] Next, the positive electrode mixture prepared above was placed on one surface of the solid electrolyte layer produced above, and compacted by pressing at a molding pressure of 200 [MPa] to produce a positive electrode active material layer (disk shape with a diameter of 10 mm and a thickness of 70 μm).

[0083] Thereafter, the (lithium ion / electron conductive structure) produced above was placed on the other surface of the solid electrolyte layer produced above. Next, after fastening the jig with a restraining pressure of 100 [MPa], leads for current extraction were connected to each electrode to produce a test cell of this example. In the test cell produced in this manner, the porosity of the solid electrolyte layer and the negative electrode (lithium ion / electron conductive structure) was 5% and 60%, respectively.

[0084] [Example 1-2] A predetermined amount of silver (Ag) powder was weighed as a metal that can alloy with lithium. Next, this was dispersed in an appropriate amount of dehydrated ethanol to prepare Solution B. And before producing the test cell, Solution B was uniformly sprayed on the negative electrode made of an electrolyte-coated stainless steel mesh (lithium ion / electron conductive structure) and allowed to dry naturally.

[0085] A test cell of this example was produced in the same manner as in Example 1-1 described above, except that the negative electrode subjected to the above treatment was used. In the test cell produced in this manner, the porosity of the solid electrolyte layer and the negative electrode (lithium ion / electron conductive structure) was 5% and 60%, respectively.

[0086] [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) prepared above, a stainless steel mesh not coated with a solid electrolyte and 7 mg of an argyrodite-type sulfide solid electrolyte (Li6PS5Cl) were simply encapsulated simultaneously, and a restraint pressure was applied under the same conditions as above. Except for this, the test cell of this comparative example was fabricated by the same method as Example 1-1 described above. In addition, the porosity of the solid electrolyte layer and the negative electrode in the test cell fabricated in this way was 5% and 60%, respectively.

[0087] [Comparative Example 1-2] In Comparative Example 1-1 described above, when arranging the negative electrode of the test cell, the test cell of this comparative example was fabricated by the same method as Comparative Example 1-1 described above, except that only a stainless steel mesh not coated with a solid electrolyte was arranged and the solid electrolyte was not encapsulated simultaneously. In addition, the porosity of the solid electrolyte layer and the negative electrode in the test cell fabricated in this way was 5% and 60%, respectively.

[0088] [Example 2-1] As a constituent material of the conductive porous body, Ketjenblack (registered trademark) (manufactured by Ketjenblack International Co., Ltd.), which is a carbon material, EC300 was prepared. Next, this carbon material was immersed in Solution A prepared above for a sufficient time. Then, it was taken out from Solution A and dried in an incubator at 150 °C for a sufficient time to fabricate an electrolyte-coated carbon material.

[0089] Subsequently, a laminate of a solid electrolyte layer and a positive electrode active material layer was fabricated by the same method as Example 1-1 described above.

[0090] Next, on the other surface of the solid electrolyte layer fabricated above, the electrolyte-coated carbon material prepared above was placed, and by performing pressure powder molding at a molding pressure of 100 [MPa], a negative electrode (lithium ion / electron conductive structure) (in the shape of a disk with a diameter of 10 mm and a thickness of 70 μm) was fabricated. Thereafter, leads for current extraction were connected to each electrode to fabricate a test cell of this Example. Note that the porosity of the solid electrolyte layer and the negative electrode (lithium ion / electron conductive structure) in the test cell fabricated in this manner was 5% and 60%, respectively.

[0091] [Example 2-2] Before fabricating the test cell, Solution B prepared above was uniformly sprayed onto the electrolyte-coated carbon material and allowed to dry naturally.

[0092] A test cell of this Example was fabricated in the same manner as Example 2-1 described above, except that a negative electrode (lithium ion / electron conductive structure) was fabricated using the electrolyte-coated carbon material subjected to the above treatment. Note that the porosity of the solid electrolyte layer and the negative electrode (lithium ion / electron conductive structure) in the test cell fabricated in this manner was 5% and 60%, respectively.

[0093] [Comparative Example 2] In Example 2-1 described above, instead of the electrolyte-coated carbon material, a negative electrode was fabricated using a mixture obtained by mixing 1 mg of a carbon material (Ketjenblack EC300) and 5.6 mg of an argyrodite-type sulfide solid electrolyte with a roll mill. A test cell of this Comparative Example was fabricated in the same manner as Example 2-1 described above. Note that the porosity of the solid electrolyte layer and the negative electrode in the test cell fabricated in this manner was 5% and 60%, respectively.

[0094] [Example 3-1] A test cell of this example was fabricated by the same method as in Example 2-1 described above, except that hard carbon, another carbon material, was used as a constituent material of the conductive porous body instead of Ketjen Black (registered trademark). Note that the porosity of the solid electrolyte layer and the negative electrode (lithium ion / electron conductive structure) in the test cell fabricated in this manner was 5% and 60%, respectively.

[0095] [Example 3-2] Before fabricating the test cell, Solution B prepared above was uniformly sprayed onto the electrolyte-coated carbon material and allowed to dry naturally.

[0096] A test cell of this example was fabricated by the same method as in Example 3-1 described above, except that a negative electrode (lithium ion / electron conductive structure) was fabricated using the electrolyte-coated carbon material subjected to the above treatment. Note that the porosity of the solid electrolyte layer and the negative electrode (lithium ion / electron conductive structure) in the test cell fabricated in this manner was 5% and 60%, respectively.

[0097] [Comparative Example 3] In Example 3-1 described above, a negative electrode was fabricated using a mixture obtained by mixing 1 mg of a carbon material (hard carbon) and 5.6 mg of an argyrodite-type sulfide solid electrolyte with a roll mill instead of the electrolyte-coated carbon material. A test cell of this comparative example was fabricated by the same method as in Example 3-1 described above. Note that the porosity of the solid electrolyte layer and the negative electrode in the test cell fabricated in this manner was 5% and 60%, respectively.

[0098] 《Test Examples of Test Cells (Evaluation of Charge-Discharge Rate Characteristics)》 The charge-discharge rate characteristics of the test cells fabricated in the above-described examples and comparative examples were evaluated.

[0099] The charge-discharge test was performed at a rate condition of 0.2C (low rate condition) for charging in a constant current-constant voltage (CCCV) mode and 2C (high rate condition) for discharging in a constant current (CC) mode, respectively, within a voltage range of 4.3V / 2.5V with respect to Li. The evaluation temperature was set at 298K (25°C), and a 30-minute pause was taken between charging and discharging. Note that "1C" refers to the current value at which the battery becomes fully charged (100% charged) when charged for 1 hour at that current value.

[0100] 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 for the charge-discharge rate characteristics (the larger this value, the better the charge-discharge rate characteristics). The results are shown in Table 1 below.

[0101]

Table 1

[0102] From the results shown in Table 1, when comparing the examples and comparative examples with the same constituent material of the conductive porous body, it can be seen that the charge-discharge rate characteristics can be significantly improved by having the configuration of the present invention. Also, it can be seen that the charge-discharge rate characteristics are further improved by the negative electrode containing a metal (Ag) that can alloy with lithium.

Explanation of Symbols

[0103] 10a Stacked battery, 11’ Negative electrode current collector, 11” Positive electrode 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 Laminate film.

Claims

1. a positive electrode, a negative electrode, a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a first lithium ion conductive solid electrolyte, and having a power generation element, wherein the negative electrode includes a porous body having a porosity of 60 to 95% and made of a metal material and having conductivity (however, excluding those having a three-dimensional network structure, those having a foam shape, and those having a shape of a bonded body of metal powders), and a second lithium ion conductive solid electrolyte covering at least a part of the inner surface of the porous body, and includes a lithium ion / electron conductive structure, a lithium secondary battery, wherein the porosity of the lithium ion / electron conductive structure is larger than the porosity of the solid electrolyte layer.

2. a positive electrode, a negative electrode, a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a first lithium ion conductive solid electrolyte, and having a power generation element, wherein the negative electrode includes a porous body having a porosity of 60 to 95% and made of a metal material and having conductivity (however, excluding those having a three-dimensional network structure, those having a foam shape, and those having a shape of a bonded body of metal powders), and a second lithium ion conductive solid electrolyte covering at least a part of the inner surface of the porous body, and includes a lithium ion / electron conductive structure, wherein the porosity of the lithium ion / electron conductive structure is larger than the porosity of the solid electrolyte layer, and a lithium secondary battery, wherein metallic lithium is held in the pores of the lithium ion / electron conductive structure.

3. The lithium secondary battery according to claim 1 or 2, wherein the porous body having conductivity includes a metal material having a shape of a mesh, an expanded grid (expanded metal) or a punched metal.

4. The lithium secondary battery according to claim 3, wherein the porous body having conductivity includes stainless steel or nickel.

5. The lithium secondary battery according to any one of claims 1 to 4, wherein the negative electrode includes a metal capable of alloying with lithium selected from the group consisting of magnesium, zinc, bismuth, indium, ruthenium, rhodium, iridium, palladium, platinum, silver, gold, cadmium, gallium and thallium.

6. The lithium secondary battery according to claim 5, wherein the metal capable of alloying with lithium is silver.

7. The lithium secondary battery according to any one of claims 1 to 6, wherein the first lithium ion conductive solid electrolyte and the second lithium ion conductive solid electrolyte contain a sulfide solid electrolyte.

8. The lithium secondary battery according to any one of claims 1 to 7, which is an all-solid-state lithium secondary battery.

Images